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Short Message Peer-to-Peer
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Operation
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Versions The SMPP standard has evolved during the time. The most commonly used versions of SMPP are: SMPP 3.3 the oldest used version (despite its limitations, it is still widely used); supports GSM only. Generates an immediate response for each message sent.
SMPP 3.4 adds optional tag–length–value (TLV) parameters, support of non-GSM SMS technologies and the transceiver support (single connections that can send and receive messages). The exchange of SMPP request and response PDUs between an ESME Transmitter and SMSC may occur synchronously or asynchronously.
SMPP 5.0 is the latest version of SMPP; adds support for cell broadcasting, smart flow control. As of 2023, it is not widely used.The applicable version is passed in the interface_version parameter of a bind command.
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Short Message Peer-to-Peer
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PDU format (after version 3.4)
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The SMPP PDUs are binary encoded for efficiency. They start with a header which may be followed by a body: PDU header Each PDU starts with a header. The header consists of 4 fields, each of length of 4 octets: command_length Is the overall length of the PDU in octets (including command_length field itself); must be ≥ 16 as each PDU must contain the 16 octet header command_id Identifies the SMPP operation (or command). If the most significant bit is cleared, this is a request operation. Otherwise it is a response.
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Short Message Peer-to-Peer
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PDU format (after version 3.4)
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command_status Always has a value of 0 in requests; in responses it carries information about the result of the operation sequence_number Is used to correlate requests and responses within an SMPP session; allows asynchronous communication (using a sliding window method)All numeric fields in SMPP use the big endian order, which means that the first octet is the Most Significant Byte (MSB).
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Short Message Peer-to-Peer
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Example
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This is an example of the binary encoding of a 60-octet submit_sm PDU. The data is shown in Hex octet values as a single dump and followed by a header and body break-down of that PDU.
This is best compared with the definition of the submit_sm PDU from the SMPP specification in order to understand how the encoding matches the field by field definition.
The value break-downs are shown with decimal in parentheses and Hex values after that. Where you see one or several hex octets appended, this is because the given field size uses 1 or more octets encoding.
Again, reading the definition of the submit_sm PDU from the spec will make all this clearer.
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Short Message Peer-to-Peer
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Example
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PDU header 'command_length', (60) ... 00 00 00 3C 'command_id', (4) ... 00 00 00 04 'command_status', (0) ... 00 00 00 00 'sequence_number', (5) ... 00 00 00 05 PDU body 'service_type', () ... 00 'source_addr_ton', (2) ... 02 'source_addr_npi', (8) ... 08 'source_addr', (555) ... 35 35 35 00 'dest_addr_ton', (1) ... 01 'dest_addr_npi', (1) ... 01 'dest_addr', (555555555) ... 35 35 35 35 35 35 35 35 35 00 'esm_class', (0) ... 00 'protocol_id', (0) ... 00 'priority_flag', (0) ... 00 'schedule_delivery_time', (0) ... 00 'validity_period', (0) ... 00 'registered_delivery', (0) ... 00 'replace_if_present_flag', (0) ... 00 'data_coding', (3) ... 03 'sm_default_msg_id', (0) ... 00 'sm_length', (15) ... 0F 'short_message', (Hello Wikipedia) ... 48 65 6C 6C 6F 20 57 69 6B 69 70 65 64 69 61 Note that the text in the short_message field must match the data_coding. When the data_coding is 8 (UCS2), the text must be in UCS-2BE (or its extension, UTF-16BE). When the data_coding indicates a 7-bit encoding, each septet is stored in a separate octet in the short_message field (with the most significant bit set to 0). SMPP 3.3 data_coding exactly copied TP-DCS values of GSM 03.38, which make it suitable only for GSM 7-bit default alphabet, UCS2 or binary messages; SMPP 3.4 introduced a new list of data_coding values: The meaning of the data_coding=4 or 8 is the same as in SMPP 3.3. Other values in the range 1-15 are reserved in SMPP 3.3. Unfortunately, unlike SMPP 3.3, where data_coding=0 was unambiguously GSM 7-bit default alphabet, for SMPP 3.4 and higher the GSM 7-bit default alphabet is missing in this list, and data_coding=0 may differ for various Short message service centers—it may be ISO-8859-1, ASCII, GSM 7-bit default alphabet, UTF-8 or even configurable per ESME. When using data_coding=0, both sides (ESME and SMSC) must be sure they consider it the same encoding. Otherwise it is better not to use data_coding=0. It may be tricky to use the GSM 7-bit default alphabet, some Short message service centers requires data_coding=0, others e.g. data_coding=241.
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Short Message Peer-to-Peer
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Quirks
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Despite its wide acceptance, the SMPP has a number of problematic features: No data_coding for GSM 7-bit default alphabet Not standardized meaning of data_coding=0 Unclear support for Shift-JIS encoding Incompatibility of submit_sm_resp between SMPP versions Using of SMPP 3.3 SMSC Delivery Receipts, especially the Message Id format in them No data_coding for GSM 7-bit default alphabet Although data_coding value in SMPP 3.3 are based on the GSM 03.38, since SMPP 3.4 there is no data_coding value for GSM 7-bit alphabet (GSM 03.38). However, it is common for DCS=0 to indicate the GSM 7-bit alphabet, particularly for SMPP connections to SMSCs on GSM mobile networks. It is further ambiguous whether the 7-bit alphabet is packed, as in GSM, allowing sending 160 characters in 140 octets, or whether the each 7-bit character takes up an entire octet (with the high bit set to zero, as with ASCII).
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Short Message Peer-to-Peer
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Quirks
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Not standardized meaning of data_coding=0 According to SMPP 3.4 and 5.0 the data_coding=0 means ″SMSC Default Alphabet″. Which encoding it really is, depends on the type of the SMSC and its configuration.
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Short Message Peer-to-Peer
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Quirks
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Unclear support for Shift-JIS encoding One of the encodings in CDMA standard C.R1001 is Shift-JIS used for Japanese. SMPP 3.4 and 5.0 specifies three encodings for Japanese (JIS, ISO-2022-JP and Extended Kanji JIS), but none of them is identical with CDMA MSG_ENCODING 00101. It seems that the Pictogram encoding (data_coding=9) is used to carry the messages in Shift-JIS in SMPP.
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Short Message Peer-to-Peer
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Quirks
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Incompatibility of submit_sm_resp between SMPP versions When a submit_sm fails, the SMSC returns a submit_sm_resp with non-zero value of command_status and ″empty″ message_id.
SMPP 3.3 explicitly states about the message_id field ″If absent this field must contain a single NULL byte″. The length of the PDU is at least 17 octets.
SMPP 3.4 contains an unfortunate note in the SUBMIT_SM_RESP section ″The submit_sm_resp PDU Body is not returned if the command_status field contains a non-zero value.″ Then the length of the PDU is 16 octets.
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Short Message Peer-to-Peer
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Quirks
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SMPP 5.0 just specifies that message_id is a mandatory parameter of the type C-Octet string of the submit_sm_resp message. According to the section 3.1.1 NULL Settings, ″A NULL string ″″ is encoded as 0x00″. The length of the PDU is at least 17 octets.For the best compatibility, any SMPP implementation should accept both variants of negative submit_sm_resp regardless of the version of SMPP standard used for the communication.
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Short Message Peer-to-Peer
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Quirks
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The original intention of error scenarios was that no body would be returned in the PDU response. This was the standard behavior exhibited on all Aldiscon/Logica SMSC and also in most of the other vendors. When SMPP 3.4 was being taken on by the WAP forum, several clarifications were requested on whether a body should be included with NACKed response and measures were taken to clarify this in several places in the specification including the submit_sm section and also in the bind_transceiver section. What should have been done was to add the clarification that we eventually added in V5.0.. that bodies are not supposed to be included in error responses. Some vendors have been very silly in their implementations including bodies on rejected bind_transmitter responses but not on bind_transceiver responses etc. The recommendation I would make to vendors.. as suggested above.. accept both variants. But its also wise to allow yourself issue NACKed submit_sm_resp and deliver_sm_resp PDUs with and without an empty body. In the case of these two PDUs, that empty body will look like a single NULL octet at the end of the stream. The reason you may need this ability to include what I call dummy bodies with NACKed requests is that the other side of the equation may be unable or unwilling to change their implementation to tolerate the missing body. (I worked on three versions of SMPP specification in Aldiscon/Logica and designed the ESME solution for Openmind Networks) Message ID in SMPP 3.3 SMSC Delivery Receipts The only way to pass delivery receipts in SMPP 3.3 is to put information in a text form to the short_message field; however, the format of the text is described in Appendix B of SMPP 3.4, although SMPP 3.4 may (and should) use receipted_message_id and message_state TLVs for the purpose. While SMPP 3.3 states that Message ID is a C-Octet String (Hex) of up to 8 characters (plus terminating '\0'), the SMPP 3.4 specification states that the id field in the Delivery Receipt Format is a C-Octet String (Decimal) of up to 10 characters. This splits SMPP implementations to 2 groups: Implementations using the decimal representation of an integer Message Id in the id field of the Delivery Receipt body and the hexadecimal representation of an integer Message Id in message_id and receipted_message_id fields Implementations using the same hexadecimal number (or even the same arbitrary string) both in message_id parameter and in the id field of the Delivery Receipt bodyThe SMPP 3.4 specification does however state that the delivery receipt format is SMSC vendor specific, and therefore the format included in the specification is merely one possibility. As noted above, when using SMPP 3.4 receipted_message_id and message_state TLVs should be used to convey the outcome of a message.
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Short Message Peer-to-Peer
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Extensibility, compatibility and interoperability
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Since introduction of TLV parameters in version 3.4, the SMPP may be regarded an extensible protocol. In order to achieve the highest possible degree of compatibility and interoperability any implementation should apply the Internet robustness principle: ″Be conservative in what you send, be liberal in what you accept″. It should use a minimal set of features which are necessary to accomplish a task. And if the goal is communication and not quibbling, each implementation should overcome minor nonconformities with standard: Respond with a generic_nack with command_status=3 to any unrecognised SMPP command, but do not stop the communication.
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Short Message Peer-to-Peer
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Extensibility, compatibility and interoperability
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Ignore any unrecognised, unexpected or unsupported TLV parameters.
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Short Message Peer-to-Peer
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Extensibility, compatibility and interoperability
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The borders of PDUs are always given by the PDUs' command_length field. Any message field must not exceed the end of PDU. If a field is not properly finished, it should be treated as truncated at the end of PDU, and it should not affect further PDUs.Information applicable to one version of SMPP can often be found in another version of SMPP, for example with the case of SMPP 3.4 describing the only mechanism of delivery receipts in SMPP 3.3 described above.
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Short Message Peer-to-Peer
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Security
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The SMPP protocol is designed on a clear-text binary protocol which needs to be considered if using for potentially sensitive information such as one-time passwords via SMS. There are, however, implementations of SMPP over secure SSL/TLS if required.
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EA-2012
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EA-2012
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EA-2012 is an extremely toxic organophosphate nerve agent. It's an extremely potent acetylcholinesterase inhibitor that is resistant to atropine and oxime treatment.
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Pixia
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Pixia
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Pixia is a freeware raster graphics editor program for Windows, created by Isao Maruoka. It was originally designed for the anime/manga community but has also been used in other branches of art. Besides the primary Japanese interface, it is also available in English, French, Italian, Spanish, Hungarian, Chinese Simplified, Chinese Traditional, Polish, Korean and German. The program supports multiple layers, transparency effects, standard file formats and a number of RGB file formats including .PSD. The main file extension used by this program is .PXA. The program also has a native support for Wacom tablets, for example the 4.2a version added support for Wacom Bamboo tablets. An advanced version of this software called Phierha with better UI and more functions is also available.
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Pixia
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Reception
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A CNET Editors' Review in January 2011 called Pixia "one of the most capable and professional Photoshop alternatives we've tried."
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AppleColor High-Resolution RGB Monitor
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AppleColor High-Resolution RGB Monitor
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Apple Inc. sold a variety of LCD and CRT computer displays in the past. Apple paused production of their own standalone displays in 2016 and partnered with LG to design displays for Macs. In June 2019, the Pro Display XDR was introduced, however it was expensive and targeted for professionals. Nearly three years later, in March 2022, the Studio Display was launched as a consumer-targeted counterpart to the professional monitor. These two are currently the only Apple-branded displays available.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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In the beginning (throughout the 1970s), Apple did not manufacture or sell displays of any kind, instead recommending users plug-into their television sets or (then) expensive third party monochrome monitors. However, in order to offer complete systems through its dealers, Apple began to offer various third party manufactured 12″ monochrome displays, re-badged as the Monitor II.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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First generation Apple's manufacture history of CRT displays began in 1980, starting with the Monitor /// that was introduced alongside and matched the Apple III business computer. It was a 12″ monochrome (green) screen that could display 80×24 text characters and any type of graphics, however it suffered from a very slow phosphor refresh that resulted in a "ghosting" video effect. So it could be shared with Apple II computers, a plastic stand was made available to accommodate the larger footprint of the display.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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Three years later came the introduction of the Apple manufactured Monitor //, which as the name implies, was more suited in look and style for the Apple II line and at the same time added improvements in features and visual quality. In 1984 a miniature 9″ screen, called the Monitor IIc, was introduced for the Apple IIc computer to help complement its compact size. This display was also the first to use the brand new design language for Apple's products called Snow White, as well as being the first display not in a beige color, but rather a bright, creamy off-white. By early 1985 came the first color CRTs, starting with the Monitor 100, a digital RGB display for the Apple III and Apple IIe (with appropriate card), followed shortly by the 14″ ColorMonitor IIe (later renamed to AppleColor Composite Monitor IIe) and ColorMonitor IIc (later renamed to AppleColor Composite Monitor IIc), composite video displays for those respective models. All of these Apple displays support the maximum Apple II Double Hi-Res standard of 560×192.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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In 1986 came the introduction of the AppleColor RGB Monitor, a 12″ analog RGB display designed specifically for the Apple IIGS computer. It supported a resolution of 640×400 interlaced (640×200 non-interlaced) and could be used by the Macintosh II, in a limited fashion, with the Apple High Resolution Display Video Card. Also introduced that year was the Apple Monochrome Monitor, which cosmetically was identical to the former model but was a black and white composite display suitable in external appearance for the Apple IIGS, Apple IIc or Apple IIc Plus.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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Second generation The second generation of displays were built into the Lisa and Macintosh computers. The Macintosh had a 9-inch monochrome display that could display 512×342 pixels which would be used in all monochrome Compact Macintosh computers.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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A new external AppleColor High-Resolution RGB Monitor was introduced in 1987 for the Macintosh II. It had a 13″ Trinitron CRT (the first Apple display to use an aperture grille CRT) with a fixed resolution of 640×480 pixels. The Macintosh II was a modular system with no internal display and was able to drive up to six displays simultaneously using multiple graphics cards. The desktop spanned multiple displays, and windows could be moved between displays or straddle them. In 1989, Apple introduced a series of monochrome displays for the Macintosh, the 20″ Macintosh Two Page Monochrome Display which could display two pages side by side, the 15″ Macintosh Portrait Display with a vertical orientation to display one page, and the 12″ High-Resolution Monochrome Monitor. In 1990, two 12″ displays were introduced for the low end, a 640×480 monochrome model and a 512×384 color model (560×384 for compatibility with Apple IIe Card), meant for the Macintosh LC. These were succeeded by the Macintosh Color Display series in 1992, which came in 14", 16" and 20" models, with resolutions of 640×480, 832×624, and 1152×870 respectively. There was also the Apple Performa Plus Display (a low-end Goldstar-built 14″ display with 640×480 resolution) for the Macintosh Performa series and the Apple Color Plus 14″ Display.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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Third generation The third generation of displays marked the end of the monochrome display era and the beginning of the multimedia era. The first display to include built-in speakers was introduced in 1993 as the Apple AudioVision 14 Display. The "Multiple Scan" series of displays began with the Multiple Scan 17 and 20 with Trinitron CRTs and the Multiple Scan 14 with shadow mask CRT, and would ultimately become Apple's value line of shadow mask displays. The AppleVision series of displays then became the high-end display line, using 17″ and 20″ Trinitron CRTs and with AV versions containing integrated speakers. The AppleVision line was later renamed to "ColorSync" display line when Steve Jobs returned to Apple.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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The Macintosh Color Classic introduced a 10″ color Trinitron display to the Classic compact Macintosh, with a slightly enhanced resolution of 512×384 (560×384 to accommodate the Apple IIe Card) like the standalone 12″ color display. Apple continued the all-in-one series with the larger 14″ Macintosh LC 500 series, featuring a 14″, 640×480 Trinitron CRT until the LC 580 in 1995, which heralded the switch to shadow mask CRTs for the remainder of Apple's all-in-one computers until the switch to LCDs in 2002. The last Macintosh to include an integrated CRT was the eMac, which boosted the display area to 17″ with support up to 1280×960 resolution. It used a 4th generation flat-screen CRT and was discontinued in 2006.
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AppleColor High-Resolution RGB Monitor
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CRT displays
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Fourth generation The fourth generation of displays were introduced simultaneously with the Blue & White Power Macintosh G3 in 1999, which included the translucent plastics of the iMac (initially white and blue "blueberry", then white and grey "graphite" upon the introduction of the Power Mac G4). The displays were also designed with same translucent look. The "Apple Studio Display" series of CRT displays were available in a 17″ Diamondtron and a 21″ Trinitron CRT, both driven by an LG-Manufactured chassis. The 17″ displays were notorious for faulty flybacks and failing in a manner that could destroy the monitor and catch fire. It's also reported that these monitors can destroy GPUs, and sometimes the entire computer. The last Apple external CRT display was introduced in 2000 along with the Power Mac G4 Cube. Both it and the new "LCD Studio Displays" featured clear plastics to match the Cube, and the new Apple Display Connector, which provided power, USB, and video signals to the display through a single cable. It was available only in a 17″ flat screen Diamondtron CRT. It was discontinued the following year.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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The history of Apple LCDs started in 1984 when the Apple Flat Panel Display was introduced for the Apple IIc computer, principally to enhance the IIc's portability (see Apple IIc Portability enhancements). This monochrome display was capable of 80 columns by 24 lines, as well as double hi-res graphics, but had an odd aspect ratio (making images look vertically squished) and required a very strong external light source, such as a desk lamp or direct sunlight to be used. Even then it had a very poor contrast overall and was quite expensive (US$600), contributing to its poor sales and consequently it dropping from the market not long after its introduction. An estimated 10,000 IIc LCD displays were produced.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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Portable displays The next attempt at a flat panel was with the Macintosh Portable. More of a "luggable" than a laptop, it contained a high-resolution, active-matrix, 1-bit black & white, 9.8″ LCD with 640×400 resolution. Like the IIc Flat Panel, it was not backlit and required a bright light source to be used. A second generation model employed a backlit LCD. The PowerBook and MacBook series would continue to use LCD displays, following an industry-wide evolution from black-and-white to grayscale to color and ranging from 9″ to 17″. Two primary technologies were used, active matrix (higher quality and more expensive) and passive matrix displays (lower quality and cheaper). By 1998 all laptops would use active-matrix color LCDs, though the Newton products and eMate portables would continue to use black and white LCDs. Apple's current MacBook portable displays include LED backlighting and support either 2560×1600 or 2880×1800 pixel resolutions depending on screen size. The iPod series used black-and-white or color LCDs, the iPhone line uses LCD and OLED displays, and the Apple Watch uses OLED.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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All-In-Ones In 1997, Apple released the Twentieth Anniversary Macintosh (TAM), its first all-in-one desktop with an LCD display. Drawing heavily from PowerBook technology, the TAM featured a 12.1″ active matrix LCD capable of displaying up to 16 bit color at 800×600. While Apple chose to retain traditional and cheaper CRTs for its all-in-one desktop line for the next 4 years, the TAM is undoubtedly the predecessor for the successful LCD-based iMac line of all-in-one desktops starting with the iMac G4 released in 2002. A substantial upgrade over the TAM, it contained a 15″ LCD supporting up to 1024×768 resolution. It was followed by a 17″ and 20″ models boasting resolution of up to 1680 × 1050. In 2005, the iMac G5 dropped the 15″ configuration and in 2007, the new iMac dropped the 17″ and added a 24″ to the line-up, further boosting resolution to 1920 x 1200. In October 2009, new iMac models moved to 16:9 aspect ratio screens at 21.5 and 27 inches.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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External displays The first desktop color flat-panel was introduced on March 17, 1998, with the 15″ Apple Studio Display (15-inch flat panel) which had a resolution of 1024×768. After the eMate, it was one of the first Apple products to feature translucent plastics, two months before the unveiling of the iMac. Apple called its dark blue color "azul". It had a DA-15 input as well as S-video, composite video, ADB and audio connectors, though no onboard speakers. In January 1999 the coloring was changed to match the blue and white of the new Power Macintosh G3s, and the connector changed to DE-15 VGA.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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The 22″ widescreen Apple Cinema Display was introduced in August 1999, simultaneously with the Power Mac G4 and in the beginning was sold only as an option to the Power Mac G4, selling for US$3,999. It had a native resolution of 1600×1024 and used a DVI connector. The display had a striped look on the bezel, similar to previous Studio Displays and iMacs. In December, the colors of the 15″ display were changed to "graphite" to match the new Power Mac G4s, and the input was changed from VGA to DVI, the audio and video features dropped, and the ADB functionality replaced by a two-port USB hub.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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In 2000 the 22″ Cinema Displays switched to the ADC interface, and the 15″ Studio Display was remodeled to match the Cinema Display's easel-like form factor and also featured the Apple Display Connector. In 2001 an LCD-based 17″ Studio Display was introduced, with a resolution of 1280×1024. In 2002 Apple introduced the Cinema Display HD which had a 23″ widescreen display with a resolution of 1920×1200. In 2003 Apple introduced the 20″ Cinema Display with a resolution of 1680×1050 to replace the discontinued 22″ display.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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In 2004 a new line was introduced, utilizing the same 20″ and 23″ panels alongside a new 30″ model, for $3,299. The displays had a sleek aluminum enclosure with a much narrower bezel than their predecessors. The 20″ model featured a 1680×1050 resolution, the 23″ 1920×1200, and the 30″ 2560×1600. The 30″ version requires a dual-link interface, because a single-link DVI connection (the most common type) doesn't have enough bandwidth to provide a picture to a display of this resolution. Initially, the only graphics cards that could power the new 30″ display were the Nvidia GeForce 6800 DDL series, available in both GT and Ultra forms. The DDL suffix signified the dual-link DVI capability. The less expensive of the two cards retailed for US$499, raising the net cost of owning and using the display to nearly $3,800. Later graphics options included the NVIDIA Quadro FX 4500; the card included two dual-link DVI connectors which allowed a Power Mac G5 to run two 30″ Cinema Displays simultaneously with the total number of pixels working out to 8.2 million.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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In 2006 along with the introduction of the Mac Pro, Apple lowered the price of the 30″ Cinema Display to US$1999. The Mac Pro featured an NVIDIA GeForce 7300GT as the graphics card in its base configuration which is capable of running a 30″ Cinema Display and another 23″ display simultaneously. The Mac Pro is also available with both the ATI Radeon X1900XT card and the NVIDIA Quadro FX 4500 as build-to-order options. Each of these cards is capable of driving two 30″ Cinema Displays.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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LED Cinema Display With the introduction of the Unibody MacBook family, Apple introduced the 24-inch LED Cinema Display, its first desktop display to use the new Mini DisplayPort connector, and also the first with an LED-backlit LCD. It had built-in speakers, a powered 3-port USB hub on the rear, an iSight camera and microphone, and a MagSafe power adapter for laptops. It also connected by USB for peripherals. It has a resolution of 1920×1200 and retailed for US$899.00. In 2010 it was replaced with a new 27-inch version with a resolution of 2560×1440.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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Thunderbolt Display In 2011 Apple released the Apple Thunderbolt Display, replacing the Mini DisplayPort and USB connector with a Thunderbolt plug for display and data. A Gigabit Ethernet port, a FireWire 800 port and a Thunderbolt 2 port were added as well, and the iSight camera was upgraded with a 720p FaceTime camera. On June 23, 2016, Apple announced it had discontinued the Thunderbolt Display, ending Apple's production of standalone displays.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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LG UltraFine After Apple discontinued production of standalone displays in 2016, they partnered with LG to design the UltraFine line, with a 21.5-inch 4K display (22MD4KA-B) and 27-inch 5K display (27MD5KA-B), released in November 2016 alongside the Thunderbolt 3-enabled MacBook Pro. Both displays use a USB-C connector, with the 27-inch version integrating Thunderbolt 3 connectivity. On the rear of the displays is a three port USB-C hub. The 21.5-inch version provides up to 60W charging power, while the 27-inch provides up to 85W. The 21.5-inch is compatible with all Macs with a USB-C port, while the 27-inch version can only be used natively at full resolution with Macs with Thunderbolt 3, which includes all Macs with USB-C except the Retina MacBook. The 27-inch model is compatible with older Thunderbolt 2-equipped Macs using an adapter, but is limited to displaying their maximum output resolution. Both models include integrated stereo speakers, while the 27-inch model also includes a FaceTime camera. Like previous Apple displays, there are no physical buttons on the display, and brightness and speaker volume are controlled by a connected computer.In May 2019 the 21.5-inch model was discontinued and replaced with a 23.7-inch model (24MD4KL-B) which added Thunderbolt 3 connectivity and increased the power output to 85W. In July 2019, the 27-inch model (27MD5KL-B) was updated with USB-C video input, adding compatibility with the 3rd generation iPad Pro at 4K resolution, and increased power output to 94W. Apple stopped selling the 27-inch model in March 2022 following the release of the Apple Studio Display, but the display is still in production according to LG.
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AppleColor High-Resolution RGB Monitor
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Flat panel displays
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Pro Display XDR Apple announced the Pro Display XDR at the 2019 WWDC, the first Apple-branded display since the Apple Thunderbolt Display was discontinued in 2016. The display contains a 6016×3384 6K color-calibrated Extreme Dynamic Range (XDR) panel.
Studio Display Apple announced the Apple Studio Display at the March 2022 Apple Special Event. It features a 27-inch, 5K Retina monitor, with 5120-by-2880 resolution at 218 pixels per inch, 600 nits brightness, wide color (P3), and True Tone technology.
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AppleColor High-Resolution RGB Monitor
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Connectors
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Apple has employed a large number of display connector designs over the years: Original DA-15 (commonly but incorrectly known as a DB-15) used on all modular desktop Macs until the 1999 Blue and White Power Macintosh G3.
A 13W3 connector (as on Sun Microsystems machines) used on the Macintosh Portrait Display A non-standard "mini-15" connector used on early PowerBooks which allowed an Apple display to be attached via a short adaptor cable.
The HDI-45 used on some "AV" model Centris, Quadra and the first-generation (NuBus) Power Macintosh machines.
Standard 15-pin high-density DE-15 VGA connector, first included on some Power Macintosh 9600 models and most PowerPC PowerBooks, and available on all current Macintoshes via a short adaptor cable.
The Apple Display Connector (ADC), which carries DVI, VGA, USB and power in one connector, was used on the PowerMac G4 and early models of the PowerMac G5.
A DVI connector was used on the 2001-2002 titanium PowerBook G4; all aluminum PowerBook G4 15″ and 17″; all aluminum MacBook Pro 15″ and 17″ models; Mac Mini G4, Power Mac G4, G5; Intel Mac Mini, and Mac Pro 2006–2012. PowerBook G4 12″, iMac G5 and Intel white iMacs mini-DVI ports.
A mini-VGA connector, which can provide VGA via a short adaptor cable. It appears on the white iBook, eMac, iMac G4 and G5, and first generation 12-inch PowerBook G4. Later models also support a composite and S-video adapter attached to this port.
A mini-DVI connector used on the 12″ PowerBook G4 (except first generation,) Intel-based iMacs, MacBooks, and Mac Minis.
A micro-DVI connector was used in the first generation MacBook Air to accommodate its small form factor.
A mini DisplayPort connector was used on some MacBook Air, MacBook Pro, iMac, Mac Mini and Mac Pro models.
Currently all Macs feature Thunderbolt connectors.
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AppleColor High-Resolution RGB Monitor
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Connectors
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The Retina MacBook introduced USB-C connectivity for displays. The 2016 MacBook Pro uses a combination Thunderbolt 3 USB-C connector. They are backwards compatible with HDMI and DisplayPort.Additionally, various Apple computers have been able to output: S-video via standard 4-pin mini-DIN connector Composite video, via: S-video port and use of short adaptor cable (PowerBooks) Standard phono connector (AV Macs) Phono connector video out on the Apple II, II+, IIe, IIc, IIc+, IIGS, III, and III+. While not technically NTSC or PAL compatible, a suitable image would display on NTSC/PAL television monitors A non-standard 3.5 mm jack that functions as either a headphone jack, or stereo audio and composite video out via an adaptor cable (FireWire Special Edition Clamshell iBooks and early "Dual USB" iBooks with external reset button) S-video, Composite video, or VGA, via: Mini-VGA when using an Apple Video Output Adapter (S-video & Composite or VGA) The Apple Video Adapter was specially designed to allow users to connect to S-video or composite video devices. The video adapter cable plugs into the video output port (Mini-VGA) built into the back of certain Macintosh computers. The video output port supports VGA, S-Video and Composite video out. The Apple Video Adapter is for S-Video or Composite video output only, use a separate Apple VGA Adapter for VGA video output options. With the Apple Video Adapter you can connect to your TV, VCR, or overhead projector via S-Video or Composite cables.Compatible with: iBook without an external reset button, 12-inch PowerBook G4, Mac Mini, eMac, iMac G5, or 17-inch iMac (1 GHz) with Mini-VGA port.The Apple VGA Display Adapter was specially designed to allow users to connect certain Macintosh computers to an extra VGA display or external projector (equipped with VGA) for 24-bit video-mirroring. The VGA cable from your external display or projector cable plugs into the Mini-VGA video port built into your Macintosh via the Apple VGA Display Adapter.Compatible with: eMac, iMac G5, iMac G4 flat-panel, 12-inch PowerBook G4, or iBooks having a Mini-VGA port. Most Macintosh computers with the Mini-VGA port can also use the Apple Video Adapter for S-video & Composite output options.12-inch PowerBook G4 (first generation) models supported video-mirroring and extended video desktop modes through a mini-VGA port. All 15 and 17 inch PowerBook G4 models have a DVI port as well as an S-Video out port. The mini-VGA port on the 12-inch PowerBook was replaced by a mini-DVI port starting with the second revision of the machine.
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AppleColor High-Resolution RGB Monitor
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Connectors
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The Retina MacBook Pro supports HDMI output from a built-in connector in addition to its two Thunderbolt connectors.
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Benesi–Hildebrand method
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Benesi–Hildebrand method
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The Benesi–Hildebrand method is a mathematical approach used in physical chemistry for the determination of the equilibrium constant K and stoichiometry of non-bonding interactions. This method has been typically applied to reaction equilibria that form one-to-one complexes, such as charge-transfer complexes and host–guest molecular complexation.
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Benesi–Hildebrand method
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Benesi–Hildebrand method
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HG The theoretical foundation of this method is the assumption that when either one of the reactants is present in excess amounts over the other reactant, the characteristic electronic absorption spectra of the other reactant are transparent in the collective absorption/emission range of the reaction system. Therefore, by measuring the absorption spectra of the reaction before and after the formation of the product and its equilibrium, the association constant of the reaction can be determined.
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Benesi–Hildebrand method
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History
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This method was first developed by Benesi and Hildebrand in 1949, as a means to explain a phenomenon where iodine changes color in various aromatic solvents. This was attributed to the formation of an iodine-solvent complex through acid-base interactions, leading to the observed shifts in the absorption spectrum. Following this development, the Benesi–Hildebrand method has become one of the most common strategies for determining association constants based on absorbance spectra.
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Benesi–Hildebrand method
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Derivation
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To observe one-to-one binding between a single host (H) and guest (G) using UV/Vis absorbance, the Benesi–Hildebrand method can be employed. The basis behind this method is that the acquired absorbance should be a mixture of the host, guest, and the host–guest complex.
HG +AG+AH With the assumption that the initial concentration of the guest (G0) is much larger than the initial concentration of the host (H0), then the absorbance from H0 should be negligible.
HG +AG The absorbance can be collected before and following the formation of the HG complex. This change in absorbance (ΔA) is what is experimentally acquired, with A0 being the initial absorbance before the interaction of HG and A being the absorbance taken at any point of the reaction.
ΔA=A−A0 Using the Beer–Lambert law, the equation can be rewritten with the absorption coefficients and concentrations of each component.
HG HG ]b+εG[G]b−εG[G]0b Due to the previous assumption that [G]0≫[H]0 , one can expect that [G] = [G]0. Δε represents the change in value between εHG and εG.
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Benesi–Hildebrand method
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Derivation
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HG ]b A binding isotherm can be described as "the theoretical change in the concentration of one component as a function of the concentration of another component at constant temperature." This can be described by the following equation: HG ]=[H]0Ka[G]1+Ka[G] By substituting the binding isotherm equation into the previous equation, the equilibrium constant Ka can now be correlated to the change in absorbance due to the formation of the HG complex.
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Benesi–Hildebrand method
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Derivation
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ΔA=bΔε[H]0Ka[G]01+Ka[G]0 Further modifications results in an equation where a double reciprocal plot can be made with 1/ΔA as a function of 1/[G]0. Δε can be derived from the intercept while Ka can be calculated from the slope.
1ΔA=1bΔε[G]0[H]0Ka+1bΔε[H]0
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Benesi–Hildebrand method
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Limitations and alternatives
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In many cases, the Benesi–Hildebrand method provides excellent linear plots, and reasonable values for K and ε. However, various problems arising from experimental data have been noted from time to time. Some of these issues include: different values of ε with different concentration scales, lack of consistency between the Benesi–Hildebrand values and those obtained from other methods (e.g. equilibrium constants from partition measurements), and zero and negative intercepts. Concerns have also surfaced over the accuracy of the Benesi–Hildebrand method as certain conditions cause these calculations to become invalid. For instance, the reactant concentrations must always obey the assumption that the initial concentration of the guest ([G]0) is much larger than the initial concentration of the host ([H]0). In the case when this breaks down, the Benesi–Hildebrand plot deviates from its linear nature and exhibits scatter plot characteristics. Also, in the case of determining the equilibrium constants for weakly bound complexes, it is common for the formation of 2:1 complexes to occur in solution. It has been observed that the existence of these 2:1 complexes generate inappropriate parameters that significantly interfere with the accurate determination of association constants. Due to this fact, one of the criticisms of this method is the inflexibility of only being able to study reactions with 1:1 product complexes.
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Benesi–Hildebrand method
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Limitations and alternatives
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These limitations can be overcome by using a computational method which is more generally applicable, a non-linear least-squares minimization method. The two parameters, K or ε are determined by using the Solver module a spreadsheet, by minimizing a sum of squared differences between observed and calculated quantities with respect to the equilibrium constant and molar absorbance or chemical shift values of the individual chemical species involved. The use of this and more sophisticated methods have the additional advantage that they are not limited to systems where a single complex is formed.
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Benesi–Hildebrand method
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Modifications
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Although initially used in conjunction with UV/Vis spectroscopy, many modifications have been made that allow the B–H method to be applied to other spectroscopic techniques involving fluorescence, infrared, and NMR.Modifications have also been done to further improve the accuracy in the determination of K and ε based on the Benesi–Hildebrand equations. One such modification was done by Rose and Drago. The equation that they developed is as follows: HG HG Their method relied on a set of chosen values of ε and the collection of absorbance data and initial concentrations of the host and guest. This would thus allow the calculation of K−1. By plotting a graph of εHG versus K−1, the result would be a linear relationship. When the procedure is repeated for a series of concentrations and plotted on the same graph, the lines intersect at a point giving the optimum value of εHG and K−1. However, some problems have surfaced with this modified method as some examples displayed an imprecise point of intersection or no intersection at all.More recently, another graphical procedure has been developed in order to evaluate K and ε independently of each other. This approach relies on a more complex mathematical rearrangement of the Benesi–Hildebrand method but has proven to be quite accurate when compared to standard values.
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Birefringence
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Birefringence
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Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress. Birefringence is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking slightly different paths. This effect was first described by Danish scientist Rasmus Bartholin in 1669, who observed it in calcite crystals which have one of the strongest birefringences. In the 19th century Augustin-Jean Fresnel described the phenomenon in terms of polarization, understanding light as a wave with field components in transverse polarization (perpendicular to the direction of the wave vector). Birefringence plays an important role in achieving phase-matching for a number of nonlinear optical processes.
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Birefringence
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Explanation
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A mathematical description of wave propagation in a birefringent medium is presented below. Following is a qualitative explanation of the phenomenon.
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Birefringence
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Explanation
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Uniaxial materials The simplest type of birefringence is described as uniaxial, meaning that there is a single direction governing the optical anisotropy whereas all directions perpendicular to it (or at a given angle to it) are optically equivalent. Thus rotating the material around this axis does not change its optical behaviour. This special direction is known as the optic axis of the material. Light propagating parallel to the optic axis (whose polarization is always perpendicular to the optic axis) is governed by a refractive index no (for "ordinary") regardless of its specific polarization. For rays with any other propagation direction, there is one linear polarization that would be perpendicular to the optic axis, and a ray with that polarization is called an ordinary ray and is governed by the same refractive index value no. For a ray propagating in the same direction but with a polarization perpendicular to that of the ordinary ray, the polarization direction will be partly in the direction of the optic axis, and this extraordinary ray will be governed by a different, direction-dependent refractive index. Because the index of refraction depends on the polarization when unpolarized light enters a uniaxial birefringent material, it is split into two beams travelling in different directions, one having the polarization of the ordinary ray and the other the polarization of the extraordinary ray.
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Birefringence
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Explanation
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The ordinary ray will always experience a refractive index of no, whereas the refractive index of the extraordinary ray will be in between no and ne, depending on the ray direction as described by the index ellipsoid. The magnitude of the difference is quantified by the birefringence: Δn=ne−no.
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Birefringence
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Explanation
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The propagation (as well as reflection coefficient) of the ordinary ray is simply described by no as if there were no birefringence involved. The extraordinary ray, as its name suggests, propagates unlike any wave in an isotropic optical material. Its refraction (and reflection) at a surface can be understood using the effective refractive index (a value in between no and ne). Its power flow (given by the Poynting vector) is not exactly in the direction of the wave vector. This causes an additional shift in that beam, even when launched at normal incidence, as is popularly observed using a crystal of calcite as photographed above. Rotating the calcite crystal will cause one of the two images, that of the extraordinary ray, to rotate slightly around that of the ordinary ray, which remains fixed.When the light propagates either along or orthogonal to the optic axis, such a lateral shift does not occur. In the first case, both polarizations are perpendicular to the optic axis and see the same effective refractive index, so there is no extraordinary ray. In the second case the extraordinary ray propagates at a different phase velocity (corresponding to ne) but still has the power flow in the direction of the wave vector. A crystal with its optic axis in this orientation, parallel to the optical surface, may be used to create a waveplate, in which there is no distortion of the image but an intentional modification of the state of polarization of the incident wave. For instance, a quarter-wave plate is commonly used to create circular polarization from a linearly polarized source.
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Birefringence
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Explanation
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Biaxial materials The case of so-called biaxial crystals is substantially more complex. These are characterized by three refractive indices corresponding to three principal axes of the crystal. For most ray directions, both polarizations would be classified as extraordinary rays but with different effective refractive indices. Being extraordinary waves, the direction of power flow is not identical to the direction of the wave vector in either case.
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Birefringence
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Explanation
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The two refractive indices can be determined using the index ellipsoids for given directions of the polarization. Note that for biaxial crystals the index ellipsoid will not be an ellipsoid of revolution ("spheroid") but is described by three unequal principle refractive indices nα, nβ and nγ. Thus there is no axis around which a rotation leaves the optical properties invariant (as there is with uniaxial crystals whose index ellipsoid is a spheroid).
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Birefringence
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Explanation
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Although there is no axis of symmetry, there are two optical axes or binormals which are defined as directions along which light may propagate without birefringence, i.e., directions along which the wavelength is independent of polarization. For this reason, birefringent materials with three distinct refractive indices are called biaxial. Additionally, there are two distinct axes known as optical ray axes or biradials along which the group velocity of the light is independent of polarization.
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Birefringence
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Explanation
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Double refraction When an arbitrary beam of light strikes the surface of a birefringent material at non-normal incidence, the polarization component normal to the optic axis (ordinary ray) and the other linear polarization (extraordinary ray) will be refracted toward somewhat different paths. Natural light, so-called unpolarized light, consists of equal amounts of energy in any two orthogonal polarizations. Even linearly polarized light has some energy in both polarizations, unless aligned along one of the two axes of birefringence. According to Snell's law of refraction, the two angles of refraction are governed by the effective refractive index of each of these two polarizations. This is clearly seen, for instance, in the Wollaston prism which separates incoming light into two linear polarizations using prisms composed of a birefringent material such as calcite.
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Birefringence
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Explanation
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The different angles of refraction for the two polarization components are shown in the figure at the top of this page, with the optic axis along the surface (and perpendicular to the plane of incidence), so that the angle of refraction is different for the p polarization (the "ordinary ray" in this case, having its electric vector perpendicular to the optic axis) and the s polarization (the "extraordinary ray" in this case, whose electric field polarization includes a component in the direction of the optic axis). In addition, a distinct form of double refraction occurs, even with normal incidence, in cases where the optic axis is not along the refracting surface (nor exactly normal to it); in this case, the dielectric polarization of the birefringent material is not exactly in the direction of the wave's electric field for the extraordinary ray. The direction of power flow (given by the Poynting vector) for this inhomogenous wave is at a finite angle from the direction of the wave vector resulting in an additional separation between these beams. So even in the case of normal incidence, where one would compute the angle of refraction as zero (according to Snell's law, regardless of the effective index of refraction), the energy of the extraordinary ray is propagated at an angle. If exiting the crystal through a face parallel to the incoming face, the direction of both rays will be restored, but leaving a shift between the two beams. This is commonly observed using a piece of calcite cut along its natural cleavage, placed above a paper with writing, as in the above photographs. On the contrary, waveplates specifically have their optic axis along the surface of the plate, so that with (approximately) normal incidence there will be no shift in the image from light of either polarization, simply a relative phase shift between the two light waves.
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Birefringence
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Terminology
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Much of the work involving polarization preceded the understanding of light as a transverse electromagnetic wave, and this has affected some terminology in use. Isotropic materials have symmetry in all directions and the refractive index is the same for any polarization direction. An anisotropic material is called "birefringent" because it will generally refract a single incoming ray in two directions, which we now understand correspond to the two different polarizations. This is true of either a uniaxial or biaxial material.
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Birefringence
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Terminology
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In a uniaxial material, one ray behaves according to the normal law of refraction (corresponding to the ordinary refractive index), so an incoming ray at normal incidence remains normal to the refracting surface. As explained above, the other polarization can deviate from normal incidence, which cannot be described using the law of refraction. This thus became known as the extraordinary ray. The terms "ordinary" and "extraordinary" are still applied to the polarization components perpendicular to and not perpendicular to the optic axis respectively, even in cases where no double refraction is involved.
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Birefringence
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Terminology
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A material is termed uniaxial when it has a single direction of symmetry in its optical behavior, which we term the optic axis. It also happens to be the axis of symmetry of the index ellipsoid (a spheroid in this case). The index ellipsoid could still be described according to the refractive indices, nα, nβ and nγ, along three coordinate axes; in this case two are equal. So if nα = nβ corresponding to the x and y axes, then the extraordinary index is nγ corresponding to the z axis, which is also called the optic axis in this case.
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Birefringence
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Terminology
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Materials in which all three refractive indices are different are termed biaxial and the origin of this term is more complicated and frequently misunderstood. In a uniaxial crystal, different polarization components of a beam will travel at different phase velocities, except for rays in the direction of what we call the optic axis. Thus the optic axis has the particular property that rays in that direction do not exhibit birefringence, with all polarizations in such a beam experiencing the same index of refraction. It is very different when the three principal refractive indices are all different; then an incoming ray in any of those principal directions will still encounter two different refractive indices. But it turns out that there are two special directions (at an angle to all of the 3 axes) where the refractive indices for different polarizations are again equal. For this reason, these crystals were designated as biaxial, with the two "axes" in this case referring to ray directions in which propagation does not experience birefringence.
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Birefringence
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Terminology
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Fast and slow rays In a birefringent material, a wave consists of two polarization components which generally are governed by different effective refractive indices. The so-called slow ray is the component for which the material has the higher effective refractive index (slower phase velocity), while the fast ray is the one with a lower effective refractive index. When a beam is incident on such a material from air (or any material with a lower refractive index), the slow ray is thus refracted more towards the normal than the fast ray. In the example figure at top of this page, it can be seen that refracted ray with s polarization (with its electric vibration along the direction of the optic axis, thus called the extraordinary ray) is the slow ray in given scenario.
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Birefringence
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Terminology
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Using a thin slab of that material at normal incidence, one would implement a waveplate. In this case, there is essentially no spatial separation between the polarizations, the phase of the wave in the parallel polarization (the slow ray) will be retarded with respect to the perpendicular polarization. These directions are thus known as the slow axis and fast axis of the waveplate.
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Birefringence
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Terminology
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Positive or negative Uniaxial birefringence is classified as positive when the extraordinary index of refraction ne is greater than the ordinary index no. Negative birefringence means that Δn = ne − no is less than zero. In other words, the polarization of the fast (or slow) wave is perpendicular to the optic axis when the birefringence of the crystal is positive (or negative, respectively). In the case of biaxial crystals, all three of the principal axes have different refractive indices, so this designation does not apply. But for any defined ray direction one can just as well designate the fast and slow ray polarizations.
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Birefringence
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Sources of optical birefringence
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While the best known source of birefringence is the entrance of light into an anisotropic crystal, it can result in otherwise optically isotropic materials in a few ways: Stress birefringence results when a normally isotropic solid is stressed and deformed (i.e., stretched or bent) causing a loss of physical isotropy and consequently a loss of isotropy in the material's permittivity tensor; Form birefringence, whereby structure elements such as rods, having one refractive index, are suspended in a medium with a different refractive index. When the lattice spacing is much smaller than a wavelength, such a structure is described as a metamaterial; By the Pockels or Kerr effect, whereby an applied electric field induces birefringence due to nonlinear optics; By the self or forced alignment into thin films of amphiphilic molecules such as lipids, some surfactants or liquid crystals; Circular birefringence takes place generally not in materials which are anisotropic but rather ones which are chiral. This can include liquids where there is an enantiomeric excess of a chiral molecule, that is, one that has stereo isomers; By the Faraday effect, where a longitudinal magnetic field causes some materials to become circularly birefringent (having slightly different indices of refraction for left- and right-handed circular polarizations), similar to optical activity while the field is applied.
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Birefringence
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Common birefringent materials
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The best characterized birefringent materials are crystals. Due to their specific crystal structures their refractive indices are well defined. Depending on the symmetry of a crystal structure (as determined by one of the 32 possible crystallographic point groups), crystals in that group may be forced to be isotropic (not birefringent), to have uniaxial symmetry, or neither in which case it is a biaxial crystal. The crystal structures permitting uniaxial and biaxial birefringence are noted in the two tables, below, listing the two or three principal refractive indices (at wavelength 590 nm) of some better-known crystals.In addition to induced birefringence while under stress, many plastics obtain permanent birefringence during manufacture due to stresses which are "frozen in" due to mechanical forces present when the plastic is molded or extruded. For example, ordinary cellophane is birefringent. Polarizers are routinely used to detect stress, either applied or frozen-in, in plastics such as polystyrene and polycarbonate.
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Birefringence
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Common birefringent materials
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Cotton fiber is birefringent because of high levels of cellulosic material in the fibre's secondary cell wall which is directionally aligned with the cotton fibers.
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Birefringence
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Common birefringent materials
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Polarized light microscopy is commonly used in biological tissue, as many biological materials are linearly or circularly birefringent. Collagen, found in cartilage, tendon, bone, corneas, and several other areas in the body, is birefringent and commonly studied with polarized light microscopy. Some proteins are also birefringent, exhibiting form birefringence.Inevitable manufacturing imperfections in optical fiber leads to birefringence, which is one cause of pulse broadening in fiber-optic communications. Such imperfections can be geometrical (lack of circular symmetry), or due to unequal lateral stress applied to the optical fibre. Birefringence is intentionally introduced (for instance, by making the cross-section elliptical) in order to produce polarization-maintaining optical fibers. Birefringence can be induced (or corrected!) in optical fibers through bending them which causes anisotropy in form and stress given the axis around which it is bent and radius of curvature.
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Birefringence
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Common birefringent materials
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In addition to anisotropy in the electric polarizability that we have been discussing, anisotropy in the magnetic permeability could be a source of birefringence. At optical frequencies, there is no measurable magnetic polarizability (μ=μ0) of natural materials, so this is not an actual source of birefringence.
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Birefringence
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Measurement
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Birefringence and other polarization-based optical effects (such as optical rotation and linear or circular dichroism) can be observed by measuring any change in the polarization of light passing through the material. These measurements are known as polarimetry. Polarized light microscopes, which contain two polarizers that are at 90° to each other on either side of the sample, are used to visualize birefringence, since light that has not been affected by birefringence remains in a polarization that is totally rejected by the second polarizer ("analyzer"). The addition of quarter-wave plates permits examination using circularly polarized light. Determination of the change in polarization state using such an apparatus is the basis of ellipsometry, by which the optical properties of specular surfaces can be gauged through reflection.
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Birefringence
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Measurement
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Birefringence measurements have been made with phase-modulated systems for examining the transient flow behaviour of fluids. Birefringence of lipid bilayers can be measured using dual-polarization interferometry. This provides a measure of the degree of order within these fluid layers and how this order is disrupted when the layer interacts with other biomolecules.
For the 3D measurement of birefringence, a technique based on holographic tomography [1] can be used.
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Birefringence
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Applications
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Birefringence is used in many optical devices. Liquid-crystal displays, the most common sort of flat-panel display, cause their pixels to become lighter or darker through rotation of the polarization (circular birefringence) of linearly polarized light as viewed through a sheet polarizer at the screen's surface. Similarly, light modulators modulate the intensity of light through electrically induced birefringence of polarized light followed by a polarizer. The Lyot filter is a specialized narrowband spectral filter employing the wavelength dependence of birefringence. Waveplates are thin birefringent sheets widely used in certain optical equipment for modifying the polarization state of light passing through it.
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Birefringence
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Applications
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Birefringence also plays an important role in second-harmonic generation and other nonlinear optical components, as the crystals used for this purpose are almost always birefringent. By adjusting the angle of incidence, the effective refractive index of the extraordinary ray can be tuned in order to achieve phase matching, which is required for the efficient operation of these devices.
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Birefringence
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Applications
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Medicine Birefringence is utilized in medical diagnostics. One powerful accessory used with optical microscopes is a pair of crossed polarizing filters. Light from the source is polarized in the x direction after passing through the first polarizer, but above the specimen is a polarizer (a so-called analyzer) oriented in the y direction. Therefore, no light from the source will be accepted by the analyzer, and the field will appear dark. Areas of the sample possessing birefringence will generally couple some of the x-polarized light into the y polarization; these areas will then appear bright against the dark background. Modifications to this basic principle can differentiate between positive and negative birefringence.
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Birefringence
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Applications
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For instance, needle aspiration of fluid from a gouty joint will reveal negatively birefringent monosodium urate crystals. Calcium pyrophosphate crystals, in contrast, show weak positive birefringence. Urate crystals appear yellow, and calcium pyrophosphate crystals appear blue when their long axes are aligned parallel to that of a red compensator filter, or a crystal of known birefringence is added to the sample for comparison.
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Birefringence
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Applications
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The birefringence of tissue inside a living human thigh was measured using polarization-sensitive optical coherence tomography at 1310 nm and a single mode fiber in a needle. Skeletal muscle birefringence was Δn = 1.79 × 10−3± 0.18×10−3, adipose Δn = 0.07 × 10−3 ± 0.50 × 10−3, superficial aponeurosis Δn = 5.08 × 10−3 ± 0.73 × 10−3 and interstitial tissue Δn = 0.65 ×10−3 ±0.39 ×10−3. These measurements may be important for the development of a less invasive method to diagnose Duchenne muscular dystrophy.
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Birefringence
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Applications
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Birefringence can be observed in amyloid plaques such as are found in the brains of Alzheimer's patients when stained with a dye such as Congo Red. Modified proteins such as immunoglobulin light chains abnormally accumulate between cells, forming fibrils. Multiple folds of these fibers line up and take on a beta-pleated sheet conformation. Congo red dye intercalates between the folds and, when observed under polarized light, causes birefringence.
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Birefringence
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Applications
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In ophthalmology, binocular retinal birefringence screening of the Henle fibers (photoreceptor axons that go radially outward from the fovea) provides a reliable detection of strabismus and possibly also of anisometropic amblyopia. In healthy subjects, the maximum retardation induced by the Henle fiber layer is approximately 22 degrees at 840 nm. Furthermore, scanning laser polarimetry uses the birefringence of the optic nerve fibre layer to indirectly quantify its thickness, which is of use in the assessment and monitoring of glaucoma. Polarization-sensitive optical coherence tomography measurements obtained from healthy human subjects have demonstrated a change in birefringence of the retinal nerve fiber layer as a function of location around the optic nerve head. The same technology was recently applied in the living human retina to quantify the polarization properties of vessel walls near the optic nerve.Birefringence characteristics in sperm heads allow the selection of spermatozoa for intracytoplasmic sperm injection. Likewise, zona imaging uses birefringence on oocytes to select the ones with highest chances of successful pregnancy. Birefringence of particles biopsied from pulmonary nodules indicates silicosis.
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Birefringence
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Applications
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Dermatologists use dermatoscopes to view skin lesions. Dermoscopes use polarized light, allowing the user to view crystalline structures corresponding to dermal collagen in the skin. These structures may appear as shiny white lines or rosette shapes and are only visible under polarized dermoscopy.
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Birefringence
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Applications
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Stress-induced birefringence Isotropic solids do not exhibit birefringence. When they are under mechanical stress, birefringence results. The stress can be applied externally or is "frozen in" after a birefringent plastic ware is cooled after it is manufactured using injection molding. When such a sample is placed between two crossed polarizers, colour patterns can be observed, because polarization of a light ray is rotated after passing through a birefringent material and the amount of rotation is dependent on wavelength. The experimental method called photoelasticity used for analyzing stress distribution in solids is based on the same principle. There has been recent research on using stress induced birefringence in a glass plate to generate an Optical vortex and full Poincare beams (optical beams that have every possible polarization state across a cross-section).
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Birefringence
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Applications
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Other cases of birefringence Birefringence is observed in anisotropic elastic materials. In these materials, the two polarizations split according to their effective refractive indices, which are also sensitive to stress.
The study of birefringence in shear waves traveling through the solid Earth (the Earth's liquid core does not support shear waves) is widely used in seismology.Birefringence is widely used in mineralogy to identify rocks, minerals, and gemstones.
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Birefringence
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Theory
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In an isotropic medium (including free space) the so-called electric displacement (D) is just proportional to the electric field (E) according to D = ɛE where the material's permittivity ε is just a scalar (and equal to n2ε0 where n is the index of refraction). In an anisotropic material exhibiting birefringence, the relationship between D and E must now be described using a tensor equation: where ε is now a 3 × 3 permittivity tensor. We assume linearity and no magnetic permeability in the medium: μ = μ0. The electric field of a plane wave of angular frequency ω can be written in the general form: where r is the position vector, t is time, and E0 is a vector describing the electric field at r = 0, t = 0. Then we shall find the possible wave vectors k. By combining Maxwell's equations for ∇ × E and ∇ × H, we can eliminate H = 1/μ0B to obtain: With no free charges, Maxwell's equation for the divergence of D vanishes: We can apply the vector identity ∇ × (∇ × A) = ∇(∇ ⋅ A) − ∇2A to the left hand side of eq. 3a, and use the spatial dependence in which each differentiation in x (for instance) results in multiplication by ikx to find: The right hand side of eq. 3a can be expressed in terms of E through application of the permittivity tensor ε and noting that differentiation in time results in multiplication by −iω, eq. 3a then becomes: Applying the differentiation rule to eq. 3b we find: Eq. 4b indicates that D is orthogonal to the direction of the wavevector k, even though that is no longer generally true for E as would be the case in an isotropic medium. Eq. 4b will not be needed for the further steps in the following derivation.
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Birefringence
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Theory
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Finding the allowed values of k for a given ω is easiest done by using Cartesian coordinates with the x, y and z axes chosen in the directions of the symmetry axes of the crystal (or simply choosing z in the direction of the optic axis of a uniaxial crystal), resulting in a diagonal matrix for the permittivity tensor ε: where the diagonal values are squares of the refractive indices for polarizations along the three principal axes x, y and z. With ε in this form, and substituting in the speed of light c using c2 = 1/μ0ε0, the x component of the vector equation eq. 4a becomes where Ex, Ey, Ez are the components of E (at any given position in space and time) and kx, ky, kz are the components of k. Rearranging, we can write (and similarly for the y and z components of eq. 4a) This is a set of linear equations in Ex, Ey, Ez, so it can have a nontrivial solution (that is, one other than E = 0) as long as the following determinant is zero: Evaluating the determinant of eq. 6, and rearranging the terms according to the powers of ω2c2 , the constant terms cancel. After eliminating the common factor ω2c2 from the remaining terms, we obtain In the case of a uniaxial material, choosing the optic axis to be in the z direction so that nx = ny = no and nz = ne, this expression can be factored into Setting either of the factors in eq. 8 to zero will define an ellipsoidal surface in the space of wavevectors k that are allowed for a given ω. The first factor being zero defines a sphere; this is the solution for so-called ordinary rays, in which the effective refractive index is exactly no regardless of the direction of k. The second defines a spheroid symmetric about the z axis. This solution corresponds to the so-called extraordinary rays in which the effective refractive index is in between no and ne, depending on the direction of k. Therefore, for any arbitrary direction of propagation (other than in the direction of the optic axis), two distinct wavevectors k are allowed corresponding to the polarizations of the ordinary and extraordinary rays.
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Birefringence
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Theory
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For a biaxial material a similar but more complicated condition on the two waves can be described; the locus of allowed k vectors (the wavevector surface) is a 4th-degree two-sheeted surface, so that in a given direction there are generally two permitted k vectors (and their opposites). By inspection one can see that eq. 6 is generally satisfied for two positive values of ω. Or, for a specified optical frequency ω and direction normal to the wavefronts k/|k|, it is satisfied for two wavenumbers (or propagation constants) |k| (and thus effective refractive indices) corresponding to the propagation of two linear polarizations in that direction.
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Birefringence
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Theory
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When those two propagation constants are equal then the effective refractive index is independent of polarization, and there is consequently no birefringence encountered by a wave traveling in that particular direction. For a uniaxial crystal, this is the optic axis, the ±z direction according to the above construction. But when all three refractive indices (or permittivities), nx, ny and nz are distinct, it can be shown that there are exactly two such directions, where the two sheets of the wave-vector surface touch; these directions are not at all obvious and do not lie along any of the three principal axes (x, y, z according to the above convention). Historically that accounts for the use of the term "biaxial" for such crystals, as the existence of exactly two such special directions (considered "axes") was discovered well before polarization and birefringence were understood physically. These two special directions are generally not of particular interest; biaxial crystals are rather specified by their three refractive indices corresponding to the three axes of symmetry.
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Birefringence
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Theory
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A general state of polarization launched into the medium can always be decomposed into two waves, one in each of those two polarizations, which will then propagate with different wavenumbers |k|. Applying the different phase of propagation to those two waves over a specified propagation distance will result in a generally different net polarization state at that point; this is the principle of the waveplate for instance. With a waveplate, there is no spatial displacement between the two rays as their k vectors are still in the same direction. That is true when each of the two polarizations is either normal to the optic axis (the ordinary ray) or parallel to it (the extraordinary ray).
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Birefringence
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Theory
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In the more general case, there is a difference not only in the magnitude but the direction of the two rays. For instance, the photograph through a calcite crystal (top of page) shows a shifted image in the two polarizations; this is due to the optic axis being neither parallel nor normal to the crystal surface. And even when the optic axis is parallel to the surface, this will occur for waves launched at non-normal incidence (as depicted in the explanatory figure). In these cases the two k vectors can be found by solving eq. 6 constrained by the boundary condition which requires that the components of the two transmitted waves' k vectors, and the k vector of the incident wave, as projected onto the surface of the interface, must all be identical. For a uniaxial crystal it will be found that there is not a spatial shift for the ordinary ray (hence its name) which will refract as if the material were non-birefringent with an index the same as the two axes which are not the optic axis. For a biaxial crystal neither ray is deemed "ordinary" nor would generally be refracted according to a refractive index equal to one of the principal axes.
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Vacuum blasting
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Vacuum blasting
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Vacuum blasting is an abrasive blasting method, also referred to as dustless blasting or closed loop abrasive blasting. The method is characterized by a blast tool that does abrasive blasting and collects both used blast media, and loosened particles from the surface to be treated, simultaneously.
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Vacuum blasting
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Procedure
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The blast tool is equipped with a blast hose and a suction hose, that both run from the blast tool to a control unit. The control unit supplies the blast tool with pressurized air mixed with blast media, and sucks back dust, loosened particles and used blast media. The control unit continuously separates dust and loosened particles from the used blast media, and sends used blast media back into the pressurized air flow. The dust and loosened particles are collected in a waste container.
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Vacuum blasting
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Applications
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The method is typically used in areas where dust and spill from regular abrasive blasting is not wanted, for example due to HSE-considerations. The blast process itself is slower than regular abrasive blasting, but requires less sheeting and scaffolding
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Myogel
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Myogel
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Myogel is a trade name for a human-based extracellular matrix used in cancer research to provide a 3D cell culture environment for cancer cells. Unlike other synthesized matrices such as matrigel which originated from mice sarcoma, myogel is extracted from a human benign tumor tissue called leiomyoma. Myogel was developed in Tuula Salo's lab at the University of Oulu. The idea started in 2009 by culturing cancer cells on myoma discs. Later in 2015, these myoma tissues were processed following matrigel receipt, to extract a gel form called Myogel. Myogel was compared with matrigel and found to be superior in term of enhancing cancer cells proliferation, migration and invasion.
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Irene Tracey
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Irene Tracey
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Irene Mary Carmel Tracey (born 30 October 1966) is Vice-Chancellor of the University of Oxford and former Warden of Merton College, Oxford. She is also Professor of Anaesthetic Neuroscience in the Nuffield Department of Clinical Neurosciences and formerly Pro-Vice-Chancellor (without portfolio) at the University of Oxford. She is a co-founder of the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), now the Wellcome Centre for Integrative Neuroimaging. Her team’s research is focused on the neuroscience of pain, specifically pain perception and analgesia as well as how anaesthetics produce altered states of consciousness. Her team uses multidisciplinary approaches including neuroimaging.
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Irene Tracey
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Early life and education
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Tracey was born at the Radcliffe Infirmary in Oxford and educated at St. Thomas More R.C. Primary School and Gosford Hill School in Kidlington. She completed her undergraduate and graduate studies at Merton College, Oxford in Biochemistry under the supervision of Eric Newsholme and George Radda. She graduated with joint-top first class degree winning the Gibb’s Prize as an undergraduate and was a Wellcome Trust prize student and senior scholar at Merton College for her graduate work. Her graduate research was supervised by Jeffrey F. Dunn and investigated the use of magnetic resonance imaging methods to study disease in humans.
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Irene Tracey
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Career
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As an early career researcher, Tracey held a postdoctoral position at Harvard Medical School, working at the MGH-NMR imaging centre (now Martinos) applying magnetic spectroscopy techniques to understand AIDS Dementia Complex. During this period she became interested in pain, the research field she would eventually focus on. Tracey returned to Oxford in 1997, where she helped to found the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), later renamed the Wellcome Centre for Integrative Neuroimaging; she served as its Director from 2005 until 2015. She was appointed university lecturer in 2001 at the Department of Physiology, Anatomy and Genetics; during this time, she was also a tutor in medicine and Fellow of Christ Church. Between 2007 and 2019, Tracey was Nuffield Chair in Anaesthetic Sciences and a Fellow of Pembroke College, where she is now an Honorary Fellow. In October 2016, she became Head of the Nuffield Department of Clinical Neurosciences.In October 2017, Tracey was announced as the next Warden of Merton College, in succession to Sir Martin Taylor. She was installed as Warden on 5 October 2019, becoming the college’s 51st warden.On 9 May 2022, it was announced that Tracey would be the next Vice-Chancellor of the University of Oxford, with effect from 2023, in succession to Louise Richardson. She said of her nomination: ‘I am deeply committed to growing Oxford's impact through supporting its ground-breaking discovery research, its excellence in teaching and its drive to create a global innovation powerhouse.’Tracey has served on various scientific committees, including the International Association for the Study of Pain (IASP), British Neuroscience Association, and Lundbeck Brain Prize Committee. She is a member of the Council of the Medical Research Council (MRC) and President of the Federation of European Neuroscience Societies (FENS). She is a passionate advocate for women in science and, as Warden of Merton College, championed greater inclusion and diversity.
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Irene Tracey
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Career
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Research Tracey's research centers on investigating what she calls "the cerebral signature for pain perception" − how key regions of the human brain give rise to pain − and on developing objective, reliable, scientific ways of measuring what has always been considered a highly subjective experience. In particular, Tracey and her colleagues have used fMRI brain scanning techniques to discover the various neural sites and mechanisms that underlie pain, to distinguish between the experience of pain and the anticipation of that experience, and to explore differences in how people experience the same pain in different ways at different times. Her team has also investigated how pain-relief treatments can produce altered states of consciousness and how religious beliefs can affect and alleviate pain. One key finding is that pain is complex and cognitive, and, in Tracey’s words, "sensitive to various mental processes such as the feelings and beliefs that someone has", so it doesn't arise exclusively from a single painful input, such as a pinprick or burn. Her objective is to improve the understanding of chronic pain, its diagnosis, and treatment, partly through the development of more effective drugs.
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