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Derivation of the Schwarzschild solution
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Using the field equations to find A(r) and B(r)
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To determine A and B , the vacuum field equations are employed: Rαβ=0 Hence: Γβα,ρρ−Γρα,βρ+ΓρλρΓβαλ−ΓβλρΓραλ=0, where a comma is used to set off the index that is being used for the derivative. The Ricci curvature is diagonal in the given coordinates: Rtt=−14B′A(A′A−B′B+4r)−12(B′A)′, Rrr=−12(B′B)′−14(B′B)2+14A′A(B′B+4r), Rθθ=1−(rA)′−r2A(A′A+B′B), sin 2(θ)Rθθ, where the prime means the r derivative of the functions.
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Derivation of the Schwarzschild solution
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Using the field equations to find A(r) and B(r)
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Only three of the field equations are nontrivial and upon simplification become: 4A′B2−2rB″AB+rA′B′B+rB′2A=0, rA′B+2A2B−2AB−rB′A=0, −2rB″AB+rA′B′B+rB′2A−4B′AB=0 (the fourth equation is just sin 2θ times the second equation). Subtracting the first and third equations produces: A′B+AB′=0⇒A(r)B(r)=K where K is a non-zero real constant. Substituting A(r)B(r)=K into the second equation and tidying up gives: rA′=A(1−A) which has general solution: A(r)=(1+1Sr)−1 for some non-zero real constant S . Hence, the metric for a static, spherically symmetric vacuum solution is now of the form: sin 2θdϕ2)+K(1+1Sr)dt2 Note that the spacetime represented by the above metric is asymptotically flat, i.e. as r→∞ , the metric approaches that of the Minkowski metric and the spacetime manifold resembles that of Minkowski space.
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Derivation of the Schwarzschild solution
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Using the weak-field approximation to find K and S
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The geodesics of the metric (obtained where ds is extremised) must, in some limit (e.g., toward infinite speed of light), agree with the solutions of Newtonian motion (e.g., obtained by Lagrange equations). (The metric must also limit to Minkowski space when the mass it represents vanishes.) 0=δ∫dsdtdt=δ∫(KE+PEg)dt (where KE is the kinetic energy and PEg is the Potential Energy due to gravity) The constants K and S are fully determined by some variant of this approach; from the weak-field approximation one arrives at the result: 44 =K(1+1Sr)≈−c2+2Gmr=−c2(1−2Gmc2r) where G is the gravitational constant, m is the mass of the gravitational source and c is the speed of light. It is found that: K=−c2 and 1S=−2Gmc2 Hence: A(r)=(1−2Gmc2r)−1 and B(r)=−c2(1−2Gmc2r) So, the Schwarzschild metric may finally be written in the form: sin 2θdϕ2)−c2(1−2Gmc2r)dt2 Note that: 2Gmc2=rs is the definition of the Schwarzschild radius for an object of mass m , so the Schwarzschild metric may be rewritten in the alternative form: sin 2θdϕ2)−c2(1−rsr)dt2 which shows that the metric becomes singular approaching the event horizon (that is, r→rs ). The metric singularity is not a physical one (although there is a real physical singularity at r=0 ), as can be shown by using a suitable coordinate transformation (e.g. the Kruskal–Szekeres coordinate system).
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Derivation of the Schwarzschild solution
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Alternate derivation using known physics in special cases
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The Schwarzschild metric can also be derived using the known physics for a circular orbit and a temporarily stationary point mass. Start with the metric with coefficients that are unknown coefficients of r :−c2=(dsdτ)2=A(r)(drdτ)2+r2(dϕdτ)2+B(r)(dtdτ)2.
Now apply the Euler–Lagrange equation to the arc length integral J=∫τ1τ2−(ds/dτ)2dτ.
Since ds/dτ is constant, the integrand can be replaced with (ds/dτ)2, because the E–L equation is exactly the same if the integrand is multiplied by any constant. Applying the E–L equation to J with the modified integrand yields: A′(r)r˙2+2rϕ˙2+B′(r)t˙2=2A′(r)r˙2+2A(r)r¨0=2rr˙ϕ˙+r2ϕ¨0=B′(r)r˙t˙+B(r)t¨ where dot denotes differentiation with respect to τ.
In a circular orbit r˙=r¨=0, so the first E–L equation above is equivalent to 2rϕ˙2+B′(r)t˙2=0⇔B′(r)=−2rϕ˙2/t˙2=−2r(dϕ/dt)2.
Kepler's third law of motion is T2r3=4π2G(M+m).
In a circular orbit, the period T equals 2π/(dϕ/dt), implying (dϕdt)2=GM/r3 since the point mass m is negligible compared to the mass of the central body M.
So B′(r)=−2GM/r2 and integrating this yields B(r)=2GM/r+C, where C is an unknown constant of integration. C can be determined by setting M=0, in which case the spacetime is flat and B(r)=−c2.
So C=−c2 and B(r)=2GM/r−c2=c2(2GM/c2r−1)=c2(rs/r−1).
When the point mass is temporarily stationary, r˙=0 and 0.
The original metric equation becomes t˙2=−c2/B(r) and the first E–L equation above becomes A(r)=B′(r)t˙2/(2r¨).
When the point mass is temporarily stationary, r¨ is the acceleration of gravity, −MG/r2.
So A(r)=(−2MGr2)(−c22MG/r−c2)(−r22MG)=11−2MG/(rc2)=11−rs/r.
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Derivation of the Schwarzschild solution
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Alternative form in isotropic coordinates
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The original formulation of the metric uses anisotropic coordinates in which the velocity of light is not the same in the radial and transverse directions. Arthur Eddington gave alternative forms in isotropic coordinates. For isotropic spherical coordinates r1 , θ , ϕ , coordinates θ and ϕ are unchanged, and then (provided r≥2Gmc2 )r=r1(1+Gm2c2r1)2 , dr=dr1(1−(Gm)24c4r12) , and (1−2Gmc2r)=(1−Gm2c2r1)2/(1+Gm2c2r1)2 Then for isotropic rectangular coordinates x , y , z sin cos (ϕ), sin sin (ϕ), cos (θ) The metric then becomes, in isotropic rectangular coordinates: ds2=(1+Gm2c2r1)4(dx2+dy2+dz2)−c2dt2(1−Gm2c2r1)2/(1+Gm2c2r1)2
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Derivation of the Schwarzschild solution
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Dispensing with the static assumption – Birkhoff's theorem
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In deriving the Schwarzschild metric, it was assumed that the metric was vacuum, spherically symmetric and static. The static assumption is unneeded, as Birkhoff's theorem states that any spherically symmetric vacuum solution of Einstein's field equations is stationary; the Schwarzschild solution thus follows. Birkhoff's theorem has the consequence that any pulsating star that remains spherically symmetric does not generate gravitational waves, as the region exterior to the star remains static.
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Distributed file system for cloud
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Distributed file system for cloud
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A distributed file system for cloud is a file system that allows many clients to have access to data and supports operations (create, delete, modify, read, write) on that data. Each data file may be partitioned into several parts called chunks. Each chunk may be stored on different remote machines, facilitating the parallel execution of applications. Typically, data is stored in files in a hierarchical tree, where the nodes represent directories. There are several ways to share files in a distributed architecture: each solution must be suitable for a certain type of application, depending on how complex the application is. Meanwhile, the security of the system must be ensured. Confidentiality, availability and integrity are the main keys for a secure system.
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Distributed file system for cloud
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Distributed file system for cloud
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Users can share computing resources through the Internet thanks to cloud computing which is typically characterized by scalable and elastic resources – such as physical servers, applications and any services that are virtualized and allocated dynamically. Synchronization is required to make sure that all devices are up-to-date.
Distributed file systems enable many big, medium, and small enterprises to store and access their remote data as they do local data, facilitating the use of variable resources.
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Distributed file system for cloud
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Overview
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History Today, there are many implementations of distributed file systems. The first file servers were developed by researchers in the 1970s. Sun Microsystem's Network File System became available in the 1980s. Before that, people who wanted to share files used the sneakernet method, physically transporting files on storage media from place to place. Once computer networks started to proliferate, it became obvious that the existing file systems had many limitations and were unsuitable for multi-user environments. Users initially used FTP to share files. FTP first ran on the PDP-10 at the end of 1973. Even with FTP, files needed to be copied from the source computer onto a server and then from the server onto the destination computer. Users were required to know the physical addresses of all computers involved with the file sharing.
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Distributed file system for cloud
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Overview
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Supporting techniques Modern data centers must support large, heterogenous environments, consisting of large numbers of computers of varying capacities. Cloud computing coordinates the operation of all such systems, with techniques such as data center networking (DCN), the MapReduce framework, which supports data-intensive computing applications in parallel and distributed systems, and virtualization techniques that provide dynamic resource allocation, allowing multiple operating systems to coexist on the same physical server.
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Distributed file system for cloud
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Overview
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Applications Cloud computing provides large-scale computing thanks to its ability to provide the needed CPU and storage resources to the user with complete transparency. This makes cloud computing particularly suited to support different types of applications that require large-scale distributed processing. This data-intensive computing needs a high performance file system that can share data between virtual machines (VM).Cloud computing dynamically allocates the needed resources, releasing them once a task is finished, requiring users to pay only for needed services, often via a service-level agreement. Cloud computing and cluster computing paradigms are becoming increasingly important to industrial data processing and scientific applications such as astronomy and physics, which frequently require the availability of large numbers of computers to carry out experiments.
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Distributed file system for cloud
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Architectures
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Most distributed file systems are built on the client-server architecture, but other, decentralized, solutions exist as well.
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Distributed file system for cloud
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Architectures
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Client-server architecture Network File System (NFS) uses a client-server architecture, which allows sharing of files between a number of machines on a network as if they were located locally, providing a standardized view. The NFS protocol allows heterogeneous clients' processes, probably running on different machines and under different operating systems, to access files on a distant server, ignoring the actual location of files. Relying on a single server results in the NFS protocol suffering from potentially low availability and poor scalability. Using multiple servers does not solve the availability problem since each server is working independently. The model of NFS is a remote file service. This model is also called the remote access model, which is in contrast with the upload/download model: Remote access model: Provides transparency, the client has access to a file. He sends requests to the remote file (while the file remains on the server).
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Distributed file system for cloud
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Architectures
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Upload/download model: The client can access the file only locally. It means that the client has to download the file, make modifications, and upload it again, to be used by others' clients.The file system used by NFS is almost the same as the one used by Unix systems. Files are hierarchically organized into a naming graph in which directories and files are represented by nodes.
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Distributed file system for cloud
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Architectures
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Cluster-based architectures A cluster-based architecture ameliorates some of the issues in client-server architectures, improving the execution of applications in parallel. The technique used here is file-striping: a file is split into multiple chunks, which are "striped" across several storage servers. The goal is to allow access to different parts of a file in parallel. If the application does not benefit from this technique, then it would be more convenient to store different files on different servers. However, when it comes to organizing a distributed file system for large data centers, such as Amazon and Google, that offer services to web clients allowing multiple operations (reading, updating, deleting,...) to a large number of files distributed among a large number of computers, then cluster-based solutions become more beneficial. Note that having a large number of computers may mean more hardware failures. Two of the most widely used distributed file systems (DFS) of this type are the Google File System (GFS) and the Hadoop Distributed File System (HDFS). The file systems of both are implemented by user level processes running on top of a standard operating system (Linux in the case of GFS).
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Distributed file system for cloud
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Architectures
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Design principles Goals Google File System (GFS) and Hadoop Distributed File System (HDFS) are specifically built for handling batch processing on very large data sets.
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Distributed file system for cloud
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Architectures
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For that, the following hypotheses must be taken into account: High availability: the cluster can contain thousands of file servers and some of them can be down at any time A server belongs to a rack, a room, a data center, a country, and a continent, in order to precisely identify its geographical location The size of a file can vary from many gigabytes to many terabytes. The file system should be able to support a massive number of files The need to support append operations and allow file contents to be visible even while a file is being written Communication is reliable among working machines: TCP/IP is used with a remote procedure call RPC communication abstraction. TCP allows the client to know almost immediately when there is a problem and a need to make a new connection.
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Distributed file system for cloud
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Architectures
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Load balancing Load balancing is essential for efficient operation in distributed environments. It means distributing work among different servers, fairly, in order to get more work done in the same amount of time and to serve clients faster. In a system containing N chunkservers in a cloud (N being 1000, 10000, or more), where a certain number of files are stored, each file is split into several parts or chunks of fixed size (for example, 64 megabytes), the load of each chunkserver being proportional to the number of chunks hosted by the server. In a load-balanced cloud, resources can be efficiently used while maximizing the performance of MapReduce-based applications.
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Distributed file system for cloud
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Architectures
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Load rebalancing In a cloud computing environment, failure is the norm, and chunkservers may be upgraded, replaced, and added to the system. Files can also be dynamically created, deleted, and appended. That leads to load imbalance in a distributed file system, meaning that the file chunks are not distributed equitably between the servers.
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Distributed file system for cloud
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Architectures
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Distributed file systems in clouds such as GFS and HDFS rely on central or master servers or nodes (Master for GFS and NameNode for HDFS) to manage the metadata and the load balancing. The master rebalances replicas periodically: data must be moved from one DataNode/chunkserver to another if free space on the first server falls below a certain threshold. However, this centralized approach can become a bottleneck for those master servers, if they become unable to manage a large number of file accesses, as it increases their already heavy loads. The load rebalance problem is NP-hard.In order to get a large number of chunkservers to work in collaboration, and to solve the problem of load balancing in distributed file systems, several approaches have been proposed, such as reallocating file chunks so that the chunks can be distributed as uniformly as possible while reducing the movement cost as much as possible.
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Distributed file system for cloud
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Architectures
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Google file system Description Google, one of the biggest internet companies, has created its own distributed file system, named Google File System (GFS), to meet the rapidly growing demands of Google's data processing needs, and it is used for all cloud services. GFS is a scalable distributed file system for data-intensive applications. It provides fault-tolerant, high-performance data storage a large number of clients accessing it simultaneously.
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Distributed file system for cloud
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Architectures
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GFS uses MapReduce, which allows users to create programs and run them on multiple machines without thinking about parallelization and load-balancing issues. GFS architecture is based on having a single master server for multiple chunkservers and multiple clients.The master server running in dedicated node is responsible for coordinating storage resources and managing files's metadata (the equivalent of, for example, inodes in classical file systems).
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Distributed file system for cloud
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Architectures
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Each file is split into multiple chunks of 64 megabytes. Each chunk is stored in a chunk server. A chunk is identified by a chunk handle, which is a globally unique 64-bit number that is assigned by the master when the chunk is first created.
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Distributed file system for cloud
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Architectures
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The master maintains all of the files's metadata, including file names, directories, and the mapping of files to the list of chunks that contain each file's data. The metadata is kept in the master server's main memory, along with the mapping of files to chunks. Updates to this data are logged to an operation log on disk. This operation log is replicated onto remote machines. When the log becomes too large, a checkpoint is made and the main-memory data is stored in a B-tree structure to facilitate mapping back into the main memory.
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Distributed file system for cloud
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Architectures
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Fault tolerance To facilitate fault tolerance, each chunk is replicated onto multiple (default, three) chunk servers. A chunk is available on at least one chunk server. The advantage of this scheme is simplicity. The master is responsible for allocating the chunk servers for each chunk and is contacted only for metadata information. For all other data, the client has to interact with the chunk servers.
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Distributed file system for cloud
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Architectures
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The master keeps track of where a chunk is located. However, it does not attempt to maintain the chunk locations precisely but only occasionally contacts the chunk servers to see which chunks they have stored. This allows for scalability, and helps prevent bottlenecks due to increased workload.In GFS, most files are modified by appending new data and not overwriting existing data. Once written, the files are usually only read sequentially rather than randomly, and that makes this DFS the most suitable for scenarios in which many large files are created once but read many times.
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Distributed file system for cloud
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Architectures
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File processing When a client wants to write-to/update a file, the master will assign a replica, which will be the primary replica if it is the first modification. The process of writing is composed of two steps: Sending: First, and by far the most important, the client contacts the master to find out which chunk servers hold the data. The client is given a list of replicas identifying the primary and secondary chunk servers. The client then contacts the nearest replica chunk server, and sends the data to it. This server will send the data to the next closest one, which then forwards it to yet another replica, and so on. The data is then propagated and cached in memory but not yet written to a file.
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Distributed file system for cloud
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Architectures
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Writing: When all the replicas have received the data, the client sends a write request to the primary chunk server, identifying the data that was sent in the sending phase. The primary server will then assign a sequence number to the write operations that it has received, apply the writes to the file in serial-number order, and forward the write requests in that order to the secondaries. Meanwhile, the master is kept out of the loop.Consequently, we can differentiate two types of flows: the data flow and the control flow. Data flow is associated with the sending phase and control flow is associated to the writing phase. This assures that the primary chunk server takes control of the write order.
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Distributed file system for cloud
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Architectures
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Note that when the master assigns the write operation to a replica, it increments the chunk version number and informs all of the replicas containing that chunk of the new version number. Chunk version numbers allow for update error-detection, if a replica wasn't updated because its chunk server was down.Some new Google applications did not work well with the 64-megabyte chunk size. To solve that problem, GFS started, in 2004, to implement the Bigtable approach.
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Distributed file system for cloud
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Architectures
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Hadoop distributed file system HDFS , developed by the Apache Software Foundation, is a distributed file system designed to hold very large amounts of data (terabytes or even petabytes). Its architecture is similar to GFS, i.e. a server/client architecture. The HDFS is normally installed on a cluster of computers.
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Distributed file system for cloud
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Architectures
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The design concept of Hadoop is informed by Google's, with Google File System, Google MapReduce and Bigtable, being implemented by Hadoop Distributed File System (HDFS), Hadoop MapReduce, and Hadoop Base (HBase) respectively. Like GFS, HDFS is suited for scenarios with write-once-read-many file access, and supports file appends and truncates in lieu of random reads and writes to simplify data coherency issues.An HDFS cluster consists of a single NameNode and several DataNode machines. The NameNode, a master server, manages and maintains the metadata of storage DataNodes in its RAM. DataNodes manage storage attached to the nodes that they run on. NameNode and DataNode are software designed to run on everyday-use machines, which typically run under a Linux OS. HDFS can be run on any machine that supports Java and therefore can run either a NameNode or the Datanode software.On an HDFS cluster, a file is split into one or more equal-size blocks, except for the possibility of the last block being smaller. Each block is stored on multiple DataNodes, and each may be replicated on multiple DataNodes to guarantee availability. By default, each block is replicated three times, a process called "Block Level Replication".The NameNode manages the file system namespace operations such as opening, closing, and renaming files and directories, and regulates file access. It also determines the mapping of blocks to DataNodes. The DataNodes are responsible for servicing read and write requests from the file system's clients, managing the block allocation or deletion, and replicating blocks.When a client wants to read or write data, it contacts the NameNode and the NameNode checks where the data should be read from or written to. After that, the client has the location of the DataNode and can send read or write requests to it.
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Distributed file system for cloud
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Architectures
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The HDFS is typically characterized by its compatibility with data rebalancing schemes. In general, managing the free space on a DataNode is very important. Data must be moved from one DataNode to another, if free space is not adequate; and in the case of creating additional replicas, data should be moved to assure system balance.
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Distributed file system for cloud
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Architectures
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Other examples Distributed file systems can be optimized for different purposes. Some, such as those designed for internet services, including GFS, are optimized for scalability. Other designs for distributed file systems support performance-intensive applications usually executed in parallel. Some examples include: MapR File System (MapR-FS), Ceph-FS, Fraunhofer File System (BeeGFS), Lustre File System, IBM General Parallel File System (GPFS), and Parallel Virtual File System.
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Distributed file system for cloud
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Architectures
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MapR-FS is a distributed file system that is the basis of the MapR Converged Platform, with capabilities for distributed file storage, a NoSQL database with multiple APIs, and an integrated message streaming system. MapR-FS is optimized for scalability, performance, reliability, and availability. Its file storage capability is compatible with the Apache Hadoop Distributed File System (HDFS) API but with several design characteristics that distinguish it from HDFS. Among the most notable differences are that MapR-FS is a fully read/write filesystem with metadata for files and directories distributed across the namespace, so there is no NameNode.Ceph-FS is a distributed file system that provides excellent performance and reliability. It answers the challenges of dealing with huge files and directories, coordinating the activity of thousands of disks, providing parallel access to metadata on a massive scale, manipulating both scientific and general-purpose workloads, authenticating and encrypting on a large scale, and increasing or decreasing dynamically due to frequent device decommissioning, device failures, and cluster expansions.BeeGFS is the high-performance parallel file system from the Fraunhofer Competence Centre for High Performance Computing. The distributed metadata architecture of BeeGFS has been designed to provide the scalability and flexibility needed to run HPC and similar applications with high I/O demands.Lustre File System has been designed and implemented to deal with the issue of bottlenecks traditionally found in distributed systems. Lustre is characterized by its efficiency, scalability, and redundancy. GPFS was also designed with the goal of removing such bottlenecks.
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Distributed file system for cloud
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Communication
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High performance of distributed file systems requires efficient communication between computing nodes and fast access to the storage systems. Operations such as open, close, read, write, send, and receive need to be fast, to ensure that performance. For example, each read or write request accesses disk storage, which introduces seek, rotational, and network latencies.The data communication (send/receive) operations transfer data from the application buffer to the machine kernel, TCP controlling the process and being implemented in the kernel. However, in case of network congestion or errors, TCP may not send the data directly. While transferring data from a buffer in the kernel to the application, the machine does not read the byte stream from the remote machine. In fact, TCP is responsible for buffering the data for the application.Choosing the buffer-size, for file reading and writing, or file sending and receiving, is done at the application level. The buffer is maintained using a circular linked list. It consists of a set of BufferNodes. Each BufferNode has a DataField. The DataField contains the data and a pointer called NextBufferNode that points to the next BufferNode. To find the current position, two pointers are used: CurrentBufferNode and EndBufferNode, that represent the position in the BufferNode for the last write and read positions.
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Distributed file system for cloud
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Communication
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If the BufferNode has no free space, it will send a wait signal to the client to wait until there is available space.
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Distributed file system for cloud
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Cloud-based Synchronization of Distributed File System
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More and more users have multiple devices with ad hoc connectivity. The data sets replicated on these devices need to be synchronized among an arbitrary number of servers. This is useful for backups and also for offline operation. Indeed, when user network conditions are not good, then the user device will selectively replicate a part of data that will be modified later and off-line. Once the network conditions become good, the device is synchronized. Two approaches exist to tackle the distributed synchronization issue: user-controlled peer-to-peer synchronization and cloud master-replica synchronization.
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Distributed file system for cloud
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Cloud-based Synchronization of Distributed File System
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user-controlled peer-to-peer: software such as rsync must be installed in all users' computers that contain their data. The files are synchronized by peer-to-peer synchronization where users must specify network addresses and synchronization parameters, and is thus a manual process.
cloud master-replica synchronization: widely used by cloud services, in which a master replica is maintained in the cloud, and all updates and synchronization operations are to this master copy, offering a high level of availability and reliability in case of failures.
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Distributed file system for cloud
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Security keys
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In cloud computing, the most important security concepts are confidentiality, integrity, and availability ("CIA"). Confidentiality becomes indispensable in order to keep private data from being disclosed. Integrity ensures that data is not corrupted.
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Distributed file system for cloud
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Security keys
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Confidentiality Confidentiality means that data and computation tasks are confidential: neither cloud provider nor other clients can access the client's data. Much research has been done about confidentiality, because it is one of the crucial points that still presents challenges for cloud computing. A lack of trust in the cloud providers is also a related issue. The infrastructure of the cloud must ensure that customers' data will not be accessed by unauthorized parties.
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Distributed file system for cloud
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Security keys
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The environment becomes insecure if the service provider can do all of the following: locate the consumer's data in the cloud access and retrieve consumer's data understand the meaning of the data (types of data, functionalities and interfaces of the application and format of the data).The geographic location of data helps determine privacy and confidentiality. The location of clients should be taken into account. For example, clients in Europe won't be interested in using datacenters located in United States, because that affects the guarantee of the confidentiality of data. In order to deal with that problem, some cloud computing vendors have included the geographic location of the host as a parameter of the service-level agreement made with the customer, allowing users to choose themselves the locations of the servers that will host their data.
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Distributed file system for cloud
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Security keys
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Another approach to confidentiality involves data encryption. Otherwise, there will be serious risk of unauthorized use. A variety of solutions exists, such as encrypting only sensitive data, and supporting only some operations, in order to simplify computation. Furthermore, cryptographic techniques and tools as FHE, are used to preserve privacy in the cloud.
Integrity Integrity in cloud computing implies data integrity as well as computing integrity. Such integrity means that data has to be stored correctly on cloud servers and, in case of failures or incorrect computing, that problems have to be detected.
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Distributed file system for cloud
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Security keys
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Data integrity can be affected by malicious events or from administration errors (e.g. during backup and restore, data migration, or changing memberships in P2P systems).Integrity is easy to achieve using cryptography (typically through message-authentication code, or MACs, on data blocks).There exist checking mechanisms that effect data integrity. For instance: HAIL (High-Availability and Integrity Layer) is a distributed cryptographic system that allows a set of servers to prove to a client that a stored file is intact and retrievable.
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Distributed file system for cloud
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Security keys
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Hach PORs (proofs of retrievability for large files) is based on a symmetric cryptographic system, where there is only one verification key that must be stored in a file to improve its integrity. This method serves to encrypt a file F and then generate a random string named "sentinel" that must be added at the end of the encrypted file. The server cannot locate the sentinel, which is impossible differentiate from other blocks, so a small change would indicate whether the file has been changed or not.
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Distributed file system for cloud
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Security keys
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PDP (provable data possession) checking is a class of efficient and practical methods that provide an efficient way to check data integrity on untrusted servers: PDP: Before storing the data on a server, the client must store, locally, some meta-data. At a later time, and without downloading data, the client is able to ask the server to check that the data has not been falsified. This approach is used for static data.
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Distributed file system for cloud
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Security keys
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Scalable PDP: This approach is premised upon a symmetric-key, which is more efficient than public-key encryption. It supports some dynamic operations (modification, deletion, and append) but it cannot be used for public verification.
Dynamic PDP: This approach extends the PDP model to support several update operations such as append, insert, modify, and delete, which is well suited for intensive computation.
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Distributed file system for cloud
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Security keys
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Availability Availability is generally effected by replication. Meanwhile, consistency must be guaranteed. However, consistency and availability cannot be achieved at the same time; each is prioritized at some sacrifice of the other. A balance must be struck.Data must have an identity to be accessible. For instance, Skute is a mechanism based on key/value storage that allows dynamic data allocation in an efficient way. Each server must be identified by a label in the form continent-country-datacenter-room-rack-server. The server can reference multiple virtual nodes, with each node having a selection of data (or multiple partitions of multiple data). Each piece of data is identified by a key space which is generated by a one-way cryptographic hash function (e.g. MD5) and is localised by the hash function value of this key. The key space may be partitioned into multiple partitions with each partition referring to a piece of data. To perform replication, virtual nodes must be replicated and referenced by other servers. To maximize data durability and data availability, the replicas must be placed on different servers and every server should be in a different geographical location, because data availability increases with geographical diversity. The process of replication includes an evaluation of space availability, which must be above a certain minimum thresh-hold on each chunk server. Otherwise, data are replicated to another chunk server. Each partition, i, has an availability value represented by the following formula: availi=∑i=0|si|∑j=i+1|si|confi.confj.diversity(si,sj) where si are the servers hosting the replicas, confi and confj are the confidence of servers i and j (relying on technical factors such as hardware components and non-technical ones like the economic and political situation of a country) and the diversity is the geographical distance between si and sj .Replication is a great solution to ensure data availability, but it costs too much in terms of memory space. DiskReduce is a modified version of HDFS that's based on RAID technology (RAID-5 and RAID-6) and allows asynchronous encoding of replicated data. Indeed, there is a background process which looks for widely replicated data and deletes extra copies after encoding it. Another approach is to replace replication with erasure coding. In addition, to ensure data availability there are many approaches that allow for data recovery. In fact, data must be coded, and if it is lost, it can be recovered from fragments which were constructed during the coding phase. Some other approaches that apply different mechanisms to guarantee availability are: Reed-Solomon code of Microsoft Azure and RaidNode for HDFS. Also Google is still working on a new approach based on an erasure-coding mechanism.There is no RAID implementation for cloud storage.
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Distributed file system for cloud
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Economic aspects
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The cloud computing economy is growing rapidly. The US government has decided to spend 40% of its compound annual growth rate (CAGR), expected to be 7 billion dollars by 2015.More and more companies have been utilizing cloud computing to manage the massive amount of data and to overcome the lack of storage capacity, and because it enables them to use such resources as a service, ensuring that their computing needs will be met without having to invest in infrastructure (Pay-as-you-go model).Every application provider has to periodically pay the cost of each server where replicas of data are stored. The cost of a server is determined by the quality of the hardware, the storage capacities, and its query-processing and communication overhead. Cloud computing allows providers to scale their services according to client demands.
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Distributed file system for cloud
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Economic aspects
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The pay-as-you-go model has also eased the burden on startup companies that wish to benefit from compute-intensive business. Cloud computing also offers an opportunity to many third-world countries that wouldn't have such computing resources otherwise. Cloud computing can lower IT barriers to innovation.Despite the wide utilization of cloud computing, efficient sharing of large volumes of data in an untrusted cloud is still a challenge.
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Aggressive NK-cell leukemia
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Aggressive NK-cell leukemia
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Aggressive NK-cell leukemia is a disease with an aggressive, systemic proliferation of natural killer cells (NK cells) and a rapidly declining clinical course.It is also called aggressive NK-cell lymphoma.
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Aggressive NK-cell leukemia
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Signs and symptoms
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Patients usually present with constitutional symptoms (malaise, weight loss, fatigue), and hepatosplenomegaly is commonly found on physical exam. Lymphadenopathy is also found to a lesser extent. Due to the aggressive nature of the disease, patients may initially present at a more advanced stage, with coagulopathies, hemophagocytic syndrome, and multi-organ failure. Rarely, individuals who have an aggressive NK cell lymphoma that is associated with latent infection with the Epstein-Barr virus (see next section) present with or develop extensive allergic reactions to mosquito bites. The symptoms of these reactions range from a greatly enlarged bite site that may be painful and involve necrosis to systemic symptoms (e.g. fever, swollen lymph nodes, abdominal pain, and diarrhea), or, in extremely rare cases, to life-threatening anaphylaxis.
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Aggressive NK-cell leukemia
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Cause
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This disease has a strong association with the Epstein–Barr virus (EBV), but the true pathogenesis of this disease has yet to be described. The cell of origin is believed to be an NK cell. Blastoid NK cell lymphoma appears to be a different entity and shows no association with EBV.
Sites of involvement This disease is typically found and diagnosed in peripheral blood, and while it can involve any organ, it is usually found in the spleen, liver, and bone marrow.
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Aggressive NK-cell leukemia
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Diagnosis
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Leukemic cells are invariably present in samples of peripheral blood to a variable extent. Pancytopenia (anemia, neutropenia, thrombocytopenia) is commonly seen as well.
Peripheral blood The leukemic cells have a diameter mildly greater than a large granular lymphocyte (LGL) and have azurophilic granules and nucleoli of varying prominence. Nuclei may be irregular and hyperchromatic.
Bone marrow Bone marrow involvement runs the spectrum between an inconspicuous infiltrate to extensive marrow replacement by leukemic cells. Reactive histiocytes displaying hemophagocytosis can be seen interspersed in the neoplastic infiltrate.
Other organs Leukemic involvement of organs is typically destructive on tissue sections with necrosis and possibly angioinvasion, and the monotonous infiltrate may be diffuse or patchy.
Immunophenotype The immunophenotype of this disease is the same as extranodal NK/T-cell lymphoma, nasal type and is shown in the table below. CD11b and CD16 show variable expression.
Genetic findings Due to the NK lineage, clonal rearrangements of lymphoid (T cell receptor; B cell receptor) genes are not seen. The genome of the Epstein Barr virus (EBV) is detected in many cases, along with a variety of chromosomal abnormalities.
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Aggressive NK-cell leukemia
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Treatment
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Currently Aggressive NK-cell leukemia, being a subtype of PTCL, is treated similarly to B-cell lymphomas. However, in recent years, scientists have developed techniques to better recognize the different types of lymphomas, such as PTCL. It is now understood that PTCL behaves differently from B-cell lymphomas and therapies are being developed that specifically target these types of lymphoma. Currently, however, there are no therapies approved by the U.S. Food and Drug Administration (FDA) specifically for PTCL. Anthracycline-containing chemotherapy regimens are commonly offered as the initial therapy. Some patients may receive a stem cell transplant. Novel approaches to the treatment of PTCL in the relapsed or refractory setting are under investigation.
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Aggressive NK-cell leukemia
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Epidemiology
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This rare form of leukemia is more common among Asians in comparison to other ethnic groups. It is typically diagnosed in adolescents and young adults, with a slight predominance in males.
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Aggressive NK-cell leukemia
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Research directions
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Pralatrexate is one compound currently under investigations for the treatment of PTCL.
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FR-4
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FR-4
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FR-4 (or FR4) is a NEMA grade designation for glass-reinforced epoxy laminate material. FR-4 is a composite material composed of woven fiberglass cloth with an epoxy resin binder that is flame resistant (self-extinguishing).
"FR" stands for "flame retardant", and does not denote that the material complies with the standard UL94V-0 unless testing is performed to UL 94, Vertical Flame testing in Section 8 at a compliant lab. The designation FR-4 was created by NEMA in 1968.
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FR-4
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FR-4
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FR-4 glass epoxy is a popular and versatile high-pressure thermoset plastic laminate grade with good strength to weight ratios. With near zero water absorption, FR-4 is most commonly used as an electrical insulator possessing considerable mechanical strength. The material is known to retain its high mechanical values and electrical insulating qualities in both dry and humid conditions. These attributes, along with good fabrication characteristics, lend utility to this grade for a wide variety of electrical and mechanical applications.
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FR-4
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FR-4
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Grade designations for glass epoxy laminates are: G-10, G-11, FR-4, FR-5 and FR-6. Of these, FR-4 is the grade most widely in use today. G-10, the predecessor to FR-4, lacks FR-4's self-extinguishing flammability characteristics. Hence, FR-4 has since replaced G-10 in most applications.
FR-4 epoxy resin systems typically employ bromine, a halogen, to facilitate flame-resistant properties in FR-4 glass epoxy laminates. Some applications where thermal destruction of the material is a desirable trait will still use G-10 non flame resistant.
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FR-4
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Properties
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Which materials fall into the "FR-4" category is defined in the NEMA LI 1-1998 standard. Typical physical and electrical properties of FR-4 are as follows. The abbreviations LW (lengthwise, warp yarn direction) and CW (crosswise, fill yarn direction) refer to the conventional perpendicular fiber orientations in the XY plane of the board (in-plane). In terms of Cartesian coordinates, lengthwise is along the x-axis, crosswise is along the y-axis, and the z-axis is referred to as the through-plane direction. The values shown below are an example of a certain manufacturer's material. Another manufacturer's material will usually have slightly different values. Checking the actual values, for any particular material, from the manufacturer's datasheet, can be very important, for example in high frequency applications.
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FR-4
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Properties
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where: LW Lengthwise CW Crosswise PF Perpendicular to laminate face
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FR-4
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Applications
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FR-4 is a common material for printed circuit boards (PCBs). A thin layer of copper foil is typically laminated to one or both sides of an FR-4 glass epoxy panel. These are commonly referred to as copper clad laminates. The copper thickness or copper weight can vary and so is specified separately. FR-4 is also used in the construction of relays, switches, standoffs, busbars, washers, arc shields, transformers and screw terminal strips.
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Potassium trichloridocuprate(II)
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Potassium trichloridocuprate(II)
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Potassium trichloridocuprate(II) is a salt with chemical formula KCuCl3, more properly [K+]2[Cu2Cl2−4].It is a member of the "halide" sub-family of perovskite materials with general formula ABX3 where A is a monovalent cation, B is a divalent cation, and X is a halide anion.The compound occurs in nature as the bright red mineral sanguite.The compound is also called potassium trichlorocuprate(II), potassium copper(II) trichloride, potassium cupric chloride and other similar names. The latter is used also for potassium tetrachloridocuprate(II) K2CuCl4.
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Potassium trichloridocuprate(II)
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Preparation and properties
|
The compound can be obtained by evaporation of a solution of potassium chloride KCl and copper(II) chloride CuCl2 in 1:1 mole ratio.The anhydrous form is garnet-red. It can be crystallized from a molten mixture of potassium chloride KCl and copper(II) chloride CuCl2. or by evaporation from a solution of the salts in ethanol. It is very hygroscopic, and soluble in methanol and ethanol. It is antiferromagnetic below 30 K, and pleochroic, with maximum visible absorption when the electric vector is parallel to the Cu–Cu vector of the dimer.
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Potassium trichloridocuprate(II)
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Structure
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Anhydrous The anhydrous mineral form (sanguite) has the monoclinic crystal structure, with symmetry group P21/c and lattice parameters a = 402.81 pm, b = 1379.06 pm, c = 873.35 pm, and β = 97.137°, cell volume V = 0.48138 nm3, and formulas per cell Z = 4. The measured density is 2.86 g/cm3, close to the calculated one 2.88 g/cm3. It contains discrete almost planar anions [Cu2Cl6]2−, each with the two copper atoms connected by two bridging chlorine atoms. These anions are arranged in columns consisting of distorted edge-sharing CuCl6 octahedra, stacked in double chains parallel to the a axis. The columns occupy the edges and the centre of the cell's projection on the bc plane. The potassium atoms are located between these columns; each K+ cation is surrounded by nine chlorine atoms. The mineral is optically biaxial (negative), with α = 1.653, β = 1.780, γ = 1.900', 2V= 85°. The mineral is named from the Latin sanguis (blood), alluding to its color.Theoretical calculations for this topology give the lattice parameters as a = 1388.1 pm, b = 427.7 pm, c = 896.5 pm, α = 79.855°, cell volume V = 0.523891 nm3, calculated density 2.65 g/cm3.
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Potassium trichloridocuprate(II)
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Structure
|
Theoretical An alternative theoretical structure for the compound has a cubic crystal system, symmetry group Pm3m[221], with the copper atoms arranged as corners of a cubic grid, a potassium atom at the center of each cube and a chlorine atom at the midpoint of each edge. The latice parameters are a = b = c = 485.8 pm, V = 0.114684 nm3, predicted density 3.03 g/cm3.
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Penis envy
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Penis envy
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Penis envy (German: Penisneid) is an idea in psychoanalytic theory. This is a stage theorized by Sigmund Freud regarding female psychosexual development, in which young girls experience anxiety upon realization that they do not have a penis. Freud considered this realization a defining moment in a series of transitions toward a mature female sexuality. In Freudian theory, the penis envy stage begins the transition from an attachment to the mother to competition with the mother for the attention, recognition and affection of the father. The parallel reaction of a boy's realization that women do not have a penis is castration anxiety.
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Penis envy
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Penis envy
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Freud's theory on penis envy was criticized and debated by other psychoanalysts, such as Karen Horney, Ernest Jones, Helene Deutsch, and Melanie Klein, specifically on the treatment of penis envy as a fixed operation as opposed to a formation constructed or used in a secondary manner to fend off earlier wishes.
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Penis envy
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Freud's theory
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Freud introduced the concept of interest and envy of the penis in his 1908 article "On the Sexual Theories of Children." It was not mentioned in the first edition of Freud's earlier Three Contributions to the Theory of Sex (1905), but a synopsis of the 1908 article was added to the third edition in 1915. In On Narcissism (1914) he described how some women develop a masculine ideal as "a survival of the boyish nature that they themselves once possessed". The term grew in significance as Freud gradually refined his views of sexuality, coming to describe a mental process he believed occurred as one went from the phallic stage to the latency stage (see Psychosexual development.) Psychosexual development Child Penis envy stems from Freud's concept of the Oedipus complex in which the phallic conflict arises for males, as well as for females. Though Carl Jung made the distinction between the Oedipus complex for males and the Electra complex for females in his work The Theory of Psychoanalysis, Freud rejected this latter term, stating that the feminine Oedipus complex is not the same as the male Oedipus because, "It is only in the male child that we find the fateful combination of love for the one parent and simultaneous hatred of the other as a rival." This development of the female Oedipus complex according to Freud begins when the female makes comparisons with another male, perceiving this not as a sex characteristic; but rather, by assuming that she had previously possessed a penis, and had lost it by castration. This leads to the essential difference between the male and female Oedipus complex that the female accepts castration as a fact, while the boy fears it happening.Freud felt that penis envy may lead to: Resentment towards the mother who failed to provide the daughter with a penis Depreciation of the mother who appears to be castrated Giving up on phallic activity (clitoral masturbation) and adopting passivity (vaginal intercourse) A symbolic equivalence between penis and childThis envy towards the penis leads to various psychical consequences according to Freud, so long as it does not form into a reaction-formation of a masculinity complex. One such consequence is a sense of inferiority after becoming aware of the wound inflicted upon her narcissism. After initially attempting to explain this lack of a penis as a punishment towards her, she later realizes the universality of her female situation, and as a result begins to share the contempt that men have towards women as a lesser (in the important respect of a lack of a penis), and so insists upon being like a man. A second consequence of penis envy involves the formation of the character-trait of jealousy through displacement of the abandoned penis envy upon maturation. Freud concludes this from considering the common female fantasy of a child being beaten to be a confession of masturbation, with the child representing the clitoris. A third consequence of penis envy involves the discovery of the inferiority of this clitoris, suggested through the observation that masturbation is further removed from females than from males. This is, according to Freud, because clitoral masturbation is a masculine activity that is slowly repressed throughout puberty (and shortly after discovering the penis envy) in an attempt to make room for the female's femininity by transitioning the erotogenic zone from the clitoris to the vagina.The result of these anxieties culminates in the girl giving up on her desire for the penis, and instead puts it in the place of the wish for a child; and, with that goal in mind, she takes her father as the love-object and makes the mother into the object of her jealousy.
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Penis envy
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Freud's theory
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Adult Freud considered that in normal female development penis envy transformed into the wish for a man and/or a baby.Karl Abraham differentiated two types of adult women in whom penis envy remained intense as the wish-fulfilling and the vindictive types: The former were dominated by fantasies of having or becoming a penis—as with the singing/dancing/performing women who felt that in their acts they magically incorporated the (parental) phallus. The latter sought revenge on the male through humiliation or deprivation (whether by removing the man from the penis or the penis from the man).
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Penis envy
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Society and culture
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Within psychoanalytic circles Freud's theories regarding psychosexual development, and in particular the phallic stage, were challenged early by other psychoanalysts, such as Karen Horney, Otto Fenichel and Ernest Jones, though Freud did not accept their view of penis envy as a secondary, rather than a primary, female reaction. Later psychologists, such as Erik Erikson and Jean Piaget, challenged the Freudian model of child psychological development as a whole.
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Penis envy
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Society and culture
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Jacques Lacan, however, took up and developed Freud's theory of the importance of what he called "penisneid in the unconscious of women" in linguistic terms, seeing what he called the phallus as the privileged signifier of humanity's subordination to language: "the phallus (by virtue of which the unconscious is language)". He thereby opened up a new field of debate around phallogocentrism—some figures like Juliet Mitchell endorsing a view of penis envy which "uses, not the man, but the phallus to which the man has to lay claim, as its key term", others strongly repudiating it.Ernest Jones attempted to remedy Freud's initial theory penis envy by giving three alternative meanings: The wish to acquire a penis, usually by swallowing it and retaining it within the body, often converting it there into a baby The wish to possess a penis in the clitoris region The adult wish to enjoy a penis in intercourse Feminist criticisms In Freud's theory, the female sexual center shifts from the clitoris to the vagina during a heterosexual life event. Freud believed in a duality between how genders construct mature sexuality in terms of the opposite gender, whereas feminists reject the notion that female sexuality can only be defined in relation to the male. Feminist development theorists instead believe that the clitoris, not the vagina, is the mature center of female sexuality because it allows a construction of mature female sexuality independent of the penis.Karen Horney — a German psychoanalyst who also placed great emphasis on childhood experiences in psychological development — was a particular advocate of this view. She asserted the concept of "womb envy", and saw "masculine narcissism" as underlying the mainstream Freudian view.
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Penis envy
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Society and culture
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Some feminists argue that Freud's developmental theory is heteronormative and denies women a mature sexuality independent of men; they also criticize it for privileging the vagina over the clitoris as the center of women's sexuality. They criticize the sociosexual theory for privileging heterosexual sexual activity and penile penetration in defining women's "mature state of sexuality". Others claim that the concept explains how, in a patriarchal society, women might envy the power accorded to those with a phallus.In her academic paper "Women and Penis Envy" (1943), Clara Thompson reformulated the latter as social envy for the trappings of the dominant gender, a sociological response to female subordination under patriarchy.Betty Friedan referred to penis envy as a purely parasitic social bias typical of Victorianism and particularly of Freud's own biography, and showed how the concept played a key role in discrediting alternative notions of femininity in the early to mid twentieth century: "Because Freud's followers could only see woman in the image defined by Freud – inferior, childish, helpless, with no possibility of happiness unless she adjusted to being man's passive object – they wanted to help women get rid of their suppressed envy, their neurotic desire to be equal. They wanted to help women find sexual fulfillment as women, by affirming their natural inferiority".A small but influential number of feminist philosophers, working in psychoanalytic feminism, and including Luce Irigaray, Julia Kristeva, and Hélène Cixous, have taken varying post-structuralist views on the question, inspired or at least challenged by figures such as Jacques Lacan and Jacques Derrida.
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Hypotrichosis with juvenile macular dystrophy
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Hypotrichosis with juvenile macular dystrophy
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Hypotrichosis with juvenile macular dystrophy (HJMD or CDH3) is an extremely rare congenital disease characterized by sparse hair growth (hypotrichosis) from birth and progressive macular corneal dystrophy.
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Hypotrichosis with juvenile macular dystrophy
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Signs and symptoms
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Hair growth on the head is noticeably less full than normal, and the hairs are very weak; the rest of the body shows normal hair. The macular degeneration comes on slowly with deterioration of central vision, leading to a loss of reading ability. Those affected may otherwise develop in a completely healthy manner; life expectancy is normal.
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Hypotrichosis with juvenile macular dystrophy
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Cause
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Hypotrichosis with juvenile macular dystrophy is an autosomal recessive hereditary disease. It is caused by a combination of mutations (compound heterozygosity) in the CDH3 gene, which codes for Cadherin-3 (also known as P-Cadherin), a calcium-binding protein that is responsible for cellular adhesion in various tissues.
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Hypotrichosis with juvenile macular dystrophy
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Diagnosis
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The markedly anomalous hair growth should lead to a retinal examination by school entry at the latest, since weak vision will not necessarily be detected in the course of normal medical check-ups. Confirmation of a diagnosis, which is necessary for any future therapeutic options, is only possible by means of a molecular genetic diagnosis in the context of genetic counseling.
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Hypotrichosis with juvenile macular dystrophy
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Diagnosis
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Examination method The extent of retinal damage is assessed by fluorescent angiography, retinal scanning and optical coherence tomography; electrophysiological examinations such as electroretinography (ERG) or multifocal electroretinography (mfERG) may also be used.
Differential diagnosis Anomalies of the hair shaft caused by ectodermal dysplasia should be ruled out. Mutations in the CDH3 gene can also appear in EEM syndrome.
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Hypotrichosis with juvenile macular dystrophy
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Treatment
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There is no treatment for the disorder. A number of studies are looking at gene therapy, exon skipping and CRISPR interference to offer hope for the future. Accurate determination through confirmed diagnosis of the genetic mutation that has occurred also offers potential approaches beyond gene replacement for a specific group, namely in the case of diagnosis of a so-called nonsense mutation, a mutation where a stop codon is produced by the changing of a single base in the DNA sequence. This results in premature termination of protein biosynthesis, resulting in a shortened and either functionless or function-impaired protein. In what is sometimes called "read-through therapy", translational skipping of the stop codon, resulting in a functional protein, can be induced by the introduction of specific substances. However, this approach is only conceivable in the case of narrowly circumscribed mutations, which cause differing diseases.
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Hypotrichosis with juvenile macular dystrophy
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Treatment
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Life planning A disease that threatens the eyesight and additionally produces a hair anomaly that is apparent to strangers causes harm beyond the physical. It is therefore not surprising that learning the diagnosis is a shock to the patient. This is as true of the affected children as of their parents and relatives. They are confronted with a statement that there are at present no treatment options. They probably have never felt so alone and abandoned in their lives. The question comes to mind, "Why me/my child?" However, there is always hope and especially for affected children, the first priority should be a happy childhood. Too many examinations and doctor appointments take up time and cannot practically solve the problem of a genetic mutation within a few months. It is therefore advisable for parents to treat their child with empathy, but to raise him or her to be independent and self-confident by the teenage years. Openness about the disease and talking with those affected about their experiences, even though its rarity makes it unlikely that others will be personally affected by it, will together assist in managing life.
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Hypotrichosis with juvenile macular dystrophy
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Epidemiology
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It is estimated to affect less than one in a million people. Only 50 to 100 cases have so far been described.
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Hypotrichosis with juvenile macular dystrophy
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History
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The disease was first described in 1935 by Hans Wagner, a German physician.
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Hypotrichosis with juvenile macular dystrophy
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Sources
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"A Rare Syndrome: Hypotrichosis with Juvenile Macular Dystrophy (HJMD)". Investigative Ophthalmology & Visual Science. 55 (13): 6424. April 2014.
Online Mendelian Inheritance in Man (OMIM): CADHERIN 3 - 114021 Samuelov, L; Sprecher, E; Tsuruta, D; Bíró, T; Kloepper, J. E.; Paus, R (2012). "P-cadherin regulates human hair growth and cycling via canonical Wnt signaling and transforming growth factor-β2". Journal of Investigative Dermatology. 132 (10): 2332–41. doi:10.1038/jid.2012.171. hdl:2437/149863. PMID 22696062.
Nagel-Wolfrum, K; Möller, F; Penner, I; Wolfrum, U (2014). "Translational read-through as an alternative approach for ocular gene therapy of retinal dystrophies caused by in-frame nonsense mutations". Visual Neuroscience. 31 (4–5): 309–16. doi:10.1017/S0952523814000194. PMID 24912600. S2CID 13191204. (Review).
Gregory-Evans, C. Y.; Wang, X; Wasan, K. M.; Zhao, J; Metcalfe, A. L.; Gregory-Evans, K (2014). "Postnatal manipulation of Pax6 dosage reverses congenital tissue malformation defects". Journal of Clinical Investigation. 124 (1): 111–116. doi:10.1172/JCI70462. PMC 3871240. PMID 24355924.
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Hypotrichosis with juvenile macular dystrophy
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Sources
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Schwarz, N.; Carr, A.-J.; Lane, A.; Moeller, F.; Chen, L. L.; Aguila, M.; Nommiste, B.; Muthiah, M. N.; Kanuga, N.; Wolfrum, U.; Nagel-Wolfrum, K.; Da Cruz, L.; Coffey, P. J.; Cheetham, M. E.; Hardcastle, A. J. (2014). "Translational read-through of the RP2 Arg120stop mutation in patient iPSC-derived retinal pigment epithelium cells". Human Molecular Genetics. 24 (4): 972–86. doi:10.1093/hmg/ddu509. PMC 4986549. PMID 25292197.
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MechQuest
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MechQuest
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MechQuest is an online Flash based single-player sci-fi role-playing video game developed by Artix Entertainment. MechQuest centers on mecha combat and was updated on a weekly basis. Players can play for free or pay a one time fee which grants access to more game content like: a Starship, missions/events, and special Mechas.
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MechQuest
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Gameplay
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MechQuest is a single player RPG; however the character data is stored on a server. Players control their character via pointing and clicking on the screen in various areas to navigate the player character to the point where they click. Most items are activated either simply by running into them, or by pressing a button that will appear when the point is reached (when outside of battle). Battles are presented in two ways, Mecha battles and energy blade battles, both battle styles are similar to a traditional RPG in that much of its game play revolves around fighting enemies in a turn based system. Mecha Battles features a set of many types of attacks but the player must spend energy points to use them.
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MechQuest
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Gameplay
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G.E.A.R.S. University Houses G.E.A.R.S. University Houses are groups that the players can join so they can participate in competitive activities. There are three houses available for players to join: house WolfBlade holds G.E.A.R.S. warriors and heroes, house of RuneHawk is a refuge for science and magic alike, and house of MystRaven is for tricksters who enjoy pranks and shenanigans.
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MechQuest
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Plot
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The player controls a mecha pilot from an unknown location. The game begins with the player on a starship heading towards the planet Loreon, where the player will attend G.E.A.R.S. University in Soluna City. After joining the university, the player is educated and trained in the art of mecha and energy blade combat. The player soon discovers an alien empire called the Shadowscythe, who plan to assimilate the entire galaxy, and uses their newly obtained skills to stop the empire's evil plans.
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MechQuest
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Plot
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Holiday events MechQuest has several recurring holiday events. These include New Years Day, Valentine's Day, April Fools' Day Halloween(named "Mogloween" in game), Christmas (named Frostval in game), Friday the 13th, Talk Like a Pirate Day and Thanksgiving.
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MechQuest
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Critical reception
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Nic Stransky complimented the graphics and simplicity of the game, but wrote that melee could feel inconsistent and that players may wish for more strategy. MMOHuts praised MechQuest for: "Running on flash, for having a classic RPG style turn-based combat, and plenty of gear available for purchase."
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MicroKORG
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MicroKORG
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The microKORG is a MIDI-capable digital synthesizer/vocoder from Korg featuring DSP-based analog modelling. The synthesizer is built in such a way that it is essentially a Korg MS-2000 with a programmable step arpeggiator (the MS-2000 has only six simple patterns), a less advanced vocoder (8 bands instead of 16 bands on the MS-2000), lack of motion sequencing (MS-2000 had three motion sequences), lack of an XLR microphone input, and in a smaller case with fewer real-time control knobs.
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MicroKORG
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MicroKORG
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The microKORG was released in 2002 and is still in production as of 2022. It is considered one of the most popular music synthesizers in recent history, with an estimated 100,000 units sold as of May 2009. In September 2007 Korg released a limited edition of the microKORG with reverse-color keys, although the functionality was otherwise unchanged. At NAMM 2008, a successor dubbed the microKORG XL was introduced. Available since early 2009, it uses Korg's MMT (Multi Modeling Technology) engine, borrowed from the newer and more powerful Radias/R3 synthesizers. Also, in late 2016, a slightly updated version was released, dubbed the MicroKORG S. This edition retains the same sound engine as the original MicroKORG, but offers an integrated speaker system (stereo + sub), updated color scheme & twice the patch memory. In 2022, a VST Version was released as part of the Korg Collection.
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MicroKORG
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Synthesis
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The microKORG features a DSP-based synthesis engine, designed around the same engine found in the Korg MS2000. In Korg's terminology, the fundamental unit of sound is referred to as the "timbre". Each timbre consists of a pair of multi-function oscillators. Two timbres can be combined in one patch to create a four-oscillator "layer", which can in turn be used to create more complex sounds (although doing so halves the polyphony from four notes to two) Oscillator one (OSC1) can produce one of several virtual analog-style waveforms, including sawtooth, square, triangle, and sine waves. Alternatively, OSC1 can produce a so-called "VOX" wave (which simulates human vocal formants), white noise, and one of 64 different digital waveforms created via harmonic additive synthesis. Some of these 64 waveforms (which are really single-cycle wavetables) were originally featured in the Korg DW-6000 & DW-8000 digital-analog hybrid synthesizers of the mid 1980s. The second oscillator (OSC2) is limited to sawtooth, square, and triangle waveforms.
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MicroKORG
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Synthesis
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Each waveform on OSC1 has a unique modulation feature, including wave morphing, Pulse-width modulation, and FM. OSC2 can be detuned, synchronized, and/or ring-modulated with OSC1 in order to create more complex sounds. OSC1 can also be replaced with the signal from one of the line-level inputs on the back of the unit, allowing for external signals to be processed as if they were an oscillator (via the filters, effects, or even ring-modulated by OSC2).
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MicroKORG
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Synthesis
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For further shaping of the sound, the microKORG offers several types of digital filters, including Low Pass (-12dB/Oct and -24dB/Oct), Band Pass (-12dB/Oct), and High Pass (-12dB/Oct) modes.Additionally, the unit provides a number of built-in effects, such as flanger, ensemble (chorus), phaser, and digital delay, all of which can be applied to external signals. For modulation, there are two independent LFOs, with six different waveforms, allowing for the creation of more complex, time-varying patches.
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MicroKORG
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Synthesis
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When playing a single timbre, the keyboard is limited to four-voice polyphony. In layer mode it generally has only two-voice polyphony, although one combination of polyphonic/mono layers allows for effective three-voice polyphony of the second timbre.
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MicroKORG
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Synthesis
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The microKORG groups its 128 factory preset sound patches into 8 groups: Trance Techno/House Electronica D'n'B/Breaks Hip hop/Vintage Retro Special Effects/Hit VocoderA large knob changes the selected sound group. Each group has 16 different patches (two banks of eight); the active patch is selected by the eight LED-illuminated buttons on the front panel, while the accompanying A/B switch toggles between the two banks. All patches are user editable, and do not necessarily have to align with the genre groupings listed on the faceplate.
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MicroKORG
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microKORG S
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In 2016, Korg reissued the microKORG as the modified 'microKORG S'. This edition retains the engine and features of the original microKORG (as opposed to the XL/XL+, see below), but includes a new lighter-colored housing, built-in speakers, twice the original patch memory (256 slots) and a Favorites feature to assign 8 patches to the program buttons for easier selection.
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MicroKORG
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microKORG XL
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The direct successor to the microKORG, the 'microKORG XL', utilizes the MMT (Multi Modelling Technology) engine, and is based on Korg's own R3 synthesizer. The XL features a brand-new LCD display and two large Program Select knobs for easier patch access, though has fewer real-time controls than the original microKORG.
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MicroKORG
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microKORG XL
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The microKORG XL groups its 128 factory preset sound patches into 8 groups: Vintage Synth Rock/Pop R&B/Hip Hop Jazz/Fusion TechnoTrance House/Disco D'N'B/Breaks Favouriteand several sub categories: Poly Synth Bass Lead Arp/Motion Pad/Strings Keyboard/Bell Special Effects/Hit Vocoder New features specific to the microKORG XL Notably, the 'microKORG XL' features 17 different KAOSS derived effects, including phaser, flange, decimation, vibrato, tremolo and retrigger. The XL also features several included PCM Waveforms, including Piano, Brass Ensemble, nine Electric Piano and Clavinet, seven organ sounds (one of which emulates the Korg M1 Organ), a full String Orchestra, two variable formant waves and more than 32 digitally generated waveforms (SYNWAVE 6 is a ramp wave/inverted sawtooth). The XL adds two additional Waveform Modulation types: Phase Modulation and Unison (in which five stacked oscillators within 1 oscillator can be detuned and phased to achieve a richer sound.) The Unison Simulator is similar to the Supersaw waveform on the Roland JP-8000. The included "OSC MOD WAVEFORM" and "OSC2 SYNC" controllers are reminiscent of the Poly-Mod feature in the Sequential Circuits Prophet-5.
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