虛擬儀器（virtual instrumention）是基于計算機的儀器。計算機和儀器的密切結合是目前儀器發(fā)展的一個重要方向。粗略地說這種結合有兩種方式，一種是將計算機裝入儀器，其典型的例子就是所謂智能化的儀器。隨著計算機功能的日益強大以及其體積的日趨縮小，這類儀器功能也越來越強大，目前已經(jīng)出現(xiàn)含嵌入式系統(tǒng)的儀器。另一種方式是將儀器裝入計算機。以通用的計算機硬件及操作系統(tǒng)為依托，實現(xiàn)各種儀器功能。虛擬儀器主要是指這種方式。下面的框圖反映了常見的虛擬儀器方案。 虛擬儀器的主要特點有： n 盡可能采用了通用的硬件，各種儀器的差異主要是軟件。 n 可充分發(fā)揮計算機的能力，有強大的數(shù)據(jù)處理功能，可以創(chuàng)造出功能更強的儀器。 n 用戶可以根據(jù)自己的需要定義和制造各種儀器。 虛擬儀器實際上是一個按照儀器需求組織的數(shù)據(jù)采集系統(tǒng)。虛擬儀器的研究中涉及的基礎理論主要有計算機數(shù)據(jù)采集和數(shù)字信號處理。目前在這一領域內(nèi)，使用較為廣泛的計算機語言是美國NI公司的labview。 虛擬儀器的起源可以追朔到20世紀70年代，那時計算機測控系統(tǒng)在國防、航天等領域已經(jīng)有了相當?shù)陌l(fā)展。PC機出現(xiàn)以后，儀器級的計算機化成為可能，甚至在Microsoft公司的Windows誕生之前，NI公司已經(jīng)在Macintosh計算機上推出了labview2.0以前的版本。對虛擬儀器和labview長期、系統(tǒng)、有效的研究開發(fā)使得該公司成為業(yè)界公認的權威。 普通的PC有一些不可避免的弱點。用它構建的虛擬儀器或計算機測試系統(tǒng)性能不可能太高。目前作為計算機化儀器的一個重要發(fā)展方向是制定了VXI標準，這是一種插卡式的儀器。每一種儀器是一個插卡，為了保證儀器的性能，又采用了較多的硬件，但這些卡式儀器本身都沒有面板，其面板仍然用虛擬的方式在計算機屏幕上出現(xiàn)。這些卡插入標準的VXI機箱，再與計算機相連，就組成了一個測試系統(tǒng)。VXI儀器價格昂貴，目前又推出了一種較為便宜的PXI標準儀器。 虛擬儀器研究的另一個問題是各種標準儀器的互連及與計算機的連接。目前使用較多的是IEEE 488或GPIB協(xié)議。未來的儀器也應當是網(wǎng)絡化的。
上傳時間： 2013-10-15
上傳用戶：gaoliangncepu
Abstract: This application note helps system designers choose the correct external components for use with the MAX16948 dualremote antenna LDO/switch, thus ensuring that automobile-regulated phantom antenna supply and output-current-monitoring circuitrymeet performance objectives. An electronic calculator is provided that helps specify the critical external components for theMAX16948, thus reducing design time. The calculator also determines the device's analog output voltage, output current-limitthreshold, and output current-sensing accuracies. The calculator includes new automatic Step By Step feature that assists designerswith component choice. To use the new automatic feature, click on the Step By Step button relative to the desired section.
上傳時間： 2013-11-04
上傳用戶：lhll918
Attributes, Constraints, and Carry Logic Overview Information for Mentor Customers Schematic Syntax UCF/NCF File Syntax Attributes/Logical Constraints Placement Constraints relative Location (RLOC) Constraints Timing Constraints Physical Constraints Relationally Placed Macros (RPM) Carry Logic in XC4000 FPGAs Carry Logic in XC5200 FPGAs
標簽： Constraints Information Attributes Customers
上傳時間： 2015-05-12
上傳用戶：cc1015285075
The government of a small but important country has decided that the alphabet needs to be streamlined and reordered. Uppercase letters will be eliminated. They will issue a royal decree in the form of a String of B and A characters. The first character in the decree specifies whether a must come ( B )Before b in the new alphabet or ( A )After b . The second character determines the relative placement of b and c , etc. So, for example, "BAA" means that a must come Before b , b must come After c , and c must come After d . Any letters beyond these requirements are to be excluded, so if the decree specifies k comparisons then the new alphabet will contain the first k+1 lowercase letters of the current alphabet. Create a class Alphabet that contains the method choices that takes the decree as input and returns the number of possible new alphabets that conform to the decree. If more than 1,000,000,000 are possible, return -1. Definition
標簽： government streamline important alphabet
上傳時間： 2015-06-09
上傳用戶：weixiao99
The EM algorithm is short for Expectation-Maximization algorithm. It is based on an iterative optimization of the centers and widths of the kernels. The aim is to optimize the likelihood that the given data points are generated by a mixture of Gaussians. The numbers next to the Gaussians give the relative importance (amplitude) of each component.
標簽： algorithm Expectation-Maximization iterative optimi
上傳時間： 2015-06-17
上傳用戶：獨孤求源
Encoding and decoding of the binary extended (24,12,8) Golay code: An arithmetic decoding algorithm. It is a very close relative of the error-trapping decoding algorithms developed by Kasami in the 1960s.
標簽： decoding arithmetic Encoding algorith
上傳時間： 2014-07-01
上傳用戶：lps11188
This the implementation of structural SVM for training complex alignment models for protein sequence alignment, especially for homology modeling. The structural SVM algorithm can incorporate many relevant features like secondary structure, relative exposed surface area, profiles and their various interaction into the alignment model. It was developed under Linux and compiles under gcc, built upon the svm^light software by Thorsten Joachims.
標簽： implementation structural for alignment
上傳時間： 2014-01-11
上傳用戶：chenbhdt
fwknop stands for "Firewall Knock Operator" and is an upcoming piece of software that will be released at the DEFCON 12 conference in July, 2004 in Las Vegas. fwknop implements network access controls (via iptables) based on a flexible port knocking mini-language, but with a twist it combines port knocking and passive operating system fingerprinting to make it possible to do things like only allow, say, Linux-2.4/2.6 systems to connect to your SSH daemon. fwknop supports shared, multi-protocol port knock sequences along with both relative and absolute timeouts, and coded port knock sequences encrypted with the Rijndael block cipher.
標簽： Firewall Operator software upcoming
上傳時間： 2016-12-04
上傳用戶：牛津鞋
SuperLU is a general purpose library for the direct solution of large, sparse, nonsymmetric systems of linear equations on high performance machines. The library is written in C and is callable from either C or Fortran. The library routines will perform an LU decomposition with partial pivoting and triangular system solves through forward and back substitution. The LU factorization routines can handle non-square matrices but the triangular solves are performed only for square matrices. The matrix columns may be preordered (before factorization) either through library or user supplied routines. This preordering for sparsity is completely separate from the factorization. Working precision iterative refinement subroutines are provided for improved backward stability. Routines are also provided to equilibrate the system, estimate the condition number, calculate the relative backward error, and estimate error bounds for the refined solutions.
標簽： nonsymmetric solution SuperLU general
上傳時間： 2017-02-20
上傳用戶：lepoke
用jquery實現(xiàn)的漸變式下拉菜單jQuery 漸變下拉菜單。使用slideToggle和slideUp來實現(xiàn).當然,也可以使用hide/show, fadeIn/fadeOut等來實現(xiàn),只是效果不同,實現(xiàn)的方法還是相同的.需要注意的是,要給.dropdown加上position:relative 防止閃爍
標簽： slideToggle fadeOut slideUp jquery
上傳時間： 2014-01-19
上傳用戶：SimonQQ
