虚拟仪器（virtual instrumention）是基于计算机的仪器。计算机和仪器的密切结合是目前仪器发展的一个重要方向。粗略地说这种结合有两种方式，一种是将计算机装入仪器，其典型的例子就是所谓智能化的仪器。随着计算机功能的日益强大以及其体积的日趋缩小，这类仪器功能也越来越强大，目前已经出现含嵌入式系统的仪器。另一种方式是将仪器装入计算机。以通用的计算机硬件及操作系统为依托，实现各种仪器功能。虚拟仪器主要是指这种方式。下面的框图反映了常见的虚拟仪器方案。 虚拟仪器的主要特点有： n 尽可能采用了通用的硬件，各种仪器的差异主要是软件。 n 可充分发挥计算机的能力，有强大的数据处理功能，可以创造出功能更强的仪器。 n 用户可以根据自己的需要定义和制造各种仪器。 虚拟仪器实际上是一个按照仪器需求组织的数据采集系统。虚拟仪器的研究中涉及的基础理论主要有计算机数据采集和数字信号处理。目前在这一领域内，使用较为广泛的计算机语言是美国NI公司的labview。 虚拟仪器的起源可以追朔到20世纪70年代，那时计算机测控系统在国防、航天等领域已经有了相当的发展。PC机出现以后，仪器级的计算机化成为可能，甚至在Microsoft公司的Windows诞生之前，NI公司已经在Macintosh计算机上推出了labview2.0以前的版本。对虚拟仪器和labview长期、系统、有效的研究开发使得该公司成为业界公认的权威。 普通的PC有一些不可避免的弱点。用它构建的虚拟仪器或计算机测试系统性能不可能太高。目前作为计算机化仪器的一个重要发展方向是制定了VXI标准，这是一种插卡式的仪器。每一种仪器是一个插卡，为了保证仪器的性能，又采用了较多的硬件，但这些卡式仪器本身都没有面板，其面板仍然用虚拟的方式在计算机屏幕上出现。这些卡插入标准的VXI机箱，再与计算机相连，就组成了一个测试系统。VXI仪器价格昂贵，目前又推出了一种较为便宜的PXI标准仪器。 虚拟仪器研究的另一个问题是各种标准仪器的互连及与计算机的连接。目前使用较多的是IEEE 488或GPIB协议。未来的仪器也应当是网络化的。
上传时间： 2013-10-15
上传用户：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.
上传时间： 2013-11-04
上传用户：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
标签： Constraints Information Attributes Customers
上传时间： 2015-05-12
上传用户：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
标签： government streamline important alphabet
上传时间： 2015-06-09
上传用户：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.
标签： algorithm Expectation-Maximization iterative optimi
上传时间： 2015-06-17
上传用户：独孤求源
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.
标签： decoding arithmetic Encoding algorith
上传时间： 2014-07-01
上传用户：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.
标签： implementation structural for alignment
上传时间： 2014-01-11
上传用户：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.
标签： Firewall Operator software upcoming
上传时间： 2016-12-04
上传用户：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.
标签： nonsymmetric solution SuperLU general
上传时间： 2017-02-20
上传用户：lepoke
用jquery实现的渐变式下拉菜单jQuery 渐变下拉菜单。使用slideToggle和slideUp来实现.当然,也可以使用hide/show, fadeIn/fadeOut等来实现,只是效果不同,实现的方法还是相同的.需要注意的是,要给.dropdown加上position:relative 防止闪烁
标签： slideToggle fadeOut slideUp jquery
上传时间： 2014-01-19
上传用户：SimonQQ
