real-time的基础知识.doc

合集下载

玩转四驱(1) 四驱基础知识讲解篇

玩转四驱（1）四驱基础知识讲解篇四驱，是一个很值得讨论的话题，我们在大街上经常能看到贴着4×4或AWD商标的汽车。

相信“四驱”这个概念在每个网友心里都有不同的解释，其实很简单，就是四个车轮都有动力的车就是四驱汽车。

但是要是再往进一步说，四驱车的结构都是一样的嘛？为什么有些恶劣地形有的四驱车能过去有的四驱车过不去？发烧级的四驱车仅仅是外观比较威猛？如果您对这些问题还有疑问，不用着急，在这里可以让您对四驱的一切变得明晰。

一、差速器/差速锁——不能混淆的基础概念！①差速器从世界上第一辆汽车的诞生之后不久，差速器这个东西也就随之诞生了，它存在的意义只有一个——为了汽车能正常转弯。

过去的马车两侧车轮是通过一根硬轴链接的，所以两侧的车轮的转速永远是相同的，因为无法差速，转弯的时候内侧的车轮除了滚动摩擦外还会有滑动摩擦，还好马车的车轮是木头做的，耐磨……同理汽车在转弯的时候也会有同样的问题，如果还是采用一根硬轴链接，那么转弯时汽车的轮胎等部件将会受到严重的损伤。

为了解决这个问题，当今汽车都是两个半轴的设计，将两个半轴链接起来的就是差速器，有了差速器也就允许两侧车轮有转速差。

『直行状态下差速器不工作』『转弯状态下差速器工作』能达到实现两侧车轮转速不一样，最重要的是差速器里面的一组行星齿轮。

为了通俗易懂，我们做一个比喻：差速器壳体里面的一组行星齿轮就可以抽象地看作为只有一个齿的“齿轮”，也就是一根棍子，这个棍子可以链接两侧的半轴，并带动两个半轴旋转。

注意，这个棍子除了随着传动轴公转，同时还可以自转。

如果两侧的车辆受到的摩擦力是相同的，那么这根棍子就不会有自转，即两侧车轮转速也相同；如果有一侧车轮受到的摩擦力大于另一侧，那么这根棍子本身就会发生自转，这样在不改变公转转速的情况加上自转，就可以达到两侧转速不一样的目的。

也就是说，如果一侧的轮子被卡死不能转动了，那也无妨，虽然动力依然存在，但这个会自转的棍子就会带动那个没有被卡死的轮子转动。

实时荧光定量PCR介绍

BLAST检索确认Probe特异性
实时荧光定量PCR介绍
4/14/2021 • 18
反应性能确认
实时荧光定量PCR介绍
线性关系、扩增效率确认
相关系数（r2）：大于0.98 PCR扩增效率（E）：0.8-1.2
检测灵敏度确认
35Cycles内可得到好的定量结果。如果采用SYBR检测方法， 30Cycles内无非特异性产物扩增。
105 104103102101100
105 104 103 102 101 100
• 标准品梯度的选择：5～6个梯度 • 标准品稀释倍数的选择：标准品稀释倍数通常为10
实时荧光定量PCR介绍
4/14/2021 • 21
标准品的种类
DNA样品定量标准品 RNA样品定量标准品
基因组DNA 质粒
Total RNA & cDNA 体外转录RNA
No Template Control确认
30Cycles内无引物二聚体产生。
4/14/2021 • 19
主要内容
1. 标准曲线分析
2. 融解曲线分析
3
Real Time PCR解析方法
3. 绝对定量和相对定量解析方法
实时荧光定量PCR介绍
4/14/2021 • 20
标准曲线制作
扩增曲线
标准曲线
（Perfect Real Time）（DRR064）
仪器 Smart Cycler Ⅱ
实时荧光定量PCR介绍
4/14/2021 • 36
绝对定量应用例对SARS培养液中所含SARS病毒RNA进行定量
SARS Control RNA构建
SYN247 F01
SYN247 F02

real-time PCR 数据分析

real-time PCR 数据分析无论所使用的real-time PCR是何种型号，正确的数据分析对于获得有效的实验结果都是至关重要的。

这里介绍有关real-time PCR数据分析的知识。

在讨论基本分析过程之前，先介绍如何设计一个好的实验。

如果你是自己设计的引物和探针，那有助于下一步的工作。

但是在有些情况下，人们使用出版文献上的序列会更方便。

记住，即便是出版物提供的序列也不能保证会得到优化的实验结果。

而且排版错误的可能性也需要考虑在内。

所以进入实验室之前使用BLAST对全部序列进行核实确保他们是正确的。

下订单前先检察引物和探针的序列和Tm值是实验设计的基本要求。

标准曲线是判断实验质量的重要手段。

使用一个已知的模板，PCR产物，合成的寡核苷酸或转录的RNA做个标准曲线能够确定PCR的效率，敏感性，动态范围和其他的参数。

建立标准曲线时使用OD260的模板样本。

模板的总量以DNA分子的数量来描述，把质量转化为DNA含量的公式如下：（质量（克）*阿伏伽德罗常数）每个碱基的平均质量*模板的长度。

例如，合成70-mer的单链DNA，样本质量为0.8*10ˆ-11gm。

代入公式得：（0.8*10ˆ-11*6.023*10ˆ23molecules/mole）330gm/mole/base*70 base。

如果使用双链的模板，则碱基的平均质量为660gm/mole/base。

标准曲线使用的模板含量从1*10ˆ7开始连续稀释7次每次稀释10倍，最终得到10个模板拷贝。

这样的浓度有助于得到最高的ΔRn和最低的Ct。

用Excel画曲线时以模板数量的对数值为X，Ct（cycle threshold）值为Y轴。

标准曲线的计算公式如下：y=mx+b。

y就是Ct，m是斜率，x=log10template amount，b=y-intercept。

用斜率计算出实验效率Efficiency【10ˆ（-1/斜率）】-1。

实验效率告诉我们PCR反应的执行情况。

实时荧光定量PCR介绍

July 25, 2013
•
实时荧光定量PCR介绍
33
相对定量解析方法
管家基因
维持细胞基本代谢活动所必须的基因,
如：GAPDH、β-actin等。
筛选方法
根据文献提供通过具体实验筛选
实时荧光定量PCR介绍
July 25, 2013
•
34
主要内容
1
Real Time PCR基础知识
绝对定量
2
Real Time PCR实验方法 ◇ 对SARS病毒培养液中所含SARS病毒RNA进行定量分析
△ 引物内部或两条引物之间避免3 base以上的互补序列 △ 引物3’ 末端避免2 base以上的互补序列
使用BLAST检索，确认引物特异性尽量在Exon junction上设计引物，限制基因组DNA扩增
July 25, 2013
•
实时荧光定量PCR介绍
17
Real Time PCR探针设计原则
Real Time PCR用TaqMan探针设计原则
Probe长度 Tm值序列 5’ 末端序列互补性
特异性
★★ ★★★ ★ ★ ★★★ ★★★
20-24 bp 探针的Tm比引物高8-10℃
△ 目的序列GC含量相对较高的区域设计 △ 整体上碱基不能过偏 △ 个别部分避免GC rich或AT rich (特别是3’
Real Time PCR解析方法
3. 绝对定量和相对定量解析方法
实时荧光定量PCR介绍
July 25, 2013
•
20
标准曲线制作
扩增曲线标准曲线
105 104 3 10 2 10 1 10 0 10
105 104 103 102 101 100

视频通信基础知识

议程
视频通信的基本概念视频通信网络的组成视频通信标准 H.320 视频通信系统组网 H.323 视频通信系统组网
视频通信基础知识
视频通信的基本概念
视频通信基础知识
Video Conference 视频会议视讯会议电视会议会议电视
电视会议
视频通信基础知识
Video Communication
• Quarter CIF (QCIF) – 176 x 144
– Refresh rates
• 30, 15, 10, 7.5 times per second
视频通信基础知识
Video Standard - H.261
• Is what traditional videoconferencing has used
29
30
视频通信基础知识
视频通信网络的组成
视频通信基础知识
视频通信
Video Server
视频通信基础知识
视频通信网络的组成
网络
终端 (Endpoint) 视频通信基础知识
终端
视频输入设备
视频输出设备
网络接口
编解码器（CODEC)
Network
音频输入设备
音频输出设备
视频通信基础知识
视频通信终端分类
▪ 需要大量带宽 ▪ 功能定义 ▪ 服务质量保证 ▪ 目前已很成熟
视频通信基础知识
Video Standard - H.261
• H.261
– Video coding and decoding – Defined image format
• Common Intermediate Format (CIF) – 352 pixels x 288 lines

视频基础知识

一．视频基础知识1. 视频编码原理视频图像数据有极强的相关性，也就是说有大量的冗余信息。

其中冗余信息可分为空域冗余信息和时域冗余信息。

压缩技术就是将数据中的冗余信息去掉（去除数据之间的相关性），压缩技术包含帧内图像数据压缩技术、帧间图像数据压缩技术和熵编码压缩技术。

1.1去时域冗余信息使用帧间编码技术可去除时域冗余信息，它包括以下三部分：A．运动补偿:运动补偿是通过先前的局部图像来预测、补偿当前的局部图像，它是减少帧序列冗余信息的有效方法。

B．运动表示:不同区域的图像需要使用不同的运动矢量来描述运动信息。

运动矢量通过熵编码进行压缩。

C．运动估计:运动估计是从视频序列中抽取运动信息的一整套技术。

注：通用的压缩标准都使用基于块的运动估计和运动补偿。

1.2去空域冗余信息主要使用帧内编码技术和熵编码技术：A．变换编码:帧内图像和预测差分信号都有很高的空域冗余信息。

变换编码将空域信号变换到另一正交矢量空间，使其相关性下降，数据冗余度减小。

B．量化编码:经过变换编码后，产生一批变换系数，对这些系数进行量化，使编码器的输出达到一定的位率。

这一过程导致精度的降低。

C．熵编码:熵编码是无损编码。

它对变换、量化后得到的系数和运动信息，进行进一步的压缩。

2. 视频编码解码标准2.1 H.264H.264是国际标准化组织（ISO）和国际电信联盟（ITU）共同提出的继MPEG4之后的新一代数字视频压缩格式，它即保留了以往压缩技术的优点和精华又具有其他压缩技术无法比拟的许多优点。

H.264最大的优势是具有很高的数据压缩比率，在同等图像质量的条件下，H.264的压缩比是MPEG-2的2倍以上，是MPEG-4的1.5～2倍。

举个例子，原始文件的大小如果为88GB，采用MPEG-2压缩标准压缩后变成3.5GB，压缩比为25∶1，而采用H.264压缩标准压缩后变为879MB，从88GB到879MB，H.264的压缩比达到惊人的102∶1。

Unit 1 科技英语基础知识(一)

4
例1 This electron beam sweeps across each line at a uniform rate，then flies back to scan another line directly below the ， previous one and so on，until the horizontal lines into which it is ， desired to break or split the picture have been scanned in the desired sequence．．此句可先分解和简化为如下的简单句: 此句可先分解和简化为如下的简单句 beam sweeps each line，， then flies back to scan another line，， it is desired to break picture into lines in desired sequence．．全句译为: 电子束以均匀的速率扫描每一行，然后飞速返回全句译为电子束以均匀的速率扫描每一行，去扫描下一行，直到把被扫描的图像按所希望的顺序分割成行。去扫描下一行，直到把被扫描的图像按所希望的顺序分割成行。
9
要成为一个名副其实的内行，需要学到老。例6 要成为一个名副其实的内行，需要学到老。这句中，这句中，有“成为”、“需要”、“学”三个表示动作成为” 需要” 的词，本句译成英语的词，本句译成英语: To be a true professional requires lifelong learning. 可以看出，作为谓语，可以看出，选“需要(require)”作为谓语，其余两个动需要作为谓语作中的“成为”用不定式形式to be，“学”用动名词形式作中的“成为”用不定式形式， learning，这样才能符合英语语法的要求。，这样才能符合英语语法的要求。把水加热并不会改变水的化学成分。例7 把水加热并不会改变水的化学成分。本句有两个动作，本句有两个动作，即“加热”和“改变”，译成英语: 加热” 改变” 译成英语 Heating water does not change its chemical composition. 本句将“改变”用作谓语，而将“加热” 本句将“改变”用作谓语，而将“加热”(heating)处理处理为动名词，连同其宾语作为本句主语。为动名词，连同其宾语water作为本句主语。作为本句主语

Real_Time_PCR

R
核糖核苷酸
Q
Cycling Probe法基本原理
热变性退火酶切延伸
SYBR Green I法vs Probe法
SYBR Green I 法
◆优点：价栺便宜、使用方便、无需合成特异性探针。 ◆缺点：引物要求高（要求特异性扩增）、不能进行多重PCR。
Probe法
◆优点：特异性强，能进行多重PCR。 ◆缺点：需要设计特异性探针，成本高、有时设计困难。
实时荧光定量PCR
（Real Time PCR）
主要内容
Real Time PCR 基础知识 Real Time PCR 实验方法
Real Time PCR 解析方法
Real Time PCR 应用实例
Real Time PCR 基础知识
Real Time PCR 的用途及原理
Real Time PCR 检测方法
互补性
特异性
★★★
★★★
RT-PCR用引物 ★★
★号表示重要程度，★号越多，表示该参数越重要，设计时要优先考虑
Real Time PCR引物及探针设计
好的引物需要寻找好的参照序列
目的基因目的基因序列获得引物设计分析序列
RefSeq序列
特异性确认
基因组序列确认 Real Time RT-PCR 引物
Real Time PCR 检测系统
Real Time PCR 用途
定性分析
病毒和病原菌检测生物品种鉴定
绝对定量
病毒和病原菌定量分析导入基因拷贝数解析
相对定量
差异显示结果验证基因芯片结果验证 siRNA效果确认 mRNA表达量分析
SNP解析
GMO定量检测
操作简单，无需电泳，检测快速，降低污染几率，适用于大量样品检测，检测灵敏度高；可以在宽广范围内进行准确定量。

实时操作系统

Real-Time Systems,28,237±253,2004#2004Kluwer Academic Publishers.Manufactured in The Netherlands. Real-Time Operating SystemsJOHN A.STANKOVICUniversity of VirginiaR.RAJKUMARCarnegie Mellon University1.IntroductionReal-time operating systems(RTOSs)provide basic support for scheduling,resource management,synchronization,communication,precise timing,and I/O.RTOSs have evolved from single-use specialized systems to a wide variety of more general-purpose operating systems(such as real-time variants of L inux).We have also seen an evolution from RTOSs which are completely predictable and support safety-critical applications to those which support soft real-time applications.Such support includes the concept of quality of service(QoS)for open real-time systems,often applied to multimedia applications as well as large,complex distributed real-time systems.Researchers in real-time operating system have developed new ideas and paradigms that enhance traditional operating systems to be more ef®cient and predictable.Some of these ideas are now found in traditional operating systems and many other ideas are found in the wide variety of RTOS on the market today.The RTOS market includes many proprietary kernels, composition-based kernels,and real-time versions of popular OSs such as Linux and Windows-NT.Many industry standards have been in¯uenced by RTOS research including POSIX real-time extensions,Real-Time Speci®cation for Java,OSEK(automotive RTOS standard),Ada83and Ada95.This paper provides an overview of the architectures, principles,paradigms,and new ideas developed in RTOS research over the past20years. The paper concentrates on research done within the context of complete RTOSs.Note that much more research on RTOSs has been accomplished and published as speci®c aspects on RTOS.For example,real-time synchronization and memory management research has many exciting results.Also,many ideas found in the companion paper on real-time scheduling can be found in various RTOSs as well.2.RTOS Taxonomy and ArchitecturesReal-time operating systems emphasize predictability,ef®ciency,and include features to support timing constraints.Several general categories of real-time operating systems exist:small,proprietary kernels(commercially available as well as homegrown kernels), real-time extensions to commercial timesharing operating systems such as Unix and238STANKOVIC AND RAJKUMAR Linux,component-based kernels,QoS-based kernels,and(largely)University-based research kernels.2.1.Small,Fast,Proprietary KernelsThe small,fast,proprietary kernels come in two varieties:homegrown1and commercial offerings.2Both varieties are often used for small embedded systems when very fast and highly predictable execution must be guaranteed.The homegrown kernels are usually highly specialized to the application.The cost of uniquely developing and maintaining a homegrown kernel,as well as the increasing quality of the commercial offerings is signi®cantly reducing the practice of generating homegrown kernels.In addition, component-based OSs(see Section2.3)are also reducing the need for homegrown kernels.For both varieties of proprietary kernels,to achieve speed and predictability,the kernels are stripped down and optimized versions of timesharing operating systems.To reduce the run-time overheads incurred by the kernel and to make the system fast,the kernel:*has a fast context switch,*has a small size(with its associated minimal functionality),*responds to external interrupts quickly(sometimes with a guaranteed maximum latency to post an event but,generally,no guarantee is given as to when processing of the event will be completed;this later guarantee can sometimes be computed if priorities are assigned correctly),*minimizes intervals during which interrupts are disabled,*provides®xed or variable sized partitions for memory management(i.e.,no virtual memory)as well as the ability to lock code and data in memory,*provides special sequential(often memory-based)®les that can accumulate data at a fast rate.To deal with timing requirements,the kernel*supports multi-tasking,*provides a priority-based preemptive scheduling mechanism,*provides bounded execution time for most primitives,*maintains a high-resolution real-time clock,REAL-TIME OPERATING SYSTEMS239 *provides for special alarms and timeouts,*supports real-time queuing disciplines such as earliest deadline®rst and primitives for jamming a message into the front of a queue,*provides primitives to delay processing by a®xed amount of time and to suspend/ resume execution.In general,the kernels also perform multi-tasking and inter-task communication and synchronization via standard primitives such as mailboxes(message queues),events, signals,mutexes,and semaphores.While all these latter features are designed to be fast, ``fast''is a relative term and not suf®cient when dealing with real-time constraints. Nevertheless,many real-time system designers use these features as a basis upon which to build real-time systems.This has been effective in small embedded applications such as instrumentation,communication front-ends,intelligent peripherals and many areas of process control.Since these applications are simple,it is relatively easy to show that all timing constraints are met.Consequently,the kernels provide exactly the minimal functionality that is needed.However,as applications become more complex,it becomes more and more dif®cult to craft a solution based on priority-driven scheduling where all timing,computation time,resource,precedence,and value requirements are mapped to a single priority for each task.In these situations,demonstrating predictability can be rather dif®cult.2.2.Real-Time Extensions to Commercial Operating SystemsA second approach to real-time operating systems is the extension of commercial products,for example,extending Unix to RT-Unix(Furht et al.,1991),Linux to RT-Linux(FSLLabs;Niehaus,KURT;RedIce Linux),or POSIX to RT-POSIX,or MACH to RT-MACH(Tokuda et al.,1990),or CHORUS to a real-time version(CHORUS system). The real-time version of commercial operating systems are generally slower and less predictable than the proprietary kernels,but have greater functionality and better software development environmentsÐvery important considerations in many large or complex applications.Another signi®cant advantage is that they are based on a set of familiar interfaces(standards)that facilitate portability.For Unix,since many variations of Unix have evolved,an IEEE standardization effort,called POSIX,has de®ned a common set of user-level interfaces for operating systems.The effort has focussed on eleven important real-time related functions:timers,priority scheduling,shared memory,real-time®les, semaphores,interprocess communication,asynchronous event noti®cation,process memory locking,asynchronous I/O,synchronous I/O,and threads.Various problems exist when attempting to convert a non real-time operating system to a real-time version.These problems can exist both at the system interface as well as in the implementation.For example,in Unix,interface problems exist in process scheduling due to the nice and setpriority primitives and its round-robin scheduling policy.In addition, the timer facilities are too coarse,memory management(of some versions)contains no240STANKOVIC AND RAJKUMAR method for locking pages into memory,and interprocess communication facilities do not support fast and predictable communication often resulting in different forms of priority inversion(Sha et al.,1990).The implementation problems include intolerable overhead, excessive latency in responding to interrupts,partly but very importantly,due to the non-preemptability of the kernel,and internal FIFO queues.These and other problems can and have been solved to result in a real-time operating system that is used for both real-time and non real-time processing.However,because the underlying paradigm of timesharing systems still exists,application developers must be careful not to use certain non real-time features that might insidiously impact the real-time tasks.Real-time capabilities can be added to operating systems in multiple ways.It is illustrative to study how many real-time versions of Linux have been created and commercialized in recent years.These versions can be grouped into the following categories.*Compliant kernels:In this approach,an existing real-time operating system is modi®ed such that L inux binaries can be run without any modi®cation.Essentially, the functionality and semantics of Linux system calls need to be appropriately emulated under the native operating system.For example,L ynxOS from L ynuxWorks adopts this approach.*Dual kernels:In this approach,a hard but thin real-time kernel sits below the native operating system(such as Linux or FreeBSD),and traps all accesses to and interrupts from the underlying hardware.The thin kernel schedules several hard real-time tasks co-located with it,and runs the native OS as its lowest priority task.As a result,native applications can be run without change,while hard real-time tasks can get excellent performance and predictability.A means of(non-real-time)communication is also provided between the thin real-time kernel and the native non-real-time kernel for data exchange purposes.The downside of this approach is that there is no memory protection between the real-time tasks and the native/thin kernels.As a result,the failure of any real-time task can lead to a complete system crash.The thin real-time kernel also needs to have its own set of device drivers for real-time functionality.RT-Linux(FSLLabs)is an example of this approach.*Core kernel modi®cations:In this approach,changes are made to the core of a non-real-time kernel in order to make it predictable and deterministic enough so as to behave as a real-time ing®xed-priority scheduling with a O(1)scheduler, employing high-resolution timers,making the kernel preemptive(so that a lower priority process in the kernel space due to an ongoing system call can be preempted by a higher priority process that becomes eligible to run),support for priority inheritance protocols to minimize priority inversion,making interrupt handlers schedulable using kernel threads,the use of periodic processes,replacing FIFO queues with priority queues and optimizing long paths through the kernel are typical means of accomplishing this goal.TimeSys L inux(based on CMU's L inux/RK (Oikawa and Rajkumar,1999)discussed in Section2.5.5)and to a smaller extent MontaVista Linux fall under this category.REAL-TIME OPERATING SYSTEMS241 *The Resource kernel approach:In this approach,the kernel is extended to provide support for resource reservations in addition to the traditional®xed-priority preemptive scheduling approach.The latter approach can run into problems when a relatively high-priority process overruns its expected execution time or even goes into an in®nite loop.Resource kernels support and enforce resource reservation,such that no misbehaving task can directly impact the timing behavior of another task.CMU's Linux/RK and its commercial cousin,TimeSys Linux,and fall into this category. ponent-BasedKernelsA number of systems such as OS-Kit(Ford et al.,1997),Coyote(Bhatti et al.,1999), PURE(Beuche et al.,1999),2K(Kon et al.,1998),MMLite(Helander and Forin,1998), and Pebble(Gabber et al.,1999)have a common intent to deal with operating system construction through composition.They de®ne OS components that can be selectively included to compose an RTOS that can be tailored to the application(s)at hand.OS-Kit provides a set of operating system components that can be combined to con®gure an operating system.However,it does not supply any rules to help build an operating system.Coyote is focussed on communication protocols,and its ability for re-con®guration might be adopted for operating system and embedded application areas. PURE is explicitly concerned with providing operating system components for con®guration and composition of operating systems for embedded applications.PURE uses an object-oriented methodology to provide different components for con®guration and customization of operating systems for embedded applications.2K emphasizes adaptability issues to allow applications to be as customizable as possible.2K is also concerned with component-based software for small mobile devices,or personal digital assistants(PDAs).To explore the concepts of a component-based RTOS,consider two component-based RTOSs in more detail.MML ite is an object-based,modular system architecture that provides a menu of components for use at compile-time,link-time,or runtime to construct a wide range of applications.A component in MML ite consists of one or more objects.Multiple objects can reside in a single namespace.When an object needs to send a message to an object in another namespace for the®rst time,a proxy object is created in the sending object's namespace that transparently handles the marshaling of parameters.A unique aspect of MMLite is its focus on support for transparently replacing components while these components are in use(mutation).MML ite uses COM interfaces, which in turn support dynamic recon®gurability on a per-object and per-component basis. However,COM does not provide protection between the components.The base menu of the MMLite system contains components for heap management,dynamic on-demand loading of new components,machine initialization,timer and interrupt drivers,scheduler, threads and synchronization,namespaces,®le system,network,and virtual memory. These components are typically very small(500±3000bytes on the386architecture), although the network component is much larger(84,832bytes on386).The resulting MMLite system can be quite small:the base system is26Kbytes on386,and20Kbytes242STANKOVIC AND RAJKUMAR on the ARM architecture.It is not clear to what extent MML ite provides users with the ability to easily select components that the MMLite developers write,and to what extent users themselves de®ne and utilize their own new components.Although there has been an apparent emphasis on developing minimal-sized components(in number of bytes), analysis tools regarding the runtime performance of components due to namespace resolution and the creation and loading of proxy objects is lacking.Pebble is a new operating system designed to be an ef®cient application-speci®c operating system and to support component-based applications.It also supports complex embedded applications.As an operating system,it adopts a microkernel architecture with a minimal privileged-mode nucleus that is only responsible for switching between protection domains.The OS functionality is provided by user-level components(servers), which can be replaced,augmented,or layered.The programming model is client/server; client components(applications)request services from system components(servers). Examples of system components are the interrupt dispatcher,scheduler,portal manager, device driver,®le system,virtual memory,and so on.The Pebble kernel and its essential components(interrupt dispatcher,scheduler,portal manager,real-time clock,console driver,and idle task)need approximately560Kbytes of ponents are like processes,where each one executes in its own protection domain(PD).In Pebble,a PD includes a page table and a set of portals.Portals provide communication between PDs.For example,if there is a portal from PD1to PD2,then a thread executing in PD1can invoke a speci®c service(entry point)of PD2.Therefore, components communicate through transferring threads from one PD to another using portals.The PD concept together with the portal concept can be understood as a component infrastructure.While Pebble PDs provide the means to isolate the components,portals provide the means for components to communicate with each other.Instantiation and management of portals are performed by an operating system component,Portal Manager.For instance,the instantiation process involves the registration of a server(any system or application component)in a portal and the request of a client for that portal.In Pebble,it is possible to dynamically load and to replace system components to ful®ll applications requirements.2.4.QoS-BasedKernelsQoS research has been extensive,®rst as applied to networking then to general distributed computing.More recently,QoS has been applied to soft real-time systems.In these systems,a guarantee is given that a certain amount of resources is assigned to a task or application.In other cases,there are differentiated guarantees meaning that certain classes of tasks are guaranteed resources compared to another class of tasks.For example, tasks dealing with the control of the plant may be required to obtain twice the resources than tasks reporting the results to a command center.The resources being controlled may just be the CPU or a set of resources.Many research results exist for developing algorithms to control the guarantees.Sometimes,these algorithms are implemented as monitors on top of an RTOS.In other cases,the algorithms may be implemented asREAL-TIME OPERATING SYSTEMS243 middleware(Brandt et al.,1998).The algorithms differ in their approach and utilize many different techniques such as fair-share scheduling(Jeffay et al.,1998),proportional scheduling(Stoica et al.,1996),rate-based scheduling(Jeffay,2001),reservations,and feedback control.In this paper,we are more interested in RTOS that incorporate QoS support such as RT Mach(Tokuda et al.,1990)and Rialto(Jones et al.,1996,1997).Both of these RTOSs allow users to negotiate with the RTOS for a certain amount of resources.RT-Mach employs reservations to support QoS.RT-Mach supports multimedia applications and both real-time and non-real-time tasks.Rialto allows for multiple,independent applications to co-exist.A system-wide planner reasons about the resource allocations between applications.This is similar to the reservation and admission control type work discussed above,but here,independent applications are supported on a single platform. Rialto also has support for overload and for re-negotiation of guarantees.2.5.Research KernelsMany past and current University-based research-oriented real-time operating systems have been developed.These projects addressed many of the following research issues including:*identifying the need for new approaches which challenge the basic assumptions made by timesharing operating systems and developing those new paradigms;*developing real-time process models:*some systems use the standard process model both to program with and at execution time,*some systems use the process model to program with but translate into a different run-time model to help support predictability and on-line guarantees, *some systems use real-time threads;*developing real-time synchronization primitives such as those that support priority inheritance and priority ceiling protocols;*developing solutions that facilitate timing analysis of both the initial system and upon modi®cations(the real-time scheduling algorithms play a large role here);*strongly emphasizing predictability not only of the kernel but also providing good support for application-level predictability;*retaining signi®cant amounts of application semantics at run time;*developing support for fault tolerance;244STANKOVIC AND RAJKUMAR *investigating object-oriented approaches;*providing support for multiprocessor and distributed real-time systems including end-to-end timing constraints;*developing support for QoS;*attempting to de®ne a real-time micro-kernel;*providing support for real-time programming languages such as the Real-Time Speci®cation of Java(JSR-00001).We survey several research projects as representative of a much wider set of work in the®eld.2.5.1.MARSThe MARS kernel(Damm et al.,1989;Kopetz et al.,1989)offers support for controlling a distributed application based entirely on the passage of time(rather than asynchronous events)from the environment.Emphasis is placed on an a priori static analysis to demonstrate that all the timing requirements are met.An important feature of this system is that¯ow control on the maximum number of events that the system handles is automatic and this fact contributes to the predictability analysis.This system is based on a paradigm,that is,the time-triggered model,that is different than what is found in timesharing systems.The scheduling approach is static and table-driven.Support for distributed real-time systems includes a hardware-based clock synchronization algorithm and a TDMA-like protocol to guarantee timely message delivery.A number of extensions to the original work have added¯exibility to handle more dynamic situations.The time-triggered approach advocated in MARS has seen success in the automotive industry and in several other safety-critical application domains.2.5.2.SPRINGThe Spring kernel(Stankovic and Ramamritham,1995;Stankovic et al.,1999)contains real-time support for multiprocessors and distributed systems.A novel aspect of the kernel is the dynamic planning-based scheduling of tasks that arrive dynamically.Such tasks are subject to admission control and dynamically acquire reservations for resources. This takes tasks'time and resource constraints into account and avoids the need to a priori compute worst-case blocking times.Safety-critical tasks are dealt with through static table-driven scheduling.The kernel also embodies a re¯ective architecture (Stankovic and Ramamritham,1995)that retains a signi®cant amount of application semantics at run time.This approach provides a high degree of¯exibility along withREAL-TIME OPERATING SYSTEMS245 support for graceful degradation.These planning and application semantic features are integrated to provide direct support for achieving both application-and system-level predictability.The kernel also uses global replicated memory to achieve predictable distributed communication.The abstractions provided by the Kernel include dynamic guarantees,reservations,planning,and end-to-end timing support.Spring,like MARS, presents a new paradigm for real-time operating systems,but unlike MARS it strives for a more¯exible combination of off-line and on-line techniques.Concepts of admission control,re¯ection and reservations found in the Spring kernel have been used by many other systems.2.5.3.ARTSThe ARTS kernel(Tokuda and Merger,1989)provides a distributed real-time computing environment that works in conjunction with the static priority-driven preemptive scheduling paradigm.The kernel supports the notion of real-time objects and real-time threads.Each real-time object is time-encapsulated.This is enforced by a time fence mechanism which provides a run-time check that ensures that the slack time is greater than the worst-case execution time for an object invocation about to be performed.If it is, the operation proceeds,else it is aborted.Each real-time thread can have a value function, timing constraints,worst-case execution time,phase,and delay value associated with it. Communication(object invocation)proceeds in a request±accept±reply fashion,but does not address deadlines for messages.A real-time transport protocol has been developed. The ARTS kernel is also tied to various tools that a priori analyze the system-wide schedulability of the system.2.5.4.HARTOSThe hexagonal architecture for real-time systems(HARTS)consists of multiple sites connected by a hexagonal mesh network.Each site may be a uniprocessor or multiprocessor and contains an intelligent network processor.The intelligent network processor handles much of the low-level communication functions.An experimental operating system called HARTOS(Kandlur et al.,1992)is a distributed real-time kernel running on HARTS.On each site,HARTOS runs in conjunction with the commercial uniprocessor OS,pSOS.Hence,by itself,HARTOS is not a full operating system.Rather, HARTOS focusses on interprocess communication,thereby providing some support for distributed real-time systems.In particular,HARTOS supports message send and receive, non-queued event signals,reliable streams,and message scheduling that provides a best-effort approach in delivering a message by its deadline.Support for fault-tolerant routing, clock synchronization,and for replicated processes are also planned.246STANKOVIC AND RAJKUMAR 2.5.5.RKIn extensions to Real-Time Mach,Mercer et al.(1994)added the notion of processor reservations based on the Liu and Layland periodic task model of each task obtaining C i units of time every T i units of time.Rajkumar et al.(1998)generalized this concept to the notion of a resource kernel,which is de®ned as one which provides guaranteed,timely and enforced access for applications to system resources.In addition,scheduling policies could be changed within the OS without affecting any guarantees.Resources that could be guaranteed access to can include CPU cycles(Rajkumar et al.,1988),disc bandwidth (Molano et al.,1997;Saewong and Rajkumar,2003),network bandwidth(Ghosh and Rajkumar,2002)or memory space(Easwaran and Rajkumar,2004).Resource reservations on multiple resources could also be combined to form a resource set to which one or more applications could be bound.An application bound to a resource set essentially has access to a``virtual machine''that comprises a time-or space-multiplexed subset of the underlying physical resources.This virtualization also enabled the binding of binary images to be bound to arbitrarily sized reservations(w/o access to source).An interesting variation of the priority inversion problem occurs when processes bound to two(or more)different reservations need to share a resource(such as the X-windows server).Solutions to this problem are also based on variants of priority inheritance and led to reservation inheritance protocols(de Niz et al.,2001).Counter-intuitive as it may seem,the reservation model of guaranteeing and enforcing C i units of time every T i units of time is not just useful for periodic tasks.It can also act as a traf®c shaper to aperiodic tasks in the exact same spirit of a deferrable(Sprunt et al., 1989)or sporadic server(Strosnider et al.,1995).3.ParadigmsReal-time operating systems utilize various paradigms.Key concepts found in these paradigms include:hard and soft real-time guarantees,admission control,re¯ection, reservations,and resource kernels.Many of these key concepts work together in achieving the overarching paradigm presented by a particular kernel.3.1.HardandSoft Real-Tim e GuaranteesIn general,the smaller,more deterministic kernels provide support for hard deadline systems.Here all the inputs and system details are known,and careful design and analysis can result in meeting hard deadline requirements.In performing the analysis it is also possible to carefully account for the kernel overheads.Safety-critical hard real-time systems also typically employ comfortable margins on resource utilization(such as ensuring that total utilization on a resource does not exceed50±60%).The larger,more dynamic,more probabilistic kernels provide support for soft real-time systems.Here quality of service guarantees are de®ned and shown to be met in aREAL-TIME OPERATING SYSTEMS247 probabilistic sense.We sometimes®nd hierarchical real-time scheduling or partitioned scheduling to handle different classes of tasks.3.2.Admission ControlAdmission control is a function that decides if new work entering the system should be admitted or not.The key ingredients of admission control include a model of the state of system resources,knowledge about the incoming request,the exact algorithm to make the admission control decision,and policies for the actions to take upon admission and upon rejection.First consider hard real-time systems.Many hard real-time systems are statically scheduled and operate in highly deterministic fashion.This facilitates the timing analysis required of these systems and there is no notion of admission control.But,many hard real-time systems operate in dynamic environments where static scheduling is too costly or rigid.What is required is a solution that enables on-line careful timing analysis and dynamic scheduling.A solution provided in the Spring kernel (Stankovic and Ramamritham,1989,1995)included the synergistic combination of admission control,resource reservation,and re¯ection;so this concept already exists in the hard real-time domain.Here the model of the state of the system is a detailed timeline that identi®es the start and®nish time(based on a worst-case execution time model)for each admitted task on each resource that it requires.Signi®cant re¯ective information is known about each incoming task because they are pre-analyzed for a particular real-time system;there are no general purpose on-the-¯y tasks created.The re¯ective information known about the requested work includes the worst-case execution time,shared data required by this task,precedence constraints,importance level,which tasks communicate with this task,deadline,etc.The algorithm is a heuristic that schedules the task on the detailed time line along with all the previously admitted tasks in such a manner that if successful,all the tasks will meet their deadlines.See Zho et al.(1987)for a detailed description of the algorithm.If the task is admitted,it has been assigned a very speci®c time-slice(although it may actually execute early under certain conditions).If it is not admitted,then a separate policy is invoked to decide what action to take.Typical actions include:try a simpler version of the task if any exists,or if the deadline is far away try to schedule the task on another node,or if the deadline is close then just reject this task. These policies can be modi®ed based on the importance of the task.The low-level details of the entire guaranteed schedule are available to the application.A large amount of application semantic information is pushed into the kernel(via the compiler and a special system description language).For example,the process control block(PCB)contains,in addition to the typical information,worst case execution times,deadline information, precedence requirements,a communication graph,fault-tolerance information,etc. Work on supporting QoS for audio and video has also used admission control and reservations.In many systems,various amounts and types of re¯ective information are also used.The typical model of the system has been utilizations identi®ed independently for multiple resources such as CPU,network bandwidth,disc,and memory.The precise admission control algorithm has varied from system to system,but it is usually based on。

超声知识

一、超声波的频率超声波频率 f ≥ 20KHz ，诊断超声波频率一般范围在 0.5-80MHz ，其中3-10MHz 最常用。

二、超声波的发生超声波可由多种物理能量转变而成，需经过换能器进行转换。

目前最常用的换能器是压电陶瓷即压电晶体，在交变电场的作用中产生厚度的交替改变即声振动 , 当电场交变频率与压电晶体的固有频率一致时，换能器的电转换（电 ? 声）效率最高，即晶体的振幅最大。

压电晶体常具有两种可逆的能量转变效应：由电能转变为声能时称逆压电效应；相反，由声波的压力变化传至压电晶体后其两端的电极随声波的压缩（压力）与张弛（负压）发生正负电位交替变化，称正压电效应。

在逆压电效应中压电晶体成为超声发生器；在正压电效应中压电晶体成为回声接收器。

天然的压电晶体以石英为代表，另有机压电薄膜材料（聚偏氟乙烯 PVDF ）其声阻抗与人体软组织声抗十分相近，检查时减少中间传递的声能量损失。

压晶体在制成一个器件后称超声探头，探头在发生超声时称为声源。

第二节超声的传播从声源发生的声能抵达另一物体时为超声的传播，超声是以波的形式传播的，分纵波、横波、板体波、表面波等。

人体内除骨骼外，在所有软组织中几乎所有都是以纵波的形式传播的。

1 、频率 f ：由声源决定。

周期 T=1/f2 、声速 c ：由传播媒质决定。

3 、波长 l ： l =c/f=CT4 、声扬：声源发出的声波在介质内所影响涉及的范围。

A ）指向性：声源直径大于波长时，声束集中在一个狭小的立体角内发射的特性。

B ）近场：以接近于圆柱样的形态传播，称 Fresnel 区。

C ）远场：呈倒圆椎形分布。

D ）声轴、声束、束宽（ beam axis 、 beam 、 beam width)E ）分辨力：是指超声波辨别两个相邻物体的能力。

侧向分辨力取决于激励电脉冲的长度及探头的阻尼程度，横向分辨力取决于声束的宽度；用减少脉冲的乙及增加探头的阻尼以提高轴向分辨力，用声束聚焦的方法可以提高横向分辨力。

realtimePCR和RT-PCR详解及其区别要点

real-time PCR技术的原理及应用摘要：一、实时荧光定量PCR原理（一）定义：在PCR反应体系中加入荧光基团，利用荧光信号累积实时监测整个PCR进程，最后通过标准曲线对未知模板进行定量分析的方法。

（二）实时原理 1、常规PCR技术：对PCR扩增反应的终点产物进行定量和定性分析无法对起始模板准一、实时荧光定量PCR原理（一）定义：在PCR反应体系中加入荧光基团，利用荧光信号累积实时监测整个PCR进程，最后通过标准曲线对未知模板进行定量分析的方法。

（二）实时原理1、常规PCR技术：对PCR扩增反应的终点产物进行定量和定性分析无法对起始模板准确定量，无法对扩增反应实时检测。

2、实时定量PCR技术：利用荧光信号的变化实时检测PCR扩增反应中每一个循环扩增产物量的变化，通过Ct值和标准曲线的分析对起始模板进行定量分析3、如何对起始模板定量？通过Ct值和标准曲线对起始模板进行定量分析.4、几个概念：（1）扩增曲线：（2）荧光阈值：（3）Ct值：CT值的重现性：5、定量原理：理想的PCR反应： X=X0*2n非理想的PCR反应： X=X0 (1+Ex)nn：扩增反应的循环次数X：第n次循环后的产物量X0：初始模板量Ex：扩增效率5、标准曲线6、绝对定量1）确定未知样品的 C(t)值2）通过标准曲线由未知样品的C(t)值推算出其初始量7、DNA的荧光标记：二、实时荧光定量PCR的几种方法介绍方法一：SYBR Green法（一）工作原理1、SYBR Green 能结合到双链DNA的小沟部位2、SYBR Green 只有和双链DNA结合后才发荧光3、变性时，DNA双链分开，无荧光4、复性和延伸时，形成双链DNA， SYBR Green 发荧光，在此阶段采集荧光信号。

PCR反应体系的建立及优化:1、SYBR Green 使用浓度:太高抑制Taq酶活性，太低，荧光信号太弱，不易检测2、Primer：引物的特异性高，否则扩增有杂带，定量不准3、MgCl2的浓度:可以降低到1.5mM,以减少非特异性产物4、反应Buffer 体系的优化5、反应温度和时间参数:由酶和引物决定6、其他与常规PCR相同（二）应用范围1、起始模板的测定；2、基因型的分析；3、融解曲线分析：可以优化PCR反应的条件，对常规PCR有指导意义，如对primer的评价；可以区分单一引物、引物二聚体、变异产物、多种产物。

real-time pcr原理

real-time pcr原理
实时聚合酶链反应（real-time PCR）是一种广泛应用于分子生
物学研究中的技术，用于检测和定量DNA或RNA的存在。

与传统聚合酶链反应（PCR）相比，实时PCR能够提供更快、更准确的结果。

实时PCR基于聚合酶链反应原理，通过扩增目标DNA或
RNA序列来检测其存在。

实时PCR使用一对特异性引物，即
前向引物和反向引物，与目标序列的两侧结合。

在反应过程中，DNA聚合酶会复制模板DNA，并在每个引物的结合位点依次
合成新的DNA链。

然而，与传统PCR不同的是，实时PCR在反应混合物中加入
了一种叫做探针的荧光探测剂。

这种探针通常由一个引物和一个荧光信号发生器组成。

当探针与目标序列结合时，引物会选择性地与模板DNA结合，并将荧光信号发生器离开。

在PCR
反应进行的同时，荧光信号会产生，并且可以实时监测到
PCR反应的进程。

实时PCR设备一般配备了一个光学系统，可以记录PCR反应
过程中产生的荧光信号。

光学系统能够定量检测荧光信号的强度，并将其转化为DNA或RNA的相对数量。

这使得实时
PCR能够定量目标DNA或RNA序列在样本中的存在量。

总的来说，实时PCR结合了PCR的增幅特性和荧光技术的快
速检测特性，可以在PCR反应进行的同时实时监测和定量目
标DNA或RNA序列的存在量。

这使得实时PCR成为现代分子生物学研究中的重要工具。

计算机应用基础复习资料

计算机应用基础复习资料2005年6月第1章计算机基础知识⒈计算机的发展过程分为几个时代？按照什么划分的？答：计算机的发展分为四个时代。

按照所采用的电子元器件划分。

即电子管时代、晶体管时代、中小规模集成电路时代、大规模和超大规模集成电路时代。

2．计算机有哪些主要特点？答：现代计算机也称为电脑或电子计算机（Computer），是指一种能存储程序和数据、自动执行程序、快速而高效地自动完成对各种数字化信息处理的电子设备。

它能部分地代替人的脑力劳动。

计算机具有以下主要特点：（1）处理速度快（2）计算精度高（3）存储容量大（4）可靠性高（5）工作过程的全自动化（6）适用范围广，通用性强⒊计算机的主要应用领域有哪些？答：自1946年世界上地一台计算机诞生到现在，计算机的主要应用领域有：（1）科学计算（数值计算）（2）信息处理（3）过程控制（4）计算机辅助设计（CAD）和辅助制造（CAM）（5）现代教育（6）家庭生活4.计算机的发展方向是什么？答：随着计算机科学理论和制造技术的发展，现代计算机的发展表现为两个方面：一是巨型化、微型化、多媒体化、网络化和智能化5种趋向；二是朝着非冯·诺依曼结构模式发展。

5.计算机内部信息为什么要采用二进制编码表示？答：计算机中采用二进制数是因为二进制数具有如下特点：（1）简单可行，容易实现（2）运算规则简单a（3）适合逻辑运算6．什么是机器指令？它由哪两部分组成？各部分的作用是什么？什么是指令系统？答：机器指令就是给计算机下达的一道命令，它告诉计算机每一步要进行什么操作、参与此项操作的数据来自何处、操作结果又将送往哪里。

所以，一条指令必须包括操作码和地址码（或称操作数）两部分，操作码指出该指令完成操作的类型，地址码指出参与操作的数据和操作结果存放的位置。

一台计算机可能有多种多样的指令，这些指令的集合称为该计算机的指令系统。

7.试解释下列基本概念：机器语言、汇编语言、高级语言、源程序和目标程序。

rtk学习操作流程

rtk学习操作流程
RTK（Real-Time Kinematic）是一种高精度的全球定位系统，
可以提供厘米级别的定位精度。

RTK技术在土地测绘、农业、建筑
等领域有着广泛的应用。

下面将介绍RTK学习操作流程。

首先，学习RTK技术需要具备一定的基础知识，包括GPS原理、测量方法等。

可以通过阅读相关书籍、参加培训班等方式来获取这
些知识。

其次，需要了解RTK设备的组成和工作原理。

RTK系统由基站
和移动站组成，基站用来发送校正信号，移动站接收这些信号并进
行定位。

学习者需要了解这两个部分的功能和工作原理。

接着，学习者需要熟悉RTK设备的操作方法。

包括设备的开关机、设置参数、连接基站等操作。

在实际操作中，需要注意设备的
摆放位置、天线的朝向等因素，以确保获得准确的定位结果。

在进行实地测量时，学习者需要选择合适的测量方法和技术。

比如，在建筑测量中，可以采用RTK技术进行地形测量、建筑物测
量等。

在农业领域，可以利用RTK技术进行土壤测量、作物生长监
测等。

最后，学习者需要不断实践和总结经验。

通过实际操作，不断
提高自己的技术水平和应用能力。

同时，及时总结经验教训，不断
改进和完善自己的工作方法。

总的来说，学习RTK技术需要系统学习基础知识，熟悉设备的组成和工作原理，掌握操作方法和技术，不断实践和总结经验。

只有不断努力和实践，才能真正掌握RTK技术，提高定位精度，为各行业的发展贡献自己的力量。

OS基础知识

第一章操作系统引论
处理器管理(进程管理)
• 讨论如何分配CPU ----即采用什么策略把CPU分配给多个进程，从而决定了操作系统的性质或类型。
第一章操作系统引论
存储管理
• • • • 主存空间的分配与回收逻辑地址与物理地址的映射主存的共享与保护，体现OS是否真正有效利用了资源。
特点：资源共享、通信功能
第一章操作系统引论
六、分布式操作系统
①系统中任两台计算机可通过通信来交换信息；
②各个计算机无主次之分；
③系统中的资源为所有用户共享； ④若干台计算机相互协作完成一件共同的任务。七、当代操作系统的两大发展方向 ----宏观应用与微观应用
推动OS发展的主要动力：
1、不断提高计算机资源利用率的需要；2、方便用户；3、器件的不断更新换代；
第一章操作系统引论
二、 OS作为计算机系统资源的管理者在一个计算机系统中，通常都含有各种各样的硬件和软件资源。作为资源，就是要“物尽其用”，即最大限度地提高资源利用率。如：①CPU与外设并行工作； ②提高内存的利用率。 OS确是计算机系统资源的管理者。事实上，当今世界上广为流行的一个关于 OS 作用的观点，正是把 OS 作为计算机系统的资源管理者。
第一章操作系统引论
设备管理
—是OS中最复杂、最具多样性的部分
• 外围设备的分配: --独占型设备的分配共享型磁盘的驱动调度 Spooling技术与虚拟设备设备的启动设备的中断处理
第一章操作系统引论
文件管理
—是用户直接可见的部分，体现OS是否真正方便用户。
• 外存空间的分配与回收 • 实现逻辑文件与物理文件的转换 • 建立文件目录实现按名存取 • 提供合适的存取方法以适应不同的应用 • 实现文件的共享、保护与保密 • 提供一组文件操作来使用文件

多媒体技术基础知识

多媒体技术基础知识21世纪是信息化社会，以信息技术为主要标志的高新技术产业在整个经济中的比重不断增长，多媒体技术及其产品是当今世界计算机产业发展的新领域。

多媒体技术使计算机具有综合处理声音、文字、图像和视频的能力，它以形象丰富的声、文、图信息和方便的交互性，极大地改善了人机界面，改变了使用计算机的方式，从而为计算机进入人类生活和生产的各个领域打开了方便之门，给人们的工作、生活、学习和娱乐带来深刻的变化。

本章主要内容：•多媒体技术的概念、发展历程；•流媒体技术；•多媒体技术的研究内容和应用领域；•多媒体产品的开发模式、开发工具以及开发流程；•多媒体产品的版权问题。

1.1概述在当今数字化时代，多媒体已经从一个时髦的概念变成一种实用的技术。

计算机是人们应掌握的基本技能之一，而使用计算机必然用到多媒体。

多媒体技术不仅应用到教育、通信、工业、军事等领域，也应用到动漫、虚拟现实、音乐、绘画、建筑、考古等艺术领域，为这些领域的研究和发展带来勃勃生机。

多媒体技术影响着科学研究、工程制造、商业管理、广播电视、通信网络和人们的生活。

多媒体技术是20世纪后期发展起来的一门新型技术，它大大改变了人们处理信息的方式。

早期的信息传播和表达信息的方式，往往是单一的和单向的。

后来随着计算机技术、通信和网络技术、信息处理技术和人机交互技术的发展，拓展了信息的表示和传播方式，形成了将文字、图形图像、声音、动画和超文本等各种媒体进行综合、交互处理的多媒体技术。

1.1.1多媒体技术的基本概念1．媒体的概念及类型媒体（medium）是信息表示和传播的载体。

媒体在计算机领域有两种含义：一种是指媒质，即存储信息的实体，如磁盘、光盘、磁带、半导体存储器等；二是指传递信息的载体，如数字、文字、声音、图形和图像等。

国际电话与电报咨询委员会（CCITT）将媒体做如下分类。

1）感觉媒体感觉媒体（perception media）指能直接作用于人的感官，使人直接产生感觉的媒体。

流媒体基础知识

流媒体基础知识(上)一、前言随着越来越多的朋友开始选择ADSL、Cable Modem或FTTB+ LAN作为首要的上网方式，宽频时代即将到来，这使我们“宽频 KTV、影音聊天室、线上电影院、远程教育”的梦想即将成为现实，而与其密切相关的“流媒体(Streaming Media)”也成了许多人谈论的热门话题，因为“流媒体”正是实现这些宽频应用的技术动力。

宽频时代的到来还使得网民们不再满足于仅仅作为一项服务的受众，他们需要更大规模的交流，从中体现个体的价值，因此，许多朋友开始用自己的计算机，搭建网络广播和点播站点。

他们充满着满腔的热情，但不可否认的是，中国网民先天技术上的不足，让他们在建设这样的站点时遇到重重险阻，以至于放弃。

如何将这种热情在技术的引导下成为动力，这正是我们家用电脑所要做的，所以，在今天，在这里，我就将给大家介绍如何打造属于自己的流媒体服务器。

不过，在开始正式的流媒体服务器架设之前，请让我们先了解一下流媒体服务器的基础知识。

二、流媒体基础知识什么是流媒体？目前，在网络上传输音/视频等多媒体信息有两种解决方案，即http或ftp下载以及流式传输。

http或ftp下载使用标准的http和ftp协议，但由于多媒体信息个头巨大，下载一个多媒体文件一般需要几分钟或几小时的时间，这就造成为了看一个并不知道内容的视频，首先需要耗费可能比整个视频都要长的时间来完成下载。

这些被下载的文件还必须在下载前制作完成，放在网络服务器上，这样造成的直接后果就是：网络带宽不断提高，人们下载的等待时间越来越少，但最终还是不能观看网上现场直播。

流式传输时，声音、影像或动画等多媒体信息由流媒体服务器向用户计算机连续、实时传送，它首先在使用者端的电脑上创建一个缓冲区，于播放前预先下载一段资料作为缓冲，用户不必等到整个文件全部下载完毕，而只需经过几秒或十数秒的启动延时即可进行观看。

当多媒体信息在客户机上播放时，文件的剩余部分将在后台从服务器内继续下载。