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Đo lường quang học P6
Holography Holography is the synthesis of interference and diffraction. In recording a hologram, two waves interfere to form an interference pattern on the recording medium. When reconstructing the hologram, the reconstructing wave is diffracted by the hologram. When looking at the reconstruction of a 3-D object, it is like looking at the real object. It is therefore said that: ‘A photograph tells more than a thousand words and a hologram tells more than a thousand photographs’. Although holography requires coherent light, it was invented by Gabor back in 1948, more than a decade before the invention of the laser....
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Đo lường quang học P7
Moir´ Methods. Triangulation e Figure 3.2 is an illustration of two interfering plane waves. Let us look at the figure for what it really is, namely two gratings that lie in contact, with a small angle between the grating lines. As a result, we see a fringe pattern of much lower frequency than the individual gratings. This is an example of the moir´ effect and the resulting fringes are e called moir´ fringes or a moir´ pattern. Figures 3.4, 3.8 and 3.9 are examples of the same e e effect. The mathematical description of moir´ patterns resulting from the superposition e...
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Đo lường quang học P8
Speckle Methods When looking at the laser light scattered from a rough surface, one sees a granular pattern as in Figure 8.2. This so-called speckle pattern can be regarded as a multiple wave interference pattern with random individual phases. In the years following the advent of the laser, this pattern was considered a mere nuisance, especially in holography (and it still is!). But from the beginning of 1970 there were several reports from experiments in which speckle was exploited as a measuring tool. In this chapter the basic principles of the different techniques of speckle metrology will be described....
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Đo lường quang học P9
Photoelasticity and Polarized Light Up to now we have treated the light field as a scalar quantity. The electromagnetic field, however, is a vector quantity which is perpendicular to the direction of propagation and with a defined orientation in space. This property is known as the polarization of light. In our treatments of interferometry and holography it is silently understood that the interfering waves have the same polarization. In practice, however, this condition is fulfilled to a greater or lesser degree....
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Đo lường quang học P10
Digital Image Processing The electronic camera/frame grabber/computer combination has made it easy to digitize, store and manipulate images. These possibilities have made a great impact on optical metrology in recent years. Digital image processing has evolved as a specific scientific branch for many years. Many of the methods and techniques developed here are directly applicable to problems in optical metrology. In this chapter we go through some of the standard methods such as edge detection, contrast stretching, noise suppression, etc. Besides, algorithms for solving problems specific for optical metrology are needed. Such methods will be treated in Chapter 11. ...
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Đo lường quang học P11
Fringe Analysis In Chapters 3 and 6–9 we have given a description of classical interferometry, holographic interferometry, moir´ , speckle and photoelasticity. The outcome of all these techniques is e a set of fringes called interferograms. For many years, the analysis of these interferograms has been a matter of manually locating the positions and numbering of the fringes. With the development and decreasing cost of digital image processing equipment, a lot of effort has been made into what is termed digital fringe pattern measurement techniques....
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Đo lường quang học P12
Computerized Optical Processes For almost 30 years, the silver halide emulsion has been first choice as the recording medium for holography, speckle interferometry, speckle photography, moir´ and optical e filtering. Materials such as photoresist, photopolymers and thermoplastic film have also been in use. There are two main reasons for this success. In processes where diffraction is involved (as in holographic reconstruction), a transparency is needed. The other advantage of film is its superior resolution. Film has, however, one big disadvantage; it must undergo some kind of processing...
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Đo lường quang học P13
Fibre Optics in Metrology With a carrier frequency of some 1014 Hz, light has the potential of being modulated at much higher frequencies than radio waves. Since the mid-1960s the idea of communication through optical fibres has developed into a vital branch of electro-optics. Great progress has been made and this is now an established technique in many communication systems. From the viewpoint of optical metrology, optical fibres are an attractive alternative for the guiding of light. An even more important reason for studying optical fibres is their potential for making new types of sensors. ...
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Hiệu suất của hệ thống thông tin máy tính P1
IN this chapter we discuss the aim of and the approach normall evaluation of computer and communication systems in Section 1.1. A classification solution techniques is presented in Section 1.2. The fact that we will need stochastic models is motivated in Section 1.3. As a special case of these, we then introduce queueing models in Section 1.4. Finally, in Section 1.5, we discuss the use of software tools for model construction and solution.
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Hiệu suất của hệ thống thông tin máy tính P2
In this section we will introduce evaluation: lies in the fact that it can be applied almost unconditionally to all queueing models and at many levels of abstraction. Its strength furthermore lies in the fact that its form is both intuitively appealing and simple. Little’s law and explain it intuitively. A more thorough In Section 2.1.1 we introduce proof is given in
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Hiệu suất của hệ thống thông tin máy tính P3
Chapter Stochastic 3 processes is to provide evaluation rigour. as outlined processes stochastic 3.2. We follow in Section discusses the necessary purposes. It is assumed in Appendix and classify process with A. them in Section 3.1, after which we with chains classes in more the study 3.4 in which general detail. We start Markov chains special in Sections as arrival in Section chains. background that the reader in stochastic processes in this T about HE aim of this chapter for practical probability define a number processes performance theory, nor at mathematical stochastic of different in Section Then, ...
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Hiệu suất của hệ thống thông tin máy tính P4
IN the previous chapter we have already presented birth-death processes as an important class of CTMCs. In this chapter, we will see that a birth-death model can be used for analysing various types of elementary queueing stations.
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Hiệu suất của hệ thống thông tin máy tính P5
IN the previous chapter we have discussed a number of Markovian shown various applications of them. In practice,however, there are systems for which the negative exponential service times that were assumed in these models are not realistic. There exist, however, also single server models that require less strict assumptions regarding model, the GIG11 model and the used service time distributions. Examples are the MjGll the GiPHll model. The analysis of these models is more complicated than that of the simple birth-death models encountered in Chapter 4. In this chapter we focus on the MlGll applicable in environments where multiple are...
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Hiệu suất của hệ thống thông tin máy tính P6
IN this chapter we continue the study of MlGjl q ueueing models. In particular, we will study the influence of various new scheduling disciplines, in comparison to the FCFS scheduling we have addressed in Chapter 5. We address non-preemptive priority scheduling in Section 6.1 and preemptive priority scheduling in Section 6.2. A limiting case of the non-preemptive priority scheduling is shortest job next scheduling, which is discussed in Section 6.3.
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Hiệu suất của hệ thống thông tin máy tính P7
GIMIl-FCFS and GIGI&FCFS queueing models N Chapters 5 and 6 we have addressed queues with generally distributed service time distributions, but still with Poisson arrivals. In this chapter we focus on queues with more general interarrival time distributions. In Section 7.1 we address the GlMll queue, the important “counterpart” of the MIGil q ueue. Then, in Section 7.2, we present an exact result for the GIG11 q ueue. Since this result is more of theoretical than of any practical interest, we conclude in Section 7.3 with a well-known approximate result for the GIG11 queue. ...
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Hiệu suất của hệ thống thông tin máy tính P8
IN this chapter numerical the class of PHlPH however, as special cases of GIGI 1 queues; due to the specific methods efficient solution. known as matrix-geometric is not to present solution. efficient organised Instead, solution insight The aim of this chapter and their matrix-geometric geometric models, queueing methods, together models. is further with their all the known operation, material our aim is to show the usefulness and to show that techniques, are a good alternative 8.1 we readdress to provide into their This chapter matrix-geometric play an important...
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Hiệu suất của hệ thống thông tin máy tính P9
These days, intelligent file or computing servers via a shared communication medium that grants access using a polling scheme. Also in other fields, e.g., manufacturing, logistics and maintenance, the principle of polling is often encountered. When trying to analyse systems that operate along some polling scheme, so-called polling models are needed. In this chapter we provide a concise overview of the theory and application of polling models. Although we do provide some mathematical derivations, sometimes polling our main aim is...
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Hiệu suất của hệ thống thông tin máy tính P10
In practice, many systems consist of multiple, fairly independent service providing entities, each with their own queue. Jobs in such systems “travel” from queueing station to queueing station in order to complete. Instances of these so-called queueing networks can be observed at many places: in computer systems where a number of users are trying to get things done by a set of processors and peripherals
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Hiệu suất của hệ thống thông tin máy tính P11
Chapter 10 we addressed queueing networks with, in principle, an unbounded number of customers. In this chapter we will focus on the class of queueing networks with a fixed number of customers. The simplest case of this class is represented by the so-called GordonNewell queueing networks; they are presented in Section 11.1. As we will see, although the state space of the underlying Markov chain is finite, the solution of the steady-state probabilities is not at all straightforward (in comparison to Jackson networks). A recursive scheme to calculate the steady-state probabilities in Gordon-Newell queueing networks is presented in Section...
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Hiệu suất của hệ thống thông tin máy tính P12
The previous chapter it has become clear that the evaluation of large closed queueing networks can be quite unattractive from a computational point of view; this was also the reason for addressing approximation schemes and bounding methods. In this chapter we go a different way to attack large queueing network models: hierarchical modelling and evaluation. We address a modelling and evaluation approach where large submodels are solved in isolation and where the results of such an isolated evaluation are used in other models. To be able to do so, however, we need load-dependent queueing stations, that is, queueing nodes in...
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Hiệu suất của hệ thống thông tin máy tính P13
The seminal paper on this class of queueing networks, published by Baskett, Chandy, Muntz and Palacios in 1975, is probably the most referenced paper in the performance evaluation literature. We present the BCMP result in Section 13.1, and then we discuss a number of computational algorithms in Section 13.2. It is important to note that we do not strive for completeness in this chapter; we merely selected a few computational algorithms to show their similarity to the algorithms discussed so far and to comment on their computational complexity. ...
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Hiệu suất của hệ thống thông tin máy tính P14
IN this chapter the basic theory theory SPNs grew out of the general 1960s through of (non-timed) of stochastic nets developed in these models. the early the introduction for an overview. networks, papers in the field of stochastic to the end of the chapter SPNs are, like queueing easy specification the involved numerically, butions to an underlying In this chapter computed. performance CTMCs Note that modelling. Notation
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Hiệu suất của hệ thống thông tin máy tính P15
In this chapter, of infinite-state we focus on the solution with a finite, but possibly specification. 4 (birth-death state space, once they have been generated CTMCs from a high-level The solution has been discussed in Chapter queueing models), Chapter 8 (quasi-birth-death queueing models) and Chapter models) and will be discussed further in Chapter 17. Finite haviour.
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Hiệu suất của hệ thống thông tin máy tính P16
In this chapter we address a number of applications of the use of SPN models. All the addressed applications include aspects that are very difficult to capture by other performance evaluation techniques. The aim of this chapter is not to introduce new theory, but to make the reader more familiar with the use of SPNs. We start with SPN models of a multiprogramming computer system in Section 16.1. We will show how to use exact SPN models for multiprogramming models including paging phenomena
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Hiệu suất của hệ thống thông tin máy tính P17
THE SPNs we have addressed in the previous finite state space. In this chapter we focus on a special class of stochastic SPNs with unbounded state space, known as one-place unbounded SPNs or infinite-state (abbreviated as iSPNs). In particular, we focus on a class of SPNs of which the underlying CTMC has a QBD structure, for which efficient solution methods exist (see Chapter 8). The properties an SPN has to fulfill to belong to this class can be verified at the SPN level, without having to construct the reachability graph....
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Hiệu suất của hệ thống thông tin máy tính P18
In the previous chapters we have addressed models that can be solved by analytical or numerical means. Although the class of addressed models has been very wide, there are still models that cannot be solved adequately with the presented techniques. These models, however, can still be analysed using simulation. With simulation there are no fundamental restrictions towards what models can be solved. Practical restrictions do exist since the amount of computer time or memory required for running a simulation can be prohibitively large....
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Giai đoạn mảng anten P1
ARRAY BACKGROUND Discovery of the first works on array antennas is a task best left to historians, but the two decades before 1940 contained much activity on array theory and experimentation. Some of the researchers were G. H. Brown, E. Bruce, P. S. Carter, C. W. Hansell, A. W. Ladner, N, E. Lindenblad, A. A. Pistolkors, S. A. Schelkunoff, G. C. Southworth, E. J. Sterba, and T. Walmsley. Primary journals were Proc. IRE, Proc. IEE, BSTJ, RCA Review, and Marconi Review. During World War II, much array work was performed in the United States and Britain....
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Giai đoạn mảng anten P2
Basic Array Characteristics This chapter is concerned with basic characteristics of linear and planar arrays, primarily with uniform excitation. The theory of, and procedures for, the design of array distributions to produce narrow-beam, low-sidelobe patterns, or shaped beams, are covered in detail in Chapter 3. Impedance effects due to mutual coupling are treated in Chapter 7.
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Giai đoạn mảng anten P3
Linear Array Pattern Synthesis The fields radiated from a linear array are a superposition (sum) of the fields radiated by each element in the presence of the other elements. Each element has an excitation parameter, which is current for a dipole, voltage for a slot
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Giai đoạn mảng anten P4
Many aircraft radars are now equipped with flat plane slot arrays instead of dish antennas, where the outline is approximately circular. These are usually fixed narrow-beam antennas with controlled sidelobes. Pattern synthesis typically usesthe product of two linear syntheses;one along the slot “sticks,” and a second across the sticks. These are often designed as Taylor ii patterns, as described in Chapter 3. Since the sticks near the edge are shorter, with fewer slots, than those at the center, the overall pattern will deviate somewhat from the product of the two orthogonal patterns...
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