vb.net 2d barcode dll The Operator in .NET

Embed DataMatrix in .NET The Operator

So far, all of the variables that we have been using are declared at the start of the Main( ) method. However, C# allows a local variable to be declared within any block. As explained in 1, a block begins with an opening curly brace and ends with a closing curly brace. A block defines a scope. Thus, each time you start a new block, you are creating a new scope. A scope determines what names are visible to other parts of your program without qualification. It also determines the lifetime of local variables. The most important scopes in C# are those defined by a class and those defined by a method. A discussion of class scope (and variables declared within it) is deferred until later in this book, when classes are described. For now, we will examine only the scopes defined by or within a method. The scope defined by a method begins with its opening curly brace and ends with its closing curly brace. However, if that method has parameters, they too are included within the scope defined by the method. As a general rule, local variables declared inside a scope are not visible to code that is defined outside that scope. Thus, when you declare a variable within a scope, you are protecting it from access or modification from outside the scope. Indeed, the scope rules provide the foundation for encapsulation. Scopes can be nested. For example, each time you create a block of code, you are creating a new, nested scope. When this occurs, the outer scope encloses the inner scope. This means that local variables declared in the outer scope will be visible to code within the inner scope.

FIGURE 25-1

FileStream fin = new FileStream("test.dat", FileMode.Open, FileAccess.Read);

S parameters characterize any RF device s behavior at different frequencies and bias points. With the information that S parameters supply, the designer can calculate a device s gain, return loss, stability, reverse isolation, and its input and output impedances. Knowing the transistor s port impedances is required so that the necessary matching network can easily be designed for a proper impedance match from stage to stage. This matching is vital so that maximum power is delivered to the load at a high return loss (minimum power reflected back toward the source from the load). Impedance matching of active devices is essential because not only will the typical transistor not have a 50-ohm resistive ZIN and ZOUT, but its reactances will also vary over frequency. This means that for maximum power transfer into the system s impedance, which is normally 50 ohms, a matching network must be used to match the active device to the system s impedance, and sometimes over a wide band of frequencies. However, utilizing LC components is the dominant matching technique, so the match will be perfect only over a very narrow band of frequencies. There are, nevertheless, techniques for impedance matching that work quite well over a very wide band of frequencies, and these will be discussed. For further information, consult the influential work on practical amplifier design RF Circuit Design by Chris Bowick. As mentioned above, a device that must be matched will normally not be at 50 ohms resistive and furthermore will be either inductive or capacitive. This combination resistive and reactive elements in the active device s ZIN and ZOUT is referred to as a complex impedance. So the matching network s job is not only to match the active device to the system s impedance, but also to cancel the reactive element to allow for a 50 j0 match (or 50 ohms resistive, with no capacitive or inductive reactances). This is called conjugate matching, and supplies a perfect impedance match. Nevertheless, in order to decrease the gain of a transistor at various desired frequencies for gain flattening, or to purposely design an amplifier with less gain within its bandpass, as well as for optimal noise figure (NF), a perfect match may not be desired for certain amplifier applications. It is usually advisable that all circuits, even discrete circuits in the middle of an IF chain, have a ZIN and ZOUT of 50 ohms. Although we could match at any sensible impedance from discrete stage to discrete stage, it would make it quite difficult to perform accurate interstage tests with the 50-ohm test gear commonly available. Thus, after each stage is tested, a 50-ohm circuit can then be confidently placed within the system for reliable cascaded operation. When designing matching networks, we will take the S-parameter 2-port representation of the transistor, ignoring any effect the DC biasing network may have on these parameters in the final design. This is quite valid if only small amounts of RF feedback are produced by high values of Rf (Fig. 3.15; the feedback resistor) in an amplifier s bias network. In this way, the S parameters will be satisfactory for computing not only the matching networks, but also for the software simulations of the circuit s responses. However, if an amplifier utilizes a low value resistor for Rf in order to employ heavy feedback,

Another key consideration in the ability of the CD-ROM drive to deliver information is the data transfer rate. In many ways, the data transfer rate is more important than the access time in assessing performance, since it measures the ability of the CD-ROM drive to move data from the disc surface to the host computer. Mainstream 24x CD-ROM drives theoretically deliver data at an impressive 3600K bytes per second. However, if you develop a CD-ROM in anticipation of this kind of performance, you may suffer seriously degraded performance on the multitude of low-speed drives still installed in the marketplace. In many cases you will want to deliver content to the largest installed base of equipment, a factor that imposes rather stern limitations on the scope and execution of your project. While the bulk of the installed base is rapidly shifting from 12x and 16x drives to 24x and 32x drives (largely because of price reductions in high-performance equipment), you can never reliably count on the majority of your audience having high-performance CD-ROM drives. At this point in time, your best bet is to optimize your CD-ROM production to perform at its best on a 12x drive. This may handicap you in some ways, but it will also challenge you to nd the best techniques to keep data barrelling through the pipe. For certain types of productions, perhaps those where the mass market is less important and you have control

This query produces a sequence that contains objects that encapsulate the name and the instock status of an inventory item. This information is synthesized from joining the two lists items and statusList. The following version reworks this query so that it uses the Join( ) method rather than the C# query syntax:

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This ultimately leads to more profits for the Service Provider because they avoid the significant costs incurred during the acquisition of new customers to replace those who leave. Figure 1.17 shows a scenario illustrating the significant revenue benefits of delivering Ethernet services over traditional TDM services. Two Service Providers, A and B, start out delivering Internet access services and employing Ethernet and E-1, respectively. Assuming similar pricing and growth opportunities at both Service Providers and a better customer retention rate for Service Provider A (as noted previously, a Service Provider offering Ethernet service is better positioned to deliver almost all of a customer s service requests), we find that Service Provider A will, with time, receive higher revenues than Service Provider B. By the fifth year, Service Provider A will, in fact, receive 2.6 times more revenues than Service Provider B across a similar customer base of 100 customers.51 Market assessments indicate a rapidly growing demand for Ethernet services for all the reasons discussed previously in this section.52 According to Infonetics, over 86 percent of Service Providers indicated high customer demand for new Ethernet services with about 57 percent wanting to migrate from Frame Relay and ATM to Ethernet services. Naturally, Service Providers find this demand appealing and are scurrying to provide Ethernet service; in the North American market alone, over 200 Carriers are providing some form of Ethernet service. In other global markets such as Asia, customer demand follows an even more aggressive trend. These different trends are discussed in detail in 3.

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6. Dynamic characteristics of the bridge, longitudinal and torsional mode shapes, frequency of vibrations and damping effects can be effectively studied. 7. For bridges located in severe earthquake zones, earthquake response can be studied by measuring bridge frequency, vibration and damping. 8. Vibration tests are usually performed by portable sinusoidal shakers, impulsive devices such as hammers, sudden release of applied de ections and sudden braking of vehicles. For modal frequency, mode shapes and damping ratios, accelerometers are used. 9. Weigh in motion testing (WIM) is commonly used to survey the truck volume and weight spectra. By using axle sensors, WIM tests provide data on vehicle arrivals, speed and axle loads.