Sources radiated power

Sound power is the total energy emitted from a fan that is a function of the fan s speed and point of operation and is independent of the fan s installation and surrounding environment Sound power level is the acoustical power expressed in decibels (dB) radiating from a source. Sound power can be converted into predictable pressure levels (dBA) after the acoustical environment surrounding the fan is defined. Sound pressure for a specific fan varies with... 

The conversion of radiated power (P in watts) to luminous flux (F in lumens) is achieved by considering the variation with wavelength of the human eye s photopie response. Then the spectral power from the source (PA in, lor example, W/nnt) is convoluted with the relative spectral response of the eye (V tabulated by the CIE) according to ... 

Although the methods and materials described are adequate to construct commercial irradiators today, economic forces will ultimately require the use of higher specific activities than are used today. An example will perhaps illustrate this point. Suppose one desires to build an irradiator to pasteurize strawberries. Peak loads and therefore design loads would be about 10,000 pounds per hour. About 10 kw. of radiation power at reasonable over-all efficiencies, or about 670,000 curies of 60Co, would be required. If the radiation source were made up at 2 curies per gram, one would require 4000 BNL strips in 1000 irradiation cans at a cost of 100,000 at 20 curies per gram, 400 strips in 100 irradiation cans at a cost of 10,400 ... 

Centralized Control As mentioned previously, motor starters may be located either at the motor or at some remote point. Frequently they are grouped at a location convenient to the source of power. The feeders radiate from this point to the individual motor loads. A convenient method is the control-center modular structure for low-voltage control, into which are assembled motor starters and other control devices. The individual starters can be drawn out of the structure for rapid, easy maintenance and adjustment. With this construction it is easy to change starter size or add additional starters. All the starters are in one location, so that interwiring is simple and easy to check. Auxiliary relays, control transformers, and other special control devices can also be included. See Fig. 29-7. 

Promethium has limited uses. It can be used as a source of power. The radiation it gives off provides energy, similar to that from a battery. A promethium battery can be used in places where other kinds of batteries would be too heavy or large to use, as on satellites or space probes. Such batteries are far too expensive for common use, however. 

In atomic fluorescence spectroscopy, an external source is used just as in atomic absorption, as shown in Figure 24-6. Instead of measuring the attenuated source radiant power, however, the radiant power of fluorescence, Pp, is measured, usually at right angles to the source beam. In such experiments, we must avoid or discriminate against scattered source radiation. Atomic fluorescence is often measured at the same wavelength as the source radiation, in which case it is called resonance fluorescence. 

Figure 28-1 6 Block diagram of a single-beam atomic absorption spectrometer. Radiation from a line source is focused on the atomic vapor in a flame or an electrothermal atomizer. The attenuated source radiation then enters a monochromator, which isolates the line of interest. Next, the radiant power from the source, attenuated by absorption, is measured by the photomultiplier tube (PMT). The signal is then processed and directed to a computer system for output.

A natural question that arises in the context of possible applications is how much radiation power is necessary to produce such magneto-resistance oscillations In order to answer this question, we exhibit the dependence of the radiation-induced magnetoresistance oscillations on the absolute radiation intensity in Fig. 4. Here, the quoted radiation intensities are the measured values at the microwave source, and they do not reflect losses that come about in the transmission of the radiation from the source to... 

Fig. 4 shows that the source radiation intensity can be reduced from 1000 microwatts [/cm ] to 10 microwatts [/cm ], without a tremendous loss in the oscillatory resistance signal. Indeed, even 1 microwatt [/cm ] yields observable oscillations withont supplementary electronic enhancement. We expect that the application of balanced bridge and/or modulation techniques ate likely to provide sensitivity to even lower power levels, into the nanowatt [/cm ] level. 

There is a subtle but important difference between the terms Sound Power Level (PWL), and Sound Pressure Level (SPL). Sound power level is used to indicate the total energy emitting ability of a sound source. In other words, sound power is an attribute of the source itself. Sound pressure level, on the other hand, is used to indicate the intensity of sound received at any point of interest, from one or more sources. The illustration in Eigure 8.4 shows the formula to calculate the SPL to be expected at a distance r from a spherically radiating source of power level L. ... 

Directivity factor ratio of the mean-square pressure (or intensity) on the axis of a transducer at a certain distance to the mean-square pressure (or intensity) that a spherical source radiating the same power would produce at that point. 

A/ is the intensity decrease on traversing unit distance in a sample with ground-state population density of A typical value of 5 is 10" ° cm" s photon" molecule" and at 1 torr pressure Ng is about 10 molecules cm . In this case a relative attenuation A/// of 10" is obtained at 7=10 photons cm" s", i.e., about 10 watt cm" s" for visible radiation. Powers of these orders of magnitude, at narrow frequency bandwidths, are practical only with laser sources. For TPE applications, lasers are often (not always) operated in a pulsed mode, allowing easy... 

Radiation Power Rate. For sources consisting of a known weight of a single radioisotope whose decay properties are known, the power in Mev/g-sec can be computed from Eq. (10-14) or (10-16). Conversion to watts is then made on the basis that 1 Mev/sec = 1.6 X 10 watt. The addition of other radioisotopes to the volume source requires a summation of the power value calculated for each isotope as described. The power liberation from a complex mixture of radioisotopes such as found in the fission products of U fuel is time-consuming to calculate. Figure 10-7 avoids the necessity of this by giving the and y power, curies and composition of the radioactive isotopes, all as a function of elapsed time after the fuel is pulled from the reactor. This elapsed time is known as the radiation cooling period. 

In the double-beam system, the source radiation is split into two beams of equal intensity. The two beams traverse two light paths identical in length a reference cell is put in one path and the sample cell in the other. The intensities of the two beams after passing through the cells are then compared. Variation in radiation intensity due to power fluctuations, radiation lost to the optical system (e.g., cell surfaces, mirrors, etc.), radiation absorbed by the solvent, and so on should be equal for both beams, correcting for these sources of error. A dispersive spectrometer used for absorption spectroscopy that has one or more exit slits and photoelectric detectors that ratio the intensity of two light beams as a function of wavelength is called a spectrophotometer. 

This problem is overcome most simply by modulation of the radiation source. Modulation means that the source radiation is switched on and off very rapidly. This can be done by using a rotating mechanical chopper placed directly in front of the source. A chopper is shown in Figs. 6.8 and 6.14. The mechanical chopper is a circle of metal sheet with opposite quadrants cut out. Every quarter turn of the chopper alternately blocks and passes the source radiation. Another way to modulate the source is by pulsing the power to the lamp at a given frequency. When modulated, the signal from the source is... 

Table I lists typical pulse repetition rates, fundamental peak power densities and frequency doubling efficiencies obtainable with various visible laser sources. For the cw and quasi-cw dye laser sources, peak power densities are estimated assuming that 1.0 watt of visible radiation is focused to a 50 ym spot within the frequency doubling crystal. Because the beam energy is bunched into short duration pulse packets with the quasi-cw source, the obtainable focused peak power density and the resultant second harmonic generation efficiency are much larger with this source than with a cw dye laser source. 

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