Spectral distributions

The spectral distribution is properly described by Schwinger (1949). The instantaneous power radiated by a monoenergetic electron in circular motion expressed as energy per unit time per unit angle per unit wavelength is given by 

The spectral distribution of the emitted light has been determined by a wavelength filter method. Ashby (136) found that the PMT anode current was attenuated about 50% by interposing a filter that absorbed light of the wavelengths shorter than 420 nm between the polymer and the PMT. No current could be detected if a filter was interposed that absorbed light of wave- 

The resulting spectrum consisted of a broad peak from 400-610 nm with a maximum at about 540 nm. A shoulder peak was observed at about 475 nm. Also using wavelength filters, de Rock and Hoi (140) obtained the OL spectrum of dicumyl peroxide in polypropylene. The OL curve extended from 360 nm to about 500 nm with a peak maximum at 420 nm. It was very similar to the phosphorescence spectrum of acetophenone dissolved in poly(methyl methacrylate) in fact, the peak maximas were exactly the same. 

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C is the concentration of limiting reactant in mol/L, c is the chemiluminescence quantum yield in ein/mol, and P is a photopic factor that is determined by the sensitivity of the human eye to the spectral distribution of the light. Because the human eye is most responsive to yellow light, where the photopic factor for a yellow fluorescer such as fluorescein can be as high as 0.85, blue or red formulations have inherently lower light capacities. 

M. P. Thekaekara, "Survey of Quantitative Data on the Solar Energy and its Spectral Distribution," Conference of COMPEES, Dahran, Saudi Arabia, Nov. 1975. 

The spectral distribution of energy flux from a black body is expressed by Planck s law ... 

In photoluminescence one measures physical and chemical properties of materials by using photons to induce excited electronic states in the material system and analyzing the optical emission as these states relax. Typically, light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distribution and time dependence of the emission are related to electronic transition probabilities within the sample, and can be used to provide qualitative and, sometimes, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. 

The extent to which a ventilation noise is perceived as disturbing depends not only on its dB(A) level, but also on the spectral distribution and the presence of tones or intermittent components in the noise. From an experiment carried out on respondents exposed to ventilation noises with different characteristics in a simulated office room, it emerged that the highest acceptable level was about 7 dB higher for ventilation noise with a superimposed tone at 30 Fiz than for other types of noise. In another experiment, it was found that the tolerance level was much higher for a tone than for a noise at 100 Hz, whereas the opposite tendency applied at 1000 Hz. ... 

Viviani, V. R., and Bechara, E. J. H. (1995). Bioluminescence of Brazilian fireflies (Coleoptera Lampyridae) Spectral distribution and pH effect on luciferase-elicited colors. Comparison with Elaterid and phengodid luciferases. Photochem. Photobiol. 62 490-495. 

A means for describing the volumetric efficiency of a flare is the radiant energy per steradian per unit flare volume (W-sec/ster cm3), the RED (Ref 133, p 227), such that the RED, the bum time of the flare and the curve of the spectral distribution constitutey for most purposes, 2 full description of a flare... 

Sodium has 1 valence electron, and 10 bound electrons. The first two excited states are the 3 Pi/2 and the 3 P3/2 states. Transitions to these levels give rise to the Di and D2 transitions respectively. There are two h)q)erfine levels in the 3 ground state, and four h)q)erfine levels in the 3 Pa/2 excited state (Fig. 3). There is no significant energy difference between the h)q)erfine levels in the 3 Pa/2 state. Thus, the six permitted fines appear in two groups, producing a double peaked spectral distribution, with the peaks separated by 1.772 GHz. 

The fundamental quantity for interferometry is the source s visibility function. The spatial coherence properties of the source is connected with the two-dimensional Fourier transform of the spatial intensity distribution on the ce-setial sphere by virtue of the van Cittert - Zemike theorem. The measured fringe contrast is given by the source s visibility at a spatial frequency B/X, measured in units line pairs per radian. The temporal coherence properties is determined by the spectral distribution of the detected radiation. The measured fringe contrast therefore also depends on the spectral properties of the source and the instrument. 

The main consequences are twice. First, it results in contrast degradations as a function of the differential dispersion. This feature can be calibrated in order to correct this bias. The only limit concerns the degradation of the signal to noise ratio associated with the fringe modulation decay. The second drawback is an error on the phase closure acquisition. It results from the superposition of the phasor corresponding to the spectral channels. The wrapping and the nonlinearity of this process lead to a phase shift that is not compensated in the phase closure process. This effect depends on the three differential dispersions and on the spectral distribution. These effects have been demonstrated for the first time in the ISTROG experiment (Huss et al., 2001) at IRCOM as shown in Fig. 14. 

The Compton scattering cannot be neglected, but it is independent of molecular structure. Then, fitting experimental data to formulas from gas phase theory, the concentration of excited molecules can be determined. Another problem is that the undulator X-ray spectrum is not strictly monochromatic, but has a slightly asymmetric lineshape extending toward lower energies. This problem may be handled in different ways, for example, by approximating its spectral distribution by its first spectral moment [12]. 

Air or water cooled mercury discharge lamps find many uses, one of the more obvious of which is the study of photochemical reactions. These lamps are usually made of vitreous silica because of its low thermal expansion, high melting point and its transparency to ultraviolet radiation. Their operating pressure has a profound effect on the spectral distribution of the radiation produced and therefore it is important to consider the requirements in the design of such lamps. 

The expression in brackets in Eq. (87) is of the form (sin x/x)2t where x = (tom — o>)tf 2. Thus, for a given time t for the duration of the perturbation, the spectrum, e.g. the transition probability as a function of the ahgular frequency w is as shown in Fig. 2. The width at half-maximum of this spectral feature is represented by A for a given value of the time, t. If, for example, the perturbation time is increased by a factor of four, the width of the spectral distribution is reduced by the same factor, as shown by (he solid tine in Fig. 2. Equation (87) expresses the probability that the system, initially in die state k = n, will be in the state m after a sinusoidal perturbation over a relatively short period of time t. 

Thus they were able to calculate the velocity intensity from the mass-transfer intensity and the spectral distribution function of mass-transfer fluctuations. By measuring and correlating mass-transfer fluctuations at strip electrodes in longitudinal and circumferential arrays, information was obtained about the structure of turbulent flow very close to the wall, where hot wire anemometer techniques become unreliable. A concise review of this work has been given by Hanratty (H2). 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

The spectral distribution of this radiation is given in Table 4.3, from which we can easily see that radiation with wavelengths below 150nm represents only a tiny fraction of the total. The energy distribution of the solar radiation corresponds to that from a black body with a temperature of around 5,000 K. 

Table 4.3 Spectral distribution of the optical solar radiation in the Earth s atmosphere. Data taken from the Smithsonian Physical Tables (1959)...

Specific solar radiation conditions are defined by the air mass (AM) value. The spectral distribution and total flux of radiation outside the Earth s atmosphere, similar to the radiation of a black body of 5,900 K, has been defined as AM-0. The AM-1 and AM-1.5 are defined as the path length of the solar light relative to a vertical position of the Sun above the terrestrial absorber, which is at the equator when the incidence of sunlight is vertical (90°) and 41.8°, respectively. The AM-1.5 conditions are achieved when the solar flux is 982 Wm2. However, for convenience purpose the flux of the standardized AM-1.5 spectrum has been corrected to 1,000 Wm2. 

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