White spectrum

An experimental teclmique that is usefiil for structure studies of biological macromolecules and other crystals with large unit cells uses neither the broad, white , spectrum characteristic of Lane methods nor a sharp, monocliromatic spectrum, but rather a spectral band with AX/X 20%. Because of its relation to the Lane method, this teclmique is called quasi-Laue. It was believed for many years diat the Lane method was not usefiil for structure studies because reflections of different orders would be superposed on the same point of a film or an image plate. It was realized recently, however, that, if there is a definite minimum wavelengdi in the spectral band, more than 80% of all reflections would contain only a single order. Quasi-Laue methods are now used with both neutrons and x-rays, particularly x-rays from synclirotron sources, which give an intense, white spectrum. 

Photon noise is stochastic phenomena and has a white spectrum over the electronic frequency domain. 

This corresponds to prior knowledge of an equal-energy white spectrum. Combining Eqs. (16) and (20) then yields... 

In summary, it makes more sense for maximum ignorance about a spectrum to mean an infinity of equally likely possibilities (33) than to imply the unique, equal-energy white spectrum (31). 

Time-correlation functions can also be computed from their continued fraction representations (see section III.D) by exploiting a hierarchy of approximations of the following kind. Suppose that the nth order random force has a white spectrum.34 It then follows that... 

This method of approximation is illustrated on the velocity correlation function, although it can be applied to the other time-correlation functions that have been discussed. For the purpose of this illustrative example let us assume that the second-order random force has a white spectrum. Then the continued fraction representation of i(S) is... 

X rays can be produced either (i) by sharp deceleration of fast-moving electrons, or (ii) by ionizing collisions of these electrons with atoms of a suitable (metallic) target. Process (i) gives a continuous white spectrum (because the energy of a free electron is not quantized), whilst (ii) gives narrow characteristic lines. The latter occur when the energy... 

It should also be noted that the spectral power distribution for the "cool white" lamp given in ISO 10977 1993(E) is not that of "cool white" fluorescent lamp but that of a the visible "cool white" spectrum to which the mercury lines have been added (30). This lamp also has a CCT of approximately 4100 K. There is one known notable exception to this last statement and that is Luzchem Research Inc. (33), which does supply a spectrum for each lamp that they sell if it is to be used for ICH photostability testing. 

The multiplex advantage has been lost completely, and the FT spectrometer has the same SNR as a single-channel scanning system, in the case of a flat spectrum. For spectra more complex than a single peak, but not to the limit of a flat (i.e., white ) spectrum, SNRft will lie between the limits described by Eqs. (4.38) and (4.39). 

Neutrons are usually produced in nuclear reactors they have variable energy and therefore, a white spectrum. Maximum flux of neutrons is usually obtained in an angstrom range of wavelengths. The main differences when compared to x-rays are as follows i) neutrons are scattered by nuclei, which are much smaller than electron clouds, and the scattering occurs on... 

Figure 11 Some well characterized Fourier pairs. The white spectrum and the impulse function (a), the boxcar and sine functions (b), the triangular and sintf functions (c), and the Gaussian pair (d)...

Recently, it was demonstrated that the Schlieren effect can be more effectively circumvented when component B prevails [3]. As the related spectrum approaches an ideal white spectrum, the intensity of the effect is not wavelength dependent and hence quantitative suppression by DWS can be attained. Paradoxically, it has often been emphasised that the Schlieren effect becomes less pronounced as mixing conditions are improved. However, under good mixing conditions, component A of the Schlieren effect is dominant. Hence, the DWS efficiency is somewhat... 

The 111 plane of germanium (2d = 6.53 A) or silicon (2d = 6.32 A) is often used as the 222 reflection is forbidden. The monochromatic beam is convergent, resulting in a line at the focus of the bent crystal. This simple setup can be used because the incident white spectrum does not provide wavelengths of the third- and higher-order harmonics... 

For most liquids, t is 10 ° sec. and 0)/ is usually 10 sec. consequently cOjT is therefore much less than unity (Fig. 1) and the value of is more or less independent of co and hence of the applied magnetic field strength. This region of the correlation spectrum is called the white spectrum". 

In the case of dipolar coupling, the transitions Wq, W2 and are all allowed. However it can be shown that the nuclear—electron coupling parameter p is always positive. Under optimum conditions (white spectrum) the ratios of lUo lUi 11 2 are and thus p has a value... 

Effect of aging on the white spectrum. The device was operated continuously at SOmA/cm DC and 40°C. (Reproduced from Hatwar, T.K. and Spindler, J.P. SID Int. Symp. Dig. Tech. Papers, 39, 814, 2008. With permission.)... 

Early experimenters with x-radiation [1,9] noted that x-rays could be polarized like other forms of electromagnetic radiation. Barkla [9] showed that the primary bremsstrahlung radiation was partially polarized. A later investigator, Ross [10], showed that at the high-energy limit of the white spectrum, the x-ray photons were very nearly completely plane polarized. This is in sharp contrast to primary characteristic x-rays, which are unpolarized. 

These effects have been used by investigators to reduce the background radiation levels in x-ray spectroscopy. For Bremsstrahlung radiation, the maximum polarization vector is parallel to the electron path in the x-ray tube. In many conventional-wavelength spectrometer designs, the specimen and crystal surfaces will become parallel when 26 equals the takeoff angle 2 ( 45°). In addition, the x-ray tube axis and the rotational axes of the crystal and detector are parallel. This so-called parallel optics cannot take advantage of the polarization of the white spectrum. If, however, the surface plane of the crystal and specimen remain perpendicular... 

Considerable interest in pure nuclear back-reflections arises also from application to y-optical devices, such as the filtering of Mossbauer radiation from the white spectrum of synchrotron radiation. 

X-rays are divided into continuous and characteristic. Continuous X-rays occur as a result of the stopping of very fast charged particles (e.g. electrons) in the target substance and have a white spectrum. Characteristic X-ray emission radiation is emitted by target atoms after their collisions with hot electrons... 

If white light falls on a diffraction grating each of the main maxima is broadened. The width of a white spectrum is defined by boundary wavelengths 0.4-0.7 pm of visible light. Spectrum of adjacent orders can sometimes overlap. This overlapping is shown in Figure 6. lb where, for clarity, spectra of different orders are given on a different vertical level. It can be seen that spectra of zero-, first- and second-orders exist separately, whereas spectra of the third- and fourth-orders are partially overlapped. 

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