Atomic interferences

Solid solutions are more rare. Crystals are stable because of the regularity of the positioning of the atoms. A foreign atom interferes with this regularity and hence with the crystal stability. Therefore, as a crystal forms, it tends to exclude foreign atoms. That is why crystallization provides a good method for purification. 

Steel is an alloy of about 2% or less carbon in iron. Carbon atoms are much smaller than iron atoms, and so they cannot substitute for iron in the crystal lattice. Indeed, they are so small that they can fit into the interstices (the holes) in the iron lattice. The resulting material is called an interstitial alloy (Fig. 5.48). For two elements to form an interstitial alloy, the atomic radius of the solute element must be less than about 60% of the atomic radius of the host metal. The interstitial atoms interfere with electrical conductivity and with the movement of the atoms forming the lattice. This restricted motion makes the alloy harder and stronger than the pure host metal would be. 

Inertial sensors are useful devices in both science and industry. Higher precision sensors could find practical scientific applications in the areas of general relativity (Chow et ah, 1985), geodesy and geology. Important applications of such devices occur also in the field of navigation, surveying and analysis of earth structures. Matter-wave interferometry has recently shown its potential to be an extremely sensitive probe for inertial forces (Clauser, 1988). First, neutron interferometers have been used to measure the Earth rotation (Colella et ah, 1975) and the acceleration due to gravity (Werner et ah, 1979) in the end of the seventies. In 1991, atom interference techniques have been used in... 

X-ray diffraction (XRD) and scattering experiments involve placing the sample in the path of a monochromatized X-ray beam of low divergence. The scattered X-rays from the regularly placed atoms interfere with each other, giving strong diffraction signals in particular directions. The directions of the diffracted beams are related to the slope and dimensions of the unit cell of the crystalline lattice, and the diffraction intensity depends on the disposition of the atoms within the unit cell [5]. 

All chlorofluorocarbons have some fire-extinguishing properties even carbon tetrachloride was used at one time in small, handheld fire extinguishers. Flowever, bromofluorocarbons (BFCs) are exceptional because the bromine atom interferes most effectively with the radical propagation mechanism of the flame. Table 1 includes the three, commercially available bromofluorocarbons used as fire-fighting agents which are generally referred to industrially by the term Flalon . 

For the purposes of this review it is convenient to focus attention on that class of molecules in which the valence electrons are easily distinguished from the core electrons (e.g., -n electron systems) and which have a large number of vibrational degrees of freedom. There have been several studies of the photoionization of aromatic molecules.206-209 In the earliest calculations either a free electron model, or a molecule-centered expansion in plane waves, or coulomb functions, has been used. Only the recent calculation by Johnson and Rice210 explicitly considered the interference effects which must accompany any process in a system with interatomic spacings and electron wavelength of comparable magnitude. The importance of atomic interference effects in the representation of molecular continuum states has been emphasized by Cohen and Fano,211 but, as far as we know, only the Johnson-Rice calculation incorporates this phenomenon in a detailed analysis. 

Rays coming from two neighboring atoms interfere constructively if the difference in path-length is just an integer number of wavelengths. This is the case for... 

Reference to atomic interference is of interest for other reasons, too. One can study the properties of elementary particles by observing and precisely measuring various fine effects in the bound states. From such measurements, in principle, one can obtain such details as the behaviour of interactions at short distances, which otherwise are manifested only at very high energies. Optical measurements are probably among the most precise. If one adopts this form of measurement it is natural to ask whether it is possible to consider some phenomena of atomic physics within spec-... 

At the same time, a two electrode interferometer, which is convenient in operation, and which can be adjusted relatively easily with respect to a strictly collimated beam of hydrogen atoms, permits the study of many specific features of atomic interference. 

In the experiments described above, it has been shown that when the two phase-shifted components of the 2p (or 2s) atomic hydrogen state interfere, some net curve - the superposition of separate curves corresponding to transitions between the components of the hyperfine 2s and 2p level structure - is registered. Further study of atomic interference has shown that hyperfine splitting can also be obtained in other ways. 

Aromaticity in the larger (4A+2) annulenes depends on whether the molecule can adopt the necessary planar conformation. In the all-cis [10]annulene, the planar conformation requires an excessive amount of angle strain. The [10]annulene isomer with two trans double bonds cannot adopt a planar conformation either, because two hydrogen atoms interfere with each other. Neither of these [10]annulene isomers is aromatic, even though each has (4/V+2) pi electrons, with N = 2. If the interfering hydrogen atoms in the partially trans isomer are removed, the molecule can be planar. When these hydrogen atoms are replaced with a bond, the aromatic compound naphthalene results. 

Brevetoxin B is one of a family of polyethers found in a sea creature (a dinoflagellate Gymnodinjum breve, hence the name) which sometimes multiplies at an amazing rate and creates red tides around the coasts of the Gulf of Mexico. Rsh die in shoals and so do people if they eat the shellfish that have eaten the red tide. The brevetoxins are the killers. The many ether oxygen atoms interfere with sodium ion (Na+) metabolism. 

Similar phenol couplings have been attempted in the laboratory with compounds in the benzyl isoquinoline series but the nitrogen atom interferes if it is at all basic. When it has a carbonyl substituent the reactions do work reasonably well, but the yields are poor. Nature is still much better at this reaction than we are. 

Scattered waves from neighbouring atoms interfere in exactly the same way and unless the atoms are ordered as in a crystal, the total diffraction pattern is a function of the radial distribution of scattering density (atoms) only. This is the mechanism whereby diffraction patterns arise during gas-phase electron diffraction, scattering by amorphous materials, and diffraction... 

This quantity (which in the case of X-rays is identical with the atom form factor F) has a distinctive magnitude, and depends on the angle in a distinctive way, for each kind of atom. It also gives the effect which intra-atomic interference has in diminishing the scattered intensity, and is calculated on the basis of ... 

Interstitial atoms interfere with electrical conductivity and the movement of atoms. 

Fish die in shoals and so do people if they eat the shellfish that have eaten the red tide. The brevetoxins are the killers. The many ether oxygen atoms interfere with sodium ion (Na+) metabolism. 

Here I(Q) is the X-ray interference function, representing the wave number dependence of the X-ray intensity after dividing by the squared structure factor f(Q) in order to remove the <2 d P > d nce due to intra-atomic interference effects. The function I(Q) has also been corrected for by several other structure-independent quantities such as polarization, absorption and geometrical factors. 

The inner diffraction effect is produced when the individual particles of the atom capable of vibration, i.e. the electrons contained in the atoms, are dispersed and give rise to secondary radiations which interfere with one another. In a liquid built up of single atoms— A, Kr, Xe, Hg, Ga— the result is that, on account of intra-atomic interference, the dependence of intensity distribution on the angle of diffraction is already affected. This influence is generally expressed by a factor, which, because of its origin, is called the atomic form factor its action is that more intensity is scattered in the directions near the primary beam than if the interaction of the individual electrons is not taken into account. 

Fiydride generation (and cold-vapor) techniques significantly improve atomic absorption spectrometry (AAS) concentration detection limits while offering several advantages (1) separation of the analyte from the matrix is achieved which invariably leads to improved accuracy of determination (2) preconcentration is easily implemented (3) simple chemical speciation may be discerned in many cases and (4) the procedures are amenable to automation. Disadvantages with the approach that are frequently cited include interferences from concomitant elements (notably transition metals), pH effects, oxidation state influences (which may be advantageously used for speciation) and gas-phase atomization interferences (mutual effect from other hydrides). 

In siammary, the preliminary results presented in this contribution already demonstrate that time resolving polarization spectroscopy offers a number of favourable and new features for direct observation of fast evolving events on a femtosecond time scale and detection of oscillations up to the THz-range. The described technique can be applied to free atoms, liquids and solids to measure coherent transients in groimd and excited states. Since the observed beats result from an atomic interference effect, narrow structures which may be hidden by inhomogeneous broadening mechanisms can still be resolved. 

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