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Various types of spectral interferences in atomic absorption spectroscopy were investigated. Of particular concern were interferences in which atomic electronic processes are a problem. Source emission of multiplets and other radiation near the analysis line can cause nonlinear analytical curves and poor detection limits. Direct absorption spectral overlaps were found to be of importance in some analyses, particularly for transition elements. Comprehensive lists of observed and predicted spectral interferences are presented. It is concluded that spectral interferences may be of more importance than previously supposed in routine analytical situations. Further, there should be an optimal spectral bandpass for each analytical transition.

Correlated random walk statistics are used to derive an expression for the diffusion coefficient for vacancies in a linear chain containing impurities. The results are applied to the problem of anion mobility in the calcium apatites. For fluorapatite the analysis indicates energies of motion for fluorine and oxygen ions to be 0.77 and 2.0 eV, respectively. Le coefficient de diffusion des lacunes, dans une chaǐne lineaire contenant des impuretes, est obtenu a ľaide de statistique ďevenements aleatoires non independants. Le resultat est applique au probleme de la mobilitye des anions dans les apatites de calcium. Pour la fluorapatite, ľanalyse indique des energies de motion des ions fluor et oxygene de 0,77 et 2,0 eV, respectivement.

The presence of residual elastic strains in deformed bulk specimens can contribute to the shifts of X-ray reflections. This is important in elastically anisotropic face-centered cubic metals and can contribute to calculations of stacking fault probabilities. An example of such an effect in measurements on zone-refined lead at 4.2 K is examined.

Calculations are presented for the energy of Schottky pair formation and for the activation energy of cation vacancy migration in potassium azide (KN3). Parameters for the repulsive overlap energy of the azide molecule ion have been derived from a Born model treatment of the lattice interactions with the cohesive energy and its first and second derivatives used in the fitting procedure. Three different representations of the repulsive potential are considered. Point defect calculations are performed first in a rigid lattice approximation and then with the effects of polarization and relaxation included. The polarization energy is calculated by a generalized Mott and Littleton method, which accounts for the anisotropy of the lattice, in both zeroth and first order approximations. Relaxations include displacements and rotations of nearest neighbors of the defect configurations. The sensitivity of the results t o the choice of a repulsive potential are discussed. L'energie de formation d'une paire de Schottky et l'energie d'activation pour la migration d'une lacune de cation ont ete calculees pour le nitrure de potassium (KN3). Des parametres pour l'energie de repulsion venant du chevauchement de l'ion-molecule nitrure ont At obtenus en traitant les interactions du reseau a l'aide d'un modiele de Born, et l'energie de cohesion ainsi que ses derivees premiere et seconde ont ete utilisees pour obtener la meilleure correlation. Trois differentes representations du potentiel de repulsion sont considerees. Les calculs sur les defauts ponctuels sont faits d'abord dans I'approximation du reseau rigide, ensuite en tenant compte des effects de polarisation et de relaxation. L'energie de polarisation est calculee par une methode de Mott et Littleton generalisee, qui tient compte de I'anisotropie du reseau dans I'approximation d'ordre zero et dans celle du premier ordre. Les phenomienes de relaxation comprennent les deplacements et les rotations des plus proches voisins du complexe du defaut. La depenidance des resultats au choix des potentiels de repulsion est discutee.

Experiments are reported in which the diffusion coefficients for the migration of Ca2+, PO, and OD− ions have been measured in single crystals of fluorapatite for directions parallel and perpendicular to the crystalline c-axis. The measurements have been made over the temperature range between 1000 and 1800 K. Parallel to the c-axis the Ca2+ selfdiffusion coefficient can be empirically represented by D∥(Ca) = 9.3 × 106exp (−5.64/kT) + 3.6 × 10−3 exp (− 2.46/kT) cm2 s−1 and perpendicular to the c-axis by D⟂(Ca) = = 1.28 × 108 exp (−6.0/kT) + 7.92 × 10−8 exp (−1.15/kT) cm2 s−1. The diffusion coefficient of the phosphate ions is found to be at least two orders of magnitude smaller than that of calcium ions at 1700 K with D∥ (PO4) = 1.2 × 10−12 cm2 s−1 and D⟂(PO4) = 3.6 × 10−12 cm2 s−1. Preliminary data on the diffusion of OD− ions are also presented. A theoretical model for the calcium diffusion coefficients is discussed. The biological implications of the data are briefly examined. Les coefficients de diffusion correspondant a la migration des ions Ca2+, PO et OD− dans des monocristaux de fluorapatite, ont ete mesures, dans les directions parallele et perpendiculaire a l'axe cristallographique c. Les mesures on ete faites dans le domaine de temperature 1000 a 1800 K. Parallelement a l'axe c, le coefficient d'auto-diffusion de Ca2+ peut ětre represente empiriquement par D∥(Ca) = 9,3 × 106 exp (−5,64/kT) + 3,6 × 10−3 exp (−2,46/kT) cm2 s−1 et perpendiculairement a l'axe c par D⟂(Ca) = 1,28 × 108 exp (−6,0/kT) + 7,92 × 10−8 exp (−1,15/kT) cm2 s−1. Les coefficients de diffusion des ions phosphates sont au moins cent fois plus faibles que ceux des ions calcium a 1700 K avec D∥(PO4) = 1,2 × 10−12 cm2 s−1 and D⟂(PO4) = 3,6 × 10−12 cm2 s−1. Le premiers resultats sur la diffusion des ions OD− sont egalement presentes, ainsi qui une discussion d'un modele theorique pour les coefficients de diffusion du calcium, et une breve revue des implications biologiques de ces resultats.

The changes in the x-ray Debye–Scherrer diffraction pattern, as a function of plastic strain, have been measured for a silicon bronze (Cu–6·6 at. % Si–1·2 at. % Mn) tensile specimen. Analysis of line positions and line breadths gave the following results. The stacking-fault probability increased with extension, and near fracture (70–75% extension and about 70 Kg/mm2 stress) its value was around 0·008. The extrapolated, or ‘true’ lattice parameter, measured in the radial direction, decreased, but not smoothly. The longitudinal stress calculated, using known elastic constants and theory, from the changes in lattice parameters accompanying the plastic deformation, compared favourably with that of the stress–strain curve from a standard mechanical test. This was also true when the stress was calculated from the changes in separation of the 111–200 peaks, provided a correction was made for the effect of stacking faults. If this correction was not made, then the calculated stresses fell below the value...

The energies of motion of F−, OH− and O2− ions in the apatite lattice have been calculated using a Born model of the crystal. Attention was confined to migration parallel to the c-axis by a vacancy mechanism. In contrast to most ionic crystals the barrier to migration is electrostatic rather than repulsive in character. It is found that the migration energy in a given crystal is least for F−, intermediate for O2− and largest for OH−.

Existing theories of slope development are questioned in that changes over time are not supported by direct evidence. Field data are presented which relate changes in the slope characteristics of recessional moraines to a time scale controlled by actual dates. Recently exposed moraines have irregular surfaces and show a wide range of slope angles. Frost-heaving and surface runoff create smooth slopes of 25°-30° inclination. These changes take place uniformly with respect to time. No significant changes take place after 35 years.

Measurements are reported in which the number of F2-centers produced by warming crystals previously X-irradiated at liquid nitrogen temperatures is studied as a function of temperature and crystal purity. These data are analysed in terms of a diffusion model in which the energy of migration and the initial F+-center distribution are adjustable parameters. It is shown that the best fit is obtained with an energy of motion of negative ion vacancies (F+-centers) of 0.66 eV and a vacancy distribution such that the F+-centres tend to be within five nearest neighbor distances of the F-centers. Nous avons fait une etude experimentale du nombre de centres F2 produits lors du recuit de cristaux ayant ete auparavent irradies aux rayons X a la temperature de l'azote liquide, en fonction de la tempeture et de la purete cristalline. Ces resultats sont etudies a l'aid d'un modele de diffusion pour lequel l'energie de migration et la distribution initiale des centres F+ sont des parametres ajustables. Nous montrons que la meilleure concordance est obtenue pour une energie de motion des lacunes d'ions negatifs (centres F+) de 0,66 eV et une distribution de lacunes telle que les centres F+ ont tendance a ětre a une distance des centres F inferieure a cinq fois la distance des plus proches coisins.

The temperature dependence of the dynamic equilibrium between F- and F2,-centers has been studied in KCl during X-irradiation. Three distinct regions have been identified, a high temperature region corresponding in its temperature dependence of the equilibrium constant to the corresponding temperature range in additively colored crystals and two low temperature regions in which the equilibrium constant increases with increasing temperature with an apparent activation energy of 0.25 and 0.85 eV. A kinetic model is developed to explain these observations which involves the random creation of point defects by the radiation together with an enhanced creation probability near existing F-centers.

A general expression for the relaxation strength Δ M for Zener relaxation is obtained in terms of the rates of change with strain of the short-range order parameters and of the assumed pair-wise interaction energies between atoms. A Bethe-Peierls description of the degree of order yielded values of Δ M in agreement with experiment (Le Claire and Lomer 1954) but is unable to explain more recent observations in a AgZn and LiMg alloys of (1) a marked anisotropy of Δ M (Seraphim and Nowick 1961) and (2) a positive critical temperature, increasing with solute concentration, in the Curie-Weiss type temperature dependence of Δ M (Li and Nowick 1961). Both these defects are fully remedied when the more complete Cowley (1950, 1960) equations are used to describe the degree of order. First and second nearest-neighbour interaction energies only need to be taken into account and order parameters out to eighth neighbours. Good agreement with experimental measurements on a AgZn alloys is obtained with a choice...

THE eukaryotic genome is composed primarily of DNA and a complex and heterogeneous array of proteins. Evidence is rapidly accumulating to suggest that these chromosomal proteins are important in determining structural as well as functional properties of the genome1–6. In addition to being implicated in packaging of the cell's genetic information7–12, chromosomal proteins render limited and defined genetic sequences available for transcription13–23. But the specific properties and mode of interaction of genome components remain to be resolved. We present here evidence that several molecular weight classes of chromosomal proteins are glycoproteins. Furthermore, we report the association of glycosaminoglycans, another class of carbohydrate-containing macromolecules, with the eukaryotic genome.

It is shown that the crust of pulsars can deform in a gradual plastic manner in spite of its extreme density and strength. This deformation leads to stronger damping of pulsar rotation and to higher magnetic moments and also to rarer starquakes than calculated for a rigid crust.