Crystal structure of synthesized CuGaTe2 determined by X-ray powder diffraction using the Rietveld method

A full profile X-ray powder diffraction structure refinement has been carried out on a sample of synthesized CuGaTe₂ using graphite monocromatized CuK step-scan data and a profile shape of the Pearson VII type. The most satisfactory convergence was achieved at R _p = 0.0666, R _wp = 0.0884, R _B = 0.0106 and R _F = 0.0102. The derived structural parameters at 26.5°C are: a = 0.602348(7), c = 1.193979(2) nm and x(Te) = 0.256(6). The ratio between lattice parameters, = c/2a = 0.9911 (0), differs from 1.0, indicating a tetragonal distortion, and non-ideal anion displacements, x(Te)1/4, is manifested by the existence of bond alternation of Cu-Te and Ga-Te with interatomic distances of 0.262(5) and 0.2578(5) nm, respectively. These results show a light tetrahedral deformation produced by four-fold tetrahedra of the copper cation in the CuGaTe₂ chalcopyrite-type structure.     

A model for the compressive buckling of extended chain polymers

A model for the compressive buckling of an extended polymer chain is presented. The application of classical elastic instability analysis to an idealized polymer chain reveals that the bending rigidity and critical buckling loads for a chain are proportional to the force constants for valence bond angle bending and torsion. Highly oriented polymer fibres are treated as a collection of elastic chains that interact laterally. The critical stresses to buckle this collection of chains are calculated following a procedure developed to predict the compressive strengths of fibre-reinforced composites. This buckling stress is predicted to be equal to the shear modulus of the fibres and is the limiting value of compressive strength. Comparison of experimental and predicted values shows that the theory overestimates the compressive strength, but that there is a correlation of shear modulus with axial compressive strength. Consideration of flaws in both the theory and the material indicate that the compressive strength should be proportional to either the shear modulus or shear strength of the fibres.Nomenclature P axial compressive load (force) - P _cr critical buckling load (force) - M,M _i bending moments - l length of a link - p number of links - k elastic hinge constant - , _i angular rotation of hinges - L overall chain or column length - v,v _i lateral deflection of buckled chain or column - x, y, z Cartesian coordinate axes - E Young's modulus of isotropic column - I moment of inertia - a _ij matrix coefficients - A _p coefficient for exact buckling loads of chains - T energy change due to work of external load on buckled column or chain - U ₁ bending strain energy change of buckled column or chain - U ₂, U ₂ ^e , U ₂ ^s strain energy changes in elastic foundation, where e refers to extension mode buckling and s refers to shear mode buckling - E _t transverse modulus - G longitudinal shear modulus - b dimension associated with chain packing - A cross-sectional area per chain (=b ²) - f(x) curve fitted to shape of buckled chain - m,n,r integers - a _n coefficients of trigonometric series - _y normal strain iny-direction - _y normal stress iny-direction - xy shear strain inxy plane - xy shear stress inxy plane - u _x displacement inx-direction - u _y displacement iny-direction - V volume     

Corrosion and wear properties of multipurpose coatings deposited by ion-beam-assisted deposition

Electrochemical measurements and wear tests were performed on aluminium and aluminium alloy coatings containing magnesium for uniform and local pitting corrosion protection of low carbon steel substrates. Final hard chromium nitride and aluminium nitride layers were deposited at the surface of the protective films in order to lower friction and wear. The results show that wear and corrosion protection can be improved by use of bifunctional multilayers. The coatings for multipurpose application were generated by ion-beam-assisted deposition. The defined intrinsic film stress controlled by the ion-to-atom arrival ratio influences the corrosion properties. Increasing the ion-to-atom ratios usually improves the corrosion resistance.     

Effect of Inhomogeneities on the Apparent Location and Magnitude of a Cardiac Current Dipole Source

A mathematical model was used to investigate the effects of electrical inhomogeneities introduced by the intracavitary blood mass and the lungs on the apparent location and magnitude of a current dipole source representing local activity in the myocardium. Radial and tangential current source moments were considered, and lung conductivity was taken as a variable parameter. Both the blood mass and the lungs cause a current source to appear closer to the heart center than it actually is. The effect increases as the source moves away from the endocardial surface, and maximum displacement is estimated to be of the order of 1 cm. The net effect of the inhomogeneities is to increase the magnitude of the radial component of a source dipole while diminishing its tangential component. These effects depend on source location.     

Analytical studies on the temperature distribution in spiral plate heat exchangers: Straightforward design formulae for efficiency and mean temperature difference

The temperature distribution in spiral plate heat exchangers has been calculated numerically to obtain the efficiency and the logarithmic mean temperature difference (LMTD) correction factors F as a function of the number of transfer units N, the number of turns n, and the heat capacity rate ratio C. It has been found that the LMTD correction factors, when plotted against the number of transfer units per turn N/n, fall approximately on a single curve. That curve for balanced countercurrent operation (C = −1) can be very closely represented by the simple formula F = (n/N)tanh(N/n). From that simple analytic representation of our numerical results it was concluded that a simpler physical model might exist to represent the overall behaviour of a spiral plate heat exchanger equally well. In fact, a countercurrent cascade of n cocurrent heat exchangers does result exactly in the above-mentioned formula for the LMTD correction factor. From that model the F-factors for other heat capacity rate ratios C (−1 < C 0) can also be calculated and they are in sufficient agreement with the numerical results.     

Monoterpene concentrations in fresh,senescent, and decaying foliage of singleleaf pinyon (Pinus monophylla Torr. & Frem.: Pinaceae) from the western Great Basin

Senescent foliage from pines is potentially a large contributor to the total monoterpene content of the litter layer, and the availability of these compounds as phytotoxins may result from release of these compounds into the vapor phase. In order to determine the fate of several monoterpene hydrocarbons in the natural environment, we examined their concentrations in fresh, senescent, and decaying needles from 32 single-leaf pinyon pine (Pinus monophylla Torr. & Frem.: Pinaceae) trees growing at two different locations. Total monoterpene content was highest in the fresh needles (mean=5.6 ± 2.2 mg/g extracted air dry weight), but also remained relatively high in senescent needles (mean=3.6 ±1.8 mg/g extracted air dry weight), either still attached to the tree or forming the freshest layer of understory litter. Decaying needles within a dark decomposing layer of litter material 5–20 cm from the surface were found to contain much lower amounts of total monoterpenes (average: =0.12 ±0.06 mg/g extracted air dry weight). Further investigation of the fate of these compounds in the pinyon understory is required to determine if these hydrocarbons are indeed exerting phytotoxic characteristics.     

Host odor and visual stimulus interaction during intratree host finding behavior ofRhagoletis pomonella flies

Responses ofRhagoletis pomonella (Walsh) (Diptera: Tephritidae) flies to host fruit visual stimuli (apples or models of apples) and chemical stimuli (synthetic apple volatile blend) were studied in semidwarf field-caged apple trees. Three different fruit or model densities (1, 4, or 16 fruit or models/ tree) and two odor release rates [ca. 0.7g/hr (close to the natural release rate of a ripe apple) and ca. 500g/hr (amount of odor released by commercially sold apple maggot traps)] were tested. Individually released flies were followed as they moved within a tree for a maximum of 20 min. We recorded three-dimensional search paths followed by foraging flies and computed such variables as total relative distance traveled before alighting on a fruit or model, track length between individual alightment sites, and directness of flight to fruits or models. Effect of odor on propensity to alight on fruit or models and host-searching behavior prior to alighting on fruit or on models varied according to fruit or model color and density. If the fruit visual stimulus was strong (e.g., red color), odor did not increase the probability of finding fruit or fruit models. As the visual stimulus became progressively weaker (red to green to clear), odor (irrespective of concentration) appeared to aid flies during the fruit-finding process. As density of fruit or models increased, the probability of flies finding a fruit or model also increased (e.g., 50% of flies found a red fruit model at 1 model/tree while 90% found a red model at 16 models/tree; 4% of flies found a clear model with odor at 1 model/tree while 35% found a clear model with odor at 16 models/tree). Findings reported elsewhere indicate thatR. pomonella flies are able to discover a point source of odor (an odor-bearing tree in a patch of trees) by flying upwind (in the tree patch) in response to intermittent exposure to odor. Findings here indicate that after arrival on a host tree (point source), flies discover individual apparent and abundant host fruit on the basis of vision. If fruit are less apparent or scarce, odor appears to interact with vision during the fruit-finding process.