Ultrasonic attenuation of metals at low temperatures

At very low temperatures when the mean free path of the electrons in metals becomes large but less than the wavelength of sound wave a relationship between electrical conductivity and attenuation in the normal state has been deduced byMason using the mean free path associated with the electrical conductivity. Similarly, a relationship between thermal conductivity and attenuation can be deduced using the mean free path associated with the thermal conductivity. It has been shown from experimental results that the relationship thus deduced agrees better in the temperature region discussed in the paper. When the mean free path becomes greater than the wavelength, α_s/α_n, the ratio of superconducting attenuation to that in the normal state can be determined in accordance with the theory ofBardeen, Cooper andSchrieffer. It is apparent from experimental results that in the limited region where the scattering of electrons is predominantly by lattice vibrations, K_s/K_n, the ratio of superconducting thermal conductivity to that in the normal state is equal to α_s/α_n.     

Effect of impurities on superconduction in tin

Ultrasonic absorption peaks were observed in a single crystal of tin doped with 0.0093 at % indium. The results are discussed here.     

An Economic Order Quantity Model for Items with Two Levels of Storage for a Linear Trend in Demand

A deterministic inventory model with two levels of storage (own warehouse and rented warehouse) is studied by considering a linear (positive) trend in demand. Firstly, the model is formulated and solved without allowing backlogging. Secondly, the model is reformulated and solved under the assumptions that shortages in inventory are allowed and backlogged. The results are illustrated with the help of numerical examples.     

Constrained deformation of a confined solid: anomalous failure by nucleation of smectic bands

We report results of computer simulations of the deformation and failure behavior of a thin crystalline strip of "hard disks" in two dimensions confined within a quasi-one-dimensional "hard-wall" channel of fixed width corresponding to a few disk diameters. Starting from a commensurate triangular solid, stretching the strip along its length introduces a rectangular distortion. This, beyond a critical strain, leads to failure of the solid by "phase separation" into alternating bands of solid and smectic-like phases. The critical strain is inversely proportional to the channel width, i.e., thinner strips are stronger. The large plastic deformation which precedes failure is observed to be reversible.     

Optical absorption and photoluminescence spectroscopy of the growth of silver nanoparticles

Results obtained from the optical absorption and photoluminescence (PL) spectroscopy experiments have shown the formation of excitons in the silver-exchanged glass samples. These findings are reported here for the first time. Further, we investigate the dramatic changes in the photoemission properties of the silver-exchanged glass samples as a function of postannealing temperature. Observed changes are thought to be due to the structural rearrangements of silver and oxygen bonding during the heat treatments of the glass matrix. In fact, photoelectron spectroscopy does reveal these chemical transformations of silver-exchanged soda glass samples caused by the thermal effects of annealing in a high vacuum atmosphere. An important correlation between temperature-induced changes of the PL intensity and thermal growth of the silver nanoparticles has been established in this Letter through precise spectroscopic studies.     

X-ray elucidation of 17α-pregna-2,4-dien-20-yne-(2,3-d) isoxazole-17β-ol

Synthetic pregnen steroid 17-pregna-2,4-dien-20-yne-(2,3-d) isoxazole-17-ol crystallizes in the orthorhombic space group P2₁2₁2₁, with a = 6.601(4), b = 10.530(4), c = 26.177(9) Å, and Z = 4. The structure was solved from Enraf Nonius CAD4 diffractometer data by direct methods and refined to R = 0.0399 for 2041 observed reflections (I > 2(I)). The molecule contains five rings of which rings A, B, and C are cyclohexene; ring D is cyclopentene; and ring E is heterocyclic cyclopentene. Ring A acquires the conformation of a half-chair; ring B tends toward a half-chair conformation with a bias toward a chair conformation that contains a hydrogen at C8 and an hydrogen at C9. Ring C acquires a near chair conformation with an hydrogen at C14. Ring D is a 13, 14-half chair, and ring E is a O3-envelope. Both the ring junctions A/B and A/E are quasi-trans, whereas the ring junctions B/C and C/D are both trans. The molecule as a whole is slightly convex toward the -side, with an angle of 16.7(2)° between the C10–C19 and C13–C18 vectors. Structural association is due to hydrogen bonding and stacking interactions.     

Study of ultrasonic absorption in the intermediate state of pure superconducting tin

Ultrasonic absorption studies in the intermediate state of superconducting tin have revealed sharp resonance peaks. Measurements have been made under wide variations of ultrasonic pulse frequencies. The possibility of correlating this study with a model proposed by Claiborne and Einspruch for hard superconducting alloys has been explored.     

Exchange interaction in trinuclear transition-metal complexes

Heterotrinuclear transition-metal complexes are of interest for the study of long-range magnetic interactions and as model compounds for the investigation of biological electron transport chains. The systems under study here contain paramagnetic Fe¹¹¹-containing terminal units and a bridging unit with M¹¹=Zn, Cu, Ni, Co, Fe, Mn. The spectroscopic methods applied include Mössbauer, — EPR- and magnetic susceptibility investigations. The spin-Hamiltonian analysis of the measured results yields information about the intramolecular super-exchange interactions among the various magnetic transmition-metal sites. In view of the 7Å separation between the two terminal Fe¹¹¹ sites, the Fe¹¹¹...Fe¹¹¹ exchange coupling of the order ?10cm^?1 is large.     

Two step-down tests for equality of covariance matrices

The classical problem of testing the equality of the covariance matrices from k ? 2 p-dimensional normal populations is reexamined. The likelihood ratio (LR) statistic, also called Bartlett’s statistic, can be decomposed in two ways, corresponding to two distinct component-wise decompositions of the null hypothesis in terms of the covariance matrices or precision matrices, respectively. The factors of the LR statistic that appear in these two decompositions can be interpreted as conditional and unconditional LR statistics for the component-wise null hypotheses, and their mutual independence under the null hypothesis allows the determination of the overall significance level.