High temperature NMR in vanadium: Electron paramagnetism and atomic diffusion effects

We present preliminary results on Knight shift T₁ and T₂ measurements between 300 and 1700 K. We have observed the motional narrowing due to the self diffusion as well as a strong quadrupolar contribution to T₁ due to the diffusion of interstitial gases. K varies from 0.58 to 0.63%. This temperature dependence is shown to be mainly due to an intrinsic temperature effect. The high temperature Korringa like behaviour of T₁ with T₁T = 1.05 sec. K is explained in terms of the temperature dependence of the d spin contribution.     

UPS measurements of molecular energy level of condensed gases

There have been numerous attempts to use ultraviolet photoemission spcctroscopy (UPS) to monitor the chemical states of adsorbed gas molecules on metal surfaces. To interpret the data correctly, one has to determine the effect of photoemission on the measured energy levels of the molecule. We have measured the UPS spectra of seven gases (C₆H₆, C₅H₅N, CH₃OH, C₂H₅OH, H₂CO, H₂O, NH₃) condensed on a LN₂ cooled MoS₂ substrate at hv = 21.2 eV. The inertness of the MoS₂ substrate assures that no strong chemical bonding exists between the substrate and adsorbed molecules. For each gas, the spectrum of the condensed phase is similar to the corresponding spectrum of the gas phase except all the energy levels are shifted up by the same amount. This shift ranges from 1 to 1.65 eV for the gases studied. The energy shift is attributed to the dielectric screening of the hole produced during the optical excitation.     

Anomalous ultrasonic velocity of the transverse wave in KH3(SeO3)2

The ultrasonic velocity of the transverse wave with q = [010] and ξ = [001] measured as a function of temperature at 5 MHz in centrosymmetric KH₃(SeO₃)₂ shows a large anomaly with a tendency to approach zero at the transition temperature.     

Application of the sequential gradient-restoration algorithm to thermal convective instability problems

The problem of the thermal stability of a horizontal incompressible fluid layer with linear and nonlinear temperature distributions is solved by using the sequential gradient-restoration algorithm developed for optimal control problems. The hydrodynamic boundary conditions for the layer include a rigid or free upper surface and a rigid lower surface. The resulting disturbing equations are solved as a Bolza problem in the calculus of variations. The results of the study are compared with the existing works in the literature.The authors acknowledge valuable discussions with Dr. A. Miele.     

An exact algorithm for solving a capacitated location-routing problem

In location-routing problems, the objective is to locate one or many depots within a set of sites (representing customer locations or cities) and to construct delivery routes from the selected depot or depots to the remaining sites at least system cost. The objective function is the sum of depot operating costs, vehicle acquisition costs and routing costs. This paper considers one such problem in which a weight is assigned to each site and where sites are to be visited by vehicles having a given capacity. The solution must be such that the sum of the weights of sites visited on any given route does not exceed the capacity of the visiting vehicle. The formulation of an integer linear program for this problem involves degree constraints, generalized subtour elimination constraints, and chain barring constraints. An exact algorithm, using initial relaxation of most of the problem constraints, is presented which is capable of solving problems with up to twenty sites within a reasonable number of iterations.     

Hyperfine field and diffusion of μ+ in Fe single crystals

In recent positive-muon spin rotation experiment at TRIUMF on single crystal Fe, a clear temperature dependent change has been observed, for the first time, both in frequency and depolarization rates from 300 K down to 23 K. The μ⁺ depolarization was explained by the μ⁺ diffusion through inhomogeneous dipolar fields and the diffusion constant was found to obey an Arrhenius law (activation energy 17 meV) above 70 K but surprisingly deviated from this at lower temperatures, indicating quantum diffusion. We have also found that the μ⁺ hyperfine field has a temperature dependence slightly stronger than that of the magnetization.     

Influence of magnetoelastic effects on lattice vibrations in the ferromagnetic invar alloy Fe0.65Ni0.35

Neutron scattering measurements have been made of phonons in a Fe₆₅Ni₃₅ crystal at several temperatures. Marked softening of the [110] acoustic shear modes and a dip in the dispersion relation are found at low temperatures. Above the magnetic ordering temperature T_c, the frequency shift is removed completely, which suggests phonon perturbation by magnetoelastic coupling.     

EPR of cadmium ferric voltaite above the ferrimagnetic transition

A single isotropic EPR line of Fe³⁺ in synthetic cadmium ferric voltaite, (NH₄)₂Cd₅Fe₃Al(SO₄)₁₂ · 18H₂O, was observed in a wide temperature range from 295 to 1.57°K. The ferrimagnetic transition temperature of CdFe voltaite was determined to be ～ 0.7°K using the temperature dependence of the g-factor and the line width. The cubic crystal field parameter, a, for Fe³⁺ in CdFe voltaite is extracted from the EPR line width measurement using the exchange-narrowed line width model of Anderson and Weiss. The parameter a for Fe³⁺ in CdFe voltaite at 4.2°K is 157 × 10^-4cm^-1 which is consistent with the corresponding values for Fe³⁺ in other cubic structures.     

Spatial resolution of X-ray line emission in laser produced plasma by shadow techniques

Spatial resolution of X-ray emission from laser-produced plasmas is obtained by placing a 500 μm wire between the plasma and a slitless crystal spectrometer. The sizes of emitting regions of various spectral lines, as well as electron temperature and density spatial profiles are deduced for an Al plasma.     

Pressure dependence of the electric field gradient and knight shift tensors of single crystal gallium

Nuclear pure quadrupole resonance has been observed in single crystal gallium as a function of hydrostatic pressure up to 7 kbar at temperatures of 77, 198 and 273 K. The resonance frequency v_Q increases linearly with pressure and the slope ($\text{δv}{}_{\mathrm{O}}\text{δP}$)_T is 13.7, 15.5 and 16.3 Hz/bar at 77, 198 and 273 K respectively. The asymmetry parameter decreases nonlinearly with pressure. Using compressibility and thermal expansion data, the volume dependence of the major principle component of the electric field gradient was deduced. The principal components K_x, K_y and K_z of the Knight shift tensor have been measured as a function of pressure to 6 kbar at 77 K. The isotropic and anisotropic components of the Knight shift were deduced as a function of pressure, and K_iso is found to vary with volume as V^{4.95 ± 0.80}.