Phase diagram and magnetocaloric effect of alloys

We propose the phase diagram of a new pseudo-ternary compound, CoMnGe_1-xSn_x, in the range x0.1. Our phase diagram is a result of magnetic and calorimetric measurements. We find that the separate magnetic and structural transitions in CoMnGe are tuned together as the level of Sn substitution is increased. We demonstrate the appearance of a hysteretic magnetostructural phase transition in the range x=0.04–0.055, similar to that observed in CoMnGe under hydrostatic pressure. From magnetisation measurements, we show that the isothermal entropy change associated with the magnetostructural transition can be as high as in a field of 1 T. However, the large thermal hysteresis in this transition () will limit its straightforward use in a magnetocaloric device.     

Strong-coupling expansions for multiparticle excitations: continuum and bound states

We present a new linked cluster expansion for calculating properties of multiparticle excitation spectra to high orders. We use it to obtain the two-particle spectra for systems of coupled spin-half dimers. We find that even for weakly coupled dimers the spectrum is very rich, consisting of many bound states. The number of bound states depends on both geometry of coupling and frustration. Many of the bound states can only be seen by going to sufficiently high orders in the perturbation theory, showing the extended character of the pair attraction.     

Vibrotacile masking of Pacinian and non-Pacinian channels

Vibrotactile masking functions were determined using sinusoidal and noise maskers. Results were nearly identical within the Pacinian (P) and non-Pacinian (NP) channels. At low maskers SLs there was a substantial amount of negative masking which proved not be an artifact of stimulus definition. The critical parameters for successful prediction of the data were a peripheral threshold and internal Gaussian noise. Threshold shifts in cross-channel stimulation can be attributed to the masker exceeding the detection threshold of the signal channel.     

Synthesis of 9-substituted homoadamantanes

9-Homoadamantanone was prepared conveniently from 1-homoadamantanol via $\text{10-homop}$rotoadamantan-4-one in 58% overall yield.     

O- and N-substituted products from the treatment of 3,5-dichioro-2-pyridone with benzenesulfonyl chlorides

Treatment of 3,5-dichloro-2-pyridone with various benzenesulfonyl chlorides in the presence of triethylamine at 25° yielded both O- and N-sulfonylated products. These isomers were isolable, relatively stable compounds which were distinguished by their ir and uv spectra.     

Renormalization of anisotropy and glueball masseson tadpole improved lattice gauge action

The Numerical calculations for tadpole-improved U(1) lattice gauge theory in three-dimensions on anisotropic lattices have been performed using standard path integral Monte Carlo techniques. Using average plaquette tadpole renormalization scheme, simulations were done with temporal lattice spacings much smaller than the spatial ones and results were obtained for the string tension, the renormalized anisotropy and scalar glueball masses. We find, by comparing the regular and sideways potentials, that tadpole improvement results in very little renormalization of the bare anisotropy and reduces the discretization errors in the static quark potential and in the glueball masses.Received: 19 March 2003, Revised: 26 August 2003, Published online: 24 October 2003     

Radiative recombination in iridium-doped silver bromide single crystals

The infrared emission spectrum of iridium-doped silver bromide results from a process that is competitive with the visible emission due to iodide centers in pure AgBr crystals. The emitting species is Ir³⁺, and experiments are described which help elucidate the nature of the radiative processes involved.     

Statistical model cross sections for overlapping resonances

The cross section for a reaction dominated by numerous incoherent resonances is studied, as a function of the average resonance width $\text{Λ}$ divided by the spacing D. Both the Bohr and Wheeler formulae for the average cross sections, and the standard Ericson analysis of fluctuations, are found to be valid only for weakly overlapping resonances, $\text{Λ}\text{D}\text{?}\text{n}\text{2π}$, where n is the number of open scattering channels. Two different models are presented which respect unitarity whatever the resonance widths, namely a K-matrix or Weisskopf-Wigner model, and an eikonal type model. The cross sections are found to saturate either the elastic or the inelastic unitarity bound for strongly overlapping resonances, $\text{Λ}\text{D}\text{?}\text{n}\text{2π}$; and the fluctuations in the cross sections are found to have a coherence length of order nD, rather than $\text{Λ}$.     

Lattice model calculations for SU(2) Yang-Mills theory in 1 + 1 dimensions

Lattice model techniques are employed to study the low-energy spectrum of SU(2) Yang-Mills theory in 1 + 1 dimensions. The Hamiltonian formulation of Kogut and Susskind is employed. The strong coupling expansion is carried to eighth order for a few of the lower-lying states. These expansions are extrapolated to the continuum limit using Padé approximants, both for finite quark masses and in the non-relativistic limit (quark mass goes to infinity). These methods succeed in giving a qualitative picture of the spectrum, but their quantitative accuracy is poor.