Raman spectrographic system for quantitative analysis of isotopic hydrogen mixtures for muon catalysis experiments

We show that Raman spectral lines from H₂, D₂, T₂, HD, HT and DT are readily resolved, permitting an effective means to analyze isotopic hydrogen mixtures used in muon-catalyzed fusion experiments. We propose a Raman spectrographic system to allow for real-time analysis of targets involving all three isotopes of hydrogen.     

RAPID: Randomized pharmacophore identification for drug design

This paper describes a randomized approach for finding invariants in a set of flexible and chemically distinct ligands (drug molecules) that underlies an integrated software system called RAPID currently under development. An invariant is a collection of features embedded in ³ which is present in one or more of the possible low-energy conformations of each ligand. Such invariants are called pharmacophores and contain the parts of the ligand that are primarily responsible for its binding with a receptor. The identification of pharmacophores is crucial in drug design since frequently the structure of targeted receptor is unknown but a number of molecules that interact with it have been discovered by experiments. In these cases the pharmacophore is used as a template for building more effective drugs. It is expected that our techniques and results will prove useful in other applications such as molecular database screening and comparative molecular field analysis.     

Inelastic mean free paths for electrons in bulk jellium

Bulk inelastic mean free paths, λ, of electrons in jellium are given in graphical form as a function of the electron spacing parameter r_s and the electron energy E, based on self-energy results of Lundqvist. The results are suggested as a useful guide to the dependence of λ on the material in the energy range near the minimum of λ.     

Hydrostatic pressure effects on the superconducting properties of Ag1−xSn1+xSe2

The superconducting transition temperature, T_c, of NaCl structure compounds in the series Ag_1?xSn_1+xSe₂ is found to be exceptionally sensitive to hydrostatic pressures up to 21 kbar. For five samples of varying composition, T_c is suppressed smoothly at a rate of ?(6?8)×10^?5K·bar^?1. These results are discussed with respect to the volume sensitivity of the electron-phonon interaction responsible for superconductivity.     

Molecular frame distortion and molecular pair polarizability

The contribution of frame distortion to the collision-induced polarizability of the isotropic molecules CH₄, CF₄, CCl₄ and SF₆ is estimated and found to be negligible     

A perturbation scheme for spherical arrangements with application to molecular modeling

We describe a software package for computing and manipulating the subdivision of a sphere by a collection of (not necessarily great) circles and for computing the boundary surface of the union of spheres. We present problems that arise in the implementation of the software and the solutions that we have found for them. At the core of the paper is a novel perturbation scheme to overcome degeneracies and precision problems in computing spherical arrangements while using floating point arithmetic. The scheme is relatively simple, it balances between the efficiency of computation and the magnitude of the perturbation, and it performs well in practice. In one O(n) time pass through the data, it perturbs the inputs necessary to insure no potential degeneracies and then passes the perturbed inputs on to the geometric algorithm. We report and discuss experimental results. Our package is a major component in a larger package aimed to support geometric queries on molecular models; it is currently employed by chemists working in “rational drug design”. The spherical subdivisions are used to construct a geometric model of a molecule where each sphere represents an atom.     

Embedding a quantum rank three quadric in a quantum P3

We continue the classification, begun in [11], [14] and [12], of quadratic Artin-Schelter regular algebras of global dimension 4 which map onto a twisted homogeneous coordinate ring of a quadric hypersurfcice in P³. In this paper, we consider those cases where the quadric has rank 3. We also give sufficient conditions for the point scheme of any quadratic regular algebra of global dimension 4 to be the graph of an automorphism.     

Measurement of temperature, density, and particle transport with localized dopants in wire-array Z pinches

Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.     

Calculations of the effect of tunneling on the Swain-Schaad exponents (SSEs) for the 1,5-hydrogen shift in 5-methyl-1,3-cyclopentadiene. Can SSEs be used to diagnose the occurrence of tunneling?

MPW1K density functional calculations, carried out with the 6-31+G(d,p) basis set, have been combined with canonical variational transition state theory (CVT) and small-curvature tunneling (SCT) corrections in order to compute the primary kinetic isotope effects for rearrangement of 5-methyl-1,3-cyclopentadiene (1) to 1-methyl-1,3-cyclopentadiene (2). The Swain-Schaad exponents, SSE = ln(kH/kT)/ln(kD/kT), for this reaction have been computed over the temperature range 100-600 K. Tunneling results in both large positive and large negative deviations from the value of SSE = 3.26, expected from consideration of only the effect of the isotopic mass on passage over the reaction barrier. In the rearrangement of 1 to 2, SSE approximately 3.26, not only at temperatures >400 K, where tunneling is relatively unimportant, but also around 170 K, where tunneling by both H and D is the dominant mode of reaction. Thus, from an experimental finding that SSE approximately 3.26 at a single temperature, it cannot be rigorously concluded that tunneling is unimportant. Measurement of SSEs over a broad temperature range is advisable; but measurement of the temperature dependence of just kH/kD can be used to establish more unequivocally whether tunneling is important, without the necessity of measuring kT.