Differential non-destructive image current detection in a fourier transform quadrupole ion trap

Dual-detector differential non-destructive Fourier transform detection in a quadrupole ion trap is shown to improve signal intensity and reduce noise compared with spectra recorded using a single detector. A larger area detector in each end-cap electrode is machined to fit its hyperbolic shape and so minimize field imperfections on the z-axis. Argon, acetophenone and bromobenzene spectra were recorded to allow a comparison between single- and dual-detector (differential) modes of detection and to demonstrate the improvement achieved with differential detection. Copyright 1999 John Wiley & Sons, Ltd.     

Structures and stabilization energies of methyl anions with main group substituents from the first five periods

The effects of substituents (X) on the structures and stabilities of CH₂X^? anions for groups comprised of fourth- and fifth-period main group elements (X = K, CaH, GaH₂, GeH₃, AsH₂, SeH, Br, Rb, SrH, InH₂, SnH₃, SbH₂, TeH, and I) have been investigated by ab initio pseudopotential calculations. Full geometry optimizations have been carried out on the CH₂X^? anions and the corresponding neutral parent molecules, CH₃X, at HF/DZP + and MP2/DZP + levels. Results for substituents from the second (X = Li? F) and third (X = Na? Cl) periods provide comparisons of substituent effects of the main group elements of the first four rows of the periodic table on methyl anions. Frequency calculations characterize the nature of stationary points and show pyramidal CH₂X^? anion structures to be the most stable unless π acceptor interactions (e.g., with BH₂, AlH₂, GaH₂, and InH₂ favor planar geometries. The CH₂X^? stabilization energies [at QCISD(T)/DZP + /MP2/DZP + + ZPE level for X = K? I and QCISD(T)/6?31 + G*/MP2/6?31 + G* + ZPE level] for X = Li? Cl) also show strong π-stabilizing effects for the same substituents. With the exception of CH₃ and NH₂, all substituents stabilize methyl anions, although the σ stabilization by OH and F is small. The SiH₃? PH₂? SH? Cl, GeH₃? AsH₂? SeH? Br, and SnH₃? SbH₂? TeH? I sets of substituents give stabilization energies between 19 and 30 kcal/mol. The stability of methyl anions substituted by the halogens and the chalcogens (X = OH, SH, SeH, and TeH) increases down a group in accord with the increasing substituent polarizability, while for π acceptors (BH₂, AlH₂, GaH₂, and InH₂) the stability decreases down a group in line with their π-accepting ability. © 1994 by John Wiley & Sons, Inc.     

Temperature hysteretic effect and its influence on colossal magnetoresistance of La0.33Nd0.33Ca0.33MnO3

Electrical resistance (R) measurements of a bulk La_0.33Nd_0.33Ca_0.33MnO₃ perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T _MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance and shifts T _MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than in the warming path leading to the hysteretic resistance ratio (R _cool/R _warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and 40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence of La-rich and Nd-rich domains assumed to be distributed randomly in the compound.     

ac Conductivity of mixed spinel NiAl0.7Cr0.7Fe0.6O4

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl_0.7Cr_0.7Fe_0.6O₄. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.     

The study of compatibility of polyethylene and polypropylene by using irradiated polyethylene wax

The modification of the compatibility between polyethylene (PE) and polypropylene (PP) by using irradiated PE wax (PE wax) is the purpose of this study. In this part, polymer blends based on various ratios of PE and PP were blended with 2.5% PE wax in all the blend ratios to determine the optimum ratio of the blend to be compatabilized. The influence of PE wax as a compatibilizing agent for PE and PP blend was investigated through the measurements of thermal, mechanical and morphological properties. The PP/PE blends modified by this method showed higher mechanical properties than those of the unmodified blends. Also, stress and strain of the modified blend having ratio (60/40) PP/PE blend recorded the maximum mechanical behavior. Scanning electron microscopy (SEM) micrographs of modified blends showed an indication of strong interfacial adhesion and a smooth continuous surface in which giving a support to the effect of irradiated PE wax as a tool for improving the compatibility.     

On the theory of slowing down gracefully

We discuss the transport of a tracer particle through the Bose?CEinstein condensate of a Bose gas. The particle interacts with the atoms in the Bose gas through two-body interactions. In the limiting regime where the particle is very heavy and the Bose gas is very dense, but very weakly interacting (??mean-field limit??), the dynamics of this system corresponds to classical Hamiltonian dynamics. We show that, in this limit, the particle is decelerated by emission of gapless modes into the condensate (Cerenkov radiation). For an ideal gas, the particle eventually comes to rest. In an interacting Bose gas, the particle is decelerated until its speed equals the propagation speed of the Goldstone modes of the condensate. This is a model of ??Hamiltonian friction??. It is also of interest in connection with the phenomenon of ??decoherence?? in quantum mechanics. This note is based on work we have carried out in collaboration with D Egli, I M Sigal and A Soffer.     

Local canted spin behaviour in Co1.4−x Zn x Ge0.4Fe1.2O4 spinels: A macroscopic, mesoscopic and microscopic study

DC magnetization, neutron depolarization and neutron diffraction (with both polarized and unpolarized neutrons) measurements have been reported for the Co_1.1−x Zn _x Ge_0.1Fe_1.2O₁ spinels with x=0.5, 0.6 and 0.7. Neutron depolarization and neutron diffraction measurements confirm the presence of a long range ferrimagnetic ordering of the local canted spins in these ferrite samples. The observed features of low field magnetization have been explained under the framework of thermally activated domain wall movement of ferrimagnetic arrangement of local canted spins. An important role of magnetic anisotropy (due to the presence of Co²⁺ ions) in establishing the magnetic ordering and domain kinetics in these ferrites has been observed.     

Iodometric microgram determination of chromium(III) and (VI) by use of chemical amplification reactions

A simple, rapid and sensitive method is described for the iodometric determination of microgram amounts of chromium(III), based on the oxidation of chromium(III) with periodate at pH 3.2, removal of the unreacted periodate by masking with molybdate and subsequent iodometric determination of the liberated iodate. Chromium(VI) can be determined by this method after prior reduction to chromium(III) with sodium sulphite. The method can also be used for the analysis of organochromium compounds.