Automorphisms of the symplectic group over a local ring

Let R denote a commutative local ring with maximal ideal m and residue field K = R/m. Let V be a symplectic space over R. In this paper we determine the group automorphisms of the symplectic group Sp_n(V) when n 6, the characteristic of k is not 2, and k is not the finite field of three elements.     

CdCu3(OH)6Cl2: A new layered hydroxide chloride

A new transition metal hydroxide chloride containing kagomé layers of magnetic ions, CdCu₃(OH)₆Cl₂, has been synthesized and structurally characterized. The actual low symmetry P2₁/n structure can be derived from the ideal trigonal one with a change in cation distribution and coherent distortions of the anion framework. The result is a fundamentally different Cu²⁺ kagomé framework than found in the related Herbertsmithite and Kapellasite minerals. Magnetization measurements show no transition to long range magnetic order above T=2 K, despite strong antiferromagnetic interactions with a Weiss temperature of θ_w=−150 K. Furthermore, we show that the structure of CdCu₃(OH)₆Cl₂ and related hydroxide chlorides can be rationalized on the basis of [(OH)₃Cl]⁴⁻ pseudopolyatomic anions that pack and rotate, in much the same way as do traditional polyatomic anions. This opens the door to rational design of new and useful hydroxide chloride materials.     

On low frequency and 1/f noise from diffusion like processes

The noise spectrum resulting from diffusion like processes is calculated in two and three dimensions for two different forms of free energy fluctuation. For example it is shown that in a three dimensional system with ideal non-interacting particles the noise is almost white up to a certain frequency. In a two dimensional system where the free energy fluctuations are proportional to the gradient of a parameter modulating the electrical conductivity a 1/f noise power spectrum is expected in a certain frequency interval.     

PbMn(SO4)2: A new chiral antiferromagnet

PbMn(SO₄)₂ has been synthesized in an evacuated quartz tube. The nuclear and magnetic crystal structures have been determined using powder X-ray and neutron diffraction. This material crystallizes in the enantiomorphic space group pair P4₁2₁2(92) and P4₃2₁2(96), forming a double-helical arrangement of Pb²⁺ and Mn²⁺ cations. The Mn²⁺O₆ octahedra are distorted. Each 3d⁵ Mn²⁺ has four nearest-neighbors and four next-nearest-neighbors adopting a frustrating arrangement. The compound orders antiferromagnetically at 5.5 K. Field dependent specific heat and magnetization measurements show that T_N is suppressed to 3.3 K when μ₀H=9 T.     

Electron spin density distribution in the polymer phase of CsC60: assignment of the NMR spectrum

We present high resolution 133Cs-13C double resonance NMR data and 13C-13C NMR correlation spectra of 13C enriched samples of the polymeric phase of CsC60. These data lead to a partial assignment of the lines in the 13C NMR spectrum of CsC60 to the carbon positions on the C60 molecule. A plausible completion of the assignment can be made on the basis of an ab initio calculation. The data support the view that the conduction electron density is concentrated at the C60 "equator," away from the interfullerene bonds.     

Applications of a simple theory of the acoustic motion of fibrous networks in viscous media

The rupture of blood capillaries in the spinal chords of rats by pulsed ultrasound and the motion of fibrils in the corneal stroma are analysed in detail in terms of a simple theory of wave propagation in a fibrous network permeated by a viscous medium. The advantages of inelastic light scattering experiments in connection with studies of ultrasound are emphasized.     

Autoreduction of Pd-Co and Pt-Co cyanogels: exploration of cyanometalate coordination chemistry at elevated temperatures

Cyanogels are coordination polymers made from the reaction of a chlorometalate and a cyanometalate in aqueous solution, which undergo a sol-gel transition to form stable gels. At temperatures above 240 degrees C, the cyanide ligand acts as a reducing agent and reduces the metal centers to lower oxidation states. To understand the mechanism of the autoreduction, the thermal reduction of the Pd-Co cyanogel system formed by the reaction of PdCl4(2-) and Co(CN)6(3-) was studied in an inert atmosphere. It was found that the reduction proceeds through two polymeric cyanide-containing intermediates, CoPd(CN)4 and Pd(CN)2, that form upon reduction of Co(3+) to Co(2+) and involves a significant rearrangement of the coordination structure. The two intermediates upon further heating reduce to metallic products, which by solid-state diffusion form a single Pd/Co alloy product. CoPd(CN)4 was found to have a hydrated form Co(H2O)2Pd(CN)4 x 4 H2O with a layered structure crystallizing in an orthorhombic Pnma space group. The Pt-Co cyanogel was found to autoreduce via a similar route. CoPt(CN)4 was confirmed as an intermediate. Understanding of the mechanism of the cyanogel autoreduction is an important step toward better understanding of opportunities that cyanogels offer in materials chemistry, as well as an expansion of the knowledge of coordination chemistry at elevated temperatures in general.     

Multiple Threshold Percolation in Polymer/Filler Composites

Local variations in filler particle concentration and/or shape and orientation in static filler/polymer composites are modelled as distributions of percolation thresholds. The concentration variations can be due to insufficient mixing, formation of semicrystalline voids during cooling from the melt, shrinkage during polymer curing, flow during physical compression or the like. Irregular filler shapes, especially elongated shapes, reduce the percolation threshold; thus natural variations in the shapes and orientations of filler particle aggregates lead to locally varying percolation thresholds. A distribution of percolation thresholds leads to an apparent percolation threshold based on the conductivity below the mean percolation threshold. For filler concentrations above the apparent percolation threshold the dielectric constant continues to increase before reaching a lowered peak value at the mean percolation threshold and then decreasing. Own experimental results on EBA /carbon black composites support the theory.