Fast intramolecular dynamics of triphenyl phosphite investigated by <Emphasis Type="Bold">2</Emphasis>H NMR

The first analysis of rapid intramolecular motions of triphenyl phosphite by ²H NMR is presented. The fragile slowing down of the primary relaxation is followed by a solid-echo method. The occurrence of a fast reorientation of the phenyl side groups is demonstrated in the supercooled liquid state, identified as a two-fold flip on the basis of simple lineshape simulations. Coexistence of both static and motionally averaged components in “two phase” spectra indicate a broad distribution of correlation times for this relaxation. This dynamical behavior is shown to persist in the glacial phase. Received 28 May 2002 / Received in final form 1st October 2002 Published online 31 December 2002     

Preparation of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowires by calcining the precursor powders synthesized in a novel inverse microemulsion

Manganese oxide (hausmannite) nanowires were prepared by annealing precursor powders at a temperature of 800 °C for 3 h, which were produced in a novel inverse microemulsion (IμE) system. The microstructures of the as-prepared Mn₃O₄ nanowires were investigated by means of X-ray diffraction, transmission electron microscopy, and Raman spectra. It has been found that the Mn₃O₄ nanowires were relatively straight and their surfaces were smooth with a typical diameter of 75–150 nm. The formation mechanism of the Mn₃O₄ nanowires is discussed. Received: 30 May 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn     

A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals

One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond, through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)₂₃C₆, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic theory during quenching from HPHT to room temperature and ambient pressure. Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn     

Spectroscopic studies of erbium-doped potassium-lead double chloride crystals KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript>:Er<Superscript>3+</Superscript>: 1. Optical spectra and relaxation of excited states of the erbium ion in potassium-lead double chloride crystals

Optical spectra, intensities of radiative and nonradiative transitions, and luminescence kinetics in erbium-doped potassium-lead double chloride crystals KPb₂Cl₅:Er³⁺s(KPC:Er³⁺) were investigated. The crystals were grown by the Bridgman-Stockbarger method. Their absorption and luminescence spectra were studied experimentally. The crystal-matrix absorption edge was determined at 80 and 300 K. Intensity parameters, radiative transition probabilities, branching ratios, and nonradiative relaxation rates were estimated by the Judd-Ofelt method. The luminescence kinetics from the emitting levels ⁴ G _11/2, ² G _9/2, ⁴ S _3/2, and ⁴ F _9/2 upon selective excitation was studied.     

Inverses and regularity of band preserving operators

The following four main results are proved here. Theorem 3.3.For each one-to-one band preserving operatorT:X → Xon a vector lattice its inverseT⁻¹:T(X) → Xis also band preserving. This answers a long standing open question. The situation is quite different if we move from endomorphisms to more general operators. Theorem 4.2.For a vector lattice X the following two conditions are equivalent:

1.

i)|For each one-to-one band preserving operator T:X → X^u from X to its universal completion X^u the inverse T⁻¹ is also band preserving.

2.

ii)|For each non-zero x ? X and each non-zero band U ⊂ {x}^dd there exists a non-zero semi-component of x in U.

Theorem 5.1.For a vector lattice X the following two conditions are equivalent.

1.

i)|Each band preserving operator T:X → X^u is regular.

2.

ii)|The d-dimension of X equals 1.

Corollary 5.9.Let X be a vector sublattice of C(K) separating points and containing the constants, where K is a compact Hausdorff space satisfying any one of the following three conditions: K is metrizable, or connected, or locally connected. Then each band preserving operatorT: X → Xis regular.     

First-stage enrichment in CO2-laser-induced13C separation by a two-stage IRMPD process: IRMPD of CHClF2/Br2 mixtures

We have been studying the practical CO₂-laser-induced¹³C separation by a two-stage IRMPD process. The IRMPD of natural CHClF₂ in the presence of Br₂ mainly produced CBr₂F₂, which was found to be highly enriched with¹³C. The yield and¹³C-atom fraction of CBr₂F₂ were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br₂ pressure using a CO₂ TEA laser with an output less than 1 J pulse^–1 in order to optimize experimental conditions for¹³C separation. For example, we obtained CBr₂F₂ at a¹³C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF₂ and 10-Torr Br₂ with the laser radiation at a wavenumber of 1045.02 cm^–1 and at a fluence of 3.4 J cm^–2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10^–4 g of¹³C-enriched CBr₂F₂ (¹³C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher¹³C by the second-stage IRMPD of the CBr₂F₂ in the presence of oxygen.     

The influence of contact surface microstructure on vacuum arcstability and voltage

The authors present the results of DC vacuum arc lifetime and voltage measurements for contacts with different surface microstructures. This was realized by treating the contact surface with emery paper of varying roughness. The contact surface microstructure was found to have a large effect on the DC arc lifetime (several tens of times difference at the most) and arc voltage (30% difference at the most). The mechanism of the surface microstructure effect on DC arc stability was analyzed and is explained preliminarily. The rougher the contact surface is, the longer the arc lifetime and the more stable. The arc itself has a tendency to condition the surface in a way that is unfavorable for a sustained arc lifetime. The crater size for a rough surface is smaller than for a smooth one. The rougher the contact is, the lower the arc voltage (both DC and HF components). The arc erosion has a tendency to increase the arc voltage. It is probable that type I cathode spots (fast motion, small crater size) correspond not only to the surface contamination, but also to the surface roughness     

Measuring the Polarization Parameters of Rain by Inverse Scattering

The theory is presented for one method of determining the effective polarization parameters of the rain medium in the problem of polarization information processing of detecting target. The determination of the effective polarization parameters of the propagation medium is from the data of propagation measurements over a line-of-sight link. The polarization parameters the effective average value, the effective standard deviation and F the effective shape parameter of the propagation medium are obtained by means of the method of inverse scattering, showing a good agreement with the data from direct measurements.     

Study of the Anglular Structure of Emission from the Radio Galaxy 3C295 in the Decameter Wavelength Range

We present the results of observations of the angular structure of the radio source 3C295 at decameter waves using the URAN-1 and URAN-2 interferometers. It is shown that the radio image of 3C295 at these frequencies differs drastically from the structure of this object observed at higher frequencies. The simplest model of the structure of this radio galaxy, comprising one component with a Gaussian brightness distribution of angular size (7.4 ± 0.4)× (8.7± 0.4) at 25 MHz and (9.1± 0.5)× (10.6 ± 0.5) at 20 MHz, is determined. A decrease in the spectral density of the emission with decreasing frequency, observed below 50 MHz, is explained.     

Quantisation of 2D- gravity with Weyl and area- preserving diffeomorphism invariances

The constraint structure of the induced 2D-gravity with the Weyl and area-preserving diffeomorphism invariances is analysed in the ADM formulation. It is found that when the area-preserving diffeomorphism constraints are kept, the usual conformal gauge does not exist, whereas there is the possibility to choose the so-called “quasi-light-cone” gauge, in which besides the area-preserving diffeomorphism invariance, the reduced Lagrangian also possesses the SL(2, R) residual symmetry. This observation indicates that the claimed correspondence between the SL(2, R) residual symmetry and the area-preserving diffeomorphism invariance in both regularisation approaches does not hold. The string-like approach is then applied to quantise this model, but a fictitious non-zero central charge in the Virasoro algebra appears. When a set of gauge-independent SL(2, R) current-like fields is introduced instead of the string-like variables, a consistent quantum theory is obtained, which means that the area-preserving diffeomorphism invariance can be maintained at the quantum level.