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31.
Mössbauer spectra of119Sn in Sn1–z
Eu
z
Mo6S8 (z=0, 1/3, 2/3) have been measured in the temperature range 4.9 KT293 K. The spectra consist of a quadrupole doublett with unequal intensities at all temperatures. The Debye-Waller factor, the isomeric shift and the asymmetry of the intensity of the quadrupole components show irregularities between 50 K and 110 K which are interpreted as arising from a structural phase transition. The temperature dependence of the Debye-Waller factor can be approximated by a simple phonon spectrum. No quantitative explanation can be given for the large values of the asymmetry. Evidence is presented that this behavior is connected with the properties of the librational modes of the Mo6S8-units in the crystal. 相似文献
32.
Free standing ferroelectric films in a rotating electric field have been investigated. Depending upon the applied voltage and the period of the field rotation different structure formations could be observed. At high fields, a homogeneous orientation is obtained. In the case of very low fields, a schlieren texture results. Under special conditions, a stable ring system appears. The dynamics of these rings have been studied. The dependence of the structure formation on the relation between the impulse length of the applied field and the reorientation time is discussed. 相似文献
33.
W. Jost H. E. Hauck und F. Eisenbeiß 《Fresenius' Journal of Analytical Chemistry》1984,318(3-4):300-301
34.
Complexes of Rhenium with Planar ReN2S2 Rings. Syntheses and Crystal Structures of AsPh4[ReCl4(N2S2)] and PPh4[ReBr4(N2S2)] The complex [ReCl4(N2S2)]? can be obtained as PPh4⊕ or AsPh4⊕ salt by the action of S(NSiMe3)2 and of diphenylacetylene, respectively, on the chlorothionitrene complex [ReCl4(NSCl)2]?. Another method of synthesis is the reaction of [ReCl3(NSCl)2(POCl3)] with SbPh3. [ReBr3(N2S2)]2 is obtained from excess Me3SiBr and [ReCl3(NSCl)2(POCl3)]. The anionic complex [ReBr4(N2S2)]? forms from either [ReCl4(NSCl)2]? or [ReCl4(N2S2)]? with Me3SiBr. All compounds are black, diamagnetic, and sensitive to moisture; the PPh4⊕ and AsPh4⊕ salts are soluble in CH2Cl2 and CH2Br2. The IR spectra are reported. The crystal structures of AsPh,4[ReCl4(N2S2)] and PPh4[ReBr4(N2S2)] were determined by X-ray diffraction. AsPh4[ReCl4(N2S2)]: space group P2/n, Z = 2, a = 1244.5, b = 1429.3, c = 791.1 pm, γ = 96.89° (1715 observed reflexions, R = 0.082). PPh4[ReBr4[ReBr4(N2S2)]: space group P21/n, Z = 4, a = 961.7, b = 1397.4, c = 2205.7 pm, β = 102.10° (1787 observed reflexions, R = 0.073). In both compounds the [ReX4(N2S2)]? anions have the same type of structure, the Re atoms forming part of planar ReN2S2 rings; the bond lengths are ReN 177 pm, NS 152 pm, and SS 259 for the chloro compound and ReN 184 pm, NS 153 pm, and SS 264 pm for the bromo compound. In AsPh4[ReCl4(N2S2)] the cations are stacked to form columns in the c-direction; in PPh4[ReBr4(N2S2)], there is considerable distortion form this packing principle. 相似文献
35.
Mössbauer spectra of119Sn in Sn1–z
Eu
z
Mo6S8 (z=0, 1/3, 2/3) have been measured in the temperature range 4.9 KT293 K. The spectra consist of a quadrupole doublett with unequal intensities at all temperatures. The Debye-Waller factor, the isomeric shift and the asymmetry of the intensity of the quadrupole components show irregularities between 50 K and 110 K which are interpreted as arising from a structural phase transition. The temperature dependence of the Debye-Waller factor can be approximated by a simple phonon spectrum. No quantitative explanation can be given for the large values of the asymmetry. Evidence is presented that this behavior is connected with the properties of the librational modes of the Mo6S8-units in the crystal. 相似文献
36.
Summary The introduction of a cyano-modified, pre-coated layer substantially widens the selectivity of stationary phases in thin-layer
chromatography. This is a moderately polar sorbent based on silica gel 60, which can be used both in adsorption chromatography
and in reversed-phase chromatography. This new pre-coated layer is particularly suitable for separation of steroids, alkaloids
and derivatized amino acids. The possibility of separating habitforming drugs and preservatives in the presence of ionpair
reagents is also discussed. 相似文献
37.
We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR
2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the
FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein
field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity.
Some new and interesting potentials are noted in the presence of R
2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover
approximation. 相似文献
38.
S. Croft L.G. Evans A. Favalli D.K. Hauck D. Henzlova P. Santi 《Radiation measurements》2012,47(7):467-474
A standard nondestructive assay technique for determining the mass of plutonium in an item is passive neutron coincidence counting. In passive neutron coincidence counting, the dead time or rate loss corrections for the singles and doubles neutron counting rates are routinely made using empirical relationships that are based on the design and performance of the individual counter used to make the measurements. The empirical methods were developed ahead of any supporting theory for dead time losses and have worked well to date for the majority of safeguards measurement scenarios. Modern applications using highly efficient systems with short neutron lifetimes together with the challenges posed by highly multiplying items mean dead time corrections of higher fidelity are needed. While many attempts have been made to develop dead time corrections that are based on the physical principles of the measurements being performed, these corrections have often been found to be difficult to implement in a real system. For instance, Matthes and Haas developed an approach in 1985 which did not gain favor largely because the form of the doubles correction apparently required numerical integration which was difficult to implement with the computer technology of that time. A recent review into the approach that was developed by Matthes and Haas has determined that a straightforward analytical expression can be derived for the doubles correction that is similar to the singles rate correction that was developed in their original work. An analysis of the expressions is presented here to show how they relate to the traditional empirical methods. Further, we illustrate their implications and limitations. For instance the empirical methods do not address within burst losses i.e. rate related losses due to the correlated neutron bursts from fission, whereas the Matthes and Hass expression for singles counting does exhibit such an effect. 相似文献
39.
[PPh3Cl]⊕[ReCl4(N2S2)]?; Synthese, IR-Spektrum und Kristall Strukture The title compound is prepared by the reaction of [ReCl3(NSCl)2(POCl3)] with triphenylphosphane; it formes black crystals. The crystal structure determination was solved with X-ray methods (2861 observed independent reflexions, R = 0.038). The compound crystallizes monoclinic in the space group P21/n with four formula units per unit cell. The structure consists of [PPh3Cl]⊕ cations and [ReCl4(N2S2)]? anions, in which the rhenium atom is surrounded octahedrally by four chlorine ligands and the N atoms of a ReN2S2-five-membered ring in cis-position (symmetry C2v). The Re? N bond lengths (181 pm) and the NS bond lengths (152 pm) are in the range of double bonds; the S? S distance is very long (253 pm). The i.r. spectrum is reported. 相似文献
40.
We present a method for the simple production of a pair of real non-negative pupil functions p?1,p?2, that act together to yield a bipolar system spread function P>(x) = |p1|p2 ? |p2|p2. The subtraction can be perf ormed by electronic means. 相似文献