XANES and USXES studies of interatomic interactions in (Co41Fe39B20)x(SiO2)1 ? x nanocomposites

The electronic structure and phase composition of (Co₄₁Fe₃₉B₂₀) _x (SiO₂)_{1 − x} nanocomposites are studied by x-ray absorption near-edge spectroscopy, which is extremely sensitive to the chemical environment of elements in multicomponent compounds. An analysis of the recorded Fe L _{2, 3}, Co L _{2, 3}, B K, Si L _{2, 3}, and O K absorption spectra demonstrates interatomic interactions between the elements of the metallic and dielectric components of the nanocomposites. As a result of these interatomic interactions, a complex multiphase system, whose electronic structure should determine the transport and magnetic properties of the nanocomposites, forms. In particular, the transformation of the fine structure of the iron L _{2, 3} spectra reflects a change in the ratio of divalent to trivalent iron in its oxides and/or silicates. CoO and complex boron oxides are found to exist in the nanocomposites. The electrical conductivity of a FeO · F₂O₃ · CoO grain embedded in the silicate-oxide medium of the nanocomposites is controlled by electron exchange between Co²⁺, Fe²⁺, and Fe³⁺ ions. The dielectric component consists of a mixture of silicon oxide and the silicates/borosilicates of transition metals. Original Russian Text ? é.P. Domashevskaya, S.A. Storozhilov, S.Yu. Turishchev, V.M. Kashkarov, V.A. Terekhov, O.V. Stogneĭ, Yu.E. Kalinin, A.V. Sitnikov, S.L. Molodtsov, 2008, published in Fizika Tverdogo Tela, 2008, Vol. 50, No. 1, pp. 135–141.     

Observation of a superfluid phase in solid helium

Evidence of a superfluid liquid phase present in polycrystalline helium at a temperature of 0.2 K and a pressure of 51 bar has been obtained by means of inelastic neutron scattering. The superfluid component is absent at a temperature of 0.6 K and the same pressure. Thus, a “solid helium-superfluid helium” phase transition has been discovered. The sample of solid helium in a porous medium (silica aerogel) has been prepared with the use of a capillary blocking technique. The shape of the structure factor of the superfluid phase indicates the presence of clusters or the effects of a restricted geometry. The results may be used to explain the nonclassical rotational inertia phenomenon in solid helium (often referred to as supersolidity, Nature, 2004).     

Towards experiments with highly charged ions at HESR

The atomic physics collaboration SPARC is a part of the APPA pillar at the future Facility for Antiproton and Ion Research. It aims at atomic-physics research across virtually the full range of atomic matter. An emphasis of this contribution are the atomic physics experiments addressing the collision dynamics in strong electro-magnetic fields as well as the fundamental interactions between electrons and heavy nuclei at the HESR. Here we give a short overview about the central instruments for SPARC experiments at this storage ring.     

Synthesis and unusual [2+2]-cycloaddition reactions of ethyl 4-chloro-2-oxobut-3-ynoate with unactivated alkenes

The highly activated acetylenes, ethyl 4-chloro-2-oxobut-3-ynoate and ethyl 4-bromo-2-oxobut-3-ynoate, were prepared from readily available bis(trimethylstannyl)acetylene in two steps with high overall yield. An unusual ability of the former to furnish [2+2]-cycloadducts with 1,1-disubstituted alkenes in the absence of irradiation and catalysts was discovered. The cycloaddition of ethyl 4-chloro-2-oxobut-3-ynoate to the 1,2-disubstituted alkenes was shown to be effectively catalyzed with stannic chloride.     

Synthesis of boron-containing derivatives of pyropheophorbide <Emphasis Type="ItalicUnderline">a</Emphasis> and investigation of their photophysical and biological properties

Proceeding from pyropheophorbide a and 9-hydroxymethyl-m-carborane, 1-hydroxymethyl-o-carborane, and 3-amino-o-carborane new carboranylchlorins were prepared, and their photophysical and biological properties were investigated.     

Probability distribution analysis of single-molecule fluorescence anisotropy and resonance energy transfer

Analysis of anisotropy in single-molecule fluorescence experiments using the probability distribution analysis (PDA) method is presented. The theory of anisotropy-PDA is an extension of the PDA theory recently developed for the analysis of F?rster resonance energy transfer (FRET) signals [Antonik, M.; et al. J. Phys. Chem. B 2006, 110, 6970]. The PDA method predicts the shape of anisotropy histograms for any given expected ensemble anisotropy, signal intensity distribution, and background. Further improvements of the PDA theory allow one to work with very low photon numbers, i.e., starting from the level of background signal. Analysis of experimental and simulated data shows that PDA has the major advantage to unambiguously distinguish between shot noise broadening and broadening caused by heterogeneities in the sample. Fitting of experimental histograms yields anisotropy values of individual species, which can be directly compared with those measured in ensemble experiments. Excellent agreement between the ensemble data and the results of PDA demonstrates a good absolute accuracy of the PDA method. The precision in determination of mean values depends mainly on the total number of photons, whereas the ability of PDA to detect the presence of heterogeneities strongly depends on the time window length. In its present form PDA can be also applied to computed fluorescence parameters such as FRET efficiency and scatter-corrected fluorescence anisotropy. Extension of the PDA theory to low photon numbers makes it possible to apply PDA to dynamic systems, for which high time resolution is required. In this way PDA is developed as a sensitive tool to detect biomolecular heterogeneities in space and time.     

Method for Recirculation of Signals in the Problem of Observation of a Point Object above a Metal Surface

Technical Physics - Application of ultrawideband centimeter-wavelength signals using recirculation of signals in spatial recirculation loops (emitter–target–element of the receiving...     

Study of the Involvement of <Superscript>8</Superscript>Be and <Superscript>9</Superscript>B Nuclei in the Dissociation of Relativistic <Superscript>10</Superscript>C, <Superscript>10</Superscript>B,and <Superscript>12</Superscript>C Nuclei

The results obtained by estimating the contribution of 8Be and 9B nuclei to the coherent dissociation of ¹⁰C, ¹⁰B, and ¹²C relativistic nuclei in nuclear track emulsions (“white” stars) are presented. The selection of white stars accompanied by 9B leads to a distinct peak appearing in the distribution of the excitation energy of 2α2p ensembles and having a maximum at 4.1 ± 0.3 MeV. A 8Be nucleus manifests itself in the coherent-dissociation reaction ¹⁰B → ²He + H with a probability of (25 ± 5)%, (14 ± 3)% of it being due to 9B decays. The ratio of the branching fractions of the ⁹B + n and ⁹Be + p mirror channels is estimated at 6 ± 1. An analysis of the relativistic dissociation of ¹²C nuclei in a nuclear track emulsion revealed nine 3α events corresponding to the Hoyle state.     

Effect of heat treatment on the structure and the thermoelectric properties of Sb<Subscript>0.9</Subscript>Bi<Subscript>1.1</Subscript>Te<Subscript>2.9</Subscript>Se<Subscript>0.1</Subscript> thin films and composites based on them

This work considers the effect of vacuum annealing on the thermoelectric properties of Sb_0.9Bi_1.1Te_2.9Se_0.1 thin film and Sb_0.9Bi_1.1Te_2.9Se_0.1–C composites with various carbon contents produced by ion-beam deposition in an argon atmosphere. The electrical resistivity and the thermopower of Sb_0.9Bi_1.1Te_2.9Se_0.1–C nanocomposites are found to be dependent on not only the carbon concentration but also the type and the concentration of intrinsic point defects of the Sb_0.9Bi_1.1Te_2.9Se_0.1 solid solution, which determine the type of conductivity of Sb_0.9Bi_1.1Te_2.9Se_0.1 granules. The power factors are estimated for films of Sb_0.9Bi_1.1Te_2.9Se_0.1 solid solution and films of Sb_0.9Bi_1.1Te_2.9Se_0.1–C composites and found to have values comparable with the values for nanostructured materials on the basis of (Bi,Sb)₂(Te,Se)₃ solid solutions.