Transient magnetic fields in silicon ions traversing thin foils of Fe and Gd at high velocity

Spin precessions of the²⁸Si first 2⁺ state, caused by transient magnetic fields in thin Fe and Gd foils, were measured at a mean ion velocity of 7.5v ₀ (v ₀=c/137). Transient fields of 1.8 (3) kT and 1.1 (2) kT have been deduced for Fe and Gd, respectively. The observed field strengths are discussed in terms of the electron mean polarization in the SiK shell.     

Transient field precessions and electron polarizations for sulphur ions at high velocity

Effective transient magnetic fields have been measured for S ions traversing thin ferromagnetic foils of Fe, Ni and Gd at mean velocities of 8.0v ₀ (v ₀ =c/137). The deduced polarizations attached to 1s electrons are discussed together with all data available for light ions considering spin exchange scattering as polarization mechanism.     

磁致冷材料钆硅锗系合金中Si和Gd的重量法联测的研究

参考了HClO4脱水重量法测定Si及草酸盐重量法测定Gd的方法,建立了钆硅锗系合金中主成分Si和Gd联合测定的方法,并详细考查了共存元素及杂质元素对测定的影响。合金共存元素Ge在HCl的存在下,绝大部分可以GeCl4的形式被蒸发,达到与被测元素分离的目的。熔样过程引入的杂质元素Ni可与被测元素Gd,用氨水沉淀分离,残留Ni不足以影响Gd的测定。方法回收率在98.5%以上,Si和Gd的测量相对标准偏差分别在2.6%~3.0%和0.4%~0.5%。     

Interaction second virial coefficients at low temperatures for NeKr and NeO2 systems

Published results of vapour—liquid and vapour—solid equilibrium studies for neon—krypton and neon—oxygen mixtures have been analysed to give values for the interaction second virial coefficients. B₁₂. Comparisons are made with other results for the NeKr system and with the predictions of some proposed intermolecular potentials.     

Electronic stopping powers of Ni, Gd and Pd metals for 19F ions at low energy

Summary Electronic stopping power of ¹⁹F in Ni, Pd and Gd was measured and compared to Mstar and SRIM calculation as well as experimental results published in literature. It turns out that the present electronic stopping power agrees reasonably well with them.     

Dual Emission from Precious Metal-Free Luminophores Consisting of C,H, O,Si, and S/P at Room Temperature

Fluorescence–phosphorescence dual-emissive compounds are valuable tools for ratiometric luminescence sensing. Herein, it is reported that 2,5-bis(phenylsulfonyl)- and 2,5-bis[bis(4-methoxyphenyl)phosphinyl]-1,4-disiloxybenzenes exhibit dual emission with emission peaks that were easily identified without performing time-gated measurement. The disiloxybenzenes in powder simultaneously fluoresced and phosphoresced at 358–374 and 457–470 nm, respectively, under vacuum. The intensity ratios of the phosphorescence/fluorescence maxima of the disiloxybenzenes in powder and in a thin film of poly(methyl methacrylate) were sensitive to temperature and molecular oxygen, respectively. The plots of the relative intensity versus temperature or partial pressure of molecular oxygen were well fitted with calibration curves defined by an exponential approximation with excellent correlation coefficients R² (0.9708–0.9921), demonstrating the high potential of the disiloxybenzenes as precious metal-free probes applicable to ratiometric luminescence sensing.     

Theoretical Studies on Structure,Isomerization, and Stability of [Si,O, S]

The structures, energetics, and isomerization of a possible interstellar [Si, O, S] system were explored at the CCSD(T)/aug-cc-pVQZ//CCSD(T)/aug-cc-pVTZ level. On the schemaitc potential energy surface(PES), we found that silicon oxysulfide(OSiS) produced in laboratory is the global minimum. An analysis of the Wiberg bond index(WBI), bond order and the bond length, shows that silicon oxysulfide contains SiO and SiS double bonds in accordance with the results of Schn?ckel. Besides silicon oxysulfide, another interesting cyclic minimum(c-SiOS) was found to have a very high kinetic stability stabilized by the least barrier of 120.9 kJ/mol. In light of the fact that no cyclic sulfide-containing species has been detected in space, c-SiOS could be a very promising candidate. The presented results might provide useful information on detected interstellar molecules O=Si=S and c-SiOS.     

Preparation of Gd2O3:Yb,Er and Gd2O2S:Yb,Er infrared-to-visible conversion phosphor ultrafine particles using an emulsion liquid membrane system

Upconverting phosphor fine particles (Gd2O3:Yb,Er and Gd2O2S:Yb,Er) have been prepared, using an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system. The composite Gd-Yb-Er oxalate particles obtained in the ELM system were mainly 20-60 nm in size, together with a smaller amount of submicrometer-sized spherical particles. Nanometer-sized Gd2O3:Yb,Er and Gd2O2S:Yb,Er particles were obtained by calcination in air and in sulfur atmosphere, respectively, of the precursor oxalate particles prepared in the ELM system. Upconversion emissions (red and green) were obtained from the Gd2O3:Yb,Er and Gd2O2S:Yb,Er particles prepared in the ELM system under infrared excitation (lambdaex=980 nm) via a two-photon process. Upconversion phosphor fine particles, about 50 nm in diameter, may be applied to the luminescent reporter material for the detection of the targeted analyte in immunoassays or DNA assays.     

Theoretical Study on the Structure and Stability of Si5X （X = Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl） Clusters

1 INTRODUCTION In the later 60s of last century, silicon substituted for germanium to present as mainstream in semicon- ductor. The semi-conductive devices made by silicon have many advantages, for example, refractory pro- perty, high radioresistance, simple and stable process- ing technic, high machinability and low cost. So it was widely used to manufacture large power appara- tuses, for instance, digit and linear integrated circuit, large scale integrated circuit (LSI), etc. Thus, th…     

Strong enhancement of transient magnetic fields in Gd over Fe for oxygen ions at high velocities

Precision data on transient magnetic fields (TF) in ferromagnetic Gd and Fe were obtained for oxygen ions at velocities between 2 and 8v ₀ (v ₀=c/137) using the¹⁶O(3^?) state as probe. At the high velocities the TF in Gd were found to be twice as large as in Fe which is in contrast to the generally observed scaling with the polarization density of the hosts. Degrees of polarization could be deduced from TF strengths using measured ion fractions of singly occupiedK-shell. The values derived were compared with theoretical estimates based on spin exchange scattering as a possible polarization mechanism.     

Y2O2S:Eu,Ti,Mg的光谱性质和长时发光特性

研究了Ti, Mg, Eu等离子掺杂的Y2O2S材料的光谱性质和长时发光特性, 并发现了光致激发下Y2O2S∶Ti中峰值为594nm的宽带发射及长时发光现象. 根据发射光谱和衰减曲线的分析, 认为Ti掺杂后在Y2O2S晶体中形成施主能级, 有效地捕获离化的电子, 造成长时发光现象. 共掺入Mg进行电荷补偿可增强初始发光亮度和发光时间. 在红色长时发光材料Y2O2S∶Eu, Ti, Mg中, Eu3 作为发光中心, 接受被俘获的电子和空穴重新复合后释放的能量, 发射Eu3 的626和616 nm等特征光谱.     

Catalysis in the Synthesis of S,N-Heterocycles and O,N-, S,N-, and O,S,N-Macroheterocycles

The review systemizes and generalizes published data on the catalytic syntheses of six-, seven-, and eight-membered S,N-heterocycles and O,N-, S,N-, and O,S,N-macroheterocycles.     

Spin dynamics of the radical pair in a low magnetic field studied by the transient absorption detected magnetic field effect on the reaction yield and switched external magnetic field

The spin dynamics of the radical pair generated from the photocleavage reaction of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TMDPO) in micellar solutions was studied by the time-resolved magnetic field effect (MFE) on the transient absorption (TA) and by a novel technique, absorption detected switched external magnetic field (AD-SEMF). Thanks to the large hyperfine coupling constant (A = 38 mT), a characteristic negative MFE on the radical yield was observed at a magnetic field lower than 60 mT whereas a positive effect due to the conventional hyperfine (HFM) and relaxation mechanisms (RM) was observed at higher magnetic field. The negative effect can be assigned to the mechanism "so-called" low field effect (LFE) mechanism and has been analyzed thoroughly using a model calculation incorporating a fast spin dephasing process. The time scale of the spin mixing process of LFE studied by AD-SEMF is shorter than the lifetime of the recombination kinetics of the radical pair. These results indicate that the LFE originates from the coherent spin motion. This can be interfered from the fast spin dephasing caused by electron spin interaction fluctuations.     

Ethanol steam reforming over Ni-Cu/Al2O3-MyOz （M = Si, La, Mg, and Zn） catalysts

Ni-based catalysts doped with copper additives were studied on their role in ethanol steam reforming reaction.The effects of Ca content,support species involving Al2O3-SiO2,Al2O3-MgO,Al2O3-ZnO,and Al2O3-La2O3,on the catalytic performance were studied.Characterizations by TPR,XRD,NH3-TPD,XPS,and TGA indicated that catalysts 30Ni5Cu/Al2O3-MgO and 30NiSCu/Al2O3-ZnO have much higher H2 selectivity than 30NiSCu/Al2O3-SiO2,as well as good coke resistance.H2 selectivity for 30Ni5Cu/Al2O3-MgO catalyst was 73.3% at 450℃ and increased to 94.0% at 600 ℃,whereas for 30NiSCu/Al2O3-ZnO catalyst,the H2 selectivity was 63.6% at 450 ℃ and 95.2% at 600 ℃.These Al2O3-MgO and Al2O3-ZnO supported Ni-Cu bimetallic catalysts may have important applications in the production of hydrogen by ethanol steam reforming reactions.     

Collective relaxation of protein protons at very low magnetic field: a new window on protein dynamics and aggregation

Since the recent availability of high sensitivity field-cycling relaxometers, it has become possible to measure the protein proton relaxation in millimolar protein solutions as a function of magnetic field. In principle, this provides direct access to the so-called spectral density function of protein protons and, hence, to a full set of dynamic parameters. Understanding the dynamic behavior of biological molecules is increasingly appreciated as crucial to understanding their function. However, theoretical tools to analyze the collective relaxation behavior of protons in solute macromolecules over a wide range of magnetic fields are lacking. A complete relaxation matrix analysis of such behavior is described here. This analysis provides excellent predictions of the experimental proton magnetization decays/recoveries-measured to an unprecedented level of accuracy by a last-generation fast field-cycling relaxometer-of two different globular proteins, hen egg white lysozyme and human serum albumin. The new experimentally validated theoretical model is then used to extract dynamic information on these systems. A "collective" order parameter SC2, different from, but complementary to, that commonly extracted from heteronuclear relaxation measurements at high field, is defined and measured. An accurate estimate of the rotational correlation time is obtained: in the case of lysozyme it agrees very well with theoretical predictions; in the case of serum albumin it provides evidence for aggregation at millimolar concentration.     

Pseudo-Jahn-Teller origin of geometry and pseudorotations in second row tetra-atomic clusters X4 (X=Na, Mg, Al, Si, P, S)

Experimentally determined or ab initio calculated molecular geometries carry no information about their origin. Employing the Jahn-Teller (JT) vibronic coupling effects as the only source of instability and consequent distortions of high-symmetry molecular configurations, we have worked out a procedure that allows us to trace the origin of particular geometries and determine the detailed electronic mechanism of their formation. This procedure is illustrated by considering a series of X(4) clusters with X=Na, Mg, Al, Si, P, and S. It shows explicitly why Na(4), Si(4), and Al(4) have a rhombic geometry in the ground state, while Mg(4) and P(4) are tetrahedral, whereas S(4) is a trapezium. Even when the minimum-energy geometries are the same (as in the case of rhombic Na(4), Si(4), and Al(4)), the electronic mechanism of their formation is quite different. In particular, in Na(4) and Si(4) the rhombic minima are produced by a strong pseudo JT coupling between two excited states in the square-planar configuration (different in the two cases) that stabilizes one of them and makes it the ground state by rhombic distortions. The rhombic configuration of Al(4) is due to the pseudo JT effect in its ground-state square-planar configuration, and the trapezium in S(4) is formed by two pseudo JT couplings essentially involving excited states. In several cases this analysis shows also the tunneling paths between equivalent configurations.     

Gd(1.33)Pt(3)(Al,Si)(8) and Gd(0.67)Pt(2)(Al,Si)(5): two structures containing a disordered Gd/Al layer grown in liquid aluminum

Gd(1.33)Pt(3)Al(8) was synthesized by the combination of Gd and Pt in excess liquid aluminum. Addition of silicon resulted in the incorporation of a small amount of this element into the material to form the isostructural Gd(1.33)Pt(3)Al(7)Si. Both compounds grow as rodlike crystals with hexagonal cross section. The structures were refined in the rhombohedral space group R(-)3m, with cell parameters a = 4.3359(6) A and c = 38.702(8) A for the ternary and a = 4.3280(8) A and c = 38.62(1) A for the quaternary compound. The structure is comprised of stuffed arsenic-like PtAl(2) layers and disordered Gd/Al layers. Analysis of the hk0 zone reflections indicate the presence of an a = radical 3a supercell, but the structure is not ordered along c, as revealed by the highly diffuse reflections in the 0kl zone photos. Therefore, the compounds are disordered variants of the Gd(4)Pt(9)Al(24) type. Magnetic susceptibility studies reveal antiferromagnetic transitions at 15 K for the ternary and 7 K for the quaternary compound. Variation of the reactant ratio produces a different structure comprised of the same structural blocks, including the disordered Gd/Al layer. Gd(0.67)Pt(2)Al(5) and its quaternary analogue Gd(0.67)Pt(2)Al(4)Si form in the hexagonal system P6(3)/mmc with cell parameters a = 4.2907(3) A and c = 16.388(2) A for the ternary and a = 4.2485(6) A and c = 16.156(3) A for the quaternary compound.