Ab initio studies of copper hydrides under high pressure

The crystal structure, electronic structure, and superconductivity of copper hydrides at high pressure have been studied by ab initio calculation. Consistent with experimental report, results show that the predicted stoichiometry Cu₂H with the P-3m1 space group is stable above 16.8 GPa. The stoichiometry of CuH with the Fm-3m space group is predicted to be synthesized above 30 GPa, but it is metastable and dynamical instable up to 120 GPa. The electronic band calculations reveal that Cu₂H is a good metal at a stable pressure range, whereas CuH is an insulator. Moreover, the other hydrogenrich compounds CuH₂ and CuH₃ are thermodynamically and dynamically unstable, respectively. The calculated superconducting transition temperature (T _c) of Cu₂H at 40 GPa is 0.028 K by using the Allen-Dynes modified McMillan equation.     

SOLEIL shining on the solution‐state structure of biomacromolecules by synchrotron X‐ray footprinting at the Metrology beamline

Synchrotron X‐ray footprinting complements the techniques commonly used to define the structure of molecules such as crystallography, small‐angle X‐ray scattering and nuclear magnetic resonance. It is remarkably useful in probing the structure and interactions of proteins with lipids, nucleic acids or with other proteins in solution, often better reflecting the in vivo state dynamics. To date, most X‐ray footprinting studies have been carried out at the National Synchrotron Light Source, USA, and at the European Synchrotron Radiation Facility in Grenoble, France. This work presents X‐ray footprinting of biomolecules performed for the first time at the X‐ray Metrology beamline at the SOLEIL synchrotron radiation source. The installation at this beamline of a stopped‐flow apparatus for sample delivery, an irradiation capillary and an automatic sample collector enabled the X‐ray footprinting study of the structure of the soluble protein factor H (FH) from the human complement system as well as of the lipid‐associated hydrophobic protein S3 oleosin from plant seed. Mass spectrometry analysis showed that the structural integrity of both proteins was not affected by the short exposition to the oxygen radicals produced during the irradiation. Irradiated molecules were subsequently analysed using high‐resolution mass spectrometry to identify and locate oxidized amino acids. Moreover, the analyses of FH in its free state and in complex with complement C3b protein have allowed us to create a map of reactive solvent‐exposed residues on the surface of FH and to observe the changes in oxidation of FH residues upon C3b binding. Studies of the solvent accessibility of the S3 oleosin show that X‐ray footprinting offers also a unique approach to studying the structure of proteins embedded within membranes or lipid bodies. All the biomolecular applications reported herein demonstrate that the Metrology beamline at SOLEIL can be successfully used for synchrotron X‐ray footprinting of biomolecules.     

基于DMD光谱可调的星模拟器光源光学系统设计

为满足在各种谱线分布下对星敏感器探测能力的高准确度标定,提出了一种基于数字微镜器件的光谱可调星模拟器光源光学系统设计方法,以解决星模拟器与星敏感器观星色温不匹配对星敏感器光信号定标准确度产生的问题.首先,根据设计指标选取Czerny-Turner型光学系统为光源光学系统,对Czerny-Turner型光学系统的彗差和象散进行分析,选取消彗差的Czerny-Turner结构;其次利用MATLAB程序求解Czerny-Turner型光学系统初始结构并应用ZEMAX对其进行优化;最后对光学系统进行公差分析.公差分析结果表明,在400~1 100nm的工作谱段范围内,光学系统的光谱分辨率小于2nm,设计结果满足要求,有效降低了光谱不匹配带来的定标误差.     

Opinion formation in a social network: The role of human activity

The model of opinion formation in human population based on social impact theory is investigated numerically. On the basis of a database received from the on-line game server, we examine the structure of social network and human dynamics. We calculate the activity of individuals, i.e. the relative time devoted daily to interactions with others in the artificial society. We study the influence of correlation between the activity of an individual and its connectivity on the process of opinion formation. We find that such correlations have a significant influence on the temperature of the phase transition and the effect of the mass media, modeled as an external stimulation acting on the social network.     

Surface‐enhanced Raman scattering study of monolayers formed from mixtures of 4–mercaptobenzoic acid and various aromatic mercapto‐derivative bases

Monolayers formed from aromatic compounds have many potential applications, for example in construction of bioelectronic elements having high efficiency of electron transfer. In this paper, the composition of monolayers formed on silver surfaces from mixtures of 4‐mercaptobenzoic acid (MBA) and four model (stable and easily available) aromatic thiols with strong base properties: 4,6‐diamino‐2‐mercaptopyrimidine (APY), 1H‐1,2,4‐triazole‐3‐thiol (HTR), 4‐methyl‐4H‐1,2,4‐triazole‐3‐thiol (MTR) and 3‐amino‐1,2,4‐triazole‐5‐thiol (ATR), were determined from surface‐enhanced Raman scattering (SERS) measurements. Our investigations showed that among studied aromatic bases, APY is the most promising candidate for the formation of mixed monolayers with MBA. In the whole pH range studied (2–12.5), mixed MBA + APY monolayers with similar surface concentration of both components are formed during the adsorption from the 0.5 mM MBA + 0.5 mM APY aqueous solution. Desorption of MBA and APY from the mixed monolayer is, however, significantly different. During immersion in water, surface concentration of APY decreases significantly faster than MBA (a significant part of the adsorbed MBA molecules is present on the silver surface even after 2 h of soaking in water). Presence of chlorides, bovine serum albumin or laccase in the surrounding solution does not observably influence the structure of MBA + APY monolayers. The properties of monolayers formed from MBA and substituted triazoles were found to be significantly different than those of MBA + APY monolayers. Copyright © 2009 John Wiley & Sons, Ltd.     

Vibrational spectra of two BEDT-TTF-based organic conductors: charge order

Infrared and Raman investigations of two phases of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) based organic conductors with the same CF₃CF₂SO₃⁻ anion: β′-(BEDT-TTF)₂CF₃CF₂SO₃ and δ′-(BEDT-TTF)₂CF₃CF₂SO₃, are shortly reviewed and compared with the most typical infrared properties of the family of (BEDT-TTF)₂RR′SO₃ organic conductors, where R = SF₅, CF₃, and R′ are CH₂, CF₂, CHF, CHFCF₂, and CH₂CF₂. The role of the molecular structur and spatial organization of the counterions is discussed. Presented at 2-nd International Conference on Functional Materials and Devices, ICFMD 2008, June 16–19, 2008, Kuala Lumpur, Malaysia     

A DFT/TD‐DFT study for the ground and excited states of peramine and some pyrrolopyrazinone compounds

Peramine, a heterocyclic natural molecule, reveals two main, different in nature, electronic absorption bands. Theoretical calculations at the TD‐B3LYP/6–311++G(d,p) level of theory show that the electronic excitations are connected predominantly with π → π^* and charge‐transfer (CT) transitions. Excitation of electrons from the pyrrolopyrazinone ring to the side chain plays a role in creating the CT transition. The character and energy of the first 30 singlet–singlet electronic transitions have also been investigated for the most stable conformation of peramine. Copyright © 2009 John Wiley & Sons, Ltd.     

Bump time-frequency toolbox: a toolbox for time-frequency oscillatory bursts extraction in electrophysiological signals

Background  

oscillatory activity, which can be separated in background and oscillatory burst pattern activities, is supposed to be representative of local synchronies of neural assemblies. Oscillatory burst events should consequently play a specific functional role, distinct from background EEG activity – especially for cognitive tasks (e.g. working memory tasks), binding mechanisms and perceptual dynamics (e.g. visual binding), or in clinical contexts (e.g. effects of brain disorders). However extracting oscillatory events in single trials, with a reliable and consistent method, is not a simple task.     

Effect of Carbonized Conditions on Residual Strain and Crystallinity Quality of Heteroepitaxial Growth 3C-SiC Films

Heteroepitaxial growth of SiC on n-Si（111） substrates is performed by a low pressure chemicaJ vapor deposition process. The effects of different carbonized temperature and carbonized time on the crystalline quality and the residual strain of 3C-SiC films are discussed. The results show that the residual strain is obviously reduced and the crystalline quality is greatly improved at the best carbonized temperature of 1000℃ and the carbonized time of 5 min. Under these optimized carbonization conditions, thick epitaxial films of about 15 μm with good crystalline quality and low residual strain can be obtained.     

Effect of poly (ethylene glycol) coating on the magnetic and thermal properties of biocompatible magnetic liquids

The aim of this study was to investigate the influence of poly(ethylene glycol) surface-active coating on the magnetic and thermal properties of biocompatible magnetic liquids. The data were analyzed using the high-temperature approximation model taking into account polydispersity of a system. Heating ability of the PEG-stabilized magnetic fluids was determined by the calorimetric measurement of specific absorption rate (SAR) at a frequency of 750 kHz and a magnetic field of 0-2 kA/m. MF-Oleate/PEG heating properties were found to be comparable to the ones of MF-Oleate. The PEG shell thus does not seem to effect the thermal characteristics and SAR values and might make the magnetic fluid useful for application in hyperthermia treatment.