Superconductivity in the alkali metals

At ambient pressure there are 29 elemental superconductors in the periodic table, none of which is an alkali metal. The first alkali metal to become superconducting under high pressure is Cs followed years later by Li. Alkali metals are believed to be exemplary free-electron systems. The fact that an alkali metal becomes superconducting at all is surprising and is a result of the fact that under pressure it shows marked deviations from free-electron behaviour where, counterintuitively, bands narrow and gaps widen. For this reason the alkali metals are among the most interesting systems known to study in high-pressure experiments and superconductivity is one of their most fascinating properties.     

A one step synthesis of novel 4-alkoxy-β-lactams by high pressure promoted [2 + 21 cycloadditions of enol ethers and isocyanates derived from amino acids

Abstract

Novel moni-β-lactams derived from esters of amino acids have been prepared in one step by the high pressure promoted [2 + 2] cycloaddition of enol ethers with isocyanates derived from esters of amino acids. The effect of substituents in the enol ether and in the isocyanate on the scope of the synthesis has been demonstrated.     

The Morphology and Mechanical Properties of Isotactic Polypropylene Injection-Molded Samples with the Presence of β-Nucleation Agent and Periodical Shear Field

The pressure vibration injection molding (PVIM) method was used to prepare β-nucleated isotactic polypropylene samples (PVIM β-iPP samples); a relatively low, periodical shear was imposed on the polymer melt in the mold at the filling and packing stages. The crystal structures and crystal orientation of the PVIM β-iPP samples were investigated by polarizing light microscopy (PLM), scanning electron microscopy (SEM), and synchrotron two-dimensional wide-angle X-ray diffraction (2D-WAXD). The PLM observations indicated that a cylindrite layer, rather than the transition layer, was found in PVIM β-iPP samples, which is different from the conventional injection-molded (CIM) samples. In addition, the thickness of the oriented layer of the PVIM samples was obviously greater than that of the CIM samples. The SEM observations demonstrated that a large amount of shish-kebab structures appeared in the shear layer of the PVIM β-iPP samples; at the same time, numerous β-spherulites were formed in the core layer. The 2D-WAXD data indicated that orientation homogeneity, to some degree, could be obtained by the periodical shear during PVIM. As a result, the above-mentioned morphology of the PVIM β-iPP samples leads to potentially useful prominent reinforcement and toughening of the material.     

Functional magnetic resonance imaging of tonic pain and vasopressor effects in rats

In functional magnetic resonance imaging (fMRI) studies, an elevation in blood pressure (BP) in individuals with a poor autoregulatory response may increase cerebral blood flow, potentially enhancing the blood oxygenation level dependent response. To investigate the role of BP changes, the cerebral activation to either tonic pain or the infusion of the vasopressor norepinephrine was correlated with the accompanying BP changes in alpha-chloralose anesthetized rats. Immediately after formalin (2%) injection into the forepaw, fMRI detected an activation that was correlated with the BP increase and additional activations that were independent of blood pressure changes 5–40 minutes later. The activation detected with the administration of the vasopressor norepinephrine, which does not cross the blood-brain barrier was correlated to both the amount and rate of increase in BP. The response ranged from being sparse, localized within cortex or widespread during modest, moderate or severe elevations in BP, respectively. The cerebral circulatory effects of hypertension should be considered as contributing to changes in cerebral blood oxygenation in fMRI studies involving increases in BP.     

Derivation of a new class of distributions for the microcanonical ensemble

A new class of distributions for the microcanonical ensemble, which are shown to be stable laws, are derived by applying the central limit theorem to the canonical ensemble. This opens up a whole new host of phenomena that can be treated from a unified thermodynamic point of view. Pressure broadening of line shapes is used as an illustration.1. Work supported, in part, by contributions from the Consiglio Nazionale di Ricerche and the Ministero dell'Università e della Ricerca Scientifica e Tecnologica.2. The interaction parameterC is proportional to the mean square dipole moment. As an order of magnitude of the dipole moment, we can take it as the product of the electric charge and a typical atomic radius for a moderately excited state, which is several times the Bohr radius. Multiplication by the fine structure constant converts the Bohr radius into the Compton wavelength, thereby reducing the magnitude of the interaction by 1/137.     

Computation of collective modes and acoustic investigations at different temperatures of vitrous silica

This paper is mainly concerned with elastic and acoustic properties of vitrous silica besides the computation of phonon frequencies. Thus the phonon frequencies of vitrous silica have been calculated assuming the electronic bulk modulus,K _e, as equal to zero. New equations have been derived to relate the pressure derivatives of second order elastic constants to the acoustic Gruneisen’s parameters using both Bhatia-Singh’s parameters and Schofield’s equations. The calculated longitudinal and transverse Gruneisen’s parameters and the predicted absorption band spectra from Nagendranath’s equation and Bhatia Singh’s parameters are in good agreement with experiment. The calculated mean acoustic mode Gruneisen’s parameter evaluated from the pressure derivative of Nagendranath’s equation is also in good agreement with experiment. An erratum to this article is available at .     

Atmospheric pressure plasma treatment on graphene grown by chemical vapor deposition

We demonstrate the surface treatment of graphene using an atmospheric pressure plasma jet (APPJ) system. The graphene was synthesized by a thermal chemical vapor deposition with methane gas. A Mo foil and a SiO₂ wafer covered by Ni films were employed to synthesize monolayer and mixed-layered graphene, respectively. The home-built APPJ system was ignited using nitrogen gas to functionalize the graphene surface, and we studied the effect of different treatment times and interdistance between the plasma jet and the graphene surface. After the APPJ treatment, the hydrophobic character of graphene surface changed to hydrophilic. We found that the change is due to the formation of functionalities such as hydroxyl and carboxyl groups. Furthermore, it is worth noting that the nitrogen plasma treatment induced charge doping on graphene, and the pyridinic nitrogen component in the X-ray photoelectron spectroscopy spectrum was significantly enhanced. We conclude that the atmospheric pressure plasma treatment enables controlling the graphene properties without introducing surface defects.     

Pressure induced lattice anomalies in pnictides

Hydrostatic pressure Raman and synchrotron XRD measurements at room temperature have been carried out on a series of NdFeAsO_1−xF_y (Nd1111) oxypnictides in order to investigate pressure-induced lattice modifications. The synchrotron XRD data indicate that there is an increased deviation of the lattice constants from smooth pressure dependence in the superconducting compound, in close agreement with the results from SmFeAsO_1−xF_x (Sm1111), although the effect is less pronounced in Nd1111. As in Sm1111 the hydrostatic pressure Raman measurements show that the A_1g mode of the rare earth atom deviates from the linear pressure dependence. Anomalous pressure dependence and a hysteresis is observed in the phonon width of the phonon modes. The calculated Grüneisen parameter for the Nd phonon is very similar to the corresponding value for SmFeAsO_1−xF_x compound and it does not vary with substitution. For the As mode it has a lower value indicating a stiffer phonon with the increased ion size. In connection with the XRD measurements the Raman data show a sudden increase of the pressure-induced lattice anomalies close to doping where the compounds become superconducting.     

Kinetic modeling of a high power fast-axial-flow CO2 laser with computational fluid dynamics method

A new computational fluid dynamics (CFD) method for the simulation of fast-axial-flow CO2 laser is developed.The model which is solved by CFD software uses a set of dynamic differential equations to describe the dynamic process in one discharge tube.The velocity,temperature,pressure and turbulence energy distributions in discharge passage are presented.There is a good agreement between the theoretical prediction and the experimental results.This result indicates that the parameters of the laser have significant effect on the flow distribution in the discharge passage.It is helpful to optimize the output of high power CO2 laser by mastering its kinetic characteristics.     

三维跨音速叶栅自动气动优化设计

应用三维叶栅自动设计参数化方法,选择E3约束的条件下进行了自动气动优化设计.优化后,最优叶栅的总压恢复系数比参考叶栅提高了0.8%,流量和出口气流角都在约束范围内.对优化结果的详细气动分析表明,叶栅性能有显著的改善,表明该算法具有良好的优化性能.