Pressure-induced phase transition of zinc-blende AlN: An ab initio molecular dynamics study

An ab initio constant pressure technique is carried out to study the pressure-induced phase transition of the zinc blende AlN (aluminum nitride). A first order phase transformation into a rock salt structure is observed in the constant pressure simulations. The transformation is accompanied by an initial tetragonal distortion and a subsequent shearing, similar to that found in the other zinc blende structured materials. This phase transition should occur around 6.2 GPa based upon the enthalpy calculations.     

Catalytic decomposition of hydrogen peroxide by Cu/M heterobimetallic complexes (M = Mn, Zn) with Schiff bases in the presence of electrolytes

A study was carried out on the effect of electrolytes KCl, CaCl₂, MnCl₂, ZnCl₂, CuCl₂, KNO₃, Ca(NO₃)₂, Mn(NO₃)₂, Zn(NO₃)₂, and Cu(NO₃)₂ on the kinetics of the decomposition of H₂O₂ catalyzed by [Cu(L¹/L²)][MCl₄] complexes (M = Zn, Mn; L¹ is 4,6,6-trimethyl-1,9-diamino-3,7-diaza-3-nonene, L² is 1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetraaza-6-pentadecene). The chloride ions were found to reversibly inhibit the catalyst. The major kinetic characteristics of this reaction were obtained using a mathematical model taking account of the reversible and irreversible inhibition of the catalyst. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 4, pp. 240–247, July–August, 2008.     

Relaxations in chitin: Evidence for a glass transition

Relaxations in chitin have been investigated in the temperature range 298–523 K using impedance spectroscopy in the frequency range 10⁻¹–10⁸ Hz. The objective was to detect a glass‐transition temperature for this naturally occurring, semicrystalline polysaccharide. The impedance study was complemented with X‐ray diffraction, thermogravimetric, and differential scanning calorimetry measurements. Preliminary impedance data treatment includes the subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content for further analysis. When all these aspects are taken into account, two relaxations are clearly revealed in the impedance data. For the first time, evidence is presented for a relaxation process, which exhibits a non‐Arrhenius temperature dependence, in dry α‐chitin (∼0.1% moisture content), and likely represents the primary α‐relaxation. This evidence suggests a glass transition temperature for chitin of 335 ± 10 K estimated on the basis of the temperature dependence of the conductivity and of the relaxation time. A second relaxation in dry α‐chitin, not previously reported in the literature, is observed from 353 K to the onset of thermal degradation (∼483 K) and is identified as the σ‐relaxation often associated with proton mobility. It exhibits a normal Arrhenius‐type temperature dependence with activation energy of 113 ± 3 kJ/mol. The latter has not been previously reported in the literature. A high frequency secondary β‐relaxation is also observed with Arrhenius activation energy of 45 ± 1 kJ/mol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 932–943, 2009     

Some exact expressions for the bulk-arrival queue mx/M/1

For a M/M/1 queueing system with group arrivals of random size the transition probabilities of the queue size process and the distribution of the maximal queue size during a time interval [0,t) are calculated. Simple formulae for the corresponding Laplace transforms are given.     

Zr70Cu30非晶合金退火时结构弛豫过程的压力效应

 本文研究了Zr₇₀Cu₃₀非晶合金在压力下低于玻璃化温度退火时，表征结构中几何短程有序化过程的超导转变温度（T_c）的弛豫行为。结果表明，结构弛豫使T_c下降。压力退火则阻碍T_c的热弛豫下降趋势，但过程的动力学仍保持和常压弛豫相似的对数特征。作者应用压力促使非晶结构中局域张应力减小的观点来解释上述现象。     

Sound velocity in dense stellar matter with strangeness and compact stars

The phase state of dense matter in the intermediate density range (\begin{document}$\sim$\end{document}1-10 times the nuclear saturation density) is both intriguing and unclear and can have important observable effects in the present gravitational wave era of neutron stars. As matter density increases in compact stars, the sound velocity is expected to approach the conformal limit (\begin{document}$c_s/c=1/\sqrt{3}$\end{document}) at high densities and should also fulfill the causality limit (\begin{document}$c_s/c<1$\end{document}). However, its detailed behavior remains a prominent topic of debate. It was suggested that the sound velocity of dense matter could be an important indicator of a deconfinement phase transition, where a particular shape might be expected for its density dependence. In this work, we explore the general properties of the sound velocity and the adiabatic index of dense matter in hybrid stars as well as in neutron stars and quark stars. Various conditions are employed for the hadron-quark phase transition with varying interface tension. We find that the expected behavior of the sound velocity can also be achieved by the nonperturbative properties of the quark phase, in addition to a deconfinement phase transition. Moreover, it leads to a more compact star with a similar mass. We then propose a new class of quark star equation of states, which can be tested by future high-precision radius measurements of pulsar-like objects.     

Determining Causal Skeletons with Information Theory

Modeling a causal association as arising from a communication process between cause and effect, simplifies the discovery of causal skeletons. The communication channels enabling these communication processes, are fully characterized by stochastic tensors, and therefore allow us to use linear algebra. This tensor-based approach reduces the dimensionality of the data needed to test for conditional independence, e.g., for systems comprising three variables, pair-wise determined tensors suffice to infer the causal skeleton. The only thing needed is a minor extension to information theory, namely the concept of path information.     

Pressure-induced anomalous insulating behavior in frustrated iridate La_3Ir_3O_(11)

The geometrically frustrated iridate La_3Ir_3O_(11) with strong spin–orbit coupling and fractional valence was recently predicted to be a quantum spin liquid candidate at ambient conditions. Here, we systematically investigate the evolution of structural and electronic properties of La_3Ir_3O_(11) under high pressure. Electrical transport measurements reveal an abnormal insulating behavior rather than metallization above a critical pressure P_c ～ 38.7 GPa. Synchrotron x-ray diffraction(XRD)experiments indicate the stability of the pristine cubic KSbO_3-type structure up to 73.1 GPa. Nevertheless, when the pressure gradually increases across P_c, the bulk modulus gets enhanced and the pressure dependence of bond length d_(Ir-Ir) undergoes a slope change. Consistent with the XRD data, detailed analyses of Raman spectra reveal an abnormal redshift of Raman mode and a change of Raman intensity around P_c. Our results demonstrate that the pressure-induced insulating behavior in La_3Ir_3O_(11) can be assigned to the structural modification, such as the distortion of IrO_6 octahedra. These findings will shed light on the emergent abnormal insulating behavior in other 5 d iridates reported recently.     

Equilibrium folding and unfolding dynamics to reveal detailed free energy landscape of src SH3 protein by magnetic tweezers

Src SH3 protein domain is a typical two-state protein which has been confirmed by research of denaturant-induced unfolding dynamics. Force spectroscopy experiments by optical tweezers and atomic force microscopy have measured the force-dependent unfolding rates with different kinds of pulling geometry. However, the equilibrium folding and unfolding dynamics at constant forces has not been reported. Here, using stable magnetic tweezers, we performed equilibrium folding and unfolding dynamic measurement and force-jump measurement of src SH3 domain with tethering points at its N-and C-termini. From the obtained force-dependent transition rates, a detailed two-state free energy landscape of src SH3 protein is constructed with quantitative information of folding free energy, transition state barrier height and position,which exemplifies the capability of magnetic tweezers to study protein folding and unfolding dynamics.