Molecular Dynamics Simulations of Liquid Phosphorus at High Temperature and Pressure

By performing ab initio molecular dynamics simulations, we have investigated the microstructure, dynamical and electronic properties of liquid phosphorus （P） under high temperature and pressure. In our simulations, the calculated coordination number （CN） changes discontinuously with density, and seems to increase rapidly after liquid P is compressed to 2.5 g/cm3. Under compression, liquid P shows the first-order liquid-liquid phase transition from the molecular liquid composed of the tetrahedral P4 molecules to complex polymeric form with three-dimensional network structure, accompanied by the nonmetal to metal transition of the electronic structure. The order parameters Q6 and Q4 are sensitive to the microstructural change of liquid P. By calculating diffusion coefficients, we show the dynamical anomaly of liquid P by compression. At lower temperatures, a maximum exists at the diffusion coefficients as a function of density; at higher temperatures, the anomalous behavior is weakened. The excess entropy shows the same phenomena as the diffusion coefficients. By analysis of the angle distribution functions and angular limited triplet correlation functions, we can clearly find that the Peierls distortion in polymeric form of liquid P is reduced by further compression.     

Superconductivity of bilayer phosphorene under interlayer compression

According to first-principles calculations, it is our prediction that bilayer phosphorene(BLP) will become a quasitwo-dimensional superconductor under a certain degree of interlayer compression. A decreasing interlayer distance may realize the transition in the BLP from a semiconducting phase to a metallic phase. On the other hand, a severe vertical compression may make the BLP lattice become dynamically unstable. It is found that in the stable metallic phase of the BLP, interlayer phonon modes dominate the electron-phonon coupling λ. The obtained λ can be greater than 1 and the superconducting temperature T_c can be higher than 10 K.     

Exothermic Supercooled Liquid-Liquid Transition in Amorphous Sulfur

Amorphous sulfur （a-S） is prepared by rapidly compressing molten sulfur to high pressure. From differential scanning calorimeter measurements, a large exothermic peak has been observed around 396K. Online wide-angled x-ray scattering spectra indicate that no crystallization occurs in the temperature range 295-453K, suggesting that the exothermal process corresponds to an amorphous-to-amorphous transition. The transition from amor- phous sulfur to liquid sulfur is further verified by the direct observation of sulfur melt at the temperature of the associated transition. This is the first time of reporting that a-S transforms to liquid sulfur directly, which has avoided a crystallization process. What is more, the transition is an exothermic and a volume expansion process.     

Pd-Si Binary Bulk Metallic Glass Prepared at Low Cooling Rate

We report that binary bulk metallic glasses can be made up to 6ram in diameter in a Pd Si ahoy system by air cooling at slow cooling rate (about 8 K/s). The high stability of the undercooled liquid and the large glass-forming ability (GFA) of the binary alloy are contributed to the removing of heterogeneous impurities in the alloy melt by employing the fluxing technique. It has been found that decreasing cooling rate can increase the supercooled liquid region and thermal stability of the glassy alloy. After fluxing, a wider supercooled liquid region (△T = 58 K) and higher glass-forming ability have been obtained in a Pd81Si19 binary glassy alloy prepared by slow cooling rate.     

Preparation of Thermo-Stable Bulk Metallic Glass of Nd10Cu20Ni10Al10 by Rapid Compression

Melt of Nd60Cu20NiloAl10 alloy is solidified by rapid compression from 0.1 to 5.5 GPa at 793K and from 0.1 to 3.2GPa at 873K within 20ms, separately. A fully bulk metallic glass is obtained by the rapid compression method. By comparing with as-cast bulk metallic glass （BMG）, it is found that Nd60Cu20Ni10Al10 BMG prepared by rapid compression exhibits a higher thermodynamic stability and a paramagnetic property. The relationship between the glass-formation temperature and the pressure in rapid compression for the BMG is demonstrated in the P - T phase diagram.     

P-V criticality and Joule-Thomson expansion of charged AdS black holes in the Rastall gravity

We discuss the P-V criticality and the Joule-Thomson expansion of charged AdS black holes in the Rastall gravity. We find that although the equation-of-state of a charged AdS black hole in the Rastall gravity is related to the Rastall parameter λ, its reduced equation-of-state at the critical point is independent of the Rastall parameter λ, as is the case in the Einstein gravity where λ=0. This is the reason why the critical exponents are not related to the Rastall parameter λ. We also find that the inversion temperature T_i is related to the Rastall parameter λ,but that the minimum inversion temperature T_i~(min) and the ratio ε between the minimum inversion temperature and the critical temperature are both independent of the Rastall parameter λ. At the critical point, the thermodynamic evolution of a charged AdS black hole in the Rastall gravity behaves as in the van der Waals fluid and charged AdS black hole in the Einstein gravity. We show the inversion curves and isenthalpic curves in the T-P plane and analyze the effect of the Rastall constant λ on the inversion curves of a charged AdS black hole during the Joule-Thomson expansion.     

Thermal Expansion Anomaly and Spontaneous Magnetostriction of Y2Fe14Al3 Compound

The structure and magnetic properties of Y2Fe14Al3 compound are investigated by means of x-ray diffraction and magnetization measurements. The Y2Fe14Al3 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion is found in Y2Fe14Al3 compound in the temperature range from 403 to 491K by x-ray dilatometry. The coefficient of the average thermal expansion is α^- = -2.54Х 10^-5 K^-1. The spontaneous magnetostrictive deformations from 283 to 470 K are caJculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 5.74 × 10^-3 to nearly zero with temperature increasing from 283 to 470K, the spontaneous linear magnetostrictive deformation λc along the c-axis is larger than the spontaneous linear magnetostrictive deformation λa in basal-plane in the same temperature below 350 K.     

Reverse Monte Carlo study on structural order in liquid and glassy AlFe alloys

This paper reports that anomalous local order in liquid and glassy AlFeCe alloy has been detected by x-ray diffraction measurements. The addition of the element Ce has a great effect on this local structural order. The element Ce favours interpenetration of the icosahedra by sharing a common face and edges. It argues that frustration between this short-range order and the long-range crystalline order controls the glass-forming ability of these liquids. The obtained results suggest that a system having a stronger tendency to show local icosahedral order should be a better glass-former. This scenario also naturally explains the close relationship between the local icosahedral order in a liquid, glass-forming ability, and the nucleation barrier. Such topological local order has also been analysed directly using the reverse Monte Carlo method. It also estimated the fraction of local ordered and disordered structural units in a glassy AlFeCe alloy.     

Thermal Entanglement of Anisotropic XY Chains in a Transverse Field

By using the concept of concurrence, we numerically investigate the thermal entanglement between any two nearest-neighbour spins in uniform and periodic anisotropic XY chains in a transverse field at finite temperature T. It is found that the entanglement has more than one critical temperatures on some parameter regions for uniform and periodic chains. We also discuss the behaviour of the thermal entanglement at the vicinity of quantum phase transition of periodic anisotropic XY chains and find that a11 the derivatives aλC have similar behaviour as that of the uniform chain.     

Decondensation behavior of DNA chains induced by multivalent cations at high salt concentrations:Molecular dynamics simulations and experiments

Using molecular dynamics simulations and atomic force microscopy(AFM), we study the decondensation process of DNA chains induced by multivalent cations at high salt concentrations in the presence of short cationic chains in solutions.The typical simulation conformations of DNA chains with varying salt concentrations for multivalent cations imply that the concentration of salt cations and the valence of multivalent cations have a strong influence on the process of DNA decondensation. The DNA chains are condensed in the absence of salt or at low salt concentrations, and the compacted conformations of DNA chains become loose when a number of cations and anions are added into the solution. It is explicitly demonstrated that cations can overcompensate the bare charge of the DNA chains and weaken the attraction interactions between the DNA chains and short cationic chains at high salt concentrations. The condensation-decondensation transitions of DNA are also experimentally observed in mixing spermidine with λ-phage DNA at different concentrations of Na Cl/Mg Cl2 solutions.     

Experimental Study on Liquid Free Surface in Buoyant-Thermocapillary Convection

We investigate the surface deformations of buoyant-thermocapillary convection in a rectangular cavity due to gravity and temperature gradient between the two sidewalls. The cavity is 52mm×42 mm in horizontal cross section, the thickness of liquid layer h is changed from 2.5 mm to 6.5 mm. Surface deformations of h = 3.5 mm and 6.0mm are discussed and compared. Temperature difference is increased gradually, and the flow in the liquid layer will change from stable convection to unstable convection. Two kinds of optical diagnostic system with image processor are developed for study of the kinetics of buoyant-thermocapillary convection, they give out the information of liquid free surface. The quantitative results are calculated by Fourier transform and correlation analysis, respectively. With the increasing temperature gradient, surface deformations calculated are more declining. It is interesting phenomenon that the inclining directions of the convections in thin and thick liquid layers are different. For a thin layer, the convection is mainly controlled by thermocapillary effect. However, for a thick layer, the convection is mainly controlled by buoyancy effect. The surface deformation theoretically analysed is consistent with our experimental results. The present experiment proves that surface deformation is related to temperature gradient and thickness of the liquid layer. In other words, surface deformation lies on capillary convection and buoyancy convection.     

Transition to Chaos in the Floating Half Zone Convection

The transition process from steady convection to chaos is experimentally studied in thermocapillary convections of floating half zone. The onset of temperature oscillations in the liquid bridge of floating half zone and further transitions of the temporal convective behaviour are detected by measuring the temperature in the liquid bridge. The fast Fourier transform reveals the frequency and amplitude characteristics of the flow transition. The experimental results indicate the existence of a sequence of period-doubling bifurcations that culminate in chaos. The measured Feigenbaum numbers are δ2 =4.69 and δ4 = 4.6, which are comparable with the theoretical asymptotic value δ=4.669.     

Investigation of the free volume and ionic conducting mechanism of poly（ethylene oxide）-LiClO_4 polymeric electrolyte by positron annihilating lifetime spectroscopy

The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite（OREC） content and temperature in a range from 160 K to 300 K.According to the variation of ortho-positronium（o-Ps） lifetime with temperature,the glassy transition temperature is determined.The continuous maximum entropy lifetime（MELT） analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution.The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher（VTF） and Williams-Landel-Ferry（WLF） equations,implying a free-volume transport mechanism.A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation.It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte,which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.     

Investigation of the free volume and ionic conducting mechanism of poly（ethylene oxide）-LiClO₄ polymeric electrolyte by positron annihilating lifetime spectroscopy

The positron annihilation lifetime and ionic conductivity are each measured as a function of organophilic rectorite(OREC) content and temperature in a range from 160 K to 300 K.According to the variation of ortho-positronium(o-Ps) lifetime with temperature,the glassy transition temperature is determined.The continuous maximum entropy lifetime(MELT) analysis clearly shows that the OREC and temperature have important effects on o-Ps lifetime and free volume distribution.The experimental results show that the temperature dependence of ionic conductivity obeys the Vogel-Tammann-Fulcher(VTF) and Williams-Landel-Ferry(WLF) equations,implying a free-volume transport mechanism.A linear least-squares procedure is used to evaluate the apparent activation energy related to the ionic transport in the VTF equation and several important parameters in the WLF equation.It is worthwhile to notice that a direct linear relationship between the ionic conductivity and free volume fraction is established using the WLF equation based on the free volume theory for nanocomposite electrolyte,which indicates that the segmental chain migration and ionic migration and diffusion could be explained by the free volume theory.     

Stability of conductance oscillations in carbon atomic chains

The conductance stabilities of carbon atomic chains(CACs) with different lengths are investigated by performing theoretical calculations using the nonequilibrium Green's function method combined with density functional theory.Regular even–odd conductance oscillation is observed as a function of the wire length.This oscillation is influenced delicately by changes in the end carbon or sulfur atoms as well as variations in coupling strength between the chain and leads.The lowest unoccupied molecular orbital in odd-numbered chains is the main transmission channel,whereas the conductance remains relatively small for even-numbered chains and a significant drift in the highest occupied molecular orbital resonance toward higher energies is observed as the number of carbon atoms increases.The amplitude of the conductance oscillation is predicted to be relatively stable based on a thiol joint between the chain and leads.Results show that the current–voltage evolution of CACs can be affected by the chain length.The differential and second derivatives of the conductance are also provided.     

The vibron dressing in α-helicoidal macromolecular chains

We present a study of the physical properties of the vibrational excitation in α-helicoidal macromolecular chains,caused by the interaction with acoustical and optical phonon modes. The influence of the temperature and the basic systemparameters on the vibron dressing have been analyzed by employing the simple mean-field approach based on the variationalextension of the Lang-Firsov unitary transformation. The applied approach predicts a region in system parameter spacewhere one has an abrupt transition from a partially dressed (light and mobile) to a fully dressed (immobile) vibron state.We found that the boundary of this region depends on system temperature and the type of bond among structural elementsin the macromolecular chain.     

Luminescence mechanism and energy level structure of Eu-doped GaN powders investigated by cathodoluminescence spectroscopy

1.5at% Eu-doped GaN powders were prepared by a co-precipitation method.Powder X-ray diffraction(XRD)results shows that there is only the wurtzite phase.Cathodoluminescence spectra were measured at room temperature and liquid nitrogen temperature,respectively.The band-to-band luminescence of GaN was shifted from 373 nm to 368 nm with the temperature decreasing from room temperature to liquid nitrogen temperature.The luminescence peaks at 537,557,579,590,597,614,653 and 701 nm are attributed to the Eu ions related transitions in the host of GaN powders and the peak positions were not influenced by the variation of temperature.With the increase of accelerating voltage,the intensity of all luminescence peaks was increased.The strongest luminescence peak at 614 nm shows non-symmetrical shape and is composed of 612,615 and 621 nm through Lorentzian fitting,which indicates there are oxygen and nitrogen environments of the Eu3+ions in the Eu-doped GaN powders.     

Excellent Magnetocaloric Effect in Er60Al18Co22 Bulk Metallic Glass

Excellent magnetocaloric effect with a maximum entropy change and refrigeration capacity of 17.6 J·kg^-1·K^-1 and 546 J·kg^-1, respectively, has been discovered in the Er60Al18Co22 bulk metallic glass under the field of 50 kOe in the temperature range of helium liquefaction. This MCE results from the second-order magnetic transition from the paramagnetic to the ferromagnetic state. Our analysis based on mean-field theory suggests that the excellent MCE is attributed to the strong exchange of magnetic moment in the glassy structure.     

Industrial diamonds grown in Ni70Mn25Co5--graphite--sulfur system under HPHT

This paper reports that diamond single crystals were synthesized from sulfur-added Ni70Mn25Co5+C system under high pressure and high temperature(HPHT).It was found that additive sulfur had inhibited the nucleation and growth of diamond to some extent.X-ray diffraction of the collected sample indicated that under the synthesis conditions,a new compound MnS had been formed through the reaction of additive sulfur with manganese in the catalyst.The MnS has a fcc structure,and its average crystal size was about 30 nm.By scanning electron microscope,the {111} surface of diamond was found to be flat,while there was usually a large depression on the central region of {100}.Further observation showed that there were many small upside-down pyramidal pits in the expression.The results of x-ray photoelectron spectroscopy shows that MnS can only be detected in the depression in the range of detection precision.It was inferred that MnS had been dissolved in the melted alloy during the growth experiment,and precipitated in the sequent quenching process.     

A Quorum Sensing Active Matter in a Confined Geometry

Inspired by the problem of biofilm growth, we numerically investigate clustering in a two-dimensional suspension of active(Janus) particles of finite size confined in a circular cavity. Their dynamics is regulated by a non-reciprocal mechanism that causes them to switch from active to passive above a certain threshold of the perceived near-neighbor density(quorum sensing). A variety of cluster phases, i.e., glassy, solid(hexatic) and liquid, are observed, depending on the particle dynamics at th...