Molecular dynamics study for the melting curve of MgO at high pressure

Shell-model molecular dynamics method is used to study the melting temperatures of MgO at elevated temperatures and high pressures using interaction potentials. Equations of state for MgO simulated by molecular dynamics are in good agreement with available experimental data. The pressure dependence of the melting curve of MgO has been calculated. The surface melting and superheating are considered in the correction of experimental data and the calculated values, respectively. The results of corrections are compared with those of previous work. The corrected melting temperature of MgO is consistent with corrected experimental measurements. The melting temperature of MgO up to 140GPa is calculated.     

A compact pulse generator for radiographic source supply

Radiography of short-living objects using X-pinch radiation is a new perspective direction in diagnostics developed at the P. N. Lebedev Institute of Physics. High spatial (up to a few tenth of a micrometer) and temporal resolutions (up to 0.1 ns) achieved with the use of the X pinch is extremely interesting to the researches of transient processes and substances in extreme states. The X pinch is produced by two or more crossed wires (with wire diameters up to 30 μm) exploded under the influence of current running through them. Scanning radiation is generated in a dense high-temperature plasma (up to several kiloelectron volts) arising in the region of wire crossing. Among the main requirements on the generator used to create the X pinch are current amplitudes of 150–300 kA and rates of current increase of 1–2 kA/ns. Up to now, these current pulse parameters have been provided only by bulky stationary generators weighing from 300 kg to several tons. In the present paper, a small-size (weighing 70 kg) high-current pulse generator (with current amplitude exceeding 300 kA and pulse rise time of 200 ns) of soft x-ray radiation from high-temperature X-pinch plasma is described. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 87–92, February, 2007.     

Continuous Variable Entanglement of Two Mesoscopic Josephson Junctions Induced by a Thermal Radiation Field

The continuous-variable （CV） entanglement between two mesoscopic Josephson junctions is studied and the time-dependent characteristic function in Wigner representation for the Josephson junction subsystem driven by a singlemode thermal field is analytically obtained. It is found that an initial lowest energy state of the junction subsystem can evolve into a two-mode entangled Gaussian state through the interaction with the thermal radiation field. Furthermore, we investigate the influence of the temperature on the entanglement of the junctions and find that the CV entanglement of the two junctions shows the critical behavior with respect to the temperature.     

Total Dose Radiation Tolerance of Phase Change Memory Cell with GeSbTe Alloy

Phase change memory （PCM） cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state （higher resistance state） to the crystalline state （lower resistance state）. The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low （only several μA）. An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad（Si）, which makes it attractive for space-based applications.     

Improved method for analyzing quasi-optical launchers

An improved method for analyzing the radiation characteristic of the quasi-optical launcher is presented. The launcher is decomposed into an open-ended waveguide and a helical cut according to the proposed method. The radiation from the open-ended waveguide is obtained by using the Stratton-Chu formulation. The helical cut＇s radiation is calculated based on its current distribution, gained by several iterative computations, which helps to improve the calculation accuracy since the diffraction effect introduced by the helical cut is considered during the calculation. The proposed method is used to study different launches, and the results are compared with the existing results. Good agreement is achieved between the results obtained from our proposed method and the reported results. The present results provide an alternative for analysis and synthesis of the optical-mode converter.     

ORNL-HRIBF 6GHzECR离子源的最新结果

Experimental studies were conducted to characterize and improve the performance of the flat-B ECR ion source.The emittance of the source was investigated for the first time.The output beam currents of high-charge-states of Ar(q>8)were nearly doubled by increasing the plasma electrode aperture from 4mm to 6mm in diameter.To investigate possible enhancements with broadband microwave radiation,a"white"Gaussian noise generator was employed with a TWT amplifier to generate microwave radiation with a bandwidth of～200MHz.The performance of the flat-B ECR ion source was found to be much better with narrow bandwidth radiation when the source was operated in the flat-B region.However,the ion beam intensities and charge state distributions were improved with the broadband radiation when the source was tuned off the flat-B region.     

Electron Capture Process in Collisions of Proton with Excited State of Helium

Total and star,selective cross sections for single electron capture （SEC） from the n = 2 excited state of helium colliding by protons are calculated in the energy range of 1.0-100.0 ke V/u by using the two-center atomic orbital close-coupling method. The interaction of the active electron with helium ion is represented by a model potential. Total SEC cross sections show a monotonic decreasing trend with increasing collision energy, and display a different behavior compared with the case from the ground state of helium. It is also found that the dominant reaction channel is captured to the H（2p） state up to 40 keV//u, and then the capture to the H（1s） or H（2s） state becomes more pronounced. Moreover, the alignment dependence on the initial states is obtained for the electron capture from He（2p0） and He （2p1）.     

Carrier Envelope Phase Controlled High-Order Harmonic Generation in Ultrashort Laser Pulse

We investigate the carrier envelope phase （CEP） effects on high-order harmonic generation （HHG） in ultrashort pulses with the pulse duration 2.5 fs when the laser intensity is high enough so that the initial state is ionized effectively during the laser pulse but remains about 20% population at the end of the laser pulse. We find that the ionization process of the initial state is very sensitive to the CEP during the laser pulse. The ionization process of the initial state determines the continuum state population and hence influences dramatically the weights of the classical trajectories that contribute to HHG. In such a case we can not predict the cutoff and the structure of the harmonic spectrum only by the number and the kinetic energy of the classical trajectories. The harmonic spectrum exhibits abundant characters for different CEP cases. As a result, we can control the cutoff frequency and the plateau structure of the harmonic spectrum with CEP by controlling the time behaviour of the ionization of the initial state.     

Sudden Death of Entanglement between Two Atoms with Initial Tripartite Entangled State in the Tavis--Cummings Model

We study the entanglement dynamics of two atoms with initial tripartite entangled W-like state in the Tavis-Cummings model. We find that the entanglement evolvement is sensitive not only to the entanglement degree of the initial state but also to the concrete form of the initial state. The so-called sudden death effect occurs only for some initial states.     

A high-pressure study of PbCO3 by XRD and Raman spectroscopy

The pressure-induced phase transitions of PbCO3 are studied using synchrotron radiation in a diamond anvil cell at room temperature. The XRD measurement indicates that PbCO3 with an initial phase of aragonite-type structure undergoes two phase transitions at ～7.8GPa and ～15.7GPa respectively. The higher-pressure phase appearing at ～ 15.7GPa is stable up to 51.8GPa. The two phase transitions are further confirmed by Raman scattering up to 23.3GPa. During the decompression process, the high-pressure phases of PbCO3 are gradually recovered to the starting aragonite-type structure, but exhibit some hysteresis. The bulk modulus B0 of the aragonite-type structure is obtained to be 63±(3) GPa by fitting the volume-pressure data to the Birch-Murnaghan equation of states with B0 fixed to 4.     

A MEMS-Based Piezoelectric Power Generator for Low Frequency Vibration Energy Harvesting

A novel power generator has been achieved to convert vibration to electrical energy via the piezoelectric effect. The generator obtained by micro fabrication process mainly consists of silicon based frame and composite cantilever. The prototype tested at resonant vibration generates 1.15μW of effective power to a 20.4-kΩ resistance load. The potential of this work is to offer miniaturization solutions for power generators, and with the proposed method the ambient ubiquitous vibration can be harvested effectively as endless energy source to form an integrated self-powering system.     

Equation of State of the Fluid He-Ne Binary Mixtures at High Pressures and High Temperatures

The fluid variational free energy model is applied to calculate the equation of state (EOS) of the fluid (Ne/3,2He/3) mixtures at 296K. The pair potential is used to describe the He-Ne interaction. The calculated EOSs at 296Kare compared with the experiments for solid Ne(He)2. The validity of the potential and the calculated model is verified by comparison. The present model is extended to calculate the equation of state of the fluid He-Ne mixtures with different He:Ne compositions in the pressure 0-160 GPa and temperature up to 10000 K.     

Entanglement Distillation for Mixed States Using Particle Statistics

We extend the idea of entanglement concentration protocol for pure states （Phys. Rev. Lett. 88, 187903） to the case of entanglement distillation for mixed states. The scheme works only with particle statistics and local operations, without the need of any other interactions. We show that the maximally entangled state can be distilled out when the initial state is pure, otherwise the entanglement distilled depends on the off-diagonal element of density matrix of the initial state. Because of the requirement for density matrix, the entanglement distilled is always less than one, and this result is the same for both fermionic and bosonic particles. The distillation efficiency is a product of the diagonal elements of the initial state, it takes the maximum 50%, the same as that in the case for pure states.We extend the idea of entanglement concentration protocol for pure states （Phys. Rev. Lett. 88, 187903） to the case of entanglement distillation for mixed states. The scheme works only with particle statistics and local operations, without the need of any other interactions. We show that the maximally entangled state can be distilled out when the initial state is pure, otherwise the entanglement distilled depends on the off-dlagonal element of density matrix of the initial state. Because of the requirement for density matrix, the entanglement distilled is always less than one, and this result is the same for both fermionic and bosonic particles. The distillation effciency is a product of the diagonal elements of the initial state, it takes the maximum 50%, the same as that in the case for pure states.     

Quantum circuits for realizing deterministic and exact teleportation via two partially entangled pairs of particles

Deterministic and exact teleportation can be achieved via two partially entangled pairs of particles [Gu Y J 2006 {\em Opt. Comm.} {\bf 259} 385]. The key point of the protocol is a generalized measurement described by a positive operator-valued measure, which can be realized by performing a unitary operation in the extended space and a conventional Von Neumann orthogonal measurement. By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the teleportation. Our method for constructing quantum circuits differs from the usual methods based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements.     

A Lower Bound on the Entanglement in the Jaynes-Cummings Model

The entanglement between an atom and field is investigated by using the 3aynes-Cummings model. The initial atomic state is supposed in a mixed state and the field is in a squeezed state. The lower bound on the entanglement quantified by concurrence is calculated. It is found that the entanglement with the atom being initially in a mixed state can be larger than that with the atom being initially in a pure state. The entanglement is not a monotone function of the squeezing parameter r of the field and it achieves the maximum for certain r and then decreases with further increase of r.     

Effect of cavity dissipation on the emission spectrum of an atom interacting with a field in the dispersive approximation

The emission spectrum of a two-level atom interacting dispersively with a single mode radiation field in the dissipative cavity is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in coherent state are calculated. It is found that the spectrum structure is influenced significantly by the cavity damping constant \kappa , and the spectrum structure is dependent on the interaction time T when the cavity dissipation is present. Only one peak located at Ω_a appears in the atomic spectra for larger T.     

Decoherence from a spin chain with Dzyaloshinskii—Moriya interaction

We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a spin chain with Dzyaloshinsky-Moriya interaction.In the case of a two-qubit with an initial pure state,quantum correlations decay to zero at the critical point of the environment in a very short time.In the case of a two-qubit with initial mixed state,it is found that quantum discord may get maximized due to the quantum critical behavior of the environment,while entanglement vanishes under the same condition.Besides,we observed a sudden transition between classical and quantum decoherence when only a single qubit interacts with the environment.The effects of Dzyaloshinsky-Moriya interaction on quantum correlations are considered in the two cases.The decay of quantum correlations is always strengthened by Dzyaloshinsky-Moriya interaction.     

Simulation of radiation losses using non-coronal model on HL-2A

In this paper, the radiation losses of impurity on HL-2A have been simulated by assuming the profiles electron temperature and density and solving ionization rate equation under conditions of non-coronal radiation. The time required for an impurity species to establish equilibrium is proved to be sensitively dependent on the plasma electron temperature, and it is strongly correlated with the ionization state distribution during equilibrium establishment of impurity species. It is found from simulation results that the residence parameter plays an important role in the enhancement of radiation losses of plasma.     

Prisoner's Dilemma Game on Clustered Scale-Free Networks under Different Initial Distributions

The evolutionary prisoner＇s dilemma game is investigated under different initial distributions for cooperators and defectors on scale-free networks with a tunable clustering coefficient. It is found that, on the one hand, cooperation can be enhanced with the increasing clustering coefficient when only the most connected nodes are occupied by cooperators initially. On the other hand, if cooperators just occupy the lowest-degree nodes at the beginning, then the higher the value of the clustering coefficient, the more unfavorable the environment for cooperators to survive for the increment of temptation to defect. Thereafter, we analytically argue these nontrivial phenomena by calculating the cooperation probability of the nodes with different degrees in the steady state, and obtain the critical values of initial frequency of cooperators below which cooperators would vanish finally for the two initial distributions.     

X-ray beam hardening correction for measuring density in linear accelerator industrial computed tomography

Due to X-ray attenuation being approximately proportional to material density,it is possible to measure the inner density through Industrial Computed Tomography（ICT） images accurately. In practice,however,a number of factors including the non-linear effects of beam hardening and diffuse scattered radiation complicate the quantitative measurement of density variations in materials. This paper is based on the linearization method of beam hardening correction,and uses polynomial fitting coecient which is obtained by the curvature of iron polychromatic beam data to fit other materials. Through theoretical deduction,the paper proves that the density measure error is less than 2% if using pre-filters to make the spectrum of linear accelerator range mainly 0.3 MeV to 3 MeV. Experiment had been set up at an ICT system with a 9 MeV electron linear accelerator. The result is satisfactory. This technique makes the beam hardening correction easy and simple,and it is valuable for measuring the ICT density and making use of the CT images to recognize materials.