arXiv subjects
Publications and source records attributed to J. Yang.
Using equations, governing np pairing correlations in S=1, T=0 pairing channel (PRC 63 (2001) 021304(R)), it is shown that at low densities equations for the energy gap in the spectrum of quasiparticles and chemical potentials of protons and neutrons allow solutions with negative chemical potential. This corresponds to appearance of Bose--Einstein condensate (BEC) of deuterons in low density region of nuclear matter.
The possibility of ferromagnetic and antiferromagnetic phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the effective Gogny interaction. It is shown that at some critical density nuclear matter with D1S effective force undergoes a phase transition to the antiferromagnetic spin state (the opposite direction of neutron and proton spins). The self--consistent equations of spin polarized nuclear matter with D1S force have no solutions, corresponding to the ferromagnetic spin ordering (the same direction of neutron and proton spins) and, hence, the ferromagnetic transition does not appear. The dependence of antiferromagnetic spin polarization parameter as a function of density is found at zero temperature.
The effect of Cu-doping at Mn-site on structural, magnetic and transport properties in electron-doped manganites La0.85Te0.15Mn1-xCuxO3 has been investigated. Based on the analysis of structural parameter variations, the valence state of the Cu ion in Cu-doped manganites is suggested to be +2. All samples undergo the paramagnetic-ferromagnetic (PM-FM) phase transition. The Curie temperature decreases and the transition becomes broader with increasing Cu-doping level, in contrast, the magnetization magnitude of Cu-doping samples at low temperatures increase as x \leq 0.15. The insulator-metal (I-M) transition moves to lower temperatures with increasing Cu-doping content and disappears as x > 0.1. In addition, the higher temperature resistivity r peak in double-peak-like r(T) curves observed in no Cu-doping sample is completely suppressed as Cu-doping level x = 0.1 and r(T) curve only shows single I-M transition at the low temperature well below . The results are discussed according to the change of magnetic exchange interaction caused by Cu-doping.
The possible redox (oxidation reduction) chemical methods for precisely determining the oxygen content in the perovskite manganites including hole-doped La1-xCaxMnOy and electron-doped La1-xTexMnOy compounds are described. For manganites annealed at different temperatures, the oxygen content of the samples was determined by a redox back titration in which the powder samples taken in a quartz crucible were dissolved in (1+1) sulfuric acid containing an excess of sodium oxalate, and the excess sodium oxalate was titrated with permanganate standard solution. The results indicate that the method is effective and highly reproducible. Moreover, the variation of oxygen content is also reflected in significantly affecting the electrical transport property of the samples, which is mainly considered to be closely related to introduce oxygen vacancies in the Mn-O-Mn network.
The effect of grain size on structural, magnetic and transport properties in electron-doped manganites La0.9Te0.1MnO3 has been investigated. All samples show a rhombohedral structure with the space group at room temperature. It shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases with the increase of grain size. All samples undergo paramagnetic (PM)-ferromagnetic (FM) phase transition and an interesting phenomenon that both magnetization and the Curie temperature decrease with increasing grain size is observed, which is suggested to mainly originate from the increase of the Mn-O bond length . Additionally, obviously increases with decreasing grain size due to the increase of both the height and width of tunneling barriers with decreasing the grain size. The results indicate that both the intrinsic colossal magnetoresistance (CMR) and the extrinsic the extrinsic interfacial magnetoresistance (IMR) can be effectively tuned in La0.9Te0.1MnO3 by changing grain size.
The structural, electrical transport and magnetic properties of perovskite oxides La1-xTexMnO3 have been investigated and thus the magnetic phase diagram of La1-xTexMnO3 compounds as a function of temperature and the doping level x has been obtained. All samples have rhombohedral structure and undergo paramagnetic-ferromagnetic (PM-FM) transition accompanied with metal-insulator transition (MIT). Whereas a charge ordering (CO) transition begins to appear at for the sample with x=0.60. Moreover, the variation of the Curie temperature and the MIT temperature is quite complex and the results are discussed in terms of three factors including the average A-site cation radius , the size mismatch and the Te content. In addition, there has an evident magnetoresistance (MR) at low temperatures for all samples.
The effect of the variation of oxygen content on structural, magnetic and transport properties in the electron-doped manganites La0.9Te0.1MnOy has been investigated. All samples show a rhombohedral structure with the space group . The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM) transition becomes broader with the reduction of oxygen content. The resistivity of the annealed samples increases slightly with a small reduction of oxygen content. Further reduction in the oxygen content, the resistivity maximum increases by six orders of magnitude compared with that of the as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83 display the semiconducting behavior () in both high-temperature PM phase and low-temperature FM phase, which is considered to be related to the appearance of superexchange ferromagnetism (SFM) and the localization of carriers. The results are discussed in terms of the combined effects of the increase in the Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE) interaction, and the localization of carriers due to the introduction of oxygen vacancies in the Mn-O-Mn network.
The effect of Pr-doping on structural, magnetic and transport properties in electron-doped manganites La0.9-xPrxTe0.1MnO3 with fixed carrier concentration are investigated. The room temperature structural transition from rhombohedral (R3C) to orthorhombic (Pbnm) symmetry is found in the samples with by the Rietveld refinement of x-ray powder diffraction patterns. The Curie temperature of samples decreases and the transition becomes broader with increasing Pr-doping level. For the samples with, there exist insulator-metal (I-M) transition. And the low-temperature I-M transition is observed at about 66K for the sample with x = 0.36, which may be related to the opening of a new percolation channel. For the samples with, r(T) curves display the semiconducting behavior (dρ/dT < 0) in both high-temperature PM phase and low-temperature FM phase. The results are discussed in terms of the increased bending of the Mn-O-Mn bond with decreasing the average ionic radius of the A-site element and the tolerance factor, resulting in the narrowing of the bandwidth, the decrease of the mobility of electrons and the weakening of DE interaction caused by the substitution of smaller Pr3+ ions for larger La3+ ion.
The possibility of appearance of spin polarized states in symmetric and strongly asymmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the Skyrme effective interaction. The zero temperature dependence of the neutron and proton spin polarization parameters as functions of density is found for SkM$^*$, SGII (symmetric case) and SLy4, SLy5 (strongly asymmetric case) effective forces. By comparing free energy densities, it is shown that in symmetric nuclear matter ferromagnetic spin state (parallel orientation of neutron and proton spins) is more preferable than antiferromagnetic one (antiparallel orientation of spins). Strongly asymmetric nuclear matter undergoes at some critical density a phase transition to the state with the oppositely directed spins of neutrons and protons while the state with the same direction of spins does not appear. In comparison with neutron matter, even small admixture of protons strongly decreases the threshold density of spin instability. It is clarified that protons become totally polarized within a very narrow density domain while the density profile of the neutron spin polarization parameter is characterized by the appearance of long tails near the transition density.
We present ~2"-4" aperture synthesis observations of the circumstellar disk surrounding the nearby young star TW Hya in the CO J=2--1 and J=3--2 lines and associated dust continuum obtained with the partially completed Submillimeter Array. The extent and peak flux of the 230 and 345 GHz dust emission follow closely the predictions of the irradiated accretion disk model of Calvet et al. (2002). The resolved molecular line emission extends to a radius of at least 200 AU, the full extent of the disk visible in scattered light, and shows a clear pattern of Keplerian rotation. Comparison of the images with 2D Monte Carlo models constrains the disk inclination angle to 7+/-1 degrees. The CO emission is optically thick in both lines, and the kinetic temperature in the line formation region is ~20K. Substantial CO depletion, by an order of magnitude or more from canonical dark cloud values, is required to explain the characteristics of the line emission.
In the framework of a Fermi liquid theory it is considered the possibility of appearance of spin polarized states in strongly asymmetric nuclear matter with Skyrme effective interaction. The zero temperature dependence of neutron and proton spin polarization parameters as functions of density is found for SLy4, SLy5 effective forces. It is shown that at some critical density it will be formed the state with the oppositely directed spins of neutrons and protons, while the state with the same direction of spins does not appear. In comparison with neutron matter, even small admixture of protons strongly decreases the threshold density of spin instability. It is clarified that protons become totally polarized within very narrow density domain while in the density profile of neutron spin polarization parameter their appear long tails near the transition density.
Stable embedded solitons are discovered in the generalized third-order nonlinear Schroedinger equation. When this equation can be reduced to a perturbed complex modified KdV equation, we developed a soliton perturbation theory which shows that a continuous family of sech-shaped embedded solitons exist and are nonlinearly stable. These analytical results are confirmed by our numerical simulations. These results establish that, contrary to previous beliefs, embedded solitons can be robust despite being in resonance with the linear spectrum.
We derive the soliton matrices corresponding to an arbitrary number of higher-order normal zeros for the matrix Riemann-Hilbert problem of arbitrary matrix dimension, thus giving the complete solution to the problem of higher-order solitons. Our soliton matrices explicitly give all higher-order multi-soliton solutions to the nonlinear partial differential equations integrable through the matrix Riemann-Hilbert problem. We have applied these general results to the three-wave interaction system, and derived new classes of higher-order soliton and two-soliton solutions, in complement to those from our previous publication [Stud. Appl. Math. \textbf{110}, 297 (2003)], where only the elementary higher-order zeros were considered. The higher-order solitons corresponding to non-elementary zeros generically describe the simultaneous breakup of a pumping wave $(u_3)$ into the other two components ($u_1$ and $u_2$) and merger of $u_1$ and $u_2$ waves into the pumping $u_3$ wave. The two-soliton solutions corresponding to two simple zeros generically describe the breakup of the pumping $u_3$ wave into the $u_1$ and $u_2$ components, and the reverse process. In the non-generic cases, these two-soliton solutions could describe the elastic interaction of the $u_1$ and $u_2$ waves, thus reproducing previous results obtained by Zakharov and Manakov [Zh. Eksp. Teor. Fiz. \textbf{69}, 1654 (1975)] and Kaup [Stud. Appl. Math. \textbf{55}, 9 (1976)].
We present molecular line and submillimeter dust continuum observations of the Lynds 870 cloud in the vicinity of IRAS 20231+3440. Two submillimeter cores, SMM1 and SMM2, are identified mapping the 870 micron dust continuum and ammonia emission. The total molecular mass is ~70-110 solar mass. The northern core is warmer and denser than the southern one. Molecular outflows are discovered in both cores. In the northern one a significant amount of low velocity (1.3-2.8 km/s) outflowing gas is found, that is hidden in the relatively broad CO lines but that is revealed by the narrower HCO+ spectra. While IRAS 20231+3440 is most likely the exciting star of the northern outflow, the driving source of the southern outflow is not detected by infrared surveys and must be deeply embedded in the cloud core. Large scale (~0.2 pc) infall motion is indicated by blue asymmetric profiles observed in the HCO+ J = 3-2 spectra. Red K_s band YSO candidates revealed by the 2MASS survey indicate ongoing star formation throughout the cloud. The calculated masses and the measured degree of turbulence are also reminiscent of clouds forming groups of stars. The excitation of the molecular lines, molecular abundances, and outflow properties are discussed. It is concluded that IRAS 20231+3440 is a ClassI object, while the southern core most likely contains a Class0 source.
We describe the construction of a high performance parallel computer composed of PC components, as well as the performance test in lattice QCD.
We show that the dynamic approach to Lévy statistics is characterized by aging and multifractality, induced by an ultra-slow transition to anomalous scaling. We argue that these aspects make it a protoptype of complex systems.
Using the Karpman-Solov'ev method we derive the equations for the 2-soliton adiabatic interaction for solitons of the modified nonlinear Schrodinger equation (MNSE). Then we generalize these equations to the case of N interacting solitons with almost equal velocities and widths. On the basis of this result we prove that the N MNSE-soliton train interaction (N>2) can be modeled by the completely integrable complex Toda chain (CTC). This is an argument in favor of universality of the complex Toda chain which was previously shown to model the soliton train interaction for nonlinear Schrodinger solitons. The integrability of the CTC is used to describe all possible dynamical regimes of the N-soliton trains which include asymptotically free propagation of all N solitons, N-soliton bound states, various mixed regimes, etc. It allows also to describe analytically the manifolds in the 4N-dimensional space of initial soliton parameters which are responsible for each of the regimes mentioned above. We compare the results of the CTC model with the numerical solutions of the MNSE for 2 and 3-soliton interactions and find a very good agreement.
We present a systematic study of the kaon to pion multiplicity ratios (K+/pi+ and K-/pi-) in heavy-ion collisions from AGS to RHIC energy using the Relativistic Quantum Molecular Dynamics (RQMD) model. The model satisfactorily describes the available experimental data on K+/pi+ and K-/pi-. Within the model, we find that the strong increase of the ratios with the number of participants is mainly due to hadronic rescattering of produced mesons with ingoing baryons and their resonances. The enhancement of K/pi in heavy-ion collisions with respect to elementary p+p interactions is larger at AGS energy than SPS energy, and decreases smoothly with bombarding energy. The total multiplicity ratios at RHIC energy are predicted by RQMD to be K+/pi+ = 0.19 and K-/pi- = 0.15.