共查询到20条相似文献,搜索用时 46 毫秒
1.
An extended quark sigma model which includes higher-order mesonic interactions is studied at the finite baryonic chemical potential u B and temperature T. The field equations have been solved in the mean-field approximation by using the modified iteration method at finite baryonic chemical potential u B and temperature T. The Goldstone theorem is satisfied below a critical temperature in the chiral limit for u B = 0. As expected from general universality, the chiral phase transition is second-order. By including the higher-order mesonic interactions, the critical temperature is reduced compared to that found in recent works and is in good agreement with lattice QCD results. The nucleon mass is examined in the (u B , T) plane, showing a strong dependence on u B and T. We find that an increase in both the baryonic chemical potential u B and the temperature T leads to an increase in the values of the nucleon mass. This is evidence for the quark-gluon deconfinement phase transition at higher values of temperature. 相似文献
2.
Erhan Albayrak 《Journal of magnetism and magnetic materials》2011,323(7):992-996
The ABpC1−p type of mixed ferromagnetic-ferrimagnetic ternary-alloy with A (spin-3/2), B (spin-1) and C (spin-5/2) ions was studied on the Bethe lattice with the odd numbered shells containing only A ions, while the even numbered shells either containing B or C ions randomly. The phase diagrams were obtained on the (R=|JAC|/JAB,kTc/JAB) and (p, kTc/JAB) planes for given values of p and R, respectively, with the coordination numbers z=3, 4, 5 and 6. The explicit dependence of the phase diagrams on z and each shell of the Bethe lattice having only one type of ion lead to some differences when compared with the previous works. The model presents one or two compensation temperatures for appropriate values of the system parameters. 相似文献
3.
We give an exact formulation of a mixed spin-1 and spin-3/2 Ising model on the Bethe lattice, which shows ferrimagnetism and compensation points. The model incorporates antiferromagnetic nearest-neighbor interaction which is relevant to describe ferrimagnetism. The influence of two sublattice crystal fields, DA and DB, on compensation points is studied in detail. For certain crystal-field values, the single or double compensation temperature may occur in the present system. 相似文献
4.
P. Fozooni K. Djerfi Anders Kristensen M. J. Lea P. J. Richardson A. Santrich-Badal A. Blackburn R. W. van der Heijden 《Czechoslovak Journal of Physics》1996,46(1):327
The magnetoconductivity σ(B) of a classical 2D electron crystal on superfluid4He is non-linear. Experimentally we find a contribution to σ(B) which at constant field, gives σ(B)∞J x, the current density, while at constant current, σ(B) ∞ 1/B. In this region the Hall velocity νH slowly approaches the ripplon velocity νI at the first reciprocal lattice vector, due to strong electron-ripplon interactions with the helium. The magnetoconductivity decreases sharply for νH>νI. Fluctuations in σ(B) are seen above the melting temperature. 相似文献
5.
E. N. Tkachev T. I. Buryakov V. L. Kuznetsov S. I. Moseenkov I. N. Mazov S. I. Popkov K. A. Shaikhutdinov 《Journal of Experimental and Theoretical Physics》2013,116(5):860-865
Electrical conductivity σ(T) of the paper consisting of multiwalled carbon nanotubes (MWCNTs) is studied in the temperature range 4.2-295 K, and its magnetoresistivity ρ(B) at various temperatures in magnetic fields up to 9 T is analyzed. The temperature dependence of the paper electrical conductivity σ(T) exhibits two-dimensional quantum corrections to the conductivity below 10 K. The dependences of negative magnetoresistivity ρ(B) measured at various temperatures are used to estimate the wavefunction phase breakdown length L φ of conduction electrons and to obtain the temperature dependence L φ = constT ?p/2, where p ≈ 1/3. Similar dependences of electrical conductivity σ(T), magnetoresistivity ρ(B), and phase breakdown length L φ(T) are detected for the initial MWCNTs used to prepare the paper. 相似文献
6.
A. V. Kornilov V. M. Pudalov Y. Kitaoka K. Ishida G. -q. Zheng T. Mito J. S. Qualls 《JETP Letters》2003,78(1):21-24
Phase transitions occuring in a quasi-one-dimensional organic compound (TMTSF)2PF6 near the boundaries between the paramagnetic metallic (PM), antiferromagnetic insulator (AFI), and superconducting (SC) states were studied experimentally. A controlled transition through the phase boundary was achieved by maintaining the sample at fixed temperature T and pressure P, while the critical pressure was tuned by varying a magnetic field B. When the PM/AFI phase boundary was crossed due to the variation of a magnetic field, history effects were observed: the resistance was found to depend on the trajectory described by the system before arriving at a given point (P-B-T) of the phase space. The results of the experiment give evidence for the formation of a macroscopically inhomogeneous state characterized by the inclusions of a minor phase that is spatially separated from the major phase. Away from the phase boundary, the homogeneous state is restored. After this, upon approaching the phase boundary in the back direction, the system exhibits no features of the minor phase up to the very boundary. 相似文献
7.
We have used X-ray diffraction to study the structural phase of CeCoIn5 in external pressure. Using high-pressure X-ray diffraction, we find that the crystalline phase is stable in the P4/mmm phase for pressures ≤51.2 GPa. From our measured equation of state, we find a bulk modulus given by B 0 = 72.8 ± 2.9 GPa and a first pressure derivative of B ′ = 5.1 ± 0.3. Measurement of the electrical resistivity of CeCoIn5 to pressures as high as 34.4 GPa shows the existence of a peak in resistivity at p ? = 8.2 ± 0.2 GPa. 相似文献
8.
We study the site-bond percolation problem for clusters of holes and particles with antiferromagnetic order by means of the Bethe cluster approximation. We find that the droplets (i.e.P B =1?e ?|K|/2) diverge at the antiferromagnetic critical pointH=0,T=T c; however forH≠0 they diverge along a percolation line which is different from the Antiferromagnetic Phase Boundary except atT=0. 相似文献
9.
For a two-surface B tending to an infinite-radius round sphere at spatial infinity, we consider the Brown-York boundary integral HB belonging to the energy sector of the gravitational Hamiltonian. Assuming that the lapse function behaves as N∼1 in the limit, we find agreement between HB and the total Arnowitt-Deser-Misner energy, an agreement first noted by Braden, Brown, Whiting, and York. However, we argue that the Arnowitt-Deser-Misner mass-aspect differs from a gauge invariant mass-aspect by a pure divergence on the unit sphere. We also examine the boundary integral HB corresponding to the Hamiltonian generator of an asymptotic boost, in which case the lapse N∼xk grows like one of the asymptotically Cartesian coordinate functions. Such a two-surface integral defines the kth component of the center of mass for (the initial data belonging to) a Cauchy surface Σ bounded by B. In the large-radius limit, we find agreement between HB and an integral introduced by Beig and Murchadha as an improvement upon the center-of-mass integral first written down by Regge and Teitelboim. Although both HB and the Beig- Murchadha integral are naively divergent, they are in fact finite modulo the Hamiltonian constraint. Furthermore, we examine the relationship between HB and a certain two-surface integral which is linear in the spacetime Riemann curvature tensor. Similar integrals featuring the curvature appear in works by Ashtekar and Hansen, Penrose, Goldberg, and Hayward. Within the canonical 3+1 formalism, we define gravitational energy and center of mass as certain moments of Riemann curvature. 相似文献
10.
J.H Jung S.A SeoT.W Noh P.A Sharma N Hur S.-W Cheong 《Solid State Communications》2003,126(4):175-179
We measured reflectivity spectra of polycrystalline Mg1−xB2 samples, which show a metal-insulator transition with x. After performing the Kramers-Kronig analysis, the obtained optical conductivity spectra σ(ω) of MgB2 show a narrow Drude peak in the far-infrared region and a broad peak in the mid-infrared region. As x increases, the spectral weight of the Drude peak is strongly suppressed and that of the broad peak becomes enhanced a little. The existence of the broad mid-infrared peak in the insulating sample suggests that this peak might not be related to the free carriers in MgB2. In the far-infrared region, we also observe that the low energy dielectric constant of Mg1−xB2 diverges near the metal-insulator phase boundary (i.e. x=0.08). This result implies the possibility of a phase separation and a percolative metal-insulator transition in Mg1−xB2. 相似文献
11.
The model of hadron-quark phase transitions proposed by Cleymans et al. is modified by taking into account the fact that the nuclear repulsive force is operative between a pair of nucleons or a pair of antinucleons but not between a nucleon and an antinucleon. The phase boundary in the temperature (T)-chemical potential (μ) plane is calculated for some values of the bag constantB and the hard core radiusR. Stability of the normal nuclear matter together with the bag picture for the nucleon yields rather stringent bounds forB as functions ofR. The most probable range of values is estimated to beB 1/4?150~200 MeV being consistent with the estimate from hadron spectroscopy. For this range ofB, it is improbable to realize the broken chiral phase with deconfining constituent quarks and Goldstone pions at someT and μ. 相似文献
12.
Z. Arnold O. Isnard H. Mayot M. Mí?ek J. Kamarád 《Journal of magnetism and magnetic materials》2010,322(9-12):1117-1119
The effect of pressure on magnetic properties of YCo12B6 and CeCo12B6 was studied in temperature range 5–300 K at pressures up to 9 kbar. The Curie temperature TC and spontaneous magnetization MS decrease with pressure for both compounds. The decrease can be attributed mostly to the volume dependence of both, the Co magnetic moment and the exchange interactions. The hybridization of the p–d states as a consequence of small distances between the Co and B atoms can be one reason of the relatively low pressure effects (ΔTC/Δp=?0.39±0.02 K/kbar, d ln MS/dp=?0.0013±0.0002 kbar?1) in YCo12B6. Higher volume sensitivity of magnetic properties of CeCo12B6 in comparison with YCo12B6 can be attributed to the pressure induced changes of the Ce f- and Co d-states. 相似文献
13.
Yong Hu 《Journal of magnetism and magnetic materials》2010,322(7):844-17687
A modified Monte Carlo Metropolis method is performed to simulate the blocking temperature (TB) in an “alloy-like” heterogeneous system with geometrical frustration. It is found that the blocking temperature, at which the field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves are splitting, changes little for x≤0.5 initially, then decreases obviously with the increase in x. Some discrete error bars emerge for large x owing to the superparamagnetic or agglomerate behavior of the small antiferromagnet. Using a thermal fluctuation model, an analytic expression for TB as a function of x is obtained. By calculating the curves of temperature derivative of the difference between FC and ZFC magnetizations and analyzing the distribution of energy barriers, we interpret the dependence of TB on different proportions of ferromagnetic phase in detail. 相似文献
14.
We have studied the low-field (B ≦ 10?2 T) d.c. susceptibility χ of the austenitic stainless-steel alloy Fe69Mn26Cr5 as a function of the magnetic field B and temperature T. χ(T) shows structure, strong B dependence, and typical irreversible effects. The range of temperatures studied comprises three distinct regions. In the high-temperature region (300 K ≦ T ≦ 380 K) a blunt peak in the susceptibility is noticed at T2 = 340 K. T2 was not sensitive to thermal cycling. χ(T) displayed a sharp cusp at T1 = 200 K. This peak was sensitive to the thermal history of the sample and was strongly suppressed by B. Between T1 and T2 a shallow valley with some hysteresis was observed. We interpret this behavior to be due to a low-temperature pure spin-glass phase, a high temperature conventional paramagnetic phase, and coexisting antiferromagnetic and spin-glass phases between T1 and T2. 相似文献
15.
Essam R. Shaaban 《Physica B: Condensed Matter》2011,406(3):406-411
Glasses with compositions 70B2O3-30Bi2O3 and 70B2O3-30PbO have been prepared and studied by differential thermal analysis (DTA). The crystallization kinetics of the glasses were investigated under non-isothermal conditions. From the dependence of glass-transition temperature (Tg) on heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as glass-transition temperature, Tg, onset temperature of crystallization, Tin, temperature corresponding to the maximum crystallization rate, Tp, beside the kinetic parameters, K(Tg) and K(Tp). The results revealed that 70B2O3-30PbO is more stable than 70B2O3-30Bi2O3. The crystallization mechanism is characterized for both 70B2O3-30Bi2O3 and 70B2O3-30PbO glasses (kinetic exponent n=2.06 for 70B2O3-30Bi2O3, and n=3.03 for 70B2O3-30PbO). The phases at which the glass crystallizes after the thermal process were identified by X-ray diffraction. 相似文献
16.
O. Hudak 《Physics letters. A》2009,373(3):359-362
Recently the ground state and some excited states of the half-filled case of the 1d Hubbard model were discussed exactly for an open chain with L sites. The case when the boundary site has the chemical potential −p and the Hubbard coupling U is positive was considered. We model CeAl2 nanoparticles, in which a valence of 4f electron number changes on surface Ce atoms, by this Hubbard model. A surface phase transition exists at some critical value pc3 of chemical potential (its absolute value) p in the model; when p<pc3 all the charge excitations have the gap, while there exists a massless charge mode when p>pc3. The aim of this Letter is to find whether this surface phase transition is of the first order or of the second order. We have found that the entanglement entropy and its derivative has a discontinuity at pc3 in general and thus this transition is of the first order (with exception of two points for the probability w2 of occurrence of two electrons with opposites spins on the same site). There is a divergence in the difference of entanglement entropy for points w2=0 and . The first point w2=0 corresponds to ferro- (antiferro-) magnetic state at half-filled case. The second point does not correspond to any state for halffilled case. In the first case there is present the surface phase transition of the second order type. 相似文献
17.
18.
Erhan Albayrak 《Journal of magnetism and magnetic materials》2011,323(22):2846-2850
The effects of crystal field (Δ) which is randomly turned on with probability p or turned off with probability 1−p on the sites of the Bethe lattice are investigated to study the critical behavior of the spin-3/2 Blume-Capel model. The order-parameters are obtained in terms of the recursion relations and then the possible phase diagrams are calculated at finite temperatures for given system parameters p, Δ and coordination numbers z=3, 4, 5 and 6. It was found that the phase diagrams change drastically for given probability and randomness. The first-order phase transitions are only found for higher p values and the lines of which get shorter and eventually disappear as p decreases. The critical lines do not present any qualitative differences with z, but they are seen at higher temperatures for higher z. 相似文献
19.
We study the thermodynamic behavior of a ferromagnetic Ising system on a Bethe lattice in the presence of given boundary conditions. More specifically, we study the interface of the system when the spins on half of the surface are fixed opposite to the spins on the other half. We find an interface width that remains finite in the whole range (0,T
c
), a feature due to the special topology of the Bethe lattice. We also study the case where the spin on a certain lattice site belonging to a domain is fixed in a direction opposite to the domain magnetization at all temperaturesT
c
. We obtain the influence of that spin on the local magnetization, and we find that the fixed spin nucleates a local domain that extends over a distance of only a few lattice sites from it at all temperaturesT
c
. 相似文献
20.
Stefan Boettcher 《Physica A》2007,386(2):640-643
Based on a recently developed algorithm for the exploration of ground states in bond-diluted lattice spin glasses, we determine the scaling of defect energies with system size for Ising spin glasses at the bond percolation threshold pc. The results can be related by well-known scaling relations to the shape of the transition temperature Tg∼(p-pc)φ between the paramagnetic and glassy regime for p→pc. The numerical results in three dimensions are consistent with rather old experimental data for (FexNi1-x)75P16B6A3, suggesting that new experimental work may be able to put those numerical predictions to the test. 相似文献