Crossover behaviour in random uniaxial ferromagnets with dipolar interactions

The crossover behaviour of random uniaxial ferromagnets with dipolar interactions is studied by a numerical solution of the renormalization group equations. It is found that as a function of temperature the crossover from pure behaviour to asymptotic random behaviour stretches over many decades on the temperature scale and is practically unobservable. However the effective critical exponent becomes nonuniversal for observable temperature distances from the critical point and depends on the impurity concentration. We also predict a similar nonuniversal behaviour for the measurable four spin coupling in these systems.     

Computer simulation of some dynamical properties of the Lorentz gas

We carried out molecular dynamics simulations of a Lorentz gas, consisting of a lone hydrogen molecule moving in a sea of stationary argon atoms. A Lennard-Jones form was assumed for the H₂-Ar potential. The calculations were performed at a reduced temperatureK ^* =kT/_{H 2–Ar} = 4.64 and at reduced densities ^*= _{Ar Ar} ³ in the range 0.074–0.414. The placement of Ar atoms was assumed to be random rather than dictated by equilibrium considerations. We followed the trajectories of many H₂ molecules, each of which is assigned in turn a velocity given by the Maxwell-Boltzmann distribution at the temperature of the simulation. Solving the equations of motion classically, we obtained the translational part of the incoherent dynamic structure factor for the H₂ molecule,S _tr(q, ). This was convoluted with the rotational structure factorS _rot(q, ) calculated assuming unhindered rotation to obtain the total structure factorS(q, ). Our results agree well with experimental data on this function obtained by Egelstaffet al. At the highest density ( ^*=0.414) we studied the dependence ofS(q, ) on system size (number of Ar atoms), number of H₂ molecules for which trajectories are generated, and the length of time over which these trajectories are followed.     

Concentrations and velocity distributions of positive ions in laser ablation of copper

It is shown that the generation of secondary electrons by excited neutrals hitting a surface makes the so-called probe method unsuited for measuring the positive ion fraction in laser ablation plumes. Experiments have been performed in a modified set-up, in which the disturbance by secondary electrons is avoided. For a typical case of Cu irradiated in ultra-high vacuum by nanosecond excimer laser pulses of 3 J cm^–2 the ionized fraction is about 10^–8 at a distance of 60 cm. This number is in fair agreement with Saha-Langmuir predictions based on the assumption of local thermal equilibrium at an estimated temperature of about 3000K. Angular-resolved time-of-flight measurements show that there are three different ion velocity distributions. A slow contribution (kinetic energy 2eV) with an angular distribution peaked along the normal, and two fast, isotropic contributions (kinetic energy 20–50 eV). The fast contributions are attributed to ions involved in a Coulomb explosion.     

Isotope effects in the interaction of hydrogen and deuterium with a rhodium (110) surface

The adsorption of H₂ and D₂ on a Rh (110) surface at 100 K leads to a sequence of ordered phases, among others 1×2 phases at _H =0.5 and at _H =1.5 which likely involve a partial surface reconstruction consisting of a small perpendicular displacement of Rh surface atoms. The structure of the adsorbate phases is strongly correlated with the binding energy of the adsorbed phases. Three H (D) binding states (₁,₂ and) are populated at saturation as determined by thermal desorption spectroscopy (TDS). Whereas the peak temperature of the state is invariant with the hydrogen isotope, the D ₁ state appears at a 8 Klower and theD ₂ state at a 5 Khigher temperature than the respective H states. Generally the D phases exhibit a better long-range order than the H phases. The rate of adsorption is identical for the first three adsorbed phases but D₂ adsorbs appreciably faster in the 1×2–3H and the final l×1–2H phases.Zero point energy effects as well as a H coverage dependent local interaction model could account for the observed effects.     

Competing ordered phases in URu2Si2: hydrostatic pressure and rhenium substitution

A persistent kink in the pressure dependence of the "hidden order" (HO) transition temperature of URu(2-x)RexSi2 is observed at a critical pressure P(c)=15 kbar for 0 相似文献   

Local Resolvent Estimates for <Emphasis Type="Italic">N</Emphasis>-body Stark Hamiltonians

For an N-body Stark Hamiltonian , the resolvent estimate holds uniformly in with Re and Im , where , and is a compact interval. This estimate is well known as the limiting absorption principle. In this paper, we report that by introducing the localization in the configuration space, a refined resolvent estimate holds uniformly in with Re and Im . Dedicated to Professor Hideo Tamura on the occasion of his 60th birthday     

Higher Dimensional Cosmological Model With Gravitational and Cosmological "Constants"

In this paper we have considered a cosmological model representing a flat viscous universe with variable G and in the context of higher dimensional spacetime. It has been observed that in this model the particle horizon exists and the cosmological term varies as inverse square of time. The deceleration parameter and temperature are well within the observational limits. The model indicates matter and entropy generation in the early stages of the universe. Further, it is shown that our model generates all models obtained by Arbab and Singh et al. in four-dimensional space-time.     

Massive and massless neutrinos on unbalanced seesaws

The observation of neutrino oscillations requires new physics beyond the standard model (SM).A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU(2)L x U(1)y gauge symmetry.The overall neutrino mass matrix M turns out to be a symmetric (p+q) x (p+q) matrix.Given p＞q,the rank of M is in general equal to 2q,corresponding to 2q non-zero mass eigenvalues.The existence of (p-q) massless left-handed Majorana neutrinos is an exact consequence of the model,independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p x p light Majorana neutrino mass matrix M,and the q x q heavy Majorana neutrino mass matrix MR.In other words,the numbers of massive left- and right-handed neutrinos are fairly matched.A good example to illustrate this "seesaw fair play rule"is the minimal seesaw model with p ＝ 3 and q ＝ 2,in which one masslese neutrino sits on the unbalanced seesaw.     

Structure and physical properties of ceramics in a section of the system Mg-Cu-Fe-O

The concentration dependences of the crystal lattice parameter and the Curie temperature of the magnetic ceramic, obtained in air at a calcination temperature of 1100°C from charges with the composition (1–x)MgFe₂O₄+x(0.5 CuO × 1.25 Fe₂O₃), where 0x1, were studied. The dependences of the magnetic parameters of the hysteresis loop as well as the resistivity on the composition of the charge were investigated. The single-phase ceramic, having the structure of spinel, is formed for x < 0.5, and in samples with x > 0.5 a tetragonal phase and -Fe₂O₃ are present. The maximum squareness ratio of the hysteresis loop (SHL) is observed in the region x=0.1–0.4. The region of high values of the squareness ratio is also the region of solid solutions containing defects, when -Fe₂O₃ quasiparticles, having the structure of imperfect spinel, are present in the solution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 84–86, December, 1990.     

Probing nucleon strange asymmetry from charm production in neutrino deep inelastic scattering

We propose a means to detect the nucleon strange quark-antiquark asymmetry, which is predicted as a non-perturbative effect, but still unchecked directly by available experiments. The difference for the and meson production cross sections in neutrino and antineutrino induced charged current deep inelastic scattering is illustrated to be sensitive to the nucleon strange asymmetry. A prospect is given and the effect due to the light quark fragmentation is also discussed for the extraction of the strange asymmetry in future experiments.Received: 23 April 2005, Published online: 27 July 2005PACS: 14.60.Pq, 12.15.Ff     

Calculating the jet quenching parameter

Models of medium-induced radiative parton energy loss account for the strong suppression of high-p(T) hadron spectra in square root of (S)NN=200 GeV Au-Au collisions at BNL RHIC in terms of a single "jet quenching parameter" q. We observe that q can be given a model-independent, nonperturbative, quantum field theoretic definition in terms of the short-distance behavior of a particular lightlike Wilson loop. We then use the anti-de Sitter/conformal-field-theory correspondence to obtain a strong-coupling calculation of q in hot N=4 supersymmetric QCD, finding q(SYM)=26.69 square root of alpha(SYM)N(c)T(3) in the limit in which both N(c) and 4pialpha(SYM)N(c) are large. Thus, at strong coupling q is not proportional to the entropy density s, or to some "number density of scatterers" since, unlike the number of degrees of freedom, q does not grow like N(c)(2).     

Remote radio determination of the altitude gradient ot the temperature in the near-surface layer of the atmosphere

A procedure is proposed for the determination of the value of the near-surface temperature gradient of the atmosphere a averaged over the near-surface layer of the atmosphere (several hundred meters thick) from the brightness temperatures at two viewing angles. It is shown that the optimal absorption line for making the measurements is the 5 mm (v 59–62 GHz) oxygen multiplet. It is noted that the accuracy of the determination of the quantity by the proposed procedure is several times higher than by the usual procedure of recovering the temperature distributions of the atmosphere at frequencies = 53–55 GHz.Radiophysical Scientific Research Institute. Translated from Izvestiya Vysshilkh Uchebnykh Zavedenii, Radiofizika, Vol. 25, No. i0, pp. 1119–1130, October, 1982.     

Current controlled negative resistance phenomenon in SbPbSe system

Thin film Al/Sb₂Pb₁Se₇/Al metal-glass-metal sandwiched structures prepared using thermal evaporation technique have been studied. The I–V measurements showed that the devices switched from high resistance OFF state to a low resistance ON state when a particular voltage appeared across it. The OFF state I–V characteristics showed non-ohmic behaviour while in the ON state the devices displayed purely linear characteristics. The switching voltage (V _th) was found to depend on film thickness and temperature of the device. A linear relation between V_th and temperature was observed.     

Adhered Supported Carbon Nanotubes

Carbon nanotubes (NTs) in excess of 200 m long are grown by catalytic pyrolysis of hydrocarbon vapors. The nanotubes grow continuously without the typical extinction due to catalyst encapsulation. A woven metal mesh supports the nanotubes creating a metal supported nanotube (MSNT) structure. The 140 m wide mesh openings are completely filled by 70 nm diameter multiwalled nanotubes (MWNTs). The MWNTs are straight, uniform and highly crystalline. Their wall thickness is about 10 nm (30 graphite layers). The adherent NTs are not removed from the support in a Scotch tape pull test. A 12.5 cm² capacitor made from two MSNT structures immersed in 1 M KCl has a capacitance of 0.35 F and an equivalent series resistance of 0.18 . Water flows through the MSNT at a flow velocity of 1 cm/min with a pressure drop of 15 inches of water. With the support removed, the MWNTs naturally form a carbon nanocomposite (CNC) paper with a specific area of 80 m²/gm, a bulk density of 0.21 g/cm³, an open pore fraction of 0.81, and a resistivity of 0.16 -cm.     

Microscopic selection principle for a diffusion-reaction equation

We consider a model of stochastically interacting particles on , where each site is assumed to be empty or occupied by at most one particle. Particles jump to each empty neighboring site with rate/2 and also create new particles with rate 1/2 at these sites. We show that as seen from the rightmost particle, this process has precisely one invariant distribution. The average velocity of this particle V() then satisfies ^–1/2V() as. This limit corresponds to that of the macroscopic density obtained by rescaling lengths by a factor ^1/2 and letting. This density solves the reaction-diffusion equation , and under Heaviside initial data converges to a traveling wave moving at the same rate .     

Decay of the Bethe–Salpeter Kernel and Bound States for Lattice Classical Ferromagnetic Spin Systems at High Temperature

We consider lattice classical ferromagnetic spin systems at high temperature (1) with nearest neighbor interactions and even single-spin distributions (ssd). Associated with each system is an imaginary time lattice quantum field theory. It is known that there is a particle of mass m–ln in the energy-momentum spectrum. If s ⁴–3s ²²<0, where s ^k is the kth moment of the ssd, and is sufficiently small, we show that in the two-particle subspace there is no mass spectrum up to 2m. For >0 we show that the only mass spectrum in (m, 2m) is a bound state of mass m _b=2m+ln(1–)+O(), where =(+2s ²²)^–1. A bound on the decay of the kernel of a Bethe–Salpeter equation is obtained and used to prove these results.     

Equation of state and symmetry energy within the stability valley

We apply the direct variational method to derive the equation of state for finite nuclei within the stability valley. The extended Thomas-Fermi approximation for the energy functional with Skyrme forces is used. Applying the leptodermous expansion for the profile nucleon densities, we have studied the neutron coat and the isospin symmetry energy for neutron-rich nuclei. Using the equation of state for the pressure, we derive the region of spinodal instability of finite nuclei and its dependence on the mass number, the asymmetry parameter and the Skyrme force parameters. We suggest the procedure of derivation of the isospin symmetry energy from the analysis of the isospin shift of the chemical potential = - beyond the beta-stability line. We show that both the structure of the neutron coat and the position of the drip line depend significantly on the Skyrme force parameters.     

Ion Mobility Measurements and Ion Chemical Reaction Studies at Heavy Elements in a Buffer Gas Cell

Drift time measurements of ions in a buffer gas cell filled with argon have been performed from which changes of the ion mobility and ionic radii for various heavy elements and their compounds were determined. The ionic radius of americium shrinks by (3.1 1.3)% with respect to that of plutonium, and an increase of the radius by (28 2)% of plutonium oxide with respect to plutonium was found. Ion chemical reactions of erbium ions were studied online in an argon buffer gas cell to which the reaction gases oxygen (O) and methane (CH) were added. The erbium ions were implanted into the buffer gas cell with an energy of 50 MeV. The online measured reaction constant = (3.2 0.4) 10 cm/(molecule s) for the reaction Er + O ErO + O agrees with a reference measurement = (3.6 0.4) 10 cm/(molecule s), performed with a Fourier-Transform-Mass-Spectrometer.     

Resistivity of lanthanum and cerium

Conclusions The temperature dependence of the resistivity of cerium and lanthanum has been measured. The resistivity has been shown to decrease with increasing purity. The observed hysteresis in the temperature dependence of the resistivity of lanthanum is due to the martensite nature of the conversions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 6, pp. 107–109, June, 1970.     

Quantification of Effector Binding to the Hemoglobin Central Cavity by Intrinsic and Extrinsic Steady-State Fluorescence

The relative intrinsic and extrinsic fluorescence of hemoglobins are established markers of the R (oxy) T (deoxy) transition and reveal site-specific conformational differences amongst hemoglobin (Hb) mutants. The Hb central cavity has been probed by binding the fluorescent analogue of 2,3-diphosphoglycerate, 8-hydroxy-1,3,6-pyrenetrisulfonate (HPT). An approach to quantify binding of HPT to HbC (6 Lys) and HbA (6 Glu), by steady-state front-face fluorescence spectroscopy using both the intrinsic and extrinsic emissions, is presented. When HPT specifically binds to Hb, efficient fluorescence energy transfer from the intrinsic fluorescence of Hb to HPT occurs, decreasing the intrinsic fluorescence of Hb that plateaus upon stoichiometric binding. HPT fluorescence is significantly but not totally quenched upon binding to HbA and HbC. HPT exhibits a molecular binding ratio of 2:1 to HbC, in contrast to HbA (1:1 binding). The apparent secondary binding site for HbC is weaker (K_D1 = 25 M vs. K_D2 = 0.15 mM). Conformational alterations of HbC at the and clefts of the central cavity are further supported by these data.