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1.
A dynamical theory is studied in which a scalar field ϕ in Einstein-Minkowski space is coupled to the four-velocity N
μ of a preferred inertial observer in that space. As a consistent requirement on this coupling we study a principle of duality
invariance of the dynamical mass term of ϕ at some universal length in the small-distance regime. In the large-distance regime
duality breaking can be introduced by giving a background value to ϕ and a background direction to N
μ. It is shown that, in an appropriate approximation, duality breaking can be related to the emergence of a characteristic
phase in which the condensation of the ground state allows massive excitations with a characteristic scale of squared mass
which agrees with the present observational bound for the cosmological constant. 相似文献
2.
X-ray diffraction studies showed substitution of nonmagnetic lanthanum for terbium in the TbMnSi polycrystalline compound to initiate a structural transition from a TiNiSi-type orthorhombic structure (for TbMnSi) to a CeFeSi-type tetragonal phase (for Tb 0.5La 0.5MnSi). Magnetic measurements (of the magnetization, magnetostriction, thermal expansion) performed on Tb 0.5La 0.5MnSi revealed a change in the character of magnetic ordering, the appearance of a ferromagnetic component in the Mn magnetic moment, a strong increase in magnetization as compared to TbMnSi, and the appearance of a spontaneous magnetic moment. Insertion of the lanthanum ion onto the rare-earth sublattice of TbMnSi brings about a change in the unit cell size and, hence, in the Mn-Mn, Mn-Si, and R-Mn interatomic distances, which causes, in turn, a change in the character of exchange interactions in Tb 0.5La 0.5MnSi and the formation of a complex magnetic structure. 相似文献
3.
It is found that a fixed point of the renormalization group equation corresponding to a system of a unimodal map with extremum
of power κ and a map summarizing values of a function of the dynamical variable of the first subsystem, undergoes a bifurcation in the
course of increase of κ. It occurs at κ
c
=1.984396 and results in a birth of the period-2 stationary solution of the RG equation. At κ=2 this period-2 solution corresponds to the universal period-doubling behavior discovered earlier and denoted as the C-type
criticality (Kuznetsov and Sataev in Phys. Lett. A 162:236–242, 1992). By combination of analytical methods and numerical computations we obtain and analyze an asymptotic expansion of the period-2
solution in powers of Δ κ= κ− κ
c
. The developed approach resembles the ε-expansion in the phase transition theory, in which a “trivial” stationary point of the RG transformation undergoes a bifurcation
that gives rise to a new fixed point responsible for the critical behavior with nontrivial critical indices. 相似文献
4.
The formation of a system of one-dimensional quantum conductors in porous multilayer In xGa 1?xAs/GaAs structures with a two-dimensional charge-carrier gas in the In xGa 1?xAs layers is discussed. The transition from the single-crystalline to porous matrix is studied with scanning atomic force microcopy. A decrease in the dimensionality of the electron-hole gas in the objects, i.e., a transition from the two-dimensional to a one-dimensional system, is established by analyzing the dependences of the position and width of a spectral line in the photoluminescence spectra on the etching time. Both multilayer periodic superlattices and a structure with a single In xGa 1?xAs layer located near the surface of gallium arsenide are studied. The electrophysical characteristics of electrons in the porous superlattices are measured as functions of temperature. They confirm the formation of a new structure and indicate a change in the mechanism of electron scattering in the quasi-one-dimensional transport channels formed in the system. 相似文献
5.
Ferrofluid spin-up flow is studied within a sphere subjected to a uniform rotating magnetic field from two surrounding spherical coils carrying sinusoidally varying currents at right angles and 90° phase difference. Ultrasound velocimetry measurements in a full sphere of ferrofluid shows no measureable flow. There is significant bulk flow in a partially filled sphere (1-14 mm/s) of ferrofluid or a finite height cylinder of ferrofluid with no cover (1-4 mm/s) placed in the spherical coil apparatus. The flow is due to free surface effects and the non-uniform magnetic field associated with the shape demagnetizing effects. Flow is also observed in the fully filled ferrofluid sphere (1-20 mm/s) when the field is made non-uniform by adding a permanent magnet or a DC or AC excited small solenoidal coil. This confirms that a non-uniform magnetic field or a non-uniform distribution of magnetization due to a non-uniform magnetic field are causes of spin-up flow in ferrofluids with no free surface, while tangential magnetic surface stress contributes to flow in the presence of a free surface.Recent work has fitted velocity flow measurements of ferrofluid filled finite height cylinders with no free surface, subjected to uniform rotating magnetic fields, neglecting the container shape effects which cause non-uniform demagnetizing fields, and resulting in much larger non-physical effective values of spin viscosity η′∼10 −8−10 −12 N s than those obtained from theoretical spin diffusion analysis where η′≤10 −18 N s. COMSOL Multiphysics finite element computer simulations of spherical geometry in a uniform rotating magnetic field using non-physically large experimental fit values of spin viscosity η′∼10 −8−10 −12 N s with a zero spin-velocity boundary condition at the outer wall predicts measureable flow, while simulations setting spin viscosity to zero ( η′ =0) results in negligible flow, in agreement with the ultrasound velocimetry measurements. COMSOL simulations also confirm that a non-uniform rotating magnetic field or a uniform rotating magnetic field with a non-uniform distribution of magnetization due to an external magnet or a current carrying coil can drive a measureable flow in an infinitely long ferrofluid cylinder with zero spin viscosity ( η′ =0). 相似文献
7.
We have developed a simple assessment method for the overlap between spheroidal particles, which neither requires the complex manipulation of vectors and matrices that is indispensable in the ordinary methods, nor is based on a model potential. Moreover, we have developed an evaluation method for the interaction energy arising from the overlap of the steric layer coating spheroidal particles. This is based on a sphere-connected particle model, but some modifications are introduced in order to express an appropriate repulsive interaction energy at the deepest overlapping position. We have investigated the phase change in a magnetic spheroidal particle suspension for a two-dimensional system by means of Monte Carlo simulations. In the case of no external magnetic field, if the magnetic particle-particle interaction is sufficiently strong to favour cluster formation, long raft-like clusters tend to be formed in a dilute situation. With decreasing values of area fraction, a chain-like structure in a dense situation transforms into a raft-like structure within a narrow range of the particle area fraction. Similarly, the raft-like clusters are preferred in a weak applied magnetic field, but an increase in the field strength induces a phase change from a raft-like into a chain-like structure.Highlights of the present paper: A simple assessment method has been proposed for the overlap between two spheroidal particles. The particle overlap assessment is free from a complex mathematical manipulation regarding vectors and matrices. A modified sphere-connected model has been proposed in order to more accurately evaluate a repulsive interaction due to the overlap of the steric layers coating spheroidal particles. 2D Monte Carlo simulations have been performed to elucidate the phenomenon of a phase change by magnetic spheroidal particles on a material plane surface. A phase change between a raft-like and a chain-like aggregate structure is able to be controlled by the area fraction of particles and an external magnetic field. 相似文献
8.
This proposes a new theory of Quantum measurement; a state reduction theory in which reduction is to the elements of the number
operator basis of a system, triggered by the occurrence of annihilation or creation (or lowering or raising) operators in
the time evolution of a system. It is from these operator types that the acronym ‘LARC’ is derived. Reduction does not occur
immediately after the trigger event; it occurs at some later time with probability P
t
per unit time, where P
t
is very small. Localisation of macroscopic objects occurs in the natural way: photons from an illumination field are reflected
off a body and later absorbed by another body. Each possible absorption of a photon by a molecule in the second body generates
annihilation and raising operators, which in turn trigger a probability per unit time P
t
of a state reduction into the number operator basis for the photon field and the number operator basis of the electron orbitals
of the molecule. Since all photons in the illumination field have come from the location of the first body, wherever that
is, a single reduction leads to a reduction of the position state of the first body relative to the second, with a total probability
of mP
t
, where m is the number of photon absorption events. Unusually for a reduction theory, the larc theory is naturally relativistic. 相似文献
9.
We study localized modes on a single magnetic impurity positioned in the bulk or at the surface of a one-dimensional chain, in the presence of a magnetic field B acting at the impurity site. The strong on-site nonlinear interaction U between two electrons of opposite spin at the impurity site, modelled here as a nonlinear local term, and the presence of the external field induce a strong correlation between parallel and antiparallel spin bound states. We find that, for an impurity in the bulk, a localized vector mode (with up and down spin components) is always possible for any given value of U and B, while for a surface impurity, a minimum value of both, U and B is needed to create a vector mode. In this case, up to two localized modes are possible, but only one of them is stable. The presence of the surface seems to destabilize the bulk mode in the parameter region U∼ B, creating a “forbidden strip” region in parameter space, bounded by U= B+ V and U= B− V, approximately. 相似文献
10.
We construct new supersymmetric solutions of D = 11 supergravity describing n orthogonally “overlapping” membranes and fivebranes for n = 2,…,8. Overlapping branes arise after separating intersecting branes in a direction transverse to all of the branes. The solutions, which generalize known intersecting brane solutions, preserve at least 2 −n of the supersymmetry. Each pairwise overlap involves a membrane overlapping a membrane in a 0-brane, a fivebrane overlapping a fivebrane in a 3-brane or a membrane overlapping a fivebrane in a string. After reducing n overlapping membranes to obtain n overlapping D-2-branes in D = 10, T-duality generates new overlapping D-brane solutions in type IIA and type IIB string theory. Uplifting certain type IIA solutions leads to the D = 11 solutions. Some of the new solutions reduce to dilaton black holes in D = 4. Additionally, we present a D = 10 solution that describes two D-5-branes overlapping in a string. T-duality then generates further D = 10 solutions and uplifting one of the type IIA solutions gives a new D = 11 solution describing two fivebranes overlapping in a string. 相似文献
11.
In order to elucidate the anomalous magnetic properties in the ferromagnetically ordered state of SmNi 4Ga GdNi 4Ga and TbNi 4Ga, we have carried out a detailed study with magnetization and specific heat (SH) measurements. GdNi 4Ga shows the possibility of a filled 3d band and a helical spin arrangement below the ordering temperature. TbNi 4Ga shows a dominant crystal field effect resulting in a deviation of TC from the de-Gennes scaling and possible Schottky anomalies in the SH. SmNi 4Ga shows a large coercivity at low temperatures. A rough estimate of the domain wall thickness in SmNi 4Ga gives a value of 8 Å. 相似文献
12.
Two new ponderomotive effects in black hole physics are indicated: (i) the precession of the rotation axis of a charged black hole in an external magnetic field, (ii) the drift of a non-charged rotating hole in an asymmetric homogeneous electromagnetic field posessing a non-zero Poynting vector. The precession time for a black hole of solar mass with Q = 10 ?5M in a magnetic field B ~ 10 12G is about a year. 相似文献
13.
A simple “chimney” method was used to eliminate the voids in an arrangement of quantum dots sized 2 nm on a solid substrate, which resulted in a large well ordered superlattice of area in the order more than 1 μm 2. Based on the principle of speeding up the interparticle interaction of nanoparticles to overcome the particle-substrate one, a lateral centripetal force originated from a glass tube acting as a chimney in a simple evaporation device is imposed. This method allows the packing process to be controlled in a mechanical force field, that is, with the same nanogold dispersion different patterns on a substrate—from separate dots to an ordered compact monolayer or even a multilayer structure—could be easily obtained. 相似文献
14.
Two-magnon Raman scattering in dielectric, as well as superconducting, YBa 2Cu 3O 6 + x single crystals with mobile oxygen content x = 0.2–0.7 and superconducting transition temperature T c = 0–74 K is studied in detail. Doping with oxygen in the range of x = 0.2–0.5 leads to two-magnon scattering peak broadening and a shift in the spectral position of the peak towards lower energies. The most significant qualitative changes in two-magnon scattering in YBa 2Cu 3O 6 + x crystals are observed in a narrow oxygen concentration range near x = 0.7. This is explained by a considerable decrease in the correlation length ξ AF of antiferromagnetic (AF) correlations upon an increase in the concentration of free carriers. For instance, doping is accompanied with a reduction of ξ AF to values of several lattice constants a for x ≈ 0.7, a transition to the regime of short-range AF order, and local scattering of light from a small AF cluster with a size of 3 × 4 lattice constants. An increase in the free charge carrier concentration destroys the short-range AF order in a narrow range of the stoichiometry index near x = 0.7. Experimental data also indicate heterogeneity of cuprate planes at microscopic level, which leads to coexistence of superconducting and AF regions in YBa 2Cu 3O 6 + x super-conducting crystals. 相似文献
15.
Solutions of the nonlinear Ginzburg-Landau equations in cylindrical symmetry have been computed for a type I superconductor. From these solutions the behaviour of a circular cylinder of infinite length in a magnetic field parallel to its axis has been deduced. For a series of values of the magnetic field solutions are given in two cases. The first case was calculated with the assumption of no fluxoid frozen in (fluxoid quantum number n=0), whereas in the second case a vortex with fluxoid quantum number n=1 was assumed on the axis of the cylinder. For both series of solutions investigation of the thermodynamic stability was carried out. This and further thermodynamic considerations led to the result that in a gedankenexperiment the transition from the normal to the superconducting state and vice versa can be performed in a reversible manner. The expulsion of the magnetic field from the sample during the reversible transition to the superconducting state (Meissner-Effect) is also described by the solutions. Further results are the existence of a supercooled state down to a magnetic field H c2=κ√2H cb and of a superheated state up to a field H c1> H cb. The value of H c1 depends on the radius of the cylinder. If a condensation to the superconducting state takes place at a field H 0 where H c2< H 0< H cb, condensation with n=0 seems to be preferred in comparison to that with n=1. 相似文献
16.
Raman measurements on solid hydrogen show a maximum in the vibrational frequency of a H 2 molecule as a function of pressure, around 350 Kbar. We give an interpretation of this experimental data by considering a model in which a single H 2 molecule is immersed in a dielectric medium, and enclosed in a spheroidal box to simulate the effect of pressure. The maximum results from a balance between a decreasing equilibrium bond length of H 2 with pressure at low pressures and a term which reflects the pressure dependence of the dielectric constant. Our results are consistent with available calculations which give a much lower vibrational frequency at a much higher pressure, for a H 2 molecule embedded in a metallic medium. 相似文献
17.
Abstract Tests were made for a quantitative decomposition of N 2O to N 2 and for the setting of a statistical equilibrium in mixtures with gaseous nitrogen of nonrandom distribution by emission spectrometric continuous-flow-measurements. Under high-frequency-discharge conditions a residence time of 0.5 seconds is enough for a quantitative decomposition. In this time the statistical balance in the mixture of N 2O and N 2 is reached. The determination of the relative 15N abundance in pure N 2O or N 2 gases or in mixtures of N 2O and N 2 in a continuous-flow-emissionspectrometer can directly be achieved. 相似文献
18.
By using a CO 2 laser operated at 10.6μm, a bimolecular reaction was induced in a binary SO 2/O 2 gas mixture, with a sensitizer gas (SF 6) as photo-absorbing species.The infrared (IR) synthesis of SO 3 was performed in a flowing gas device equipped with a continuous trapping system of the reaction product. Vibrational energy transfer processes presumably should play a specific role in SO 2 excitation and reaction in the presence of SF 6. 相似文献
19.
An analysis of the experimental data on one-pion and two-pion production in the p( ??, ????) X reaction studied in a semi-exclusive experiment at an energy of E ?? = 4.2 GeV has been performed. The obtained results demonstrate that the inelastic ??-particle scattering on the proton at the energy of the experiment proceeds either through excitation and decay of the ?? resonance in the projectile ?? particle, or through excitation in the target proton of the Roper resonance, which decays into a nucleon and a pion, or a nucleon and a ?? meson??a system of two pions in the isospin I = 0, S-wave state. 相似文献
20.
The Magnaporthe grisea is a fungus whose spores strongly adhere to plant leaves, and to solid surfaces in general. In this note, we give an estimate of the adhesion force, Fdet, of a spore on a glass surface, in water. Fdet is defined as the force to be applied to a spore to pull it out from the surface. In our experiments, spores are detached from the glass in a few milliseconds by means of a capillary force. The latter is provided by a water/air or a water/oil interface, in contact with the spore body. We thus find Fdet of the order of 10 −6 N. 相似文献
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