The classical field limit ofP(ϕ)2 quantum field theory

It will be shown that, for a convex polynomialP, theP()₂ quantum field theory without cutoff has a classical field limit as Planck's constanth tends to zero. This extends work of Hepp [1], who considered theories with a space cutoff.     

Steady-state sound field in enclosures

The classical normal-mode theory expresses the steady-state soundfield in an enclosure produced by a sound source as a series of normal modes ofvibration.Experimental facts are not often explained by this theory,and it wasconjectured that the normal-mode expression is not the complete solution ofthe wave equation in the enclosure,but only the reverberant part of it,and thereshould be an additional term representing the direct spherical radiation to makethe solution complete.The problem is examined by critically reviewing the de-rivation of the normal-mode expression,and by theoretical analysis of thesteady-state sound field in the room and experimental measurements therein.The conjecture is thus confirmed,and it is definitely shown that the sound fieldshould contain the direct wave as well as the standing waves(normal modes)formed by the confinement of the boundary surfaces.Relevant mathematicalexpressions are derived.     

The near field acoustic holography technique for cyclostationary sound field and its experimental research

One near field acoustic holography (NAH) technique is proposed for analyzing cyclostationary sound field. The signal of this kind of sound field has very serious modulation phenomenon generally, in spectrum of which obvious sidebands exist. It is difficult for the traditional NAH to possess demodulation function, so virtual power of sidebands exists in its hologram. Replacing the Fourier's transform with the second-order cyclic statistics, the proposed NAH technique uses the cyclic spectrum density (CSD) function as reconstructed physical quantity, instead of the spectrum or power spectrum density of sound pressure signal. The CSD function can demodulate cyclostationary signals, which makes no virtual power of sidebands in its hologram. The results of simulation and experiment show that the proposed NAH can extract more information about cyclostationary sound field than traditional NAH, by which sound field can be known more clearly.     

The extended conformal Einstein field equations with matter: The Einstein–Maxwell field

A discussion is given of the conformal Einstein field equations coupled with matter whose energy–momentum tensor is trace-free. These resulting equations are expressed in terms of a generic Weyl connection. The article shows how in the presence of matter it is possible to construct a conformal gauge which allows to know a priori the location of the conformal boundary. In vacuum this gauge reduces to the so-called conformal Gaussian gauge. These ideas are applied to obtain (i) a new proof of the stability of Einstein–Maxwell de Sitter-like spacetimes; (ii) a proof of the semi-global stability of purely radiative Einstein–Maxwell spacetimes.     

Superconductive superheating field for finiteκ

We have calculated analytically the superheating fieldH _sh for bulk superconductors, correct to second order in. We find , which agrees well with numerical computations for<0.5. The surface order parameter is , and the penetration depth is .     

Lagrange–Poincaré field equations

The Lagrange–Poincaré equations of classical mechanics are cast into a field theoretic context together with their associated constrained variational principle. An integrability/reconstruction condition is established that relates solutions of the original problem with those of the reduced problem. The Kelvin–Noether Theorem is formulated in this context. Applications to the isoperimetric problem, the Skyrme model for meson interaction, and molecular strands illustrate various aspects of the theory.     

Three dimensional active sound field cancellation

In this paper, a novel method for Three dimensional active sound field cancellation is proposed. The optimum sound cancellations in different situations may be obtained. An array whose elements lie on a set of rings placed on the surface of a scattering object is considered as the device. It is quite possible to cancel the scattered sound field to any arbitrary level over either the whole space or a partial area of interest, as long as the number of the array elements is sufficient.     

High field magnetization and57Fe hyperfine field in amorphous RuxFe80−xB20 alloys

Magnetism in amorphous alloys of Ru_xFe_80–xB₂₀, 0 × 22 has been investigated using high field magnetization and Mössbauer spectroscopy. The average Fe hyperfine field in Ru₁₈Fe₆₂B₂₀ shows an anomalous rise at low temperatures. In Ru rich alloys a low field component appears in the hyperfine field distribution and the alloys do not saturate magnetically in 80 kG fields. It is inferred that their magnetic structure is non collinear and that antiferromagnetic exchange in the system increases with Ru concentration.     

Radiation from relativistic electrons during entry into a magnetic field andβ decay in the field

This paper considers the radiation emitted when a nucleus experiences decay in a magnetic field, producing relativistic electrons. The spectral-angular distribution of the radiation from relativistic electrons in a sharply delineated magnetic field was also found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 92–95, March, 1976.In conclusion, the authors express their gratitude to Prof. A. A. Sokolov for the stimulating interest he took in the paper and extend their thanks to V. Ch. Zhukovskii for his helpful discussion of the results obtained.     

Electric field control of spin splitting in III–V semiconductor quantum dots without magnetic field

We provide an alternative means of electric field control for spin manipulation in the absence of magnetic fields by transporting quantum dots adiabatically in the plane of two-dimensional electron gas. We show that the spin splitting energy of moving quantum dots is possible due to the presence of quasi-Hamiltonian that might be implemented to make the next generation spintronic devices of post CMOS technology. Such spin splitting energy is highly dependent on the material properties of semiconductor. It turns out that this energy is in the range of meV and can be further enhanced with increasing pulse frequency. In particular, we show that quantum oscillations in phonon mediated spin-flip behaviors can be observed. We also confirm that no oscillations in spin-flip behaviors can be observed for the pure Rashba or pure Dresselhaus cases.     

Is the electromagnetic field an invariant superposition of the 42 states of a basic field?

It is shown that an invariant superposition of 42 symmetry-related states of a basic field can account for the experimental value of the fine-structure constant. Such a theory yields the formulac/e ²=N(N–1)/4=137.0324, withN=42 the order of the invariance group.     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

What is a mean gravitational field?

The equations of General Relativity are non-linear. This makes their averaging non-trivial. The notion of mean gravitational field is defined and it is proven that this field obeys the equations of General Relativity if the unaveraged field does. The workings of the averaging procedure on Maxwells field and on perfect fluids in curved space-times are also discussed. It is found that Maxwells equations are still verified by the averaged quantities but that the equation of state for other kinds of matter generally changes upon average. In particular, it is proven that the separation between matter and gravitational field is not scale-independent. The same result can be interpreted by introducing a stress-energy tensor for a mean-vacuum. Possible applications to cosmology are discussed. Finally, the work presented in this article also suggests that the signature of the metric might be scale-dependent too.Received: 16 October 2003, Published online: 15 March 2004PACS: 04.20.Cv Fundamental problems and general formalism 04.40.Nr Einstein-Maxwell spacetimes, spacetimes with fluids, radiation or classical fields - 95.35. + d Dark matter (stellar, interstellar, galactic, and cosmological)     

Luis Santaló and classical field theory

Considered one of the founding fathers of integral geometry, Luis Santaló has contributed to various areas of mathematics. His work has applications in number theory, in the theory of differential equations, in stochastic geometry, in functional analysis, and also in theoretical physics. Between the 1950’s and the 1970’s, he wrote a series of papers on general relativity and on the attempts at generalizing Einstein’s theory to formulate a unified field theory. His main contribution in this subject was to provide a classification theorem for the plethora of tensors that were populating Einstein’s generalized theory. This paper revisits his work on theoretical physics.

     

Cauchy magnetic field component and magnitude distribution studied by the zero‐field muon spin relaxation technique

Zero‐field muon spin relaxation (ZF‐μSR) data for dilute spin magnetic systems have been widely interpreted with what is called a Kubo–Toyabe form based on a Lorentzian distribution of local field components. We derive here the proper magnetic field magnitude distribution using independent and uncorrelated component distributions. Our result is then compared to the previously accepted formula for ZF‐μSR. We discuss the origins of the magnetic field component and magnitude distributions. Further, we found that after rescaling the magnetic field, the differences that are amenable to experimental examination are quite small, although the interpretations behind them are quite different. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theory of sound field in a room

In the normal-mode theory of Morse, it gives a series of normal modes as the solution of forced vibration in a room. But actually there is always the direct radiation besides the normal modes which represent the reverbrant sound field only. The reason is that the normal modes were assumed only in the source, and naturally normal modes only are obtained in the solution. A theory of double source is proposed, that the sound source is both the source of the direct radiation as if in free space before the boundary surfaces were reached by the direct radiation, and after the first reflection from the boundary surfaces, the source of the reflected wavelets, randomly distributed both in space an in time on the boundary surfaces that build up the normal modes after further reflections. The wave equation is formed accordingly, and the solution of the wave equation, the sound field in a room, contains explicitly both the direct radiation and the reverberant sound formed of normal modes. The approximate mean square sound pressure is found to be the dircet sound determined by the sound power of the source,and reverberant sound determined by the sound power reduced by a factor of π/2, different slightly from the result obtained from energy consideration, if the source is pure tone. There is essentially no difference for a source of band noise.     

Carbon nanotube emitters and field emission triode

Based on our study on field emission from multi-walled carbon nanotubes (MWNTs), we experimentally manufactured field emission display (FED) triode with a MWNTs cold cathode, and demonstrated an excellent performance of MWNTs as field emitters. The measured luminance of the phosphor screens was 1.8 × 103 cd/m2 for green light. The emission is stable with a fluctuation of only 1.5% at an average current of 260 μA.     

Random‐field experiments in dilute antiferromagnets

Experiments in d = 2 and d = 3 random-field Ising systems are reviewed. Random fields destroy the phase transition for the d = 2 system Rb₂Co _x Mg_1-xF₄. The d = 3 Fe _x Zn_1-xF₄ system shows a new phase transition with unusual dynamics. Extreme critical slowing down plays an essential role in the d = 3 measurements. Experiments on the related d = 3 systems Mn _x Zn_1-xF₂ and Fe _x Mg_1-xC1₂ are also discussed.     

Zero—field—cooled and field—cooled magnetizations and magnetic susceptibility of itinerant ferromagnet SrRuO3

Zero-field-cooled(ZFC) magnetization,field-cooled(FC) magnetization,ac magnetic susceptibility and major hysteresis loops of itinerant ferromagnet SrRuO3 have been measured at magnetic ordering temperatures ranging from 5 to 160K.An empirical model is proposed to calculate the measured ZFC magnetization.The result indicates that the calculated ZFC magnetization compares well with the measured one.Based on the generalized Preisach model.both the ZFC and FC curves are reproduced by numerical simulations.The critical temperature and critical exponents are determined by measuring the ac magnetic susceptibility in different bias magnetic fields at temperatures in the vicinity of the point of phase transition.