Showing papers on "Field (physics) published in 1996"
TL;DR: In this paper, a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer is proposed, and the qualitative features of this model are reproduced by a numerical calculation of the spin distribution.
Abstract: Nickel ferrite nanoparticles exhibit anomalous magnetic properties at low temperatures: low magnetization with a large differential susceptibility at high fields, hysteresis loops which are open up to 160 kOe, time-dependent magnetization in 70 kOe applied field, and shifted hysteresis loops after field cooling. We propose a model of the magnetization within these particles consisting of ferrimagnetically aligned core spins and a spin-glass-like surface layer. We find that qualitative features of this model are reproduced by a numerical calculation of the spin distribution. Implications of this model for possible macroscopic quantum tunneling in these materials are discussed.
1,407 citations
Book•
01 Jan 1996
TL;DR: An essential volume in industry and to all researchers who, whatever their background and level of experience, are interested in this rapidly expanding field as discussed by the authors, is a good resource for anyone interested in the field.
Abstract: An essential volume in industry and to all researchers who, whatever their background and level of experience, are interested in this rapidly expanding field.
1,144 citations
TL;DR: In this article, the relativistic mean field theory for finite nuclei is reviewed and a field theoretical theory for pairing relations is presented and new results for realistic pairing interactions are discussed.
1,138 citations
TL;DR: In this article, the decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density, which is not present in the decay of the weaker fields associated with ordinary radio pulsars.
Abstract: We calculate the quiescent X-ray, neutrino, and Alfven wave emission from a neutron star with a very strong magnetic field, Bdipole ~ 1014 − 1015 G and Binterior ~ (5–10) × 1015 G. These results are compared with observations of quiescent emission from the soft gamma repeaters and from a small class of anomalous X-ray pulsars that we have previously identified with such objects. The magnetic field, rather than rotation, provides the main source of free energy, and the decaying field is capable of powering the quiescent X-ray emission and particle emission observed from these sources. New features that are not present in the decay of the weaker fields associated with ordinary radio pulsars include fracturing of the neutron star crust, strong heating of its core, and effective suppression of thermal conduction perpendicular to the magnetic field. As the magnetic field is forced through the crust by diffusive motions in the core, multiple small-scale fractures are excited, as well as a few large fractures that can power soft gamma repeater bursts. The decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density. The strongest prediction of the model is that these sources will show no optical emissions associated with X-ray heating of an accretion disk.
1,128 citations
TL;DR: The theory predicts that, close to the depinning transition, the transverse Meissner effect is accompanied by stretched exponential relaxation of the field into the bulk and a diverging penetration depth.
Abstract: We study the localization transitions which arise in both one and two dimensions when quantum mechanical particles described by a random Schr\"odinger equation are subjected to a constant imaginary vector potential. A path-integral formulation relates the transition to flux lines depinned from columnar defects by a transverse magnetic field in superconductors. The theory predicts that, close to the depinning transition, the transverse Meissner effect is accompanied by stretched exponential relaxation of the field into the bulk and a diverging penetration depth.
1,000 citations
TL;DR: The Finite Integration Theory (FI) as mentioned in this paper is a generalization of the Yee's algorithm to the time domain and can be applied to a wide range of problems, such as waveguide transition analysis, lossy materials and fields of moving charges.
Abstract: The solution of Maxwell's equations in the time domain has now been in use for almost three decades and has had great success in many different applications. The main attraction of the time domain approach, originating in a paper by Yee (1966), is its simplicity. Compared with conventional frequency domain methods it takes only marginal effort to write a computer code for solving a simple scattering problem. However, when applying the time domain approach in a general way to arbitrarily complex problems, many seemingly simple additional problems add up. We describe a theoretical framework for solving Maxwell's equations in integral form, resulting in a set of matrix equations, each of which is the discrete analogue to one of the original Maxwell equations. This approach is called Finite Integration Theory and was first developed for frequency domain problems starting about two decades ago. The key point in this formulation is that it can be applied to static, harmonic and time dependent fields, mainly because it is nothing but a computer-compatible reformulation of Maxwell's equations in integral form. When specialised to time domain fields, the method actualy contains Yee's algorithm as a subset. Further additions include lossy materials and fields of moving charges, even including fully relativistic analysis.
For amny practical problems the pure time domain algorithm is not sufficient. For instance a waveguide transition analysis requires knowledge of the incoming and outgoing mode patterns for proper excitation in the time domain. This is a typical example where both frequency and time domian analysis are essential and only the combinatin yields the successful result. Typical engineers may wonder why at all one should apply time domain analysis to basically monochromatic field problems. The answer is simple: it is much faster, needs less computer memory, is more general nad typically more accurate. Speed-up factors of over 200 have been reached for realistic problems in filter and waveguide design. The small core space requirement makes time domain methods applicable on desktop computers using milions of cells, and six unknowns per cell—a dimension that has not yet been reached by frequency domain approaches. This enormous amount of mesh cells is absolutely neceesary when complex structures or structures with spacial dimensions of many wavelengths are to be studied. Our personal recod so far is a waveguide problem in which we used 72,000,000 unknowns.
701 citations
TL;DR: In this article, the authors constructed the quantum versions of the monodromy matrices of KdV theory, called as T-operators, which act in highest weight Virasoro modules.
Abstract: We construct the quantum versions of the monodromy matrices of KdV theory. The traces of these quantum monodromy matrices, which will be called as “T-operators,” act in highest weight Virasoro modules. TheT-operators depend on the spectral parameter λ and their expansion around λ=∞ generates an infinite set of commuting Hamiltonians of the quantum KdV system. TheT-operators can be viewed as the continuous field theory versions of the commuting transfermatrices of integrable lattice theory. In particular, we show that for the values\(c = 1 - 3\frac{{3(2n + 1)^2 }}{{2n + 3}}\),n=1,2,3 .... of the Virasoro central charge the eigenvalues of theT-operators satisfy a closed system of functional equations sufficient for determining the spectrum. For the ground-state eigenvalue these functional equations are equivalent to those of the massless Thermodynamic Bethe Ansatz for the minimal conformal field theoryM2,2n+3; in general they provide a way to generalize the technique of the Thermodynamic Bethe Ansatz to the excited states. We discuss a generalization of our approach to the cases of massive field theories obtained by perturbing these Conformal Field Theories with the operator Φ1,3. The relation of theseT-operators to the boundary states is also briefly described.
598 citations
TL;DR: In this article, the authors present a method for the determination of Fractal Dimension in Point Field Models, based on the Hausdorff measure and dimension of a point field.
Abstract: FRACTALS AND METHODS FOR THE DETERMINATION OF FRACTAL DIMENSIONS. Hausdorff Measure and Dimension. Deterministic Fractals. Random Fractals. Methods for the Empirical Determination of Fractal Dimension. THE STATISTICS OF SHAPES AND FORMS. Fundamental Concepts. Representation of Contours. Set Theoretic Analysis. Point Description of Figures. Examples. POINT FIELD STATISTICS. Fundamentals. Finite Point Fields. Poisson Point Fields. Fundamentals of the Theory of Point Fields. Statistics for Homogeneous Point Fields. Point Field Models. Appendices. References. Index.
577 citations
TL;DR: In this paper, the authors investigate field theories defined on spaces with non-commutative coordinates corresponding to deformations of flat spaces as e.g. the Euclidean plane or Minkowski space.
536 citations
TL;DR: In this article, the symmetry aspects of the crystal field and the parametrization of the energy level scheme are discussed and the determination of phenomenological crystal-field parameters is described.
Abstract: Publisher Summary This chapter describes the symmetry aspects of the crystal field and the parametrization of the energy level scheme. It provides an overview of the experimental data of trivalent lanthanide ions doped into crystalline host matrices. The selection rules for induced electric dipole (ED) and magnetic dipole (MD) transitions for systems with even or odd numbers of f electrons in different site symmetries are presented. Methods for the assignment of crystal-field levels are discussed and the determination of phenomenological crystal-field parameters is described. Such a set of crystal-field parameters in combination with a suitable set of free-ion parameters allows calculating crystal-field energy levels and reconstructing the energy diagram of the 4fn configuration. In this way, it is not only possible to check the validity of the crystal-field model but also to get information about energy levels, which cannot be detected experimentally.
412 citations
TL;DR: In this paper, the authors present an approximate formula to calculate the horizontal electric field from lightning that is applicable for close, intermediate, and long distances to the lightning, at ground level and at a height above ground.
Abstract: We present an approximate formula to calculate the horizontal electric field from lightning that is applicable for close, intermediate, and long distances to the lightning, at ground level and at a height above ground. The formula is analytically simple and can be readily implemented for numerical calculations in the frequency and in the time domains. The formula can be particularly useful for lightning induced voltage calculations. A test of the formula by comparison with the results obtained using good approximations to Sommerfeld's integrals is presented. The results compare favorably for a wide range of distances. Theoretical waveforms obtained with a return stroke model and the formula predict that, for negative ground lightning, the horizontal component of the electric field at close range and at a height of a few meters above the ground starts with a sharp pulse directed toward the lightning channel and is followed by a slower field change of opposite polarity.
TL;DR: A cavity QED interaction which forces the ground state of a cavity field mode to evolve into an arbitrary quantum state at a prechosen time does not involve either atom-field state entanglement or the projections characteristic of quantum measurement.
Abstract: We present a cavity QED interaction which forces the ground state of a cavity field mode to evolve into an arbitrary quantum state at a prechosen time ${t}^{*}$. This method does not involve either atom-field state entanglement or the projections characteristic of quantum measurement.
TL;DR: In this paper, a complete analysis of all potentially dangerous directions in the field space of the minimal supersymmetric standard model is carried out, and corresponding new constraints on the parameter space are given in an analytic form, representing a set of necessary and sufficient conditions to avoid dangerous directions.
TL;DR: In this article, the authors presented the most general rotating black hole solution of five-dimensional N = 4 super-string vacua that conforms to the no-hair theorem.
TL;DR: It is proved that the density of states distribution, as a function of color charge density, is Gaussian, confirming the assumption made by McLerran and Venugopalan.
Abstract: We consider a very large ultrarelativistic nucleus. Assuming a simple model of the nucleus and weak coupling we find a classical solution for the gluon field of the nucleus and construct the two-dimensional color charge density for McLerran-Venugopalan model out of it. We prove that the density of states distribution, as a function of color charge density, is Gaussian, confirming the assumption made by McLerran and Venugopalan.
TL;DR: In this article, a condition on the wave front set for the corresponding n-point distributions, called "microlocal spectrum condition" (μSC), is discussed, and all Wick polynomials including the energy-momentum tensor for this field are constructed as operator valued distributions on the manifold.
Abstract: Quantum fields propagating on a curved spacetime are investigated in terms of microlocal analysis. We discuss a condition on the wave front set for the correspondingn-point distributions, called “microlocal spectrum condition” (μSC). On Minkowski space, this condition is satisfied as a consequence of the usual spectrum condition. Based on Radzikowski's determination of the wave front set of the two-point function of a free scalar field, satisfying the Hadamard condition in the Kay and Wald sense, we construct in the second part of this paper all Wick polynomials including the energy-momentum tensor for this field as operator valued distributions on the manifold and prove that they satisfy our “microlocal spectrum condition”.
TL;DR: The dynamic properties of a trapped Bose-condensed gas under variations of the confining field are discussed and analytical scaling solutions for the evolving coherent state ~condensate!.
Abstract: We discuss the dynamic properties of a trapped Bose-condensed gas under variations of the confining field and find analytical scaling solutions for the evolving coherent state (condensate). We further discuss the characteristic features and the depletion of this coherent state.
01 Jan 1996
TL;DR: In this article, the casimir effect and radiative reaction in an optical cavity were discussed. But the authors did not consider the effect of the atom-photon interactions in the optical cavity.
Abstract: New aspects of the casimir effect - fluctuations and radiative reaction, G. Barton non-perturbative atom-photon interactions in an optical cavity, H.J. Carmichael et al single atom emission in an optical resonator, J.J. Childs et al one electron in a cavity, G. Gabrielse and J. Tan manipulation of non-classical field states in a cavity by atom interferometry, S. Haroche and J.M. Raimond perturbative cavity quantum electrodynamics, E.A. Hinds structure and dynamics in cavity quantum electrodynamics, H.J. Kimble spontaneous emission by moving atoms, P. Meystre and M. Wilkens quantum optics of driven atoms in coloured vacua, T.W. Mossberg and M. Lewenstein the micromaser - a proving ground for quantum physics, G. Raithel et al.
TL;DR: The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization.
Abstract: In the intense field (long-wavelength) limit, the oscillating motion of an electron wave packet leads to multiple passes by the scattering Coulomb center. The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization. Our calculations show enhancement by more than an order of magnitude for multiphoton double ionization of He at 0.8 \ensuremath{\mu}m.
TL;DR: A detection method is presented that removes inhomogeneity while retaining chemical shift differences and J couplings with existing inhomogeneous magnets, and could nearly double the largest resonance frequency available for high-resolution NMR.
Abstract: Researchers interested in high-resolution nuclear magnetic resonance (NMR) spectroscopy have long sought higher magnetic fields to enhance resolution and simplify spectra Magnets with substantially larger fields than those available in the best commercial spectrometers are available, but the inhomogeneity is unacceptable for high-resolution spectra A detection method (termed HOMOGENIZED) is presented that removes inhomogeneity while retaining chemical shift differences and J couplings With existing inhomogeneous magnets, this method could nearly double the largest resonance frequency available for high-resolution NMR The HOMOGENIZED sequence is based on observations of intermolecular zero-quantum coherences between a solute molecule and solvent molecules that are micrometers away; as long as the field is homogeneous over this short distance, sharp resonances are recovered without echoes Experimental demonstrations and a detailed density matrix theory to explain the effect are presented
TL;DR: Three theorems in general relativity are proved which rule out classical scalar hair of static, spherically symmetric, possibly electrically charged black holes.
Abstract: We prove three theorems in general relativity which rule out classical scalar hair of static, spherically symmetric, possibly electrically charged black holes. We first generalize Bekenstein's no-hair theorem for a multiplet of minimally coupled real scalar fields with not necessarily quadratic action to the case of a charged black hole. We then use a conformal map of the geometry to convert the problem of a charged (or neutral) black hole with hair in the form of a neutral self-interacting scalar field nonminimally coupled to gravity to the preceding problem, thus establishing a no-hair theorem for the cases with a nonminimal coupling parameter $\ensuremath{\xi}l0$ or $\ensuremath{\xi}g~\frac{1}{2}$. The proof also makes use of a causality requirement on the field configuration. Finally, from the required behavior of the fields at the horizon and infinity we exclude hair of a charged black hole in the form of a charged self-interacting scalar field nonminimally coupled to gravity for any $\ensuremath{\xi}$.
TL;DR: In this article, the authors present solutions for mode I and mode II crack tip fields for plane strain deformations of an elastic-plastic solid whose constitutive behavior depends on both strains and strain gradients.
Abstract: Solutions are presented for mode I and mode II crack tip fields for plane strain deformations of an elastic-plastic solid whose constitutive behavior depends on both strains and strain gradients. The constitutive law is the simplest generalization of the J2 deformation theory of plasticity to include strain gradient effects. Only one new constitutive parameter enters, a length parameter characterizing the scale over which gradient effects become important. The formulation is cast within the framework of coupled stress theory. Crack tip solutions are obtained which display the transition from the HRR fields, governing behavior in an intermediate region with the plastic zone, to the dominant fields at the tip. The dominant fields are obtained in closed form, and finite element methods have been used to produce the solution over the entire field. Some of the difficulties encountered in arriving at an accurate numerical scheme are detailed. Implications of the solutions for fracture are discussed, as are avenues for further research.
TL;DR: In this paper, the Bethe ansatz technique is applied for the calculation of the observables in the strong coupling region of the sine-Gordon model and the results are in the exact agreement with ones following from the sigma model action, which is a two-parameter U (1) ⊗ ( 1) symmetrical deformation of the O(4) non-finear sigma Model.
TL;DR: In this article, the authors detected Zeeman splitting of the Fe I line (geff = 2.5) at 8468.40 A in the very active M4.5 Ve stars Gliese 729 and Glieses 873 (EV Lac).
Abstract: We have detected Zeeman splitting of the Fe I line (geff = 2.5) at 8468.40 A in the very active M4.5 Ve stars Gliese 729 and Gliese 873 (EV Lac). High-resolution (R = 120,000), low-noise (~0.5%) spectra show clear Zeeman-shifted σ components from which we infer field strengths of 2-4 kG, independent of uncertainties in model atmospheres. Similar observations of a sequence (M0 V-M5 V) of low-activity M dwarfs demonstrate that the wing components in the 8468.40 A line are not due to the ubiquitous TiO lines in the vicinity. This strongly suggests that discrepancies in the shape of the magnetically sensitive iron line are due to magnetic fields rather than differences in photospheric temperature. By fitting the ratio of active to inactive line profiles with simple one-component models, we estimate that 50 ± 13% of the photosphere of EV Lac is covered by 3.8 ± 0.5 kG magnetic fields, while 50 ± 13% of Gliese 729 is covered by 2.6 ± 0.3 kG fields. This confirms earlier reports of large magnetic fields on M dwarf flare stars. We see evidence for a distribution of magnetic field strength, spatially across the surface and/or with depth. The twofold increase in field strength relative to G and K dwarfs is predicted by flux tube equilibrium arguments, but the 1 kG difference in the measured field strengths for these two stars suggests that field strengths may also grow with activity as the photospheric filling factor approaches unity.
TL;DR: In this paper, a method of computing the excited state energies in Integrable Quantum Field Theories (IQFT) in finite geometry, with spatial coordinate compactified on a circle of circumference R, was developed.
Abstract: We develop a method of computing the excited state energies in Integrable Quantum Field Theories (IQFT) in finite geometry, with spatial coordinate compactified on a circle of circumference R. The IQFT ``commuting transfer-matrices'' introduced by us (BLZ) for Conformal Field Theories (CFT) are generalized to non-conformal IQFT obtained by perturbing CFT with the operator $\Phi_{1,3}$. We study the models in which the fusion relations for these ``transfer-matrices'' truncate and provide closed integral equations which generalize the equations of Thermodynamic Bethe Ansatz to excited states. The explicit calculations are done for the first excited state in the ``Scaling Lee-Yang Model''.
TL;DR: The application of electromagnetic- field-induced transparency and quantum interference effects in the cooperative phenomenon, such as optical bistability, and the possibility of control-field-induced multistability in two-level systems are demonstrated.
Abstract: We demonstrate the application of electromagnetic-field-induced transparency and quantum interference effects in the cooperative phenomenon, such as optical bistability. The control field used in tandem with the usual electromagnetic field of the two-level scheme results in a considerable lowering of the threshold intensity. We discuss the transient response of the system in the mean-field limit and describe the regression to the steady state when perturbed away from it; the regression exponent is itself dependent on the control field. We also demonstrate the possibility of control-field-induced multistability in two-level systems. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, the authors describe spinor fields with nonvanishing winding number on a truncated (fuzzy) sphere, and the corresponding field theory actions conserve all basic symmetries of the standard commutative version (space isometries and global chiral symmetry).
Abstract: In the framework of noncommutative geometry we describe spinor fields with nonvanishing winding number on a truncated (fuzzy) sphere. The corresponding field theory actions conserve all basic symmetries of the standard commutative version (space isometries and global chiral symmetry), but due to the noncommutativity of the space the fields are regularized and they contain only a finite number of modes.
TL;DR: A fast and robust method for correcting magnetic resonance image distortion due to field in homogeneity is proposed and applied to spiral k‐space scanning and can be used in combination with other deblurring methods.
Abstract: A fast and robust method for correcting magnetic resonance image distortion due to field inhomogeneity is proposed and applied to spiral k-space scanning. The method consists of acquiring a local field map, finding the best fit to a linear map, and using it to deblur the image distortions due to local frequency variations. The linear field map is determined using a maximum likelihood estimator with weights proportional to the pixel intensity. The method requires little additional computation and is robust in low signal regions and near abrupt field changes. Additionally, it can be used in combination with other deblurring methods. The application of this method is illustrated in conjunction with a multislice, T2-weighted, breath-held spiral scan of the liver.