The equilibrium polarization of an optically pumped3He target

The nuclear polarization of an optically pumped³He target can be determined by optical methods if one makes some assumptions on the kinetics of the pumping process. Experiments and calculations have been carried out to examine whether these postulates are permissible. A good agreement between experiments and theory confirms the correctness of the assumptions and consequently justify the determination of the nuclear polarization by optical methods.     

Microscopic,quantal theory of Brownian motion applied to deep inelastic heavy-ion collisions

The present understanding of the statistical features of deep inelastic heavy ion collisions can be improved considerably by following the lines of modern molecular theory of Brownian motion. Only a few assumptions are necessary, which are direct consequences of the underlying physical picture. The physical interpretation of these assumptions leads to simple estimates of their validity. The theory is a quantum mechanical, strong coupling, transport theory. Collective vibrations can be included in a simple and straightforward manner.     

Maximum-entropy data analysis

The reconstruction of physical quantities from (computer-) experimental data is very often hampered by the presence of noise, insufficient information and above all by the ill-posed nature of the underlying inversion problem. It will be demonstrated that the maximum entropy concepts is particularly suited for this type of data-analysis problems. It is based on Bayesian statistics and provides a consistent probabilistic theory to obtain unbiased results, independent of any model assumptions. This is particularly desirable if there is no additional information to justify these hypotheses. If, on the other hand, additional prior knowledge is available, it can be effectively incorporated into the computation, leading to more stringent confidence intervals.     

Fields over unsharp coordinates

It has been shown that space-time coordinates can exhibit only very few types of short-distance structures, if described by linear operators: they can be continuous, discrete, or "unsharp" in one of two ways. In the literature, various quantum gravity models of space-time at short distances point towards one of these two types of unsharpness. Here, we investigate the properties of fields over such unsharp coordinates. We find that these fields are continuous--but possess only a finite density of degrees of freedom, similar to fields on lattices. As a special case we recover the Shannon sampling theorem of information theory.     

Resurgence in quasiclassical scattering

In quasiclassical spectral theory, "resurgence" means that long periodic orbits can be expressed by short ones in such a way that the spectral determinant is real. The question has thus long been posed whether long scattering orbits can be expressed by short orbits in such a way as to make the quasiclassical scattering matrix unitary. We here find a resurgent and manifestly Hermitean expression for Wigner's R matrix, implying a unitary scattering matrix. The result is particularly important if the average resonance width is comparable with the average resonance spacing.     

A new approach to the theory of relativity. II. The general theory of relativity

The considerations of Part I are extended and the experimental data and hypotheses that led to the establishment of the general theory of relativity are analyzed. It is found that one of the fundamental assumptions is that light is propagated homogeneously; i.e., by using arbitrary systems of coordinates, propagation of light can be represented by a homogeneous quadratic form. This is shown to be an assumption that can be verified by experiment, at least in principle. As a result of adding a number of further assumptions to this, the usual formalism of the general theory of relativity can be established. In the above point of view, the general theory of relativity—like any other theory—cannot be built upad hoc, but is built on distinct physical hypotheses, each of which can be subjected to test by experiment.     

The gravitational anomaly: An elementary,coordinate-space approach

Alvarez-Gaumé and Witten have shown that energy-momentum conservation must be violated in certain parity-violating quantum field theories involving gravity. In two dimensions this effect can be studied without the aid of Feynman diagrams or calculations in momentum space. The arguments parallel those for the conformal (trace) anomaly; as in that case, there are two kinds of arguments, one based on the conservation equations themselves with some very general assumptions, and the other based on explicit calculations and renormalization in a model theory with a linear field equation. The basic point is that if matter is created at all by the gravitational field, it must appear in both left-moving and right-moving modes if the conservation law is to hold always.This essay received an honourable mention (1985) by the Gravity Research Foundation—Ed.     

Classical magnetostriction of nickel in high magnetic field

A simple model is proposed as a possible explanation for the checkerboard pattern of modulations in the hole density observed in recent tunneling experiments on underdoped cuprates. Two assumptions are made; first, an enhanced hole density near the acceptor dopants and secondly short range correlations in the positions of these dopants caused by their electrostatic and anisotropic elastic interactions. Together these can lead to a structure factor in qualitative agreement with experiment.     

A combination of laser-induced grating and transient-absorption experiments for investigation of laser pulse properties and fast molecular relaxation processes

A repetitive low-power laser-pulse apparatus has been developped which allows both absorption relaxation and light-induced grating experiments without changing geometry or components. The influence of pulse width and coherence time on the diffracted intensity correlation function is discussed for a weak amplitude grating in terms of a simplified theory. From the corresponding absorption relaxation signals including the coherent coupling contribution some easy ways for detecting vibronic-relaxation, intersystem-crossing and orientational-relaxation times are deduced. The advantage of the in-situ measurement of the amplitude grating autocorrelation function leads to a precise zero-delay calibration of the transient absorption equipment. Furthermore one gets the response function for the absorption experiments from the grating experiments, if stable mode-locking operation of the argon laser is reached. This condition can be controlled either by the time course of the absorption or grating signals. A surprisingly short coherence length is detected for the cavity-dumped laser beam. A reliable check of the coherent-coupling theory confirms the theoretical assumptions incorporated into the fast-relaxation signal analysis. Experiments on dye molecules show high triplet yield of heavy-atom substituted dyes and fast rotational diffusion of oblong molecular rotors.     

Determinant Bounds and the Matsubara UV Problem of Many-Fermion Systems

It is known that perturbation theory converges in fermionic field theory at weak coupling if the interaction and the covariance are summable and if certain determinants arising in the expansion can be bounded efficiently, e.g. if the covariance admits a Gram representation with a finite Gram constant. The covariances of the standard many–fermion systems do not fall into this class due to the slow decay of the covariance at large Matsubara frequency, giving rise to a UV problem in the integration over degrees of freedom with Matsubara frequencies larger than some Ω (usually the first step in a multiscale analysis). We show that these covariances do not have Gram representations on any separable Hilbert space. We then prove a general bound for determinants associated to chronological products which is stronger than the usual Gram bound and which applies to the many–fermion case. This allows us to prove convergence of the first integration step in a rather easy way, for a short–range interaction which can be arbitrarily strong, provided Ω is chosen large enough. Moreover, we give – for the first time – nonperturbative bounds on all scales for the case of scale decompositions of the propagator which do not impose cutoffs on the Matsubara frequency.     

Kochen-Specker Theorem as a Precondition for Quantum Computing

We study the relation between the Kochen-Specker theorem (the KS theorem) and quantum computing. The KS theorem rules out a realistic theory of the KS type. We consider the realistic theory of the KS type that the results of measurements are either +1 or ?1. We discuss an inconsistency between the realistic theory of the KS type and the controllability of quantum computing. We have to give up the controllability if we accept the realistic theory of the KS type. We discuss an inconsistency between the realistic theory of the KS type and the observability of quantum computing. We discuss the inconsistency by using the double-slit experiment as the most basic experiment in quantum mechanics. This experiment can be for an easy detector to a Pauli observable. We cannot accept the realistic theory of the KS type to simulate the double-slit experiment in a significant specific case. The realistic theory of the KS type can not depicture quantum detector. In short, we have to give up both the observability and the controllability if we accept the realistic theory of the KS type. Therefore, the KS theorem is a precondition for quantum computing, i.e., the realistic theory of the KS type should be ruled out.     

Numerical evaluation of boundary layer assumptions for laminar diffusion flames in microgravity

A systematic numerical study of a low Reynolds number laminar diffusion flame is presented. The configuration used is that of a boundary layer flow established over a flat plate burner. The importance of this configuration relies on its potential use for the assessment of the flammability of materials to be used in space vehicles. The study focuses on the validity of boundary layer formulations to the study of these flames. The characteristic velocities are representative of microgravity environments [O(100 mm/s)]. Parietal injection results eventually in flow separation establishing two characteristic regimes: non-separated and separated flows. Non-separated flows show an increased local acceleration but allow the use of two-dimensional assumptions at the plane of symmetry. It was demonstrated that classical boundary layer assumptions can be used if the flow is non-separated. Three-dimensional flow fields at the trailing edge of the injection zone characterize separated flows. Energy release enhances the positive pressure perturbations and leads to flow acceleration that cannot be damped by viscous shear. Acceleration appears at the vicinity of the flame, thus it is dramatically amplified by the decreased density in this region. Significant errors are generated if boundary layer assumptions are used to describe diffusion flames established in separated flows.     

Quantum Theory and the Limits of Objectivity

Three recent arguments seek to show that the universal applicability of unitary quantum theory is inconsistent with the assumption that a well-conducted measurement always has a definite physical outcome. In this paper I restate and analyze these arguments. The import of the first two is diminished by their dependence on assumptions about the outcomes of counterfactual measurements. But the third argument establishes its intended conclusion. Even if every well-conducted quantum measurement we ever make will have a definite physical outcome, this argument should make us reconsider the objectivity of that outcome.     

Near molecular-scale growth of natural minerals: Experimental methods and errors in length-dependent step speeds with scanning probe microscopy

Experimental observation of step (i.e., a linear discontinuity in a surface) growth on calcium carbonate and barium sulfate surfaces was performed using in situ scanning probe microscopy (SPM) in aqueous solutions. Step speeds at very short step lengths (<300 nm) were found to increase with step length, but scatter in the data precluded comparison of different theoretical models with regard to the experimental data. Analysis of experimental errors revealed that the data scatter was not unusual and further suggested that significant experimental bias in the determination of step properties such as the step free energy and kinetics of kink propagation and nucleation are introduced if the instrument bandwidth is not appropriate for the specific dynamics of the step. In light of step growth models based on either equilibrium assumptions or non-equilibrium assumptions, these biases tend to favor one model over the other.     

Local aspects of superselection rules

We study a theory of short range forces in terms of local observable quantities; among the superselection structure determined by the algebra of all local observables, to each additive independent charge we associate local observables having a meaning analogous to the regularized integrals of charge density fields over a finite volume. Among other assumptions, we require that parastatistics are absent from the theories considered.     

Gauge Fields in General Parametrical Approach and Their Finslerian Reduction

The covariance principle of general relativity is extended to internal space. Associated gauge fields and tensors are systematically described, whereupon the variational principle is set up for all gauge fields by applying a Palatini-type method, thereby giving rise to an attractive self-contained theory in which the Einstein equations are intrinsically synthesized with the generalized Yang-Mills equations. General gauge-covariant physical field equations are formulated, showing that currents, external + internal spin tensors, and energy-momentum tensors can be introduced unambiguously under these general conditions and that the associated conservation laws can be derived. The electromagnetic field finds its gauge-geometric origin as the gauge field related to internal densities. To be operative with the tensor indices of external and internal types, this general theory must be bimetric. The assumptions that the gauge-covariant derivatives of metric tensors should vanish simplify the theory to the level of a Finslerian gauge approach.     

Definition and existence of multichannel scattering states

The field theoretical formulation of quantum mechanics is used to consider the nonrelativistic multichannel scattering theory. With the help of appropriately constructed time dependent creation operators, Hilbert vectors are formed whose limits in time can be defined as multichannel scattering states in the usual sense. The existence of these states is proved under certain assumptions for the potential, by showing the convergence of the above mentioned operators. The commutation relations for the limits of these operators are given.     

Nonlinear vibration of carbon nanotube embedded in viscous elastic matrix under parametric excitation by nonlocal continuum theory

In the present work, the nonlinear vibration of a carbon nanotube which is subjected to the external parametric excitation is studied. By the nonlocal continuum theory and nonlinear von Kármán beam theory, the governing equation of the carbon nanotube is derived with the consideration of the large deformation. The principle parametric resonance of the nanotube is discussed and the approximation explicit solution is presented by the multiple scale method. Numerical calculations are performed. It can be observed that when the mode number is 1, the stable region can be significantly changed by the parametric excitation, length-to-diameter ratio and matrix stiffness. This phenomenon becomes different to appear if the mode number increases. Moreover, the small scale effects have great influences on the positive bifurcation point for the short carbon nanotube, and the nonlocal continuum theory can present the proper model.     

关于强磁场下输运过程的附注

这篇短文是对论文[1]的补充,同时也是对论文[2]中一些论点的答复,我们强调的一点是在久保公式中首先令ν→∞,然后令△t→∞,就会得到正确的输运系数,依据趋近平衡的理论来表达输运系数能使之充分确定,而在力学形式体系中它是不确定的,并且指出在输运理论中引进宏观流算符是不必要的。 关键词：