Abstract: We describe a class of continuously phase-modulated radiation pulses that result in coherent population inversion on resonance as well as over a large range of transition frequencies and radiation field strengths. This is a population-inversion analogy to self-induced transparency. Simulations of the inversion properties of the modulated inversion pulse (MIP) are presented. It is shown that the inversion behavior can be explained by treating the MIP as a highly efficient adiabatic sweep. Criteria for establishing adiabaticity are discussed in detail. Finally, a method is presented for generating a sequence of phase-shifted radio-frequency pulses, from the continuously modulated pulse, which can be implemented on modern NMR and coherent optical spectrometers; experimental confirmation is given.

Abstract: Etude des conditions de jonction pour un fluide isotropique sans cisaillement subissant un ecoulement de chaleur radiale avec un rayonnement non polarise sortant

Abstract: A generalization of reduced magnetohydrodynamics is constructed from moments of the Fokker–Planck equation. The new model uses familiar aspect‐ratio approximations but allows for (i) evolution as slow as the diamagnetic drift frequency, thereby including certain finite Larmor radius effects, (ii) pressure gradient terms in a generalized Ohm’s law, thus making accessible the adiabatic electron limit, and (iii) plasma compressibility, including the divergence of both parallel and perpendicular flows. The system is isothermal and surprisingly simple, involving only one additional field variable, i.e., four independent fields replace the three fields of reduced magnetohydrodynamics. It possesses a conserved energy. The model’s equilibrium limit is shown to reproduce not only the large‐aspect‐ratio Grad–Shafranov equation, but also such finite Larmor radius effects as the equilibrium ion parallel flow. Its linearized version reproduces, among other things, crucial physics of the long mean‐free‐path electron response. Nonlinearly, the four‐field model is shown to describe diffusion in stochastic magnetic fields with good qualitative accuracy.

Abstract: Theoretical Foundations Basic Description of the Rules Leading to the Adiabatic Elimination of Fast Variables Continued Fractions in the Theory of Relaxation Memory Function Methods in Solid State Physics Molecular Dynamics: Intense External Fields Non Linear Effects in Molecular Dynamics of the Liquid State Dynamical Properties of Hydrogen-Bonded Liquids Slow Motion EPR Spectra in Terms of a Generalized Langevin Equation The Theory of Chemical Reaction Rates Experimental Investigation on the Effect of Multiplicative Noise by Means of Electric Circuits Interdisciplinary Subjects: The Time Properties of a Model of Random Fluctuating Selection Stochastic Processes in Astrophysics: Stellar Formation and Galactic Evolution Author and Subject Indexes.

Abstract: The dynamic features of combustion are discussed for four important cases: ignition, inflammation, explosion, and detonation. Ignition, the initiation of a self-sustained exothermic process, is considered in the simplest case of a closed thermodynamic system and its stochastic distribution. Inflammation, the initiation and propagation of self-sustained flames, is presented for turbulent flow. Explosion, the dynamic effects caused by the deposition of exothermic energy in a compressible medium, is illustrated by self-similar blast waves with energy deposition at the front and the adiabatic non-self-similar wave. Detonation, the most comprehensive illustration of all the dynamic effects of combustion, is discussed with a phenomenological account of the development and structure of the wave.

Abstract: Time evolution of hot drops of matter containing approx.230 or approx.130 particles is studied by classical molecular dynamics. Initially, the drops have uniform density and a sharp surface. The chosen initial conditions include three values of density and a range of temperatures wide enough to study the phenomena of evaporation, fragmentation, and total vaporization in a unified fashion. The average density and temperature of central matter is measured periodically to obtain trajectories of the evolution in the rho,T plane. These trajectories indicate that the matter expands almost adiabatically until it reaches the region of adiabatic instabilities. Density inhomogeneities develop in this region, but the matter fragments only if the expansion continues to average densities of less than one-fourth the liquid density, otherwise it recondenses into a single blob. The recondensed matter and fragments have very crooked surfaces. If the temperature is high enough, the expanding matter does not enter the region of adiabatic instabilities and totally vaporizes. For initial densities of the order of equilibrium density, matter does not fragment or develop large inhomogeneities in the region enclosed by the isothermal and adiabatic spinodals. Thus it appears unlikely that fragmentation of small drops (nuclei) can be used to study themore » isothermal critical region of gas-liquid phase transition. A detailed tabulation of the energies and number of monomers, dimers, light, and heavy fragments emitted in each event is presented.« less

Abstract: The nonlinear evolution of the free-electron-laser amplifier is investigated numerically for a configuration consisting of a helical wiggler and axial guide magnetic fields. A set of coupled nonlinear differential equations is derived in three dimensions which governs the self-consistent evolution of either the TE or TM modes in a loss-free cylindrical waveguide and the trajectories of an ensemble of electrons. The initial conditions are chosen to model the adiabatic injection of a cold, cylindrically symmetric electron beam into an interaction region in which the wiggler amplitude rises slowly from zero to a constant level in ten wiggler periods. Both self-field and space-charge effects have been neglected in the formulation, and the analysis is valid for the high-gain Compton regime of operation. Numerical simulations are conducted to model an amplifier operating in the neighborhood of 35 GHz, and for electron-beam energies of 250 keV and 1 MeV. (The free-electron-laser operating at electron-beam energies less than 500 keV is called the ubitron.) The growth rate in the linear regime prior to saturation is found to be in substantial agreement with the predictions based on a linear theory of the instability, and the saturation efficiency is consistent with that expected on the basismore » of simple, heuristic phase-trapping arguments. Substantial enhancements in the efficiency are found to occur due to the presence of the axial guide field.« less

Abstract: : We have developed a numerical model to study the steady state behavior of a fully ionized plasma (H+, O+ and the electrons) encompassing the geomagnetic field lines. The theoretical formulation is based on the 16-moment system of transport equations. The electron gas is collision is dominated below 2500 km. Above this altitude electron temperature anisotropy develops with temperature perpendicular to the field line being higher than that parallel to the field line. The H+ ion temperature anisotropy shows H+ temperature parallel to the field line being higher than that perpendicular to the field line. H+ ion temperature also exhibits adiabatic cooling as to the supersonic ion gas cools down as it expands in a diverging magnetic field. Our results are in good agreement with the pervious theoretical studies of the polar wind and recent experimental observations. This is the first successful steady state solution to the 16-moment set of transport equations. Keywords include: Polar wind, Temperature anisotropy, and Adiabatic cooling.

Abstract: It is well known that acoustic disturbances incident upon the boundary layer may cause Tollmien-Schlichting waves. An intense generation of these waves is observed in local inhomogeneities of the flow [1]. To investigate this phenomenon we shall consider a two-dimensional gas flow about a flat plate directed along a free-stream flow (fig.1). The free-stream velocity U∞ is taken to be subsonic with M < 1. Introduce cartesian coordinates x′, y′ aligning their origin with the plate leading edge and orienting x′ along the plate surface. Denote velocity vector components in this coordinate system by u′ and v′, density by p′, and viscosity coefficient by μ′ . Let the gas under consideration have an adiabatic constant r and its thermodynamic state be described by the Clapeyron equation.

Abstract: A set of coordinates suitable for the three-body problem is introduced. In this case the three-body wavefunction possesses the remarkable property of being compatible with the physical boundary conditions in the adiabatic representation.

Abstract: A Matter of Stability: Professor Paul Ledoux.- Irregular Stellar Variability.- Cosmic Arrhythmias.- A Perturbative Approach to Stellar Pulsations.- Chaos and Noise.- Clues to Strange Attractors.- Information Aspects of Strange Attractors.- On the Rapid Generation of Magnetic Fields.- Ordered and Chaotic Motions in Hamiltonian Systems and the Problems of Energy Partition.- The Transition to Chaos in Galactic Models of Two and Three Degrees of Freedom.- Nonlinear Nonradial Adiabatic Stellar Oscillations: Numerical Results for Many-Mode Couplings.- Chaotic Oscillations in a Simple Stellar Model - A Mechanism for Irregular Variability.- X-Ray Bursters - The Hot Road to Chaos?.- Compressible MHD Turbulence: An Efficient Mechanism to Heat Stellar Coronae.

Abstract: One of us has previously developed a technique for obtaining the leading terms in a perturbation expansion of the Born–Oppenheimer energies and derivative couplings for the X3 system near the conical intersection at a C3v configuration. In a preceding paper, these leading terms have been utilized to study various aspects of the adiabatic approximation for both model and real systems of this type. In the present article, this technique is generalized and extended to all orders, yielding rigorous functional forms for both energies and derivative couplings. In particular, the ‘‘nonremovable’’ part of the derivative coupling, which cannot be transformed away by going to a diabatic basis, is explicitly exhibited. Convenient approximations for both removable and nonremovable couplings are also obtained. These should facilitate the estimation of the effect of the different couplings in various situations.

Abstract: From 3 to 10% of the time, the solar wind has a radial proton temperature between 15,000/sup 0/K and 3500/sup 0/K (the lowest recorded temperature). This ''cold'' component shows some very important features that make it worthy of special study. It shows a temperature dependence on heliocentric distance that is nearly adiabatic. When extrapolated back to 3 R/sub s/, assuming adiabatic cooling, the resulting temperature for this cold component is in good agreement with coronal temperatures near the sonic point. Most importantly, the proton velocities and densities associated with this cold component match those predicted by solar wind models that do not incorporate significant wave heating. We conclude that this is one solar wind component that fit well with appropriate models.

Abstract: The concept of time in quantal tunneling processes is reexamined. We find that the Wigner–Eisenbud definition of real time and the definition of imaginary time may be understood in terms of stationary phase analysis in complex time of the microcanonical flux–flux correlation function. This analysis explains why the real time should not be used to justify adiabatic approximations for perpendicular degrees of freedom at tunneling energies. A semiclassical analysis shows that, as suggested by Buettiker and Landauer, the imaginary time should be used to determine the validity of the adiabatic approximation for tunneling processes. Numerical examples for the hydrogen exchange reaction are provided. The implications on adiabatic and sudden approximations in reactive scattering are discussed. A theory unifying the two approaches is outlined.

Abstract: The formation of adiabatic shear bands in ductile metals under dynamic loading conditions is generally thought to result from a material instability, which is associated with a peak in the curve of engineering plastic flow stress vs. engineering shear strain. This instability arises from the effect of thermal softening, caused by irreversible adiabatic heating, which counteracts the tendency of the material to harden with increasing plastic strain. An approximate linear stability analysis of a one-dimensional rigid-thermoviscoplastic model, based on data taken from dynamic torsion experiments on thin-walled tubes of mild steel, shows that shear band formation in this situation can be interpreted as a bifurcation from a homogeneous simple shearing deformation which occurs at the peak in the homogeneous stess vs. strain curve. The asymptotic method of multiple scales is used to show that the growth rate of small perturbations on the homogeneous deformation is controlled by the ratio of the slope of the homogeneous stress vs. strain curve to the material viscosity, i.e., the rate of change of the plastic flow stress with respect to the strain-rate. In addition, it is shown that this growth rate is essentially independent of wavelength in any small perturbation. Numerical methods are usedmore » to show that this growth rate beyond the bifurcation point may not be sufficiently large for the model to account for the experimental data, and some suggestions are made on how to modify the constitutive equation so that it better fits the experimental data.« less

Abstract: Adiabatic positive displacement gas cycle machinery is designed with explicit control of the heat flow between the gas and the walls. The control is achieved by maintaining near-laminar flow and a small wall area to volume ratio. The most stable near-laminar flow in a cylinder is an axial vortex because of symmetry, and hence the induction port design should establish an axial vortex and a low velocity. Induction and exhaust port designs to achieve this flow are applied to a vane pump, an adiabatic air compressor, a diesel engine, and two and four stroke Otto cycle engines. The gain in thermal efficiency for these designs can be significant, up to a factor of 2, since the largest inefficiency in nearly all positive displacement machinery is imperfect control of heat flow.

Abstract: The authors report results on one- and two-photon detachment cross sections of negative hydrogen ions from the 1Se ground state in lowest-order perturbation theory using an adiabatic hyperspherical approximation.

Abstract: In order to improve the Born–Oppenheimer treatment of adiabaticity we impose to the electronic and nuclear wave functions to have a well defined phase difference. It enables us to correctly evaluate matrix elements of such quantities as momenta which are poorly evaluated in the Born–Oppenheimer description. The phase factor obeys an equation which we solve by successive approximations and leads to simple expressions for this phase factor. Taking the coupling of two harmonic oscillators as an exactly soluble example which may also be treated within this adiabatic approximation we show that the proposed formalism is rather easy to use and leads to significant improvements with respect to Born–Oppenheimer treatments. We suggest that this framework might be useful when treating systems which are weakly coupled but are not so different in their time evolutions as are electrons and nuclei.

Abstract: The Eisenbud–Wigner time delay matrix is used to study the dynamics of reaction close to vibrationally adiabatic barrier energies. Maxima in the time delay are predicted and are found to be in excellent agreement with vibrationally adiabatic barrier energies determined by quantized pods. The actual time spent in the vicinity of the barriers is estimated by separating out the free particle time. This ‘‘real time’’ is then used to analyze the validity of the adiabatic and sudden approaches to reactive scattering in the 3D H+H2 and D+H2 reactions.

Abstract: On reevalue des donnees trouvees dans une precedente etude sur le transfert de chaleur par convection a partir de jets au plafond dus a un parametre flottant, et on developpe une estimation independante pour de la distribution de temperature au plafond. L'analyse prend en compte les effets de radiation du plafond et on utilise la similarite etablie anterieurement entre le phenomene de transfert de chaleur mur/jet et panache/plafond

Abstract: Neutral exospheric temperatures from Thomson scatter measurements made between 1970 and 1980 at Millstone Hill (426°N) are examined for seasonal and solar cycle variations during geomagnetically undisturbed times Analysis reveals unexpectedly large diurnal temperature amplitudes during solar cycle 21 at moderate to high levels of solar activity pointing to the increased role of ion drag in the adiabatic compression of the thermosphere A heuristic model assuming momentum balance between the pressure gradient and ion drag, and thermal balance between EUV heating, its vertical conduction and adiabatic compression serves to illustrate modulation of adiabatic cooling efficiency by enhanced ion drag effect

Abstract: We derive and discuss the behavior of several multilevel models relevant to the problem of molecular multiphoton excitation under the action of a quasimonochromatic laser field, the amplitude of which rises slowly and falls rapidly on a certain internal time scale. Our method is suitable for the numerical solution of problems involving the adiabatic excitation of large multilevel systems. We find adiabatic inversion to be a general characteristic of the models considered. The fact that adiabatic inversion is accompanied by marked qualitative and quantitative changes in the expectation value of the dipole operator makes our results useful for understanding the propagation of laser pulses. An explicit expression that is especially convenient for numerical evaluation is presented for determining the limiting internal time scale, which is determined by the energy levels and transition moments of the system and the laser frequency. We illustrate the criterion for adiabatic inversion by applying it to a particular multilevel model. From a density-matrix treatment we conclude that collisional damping destroys the coherence required for adiabatic inversion. On the basis of our results we believe that the adiabatic approximation may be appropriate for some experiments of current interest.

Abstract: In this short contribution we present a commentary on the interpretation of our thermal activation data obtained in the quantum regime of a SQUID, as discussed in part I [Bol et al., Physica B 133 (1985) 196]. Under certain circumstances a superconducting ring containing a weak superconducting junction, a SQUID, has two metastable magnetic flux states separated by a potential energy barrier ΔV. In this metabistable system stochastic magnetic flux transitions were observed due to intrinsic thermal activation. It was found that the transition rate was strongly reduced compared with the predictions of the classical thermal activation theory of Kramers or with the modern thermal activation theory of Grabert and Weiss which is an extension to the quantum regime where kT ⪅ h ω0 (ω0 being the free oscillation frequency corresponding to the metastable potential well). In these theories the transition rate is proportional to exp(-ΔV/kT), in which V is treated as a temperature independence potential just as in the case in microscopic activated processes. In fact, however, from the thermodynamic point of view the relevant quantity in the exponent is the magnetic availability of the system with respect to the surroundings fixed by the temperature of the heat bath and the external magnetic field. Only when the system is completely isothermal can the potential V be identified with the Gibbs function. But in general when a flux transition takes place between the metastable potential wells, some energy will be dissipated possibly causing a temporary temperature rise due to self-heating. In principle, therefore, the system behaves neither perfectly isothermal nor adiabatic.