For the Lyman-α line of Ti xxii emitted from the JT-60 tokamak plasma, the intensity ratio of its fine-structure components (1 ${}_{}{}^2{}_{}{}^{}$${\mathit{S}}_{1/2–}$2 ${}_{}{}^2{}_{}{}^{}$${\mathit{P}}_{1/2,3/2}$) has been measured with a crystal spectrometer. Dependences of the ratio on plasma parameters have been investigated systematically in discharges with various heating modes. The ratio is found to vary by ∼10%. No satisfactory interpretation is given to the observed variation.

The classical method of moments is applied to determine the dispersion law of the quasi-two-dimensional Coulomb-system soft collective mode. An interpolation formula is found for the longitudinal dielectric permeability, satisfying all known exact relations and sum rules. The sum rules (the inverse-dielectric-permeability imaginary-part frequency moments) are calculated, taking into account the magnetic interaction between electrons.

Electron distribution functions in nonthermal cold plasmas generated by classical electrical discharges have been calculated from a powerful Boltzmann equation solution and an original Monte Carlo simulation. In these two methods both classical (i.e., elastic, inelastic, and superelastic) electron-atom (or molecule) collisions and electron-electron interactions are taken into account. The approximations considered to include long-range (electron-electron) and short-range (electron-atom) interactions in the same Monte Carlo algorithm are first validated by comparing with Boltzmann equation results. Then, the influence of electron-electron interactions on electron distribution functions, swarm parameters, and reaction rates under nonthermal cold plasma conditions are analyzed and discussed as a function of reduced electric field E/N and ionization degree ${\mathit{n}}_{\mathit{e}}$/N for different atomic and molecular gases.

We report accurate measurements of excess electron mobility in high-density Ar gas at a temperature T≃163 K in the density range (4<N<70)×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$ as a function of the electric-field strength. The positive-density effect shown by the zero-field density-normalized mobility ${\mathrm{\mu }}_0$N can be explained within the same theoretical framework recently used for neon gas, where ${\mathrm{\mu }}_0$N shows a negative-density effect. Thus the analysis of our present measurements indicates that there is no need for two separate theories for both negative- and positive-scattering-length gases.

Nonthermal dusty plasmas can be found in plasma-processing applications as well as in space phsyics. A model based on a particle-in-cell Monte Carlo simulation has been developed to study the physical properties of such plasmas and the plasma-dust particle interactions. Assuming a uniform dusty plasma with a given size and concentration of dust particles, the model provides self-consistently the average electric field necessary to sustain the plasma for a given current density flowing through it, the charge and floating potential of the dust particles, the potential distribution, and the velocity distribution functions of electrons and positive ions. The model has been applied to situations where the distance between dust particles is much smaller than the electron Debye length (particulates interact electrostatically with each other) as well as situations where the distance between dust particles is larger than the Debye length (particulates are isolated electrostatically from each other). Questions concerning the momentum and energy transfer from electrons and ions to dust particles are also discussed. Simple scaling laws are also derived and compared with the numerical results.

Self-consistent fluid and particle-in-cell Monte Carlo (PIC-MC) models in conjunction with experimental measurements have been used to study the electrical characteristics of rf discharges in pure argon and in argon contaminated with dust particles (at 0.11 torr argon, 13.56 MHz). In the experiments, the dust particles were first created in a silane-argon rf discharge and subsequently trapped in an argon discharge in order to stop the growth process. The concentration and radius of the dust particles were measured experimentally and found equal to ${10}^8$ ${\mathrm{cm}}^{\mathrm{-}3}$ and 0.05 μm, respectively. The PIC-MC discharge model has been used to check the validity of the fluid model in pure argon. The discharge in dusty argon has been described with a fluid model modified to account for the presence of dust particles. This model uses as input data the number of negative charges carried by the dust particles and the frequency of electron loss to the particles deduced from a two-dimensional particle-in-cell Monte Carlo simulation of a dusty dc plasma. The results show good agreement between experiments and models within the whole range of rf voltages considered and for the pure and dusty argon plasmas. The presence of dust particles in the plasma modifies considerably the discharge impedance, which becomes much more resistive. The electron number density in the plasma is much smaller than the positive ion density and than the number density of negative charges carried by the dust particles. It appears that the phase shift between current and voltage is very sensitive to the presence of powders. This property could be useful for the detection of powder formation in a processing plasma.

We derive here a one-dimensional generalized dispersion relation for a free-electron laser, describing, at the same time, the steady-state instability, the superradiant instability, and the sideband instability. Intermediate forms of instability are discussed, where the sideband instability and the superradiant instability are seen to occur together. Numerical simulations have been carried out in order to test the analytical results and investigate the nonlinear evolution of the perturbation of different equilibrium states. We show that both the superradiant instability and the sideband instability can lead to the growth of superradiant spikes.

The nonlinear beam dynamics of transverse betatron oscillations were studied experimentally at the Indiana University Cyclotron Facility cooler ring. Motion in one dimension was measured for betatron tunes near the third, fourth, fifth, and seventh integer resonances. This motion is described by coupling between the transverse modes of motion and nonlinear field errors. The Hamiltonian for nonlinear particle motion near the third- and fourth-integer-resonance conditions has been deduced.

The Burgers equation is solved for Reynolds numbers ≲8000 in a representation using coarse-scale scaling functions and a subset of the wavelets at finer scales of resolution. Situations are studied in which the solution develops a shocklike discontinuity. Extra wavelets are kept for several levels of higher resolution in the neighborhood of this discontinuity. Algorithms are presented for the calculation of matrix elements of first- and second-derivative operators and a useful product operation in this truncated wavelet basis. The time evolution of the system is followed using an implicit time-stepping computer code. An adaptive algorithm is presented which allows the code to follow a moving shock front in a system with periodic boundary conditions.

The elastic deformation and adhesion of two convex bodies that interact via surface forces of finite range are calculated self-consistently. Hertz theory is compared to the result of an exponential repulsion, and it is found to be valid in the limit of short-ranged forces and high loads. A Lennard-Jones law is used to examine the classical theories of adhesion, which relate the surface energy to the pull-off force, and their regime of validity is explored. Explicit expressions are given for the displacement prior to contact, and for the jump instabilities due to elastic deformation, which occur for compliant bodies with rapidly changing surface forces. The loading-unloading cycle is shown to be hysteretic for large adhesions, and this is correlated with the onset of jumps. In these cases the pull-off force is demonstrated to depend upon the history of the sample, and it increases with increasing maximum applied loads.

We consider a nonlinear diatomic lattice of the Klein-Gordon type composed of particles with two different masses. The linear spectrum of this model exhibits a gap, which is proportional to the mass difference in addition to the natural gap stipulated by a nonlinear substrate potential. We analyze the coupled nonlinear excitations of such a diatomic chain which have a similar origin as the well-known gap solitons appearing in nonlinear (e.g., optical) systems with a spatial periodicity. We also describe dark-profile localized structures with a frequency lying below the gap. In the limit when the gap disappears, i.e., for the case of a monoatomic chain, the gap solitons do not exist but instead there exist localized structures of a distinct type created by the nonlinearity-induced symmetry breaking between two equivalent eigenmodes of the lattice, the so-called self-supporting gap solitons.

A unified variational theory is developed for collapse, folding, and glass transitions of the proteins modeled by associative-memory Hamiltonians. The mechanisms and conditions of transitions are studied, and the phase diagram is discussed. A quantitative measure of feasibility of folding and an upper bound of memory capacity are derived. The variational method gives several insights to improve simulations for protein-structure predictions.

Reflection interference microscopy in combination with real-time image processing was applied to determine the spatial spectrum of the mean-square amplitude of erythrocyte flickering in the wave-vector regime 0.3≤q≤4 μ${\mathrm{m}}^{\mathrm{-}1}$. The mean-square amplitude scales as ${\mathit{q}}^{4\pm \mathrm{\epsilon }}$ for q≥0.7 μ${\mathrm{m}}^{\mathrm{-}1}$, suggesting that flickering is dominated mainly by bending stiffness. We measured a bending modulus of ${\mathit{K}}_{\mathit{c}}$=(2±0.5)×${10}^{\mathrm{-}20}$ N m as compared to ${\mathit{K}}_{\mathit{c}}$=(5±1.5)×${10}^{\mathrm{-}20}$ N m found for dimyristoylphosphatidylcholine (DMPC) vesicles with the same technique.

We have modified the self-consistent phonon approach to treat DNA double helices modeled with a large repeating unit (N base pairs) so that melting behaviors of DNA polymers of various base-pair sequences can be studied. The melting temperatures of DNA polymers of different G-C–to–A-T ratios were calculated (G, C, A, and T denote guanine, cytosine, adenine, and thymine, respectively). It is shown that a DNA polymer with a relatively higher content of A-T melts at a lower temperature than DNA with a higher content of G-C. The melting temperature increases linearly when the G-C content in a DNA polymer increases. This is in agreement with both experimental observations and theoretical analysis.

A simple and accurate formula for the first derivative of the hard-sphere radial distribution function at contact as a function of density is proposed, suggested by the solution of the Percus-Yevick equation for a fluid of hard spheres.

We discuss scaling properties of random walks, density of states, and crossover behavior in a bifractal, which is defined as a Cartesian product of two fractals.

The decay of a metastable state is studied by means of a functional-integral approach. Depending on the shape of the potential barrier, the crossover from thermal activation to thermally assisted quantum tunneling is either a first- or second-order phase transition on temperature. Below the crossover temperature, first-order transitions between different tunneling regimes are possible. The general features of these transitions, and the possibilities to observe them, are discussed.

This work presents a semiclassical calculation for the time-dependent transition rates (TDTR’s) of a multilevel quantum system interacting with a reservoir characterized by a power-law distribution of relaxation times. Some simple asymptotic expressions for these TDTR’s are given, which can be very useful in order to be used in non-Markovian master equations.

Recently, Liem, Brown, and Clarke [Phys. Rev. A 45, 3706 (1992)] have compared the results obtained from the homogeneous-shear and the sliding-boundary nonequilibrium molecular-dynamics methods to generate shear flow. Here the comparison is carried out by using a kinetic theory description.

We reexamine the frequency conversion of radiation pulses in the presence of electron plasma waves. An analytical formulation, describing the dependence of pulse frequency on the plasma density and electron-density perturbation, is derived from the plasma dispersion relation and phase-matching condition. The basic issues of photon-accelerator schemes are discussed based upon the calculation results.