Table of contents

It is shown that if the Lorentz condition is discarded, the Maxwell–Heaviside field equations become the Lehnert equations, indicating the presence of charge density and current density in the vacuum. The Lehnert equations are a subset of the O(3) Yang–Mills field equations. Charge and current density in the vacuum are defined straightforwardly in terms of the vector potential and scalar potential, and are conceptually similar to Maxwell's displacement current, which also occurs in the classical vacuum. A demonstration is made of the existence of a time dependent classical vacuum polarization which appears if the Lorentz condition is discarded. Vacuum charge and current appear phenomenologically in the Lehnert equations but fundamentally in the O(3) Yang–Mills theory of classical electrodynamics. The latter also allows for the possibility of the existence of vacuum topological magnetic charge density and topological magnetic current density. Both O(3) and Lehnert equations are superior to the Maxwell–Heaviside equations in being able to describe phenomena not amenable to the latter. In theory, devices can be made to extract the energy associated with vacuum charge and current.

We study an N-component, symmetrically coupled system of Korteweg-de Vries (KdV) equations that is integrable in the context of the sl(N + 1) AKNS hierarchy. We show how the coupled system can be solved through a combination of the well-known inverse-scattering transform for (one-component) KdV and the solution of a linear equation with nonconstant coefficients. The coupled KdV system may be viewed as a phenomenological model for the sharing of mass among interacting solitons of the (one-component) KdV equation. Results for the scattering theory of solutions of the nonconstant coefficient linear equation arising in the solution of the coupled system are used to quantify the redistribution of mass during soliton collisions within the framework of the coupled KdV model.

The Carleman embedding method is applied to find the first integrals of nonlinear acoustic gravity wave equations. Several new results are obtained.

Equations for geodesic deviation (GDE) are deduced for the space-time metric of Gödel type. The equation turns out to be a matrix Schrödinger problem. It is then demonstrated that one can generate nonlinear equations for the coefficient functions of the metric if a "time" evolution equation is adjoined to the GDE. Soliton like solutions for the metric functions can be obtained through an inverse scattering transform of the matrix Schrödinger problem. Thereby a solution of the GDE equation is also determined by the wave function of the IST.

Accelerator mass spectrometry (AMS) is a highly sensitive method for counting atoms. It is used for detecting very low concentrations of both radionuclides and stable nuclides. The main advantages of AMS compared to conventional radiometric methods are the use of smaller samples (mg size) and shorter measuring times (less than one hour). In AMS, rare isotopes from a sample material placed in the ion source of an electrostatic tandem accelerator are measured by counting individual atoms with nuclear detection techniques after acceleration to energies in the MeV range. A dramatic improvement in background rejection for AMS systems has, in the best cases, led to a 10⁸ increase in sensitivity for isotope ratio measurements compared to the older technique of mass spectrometry. In this report some current applications of the AMS technique at the Lund Pelletron accelerator, as well as the recent improvements of the Lund system, are presented.

We argue that the commonly used procedure of extracting the static potential from lattice Wilson loop measurements may contain an underestimated systematic uncertainty at large quark separations. To illustrate the point, we extract the potential by the standard lattice method in a model vacuum made of instantons. A beautiful infinitely rising linear potential is obtained in the case where the true potential is in fact flattening. We argue that the flux tube formation might also be an artifact of the lattice procedure and not necessarily a measured physical effect.

We conclude that at present the rising potential is known for sure up to no more than about 0.7 fm. It may explain why no screening has been clearly observed so far for adjoint sources or for fundamental sources but with dynamical fermions.

Finally, we speculate on how confinement could be achieved despite the absense of the infinitely rising potential in the pure glue theory.

In this paper the equation of state of hot neutron matter is calculated. Involving the Oppenheimer-Volkov-Tolman equation global parameters of a neutron star at finite temperature are obtained.

Excitation functions for ⁸⁹Y [(α,3n); (α,4n); (α,p3n); (α,αn); (α,α2n)] reactions were measured up to 50 MeV using stacked foil activation technique and HPGe gamma ray spectroscopy method. The experimental data were compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann (ALICE/90). For (α,xnyp) type of reactions, the precompound contributions are described by the model. There seems to be indications of direct inelastic scattering effects in (α,αxn) type of reactions. To the best of our knowledge, the excitation functions for (α,4n), (α,p3n), (α,αn) and (α,α2n) reactions were measured for the first time.

A plasma of argon produced with a plasma focus discharge has been observed between 3.8 and 4.2 Å. Spectra registered with a spectral resolution of 0.03 Å/mm show satellite lines of Ar which were measured and compared with two independent theoretical calculations. Seven transitions of Li-like, eleven of Be-like. twelve of B-like, twenty of C-like, nine of N-like, seven of O-like and two of F-like argon have been identified. The agreement between the observations and the calculations and also between the two sets of calculations is generally good.

Core-polarization and configuration interaction effects are investigated in singly ionized copper. It is shown that these effects are responsible, to a large extent, for the discrepancies observed between recent relativistic Hartree–Fock (HFR) and configuration-interaction (CIV3) calculations and accurate beam-laser experimental results. A new set of transition rates is obtained using the HFR + Core Polarization formalism leading to theoretical lifetime and transition probability values in fair agreement with the experiment. An indicative calculation performed with the configuration - interaction code SUPERSTRUCTURE demonstrates the importance of semi-empirical term energy corrections in producing reliable transition rates in a case like the present one.

The foreign-gas broadening parameters for fluoroform molecules interacting with spherical (He, Ne, Ar, Kr, Xe, CH₄, CCl₄) perturbers have been measured. The results are pressure broadening coefficients (in kHz/Pa) for J = 1 ← 0 transition of CHF₃: C_w(He) = 23.8±0.4, C_w(Ne) = 16.4±0.5, C_w(Ar) = 18.5±0.4, C_w(Kr) = 19.7±0.6, C_w(Xe) = 21.7±0.5, C_w(CH4) = 26.3±0.7, C_w(CCl4) = 34.7±0.7. Experimental linewidth parameters are interpreted using Anderson–Tsao–Curnutte as well as Murphy–Boggs theories for the mixed-interactions case. The first-order London dispersion forces, induction forces and exchange forces were taken into account.

The work reports the calculation of cross sections of inelastic electron scattering on metallic La, exciting the inner 3d-shell. The calculations are based on an atomic physics description of the triply ionized free atom. The large spin-orbit coupling constant of the 3d-hole leads to an approximate jK-coupling. The resulting excitation strength is formulated in terms of the Born amplitude including resonant contributions. The intensity is folded with a Lorentzian broadening with full width at half maximum (FWHM) parameter Γ. This parameter is considered to be dependent on the projectile electron energy so that the dynamic effects found in experimental EELS may be addressed. The systematic variation of the relative intensities of the spin-orbit doublet structures with excitation energy found in experiment is partly accounted for as Γ is varied from the experimentally measured values of 0.7 eV–0.5 eV and beyond.

The asymptotic theory is used for evaluation of the cross section of resonant charge exchange for most elements of the periodical system. An analysis is given of the accuracy of the data obtained. The error for the cross sections at collision energies of the order of 1 eV varies from 1% for hydrogen and elements of the first and second groups of the periodic table up to about 10% for elements of intermediate groups where coupling of electrons of the valent electron shell is of importance and the accuracy of the atomic wave function for transiting electrons at large distances from the core is less.

The method of superposition of configurations has been used to obtain accurate oscillator strengths and transition probabilities for transitions between the 3s²3p^5 2P° ground state and the 3s3p⁶, 3s²3p⁴3d and 3s²3p⁴4s states of doubly-ionized potassium, triply-ionized calcium and four-times-ionized scandium. The CIV3 code was used to perform calculations both in LS coupling and in intermediate (or LSJ) coupling, using an extensive set of correlation configurations. The present results are believed to be the most accurate available and are compared with previous theoretical work.

The reflection from a semi-infinite chiral medium is analyzed rigourously by obtaining the Fresnel coefficients of reflection as well as the depolarization coefficients for the case of illumination by a plane wave with linear polarization. The chiral material is described electromagnetically by the constitutive relations D = ε₀E + iξ_cB and H = iξ_cE + (1/µµ₀)B, where ε_ij = ε_⊥(δ_ij - n_in_j) + ε_IIn_in_j is the dielectric tensor of the chiral substrate (z ≤ 0), n is the normal vector to the half-space, µ is the magnetic permeability, ε₀ and µ₀ are vacuum permittivity and permeability, ξ_c[Ω^-1] is the chiral component of the polymer admittance. The constants ε_⊥(ω), ε_II(ω), ξ_c(ω), µ(ω) are supposed to be complex and to have values that are determined by usual ellipsometric measurements. For small values of the dimensionless chirality parameter |g_c| = √(µ₀/ε₀)|ξ_c| and by supposing ε_⊥ = ε_II = ε = ε₁ + iε₂, µ = 1 (the isotropic nonmagnetic case) and appropriate perturbation theory is developed. Ellipsometric characterization (and its interpretation) for the polymer sample P7MB (poli-bi-benzoate with spacers containing 7 ethylene units) is given.

A high power laser of finite spot size, propagating through a high Z plasma embedded with light ions, exerts ponderomotive forces on the electrons. As the electrons move out of the axial region, a strong space charge field sets in that pulls the lighter and heavier ions together with the electrons. Thus a plasma channel evolves on a time scale τ = r₀/c_s where r₀ is the spot size of the laser and c_s is the characteristic sound speed. The ratio of fractional ion depletion to heavy ion depletion from the axial region is (Δn_l/n_l)/(Δn_h/n_h) = m_hZ_ln⁰_0l/m_lZ_hn⁰_0h where m_h and m_l are the heavy and light ion masses, Z_h and Z_l, are the heavy and light ion charges, n_h and n_l are the heavy and light ion densities respectively. The channel is capable of self-ducting/self-focusing the laser when the power of the laser exceeds a threshold value.

An electrostatic collisional sheath of a dusty plasma is investigated. The plasma is assumed to be highly neutralized so that most collisions arise from the interaction between ions and neutral gas. Dust particles are considered as spherical grains whose charges can be determined by the collisional probe theory. We assume that the dust particles are motionless with uniform density. It is shown that the species of neutral gas as well as the ion to electron density ratio can have a strong influence on the sheath potential profile and dust charges.

The full nonlinear evolution of a four-field plasma model with vanishing resistivity reveals that the eventual nonlinear saturation regime is markedly different from extrapolations suggested by investigations of the early nonlinear stage, and that topological transitions akin to filamentation in pressure and current density occur, driven by the nonlinear evolution of the fluid motion.

The energy loss of a test charge in an unmagnetized dusty plasma is estimated for different dust parameters (such as dust charge state, dust number density, dust charge fluctuations and dust-neutral collisions) using Krook and BGK-type collisional models. We find that the higher the dust-charge-state the more pronounced is the wake-fleld (which extends up to several Debye lengths). The variation of the dust number density shows a similar behavior. For large dust-neutral collisions a weakly damped large amplitude wake-field is observed which jumps ahead of the test charge position for higher collision frequencies. The dust neutral collisions are also found to enhance the energy loss for test charge velocities greater than the dust acoustic speeds in contrast with the dust charge fluctuations which enhances the energy loss only for test charge velocities smaller than the dust acoustic speeds.

Under sealed blackbody cavity conditions, pressure gradients typically take three forms: (a) statistical fluctuations, (b) transients associated with the system relaxing toward equilibrium, and (c) equilibrium pressure gradients, such as those associated with static gravitational potentials. In this paper a new type of pressure gradient is introduced, one which arises if a gravitator has surfaces with different trapping probabilities for suprathermal gas collisions. Three-dimensional test particle simulations of this system using realistic physical parameters support this hypothesis. This gas phase is inherently nonequilibrium in character and represents an unstudied thermodynamic regime involving low-density gas-surface interactions. This is the gravitational analog of a previously studied, chemically-induced pressure gradient (D P Sheehan 1998 Phys. Rev. E 57 6660).