Charge transfer and rapidity gap analysis inp(π+)n interactions at 195GeV/c

We present charge transfer probabilities between CM hemispheres inpn and π⁺ n interactions at 195 GeV/c. The relative probabilities for charge exchanges |ΔQ|>1 as a function of rapidity gap length,r, are given. Both results are compared with those of π^? p interactions at 200GeV/c. The average ofr, viz. <r>, is given as a function of the gap number and of ΔQ for various multiplicities, and the reduced average gap lengths <r>/y _max forpn interactions are compared with data at a lower energy.     

On a proposed phenomenological determination of the strength of the dissipative forces in heavy ion reactions

We investigate a mechanism which shows that the experimental determination of the direction of the final spins of the nuclei in deep inelastic collisions yields distinct information on the strength of the radial dissipative forces since, in certain systems, the classical trajectories are accordingly scattered to positive or to negative deflection angles. The radial friction constant marking off both regions from each other amounts to c_r ≈ 2 × 10^?21 MeV fm sec for Ar + Th at E_lab^inc = 388 MeV and to c_r ≈ 1 × 10^?21 MeV fm sec for O + Pb at E_lab^inc = 315 MeV.     

Approach to saturation of the magnetization of dilute AuFe alloys

We present a reinterpretation of our recent measurements of the magnetic properties of some dilute AuFe alloys. We find that the observed approach to saturation of the magnetization for these AuFe alloys can be understood if both single-impurity (Kondo) effects and effects due to interactions between impurities via the Rudeman-Kittel-Kasuya-Yosida (RKKY) interaction, V(r) = (V₀ cos 2k_Fr)/r³, are properly included in the analysis. The analysis yields for the strength of the RKKY interaction V₀ = (1.1 ± 0.3) × 10^-36ergcm³, for the s-d exchange parameter |J| = (1.9 ± 0.3) eV, and for the Kondo temperature T_K = (0.8 ± 0.1) K. We conclude that mean free path effects do not significantly influence the observed approach to saturation of the magnetization for the AuFe alloys studied.     

Screening of excitonic states by low-density 2D charge carriers in GaAs/AlGaAs quantum wells

Screening of excitonic states by a system of 2D electrons (or holes) in GaAs/AlGaAs single quantum wells is studied. With increasing concentration of 2D charge carriers, a threshold-type disappearance of excitonic states is observed in both luminescence and reflectance spectra. The higher the quality of the 2D system, the lower the corresponding threshold concentration. In the best systems, the collapse of excitonic states occurs at unexpectedly low electron densities n _e =5×10⁹ cm^?2, which correspond to the mean dimensionless distance between the particles r _s =8. This value far exceeds the threshold values observed for 3D systems (r _s ≈2), as well as the values obtained for quantum wells in previous studies. The problem of measuring the concentration of low-density 2D charge carriers in photoexcitation conditions is solved by applying the method of optical detection of the dimensional magnetoplasma resonance. This method provides reliable measurements of the density of a 2D system to the values about 10⁹ cm^?2.     

Klein paradox in the Breit equation

We demonstrate that in the Breit equation with a central potentialV(r) having the propertyV(r ₀)=E there appears a Klein paradox atr=r ₀. This phenomenon, besides the previously found Klein paradox arr→∞ appearing ifV(r)→∞ atr→∞, seems to indicate that in the Breit equation valid in the singleparticle theory the sea of particle-antiparticle pairs is not well separated from the considered two-body configuration. We conjecture that both phenomena should be absent from the Salpeter equation which is consistent with the hole theory. We prove this conjecture in the limit ofm ⁽¹⁾→∞ andm ⁽²⁾→∞, where we neglect the terms ～1/m ⁽¹⁾ and 1/m ⁽²⁾. In Appendix I we show that in the Breit equation the oscillations accumulating atr=r ₀ in the case ofm ⁽¹⁾≠m ⁽²⁾ are normalizable to the Dirac δ-function. In Appendix II the analogical statement is justified for the nonoscillating singular behaviour appearing atr=r ₀ in the case ofm ⁽¹⁾=m ⁽²⁾.     

Instability of layered quantum liquids: 6. Strongly correlated bosons

We calculate the local-field corrections G(q, q _z) for charged bosons at zero temperature in a superlattice with interlayer distance d. An analytical expression for the local-field correction is described. The sum-rule version of the self-consistent approach for the local-field correction is used to discuss the effects of correlation. The RPAparameter r _s and the ratio d/a* determine correlation effects. a* is the effective Bohr radius. The stability region for the Bose condensate r _s < r _sc as a function of d/a* is determined: r _sc ≈ (d/a*)^3/4. The ground-state energy of the layered Bose condensate is calculated and optical and acoustical plasmons are discussed. We predict a roton structure for optical plasmons for r _s > r _sr with r _sr ≈ 0.5 (d/a*)^3/4.     

Natural operators of smooth mappings of manifoldswith metric fields

In this paper we introduce the concepts of both a natural bundle and a natural operator generalized for the case of the category Mf_m × Mf_m of cartesian products of two manifolds and products of local diffeomorphisms. It is shown that any r-th order natural bundle over M × N has a structure of an associated bundle (P^rM × P^rN)Z G_{m^r × Gm^r}]. We consider prolongations of such associated bundles and their reduction with respect to a chosen subgroup. The existence of a bijective correspondence between natural operators of order k and the equivariant mappings of the corresponding type fibers are proved. A basis of invariants of arbitrary order is constructed for natural operators of smooth mappings of manifolds endowed with metric fields or connections, with values in a natural bundle of order one.     

Wavefunctions of helium-like systems in limiting regions

We find an approximate analytic form for the solution ψ(r ₁, r ₂, r ₁₂) of the Schrödinger equation for a system of two electrons bound to a nucleus in the spatial regions r ₁ = r ₂ = 0 and r ₁₂ = 0, which are of great importance for a number of physical processes. The forms are based on the well-known behavior of ψ(r ₁, r ₂, r ₁₂) near the singular triple coalescence point. The approximate functions are compared to the locally exact ones obtained earlier by the correlation function hyperspherical harmonic (CFHH) method for the helium atom, light helium-like ions, and the negative ion of hydrogen H^?. The functions are shown to determine a natural basis for the expansion of CFHH functions in the considered spatial region. We demonstrate how these approximate functions simplify calculations of high-energy ionization processes.     

Coulomb energies and nuclear radii in the energy density formalism

The relation between Coulomb displacement energies,ΔE _c , andΔr=r _n -r _p , the difference between the rms radii of neutrons and protons in nuclei, is investigated within the energy density formalism (EDF). The variational equation, obtained by minimizing the Coulomb plus symmetry energies, is solved assuming the symmetry interaction is a simple functional of the local nuclear matter density. Varying parameters of the model, rather unique relation betweenΔE _c andΔr is obtained (within ±50 keV).ΔE _c isindependent ofr _ex, the rms radius of the excess neutrons distribution. Using the experimental values ofr _p and adjusting the model to reproduce the recent data onΔr (Δr∽~0.05 fm for⁴⁸Ca and²⁰⁸Pb), which are significantly smaller than those obtained from current Hartree-Fock calculations, the calculatedΔE _c agree with the experimental results. Using the value ofΔr～0.05 fm and the experimental values ofr _ex, a small compression (<0.02 fm) of the proton core in the analogue state relative to its parent state emerges, thus contributing an additional electrostatic term to the Coulomb displacement energy. The size of this relative core-compression effect depends on the values assumed forΔr andr _ex, it increases with the decreasing ofΔr and the increasing ofr _ex. IfΔr～0.05 fm the effect is large enough to remove the long standing Coulomb energy anomaly. The main result of the present work is the correlation betweenΔE _c andΔr, suggesting that the difficulties of current Hartree-Fock calculations in reproducing isotope shifts ofr _p , the small value ofr _n ?r _p and the values ofΔE _c may all be different manifestations of some missing residualp n effective interaction.     

A theorem on the order of levels in confining potentials

We prove that in a two-body, non-relativistic system interacting via a potential V = ?g²/r + V_c(r), where V_c is a confining potential non-singular at the origin, the 2S level is above the 2P level if V_c satisfies the following sufficient condition: This covers the well-known cases of linear potentials or harmonic oscillator potentials, which were considered in charmonium models, but also more generally, for instance, V_c(r) = r^α, α >0.     

Implicit finite-size effects in computer simulations

The influence of periodic boundary conditions (implicit finite-size effects) on the anisotropy of pair correlations in computer simulations is studied for a dense classical fluid of pair-wise interacting krypton atoms near the triple point. Molecular dynamics simulation data for the pair distribution function g _N(r) ≡ g _N(r, θ, ?) N-particle systems, as a function of radial distance r, polar angle θ, and azimuthal angle ?, are compared directly with corresponding theoretical predictions [L. R. Pratt and S. W. Haan, J. Chem. Phys. 74, 1864 (1981)]. For relatively small systems of N = 60, 80, and 108 atoms, significant angular variation is observed, which is qualitatively, and in several cases quantitatively, well predicted by theory. Finite-size corrections to the spherically-averaged radial distribution function g _N(r), however, are found to be comparable to random statistical errors for runs of 10⁵ time steps.     

On radii of neutron distributions in nuclei

We consider the analyses of the differences between rms radii (Δ = r_n ? r_p) of neutron and proton distributions in a wide variety of nuclei. We note that apart from its own intrinsic interest, the quantity Δ is of importance for isotope shifts, core polarization contributions to the Coulomb energy differences of mirror pairs (Nolen-Schiffer anomaly) and the renormalization of the effective interaction. For example, if Δ were very small in ⁴⁸Ca then the Nolen-Schiffer anomaly could be explained by a core polarization mechanism. We consider critically the various methods of determining Δ and conclude that at present probably the most reliable method is high energy (≈ 1 GeV) proton-nucleus scattering. The different theoretical analyses based upon, e.g., the multiple diffraction theory (where Glauber amplitude is the leading term) or the optical potential (KMT) formalisms appear to be converging to essentially the same answer when analyzing the same data. High energy α-particles and medium energy pions can also become useful sources of information if higher order optical potentials are treated with care. We find that Δ is rather large in ⁴⁸Ca, i.e. there is a neutron skin, so that the Nolen-Schiffer anomaly cannot be explained by a core polarization mechanism. The results of high energy proton-nucleus scattering are in excellent agreement with current density dependent Hartree-Fock calculations.     

Extracting d-orbital occupancy from magnetic Compton scattering in bilayer manganites

We consider the shape of the magnetic Compton profile (MCP), J_mag(p_z), in La_1.2Sr_1.8Mn₂O₇ for momentum transfer p_z along the [110] direction and the associated reciprocal form factor B(r) defined by taking the one-dimensional Fourier transform of J_mag(p_z). B(r) is shown to contain a prominent dip at r≈1 Å, where the minimum value B_min of B(r) can be related to the occupancies of the e_g orbitals of dx²−y² and d3z²−r² symmetry in the system. We illustrate our procedure in detail by analyzing the measured MCP at 5 K and the MCP computed within the framework of the local spin density approximation (LSDA) and comment on the differences between the measured and computed e_g occupancies as a reflection of the limitations of the LSDA in treating electron correlation effects.     

Rotational diffusion of a tracer colloid particle: I. Short time orientational correlations

We extend the generalized Smoluchowski equation to descrbe the diffusional relaxation of position and orientation in a suspension of interacting spherical colloid particles. Considering a tracer particle which interacts with other particles through spherically symmetric pair potentials and with an external field we obtain a cluster expansion representation of the orientational time correlation functions for the tracer. The one and two body cluster contributions are studied explicitly at short times. Working to first order in volume fraction φ we show that the initial slope of the time correlation functions is described by a modified diffusion coefficient D^r = D^r₀(1 −C^rφ) where C^r is a number determined by hydrodynamic and potential interactions. We evaluate C^r numerically for spheres with slip-stick hydrodynamic boundary conditions and also for permeable spheres.     

Ritz assignment and Watson fits of the high-resolution ring-puckering spectrum of oxetane

Oxetane is a four-membered ring molecule exhibiting a large-amplitude ring-puckering motion. In order to analyze this vibration we recorded a rotationally resolved far-infrared spectrum between 50 and 145 cm⁻¹. The analysis of the ring-puckering fundamental band with the assignment of 1108 lines, has been presented in a previous paper. In the present work we present a list of further 6531 assigned transitions between the five lowest excited ring-puckering states. The 4983 term values involved in the transitions assigned in this and in the preceding work have been evaluated by the “Ritz” program, and are now available. An A-reduced Watson Hamiltonian in any of the three representations I^r, II^r, and III^r was used to perform a fit of the assigned transitions. Precise rotational constants and quartic as well as a full set of sextic centrifugal distortion constants were obtained for the investigated ring-puckering states. For the first time, high-resolution values for the vibrational G_v parameters have been obtained, and we have added terms in x⁶ and x⁸ to the double minimum-potential well describing the ring-puckering motion, in order to reproduce their values within the experimental accuracy. The same potential still reproduces the lower resolution values of the Q-branch origins involving higher ring-puckering states up to v_rp=14 found in the previous literature.     

Influence of quantum dot density on excitonic transport and recombination in CdZnTe/ZnTe QD structures

We report on dynamics of excitons in Cd_xZn_1−xTe/ZnTe quantum dots (QDs) and present information of excitonic transport and recombination. Due to different growth methods, samples with different QD's densities were obtained. Time-resolved measurements reveal three decay mechanisms: (i) radiative recombination of excitons in the individual QDs; (ii) thermally activated escape of excitons and (iii) escape due to tunneling (hopping). In the high QD-density samples the hopping (r_HB=2700 ns⁻¹) is two orders of magnitude more efficient than in the low QD-density samples (r_HB=33 ns⁻¹). Radiative recombination rates are similar in both types of samples, r_R=1-1.3 ns⁻¹. Due to the good radiative to nonradiative recombination ratio, the low-density QDs can be a potential source of entangled photon pairs.     

An Integro-Differential Equation for Bose�CEinstein Condensates

We present an integro-differential equation describing systems with large number of bosons. The new equation includes the two-body correlations exactly into account and the kernel has a simple analytic form. The equation has been employed to obtain results for ${A\in\{10,100\}}$ ⁸⁷Rb atoms confined by an externally applied trapping potential V _trap(r). Our results are in excellent agreement with those of the Potential Harmonic Expansion Method (PHEM) and the Diffusion Monte Carlo (DMC) method.     

Theory of the radial distribution functions in α-AgI

The three partial radial distribution functions g_Ag-Ag(r), g_Ag-I(r) and g_I-I(r) in α-AgI are calculated on the basis of the fact that I-ions form a bcc lattice and Ag-ions are randomly distributed over the 12(d) sites. The short-range order between the Ag-ions is described in terms of the microcrystalline model which has been recently divised by the present author on the occasion of the study on the superionic transition in CuI. The calculated results are in good agreement with those of the computer simulation of Vashishta and Rahman. We have an evidence that the Ag-ions are correlated in order to decrease the Coulomb interaction between them (not core-core repulsion) and the microcrystalline model is suitable to represent the correlated region. We discuss the relation between the microcrystalline model and the caterpillar mechanism.     

Some properties of the two-point functions in a dilatationally covariant field theory

The object of our concern are some properties of the two-point functions in a model of dilatationally covariant field theory. We examine the one- and two-dimensional irreducible representations of the dilatation group. For the one-dimensional case we obtain either a massless free field theory or a theory of an interacting field which does not contribute on the mass shell μ=p²=0 and is characterized by a spectral function μ^r₊?1. In the two-dimensional case both fields differ from the free field, their spectral functions ρ_ij(μ) do not vanish identically and are products of two factors, a polynomial of order up to two in ln μ and μ^r₊?-1. The differences between the case of internal symmetry and the case of dilatations are emphasized. The formula for the form factor in the Araki-Haag limit is given.