Wave Cross Sections Research Articles

Partial Wave Cross Sections for Collisions between HeliumAtoms and Hydrogen Halide Molecules

The close-coupling method is utilized to calculate partial crosssections for elastic and inelastic scattering of He atoms with HX (X=F,Cl, Br) molecule based on the CCSD (T) potential energy surfacesobtained in the previous research. The calculation is performed at theincident energy of 200 meV. The rationality of our results has beenconfirmed by comparison with the available theoretical results. Thetendency of the elastic and inelastic rotational excitation partialwave cross sections varying with the reduced mass of the three systemsis obtained.

Controllable metamaterial electrmagnetic structure research on applying to stealth technology

AbstractIn this article, we present a new kind of a controllable metamaterial electromagnetic structure that it may be applied into stealth design and stealth technology in the future, in which the transmission coefficient of electromagnetic wave and single radar cross section (RCS) of structure are both electrically controlled, simulated, and characterized between 7 and 12 GHz. This structure is constructed with split ring resonators (SRRs) and metallic wire arrays including pin diodes, pin diodes are periodically inserted at these discontinuous each 10 mm to control the electrical continuity of the wires, and they can be either in an on state or in an off state depending on the voltage. the simulation and test prove that this structure could absorb electromagnetic incident wave, and have reduced RCS markedly with the largest scope of ‐6 dBm around frequency 9.0 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1616–1619, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22521

Partial wave scattering cross sections for He–HBr collision

A new anisotropic potential is fitted to ab initio data. The close-coupling approach is utilized to calculate state-to-state rotational excitation partial wave cross sections for elastic and inelastic collisions of He atom with HBr molecule based on the fitted potential. The calculation is performed separately at the incident energies: 75, 100 and 200 meV.The tendency of the elastic and inelastic rotational excitation partial wave cross sections varying with total angular quantum number J is obtained.

H¯−Liscattering and enhancedH¯cooling

The $s$-wave elastic phase shifts and cross sections for the $\overline{\mathrm{H}}\text{\ensuremath{-}}\mathrm{Li}$ system are predicted using an ab initio and nonadiabatic quantal method at very low energies. The smooth and monotonic change of the phase shifts with added eigenstates indicates that the leptonic potential for the present system has no barrier as noticed in the case of the $\overline{\mathrm{H}}\text{\ensuremath{-}}\mathrm{He}$ system, or even a hump which is present in $\overline{\mathrm{H}}\text{\ensuremath{-}}\mathrm{H}$ interaction. The very high value of the $s$-wave elastic cross section at zero or near zero energy implies that Li will be a more efficient buffer gas in cooling the antiatom to ultralow temperatures. This study may stimulate new experiments in thermalizing $\overline{\mathrm{H}}$ atom.

Orthopositronium-orthopositronium scattering using the close-coupling approximation at medium energies

Elastic and excitation (single and double) cross sections $(n\ensuremath{\leqslant}3)$ of orthopositronium-orthopositronium $(o\text{\ensuremath{-}}\mathrm{Ps}--o\text{\ensuremath{-}}\mathrm{Ps})$ scattering system are predicted using eigenstate close-coupling approximation at medium energies. The partial wave cross sections have shown a peculiar feature. The static exchange results and other inelastic cross sections for even parity transitions only survive for even values of partial wave and vice versa like Born-Oppenheimer (BO) cross sections. To the best of our knowledge, this feature has not been noticed for other systems. Our results are nearly convergent with added eigenstates and elastic and excitation cross sections are compared with their corresponding BO predictions.

Viscous relaxation and collective oscillations in a trapped Fermi gas near the unitarity limit

The viscous relaxation time of a trapped two-component gas of fermions in its normal phase is calculated as a function of temperature and scattering length, with the collision probability being determined by an energy-dependent s-wave cross section. The result is used for calculating the temperature dependence of the frequency and damping of collective modes studied in recent experiments, starting from the kinetic equation for the fermion distribution function with mean-field effects included in the streaming terms.

H¯−Heelastic scattering at low energies: Contribution of nonzero partial waves

The present study reports the nonzero partial wave elastic cross sections together with $s$-wave results for the scattering of an antihydrogen atom off a gaseous helium target at thermal energies (up to ${10}^{\ensuremath{-}2}\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$). We have used a nonadiabatic atomic orbital method having different basis sets to investigate the system. The consideration of all the significant partial waves (up to $J=24$) reduces the oscillatory nature present in the individual partial wave cross section. The added elastic cross section is almost constant up to ${10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ and then decreases steadily and very slowly with increasing energy.

Multichannel Calculation ofDs*Vector States and theDsJ+(2632)Resonance

We study bound states below threshold and resonances above threshold in the ${D}^{0}{K}^{+}$ and ${D}_{s}^{+}\ensuremath{\eta}$ systems, using a many-coupled-channel model for nonexotic meson-meson scattering applied to states with the quantum numbers of $c\overline{s}$ quark-antiquark vector mesons. We fit the ground state at 2.112 GeV, whence the lowest resonances in ${D}^{0}{K}^{+}$ come out at 2.61, 2.72, 3.03, and 3.08 GeV. The resonance at 2.61 GeV acquires a width of about 8 MeV, while its partial $P$ wave cross section is up to 6 times larger in ${D}_{s}\ensuremath{\eta}$ than in ${D}^{0}{K}^{+}$, provided a mechanism accounting for Okubo-Zweig-Iizuka--forbidden decays is included. The latter finding is in agreement with the observations of the SELEX Collaboration with respect to the recently reported ${D}_{sJ}^{+}(2632)$ resonance. Therefore, we conclude that the ${D}_{sJ}^{+}(2632)$ is probably the first recurrence of the ${D}_{s}^{*}(2112)$ meson.

Analysis of structures in the cross sections for elastic scattering and spin exchange in low-energyH++Hcollisions

Elastic scattering and spin exchange cross sections in ${\mathrm{H}}^{+}+\mathrm{H}$ collisions are computed using accurate adiabatic potential curves for the center-of-mass energy range ${10}^{\ensuremath{-}4}lEl100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Both cross sections show considerable structure which necessitates computation on a fine energy grid to resolve them. We analyze the structures using a comparison equation method to find the poles of the scattering matrix in the complex energy plane. We show that many features of the cross sections can be correlated with these poles and tabulate the positions of the most important poles. Finding stationary phases in the partial wave cross sections, we also explain in all details the glory oscillations of the elastic cross section that extends below $100\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ down to the lowest energies.

Fully dispersive nonlinear water wave model in curvilinear coordinates

A vertically integrated fully dispersive nonlinear wave model is expressed in curvilinear coordinates with non-orthogonal grids for the simulation of broad-banded nonlinear random water waves in regions of arbitrary geometry. The transformation is performed for both dependent and independent variables, hence an irregular physical domain is converted into a rectangular computational domain with contravariant velocities. Use of contravariant velocity components as dependent variables ensures easy and accurate satisfaction of the wall condition for lateral enclosures surrounding a physical domain, such as a coastal area, channel, or harbor. The numerical scheme is based on finite-difference approximations with staggered grids which results in implicit formulations for the momentum equations and a semi-explicit formulation for the continuity equation. Linear long wave propagation in a channel of varying cross-section and linear random wave propagation in a circular channel are presented as test cases for comparisons with the corresponding analytical solutions. Cnoidal and Stokes waves in a circular channel are also simulated as examples to nonlinear wave propagation within curved walls.

Total elastic cross section forH¯−Hscattering at thermal energies

This paper reports the elastic scattering cross sections for a few low-lying partial waves and also the converged elastic cross sections with added partial waves in the energy range ${10}^{\ensuremath{-}10}--{10}^{\ensuremath{-}2}$ a.u. for the $\mathrm{H}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{-}\mathrm{H}$ system using atomic orbital techniques. The present s-wave predictions are in good agreement with the other existing theoretical estimates. Nonzero low-order partial-wave elastic cross sections show dips like for s-wave scattering. The converged elastic cross section shows structurelike behavior in the energy range $4.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}2}\mathrm{a}.\mathrm{u}.$

Reaction Dynamics at the Barrier for Heavy Compound

To investigate basic properties of the fusion reaction dynamics for heavy compound systems the partial wave distribution σ l extracted from measured γ multiplicities can be employed as an alternative to the classically used fusion/fission excitation functions. A variety of reactions leading to compound nuclei (CN) in the Pb region can be used to investigate features like the fusion-fission competition, the role of deformation in the fusion of heavy systems and a possible effect of the Z=82 shell on the enhancement of evaporation residue (ER) production. The measured spin distribution (SD) can provide information on the single partial wave cross sections which is hidden in the integral fusion cross section. We started a series of experiments to measure those properties for the reactions at the Laboratori Nazionali di Legnaro, Italy. In order to extract the CN spin distribution, γ multiplicities are measured by using the γ-detector array GASP and its inner ball in the multiplicity filter mode.

Hyperspherical close-coupling calculations for charge transfer cross sections in Si4+ + H(D) andBe4+ + Hcollisions at low energies

Total and partial electron capture cross sections are calculated for Si4+ + H(1s)/D(1s)collisions from 1 meV amu−1to 1 keV amu−1, and for Be4+ + H(1s)collisions from 2.5 eV amu−1up to 1 keV amu−1,using the recently developed hyperspherical close-coupling (HSCC) approach. For bothsystems, our results are in good agreement with calculations based on the molecularorbital expansion method in reaction coordinates (RC). For Si4+ + D(1s)our total charge transfer cross sections agree well withexperiment, but not the partial cross sections. For Be4+ + H,we show that partial wave cross sections from the RC method have moreoscillatory structures than those from the HSCC method, even though the totalcross sections agree. In comparison with the RC method, the HSCC approachdoes not require the introduction of any ad hoc external parameters in theformulation.

Reaction dynamics at the barrier for heavy compound systems

To investigate basic properties of the fusion reaction dynamics for heavy compound systems, the partial wave distribution σl extracted from measured γ multiplicities can be employed as an alternative to the classically used fusion/fission excitation functions. A variety of reactions leading to compound nuclei in the Pb region can be used to investigate features like the fusion-fission competition, the role of deformation in the fusion of heavy systems, and a possible effect of the Z=82 shell on the enhancement of evaporation residue production. The measured spin distribution can provide information on the single partial wave cross sections, which is hidden in the integral fusion cross section. Moreover, it can reveal signatures in the high-spin region, which could be an indication of a stabilization due to an increase in the potential hole by shell correction energies Eshell in the vicinity of a closed shell. The systematic investigation and understanding of the fusion-fission reaction dynamics, together with the understanding of the structure of transfermium nuclei, which are stabilized only via shell effects, are essential for a successful program aiming at the synthesis of new elements at GSI, Dubna, or elsewhere. We started a series of experiments to measure those properties for the reactions at the Laboratori Nazionali di Legnaro, Italy. In order to extract the compound nucleus spin distribution, γ multiplicities are measured using the γ-detector array GASP and its inner ball in the multiplicity filter mode.

Relativistic calculation of nuclear transparency in(e,e′p)reactions

Nuclear transparency in (e,e'p) reactions is evaluated in a fully relativistic distorted wave impulse approximation model. The relativistic mean field theory is used for the bound state and the Pauli reduction for the scattering state, which is calculated from a relativistic optical potential. Results for selected nuclei are displayed in a Q^2 range between 0.3 and 1.8 (GeV/c)^2 and compared with recent electron scattering data. For Q^2 = 0.3 (GeV/c)^2 the results are lower than data; for higher Q^2 they are in reasonable agreement with data. The sensitivity of the model to different prescriptions for the one-body current operator is investigated. The off-shell ambiguities are rather large for the distorted cross sections and small for the plane wave cross sections.

Positronium scattering by atomic hydrogen with inclusion of target excitation channels

Calculations are reported for positronium (Ps) scattering by atomic hydrogen (H) in the energy range 0--6.5 eV in a coupled-pseudostate approximation in which excitation and ionization channels of both the Ps and the H are taken into account. The approximation contains an accurate representation of the van der Waals coefficient. Results are presented for phase shifts, scattering lengths, effective ranges, and various cross sections including partial wave, total, and ortho-para conversion cross sections. An analysis of the possible spin transitions is provided and the energy of the positronium hydride (PsH) bound state is determined. Substantial differences are found from earlier work within the frozen target approximation, now clearly confirming the importance of target excitation channels. Good agreement is obtained with recent calculations of S-wave phase shifts and scattering lengths using the stabilization method. Convergence to the exact binding energy for PsH appears to be slow. Resonances corresponding to unstable states of the positron orbiting ${\mathrm{H}}^{\ensuremath{-}}$ are seen in the electronic spin singlet partial waves. The importance of the ${\mathrm{H}}^{\ensuremath{-}}$ formation channel is discussed.

Spin correlations inp→p→→pnπ+pion production near threshold

A first measurement of longitudinal as well as transverse spin correlation coefficients for the reaction $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pn}{\ensuremath{\pi}}^{+}$ is made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 325-, 350-, 375-, and 400-MeV beam energies. The spin correlation coefficients ${A}_{\mathrm{xx}}{+A}_{\mathrm{yy}},$ ${A}_{\mathrm{xx}}\ensuremath{-}{A}_{\mathrm{yy}},$ ${A}_{\mathrm{zz}},$ and ${A}_{\mathrm{xz}}$ and the analyzing power ${A}_{y},$ as well as angular distributions for $\ensuremath{\sigma}({\ensuremath{\theta}}_{\ensuremath{\pi}})$ and the polarization observables ${A}_{\mathrm{ij}}({\ensuremath{\theta}}_{\ensuremath{\pi}}),$ are extracted. Partial wave cross sections for dominant transition channels are obtained from a partial-wave analysis that included transitions with final-state angular momenta of $l<~1.$ The measurements of the $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pn}{\ensuremath{\pi}}^{+}$ polarization observables are compared with the predictions from the J\"ulich meson exchange model. The agreement is very good at 325 MeV, but it deteriorates increasingly for the higher energies. At all energies agreement with the model is better than for the reaction $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\rightarrow}\mathrm{pp}{\ensuremath{\pi}}^{0}.$

INTERACTION OF TACHYONS WITH MATTER

A new interaction mechanism of superluminal particles with matter is suggested. Tachyons are described by a real Proca field with negative mass square, coupled to a current of subluminal matter. The potential of a static point source in this field theory is a damped periodic function with 1/r-decay. We treat this potential as a perturbation of the Coulomb potential, and study its effects on cross-sections and energy levels. In the limit of large impact parameter, the periodicity of the potential has a pronounced effect on the classical cross-section, which gets singular at the accumulating extrema of the scattering angle. In this limit we define the cross-section wave mechanically, by semiclassical rainbow scattering. The impact of the tachyon potential on the energy levels of hydrogen and hydrogenic ions is calculated by means of Bohr–Sommerfeld quantization. Estimates for the tachyon mass (3 keV) and the coupling constant of the tachyon potential are derived on the basis of high-precision Lamb shift measurements.

Analysis of discrepancies between quantal and semiclassical calculations of electron impact broadening in plasmas

In this work we analyse the serious discrepancies found between quantal calculations and non-perturbative semiclassical calculations of electron impact broadening in the case of B 2+2 s–2 p. We use the Coulomb Bethe (CB) approximation to calculate both electron impact broadening and excitation of 2 s–2 p for comparison with the other methods. We find good agreement between CB and the non-perturbative semiclassical method for the line width contributions of individual partial waves, except for low L, where strong collision effects enter. We also find good agreement between CB and the R-matrix and Coulomb Born methods for the excitation cross section partial wave contributions, again except for low L. There is disagreement for the high partial wave cross sections between the non-perturbative semiclassical method and all of the quantum methods; this is resolved by applying a symmetrized method, for which we demonstrate excellent agreement with CB. The area in which the semiclassical, Coulomb–Born and R-matrix methods disagree has been reduced to the first three partial waves, and the disagreement must be due to the treatment of strong collisions.

Research on the development of a method of spatially temporary smoothing of a high-power laser beam

The investigations of the influence of various types of wavefront distortions, varying in time, on the intensity distribution on the surface of a target are carried out. It is shown that distortions of a wavefront, equivalent to transverse displacement in time of a beam in far field at an angle of approximately 10 diffraction angles, results in practically full smoothing of a specl-structure of intensity distribution. Creation of phase distortions of a beam assigned as running in a cross section wave with an amplitude of more than 3 radian and with a spatial size exceeding 20–30 times the size of the kinoform phase plate element, permits us to reduce the depth of modulation in distribution of intensity in far field also. The capability of application is considered as a smoothing device of the dynamic plasma layer, based on the volume-structured medium. The model of energy transport process in such media is developed. Matching of calculation and experimental results is conducted.