Double Continuum Research Articles

Modelling of three-body effects in a double continuum

Theoretical calculations of double ionisation by electron or photon impact require a final state wavefunction which takes account both of the Coulomb repulsion between the pair of free electrons and of their interaction with the residual ionic core. It is desirable that this should be separable so as to facilitate the introduction of electron-pair correlations in the initial state wavefunction for the collision system. We propose a method for calculating coupled classical trajectories for the free electrons and deducing from these potentials from which their quantum mechanical wavefunctions may be obtained. Test calculations are reported for electron impact single ionisation of hydrogen

Theoretical study of the differential cross section of the ionization of hydrogen (2s) by electron impact

Electron impact ionization of hydrogen in is 2s metastable state is investigated theoretically. An ab initio calculation is proposed which includes the correlated double continuum Brauner-Briggs-Klar (BBK) wavefunction. The results of this model are compared with those given by the use of the second Born approximation. Some interesting kinematical situations are explored for future experiments.

A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

view Abstract Citations (20) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Circumstellar Molecular Gas Structure Associated with the Massive Young Star Cepheus A--HW 2 Torrelles, Jose M. ; Rodriguez, Luis F. ; Canto, Jorge ; Ho, Paul T. P. Abstract We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier). Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/186747 Bibcode: 1993ApJ...404L..75T Keywords: Early Stars; Massive Stars; Molecular Gases; Stellar Envelopes; Very Large Array (Vla); Ammonia; Data Processing; Data Reduction; Radio Astronomy; Astrophysics; ISM: MOLECULES; ISM: INDIVIDUAL NAME: CEPHEUS A; ISM: JETS AND OUTFLOWS; ISM: H II REGIONS full text sources ADS | data products SIMBAD (2)

The Effect of Correlation on the Double Ionization of Helium by Fast Electrons

Abstract The double ionization of helium by fast electrons is studied by using a correlated double continuum wave function describing the two ejected electrons.

High resolution X-ray excited inner valence photoelectron spectra of HBr and DBr

High resolution valence photoelectron spectra of HBr and DBr induced by an AlKα X-ray source are reported. The valence electron X-ray excited spectra have been recorded in an extended energy range including the double ionization continuum up to 10 eV above the first double ionization threshold. For the outer valence A state UV excited results are also reported. Isotope effects in HBr and DBr are observed in the high energy excited spectra. Using a line profile analysis potential curves are sketched and it is concluded that in analogy with HCl most of the inner valence lines belong to the 4σ −1 2Σ + manifold owing to the final ionic state configuration interaction. However, as in the case of HCl one narrow line can probably be associated with a 2Π state corresponding to a shake-up transition in the outer valence region.

Loops and unoriented strings

We derive and analyze Schwinger-Dyson equations for Dyson's Coulomb gas at arbitrary temperature. This system interpolates between theories of oriented and unoriented strings. The Schwinger-Dyson equations can be formulated as Virasoro constraints constructed from a boson with a temperature-dependent background charge. We describe a geometric interpretation of these equations, calculate correlation functions perturbatively in 1/ N and discuss a high-low temperature duality exhibited by the Coulomb gas. We also interpret the double scaling continuum limit of the loop equations.

Interaction of local inhomogeneities of a fluidized bed

In connection with an analysis of transport processes in fluidized beds a study is made of the steady motion of a system of local inhomogeneities of the bed porosity, which are modeled by packets of particles. The interaction of the inhomogeneities is taken into account on the basis of a cell model. The velocity fields and the pressure distributions of the solid and gas phases together with the rising and sinking velocities of the system of packets are determined in the approximation of a double continuum. The flow regimes of the fluidizing agent are investigated. It is shown that with increasing concentration of packets in the bed the velocity of their motion decreases, and the circulation region of the dispersion medium surrounding a packet or trapped within it contracts. The dependence of the rate of flow of the fluidizing agent through the transverse section of the reactor on the concentration of packets in the bed is found.

Double continuum fragmentation in the vibrational predissociation X⋅⋅⋅BC(v)⋅⋅⋅Y→BC(v′<v)+X+Y of van der Waals complexes: A perturbative treatment

We present an approximate quantal model to study the double continuum problem arising in the complete fragmentation of X⋅⋅⋅BC(v)⋅⋅⋅Y van der Waals(vdW) complexes, where BC is a conventional diatomic molecule vibrationally excited and X and Y are rare gas atoms, through vibrational predissociation (VP). Assuming a near equilibrium geometry of the complex and using an adiabatic approximation for describing the oscillation in the angle formed by the BC⋅⋅⋅X and BC⋅⋅⋅Y weak bonds, the rates for complete fragmentation are expressed in the frame of Fermi’s ‘‘Golden Rule’’. Double continuum wave functions may be obtained by a perturbative treatment that allows one to take properly into account the symmetry of the problem in the particular and very frequent case X≡Y.

Aperture Synthesis Observations of CS, NH3, and Continuum in the Bipolar Flow Source NGC2071-IRS

ABSTRACT.We have made aperture synthesis observations of CS(J=l-0, 2-1) and NH3(1,1) lines and 49, 98, and 110 GHz continuum in NGC2071-1RS with the Nobeyama Millimeter Array. Wfe have obtained maps of these lines and continuum maps with 2”. 7-20” resolution, ffe have found that dense molecular gas has a disk structure with a radial scale ranging 0.01 pc - 0.1 pc and has a ring-like structure with expanding motion at the central 5000 AU region. We also have found that there exists double dust continuum sources which are separated by 2500 AU in projection and are apparently located at the inner edges of the ring. Our observational results suggest that the disk of molecular gas has a central hole formed by wind and UV radiation from a central young stellar object, the central part is expanding, and that dust continuum emission comes from tangential parts of the shock compressed ring (r~1300 AU, M(H2)~ 21-34 Mo, and n(H2)~ 109) at the most inner side of the disk structure. The other possible model of the dust continuum sources is a binary system of self-luminous young stellar objects.

Soft modes in the one-dimensional Heisenberg antiferromagnet near saturation.

The elementary excitations of the one-dimensional spin-S Heisenberg antiferromagnet near saturation are explained, with special attention to the soft mode, in terms of a gas of interacting magnons. Recent numerical studies of the antiferromagnet in a magnetic field uncovered the presence of the soft mode at a magnetization-dependent wave number for large magnetizations. We show that very near saturation and for large spins the antiferromagnet can be written in terms of a gas of magnons interacting via repulsive \ensuremath{\delta}-function potentials, a system with a known Bethe-ansatz solution. The soft mode can then be explained as a Kohn-anomaly-type excitation above a quasi-Fermi-sea. Other elementary excitations form a particle-hole-type double continuum. The soft mode's apparent physical observability is indicated by a shoulder at the appropriate wave number in the integrated longitudinal intensity.

Quantal treatment of three-particle break-up: collisional detachment

A full quantum mechanical treatment of three-particle break-up in the negative-ion-atom collision A-+B to A+B+e- is presented. The continuum states of the heavy-particle motion are described as a superposition of the AB relative motion in an arbitrary large box. The double continuum problem is then reduced to a pseudo-associative detachment problem: A-+B to AB( nu )+e-. Results for the detachment probability, as well as a histogram representation of the spectrum of ejected electrons, are presented for a model problem in which the ejected electron has p-wave character. This allows for a discussion of the method as well as of some of the characteristics of this detachment process.

Satellite Intensities in Photoelectron Spectroscopy and Electron Momentum Spectroscopy-Synchrotron Radiation Studies of Argon 3s and Xenon 5s Photoionisation (hv - 60?130 eV)

Binding energy spectra for the main line, satellite lines and associated double ionization continuum for argon 3s and xenon 5s photoionisation have been measured in the photon energy range 60-130 eV using monochromatised synchrotron radiation and magic angle photoelectron spectroscopy. In particular the ratio of satellite to main line intensities has been investigated and compared with the results of earlier experiments using X-ray and ultraviolet photoelectron spectroscopy as well as with recent measurements by electron momentum [i.e. binary (e,2e)] spectroscopy. The results of the presently reported photoelectron measurements show that the satellite intensity relative to that of the main ns -1 line increases with increasing photon energy and approaches the value given by electron momentum spectroscopy. These findings are contrary to predictions based on recent calculations of photoelectron intensities. The present work lends support to the direct interpretation of satellite intensities (pole strengths or spectroscopic factors) in binary� (e, 2e) spectroscopy using the plane wave impulse approximation. The need for improved calculations of photoionisation intensities as well as further photoelectron measurements in the X-ray region is stressed.

On inertial effects on discontinuities in the concentration of the solid phase in a disperse medium

A system of conditions for the conservation of mass and momentum of a fluid and a solid phase on the surface of discontinuity in a disperse medium is analysed within the framework of the double continuum model /1/. The case when there is a high concentration of solid particles on one side of the discontinuity and a low or zero concentration of them on the other side is considered. Under these conditions in the region of a high concentration of the solid phase remote from the discontinuity, the inertial force of the fluid phase is small compared with the interphase interaction force and Darcy's law holds while both forces are of the same order of magnitude in the thin transition lower close to the surface of discontinuity. It is assumed that the surface of discontinuity is impermeable to the particles of the solid phase. Effects due to the possible occurrence of surface tension on the discontinuity are not considered. Subject to the assumptions which have been made, a solution of the initial system of equations of motion and continuity of the phases is constructed in the stationary approximation taking account of the transition layer which satisfies the condition of the continuity of the pressure and the velocity of the fluidizing agent on the boundaries of the layer. Replacement of the transition layer by a discontinuity leads to a jumpwise change in the above-mentioned parameters upon crossing the discontinuity which, in the case being considered, necessitates a modification of the whole system of boundary conditions on the surface of discontinuity /1–3/. Examples of the construction of the flow fields of the fluid and solid phases during the motion of a local inhomogeneity in the concentration of the particles in the pseudofluidized layer are presented. Inertial (dynamic) effects on the discontinuities during the slow filtration of a gas in porous media have been considered previously /4, 5/. The inertialess model of a fluidizing agent has been used (6, 7/, etc.) to analyse the motion of bubbles in a pseudofluidized bed.

Intensities of the 3s ionisation spectrum of argon

A critical comparison of experimental data and theoretical calculations of the relative strengths for populating the Ar II 2Se states following high-energy photoionisation ( gamma , e) and binary (e, 2e) processes is presented. There is a difference in reported pole strengths (peak areas) of the discrete Ar II states (formed by the ejection of a 3s electron) derived from the two techniques. In addition, the lack of strength in the Ar II continuum (i.e. for Ar2++e) reported in the ( gamma ,e) experiments is in contrast with theoretical calculations and binary (e, 2e) experiments. The possible problems of background subtraction in the ( gamma , e) experiment are discussed and it is noted that if the background function is determined in a region of the spectrum where considerable strength in the double ionisation continuum exists, the relative strengths for the satellite lines will be systematically underestimated. It is shown that removal of this defect in the interpretation of the ( gamma , e) experiment should result in similar discrepancies between the ( gamma , e) and binary (e, 2e) measurements.

Detection of iron lines in the persistent emission of some X-ray burst sources observed by EXOSAT

We have observed the X-ray burst sources 4U1728-33 and 4U1813-14 with the ME detectors aboard EXOSAT, and present here results of a spectral analysis of their persistent emissions. For both sources the data can be well fitted by a double blackbody continuum and a Gaussian emission line. The two spectral components can be interpreted in terms of a blackbody radiation from the neutron star, and emission from the inner part of an accretion disc. The line feature is consistent with the 6.7 keV iron emission line expected in the presence of a hot extended object (X-ray corona) around the neutron star.

Electron spectroscopy study of the 27.5 eV satellite line in acetylene excited by synchrotron radiation

Valence electron spectra from acetylene using synchrotron radiation with 50 and 70 eV excitation energy are presented. The 27.5 eV satellite line is resolved into two components. The intensities of these satellite lines are compared to the previously measured intensities at 1487 eV excitation energy. β values for the satellite lines and for all the valence levels are determined at 70 eV excitation enery. A previously unknown satellite line is found at 31.0 eV binding energy. This line corresponds to an onset of the double ionization continuum.

Continuous Double Adiabatic Spectrum in Toroidal Plasmas

The continuous spectrum of an anisotropic and axisymmetric toroidal plasma is investigated using the double adiabatic theory. The continuum is given by an eigenvalue problem of a fourth order system of ordinary differential equations. In contrast to the magnetohydrodynamic continuum the double adiabatic continuum may become unstable. The stability depends upon the parallel and perpendicular pressure distributions along the field lines. In absence of a toroidal magnetic field, the fourth order system decouples into two second order differential equations for which specific stability criteria are derived.

Zero-temperature dynamics of the [formula omitted] linear Heisenberg antiferromagnet in a magnetic field

Analytic calculations in the Bethe formalism and finite-chain calculations show that the dynamic spin-correlation function in ( q, ω)-space of the s= 1 2 linear Heisenberg antiferromagnet at T> = 0 in a uniform magnetic field is governed by a double continuum of excitations. Appropriate neutron scattering experiments are expected to show double-peak spectra.

Quantum effects in the spin dynamics of the linear Heisenberg antiferromagnet

We present an approximate analytic expression for the dynamical spin correlation function of the S=1/2 linear Heisenberg antiferromagnet at T=0. The basis for our approach is that in zero field the spectrum is dominated by a double continuum [in (q,ω) -space] of triplet spin wave excitations. The S=1/2 integrated intensity agrees very well with recent neutron scattering results on CPC, unlike the corresponding classical intensity. Moreover, the S=1/2 spectral weight function shows increasing asymmetry as q→π, a quantum effect, observable in more recent neutron scattering data. In non-zero magnetic field, there exist two, partly overlapping, double continua, each giving rise to a peak situated at the lower boundary. The (zz component of) spectral weight function therefore has a double-peaked structure, as observed experimentally. Theory and experiment are in apparent agreement concerning the energy difference between the peaks.

Zero-Temperature Dynamics of theS=12Linear Heisenberg Antiferromagnet

We present an analytical expression for the dynamical spin-correlation function of the $S=\frac{1}{2}$ linear Heisenberg antiferromagnet based on the fact that the spectrum is dominated by a double continuum of spin-wave excitations. Our expression is not exact, but exact sum rules show that the degree of approximation is small. We predict that in a uniform magnetic field the spectral weight function will display a double-peaked structure. Such a feature is observed in recent neutron-scattering experiments.