Large-angle scattering of heavy ions: (I). General structure of elastic cross section

Closed-form expressions are derived for the differential cross section of elastic heavy-ion scattering at large angles. The derivation is based on the general form of the elastic partial-wave S-matrix in real l-space. By a generalization of analytic techniques developed in earlier work, it is shown that the large-angle scattering cross section has a universal structure involving combinations of Bessel functions and the Fourier transforms of the rapidly varying parts of the S-matrix, irrespective of their dynamical origin. Anomalous large-angle scattering is attributed to deviations of the S-matrix from its “normal strong-absorption profile”, and general conditions for backward-angle enhancement are given. Our model-independent formulation provides the framework for an “inductive” method of analyzing experimental angular distributions and excitation functions aimed at identifying, as uniquely as possible, the dynamical mechanisms that operate in large-angle heavy-ion scattering. Extensions of the formalism to inelastic scattering and transfer reactions, and applications of the analytic method, will be described in subsequent papers.     

Quantum theory of atom-surface scattering: Incommensurate and fluid adsorbates

The problem of atomic scattering from adsorbate-covered surfaces, treated earlier for the case of commensurate overlayers, is considered again in the eikonal approximation for incommensurate lattice phases and for fluid phases. Stochastic methods are employed and for a specific model (hard bosses on a plane) it is shown how the statistical and geometric problems can be separately solved. In order to explain the meaning of the coherent and incoherent scattering contributions a time-dependent theory is introduced and it is shown that the incoherent “elastic” scattering is in fact weakly inelastic and (for classical diffusion with diffusion coefficient D) has an energy width of the order ?DQ², where Q is the parallel momentum transfer. The problem of the decay of substrate diffraction intensities when the coverage of random impurities is increased is also discussed.     

Hadron scattering in two-dimensional QCD: (I). Formalism and leading order calculations

Two-dimensional quantum chromodynamics in the 1/N_c expansion is explored as a model for hadronic interactions. In meson-meson scattering, order 1/N_c terms exhibit embryonic “Regge” behaviour, with the crossed channel factorization, signature and exchange degeneracy properties found in dual Regge models. “Regge” intercepts are additive in the quark quantum numbers exchanged, and have a lower limit for large quark masses. Residues also factorize in the direct channel. An analogue for fixed angle scattering is presented which has deviations from dimensional counting rules related to form factors and Regge intercepts.     

Topology and hydrogen connectivity in supercritical water

The experimental density dependences of relative fractions of the “liquid-like” and “gas-like” components of supercritical water have been adequately described in terms of the two-component structural dynamic model proposed earlier for interpreting the experimental results on neutron scattering by supercritical water (on the isotherm at 400°C, the density range 0.005 < ρ < 0.32 g/cm³) using the data on the hydrogen connectivity in supercritical water obtained by the molecular dynamics method.     

A topological approach to high-energy large transverse momentum interactions

We discuss the high p_T strong interaction from a topological (1/N_f) expansion viewpoint. Topology of quark line graphs is used to classify the underlying process rather than constituent scattering, all constituents being implicitly confined. The distinction between “jets” and “background” is clarified in a very simple dynamical model. Although the model does not require quarks as dynamical entities, many of its features are in agreement with parton model predictions.     

Some evidence of LOTO splitting in disordered ZnCl2

We report evidence for the existence of LOTO splitting effects in glassy and molten zinc chloride. The Raman scattering measurements compared with the literature existing IR data, allow to assign in our system all the optical modes characteristic of the T_d symmetry and the “lattice” mode convuluted with the “acoustic” contribution. Some calculations of microscopic quantities in the framework of Payne and Inkson model are performed to test the degenerate optical splitting mode hypothesis.     

Neutron diffuse scattering in Fe3O4 due to molecular polarons

The results of a precise re-examination of neutron diffuse scattering above the Verwey transition of Fe₃O₄ are reported. A model to describe the properties of valence fluctuations at the B-site Fe-ions are proposed, which assumes the existance of “molecular polarons”. The experimental results of anisotropic distribution of diffuse scattering seem to give an evidence for the feasibility of the proposed model.     

Neutron scattering study of anisotropic spin correlations in quasi two-dimensional antiferromagnet MnTiO3

An anisotropic three-dimensional neutron critical scattering has been observed from a “quasi” two-dimensional antiferromagnet MnTiO₃ in the vicinity of the Néel temperature. When temperature increases, the scattering profile transforms gradually to a ridge-like form, indicating that “cross-over” from three-dimensional to two-dimensional character appears at about 16 degrees above T_N.     

Raman scattering excited with 532 nm laser in bisphenol “AF” and its connection with bisphenol “A” and “S”

Bisphenol “AF,” a chemically similar replacement substitute for Bisphenol “A” which is a widespread environmental hormone, is studied by Raman spectroscopy (250–3500?cm^–1). Experimentally observed scattering peaks are illuminated by Density Functional Theory calculations. Principal component analysis is executed on the experimental Raman spectra of Bisphenol “AF” together with spectra of Bisphenol “A” and “S” reported earlier. Eight correlating molecular frequencies of Bisphenol “AF,” “A,” and “S” are found in contrast to 12 such frequencies of Bisphenol “A” and “S” only. The refined list of correlating frequencies manifests the existence of correlation in bisphenol family and clue toward their grouping, identification, detection, and screening together with mechanism responsible for toxicity.     

Concerning the semimetallic characters of TiS2 and TiSe2

Recent data on TiS₂ are discussed in terms of the dirty semiconductor model rather than the semimetallic model. The “T²” resistivity is attributed to scattering by “Fivaz-mode”, optic homopolar phonons rather than to electron-hole scattering.A slight semimetallic p-d overlap is finally obtained by TiSe₂ and leads to phenomena of the type expected for the ‘excitonic insulator’.     

Improved theoretical pion-nucleus optical potentials

An approach which makes the first order pion-nucleus optical potential theoretically sound is presented. This study should permit higher order improvements to the potential to be more meaningful and the nuclear structure information extracted from pi-nucleus scattering to be more reliable. Based on multiple scattering theory, three optical potentials are constructed and studied in momentum space. These models are the popular Kisslinger potential, the local “Laplacian” potential, and an “improved off-shell potential;” the latter one is derived from absorptive separable pion-nucleon potentials which exactly reproduce on-shell πN scattering. By working in momentum space and explicitly including πN resonances and off-shell effects in the definition of the optical potential, the approach described here is capable of handling any number of pi-nucleon partial waves, is applicable over a very wide energy region, is based on a physical model for off-shell behavior, and is extended easily to include higher order effects. The optical potentials are inserted into two different relativistic wave equations to determine the total cross section and elastic differential cross section for pi-nucleus scattering. It is found that the various models for off-shell πN scattering determine significantly different πC¹² scattering, with the improved off-shell model preferred on theoretical grounds. Also discussed is the importance of properly transforming πN scattering to the pi-nucleus c.m. system, the origin of the shift in the peak position of the π^?C total cross section, and the reason for the increased diffractive nature of the differential cross section at 180 MeV.     

On the prediction of impact noise,V: The noise from drop hammers

In earlier papers in this series, the concepts of “acceleration” and “ringing” noise have been studied in relation to impact machines, and values of radiation efficiency have been obtained for the various types of structural components. In the work reported in this paper the predicted and measured noise radiation from a drop hammer, both in full-scale and in $\text{1}\text{3}\text{-}\text{scale}$ model form, were examined. It is found that overall noise levels (L_eq per event) can be predicted from vibration measurements to within ± 1·5 dB, and to within ±2·5 dB in one-third octave bands. In turn this has permitted noise reduction techniques to be examined by studies of local component vibration levels rather than overall noise, a method which provides considerable enlightenment at the design stage. It is shown that on one particular drop hammer, the noise energy is shared surprisingly uniformly over four or five sources, and that when these have been reduced, the overall noise reduction is severely limited by the “acceleration” noise from the “tup” or “hammer” itself. As this is difficult to eliminate without a basic change in forging technology, it follows that “tup” enclosure or modification of the sharpness of the final “hard” impact are the only means available for any serious noise reduction. Also indicated is the reliability of using model techniques, suitably scaled in frequency and impulse magnitude, in developing machinery with impact characteristics.     

QCD asymptotics and kinematic thresholds in deep inelastic scattering

The Nachtmann moments of deep inelastic scattering structure functions are required by kinematics to contain a so far neglected threshold factor which is dependent on both n and q². Its presence significantly affects the “moment analysis” in the usual QCD phenomenology and it resolves the difficulties connected with improper threshold behavior of the “ξ-scaling” analysis of structure functions.     

Relative intensities in X-ray photoelectron spectra: Part XI. Calculation of photoionization cross sections for valence levels of SiF4

Partial photoionization cross sections for valence MOs of SiF₄ have been calculated by the method of multiple scattering with atomic amplitudes (MSAA) for excitation energies ranging from the ionization threshold to 60 eV. The cross section behavior near the ionization thresholds is determined mainly by the shape resonances of t₂ and e symmetries. The resonance structure of photoionization cross sections is treated in terms of deviations from the additive model, and of conceptions of “quasi-stationary” states and “quasi-forbidden” bands. The energy positions of quasi-stationary states in SiF₄ are compared with the data obtained from X-ray absorption spectra. The dependence of theoretical cross sections on the inter-nuclear distances is studied.     

6Li scattering: A failure of the double-folded potential model

Data for ⁶Li scattering elastically from various nuclei were analyzed using the double-folding model together with a recently introduced “realistic” effective interaction which has reproduced the potentials for heavier ions. However, it is concluded that the potential for ⁶Li is not given by this model which systematically overestimates it by nearly a factor of two.     

On-shell faddeev equations: A democritean approach to the three-body problem

Coupling the mass-energy relationδE≧mc² to the uncertainty relationδE δt ≧ ? produces fluctuations in the number of particles at short distances and scatterings of particle pairs independent of any specific “interaction” mechanism. This observation allows the construction of a scattering theory in which there are only particles and the void, but particle number can change. We consider a system of three massive particles (hadrons) in the energy region below the first production threshold for a fourth hadron and above the first anomalous threshold for the presence of a fourth “virtual” hadron. The on-shell Faddeev equations, containing only two-particle scattering phases for positive two particle energies, provide a convergent, unitary, and readily soluble dynamics for this system. If any of the pairs can coalesce into a different particle with a rest energy less than the sum of the rest energies of the pair, the equations can be readily extended to describe 3-2 and 2–3 transitions involving this particle (coalescence, breakup) elastic scattering from it, and if there is more than one such particle 2-2 rearrangements. The three-body “bound state” requires a well defined analytic continuation. Features of more conventional calculations of three-nucleon problems which provide examples of this structure are discussed. Since only free particles occur in the theory, and the only failure of energy conservation is that required by the uncertainty principle for (free-particle) intermediate states, these one-variable equations might be extended to particles with the relativistic connection between mass, energy and momentum, and transitions in which the full rest energy of the particle which appears or disappears must be provided. The non-linear “crossed” theory for such particles has not been written down, but if the relativistic boundary condition model of Brayshaw is viewed as representing these crossed processes by a phenomenological core, then a crossed theory requiring the π to be a bound state of three π's might predict the π-π S-wave scattering length in theI=0 state in terms of the pion Compton wavelength (and hence the position and the width of the?) and will then show that the? in turn generates asingle ω resonance at about the right place. Implications are discussed.     

Elementary particle component of the deuteron

The low energy nucleon-nucleon system is analyzed by means of a model interaction which includes coupling of the nucleons to an “elementary deuteron” state. The probability of the elementary particle component, or “elementarity”, of the physical deuteron is investigated. It is found that, contrary to earlier assertions, the low energy scattering parameters do not determine the elementarity of the deuteron in a model-independent way.     

On the occupation of interstitial sites by hydrogen atoms in intermetallic hydrides: A quantitative model

A simple model to predict the relative occupation numbers of various interstitial sites in intermetallic hydrides is proposed. The model assumes that the occupation numbers are determined by Boltzmann distribution function as well as by the heat of formation of the “imaginary binary hydrides” formed between the hydrogen atoms and the host metallic atoms forming the interstitial sites. Comparison of our calculations with recent neutron scattering data on various hydrides indicate good agreement at T=300 K.     

Exakte Lösungen von Low-Gleichungen

The general solution of the Low equation for a family of two-dimensional crossingmatrices is constructed. It depends on 2 arbitrary functions and its Riemann surface has an infinity of distinct sheets. Furthermore a subclass of solutions of the 3dimensional and 4dimensional pseudoscalar symmetricπ-N scattering theory is constructed, the former depending on 2 arbitrary functions, the latter on 3. The criterion of minimal zeros in the scattering functions on the physical sheet is applied, to restrict this manyfold. In the threedimensional case the restricted solution depends on 2 parameters which may be interpreted as “coupling constant” and “cut off”. In the 4dimensional case the criterion of minimal zeros in the scattering functions gives a solution which depends on 5 parameters and thus is not uniquely determined by a “coupling constant” and a “cut off”.