Model-independent separation of structure functions over an extended kinematical region

A method for the separation of structure functions in (e, e p) experiments is proposed, which is an extension of the traditional Rosenbluth-type techniques of [1,2]. In our approach, we use a very flexible Ansatz to describe the structure functions within an extended kinematical regionG and determine its free parameters with a x² minimization. The procedure is tested by pseudo data (¹²C(e, ep)¹¹B_g.s.) in the quasi-free region.Part of the doctorate-thesis of Thomas Veit     

Optical spectrum and local lattice structure for ruby

We perform ab initio calculations using a pseudo-potential plane-wave method based on density functional theory, within the local density approximation and generalized gradient approximation, in order to determine and predict the pressure dependence of structural and elastic properties of spinel compounds: MgAl₂O₄, MgGa₂O₄ and MgIn₂O₄. The results are in agreement with the available experimental data and other theoretical calculations.     

Effects of the form factor on exclusive (e, e′p) reactions

For the exclusive (e, e′p) reaction, we discuss the possibility of observing effects due to swollen nucleons in the nuclear medium, such as ⁴⁰Ca and ²⁰⁸Pb, by introducing form factors of the nucleon in the nuclear medium. These form factors include effectively the change of nucleon properties in the nuclear medium. This calculation is performed by using a Dirac-Hartree single particle model for a bound state and a relativistic optical model for a continuum state with inclusion of the electron Coulomb distortion. The effect of the form factor, which increases with higher momentum transfer (q ≥ 400MeV/c) is too small to be discerned from the errors on the available experimental data. But it affects the determination of spectroscopic factors to some extent.     

High pressure study of the organic compound (TMTTF)<Subscript>2</Subscript>BF<Subscript>4</Subscript>

High pressure resistivity measurements of the organic compound (TMTTF)₂BF₄ have been performed in a newly developped Bridgman cell providing good pressure conditions on a wide pressure range. For the first time in this compound a zero resistance superconducting state is observed between 3 and 4 GPa. At temperatures above the superconducting transition, the resistivities of the two high quality samples show a different behavior. One sample, provides indications for a magnetic quantum critical point at the maximum of T_c, whereas in the other antiferromagnetic spin-fluctuations are present above T_c.     

Electronic and magnetic properties and their response to pressure in Ni2MnB

The electronic structure and magnetic properties of Ni₂MnB upon pressure up to 20 GPa have been studied by using the density functional theory (DFT) method. The results indicate that ferromagnetic ordered Ni₂MnB in L2₁ structure is more stable than the nonmagnetic one. The magnetic moments of Ni and Mn atoms as well as the total magnetic moment of Ni₂MnB are found to decrease weakly with increasing pressure. The pressure derivative of the total magnetic moment is −3.07×10⁻³ GPa⁻¹. The equilibrium bulk modulus and its derivative from the Murnaghan equation of state (EOS) are B₀=247.7 GPa, B′=4.98.     

Mantle convection: A review

The solid-state convection in the Earth mantle is characterized by plate tectonics, which shapes the tectonic activities of the Earth, and superplumes as broad hot regions chemically distinct from the surrounding regions in deep lower mantle. Recent numerical studies of mantle convection suggest that the rigidly moving plates occur on the Earth because the rupture strength of plate margins is sufficiently low, while that of plate interiors is high enough to inhibit spontaneous formation of new plate boundaries by the weight of the plates themselves. This implies that the activity of plate tectonics has fluctuated much in the Earth history. Recent numerical studies also suggest that the superplumes develop owing to the chemical differentiation of the mantle by ridge magmatism. Superplumes have probably induced frequent and vigorous hot spot volcanism in the early Earth. It is now within reach to construct an integrated model for tectonic and structural evolution of the mantle in the Earth and other terrestrial planets.     

On the behavior of the nuclear spectral function at high momentum and removal energy

We propose a procedure to extrapolate the nuclear spectral function P(|k|E) obtained from nonrelativistic many-body theory to large values of three-momentum and removal energy. Our approach is based on phenomenological information extracted from both soft hadron-nucleus interactions, in the regime where the proton inclusive spectrum is dictated by Regge asymptotic, and deep-inelastic lepton-nucleus collisions. The extrapolated P(|k|E) is used to compute the semi-inclusive spectra of backward protons produced in electron-nucleus scattering. Received: 1 December 1998 / Revised version: 19 January 1999     

Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding

The electric form factor of the neutron G _E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q ²= 0.15 (GeV/c)² in a measurement of the recoil polarisation ratio P _x/P_z in the quasifree reaction D(e,e′n)p. At this Q ² the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenh?vel et al.. After the corresponding corrections a value of G _E,n(0.15 (GeV/c)²) = 0.0481±0.0065_stat±0.0053_syst is obtained. Received: 12 April 1999     

On the treatment of the Δ-contributions in electromagnetic pp-knockout reactions

The treatment of the Δ-current and its contribution in the exclusive ¹⁶O (e, e'pp)¹⁴C and ¹⁶O (γ, pp)¹⁴C knockout reactions are investigated in combination with the effects of correlations. Different parametrizations of the effective Δ-current and different treatments of correlations in the two-nucleon overlap function are considered. The results are presented and discussed for a suitable choice of kinematics. It is found that the investigation of different mutually supplementing kinematics is necessary to resolve the uncertainties in the theoretical ingredients and extract clear and unambiguous information on correlations.     

A simple model of resonance-dominated quasi-elastic scattering

We examine a highly simplified model of projectile-nucleus scattering in which the elementary interactions are resonance dominated. The essential element introduced into the nuclear dynamics is a shift of spectral strength to an energy comparable with or greater than the resonance half-width. The interplay of the energy dependences yields strong sensitivity to the underlying dynamics. Phenomenological treatments based on simplified nuclear dynamics, such as the -hole model, are seen to reproduce inclusive observables. They do less well on more exclusive observables and can be misleading in their implications for the underlying physics.Communicated by F. Lenz