Spin content of the nucleon in a non-topological chiral soliton model

The spin content of the proton is investigated by studying the flavor singlet axial structure of the nucleon in a non-topological chiral soliton model. In order to construct a nucleon state we used the generator coordinate projection method as well as a coherent state for the meson wave function. Using a standard set of parameters we found the value g _A ⁰ ? 0.44 for the flavor singlet axial vector coupling constant. This result is not far from that of a typical valence quark model.     

Interlayer pairing in high temperature superconductors: effect of nonmagnetic impurities

The influence of impurity scattering is studied theoretically in a two-layer model for the high-T _c superconductor Y₁Ba₂Cu₃O_7– with intra- and inter-layer pairing. Two types of impurities are considered: (I) impurities which conserve the reflection symmetry of the two layers and (II) impurities which break it. Impurities of type (I) have no influence on the critical temperature. Type (II) impurities have strong influence onT _c as well as onH _c2 if there is a pairing interaction between carriers of different layers. The treatment of type (II) impurities is generalized to a periodic layer model appropriate for La_2–x Ba _x CuO₄. Available experiments on impurities in Y₁Ba₂Cu₃O_7– and La_2–x Ba _x CuO₄ are interpreted with our theory.     

Optimization of scrapping decisions: Theory and applications

Contrary to the variety of models and procedures for optimizing the ordering decision in inventory control theory, no comparable tools exist for the scrapping decision. Thus, the current paper constitutes a step in this direction. Using a simple deterministic model, the basic economics and structure of the problem are introduced first. Then we determine explicitly scrap-optimal turn-around-times as well as the corresponding scrap- and rest-quantities. Accounting for the stochastic nature of demand, the model is generalized and algorithms for determination of optimal scrapping decision are discussed. Finally we compare the results and discuss practical applications.     

Radiative processes and non-equilibrium thermodynamics

With the assumption of an elementary physical concept meteorologically effective radiative processes (absorption-emission, scattering) can be included consistently in nonequilibrium thermodynamics of irreversible phenomena. Analogously to the usual Gibbs relations a fundamental equation was formulated for monochromatic light rays as the nucleus of the theory.Using the methods of classical irreversible theory, a complete entropy balance equation is derived in which the entropy variations of the mass as well as of the radiation field are explicitly represented. The resulting entropy source strength function through its analytical structure reveals the dynamical character of the irreversible variation terms. The-expression being positive according to the second law of thermodynamics is found to have a bilinear form as a function of the irreversible fluxes representing the entropy generating radiative processes and their conjugated thermodynamic forces. The mathematical structure and the positive sign of, following the usual line of reasoning, motivate the assumption of constitutive relations for the irreversible radiative processes. These equations developed from purely thermodynamical reasoning turn out to be equivalent to the usual radiative transfer equation which is founded on a very different theoretical concept. A very fundamental relationship can be deduced in this context from the entropy production function. It provides a direct thermodynamical proof that in nonscattering media the definition of a local temperature is necessarily accompanied by the validity of the Kirchhoff law.     

Magnetic excitations in the quasi one-dimensional antiferromagnetic singlet groundstate system CsFeBr3

We have measured the magnetic excitations in CsFeBr₃ along the chain direction (z-axis) and perpendicular to it by inelastic neutron scattering. The measured dispersion curves can be reproduced by the formula $$\omega ^2 (q) = A^2 - 8A[J\cos (\pi q_c ) + J'\gamma (2\pi q_ \bot )]R(T)$$ which is very different from dispersion relations for usual 1 D antiferromagnets, because of the singlet groundstate of this system. The large value of the anisotropy energyA/k=29.8±0.5 K, which is independent of temperature, causes the singlet groundstate. The intra-and inter-chain exchange parameters areJ/k=?3.2±0.15K andJ'/k=?0.32±0.02 K determined atT=1.4 K. At 1.4 K the renormalisation factor is taken to beR(T)=1. AtT=30 K the value forR(T) was found to be 0.5±0.1 keepingJ andJ' unchanged. The excitations at (1/3 1/31) show soft mode behaviour but no phase transition. The observed intensities are interpreted by a heuristic model for the eigenvectors in the excited state including antiferro-as well as ferromagnetic configurations of the fluctuations.     

Exciton-related optical nonlinearities in semiconductors and semiconductor microcrystallites

We report on large optical nonlinearities due to specific many-body effects in high-density electron-hole pair systems. On bulk CdS we study the effect of free-carrier screening on the absorption and refraction in the vicinity of the band-gap at room temperature. Steady-state saturable absorption at mW-power levels and four-wave mixing with first-order efficiencies as large as 2% of the incoming light are demonstrated on a 1m slab. On CuBr microcrystallites embedded in glass we investigate the changes of the exciton absorption caused by many-exciton effects both at cryo and room temperature. In contrast to bulk semiconductors, we observe a blue shift of the exciton peak at resonant optical excitation. In addition, strong saturation of absorption with very large contrast shows up. We find Lorentzian saturation intensities in the 100 kW/cm² range.     

The magnetic moment of the 10+ isomer in140Ce andE1 transitions inN=82 isotones caused by outer subshell configurations

Using the reaction¹³⁸Ba(α,2n)¹⁴⁰Ce the magnetic moment of the 10 ₁ ⁺ isomer atE _x =3714.7 keV in theN=82 nucleus¹⁴⁰Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ _N . Measuredg-factors in¹⁴⁰Ce are compared to calculations within the shell model with configuration mixing. For the 10 ₁ ⁺ isomer in¹⁴⁰Ce the four proton configuration π(1g ₇ ^2/2 ,2d ₅ ^2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d _3/2,π3s ₁ ² or π1h ₁₁ ² shells and admixtures of neutron excitations to the wave function of the 10 ₁ ⁺ state could be excluded. The strongE1γ-branch of the deexcitation of the 10 ₁ ⁺ isomer in¹⁴⁰Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f _7/2 andπ1h _9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei¹⁴⁰Ce,¹⁴¹Pr and¹⁴⁵Eu may be understood.     

New aspect in transient magnetic fields using heavy ion beams

Transient field precessions have been measured with the first excited 2 ₁ ⁺ -state as probe for ions of²⁸Si traversing Fe at v_ion?1v₀ and 13v₀(v₀=c/137) and⁶²Ni being stopped in Fe. The degree of polarization deduced for the Si ions, p_1s=0.19(6), is consistent with low-velocity data. There is clear evidence that the field strength is attenuated by heavy ion beams. For the⁶²Ni(2 ₁ ⁺ ) state at 1.173 MeV a g-factor value of g=0.34(7) was obtained in good agreement with a previous result.     

Optical humidity and ammonia gas sensors using Reichardt's dye-polymer composites

Optical intensity reflected at 750 nm by Reichardt's betain dye-polymer (PMMA or PEO) composite increased with an increase in humidity and was not affected by ammonia vapor. For the composites treated with hydrochloric acid, the intensity at around 590 nm decreased with an increase in ammonia concentration, and the sensitivity was enhanced by the presence of water vapor. The treatment with hydrochloric acid induced the formation of phenolic group, O⁻---H⁺ and N⁺---Cl⁻ in the dye. The sorption of NH₃ decreases the ionic interactions.