Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

BAMLSS: Bayesian Additive Models for Location,Scale, and Shape (and Beyond)

Bayesian analysis provides a convenient setting for the estimation of complex generalized additive regression models (GAMs). Since computational power has tremendously increased in the past decade, it is now possible to tackle complicated inferential problems, for example, with Markov chain Monte Carlo simulation, on virtually any modern computer. This is one of the reasons why Bayesian methods have become increasingly popular, leading to a number of highly specialized and optimized estimation engines and with attention shifting from conditional mean models to probabilistic distributional models capturing location, scale, shape (and other aspects) of the response distribution. To embed many different approaches suggested in literature and software, a unified modeling architecture for distributional GAMs is established that exploits distributions, estimation techniques (posterior mode or posterior mean), and model terms (fixed, random, smooth, spatial,…). It is shown that within this framework implementing algorithms for complex regression problems, as well as the integration of already existing software, is relatively straightforward. The usefulness is emphasized with two complex and computationally demanding application case studies: a large daily precipitation climatology, as well as a Cox model for continuous time with space-time interactions. Supplementary material for this article is available online.     

Crystalline field effects in superconducting La1−xTbxAl2 under pressure

The pressure dependence of the superconducting transition temperature of LaAl₂ and alloys with Tb and Gd impurities has been measured. The results are compared with a theoretical calculation of the pressure dependence ofT _c , which is based on the variation by pressure of the crystalline field experienced by the Tb ions. Measurements onLaGdAl₂ where crystal field effects are absent have been used to study the influence of pressure on the scattering rate.     

Low temperature properties of (La,Nd)Sn3 alloys

Dilute (La_1–x Nd _x )Sn₃ alloys with 0.01<x<0.15 are characterized by determination of the superconducting transition temperatureT _c as well as low temperature measurements of the specific heat and inelastic neutron scattering. As an important result of these experiments we found that the Nd impurities in LaSn₃ exist as stable trivalent ions, in contrast to all other light rare earths. In addition, specific heat and neutron scattering results revealed the scheme of crystal field (CF) levels of Nd³⁺.Using this level scheme, the concentration dependence of the superconducting transition temperature,T _c (x), could be quantitatively fitted up tox9 at % by the theory of Keller and Fulde [J. Low. Temp. Phys.4, 289 (1971)]. From the relatively high initial slope ofT _c (x) we inferred that — besides isotropic spin exchange — other pair-breaking processes are important.In contrast toT _c (x), the reduced specific heat jumpsC/C ₀ as a function ofT _c /T _c0 (whereT _c0 andC ₀ refer to LaSn₃) were found to lie considerably below the theoretical curve for isolated Nd³⁺ ions. This is explained by Nd—Nd interactions resulting in a mean Zeeman splitting (<k _B T _c ) of the CF ground state, which could be directly observed in the form of broadened Schottky humps in the normal state specific heats.     

Wärmeleitung und kalorische Effekte in supraleitendem Niobium

The thermal conductivity in the mixed state of Nb is not only a function of the average energy gap. An extra scattering arising from the spatial modulation of the gap must be considered. The characteristic minimum of thermal conductivity is influenced by magnetic hysteresis. This effect is explained byBean's model of flux-penetration. The forgoing results run out from measurements of thermal conductivity and magnetization of several niobium samples in a longitudinal magnetic field.     

The electronic structure of from high energy spectroscopy

We report the results of a detailed study of the occupied and unoccupied electronic structure of dimers of the new heterofullerene by means of photoemission and electron energy-loss spectroscopy. A close similarity is found between the electronic structures of pristine and with an additional broadening of the spectra in the former due to the distortion of the fullerene cage caused both by dimerization and the chemical substitution. Both the occupied and unoccupied electronic states, as well as the interband transitions between them, attest to the high degree of molecular character retained in the solid state. Comparison of the shake-up structures in the and X-ray photoemission spectra confirm that the highest lying occupied states in the heterofullerene have a strong degree of N character, whereas the lowest lying unoccupied states have mainly C character. We also present the optical conductivity of the heterofullerene (derived from the loss function), which shows an optical gap of 1.4 eV, some 0.4 eV smaller than that of . Received: 25 August 1997 / Revised: 22 September 1997 / Accepted: 16 October 1997     

Nuclear orientation of183Re and184Re in iron

The temperature dependence of the anisotropy of γ-rays from the decay of oriented¹⁸³,¹⁸⁴Re nuclei situated in an iron matrix was measured between 14 and 33 mK. Magnetic hyperfine splitting constants ofgH _HF=5.04(9) × 10^?18 erg andgH _HF=3.21 (13) × 10^?18 erg were determined for the groundstates of¹⁸³Re and¹⁸⁴Re, respectively. With the previously known hyperfinefield of ?760(15) kG for Re in iron the followingg-factors were deduced:¹⁸³Reg=1.32 (5) and¹⁸⁴Reg=0.84 (5). The E2/M1 mixing ratio of the 793 keV 2⁺ ?2⁺ transition in¹⁸⁴W was accurately determined to δ (793 keV)=+16.65 (85).     

The influence of crystal field split impurities (Tb) on the superconducting properties of LaAl2

The superconducting transition temperatures of the system La_1-xTbxAl₂ have been measured. By making use of the theory of Keller and Fulde the energy splitting between the ground state and the first excited state of Tb³⁺ is found to be 5 ± 1 K. Furthermore, we have determined the upper critical field H_c2(T) of these alloys and compared the results with those found for La_1-xGd_xAl₂. In this way the influence of the crystal field splitting of Tb³⁺ on the critical field data is clearly demonstrated.     

Anomalous thermal expansion of CeAl3 due to valence mixing

The lattice parameters of the compounds CeAl₃, LaAl₃, PrAl₃, and GdAl₃ have been measured with x-rays in the range $\text{5}\text{K}{}^{\mathrm{\le }}\text{T}{}^{\mathrm{\le }}\text{300}\text{K}$. In spite of their similarity, a significant difference between CeAl₃ and the other compounds is found in the relative volume change $\text{Δ}\text{V}\text{V}\text{(}\text{T}\text{)}$. This is attributed to an increasing admixture of Ce⁴⁺ with decreasing temperature. Furthermore, cristalline-field effects are observed in the case of PrAl₃.