Single \mathrm{\ensuremath{\pi^{-}}} production in np collisions for excess energies up to 90 MeV

The quasifree reaction was studied in a kinematically complete experiment by bombarding a liquid-hydrogen target with a deuteron beam of momentum 1.85GeV/c and analyzing the data along the lines of the spectator model. In addition to the three charged ejectiles the spectator proton was also detected in the large-acceptance time-of-flight spectrometer COSY-TOF. It was identified by its momentum and flight direction thus yielding access to the Fermi motion of the bound neutron and to the effective neutron 4-momentum vector _n which differed from event to event. A range of almost 90MeV excess energy above threshold was covered. Energy-dependent angular distributions, invariant-mass spectra as well as fully covered Dalitz plots were deduced. Sizeable pp FSI effects were found as were contributions of p and d partial waves. In comparison with existing literature data the results provide a sensitive test of the spectator model. The behavior of the elementary cross-section σ₀₁ close to threshold is discussed in view of new cross-section data.     

Irreducible pionic effects in nucleon-deuteron scattering below 20 MeV

The consequences of a recently introduced irreducible pionic effect in low-energy nucleon-deuteron scattering are analyzed. Differential cross-sections, nucleon (vector) and deuteron (vector and tensor) analyzing powers, and four different polarization transfer coefficients are considered. This 3NF-like effect is generated by the pion exchange diagram in presence of a two-nucleon correlation and is partially cancelled by meson retardation contributions. Indications are provided that such type of effects are capable to selectively increase the vector (nucleon and deuteron) analyzing powers, while in the considered energy range they are almost negligible on the differential cross-sections. These indications, observed with different realistic nucleon-nucleon interactions, provide additional evidences that such 3NF-like effects have indeed the potential for solving the puzzle of the vector analyzing powers. Smaller but non-negligible effects are observed for the other spin observables. In some cases, we find that the modifications introduced by such pionic effects on these spin observables (other than the vector analyzing powers) are significant and interesting and could be observed by experiments. Received: 21 November 2001 / Accepted: 18 March 2002     

Crystal inclusion chemistry of zinc-tetra(4-bromophenyl)porphyrin

The structural patterns of Zn(II)-tetra(4-bromophenyl)porphyrin and several of its newly prepared complexes and clathrates in the solid phase were determined by X-ray crystallography. The molecular structure of the porphyrin compound is characterized by a nearly perfect planarity of the metalloporphyrin core due to effective Zn...;Br intermolecular interactions in the crystalline lattice. The composite materials show three different kinds of interporphyrin organization, dominated to a large extent by the molecular shape, often exhibited by related tetraphenylporphyrin derivatives. These include monoclinic herringbone packing modes without any apparent involvement of the halogen atoms in specific interactions, chained interporphyrin arrangements exhibiting C-Br...; close approach, and porous layered networks of the porphyrin species revealing direct Br...;Br contacts. The latter two forms are also affected by C-H...;Br attractions. Four-, five- and six-coordination of the central zinc ion was observed, but there is no apparent correlation between the coordination number and the crystal packing type. Thermal analysis revealed the relative strength of binding of the ligand and solvate species to the porphyrin lattice. The bromophenyl-substituted porphyrin building block forms only a small number of crystalline heteromolecular materials with other components, and occurrence of the uniquely structured porous porphyrin networks is not as dominant as in the analogous chlorophenyl derivatives. Estimates of interporphyrin packing stabilization energies suggest that the stability of these layered patterns is affected primarily by dipolar attractions, which are less significant in solids containing the Br, rather than Cl, groups. Supplementary Data relating to this article have been deposited with the British Library as supplementary publication No. SUP 82200 (40 pages).     

茂型稀土金属有机配合物催化甲基丙烯酸酯类聚合研究进展

综述了茂型稀土金属有机配合物催化甲基丙烯酸酯类聚合的研究现状和最新进展。系统地介绍了不同的茂型稀土金属有机催化体系中温度、反应时间、溶剂等条件对催化甲基丙烯酸酯类聚合的影响规律,并研究其催化反应机理,最后展望茂型稀土金属有机化学今后的研究方向及前景。     

Synthetic Polyphosphonates,Polyphosphates, and Phosphonocarboxylates as Allosteric Effectors of Hemoglobin

Abstract

Synthetic phosphonocarboxylates, diphosphonates, polyphosphates, and some triphosphonic acids were studied as effectors in the binding of dioxygen to human hemoglobin. Ethane-1,2-diphosphonic acid, and triphosphate anion were strong effectors.     

A class of one-dimensional geometric variational problems with energy involving the curvature and its derivatives: a geometric measure-theoretic approach

The notions of Legendrian and Gaussian towers are defined and investigated. Then applications in the context of one-dimensional geometric variational problems with the energy involving the curvature and its derivatives are provided. Particular attention is paid to the case when the functional is defined on smooth boundaries of plane sets.      

Kinetics of muon catalyzed fusion processes in solid H/D mixture

This paper presents the final results of an experimental study of the kinetics of the muon catalysed fusion (MCF) in solid hydrogen-deuterium mixtures (H/D) at a temperature of 3 K. The experiment E742 was carried out on a TRIUMF meson facility in Canada. Four exposures were performed at different deuterium concentrations in the H/D mixture: c_d = 0.0005, 0.02, 0.15 and 0.75. A simultaneous analysis of the measured time distributions of the 5.5 MeV γ-quanta and the 5.3 MeV conversion muons obtained from nuclear fusion in the pdμ molecule allowed to extract the values of MCF chain parameters in the H/D mixture: the fusion partial rates for different nuclear spin states of the pdμ molecule, and the pdμ molecule formation rate. The experimental data fitting procedure was conducted in two ways: using solely the analytical formulae describing the kinetics of the MCF processes in the H/D mixture, and the detailed Monte Carlo simulation of the entire experiment. The results obtained by these two methods are consistent with each other and confirm the existence of the Wolfenstein-Gerstein effect.     

A NEW CLASS OF BILEVEL GENERALIZED MIXED EQUILIBRIUM PROBLEMS IN BANACH SPACES

A new class of bilevel generalized mixed equilibrium problems involving setvalued mappings is introduced and studied in a real Banach space. By using the auxiliary principle technique, new iterative algorithms for solving the generalized mixed equilibrium problems and bilevel generalized mixed equilibrium problems involving set-valued mappings are suggested and analyzed. Existence of solutions and strong convergence of the iterative sequences generated by the algorithms are proved under quite mild conditions. The behavior of the solution set of the generalized mixed equilibrium problems and bilevel generalized mixed equilibrium problems is also discussed. These results are new and generalize some recent results in this field.     

πphotoproduction on the deuteron via Δ-excitation using the Lorentz Integral Transform

The Lorentz Integral Transform method (LIT) is extended to pion photoproduction in the Δ-resonance region. The main focus lies on the solution of the conceptual difficulties which arise if energy-dependent operators for nucleon resonance excitations are considered. In order to demonstrate the applicability of our approach, we calculate the inclusive cross-section for π⁰-photoproduction off the deuteron within a simple pure resonance model.