Convergence properties of relaxation algorithms

Nonadaptive relaxation algorithms require strong continuity assumptions and adaptive relaxation algorithms are computationally costly. To remedy that situation, an anti-jamming procedure similar to the one used by the author for the method of feasible directions is proposed. The resulting algorithms are compared with the existing ones for solving unconstrained optimization problem inE ⁿ .     

Structure of sulfur-stabilized carbanions. A 13C NMR study of some α-lithio-sulfoxides and sulfones

¹³C chemical shifts and ¹J(¹³CH) coupling constants provide information on the structures of some α-lithio-sulfoxides and sulfones.     

Towards supersymmetric subconstituent models

't Hooft's consistency equations for subconstituent models are generalized to supersymmetric theories and a few solutions are outlined.     

Unusual transformations of the chrysanthemic nitrile skeleton by sodium hydride in n,n-dimethylformamide

It is shown that the title transformations occurred through basecatalyzed opening of the cyclopropane ring into the dienic nitrile $\text{4}$which then reacted with the in situ formed formaldehyde to yield the bicyclic compound $\text{5}$.     

NMR (195Pt and 13C) contribution to the study of some Pt(II), Pt(IV) and mixed-valence thioamido complexes

The ¹⁹⁵Pt and ¹³C chemical shifts (δ_Pt and δ_c) are reported for platinum(II), platinum(IV) and class II mixed-valence complexes, with general formula [PtL₄]X₂, cis- and trans-PtL₂X₂, PtL₂X₄ and Pt₂L₄X₆ (where L may be thiourea, 2-imidazolidine-thione, tetrahydro 2-pyrimidinethione, thiocaprolactam, pyridine-2-thione and tetramethylthiourea, and X may be Cl or Br). The ¹⁹⁵Pt chemical shifts can be understood in view of ¹³C data in terms of variations of electronegativities and σ-donor abilities of ligands attached to platinum.     

A simple jitter-free picosecond streak camera

Using a DC-biased room-temperature photoconductive switching element, a picosecond resolution optical streak camera is operated at sweep rates up to 7 ps/mm. Single-shot jitter is 2 ps with complete absence of short and long-term drift characteristic of all other sweep drivers. This high accuracy allows the streak camera to be used in a single-shot averaging mode which leads to a sub-picosecond absolute timing accuracy. When operated in this manner, the streak camera becomes a highly reliable and accurate device for measuring transient events on a time scale of single picoseconds. The simplicity of this method makes it highly attractive for many applications in laser fusion and picosecond chemistry and photophysics studies where reliable no-drift operation is highly desirable.     

Preparation of bis(μ-chalcogeno) complexes [(η5-RC5H4)2M(μ-E)]2 M = Zr,Hf; R = H,t-Bu; E = S or Se from metallocene dichlorides,and isolation of the mixed μ-complexes [(t-BuC5H4)2Zr2](μ-O)(μ-E)

Metallocene dichlorides (RCp)₂MCl₂ (M = Zr, Hf; R = H, t-Bu) react with E/2HLiBEt₃ (E = S, Se) to give the symmetrical dinuclear compounds [(RCp)₂M(μ-E)]₂. UV irradiation in toluene of [(t-BuCp)₂Zr(CH₃)]₂(μ-O) in the presence of powdered sulfur or gray selenium gives the new compounds [(t-BuCp)₂Zr₂](μ-O)(μ-E).     

Band model describing the magnetic properties of Fe2−xMxP1−yAsy type compounds with hexagonal structure

The variation of the magnetic properties of the system Fe₂P_1?yAs_y, in the structure range of Fe₂P, enables us to derive a band model for these compounds. It is characterized by very narrow d bands splitted by the crystal-field. The bandwidth is close to the exchange interactions and to the crystal-field splitting. The model, extended to the series Fe_2?xM_xP_1?yAs_y, where M = Mn, Fe, Co, Ni is able to explain magnetic, electric and hyperfine results.