Realization of dual,tunable, ordinary- and quantized-Hall resistances in doubly connected GaAs/AlGaAs heterostructures

An experimental configuration based on gated, double boundary GaAs/AlGaAs devices provides the first demonstration of dual distinct, tunable Hall resistances in the same sample over the weak- and strongmagnetic field limits, including the simultaneous observability of dual quantized Hall effects of dissimilar filling factors. These experiments suggest that the ordinary Hall resistance examined in experiment is essentially a topological resistance determined by connectivity, which need not reflect all “local” values of the off-diagonal resistivity, θ _M ρ _xy .     

Packing triangles in low degree graphs and indifference graphs

We consider the problems of finding the maximum number of vertex-disjoint triangles (VTP) and edge-disjoint triangles (ETP) in a simple graph. Both problems are NP-hard. The algorithm with the best approximation ratio known so far for these problems has ratio 3/2+?, a result that follows from a more general algorithm for set packing obtained by Hurkens and Schrijver [On the size of systems of sets every t of which have an SDR, with an application to the worst-case ratio of heuristics for packing problems, SIAM J. Discrete Math. 2(1) (1989) 68-72]. We present improvements on the approximation ratio for restricted cases of VTP and ETP that are known to be APX-hard: we give an approximation algorithm for VTP on graphs with maximum degree 4 with ratio slightly less than 1.2, and for ETP on graphs with maximum degree 5 with ratio 4/3. We also present an exact linear-time algorithm for VTP on the class of indifference graphs.     

Photo-excited zero-resistance states in quasi-two-dimensional GaAs / AlxGa1−xAs devices

We illustrate some experimental features of the recently discovered radiation-induced zero-resistance states in the high-mobility GaAs/AlGaAs system, with a special emphasis on the interplay between the radiation-induced changes in the diagonal resistance and the Hall effect. We show that, quantum Hall effects, i.e., quantum Hall plateaus, disappear under photoexcitation, at the minima of the radiation-induced magnetoresistance oscillations.     

Frequency distribution function and critical points for phonons in graphite

A molecular force field for the study of the dynamics of graphite has been reported earlier (Mani and Ramani 1974). In the present paper we present calculations of the single phonon density of states and the lattice specific heat. Most of the peaks in the frequency distribution function have been identified and classified using symmetry-required critical points. The validity of the force field used has also been discussed.     

Preparation of radioidinated insulin and thyroid stimulating hormone using 1,3,4,6-tetrachloro-3α, 6α-diphenylglycouril (Iodogen) for radioimmunoassay

Radioiodinated insulin and thyroid stimulating hormones were prepared using 1,3,4,6-tetrachloro-3, 6-diphenylglycouril (Iodogen). Conditions of iodination like concentration of iodogen, reaction time, etc., were optimized to get maximum yield. Stability studies of iodogen coated tubes were carried out over a period of time. The dependence of iodination yield on varying amounts of activity and protein concentration were investigated. Iodination yield over a range of pH was also studied. The radiolabelled hormones prepared by this method were used in radioimmunoassay and were compared with tracers prepared by the Chloramine-T method.     

Gleichungen und Ungleichungen für die Gerüste von konvexen Polytopen und Zellenkomplexen

Ohne Zusammenfassung Der erste Verfasser ist von einer Harkness Fellowship des Commonwealth Fund unterstützt worden, der zweite Verfasser von einem Stipendium des Schweizerischen Nationalfonds     

Studies on Trace Labelling of Bromsulphalein (BSP) with Radioiodine

Two methods have been studied for high specific activity trace iodination of Bromsulphalein (BSP) with radioiodine (¹³¹I). In the first method, BSP in aqueous solution is reacted with iodine and an oxidising agent – hydrogen peroxide or chloramine T. In the second method, iodination is carried out by electrolytically liberated iodine. The electrolytic method gives labelled BSP free from any labelled degradation products. The stability of ¹³¹I-labelled BSP in aqueous solution has been studied. The product has been found to remain more stable in aqueous solutions at a slightly acid pH (4…6.5) than in dilute alkaline solutions (pH 7…9.5).     

Copper(I) Derivative of Pyridine-3-carbaldehyde-N-ethylthiosemicarbazone and Triphenylphosphine—First Case of Crystal Structure Study

The synthesis and crystal structure of pyridine-3-carbaldehyde-N-ethylthiosemicarbazone (3-pytscH-NHEt) 1, and its Cu^I complex of stoichiometry, [CuCl(3-pytscH-NHEt)(PPh₃)₂] 2, studied using single crystal X-ray crystallography, are reported in this paper. Crystal data: 1, monoclinic, P2₁/n, a?=?6.6322(3), b?=?21.1200(8), c?=?7.2989(3) Å; β?=?91.883(4), T?=?173(2), R factor?=?0.0457; 2: triclinic, P-1, a?=?19.3600(5), b?=?20.6241(6), c?=?23.8015(6) Å,α?=?92.647(2), β?=?104.388(2), γ?=?114.377(3), R factor?=?0.0662. The thio-ligand, as a neutral entity, is coordinating to Cu through its S donor atom in complex 2. It has exhibited an unusual feature of forming four independent molecules (A, B, C, D) in the unit cell, with minor differences in the bond angles / distances / torsion angles. The geometry of each molecule of 2 is distorted tetrahedral. Crystal packing, as well as Infrared, electronic absorption and proton NMR spectroscopic studies, are also reported. Copper compound 2 represents the first example of a structurally studied copper coordination compound of 3-pyridyl based thiosemicarbazones.

Graphical Abstract

Copper(I) chloride with pyridine-3-carbaldehyde-N-ethylthiosemicarbazone and PPh₃ in CH₃CN yielded a copper compound, 2 (Green-Cl, blue-N; aqua-Cu, orange-S, magneta-P).