Synthetic studies toward aryl-(4-aryl-4H-[1,2,4]triazole-3-yl)-amine from 1,3-diarylthiourea as urea mimetics

A thiophile-promoted synthesis of disubstituted 4H-[1,2,4]triazole-3-yl-amines as urea mimetics from the corresponding 1,3-disubstituted thioureas has been studied, and the scope and limitations of this reaction are presented. The reaction proceeds through the formation of a carbodiimide, followed by a sequential addition--dehydration with acyl hydrazides. 1,3-Branched dialkylthioureas result in the formation of the corresponding ureas. The electronic and steric effects of the substitution on the phenyl rings of the 1,3-diarylthioureas play an important role in the formation of the intermediary carbodiimde and the direction of the subsequent ring closure of the N-acyl hydrazide adduct.     

On the number of regular vertices of the union of jordan regions

Let \C be a collection of n Jordan regions in the plane in general position, such that each pair of their boundaries intersect in at most s points, where s is a constant. If the boundaries of two sets in \C cross exactly twice, then their intersection points are called regular vertices of the arrangement \A(\C) . Let R(\C) denote the set of regular vertices on the boundary of the union of \C . We present several bounds on |R(\C)| , depending on the type of the sets of \C . (i) If each set of \C is convex, then |R(\C)|=O(n ^1.5+\eps ) for any \eps>0 . (ii) If no further assumptions are made on the sets of \C , then we show that there is a positive integer r that depends only on s such that |R(\C)|=O(n ^2-1/r ) . (iii) If \C consists of two collections \C ₁ and \C ₂ where \C ₁ is a collection of m convex pseudo-disks in the plane (closed Jordan regions with the property that the boundaries of any two of them intersect at most twice), and \C ₂ is a collection of polygons with a total of n sides, then |R(\C)|=O(m ^2/3 n ^2/3 +m +n) , and this bound is tight in the worst case. Received December 4, 1998, and in revised form June 3, 2000. Online publication Feburary 1, 2001.     

Surface specific heat of 3He and Andreev bound states

High resolution measurements of the specific heat of liquid 3He in the presence of a silver surface have been performed at temperatures near the superfluid transition in the pressure range of 1-29 bar. The surface contribution to the heat capacity is identified with Andreev bound states of quasiparticles that have a range of half a coherence length.     

Cognitive dysfunction in NF1 knock-out mice may result from altered vesicular trafficking of APP/DRD3 complex

Background  

It has been estimated that more than 50% of patients with Neurofibromatosis type 1 (NF1) have neurobehavioral impairments which include attention deficit/hyperactivity disorder, visual/spatial learning disabilities, and a myriad of other cognitive developmental problems. The biological mechanisms by which NF1 gene mutations lead to such cognitive deficits are not well understood, although excessive Ras signaling and increased GABA mediated inhibition have been implicated. It is proposed that the cognitive deficits in NF1 are the result of dysfunctional cellular trafficking and localization of molecules downstream of the primary gene defect.     

Anomalous attenuation of transverse sound in 3He

We present the first measurements of the attenuation of transverse sound in superfluid 3He-B. We use fixed path length interferometry combined with the magnetoacoustic Faraday effect to vary the effective path length by a factor of 2, resulting in absolute values of the attenuation. We find that attenuation is significantly larger than expected from the theoretical dispersion relation, in contrast with the phase velocity of transverse sound. We suggest that the anomalous attenuation can be explained by surface Andreev bound states.     

The kinetics of the R- and UV-band photoconductivity (PC) in radiation damaged diamond

Illumination in the UV-band of radiation damaged diamond was found to enhance the PC in the red (the RPC). Continuous R-illumination then caused the RPC to decay hyperbolically to zero. R-band illumination also enhanced the PC in the UV band (UPC). Continuous illumination in the UV-band then caused the UPC to decay to a level about half of the maximum UPC. A two-level model was proposed in which exchange of holes between the U- and R-levels via the valence band was assumed to take place under illumination. The differential equations obtained from the kinetics of the transitions were solved with some approximations, and were found to give an excellent agreement with the experimental results. Further support for the model was obtained from numerical integration of the differential equations. When compared with the experimental results this provided information on the crystal parameters involved. The transition rates for valence-band holes into the levels R and U were found to be: A_R= U_U = 2.3 × 10^?11m³sec^?1, which gave for the capture-cross-sections at 290 K of these centres S = 3.2 × 10^?17m². Surprisingly low densities of the order of 10¹²m^?3 were obtained for R and U, indicating that only a small fraction of the damage-produced defects play a role in the UPC and RPC.