Electron distribution in 1-organo-1H-tetrazole-5-thiols. Crystal and molecular structure of 1-methyl-1H-tetrazole-5-thiol and its potassium (18-crown-6) salt

The crystal and molecular structures of both neutral and anionic 1-methyl-1H-tetrazole-5-thiol, as its potassium(18-crown-6) salt, are reported. In the solid state, the molecular thiotetrazole adopts a planar, dimeric arrangement, in which two neighboring molecules are hydrogen bridged. Each monomeric unit exhibits considerable π electron delocalization over the CN₂S fragment. The anionic form displays extensive, but not uniform, π electron delocalization within the ring, which also extends to the exocyclic carbon–sulfur bond, the structure being best described as a hybrid. The potassium cation is coordinated to the macrocyclic 18-crown-6 ether as expected, but it also interacts with the NCS fragment of the tetrazolethiolate ring.     

Reactions of transition metal compounds with macrocyclic alkadiynes : II. Cyclopentadienylnickel and dicobalt hexacarbonyl complexes retaining the macrocyclic alkadiyne structure unit

The macrocyclic alkadiynes 1,7-cyclododecadiyne, 1,7-cyclotridecadiyne, 1,7-cyclotetradecadiyne, 1,8-cyclotetradecadiyne, and 1,8-cyclopentadecadiyne react with [C₅H₅NiCO]₂ in boiling benzene to give the dark green tetrametallic derivatives (alkadiyne) (NiC₅H₅)₄ and with Co₂(CO)₈ in pentane at room temperature to give the dark red tetrametallic derivatives (alkadiyne)[Co₂(CO)₆]₂. The reactions of 1,7-cyclododecadiyne with [C₅H₅NiCO]₂ and Co₂(CO)₈ can also be made to give the crystalline bimetallic derivatives 1,7-C₁₂H₁₆(NiC₅H₅)₂ and 1,7-C₁₂H₁₆Co₂(CO)₆. The macrocyclic alkadiyne ring system is retained in all of these new complexes.     

Electric field tunability of nuclear and electronic spin dynamics due to the hyperfine interaction in semiconductor nanostructures

We present formulas for the nuclear and electronic spin relaxation times due to the hyperfine interaction for nanostructed systems and show that the times depend on the square of the local density of electronic states at the nuclear position. A drastic sensitivity (orders of magnitude) of the electronic and nuclear spin coherence times to small electric fields is predicted for both uniformly distributed nuclear spins and delta-doped layers of specific nuclei. This sensitivity is robust to nuclear spin diffusion.     

Preparation of counterion stabilized concentrated silver sols

A strategy for obtaining stable concentrated silver dispersions without dedicated stabilizing agents is presented. This approach consists of rapidly mixing aqueous solutions of silver salicylate and ascorbic acid. By using salicylate as Ag(+) counterion, it is possible to prepare stable sols with metal concentrations up to two orders of magnitude higher than with silver nitrate. The stabilizing effect of the counterion is the result of a decreased ionic strength due to salicylate protonation and its adsorption on the surface of silver. Both effects increase the range of the electrostatic repulsive forces by expanding the electrical double layer.     

The FENE Dumbbell Polymer Model: Existence and Uniqueness of Solutions for the Momentum Balance Equation

We consider the FENE dumbbell polymer model which is the coupling of the incompressible Navier-Stokes equations with the corresponding Fokker–Planck–Smoluchowski diffusion equation. We show global well-posedness in the case of a 2D bounded domain. We assume in the general case that the initial velocity is sufficiently small and the initial probability density is sufficiently close to the equilibrium solution; moreover an additional condition on the coefficients is imposed. In the corotational case, we only assume that the initial probability density is sufficiently close to the equilibrium solution.     

Thermal decomposition of ammonia. N2H4-an intermediate reaction product

The paper reports the thermal decomposition of ammonia under dynamic conditions at 800°C in a quartz reactor. Its purpose is to confirm the homogeneous-heterogeneous degenerated branched chain mechanism established in previous studies, which assume the formation of N₂H₄ as a molecular intermediate; this paper identifies hydrazine as a product of thermal decomposition using FT-IR and UV-VIS spectroscopies.     

Three-dimensional numerical simulation of the reciprocating flow in a branching tube network

The paper deals with the three dimensional numerical simulation of the reciprocating flow in a branching network, a phenomenon that might be found for example in the human bronchi. As the first approximation, the working fluid was water with laminar flow regime. The main issue was to elucidate the mechanism of the air exchange in the human lungs. The model used in this simulation consists of two branching generations. Three different cases have been analyzed with various frequency, Re and Wo numbers.     

Numerical stochastic model for the magnetic relaxation time of the fine particle system with dipolar interactions

This paper presents the results obtained by numerical simulations, the magnetic relaxation time simulation for a fine particle system with dipolar magnetic interaction. We used a 3D simulation model for fine magnetic particles with spherical shape and lognormal distribution for their diameters. Starting from Dormann–Bessais–Fiorani model, the 3D model we used is more realistic if we consider that the particles are randomly arranged into a preset volume, following a Gaussian distribution generated with the Box–Mueller transformation.     

Calculation of the quantum efficiency for the absorption on confinement levels in quantum dots

The quantum efficiency of the absorption on quantum confinement levels is investigated. This is achieved by modeling the electron confinement in a spherical quantum dot (QD). The confinement levels are calculated using both infinite and finite rectangular quantum wells. The spectral internal quantum efficiency is evaluated within both the models, by computing Einstein’s coefficients for the transitions between confinement levels. The size of QDs (1–3 nm radius) leads to negligible many body effects. The nature of the QD material and of the matrix embedding is taken into account in the finite rectangular quantum well approximation and introduces only a small correction. The temperature dependence of the efficiency is also taken into account. A numerical application is performed for a silicon QD of 2.5 nm radius, embedded in amorphous silica. It is proved that the absorption threshold shifts toward the far infrared limit and that the spectral internal quantum efficiency reaches 4–5% at the threshold.     

Electronic transport of a T-shaped double-quantum-dot system in the Coulomb blockade regime

We studied the electronic transport properties of a T-shaped double-quantum-dot system in the Coulomb blockade regime when the onsite Coulomb interaction parameters U ₁ and U ₂ have finite values in both component dots. Our analysis is done in the so-called beyond Hartree-Fock approximation that includes contributions related to both normal and mixed averages of various number-like operators in the system. We provide an analytic formula for the main’s dot Green function in the case of large onsite Coulomb interaction parameters (U ₁ = U ₂ → ∞), and find that with a good approximation, this limit is realized when the ratio U ₁/t = U ₂/t ≥ 30, t being the interdot electron tunneling between the two component dots of the structures. In the most general situation of the Coulomb blockade regime (U ₁ ≠ U ₂) the system conductivity presents two dips corresponding to the Fano-Kondo effect and the system’s shot noise and electronic current present a series of plateaus that should be visible in experimental setups.