Dependence of hot carriers temperature on lattice temperature in CdS

Non-equilibrium carrier distributions were obtained in CdS at various temperatures from 77 to 400K. A study is made of the influence of the lattice temperature on the carrier temperature. It is found that the higher the lattice temperature the lower is the difference between carrier and lattice temperatures, though carriers are always thermalized among themselves. The results can be accounted for by carrier relaxation through optical polar phonon emission.     

Temperature effect (300-1500 K) on the infrared photon transport inside an X-ray microtomographic reconstructed porous silica glass

A Monte Carlo Ray Tracing program has been developed to predict the thermal radiative properties of an X-ray microtomographic reconstructed silica glass containing gas bubbles, for a large domain of wavelength (1-25 μm) and for a large domain of temperature (300-1500 K). The main input of the program is the complex optical index of the corresponding homogeneous silica glass. Validity of the model is checked by comparing a simulated normal spectral emittance, obtained on the reconstructed glass, with the experimental one recorded at .     

Selective protodeboronation: synthesis of 4-methyl-2-thiopheneboronic anhydride and demonstration of its utility in Suzuki-Miyaura reactions

An efficient synthesis of 4-methyl-2-thiopheneboronic anhydride is reported. Regioselective lithiation of 3-methylthiophene followed by reaction with triisopropylborate and hydrolysis provides a 92:8 ratio of 4-methyl-2-thiopheneboronic acid (1) and regioisomeric 2-methyl-3-thiopheneboronic acid (3). The undesired regioisomer is selectively protodeboronated with concentrated acid to provide only the desired 4-methyl-2-thiopheneboronic acid (1). The title compound is isolated by dehydration/crystallization and employed in several Suzuki-Miyaura reactions.     

Electron transfer to sulfides and disulfides: intrinsic barriers and relationship between heterogeneous and homogeneous electron-transfer kinetics

The electron-acceptor properties of series of related sulfides and disulfides were investigated in N,N-dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron-transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the C(alkyl)--S or S--S bond. A generalized picture of how the intrinsic electron-transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative- and nondissociative-type acceptors, and this led to verification that the heterogeneous and the homogeneous data correlate as predicted by the Hush theory.     

Structure and lattice dynamics of binary lead silicate glasses investigated by infrared spectroscopy

The polar lattices dynamics of seven binary lead silicate glasses have been studied by infrared spectroscopy. The analysis of the reflectivity spectra with a dielectric function model, based on a modified Gaussian profile, allows a quantitative evaluation of the presence of lead cations within different structural sites. From the role of the lead cations versus the degree of polymerization of the silicate network and the comparison with literature results, we may to give a scenario for explaining the observed structural evolution of the glass matrix and more particularly the drastic change occurring around 45% of lead content. Below this threshold, lead cations act only as modifiers of the silicate network. Above, the glass structure is deeply modified; a lead network involving around 10% of the lead content appears in glasses whose composition is just above the threshold and progressively grows at the expense of the silicate network with the increase of lead content. For high lead content, lead cations can act as modifiers of the silicate network or as network formers. Results also show that the analysis of far infrared measurements combined with the knowledge of the UV edge optical response is very promising to characterize the local disorder around cations in glasses.     

Crystal Structures and Hydrogen Bonding of Two Complexes containing the [Ammine‐chlorido‐ethylenediamine‐bis(pyridine)cobalt(III)]2+ Cation

The crystal structures of two classical cobalt(III) complexes comprising the [CoCl(NH₃)(en)(py)₂]²⁺ cation were determined by single‐crystal X‐ray diffraction. Both complexes, dark red [CoCl(NH₃)(en)(py)₂]Cl₂ · H₂O ( 1 ) and purple [CoCl(NH₃)‐(en)(py)₂][HgCl₄] · 1.125H₂O ( 2 ), crystallize in the triclinic space group P1 . In both compounds, the Co atom exhibits a typical octahedral coordination and the configuration index of the complex is OC‐6‐43. In the case of the chloride ( 1 ), the asymmetric unit comprises one formula unit, whereas there are two formula units in the case of the tetrachloridomercurate ( 2 ). Complex cations, anions, and crystal water molecules are interconnected by various N–H ··· N, N–H ··· Cl, N–H ··· O, O–H ··· Cl, and O–H ··· O bridge bonds. As a result, compound 1 features a two‐dimensional layer structure and compound 2 exists as a three‐dimensional network.     

Tailoring of polymer properties in segmented block copolymers

Linking segments of two different polymers in block copolymers offers the opportunity to combine their macroscopic properties and to design tailor‐made materials. This is shown for segmented block copolymers (A‐B)_n in which the basic segment is polysulfone. Incorporation of either hydrophilic and or hydrophobic segments results in a dramatic change of surface properties which is also correlated to the bulk structure of the block copolymers.     

Data structures for speeding up Tabu Search when solving sparse quadratic unconstrained binary optimization problems

Journal of Heuristics - The quadratic unconstrained binary optimization (QUBO) problem belongs to the NP-hard complexity class of problems and has been the subject of intense research since the...