Entropy production as a regularization factor in solving an inverse diffusion problem

Inverse diffusion problems allow the diffusion coefficients to be determined from experimental concentration profiles. Solutions of the inverse diffusion problem are unstable toward perturbations of the initial concentration profiles. By the example of inverse diffusion problem solution for a model binary system it is demonstrated that the use of the production entropy to minimize the discrepancy functional stabilizes the solution even for significant perturbations of the initial concentration profile. The choice of the entropy production for the smoothing component of the discrepancy functional is physically adequate to the formulated problem, and the entropy production can be used to solve inverse problems of heat and mass transfer. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 79–83, June, 2006.     

Reactions of aromatic acetylenic ethers with triethylgermane

Conclusions The addition of Et₃GeH to the phenoxy- and phenylthioacetylenes under the influence of (Ph₃P)₃RhCl is both nonstereo- and nonregiospecific. The analogous reaction with 3-aroxy-1-propynes is stereospecific but nonregioselective.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2618–2620, November, 1982.     

Hydrosilylation of 2-(2-Propynyl)-2,3-dihydro-1,2-benzothiazol-3-one 1,1-Dioxide with 1-Alkynyl(dimethyl)- and Bis(1-alkynyl)methylsilanes

Hydrosilylation of 2-(2-propynyl)-2,3-dihydro-1,2-benzothiazol-3-one 1,1-dioxide with 1-alkynyldimethyl- and bis(1-alkynyl)methylsilanes of the general formula Me _n HSi(C=-CR)₃-n (n = 1, 2) in the presence of H₂PtCl₆ (Speier's catalyst) occurs in a nonregioselective but stereoselective fashion, yielding mixtures of the corresponding trans-- and -adducts. The fraction of the latter ranges from 50 to 70%, depending mainly on the substrate nature rather than on the nature of substituent at the triple bond of the reagent.     

Heterocyclic analogs of pleiadiene. 55. 2-Azidoperimidines: Stability of the tetrazole form

2-Azidoperimidine and its 1-methyl, 1-benzyl, and 1-phenyl derivatives were synthesized by the action of sodium azide on the corresponding 2-chloroperimidines. The IR spectra constitute evidence for the existence of all of these compounds in both the solid state and in solution in exclusively the tetrazolo [1,5-a]perimidine form.See [1] for Communication 54.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1114–1117, August, 1981.     

Structural aspects of catalytic mechanisms of endonucleases and their binding to nucleic acids

Endonucleases (EC 3.1) are enzymes of the hydrolase class that catalyze the hydrolytic cleavage of deoxyribonucleic and ribonucleic acids at any region of the polynucleotide chain. Endonucleases are widely used both in biotechnological processes and in veterinary medicine as antiviral agents. Medical applications of endonucleases in human cancer therapy hold promise. The results of X-ray diffraction studies of the spatial organization of endonucleases and their complexes and the mechanism of their action are analyzed and generalized. An analysis of the structural studies of this class of enzymes showed that the specific binding of enzymes to nucleic acids is characterized by interactions with nitrogen bases and the nucleotide backbone, whereas the nonspecific binding of enzymes is generally characterized by interactions only with the nucleic-acid backbone. It should be taken into account that the specificity can be modulated by metal ions and certain low-molecular-weight organic compounds. To test the hypotheses about specific and nonspecific nucleic-acid-binding proteins, it is necessary to perform additional studies of atomic-resolution three-dimensional structures of enzyme-nucleic-acid complexes by methods of structural biology.     

Dynamic Model of Elastoplastic Normal Collision of Spherical Particles under Nonlocal Plasticity

Physics of the Solid State - The problem of normal collision of a spherical particle with a half-space is considered with allowance for nonlocal plastic deformation in the case where the strength...     

α-Acetylene Hydrosilanes as Hydrosilylating Agents for Terminal Arylacetylenes

The hydrosilylation of a number of acetylenes RCCH (R, R' = Ph, CH₂OPh, CH₂SPh) with -ethynylhydrosilanes Me₂SiHCHCR' in the presence of H₂PtCl₆ was investigated. The addition did not occur regioselectively, but was stereospecific and afforded a mixture of - and trans--adducts. The replacement of phenyl substituent by phenoxymethyl both in the molecule of ethynylsilane and the acetylene substrate resulted in growing proportion of the -adduct in the reaction mixture up to 10-60%.     

Evolution of the Electroluminescence Spectra and the Acoustic Emission of the Epitaxial Structures of GaAsP

The dependence of the spectral position of the electroluminescence bands of epitaxial light-emitting diode n ⁺–n–p structures (GaAs_0.15P_0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short-term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (100–200 A/cm²).