Solving reactor problems to determine the multiplication: A new method of accelerating outer iterations

A new cyclic iterative method with variable parameters is proposed for accelerating the outer iterations in a process used to calculate K _eff in multigroup problems. The method is based on the use of special extremal polynomials that are distinct from Chebyshev polynomials and take into account the specific nature of the problem. To accelerate the convergence with respect to K _eff, the use of three orthogonal functionals is proposed. Their values simultaneously determine the three maximal eigenvalues. The proposed method was incorporated in the software for neutron-physics calculations for WWER reactors.     

Low energy supersymmetry from the heterotic string landscape

We study possible correlations between properties of the observable and hidden sectors in heterotic string theory. Specifically, we analyze the case of the Z6-II orbifold compactification which produces a significant number of models with the spectrum of the supersymmetric standard model. We find that requiring realistic features does affect the hidden sector such that hidden sector gauge group factors SU(4) and SO(8) are favored. In the context of gaugino condensation, this implies low energy supersymmetry breaking.     

Electrical conductivity of double-walled carbon nanotubes in the framework of the Hubbard model

The electrical conductivity of double-walled carbon nanotubes of the “armchair” type with the ABAB packing of layers is investigated theoretically. The temperature dependences of the longitudinal electrical conductivity σ(T) for a number of double-walled carbon nanotubes, such as the (3, 3)@(8, 8), (5, 5)@(10, 10), (8, 8)@(13, 13), (10, 10)@(15, 15), and (15, 15)@(20, 20) nanotubes, are obtained in the framework of the Hubbard model with the use of the Green’s function method. It is revealed that the dependences of the electrical conductivity for single-walled and double-walled carbon nanotubes exhibit different behavior in the temperature range from 30 to 60 K. In particular, the dependence of the electrical conductivity for the double-walled carbon nanotubes flattens out in this temperature range.     

Electrospray ionization tandem mass spectrometry sequencing of novel skin peptides from Ranid frogs containing disulfide bridges

Tandem mass spectrometry sequencing, as well as Edman sequencing of peptides belonging to the Rana genus, represents a difficult task due to the presence of a disulfide bridge at the C-terminus and their rather high molecular masses (over 2000 Da). The present study throws light upon the sequence of three rather long peptides (more than 20 amino acid residues each) isolated from the skin secretion of Russian frogs, Rana ridibunda and Rana arvalis. This novel aspect involves the fact that the sequences (including two sequences established de novo) were determined exclusively by means of mass spectrometry. A combination of electron capture dissociation (ECD) and collision-induced dissociaiton (CID) data accompanied by exact mass measurements (LTQ Fourier transform ion cyclotron resonance mass spectrometer) facilitated reaching the goal. To overcome the difficulty dealing with disulphide bridges ("Rana box"), reduction of the S-S bond with dithiotreitol followed by derivatization of Cys residues with iodoacetamide was used. The sequence was determined using combined spectral data on y and b series of fragment ions. A multiple mass spectrometry (MS(3)) experiment was also used to elucidate the sequence inside the "Rana box" after cysteine derivatization. Exact mass measurements were used to differentiate between Lys and Gln residues, while characteristic losses of 29 and 43 Da (d and w fragment ions) in CID and ECD experiments allowed us to distinguish between Ile and Leu isomeric acids.     

Mass spectrometry in the study of mechanisms of aquatic chlorination of organic substrates

Chlorination is an effective method of water disinfection. However, it has been identified as contributing to the formation of a wide variety of disinfection by-products that have been associated with adverse health effects. Natural humic matter and anthropogenic pollutants are responsible for the formation of these by-products. Mass spectrometry is the most efficient tool to analyze the rates of conversion, the nature and levels of by-products in the reactions of chlorinating agents with model organic compounds. More than 30 substrates with various functional groups were studied, while gaseous chlorine and sodium hypochlorite were used as chlorinating agents. The effects of pH, substrate/active chlorine ratio, addition of metal cations and bromides and iodides on the aqueous chlorination process of various organic substrates were investigated. Transformation schemes were proposed for the studied compounds.     

Passive scalar in a large-scale velocity field

We consider advection of a passive scalar θ(t,r) by an incompressible large-scale turbulent flow. In the framework of the Kraichnan model all PDF’s (probability distribution functions) for the single-point statistics of θ and for the passive scalar difference θ(r ₁)−θ(r ₂) (for separations r ₁−r ₂ lying in the convective interval) are found. Zh. éksp. Teor. Fiz. 115, 920–939 (March 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Differential Thermal EMF of Carbon Zigzag-Type Nanotubes in an External Electric Field

Physics of the Solid State - The thermoelectric characteristics of carbon nanotubes are studied theoretically. The behavior of the differential thermal EMF of single-layer carbon zigzag-type...     

Analysis of Angular $$\boldsymbol{t{-}\gamma}$$ Correlations in the Reaction $${}^{\boldsymbol{27}}$$ Al $$\boldsymbol{(\alpha,t)^{28}}$$ Si(2 $${}^{\boldsymbol{+}}$$ )

Physics of Atomic Nuclei - Angular $$t$$ – $$\gamma$$ correlations measured earlier in the reaction $${}^{27}$$ Al $$(\alpha,t)^{28}$$ Si(2 $${}^{+}$$ ) occurring at $$E_{\alpha}=30.3$$ MeV...     

Microwave-Assisted Solution Synthesis of Metastable Intergrowth of AgInS2 Polymorphs

The intergrowth of stable and metastable AgInS₂ polymorphs was synthesized using a microwave-assisted synthesis. The samples were synthesized in water and in a deep eutectic solvent (DES) consisting of choline chloride and thiourea. An increase in the metal precursor concentration improved the crystallinity of the synthesized samples and affected the particle size. AgInS₂ cannot be synthesized from crystalline binary Ag₂S or In₂S₃ via this route. The solution synthesis reported here results in the intergrowth of the thermodynamically stable polymorph (space group I4¯2d, chalcopyrite structure) and the high-temperature polymorph (space group Pna2₁, wurtzite-like structure) that is metastable at room temperature. A scanning transmission microscopy (STEM) study revealed the intergrowth of tetragonal and orthorhombic polymorphs in a single particle and unambiguously established that the long-thought hexagonal wurtzite polymorph has pseudo-hexagonal symmetry and is best described with the orthorhombic unit cell. The solution-synthesized AgInS₂ polymorphs intergrowth has slightly lower bandgap values in the range of 1.73 eV–1.91 eV compared to the previously reported values for tetragonal I4¯2d (1.86 eV) and orthorhombic Pna2₁ (1.98 eV) polymorphs.