On the Tender X-Ray Flat-Field Spectrograph with a Concave VLS Grating

Journal of Russian Laser Research - We analyze the way of advancing to tender X-rays the short-wavelength bound of the operating range of flat-field grating spectrographs. We design two VLS grating...     

Study of coherent diffractive production reactions ofp+C→[Y 0 K +]+C type and observation of narrow structures in ∑ (1385)0 K + and ∑0 K + effective mass spectra

In the experiments at the SPHINX facility in 70 GeV proton beam of the IHEP accelerator the coherent diffractive production reactions on carbon nucleip+C [(1385)⁰ K ⁺+C andp+C[⁰ K ⁺]+C were investigated. The evidences for new baryon states were obtained in the study of hyperon-kaon effective mass spectra in these two reactions:X (2050) with massM=(2052±6) MeV and width =(35 _–35 ⁺²² ) MeV inM[(1385)⁰ K ⁺] andX(2000) withM=1999±6 MeV and =91±17 MeV inM[⁰ K ⁺]. The unusual features of these massive states (small enough decay widths, anomalously large branching ratios for decays with strange particles emission) make them very serious candidates for cryptoexotic pentaquark baryons with hidden strangeness.     

Carbohydrates Exhibit a Distinct Preferential Solvation Pattern in Binary Aqueous Solvent Mixtures

Molecular dynamics simulations reveal the entire solvation shell around a model disaccharide dissolved in the binary 1:3 molar mixture of dimethyl sulfoxide and water becomes distinctly structured (see drawing). Such preferential solvation is due to the large number of hydroxyl groups and the rich network of hydrogen bonds of a disaccharide formed with the solvent.     

Normal-Incidence Imaging Spectrograph Based on an Aperiodic Spherical Grating for the Vacuum Spectral Region

Optics and Spectroscopy - The possibility of astigmatism compensation in a wide wavelength range in normal incidence schemes based on a spherical diffraction grating with variable groove density...     

Symmetrical triindole as a central unit in the fluorene-containing polyphenol assembly

A new strategy was proposed for the synthesis of fluorene-containing indole polyphenols, based on the Suzuki–Miyaura reaction of hexabrominated symmetric indole trimer with the monoboryl N,N'-di[9,9'-bis(3',5'-dimethoxybenzyl)fluoren-2'-yl]aniline derivative and subsequent chemical transformations. The prepared compound was applicable for the development of a promising positive resist for electron-beam nanolithography capable of forming patterns with a 12 nm resolution.     

Excitation of velocity fluctuations and noise in a wind tunnel

The aim of this paper is to develop a theory, consistent with the observations, of the nature and location of the structures that determine self-excitation and the emission of the narrow-band components of the noise generated by the open working section of wind tunnels. At the same time, the theory is applied by using it as a basis for constructive solutions.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.4, pp. 165–173, July–August, 1992.     

An iterative method for improving the quality of reconstruction of a three-dimensional surface

A complex image with constraints imposed on the amplitude and phase image components is processed using the Gerchberg iterative algorithm for the first time. The use of the Gerchberg iterative algorithm makes it possible to improve the quality of a three-dimensional surface profile reconstructed by the previously proposed method that is based on the multiangle projection of fringes and the joint processing of the obtained images by Fourier synthesis.     

Calculation of chemical potentials of chain molecules by the incremental gauge cell method

The gauge cell Monte Carlo method is extended to calculations of the incremental chemical potentials and free energies of linear chain molecules. The method was applied to chains of Lennard-Jones beads with stiff harmonic bonds up to 500 monomers in length. We show that the suggested method quantitatively reproduces the modified Widom particle insertion method of Kumar et al. [S. K. Kumar, I. Szleifer, and A. Z. Panagiotopoulos, Phys. Rev. Lett. 66(22), 2935 (1991)], and is by an order of magnitude more efficient for long chains in terms of the computational time required for the same accuracy of chemical potential calculations. The chain increment ansatz, which suggests that the incremental chemical potential is independent of the chain length, was tested at different temperatures. We confirmed that the ansatz holds only for coils above the θ temperature. Special attention is paid to the effects of the magnitude of adsorption potential and temperature on the behavior of single chains in confinements that are comparable in size with the free chain radius of gyration. At sufficiently low temperatures, the dependence of the incremental chemical potential on the chain length in wetting pores is superficially similar to a capillary condensation isotherm, reflecting monolayer formation following by pore volume filling, as the chain length increases. We find that the incremental gauge cell method is an accurate and efficient technique for calculations of the free energies of chain molecules in bulk systems and nanoconfinements alike. The suggested method may find practical applications, such as modeling polymer partitioning on porous substrates and dynamics of chain translocation into nanopores.     

Molecular modeling of organophosphorous agents and their aqueous solutions

Using molecular dynamics simulations, we modeled solvation and diffusion in aqueous solutions of organophosphorous compounds, including nerve G-agents sarin and soman (methylphosphonofluoridates) and their common simulants DMMP (dimethyl methylphosphonate) and DIFP (diisopropyl fluorophosphate). The aqueous solutions of the organophosphorous compounds were found to display complex molecular scale structures and dynamic properties due to competing interactions between strongly hydrophobic and hydrophilic groups. The mixing of agents with water was proved to be exothermic with negative excess mixing volume, indicating a strongly hydrophilic solvation. This effect was confirmed in a specially performed experiment. We discuss to what extent DMMP and DIFP are suitable simulants for G-agents in experimental studies, as far as their interactions with water are concerned. We also focus on the relevance of the structural features and mobilities of agents in water to their interactions with permselective polyelectrolyte membranes that may be employed as protective barriers against chemical warfare agents.     

Molecular dynamics simulation of nanoscale distribution and mobility of water and dimethylmethylphosphonate in sulfonated polystyrene

The interest in a better understanding of the specific interactions of phosphor-organic compounds and water with sulfonated polystyrene (sPS) is motivated by the use of block copolymers as protective membranes against chemical warfare agents. Using classical molecular dynamics simulations, we explored the nanoscale segregation and diffusion of water and nerve gas simulant dimethylmethylphosphonate (DMMP) in sPS neutralized with calcium counterions at different sulfonation and hydration levels. The water content was varied from 15 to 54% of dry polymer weight, and the DMMP content was varied from 0 to 100 wt %. We found that, in the 40% sulfonated polystyrene, water forms well defined aggregates, which grow in size as the hydration increases, reaching approximately 20 A at the maximum water content. In the 100% sulfonated polystyrene, the overall structure of hydrated polymer is more uniform with smaller water aggregates. Diffusion of water at the same number of water molecules per sulfonate group is faster at a lower sulfonation level. The solvation of sPS in water-DMMP binary mixtures was found to differ substantially from Nafion, where DMMP forms a layer between the hydropholic and hydrophobic subphases. In sPS with divalent Ca(2+) counterions, DMMP and water compete for the solvation of the sulfonate group. At high water and DMMP contents, the diffusion of DMMP turned out to be rather fast with a diffusion coefficient of ca. 30% of that of water. At the same time, water diffusion slows down as the DMMP concentration increases. This observation suggests that although sPS is permeable for both solvents, water and DMMP are partially segregated on the scale of 1-2 nm and have different pathways through the system. The nonuniform nanoscale distribution of water and DMMP in sPS is confirmed by analyses of different pair correlation functions. This feature may significantly affect the perm-selective properties of sPS-contained block copolymer membranes.