More efficient Brownian dynamics algorithms

We examine the relative efficiencies of three- algorithms for performing Brownian Dynamics simulations without many-body hydrodynamics. We compare the conventional Brownian Dynamics algorithm of Ermak (CBD), Smart Monte Carlo (SMC) which incorporates Boltzmann sampling into essentially a CBD procedure, and the Stochastic Runge Kutta (SRK) method. We show, using the repulsive potential φ(r) = ε(σ/r) ⁿ , where n = 36 and 72, that the SRK algorithm gives the most accurate short-time dynamics for the mean-square displacements. The SRK algorithm static and dynamical properties converge better with a reducing time step to the exact values, than those generated by the CBD algorithm; giving efficiency gains typically of a factor of 3–4. Both CBD and SMC have the incorrect sign for the first correction term to the mean square displacement in a time step, whereas the SRK algorithm gives essentially the exact solution to order Δt ², where Δt is the simulation time step. In fact, these correction terms are almost equal and opposite in sign. Expressions for these terms were derived in terms of the average interaction energy per particle. The force, shear and bulk stress autocorrelation functions were calculated. The average energy per particle and time correlation functions at short time have values in excess of the exact values, while the corresponding quantities for SRK are below this. This difference in behaviour can be traced back to the extent of compliance of the particle trajectories with the exact expansion of the Smoluchowski equation. The accuracy, at a given value of the time step, of the stochastic algorithms can significantly depend on the form of the interaction potential between particles. It is also demonstrated that the long time limits of various correlation functions are fairly insensitive to a particular scheme (SRK or CBD) used in the simulations. All the correlation functions have a stretched exponential region at intermediate to long times, and the values of the exponents on density and force law steepness have been determined.     

Thermogravitational convection in ionospheric plasma modified by high-power decametric radiowaves

Quality theoretical analysis allows us to assume that artificial plasma inhomogeneities in the ionosphere modified by high-power decametric radiowaves could be space modes of thermogravitational convection. Effects observed in the scattering of test 10-m radiowaves are interpreted as anindication of thermogravitational convection in heated ionospheric plasma.Translated from Izvestiya Vyssikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 5, pp. 568–578, May, 1996.     

Dimethyldioxirane as a New Reagent for the Synthesis of Benzoxazines

Russian Journal of Organic Chemistry -     

Synthesis and chemical reactions of 2-RS-methyl-7-methyl-5-oxo-5H-1,3,4-thiadiazolo[3,2-a]pyrimidines

The corresponding sulfides have been synthesized starting from 2-chloromethyl-7-methyl-5-oxo-5H-1,3,4-thiadiazolo[3,2-a]pyrimidine and some of their reactions have been studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 549–552, April, 1996.     

Brightening in the UV region of GSGG crystals after γ-irradiation

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 1, pp. 124–127, January, 1988.     

Some transformations of 2-chloromethyl-7-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one

The reactions of 2-chloromethyl-7-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one withtert-butyl hypochlorite and molecular bromine and the replacement of the chlorine atom in the chloromethyl group through the action of piperidine and morpholine were investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 908–910, May, 1994.     

Glutamate receptor blockers from venoms of the spiders Argiope lobata and Araneus tartaricus

The presence of glutamate receptor blockers with molecular masses below 1000 Da and pI9 has been detected in the venoms of the spidersArgiope lobata andAraneus tartaricus.Institute of Physiology, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 532–537, July–August, 1990.     

Reactions of N- and C-Alkenylanilines: IV. Synthesis of Heterocycles by Oxidation of N-Acyl-o-(1-alkenyl)anilines with Hydrogen Peroxide

Heterocyclic compounds of the 4H-3,1-benzoxazine and cyclopenta[b]indole series were syn- thesized by oxydation of N-acyl derivatives of 2-(1-alkenyl)anilines with hydrogen peroxide. The structure of the oxidation products is determined by the reaction conditions, substituent in the ortho-position of the aromatic ring, protecting group, and alkenyl radical structure.     

Synthesis of derivatives of a new heterocyclic system, 9-oxo-1,3,4-thiadiazolo[3,2-a]pyrido[3,2-e]pyrimidine

Reaction of 2-substituted 5-imino-7-oxo-1,3,4-thiadiazolo[3,2-a]pyrimidines with pentane-2,4-dione in polyphosphoric acid yields 9-oxo-1,3,4-thiadiazolo[3,2-a]pyrido[3,2-e]pyrimidines.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2037–2038, October, 1995.The authors are grateful to V. A. Dorokhov for the skilled preparation of the paper for publication.