314 research outputs found
Discontinuous molecular dynamics for rigid bodies: Applications
No full textEvent-driven molecular dynamics simulations are carried out on two rigid-body systems which differ in the symmetry of their molecular mass distributions. First, simulations of methane in which the molecules interact via discontinuous potentials are compared with simulations in which the molecules interact through standard continuous Lennard-Jones potentials. It is shown that under similar conditions of temperature and pressure, the rigid discontinuous molecular dynamics method reproduces the essential dynamical and structural features found in continuous-potential simulations at both gas and liquid densities. Moreover, the discontinuous molecular dynamics approach is demonstrated to be between 3 and 100 times more efficient than the standard molecular dynamics method depending on the specific conditions of the simulation. The rigid discontinuous molecular dynamics method is also applied to a discontinuous-potential model of a liquid composed of rigid benzene molecules, and equilibrium and dynamical properties are shown to be in qualitative agreement with more detailed continuous-potential models of benzene. The few qualitative differences in the angular dynamics of the two models are related to the relatively crude treatment of variations in the discontinuous repulsive interactions as one benzene molecule rotates by another. (c) 2007 American Institute of Physics.PT: J; CR: ALDER BJ, 1959, J CHEM PHYS, V31, P459 BELLEMANS A, 1980, MOL PHYS, V39, P781 CACELLI I, 2004, J AM CHEM SOC, V126, P14278 CHAPELA GA, 1984, MOL PHYS, V53, P139 CHAPELA GA, 1989, CHEM PHYS, V129, P201 DELAPENA LH, 2007, J CHEM PHYS, V126 DEMICHELE C, 2006, J PHYS CHEM B, V110, P8064 DING F, 2003, PROTEINS, V53, P220 DUANE S, 1987, PHYS LETT B, V195, P216 DULLWEBER A, 1997, J CHEM PHYS, V107, P5840 FALCONE DR, 1967, J PHYS CHEM-US, V71, P2754 MACKERELL AD, 1998, J PHYS CHEM B, V102, P3586 NGUYEN HD, 2006, J AM CHEM SOC, V128, P1890 PRESS WH, 1992, NUMERICLA RECIPES FO RAPAPORT DC, 1979, J CHEM PHYS, V71, P3299 RAPAPORT DC, 2004, ART MOL DYNAMICS SIM VANZON R, CONDMAT0612404 VANZON R, IN PRESS J COMPUT PH ZACHAROPOULOS N, 2005, J CHEM PHYS, V122 ZHOU YQ, 1999, J MOL BIOL, V293, P917; NR: 20; TC: 0; J9: J CHEM PHYS; PG: 12; GA: 138VLSource type: Electronic(1
Discontinuous molecular dynamics for semiflexible and rigid bodies
No full textA general framework for performing event-driven simulations of systems with semiflexible or rigid bodies interacting under impulsive forces is outlined. The method consists of specifying a means of computing the free evolution of constrained motion, evaluating the times at which interactions occur, and determining the consequences of interactions on subsequent motion. Algorithms for computing the times of interaction events and carrying out efficient event-driven simulations are discussed. The semiflexible case and the rigid case differ qualitatively in that the free motion of a rigid body can be computed analytically and need not be integrated numerically. (c) 2007 American Institute of Physics.PT: J; CR: ABRAMOWITZ M, 1965, HDB MATH FUNCTIONS F ALDER BJ, 1959, J CHEM PHYS, V31, P459 ALDER BJ, 1960, J CHEM PHYS, V33, P1439 ALLEN MP, 1987, COMPUTER SIMULATION ALLEN MP, 1989, COMPUT PHYS REP, V9, P301 ANDERSEN HC, 1983, J COMPUT PHYS, V52, P24 BARAFF D, 1989, COMPUT GRAPH, V23, P223 BARAFF D, 1992, THESIS CORNELL U BRENT RP, 1973, ALGORITHMS MINIMIZAT CARTER EA, 1989, CHEM PHYS LETT, V156, P472 CHAPELA GA, 1984, MOL PHYS, V53, P139 CHAPELA GA, 1989, CHEM PHYS, V129, P201 CICCOTTI G, 2004, J STAT PHYS, V115, P701 DELAPENA LH, UNPUB DELAPENA LH, 2005, J CHEM PHYS, V126 DEMICHELE C, 2006, J PHYS CHEM B, V110, P8064 DONEV A, 2005, J COMPUT PHYS, V202, P737 DONEV A, 2005, J COMPUT PHYS, V202, P765 ERPENBECK JJ, 1977, STAT MECH B FIXMAN M, 1974, P NATL ACAD SCI USA, V71, P3050 FRENKEL D, 2004, UNDERSTANDING MOL DY GALASSI M, 2005, GNU SCI LIB REFERENC GOLDSTEIN H, CLASSICAL MECH JACOBI CGJ, 1849, J CRELLE, V39, P293 KNOPP K, 1947, THEORY FUNCTIONS 2 LANDAU LD, 1976, MECHANICS LUBACHEVSKY BD, 1991, J COMPUT PHYS, V94, P255 MARIN M, 1993, J COMPUT PHYS, V109, P306 MARIN M, 1995, COMPUT PHYS COMMUN, V92, P214 MARSDEN JE, 2002, INTRO MECH SYMMETRY MASUTANI Y, 1994, P IEEE INT C ROB AUT, V2, P1066 MELCHIONNA S, 2000, PHYS REV E A, V61, P6165 MOSHIER SL, 1989, METHODS PROGRAMS MAT PRESS WH, 1992, NUMERICLA RECIPES FO RAMSHAW JD, 1986, PHYS LETT A, V116, P110 RAPAPORT DC, 1980, J COMPUT PHYS, V34, P184 RAPAPORT DC, 2004, ART MOL DYNAMICS SIM RUEB AS, 1834, THESIS UTRECHT NETHE RYCKAERT JP, 1977, J COMPUT PHYS, V23, P327 TUCKERMAN ME, 1999, EUROPHYS LETT, V45, P149 TUCKERMAN ME, 2001, J CHEM PHYS, V115, P1678 VANZON R, IN PRESS J COMPUT PH VANZON R, 2002, PHYS REV E 1, V65 WHITTAKER ET, 1937, TREATISE ANAL DYMANI; NR: 44; TC: 1; J9: J CHEM PHYS; PG: 13; GA: 138VLSource type: Electronic(1
'Teraz' u Parminidesa: B 8.5 ('NOW' ACCORDING TO PARMENIDES: B 8.5)
No full textThe main purpose of this paper is to analyze the concept of time in Parmenides' poem. The author begins with comparison between Parmenides and the concept of eternity in Plato's Timaeus. Some historian agree, that concept of eternity was alien for Parmenides and argue from fragm. 8, 5-6, where Parmenides uses the term 'now' - nyn in non-eternal sense. The author reads the conceptions of Schofield, Kahn, Gallop and Groarke (and many other writers) and observe some difficulties with their interpretations. He makes entrance with strictly philological analysis of nyn (Plato, Sophocles, Aristotle) and compares their use of 'now' with poems of Pindar. The author introduces the concept of 'cyclical' time, where order of moments is irrelevant and men can achieve salvation relatively easy to access
A European union and Canadian review of public health nursing preparation and practice.
No full textThis study explores the preparation and role of the public health nurse (PHN) across European Union (EU) countries (Finland, Sweden, and the United Kingdom) and Canadian provinces (Alberta, New Brunswick, and Prince Edward Island)
The role of collective motion in examples of coarsening and self-assembly
No full textThe simplest prescription for building a patterned structure from its constituents is to add particles, one at a time, to an appropriate template. However, self-organizing molecular and colloidal systems in nature can evolve in much more hierarchical ways. Specifically, constituents (or clusters of constituents) may aggregate to form clusters (or clusters of clusters) that serve as building blocks for later stages of assembly. Here we evaluate the character and consequences of such collective motion in a set of prototypical assembly processes. We do so using computer simulations in which a system's capacity for hierarchical dynamics can be controlled systematically. By explicitly allowing or suppressing collective motion, we quantify its effects. We find that coarsening within a two dimensional attractive lattice gas (and an analogous off-lattice model in three dimensions) is naturally dominated by collective motion over a broad range of temperatures and densities. Under such circumstances, cluster mobility inhibits the development of uniform coexisting phases, especially when macroscopic segregation is strongly favored by thermodynamics. By contrast, the assembly of model viral capsids is not frustrated but is instead facilitated by collective moves, which promote the orderly binding of intermediates consisting of several monomers
Cell cycle coordination and regulation of bacterial chromosome segregation dynamics by polarly localized proteins
No full textA Landmark Protein Essential for Establishing and Perpetuating the Polarity of a Bacterial Cell
No full textSummaryPolarity is often an intrinsic property of the cell, yet little is known about its origin or its maintenance over generations. Here we identify a landmark protein, TipN, which acts as a spatial and temporal cue for setting up the correct polarity in the bacterium Caulobacter crescentus. TipN marks the new pole throughout most of the cell cycle, and its relocation to the nascent poles at the end of division provides a preexisting reference point for orienting the polarity axis in the progeny. Deletion of tipN causes pleiotropic polarity defects, including frequently reversed asymmetry in progeny size and mislocalization of proteins and organelles. Ectopic localization of TipN along the lateral side of the cell creates new axes of polarity leading to cell branching and formation of competent cell poles. Localization defects of the actin-like protein MreB in the ΔtipN mutant suggest that TipN is upstream of MreB in regulating cell polarity
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
Early Air Force Flight Test Center (AFFTC) experience with Peripheral Vision Horizon Displays (PVHD)
No full textThree separate Air Force Flight Test Center (AFFTC) tests were conducted in 1980 and 1981 on two models of the peripheral vision horizon displays (PVHD) (Malcolm Horizon). A fixed base simulator test was conducted with twenty test pilot subjects using the Flight Simulator Demonstration Model which incorporated a Helium Neon laser as the light bar medium. Two separate flight tests were conducted by the Test Pilot School classes 80A and 80B in a Twin Otter commuter aircraft using the Stage A Model PVHD. The Xenon lighted A Model was tested in its original configuration by class 80A. Class 80B used a modified configuration which incorporated an AFFTC designed and manufactured hood. With the hood, the PVHD projected a thinner, distinct light bar. Only a few general remarks concerning the tests and unrestricted, overall conclusions reached by the author are presented. The conclusions of all three AFFTC evaluations of the PVHD concept were that it has not yet been adequately evaluated. There seems to be a significant learning curve associated with the PVHD and the project pilots for Test Pilot School Class 80B only got a good start on the learning curve. A lengthy learning curve for the PVHD should be anticipated in view of the training period required for the attitude display indicator (ADI). This does seem to point out that the PVHD, in its present form, is simply not as compelling as the natural horizon. It can also be concluded that any attempt at a valid evaluation of the PVHD concept can be done only under instrument meteorological conditions (IMC) or validly simulated IMC conditions. The knee in the learning curve, however, may be reached without full IMC, although it may take much longer to reach
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