178 research outputs found
A contact cavity-biased method for grand canonical Monte Carlo simulations
A modification of the cavity-biased grand canonical Monte Carlo (GCMC) proposed by Mezei is introduced here. Instead of on a fixed grid, test points of cavities are generated at the contact positions around the centers of existing particles. The increase in the probability or bias of finding a cavity is related to the radial distribution function and can hence be corrected. With this new cavity-biased implementation, an improved convergence to equihbrium is demonstrated and higher densities can be attained. Comparisons with the standard GCMC method, and the original cavity-biased scheme of Mezei are made. © 1994 American Institute of Physics.published_or_final_versio
Logarithmic interaction under periodic boundary conditions: Closed form formulas for energy and forces
A method is given to obtain closed form formulas for the energy and forces
for an aggregate of charges interacting via a logarithmic interaction under
periodic boundary conditions. The work done here is a generalization of
Glasser's results [M. L. Glasser, J. Math. Phys. 15, 188 (1974)] and is
obtained with a different and simpler method than that by Stremler [M. A.
Stremler, J. Math. Phys. 45, 3584 (2004)]. The simplicity of the formulas
derived here makes them extremely convenient in a computer simulation
Yukawa potentials in systems with partial periodic boundary conditions II : Lekner sums for quasi-two dimensional systems
Yukawa potentials may be long ranged when the Debye screening length is
large. In computer simulations, such long ranged potentials have to be taken
into account with convenient algorithms to avoid systematic bias in the
sampling of the phase space. Recently, we have provided Ewald sums for
quasi-two dimensional systems with Yukawa interaction potentials [M. Mazars,
{\it J. Chem. Phys.}, {\bf 126}, 056101 (2007) and M. Mazars, {\it Mol. Phys.},
Paper I]. Sometimes, Lekner sums are used as an alternative to Ewald sums for
Coulomb systems. In the present work, we derive the Lekner sums for quasi-two
dimensional systems with Yukawa interaction potentials and we give some
numerical tests for pratical implementations. The main result of this paper is
to outline that Lekner sums cannot be considered as an alternative to Ewald
sums for Yukawa potentials. As a conclusion to this work : Lekner sums should
not be used for quasi-two dimensional systems with Yukawa interaction
potentials.Comment: 25 pages, 5 figures and 1 tabl
Lekner summations and Ewald summations for quasi-two dimensional systems
Using the specific model of a bilayer of classical charged particles (bilayer
Wigner crystal), we compare the predictions for energies and pair distribution
functions obtained by Monte Carlo simulations using three different methods
available to treat the long range Coulomb interactions in systems periodic in
two directions but bound in the third one. The three methods compared are: the
Ewald method for quasi-two dimensional systems [D.E. Parry, Surf. Sci.
, 433 (1975); \it{ibid.}, , 195 (1976)], the Hautman-Klein
method [J. Hautman and M.L. Klein, Mol. Phys. , 379 (1992)] and the
Lekner summations method [J. Lekner, Physica A, 485 (1991)]. All of
the three method studied in this paper may be applied to any quasi-two
dimensional systems, including those having not the specific symmetry of slab
systems. For the particular system used in this work, the Ewald method for
quasi-two dimensional systems is exact and may be implemented with efficiency;
results obtained with the other two methods are systematically compared to
results found with the Ewald method. General recommendations to implement with
accuracy, but not always with efficiency, the Lekner summations technique in
Monte Carlo algorithms are given.Comment: 50 pages, 9 figures, 4 table
Maternal sepsis complicating arabin cervical pessary placement for the prevention of preterm birth: a case report
Preterm delivery is a major health problem and contributes to more than 50% of all neonatal and infant deaths. Recently, there has been a renewed interest in the use of cervical pessaries as a safe and effective intervention with few maternal side-effects for the prevention of preterm birth in both single and twin pregnancies
Yukawa potentials in systems with partial periodic boundary conditions I : Ewald sums for quasi-two dimensional systems
Yukawa potentials are often used as effective potentials for systems as
colloids, plasmas, etc. When the Debye screening length is large, the Yukawa
potential tends to the non-screened Coulomb potential ; in this small screening
limit, or Coulomb limit, the potential is long ranged. As it is well known in
computer simulation, a simple truncation of the long ranged potential and the
minimum image convention are insufficient to obtain accurate numerical data on
systems. The Ewald method for bulk systems, i.e. with periodic boundary
conditions in all three directions of the space, has already been derived for
Yukawa potential [cf. Y., Rosenfeld, {\it Mol. Phys.}, \bm{88}, 1357, (1996)
and G., Salin and J.-M., Caillol, {\it J. Chem. Phys.}, \bm{113}, 10459,
(2000)], but for systems with partial periodic boundary conditions, the Ewald
sums have only recently been obtained [M., Mazars, {\it J. Chem. Phys.}, {\bf
126}, 056101 (2007)]. In this paper, we provide a closed derivation of the
Ewald sums for Yukawa potentials in systems with periodic boundary conditions
in only two directions and for any value of the Debye length. A special
attention is paid to the Coulomb limit and its relation with the
electroneutrality of systems.Comment: 40 pages, 5 figures and 4 table
Morphine induces preconditioning via activation of mitochondrial KCa channels
PURPOSE: Mitochondrial calcium sensitive potassium (mK(Ca)) channels are involved in cardioprotection induced by ischemic preconditioning. In the present study we investigated whether morphine-induced preconditioning also involves activation of mK(Ca) channels. METHODS: Isolated rat hearts (six groups; each n = 8) underwent global ischemia for 30 min followed by a 60-min reperfusion. Control animals were not further treated. Morphine preconditioning (MPC) was initiated by two five-minute cycles of morphine 1 muM infusion with one five-minute washout and one final ten-minute washout period before ischemia. The mK(Ca) blocker, paxilline 1 muM, was administered, with and without morphine administration (MPC + Pax and Pax). As a positive control, we added an ischemic preconditioning group (IPC) alone and combined with paxilline (IPC + Pax). At the end of reperfusion, infarct sizes were determined by triphenyltetrazoliumchloride staining. RESULTS: Infarct size was (mean +/- SD) 45 +/- 9% of the area at risk in the Control group. The infarct size was less in the morphine or ischemic preconditioning groups (MPC: 23 +/- 8%, IPC: 20 +/- 5%; each P < 0.05 vs Control). Infarct size reduction was abolished by paxilline (MPC + Pax: 37 +/- 7%, P < 0.05 vs MPC and IPC + Pax: 36 +/- 6%, P < 0.05 vs IPC), whereas paxilline alone had no effect (Pax: 46 +/- 7%, not significantly different from Control). CONCLUSION: Cardioprotection by morphine-induced preconditioning is mediated by activation of mK(Ca) channel
De novo copy number variations in candidate genomic regions in patients of severe autism spectrum disorder in Vietnam
Autism spectrum disorder (ASD) is a developmental disorder with a prevalence of around 1% children worldwide and characterized by patient behaviour (communication, social interaction, and personal development). Data on the efficacy of diagnostic tests using copy number variations (CNVs) in candidate genes in ASD is currently around 10% but it is overrepresented by patients of Caucasian background. We report here that the diagnostic success of de novo candidate CNVs in Vietnamese ASD patients is around 6%. We recruited one hundred trios (both parents and a child) where the child was clinically diagnosed with ASD while the parents were not affected. We performed genetic screening to exclude RETT syndrome and Fragile X syndrome and performed genome-wide DNA microarray (aCGH) on all probands and their parents to analyse for de novo CNVs. We detected 1708 non-redundant CNVs in 100 patients and 118 (7%) of them were de novo. Using the filter for known CNVs from the Simons Foundation Autism Research Initiative (SFARI) database, we identified six CNVs (one gain and five loss CNVs) in six patients (3 males and 3 females). Notably, 3 of our patients had a deletion involving the SHANK3 gene–which is the highest compared to previous reports. This is the first report of candidate CNVs in ASD patients from Vietnam and provides the framework for building a CNV based test as the first tier screening for clinical management
Development and Notch Signaling Requirements of the Zebrafish Choroid Plexus
The choroid plexus (CP) is an epithelial and vascular structure in the ventricular system of the brain that is a critical part of the blood-brain barrier. The CP has two primary functions, 1) to produce and regulate components of the cerebral spinal fluid, and 2) to inhibit entry into the brain of exogenous substances. Despite its importance in neurobiology, little is known about how this structure forms.Here we show that the transposon-mediated enhancer trap zebrafish line Et(Mn16) expresses green fluorescent protein within a population of cells that migrate toward the midline and coalesce to form the definitive CP. We further demonstrate the development of the integral vascular network of the definitive CP. Utilizing pharmacologic pan-notch inhibition and specific morpholino-mediated knockdown, we demonstrate a requirement for Notch signaling in choroid plexus development. We identify three Notch signaling pathway members as mediating this effect, notch1b, deltaA, and deltaD.This work is the first to identify the zebrafish choroid plexus and to characterize its epithelial and vasculature integration. This study, in the context of other comparative anatomical studies, strongly indicates a conserved mechanism for development of the CP. Finally, we characterize a requirement for Notch signaling in the developing CP. This establishes the zebrafish CP as an important new system for the determination of key signaling pathways in the formation of this essential component of the vertebrate brain
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