170 research outputs found
DynamO: A free O(N) general event-driven molecular-dynamics simulator
Molecular-dynamics algorithms for systems of particles interacting through
discrete or "hard" potentials are fundamentally different to the methods for
continuous or "soft" potential systems. Although many software packages have
been developed for continuous potential systems, software for discrete
potential systems based on event-driven algorithms are relatively scarce and
specialized. We present DynamO, a general event-driven simulation package which
displays the optimal O(N) asymptotic scaling of the computational cost with the
number of particles N, rather than the O(N log(N)) scaling found in most
standard algorithms. DynamO provides reference implementations of the best
available event-driven algorithms. These techniques allow the rapid simulation
of both complex and large (>10^6 particles) systems for long times. The
performance of the program is benchmarked for elastic hard sphere systems,
homogeneous cooling and sheared inelastic hard spheres, and equilibrium
Lennard-Jones fluids. This software and its documentation are distributed under
the GNU General Public license and can be freely downloaded from
http://marcusbannerman.co.uk/dynamo
Thermodynamics of Portland Cement Clinkering
Acknowledgements The authors would like to thank Gulf Organization for Research and Development (GORD, Qatar) for funding.Postprin
Collision statistics in sheared inelastic hard spheres
The dynamics of sheared inelastic-hard-sphere systems are studied using
non-equilibrium molecular dynamics simulations and direct simulation Monte
Carlo. In the molecular dynamics simulations Lees-Edwards boundary conditions
are used to impose the shear. The dimensions of the simulation box are chosen
to ensure that the systems are homogeneous and that the shear is applied
uniformly. Various system properties are monitored, including the one-particle
velocity distribution, granular temperature, stress tensor, collision rates,
and time between collisions. The one-particle velocity distribution is found to
agree reasonably well with an anisotropic Gaussian distribution, with only a
slight overpopulation of the high velocity tails. The velocity distribution is
strongly anisotropic, especially at lower densities and lower values of the
coefficient of restitution, with the largest variance in the direction of
shear. The density dependence of the compressibility factor of the sheared
inelastic hard sphere system is quite similar to that of elastic hard sphere
fluids. As the systems become more inelastic, the glancing collisions begin to
dominate more direct, head-on collisions. Examination of the distribution of
the time between collisions indicates that the collisions experienced by the
particles are strongly correlated in the highly inelastic systems. A comparison
of the simulation data is made with DSMC simulation of the Enskog equation.
Results of the kinetic model of Montanero et al. {[}Montanero et al., J. Fluid
Mech. 389, 391 (1999){]} based on the Enskog equation are also included. In
general, good agreement is found for high density, weakly inelastic systems.Comment: 10 figures, 1 table, 27 page
Preclinical evaluation of the antitumor activity of bortezomib in combination with vitamin C or with epigallocatechin gallate, a component of green tea
Glutamatergic dysfunction leads to a hyper-dopaminergic phenotype through deficits in short-term habituation: a mechanism for aberrant salience
Psychosis in disorders like schizophrenia is commonly associated with aberrant salience and elevated striatal dopamine. However, the underlying cause(s) of this hyper-dopaminergic state remain elusive. Various lines of evidence point to glutamatergic dysfunction and impairments in synaptic plasticity in the etiology of schizophrenia, including deficits associated with the GluA1 AMPAR subunit. GluA1 knockout (Gria1−/−) mice provide a model of impaired synaptic plasticity in schizophrenia and exhibit a selective deficit in a form of short-term memory which underlies short-term habituation. As such, these mice are unable to reduce attention to recently presented stimuli. In this study we used fast-scan cyclic voltammetry to measure phasic dopamine responses in the nucleus accumbens of Gria1−/− mice to determine whether this behavioral phenotype might be a key driver of a hyper-dopaminergic state. There was no effect of GluA1 deletion on electrically-evoked dopamine responses in anaesthetized mice, demonstrating normal endogenous release properties of dopamine neurons in Gria1−/− mice. Furthermore, dopamine signals were initially similar in Gria1−/− mice compared to controls in response to both sucrose rewards and neutral light stimuli. They were also equally sensitive to changes in the magnitude of delivered rewards. In contrast, however, these stimulus-evoked dopamine signals failed to habituate with repeated presentations in Gria1−/− mice, resulting in a task-relevant, hyper-dopaminergic phenotype. Thus, here we show that GluA1 dysfunction, resulting in impaired short-term habituation, is a key driver of enhanced striatal dopamine responses, which may be an important contributor to aberrant salience and psychosis in psychiatric disorders like schizophrenia
Risk of Uterine Rupture and Placenta Accreta With Prior Uterine Surgery Outside of the Lower Segment
Objective—Women with a prior myomectomy or prior classical cesarean delivery are often delivered early by cesarean due to concern for uterine rupture. Although theoretically at increased risk for placenta accreta, this risk has not been well quantified. Our objective was to estimate and compare the risks of uterine rupture and placenta accreta in women with prior uterine surgery. Methods—Women with prior myomectomy or prior classical cesarean delivery were compared to women with a prior low transverse cesarean to estimate rates of both uterine rupture and placenta accreta. Results—One hundred seventy-six women with a prior myomectomy, 455 with a prior classical cesarean delivery, and 13,273 women with a prior low transverse cesarean were evaluated. Mean gestational age at delivery differed by group (p0.99) or in the prior classical cesarean delivery group (0.88%, p=0.13). Placenta accreta occurred in 0% (95% CI 0-1.98%) of prior myomectomy compared with 0.19% in the low transverse cesarean group (p>0.99) and 0.88% in the prior classical cesarean delivery group (p=0.01 relative to low transverse cesarean). The adjusted OR for the prior classical cesarean delivery group (relative to low transverse cesarean) was 3.23 (1.11-9.39) for uterine rupture and 2.09 (0.69-6.33) for accreta. The frequency of accreta for those with previa was 11.1% for the prior classical cesarean delivery and 13.6% for low transverse cesarean groups (p>0.99=1.0). Conclusion—A prior myomectomy is not associated with higher risks of either uterine rupture or placenta accreta. The absolute risks of uterine rupture and accreta after prior myomectomy are low
TEMPORAL TRENDS IN THE SPATIAL DISTRIBUTION OF IMPERVIOUS COVER RELATIVE TO STREAM LOCATION
Use of impervious cover is transitioning from an indicator of surface water condition to one that also guides and informs watershed planning and management, including Clean Water Act (33 U.S.C. §1251 et seq.) reporting. Whether it is for understanding surface water condition or planning and management, impervious cover is most commonly expressed as summary measurement (e.g., percentage watershed in impervious cover). We use the National Land Cover Database to estimate impervious cover in the vicinity of surface waters for three time periods (2001, 2006, 2011). We also compare impervious cover in the vicinity of surface waters to watershed summary estimates of impervious cover for classifying the spatial pattern of impervious cover. Between 2001 and 2011, surface water shorelines (streams and water bodies) in the vicinity of impervious cover increased nearly 10,000 km. Across all time periods, approximately 27% of the watersheds in the continental United States had proximally distributed impervious cover, i.e., the percentage of impervious cover in the vicinity of surface waters was higher than its watershed summary expression. We discuss how impervious cover spatial pattern can be used to inform watershed planning and management, including reporting under the Clean Water Act
Absent sleep EEG spindle activity in GluA1 (Gria1) knockout mice:relevance to neuropsychiatric disorders
Sleep EEG spindles have been implicated in attention, sensory processing, synaptic plasticity and memory consolidation. In humans, deficits in sleep spindles have been reported in a wide range of neurological and psychiatric disorders, including schizophrenia. Genome-wide association studies have suggested a link between schizophrenia and genes associated with synaptic plasticity, including the Gria1 gene which codes for the GluA1 subunit of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor. Gria1−/− mice exhibit a phenotype relevant for neuropsychiatric disorders, including reduced synaptic plasticity and, at the behavioural level, attentional deficits leading to aberrant salience. In this study we report a striking reduction of EEG power density including the spindle-frequency range (10–15 Hz) during sleep in Gria1−/− mice. The reduction of spindle-activity in Gria1−/− mice was accompanied by longer REM sleep episodes, increased EEG slow-wave activity in the occipital derivation during baseline sleep, and a reduced rate of decline of EEG slow wave activity (0.5–4 Hz) during NREM sleep after sleep deprivation. These data provide a novel link between glutamatergic dysfunction and sleep abnormalities in a schizophrenia-relevant mouse model
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