420 research outputs found
Ewald Sums for One Dimension
We derive analytic solutions for the potential and field in a one-dimensional
system of masses or charges with periodic boundary conditions, in other words
Ewald sums for one dimension. We also provide a set of tools for exploring the
system evolution and show that it's possible to construct an efficient
algorithm for carrying out simulations. In the cosmological setting we show
that two approaches for satisfying periodic boundary conditions, one overly
specified and the other completely general, provide a nearly identical
clustering evolution until the number of clusters becomes small, at which time
the influence of any size-dependent boundary cannot be ignored. Finally we
compare the results with other recent work with the hope of providing
clarification over differences these issues have induced. We explain that
modern formulations of physics require a well defined potential which is not
available if the forces are screened directly.Comment: 2 figures added references expanded discussion of algorithm corrected
figures added discussion of screened forc
On the morphology of the electron-positron annihilation emission as seen by SPI/INTEGRAL
The 511 keV positron annihilation emission remains a mysterious component of
the high energy emission of our Galaxy. Its study was one of the key scientific
objective of the SPI spectrometer on-board the INTEGRAL satellite. In fact, a
lot of observing time has been dedicated to the Galactic disk with a particular
emphasis on the central region. A crucial issue in such an analysis concerns
the reduction technique used to treat this huge quantity of data, and more
particularly the background modeling. Our method, after validation through a
variety of tests, is based on detector pattern determination per ~6 month
periods, together with a normalisation variable on a few hour timescale. The
Galactic bulge is detected at a level of ~70 sigma allowing more detailed
investigations. The main result is that the bulge morphology can be modelled
with two axisymmetric Gaussians of 3.2 deg. and 11.8 deg. FWHM and respective
fluxes of 2.5 and 5.4 x 10^-4 photons/(cm^2.s^1). We found a possible shift of
the bulge centre towards negative longitude at l=-0.6 +/- 0.2 degrees. In
addition to the bulge, a more extended structure is detected significantly with
flux ranging from 1.7 to 2.9 x10^-3 photons/(cm^2.s^1) depending on its assumed
geometry (pure disk or disk plus halo). The disk emission is also found to be
symmetric within the limits of the statistical errors.Comment: This paper has 12 pages and 14 figures. Accepted for publication by
the Astrophysical Journa
Formation of fractal structure in many-body systems with attractive power-law potentials
We study the formation of fractal structure in one-dimensional many-body
systems with attractive power-law potentials. Numerical analysis shows that the
range of the index of the power for which fractal structure emerges is limited.
Dependence of the growth rate on wavenumber and power-index is obtained by
linear analysis of the collisionless Boltzmann equation, which supports the
numerical results.Comment: accepted by PR
A continuous non-linear shadowing model of columnar growth
We propose the first continuous model with long range screening (shadowing)
that described columnar growth in one space dimension, as observed in plasma
sputter deposition. It is based on a new continuous partial derivative equation
with non-linear diffusion and where the shadowing effects apply on all the
different processes.Comment: Fast Track Communicatio
Rapid and MR-Independent IK1 activation by aldosterone during ischemia-reperfusion
In ST elevation myocardial infarction (STEMI) context, clinical studies have shown the deleterious
effect of high aldosterone levels on ventricular arrhythmia occurrence and cardiac
mortality. Previous in vitro reports showed that during ischemia-reperfusion, aldosterone
modulates K+ currents involved in the holding of the resting membrane potential (RMP).
The aim of this study was to assess the electrophysiological impact of aldosterone on IK1
current during myocardial ischemia-reperfusion. We used an in vitro model of “border zone”
using right rabbit ventricle and standard microelectrode technique followed by cell-attached
recordings from freshly isolated rabbit ventricular cardiomyocytes. In microelectrode experiments,
aldosterone (10 and 100 nmol/L, n=7 respectively) increased the action potential
duration (APD) dispersion at 90% between ischemic and normoxic zones (from 95±4ms to
116±6 ms and 127±5 ms respectively, P<0.05) and reperfusion-induced sustained premature
ventricular contractions occurrence (from 2/12 to 5/7 preparations, P<0.05). Conversely,
potassium canrenoate 100 nmol/L and RU 28318 1 μmol/l alone did not affect AP
parameters and premature ventricular contractions occurrence (except Vmax which was
decreased by potassium canrenoate during simulated-ischemia). Furthermore, aldosterone
induced a RMP hyperpolarization, evoking an implication of a K+ current involved in the
holding of the RMP. Cell-attached recordings showed that aldosterone 10 nmol/L quickly
activated (within 6.2±0.4 min) a 30 pS K+-selective current, inward rectifier, with pharmacological
and biophysical properties consistent with the IK1 current (NPo =1.9±0.4 in control vs
NPo=3.0±0.4, n=10, P<0.05). These deleterious effects persisted in presence of RU 28318,
a specific MR antagonist, and were successfully prevented by potassium canrenoate, a non
specific MR antagonist, in both microelectrode and patch-clamp recordings, thus indicating
a MR-independent IK1 activation. In this ischemia-reperfusion context, aldosterone induced
rapid and MR-independent deleterious effects including an arrhythmia substrate (increased
APD90 dispersion) and triggered activities (increased premature ventricular contractions
occurrence on reperfusion) possibly related to direct IK1 activation
An integrating factor matrix method to find first integrals
In this paper we developed an integrating factor matrix method to derive
conditions for the existence of first integrals. We use this novel method to
obtain first integrals, along with the conditions for their existence, for two
and three dimensional Lotka-Volterra systems with constant terms. The results
are compared to previous results obtained by other methods
Characteristics of the summit lakes of Ambae volcano and their potential for generating lahars
Volcanic eruptions through crater lakes often generate lahars, causing loss of life and property. On Ambae volcano, recent eruptive activities have rather tended to reduce the water volume in the crater lake (Lake Voui), in turn, reducing the chances for outburst floods. Lake Voui occupies a central position in the summit caldera and is well enclosed by the caldera relief. Eruptions with significantly higher magnitude than that of 1995 and 2005 are required for an outburst. A more probable scenario for lahar events is the overflow from Lake Manaro Lakua bounded on the eastern side by the caldera wall. Morphology and bathymetry analysis have been used to identify the weakest point of the caldera rim from which water from Lake Manaro Lakua may overflow to initiate lahars. The 1916 disaster described on south-east Ambae was possibly triggered by such an outburst from Lake Manaro Lakua. Taking into account the current level of Lake Manaro Lakua well below a critical overflow point, and the apparently low potential of Lake Voui eruptions to trigger lahars, the Ambae summit lakes may not be directly responsible for numerous lahar deposits identified around the Island
Going beyond children’s single-text comprehension:The role of fundamental and higher–level skills in 4th graders’ multiple-document comprehension
Background: Children's comprehension of single texts relies on both foundational and higher-level skills. These are also assumed to support multiple-document comprehension, but their relative importance has not been examined, to date. Multiple-document comprehension additionally requires the identification and use of information about each document's source. Aims: This study examined multiple-document comprehension in primary school-aged children. It sought to determine the relative importance of skills proposed to be common to both single-text and multiple-document comprehension (word reading fluency, verbal working memory, comprehension monitoring) and specific to the latter (source use). Single-text comprehension and prior topic knowledge were considered as moderator and control. Sample: Participants were 94 children in the fourth year (mean age = 9; 7 years; 52% females). Methods: Children read three documents on each of two topics (chocolate and video games). Multiple-document comprehension and source use were assessed through short essays. Independent measures of the fundamental and higher-level skills were used. Results: There was a significant direct and indirect influence of word reading fluency on comprehension of multiple documents on videogames and also an indirect influence of comprehension monitoring. Indirect influences of word reading fluency and comprehension monitoring on multiple-document comprehension for both topics were also apparent. Verbal working memory was not a unique predictor. When source information was identified, it was included to support the argument in the composition. Conclusions: Efficient word reading, comprehension monitoring, and single-text comprehension are important for multiple-document comprehension in young readers. Implications of these findings and differences between the two document sets are discussed
Drug resistance is widespread among children who receive long-term antiretroviral treatment at a rural Tanzanian hospital
To assess long-term virological efficacy and the emergence of drug resistance in children who receive antiretroviral treatment (ART) in rural Tanzania.
Haydom Lutheran Hospital has provided ART to HIV-infected individuals since 2003. From February through May 2009, a cross-sectional virological efficacy survey was conducted among children (200 copies/mL.
Virological response was measured in 19 of 23 eligible children; 8 of 19 were girls and median age at ART initiation was 5 years (range 2–14 years). Median duration of ART at the time of the survey was 40 months (range 11–61 months). Only 8 children were virologically suppressed (≤40 copies/mL), whereas 11 children had clinically relevant resistance mutations in the reverse transcriptase gene. The most frequent mutations were M184V (n = 11), conferring resistance to lamivudine and emtricitabine, and Y181C (n = 4), G190A/S (n = 4) and K103N (n = 4), conferring resistance to NNRTIs. Of concern, three children had thymidine analogue mutations, associated with cross-resistance to all nucleoside reverse transcriptase inhibitors. Despite widespread resistance, however, only one child experienced a new WHO stage 4 event and none had a CD4 cell count of <200 cells/mm3.
Among children on long-term ART in rural Tanzania, >50% harboured drug resistance. Results for children were markedly poorer than for adults attending the same programme, underscoring the need for improved treatment strategies for children in resource-limited settings
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