3,461 research outputs found
Multi-scale analysis of timber framed structures filled with earth and stones
This paper deals with the seismic analysis of timber framed houses filled by stones and earth mortar using a multi-scale approach going from the cell to the wall and then to the house. At the scale of the elementary cells, experimental results allow fitting the parameters of a new versatile hysteretic law presented herein through the definition of a macro-element. Then, at the scale of wall, the numerical simulations are able to predict its behavior under quasi-static cyclic loading and is compared to experimental results allowing validating the macro-element model
L\u27Amour C\u27est Comme La Salade : Chanson Comique
https://digitalcommons.library.umaine.edu/mmb-vp/1934/thumbnail.jp
Statistical Methods for Thermonuclear Reaction Rates and Nucleosynthesis Simulations
Rigorous statistical methods for estimating thermonuclear reaction rates and
nucleosynthesis are becoming increasingly established in nuclear astrophysics.
The main challenge being faced is that experimental reaction rates are highly
complex quantities derived from a multitude of different measured nuclear
parameters (e.g., astrophysical S-factors, resonance energies and strengths,
particle and gamma-ray partial widths). We discuss the application of the Monte
Carlo method to two distinct, but related, questions. First, given a set of
measured nuclear parameters, how can one best estimate the resulting
thermonuclear reaction rates and associated uncertainties? Second, given a set
of appropriate reaction rates, how can one best estimate the abundances from
nucleosynthesis (i.e., reaction network) calculations? The techniques described
here provide probability density functions that can be used to derive
statistically meaningful reaction rates and final abundances for any desired
coverage probability. Examples are given for applications to s-process neutron
sources, core-collapse supernovae, classical novae, and big bang
nucleosynthesis.Comment: Accepted for publication in J. Phys. G Focus issue "Enhancing the
interaction between nuclear experiment and theory through information and
statistics
STARLIB: A Next-Generation Reaction-Rate Library for Nuclear Astrophysics
STARLIB is a next-generation, all-purpose nuclear reaction-rate library. For
the first time, this library provides the rate probability density at all
temperature grid points for convenient implementation in models of stellar
phenomena. The recommended rate and its associated uncertainties are also
included. Currently, uncertainties are absent from all other rate libraries,
and, although estimates have been attempted in previous evaluations and
compilations, these are generally not based on rigorous statistical
definitions. A common standard for deriving uncertainties is clearly warranted.
STARLIB represents a first step in addressing this deficiency by providing a
tabular, up-to-date database that supplies not only the rate and its
uncertainty but also its distribution. Because a majority of rates are
lognormally distributed, this allows the construction of rate probability
densities from the columns of STARLIB. This structure is based on a recently
suggested Monte Carlo method to calculate reaction rates, where uncertainties
are rigorously defined. In STARLIB, experimental rates are supplemented with:
(i) theoretical TALYS rates for reactions for which no experimental input is
available, and (ii) laboratory and theoretical weak rates. STARLIB includes all
types of reactions of astrophysical interest to Z = 83, such as (p,g), (p,a),
(a,n), and corresponding reverse rates. Strong rates account for thermal target
excitations. Here, we summarize our Monte Carlo formalism, introduce the
library, compare methods of correcting rates for stellar environments, and
discuss how to implement our library in Monte Carlo nucleosynthesis studies. We
also present a method for accessing STARLIB on the Internet and outline updated
Monte Carlo-based rates.Comment: Accepted for publication in the Astrophysical Journal Supplement
Series; 96 pages, 22 figure
The reactions and ashes of thermonuclear explosions on neutron stars
This paper reports on the detailed rp-process reaction flow on an accreting
neutron star and the resulting ashes of a type I X-ray burst. It is obtained by
coupling a 298 isotope reaction network to a self-consistent one-dimensional
model calculation with a constant accretion rate of dM/dt=1.0e17g/s (0.09
Eddington).Comment: 4 pages, 2 figures, submitted to the INPC2004 proceeding
Second-Order Nonlinear Optical Properties of Multiaddressable Indolinooxazolidine Derivatives: Joint Computational and Hyper-Rayleigh Scattering Investigations
The linear and nonlinear optical (NLO) properties of two indolinooxazolidine derivatives acting as multiaddressable switches are reported. The second-order hyperpolarizability contrasts upon commutation between their closed and open forms are characterized using hyper-Rayleigh scattering (HRS) measurements, and rationalized by means of density functional theory and post Hartree–Fock ab initio calculations. It is evidenced that the addition of a withdrawing substituent on the indolinic subunit leads to a more effective photoinduced charge transfer while decreasing the transition energy of the S0 → S1 transition, which induces a significant enhancement of the HRS response of the open form. This substitution is however detrimental to the NLO contrast, due to the concomitant increase of the HRS response of the closed form
Development and Characterisation of a Gas System and its Associated Slow-Control System for an ATLAS Small-Strip Thin Gap Chamber Testing Facility
A quality assurance and performance qualification laboratory was built at
McGill University for the Canadian-made small-strip Thin Gap Chamber (sTGC)
muon detectors produced for the 2019-2020 ATLAS experiment muon spectrometer
upgrade. The facility uses cosmic rays as a muon source to ionise the quenching
gas mixture of pentane and carbon dioxide flowing through the sTGC detector. A
gas system was developed and characterised for this purpose, with a simple and
efficient gas condenser design utilizing a Peltier thermoelectric cooler (TEC).
The gas system was tested to provide the desired 45 vol% pentane concentration.
For continuous operations, a state-machine system was implemented with alerting
and remote monitoring features to run all cosmic-ray data-acquisition
associated slow-control systems, such as high/low voltage, gas system and
environmental monitoring, in a safe and continuous mode, even in the absence of
an operator.Comment: 23 pages, LaTeX, 14 figures, 4 tables, proof corrections for Journal
of Instrumentation (JINST), including corrected Fig. 8b
Maternal self-reported prenatal depressive symptoms predict infant NR3C1 1F and BDNF IV DNA methylation.
Prenatal maternal psychological distress increases risk for adverse infant outcomes.
However, the biological mechanisms underlying this association remain unclear.
Prenatal stress can impact fetal epigenetic regulation that could underlie changes in
infant stress responses. It has been suggested that maternal glucocorticoids may
mediate this epigenetic effect. We examined this hypothesis by determining the
impact of maternal cortisol and depressive symptoms during pregnancy on infant
NR3C1 and BDNF DNA methylation. Fifty-seven pregnant women were recruited
during the second or third trimester.
Participants self-reported depressive symptoms
and salivary cortisol samples were collected diurnally and in response to a stressor.
Buccal swabs for DNA extraction and DNA methylation analysis were collected from
each infant at two months of age, and mothers were assessed for postnatal depressive
symptoms. Prenatal depressive symptoms significantly predicted increased NR3C1 1F
DNA methylation in male infants ( 2.147 = س , P = 0.044). Prenatal depressive
symptoms also significantly predicted decreased BDNF IV DNA methylation in both
male and female infants ( -3.244 = س , P = 0.013). No measure of maternal cortisol
during pregnancy predicted infant NR3C1 1F or BDNF promoter IV DNA
methylation. Our findings highlight the susceptibility of males to changes in NR3C1
DNA methylation and present novel evidence for altered BDNF IV DNA methylation
in response to maternal depression during pregnancy. The lack of association between
maternal cortisol and infant DNA methylation suggests that effects of maternal
depression may not be mediated directly by glucocorticoids. Future studies should
consider other potential mediating mechanisms in the link between maternal mood
and infant outcome
First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
The first direct mass-measurement of He has been performed with the
TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the
mass of He was determined with improved precision over our previous
measurement. The obtained masses are (He) = 6.018 885 883(57) u and
(He) = 8.033 934 44(11) u. The He value shows a deviation from
the literature of 4. With these new mass values and the previously
measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and
1.959(16) fm for He and He respectively. We present a detailed
comparison to nuclear theory for He, including new hyperspherical harmonics
results. A correlation plot of the point-proton radius with the two-neutron
separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure
Non-linear optical susceptibilities, Raman efficiencies and electrooptic tensors from first-principles density functional perturbation theory
The non-linear response of infinite periodic solids to homogenous electric
fields and collective atomic displacements is discussed in the framework of
density functional perturbation theory. The approach is based on the 2n + 1
theorem applied to an electric-field-dependent energy functional. We report the
expressions for the calculation of the non-linear optical susceptibilities,
Raman scattering efficiencies and electrooptic coefficients. Different
formulations of third-order energy derivatives are examined and their
convergence with respect to the k-point sampling is discussed. We apply our
method to a few simple cases and compare our results to those obtained with
distinct techniques. Finally, we discuss the effect of a scissors correction on
the EO coefficients and non-linear optical susceptibilities
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