1,788 research outputs found
Kinetic energy of protons in ice Ih and water: a path integral study
The kinetic energy of H and O nuclei has been studied by path integral
molecular dynamics simulations of ice Ih and water at ambient pressure. The
simulations were performed by using the q-TIP4P/F model, a point charge
empirical potential that includes molecular flexibility and anharmonicity in
the OH stretch of the water molecule. Ice Ih was studied in a temperature range
between 210-290 K, and water between 230-320 K. Simulations of an isolated
water molecule were performed in the range 210-320 K to estimate the
contribution of the intramolecular vibrational modes to the kinetic energy. Our
results for the proton kinetic energy, K_H, in water and ice Ih show both
agreement and discrepancies with different published data based on deep
inelastic neutron scattering experiments. Agreement is found for water at the
experimental melting point and in the range 290-300 K. Discrepancies arise
because data derived from the scattering experiments predict in water two
maxima of K_H around 270 K and 277 K, and that K_H is lower in ice than in
water at 269 K. As a check of the validity of the employed water potential, we
show that our simulations are consistent with other experimental thermodynamic
properties related to K_H, as the temperature dependence of the liquid density,
the heat capacity of water and ice at constant pressure, and the isotopic shift
in the melting temperature of ice upon isotopic substitution of either H or O
atoms. Moreover, the temperature dependence of K_H predicted by the q-TIP4P/F
model for ice Ih is found to be in good agreement to results of path integral
simulations using ab initio density functional theory.Comment: 11 pages, 6 figures, 2 table
The underlying physical meaning of the relation
Asteroseismology of stars that exhibit solar-like oscillations are enjoying a
growing interest with the wealth of observational results obtained with the
CoRoT and Kepler missions. In this framework, scaling laws between
asteroseismic quantities and stellar parameters are becoming essential tools to
study a rich variety of stars. However, the physical underlying mechanisms of
those scaling laws are still poorly known. Our objective is to provide a
theoretical basis for the scaling between the frequency of the maximum in the
power spectrum () of solar-like oscillations and the cut-off
frequency (). Using the SoHO GOLF observations together with
theoretical considerations, we first confirm that the maximum of the height in
oscillation power spectrum is determined by the so-called \emph{plateau} of the
damping rates. The physical origin of the plateau can be traced to the
destabilizing effect of the Lagrangian perturbation of entropy in the
upper-most layers which becomes important when the modal period and the local
thermal relaxation time-scale are comparable. Based on this analysis, we then
find a linear relation between and , with a
coefficient that depends on the ratio of the Mach number of the exciting
turbulence to the third power to the mixing-length parameter.Comment: 8 pages, 11 figures. Accepted in A&
Mpemba Effect, Shechtman's Quasicrystals and Students' Exploring Activities
In the 1960s, Tanzanian student Erasto Mpemba and his teacher published an
article with the title "Cool" in the journal Physics Education (Mpemba, E. B. -
Osborne, D. G.: Cool?. In: Physics Education, vol.4, 1969, pp. 172-175.). In
this article they claimed that hot water freezes faster than cold water. The
article raised not only a wave of discussions, and other articles about this
topic, but also a whole series of new experiments, which should verify this
apparent thermodynamic absurdity and find an adequate explanation. Here we give
a review with references to explanations and we bring some proposals for
experimental student work in this area. We introduce Mpemba Effect not only as
a paradoxical physics phenomenon, but we shall present a strong educational
message that the Mpemba story brings to the teachers and their students. This
message also creates a bridge between this phenomenon and the discovery for
which the 2011 Nobel Prize in Chemistry was awarded. It leads to critical
adoption of traditional knowledge and encourages resilience in investigative
exploration of new things
A large sample of calibration stars for Gaia: log g from Kepler and CoRoT
Asteroseismic data can be used to determine surface gravities with precisions
of < 0.05 dex by using the global seismic quantities Deltanu and nu_max along
with Teff and [Fe/H]. Surface gravity is also one of the four stellar
properties to be derived by automatic analyses for 1 billion stars from Gaia
data (workpackage GSP_Phot). We explore seismic data from MS F, G, K stars
(solar-like stars) observed by Kepler as a potential calibration source for
methods that Gaia will use for object characterisation (log g). We calculate
log g for bright nearby stars for which radii and masses are known, and using
their global seismic quantities in a grid-based method, we determine an
asteroseismic log g to within 0.01 dex of the direct calculation, thus
validating the accuracy of our method. We find that errors in Teff and mainly
[Fe/H] can cause systematic errors of 0.02 dex. We then apply our method to a
list of 40 stars to deliver precise values of surface gravity, i.e. sigma <
0.02 dex, and we find agreement with recent literature values. Finally, we
explore the precision we expect in a sample of 400+ Kepler stars which have
their global seismic quantities measured. We find a mean uncertainty
(precision) on the order of <0.02 dex in log g over the full explored range 3.8
< log g < 4.6, with the mean value varying only with stellar magnitude (0.01 -
0.02 dex). We study sources of systematic errors in log g and find possible
biases on the order of 0.04 dex, independent of log g and magnitude, which
accounts for errors in the Teff and [Fe/H] measurements, as well as from using
a different grid-based method. We conclude that Kepler stars provide a wealth
of reliable information that can help to calibrate methods that Gaia will use,
in particular, for source characterisation with GSP_Phot where excellent
precision (small uncertainties) and accuracy in log g is obtained from seismic
data.Comment: Accepted MNRAS, 15 pages (10 figures and 3 tables), v2=some rewording
of two sentence
The 190 kDa centrosome-associated protein of Drosophila melanogaster contains four zinc finger motifs and binds to specific sites on polytene chromosomes
Microinjection of a bacterially expressed, TRITC labelled fragment of the centrosome-associated protein CP190 of Drosophila melanogaster, into syncytial Drosophila embryos, shows it to associate with the centrosomes during mitosis, and to relocate to chromatin during interphase. Indirect immunofluorescence staining of salivary gland chromosomes of third instar Drosophila larvae, with antibodies specific to CP190, indicate that the protein is associated with a large number of loci on these interphase polytene chromosomes. The 190 kDa CP190 protein is encoded by a 4.1 kb transcript with a single, long open reading frame specifying a polypeptide of 1,096 amino acids, with a molecular mass of 120 kDa, and an isoelectric point of 4.5. The central region of the predicted amino acid sequence of the CP190 protein contains four CysX₂CysX₁₂HisX₄His zinc-finger motifs which are similar to those described for several well characterised DNA binding proteins. The data suggest that the function of CP190 involves cell cycle dependent associations with both the centrosome, and with specific chromosomal loci
The 190 kDa centrosome-associated protein of Drosophila melanogaster contains four zinc finger motifs and binds to specific sites on polytene chromosomes
Microinjection of a bacterially expressed, TRITC labelled fragment of the centrosome-associated protein CP190 of Drosophila melanogaster, into syncytial Drosophila embryos, shows it to associate with the centrosomes during mitosis, and to relocate to chromatin during interphase. Indirect immunofluorescence staining of salivary gland chromosomes of third instar Drosophila larvae, with antibodies specific to CP190, indicate that the protein is associated with a large number of loci on these interphase polytene chromosomes. The 190 kDa CP190 protein is encoded by a 4.1 kb transcript with a single, long open reading frame specifying a polypeptide of 1,096 amino acids, with a molecular mass of 120 kDa, and an isoelectric point of 4.5. The central region of the predicted amino acid sequence of the CP190 protein contains four CysX₂CysX₁₂HisX₄His zinc-finger motifs which are similar to those described for several well characterised DNA binding proteins. The data suggest that the function of CP190 involves cell cycle dependent associations with both the centrosome, and with specific chromosomal loci
The Effect of Enhanced Depression Care on Anxiety Symptoms in Acute Coronary Syndrome Patients: Findings from the COPES Trial
Similar to depression, anxiety is common after acute coronary syndromes (ACS), and is an independent predictor of worse outcomes [1,2,3]. Yet, post-ACS psychological interventions have focused on treating depression. We previously reported that an enhanced depression care intervention involving patient preference for problem-solving therapy (PST), antidepressant medications, or both followed by stepped care according to treatment response was effective at reducing depressive symptoms after ACS with an effect size of 0.59 SD [4]. We report here the independent effect of this intervention on anxiety
A closure model with plumes II. Application to the stochastic excitation of stellar p modes
Our goal is to improve the theoretical modelling of stochastic excitation of
p modes by turbulent convection. With the help of the closure model with plume
(CMP) developed in a companion paper, we refine the theoretical description of
the excitation by the turbulent Reynolds stress term. The CMP is generalized
for two-point correlation products so as to apply it to the formalism developed
by Samadi & Goupil (2001). The excitation source terms are then computed with
this improvement, and a comparison with solar data from the GOLF instrument is
performed. The present model provides a significant improvement when comparing
absolute values of theoretical ampplitudes with observational data. It gives
rise to a frequency dependence of the power supplied to solar p modes, which
agrees with GOLF observations. It is shown that the asymmetry of the turbulent
convection zone (up- and downflows) plays a major role in the excitation
processes. Despite an increase in the Reynolds stress term contribution due to
our improved description, an additional source of excitation, identified as the
entropy source term, is still necessary for reproducing the observational data.
Theoretical excitation rates in the frequency range [2.5 mHz, 4 mHz] now are in
agreement with the observational data from the GOLF instrument. However, at
lower frequencies, it exhibits small discrepancies at the maximum level of a
few per cent. Improvements are likely to come from a better physical
description of the excitation by entropy fluctuations in the superadiabatic
zone.Comment: 9 pages, accepted for publication in A&
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