3,646 research outputs found
Contribution of time of day and the circadian clock to the heat stress responsive transcriptome in Arabidopsis.
In Arabidopsis, a large subset of heat responsive genes exhibits diurnal or circadian oscillations. However, to what extent the dimension of time and/or the circadian clock contribute to heat stress responses remains largely unknown. To determine the direct contribution of time of day and/or the clock to differential heat stress responses, we probed wild-type and mutants of the circadian clock genes CCA1, LHY, PRR7, and PRR9 following exposure to heat (37 °C) and moderate cold (10 °C) in the early morning (ZT1) and afternoon (ZT6). Thousands of genes were differentially expressed in response to temperature, time of day, and/or the clock mutation. Approximately 30% more genes were differentially expressed in the afternoon compared to the morning, and heat stress significantly perturbed the transcriptome. Of the DEGs (~3000) specifically responsive to heat stress, ~70% showed time of day (ZT1 or ZT6) occurrence of the transcriptional response. For the DEGs (~1400) that are shared between ZT1 and ZT6, we observed changes to the magnitude of the transcriptional response. In addition, ~2% of all DEGs showed differential responses to temperature stress in the clock mutants. The findings in this study highlight a significant role for time of day in the heat stress responsive transcriptome, and the clock through CCA1 and LHY, appears to have a more profound role than PRR7 and PRR9 in modulating heat stress responses during the day. Our results emphasize the importance of considering the dimension of time in studies on abiotic stress responses in Arabidopsis
Pairing interactions and pairing mechanism in high temperature copper oxide superconductors
The polaron binding energy E_{p} in undoped parent cuprates has been
determined to be about 1.0 eV from the unconventional oxygen-isotope effect on
the antiferromagnetic ordering temperature. The deduced value of E_{p} is in
quantitative agreement with that estimated from independent optical data and
that estimated theoretically from the measured dielectric constants. The
substantial oxygen-isotope effect on the in-plane supercarrier mass observed in
optimally doped cuprates suggests that polarons are bound into the Cooper
pairs. We also identify the phonon modes that are strongly coupled to
conduction electrons from the angle-resolved photoemission spectroscopy,
tunneling spectra, and optical data. We consistently show that there is a very
strong electron-phonon coupling feature at a phonon energy of about 20 meV
along the antinodal direction and that this coupling becomes weaker towards the
diagonal direction. We further show that high-temperature superconductivity in
cuprates is caused by strong electron-phonon coupling, polaronic effect, and
significant coupling with 2 eV Cu-O charge transfer fluctuation.Comment: 11 pages, 7 figure
Optical Conductivity of Ferromagnetic Semiconductors
The dynamical mean field method is used to calculate the frequency and
temperature dependent conductivity of dilute magnetic semiconductors.
Characteristic qualitative features are found distinguishing weak,
intermediate, and strong carrier-spin coupling and allowing quantitative
determination of important parameters defining the underlying ferromagnetic
mechanism
Scattering of a proton with the Li4 cluster: non-adiabatic molecular dynamics description based on time-dependent density-functional theory
We have employed non-adiabatic molecular dynamics based on time-dependent
density-functional theory to characterize the scattering behaviour of a proton
with the Li cluster. This technique assumes a classical approximation for
the nuclei, effectively coupled to the quantum electronic system. This
time-dependent theoretical framework accounts, by construction, for possible
charge transfer and ionization processes, as well as electronic excitations,
which may play a role in the non-adiabatic regime. We have varied the incidence
angles in order to analyze the possible reaction patterns. The initial proton
kinetic energy of 10 eV is sufficiently high to induce non-adiabatic effects.
For all the incidence angles considered the proton is scattered away, except in
one interesting case in which one of the Lithium atoms captures it, forming a
LiH molecule. This theoretical formalism proves to be a powerful, effective and
predictive tool for the analysis of non-adiabatic processes at the nanoscale.Comment: 18 pages, 4 figure
Temperature Dependence of Low-Lying Electronic Excitations of LaMnO_3
We report on the optical properties of undoped single crystal LaMnO_3, the
parent compound of the colossal magneto-resistive manganites. Near-Normal
incidence reflectance measurements are reported in the frequency range of
20-50,000 cm-1 and in the temperature range 10-300 K. The optical conductivity,
s_1(w), is derived by performing a Kramers-Kronig analysis of the reflectance
data. The far-infrared spectrum of s_1(w) displays the infrared active optical
phonons. We observe a shift of several of the phonon to high frequencies as the
temperature is lowered through the Neel temperature of the sample (T_N = 137
K). The high-frequency s_1(w) is characterized by the onset of absorption near
1.5 eV. This energy has been identified as the threshold for optical
transitions across the Jahn-Teller split e_g levels. The spectral weight of
this feature increases in the low-temperature state. This implies a transfer of
spectral weight from the UV to the visible associated with the paramagnetic to
antiferromagnetic state. We discuss the results in terms of the double exchange
processes that affect the optical processes in this magnetic material.Comment: 7 pages, 5 figure
Lifetime of electronic excitations in metal nanoparticles
9 páginas, 4 figuras.-- Trabajo presentado al "6th International Meeting on Photodynamics" celebrado en La Habana (Cuba) del 1 al 5 de febrero de 2010.Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a one-electron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The well-known quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finite-size systems.We acknowledge the partial support of the Basque Government, the University of the
Basque Country UPV/EHU (grant no. 9/UPV 00206.215-13639/2001) and the Spanish
MEC (grants FIS2007-66711-C02-02 and MAT2008-06843-C03-01). JAA acknowledges the
financial support of Ikerbasque.Peer reviewe
Lifetime of electronic excitations in metal nanoparticles
9 páginas, 4 figuras.-- Trabajo presentado al "6th International Meeting on Photodynamics" celebrado en La Habana (Cuba) del 1 al 5 de febrero de 2010.Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a one-electron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The well-known quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finite-size systems.We acknowledge the partial support of the Basque Government, the University of the
Basque Country UPV/EHU (grant no. 9/UPV 00206.215-13639/2001) and the Spanish
MEC (grants FIS2007-66711-C02-02 and MAT2008-06843-C03-01). JAA acknowledges the
financial support of Ikerbasque.Peer reviewe
Dynamics of metallic stripes in cuprates
We study the dynamics of metallic vertical stripes in cuprates within the
three-band Hubbard model based on a recently developed time dependent
Gutzwiller approximation. As doping increases the optical conductivity shows
transfer of spectral weight from the charge transfer band towards i) an
incoherent band centered at 1.3eV, {ii} a Drude peak, mainly due to motion
along the stripe, {iii} a low energy collective mode which softens with doping
and merges with ii} at optimum doping in good agreement with experiment. The
softening is related to the quasidegeneracy between Cu centered and O centered
mean-field stripe solutions close to optimal doping.Comment: 4 pages, 5 figures, corrections to Fig.
Determination of pulsation periods and other parameters of 2875 stars classified as MIRA in the All Sky Automated Survey (ASAS)
We have developed an interactive PYTHON code and derived crucial ephemeris
data of 99.4% of all stars classified as 'Mira' in the ASAS data base,
referring to pulsation periods, mean maximum magnitudes and, whenever possible,
the amplitudes among others. We present a statistical comparison between our
results and those given by the AAVSO International Variable Star Index (VSX),
as well as those determined with the machine learning automatic procedure of
Richards et al. 2012. Our periods are in good agreement with those of the VSX
in more than 95% of the stars. However, when comparing our periods with those
of Richards et al, the coincidence rate is only 76% and most of the remaining
cases refer to aliases. We conclude that automatic codes require still more
refinements in order to provide reliable period values. Period distributions of
the target stars show three local maxima around 215, 275 and 330 d, apparently
of universal validity, their relative strength seems to depend on galactic
longitude. Our visual amplitude distribution turns out to be bimodal, however
1/3 of the targets have rather small amplitudes (A 2.5) and could
refer to semi-regular variables (SR). We estimate that about 20% of our targets
belong to the SR class. We also provide a list of 63 candidates for period
variations and a sample of 35 multiperiodic stars which seem to confirm the
universal validity of typical sequences in the double period and in the
Petersen diagramsComment: 14 pages, 14 figures, and 8 tables. Accepted to The Astrophysical
Journal Supplement Series, September 201
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