478 research outputs found
Interface hole-doping in cuprate-titanate superlattices
The electronic structure of interfaces between YBaCuO and
SrTiO is studied using local spin density approximation (LSDA) with
intra-atomic Coulomb repulsion (LSDA+U). We find a metallic state in
cuprate/titanate heterostructures with the hole carriers concentrated
substantially in the CuO-layers and in the first interface TiO and SrO
planes. This effective interface doping appears due to the polarity of
interfaces, caused by the first incomplete copper oxide unit cell.
Interface-induced high pre-doping of CuO-layers is a key mechanism
controlling the superconducting properties in engineered field-effect devices
realized on the basis of cuprate/titanate superlattices.Comment: 5 pages, 5 figure
Thermodynamics of the \phi^4 theory in tadpole approximation
Relying on the Luttinger-Ward theorem we derive a thermodynamically
selfconsistent and scale independent approximation of the thermodynamic
potential for the scalar theory in the tadpole approximation. The
resulting thermodynamic potential as a function of the temperature is similar
to the one of the recently proposed screened perturbation theory.Comment: 6 pages, including 1 eps figur
The Low-Mass Companion to the Lithium-Depleted, Spectroscopic Binary HBC 425 (St 34)
We present high angular resolution, near-infrared imaging and spectroscopy of
a low-mass companion to the lithium-depleted, double-line spectroscopic binary
HBC 425 (St 34) obtained using the Near Infrared Spectrograph (NIRSPEC) and the
Keck II adaptive optics system. Positioned 1.23" southeast of the primary pair,
the companion, HBC 425C, is ~2.4 magnitudes fainter at 2.2 microns.
Moderate-resolution (R~2500) J- and K-band spectroscopy reveal HBC 425C to have
an M5.5 (+/-0.5) spectral type. Comparisons with pre-main sequence evolutionary
models imply a mass of ~0.09 M(Sun) and ages of 8-10 Myr, assuming the nominal
distance of Taurus-Auriga (~140 pc), or ~25 Myr if placed at ~90 pc. We also
present high dispersion, optical spectra of HBC 425 and HBC 425C obtained using
the High Resolution Echelle Spectrometer (HIRES) on Keck I. We detect strong Li
I 6708 absorption in the spectrum of HBC 425C. Using curves of growth for the
Li I 6708 doublet, we estimate its abundance level to lie between log N(Li)=1.9
and 3.1 dex. The spectrum of HBC 425 exhibits Ca II H & K, He I 5876, 6678, and
strong Balmer line emission, consistent with accretion. We place more
restrictive upper limits on the surface abundance of lithium and find that HBC
425 retains less than ~0.1% of its primordial abundance. The presence of
lithium in the photosphere of HBC 425C does not resolve the discrepancy between
isochronal and lithium depletion ages for the primary pair. However, if lithium
were depleted relative to interstellar abundance levels, even minimally,
considerable support would be gained for the more advanced age of this
hierarchical triple system.Comment: 16 pages, 6 figures, accepted for publication in the Publications of
the Astronomical Society of the Pacifi
Cyclic brightening in the short-period WZ Sge-type cataclysmic variable SDSS J080434.20+510349.2
We have observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 and
study the origin of a long-term variability found in its light curve.
Multi-longitude time-resolved photometric observations were carried out to
analyze the uncommon behavior also found recently in two newly discovered CVs.
This study of SDSS J080434.20+510349.2 mainly concerns the understanding of the
nature of the observed double-humped light curve and its relation to a cyclic
brightening occurring during quiescence. The observations were obtained early
in 2007, when the object was at about V~17.1, 0.4 mag brighter than the
pre-outburst magnitude. The light curve shows a sinusoidal variability with an
amplitude of about 0.07 mag and a periodicity of 42.48 min, which is half of
the orbital period of the system. In addition, we have observed two
"mini-outbursts" of the system up to 0.6 mag, with a duration of about 4 days
each. The "mini-outburst" had a symmetric profile and repeated in about 32
days. Subsequent monitoring of the system shows a cyclical behaviour of such
"mini-outbursts" with a similar recurrence period. The origin of the
double-humped light curve and the periodic brightening is discussed in the
light of the evolutionary state of SDSS J080434.20+510349.2.Comment: 7 pages, 6 figures, Accepted by A&A, typos added, figure correcte
A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey
We describe the pre-OmegaTranS project, a deep survey for transiting
extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we
observed a single dense stellar field with a very high cadence of ~2min using
the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical
Wide-field System for Europe and the Munich Difference Imaging Analysis
pipeline, a module that has been developed for this project, we created the
light curves of 16000 stars with more than 4000 data points which we searched
for periodic transit signals using a box-fitting least-squares detection
algorithm. All light curves are publicly available. In the course of the
pre-OmegaTranS project we identified two planet candidates - POTS-1b and
POTS-C2b - which we present in this work. With extensive follow-up observations
we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K
dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup
and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun
and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag
the follow-up and confirmation of POTS-1b was particularly challenging and
costly.Comment: 18 pages, 23 figures, accepted for publication in MNRA
The First Substellar Subdwarf? Discovery of a Metal-poor L Dwarf with Halo Kinematics
We present the discovery of the first L-type subdwarf, 2MASS
J05325346+8246465. This object exhibits enhanced collision-induced H
absorption, resulting in blue NIR colors (). In
addition, strong hydride bands in the red optical and NIR, weak TiO absorption,
and an optical/J-band spectral morphology similar to the L7 DENIS 02051159AB
imply a cool, metal-deficient atmosphere. We find that 2MASS 0532+8246 has both
a high proper motion, = 2\farcs60\pm0\farcs15 yr, and a
substantial radial velocity, km s, and its
probable proximity to the Sun (d = 10--30 pc) is consistent with halo
membership. Comparison to subsolar-metallicity evolutionary models strongly
suggests that 2MASS 0532+8246 is substellar, with a mass of 0.077 M
0.085 M_{\sun} for ages 10--15 Gyr and metallicities Z_{\sun}. The discovery of this object clearly indicates that star
formation occurred below the Hydrogen burning mass limit at early times,
consistent with prior results indicating a flat or slightly rising mass
function for the lowest-mass stellar subdwarfs. Furthermore, 2MASS 0532+8246
serves as a prototype for a new spectral class of subdwarfs, additional
examples of which could be found in NIR proper motion surveys.Comment: 9 pages, 3 figures, accepted to Ap
Proton Wires in an Electric Field: the Impact of Grotthuss Mechanism on Charge Translocation
We present the results of the modeling of proton translocation in finite
H-bonded chains in the framework of two-stage proton transport model. We
explore the influence of reorientation motion of protons, as well as the effect
of electric field and proton correlations on system dynamics. An increase of
the reorientation energy results in the transition of proton charge from the
surrounding to the inner water molecules in the chain. Proton migration along
the chain in an external electric field has a step-like character, proceeding
with the occurrence of electric field threshold-type effects and drastic
redistribution of proton charge. Electric field applied to correlated chains
induces first a formation of ordered dipole structures for lower field
strength, and than, with a further field strength increase, a stabilization of
states with Bjerrum D-defects. We analyze the main factors responsible for the
formation/annihilation of Bjerrum defects showing the strong influence of the
complex interplay between reorientation energy, electric field and temperature
in the dynamics of proton wire.Comment: 28 pages, 9 figure
IN VITRO EXPERIMENTAL REWIRING OF 4 NEUTROPHILIC GRANULOCYTE SUBSETS FROM THE PRO-INFLAMMATORY TO THE ANTI-INFLAMMATORY PHENOTYPE IN CHILDREN WITH SURGICAL PURULENT INFECTION OF SOFT TISSUE
Treatment of young children with atypical or recurrent purulent soft tissue infections (PSTD) that do not respond well to surgery and antibiotics is most challenging. PSTD occurs against the background of impaired functioning of the immune system and, first of all, the system of neutrophilic granulocytes (NG). The vector effect of immunotropic therapy on a specific NG subsets may allow the correction of NG dysfunctions without compromising host protection, including strategies to enhance, inhibit or restore their functions.The aim of study: to evaluate in vitro the modulating effects of arginyl-alpha-aspartyl-lysyl-valyl-tyrosyl-arginine (HP) on the transformed phenotype of 4 NG subsets, as well as on the functional activity of NG in children with purulent-inflammatory soft tissue diseases.We studied samples of peripheral blood (PB) from young children 2-4 years old: 17 children with atypical acute PSTD and 10 apparently healthy children. At stage I, a comparative assessment of the content and phenotype of 4 NG subsets CD16+CD62L+СD63- , CD16+CD62L+СD63+, СD64- CD16+CD32+CD11b+, СD64+CD16+CD32+CD11b+, phagocytic and microbicidal functions of NG was carried out. At stage II, the in vitro system determined the effects of HP on NG in children with PSTD according to the studied parameters. By the method of flow cytometry (FC500 “Beckman Coulter” (USA), conjugates of MkAT “Beckman Coulter International S.A.” (France)), the relative number of NGs of the studied subsets and the density of receptor expression (MFI) were determined. To assess the phagocytic function of NG a microbiological method was used to assess the completeness of phagocytosis with S. aureus (strain 209). The activity of NG NADPH oxidase was investigated in the NBT-spontaneous test (NBTsp.) and in the in vitro NBT-induced test (NBTind.). A comparative study of PB samples from conventionally healthy children and children with PSTD made it possible to identify various variants of transformation of the phenotype of the studied NG subsets, associated with defects in their functional activity. In the in vitro system the effects of HP were demonstrated, manifested by a decrease in the amount of CD16+CD62L+CD63+NG and an increase in CD16+CD62L+CD63- NG, modulation of the negatively altered phenotype of subsets CD64- CD32+CD16+CD11b+NG and CD64+CD32+CD16+CD11b+NG, aimed at restoring phagocytic function and maintaining the tension of NADPH oxidases.As a result of the study it was found the immunomodulatory effects of HP, which is manifested in the reorientation of NG from the pro-inflammatory phenotype to the anti-inflammatory one, which can be used in the future when creating personalized targeted immunotherapy aimed at correcting defective functioning NG in early children, suffering from PSTD
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