1,989 research outputs found
Resistance to human immunodeficiency virus type 1 infection conferred by transduction of human peripheral blood lymphocytes with ribozyme, antisense, or polymeric trans-activation response element constructs.
Mean parameter model for the Pekar-Fr\"{o}hlich polaron in a multilayered heterostructure
The polaron energy and the effective mass are calculated for an electron
confined in a finite quantum well constructed of
layers. To simplify the study we suggest a model in which parameters of a
medium are averaged over the ground-state wave function. The rectangular and
the Rosen-Morse potential are used as examples.
To describe the confined electron properties explicitly to the second order
of perturbations in powers of the electron-phonon coupling constant we use the
exact energy-dependent Green function for the Rosen-Morse confining potential.
In the case of the rectangular potential, the sum over all intermediate virtual
states is calculated. The comparison is made with the often used leading term
approximation when only the ground-state is taken into account as a virtual
state. It is shown that the results are quite different, so the incorporation
of all virtual states and especially those of the continuous spectrum is
essential.
Our model reproduces the correct three-dimensional asymptotics at both small
and large widths. We obtained a rather monotonous behavior of the polaron
energy as a function of the confining potential width and found a peak of the
effective mass. The comparison is made with theoretical results by other
authors. We found that our model gives practically the same (or very close)
results as the explicit calculations for potential widths .Comment: 12 pages, LaTeX, including 5 PS-figures, subm. to Phys. Rev. B, new
data are discusse
Quantum Monte Carlo study of the one-dimensional Holstein model of spinless fermions
The Holstein model of spinless fermions interacting with dispersionless
phonons in one dimension is studied by a Green's function Monte Carlo
technique. The ground state energy, first fermionic excited state, density wave
correlations, and mean lattice displacement are calculated for lattices of up
to 16 sites, for one fermion per two sites, i.e., a half-filled band. Results
are obtained for values of the fermion hopping parameter of ,
, and where is the phonon frequency. At a finite
fermion-phonon coupling there is a transition from a metallic phase to an
insulating phase in which there is charge-density-wave order. Finite size
scaling is found to hold in the metallic phase and is used to extract the
coupling dependence of the Luttinger liquid parameters, and ,
the velocity of charge excitations and the correlation exponent, respectively.
For free fermions () and for strong coupling () our
results agree well with known analytic results. For and
our results are inconsistent with the metal-insulator transition being a
Kosterlitz-Thouless transition.\\Comment: 16 pages of ReVTeX, 11 figures in uuencoded compressed tar file.
Minor changes to text. Our results are inconsistent with the metal-insulator
transition studied being a Kosterlitz-Thouless transition. The figures are
now in the correct order. To appear in Physical Review B, April 15, 199
Nuclear receptors in vascular biology
Nuclear receptors sense a wide range of steroids and hormones (estrogens, progesterone, androgens, glucocorticoid, and mineralocorticoid), vitamins (A and D), lipid metabolites, carbohydrates, and xenobiotics. In response to these diverse but critically important mediators, nuclear receptors regulate the homeostatic control of lipids, carbohydrate, cholesterol, and xenobiotic drug metabolism, inflammation, cell differentiation and development, including vascular development. The nuclear receptor family is one of the most important groups of signaling molecules in the body and as such represent some of the most important established and emerging clinical and therapeutic targets. This review will highlight some of the recent trends in nuclear receptor biology related to vascular biology
Pentacene perfluoropentacene bilayers on Au 111 and Cu 111 Impact of organic metal coupling strength on molecular structure formation
As crucial element in organic opto electronic devices, heterostructures are of pivotal importance. In this context, a comprehensive study of the properties on a simplified model system of a donor acceptor D A bilayer structure is presented, using ultraviolet photoelectron spectroscopy UPS , X ray photoelectron spectroscopy XPS , low energy electron diffraction LEED and normal incidence X ray standing wave NIXSW measurements. Pentacene PEN as donor and perfluoropentacene PFP as acceptor material are chosen to produce bilayer structures on Au 111 and Cu 111 by sequential monolayer deposition of the two materials. By comparing the adsorption behavior of PEN PFP bilayers on such weakly and strongly interacting substrates, it is found that i the adsorption distance of the first layer PEN or PFP indicates physisorption on Au 111 , ii the characteristics of the bilayer structure on Au 111 are almost independent of the deposition sequence, and hence, iii in both cases a mixed bilayer is formed on the Au substrate. This is in striking contrast to PFP PEN bilayers on Cu 111 , where strong chemisorption pins PEN molecules to the metal surface and no intermixing is induced by subsequent PFP deposition. The results illustrate the strong tendency of PEN and PFP molecules to mix, which has important implications for the fabrication of PEN PFP heterojunction
The astrometric Gaia-FUN-SSO observation campaign of 99 942 Apophis
Astrometric observations performed by the Gaia Follow-Up Network for Solar
System Objects (Gaia-FUN-SSO) play a key role in ensuring that moving objects
first detected by ESA's Gaia mission remain recoverable after their discovery.
An observation campaign on the potentially hazardous asteroid (99 942) Apophis
was conducted during the asteroid's latest period of visibility, from
12/21/2012 to 5/2/2013, to test the coordination and evaluate the overall
performance of the Gaia-FUN-SSO . The 2732 high quality astrometric
observations acquired during the Gaia-FUN-SSO campaign were reduced with the
Platform for Reduction of Astronomical Images Automatically (PRAIA), using the
USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. The astrometric
reduction process and the precision of the newly obtained measurements are
discussed. We compare the residuals of astrometric observations that we
obtained using this reduction process to data sets that were individually
reduced by observers and accepted by the Minor Planet Center. We obtained 2103
previously unpublished astrometric positions and provide these to the
scientific community. Using these data we show that our reduction of this
astrometric campaign with a reliable stellar catalog substantially improves the
quality of the astrometric results. We present evidence that the new data will
help to reduce the orbit uncertainty of Apophis during its close approach in
2029. We show that uncertainties due to geolocations of observing stations, as
well as rounding of astrometric data can introduce an unnecessary degradation
in the quality of the resulting astrometric positions. Finally, we discuss the
impact of our campaign reduction on the recovery process of newly discovered
asteroids.Comment: Accepted for publication in A&
Small Polarons in Transition Metal Oxides
The formation of polarons is a pervasive phenomenon in transition metal oxide
compounds, with a strong impact on the physical properties and functionalities
of the hosting materials. In its original formulation the polaron problem
considers a single charge carrier in a polar crystal interacting with its
surrounding lattice. Depending on the spatial extension of the polaron
quasiparticle, originating from the coupling between the excess charge and the
phonon field, one speaks of small or large polarons. This chapter discusses the
modeling of small polarons in real materials, with a particular focus on the
archetypal polaron material TiO2. After an introductory part, surveying the
fundamental theoretical and experimental aspects of the physics of polarons,
the chapter examines how to model small polarons using first principles schemes
in order to predict, understand and interpret a variety of polaron properties
in bulk phases and surfaces. Following the spirit of this handbook, different
types of computational procedures and prescriptions are presented with specific
instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure
Organotypic Brain Cultures for Metastasis Research
We thank members of Brain Metastasis Group for critical discussion. Research in the Brain Metastasis Group is supported by MINECO-Retos SAF2017-89643-R (M.V.), Cancer Research Institute CLIP Award 2018 (M.V.), AECC (GCTRA16015SEOA) (M.V.), Bristol-Myers Squibb Melanoma Research Alliance Young Investigator Award 2017 (M.V.), Beug Foundationâs Prize for Metastasis Research 2017 (M.V.), Worldwide Cancer Research (19-0177) (M.V.), H2020-FETOPEN (828972) (M.V.), FundaciĂłn RamĂłn Areces (CIVP19S8163), and La Caixa-Severo Ochoa International PhD Program Fellowship (L.Z.). M.V. is a RamĂłn y Cajal Investigator (RYC-2013-13365) and an EMBO YIP investigator.N
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
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