3,304 research outputs found
Extended quintessence, inflation, and stable de Sitter spaces
A new gauge-invariant criterion for stability against inhomogeneous
perturbations of de Sitter space is applied to scenarios of dark energy and
inflation in scalar-tensor gravity. The results extend previous studies.Comment: 16 pages, LaTeX, to appear in Class. Quantum Gra
Plasmon-phonon coupling in large-area graphene dot and antidot arrays
Nanostructured graphene on SiO2 substrates pave the way for enhanced
light-matter interactions and explorations of strong plasmon-phonon
hybridization in the mid-infrared regime. Unprecedented large-area graphene
nanodot and antidot optical arrays are fabricated by nanosphere lithography,
with structural control down to the sub-100 nanometer regime. The interaction
between graphene plasmon modes and the substrate phonons is experimentally
demonstrated and structural control is used to map out the hybridization of
plasmons and phonons, showing coupling energies of the order 20 meV. Our
findings are further supported by theoretical calculations and numerical
simulations.Comment: 7 pages including 6 figures. Supporting information is available upon
request to author
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High-Quality Draft Genome Sequence of Desulfovibrio carbinoliphilus FW-101-2B, an Organic Acid-Oxidizing Sulfate-Reducing Bacterium Isolated from Uranium(VI)-Contaminated Groundwater.
Desulfovibrio carbinoliphilus subsp. oakridgensis FW-101-2B is an anaerobic, organic acid/alcohol-oxidizing, sulfate-reducing δ-proteobacterium. FW-101-2B was isolated from contaminated groundwater at The Field Research Center at Oak Ridge National Lab after in situ stimulation for heavy metal-reducing conditions. The genome will help elucidate the metabolic potential of sulfate-reducing bacteria during uranium reduction
Study of the auto-ignition phenomenon of PRFs under HCCI conditions in a RCEM by means of spectroscopy
An investigation of the effects of contour conditions and fuel properties on the auto-ignition and combustion
process under HCCI conditions is presented in this study. A parametric variation of initial temperature,
intake pressure, compression ratio, oxygen concentration and equivalence ratio has been carried out
for Primary Reference Fuels in a Rapid Compression Expansion Machine while applying spectroscopy. The
results have also been contrasted with natural chemiluminescence measurements. Additionally, the
experiments have been simulated in CHEMKIN and the results derived from the optical techniques have
been compared with the results from the chemical kinetics of the process, validating the chemical kinetic
mechanism and an additional sub-model of excited OH
. Two different scenarios can be seen according to
the results from the spectrograph. For very lean or very low-temperature combustions no peak of OH is
seen at 310 nm of wavelength, proving that the luminosity came from the CO continuum rather than
from the OH
. However, for more intense combustions (richer equivalence ratios, higher temperatures
or lower EGR rates) spectrography shows a clear peak of OH that has much longer time of life than
the corresponding to the CO continuum. The main chemical reaction that causes this two scenarios
has been identified as H þ HO2 ) 2OH. The increase of relevance of this reaction at high combustion temperatures
causes a higher OH accumulation, which leads to a brighter OH emission. Finally, for low temperature
combustions the CO continuum out-shines the OH radiation so the light emitted by this radical
cannot be detected by means of natural chemiluminescence.
201The authors would like to thank different members of the LAV team of the ETH-Zurich for their contribution to this work. The authors are grateful to the Universitat Politecnica de Valencia for financing the Ph.D. studies of W. Vera-Tudela (FPI SP1 grant 30/05/2012) and his stay at ETH-Zurich (grant 30/12/2014). Finally, the authors would like to thank the Spanish Ministry of Education for financing the Ph.D. studies of Dario Lopez-Pintor (grant FPU13/02329) and his stay at ETH-Zurich (grant EST14/00626).Desantes Fernández, JM.; García Oliver, JM.; Vera-Tudela-Fajardo, WM.; López Pintor, D.; Schneider, B.; Boulouchos, K. (2016). Study of the auto-ignition phenomenon of PRFs under HCCI conditions in a RCEM by means of spectroscopy. Applied Energy. 179:389-400. https://doi.org/10.1016/j.apenergy.2016.06.134S38940017
Bulk-sensitive photoemission spectroscopy of A_2FeMoO_6 double perovskites (A=Sr, Ba)
Electronic structures of Sr_2FeMoO_6 (SFMO) and Ba_2FeMoO_6 (BFMO) double
perovskites have been investigated using the Fe 2p->3d resonant photoemission
spectroscopy (PES) and the Cooper minimum in the Mo 4d photoionization cross
section. The states close to the Fermi level are found to have strongly mixed
Mo-Fe t_{2g} character, suggesting that the Fe valence is far from pure 3+. The
Fe 2p_{3/2} XAS spectra indicate the mixed-valent Fe^{3+}-Fe^{2+}
configurations, and the larger Fe^{2+} component for BFMO than for SFMO,
suggesting a kind of double exchange interaction. The valence-band PES spectra
reveal good agreement with the LSDA+U calculation.Comment: 4 pages, 3 figure
High spatial resolution X-ray spectroscopy of SNR Cassiopeia A with {\sl Chandra}
We present high spatial resolution X-ray spectroscopy of supernova remnant
Cassiopeia A with the {\sl Chandra} observations. The X-ray emitting region of
this remnant was divided into 38 34 pixels with a scale of 10\arcsec
10\arcsec each. Spectra of 960 pixels were created and fitted with
an absorbed two component non-equilibrium ionization model. With the spectral
analysis results we obtained maps of absorbing column density, temperatures,
ionization ages, and the abundances for Ne, Mg, Si, S, Ca and Fe. The Si, S and
possibly Ca abundance maps show obviously jet structures, while Fe doesn't
follow the jet but seems to be distributed perpendicular to it. In the range of
about two orders of magnitude, the abundances of Si, S and Ca show tight
correlations between each other, suggesting them to be ejecta from explosive
O-burning and incomplete Si-burning. Meanwhile, Ne abundance is well correlated
with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The
Fe abundance is positively correlated with that of Si when Si abundance is
lower than 3 solar abundances, but a negative correlation appears when the Si
abundance is higher. We suggest that such a two phase correlation is the
results of different ways in which Fe is synthesized.Comment: accepted by ChJA
Resonant Visible Light Modulation with Graphene
Fast modulation and switching of light at visible and near-infrared (vis-NIR)
frequencies is of utmost importance for optical signal processing and sensing
technologies. No fundamental limit appears to prevent us from designing
wavelength-sized devices capable of controlling the light phase and intensity
at gigaherts (and even terahertz) speeds in those spectral ranges. However,
this problem remains largely unsolved, despite recent advances in the use of
quantum wells and phase-change materials for that purpose. Here, we explore an
alternative solution based upon the remarkable electro-optical properties of
graphene. In particular, we predict unity-order changes in the transmission and
absorption of vis-NIR light produced upon electrical doping of graphene sheets
coupled to realistically engineered optical cavities. The light intensity is
enhanced at the graphene plane, and so is its absorption, which can be switched
and modulated via Pauli blocking through varying the level of doping.
Specifically, we explore dielectric planar cavities operating under either
tunneling or Fabry-Perot resonant transmission conditions, as well as Mie modes
in silicon nanospheres and lattice resonances in metal particle arrays. Our
simulations reveal absolute variations in transmission exceeding 90% as well as
an extinction ratio >15 dB with small insertion losses using feasible material
parameters, thus supporting the application of graphene in fast electro-optics
at vis-NIR frequencies.Comment: 17 pages, 13 figures, 54 reference
Phenotypic and functional analyses show stem cell-derived hepatocyte-like cells better mimic fetal rather than adult hepatocytes
Background & Aims: Hepatocyte-like cells (HLCs), differentiated from pluripotent stem cells by the use of soluble factors, can model human liver function and toxicity. However, at present HLC maturity and whether any deficit represents a true fetal state or aberrant differentiation is unclear and compounded by comparison to potentially deteriorated adult hepatocytes. Therefore, we generated HLCs from multiple lineages, using two different protocols,
for direct comparison with fresh fetal and adult hepatocytes.
Methods: Protocols were developed for robust differentiation. Multiple transcript, protein and functional analyses compared HLCs to fresh human fetal and adult hepatocytes.
Results: HLCs were comparable to those of other laboratories by multiple parameters. Transcriptional changes during differentiation mimicked human embryogenesis and showed more similarity to pericentral than periportal hepatocytes. Unbiased proteomics demonstrated greater proximity to liver than 30 other human organs or tissues. However, by comparison to fresh material,
HLC maturity was proven by transcript, protein and function to be fetal-like and short of the adult phenotype. The expression of 81% phase 1 enzymes in HLCs was significantly upregulated and half were statistically not different from fetal hepatocytes. HLCs secreted albumin and metabolized testosterone (CYP3A) and dextrorphan (CYP2D6) like fetal hepatocytes. In seven bespoke tests,
devised by principal components analysis to distinguish fetal from adult hepatocytes, HLCs from two different source laboratories consistently demonstrated fetal characteristics.
Conclusions: HLCs from different sources are broadly comparable with unbiased proteomic evidence for faithful differentiation down the liver lineage. This current phenotype mimics human fetal rather than adult hepatocytes
Modelling of strain effects in manganite films
Thickness dependence and strain effects in films of
perovskites are analyzed in the colossal magnetoresistance regime. The
calculations are based on a generalization of a variational approach previously
proposed for the study of manganite bulk. It is found that a reduction in the
thickness of the film causes a decrease of critical temperature and
magnetization, and an increase of resistivity at low temperatures. The strain
is introduced through the modifications of in-plane and out-of-plane electron
hopping amplitudes due to substrate-induced distortions of the film unit cell.
The strain effects on the transition temperature and transport properties are
in good agreement with experimental data only if the dependence of the hopping
matrix elements on the bond angle is properly taken into account.
Finally variations of the electron-phonon coupling linked to the presence of
strain turn out important in influencing the balance of coexisting phases in
the filmComment: 7 figures. To be published on Physical Review
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