6,615 research outputs found
Electronic structure of the molecule based magnet Cu PM(NO3)2 (H2O)2
We present density functional calculations on the molecule based S=1/2
antiferromagnetic chain compound Cu PM(NO3)2 (H2O)2; PM = pyrimidine. The
properties of the ferro- and antiferromagnetic state are investigated at the
level of the local density approximation and with the hybrid functional B3LYP.
Spin density maps illustrate the exchange path via the pyrimidine molecule
which mediates the magnetism in the one-dimensional chain. The computed
exchange coupling is antiferromagnetic and in reasonable agreement with the
experiment. It is suggested that the antiferromagnetic coupling is due to the
possibility of stronger delocalization of the charges on the nitrogen atoms,
compared to the ferromagnetic case. In addition, computed isotropic and
anisotropic hyperfine interaction parameters are compared with recent NMR
experiments
Influence of a Corpus Luteum Tissue Extract on Rabbit Ovarian Mesothelial Cells
This study investigates rabbit ovarian mesothelial (OM) cells exposed in vitro to a crude corpus luteum extract (CLE; 60 μg/ml). The growth of OM cells was evaluated by measuring the change in cell number (mean % ± standard error of mean, SEM), the number of cell population doublings (CPD ± SEM), and the cell population doubling time in hours (CPDT ± SEM) after 7.5 days of culture in a serum-poor medium. Quantitative estimates of surface morphology changes were obtained by analyzing the total number (mean no. ± SEM), density (mean no./100 μ.m2 ± SEM), and length-to-diameter ratio (mean L/D ± SEM) of microvilli. OM cells in control medium formed loosely cohesive monolayers, and grew 152.53 ± 11.01% with a CPD of 0.59 ± 0.08 and a CPDT of 117.29 ± 6.43 hours. The exposed surface area of these cells was over 8,000 μ.m2 and was covered in its epinuclear region by long and slender microvilli with a L/D of 6.01 ± 0.29. The total number of microvilli in each control cell was 1977.52 ± 120.49 with a density of 0.58 ± 0.03/100 μ.m2 in the epinuclear region and of 0.05 ± 0.003/150 μ.m2 in the remaining surface area (5,161.62 ± 354.43 μ.m2). In contrast, CLE-rich cells cultures grew 329.57 ± 16.65%, with a CPD of 1.71 ± 0.07 and a CPDT of 53.43 + 2.93 hours. These cells formed confluent monolayers of smaller (2104.86 ± 103.71 μ.m2), tightly juxtaposed epithelioid cells with a microvillar density of 0.70 ± 0.03/100 μ.m2 in over 78% of their surface. These data support the existence of an intra-ovarian factor capable of enhancing growth and differentiation of OM cells
Tat-SF1 Is Not Required for Tat Transactivation but Does Regulate the Relative Levels of Unspliced and Spliced HIV-1 RNAs
.To directly address the involvement of Tat-SF1 in HIV-1 gene expression, we depleted Tat-SF1 in HeLa cells by conventional expression of shRNAs and in T- Rex -293 cells containing tetracycline-inducible shRNAs targeting Tat-SF1. We achieved efficient depletion of Tat-SF1 and demonstrated that this did not affect cell viability. HIV-1 infectivity decreased in Tat-SF1-depleted cells, but only when multiple rounds of infection occurred. Neither Tat-dependent nor basal transcription from the HIV-1 LTR was affected by Tat-SF1 depletion, suggesting that the decrease in infectivity was due to a deficiency at a later step in the viral lifecycle. Finally, Tat-SF1 depletion resulted in an increase in the ratio of unspliced to spliced viral transcripts.Tat-SF1 is not required for regulating HIV-1 transcription, but is required for maintaining the ratios of different classes of HIV-1 transcripts. These new findings highlight a novel, post-transcriptional role for Tat-SF1 in the HIV-1 life cycle
High-speed noise-free optical quantum memory
Quantum networks promise to revolutionise computing, simulation, and
communication. Light is the ideal information carrier for quantum networks, as
its properties are not degraded by noise in ambient conditions, and it can
support large bandwidths enabling fast operations and a large information
capacity. Quantum memories, devices that store, manipulate, and release on
demand quantum light, have been identified as critical components of photonic
quantum networks, because they facilitate scalability. However, any noise
introduced by the memory can render the device classical by destroying the
quantum character of the light. Here we introduce an intrinsically noise-free
memory protocol based on two-photon off-resonant cascaded absorption (ORCA). We
consequently demonstrate for the first time successful storage of GHz-bandwidth
heralded single photons in a warm atomic vapour with no added noise; confirmed
by the unaltered photon statistics upon recall. Our ORCA memory platform meets
the stringent noise-requirements for quantum memories whilst offering technical
simplicity and high-speed operation, and therefore is immediately applicable to
low-latency quantum networks
Radiative Heating on the After-Body of Martian Entry Vehicles
This paper presents simulations of the radiative heat flux imparted on the after-body of vehicles entering the Martian atmosphere. The radiation is dominated by CO2 bands emitting in the mid-wave infrared spectral region. This mechanism has traditionally not been considered in the design of past Mars entry vehicles. However, with recent analysis showing that the CO2 radiation can be greater than convective heating in the wake, and with several upcoming and proposed missions to Mars potentially affected, an investigation of the impact of this radiation is warranted. The focus of this paper is to provide a better understanding of the impact to aerothermal heating predictions and to provide comparisons between NASA's two main radiation codes, NEQAIR and HARA. The tangent slab approximation is shown to be overly conservative, by as much as 58 percent, for most back- shell body point locations compared to using a full angular integration method. However, due to the complexity of the wake flow, it is also shown that tangent slab does not always represent an upper limit for radiative heating. Furthermore, analysis in this paper shows that it is not possible to provide a general knock-down factor from the tangent slab results to those obtained using the more rigorous full integration method. When the radiative heating is accounted for on the after-body, the unmargined total heat flux can be as high as 14 watts per square centimeter
Optimal Coherent Filtering for Single Noisy Photons
We introduce a filter using a noise-free quantum buffer with large optical
bandwidth that can both filter temporal-spectral modes, as well as
inter-convert them and change their frequency. We show that such quantum
buffers optimally filter out temporal-spectral noise; producing identical
single-photons from many distinguishable noisy single-photon sources with the
minimum required reduction in brightness. We then experimentally demonstrate a
noise-free quantum buffer in a warm atomic system that is well matched to
quantum dots and can outperform all intensity (incoherent) filtering schemes
for increasing indistinguishability.Comment: 5 pages, 4 Figure
Locally Biased Galaxy Formation and Large Scale Structure
We examine the influence of the morphology-density(MD) relation and a wide
range of simple models for biased galaxy formation on statistical measures of
large scale structure. We contrast the behavior of local biasing models, in
which the efficiency of galaxy formation is determined by density, geometry, or
velocity dispersion of the local mass distribution, with that of non-local
biasing models, in which galaxy formation is modulated coherently over scales
larger than the galaxy correlation length. If morphological segregation of
galaxies is governed by a local MD relation, then the correlation function of
E/S0 galaxies should be steeper and stronger than that of spiral galaxies on
small scales, as observed, while on large scales the correlation functions of
E/S0 and spiral galaxies should have the same shape but different amplitudes.
Similarly, all of our local bias models produce scale-independent amplification
of the correlation function and power spectrum in the linear and mildly
non-linear regimes; only a non-local biasing mechanism can alter the shape of
the power spectrum on large scales. Moments of the biased galaxy distribution
retain the hierarchical pattern of the mass moments, but biasing alters the
values and scale-dependence of the hierarchical amplitudes S3 and S4.
Pair-weighted moments of the galaxy velocity distribution are sensitive to the
details of the biasing prescription. The non-linearity of the relation between
galaxy density and mass density depends on the biasing prescription and the
smoothing scale, and the scatter in this relation is a useful diagnostic of the
physical parameters that determine the bias. Although the sensitivity of galaxy
clustering statistics to the details of biasing is an obstacle to testing
cosmological models, it is an asset for testing galaxy formation theories.Comment: 47 pages including 17 Figures, submitted to Ap
High resolution mid-infrared spectroscopy of ultraluminous infrared galaxies
(Abridged) We present R~600, 10-37um spectra of 53 ULIRGs at z<0.32, taken
using the IRS on board Spitzer. All of the spectra show fine structure emission
lines of Ne, O, S, Si and Ar, as well as molecular Hydrogen lines. Some ULIRGs
also show emission lines of Cl, Fe, P, and atomic Hydrogen, and/or absorption
features from C_2H_2, HCN, and OH. We employ diagnostics based on the
fine-structure lines, as well as the EWs and luminosities of PAH features and
the strength of the 9.7um silicate absorption feature (S_sil), to explore the
power source behind the infrared emission in ULIRGs. We show that the IR
emission from the majority of ULIRGs is powered mostly by star formation, with
only ~20% of ULIRGs hosting an AGN with a comparable or greater IR luminosity
than the starburst. The detection of the 14.32um [NeV] line in just under half
the sample however implies that an AGN contributes significantly to the mid-IR
flux in ~42% of ULIRGs. The emission line ratios, luminosities and PAH EWs are
consistent with the starbursts and AGN in ULIRGs being more extincted, and for
the starbursts more compact, versions of those in lower luminosity systems. The
excitations and electron densities in the NLRs of ULIRGs appear comparable to
those of lower luminosity starbursts, though there is evidence that the NLR gas
in ULIRGs is more dense. We show that the combined luminosity of the 12.81um
[NeII] and 15.56um [NeIII] lines correlates with both IR luminosity and the
luminosity of the 6.2 micron and 11.2 micron PAH features in ULIRGs, and use
this to derive a calibration between PAH luminosity and star formation rate.
Finally, we show that ULIRGs with 0.8 < S_sil < 2.4 are likely to be powered
mainly by star formation, but that ULIRGs with S_sil < 0.8, and possibly those
with S_sil > 2.4, contain an IR-luminous AGN.Comment: 62 pages in preprint format, 4 tables, 23 figures. ApJ accepte
Galaxy and Cluster Biasing from Local Group Dynamics
Comparing the gravitational acceleration induced on the Local Group of
galaxies by different tracers of the underline density field we estimate,
within the linear gravitational instability theory and the linear biasing
ansatz, their relative bias factors. Using optical SSRS2 galaxies, IRAS (PSCz)
galaxies and Abell/ACO clusters, we find b_{O,I} ~ 1.21 +- 0.06 and b_{C,I} ~
4.3 +- 0.8, in agreement with other recent studies. Finally, there is an
excellent one-to-one correspondence of the PSCz and Abell/ACO cluster dipole
profiles, once the latter is rescaled by b_{C,I}, out to at least ~150 h^{-1}
Mpc.Comment: 7 pages, 5 figures, accepted for publication in MNRA
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