10,435 research outputs found
Tracing Quasar Narrow-Line Regions Across Redshift: A Library of High S/N Optical Spectra
In a single optical spectrum, the quasar narrow-line region (NLR) reveals low
density, photoionized gas in the host galaxy interstellar medium, while the
immediate vicinity of the central engine generates the accretion disk continuum
and broad emission lines. To isolate these two components, we construct a
library of high S/N optical composite spectra created from the Sloan Digital
Sky Survey (SDSS-DR7). We divide the sample into bins of continuum luminosity
and Hbeta FWHM that are used to construct median composites at different
redshift steps up to 0.75. We measure the luminosities of the narrow-emission
lines [NeV]3427, [NeIII]3870, [OIII]5007, and [OII]3728 with ionization
potentials (IPs) of 97, 40, 35, and 13.6 eV respectively. The high IP lines'
luminosities show no evidence of increase with redshift consistent with no
evolution in the AGN SED or the host galaxy ISM illuminated by the continuum.
In contrast, we find that the [OII] line becomes stronger at higher redshifts,
and we interpret this as a consequence of enhanced star formation contributing
to the [OII] emission in host galaxies at higher redshifts. The SFRs estimated
from the [OII] luminosities show a flatter increase with z than non-AGN
galaxies given our assumed AGN contribution to the [OII] luminosity. Finally,
we confirm an inverse correlation between the strength of the FeII4570 complex
and both the [OIII] EW (though not the luminosity) and the width of the Hbeta
line as known from the eigenvector 1 correlations.Comment: 17 pages, colour figures, accepted for publication in MNRA
Seeking large-scale magnetic fields in a pure-disk dwarf galaxy NGC 2976
It is still unknown how magnetic field-generation mechanisms could operate in
low-mass dwarf galaxies. Here, we present a detailed study of a nearby
pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this
galaxy possesses a clearly defined disk. For the purpose of our studies, we
performed deep multi-frequency polarimetric observations of NGC 2976 with the
VLA and Effelsberg radio telescopes. Additionally, we supplement them with
re-imaged data from the WSRT-SINGS survey. The magnetic field morphology
discovered in NGC 2976 consists of a southern polarized ridge. This structure
does not seem to be due to just a pure large-scale dynamo process (possibly
cosmic-ray driven) at work in this object, as indicated by the RM data and
dynamo number calculations. Instead, the field of NGC 2976 is modified by past
gravitational interactions and possibly also by ram pressure inside the M 81
galaxy group environment. The estimates of total (7 muG) and ordered (3 muG)
magnetic field strengths, as well as degree of field order (0.46), which is
similar to those observed in spirals, suggest that tidally generated magnetized
gas flows can further enhance dynamo action in the object. NGC 2976 is
apparently a good candidate for the efficient magnetization of its
neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic
field into the intergalactic space up to a distance of about 5 kpc. Tidal
interactions (and possibly also ram pressure) can lead to the formation of
unusual magnetic field morphologies (like polarized ridges) in galaxies out of
the star-forming disks, which do not follow any observed component of the
interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to
provide ordered magnetic fields far out of their main disks.Comment: 16 page
Strongly correlated gases of Rydberg-dressed atoms: quantum and classical dynamics
We discuss techniques to generate long-range interactions in a gas of
groundstate alkali atoms, by weakly admixing excited Rydberg states with laser
light. This provides a tool to engineer strongly correlated phases with reduced
decoherence from inelastic collisions and spontaneous emission. As an
illustration, we discuss the quantum phases of dressed atoms with dipole-dipole
interactions confined in a harmonic potential, as relevant to experiments. We
show that residual spontaneous emission from the Rydberg state acts as a
heating mechanism, leading to a quantum-classical crossover.Comment: 4 pages, 4 figure
Heparin oligosaccharides: inhibitors of the biological activity of bFGF on Caco-2 cells.
A number of growth factors, including members of the fibroblast growth factor (FGF) family - hepatocyte growth factor, vascular endothelial growth factor and heparin-binding epidermal growth factor - are dependent on heparan sulphate (HS) for biological activity mediated through their high-affinity signal-transducing receptors. This obligate requirement for HS prompted the search for antagonists of HS function that could be used as anti-growth factor drugs for the treatment of cancer. Basic FGF (bFGF) was the focus of this study. Caco-2, a human colon carcinoma cell line, was adapted to growth in serum-free medium so that investigation of its growth factor requirements for growth and migration could be performed in defined conditions (Jayson GC, Evans GS, Pemberton PW, Lobley RW, Allen T 1994, Cancer Res, 54, 5718-5723). This cell line multiplied and moved in a dose-dependent manner in response to bFGF. Here, we show that the mitogenic response to bFGF is dependent on the presence of heparan sulphate. A library of heparin oligosaccharides with uniform composition but variable length was generated [general formula [IdoA(2S)-GlcNS(6S)n], and oligosaccharides of defined lengths were tested for their ability to inhibit the biological activity of bFGF. While intact heparin and heparin-derived fragments of 12 monosaccharide units did not affect bFGF-induced cell division or bFGF-induced cell migration, octasaccharides and decasaccharides potently inhibited the bFGF-induced growth and migration responses. In particular, octasaccharides completely inhibited these biological activities at 10 microg ml-, a clinically achievable and tolerable concentration. This study shows that the length of an oligosaccharide determines its ability to block the biological activity of bFGF. The observation that the biological activity of cell-surface heparan sulphate can be antagonized in this way in a human carcinoma cell line suggests that oligosaccharides should be investigated further as anti-growth factor agents for the treatment of cancer. In addition, the results suggest that the clinical evaluation of low-molecular weight heparin (LMWH) as an anti-cancer agent might benefit from subfractionation of the LMWH, to remove oligosaccharides of 12 or more residues
Synthesis and analysis of jet fuel from shale oil and coal syncrudes
Thirty-two jet fuel samples of varying properties were produced from shale oil and coal syncrudes, and analyzed to assess their suitability for use. TOSCO II shale oil and H-COAL and COED syncrudes were used as starting materials. The processes used were among those commonly in use in petroleum processing-distillation, hydrogenation and catalytic hydrocracking. The processing conditions required to meet two levels of specifications regarding aromatic, hydrogen, sulfur and nitrogen contents at two yield levels were determined and found to be more demanding than normally required in petroleum processing. Analysis of the samples produced indicated that if the more stringent specifications of 13.5% hydrogen (min.) and 0.02% nitrogen (max.) were met, products similar in properties to conventional jet fuels were obtained. In general, shale oil was easier to process (catalyst deactivation was seen when processing coal syncrudes), consumed less hydrogen and yielded superior products. Based on these considerations, shale oil appears to be preferred to coal as a petroleum substitute for jet fuel production
Clustering of solutions in the random satisfiability problem
Using elementary rigorous methods we prove the existence of a clustered phase
in the random -SAT problem, for . In this phase the solutions are
grouped into clusters which are far away from each other. The results are in
agreement with previous predictions of the cavity method and give a rigorous
confirmation to one of its main building blocks. It can be generalized to other
systems of both physical and computational interest.Comment: 4 pages, 1 figur
Dynamics of Low-Density Ultracold Rydberg Gases
Population dynamics in weakly-excited clouds of ultracold Rb Rydberg
atoms were studied by means of trap loss, fluorescence detection, and state
dependent stimulated emission. Rydberg atoms were excited to various nl Rydberg
states via continuous two-photon excitation from a magneto-optical trap. A
stimulated emission probe laser was then used to bring the Rydberg atoms down
to the 6P state, allowing state-dependent detection of the Rydberg
atoms. Measurements of trap loss and fluorescent emission reveal information
about the evolution of the Rydberg populations. In particular, population in
the initial Rydberg state quickly transfers to other Rydberg states by a
non-collisional mechanism, likely superradiant emission. The trap-loss
measurements are consistent with black-body ionization as the dominant loss
mechanism.Comment: 9 pages, 7 figure
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