15,812 research outputs found
Radio Observations of Infrared Luminous High Redshift QSOs
We present Very Large Array (VLA) observations at 1.4 GHz and 5 GHz of a
sample of 12 Quasi-stellar Objects (QSOs) at z = 3.99 to 4.46. The sources were
selected as the brightest sources at 250 GHz from the recent survey of Omont et
al. (2001). We detect seven sources at 1.4 GHz with flux densities, S_{1.4} >
50 microJy. These centimeter (cm) wavelength observations imply that the
millimeter (mm) emission is most likely thermal dust emission. The
radio-through-optical spectral energy distributions for these sources are
within the broad range defined by lower redshift, lower optical luminosity
QSOs. For two sources the radio continuum luminosities and morphologies
indicate steep spectrum, radio loud emission from a jet-driven radio source.
For the remaining 10 sources the 1.4 GHz flux densities, or limits, are
consistent with those expected for active star forming galaxies. If the radio
emission is powered by star formation in these systems, then the implied star
formation rates are of order 1e3 M_solar/year. We discuss the angular sizes and
spatial distributions of the radio emitting regions, and we consider briefly
these results in the context of co-eval black hole and stellar bulge formation
in galaxies.Comment: to appear in the A
The ASCA spectrum of the z=4.72 blazar, GB 1428+4217
The X-ray luminous quasar GB 1428+4217 at redshift 4.72 has been observed
with ASCA. The observed 0.5-10 keV flux is 3.2E-12 erg/s/cm2. We report here on
the intrinsic 4-57 keV X-ray spectrum, which is very flat (photon index of
1.29). We find no evidence for flux variability within the ASCA dataset or
between it and ROSAT data. We show that the overall spectral energy
distribution of GB 1428+4217 is similar to that of lower redshift MeV blazars
and present models which fit the available data. The Doppler beaming factor is
likely to be at least 8. We speculate on the number density of such high
redshift blazars, which must contain rapidly-formed massive black holes.Comment: 5 pages, 3 Postscript figures, to appear in MNRA
HDAC inhibitors increase NRF2-signaling in tumour cells and blunt the efficacy of co-adminstered cytotoxic agents
The NRF2 signalling cascade provides a primary response against electrophilic chemicals and oxidative stress. The activation of NRF2-signaling is anticipated to have adverse clinical consequences; NRF2 is activated in a number of cancers and, additionally, its pharmacological activation by one compound can reduce the toxicity or efficiency of a second agent administered concomitantly. In this work, we have analysed systematically the ability of 152 research, pre-clinical or clinically used drugs to induce an NRF2 response using the MCF7-AREc32 NRF2 reporter. Ten percent of the tested drugs induced an NRF2 response. The NRF2 activators were not restricted to classical cytotoxic alkylating agents but also included a number of emerging anticancer drugs, including an IGF1-R inhibitor (NVP-AEW541), a PIM-1 kinase inhibitor (Pim1 inhibitor 2), a PLK1 inhibitor (BI 2536) and most strikingly seven of nine tested HDAC inhibitors. These findings were further confirmed by demonstrating NRF2-dependent induction of endogenous AKR genes, biomarkers of NRF2 activity. The ability of HDAC inhibitors to stimulate NRF2-signalling did not diminish their own potency as antitumour agents. However, when used to pre-treat cells, they did reduce the efficacy of acrolein. Taken together, our data suggest that the ability of drugs to stimulate NRF2 activity is common and should be investigated as part of the drug-development process
PMN J0525-3343: soft X-ray spectral flattening in a blazar at z=4.4
We report optical, radio and X-ray observations of a new distant blazar, PMN
J0525-3343, at a redshift of 4.4. The X-ray spectrum measured from ASCA and
BeppoSAX flattens below a few keV, in a manner similar to the spectra of two
other z>4 blazars, GB 1428+4217 (z=4.72) reported by Boller et al and RXJ
1028.6-0844 (z=4.28) by Yuan et al. The spectrum is well fitted by a power-law
continuum which is either absorbed or breaks at a few keV. An intrinsic column
density corresponding to 2 x 10^23 H-atoms cm-2 at solar abundance is required
by the absorption model. This is however a million times greater than the
neutral hydrogen, or dust, column density implied by the optical spectrum,
which covers the rest-frame UV emission of the blazar nucleus. We discuss the
problems raised and suggest that, unless there is intrinsic flattening in the
spectral distribution of the particles/seed photons producing X-rays via
inverse Compton scattering, the most plausible solution is a warm absorber
close to the active nucleus.Comment: 7 pages, 7 figures; MNRAS, in pres
Calculating Nonlocal Optical Properties of Structures with Arbitrary Shape
In a recent Letter [Phys. Rev. Lett. 103, 097403 (2009)], we outlined a
computational method to calculate the optical properties of structures with a
spatially nonlocal dielectric function. In this Article, we detail the full
method, and verify it against analytical results for cylindrical nanowires.
Then, as examples of our method, we calculate the optical properties of Au
nanostructures in one, two, and three dimensions. We first calculate the
transmission, reflection, and absorption spectra of thin films. Because of
their simplicity, these systems demonstrate clearly the longitudinal (or
volume) plasmons characteristic of nonlocal effects, which result in anomalous
absorption and plasmon blueshifting. We then study the optical properties of
spherical nanoparticles, which also exhibit such nonlocal effects. Finally, we
compare the maximum and average electric field enhancements around nanowires of
various shapes to local theory predictions. We demonstrate that when nonlocal
effects are included, significant decreases in such properties can occur.Comment: 30 pages, 12 figures, 1 tabl
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