11,352 research outputs found
Macrophage-sensory neuronal interaction in HIV-1 gp120-induced neurotoxicity
Acknowledgements We thank Dr Jim Perkins of University College London for his help with the statistical analysis of our gene array data. We thank Prof. Maria Papathanasopoulos from the University of the Witwatersrand, Johannesburg, for the gift of gp120Bal.Peer reviewedPublisher PD
The external benefits of higher education
The private market benefits of education are widely studied at the micro level, although the magnitude of their macroeconomic impact is disputed. However, there are additional benefits of education, which are less well understood. In this paper the macroeconomic effects of external benefits of higher education are estimated using the âmicro-to-macroâ simulation approach. Two types of externalities are explored: technology spillovers and productivity spillovers in the labour market. These links are illustrated and the results suggest they could be very large. However, this is qualified by the dearth of microeconomic evidence, for which we hope to encourage further work
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
Revealing Cosmic Rotation
Cosmological Birefringence (CB), a rotation of the polarization plane of
radiation coming to us from distant astrophysical sources, may reveal parity
violation in either the electromagnetic or gravitational sectors of the
fundamental interactions in nature. Until only recently this phenomenon could
be probed with only radio observations or observations at UV wavelengths.
Recently, there is a substantial effort to constrain such non-standard models
using observations of the rotation of the polarization plane of cosmic
microwave background (CMB) radiation. This can be done via measurements of the
-modes of the CMB or by measuring its TB and EB correlations which vanish in
the standard model. In this paper we show that correlations-based
estimator is the best for upcoming polarization experiments. The based
estimator surpasses other estimators because it has the smallest noise and of
all the estimators is least affected by systematics. Current polarimeters are
optimized for the detection of -mode polarization from either primordial
gravitational waves or by large scale structure via gravitational lensing. In
the paper we also study optimization of CMB experiments for the detection of
cosmological birefringence, in the presence of instrumental systematics, which
by themselves are capable of producing correlations; potentially mimicking
CB.Comment: 10 pages, 3 figures, 2 table
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
Discovery of three z>6.5 quasars in the VISTA Kilo-degree Infrared Galaxy (VIKING) survey
Studying quasars at the highest redshifts can constrain models of galaxy and
black hole formation, and it also probes the intergalactic medium in the early
universe. Optical surveys have to date discovered more than 60 quasars up to
z~6.4, a limit set by the use of the z-band and CCD detectors. Only one z>6.4
quasar has been discovered, namely the z=7.08 quasar ULAS J1120+0641, using
near-infrared imaging. Here we report the discovery of three new z>6.4 quasars
in 332 square degrees of the Visible and Infrared Survey Telescope for
Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the
number from 1 to 4. The newly discovered quasars have redshifts of z=6.60,
6.75, and 6.89. The absolute magnitudes are between -26.0 and -25.5, 0.6-1.1
mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the MgII
emission line in all three objects. The quasars are powered by black holes with
masses of ~(1-2)x10^9 M_sun. In our probed redshift range of 6.44<z<7.44 we can
set a lower limit on the space density of supermassive black holes of
\rho(M_BH>10^9 M_sun) > 1.1x10^(-9) Mpc^(-3). The discovery of three quasars in
our survey area is consistent with the z=6 quasar luminosity function when
extrapolated to z~7. We do not find evidence for a steeper decline in the space
density of quasars with increasing redshift from z=6 to z=7.Comment: 14 pages, 9 figures. Published in Ap
Fundamental Behavior of Electric Field Enhancements in the Gaps Between Closely Spaced Nanostructures
We demonstrate that the electric field enhancement that occurs in a gap
between two closely spaced nanostructures, such as metallic nanoparticles, is
the result of a transverse electromagnetic waveguide mode. We derive an
explicit semianalytic equation for the enhancement as a function of gap size,
which we show has a universal qualitative behavior in that it applies
irrespective of the material or geometry of the nanostructures and even in the
presence of surface plasmons. Examples of perfect electrically conducting and
Ag thin-wire antennas and a dimer of Ag spheres are presented and discussed.Comment: 9 pages and 4 figure
What do women undergoing in vitro fertilization (IVF) understand about their chance of IVF success?
Funding No external funding was used for this study. S.L. is supported by a NHMRC Investigator Grant (APP1195189). R.W. is supported by a NHMRC Investigator Grant (GNT2009767). B.W.M. is supported by a NHMRC Investigator Grant (GNT1176437) and has received research funding and travel funding from MerckPeer reviewedPublisher PD
New Measurements of Fine-Scale CMB Polarization Power Spectra from CAPMAP at Both 40 and 90 GHz
We present new measurements of the cosmic microwave background (CMB)
polarization from the final season of the Cosmic Anisotropy Polarization MAPper
(CAPMAP). The data set was obtained in winter 2004-2005 with the 7 m antenna in
Crawford Hill, New Jersey, from 12 W-band (84-100 GHz) and 4 Q-band (36-45 GHz)
correlation polarimeters with 3.3' and 6.5' beamsizes, respectively. After
selection criteria were applied, 956 (939) hours of data survived for analysis
of W-band (Q-band) data. Two independent and complementary pipelines produced
results in excellent agreement with each other. A broad suite of null tests as
well as extensive simulations showed that systematic errors were minimal, and a
comparison of the W-band and Q-band sky maps revealed no contamination from
galactic foregrounds. We report the E-mode and B-mode power spectra in 7 bands
in the range 200 < l < 3000, extending the range of previous measurements to
higher l. The E-mode spectrum, which is detected at 11 sigma significance, is
in agreement with cosmological predictions and with previous work at other
frequencies and angular resolutions. The BB power spectrum provides one of the
best limits to date on B-mode power at 4.8 uK^2 (95% confidence).Comment: 19 pages, 17 figures, 2 tables, submitted to Ap
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