66 research outputs found
An Unbiassed Census of Active Galactic Nuclei in the Two Micron All Sky Survey
(Abridged) We present an unbiassed near-IR selected AGN sample, covering
12.56 square degrees down to K ~ 15.5, selected from the Two Micron All Sky
Survey (2MASS). Our only selection effect is a moderate color cut (J-K>1.2)
designed to reduce contamination from galactic stars. We observed both
point-like and extended sources. Using the brute-force capabilities of the 2dF
multi-fiber spectrograph on the Anglo-Australian Telescope, we obtained spectra
of 65% of the target list: an unbiassed sub-sample of 1526 sources.
80% of the 2MASS sources in our fields are galaxies, with a median redshift
of 0.15. The remainder are K- and M-dwarf stars.
Seyfert-2 Galaxies are roughly three times more common in this sample than in
optically selected galaxy samples (once corrections have been made for the
equivalent width limit and for different aperture sizes).
We find 14 broad-line (Type-1) AGNs, giving a surface density down to K<15
comparable to that of optical samples down to B=18.5. Half of our Type-1 AGNs
could not have been found by normal color selection techniques. In all cases
this was due host galaxy light contamination rather than intrinsically red
colors.
We conclude that the Type-1 AGN population found in the near-IR is not
dramatically different from that found in optical samples. There is no evidence
for a large population of AGNs that could not be found at optical wavelengths,
though we can only place very weak constraints on any population of dusty
high-redshift QSOs.Comment: AJ in pres
An HST/WFPC2 Snapshot Survey of 2MASS-Selected Red QSOs
Using simple infrared color selection, 2MASS has found a large number of red,
previously unidentified, radio-quiet QSOs. Although missed by UV/optical
surveys, the 2MASS QSOs have K-band luminosities that are comparable to
"classical" QSOs. This suggests the possible discovery of a previously
predicted large population of dust-obscured radio-quiet QSOs. We present the
results of an imaging survey of 29 2MASS QSOs observed with WFPC2 onboard the
Hubble Space Telescope. I-band images, which benefit from the relative
faintness of the nuclei at optical wavelengths, are used to characterize the
host galaxies, measure the nuclear contribution to the total observed I-band
emission, and to survey the surrounding environments. The 2MASS QSOs are found
to lie in galaxies with a variety of morphologies, luminosities, and dynamical
states, not unlike those hosting radio-quiet PG QSOs. Our analysis suggests
that the extraordinary red colors of the 2MASS QSOs are caused by extinction of
an otherwise typical QSO spectrum due to dust near the nucleus.Comment: 23 pages including 9 figures and 7 tables, accepted for publication
in ApJ, higher resolution HST images at:
http://shapley.as.arizona.edu/~amarble/papers/twomq
Pinning of quantized vortices in helium drop by dopant atoms and molecules
Using a density functional method, we investigate the properties of liquid
4He droplets doped with atoms (Ne and Xe) and molecules (SF_6 and HCN). We
consider the case of droplets having a quantized vortex pinned to the dopant. A
liquid drop formula is proposed that accurately describes the total energy of
the complex and allows one to extrapolate the density functional results to
large N. For a given impurity, we find that the formation of a
dopant+vortex+4He_N complex is energetically favored below a critical size
N_cr. Our result support the possibility to observe quantized vortices in
helium droplets by means of spectroscopic techniques.Comment: Typeset using Revtex, 3 pages and 5 figures (4 Postscript, 1 jpeg
Surface Region of Superfluid Helium as an Inhomogeneous Bose-Condensed Gas
We present arguments that the low density surface region of self-bounded
superfluid He systems is an inhomogeneous dilute Bose gas, with almost all
of the atoms occupying the same single-particle state at . Numerical
evidence for this complete Bose-Einstein condensation was first given by the
many-body variational calculations of He droplets by Lewart, Pandharipande
and Pieper in 1988. We show that the low density surface region can be treated
rigorously using a generalized Gross-Pitaevskii equation for the Bose order
parameter.Comment: 4 pages, 1 Postscript figur
Optical Magnetometry
Some of the most sensitive methods of measuring magnetic fields utilize
interactions of resonant light with atomic vapor. Recent developments in this
vibrant field are improving magnetometers in many traditional areas such as
measurement of geomagnetic anomalies and magnetic fields in space, and are
opening the door to new ones, including, dynamical measurements of bio-magnetic
fields, detection of nuclear magnetic resonance (NMR), magnetic-resonance
imaging (MRI), inertial-rotation sensing, magnetic microscopy with cold atoms,
and tests of fundamental symmetries of Nature.Comment: 11 pages; 4 figures; submitted to Nature Physic
Resonant nonlinear magneto-optical effects in atoms
In this article, we review the history, current status, physical mechanisms,
experimental methods, and applications of nonlinear magneto-optical effects in
atomic vapors. We begin by describing the pioneering work of Macaluso and
Corbino over a century ago on linear magneto-optical effects (in which the
properties of the medium do not depend on the light power) in the vicinity of
atomic resonances, and contrast these effects with various nonlinear
magneto-optical phenomena that have been studied both theoretically and
experimentally since the late 1960s. In recent years, the field of nonlinear
magneto-optics has experienced a revival of interest that has led to a number
of developments, including the observation of ultra-narrow (1-Hz)
magneto-optical resonances, applications in sensitive magnetometry, nonlinear
magneto-optical tomography, and the possibility of a search for parity- and
time-reversal-invariance violation in atoms.Comment: 51 pages, 23 figures, to appear in Rev. Mod. Phys. in Oct. 2002,
Figure added, typos corrected, text edited for clarit
Moving magnetoencephalography towards real-world applications with a wearable system
Imaging human brain function with techniques such as magnetoencephalography1 (MEG) typically requires a subject to perform tasks whilst their head remains still within a restrictive scanner. This artificial environment makes the technique inaccessible to many people, and limits the experimental questions that can be addressed. For example, it has been difficult to apply neuroimaging to investigation of the neural substrates of cognitive development in babies and children, or in adult studies that require unconstrained head movement (e.g. spatial navigation). Here, we develop a new type of MEG system that can be worn like a helmet, allowing free and natural movement during scanning. This is possible due to the integration of new quantum sensors2,3 that do not rely on superconducting technology, with a novel system for nulling background magnetic fields. We demonstrate human electrophysiological measurement at millisecond resolution whilst subjects make natural movements, including head nodding, stretching, drinking and playing a ball game. Results compare well to the current state-of-the-art, even when subjects make large head movements. The system opens up new possibilities for scanning any subject or patient group, with myriad applications such as characterisation of the neurodevelopmental connectome, imaging subjects moving naturally in a virtual environment, and understanding the pathophysiology of movement disorders
HTLV-1 infection in solid organ transplant donors and recipients in Spain
Background: HTLV-1 infection is a neglected disease, despite infecting 10–15 million people worldwide and
severe illnesses develop in 10% of carriers lifelong. Acknowledging a greater risk for developing HTLV-1
associated illnesses due to immunosuppression, screening is being widely considered in the transplantation
setting. Herein, we report the experience with universal HTLV testing of donors and recipients of solid organ
transplants in a survey conducted in Spain.
Methods: All hospitals belonging to the Spanish HTLV network were invited to participate in the study. Briefly, HTLV
antibody screening was performed retrospectively in all specimens collected from solid organ donors and recipients
attended since the year 2008.
Results: A total of 5751 individuals were tested for HTLV antibodies at 8 sites. Donors represented 2312
(42.2%), of whom 17 (0.3%) were living kidney donors. The remaining 3439 (59.8%) were recipients. Spaniards
represented nearly 80%.
Overall, 9 individuals (0.16%) were initially reactive for HTLV antibodies. Six were donors and 3 were recipients.
Using confirmatory tests, HTLV-1 could be confirmed in only two donors, one Spaniard and another from
Colombia. Both kidneys of the Spaniard were inadvertently transplanted. Subacute myelopathy developed
within 1 year in one recipient. The second recipient seroconverted for HTLV-1 but the kidney had to be
removed soon due to rejection. Immunosuppression was stopped and 3 years later the patient remains in
dialysis but otherwise asymptomatic.
Conclusion: The rate of HTLV-1 is low but not negligible in donors/recipients of solid organ transplants in
Spain. Universal HTLV screening should be recommended in all donor and recipients of solid organ
transplantation in Spain. Evidence is overwhelming for very high virus transmission and increased risk along
with the rapid development of subacute myelopath
Rapid subacute myelopathy following kidney transplantation from HTLV-1 donors: role of immunosuppresors and failure of antiretrovirals
Two kidney transplant recipients from a single donor became infected with HTLV-1 (human T-lymphotropic virus type 1) in Spain. One developed myelopathy 8 months following surgery despite early prescription of antiretroviral therapy. The allograft was removed from the second recipient at month 8 due to rejection and immunosuppressors discontinued. To date, 3 years later, this patient remains infected but asymptomatic. HTLV-1 infection was recognized retrospectively in the donor, a native Spaniard who had sex partners from endemic regions. Our findings call for a reappraisal of screening policies on donor-recipient organ transplantation. Based on the high risk of disease development and the large flux of persons from HTLV-1 endemic regions, pre-transplant HTLV-1 testing should be mandatory in Spain
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