5,127 research outputs found
Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph
We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph
observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were
obtained as part of a coordinated observing program including X-ray
observations with the Chandra/High Energy Transmission Grating (HETG)
Spectrometer and Suzaku. We detected nine kinematic components of UV
absorption, which were previously identified using the HST/Space Telescope
Imaging Spectrograph. None of the absorption components showed evidence for
changes in column density or profile within the \sim 10 yr between the STIS and
COS observations, which we interpret as evidence of 1) saturation, for the
stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the
weaker components. After applying a +200 km s^-1 offset to the HETG spectrum,
we found that the radial velocities of the UV absorbers lay within the O VII
profile. Based on photoionization models, we suggest that, while UV components
2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray
absorption detected in the HETG analysis occurs in more highly ionized gas.
Moreover, the mass loss rate is dominated by high ionization gas which lacks a
significant UV footprint.Comment: 41 pages, 10 Figures; accepted for publication in the Astrophysical
Journa
Generalized Entropies
We study an entropy measure for quantum systems that generalizes the von
Neumann entropy as well as its classical counterpart, the Gibbs or Shannon
entropy. The entropy measure is based on hypothesis testing and has an elegant
formulation as a semidefinite program, a type of convex optimization. After
establishing a few basic properties, we prove upper and lower bounds in terms
of the smooth entropies, a family of entropy measures that is used to
characterize a wide range of operational quantities. From the formulation as a
semidefinite program, we also prove a result on decomposition of hypothesis
tests, which leads to a chain rule for the entropy.Comment: 21 page
Study of quasi-optical circuit techniques in varactor multipliers
Quasi-optical circuit techniques in varactor multiplier
One laptop per child: Vision vs. reality
Nicholas Negroponte presents the idea of One Laptop Per Child (OLPC), a 20 million in startup investment, sponsorships and partnerships with major IT industry players, and interest from developing countries. Some developing countries are deploying OLPC laptops, while some have cancelled the deployments on the results of pilot projects. The OLPC organization (www.olpc.com) is also struggling with key staff defections, budget cuts, and ideological disillusionment. OLPC is also motivating the PC industry to develop lower-cost, education-oriented PCs, and providing developing countries with low-cost computing options along with its own innovation. OLPC also has developed a novel technology, the XO laptop, with a focus on the needs of students in poor rural areas
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One Laptop Per Child (OLPC): A novel computerization movement?
This study applies concepts about computerization movements (CMs) to a case study of the diffusion of innovation in the developing world and thereby to draw lessons for undertaking similar technology projects. We identify the key characteristics of a computerization movement in the scholarly literature and then review the One Laptop Per Child (OLPC) Project in terms of each, identifying where OLPC adds new understanding about CMs. The OLPC project is an example of a computerization movement that has launched a new generation of low-cost computers in the developing world, while failing in its own ambitious goals. The OLPC project provides insights into the nature of computerization movements, in particular the process of mobilization, the diffusion of innovations in the developing world, and the overlap of multiple movements. OLPC's limited success to date illustrates the importance of having: (1) financial resources beyond deployment for economic sustainability, (2) local skills, infrastructure and deployment capability for operational sustainability, and (3) a replicable and scalable deployment model for ease of implementation across many sites. © 2011 IEEE
Observation of Feshbach-like resonances in collisions between ultracold molecules
We observe magnetically tuned collision resonances for ultracold Cs2
molecules stored in a CO2-laser trap. By magnetically levitating the molecules
against gravity, we precisely measure their magnetic moment. We find an avoided
level crossing which allows us to transfer the molecules into another state. In
the new state, two Feshbach-like collision resonances show up as strong
inelastic loss features. We interpret these resonances as being induced by Cs4
bound states near the molecular scattering continuum. The tunability of the
interactions between molecules opens up novel applications such as controlled
chemical reactions and synthesis of ultracold complex molecules
VLA OH and H I Zeeman Observations of the NGC 6334 Complex
We present OH and H I Zeeman observations of the NGC 6334 complex taken with
the Very Large Array. The OH absorption profiles associated with the complex
are relatively narrow (del-v_FWHM ~ 3 km s^1) and single-peaked over most of
the sources. The H I absorption profiles contain several blended velocity
components. One of the compact continuum sources in the complex (source A) has
a bipolar morphology. The OH absorption profiles toward this source display a
gradient in velocity from the northern continuum lobe to the southern continuum
lobe; this velocity gradient likely indicates a bipolar outflow of molecular
gas from the central regions to the northern and southern lobes. Magnetic
fields of the order of 200 microG have been detected toward three discrete
continuum sources in the complex. Virial estimates suggest that the detected
magnetic fields in these sources are of the same order as the critical magnetic
fields required to support the molecular clouds associated with the sources
against gravitational collapse.Comment: 14 pages, 9 postscript figures, accepted for publication in the
Astrophysical Journal (ApJ), tentatively scheduled for vol. 533, Apr. 20,
2000; also available at
http://www.pa.uky.edu/~sarma/RESEARCH/aps_research.htm
Recovery of intracranial stenoses in varicella zoster virus vasculitis after long-term treatment with valacyclovir and prednisolone
BACKGROUND AND PURPOSE: Optimal treatment of intracranial stenoses in varicella zoster virus (VZV)-associated vasculitis is unknown. This study aims to evaluate the merits and potential pitfalls of a specific therapeutic strategy, initially proposed by Don Gilden in 2015. METHODS: We describe three patients with intracranial stenoses caused by VZV vasculitis successfully treated by a long-term combination of valacyclovir and prednisolone. RESULTS: All three patients were young men suffering from stroke. Only one reported a first contact to VZV in adulthood. All three presented stenoses in the intracranial part of the internal carotid artery or the proximal segments of the middle cerebral artery as well as an elevated cell count and positive VZV antibody index in cerebrospinal fluid. They received a combination therapy regimen with prednisone and valacyclovir about a minimum of one year. Intracranial stenoses improved markedly in one and almost resolved completely in the other two patients. Side effects of corticosteroid treatment occurred in two patients. CONCLUSIONS: Long-term combination treatment with prednisone and valacyclovir proved to be effective in three young men suffering from intracranial stenosis due to VZV vasculitis
The Kinematics and Physical Conditions pf the Ionized Gas in Markarian 509. II. STIS Echelle Observations
We present observations of the UV absorption lines in the luminous Seyfert 1
galaxy Mrk 509, obtained with the medium resolution (lambda/Delta-lambda ~
40,000) echelle gratings of the Space Telescope Imaging Spectrograph on the
Hubble Space Telescope. The spectra reveal the presence of eight kinematic
components of absorption in Ly-alpha, C IV, and N V, at radial velocities of
-422, -328, -259, -62, -22, +34, +124, and +210 km s^-1 with respect to an
emission-line redshift of z = 0.03440, seven of which were detected in an
earlier Far Ultraviolet Spectrographic Explorer (FUSE) spectrum. The component
at -22 km s^-1 also shows absorption by Si IV. The covering factor and velocity
width of the Si IV lines were lower than those of the higher ionization lines
for this component, which is evidence for two separate absorbers at this
velocity. We have calculated photoionization models to match the UV column
densities in each of these components. Using the predicted O VI column
densities, we were able to match the O VI profiles observed in the FUSE
spectrum. Based on our results, none of the UV absorbers can produce the X-ray
absorption seen in simultaneous Chandra observations; therefore, there must be
more highly ionized gas in the radial velocity ranges covered by the UV
absorbers.Comment: 30 pages, three figures (Figure 1 is in color). Accepted for
publication in the Astrophysical Journa
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