47,580 research outputs found
Primary aragonite and high-Mg calcite in the late Cambrian (Furongian) : Potential evidence from marine carbonates in Oman
Acknowledgements Fieldwork and sampling was funded by Petroleum Development Oman during S. Al Marjibis's Ph.D. Their help is gratefully acknowledged. We also thank colleagues at the University of Aberdeen, Julie Dougans (SUERC) for assisting with stable isotope analysis and Dr. Richard Hinton (EIMF) for assistance with ion microprobe analysis. Profs. Kiessling, Tucker, Bosence, Coleman, Dr. Dickson and an anonymous reviewer are thanked for their helpful and encouraging comments.Peer reviewedPostprin
Modeling Variable Emission Lines in AGNs: Method and Application to NGC 5548
We present a new scheme for modeling the broad line region in active galactic
nuclei (AGNs). It involves photoionization calculations of a large number of
clouds, in several pre-determined geometries, and a comparison of the
calculated line intensities with observed emission line light curves. Fitting
several observed light curves simultaneously provides strong constraints on
model parameters such as the run of density and column density across the
nucleus, the shape of the ionizing continuum, and the radial distribution of
the emission line clouds. When applying the model to the Seyfert 1 galaxy NGC
5548, we were able to reconstruct the light curves of four ultraviolet
emission-lines, in time and in absolute flux. This has not been achieved by any
previous work. We argue that the Balmer lines light curves, and possibly also
the MgII2798 light curve, cannot be tested in this scheme because of the
limitations of present-day photoionization codes. Our fit procedure can be used
to rule out models where the particle density scales as r^{-2}, where r is the
distance from the central source. The best models are those where the density
scales as r^{-1} or r^{-1.5}. We can place a lower limit on the column density
at a distance of 1 ld, of N_{col}(r=1) >~ 10^{23} cm^{-2} and limit the
particle density to be in the range of 10^{12.5}>N(r=1)>10^{11} cm^{-3}. We
have also tested the idea that the spectral energy distribution (SED) of the
ionizing continuum is changing with continuum luminosity. None of the
variable-shape SED tried resulted in real improvement over a constant SED case
although models with harder continuum during phases of higher luminosity seem
to fit better the observed spectrum. Reddening and/or different composition
seem to play a minor role, at least to the extent tested in this work.Comment: 12 pages, including 9 embedded EPS figures, accepted for publication
in Ap
Unsteady Crack Motion and Branching in a Phase-Field Model of Brittle Fracture
Crack propagation is studied numerically using a continuum phase-field
approach to mode III brittle fracture. The results shed light on the physics
that controls the speed of accelerating cracks and the characteristic branching
instability at a fraction of the wave speed.Comment: 11 pages, 4 figure
On the Maximum Mass of Accreting Primordial Supermassive Stars
Supermassive primordial stars are suspected to be the progenitors of the most
massive quasars at z~6. Previous studies of such stars were either unable to
resolve hydrodynamical timescales or considered stars in isolation, not in the
extreme accretion flows in which they actually form. Therefore, they could not
self-consistently predict their final masses at collapse, or those of the
resulting supermassive black hole seeds, but rather invoked comparison to
simple polytropic models. Here, we systematically examine the birth, evolution
and collapse of accreting non-rotating supermassive stars under accretion rates
of 0.01-10 solar masses per year, using the stellar evolution code KEPLER. Our
approach includes post-Newtonian corrections to the stellar structure and an
adaptive nuclear network, and can transition to following the hydrodynamic
evolution of supermassive stars after they encounter the general relativistic
instability. We find that this instability triggers the collapse of the star at
masses of 150,000-330,000 solar masses for accretion rates of 0.1-10 solar
masses per year, and that the final mass of the star scales roughly
logarithmically with the rate. The structure of the star, and thus its
stability against collapse, is sensitive to the treatment of convection, and
the heat content of the outer accreted envelope. Comparison with other codes
suggests differences here may lead to small deviations in the evolutionary
state of the star as a function of time, that worsen with accretion rate. Since
the general relativistic instability leads to the immediate death of these
stars, our models place an upper limit on the masses of the first quasars at
birth.Comment: 5 pages, 4 figures. Accepted ApJ letter
Non-Volatile Magnonic Logic Circuits Engineering
We propose a concept of magnetic logic circuits engineering, which takes an
advantage of magnetization as a computational state variable and exploits spin
waves for information transmission. The circuits consist of magneto-electric
cells connected via spin wave buses. We present the result of numerical
modeling showing the magneto-electric cell switching as a function of the
amplitude as well as the phase of the spin wave. The phase-dependent switching
makes it possible to engineer logic gates by exploiting spin wave buses as
passive logic elements providing a certain phase-shift to the propagating spin
waves. We present a library of logic gates consisting of magneto-electric cells
and spin wave buses providing 0 or p phase shifts. The utilization of phases in
addition to amplitudes is a powerful tool which let us construct logic circuits
with a fewer number of elements than required for CMOS technology. As an
example, we present the design of the magnonic Full Adder Circuit comprising
only 5 magneto-electric cells. The proposed concept may provide a route to more
functional wave-based logic circuitry with capabilities far beyond the limits
of the traditional transistor-based approach
The Effectiveness of Facilitated Business-to-Business Word-of Mouth Marketing Strategies on Target Participantsâ Information Sharing Behavior
This study examines the impact of facilitated business-to-business (B2B) word-of-mouth (WOM) on participants' information transmission decisions. We also examine characteristics of WOM participants and determine the types of participants who spread information. Understanding WOM participants' information sharing decisions is extremely important to agribusinesses using WOM in their marketing mix. For an expendable crop input, the most important factor in determining whether producers share WOM initiative information with peers is how often they are asked for advice by their peers. In contrast, for an expendable companion animal product the most important factor in determining whether veterinarians share WOM initiative information with peers is whether they had a satisfactory experience in the WOM initiative.facilitated B2B WOM, effectiveness of facilitated B2B WOM, indirect impact of facilitated B2B WOM, agribusiness firmsâ information sharing decisions, Agribusiness, Industrial Organization, Marketing, Teaching/Communication/Extension/Profession, Q10, Q13,
Ticklish Sensation : One Step - Two Step or Trot
https://digitalcommons.library.umaine.edu/mmb-ps/2633/thumbnail.jp
Epidemiology and potential preventative measures for viral infections in children with malignancy and those undergoing hematopoietic cell transplantation.
In pediatric patients with malignancy and those receiving hematopoietic stem cell transplants, bacterial and fungal infections have been the focus of fever and neutropenia episodes for decades. However, improved diagnostic capabilities have revealed viral pathogens as a significant cause of morbidity and mortality. Because of limited effective antiviral therapies, prevention of viral infections is paramount. Pre-exposure and post-exposure prophylaxis and antiviral suppressive therapeutic approaches are reviewed. Additionally, infection control practices specific to this patient population are discussed. A comprehensive approach utilizing each of these can be effective at reducing the negative impact of viral infections
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