169 research outputs found
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The Evolution of Low-Level Radioactive Waste (LLW) Disposal Practices at the Savannah River Site Coupled with Vigorous Stakeholder Interaction
Low-level radioactive waste (LLW) disposal practices at SRS evolved from trench disposal with little long-term performance basis to disposal in robust concrete vaults, again without modeling long-term performance. Now, based on an assessment of long-term performance of various waste forms and methods of disposal, the LLW disposal program allows for a ''smorgasbord'' of various disposal techniques and waste forms, all modeled to ensure long-term performance is understood. New disposal techniques include components-in-grout, compaction/volume reduction prior to disposal, and trench disposal of extremely low activity waste. Additionally, factoring partition coefficient (Kd) measurements based on waste forms has been factored into performance models. This paper will trace the development of the different disposal methods, and the extensive public communications effort that resulted in endorsement of the changes by the SRS Citizens Advisory Board
The Mikheyev-Smirnov-Wolfenstein Effect as a Probe of the Solar Interior
We relate the MSW effect to the efective absorption of the electronic
collective motion energy by retaining the imaginary part of the index of
refraction associated with the charged-current scattering and show that the
small angle MSW solution to the solar neutrino anomaly can be used as a probe
of the physical conditions of the solar interior if it is correct. We find that
the constraint on the absorption imposed by the small angle MSW solution and
the theoretical estimate of the absorption by the Boltzmann kinetic theory are
consistent, which shows that a consistent theoretical picture can be developed
when plasma absorption processes are taken into account.Comment: 4 pages, no figure, REVTeX, to appear in Phys. Rev.
A general nonlinear fluid model for reacting plasma-neutral mixtures
A generalized, computationally tractable fluid model for capturing the effects of neutral particles in plasmas is derived. The model derivation begins with Boltzmann equations for singly charged ions, electrons, and a single neutral species. Electron-impact ionization, radiative recombination, and resonant charge exchange reactions are included. Moments of the reaction collision terms are detailed. Moments of the Boltzmann equations for electron, ion, and neutral species are combined to yield a two-component plasma-neutral fluid model. Separate density, momentum, and energy equations, each including reaction transfer terms, are produced for the plasma and neutral equations. The required closures for the plasma-neutral model are discussed
First Simultaneous NIR/X-ray Detection of a Flare from SgrA*
We report on the first simultaneous near-infrared/X-ray detection of the Sgr
A* counterpart which is associated with the massive black hole at the center of
the Milky Way. The observations have been carried out using the NACO adaptive
optics (AO) instrument at the European Southern Observatory's Very Large
Telescope and the ACIS-I instrument aboard the Chandra X-ray Observatory. We
also report on quasi-simultaneous observations at a wavelength of 3.4 mm using
the Berkeley-Illinois-Maryland Association (BIMA) array. A flare was detected
in the X-domain with an excess 2-8 keV luminosity of about 6
erg/s. A fading flare of Sgr A* with 2 times the interim-quiescent flux was
also detected at the beginning of the NIR observations, that overlapped with
the fading part of the X-ray flare. Compared to 8-9 hours before the NIR/X-ray
flare we detected a marginally significant increase in the millimeter flux
density of Sgr A* during measurements about 7-9 hours afterwards. We find that
the flaring state can be conveniently explained with a synchrotron self-Compton
model involving up-scattered sub-millimeter photons from a compact source
component, possibly with modest bulk relativistic motion. The size of that
component is assumed to be of the order of a few times the Schwarzschild
radius. The overall spectral indices
() of both states are quite comparable with a
value of 1.3. Since the interim-quiescent X-ray emission is spatially
extended, the spectral index for the interim-quiescent state is probably only a
lower limit for the compact source Sgr A*. A conservative estimate of the upper
limit of the time lag between the ends of the NIR and X-ray flare is of the
order of 15 minutes.Comment: Reviewed version; minor changes; added quasi-simultaneous submm
observation
Foundations of Black Hole Accretion Disk Theory
This review covers the main aspects of black hole accretion disk theory. We
begin with the view that one of the main goals of the theory is to better
understand the nature of black holes themselves. In this light we discuss how
accretion disks might reveal some of the unique signatures of strong gravity:
the event horizon, the innermost stable circular orbit, and the ergosphere. We
then review, from a first-principles perspective, the physical processes at
play in accretion disks. This leads us to the four primary accretion disk
models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin)
disks, slim disks, and advection-dominated accretion flows (ADAFs). After
presenting the models we discuss issues of stability, oscillations, and jets.
Following our review of the analytic work, we take a parallel approach in
reviewing numerical studies of black hole accretion disks. We finish with a few
select applications that highlight particular astrophysical applications:
measurements of black hole mass and spin, black hole vs. neutron star accretion
disks, black hole accretion disk spectral states, and quasi-periodic
oscillations (QPOs).Comment: 91 pages, 23 figures, final published version available at
http://www.livingreviews.org/lrr-2013-
Physical comorbidities in men with mood and anxiety disorders: a population-based study
Background : The mind-body nexus has been a topic of growing interest. Further data are however required to understand the specific relationship between mood and anxiety disorders and individual physical health conditions, and to verify whether these psychiatric disorders are linked to overall medical burden. Methods : This study examined data collected from 942 men, 20 to 97 years old, participating in the Geelong Osteoporosis Study. A lifetime history of mood and anxiety disorders was identified using the Structured Clinical Interview for DSM-IV-TR Research Version, Non-patient edition (SCID-I/NP). The presence of medical conditions (lifetime) was self-reported and confirmed by medical records, medication use or clinical data. Anthropometric measurements and socioeconomic status (SES) were determined and information on medication use and lifestyle was obtained via questionnaire. Logistic regression models were used to test the associations. Results : After adjustment for age, socioeconomic status, and health risk factors (body mass index, physical activity and smoking), mood disorders were associated with gastro oesophageal reflux disease (GORD), recurrent headaches, blackouts and/or epilepsy, liver disorders and pulmonary disease in older people, whilst anxiety disorders were significantly associated with thyroid, GORD and other gastrointestinal disorders, and psoriasis. Increased odds of high medical burden were associated with both mood and anxiety disorders. Conclusions : Our study provides further population-based evidence supporting the link between mental and physical illness in men. Understanding these associations is not only necessary for individual management, but also to inform the delivery of health promotion messages and health care
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