2,813 research outputs found
Electronic Selection Rules Controlling Dislocation Glide in bcc Metals
The validity of the structure-property relationships governing the
deformation behavior of bcc metals was brought into question with recent {\it
ab initio} density functional studies of isolated screw dislocations in Mo and
Ta. These existing relationships were semiclassical in nature, having grown
from atomistic investigations of the deformation properties of the groups V and
VI transition metals. We find that the correct form for these
structure-property relationships is fully quantum mechanical, involving the
coupling of electronic states with the strain field at the core of long
screw dislocations.Comment: 4 pages, 2 figure
Grain Physics and Rosseland Mean Opacities
Tables of mean opacities are often used to compute the transfer of radiation
in a variety of astrophysical simulations from stellar evolution models to
proto-planetary disks. Often tables, such as Ferguson et al. (2005), are
computed with a predetermined set of physical assumptions that may or may not
be valid for a specific application. This paper explores the effects of several
assumptions of grain physics on the Rosseland mean opacity in an oxygen rich
environment. We find that changing the distribution of grain sizes, either the
power-law exponent or the shape of the distribution, has a marginal effect on
the total mean opacity. We also explore the difference in the mean opacity
between solid homogenous grains and grains that are porous or conglomorations
of several species. Changing the amount of grain opacity included in the mean
by assuming a grain-to-gas ratio significantly affects the mean opacity, but in
a predictable way.Comment: 19 pages, 6 figures, accepted for publication in Ap
Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574
While following up L dwarf candidates selected photometrically from the Two
Micron All Sky Survey, we uncovered an unusual object designated 2MASS
J01415823-4633574. Its optical spectrum exhibits very strong bands of vanadium
oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium.
Morphologically such spectroscopic characteristics fall intermediate between
old, field early-L dwarfs (log(g)~5) and very late M giants (log(g)~0), leading
us to favor low gravity as the explanation for the unique spectral signatures
of this L dwarf. Such a low gravity can be explained only if this L dwarf is
much lower in mass than a typical old field L dwarf of similar temperature and
is still contracting to its final radius. These conditions imply a very young
age. Further evidence of youth is found in the near-infrared spectrum,
including a triangular-shaped H-band continuum reminiscent of young brown dwarf
candidates discovered in the Orion Nebula Cluster. Using the above information
along with comparisons to brown dwarf atmospheric and interior models, our
current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of
6-25 M_Jupiter. The location of 2MASS 0141-4633 on the sky coupled with a
distance estimate of ~35 pc and the above age estimate suggests that this
object may be a brown dwarf member of either the 30-Myr-old Tucana/Horologium
Association or the ~12-Myr-old beta Pic Moving Group.Comment: Accepted for publication in the 10 March 2006 issue (volume 639) of
the Astrophysical Journa
Treatment of metastatic spinal lesions with a navigational bipolar radiofrequency ablation device: A multicenter retrospective study
A High Power Density Power System Electronics for NASA's Lunar Reconnaissance Orbiter
A high power density, modular and state-of-the-art Power System Electronics (PSE) has been developed for the Lunar Reconnaissance Orbiter (LRO) mission. This paper addresses the hardware architecture and performance, the power handling capabilities, and the fabrication technology. The PSE was developed by NASA s Goddard Space Flight Center (GSFC) and is the central location for power handling and distribution of the LRO spacecraft. The PSE packaging design manages and distributes 2200W of solar array input power in a volume less than a cubic foot. The PSE architecture incorporates reliable standard internal and external communication buses, solid state circuit breakers and LiIon battery charge management. Although a single string design, the PSE achieves high reliability by elegantly implementing functional redundancy and internal fault detection and correction. The PSE has been environmentally tested and delivered to the LRO spacecraft for the flight Integration and Test. This modular design is scheduled to flight in early 2009 on board the LRO and Lunar Crater Observation and Sensing Satellite (LCROSS) spacecrafts and is the baseline architecture for future NASA missions such as Global Precipitation Measurement (GPM) and Magnetospheric MultiScale (MMS)
Ubiquitination directly enhances activity of the deubiquitinating enzyme ataxinâ3
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/1/emboj2008289-sup-0001.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102210/2/emboj2008289.pd
Structural basis for the binding of tryptophan-based motifs by δ-COP.
Coatomer consists of two subcomplexes: the membrane-targeting, ADP ribosylation factor 1 (Arf1):GTP-binding βγδΜ-COP F-subcomplex, which is related to the adaptor protein (AP) clathrin adaptors, and the cargo-binding ιβ'Îľ-COP B-subcomplex. We present the structure of the C-terminal Îź-homology domain of the yeast δ-COP subunit in complex with the WxW motif from its binding partner, the endoplasmic reticulum-localized Dsl1 tether. The motif binds at a site distinct from that used by the homologous AP Îź subunits to bind YxxÎŚ cargo motifs with its two tryptophan residues sitting in compatible pockets. We also show that the Saccharomyces cerevisiae Arf GTPase-activating protein (GAP) homolog Gcs1p uses a related WxxF motif at its extreme C terminus to bind to δ-COP at the same site in the same way. Mutations designed on the basis of the structure in conjunction with isothermal titration calorimetry confirm the mode of binding and show that mammalian δ-COP binds related tryptophan-based motifs such as that from ArfGAP1 in a similar manner. We conclude that δ-COP subunits bind Wxn(1-6)[WF] motifs within unstructured regions of proteins that influence the lifecycle of COPI-coated vesicles; this conclusion is supported by the observation that, in the context of a sensitizing domain deletion in Dsl1p, mutating the tryptophan-based motif-binding site in yeast causes defects in both growth and carboxypeptidase Y trafficking/processing.We should like to thank the beamline scientists at the Diamond Light Source and Mike Lewis (MRC LMB), Gerry Johnston (Dalhousie University), and Mark Rose (Princeton University) for helpful discussions and technical advice. RJS and DJO are funded by a Wellcome Trust fellowship to DJO (090909). PPP was funded by Canadian Institute of Health Research. RD acknowledges support from the DFG Excellence Cluster âInflammation and Interfacesâ (ECX306) and the University of LĂźbeck. SMT and FMH acknowledge support from NIH (GM071574). PRE is funded by MRC grant U105178845This is the author accepted manuscript. The final version is available from PNAS via http://dx.doi.org/10.1073/pnas.150618611
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Risk-based prioritization for the interim remediation of inactive low-level liquid radioactive waste underground storage tanks at Oak Ridge National Laboratory, Oak Ridge, Tennessee
The paper presents a risk-based approach for rapid prioritization of low-level liquid radioactive waste underground storage tanks (LLLW USTs), for possible interim corrective measures and/or ultimate closure. The ranking of LLLW USTs is needed to ensure that tanks with the greatest potential for adverse impact on the environment and human health receive top priority for further evaluation and remediation. Wastes from the LLLW USTs at Oak Ridge National Laboratory were pumped out when the tanks were removed from service. The residual liquids and sludge contain a mixture of radionuclides and chemicals. Contaminants of concern that were identified in the liquid phase of the inactive LLLW USTs include the radionuclides [sup 90]Sr, [sup 137]Cs, and [sup 233]U and the chemicals carbon tetrachloride, trichloroethane, tetrachloroethene, methyl ethyl ketone, mercury, lead, and chromium. The risk-based approach for prioritization of the LLLW USTs is based upon three major criteria: (1) leaking characteristics of the tank, (2) location of the tanks, and (3) toxic potential of the tank contents. Leaking characteristics of LLLW USTs will aid in establishing the potential for the release of contaminants to environmental media. In this study, only the liquid phase was assumed to be released to the environment. Scoring criteria for release potential of LLLW USTs was determined after consideration of the magnitude of any known leaks and the tank type for those that are not known to leak
Neutrino physics and the mirror world: how exact parity symmetry explains the solar neutrino deficit, the atmospheric neutrino anomaly and the LSND experiment
Evidence for oscillations has been
reported at LAMPF using the LSND detector. Further evidence for neutrino mixing
comes from the solar neutrino deficit and the atmospheric neutrino anomaly. All
of these anomalies require new physics. We show that all of these anomalies can
be explained if the standard model is enlarged so that an unbroken parity
symmetry can be defined. This explanation holds independently of the actual
model for neutrino masses. Thus, we argue that parity symmetry is not only a
beautiful candidate for a symmetry beyond the standard model, but it can also
explain the known neutrino physics anomalies.Comment: 27 pages, LaTeX, no figures, additional discussion on big bang
nucleosynthesis, some additional references, to appear in Phys. Rev.
Standing in a Garden of Forking Paths
According to the Path Principle, it is permissible to expand your set of beliefs iff (and because) the evidence you possess provides adequate support for such beliefs. If there is no path from here to there, you cannot add a belief to your belief set. If some thinker with the same type of evidential support has a path that they can take, so do you. The paths exist because of the evidence you possess and the support it provides. Evidential support grounds propositional justification.
The principle is mistaken. There are permissible steps you may take that others may not even if you have the very same evidence. There are permissible steps that you cannot take that others can even if your beliefs receive the same type of evidential support. Because we have to assume almost nothing about the nature of evidential support to establish these results, we should reject evidentialism
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