3,402 research outputs found
Anthropically Selected Baryon Number and Isocurvature Constraints
The similarity of the observed baryon and dark matter densities suggests that
they are physically related, either via a particle physics mechanism or
anthropic selection. A pre-requisite for anthropic selection is the generation
of superhorizon-sized domains of different Omega_{B}/Omega_{DM}. Here we
consider generation of domains of different baryon density via random
variations of the phase or magnitude of a complex field Phi during inflation.
Baryon isocurvature perturbations are a natural consequence of any such
mechanism. We derive baryon isocurvature bounds on the expansion rate during
inflation H_{I} and on the mass parameter mu which breaks the global U(1)
symmetry of the Phi potential. We show that when mu < H_{I} (as expected in
SUSY models) the baryon isocurvature constraints can be satisfied only if H_{I}
is unusually small, H_{I} < 10^{7} GeV, or if non-renormalizable
Planck-suppressed corrections to the Phi potential are excluded to a high
order. Alternatively, an unsuppressed Phi potential is possible if mu is
sufficiently large, mu > 10^{16} GeV. We show that the baryon isocurvature
constraints can be naturally satisfied in Affleck-Dine baryogenesis, as a
result of the high-order suppression of non-renormalizable terms along MSSM
flat directions.Comment: 8 pages, 1 eps figure, LaTeX. Minor typo correcte
Alien Registration- Mcdonald, John J. (Bangor, Penobscot County)
https://digitalmaine.com/alien_docs/11827/thumbnail.jp
Binary Capture Rates for Massive Protostars
The high multiplicity of massive stars in dense, young clusters is
established early in their evolution. The mechanism behind this remains
unresolved. Recent results suggest that massive protostars may capture
companions through disk interactions with much higher efficiency than their
solar mass counterparts. However, this conclusion is based on analytic
determinations of capture rates and estimates of the robustness of the
resulting binaries. We present the results of coupled n-body and SPH
simulations of star-disk encounters to further test the idea that disk-captured
binaries contribute to the observed multiplicity of massive stars.Comment: 4 pages, 3 figures, accepted to ApJ
New Q-ball Solutions in Gauge-Mediation, Affleck-Dine Baryogenesis and Gravitino Dark Matter
Affleck-Dine (AD) baryogenesis along a d=6 flat direction in gauge-mediated
supersymmetry-breaking (GMSB) models can produce unstable Q-balls which
naturally have field strength similar to the messenger scale. In this case a
new kind of Q-ball is formed, intermediate between gravity-mediated and
gauge-mediated type. We study in detail these new Q-ball solutions, showing how
their properties interpolate between standard gravity-mediated and
gauge-mediated Q-balls as the AD field becomes larger than the messenger scale.
It is shown that E/Q for the Q-balls can be greater than the nucleon mass but
less than the MSSM-LSP mass, leading to Q-ball decay directly to Standard Model
fermions with no MSSM-LSP production. More significantly, if E/Q is greater
than the MSSM-LSP mass, decaying Q-balls can provide a natural source of
non-thermal MSSM-LSPs, which can subsequently decay to gravitino dark matter
without violating nucleosynthesis constraints. The model therefore provides a
minimal scenario for baryogenesis and gravitino dark matter in the
gauge-mediated MSSM, requiring no new fields.Comment: 13 pages, 9 figures. Some corrections and additional discussion.
Version published in JCA
Tuning biexciton binding and anti-binding in core/shell quantum dots
We use a path integral quantum Monte Carlo method to simulate excitons and
biexcitons in core shell nanocrystals with Type-I, II and quasi-Type II band
alignments. Quantum Monte Carlo techniques allow for all quantum correlations
to be included when determining the thermal ground state, thus producing
accurate predictions of biexciton binding. These subtle quantum correlations
are found to cause the biexciton to be binding with Type-I carrier localization
and strongly anti-binding with Type-II carrier localization, in agreement with
experiment for both core shell nanocrystals and dot in rod nanocrystal
structures. Simple treatments based on perturbative approaches are shown to
miss this important transition in the biexciton binding. Understanding these
correlations offers prospects to engineer strong biexciton anti-binding which
is crucial to the design of nanocrystals for single exciton lasing
applications.Comment: 10 pages, 11 figure
New proof-of-concept in viral inactivation: virucidal efficacy of 405Â nm light against feline calicivirus as a model for norovirus decontamination
The requirement for novel decontamination technologies for use in hospitals is ever present. One such system uses 405 nm visible light to inactivate microorganisms via ROS-generated oxidative damage. Although effective for bacterial and fungal inactivation, little is known about the virucidal effects of 405 nm light. Norovirus (NoV) gastroenteritis outbreaks often occur in the clinical setting, and this study was designed to investigate potential inactivation effects of 405 nm light on the NoV surrogate, feline calicivirus (FCV). FCV was exposed to 405 nm light whilst suspended in minimal and organically-rich media to establish the virucidal efficacy and the effect biologically-relevant material may play in viral susceptibility. Antiviral activity was successfully demonstrated with a 4 Log10 (99.99%) reduction in infectivity when suspended in minimal media evident after a dose of 2.8 kJ cm−2. FCV exposed in artificial faeces, artificial saliva, blood plasma and other organically rich media exhibited an equivalent level of inactivation using between 50–85% less dose of the light, indicating enhanced inactivation when the virus is present in organically-rich biologically-relevant media. Further research in this area could aid in the development of 405 nm light technology for effective NoV decontamination within the hospital environment
Efficient Compression of Digital Holograms for Internet Transmission of Three-Dimensional Images
We compress phase-shift digital holograms (whole Fresnel fields) for the transmission of three-dimensional images. For real-time networking applications, the time required
to compress can be as critical as compression rate. We achieve lossy compression through quantization of both the real and imaginary streams, followed by a bit packing
operation. We define a speedup metric that combines space gains due to compression with temporal overheads due to the compression routine and transmission
serialization. We empirically verify transmission speedup due to compression, using a special-purpose Internet-based networking application
Applicability of tandem affinity purification MudPIT to pathway proteomics in yeast
A combined multidimensional chromatography-mass spectrometry approach known as "MudPIT" enables rapid identification of proteins that interact with a tagged bait while bypassing some of the problems associated with analysis of polypeptides excised from SDS-polyacrylamide gels. However, the reproducibility, success rate, and applicability of MudPIT to the rapid characterization of dozens of proteins have not been reported. We show here that MudPIT reproducibly identified bona fide partners for budding yeast Gcn5p. Additionally, we successfully applied MudPIT to rapidly screen through a collection of tagged polypeptides to identify new protein interactions. Twenty-five proteins involved in transcription and progression through mitosis were modified with a new tandem affinity purification (TAP) tag. TAP-MudPIT analysis of 22 yeast strains that expressed these tagged proteins uncovered known or likely interacting partners for 21 of the baits, a figure that compares favorably with traditional approaches. The proteins identified here comprised 102 previously known and 279 potential physical interactions. Even for the intensively studied Swi2p/Snf2p, the catalytic subunit of the Swi/Snf chromatin remodeling complex, our analysis uncovered a new interacting protein, Rtt102p. Reciprocal tagging and TAP-MudPIT analysis of Rtt102p revealed subunits of both the Swi/Snf and RSC complexes, identifying Rtt102p as a common interactor with, and possible integral component of, these chromatin remodeling machines. Our experience indicates it is feasible for an investigator working with a single ion trap instrument in a conventional molecular/cellular biology laboratory to carry out proteomic characterization of a pathway, organelle, or process (i.e. "pathway proteomics") by systematic application of TAP-MudPIT
Robust Tracking for Real-Time Dense RGB-D Mapping with Kintinuous
This paper describes extensions to the Kintinuous algorithm for spatially extended KinectFusion, incorporating the following additions: (i) the integration of multiple 6DOF camera odometry estimation methods for robust tracking; (ii) a novel GPU-based implementation of an existing dense RGB-D visual odometry algorithm; (iii) advanced fused real-time surface coloring. These extensions are validated with extensive experimental results, both quantitative and qualitative, demonstrating the ability to build dense fully colored models of spatially extended environments for robotics and virtual reality applications while remaining robust against scenes with challenging sets of geometric and visual features
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