1,290 research outputs found
False vacuum decay in Jordan-Brans-Dicke cosmologies
The bubble nucleation rate in a first-order phase transition taking place in a background Jordan-Brans-Dicke cosmology is examined. The leading order terms in the nucleation rate when the Jordan-Brans-Dicke field is large (i.e., late times) are computed by means of a Weyl rescaling of the fields in the theory. It is found that despite the fact that the Jordan-Brans-Dicke field (hence the effective gravitational constant) has a time dependence in the false vacuum at late times the nucleation rate is time independent
Culture Research Landscape Throughout the United States Department of Defense
This contribution delineates the U.S. Department of Defense (DoD) regional expertise and culture (REC) research landscape from 2005 through 2011, including major research efforts and topics of study, key contributors and publications, collaborative practices, and future research opportunities. Through interviews and survey responses, subject matter experts (SMEs) in REC research noted the need for better REC research coordination, more social science expertise and personnel, and greater collaborative practices. Key contributors to REC research across the DoD are located at AFCLC, ARI, ARL, AFRL, CAOCL, NAWCTSD, TRADOC, and the HSCB Modeling program. Opportunities for future research include: (1) Validation studies for 3C requirements; (2) Validation studies of REC training and education programs; (3) Role of technology in culture training; (4) Mitigating Cognitive Dissonance: Crossing the Culture Divide; (5) Navigating Culture During a High Stakes Mission; (6) Team cohesion in a multinational context
What’s Brewing? A Statistics Education Discovery Project
We believe that students learn best, are actively engaged, and are genuinely interested when working on real-world problems. This can be done by giving students the opportunity to work collaboratively on projects that investigate authentic, familiar problems. This article shares one such project that was used in an introductory statistics course. We describe the steps taken to investigate why customers are charged more for iced coffee than hot coffee, which included collecting data and using descriptive and inferential statistical analysis. Interspersed throughout the article, we describe strategies that can help teachers implement the project and scaffold material to assist students who may have gaps in their mathematical background and offer suggestions if using the lesson with students who are mathematically stronger. Students were highly motivated and enthusiastic to work on a problem with a rich, readily understood context. This article provides teachers with an alternative way to assess student learning, and gives students the opportunity to work the way statisticians work
The Vacuole Model: New Terms in the Second Order Deflection of Light
The present paper is an extension of a recent work (Bhattacharya et al. 2010)
to the Einstein-Strauss vacuole model with a cosmological constant, where we
work out the light deflection by considering perturbations up to order M^3 and
confirm the light bending obtained previously in their vacuole model by Ishak
et al. (2008). We also obtain another local coupling term
-((5{\pi}M^2{\Lambda})/8) related to {\Lambda}, in addition to the one obtained
by Sereno (2008, 2009). We argue that the vacuole method for light deflection
is exclusively suited to cases where the cosmological constant {\Lambda}
disappears from the path equation. However, the original Rindler-Ishak method
(2007) still applies even if a certain parameter {\gamma} of Weyl gravity does
not disappear. Here, using an alternative prescription, we obtain the known
term -(({\gamma}R)/2), as well as another new local term ((3{\pi}{\gamma}M)/2)
between M and {\gamma}. Physical implications are compared, where we argue that
the repulsive term -(({\gamma}R)/2) can be masked by the Schwarzschild term
((2M)/R) in the halo regime supporting attractive property of the dark matter.Comment: 15 page
A New Independent Limit on the Cosmological Constant/Dark Energy from the Relativistic Bending of Light by Galaxies and Clusters of Galaxies
We derive new limits on the value of the cosmological constant, ,
based on the Einstein bending of light by systems where the lens is a distant
galaxy or a cluster of galaxies. We use an amended lens equation in which the
contribution of to the Einstein deflection angle is taken into
account and use observations of Einstein radii around several lens systems. We
use in our calculations a Schwarzschild-de Sitter vacuole exactly matched into
a Friedmann-Robertson-Walker background and show that a -contribution
term appears in the deflection angle within the lens equation. We find that the
contribution of the -term to the bending angle is larger than the
second-order term for many lens systems. Using these observations of bending
angles, we derive new limits on the value of . These limits constitute
the best observational upper bound on after cosmological constraints
and are only two orders of magnitude away from the value determined by those
cosmological constraints.Comment: 5 pages, 1 figure, matches version published in MNRA
Numerical Evolution of General Relativistic Voids
In this paper, we study the evolution of a relativistic, superhorizon-sized
void embedded in a Friedmann-Robertson-Walker universe. We numerically solve
the spherically symmetric general relativistic equations in comoving,
synchronous coordinates. Initially, the fluid inside the void is taken to be
homogeneous and nonexpanding. In a radiation- dominated universe, we find that
radiation diffuses into the void at approximately the speed of light as a
strong shock---the void collapses. We also find the surprising result that the
cosmic collapse time (the -crossing time) is much smaller than
previously thought, because it depends not only on the radius of the void, but
also on the ratio of the temperature inside the void to that outside. If the
ratio of the initial void radius to the outside Hubble radius is less than the
ratio of the outside temperature to that inside, then the collapse occurs in
less than the outside Hubble time. Thus, superhorizon-sized relativistic void
may thermalize and homogenize relatively quickly. These new simulations revise
the current picture of superhorizon-sized void evolution after first-order
inflation.Comment: 37 pages plus 12 figures (upon request-- [email protected])
LaTeX, FNAL-PUB-93/005-
Uncovering the Origins of Spiral Structure by Measuring Radial Variation in Pattern Speeds
Current theories of spiral and bar structure predict a variety of pattern
speed behaviors, calling for detailed, direct measurement of the radial
variation of pattern speeds. Our recently developed Radial Tremaine-Weinberg
(TWR) method allows this goal to be achieved for the first time. Here we
present TWR spiral pattern speed estimates for M101, IC 342, NGC 3938 and NGC
3344 in order to investigate whether spiral structure is steady or winding,
whether spirals are described by multiple pattern speeds, and the relation
between bar and spiral speeds. Where possible, we interpret our pattern speeds
estimates according to the resonance radii associated with each (established
with the disk angular rotation), and compare these to previous determinations.
By analyzing the high-quality HI and CO data cubes available for these
galaxies, we show that it is possible to determine directly multiple pattern
speeds within these systems, and hence identify the characteristic signatures
of the processes that drive the spiral structure. Even this small sample of
galaxies reveals a surprisingly complex taxonomy, with the first direct
evidence for the presence of resonant coupling of multiple patterns found in
some systems, and the measurement of a simple single pattern speed in others.
Overall, this study demonstrates that we are now in a position to uncover more
of the apparently complex physics that lies behind spiral structure.Comment: 15 pages in emulateapj format, 12 figures, accepted for publication
in Ap
A family-based study of gene variants and maternal folate and choline in neuroblastoma: a report from the Children’s Oncology Group
Neuroblastoma is a childhood cancer of the sympathetic nervous system with embryonic origins. Previous epidemiologic studies suggest maternal vitamin supplementation during pregnancy reduces the risk of neuroblastoma. We hypothesized offspring and maternal genetic variants in folate-related and choline-related genes are associated with neuroblastoma and modify the effects of maternal intake of folate, choline and folic acid
Bidirectional Transcription Directs Both Transcriptional Gene Activation and Suppression in Human Cells
Small RNAs targeted to gene promoters in human cells have been shown to modulate both transcriptional gene suppression and activation. However, the mechanism involved in transcriptional activation has remained poorly defined, and an endogenous RNA trigger for transcriptional gene silencing has yet to be identified. Described here is an explanation for siRNA-directed transcriptional gene activation, as well as a role for non-coding antisense RNAs as effector molecules driving transcriptional gene silencing. Transcriptional activation of p21 gene expression was determined to be the result of Argonaute 2–dependent, post-transcriptional silencing of a p21-specific antisense transcript, which functions in Argonaute 1–mediated transcriptional control of p21 mRNA expression. The data presented here suggest that in human cells, bidirectional transcription is an endogenous gene regulatory mechanism whereby an antisense RNA directs epigenetic regulatory complexes to a sense promoter, resulting in RNA-directed epigenetic gene regulation. The observations presented here support the notion that epigenetic silencing of tumor suppressor genes, such as p21, may be the result of an imbalance in bidirectional transcription levels. This imbalance allows the unchecked antisense RNA to direct silent state epigenetic marks to the sense promoter, resulting in stable transcriptional gene silencing
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