61,897 research outputs found
The numerical solution of fractional differential equations: Speed versus accuracy
This paper discusses the development of efficient algorithms for a certain fractional differential equation.Manchester Centre for Computational Mathematic
Embedded Clusters in Molecular Clouds
Stellar clusters are born embedded within giant molecular clouds (GMCs) and
during their formation and early evolution are often only visible at infrared
wavelengths, being heavily obscured by dust. Over the last 15 years advances in
infrared detection capabilities have enabled the first systematic studies of
embedded clusters in galactic molecular clouds. In this article we review the
current state of empirical knowledge concerning these extremely young
protocluster systems. From a survey of the literature we compile the first
extensive catalog of galactic embedded cluster properties. We use the catalog
to construct the mass function and estimate the birthrate for embedded clusters
within roughly 2 Kpc of the Sun. We find that the embedded cluster birthrate
exceeds that of visible open clusters by an order of magnitude or more
indicating a high infant mortality rate for protocluster systems. Less than
4-7% of embedded clusters survive emergence from molecular clouds to become
bound clusters of Pleiades age. The vast majority (90%) of stars that form in
embedded clusters form in rich clusters of 100 or more members with masses in
excess of 50 solar masses. We review the role of embedded clusters in
investigating the nature of the IMF which, in one nearby example, has been
measured over the entire range of stellar and substellar mass, from OB stars to
subsellar objects near the deuterium burning limit. We also review the role
embedded clusters play in the investigation of circumstellar disk evolution and
the important constraints they provide for understanding the origin of
planetary systems. Finally, we discuss current ideas concerning the origin and
dynamical evolution of embedded clusters and the implications for the formation
of bound open clusters.Comment: To appear in Annual Reviews of Astronomy and Astrophysics v41.
Manuscript consists of 73 pages with 14 figures. Due to space limitations 5
figures are included as separate low quality jpeg figures. A complete
manuscript with full resolution figures can be downloaded from
http://cfa-www.harvard.edu/~clada/preprints.htm
Floating nut retention system
A floating nut retention system includes a nut with a central aperture. An inner retainer plate has an opening which is fixedly aligned with the nut aperture. An outer retainer member is formed of a base plate having an opening and a surface adjacent to a surface of the inner retainer plate. The outer retainer member includes a securing mechanism for retaining the inner retainer plate adjacent to the outer retainer member. The securing mechanism enables the inner retainer plate to float with respect to the outer retainer number, while simultaneously forming a bearing surface for inner retainer plate
Potential relationship of epistemic games to group dynamics and learning orientations towards physics problem solving
Current investigations into pedagogical goals of introductory algebra-based
physics students at the University of Central Arkansas, by learning orientation
towards an in-class metacognitive group problem solving task, seek to determine
possible relationships with attitudinal shifts and course performance. Students
thus far have been untreated with known group-based learning pedagogies, so as
to establish trends of common group habits, and ultimately to properly inform
implementation of group-based pedagogies in reaction to these trends. However,
students' group dynamics and learning orientations prove difficult to map to
group-based measurements; an estimate of group learning orientation and
preferred working group dynamic is here explored as a potential means of
interpreting students' use of problem solving strategies. A means of "sampling"
audiovisual data in a live classroom of several simultaneous groups is also
presented as a way to estimate the frequency of chosen strategies to this end.Comment: 4 pages, 2 figures, 2 tables, conference proceeding
Adaptation of WASH Services Delivery to Climate Change and Other Sources of Risk and Uncertainty
This report urges WASH sector practitioners to take more seriously the threat of climate change and the consequences it could have on their work. By considering climate change within a risk and uncertainty framework, the field can use the multitude of approaches laid out here to adequately protect itself against a range of direct and indirect impacts. Eleven methods and tools for this specific type of risk management are described, including practical advice on how to implement them successfully
On Measurement of Helicity Parameters in Top Quark Decay
To enable an evaluation of future measurements of the helicity parameters for
" t --> W b " decay in regard to " T_FS violation", this paper considers the
effects of an additional pure-imaginary coupling, (i g/2 Lambda) or (i g),
associated with a specific, single additional Lorentz structure, i = S, P, S +
P, ... Sizable " T_FS violation" signatures can occur for low-effective mass
scales (< 320 GeV), but in most cases can be more simply excluded by 10%
precision measurement of the probabilities P(W_L) and P(b_L). Signatures for
excluding the presence of " T_FS violation" associated with the two dynamical
phase-type ambiguities are investigated.Comment: 15 pages, 1 table, 7 figures, no macro
Sexual differentiation and gonad development in striped mullet (Mugil cephalus L.) from South Carolina estuaries*
This study examined the sexual differentiation and reproductive dynamics of striped mullet (Mugil cephalus L.) in the estuaries of South Carolina. A total of 16,464 specimens were captured during the study and histological
examination of sex and maturity was performed on a subsample of 3670 fish. Striped mullet were sexually
undifferentiated for the first 12 months, began differentiation at 13 months, and were 90% fully differentiated by 15 to 19 months of age and 225 mm total
length (TL). The defining morphological characteristics for differentiating males was the elongation of the protogonial
germ tissue in a corradiating pattern towards the center of the lobe, the development of primary and secondary ducts, and the lack of any recognizable ovarian wall structure. The
defining female characteristics were the formation of protogonial germ tissue into spherical germ cell nests, separation of a tissue layer from the outer epithelial layer of the lobe-forming ovarian walls, a tissue bud growing from the suspensory tissue that helped form
the ovary wall, and the proliferation of oogonia and oocytes. Sexual maturation in male striped mullet first occurred at 1 year and 248 mm TL and 100% maturity occurred at age 2 and 300 mm TL. Female striped mullet first matured at 2 years and 291 mm total length and 100% maturity occurred at 400 mm TL and age 4. Because of the open ocean spawning behavior of striped mullet, all stages of maturity were observed in males and females except for functionally mature females with hydrated oocytes. The spawning season
for striped mullet recruiting to South Carolina estuaries lasts from October to April; the majority of spawning activity, however, occurs from November to January. Ovarian atresia was observed to have four distinct phases. This study presents morpholog ical analysis of reproductive ontogeny in relation to size and age in South Carolina striped mullet. Because of the length of the undifferentiated gonad stage in juvenile striped mullet, previous studies have proposed the possibility of protandric
hermaphrodism in this species. The results of our study indicate that striped mullet are gonochoristic but capable of exhibiting nonfunctional hermaphroditic characteristics in differentiated mature gonads
Semi-inclusive hadronic B decays as null tests of the Standard Model
We propose a new set of observables that can be used as experimental null
tests of the Standard Model in charged and neutral B decays. The CP asymmetries
in hadronic decays of charged B mesons into inclusive final states containing
at least one of the following mesons: K_{S,L}, eta', c\bar c bound states or
neutral K^* or D mesons, for all of which a U-spin rotation is equivalent to a
CP conjugation, are CKM suppressed and furthermore vanish in the exact U-spin
limit. We show how this reduces the theoretical error by using Soft Collinear
Effective Theory to calculate the CP asymmetries for K_{S,L} X_{s+d}, K^*
X_{s+d} and eta' X_{s+d} final states in the endpoint region. For these CP
asymmetries only the flavor and not the charge of the decaying B meson needs to
be tagged up to corrections of NLO in 1/m_b, making the measurements more
accessible experimentally.Comment: 8 pages, significantly expanded after the observation that both
neutral and charged B decays can be used, calculation for decays involving
eta' adde
Glucocorticoid receptor action in metabolic and neuronal function [version 1; referees: 3 approved]
Glucocorticoids via the glucocorticoid receptor (GR) have effects on a variety of cell types, eliciting important physiological responses via changes in gene expression and signaling. Although decades of research have illuminated the mechanism of how this important steroid receptor controls gene expression using in vitro and cell cultureâbased approaches, how GR responds to changes in external signals in vivo under normal and pathological conditions remains elusive. The goal of this review is to highlight recent work on GR action in fat cells and liver to affect metabolism in vivo and the role GR ligands and receptor phosphorylation play in calibrating signaling outputs by GR in the brain in health and disease. We also suggest that both the brain and fat tissue communicate to affect physiology and behavior and that understanding this âbrain-fat axisâ will enable a more complete understanding of metabolic diseases and inform new ways to target them
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