1,622 research outputs found
No-vent fill pressurization tests using a cryogen simulant
The results are described of an experimental program which studied the performance of various no-vent fill techniques for tank-to-tank liquid transfer. The tests were performed using a cryogen simulant (Freon-114) and a test bed consisting of a multiple tank/plumbing network that enabled studies of a variety of different inlet flow and active mixing regimes. Several results and conclusions were drawn from the 26 transfer experiments comprising the program. Most notable was the significant improvement in fill performance (i.e., minimized fill time and maximized fill fraction) with increased agitation of the liquid surface. Another was the close correlation between measured condensation rates and those predicted by recent theories which express condensation as a function of turbulent eddy effects on the liquid surface. In most cases, test data exhibited strong agreement with an analytical model which accounts for tank heat transfer and thermodynamics in a 1 g environment
Hominids adapted to metabolize ethanol long before human-directed fermentation
Paleogenetics is an emerging field that resurrects ancestral proteins from now-extinct organisms to test, in the laboratory, models of protein function based on natural history and Darwinian evolution. Here, we resurrect digestive alcohol dehydrogenases (ADH4) from our primate ancestors to explore the history of primate-ethanol interactions. The evolving catalytic properties of these resurrected enzymes show that our ape ancestors gained a digestive dehydrogenase enzyme capable of metabolizing ethanol near the time that they began using the forest floor, about 10 million y ago. The ADH4 enzyme in our more ancient and arboreal ancestors did not efficiently oxidize ethanol. This change suggests that exposure to dietary sources of ethanol increased in hominids during the early stages of our adaptation to a terrestrial lifestyle. Because fruit collected from the forest floor is expected to contain higher concentrations of fermenting yeast and ethanol than similar fruits hanging on trees, this transition may also be the first time our ancestors were exposed to (and adapted to) substantial amounts of dietary ethanol
Electron-based crystalline undulator
We discuss the features of a crystalline undulator of the novel type based on
the effect of a planar channeling of ultra-relativistic electrons in a
periodically bent crystals. It is demonstrated that an electron-based undulator
is feasible in the tens of GeV range of the beam energies, which is noticeably
higher than the energy interval allowed in a positron-based undulator.
Numerical analysis of the main parameters of the undulator as well as the
characteristics of the emitted undulator radiation is carried out for 20 and 50
GeV electrons channeling in diamond and silicon crystals along the (111)
crystallographic planes.Comment: 16 pages, 8 figures, Latex, IOP styl
PSR J1856+0245: Arecibo Discovery of a Young, Energetic Pulsar Coincident with the TeV Gamma-ray Source HESS J1857+026
We present the discovery of the Vela-like radio pulsar J1856+0245 in the
Arecibo PALFA survey. PSR J1856+0245 has a spin period of 81ms, a
characteristic age of 21kyr, and a spin-down luminosity Edot = 4.6 x 10^36
ergs/s. It is positionally coincident with the TeV gamma-ray source HESS
J1857+026, which has no other known counterparts. Young, energetic pulsars
create wind nebulae, and more than a dozen pulsar wind nebulae have been
associated with very-high-energy (100GeV-100TeV) gamma-ray sources discovered
with the HESS telescope. The gamma-ray emission seen from HESS J1857+026 is
potentially produced by a pulsar wind nebula powered by PSR J1856+0245; faint
X-ray emission detected by ASCA at the pulsar's position supports this
hypothesis. The inferred gamma-ray efficiency is epsilon_gamma = L_gamma/Edot =
3.1% (1-10TeV, for a distance of 9kpc), comparable to that observed in similar
associations.Comment: 13 pages, 1 figure, accepted for publication in The Astrophysical
Journal Letter
Improved Experimental Limits on the Production of Magnetic Monopoles
We present new limits on low mass accelerator-produced point-like Dirac
magnetic monopoles trapped and bound in matter surrounding the D\O collision
region of the Tevatron at Fermilab (experiment E-882). In the context of a
Drell-Yan mechanism, we obtain cross section limits for the production of
monopoles with magnetic charge values of 1, 2, 3, and 6 times the minimum Dirac
charge of the order of picobarns, some hundred times smaller than found in
similar previous Fermilab searches. Mass limits inferred from these cross
section limits are presented.Comment: 5 pages, 4 eps figures, REVTe
A Framework to Manage the Complex Organisation of Collaborating: Its Application to Autonomous Systems
In this paper we present an analysis of the complexities of large group
collaboration and its application to develop detailed requirements for
collaboration schema for Autonomous Systems (AS). These requirements flow from
our development of a framework for collaboration that provides a basis for
designing, supporting and managing complex collaborative systems that can be
applied and tested in various real world settings. We present the concepts of
"collaborative flow" and "working as one" as descriptive expressions of what
good collaborative teamwork can be in such scenarios. The paper considers the
application of the framework within different scenarios and discuses the
utility of the framework in modelling and supporting collaboration in complex
organisational structures
An Exploratory Study into the Factors Impeding Ethical Consumption
Although consumers are increasingly engaged with ethical factors when forming opinions about products and making purchase decisions, recent studies have highlighted significant differences between consumersâ intentions to consume ethically, and their actual purchase behaviour. This article contributes to an understanding of this âethical purchasing gapâ through a review of existing literature, and the inductive analysis of focus group discussions. A model is suggested which includes exogenous variables such as moral maturity and age which have been well covered in the literature, together with further impeding factors identified from the focus group discussions. For some consumers, inertia in purchasing behaviour was such that the decision-making process was devoid of ethical considerations. Several manifested their ethical views through post-purchase dissonance and retrospective feelings of guilt. Others displayed a reluctance to consume ethically due to personal constraints, a perceived negative impact on image or quality, or an outright negation of responsibility. Those who expressed a desire to consume ethically often seemed deterred by cynicism, which caused them to question the impact they, as an individual, could achieve. These findings enhance the understanding of ethical consumption decisions and provide a platform for future research in this area
The influence of the dechanneling process on the photon emission by an ultra-relativistc positron channeling in a periodically bent crystal
We investigate, both analytically and numerically, the influence of the
dechanneling process on the parameters of undulator radiation generated by
ultra-relativistic positron channelling along a crystal plane, which is
periodically bent. The bending might be due either to the propagation of a
transverse acoustic wave through the crystal, or due to the static strain as it
occurs in superlattices. In either case the periodically bent crystal serves as
an undulator which allows to generate X-ray and gamma-radiation.
We propose the scheme for accurate quantitative treatment of the radiation in
presence of the dechanneling. The scheme includes (i) the analytic expression
for spectral-angular distribution which contains, as a parameter, the
dechanneling length, (ii) the simulation procedure of the dechanneling process
of a positron in periodically bent crystals. Using these we calculate the
dechanneling lengths of 5 GeV positrons channeling in Si, Ge and W crystals,
and the spectral-angular and spectral distributions of the undulator over broad
ranges of the photons. The calculations are performed for various parameters of
the channel bending.Comment: published in J. Phys. G: Nucl. Part. Phys. 27 (2001) 95-125,
http://www.iop.or
Length of Anticoagulation in Provoked Venous Thromboembolism: A Multicenter Study of How Real-World Practice Mirrors Guideline Recommendations
Background For more than a decade, guidelines have recommended a limited 3âmonths of anticoagulation for the treatment of provoked venous thromboembolism (VTE). How closely real-world practice follows guideline recommendations is not well described. Methods and Results In our multicenter, retrospective cohort study, we evaluated trends in anticoagulation duration for patients enrolled in the MAQI(2) (Michigan Anticoagulation Quality Improvement Initiative) registry who were receiving anticoagulation for a provoked VTE. The MAQI(2) registry comprises 6 centers in Michigan that manage patients\u27 long-term anticoagulation. We identified 474 patients on warfarin and 302 patients on direct oral anticoagulants who were receiving anticoagulation for a primary indication of provoked VTE between 2008 and 2020. Using a predefined threshold of 120âdays (3 months plus a buffer period), predictors of extended anticoagulant use were identified using multivariable logistic regression. Most patients received \u3e120âdays of anticoagulation, regardless of which medication was used. The median (25th-75th percentile) length of treatment for patients taking warfarin was 142 (91-234) days and for direct oral anticoagulants was 180 (101-360) days. Recurrent VTE (odds ratio [OR], 2.75 [95% CI, 1.67-4.53]), history of myocardial infarction (OR, 3.92 [95% CI, 1.32-11.7]), and direct oral anticoagulant rather than warfarin use (OR, 2.22 [95% CI, 1.59-3.08]) were independently associated with prolonged anticoagulation. Conclusions In our cohort of patients with provoked VTE, most patients received anticoagulation for longer than the guideline-recommended 3âmonths. This demonstrates a potential opportunity to improve care delivery and reduce anticoagulant-associated bleeding risk
Tevatron Beam Halo Collimation System: Design, Operational Experience and New Methods
Collimation of proton and antiproton beams in the Tevatron collider is
required to protect CDF and D0 detectors and minimize their background rates,
to keep irradiation of superconducting magnets under control, to maintain
long-term operational reliability, and to reduce the impact of beam-induced
radiation on the environment. In this article we briefly describe the design,
practical implementation and performance of the collider collimation system,
methods to control transverse and longitudinal beam halo and two novel
collimation techniques tested in the Tevatron.Comment: 25 p
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