18,635 research outputs found
Transient heat and mass transfer analysis of supercritical cryogenic storage systems with spherical static heaters Final report
Transient heat and mass transfer analysis of supercritical cryogenic storage systems with spherical static heaters by computer progra
Nonlinear double-diffusive intrusions at the equator
Previous, linear analysis has suggested that observations of interleaving, quasi-horizontal layers in the equatorial oceans may be explained by double-diffusive or inertial instability. Here we describe an idealized, two-dimensional, numerical investigation of the nonlinear development of these instabilities, focusing almost exclusively on the double-diffusive case. We consider the mechanisms for equilibration and maintenance of the interleaving intrusions and perform a thorough sensitivity analysis. Nonlinearity arising from changes in diffusive regime is found to be more important than advective nonlinearity in promoting global equilibration. When variations in effective flux ratio are weak, local constraints prevent equilibration until large amplitudes are reached. When variations in flux ratio with density ratio are allowed, small-scale staircase and mesoscale intrusive instabilities coexist, leading to staircase-like intrusions with sharp, steppy interfaces. Solutions are found to equilibrate at between 3 and 13 times the amplitude where mean salinity gradients overturn. Cross-equatorial diffusivities between 20 and 400 m2 s-1 are found in realistic cases with intrusion lengths of up to 40 km. A modified estimate of the effective cross-equatorial diffusivity based on a balance of lateral advection and vertical diffusion tends to overestimate the sensitivity to the mean horizontal and vertical gradients of salinity and underestimates the sensitivity to the vertical diffusivity but does give values within an order of magnitude of those derived from numerical experiments.
For comparison, we give a single example of inertially driven interleaving layers which reach 190 km in length giving cross-equatorial heat fluxes four times larger than realistic doublediffusively driven cases. Although the inertial case is not considered in detail, we speculate that observed interleaving is more likely to be created by inertial than double-diffusive instability
The effect of parallel static and microwave electric fields on excited hydrogen atoms
Motivated by recent experiments we analyse the classical dynamics of a
hydrogen atom in parallel static and microwave electric fields. Using an
appropriate representation and averaging approximations we show that resonant
ionisation is controlled by a separatrix, and provide necessary conditions for
a dynamical resonance to affect the ionisation probability.
The position of the dynamical resonance is computed using a high-order
perturbation series, and estimate its radius of convergence. We show that the
position of the dynamical resonance does not coincide precisely with the
ionisation maxima, and that the field switch-on time can dramatically affect
the ionisation signal which, for long switch times, reflects the shape of an
incipient homoclinic. Similarly, the resonance ionisation time can reflect the
time-scale of the separatrix motion, which is therefore longer than
conventional static field Stark ionisation. We explain why these effects should
be observed in the quantum dynamics.
PACs: 32.80.Rm, 33.40.+f, 34.10.+x, 05.45.Ac, 05.45.MtComment: 47 pages, 20 figure
A shallow water ferrous-hulled shipwreck reveals a distinct microbial community.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Shipwrecks act as artificial reefs and provide a solid surface in aquatic systems for many different forms of life to attach to, especially microbial communities, making them a hotspot of biogeochemical cycling. Depending on the microbial community and surrounding environment, they may either contribute to the wreck’s preservation or deterioration. Even within a single wreck, preservation and deterioration processes may vary, suggesting that the microbial community may also vary. This study aimed to identify the differences through widespread sampling of the microbial communities associated with the Pappy Lane shipwreck (NC shipwreck site #PAS0001), a shallow water ferrous-hulled shipwreck in Pamlico Sound, North Carolina to determine if there are differences across the wreck as well as from its surrounding environment. Loose shipwreck debris, drilled shipcores, surrounding sediment, and seawater samples were collected from the Pappy Lane shipwreck to characterize the microbial communities on and around the shipwreck. Results indicated that the shipwreck samples were more similar to each other than the surrounding sediment and aquatic environments suggesting they have made a specialized niche associated with the shipwreck. There were differences between the microbial community across the shipwreck, including between visibly corroded and non-corroded shipwreck debris pieces. Relative abundance estimates for neutrophilic iron-oxidizing bacteria (FeOB), an organism that may contribute to deterioration through biocorrosion, revealed they are present across the shipwreck and at highest abundance on the samples containing visible corrosion products. Zetaproteobacteria, a known class of marine iron-oxidizers, were also found in higher abundance on shipwreck samples with visible corrosion. A novel Zetaproteobacteria strain, Mariprofundus ferrooxydans O1, was isolated from one of the shipwreck pieces and its genome analyzed to elucidate the functional potential of the organism. In addition to iron oxidation pathways, the isolate has the genomic potential to perform carbon fixation in both high and low oxygen environments, as well as perform nitrogen fixation, contributing to the overall biogeochemical cycling of nutrients and metals in the shipwreck ecosystem. By understanding the microbial communities associated with shallow water ferrous-hulled shipwrecks, better management strategies and preservation plans can be put into place to preserve these artificial reefs and non-renewable cultural resources.ECU Open Access Publishing Support Fun
Step Position Distributions and the Pairwise Einstein Model for Steps on Crystal Surfaces
The Pairwise Einstein Model (PEM) of steps not only justifies the use of the
Generalized Wigner Distribution (GWD) for Terrace Width Distributions (TWDs),
it also predicts a specific form for the Step Position Distribution (SPD),
i.e., the probability density function for the fluctuations of a step about its
average position. The predicted form of the SPD is well approximated by a
Gaussian with a finite variance. However, the variance of the SPD measured from
either real surfaces or Monte Carlo simulations depends on , the
length of step over which it is calculated, with the measured variance
diverging in the limit . As a result, a length scale
can be defined as the value of at which the measured and
theoretical SPDs agree. Monte Carlo simulations of the terrace-step-kink model
indicate that , where is the correlation
length in the direction parallel to the steps, independent of the strength of
the step-step repulsion. can also be understood as the length over
which a {\em single} terrace must be sampled for the TWD to bear a "reasonable"
resemblence to the GWD.Comment: 4 pages, 3 figure
AGN and starbursts at high redshift: High resolution EVN radio observations of the Hubble Deep Field
We present deep, wide-field European VLBI Network (EVN) 1.6 GHz observations
of the Hubble Deep Field (HDF) region with a resolution of 0.025 arcseconds.
Above the 210 microJy/beam (5sigma) detection level, the EVN clearly detects
two radio sources in a field that encompasses the HDF and part of the Hubble
Flanking Fields (HFF). The sources detected are: VLA J123644+621133 (a z=1.013,
low-luminosity FR-I radio source located within the HDF itself) and VLA
J123642+621331 (a dust enshrouded, optically faint, z=4.424 starburst system).
A third radio source, J123646+621404, is detected at the 4sigma level. The VLBI
detections of all three sources suggest that most of the radio emission of
these particular sources (including the dusty starburst) is generated by an
embedded AGN.Comment: 4 pages, 1 figure; Accepted by Astron. & Astrophys Letters ... See
http://www.nfra.nl/~mag/hdf_evn.htm
The One-loop Open Superstring Massless Five-point Amplitude with the Non-Minimal Pure Spinor Formalism
We compute the massless five-point amplitude of open superstrings using the
non-minimal pure spinor formalism and obtain a simple kinematic factor in pure
spinor superspace, which can be viewed as the natural extension of the
kinematic factor of the massless four-point amplitude. It encodes bosonic and
fermionic external states in supersymmetric form and reduces to existing
bosonic amplitudes when expanded in components, therefore proving their
equivalence. We also show how to compute the kinematic structures involving
fermionic states.Comment: 38 pages, harvmac TeX, v2: fix typo in (4.2) and add referenc
A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function
The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC)
of e+e- -> hadrons is calculated to high precision and the results are shown to
be larger than previously reported. The consistency with the leading logarithm
approximation and the accurate cancellation of infrared singularities exhibited
by the new calculation suggest that it is reliable. We offer evidence that the
source of the disagreement with previous results lies in the regulation of
double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper
as PostScript file (125 kB) available at:
http://www.phys.washington.edu/~clay/eecpaper1/paper.htm
Advancing the Evidence Base of Sport for Development: A New Open-Access, Peer-Reviewed Journal
We are pleased to release the first edition of the Journal of Sport for Development (JSFD) and we would like to take this opportunity to briefly describe its origins and objectives. In doing so, we endeavour to clarify for researchers, implementers, funders and policy-makers how we believe JSFD fits into the expanding sport for development (SFD) landscape. It is widely accepted that the United Nations International Year of Sport and Physical Education (IYSPE) in 2005 was an advocacy success and sparked a mass expansion in the SFD sector.1 This built on several previous international resolutions that recognised recreational play as a human right and emphasised the social potential of sport.2-9 Over the last decade, SFD has enjoyed widespread and international growth, in terms of resources, constituents, and public awareness.10 During this period several entities have attempted to define and demarcate the SFD sector. We believe that establishing a common definition is a critical step towards unifying a diverse range of stakeholders, many of which separately articulate the role of sport for social change and peace. However, we prefer to view these areas as integral parts of the sector and have adapted a previously described broad and inclusive definition for SFD
Perceived acceptability of partial enteral nutrition (PEN) using oral nutritional supplement drinks in adolescent and adult Crohn’s Disease outpatients: a feasibility study
BACKGROUND AND AIMS: Studies, mainly in Japanese cohorts, have shown that partial enteral nutrition (PEN) including oral nutritional supplement (ONS) drinks can prolong disease remission and increase drug effectiveness in Crohn’s disease (CD). Acceptability is a key feasibility parameter to determine whether PEN is a viable treatment option in UK CD patients. We report the results of a single centre cross-sectional feasibility study carried out to investigate perceived acceptability of PEN using ONS drinks and whether ONS preference varies with sex, nutritional status or phenylthiocarbamide (PTC) sensitivity. METHODS: Patients with a confirmed CD diagnosis were recruited using convenience sampling from an adult and adolescent gastroenterology outpatient clinic over 3 years. Blind taste testing of 5 polymeric ONS drinks was conducted using a validated 9-point hedonic rating scale followed by completion of the acceptability questionnaire based on the preferred ONS drink. A subset of patients took home the preferred ONS for a 7-day study. RESULTS: 105 CD patients (55 males), aged 34.9 (±15.4) years were recruited and 28 patients completed the 7-day ONS study. Overall impression scores did not significantly vary with nutritional status, sex, BMI, handgrip strength (HGS), mid-upper arm circumference (MUAC) or PTC sensitivity. Ensure plus™ milkshake rated highest for overall impression (6.5, p=<0.0001) and all other organoleptic properties (p<0.0001). The main perceived benefits of using ONS drinks as PEN related to assurance of nutrient intake (89.3%), convenience (85.7%), and improvement of gut symptoms (84.6%). The main perceived barriers related to reduction in pleasure from eating and drinking (55.6%), struggle with drink storage (53.6%) and increased tiredness than if eating 3 solid meals daily (52%%). 64.8% of patients would consider using PEN as a maintenance treatment option. 81.0% of patients felt confident about consuming ONS drinks daily as PEN for three months but this dropped to 63.8% and 37.1% at 6 and 12 months, respectively. There was a significant drop in perceived ease of use as PEN after the 7-day ONS study (P=0.01). CONCLUSION: Use of ONS drinks as PEN have high perceived benefits and appear to be a feasible option for short-term use of 3-6 months in CD patients. However, confidence in long-term use of ONS drinks as PEN is low mainly due to the perceived social impact. Future studies should assess longer trial periods and volume of ONS drinks to increase the validity of these findings
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