3,620 research outputs found
Comparison of uniform perturbation solutions and numerical solutions for some potential flows past slender bodies
Approximate solutions for potential flow past an axisymmetric slender body and past a thin airfoil are calculated using a uniform perturbation method and then compared with either the exact analytical solution or the solution obtained using a purely numerical method. The perturbation method is based upon a representation of the disturbance flow as the superposition of singularities distributed entirely within the body, while the numerical (panel) method is based upon a distribution of singularities on the surface of the body. It is found that the perturbation method provides very good results for small values of the slenderness ratio and for small angles of attack. Moreover, for comparable accuracy, the perturbation method is simpler to implement, requires less computer memory, and generally uses less computation time than the panel method. In particular, the uniform perturbation method yields good resolution near the regions of the leading and trailing edges where other methods fail or require special attention
The 8 o'clock Arc: A Serendipitous Discovery of a Strongly Lensed Lyman Break Galaxy in the SDSS DR4 Imaging Data
We report on the serendipitous discovery of the brightest Lyman Break Galaxy
(LBG) currently known, a galaxy at z=2.73 that is being strongly lensed by the
z=0.38 Luminous Red Galaxy (LRG) SDSS J002240.91+143110.4. The arc of this
gravitational lens system, which we have dubbed the "8 o'clock arc" due to its
time of discovery, was initially identified in the imaging data of the Sloan
Digital Sky Survey Data Release 4 (SDSS DR4); followup observations on the
Astrophysical Research Consortium (ARC) 3.5m telescope at Apache Point
Observatory confirmed the lensing nature of this system and led to the
identification of the arc's spectrum as that of an LBG. The arc has a spectrum
and a redshift remarkably similar to those of the previous record-holder for
brightest LBG (MS 1512-cB58, a.k.a "cB58"), but, with an estimated total
magnitude of (g,r,i) = (20.0,19.2,19.0) and surface brightness of
(mu_g,mu_r,mu_i) = (23.3, 22.5, 22.3) mag/arcsec^2, the 8 o'clock arc is thrice
as bright. The 8 o'clock arc, which consists of three lensed images of the LBG,
is 162deg (9.6arcsec) long and has a length-to-width ratio of 6:1. A fourth
image of the LBG -- a counter-image -- can also be identified in the ARC 3.5m
g-band images. A simple lens model for the system assuming a singular
isothermal ellipsoid potential yields an Einstein radius of 2.91+/-0.14 arcsec,
a total mass for the lensing LRG (within the (10.6+/-0.5)/h kpc enclosed by the
lensed images) of 1.04x10^12/h Msun, and a magnification factor for the LBG of
12.3(+15/-3.6). The LBG itself is intrinsically quite luminous (approximately
6L*) and shows indications of massive recent star formation, perhaps as high as
160/h Msun/year.Comment: 4 pages 5 figures, submitted to ApJ Letter
A New Limit on the Antiproton Lifetime
Measurements of the cosmic ray pbar/p ratio are compared to predictions from
an inhomogeneous disk-diffusion model of pbar production and propagation within
the Galaxy, combined with a calculation of the modulation of the interstellar
cosmic ray spectra as the particles propagate through the heliosphere to the
Earth. The predictions agree with the observed pbar/p spectrum. Adding a finite
pbar lifetime to the model, we obtain the limit tau_pbar > 0.8 Myr (90 % C.L.).Comment: 13 pages, 3 encapsulated Postscript figures, uses AASTeX; accepted by
Astrophysical Journal; minor change
Fecundity of Blue Crab, Callinectes Sapidus, in Chesapeake Bay: Biological, Statistical and Management Considerations
Ovigerous blue crabs were collected from the mouth of Chesapeake Bay during the 1986 and 1987 spawning seasons. Mean carapace width was 14.7 cm; mean fecundity was 3.2×106 eggs. Fecundity was significantly related to carapace width, and did not vary significantly with developmental stage of the eggs. Mean fecundities were 2.6×106 eggs in 1986, and 4.0×106 eggs in 1987. An additive model with year and size effects described the observed fecundities reasonably well, was compact, and was easier to interpret than a multiplicative model. To fit a more general model without year effects, the authors took the mean of 1986 and 1987 results, and modeled fecundity as E=-2.25+0.38W, where E is predicted fecundity (106 eggs), and W is carapace width (cm)
Estimates of Spawning Stock Size of Blue Crab, Callinectes Sapidus, in Chesapeake Bay, 1986-1987
The 1986 spawning stock exhibited a single abundance peak, increasing from 1.0×105 individuals in early July to 9.3×106 in late July, maintaining high levels throughout the summer, and declining in the fall to 7.4×105 individuals. The 1987 spawning stock showed 2 peaks of abundance. The population reached the lesser peak, 1.0×106 individuals, in late July; the greater peak, 1.5×106, in late August. By late September, the population had declined to 6.5×105 individuals. The peak abundance of the 1987 female spawning stock was only 16% as great as the peak abundance in 1986; the 1987 spawning stock size in 1986. Variability of this magnitude calls for continued monitoring and watchful management, to prevent fishing pressure from exceeding the reproductive capacity of the stock
The effectiveness of interventions in workplace health promotion as to maintain the working capacity of health care personal
Background: The increasing proportion of elderly people with respective care requirements and within the total population stands against aging personnel and staff reduction in the field of health care where employees are exposed to high load factors. Health promotion interventions may be a possibility to improve work situations and behavior. Methods: A systematic literature search is conducted in 32 databases limited to English and German publications since 1990. Moreover, internet-searches are performed and the reference lists of identified articles are scanned. The selection of literature was done by two reviewers independently according to inclusion and exclusion criteria. Data extraction and tables of evidence are verified by a second expert just like the assessment of risk of bias by means of the Cochrane Collaboration’s tool. Results: We identified eleven intervention studies and two systematic reviews. There were three randomized controlled trials (RCT) and one controlled trial without randomization (CCT) on the improvement of physical health, four RCT and two CCT on the improvement of psychological health and one RCT on both. Study duration ranged from four weeks to two years and the number of participants included from 20 to 345, with a median of 56. Interventions and populations were predominantly heterogeneous. In three studies intervention for the improvement of physical health resulted in less complaints and increased strength and flexibility with statistically significant differences between groups. Regarding psychological health interventions lead to significantly decreased intake of analgesics, better stress management, coping with workload, communication skills and advanced training. Discussion: Taking into consideration the small to very small sample sizes, other methodological flaws like a high potential of bias and poor quality of reporting the validity of the results has to be considered as limited. Due to the heterogeneity of health interventions, study populations with differing job specializations and different lengths of study durations and follow-up periods, the comparison of results would not make sense. Conclusions: Further research is necessary with larger sample sizes, with a sufficient study duration and follow-up, with a lower risk of bias, by considering of relevant quality criteria and with better reporting in publications
Breaking Eight-fold Degeneracies in Neutrino CP Violation, Mixing, and Mass Hierarchy
We identify three independent two-fold parameter degeneracies (\delta,
\theta_{13}), sgn(\delta m^2_{31}) and (\theta_{23}, \pi/2-\theta_{23})
inherent in the usual three-neutrino analysis of long-baseline neutrino
experiments, which can lead to as much as an eight-fold degeneracy in the
determination of the oscillation parameters. We discuss the implications these
degeneracies have for detecting CP violation and present criteria for breaking
them. A superbeam facility with a baseline at least as long as the distance
between Fermilab and Homestake (1290 km) and a narrow band beam with energy
tuned so that the measurements are performed at the first oscillation peak can
resolve all the ambiguities other than the (\theta_{23}, \pi/2-\theta_{23})
ambiguity (which can be resolved at a neutrino factory) and a residual (\delta,
\pi-\delta) ambiguity. However, whether or not CP violation occurs in the
neutrino sector can be ascertained independently of the latter two ambiguities.
The (\delta,\pi-\delta) ambiguity can be eliminated by performing a second
measurement to which only the \cos\delta terms contribute. The hierarchy of
mass eigenstates can be determined at other oscillation peaks only in the most
optimistic conditions, making it necessary to use the first oscillation
maximum. We show that the degeneracies may severely compromise the ability of
the proposed SuperJHF-HyperKamiokande experiment to establish CP violation. In
our calculations we use approximate analytic expressions for oscillation
probabilitites that agree with numerical solutions with a realistic Earth
density profile.Comment: Revtex (singlespaced), 35 pages, 15 postscript figures, uses
psfig.st
On the complementarity of Hyper-K and LBNF
The next generation of long-baseline experiments is being designed to make a
substantial step in the precision of measurements of neutrino-oscillation
probabilities. Two qualitatively different proposals, Hyper-K and LBNF, are
being considered for approval. This document outlines the complimentarity
between Hyper-K and LBNF.Comment: 5 pager
Heavy quark production via leptoquarks at a neutrino factory
The proposed neutrino factory (NF) based on a muon storage ring (MSR) is an
ideal place to look for heavy quark production via neutral current (NC) and
charged current (CC) interactions. In this article, we address the issue of
contribution coming from mediating leptoquarks (LQ) in interactions leading to the production of at a
MSR and investigate the region where LQ interactions are significant in the
near-site experiments.Comment: 12 pages latex, 10 ps figures, uses axocolour.sty, Slightly revised
version to appear in PR
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