2,315 research outputs found
Flow establishment in a generic scramjet combustor
The establishment of a quasi-steady flow in a generic scramjet combustor was studied for the case of a time varying inflow to the combustor. Such transient flow is characteristic of the reflected shock tunnel and expansion tube test facilities. Several numerical simulations of hypervelocity flow through a straight duct combustor with either a side wall step fuel injector or a centrally located strut injector are presented. Comparisons were made between impulsively started but otherwise constant flow conditions (typical of the expansion tube or tailored operations of the reflected shock tunnel) and the relaxing flow produced by the 'undertailored' operations of the reflected shock tunnel. Generally the inviscid flow features, such as the shock pattern and pressure distribution, were unaffected by the time varying inlet conditions and approached steady state in approx. the times indicated by experimental correlations. However, viscous features, such as heat transfer and skin friction, were altered by the relaxing inlet flow conditions
Cryptorchidism and hypospadias in sons of gardeners and farmers.
Cryptorchidism and hypospadias have been related to prenatal estrogen exposure in animal models. Some chemicals used in farming and gardening have been shown to possess estrogenic and other hormone-disrupting effects. Earlier studies have indicated increased risks of urogenital malformations in the sons of pesticide appliers. In the present study, parental occupation in the farming and gardening industry among 6,177 cases of cryptorchidism, 1,345 cases of hypospadias, and 23,273 controls, born live from 1983 to 1992 in Denmark, was investigated in a register-based case-control study. A significantly increased risk of cryptorchidism but not hypospadias was found in sons of women working in gardening (adjusted odds ratio = 1.67; 95% confidence interval, 1.14-2.47). The risks were not increased in sons of men working in farming or gardening. The increased risk of cryptorchidism among sons of female gardeners could suggest an association with prenatal exposure to occupationally related chemicals
Complications After Systematic, Random and Image-guided Prostate Biopsy
CONTEXT: Prostate biopsy (PB) represents the gold standard method to confirm the presence of cancer. In addition to traditional random or systematic approaches, a magnetic resonance imaging (MRI)-guided technique has been introduced recently. OBJECTIVE: To perform a systematic review of complications after transrectal ultrasound (TRUS)-guided, transperineal, and MRI-guided PB. EVIDENCE ACQUISITION: We performed a systematic literature search of Web of Science, Embase, and Scopus databases up to October 2015, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Complications and mortality following random, systematic, and image-guided PBs were reviewed. Eighty-five references were included. EVIDENCE SYNTHESIS: The most frequent complication after PB was minor and self-limiting bleeding (hematuria and hematospermia), regardless of the biopsy approach. Occurrence of rectal bleeding was comparable for traditional TRUS-guided and image-guided PBs. Almost 25% of patients experienced lower urinary tract symptoms, but only a few had urinary retention, with higher rates after a transperineal approach. Temporary erectile dysfunction was not negligible, with a return to baseline after 1-6 mo. The incidence of infective complications is increasing, with higher rates among men with medical comorbidities and older age. Transperineal and in-bore MRI-targeted biopsy may reduce the risk of severe infectious complications. Mortality after PB is uncommon, regardless of biopsy technique. CONCLUSIONS: Complications after PB are frequent but often self-limiting. The incidence of hospitalization due to severe infections is continuously increasing. The patient's general health status, risk factors, and likelihood of antimicrobial resistance should be carefully appraised before scheduling a PB. PATIENT SUMMARY: We reviewed the variety and incidence of complications after prostate biopsy. Even if frequent, complications seldom represent a problem for the patient. The most troublesome complications are infections. To minimize this risk, the patient's medical condition should be carefully evaluated before biopsy
Gauged N=4 supergravities
We present the gauged N=4 (half-maximal) supergravities in four and five
spacetime dimensions coupled to an arbitrary number of vector multiplets. The
gaugings are parameterized by a set of appropriately constrained constant
tensors, which transform covariantly under the global symmetry groups SL(2) x
SO(6,n) and SO(1,1) x SO(5,n), respectively. In terms of these tensors the
universal Lagrangian and the Killing Spinor equations are given. The known
gaugings, in particular those originating from flux compactifications, are
incorporated in the formulation, but also new classes of gaugings are found.
Finally, we present the embedding chain of the five dimensional into the four
dimensional into the three dimensional gaugings, thereby showing how the
deformation parameters organize under the respectively larger duality groups.Comment: 36 pages, v2: references added, comments added, v3: published
version, references added, typos corrected, v4: sign mistakes in footnote 4
and equation (2.13) correcte
The evolution of luminosity, colour and the mass-to-luminosity ratio of Galactic open clusters: comparison of discrete vs. continuous IMF models
(abridged) We found in previous studies that standard Simple Stellar
Population (SSP) models are unable to describe or explain the colours of
Galactic open clusters both in the visible and in the NIR spectral range. (...)
We construct a numerical SSP-model, with an underlying Salpeter IMF, valid
within an upper and lower stellar mass range, and with total masses
typical of open clusters. We assume that the mass
loss from a cluster is provided by mass loss from evolved stars and by the
dynamical evaporation of low-mass members due to two-body relaxation. The data
for the latter process were scaled to the models from high-resolution N-body
calculations. We also investigate how a change of the -limit influences
magnitudes and colours of clusters of a given mass and derive a necessary
condition for a luminosity and colour flash. The discreteness of the IMF leads
to bursts in magnitude and colour of model clusters at moments when red
supergiants or giants appear and then die. The amplitude of the burst depends
on the cluster mass and on the spectral range; it is strongly increased in the
NIR compared to optical passbands. In the discrete case, variations of the
parameter are able to substantially change the magnitude-age and
-age relations. For the colours, the lowering of considerably
amplifies the discreteness effect. The influence of dynamical mass loss on
colour and magnitude is weak, although it provides a change of the slopes of
the considered relations, improving their agreement with observations. For the
Galactic open clusters we determined luminosity and tidal mass independent of
each other. The derived mass-to-luminosity ratio shows, on average, an increase
with cluster age in the optical, but gradually declines with age in the NIR.
The observed flash statistics can be used to constrain in open clusters.Comment: 15 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
The general gaugings of maximal d=9 supergravity
We use the embedding tensor method to construct the most general maximal
gauged/massive supergravity in d=9 dimensions and to determine its extended
field content. Only the 8 independent deformation parameters (embedding tensor
components, mass parameters etc.) identified by Bergshoeff \textit{et al.} (an
SL(2,R) triplet, two doublets and a singlet can be consistently introduced in
the theory, but their simultaneous use is subject to a number of quadratic
constraints. These constraints have to be kept and enforced because they cannot
be used to solve some deformation parameters in terms of the rest. The
deformation parameters are associated to the possible 8-forms of the theory,
and the constraints are associated to the 9-forms, all of them transforming in
the conjugate representations. We also give the field strengths and the gauge
and supersymmetry transformations for the electric fields in the most general
case. We compare these results with the predictions of the E11 approach,
finding that the latter predicts one additional doublet of 9-forms, analogously
to what happens in N=2, d=4,5,6 theories.Comment: Latex file, 43 pages, reference adde
Universal Negative Poisson Ratio of Self Avoiding Fixed Connectivity Membranes
We determine the Poisson ratio of self-avoiding fixed-connectivity membranes,
modeled as impenetrable plaquettes, to be sigma=-0.37(6), in statistical
agreement with the Poisson ratio of phantom fixed-connectivity membranes
sigma=-0.32(4). Together with the equality of critical exponents, this result
implies a unique universality class for fixed-connectivity membranes. Our
findings thus establish that physical fixed-connectivity membranes provide a
wide class of auxetic (negative Poisson ratio) materials with significant
potential applications in materials science.Comment: 4 pages, 3 figures, LaTeX (revtex) Published version - title changed,
one figure improved and one reference change
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