814 research outputs found
Revisiting the 26.5°C Sea Surface Temperature Threshold for Tropical Cyclone Development
Abstract
A high sea surface temperature is generally accepted to be one of the necessary ingredients for tropical cyclone development, indicative of the potential for surface heat and moisture fluxes capable of fueling a self-sustaining circulation. Although the minimum 26.5°C threshold for tropical cyclogenesis has become a mainstay in research and education, the fact that a nonnegligible fraction of storm formation events (about 5%) occur over cooler waters casts some doubt on the robustness of this estimate. Tropical cyclogenesis over subthreshold sea surface temperatures is associated with low tropopause heights, indicative of the presence of a cold trough aloft. To focus on this type of development environment, the applicability of the 26.5°C threshold is investigated for tropical transitions from baroclinic precursor disturbances in all basins between 1989 and 2013. Although the threshold performs well in the majority of cases without appreciable environmental baroclinicity, the potential for development is underestimated by up to 27% for systems undergoing tropical transition. An alternative criterion of a maximum 22.5°C difference between the tropopause-level and 850-hPa equivalent potential temperatures (defined as the coupling index) is proposed for this class of development. When combined with the standard 26.5°C sea surface temperature threshold for precursor-free environments, error rates are reduced to 3%–6% for all development types. The addition of this physically relevant representation of the deep-tropospheric state to the ingredients-based conceptual model for tropical cyclogenesis improves the representation of the important tropical transition-based subset of development events.</jats:p
Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data
This paper presents data from first GPS measurements of global response of
the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The
analysis used novel technology of a global detection of ionospheric effects
from solar flares (GLOBDET) as developed by one of the authors (Afraimovich E.
L.). The essence of the method is that use is made of appropriate filtering and
a coherent processing of variations in total electron content (TEC) in the
ionosphere which is determined from GPS data, simultaneously for the entire set
of visible (over a given time interval) GPS satellites at all stations used in
the analysis. It was found that fluctuations of TEC, obtained by removing the
linear trend of TEC with a time window of about 5 min, are coherent for all
stations and beams to the GPS satellites on the dayside of the Earth. The time
profile of TEC responses is similar to the time behavior of hard X-ray emission
variations during flares in the energy range 25-35 keV if the relaxation time
of electron density disturbances in the ionosphere of order 50-100 s is
introduced. No such effect on the nightside of the Earth has been detected yet.Comment: EmTeX-386, 13 pages, 5 figure
The Impact of Ghrelin on the Survival and Efficacy of Dopaminergic Fetal Grafts in the 6-OHDA-Lesioned Rat
Ghrelin is a peptide produced in the gut with a wide range of physiological functions. Recent studies have suggested it may have potential as a neuroprotective agent in models of Parkinson’s disease, reducing the impact of toxic challenges on the survival of nigral dopaminergic neurons. The presence of the ghrelin receptor (GHSR1a) on the dopaminergic neurons of the substantia nigra raises the possibility that a potential application for this property of ghrelin may be as an adjunctive neuroprotective agent to enhance and support the survival and integration of dopaminergic cells transplanted into the striatum. Thus far, inconsistent outcomes in clinical trials for fetal cell transplantation have been linked to low rates of cell survival which we hypothesize could be ameliorated by the presence of ghrelin. To explore this, we confirmed the expression of the GHSR1a and related enzymes on e14 ventral mesencephalon. To determine a functional effect, five groups of female Sprague–Dawley rats received a unilateral 6-OHDA lesion to the medial forebrain bundle and four received an intrastriatal graft of e14 ventral mesencephalic cells. Grafted rats received saline; acyl-ghrelin (10 µg/kg); acyl-ghrelin (50 µg/kg) or the ghrelin agonist JMV-2894 (160 µg/kg) i.p. for 8 weeks. An effect of ghrelin at low dose on hippocampal neurogenesis indicated blood–brain barrier penetrance and attainment of biologically relevant levels but neither acyl-ghrelin nor JMV-2894 improved graft survival or efficacy
Perceptions of alcohol health warning labels in a large international cross-sectional survey of people who drink alcohol
Aims
This paper aimed to explore perceptions of alcohol health warning labels amongst a large international sample of people who drink alcohol.
Methods
The Global Drug Survey (GDS) is the world’s largest annual cross sectional survey of drug use. Seven health warning labels were presented (relating to heart disease, liver, cancer, calories, violence, taking two days off and the myth of benefits to moderate drinking). People were asked if they were aware of the information, believed it, if it was personally relevant, and if it would change their drinking. This paper included data from 75,969 respondents from 29 countries/regions who reported the use of alcohol in the last 12 months, collected during November–December 2017 (GDS2018).
Results
The fact that drinking less can reduce the risk of seven types of cancer was the least well known, and yet was demonstrated to encourage almost 40% of drinkers to consider drinking less. Women and high risk drinkers were more likely to indicate they would reduce their drinking in response to all labels. Personal relevance was identified as a key predictor of individual responses.
Conclusion
Findings highlight the potential of a range of health messages displayed on alcoholic beverages to raise awareness of alcohol-related harms and potentially support a reduction in drinking. Further research should explore what influences personal relevance of messages as this may be a barrier to effectiveness
The use of GPS-arrays in detecting shock-acoustic waves generated during rocket launchings
This paper is concerned with the form and dynamics of shock-acoustic waves
(SAW) generated during rocket launchings. We have developed a method for
determining SAW parameters (including angular characteristics of the wave
vector, and the SAW phase velocity, as well as the direction towards the
source) using GPS-arrays whose elements can be chosen out of a large set of
GPS-stations of the global GPS network. The application of the method is
illustrated by a case study of ionospheric effects from launchings of launch
vehicles (LV) Proton and Space Shuttle from space-launch complexes Baikonur and
Kennedy Space Center (KSC) in 1998 and 1999 (a total of five launchings). The
study revealed that, in spite of a difference of LV characteristics, the
ionospheric response for all launchings had the character of an N - wave
corresponding to the form of a shock wave, regardless of the disturbance source
(rocket launchings, industrial explosions). The SAW period T is 270--360 s, and
the amplitude exceeds the standard deviation of TEC background fluctuations in
this range of periods under quiet and moderate geomagnetic conditions by
factors of 2 to 5 as a minimum. The angle of elevation of the SAW wave vector
varies from 30 degree to 60 degree, and the SAW phase velocity (900-1200 m/s)
approaches the sound velocity at heights of the ionospheric F-region maximum.Comment: EmTeX-386, 23 pages, 6 figure
Scattering of light and atoms in a Fermi-Dirac gas with BCS pairing
We theoretically study the optical properties of a Fermi-Dirac gas in the
presence of a superfluid state. We calculate the leading quantum-statistical
corrections to the standard column density result of the electric
susceptibility. We also consider the Bragg diffraction of atoms by means of
light-stimulated transitions of photons between two intersecting laser beams.
Bardeen-Cooper-Schrieffer pairing between atoms in different internal levels
magnifies incoherent scattering processes. The absorption linewidth of a
Fermi-Dirac gas is broadened and shifted. Bardeen-Cooper-Schrieffer pairing
introduces a collisional local-field shift that may dramatically dominate the
Lorentz-Lorenz shift. For the case of the Bragg spectroscopy the static
structure function may be significantly increased due to superfluidity in the
nearforward scattering.Comment: 13 pages, 6 figures; to appear in PR
Traveling wave packets of total electron content disturbances as deduced from global GPS network data
We identified a new class of mid-latitude medium-scale traveling ionospheric
disturbances (MS TIDs), viz. traveling wave packets (TWPs) of total electron
content (TEC) disturbances. For the first time, the morphology of TWPs is
presented for 105 days. Using the technique of GPS interferometry of TIDs we
carried out a detailed analysis of the spatial-temporal properties of TWPs by
considering an example of the most conspicuous manifestation of TWPs on October
18, 2001 over California, USA. The velocity and direction of TWPs correspond to
those of mid-latitude MS TIDs obtained previously from analyzing the phase
characteristics of HF radio signals as well as signals from geostationary
satellites and discrete cosmic radio sources.Comment: LaTeX2.09, 28 pages, 9 figure
Vector boson production at hadron colliders: hard-collinear coefficients at the NNLO
We consider QCD radiative corrections to vector-boson production in hadron
collisions. We present the next-to-next-to-leading order (NNLO) result of the
hard-collinear coefficient function for the all-order resummation of
logarithmically-enhanced contributions at small transverse momenta. The
coefficient function controls NNLO contributions in resummed calculations at
full next-to-next-to-leading logarithmic accuracy. The same coefficient
function is used in applications of the subtraction method to perform
fully-exclusive perturbative calculations up to NNLO.Comment: 13, pages, no figures. arXiv admin note: text overlap with
arXiv:1106.465
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
The transverse momentum distribution is computed for inclusive Higgs
boson production at the energy of the CERN Large Hadron Collider. We focus on
the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and
incorporate contributions from the quark-gluon and quark-antiquark channels.
Using an impact-parameter -space formalism, we include all-orders
resummation of large logarithms associated with emission of soft gluons. Our
resummed results merge smoothly at large with the fixed-order
expectations in perturbative quantum chromodynamics, as they should, with no
need for a matching procedure. They show a high degree of stability with
respect to variation of parameters associated with the non-perturbative input
at low . We provide distributions for Higgs boson masses
from to 200 GeV. The average transverse momentum at zero rapidity
grows approximately linearly with mass of the Higgs boson over the range ~GeV. We provide analogous results
for boson production, for which we compute GeV. The
harder transverse momentum distribution for the Higgs boson arises because
there is more soft gluon radiation in Higgs boson production than in
production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in
wording. Published in Phys. Rev. D67, 034026 (2003
Nuclear dependence coefficient for the Drell-Yan and J/ production
Define the nuclear dependence coefficient in terms of ratio
of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon
collisions: . We argue that in small region, the
for the Drell-Yan and J/ production is given by a universal function:\
, where parameters a and b are completely determined by either
calculable quantities or independently measurable physical observables. We
demonstrate that this universal function is insensitive to the
A for normal nuclear targets. For a color deconfined nuclear medium, the
becomes strongly dependent on the A. We also show that our
for the Drell-Yan process is naturally linked to perturbatively
calculated at large without any free parameters, and the
is consistent with E772 data for all .Comment: latex, 28 pages, 10 figures, updated two figures, and add more
discussion
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