5,707 research outputs found
Methane storms as a driver of Titan's dune orientation
Titan's equatorial regions are covered by eastward propagating linear dunes.
This direction is opposite to mean surface winds simulated by Global Climate
Models (GCMs), which are oriented westward at these latitudes, similar to trade
winds on Earth. Different hypotheses have been proposed to address this
apparent contradiction, involving Saturn's gravitational tides, large scale
topography or wind statistics, but none of them can explain a global eastward
dune propagation in the equatorial band. Here we analyse the impact of
equinoctial tropical methane storms developing in the superrotating atmosphere
(i.e. the eastward winds at high altitude) on Titan's dune orientation. Using
mesoscale simulations of convective methane clouds with a GCM wind profile
featuring superrotation, we show that Titan's storms should produce fast
eastward gust fronts above the surface. Such gusts dominate the aeolian
transport, allowing dunes to extend eastward. This analysis therefore suggests
a coupling between superrotation, tropical methane storms and dune formation on
Titan. Furthermore, together with GCM predictions and analogies to some
terrestrial dune fields, this work provides a general framework explaining
several major features of Titan's dunes: linear shape, eastward propagation and
poleward divergence, and implies an equatorial origin of Titan's dune sand.Comment: Published online on Nature Geoscience on 13 April 201
The partitioning of poleward energy transport response between the atmosphere and Ekman flux to prescribed surface forcing in a simplified GCM
Recent studies have indicated that ocean circulation damps the atmospheric energy transport response to hemispherically differential energy perturbations, thereby muting the shifts of the Inter-Tropical Convergence Zone (ITCZ). Here, we focus on the potential role of Ekman heat transport in modulating this atmospheric response. An idealized representation of Ekman-driven heat transport (FE) is included in an aquaplanet slab ocean coupled to a gray radiation atmospheric model. We first alter the strength of FE in the control climate by tuning the gross stability of the Ekman layer SE. For a wide range of FE, the total poleward transport of energy remains nearly unchanged, but the ocean transports an increasing share for larger SE. The control climate is then perturbed by adding surface cooling in the Southern Hemisphere and warming in the Northern Hemisphere. The Ekman coupling damps the atmospheric energy transport response, as in previous coupled model experiments with full ocean dynamics. The ratio of the changes in Ekman to atmospheric energy transport is determined by the ratio of the gross stability in the Ekman layer to the atmosphere in the control climate, and is insensitive to the amplitude and location of forcing. We find that an unrealistically large SE is needed to reproduce the ratio of the changes in cross-equatorial oceanic to atmospheric energy transport in fully coupled models. The limited damping effect of Ekman transport highlights the need to examine the roles of deep circulation and subtropical gyres, as well as ocean heat uptake processes
Distinct Binding and Immunogenic Properties of the Gonococcal Homologue of Meningococcal Factor H Binding Protein
Neisseria meningitidis is a leading cause of sepsis and meningitis. The bacterium recruits factor H (fH), a negative regulator of the complement system, to its surface via fH binding protein (fHbp), providing a mechanism to avoid complement-mediated killing. fHbp is an important antigen that elicits protective immunity against the meningococcus and has been divided into three different variant groups, V1, V2 and V3, or families A and B. However, immunisation with fHbp V1 does not result in cross-protection against V2 and V3 and vice versa. Furthermore, high affinity binding of fH could impair immune responses against fHbp. Here, we investigate a homologue of fHbp in Neisseria gonorrhoeae, designated as Gonococcal homologue of fHbp (Ghfp) which we show is a promising vaccine candidate for N. meningitidis. We demonstrate that Gfhp is not expressed on the surface of the gonococcus and, despite its high level of identity with fHbp, does not bind fH. Substitution of only two amino acids in Ghfp is sufficient to confer fH binding, while the corresponding residues in V3 fHbp are essential for high affinity fH binding. Furthermore, immune responses against Ghfp recognise V1, V2 and V3 fHbps expressed by a range of clinical isolates, and have serum bactericidal activity against N. meningitidis expressing fHbps from all variant groups
The Sister-Chromatid Exchange Assay in Human Cells
The semiconservative nature of DNA replication allows the differential labeling of sister chromatids that isthe fundamental requirement to perform the sister-chromatid exchange (SCE) assay. SCE assay is apowerful technique to visually detect the physical exchange of DNA between sister chromatids. SCEscould result as a consequence of DNA damage repair by homologous recombination (HR) during DNAreplication. Here, we provide the detailed protocol to perform the SCE assay in cultured human cells. Cellsare exposed to the thymidine analog 5-bromo-20-deoxyuridine (BrdU) during two cell cycles, resulting inthe two sister chromatids having differential incorporation of the analog. After metaphase spreads prepara-tion and further processing, SCEs are nicely visualized under the microscope
Cardiac-Specific Disruption of Bin1 in Mice Enables a Model of Stress- and Age-Associated Dilated Cardiomyopathy
Comparative survey of Complementary and Alternative Medicine (CAM) attitudes, use, and information-seeking behaviour among medical students, residents & faculty
BACKGROUND: There is significant and growing national interest for introducing Complementary and Alternative Medicine (CAM) instruction into allopathic medical education. We measured CAM attitudes, use, and information-seeking behaviors as a baseline to evaluate future planned CAM instruction. METHODS: Cross-sectional and longitudinal survey data on CAM attitudes, modality use, and common information resources was collected for (a) medical students (n = 355), (b) interns entering residencies in medical and surgical disciplines (n = 258), and (c) faculty from diverse health professions attending workshops on evidence-based CAM (n = 54). One student cohort was tracked longitudinally in their first, second and third years of training. RESULTS: Compared to medical students and interns, faculty who teach or intend to integrate CAM into their instruction had significantly (p < .0005) more positive attitudes and used CAM modalities significantly (p < .0005) more often. Medical students followed longitudinally showed no change in their already positive attitudes. The 3 survey groups did not differ on the total number of CAM information resources they used. Each group surveyed used about two out of the five common information sources listed, with the Internet and journals most frequently cited. CONCLUSION: Students, interns and a selected faculty group demonstrate positive attitudes toward CAM and frequently use various CAM modalities. CAM instruction should therefore be focused on acquiring knowledge of available CAM modalities and skills to appraise evidence to appropriately advise patients on best approaches to CAM use. Trainees may benefit from exposure to a wider array of CAM information resources
Prehistory of Transit Searches
Nowadays the more powerful method to detect extrasolar planets is the transit
method. We review the planet transits which were anticipated, searched, and the
first ones which were observed all through history. Indeed transits of planets
in front of their star were first investigated and studied in the solar system.
The first observations of sunspots were sometimes mistaken for transits of
unknown planets. The first scientific observation and study of a transit in the
solar system was the observation of Mercury transit by Pierre Gassendi in 1631.
Because observations of Venus transits could give a way to determine the
distance Sun-Earth, transits of Venus were overwhelmingly observed. Some
objects which actually do not exist were searched by their hypothetical
transits on the Sun, as some examples a Venus satellite and an infra-mercurial
planet. We evoke the possibly first use of the hypothesis of an exoplanet
transit to explain some periodic variations of the luminosity of a star, namely
the star Algol, during the eighteen century. Then we review the predictions of
detection of exoplanets by their transits, those predictions being sometimes
ancient, and made by astronomers as well as popular science writers. However,
these very interesting predictions were never published in peer-reviewed
journals specialized in astronomical discoveries and results. A possible
transit of the planet beta Pic b was observed in 1981. Shall we see another
transit expected for the same planet during 2018? Today, some studies of
transits which are connected to hypothetical extraterrestrial civilisations are
published in astronomical refereed journals. Some studies which would be
classified not long ago as science fiction are now considered as scientific
ones.Comment: Submiited to Handbook of Exoplanets (Springer
Age-related hyperkyphosis, independent of spinal osteoporosis, is associated with impaired mobility in older community-dwelling women
While many assume hyperkyphosis reflects underlying spinal osteoporosis and vertebral fractures, our results suggest hyperkyphosis is independently associated with decreased mobility. Hyperyphosis is associated with slower Timed Up and Go performance times and may be a useful clinical marker signaling the need for evaluation of vertebral fracture and falling risk.
While multiple studies have demonstrated negative effects of hyperkyphosis on physical function, none have disentangled the relationship between hyperkyphosis, impaired function, and underlying spinal osteoporosis. The purpose of this study is to determine whether kyphosis, independent of spinal osteoporosis, is associated with mobility on the Timed Up and Go, and to quantify effects of other factors contributing to impaired mobility.
We used data for 3,108 community-dwelling women aged 55-80 years in the Fracture Intervention Trial. All participants had measurements of kyphosis, mobility time on the Timed Up and Go test, height, weight, total hip bone mineral density (BMD), grip strength, and vertebral fractures at baseline visits in 1993. Demographic characteristics included age and smoking status. We calculated mean Timed Up and Go time by quartile of kyphosis. Using multivariate linear regression, we estimated the independent association of kyphosis with mobility time, and quantified effects of other covariates on mobility.
Mean mobility time increased from 9.3 s in the lowest to 10.1 s in the highest quartile of kyphosis. In a multivariate-adjusted model, mobility time increased 0.11 s (p = 0.02) for each standard deviation (11.9°) increase in kyphosis. Longer performance times were significantly associated with increasing age, decreasing grip strength, vertebral fractures, body mass index ≥25, and total hip BMD in the osteoporotic range.
Kyphosis angle is independently associated with decreased mobility on the Timed Up and Go, which is in turn correlated with increased fall risk. Hyperkyphosis may be a useful clinical marker signaling the need for evaluation of vertebral fracture and falling risk
Chromosomes of Theridiidae spiders (Entelegynae): Interspecific karyotype diversity in Argyrodes and diploid number intraspecific variability in Nesticodes rufipes
Theridiidae is a derived family within the Araneoidea clade. In contrast to closely related groups, the 2n(male) = 20+X1 X 2 with acro/telocentric chromosomes is the most widespread karyotype among the theridiid spiders. In this work, the cytogenetic analysis of Argyrodes elevatus revealed original chromosome features different from those previously registered for Theridiidae, including the presence of 2n(male) = 20+X with meta/submetacentric chromosomes. Most individuals of Nesticodes rufipes showed family conserved karyotype characteristics. However, one individual had a 2n(male) = 24 due to the presence of an extra chromosome pair, which exhibited regular behavior and reductional segregation during meiosis. After silver staining, mitotic cells exhibited NORs localized on the terminal regions of the short arms of pairs 2, 3, and 4 of A. elevatus and on the terminal regions of long arms of pair 4 of N. rufipes. The comparative analysis with data from phylogenetically related species allowed the clarification of the origin of the interspecific and intraspecific chromosome variability observed in Argyrodes and in N. rufipes, respectively
The Linear Algebraic Method for Electron-Molecule Collisions
In order to find numerical solutions to many problems in physics, chemistry and engineering it is necessary to place the equations of motion (classical or quantal) of the variables of dynamical interest on a discrete mesh. The formulation of scattering theory in quantum mechanics is no exception and leads to partial differential or integral equations which may only be solved on digital computers. Typical approaches introduce a numerical grid or basis set expansion of the scattering wavefunction in order to reduce `the problem to the solution of a set of algebraic equations. Often it is more convenient to deal with the scattering matrix or phase amplitude rather than the wavefunction but the essential features of the numerics are unchanged. In this section we will formulate the Linear Algebraic Method (LAM) for electron-atom/molecule scattering for a simple, one-dimensional radial potential. This will illustrate the basic approach and enable the uninitiated reader to follow the subsequent discussion of the general, multi-channel, electron-molecule formulation without undue difficulty. We begin by writing the Schroedinger equation for the s-wave scattering of a structureless particle by a short-range, local potential
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