3,269 research outputs found
Champagne Flutes and Brandy Snifters: Modelling Protostellar Outflow-Cloud Chemical Interfaces
A rich variety of molecular species has now been observed towards hot cores
in star forming regions and in the interstellar medium. An increasing body of
evidence from millimetre interferometers suggests that many of these form at
the interfaces between protostellar outflows and their natal molecular clouds.
However, current models have remained unable to explain the origin of the
observational bias towards wide-angled "brandy snifter" shaped outflows over
narrower "champagne flute" shapes in carbon monoxide imaging. Furthermore,
these wide-angled systems exhibit unusually high abundances of the molecular
ion HCO. We present results from a chemo-dynamic model of such regions
where a rich chemistry arises naturally as a result of turbulent mixing between
cold, dense molecular gas and the hot, ionized outflow material. The injecta
drives a rich and rapid ion-neutral chemistry in qualitative and quantitative
agreement with the observations. The observational bias towards wide-angled
outflows is explained naturally by the geometry-dependent ion injection rate
causing rapid dissociation of CO in the younger systems.Comment: Accepted to MNRAS. 12 pages, 8 Figure
Amphibian Immune Defenses against Chytridiomycosis: Impacts of Changing Environments
Eco-immunology is the field of study that attempts to understand the functions of the immune system in the context of the host's environment. Amphibians are currently suffering devastating declines and extinctions in nearly all parts of the world due to the emerging infectious disease chytridiomycosis caused by the chytrid fungus, Batrachochytrium dendrobatidis. Because chytridiomycosis is a skin infection and remains confined to the skin, immune defenses of the skin are critical for survival. Skin defenses include secreted antimicrobial peptides and immunoglobulins as well as antifungal metabolites produced by symbiotic skin bacteria. Low temperatures, toxic chemicals, and stress inhibit the immune system and may impair natural defenses against B. dendrobatidis. Tadpoles' mouth parts can be infected by B. dendrobatidis. Damage to the mouth parts can impair growth, and the affected tadpoles maintain the pathogen in the environment even when adults have dispersed. Newly metamorphosing frogs appear to be especially vulnerable to infection and to the lethal effects of this pathogen because the immune system undergoes a dramatic reorganization at metamorphosis, and postmetamorphic defenses are not yet mature. Here we review our current understanding of amphibian immune defenses against B. dendrobatidis and the ability of the pathogen to resist those defenses. We also briefly review what is known about the impacts of temperature, environmental chemicals, and stress on the host-pathogen interactions and suggest future directions for researc
Parametric Amplification of Nonlinear Response of Single Crystal Niobium
Giant enhancement of the nonlinear response of a single crystal Nb sample,
placed in {\it a pumping ac magnetic field}, has been observed experimentally.
The experimentally observed amplitude of the output signal is about three
orders of magnitude higher than that seen without parametric pumping. The
theoretical analysis based on the extended double well potential model provides
a qualitative explanation of the experimental results as well as new
predictions of two bifurcations for specific values of the pumping signal.Comment: 6 pages, 10 figure
Characterization of the stretched exponential trap-time distributions in one-dimensional coupled map lattices
Stretched exponential distributions and relaxation responses are encountered
in a wide range of physical systems such as glasses, polymers and spin glasses.
As found recently, this type of behavior occurs also for the distribution
function of certain trap time in a number of coupled dynamical systems. We
analyze a one-dimensional mathematical model of coupled chaotic oscillators
which reproduces an experimental set-up of coupled diode-resonators and
identify the necessary ingredients for stretched exponential distributions.Comment: 8 pages, 8 figure
Low energy polarization sensitivity of the Gas Pixel Detector
An X-ray photoelectric polarimeter based on the Gas Pixel Detector has been
proposed to be included in many upcoming space missions to fill the gap of
about 30 years from the first (and to date only) positive measurement of
polarized X-ray emission from an astrophysical source. The estimated
sensitivity of the current prototype peaks at an energy of about 3 keV, but the
lack of readily available polarized sources in this energy range has prevented
the measurement of detector polarimetric performances.
In this paper we present the measurement of the Gas Pixel Detector
polarimetric sensitivity at energies of a few keV and the new, light, compact
and transportable polarized source that was devised and built to this aim.
Polarized photons are produced, from unpolarized radiation generated with an
X-ray tube, by means of Bragg diffraction at nearly 45 degrees.
The employment of mosaic graphite and flat aluminum crystals allow the
production of nearly completely polarized photons at 2.6, 3.7 and 5.2 keV from
the diffraction of unpolarized continuum or line emission. The measured
modulation factor of the Gas Pixel Detector at these energies is in good
agreement with the estimates derived from a Monte Carlo software, which was up
to now employed for driving the development of the instrument and for
estimating its low energy sensitivity. In this paper we present the excellent
polarimetric performance of the Gas Pixel Detector at energies where the peak
sensitivity is expected. These measurements not only support our previous
claims of high sensitivity but confirm the feasibility of astrophysical X-ray
photoelectric polarimetry.Comment: 15 pages, 12 figures. Accepted for publication in NIM
Postseismic Deformation Following the 2015 M_w7.8 Gorkha (Nepal) Earthquake: New GPS Data, Kinematic and Dynamic Models, and the Roles of Afterslip and Viscoelastic Relaxation
We report Global Positioning System (GPS) measurements of postseismic deformation following the 2015 M_w7.8 Gorkha (Nepal) earthquake, including previously unpublished data from 13 continuous GPS stations installed in southern Tibet shortly after the earthquake. We use variational Bayesian Independent Component Analysis (vbICA) to extract the signal of postseismic deformation from the GPS time series, revealing a broad displacement field extending >150 km northward from the rupture. Kinematic inversions and dynamic forward models show that these displacements could have been produced solely by afterslip on the Main Himalayan Thrust (MHT) but would require a broad distribution of afterslip extending similarly far north. This would require the constitutive parameter (a â b)Ď to decrease northward on the MHT to â¤0.05 MPa (an extreme sensitivity of creep rate to stress change) and seems unlikely in light of the low interseismic coupling and high midcrustal temperatures beneath southern Tibet. We conclude that the northward reach of postseismic deformation more likely results from distributed viscoelastic relaxation, possibly in a midcrustal shear zone extending northward from the seismogenic MHT. Assuming a shear zone 5â20 km thick, we estimate an effective shearâzone viscosity of ~3¡10šâśâ3¡10š⡠Pa¡s over the first 1.12 postseismic years. Nearâfield deformation can be more plausibly explained by afterslip itself and implies (a â b)Ď ~ 0.5â1 MPa, consistent with other afterslip studies. This nearâfield afterslip by itself would have reâincreased the Coulomb stress by âĽ0.05 MPa over >30% of the Gorkha rupture zone in the first postseismic year, and deformation further north would have compounded this reloading
Research priorities for improving infant and young child feeding in humanitarian emergencies
Background
There are many challenges during emergencies to ensure that optimal infant and young child feeding is protected, promoted and supported, but there is a dearth of evidence on strategies and programmes to improve Infant and Young Child Feeding in Emergencies (IYCF-E) and a need to determine research priorities.
Methods
Based on interviews with key informants who are experts in the subject, we developed a list of 48 research questions on IYCF-E. A framework, following the Child Health and Nutrition Research Initiative method to set priorities in child health research, was developed to rank the research questions. Four criteria were applied to create a ranking based on answerability, operational relevance, disease burden reduction and prevention, and originality. Using an on-line survey, prioritisation of research questions was done by 27 people from 14 NGOs, universities and research institutions, and UN organisations.
Results
The top-ten research questions identified focused on the following:
⢠Use of cash-transfer to buy breast-milk substitutes;
⢠Effectiveness of complementary feeding strategies;
⢠Long-term effect of IYCF-E interventions;
⢠Design of IYCF-E programmes in a context where breastfeeding rates are low and breast milk substitutes use is high;
⢠Design of effective re-lactation interventions;
⢠Provision of psychological support to young childrenâs care-takers;
⢠Determination of number of beneficiaries and coverage of IYCF-E programmes;
⢠Pros and cons of distributing ready-to-use infant formula compared with distributing powdered infant formula plus kit for safer use of BMS, when use of infant formula is necessary;
⢠Assessment of the impact of specific IYCF-E programmes on nutritional status, morbidity and mortality;
⢠Linking and mainstreaming IYCF-E interventions with other sectors such as health, WASH, food security and child protection.
Conclusion
The questions found by this study could form the basis of future research on IYCF-E and could be integrated into the agenda of relevant stakeholders. Results of studies based on these questions will be fundamental to fill the evidence gap in IYCF-E, improve IYCF-E programming and ultimately contribute to the reduction in morbidity and mortality among infants and young children in humanitarian emergencies
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