22,141 research outputs found
Studying the interaction between microquasar jets and their environments
In high-mass microquasars (HMMQ), strong interactions between jets and
stellar winds at binary system scales could occur. In order to explore this
possibility, we have performed numerical 2-dimensional simulations of jets
crossing the dense stellar material to study how the jet will be affected by
these interactions. We find that the jet head generates strong shocks in the
wind. These shocks reduce the jet advance speed, and compress and heat up jet
and wind material. In addition, strong recollimation shocks can occur where
pressure balance between the jet side and the surrounding medium is reached.
All this, altogether with jet bending, could lead to the destruction of jets
with power . The conditions around the outflow shocks
would be convenient for accelerating particles up to TeV energies. These
accelerated particles could emit via synchrotron and inverse Compton (IC)
scattering if they were leptons, and via hadronic processes in case they were
hadrons.Comment: 4 pages. Contribution to the proceedings of High Energy Phenomena in
Relativistic Outflows, held in Dublin, Ireland, September 24-28, 200
Compatibility and stability of hyoscine n-butyl bromide and furosemide admixtures for use in palliative care
In order to avoid separate injections, admixtures of drugs are frequently used in palliative care settings. There are different factors that can influence the compatibility and stability of the mixture: drug type, concentration, solvent, container, temperature and light. There are some mixtures of drugs with proven stability, but there is lack of evidence about the stability and compatibility of the combination of hyoscine N-butyl bromide and furosemide.Universidad de MĂĄlaga,Campus de Excelencia Internacional AndalucĂa Tec
Non-linear Relaxation of Interacting Bosons Coherently Driven on a Narrow Optical Transition
We study the dynamics of a two-component Bose-Einstein condensate (BEC) of
Yb atoms coherently driven on a narrow optical transition. The
excitation transfers the BEC to a superposition of states with different
internal and momentum quantum numbers. We observe a crossover with decreasing
driving strength between a regime of damped oscillations, where coherent
driving prevails, and an incoherent regime, where relaxation takes over.
Several relaxation mechanisms are involved: inelastic losses involving two
excited atoms, leading to a non-exponential decay of populations; Doppler
broadening due to the finite momentum width of the BEC and inhomogeneous
elastic interactions, both leading to dephasing and to damping of the
oscillations. We compare our observations to a two-component Gross-Pitaevskii
(GP) model that fully includes these effects. For small or moderate densities,
the damping of the oscillations is mostly due to Doppler broadening. In this
regime, we find excellent agreement between the model and the experimental
results. For higher densities, the role of interactions increases and so does
the damping rate of the oscillations. The damping in the GP model is less
pronounced than in the experiment, possibly a hint for many-body effects not
captured by the mean-field description.Comment: 7 pages, 4 figures; supplementary material available as ancillary
fil
Clock spectroscopy of interacting bosons in deep optical lattices
We report on high-resolution optical spectroscopy of interacting bosonic
Yb atoms in deep optical lattices with negligible tunneling. We prepare
Mott insulator phases with singly- and doubly-occupied isolated sites and probe
the atoms using an ultra-narrow "clock" transition. Atoms in singly-occupied
sites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are
strongly affected by interatomic interactions, and we measure their inelastic
decay rates and energy shifts. We deduce from these measurements all relevant
collisional parameters involving both clock states, in particular the intra-
and inter-state scattering lengths
Exploring Particle Acceleration in Gamma-Ray Binaries
Binary systems can be powerful sources of non-thermal emission from radio to
gamma rays. When the latter are detected, then these objects are known as
gamma-ray binaries. In this work, we explore, in the context of gamma-ray
binaries, different acceleration processes to estimate their efficiency: Fermi
I, Fermi II, shear acceleration, the converter mechanism, and magnetic
reconnection. We find that Fermi I acceleration in a mildly relativistic shock
can provide, although marginally, the multi-10 TeV particles required to
explain observations. Shear acceleration may be a complementary mechanism,
giving particles the final boost to reach such a high energies. Fermi II
acceleration may be too slow to account for the observed very high energy
photons, but may be suitable to explain extended low-energy emission. The
converter mechanism seems to require rather high Lorentz factors but cannot be
discarded a priori. Standard relativistic shock acceleration requires a highly
turbulent, weakly magnetized downstream medium; magnetic reconnection, by
itself possibly insufficient to reach very high energies, could perhaps
facilitate such a conditions. Further theoretical developments, and a better
source characterization, are needed to pinpoint the dominant acceleration
mechanism, which need not be one and the same in all sources.Comment: 7 pages, 1 figure, proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics Applications
(Villa Olmo, Como 3-7 October 2011
Person to Person in Norway
While still in the midst of their study abroad experiences, students at Linfield College write reflective essays. Their essays address issues of cultural similarity and difference, compare lifestyles, mores, norms, and habits between their host countries and home, and examine changes in perceptions about their host countries and the United States. In this essay, Amber Hay describes her observations during her study abroad program at Telemark University College in BĂž, Norway
The development of power specific redlines for SSME safety monitoring
Over the past several years, there has been an increased awareness in the necessity for rocket engine health monitoring because of the cost and complexity of present and future systems. A current rocket engine system, the Space Shuttle Main Engine (SSME), combines a limited redline system with closed-loop control of the engine's thrust level and mixture ratio. Despite these features, 27 tests of the SSME have resulted in major incidents. A SSME transient model was used to examine the effect of variations in high pressure turbopump performance on various engine parameters. Based on analysis of the responses, several new parameters are proposed for further investigation as power-level specific redlines
Remote sensing observatory validation of surface soil moisture using Advanced Microwave Scanning Radiometer E, Common Land Model, and ground based data: Case study in SMEX03 Little River Region, Georgia, U.S.
Optimal soil moisture estimation may be characterized by intercomparisons among remotely sensed measurements, groundâbased measurements, and land surface models. In this study, we compared soil moisture from Advanced Microwave Scanning Radiometer E (AMSRâE), groundâbased measurements, and a SoilâVegetationâAtmosphere Transfer (SVAT) model for the Soil Moisture Experiments in 2003 (SMEX03) Little River region, Georgia. The Common Land Model (CLM) reasonably replicated soil moisture patterns in dry down and wetting after rainfall though it had modest wet biases (0.001â0.054 m3/m3) as compared to AMSRâE and ground data. While the AMSRâE average soil moisture agreed well with the other data sources, it had extremely low temporal variability, especially during the growing season from May to October. The comparison results showed that highest mean absolute error (MAE) and root mean squared error (RMSE) were 0.054 and 0.059 m3/m3 for short and long periods, respectively. Even if CLM and AMSRâE had complementary strengths, low MAE (0.018â0.054 m3/m3) and RMSE (0.023â0.059 m3/m3) soil moisture errors for CLM and soil moisture low biases (0.003â0.031 m3/m3) for AMSRâE, care should be taken prior to employing AMSRâE retrieved soil moisture products directly for hydrological application due to its failure to replicate temporal variability. AMSRâE error characteristics identified in this study should be used to guide enhancement of retrieval algorithms and improve satellite observations for hydrological sciences
The trade-offs of social assistance programs in the labor market: The case of the âSeguro Popularâ program in Mexico
In 2002, the Mexican government began a tremendous financial effort to provide health insurance, Seguro Popular (SP), to the 50 million uninsured in Mexico. In doing so, the states and municipalities offered virtually free health insurance to uncovered self-employed and informal salaried workers substantially altering the incentives for workers and firms to operate in the formal economy. We take advantage of the staggered implementation of the program across municipalities to estimate the effects of the SP in the labor market. We find that the SP had a negative effect in the creation of formal jobs, especially in small and medium sized firms. According to our estimates, had the program not been in place, 31.000 more employers and 300.000 new formal jobs should have been registered with Mexican social security. These represent 3.8% and 2.4% of the stock of registered employers and employees in 2002 when the program started.social assistance program, informality, labor market, Mexico
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