776 research outputs found
On The Origin Of The Gamma Rays From The Galactic Center
The region surrounding the center of the Milky Way is both astrophysically
rich and complex, and is predicted to contain very high densities of dark
matter. Utilizing three years of data from the Fermi Gamma Ray Space Telescope
(and the recently available Pass 7 ultraclean event class), we study the
morphology and spectrum of the gamma ray emission from this region and find
evidence of a spatially extended component which peaks at energies between 300
MeV and 10 GeV. We compare our results to those reported by other groups and
find good agreement. The extended emission could potentially originate from
either the annihilations of dark matter particles in the inner galaxy, or from
the collisions of high energy protons that are accelerated by the Milky Way's
supermassive black hole with gas. If interpreted as dark matter annihilation
products, the emission spectrum favors dark matter particles with a mass in the
range of 7-12 GeV (if annihilating dominantly to leptons) or 25-45 GeV (if
annihilating dominantly to hadronic final states). The intensity of the
emission corresponds to a dark matter annihilation cross section consistent
with that required to generate the observed cosmological abundance in the early
universe (sigma v ~ 3 x 10^-26 cm^3/s). We also present conservative limits on
the dark matter annihilation cross section which are at least as stringent as
those derived from other observations.Comment: 13 pages, 11 figure
Frame-dragging effects on magnetic fields near a rotating black hole
We discuss the role of general relativity frame dragging acting on magnetic
field lines near a rotating (Kerr) black hole. Near ergosphere the magnetic
structure becomes strongly influenced and magnetic null points can develop. We
consider aligned magnetic fields as well as fields inclined with respect to the
rotation axis, and the two cases are shown to behave in profoundly different
ways. Further, we construct surfaces of equal values of local electric and
magnetic intensities, which have not yet been discussed in the full generality
of a boosted rotating black hole.Comment: to appear in the proceedings of "The Central Kiloparsec in Galactic
Nuclei (AHAR 2011)", Journal of Physics: Conference Series (JPCS), IOP
Publishin
Comparative evaluation of synergy of combinations of \u3b2-lactams with fluoroquinolones or macrolides in Streptococcus pneumoniae
OBJECTIVES: Streptococcus pneumoniae has shown a great ability to develop
efficacious mechanisms of resistance to the main drugs for the treatment of
pneumonia, such as \u3b2-lactams, macrolides and fluoroquinolones. The present study
aimed to compare the antipneumococcal activity of combinations of respiratory
fluoroquinolones with cephalosporins (either parenteral or oral) or protected
penicillin versus the standard combinations (i.e. a macrolide with a protected
penicillin or cephalosporin) against 100 isolates with different susceptibilities
to macrolides and/or penicillin.
METHODS: Chequerboard assays for all isolates and time-kill curves for nine
isolates with different patterns of susceptibility were performed. Synergy
between antibiotics at serum peak concentrations was also determined.
RESULTS: The combination of levofloxacin with ceftriaxone produced the highest
rate of synergy (54/100), mainly against macrolide-resistant strains (22/30).
Antagonism was not observed for any tested combination apart from clarithromycin
with amoxicillin/clavulanic acid (22/100 isolates). Although the killing
activities of all antibiotics improved when they were tested in combination,
synergy was observed only for some combinations after 12 and/or 24 h. Serum
concentrations were effective in inhibiting the growth of the tested strains.
CONCLUSIONS: Combinations of levofloxacin with parenteral cephalosporins were the
most active among all the tested combinations, while antagonism occurred when
clarithromycin and amoxicillin/clavulanic acid were tested
Smart Climate Hydropower Tool: A Machine-Learning Seasonal Forecasting Climate Service to Support Cost–Benefit Analysis of Reservoir Management
This study proposes a climate service named Smart Climate Hydropower Tool (SCHT) and designed as a hybrid forecast system for supporting decision-making in a context of hydropower production. SCHT is technically designed to make use of information from state-of-art seasonal forecasts provided by the Copernicus Climate Data Store (CDS) combined with a range of different machine learning algorithms to perform the seasonal forecast of the accumulated inflow discharges to the reservoir of hydropower plants. The machine learning algorithms considered include support vector regression, Gaussian processes, long short-term memory, non-linear autoregressive neural networks with exogenous inputs, and a deep-learning neural networks model. Each machine learning model is trained over past decades datasets of recorded data, and forecast performances are validated and evaluated using separate test sets with reference to the historical average of discharge values and simpler multiparametric regressions. Final results are presented to the users through a user-friendly web interface developed from a tied connection with end-users in an effective co-design process. Methods are tested for forecasting the accumulated seasonal river discharges up to six months in advance for two catchments in Colombia, South America. Results indicate that the machine learning algorithms that make use of a complex and/or recurrent architecture can better simulate the temporal dynamic behaviour of the accumulated river discharge inflow to both case study reservoirs, thus rendering SCHT a useful tool in providing information for water resource managers in better planning the allocation of water resources for different users and for hydropower plant managers when negotiating power purchase contracts in competitive energy markets
Smart climate hydropower tool: A machine-learning seasonal forecasting climate service to support cost–benefit analysis of reservoir management
This study proposes a climate service named Smart Climate Hydropower Tool (SCHT) and designed as a hybrid forecast system for supporting decision-making in a context of hydropower production. SCHT is technically designed to make use of information from state-of-art seasonal forecasts provided by the Copernicus Climate Data Store (CDS) combined with a range of different machine learning algorithms to perform the seasonal forecast of the accumulated inflow discharges to the reservoir of hydropower plants. The machine learning algorithms considered include support vector regression, Gaussian processes, long short-term memory, non-linear autoregressive neural networks with exogenous inputs, and a deep-learning neural networks model. Each machine learning model is trained over past decades datasets of recorded data, and forecast performances are validated and evaluated using separate test sets with reference to the historical average of discharge values and simpler multiparametric regressions. Final results are presented to the users through a user-friendly web interface developed from a tied connection with end-users in an effective co-design process. Methods are tested for forecasting the accumulated seasonal river discharges up to six months in advance for two catchments in Colombia, South America. Results indicate that the machine learning algorithms that make use of a complex and/or recurrent architecture can better simulate the temporal dynamic behaviour of the accumulated river discharge inflow to both case study reservoirs, thus rendering SCHT a useful tool in providing information for water resource managers in better planning the allocation of water resources for different users and for hydropower plant managers when negotiating power purchase contracts in competitive energy markets
Similar glycaemic control and risk of hypoglycaemia with patient- versus physician-managed titration of insulin glargine 300 U/mL across subgroups of patients with T2DM: a post hoc analysis of ITAS
Aims: The Italian Titration Approach Study (ITAS) demonstrated comparable HbA1c reductions and similarly low hypoglycaemia risk at 6 months in poorly controlled, insulin-naïve adults with T2DM who initiated self- or physician-titrated insulin glargine 300 U/mL (Gla-300) in the absence of sulphonylurea/glinide. The association of patient characteristics with glycaemic and hypoglycaemic outcomes was assessed. Methods: This post hoc analysis investigated whether baseline patient characteristics and previous antihyperglycaemic drugs were associated with HbA1c change and hypoglycaemia risk in patient- versus physician-managed Gla-300 titration. Results: HbA1c change, incidence of hypoglycaemia (any type) and nocturnal rates were comparable between patient- and physician-managed arms in all subgroups. Hypoglycaemia rates across subgroups (0.03 to 3.52 events per patient-year) were generally as low as observed in the full ITAS population. Small increases in rates of 00:00–pre-breakfast and anytime hypoglycaemia were observed in the ≤ 10-year diabetes duration subgroup in the patient- versus physician-managed arm (heterogeneity of effect; p < 0.05). Conclusions: Comparably fair glycaemic control and similarly low hypoglycaemia risk were achieved in almost all patient subgroups with patient- versus physician-led Gla-300 titration. These results reinforce efficacy and safety of Gla-300 self-titration across a range of phenotypes of insulin-naïve people with T2DM. Clinical trial registration: EudraCT 2015-001167-3
Single Hole Green's Functions in Insulating Copper Oxides at Nonzero Temperature
We consider the single hole dynamics in a modified model at finite
temperature. The modified model includes a next nearest () and next-next
nearest () hopping. The model has been considered before in the zero
temperature limit to explain angle resolved photo-emission measurements. We
extend this consideration to the case of finite temperature where long-range
anti-ferromagnetic order is destroyed, using the self-consistent Born
approximation. The Dyson equation which relates the single hole Green's
functions for a fixed pseudo-spin and for fixed spin is derived. The Green's
function with fixed pseudo-spin is infrared stable but the Green's function
with fixed spin is close to an infrared divergency. We demonstrate how to
renormalize this Green's function in order to assure numerical convergence. At
non-zero temperature the quasi-particle peaks are found to shift down in energy
and to be broadened.Comment: 7 pages, RevTex, 5 Postscript figure
Whistler waves generated inside magnetic dips in the young solar wind: observations of the Search-Coil Magnetometer on board Parker Solar Probe
Context. Whistler waves are electromagnetic waves produced by electron-driven
instabilities, that in turn can reshape the electron distributions via
wave-particle interactions. In the solar wind, they are one of the main
candidates for explaining the scattering of the strahl electron population into
the halo at increasing radial distances from the Sun and for subsequently
regulating the solar wind heat flux. However, it is unclear what type of
instability dominates to drive whistlers in the solar wind. Aims. Our goal is
to study whistler wave parameters in the young solar wind sampled by Parker
Solar Probe (PSP). The wave normal angle (WNA) in particular is a key parameter
to discriminate between the generation mechanisms of these waves. Methods. We
analyze the cross-spectral matrices of magnetic fieldfluctuations measured by
the Search-Coil Magnetometer (SCM) and processed by the Digital Fields Board
(DFB) from the FIELDS suite during PSP's first perihelion. Results. Among the
2701 wave packets detected in the cross spectra, namely individual bins in time
and frequency, most were quasi-parallel to the background magnetic field but a
significant part (3%) of observed waves had oblique (> 45{\deg}) WNA. The
validation analysis conducted with the time-series waveforms reveal that this
percentage is a lower limit. Moreover, we find that about 64% of the whistler
waves detected in the spectra are associated with at least one magnetic dip.
Conclusions. We conclude that magnetic dips provides favorable conditions for
the generation of whistler waves. We hypothesize that the whistlers detected in
magnetic dips are locally generated by the thermal anisotropy as quasi-parallel
and can gain obliqueness during their propagation. We finally discuss the
implication of our results for the scattering of the strahl in the solar wind.Comment: 15 pages, 14 figures, recommended for publication in A&
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