21,552 research outputs found
High-energy emission from Gamma-Ray Bursts
The number of Gamma-Ray Bursts (GRBs) detected at high energies
( GeV) has seen a rapid increase over the last decade, thanks to
observations from the Fermi-Large Area Telescope. The improved statistics and
quality of data resulted in a better characterisation of the high-energy
emission properties and in stronger constraints on theoretical models. In spite
of the many achievements and progresses, several observational properties still
represent a challenge for theoretical models, revealing how our understanding
is far from being complete. This paper reviews the main spectral and temporal
properties of GeV emission from GRBs and summarises the most
promising theoretical models proposed to interpret the observations. Since a
boost for the understanding of GeV radiation might come from observations at
even higher energies, the present status and future prospects for observations
at very-high energies (above 100 GeV) are also discussed. The improved
sensitivity of upcoming facilities, coupled to theoretical predictions,
supports the concrete possibility for future ground GRB detections in the
high/very-high energy domain.Comment: Invited review article, IJMPD (in press
Elliptic genera from multi-centers
I show how elliptic genera for various Calabi-Yau threefolds may be
understood from supergravity localization using the quantization of the phase
space of certain multi-center configurations. I present a simple procedure that
allows for the enumeration of all multi-center configurations contributing to
the polar sector of the elliptic genera\textemdash explicitly verifying this in
the cases of the quintic in , the sextic in
, the octic in and the
dectic in . With an input of the corresponding
`single-center' indices (Donaldson-Thomas invariants), the polar terms have
been known to determine the elliptic genera completely. I argue that this
multi-center approach to the low-lying spectrum of the elliptic genera is a
stepping stone towards an understanding of the exact microscopic states that
contribute to supersymmetric single center black hole entropy in
supergravity.Comment: 30+1 pages, Published Versio
Quantity Competition in Networked Markets Outflow and Inflow Competition
This paper investigates how quantity competition operates in economies in which a network describes the set of feasible trades. A general equilibrium model is presented in which prices and .ows of goods are endogenously determined. In such economies equilibrium dictates whether an individual buys, sells or does both (which is possible). The first part of the analysis provides sufficient conditions for pure strategy equilibrium existence; characterizes equilibrium prices, flows and markups; and details negative effects on welfare of changes in the network structure. The main contributions show that goods do not cycle, since prices strictly increase along the supply chains; that not all connected players with different marginal rates of substitution trade; and that adding trading relationships may decrease individual and social welfare. The second part of the analysis provides necessary and sufficient conditions for a networked economy to become competitive as the number of players grows large. In this context it shown that no economy in which goods are resold can ever be competitive; and that large well connected economies are competitive.
Land Use and Water Management in Israel- Economic and environmental analysis of sustainable reuse of wastewater in agriculture
We will analyze land use and water management issues in Israel by focusing on wastewater irrigation. Irrigation with treated effluents has become an important water source in Israel due to scarcity of natural water resources. Treated wastewater reuse serves as source of water and nutrients and assists with wastewater discard. Wastewater also carries pollutants including micro and macro organic and inorganic matter and its treatment and use should adapt to sustainability criteria. Wastewater treatment processes can decrease pollutants levels, while salinity is not influenced unless combining relatively expensive desalination processes. Advantages of using wastewater in irrigation include: supporting agricultural production, highly reliable supply, low cost water source, solution for effluent disposal and saving of chemical fertilizers. Disadvantages include quality problems as related to human health, damage to crops, contamination of groundwater, problems related to irrigation system, increased water requirement and need for continuous follow up and control. The higher is the treatment level, the higher are the treatment costs but the environmental potential hazards are lower. Regarding sustainable use we will assess advantages and disadvantages of treating and irrigating with treated effluents. We will focus on the economic and environmental analysis of sustainable reuse of wastewater in agriculture regarding its impact on groundwater, soil and society.
The Effectiveness of Personalized Movie Explanations : An Experiment Using Commercial Meta-data
Preprin
Anisotropic CR diffusion and gamma-ray production close to supernova remnants, with an application to W28
Cosmic rays that escape their acceleration site interact with the ambient
medium and produce gamma rays as the result of inelastic proton-proton
collisions. The detection of such diffuse emission may reveal the presence of
an accelerator of cosmic rays, and also constrain the cosmic ray diffusion
coefficient in its vicinity. Preliminary results in this direction have been
obtained in the last years from studies of the gamma-ray emission from
molecular clouds located in the vicinity of supernova remnants, which are the
prime candidate for cosmic ray production. Hints have been found for a
significant suppression of the diffusion coefficient with respect to the
average one in the Galaxy. However, most of these studies rely on the
assumption of isotropic diffusion, which may not be very well justified. Here,
we extend this study to the case in which cosmic rays that escape an
accelerator diffuse preferentially along the magnetic field lines. As a first
approximation, we further assume that particles are strongly magnetized and
that their transport perpendicular to the magnetic field is mainly due to the
wandering of the field lines. The resulting spatial distribution of runaway
cosmic rays around the accelerator is, in this case, strongly anisotropic. An
application of the model to the case of the supernova remnant W28 demonstrates
how the estimates of the diffusion coefficient from gamma-ray observations
strongly depend on the assumptions made on the isotropy (or anisotropy) of
diffusion. For higher levels of anisotropy of the diffusion, larger values of
the diffusion coefficient are found to provide a good fit to data. Thus,
detailed models for the propagation of cosmic rays are needed in order to
interpret in a correct way the gamma-ray observations.Comment: 10 pages, 5 figures, submitted to MNRA
SAsSy - Making Decisions Transparent with Argumentation and Natural Language Generation
Peer reviewedPublisher PD
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