1,721,177 research outputs found
Exact versus approximate equitemporal surfaces in gamma-ray burst afterglows
No full textBy integrating the relativistic hydrodynamic equations introduced by Taub, we have determined the exact equitemporal surfaces for the gamma-ray burst afterglows. These surfaces are compared and contrasted to the ones obtained, using approximate methods, by Panaitescu & Meszaros, Sari, and Granot et al
On the exact analytic expressions for the equitemporal surfaces in gamma-ray burst afterglows
No full textWe have recently shown that marked differences exist between the equitemporal surfaces ( EQTSs) for the gamma- ray burst ( GRB) afterglows numerically computed by the full integration of the equations of motion and the ones found in the current literature expressed analytically on the grounds of various approximations. In this Letter, the exact analytic expressions of the EQTSs are presented both in the case of fully radiative and adiabatic regimes. The new EQTS analytic solutions validate the numerical results recently obtained by Bianco & Ruffini and offer a powerful tool to analytically perform the estimates of the physical observables in GRB afterglows
Exact versus approximate solutions in gamma-ray burst afterglows
No full textWe have recently obtained the exact analytic solutions for the relativistic equations relating the radial and timecoordinates of a relativistic, thin uniform shell expanding in the interstellar medium in the fully radiative and fully adiabatic regimes. Here we reexamine the validity of the constant-index power-law relation between the Lorentz gamma factor and its radial coordinate, which is usually adopted in the gamma-ray burst (GRB) literature on the grounds of an "ultrarelativistic" approximation. Such expressions are found to be mathematically correct but only approximately valid in a very limited range of physical and astrophysical parameters and in an asymptotic regime that is reached for a very short time only, if at all, and they are shown to be nonapplicable to GRBs
Theoretical interpretation of GRB 011121
No full textGRB 011121 is analyzed as a prototype to understand the "flares" recently observed by Swift in the afterglow of many GRB sources. Detailed theoretical computation of the GRB 011121 light curves in selected energy bands are presented and compared and contrasted with observational BeppoSAX data
The role of soil amendments in limiting the leaching of agrochemicals: Laboratory assessment for copper sulphate and dicamba
Full text linkAgriculture is among the major contributors to soil and groundwater pollution, primarily through the widespread
leaching of pesticides and fertilizers from crops, as well as accidental releases from point sources. Therefore,
alongside restrictions on the use of highly soluble agrochemicals and enhanced application guidelines, there is a
significant demand for low-impact and cost-effective solutions aimed at reducing the mobility of agrochemicals
in the soils. This study evaluates the potential of soil amendments—commonly used to enhance soil structural
properties, water holding capacity, and fertility—to also absorb highly soluble pesticides, thereby controlling
their leaching into the subsoil. Specifically, zeolite, biochar, and milled corncob were examined in laboratory
tests under static (batch tests) and dynamic (column leaching tests) conditions to assess their effectiveness in
adsorbing two widely used pesticides, copper sulphate and dicamba. Batch adsorption tests were performed
using the amendments as pure materials and in mixtures with sand at various application rates (1–20% by
weight). The highest affinity to copper sulphate was recorded for biochar, while dicamba exhibited a higher
affinity to corncob, thanks to its higher content of organic carbon. Column leaching tests, performed at an
amendment application rate of 5%, confirmed the different affinity observed in batch tests among pesticides and
amended soil. Less than 2% of copper sulphate leached out from biochar- and zeolite-sand columns, while a
recovery of 10% and 56% was observed for the corncob-sand mixture and for pure sand, respectively. Dicamba
leaching from biochar- and corncob-sand columns was halved compared to pure sand. In conclusion, the tested
soil amendments resulted highly effective in reducing pesticide leaching, opening the way for their possible
applications in agriculture to reduce or prevent both diffuse and punctual contamination
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
MNMs: a model for the simulation of depth filtration of non-Newtonian suspensions in granular media
No full textMNMs is a software (www.polito.it/groundwater/software) able to simulate transport, attachment/detachment processes and clogging occurring during depth filtration in granular porous media. The software was developed in the framework of the FP7 NANOREM project with the aim of simulating the transport of non-Newtonian suspensions of micro- and nanoparticles in saturated porous media (e.g. aquifer systems). Colloid transport mechanisms are controlled by particle-collector and particle-particle interactions, modelled by a non equilibrium kinetic model accounting for deposition and release processes. The key aspects included in MNMs are: influence of water chemistry (changes in ionic strength), clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid. The influence of colloid transport on porosity, permeability, and fluid viscosity is explicitly lumped into the model by a modified Darcy law generalized for non Newtonian fluids. MNMs was used for the simulation of: (i) clogging processes and pressure buildup during depth filtration [2,3], (ii) distribution of micro- and nanoscale iron particles suspended in shear thinning fluids for the remediation of contaminated aquifer systems [2,3], (iii) attachment and detachment of colloidal particles under variable ionic strength [1
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