630 research outputs found
Changing the University System Management: a study of the Italian scenario
Over recent years, the Italian University System has been handling a phase of deep
changes, which have had significant impact on its mission and on the way it operates.
The most important of these changes have been to the organisation of universities, their
recruitment procedures and in terms of improvements to the quality and efficiency of
the university system itself. In this perspective, the objective of this research was to carry
out a critical analysis of the process of change, with special reference to improving
efficiency by making the transition from cash-based accounting to accrual accounting. In
order to achieve this objective, the starting point was the legislation of reference that
sets out the terms for the move to financial accrual accounting. A comparative analysis
was then carried out at an international level, with the purpose of highlighting the
strengths and weaknesses identified during the implementation of these new
procedures within the public field. This was followed by an analysis of the details of the
theory defining the accounting principles to be used in the process of preparing
university’s financial statements. Finally, the study identified the main critical points
relating to implementation of the new accounting system, offering, at the same time,
several thoughts concerning possible subsequent analyses on this topic
Structure of Gamma-Ray Burst jets: intrinsic versus apparent properties
With this paper we introduce the concept of apparent structure of a GRB jet,
as opposed to its intrinsic structure. The latter is customarily defined
specifying the functions epsilon(theta) (the energy emitted per jet unit solid
angle) and Gamma(theta) (the Lorentz factor of the emitting material); the
apparent structure is instead defined by us as the isotropic equivalent energy
E_iso(theta_v) as a function of the viewing angle theta_v. We show how to
predict the apparent structure of a jet given its intrinsic structure. We find
that a Gaussian intrinsic structure yields a power law apparent structure: this
opens a new viewpoint on the Gaussian (which can be understood as a proxy for a
realistic narrow, well collimated jet structure) as a possible candidate for a
quasi-universal GRB jet structure. We show that such a model (a) is consistent
with recent constraints on the observed luminosity function of GRBs; (b)
implies fewer orphan afterglows with respect to the standard uniform model; (c)
can break out the progenitor star (in the collapsar scenario) without wasting
an unreasonable amount of energy; (d) is compatible with the explanation of the
Amati correlation as a viewing angle effect; (e) can be very standard in energy
content, and still yield a very wide range of observed isotropic equivalent
energies.Comment: 10 pages, 8 figures, 1 table. Accepted by MNRA
Afterglows from precursors in Gamma Ray Bursts. Application to the optical afterglow of GRB 091024
About 15% of Gamma Ray Bursts have precursors, i.e. emission episodes
preceding the main event, whose spectral and temporal properties are similar to
the main emission. We propose that precursors have their own fireball,
producing afterglow emission due to the dissipation of the kinetic energy via
external shock. In the time lapse between the precursor and the main event, we
assume that the central engine is not completely turned off, but it continues
to eject relativistic material at a smaller rate, whose emission is below the
background level. The precursor fireball generates a first afterglow by the
interaction with the external circumburst medium. Matter injected by the
central engine during the "quasi-quiescent" phase replenishes the external
medium with material in relativistic motion. The fireball corresponding to the
main prompt emission episode crashes with this moving material, producing a
second afterglow, and finally catches up and merges with the first precursor
fireball. We apply this new model to GRB 091024, an event with a precursor in
the prompt light curve and two well defined bumps in the optical afterglow,
obtaining an excellent agreement with the existing data.Comment: 11 pages, 6 figures, 3 tables. Accepted for publication in MNRAS,
Main Journa
Luminosity function and jet structure of Gamma Ray Bursts
The structure of Gamma Ray Burst (GRB) jets impacts on their prompt and
afterglow emission properties. The jet of GRBs could be uniform, with constant
energy per unit solid angle within the jet aperture, or it could instead be
structured, namely with energy and velocity that depend on the angular distance
from the axis of the jet. We try to get some insight about the still unknown
structure of GRBs by studying their luminosity function. We show that low
(1e46-1e48 erg/s) and high (i.e. with L > 1e50 erg/s) luminosity GRBs can be
described by a unique luminosity function, which is also consistent with
current lower limits in the intermediate luminosity range (1e48-1e50} erg/s).
We derive analytical expressions for the luminosity function of GRBs in uniform
and structured jet models and compare them with the data. Uniform jets can
reproduce the entire luminosity function with reasonable values of the free
parameters. A structured jet can also fit adequately the current data, provided
that the energy within the jet is relatively strongly structured, i.e. E propto
theta^{-k} with k > 4. The classical E propto theta^{-2} structured jet model
is excluded by the current data.Comment: 11 pages, 2 tables, 7 figures, submitted to MNRA
Nonlinear filtering for Markov systems with delayed observations
Versione iniziale di un lavoro successivamente pubblicato
(altra versione disponible su)
http://www.mat.uniroma1.it/people/nappo/papers.pdf/CFN-JAMCS-DelayMarkov.pd
Factors that lead to the use of crack cocaine in combination with marijuana in Brazil: a qualitative study
Limits to tDCS effects in language:failures to modulate word production in healthy participants with frontal or temporal tDCS
Transcranial direct current stimulation (tDCS) is a method of non-invasive brain stimulation widely used to modulate cognitive functions. Recent studies, however, suggests that effects are unreliable, small and often non-significant at least when stimulation is applied in a single session to healthy individuals. We examined the effects of frontal and temporal lobe anodal tDCS on naming and reading tasks and considered possible interactions with linguistic activation and selection mechanisms as well possible interactions with item difficulty and participant individual variability. Across four separate experiments (N, Exp 1A = 18; 1B = 20; 1C = 18; 2 = 17), we failed to find any difference between real and sham stimulation. Moreover, we found no evidence of significant effects limited to particular conditions (i.e., those requiring suppression of semantic interference), to a subset of participants or to longer RTs. Our findings sound a cautionary note on using tDCS as a means to modulate cognitive performance. Consistent effects of tDCS may be difficult to demonstrate in healthy participants in reading and naming tasks, and be limited to cases of pathological neurophysiology and/or to the use of learning paradigms
Bulk Lorentz factors of Gamma-Ray Bursts
Knowledge of the bulk Lorentz factor of GRBs allows us to
compute their comoving frame properties shedding light on their physics. Upon
collisions with the circumburst matter, the fireball of a GRB starts to
decelerate, producing a peak or a break (depending on the circumburst density
profile) in the light curve of the afterglow. Considering all bursts with known
redshift and with an early coverage of their emission, we find 67 GRBs with a
peak in their optical or GeV light curves at a time . For another
106 GRBs we set an upper limit . We show that
is due to the dynamics of the fireball deceleration and not to the passage of a
characteristic frequency of the synchrotron spectrum across the optical band.
Considering the of 66 long GRBs and the 85 most constraining upper
limits, using censored data analysis methods, we reconstruct the most likely
distribution of . All are larger than the time when the prompt emission peaks, and are much larger than the time when the fireball becomes transparent. The reconstructed distribution of
has median value 300 (150) for a uniform (wind) circumburst
density profile. In the comoving frame, long GRBs have typical isotropic
energy, luminosity, and peak energy erg, erg s ,
and keV in the homogeneous (wind) case. We
confirm that the significant correlations between and the rest frame
isotropic energy (), luminosity () and peak energy
() are not due to selection effects. Assuming a typical opening
angle of 5 degrees, we derive the distribution of the jet baryon loading which
is centered around a few .Comment: 19 pages, 11 figures, 6 tables. Accepted for publication on Astronomy
& Astrophysic
Airborne Measurements of Gravity Wave Breaking at the Tropopause
2000 FLORIDA AVE NW, WASHINGTON, DC,
2000
How should eosinophilic cystitis be treated in patients with chronic granulomatous disease?
Chronic granulomatous disease (CGD) is a primary immunodeficiency resulting from the absence or malfunction of oxidative mechanism in phagocytic cells. The disease is due to a mutation in one of four genes that encode subunits of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. Affected patients experience severe infections and granuloma formation due to exuberant inflammatory responses. Some evidence suggests that eosinophilic cystitis (EC) is included in the spectrum of inflammatory manifestations. EC is an inflammatory disease, rare in childhood, which may require different, nonstandardized therapeutic approaches, ranging from antihistamines to cyclosporine
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