7,729 research outputs found
A Type Inference Algorithm for Secure Ambients
We consider a type discipline for the Ambient Calculus that associates ambients with security levels and constrains them to be traversed by or opened in ambients of higher security clearance only. We present a bottom-up algorithm that, given an untyped process , computes a minimal set of constraints on security levels such that all actions during runs of are performed without violating the security level priorities. Such an algorithm appears to be a prerequisite to use type systems to ensure security properties in the web scenario
Computer simulation of the microstructure and rheology of semi-solid alloys under shear
The rheological behavior of metallic alloys containing both solid and liquid
phases is investigated in the low solid fraction range (<50%). This behavior
depends on both the solid fraction and the shear rate. The concept of Effective
Volume Fraction (EVF) is used to decorrelate the influence of these two
parameters. At high shear rate the slurry behaves like a suspension of hard
spheres, whereas at lower shear rate, particles tend to aggregate in clusters,
entrapping liquid and thus, increasing the EVF and the viscosity. A lattice
model is introduced to simulate the aggregation / break-up processes within a
slurry under shear. When the steady state is reached, the entrapped liquid
fraction is calculated, leading to a viscosity estimation. Simulation results
for the viscosity and 3D cluster structure are in good agreement with
experimental results.Comment: 30 pages, 17 figures, to be published in Acta Mate
Searching for pulsed emission from XTE J0929-314 at high radio frequencies
The aim of this work is to search for radio signals in the quiescent phase of
accreting millisecond X-ray pulsars, in this way giving an ultimate proof of
the recycling model, thereby unambiguously establishing that accreting
millisecond X-ray pulsars are the progenitors of radio millisecond pulsars.
To overcome the possible free-free absorption caused by matter surrounding
accreting millisecond X-ray pulsars in their quiescence phase, we performed the
observations at high frequencies. Making use of particularly precise orbital
and spin parameters obtained from X-ray observations, we carried out a deep
search for radio-pulsed emission from the accreting millisecond X-ray pulsar
XTE J0929-314 in three steps, correcting for the effect of the dispersion due
to the interstellar medium, eliminating the orbital motions effects, and
finally folding the time series.
No radio pulsation is present in the analyzed data down to a limit of 68
microJy at 6.4 GHz and 26 microJy at 8.5 GHz.
We discuss several mechanisms that could prevent the detection, concluding
that beaming factor and intrinsic low luminosity are the most likely
explanations.Comment: 7 pages, 4 figures. Accepted for publication in Astronomy &
Astrophysic
Measuring the spin up of the Accreting Millisecond Pulsar XTE J1751-305
We perform a timing analysis on RXTE data of the accreting millisecond pulsar
XTE J1751-305 observed during the April 2002 outburst. After having corrected
for Doppler effects on the pulse phases due to the orbital motion of the
source, we performed a timing analysis on the phase delays, which gives, for
the first time for this source, an estimate of the average spin frequency
derivative = (3.7 +/- 1.0)E-13 Hz/s. We discuss the torque resulting
from the spin-up of the neutron star deriving a dynamical estimate of the mass
accretion rate and comparing it with the one obtained from X-ray flux.
Constraints on the distance to the source are discussed, leading to a lower
limit of \sim 6.7 kpc.Comment: 7 pages, 3 figures, Accepted for publication by MNRA
The Status of a PA Endangered Bird- the Upland Sandpiper
The upland sandpiper (Bartramia Longuardia) has experienced a steep population decline in the northeastern U.S. since the mid-20th Century. In Pennsylvania it was found in less than 0.5% of atlas blocks during the Second Atlas of Breeding Birds in Pennsylvania project (2nd PBBA; 2004-09) and breeding was confirmed at only two locations. Due to continued declines and a small population size, the upland sandpiper was listed as PA endangered in 2012. During May 2012 the areas around 15 2nd PBBA upland sandpiper sightings were resurveyed by Gettysburg College students and volunteer birdwatchers. The aim was to establish whether the atlas records related to persisting populations. We used five-minute audio playback at up to 10 locations within 4km of the atlas sightings. A maximum of 19 pairs/calling male upland sandpipers were found across the state in 2012, most of them on or close to reclaimed surface mines. However, locating such a scarce species can be problematic, and it is still not known to what extent the species is under-reported. To help direct future surveys we analyzed data from the 2nd PBBA and the 2012 survey to produce a habitat suitability model for the upland sandpiper in Pennsylvania. We used a GIS framework to determine areas of suitable habitat and then stratified these by proximity to recent (2004-2012) upland sandpiper sightings. We recommend that our suitability model be used to establish a sampling protocol for more thorough statewide upland sandpiper survey every five years, in order that the species’ precarious status can be closely monitored
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Educational strategies in data journalism: A comparative study of six European countries
The article explores training programs in higher education with regard to data journalism from a multi-national perspective. By carrying out a comparative analysis in six European countries (Germany, Switzerland, the Netherlands, Italy, Poland, and the United Kingdom), it covers different models of media systems and journalistic cultures envisaged by Hallin and Mancini. Based on a desk review and in-depth interviews with instructors of data journalism in each country, the article identifies different approaches to the way data journalism is taught. In Europe, such programs are offered by four types of organizations: academic, vocational, professional, and civic. The role played by those organizations can be explained as a result of the peculiarities of national media systems. But there are also commonalities, for example, non-academic institutions (such as the European Journalism Center or the Center for Investigative Journalism) and major international news outlets (such as The Guardian and The New York Times) seem to take over a leading role in all of the analyzed countries. Generally speaking, data journalism education appears to be a very young discipline that frequently neglects fundamental journalistic topics such as ethical issues, transparency, accountability, and responsiveness although they are crucial in a journalistic field as sophisticated tools to reveal hidden aspects of reality
Timing of the Accreting Millisecond Pulsar XTE J1814-338
We present a precise timing analysis of the accreting millisecond pulsar XTE
J1814-338 during its 2003 outburst, observed by RXTE. A full orbital solution
is given for the first time; Doppler effects induced by the motion of the
source in the binary system were corrected, leading to a refined estimate of
the orbital period, P_orb=15388.7229(2)s, and of the projected semimajor axis,
a sini/c= 390.633(9) lt-ms. We could then investigate the spin behaviour of the
accreting compact object during the outburst. We report here a refined value of
the spin frequency (nu=314.35610879(1) Hz) and the first estimate of the spin
frequency derivative of this source while accreting (nu^dot=(-6.7 +/- 0.7)
10^(-14) Hz/s). This spin down behaviour arises when both the fundamental
frequency and the second harmonic are taken into consideration. We discuss this
in the context of the interaction between the disc and the quickly rotating
magnetosphere, at accretion rates sufficiently low to allow a threading of the
accretion disc in regions where the Keplerian velocity is slower than the
magnetosphere velocity. We also present indications of a jitter of the pulse
phases around the mean trend, which we argue results from movements of the
accreting hotspots in response to variations of the accretion rate.Comment: 7 pages, 4 figures, Accepted for publication by MNRA
Appraisal Value and Assessed Value in Italy.
The appraisal value is an appraiser's opinion (not determination) of
the current worth of a property on the real estate market. The assessed value is
the value placed on real estate property by government assessors for
determining ad valorem taxes. Assessed value is used rarely as basis for
appraisal value. The Italian appraisal practice is characterized by valuations
developed in subjective opinions formulated by the valuers, according to the
experience and the competence rather than on the survey of the market data of
comparable properties. These opinions are indicated by the term expertise,
borrowed from the estimates made in the art market. In Italy, the valuation of
the properties applies a form of expertise based on subjective opinion rather
than on the market prices. The basis of the expertise is one synthetic estimate of
the value based on a single parameter, often derived from generic list of interval
values quotations
Multilevel methodology approach for the construction of real estate monthly index numbers
In this paper, we evaluate price indices and hedonic price indices for Italian real estate data using multilevel models. The methodology is based on a random coefficient panel data model. We propose a Laspeyres-type price index and hedonic prices indexes based on some characteristics of the sold properties. The multilevel hierarchical analysis has the advantage of allowing the appraisal analysis for groups, and identified in the same sample data the hierarchical structures of market segmentation according to the parameters of the real estate segment. It allows getting a lot of regression functions as the number of groups identified. Obviously, this depends on the sample size and the variability between groups. Specifically, if the data are also grouped by date, the model allows an analysis of the time series which makes possible the calculation of index numbers and the overall monthly index numbers of real estate properties, consistent with collected data
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