7,060 research outputs found
Performance Analysis and Design of Maximum Ratio Combining in Channel-Aware MIMO Decision Fusion
In this paper we present a theoretical performance analysis of the maximum
ratio combining (MRC) rule for channel-aware decision fusion over
multiple-input multiple-output (MIMO) channels for (conditionally) dependent
and independent local decisions. The system probabilities of false alarm and
detection conditioned on the channel realization are derived in closed form and
an approximated threshold choice is given. Furthermore, the channel-averaged
(CA) performances are evaluated in terms of the CA system probabilities of
false alarm and detection and the area under the receiver operating
characteristic (ROC) through the closed form of the conditional moment
generating function (MGF) of the MRC statistic, along with Gauss-Chebyshev (GC)
quadrature rules. Furthermore, we derive the deflection coefficients in closed
form, which are used for sensor threshold design. Finally, all the results are
confirmed through Monte Carlo simulations.Comment: To appear in IEEE Transactions on Wireless Communication
Uso delle tecniche GNSS a supporto dei rilievi di infortunistica stradale
In the context of scientific research developed in recent years by DICAM, University of Palermo, a
trend that is particularly interesting and multidisciplinary concerning the use of GNSS techniques in
NRTK for applications of road accidents.
The detections of the information relating to the left road today are conducted with standardized
mode between those of local police; regarding the real relief it is realized with triangulation
techniques, with the aid of manual instrumentation consists casters metrics in plastic or steel wires.
The GNSS techniques in NRTK lend themselves well to this type of survey, the high information
content and to manage different metadata (maps, coordinates, photographs, details of the accident)
that are useful for the detection of claims.
This paper reports the experience that has been conducted in teams to aid detection of road
accidents in the body of the Municipal Police of Palermo using the Topcon GNSS instrumentation,
and in particular a GNSS receiver GRS1 equipped with software TopCRASH.
The first results are very encouraging and lead to the conclusion that the GNSS in NRTK is ripe for
interdisciplinary applications such as those related to road acciden
Pedestrian access to a network of public transport
The location of the bus stops is very important in urban and suburban contexts. The same importance of safety perception and comfort during transport operations is attributed to accessibility to bus stops. The placement of bus stops is a crucial factor to increase safety of passengers and pedestrians as well as the efficacy and efficiency of local public transport operations. To correctly localize these infrastructures, designers use physical parameters, such as maximum walking distance and travel time. While critical factors related to the quality of pedestrian access to the bus stop, to the real walked distance or to land use of bus stop areas are not taken in to account. The purpose of this paper is to propose a GIS methodology, which may correlate qualitative and quantitative factors that characterize the pedestrian access network to the bus stops
POTENTIAL DEMAND AND PRELIMINARY DESIGN OF DOOR TO DOOR DIAL A RYDE SYSTEMS
The paper aims to provide a framework for the preliminary design of dial a ride system. In this context we have carried out a stated preference survey to evaluate the potential
demand of service, taking into account a sample of citizens with limited disability to move.
Thus, we have submitted a questionnaire to users of some clinics of Palermo, considering in
the choice competitive scenario the dial a ride system. Furthermore a multinomial logit model
has been calibrated. Finally a preliminary design of service has been proposed
Chandra Observation of the Persistent Emission from the Dipping Source XB 1916-053
We present the results of a 50 ks long Chandra observation of the dipping
source XB 1916-053. During the observation two X-ray bursts occurred and the
dips were not present at each orbital period. From the zero-order image we
estimate the precise X-ray coordinates of the source with a 90% uncertainty of
0.6''. In this work we focus on the spectral study of discrete absorption
features, during the persistent emission, using the High Energy Transmission
Grating Spectrometer on board the Chandra satellite. We detect, for the first
time in the 1st-order spectra of XB 1916-053, absorption lines associated to Ne
X, Mg XII, Si XIV, and S XVI, and confirm the presence of the Fe XXV and Fe
XXVI absorption lines with a larger accuracy with respect to the previous XMM
EPIC pn observation. Assuming that the line widths are due to a bulk motion or
a turbulence associated to the coronal activity, we estimate that the lines are
produced in a photoionized absorber distant from the neutron star 4 x 10^{10}
cm, near the disk edge.Comment: 20 pages, 10 figures, submitted to ApJ on 2005-09-22, accepted by ApJ
on 2006-05-0
Bus speed estimation by neural networks to improve the automatic fleet management
In the urban areas, public transport service interacts with the private mobility. Moreover, on each link
of the urban public transport network, the bus speed is affected by a high variability over time. It depends
on the congestion level and the presence of bus way or no. The scheduling reliability of the public
transport service is crucial to increase attractiveness against private car use. A comparison between a
Radial Basis Function network (RBF) and Multi layer Perceptron (MLP) was carried out to estimate the
average speed, analysing the dynamic bus location data achieved by an AVMS (Automatic Vehicle
Monitoring System). Collected data concern bus location, geometrical parameters and traffic conditions.
Public Transport Company of Palermo provided these data
Broad-band Spectral Evolution of Scorpius X-1 along its Color-Color Diagram
We analyze a large collection of RXTE archive data from April 1997 to August
2003 of the bright X-ray source Scorpius X-1 in order to study the broadband
spectral evolution of the source for different values of the inferred mass
accretion rate by studying energy spectra from selected regions in the Z-track
of its Color-Color Diagram. A two-component model, consisting of a soft thermal
component interpreted as thermal emission from an accretion disk and a thermal
Comptonization component, is unable to fit the whole 3--200 keV energy spectrum
at low accretion rates. Strong residuals in the highest energy band of the
spectrum require the addition of a third component that can be fitted with a
power-law component, that could represent a second thermal Comptonization from
a much hotter plasma, or a hybrid thermal/non-thermal Comptonization. We
discuss the physical implications derived from the results of our analysis,
with a particular emphasis on the hardest part of the X-ray emission and its
possible origins.Comment: 18 pages. Accepted for publication in Ap
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
A multidisciplinary approach using LCCA and micro-simulation 10 model for the management of the urban pavements
The maintenance and the rehabilitation of the urban road pavements are not often based on
systematic program and scheduling but rather on emergency or on other not identified reasons.
Moreover the Life Cycle Cost Analysis (LCCA), the only peculiar procedure for the
management pavement, finds its own application for highway and motorway, even if it is
possible to search the best investment for the urban interstate and arterials.
By the light of the quantity of the involved resources, it seems necessary to define an operative
methodology for programming the maintenance and rehabilitation activities for the urban
pavement. The paper is oriented towards the development of a multidisciplinary approach to
make decision on management of urban pavement using the basic concepts of the LCCA and
micro-simulation model to define a scheme of work zone that minimizes the delay on the traffic
flow.
The best rehabilitation strategy should be characterized by the lowest users\u2019 cost that depends on
the time period of the work zone, which is conditioned by both own scheme and the provided
treatment, and on \u201csocial cost\u201d as increased travel time for queue generation .
Different scenarios for different work zone plans were developed and a micro-simulation model
was used to assess increased total travel time of a traffic flow within the maintenance area.
In this work an analysis by means of the above mentioned approach was carried out on real scenario in the city of Palermo in order to point out the several frames of the adopted
methodology
The role of General Relativity in the evolution of Low Mass X-ray Binaries
We study the evolution of Low Mass X-ray Binaries (LMXBs) and of millisecond
binary radio pulsars (MSPs), with numerical simulations that keep into account
the evolution of the companion, of the binary system and of the neutron star.
According to general relativity, when energy is released, the system loses
gravitational mass. Moreover, the neutron star can collapse to a black hole if
its mass exceeds a critical limit, that depends on the equation of state. These
facts have some interesting consequences: 1) In a MSP the mass-energy is lost
with a specific angular momentum that is smaller than the one of the system,
resulting in a positive contribution to the orbital period derivative. If this
contribution is dominant and can be measured, we can extract information about
the moment of inertia of the neutron star, since the energy loss rate depends
on it. Such a measurement can therefore help to put constraints on the equation
of state of ultradense matter. 2) In LMXBs below the bifurcation period (\sim
18 h), the neutron star survives the period gap only if its mass is smaller
than the maximum non-rotating mass when the companion becomes fully convective
and accretion pauses. Therefore short period (P < 2h) millisecond X-ray pulsar
like SAX J1808.4-3658 can be formed only if either a large part of the
accreting matter has been ejected from the system, or the equation of state of
ultradense matter is very stiff. 3) In Low Mass X-ray binaries above the
bifurcation period, the mass-energy loss lowers the mass transfer rate. As side
effect, the inner core of the companion star becomes 1% bigger than in a system
with a non-collapsed primary. Due to this difference, the final orbital period
of the system becomes 20% larger than what is obtained if the mass-energy loss
effect is not taken into account.Comment: 7 pages, 3 figures, accepted by the MNRA
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