5,219 research outputs found
A strong form of the Quantitative Isoperimetric inequality
We give a refinement of the quantitative isoperimetric inequality. We prove
that the isoperimetric gap controls not only the Fraenkel asymmetry but also
the oscillation of the boundary
Push & Pull: autonomous deployment of mobile sensors for a complete coverage
Mobile sensor networks are important for several strategic applications
devoted to monitoring critical areas. In such hostile scenarios, sensors cannot
be deployed manually and are either sent from a safe location or dropped from
an aircraft. Mobile devices permit a dynamic deployment reconfiguration that
improves the coverage in terms of completeness and uniformity.
In this paper we propose a distributed algorithm for the autonomous
deployment of mobile sensors called Push&Pull. According to our proposal,
movement decisions are made by each sensor on the basis of locally available
information and do not require any prior knowledge of the operating conditions
or any manual tuning of key parameters.
We formally prove that, when a sufficient number of sensors are available,
our approach guarantees a complete and uniform coverage. Furthermore, we
demonstrate that the algorithm execution always terminates preventing movement
oscillations.
Numerous simulations show that our algorithm reaches a complete coverage
within reasonable time with moderate energy consumption, even when the target
area has irregular shapes. Performance comparisons between Push&Pull and one of
the most acknowledged algorithms show how the former one can efficiently reach
a more uniform and complete coverage under a wide range of working scenarios.Comment: Technical Report. This paper has been published on Wireless Networks,
Springer. Animations and the complete code of the proposed algorithm are
available for download at the address:
http://www.dsi.uniroma1.it/~novella/mobile_sensors
Chandra Observation of a 300 kpc Hydrodynamic Instability in the Intergalactic Medium of the Merging Cluster of Galaxies A3667
We present results from the combination of two Chandra pointings of the
central region of the cluster of galaxies A3667. From the data analysis of the
first pointing Vikhlinin et al. reported the discovery of a prominent cold
front which is interpreted as the boundary of a cool gas cloud moving through
the hotter ambient gas. Vikhlinin et al. discussed the role of the magnetic
fields in maintaining the apparent dynamical stability of the cold front over a
wide sector at the forward edge of the moving cloud and suppressing transport
processes across the front. In this Letter, we identify two new features in the
X-ray image of A3667: i) a 300 kpc arc-like filamentary X-ray excess extending
from the cold gas cloud border into the hotter ambient gas; ii) a similar
arc-like filamentary X-ray depression that develops inside the gas cloud. The
temperature map suggests that the temperature of the filamentary excess is
consistent with that inside the gas cloud while the temperature of the
depression is consistent with that of the ambient gas. We suggest that the
observed features represent the first evidence for the development of a large
scale hydrodynamic instability in the cluster atmosphere resulting from a major
merger. This result confirms previous claims for the presence of a moving cold
gas cloud into the hotter ambient gas. Moreover it shows that, although the gas
mixing is suppressed at the leading edge of the subcluster due to its magnetic
structure, strong turbulent mixing occurs at larger angles to the direction of
motion. We show that this mixing process may favor the deposition of a
nonnegligible quantity of thermal energy right in the cluster center, affecting
the development of the central cooling flow.Comment: Replaced to match version accepted for publication in ApJL; some
changes on text. 4 pages, 3 color figures and 2 BW figures, emulateapj
Effect of Ferric Sodium EDTA administration, in combination with vitamin C, folic acid, copper gluconate, zinc gluconate and selenomethionine, on cardiovascular risk evaluation: exploration of the HRV frequency domain
diseases. Using the Heart Rate Variability (HRV) analysis is possible to provide an evaluation of the safety and the
effectiveness of intervention.
Objective: To evaluate the efficacy and safety of Ferric Sodium EDTA in combination with vitamin C, folic acid, copper
gluconate, zinc gluconate and selenomethionine (Ferachel forte®) 2 tabs/day for 24 days in elderly patients with secondary
anaemia, by exploring the HRV frequency domain.
Methods: In 45 elderly patients with secondary anaemia and/or low-moderate kidney failure, laboratory values after
administration of Ferric Sodium EDTA, 2 tabs a day, in combination with vitamin C, folic acid, copper gluconate, zinc
gluconate and selenomethionine (Ferachel forte®) for 24 days (N=16 patients) or ferrous gluconate 63 mg/day added to
saline solution, administered using intravenous access during the hospitalization period of 15 ± 5 days (N=29 patients)
were evaluated. Also, ECG signals and bioelectrical impedance (BIA) were measured.
Results: Oral iron supplementation with Ferric Sodium EDTA, in combination with vitamin C, folic acid, copper gluconate,
zinc gluconate and selenomethionine (Ferachel forte®) confirmed to be effective and safe about the cardiovascular risk
in old patients. This study showed the real superiority of the oral administration about the cardiovascular risk in elderly
patients in comparison with intravenous administration of ferrous gluconate.
Conclusion: This study confirms that Ferric Sodium EDTA combination (Ferachel forte®) can be a valid alternative to ferrous
gluconate intravenous therapy (gold standard) in the treatment of secondary anaemia in elderly patients. In fact, during
the treatment, efficacy results have been maintained without statistically significant variations about cardiovascular risk,
evaluated by exploring the HRV frequency domain
INTEGRAL discovery of non-thermal hard X-ray emission from the Ophiuchus cluster
We present the results of deep observations of the Ophiuchus cluster of
galaxies with INTEGRAL in the 3-80 keV band. We analyse 3 Ms of INTEGRAL data
on the Ophiuchus cluster with the IBIS/ISGRI hard X-ray imager and the JEM-X
X-ray monitor. In the X-ray band using JEM-X, we show that the source is
extended, and that the morphology is compatible with the results found by
previous missions. Above 20 keV, we show that the size of the source is
slightly larger than the PSF of the instrument, and is consistent with the soft
X-ray morphology found with JEM-X and ASCA. Thanks to the constraints on the
temperature provided by JEM-X, we show that the spectrum of the cluster is not
well fitted by a single-temperature thermal Bremsstrahlung model, and that
another spectral component is needed to explain the high energy data. We detect
the high energy tail with a higher detection significance (6.4 sigma) than the
BeppoSAX claim (2 sigma). Because of the imaging capabilities of JEM-X and
ISGRI, we are able to exclude the possibility that the excess emission comes
from very hot regions or absorbed AGN, which proves that the excess emission is
indeed of non-thermal origin. Using the available radio data together with the
non-thermal hard X-ray flux, we estimate a magnetic field B ~ 0.1-0.2 mu G.Comment: 8 pages, 9 figures, accepted by A&
Analysis of Road Safety Speed from Floating Car Data
Intelligent Transportation Systems aims at improving efficiency and safety of the transportation system by acting either on vehicle performances or assisting the driver with information on vehicle and traffic status. Although digital road graphs are available to derive quantitative parameters that describe the road geometry, the information provided usually includes speed limits and repetition of road signs. On the other hand, a huge amount of data is available on individual vehicle speeds and trajectories collected as Floating Car Data (FCD) but they are not combined with road parameters to derive information on how drivers perceive the infrastructure and behave when traveling on it. In the paper, a methodology is presented to evaluate the consistency between drivers' behavior and a theoretical safety speed determined from road geometry. The azimuth profile is progressively built for a road layout, based on the geometry described by a digital graph. Consecutive elements with the constant azimuth variation are identified as circular curves and their radii are computed by circle fitting. The safety speed with respect to longitudinal stability is estimated. The obtained safety speed is then compared to the distribution of speeds observed from about 200 million FCD collected on the regional road network of Latium. The obtained results permit to individuate critical points of the network in terms of road safety
The Surface Diffusion Flow with Elasticity in Three Dimensions
We establish the short-time existence of a smooth solution to the surface diffusion equation with an elastic term and without an additional curvature regularization in three space dimensions. We also prove the asymptotic stability of strictly stable stationary sets
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