178,111 research outputs found
Modeling and experimentation of through-the-body RFID links and application to smart prosthesis
No full textThe Internet of Things (IoT) is the natural evolution of the current concept of Internet in which even the common objects of our daily lives, uniquely identifiable and equipped with sensing capabilities
will be globally connected and able to communicate and cooperate each others to improve the quality of our life. In this scenario even the human body could become a sensing node of the
network, able to communicate its needs and health status to healthcare center, boosting the traditional medical model towards the new idea of Pervasive Healthcare. The practical implementation of such Smart-Health services requires an enabling technology, completely
transparent to the user and with high degree of pervasiveness as low cost, long lifetime and low power consumption. In this regard, Radio Frequency Identification (RFID) technology can play a key
role in the development and implementation of IoT-based personal Healthcare systems. A RFID tag, together with its identification code is in fact able to carry information about the tagged objects
e.g. detecting the presence in the environment of gases or humidity when it is functionalized with special chemical compounds, or can be connected to sensors to monitor the temperature or other physical parameters. Moreover, these non-intrusive devices could be spread in the living environments, easily integrated inside clothes or embedded into implanted prosthesis, cardio-vascular stents, realizing in the latter case “augmented” devices able to take care of the human health “from the inside”. This Thesis, investigates the feasibility of passive UHF RFID implants
in the human body with particular regard to the area of the limbs in which, normally are implanted orthopedic prostheses, as a result of fractures or degenerative diseases of the musculoskeletal
system.
The structure of the Thesis is the following:
Part I (chapter 1) describes the key role of RFID technology in the implementation of a new model of healthcare in the frame of IoT with some examples of application in the monitoring of environmental parameters (temperature, presence of gases and humidity) and human behavior. The chapter 2 is devoted to the mathematical model to be applied for the analysis of the UHF-RFID radio channel consisting in a region of the human body wherein a passive tag is implanted.
Part II investigates the performance of through-the-body channel with reference to a human torso and limb simulators (chapter 3) introducing power budget indicators to determine the feasibility
and reliability of the wireless communications. In particular, with regard to implants in the limbs, the analysis will be enhanced by a campaign of measurements carried out on an experimental phantom
manufactured with meat and bovine bone, and using a loop antenna as a reference (chapter 4).
Part III of this work deals with the integration of a passive tag inside an orthopedic prosthesis (chapter 5). An intramedullary nail will be particularly considered in the analysis but the same considerations can be applied to other types of prosthesis. Also in this case the problem will be addressed either using both numerical simulations and experimental measurements on a prototype of the functionalized intramedullary nail inserted into a limb phantom
Evolution of supermassive black hole binaries in gaseous environments
No full textIn this contribution, I discuss some aspects of the dynamical evolution of supermassive black hole binaries and their accretion discs. Firstly, I discuss the issue of alignment of the spins of the two binary component, which has important implications for the shape of the gravitational wave emitted at merger and for the possibility of a strong recoil of the remnant black hole. Even under the favourable assumption that mass flow through the gap is not inhibited by tidal torque, we demonstrate that differential accretion onto the two components of the systems results in a very different spin evolution of the two black holes. Secondly, I revisit the issue of how much mass can flow within the cavity carved in the disc by an equal mass binary. Recent simulations have shown that the tidal torque of the binary is generally not sufficient to prevent accretion onto the binary component. Here, I demonstrate that such results are heavily dependent on the disc thickness. While for H/R ∼ 0.1 (the value adopted in most simulations to date), we reproduce the previous results, we show that as H/R is decreased to ∼ 0.01, mass flow through the gap is essentially shut off almost completely. Thirdly, I show numerical simulations of the process of gas squeezing during the merger proper, demonstrating that most of the disc mass is accreted producing a super-Eddington flare
The Physics of Accretion Discs, Winds and Jets in Tidal Disruption Events
No full textAccretion onto black holes is an efficient mechanism in converting the gas mass-energy into energetic outputs as radiation, wind and jet. Tidal disruption events, in which stars are tidally torn apart and then accreted onto supermassive black holes, offer unique opportunities of studying the accretion physics as well as the wind and jet launching physics across different accretion regimes. In this review, we systematically describe and discuss the models that have been developed to study the accretion flows and jets in tidal disruption events. A good knowledge of these physics is not only needed for understanding the emissions of the observed events, but also crucial for probing the general relativistic space-time around black holes and the demographics of supermassive black holes via tidal disruption events
A Structural Antenna for UHF-RFID Implant into Limb Prosthesis
No full textOrthopaedic prosthesis of the near future will incorporate
sensing and communication capabilities. An integrated
radiofrequency tag, suitable to cohabitation with a realistic
metallic prosthesis is here proposed by applying the technology
of structural antennas that is well assessed in the avionic
and naval communications. The resulting Prosthetic Structural
Tag (PST) is suitable to energy harvesting and radiofrequency
identifications. Simulation and laboratory experimentations over
phantoms demonstrated a read distance of more that 35cm at
870-960 MHz with an interesting power margin to enable also
sensing applications
Numerical and experimental characterization of through-the-body UHF-RFID links for passive tags implanted into human limbs
No full textAppropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Stellar disruption by a supermassive black hole : is the light curve really proportional to t^(-5/3)?
No full textIn this paper, we revisit the arguments for the basis of the time evolution of the flares expected to arise when a star is disrupted by a supermassive black hole. We present a simple analytic model relating the light curve to the internal density structure of the star. We thus show that the standard light curve proportional to t−5/3 only holds at late times. Close to the peak luminosity the light curve is shallower, deviating more strongly from t−5/3 for more centrally concentrated (e.g. solar type) stars. We test our model numerically by simulating the tidal disruption of several stellar models, described by simple polytropic spheres with index γ . The simulations agree with the analytical model given two considerations. First, the stars are somewhat inflated on reaching pericentre because of the effective reduction of gravity in the tidal field of the black hole. This is well described by a homologous expansion by a factor which becomes smaller as the polytropic index becomes larger. Secondly, for large polytropic indices wings appear in the tails of the energy distribution, indicating that some material is pushed further away from parabolic orbits by shocks in the tidal tails. In all our simulations, the t−5/3 light curve is achieved only at late stages. In particular, we predict that for solar-type stars, this happens only after the luminosity has dropped by at least 2 mag from the peak. We discuss our results in the light of recent observations of flares in otherwise quiescent galaxies and note the dependence of these results on further parameters, such as the star/hole mass ratio and the stellar orbit
The evolution of misaligned accretion discs and spinning black holes
No full textIn this paper, we consider the process of alignment of a spinning black hole and a surrounding misaligned accretion disc. We use a simplified set of equations, that describe the evolution of the system in the case where the propagation of warping disturbances in the accretion disc occurs diffusively, a situation likely to be common in the thin discs in active galactic nuclei (AGN). We also allow the direction of the hole spin to move under the action of the disc torques. In such a way, the evolution of the hole-disc system is computed self-consistently. We consider a number of different situations and we explore the relevant parameter range, by varying the location of the warp radius R-w and the propagation speed of the warp. We find that the dissipation associated with the twisting of the disc results in a large increase in the accretion rate through the disc, so that AGN accreting from a misaligned disc are likely to be significantly more luminous than those accreting from a flat disc. We compute explicitly the time-scales for the warping of the disc and for the alignment process and compare our results with earlier estimates based on simplified steady-state solutions. We also confirm earlier predictions that, under appropriate circumstances, accretion can proceed in a counter-aligned fashion, so that the accreted material will spin-down the hole, rather than spinning it up. Our results have implication in a number of different observational features of AGN such as the orientation and shape of jets, the shape of X-ray iron lines and the possibility of obscuration and absorption of X-ray by the outer disc as well as the general issue of the spin history of black holes during their growth
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