1,721,037 research outputs found
Design issues and performance analysis of CCM boost converters with RHP zero mitigation via inductor current sensing
Full text linkThe right-half plane (RHP) zero in the control to output voltage transfer function of a boost converter operating in the continuous conduction mode limits the loop bandwidth. By injecting a scaled version of the inductor current into the loop, it is possible to shift the zero from the right-half plane to the left-half plane, which leads to increased stability of the control loop. This solution generates a static voltage error at the output of the converter (tracking error), which may be unacceptable in practical applications. A few strategies to mitigate or correct this tracking error have been suggested. However, they have never been fully assessed. This paper thoroughly investigates the impact of the RHP zero mitigation technique on the dynamic performance of a boost converter, and identifies the complex trade-off between the system stability, transient response, and tracking error correction capability. Based on these findings, design guidelines are provided to help maximize system performance. A representative case study is considered to highlight the performance benefits and simulation results are presented to validate the analysis
A distributed message-optimal assignment on rings
No full textConsider a set of items and a set of m colors, where each item is associated to one color. Consider also n computational agents connected by a ring. Each agent holds a subset of the items and items of the same color can be held by different agents. We analyze the problem of distributively assigning colors to agents in such a way that (a) each color is assigned to one agent only and (b) the number of different colors assigned to each agent is minimum. Since any color assignment requires the items be distributed according to it (e.g. all items of the same color are to be held by only one agent), we define the cost of a color assignment as the amount of items that need to be moved, given an initial allocation. We first show that any distributed algorithm for this problem requires a message complexity of Ω(n⋅m) and then we exhibit an optimal message complexity algorithm for synchronous and asynchronous rings that in polynomial time determines a color assignment with cost at most three times the optimal. We show that the approximation is tight and how to get a better cost solution at the expenses of either the message or the time complexity. Finally, we present some experiments showing that, in practice, our algorithm performs much better than the theatrical worst case scenario
Electromagnetic and Thermal Models of a Water Cooled Dipole Radiating in a Biological Tissue
No full textAn insulated, water-cooled dipole, radiating in a biological tissue, is analyzed with a theoretical electromagnetic and thermal model. The SAR and temperature distributions are calculated taking into account the effect of the water flowing inside the applicator. The steady-state temperatures in a dissipative medium, interacting with the dipole, are evaluated for several thicknesses of the external casing, water temperatures and blood perfusions. A correct design of the external casing thickness and a proper choice of the temperature and flow velocity of water allows to control the wall temperature of the applicator within physiological limits. The influence of the blood perfusion on the temperature distribution is investigated
Analysis of electromagnetic scattering by artificially soft discs
No full textAn analysis of the electromagnetic behaviour of corrugated artificially soft discs, illuminated by a vertical dipole, was carried out by using both numerical and asymptotic methods. The finite-difference time-domain method was used to find near-field distributions. This allows the consistency of the artificially soft model to be tested; furthermore, the near-field data are used to find the radiation pattern by using near-to-far-field transformations. The direct scattering in the far zone was also obtained by using edge integration of incremental diffraction coefficients; these are derived by applying the localisation process of the incremental theory of diffraction to a wedge with perfectly soft boundary conditions on one face and perfectly electric boundary conditions on the other. The effect of the corrugations is analysed in the far-field limit by comparison with a perfectly conducting disc
Distributed balanced color assignment on arbitrary networks
No full textConsider a scenario in which a set of n agents hold items, where each item can be of one out of m possible types (colors). The agents are connected by an arbitrary network and have to distributively find a repartition of the colors such that the amount of colors for each agent is as balanced as possible: in the particular case where m is a multiple of n, each agent must have exactly m/n colors. More formally, the goal is to let the agents agree on an assignment of colors to agents such that the following two conditions hold: (i) each color is assigned to exactly one agent; (ii) each agent has at least ⌊m/n⌋ and at most ⌈m/n⌉ colors. Among all possible such repartitions, we seek for the one that minimizes the number of “changes” (measured in terms of misplaced items) with respect to the initial configuration. In other words, our aim is to design a distributed algorithm that finds a balanced coloring of minimum cost, where the cost of a coloring is the number of items that need to be relocated. This kind of questions, usually modeled as generalized bipartite matching problems, have been studied in the distributed setting only on clusters of commodity nodes with the aim of copying with real-world massive instances, which may involve millions of agents and colors. Here we propose the first distributed algorithm designed to run on an arbitrary network with the agents as nodes. Our algorithm turns out to be efficient in terms of both time and message complexity for a large class of graphs. Our results can be outlined as follows. We prove a lower bound Ω(m/n⋅D2) on message complexity, where D is the diameter of the graph, that holds for any approximation algorithm whose solution has cost at most 2(α−2)/α times the cost of any optimal solution, for every constant α>2. We give a distributed deterministic algorithm with time complexity O(maxn2,Dlogq) and message complexity?>O(nlogn⋅(logq+mlogm)), where q is the maximum number of items of a given color held by any agent. We show that the cost of our solution for arbitrary graphs is at most (2+δ) times the optimal cost, for any δ>0. We finally observe that, for large diameter graphs (i.e., D=Ω(nε), ε>0), we get matching lower and upper bounds on message complexity for the vast majority of instances of potential interest, that is, instances with polynomial number of colors and (up to) super-exponential number of items
Re-identification Attack based on Few-Hints Dataset Enrichment for Ubiquitous Applications
No full textUbiquitous and pervasive applications record a large amount of data about users, to provide context-aware and tailored services. Although this enables more personalized applications, it also poses several questions concerning the possible misuse of such data by a malicious entity, which may discover private and sensitive information about the users themselves. In this paper we propose an attack on ubiquitous applications pseudo-anonymized datasets which can be leaked or accessed by the attacker. We enrich the data with true information which the attacker can obtain from a multitude of sources, which will eventually spark a chain reaction on the records of the dataset, possibly re-identifying users. Our results indicate that through this attack, and with few hints added to the dataset, the possibility of re-identification are considerable, achieving more than 70% re-identified users on a public available dataset. We compare our proposal with the state of the art, showing the improved performance figures obtained thanks to the graph-modeling of the dataset records and the novel hint structure
Analisi del comportamento elettromagnetico e termico di applicatori interstiziali ed endocavitari
No full textA Dipole-type Intracavitary Hyperthermic Applicator with a Metallic Reflector: Experiments and Theoretical Analysis
No full textA water-cooled electromagnetic (EM) dipole, for intracavitary hyperthermia, embodying a metallic reflector to give directional characteristics to the SAR and then to the heating pattern in the biological tissue, is considered. The influence of the reflector on the SAR deposition has been theoretically modelled with an EM analysis which uses the method of moments (MOM). A thermal model, based on the heat transfer equation, is used to predict temperature distribution, which exhibits a directivity related to the angular extension of the reflector. Experiments have been carried out in a polyacrylamide phantom. The temperature distribution detected with a liquid crystal sheet shows fairly good agreement with theoretical predictions
- …
