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981.
In this paper, we consider a finite difference grid-based semi-Lagrangian approach for solving the Vlasov–Poisson (VP) system. Many of existing methods are based on dimensional splitting, which decouples the problem into solving linear advection problems, see Cheng and Knorr (J Comput Phys 22:330–351, 1976). However, such splitting is subject to the splitting error. If we consider multi-dimensional problems without splitting, difficulty arises in tracing characteristics with high order accuracy. Specifically, the evolution of characteristics is subject to the electric field which is determined globally from the distribution of particle density via Poisson’s equation. In this paper, we propose a novel strategy of tracing characteristics high order in time via a two-stage multi-derivative prediction–correction approach and by using moment equations of the VP system. With the foot of characteristics being accurately located, we propose to use weighted essentially non-oscillatory interpolation to recover function values between grid points, therefore to update the solution at the next time level. The proposed method does not have time step restriction as the Eulerian approach and enjoys high order spatial and temporal accuracy. The performance of the proposed schemes are numerically demonstrated via classical test problems such as Landau damping and two stream instabilities. 相似文献
982.
Giovanni B. Broggiato Francesca Campana Edoardo Mancini 《Engineering with Computers》2013,29(3):319-327
Computer-aided engineering methods are extensively applied to sheet metal forming integrated design. The adoption of a new class of materials, the advanced high strength steels, has increased the occurrence of springback, and consequently the request for tools oriented to springback reduction and optimization. This paper presents an approximated formulation to compute the springback field after stamping through the finite element analysis of the process. This can be found assuming that the residual field of nodal forces after stamping produces a springback shape referable to a linear combination of n modes of vibration of the nominal shape of the component. The aim of this formulation is not that of substituting the finite element analysis of the springback but rather to make use of the coefficients of the linear combination, so to define a global quality function for springback. In this way, Robust Design methods or other current optimization procedures to improve the stamping process as for structural defects (such wrinkling, necking and flatness) can be applied also for the reduction of springback. The meaning of these coefficients will be shown through three test cases and the consistency of the formulation will be discussed according to the number of modes of vibration included in the computation. 相似文献
983.
Giovanni Forzieri Fabio Castelli Federico Preti 《International journal of remote sensing》2013,34(2):630-654
Riparian vegetation plays a crucial role in affecting the floodplain hydraulic roughness, which in turn significantly influences the dynamics of flood waves. Systematic detection, identification and assessment of flow resistance factors using conventional field sampling is often unfeasible as these techniques are time-consuming and expensive. As in many other environmental monitoring problems, remote sensing may provide unprecedented mapping capabilities. In this article we present an overview focusing on the different methods that can be used to remotely derive floodplain hydraulic roughness. The overview is based on an extensive literature review on recent estimation techniques of riparian roughness using remote sensing data from different platforms. The outlined methods of floodplain roughness parameterization include: (1) classification-derived hydraulic roughness maps and (2) estimation of vegetation hydrodynamic properties. Possible directions for a multiscale analysis of riparian flow resistance are also described in a short section by focusing on the potential of data assimilation methods for the estimation of floodplain roughness. The literature reveals that many valuable remote-sensing techniques have been developed for riparian corridor parameterization. Methodologies based on the fusion of multispectral/temporal imagery with data of different origin, such as light detection and ranging (LiDAR) and radar/microwave, appear to be powerful tools for characterizing riparian ecosystems for hydraulic purposes. 相似文献
984.
ISWEC: A gyroscopic mechanism for wave power exploitation 总被引:1,自引:0,他引:1
Giovanni Bracco Ermanno GiorcelliGiuliana Mattiazzo 《Mechanism and Machine Theory》2011,46(10):1411-1424
In the past four decades, hundreds of Wave Energy Converters (WECs) have been proposed and studied, but so far a final architecture to harvest wave power has not been identified. Many engineering problems are still to be solved, like survivability, durability and effective power capture in a variable wave climate. ISWEC (Inertial Sea Wave Energy Converter) is a system using the gyroscopic reactions provided from a spinning flywheel to extract power. The flywheel works inside a sealed floating body in order to be protected from the outer environment and grant a reliable and durable operation. The article summarizes the design procedure of a 1:45 scaled ISWEC device with rated power 2.2 W and the tank tests performed with a simplified plain float to verify the actual prototype power capabilities. The article then focuses on the implementation of a non-linear coupled model (mechanics + hydrodynamics) to improve the float shape in order to maximize the power absorption. The final result is a float shape capable to absorb a power almost three times bigger (5.96 W) than the initial float shape. 相似文献
985.
We introduce efficient margin-based algorithms for selective sampling and filtering in binary classification tasks. Experiments
on real-world textual data reveal that our algorithms perform significantly better than popular and similarly efficient competitors.
Using the so-called Mammen-Tsybakov low noise condition to parametrize the instance distribution, and assuming linear label
noise, we show bounds on the convergence rate to the Bayes risk of a weaker adaptive variant of our selective sampler. Our
analysis reveals that, excluding logarithmic factors, the average risk of this adaptive sampler converges to the Bayes risk
at rate N
−(1+α)(2+α)/2(3+α) where N denotes the number of queried labels, and α>0 is the exponent in the low noise condition. For all $\alpha>\sqrt{3}-1\approx0.73$\alpha>\sqrt{3}-1\approx0.73 this convergence rate is asymptotically faster than the rate N
−(1+α)/(2+α) achieved by the fully supervised version of the base selective sampler, which queries all labels. Moreover, for α→∞ (hard margin condition) the gap between the semi- and fully-supervised rates becomes exponential. 相似文献
986.
We provide a logical analysis of private international law, a rather esoteric, but increasingly important, domain of the law. Private international law addresses overlaps and conflicts between legal systems by distributing cases between the authorities of such systems (jurisdiction) and establishing what rules these authorities have to apply to each case (choice of law). A formal model of the resulting interactions between legal systems is proposed based on modular argumentation. It is argued that this model may also be useful for governing the interactions between heterogeneous agents, belonging to different and differently regulated virtual societies, without recourse to a central regulatory agency. The model also provides for multiple interpretations concerning rules of private international law as well as substantive rules of the different legal systems. 相似文献
987.
Irene Amerini Giovanni Ballocca Rudy Becarelli Roberto Borri Roberto Caldelli Francesco Filippini 《Multimedia Tools and Applications》2010,50(2):381-414
In the last decade with the growth of Interactive Digital Television (IDTV) we have seen the end of passive television. An
example of this trend is Internet access through television by means of the last generation Set Top Boxes (STBs). The chance
to enjoy web contents through digital television Set Top Boxes, delivering a satisfying browsing experience across this platform,
could provide the opportunity to promote social inclusion and bridging the “digital divide”. In this paper we present WebClimb, a web browser that would pursue an effective integration of Digital Terrestrial Television (DTT) and Internet in the DVB-MHP
platform. WebClimb is a Java-based web browser that enables users to browse the web by interacting with an easy to use Graphical User Interface
(GUI), driven by a common TV remote control without asking for reformatting such a content on the server side. In addition
to this, the main requirement has been to design and develop an MHP browser application to be broadcast through a TV channel
and not embedded in a specific device, though it could be too. Experimental results and a comparison with other possible solutions
are provided. 相似文献
988.
Gustavo Marfia Claudio E. Palazzi Giovanni Pau Mario Gerla Marco Roccetti 《Computer Networks》2010,54(14):2327-2344
The Transmission Control Protocol (TCP), the most widely used transport protocol over the Internet, has been advertised to implement fairness between flows competing for the same narrow link. However, when session round-trip-times (RTTs) radically differ, the share may be anything but fair. This RTT-unfairness represents a problem that severely affects the performance of long-RTT flows and whose solution requires a revision of TCP’s congestion control scheme. To this aim, we discuss TCP Libra, a new transport protocol able to ensure fairness and scalability regardless of the RTT, while remaining friendly towards legacy TCP. As main contributions of this paper: (i) we focus on the model derivation and show how it leads to the design of TCP Libra; (ii) we analyze the role of its parameters and suggest how they may be adjusted to lead to asymptotic stability and fast convergence; (iii) we perform model-based, simulative, and real testbed comparisons with other TCP versions that have been reported as RTT-fair in the literature. Results demonstrate the ability of TCP Libra in ensuring RTT-fairness while remaining throughput efficient and friendly towards legacy TCP. 相似文献
989.
Franco Chialva Peter A. P. Liddle Giovanni Doglia 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1983,176(5):363-366
Summary A series of essential oils obtained from samples ofArtemisia absinthium L. from various geographical origins and collected at different heights were analysed by means of glass-capillary gas chromatography. The main components were identified by means of GC, GC-MS, IR,1HNMR and13CNMR.Several chemotypes were detected: in the western Alpine arc (Italy) the most important chemotype, above 1,000 m., was acis-epoxy-ocimene type, while at lower levels a-thujone type predominated.Plants originating from France could be divided into a chrysanthenyl acetate and a saßinyl acetate chemotype; plants from Siberia, Rumania and some from Valle d'Aosta belonged to a mixed type.
Chemotaxonomie von Wermut (Artemisia absinthum L.)I. Zusammensetzung des ätherischen Öls einiger Chemotypen
Zusammenfassung Die ätherischen Öle des Wermuts, aus mehreren Herkunften und aus verschiedenen Höhen, wurden durch Capillargaschromatographie bestimmt und durch MS, IR,1HNMR,13CNMR identifiziert.Dabei konnten verschiedene Chemotypen festgestellt werden. In den Westalpen ist der cis-Epoxycimen Typ über 1000 m der wichtigste Typ, während der-Thujon-Typ in niedrigeren Zonen vorherrscht.Französische Muster gehörten zu den Chrysanthenylacetat-und Sabinylacetat-Chemotypen, Muster aus Sibirien, Rumänien und dem Aostatal dagegen zu einem gemischten Typ.相似文献