Narrow-band filtering by means of triangular meta-material resonators based on RF MEMS cantilevers in CPW configuration

Microsystem Technologies - Triangular resonators, designed by using Radio Frequency Micro Electro Mechanical Systems (RF MEMS) cantilevers in coplanar waveguide (CPW) configuration, have been...     

A High Order Multi-Dimensional Characteristic Tracing Strategy for the Vlasov–Poisson System

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.     

Computer-aided engineering for sheet metal forming: definition of a springback quality function

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.     

Advances in remote sensing of hydraulic roughness

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.     

ISWEC: A gyroscopic mechanism for wave power exploitation

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.     

Learning noisy linear classifiers via adaptive and selective sampling

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.     

The modular logic of private international law

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.     

Wireless multimedia delivery over 802.11e with cross-layer optimization techniques

The use of wireless networks has spread further than simple data transfer to delay sensitive and loss tolerant multimedia applications. Over the past few years, wireless multimedia transmission across Wireless Local area Networks (WLANs) has gained a lot of attention because of the introduction of technologies such as Bluetooth, IEEE 802.11, 3G, and WiMAX. The IEEE 802.11 WLAN has become a dominating technology due to its low cost and ease of implementation. But, transmitting video over WLANs in real time remains a challenge because it imposes strong demands on video codec, the underlying network, and the Media Access Control (MAC) layer. This paper presents a cross-layer mapping algorithm to improve the quality of transmission of H.264 (a recently-developed video coding standard of the ITU-T Video Coding Experts Group) video stream over IEEE 802.11e-based wireless networks. The major goals of H.264 standard were on improving the rate distortion and the enhanced compression performance. Our proposed cross-layer design involves the mapping of H.264 video slices (packets) to appropriate access categories of IEEE 802.11e according to their information significance. We evaluate the performance of our proposed cross-layer design and the results obtained demonstrate its effectiveness in exploiting characteristics of the MAC and application layers to improve the video transmission quality.     

A DVB-MHP web browser to pursue convergence between Digital Terrestrial Television and Internet

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.     

TCP Libra: Derivation,analysis, and comparison with other RTT-fair TCPs

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.