1,515 research outputs found
On a necessary condition for B-spline Gabor frames
No full textIn a previous note K. Grochenig et al. prove that if g is a continuous function with compact support such that the translates of g form a partition of unity, then g cannot generate a Gabor frame for integer values of the frequency shift parameter b greater than 1. We give a simpler proof of this result which applies also to windows g which are neither continuous nor with compact support. Our proof is based on a necessary condition for Gabor frames due to C. E. Heil and D. F. Walnut
Computer Aided Modelling of Rubber Pad Forming Process
No full textRubber pad forming (RPF) is a novel method for sheet metal forming that has been increasingly used for: automotive, energy, electronic and aeronautic applications. Compared with the conventional forming processes, this method only requires one rigid die, according to the shape of the part, and the other tool is replaced by a rubber pad. This method can greatly improve the formability of the blank because the contact surface between the rigid die and the rubber pad is flexible. By this way the rubber pad forming enables the production of sheet metal parts with complex contours and bends. Furthermore, the rubber pad forming process is characterized by a low cost of the die because only one rigid die is required.
The conventional way to develop rubber pad forming processes of metallic components requires a burdensome trial-and-error process for setting-up the technology, whose success chiefly depends on operator’s skill and experience. In the aeronautical field, where the parts are produced in small series, a too lengthy and costly development phase cannot be accepted. Moreover, the small number of components does not justify large investments in tooling. For these reasons, it is necessary that, during the conceptual design, possible technological troubles are preliminarily faced by means of numerical simulation.
In this study, the rubber forming process of an aluminum alloy aeronautic component has been explored with numerical simulations and the significant parameters associated with this process have been investigated. Several effects, depending on: stamping strategy, component geometry and rubber pad characterization have been taken into account.
The process analysis has been carried out thanks to an extensive use of a commercially finite element (FE) package useful for an appropriate set-up of the process model. These investigations have shown the effectiveness of simulations in process design and highlighted the critical parameters which require necessary adjustments before physical tests
Frames and oversampling formulas for band limited functions
No full textIn this article, we obtain families of frames for the space B (omega) of functions with band in [-omega, omega] by using the theory of shift-invariant spaces. Our results are based on the Gramian analysis of Ron and Shen and a variant, due to Bownik, of their characterization of families of functions whose shifts form frames or Riesz bases. We give necessary and sufficient conditions for the translates of a finite number of functions (generators) to be a frame or a Riesz basis for B (omega) . We also give explicit formulas for the dual generators, and we apply them to Hilbert transform sampling and derivative sampling. Finally we provide numerical experiments that support the theory
Il paesaggio vegetale della conca del Lago Torbido e del Lago Turchino al Monte Rondinaio (Appennino lucchese-modenese). II contributo. Note miscellanee su alcune piante rare o di interesse fitogeografico
No full textInvestigation of new cae tools features to take in account the metal forming process memory of stamped parts for massive production of structural members in automotive applications
No full text
Efficiency measurement and uncertainty discussion of an electric engine powered by a ‘self-breathing’ and ‘self-humidified’ proton exchange membrane fuel cell
No full textThe efficiency of an automotive engine based on a “self-breathing” and “self-humidified” proton exchange membrane fuel cell stack PEM FC connected to a dc brushless electrical motor was measured under variable power load conditions. Experiments have been carried out on a small scale 150 W engine model. After determining the fuel cell static polarization curve and the time response to power steps, the system was driven to copy on the test bench a “standard urban load cycle” and its instantaneous efficiencies were measured at an acquisition rate of 5 Hz. The integral system efficiency over the entire urban load cycle, comprising the losses of the unavoidable auxiliary components of the engine, was then calculated. The fuel cell stack was operated mainly in “partial” dead-end mode, with a periodic anode flow channel purging, and one test was carried out in “pure” dead-end mode, with no anode channel purging. An uncertainty analysis of the efficiencies was carried out, taking into account either type A and type B evaluation methods, strengthening the discussion about the outcomes obtained for a system based on this novel simplified FC type. For our small scale engine we measured over the standard urban cycle, on the basis of the H2 high heating
value HHV, a tank-to-wheel integral efficiency of 18.2±0.8%, when the fuel cell was operated with periodic flow channel purging, and of 21.5±1.3% in complete dead-end operation mode
Il paesaggio vegetale della conca del Lago Torbido e del Lago Turchino al Monte Rondinaio (Appennino lucchese-modenese). I contributo
No full textWENDY: a Wireless Environmental Monitoring Device Prototype
No full textRecent studies show how air quality monitoring activities are fundamental because the environment has always played a vital role in the life-cycle of an artwork/monument, due to interaction with the materials. For this reason, we propose and present a measuring device able to detects different parameters. The device is instrumented with a microcontroller that detects signals from an inertial sensor with nine degrees of freedom, a sensor for climate parameters, four gas sensors (SO2, O3, NO, NO2), a lux-meter and particles matter analyzer. The goal of this study is to realize a small- size and low-cost sensor system able to evaluate and classify the effects of different factors in an original way: through a global Risk Index. The proposed and projected system allows monitoring: (a) daily thermal variations; (b) the vibrations that occur on the structure and (c) pollutant – both reductant, oxidant and deposit agents. In this paper, the structure (hardware and software) of the environmental monitoring device is presented and expounded in detail. A Risk Analysis Algorithm is proposed and evaluated. It shows how the global degrading risk is always lower than the threshold level, even if the single compound could exceed its own threshold
- …
