1,722,647 research outputs found
Relativistic electrons-based thz sources: Principles of operation and the ENEA experience
No full textAn introduction to the general theory of free electron sources of coherent radiation is reported. The basic mechanisms for the generation of electromagnetic waves as spontaneous emission process are described together with the more sophisticated theory of gain for the description of the stimulated process. The ENEA experience in the realisation of compact free electron sources is reported jointly with the "tricks" that allowed the Frascati group to shorten the device dimensions while maintaining important performances. © 2014 Springer Science+Business Media Dordrecht
Framed harvesters for collecting energy from vibrations in industrial plants
No full textThe idea of increasing the number of resonance conditions of a cantilever piezoelectric harvester by coup ling the harvester with a frame that surrounds the harvester’s body is presented and discussed. Experimental tests on prototypes show that it is possible to design framed harvesters able to generate significant powers at two frequencies. Since the framed harvesters will be used for harvesting energy from p eriodic vibrations characterized by multiple harmonics, a tuning method is needed. For this reason a numerical sensitivity analysis is performed to analyze the effect on harvester tuning of small masses mounted on the frame. A prototype tuned to 40 and 80 Hz is developed and tested, its performance is compared with the one of a system of two simple harvesters tuned to the same frequencie
Hybrid (Oscillator-Amplifier) Free Electron Laser and New Proposals
No full textThe present work analyses a hybrid free electron laser (FEL) scheme where the oscillator is based on a radiation source operating with a slow-wave guiding structure as, for instance, a Cerenkov FEL or a Smith–Purcell FEL. Such devices, often running in transverse magnetic (TM) modes, present a longitudinal electric field which can easily affect the longitudinal electrons’ velocities, inducing an energy modulation on the beam. Such a modulation, properly controlled, can induce a strong radiation emission in a magnetic undulator properly designed to operate as a radiator. General considerations will be exposed together with a practical numerical example in the far infrared region of the spectrum
Experimental vibration analysis and development of the dynamic model of a uav for aerial manipulation
No full textIn the near future, aerial manipulators will be employed in important field applications, such as inspection and maintenance of bridges, tall buildings, wind farms, and offshore and nuclear plants, and search and rescue or structure assembly in hazardous environments. Unfortunately, the precision of aerial manipulators is seriously affected by the dynamic interaction between the Unmanned Aerial Vehicle (UAV) and the robot manipulator. Indeed, on the one hand, the manipulator transfers forces and torques to the UAV, which affect the UAV position and attitude. On the other hand, the UAV induces undesired vibrations on the manipulator. In this paper, first, Experimental Modal Analysis (EMA) has been used to find the experimental vibration modes of a heavy payload UAV. Then, simplified Mass-Spring-Damper (MSD) dynamic models of the UAV have been proposed, to model the most relevant experimental modes of vibration. Finally, a simple 3-Degrees-of-Freedom (3-DOFs) MSD model has been proposed to model the whole system, which eigenfrequencies and vibration modes are in good agreement with the experimental data. The developed model has been used to simulate the system response in the real scenario of a sudden variation in the lift force due to turbulence
Nephritogenic-antinephritogenic antibody network in lupus glomerulonephritis
No full textLupus glomerulonephritis (LGN) is one of the most threatening manifestations of systemic lupus erythematosus (SLE) and a major predictor of poor prognosis. The mechanisms leading to kidney inflammation are not completely clear; however, autoantibodies seem to play a pivotal role. Apoptosis dysregulation in SLE is likely to trigger generation of autoantibodies, the released nucleosomes being the driving autoantigen for further epitope amplification and selection of DNA or nucleosome-specific B cells. Growing evidence supports a multistep path to LGN involving initial autoantibody binding to chromatin fragments in the mesangial matrix, where they can induce mesangial inflammation leading to a shut-down of the renal DNase gene, generation and deposition of secondary necrotic chromatin on the glomerular basement membrane favouring antibody binding, complement activation and development of membrano-proliferative glomerular lesions. Anti-DNA IgG antibodies display the major pathogenetic potential in LGN initiation; however, other isotypes (IgA or IgE) as well as autoantibodies targeting other molecules (e.g. anti-C1q, anti-C reactive protein) can perpetuate renal injury. Conversely, protective autoantibodies are also likely in SLE which can contain renal damage targeting either DNA (i.e. IgM anti-DNA) or other molecules (e.g. pentraxin 3). Thus, lupus nephritogenic-antinephritogenic antibodies orchestrate the balance between harm and defence of renal tissue
Dynamics of cylindrical parts for vibratory conveying
Full text linkVibratory conveyors are widely used to feed raw materials and small parts to processing equipment. Up to now, most of the research has focused on materials and parts that can be modeled as point masses or small blocks. This paper focuses on the conveying of cylindrical parts. In this case, the rolling motion is an essential feature of conveyor dynamics. First, the dynamic equations governing the rolling motion are stated, and the effects of friction and rolling resistance coefficients on the behavior of the system are analyzed. Then, a non-linear numerical model is developed in MATLAB. It takes into account the transition between pure rolling and rolling with sliding and the impacts of the cylindrical part on the edges of the conveyor. Numerical results showing the effect of the operative parameters of the conveyor and of friction properties on the traveled distance are presented and discussed. Finally, a comparison between numerical and experimental results is presented
Carta remitida por Raimundo Doria a Manuel María Mosquera
No full textCarta remitida por Raimundo Doria a Manuel María Mosquera sobre asuntos personales. Fechada en Bogotá
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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