89,183 research outputs found
Capacitance study of thin film SnO2:F/p-type a-Si:H heterojunctions
No full textWe characterized SnO2:F/p-type a-Si:H heterojunctions by current-voltage (I-V) and capacitance-voltage (C-V) measurements at
room temperature to determine the junction parameters. Samples with circular geometry and different diameters were
characterized. The current scales with the junction area, and the current density J as a function of the voltage V is a slightly
asymmetric curve with a super-linear behaviour (cubic law) for high voltages. Using a transmission line model valid for devices
with circular geometry, we studied the effects of the SnO2:F resistivity on the measured capacitance when the SnO2:F layer
works as an electrical contact. The measured C-V curve allows us to determine junction parameters as doping of p-type a-Si:H,
built-in potential and depletion width for the heterojunction with the smallest diameters, demonstrating that for these samples the
TCO effects can be neglected. We compared theoretical and measured data to explain qualitatively the transport mechanism in
this heterojunction
Barclay & Crousse. Segnali di vita tra i due deserti. Barclay & Crousse. Señales de vida entre dos desiertos
No full textLa costa desertica peruviana: una lunghissima linea sul Pacifico che si estende da nord a sud per circa 2400 km, scandita da un sistema regolare di oasi trasversali. Ogni traccia della presenza dell’uomo è spesso occultata da questa natura estrema. Anche le rovine precolombiane, che di rado si incontrano ai margini delle oasi, appaiono come tracce astratte di una natura geometrizzata.
La condizione geografica dell’intero Perù è tale da replicare, sia alla grande sia alla piccola scala, analoghe condizioni insediative. Ogni sua porzione si distingue nettamente dal paesaggio desertico a cui si contrappone, che sia l’immensa distesa oceanica, l’impervio altopiano andino o l’impenetrabile foresta pluviale. Tutti gli insediamenti umani, città o edifici, si configurano spesso come strategiche isole di confine tra due frammenti di deserto.
In questa radicale condizione si inserisce il lavoro che Sandra Barclay e Jean Pierre Crousse sviluppano dalla fine degli anni ’90 fino ad oggi raccontato dal libro di Cacciatore e Foti. Dieci case, progettate e costruite sulla costa pacifica, esprimono chiaramente le straordinarie potenzialità architettoniche insite in questo contesto
Carrier transport mechanism in the SnO2:F/p-type a-Si:H heterojunction
No full textWe characterize SnO2:F/p-type a-Si:H/Mo structures by current-voltage (I-V) and capacitance-voltage (C-V) measurements at different temperatures to determine the transport mechanism in the SnO2:F/p-type a-Si:H heterojunction. The experimental I-V curves of these structures, almost symmetric
around the origin, are ohmic for |V| 0.1 V. The structure can be modeled as two diodes back to back connected so that the main current transport mechanisms are due to the reverse current of the diodes. To explain the measured C-V curves, the capacitance of the heterostructure is modeled as the series connection of the depletion capacitances of the two back to back connected SnO2:F/p-type a-Si:H and Mo/p-type a-Si:H junctions. We simulated the reverse I-V curves of the SnO2:F/p-type a-Si:H heterojunction at different
temperatures by using the simulation software SCAPS 2.9.03. In the model the main transport mechanism is generation of holes enhanced by tunneling by acceptor-type interface defects with a trap energy of 0.4 eV above the valence bandedge of the p-type a-Si:H layer and with a density of
4.0 10^13 cm^-2. By using I-V simulations and the proposed C-V model the built-in potential (Vbi) of the SnO2:F/p-type a-Si:H (0.16 V) and p-type a-Si:H/Mo (0.14 V) heterojunctions are extracted and a band diagram of the characterized structure is proposed
On the estimation of von mises equivalent stress in random vibration analysis
No full textLinear random vibration analysis aims to the probabilistic characterization of response functions; classical procedures are targeted to the time histories of output kinematic variables, such as displacement, velocity and acceleration, and to parameters which are linearly related to them, such as internal forces, deformations, stress components ecc. Much less attention has been devoted, by researcher and developers, to the case of response variables which are non-linearly dependent of the lagrangian coordinates or their derivatives; the most typical among these is the Von Mises equivalent stress, whose square value is quadratic in the components of the stress tensor, and thus in the lagrangian coordinates. The topic is of relevance especially for the structural safety of industrial equipment and systems, which is usually based on local stress integrity assessment. In the paper an innovative analytical procedure to deal with the probabilistic characterization of the VM stress is proposed as an extension of the classical approach adopted for linear output parameters. To this aim the matrix of the quadratic form delivering is decomposed into the sum of suitable factors; each of them deserves the same treatment as for linear parameters. The various features related to the numerical implementation of the procedure for stationary or non-stationary (evolutionary) random excitation are discussed, with reference to both the application via direct frequency domain treatment and to the modal superposition approach; an example is finally shown and commented
Un progetto per Bologna: l'area Staveco da cittadella militare a Campus Universitario. Ateliermap
No full textJohn F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
Sous-facteurs de L(F∞) d'indice 4cos2π/n,n≥3
No full textLet Q be a factor of type II1, λ a number in the Jones discrete series {4cosπ/m:m≥3}, and {ei} the Jones projections associated with λ. Denote by A2n and A1n the finite-dimensional von Neumann algebras generated, respectively, by {1,e2,⋯,en} and {1,e1,⋯,en}, with the corresponding traces. The author shows that, for n sufficiently large, the index of the inclusion An=(Q⊗A2n)∗A2nA1n⊂(Q⊗A2n+1)∗A2n+1A1n+1=An+1 is equal to λ (here ∗ denotes the reduced, amalgamated free product of the algebras in question). Using the random matrix model of Voiculescu, he proves that if Q is the von Neumann algebra L(F∞) of the free group with infinitely many generators, then An is isomorphic to L(F∞).
The two facts together imply the existence, for any λ in the Jones discrete series, of an irreducible subfactor of L(F∞) of index λ. This constitutes the first example of a nonhyperfinite, non-Γ II1 factor such that its Jones invariant is fully computable (the existence of nonirreducible subfactors of L(F∞) for any index ≥4 is a simple consequence of known results)
Comparison between textured SnO_2:F and Mo contacts with the p-type layer in p–i–n hydrogenate amorphous silicon solar cells by forward bias impedance analysis
No full textIn this paper we compare the performance of the textured SnO_2:F and Mo contacts with the p-type layer in p–i–n hydrogenate amorphous silicon (a-Si:H) solar cells. We use standard current–voltage (I–V) electrical characterization methods coupled with forward bias small signal impedance analysis. We show the efficacy of this technique to determine the effective carrier lifetime in photovoltaic cells. We
show that such effective lifetimes are indeed directly connected to the respective dark diode saturation currents. We also find that the effective lifetime is constant with the temperature in the 0–70 °C range and it is significantly better for the solar cell with Mo diode contact. This also explains well the higher open circuit voltage Voc found under illumination in the Mo/p–i–n cell compared to the SnO_2:F/p–i–n one
A stochastic and continuous model of aeolian vibrations of conductors equipped with stockbridge dampers
No full textSuspended conductors and guard wires of overhead electrical transmission lines (OHL) are prone to aeolian vibrations, resulting from the alternate shedding of vortices in the wake of the cable. These vibrations can occur under light to moderate wind and, whenever not properly controlled, can induce wear damage and fatigue failures of the cables. Nonlinear passive control devices such as Stockbridge dampers, hence, are often installed along the line spans to reduce the vibration severity. The technical approach to the assessment of aeolian vibrations is based on the Energy Balance Method (EBM) and relies on the simplifying assumption of mono-modal oscillations. Typical aeolian vibration records, however, clearly show that several modes can be simultaneously excited due to wind variations in time and along the span. Aiming at overcoming the mono-modal vibration assumption of the EBM, in the present paper wind forces are modeled as a narrow band stochastic process, centered around the Strouhal frequency of the conductor and with arbitrary cross-correlation in space. A new approach, based on the well-known smooth endochronic Bouc-Wen model, is developed to describe the hysteretic dynamic response of Stockbridge dampers. An iterative solution strategy based on a stochastically equivalent linear damper model is then developed to investigate aeolian vibrations of a suspended cable with a Stockbridge damper attached along its length
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