A 16 moments model in relativistic extended thermodynamics of rarefied polyatomic gas

A model with 16 moments is here presented in the framework of RET of polyatomic gases. It furnishes as principal subsystem the relativistic counterpart of a work by Arima T., Ruggeri T., Sugiyama M.; this is present in literature and treats the non relativistic case which incorporates relaxation processes of molecular rotation and vibration. Another principal subsystem is the natural extension of the 14 moments model by Pennisi S. and Ruggeri T.; this is also present in literature in the relativistic framework but where the trace of the third balance equation is neglected. Its extension is found here for the case when this trace isn’t neglected.

     

Extended thermodynamics of the Blotekjaer hydrodynamical model for semiconductors

The Blotekjaer hydrodynamical model for charge carriers transport in semiconductors is reconsidered from the viewpoint of extended thermodynamics. In particular the Blotekjaer original closure of the moment equations is shown to be equivalent to that obtained by applying the entropy principle.Work partially supported by C.N.R. (MMI-P.S IPPMI, U.O Mathematical Models of Semiconductors)     

Extended approaches to covariant Maxwell electrodynamics

The field equations of covariant Maxwell electrodynamics are a set I of 8 equations for the determination of 6 variables, i.e., the independent components of the skew-symmetric Maxwell tensorF . Obviously 2 of these equations are not evolutive; however they cannot be eliminated without losing manifest covariance. This paper presents a new hyperbolic set S of 8 equations in the 8 variablesF ,x, y, wherex, y are new auxiliary quantities. The solutions of S withx =y = 0 are those of the set I. Moreover, S is expressed in covariant form and is equivalent to a symmetric hyperbolic system.     

Experimental investigation and analytical description of a vibro-impact NES coupled to a single-degree-of-freedom linear oscillator harmonically forced

In this paper, the dynamics of a system composed of a harmonically forced single-degree-of-freedom linear oscillator coupled to a vibro-impact nonlinear energy sink (VI-NES) is experimentally investigated. The mass ratio between the VI-NES and the primary system is about \(1\%\). Depending on the external force’s amplitude and frequency, either a strongly modulated response (SMR) or a constant amplitude response (CAR) is observed. In both cases, an irreversible transfer of energy occurs from the linear oscillator toward the VI-NES: process known in the literature as passive targeted energy transfer. Furthermore, the problem is analytically studied by using the method of multiple scales. The obtained slow invariant manifold shows the existence of a stable and of an unstable branch of solutions, as well as of an energy threshold (a saddle-node bifurcation) for the solutions to appear. Subsequently, the fixed points of the problem are calculated. When a stable fixed point is reached, the system is naturally drawn to it and a CAR is established, whereas when no stable point is attained, the system exhibits a SMR regime. Finally, a good correlation between the experimental and the analytical results is presented.     

Quantum size effects and negative resistance in MOS structure with polycrystalline InSb (n-type)

Summary The tunnel characteristics (J vs. V) of Al−Al₂O₃−InSb (n type) structures with thin (100÷400)? semiconducting electrode are presented. They are analysed by utilizing the model proposed by Chang, Esaki and Styles. The data obtained by a nonlinear best fit on experimental points describe the MOS structure and the negative-resistance region exibited by the characteristics. Furthermore, the semiconductor gap shows a dependence on the thickness and this variation is explainable with the quantum effects presence in the thinnest films.

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Riassunto Le caratteristiche tunnel (J vs. V) di strutture Al−Al₂O₃−InSb (n type) con eletrodo semiconduttore sottile (100÷400) ? sono presentate. Esse sono analizzate utilizzando il modello proposto da Chang, Esaki e Styles; i dati ottenuti da un adattamento ottimale non lineare sui punti sperimentali descrivono la struttura MOS e la regione a resistenza negativa esibita dalle caratteristiche. Inoltre si osserva che il gap del semiconduttore varia con lo spessore; tale variazione è interpretata mediante la presenza di effetti quantistici di dimensione nei films più sottili.

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Резюме Приводятся туннельные характеристики (J в зависимости отV) для Al−Al₂O₃−InSb (n-типа) структур с тонким (100÷400) ? сверхпроводящим злектродом. Эти нарактеристики анализируются с помощью модели, предложенной Ченгом, Есаки и Стайлсом. Данные, полученные путем нелинейной подгонки, описывают MOS структуры и область отрицательного сопротивления, обнаруженного в характеристиках. Кроме того, щель в свернпроводнике обнаруживает зависимость от толщины. Изменение щели объясняется наличием квантовых эффектов, связанных с размерами образцов, в тончайших пленках.

     

Quantum size effects and band structure in InSb

Quantum Size Effects (Q.S.E.) in InSb films have been detected by different experimental procedures.The work function dependence on thickness obtained from photoelectric emission threshold measurements is compared with prior results obtained with the retarding potential method. With both methods, the measured work function values are comparable. They are less than the corresponding bulk values, conforming to current theoretical predictions.The interband energy gap has been determined from photoelectric absorption band edge data: its value differs with respect to the bulk one, by the location of the first allowed energy subband in the conduction band due to the presence of Q.S.E.Some evidence is given for absence of a band structure dependence on Q.S.E.     

Wave speeds in the macroscopic relativistic extended model with many moments

An exact macroscopic extended model for relativistic gases, with an arbitrary number of moments, is present in the literature. It is determined except for a numberable family $\mathcal {F}$ of single variable functions whose physical meaning remains an open problem; a possibility is that it allows to apply the theory to a wider set of materials. Other models appearing in literature are particular cases of this macroscopic one when all these arbitrary functions are zero. Here we exploit equations determining wave speeds for that model. We find interesting results; for example, the whole system for their determination can be divided into independent subsystems which are expressed by linear combinations, through scalar coefficients, of tensors all of the same order. As expected, these wave speeds for the macroscopic model depend on $\mathcal {F}$ . Moreover, some wave speeds (but not all of them) are expressed by square roots of rational numbers.     

Fast numerical method for crack problem in the porous elastic material

The present paper discusses the crack problem in the linear porous elastic plane using the model developed by Nunziato and Cowin. With the help of Fourier transform the problem is reduced to an integral equation over the boundary of the crack. Some analytical transformations are applied to calculate the kernel of the integral equation in its explicit form. We perform a numerical collocation technique to solve the derived hyper-singular integral equation. Due to convolution type of the kernel, we apply, at each iteration step, the classical iterative conjugate gradient method in combination with the Fast Fourier technique to solve the problem in almost linear time. There are presented some numerical examples for materials of various values of porosity.     

Superheating of silicon nanocrystals observed by Raman spectroscopy

In the Raman spectra of silicon nanocrystals a new anomalous component was detected. Close to the usual first order Raman peak situated for a bulk crystal at 521 cm⁻¹ at room temperature, two peaks arise shifting towards lower energy and demonstrating a huge temperature increase, as measured by the ratio of the Stokes/anti-Stokes peak intensities. This behavior is dependent on the laser power and on the morphology of the nanocrystals. We can exclude, however, confinement effects, although surface enhanced phonon modes could be responsible of such superheating. Alternative explanations are also suggested and discussed.