Conductivity of irradiated Kapton in relation to energy loss of ions and electrons

Abstract

We have studied the effects of 2.5 MeV electron irradiation and ion (C, N, F, Si and Kr) bombardment on the electrical conductivity of a polyimide (Kapton-H) with ion energies ranging between 320 keV (N) and 1.25 GeV (Kr). In this wide range of situations we have tried to sort out the respective effects of nuclear and electronic excitation energy losses.

For all ion irradiation the conductivity is found to scale with the electronic excitation absorbed dose: i.e. a power law of conductivity versus absorbed dose with an exponent around 9 is observed. At a given absorbed dose (in Gray units) the efficiency of each ion to enhance conductivity is found to be proportional to the electronic energy loss; electrons are much less efficient than ions and thus collective excitations are required to achieve this process.

The nuclear energy loss can perhaps play some role at conductivities higher than 100 Ω^?1 m^?1, but its effects are negligible in the range explored here.     

On the natural frequencies of a stepped thickness Timoshenko shaft

Summary In this note the free vibrations of stepped thickness shafts are investigated taking into account the effects of rotatory inertia and transverse shear force. The solution of the system of indefinite equations is written first, together with boundary and continuity conditions. Then, a practical application is presented and the values of the first six natural frequencies are given, using both the Timoshenko and Euler-Bernoulli theories. Finally, the dependence of the eigenvalues on the extension of the central, thicker portion of the shaft, are studied.

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Sommario In questa nota si studiano le vibrazioni libere degli alberi con sezione uniforme a tratti, tenendo conto degli effetti dello sforzo di taglio e dell'inerzia rotazionale. Dopo aver riassunto il metodo e scritto le condizioni al contorno e di continuità, viene esaminato un caso di concreto interesse e si forniscono i valori delle prime sei frequenze naturali ottenute sia dalla teoria di Timoshenko che da quella di Eulero-Bernoulli. Viene infine studiata la dipendenza delle frequenze dall'estenzione della parte centrale, più tozza, dell'albero.

     

The effect of ideology on policy outcomes in proportional representation systems

In this paper we propose a model in which there are ideological and strategic voters who vote under proportional rule. We prove that the behavior of ideological voters matters for the determination of the outcome. We show that a subset of strategic voters partially counteracts the votes of the ideological voters.     

Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I⁻/I³⁻ and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]³⁺/²⁺; dtb = 4,4′ditert-butyl-2,2′-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I⁻/I³⁻-based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte.     

Unilaterality and Dry Friction: A Geometric Formulation for Two-Dimensional Rigid Body Dynamics

The dynamics of a rigid body simply supported on a moving rigid ground in the presence of dry friction is investigated. Rigid body kinematics, in terms of generalized coordinates, and features of contact are discussed. According to the contact laws, a variational formulation is adopted to describe the dynamics and to analyze, in the case of contact, the connection between dynamically possible motions and actual evolution of the system. A geometric method is then proposed which allows the dynamic evolution to be determined without any direct evaluation of the contact forces. Though different situations are possible, depending on the instantaneous values of relative position, velocity and active forces, a unique solution is identified. Examples illustrating applications of the theory are presented.     

Modelling the dynamics of large block structures

This paper summarizes the main critical points that arise when the problem of modelling the dynamics of block structures is tackled. In the first sections, a rigorous formulation of dynamics and impact problem is presented for a single rigid block freely supported on rigid ground, in order to illustrate the basic difficulties concerning the modelling of more complicated structures. Then, a critical review is presented on the numerous researches performed on this subject and the results achieved, and the problems still open, are put in evidence.

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Sommario In questo lavoro, si illustrano i punti salienti e critici che devono essere affrontati nella modellazione del comportamento dinamico di structture costituite da grandi blocchi assemblati a secco. Nei primi paragrafi, viene presentato e discusso il problema generale della dinamica e dell' urto del blocco singolo semplicemente appoggiato su suolo rigido: è questa la base necessaria per affrontare in modo rigoroso la modellazione di strutture più complesse. Viene quindi presentata una rassegna critica di vari modelli proposti in letteratura, evidenziando i problemi risolti e quelli ancora aperti.

     

A spatial voting model where proportional rule leads to two-party equilibria

In this paper we show that in a simple spatial model where the government is chosen under strict proportional rule, if the outcome function is a linear combination of parties’ positions, with coefficient equal to their shares of votes, essentially only a two-party equilibrium exists. The two parties taking a positive number of votes are the two extremist ones. Applications of this result include an extension of the well-known Alesina and Rosenthal model of divided government as well as a modified version of Besley and Coate’s model of representative democracy.