A simple model of ac hopping surface conductivity in ionic liquids

The boundary conditions proposed to discuss the charge exchange taking place in an ionic liquid in contact with non-blocking electrodes are reconsidered in a dynamic situation. Assuming that the variation of the bulk ionic current density depends linearly on the surface value of the ionic current density, the frequency dependence of the phenomenological parameter is determined. The analysis has been performed in the framework where the relaxation times are smaller than a maximum relaxation time τM, and that the response function is independent on the value of the relaxation time. Using simple physical considerations, an expression for the surface conductivity describing the ionic charge exchange at the electrode is obtained. According to our calculations, its frequency dependence is similar to that predicted for the electric conductivity in disordered materials when the mechanism is of the hopping type. From measurements of impedance spectroscopy, by the best fit of the experimental data, the temperature dependence of the hopping time, of the dc surface conductivity, and of the diffusion coefficient are derived. They are in good agreement with the theoretical predictions obtained with the random distribution of surface energy barrier. Keywords: Ionic liquids, Non-blocking electrodes, Electrical impedance spectroscopy, AC hopping surface conductivit

Ring-Pattern Dynamics in Smectic-C* and Smectic-C_A* Freely Suspended Liquid Crystal Films

Ring patterns of concentric 2pi-solitons in molecular orientation, form in freely suspended chiral smectic-C films in response to an in-plane rotating electric field. We present measurements of the zero-field relaxation of ring patterns and of the driven dynamics of ring formation under conditions of synchronous winding, and a simple model which enables their quantitative description in low polarization DOBAMBC. In smectic C_A* TFMHPOBC we observe an odd-even layer number effect, with odd number layer films exhibiting order of magnitude slower relaxation rates than even layer films. We show that this rate difference is due to much larger spontaneous polarization in odd number layer films.Comment: 4 RevTeX pgs, 4 eps figures, submitted to Phys. Rev. Let

IMPLEMENTATION OF THE ANDROID SOURCE CODE FOR “COHEN QUESTIONNAIRE – TO IDENTIFY THE LEVEL OF STRESS”

This paper aims to present the study on the implementation of the source code for a Cohen questionnaire meant to detect stress level. The importance of this study consists in a unique mobile app for Cohen test. The results can be used for several research’s studies. We used instruments such us HTML, CSS, JavaScript, PHP, server web and MYSQL to develop the application for Android.The application is composed of 10 questions and at the end of test the users we received some recommendations to reduce stress at work

DESIGN AND DEVELOPMENT OF A MOBILE APPLICATION ANDROID FOR THE MEASUREMENT OF STRESS LEVEL

The case study presented in this article consists in a mobile aplication created on the basis of the Cohen questionnaire meant to detect stress level. The study is a novelty because the mobile app can be used on an undefined number of Android terminals. The test can be performed several times by the same person, and the data can be used later for various reports due to the authentication and in-app account creation feature.To design the application were used the follow instruments: PhoneGap, HTML, CSS, JavaScript, PHP, server web, MYSQL and Adobe photoshop.The application can be used in any medium that requires rapid detection of stress on the Cohen test of a large number of respondents. Data obtained through the application can be used to carry out research studies in universities, psychology offices, recruitment companies, and so on

Analysis and management of avariation to a fluvial transport vessel caused by collision

In general, the body of the ship is a welded metal structure made up of the shell and bone. The paper aims is to analyze and present the solution for the collision damage to a river transport vessel. The problem is treated as in the case of a typical failure of welded constructions. In this regard, the fault will be described, after which the stages of the fault remedy will be presented

The failure of the floating cover of a vertical cylindrical tank

The location of oil tanks for the storage of volatile hydrocarbons could be done in geographical areas where the standard unit weight of the snow layer on the horizontal surface of the land reached 1500 ... 2000 N / m2 . The snow layer deposited on the floating cover under heavy weather conditions can cause a compressive force between 4500 and 6000 N / m2 . This creates problems in the operation of the tank and consequently the constructive structure of the floating cover can not bear this unitary load from the snow load, inevitably causing the damage. The capacities of the floating cover should be considered not only in terms of limitations on load-bearing considerations in general, but also in terms of the distribution of loads on the surface of the floating cover. The paper presents the aspect of the failure of a floating cover of a vertical cylindrical tank used to store liquid hydrocarbons under heavy climatic conditions

Considerations on damage to bulb turbine shafts from iron Gates II

During operation, the turbine bulb shaft is subjected to static specific stresses (tension, compression, torsion) and dynamic (fatigue, random vibrations). These stresses are the effect of hydraulic forces and moments developed on the rotor blade, the weight of the rotor (with or without oil) in the console and inevitable vibrations, which creates a rotating mass unevenly distributed over the axis of symmetry of the turbine. Observations made on the turbine bulb shafts of the Iron Gate II CHE have revealed cracks in the connection area of a shaft flange that engages it with the turbine rotor. Examination of these cracks leads to the conclusion that they are specific to the inevitable fatigue demands in exploiting the tree and enhancing the environment in which they work. Therefore, in the paper, a presentation and analysis of the damage of bulb turbine shafts from CHE Porţile de Fier II, after a significant number of hours of operation

Charge transport and trapping in Cs-doped poly(dialkoxy-p-phenylene vinylene) light-emitting diodes

Al/Cs/MDMO-PPV/ITO (where MDMO-PPV stands for poly[2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4phenylene vinylene] and ITO is indium tin oxide) light-emitting diode (LED) structures, made by physical vapor deposition of Cs on the emissive polymer layer, have been characterized by electroluminescence, current-voltage, and admittance spectroscopy. Deposition of Cs is found to improve the balance between electron and hole currents, enhancing the external electroluminescence efficiency from 0.01 cd A-1 for the bare Al cathode to a maximum of 1.3 cd A-1 for a Cs coverage of only 1.5×1014 atoms/cm2. By combining I-V and admittance spectra with model calculations, in which Cs diffusion profiles are explicitly taken into account, this effect could be attributed to a potential drop at the cathode interface due to a Cs-induced electron donor level 0.61 eV below the lowest unoccupied molecular orbital. In addition, the admittance spectra in the hole-dominated regime are shown to result from space-charge-limited conduction combined with charge relaxation in trap levels. This description allows us to directly determine the carrier mobility, even in the presence of traps. In contrast to recent literature, we demonstrate that there is no need to include dispersive transport in the description of the carrier mobility to explain the excess capacitance that is typically observed in admittance spectra of p-conjugated materials

The laser-hybrid accelerator for radiobiological applications

The `Laser-hybrid Accelerator for Radiobiological Applications', LhARA, is conceived as a novel, uniquely-flexible facility dedicated to the study of radiobiology. The technologies demonstrated in LhARA, which have wide application, will be developed to allow particle-beam therapy to be delivered in a completely new regime, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates. LhARA will be a hybrid accelerator system in which laser interactions drive the creation of a large flux of protons or light ions that are captured using a plasma (Gabor) lens and formed into a beam. The laser-driven source allows protons and ions to be captured at energies significantly above those that pertain in conventional facilities, thus evading the current space-charge limit on the instantaneous dose rate that can be delivered. The laser-hybrid approach, therefore, will allow the vast ``terra incognita'' of the radiobiology that determines the response of tissue to ionising radiation to be studied with protons and light ions using a wide variety of time structures, spectral distributions, and spatial configurations at instantaneous dose rates up to and significantly beyond the ultra-high dose-rate `FLASH' regime. It is proposed that LhARA be developed in two stages. In the first stage, a programme of in vitro radiobiology will be served with proton beams with energies between 10MeV and 15MeV. In stage two, the beam will be accelerated using a fixed-field accelerator (FFA). This will allow experiments to be carried out in vitro and in vivo with proton beam energies of up to 127MeV. In addition, ion beams with energies up to 33.4MeV per nucleon will be available for in vitro and in vivo experiments. This paper presents the conceptual design for LhARA and the R&D programme by which the LhARA consortium seeks to establish the facility