1. Electric field driven reconfigurable multistable topological defect patternsSaša Harkai, Bryce S. Murray, Charles Rosenblatt, Samo Kralj, 2020, izvirni znanstveni članek Opis: Topological defects appear in symmetry breaking phase transitions and are ubiquitous throughout Nature. As an ideal testbed for their study, defect configurations in nematic liquid crystals (NLCs) could be exploited in a rich variety of technological applications. Here we report on robust theoretical and experimental investigations in which an external electric field is used to switch between predetermined stable chargeless disclination patterns in a nematic cell, where the cell is sufficiently thick that the disclinations start and terminate at the same surface. The different defect configurations are stabilized by a master substrate that enforces a lattice of surface defects exhibiting zero total topological charge value. Theoretically, we model disclination configurations using a Landau-de Gennes phenomenological model. Experimentally, we enable diverse defect patterns by implementing an in-house-developed atomic force measurement scribing method, where NLC configurations are monitored via polarized optical microscopy. We show numerically and experimentally that an “alphabet” of up to 18 unique line defect configurations can be stabilized in a 4 × 4 lattice of alternating �=±1 surface defects, which can be “rewired” multistably using appropriate field manipulation. Our proof-of-concept mechanism may lead to a variety of applications, such as multistable optical displays and rewirable nanowires. Our studies also are of interest from a fundamental perspective. We demonstrate that a chargeless line could simultaneously exhibit defect-antidefect properties. Consequently, a pair of such antiparallel disclinations exhibits an attractive interaction. For a sufficiently closely spaced pair of substrate-pinned defects, this interaction could trigger rewiring, or annihilation if defects are depinned. Ključne besede: line defects, topological defects, nematic liquid crystals, electric field, atomic force microscopy, numerical techniques, polarized optical microscopy Objavljeno v DKUM: 18.11.2024; Ogledov: 0; Prenosov: 2
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2. The external bias-dependent electric field at hole-injecting electrode/[alpha]-NPD junction and its relationship to Gaussian disordered interface statesBruno Cvikl, 2019, izvirni znanstveni članek Opis: An alternative interpretation of two different sets of published temperature-dependent current-voltage a-NPD (i.e. N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,11-biphenyl)-4,4'-diamine) organic semiconductor data is presented. The measurements are described in terms of the hole drift current density expressed with two parameters: the electric field at the hole-injecting interface, Eint, and, ?max, the hole mobility determined by the measured current density at the maximum value of the externally applied electric field, Ea, in a given experiment. The former parameter, depending on the contact résistance, may be a function of Ea but the latter is Ea independent, The fixed value of Eint signifies the occurrence of the space charge limited current, SCLC, within the electrode/a-NPD structures and the contact is ohmic. Then, the calculated weak bias-dependent hole drift mobility, a function of Eint, equals the well%known exponential bias-dependent mobility, and saturates. The data not displaying SCLC characteristics are used for the calculation of Eint dependence on the applied field, Ea. It is shown that the quasi-ohmic contacts cause Eint to become a strong double-valued function of the externally applied electric field, Ea, described in terms of the distorted, inverted, high order parabola. The corresponding bias-dependent hole drift mobility is non-exponential and evolves on a considerably lower level than in SCLC cases. It is found that a sufficiently increased Ea alters the quasi-ohmic contact/a-NPD region into the ohmic one. A simple model of a thin, net hole charged, electrode/a-NPD interface enables the relationship between the deduced interfacial electric field, Eint, and the Ea dependent Gaussian width, as well as the energy shift of its peak along the negative binding energy is to be investigated. The currentvoltage method appears to be a helpful expedient for the investigation of the electric field at hole-injecting electrode/organic interfaces. Ključne besede: electrode/organic electric field, contact affected hole mobility, organic interface disorder parameters Objavljeno v DKUM: 22.12.2023; Ogledov: 572; Prenosov: 7
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3. Electric and magnetic field measurements for high voltage transmission lines : the case of TurkeyMehmet Zeki Çelik, Mehmet Murat Ispirli, Yusuf Öner, Bülent Oral, 2019, strokovni članek Opis: A power system is a facility that creates low-frequency electromagnetic fields (EMF) with its highvoltage level and high electric current capacity. In this respect, these electromagnetic fields need to be significantly evaluated from the aspects of both those who are exposed to the fields due to the structure of the facility during their daily lives and those who are exposed to the fields due to their occupation. In this study, the transmission lines and substations in the power system of Turkey are evaluated on account of electric and magnetic field measurements. Firstly, the people living in general public zones near the transmission line or substation were examined. In another part of the study, measurements were made in the occupational exposure of the staff in the energy zone. The results obtained from measurements are compared with the limit values provided by the International Commission on Non%Ionizing Radiation Protection (ICNIRP). The measurements were performed by NARDA EFA-300 electromagnetic field measurement. The closest point to the ground was determined as the reference point for the measurements performed on transmission lines. The results for different distances were obtained by performing measurements following those reference points with fixed distances. Ključne besede: electric field, ELF, electromagnetic filed, ICNIRP, magnetic field Objavljeno v DKUM: 05.12.2023; Ogledov: 424; Prenosov: 7
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4. Assessment of human exposure to electric and magnetic fields near transmission lines using FEMMBojan Glushica, Blagoja Markovski, Andrijana Kuhar, Vesna Arnautovski Toseva, 2023, izvirni znanstveni članek Opis: The intensity of ELF electric and magnetic fields near transmission lines is of particular interest in environmental and equipment protection studies. The use of numerical tools is the most efficient method for their assessment. In this paper, we numerically compute the electric and magnetic fields near different configurations of high-voltage transmission lines using the open- source software FEMM 4.2. Computed fields are compared with reference levels related to human exposure to electromagnetic fields. The accuracy of the applied method is validated with published, numerically computed and measured results. Ključne besede: finite elements method, transmission lines, electric field, magnetic field, electromagnetic computation Objavljeno v DKUM: 11.10.2023; Ogledov: 525; Prenosov: 7
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5. Finite size effects in soft matter under an electric field stimulusSaša Harkai, 2016, magistrsko delo Opis: In this thesis, we study the effect of an external electric field on the properties of glass forming liquids. We present the properties relevant and important for understanding the phenomenon, such as the transition temperature and the temperature dependence of viscosity. We create a numerical model and use a method called molecular dynamics with the Lennard-Jones potential and an added external field as the interatomic potential to simulate molecular motion within a glass forming liquid. We implement analysis methods to calculate properties such as the radial distribution function, static structure factor, diffusion coefficient, non-Gaussian parameter, and relaxation time. We use the implemented methods to evaluate the molecular behaviour of the simulation and compare the results with theoretical predictions. Ključne besede: finite size, glass transition, diffusion constant, dynamic heterogeneity, electric field Objavljeno v DKUM: 21.09.2016; Ogledov: 1529; Prenosov: 121
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