PRESKUS PRIMERNOSTI NFC V SISTEMU ZA REGISTRACIJO ČASADavid Sakelšek
, 2009, diplomsko delo
Opis: V nalogi smo preučili primernost tehnologije NFC (Near Field Communication) na primeru razvoja sistema za registracijo dela. Opisali smo glavne tehnološke značilnosti te tehnologije. Podana je primerjava z ostalimi brezžicnimi tehnologijami kot so Bluetooth, WiFi in 3G. V nalogi je razvita aplikacija MobileTime, ki uporablja NFC za registracijo dogodkov. Razvit je strežniški in odjemalski modul rešitve. Preskus je pokazal, da tehnologija ustreza poslovnim zahtevam, omejitev pa je majhno število mobilnih odjemalcev z vgrajenim vezjem NFC.
Ključne besede: Near Field Communication, Sistemi za registracijo časa, Mobilne naprave, Java, .NET Framework
Objavljeno: 22.01.2010; Ogledov: 1390; Prenosov: 99
Celotno besedilo (4,05 MB)
A FEM method for eddy current analysis in laminated mediaOszkar Biró
, Kurt Preis
, Igor Tičar
, 2005, izvirni znanstveni članek
Opis: A method is presented to compute three-dimensional eddy current distributions in laminated media by means of the finite element method. In a first step, the laminated medium is assumed to have an anisotropic conductivity with zero (or very low) value in the direction normal to the laminations. In a second step, the eddy currents within the laminates are computed by solving the quasistatic electromagnetic field individually in each sheet. In these essentially two-dimensional analyses, the boundary conditions are taken from the three dimensional field distribution determined in the first step. Comparisons with results obtained from a finite element model taking account of each laminate prove the validity of the method.
Ključne besede: electromagnetic field, eddy currents, finite element method analysis, laminates
Objavljeno: 01.06.2012; Ogledov: 904; Prenosov: 5
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Ecological alternatives to the reduction and oxidation processes in dyeing with vat and sulphur dyesMojca Božič
, Vanja Kokol
, 2008, pregledni znanstveni članek
Opis: This article gives a summary of the most commonly used ecologically unfriendly processes for the reduction and oxidation of vat and sulphur dyes. It also describes the new alternatives that are in the development stage and could be important in the near future. Sodium dithionite as the dominant reducing agent produces large amounts of sodium sulphate, and also toxic sulphite and thiosulphate as by-products. Consequently, high amounts of hydrogen peroxide and alkali are required for the treatment of effluents, which add to the cost of the process. Attempts have been made to use organic biodegradable reducing agents, enzymes, catalytic hydrogenation, and also indirect or direct, electrochemical reductive methods that employ a redox mediator (electron-carrier). The reduction has also been carried out via the dye radical molecule or, in the case of indigo, by direct electrochemical reduction using graphite as the electrode material. Physical techniques, for example using ultrasound, magnetic fields or UV have been shown to be effective only when used to accelerate methods using classical reduction and oxidation processes. However, although these methods offer some environmental benefits, there is still no satisfactory alternative reducing and/or oxidising agent available today.
Ključne besede: textile dyeing, vat dyes, sulphur dyes, reduction, oxidation, catalysis, ecology, organic agents, electrochemistry, ultrasound, magnetic field, UV application, biotechnology
Objavljeno: 01.06.2012; Ogledov: 873; Prenosov: 14
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STABILITY AND METASTABILITY OF NEMATIC GLASSESAmid Ranjkesh Siahkal
, 2014, doktorska disertacija
Opis: Structures exhibiting continuous symmetry breaking are extremely susceptible to various perturbations. The reason behind is the existence of Goldstone modes in the gauge
component of the order parameter describing broken symmetry. The so-called Larkin-Imry–Ma argument claims that even infinitesimally weak random field-type disorder destroys long range order (LRO) which would otherwise be present in the absence of random disorder. Furthermore, it claims that the system breaks into domain type configuration having short range order (SRO), where the characteristic domain size scales as ksi= W^-2/(4-d). Here W measures the strength of random field interaction and d is the dimensionality of space. However, some studies claim that structures with quasi long range order (QLRO) are established instead of SRO. The main focus of this doctor thesis is the character of nematic structures in the random field. I studied theoretically and numerically nematic structures that are obtained by continuous symmetry breaking in orientational degrees of freedom on
decreasing the temperature T, starting from the ordinary liquid, the so called isotropic phase. In particular, I investigated conditions for which the Larkin-Imry-Ma theorem holds true. So far statistical interpretations of such systems have typically used two different semi-
microscopic type models: i) the Random Anisotropic Nematic (RAN) and ii) the Sprinkled Silica Spin (SSS) model. The RAN model is a Lebwohl-Lasher (LL) model with nematic molecules locally coupled with uncorrelated random anisotropic field at each site, while the SSS model has a finite concentration of impurities frozen in random directions. I used a three dimensional (d = 3) model intermediate between SSS and RAN models, with finite
concentration p of frozen impurities, where p < pc (pc stands for the percolation threshold). The simulations were performed at different temperatures for temperature-quenched (TQH) and ﬁeld-quenched histories (FQH), as well as for temperature-annealed histories (AH). The
ﬁrst two of these limits represent extreme histories encountered in typical experimental studies. Numerically, I studied the impact of control parameters (T, p, W) and history of samples (TQH, FQH, AH) on structural properties of the system. Within the model I was varying p, temperature T, interaction strength W and also sample histories. From final configurations, I calculated orientational order parameters and two-point correlation
functions. Next, I estimated the size of the Larkin-Imry-Ma domains d. Finite size-scaling was also used to determine the range of the orientational ordering, as a function of W, p, T and sample history. The main results of my study are the following. In general, the system exhibited strong memory effects, indicating important role of history of samples. Furthermore, obtained results were relatively robust (from macroscopic point of view), indicating substantial energy barriers among competing states. On increasing the strength W, I typically obtained the following sequence of orders: LRO, QLRO, and SRO. For some concentrations p,however, SRO was absent. The crossover anchoring strength between QLRO and SRO strongly depends on history of samples, and it has the lowest values for TQH. From my simulations it follows that for the model used the Larkin-Imry-Ma argument holds only in limited range of model parameters. In most cases I obtain QLRO instead of SRO. However, in all structures there is imprint of Larkin-Imry-Ma domains, exhibiting scaling d 1/ (W2p) in the weak anchoring regime. This suggests that we do not have a “classical ” QLRO with algebraic decay with distance. Similar results were obtained in the studies of magnetic systems.
Ključne besede: nematic liquid crystals, topological defect, order parameter, symmetry breaking, domains, Random field, larkin-Imry–Ma theorem, speroNematics
Objavljeno: 15.07.2014; Ogledov: 828; Prenosov: 43
Celotno besedilo (2,86 MB)
The golden mean in the topology of four-manifolds, in conformal field theory, in the mathematical probability theory and in Cantorian space-timeLeila Marek-Crnjac
, 2006, izvirni znanstveni članek
Opis: Pokažemo povezavo med topologijo štiri-mnogoterosti, konformno teorijo, verjetnostno teorijo in Cantorjevim prostorom. Na vseh štirih matematičnih področjih najdemo kot najpomembnejšo skupno povezavo pojav zlatega reza.
Ključne besede: matematika, topologija, zlati rez, konformna teorija, Cantorjev prostor-čas, E-neskončno teorija, mathematics, topology, golden mean, conformal field theory, Cantorian space-time, E-infinity theory
Objavljeno: 10.07.2015; Ogledov: 177; Prenosov: 7
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, G. W. Gibbons
, Christopher N. Pope
, 2015, izvirni znanstveni članek
Opis: We present explicit solutions of the time-symmetric initial value constraints, expressed in terms of freely specifiable harmonic functions for examples of supergravity theories, which emerge as effective theories of compactified string theory. These results are a prerequisite for the study of the time-evolution of topologically non-trivial initial data for supergravity theories, thus generalising the "Geometrodynamics" program of Einstein-Maxwell theory to that of supergravity theories. Specifically, we focus on examples of multiple electric Maxwell and scalar fields, and analyse the initial data problem for the general Einstein-Maxwell-Dilaton theory both with one and two Maxwell fields, and the STU model. The solutions are given in terms of up to eight arbitrary harmonic functions in the STU model. As a by-product, in order compare our results with known static solutions, the metric in isotropic coordinates and all the sources of the non-extremal black holes are expressed entirely in terms of harmonic functions. We also comment on generalizations to time-nonsymmetric initial data and their relation to cosmological solutions of gauged so-called fake supergravities with positive cosmological constant.
Ključne besede: black holes, supergravity, string theory, conformal field models, string duality
Objavljeno: 14.06.2017; Ogledov: 87; Prenosov: 11
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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: 21.09.2016; Ogledov: 349; Prenosov: 23
Celotno besedilo (1,38 MB)