| | SLO | ENG | Piškotki in zasebnost

Večja pisava | Manjša pisava

Iskanje po katalogu digitalne knjižnice Pomoč

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju


1 - 10 / 28
Na začetekNa prejšnjo stran123Na naslednjo stranNa konec
Raman spectroscopy of multiphonon emission process in Ni-doped PbTe
Nebojša Romčević, J. Trajić, B. Hadžić, M. Romčević, D. Stojanović, Z. Lazarević, T. A. Kuznetsova, D. Khokhlov, Rebeka Rudolf, Ivan Anžel, 2009, objavljeni znanstveni prispevek na konferenci

Opis: In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1* 1019 at./cm3. Well resolved peaks appear at about 126, 143, 181, 362 and 724 cm-1. The modes at 126 and 143 cm-1, which are also observed in other telluride compounds, originate from vibrations in TeO2. We assume that the mode at about 181 cm-1 is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor Ni3+ state). Modes at about 362 cm-1 and 724 cm-1 are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
Ključne besede: crystals, Raman scattering
Objavljeno: 31.05.2012; Ogledov: 955; Prenosov: 67
URL Povezava na celotno besedilo

Porosity sensor by using quartz crystals and two excitation signals
Vojko Matko, 2003, objavljeni znanstveni prispevek na konferenci

Opis: In response to a need for a more accurate porosity measuring method for small solid samples (app. 1 g in mass) the porosity measurement sensor using a sensitive capacitive-dependent crystal was developed. This paper presents the new sensor and the probe sensitivity, frequency dependence on the volume. In addition, the new idea of excitation of the entire sensor with stochastic test signals is described, and the porosity measuring method is provided. The latter includes the influence of test signals on the weighting function uncertainty. The experimental results of the porosity determination in volcanic rock samples are presented. The uncertainty of porosity measurements is less than 0.1% in the temperature range 10 - 30°C.
Ključne besede: electrical measurements, porosity, soil, capacitive dependent crystals, sensor, glass test tube, direct digital method
Objavljeno: 01.06.2012; Ogledov: 1199; Prenosov: 62
URL Povezava na celotno besedilo

Liquid crystal - anisotropic nanoparticles mixtures
Vlad Popa-Nita, Matej Cvetko, Samo Kralj, 2011, samostojni znanstveni sestavek ali poglavje v monografski publikaciji

Ključne besede: liquid crystals, nano particles, phase behavior
Objavljeno: 07.06.2012; Ogledov: 772; Prenosov: 60
URL Povezava na celotno besedilo

Competition between local disordering and global ordering fields in nematic liquid crystals
Matej Cvetko, Milan Ambrožič, Samo Kralj, 2010, izvirni znanstveni članek

Opis: We study the influence of external electric or magnetic field B on orientational ordering of nematic liquid crystals or of other rod-like objects (e.g. nanotubes immersed in a liquid) in the presence of random anisotropy field type of disorder. The Lebwohl-Lasher lattice type of semi-microscopic approach is used at zero temperature. Therefore, results are valid well below the transition into the isotropic phase. We calculate the correlation function of systems as a function of B, concentration p of impurities imposing random anisotropy field disorder, the disorder strength W and system dimensionality (2D and 3D systems). In order to probe memory effects we calculate correlation length ▫$xi$▫ for random and homogeneous initial configurations. We determine the crossover fields Bc(p) separating roughly the ordered and disordered regime. Memory effects are apparent only in the latter case, i.e. for B < Bc.
Ključne besede: disorder, Imry-Ma theorem, liquid crystals, memory effect, orientational order
Objavljeno: 07.06.2012; Ogledov: 741; Prenosov: 147
.pdf Celotno besedilo (747,18 KB)
Gradivo ima več datotek! Več...

Finite-size effects on order reconstruction around nematic defects
Samo Kralj, Riccardo Rosso, Epifanio G. Virga, 2010, izvirni znanstveni članek

Opis: By use of the Landau-de Gennes phenomenological theory, we study the texture of a nematic liquid crystal confined within a hybrid cell. Precisely, we consider cylindrically symmetric solutions containing topological defects dictated by appropriate boundary conditions. We focus our attention on cells whose dimensions are comparable with the biaxial correlation length ▫$xi_b$▫. For such severe confinements the order reconstruction (OR) configuration could be stable. Its structural details reflect the balance among boundary-enforced frustration, elastic penalties, and finite-size effects. In particular, we analyze the interplay between finite-size effects and topological defects. We show that defects are always pinned to the negatively (planar) uniaxial sheet of the OR structure. The presence of a ring defect can dramatically increase the critical threshold below which the OR structure is stable.
Ključne besede: physics, liquid crystals, nematic crystals, nematic defects, structural transitions
Objavljeno: 07.06.2012; Ogledov: 919; Prenosov: 49
URL Povezava na celotno besedilo

Memory effects in randomly perturbed systems exhibiting continuous symmetry breaking
Matej Cvetko, Milan Ambrožič, Samo Kralj, 2009, izvirni znanstveni članek

Opis: We studied pattern characteristics in randomly perturbed structures exhibitingcontinuous symmetry breaking. A Lebwohl-Lasher-type lattice model was used which described well the onset of orientational ordering of a system of rod-like objects. For example, such systems mimic the orientational ordering tendency in liquid crystals or in an ensemble of nanotubes. We set impurities to impose a random anisotropy type of disorder on the objects. Structural characteristics were studied as a function of concentration of impurities, interaction strength w between impurities and rod-like objects, external ordering strength and history of samples. We showed that the characteristic linear size of patterns and range of ordering strongly depend on the history of samples for weak enough strength w. The two-dimensional and three-dimensional simulations yielded qualitatively similar results.
Ključne besede: liquid crystals, memory effect, nanotubes, structural order, percolation
Objavljeno: 07.06.2012; Ogledov: 746; Prenosov: 67
URL Povezava na celotno besedilo

The influence of disorder on thermotropic nematic liquid crystals phase behavior
Vlad Popa-Nita, Ivan Gerlič, Samo Kralj, 2009, pregledni znanstveni članek

Opis: We review the theoretical research on the influence of disorder on structure and phase behavior of condensed matter system exhibiting continuous symmetry breaking focusing on liquid crystal phase transitions. We discuss the main properties of liquid crystals as adequate systems in which several open questions with respect to the impact of disorder on universal phase and structural behavior could be explored. Main advantages of liquid crystalline materials and different experimental realizations of random field-type disorder imposed on liquid crystal phases are described.
Ključne besede: liquid crystals, random fields, phase transition, disorder, nematic structures
Objavljeno: 07.06.2012; Ogledov: 1275; Prenosov: 144
.pdf Celotno besedilo (864,80 KB)
Gradivo ima več datotek! Več...

Alignment of carbon nanotubes in nematic liquid crystals
Paul van der Schoot, Vlad Popa-Nita, Samo Kralj, 2008, izvirni znanstveni članek

Opis: The self-organizing properties of nematic liquid crystals can be used to aligncarbon nanotubes dispersed in them. Because the nanotubes are so much thinner than the elastic penetration length, the alignment is caused by the coupling of the unperturbed director field to the anisotropic interfacial tension of the nanotubes in the nematic host fluid. In order to relate the degree of alignment of the nanotubes to the properties of the nematic liquid crystal, we treat the two components on the same footing and combine Landau-deGennes free energies for the thermotropic ordering of the liquid crystal and for the lyotropic nematic ordering of carbon nanotubes caused by their mutually excluded volumes. The phase ordering of the binary mixture is analyzed as a function of the volume fraction of the carbon nanotubes, the strength of the coupling and the temperature. We find that the degree of ordering of the nanorods is enslaved by the properties of the host liquid and that it can be tuned by raising or lowering the temperature or by increasing or decreasing their concentration. By comparing the theory to recent experiments, we find the anchoring energy of multiwalled carbon nanotubes to be in the range from 10-10 to 10-7 N m-1.
Ključne besede: liquid crystals, nematic crystals, molecular dynamics, stability, elasticity, carbon nanotubes
Objavljeno: 07.06.2012; Ogledov: 955; Prenosov: 35
URL Povezava na celotno besedilo

Fingered core structure of nematic boojums
Samo Kralj, Riccardo Rosso, Epifanio G. Virga, 2008, izvirni znanstveni članek

Opis: Using the Landau-de Gennes phenomenological approach, we study the fine biaxial core structure of a boojum residing on the surface of a nematic liquid crystal phase. The core is formed by a negatively uniaxial finger, surrounded by a shell with maximal biaxiality. The characteristic finger's length and the shell's width are comparable to the biaxial correlation length. The finger tip is melted for topological reasons. Upon decreasing the surface anchoring strength below a critical value, the finger gradually leaves the bulk and it is expelled through the surface.
Ključne besede: physics, liquid crystals, nematic crystals, line defects, surface phenomena
Objavljeno: 07.06.2012; Ogledov: 761; Prenosov: 50
URL Povezava na celotno besedilo

Annihilation of defects in liquid crystals
Milan Svetec, Milan Ambrožič, Samo Kralj, 2007, objavljeni znanstveni prispevek na konferenci

Opis: The annihilation of defect is studied theoretically in liquid crystals (LCs). We consider the annihilation of point disclinations in nematic and line edge dislocations in smectic A LC phase, respectively. We stres s qualitative similarities in these processes. The whole annihilation regime is taken into account, consisting of the pre-collision, collision, and post-collision stage.
Ključne besede: physics, liquid crystals, annihilation, defects, point defects, point disclinations, edge dislocations
Objavljeno: 07.06.2012; Ogledov: 698; Prenosov: 48
URL Povezava na celotno besedilo

Iskanje izvedeno v 0.31 sek.
Na vrh
Logotipi partnerjev Univerza v Mariboru Univerza v Ljubljani Univerza na Primorskem Univerza v Novi Gorici