Physical properties of the intermetallic catalyst compound ZnPd

Kataliza se uporablja v znanosti in tehnologiji za spreminjanje poteka kemijskih reakcij preko znižanja aktivacijske energije, ki je potrebna za reakcijo. Najpreprostejši katalizator dobimo, če vzamemo kovinski element brez podlage. Slabost take izbire je zelo omejeno število elementov, ki so katalitsko aktivni za dano kemijsko reakcijo. Alternativni materiali za heterogeno katalizo so strukturno urejene intermetalne spojine. Gre za spojine iz dveh ali več kovinskih elementov, ki se nahajajo levo ali v okolici Zintlove črte v periodnem sistemu elementov. Njihova struktura je popolnoma ali delno urejena in se razlikuje od strukture elementov, ki tvorijo spojino. Stabilnost intermetalnih spojin med kemijsko reakcijo je povezana z njihovo elektronsko in geometrijsko strukturo. Prednost uporabe intermetalnih spojin za katalizo je možnost izbire elektronske in geometrijske strukture. Intermetalne spojine lahko razpadejo pred ali med katalizo, tako da iz njih nastane katalizator z veliko aktivno površino. Intermetalne spojine lahko nastanejo tudi med kemijsko reakcijo pri reakciji med aktivno kovino in podlago ali med različnimi materiali s podlago. V izogib tem težavam je bil nedavno sprejet pristop, da se kot stabilne katalizatorje brez podlage uporablja intermetalne spojine z urejeno kristalno strukturo. V Magistrskem delu smo opravili karakterizacijo vzorca ZnPd s pomočjo mikroskopije SEM, ki je bila izvedena na Kemijskem institutu v Ljubljani. Ostale meritve so bile izvedene na Institutu »Jožef Stefan« v Ljubljani. Z napravo PPMS (angl. Physical Property Measurement System) proizvajalca Quantum Design smo izmerili fizikalne lastnosti ZnPd. Pri določanju magnetnega stanja vzorca pa smo uporabili magnetometer MPMS (angl. Magnetic Property Measurement System) XL-5 proizvajalca Quantum Design. V Magistrskem delu smo prav tako dopolnili nedavne študije fizikalnih lastnostih intermetalnih katalizatorjev GaPd in InPd.Catalysis is used in science and technology to change the path of chemical reactions by modifying their activation energies. The simplest catalyst is an unsupported metal element. The downside of such choice is a very limited number of elements that are catalytically active for a specific chemical reaction. Alternative materials for heterogeneous catalysis are structurally ordered intermetallic alloys. Intermetallic alloys are composed of two or more metallic elements. The completely or partially ordered structure of intermetallic alloys is different form the structure of individual elements that form the alloy. Stability of intermetallic alloys during chemical reactions depends on their electronic and geometrical structure. The great advantage of intermetallic alloys is the possibility to choose their electronic and geometric structure before use. Intermetallic alloys can decompose before or during catalysis. They form catalysts with large active surfaces. Intermetallic alloys can also form during the chemical reaction between active metal and supporting material or between different supporting materials. To avoid difficulties, an approach to use intermetallic alloys with ordered crystal structure as stable unsupported catalysts has recently been accepted. In this Master\u27s thesis, we characterized a ZnPd sample using SEM microscope at the Chemistry Institute in Ljubljana. Physical properties of the sample were measured at the Jožef Stefan Institute in Ljubljana. With the Physical Property Measurement System (PPMS) we measured specific heat and electrical resistivity. To determine the magnetic state of the sample we used the Magnetic Property Measurement System (MPMS XL-5). We have also supplemented recent studies of physical properties of intermetallic catalysts GaPd and InPd

Analytical mechanics

Pri predmetu Analitična mehanika obravnavamo številne probleme iz mehanike, predvsem dinamike, na bolj matematično sistematičen način, kot je navada pri običajnih fizikalnih nalogah, npr. v zvezi z drugim Newtonovim zakonom. S tem lahko vključimo tudi kompleksnejše geometrije pri gibanju teles. Ključni del analitične mehanike je vpeljava generaliziranih koordinat kot neodvisnih spremenljivk gibanja, s katerimi izrazimo Lagrangeevo funkcijo ali pa Hamiltonian. Nazadnje moramo rešiti ustrezne diferencialne enačbe, da najdemo časovno odvisnost generaliziranih koordinat. Gravitacija in nihanje sta značilni področji, kjer koristno uporabimo matematični formalizem analitične mehanike.In the course Analytical mechanics numerous problems in mechanics, particularly topics from dynamics, are treated in a more systematic way, as compared to ordinary physical problems, e.g., in relation to second Newton law. In this way, we can also include more complex geometries in the motion of bodies. The key part od analytical mechanics is introduction of generalized coordinates as independent variables of motion, used to express either Lagrange function or Hamiltonian. Finally, the corresponding differential equations must be solved in order to find the time development of generalized coordinates. Gravitation and oscillation are typical areas where the mathematical formalism of analytical mechanics can be used

Stable assemblies of topological defects in nematic orientational order

We considered general mechanisms enabling the stabilization of localized assemblies of topological defects (TDs). There is growing evidence that physical fields represent fundamental natural entities, and therefore these features are of interest to all branches of physics. In general, cores of TDs are energetically costly, and consequently, assemblies of TDs are unfavorable. Owing to the richness of universalities in the physics of TDs, it is of interest to identify systems where they are easily experimentally accessible, enabling detailed and well-controlled analysis of their universal behavior, and cross-fertilizing knowledge in different areas of physics. In this respect, thermotropic nematic liquid crystals (NLCs) represent an ideal experiment testbed for such studies. In addition, TDs in NLCs could be exploited in several applications. We present examples that emphasize the importance of curvature imposed on the phase component of the relevant order parameter field. In NLCs, it is represented by the nematic tensor order parameter. Using a simple Landau-type approach, we show how the coupling between chirality and saddle splay elasticity, which can be expressed as a Gaussian curvature contribution, can stabilize Meron TDs. The latter have numerous analogs in other branches of physics. TDs in 2D curved manifolds reveal that the Gaussian curvature dominantly impacts the assembling and stabilization of TDs. Furthermore, a strong enough curvature that serves as an attractor for TDs is a respective field that could be imposed in a fast enough phase transition. Assemblies of created TDs created in such a disordered environment could be stabilized by appropriate impurities

Impact of random-field-type disorder on nematic liquid crystalline structures

We study bicomponent systems where one component represents a liquid crystalline (LC) phase, and the other component randomly perturbs the LC order. Such systems can serve as a testbed to systematically analyse the impact of qualitatively different types of random-type sources of perturbation on the orientational and/or translational order. This mini-review presents typical representatives of such systems, where orientational and translational order is probed in nematic and smectic A LCs, respectively. As a source of perturbation, we consider either different porous matrices (control-pore glass, aerogels) or aerosil nanoparticles, which can form in LCs' different fractal-like network organizations. In such complex systems, LC ordering fingerprints the interplay among LC elastic forces, interfacial forces, and randomness. The resulting LC behaviour could be characterised by either long-range, quasi long-range, or short-range order. We demonstrate under which conditions random-field-like phenomena or interfacial effects dominate. However, these effects are relatively strongly entangled in most experimental systems, and individual impacts cannot be precisely identified