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Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles
Marjan Krašna, Matej Cvetko, Milan Ambrožič, 2010, izvirni znanstveni članek

Opis: Orientational ordering of a homogeneous mixture of uniaxial liquid crystalline(LC) molecules and magnetic nanoparticles (NPs) is studied using the Lebwohl-Lasher lattice model. We consider cases where NPs tend to be oriented perpendicularly to LC molecules due to elastic forces. We study domain-type configurations of ensembles, which are quenched from the isotropic phase. We show that for large enough concentrations of NPs the long range uniaxial nematic ordering is replaced by short range order exhibiting strong biaxiality. This suggests that the impact of NPs on orientational ordering of LCs for appropriate concentrations of NPs is reminiscent to the influence of quenched random fields which locally enforce a biaxial ordering.
Ključne besede: liquid crystals, nanoparticles, disorder, orientational order, quenched disorder, symmetry breaking
Objavljeno: 03.08.2017; Ogledov: 31; Prenosov: 0
.pdf Polno besedilo (447,84 KB)

Inheritance patterns in citation networks reveal scientific memes
Tobias Kuhn, Matjaž Perc, Dirk Helbing, 2014, izvirni znanstveni članek

Opis: Memes are the cultural equivalent of genes that spread across human culture by means of imitation. What makes a meme and what distinguishes it from other forms of information, however, is still poorly understood. Our analysis of memes in the scientific literature reveals that they are governed by a surprisingly simple relationship between frequency of occurrence and the degree to which they propagate along the citation graph. We propose a simple formalization of this pattern and validate it with data from close to 50 million publication records from the Web of Science, PubMed Central, and the American Physical Society. Evaluations relying on human annotators, citation network randomizations, and comparisons with several alternative approaches confirm that our formula is accurate and effective, without a dependence on linguistic or ontological knowledge and without the application of arbitrary thresholds or filters.
Ključne besede: memes, inheritance, genes, network science, complex systems
Objavljeno: 03.08.2017; Ogledov: 19; Prenosov: 0
.pdf Polno besedilo (2,85 MB)

Correlation of positive and negative reciprocity fails to confer an evolutionary advantage: phase transitions to elementary strategies
Attila Szolnoki, Matjaž Perc, 2013, izvirni znanstveni članek

Opis: Economic experiments reveal that humans value cooperation and fairness. Punishing unfair behavioris therefore common, and according to the theory of strong reciprocity, it is also directly related to rewarding cooperative behavior. However, empirical data fail to confirm that positive and negative reciprocity are correlated. Inspired by this disagreement, we determine whether the combined application of reward and punishment is evolutionarily advantageous. We study a spatial public goods game, where in addition to the three elementary strategies of defection, rewarding, and punishment, a fourth strategy that combines the latter two competes for space. We find rich dynamical behavior that gives rise to intricate phase diagrams where continuous and discontinuous phase transitions occur in succession. Indirect territorial competition, spontaneous emergence of cyclic dominance, as well as divergent fluctuations of oscillations that terminate in an absorbing phase are observed. Yet, despite the high complexity of solutions, the combined strategy can survive only in very narrow and unrealistic parameter regions. Elementary strategies, either in pure or mixed phases, are much more common and likely to prevail. Our results highlight the importance of patterns and structure in human cooperation, which should be considered in future experiments.
Ključne besede: public goods, punishment, reward, evolutionary games, collective phenomena, phase transitions, physics of social systems
Objavljeno: 03.08.2017; Ogledov: 20; Prenosov: 1
.pdf Polno besedilo (667,46 KB)

Comparison of cultivable acetic acid bacterial microbiota in organic and conventional apple cider vinegar
Aleksandra Mori Štornik, Barbara Skok, Janja Trček, 2016, izvirni znanstveni članek

Opis: Organic apple cider vinegar is produced from apples that go through very restricted treatment in orchard. During the first stage of the process, the sugars from apples are fermented by yeasts to cider. The produced ethanol is used as a substrate by acetic acid bacteria in a second separated bioprocess. In both, the organic and conventional apple cider vinegars the ethanol oxidation to acetic acid is initiated by native microbiota that survived alcohol fermentation. We compared the cultivable acetic acid bacterial microbiota in the production of organic and conventional apple cider vinegars from a smoothly running oxidation cycle of a submerged industrial process. In this way we isolated and characterized 96 bacteria from organic and 72 bacteria from conventional apple cider vinegar. Using the restriction analysis of the PCR-amplified 16S-23S rRNA gene ITS regions, we identified four different HaeIII and five different HpaII restriction profiles for bacterial isolates from organic apple cider vinegar. Each type of restriction profile was further analyzed by sequence analysis of the 16S-23S rRNA gene ITS regions, resulting in identification of the following species: Acetobacter pasteurianus (71.90 %), Acetobacter ghanensis (12.50 %), Komagataeibacter oboediens (9.35 %) and Komagataeibacter saccharivorans (6.25 %). Using the same analytical approach in conventional apple cider vinegar, we identified only two different HaeIII and two different HpaII restriction profiles of the 16S‒23S rRNA gene ITS regions, which belong to the species Acetobacter pasteurianus (66.70 %) and Komagataeibacter oboediens (33.30 %). Yeasts that are able to resist 30 g/L of acetic acid were isolated from the acetic acid production phase and further identified by sequence analysis of the ITS1-5.8S rDNA‒ITS2 region as Candida ethanolica, Pichia membranifaciens and Saccharomycodes ludwigii. This study has shown for the first time that the bacterial microbiota for the industrial production of organic apple cider vinegar is clearly more heterogeneous than the bacterial microbiota for the industrial production of conventional apple cider vinegar. Further chemical analysis should reveal if a difference in microbiota composition influences the quality of different types of apple cider vinegar.
Ključne besede: microbiology, acetic acid bacteria, apple cider vinegar
Objavljeno: 24.07.2017; Ogledov: 37; Prenosov: 1
.pdf Polno besedilo (289,47 KB)

16S rRNA in situ hybridization followed by flow cytometry for rapid identification of acetic acid bacteria involved in submerged industrial vinegar production
Janja Trček, Luka Lipoglavšek, Gorazd Avguštin, 2016, izvirni znanstveni članek

Opis: Acetic acid bacteria are involved in many biotechnological processes such as vitamin C, gluconic acid, miglitol or acetic acid production, and others. For a technologist trying to control the industrial process, the ability to follow the microbiological development of the process is thus of importance. During the past few years hybridization in a combination with flow cytometry has oft en been used for this purpose. Since vinegar is a liquid, it is an ideal matrix for flow cytometry analysis. In this work we have constructed a specific probe for highly acetic acid-resistant species of the acetic acid bacteria and a protocol for in situ hybridization, which in combination with flow cytometry enables direct monitoring of bacteria producing vinegar with >10 % of acetic acid. The approach was successfully applied for monitoring microbiota during industrial vinegar production.
Ključne besede: microbiology, acetic acid bacteria, flow cytometry
Objavljeno: 24.07.2017; Ogledov: 38; Prenosov: 0
.pdf Polno besedilo (500,81 KB)

Razvoj testne lutke za preučevanje delovanja senzorja za zaznavo pešcev ob trku z osebnim vozilom pri velikih naletnih hitrostih
Taja Svetina, 2017, magistrsko delo

Opis: V magistrskem delu predstavimo razvoj nadomestne testne lutke za testno lutko Flex-PLI, ki bi jo uporabljali pri testih preučevanja delovanja senzorja za zaznavo pešcev ob trku z vozilom pri velikih naletnih hitrostih. Razvoj zajema določanje ciljnih krivulj, ki predstavljajo lastnosti testne lutke Flex-PLI med trkom, simulacijo trkov ter oblikovanje nove testne lutke, določanje njenih lastnosti med trkom in primerjanje teh lastnosti z lastnostmi testne lutke Flex-PLI. Podane so tudi dinamika togega telesa, fizika trkov ter možnosti zaščite pešcev pri trku z vozilom. Uspelo nam je razviti nadomestno testno lutko, ki zadostno oponaša obnašanje testne lutke Flex-PLI pri trkih z velikimi naletnimi hitrostmi in ki zadostuje zadanemu cilju, da naj bi bila nadomestna testna lutka čim bolj enostavna in posledično v primerjavi s testno lutko Flex-PLI cenovno ugodna. Podali smo različico možnega prototipa nadomestne testne lutke
Ključne besede: trki, gibalna količina, poškodbe pri trkih, zaščita pešcev, kinetična energija, testna lutka, tlačni senzor za zaznavo pešcev, deformacije
Objavljeno: 21.07.2017; Ogledov: 53; Prenosov: 0
.pdf Polno besedilo (3,49 MB)

Curvature-controlled topological defects
Luka Mesarec, Pavlo Kurioz, Aleš Iglič, Wojciech Góźdź, Samo Kralj, izvirni znanstveni članek

Opis: Effectively, two-dimensional (2D) closed films exhibiting in-plane orientational ordering (ordered shells) might be instrumental for the realization of scaled crystals. In them, ordered shells are expected to play the role of atoms. Furthermore, topological defects (TDs) within them would determine their valence. Namely, bonding among shells within an isotropic liquid matrix could be established via appropriate nano-binders (i.e., linkers) which tend to be attached to the cores of TDs exploiting the defect core replacement mechanism. Consequently, by varying configurations of TDs one could nucleate growth of scaled crystals displaying different symmetries. For this purpose, it is of interest to develop a simple and robust mechanism via which one could control the position and number of TDs in such atoms. In this paper, we use a minimal mesoscopic model, where variational parameters are the 2D curvature tensor and the 2D orientational tensor order parameter. We demonstrate numerically the efficiency of the effective topological defect cancellation mechanism to predict positional assembling of TDs in ordered films characterized by spatially nonhomogeneous Gaussian curvature. Furthermore, we show how one could efficiently switch among qualitatively different structures by using a relative volume v of ordered shells, which represents a relatively simple naturally accessible control parameter.
Ključne besede: topological defects, Gaussian curvature, self-assembling, crystal growth nucleation
Objavljeno: 20.07.2017; Ogledov: 32; Prenosov: 0
.pdf Polno besedilo (6,77 MB)

Ontogenetski vidik modularne organizacije lobanje navadnega polha, Glis glis (Linnaeus, 1766)
Saša Zavratnik, 2017, magistrsko delo

Opis: Glodavci spadajo med najuspešnejše sodobne sesalce. Lobanja sesalcev je kompleksna struktura, primerna za proučevanje postnatalne ontogenije pri malih sesalcih. Deluje kot celota, deli pa so med seboj neenakomerno povezani in razdeljeni v module. Material, uporabljen v študiji, so bile ventralne strani lobanj navadnega polha, Glis glis (Linnaeus, 1766) iz lokalitete Krim, Slovenija, shranjene v Prirodoslovnem muzeju Slovenije. Lobanje smo na podlagi erupcije meljakov razdelili v šest starostnih skupin. Raziskovali smo postnatalno variabilnost v obliki in velikosti ventralne strani lobanje, predvsem z vidika modularne organizacije, morfološke integracije ter alometrije. Do sedaj podobna raziskava še ni bila izvedena. Z metodami geometrijske morfometrije smo primerjali stopnjo modularnosti med juvenilnimi in adultnimi osebki. Hipotetično modularnost smo na osnovi Escoufierjevega RV koeficienta testirali na 224 lobanjah. Hipotezo o modularnosti pri mladih živalih smo zavrnili, pri odraslih osebkih pa so rezultati delno podprli delitev lobanje na obrazni in možganski del. Stopnja integracije med moduloma je večja pri mladih osebkih in se s starostjo zmanjšuje. Lobanja navadnega polha raste alometrično. Čeprav je lahko alometrija močan integracijski faktor, je imela na hipotetično modularnost lobanje navadnega polha majhen vpliv. Sklepamo, da je sprememba v stopnji integracije med obraznim in možganskim delom lobanje v času ontogenije posledica specializacije obeh funkcionalnih modulov ter prehoda s sesanja mleka na mehansko obdelavo trše hrane.
Ključne besede: geometrijska morfometrija, modularnost, alometrija, RV koeficient, ontogenija, lobanja, Glis glis
Objavljeno: 19.07.2017; Ogledov: 51; Prenosov: 13
.pdf Polno besedilo (1,50 MB)

Določitev površinske napetosti nematskega tekočega kristala in nekaterih izotropnih kapljevin na obdelanih steklenih površinah z metodo kapilarnega dviga
Denis Rajh, 2017, magistrsko delo

Opis: V magistrskem delu so predstavljene meritve močenja in kapilarnega dviga vode, glicerola, silikonskega olja in tekočega kristala na obdelanih steklenih površinah z namenom določitve površinske napetosti. Delo je sestavljeno iz teoretičnega opisa kapilarnih pojavov s poudarkom na računanju oblike meniskusa in višine kapilarnega dviga, predstavitve fizikalnih lastnosti uporabljenih materialov in eksperimentalnih metod ter rezultatov. Razvil sem postopek merjenja kontaktnih kotov kapljevin na ravnih podlagah s prilagojenim optičnim mikroskopom s horizontalno postavitvijo objektivov, ki je bil uporaben tudi za določanje oblike meniskusov in meritve višin kapilarnih dvigov v cilindričnih kapilarah. Ugotovil sem, da ima obdelava steklenih površin s silanom različen vpliv na močenje polarnih in nepolarnih kapljevin, kar se pozna tudi pri spreminjanju višine kapilarnih dvigov. Pokazal sem tudi, da se anizotropne lastnosti nematskega tekočega kristala izrazijo v anizotropiji površinske napetosti, ki je odvisna od robnih pogojev na površini stekla. Metoda kapilarnega dviga v ozkih cilindričnih kapilarah se je izkazala kot enostaven, učinkovit, ponovljiv in dovolj natančen način določanja površinske napetosti različnih vrst kapljevin, ki je uporabna tudi za raziskovanje vpliva kemijske funkcionalizacije površin na lastnosti močenja.
Ključne besede: kapilarni dvig, močenje, površinska napetost, kapljevine, tekoči kristali
Objavljeno: 19.07.2017; Ogledov: 39; Prenosov: 4
.pdf Polno besedilo (5,87 MB)

Möbiusove transformacije in dvojne spirale
Katja Breznik, 2017, magistrsko delo

Opis: V pričujočem magistrskem delu se najprej seznanimo s Kleinovim konceptom geometrije. Ta nam med drugim omogoča, da med različnimi geometrijami, ki jih lahko razumemo kot dokaj neodvisne matematične teorije, vzpostavimo medsebojne relacije. V drugem poglavju preidemo na geometrijo kompleksnih števil. Sledi osrednje poglavje s podrobno obravnavo Möbiusovih transformacij. Seznanimo se z definicijo, lastnostmi in s klasifikacijo Möbiusovih transformacij. Predstavljeno teorijo podkrepimo s primeri. Za konec opišemo primer dvojne spirale, ki jo zgradimo s pomočjo loksodromične Möbiusove transformacije, podane s predpisom T(z)=((2+i)z+2+4i):(z+2+i), kar je tudi osrednji cilj magistrskega dela.
Ključne besede: geometrija, grupa, transformacijska grupa, kompleksna števila, stereografska projekcija, Riemannova sfera, Möbiusove transformacije, klasifikacija Möbiusovih transformacij, dvojna spirala
Objavljeno: 19.07.2017; Ogledov: 39; Prenosov: 10
.pdf Polno besedilo (724,80 KB)

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