"The last fifteen years have seen much success in the analysis of quasi-static evolution for Griffith fracture, which is the mathematically natural starting point for studying fracture. At the same time, attempts have been made to show existence for similar models based on cohesive fracture rather than Griffith. These models are generally viewed as physically more realistic than Griffith, in that they are better models for crack nucleation. These attempts at existence proofs have been unsuccessful without very strong additional assumptions, for example, specifying the crack path a priori. The main purpose of this thesis is to characterize as well as possible the mathematical difficulties in cohesive fracture, and to make progress toward an existence result without the prescribed crack path assumption. So far, the most powerful method for existence proofs is to build a sequence of approximate solutions, based on time discretization, and take the limit as the time steps go to zero. We show that there are mainly two complications on the cracks of these approximate solutions that we need to rule out in order to show existence. The first one is due to the potential oscillation of the crack path. The second is due to the potential splitting of a crack into two or more nearby cracks, with the same total jump in displacement. We begin by first constructing an example illustrating how oscillations described above can affect the minimality of the limit. Then we prove that the splitting described above can be ruled out for any sequence of unilateral minimizers. With this result, we show how exactly oscillation affect the minimality on the limit of the sequence. We then move to the evolution problem and show the convergence of energy for almost every t. Based on this result we develop a method that allows us to analyze the problem using only a finite set of times. An application of this method is a proof of absolute continuity. Future work will be aimed at using the tools we developed to rule out oscillation and finally to prove existence results under more general assumptions."

Listeria monocytogenes is a major concern for the food industry. It is one of the major agents causing listeriosis. The objective of the first part of this study is to evaluate the effect of hydration level on attached listeria monocytogenes on stainless steel/High density polyethylene transferred to food products. Attached cells were prepared on stainless steel/High density polyethylene. Transfer experiments were conducted from inoculated surface material slides to cold smoked salmon fillets. This experiment was repeated 6 times. The results were analyzed with an analysis of variance by SAS. The differences between the different RH% and surface conditions were not statistically significant. There was variability in between packages, brands and over the course of storage after opening, and likely contributed to the variability of transfer observed in this set of experiments. The objective of the second part of the research is to study the effect of hydration level on the detachment of Listeria monocytogenes biofilm growing on stainless steel by using Atomic force microscope. Biofilms were grown on stainless steel in drip flow bioreactor at 32 °C for 72 h. Then biofilms were equilibrated over saturated salt solution at 20 °C for 48 h before the Atomic Force Microscope experiment. The results showed that cohesive energy value of the biofilm increased with biofilm depth. Only square shaped displaced 2.5X2.5 μm region were visualized after serious of raster scanning under high load which means that moisture condition of Listeria monocytogenes biofilm can significantly affect the cohesiveness between of Listeria monocytogenes biofilm.

Wet web paper cohesive properties behave in a similar way than tensile strength properties. The result was obtained using an unique apparatus developed by the IPST, which allows the cohesive strength determination for different wet web solids content. With the results a linear relation can be established between the cohesive strength index (obtained with the splitting apparatus) and the tensile strength index (obtained with the Instron). The splitting apparatus results can be used to calculate strain based on the work of Osterberg.

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<p>U ovoj doktorskoj disertaciji izloženi su rezultati&nbsp;analize eksperimentalno i teorijski dobijene&nbsp;raspodele gustine naelektrisanja dva derivata&nbsp;tiosemikarbazida, 4-metil-3-tiosemikarbazida&nbsp;(MeTSC) i 4-metil-3-tiosemikarbazon 2-piridinformamida (TSC4). &nbsp;Analiza&nbsp;eksperimentalno dobijene gustine naelektrisanja je&nbsp;zasnovana&nbsp; na preciznim &nbsp;podacima dobijenim&nbsp;difrakcijom rendgenskog zračenja visoke&nbsp;rezolucije. Teorijska istraživanja bazirana su na&nbsp;teorijskim strukturnim faktorima dobijenim&nbsp;primenom programa CRYSAL09 polazeći od&nbsp;geometrije&nbsp; molekula određene nakon multipol&nbsp;utačnjavanja eksperimentalno dobijene gustine&nbsp;naelektrisanja. Za opisivanje eksperimentalne i&nbsp;teorijske ukupne elektronske gustine kori&scaron;ćen je&nbsp;Hansen-Coppens-ov multipol-model.&nbsp; Takođe je&nbsp;urađena i topolo&scaron;ka analizahemijskih veza i&nbsp;interakcija &nbsp;i ispitivana su elektrostatička svojstva&nbsp;atoma sumpora.</p><p>Analizom eksperimentalne gustine&nbsp;naelektrisanja kristalnih struktura MeTSC i TSC4&nbsp;uočeno je da deformaciona gustina slobodnih&nbsp;elektronskih parova S atoma ima &nbsp;oblik torusa, da&nbsp;je unutar njega raspodela elektronske gustine&nbsp;nehomogena i da položaj samog torusa može biti&nbsp;ortogonalan (SalTSC) ili pod uglom (MeTSC,&nbsp;<br />TSC4).&nbsp; Na osnovu raspodele deformacione&nbsp;gustine i elektrostatičkog potencijala, kao &nbsp;i na&nbsp;osnovu topolo&scaron;ke analize ukupne eksperimentalne&nbsp;gustine naelektrisanja &rho;_ktv&nbsp; i njenog Laplasijana &nabla;²&rho;_ktv zaključeno je da atom sumpora ima izrazitu&nbsp;fleksibilnost i sposobnost da prilagodi svoju&nbsp;elektronsku gustinu slobodnih elektronskih &nbsp;parova&nbsp;prostornom rasporedu donornih grupa koje&nbsp;učestvuju u interakcijama sa S akceptorom.&nbsp; U&nbsp;kristalnim strukturama MeTSC i TSC4 utvrđeno&nbsp;je da S atom istovremeno gradi četiri, odnosno&nbsp;prosečno &scaron;est međumolekulskih interakcija.</p><p>U cilju upotpunjavanja eksperimentalnih&nbsp;rezultata analizirana je teorijski dobijena gustina&nbsp;naelektrisanja oba molekula, a zatim su ispitivane&nbsp;karakteristike sumpora kao akceptora i to u&nbsp;sistemima različite složensti polazeći od&nbsp;izolovanih monomera, preko izdvojenih dimer do&nbsp;kristalnogokruženja. Ovom analizom je utvrđeno&nbsp;da se simultanim angažovanjem S atoma u vi&scaron;e&nbsp;interakcija ne umanjuje njegova akceptorska&nbsp;sposobnost.</p><p>Vodonične vezekoje uključuju S akceptor su&nbsp;ispitivane sa aspekta &nbsp;energijskih svojstava dimera&nbsp;koji suprisutni u MeTSCi TSC4, kaoi u dodatno&nbsp;konstruisanim&nbsp; sistemima&nbsp; MeTSC/MeOH&nbsp; i&nbsp;aceton/MeOH. Energijske&nbsp; karakteristike&nbsp; su&nbsp;proučavane u pogledu elektrostatičke energije&nbsp;interakcije (E_es) i kohezione energije(E_coh). Za&nbsp;<br />dva odabrana&nbsp; MeTSC/MeOH i aceton/MeOH&nbsp;sistema je primenjena metoda &nbsp;kuplovanih klastera&nbsp;kao&scaron;to&nbsp; je&nbsp;<em> ab initio</em>&nbsp; CCSD(T)&nbsp; metod.&nbsp; Za&nbsp;MeTSC/MeOH sistem je &nbsp;urađena potpuna&nbsp;optimizacija i za tako dobijenu ravnotežnu&nbsp;geometriju je izračunata energija sistema&nbsp;∆E_CCSD(T),CBS.</p> / <p>In this dissertation the analysis of the experimental and theoretically obtained electron &nbsp;density of two derivatives of thiosemicarbasides, 4-methyl-3-thiosemicarbaside (MeTSC) and 4-methyl-3-thiosemikabazone 2-piridinformamide (TSC4) are presented.&nbsp; The analysis of experimentally obtained electron density is based on &nbsp;accurate X-ray diffraction data of high resolution. Theoretically calculated electron densities are obtained from periodic quantum mechanical calculation using CRYSTAL09 and the accurate structural parameters from high resolution X-ray&nbsp;experiment. For the description of the theoretical and experimental electron density the Hansen-Coppens multipol model was used. Further topological analysis of chemical bonds and interactions was performed in order to explain the electrostatic properties of sulfur.</p><p>In this work it has been observed that in the experimentally obtained electron density of the MeTSC and TSC4 crystal structures, the deformational electron density of sulfur free electron pairs forms a toroidal shape. Further, this torus is not homogeneously filled but shows pronounced local accumulations and its position can be either orthogonal (like in SalTSC) or tilted (MeTSC, TSC4). Based on the distribution of the&nbsp;deformational electron&nbsp; density and electrostatic potential, as well as the topological analysis of the total electron density &rho;_ktv and its Laplasian &nabla;²&rho;_ktv&nbsp;it can be concluded that the S atom has a remarkable flexibility and ability to adapt his deformation electron density of free electron pairs into toruses corresponding to the position of donor groups surrounding him. In the crystal structures of MeTSC and TSC4 it was determined that the S atom participates in four and six interactions, respectively.</p><p>In order to supplement&nbsp; the experimentally obtained results a theoretically calculated electron density of both molecules (MeTSC and TSC4) was performed and the properties of the S atom as a hydrogen acceptor have been studied. The analysis was &nbsp;performed on systems of various complexity, starting with isolated monomers, then on &nbsp;dimers and up to the whole crystal packing. From this work it has been concluded that &nbsp;the acceptor capabilities of the S atom are not diminished with the increasing number &nbsp;of interactions.&nbsp;&nbsp;&nbsp;&nbsp;</p><p>The hydrogen bonding involving thioureido S&nbsp;acceptor is also investigated in terms of the energetic properties of the MeTSC and TSC4 dimers existing in the crystal structure, and additional MeTSC/MeOH and acetone/MeOH systems. Energetic features were thoroughly studied through electrostatic interactions energies (E_es) and &nbsp;cohesive energies (E_coh). For two selected MeTSC/MeOH and acetone/MeOH systems an ab initio approach&nbsp;employing the coupled-cluster singles and doubles augmented by a perturbational correction for connected triple excitations (CCSD(T)) method were applied. Finaly, for MeTSC/MeOH system full geometry optimization was &nbsp;performed and for resulting equilibrium geometry the energy of the system (∆E_CCSD(T),CBS) was calculated.</p>