Ancient DNA analysis of archaeological wheat remains may serve to clarify unknown or controversial points in the history of wheat. In the first part of this study, extraction and amplification of DNA from Anatolian charred ancient wheat seeds obtained from different locations and ages was attempted. None of the our extraction samples yielded any PCR amplification. The possible reasons for this result were investigated by constructing an artificial charring experiment. The results suggest that the chances of obtaining DNA from the charred archaeological samples used in this study by the methods used are very low. Moreover, strong PCR inhibition by these charred seed extracts was observed. The second part of the study aimed to develop new DNA based markers for ancient wheat DNA analysis. Markers linked to the brittle rachis character exhibiting domestication status were sought, but no result was obtained. Primers targeting plasmon sequences were developed and tested. A primer pair amplifying a 400 bp portion of the chloroplast TrnLTrnF intergenic region was focused upon. A short piece of this region was amplified using ancient wheat DNA extracted in another study. This short piece appeared non-polymorphicupon sequencing. The sequence spanning a wider portion of this region contained a number of length polymorphisms. Phylogenetic reconstruction using maximum parsimony showed that these polymorphisms were able to distinguish wheat taxa at the maternal ancestor level.

Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.

Impact of rain drops at relatively high velocities, which is known as rain erosion, causes severe damages on various materials. Every material can withstand the rain erosion up to a specific impact velocity. However, this damage is critical for optical windows which are very important components for Electro-Optical (EO) systems such as thermal camera. Even a small scratch may affect the transmission capability of the optical window adversely and leads to some functional problems in the device due to insufficient transmitted data. Since it has a vital effect on the EO systems, the rain erosion is needed to be investigated on the special optical windows, particularly for determining the velocity that a damage initiates. In this study, the rain erosion is investigated on germanium which is a kind of optical window, by means of numerical simulations in LS-DYNA. Damage Threshold Velocity (DTV) is examined for two different water shapes (which are spherical water drop and water jet) within a velocity range between 100 and 250 m/s. Both single and multiple impact cases are considered for both water shapes up to ten consecutive collisions. By using the results, the &ldquo / DTV versus number of impact curves&rdquo / are obtained in order to understand the amount of damage with respect to both single and multiple impacts. Results are compared with both literature and the experimental data within the scope of DTV and shape of the damage. In the numerical simulations, ALE (Arbitrary Lagrangian Eulerian) method is used for modelling water. &ldquo / JOHNSON-HOLMQUIST-CERAMICS (JH-2)&rdquo / which is recommended for both ceramics and glass applications is used as the material model for Germanium. JH-2 is a complete material model which contains damage effects, failure criteria, and Equation of State (EOS) all together. Among the material models available in the library of LS-DYNA, &ldquo / MAT-NULL + EOS-GRUNEISEN&rdquo / is used for water.

Fracture of polymer-metal interfaces is one of the main failure modes occurring in micro-electronic components. This phenomenon is particularly true when considering the delamination of several layers of an interconnect structure. In order to predict the failure nucleation and the crack propagation into the composite material, the finite element analysis is one of the key procedures. Even though simple linear models have been considered for years, we are now facing the necessity of using more complex models including non-linearity which can occur, in this case, with the presence of high local stresses near the crack front. However, the computational time can sometimes be incredibly long. Moreover, the fact that the considered materials are quasi-brittle brings some numerical difficulties such as sharp snap-back and snap-through. The actual challenge resides in obtaining a reliable result in a reasonable time of calculation. The present work considers the implementation of a new non-linear finite element solver, developed for the MSc. Marc/Mentat package software. It is based on a general arc-length constraint which considers the energy released during the propagation of the crack. This offers the advantage of being directly linked to the failure process, and no previous knowledge of the failure behavior is required. The models considered in this work represent the simulation of crack propagations in multilayer electronic systems, such as SIP devices, and are based on a cohesive zone approach. In order to clearly understand the issues of this problem, this work includes a brief description of the fracture mechanics and reviews the existing nonlinear finite element solvers. After explaining the principle of the energy release solver and the different issues due to its implementation, its efficiency is compared to pre-implemented solvers, such as the Crisfield method. The results show a significant improved robustness of the new energy released method compared to the previous arc-length methods.

Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.

To date, efforts to model fracture and crack propagation have focused on two broad approaches: discrete and continuum damage descriptions. The discrete approach incorporates a discontinuity into the displacement field that must be tracked and updated. Examples of this approach include XFEM, element deletion, and cohesive zone models. The continuum damage, or smeared crack, approach incorporates a damage parameter into the model that controls the strength of the material. An advantage of this approach is that it does not require interface tracking since the damage parameter varies continuously over the domain. An alternative approach is to use a phase-field to describe crack propagation. In the phase-field approach to modeling fracture the problem is reformulated in terms of a coupled system of partial differential equations. A continuous scalar-valued phase-field is introduced into the model to indicate whether the material is in the unfractured or fractured ''phase''. The evolution of the phase-field is governed by a partial differential equation that includes a driving force that is a function of the strain energy of the body in question. This leads to a coupling between the momentum equation and the phase-field equation. The phase-field model also includes a length scale parameter that controls the width of the smooth approximation to the discrete crack. This allows discrete cracks to be modeled down to any desired length scale. Thus, this approach incorporates the strengths of both the discrete and continuum damage models, i.e., accurate modeling of individual cracks with no interface tracking. The research presented in this dissertation focuses on developing phase-field models for dynamic fracture. A general formulation in terms of the usual balance laws supplemented by a microforce balance law governing the evolution of the phase-field is derived. From this formulation, small-strain brittle and large-deformation ductile models are then derived. Additionally, a fourth-order theory for the phase-field approximation of the crack path is postulated. Convergence and approximation results are obtained for the proposed theories. In this work, isogeometric analysis, and particularly T-splines, plays an important role by providing a smooth basis that allows local refinement. Several numerical simulations have been performed to evaluate the proposed theories. These results show that phase-field models are a powerful tool for predicting fracture. / text

Recently, the portfolio of compounds approved for inhalation therapy has expanded rapidly for lung disease therapies. The rationale for this delivery approach includes a more targeted and localized delivery to the diseased site with reduced systemic exposure, potentially leading to decreased adverse side effects. We have proposed that brittle matrix powders prepared by thin film freezing (TFF) are a suitable platform for pulmonary drug delivery which can achieve high lung concentrations while limit the corresponding systemic levels associated with toxicity, and enhanced physicochemical and aerodynamic properties can be obtained by varying TFF processing parameters. In Chapter 2, the in vitro and in vivo performance of an amorphous formulation prepared by TFF and a crystalline micronized formulation produced by milling was compared for Tacrolimus (TAC). TFF processed matrix powders was capable of achieving deep lung delivery due to its low density, highly porous and brittle characteristics. When emitted from a Miat® monodose inhaler, TFF processed TAC formulations exhibited a fine particle fraction (FPF) of 83.3% and a mass median aerodynamic diameter (MMAD) of 2.26 µm. Single dose 24-h pharmacokinetic studies in rats demonstrated that the TAC formulation prepared by TFF exhibited higher pulmonary bioavailability with a prolonged retention time in the lung, possibly due to decreased clearance (e.g., macrophage phagocytosis), compared to the micronized TAC formulation. Additionally, TFF formulation generated a lower systemic TAC concentration with smaller variability than the micronized formulation following inhalation, potentially leading to reduced side effects related to the drug in systemic circulation. Chapter 3 investigated the impact of processing parameters in the TFF process on the physicochemical and aerodynamic properties of the resulting formulations. All of these enhanced powder properties resulted from higher freezing rate contributed to a better aerodynamic performance of the obtaining formulations. Moreover, a decreasing trend of FPF was observed for these TFF powders when the initial solid concentrations increased. The variation of the freezing rate and initial solid loading in the TFF process enabled the production of formulations with enhanced physicochemical properties and improved aerodynamic performance. / text

The quest to answer fundamental questions and solve complex problems is a principal tenet of Earth science. The pursuit of scientific knowledge has generated profuse research, resulting in a plethora of information-rich resources. This phenomenon offers great potential for scientific discovery. However, a deficiency in information connectivity and processing standards has become evident. This deficiency has resulted in a demand for tools to facilitate and process this upsurge in information. This ontology project is an answer to the demand for information processing tools. The primary purpose of this domain-specific ontology and knowledge base is to organize, connect, and correlate research data related to brittle deformation microstructures. This semantically enabled ontology may be queried to return not only asserted information, but inferred knowledge that may not be evident. In addition, its standardized development in OWL-DL (Web Ontology Language-Description Logic) allows the potential for sharing and reuse among other geologic science communities.

The objective of the research presented in this thesis is to validate the parallel-bonded modeling method in the context of coupled thermo-mechanical simulations. The simulation results were compared with analytical and experimental data, in the attempt to assess the usability of this particular modeling method. Previous studies of numerical approaches that related to the thermal fracturing of hard rock had used continuum-based models with constitutive relations. The simulations in the thesis were conducted using Particle Flow Code (PFC) which was chosen for the research because of its several benefits. The code has unique features such as spontaneous damage development without imposed conditions, and emergent properties such as material heterogeneity, and dynamic behavior giving possibility to monitor synthetic seismic events. The basic code has been available since 1995 and research using the code has produced hundreds of publications. The thermal option for the code is a recent addition and lacked verification, validation and applications. The thesis is the answer for that. In the course of the research work new particle clustering and grouping routines were developed and tested. Three modeling studies were conducted varying from laboratory to field scales. The 2D modeling study of the heated cylinder experiment yielded similar results both in fracture-behavioral and acoustic emission (AE) magnitude ranges when compared with the laboratory data. The 3D cubic numerical specimens, created with breakable particle clusters, were heated, and the induced damage was observed by P wave velocity measurements. The results showed trends comparable to the laboratory data: P wave velocity decreases with rising temperatures of up to 250°C and cluster-boundary cracking occurs, comparable to grain-boundary cracking in the heated rock samples. The large 2D tunnel models captured the phenomena observed in-situ displaying the difference in the damage to the roof and floor regions, respectively. This damage was due to the filling material confinement of about 100 kPa on the tunnel floor. In general, the results of the thermo-mechanical simulations were in accordance with the experimental data. The modeled temperature evolutions during the heating and cooling periods were also in accordance with the experimental and analytical data.

Research area and topicality of the work. Mechanical properties and their evolution under loading are the most significant factors for the development of various mechanical structures, technologies and equipment. It seems to be natu-ral that deeper understanding of the behaviour of existing and design of new materials presents a challenge in different research areas. It should be noted, that all the materials are heterogeneous in meso- and micro- scales. They exhibit essential differences, compared to the macroscopic continuum behaviour. Basically, both experimental and numerical simulation methods are extensively applied for investigation purposes. Experimental techniques, capable of giving a realistic view of the inside of the material and extracting the real data, are very expensive. Therefore, the nu-merical simulation tools are extensively used as an alternative for investigation purposes. They have considerable advantages allowing the reproduction of multiple experiments and providing comprehensive data about ongoing phe-nomena. Recently, numerical technologies have become highly multidisciplinary subjects. They comprise phenomenological and statistical ideas, while mathe-matical models employ the relations of continuum mechanics, classical discre-tization methods and molecular dynamics. The Discrete Element Method (DEM) is one of new methods. It is aimed at simulating the dynamic behaviour of the contacting particles. Variable topology of the system of particles is an... [to full text] / Tyrimų sritis ir darbo aktualumas. Kuriant modernias ��vairios paskirties mechanines sistemas, technologijas ir įrangą, svarbiomis tampa jas sudarančios medžiagos. Savaime suprantama, kad žinomos ir naujai kuriamos medžiagos dabar kur kas išsamiau nagrinėjamos daugelyje mokslo šakų, įskaitant ir me-džiagų mechaniką. Visos medžiagos mezo- ir mikrostruktūros požiūriu yra ne-vienalytės. Jų mikroskopinės savybės skirtingos, lyginant su įprastu kontinuu-mu. Medžiagų savybėms tirti dažniausiai taikomi eksperimentiniai metodai. Eksperimentiniais metodais ištirti medžiagos struktūras ir jose vykstančius procesus ir įvertinti tam tikras jų savybes labai brangu. Tai viena priežasčių, kodėl skaitinis modeliavimas tampa realia tyrimų alternatyva. Skaitinį eksperi-mentą galima kartoti daug kartų, valdant bandinio parametrus, išlaikant tas pa-čias sąlygas, ir stebėti reiškiniui būdingus rodiklius visame tūryje. Šiuolaikiniai modeliavimo metodai yra kompleksiniai. Jie jungia fenome-nologines ir statistines idėjas, o matematiniai modeliai sudaromi taikant konti-nuumo mechanikos ir jų diskrečiųjų modelių bei molekulinės dinamikos pri-klausomybes. Diskrečiųjų elementų metodas (DEM) taip pat priskiriamas šiuo-laikinių metodų kategorijai. Jis skirtas kontaktuojančių dalelių sistemų dinami-niam modeliavimui. Kintanti dalelių sistemos topologija – būdingas metodo požymis. Pastaruoju metu DEM jau taikomas kontinuumui modeliuoti ir praktikoje aktualiems irimo uždaviniams spręsti. Reikia pastebėti... [toliau žr. visą tekstą]