Disertacijoje nagrinėjami reguliuotų upelių natūralizacijos klausimai. Tyrimo objektas yra Pietryčių Lietuvos sausinimo reikmėms reguliuoti upeliai, esantys kalvoto reljefo regione. Savaiminė natūralizacija tirta tik lyguminiame reljefe. Kadangi natūralizacijos procesai vyksta skirtingai, nuspręsta įvertinti juos kalvotame Pietryčių Lietuvos regione. Reguliuotų upelių tyrimai svarbūs tuo, kad reguliuotų upelių natūralizacija, sumedėjusiai augalijai augant ant upelio vagos šlaitų, beveik nemažina jų hidraulinio laidumo, tačiau padeda atkurti natūralių tėkmių režimą ir tuo pačiu atstatyti pažeistas vandens ekosistemas. Pagrindinis tyrimų tikslas – nustatyti reguliuotų upelių savaiminio apaugimo sumedėjusia augalija dėsningumus ir įvertinti jos pasiskirstymo įtaką vagos hidrauliniam laidumui bei potvynių dinamikai. Darbe sprendžiami šie uždaviniai: sumedėjusios augalijos rūšinės sudėties, dažnio, tankio pasiskirstymo dėsningumai, sumedėjusios ir žolinės augalijos poveikis reguliuotų upelių hidrauliniam laidumui. Disertaciją sudaro įvadas, penki skyriai, bendrosios išvados, rekomendacijos. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, pateiktas darbo tikslas, uždaviniai, aprašomas mokslinis darbo naujumas, pristatomi mokslinių konferencijų pranešimai ir publikacijos. Pirmasis skyrius skirtas natūralių upelių reguliavimo tendencijoms analizuoti. Apibūdintas augalijos plitimas reguliuotuose upeliuose, jų įtaka hidrauliniam vagos laidumui. Antrajame skyriuje pateikta... [toliau žr. visą tekstą] / Issues of regulated streams naturalization were analyzed in the dissertation. Subject of the research was the streams regulated for drainage purposes in a hilly relief region of the Southeast Lithuania. Self-naturalization was researched only in plain relief. Since naturalization processes are running differently, it was decided to evaluate them in a hilly relief in the region of the Southern Lithuania. Researches of regulated streams are important due to the fact, that naturalization of regulated streams with growing woody vegetation on the slopes of a stream bed almost does not decrease its hydraulic conductivity but helps to restore regime of natural flows and restore damaged aqueous ecosystems at the same times. The main target of the research is to determine regularities of self-overgrowth of regulated streams with woody vegetation and assess influence of its distribution on bed’s hydraulic conductivity and flood dynamics. Following tasks are solved in the work: regularities of woody vegetation specie composition, frequency, density distribution, influence of woody and grass vegetation on regulated stream’s hydraulic conductivity. The dissertation is composed of introduction, five chapters, general conclusions, recommendations. Introduction describes relevance of the problem, aim of the work, tasks are introduced, scientific novelty of the work is described, presentations on scientific conferences and publications are introduced. Chapter one is dedicated for analysis of... [to full text]

Pagrindinis disertacijos tikslas – optinio ZnMgRE (RE = Y, Ho, Er) kvazikristalų atsako tyrimais atskleisti jų elektroninės posistemės ypatumus. Disertaciją sudaro eksperimentiniai rentgeno-difrakciniai (XRD) ir optiniai spektroskopiniai tyrimai, kvazikristalų elektroninės posistemės modelio konstravimas ir teorinis jų optinio atsako aprašymas. Atliktais eksperimentiniais XRD tyrimais buvo siekiama atskleisti kvazikristalų atvirkštinės gardelės vektorius, apibrėžiančius potencinį kvazikristalinį lauką, veikiantį į elektroninę posistemę. Optiniai spektroskopiniai tyrimai buvo atlikti kombinuotu spektroskopinės elipsometrijos ir atspindžio spektroskopijos metodu, paremtu darbe pasiūlyta inkaro lango duomenų analizės schema. Naudotas spektroskopinių tyrimų metodas įgalino atskleisti patikimus ZnMgRE optinio laidumo spektrus plačioje, 0.01 – 6 eV, spektrinėje srityje. Darbe išplėstas ZnMgRE elektronų posistemės modelis, kuris anksčiau buvo pasiūlytas kvazikristalų fotoemisinio atsako analizei. Nepriklausomų Fermi paviršiaus sankirtų su Bragg’ų plokštumomis schema formuluota išplėstiniame juostiniame atvaizdavime. Teorinė optinio laidumo skaičiavimų schema, anksčiau pasiūlyta kristalinių junginių optinio laidumo skaičiavimams, šiame darbe išplėsta įskaitant įvairias Fermi lygmens padėtis pseudotarpo atžvilgiu. Teoriniai ZnMgRE optinio laidumo skaičiavimai, atlikti darbe pasiūlyto elektroninės posistemės modelio rėmuose, detaliai atkartoja eksperimentinius optinio laidumo spektrus... [toliau žr. visą tekstą] / The main goal of the dissertation was to reveal the electronic structure of ZnMgRE (RE = Y, Ho, Er) quasicrystals by investigations of their optical response. The thesis comprises experimental X-ray diffraction (XRD) and optical spectroscopy studies of the quasicrystals, a construction of their electron subsystem model, and a theoretical description of their optical response. The XRD studies were carried out to determine the reciprocal quasicrystalline lattice vectors, which define the atomic potential field acting on an electron subsystem. The optical spectroscopy studies were carried out by the combined spectroscopic ellipsometry and reflectance spectroscopy technique, based on a suggested anchor-window method. High-accuracy ZnMgRE optical conductivity spectra were recorded in the wide, 0.01 – 6 eV, spectral range. The model of ZnMgRE electron energy spectrum, previously suggested for an interpretation of experimental ZnMgRE photoemission spectra, was developed. The nearly-free-electron gas model of independent intersections was formulated in the extended zone presentation. A scheme of the theoretical optical conductivity calculations was extended to account for various positions of the Fermi level with respect to a pseudogap. The experimental ZnMgRE optical conductivity spectra can be reproduced in detail by theoretical calculations performed within the framework of the suggested electron energy spectrum model. The set of the electron energy spectrum parameters determined... [to full text]

The main goal of the dissertation was to reveal the electronic structure of ZnMgRE (RE = Y, Ho, Er) quasicrystals by investigations of their optical response. The thesis comprises experimental X-ray diffraction (XRD) and optical spectroscopy studies of the quasicrystals, a construction of their electron subsystem model, and a theoretical description of their optical response. The XRD studies were carried out to determine the reciprocal quasicrystalline lattice vectors, which define the atomic potential field acting on an electron subsystem. The optical spectroscopy studies were carried out by the combined spectroscopic ellipsometry and reflectance spectroscopy technique, based on a suggested anchor-window method. High-accuracy ZnMgRE optical conductivity spectra were recorded in the wide, 0.01 – 6 eV, spectral range. The model of ZnMgRE electron energy spectrum, previously suggested for an interpretation of experimental ZnMgRE photoemission spectra, was developed. The nearly-free-electron gas model of independent intersections was formulated in the extended zone presentation. A scheme of the theoretical optical conductivity calculations was extended to account for various positions of the Fermi level with respect to a pseudogap. The experimental ZnMgRE optical conductivity spectra can be reproduced in detail by theoretical calculations performed within the framework of the suggested electron energy spectrum model. The set of the electron energy spectrum parameters determined... [to full text] / Pagrindinis disertacijos tikslas – optinio ZnMgRE (RE = Y, Ho, Er) kvazikristalų atsako tyrimais atskleisti jų elektroninės posistemės ypatumus. Disertaciją sudaro eksperimentiniai rentgeno-difrakciniai (XRD) ir optiniai spektroskopiniai tyrimai, kvazikristalų elektroninės posistemės modelio konstravimas ir teorinis jų optinio atsako aprašymas. Atliktais eksperimentiniais XRD tyrimais buvo siekiama atskleisti kvazikristalų atvirkštinės gardelės vektorius, apibrėžiančius potencinį kvazikristalinį lauką, veikiantį į elektroninę posistemę. Optiniai spektroskopiniai tyrimai buvo atlikti kombinuotu spektroskopinės elipsometrijos ir atspindžio spektroskopijos metodu, paremtu darbe pasiūlyta inkaro lango duomenų analizės schema. Naudotas spektroskopinių tyrimų metodas įgalino atskleisti patikimus ZnMgRE optinio laidumo spektrus plačioje, 0.01 – 6 eV, spektrinėje srityje. Darbe išplėstas ZnMgRE elektronų posistemės modelis, kuris anksčiau buvo pasiūlytas kvazikristalų fotoemisinio atsako analizei. Nepriklausomų Fermi paviršiaus sankirtų su Bragg’ų plokštumomis schema formuluota išplėstiniame juostiniame atvaizdavime. Teorinė optinio laidumo skaičiavimų schema, anksčiau pasiūlyta kristalinių junginių optinio laidumo skaičiavimams, šiame darbe išplėsta įskaitant įvairias Fermi lygmens padėtis pseudotarpo atžvilgiu. Teoriniai ZnMgRE optinio laidumo skaičiavimai, atlikti darbe pasiūlyto elektroninės posistemės modelio rėmuose, detaliai atkartoja eksperimentinius optinio laidumo spektrus... [toliau žr. visą tekstą]

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<p><font face="TimesNewRoman"> <p align="left">Research findings in current study provide a new insight into the fractured rock aquifers in the TMG area. Some of the results will have wide implications on the groundwater management and forms a solid basis the further study of the TMG aquifers.</p> </font></p>

Glass materials surround us, impacting our lives on a daily basis, whether geologically deposited by volcanic activity or synthesized in large volume by industry. These amorphous oxide materials are vastly important due to their variety of applications including solid electrolytes, cookware, and storage of high-level nuclear waste. Although they are used for different applications, one common characteristic of these materials is the absence of long-range periodic order. This makes it difficult to use traditional solid-state characterization methods such as x-ray and neutron diffraction to study glass structure. Nuclear magnetic resonance (NMR), is ideally suited to study materials that exhibit short-range non-periodic order as it probes directly at a nucleus of interest and is sensitive to its local structural environment. This ability of solid-state NMR is illustrated by revealing local structural features in various oxide materials presented in this thesis. Within is a compilation of studies looking at basic borates, followed by borovanadates and complex borosilicate glasses. A multinuclear application of using quantum chemical calculations, single and double resonance methods and charge-balance models are discussed to deconvolute the complex structures of these disordered materials. This is followed by a study of a difficult low-gamma nucleus, 73Ge, (once considered “impossible” for solid-state NMR) which is explored for future material studies by looking at 73Ge NMR of crystalline and glassy germanates. 73Ge chemical shifts were related to coordination environments and quadrupolar coupling constants were related to bond length distortions.

Bipolar electrochemistry deals with the exposure of an isolated conducting substrate that has no direct connection with a power supply except via an electric field. Therefore it can be considered as a "wireless technique". The polarization of the substrate with respect to the surrounding medium generates a potential difference between its opposite ends which can support localized electrochemical oxidation reduction reactions and break the surface symmetry of the substrate. The method was applied in the present thesis to materials science and biological systems. In the frame of designing asymmetric particles, also called "Janus" particles, bipolar electrochemistry was adapted for the bulk preparation of these objects. Conductive substrates with different nature, sizes and shapes have been modified with various materials such as metals, ionic and inorganic compounds using this approach. Moreover, a control over the deposit topology could be achieved for substrates at different length scales. Bipolar electrodeposition is also a good tool for investigating the generation of different metal morphologies. Further developments in the bipolar setup allowed us to use the technology for microstructuration of conductive objects. Furthermore the concept has shown to be very useful in the field of the induced motion of particles. The asymmetric objects that have been prepared by bipolar electrodeposition were employed as microswimmers which could show both translational and rotational motion. The application of electric fields in the bipolar setup can be used for the direct generation of motion of isotropic objects through bubble generation. A levitation motion of objects combined with light emission was possible using this concept. Finally, bipolar electrochemistry was also used for studying the intrinsic conductivity of biological molecules (DNA), which is of great importance in the nanotechnology.

The charge-density-wave (CDW) material orthorhombic tantalum trisulfide (TaS3) is a quasi-one dimensional material that forms long ribbon shaped crystals, and exhibits unique physical behavior. We have measured the dependence of the hysteretic voltage-induced torsional strain (VITS) in TaS3, which was first discovered by Pokrovskii et. al. in 2007, on temperature and applied torque. Our experimental results shows that the application of torque to the crystal could also change the VITS time constant, magnitude, and sign. This suggests that the VITS is a consequence of residual torsional strain originally present in the sample which twists the polarizations of the CDW when voltage is applied. This polarization twist then results in torque on the crystal. Another group of materials that may attract interest is that of small-molecule soluble organic semiconductors. Due to their assumed small phonon thermal conductivities and higher charge carrier mobilities, which will increase their seebeck coefficients with doping as compared to polymers, the small-molecule organic materials are promising for thermoelectric applications. In our experiments, we have measured the interlayer thermal conductivity of rubrene (C42H28), using ac-calorimetry. For rubrene, we find that the interlayer thermal conductivity, ≈ 0.7 mW/cm·K, is several times smaller than the (previously measured) in-plane value. Also, we have measured the interlayer and in-plane thermal conductivities of 6,13-bis((triisopropylsilyl)ethynyl) pentacene (TIPS-Pn). The in-plane value is comparable to that of organic metals with excellent π-orbital overlap. The interlayer (c-axis) thermal diffusivity is at least an order of magnitude larger than the in-plane, and this unusual anisotropy implies very strong dispersion of optical modes in the interlayer direction, presumably due to interactions between the silyl-containing side groups. Similar values for both in-plane and interlayer conductivities have been observed for several other functionalized pentacene semiconductors with related structures.

Solid oxide fuel cells are considered as one of the main alternatives for future sources of clean energy. To further improve their performance, theoretical methods able to describe the diffusion process in candidate electrolyte materials at finite temperatures are needed. The method of choice for simulating systems at finite temperature is molecular dynamics. However, if the forces are calculated directly from the Schrödinger equation (first-principles molecular dynamics) the computational expense is too high to allow long enough simulations to properly capture the diffusion process in most materials. This thesis introduces a method to deal with this problem using an external force field to speed up the diffusion process in the simulation. The method is applied to study the diffusion of oxygen ions in Sm-doped ceria, which has showed promise in its use as an electrolyte. Good agreement with experimental data is demonstrated, indicating high potential for future applications of the method.

Rapportens huvudsyfte är att ta fram en isoleringskombination av högpresterande material, som ska bidra till ett förbättrat U-värde och reducerad väggtjocklek. Konstruktionen är baserad på en befintlig sandwichvägg från Strängbetong, där författarna ersatt den ursprungliga isoleringen med det utvecklade isolerskiktet för att slutligen studera väggarna med lika villkor. Den framtagna väggens isolerings- förmåga presenteras genom handberäkningar, där det erhålls U-värde och temperaturfördelningar mellan elementens olika skikt vid stationära förhållanden. Det har även utförts värmesimuleringar för att analysera samma fysikaliska faktorer dock baserat på 3D förhållanden. I samarbete med företag har flera högpresterande isoleringsmaterial valts ut att ingå i väggkonstruktionen. Genom fördjupade studier av materialens fysikaliska egenskaper kunde en komplett isoleringskombination utvecklas och fick namnet InsuFlex. InsuFlex applicerades sedan i en sandwichkonstruktion för vidare analyser och värmesimuleringar. De nya väggresultaten visade mycket goda förbättringar av den ursprungliga sandwichväggen, tack vare det utvecklade skiktet av InsuFlex. Genom utförda beräkningar kunde författarna konstatera att isoleringsförmågan förbättrats med 46,5- samt 29 %, samtidigt som tjockleken reducerats med 5,5- samt 16,5 %, i jämförelse med Strängbetongs befintliga produkt. Den nya väggen erbjuder goda förutsättningar att reducera energiförlusterna och komma närmare framtida energikrav. Isoleringsmetoden förväntas även kunna appliceras i flera olika konstruktionselement. / The main objective of this report is development of an insulation-layer of high performance materials for a sandwich structure, which will contribute to an improved U-value and reduced wall thickness. The design is based on an existing sandwich wall, where the authors replaced the original insulation with the developed insulation-layer, to study the walls with equal conditions. The insulating ability is presented through calculations and thermal simulation to analyze the thermal aspects of the stationary conditions and 3D conditions. A complete insulation combination was developed through extensive studies of material’s physical properties, and named “InsuFlex”. The insulation-layer was then applied in a sandwich construction for further analysis and thermal simulations. The new design showed improvements in several areas.