The thesis is dedicated to carrier recombination investigations in wide-band-gap semiconductors and their structures. The complex experimental studies were performed by combining several different techniques. Carrier dynamics in GaN epilayers were investigated under extremely low and high excitation conditions. A new method for interpreting photoluminescence decay kinetics was suggested by interrelating luminescence and light-induced grating decay transients. The new approach for studies of yellow band in GaN was shown by linking the carrier lifetime with yellow band intensity. Two AlGaN epilayers grown by different novel growth techniques were compared and the factors limiting carrier lifetime were identified. Moreover, more evidence on alloy mixing and band potential fluctuations in AlGaN was provided by our study. Essential knowledge was attained about carrier dynamics in high-Al-content AlGaN/AlGaN multiple quantum well structures: the influence of built-in electric field and carrier localization on carrier dynamics. Most of the samples under study were grown by MEMOCVDTM growth technique, and our study confirmed the high potential of this innovative growth technique for improving material quality. / Disertacija skirta krūvininkų rekombinacijos tyrimams plačiatarpiuose nitridiniuose puslaidininkiuose bei jų dariniuose. Kompleksiniai eksperimentiniai tyrimai buvo atlikti naudojant kelias skirtingas metodikas. Atlikti krūvininkų dinamikos GaN sluoksniuose tyrimai labai žemų ir aukštų sužadinimų sąlygomis. Pasiūlytas naujas liuminescencijos gesimo kinetikų interpretavimo metodas, siejant liuminescencijos ir šviesa indukuotų dinaminių gardelių kinetikas. Naujas požiūris į geltonosios liuminescencijos juostą GaN sluoksniuose leido susieti geltonosios liuminescencijos intensyvumą su krūvininkų gyvavimo trukme. Skirtingomis technologijomis augintų AlGaN sluoksnių palyginimas suteikė informacijos apie juostos potencialo fliuktuacijas bei krūvininkų gyvavimo trukmę ribojančius veiksnius AlGaN medžiagose. Atskleista naujų krūvininkų dinamikos daugialakštėse AlGaN/AlGaN kvantinėse duobėse ypatumų – vidinio elektrinio lauko bei kvantinės duobės pločio fliuktuacijų sąlygotos lokalizacijos įtaka krūvininkų dinamikai. Dauguma tirtų bandinių buvo auginti naudojant MEMOCVDTM technologiją ir tyrimai patvirtino šios technologijos potencialą siekiant pagerinti medžiagų kokybę.

The thesis is aimed at gaining new knowledge on carrier localization and recombination in InGaN epilayers and structures by using photoluminescence spectroscopy with sub-micrometer spatial resolution. Optical characterization is combined with the structural analysis to provide a deeper insight into peculiarities of InGaN luminescence. Studies of InGaN epitaxial layers showed the relaxed layers to contain nanocolumn-like structures that additionally contribute to inhomogeneous photoluminescence distribution in InGaN layers. The feasibility of suppressing the defect-related emission in InGaN epilayers by laser annealing is demonstrated. The influence of unintentional annealing at elevated temperatures during fabrication of InGaN structures is revealed. A novel interpretation for negative correlation between photoluminescence intensity and band peak wavelength in high-indium-content InGaN multiple quantum wells is suggested. The enhancement of emission efficiency in InGaN quantum wells due to coupling of the optical dipole with localized surface plasmons in silver nanoparticles is investigated and the influence of potential fluctuations on the coupling with localized surface plasmons is revealed. / Disertacija yra skirta krūvininkų lokalizacijos ir rekombinacijos tyrimams InGaN epitaksiniuose sluoksniuose ir dariniuose panaudojant fotoliuminescencinę spektroskopiją su submikrometrine erdvine skyra. Optinius bandinių tyrimus papildo struktūrinė analizė. Darbe parodyta, jog relaksavusiuose InGaN sluoksniuose egzistuoja į nanokolonas panašūs dariniai, kurie papildomai prisideda prie netolygaus fotoliuminescencijos pasiskirstymo InGaN epitaksiniuose sluoksniuose. Pademonstruota galimybė nuslopinti priemaišinės kilmės liuminescenciją InGaN sluoksnyje jį iškaitinus lazerio spinduliuote. Atskleistas netyčinis InGaN darinių aktyviojo sluoksnio iškaitinimas, vykstantis formuojant p tipo sluoksnius, kuris keičia InGaN kvantinių darinių optines sąvybes. Išnagrinėta neigiama koreliacja tarp fotoliuminescencijos intensyvumo ir juostos viršūnės bangos ilgio InGaN kvantiniuose dariniuose ir pasiūlytas naujas šios ypatybės interpretavimo modelis. Lokaliai stebėtas liuminescencijos intensyvumo padidėjimas dėl sąveikos su lokalizuotais paviršiniais plazmonais, indukuotais sidabro nanodalelėse. Parodytas potencialo fliuktuacijų daromas poveikis rezonansinei sąveikai tarp optinių dipolių kvantinėse duobėse ir lokalizuotų paviršinių plazmonų.

Disertacija yra skirta krūvininkų lokalizacijos ir rekombinacijos tyrimams InGaN epitaksiniuose sluoksniuose ir dariniuose panaudojant fotoliuminescencinę spektroskopiją su submikrometrine erdvine skyra. Optinius bandinių tyrimus papildo struktūrinė analizė. Darbe parodyta, jog relaksavusiuose InGaN sluoksniuose egzistuoja į nanokolonas panašūs dariniai, kurie papildomai prisideda prie netolygaus fotoliuminescencijos pasiskirstymo InGaN epitaksiniuose sluoksniuose. Pademonstruota galimybė nuslopinti priemaišinės kilmės liuminescenciją InGaN sluoksnyje jį iškaitinus lazerio spinduliuote. Atskleistas netyčinis InGaN darinių aktyviojo sluoksnio iškaitinimas, vykstantis formuojant p tipo sluoksnius, kuris keičia InGaN kvantinių darinių optines sąvybes. Išnagrinėta neigiama koreliacja tarp fotoliuminescencijos intensyvumo ir juostos viršūnės bangos ilgio InGaN kvantiniuose dariniuose ir pasiūlytas naujas šios ypatybės interpretavimo modelis. Lokaliai stebėtas liuminescencijos intensyvumo padidėjimas dėl sąveikos su lokalizuotais paviršiniais plazmonais, indukuotais sidabro nanodalelėse. Parodytas potencialo fliuktuacijų daromas poveikis rezonansinei sąveikai tarp optinių dipolių kvantinėse duobėse ir lokalizuotų paviršinių plazmonų. / The thesis is aimed at gaining new knowledge on carrier localization and recombination in InGaN epilayers and structures by using photoluminescence spectroscopy with sub-micrometer spatial resolution. Optical characterization is combined with the structural analysis to provide a deeper insight into peculiarities of InGaN luminescence. Studies of InGaN epitaxial layers showed the relaxed layers to contain nanocolumn-like structures that additionally contribute to inhomogeneous photoluminescence distribution in InGaN layers. The feasibility of suppressing the defect-related emission in InGaN epilayers by laser annealing is demonstrated. The influence of unintentional annealing at elevated temperatures during fabrication of InGaN structures is revealed. A novel interpretation for negative correlation between photoluminescence intensity and band peak wavelength in high-indium-content InGaN multiple quantum wells is suggested. The enhancement of emission efficiency in InGaN quantum wells due to coupling of the optical dipole with localized surface plasmons in silver nanoparticles is investigated and the influence of potential fluctuations on the coupling with localized surface plasmons is revealed.

Oil companies need to evaluate the risk of annular fluid or gas migration if cement fails during the life of the well. Sustained casing pressure can lead to shutting in the wells to avoid health, safety, and environment (HSE) risks and government fines. To understand the long-term integrity of cement in high temperature and high pressure (HTHP) conditions and the mechanical properties that affect the ability of cements to seal fluids, this project used finite-element models (FEMs) to study the stress-causing phenomena. FEM analyses in ABAQUS version 6.11 were used to determine the potential of cement failure in oil wells. The model uses a 3D section of a well that can be used for different casing and formation types under different loading conditions. The model built in ABAQUS version 6.11 allows incorporating materials with nonlinear mechanical properties; it also uses FEM analysis to forecast fractures inside the cement under different loading scenarios like hydraulic fracture jobs or casing tests. The finite-element model included cases for cement cracking, cement debonding, and plastic deformation of the cement and rock that can generate loss of zonal isolation. Linear manner: set cements behave elastically until a failure criterion is reached, and then they can behave plastically. The FEM approach can reproduce stresses, strains, and volume changes in the material under different environmental HTHP conditions. Cemented wells have both tensile and compressive stresses that make some parts of the cement sheath experience fracture initiation, plastic deformation, or debonding. This dissertation provides a model that will help drillers design the set cement for long-term integrity in HPHT well conditions. The FEM predicts if the cement sheath can develop debonding, cracks or plastic deformations during the life of the well. The cement sheath needs to be designed for long-term zonal isolation to avoid interzonal communications, remedial costs and environmental problems related to cement seal. A CMS™-300 Automated Permeameter, a mechanical properties analyzer, HPHT cement consistometer, annular expansion molds, and tri-axial test equipment were used in this study to test cements for specific applications in three Colombian oil fields, including an oil field with in-situ combustion project.

<p>The Orange Basin was formed during the late Jurassic to early Cretaceous periods due to Gondwana breakup and rifting and later drifting apart of the African and South American plates. The basin consists of siliciclastic sandstone which took its sediment supply from river system with a rivalling delta to the north of the basin. Geological and petrophysical studies were carried out to evaluate the reservoir potential of the wells in the study area. This study considered five wells (A-G1, A-W1, A-K1, A-K2 and A-Y1) in the Orange Basin with attention to the Albian age sandstone. Only three of the studied wells (A-G1, A-W1 and A-K1) have core samples for analysis. The methods used for the execution of this study include the description and calibration of spot cores with conventional standard logging record responses, wireline log interpretation using sequence stratigraphy approach, detailed petrographic (SEM, HR-TEM, XRD and thin section) and geochemical (pore water geochemistry, FTIR and XRF) analyses, and petrophysical analysis to unravel the complexities with regard to facies association, depositional environment and diagenesis. Linking diagenesis to depositional facies and sequence stratigraphy has given a clearer picture to the spatial and temporal distribution of diagenetic alterations and thus of evolution of reservoir quality in the studied wells. Three depositional lithofacies were identified based on a detailed core description [fine grained sandstone (F1), very fine grained sandstone (F2) and mudstone (F3)]. Fluvio-deltaic and shallow marine environments were also interpreted from the core description based on the sedimentary structures and mineral assemblage while the log interpretation shows that the different reservoir units range between LST, TST and HST but mostly of LST. Mineralogical predictions were made possible in the wells without core samples (A-K2 and A-Y1) through the use of density-neutron cross plot, these reveal that the two wells contain some considerable amount of clay minerals like kaolinite, chlorite and illite.</p>

Darbo tikslas – įvertinti šachtinių šulinių geriamojo vandens kokybę ir jo gerinimo galimybes Pakruojo rajone. Uždaviniai: 1. Įvertinti šachtinių šulinių geriamojo vandens kokybės rodiklius. 2. Nustatyti nėščių moterų ir moterų, kurios augina kūdikius iki 6 mėn. amžiaus, požiūrį į naudojamo vandens kokybę ir tyrimo rodiklius. 3. Įvertinti šachtinių šulinių geriamojo vandens kokybės gerinimo galimybes. Tyrimo metodika. Anketinė nėščių moterų ir kūdikius iki 6 mėn. amžiaus auginančių moterų (n=167, atsako dažnis 100 proc.) apklausa. Šachtinių šulinių geriamojo vandens kokybės rodiklių tyrimo protokolų analizė (n = 270) ir visuomenės sveikatos centro ir biuro specialistų, rajono ekologo (n=3, atsako dažnis 100 proc.) interviu. Apklausos duomenys analizuoti „SPSS 15.0 for Windows“ programa. Hipotezės tikrintos, taikant χ² testą, nustatčius reikšmingumo lygį p<0,05. Rezultatai. Tyrimo metu buvo nustatyta, kad respondentės, naudojančios užterštų šachtinių šulinių vandenį, dažniausiai gyvena kaimo vietovėse, turi mažas metines pajamas, yra bedarbės. 95,8 % respondenčių gavo informaciją apie šachtinių šulinių vandens kokybę ir patarimus, kaip apsaugoti save ir kūdikius. Moterys, turinčios žemesnį išsilavinimą, informavus apie vandens tyrimo rezultatus bei riziką sveikatai, vartoja užterštą geriamąjį vandenį nitratais ir nesiima jokių veiksmų jo kokybei gerinti. Netinkamai tvarkoma šulinio aplinka, kuri gali sąlygoti užteršimą: apie šulinį auginami augalai, kurie yra tręšiami... [toliau žr. visą tekstą] / The Aim of the study. To asses the quality of the possibilities of improving of water quality. Objectives : 1. Estimate the quality of drinking water. 2. Evaluate the attitude of pregnant women and the women growing up babies sunder the age of six (6) months to the wells water quality indicators. 3. Estimate the opportunities for improvements of quality of drinking water. Research methods. Questionnaire of pregnant women and the women raising infants under six months (n=167), response rate -100 percent. The analysis of the wells for drinking water quality indicators (n=270) was done by the public health center. Interview of the public health professionals of the region: (n=3, response rate 100 percent). Survey data, was analyzed at “SPSS15.0 for Windows” program. The Hypothesis is verified by using the test χ2 , significance level p<0,05. Results. 95.8 % of respondents have received enough information concerning the quality of the water in their wells. The women with lower education were informed about the test results of their water, about health risks using the water, but they still are using contaminated by nitrates drinking water and don’t take any actions to improve it’s quality. Improperly maintenance of wells and their environment may lead to contamination of drinking water: the plants growing near the wells are fertilized with organic fertilizers, sewage is loaded on the ground. The pregnant women with higher education show better knowledge for improvement of water... [to full text]

In his writing on the nature and purpose of the novel between 1895 and 1911, Wells endorses artistic principles for their social effects. His public lecture on “The Contemporary Novel,” written in 1911 in response to a debate with Henry James, is the most lucid articulation of his artistic principles, and his later autobiographical reflections on the debate obscure the clarity of the earlier version. Wells’s artistic principles emerge in his reviews of contemporary fiction for the Saturday Review (1895–1897), where he extends Poe’s concept of “unity of effect” to the novel and justifies his preference for social realism with a theory of cultural evolution. His views develop further in the context of sociological and philosophical debates between 1901 and 1905. Wells commenced the century with a sceptical view on the social effects of literature, but his exposure to British Pragmatism encouraged him to revive the principles developed in his reviewing. The view on Wells’s conception of the novel presented in this thesis challenges the prevailing view that he began his career with a set of purely artistic principles, adding sociological and intellectual apparatus after the turn of the century.

Aquifer storage and recovery (ASR) is a particular scheme of artificial recharge of groundwater by injecting fresh water into aquifers and subsequently recovering the stored water during times of peak demand or extended drought. In the era of combating climate change, ASR, as an effective means for water reuse and sustainable management of water resources in concert with the natural environment, represents a huge opportunity for climate change adaptation to mitigate water availability stress.The success of an ASR scheme is quantified by the recovery efficiency (RE), defined as the volume of stored water that can be recovered for supply purposes divided by the total volume injected. It is not uncommon that RE may be significantly lower than 100% because of the water quality changes as a consequence of the mixing between the injected water and native groundwater and the interaction between injected water and soil. Thus, the key of a successful ASR scheme is (1) to select appropriate aquifers and (2) to design optimal operational processes to build up a bubble of injected water with minimized negative impact from such mixing and interaction. To achieve this, this thesis develops an integrated knowledge base with sound interdisciplinary science and understanding of the mixing processes under operational ASR management in aquifers with various hydrogeological conditions. Analytical and numerical modeling are conducted to improve the scientific understanding of mixing processes involved in ASR schemes and to provide specific technical guidance for improving ASR efficiency under complex hydrogeological conditions. (1) An efficient approach is developed to analytically evaluate solute transport in a horizontal radial flow field with a multistep pumping and examine the ASR performance in homogeneous, isotropic aquifer with advective and dispersive transport processes. (2) Numerical and analytical studies are conducted to investigate the efficiency of an ASR system in dual-domain aquifers with mass transfer limitations under various hydrogeological and operational conditions. Simple and effective relationships between transport parameters and ASR operational parameters are derived to quantify the effectiveness and ascertain the potential of ASR systems with mass transfer limitations.(3) Effects of hydrogeological and operational parameters on ASR efficiency are assessed in homogeneous/stratified, isotropic/anisotropic coastal aquifers. Effects of transverse dispersion are particularly investigated in such aquifers.(4) Finally, we test and study an innovative ASR scheme for improving the RE in brackish aquifers: injection through a fully-penetrated well and recovery through a partially-penetrated well.

Darbo objektas: Marijampolės miesto geriamasis vanduo. Darbo tikslas: įvertinti Marijampolės miesto geriamojo vandens kokybę 2005-2013 metais. Darbo metodai: Tyrimai vykdyti UAB „Sūduvos vandenys“ 2005–2013 metais Marijampolės mieste. Eksperimento metu skirtingais metais tirta dviejų vandenviečių cheminė vandens kokybė. Indikatoriniams ir cheminiams geriamojo vandens kokybės tyrimams Marijampolės vandenvietėse vanduo imamas iš gręžinių. Požeminio vandens mėginiai jo cheminės būklės/kokybės vertinimui imami tiesiogiai iš eksploatacinių gręžinių ir vandens mišinio vieną – du kartus per metus, pavasarį ir rudenį. Požeminio vandens mėginiai imami vadovaujantis nustatyta tvarka (LST ISO 5667-11:2009 „Vandens kokybė. Bandinių ėmimas. 11-oji dalis. Nurodymai, kaip imti gruntinio vandens bandinius“; LST EN ISO 5667-3:2006 „Vandens kokybė. Mėginių ėmimas. 3-oji dalis. Nurodymai, kaip konservuoti ir gabenti mėginius“). Darbo rezultatai: Įvertinus Marijampolės miesto eksploatacinių gręžinių geriamojo vandens kokybę nustayta, kad I-ojoje vandenvietėje amonio jonų ir bendrosios geležies koncentracijos yra didesnės nei II-osios vandenvietės vandens mišinyje iš visų artezinių gręžinių ir viršija nustatytas ribines vertes. Marijampolės miesto I-osios vandenvietės vandenyje 2005-2013 metais prieš nugeležinimą didėjo bendrosios geležies koncentracija, mažėjo permanganato indekso vertė. Po nugeležinimo didėjo chloridų, nitratų koncentracijos, mažėjo permanganato indekso vertė. II-osios... [toliau žr. visą tekstą] / The object: of the two Marijampoles watering places city drinking water. To identify: Marijampoles urban drinking water quality dynamics. Working methods: The study was carried UAB „Sūduvos waters“ in 2005-2013 Marijampoles city. During the experiment, two different years studied waterworks chemical quality of the water. The indicator and chemical quality of drinking water research Marijampoles waterworks water taken from wells. Groundwater samples of the chemical status/quality assessment are taken directly from wells and water one - two times a year, in spring and autumn. Groundwater samples shall be taken in accordance with established procedures (ISO 5667-11:2009 Water quality. Sampling. 11th part. Guidance on sampling of groundwater samples "BS EN ISO 5667-3:2006 Water quality. Sampling. 3rd part. Guidance on the preservation and handling of samples). The results: Assessment Marijampoles city wells for drinking water quality Preset that I th wellfield ammonium ion and total iron concentration is higher than in the II-nd watering of water from the artesian well and exceeds the threshold value. Marijampoles town I th watering water year 2005-2013 against the removal of iron increased total iron concentration decreased permanganate index value. After the removal of iron increased chloride, nitrate concentrations decreased permanganate index value. II th watering water before removal of iron decreased the pH value. After the removal of iron increased chloride, nitrate... [to full text]

H. G Wells’s novel The Time Machine is a significant work of science fiction that dramatizes the themes of degeneration and social inequality, themes that were very relevant during the Victorian era in relation to the discovery of evolution. Degeneration was seen as the degradation of society into primitiveness far from the Victorian standards, and the problem of social difference, where the gap between poor and rich was very wide, became the visible proof of the difference between the evolved and civilized and the degenerated and primitive. The purpose of this essay is to analyse how the frame narrative, the story surrounding the main adventure, affects the theme of degeneration in the novel. The framework reveals the reactions of the people present at the dinner parties, where the Time Traveller recounts his journey into a degenerated future. The guests are all representing different factions of Victorian society, such as the Provincial Mayor, the Very Young Man and the Editor who all have their own motives and agendas in relation to degeneration, social differences and time travel. By examining the guests’ individual motives, the essay argues that they do not want to believe in time travel since it would include believing in a degenerated future where all the glory of their present-day Victorian era would crumble into chaos and pandemonium. This essay shows that by denying the relevance of the Time Traveller’s story, despite the evidence presented, the dinner guests are condemning themselves to the degenerated future they are afraid of, hence making the novel a warning example of not accepting new ideas.