Spray cooling is a high heat removal technique which has been used widely in many industries, especially metallurgical, where the control of the temperatures of metals is an important factor to obtain the desired microstructure; and also in microelectronics where is very important to obtain high heat fluxes at relatively low surface temperatures. In this study, an open loop spray cooling system has been fabricated to provide an upward-facing spray over a 12 mm diameter test surface. A full cone spray nozzle was used to deliver deionized water to the test surface at five pressures (10, 15, 20, 25 and 30 psi), and at three different distances to the test surface (3, 7 and 12 mm). The volumetric flow rate at the surface used in the experiments depended on both the pressures and the distances. For a distance of 3 mm and 7 mm, the volumetric flow rate range from 336.6 to 627 ml/min while for 12 mm, the range was from 336.6 to 484.28 ml/min. Heat fluxes of 1.92 to 451 W/cm2, 2.1 to 417.3 W/cm2 and 1.9 to 409.5 W/cm2 for distances of 3, 7 and 12 mm respectively were registered at different input power levels. For all the three distances, the volumetric flow rate affects the heat flux, especially for 3 mm; and this effect decreases for higher distances. However, the distance between the nozzle and the test surface has little effect on the heat flux at low pressures but at higher pressures, the difference in heat flux is mainly due to the fact that part of the spray does not impinge the test surface.

This report discusses the use of micro-fabrication techniques for creating experimental test sections containing trees of micro-finned conducting pathways, also referred to as constructal trees, for cooling a heat generating substrate. These trees are made of copper and contain branches that bifurcate at 90° angles to form constructal patterns. The patterns for the finalized test sections were created using photolithography techniques, and copper was deposited via thermal evaporation onto a 1 cm² substrate to create the trees. Certain test section design parameters were varied including the geometric complexity of the constructal trees, the volume of copper used between tree complexities, choice of material for the substrate, and the height, or thickness, of the trees. Also described in this report is an experimental methodology and testing apparatus designed to assess the cooling performance of the test sections. This methodology includes using controlled uniform heating applied to the bottom of each test section, while cooled nitrogen is impinged on the tip of the constructal tree to create a heat sink. / text

En la presente tesis doctoral se ha realizado un estudio computacional de las propiedades electrónicas de sistemas basados en cadenas metálicas monodimensionales de la familia de los llamados nanowires, concretamente su magnetismo y conductividad. Estas cadenas lineales se sustentan gracias a los ligandos orgánicos que se organizan a su alrededor, cuyo número de sitios de unión determina la nuclearidad de la cadena. Para estas moléculas, llamadas cadenas metálicas extendidas, se han calculado los parámetros de acoplamiento magnético con el método CASPT2. El uso del Hamiltoniano de Heisenberg estándar para los sistemas M3(dpa)4Cl2 cuando hay dos electrones no desapareados en cada centro, ha sido examinado mediante el cálculo del valor de λ mediante cálculos DFT. Las diferentes conductividades eléctricas observadas en las cadenas MMX [Ni2(dta)4I]∞ y [Pt2(dta)4I]∞ (dta = CH3CS2) y sus estados de ordenación de carga han sido analizados con parámetros de estructura electrónica extraídos a partir de cálculos DFT periódicos y de correlación combinados con la teoría del Hamiltoniano efectivo. / In the present thesis, magnetic and conducting properties of systems, one-dimensional chains of the family of so-called nanowires, have been studied computationally. These linear chains are supported by organic ligands surrounding the metal backbone where the number of binding sites determines the nuclearity of the chain. For these molecules, also called extended metal atom chains, magnetic coupling parameters have been calculated with the CASPT2 method. The use of standard Heisenberg Hamiltonian for systems M3(dpa)4Cl2 when two unpaired electrons are localized on each magnetic center has been examined by calculating the value of λ from DFT calculations. The different electrical conductivities observed in MMX chains [Ni2(dta)4I]∞ and [Pt2(dta)4I]∞ (dta = CH3CS2) and the charge ordering state have been analyzed with DFT periodic calculations and also through the comparison of extracted electronic structure parameters from ab initio calculations combined with the effective Hamiltonian theory.

Les solides ioniques sont des composés dont la structure cristalline est généralement bien connue. La répétition d'un motif simple parallèlement à un groupe de trois vecteurs de translation suffit à la construction du réseau. Pourtant, il a fallu considérablement sophistiquer ce modèle pour calculer avec succès l'énergie de cohésion de simples cristaux cubiques faces centrées, comme le réseau de chlorure de sodium. Bien qu'apparemment moins compliqués, les cristaux de structure de type du chlorure de césium ont été, en revanche beaucoup moins étudiés. Il s'en suit une certaine méconnaissance du potentiel intercristallin de ces cristaux ce qui interdit corrélativement une bonne compréhension des phénomènes inhérents à la structure cristalline. N'ayant trouvé aucune théorie satisfaisante permettant d'atteindre le potentiel d'un solide ionique de structure cubique simple, nous présentons dans la première partie de nos travaux une étude sur la détermination des énergies potentielles des réseaux cubiques simples.

Per paskutinį dešimtmetį anglies nanostuktūros – amorfinės anglies plėvelės, fulerenai, o ypač nanovamzdeliai patraukė daugelio tyrėjų dėmesį. Šios struktūros yra daug žadančios puslaidininkių pramonėje, dėl galimybių prietaisų miniatiūrizavimui. Šiuo metu nanotechnologija patraukia vis didesnį dėmesį. Neabejojama anglies ir kitų nanostruktūrų išskirtinėmis savybėmis ir bandoma jas pritaikyti įvairiose srityse, tačiau šių struktūrų įdiegimą riboja tai, kad sunku pagaminti norimų struktūrų ir išmatavimų anglies nanodarinius, nes būtent anglies nanodarinių struktūra nulemia šių darinių fizikines savybes, taipogi ir laidumą. / Carbon nanodivices have attracted the attention of many researchers since their discovery last decade. These carbon molecules are tiny tubes with diameters down to 0.4 nm, while their lengths can grow up to a million times their diameter. Using their remarkable electrical properties, simple electronic logic circuits have been built. These structures are promising for the semiconductor industry which is leading the search of miniaturization. They are not only very good conductors, but they also appear to be the yet found material with the biggest specific stiffness, having half the density of aluminium. They also have great active surface. The aim of this work is to analyse the variable range hopping ( VRH ) conduction, which can describe conduction mechanism in carbon films. Also, to find conduction parameters, whish describe the conduction mechanism in carbon films and carbon nanotubes networks. In that work was analysed impacts of photon – assisted tunneling on electrical conductivity in carbon nanotubes networks mechanism.

Baigiamajame magistro darbe nagrinėjamos OpenMP, UPC, MPI ir BSP lygiagrečiojo programavimo technologijos sprendžiant dvimatį šilumos laidumo uždavinį lygiagrečiuoju Jakobio iteraciniu metodu. Kiekvienai technologijai sudaromi lygiagretieji algoritmai, aptariamas jų realizacijos sudėtingumas programuotojo požiūriu ir efektyvumas skirtingose kompiuterių architektūrose. Dabą sudaro 6 dalys: įvadas, technologijų apžvalga, šilumos laidumo uždavinys, programų realizacija, rezultatų palyginimas, išvados, literatūra. Darbo apimtis – 38 p. teksto be priedų, 9 paveikslėliai, 3 lentelės, 10 bibliografinių šaltinių. / In this thesis, we consider OpenMP, UPC, MPI and BSP parallel programming technologies - solving two dimensional heat equation, using parallel Jacobi iterative method. Parallel algorithms are constructed and implemented for each technology. Their effectiveness in different computer architectures is discussed as well as the complexity of different implementations from programmer’s point of view. Thesis consists of 6 parts: introduction, technology overview, heat conduction problem, program implementations, comparison of the results, conclusions and references. Thesis consist of: 38 p. text without appendixes, 9 pictures, 3 tables, 10 bibliographical entries.

Habilitacinei procedūrai teikiamų darbų apžvalgoje yra pateikiama autoriaus atlikta ir kitų autorių įvairių kristalinių (ZnS, ZnSe) ir organinių junginių diodų, nanovamzdelių, plonų plėvelių, nanofibrų, ir kitų nanodarinių mokslinėje literatūroje skelbtų eksperimentinių elektrinio laidumo tyrimų rezultatų analizė bei šių rezultatų sugretinimas su fononais stimuliuoto tuneliavimo (FST) teorijų pagrindu paskaičiuotomis tuneliavimo tikimybių priklausomybėmis. Tyrimo rezultatai leido išsiaiškinti tai, kad krūvininkų generacijos procesas yra jų tuneliavimas iš gaudiklių dalyvaujant fononams. Įrodyta, kad organiniuose dariniuose (jų tarpe ir nanodariniuose) stebimą virsmą iš puslaidininkinio laidumo į metalinį laidumą (kai virsmo temperatūra TC) galima paaiškinti krūvininkų tunelinio proceso metu susidariusiu balansu tarp fononų absorbcijos ir jų generacijos, kai proceso metu elektrinis laukas krūvininkus išlaisvina iš lokalizuotos būsenos į laidumo būseną. Toje temperatūrų srityje, kur T < TC, tuneliavime dominuoja fononų absorbcija, ir todėl ten tunelinio perėjimo tikimybė, temperatūrai augant, padidėja. Priešingai, tose srityse, kur T > TC, procese dominuoja fononų emisija ir todėl ji sumažina krūvininkų tuneliavimo tikimybę, tuo pačiu iššaukdama elektrinio laidumo sumažėjimą kylant temperatūrai. Tokio FST modelio pagrįstumą įrodo ir tai, kad tiek plačiame elektrinių laukų, tiek ir temperatūrų intervale, tuneliavimo procesas yra vieningai aprašomas tų pačių parametrų... [toliau žr. visą tekstą] / Habilitation procedure review is for to clarify the conductance mechanism in polymers and other conducting nanodevices. The model based on the phonon-assisted tunnelling (PhAT) process, initiated by an electric field. An advantage of this PhAT model over the other models is the possibility to describe the behaviour of conductivity data measured at both low and high temperatures with the same set of parameters: εT - the energetic depth of the center, m* - the effective mass, T- temperature, E- the electric field, ħω - the phonon energy and a- the electron-phonon interaction constant. From these ones only the electron-phonon coupling constant a, and the phonon energy ħω are the fitting parameters estimated from the best fitting of the experimental data and the theory. Other parameters are from experiments or from literary sources known. Therefore, the PhAT mechanism could be dominant in the conductance of the MWNT, so as was shown, also in the case of the single-wall nanotubes. On the basis of this proposed model, the phenomenon of the crossover from non-metallic to metallic behavior of the conductivity is also explained. The decrease of conductivity in the framework of this model occurs at the temperatures T > TC when the phonon emission in the process of tunnelling dominates over the phonon absorption. The obtained agreement between the theoretical and experimental results, is not accidental but is due to the fact that the proposed model includes ultimate pictures of charge... [to full text]

Organic semiconductors are very attractive for thin film Organic Photodetectors (OPDs) since they possess a number of desirable attributes for optical sensing including high absorption coefficients over visible and ultraviolet wavelengths and compatibility with large-area deposition processes such as ink-jet, screen printing, and solution processing. OPDs, in general, utilize a vertical device architecture where the photoactive organic semiconductor layers are sandwiched between top and bottom electrodes that provide electrical contact. More recently, an interest in utilizing a lateral device architecture instead of the vertical one, has emerged. In this architecture, the two contacts are positioned on the two sides of the photoactive material with respect to the direction of the incoming signal, separated by a small gap. However, the factors governing lateral OPDs’ photo-response are still not well understood. In this thesis, we fabricate top-contact lateral OPDs using a thermal evaporation only fabrication process. We study the factors governing both the dark and photo currents of lateral OPDs. The effect of the wide gap between the two electrodes on the current-voltage characteristics is discussed and the role of space charge limited conduction is investigated. The contributions in the photoresponse of light scattering through the active layers as well as the back reflection of light at the metallic contacts are emphasized. The reproducibility over repeated operation cycles of both dark and photo currents values is explored. Exposure to light of the lateral OPD is found to lead to a significant increase in the dark current. The role of the conductivity enhancement in the channel due to light-induced trap filling is investigated. External quantum efficiency and detectivity estimates are given for deep ultraviolet lateral (DUV) OPDs. A comparison with vertical DUV OPDs performances is provided. Finally, the use of a phosphorescent sensitizer doped in the absorbing bottom layer to improve top-contact lateral OPDs efficiency is discussed.

Experimental measurements are never perfect, even with sophisticated modern instruments. One of the fundamental problems in signal measurement is distinguishing the noise from the signal. Sometimes the two can be partly distinguished on the basis of frequency components: for example, the signal may contain mostly low-frequency components and the noise may be located at higher frequencies. This is the basis of filtering. This thesis discusses some changes in the experimental protocol such as determining a suitable stimulation site to elicit full compound nerve action potentials (CNAP). The effect of sampling frequency and smoothing techniques to improve the resolution of the conduction velocity distribution (CVD) estimates will also be discussed. A change in stimulation site to elicit the full CNAPs is proposed after realizing that it is relatively difficult to stimulate at the same location to recruit the nerve fibers repeatedly at the elbow. Thus, the stimulation site was changed from elbow to wrist to elicit the full CNAPs. From the simulations it is evident that there was some signal information beyond 2.5 kHz frequency resulting in an increase in the sampling rate from 5 kHz to 10 kHz. The results obtained after employing smoothing techniques improved the CVD resolution. The simulation results were corroborated with the experimental results obtained. Another aspect of this thesis is to check the error tolerance of the EMG decomposition algorithm. Once the muscle electrical activity is recorded, MU trains undergo an automatic decomposition process. Decomposition errors are present in most contractions, thus a human operator has to make changes/correct the values of the motor unit firing times. From the data acquired, false negatives, false positives and false negative-positive errors have been introduced. Different levels of errors to measure the coherence between two motor-unit firing trains from a muscle contraction were also introduced. The firing rate curves are computed for each MU to analyze the interactions between two motor units (MU). The false negatives type of errors was found to be least detrimental. Whereas the false positives and false negative-positive errors affected coherence the most, their error tolerance was only a single error per 5 seconds.

Tvarkingą širdies darbą užtikrina širdies laidžioji sistema (ŠLS). Ją pažeidus sutrinka širdies darbas. Pažeidimo rizika atsiranda operacijos metu, kadangi ŠLS yra raumeninės kilmės audinys ir vizualiai neatskiriamas nuo aplinkinių audinių. ŠLS pažeidimo galima būtų išvengti, jei būtų žinomas tikslus ŠLS išsidėstymas arba egzistuotų ŠLS vaizdinimo metodika. Deja, bet atskirų ŠLS dalių tikslus išsidėstymas vis dar tikslinamas, o patologijų atvejais apskritai nėra žinomas. ŠLS vaizdinimo metodikos, tinkančios in vivo taikymams, taipogi nėra. Atlikus širdies audinių tyrimus nustoviąja fluorescencine spektroskopija nustatyti charakteringi intensyvumų skirtumai. Remiantis šiais skirtumais sukurta ŠLS atskyrimo metodika, paremta intensyvumų santykių skaičiavimu. Suskaičiuota vertė R = I(330)/I(380) yra skirtinga ŠLS, miokardui (MK) ir jungiamąjam audiniui (JA).Tokia metodika yra nejautri tyrimo sąlygoms ir gali būti naudojama ŠLS nustatymui. Ištyrus širdies audinius laikinės skyros spektroskopija nustatyta, kad ŠLS ir MK fluorescencijos gyvavimo trukmė bei santykinė sudėtis reikšmingai nesiskiria, tuo tarpu JA ir ŠLS tiek fluorescencijos gyvavimo trukmės, tiek santykinė komponentinė sudėtis yra skirtinga. Ištyrus širdies audinius konfokaliniu atspindžio mikroskopu nustatyta, jog dėl skirtingų šviesą atspindinčių komponentų bei skirtingo jų išsidėstymo galima identifikuoti MK, JA, Purkinje ląsteles ir ŠLS pluoštus. Atlikus tyrimus in vivo nustatyta, jog operacijos metu... [toliau žr. visą tekstą] / Rhythmical contraction of the heart is controlled by the cardiac conduction system (CCS). However, this highly important system visually could not be distinguished from the surrounding heart tissues – myocardium (MC) and connective tissue (CT); therefore during surgical procedures CCS could be damaged. The reliable method for CCS identification either in vivo or ex vivo does not exist therefore there is a definite need for developing a CCS imaging method. Fluorescence spectroscopy studies of cardiac tissues revealed, that most distinct spectral differences between CCS and the surrounding tissues were observed in 400 nm – 550 nm region under excitation from 330 nm – 380 nm region. The visualization method, based on the intensity ratios calculated for two excitation wavelengths, has been established. The calculated ratio R = I(330)/I(380) is different for CCS, CT and MC tissues, therefore the method may be used for identification of CCS. Time resolved fluorescence spectroscopy revealed no significant difference in composition and lifetimes between CCS and MC. On the other hand, the lifetimes and the relative spectral composition of CT differed significantly from those of CCS. Reflection confocal microscopy allows visualizing MC, CT, Purkinje cells and CCS bundles because of different reflection properties of tissue components and their specific distribution inside the tissue. The results of in vivo performed procedure revealed, that the distribution of fluorescence intensities... [to full text]