The horizontal well with multiple transverse fractures has proven to be an effective strategy for shale gas reservoir exploitation. Some operators are successfully producing shale oil using the same strategy. Due to its higher viscosity and eventual 2-phase flow conditions when the formation pressure drops below the oil bubble point pressure, shale oil is likely to be limited to lower recovery efficiency than shale gas. However, the recently discovered Eagle Ford shale formations is significantly over pressured, and initial formation pressure is well above the bubble point pressure in the oil window. This, coupled with successful hydraulic fracturing methodologies, is leading to commercial wells. This study evaluates the recovery potential for oil produced both above and below the bubble point pressure from very low permeability unconventional shale oil formations. We explain how the Eagle Ford shale is different from other shales such as the Barnett and others. Although, Eagle Ford shale produces oil, condensate and dry gas in different areas, our study focuses in the oil window of the Eagle Ford shale. We used the logarithmically gridded locally refined gridding scheme to properly model the flow in the hydraulic fracture, the flow from the fracture to the matrix and the flow in the matrix. The steep pressure and saturation changes near the hydraulic fractures are captured using this gridding scheme. We compare the modeled production of shale oil from the very low permeability reservoir to conventional reservoir flow behavior. We show how production behavior and recovery of oil from the low permeability shale formation is a function of the rock properties, formation fluid properties and the fracturing operations. The sensitivity studies illustrate the important parameters affecting shale oil production performance from the stimulated reservoir volume. The parameters studied in our work includes fracture spacing, fracture half-length, rock compressibility, critical gas saturation (for 2 phase flow below the bubble point of oil), flowing bottom-hole pressure, hydraulic fracture conductivity, and matrix permeability. The sensitivity studies show that placing fractures closely, increasing the fracture half-length, making higher conductive fractures leads to higher recovery of oil. Also, the thesis stresses the need to carry out the core analysis and other reservoir studies to capture the important rock and fluid parameters like the rock permeability and the critical gas saturation.

This licentiate thesis is focusing on conditions for teaching and learning in a project based vocational education in a Swedish upper secondary school.  To address this topic the aim is to increase the understanding of opportunities for teaching and learning provided in a project-bases vocational educational and training. From this aim, following research questions is addressed through article I as: (1) What kinds of competence are the students able to develop in a PBLE? (2) In what ways do the developed competence and vocational skills relate to the specific course syllabuses? (3) How is the students’ vocational competence constituted? And through article II as: How do teachers view PBVET as (a) framing possibilities for their practice, (b) affecting students learning, and (c) presenting challenges in this learning environment?  A methodological approach that involved stimulated recall inspired interviews that were based on field notes was used in the empirical gathering and was found highly useful. The theoretical approach is based on activity theory according to Vygotskij, Leontiev and Engeströms thoughts and from Ellströms idea of learning.  The result indicates that different activities are affecting the teachers’ opportunities for teacher guidance as well as their ability to engage students into tasks. For the students to develop vocational skills a slow progress in the building process is affecting their ability to perform tasks. The vocational competences that they develop are mainly set as a reproductive learning that in some easy tasks can move to a higher, re-productive learning. As for the relationship between teacher guidance and students ability to develop vocational skills, the hierarchic structure identified in this study indicates that the educational system is overridden by the production system that sets the outer frame for the opportunities that are provided in this educational setting.

In this dissertation I examine the properties and origins of the most energetic component of Mercury's atmosphere and how it couples to the planet's magnetosphere and space environment. Mercury' s atmosphere consists of particles liberated from its surface that follow ballistic, collisionless trajectories under the influence of gravity and solar radiation pressure. This tenuous atmosphere can be classified as an exosphere where the exobase boundary is the planet's surface. To explain how this exosphere is sustained, a number of theories have been presented: (1) thermal evaporation from the hot surface; (2) photo-desorption of surface materials by UV solar radiation; (3) sputtering by plasma surface interactions; and (4) vaporization of the surface by micro-meteorite impacts. Using a 3-dimensional numerical model, I determine the role each source has in populating the exosphere. New observations of Mercury's escaping atmosphere are presented using novel imaging techniques in which sodium acts as a tracer to identify atmospheric sources. I discuss the implications of these measurements for our understanding of the physical processes at work in the exosphere, and provide a foundation for modeling such processes. For the first time, this work quantifies the variability in the loss of Mercury's sodium as a seasonal effect. My observations show that atmospheric escape can, at times, exceed 10^24 Na atoms s^-1, nearly twice the highest rate previously reported. By forward modeling Mercury's atmospheric escape, I place new constraints on the source properties and eliminate the prevailing theory that the escaping tail is sputtered from the surface by solar wind ions. The MESSENGER spacecraft has recently discovered that sodium is distributed unevenly over the surface and that the magnetosphere is offset from the planet's center. Using the first model to include these effects, I demonstrate the magnetosphere's influence upon exospheric sources by simulating asymmetries observed in the escaping atmosphere. I conclude that the exosphere is sustained by a combination of micro-meteorite impact vaporization and photo-desorption that is locally enhanced by precipitating ions.

Stimulated Raman Scattering (SRS) is a Coherent Raman microscopy method that has been increasingly employed in recent years for highly-specific, label-free, and high-speed bioimaging. Compared to a similar Coherent Raman method, the so-called Coherent Anti-Stokes Scattering (CARS) microscopy, it exhibits advantages such as the absence of nonresonant background (NRB) and the linearity of the signal intensity on the concentration of molecules of interest. However, SRS can be affected by unwanted background signals that hinder the acquisition of an accurate Raman information. These unwanted signals are generated by parasitic effects that are difficult to suppress in standard SRS setups. Here, I present a frequency-modulation (FM) SRS technique via an Acousto-Optic Tunable ioilter (AOTF), describing its implementation on Vibra Lab setup and assessing its efficiency with imaging results. The FM technique provides a cancellation of the unwanted background signals, maintaining intact the SRS information. It is based on the weak spectral dependence of the parasitic effects as compared to the high spectral specificity of the SRS signal. The proposed scheme presents a few advantages when compared with other solutions presented in the literature. In particular, it doesn't require a complex setup configuration, and it can be used seamlessly in a very broad range of the vibrational spectrum.

<p> The major purpose of the work described in this thesis has been the development of an analytical model for the electron-beam pumped semiconductor laser system consistent with the main dynamic effects observed experimentally in the stimulated emission. The lasing mat4:!rials used in this study were single crystals of CdS, CdS1e and GaAs. The choice was made on the basis of the availability of high purity single crystals and for representation of both II-VI and III-V materials in the study. </p> <p> Generally, the light output from a pulse-excited semiconductor laser changes in both wavelength and far-field pattern as a function of time during the excitation pulse. The effects investigated divide naturally into two parts. The first part deals with the tuning of the peak output of the stimulated emission toward lower energies during the excitation pulse. The second part deals with a deviation of the far-field radiation pattern of the spatial laser mode with respect to the cavity axis and the changes of this angle with time during the pump pulse. </p> <p> In parallel with these investigations, a theoretical model of the semiconductor laser was developed. This model takes into account spatial variations in the gain and refractive index in the semiconductor material and changes in these profiles with time. The analysis, in terms of the experimental parameters, leads to a prediction of angular tuning of the far-field mode and can account for certain features of faster-than-bandgap wavelength tuning in a number of disparate laser materials. A particularly significant consequence of the model is the prediction of dramatic variations in cavity loss as a function of time. The major consequences of this effect for laser dynamics are discussed. </p> / Thesis / Doctor of Philosophy (PhD)

No description available.

Föreliggande studie har som syfte att undersöka barns lärandepraktiker och meningsskapande samspel när de spelar digitala spel tillsammans. Barn i årskurs två har delats in i fyra grupper. Två av grupperna har spelat datorspelet Labyrint och de båda andra grupperna har spelat datorspelet Bloxorz. Data samlades in i två steg: först genom videoobservation av spelsituationerna i ett första skede och sedan genom ett påföljande stimulated recall-samtal där den inspelade spelsituationen diskuterades tillsammans med barnen. Data har sedan analyserats med en interaktionsanalytisk metod som undersöker hur barnen använder verbal och ickeverbal kommunikation i samspel med varandra, kontexter och teknologier för att lösa olika typer av uppgifter i spelen. Studien leder till slutsatsen att olika former av samspel äger rum mellan spelare och åskådare, man skapar gemensamt strategier för problemlösning. Strategierna realiseras genom arbetsfördelning mellan barnen, där fördelningen kan vara större eller mindre. En relevant parameter är utsträckningen i vilken spelaren antingen är en fullt agerande spelare med eget initiativtagande, eller som motsats intar rollen av utförare av åskådarnas instruktioner. En annan parameter relevant för samtliga strategier är huruvida barnet utgår från ett situerat avatar-perspektiv eller ett mer holistiskt nivå-perspektiv vid val av strategi. Spel har en enorm motiverande kraft och barn samlas gärna kring datorn och spelar dataspel. Där kan de använda sina samlade kunskaper och inre motivation för att prova olika strategier vid problemlösning. Flera olika fenomen känns igen från tidigare forskning; flow, inre motivation, utforskande spelstrategier och målsökande spelstrategier. Den aktuella studien bidrar med en metod, en analysmodell samt begrepp för ökad förståelse av gemensamt lärande.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

The purpose of this dissertation is to advance the understanding of SrS-based a. c. thin film electroluminescent (ACTFEL) devices. The role of traps in the bulk phosphor layer in the light emission mechanism from ACTFEL devices is studied, characterized and modeled. Experiments were performed to observe the response of the ACTFEL devices to tailored voltage excitations. A physical model was developed to describe the optoelectronic processes taking place in the phosphor; analytical equations were written and numerically simulated to plot the flux and luminance responses of the device to similarly tailored voltage excitations. The voltage excitation parameters such as amplitude, rise times and fall times were varied both experimentally and in simulations and their effect on the opto-electronic response of the device was studied. Thermally stimulated luminance studies were performed to determine critical device parameters. Theoretical predictions matched the experimental data in a qualitative manner. A much improved quantitative accuracy is obtained when the role of dipoles in the EL mechanisms is incorporated into the model.

Previous work has shown that laser-induced desorption (LID) can prove useful for the determination of surface contamination. However, because of the nature of small-spot sampling utilized in the previous work, it proved rather difficult to gather statistically significant data. A solution to this problem that still allowed sampling the surface with small focused laser spots was to automate the sample manipulation, laser control, and data acquisition of the system. With the automation of the LID facility in place, a detailed study of the LID of water/heavy water (H₂O/D₂O) was undertaken. As in the earlier work, samples were irradiated with a hydrogen fluoride/deuterium fluoride (HF/DF) laser beam focused inside an ultrahigh vacuum (UHV) chamber. The molecules desorbed from the sample surface were partially contained in a glass envelope that also contained a quadrupole mass analyzer. Samples consisted of bulk-etched CaF₂ and optical thin-film coatings of CaF₂--undosed or H₂O/D₂O dosed--on a variety of substrates. Some analysis was performed on cleaved, single-crystal alkali halides. The focused laser spot size was 155 μm (l/e² diameter) for the HF laser and 138 μm (l/e² diameter) for the DF laser. Between 400 and 800 sites per sample were tested for each desorption onset analysis. A study was also performed to test the possibility of correlation between (1) laser-induced damage and defects and (2) laser-induced desorption and adsorption sites for some of the samples listed above. Attempts to deuterate and hydrate CaF₂ thin films met with limited success as laser-induced desorption samples. Other analysis techniques showed that dosing during the coating process produced a more ordered coating; in fact, dosing with H₂O reduced the optical absorption in the "H₂O" band, modified the damage morphology, and, along with a low temperature bakeout, raised the laser-damage threshold.