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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Gravitational Microlensing

Barnes, Wesley M 01 January 2017 (has links)
A gravitational microlensing event occurs when a foreground star passes near our line of site to a background source star. The foreground star acts as a lens, perturbing the image of the source star and amplifying the apparent intensity. Because the lens is in motion relative to the source star, the amplification is a function in time, resulting in a characteristic microlensing light curve. If the lens happens to have a planetary companion, the resulting light curve will be perturbed due the planet and the characteristics of the binary system can be ascertained.

Understanding and Design of an Arduino-based PID Controller

Bista, Dinesh 01 January 2016 (has links)
This thesis presents research and design of a Proportional, Integral, and Derivative (PID) controller that uses a microcontroller (Arduino) platform. The research part discusses the structure of a PID algorithm with some motivating work already performed with the Arduino-based PID controller from various fields. An inexpensive Arduino-based PID controller designed in the laboratory to control the temperature, consists of hardware parts: Arduino UNO, thermoelectric cooler, and electronic components while the software portion includes C/C++ programming. The PID parameters for a particular controller are found manually. The role of different PID parameters is discussed with the subsequent comparison between different modes of PID controllers. The designed system can effectively measure the temperature with an error of ± 0.6℃ while a stable temperature control with only slight deviation from the desired value (setpoint) is achieved. The designed system and concepts learned from the control system serve in pursuing inexpensive and precise ways to control physical parameters within a desired range in our laboratory.

Attrition in University Physics : a narrative study of individuals reacting to a collectivist environment

Johannsen, Bjørn Friis January 2007 (has links)
No description available.

Students' depictions of quantum mechanics : a contemporary review and some implications for research and teaching

Falk, Johan January 2007 (has links)
This thesis presents a comprehensive review of research into students’ depictions of quantum mechanics. A taxonomy to describe and compare quantum mechanics education research is presented, and this taxonomy is used to highlight the foci of prior research. A brief history of quantum mechanics education research is also presented. Research implications of the review are discussed, and several areas for future research are proposed. In particular, this thesis highlights the need for investigations into what interpretations of quantum mechanics are employed in teaching, and that classical physics – in particular the classical particle model – appears to be a common theme in students’ inappropriate depictions of quantum mechanics. Two future research projects are presented in detail: one concerning interpretations of quantum mechanics, the other concerning students’ depictions of the quantum mechanical wave function.This thesis also discusses teaching implications of the review. This is done both through a discussion on how Paper 1 can be used as a resource for lecturers and through a number of teaching suggestions based on a merging of the contents of the review and personal teaching experience.

The gendered doing of physics : a conceptual framework and its application for exploring undergraduate physics students' identity formation in relation to laboratory work

Danielsson, Anna January 2007 (has links)
No description available.

Physics Students' Experiences of the Disciplinary Discourse Encountered in Lectures in English and Swedish

Airey, John January 2006 (has links)
No description available.

Ink-paper interactions and effect on print quality in inkjet printing

Lundberg, Anna January 2011 (has links)
This thesis concerns paper and ink interactions related to inkjet printing. The main purpose of this work was to gain a deeper understanding in which parameters control the flow of ink into papers and how the ink interacts with the paper surface. The overall objective was to find key parameters to optimize the print quality in inkjet printing. Characterization of paper-surfaces in terms of porosity, surface roughness and surface energy was made. Objective and subjective measurements were used for print quality evaluation. Light microscopy imaging and SEM was used to see how ink interacts with the paper surface in a printed image. A high speed camera was used to study the absorption of picolitre sized inkjet droplets into fine papers. An initial study on the effect of paper properties on print quality was made. Result indicated that there were small differences in print quality for pilot papers with different composition (in a specific parameter window) and the commercial paper COLORLOK® reproduced a noticeable high colour gamut compared to the other samples.Research was made to see how surface fixation can affect the print quality for printouts made with pigmented ink. Surface fixation promotes retention of the pigmented colorant in the outermost surface layer of the paper and has been denoted “colorant fixation” in this thesis. It was shown that applying colorant fixation onto a paper surface before printing can increase the detail reproduction in a printed image. Different concentrations of calcium chloride were applied onto the paper surface on fullscale produced non-commercial papers. Test printing was made with a SoHo (Small office/Home office) printer using pigmented ink and results showed that using calcium chloride as surface treatment can lead to aggregation of pigments at the surface resulting in a higher detail reproduction. Fast absorption of the carrier liquid into the paper and fast fixation of colourants on the surface is important in inkjet printing to avoid colour to colour bleeding. These demands will be more pronounced when the printing speed increases. It is important to understand which parameters affect the absorption process to be able to control the mechanisms and to optimize the print quality. A study of absorption of picolitre size inkjet droplets into fine paper was made in this work. Theoretical equations describing fluid absorption into capillaries were tested and compared with experimental results. The result showed that the time dependence in the Lucas-Washburn (L-W) equation fits fairly well to data whereas the L-W equation overestimates the penetration depth. The results are directly applicable to paper and printing industry and can be used as a base for future studies of absorption of picolitre sized droplets into porous materials and for studies of aggregation of colloidal particles on surfaces. / Presentationen hölls den 2011-02-25 / Next generation substrates for inkjet printing

Sample and hold measurement for binary detection of a quantum state

Walter, Jochen January 2004 (has links)
<p>Measuring the dynamics of a quantum bit (qubit) relies on the accurate detection of the quantum state of the system. A widely used method to measure the state of a solid state Josephson junction qubit is to measure the switching current of a Josephson device.</p><p>This work investigates the measurement of the switching current of SQUID samples by means of fast current pulses. The response of a SQUID to a square current pulse has to be measured at the top of a dilution refrigerator through long cables, resulting in bandwidth limitations. A switch in the last instance of a pulse will not be detected, resulting in uncertainties in the detection. We explain how a square bias pulse that is directly followed by a hold level of lower amplitude can be used to circumvent the bandwidth limitations by latching the state of the system it was in after the bias pulse. This corresponds to a sample and hold measurement.</p><p>Every single measurement in a quantum mechanical probability measurement has to be statistically independent. We show correlation measurements for di erent settings of the pulse parameters and at di erent magnitudes of the switching current. A gure of merit for a quantum detector is its resolution. The measurements show that with the sample and hold technique good current resolutions can be obtained, even at very small magnitudes and short pulse durations. In order to make a fast measurement of the switching current, the switching process must occur during the bias pulse. We show in both measurements and computer simulations that a fast switch pulse can induce switching by the hold level,even when the hold level was initially adjusted to a value where it never switched the sample. The computer simulations show that by choosing the hold amplitude low enough, switching occurs rapidly, determined by the bias pulse alone.</p>

Gravitational Wave Production through Decay of the Inflaton into Intermediary Fields During Slow Roll Inflation

Cook, Jessica Lauren 01 September 2013 (has links)
This dissertation looks for possible observable signals of tensor metric perturbations sourced during slow roll inflation from decay of the inflaton field into other intermediary fields. We focus on two main scenarios, one of explosive production of intermediary fields for a short period during inflation and another of prolonged production of vectors due to a derivative coupling of the vectors with the inflaton field. We only find a possible observable signal of tensor perturbations in the second case.


Ahmad, Bilal Syed 04 1900 (has links)
<p>Radiation induced bystander effects have given the cancer risk analysis a whole new paradigm. However the actual mechanism involved in producing the effects is still not clear. The basic bystander signal is assumed to be a biological signal. In this study we proposed and tried to quantify the presence of a physical signal in the form of electromagnetic radiation that can trigger a biological response in the bystander cells. In bystander effect studies where the cells are exposed to very low fluence of charged particles there could be several regions that can produce electromagnetic radiation due to the process of atomic/molecular excitations and relaxations. We focused on quantifying the number of ultraviolet photons emitted when charged particles pass through different media that have relevance to radiation biology experiments. The choice of UV photons was made due to the reason that its effects on living cells are very well documented. For this purpose we developed a system which employed the technique of single photon counting to measure the light emitted from samples irradiated under vacuum by a charged particle beam. Photon counting was done using a fast photomultiplier tube (Hamamatsu R7400p) with a peak cathode response at 420 nm wavelength.</p> <p>In the early set of “proof of principle experiments” we tested polystyrene targets for ion beam induced luminescence. Polystyrene is one of the materials that are used as a cell substrate for radiation biology experiments. The luminescence yield from polystyrene was measured in terms of absolute value i.e. number of photons per second per unit solid angle. The output appeared to have a non-linear behavior with the incident Ion fluence: it rose exponentially to an asymptotic value. We irradiated the samples with beam energies varying from 1 MeV to 2.0 MeV and showed saturation at or before an incident fluence rate of 3×10<sup>13</sup> H<sup>+</sup>/cm<sup>2</sup>s. The average saturation value for the photon output was found to be 40 × 10<sup>6</sup> cps. Some measurements were performed using filters to study the emission at specific wavelengths. In the case of filtered light measurements, the photon output was found to saturate at 28×10<sup>3</sup>, 10×10<sup>6</sup>, and 35×10<sup>6</sup> cps for wavelengths of 280±5 nm, 320±5 nm and 340±5 nm respectively. Using the IBIL signal evolution characteristics with the ion fluence we determined the ions produce a damage having a cross section of the order of 10<sup>-14</sup> cm<sup>2</sup> in polystyrene. The average radiant intensity was found to increase at wavelengths of 280 nm and 320 nm when the proton energy was increased. Having found an evidence of a significant production of UV in ion irradiated, biologically relevant, material we extended this study further into the measurements from other relevant materials in radiation biology.</p> <p>Here charged particle irradiation was performed using positively charged protons (H<sup>+</sup>) ranging in energy from 1.2 MeV to 2.2 MeV at a fluence rate of 2.7×10<sup>10</sup> protons mm<sup>-2</sup>s<sup>-1</sup>.The materials chosen for this study were polypropylene, Mylar, Teflon, and Cellophane as they are all materials commonly used in radiation biology experiments as cell substrates or containers. In addition, we performed measurements of two NIST standard materials derived from living cells: oyster tissue and citrus leaves. These materials were measured as a powder.</p> <p>All the container materials were found to emit UV frequency photons at emission levels that are significant enough to warrant further investigation of the potential biological consequences. In addition, the NIST standard reference materials oyster tissue and citrus leaves also emitted UV when irradiated. This suggested that biological materials may themselves emit UV at significant levels when irradiated with charged particles.</p> <p>We established this further by irradiated cells with β-particles. Cells were plated in Petri-dishes of two different sizes, having different thicknesses of polystyrene (PS) substrate. Exposure of the cell substrates (polystyrene) only resulted in the production of 1035 photons per unit activity in μCi of <sup>90</sup>Y which was equivalent to an exposure of 840 <em>β</em>-particles/cm<sup>2</sup> to the substrate. For a collimated electron beam exposure, we observed 158-167 photons per unit μCi (18 β-particles per cm<sup>2</sup> on the substrate) for different thicknessesof the substrate. Upon irradiating HPV-G cells plated on the PS dishes we determined that the luminescence gradually increased with the increasing exposure of β-particles; reaching up to 250 % of that of the luminescence without any cells for an activity of 180 μCi. For general irradiation conditions we found statistically significant difference in luminescence output for varying cellular densities with cells only and with the application of medium on top of the cells. The colourless medium increased the total luminescence yield while the coloured medium decreased it. When the cells were irradiated using a collimated beam of electrons it was found that the luminescence decreases with the increasing cellular density thus providing an evidence of re-absorption of photons within the surroundings.</p> <p>After establishing the fact that charged particles induce light emission from the materials that have a relevance to the radiation biology experiments. We extended our study further to find out other sources of radiation that could affect the dose distribution in radiation biology experiments. In radiation biology experiments the low doses of radiation are usually delivered usingamicrobeam charged particle accelerator. Microbeams delivers a highly localized and small dose to the biological medium by using a set of collimators that confine the charged particle beam to a very narrow (micron level) region. Since the collimation block a significant proportion of the beam therefore there is a chance of the production of low energy x-rays and secondary electrons. We used Monte Carlo simulations to investigate the production of particle induced x-rays and secondary electrons in the collimation system and its possible effects on the final dose delivery to the biological medium. We found no evidence of the escape of x-rays or secondary electrons from the collimation system for proton energies of up to 3 MeV. The thickness of the collimators was sufficient to reabsorb all the generated low energy x-rays and secondary electrons. However if the proton energy exceeds 3 MeV then a significant proportion of 10 keV and 59 keV (K-α) x-rays can be emitted by the collimator. Further it was established that due to the phase space distribution of particles in various orientations with the beam axis there are significant chances of hitting non-targetted cells in microbeams that employ a collimator to confine the beam.This may happen due to the beam particles travelling obliquely with the beam axis thus passing the collimator edge and hitting the non-targetted cells. Another reason could be the scatter of beam particles inside the collimator.</p> <p>The evidence of the production of UV in materials relevant to the radiation biology experiments suggest that the conclusions and hypotheses derived from some radiation bystander experiments need to be re-thought, as charged particle irradiation leads to some level of UV emission in experimental materials which may be the cause of some “non-targeted” effects.</p> / Doctor of Philosophy (PhD)

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