Department: Physics ![[clear]](close-x.png "Remove this limiter")
31 matches in the database.
These are records: 1 - 30.
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1.
Abbas, Mohamad.
A search for Long-Period Variable Stars in the Globular Cluster NGC 6496.
Degree: MS, Physics, 2011, Bowling Green State University
► Studying the late stages of stars is essential to understand the process…
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▼ Studying the late stages of stars is essential to understand the process of stellar evolution. Depending on their masses and properties, some stars become unstable at the end of their evolutionary state and hence they start pulsating. Their brightness and surface temperature change with their pulsations and hence we see them as variable stars. We are looking for long period variable stars (LPVs) in the globular cluster NGC 6496. We observed the cluster from February 2009 till October 2010 using a 0.41m telescope in the V and I bandpasses. We have identified 11 variable stars in the cluster. 6 of them are new discovered LPVs in which 3 of them are semiregular LPVs and the rest 3 are irregular LPVs. We plotted the color magnitude diagram (CMD) of this cluster and all our LPVs were detected on the RGB/AGB. 5 of the 11 variable stars are short period variable stars in which 4 of them are W UMa binary stars and 1 is an Algol binary star. The light curves of all these stars are plotted in this paper and the periods were detected using different period-finding methods.
Advisors/Committee Members: Andrew, Layden.
Subjects: Astronomy; Astrophysics; Physics
Keywords: astronomy; observational; NGC 6553; globular cluster; metal-rich; variable stars; long period variable stars; mira; DAOPHOT; ALLSTAR; ALLFRAME; DAOMASTER; irregular; semi-regular; pulsation
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2.
Abeyratne, Sumana.
QUANTUM STRATEGIES AND QUANTUM GAMBLING.
Degree: MS, Physics, 2006, Bowling Green State University
► The main purpose of this thesis is to show that quantum strategies…
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▼ The main purpose of this thesis is to show that quantum strategies have distinct advantages over classical strategies. To accomplish this task, this study generalizes two existing quantum game protocols. The first part of the thesis discusses the coin tossing game, which can be played both classically and quantum mechanically. The discussion includes the analysis of a previously studied quantum coin tossing game. The analysis starts with the simplest coin tossing game between two players, which involves two games, and examines all possible classical and quantum game combinations. Similarly, as an extension, three games between two players with all possible game combinations are analyzed. At the end, it becomes clear that quantum strategies always dominate classical strategies. The second part of the thesis investigates an interesting quantum gambling game between two distant mistrustful parties, which has also been previously studied. Since this game appears to be unfair for the gambler, the problem is generalized and investigated for the requirements for a fair quantum gambling game. Consequently, it is discovered that a fair quantum gambling game between two distant mistrustful parties can be defined. Quantum gambling between such parties, however, does not have a classical counterpart.
Advisors/Committee Members: Xi, Haowen.
Subjects: Physics, General
Keywords: quantum games; quantum strategies; quantum coin tossing; quantum gambling
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3.
Anderson, Tyler.
Determining Interstellar Reddening Using Intrinsic Colors of C- Type RR-Lyrae Variables.
Degree: MS, Physics, 2012, Bowling Green State University
► We present calibrated VI light curves for 13 field c-type RR Lyraes.…
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▼ We present calibrated VI light curves for 13 field c-type RR Lyraes. We determine the stars' mean-intensity magnitudes, light amplitudes, periods, and both mean colors and colors at `minimum light.' We explore the application of the defined phase window of `minimum light' to RRc's and find mean color to be a more accurate and physically meaningful quantity for use in determining interstellar reddening. Relations to determine reddening involving period, light amplitude, and metallicity using both mean and minimum light color are presented. The strongest relation, involving data from the best 39 stars between our field stars and RRc's across five GCs, finds (V-I)_mean = 0.924* Period + 0.036 mag, with an rms scatter of 0.031 mag.
Advisors/Committee Members: Layden, Andrew.
Subjects: Astronomy
Keywords: RR Lyrae; Variable stars; Interstellar Reddening; c-type RR Lyrae; Color; Intrinsic Color; Minimum light; RRL; RRc
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4.
Attanayake, Harsha.
Transport Properties of 40% La Filled Skutterudite Thin Films - Theory and Instrumentation.
Degree: MS, Physics, 2008, Bowling Green State University
► This study researches thin films fabricated by pulsed-laser ablation on tempered glass…
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▼ This study researches thin films fabricated by pulsed-laser ablation on tempered glass substrates using 40% La filled-Skutterudite. In general, laser ablated films exhibit up to 70% amorphous structure and vary in thickness by about 20% from center to edge. The thermoelectric figure of merit determined using a modified version of the Harman equation at room temperature approaches a value of 18. The modifications include the effects of the substrate and its thickness. An empirical figure of merit obtained using the voltage measurements under adiabatic and isothermal conditions was extrapolated to zero substrate thickness. A total of 16 samples were prepared in three ablation runs with different substrate thickness and with an average film thickness of 95 nm. The higher figure of merit obtained compared to bulk samples can be the result of a variety of possibilities: enhanced Seebeck coefficient and size limited thermal conductivity in both electronic and lattice components due to limited mean free path.
Advisors/Committee Members: Boughton, Robert I.
Subjects: Energy; Materials science; Physics
Keywords: thermoelectric; figure of merit; skutterudite
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5.
Bas, Derek.
Laser Beam Steering with Thin Film GaAs on Plastic.
Degree: MS, Physics, 2010, Bowling Green State University
► Optical networking requires the use of microelectromechanical systems (MEMS) as beam steering…
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▼ Optical networking requires the use of microelectromechanical systems (MEMS) as beam steering components. Since current techniques require an external mechanical or electrical source to control output, they introduce obstacles to speed and efficiency that could be overcome by the use of all-optical components. Thin film GaAs has been observed to exhibit optical properties that would be useful in creating a new all-optical beam steering device. The objective of the current project is to more clearly understand the mechanics behind the properties that were observed. Results were obtained and studied and several preliminary designs for optical logic gate applications are discussed.
Advisors/Committee Members: Ullrich, Bruno.
Subjects: Experiments; Materials science; Optics; Physics
Keywords: optical switch; laser; beam steering; thin film; semiconductors; GaAs; logic gate; all-optical; photonics; absorption; thermal expansion
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6.
Bhowmick, Mithun.
Investigation of Optoelectronic Properties in Thin-Film and Crystalline Cadmium Sulfide.
Degree: MS, Physics, 2007, Bowling Green State University
► Photocurrent (PC), transmission and photoluminescence (PL) properties were measured in cadmium sulfide…
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▼ Photocurrent (PC), transmission and photoluminescence (PL) properties were measured in cadmium sulfide (CdS). A thin-film (G69) and a single crystal of CdS were used for the measurements. These measured spectra were compared to theoretical values using two different models. In each of the comparisons, a theoretical absorption spectrum was used for the analysis. Along with these experiments, reflectivity of the material was measured to find the thickness of the film. The PL spectrum was used to determine crystal orientation. Based on these measurements, efficiency of the model as well as the material was verified.
Advisors/Committee Members: Ullrich, Bruno.
Subjects: Physics, Optics
Keywords: Photocurrent; THIN-FILM; CdS; crystal; photoluminescence; TRANSMITTANCE; semiconductors
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7.
Cardona Velasquez, Gustavo Adolfo.
Properties of Bright Variable Stars in Unusual Metal Rich Cluster NGC 6388.
Degree: MS, Physics, 2011, Bowling Green State University
► We have searched for Long Period Variable (LPV) stars in the metal-rich…
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▼ We have searched for Long Period Variable (LPV) stars in the metal-rich cluster NGC 6388 using time series photometry in the V and I bandpasses. A CMD was created, which displays the tilted red HB at V = 17.5 mag. and the unusual prominent blue HB at V = 17 to 18 mag. Time-series photometry and periods have been presented for 63 variable stars, of which 30 are newly discovered variables. Of the known variables nine are LPVs. We are the first to present light curves for these stars and to classify their variability types. We find 3 LPVs as Mira, 6 as Semi-regulars (SR) and 1 as Irregular (Irr.), 18 are RR Lyrae, of which we present complementary time series and period for 14 of these stars, and 7 are Population II Cepheids, of which we present complementary time series and period for 4 of them. The newly discovered variables are all suspected LPV stars and we classified them, using time series photometry and periods, as Mira for 1 star, SR for 15 stars, Irr for 7 stars, Suspected Variables for 7 stars, out of which there are 3 very bright stars that could have overexposed the CCD, with no definite borderline between the SR and Irr stars. Once classified we used probable distance for the cluster center and location on the CMD to establish possible membership, which left us with 63 possible cluster members, but the crowdedness of the cluster and the fact that the cluster is located near the bulge of the Milky Way prevents us from establishing a better certainty for its membership.
Advisors/Committee Members: Layden, Andrew C.
Subjects: Astronomy; Astrophysics; Physics
Keywords: NGC 6388; globular cluster; metal-rich; variable stars; long period variable stars; mira; ISIS; DAOPHOT; ALLSTAR; ALLFRAME; DAOMASTER; irregular; semi-regular; pulsation
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8.
Diederich, Geoffrey M.
Synthesis of Zinc Telluride/Cadmium Selenide/Cadmium Sulfide Quantum Dot Heterostructures for use in Biological Applications.
Degree: MS, Physics, 2012, Bowling Green State University
► This study investigates the synthesis of charge-separating quantum dots specifically engineered to…
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▼ This study investigates the synthesis of charge-separating quantum dots specifically engineered to be used as voltage sensitive probes in mapping of neuronal networks. ZnTe/CdSe/CdS core/shell/shell is the proposed system. The dots spatially separate charges and show the Stark effect under applied voltages, making them perfect for use as voltage sensitive probes. Synthesis techniques and characterization methods are given.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Physics
Keywords: Quantum Dots, Type II, VSP, Charge Separating
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9.
Divaratne, Dilupama Ayeshani.
Transport Properties of 40% La Filled Skutterudite Thin Films Sample Preparation and Data Analysis.
Degree: MS, Physics, 2008, Bowling Green State University
► The efficiency of thermoelectric energy conversion devices is a function of the…
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▼ The efficiency of thermoelectric energy conversion devices is a function of the thermoelectric figure of merit ZT where T is the absolute temperature and Z is defined as Z = S2σ/κ. Large values of ZT require high Seebeck coefficient S, high electrical conductivity σ, and low thermal conductivity κ. It is difficult to increase Z in bulk thermoelectric material because these three material's properties are coupled to each other.In this project we studied thin skutterudite films. In order to measure the figure of merit we used a method (Harman's method) of measuring both adiabatic and isothermal voltages across the sample. A fraction of the conduction heat current flows through the glass substrate as well as through the thin film sample. The heat conductivity through the substrate is directly proportional to its thickness. The key idea of this study is to determine the relationship between the experimental figure of merit and the substrate thickness at constant temperature, thus obtaining the limiting Figure of Merit value for skutterudite thin films. We obtained an average value of 18.901.43, which is higher than bulk skutterudite. The lower dimensionality, the amorphous structure, and the higher Seebeck coefficient of thin films are possible causes of the higher value of the limiting F.O.M.
Advisors/Committee Members: Boughton, Prof. Robert.
Subjects: Materials science; Physics
Keywords: skutterudite, thermoelectric, thin film, figure of merit
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10.
Goldsmith, Neil.
Calcium Movement in the Sarcomere and its Connection to Muscle Contraction: A Pilot Study.
Degree: MS, Physics, 2008, Bowling Green State University
► The human body uses calcium as an activator for muscle contraction. A…
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▼ The human body uses calcium as an activator for muscle contraction. A muscle contraction begins with the release of calcium from the terminal cisternae into the sarcomere. The interaction of calcium with myoplasmic proteins then causes the muscle to contract. A biophysical model of the sarcomere will be developed in order to use the model to connect chemical concentrations with force production by the muscle. Since the sarcomere is the base contractile unit of muscle, it should therefore be the appropriate starting point for such a model. The model includes calcium release, diffusion, binding, and uptake. Magnesium concentrations are also modeled as they compete for calcium binding sites on parvalbumin, ATP, and troponin. The binding of calcium to troponin is of special importance because it results in unblocking of the actin sites. The actin will then interact with myosin in a multi-step process that is well understood but poorly quantified. This interaction leads to contraction of the sarcomere and thus the production of force.
Advisors/Committee Members: Fulcher, Lewis.
Subjects: Biophysics
Keywords: CALCIUM; diffusion; MUSCLE; SERCA pump; CONTRACTION; SARCOMERE
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11.
Gurusinghe, Nilanka Praveena.
Investigation of optoelectronic properties of thin film n-type ZnS on p-type Si.
Degree: MS, Physics, 2008, Bowling Green State University
► This project investigated optoelectronic properties of thin film n-type ZnS on p-type…
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▼ This project investigated optoelectronic properties of thin film n-type ZnS on p-type Si substrate, which have been fabricated using pulsed-laser deposition (PLD) technique. The photocurrent (PC) response of the above heterostructure was measured using the lock-in technique. The experimental PC response spectrum was compared with the theoretical spectrum using density of states (DOS), modified Urbach rule,and the surface recombination of a thin film. In addition, current-voltage (I/V) characteristics was employed to determine the electronic features of the thin-film sample.
Advisors/Committee Members: Ullrich, Dr. Bruno.
Subjects: Optics; Physics
Keywords: photocurrent of ZnS thin films; AC photocurrent measurements; ZnS thin films
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12.
Hemantha, Maddumage Don Prasad.
FINANCIAL MARKET MODELING WITH MINORITY AND MAJORITY RULES.
Degree: MS, Physics, 2006, Bowling Green State University
► Two multi-agent models are proposed and the characteristics of each model is…
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▼ Two multi-agent models are proposed and the characteristics of each model is measured through numerical simulation. Agents in both models use the same two strategies. First model is based on the minority rule and an exponential return distribution was observed, while majority rule based second model generates a power law decay of probability. These models are capable of reproducing every stylized fact of financial markets: autocorrelation of return and absolute return, log-normal volatility distribution, leverage effect, and multifractal properties.
Advisors/Committee Members: Xi, Haowen.
Subjects: Physics, Condensed Matter
Keywords: volatility; ï¬nancial; 1E-3; autocorrelation; MARKET; effect
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13.
Hewa-Kasakarage, Nishshanka Niroshan.
Charge Separation in Heterostructured Semiconductor Nanocrystals.
Degree: MS, Physics, 2010, Bowling Green State University
► Hybrid semiconductor nanocrystals (NCs) consisting of separate donor-acceptor domains are viewed as…
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▼ Hybrid semiconductor nanocrystals (NCs) consisting of separate donor-acceptor domains are viewed as promising candidates for increasing the efficiency in present-day photovoltaic and photocatalytic applications. Properties of colloidal heterostructured nanocrystals are largely determined by the spatial distribution of photogenerated carriers across the junction of semiconductor materials that form the heterostructure. The two known types of carrier distributions are identified based on whether both carriers reside within the same (type I) or opposite (type II) sides of the heterojunction. Herein, we report on organometallic synthesis of semiconductor heterostructured nanocrystals (nanorods, core/shell nanocrystals, Alloy nanocrystals and nanobarbells) that produce a number of unique properties including enhanced magnitude of quantum confined Stark effect, efficient spatial separation of carriers in between acceptor and donor, and subnanosecond switching of absorption energies that can find practical applications in electroabsorption switches, solar cell and ultrasensitive charge detectors.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Physics
Keywords: Heterostructured Semiconductor Nanocrystals
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14.
Kager, Elisabeth.
Pulsation Properties of Long Period Variable Stars in Globular Cluster NGC 6553.
Degree: MS, Physics, 2010, Bowling Green State University
► Photometry for the metal-rich globular cluster NGC 6553 has been done and…
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▼ Photometry for the metal-rich globular cluster NGC 6553 has been done and is presented in both V and I banpasses. A color magnitude diagram for this cluster was created which indicates the presence of two distinct giant branches that separate the cluster population from the field population at I = 12.2 mag. Time-series photometry is presented for 49 stars, 22 of which are considered cluster members. Cluster membership was found by locating them on the cluster giant branch. Ten of these 22 cluster members are new discoveries while the other twelve were found during a study done by Lloyed Evans and Menzies in 1972. Where possible, properties, such as average period, average amplitude, and the observed range of magnitudes of the variable star candidates are discussed. Lloyd Evans and Menzies did not investigate the stars' properties, but they provided generalized sub-classifications for them. Their findings included eleven irregular/semi-regular variables and one Mira variable. We, on the other hand, provide specific sub-classifiactions for the individual stars. Comparing our results of the same twelve stars to Lloyd Evans and Menzies', we find that we sub-classified them as ten irregular/semi-regular variables, one Mira variable, and one possible binary star system. We do not find a definite borderline between the irregular and the semi-regular variable star classes. Also, we have made the observation that there is no trend of sub-classes with respect to the position on the giant branch. This leads to the conclusion that there is no smooth transition from the position of irregular/semi-regular variables to the position occupied by Mira-type variables, but rather a sudden jump. This same phenomenon has been observed by Lebzelter and Wood in a paper published in 2005.
Advisors/Committee Members: Layden, Andrew.
Subjects: Astronomy; Astrophysics; Physics
Keywords: astronomy; observational; NGC 6553; globular cluster; metal-rich; variable stars; long period variable stars; mira; DAOPHOT; ALLSTAR; ALLFRAME; DAOMASTER; irregular; semi-regular; pulsation
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15.
Kinder, Erich W.
Fabrication of All-Inorganic Optoelectronic Devices Using Matrix Encapsulation of Nanocrystal Arrays.
Degree: MS, Physics, 2012, Bowling Green State University
► A general strategy for low-temperature processing of colloidal semiconductor nanocrystals into fully…
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▼ A general strategy for low-temperature processing of colloidal semiconductor nanocrystals into fully inorganic films is reported. This methodology improves on the traditional organic ligand-interlinking process, replacing the organic molecules in the nanocrystal array with a matrix of a wide-band gap semiconductor. This preserves optoelectronic properties of the individual nanoparticles while rendering the nanocrystal film photoconductive. Fabricated solids exhibit improved thermal stability over their organic counterparts. This is attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces. Compelling light-harvesting performance is shown in prototype solar cells.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Chemistry; Physics
Keywords: Nanocrystal; Solar Cell; SMENA; Semiconductor; Photovoltaic; Depleted Heterojunction
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16.
Kirsanova, Maria.
ZnSe/CdS Core/Shell Nanostructures and Their Catalytic Properties.
Degree: MS, Physics, 2012, Bowling Green State University
► The study focused on developing synthetic routes for the colloidal synthesis of…
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▼ The study focused on developing synthetic routes for the colloidal synthesis of ZnSe/CdS semiconductor heterostructures, various in size and geometry, and evaluating their applicability to practical realizations. Such composite semiconductor nanocrystals (NCs) with core/shell morphology can be designed to drive an efficient separation of photoinduced charges. As a preliminary, high-quality ZnSe/CdS core/shell quantum dots (QDs), exhibiting a type II carrier localization regime, were fabricated via a traditional pyrolysis of organometallic precursors. An efficient spatial separation of electrons and holes between the core and the shell was observed for heterostructures containing more than 3 monolayers of CdS, which allows for their potential applications in areas of biomedical imaging, solar cells, and QD based lasers. Furthermore, colloidal synthesis of ZnSe/CdS barbell-shaped NCs, comprising a type II heterojunction of ZnSe and CdS domains, showed compelling evidence of photoinduced charge separation at the interface of semiconductor materials. The nanobarbells were fabricated in a two-step procedure by growing ZnSe caps onto polar facets of CdS nanorods. Finally, time-resolved spectroscopy and electrochemistry techniques were used to demonstrate that the attachment of a hole-scavenging surfactant to ZnSe/CdS nanocrystals promotes an efficient transfer of holes to the surface. Specifically, the effect of the shell thickness in core/shell NCs on the ability of core-localized charges to perform oxidative reactions was determined. More importantly, it was observed that holes can be extracted from the core much faster than they recombine with shell-localized electrons, indicating that most of photoinduced holes in these nanostructures can be made available to drive catalytic reactions.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Industrial Engineering; Nanoscience; Nanotechnology; Physics; Solid State Physics
Keywords: Nanoscience; Nanotechnology; Quantum dots; Semiconductor; Nanocrystals; Catalysis; Photocatalysis; ZnSe/CdS; Core/Shell; Colloidal Synthesis
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17.
Lark, Adam Christopher.
STUDENT MISCONCEPTIONS IN NEWTONIAN MECHANICS.
Degree: MS, Physics, 2007, Bowling Green State University
► A general understanding of Newton’s first and second law is demonstrated in…
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▼ A general understanding of Newton’s first and second law is demonstrated in the literature to be severely lacking or seemingly absent in most students. While several studies found some degree of success involving experimental teaching methods in high school and college classes, this study seeks to address the foundation of students’ knowledge in Newtonian Mechanics: early education. Fourth grade and sixth grade students were first interviewed, testing for current understanding of forces and motion, and subsequently taught four lessons on the topic. Lessons were designed (based on successful classroom ideas described by the literature) to target common misconceptions students have involving forces and motion. Pre-interviews confirm the lack of general understanding of many concepts described by the literature, while post-interviews show statistically significant conceptual changes in many of the targeted conceptual areas. The lessons involved in this study successfully changed student ideas on topics involving friction, forces stopping objects’ motion (as opposed to it stopping on its own), an understanding of the different ways motion can change, and that forces are what change motion. Unfortunately, the one topic described by the literature as hardest to alter remained prevalent in the students. Post-interviews show student still answering either “the force of the push” or “some external force that would keep the object moving” when asked what keeps an object in motion. A second phase of this study (a longitudinal study) will examine whether this particular misconception, after several years of these lessons, can promote stronger conceptual growth.
Advisors/Committee Members: Van Hook, Stephen.
Subjects: Education, Physical
Keywords: Misconceptions; Newton; Mechanics; Elementary; Education; Early Childhood
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18.
Li, Jun.
Intraglottal Glottal Pressure Distributions for Three Oblique Glottal Angles.
Degree: MS, Physics, 2010, Bowling Green State University
► Glottal obliquity occurs when the centerline of the glottis is not vertical,…
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▼ Glottal obliquity occurs when the centerline of the glottis is not vertical, a consequence of oscillations of the vocal folds that are not mirror images of each other. This study examined the intraglottal surface pressure distributions for three cases of obliquity: 2.5, 5, and -3.75 degrees, relatively small oblique angles. These correspond to included glottal angles that are convergent, uniform, and divergent, respectively. The Plexiglas model M5 of the laryngeal airway with rectangular glottal ducts and insertable vocal fold pieces was used to obtain the pressure distributions. Glottal diameter and transglottal pressure were primary parameters for each obliquity case. The glottal diameters were 0.005, 0.01, 0.02, 0.04, 0.08, 0.16, and 0.32 cm. The pressure distributions ranged from 3-25 cm H2O for most cases. For each diameter, pressures were measured along both the flow wall (to which the flow jet adheres or was directed) and the non-flow wall (the side opposite the flow wall). Results indicate that the small angle obliquity cases studied here suggest significant pressure distribution differences compared to the symmetric glottis of the same included angle for the following conditions: for the convergent glottis for medium and large diameters; for the uniform glottis for small and for large diameters. However, there was little effect on pressure distributions for the divergent glottis, for small diameters for the convergent glottis, and for medium diameters for the uniform glottis. Relative to diameter change, strong effects were found. As the diameter was reduced, the pressure distributions rose both upstream and in the glottis for the uniform glottis, and increased in the glottis for the convergent glottis. For the divergent glottis, reducing the diameter moved the minimal pressure downstream to the minimal diameter location, and increased the pressures on the inferior vocal fold surfaces. In addition, when the airflow is shifted to change which wall is the flow wall, this shifts the minimal pressure and the shape of the pressure distributions. Pressure on the flow wall is typically lower than the pressure on the non-flow wall. In general, the effects of obliquity, diameter, and flow-wall alter the intraglottal surface pressure distributions to create different forces on the vocal folds. Further computer modeling needs to be performed to determine the specific oscillatory consequences (magnitude and symmetry of motion) of the effects found here.
Advisors/Committee Members: Fulcher, Lewis.
Subjects: Physics
Keywords: glottal obliquity; vocal folds; intraglottal pressure distributions; convergent; uniform; divergent; Plexiglas model M5; glottal diameters; flow wall; non-flow wall; pressure distribution differences; symmetric glottis
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19.
Liu, Chen.
A numerical and analytical study of phonation threshold pressure and experiments with a physical model of the vocal fold mucosa.
Degree: MS, Physics, 2009, Bowling Green State University
► Titze (1988) used the surface wave model to derive an analytical expression…
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▼ Titze (1988) used the surface wave model to derive an analytical expression for threshold pressure in terms of the glottal geometry and biomechanical parameters of the larynx. This formula was tested in a series of experiments in 1995 and 1997. Since the membrane of the physical model used in the experiments becomes rounded when a fluid flows beneath it, the effects of glottal curvature were investigated. Because physical model used for the experiments could be adjusted to give a divergent prephonatory glottal geometry, an angle θ was also introduced in addition to the curvature correction. Including the curvature coefficient b and the prephonatory glottal angle θ do not seem likely candidates for discrepancies observed in the experiments because such effects are hard to distinguish from changes in the effective values of the glottal halfwidth and the damping coefficient. Nardone’s mathematical model was built from the classic, lumped element, two-mass model of Ishizaka and Flanagan. The mathematical model is based on ten, second-order, nonlinear, coupled, ordinary differential equations that are solved simultaneously using the software Mathematica. Nardone’s model was employed to study the role of vocal tract parameters and viscous damping constants in determining the threshold pressure. Calculated results were compared with Chan and Titze’s (2006) experimental data. The results indicate that the threshold pressure is consistently lowered when the vocal tract is included, which follows the same trend as the experimental results of Chan and Titze (2006). Increasing the vocal tract area in the mathematical model achieved a larger difference between the calculated results with vocal tract and with a larger vocal tract area. We have also shown that an increased viscous damping constant leads to a bigger threshold pressure differences. Comparison of the calculated results with Chan and Titze’s (2006) experiments were not able to generate a consistent fit over the entire range of glottal widths studied. Successes were recorded over parts of the range with different sets of parameters.
Advisors/Committee Members: Fulcher, Lewis.
Subjects: Biophysics
Keywords: phonation; threshold pressure; vocal fold; Titze
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20.
Mandere, Edward Ondieki.
Financial Networks and Their Applications to the Stock Market.
Degree: MS, Physics, 2009, Bowling Green State University
► Complex networks exist in many different fields of study. Recently financial networks…
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▼ Complex networks exist in many different fields of study. Recently financial networks have garnered a lot of interest mainly as a way of visualizing the relationships between financial entities. This makes them useful in assessing current market dynamics and in predicting future market conditions. The most studied network in econophysics is the correlation network of stock price returns. Stock price return correlations are used to determine a metric distance between stocks. A minimum spanning tree algorithm (Prim's or Kruskal's) is then applied to find closest stocks to create a tree. These networks can then be used to identifyand cluster stocks into economic sectors based on their proximity. Some characteristics of these networks such as topology, connectedness and size will be studied in this thesis. The use of these correlation networks in modern portfolio optimization problem will be considered. Using correlation networks to predict large and coordinated price movements will also be discussed.
Advisors/Committee Members: Xi, Haowen.
Subjects: Physics
Keywords: econophysics; Correlation Matrices; Correlation Networks; Random Matrix Theory
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22.
Nardone, Marco.
Analysis of Voice Perturbations Using an Asymmetric Model of the Vocal Folds.
Degree: MS, Physics, 2007, Bowling Green State University
► A mathematical model was developed to investigate possible causes of jitter and…
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▼ A mathematical model was developed to investigate possible causes of jitter and shimmer. The model builds from the classic, lumped element, two-mass model of Ishizaka and Flanagan. Bilateral asymmetry was incorporated into the model to facilitate the simulation of physiological and aerodynamic imbalances in the larynx. The aerodynamic driving forces on the vocal folds were derived from empirical pressure data that were obtained from a scaled-up Plexiglas model of a typical male human larynx, called M5. The mathematical model is based on ten, second-order, nonlinear, coupled, ordinary differential equations that were solved simultaneously using the software Mathematica. The solutions were analyzed graphically and numerically to identify perturbations in the fundamental frequency and amplitude of the glottal airflow. Jitter and shimmer were quantified using the jitter factor and the amplitude variability index. The results indicate that only time-dependent asymmetries result in jitter and shimmer.
Advisors/Committee Members: Fulcher, Lewis P.
Subjects: Physics, Acoustics
Keywords: voice, jitter, shimmer, Mathematica, vocal folds
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23.
Nemchinov, Alexander.
Using Colloidal Nanocrystal Matrix Encapsulation Technique for the Development of Novel Infrared Light Emitting Arrays.
Degree: MS, Physics, 2012, Bowling Green State University
► Colloidal semiconductor nanocrystals (NCs) and composite metal-semiconductor (M-S) structures are emerging as…
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▼ Colloidal semiconductor nanocrystals (NCs) and composite metal-semiconductor (M-S) structures are emerging as a promising class of nanomaterials for the development of solid state optical applications. Some of these applications require colloidal nanocrystals in form of thin films (matrices), possessing both thermal and chemical stability, and demonstrating high energy transfer efficiency. In this study, we addressed the issues of low emission yield and instability of NC matrices through the use of ligand-free encapsulation of colloidal nanocrystals within all-inorganic crystalline solids. The present methodology relies on solution-processing of CdSe nanocrystals into a crystalline matrix ofa wide bandgap semiconductor (CdS, ZnS), which replaces the original molecular ligands on nanocrystal surfaces with an inorganic medium. Such matrices efficiently protect nanoparticles from the surrounding environment and preserve the quantum confinement of electrical charges in embedded NCs. Assembly of thin film matrices from NC “inks” is cost-effective approach for the development of next-generation materials with high efficiency photoluminescence. Specifically, the main accomplishments of this work included: (i) hot-injection synthesis of CdSe/CdS core/shell semiconductor NCs; (ii) processing of NCs into light emitting solid films through spin-coating with consecutive ligand exchange; (iii) optimization of film morphology towards improving the emission yield and stability; (iv) further enhancement of developed morphology via introducing the M-S composites: a. development of chemical strategies for the fabrication of M-S nanocomposites that demonstrate an efficient and potentially tunable energy exchange between excitons in semiconductor and plasmons in metal nanoparticles; b. investigation of the nature of underlying exciton-plasmon interactions and the ultrafast electron processes in the fabricated M-S heteronanocrystals, using modern spectroscopy methods. A general strategy for the low-temperature processing assembly of all-inorganic light-emitting nanocrystal films with emission quantum yield (QY) inthe 30-52% range is reported. This technology exceeds the traditional ligand-interlinking scheme and is based on the ligand-free encapsulation of morphologically-defined nanocrystalarrays into a wide bandgap semiconductor matrix. This approach preserves optoelectronic properties of individual nanoparticles and maintains properties of the photoconductive nanocrystal film. Fabricated material shows outstanding thermal stability due to the heteroepitaxial structure of nanocrystal-matrix interfaces. In addition to strong emission, fabricated films show excellent thermal and chemical stability, and a large refractive index, which avails their integration into emerging solid-state NC devices, including light emitting diodes, solar concentrators, and quantum dot lasers. Improving the efficiency of prototype NC light emitting films was achieved through material optimization, adjustment of the thickness of semiconductor layers and the study of ligand exchange process. Light absorbance and energy transfer performance of fabricated films can also be improved by introducing M-S composites as dopant into the NC matrix inks substance.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Chemistry; Nanoscience; Nanotechnology; Physics
Keywords: nanocrystals; light emitting diodes; CdSe/CdS; matrix encapsulation
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24.
Nemitz, Ian R.
Synthesis of Nanoscale Semiconductor Heterostructures for Photovoltaic Applications.
Degree: MS, Physics, 2010, Bowling Green State University
► With the demand for renewable sources of energy on the rise, significant…
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▼ With the demand for renewable sources of energy on the rise, significant effort needs to be invested in the development of inexpensive and efficient light-harvesting materials. Among those, colloidal semiconductor nanocrystals are emerging as a promising class of nanomaterials with the potential to produce a significant technological impact on solar cell and photodetection industries. One branch, multicomponent semiconductor nanocrystals, is of special interest. NCs offer the key advantages of bulk semiconductors, thermal stability, excellent absorbance across the solar spectrum, and a high density of states in the conduction band, while their nanoscale dimensions allow for a tuning of their bandgaps and easy solution processing of as-prepared nanoparticle colloids into thin film devices. The benefit of the multicomponent nanocrystals is the ability to tailor the spatial distribution of the carriers in one of two ways. By varying the coupled semiconductor materials, both carriers can reside on one side of the materials' junction (type-I heterostructure), or on opposite sides of it (type-II heterostructure). Here we report on a colloidal synthesis of PbSe/TiO2 heterostructures, comprising small-diameter PbSe nanocrystals epitaxially grown onto the surface of TiO2 nanorods, colloidal deposition of plasmatic-size gold tips onto semiconductor nanorods under ambient light, and a colloidal synthesis of a PbSxTe1-x semiconductor nanocrystals alloy.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Physics
Keywords: quantum dots; solar cell; photodetectors; nanorods; nanoscale semiconductors; nanocrystals; type II; photovoltaics
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25.
O'Connor, Timothy F. III.
Synthesis and Dynamics of Photocatalytic Type-II ZnSe/CdS/Pt Metal-Semiconductor Heteronanostructures.
Degree: MS, Physics, 2012, Bowling Green State University
► The following presents an analysis of the energetics of photocatalytic ZnSe/CdS/Pt metal-semiconductor…
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▼ The following presents an analysis of the energetics of photocatalytic ZnSe/CdS/Pt metal-semiconductor heteronanorods capable of performing a sustained H2 reduction reaction. The study begins with an investigation of the effects of charge carrier localization on the stability and efficiency of ZnSe/CdS/Pt. By switching the seed material of the dot-in-a-rod structure from ZnSe to ZnTe, the band edge alignment of the linear system can be altered from one that expels positive holes to the surface ligands of the structure to one that localizes holes in the semiconductor core, as is energetically favorable in the ZnTe seeded system. Positive holes that are not removed from the semiconductor domain are then available to oxidize the core, compromising the structure and photocatalyic capacity of the nanocrystal. In contrast, ZnSe seeded heteronanorods capable of removing chemically active holes pass this photodegradation on to the ligand moieties, destroying the inexpensive, organic surfactants rather than the nanostructure. Interestingly, it was found that fresh ligands can be reattached after the desorption of oxidized ligands, allowing for a larger turnover of photocatalytic cycles to be achieved. After studying the effects of band edge energetics, a deeper analysis of the ultrafast charge carrier dynamics was undertaken to determine the time scales at which the three dominant charge transfer processes, namely, electron transfer from CdS to Pt, hole localization within ZnSe, and the subsequent hole transfer to the surface ligand, occur. The photocatalytic reaction rate is theorized to be limited by the slowest charge transfer mechanism, which was determined to be the removal of the hole from the semiconductor core by employing femtosecond transient absorption spectroscopy. These time resolved spectroscopic measurements yield a more complete understanding of the energetic processes at work within the nanostructures and glean insight as to methods of making more efficient photocatalytic nanoreactors.
Advisors/Committee Members: Zamkov, Dr. Mikhail.
Subjects: Chemistry; Energy; Nanoscience; Nanotechnology; Physics
Keywords: nano, nanotechnology, nanoscience, catalysis, semiconductor, nanocrystal, heterostructure, ZnSe, CdS, Pt, photo, photocatalysis, metal-semiconductor, hybrid, nanostructure, charge carrier dynamics, transient absorption.
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26.
Paul, Jagannath.
MEASUREMENT OF THE THERMOELECTRIC FIGURE OF MERIT FOR A NOVEL MATERIAL – La0.8Fe3CoSb12.
Degree: MS, Physics, 2006, Bowling Green State University
► The proposed research is an investigation of the thermoelectric figure of merit…
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▼ The proposed research is an investigation of the thermoelectric figure of merit for the filled-skutterudite material–La0.8Fe3CoSb12. The samples, in the form of thin film, were prepared using Laser Ablation method where glass plates of dimension 0.5 mm thick were used as the substrate. At room temperature, the electrical resistance of the samples was measured under adiabatic and isothermal conditions using a custom built apparatus. The ratio of adiabatic electrical resistivity to the isothermal electrical resistivity has a simple relationship with the figure of merit. Using that relation, the figure of merit of the samples was determined from the obtained data at room temperature. The results of the resistance measurements showed that the material is a relatively poor conductor; that is, the electrical resistivity is high at room temperature. Measured adiabatic and the isothermal resistances of the samples and the obtained values for the thermoelectric FOM of the three samples of the material were not consistent at room temperature. Also, these values did not agree with the desired result for the material. Previous researches with different La-fractions of the material show ZT ~ 0.2 or above can be reached at room temperature and our method of investigation failed to reach that mark. In conclusion, the measured thermoelectric figure of merit for the material indicates that the material is a poor conductor of electrical current and good conductor of thermal current. In other words, the material is not a good candidate for the desired thermoelectric applications.
Advisors/Committee Members: Boughton, Robert I.
Subjects: Physics, Condensed Matter
Keywords: Thermoelectric Figure of Merit
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27.
Schmall, Nicholas Edward.
Fabrication of Binary Quantum Solids From Colloidal Semiconductor Quantum Dots.
Degree: MS, Physics, 2009, Bowling Green State University
► In this thesis I report on an attempted colloidal synthesis of heterostructured…
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▼ In this thesis I report on an attempted colloidal synthesis of heterostructured quantum solids comprising of a staggered heterojunction of nearly lattice matched cadmium sulfide and zinc selenide semiconductor quantum dots. I present compelling evidence of photoinduced charge separation between zinc selenide and cadmium sulfide domains, via absorption and photoluminescence spectra, but can not provide conclusive evidence via transmission electron microscopy of the merging of the quantum dots. Also in this thesis I report on a colloidal synthesis of lead selenide, titanium dioxide heterostructures, comprising of small diameter lead selenide nanocrystals, grown onto the surface of titanium dioxide nanorods. The deposition of lead sulfide on titanium dioxide proceeds via formation of sub-2 nm lead selenide islands that can be controllably grown to 5 nm by introducing secondary precursor injections. Evidence of the formation of lead selenide nanocrystal islands on the titanium dioxide rods was determined via the acquisition of transmission electron microscopy images that confirm the statistically distributed formation of lead selenide islands.
Advisors/Committee Members: Zamkov, Mikhail.
Subjects: Physics
Keywords: Quantum Dots; Nanocrystals; Cadmium Sulfide Quantum Dots; Zinc Selenide Quantum Dots; Titanium Dioxide Nanorods.
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28.
Smitka, Michael Thomas.
Analysis of the Halo Globular Cluster M30 and its Variable Stars.
Degree: MS, Physics, 2007, Bowling Green State University
► Photometry of the metal-poor globular cluster M30 is presented in B, V,…
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▼ Photometry of the metal-poor globular cluster M30 is presented in B, V, R and I bandpasses. A color-magnitude diagram created from this photometry indicates that accurate magnitude measurements were obtained for stars from the red giant branch down to approximately 2.5 magnitudes fainter than the main sequence turn-off. Time-series photometry is presented for six RR Lyrae type variable stars, three of which are newly discovered. Four variable stars of other types, three of them newly discovered, are also discussed. A metallicity of [Fe/H]=-2.02 was adopted for this study. Using the RR Lyrae stars' mean colors at minimum light, a reddening of E(B-V)=0.053+-0.010 was found for this cluster as well as an extinction value of Av=0.165+-0.031. A distance modulus of mu=14.504+-0.127 and the corresponding distance of 7.958+-0.147 kpc was also computed using the RR Lyrae stars' mean magnitudes. Isochrone fitting of the color-magnitude diagram yielded a cluster age of 15.8 +-1.8 Gyr.
Advisors/Committee Members: Layden, Andrew C.
Subjects: Physics, Astronomy and Astrophysics
Keywords: M30; NGC7099; RR Lyrae; photometry; light curve; color-magnitude diagram
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29.
Steele, Matthew.
Determining Oxygen Abundance vs. Age and Iron Abundance in Halo Field Dwarfs.
Degree: MS, Physics, 2005, Bowling Green State University
► A chemical abundance analysis of a sample of 18 galactic field dwarf…
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▼ A chemical abundance analysis of a sample of 18 galactic field dwarf stars was performed with Kurucz (1993) stellar atmosphere models under Local Thermodynamic Equilibrium (LTE) assumptions. The abundance determinations were made using measurements of the 7771 Å oxygen triplet, several α-element lines, and numerous Fe lines. This study presents an examination of oxygen and α-element abundances as a function of age and metallicity. The trend of increasing [O/Fe] and [α/Fe] with age predicted by the standard model of chemical evolution is not observed. This suggests type Ia supernovae may not contribute to chemical evolution over the formation time of the halo, possibly due to type Ia supernovae onset times significantly longer than current models suggest or a halo formation model involving chemically isolated fragments with short duration star formation events. The [O/Fe] vs. [Fe/H] breakpoint is determined to be located near [Fe/H] -1.3 (within ∼ 0.2 dex), midway between previously suggested values of -1.0 and -1.7 dex.
Advisors/Committee Members: Laird, John B.
Subjects: Physics, Astronomy and Astrophysics
Keywords: halo; oxygen; iron; age; [O/Fe]; field stars
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30.
Wang, Yang.
CdS Reflection Coefficient Determination via Photocurrent Spectroscopy.
Degree: MS, Physics, 2008, Bowling Green State University
► Reflectance is a very essential property of every semiconductor and the topic…
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▼ Reflectance is a very essential property of every semiconductor and the topic of this thesis was to determine the reflection coefficient of CdS by unusual means, i.e., be using photocurrent spectroscopy. Reflectance and photocurrent of the CdS sample and a silicon photodiode was measured using the lock-in amplifier. The photocurrent of the diode was required in order to correct the CdS photocurrent spectra, which are influenced by the experimental setup. By means of photocurrent, the absorption coefficient was determined using the density of states (DOS), Urbach rule, and the appropriate expression for the photocurrent. Measurement and the theory matched very well, and finally, using the absorption coefficient the dispersion of the CdS reflection was plotted.
Advisors/Committee Members: Ullrich, Bruno.
Subjects: Physics
Keywords: Photocurrent; CdS; lock-in amplifier; photodiode; Si photodiode; Reflectance
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