Atmospheric Pressure Chemical Ionization Sources Used in The Detection of Explosives by Ion Mobility Spectrometry (open access)

Atmospheric Pressure Chemical Ionization Sources Used in The Detection of Explosives by Ion Mobility Spectrometry

Melanie Waltman's dissertation to be presented on March 24, 2010.
Date: May 1, 2010
Creator: Waltman, Melanie J.
System: The UNT Digital Library
DualTrust: A Trust Management Model for Swarm-Based Autonomic Computing Systems (open access)

DualTrust: A Trust Management Model for Swarm-Based Autonomic Computing Systems

Trust management techniques must be adapted to the unique needs of the application architectures and problem domains to which they are applied. For autonomic computing systems that utilize mobile agents and ant colony algorithms for their sensor layer, certain characteristics of the mobile agent ant swarm -- their lightweight, ephemeral nature and indirect communication -- make this adaptation especially challenging. This thesis looks at the trust issues and opportunities in swarm-based autonomic computing systems and finds that by monitoring the trustworthiness of the autonomic managers rather than the swarming sensors, the trust management problem becomes much more scalable and still serves to protect the swarm. After analyzing the applicability of trust management research as it has been applied to architectures with similar characteristics, this thesis specifies the required characteristics for trust management mechanisms used to monitor the trustworthiness of entities in a swarm-based autonomic computing system and describes a trust model that meets these requirements.
Date: May 1, 2010
Creator: Maiden, Wendy M.
System: The UNT Digital Library
Measurement of the \textit{CP} Violating Phase $\boldsymbol{\sin(2\beta_{s})}$ using $\boldsymbol{B^{0}_{s}\rightarrow J/\psi\phi}$ Decays at CDF (open access)

Measurement of the \textit{CP} Violating Phase $\boldsymbol{\sin(2\beta_{s})}$ using $\boldsymbol{B^{0}_{s}\rightarrow J/\psi\phi}$ Decays at CDF

A B{sub s}{sup 0} meson can oscillate into its anti-particle, the {bar B}{sub s}{sup 0} meson, before decaying. CP violation in this system is made possible by the presence of amplitudes from both mixed and unmixed B{sub s}{sup 0} meson decays. The CP violating phase {beta}s appears in the interference between the decay amplitudes. The quantity sin(2{beta}s) is expected to be small in the standard model. Thus, measuring a large value for sin(2{beta}s) would be an unequivocal sign of new physics participation in the B{sub s}{sup 0} mixing loop diagram. In this thesis, we present a latest measurement of sin(2{beta}s), using 5.2 fb{sup -1} of data collected at CDF from p{bar p} collisions at a center of mass energy of {radical}s = 1.96 TeV. A time-dependent angular analysis, with the production flavor of the B{sub s}{sup 0} meson identified with flavor tagging methods, is used to extract sin(2{beta}s) from {approx}6500 B{sub s}{sup 0} {yields} J/{psi}{phi} decays. Other parameters of interest, such as the B{sub s}{sup 0} lifetime and the decay width difference {Delta}{Lambda} between the heavy and light B{sub s}{sup 0} mass eigenstates are determined to high precision. Also, the effect of potential contributions to the final state from B{sub …
Date: May 1, 2010
Creator: Pueschel, Elisa
System: The UNT Digital Library
Search for Supersymmetry Using Diphoton Events in p anti-p Collisions at a center of mass energy of 1.96-TeV (open access)

Search for Supersymmetry Using Diphoton Events in p anti-p Collisions at a center of mass energy of 1.96-TeV

This dissertation presents the results of a search for supersymmetry in proton-antiproton collisions with a center of mass energy of 1.96 TeV studied with the Collider Detector at Fermilab. Our strategy is to select collisions with two photons in the final state that have the properties of being the decays of very massive supersymmetric particles. This includes looking for large total energy from the decayed particles as well as for the presence of particles that leave the detector without interacting. We find no events using 2.6 fb{sup -1} of data collected during the 2004-2008 collider run of the Fermilab Tevatron which is consistent with the background estimate of 1.4 {+-} 0.4 events. Since there is no evidence of new particles we set cross section limits in a gauge-mediated supersymmetry model with {tilde {chi}}{sub 1}{sup 0} {yields} {gamma}{tilde G}, where the {tilde {chi}}{sub 1}{sup 0} and {tilde G} are the lightest neutralino and the gravitino (the lightest supersymmetric particle), respectively. We set limits on models as a function of the {tilde {chi}}{sub 1}{sup 0} mass and lifetime, producing the world's most sensitive search for {tilde {chi}}{sub 1}{sup 0} by excluding masses up to 149 GeV/c{sup 2} for {tilde {chi}}{sub 1}{sup 0} …
Date: May 1, 2010
Creator: Lee, Eun Sin & A-M, /Texas
System: The UNT Digital Library
Search for the Standard Model Higgs Boson associated with a W Boson using Matrix Element Technique in the CDF detector at the Tevatron (open access)

Search for the Standard Model Higgs Boson associated with a W Boson using Matrix Element Technique in the CDF detector at the Tevatron

In this thesis a direct search for the Standard Model Higgs boson production in association with a W boson at the CDF detector in the Tevatron is presented. This search contributes predominantly in the region of low mass Higgs region, when the mass of Higgs boson is less than about 135 GeV. The search is performed in a final state where the Higgs boson decays into two b quarks, and the W boson decays leptonically, to a charged lepton (it can be an electron or a muon) and a neutrino. This work is organized as follows. Chapter 2 gives an overview of the Standard Model theory of particle physics and presents the SM Higgs boson search results at LEP, and the Tevatron colliders, as well as the prospects for the SM Higgs boson searches at the LHC. The dataset used in this analysis corresponds to 4.8 fb<sup>-1</sup> of integrated luminosity of p$\bar{p}$ collisions at a center of mass energy of 1.96 TeV. That is the luminosity acquired between the beginning of the CDF Run II experiment, February 2002, and May 2009. The relevant aspects, for this analysis, of the Tevatron accelerator and the CDF detector are shown in Chapter 3. …
Date: May 1, 2010
Creator: Gonzalez, Barbara Alvarez
System: The UNT Digital Library
A search for the Standard Model Higgs boson in the process ZH → ℓ<sup>+</sup>ℓ<sup>-</sup>b$\bar{b}$ in  4.1 fb<sup>-1</sup> of CDF II data (open access)

A search for the Standard Model Higgs boson in the process ZH → ℓ<sup>+</sup>ℓ<sup>-</sup>b$\bar{b}$ in 4.1 fb<sup>-1</sup> of CDF II data

The standard model of particle physics provides a detailed description of a universe in which all matter is composed of a small number of fundamental particles, which interact through the exchange of force - carrying gauge bosons (the photon, W <sup>±</sup>, Z and gluons). The organization of the matter and energy in this universe is determined by the effects of three forces; the strong, weak, and electromagnetic. The weak and electromagnetic forces are the low energy manifestations of a single electro-weak force, while the strong force binds quarks into protons and neutrons. The standard model does not include gravity, as the effect of this force on fundamental particles is negligible. Four decades of experimental tests, spanning energies from a few electron-volts (eV) up to nearly two TeV, confirm that the universe described by the standard model is a reasonable approximation of our world. For example, experiments have confirmed the existence of the top quark, the W<sup>±</sup> and the Z bosons, as predicted by the standard model. The latest experimental averages for the masses of the top quark, W<sup>±</sup> and Z are respectively 173.1 ± 0.6(stat.) ± 1.1(syst.), 80.399 ± 0.023 and 91.1876 ± 0.0021 GeV/c<sup>2</sup>. The SM is a gauge …
Date: May 1, 2010
Creator: Shalhout, Shalhout Zaki
System: The UNT Digital Library
Using Quasi-Elastic Events to Measure Neutrino Oscillations with MINOS Detectors in the NuMI Neutrino Beam (open access)

Using Quasi-Elastic Events to Measure Neutrino Oscillations with MINOS Detectors in the NuMI Neutrino Beam

MINOS (Main Injector Neutrino Oscillation Search) experiment has been designed to search for a change in the flavor composition of a beam of muon neutrinos as they travel between the Near Detector at Fermi National Accelerator Laboratory and the Far Detector in the Soudan mine in Minnesota, 735 km from the target. The MINOS oscillation analysis is mainly performed with the charged current (CC) events and sensitive to constrain high-{Delta}m{sup 2} values. However, the quasi-elastic (QEL) charged current interaction is dominant in the energy region important to access low-{Delta}m{sup 2} values. For further improvement, the QEL oscillation analysis is performed in this dissertation. A data sample based on a total of 2.50 x 10{sup 20} POT is used for this analysis. In summary, 55 QEL-like events are observed at the Far detector while 87.06 {+-} 13.17 (syst.) events are expected with null oscillation hypothesis. These data are consistent with {nu}{sub {mu}} disappearance via oscillation with {Delta}m{sup 2} = 2.10 {+-} 0.37 (stat.) {+-} 0.24 (syst.) eV{sup 2} and the maximal mixing angle.
Date: May 1, 2010
Creator: Watabe, Masaki & University, /Texas A&M
System: The UNT Digital Library
Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission (open access)

Watching Electrons Transfer from Metals to Insulators using Two Photon Photoemission

Ultrafast angle-resolved two photon photoemission was used to study the dynamics and interfacial band structure of ultrathin films adsorbed onto Ag(111). Studies focused on the image potential state (IPS) in each system as a probe for measuring changes in electronic behavior in differing environments. The energetics and dynamics of the IPS at the toluene/Ag(111) interface are strongly dependent upon coverage. For a single monolayer, the first IPS is bound by 0.81 eV below the vacuum level and has a lifetime of 50 femtoseconds (fs). Further adsorption of toluene creates islands of toluene with an exposed wetting layer underneath. The IPS is then split into two peaks, one corresponding to the islands and one corresponding to the monolayer. The wetting layer IPS shows the same dynamics as the monolayer, while the lifetime of the islands increases exponentially with increasing thickness. Furthermore, the island IPS transitions from delocalized to localized within 500 fs, and electrons with larger parallel momenta decay much faster. Attempts were made using a stochastic model to extract the rates of localization and intraband cooling at differing momenta. In sexithiophene (6T) and dihexyl-sexithiophene (DH6T), the IPS was used as a probe to see if the nuclear motion of spectating …
Date: May 1, 2010
Creator: Johns, James E.
System: The UNT Digital Library
Measurement of branching fraction ratios and CP asymmetries in B &#8594D0 CPK decays with the BABAR detector (open access)

Measurement of branching fraction ratios and CP asymmetries in B &#8594D0 CPK decays with the BABAR detector

The primary goals of the BABAR experiment are the detection of CP violation (CPV) in the B meson system, the precise measurement of some of the elements of the CKM matrix and the measurement of the rates of rare B meson decays. At present, BABAR has achieved major successes: (1) the discovery, in neutral B decays, of direct and mixing-induced CP violation; (2) accurate measurements of the magnitudes of the CKM matrix elements |V{sub cb}| and |V{sub ub}|; (3) a precise measurement of the CKM parameter {beta} {triple_bond} arg[- V{sub cd}V*{sub cb}/V{sub td}V*{sub tb}]; (4) a first measurement of the CKM parameters {alpha} {triple_bond} arg[- V{sub td}V*{sub tb}/V{sub ud}V*{sub ub}], {gamma} {triple_bond} arg[- V{sub ud}V*{sub ub}/V{sub cd}V*{sub cb}]; and (5) the observation of several rare B decays and the discovery of new particles (in the charmed and charmonium mesons spectroscopy). However, the physics program of BABAR is not yet complete. Two of the key elements of this program that still need to be achieved are: (1) the observation of direct CP violation in charged B decays, which would constitute the first evidence of direct CPV in a charged meson decay; and (2) the precise measurement of {alpha} and {gamma}, which …
Date: May 5, 2010
Creator: Marchiori, Giovanni & U., /Pisa
System: The UNT Digital Library
Immersed Boundary Methods for High-Resolution Simulation of Atmospheric Boundary-Layer Flow Over Complex Terrain (open access)

Immersed Boundary Methods for High-Resolution Simulation of Atmospheric Boundary-Layer Flow Over Complex Terrain

None
Date: May 12, 2010
Creator: Lundquist, K A
System: The UNT Digital Library
Design and Synthesis of Mixed Oxides Nanoparticles for Biofuel Applications (open access)

Design and Synthesis of Mixed Oxides Nanoparticles for Biofuel Applications

The work in this dissertation presents the synthesis of two mixed metal oxides for biofuel applications and NMR characterization of silica materials. In the chapter 2, high catalytic efficiency of calcium silicate is synthesized for transesterfication of soybean oil to biodisels. Chapter 3 describes the synthesis of a new Rh based catalyst on mesoporous manganese oxides. The new catalyst is found to have higher activity and selectivity towards ethanol. Chapter 4 demonstrates the applications of solid-state Si NMR in the silica materials.
Date: May 15, 2010
Creator: Chen, Senniang
System: The UNT Digital Library
Search for the Production of Gluinos and Squarks with the CDF II Experiment at the Tevatron Collider (open access)

Search for the Production of Gluinos and Squarks with the CDF II Experiment at the Tevatron Collider

This thesis reports on two searches for the production of squarks and gluinos, supersymmetric partners of the Standard Model (SM) quarks and gluons, using the CDF detector at the Tevatron √s = 1.96 TeV p$\bar{p}$ collider. An inclusive search for squarks and gluinos pair production is performed in events with large E<sub>T</sub> and multiple jets in the final state, based on 2 fb<sup>-1</sup> of CDF Run II data. The analysis is performed within the framework of minimal supergravity (mSUGRA) and assumes R-parity conservation where sparticles are produced in pairs. The expected signal is characterized by the production of multiple jets of hadrons from the cascade decays of squarks and gluinos and large missing transverse energy E<sub>T</sub> from the lightest supersymmetric particles (LSP). The measurements are in good agreement with SM predictions for backgrounds. The results are translated into 95% confidence level (CL) upper limits on production cross sections and squark and gluino masses in a given mSUGRA scenario. An upper limit on the production cross section is placed in the range between 1 pb and 0.1 pb, depending on the gluino and squark masses considered. The result of the search is negative for gluino and squark masses up to 392 …
Date: May 19, 2010
Creator: De Lorenzo, Gianluca
System: The UNT Digital Library
Search for lepton flavor violating decay τ<sup>-</sup> →ℓ<sup>-</sup>ℓ<sup>+</sup>ℓ<sup>-</sup>ℓ = e, μ at BaBar (open access)

Search for lepton flavor violating decay τ<sup>-</sup> →ℓ<sup>-</sup>ℓ<sup>+</sup>ℓ<sup>-</sup>ℓ = e, μ at BaBar

The Standard Model (SM) is one of the most tested and verified physical theories of all time, present experimental observations are consistent with SM expectations. On the other hand SM can not explain many physical observations: the cosmological observations possibly infer the presence of dark matter which is clearly beyond the SM expectations; the SM Higgs model, while explaining the generation of fermion masses, can not explain the hierarchy problem and a non natural fine tuning of SM is needed to cancel out quadratic divergences in the Higgs boson mass. New physics (NP) beyond SM should hence be investigated: rising the energy above NP processes thresholds, and detecting new particles or new effects not predicted by the standard model directly, is one of the possible approaches; another approach is to make precision measurements of well known processes or looking for rare processes which involve higher order contribution from NP processes, this approach need higher luminosities with respect to the previous approach but lower beam energies. Search for Lepton Flavor Violation (LFV) in charged lepton decays is promising: neutrino physics provides indeed a clear and unambiguous evidence of LFV in the neutral lepton sector via mixing processes, which have been observed …
Date: May 26, 2010
Creator: Cervelli, Alberto
System: The UNT Digital Library
Antineutrino Oscillations in the Atmospheric Sector (open access)

Antineutrino Oscillations in the Atmospheric Sector

This thesis presents measurements of the oscillations of muon antineutrinos in the atmospheric sector, where world knowledge of antineutrino oscillations lags well behind the knowledge of neutrinos, as well as a search for {nu}{sub {mu}} {yields} {bar {nu}}{sub {mu}} transitions. Differences between neutrino and antineutrino oscillations could be a sign of physics beyond the Standard Model, including non-standard matter interactions or the violation of CPT symmetry. These measurements leverage the sign-selecting capabilities of the magnetized steel-scintillator MINOS detectors to analyze antineutrinos from the NuMI beam, both when it is in neutrino-mode and when it is in antineutrino-mode. Antineutrino oscillations are observed at |{Delta}{bar m}{sub atm}{sup 2}| = (3.36{sub -0.40}{sup +0.46}(stat) {+-} 0.06(syst)) x 10{sup -3} eV{sup 2} and sin{sup 2}(2{bar {theta}}{sub 23}) = 0.860{sub -0.12}{sup +0.11}(stat) {+-} 0.01(syst). The oscillation parameters measured for antineutrinos and those measured by MINOS for neutrinos differ by a large enough margin that the chance of obtaining two values as discrepant as those observed is only 2%, assuming the two measurements arise from the same underlying mechanism, with the same parameter values. No evidence is seen for neutrino-to-antineutrino transitions.
Date: May 1, 2011
Creator: Himmel, Alexander I. & /Caltech
System: The UNT Digital Library
Measurement of low $p_{T}$ $D^{0}$ meson production cross section at CDF II. (open access)

Measurement of low $p_{T}$ $D^{0}$ meson production cross section at CDF II.

In this thesis we present a study of the production of D{sup 0} meson in the low transverse momentum region. In particular the inclusive differential production cross section of the D{sup 0} meson (in the two-body decay channel D{sup 0} {yields} K{sup -}{pi}{sup +}) is obtained extending the published CDF II measurement to p{sub T} as low as 1.5 GeV/c. This study is performed at the Tevatron Collider at Fermilab with the CDF II detector.
Date: May 1, 2011
Creator: Mussini, Manuel & U., /Bologna
System: The UNT Digital Library
A Search for the Standard Model Higgs Boson Produced in Association with a $W$ Boson (open access)

A Search for the Standard Model Higgs Boson Produced in Association with a $W$ Boson

We present a search for a standard model Higgs boson produced in association with a W boson using data collected with the CDF II detector from p{bar p} collisions at {radical}s = 1.96 TeV. The search is performed in the WH {yields} {ell}{nu}b{bar b} channel. The two quarks usually fragment into two jets, but sometimes a third jet can be produced via gluon radiation, so we have increased the standard two-jet sample by including events that contain three jets. We reconstruct the Higgs boson using two or three jets depending on the kinematics of the event. We find an improvement in our search sensitivity using the larger sample together with this multijet reconstruction technique. Our data show no evidence of a Higgs boson, so we set 95% confidence level upper limits on the WH production rate. We set limits between 3.36 and 28.7 times the standard model prediction for Higgs boson masses ranging from 100 to 150 GeV/c{sup 2}.
Date: May 1, 2011
Creator: Frank, Martin Johannes & U., /Baylor
System: The UNT Digital Library
MicroCantilever (MC) based nanomechanical sensor for detection of molecular interactions (open access)

MicroCantilever (MC) based nanomechanical sensor for detection of molecular interactions

Specific aims of this study are to investigate the mechanism governing surface stress generation associated with chemical or molecular binding on functionalized microcantilevers. Formation of affinity complexes on cantilever surfaces leads to charge redistribution, configurational change and steric hindrance between neighboring molecules resulting in surface stress change and measureable cantilever deformation. A novel interferometry technique employing two adjacent micromachined cantilevers (a sensing/reference pair) was utilized to measure the cantilever deformation. The sensing principle is that binding/reaction of specific chemical or biological species on the sensing cantilever transduces to mechanical deformation. The differential bending of the sensing cantilever respect to the reference cantilever ensures that measured response is insensitive to environmental disturbances. As a proof of principle for the measurement technique, surface stress changes associated with: self-assembly of alkanethiol, hybridization of ssDNA, and the formation of cocaine-aptamer complexes were measured. Dissociation constant (K{sub d}) for each molecular reaction was utilized to estimate the surface coverage of affinity complexes. In the cases of DNA hybridization and cocaine-aptamer binding, measured surface stress was found to be dependent on the surface coverage of the affinity complexes. In order to achieve a better sensitivity for DNA hybridization, immobilization of receptor molecules was modified to enhance …
Date: May 11, 2011
Creator: Kang, Kyung
System: The UNT Digital Library
Mesoporous silica nanoparticles as smart and safe devices for regulating blood biomolecule levels (open access)

Mesoporous silica nanoparticles as smart and safe devices for regulating blood biomolecule levels

Stimuli-responsive end-capped MSN materials are promising drug carriers that securely deliver a large payload of drug molecules without degradation or premature release. A general review of the recent progress in this field is presented, including a summary of a series of hard and soft caps for drug encapsulation and a variety of internal and external stimuli for controlled release of different therapeutics, a discussion of the biocompatibility of MSN both in vitro and in vivo, and a description of the sophisticated stimuli-responsive systems with novel capping agents and controlled release mechanism. The unique internal and external surfaces of MSN were utilized for the development of a glucose-responsive double delivery system end-capped with insulin. This unique system consists of functionalized MSNs capable of releasing insulin when the concentration of sugar in blood exceeds healthy levels. The insulin-free nanoparticles are then up taken by pancreatic cells, and release inside of them another biomolecule that stimulates the production of more insulin. The in vivo application of this system for the treatment of diabetes requires further understanding on the biological behaviors of these nanoparticles in blood vessels. The research presented in this dissertation demonstrated the size and surface effects on the interaction of MSNs …
Date: May 15, 2011
Creator: Zhao, Yan
System: The UNT Digital Library
Mesoporous silica nanoparticles for biomedical and catalytical applications (open access)

Mesoporous silica nanoparticles for biomedical and catalytical applications

Mesoporous silica materials, discovered in 1992 by the Mobile Oil Corporation, have received considerable attention in the chemical industry due to their superior textual properties such as high surface area, large pore volume, tunable pore diameter, and narrow pore size distribution. Among those materials, MCM-41, referred to Mobile Composition of Matter NO. 41, contains honeycomb liked porous structure that is the most common mesoporous molecular sieve studied. Applications of MCM-41 type mesoporous silica material in biomedical field as well as catalytical field have been developed and discussed in this thesis. The unique features of mesoporous silica nanoparticles were utilized for the design of delivery system for multiple biomolecules as described in chapter 2. We loaded luciferin into the hexagonal channels of MSN and capped the pore ends with gold nanoparticles to prevent premature release. Luciferase was adsorbed onto the outer surface of the MSN. Both the MSN and the gold nanoparticles were protected by poly-ethylene glycol to minimize nonspecific interaction of luciferase and keep it from denaturating. Controlled release of luciferin was triggered within the cells and the enzymatic reaction was detected by a luminometer. Further developments by varying enzyme/substrate pairs may provide opportunities to control cell behavior and manipulate …
Date: May 15, 2011
Creator: Sun, Xiaoxing
System: The UNT Digital Library
Self-assembled pentablock copolymers for selective and sustained gene delivery (open access)

Self-assembled pentablock copolymers for selective and sustained gene delivery

The poly(diethylaminoethyl methacrylate) (PDEAEM) - Pluronic F127 - PDEAEM pentablock copolymer (PB) gene delivery vector system has been found to possess an inherent selectivity in transfecting cancer cells over non-cancer cells in vitro, without attaching any targeting ligands. In order to understand the mechanism of this selective transfection, three possible intracellular barriers to transfection were investigated in both cancer and non-cancer cells. We concluded that escape from the endocytic pathway served as the primary intracellular barrier for PB-mediated transfection. Most likely, PB vectors were entrapped and rendered non-functional in acidic lysosomes of non-cancer cells, but survived in less acidic lysosomes of cancer cells. The work highlights the importance of identifying intracellular barriers for different gene delivery systems and provides a new paradigm for designing targeting vectors based on intracellular differences between cell types, rather than through the use of targeting ligands. The PB vector was further developed to simultaneously deliver anticancer drugs and genes, which showed a synergistic effect demonstrated by significantly enhanced gene expression in vitro. Due to the thermosensitive gelation behavior, the PB vector packaging both drug and gene was also investigated for its in vitro sustained release properties by using polyethylene glycol diacrylate as a barrier gel …
Date: May 15, 2011
Creator: Zhang, Bingqi
System: The UNT Digital Library
Studies of the structure and function of Mms6, a bacterial protein that promotes the formation of magnetic nanoparticles (open access)

Studies of the structure and function of Mms6, a bacterial protein that promotes the formation of magnetic nanoparticles

Here we report structural and functional studies of Mms6, a biomineralization protein that can promote the formation in vitro of magnetic nanoparticles with sizes and morphologies similar to the magnetites synthesized by magnetotactic bacteria. We found the binding pattern of Mms6 to ferric ion to be two-phase and multivalent. We quantatively determined that Mms6 binds one Fe{sup 3+} with a very high affinity (K{sub d} = 10{sup -16} M). The second phase of iron binding is multivalent and cooperative with respect to iron with a K{sub d} in the {mu}M range and a stoichiometry of about 20 ferric ion per protein molecule. We found that Mms6 exists in large particles of two sizes, one consisting of 20-40 monomeric units and the other of 200 units. From proteolytic digestion, ultracentrifugation and liposome fusion studies, we found that Mms6 forms a large micellar quaternary structure with the N-terminal domain self-assembling into a uniformly sized micelle and the C-terminal domain on the surface. The two-phase iron-binding pattern may be relevant to iron crystal formation. We propose that the first high affinity phase may stabilize a new conformation of the C-terminal domain that allows interaction with other C-terminal domains leading to a structural change …
Date: May 15, 2011
Creator: Wang, Lijun
System: The UNT Digital Library
The theoretical study of passive and active optical devices via planewave based transfer (scattering) matrix method and other approaches (open access)

The theoretical study of passive and active optical devices via planewave based transfer (scattering) matrix method and other approaches

In this thesis, we theoretically study the electromagnetic wave propagation in several passive and active optical components and devices including 2-D photonic crystals, straight and curved waveguides, organic light emitting diodes (OLEDs), and etc. Several optical designs are also presented like organic photovoltaic (OPV) cells and solar concentrators. The first part of the thesis focuses on theoretical investigation. First, the plane-wave-based transfer (scattering) matrix method (TMM) is briefly described with a short review of photonic crystals and other numerical methods to study them (Chapter 1 and 2). Next TMM, the numerical method itself is investigated in details and developed in advance to deal with more complex optical systems. In chapter 3, TMM is extended in curvilinear coordinates to study curved nanoribbon waveguides. The problem of a curved structure is transformed into an equivalent one of a straight structure with spatially dependent tensors of dielectric constant and magnetic permeability. In chapter 4, a new set of localized basis orbitals are introduced to locally represent electromagnetic field in photonic crystals as alternative to planewave basis. The second part of the thesis focuses on the design of optical devices. First, two examples of TMM applications are given. The first example is the design …
Date: May 15, 2011
Creator: Zhuo, Ye
System: The UNT Digital Library
Optimization of Operating Parameters for Minimum Mechanical Specific Energy in Drilling (open access)

Optimization of Operating Parameters for Minimum Mechanical Specific Energy in Drilling

Efficiency in drilling is measured by Mechanical Specific Energy (MSE). MSE is the measure of the amount of energy input required to remove a unit volume of rock, expressed in units of energy input divided by volume removed. It can be expressed mathematically in terms of controllable parameters; Weight on Bit, Torque, Rate of Penetration, and RPM. It is well documented that minimizing MSE by optimizing controllable factors results in maximum Rate of Penetration. Current methods for computing MSE make it possible to minimize MSE in the field only through a trial-and-error process. This work makes it possible to compute the optimum drilling parameters that result in minimum MSE. The parameters that have been traditionally used to compute MSE are interdependent. Mathematical relationships between the parameters were established, and the conventional MSE equation was rewritten in terms of a single parameter, Weight on Bit, establishing a form that can be minimized mathematically. Once the optimum Weight on Bit was determined, the interdependent relationship that Weight on Bit has with Torque and Penetration per Revolution was used to determine optimum values for those parameters for a given drilling situation. The improved method was validated through laboratory experimentation and analysis of published …
Date: May 25, 2011
Creator: Hamrick, Todd
System: The UNT Digital Library
Compensation Techniques in Accelerator Physics (open access)

Compensation Techniques in Accelerator Physics

Accelerator physics is one of the most diverse multidisciplinary fields of physics, wherein the dynamics of particle beams is studied. It takes more than the understanding of basic electromagnetic interactions to be able to predict the beam dynamics, and to be able to develop new techniques to produce, maintain, and deliver high quality beams for different applications. In this work, some basic theory regarding particle beam dynamics in accelerators will be presented. This basic theory, along with applying state of the art techniques in beam dynamics will be used in this dissertation to study and solve accelerator physics problems. Two problems involving compensation are studied in the context of the MEIC (Medium Energy Electron Ion Collider) project at Jefferson Laboratory. Several chromaticity (the energy dependence of the particle tune) compensation methods are evaluated numerically and deployed in a figure eight ring designed for the electrons in the collider. Furthermore, transverse coupling optics have been developed to compensate the coupling introduced by the spin rotators in the MEIC electron ring design.
Date: May 31, 2011
Creator: Sayed, Hisham Kamal
System: The UNT Digital Library