Rice University Theses and Dissertations

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Rice University makes all graduate theses and dissertations (1916-present) available online at no cost to end users. Occasionally a thesis or dissertation may be be missing from the repository. If you are unable to find a specific dissertation, please let us know and we will attempt to make it available through the repository, provided that the author has not elected for it to be embargoed.

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1, 4-Dioxane biodegradation at low temperatures in Arctic groundwater samples
(2010) Li, Mengyan; Alvarez, Pedro J.
1,4-Dioxane is an emerging groundwater contaminant and a probable human carcinogen. Its biodegradation was investigated in microcosms prepared with groundwater and soil from an impacted site in Alaska. In addition to natural attenuation conditions (i.e., no amendments), the following treatments were tested: (a) biostimulation by addition of 1-butanol (a readily available auxiliary substrate) and inorganic nutrients; and (b) bioaugmentation with Pseudonocardia dioxanivorans CB1190, a well-characterized dioxane degrading bacterium, or with Pseudonocardia antarctica DVS 5a1, a bacterium isolated from Antarctica. Biostimulation enhanced the degradation of 50 mg L-1 dioxane by indigenous microorganisms (about 0.01 mg dioxane d-1 mg protein-1) at both 4 and 14°C, with a simultaneous increase in biomass. A more pronounced enhancement was observed through bioaugmentation. Microcosms with 50 mg L -1 initial dioxane (representing source zone contamination) and augmented with CB1190 degraded dioxane fastest (0.155 +/- 0.038 mg dioxane d-1 mg protein-1) at 14°C, and the degradation rate decreased dramatically at 4°C (0.021 +/- 0.007 mg dioxane d-1 mg protein-1). In contrast, microcosms with DVS 5a1 degraded dioxane at similar rates at 4 and 14°C (0.018 +/- 0.004 and 0.015 +/- 0.006 mg dioxane d-1 mg protein-1, respectively). DVS 5a1 outperformed CB1190 when the initial dioxane concentration was low (500 microg L-1). This indicates differences in competitive advantages of these two strains. Natural attenuation microcosms also showed significant degradation over 6 months when the initial dioxane concentration was 500 microg L-1. This is the first study to report the potential for dioxane bioremediation and natural attenuation of contaminated groundwater in sensitive cold-weather ecosystems such as the Arctic.
1. A new species of Oxysomatium (Nematoda) with some remarks on the genera Oxysomatium and Aplectana, and observations on the life history. 2. A description of a trichopterous larva belonging to the genus Rhyacophila
(1930) Harwood, Paul Duane
1. Strain and diamagnetic susceptibility. 2. The mobility of positive ions in flames
(1931) Banta, Henry Eugene; Wilson, H. A.; Heaps, C. W.
STRAIN AND DIAMAGNETIC SUSCEPTIBILITY --ABSTRACT-- The magnetic susceptibility of copper and, silver wires has been measured by the Gouy method before and after various annealing processes. Also, the susceptibility has been measured before and after straining specimens beyond the elastic limit, the strains being either twists or stretches. The susceptibilities are found to he increased , by as much as 20 percent for copper and 3 percent for silver by annealing at red heat for 15 minutes in an atmosphere of CO2. This increase is probably due to release of occluded gases or to oxidation or recombination of impurities. Straining the specimens beyond the elastic limit is found to produce no measurable change of susceptibility. Francis Bitter has observed a large effect due to straining these metals beyond the elastic limit. The reason for Bitter's results is not clear, but it is pointed out that no effect is to be expected in copper, at least, because crystals of this metal are isotropic magnetically and have no observable magnetostriction. THE MOBILITY OF POSITIVE IONS IN FLAMES --ABSTRACT-- The mobility was calculated from measured values of the current density, cathode drop of potential, and the thickness of the layer at the cathode in which the potential varies rapidly. The excess of ionization over recombination in the layer was assumed to be proportional to (1—x/x0m, where x is the distance from the cathode, xi the thickness of the layer at the cathode, and m is a constant. J. J. Thomson supposed that in =0, and P. E. Boucher took in = 1. The value calculated for the mobility depends on the value assumed for m. The results give, with m 2 , a value of 1.8; with m = 3, a value of 1.07 cm/sec. per volt/cm for the mobility. It is found that the mobility is the same for salts of Rb, Cs, and K, and that it does not depend on the concentration of the salt. A small increase of mobility with electric intensity is indicated by the results.
1.7-mev anomaly in Be_
(1961) Bronson, Jeff Donaldson; Phillips, Gerald C.
100-microsecond-resolved exafs technique for studying photolyzed hemoproteins
(1984) Teng, Tsu-Yi; Huang, Huey W.; Rorschach, Harold E.; Mutchler, Gordon S.
This thesis describes a 1-jus-resolved extended x-ray absorption fine structre (EXAFS) technique for studying protein dynamics. Both the time-resolved EXAFS spectrometer and the protein samples are described in detail. About ten years ago synchrotron radiation from electron storage rings began to be used for research in condensed matter. As a result a new technique for studying local structures in non-crystalline system was developed i.e. the extended x-ray absorption fine structure. This technique has now become an important tool for the structural studies of biological systems, particularly metalloproteins. In recent years the development of wiggler and undulator magnets has increased the radiation intensity to a level that, according to photon statistics, it should be possible to measure the EXAFS of hemoproteins in their transient states. Such measurements would provide structural insight to the very difficult but important problem of protein dynamics. However the conventional method of EXAFS measurement is inefficient for time-resolved measurement. We have developed a new spectrometer to take full advantage of the intense radiation. The time resolution of our spectrometer is about 1 us; below that the measurement time would be too long. Myoglobin was chosen as our sample for its importance in protein biophysics. The complex of myoglobin and carbon monoxide (CO) can be dissociated by light (flash photolysis). Its recombination time ranges from microseconds to infinity depending on temperature. The time resolved EXAFS measurement of photolyzed carboxymyoglobin will reveal the structural changes of protein around the CO binding site during the recombination process. We made our sample in the form of a thin film so that it can meet different requirments of x-ray absorption and optical photolysis. A special procedure of sample making was developed, and a transient optical absorption spectrometer was built for testing the samples. All optical absorption properties of our samples are in agreement with known results. An actual time-resolved EXAFS experiment was performed in February, 1983. The result showed no change in EXAFS with time. This might be due to a failure in photolysis (we lacked an on-line transient optical absorption spectrometer). However, these results demonstrated the feasibility and reliability of our spectrometer.
14-18 MeV total neutron cross sections of hydrogen atom, hydrogen, lithium-7, beryllium-9, boron-10, boron-11, carbon-12, carbon-16, magnesium, aluminum-27, and sulfur-32
(1953) Cook, Charles Falk
Measurements of total neutron cross sections for nuclei using fast neutrons of various energies have been previously reported. Several of these used neutrons which were not monoenergetic. However, with the advent of monoenergetic neutrons from the reaction T(d,n)He4, investigations have been reported giving total neutron cross sections at 14 Mev using monoenergetic neutrons in "good" geometry to various accuracies. Of these various reports, the data of Coon, Graves, and Barschall point to deviations from the schematic theory of nuclear cross sections proposed by Feshbach and Weisskopf for the lighter elements as well as some of the heavier elements. A systematic deviation from a plot of the equation sT2p =kA13 sT= total neutron cross section A= atomic weight was observed for the elements Be9, B10, B11, and C12. For these four elements the cross section was observed to be a decreasing function of the atomic weight. This effect is consistent with the data of Lasday and Goodman for Be9 and C12. Neither of the latter did the boron isotopes. The data of Lasday and Goodman also represents 14 Mev total neutron cross sections. Of these investigations, no one group carried out cross section measurements at more than one particular neutron energy. It is of interest to see over what energy range these systematic deviations appear. The results of Cook, et al., show that at 90 Mev the total neutron cross section for H, D, L1 7, Be9, C12 are increasing with atomic weight. This indicates that at some point in the energy range 14 to 90 Mev these deviations disappear. The investigations carried out here are measurements of total neutron cross sections for some of the light elements over the energy range 14 to 18 Mev. In addition to checking for a systematic deviation similar to that found by Coon, et al., considerable attention was given to determination of the neutron-proton total cross section over the above energy range.
1D and 2D Methods for Modeling Floodplains under Storm Surge Conditions
(2011) Stepinski, Emilia; Bedient, Philip B.
This study evaluates a 1D and a 2D method for analyzing the combined effect of inland rainfall and hurricane-induced storm surge on a coastal floodplain. Horsepen Bayou near Clear Lake, southeast of Houston, Texas is vulnerable to storm surge, which can travel upstream into the Bayou and exacerbate flooding outside the designated floodplain. However, the current 100-year floodplain for this area is delineated using a 1D model without direct storm surge inputs. Additionally, floodplains with flat topography, like Horsepen, could be modeled more accurately using 2D models, instead of the traditional 1D approach. A 1D HEC-RAS model and a 2D XPSWMM model are used to compare the resulting floodplain from three historical storms and one synthetic storm. When compared to actual FEMA flood claims, the floodplains calculated by the 2D model are more representative of inundation hazard in Horsepen and therefore a better tool for evaluating flooding in the area.
1T-TaS2 for Nonlinear Applications in Optical Neural Networks
(2020-04-17) Wang, Yuning; Naik, Gururaj
Artificial neural networks (ANNs) are a set of algorithms which can realize many different functions, such as patterns recognition, classification and prediction. ANNs has become a well-worthy field of study in multiple industries over the past years. Much effort has been contributed to this area and it turns back with significant values in terms of commerce as well as research. However, nowadays most of the ANNs are completed based on electronic hardware, which have some natural limitations such as computation speed and energy cost. Optical neural networks (ONNs) use photons, instead of electrons to transport and compute information. ONNs can easily realize linear computation just by the interference effect of lights and directly use optical nonlinear behavior to realize the nonlinear computation. Besides, ONNs own faster speed and lower energy cost compared with electronic ANNs. However, most of the ONNs are still in the developing stage and the nonlinear activation function has not been applied to real word application. Although there exist some optical nonlinear phenomena, currently the nonliearities are either too small or too slow. Besides, it is very hard to change the optical properties at room temperature with small stimulus, which limits the application of nonlinear applications. Since most of the existing devices requests strict restrictions, researchers keep exploring new materials for better efficiency and lower cost. Here, we propose 1T-TaS2, a strongly correlated material for nonlinear behavior. The optical properties of this material are very sensitive to the external stimulus, and the response speed of this material is very fast, reaching to nano seconds, which make these materials promising in nonlinear applications in ONNs. 1T-TaS2 is one kind of the Transition Metal Dichalcogenides (TMDs). TMDs are one of the strongly correlated materials involving abundant phases, such as distorted phase, metallic phase, insulating phase, charge density wave (CDW) phase, superconducting phase and topological phase. Due to these different phases, TMDs exhibit possibilities for optical tunabilities. More attractively, 1T-TaS2 shows nearly commensurate charge density wave (NCCDWs) at room temperature, which means that its nonequilibrium states can be tuned under stimulus in a relatively easy way. In this thesis, we show that the refractive index of 1T-TaS2 can be tuned under white light excitation with intensity from 2.5 mW/cm2 to 250 mW/cm2. We also find that this tunability comes from the out-of-plane, not the in-plane, stacking difference of the material. By implementing this tunability, we design three nanophotonic nonlinear devices: reflection-tunable, transmission-tunable and angle-tunable nonlinear device. By changing the parameters of the device structures dynamically, we collect, analyze and summarize the simulation results to finalize the implementation of the most efficient devices that are meeting the expectations. And we find that by giving a specific structure, the optical limiter can offer more than 10% reflection or transmission difference under different incident light intensity. The grating device could have a significant difference on the diffraction angles with a value of 6 degree under different incident light intensities.
1T-TaS2: A new tunable optical materials platform for nanophotonics application
(2022-03-08) Li, Weijian; Naik, Gururaj V.
Many body solid-state systems have attracted increasing interest due to their diverse quantum phases and novel physical properties. Such unusual properties allow people to overcome the limitations caused by materials in many nanophotonics applications such as sensing, imaging, virtual reality, optical computing, etc. To date, many new material platforms have been proposed, improving the performance of nanophotonics devices. In this dissertation, I will demonstrate the limitation of the development of nanophotonics, and show the possible revolution raised from a two-dimensional strongly correlated material, 1T-TaS2, one of the many-body solid-state systems which exhibit quantum charge-density-wave (CDW) phases over a large temperature range. First, I will discuss the physics understanding of strongly correlated materials and charge density wave quantum phase. Next, I will present the optical characterization of 1T-TaS2 in its CDW phases under external stimuli, including light, temperature, and in-plane bias. This material exhibits a unitary order change of refractive index under white light illumination, and MHz switching speed at room temperature. Furthermore, I will propose a physics model to understand the mechanism of such tunability. Nevertheless, the tunable optical properties of 1T-TaS2 can be implemented in tunable nanophotonics applications. I will show the theoretical demonstration of some tunable nanophotonic devices by using the 1T-TaS2, and the experimental results of the tunable meta-grating and meta-color-filter. Additionally, I will present the theoretical realization of the correlation behavior of percolation systems by using the renormalization theory.
1T-TaS₂: A strongly correlated material for tunable nanophotonics
(2019-09-24) Li, Weijian; Naik, Gururaj Viveka
Tunable nanophotonics have been demonstrated for several decades and achieved to practical applications in real world in multiple ways such as imaging, sensing, signal processing, information communication and etc. Many different mechanisms have been involved in such modulating, gate tunable Fermi energy of graphene, MEMS devices, chemical reaction. However the tunabilities of all of mechanisms are either small or slow due to small capacitive gaps and large stimulus. Fortunately materials with especially electric tunable optical properties are supposed to be one of the solution for overcoming this limitation. Hence, tunable optical materials are attracting more interests and under deeply investigations. Strongly correlated materials provides a group of candidates for tunable optical materials in which electronic and phononic structures are strongly sensitive to external environments. Transition Metal Dichalcogenide (TMDs), a prototype of two-dimensional (2D) compound, is one of the well studied strongly correlated materials exhibiting numerous different interesting phases such as superconducting, charge density wave (CDW) and spin liquid from liquid Helium temperature to above room temperature. Some of them even exhibit non-Fermi liquid behaviors raised from strongly interaction among localized sub-shell electrons of transition metals atoms. Because of the diverse phase transitions and non-Fermi liquid properties, TMDs provide possible larger tunabilities of optical properties of the materials compared with normal semiconductors. Although optical properties of materials hugely differ around phase transition point, low temperature makes almost all of them hard be implemented in dynamic world optical applications. CDW is one of the quantum ground states that can happen around room temperature which makes the host materials possible platforms for tunable nanophotonic applications. This quantum phase is a result of strong interaction between electrons and phonons of the materials producing a condensate that rearranges the lattice and produces a nested Fermi surface. Many TMDs support charge density waves such as NbSe₂ and TiSe₂, but 1T-TaS₂ supports CDWs at room temperatures which attracts increasing interests of physicists due to its non-equilibrium state that can be excited by electric field and light. In this thesis, we propose that 1T-TaS₂ is a promising candidate for tunable nanophotonics due to its tunable optical properties in visible by in-plane electric bias and therm-optical effect. We demonstrate that the refractive index can be tuned up to 0.1 in visible at room temperature by both DC and AC in-plane bias and up to 0.4 by white light excitation. By implementing this tunability of optical properties of 1T-TaS₂, we theoretical propose a grating design that shift the first diffraction angle at 516 nm by 15.4° under 2.5 mW/cm2 and 250 mW/cm2 white light excitation. Finally we experimentally vary this application of 1T-TaS₂ by showing up to 1 nm diffraction peak shift at around 558 nm.
2,4,6-trinitrotoluene reduction by hydrogenase in Clostridium acetobutylicum
(2003) Watrous, Mary Margaret; Hughes, Joseph B.
Unique genetic modifications to C. acetobutylicum altered the level of hydrogenase expression, allowing study of the resulting effects on the 2,4,6-trinitrotoluene (TNT) reduction rates to be possible. A strain designed to over-express the hydrogenase gene resulted in maintained TNT reduction during late growth phases when it is not typically observed. Strains exhibiting under-expression of hydrogenase produced slower TNT rates of reduction correlating to the expected inhibition of each strain type. Hydrogenase activity, measured by hydrogen production, in Clostridium acetobutylicum correlates strongly (R2 = 0.89) to TNT reduction rates. Indications suggested that hydrogenase potentially played an integral role in catalysis of TNT transformation by reducing its nitro substituents to the corresponding hydroxylamines. A mechanistic pathway is proposed by which this transformation takes place and may enhance the understanding of commonly found hydrogenases in other microorganisms and their ability to transform nitroaromatic compounds.
2D and 3D single-molecule microscopy to enhance protein chromatography
(2022-08-02) Misiura, Anastasiia; Landes, Christy F.
Over the last decade the pharmaceutical industry has been experiencing a scientific revolution, resulting in more biological-based therapeutics, also called biologics. Biologics are largely proteins or peptides, which have created a bottleneck in optimizing their purification processes. The major problem resides in the inability to predict and apply empirical processes to protein separation and purification. One ubiquitous method of protein purification and separation is chromatography. Despite its wide industrial usage and intensive development, there is still no detailed molecular-scale picture of protein dynamics during chromatographic separation. The lack of a predictive chromatographic theory is rooted in the absence of an in-depth understanding of interactions occurring inside a chromatographic column. To advance our understanding of underlying phenomena in a chromatographic column, 2D and 3D single-molecule techniques were utilized. We uncover the differences in protein motion in mobile phases, depending on salt concentration, and correlated the results to an ensemble chromatogram. We also demonstrate the importance of the combined influence of surface properties on adsorption-desorption kinetics of proteins to the stationary phase. Overall, we have shown that single-molecule methods can uncover the details of protein dynamics and transport at the nanoscale and relate them to ensemble chromatography and apply them to protein purification at-scale.
2D Materials in Lego Style: Synthesis, Characterizations and Applications
(2015-12-04) Gong, Yongji; Ajayan, Pulickel M.; Jun, Lou; Marti, Angel
Recently, the emergence and development of 2D materials with various optical and electrical properties has opened up new routes for electronic and optoelectronic device fabrication based on atomically thin layers. For example, graphene behaves as a semi-metal with extremely high mobility, hexagonal boron nitride (h-BN) is a good insulator and monolayer TMDs such as MoS2, MoSe2 and WSe2 are semiconductors with direct band gap. This diversity offers the opportunity to construct atomically thin electronics based entirely on 2D materials. One of the most promising applications is to get 2D integrated circuits to replace the traditional silicon based ones, which will be much thinner and faster. 2D materials can be considered to be analogous to Lego blocks. The Lego game is to use different Lego blocks to get a complicated Lego building. Similarly, we can use different 2D materials to get the corresponding integrated circuits or devices for energy related applications. Based on this purpose, we need different 2D blocks, which are the most fundamental parts in the 2D world, 2D materials with tunable properties, and different strategies to combine the 2D materials together. Chapter 1 focuses on synthesis, characterization and applications of pristine 2D materials, which are the fundamental blocks for the 2D world. In this part, we synthesized different 2D materials such as insulator (h-BN), metal (graphene) and semiconductors (MX2, M = metal and X = chalcogen) for different applications. There are two directions in this part: one is to explore new 2D materials and the other one is to improve the growth of 2D materials to push them closer to their real applications. Moreover, semiconductors with different band gap (from 1.1 eV to 2.8 eV) and different type (p type and n type) have been developed. Furthermore, we improved the growth of different 2D materials to get their millimeter-scale single crystals or even continuous film. In the coming Chapter 2, we focused on the 2D alloys. The purpose of alloying 2D materials is to engineer the phase and band gap by changing the composition in the alloys. By this, we can tune the optical and electrical properties in 2D materials very easily. The first project in this part is about h-BNC system, which can open a band gap in graphene system, resulting in both high mobilities and high ON-OFF ratio in their transistors. Then we developed the MoS2-xSex (x, 0-2) alloys, in which the band gap can be continuously tuned from 1.50 eV to 1.84 eV. At last, RexMo1-xS2 (x, 0-1) system is developed to study the phase transition with different x. In Chapter 3, heterostructures based on different 2D materials are developed by different strategies. For example, we can get h-BN/h-BNC/graphene lateral heterostructure by combing a conversion method and lithography. We also developed the heterostructures based on MoS2/WS2 and MoSe2/WSe2 by a one-step growth method and two-step growth method, respectively. In both of them, we can get the in-plane and vertical heterostructures. The interface of the in-plane interface is atomically seamless and sharp and the bilayer heterostructures have fixed stacking orientations, which are more advantageous than other methods. At last, we developed more complicated heterostructures, which can be composed by 3 or 4 different 2D materials. In Chapter 4, we further developed several different 3D structures constructed by 2D materials for energy storage and conversion. Basically, this part is inspired by graphene aerogel with porous 3D structure. The porous structure enables the access of electrolyte very easily and the graphene network has very good electrical conductivity, advantageous to work as electrochemical applications. In this part, we developed several different structures for different applications, including MoS2/GO as the anode for lithium ion battery, VO2/GO as the cathode for lithium ion battery and h-BNC as ORR catalyst. For the lithium ion battery, the structures developed here have better performance than the commercial ones with higher capacity, better stability and much higher charge and discharge rate. H-BNC aerogel can even beat the performance of commercial Pt/C as the ORR catalyst. In summary, the research based on 2D materials is like the Lego game, including exploring the Lego blocks (pristine 2D materials and their alloys) and combining them together to form the functional devices (2D heterostructures and 3D porous structure from 2D materials).
2D Optoelectronics: Challenges and Opportunities
(2015-12-17) Lei, Sidong; Ajayan, Pulickel M; Lou, Jun; Kono, Junichiro
Indium Selenide (InSe) is one of atomically layered 2D materials attracting broad interests recently, because of its good optoelectronic properties. Based on the challenges of 2D optoelectronics, several topics will be covered in this defense, such as trap states and low absorption rate. InSe is selected as a platform to study these topics. The localized states and trap states in InSe system was characterized through low temperature photocurrent measurement to reveal the evolution of band structure and origin of the localized states in few layered InSe. It is found the surface electron orbitals contribute to the localized states. By modifying the surface electron via metallic ions, the Fermi level can be tuned significantly and the inertia surface of the pristine 2D surface can be sensitized for functionalization. Via this method, the InSe photodetector can be improved by organic photosensitive molecules. On the other hand, local gating can induce trap states in 2D materials, helping to improve the photoresponse, but slowing down the response speed. By utilizing this effect, 2D charge coupled device can be fabricated to serve as flexible image sensor which can help correct the optical aberration. The discussion is based on InSe, however, the principle is very universal that can be easily apply to other 2D system. The research can help to promote the research and device development in 2D optoelectronics.
2D timelapse and 3D fluorescence microscopy with applications to vascular tissue engineering
(1998) Stamatas, Georgios Nikolaou; McIntire, Larry V.
Part of the definition given to the new emerging science discipline of tissue engineering is the understanding of the structure-function relationships at the cellular level. In this context it is important for vascular tissue engineering to understand the mechanisms involved in the vascular cell responses to their mechanically active environment. This work has elucidated some aspects of the complicated puzzle of mechanotransduction in vascular smooth muscle cells (SMC) and endothelial cells (EC). Two dimensional timelapse fluorescence microscopy revealed rapid alkalinization occurring in cultured human aortic SMC exposed to well defined fluid flow profiles. The response was reversible and persisted for at least 20 min after flow initiation. The magnitude of the alkalinization (0.14 pH units) was enough to increase the nitric oxide synthase activity and account at least in part for the flow-induced increases in NO production by SMC. Use of specific inhibitors demonstrated the involvement of the Na$\sp+$/H$\sp+$ exchanger in the flow-induced response, whereas the Cl$\sp-$/HCO$\sb3\sp-$ exchanger was active even under stationary conditions. The involvement of calcium as a second messenger in the EC flow-induced mechanotransduction and the localization of possible signals within the cell was addressed by a three dimensional fluorescence microscopy technique. After 5 min of flow initiation there was a significant calcium increase in the nuclear region. The response was cytoskeleton independent. The same technique revealed early flow-induced changes in the three dimensional EC architecture. Nuclear and whole cell heights were reduced by about 1 $\mu$m with a corresponding increase in the cross-sectional area at lower optical sections. Using specific cytoskeleton disrupters we demonstrated that the whole cell height response was cytoskeleton independent and the nuclear height response was microtubule dependent. Thus, it has been shown that force imposed on the EC membrane is rapidly transmitted by microtubules to the endothelial nucleus. A mechanical equivalent model is presented to explain the cytoskeleton involvement in flow-induced structural changes based on tensegrity arguments. The early responses in the nuclear calcium and structure demonstrated in this study may be important for the shear-induced gene regulation.
3-body breakup of HE_
(1963) Simpson, Wilburn Dwain; Phillips, Gerald C.
The d(p,2p)n reaction has been studied using the recently constructed angular correlation chamber at Rice University. The two protons from the reaction have been observed for incident proton energies of 5.0, 9.0, and 10.5 MeV using the two Rice University Van de Graaff accelerators. Kinematic calculations were made to determine the shape of the curve describing allowed solutions in terms of the energy of one of the detected protons versus that of the other. Observed experimental curves of the same form have been presented along with the calculated excitation energies of the 3 possible intermediate configurations if the reaction were to proceed via sequential 2-body decay, Evidence of sequential 2-body decay to a low excited state of the n-p system is observed at particular angles for 9.0 and 10.5 MeV bombarding energies. Similar decay is not observed at 5.0 MeV, but this effect is likely due to experimental difficulties in observing the appropriate region of the energy curves at this energy. The data at all three bombarding energies and for many angles show evenly populated distributions, indicating for these cases either simultaneous 3-body decay of the He3 configuration or sequential 2-body decay through quite broad intermediate states.
3-D segmentation and volume estimation of radiologic images by a novel, feature driven, region growing technique
(1992) Agris, Jacob Martin; de Figueiredo, Rui J. P.
Magnetic Resonance (MR) imaging is a 3-D, multi-slice, radiological technique that acquires multiple intensities corresponding to each voxel. The transverse relaxation time, T$\sb1$, and the axial relaxation time, T$\sb2$, are two commonly obtained intensities that tend to be orthogonal. Automated segmentation of 3-D regions is very difficult because some borders may be delineated only in T$\sb1$ images, while others are delineated only in T$\sb2$ images. Classical segmentation techniques based on either global histogram segmentation or local edge detection often fail due to the non-unique and random nature of MR intensities. A 3-D, neighborhood based, segmentation method was developed based on both spatial and intensity criteria. The spatial criterion requires that only voxels connected by an edge or face to a voxel known to be in the region be considered for inclusion. Therefore, the region "grows" outward from an initial voxel. An intensity criterion that tries to balance local and global properties must also be satisfied. It determines the vector distance between the intensity of the voxel in question and a characteristic intensity for the neighboring voxels known to be in the region. Voxel intensities within a 95% confidence interval of the characteristic intensity are considered part of the region. The kernel size used to determine the characteristic intensity determines the balance between global and local properties. The segmentation terminates when no additional voxels satisfy both spatial and error criteria. Some regions, such as the brain compartments, are highly convoluted, resulting in a large number of border voxels containing a mixture of adjoining tissues. A sub-voxel estimate of the fractional composition is necessary for accurate quantification. A least-squares estimator was derived for the fractional composition of each voxel. Additionally, a maximum likelihood estimator was derived to globally estimate the fraction for all mixture voxels. This estimator is a minimum variance estimator in contrast to the least-squares estimator. The estimation methods in conjunction with the 3-D, neighborhood based, segmentation method resulted in an automated, highly accurate, quantification technique shown to be successful even for the brain compartments. Widespread applicability of these methods was further demonstrated by segmentation of kidneys in CT images.
3.4 centimeter cyrogenic parametric amplifier system for radio astronomy
(1970) Halpain, Joe Lee; Walters, G. King; Blackwell, L. A.
A low-noise microwave receiver was designed and fabricated to provide the necessary sensitivity to detect the helium 3 line. In order to achieve ultra-low noise amplification in the input states of this receiver, cascaded non-degenerate cryogenically cooled parametric amplifiers were used. These amplifiers were followed by a tunnel diode amplifier and a mixer-preamplifier which provides a total system gain of approximately 60 db. The parametric amplifiers were cooled to the cryogenic temperature by a closed-cycle gaseous helium refrigerator. The ambient operating temperature provided by the refrigerator was approximately 18°K. The parametric amplifiers were pumped with a Ka-band klystron which provides a signal-to-idler ratio of approximately 0.38. Gain stability was achieved by using waveguide ferrite current variable attenuators which were used to control the pump power as required to maintain a constant varactor current. The system was designed to consist of two major assemblies. One of the assemblies is packaged in a 30 x 30 x 60 inch weather proof enclosure for mounting at the focal point of the National Radio Astronomy Observatory 140 foot radio telescope. This enclosure includes a thermoelectric cooling and heating system to maintain a constant temperature inside the assembly under all weather condition. The second assembly was packaged in a standard relay rack type cabinet. This unit contains all of the receiver control, monitoring and special remote test circuits. The two assemblies were designed to operate with connecting cable lengths of up to 500 feet. During the first observing period, the noise temperature performance of the receiver was about three times that expected, i.e., 100°K. However, the stability of the system was sufficient to allow long integration periods so that usable data was obtained. To correct the noise temperature performance, the parametric amplifiers were redesigned, particularly in the area of thermal conductivity. In addition, the manufacturer and package style of the varactor was changed to terminate the high failure rate that had occurred in the diodes. In addition to the low-noise temperature and excellent gain stability achieved by this receiver, several new concepts were utilized in the design of the system which greatly improved its mechanical and thermal properties. One of these is a special non-contacting choke flange on the input line to the parametric amplifiers which allows the input line to be short and unrestricted in location. The system will be utilized again in the summer of 1970. The present performance of the system should provide data which is far superior to that obtained in the last observing period since for the same signal-to-noise ratio, the integration time should be reduced by a factor of four or more.
3.5 ANGSTROM RESOLUTION STRUCTURE OF L-ARABINOSE BINDING PROTEIN FROM E. COLI
(1977) PHILLIPS, GEORGE NEAL, JR.
37+
(2015-04-21) Trotty, William M; Schaum, Troy; Wittenberg, Gordon; Colman, Scott
Walls are edges between two distinct entities; urban forms that attempt to express neutrality as infrastructure while firmly rejecting interaction between opposing constituencies. Walls are usually contiguous lines; establishing absolute boundaries and absolute limits. Belfast, Northern Ireland is no stranger to walls. Over 100 currently exist in the city as peace-keeping mechanisms separating Catholic and Protestant neighborhoods. These highly visible urban forms create parallel communities with parallel services; producing redundant infrastructures and multiplying territorial subjectivities. The City of Belfast wants all the Interface Walls removed by 2020, but the citizens want them to stay. Of the 100 walls, it is estimated that 37 will remain. As Belfast struggles to create a new marketable image for world of a city moving forward, the interface walls spread out across the city remain a marker of its conflicted past. But there may be hope for reclaiming the city, and in turn, pushing Belfast into a more transnational urban landscape. Unlike the Berlin Wall, the walls in Belfast are non-contiguous boundaries between communities; navigating the city means commuting around and through the walls on a daily basis. The Interface Walls in Belfast do not act as literal walls dividing the city, but as symbolic walls. And as a symbol, the meaning and function of the walls can change. 37+ proposes creating this shift in the symbolic nature of the Interface Walls in Belfast by introducing more walls; a network of 221 insertions in the walls that house schools, clinics, pubs, and parks. These new lengths of Interface Walls create a datum in the city that redefines the symbol of the Interface Wall as a divisive edge; exacerbating the multiplication of infrastructures and subjects to a positive effect through serial deployment of shape, materiality, and program. This new urban identity for Belfast acknowledges and rejects the contentious territoriality extant in the city, converting urban forms dedicated to separating communities into attractors for the city that negotiate contentious space.

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