Production of intense, tunable, quasi-monochromatic X-rays using the RPI linear accelerator

Sones, Bryndol A Rensselaer Polytechnic Institute 2004 해외박사(DDOD)

This research investigated the production of parametric X-rays (PXR) using the 60-MeV electron linear accelerator at Rensselaer Polytechnic Institute. PXR is an intense, energy tunable, and polarized X-ray source derived from the interaction of relativistic electrons and the periodic structure of crystal materials. In this work, PXR photon yields and the associated bremsstrahlung background were characterized for graphite, LiF, Si, Ge, Cu, and W target crystals. A model that considers the experimental geometry and crystal mosaicity was employed to predict PXR energy broadening. Measured energy linewidths consistently agreed with predicted values except in cases using poor quality graphite in which the mosaicity was greater than the PXR characteristic angle, 8.5 mrad for 60 MeV electrons. When the predicted energy linewidth was more narrow than our Si X-ray detector resolution, a near-absorption edge transmission technique was used to measure the PXR energy linewidth for Si(400) FWHM of 134 eV at 9.0 keV (2%) and Si(220) FWHM of 540 eV at 17.7 keV (3%). An experimental study was conducted to select PXR target crystals most appropriate for X-ray production at typical mammography energies (17--20 keV). Low Z materials like graphite and LiF were most suitable for PXR production because of their low Bremsstrahlung production, electron scattering, and photon absorption. Graphite was most efficient at producing PXR photons while the LiF energy linewidth was narrower. A theoretical model that considers electron multiple scattering, electron divergence, and crystal mosaicity was used to broaden the PXR photon distribution in order to calculate predicted PXR photon yield. This approach, proposed by A. P. Potylitsin, was allowed comparison of measured and predicted PXR yields. The relative error was typically below 0.5. In some cases with LiF, the differences between predicted and measured values were as low as 2% for LiF(400) and 13% for LiF(220). Finally, this work reports for the first time PXR imaging. This was achieved using LiF(220) interacting with 56 MeV electrons with electron beam currents up to 6 muA.

Measurement of Elastic and Inelastic Neutron Scattering in the Energy Range from 0.5 to 20 MeV

Daskalakis, Adam Matthew Rensselaer Polytechnic Institute 2015 해외박사(DDOD)

Improvements were made to assess data collected by the Rensselaer Polytechnic Institute's Neutron Scattering System. Reference pulses were developed to discriminate neutron from gamma-ray events. A technique to account for erroneously classified gamma-ray events was incorporated into the data analysis. New in-beam measurements were performed to characterize the energy-dependent neutron flux shape and to characterize each detector's efficiency. These measurements were also crucial in the development of response functions needed to separate elastic and inelastic scattering. The new analysis methods and techniques were used on data collected from 238U and NatFe neutron time-of-flight scattering measurements. Results from the scattering measurements were used with an improved model of the Neutron Scattering System to benchmark nuclear evaluations. The model incorporated energy-dependent detector efficiencies, energy-dependent neutron flux shape, and a detailed geometric description. Based on the improved model and the new data analysis techniques a method to quantify systematic uncertainties was developed. The JENDL-4.0 evaluation had the best agreement with the TOF data for both the 238U and NatFe measurements.

Citizens, experts and the economy: The grassroots takeover of Kentucky's agricultural future

Fitzgerald, Jenrose Dawn Rensselaer Polytechnic Institute 2005 해외박사(DDOD)

This dissertation examines how a range of agricultural players---drawing on a variety of kinds of agricultural and economic knowledge---have approached the problems posed by globalization and economic change in Kentucky. It is a story about how a small nongovernmental organization, or NGO, came to be an active voice in the political debates about the shape that Kentucky's entry into the globalization process would take. In the last decade, Kentucky's agricultural economy has undergone a rapid transformation. Tobacco---until recently Kentucky's top cash crop---has been steadily declining as a source of agricultural income. When the tobacco companies reached their Master Tobacco Settlement agreement with states in 1998, the state of Kentucky was awarded 3.5 billion dollars over a 25-year period. Half of these funds were then set aside for agricultural development as a strategy for coping with the economic impact of tobacco's decline. The tobacco settlement mobilized a range of governmental and non-governmental actors hoping to shape the future of Kentucky's agricultural economy and funnel funds in strategic directions. This dissertation examines the processes by which NGOs, farmers and other "lay" experts have engaged with professional agricultural experts and policymakers over the appropriate approach(es) to agricultural development in the state, given the demise of tobacco. Drawing on written documents, interviews, and over two years of participant observation, I document the role of variously situated players in shaping Kentucky's agricultural economy and discourse through this transition. I pay particular attention to the role of one NGO, the Community Farm Alliance, in generating farmer-centered research and shaping the debate around post-tobacco agriculture---despite their positional disadvantage vis-a-vis more mainstream agricultural networks and institutions.

Dynamic Load Control of a Wind Turbine Blade using Synthetic Jets

Taylor, Keith Robert Rensselaer Polytechnic Institute 2014 해외박사(DDOD)

Understanding and implementing engineering techniques that serve the purpose of reducing structural vibrations and load variations in wind turbine blades is of critical importance to the goal of reducing the cost of energy of wind energy systems. The effectiveness in reducing structural vibrations and load oscillations of a finite span S809 airfoil was investigated experimentally in the Rensselaer Polytechnic Institute's low speed wind tunnel at the Center for Flow Physics and Control (CeFPaC). The structural vibrations and load oscillations arose due to prescribed dynamic pitching parameters corresponding to non-dimensional motion parameters typically seen in field conditions. Aerodynamic loading was measured through a six component load cell located at the root of the model. Two-component and three-component velocity fields were measured through the use of a stereoscopic PIV system. Structural vibrations were measured through the use of strain gauges placed at the base of the model, and tip deflection was inferred by calibrating voltage variations in the strain gauges with tip deflections measured by a laser displacement sensor. This study demonstrated that, through the introduction of periodic momentum near the leading edge of this model, the average tip deflection could be reduced under dynamic conditions. Furthermore, it was demonstrated that, at certain levels of momentum injection, tip deflections might actually be enhanced. Where load oscillations during dynamic conditions were observed, a similar trend occured. Certain levels of momentum injection resulted in higher oscillations in loading observed during dynamic pitching, where higher momentum injection levels reduced load oscillations during dynamic cycles. This work concludes with the suggestion that, moving to full scale testing of this flow control system, it will be necessary to provide sufficiently high momentum injection such that damage will not occur from the implementation and actuation of a flow control system. This process seems to be the result of changing how the flow field transitions from trailing edge separation to a fully separated flow. In a phase-averaged sense, this is defined by the creation of a phase averaged leading edge recirculation region, which interacts with the trailing edge separation. Through the introduction of momentum near the leading edge, this process can be altered, such that the phase averaged trailing edge separation region is the dominant structure present in the flow.

Enabling extreme-scale circuit modeling using massively parallel discrete-event simulations

Gonsiorowski, Elsa Rensselaer Polytechnic Institute 2016 해외박사(DDOD)

Simulation is a key step in designing complex integrated circuits, such as processors. In recent years, chip complexity has increased to the point that sequential simulation tools are no longer adequate. Many commercial gate-level simulation tools are limited in scale or require specialized hardware approaches, thus limiting effective software simulation to sub-components of the larger circuit. Parallel discrete-event simulation (PDES) is a perfect fit for this context. The key contribution of this thesis is a complete software-based workflow for transforming domain-specific designs into an accurate PDES model that is able to execute and leverage the compute capabilities of modern supercomputer systems. Circuit designs at the logic level are built upon a gate library. This library describes the physical properties of the logic components for the circuit (e.g., boolean logic gates). By using a relatively small set of logic gates, the larger circuit design, such as an entire processor, is realized. I begin by presenting a proof-of-concept example which outlines the various challenges in creating a PDES model for gate-level circuit simulation. This prototype reveals the main obstacles for creating accurate, efficient, and useful tools in this space. I meet the first challenge by presenting an automatic model generation tool which accurately transforms a gate library description from a domain-specific grammar to C. Through the exemplar LSI-10K library, this tool is able to capture both logic and timing information for each of the 166 gate types. This C-based expression of the library is combined with a novel, generic gate model for Rensselaer's Optimistic Simulation System (ROSS). Next, I present a circuit model mapping workflow. It is through this mapping that I am able to take a multi-component description of a full-scale circuit and instantiate it within ROSS. Each components original listings of logic gates connected to named wires becomes a listing of simulation objects with internal knowledge of their connections to other simulation objects. The final step is the instantiation of the components and including the high-level routing between modules. Finally, I describe an efficient parallel I/O API, called RIO, designed specifically for PDES applications. RIO enables a parallel, checkpoint-restart capability for long-running, parallel simulations. These checkpoints are compact and are written in binary format. For efficient parallel I/O operations, the metadata are stored in separate files from the pieces of simulation object data. To ensure data preservation and legacy, a human-readable description file accompanies each set of checkpoint data files.

Purification of monoclonal antibodies and Fc-fusion proteins: Protein A and beyond

Ghose, Sanchayita Rensselaer Polytechnic Institute 2005 해외박사(DDOD)

Monoclonal antibodies and Fc-fusion proteins form the largest and most rapidly expanding category of biopharmaceuticals today with annual sales exceeding $8 billion and applications across a wide range of diseases. While Protein-A affinity chromatography has been universally applied as the primary purification step for process-scale production of these molecules, it suffers from disadvantages of high cost, limited throughput and the need for extensive methods development. This thesis seeks to improve fundamental understanding of Protein-A chromatography and to address these issues. To circumvent the traditional trade-off between cost and throughput during Protein-A chromatography, a novel dual flow-rate loading strategy has been developed to enable simultaneous improvements in both capacity and throughput. In the first work of its kind, an explanation has been obtained for elution pH differences among antibodies during Protein-A chromatography. These were found to be the result antibodies interacting with the Protein-A ligand through their variable regions in preference to conventional interactions through their Fc-regions. Eliminating variable-region interactions by use of an engineered Protein-A ligand resulted in a similar elution pH for all molecules, thus enabling the use of generic process conditions for Protein-A purification. In addition, for the first time, differences in binding capacity observed among molecules have been explained through steric hindrance to binding exerted by the non-binding domain of the molecules. This work also provides the first critical exploration of selectivity and binding mechanism on commercially available "alternatives" to Protein-A chromatography (HCIC and mimetic systems). A novel formalism to explain both preparative and analytical behavior in these systems has been developed. This thesis provides an improved understanding of molecular level interactions with Protein-A chromatographic supports. The strategies developed here enable the rapid development of optimal process-scale separations, and also bear significant implications for the economics of antibody production. The development of generic operating conditions for this mode of chromatography are expected to result in significant savings in time and resources during industrial process development and to remove bottlenecks for the rapid introduction of these drug candidates into the clinic. This work has been the result of a joint collaboration between Amgen, the world's largest biotechnology company, and Rensselaer.

Physical and computational modeling of biaxial base excitation of sand deposits

El-Shafee, Omar Osama Rensselaer Polytechnic Institute 2016 해외박사(DDOD)

Natural soil is often loosely deposited, with the granular particles locked together by friction. During seismic events, shear waves overcome this frictional confinement. The force exerted by the overburden pressure causes the particles to reorient into a higher density configuration. As the solid particles of the soil densify, the water between these particles is forced out, and has to travel to the surface. This pore water motion is resisted by the permeability limitations of the soil resulting in increased pore water pressure. Pore water pressure reduces the strength of the soil by limiting the contact forces between the soil grains. Once the hydrostatic force is sufficient to carry the applied load, the inter-granular frictional forces will approach zero, and the soil will behave like liquid. This liquefaction behavior causes structures to sink or topple in the soil, creating an incredible risk to human life, and loss of property. The effects of earthquake loading on site response are complex and three dimensional. The ability to understand and predict soil response during earthquakes is an important aspect in the design and management of soil-structure systems. Numerous studies were conducted over the last four decades to analyze and quantify the response of soil deposits subjected to base excitations. Most of the previous studies, especially those dealing with physical modeling were done using uniaxial base excitation. The simulation of base excitation progressed from single frequency sine excitation, to more complex motions with variable amplitude and finally multi-frequency content. The vast majority of research is conducted using uniaxial excitation, and only few used simple biaxial shaking. The work presented herein is a centrifuge study conducted at the Center for Earthquake Engineering Simulation (CEES) of Rensselaer Polytechnic Institute (RPI) to assess the dynamic response characteristics of level deposits and SSI under multidirectional shaking. Synthetic sinusoidal waves were used as base excitations to test loose and dense models under biaxial and uniaxial shaking. Dense arrays of accelerometers were used to monitor the deposit response along with pore water pressure transducers. Three primary and calibration tests were conducted in order to assess the behavior of the RPI 2D shaker and 2D laminar box. Followed by three uniaxial tests and three bi-axial shaking tests conducted on soil models to study the impact of multidirectional shaking on the soil liquefaction. The three uniaxial shaking tests consisted of: i) Two tests with input energy similar to that of the bi-axial input shaking energy and ii) Test with 10% increase in one of the components of the biaxial shake amplitude, as commonly done in practice for uniaxial simulation of multidirectional field shaking. For biaxial tests two studied free field and one studied SSI. The observed acceleration and pore pressure are used along with non-parametric identification procedures to estimate the corresponding dynamic shear stress-strain histories. The measured results along with the obtained stress and strain histories are used to shed the light on the mechanisms of liquefaction occurring through the stratum, excess pore pressure buildup, soil contraction and the difference in soil behavior when it is subjected to biaxial shaking. This difference is evident in the strain energy generated in the biaxial test compared to that of the equivalent and traditional uniaxial tests, and the non-proportional response of the soil under biaxial shaking.

A penetration-based finite element method for hyperelastic three-dimensional biphasic tissues in contact

Un, Kerem Mustafa Rensselaer Polytechnic Institute 2002 해외박사(DDOD)

Advancements in theoretical, computational and experimental methods have enabled researchers to develop more refined and realistic models for articular cartilage. A realistic numerical simulation of cartilage mechanics under <italic> in vivo</italic> conditions requires the tissue layers to be modeled in contact, undergoing large deformation. The objective of the current research is to develop an efficient finite element procedure for numerical simulation of three-dimensional (3-D) biphasic cartilage layers in contact. To achieve that objective, the penetration method is developed as a preprocessing technique that makes use of experimentally measured joint kinematic data to derive approximate contact boundary conditions. This process eliminates the nonlinearity associated with contact mechanics, and enables independent analyses of the contacting tissues. The derived boundary conditions provide the input to a finite element procedure where the material and geometric nonlinearities, as well as the strain-dependent permeability, of the tissue layers are taken into account through a biphasic continuum model. The linear and nonlinear versions of penetration-based biphasic finite element analyses are critically evaluated using canonical problems, then applied to a physiological example, namely the glenohumeral joint of the shoulder. This work represents the first attempt to analyze contacting biphasic articular cartilage layers on physiological geometries under finite deformation. This is a numerically challenging problem and requires that conventional nonlinear solution procedures be improved. The research therefore included an examination of alternate linearizations of the nonlinear problem and line search techniques to stabilize the iterative solution scheme. Both linear and nonlinear versions of this formulation have been implemented into the object-oriented analysis framework, <italic>Trellis</italic>, of the Scientific Computation Research Center at Rensselaer Polytechnic Institute using the C++ programming language.

Lateral Spreading And Liquefaction Assessment Of Cohesionless Soils In The Free Field: An Investigation Using Centrifuge Testing

El Ganainy, Hesham Mohamed Rensselaer Polytechnic Institute 2012 해외박사(DDOD)

Liquefaction of saturated sands and other granular soils due to earthquake loading has been a major cause of damage to constructed facilities. One of the major liquefaction induced types of ground failure is lateral spreading of mildly sloping ground. Evaluation of liquefaction susceptibility of soils is an important step in many geotechnical investigations in earthquake-prone regions. There is a need for better understanding of the complex behavior of saturated granular soil deposits under earthquake shaking. Centrifuge and full scale testing have proved to be valuable tools in evaluating this behavior and the consequences of liquefaction and lateral spreading. Centrifuge modeling is particularly useful due to its reliability, time and cost effectiveness when compared to full scale testing. The work presented herein is a centrifuge study conducted at the Center for Earthquake Engineering Simulation (CEES) of Rensselaer Polytechnic Institute (RPI) to investigate liquefaction and lateral spreading phenomena under free field conditions. This study is mainly concerned with investigating the correlation between different liquefaction and lateral spreading parameters, and two soil mechanical properties; the constrained modulus (<italic>M</italic>), and the shear wave velocity (<italic>V_S</italic>). This is done in two steps: (i) the effect of relative density, soil permeability, and overconsolidation and pre-shaking history on the measured mechanical properties is investigated and quantified; and (ii) the correlation between <italic>M</italic>, <italic> V_S</italic> and different liquefaction and lateral spreading parameters (e.g. lateral ground deformation and generated excess pore pressure ratio) is then established for different soil parameters and stress history conditions. The established correlations are compared against traditional methods used to assess liquefaction susceptibility of the soil in the field. Based on this study it is concluded that the mechanical soil properties have significant advantages over geometric properties of the soil such as relative density, when correlating with the liquefaction and lateral spreading response of the soil. The cases of liquefaction and no liquefaction compared very well with field liquefaction charts found in the literature and used by practitioners over the years. Comparison with other newly developed liquefaction charts based on the cyclic strain approach showed promise but revealed that further research is needed on the engineering implications for very stiff deposits. Finally, the correlation between soil liquefaction and lateral spreading parameters, on the one hand, and soil constrained modulus (<italic>M</italic>) on the other, was established and discussed in detail, confirming that <italic>M </italic> can be an alternative soil stiffness parameter to correlate with liquefaction and lateral spreading due to earthquake shaking.

A New High Energy Resolution Neutron Transmission Detector at the Gaerttner LINAC Center and Isotopic Molybdenum Total Cross Section Measurements in the keV-Region

Bahran, Rian M Rensselaer Polytechnic Institute 2013 해외박사(DDOD)

The Gaerttner LINAC Center at Rensselaer Polytechnic Institute is home to a 60 MeV electron linear accelerator (LINAC) that is used as a pulsed neutron source for TOF nuclear data experiments. High energy resolution total cross section measurements for the stable molybdenum isotopes of Mo-95, Mo-96, Mo-98, and Mo-100 were performed with a newly developed modular neutron transmission detector positioned at a 100 m experimental flight station. This work is part of an effort to both improve existing neutron total cross section libraries and measurement capabilities at the Gaerttner LINAC Center in and above the resolved resonance energy region (from 5-620 keV). The overall design optimization process and qualification of the new high resolution detector is presented. Additionally, a new method to quantify the energy-dependent neutron and gamma-ray experimental background of the detector was developed. High resolution isotopic molybdenum total cross section data are of particular importance because stable Mo isotopes can be found in significant concentrations in a nuclear fuel cycle either as a high yield fission product or in alloyed form with applications in reactor piping, fuel cladding, and as an advanced nuclear fuel in the form of U-Mo. The measured total cross section energy range encompasses the resolved resonance region and extends into the unresolved resonance region for each molybdenum isotope. New high accuracy resonance parameters for Mo-95 were generated from fitting experimental data using the multilevel R-matrix Bayesian code SAMMY in the resolved resonance region. In the unresolved resonance region, average resonance parameters and fits to the total cross section were obtained using the Hauser-Feshbach statistical model code FITACS which is embedded in SAMMY.