Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10217/100415

Browse

Now showing 1 - 20 of 313

Open Access
Effects of background winds and temperature on bores, strong wind shears and concentric gravity waves in the mesopause region
(Colorado State University. Libraries, 2009) Yue, Jia, author; She, Chiao-Yao, advisor; Reising, Steven C., advisor
Using data from the CSU sodium lidar and Kyoto University OH airglow imager at Fort Collins, CO, this thesis provides a comprehensive, though qualitative, understanding for three different yet related observed fluid-dynamical phenomena in the mesopause region. The first project involves the convection-excited gravity waves observed in the OH airglow layer at 87 km. Case study on May 11, 2004 is discussed in detail along with statistical studies and a ray-tracing modeling. A single convection source matches the center of the concentric gravity waves. The horizontal wavelengths and periods of these gravity waves were measured as functions of both radius and time. The weak mean background wind between the lower and middle atmosphere determines the penetration of the gravity waves into higher altitude. The second project involves mesospheric bores observed by the same OH imager. The observation on October 9, 2007 suggests that when a large-amplitude gravity wave is trapped in a thermal duct, its wave front could steepen and forms bore-like structure in the mesopause. In turn, the large gravity wave and its bore may significantly impact the background. Statistical study reveals the possible link between the jet/front system in the lower atmosphere and the large-scale gravity waves and associated bores in the mesopause region. The third project involves the relationship between large wind shear generation and sustainment and convective/dynamic stabilities measured by the sodium lidar at the altitude of 80-105 km during 2002-2005. The correlation between wind shear, S, and Brunt-Vaisala frequency, N suggests that the maximum sustainable wind shear is determined by the necessary condition for dynamic instability of Richardson number, leading to the result that the maximal wind shear occurs at altitudes of lower thermosphere where the atmosphere is convectively very stable. The dominate source for sustainable large windshears appears to be the semidiurnal tidal-period perturbations with shorter vertical wavelengths and greater amplitude.
Open Access
Characterization of integrated optical waveguide devices
(Colorado State University. Libraries, 2008) Yuan, Guangwei, author
At the Optoelectronics Research Lab in ECE at CSU, we explore the issues of design, modeling and measurement of integrated optical waveguide devices of interest, such as optical waveguide biosensors and on-chip optical interconnects. A local evanescent-field array coupled (LEAC) sensor was designed to meet the needs for low-trace biological detection without florescent chemical agent aids. The measurement of LEACs sensor requires the aid of either a commercial near-field scanning optical microscope (NSOM) or new proposed buried detector arrays. LEAC sensors were first used to detect pseudo-adlayers on the waveguide top surface. These adlayers include SiNx and photoresist. The field modulation that was obtained based on NSOM measurement was approximately 80% for a 17 nm SiNx adlayer that was patterned on the waveguide using plasma reactive ion etching. Later, single and multiple regions of immunoassay complex adlayers were analyzed using NSOM. The most recent results demonstrated the capability of using this sensor to differentiate immunoassay complex regions with different surface coverage ratio. The study on buried detectors revealed a higher sensitivity of the sensor to a thin organic film on the waveguide. By detecting the optical intensity decay rate, the sensor was able to detect several nanometer thick film with 1.7 dB/mm/nm sensitivity. In bulk material analysis, this sensor demonstrated more than 15 dB/mm absorption coefficient difference between organic oil and air upper claddings. In on-chip optical interconnect research, optical waveguide test structures and leaky-mode waveguide coupled photodetectors were designed, modeled and measured. A 16-node H-tree waveguide was used to deliver light into photodetectors and characterized. Photodetectors at each end node of the H-tree were measured using near-field scanning microscopy. The 0.5 micrometer wide photodetector demonstrated up to 80% absorption ratio over just a 10 micrometer length. This absorption efficiency is the highest among reported leaky-mode waveguide coupled photodetectors. The responsivity and quantum efficiency of this photodetector are 0.35 A/W and 65%, respectively.
Open Access
Applications of extreme ultraviolet compact lasers to nanopatterning and high resolution holographic imaging
(Colorado State University. Libraries, 2008) Wachulak, Przemyslaw Wojciech, author; Marconi, Mario C., advisor
This dissertation describes two applications of extreme ultraviolet light in nanotechnology. Using radiation with a wavelength in the extreme ultraviolet (EUV) range allows to reach scales much smaller than with a conventional visible illumination. The first part of this dissertation describes a series of experiments that allowed the patterning at nanometer scales with sub-100nm resolution. Two types of photoresists (positive tone - PMMA and negative tone - HSQ) were patterned over the areas up to a few mm2 with features as small as 45nm using the interferometric lithography approach, reaching resolution equivalent to the wavelength of the illumination - 46.9nm. For the nanopatterning experiments two types of interferometers were studied in detail: Lloyd's mirror configuration and an amplitude division interferometer. Both approaches are presented and their advantages and drawbacks are discussed. The second part of the dissertation focuses on holographic imaging with ultimate resolution approaching the wavelength of the illumination. Different experiments were performed using Gabor's in-line holographic configuration and its capabilities in the EUV region were discussed. Holographic imaging was performed with different objects: AFM probes, spherical markers and carbon nanotubes. The holograms were stored in a high resolution recording medium - photoresist, digitized with an atomic force microscope and numerically reconstructed using a code based on the Fresnel propagator algorithm achieving in the reconstructed images the ultimate wavelength resolution. The resolution for the carbon nano-tubes images was assessed by two independent measurements: the knife-edge test resulting 45.5nm and an algorithm based on the correlation between the reconstructed image and a set of templates with variable resolution obtained by successive Gaussian filtering. This analysis yielded a resolution ~46nm. A similar algorithm that allowed for the simultaneous assessment of the resolution and the size of the features was used in EUV microscopy images confirming the validity and robustness of the code. A very fast, non-recursive reconstruction algorithm based on fast Fourier transform allowed for three dimensional surface reconstruction of the hologram performed by optical numerical sectioning, with a lateral resolution ~200nm and depth resolution ~2μm.
Open Access
Towards emulation of large-scale IP networks using end-to-end packet delay characteristics
(Colorado State University. Libraries, 2008) Vivanco, Daniel A., author; Jayasumana, Anura, advisor
Network emulation combines concepts from network simulation and measurements and provides a emulated network testbed over which application and protocols can be tested. Existing network emulators are not scalable due to the limitations of available computer hardware infrastructure and the reliance on one-to-one packet mapping and modeling scheme. This research proposes a measurement-based modeling methodology for the design of a network-in-a-box emulator. Methodology aims at overcoming the limitation of computational overhead and end-to-end network system characterization. A framework for large scale IP network emulation, named Overall Trend Replicating Network Emulator Tool (OTRENET), is presented. OTRENET intercepts data packet streams and modify them, based on network system models, in real-time. The complexity and overhead of packet-by-packet mapping and modeling, while producing results consistent with measurements is achieved by a traffic sampling algorithm. Such algorithm monitors traffic metrics in a per-packet level, to dynamically separate it into frames. A comprehensive study of end-to-end packet delay dynamics, in the context of network system modeling, is presented. Theoretical basis, techniques and measurements for network packet delay dynamics characterization and modeling for various sending rate conditions and network stages have been developed. Goodness-of-fit results demonstrate the modeling accuracy for both packet delay and IPG processes for cases where sending bit rate is relatively small compared to the link capacity. However, as the sending bit rate increases, as a fraction of the bandwidth, IPG becomes a better alternative for network system modeling. A novel approach for online modeling end-to-end packet delay dynamics is proposed to address non-stationarity of network systems. Proposed methodology models and captures the network system characteristics taking into account the non-stationarity of the packet delay samples. In general, results presented show that analyzing packet delay processes by modeling the segmented traces yield a better understanding of the network system dynamics.
Open Access
Rapid early design space exploration using legacy design data, technology scaling trend and in-situ macro models
(Colorado State University. Libraries, 2009) Thangaraj, Charles V. K., author; Chen, Tom, advisor
CMOS technology scaling trend, i.e. the doubling of the operating frequency and the doubling of the number of transistors on a die every eighteen months, also know as Moore's Law has been a fundamental driver for the semiconductor industry for well over three decades. Scaling CMOS technologies into deep sub micron especially into sub 100 nm dimensions have caused a significant shift in business and design philosophy, and methodology. In addition to the semiconductor industry maturation there are seven key disruptive trends impacting the semiconductor industry. They are competitive landscape changes, technology convergence, greater global connectedness, increased design complexity, commoditization, consumerization, and the soaring research, development and engineering costs. These disruptions have made traditional business models increasingly ineffective and the benefits of Moore's Law insufficient for sustained competitiveness [1]. 'More-than-Moore' approach to heterogeneous system integration and holistic system optimization strategies in addition to the benefits of technology scaling are necessary for future success [2] [3].
Open Access
Robust resource allocation in heterogeneous parallel and distributed computing systems
(Colorado State University. Libraries, 2008) Smith, James T., II, author; Siegel, H. J., advisor; Maciejewski, A. A., advisor
In a heterogeneous distributed computing environment, it is often advantageous to allocate system resources in a manner that optimizes a given system performance measure. However, this optimization is often dependent on system parameters whose values are subject to uncertainty. Thus, an important research problem arises when system resources must be allocated given uncertainty in system parameters. Robustness can be defined as the degree to which a system can function correctly in the presence of parameter values different from those assumed. In this research, we define mathematical models of robustness in both static and dynamic stochastic environments. In addition, we model dynamic environments where estimates of system parameter values are provided as point estimates where these estimates are known to deviate substantially from their actual values. The main contributions of this research are (1) mathematical models of robustness suitable for dynamic environments based on single estimates of system parameters (2) a mathematical model of robustness applicable to environments where the uncertainty in system parameters can be modeled stochastically, (3) a demonstration of the use of this metric to design resource allocation heuristics in a static environment, (4) a mathematical model of robustness in a stochastic dynamic environment, (5) we demonstrate the utility of this dynamic robustness metric through the design of resource allocation heuristics, (6) the derivation of a robustness metric for evaluating resource allocation decisions in an overlay network along with a near optimal resource allocation technique suitable to this environment.
Open Access
Robust resource-allocation methods for QOS-constrained parallel and distributed computing systems
(Colorado State University. Libraries, 2008) Shestak, Valdimir, author; Maciejewski, A. A., advisor; Siegel, Howard Jay, advisor
This research investigates the problem of robust resource allocation for distributed computing systems operating under imposed Quality of Service (QoS) constraints. Often, such systems are expected to function in a physical environment replete with uncertainty, which causes the amount of processing required over time to fluctuate substantially. In the first two studies, we show how an effective resource allocation can be achieved in the heterogeneous shipboard distributed computing system and IBM cluster based imaging system. The general form for a stochastic robustness metric is then presented based on a mathematical model where the relationship between uncertainty in system parameters and its impact on system performance are described stochastically. The utility of the established metric is exploited in the design of optimization techniques based on greedy and iterative approaches that address the problem of resource allocation in a large class of distributed systems operating on periodically updated data sets. One of the major reasons for possible QoS violations in distributed systems is a loss of resources, frequently caused by abnormal operating conditions. One aspect that makes a resource allocation problem extremely challenging in such systems is a random nature of resource failures and recoveries. The last study presented in this work describes a solution method that was developed for this case based on the concepts of the Derman-Lieberman-Ross theorem. The experimental results indicate a significant potential of this approach to generate robust resource allocations in unstable distributed systems.
Open Access
Differential gene expression in Escherichia coli following exposure to non-thermal atmospheric-pressure plasma
(Colorado State University. Libraries, 2008) Sharma, Ashish, author; Collins, George, advisor; Pruden, Amy, advisor
Plasma decontamination provides a low temperature and non-toxic means of treating objects where heating and exposure to poisonous compounds is not acceptable especially in applications relating to medical devices and food packaging. The effects of various plasma constituents (UV photons, reactive species, charged particles etc.) acting independently and/or synergistically on bacteria at the biomolecular level is not well understood. High-density oligonucleotide microarrays were used to explore the differential gene expression of the entire genome of E. coli following plasma treatment. The results indicate a significant induction of genes involved in DNA repair and recombination suggesting that plasma exposure caused substantial DNA damage in the cell. There was also evidence of oxidative stress and suppression of genes involved in housekeeping functions of energy metabolism and ion transport. Experiments were also carried out to optimize plasma operating parameters to achieve a higher rate of inactivation of microbes. Overall, the results of this study will help to further optimize non-thermal plasma applications for bacterial inactivation.
Open Access
CMOS-compatible on-chip optical interconnects
(Colorado State University. Libraries, 2009) Pownall, Robert Elliott, author; Lear, Kevin L., advisor
The increase in complexity of integrated circuits (ICs) over the past five decades has resulted increasing demands on the interconnect layers. In the past decade, the ability of conventional "electrical signal down a metal wire" interconnect to keep up with the increasing demands placed on interconnect has come more and more into question. To meet the increasing demands on interconnect and to get around the limitation of conventional "metal wire" interconnect, various forms of optical interconnect have been proposed.
Unknown
Three-dimensional water vapor retrieval using a network of scanning compact microwave radiometers
(Colorado State University. Libraries, 2009) Padmanabhan, Sharmila, author; Reising, S. C., advisor
Quantitative precipitation forecasting is currently limited by the paucity of observations on sufficiently fine temporal and spatial scales. In particular, convective storms have been observed to develop in regions of strong and rapidly evolving moisture gradients that vary spatially on sub-meso γ scales (2-5 km). Therefore, measurements of water vapor aloft with high time resolution and sufficient spatial resolution have the potential to improve forecast skill for the initiation of convective storms. Such measurements may be used for assimilation into and validation of numerical weather prediction (NWP) models. Currently, water vapor density profiles are obtained using in-situ sensors on radiosondes and remotely using lidars, GPS ground-based networks, CPS radio occultation from satellites and a relatively small number of space-borne microwave and infrared radiometers. In-situ radiosonde measurements have excellent vertical resolution but are severely limited in temporal and spatial coverage. In addition, each radiosonde takes 45-60 minutes to rise from ground level to the tropopause, and is typically advected by upper-level winds up to tens of km horizontal displacement from its launch site. Tomographic inversion applied to ground-based measurements of GPS wet delay is expected to yield data with 0.5-1 km vertical resolution at 30-minute intervals. COSMIC and CHAMP satellites in low earth orbit (LEO) provide measurements with 0.1-0.5 km vertical resolution at 30-minute intervals but only 200-600 km horizontal resolution, depending on the magnitude of the path-integrated refractivity. Microwave radiometers in low-earth orbit provide reasonable vertical resolution (2 km) and mesoscale horizontal resolution (20 km) with long repeat times. Both the prediction of convective initiation and quantitative precipitation require knowledge of water vapor variations on sub-meso γ scales (2-5 km) with update times on the order of a few tens of minutes. Due to the relatively high cost of both commercially-available microwave radiometers for network deployment and rapid radiosonde launches with close horizontal spacing, such measurements have not been available. Measurements using a network of multi-frequency microwave radiometers can provide information to retrieve the 3-D distribution of water vapor in the troposphere. An Observation System Simulation Experiment (OSSE) was performed in which synthetic examples of retrievals using a network of radiometers were compared with results from the Weather Research Forecasting (WRF) model at a grid scale of 500 m. These comparisons show that the 3-D water vapor field can be retrieved with an accuracy varying from 15-40% depending on the number of sensors in the network and the location and time of the a priori. To deploy a network of low cost radiometers, the Compact Microwave Radiometer for Humidity profiling (CMR-H) was developed by the Microwave Systems Laboratory at Colorado State University. Using monolithic microwave integrated circuit technology and unique packaging yields a radiometer that is small (24 x 18 x 16 cm), light weight (6 kg), relatively inexpensive and low-power consumption (25-50 W, depending on weather conditions). Recently, field measurements at the DOE Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma have demonstrated the potential for coordinated, scanning microwave radiometers to provide 0.5-1 km resolution both vertically and horizontally with sampling times of 15 minutes or less. This work describes and demonstrates the use of algebraic reconstruction tomography to retrieve the 3-D water vapor field from simultaneous brightness temperatures using radiative transfer theory, optimal estimation and Kalman filtering.
Unknown
The study and real-time implementation of attenuation correction for X-band dual-polarization weather radars
(Colorado State University. Libraries, 2008) Liu, Yuxiang, author; Bringi, V. N., advisor; Chandrasekar, V., advisor
Attenuation of electromagnetic radiation due to rain or other wet hydrometeors along the propagation path has been studied extensively in the radar meteorology community. Recently, use of short range dual-polarization X-band radar systems has gained momentum due to lower system cost compared with the much more expensive S-band systems. Advances in dual-polarization radar research have shown that the specific attenuation and differential attenuation between horizontal and vertical polarized waves caused by oblate, highly oriented raindrops can be estimated using the specific differential phase. This advance leads to correction of the measured reflectivity (Zh) and the differential reflectivity (Zdr) due to path attenuation. This thesis addresses via theory, simulations and data analyses the accuracy and optimal estimation of attenuation-correction procedures at X-band frequency. Real-time implementation of the correction algorithm was developed for the first generation of X-band dual-polarized Doppler radar network (Integration Project 1, IP1) operated by the NSF Center for Collaborate Adaptive Sensing of the Atmosphere (CASA). We evaluate the algorithm for correcting the Zh, and the Zdr for rain attenuation using simulations and X-band radar data under ideal and noisy situations. Our algorithm is able to adjust the parameters according to the changes in temperature, drop shapes, and a certain class of drop size distributions (DSD) with very fast convergence. The X-band radar data were obtained from the National Institute of Earth Science and Disaster Prevention (NIED), Japan, and from CASA IP1. The algorithm accurately corrects NIED's data when compared with ground truth calculated from in situ disdrometer-based DSD measurements for a Typhoon event. We have implemented, in real-time, the algorithm in all the CASA IP1 radar nodes. We also evaluate our preliminary method that separately estimates rain and wet ice attenuation using microphysical outputs from a previous supercell simulation using the CSU-RAMS (Regional Atmospheric Modeling System). The retrieved rain and wet ice specific attenuation fields were found to be in close correspondence to the 'true' fields calculated from the simulation. The concept to correct rain and wet ice attenuation separately can be also applied to the CASA IP1 network with additional constraint information possibly provided by the WSR-88D network.
Unknown
Application-aware in-network service and data fusion frameworks for distributed adaptive sensing systems
(Colorado State University. Libraries, 2009) Lee, Pan Ho, author; Jayasumana, Anura P., advisor
Distributed Collaborative Adaptive Sensing (DCAS) systems are emerging for applications, such as detection and prediction of hazardous weather using a network of radars. Collaborative Adaptive Sensing of the Atmosphere (CASA) is an example of these emerging DCAS systems. CASA is based on a dense network of weather radars that operate collaboratively to detect tornadoes and other hazardous atmospheric conditions. This dissertation presents an application-aware data transport framework to meet the data distribution/processing requirements of such mission-critical sensor applications over best-effort networks. Our application-aware data transport framework consists of overlay architecture and a programming interface. The architecture enables deploying application-aware in-network services in an overlay network to allow applications to best adapt to the network conditions. The programming interface facilitates development of applications within the architectural framework. We demonstrate the efficacy of the proposed framework by considering a DCAS application. We evaluate the proposed schemes in a network emulation environment and on Planetlab, a world-wide Internet test-bed. The proposed schemes are very effective in delivering high quality data to the multiple end users under various network conditions. This dissertation also presents the design and implementation of an architectural framework for timely and accurate processing of radar data fusion algorithms. The preliminary version of the framework is used for real-time implementation of a multi-radar data fusion algorithm, the CASA network-based reflectivity retrieval algorithm. As a part of this research, a peer-to-peer (P2P) collaboration framework for multi-sensor data fusion is presented. Simulation-based results illustrate the effectiveness of the proposed P2P framework. As multi-sensor fusion applications have a stringent real-time constraint, estimation of network delay across the sensor networks is important, particularly as they affect the quality of sensor fusion applications. We develop an analytical model for multi-sensor data fusion latency for the Internet-based sensor applications. Time scale-invariant burstiness observed across the network produces excessive network latencies. The analytical model considers the network delay due to the self-similar cross-traffic and latency for data synchronization for data fusion. A comparison of the analytical model and simulation-based results show that our model provides a good estimation for the multi-sensor data fusion latency.
Open Access
Simulation of space-based radar observations of precipitations
(Colorado State University. Libraries, 2008) Khajonrat, Direk, author; Chandra, Chandrasekar V., advisor
The Tropical Rainfall Measurement Mission (TRMM) will soon be followed on by the Global Precipitation Measurement (GPM). The GPM satellite will be the next generation observation of precipitation from space. The GPM will carry a dual-frequency precipitation radar (DPR) operating at 13.6 GHz (Ku-band) and 35.6 GHz (Ka-band), as opposed to a single-frequency 13.8 GHz (Ku-band) precipitation radar (PR) in TRMM. A greater degree of accuracy of precipitation measurements can be achieved by a dual-frequency radar using measurements from the two channels. The DPR on the GPM will be the first space-based dual-frequency precipitation radar. Since spaceborne precipitation observations have never been done in Ka-band before, extensive research on dual-frequency radar, including electromagnetic wave propagation characteristics from space and retrieval algorithms are essential for system development and system evaluations. Because the DPR is the first of its kind, a simulation-based study can provide significant assessment of the GPM system which is presented here. The research reported here focuses on developing methodologies for simulating the precipitation characteristics that would be observed from space by DPR using current space-based radar observations and earth-based radar measurements. The underlying microphysics of precipitation structures are important for developing a simulation model and a realistic model of precipitation is desired for representative simulation results. In this research; a microphysical model of precipitation is developed based on airborne radar measurements. The simulation of precipitation observations in Ku- and Ka-band are performed using both TRMM-PR observations and ground-based radar measurements. The simulation of a wide variety of precipitation regimes reveals the characteristics of the precipitation observed in Ku- and Ka-band, and allows testing of different retrieval algorithms-either the single-frequency (TRMM-like algorithm) or dual-frequency techniques. A significant degradation of signal in the Ka-band channel in intense precipitation such as an intense convective storm and tropical storms directly affect the retrieval algorithms that can be used. Vertical reflectivity profiles classification and drop size distribution parameters estimation of tropical storms are studied and results are presented here.
Open Access
Gas phase cluster studies using a desk-top size soft x-ray laser for single photon ionization
(Colorado State University. Libraries, 2009) Heinbuch, Scott, author; Rocca, Jorge G., advisor
This dissertation reports the study of the structure and reactivity of clusters using a new mass spectrometry approach in which the ionization is produced by high energy photons generated by a desk-top size soft x-ray (SXR) laser. The work was motivated by the importance that catalytic processes have in enhancing the rate of gas phase chemical reactions such as the manufacture of hydrocarbons, polymers, drugs, sulfuric acid, fertilizers, pesticides, etc., many forms of pollution control, development of robust mirror coatings for extreme ultraviolet (EUV) lithography, and hydrogen storage for clean energy applications. Extensive mass spectrometry studies have shown that gas phase nanoclusters are effective model systems to study surface reactions in the bulk phase. However, the use of multi-photon ionization or electron impact ionization sources results in cluster fragmentation, limiting the information gained about the neutral cluster parent. Our approach uses the 26.5 eV photons of a compact capillary discharge driven laser to ionize clusters by single photon events, avoiding the cluster fragmentation associated with multi-photon ionization. The high photon energy also allows the detection of neutral clusters and small molecule reaction products with high ionization energies. Experiments were conducted for several types of clusters including van der Waals clusters, metal oxides, and metal oxide reactions. Density Functional Theory (DFT) calculations were employed to elucidate cluster geometries, properties, and reaction mechanisms. For hydrogen/van der Waals clusters, the unimolecular dissociation rate constants for reactions involving loss of one neutral molecule were calculated and neutral cluster temperature were estimated. The results of metal oxide clusters experiments and calculations suggest that SO2 can be reduced and oxidized by oxygen deficient and oxygen rich vanadium oxide clusters, respectively. Three SO3 formation mechanisms are proposed, and several condensed phase catalytic cycles are suggested based on SO3 formation mechanisms. Other experiments showed that C=C bonds of alkenes can be broken on neutral vanadium oxide oxygen rich clusters with the general structure VO3(V2O 5)n=0,1,2.... DFT calculations provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes are broken. New results also help to elucidate the selective catalytic reduction of NO using NH3 on a vanadium oxide catalyst. A separate set of experiments to identify capping layer materials for extreme EUV optical coatings that are resistive to carbon contamination. Results show that oxidized Hf and Zr are much less reactive than Ti or Si oxide, and might lead to capping layers that might extend lifetimes of EUV mirror coating upon EUV irradiation. Zr oxide was found to be less reactive than Hf oxide. The set of results demonstrate the potential of compact soft-ray lasers as new tools for chemistry and photo-physics studies with intense soft x-ray light in small laboratory environments.
Open Access
Propagation and frequency conversion of ultrashort pulses in the presence of coherent nuclear motion
(Colorado State University. Libraries, 2008) Hartinger, Klaus Karl, author; Bartels, R. A., advisor
We have investigated linear as well as nonlinear propagation effects on a relatively weak ultrashort pulse arising from coherent nuclear motion. To this end, we have developed analytical and numerical models used to calculate the molecular response to a strong, ultrashort pump pulse, and propagate a weak probe pulse in the presence of the nuclear wave packet. The molecular response is described in terms of an "effective" susceptibility, which can be split into linear and nonlinear contributions. While a lot of what is discussed in terms of propagation effects is applicable to both rotational and vibrational wave packets, molecular alignment, i.e., coherent rotational motion of linear molecules, is where the focus lies. We have applied spectral interferometry to detect molecular alignment, both in scanning and single-shot configurations, to observe propagation effects due to the effective linear susceptibility, as well as carried out calculations and measurements showing the dependence of the effective third-order susceptibility on coherent nuclear motion. Lastly, a strong enhancement in the conversion efficiency to the third harmonic of a relatively weak probe pulse is observed in a variety of molecular and atomic gases.
Open Access
Networked radar systems: waveforms, signal processing and retrievals for volume targets
(Colorado State University. Libraries, 2009) Bharadwaj, Nitin, author; Venkatachalam, Chandrasekar, advisor
Networked radar systems consisting of a dense set of agile short-range high frequency radars operating as Distributed Collaborative Adaptive System (DCAS) is an emerging innovative concept for atmospheric remote sensing that offer great potential to address several challenging problems in atmospheric remote sensing. This research addresses some of the unique challenges that must be overcome to successfully deploy a networked radar system. This research also provides a novel waveform and methodology for a networked radar environment and wideband waveforms for next generation precipitation radars.
Open Access
Application-aware transport services for sensor-actuator networks
(Colorado State University. Libraries, 2007) Banka, Tarun, author; Jayasumana, Anura P., advisor; Chandrasekar, V., advisor
Many emerging mission-critical sensor actuator network applications rely on the best-effort service provided by the Internet for data dissemination. This dissertation investigates the paradigm of application-aware networking to meet the QoS requirements of the mission-critical applications over best-effort networks that do not provide end-to-end QoS support. An architecture framework is proposed for application-aware data dissemination using overlay networks. The application-aware architecture framework enables application-aware processing at overlay nodes in the best-effort network to meet the QoS requirements of the heterogeneous end users of mission-critical sensor-actuator network applications. An application-aware congestion control protocol performs data selection and real-time scheduling of data for transmission while considering different bandwidth and data quality requirements of heterogeneous end users. A packet-marking scheme is proposed that enables application-aware selective drop and forwarding of packets at intermediate overlay nodes during network congestion to further enhance the QoS received by the end users under dynamic network conditions. Effectiveness of the transport services based on application-aware architecture framework is demonstrated by one-to-many high-bandwidth time-series radar data dissemination protocol for CASA (Collaborative Adaptive Sensing of the Atmosphere) application. Experiment results demonstrate that under similar network conditions and available bandwidth, application-aware processing at overlay nodes significantly improves the quality of the time-series radar data delivered to the end users compared to case when no such application-aware processing is performed. Moreover, it is shown that application-aware congestion control protocol is friendly to the already existing TCP cross-traffic on the network as long as bandwidth requirements of the mission-critical applications are met. Scalability analysis of application-aware congestion control protocol shows that it is able to schedule data at cumulative rates of more than 700M bps without degrading the QoS received by multiple end users.
Open Access
Rainfall estimation from spaceborne and ground based radars using neural networks
(Colorado State University. Libraries, 2009) Alqudah, Amin, author; Chandra, Chandrasekar V., advisor
Rainfall observed on the ground is dependent on the four dimensional radar observations. However it is difficult to express this in a simple form. A simple Z-R relation is not sufficient and has large uncertainty and it needs to be adaptively adjusted. Prior research has shown that neural networks can be used to estimate ground rainfall from radar measurements. Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) is the first space borne observation platform for mapping precipitation over the tropics. TRMM measured rainfall is important in order to study the precipitation distribution all over the globe in the tropics. TRMM ground validation is a critical important component to ensure the measurement accuracy. However, this ground validation has quite different characteristics from TRMM in terms of resolution, scale, viewing aspect, and uncertainties. This makes the use of ground radar rainfall information to correct TRMM rainfall estimates a very challenging task. In this dissertation, rainfall estimation using neural networks is investigated in order to improve rainfall estimation based on measurements taken by ground radars and TRMM-PR. Ground Radar measurements will be used to estimate rainfall using adaptive neural networks. Improvements are also suggested and performed including the use of Principal Components Analysis, ensemble average neural network, and the use of Bayesian Neural Networks. For TRMM-PR purposes a single neural network is not efficient to extract the relation between TRMM-PR measurements and the rain gauges; this is because of the resolution differences between TRMM-PR profile and the rain gauges and the low number of TRMM overpasses over these gauges which will make the training data set to have less number of profiles and not be able to generalize. Therefore, a novel hybrid Neural Network model is presented to train ground radars for rainfall estimate using rain gauge data and subsequently the trained ground radar rain estimates to train TRMM-PR based Neural Networks for rainfall estimation. This hybrid neural network model will derive the relation between rain gauges and ground radar measurements, and transfer this relation to adaptive rainfall estimation for TRMM-PR in order to estimate rainfall and generate global rainfall maps.
Open Access
Extreme ultraviolet laser ionization mass spectrometry: probing materials at the micro and nano scales
(Colorado State University. Libraries, 2023) Rush, Lydia Alexandra, author; Menoni, Carmen S., advisor; Duffin, Andrew M., advisor; Farmer, Delphine K., committee member; Marconi, Mario C., committee member; Rocca, Jorge J., committee member
The focus of this dissertation is the use of 50 to 10 nanometer wavelength extreme ultraviolet (EUV) laser light as a next generation probe for mass spectrometry analyses at the micro (>100 nanometers) and nano (≤100 nanometer) spatial scales. While the unique properties of EUV light have revolutionized the semiconductor industry through nanoscale lithography fabrication, the use of EUV lasers with analytical instruments, like mass spectrometers, for high spatial resolution chemical analyses is a relatively untapped area. This unexplored territory is owed partly to only recently bringing EUV lasers to an accessible "bench-top" scale. Herein I show how EUV laser ionization can be used with different types of mass spectrometers as a new route for interrogating nuclear and geologic materials with micro and nano scale lateral spatial resolution. I focus on the application of a compact capillary discharge EUV laser operating at a wavelength of 46.9 nanometers connected to a time-of-flight (TOF) mass spectrometer, called the EUV TOF. I also show for the first time how the 46.9 nm EUV laser ionization source can be connected to a commercial magnetic sector mass spectrometer, called the EUV magnetic sector. Specifically, I demonstrate that the EUV TOF instrument can measure the 235U/238U isotope ratio in 100 nm sized pixels in a heterogeneous uranium fuel pellet that was made by blending different feedstocks together. The results show that the EUV TOF maps similar micrometer sized areas of 235U/238U heterogeneity as nanoscale secondary ionization mass spectrometry (NanoSIMS), indicating that EUV laser ionization can be used to accurately probe complex nuclear materials within the scope of the study. I also show that the EUV TOF can be used to measure 206Pb/238U and 232Th/238U isotope ratios at the 8 µm scale in select geologic matrices of silicates, zircons, monazites, and iron manganese within error (±2σ) using a single non-matrix matched calibration standard. However, the precision on the ratio measurements was low for useful geologic applications, ranging between 1-10% at elemental concentrations exceeding hundreds of ppm because of the limitations of using a TOF for isotope ratio measurements. To this end, I show the current development of the new EUV magnetic sector instrument that uses the EUV laser ionization source with a commercial double-focusing sector-field multi-collector mass spectrometer with the aim of achieving more precise (<1%) and sensitive (≤ppm) isotope ratio measurements at high spatial scales (<10 µm down to the nanoscale). The EUV magnetic sector is being developed to probe more complex isotopic systems in nuclear and geologic materials that was not possible with the TOF mass spectrometer. The work here shows that the 46.9 nm wavelength EUV laser ionization source can be interfaced with Thermo Fisher's commercial sector-field multi-collector mass spectrometer called the Neptune by removing its inductively coupled plasma (ICP) region. The Neptune's ion optics, electric sector, and magnetic sector were modified for acceptance of the pulsed EUV-generated ions. These modifications resulted in ions from ≤2 µm diameter craters created by EUV laser ablation and ionization being successfully focused, separated by mass, and detected using the Neptune's electron multipliers. However, further system upgrades to the Neptune's detectors are needed for accurate isotope ratio measurements at high spatial scales because the 10 to 30 nanosecond wide EUV-generated ion pulses are on the order of the electron multipliers' dead time. With proper detectors, the EUV magnetic sector's accuracy, precision, sensitivity, efficiency, and spatial resolution can be measured in future experiments. The demonstration of the EUV magnetic sector instrument here represents the first time that an EUV laser ionization source has been used with a sector-field mass spectrometer, paving the way for future high spatial resolution isotope ratio analyses.
Embargo
Advanced solutions for rainfall estimation over complex terrain in the San Francisco Bay area
(Colorado State University. Libraries, 2023) Biswas, Sounak Kumar, author; Chandrasekar, V., advisor; Cheney, Margaret, committee member; Gooch, Steven, committee member; James, Susan, committee member
Fresh water is an increasingly scarce resource in the western United States and effective management and prediction of flooding and drought have a direct economic impact on almost all aspects of society. Therefore it is critical to monitor and predict water inputs into the hydrological cycle of the Western United States (US). The complex topography of the western US poses a significant challenge in developing physically realistic and spatially accurate estimates of precipitation using remote sensing techniques. The intricate landscape presents a challenging observing environment for weather radar systems. This is further compounded by the complex microphysical processes during the cool season which are influenced by coastal air-sea interactions, as well as orographic effects along the coastal regions of the West. The placement and density of operational National Weather Service (NWS) radars (popularly known as NEXRAD or WSR-88D) pose a challenge in meeting the needs for water resource management in the western US due to the complex terrain of the region. Consequently, areas like the San Francisco Bay Area could use enhanced precipitation monitoring, in terms of amount and type, along watersheds and surrounding rivers and streams. Shorter wavelength radars such as X-Band radar systems are able to augment the WSR-88D network, to observe better the lower atmosphere with higher temporal and spatial resolution. This research investigates and documents the challenges of precipitation monitoring by radars over complex terrain and aims to provide effective and advanced solutions for accurate Quantitative Precipitation Estimation (QPE) using both WSR-88D and the gap-filling X-Band radar systems over the Bay Area on the US West Coast, with a focus on the cool season. Specifically, this study focuses on a precipitation microphysics perspective, aiming to create an algorithm capable of distinguishing orographically enhanced rainfall from cool-season stratiform rainfall using X-Band radar observations. A radar-based rainfall estimator is developed to increase the accuracy of rainfall quantification. Additionally, various other scientific and engineering challenges have been addressed including radar calibration, attenuation correction of the radar beam, radar beam blockage due to terrain, and correction of measurements of the vertical profiles of radar observables. The final QPE product is constructed by merging the X-Band based QPE product with the operational NEXRAD based QPE product, significantly enhancing the overall quality of rainfall mapping within the Bay Area. Case studies reveal that the new product is able to improve QPE accuracy by ~70% in terms of mean absolute error and root mean squared error compared to the operational products. This establishes the overall need for precipitation monitoring by gap-filling X-Band radar systems in the complex terrain of the San Francisco Bay Area.