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Broadband coherent light generation in Raman-active crystals driven by femtosecond laser fieldsZhi, Miaochan 15 May 2009 (has links)
I studied a family of closely connected topics related to the production and application
of ultrashort laser pulses. I achieved broadband cascade Raman generation
in crystals, producing mutually coherent frequency sidebands which can possibly be
used to synthesize optical pulses as short as a fraction of a femtosecond (fs). Unlike
generation using gases, there is no need for a cumbersome vacuum system when
working with room temperature crystals. Our method, therefore, shows promise for
a compact system.
One problem for sideband generation in solids is phase matching, because the
dispersion is significant. I solved this problem by using non-collinear geometry. I
observed what to our knowledge is a record-large number of spectral sidebands generated
in a popular Raman crystal PbWO4 covering infrared, visible, and ultraviolet
spectral regions, when I applied two 50 fs laser pulses tuned close to the Raman
resonance. Similar generation in diamond was also observed, which shows that the
method is universal. When a third probe pulse is applied, a very interesting 2-D color
array is generated in both crystals.
As many as 40 anti-Stokes and 5 Stokes sidebands are generated when a pair of
time-delayed linear chirped pulses are applied to the PbWO4 crystal. This shows that
pulses with picosecond duration, which is on the order of the coherence decay time,
is more effective for sidebands generation than Fourier transform limited fs pulses. I also studied the technique of fs coherent Raman anti-Stokes scattering (CARS)
which is used as a tool for detecting dipicolinic acid, the marker molecule for bacterial
spores. I observed that there is a maximum when the concentration dependence of
the near-resonant CARS signal is measured. I presented a model to describe this
behavior, and found an analytical solution that agrees with our experimental data.
Theoretically, I explored a possible application for single-cycle pulses: laser induced
nuclear fusion. I performed both classical and quantum mechanical calculations
for a system of two nuclei moving under a superintense ultrashort field. From our
calculation I noted that the nuclear collisions occur on a sub-attosecond time scale,
and are predicted to result in an emission of zeptosecond bursts of light.
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Investigation of the mechanism of phosphotriesterase: characterization of the binuclear metal active site by electron paramagnetic resonance spectroscopySamples, Cynthia Renee 15 May 2009 (has links)
Phosphotriesterase (PTE) from Pseudomonas diminuta is a zinc metalloenzyme
found in soil bacteria capable of organophosphate hydrolysis at rates approaching the
diffusion controlled limit. Interest in PTE for degradation of chemical warfare agents and
disposal of pesticides supports the need to understand the mechanism by which it
performs hydrolysis. For further mechanistic clarity, this work will provide direct
confirmation of the solvent bridge identity and the protonated species resulting in loss of
catalytic identity. Inhibitor and product binding to the metal center will also be
addressed; as well as the evaluation of the catalytic activity of Fe(II)-substituted PTE.
This work has determined that the Mn/Mn-PTE electron paramagnetic resonance
(EPR) spectrum exhibits exchange coupling that is facilitated through a hydroxide bridge.
Protonation of the bridging hydroxide results in the loss of the exchange coupling
between the two divalent cations and the loss of catalytic activity. The reversible
protonation of the bridging hydroxide has an apparent pKa of 7.3 based upon changes in
the EPR spectrum of Mn/Mn-PTE with alterations in pH. The pH-rate profile for the
hydrolysis of paraoxon by Mn/Mn-PTE shows the requirement of a single function group
that must be unprotonated with a pKa of 7.1. The comparable pKa values are proposed to
result from the protonation of the same ionizable species.
The effects of inhibitor and product binding on the magnetic properties of the
metal center and the hydroxyl bridge are investigated by accessing new EPR spectral features. This work concludes that the binding of inhibitor occurs at the metal center and
results in an increase of non-bridged hydroxyl species. These results, in conjunction with
kinetic and crystallographic data, suggest that substrate binding via the phosphoryl
oxygen at the ?-metal weakens the hydroxyl bridge coordination to the ?-metal. This
loss of coordination would increase the nucleophilic character of the bridge, and binding
of the substrate to the metal center would result in a stronger nucleophile for hydrolysis.
Lastly, Fe(II) binding and activation of apoenzyme is evaluated under anaerobic
conditions. This work concludes Fe/Fe-PTE is not catalytically active, but can bind up to
2 equivalent Fe(II) ions per active site.
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Fragment Based Protein Active Site Analysis Using Markov Random Field Combinations of Stereochemical Feature-Based ClassificationsPai Karkala, Reetal 2009 May 1900 (has links)
Recent improvements in structural genomics efforts have greatly increased the
number of hypothetical proteins in the Protein Data Bank. Several computational
methodologies have been developed to determine the function of these proteins but
none of these methods have been able to account successfully for the diversity in
the sequence and structural conformations observed in proteins that have the same
function. An additional complication is the
flexibility in both the protein active site
and the ligand.
In this dissertation, novel approaches to deal with both the ligand flexibility
and the diversity in stereochemistry have been proposed. The active site analysis
problem is formalized as a classification problem in which, for a given test protein,
the goal is to predict the class of ligand most likely to bind the active site based
on its stereochemical nature and thereby define its function. Traditional methods
that have adapted a similar methodology have struggled to account for the
flexibility
observed in large ligands. Therefore, I propose a novel fragment-based approach to
dealing with larger ligands. The advantage of the fragment-based methodology is
that considering the protein-ligand interactions in a piecewise manner does not affect
the active site patterns, and it also provides for a way to account for the problems
associated with
flexible ligands. I also propose two feature-based methodologies to account for the diversity observed
in sequences and structural conformations among proteins with the same function.
The feature-based methodologies provide detailed descriptions of the active site
stereochemistry and are capable of identifying stereochemical patterns within the
active site despite the diversity.
Finally, I propose a Markov Random Field approach to combine the individual
ligand fragment classifications (based on the stereochemical descriptors) into a single
multi-fragment ligand class. This probabilistic framework combines the information
provided by stereochemical features with the information regarding geometric constraints
between ligand fragments to make a final ligand class prediction.
The feature-based fragment identification methodology had an accuracy of 84%
across a diverse set of ligand fragments and the mrf analysis was able to succesfully
combine the various ligand fragments (identified by feature-based analysis) into one
final ligand based on statistical models of ligand fragment distances. This novel
approach to protein active site analysis was additionally tested on 3 proteins with very
low sequence and structural similarity to other proteins in the PDB (a challenge for
traditional methods) and in each of these cases, this approach successfully identified
the cognate ligand. This approach addresses the two main issues that affect the
accuracy of current automated methodologies in protein function assignment.
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Techniques in Active and Generic Software LibrariesSmith, Jacob N. 2010 May 1900 (has links)
Reusing code from software libraries can reduce the time and effort to construct software
systems and also enable the development of larger systems. However, the benefits
that come from the use of software libraries may not be realized due to limitations in
the way that traditional software libraries are constructed. Libraries come equipped
with application programming interfaces (API) that help enforce the correct use of
the abstractions in those libraries. Writing new components and adapting existing
ones to conform to library APIs may require substantial amounts of "glue" code that
potentially affects software's efficiency, robustness, and ease-of-maintenance. If, as a
result, the idea of reusing functionality from a software library is rejected, no benefits
of reuse will be realized.
This dissertation explores and develops techniques that support the construction
of software libraries with abstraction layers that do not impede efficiency. In many
situations, glue code can be expected to have very low (or zero) performance overhead.
In particular, we describe advances in the design and development of active libraries
- software libraries that take an active role in the compilation of the user's code.
Common to the presented techniques is that they may "break" a library API (in a
controlled manner) to adapt the functionality of the library for a particular use case.
The concrete contributions of this dissertation are: a library API that supports
iterator selection in the Standard Template Library, allowing generic algorithms to
find the most suitable traversal through a container, allowing (in one case) a 30-fold improvement in performance; the development of techniques, idioms, and best practices
for concepts and concept maps in C++, allowing the construction of algorithms
for one domain entirely in terms of formalisms from a second domain; the construction
of generic algorithms for algorithmic differentiation, implemented as an active
library in Spad, language of the Open Axiom computer algebra system, allowing algorithmic
differentiation to be applied to the appropriate mathematical object and
not just concrete data-types; and the description of a static analysis framework to
describe the generic programming notion of local specialization within Spad, allowing
more sophisticated (value-based) control over algorithm selection and specialization
in categories and domains.
We will find that active libraries simultaneously increase the expressivity of the
underlying language and the performance of software using those libraries.
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Active Reflection Absorption for a Three Dimensional Multidirectional Wave GeneratorCruz Castro, Oscar 2009 August 1900 (has links)
In order to implement an accurate system that allows for absorption of reflected
waves impinging to a wave maker (Active Reflection Absorption), it was required to
apply a method to estimate properly the direction of arrival of the waves that does it in
the fastest way possible. Our wavemaker control system has been prepared to handle an
algorithm provided by Bosch-Rexroth where the wave angle estimation is practically
locked to a very narrow frequency band (spatial gain-mixer). The system was evaluated
with physical tests in a 3D wave basin for different conditions of reflected waves
arriving with an angle to the wavemaker front, and acceptable performance has been
found for the 3D ARA mode. However, for certain conditions over-compensation or
sub-compensation can develop resulting in a poor absorption. This is mainly related to
not being able to determine accurately the direction from which the reflected waves
travel towards the wavemaker.
The present work employed concepts found in the areas of antenna array signal
processing and signal propagation, which were applied to this problem. This approach coupled naturally with our wavemaker system since it was prepared with 48 gages that
can be employed in an array antenna fashion. A program was codified from an algorithm
found in literature to calculate the Direction of Arrival (DOA) of the reflected waves.
The focus for the testing of this program was with regular waves.
The tests were conducted to validate the program with different angles of
incidence and show that for regular waves the program was able to detect accurately the
DOA of these in as few as 5 snapshots, with a minimum of 7 gages used as the antenna
input. With data obtained directly from the control system of our wavemaker using
regular waves, the program was able to determine the DOA. The computational burden
of the algorithm is not significant in the case of regular waves. A modification of the
program is required to analyze the DOA of reflected irregular waves, which could
increase the computational burden. Actual implementation of this program to our control
system depends on cooperation with Bosch-Rexroth.
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Enhancing the Structural Performance with Active and Semi-Active Devices Using Adaptive Control StrategyBitaraf, Maryam 2011 May 1900 (has links)
Changes in the characteristics of the structure, such as damage, have not been
considered in most of the active and semi-active control methods that have been used to
control and optimize the response of civil engineering structures. In this dissertation, a
direct adaptive control which can deal with the existence of measurement errors and
changes in structural characteristics or load conditioning is used to control the
performance of structures. A Simple Adaptive Control Method (SACM) is modified to
control civil structures and improve their performance. The effectiveness of the SACM
is verified by several numerical examples. The SACM is used to reduce the structural
response such as drift and acceleration using active and semi-active devices, and its
performance is compared with that of other control methods. Also, a probabilistic
indirect adaptive control method is developed and its behavior is compared to the SACM
using a simple numerical example. In addition to the simplicity of the SACM
implementation, the results show that SACM is very effective to reduce the response of
structures with linear and non-linear behavior in comparison with other control methods.
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Acoustics in the Klebanoff-Saric Wind Tunnel: Background Identification, Forcing, and Active ControlKuester, Matthew 2012 May 1900 (has links)
Low disturbance wind tunnels, such as the Klebanoff–Saric Wind Tunnel (KSWT), offer an ideal environment to study boundary layer transition. In particular, the leading-edge receptivity of sound can be measured by creating acoustic disturbances that interact with the leading edge of a model to create Tollmien–Schlichting Waves. The magnitude and composition (sound, turbulence) of the background disturbances can affect these experiments, so the background disturbances should be minimized and documented thoroughly.
The purpose of this thesis is to document the background acoustic signature of the KSWT and describe infrastructure upgrades for acoustic receptivity experiments. The measurements presented in this thesis will support future receptivity measurements in the KSWT.
Microphone measurements revealed several important acoustic features in the tunnel. Cross correlations showed that two sources of low-frequency unsteadiness (the extended diffuser and corner two) create large pressure fluctuations that dominate the pressure spectrum. Directional separation of waves in the test section revealed that motor and blade passing noise travels primarily upstream into the test section. Finally, the acoustic treatments in the plenum are effective at removing sound from the tunnel.
A wall of speakers was installed in the plenum to enable acoustic receptivity experiments. The speakers create both the primary downstream traveling waves and reflected upstream traveling waves in the test section. An adaptive closed loop control system was installed to reduce the amplitude of the reflected waves during acoustic forcing. Although the performance of the control system is frequency dependent, the technique was implemented successfully. The reduction in the diffuser reflection will increase the quality of future acoustic receptivity experiments in the KSWT.
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Manager Allocation under Risk Budgeting-An Empirical Study of Equity Mutual Funds in TaiwanLee, Ya-Ting 19 June 2004 (has links)
none
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Develop DSP-Based Active Power Factor Correction Controller CircuitsSu, Hung-Hsien 20 October 2006 (has links)
The thesis aims to the research of active power factor correction (PFC) circuit and develop a DSP-based digital controller. In the thesis, PI controller is the control core for the voltage loop¡Band current loop, and then achieve the function of the power factor correction of boost converter. Finally, we develop a boost converter and connect it to a DSP-based controller to measure the waveforms and verify the power factor correction. Furthermore, the research can be extended to a simulating platform which we can verify the power factor correction by just changing the control law on DSP .
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GA-based Fractal Image Compression and Active Contour ModelWu, Ming-Sheng 01 January 2007 (has links)
In this dissertation, several GA-based approaches for fractal image compression and active contour model are proposed. The main drawback of the classical fractal image compression is the long encoding time. Two methods are proposed in this dissertation to solve this problem. First, a schema genetic algorithm (SGA), in which the Schema Theorem is embedded in GA, is proposed to reduce the encoding time. In SGA, the genetic operators are adapted according to the Schema Theorem in the evolutionary process performed on the range blocks. We find that such a method can indeed speedup the encoder and also preserve the image quality. Moreover, based on the self-similarity characteristic of the natural image, a spatial correlation genetic algorithm (SC-GA) is proposed to further reduce the encoding time. There are two stages in the SC-GA method. The first stage makes use of spatial correlations in images for both the domain pool and the range pool to exploit local optima. The second stage is operated on the whole image to explore more adequate similarities if the local optima are not satisfactory. Thus not only the encoding speed is accelerated further, but also the higher compression ratio is achieved, because the search space is limited relative to the positions of the previously matched blocks, fewer bits are required to record the offset of the domain block instead of the absolute position. The experimental results of comparing the two methods with the full search, traditional GA, and other GA search methods are provided to demonstrate that they can indeed reduce the encoding time substantially. The main drawback of the traditional active contour model (ACM) for extracting the contour of a given object is that the snake cannot converge to the concave region of the object under consideration. An improved ACM algorithm is proposed in this dissertation to solve this problem. The algorithm is composed of two stages. In the first stage, the ACM with traditional energy function guides the snake to converge to the object boundary except the concave regions. In the second stage, for the control points which stay outside the concave regions, a proper energy template are chosen and are added in the external energy. The modified energy function is applied so as to move the snake toward the concave regions. Therefore, the object of interest can be completely extracted. The experimental results show that, by using this method, the snake can indeed completely extract the boundary of the given object, while the extra cost is very low. In addition, for the problem that the snake cannot precisely extract the object contour when the number of the control points on the snake is not enough, a GA-based ACM algorithm is presented to deal with such a problem. First the improved ACM algorithm is used to guide the snake to approximately extract the object boundary. By utilizing the evolutionary strategy of GA, we attempt to extract precisely the object boundary by adding a few control points into the snake. Similarly, some experimental results are provided to show the performance of the method.
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