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On Delay and Security in Network Coding
Get PDFIn this thesis, delay and security issues in network coding are considered. First, we study the delay incurred in the transmission of a fixed number of packets through acyclic networks comprised of erasure links. The two transmission schemes studied are routing with hop-by-hop retransmissions, where every node in the network simply stores and forwards its received packets, and linear coding, where nodes mix their packets by forwarding linear combinations of all their previously received packets. We show that even though the achievable rates of coding and routing are the same, network coding can have an increasingly better performance than routing as the number of packets increases.
Secondly, we investigate the security benefits of network coding. We investigate the achievable secrecy rate region in a general network of noisy wiretap channels with general communication demands. The eavesdropper has access to an unknown set of links, and on the wiretapped links observes a degraded version of the intended receiver's observation. While characterizing the capacity in general is an open problem, in the noise-free case there exist inner and outer bounds. In the noisy case, we show how one can change any of the wiretap channels to a noiseless degraded broadcast channel, so that the derived network's rate region bounds, and under certain conditions is equivalent, to that of the initial network. Specifically, we showed that in case the eavesdropper can choose only a single link to wiretap at each time, then one can change all the links in the network with corresponding noiseless ones, creating an equivalent noiseless secrecy problem. In the case where the eavesdropper can wiretap multiple links simultaneously, we derive upper and lower bounding noiseless network problems.
Finally, we consider design practical code design for the detection of adversarial errors in a distributed storage system. We build on work of functions that can fool linear polynomials to create and communicate hash functions of the data in order to detect with high probability the maliciously attacked nodes in the system.</p
Essays on Information, Competition, and Cooperation
Get PDFThis thesis consists of three papers that study the relationships between information, competition, and cooperation in two novel environments. We first examine the competitive behavior of firms with private information in two-sided matching markets. This part of the thesis employs purely game-theoretic tools. Second, we study voluntary contributions towards a linear public good by players who are connected through a network. In this environment, we use experimental and theoretical techniques to examine the effects of different information treatments and network structures on contributions.
In Chapter 2, we study the behavior of firms in a competitive market for workers. In particular, we study a game in which firms with private information compete for workers by committing to a single salary offer. Workers care only about salary and the matching process follows the deferred-acceptance approach introduced by Gale and Shapley (1962). For a two-firm, two-worker model, there exists a Bayesian-Nash equilibrium in which each firm type chooses a distributional strategy with interval support in the salary space. This equilibrium exhibits a separation of types, in the sense that types with a common most preferred worker choose non overlapping, adjacent supports. The type that makes higher offers is determined by the relative marginal value for the preferred worker. In larger markets, which replicate the two-firm, two-worker case, a comparable Bayesian-Nash equilibrium exists and the separation result endures. In the limit, there is no aggregate uncertainty about the realization of firm types, and competition is confined to the most popular worker type. Numerical results suggest that the finite market equilibrium strategies converge with replication to the corresponding equilibrium strategies in the limit case.
Chapter 3 studies individual contributions in a repeated public goods experiment. Subjects are connected through a circle network, and consumption of the public good depends on a player's own contribution and the contributions of his neighbors. We study whether contributions depend on the nature of the information players are shown about others between rounds of the repeated game. We extend the approach of Arifovic and Ledyard (2009), which merges a modified model of other-regarding preferences (ORP) with a theory of learning. Our model predicts individual behavior that ranges from free-riding, to conditional cooperation, to unconditional giving. Many subjects switch between these different behavioral strategies across games with different information treatments. Individual contributions are remarkably consistent with our model, which combines other-regarding preferences, learning, and the information treatment. Both the data and model simulations suggest that learning (to play the benchmark Nash equilibrium of the game) is differential and contagious across players. Free-riders and unconditional givers learn faster than conditional cooperators, and provide an anchor that accelerates learning by their neighbors. These results suggest that the network or neighborhood structure may be important for contributions through its effects on learning.
In Chapter 4, we extend the analysis of learning and contributions in network public goods experiments. Using a set of five different network structures, we examine three key aspects of individual behavior. First, we report a negative finding regarding the predictions from our theory of other-regarding preferences. The theory provides certain predictions about how a particular subject should and should not behave across networks. We find several violations of these predictions, particularly in small, complete network groups, but also in the larger, more interesting networks. Second, we report on the average contributions by players in groups that consist of all conditional cooperators. In the one-shot game, these groups have a continuum of equilibria, in which every player contributes the same amount. While one might expect contributions to average half of the endowment, we find in both the data and learning simulations that average contributions decline over time to less than half of the endowment. We conjecture that learning dynamics may provide a method of equilibrium selection, for players trying to coordinate on one equilibrium in the repeated game.
Our main finding in this chapter is that learning is contagious in networks other than the circle, which we studied in Chapter 3. We find considerable evidence at the individual match level that free-riders and altruists provide an anchor that stabilizes behavior and accelerates learning by their conditional cooperator neighbors. Our analysis highlights the possibility that, even when the distribution of free-riders, altruists, and conditional cooperators is the same across networks, the different neighborhood structures may affect contributions differently through their effects on learning. Thus, the main contribution of this chapter is the confirmation that learning is contagious across a range of different network structures.</p
Estimation and Inference for Grasping and Manipulation Tasks Using Vision and Kinesthetic Sensors
Get PDFThis thesis presents a novel framework for state estimation in the context of robotic grasping and manipulation. The overall estimation approach is based on fusing various visual cues for manipulator tracking, namely appearance and feature-based, shape-based, and silhouette-based visual cues. Similarly, a framework is developed to fuse the above visual cues, but also kinesthetic cues such as force-torque and tactile measurements, for in-hand object pose estimation. The cues are extracted from multiple sensor modalities and are fused in a variety of Kalman filters.
A hybrid estimator is developed to estimate both a continuous state (robot and object states) and discrete states, called contact modes, which specify how each finger contacts a particular object surface. A static multiple model estimator is used to compute and maintain this mode probability. The thesis also develops an estimation framework for estimating model parameters associated with object grasping. Dual and joint state-parameter estimation is explored for parameter estimation of a grasped object's mass and center of mass. Experimental results demonstrate simultaneous object localization and center of mass estimation.
Dual-arm estimation is developed for two arm robotic manipulation tasks. Two types of filters are explored; the first is an augmented filter that contains both arms in the state vector while the second runs two filters in parallel, one for each arm. These two frameworks and their performance is compared in a dual-arm task of removing a wheel from a hub.
This thesis also presents a new method for action selection involving touch. This next best touch method selects an available action for interacting with an object that will gain the most information. The algorithm employs information theory to compute an information gain metric that is based on a probabilistic belief suitable for the task. An estimation framework is used to maintain this belief over time. Kinesthetic measurements such as contact and tactile measurements are used to update the state belief after every interactive action. Simulation and experimental results are demonstrated using next best touch for object localization, specifically a door handle on a door.
The next best touch theory is extended for model parameter determination. Since many objects within a particular object category share the same rough shape, principle component analysis may be used to parametrize the object mesh models. These parameters can be estimated using the action selection technique that selects the touching action which best both localizes and estimates these parameters. Simulation results are then presented involving localizing and determining a parameter of a screwdriver.
Lastly, the next best touch theory is further extended to model classes. Instead of estimating parameters, object class determination is incorporated into the information gain metric calculation. The best touching action is selected in order to best discern between the possible model classes. Simulation results are presented to validate the theory.</p
New Technologies Driving Decade-Bandwidth Radio Astronomy: Quad-ridged Flared Horn and Compound-Semiconductor LNAs
Get PDFAmong the branches of astronomy, radio astronomy is unique in that it spans the largest portion of the electromagnetic spectrum, e.g., from about 10 MHz to 300 GHz. On the other hand, due to scientific priorities as well as technological limitations, radio astronomy receivers have traditionally covered only about an octave bandwidth. This approach of "one specialized receiver for one primary science goal" is, however, not only becoming too expensive for next-generation radio telescopes comprising thousands of small antennas, but also is inadequate to answer some of the scientific questions of today which require simultaneous coverage of very large bandwidths.
This thesis presents significant improvements on the state of the art of two key receiver components in pursuit of decade-bandwidth radio astronomy: 1) reflector feed antennas; 2) low-noise amplifiers on compound-semiconductor technologies. The first part of this thesis introduces the quadruple-ridged flared horn, a flexible, dual linear-polarization reflector feed antenna that achieves 5:1-7:1 frequency bandwidths while maintaining near-constant beamwidth. The horn is unique in that it is the only wideband feed antenna suitable for radio astronomy that: 1) can be designed to have nominal 10 dB beamwidth between 30 and 150 degrees; 2) requires one single-ended 50 Ohm low-noise amplifier per polarization. Design, analysis, and measurements of several quad-ridged horns are presented to demonstrate its feasibility and flexibility.
The second part of the thesis focuses on modeling and measurements of discrete high-electron mobility transistors (HEMTs) and their applications in wideband, extremely low-noise amplifiers. The transistors and microwave monolithic integrated circuit low-noise amplifiers described herein have been fabricated on two state-of-the-art HEMT processes: 1) 35 nm indium phosphide; 2) 70 nm gallium arsenide. DC and microwave performance of transistors from both processes at room and cryogenic temperatures are included, as well as first-reported measurements of detailed noise characterization of the sub-micron HEMTs at both temperatures. Design and measurements of two low-noise amplifiers covering 1--20 and 8—50 GHz fabricated on both processes are also provided, which show that the 1--20 GHz amplifier improves the state of the art in cryogenic noise and bandwidth, while the 8--50 GHz amplifier achieves noise performance only slightly worse than the best published results but does so with nearly a decade bandwidth.</p
Electronic Structure and Phonon Thermodynamics of Iron Alloys
Get PDFInelastic neutron scattering (INS) and nuclear-resonant inelastic x-ray scattering (NRIXS) were used to measure phonon spectra of FeV as a B2- ordered compound and as a bcc solid solution. Contrary to the behavior of ordering alloys studied to date, the phonons in the B2-ordered phase are softer than in the solid solution. Ordering increases the vibrational entropy, which stabilizes the ordered phase to higher temperatures. Ab initio calculations show that the number of electronic states at the Fermi level increases upon ordering, enhancing the screening between ions, and reducing the interatomic force constants. The effect of screening is larger at the V atomic sites than at the Fe atomic sites.
The phonon spectra of Au-rich alloys of fcc Au-Fe were also measured. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon density of states (DOS) with Fe concentration that increases the miscibility gap temperature. The magnitude of the effect is non- linear and it is reduced at higher Fe concentrations. Force constants were calculated for several compositions and show a local stiffening of Au–Au bonds close to Fe atoms, but Au–Au bonds that are farther away do not show this effect. Phonon DOS curves calculated from the force constants reproduced the experimental trends. The Au–Fe bond is soft and favors ordering, but a charge transfer from the Fe to the Au atoms stiffens the Au–Au bonds enough to favor unmixing. The stiffening is attributed to two main effects comparable in magnitude: an increase in electron density in the free-electron-like states, and stronger sd-hybridization.
INS and NRIXS measurements were performed at elevated temperatures on B2-ordered FeTi and NRIXS measurements were performed at high pressures. The high-pressure behavior is quasi- harmonic. The softening of the phonon DOS curves with temperature is strongly nonharmonic. Calculations of the force constants and Born-von Karman fits to the experimental data show that the bonds between second nearest neighbors (2nn) are much stiffer than those between 1nn, but fits to the high temperature data show that the former softens at a faster rate with temperature. The Fe–Fe bond softens more than the Ti–Ti bond. The unusual stiffness of the 2nn bond is explained by the calculated charge distribution, which is highly aspherical and localized preferentially in the t2g orbitals. Ab initio molecular dynamics (AIMD) simulations show a charge transfer from the t2g orbitals to the eg orbitals at elevated temperatures. The asphericity decreases linearly with temperature and is more severe at the Fe sites.</p
Limits and Tradeoffs in the Control of Autocatalytic Systems
Get PDFDespite the complexity of biological networks, we find that certain common architectures govern network structures. These architectures impose fundamental constraints on system performance and create tradeoffs that the system must balance in the face of uncertainty in the environment. This means that while a system may be optimized for a specific function through evolution, the optimal achievable state must follow these constraints. One such constraining architecture is autocatalysis, as seen in many biological networks including glycolysis and ribosomal protein synthesis. Using a minimal model, we show that ATP autocatalysis in glycolysis imposes stability and performance constraints and that the experimentally well-studied glycolytic oscillations are in fact a consequence of a tradeoff between error minimization and stability. We also show that additional complexity in the network results in increased robustness. Ribosome synthesis is also autocatalytic where ribosomes must be used to make more ribosomal proteins. When ribosomes have higher protein content, the autocatalysis is increased. We show that this autocatalysis destabilizes the system, slows down response, and also constrains the system’s performance. On a larger scale, transcriptional regulation of whole organisms also follows architectural constraints and this can be seen in the differences between bacterial and yeast transcription networks. We show that the degree distributions of bacterial transcription network follow a power law distribution while the yeast network follows an exponential distribution. We then explored the evolutionary models that have previously been proposed and show that neither the preferential linking model nor the duplication-divergence model of network evolution generates the power-law, hierarchical structure found in bacteria. However, in real biological systems, the generation of new nodes occurs through both duplication and horizontal gene transfers, and we show that a biologically reasonable combination of the two mechanisms generates the desired network
Flight Dynamics in Drosophila Through a Dynamically-scaled Robotic Approach
Get PDFFlies are particularly adept at balancing the competing demands of delay tolerance, performance, and robustness during flight, which invites thoughtful examination of their multimodal feedback architecture. This dissertation examines stabilization requirements for inner-loop feedback strategies in the flapping flight of Drosophila, the fruit fly, against the backdrop of sensorimotor transformations present in the animal. Flies have evolved multiple specializations to reduce sensorimotor latency, but sensory delay during flight is still significant on the timescale of body dynamics. I explored the effect of sensor delay on flight stability and performance for yaw turns using a dynamically-scaled robot equipped with a real-time feedback system that performed active turns in response to measured yaw torque. The results show a fundamental tradeoff between sensor delay and permissible feedback gain, and suggest that fast mechanosensory feedback provides a source of active damping that compliments that contributed by passive effects. Presented in the context of these findings, a control architecture whereby a haltere-mediated inner-loop proportional controller provides damping for slower visually-mediated feedback is consistent with tethered-flight measurements, free-flight observations, and engineering design principles.
Additionally, I investigated how flies adjust stroke features to regulate and stabilize level forward flight. The results suggest that few changes to hovering kinematics are actually required to meet steady-state lift and thrust requirements at different flight speeds, and the primary driver of equilibrium velocity is the aerodynamic pitch moment. This finding is consistent with prior hypotheses and observations regarding the relationship between body pitch and flight speed in fruit flies. The results also show that the dynamics may be stabilized with additional pitch damping, but the magnitude of required damping increases with flight speed. I posit that differences in stroke deviation between the upstroke and downstroke might play a critical role in this stabilization. Fast mechanosensory feedback of the pitch rate could enable active damping, which would inherently exhibit gain scheduling with flight speed if pitch torque is regulated by adjusting stroke deviation. Such a control scheme would provide an elegant solution for flight stabilization across a wide range of flight speeds.</p
Single Particle Mass Spectrometry and Inertial Imaging with Nanomechanical Systems
Get PDFThis thesis work describes the development of a new technology for mass spectrometry using nanoelectromechanical systems (NEMS-MS). Mass spectrometry is a technique used to identify molecules through mass measurement. Nanoelectromechanical systems (NEMS) feature low cost, scalable on-chip compatibility, and are highly sensitivity to the mass of accreted species. Using NEMS devices, we perform NEMS-MS where the inertial mass of individual molecules is directly measured. This contrasts with traditional MS techniques utilizing electromagnetic fields to measure the average mass-to-charge ratio of many molecules.
Initially, an ultra-high-vacuum apparatus is constructed to perform NEMS-MS using laser desorption techniques for molecule delivery. An existing technique, matrix assisted laser desorption ionization (MALDI), is implemented without the usual ion optics system in order to permit detection of neutral and ionized particles. This, however, is found to be incompatible with NEMS-MS due to the matrix background.
The MALDI-NEMS-MS system is then used to measure gold nanoparticles that simultaneously act as the matrix and analyte. These experiments are combined with measurements of IgM antibodies using an ESI (electrospray ionization)-NEMS-MS system to demonstrate single-particle nanomechanical mass spectrometry in real time.
Then, the laser desorption-based NEMS-MS system is upgraded to implement laser induced acoustic desorption (LIAD) for particle delivery. LIAD is a matrix-free technique in the mass spectrometry community for desorbing nonvolatile, thermally labile molecules. The LIAD-NEMS-MS system is used for the direct mass measurement of several different types of proteins and protein-complexes with single-protein quantification. Additionally, experimental data is presented that suggests the movement of surface-adsorbed particles along the device surface due to the vibration of the resonant device modes; this remains to be confirmed.
Finally, a new methodology, inertial imaging theory, is presented, which enables measurement of the mass and shape of adsorbed particles on a NEMS device. The shifts induced by particle adsorption in the modal frequencies of a resonant device are used to calculate the spatial moments of mass distribution of individual adsorbates, one-by-one, as they adsorb It is shown that the ultimate resolution in particle size of this technique is limited only by fundamental noise processes in the device and not wavelength-dependent diffraction effects. Indeed, atomic resolution is possible using existing NEMS devices.</p
Earthquake Geology of Myanmar
Get PDFThis thesis describes the active structures of Myanmar and its surrounding regions, and the earthquake geology of the major active structures. Such investigation is needed urgently for this rapidly developing country that has suffered from destructive earthquakes in its long history. To archive a better understanding of the regional active tectonics and the seismic potential in the future, we utilized a global digital elevation model and optical satellite imagery to describe geomorphologic evidence for the principal neotectonic features of the western half of the Southeast Asia mainland. Our investigation shows three distinct active structural systems that accommodate the oblique convergence between the Indian plate and Southeast Asia and the extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Each of these active deformation belts can be further separated into several neotectonic domains, in which structures show distinctive active behaviors from one to another.
In order to better understand the behaviors of active structures, we focused on the active characteristics of the right-lateral Sagaing fault and the oblique subducting northern Sunda megathrust in the second part of this thesis. The detailed geomorphic investigations along these two major plate-interface faults revealed the recent slip behavior of these structures, and plausible recurrence intervals of major seismic events. We also documented the ground deformation of the 2011 Tarlay earthquake in remote eastern Myanmar from remote sensing datasets and post-earthquake field investigations. The field observation and the remote sensing measurements of surface ruptures of the Tarlay earthquake are the first study of this kind in the Myanmar region.</p
Measurement, Simulation, and Design of the Dispersion-Engineered Traveling-Wave Kinetic Inductance Amplifier
No full textRecently, Eom et al. [1 J proposed a new concept for a low-noise cryogenic amplifier known
as a Dispersion-Engineered Traveling-Wave Kinetic Inductance (DTWKI) amplifier. This
device exploits the nonlinear kinetic inductance of superconducting thin-film nitrides to
achieve high gain-bandwidth, near quantum-limited noise, and excellent dynamic range. In
this thesis, we describe recent progress toward an experimental realization of the DTWKI; in
particular, we focus on improvements in the areas of gain-bandwidth and noise performance.
We describe a numerical model of the amplifier, and use this model to interpret experimental
results and provide insight into the effects of dispersion-engineering on gain processes.
Lastly, based on experimental results and model output, we propose some improvements to
the DTWKI device