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University of Massachusetts Amherst

2011

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Articles 1 - 30 of 216

Full-Text Articles in Physical Sciences and Mathematics

Mixed Discriminants, Eduardo Cattani, Maria Angelica Cueto, Alicia Dickenstein, Sandra Di Rocco, Bernd Strumfels Dec 2011

Mixed Discriminants, Eduardo Cattani, Maria Angelica Cueto, Alicia Dickenstein, Sandra Di Rocco, Bernd Strumfels

Eduardo Cattani

No abstract provided.

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Symmetry-Breaking Bifurcation In The Nonlinear Schrödinger Equation With Symmetric Potentials, E. Kirr, Panos Kevrekidis, D. E. Pelinovsky Dec 2011

Symmetry-Breaking Bifurcation In The Nonlinear Schrödinger Equation With Symmetric Potentials, E. Kirr, Panos Kevrekidis, D. E. Pelinovsky

Panos Kevrekidis

We consider the focusing (attractive) nonlinear Schr\"odinger (NLS) equation with an external, symmetric potential which vanishes at infinity and supports a linear bound state. We prove that the symmetric, nonlinear ground states must undergo a symmetry breaking bifurcation if the potential has a non-degenerate local maxima at zero. Under a generic assumption we show that the bifurcation is either subcritical or supercritical pitchfork. In the particular case of double-well potentials with large separation, the power of nonlinearity determines the subcritical or supercritical character of the bifurcation. The results are obtained from a careful analysis of the spectral properties of the …

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Multiple Dark-Bright Solitons In Atomic Bose-Einstein Condensates, D. Yan, J. J. Chang, C. Hamner, Panos Kevrekidis, P. Engels, V. Achilleos, D. J. Frantzeskakis, R. Carretero-Gonz´Alez, P. Schmelcher Nov 2011

Multiple Dark-Bright Solitons In Atomic Bose-Einstein Condensates, D. Yan, J. J. Chang, C. Hamner, Panos Kevrekidis, P. Engels, V. Achilleos, D. J. Frantzeskakis, R. Carretero-Gonz´Alez, P. Schmelcher

Panos Kevrekidis

Motivated by recent experimental results, we present a systematic theoretical analysis of dark-bright-soliton interactions and multiple-dark-bright-soliton complexes in atomic two-component Bose-Einstein condensates. We study analytically the interactions between two dark-bright solitons in a homogeneous condensate and then extend our considerations to the presence of the trap. We illustrate the existence of robust stationary dark-bright-soliton “molecules,” composed of two or more solitons, which are formed due to the competition of the interaction forces between the dark- and bright-soliton components and the trap force. Our analysis is based on an effective equation of motion, derived for the distance between two dark-bright solitons. …

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Session G: Nuclear Power/Climate Change – Terrapower’S Traveling Wave Reactor, Tyler Ellis Nov 2011

Session G: Nuclear Power/Climate Change – Terrapower’S Traveling Wave Reactor, Tyler Ellis

Climate Change and the Future of Nuclear Power

TerraPower is moving forward with detailed plans for a sustainable, economic, and safe nuclear reactor. The Travelling Wave Reactor (TWR) – a reactor in the 500-megawatt electric range – uses unique core physics to initiate a breed and burn wave which can be completely sustained in fertile material. This process allows the TWR to convert depleted uranium waste into usable fuel as the reactor operates, providing a sustainable base-load power source. TerraPower is the first company to create a practical engineering embodiment of this previously studied concept thanks to a powerful advanced reactor modeling interface, developed in-house, which enables the …

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Session G: Nuclear Power/Climate Change – Climate V. Climate Alarm, Richard S. Lindzen Nov 2011

Session G: Nuclear Power/Climate Change – Climate V. Climate Alarm, Richard S. Lindzen

Climate Change and the Future of Nuclear Power

The underlying physics of climate contains important elements that are widely agreed on though frequently misunderstood. In this lecture, the basic physics of greenhouse warming are simply described. It will be shown that the dynamic mixing of the troposphere is essential to the mechanism. It will further be shown that there is nothing intrinsically alarming in the basic physics. Alarm depends critically on the assertion that the climate system is dominated by large positive feedbacks that greatly amplify such warming as may be due to increasing CO2 alone. The nature of possible feedbacks will be described, and the conditions for …

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Session B: The Future Of Nuclear Power - Aim High! Thorium Energy Cheaper Than From Coal, Cavan Stone Nov 2011

Session B: The Future Of Nuclear Power - Aim High! Thorium Energy Cheaper Than From Coal, Cavan Stone

Climate Change and the Future of Nuclear Power

This century, we face significant environmental challenges. Our demand for limited natural resources is rapidly increasing and much of humanity is concerned about the consequences. Our unsustainably growing population drives these challenges, and humanely stabilizing it would alleviate these pressures. Demographic data clearly shows that prosperity stabilizes population and it also shows that prosperity critically requires energy. In spite of the pressing and demonstrable nature of these challenges however, politically there is no international consensus on global energy policy. Developing nations simply will not accept a policy that will hamper their economic growth. Yet, we do have a solution to …

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Session B: The Future Of Nuclear Power - The Fukushima Nuclear Event And Its Implications For Nuclear Power, Michael W. Golay Nov 2011

Session B: The Future Of Nuclear Power - The Fukushima Nuclear Event And Its Implications For Nuclear Power, Michael W. Golay

Climate Change and the Future of Nuclear Power

The combined strong earthquake and super tsunami of 12 March 2011 at the Fukushima nuclear power plant imposed the most severe challenges ever experienced at such a facility. Information regarding the plant response and status remains uncertain, but it is clear that severe damage has been sustained, that the plant staff have responded creatively and that the offsite implications are unlikely to be seriously threatening to the health, if not the prosperity, of the surrounding population. Reexamination of the regulatory constraints of nuclear power will occur worldwide, and some changes are likely; particularly concerning reliance upon active systems for achieving …

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Session B: The Future Of Nuclear Power - The Fundamentals And Status Of Nuclear Power, Regis A. Matzie Nov 2011

Session B: The Future Of Nuclear Power - The Fundamentals And Status Of Nuclear Power, Regis A. Matzie

Climate Change and the Future of Nuclear Power

Nuclear power has enormous potential to provide clean, safe base-load electricity to the world’s growing population. Harnessing this potential in an economic and responsible manner is not without challenges. Safety remains the principal tenet of our operating fleet, which currently provides ~20% of U.S. electricity generated. The performance of this fleet from economic and safety standpoints has improved dramatically over the past several decades. This nuclear generation also represents greater than 70% of the emission free electricity with hydroelectric power providing the majority of the remainder. There have been many lessons learned from the more than 50 years of experience …

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Conference Poster, Gerald Peterson Nov 2011

Conference Poster, Gerald Peterson

Climate Change and the Future of Nuclear Power

No abstract provided.

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Breathers In Oscillator Chains With Hertzian Interactions, Guillaume James, Panos Kevrekidis, Jesus Cuevas Nov 2011

Breathers In Oscillator Chains With Hertzian Interactions, Guillaume James, Panos Kevrekidis, Jesus Cuevas

Panos Kevrekidis

We prove nonexistence of breathers (spatially localized and time-periodic oscillations) for a class of Fermi-Pasta-Ulam lattices representing an uncompressed chain of beads interacting via Hertz's contact forces. We then consider the setting in which an additional on-site potential is present, motivated by the Newton's cradle under the effect of gravity. Using both direct numerical computations and a simplified asymptotic model of the oscillator chain, the so-called discrete p-Schr\"odinger (DpS) equation, we show the existence of discrete breathers and study their spectral properties and mobility. Due to the fully nonlinear character of Hertzian interactions, breathers are found to be much more …

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Defeating The Kalka–Teicher–Tsaban Linear Algebra Attack On The Algebraic Eraser, Dorian Goldfeld, Paul E. Gunnells Nov 2011

Defeating The Kalka–Teicher–Tsaban Linear Algebra Attack On The Algebraic Eraser, Dorian Goldfeld, Paul E. Gunnells

Paul Gunnells

The Algebraic Eraser (AE) is a public key protocol for shar- ing information over an insecure channel using commutative and non- commutative groups; a concrete realization is given by Colored Burau Key Agreement Protocol (CBKAP). In this paper, we describe how to choose data in CBKAP to thwart an attack by Kalka–Teicher–Tsaban.

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Rabi Flopping Induces Spatial Demixing Dynamics, E. Nicklas, H. Strobel, T. Zibold, C. Gross, B. A. Malomed, Panos Kevrekidis, M. K. Oberthaler Nov 2011

Rabi Flopping Induces Spatial Demixing Dynamics, E. Nicklas, H. Strobel, T. Zibold, C. Gross, B. A. Malomed, Panos Kevrekidis, M. K. Oberthaler

Panos Kevrekidis

We experimentally investigate the mixing and demixing dynamics of Bose-Einstein condensates in the presence of a linear coupling between two internal states. The observed amplitude reduction of the Rabi oscillations can be understood as a result of demixing dynamics of dressed states as experimentally confirmed by reconstructing the spatial profile of dressed state amplitudes. The observations are in quantitative agreement with numerical integration of coupled Gross-Pitaevskii equations without free parameters, which also reveals the criticality of the dynamics on the symmetry of the system. Our observations demonstrate new possibilities for changing effective atomic interactions and studying critical phenomena.

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Concurrent Sessions 1a: Ramping It Up: From Marketing To Partnerships, Jef Sharp, Michael Mahoney, Jonathan Edwards Nov 2011

Concurrent Sessions 1a: Ramping It Up: From Marketing To Partnerships, Jef Sharp, Michael Mahoney, Jonathan Edwards

Clean Energy Connections

Cleantech startups are all the rage, but what does it take for these companies to get to that next level? Marketing the new company's brand or partnering with large companies with more resources? Either of these can help get innovations to market more quickly.

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Welcome, Marla Michel, Domenic J. Sarno, Steve Goodwin Nov 2011

Welcome, Marla Michel, Domenic J. Sarno, Steve Goodwin

Clean Energy Connections

No abstract provided.

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Screening Properties And Phase Transitions In Unconventional Plasmas For Ising-Type Quantum Hall States, Egil Herland, Egor Babaev, Parsa Bonderson, Victor Gurarie, Chetan Nayak, Asle Sudbø Nov 2011

Screening Properties And Phase Transitions In Unconventional Plasmas For Ising-Type Quantum Hall States, Egil Herland, Egor Babaev, Parsa Bonderson, Victor Gurarie, Chetan Nayak, Asle Sudbø

Egor Babaev

Utilizing large-scale Monte-Carlo simulations, we investigate an unconventional two-component classical plasma in two dimensions which controls the behavior of the norms and overlaps of the quantum-mechanical wavefunctions of Ising-type quantum Hall states. The plasma differs fundamentally from that which is associated with the two-dimensional XY model and Abelian fractional quantum Hall states. We find that this unconventional plasma undergoes a Berezinskii-Kosterlitz-Thouless phase transition from an insulator to a metal. The parameter values corresponding to Ising-type quantum Hall states lie on the metallic side of this transition. This result verifies the required properties of the unconventional plasma used to demonstrate that …

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Fluctuating And Dissipative Dynamics Of Dark Solitons In Quasicondensates S., S. P. Cockburn, H. E. Nistazakis, T. P. Horikis, Panos Kevrekidis, N. P. Proukakis, D. J. Frantzeskakis Oct 2011

Fluctuating And Dissipative Dynamics Of Dark Solitons In Quasicondensates S., S. P. Cockburn, H. E. Nistazakis, T. P. Horikis, Panos Kevrekidis, N. P. Proukakis, D. J. Frantzeskakis

Panos Kevrekidis

The fluctuating and dissipative dynamics of matter-wave dark solitons within harmonically trapped, partially condensed Bose gases is studied both numerically and analytically. A study of the stochastic Gross-Pitaevskii equation, which correctly accounts for density and phase fluctuations at finite temperatures, reveals dark-soliton decay times to be lognormally distributed at each temperature, thereby characterizing the previously predicted long-lived soliton trajectories within each ensemble of numerical realizations [ S. P. Cockburn et al. Phys. Rev. Lett. 104 174101 (2010)]. Expectation values for the average soliton lifetimes extracted from these distributions are found to agree well with both numerical and analytic predictions based …

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Resolutions Of The Steinberg Module For Gl(N), Avner Ash, Paul E. Gunnells, Mark Mcconnell Oct 2011

Resolutions Of The Steinberg Module For Gl(N), Avner Ash, Paul E. Gunnells, Mark Mcconnell

Paul Gunnells

We give several resolutions of the Steinberg representation St_n for the general linear group over a principal ideal domain, in particular over Z. We compare them, and use these results to prove that the computations in [AGM4] are definitive. In particular, in [AGM4] we use two complexes to compute certain cohomology groups of congruence subgroups of SL(4,Z). One complex is based on Voronoi's polyhedral decomposition of the symmetric space for SL(n,R), whereas the other is a larger complex that has an action of the Hecke operators. We prove that both complexes allow us to compute the relevant cohomology groups, and …

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Silent, Fluorescent Labeling Of Native Neuronal Receptors, D Vytla, R E. Combs-Bachmann, A M. Hussey, I Hafez, James Chambers Oct 2011

Silent, Fluorescent Labeling Of Native Neuronal Receptors, D Vytla, R E. Combs-Bachmann, A M. Hussey, I Hafez, James Chambers

James Chambers

We have developed a minimally-perturbing strategy that enables labeling and subcellular visualization of endogenous dendritic receptors on live, wild-type neurons. Specifically, calcium-permeable non-NMDA glutamate receptors expressed in hippocampal neurons can be targeted with this novel synthetic tri-functional molecule. This ligand-directed probe was targeted towards AMPA receptors and bears an electrophilic group for covalent bond formation with an amino acid side chain on the extracellular side of the ion channel. This molecule was designed in such a way that the use-dependent, polyamine-based ligand accumulates the chemically-reactive group at the extracellular side of these polyamine-sensitive receptors, thereby allowing covalent bond formation between …

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Mass Flow Through Solid 4he Induced By The Fountain Effect, M. W. Ray, Robert B. Hallock Oct 2011

Mass Flow Through Solid 4he Induced By The Fountain Effect, M. W. Ray, Robert B. Hallock

Robert Hallock

Using an apparatus that allows superfluid liquid 4_He to be in contact with hcp solid 4_He at pressures greater than the bulk melting pressure of the solid, we have performed experiments that show evidence for 4_He mass flux through the solid and the likely presence of superfluid inside the solid. We present results that show that a thermomechanical equilibrium in quantitative agreement with the fountain effect exists between two liquid reservoirs connected to each other through two superfluid-filled Vycor rods in series with a chamber filled with solid〖 4〗_He. We use the thermomechanical effect to induce flow through the solid …

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Microscopic Derivation Of Two-Component Ginzburg-Landau Model And Conditions Of Its Applicability In Two-Band Systems, Mihail Silaev, Egor Babaev Oct 2011

Microscopic Derivation Of Two-Component Ginzburg-Landau Model And Conditions Of Its Applicability In Two-Band Systems, Mihail Silaev, Egor Babaev

Egor Babaev

We report a microscopic derivation of two-component Ginzburg-Landau (GL) field theory and the conditions of its validity in two-band superconductors. We also investigate the conditions when microscopically derived or phenomenological GL models fail and one should resort to a microscopic description. We show that besides being directly applicable at elevated temperatures, a version of a minimal two-component GL theory in certain cases also gives accurate description of certain aspects of a two-band system even substantially far from $T_c$. This shows that two-component GL model can be used for addressing a wide range of questions in multiband systems, in particular vortex …

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The Influence Of Land Use And Climate Change On Forest Biomass And Composition In Massachusetts, Usa, J. R. Thompson, D. R. Foster, R. Scheller, David B. Kittredge Oct 2011

The Influence Of Land Use And Climate Change On Forest Biomass And Composition In Massachusetts, Usa, J. R. Thompson, D. R. Foster, R. Scheller, David B. Kittredge

David B. Kittredge

Land use and climate change have complex and interacting effects on naturally dynamic forest landscapes. To anticipate and adapt to these changes, it is necessary to understand their individual and aggregate impacts on forest growth and composition. We conducted a simulation experiment to evaluate regional forest change in Massachusetts, USA over the next 50 years (2010–2060). Our objective was to estimate, assuming a linear continuation of recent trends, the relative and interactive influence of continued growth and succession, climate change, forest conversion to developed uses, and timber harvest on live aboveground biomass (AGB) and tree species composition. We examined 20 …

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Dark–Bright Ring Solitons In Bose–Einstein Condensates, J. Stockhofe, Panos Kevrekidis, D. J. Frantzeskakis, P. Schmelcher Sep 2011

Dark–Bright Ring Solitons In Bose–Einstein Condensates, J. Stockhofe, Panos Kevrekidis, D. J. Frantzeskakis, P. Schmelcher

Panos Kevrekidis

We study dark–bright (DB) ring solitons in two-component Bose–Einstein condensates. In the limit of large densities of the dark component, we describe the soliton dynamics by means of an equation of motion for the ring radius. The presence of the bright, 'filling' species is demonstrated to have a stabilizing effect on the ring dark soliton. Near the linear limit, we discuss the symmetry-breaking bifurcations of DB soliton stripes and vortex-bright soliton clusters from the DB ring and relate the stabilizing effect of filling to changes in the bifurcation diagram. Finally, we show that the stabilization by means of a second …

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Programmed Buckling By Controlled Lateral Swelling In A Thin Elastic Sheet, M. A. Dias, J. A. Hanna, Christian Santangelo Sep 2011

Programmed Buckling By Controlled Lateral Swelling In A Thin Elastic Sheet, M. A. Dias, J. A. Hanna, Christian Santangelo

Christian Santangelo

Recent experiments have imposed controlled swelling patterns on thin polymer films, which subsequently buckle into three-dimensional shapes. We develop a solution to the design problem suggested by such systems, namely, if and how one can generate particular three-dimensional shapes from thin elastic sheets by mere imposition of a two-dimensional pattern of locally isotropic growth. Not every shape is possible. Several types of obstruction can arise, some of which depend on the sheet thickness. We provide some examples using the axisymmetric form of the problem, which is analytically tractable.

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Stationary States Of A Nonlinear Schrödinger Lattice With A Harmonic Trap, V. Achilleos, G. Theocharis, Panos Kevrekidis, N. I. Karachalios, F. K. Diakonos, D. J. Frantzeskakis Sep 2011

Stationary States Of A Nonlinear Schrödinger Lattice With A Harmonic Trap, V. Achilleos, G. Theocharis, Panos Kevrekidis, N. I. Karachalios, F. K. Diakonos, D. J. Frantzeskakis

Panos Kevrekidis

We study a discrete nonlinear Schrödinger lattice with a parabolic trapping potential. The model, describing, e.g., an array of repulsive Bose-Einstein condensate droplets confined in the wells of an optical lattice, is analytically and numerically investigated. Starting from the linear limit of the problem, we use global bifurcation theory to rigorously prove that – in the discrete regime – all linear states lead to nonlinear generalizations thereof, which assume the form of a chain of discrete dark solitons (as the density increases). The stability of the ensuing nonlinear states is studied and it is found that the ground state is …

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Effect Of Side Chains On Organic Donor (D) And Acceptor (A) Complexes And Photophysical Properties Of D-A Dyads, Amarnath Bheemaraju Sep 2011

Effect Of Side Chains On Organic Donor (D) And Acceptor (A) Complexes And Photophysical Properties Of D-A Dyads, Amarnath Bheemaraju

Open Access Dissertations

This dissertation aims to understand the effect of incompatible side chains on the complexes of pi-conjugated electron-rich donors and electron-deficient acceptors in solution. The role of incompatible side chains were studied in simple mixtures of organic donor and acceptor molecules that form donor-acceptor complexes. The incompatible branched and linear alkane side chains on the acceptor and donor respectively prevented complex formation between naphthalene diimide acceptor and naphthalene ether donor. However, the incompatible hydrocarbon-fluorocarbon and polar-non polar side chain pairs did not affect complex formation between the donor and acceptor. In quaterthiophene-naphthalene diimide dyads, the incompatibility of the side chain on …

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Query-Dependent Selection Of Retrieval Alternatives, Niranjan Balasubramanian Sep 2011

Query-Dependent Selection Of Retrieval Alternatives, Niranjan Balasubramanian

Open Access Dissertations

The main goal of this thesis is to investigate query-dependent selection of retrieval alternatives for Information Retrieval (IR) systems. Retrieval alternatives include choices in representing queries (query representations), and choices in methods used for scoring documents. For example, an IR system can represent a user query without any modification, automatically expand it to include more terms, or reduce it by dropping some terms. The main motivation for this work is that no single query representation or retrieval model performs the best for all queries. This suggests that selecting the best representation or retrieval model for each query can yield improved …

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Computational Affect Detection For Education And Health, David G. Cooper Sep 2011

Computational Affect Detection For Education And Health, David G. Cooper

Open Access Dissertations

Emotional intelligence has a prominent role in education, health care, and day to day interaction. With the increasing use of computer technology, computers are interacting with more and more individuals. This interaction provides an opportunity to increase knowledge about human emotion for human consumption, well-being, and improved computer adaptation. This thesis explores the efficacy of using up to four different sensors in three domains for computational affect detection. We first consider computer-based education, where a collection of four sensors is used to detect student emotions relevant to learning, such as frustration, confidence, excitement and interest while students use a computer …

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Subjects Of Scale / Spaces Of Possibility: Producing Co-Operative Space In Theory And Enterprise, Janelle Terese Cornwell Sep 2011

Subjects Of Scale / Spaces Of Possibility: Producing Co-Operative Space In Theory And Enterprise, Janelle Terese Cornwell

Open Access Dissertations

This dissertation addresses key questions raised in Human Geography and Economic Geography concerning scale and the production of space, alternative economic geographies and co-operative economic development. It is the product of a five year ethnographic investigation with co-operative enterprises in Western Massachusetts and the broader Connecticut River Valley of Western New England. It explores neglected questions about how subjects are producing co-operative economic identities, enterprises and development strategies amid capitalist cultural dominance; and how structural, financial and governmental aspects of their enterprises participate in cultivating the desire and capacity to expand co-operative space. In line with poststructuralist feminist perspectives within …

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Generalized Expectation Criteria For Lightly Supervised Learning, Gregory Druck Sep 2011

Generalized Expectation Criteria For Lightly Supervised Learning, Gregory Druck

Open Access Dissertations

Machine learning has facilitated many recent advances in natural language processing and information extraction. Unfortunately, most machine learning methods rely on costly labeled data, which impedes their application to new problems. Even in the absence of labeled data we often have a wealth of prior knowledge about these problems. For example, we may know which labels particular words are likely to indicate for a sequence labeling task, or we may have linguistic knowledge suggesting probable dependencies for syntactic analysis. This thesis focuses on incorporating such prior knowledge into learning, with the goal of reducing annotation effort for information extraction and …

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Tree-Based Methods And A Mixed Ridge Estimator For Analyzing Longitudinal Data With Correlated Predictors, Melissa Nicole Eliot Sep 2011

Tree-Based Methods And A Mixed Ridge Estimator For Analyzing Longitudinal Data With Correlated Predictors, Melissa Nicole Eliot

Open Access Dissertations

Due to recent advances in technology that facilitate acquisition of multi-parameter defined phenotypes, new opportunities have arisen for predicting patient outcomes based on individual specific cell subset changes. The data resulting from these trials can be a challenge to analyze, as predictors may be highly correlated with each other or related to outcome within levels of other predictor variables. As a result, applying traditional methods like simple linear models and univariate approaches such as odds ratios may be insufficient. In this dissertation, we describe potential solutions including tree-based methods, ridge regression, mixed modeling, and a new estimator called a mixed …

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