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## Multipath aided rapid acquisition

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 125 p.; 615537 bytes; 611114 bytes; application/pdf; application/pdf

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Spread-spectrum systems with large transmission bandwidth present significant challenges from the standpoint of achieving synchronization before communication commences. This research investigates a rapid acquisition procedure that exploits the multipath to aid the synchronization. In particular, we consider a class of serial search strategies and determine the optimal search procedure for the uncertainty space consisting of N[sub]s total cells and N[sub]Q correct cells. We derive closed-form expressions for both the minimum and maximum mean acquisition times (MATs) and the conditions for achieving these limits. We prove that the fixed-step serial search (FSSS), with the step size N[sub]Q, achieves the near-optimal MAT. We also prove that the conventional serial search, in which consecutive cells are tested sequentially, and the FSSS with the step size N[sub]s - 1 should be avoided as they result in the maximum MAT. Analytical tools used in the research include Markov chain diagrams, the transformation of feasible spaces, and convexity theory. Our results apply to all signal-to-noise ratio values, regardless of the detection-layer decision rule and the fading distribution. The impact of this research is significant for the design, implementation...

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## Coherent multi-photon interference and compensation of polarization dispersion

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 233 p.; 1446327 bytes; 1446081 bytes; application/pdf; application/pdf

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This thesis will explore strategies for coherent manipulation of multi-photon packets. Correlated multi-photon states can arise in nonlinear optical devices. A nonlinear quantum interferometer which includes these states can have interesting and strikingly different behavior from a conventional interferometer. The special quantum states set up in these devices are degraded by loss. In this thesis, we will set up theory for describing the interesting quantum behavior of these devices and the limitations imposed by loss decoherence. The underlying structure of interferometer states is shared by all two-mode systems-including classical polarization states of a single-mode fiber. We are exploring bire-fringent systems as a possible implementation of nonlinear quantum coupler ideas, but also because of its practical importance in optical communications. Polarization mode dispersion an important source of signal distortion in high-bitrate communications arising from unwanted birefringence in the fiber. We will describe theoretical analysis of compensated PMD systems, as well as our theoretical and experimental effeots to develop novel PMD compensators.; by John Michael Fini.; Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science...

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## Quantum signal processing

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 346 p.; 3228057 bytes; 3227811 bytes; application/pdf; application/pdf

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Quantum signal processing (QSP) as formulated in this thesis, borrows from the formalism and principles of quantum mechanics and some of its interesting axioms and constraints, leading to a novel paradigm for signal processing with applications in areas ranging from frame theory, quantization and sampling methods to detection, parameter estimation, covariance shaping and multiuser wireless communication systems. The QSP framework is aimed at developing new or modifying existing signal processing algorithms by drawing a parallel between quantum mechanical measurements and signal processing algorithms, and by exploiting the rich mathematical structure of quantum mechanics, but not requiring a physical implementation based on quantum mechanics. This framework provides a unifying conceptual structure for a variety of traditional processing techniques, and a precise mathematical setting for developing generalizations and extensions of algorithms. Emulating the probabilistic nature of quantum mechanics in the QSP framework gives rise to probabilistic and randomized algorithms. As an example we introduce a probabilistic quantizer and derive its statistical properties. Exploiting the concept of generalized quantum measurements we develop frame-theoretical analogues of various quantum-mechanical concepts and results...

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## A coupling-of-modes analysis of SAW grating structures

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 274 leaves; 5833842 bytes; 5833642 bytes; application/pdf; application/pdf

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#Electrical Engineering and Computer Science.#Coupled mode theory#Acoustic surface wave devices#Signal processing#Integrated optics

by Peter Vickers Wright.; Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1981.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Includes bibliographical references.

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## Thermoelectric properties of Bi₁âxÌ³SbxÌ³ nanowires and lead salt superlattice nanowires

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 147 p.; 6876723 bytes; 6876531 bytes; application/pdf; application/pdf

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This thesis involves an extensive experimental and theoretical study of the thermoelectric-related transport properties of BilxSbx nanowires, and presents a theoretical framework for predicting the electrical properties of superlattice nanowires. A template-assisted fabrication scheme is employed to synthesize Bi-based nanowires by pressure injecting liquid metal alloys into the hexagonally packed cylindrical pores of anodic alumina. These nanowires possess a very high crystalline quality with a diameter-dependent crystallographic orientation along the wire axis. A theoretical model for Bil-Sbx nanowires is developed, taking into consideration the effects of cylindrical wire boundary, multiple and anisotropic carrier pockets, and non-parabolic dispersion relations. A unique semimetal-semiconductor (SM-SC) transition is predicted for these nanowires as the wire diameter decreases or as the Sb concentration increases. Also, an unusual physical phenomenon involving a very high hole density of states due to the coalescence of 10 hole carrier pockets, which is especially advantageous for improving the thermoelectric performance of p-type materials, is uncovered for BilxSbx nanowires. Various transport measurements are reported for Bi-related nanowire arrays as a function of temperature...

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## The optical properties of bismuth nanowires

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 177 p.; 12492215 bytes; 12514606 bytes; application/pdf; application/pdf

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The optical absorption of bismuth nanowires in the energy (wavenumber) range of 600 - 4000cm-1 is studied. Optical reflection and transmission spectra reveal that bismuth nanowires have a large and intense absorption peak as well as several smaller absorption peaks which are not measured in bulk bismuth. The smaller absorption peaks fit reasonably well to theoretical models for intersubband absorption in bismuth nanowires. The wire diameter, polarization, and doping dependencies as well as the spectral shape of the dominant peak agree with simulations of the optical absorption resulting from an L-point valence to T-point valence band electronic transition. The large absorption peak is present even for nanowires too large to exhibit quantum confinement, thus showing that the absorption results from a surface-induced effect and not from quantum confinement. The enhanced optical absorption in nanowires over bulk bismuth is attributed to a surface term in the matrix element which results from the spacial gradient of the dielectric function and the large dielectric mismatch between bismuth and the surrounding alumina or air. A comparison of the measured spectra with simulations of optical absorption resulting from direct L-point electronic transitions demonstrated that this absorption mechanism is not dominant in our materials. In order to explore the optical properties of bismuth nanowires...

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## Renewal process and diffusion models of 1/f noise

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 108 leaves; 5932731 bytes; 5932489 bytes; application/pdf; application/pdf

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#Electrical Engineering and Computer Science.#Electric resistors, Film#Autocorrelation (Statistics)#Random noise theory#Power spectra

by Marvin Stuart Keshner.; Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Bibliography: leaves 99-108.

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## Surface acoustic wave gratings of finite width

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 51 leaves; 2451394 bytes; 2451151 bytes; application/pdf; application/pdf

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#Electrical Engineering and Computer Science.#Acoustic surface wave devices#Coupled mode theory#Delay lines#Wave guides

by André Antoine Merab.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Includes bibliographical references.

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## Linear state feedback, quadratic weights, and closed loop eigenstructures

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 99 leaves; 5074333 bytes; 5074093 bytes; application/pdf; application/pdf

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by Peter Murray Thompson.; Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Includes bibliographical references.

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## Phase estimation with application to speech analysis-synthesis

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 4 leaves, 3-136 p.; 8706070 bytes; 8705826 bytes; application/pdf; application/pdf

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#Electrical Engineering and Computer Science.#Speech synthesis#Frequency response (Electrical engineering)#Signal processing#Estimation theory

by Thomas F. Quatieri, Jr.; Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1980.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Vita.; Includes bibliographical references.

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## Procedural reflection in programming languages

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 3 vol. (761 leaves); 64704430 bytes; 64704183 bytes; application/pdf; application/pdf

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#Electrical Engineering and Computer Science.#Programming languages (Electronic computers)#Programming languages (Electronic computers) Semantics#LISP (Computer program language)#Interpreters (Computer programs)#Self-knowledge, Theory of

by Brian Cantwell Smith.; Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982.; MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING.; Bibliography: leaves 756-761.

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## Applied optimal control for dynamically stable legged locomotion

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 84 p.; 5240135 bytes; 5249218 bytes; application/pdf; application/pdf

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Online learning and controller adaptation will be an essential component for legged robots in the next few years as they begin to leave the laboratory setting and join our world. I present the first example of a learning system which is able to quickly and reliably acquire a robust feedback control policy for 3D dynamic bipedal walking from a blank slate using only trials implemented on the physical robot. The robot begins walking within a minute and learning converges in approximately 20 minutes. The learning works quickly enough that the robot is able to continually adapt to the terrain as it walks. This success can be attributed in part to the mechanics of our robot, which is capable of stable walking down a small ramp even when the computer is turned off. In this thesis, I analyze the dynamics of passive dynamic walking, starting with reduced planar models and working up to experiments on our real robot. I describe, in detail, the actor-critic reinforcement learning algorithm that is implemented on the return map dynamics of the biped. Finally, I address issues of scaling and controller augmentation using tools from optimal control theory and a simulation of a planar one-leg hopping robot. These learning results provide a starting point for the production of robust and energy efficient walking and running robots that work well initially...

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## Energy allocation and transmission scheduling for wireless and space communications

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 164 p.; 4820030 bytes; 4819839 bytes; application/pdf; application/pdf

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This thesis presents two innovations to geophysical inversion. The first provides a framework and an algorithm for combining linear deconvolution methods with geostatistical interpolation techniques. This allows for sparsely sampled data to aid in image deblurring problems, or, conversely, noisy and blurred data to aid in sample interpolation. In order to overcome difficulties arising from high dimensionality, the solution must be derived in the correct framework and the structure of the problem must be exploited by an iterative solution algorithm. The effectiveness of the method is demonstrated first on a synthetic problem involving satellite remotely sensed data, and then on a real 3-D seismic data set combined with well logs. The second innovation addresses how to use wavelets in a linear geophysical inverse problem. Wavelets have lead to great successes in image compression and denoising, so it is interesting to see what, if anything, they can do for a general linear inverse problem. It is shown that a simple nonlinear operation of weighting and thresholding wavelet coefficients can consistently outperform classical linear inverse methods in terms of mean-square error across a broad range of noise magnitude in the data. Wavelets allow for an adaptively smoothed solution: smoothed more in uninteresting regions...

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## Modelling morphogenesis as an amorphous computation

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 58 leaves

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This thesis presents a programming-language viewpoint for morphogenesis, the process of shape formation during embryological development. We model morphogenesis as a self-organizing, self-repairing amorphous computation and describe how we can program large-scale shape formation by giving local instructions to cell-like objects. Our goal is to simulate systems that display properties, like robustness, regeneration, and evolvability, that are present in biological systems but ordinarily not present in computer systems. Consistent with the theory of facilitated variation from evolutionary biology, we find that many of these properties can be introduced and conserved by a hierarchical organization of growth specification.; by Arnab Bhattacharyya.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.; Includes bibliographical references (leaves 57-58).

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## From thought to action

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 146 leaves

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Systems engineering is rapidly assuming a prominent role in neuroscience that could unify scientific theories, experimental evidence, and medical development. In this three-part work, I study the neural representation of targets before reaching movements and the generation of prosthetic control signals through stochastic modeling and estimation. In the first part, I show that temporal and history dependence contributes to the representation of targets in the ensemble spiking activity of neurons in primate dorsal premotor cortex (PMd). Point process modeling of target representation suggests that local and possibly also distant neural interactions influence the spiking patterns observed in PMd. In the second part, I draw on results from surveillance theory to reconstruct reaching movements from neural activity related to the desired target and the path to that target. This approach combines movement planning and execution to surpass estimation with either target or path related neural activity alone. In the third part, I describe the principled design of brain-driven neural prosthetic devices as a filtering problem on interacting discrete and continuous random processes. This framework subsumes four canonical Bayesian approaches and supports emerging applications to neural prosthetic devices.; (cont.) Results of a simulated reaching task predict that the method outperforms previous approaches in the control of arm position and velocity based on trajectory and endpoint mean squared error. These results form the starting point for a systems engineering approach to the design and interpretation of neuroscience experiments that can guide the development of technology for human-computer interaction and medical treatment.; by Lakshminarayan Srinivasan.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

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## A Computational theory of grounding in natural language conversation

Fonte: University of Rochester. Computer Science Department.
Publicador: University of Rochester. Computer Science Department.

Tipo: Thesis; Technical Report

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#Natural language processing#Grounding#Dialogue systems#Speech act theory#Discourse#Situation-theory#Plan-execution

Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 1994.; The process of adding to the common ground between conversational participants (called grounding) has previously been either oversimplified or studied in an off-line manner. This dissertation presents a computational theory, in which a protocol is presented which can be used to determine, for any given state of the conversation, whether material has been grounded or what it would take to ground the material. This protocol is related to the mental states of participating agents, showing the motivations for performing particular grounding acts and what their effects will be. We extend speech act theory to account for levels of action both above and below the sentence level, including the level of grounding acts described above. Traditional illocutionary acts are now seen to be multi-agent acts which must be grounded to have their usual effects. A conversational agent model is provided, showing how grounding fits in naturally with the other functions that an agent must perform in engaging in conversation. These ideas are implemented within the TRAINS conversation system. Also presented is a situation-theoretic model of plan execution relations, giving definitions of what it means for an action to begin...

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## Buffering and flow control in message switched communication networks by Eberhard Frank Wunderlich.

Fonte: Electronic Systems Laboratory, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology
Publicador: Electronic Systems Laboratory, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology

Formato: 220 p.; application/pdf

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Bibliography: p. 213-218.; Prepared under Advanced Research Projects Agency Contract ONR/N00014-75-C-1183.; Originally presented as the author's thesis, (Ph.D.) in the M.I.T. Dept. of Electrical Engineering and Computer Science, 1978.

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## Source coding for communication concentrators

Fonte: Electronic Systems Laboratory, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology
Publicador: Electronic Systems Laboratory, Dept. of Electrical Engineering and Computer Science, Massachusetts Institute of Technology

Formato: 213 p.; application/pdf

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by Pierre Am?e Humblet.; Bibliography: p. 194-198.; Prepared under Advanced Research Projects Agency Grant ONR-N00014-75-C-1183.; Originally presented as the author's thesis, (Ph.D.) in the M.I.T. Dept. of Electrical Engineering and Computer Science, 1978.

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## Authorship Patterns in Computer Science Research in the Philippines

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 22/07/2015
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We studied patterns of authorship in computer science~(CS) research in the
Philippines by using data mining and graph theory techniques on archives of
scientific papers presented in the Philippine Computer Science Congresses from
2000 to 2010 involving 326~papers written by 605~authors. We inferred from
these archives various graphs namely, a paper--author bipartite graph, a
co-authorship graph, and two mixing graphs. Our results show that the
scientific articles by Filipino computer scientists were generated at a rate of
33~papers per year, while the papers were written by an average of 2.64~authors
(maximum=13). The frequency distribution of the number of authors per paper
follows a power-law with a power of $\varphi=-2.04$ ($R^2=0.71$). The number of
Filipino CS researchers increases at an annual rate of 60~new scientists. The
researchers have written an average of 1.42~papers (maximum=20) and have
collaborated with 3.70~other computer scientists (maximum=54). The frequency
distribution of the number of papers per author follows a power law with
$\varphi=-1.88$ ($R^2=0.83$). This distribution closely agrees with Lotka's
{\em law of scientific productivity} having $\varphi\approx -2$. The number of
co-authors per author also follows a power-law with $\varphi=-1.65$
($R^2=0.80$). These results suggest that most CS~papers in the country were
written by scientists who prefer to work alone or at most in small groups.
These also suggest that few papers were written by scientists who were involved
in large collaboration efforts. The productivity of the Philippines' CS
researchers...

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## Brownian Functionals in Physics and Computer Science

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/10/2005
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#Condensed Matter - Statistical Mechanics#Condensed Matter - Disordered Systems and Neural Networks#Computer Science - Data Structures and Algorithms

This is a brief review on Brownian functionals in one dimension and their
various applications, a contribution to the special issue ``The Legacy of
Albert Einstein" of Current Science. After a brief description of Einstein's
original derivation of the diffusion equation, this article provides a
pedagogical introduction to the path integral methods leading to the derivation
of the celebrated Feynman-Kac formula. The usefulness of this technique in
calculating the statistical properties of Brownian functionals is illustrated
with several examples in physics and probability theory, with particular
emphasis on applications in computer science. The statistical properties of
"first-passage Brownian functionals" and their applications are also discussed.; Comment: 21 pages, 5 .eps figures included

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