Repository of works by Caltech published authors.
Type = Thesis
Mostrando recursos 1 - 14 de 14
Models of Bottom-Up and Top-Down Visual Attention - Itti, Laurent
When we observe our visual environment, we do not perceive all its components as being equally interesting. Some objects automatically and effortlessly "pop out" from their surroundings, that is, they draw our visual attention, in a "bottom up" manner, towards them. In a first approximation, focal visual attention acts as a rapidly shiftable "spotlight," which allows only the selected information to reach higher levels of processing and representation. Most models of the bottom-up control of attention are based on the concept of a saliency map, that is, an explicit two-dimensional map that encodes the conspicuity of objects in the visual...
Synaptic learning rules for local synaptic interactions : theory and application to direction selectivity - Mo, Chunhui
This thesis is organized in two parts, both concerned with local synaptic interactions within the dendritic tree. The first part is focused on how specific synaptic arrangements that can be used to compute direct ion selectivity can be learned in an unsupervised manner. The second part consists of a double synaptic veto model that can account for the observed reverse-phi selectivity of direction-selective cells. We propose an activity-based, local learning model that may account for the direction selectivity in neurons in the visual cortex based on the local veto operation among excitation and inhibition. We implement the learning rule with...
Ab initio based grand canonical Monte-Carlo simulations of CH_4 uptake in covalent-organic frameworks (COFs) - Mendoza-Cortés, José Luis
Alternatives routes towards new energies sources have become a main stream research
worldwide. Methane has the potential to become a future fuel, however there
have been longstanding problems related to transport and storage making it not an
economically viable path. Attempts to overcome these issues include conversion to
methanol, better compression techniques and sorption into porous materials. The
latter is of special interest because of the recent discovering of new class of materials
called Covalent Organic Frameworks (COF) that are: tailored materials, highly
crystalline, have a high surface area (≥2000 m^2/g) with a high pore volume and
are made of just light atoms (C, Si, B,O and H)....
Convex Optimization Methods for Graphs and Statistical Modeling - Chandrasekaran, Venkat
An outstanding challenge in many problems throughout science and engineering is
to succinctly characterize the relationships among a large number of interacting entities.
Models based on graphs form one major thrust in this thesis, as graphs often
provide a concise representation of the interactions among a large set of variables. A
second major emphasis of this thesis are classes of structured models that satisfy certain
algebraic constraints. The common theme underlying these approaches is the development
of computational methods based on convex optimization, which are in turn useful
in a broad array of problems in signal processing and machine learning. The specific
contributions are as follows:
We propose a...
Locally controlled photonic crystal devices with coupled quantum dots: physics and applications - Faraon, Andrei
One of the most promising ways of building future nano-photonic networks for classical and quantum information processing is by using photonic crystals. Quantum dots coupled to optical modes allow for efficient control of light in these devices. In this dissertation I present the work I have done at Stanford University toward building integrated photonic crystal devices with coupled quantum dots. The most significant experiments that we performed on this platform relied on perfecting the fabrication techniques for photonic crystals, and developing technologies for local control of the cavity and quantum dot properties. In terms of fabrication, our lab is currently...
A Model of the Distribution of Mass in the Galactic System - Schmidt, Maarten
The paper deals with the distribution of mass in the Galactic System. Formulae for the potential and forces due to non-homogeneous oblate spheroids are derived (section 2). It is shown that, between the galactic centre and the sun, the central force in the galactic plane decreases almost linearly with the distance from the centre (section 3). A simple analytical expression for the densit in a non-homogeneous spheroid is found which gives such a linear decrease of the central force inside the spheroid (section 4). Section 5 summarizes the observational material which forms the basis for the construction of the mass...
Algorithms for Reaction Mechanism Reduction and Numerical Simulation of Detonations Initiated by Projectiles - Hung, Patrick
The evolution of a homogeneous, chemically reactive system with ns species forms a dy-namical
system in chemical state-space. Under suitable constraints, unique and stable equi-librium
exists and can be interpreted as zeroth-dimensional (point like) attractors in this
ns-dimensional space. At these equilibrium compositions, the rates of all reversible reac-tions
vanish and can, in fact, be determined from thermodynamics independent of chemical
Generalizing this concept, an m-dimensional Intrinsic Low Dimensional Manifold (ILDM)
represents an m-dimensional subspace in chemical state-space where all but the m-slowest
aggregate reactions are in equilibrium, and these aggregate reactions are determined by
eigenvalue considerations of the chemical kinetics. In this context, a certain composition is
Noise Reduction and Flow Characteristics in Asymmetric Dual-Stream Jets - Shupe, Rebecca S.
This research effort is motivated by the advent of asymmetric nozzle concepts for
directional suppression of jet noise from turbofan engines. The specific method addressed
is the fan flow deflection (FFD) technique, whereby aerodynamic devices deflect
downward the fan stream of the turbofan exhaust and thus create an asymmetry in the
plume of the jet exiting an otherwise coaxial nozzle. The asymmetry reduces jet noise
emissions in downward and sideward directions affecting airport communities. Flow field
and acoustic measurements were conducted to understand what flow quantities are
affected by the departure from symmetry and how their changes impact noise emission.
The experiments were complemented by computations that included...
Chemical and statistical soot modeling - Blanquart, Guillaume
The combustion of petroleum based fuels like kerosene, gasoline, or diesel leads to the formation of several kind of pollutants. Among them, soot particles are particularly bad for their severe consequences on human health. Over the past decades, strict regulations have been placed on car and aircraft engines in order to limit these particulate matter emissions. Designing low emission engines requires the use of predictive soot models which can be applied to the combustion of real fuels.
Towards this goal, the present work addresses the formation of soot particles both from a chemical and statistical point of view. As a...
Three essays in empirical industrial organization - Shum, Matthew
This thesis consists of three empirical essays on topics in industrial organization. Chapter 1 introduces the three essays and describes their main results. In chapter 2, I measure the effects of advertising on households' choices among competing brands of differentiated products when households are habit persistent. In markets characterized by habit persistent consumers, an important role for advertising may be to encourage consumers to "switch" to newer, less familiar brands. This potentially enhances competition between competing brands by reducing household-level differentiation between brands that a household is and is not experienced with, contrary to the traditional Bainian arguments that advertising...
Scheduling for today’s computer systems: bridging theory and practice - Wierman, Adam
Scheduling is a fundamental technique for improving performance in computer systems. From web servers
to routers to operating systems, how the bottleneck device is scheduled has an enormous impact on the performance of the system as a whole. Given the immense literature studying scheduling, it is easy to think that we already understand enough about scheduling. But, modern computer system designs have highlighted a number of disconnects between traditional analytic results and the needs of system designers.
In particular, the idealized policies, metrics, and models used by analytic researchers do not match the policies, metrics, and scenarios that appear in real systems.
Magnetism and Electron Transport in Magnetoresistive Lanthanum Calcium Manganite - Snyder, G. Jeffrey
It is the goal of this thesis to understand the physical properties associated with the large negative magnetoresistance found in lanthanum calcium manganite. Such large magnetoresistances have been reported that this material is being considered for use as a magnetic field sensor. However, there are many variables such as temperature, magnetic field, chemical composition and processing that greatly influence the magnitude of the magnetoresistance. After introducing the problem in Chapter 1, Chapters 2 and 3 describe the materials synthesis and physical property measurements used in this work. In Chapter 4, the intrinsic magnetic and electron transport properties of lanthanum calcium...
Cavitation and Other Free Surface Phenomena - Brennen, C.
This thesis develops a method of solving axisymmetric cavity flow problems using a relaxation or numerical technique.
Chapter 1 contains a general review of the phenomenon of cavitation in fluids. Special reference is then made to fully developed cavities in an Euler or ideal fluid for both plane and axisymmetric flow. The basic theorems and equations are presented, with the various types of mathematical model which have been suggested. Details of the fundamental feature of this type of flow, namely the phenomenon of flow separation, are given. At the conclusion of the chapter the analytic methods of solution of plane cavitating...