Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons

Open Access. Powered by Scholars. Published by Universities.®

PDF

Dartmouth College

2005

Discipline
Keyword
Publication
Publication Type

Articles 1 - 30 of 73

Full-Text Articles in Physical Sciences and Mathematics

Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola Dec 2005

Dynamical Control Of Qubit Coherence: Random Versus Deterministic Schemes, Lea F. Santos, Lorenza Viola

Dartmouth Scholarship

We reexamine the problem of switching off unwanted phase evolution and decoherence in a single two-state quantum system in the light of recent results on random dynamical decoupling methods [L. Viola and E. Knill, Phys. Rev. Lett. 94, 060502 (2005)]. A systematic comparison with standard cyclic decoupling is effected for a variety of dynamical regimes, including the case of both semiclassical and fully quantum decoherence models. In particular, exact analytical expressions are derived for randomized control of decoherence from a bosonic environment. We investigate quantitatively control protocols based on purely deterministic, purely random, as well as hybrid design, and …


A Combined Routing Method For Ad Hoc Wireless Networks, Zhenhui Jiang Dec 2005

A Combined Routing Method For Ad Hoc Wireless Networks, Zhenhui Jiang

Dartmouth College Master’s Theses

To make ad hoc wireless networks adaptive to different mobility and traffic patterns, we studied in this thesis an approach to swap from one protocol to another protocol dynamically, while routing continues. By the insertion of a new layer, we were able to make each node in the ad hoc wireless network notify each other about the protocol swap. To ensure that routing works efficiently after the protocol swap, we initialized the destination routing protocol's data structures and reused the previous routing information to build the new routing table. We also tested our approach under different network topologies and traffic …


A Steerable, Untethered, 250x60 Micron Mems Mobile Micro-Robot, Bruce R. Donald, Christopher G. Levey, Craig D. Mcgray, Igor Paprotny, Daniela Rus Dec 2005

A Steerable, Untethered, 250x60 Micron Mems Mobile Micro-Robot, Bruce R. Donald, Christopher G. Levey, Craig D. Mcgray, Igor Paprotny, Daniela Rus

Computer Science Technical Reports

We present a steerable, electrostatic, untethered, MEMS micro-robot, with dimensions of 60 µm by 250 µm by 10 µm. This micro-robot is 1 to 2 orders of magnitude smaller in size than previous micro-robotic systems. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator. These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated …


How Hard Is It To Cheat In The Gale-Shapley Stable Matching Algorithm, Chien-Chung Huang Dec 2005

How Hard Is It To Cheat In The Gale-Shapley Stable Matching Algorithm, Chien-Chung Huang

Computer Science Technical Reports

We study strategy issues surrounding the stable marriage problem. Under the Gale-Shapley algorithm (with men proposing), a classical theorem says that it is impossible for every liar to get a better partner. We try to challenge this theorem. First, observing a loophole in the statement of the theorem, we devise a coalition strategy in which a non-empty subset of the liars gets a better partner and no man is worse off than before. This strategy is restricted in that not everyone has the incentive to cheat. We attack the classical theorem further by means of randomization. However, this theorem shows …


Crawdad: A Community Resource For Archiving Wireless Data At Dartmouth, David Kotz, Tristan Henderson Dec 2005

Crawdad: A Community Resource For Archiving Wireless Data At Dartmouth, David Kotz, Tristan Henderson

Dartmouth Scholarship

Wireless network researchers are seriously starved for data about how real users, applications, and devices use real networks under real network conditions. CRAWDAD (Community Resource for Archiving Wireless Data at Dartmouth) is a new National Science Foundation-funded project to build a wireless-network data archive for the research community. It will host wireless data and provide tools and documents to make collecting and using the data easy. This resource should help researchers identify and evaluate real and interesting problems in mobile and pervasive computing. To learn more about CRAWDAD and discuss its direction, about 30 interested people gathered at a workshop …


Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour Nov 2005

Dynamics Of A Nanomechanical Resonator Coupled To A Superconducting Single-Electron Transistor, M. P. Blencowe, J. Imbers, A. D. Armour

Dartmouth Scholarship

We present an analysis of the dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor (SSET) in the vicinity of Josephson quasi-particle (JQP) and double Josephson quasi-particle (DJQP) resonances. For weak coupling and wide separation of dynamical timescales, we find that for either superconducting resonances the dynamics of the resonator are given by a Fokker–Planck equation, i.e. the SSET behaves effectively as an equilibrium heat bath, characterized by an effective temperature, which also damps the resonator and renormalizes its frequency. Depending on the gate and drain–source voltage bias points with respect to the superconducting resonance, the SSET can …


Principal Component Analysis For Predicting Transcription-Factor Binding Motifs From Array-Derived Data, Yunlong Liu, Matthew P Vincenti, Hiroki Yokota Nov 2005

Principal Component Analysis For Predicting Transcription-Factor Binding Motifs From Array-Derived Data, Yunlong Liu, Matthew P Vincenti, Hiroki Yokota

Dartmouth Scholarship

The responses to interleukin 1 (IL-1) in human chondrocytes constitute a complex regulatory mechanism, where multiple transcription factors interact combinatorially to transcription-factor binding motifs (TFBMs). In order to select a critical set of TFBMs from genomic DNA information and an array-derived data, an efficient algorithm to solve a combinatorial optimization problem is required. Although computational approaches based on evolutionary algorithms are commonly employed, an analytical algorithm would be useful to predict TFBMs at nearly no computational cost and evaluate varying modelling conditions. Singular value decomposition (SVD) is a powerful method to derive primary components of a given matrix. Applying SVD …


Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery Nov 2005

Low Magnetic Prandtl Number Dynamos With Helical Forcing, Pablo D. Mininni, David C. Montgomery

Dartmouth Scholarship

We present direct numerical simulations of dynamo action in a forced Roberts flow. The behavior of the dynamo is followed as the mechanical Reynolds number is increased, starting from the laminar case until a turbulent regime is reached. The critical magnetic Reynolds for dynamo action is found, and in the turbulent flow it is observed to be nearly independent on the magnetic Prandtl number in the range from ∼0.3 to ∼0.1. Also the dependence of this threshold with the amount of mechanical helicity in the flow is studied. For the different regimes found, the configuration of the magnetic and velocity …


Master’S Thesis Proposal: Computation Reuse In Stacking And Unstacking, Anne Loomis Nov 2005

Master’S Thesis Proposal: Computation Reuse In Stacking And Unstacking, Anne Loomis

Computer Science Technical Reports

Algorithms for dynamic simulation and control are fundamental to many applications, including computer games and movies, medical simulation, and mechanical design. I propose to explore efficient algorithms for finding a stable unstacking sequence -- an order in which we can remove every object from a structure without causing the structure to collapse under gravity at any step. We begin with a basic unstacking sequence algorithm: consider the set of all objects in a structure. Collect all possible subsets into a disassembly graph. Search the graph, testing the stability of each node as it is visited. Any path of stable nodes …


Detection Of Covert Channel Encoding In Network Packet Delays, Vincent Berk, Annarita Giani, George Cybenko Nov 2005

Detection Of Covert Channel Encoding In Network Packet Delays, Vincent Berk, Annarita Giani, George Cybenko

Computer Science Technical Reports

Covert channels are mechanisms for communicating information in ways that are difficult to detect. Data exfiltration can be an indication that a computer has been compromised by an attacker even when other intrusion detection schemes have failed to detect a successful attack. Covert timing channels use packet inter-arrival times, not header or payload embedded information, to encode covert messages. This paper investigates the channel capacity of Internet-based timing channels and proposes a methodology for detecting covert timing channels based on how close a source comes to achieving that channel capacity. A statistical approach is then used for the special case …


Towards A Precision Measurement Of The Casimir Force In A Cylinder-Plane Geometry, M. Brown-Hayes, D. A.R. Dalvit, F. D. Mazzitelli, W. J. Kim, R. Onofrio Nov 2005

Towards A Precision Measurement Of The Casimir Force In A Cylinder-Plane Geometry, M. Brown-Hayes, D. A.R. Dalvit, F. D. Mazzitelli, W. J. Kim, R. Onofrio

Dartmouth Scholarship

We report on a proposal aimed at measuring the Casimir force in the cylinder-plane configuration. The Casimir force is evaluated including corrections due to finite parallelism, conductivity, and temperature. The range of validity of the proximity force approximation is also discussed. An apparatus to test the feasibility of a precision measurement in this configuration has been developed, and we describe both a procedure to control the parallelism and the results of the electrostatic calibration. Finally we discuss the possibility of measuring the thermal contribution to the Casimir force and deviations from the proximity force approximation, both of which are expected …


Sympathetic Cooling Route To Bose-Einstein Condensate And Fermi-Liquid Mixtures, Robin Côté, Roberto Onofrio, Eddy Timmermans Oct 2005

Sympathetic Cooling Route To Bose-Einstein Condensate And Fermi-Liquid Mixtures, Robin Côté, Roberto Onofrio, Eddy Timmermans

Dartmouth Scholarship

We discuss a sympathetic cooling strategy that can successfully mitigate fermion-hole heating in a dilute atomic Fermi-Bose mixture and access the temperature regime in which the fermions behave as a Fermi liquid. We introduce an energy-based formalism to describe the temperature dynamics with which we study a specific and promising mixture, composed of 6Li and 87Rb. Analyzing the harmonically trapped mixture, we find that the favorable features of this mixture are further enhanced by using different trapping frequencies for the two species.


Noao Fundamental Plane Survey. Ii. Age And Metallicity Along The Red Sequence From Line‐Strength Data, Jenica E. Nelan, Russell J. Smith, Michael J. Hudson, Gary A. Wegner Oct 2005

Noao Fundamental Plane Survey. Ii. Age And Metallicity Along The Red Sequence From Line‐Strength Data, Jenica E. Nelan, Russell J. Smith, Michael J. Hudson, Gary A. Wegner

Dartmouth Scholarship

We present spectroscopic line-strength data for 4097 red-sequence galaxies in 93 low-redshift galaxy clusters and use these to investigate variations in average stellar populations as a function of galaxy mass. Our analysis includes an improved treatment of nebular emission contamination, which affects ~10% of the sample galaxies. Using the stellar population models of D. Thomas and collaborators, we simultaneously fit 12 observed line-strength-σ relations in terms of common underlying trends of age, [Z/H] (total metallicity), and [α/Fe] (α-element enhancement). We find that the observed line-strength-σ relations can be explained only if higher mass red-sequence galaxies are, on average, …


Combinatorial Theorems About Embedding Trees On The Real Line, Amit Chakrabarti, Subhash Khot Oct 2005

Combinatorial Theorems About Embedding Trees On The Real Line, Amit Chakrabarti, Subhash Khot

Computer Science Technical Reports

We consider the combinatorial problem of embedding a tree metric into the real line with low distortion. For two special families of trees --- the family of complete binary trees and the family of subdivided stars --- we provide embeddings whose distortion is provably optimal, up to a constant factor. We also prove that the optimal distortion of a linear embedding of a tree can be arbitrarily low or high even when it has bounded degree.


A Quasi-Ptas For Unsplittable Flow On Line Graphs, Nikhil Bansal, Amit Chakrabarti, Amir Epstein, Baruch Schieber Oct 2005

A Quasi-Ptas For Unsplittable Flow On Line Graphs, Nikhil Bansal, Amit Chakrabarti, Amir Epstein, Baruch Schieber

Computer Science Technical Reports

We study the Unsplittable Flow Problem (UFP) on a line graph, focusing on the long-standing open question of whether the problem is APX-hard. We describe a deterministic quasi-polynomial time approximation scheme for UFP on line graphs, thereby ruling out an APX-hardness result, unless NP is contained in DTIME(2^polylog(n)). Our result requires a quasi-polynomial bound on all edge capacities and demands in the input instance. Earlier results on this problem included a polynomial time (2+epsilon)-approximation under the assumption that no demand exceeds any edge capacity (the "no-bottleneck assumption") and a super-constant integrality gap if this assumption did not hold. Unlike most …


Performance Evaluation Of Distributed Security Protocols Using Discrete Event Simulation, Meiyuan Zhao Oct 2005

Performance Evaluation Of Distributed Security Protocols Using Discrete Event Simulation, Meiyuan Zhao

Dartmouth College Ph.D Dissertations

The Border Gateway Protocol (BGP) that manages inter-domain routing on the Internet lacks security. Protective measures using public key cryptography introduce complexities and costs. To support authentication and other security functionality in large networks, we need public key infrastructures (PKIs). Protocols that distribute and validate certificates introduce additional complexities and costs. The certification path building algorithm that helps users establish trust on certificates in the distributed network environment is particularly complicated. Neither routing security nor PKI come for free. Prior to this work, the research study on performance issues of these large-scale distributed security systems was minimal. In this thesis, …


Limits Of Quintessence, R. R. Caldwell, Eric V. Linder Sep 2005

Limits Of Quintessence, R. R. Caldwell, Eric V. Linder

Dartmouth Scholarship

We present evidence that the simplest particle-physics scalar-field models of dynamical dark energy can be separated into distinct behaviors based on the acceleration or deceleration of the field as it evolves down its potential towards a zero minimum. We show that these models occupy narrow regions in the phase plane of w and w′, the dark energy equation of state and its time derivative in units of the Hubble time. Restricting an energy scale of the dark energy microphysics limits how closely a scalar field can resemble a cosmological constant. These results, indicating a desired measurement resolution of order σ(w′)≈(1+w), …


Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen Sep 2005

Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen

Dartmouth Scholarship

We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission- line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P ≃ 83.38 min, ∼2.8% longer than Porb, which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of ≃5−6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which …


The Effect Of Particles On Dynamic Recrystallization And Fabric Development Of Granular Ice During Creep, Min Song, Ian Baker, David M. Cole Sep 2005

The Effect Of Particles On Dynamic Recrystallization And Fabric Development Of Granular Ice During Creep, Min Song, Ian Baker, David M. Cole

Dartmouth Scholarship

The mechanical behavior and microstructural evolution of laboratory-prepared, particle-free fresh-water ice and ice with 1 wt.% (~0.43 vol.%) silt-sized particles were investigated under creep with a stress level of 1.45 MPa at −10°C. The particles were present both within the grains and along the grain boundaries. The creep rates of specimens with particles were always higher than those of particle-free ice. Dynamic recrystallization occurred for both sets of specimens, with new grains nucleating along grain boundaries in the early stages of creep. The ice with particles showed a higher nucleation rate. This resulted in a smaller average grain-size for the …


Improving Large-Scale Network Traffic Simulation With Multi-Resolution Models, Guanhua Yan Sep 2005

Improving Large-Scale Network Traffic Simulation With Multi-Resolution Models, Guanhua Yan

Dartmouth College Ph.D Dissertations

Simulating a large-scale network like the Internet is a challenging undertaking because of the sheer volume of its traffic. Packet-oriented representation provides high-fidelity details but is computationally expensive; fluid-oriented representation offers high simulation efficiency at the price of losing packet-level details. Multi-resolution modeling techniques exploit the advantages of both representations by integrating them in the same simulation framework. This dissertation presents solutions to the problems regarding the efficiency, accuracy, and scalability of the traffic simulation models in this framework. The ``ripple effect'' is a well-known problem inherent in event-driven fluid-oriented traffic simulation, causing explosion of fluid rate changes. Integrating multi-resolution …


Dark-Energy Evolution Across The Cosmological-Constant Boundary, Robert R. Caldwell, Michael Doran Aug 2005

Dark-Energy Evolution Across The Cosmological-Constant Boundary, Robert R. Caldwell, Michael Doran

Dartmouth Scholarship

We explore the properties of dark-energy models for which the equation of state, w, defined as the ratio of pressure to energy density, crosses the cosmological-constant boundary w=−1. We adopt an empirical approach, treating the dark energy as an uncoupled fluid or a generalized scalar field. We describe the requirements for a viable model, in terms of the equation of state and sound speed. A generalized scalar field cannot safely traverse w=−1, although a pair of scalars with w>−1 and w<−1 will work. A fluid description with a well-defined sound speed can also cross the boundary. Contrary to expectations, such a crossing model does not instantaneously resemble a cosmological constant at the moment w=−1 since the density and pressure perturbations do not necessarily vanish. But because a dark energy with w<−1 dominates only at very late times, and because the dark energy is not generally prone to gravitational clustering, then crossing the cosmological-constant boundary leaves no distinct imprint.


Efficient Wait-Free Algorithms For Implementing Ll/Sc Objects, Srdjan Petrovic Aug 2005

Efficient Wait-Free Algorithms For Implementing Ll/Sc Objects, Srdjan Petrovic

Dartmouth College Ph.D Dissertations

Over the past decade, a pair of instructions called load-linked (LL) and store-conditional (SC) have emerged as the most suitable synchronization instructions for the design of lock-free algorithms. However, current architectures do not support these instructions; instead, they support either CAS (e.g., UltraSPARC, Itanium, Pentium) or restricted versions of LL/SC (e.g., POWER4, MIPS, Alpha). Thus, there is a gap between what algorithm designers want (namely, LL/SC) and what multiprocessors actually support (namely, CAS or restricted LL/SC). To bridge this gap, this thesis presents a series of efficient, wait-free algorithms that implement LL/SC from CAS or restricted LL/SC.


The Theory Of Trackability With Applications To Sensor Networks, Valentino Crespi, George Cybenko, Guofei Jiang Aug 2005

The Theory Of Trackability With Applications To Sensor Networks, Valentino Crespi, George Cybenko, Guofei Jiang

Computer Science Technical Reports

In this paper, we formalize the concept of tracking in a sensor network and develop a rigorous theory of {\em trackability} that investigates the rate of growth of the number of consistent tracks given a sequence of observations made by the sensor network. The phenomenon being tracked is modelled by a nondeterministic finite automaton and the sensor network is modelled by an observer capable of detecting events related, typically ambiguously, to the states of the underlying automaton. More formally, an input string, $Z^t$, of $t+1$ symbols (the sensor network observations) that is presented to a nondeterministic finite automaton, $M$, (the …


Natural Image Statistics For Digital Image Forensics, Siwei Lyu Aug 2005

Natural Image Statistics For Digital Image Forensics, Siwei Lyu

Dartmouth College Ph.D Dissertations

We describe a set of natural image statistics that are built upon two multi-scale image decompositions, the quadrature mirror filter pyramid decomposition and the local angular harmonic decomposition. These image statistics consist of first- and higher-order statistics that capture certain statistical regularities of natural images. We propose to apply these image statistics, together with classification techniques, to three problems in digital image forensics: (1) differentiating photographic images from computer-generated photorealistic images, (2) generic steganalysis; (3) rebroadcast image detection. We also apply these image statistics to the traditional art authentication for forgery detection and identification of artists in an art work. …


On The Design Of An Immersive Environment For Security-Related Studies, Yougu Yuan Aug 2005

On The Design Of An Immersive Environment For Security-Related Studies, Yougu Yuan

Dartmouth College Master’s Theses

The Internet has become an essential part of normal operations of both public and private sectors. Many security issues are not addressed in the original Internet design, and security now has become a large concern for networking research and study. There is an imperative need to have an simulation environment that can be used to help study security-related research problems. In the thesis we present our effort to build such an environment: Real-time Immersive Network Simulation Environment (RINSE). RINSE features flexible configuration of models using various networking protocols and real-time user interaction. We also present the Estimate Next Infection (ENI) …


Efficiently Implementing A Large Number Of Ll/Sc Objects, Prasad Jayanti, Srdjan Petrovic Aug 2005

Efficiently Implementing A Large Number Of Ll/Sc Objects, Prasad Jayanti, Srdjan Petrovic

Computer Science Technical Reports

Over the past decade, a pair of instructions called load-linked (LL) and store-conditional (SC) have emerged as the most suitable synchronization instructions for the design of lock-free algorithms. However, current architectures do not support these instructions; instead, they support either CAS (e.g., UltraSPARC, Itanium) or restricted versions of LL/SC (e.g., POWER4, MIPS, Alpha). Thus, there is a gap between what algorithm designers want (namely, LL/SC) and what multiprocessors actually support (namely, CAS or RLL/RSC). To bridge this gap, a flurry of algorithms that implement LL/SC from CAS have appeared in the literature. The two most recent algorithms are due to …


Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong Aug 2005

Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong

Dartmouth Scholarship

The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic variable star. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her–type system, or polar, featuring strong Balmer lines, He I and He II emission lines, and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius found a smoothly varying light curve with a period near 4.75 hr and one minimum per orbit, indicating that the state of the system had changed dramatically. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable …


Model Simulations Of A Shock‐Cloud Interaction In The Cygnus Loop, Daniel J. Patnaude, Robert A. Fesen Jul 2005

Model Simulations Of A Shock‐Cloud Interaction In The Cygnus Loop, Daniel J. Patnaude, Robert A. Fesen

Dartmouth Scholarship

We present optical observations and two-dimensional hydrodynamic modeling of an isolated shocked ISM cloud. Hα images taken in 1992.6 and 2003.7 of a small optical emission cloud along the southwestern limb of the Cygnus Loop were used to measure positional displacements of ~01 yr-1 for surrounding Balmer-dominated emission filaments and 0025-0055 yr-1 for internal cloud emission features. These measurements imply transverse velocities of 250 and 80-140 km s-1 for ambient ISM and internal cloud shocks, respectively. A lack of observed turbulent gas stripping at the cloud-ISM boundary in the Hα images suggests that there is not an …


Structural Analysis Of Social Networks With Wireless Users, Guanling Chen, David Kotz Jul 2005

Structural Analysis Of Social Networks With Wireless Users, Guanling Chen, David Kotz

Computer Science Technical Reports

Online interactions between computer users form Internet-based social networks. In this paper we present a structural analysis of two such networks with wireless users. In one network the wireless users participate in a global file-sharing system, and in the other they interact with each other through a local music-streaming application.


Towards Tiny Trusted Third Parties, Alexander Iliev, Sean Smith Jul 2005

Towards Tiny Trusted Third Parties, Alexander Iliev, Sean Smith

Computer Science Technical Reports

Many security protocols hypothesize the existence of a {\em trusted third party (TTP)} to ease handling of computation and data too sensitive for the other parties involved. Subsequent discussion usually dismisses these protocols as hypothetical or impractical, under the assumption that trusted third parties cannot exist. However, the last decade has seen the emergence of hardware-based devices that, to high assurance, can carry out computation unmolested; emerging research promises more. In theory, such devices can perform the role of a trusted third party in real-world problems. In practice, we have found problems. The devices aspire to be general-purpose processors but …