582 research outputs found
Large and detached eddy simulation of separated flow over 3D hill geometries with surface roughness to mimic flows over complex terrains
No full textWith the push to making wind power a significant contributor to the energy portfolio in the U.S. and Europe, there is considerable effort to deploy the currently available peta-scale computational resources to assess and improve well known simulation techniques, such as the large eddy simulation (LES) and detached eddy simulation (DES) techniques, to model the complex flows in wind farms, taken as a whole, as opposed to individual wind turbines. Simulating turbulent flows in wind farms, consisting of arrays of wind turbines, begins with the modeling and simulation of the atmospheric boundary layer (ABL) over complex terrain that is characterized by regions of separated flow with a high degree of turbulence anisotropy. Over the years there has been considerable work on applying LES and Reynolds Averaged Navier--Stokes (RANS) simulations over terrain geometries, such as the Askervein Hill, to understand turbulence closure models for flow over complex terrain. Such studies, however, have had limited success due to difficulties associated with the closure models in the near wall region of the flow. At the same time, turbulence simulations over \emph{canonical} geometries, such as the periodic and axisymmetric hills, have been shown to compare well with data obtained from laboratory scale experiments, where the inflow turbulence and boundary conditions are better characterized and defined respectively. In an effort to extend these canonical flows to be more representative of flows over complex terrain, this paper aims to present results of large and detached eddy simulations of separated flow over three dimensional hill geometries with roughness parametrization, with the objective of developing better closure models for flow over complex terrain
On defect CFT and path integral methods for entanglement in quantum field theories
No full textIn the first few chapters of the thesis, we will study defect CFT methods based on the replica trick for characterizing quantum information in quantum field theories. We calculate a coefficient that characterizes the strength of the two point function of the displacement operator in the replica twist defect placed in a holographic CFT, which controls the second order shape dependence of Renyi entropy. We introduce defect CFT methods for calculating correlation functions involving the modular Hamiltonian together with probe operators inserted at lightcone separation. We use these methods to further calculate correlation functions involving modular flows of these probe operators. Tomita-Takesaki theory constrains these correlation functions, which when combined with our defect CFT calculations, provides a proof of the Quantum Null Energy Condition.
In the last few chapters of this thesis, we will calculate entanglement measures for states that are defined by a Euclidean path integral together with a source for an operator inserted in the path integral. We provide a purely Lorentzian formula for the modular Hamiltonians for these states for flat entangling cuts which systematizes the task of writing time-ordered expressions for relative entropy of these states with respect to the vacuum to all orders in the source. We further apply this method to calculate a formula for shape deformed modular Hamiltonian for the vacuum state to all orders in the shape deformation. In the case of null shape deformation, we recover the formula for the vacuum modular Hamiltonian for null cuts. We then calculate the shape deformation of relative entropy and provide evidence for the presence of a shock in the stress tensor expectation value when one performs the Connes cocycle flow of the state.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-12-01The student, Srivatsan Balakrishnan, accepted the attached license on 2021-07-16 at 15:10.The student, Srivatsan Balakrishnan, submitted this Dissertation for approval on 2021-07-16 at 15:25.This Dissertation was approved for publication on 2021-07-19 at 10:22.DSpace SAF Submission Ingestion Package generated from Vireo submission #16990 on 2022-04-06 at 17:16:09Made available in DSpace on 2022-04-29T21:41:38Z (GMT). No. of bitstreams: 3
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Previous issue date: 2021-07-19Embargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 123298
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Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Onl
WiFi, LTE, or Both? Measuring Multi-Homed Wireless Internet Performance
No full textOver the past two or three years, wireless cellular networks have become faster than before, most notably due to the deployment of LTE, HSPA+, and other similar networks. LTE throughputs can reach many megabits per second and can even rival WiFi throughputs in some locations. This paper addresses a fundamental question confronting transport and application-layer protocol designers: which network should an application use? WiFi, LTE, or Multi-Path TCP (MPTCP) running over both?
We compare LTE and WiFi for transfers of different sizes along both directions (i.e. the uplink and the downlink) using a crowd-sourced mobile application run by 750 users over 180 days in 16 different countries. We find that LTE outperforms WiFi 40\% of the time, which is a higher fraction than one might expect at first sight.
We measure flow-level MPTCP performance and compare it with the performance of TCP running over exclusively WiFi or LTE in 20 different locations across 7 cities in the United States. For short flows, we find that MPTCP performs worse than regular TCP running over the faster link; further, selecting the correct network for the primary subflow in MPTCP is critical in achieving good performance. For long flows, however, selecting the proper MPTCP congestion control algorithm is equally important.
To complement our flow-level analysis, we analyze the traffic patterns of several mobile apps, finding that apps can be categorized as "short-flow dominated" or "long-flow dominated". We then record and replay these patterns over emulated WiFi and LTE links. We find that application performance has a similar dependence on the choice of networks as flow-level performance: an application dominated by short flows sees little gain from MPTCP, while an application with longer flows can benefit much more from MPTCP --- if the application can pick the right network for the primary subflow and the right choice of MPTCP congestion control.National Science Foundation (U.S.) (Grant 1407470)National Science Foundation (U.S.) (Grant 1161964
Understanding and improving Web page load times on modern networks
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 77-80).This thesis first presents a measurement toolkit, Mahimahi, that records websites and replays them under emulated network conditions. Mahimahi improves on prior record-and-replay frameworks by emulating the multi-origin nature of Web pages, isolating its network traffic, and enabling evaluations of a larger set of target applications beyond browsers. Using Mahimahi, we perform a case study comparing current multiplexing protocols, HTTP/1.1 and SPDY, and a protocol in development, QUIC, to a hypothetical optimal protocol. We find that all three protocols are significantly suboptimal and their gaps from the optimal only increase with higher link speeds and RTTs. The reason for these trends is the same for each protocol: inherent source-level dependencies between objects on a Web page and browser limits on the number of parallel flows lead to serialized HTTP requests and prevent links from being fully occupied. To mitigate the effect of these dependencies, we built Cumulus, a user-deployable combination of a content-distribution network and a cloud browser that improves page load times when the user is at a significant delay from a Web page's servers. Cumulus contains a "Mini-CDN"-a transparent proxy running on the user's machine-and a "Puppet": a headless browser run by the user on a well-connected public cloud. When the user loads a Web page, the Mini-CDN forwards the user's request to the Puppet, which loads the entire page and pushes all of the page's objects to the Mini-CDN, which caches them locally. Cumulus benefits from the finding that dependency resolution, the process of learning which objects make up a Web page, accounts for a considerable amount of user-perceived wait time. By moving this task to the Puppet, Cumulus can accelerate page loads without modifying existing Web browsers or servers. We find that on cellular, in-flight Wi-Fi, and transcontinental networks, Cumulus accelerated the page loads of Google's Chrome browser by 1.13-2.36×. Performance was 1.19-2.13× faster than Opera Turbo, and 0.99-1.66× faster than Chrome with Google's Data Compression Proxy.by Ravi Arun Netravali.S.M
Mahimahi: A Lightweight Toolkit for Reproducible Web Measurement
No full textThis demo presents a measurement toolkit, Mahimahi, that records websites and replays them under emulated network conditions. Mahimahi is structured as a set of arbitrarily composable UNIX shells. It includes two shells to record and replay Web pages, RecordShell and ReplayShell, as well as two shells for network emulation, DelayShell and LinkShell. In addition, Mahimahi includes a corpus of recorded websites along with benchmark results and link traces (https://github.com/ravinet/sites).
Mahimahi improves on prior record-and-replay frameworks in three ways. First, it preserves the multi-origin nature of Web pages, present in approximately 98% of the Alexa U.S. Top 500, when replaying. Second, Mahimahi isolates its own network traffic, allowing multiple instances to run concurrently with no impact on the host machine and collected measurements. Finally, Mahimahi is not inherently tied to browsers and can be used to evaluate many different applications.
A demo of Mahimahi recording and replaying a Web page over an emulated link can be found at http://youtu.be/vytwDKBA-8s. The source code and instructions to use Mahimahi are available at http://mahimahi.mit.edu/
Maximizing Water--Food--Energy Nexus Synergies at Basin Scale
No full textIn this short paper, we show how solutions for mitigating resource security in one sector can be found in another. We demonstrate—by means of a case study in Burkina Faso and Ghana—how investing in the electricity grid in the south leads to increase food security in the north. A new nexus framework was developed (‘MAXUS’) which was built to understand, simulate and optimize intersectoral (and international) development strategies in the water, food and energy sectors. We believe this new type of geospatial integral resource management, supported by the exponential increase of data availability of the twenty-first century, could finally turn nexus models into decision support tools.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Water Resource
Improving web applications with fine-grained data flows
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 131-144).Web applications have significantly increased in complexity over the past several decades to support the wide range of services and performance requirements that users have come to expect. On the client-side, browsers are multi-process systems that can handle numerous content formats, rich interactivity, and asynchronous 10 patterns. On the server-side, applications are distributed across many machines and employ multi-tier architectures to implement application logic, caching, and persistent storage. As a result, web applications have become complex distributed systems that are difficult to understand, debug, and optimize. This dissertation presents fine-grained data flows as a new mechanism for understanding and optimizing complex web applications. Fine-grained data flows comprise the set of low-level reads and writes made to distributed application state during execution. We explain how fine-grained data flows can be tracked efficiently in production systems. We then present four concrete systems that illustrate how fine-grained data flows enable powerful performance optimizations and debugging primitives. Polaris dynamically reorders client HTTP requests during a page load to maximally overlap network round trips without violating data flow dependencies, reducing page load times by 34% (1.3 seconds). Prophecy uses data flow logs to create a snapshot of a mobile page's post-load state, which clients can process to elide intermediate computations, reducing bandwidth consumption by 21%, energy usage by 36%, and load times by 53% (2.8 seconds). Vesper is the first system to accurately and automatically measure page time-to-interactivity, without using heuristics or developer annotations. Vesper determines a page's interactive state by firing event handlers and analyzing the resulting data flows. Vesper-guided optimizations improve time- to- interactivity by 32%, generating more satisfaction in user studies than systems targeting past metrics. Cascade is the first replay debugger to support distributed, fine-grained provenance tracking. Cascade also enables speculative bug fix analysis, i.e., replaying a program to a point, changing program state, and resuming replay, using data flow tracking and causal analysis to evaluate potential bug fixes.by Ravi Arun Netravali.Ph. D
Thiamin diphosphate catalysis in Escherichia coli pyruvate dehydrogenase multi-enzyme complex: activation, covalent electrophilic catalysis, and substrate channeling
No full textSpectroscopic identification and characterization of covalent and non-covalent intermediates on large enzyme complexes is an exciting and challenging area of modern enzymology. While nuclear magnetic resonance (NMR) methods which provide detailed chemical insights have been successfully employed previously, limited examples are available in the literature for large enzyme complexes. Enzymes utilizing cofactors provide promising examples for such studies when synthetic routes to labeled cofactor analogs and protocols for reconstitution of apo-enzymes with such analogs are readily available. Syntheses of key isotope enriched thiamin diphosphate (ThDP) analogs – [C2, C6’ – 13C2] ThDP, [N4’ – 15N]ThDP and [C2 – 13C]ThDP – enabled first detection of (i) various ionization/tautomerization states of ThDP during the catalytic cycle of three ThDP dependent enzymes using cross polarization magic angle spinning (CPMAS) solid state NMR (SSNMR) spectroscopy and (ii) [C2, C6’ – 13C2] ThDP covalent intermediates on the E1 component (E1p) during the catalytic cycle of E. coli pyruvate dehydrogenase multi-enzyme complex (PDHc) by filter experiments including solution 1-D 1H-13C HSQC NMR. Direct evidence was gathered for the 4’-aminopyrimidinium form (APH+) on ThDP molecules bound to (i) S. cerevisiae yeast pyruvate decarboxylase (YPDC) (ii) E1p and (iii) the E1 component of E. coli 2-oxoglutarate dehydrogenase complex (E1o) using 13C and 15N CPMAS SSNMR. The thiazolium C2-H bond was found to be slightly acidic in the cofactor bound to these enzymes. 15N SSNMR experiments confirmed the formation of the 1’,4’-iminopyrimidine tautomer in presence of substrate analogs; a mechanism is proposed for the stabilization of this biologically rare tautomer in enzyme active-sites. Using rapid chemical quench in conjunction with solution NMR, pre-steady state analyses were performed on the native PDHc and PDH complexes reconstituted with E1p active-site loop variants of very low PDHc activity. The C2-α-lactylThDP intermediate could not be detected under any of the conditions used, indicating that its formation is slower than its decarboxylation. The enamine intermediate accumulates at a rate 110 s-1 on E1p and PDHc, while the rates are 100-fold slower for the PDHc variants. 2-acetylThDP could be detected on E1p only during its reaction with pyruvate and the artificial electron acceptor DCPIP. Reductive acetylation of the lipoyl domain in a pre-steady state single turn-over experiment (a model for the E1p-E2p reductive acetyl transfer reaction) was determined by mass spectrometry. Combined, these kinetic results from artificial oxidation reactions suggest the enamine is very well stabilized by E1p and oxidation of the enamine and substrate channeling to E2p are favored by intact PDHc. These studies provide unprecedented insight into the acid-base and covalent electrophilic roles of ThDP in enzyme catalysis and the methods described herein are applicable to all such complexes.Ph.D.Includes bibliographical referencesIncludes vitaby Anand Balakrishna
Classifiers of massive and structured data problems: algorithms and applications
No full textThe last two decades have seen the emergence of vast and unprecedented data repositories. Extraordinary opportunities now present themselves for new data analysis methods that can harness these repositories. As larger and larger amounts of widely varying types of data are constantly being collected and assimilated, the
task of making use of such data opens up interesting and challenging avenues of research.
This thesis deals with specific problems in data mining and machine learning in this setting. In particular we describe algorithms and applications for classification problems where
computational restrictions become limiting (resource bounded algorithms and online/streaming algorithms) as well as models and algorithms for certain problems where the structure of the input is leveraged to provide not only accurate, but also interpretable classifiers.Ph.D.Includes bibliographical references
Recurrence-based models for improving coverage within GPS and satellite-denied mobile sensor networks
No full textThis Thesis was approved for publication on 2021-04-28 at 11:15.DSpace SAF Submission Ingestion Package generated from Vireo submission #16540 on 2021-09-16 at 17:05:08Made available in DSpace on 2021-09-17T02:34:46Z (GMT). No. of bitstreams: 3
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Previous issue date: 2021-04-28Adversarial GPS-denial and coordinate spoofing, as well as satellite jamming, serve as common obstacles to disaster-recovery and military-based teams. While such teams are often supported by UAVs that connect multiple personnel by serving as relay devices, UAV position schemes that rely on centralized controllers are also disrupted by such hurdles, as GPS and satellite-based denial will effect the ability of UAVs to communicate with the controller and drones outside line of sight. In this thesis, we design and implement a drone-relay system that allows drones to cooperatively maximize coverage in a GPS-denied and satellite-denied scenario. Here, we define coverage as the ability of one entity to speak to another entity using a drone network as an intermediate relay system and is measured as the ratio of fulfilled entity-to-entity connections to all possible entity-to-entity connections. We maximize coverage over an extended experiment duration, consisting of 300–1000 timesteps, by devising algorithms that rely on a centralized controller with full knowledge of drone and ground entity position. Particle Swarm Optimization (85% coverage), Reinforcement Learning on a Recurrent Neural Network (75% coverage), and a Time-Series based Inference Optimizer (71% coverage) were amongst the best performing movement algorithms, improving upon movement models in related works by up to 40%. We then design a distributed backend that disperses commands from a centralized controller using a distributed drone-to-drone communication scheme, also collecting observations made by each drone and relaying them to the centralized controller. This backend is additionally integrated with failure recovery and security-based protocols to ensure recovery in drone-downtime and drone-compromised scenarios; both systems feature minimal overhead, allowing drone recovery from downtime in 7% of the simulated episode length and featuring a constant time-addition from encryption that does not increase as drone count increases. Finally, we remove all notions of centrality by designing and implementing a fully decentralized system, where drones operate in squads and house their own models and decision-making protocols. In this system, drone squads are able to share observations of their surroundings with neighboring drone squads to improve predictive performance. This final system complies with GPS and satellite-denial limitations as drones only perform observations in a surrounding vision radius, assuming a camera to be mounted on each drone, and drones can only send messages to neighbors in a transmission radius, avoiding the need of sending satellite-based messages.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2023-05-01The student, Rahul Balakrishnan, accepted the attached license on 2021-04-23 at 19:58.The student, Rahul Balakrishnan, submitted this Thesis for approval on 2021-04-23 at 20:11.Embargo set by: Seth Robbins for item 118580
Lift date: 2023-09-17T02:34:57Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Onl
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