Making Networks Robust to Component Failures

In this thesis, we consider instances of component failure in the Internet and in networked cyber-physical systems, such as the communication network used by the modern electric power grid (termed the smart grid). We design algorithms that make these networks more robust to various component failures, including failed routers, failures of links connecting routers, and failed sensors. This thesis divides into three parts: recovery from malicious or misconfigured nodes injecting false information into a distributed system (e.g., the Internet), placing smart grid sensors to provide measurement error detection, and fast recovery from link failures in a smart grid communication network. First, we consider the problem of malicious or misconfigured nodes that inject and spread incorrect state throughout a distributed system. Such false state can degrade the performance of a distributed system or render it unusable. For example, in the case of network routing algorithms, false state corresponding to a node incorrectly declaring a cost of 0 to all destinations (maliciously or due to misconfiguration) can quickly spread through the network. This causes other nodes to (incorrectly) route via the misconfigured node, resulting in suboptimal routing and network congestion. We propose three algorithms for efficient recovery in such scenarios and evaluate their efficacy. The last two parts of this thesis consider robustness in the context of the electric power grid. We study the use and placement of a sensor, called a Phasor Measurement Unit (PMU), currently being deployed in electric power grids worldwide. PMUs provide voltage and current measurements at a sampling rate orders of magnitude higher than the status quo. As a result, PMUs can both drastically improve existing power grid operations and enable an entirely new set of applications, such as the reliable integration of renewable energy resources. However, PMU applications require correct (addressed in thesis part 2) and timely(covered in thesis part 3) PMU data. Without these guarantees, smart grid operators and applications may make incorrect decisions and take corresponding (incorrect) actions. The second part of this thesis addresses PMU measurement errors, which have been observed in practice. We formulate a set of PMU placement problems that aim to satisfy two constraints: place PMUs near each other to allow for measurement error detection and use the minimal number of PMUs to infer the state of the maximum number of system buses and transmission lines. For each PMU placement problem, we prove it is NP-Complete, propose a simple greedy approximation algorithm, and evaluate our greedy solutions. In the last part of this thesis, we design algorithms for fast recovery from link failures in a smart grid communication network. We propose, design, and evaluate solutions to all three aspects of link failure recovery: (a) link failure detection, (b) algorithms for pre-computing backup multicast trees, and (c) fast backup tree installation. To address (a), we design link-failure detection and reporting mechanisms that use OpenFlow to detect link failures when and where they occur inside the network. OpenFlow is an open source framework that cleanly separates the control and data planes for use in network management and control. For part (b), we formulate a new problem, Multicast Recycling, that pre-computes backup multicast trees that aim to minimize control plane signaling overhead. We prove Multicast Recycling is at least NP-hard and present a corresponding approximation algorithm. Lastly, two control plane algorithms are proposed that signal data plane switches to install pre-computed backup trees. An optimized version of each installation algorithm is designed that finds a near minimum set of forwarding rules by sharing forwarding rules across multicast groups. This optimization reduces backup tree install time and associated control state. We implement these algorithms using the POX open-source OpenFlow controller and evaluate them using the Mininet emulator, quantifying control plane signaling and installation time

Enriching personal information management with document interaction histories

Personal information management is increasingly challenging, as more and more of our personal and professional activity migrates to personal computers. Manual organization and search remain the only two options available to users, and both have significant limitations; the former requires too much effort on the part of the user, while the latter is dependent on users' ability to recall discriminating information. I pursue an alternative approach, where users' computer interactions with their workspaces are recorded, algorithms draw inferences from this interaction, and these inferences are applied to improve information management and retrieval for users. This approach requires no effort from users and enables retrieval to be more personalized, natural, and intuitive. The Passages system enhances information management by maintaining a detailed chronicle of all the text the user ever reads or edits, and making this chronicle available for rich temporal queries about the user's information workspace. Passages enables queries like, which papers and web pages did I read when writing the related work section of this paper?, and which of the emails in this folder have I skimmed, but not yet read in detail? As time and interaction history are important attributes in users' recall of their personal information, effectively supporting them creates useful possibilities for information retrieval. I present methods to collect information about the large volume of text with which the user interacts, and use this information to improve retrieval. I show through user evaluation the accuracy of Passages in building interaction history, and illustrate its capacity to both improve existing retrieval systems and enable novel ways to characterize document activity across time. Before the Passages system, I developed two other systems with similar goals. Confluence extends an existing system that identifies task-based links among users' data through their being used at proximal points in time. For example, if a user frequently interacts with a report and a graph at the same time, those documents likely share a common task even though they may have no semantic relationship. Once such links are identified, they are applied when users issue search queries, expanding traditional, text-based results with other documents that share task-based links to those results. This creates a form of task-based retrieval which is independent of document semantics, and enhances users' ability to retrieve information. The SeeTrieve system extends this concept to trace the visible text in the GUI with which the user interacts and associate this with files whose accesses occur at proximal points in time. In addition to improving retrieval for users, it creates a form of automated, task-oriented tagging of files

Analysis of Local Health Department Factors that Accelerate Population-based Intervention Strategies: Preliminary Findings

Introduction: This practice-based research study capitalized on the statewide implementation of a comprehensive, locally-driven initiative to implement evidence-based policy, system and environmental changes related to obesity and tobacco use. The study examined local health department (LHD) performance and factors such as organizational quality improvement (QI) maturity, structure and governance. Methods: State health department staff reviewed grant reports and documentation pertaining to all LHD grantees, which collectively represented all 87 counties and 4 cities in Minnesota (MN), in order to designate grantees as either: “Exceeds Expectations,” “Meets Expectations” or “Approaching Expectations.” A study team of state, local and academic partners then used select measures from the QI Maturity Tool to calculate a QI Maturity Score, and subsequently place grantees into three levels of QI maturity: low, medium and high. Multivariate regression was performed to examine the potential relationship between grantee performance and QI maturity, as well as other covariates. Results: Of the final sample of 91 counties/cities, 87 had complete data for multivariate analysis. The distribution of grantee performance was: exceeds expectations (29.7%), meets expectations (55.0%) and approaching expectations (15.3%). Organizational QI maturity was strongly, positively associated with grantee performance comparing the “exceeds expectations” to those who “met or approached expectations” (OR=4.29, 95 % CI: 1.90-9.73, p=0.0005). Implications: Organizational QI maturity was strongly associated with LHD performance. More research is needed to determine whether a more mature approach to quality improvement is merely a marker for overall LHD capacity or has its own unique contribution to performance. Findings have been used to inform the next funding cycle of this initiative and provide support to implementing annual assessment of QI maturity in MN

Tax Levy Financing for Local Public Health: Relationships between Fiscal Allocation, Fiscal Effort and Fiscal Capacity

This study examines property tax levy (local tax levy) as a source of local health department (LHD) funding during a five year period (2006-2010) in all Minnesota counties by assessing fiscal effort, fiscal allocation and fiscal capacity. Local health departments rely on pluralistic funding from local, state, federal and private sources. However, local tax levy funding is unexplored and little is known regarding the extent of fiscal allocation (tax levy used for LHD), fiscal effort (potential amount of tax levy available for LHD), and fiscal capacity (wealth of community). More important it is not known to what extent variation between local jurisdictions fluctuated over time, how they are offset by declining funding from other sources, or whether other sources supplement total tax levy reductions. It is essential to explore these issues to provide a basic understanding of fiscal drivers for ongoing services. Our findings indicate that from 2006 to 2010 the local tax levy for public health as a percent of total local health department expenditures decreased 6.7%, while local tax levy for public health as a percent of total tax levy decreased 14.6%. However, during this time period the total per capita tax levy for all services increased 25.2%

Monitoring QI Maturity of Public Health Organizations and Systems in Minnesota: Promising Early Findings and Suggested Next Steps

Public health departments and systems are increasing investments in quality improvement. This paper presents methods used to identify a select number of items from a previously validated QI Maturity Tool as the basis for calculating organizational and system-level QI maturity scores that could be followed over time. Findings suggest that the abbreviated tool measures variation in QI maturity across LHDs, and differences in scores among divisions within a state health department. Minnesota has incorporated the abbreviated tool into an annual reporting system for the MN Local Public Health Act, thereby enabling stakeholders to monitor a system median score and distribution of scores every year. Such information will be used by state and local partners to identify opportunities for system-wide improvements

Monitoring QI Maturity of Public Health Organizations and Systems in Minnesota: Promising Early Findings and Suggested Next Steps

This paper presents methods used by the MN PBRN to identify a select number of items from the QI Maturity Tool as the basis for calculating organizational and system-level QI maturity scores. The findings suggest that the abbreviated tool measures variation in QI maturity across LHDs, and differences in scores among divisions within the larger state health department. The results have several implications. This modified tool shows promise and may accelerate measurement of QI in practice settings. Future additional testing may help refine the score and assure that it reflects emerging research related to QI maturity

Wintertime weather-climate variability and its links to early spring ice-out in Maine lakes

In recent decades, Maine lakes have recorded their earliest ice-out dates in over a century. In temperate regions, seasonal lake ice-cover is a critical phenomenon linking climate, aquatic ecosystem and society. And the lengthening of the ice-free period due to warmer climate has been linked to increased algal growth and declining lake water quality, warming of water temperatures leading to alterations in aquatic biodiversity, and the shortening of ice-fishing period and other traditional winter activities over lakes. In this study, historical record of eight lakes and six benchmarked meteorological stations in Maine for the period 1950–2010 were analyzed to (1) investigate the relationship between antecedent winter (January–February) temperatures, degree-day variables, and spring-time ice breakup dates, including the identification of thresholds and (2) determine the influence of the extreme phases of select atmospheric teleconnection patterns (Tropical Northern hemisphere- TNH and North Atlantic Oscillation- NAO) on the winter degree-day quantities and spring ice-out dates. The influence of antecedent winter degree-days on spring ice-out dates was characterized by determining the threshold winter accumulated freezing and melting degree-day (AFDD and AMDD), the exceedance (non-exceedance) of which engenders early (late) spring ice-out dates. Statistical analysis between teleconnection indices and winter AFDD and/or AMDD quantities for Maine revealed an asymmetric relationship. Strongly negative phases of TNH and, to a lesser extent, positive phases of NAO are linked with spatial and temporal pattern of early spring ice breakup events in Maine lakes. These relationships taken together with observed warming trends have the potential to accelerate the decline in water quality in Maine lakes

The Role of Depressive Symptomatology in Peri- and Post-Menopause

Objectives: There is evidence that menopausal symptoms manifested at peri-menopause occur less fre- quently when compared to the symptoms experienced at post-menopause. The aim of this study was to investigate this and to test the hypothesis that depressive symptomatology mediates the relationship between menopausal stage and symptom frequency. Methods: This cross-sectional study included 213 women (M age = 52 years), of whom 125 were peri- and 88 post-menopausal. Measures comprised the Center for Epidemiologic Studies-Depression scale (CES-D) and the Women’s Health Questionnaire (WHQ) vasomotor symptoms and somatic symptoms subscales. Results: Multiple mediated regression analyses provided evidence that somatic symptoms and vasomotor symptoms were less frequent at post- compared to peri-menopause, and that these differences were mediated by depressive symptomatology. Multivariate effect sizes ranged from small to moderate, and univariate effect sizes were uniformly small with wide confidence intervals. Conclusions: The frequency of vasomotor and somatic symptoms appears to increase with depressed affect. The management of symptoms could include interventions of a psychotherapeutic nature, which may offset this effect, particularly in women for whom depressive symptoms are a feature of the climac- teric syndrome. The extent to which depression and the climacteric syndrome may be causally related to one another remains unclear and longitudinal research should further examine the mechanisms of this association

Sociodemographic differences in linkage error: An examination of four large-scale datasets

© 2018 The Author(s). Background: Record linkage is an important tool for epidemiologists and health planners. Record linkage studies will generally contain some level of residual record linkage error, where individual records are either incorrectly marked as belonging to the same individual, or incorrectly marked as belonging to separate individuals. A key question is whether errors in linkage quality are distributed evenly throughout the population, or whether certain subgroups will exhibit higher rates of error. Previous investigations of this issue have typically compared linked and un-linked records, which can conflate bias caused by record linkage error, with bias caused by missing records (data capture errors). Methods: Four large administrative datasets were individually de-duplicated, with results compared to an available 'gold-standard' benchmark, allowing us to avoid methodological issues with comparing linked and un-linked records. Results were compared by gender, age, geographic remoteness (major cities, regional or remote) and socioeconomic status. Results: Results varied between datasets, and by sociodemographic characteristic. The most consistent findings were worse linkage quality for younger individuals (seen in all four datasets) and worse linkage quality for those living in remote areas (seen in three of four datasets). The linkage quality within sociodemographic categories varied between datasets, with the associations with linkage error reversed across different datasets due to quirks of the specific data collection mechanisms and data sharing practices. Conclusions: These results suggest caution should be taken both when linking younger individuals and those in remote areas, and when analysing linked data from these subgroups. Further research is required to determine the ramifications of worse linkage quality in these subpopulations on research outcomes

Data Linkage: A powerful research tool with potential problems

Background: Policy makers, clinicians and researchers are demonstrating increasing interest in using data linked from multiple sources to support measurement of clinical performance and patient health outcomes. However, the utility of data linkage may be compromised by sub-optimal or incomplete linkage, leading to systematic bias. In this study, we synthesize the evidence identifying participant or population characteristics that can influence the validity and completeness of data linkage and may be associated with systematic bias in reported outcomes