Robust Assignments via Ear Decompositions and Randomized Rounding

Many real-life planning problems require making a priori decisions before all parameters of the problem have been revealed. An important special case of such problem arises in scheduling problems, where a set of tasks needs to be assigned to the available set of machines or personnel (resources), in a way that all tasks have assigned resources, and no two tasks share the same resource. In its nominal form, the resulting computational problem becomes the \emph{assignment problem} on general bipartite graphs. This paper deals with a robust variant of the assignment problem modeling situations where certain edges in the corresponding graph are \emph{vulnerable} and may become unavailable after a solution has been chosen. The goal is to choose a minimum-cost collection of edges such that if any vulnerable edge becomes unavailable, the remaining part of the solution contains an assignment of all tasks. We present approximation results and hardness proofs for this type of problems, and establish several connections to well-known concepts from matching theory, robust optimization and LP-based techniques.Comment: Full version of ICALP 2016 pape

New statistical disclosure attacks on anonymous communications networks

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Informática, Departamento de Ingeniería del Software e Inteligencia Artificial, leída el 5-02-2016.El anonimato es una dimensi on de la privacidad en la que una persona se reserva su identidad en las relaciones sociales que mantiene. Desde el punto de vista del area de las comunicaciones electr onicas, el anonimato posibilita mantener oculta la informaci on que pueda conducir a la identi caci on de las partes involucradas en una transacci on. Actualmente, conservar el anonimato en las transacciones de informaci on en red representa uno de los aspectos m as importantes. Con este n se han desarrollado diversas tecnolog as, com unmente denominadas tecnolog as para la mejora de la privacidad. Una de las formas m as populares y sencillas de proteger el anonimato en las comunicaciones entre usuarios son los sistemas de comunicaci on an onima de baja latencia basados en redes de mezcladores. Estos sistemas est an expuestos a una serie de ataques basados en an alisis de tr a co que comprometen la privacidad de las relaciones entre los usuarios participantes en la comunicaci on, esto es, que determinan, en mayor o menor medida, las identidades de emisores y receptores. Entre los diferentes tipos de ataques destacan los basados en la inundaci on de la red con informaci on falsa para obtener patrones en la red de mezcladores, los basados en el control del tiempo, los basados en el contenido de los mensajes, y los conocidos como ataques de intersecci on, que pretenden inferir, a trav es de razonamientos probabil sticos o de optimizaci on, patrones de relaciones entre usuarios a partir de la informaci on recabada en lotes o durante un per odo de tiempo por parte del atacante. Este ultimo tipo de ataque es el objeto de la presente tesis...Anonymity is a privacy dimension related to people's interest in preserving their identity in social relationships. In network communications, anonymity makes it possible to hide information that could compromise the identity of parties involved in transactions. Nowadays, anonymity preservation in network information transactions represents a crucial research eld. In order to address this issue, a number of Privacy Enhancing Technologies have been developed. Low latency communications systems based on networks of mixes are very popular and simple measures to protect anonymity in users communications. These systems are exposed to a series of attacks based on tra c analysis that compromise the privacy of relationships between user participating in communications, leading to determine the identity of sender and receiver in a particular information transaction. Some of the leading attacks types are attacks based on sending dummy tra c to the network, attacks based on time control, attacks that take into account the textual information within the messages, and intersections attacks, that pretend to derive patterns of communications between users using probabilistic reasoning or optimization algorithms. This last type of attack is the subject of the present work. Intersection attacks lead to derive statistical estimations of the communications patterns (mean number of sent messages between a pair of users, probability of relationship between users, etc). These models were named Statistical Disclosure Attacks, and were soon considered able to compromise seriously the anonymity of networks based on mixes. Nevertheless, the hypotheses assumed in the rst publications for the concrete development of the attacks were excessively demanding and unreal. It was common to suppose that messages were sent with uniform probability to the receivers, to assume the knowledge of the number of friends an user has or the knowledge a priori of some network parameters, supposing similar behavior between users, etc...Depto. de Ingeniería de Software e Inteligencia Artificial (ISIA)Fac. de InformáticaTRUEunpu

Fringe Benefits

This study tests the hypothesis that increased rugosity (the ratio between urban perimeter and farmland area) of the rural-urban fringe allows farms to create greater value for their regions through greater access to urban markets. Findings show that increased rugosity is not associated with farmland loss despite correlating with greater population growth. Rugosity is, instead, associated with higher agricultural sales per acre and more farm-to-city networks. Using the urban interface as a variable to understand farm production and stabilization, this paper includes a spatial statistical analysis of county-level metro-area farm products, farmland loss, and demographics in relation to the concentricity of urban morphology in the United States. Four case studies reveal spatial and social network patterns of direct farm sales and donations of raw product. Farm-to-city market director interviews ground-truth these farm-city functions in relation to county and state-level policies that govern urban and farmland morphologies and function

Street design, traffic, and fear of crime : moving from gated communities to transit villages

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2001."June 2001."Includes bibliographical references (leaves 143-149).The first phase of Tren Urbano, a rail rapid transit system in San Juan, Puerto Rico, is currently under construction, with future phases in the planning stages. San Juan's built landscape is presently dominated and dramatically fragmented by gated developments, which poses fundamental problems for the success of Tren Urbano. This thesis documents and explores the negative impacts of widespread gated communities on transit use and transit-conducive development, including inhibitions on the directness of pedestrian access to stations, the quality of the pedestrian realm, the ability to sustain mixed land uses (and thus the ability of transit riders to "trip-chain"), the ability to plan efficient feeder transit service, and residents' socio-geographical perspectives of their relationships to their neighborhoods, transit, and the form of the city. If there is a way to ameliorate residents' fears of crime and achieve the sought-after benefits of gated developments while facilitating more connective pedestrian-oriented transit-supportive settlement patterns, then alternative models should be understood and promoted. The extent to which measures less restrictive than gated developments in other cities have indeed mitigated fears of crime (and actual crime) and produced more neighborhood satisfaction could provide a new model for San Juan to follow, especially around Tren Urbano stations. To arrive at such an alternative model, this research asks why Sanjuaneros are attracted to gated communities and explores urban design paradigms that take a different tack at satisfying these concerns in a more connected context. Analysis of the underlying roots of fear of crime and other perceived benefits of gated communities in San Juan reveals a common denominator concern with the physical and sociological effects of auto traffic. Gated communities provide a lure of restricted access, a refuge from the auto which brings with it the perception of uncontrollable and unpredictable threats to personal security, neighborhood livability, sense of place, and community integrity. Delving into the related physical and sociological neighborhood impacts of auto traffic enables us to work from the ground up toward pedestrian-oriented alternative models of neighborhood development. Experiments with street modification and traffic calming in Chicago neighborhoods participating in the city's Community Security Infrastructure Program confirm that by altering perceptions and use parameters of street space as well as the strutucure of the street network, residents feel enhanced control of their neighborhood domain, enhanced personal and community safety, more comfortable using public space, and generally more satisfied with their neighborhood environment. Ultimately, from the Chicago experience emerges a set of street and neighborhood design principles, that address both the space of streets and the structure of movement networks. I outline a set of urban design principles that should be applied to residential neighborhoods to satisfy individual and communal reasons that make gated communities attractive, however based on highly-connective and rich pedestrian networks within a fabric that maintains the integrity of mixed uses oriented around transit. This fabric optimizes pedestrian permeability while maintaining defined neighborhoods where the flow of movement and the tone of activity is community-defined and set within the comfort zone of the residents. The five principles that facilitate these goals are: (1) Use street space to articulate a constructive and positive vision of neighborhood activity by physically expanding the pedestrian domain to encompass the street holistically; (2) Stress elements in the street realm that act as neighborhood amenities; (3) Use street elements that exude the symbolism of invitation and accommodation by serving the dual functions of traffic control and inter-neighborhood zones of exchange; (4) Optimize the pedestrian network and constrain the auto network with street design elements that recognize and take advantage of the potential overlapping duality of these networks and their respective relationships to the same built fabric; and (5) Extend the comfort and identification zone of "home" and "neighborhood" via permeation of integrated street design and careful articulation of boundaries, potentially encompassing the transit station. While Tren Urbano first needs to figure out why gated communities are so attractive to Sanjuaneros and develop an urban design model that meets these needs while satisfying the needs of pedestrians and transit, implementation of these design principles is the next challenge. Of the strategic options available, the current realities in San Juan make (1) the creation of development incentives for building along a parallel set of design guidelines and (2) sponsoring and marketing demonstration projects the most feasible and likely to succeed at the present in forging a new direction and opening the city's eyes to new options in urban living.by Joshua Switzky.M.C.P

Sharing and viewing segments of electronic patient records service (SVSEPRS) using multidimensional database model

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The concentration on healthcare information technology has never been determined than it is today. This awareness arises from the efforts to accomplish the extreme utilization of Electronic Health Record (EHR). Due to the greater mobility of the population, EHR will be constructed and continuously updated from the contribution of one or many EPRs that are created and stored at different healthcare locations such as acute Hospitals, community services, Mental Health and Social Services. The challenge is to provide healthcare professionals, remotely among heterogeneous interoperable systems, with a complete view of the selective relevant and vital EPRs fragments of each patient during their care. Obtaining extensive EPRs at the point of delivery, together with ability to search for and view vital, valuable, accurate and relevant EPRs fragments can be still challenging. It is needed to reduce redundancy, enhance the quality of medical decision making, decrease the time needed to navigate through very high number of EPRs, which consequently promote the workflow and ease the extra work needed by clinicians. These demands was evaluated through introducing a system model named SVSEPRS (Searching and Viewing Segments of Electronic Patient Records Service) to enable healthcare providers supply high quality and more efficient services, redundant clinical diagnostic tests. Also inappropriate medical decision making process should be avoided via allowing all patients‟ previous clinical tests and healthcare information to be shared between various healthcare organizations. Multidimensional data model, which lie at the core of On-Line Analytical Processing (OLAP) systems can handle the duplication of healthcare services. This is done by allowing quick search and access to vital and relevant fragments from scattered EPRs to view more comprehensive picture and promote advances in the diagnosis and treatment of illnesses. SVSEPRS is a web based system model that helps participant to search for and view virtual EPR segments, using an endowed and well structured Centralised Multidimensional Search Mapping (CMDSM). This defines different quantitative values (measures), and descriptive categories (dimensions) allows clinicians to slice and dice or drill down to more detailed levels or roll up to higher levels to meet clinicians required fragment

COIN@AAMAS2015

COIN@AAMAS2015 is the nineteenth edition of the series and the fourteen papers included in these proceedings demonstrate the vitality of the community and will provide the grounds for a solid workshop program and what we expect will be a most enjoyable and enriching debate.Peer reviewe