Space Exploration via Proximity Search

We investigate what computational tasks can be performed on a point set in $\Re^d$, if we are only given black-box access to it via nearest-neighbor search. This is a reasonable assumption if the underlying point set is either provided implicitly, or it is stored in a data structure that can answer such queries. In particular, we show the following: (A) One can compute an approximate bi-criteria $k$-center clustering of the point set, and more generally compute a greedy permutation of the point set. (B) One can decide if a query point is (approximately) inside the convex-hull of the point set. We also investigate the problem of clustering the given point set, such that meaningful proximity queries can be carried out on the centers of the clusters, instead of the whole point set

Ruminating on rumination: Are rumination on anger and sadness differentially related to aggression and depressed mood?

Rumination is a risk factor for aggression and depression, yet few studies have incorporated both aggression and depression in a unitary model that reflects how rumination predicts these distinct conditions. The current study examined rumination on anger and sadness to assess their unique relations with aggression and depressed mood, respectively. Analogous anger rumination and sadness rumination questionnaires were used to minimize measurement variance, and were completed by 226 undergraduate students. Factor analysis suggested one general rumination factor comprised of two distinct sub-factors of anger rumination and sadness rumination. Path analysis confirmed unique relations between anger rumination and aggression, and sadness rumination and depressed mood. Further, anger rumination and anger were independent predictors of aggression. Results supported the conceptualization of anger rumination and sadness rumination as distinct constructs and underscore the importance of pursuing research that incorporates both forms of rumination to better understand how they impact development, mental health, and behavior

Adolescent-parent attachment: Bonds that support healthy development

Adolescence is characterized by significant neurological, cognitive and sociopsychological development. With the advance of adolescence, the amount of time spent with parents typically drops while time spent with peers increases considerably. Nonetheless, parents continue to play a key role in influencing their adolescent’s development. Adolescent-parent attachment has profound effects on cognitive, social and emotional functioning. Secure attachment is associated with less engagement in high risk behaviours, fewer mental health problems, and enhanced social skills and coping strategies. The present article provides a brief synopsis of the changes that occur during adolescence and describes what attachment is, why it continues to be important and how it is transformed during adolescence. It summarizes major findings on the impact of attachment on adolescent adjustment and discusses strategies for supporting healthy adolescent-parent attachment

A reduced semantics for deciding trace equivalence using constraint systems

Many privacy-type properties of security protocols can be modelled using trace equivalence properties in suitable process algebras. It has been shown that such properties can be decided for interesting classes of finite processes (i.e., without replication) by means of symbolic execution and constraint solving. However, this does not suffice to obtain practical tools. Current prototypes suffer from a classical combinatorial explosion problem caused by the exploration of many interleavings in the behaviour of processes. M\"odersheim et al. have tackled this problem for reachability properties using partial order reduction techniques. We revisit their work, generalize it and adapt it for equivalence checking. We obtain an optimization in the form of a reduced symbolic semantics that eliminates redundant interleavings on the fly.Comment: Accepted for publication at POST'1

Smallest k-Enclosing Rectangle Revisited

Given a set of n points in the plane, and a parameter k, we consider the problem of computing the minimum (perimeter or area) axis-aligned rectangle enclosing k points. We present the first near quadratic time algorithm for this problem, improving over the previous near-O(n^{5/2})-time algorithm by Kaplan et al. [Haim Kaplan et al., 2017]. We provide an almost matching conditional lower bound, under the assumption that (min,+)-convolution cannot be solved in truly subquadratic time. Furthermore, we present a new reduction (for either perimeter or area) that can make the time bound sensitive to k, giving near O(n k) time. We also present a near linear time (1+epsilon)-approximation algorithm to the minimum area of the optimal rectangle containing k points. In addition, we study related problems including the 3-sided, arbitrarily oriented, weighted, and subset sum versions of the problem

Verification of Hierarchical Artifact Systems

Data-driven workflows, of which IBM's Business Artifacts are a prime exponent, have been successfully deployed in practice, adopted in industrial standards, and have spawned a rich body of research in academia, focused primarily on static analysis. The present work represents a significant advance on the problem of artifact verification, by considering a much richer and more realistic model than in previous work, incorporating core elements of IBM's successful Guard-Stage-Milestone model. In particular, the model features task hierarchy, concurrency, and richer artifact data. It also allows database key and foreign key dependencies, as well as arithmetic constraints. The results show decidability of verification and establish its complexity, making use of novel techniques including a hierarchy of Vector Addition Systems and a variant of quantifier elimination tailored to our context.Comment: Full version of the accepted PODS pape

Approximate Minimum Diameter

We study the minimum diameter problem for a set of inexact points. By inexact, we mean that the precise location of the points is not known. Instead, the location of each point is restricted to a contineus region (\impre model) or a finite set of points (\indec model). Given a set of inexact points in one of \impre or \indec models, we wish to provide a lower-bound on the diameter of the real points. In the first part of the paper, we focus on \indec model. We present an $O(2^{\frac{1}{\epsilon^d}} \cdot \epsilon^{-2d} \cdot n^3 )$ time approximation algorithm of factor $(1+\epsilon)$ for finding minimum diameter of a set of points in $d$ dimensions. This improves the previously proposed algorithms for this problem substantially. Next, we consider the problem in \impre model. In $d$-dimensional space, we propose a polynomial time $\sqrt{d}$-approximation algorithm. In addition, for $d=2$, we define the notion of $\alpha$-separability and use our algorithm for \indec model to obtain $(1+\epsilon)$-approximation algorithm for a set of $\alpha$-separable regions in time $O(2^{\frac{1}{\epsilon^2}}\allowbreak . \frac{n^3}{\epsilon^{10} .\sin(\alpha/2)^3} )$