Concordia University

About: Concordia University is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Control theory & Population. The organization has 13565 authors who have published 31084 publications receiving 783525 citations. The organization is also known as: Sir George Williams University & Loyola College, Montreal.

Differentially Private Histogram Publishing through Lossy Compression

Abstract: Differential privacy has emerged as one of the most promising privacy models for private data release. It can be used to release different types of data, and, in particular, histograms, which provide useful summaries of a dataset. Several differentially private histogram releasing schemes have been proposed recently. However, most of them directly add noise to the histogram counts, resulting in undesirable accuracy. In this paper, we propose two sanitization techniques that exploit the inherent redundancy of real-life datasets in order to boost the accuracy of histograms. They lossily compress the data and sanitize the compressed data. Our first scheme is an optimization of the Fourier Perturbation Algorithm (FPA) presented in \cite{RN10}. It improves the accuracy of the initial FPA by a factor of 10. The other scheme relies on clustering and exploits the redundancy between bins. Our extensive experimental evaluation over various real-life and synthetic datasets demonstrates that our techniques preserve very accurate distributions and considerably improve the accuracy of range queries over attributed histograms.

Combined inhibition of nitric oxide and prostaglandins reduces human skeletal muscle blood flow during exercise.

Abstract: The vascular endothelium is an important mediator of tissue vasodilatation, yet the role of the specific substances, nitric oxide (NO) and prostaglandins (PG), in mediating the large increases in muscle perfusion during exercise in humans is unclear. Quadriceps microvascular blood flow was quantified by near infrared spectroscopy and indocyanine green in six healthy humans during dynamic knee extension exercise with and without combined pharmacological inhibition of NO synthase (NOS) and PG by l-NAME and indomethacin, respectively. Microdialysis was applied to determine interstitial release of PG. Compared to control, combined blockade resulted in a 5- to 10-fold lower muscle interstitial PG level. During control incremental knee extension exercise, mean blood flow in the quadriceps muscles rose from 10 ± 0.8 ml (100 ml tissue)−1 min−1 at rest to 124 ± 19, 245 ± 24, 329 ± 24 and 312 ± 25 ml (100 ml tissue)−1 min−1 at 15, 30, 45 and 60 W, respectively. During inhibition of NOS and PG, blood flow was reduced to 8 ± 0.5 ml (100 ml tissue)−1 min−1 at rest, and 100 ± 13, 163 ± 21, 217 ± 23 and 256 ± 28 ml (100 ml tissue)−1 min−1 at 15, 30, 45 and 60 W, respectively (P < 0.05 vs. control). In conclusion, combined inhibition of NOS and PG reduced muscle blood flow during dynamic exercise in humans. These findings demonstrate an important synergistic role of NO and PG for skeletal muscle vasodilatation and hyperaemia during muscular contraction.

A performance modeling of connectivity in vehicular ad hoc networks (vanets)

Abstract: An emerging new type of ad hoc networks is Vehicular Ad hoc NETworks (VANETs) which envision Inter-Vehicle Communications. Since, nodes in VANETs are both mobile as well as carrier of information; the network may not have full communication connectivity all the time and they may form several clusters where the nodes in each cluster may communicate with each other directly or indirectly. Multi-clustering happens whenever the minimum distance between two adjacent nodes becomes more than the transmission range of a node. Therefore, two important performance measures which affect the functionality in VANETs are communications connectivity and path availability . In this thesis, we study the statistical properties of these performance measures in VANETs at the steady state. First, it is assumed that the nodes travel along a multi-lane highway which allows vehicles to overtake each other. We derive the probability distributions of the node population size and node's location in the highway segments. Then, we determine the mean population size in a cluster and probability that nodes will form a single cluster. Then we extend the single highway model to a network of highways with arbitrary topology. We determine the joint distribution of the node populations in the highways' segments by application of the BCMP theorem. We model the number of clusters within the node population in a network path as a Markovian birth-death process. This model enables derivation of the probability distribution of the number of clusters and determination of mean durations of continuous communication path availability and unavailability times as functions of mobility and node arrival parameters. At the end, mean packet delay is presented for end to end communication in a path. We give numerical results which illustrate the effect of mobility on continuous communication path availability and communication delay. The results of this work may be helpful in studying the optimal node transmission range assignment, routing algorithms, network throughput, optimization of cross layer design schemes and MAC protocols in VANETs.

IPO Prospectus Information and Subsequent Performance

Abstract: Initial public offerings underperform in the long run; however, there is very little evidence on their cross-sectional variation. Using a random sample of IPOs from 1987 through 1991 and gathering their prospectus data, we show that financial and operating characteristics as well as offering characteristics have a limited relation with the one-year stock returns. We also find that firms that subsequently reissue equity or merge outperform their matched-firm benchmarks over three years. Underperformance is most severe for the smaller and younger firms. We find that prospectus information is more useful to predict survival/failure compared to subsequent equity offerings or acquisitions.

The Market's Perception of the Transactional Risks of Information Technology Outsourcing Announcements

Abstract: Despite the fact that several event studies have investigated the market's reaction to information technology (IT) investment announcements, little is known about how specific transactional risks influence the market value of a firm. This study examines stock market data to assess investors' responses to various transactional risks associated with IT outsourcing. More specifically, we develop and test several hypotheses to understand how transactional risks that arise due to a range of factors (i.e., the size of outsourcing contracts, difficulties in performance monitoring, asset specificity of IT resources, vendor capability, and the lack of cultural similarity between client and vendor firms) influence investors' reactions to IT outsourcing announcements. Our results indicate that most of these factors indeed significantly influence investors' perceptions of the risks involved in IT outsourcing. We discuss these findings in a larger organizational context and offer implications for both research and practice. In particular, our study offers a theoretical rationale for why negative reactions to IT outsourcing announcements may occur, while providing practitioners with several means by which they can increase the informational value of outsourcing arrangements.