Set It and Forget It: Approximating the Set Once Strip Cover Problem

We consider the Set Once Strip Cover problem, in which n wireless sensors are deployed over a one-dimensional region. Each sensor has a fixed battery that drains in inverse proportion to a radius that can be set just once, but activated at any time. The problem is to find an assignment of radii and activation times that maximizes the length of time during which the entire region is covered. We show that this problem is NP-hard. Second, we show that RoundRobin, the algorithm in which the sensors simply take turns covering the entire region, has a tight approximation guarantee of 3/2 in both Set Once Strip Cover and the more general Strip Cover problem, in which each radius may be set finitely-many times. Moreover, we show that the more general class of duty cycle algorithms, in which groups of sensors take turns covering the entire region, can do no better. Finally, we give an optimal O(n^2 log n)-time algorithm for the related Set Radius Strip Cover problem, in which all sensors must be activated immediately.Comment: briefly announced at SPAA 201

How high frequency trading affects a market index

The relationship between a market index and its constituent stocks is complicated. While an index is a weighted average of its constituent stocks, when the investigated time scale is one day or longer the index has been found to have a stronger effect on the stocks than vice versa. We explore how this interaction changes in short time scales using high frequency data. Using a correlation-based analysis approach, we find that in short time scales stocks have a stronger influence on the index. These findings have implications for high frequency trading and suggest that the price of an index should be published on shorter time scales, as close as possible to those of the actual transaction time scale.We would like to thank Yoash Shapira, Idan Michaeli and Dustin Plotnick for all of their help. DYK and EBJ acknowledge support in part by the Tauber Family Foundation and the Maguy-Glass Chair in Physics of Complex Systems at Tel Aviv University. HES and DYK thank the support of the Office of Naval Research (ONR, Grant N00014-09-1-0380, Grant N00014-12-1-0548), Keck Foundation and the NSF (Grant CMMI 1125290) for support. This work was also supported by the Intelligence Advanced Research Projects Activity (IARPA) via Department of Interior National Business Center (DoI/NBC) contract number D12PC00285. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon. Disclaimer: The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of IARPA, DoI/NBC, or the U.S. Government. (Tauber Family Foundation; Maguy-Glass Chair in Physics of Complex Systems at Tel Aviv University; N00014-09-1-0380 - Office of Naval Research (ONR); N00014-12-1-0548 - Office of Naval Research (ONR); Keck Foundation; CMMI 1125290 - NSF; D12PC00285 - Intelligence Advanced Research Projects Activity (IARPA) via Department of Interior National Business Center (DoI/NBC))Published versio

“My attitude on telehealth has completely changed.”: Facilitators and Barriers to Implementing Technology for Care Delivery in Community Mental Health Centers

The purpose of this study was to explore facilitators and barriers aiding community mental health centers in implementing technology-assisted care during the COVID-19 pandemic. Six key informants were interviewed and 28 clinicians were surveyed from three community mental health centers. Interviews focused on technology-assisted care implementation efforts and factors that facilitated adoption. Surveys focused on clinician beliefs and experience with technology-assisted care in addition to training needs. Barriers to technology-assisted care implementation included beliefs about the quality of virtual services and a lack of technology access. An increase in service utilization was reported. Technology-assisted care facilitators included reimbursement policy changes and clinic-based factors such as clinician training and supervision efforts. Clinicians reported having the skills necessary to implement technology-assisted care however endorsed a need for training. Implementation of technology-assisted care in community mental health centers was largely successful however support is needed to help clinicians adapt services to client needs

Rethinking the Reign of ʿAbdullāhi Muhammad b. ʿAlī Abdaššakūr: Harär at the Dawn of the ‘Glocal’ Era during the Latter Part of the 19th Century

This article examines the short-lived reign of ʿAbdullāhi Muhammad b. ʿAlī Abdaššakūr, the last emir of Harär, through the prism of globalization. Harär, one of the most ancient cities in East Africa, is located east of Addis Ababa, on the south-eastern tip of the plateau that extends from the Rift Valley to the plains of the Ogaden Desert. The historical events that happened in the latter part of the 19th century turned the town into a cultural and religious intersection which brought togeth..

Dynamics of Stock Market Correlations

We present a novel approach to the study the dynamics of stock market correlations. This is achieved through an innovative visualization tool that allows an investigation of the structure and dynamics of the market, through the study of correlations. This is based on the Stock Market Holography (SMH) method recently introduced. This qualitative measure is complemented by the use of the eigenvalue entropy measure, to quantify how the information in the market changes in time. Using this innovative approach, we analyzed data from the New York Stock Exchange (NYSE), and the Tel Aviv Stock Exchange (TASE), for daily trading data for the time period of 2000–2009. This paper covers these new concepts for the study of financial markets in terms of structure and information as reflected by the changes in correlations over time.Correlation, Stock Market Holography, eigenvalue entropy, sliding window