Truthful Approximation Mechanisms for Scheduling Selfish Related Machines

We consider the problem of scheduling jobs on related machines owned by selfish agents. We provide a 5-approximation deterministic truthful mechanism, the first deterministic truthful result for the problem. Previously, Archer and Tardos showed a 2-approximation randomized mechanism which is truthful in expectation only (a weaker notion of truthfulness). In case the number of machines is constant, we provide a deterministic Fully Polynomial-Time Approximation Scheme (FPTAS) and a suitable payment scheme that yields a truthful mechanism for the problem. This result, which is based on converting FPTAS to monotone FPTAS, improves a previous result of Auletta et al., who showed a (4 + ε)-approximation truthful mechanism.     

An economic evaluation of the use of rare earth screens to reduce the radiation dose from diagnostic X-ray procedures in Israel

In Israel the diffusion of rare earth screen technology has been limited. These screens could halve the radiation dose to the patient from diagnostic X-ray radiography, with little managerial effort and without being detrimental to the quality of the diagnostic image. We estimated the total effective dose from diagnostic film radiography capable of reduction by the use of rare earth screens, based on the number of hospital and ambulatory diagnostic X-ray procedures. This number was multiplied by the computed radiation dose per body site for a series of diagnostic procedures. The annual dose was approximately 0.53 mSv per head, approximately half of which could be averted by the introduction of rare earth screen technology. Based on a fatality risk of 3% Sv-1, it is estimated that the adoption of rare earth screen technology might reduce the annual incidence of cancer by some 93 cases, half of which would be fatal after an average latency period of 18.4 years. The cost of purchasing rare earth screens on a nationwide basis is approximately $3.0 million. This cost is outweighed by a saving of $9.6 million in X-ray tube replacement costs over the period 1997-2006. Government legislation enforcing the use of rare earth screens is essential, because of the lack of prestige associated with acquiring rare earth technology, as well as institutional reluctance to accept the external benefits of reduced morbidity and mortality and/or to extend budgetary time horizons.     

Mass transfer in an electrochemical reactor with two interacting jets

An electrochemical reactor operated with two identical solution streams injected in opposite directions on the same axis, and leaving it at a normal direction was studied by measuring local and global mass transfer coefficients and visualization of solution flow patterns. This flow configuration was compared to a case where a single stream enters the reactor and leaves it on the same axis. It was found that only the data obtained for the single stream mode can be correlated by the Chilton-Colburn relation, indicating a near laminar boundary layer flow. Global mass transfer coefficients for the single stream mode were found to be slightly higher than those for the interacting jets mode. However, when comparing the two modes by taking into account the dimensionless ratio of the mass transfer coefficient (Sh) to the energy consumption (Eu), it was found that the interacting jets (IJ) mode exhibits a better performance as compared to the single stream mode. The superiority of the IJ mode increases with increasing Reynold's number (Re).Nomenclature A, B adjustable parameters - b half width of channel - C electrolyte ion concentration - d inlet pipe diameter - d microelectrode diameter - D diffusion coefficient - maximum value of mean deviation - E pumping energy - Eu Euler number - F Faraday number - i current to a single microelectrode on an active wall - i current to a single microelectrode in an inert wall - I global diffusion current - k mass transfer coefficient to a single microelectrode in an active wall - k mass transfer coefficient to a single microelectrode in an inert wall - K global mass transfer coefficient - Q volumetric flow rate - Q _T total volumetric flow rate - R radius of the electrochemical reactor - Re Reynolds number - s surface area of a microelectrode - S surface area of the working electrode - Sc Schmidt number - Sh Sherwood number - V _x axial flow velocity alongx-axis - V flow velocity at large distance from the leading edge - V mean flow velocity - x axis tangential to the surface - y axis normal to the surface - z number of electrons transferred in the reaction (z=1 in the present case) Greek letters viscosity - specific gravity - kinematic viscosity (/) - P pressure drop across the reactor - V voltage drop across the reactor Abbreviations ST single stream - IJ interacting jets     

Water desalting by means of electrochemical parametric pumping. II. Separation properties of a multistage column

Multistage electrochemical parametric pumping has been successfully carried out for water desalination. Separation was effected by electroadsorption-desorption cycles of the ions into and from the electrical double layer of high surface carbon electrodes. At steady state and total reflux, the concentration ratio between the upper and lower heads of the electrochemical column was as high as 150. Two models for the build up of the concentration profile within the column are presented. The first is based on a solution of the two-phase mass transport equation using the proper boundary and initial conditions. The second treatment is based on the mixed cells assumptions. In both treatments, interphase equilibrium is assumed using the isopotentiograms as the specific equilibrium curves. Use is also made of a fast computer for the simulation of the electrochemical paramatric pumping cycles. The two models are in good agreement with the experimental results particularly in the cases where the initial concentration is high and interphase equilibrium is maintained.     

Infrared study of salt free and salt treated cellulose pyrolysis under nitrogen atmosphere

The pyrolysis under nitrogen of salt free and salt treated cellulose was studied by infrared spectroscopy. The results confirm the unzipping mechanism suggested by DTA and TGA studies, and show this mechanism to apply to the untreated and salt treated samples. The results also show the unzipping to stop at the stage of char formation. The onset of this stage was found to occur after the volatilization of only 45–50% of the initial sample of the borax treated cellulose, compared with 65–70% of the KCl treated cellulose and 80–85% of the untreated cellulose.     

Equi-affine Invariant Geometry for Shape Analysis

Traditional models of bendable surfaces are based on the exact or approximate invariance to deformations that do not tear or stretch the shape, leaving intact an intrinsic geometry associated with it. These geometries are typically defined using either the shortest path length (geodesic distance), or properties of heat diffusion (diffusion distance) on the surface. Both measures are implicitly derived from the metric induced by the ambient Euclidean space. In this paper, we depart from this restrictive assumption by observing that a different choice of the metric results in a richer set of geometric invariants. We apply equi-affine geometry for analyzing arbitrary shapes with positive Gaussian curvature. The potential of the proposed framework is explored in a range of applications such as shape matching and retrieval, symmetry detection, and computation of Voroni tessellation. We show that in some shape analysis tasks, equi-affine-invariant intrinsic geometries often outperform their Euclidean-based counterparts. We further explore the potential of this metric in facial anthropometry of newborns. We show that intrinsic properties of this homogeneous group are better captured using the equi-affine metric.     

Deconstructing gamification: evaluating the effectiveness of continuous measurement,virtual rewards,and social comparison for promoting physical activity

Game design elements are often implemented in persuasive systems aimed to promote physical activity, a process called “gamification.” Gamification is believed to motivate users to become more active, and is commonly implemented in commercial products. However, relatively few studies rigorously evaluated the effectiveness of gamification, and they yielded contradicting findings. We set out to evaluate the effectiveness of virtual rewards and social comparison—two game elements prevalent in persuasive systems. We developed a research prototype, called “StepByStep,” aimed to promote routine walking. We created different versions of StepByStep, implemented as an application on Android-based mobile devices, and compared their effectiveness in two field studies. Study 1 showed that a quantified version of the application—offering continuous measurement of walking time, a daily goal, and real-time feedback on progress toward this goal—facilitated reflection on activity and significantly increased walking time over baseline level. Study 2 showed that gamified versions offering virtual rewards and social comparison were only as effective as the quantified version. Thus, we advise designers to facilitate reflection on meaningful aspects of physical activity by developing novel ubiquitous measures. Furthermore, our findings highlight the importance of systematic comparisons between quantified and gamified elements for better understanding their motivational affordances.     

Covalent surface functionalization of nonwoven fabrics with controlled hydrophobicity,water absorption,and pH regulation properties

A modular method for functionalization of nonwoven fabrics was developed using a two-step process. In the first step, the fabrics were grafted with a linker molecule, 10-undecenoyl chloride, via esterification, followed by attachment of a functional material under UV irradiation. Perfluorodecanethiol and 3-mercaptopropionic acid (MPA) were connected to the linker-modified fabrics using thiol-ene click chemistry. Perfluorodecanethiol modified fabrics exhibited hydrophobicity with water contact angle of about 140° while MPA-modified fabrics were able to lower the pH of a solution by about 1.6. We additionally demonstrated the possibility to connect functional polymers to the linker-modified fabrics by radical graft polymerization of acrylic acid; this produced a thin layer of the polymer on the surface of the fabric. Fabrics modified with poly(acrylic acid) exhibited increased hydrophilicity with water contact angle of 0° for both cotton and viscose-polyester fabrics, while the water absorption capability for polypropylene fabrics increased from about 50 to 1200%.     

Adaptive water management in Israel: structure and policy options

Difficulties in integrating technical, economic and institutional factors present a major gap in analytical capacity to guide water policy. This article presents an integrated framework to support water policy and guide water management choices, with application to Israel. That framework rests on the theory of economic policy originally developed by Tinbergen. It sees national water challenges as consisting of external factors, constraints, policy instruments and targets. The need for a modern implementation of the theory of economic policy is motivated by emerging environmental requirements, scarce water, growing demands for domestic use, and ongoing needs to implement existing and potential peace agreements.