Adaptive schemes for location update generation in execution location-dependent continuous queries

Cataloged from PDF version of article.An important feature that is expected to be owned by today's mobile computing systems is the ability of processing location-dependent continuous queries on moving objects. The result of a location-dependent query depends on the current location of the mobile client which has generated the query as well as the locations of the moving objects on which the query has been issued. When a location-dependent query is specified to be continuous, the result of the query can continuously change. In order to provide accurate and timely query results to a client, the location of the client as well as the locations of moving objects in the system has to be closely monitored. Most of the location generation methods proposed in the literature aim to optimize utilization of the limited wireless bandwidth. The issues of correctness and timeliness of query results reported to clients have been largely ignored. In this paper, we propose an adaptive monitoring method (AMM) and a deadline-driven method (DDM) for managing the locations of moving objects. The aim of our methods is to generate location updates with the consideration of maintaining the correctness of query evaluation results without increasing location update workload. Extensive simulation experiments have been conducted to investigate the performance of the proposed methods as compared to a well-known location update generation method, the plain dead-reckoning (pdr). © 2005 Elsevier Inc. All rights reserved

Surface Engineered Angstrom Thick ZnO-sheathed TiO2 Nanowires as Photoanode for Performance Enhanced Dye-sensitized Solar Cells

Cataloged from PDF version of article.This paper presents a systematic study on the effects of angstrom-thick atomic layer deposited (ALD) ZnO sheaths on hydrothermally-grown TiO2 nanowires (NWs) used as photoanodes in dye-sensitized solar cells (DSSCs). We designed, synthesized and characterized the samples prepared using different numbers of ZnO cycles and compared their photovoltaic (PV) performances. The device consisting of TiO2 NWs coated with the optimum thickness (two cycles) of ZnO shell exhibits a three-fold increase in efficiency compared to a control reference device. This paper reports results and features that demonstrate the passivation of surface state traps upon deposition of ZnO shells. While this passivation of surface traps provides a reduction in the back-reactions of the surface state mediated electrons (KET trap), it is speculated that ZnO-induced surface band bending (SBB) substantially reduces the recombination rate of the device by reducing the recombination rate of the conduction band (CB) electrons (KET CB). Moreover, an enhancement in the amount of dye uptake for ZnO-coated TiO2 samples is observed and explained with the isoelectric point (IEP) concept. In spite of the excellent PV power conversion efficiencies achieved by the first ZnO cycles, thicker layers impede the electron injection rate, reducing the efficiency of the device by capturing the photogenerated dye electrons in ZnO quantum wells. Here, we investigate the mechanisms contributing to this unprecedented change and correlate them with the enhancement in device efficiency. © The Royal Society of Chemistry 2014

Association rules for supporting hoarding in mobile computing environments

One of the features that a mobile computer should provide is disconnected operation which is performed by hoarding. The process of hoarding can be described as loading the data items needed in the future to the client cache prior to disconnection. Automated hoarding is the process of predicting the hoard set without any user intervention. In this paper, we describe an application independent and generic technique for determining what should be hoarded prior to disconnection. Our method utilizes association rules that are extracted by data mining techniques for determining the set of items that should be hoarded to a mobile computer prior to disconnection. The proposed method was implemented and tested on synthetic data to estimate its effectiveness. Performance experiments determined that the proposed rule-based methods are effective in improving the system performance in terms of the cache hit ratio of mobile clients especially for small cache sizes

Sampling-based path planning for multi-robot systems with co-safe linear temporal logic specifications

© 2017, Springer International Publishing AG. This paper addresses the problem of path planning for multiple robots under high-level specifications given as syntactically co-safe linear temporal logic formulae. Most of the existing solutions use the notion of abstraction to obtain a discrete transition system that simulates the dynamics of the robot. Nevertheless, these solutions have poor scalability with the dimension of the configuration space of the robots. For problems with a single robot, sampling-based methods have been presented as a solution to alleviate this limitation. The proposed solution extends the idea of sampling methods to the multiple robot case. The method samples the configuration space of the robots to incrementally constructs a transition system that models the motion of all the robots as a group. This transition system is then combined with a Büchi automaton, representing the specification, in a Cartesian product. The product is updated with each expansion of the transition system until a solution is found. We also present a new algorithm that improves the performance of the proposed method by guiding the expansion of the transition system. The method is demonstrated with examples considering different number of robots and specifications

A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provides evidence of monoperiodic variations with a frequency of 0.7572 c/d and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in other HgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star.Comment: Accepted for publication in A&A, 14 pages, 15 colour figures (revised version after language editing

An international survey on residential lighting: Analysis of winter-term results

By conducting an international survey on residential lighting, a great variety of data showing the differences and similarities in lighting conditions among Poland, Turkey, Sweden and the U.K. were collected which provided an overall perspective for raising the standards of luminous environments. A total of 500 participants (125 respondents from each country- 47.6% females, 51.2% males, and 1.2% who did not wish to specify gender) provided detailed self-assessments of the lighting conditions in their living areas. The study identified interrelated factors associated with residential lighting using descriptive statistics, correlation coefficient functions and thematic analysis. As the survey results showed, the satisfaction with daylighting quality depends on daylighting sufficiency, daylighting uniformity, and number of sunlight hours (i.e., sunlight exposure), view-out and ratio of windows in the living area. Moreover satisfaction with artificial lighting quality depends on artificial lighting sufficiency, artificial lighting uniformity, artificial lighting brightness, and artificial lighting color rendering index. Overall, the findings of the study showed the potential factors that can be used to effectively change the day- and artificial lighting in residential areas, leading to a sustainable and better lighting environment

Seed Layer Assisted Hydrothermal Deposition of Low-resistivity ZnO Thin Films

In this work, we describe the combination of hydrothermal and atomic layer deposition (ALD) for growing low-resistivity ZnO polycrystalline continuous films. The effect of the thickness of ALD seed layers on the morphology of the hydrothermal ZnO films was studied. It was shown that ZnO films hydrothermally deposited on very thin seed layer consist of separate nanorods but in the case of 20 nm seed layer ZnO films transform to uniform continuous layers comprising of closely packed vertically aligned crystallites. Photoluminescence spectra were shown to exhibit broad band behavior in the visible range, corresponding to radiative recombination processes via oxygen defects of ZnO crystalline lattice, and narrow band in the UV region, associated with band-to-band recombination processes. It was shown that the resistivity of the obtained ZnO films is decreased gradually with the increase of ZnO films thickness and determined by the presence of crystal lattice defects in the seed layer. Copyright © Materials Research Society 2017