12,998 research outputs found

    Construction of optimal multi-level supersaturated designs

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    A supersaturated design is a design whose run size is not large enough for estimating all the main effects. The goodness of multi-level supersaturated designs can be judged by the generalized minimum aberration criterion proposed by Xu and Wu [Ann. Statist. 29 (2001) 1066--1077]. A new lower bound is derived and general construction methods are proposed for multi-level supersaturated designs. Inspired by the Addelman--Kempthorne construction of orthogonal arrays, several classes of optimal multi-level supersaturated designs are given in explicit form: Columns are labeled with linear or quadratic polynomials and rows are points over a finite field. Additive characters are used to study the properties of resulting designs. Some small optimal supersaturated designs of 3, 4 and 5 levels are listed with their properties.Comment: Published at http://dx.doi.org/10.1214/009053605000000688 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

    Learning incoherent dictionaries for sparse approximation using iterative projections and rotations

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    This work was supported by the Queen Mary University of London School Studentship, the EU FET-Open project FP7- ICT-225913-SMALL. Sparse Models, Algorithms and Learning for Large-scale data and a Leadership Fellowship from the UK Engineering and Physical Sciences Research Council (EPSRC)

    Vignette Equivalence and Response Consistency; The Case of Job Satisfaction

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    We compare reported job satisfaction with vignette evaluations of hypothetical jobs by using a British, Greek and Dutch data set, containing 95 randomly assigned vignettes. In order to test comparability of international data sets recently the method of anchoring vignettes has been introduced by King et al. (2004). This intuitively and attractive idea requires the properties of vignette equivalence and response consistency. In our data set both job satisfaction and vignettes are numerically evaluated on a 0-10-scale. This fact allows us to interpret the evaluations as cardinal satisfaction values and to estimate satisfaction functions for vignettes and for the own job situation. We find that both functions differ significantly: vignette evaluations appear to depend on the own job situation and other individual characteristics. Hence, without correction for those differences in background characteristics, vignette evaluations are not comparable between individuals. Similar conclusions are reached for response consistency.vignettes, vignette equivalence, response consistency, job satisfaction, subjective well-being

    Measuring adaptation to non-permanent employment contracts using a conjoint analysis approach

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    This study attempts to uncover the ‘real’ impact of temporary contracts on workers’ perceived job quality, prior to the psychological phenomena of adaptation, coping and cognitive dissonance coming into play. This is done by using a novel conjoint analysis approach that examines the ex ante preferences over different contract statuses of a newly generated sample of low-skilled employees from seven European countries. Other things equal, it is shown that the anticipated psychological ‘costs’ of moving from a riskless permanent contract to the insecurity of a temporary job or no work at all appear to be quite significant. In contrast, temporary employees, who have presumably already adapted to the circumstances surrounding a non-permanent contract, are found to be statistically indifferent between permanent and temporary employment, and request much smaller wage premiums in order to switch from one status to the other. The well-documented distress associated with joblessness is also confirmed in our data. The methodology developed here can provide policymakers with an alternative and relatively inexpensive method of quantifying the immediate impact of any shift in their employment policies.European Commissio

    Eye movements may cause motor contagion effects

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    When a person executes a movement, the movement is more errorful while observing another person’s actions that are incongruent rather than congruent with the executed action. This effect is known as “motor contagion”. Accounts of this effect are often grounded in simulation mechanisms: increased movement error emerges because the motor codes associated with observed actions compete with motor codes of the goal action. It is also possible, however, that the increased movement error is linked to eye movements that are executed simultaneously with the hand movement because oculomotor and manual-motor systems are highly interconnected. In the present study, participants performed a motor contagion task in which they executed horizontal arm movements while observing a model making either vertical (incongruent) or horizontal (congruent) movements under three conditions: no instruction, maintain central fixation, or track the model’s hand with the eyes. A significant motor contagion-like effect was only found in the ‘track’ condition. Thus, ‘motor contagion’ in the present task may be an artifact of simultaneously executed incongruent eye movements. These data are discussed in the context of stimulation and associative learning theories, and raise eye movements as a critical methodological consideration for future work on motor contagion

    A space division multiplexed free-space-optical communication system that can auto-locate and fully self align with a remote transceiver

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    Free-Space Optical (FSO) systems offer the ability to distribute high speed digital links into remote and rural communities where terrain, installation cost or infrastructure security pose critical hurdles to deployment. A challenge in any point-to-point FSO system is initiating and maintaining optical alignment from the sender to the receiver. In this paper we propose and demonstrate a low-complexity self-aligning FSO prototype that can completely self-align with no requirement for initial manual positioning and could therefore form the opto-mechanical basis for a mesh network of optical transceivers. The prototype utilises off-the-shelf consumer electrical components and a bespoke alignment algorithm. We demonstrate an eight fibre spatially multiplexed link with a loss of 15 dB over 210 m

    From Russia with Love: The Impact of Relocated Firms on Incumbent Survival

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    We identify the impact of local firm concentration on incumbent performance with a quasi natural experiment. When Germany was divided after World War II, many firms in the machine tool industry fled the Soviet occupied zone to prevent expropriation. We show that the regional location decisions of these firms upon moving to western Germany were driven by non-economic factors and heuristics rather than existing industrial conditions. Relocating firms increased the likelihood of incumbent failure in destination regions, a pattern that differs sharply from new entrants. We further provide evidence that these effects are due to increased competition for local resources.Agglomeration, competition, firm dynamics, labor, Germany

    Downlink Coverage and Rate Analysis of Low Earth Orbit Satellite Constellations Using Stochastic Geometry

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    As low Earth orbit (LEO) satellite communication systems are gaining increasing popularity, new theoretical methodologies are required to investigate such networks' performance at large. This is because deterministic and location-based models that have previously been applied to analyze satellite systems are typically restricted to support simulations only. In this paper, we derive analytical expressions for the downlink coverage probability and average data rate of generic LEO networks, regardless of the actual satellites' locality and their service area geometry. Our solution stems from stochastic geometry, which abstracts the generic networks into uniform binomial point processes. Applying the proposed model, we then study the performance of the networks as a function of key constellation design parameters. Finally, to fit the theoretical modeling more precisely to real deterministic constellations, we introduce the effective number of satellites as a parameter to compensate for the practical uneven distribution of satellites on different latitudes. In addition to deriving exact network performance metrics, the study reveals several guidelines for selecting the design parameters for future massive LEO constellations, e.g., the number of frequency channels and altitude.Comment: Accepted for publication in the IEEE Transactions on Communications in April 202
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