Asymptotic solutions for turbulent mass transfer augmented by a first order chemical reaction

We present asymptotic solutions for turbulent mass transfer in a smooth conduit at high Schmidt number in the presence of a first-order chemical reaction in the fluid. Far-field solutions are derived for a case dominated by (1) mass transfer at the wall and (2) the first-order chemical reaction. An approximate solution is derived for the regime where both are important. The solutions are in good agreement with numerical solutions and with the literature. At high Damköhler numbers the system is governed by a reaction–diffusion equation and the observed increase in mass transfer coefficient is caused by thinning of the mass transfer boundary layer due to the fast chemical reaction in the fluid. We present closed-form far-field solutions for Dirichlet, Neumann and Robin boundary conditions and comment on grid resolution requirements to accurately resolve the mass transfer boundary layer. The solution strategy presented can be straightforwardly extended to non-linear wall- and bulk-reactions.     

Wikipedia workload analysis for decentralized hosting

We study an access trace containing a sample of Wikipedia’s traffic over a 107-day period aiming to identify appropriate replication and distribution strategies in a fully decentralized hosting environment. We perform a global analysis of the whole trace, and a detailed analysis of the requests directed to the English edition of Wikipedia. In our study, we classify client requests and examine aspects such as the number of read and save operations, significant load variations and requests for nonexisting pages. We also review proposed decentralized wiki architectures and discuss how they would handle Wikipedia’s workload. We conclude that decentralized architectures must focus on applying techniques to efficiently handle read operations while maintaining consistency and dealing with typical issues on decentralized systems such as churn, unbalanced loads and malicious participating nodes.     

Identified versus introjected approach and introjected avoidance motivations in school and in sports: The limited benefits of self-worth strivings.

On the basis of self-determination theory (Ryan & Deci, 2000), the authors examined whether 2 different types of introjected motivation—an avoidant type aimed at avoiding low self-worth and an approach type aimed at attaining high self-worth—are both associated with a less positive pattern of correlates relative to identified motivation—acting because one identifies with the value of the action. Two studies focusing on the academic and sports domains (N = 1,222) showed that children and adolescents differentiated between the 2 types of introjected motivation. Although introjected avoidance motivation was associated with a more negative pattern of affective and performance correlates than was introjected approach motivation, identified motivation was associated with a much more positive pattern of correlates than both types of introjected motivation. Furthermore, being high on introjected approach motivation did not yield any benefits even when combined with high identified motivation. Results suggest that past findings portraying introjected motivation as being less desirable than identified motivation cannot be ascribed to the avoidance component of introjected motivation. Findings are consistent with the view that even an approach-oriented introjected motivation has very limited benefits when compared with identified motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of perspective effects and accelerations in perceived three-dimensional structure-from-motion.

It has been suggested that perceived three-dimensional (3D) structure-from-motion can be accounted for by a 2-frame orthographic approximation of the flow field. This study investigated the extent to which higher order cues (perspective and acceleration) are used in addition to first-order flow. Participants matched the 3D dihedral angle of a hinged plane (probe) defined by multiple-depth cues to one defined by motion only, for stimulus sizes of 8 and 33°, using perspective and orthographic projection. The results show that perspective effects can be important even for relatively small stimuli (8°) and that accelerations contribute to perceived shape. In all conditions, large biases were found. These are well accounted for by a model in which all relevant flow measurements (first-order, perspective, and acceleration) are used together with estimates of the noise in each. The model has no built-in bias toward particular 3D shapes. Instead, the visual system may act as an optimal estimator of 3D structure-from motion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioural responses to neighbourhood reputations

Most research on the effect of neighbourhood reputations focuses on the influence on attitudes and behaviour of non-residents. Much less attention is paid to the possible effects of a poor neighbourhood reputation on behaviour of residents. In order to get a better understanding of the effect of neighbourhoods on its residents (the so-called neighbourhood effects) and the role of neighbourhoods in the urban housing market, it is necessary to fill this gap. The aim of this paper is to review the literature on the reputation of places and to give an overview of possible behavioural responses of residents to negative neighbourhood reputations. The paper develops a model of behavioural responses of residents based on Hirschman’s ‘Exit, Voice and Loyalty’ framework. Three basic responses are central to the discussion of the literature: leaving the neighbourhood, attempting to improve the neighbourhood through neighbourhood participation, and (dis)investing in social contacts within the neighbourhood.     

Herbivore-Induced Volatile Production by Arabidopsis thaliana Leads to Attraction of the Parasitoid Cotesia rubecula: Chemical, Behavioral, and Gene-Expression Analysis

Many plant species defend themselves against herbivorous insects indirectly by producing volatiles in response to herbivory. These volatiles attract carnivorous enemies of the herbivores. Research on the model plant Arabidopsis thaliana (L.) Heynh. has contributed considerably to the unraveling of signal transduction pathways involved in direct plant defense mechanisms against pathogens. Here, we demonstrate that Arabidopsis is also a good candidate for studying signal transduction pathways involved in indirect defense mechanisms by showing that: (1) Adult females of Cotesia rubecula, a specialist parasitic wasp of Pieris rapae caterpillars, are attracted to P. rapae-infested Arabidopsis plants. (2) Arabidopsis infested by P. rapae emits volatiles from several major biosynthetic pathways, including terpenoids and green leaf volatiles. The blends from herbivore-infested and artificially damaged plants are similar. However, differences can be found with respect to a few components of the blend, such as two nitriles and the monoterpene myrcene, that were produced exclusively by caterpillar-infested plants, and methyl salicylate, that was produced in larger amounts by caterpillar-infested plants. (3) Genes from major biosynthetic pathways involved in volatile production are induced by caterpillar feeding. These include AtTPS10, encoding a terpene synthase involved in myrcene production, AtPAL1, encoding phenylalanine ammonia-lyase involved in methyl salicylate production, and AtLOX2 and AtHPL, encoding lipoxygenase and hydroperoxide lyase, respectively, both involved in the production of green leaf volatiles. AtAOS, encoding allene oxide synthase, involved in the production of jasmonic acid, also was induced by herbivory.     

Distributed redirection for the World-Wide Web

Replication in the World-Wide Web covers a wide range of techniques. Often, the redirection of a client browser towards a given replica of a Web page is performed after the client’s request has reached the Web server storing the requested page. As an alternative, we propose to perform the redirection as close to the client as possible in a fully distributed and transparent manner. Distributed redirection ensures that we find a replica wherever it is stored and that the closest possible replica is always found first. By exploiting locality, we can keep latency low.