The Forgiving Graph: a distributed data structure for low stretch under adversarial attack

We consider the problem of self-healing in peer-to-peer networks that are under repeated attack by an omniscient adversary. We assume that, over a sequence of rounds, an adversary either inserts a node with arbitrary connections or deletes an arbitrary node from the network. The network responds to each such change by quick “repairs,” which consist of adding or deleting a small number of edges. These repairs essentially preserve closeness of nodes after adversarial deletions, without increasing node degrees by too much, in the following sense. At any point in the algorithm, nodes v and w whose distance would have been ? in the graph formed by considering only the adversarial insertions (not the adversarial deletions), will be at distance at most ? log n in the actual graph, where n is the total number of vertices seen so far. Similarly, at any point, a node v whose degree would have been d in the graph with adversarial insertions only, will have degree at most 3d in the actual graph. Our distributed data structure, which we call the Forgiving Graph, has low latency and bandwidth requirements. The Forgiving Graph improves on the Forgiving Tree distributed data structure from Hayes et?al. (2008) in the following ways: 1) it ensures low stretch over all pairs of nodes, while the Forgiving Tree only ensures low diameter increase; 2) it handles both node insertions and deletions, while the Forgiving Tree only handles deletions; 3) it requires only a very simple and minimal initialization phase, while the Forgiving Tree initially requires construction of a spanning tree of the network.     

Impaired Higher Order Implicit Sequence Learning on the Verbal Version of the Serial Reaction Time Task in Patients With Parkinson's Disease.

Although neuroimaging studies have strongly implicated basal ganglia involvement in implicit sequence learning, serial reaction time (SRT) studies with Parkinson's disease (PD) patients have yielded mixed results. The present research sought to examine the ability of people with PD to implicitly learn sequences with different sequential structures and to objectively assess explicit knowledge. A version of the SRT task that reduces motor demands was used to compare 19 patients with PD but not dementia and 37 matched controls. PD patients showed less implicit sequence-specific learning for both sequences and reduced response time improvement over sequential trials for the more complex sequence. A closer examination revealed that the deficit involved higher order sequential associations as well as the learning of pairwise information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multifunctional Nanochemistry: Ambient,Electroless, Template-Based Synthesis and Characterization of Segmented Bimetallic Pd/Au and Pd/Pt Nanowires as High-Performance Electrocatalysts and Nanomotors

Segmented noble-metal nanowires (NWs) represent an exciting, multifunctional, one-dimensional, structural architecture with a variety of potential applications. However, the widespread use of electrodeposition in the preparation of these systems has limited their potential to be produced on a large scale, since this protocol is costly and requires complex processes and caustic reaction media. Given the inherent limitations of electrodeposition, we report, for the first time, an ambient, surfactantless, template-based approach that is not only sustainable but also efficient for the reliable production of Pd/Pt and Pd/Au segmented NWs, possessing two spatially separated, chemically distinctive, but elementally pure, axial subunits. Our simple two-step synthetic approach allows for direct and predictable control over the relative segment lengths in these nanomaterials. Moreover, thorough structural characterization of these as-prepared samples confirms that our segmented NWs maintain high-quality, crystalline, elementally pure subunits with a well-defined interface between the constituent metals. In the context of preparing segmented NWs as multifunctional nanostructures, we demonstrate that these as-prepared NWs achieve high levels of performance when employed as both electrocatalysts and nanomotors.     

Selecting and assessing challenge problems

Abstract

Organisations conducting research programs often focus the work of their scientists and technologists on challenge problems (CPs). These challenges are designed to ensure that progress is measurable and relevant to the goals of the program sponsor. Generating and selecting pertinent CPs is difficult, as is assessing their value. We describe a method of generating and selecting CPs and its application in a highly collaborative, multi-organisation research program. Thirty-eight biologists, chemists, mathematicians and computer scientists across academic, commercial and government organisations generated and ranked their top choices from among 12 richly described candidate challenge problems. A ranked-choice voting formula was applied. Five CPs were highly scored; the remaining seven were distributed across a lower range of scores. The program sponsor subsequently directed researchers to address six CPs, including the elected five. Analysis of the rationales that participants offered for their CP rankings revealed four domain-independent dimensions of value: capability, speed, impact and synergy. These dimensions of value can help managers of interdisciplinary research programs systematically select a portfolio of CPs that will efficiently apply utilise resources towards program goals and facilitate measurement of scientific progress.     

Aromatic Halogenation by Using Bifunctional Flavin Reductase–Halogenase Fusion Enzymes

The remarkable site selectivity and broad substrate scope of flavin-dependent halogenases (FDHs) has led to much interest in their potential as biocatalysts. Multiple engineering efforts have demonstrated that FDHs can be tuned for non-native substrate scope and site selectivity. FDHs have also proven useful as in vivo biocatalysts and have been successfully incorporated into biosynthetic pathways to build new chlorinated aromatic compounds in several heterologous organisms. In both cases, reduced flavin cofactor, usually supplied by a separate flavin reductase (FR), is required. Herein, we report functional synthetic, fused FDH-FR proteins containing various FDHs and FRs joined by different linkers. We show that FDH-FR fusion proteins can increase product titers compared to the individual components for in vivo biocatalysis in Escherichia coli.     

Multi-laboratory evaluations of the performance of Catellicoccus marimammalium PCR assays developed to target gull fecal sources

Here we report results from a multi-laboratory (n = 11) evaluation of four different PCR methods targeting the 16S rRNA gene of Catellicoccus marimammalium originally developed to detect gull fecal contamination in coastal environments. The methods included a conventional end-point PCR method, a SYBR^® Green qPCR method, and two TaqMan^® qPCR methods. Different techniques for data normalization and analysis were tested. Data analysis methods had a pronounced impact on assay sensitivity and specificity calculations. Across-laboratory standardization of metrics including the lower limit of quantification (LLOQ), target detected but not quantifiable (DNQ), and target not detected (ND) significantly improved results compared to results submitted by individual laboratories prior to definition standardization. The unit of measure used for data normalization also had a pronounced effect on measured assay performance. Data normalization to DNA mass improved quantitative method performance as compared to enterococcus normalization. The MST methods tested here were originally designed for gulls but were found in this study to also detect feces from other birds, particularly feces composited from pigeons. Sequencing efforts showed that some pigeon feces from California contained sequences similar to C. marimammalium found in gull feces. These data suggest that the prevalence, geographic scope, and ecology of C. marimammalium in host birds other than gulls require further investigation. This study represents an important first step in the multi-laboratory assessment of these methods and highlights the need to broaden and standardize additional evaluations, including environmentally relevant target concentrations in ambient waters from diverse geographic regions.     

Getting off on the right foot: Subjective value versus economic value in predicting longitudinal job outcomes from job offer negotiations.

Although negotiation experiences can affect a negotiator's ensuing attitudes and behavior, little is known about their long-term consequences. Using a longitudinal survey design, the authors tested the degree to which economic and subjective value achieved in job offer negotiations predicts employees' subsequent job attitudes and intentions concerning turnover. Results indicate that subjective value predicts greater compensation satisfaction and job satisfaction and lower turnover intention measured 1 year later. Surprisingly, the economic outcomes that negotiators achieved had no apparent effects on these factors. Implications, limitations, and future directions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transport and Metabolism of the Endogenous Auxin Precursor lndole-3-Butyric Acid

T Plant growth and morphogenesis depend on the levels and distribution of the plant hormone auxin. Plants tightly regulate cellular levels of the active auxin indole-3-acetic acid (IAA) through synthesis, inactivation, and transport. Although the transporters that move IAA into and out of cells are well characterized and play important roles in development, little is known about the transport of IAA precursors. In this review, we discuss the accumulating evidence suggesting that the IAA precursor indole-3-butyric acid (IBA) is transported independently of the characterized IAA transport machinery along with the recent identification of specific IBA efflux carriers and enzymes suggested to metabolize IBA. These studies have revealed important roles for IBA in maintaining IAA levels and distribution within the plant to support normal development.