Kosha: A Peer-to-Peer Enhancement for the Network File System

The storage needs of modern scientific applications are growing exponentially, and designing economical storage solutions for such applications – especially in Grid environments – is an important research topic. This work presents Kosha, a system that aims to harvest redundant storage space on cluster nodes and user desktops to provide a reliable, shared file system that acts as a large distributed storage. Kosha utilizes peer-to-peer (p2p) mechanisms to enhance the widely-used Network File System (NFS). P2P storage systems provide location transparency, mobility transparency, load balancing, and file replication – features that are not available in NFS. On the other hand, NFS provides hierarchical file organization, directory listings, and file permissions, which are missing from p2p storage systems. By blending the strengths of NFS and p2p storage systems, Kosha provides a low overhead storage solution. Our experiments show that compared to unmodified NFS, Kosha introduces a 3.3% fixed overhead and 4.5% additional overhead as nodes are increased from two to sixteen. For larger number of nodes, the additional overhead increases slowly. Kosha achieves load balancing in distributed directories, and guarantees or better file availability.*This work was supported in part by an NSF CAREER award (ACI-0238379).Troy A. Johnson was supported by a U.S. Department of Education GAANN doctoral fellowship.     

Cytochemical localization of acetylcholine receptors at the neuromuscular junction by means of horseradish peroxidase-labeled alpha-bungarotoxin

The cytochemical localization of acetylcholine (ACh) receptors at the neuromuscular junction was investigated with a procedure utilizing alpha-bungarotoxin (alpha-BtX) labeled directly with horseradish peroxidase (HRP). Following incubation of tissues in the conjugate and reaction for peroxidase, activity was observed on the junctional folds of the motor endplate. A uniform layer of reaction product approximately 15 nm thick occurred over the apical portions of the junctional folds. Membranes at the bases of the synaptic cleft showed only small amounts of reaction product. Non-junctional regions of the muscle fiber were unreactive. Activity was also observed in the membrane of the axon facing the muscle surface, often including the axolemma overlying the "active zones" of the nerve terminal. Such presynaptic activity was still evident on nerve terminals disjuncted from the synapse by enzymatic treatment prior to incubation in the conjugate. This localization indicates the possible presence of presynaptic ACh receptors within the axolemma. In muscle denervated for 7-12 days, motor endplates were reactive and parajunctional sarcolemma showed slight activity, but most extrajunctional regions contained no obvious accumulations of reaction product. Activity at all sites was prevented by preincubation of tissues in native alpha-BTX prior to incubation in the conjugate and reaction for HRP. This procedure represents a simple and convenient method for the high resolution localization of ACh receptors.     

Competing for consciousness: Prolonged mask exposure reduces object substitution masking.

In object substitution masking (OSM) a sparse, temporally trailing 4-dot mask impairs target identification, even though it has different contours from, and does not spatially overlap with the target. Here, we demonstrate a previously unknown characteristic of OSM: Observers show reduced masking at prolonged (e.g., 640 ms) relative to intermediate mask durations (e.g., 240 ms). We propose that with prolonged exposure, the mask's visual representation is consolidated, which allows processing of the lingering target icon to be reinitiated, thereby improving performance. Our findings suggest that when the visual system is confronted with 2 temporally contiguous stimuli, although one may initially gain access to consciousness above the other, the “losing” stimulus is not irreversibly lost to awareness. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Spark Plasma Sintering of Nanostructured Aluminum: Influence of Tooling Material on Microstructure

The influence of tooling material, i.e., graphite and WC-Co, on the microstructure of a spark plasma sintering (SPS) consolidated, nanostructured aluminum alloy is studied in this paper. The results show that tooling selection influences microstructure evolution, independent of process parameters. The influence of tooling on microstructure is rationalized on the basis of the following factors: heating rate, electrical current density, localized heating, and imposed pressure. A theoretic framework, based on the physical properties of graphite and WC-Co, is formulated to explain the observed behavior.     

Dynamic Micro-Strain Analysis of Ultrafine-Grained Aluminum Magnesium Alloy Using Digital Image Correlation

Tensile tests were performed in situ on an ultrafine-grained (UFG) Al-Mg alloy using a micro-tensile module in a scanning electron microscope. The micro-strain evolution was tracked and measured using digital image correlation (DIC). A fine random speckle pattern was required to achieve high resolution and accuracy of strain measurement using DIC. To produce the speckle pattern, a patterning method was developed using electron beam lithography to deposit a gold speckle pattern. The nanoscale feature size of this gold pattern (45 nm) was useful for identifying the micro-strain among individual grains of the UFG Al-Mg alloy. Microstructural aspects of the UFG Al-Mg alloy were revealed by analysis of electron backscattered diffraction (EBSD) patterns. Finally, the effect of the UFG Al-Mg alloy microstructure on the nanoscale deformation mechanism was investigated by combining EBSD and DIC data in a contour map. This combined technique provides a method for direct measurement of micro-strain and is potentially useful for deformation studies of a wide range of nanostructured materials.     

Seaweed Allelopathy Against Coral: Surface Distribution of a Seaweed Secondary Metabolite by Imaging Mass Spectrometry

Coral reefs are in global decline, with seaweeds increasing as corals decrease. Although seaweeds inhibit coral growth, recruitment, and survivorship, the mechanism of these interactions is poorly understood. Here, we used field experiments to show that contact with four common seaweeds induces bleaching on natural colonies of Porites rus. Controls in contact with inert, plastic mimics of seaweeds did not bleach, suggesting seaweed effects resulted from allelopathy rather than shading, abrasion, or physical contact. Bioassay-guided fractionation of the hydrophobic extract from the red alga Phacelocarpus neurymenioides revealed a previously characterized antibacterial metabolite, neurymenolide A, as the main allelopathic agent. For allelopathy of lipid-soluble metabolites to be effective, the compounds would need to be deployed on algal surfaces where they could transfer to corals on contact. We used desorption electrospray ionization mass spectrometry (DESI-MS) to visualize and quantify neurymenolide A on the surface of P. neurymenioides, and we found the molecule on all surfaces analyzed, with highest concentrations on basal portions of blades.     

Evaluating the role of ivy (Hedera helix) in moderating wall surface microclimates and contributing to the bioprotection of historic buildings

The role of ivy (Hedera helix L.) on building walls is much debated, with arguments being put forward for it playing a biodeteriorative role (for example through ivy rootlets exploiting cracks and holes) as well as suggestions that it might provide some bioprotection (for example by the ivy canopy protecting the walls from other agents of deterioration such as frost). We have carried out a year-long study of the influence that ivy canopies play on wall surface microclimates at five sites across a range of climatic settings within England, using iButtons to monitor temperature and relative humidity fluctuations at the wall surface on ivy-covered and exposed walls. Hourly data illustrates a general mediating effect of ivy canopies on both temperature and relative humidity regimes. The ivy reduces extremes of temperature and relative humidity, with the most clearcut differences for temperature. Across all five sites the average daily maximum temperature was 36% higher and the average daily minimum temperature 15% lower on exposed vs ivy-covered surfaces. Differences in the exposure level of studied walls (i.e. whether they are shaded or not by trees or other walls) influenced the degree of microclimatic alteration provided by the ivy canopy. Other important factors influencing the strength of the ivy impact on microclimate were found to be thickness of the canopy and aspect of the wall. A detailed analysis of one site, Byland in North Yorkshire, illustrates the seasonal differences in impact of ivy on microclimates, with insulation against freezing being the dominant effect in January, and the removal of high temperature ‘spikes’ the dominant effect in July. The observed moderating role of ivy canopies on wall surface microclimates will reduce the likelihood of frost and salt deterioration to the building materials, thus contributing to their conservation. Further research needs to be done on other potentially deteriorative roles of ivy before an overall bioprotective role can be assumed, but the significant impact of ivy on wall surface microclimates across England is clear.     

Next-generation tools for evolutionary invasion analyses

Evolutionary invasion analysis is a powerful technique for modelling in evolutionary biology. The general approach is to derive an expression for the growth rate of a mutant allele encoding some novel phenotype, and then to use this expression to predict long-term evolutionary outcomes. Mathematically, such ‘invasion fitness’ expressions are most often derived using standard linear stability analyses from dynamical systems theory. Interestingly, there is a mathematically equivalent approach to such stability analyses that is often employed in mathematical epidemiology, and that is based on so-called ‘next-generation’ matrices. Although this next-generation matrix approach has sometimes also been used in evolutionary invasion analyses, it is not yet common in this area despite the fact that it can sometimes greatly simplify calculations. The aim of this article is to bring the approach to a wider evolutionary audience in two ways. First, we review the next-generation matrix approach and provide a novel, and easily intuited, interpretation of how this approach relates to more standard techniques. Second, we illustrate next-generation methods in evolutionary invasion analysis through a series of informative examples. Although focusing primarily on evolutionary invasion analysis, we provide several insights that apply to biological modelling in general.     

Evaluation of rib steak colour from Friesian, Hereford and Charolais heifers pastured or overwintered prior to slaughter

Heifers (n=10) were randomly selected from the slaughter line of a local factory each month for a period of 21 months. Rib steak (sampled at the 10th rib) from the left side of each carcass was taken for analysis. The cattle breeds selected during this study were Friesian, Hereford and Charolais. The mean weight of the left side for all carcasses was 146.6 (S.E.M.= 1.0kg). Graded carcasses selected for sampling during this trial were classified using the EUROP scale and the specific heifer grades chosen were factory grades EO4L and EO4H. Initial Hunter 'a' values (on the day of arrival in the laboratory) of rib steak from heifers finished between November and March (overwintered) were significantly (P<0.001) higher than Hunter 'a' values from heifers finished between April and October (pastured). After storage at 4?°C under simulated retail display conditions for 6 days, the Hunter 'a' values for overwintered samples were also significantly (P<0.001) greater than those for pastured samples. Breed also had an effect on the colour of the meat. After storage for 6 days, Hunter 'a' values of rib steak from Charolais were significantly (P<0.05) higher than either Friesian or Hereford. Pastured heifers had significantly (P<0.05) higher levels of the monounsaturated fatty acid C16.1 in the total lipid fraction of rib steak (neutral and polar) than samples taken from overwintered heifers. Pastured heifers had significantly (P<0.01) higher levels of the polyunsaturated fatty acid (PUFA) C18.3 in the phospholipid fraction than those from overwintered cattle. However, Hereford had significantly (P<0.05) higher levels of C14.0, C16.1 and C18.0 in the phospholipid fraction than those found in Friesian and Charolais. The level of α-tocopherol in the muscle was not affected by either pasturing/overwintering or breed. However, Continental breeds had significantly (P<0.05) higher levels of α-tocopherol in adipose tissue than Friesian.