Ultra High Energy Cosmic Rays

Cosmic rays with energies above $10^{18}$ eV are currently of considerable interest in astrophysics and are to be further studied in a number of projects which are either currently under construction or the subject of well-developed proposals. This paper aims to discuss some of the physics of such particles in terms of current knowledge and information from particle astrophysics at other energies.Comment: 44 pages, 17 figures. Invited review, PASA, in pres

Observation of gamma-rays from LMC X-4 above 10(16) eV

Data from the University of Adelaide air shower array at Buckland Park taken over a three year period have been analyzed to search for evidence of ultra high energy gamma-ray emission from neutron star binary X-ray sources having known orbital periods. The detection of UHE gamma-rays from LMC X-4 above 10 to the 16th power eV, is reported; the first extragalactic object to be positively detected at these energies

Learning to become an expert : reinforcement learning and the acquisition of perceptual expertise

To elucidate the neural mechanisms underlying the development of perceptual expertise, we recorded ERPs while participants performed a categorization task. We found that as participants learned to discriminate computer-generated "blob'' stimuli, feedback modulated the amplitude of the errorrelated negativity (ERN)-an ERP component thought to reflect error evaluation within medial-frontal cortex. As participants improved at the categorization task, we also observed an increase in amplitude of an ERP component associated with object recognition (the N250). The increase in N250 amplitude preceded an increase in amplitude of an ERN component associated with internal error evaluation (the response ERN). Importantly, these electroencephalographic changes were not observed for participants who failed to improve on the categorization task. Our results suggest that the acquisition of perceptual expertise relies on interactions between the posterior perceptual system and the reinforcement learning system involving medial-frontal cortex

Growth and Fecundity of Several Weed Species in Corn and Soybean

Do weeds that emerge later in the season justify additional control costs\u27? If crop yield is not reduced or few or no seeds arc added to the soil seed hank, then no control may he needed. Eight weed species were sown in corn (Zea mays L.) and soybean I Glycine max (L.) Mcrr.l (i) before crop emergence, (ii) at crop emergence, (iii) at V-1, and (iv) at V-2 stages of crop growth in 2002 and 2003. Weed seed was sown close to the crop row and thinned to 1.3 plants m 2• Weed growth and fecundity were influenced by species, time of planting, and year. Only barnyarclgrass (Echinochloa crus-galli L.), rcclroot pigwced (Amaranthus retniflexus L.), and vclvetlcaf (Abutilon theophrasti L.) survived to produce seed. Plants from the pre-emergence seeding had the largest canopy and produced the most seeds. Harnyardgrass had maximum canopy cover in early .July in corn and late .Inly in soybean hut only produced seed in corn. Rcclroot pigweecl and vclvctleaf had maximum canopy cover in late August or midSeptember, and some plants from most seeding elates survived and produced seed in both corn and soybean. However, plants that grew from seed sown at V-1 and V-2 crnp grnwth stages did not reduce yield or biomass of adjacent crop plants, had low fecundity, and may not warrant treatment. Control may be necessary, however, to prevent yield losses if weeds arc present at high densities or to prevent establishment of uncommon species

The longitudinal thickness of air-shower fronts

Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied

Uncovering the Arabidopsis thaliana nectary transcriptome: investigation of differential gene expression in floral nectariferous tissues

<p>Abstract</p> <p>Background</p> <p>Many flowering plants attract pollinators by offering a reward of floral nectar. Remarkably, the molecular events involved in the development of nectaries, the organs that produce nectar, as well as the synthesis and secretion of nectar itself, are poorly understood. Indeed, to date, no genes have been shown to directly affect the <it>de novo </it>production or quality of floral nectar. To address this gap in knowledge, the ATH1 Affymetrix^®GeneChip array was used to systematically investigate the Arabidopsis nectary transcriptome to identify genes and pathways potentially involved in nectar production.</p> <p>Results</p> <p>In this study, we identified a large number of genes differentially expressed between secretory lateral nectaries and non-secretory median nectary tissues, as well as between mature lateral nectaries (post-anthesis) and immature lateral nectaries (pre-anthesis). Expression within nectaries was also compared to thirteen non-nectary reference tissues, from which 270 genes were identified as being significantly upregulated in nectaries. The expression patterns of 14 nectary-enriched genes were also confirmed via RT PCR. Upon looking into functional groups of upregulated genes, pathways involved in gene regulation, carbohydrate metabolism, and lipid metabolism were particularly enriched in nectaries versus reference tissues.</p> <p>Conclusion</p> <p>A large number of genes preferentially expressed in nectaries, as well as between nectary types and developmental stages, were identified. Several hypotheses relating to mechanisms of nectar production and regulation thereof are proposed, and provide a starting point for reverse genetics approaches to determine molecular mechanisms underlying nectar synthesis and secretion.</p

Post Industrial Journalism: Adapting to the Present

This essay is part survey and part manifesto, one that concerns itself with the practice of journalism and the practices of journalists in the United States. It is not, however, about “the future of the news industry,” both because much of that future is already here and because there is no such thing as the news industry anymore. If you wanted to sum up the past decade of the news ecosystem in a single phrase, it might be this: Everybody suddenly got a lot more freedom. The newsmakers, the advertisers, the startups, and, especially, the people formerly known as the audience have all been given new freedom to communicate, narrowly and broadly, outside the old strictures of the broadcast and publishing models. The past 15 years have seen an explosion of new tools and techniques, and, more importantly, new assumptions and expectations, and these changes have wrecked the old clarity. Many of the changes talked about in the last decade as part of the future landscape of journalism have already taken place; much of journalism’s imagined future is now its lived-in present. (As William Gibson noted long ago, “The future is already here. It’s just unevenly distributed.”) Our goal is to write about what has already happened and what is happening today, and what we can learn from it, rather than engaging in much speculation

Patterns of fish use and piscivore abundance within a reconnected saltmarsh impoundment in the northern Indian River Lagoon, Florida

Nearly all saltmarshes in east-central, Florida were impounded for mosquito control during the 1960s. The majority of these marshes have since been reconnected to the estuary by culverts, providing an opportunity to effectively measure exchange of aquatic organisms. A multi-gear approach was used monthly to simultaneously estimate fish standing stock (cast net), fish exchange with the estuary (culvert traps), and piscivore abundance (gill nets and bird counts) to document patterns of fish use in a reconnected saltmarsh impoundment. Changes in saltmarsh fish abundance, and exchange of fish with the estuary reflected the seasonal pattern of marsh flooding in the northern Indian River Lagoon system. During a 6-month period of marsh flooding, resident fish had continuous access to the marsh surface. Large piscivorous fish regularly entered the impoundment via creeks and ditches to prey upon small resident fish, and piscivorous birds aggregated following major fish movements to the marsh surface or to deep habitats. As water levels receded in winter, saltmarsh fish concentrated into deep habitats and emigration to the estuary ensued (200% greater biomass left the impoundment than entered). Fish abundance and community structure along the estuary shoreline (although fringed with marsh vegetation) were not analogous to marsh creeks and ditches. Perimeter ditches provided deep-water habitat for large estuarine predators, and shallow creeks served as an alternative habitat for resident fish when the marsh surface was dry. Use of the impoundment as nursery by transients was limited to Mugil cephalus Linnaeus, but large juvenile and adult piscivorous fish used the impoundment for feeding. In conclusion, the saltmarsh impoundment was a feeding site for piscivorous fish and birds, and functioned as a net exporter of forage fish to adjacent estuarine waters

Timing analysis techniques at large core distances for multi-TeV gamma ray astronomy

We present an analysis technique that uses the timing information of Cherenkov images from extensive air showers (EAS). Our emphasis is on distant, or large core distance gamma-ray induced showers at multi-TeV energies. Specifically, combining pixel timing information with an improved direction reconstruction algorithm, leads to improvements in angular and core resolution as large as ~40% and ~30%, respectively, when compared with the same algorithm without the use of timing. Above 10 TeV, this results in an angular resolution approaching 0.05 degrees, together with a core resolution better than ~15 m. The off-axis post-cut gamma-ray acceptance is energy dependent and its full width at half maximum ranges from 4 degrees to 8 degrees. For shower directions that are up to ~6 degrees off-axis, the angular resolution achieved by using timing information is comparable, around 100 TeV, to the on-axis angular resolution. The telescope specifications and layout we describe here are geared towards energies above 10 TeV. However, the methods can in principle be applied to other energies, given suitable telescope parameters. The 5-telescope cell investigated in this study could initially pave the way for a larger array of sparsely spaced telescopes in an effort to push the collection area to >10 km2. These results highlight the potential of a `sparse array' approach in effectively opening up the energy range above 10 TeV.Comment: Published in Astroparticle Physic

How Plankton Swim: An Interdisciplinary Approach for Using Mathematics & Physics to Understand the Biology of the Natural World

The authors have developed and field-tested high school-level curricular materials that guide students to use biology, mathematics, and physics to understand plankton and how these tiny organisms move in a world where their intuition does not apply. The authors chose plankton as the focus of their materials primarily because the challenges faced by plankton are novel problems to most students, forcing adoption of new perspectives and making the study of plankton exciting. Additional reasons that they chose plankton to focus on include their ecological importance, their availability to most teachers and students, the ease with which they can be collected and observed, and the current focus of some scientific researchers on their movement and behavior. These curricular materials include a series of inquiry-based, hands-on exercises designed to be accessible to students with a range of backgrounds. Many of these materials could be adapted for use by middle-school, and/or college-level students. In this article, the authors describe sample lessons, summarize what worked well, and flag obstacles they encountered while integrating mathematics and physics into the biology classroom