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D. We (d + we)
Selected AbstractsPinning energy of domain walls in MnZn ferrite filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2007V. H. Calle Abstract Mn Zn ferrite films deposited on (100) MgO substrates by rf sputtering technique with different thicknesses , in the range of 30-450 nm were studied. AFM images show grain size increase as film thickness increases. Grains with diameters between L , 70 and 700 nm were observed. The mono and multidomain regime in MnZn ferrite films and their effect on the pinning energy of domain walls are observed via Magneto-optical Kerr Effect, MOKE. At , , 300 nm, the coercive field, Hc, reaches a maximum value of 80 Oe. This result indicates the existence of a multidomain regime associated to a critical grain size, Lc. We used the Jiles-Atherton model (JAM) to discuss the experimental hysteresis loops. The k pinning parameter obtained from JAM shows a maximum value of k /,o = 67 Am2 for grains with Lc , 529 nm. The total energy per unit area E was correlated with k and D. We found a simple phenomenological relationship given by E , kD; where D is the magnetic domain width. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reduction of perchlorate in river sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2006Rupert Simon Abstract The transformation of perchlorate was investigated in river sediment during laboratory batch and column studies to determine if reduction of perchlorate is a viable pathway in natural sediment without previous exposure to perchlorate. Perchlorate at an initial concentration of 10 ,M was reduced quantitatively to chloride in 3 d after a lag phase of 2 d in sediment slurries amended with lactate. Raising the initial concentration of perchlorate to 1,000 ,M increased the lag phase to 20 d before reduction occurred. At perchlorate concentrations greater than 1,000 ,M, the reduction of perchlorate was not observed within 40 d. We speculate that the high concentration of perchlorate specifically was problematic to the microbes mediating the reduction of perchlorate. High levels of nitrate inhibited the reduction of perchlorate as well. In sediment slurries amended with 870 ,M sodium nitrate, the reduction of perchlorate at an initial concentration of 100 ,M did not occur before day 15 of the experiment, but complete removal of nitrate had occurred by day four. Sediment column studies further demonstrated the dependence of perchlorate reduction on endogenous nitrate levels. [source] Effects of atrazine and iridovirus infection on survival and life-history traits of the long-toed salamander (Ambystoma macrodactylum)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2006Diane Forson Abstract Environmental contaminants and emerging infectious diseases are implicated as factors contributing to global amphibian declines. However, few studies have tested the interaction of these factors. We exposed six-week-old, larval long-toed salamanders (Ambystoma macrodactylum) to Ambystoma tigrinum virus (ATV; 0 or 103.5 plaque-forming units/ml) and sublethal concentrations of atrazine (0, 1.84, 18.4, and 184 ,g/L) in a 4 × 2 factorial design for 30 d. We tested the effects of atrazine and virus on mass and snout-vent length (SVL) at metamorphosis and larval period as well as on rates of mortality and viral infectivity. We confirmed ATV transmission to A. macrodactylum via polymerase chain reaction, but infection rates were lower than expected, consistent with the theory predicting lower pathogen transmission to nonnative hosts. Larvae exposed to both atrazine and ATV had lower levels of mortality and ATV infectivity compared to larvae exposed to virus alone, suggesting atrazine may compromise virus efficacy. The highest atrazine level (184 ,g/L) accelerated metamorphosis and reduced mass and SVL at metamorphosis significantly relative to controls. Exposure to ATV also significantly reduced SVL at metamorphosis. The present study suggests moderate concentrations of atrazine may ameliorate effects of ATV on long-toed salamanders, whereas higher concentrations initiate metamorphosis at a smaller size, with potential negative consequences to fitness. [source] Intra-Patriline Variability in the Performance of the Vibration Signal and Waggle Dance in the Honey Bee, Apis melliferaETHOLOGY, Issue 7 2008Nhi Duong We examined intra-patriline behavioral plasticity in communication behavior by generating lifetime behavioral profiles for the performance of the vibration signal and waggle dance in workers which were the progeny of three unrelated queens, each inseminated with the semen of a single, different drone. We found pronounced variability within each patriline for the tendency to produce each signal, the ontogeny of signal performance, and the persistence with which individual workers performed the signals throughout their lifetimes. Within each patriline, the number of workers that performed each signal and the distribution of onset ages for each signal were significantly different. In each patriline, workers of all ages could perform vibration signals; vibration signal production began 3,5 d before waggle dancing; and some workers began performing waggle dances at ages typically associated with precocious foraging. Most workers vibrated and waggled only 1,2 d during their lifetimes, although each patriline contained some workers that performed the signal persistently for up to 8 or 9 d. We also found marked variability in signal performance among the three worker lineages examined. Because the vibration signal and waggle dance influence task performance, variability in signaling behavior within and between subfamilies may help to organize information flow and collective labor in honey bee colonies. Inter-patriline variability may influence the total number of workers from different partrilines that perform the signals, whereas intra-patriline variability may further fine-tune signal performance and the allocation of labor to a given set of circumstances. Although intra-patriline behavioral variability is assumed to be widespread in the social insects, our study is the first to document the extent of this variability for honey bee communication signals. [source] Display Plasticity in Response to a Robotic Lizard: Signal Matching or Song Sharing in Lizards?ETHOLOGY, Issue 10 2006C. Brian Smith Many territorial songbirds alter the structure of their songs after listening to and interacting repeatedly with the same neighbors. Here, we use a robotic lizard to test for similar learned changes in signal structure in male Sagebrush lizards, Sceloporus graciosus. Subjects were exposed to two types of headbob displays (species-typical and unusual) both in short-term tests and in repeated exposures for 10 d. We found no evidence for immediate changes in signal structure to match a particular opponent (signal matching) or long-term changes after repeated exposure (,song' sharing). If anything, the lizards' displays became less like that of the robotic stimulus over time. Further tests of other taxa are needed to identify the evolutionary forces that lead to these forms of behavioral plasticity and to determine whether song sharing and signal matching are unique characteristic of songbirds. Lizards also became more agitated and produced more highly aggressive displays of their own when confronted with headbob displays that violated the basic syntactic structure of their display system, confirming that they were paying attention to subtle differences in display structure despite the artificial nature of the treatments. Thus, our study also adds to the growing evidence supporting the use of robotic playbacks to study animal communication. [source] Existence, uniqueness, and algorithmic computation of general lilypond systemsRANDOM STRUCTURES AND ALGORITHMS, Issue 3 2006Matthias Heveling The lilypond system based on a locally finite subset , of the Euclidean space ,n is defined as follows. At time 0 every point of , starts growing with unit speed in all directions to form a system of balls in which any particular ball ceases its growth at the instant that it collides with another ball. Based on a more formal definition of lilypond systems given in 1, we will prove that these systems exist and are uniquely determined. Our approach applies to the far more general setting, where , is a locally finite subset of some space ,, equipped with a pseudo-metric d. We will also derive an algorithm approximating the system with at least linearly decreasing error. Several examples will illustrate our general results. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2006 [source] | ||||||||||