Relationships among nutrient enrichment, detritus quality and quantity, and large-bodied shredding insect community structure

This is a post-peer-review, pre-copyedit version of an article published in Hydrobiologia. The final authenticated version is available online at: https://doi.org/10.1007/s10750-015-2208-2Anthropogenic nutrient enrichment of forested headwater streams can enhance detrital quality, decrease standing stocks, and alter the community structure of detrivorous insects, reducing nutrient retention and decreasing ecosystem functioning. Our objective was to determine if stoichiometric principles could be used to predict genus-specific shifts in shredding insect abundance and biomass across a dissolved nutrient and detritus food quality/quantity gradient. Detritus, insect, and water samples were collected from 12 Ozark Highland headwater streams. Significant correlations were found between stream nutrients and detrital quality but not quantity. Abundance and biomass responses of four out of five tested genera were accurately predicted by consumerresource stoichiometric theory. Low carbon:phosphorus (C:P) shredders responded positively to increased total phosphorus and/or food quality, and high C:P shredders exhibited neutral or negative responses to these variables. Genus-specific declines were correlated with decreased overall biomass in shredder assemblages, potentially causing disruptions in nutrient flows to higher level consumers with nutrient enrichment. This work provides further evidence that elevated nutrients may negatively impact shredding insect communities by altering the stoichiometry of detritus–detritivore interactions. A better understanding of stoichiometric mechanisms altering macroinvertebrate populations is needed to help inform water quality criteria for the management of headwater streams

Isolating opportunity from demographics: A case study of motor vehicle theft in Philadelphia

Considering the extent of the motor vehicle theft (MVT) problem, it is surprising that there is such a dearth of studies on these crimes at the neighborhood level. In 2008, nearly one million vehicles, valued at 6.4 billion dollars, were reported stolen in the United States. Additionally, only half of these stolen vehicles were ever recovered. The purpose of this study is to increase the limited knowledge base on the characteristics of neighborhoods that predict MVT levels. Its focus is on the identification of specific types of land use that increase MVT levels, net the impact of sociodemographics, as posited by the opportunity theories of rational choice, routine activities, and crime pattern theory. The study site is Philadelphia, Pennsylvania with its 1816 census block groups serving as the unit of analysis. The percentage of total land area for each block group utilized by various theorized criminogenic land uses is determined by Geographic Information System (GIS). Evaluated land uses include shopping centers, bars, high schools, colleges, parking lots, youth hangouts, and single family homes. A ‘proximity space’ variable is also computed consisting of the percentage of block group area that is located within one street block of the combined criminogenic land uses. Its usefulness is in determining whether the impact of crime-producing land uses spreads into the surrounding neighborhood. Negative binomial regression models test various hypotheses around the general research question “After controlling for socio-structural correlates, is the presence of certain land uses predictive of MVT levels found at the neighborhood level?” Results demonstrate that land use, both independently and through neighborhood demographic structure, promotes or suppresses MVT levels, a finding consistent with opportunity theories. Specifically, the percentage of land use in block groups utilized by shopping centers, bars, and commercial parking lots is related to higher MVT counts, but that utilized by colleges and single family homes predicts lower MVT counts, net the impact of neighborhood sociodemographics. Interaction models demonstrate that SES, racial heterogeneity, single-parent families, and percentage 15-24 year olds moderate the impact of land use on MVT. Findings are relevant to urban planners, crime practitioners, and crime theorists

Exchange-bias training effect in TbFe/ GdFe: Micromagnetic mechanism

International audienceWe present magnetization and Kerr microscopy measurements of the exchange-bias training effect in hard/ soft, Tb 12 Fe 88 /Gd 40 Fe 60 , bilayers. These experimental results, compared with micromagnetic simulations, un-ambiguously show the role of the soft GdFe layer reversal on irreversible magnetic changes in the hard TbFe layer. After a partial reversal of the GdFe magnetization layer, the next field cycle exhibits a double hysteresis loop which is due to the existence of two types of domains in the sample, and only one of these domains has been subject to the training effect. The antiferromagnetically interfacial coupling and positive exchange-bias shift permit us to exclude any direct contribution from the magnetic field to this mechanism

Mechanism of chirality reversal for planar interface domain walls in exchange-coupled hard/soft magnetic bilayers

International audienceThe mechanism of chirality reversal for a planar interface domain wall in a hard/soft magnetic bilayer has been identified by combining magnetoresistance measurements, modeling, and direct magnetic domain observations. The reversal occurs through IDW nucleation and lateral domain wall propagation. Over an unpredicted wide range of applied magnetic fields, the chirality transition takes place by an unwinding followed by a rewinding of the IDW. The chirality transition mechanism of phase transition could be identified from a micromagnetic analysis of the lateral magnetic domain wall orientation. Up to three magnetization phases coexist in the uniaxial material during reversal