Abstract CO 2 production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation – the direct breakdown of organic matter (OM) by solar irradiance – has been found to contribute to litter mass loss in dry ecosystems. Previous small‐scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO 2 . However, the contribution of photodegradation to total CO 2 losses at ecosystems scales is unknown. This study determined the proportion of the total CO 2 losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO 2 production was examined by comparing daytime CO 2 fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO 2 gradient technique, and with night‐time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO 2 fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO 2 flux from the peatland and almost 60% of the dry season CO 2 flux from the grassland, and up to 62% and 92% of the summer mid‐day CO 2 fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO 2 exchange into its gross components by assuming that total daytime CO 2 losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem–atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon–climate models.
Recently, a new class of biocompatible elastic polymers loaded with small ferrous particles (magnetoelastomer) was developed at Lawrence Livermore National Laboratory, Livermore, CA. This new material was formed as a thin film using spin casting. The deformation of this material using a magnetic field has many possible applications to microfluidics. Two methods will be used to calculate the deformation of a circular magnetoelastomeric film subjected to a magnetic field. The first method is an arbitrary Lagrangian-Eulerian (ALE) finite-element method (FEM) and the second is based on nonlinear continuum electromagnetism and continuum elasticity in the membrane limit. The comparison of these two methods is used to test/validate the FEM.
Although the social sciences have made extensive use of the term ??ghetto' as a descriptive term, they have failed to forge a robust analytical concept of the same, relying instead on the folk notions taken for granted at each epoch in the society under examination. This article constructs a relational concept of the ghetto as a Janus-faced instrument of ethnoracial closure and control by drawing on the historiography of the Jewish diaspora in Renaissance Europe, the sociology of the black American experience in the Fordist metropolis, and the anthropology of ethnic outcasts in East Asia. This reveals that a ghetto is a social-organizational device composed of four elements (stigma, constraint, spatial confinement, and institutional compartmentalization) that employs space to reconcile the two antinomic purposes of economic exploitation and social ostracization. The ghetto is not a ??natural area' coterminous with ??history of migration' (as Louis Wirth argued), but a special form of collective violence concretized in urban space. Articulating the concept of ghetto makes it possible to disentangle the relationship between ghettoization, urban poverty, and segregation, and to clarify the structural and functional differences between ghettos and ethnic clusters. It also enables us to spotlight the role of the ghetto as a symbolic incubator and matrix for the production of a spoiled identity, and suggests that it should be studied by analogy with other institutions for the forced confinement of dispossessed and dishonored groups such as the reservation, the refugee camp, and the prison.
Despite substantial clinical interest in the fracture resistance of human dentin, there is little mechanistic information in archival literature that can be usefully used to model such fracture. In fact, although the fracture event indent in, akin to other mineralized tissues like bone, is widely believed to be locally strain-controlled, there has never been any scientific proof to support this belief. The present study seeks to address this issue through the use of a novel set of in vitro experiments in Hanks' balanced salt solution involving a double-notched bend test geometry, which is designed to discern whether the critical failure events involved in the onset of fracture are locally stress- or strain-controlled. Such experiments are further used to characterize the notion of plasticity in dentin and the interaction of cracks with the salient microstructural features. It is observed that fracture in dentin is indeed locally strain-controlled and that the presence of dentinal tubules does not substantially affect this process of crack initiation and growth. The results presented are believed to be critical steps in the development ofa micromechanical model for the fracture of human dentin that takes into consideration the influence of both the microstructure and the local failure mode.
A study has been made of the fracture toughness and resistance-curve behavior of a laminate consisting of alternating layers of brittle Nb3Al intermetallic and ductile Nb metal, using layer thicknesses of ∼500 and 125 μm, respectively. Effective resistance-curve toughening of Nb3Al was achieved in such a coarse-scale layered structure with only 20 vol.% of the Nb reinforcement phase. Specifically, the toughness of Nb3Al was increased from ∼1 MPa✔m to well over 20 MPa✔m (and as high as 70 MPa✔m in certain samples) after several millimeters at stable crack growth. These values are significantly greater than other Nb/Nb3Al composites containing Nb as ∼ 20 μm sized particulates or 1–2 μm thick Nb layers (in the form of a microlaminate), both containing at least 40 vol.% of the ductile phase. The source of such ductile-phase toughening was attributed to crack blunting at, and renucleation across, the ductile Nb layers, which in turn led to extensive bridging and plastic deformation within the Nb layers in the crack wake. Since the extent of crack trapping by the ductile layer and plastic deformation are limited by layer thickness, the present coarser-scale laminates tend to display better fracture resistance compared to composites with finer-scale ductile reinforcements.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A new paradigm has emerged, in which the band structure concepts of solid-state physics are applied to electromagnetics. This has led to a profusion of scientific creativity as new forms of electromagnetic crystal structures are invented for radio and microwaves, as well as for three-dimensional (3-D) geometry of both natural crystals and those artificial crystals that can arise only in the human imagination.
