837 research outputs found
Convergence analysis of a multigrid algorithm for the acoustic single layer equation
We present and analyze a multigrid algorithm for the acoustic single layer
equation in two dimensions. The boundary element formulation of the equation is
based on piecewise constant test functions and we make use of a weak inner
product in the multigrid scheme as proposed in \cite{BLP94}. A full error
analysis of the algorithm is presented. We also conduct a numerical study of
the effect of the weak inner product on the oscillatory behavior of the
eigenfunctions for the Laplace single layer operator
Leadership Representativeness in the Australian Union Movement
This paper explores the dimensions of political and personal representativeness in the context of Australian unionism in the period since World War Two. The first part of the article is dedicated to an operationalisation of these two concepts within trade unions, paying particular attention to the social origin of union leaders and their democratic accountability. The two dimensions of representativeness generate a two-by-two matrix which allows us to identify four types of union. The bulk of the article is taken up by an assessment of representativeness in Australian unions in relation to this matrix. The article concludes with some consideration of the relationship between the two different dimensions of representativeness, and the implications of this relationship for prospects for union revival
Absolute value preconditioning for symmetric indefinite linear systems
We introduce a novel strategy for constructing symmetric positive definite
(SPD) preconditioners for linear systems with symmetric indefinite matrices.
The strategy, called absolute value preconditioning, is motivated by the
observation that the preconditioned minimal residual method with the inverse of
the absolute value of the matrix as a preconditioner converges to the exact
solution of the system in at most two steps. Neither the exact absolute value
of the matrix nor its exact inverse are computationally feasible to construct
in general. However, we provide a practical example of an SPD preconditioner
that is based on the suggested approach. In this example we consider a model
problem with a shifted discrete negative Laplacian, and suggest a geometric
multigrid (MG) preconditioner, where the inverse of the matrix absolute value
appears only on the coarse grid, while operations on finer grids are based on
the Laplacian. Our numerical tests demonstrate practical effectiveness of the
new MG preconditioner, which leads to a robust iterative scheme with minimalist
memory requirements
Phage display selected magnetite interacting Adhirons for shape controlled nanoparticle synthesis
Adhirons are robust, well expressing, peptide display scaffold proteins, developed as an effective alternative
to traditional antibody binding proteins for highly specific molecular recognition applications. This paper
reports for the first time the use of these versatile proteins for material binding, and as tools for
controlling material synthesis on the nanoscale. A phage library of Adhirons, each displaying two variable
binding loops, was screened to identify specific proteins able to interact with [100] faces of cubic
magnetite nanoparticles. The selected variable regions display a strong preference for basic residues
such as lysine. Molecular dynamics simulations of amino acid adsorption onto a [100] magnetite surface
provides a rationale for these interactions, with the lowest adsorption energy observed with lysine. These
proteins direct the shape of the forming nanoparticles towards a cubic morphology in room temperature
magnetite precipitation reactions, in stark contrast to the high temperature, harsh reaction conditions
currently used to produce cubic nanoparticles. These effects demonstrate the utility of the selected
Adhirons as novel magnetite mineralization control agents using ambient aqueous conditions. The
approach we outline with artificial protein scaffolds has the potential to develop into a toolkit of novel
additives for wider nanomaterial fabrication
High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates
Many important hominid-bearing fossil localities in East Africa are in regions that are extremely hot and dry. Although humans are well adapted to such conditions, it has been inferred that East African environments were cooler or more wooded during the Pliocene and Pleistocene when this region was a central stage of human evolution. Here we show that the Turkana Basin, Kenya—today one of the hottest places on Earth—has been continually hot during the past 4 million years. The distribution of ^(13)C-^(18)O bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 °C and often in excess of 35 °C. Similar soil temperatures are observed today in the Turkana Basin and reflect high air temperatures combined with solar heating of the soil surface. These results are specific to periods of soil carbonate formation, and we suggest that such periods composed a large fraction of integrated time in the Turkana Basin. If correct, this interpretation has implications for human thermophysiology and implies a long-standing human association with marginal environments
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The Evolution of Endurance Running and the Tyranny of Ethnography: A Reply to Pickering and Bunn (2007)
Endurance running (ER) poses a conundrum for paleoanthropologists. As summarized in Bramble and Lieberman (2004), human ER capabilities, which are unique among primates, either match or exceed those of mammals adapted for running (cursors), including dogs and equids. Because many of the biomechanical and physiological challenges of human
ER are so different from those of walking, we can conclude that human ER capabilities did not arise merely as a by-product of selection for walking. Instead, the available evidence suggests that an array of features that improve ER performance were selected in the genus Homo, and they were probably present to some extent by the appearance of Homo erectus at approximately 1.9 Ma. Yet, ER is no longer necessary for human survival, even among extant foragers such as the Hadza or the
Bushmen. Thus, a puzzle that paleoanthropologists must solve is identifying what past behaviors - behaviors no longer common among living foragers - favored the evolution of ER. Pickering and Bunn’s (2007) criticisms of the ER hypothesis center on two issues: first, that early Homo lacked the tracking abilities necessary for successful pursuit hunts, and second, that recent ethnographic evidence suggests that modern hunter-gatherers rarely use ER to either hunt or scavenge. These arguments are based on a presumptive link between modern human-
like cognition and tracking abilities, as well as the notion that the modern ethnographic record provides an adequate reflection of past behaviors. Both of these assumptions are flawed. Although tracking is complex, there is little evidence to suggest that early hominids lacked the tracking abilities of much less encephalized carnivores. Additionally, as noted by Marlowe (2005), comparatively recent inventions, such as the bow and arrow, the spear thrower, nets, and even the spear point, fundamentally altered how humans hunt and scavenge. A strict reliance on the recent ethnographic record, what Wobst (1978) termed the ‘‘tyranny of ethnography,’’ is a fundamentally
problematic way of testing hypotheses of past hunting behavior. Even so, a review of the ethnographic evidence reveals errors in Pickering and Bunn’s contentions.Anthropolog
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