2,740 research outputs found
House-Swapping with Objective Indifferences
We study the classic house-swapping problem of Shapley and Scarf (1974) in a
setting where agents may have "objective" indifferences, i.e., indifferences
that are shared by all agents. In other words, if any one agent is indifferent
between two houses, then all agents are indifferent between those two houses.
The most direct interpretation is the presence of multiple copies of the same
object. Our setting is a special case of the house-swapping problem with
general indifferences. We derive a simple, easily interpretable algorithm that
produces the unique strict core allocation of the house-swapping market, if it
exists. Our algorithm runs in square polynomial time, a substantial improvement
over the cubed time methods for the more general problem.Comment: 9 page
The Role of the Phosphatidylinositol 4-Kinase PI4KA in Hepatitis C Virus-Induced Host Membrane Rearrangement
Background: Hepatitis C virus (HCV), like other positive-sense RNA viruses, replicates on an altered host membrane compartment that has been called the ‘‘membranous web.’ ’ The mechanisms by which the membranous web are formed from cellular membranes are poorly understood. Several recent RNA interference screens have demonstrated a critical role for the host phosphatidylinositol 4-kinase PI4KA in HCV replication. We have sought to define the function of PI4KA in viral replication. Methodology/Principal Findings: Using a nonreplicative model of membranous web formation, we show that PI4KA silencing leads to aberrant web morphology. Furthermore, we find that PI4KA and its product, phosphatidylinositol 4-phosphate, are enriched on membranous webs and that PI4KA is found in association with NS5A in HCV-infected cells. While the related lipid kinase PI4KB also appears to support HCV replication, it does not interact with NS5A. Silencing of PI4KB does not overtly impair membranous web morphology or phosphatidylinositol 4-phosphate enrichment at webs, suggesting that it acts at a different point in viral replication. Finally, we demonstrate that the aberrant webs induced by PI4KA silencing require the activity of the viral NS3-4A serine protease but not integrity of the host secretory pathway. Conclusions/Significance: PI4KA is necessary for the local enrichment of PI 4-phosphate at the HCV membranous web and for the generation of morphologically normal webs. We also show that nonreplicative systems of web formation can b
Transitions between foot postures are associated with elevated rates of body size evolution in mammals
Terrestrial mammals have evolved various foot postures: flat-footed (plantigrady), tiptoed (digitigrady), and hooved (unguligrady) postures. Although the importance of foot posture on ecology and body size of mammalian species has been widely recognized, its evolutionary trajectory and influence on body size evolution across mammalian phylogeny remain untested. Taking a Bayesian phylogenetic approach combined with a comprehensive dataset of foot postures in 880 extant mammalian species, we investigated the evolutionary history of foot postures and rates of body size evolution, within the same posture and at transitions between postures. Our results show that the common ancestor of mammals was plantigrade, and transitions predominantly occurred only between plantigrady and digitigrady and between digitigrady and unguligrady. At the transitions between plantigrady and digitigrady and between digitigrady and unguligrady, rates of body size evolution are significantly elevated leading to the larger body masses of digitigrade species (∼1 kg) and unguligrade species (∼78 kg) compared with their respective ancestral postures [plantigrady (∼0.75 kg) and digitigrady]. Our results demonstrate the importance of foot postures on mammalian body size evolution and have implications for mammalian body size increase through time. In addition, we highlight a way forward for future studies that seek to integrate morphofunctional and macroevolutionary approaches
Variable tree establishment in bauxite mine restoration in south-west Australia linked to rainfall distribution, seasonal temperatures and seed rain
Reasons for variable establishment of Jarrah (Eucalyptus marginata D. Don ex Sm.) and Marri (Corymbia calophylla (Lindl). K. D. Hill & L. A. S. Johnson) on restored forest sites after bauxite mining in south‐west Australia are not well understood. To refine restoration outcomes, we compiled tree seedling density establishment data from surveys of 654 previously mined sites restored between 1998 and 2017, and applied generalised linear models to discriminate the effects of 24 climatic and restoration practice variables. Final models explained 50% and 31% of the variation in Jarrah and Marri density, respectively. Broadcast seeding and fertiliser rates were positively related to seedling density. A more even rainfall distribution in the early wet season increased seedling density. However, persistent rain later in the wet season decreased density, possibly as a result of ripline soil saturation or ponding. Higher average daily maximum temperatures in the dry season decreased seedling density probably due to drought stress, but warmer daily temperature minima in both wet and dry seasons increased density. Seed rain from surrounding unmined forest was implicated as a significant, but highly variable, source of additional seed to restored sites. Restoration practices that influence soil moisture relations (tillage, depth and texture of returned soil), shallow burial of applied seed and timing of fertiliser application are likely to be important in refining restoration outcomes
The radicalization of the Indian and Irish nationalist movements, 1914-1922 : a comparison
I initially conceived of this research when I was an honours student at the University of Tasmania. It was then that my
supervisors, Dr. Asim Roy and Dr. Richard Davis, painstakingly showed me that the interaction of the Indian and Irish nationalist movements during the nineteenth and twentieth centuries was a much neglected
field of research. Dr. Davis himself has already done some substantial work in this field. Other historians such as Dr. Mary
Cumpston, Dr. J.V. Crangle, and Dr. Howard Brasted have also contributed significant studies to this fertile area of academic
endeavour. However, most of the work on this rare domain of comparative
studies is concentrated in the nineteenth century. Dr. Cumpston, for instance, discusses the nature of Irish nationalist advocacy of Indian interests during 1851-1906. Dr. Brasted, in two welldocumented
articles which establish the Irish Home Rule influence on the development of Indian national consciousness, also confines
himself to the 1870s and 1880s. Dr. Crangle, who analyses Irish nationalist diatribes against the imperial administration of India, too, focuses his attention on the period 1880-1884
Field-controlled dynamics of skyrmions and monopoles
Magnetic monopoles, despite their ongoing experimental search as elementary
particles, have inspired the discovery of analogous excitations in condensed
matter systems. In chiral condensed matter systems, emergent monopoles are
responsible for the onset of transitions between topologically distinct states
and phases, like in the case of transitions from helical and conical phase to
A-phase comprising periodic arrays of skyrmions. By combining numerical
modeling and optical characterizations, we describe how different geometrical
configurations of skyrmions terminating at monopoles can be realized in liquid
crystals and liquid crystal ferromagnets. We demonstrate how such complex
structures can be effectively manipulated by external magnetic and electric
fields. Furthermore, we discuss how our findings may hint at similar dynamics
in other physical systems, and their potential applications
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