3,987 research outputs found
Replica-symmetry breaking in dynamical glasses
Systems of globally coupled logistic maps (GCLM) can display complex
collective behaviour characterized by the formation of synchronous clusters. In
the dynamical clustering regime, such systems possess a large number of
coexisting attractors and might be viewed as dynamical glasses. Glass
properties of GCLM in the thermodynamical limit of large system sizes are
investigated. Replicas, representing orbits that start from various initial
conditions, are introduced and distributions of their overlaps are numerically
determined. We show that for fixed-field ensembles of initial conditions, as
used in previous numerical studies, all attractors of the system become
identical in the thermodynamical limit up to variations of order
because the initial value of the coupling field is characterized by vanishing
fluctuations, and thus replica symmetry is recovered for . In
contrast to this, when random-field ensembles of initial conditions are chosen,
replica symmetry remains broken in the thermodynamical limit.Comment: 19 pages, 18 figure
Biodiversity in model ecosystems, II: Species assembly and food web structure
This is the second of two papers dedicated to the relationship between
population models of competition and biodiversity. Here we consider species
assembly models where the population dynamics is kept far from fixed points
through the continuous introduction of new species, and generalize to such
models thecoexistence condition derived for systems at the fixed point. The
ecological overlap between species with shared preys, that we define here,
provides a quantitative measure of the effective interspecies competition and
of the trophic network topology. We obtain distributions of the overlap from
simulations of a new model based both on immigration and speciation, and show
that they are in good agreement with those measured for three large natural
food webs. As discussed in the first paper, rapid environmental fluctuations,
interacting with the condition for coexistence of competing species, limit the
maximal biodiversity that a trophic level can host. This horizontal limitation
to biodiversity is here combined with either dissipation of energy or growth of
fluctuations, which in our model limit the length of food webs in the vertical
direction. These ingredients yield an effective model of food webs that produce
a biodiversity profile with a maximum at an intermediate trophic level, in
agreement with field studies
Biodiversity in model ecosystems, I: Coexistence conditions for competing species
This is the first of two papers where we discuss the limits imposed by
competition to the biodiversity of species communities. In this first paper we
study the coexistence of competing species at the fixed point of population
dynamic equations. For many simple models, this imposes a limit on the width of
the productivity distribution, which is more severe the more diverse the
ecosystem is (Chesson, 1994). Here we review and generalize this analysis,
beyond the ``mean-field''-like approximation of the competition matrix used in
previous works, and extend it to structured food webs. In all cases analysed,
we obtain qualitatively similar relations between biodiversity and competition:
the narrower the productivity distribution is, the more species can stably
coexist. We discuss how this result, considered together with environmental
fluctuations, limits the maximal biodiversity that a trophic level can host
Detection of bovine papillomavirus type 2 in the peripheral blood of cattle with urinary bladder tumours: possible biological role
Bovine papillomavirus type 2 (BPV-2) infection has been associated with urinary bladder tumours in adult cattle grazing on bracken fern-infested land. In this study, we investigated the
simultaneous presence of BPV-2 in whole blood and urinary bladder tumours of adult cattle in an attempt to better understand the biological role of circulating BPV-2. Peripheral blood samples were collected from 78 cattle clinically suffering from a severe chronic enzootic haematuria. Circulating BPV-2 DNA was detected in 61 of them and in two blood samples from healthy cows. Fifty of the affected animals were slaughtered at public slaughterhouses and neoplastic proliferations in the urinary bladder were detected in all of them. BPV-2 DNA was amplified and sequenced in 78% of urinary bladder tumour samples and in 38.9% of normal samples as a control. Circulating episomal BPV-2 DNA was detected in 78.2% of the blood samples. Simultaneous presence of BPV-2 DNA in neoplastic bladder and blood samples was detected in 37 animals. Specific viral E5 mRNA and E5 oncoprotein were also detected in blood by RT-PCR
and Western blot/immunocytochemistry, respectively. It is likely that BPV-2 can persist and be maintained in an active status in the bloodstream, in particular in the lymphocytes, as a reservoir of viral infection that, in the presence of co-carcinogens, may cause the development of urinary bladder tumours
Revisiting Sovereign Bankruptcy
Sovereign debt crises occur regularly and often violently. Yet there is no legally and politically recognized procedure for restructuring the debt of bankrupt sovereigns. Procedures of this type have been periodically debated, but so far been rejected, for two main reasons. First, countries have been reluctant to give up power to supranational rules or institutions, and creditors and debtors have felt that there were sufficient instruments for addressing debt crises at hoc. Second, fears that making debt easier to restructure would raise the costs and reduce the amounts of sovereign borrowing in many countries. This was perceived to be against the interests of both the providers of both creditors and major borrowers.
This report argues that both the nature and our understanding of sovereign debt problems have changed, over the course of the last decade, in a direction that creates a much stronger case for an orderly sovereign bankruptcy regime today than ten years ago. Pre-crisis policy mistakes are now recognized to be a much more severe problem for borrowing countries than the costs or limited availability of private financing. Recent court rulings – particularly a recent U.S. ruling that gives holdout creditors that decline a restructuring offer the right to interfere with payments to the creditors that accept such an offer. This will complicate efforts to resolve future debt crises on an ad hoc basis. Finally, sovereign debt crises are no longer just a problem in emerging markets, but a core concern in advanced countries as well – particularly in the Euro area. If the Euro is to survive, this will require both better ways to resolve debt crises and stronger, market-based incentives that prevent debt problems from occurring in the first place.
To address these problems, policy proposals are presented at two levels: for the Euro area, and globally. A Euro area sovereign debt restructuring regime could be developed by amending the Treaty establishing the European Stability Mechanism (ESM). This would both restrict the scope for lending to highly indebted countries without also restructuring their debts, and protect Euro area members receiving ESM financial assistance from legal action by holdout creditors. At the global level, a number of proposals are discussed, ranging from a coordinated introduction of aggregate collective action clauses that would allow a supermajority of bondholders across all bonds to amend bond payment terms to an amendment of the IMF articles that would limit the legal remedies of holdouts when a debt restructuring proposal has been accepted both by a majority of creditors and endorsed by the IMF
Reconstruction of time-dependent coefficients: a check of approximation schemes for non-Markovian convolutionless dissipative generators
We propose a procedure to fully reconstruct the time-dependent coefficients
of convolutionless non-Markovian dissipative generators via a finite number of
experimental measurements. By combining a tomography based approach with a
proper data sampling, our proposal allows to relate the time-dependent
coefficients governing the dissipative evolution of a quantum system to
experimentally accessible quantities. The proposed scheme not only provides a
way to retrieve full information about potentially unknown dissipative
coefficients but also, most valuably, can be employed as a reliable consistency
test for the approximations involved in the theoretical derivation of a given
non-Markovian convolutionless master equation.Comment: 11 pages, 4 figures, revised version published on PR
The shape modulation of osteoblast–osteocytetransformation and its correlationwith the fibrillar organization in secondary osteons: A SEM study employing the graded osmic maceration technique
Cortex fractured surface and graded osmic
maceration techniques were used to study the secretory
activity of osteoblasts, the transformation of osteoblast to
osteocytes, and the structural organization of the matrix
around the cells with scanning electron microscopy (SEM).
A specialized membrane differentiation at the base of the cell
was observed with finger-like, flattened processes which
formed a diffuse meshwork. These findings suggested that
this membrane differentiation below the cells had not only
functioned in transporting collagen through the membrane
but also in orienting the fibrils once assembled. Thin
ramifications arose from the large and flat membrane
foldings oriented perpendicular to the plane of the osteoblasts.
This meshwork of fine filaments could not be
visualized with SEM because they were obscured within
the matrix substance. Their 3-D structure, however, should
be similar to the canalicular system. The meshwork of large,
flattened processes was no more evident in the cells which
had completed their transformation into osteocytes
Neoplastic tissue transfiguration in vivo by recombinant human transforming growth factor-β3
Human oral squamous cell carcinomas (hSCCs) are the most common head and neck cancers now presenting with more aggressive biological and clinical features due to smoking and alcohol together with widespread viremia. Transforming growth factor-β (TGF-β) proteins are powerful morphogens that induce rapid and substantial induction of endochondral bone formation but in primates only
Using the GPU to Green an Intensive and Massive Computation System
In this paper, we present the early results of an ongoing project aimed at giving an existing software system a more eco-sustainable lease of life. We defined a strategy and a process for migrating a subject system that performs intensive and massive computation to a Graphics Processing Unit (GPU) based architecture. We validated our solutions on a software system for path finding robot simulations. An initial comparison on the energy consumption of the original system and the greened one has been also executed. The obtained results suggested that the application of our solution produced more eco-sustainable software
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