23 research outputs found
Demography-based adaptive network model reproduces the spatial organization of human linguistic groups
The distribution of human linguistic groups presents a number of interesting
and non-trivial patterns. The distributions of the number of speakers per
language and the area each group covers follow log-normal distributions, while
population and area fulfill an allometric relationship. The topology of
networks of spatial contacts between different linguistic groups has been
recently characterized, showing atypical properties of the degree distribution
and clustering, among others. Human demography, spatial conflicts, and the
construction of networks of contacts between linguistic groups are mutually
dependent processes. Here we introduce an adaptive network model that takes all
of them into account and successfully reproduces, using only four model
parameters, not only those features of linguistic groups already described in
the literature, but also correlations between demographic and topological
properties uncovered in this work. Besides their relevance when modeling and
understanding processes related to human biogeography, our adaptive network
model admits a number of generalizations that broaden its scope and make it
suitable to represent interactions between agents based on population dynamics
and competition for space
Phase behavior of parallel hard cylinders
We test the performance of a recently proposed fundamental measure density
functional of aligned hard cylinders by calculating the phase diagram of a
monodisperse fluid of these particles. We consider all possible liquid
crystalline symmetries, namely nematic, smectic and columnar, as well as the
crystalline phase. For this purpose we introduce a Gaussian parameterization of
the density profile and use it to minimize numerically the functional. We also
determine, from the analytic expression for the structure factor of the uniform
fluid, the bifurcation points from the nematic to the smectic and columnar
phases. The equation of state, as obtained from functional minimization, is
compared to the available Monte Carlo simulation. The agreement is is very
good, nearly perfect in the description of the inhomogeneous phases. The
columnar phase is found to be metastable with respect to the smectic or crystal
phases, its free energy though being very close to that of the stable phases.
This result justifies the observation of a window of stability of the columnar
phase in some simulations, which disappears as the size of the system
increases. The only important deviation between theory and simulations shows up
in the location of the nematic-smectic transition. This is the common drawback
of any fundamental measure functional of describing the uniform phase just with
the accuracy of scaled particle theory.Comment: 17 pages, 5 figure
Integrability of Stochastic Birth-Death processes via Differential Galois Theory
Stochastic birth-death processes are described as continuous-time Markov
processes in models of population dynamics. A system of infinite, coupled
ordinary differential equations (the so-called master equation) describes the
time-dependence of the probability of each system state. Using a generating
function, the master equation can be transformed into a partial differential
equation. In this contribution we analyze the integrability of two types of
stochastic birth-death processes (with polynomial birth and death rates) using
standard differential Galois theory. We discuss the integrability of the PDE
via a Laplace transform acting over the temporal variable. We show that the PDE
is not integrable except for the (trivial) case in which rates are linear
functions of the number of individuals
Competitive dominance in plant communities: Modeling approaches and theoretical predictions
Quantitative predictions about the processes that promote species coexistence
are a subject of active research in ecology. In particular, competitive
interactions are known to shape and maintain ecological communities, and
situations where some species out-compete or dominate over some others are key
to describe natural ecosystems. Here we develop ecological theory using a
stochastic, synthetic framework for plant community assembly that leads to
predictions amenable to empirical testing. We propose two stochastic
continuous-time Markov models that incorporate competitive dominance through a
hierarchy of species heights. The first model, which is spatially implicit,
predicts both the expected number of species that survive and the conditions
under which heights are clustered in realized model communities. The second one
allows spatially-explicit interactions of individuals and alternative
mechanisms that can help shorter plants overcome height-driven competition, and
it demonstrates that clustering patterns remain not only locally but also
across increasing spatial scales. Moreover, although plants are actually
height-clustered in the spatially-explicit model, it allows for plant species
abundances not necessarily skewed to taller plants
The struggle for space: Viral extinction through competition for cells
The design of protocols to suppress the propagation of viral infections is an
enduring enterprise, especially hindered by limited knowledge of the mechanisms
through which extinction of infection propagation comes about. We here report
on a mechanism causing extinction of a propagating infection due to
intraspecific competition to infect susceptible hosts. Beneficial mutations
allow the pathogen to increase the production of progeny, while the host cell
is allowed to develop defenses against infection. When the number of
susceptible cells is unlimited, a feedback runaway co-evolution between host
resistance and progeny production occurs. However, physical space limits the
advantage that the virus can obtain from increasing offspring numbers, thus
infection clearance may result from an increase in host defenses beyond a
finite threshold. Our results might be relevant to better understand
propagation of viral infections in tissues with mobility constraints, and the
implications that environments with different geometrical properties might have
in devising control strategies.Comment: 4 pages, 3 figures Accepted for publication in Physical Review
Letter
Abnormalities on 1q and 7q are associated with poor outcome in sporadic Burkitt's lymphoma. A cytogenetic and comparative genomic hybridization study
Comparative genomic hybridization (CGH) studies have demonstrated a high incidence of chromosomal imbalances in non-Hodgkin's lymphoma. However, the information on the genomic imbalances in Burkitt's Lymphoma (BL) is scanty. Conventional cytogenetics was performed in 34 cases, and long-distance PCR for t(8;14) was performed in 18 cases. A total of 170 changes were present with a median of four changes per case (range 1-22). Gains of chromosomal material (143) were more frequent than amplifications (5) or losses (22). The most frequent aberrations were gains on chromosomes 12q (26%), Xq (22%), 22q (20%), 20q (17%) and 9q (15%). Losses predominantly involved chromosomes 13q (17%) and 4q (9%). High-level amplifications were present in the regions 1q23-31 (three cases), 6p12-p25 and 8p22-p23. Upon comparing BL vs Burkitt's cell leukemia (BCL), the latter had more changes (mean 4.3 +/- 2.2) than BL (mean 2.7 +/- 3.2). In addition, BCL cases showed more frequently gains on 8q, 9q, 14q, 20q, and 20q, 9q, 8q and 14q, as well as losses on 13q and 4q. Concerning outcome, the presence of abnormalities on 1q (ascertained either by cytogenetics or by CGH), and imbalances on 7q (P=0.01) were associated with a short survival
Comparison of seven prognostic tools to identify low-risk pulmonary embolism in patients aged <50 years
publishersversionPeer reviewe
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Abstract
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries