5,275 research outputs found
Selective constraints on global plankton dispersal
Marine microbial communities are highly interconnected assemblages of organisms shaped by ecological drift, natural selection and dispersal. The relative strength of these forces determines how ecosystems respond to environmental gradients, how much diversity is resident in a community or population at any given time, and how populations reorganise and evolve in response to environmental perturbations. In this study we introduce a globally-resolved population-genetic ocean model in order to examine the interplay of dispersal, selection and adaptive evolution, and their effects on community assembly and global biogeography. We find that environmental selection places strong constraints on global dispersal, even in the face of extremely high assumed rates of adaptation. Changing the relative strengths of dispersal, selection and adaptation has pronounced effects on community assembly in the model, and suggests that barriers to dispersal play a key role in the structuring of marine communities, enhancing global biodiversity and the importance of local historical contingencies
A Descriptive Analysis of Twitter Followership of the Major Political Parties in Nigeria
The role of twitter as one of the most popular social media application for organisations and political parties has been recognized by various scholars. Twitter has been used by parties as a means of sharing information and manifestoes, and also interacting with their followers online. The study was about how the Twitter followership of major political parties in Nigeria has changed since the 2015 elections. The major political parties for this study were the All Progressive Congress, APC and the Peoples Democratic Party, PDP. An internet research was carried out using the Twitter platforms for the APC and PDP. The research showed that for APC, their growth from 2014 to 2015 was “fairly significant” from 49 followers in 2014 to 244 followers in 2015, while the PDP recorded a “very significant” growth from 5839 in 2014 to 79,516 in 2015. Even though the result showed that the APC recorded a growth on Twitter, they are significantly lagging behind on the follower count as their aggregate Twitter followers are less than the number of voters that make up a polling unit in Nigeria. The surprising fact here is that APC defeated the PDP in the Nigerian presidential election of 2015 by over 3 million votes, yet is trailing the PDP on Twitter, we then have to ask if Nigerian voters have apathy for Twitter? It is recommended that further studies be carried out to ascertain what motivates political parties in Nigeria to use Twitter if as this research has shown there is no correlation between Twitter use and earned votes. Keywords: Twitter, Social Media, Political Parties, APC, PDP, Nigeria
Delayed effects of transcriptional responses in Mycobacterium tuberculosis exposed to nitric oxide suggest other mechanisms involved in survival.
Mycobacterium tuberculosis has succeeded as a human pathogen for tens of thousands of years thanks to its ability to resist and adapt to the adverse conditions it encounters upon infection. Bacterial adaptation to stress is commonly viewed in the context of transcriptional regulation, with the implicit expectation that an initial transcriptomic response is tightly coupled to an ensuing proteomic response. However, after challenging M. tuberculosis with nitric oxide we found that the rapid transcriptional responses, detectable within minutes of nitric oxide exposure, typically took several hours to manifest on the protein level. Furthermore, early proteomic responses were dominated by the degradation of a set of proteins, specifically those containing damaged iron-sulphur clusters. Overall, our findings are consistent with transcriptional responses participating mostly in late-stage recovery rather than in generating an immediate resistance to nitric oxide stress, suggesting that survival of M. tuberculosis under acute stress is contingent on mechanisms other than transcriptional regulation. These findings provide a revised molecular understanding of an important human pathogen
A linguistic approach to the psychosis continuum: (dis)similarities and (dis)continuities in how clinical and non-clinical voice-hearers talk about their voices
Introduction: “Continuum” approaches to psychosis have generated reports of similarities and differences in voice-hearing in clinical and non-clinical populations at the cohort level, but not typically examined overlap or degrees of difference between groups. Methods: We used a computer-aided linguistic approach to explore reports of voice-hearing by a clinical group (Early Intervention in Psychosis service-users; N = 40) and a non-clinical group (spiritualists; N = 27). We identify semantic categories of terms statistically overused by one group compared with the other, and by each group compared to a control sample of non-voice-hearing interview data (log likelihood (LL) value 6.63+=p < .01; effect size measure: log ratio 1.0+). We consider whether individual values support a continuum model. Results: Notwithstanding significant cohort-level differences, there was considerable continuity in language use. Reports of negative affect were prominent in both groups (p < .01, log ratio: 1.12+). Challenges of cognitive control were also evident in both cohorts, with references to “disengagement” accentuated in service-users (p < .01, log ratio: 1.14+). Conclusion: A corpus linguistic approach to voice-hearing provides new evidence of differences between clinical and non-clinical groups. Variability at the individual level provides substantial evidence of continuity with implications for cognitive mechanisms underlying voice-hearing
Front Stability in Mean Field Models of Diffusion Limited Growth
We present calculations of the stability of planar fronts in two mean field
models of diffusion limited growth. The steady state solution for the front can
exist for a continuous family of velocities, we show that the selected velocity
is given by marginal stability theory. We find that naive mean field theory has
no instability to transverse perturbations, while a threshold mean field theory
has such a Mullins-Sekerka instability. These results place on firm theoretical
ground the observed lack of the dendritic morphology in naive mean field theory
and its presence in threshold models. The existence of a Mullins-Sekerka
instability is related to the behavior of the mean field theories in the
zero-undercooling limit.Comment: 26 pp. revtex, 7 uuencoded ps figures. submitted to PR
Crossover from Rate-Equation to Diffusion-Controlled Kinetics in Two-Particle Coagulation
We develop an analytical diffusion-equation-type approximation scheme for the
one-dimensional coagulation reaction A+A->A with partial reaction probability
on particle encounters which are otherwise hard-core. The new approximation
describes the crossover from the mean-field rate-equation behavior at short
times to the universal, fluctuation-dominated behavior at large times. The
approximation becomes quantitatively accurate when the system is initially
close to the continuum behavior, i.e., for small initial density and fast
reaction. For large initial density and slow reaction, lattice effects are
nonnegligible for an extended initial time interval. In such cases our
approximation provides the correct description of the initial mean-field as
well as the asymptotic large-time, fluctuation-dominated behavior. However, the
intermediate-time crossover between the two regimes is described only
semiquantitatively.Comment: 21 pages, plain Te
Efficient Computation of Dendritic Microstructures using Adaptive Mesh Refinement
We study dendritic microstructure evolution using an adaptive grid, finite
element method applied to a phase-field model. The computational complexity of
our algorithm, per unit time, scales linearly with system size, rather than the
quadratic variation given by standard uniform mesh schemes. Time-dependent
calculations in two dimensions are in good agreement with the predictions of
solvability theory, and can be extended to three dimensions and small
undercoolingsComment: typo in a parameter of Fig. 1; 4 pages, 4 postscript figures, in
LateX, (revtex
Array-Based FMR1 Sequencing and Deletion Analysis in Patients with a Fragile X Syndrome–Like Phenotype
Background: Fragile X syndrome (FXS) is caused by loss of function mutations in the FMR1 gene. Trinucleotide CGG-repeat expansions, resulting in FMR1 gene silencing, are the most common mutations observed at this locus. Even though the repeat expansion mutation is a functional null mutation, few conventional mutations have been identified at this locus, largely due to the clinical laboratory focus on the repeat tract. Methodology/Principal Findings: To more thoroughly evaluate the frequency of conventional mutations in FXS-like patients, we used an array-based method to sequence FMR1 in 51 unrelated males exhibiting several features characteristic of FXS but with normal CGG-repeat tracts of FMR1. One patient was identified with a deletion in FMR1, but none of the patients were found to have other conventional mutations. Conclusions/Significance: These data suggest that missense mutations in FMR1 are not a common cause of the FXS phenotype in patients who have normal-length CGG-repeat tracts. However, screening for small deletions of FMR1 may be of clinically utility
Towards a quantitative phase-field model of two-phase solidification
We construct a diffuse-interface model of two-phase solidification that
quantitatively reproduces the classic free boundary problem on solid-liquid
interfaces in the thin-interface limit. Convergence tests and comparisons with
boundary integral simulations of eutectic growth show good accuracy for
steady-state lamellae, but the results for limit cycles depend on the interface
thickness through the trijunction behavior. This raises the fundamental issue
of diffuse multiple-junction dynamics.Comment: 4 pages, 2 figures. Better final discussion. 1 reference adde
New partnerships for co-delivery of the 2030 agenda for sustainable development
Partnerships have become a corner stone of contemporary research that recognizes working across disciplines and co-production with intended users as essential to enabling sustainable resilience-building. Furthermore, research that addresses sustainable development challenges brings an urgent need to reflect on the ways that partnerships are supported, and for the disaster risk management and resilience communities, efforts to support realization of the wider 2030 Agenda for sustainable development bring particular pressures. In November 2019, the UK Disasters Research Group (DRG) brought together a number of key stakeholders focused on disaster risk, resilience, and sustainability research relevant to Official Development Assistance to consider how fit for purpose existing partnership models are for the pace of change required to deliver the priorities of the wider 2030 Agenda. Participants were invited to discuss how research partnerships across three levels (individual and project-based; national and institutional; and international) could be improved based on elements that facilitate robust partnerships and learning from aspects that hinder them. From the discussions, participants emphasized the importance of effective communication mechanisms in building partnerships, co-designing projects, and establishing shared objectives. Enhanced approaches to addressing equitable partnerships and funding more substantive timelines will be key to responding to the challenges of the 2030 Agenda
- …