Spatial epidemics with large finite range

1996 ◽  
Vol 33 (4) ◽  
pp. 933-939 ◽  
Author(s):  
Mathew D. Penrose

In the epidemic with removal with range r, each site z, once infected, remains so for a period of time Tz, the variables Tz being i.i.d. with mean μ. While infected, a site infects its healthy r-neighbours independently at total rate α. After infection, sites become immune. We show that the critical rate of infection αc (r), above which an epidemic starting from a single site may continue forever, converges to μ–1 as r →∞.

1996 ◽  
Vol 33 (04) ◽  
pp. 933-939
Author(s):  
Mathew D. Penrose

In the epidemic with removal with range r, each site z , once infected, remains so for a period of time Tz , the variables Tz being i.i.d. with mean μ. While infected, a site infects its healthy r-neighbours independently at total rate α. After infection, sites become immune. We show that the critical rate of infection αc (r), above which an epidemic starting from a single site may continue forever, converges to μ –1 as r →∞.


2012 ◽  
Vol 65 (7) ◽  
pp. 1151-1157 ◽  
Author(s):  
Catherine Blanchet ◽  
Gabriel Maltais-Landry ◽  
Roxane Maranger

Submerged aquatic vegetation (SAV) may serve as an integrative proxy of spatial and temporal nitrogen (N) availability in aquatic ecosystems as plants are physiologically capable of storing variable amounts of N. However, it is important to understand whether plant species behave similarly or differently within and among systems. We sampled different SAV species along a nutrient gradient at multiple sites within several lakes to determine variability in C:N ratios and % N content among species, among plants of the same species at a single site, among sites and among lakes. Species respond differently suggesting that not all plant types can be used universally as nutrient proxies. The greatest variability in % N and C:N ratios for Valliseneria americana was observed among lakes whereas for Elodea canadensis it was among sites within a lake and among plants within a site. This suggests that V. americana could be a particularly useful indicator of N availability at larger spatial scales (regional and within a large fluvial lake) but that E. canadensis was not a particularly useful proxy.


Africa ◽  
2018 ◽  
Vol 88 (2) ◽  
pp. 332-351 ◽  
Author(s):  
Ferdinand de Jong ◽  
Brian Valente-Quinn

AbstractRuination has recently received much attention as a defining aspect of the materiality of modernity. Less attention is given to the processes of regeneration that occur within sites of ruination. In this article, we examine how processes of ruination and regeneration are folded into each other, by looking at the materiality of a single site, a small village in the vicinity of Dakar, Senegal. By building the University of the African Future at Sébikotane, the Senegalese president has sought to rekindle the spirit of excellence that inspired education at the École normale William Ponty in a Pan-African spirit. As part of a larger plan for urban expansion, the site of Sébikotane has inspired hope for development. Examining how the different temporalities of utopian modernism and Afro-nostalgia intersect in the ruined site, this article reflects on the ruination of African futures on a site of ever renascent utopian infrastructures.


Author(s):  
Lynne Goldstein

In their Introduction to this volume, the editors note that the contextual analysis of cremation requires an understanding that is broader and more complex than we generally assume. This chapter examines what has been termed a crematory at one site, and tries to determine the accuracy of this label and its cultural implications. The research included in this chapter is not European in focus, but instead looks at the North American site of Aztalan in southern Wisconsin. Aztalan has been excavated, studied, and interpreted over a period of more than 150 years, and serves as a useful contrast to some of the European sites in this volume because research at Aztalan has drawn on different kinds of analogies, modern allusions, and different histories of development of archaeological method and theory. However, because Aztalan is also a site that represents a widespread, structured, complex, agriculturally based society, it should provide a useful comparison with similar European groups, and expand the range of understanding and examples of cremation and fiery technologies. Of course, there is not a formal link between this site and those in Europe, but many of the same kinds of processes, and especially modern allusions and interpretations, apply to both. A discussion of cremation, copper working, and fiery displays is presented first, followed by details of the Aztalan example and the feature originally labelled a crematory (Rowe 1958). Following this, an outline of the range of Aztalan mortuary practices and pertinent ethnographic and ethnohistoric data highlights the importance of both copper and fire in the Mississippian context. Rather than simply looking at the Aztalan structure as an alternative mortuary location, this chapter tries to place the feature contextually in a much broader social, physical, landscape, and behavioural frame. Since 2000, archaeological approaches to the analysis of mortuary sites have become more sophisticated, both theoretically and analytically. In this process, scholars have begun to focus on the fact that cremation practices have often been presented and interpreted as nothing more than an alternative mortuary practice, and the presence of both cremation and inhumation in a single site is often seen as representing no more than choice or a reflection of changing practices over time.


Open Biology ◽  
2017 ◽  
Vol 7 (12) ◽  
pp. 170247 ◽  
Author(s):  
Nikola S. Dzhindzhev ◽  
George Tzolovsky ◽  
Zoltan Lipinszki ◽  
Mohammed Abdelaziz ◽  
Janus Debski ◽  
...  

The conserved process of centriole duplication requires Plk4 kinase to recruit and promote interactions between Sas6 and Sas5/Ana2/STIL (respective nomenclature of worms/flies/humans). Plk4-mediated phosphorylation of Ana2/STIL in its conserved STAN motif has been shown to promote its interaction with Sas6. However, STAN motif phosphorylation is not required for recruitment of Ana2 to the centriole. Here we show that in Drosophila , Ana2 loads onto the site of procentriole formation ahead of Sas6 in a process that also requires Plk4. However, whereas Plk4 is first recruited to multiple sites around the ring of zone II at the periphery of the centriole, Ana2 is recruited to a single site in telophase before Plk4 becomes finally restricted to this same single site. When we over-ride the auto-destruction of Plk4, it remains localized to multiple sites in the outer ring of the centriole and, if catalytically active, recruits Ana2 to these sites. Thus, it is the active form of Plk4 that promotes Ana2's recruitment to the centriole. We now show that Plk4 phosphorylates Ana2 at a site other than the STAN motif, which lies in a conserved region we term the ANST (ANa2-STil) motif. Mutation of this site, S38, to a non-phosphorylatable residue prevents the procentriole loading of Ana2 and blocks centriole duplication. Thus the initiation of procentriole formation requires Plk4 to first phosphorylate a single serine residue in the ANST motif to promote Ana2's recruitment and, secondly, to phosphorylate four residues in the STAN motif enabling Ana2 to recruit Sas6. We discuss these findings in light of the multiple Plk4 phosphorylation sites on Ana2.


2021 ◽  
Author(s):  
Chris Sweetapple ◽  
Matthew John Wade ◽  
Jasmine M. S. Grimsley ◽  
Joshua T. Bunce ◽  
Peter Melville-Shreeve ◽  
...  

This paper aims to determine whether population normalisation significantly alters the SARS-CoV-2 trends revealed by wastewater-based epidemiology, and whether it is beneficial and/or necessary to provide an understanding of prevalence from wastewater SARS-CoV-2 concentrations. It uses wastewater SARS-CoV-2 data collected from 394 sampling sites, and implements normalisation based on concentrations of a) ammoniacal nitrogen, and b) orthophosphate. Wastewater SARS-CoV-2 metrics are evaluated at a site and aggregated level against three indicators prevalence, based on positivity rates from the Office for National Statistics Coronavirus Infection Survey and test results reported by NHS Test and Trace. Normalisation is shown to have little impact on the overall trends in the wastewater SARS-CoV-2 data on average. However, significant variability between the impact of population normalisation at different sites, which is not evident from previous WBE studies focussed on a single site, is also revealed. Critically, it is demonstrated that while the impact of normalisation on SARS-CoV-2 trends is small on average, it is not reasonable to conclude that it is always insignificant. When averaged across many sites, normalisation strengthens the correlation between wastewater SARS-CoV-2 data and indicators of prevalence; however, confidence in the improvement is low. Lastly, it is noted that most data were collected during periods of national lockdown and/or local restrictions, and thus the impacts and benefits of population normalisation are expected to be higher when normal travel habits resume.


1991 ◽  
Vol 253 ◽  
Author(s):  
Stephen C. Lovatt ◽  
B.L. Gyorffy ◽  
Guang-Yu Guo

ABSTRACTWe study the scattering solutions of the Dirac equation numerically for anisotropic, finite range (warped muffin-tin), potentials. In particular, we calculate the partial-wave scattering matrix, ƒAA'(ε) and S-matrix SAA′(ε), for a potential characteristic of crystalline Silicon. We illustrate the consequences of aspherical scattering with reference to Silicon.


Genetics ◽  
1988 ◽  
Vol 118 (2) ◽  
pp. 193-202
Author(s):  
M S Ciampi ◽  
J R Roth

Abstract A single site in the middle of the coding sequence of the hisG gene of Salmonella is required for most of the polar effect of mutations in this gene. Nonsense and insertion mutations mapping upstream of this point in the hisG gene all have strong polar effects on expression of downstream genes in the operon; mutations mapping promotor distal to this site have little or no polar effect. Two previously known hisG mutations, mapping in the region of the polarity site, abolish the polarity effect of insertion mutations mapping upstream of this region. New polarity site mutations have been selected which have lost the polar effect of upstream nonsense mutations. All mutations abolishing the function of the site are small deletions; three are identical, 28-bp deletions which have arisen independently. A fourth mutation is a deletion of 16 base pairs internal to the larger deletion. Several point mutations within this 16-bp region have no effect on the function of the polarity site. We believe that a small number of polarity sites of this type are responsible for polarity in all genes. The site in the hisG gene is more easily detected than most because it appears to be the only such site in the hisG gene and because it maps in the center of the coding sequence.


2016 ◽  
Vol 53 (3) ◽  
pp. 925-929
Author(s):  
Achillefs Tzioufas

AbstractWe consider translation-invariant, finite-range, supercritical contact processes. We show the existence of unbounded space-time cones within which the descendancy of the process from full occupancy may with positive probability be identical to that of the process from the single site at its apex. The proof comprises an argument that leans upon refinements of a successful coupling among these two processes, and is valid in d-dimensions.


2018 ◽  
Vol 46 (12) ◽  
pp. 6229-6237 ◽  
Author(s):  
Ishtiyaq Ahmad ◽  
Manasi Kulkarni ◽  
Aathira Gopinath ◽  
Kayarat Saikrishnan

Sign in / Sign up

Export Citation Format

Share Document