scholarly journals Circular stochastic fluctuations in SIS epidemics with heterogeneous contacts among sub-populations

2012 ◽  
Vol 81 (3) ◽  
pp. 223-231 ◽  
Author(s):  
Jia-Zeng Wang ◽  
Min Qian ◽  
Hong Qian
Keyword(s):  
Stochastic Fluctuations ◽  
Sis Epidemics

scholarly journals Orthogonal control of mean and variability of endogenous genes in a human cell line

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Alain R. Bonny ◽  
João Pedro Fonseca ◽  
Jesslyn E. Park ◽  
Hana El-Samad
Keyword(s):  
Mammalian Cells ◽  
Human Cell Line ◽  
Transcriptional Level ◽  
Clear Understanding ◽  
Gene Expression Noise ◽  
Endogenous Gene ◽  
Basal Expression ◽  
Stochastic Fluctuations ◽  
Human Genes ◽  
Synthetic Circuit

AbstractStochastic fluctuations at the transcriptional level contribute to isogenic cell-to-cell heterogeneity in mammalian cell populations. However, we still have no clear understanding of the repercussions of this heterogeneity, given the lack of tools to independently control mean expression and variability of a gene. Here, we engineer a synthetic circuit to modulate mean expression and heterogeneity of transgenes and endogenous human genes. The circuit, a Tunable Noise Rheostat (TuNR), consists of a transcriptional cascade of two inducible transcriptional activators, where the output mean and variance can be modulated by two orthogonal small molecule inputs. In this fashion, different combinations of the inputs can achieve the same mean but with different population variability. With TuNR, we achieve low basal expression, over 1000-fold expression of a transgene product, and up to 7-fold induction of the endogenous gene NGFR. Importantly, for the same mean expression level, we are able to establish varying degrees of heterogeneity in expression within an isogenic population, thereby decoupling gene expression noise from its mean. TuNR is therefore a modular tool that can be used in mammalian cells to enable direct interrogation of the implications of cell-to-cell variability.

Rational Design of Novel Materials From Polymer Microrheology

2010 ◽  
Author(s):  
Rodrigo E. Teixeira ◽  
Richard S. Graham
Keyword(s):  
Rational Design ◽  
Molecular Level ◽  
Pressure Vessels ◽  
Novel Materials ◽  
Entangled Polymers ◽  
Stochastic Fluctuations ◽  
Safety Margins ◽  
Polymer Liquids ◽  
Entangled Polymer ◽  
High Degree

The visco-elastic properties of entangled polymer liquids arise from molecular-scale topological interactions and stochastic fluctuations under flow. Here, the evolutions of individual entangled polymers were observed in rheologically relevant shear flow histories. We uncover a high degree of molecular individualism and broad conformational distributions resulting from incessant stretch-collapse cycles. The data and insights of the present study may lead to improved molecular-level models and constitutive equations. These tools, in turn, may enable the rational design of novel materials with properties tailored to accomplish specific tasks such as high-pressure vessels and piping with greater safety margins and cost-effectiveness.

scholarly journals Modeling the Variability of Drop Size Distributions in Space and Time

2007 ◽  
Vol 46 (6) ◽  
pp. 742-756 ◽  
Author(s):  
Gyu Won Lee ◽  
Alan W. Seed ◽  
Isztar Zawadzki
Keyword(s):  
Drop Size ◽  
Temporal Structure ◽  
Space Time ◽  
Cascade Model ◽  
Time Variability ◽  
Size Distributions ◽  
Precipitation Field ◽  
Stochastic Fluctuations ◽  
Taylor Hypothesis ◽  
Drop Size Distributions

Abstract The information on the time variability of drop size distributions (DSDs) as seen by a disdrometer is used to illustrate the structure of uncertainty in radar estimates of precipitation. Based on this, a method to generate the space–time variability of the distributions of the size of raindrops is developed. The model generates one moment of DSDs that is conditioned on another moment of DSDs; in particular, radar reflectivity Z is used to obtain rainfall rate R. Based on the fact that two moments of the DSDs are sufficient to capture most of the DSD variability, the model can be used to calculate DSDs and other moments of interest of the DSD. A deterministic component of the precipitation field is obtained from a fixed R–Z relationship. Two different components of DSD variability are added to the deterministic precipitation field. The first represents the systematic departures from the fixed R–Z relationship that are expected from different regimes of precipitation. This is generated using a simple broken-line model. The second represents the fluctuations around the R–Z relationship for a particular regime and uses a space–time multiplicative cascade model. The temporal structure of the stochastic fluctuations is investigated using disdrometer data. Assuming Taylor hypothesis, the spatial structure of the fluctuations is obtained and a stochastic model of the spatial distribution of the DSD variability is constructed. The consistency of the model is validated using concurrent radar and disdrometer data.

scholarly journals Synchronization-induced persistence versus selection for habitats in spatially coupled ecosystems

2013 ◽  
Vol 10 (87) ◽  
pp. 20130559 ◽  
Author(s):  
Adam Lampert ◽  
Alan Hastings
Keyword(s):  
Phase Transitions ◽  
Stochastic Systems ◽  
Environmental Changes ◽  
Heterogeneous Environments ◽  
Migration Rates ◽  
Stochastic Fluctuations ◽  
Key Factor ◽  
Spatially Extended ◽  
Unique Method ◽  
Selection For

Critical population phase transitions, in which a persistent population becomes extinction-prone owing to environmental changes, are fundamentally important in ecology, and their determination is a key factor in successful ecosystem management. To persist, a species requires a suitable environment in a sufficiently large spatial region. However, even if this condition is met, the species does not necessarily persist, owing to stochastic fluctuations. Here, we develop a model that allows simultaneous investigation of extinction due to either stochastic or deterministic reasons. We find that even classic birth–death processes in spatially extended ecosystems exhibit phase transitions between extinction-prone and persistent populations. Sometimes these are first-order transitions, which means that environmental changes may result in irreversible population collapse. Moreover, we find that higher migration rates not only lead to higher robustness to stochastic fluctuations, but also result in lower sustainability in heterogeneous environments by preventing efficient selection for suitable habitats. This demonstrates that intermediate migration rates are optimal for survival. At low migration rates, the dynamics are reduced to metapopulation dynamics, whereas at high migration rates, the dynamics are reduced to a multi-type branching process. We focus on species persistence, but our results suggest a unique method for finding phase transitions in spatially extended stochastic systems in general.

Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths

Parasitology ◽  
1995 ◽  
Vol 111 (4) ◽  
pp. 531-536 ◽  
Author(s):  
A. Saul
Keyword(s):  
Genetic Drift ◽  
Computer Model ◽  
Genetic Heterogeneity ◽  
Host Selection ◽  
Selection Pressure ◽  
Intestinal Helminths ◽  
Infection Rates ◽  
Stochastic Fluctuations ◽  
Stochastic Simulation Model ◽  
Selection Of

SUMMARYA stochastic simulation model of the transmission and maintenance of genetic heterogeneity in the absence and presence of external selection pressures is presented for polygamous intestinal helminths such as Ascaris. The model assumes that the density distribution of the adult parasites is highly aggregated and that density-dependent effects on fecundity are important. The model gives rise to stable infection rates in the host. Where the parasite population contains genetic heterogeneity, with the exception of stochastic fluctuations which models genetic drift, the ratio of the different alleles remained constant over extended periods of time. This result contrasts with that of an earlier analytical model (Anderson, R. M., May, M. R. & Gutpa S. (1989) Parasitology 99, S59–S79), in which uneven mating probabilities for the different combinations of worm possible in a host was postulated to inevitably lead to fixation of the most abundant allele. New results suggest that in spite of the restricted choice of mating available to a worm in the confines of a host, selection pressure always leads to enrichment of the parasites carrying resistant alleles.

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