Current fluctuations in a partially asymmetric simple exclusion process with a defect particle.

We study an exclusion process on a ring comprising a free defect particle in a bath of normal particles. The model is one of the few integrable cases in which the bath particles are partially asymmetric. The presence of the free defect creates localized or shock phases according to parameter values. We use a functional approach to Bethe equations resulting from a nested Bethe ansatz to calculate exactly the mean currents and diffusion constants. The results agree very well with Monte Carlo simulations and reveal the main modes of fluctuation in the different phases of the steady state.

Determinants of vaccine acceptance, knowledge, attitude, and prevention practices against COVID-19 among governmental healthcare workers in Addis Ababa and Adama, Ethiopia: A cross-sectional study.

Background and Aims: COVID-19 vaccines are vital tools for infection prevention and control of the pandemic. However, coronavirus immunization requires acceptance among healthcare workforces and by the community. In Ethiopia, studies focused on determinants of vaccine acceptance, knowledge, attitude, and prevention practices (KAP) contrary to the novel coronavirus among healthcare staff are limited. Hence, closing this gap requires research. Methods: A cross-sectional study was conducted on 844 governmental healthcare workers. A stratified, simple random sampling technique was used to select the respondents. Data were collected using a structured questionnaire. Binary and multivariable logistic regression statistical models were used to analyze the data. Results: This study indicated that only 57.9% of the participants had good COVID-19 vaccine acceptance, meaning they took at least a dose of the vaccine themselves. We found that 65%, 60.9%, and 51.3% of the participants had good knowledge, prevention practices, and attitude against the pandemic. The novel coronavirus vaccine acceptance rate was 2.19 times more likely among females (adjusted odds ratio [AOR] = 2.19 with 95% confidence interval [CI]: 1.54-3.10) than among male participants. Further, respondents who did not report having any chronic diseases were 9.40 times higher to accept COVID-19 vaccines (AOR = 9.40 with 95% CI: 4.77, 18.53) than those who reported having a chronic condition. However, healthcare workers who had a habit of chewing khat at least once per week were 4% less likely to take the vaccine (AOR = 0.04 with 95% CI: 0.01, 0.32) than those who had no habit of chewing khat. Conclusion: Many core factors influencing COVID-19 vaccine acceptance were identified. A significant number of participants had poor vaccine acceptance, KAP against COVID-19. Therefore, the government should adopt urgent and effective public health measures, including public campaigns to enhance public trust in COVID-19 vaccines. In addition, continuous, timely, and practical training should be provided to healthcare workers.

Universal properties of active membranes.

We put forward a general field theory for nearly flat fluid membranes with embedded activators and analyze their critical properties using renormalization group techniques. Depending on the membrane-activator coupling, we find a crossover between acoustic and diffusive scaling regimes, with mean-field dynamical critical exponents z=1 and 2, respectively. We argue that the acoustic scaling, which is exact in all spatial dimensions, leads to an early-time behavior, which is representative of the spatiotemporal patterns observed at the leading edge of motile cells, such as oscillations superposed on the growth of the membrane width. In the case of mean-field diffusive scaling, one-loop corrections to the mean-field exponents reveal universal behavior distinct from the Kardar-Parisi-Zhang scaling of passive interfaces and signs of strong-coupling behavior.

Renormalization group study of the dynamics of active membranes: Universality classes and scaling laws.

Motivated by experimental observations of patterning at the leading edge of motile eukaryotic cells, we introduce a general model for the dynamics of nearly-flat fluid membranes driven from within by an ensemble of activators. We include, in particular, a kinematic coupling between activator density and membrane slope which generically arises whenever the membrane has a nonvanishing normal speed. We unveil the phase diagram of the model by means of a perturbative field-theoretical renormalization group analysis. Due to the aforementioned kinematic coupling the natural early-time dynamical scaling is acoustic, that is the dynamical critical exponent is 1. However, as soon as the the normal velocity of the membrane is tuned to zero, the system crosses over to diffusive dynamic scaling in mean field. Distinct critical points can be reached depending on how the limit of vanishing velocity is realized: in each of them corrections to scaling due to nonlinear coupling terms must be taken into account. The detailed analysis of these critical points reveals novel scaling regimes which can be accessed with perturbative methods, together with signs of strong coupling behavior, which establishes a promising ground for further nonperturbative calculations. Our results unify several previous studies on the dynamics of active membrane, while also identifying nontrivial scaling regimes which cannot be captured by passive theories of fluctuating interfaces and are relevant for the physics of living membranes.

Dynamics of ribosomes in mRNA translation under steady- and nonsteady-state conditions.

Recent advances in DNA sequencing and fluorescence imaging have made it possible to monitor the dynamics of ribosomes actively engaged in messenger RNA (mRNA) translation. Here, we model these experiments within the inhomogeneous totally asymmetric simple exclusion process (TASEP) using realistic kinetic parameters. In particular, we present analytic expressions to describe the following three cases: (a) translation of a newly transcribed mRNA, (b) translation in the steady state and, specifically, the dynamics of individual (tagged) ribosomes, and (c) runoff translation after inhibition of translation initiation. In cases (b) and (c) we develop an effective medium approximation to describe many-ribosome dynamics in terms of a single tagged ribosome in an effective medium. The predictions are in good agreement with stochastic simulations.

Trichotomy of awareness, outlook and practice of food handlers towards food and water safety in food establishments in Addis Ababa, Ethiopia.

INTRODUCTION: Food and waterborne diseases are the commonest global public health problems. Specifically, in Ethiopia, public health problems associated with deterioration of food and water safety situations are much more complicated due to poverty, economic and environment related risks. Awareness, outlook and practice of food handlers are the three important factors that play major roles in the occurrence and outbreak of food borne diseases. Therefore, this study aimed to evaluate awareness, outlook and practice of food handlers towards food and water safety. METHODS: Institution based cross sectional study was conducted among food handlers of Addis Ababa city administration. In this study, 416 participants were selected using a stratified, simple random sampling technique; and were interviewed using structured questionnaire. Linear Regression Model and analysis of variance were used for data analysis. RESULTS: In this study, 55.5%, 66.1% and 60.6% of the food handlers had good awareness, outlook and proper hygiene practices respectively. This study revealed that, 17.5% and 23.1% of the respondents did not know about food and water borne disease respectively. Only 39.4% of the participants had proper practice of covering mouth with tidy cloth when they cough. Moreover, 75.7% of the food handlers reported that they did not wear personal protective devices during the working time. Predictor variables like educational status and length of work experience were correlated positively and significantly with awareness. However, being married was correlated negatively with awareness. CONCLUSION: Assessing awareness, outlook and practice of food handlers regarding food and water safety is a vital activity to reduce public health problems. Significant number of food handlers had poor awareness, outlook and practice towards food and water safety. There is a call for enhancing the awareness, outlook and practice of food and water safety to achieve an excellent practice. Better food and water safety policy and firm regulatory actions are needed.

Determinants of Sanitation and Hygiene Status Among Food Establishments in Addis Ababa, Ethiopia.

INTRODUCTION: Despite advancements in food science and technology, foodborne disease remains one of the major public health problems. Poor sanitation and hygiene conditions of food establishments are the major causes for the occurrence of foodborne disease. Therefore, this study aimed to investigate core determinants of sanitation and hygiene status among food establishments. METHODS: Institution-based cross-sectional study design was conducted in Addis Ababa city. A stratified random sampling technique was deployed to select 413 study participants. Data were collected through interview and using observational checklist. Sample size was determined by using a single population proportion formula. To analyze the data, binary logistic regression and multivariable logistic regression analysis was conducted. In all analysis, P-value less than .05 were considered statistically significant. RESULTS: The study revealed that 57.4% of the food establishments were under poor sanitation status. In the multivariable analysis, presence of trained managers on hygiene and sanitation (adjusted odds ratio [AOR] = 6.10 with 95% confidence interval [CI]: 2.41-15.45), presence of renewed licenses (AOR = 3.07 with 95% CI: 1.18-7.99), absence of bureaucratic function to obtain permission to renew the food establishment buildings (AOR = 2.43 with 95% CI: 1.25-4.70), and presence of at least 10-m distance between toilet and kitchen (AOR = 9.19, at 95% CI: 5.63-15.02) were associated significantly with sanitation and hygiene status. CONCLUSIONS: Above average of the food establishments were found to be in poor sanitation and hygiene state. Many core determinant factors that influence sanitation and hygienic status of food establishments were identified. The researchers suggest that formal training on sanitation and hygiene for managers of food establishments should be provided to reduce the occurrence of foodborne diseases. Moreover, strong food and water safety policy and strategy should be promulgated to improve sanitation and hygiene status of food establishments.

Diarrheal disease and associated behavioural factors among food handlers in Addis Ababa, Ethiopia.

INTRODUCTION: Diarrheal diseases are threat everywhere, but its frequency and impact are more severe in developing countries. Diarrhea occurs world-wide and causes 4% of all deaths and 5% of health loss to disability. In 2016, it was the eighth leading cause of mortality. Moreover, data from the World Health Organization indicated that diarrheal diseases are causes for an estimated 2 million deaths annually. Therefore, this study aimed to assess diarrheal diseases and associated behavioural factors. METHOD: An institution based cross-sectional study was conducted. A stratified random sampling method was employed to select 1050 study participants. Participants were interviewed using structured questionnaire. To analysis the data, binary logistic regression and multivariable logistic regression analysis was conducted. RESULTS: The two weeks prevalence of diarrhea was found to be 3.4%. Further, 1.6%, 10.5%, 10.7% and 9% of the food handlers had acute watery diarrhea, cough, an infection of runny nose and incidence of any fever respectively. Regular hand washing after toilet (AOR = 0.13 with 95% CI: 0.024, 0.72), using toilet while wearing protective clothes/gown (AOR = 5.39 with 95% CI; 1.59, 18.32), habit of eating raw beef and raw vegetables (AOR = 6.27 with 95% CI: 1.89-20.78), type of toilet (AOR = 4.07 with 95% CI: 0.29-6.67 were associated significantly with diarrhea. CONCLUSION: This assessment proved to be an essential activity for reduction of community diarrheal diseases, as a significant number of food handlers had diarrhea. Good sanitation, hygiene practice and a healthy lifestyle behavior can prevent diarrhea. A strong political commitment with appropriate budgetary allocation is essential for the control of diarrheal diseases.

Solvable model of a many-filament Brownian ratchet.

We construct and exactly solve a model of an extended Brownian ratchet. The model comprises an arbitrary number of heterogeneous, growing and shrinking filaments which together move a rigid membrane by a ratchet mechanism. The model draws parallels with the dynamics of actin filament networks at the leading edge of the cell. In the model, the filaments grow and contract stochastically. The model also includes forces which derive from a potential dependent on the separation between the filaments and the membrane. These forces serve to attract the filaments to the membrane or generate a surface tension that prevents the filaments from dispersing. We derive an N-dimensional diffusion equation for the N filament-membrane separations, which allows the steady-state probability distribution function to be calculated exactly under certain conditions. These conditions are fulfilled by the physically relevant cases of linear and quadratic interaction potentials. The exact solution of the diffusion equation furnishes expressions for the average velocity of the membrane and critical system parameters for which the system stalls and has zero net velocity. In the case of a restoring force, the membrane velocity grows as the square root of the force constant, whereas it decreases once a surface tension is introduced.

Phenotypic Switching Can Speed up Microbial Evolution.

Stochastic phenotype switching has been suggested to play a beneficial role in microbial populations by leading to the division of labour among cells, or ensuring that at least some of the population survives an unexpected change in environmental conditions. Here we use a computational model to investigate an alternative possible function of stochastic phenotype switching: as a way to adapt more quickly even in a static environment. We show that when a genetic mutation causes a population to become less fit, switching to an alternative phenotype with higher fitness (growth rate) may give the population enough time to develop compensatory mutations that increase the fitness again. The possibility of switching phenotypes can reduce the time to adaptation by orders of magnitude if the "fitness valley" caused by the deleterious mutation is deep enough. Our work has important implications for the emergence of antibiotic-resistant bacteria. In line with recent experimental findings, we hypothesise that switching to a slower growing - but less sensitive - phenotype helps bacteria to develop resistance by providing alternative, faster evolutionary routes to resistance.

Predicting the dynamics of bacterial growth inhibition by ribosome-targeting antibiotics.

Understanding how antibiotics inhibit bacteria can help to reduce antibiotic use and hence avoid antimicrobial resistance-yet few theoretical models exist for bacterial growth inhibition by a clinically relevant antibiotic treatment regimen. In particular, in the clinic, antibiotic treatment is time-dependent. Here, we use a theoretical model, previously applied to steady-state bacterial growth, to predict the dynamical response of a bacterial cell to a time-dependent dose of ribosome-targeting antibiotic. Our results depend strongly on whether the antibiotic shows reversible transport and/or low-affinity ribosome binding ('low-affinity antibiotic') or, in contrast, irreversible transport and/or high affinity ribosome binding ('high-affinity antibiotic'). For low-affinity antibiotics, our model predicts that growth inhibition depends on the duration of the antibiotic pulse, and can show a transient period of very fast growth following removal of the antibiotic. For high-affinity antibiotics, growth inhibition depends on peak dosage rather than dose duration, and the model predicts a pronounced post-antibiotic effect, due to hysteresis, in which growth can be suppressed for long times after the antibiotic dose has ended. These predictions are experimentally testable and may be of clinical significance.

Growth-dependent bacterial susceptibility to ribosome-targeting antibiotics.

Bacterial growth environment strongly influences the efficacy of antibiotic treatment, with slow growth often being associated with decreased susceptibility. Yet in many cases, the connection between antibiotic susceptibility and pathogen physiology remains unclear. We show that for ribosome-targeting antibiotics acting on Escherichia coli, a complex interplay exists between physiology and antibiotic action; for some antibiotics within this class, faster growth indeed increases susceptibility, but for other antibiotics, the opposite is true. Remarkably, these observations can be explained by a simple mathematical model that combines drug transport and binding with physiological constraints. Our model reveals that growth-dependent susceptibility is controlled by a single parameter characterizing the 'reversibility' of ribosome-targeting antibiotic transport and binding. This parameter provides a spectrum classification of antibiotic growth-dependent efficacy that appears to correspond at its extremes to existing binary classification schemes. In these limits, the model predicts universal, parameter-free limiting forms for growth inhibition curves. The model also leads to nontrivial predictions for the drug susceptibility of a translation mutant strain of E. coli, which we verify experimentally. Drug action and bacterial metabolism are mechanistically complex; nevertheless, this study illustrates how coarse-grained models can be used to integrate pathogen physiology into drug design and treatment strategies.

Inherent variability in the kinetics of autocatalytic protein self-assembly.

In small volumes, the kinetics of filamentous protein self-assembly is expected to show significant variability, arising from intrinsic molecular noise. This is not accounted for in existing deterministic models. We introduce a simple stochastic model including nucleation and autocatalytic growth via elongation and fragmentation, which allows us to predict the effects of molecular noise on the kinetics of autocatalytic self-assembly. We derive an analytic expression for the lag-time distribution, which agrees well with experimental results for the fibrillation of bovine insulin. Our expression decomposes the lag-time variability into contributions from primary nucleation and autocatalytic growth and reveals how each of these scales with the key kinetic parameters. Our analysis shows that significant lag-time variability can arise from both primary nucleation and from autocatalytic growth and should provide a way to extract mechanistic information on early-stage aggregation from small-volume experiments.

Constraint-driven condensation in large fluctuations of linear statistics.

Condensation is the phenomenon whereby one of a sum of random variables contributes a finite fraction to the sum. It is manifested as an aggregation phenomenon in diverse physical systems such as coalescence in granular media, jamming in traffic, and gelation in networks. We show here that the same condensation scenario, which normally happens only if the underlying probability distribution has tails heavier than exponential, can occur for light-tailed distributions in the presence of additional constraints. We demonstrate this phenomenon on the sample variance, whose probability distribution conditioned on the particular value of the sample mean undergoes a phase transition. The transition is manifested by a change in behavior of the large deviation rate function.

Speed of invasion of an expanding population by a horizontally transmitted trait.

Range expansions are a ubiquitous phenomenon, leading to the spatial spread of genetic, ecological, and cultural traits. While some of these traits are advantageous (and hence selected), other, nonselected traits can also spread by hitchhiking on the wave of population expansion. This requires us to understand how the spread of a hitchhiking trait is coupled to the wave of advance of its host population. Here, we use a system of coupled Fisher-Kolmogorov-Petrovsky-Piskunov (F-KPP) equations to describe the spread of a horizontally transmitted hitchhiking trait within a population as it expands. We extend F-KPP wave theory to the system of coupled equations to predict how the hitchhiking trait spreads as a wave within the expanding population. We show that the speed of this trait wave is controlled by an intricate coupling between the tip of the population and trait waves. Our analysis yields a new speed selection mechanism for coupled waves of advance and reveals the existence of previously unexpected speed transitions.

Effect of partial absorption on diffusion with resetting.

The effect of partial absorption on a diffusive particle which stochastically resets its position with a finite rate r is considered. The particle is absorbed by a target at the origin with absorption "velocity" a; as the velocity a approaches ∞ the absorption property of the target approaches that of a perfectly absorbing target. The effect of partial absorption on first-passage time problems is studied, in particular, it is shown that the mean time to absorption (MTA) is increased by an additive term proportional to 1/a. The results are extended to multiparticle systems where independent searchers, initially uniformly distributed with a given density, look for a single immobile target. It is found that the average survival probability P(av) is modified by a multiplicative factor which is a function of 1/a, whereas the decay rate of the typical survival probability P(typ) is decreased by an additive term proportional to 1/a.

Explosive condensation in a mass transport model.

We study a far-from-equilibrium system of interacting particles, hopping between sites of a 1D lattice with a rate which increases with the number of particles at interacting sites. We find that clusters of particles, which initially spontaneously form in the system, begin to move at increasing speed as they gain particles. Ultimately, they produce a moving condensate which comprises a finite fraction of the mass in the system. We show that, in contrast with previously studied models of condensation, the relaxation time to steady state decreases as an inverse power of lnL with system size L and that condensation is instantaneous for L→∞.

Diffusion with stochastic resetting.

We study simple diffusion where a particle stochastically resets to its initial position at a constant rate r. A finite resetting rate leads to a nonequilibrium stationary state with non-Gaussian fluctuations for the particle position. We also show that the mean time to find a stationary target by a diffusive searcher is finite and has a minimum value at an optimal resetting rate r*. Resetting also alters fundamentally the late time decay of the survival probability of a stationary target when there are multiple searchers: while the typical survival probability decays exponentially with time, the average decays as a power law with an exponent depending continuously on the density of searchers.

Switching and growth for microbial populations in catastrophic responsive environments.

Phase variation, or stochastic switching between alternative states of gene expression, is common among microbes, and may be important in coping with changing environments. We use a theoretical model to assess whether such switching is a good strategy for growth in environments with occasional catastrophic events. We find that switching can be advantageous, but only when the environment is responsive to the microbial population. In our model, microbes switch randomly between two phenotypic states, with different growth rates. The environment undergoes sudden catastrophes, the probability of which depends on the composition of the population. We derive a simple analytical result for the population growth rate. For a responsive environment, two alternative strategies emerge. In the no-switching strategy, the population maximizes its instantaneous growth rate, regardless of catastrophes. In the switching strategy, the microbial switching rate is tuned to minimize the environmental response. Which of these strategies is most favorable depends on the parameters of the model. Previous studies have shown that microbial switching can be favorable when the environment changes in an unresponsive fashion between several states. Here, we demonstrate an alternative role for phase variation in allowing microbes to maximize their growth in catastrophic responsive environments.

Dynamical phase transition in a model for evolution with migration.

We study a simple quasispecies model for evolution in two different habitats, with different fitness landscapes, coupled through one-way migration. Our key finding is a dynamical phase transition at a critical value of the migration rate, at which the time to reach the steady state diverges. The genetic composition of the population is qualitatively different above and below the transition. Using results from localization theory, we show that the critical migration rate may be very small-demonstrating that evolutionary outcomes can be very sensitive to even a small amount of migration.