Stationary Population Research Articles

Economic Irreversibility in Pandemic Control Processes: Rigorous Modeling of Delayed Countermeasures and Consequential Cost Increases

After the first lockdown in response to the COVID-19 outbreak, many countries faced difficulties in balancing infection control with economics. Due to limited prior knowledge, economists began researching this issue using cost-benefit analysis and found that infection control processes significantly affect economic efficiency. A UK study used economic parameters to numerically demonstrate an optimal balance in the process, including keeping the infected population stationary. However, universally applicable knowledge, which is indispensable for the guiding principles of infection control, has not yet been clearly developed because of the methodological limitations of simulation studies. Here, we propose a simple model and theoretically prove the universal result of economic irreversibility by applying the idea of thermodynamics to pandemic control. This means that delaying infection control measures is more expensive than implementing infection control measures early while keeping infected populations stationary. This implies that once the infected population increases, society cannot return to its previous state without extra expenditures. This universal result is analytically obtained by focusing on the infection-spreading phase of pandemics, and is applicable not just to COVID-19, regardless of "herd immunity." It also confirms the numerical observation of stationary infected populations in its optimally efficient process. Our findings suggest that economic irreversibility is a guiding principle for balancing infection control with economic effects.

On the efficiency of laser pumping of hyperfine structure sublevels of Rubidium-87 and Cesium-133 atoms

The evolution of the hyperfine structure magnetic sublevel populations of 87Rb and 133Cs atoms in resonant linearly polarized laser fields is theoretically analyzed. Analytical expressions are obtained for stationary populations of the magnetic sublevels of the ground state 52S1/2 Fg = 1, Ff = 2 in 87Rb and 62S1/2 Fg = 3, Ff = 4 in 133Cs under optical pumping at the Fg ↔ Fe = Fg and Ff ↔ Fe = Ff transitions of the D2 lines (n 2S1/2 n 2P3/2) versus the initial populations. The characteristic population stabilization time are obtained by numerical solution for the density matrix equations, depending on the intensity of the laser fields and the detuning of the optical resonance. It is shown that the alternation of the polarization direction of the laser field at the transition Ff ↔ Fe = Ff almost completely transfers atoms to the lower sublevel of the “clock” M1 transition Fg M = 0 ↔ Ff M = 0 in rubidium and cesium frequency standards, which proportionally increases the signal of the recording system.

Dissipation-Driven Selection under Finite Diffusion: Hints from Equilibrium and Separation of Time Scales.

When exposed to a thermal gradient, reaction networks can convert thermal energy into the chemical selection of states that would be unfavourable at equilibrium. The kinetics of reaction paths, and thus how fast they dissipate available energy, might be dominant in dictating the stationary populations of all chemical states out of equilibrium. This phenomenology has been theoretically explored mainly in the infinite diffusion limit. Here, we show that the regime in which the diffusion rate is finite, and also slower than some chemical reactions, might bring about interesting features, such as the maximisation of selection or the switch of the selected state at stationarity. We introduce a framework, rooted in a time-scale separation analysis, which is able to capture leading non-equilibrium features using only equilibrium arguments under well-defined conditions. In particular, it is possible to identify fast-dissipation sub-networks of reactions whose Boltzmann equilibrium dominates the steady-state of the entire system as a whole. Finally, we also show that the dissipated heat (and so the entropy production) can be estimated, under some approximations, through the heat capacity of fast-dissipation sub-networks. This work provides a tool to develop an intuitive equilibrium-based grasp on complex non-isothermal reaction networks, which are important paradigms to understand the emergence of complex structures from basic building blocks.

Bcl-xL Is Required by Primary Hippocampal Neurons during Development to Support Local Energy Metabolism at Neurites

Simple SummaryB-cell lymphoma-extra large (Bcl-xL) is an anti-apoptotic protein that regulates energy metabolism in neurons. In this study, we found that primary hippocampal neurons transduced with Bcl-xL shRNA or treated with a pharmacological inhibitor of Bxl-xL had a decrease in the population of motile mitochondria. Primary hippocampal neurons lacking Bcl-xL failed to retain ATP at their neurites, which hindered the formation of complex neurite arbors, and ultimately had enhanced vulnerability to excitotoxic challenge.B-cell lymphoma-extra large (Bcl-xL) is a mitochondrial protein known to inhibit mitochondria-dependent intrinsic apoptotic pathways. An increasing number of studies have demonstrated that Bcl-xL is critical in regulating neuronal energy metabolism and has a protective role in pathologies associated with an energy deficit. However, it is less known how Bcl-xL regulates physiological processes of the brain. In this study, we hypothesize that Bcl-xL is required for neurite branching and maturation during neuronal development by improving local energy metabolism. We found that the absence of Bcl-xL in rat primary hippocampal neurons resulted in mitochondrial dysfunction. Specifically, the ATP/ADP ratio was significantly decreased in the neurites of Bcl-xL depleted neurons. We further found that neurons transduced with Bcl-xL shRNA or neurons treated with ABT-263, a pharmacological inhibitor of Bcl-xL, showed impaired mitochondrial motility. Neurons lacking Bcl-xL had significantly decreased anterograde and retrograde movement of mitochondria and an increased stationary mitochondrial population when Bcl-xL was depleted by either means. These mitochondrial defects, including loss of ATP, impaired normal neurite development. Neurons lacking Bcl-xL showed significantly decreased neurite arborization, growth and complexity. Bcl-xL depleted neurons also showed impaired synapse formation. These neurons showed increased intracellular calcium concentration and were more susceptible to excitotoxic challenge. Bcl-xL may support positioning of mitochondria at metabolically demanding regions of neurites like branching points. Our findings suggest a role for Bcl-xL in physiological regulation of neuronal growth and development.

Atomic population inversion in a two-level atom for shaped and chirped laser pulses: Exact solutions of Bloch equations with dephasing

We perform a theoretical analysis of the Bloch equations of a two-level atom with dephasing. Exact analytical solutions with two different chirped and time-dependent detuned laser pulses are derived. The atomic population inversion as well as the coherence are explored for different initial populations. We show that the stationary population inversion can be controlled.

Exact simulation of the genealogical tree for a stationary branching population and application to the asymptotics of its total length

AbstractWe consider a model of a stationary population with random size given by a continuous-state branching process with immigration with a quadratic branching mechanism. We give an exact elementary simulation procedure for the genealogical tree of n individuals randomly chosen among the extant population at a given time. Then we prove the convergence of the renormalized total length of this genealogical tree as n goes to infinity; see also Pfaffelhuber, Wakolbinger and Weisshaupt (2011) in the context of a constant-size population. The limit appears already in Bi and Delmas (2016) but with a different approximation of the full genealogical tree. The proof is based on the ancestral process of the extant population at a fixed time, which was defined by Aldous and Popovic (2005) in the critical case.

Mechanistic Insights about Electrochemical Proton-Coupled Electron Transfer Derived from a Vibrational Probe.

Proton-coupled electron transfer (PCET) is a fundamental step in a wide range of electrochemical processes, including those of interest in energy conversion and storage. Despite its importance, several mechanistic details of such reactions remain unclear. Here, we have combined a proton donor (tertiary ammonium) with a vibrational Stark-shift probe (benzonitrile), to track the process from the entry of the reactants into the electrical double layer (EDL), to the PCET reaction associated with proton donation to the electrode, and the formation of products. We have used operando vibrational spectroscopy and periodic density functional theory under electrochemical bias to assign the reactant and product peaks and their Stark shifts. We have identified three main stages for the progress of the PCET reaction as a function of applied potential. First, we have determined the potential necessary for desolvation of the reactants and their entry into the polarizing environment of the EDL. Second, we have observed the appearance of product peaks prior to the onset of steady state electrochemical current, indicating formation of a stationary population of products that does not turn over. Finally, more negative of the onset potential, the electrode attracts additional reactants, displacing the stationary products and enabling steady state current. This work shows that the integration of a vibrational Stark-shift probe with a proton donor provides critical insight into the interplay between interfacial electrostatics and heterogeneous chemical reactions. Such insights cannot be obtained from electrochemical measurements alone.

Pattern Formation in a Three-Species Cyclic Competition Model.

In nature, different species compete among themselves for common resources and favorable habitat. Therefore, it becomes really important to determine the key factors in maintaining the bio-diversity. Also, some competing species follow cyclic competition in real world where the competitive dominance is characterized by a cyclic ordering. In this paper, we study the formation of a wide variety of spatiotemporal patterns including stationary, periodic, quasi-periodic and chaotic population distributions for a diffusive Lotka-Volterra type three-species cyclic competition model with two different types of cyclic ordering. For both types of cyclic ordering, the temporal dynamics of the corresponding non-spatial system show the extinction of two species through global bifurcations such as homoclinic and heteroclinic bifurcations. For the spatial system, we show that the existence of Turing patterns is possible for a particular cyclic ordering, while it is not the case for the other cyclic ordering through both the analytical and numerical methods. Further, we illustrate an interesting scenario of short-range invasion as opposed to the usual invasion phenomenon over the entire habitat. Also, our study reveals that both the stationary and dynamic population distributions can coexist in different parts of a habitat. Finally, we extend the spatial system by incorporating nonlocal intra-specific competition terms for all the three competing species. Our study shows that the introduction of nonlocality in intra-specific competitions stabilizes the system dynamics by transforming a dynamic population distribution to stationary. Surprisingly, this nonlocality-induced stationary pattern formation leads to the extinction of one species and hence, gives rise to the loss of bio-diversity for intermediate ranges of nonlocality. However, the bio-diversity can be restored for sufficiently large extent of nonlocality.

Reconciling conformational heterogeneity and substrate recognition in cytochrome P450

Cytochrome P450, the ubiquitous metalloenzyme involved in detoxification of foreign components, has remained one of the most popular systems for substrate-recognition process. However, despite being known for its high substrate specificity, the mechanistic basis of substrate-binding by archetypal system cytochrome P450cam has remained at odds with the contrasting reports of multiple diverse crystallographic structures of its substrate-free form. Here, we address this issue by elucidating the probability of mutual dynamical transition to the other crystallographic pose of cytochrome P450cam and vice versa via unbiased all-atom computer simulation. A robust Markov state model, constructed using adaptively sampled 84-μs-long molecular dynamics simulation trajectories, maps the broad and heterogenous P450cam conformational landscape into five key substates. In particular, the Markov state model identifies an intermediate-assisted dynamic equilibrium between a pair of conformations of P450cam, in which the substrate-recognition sites remain “closed” and “open,” respectively. However, the estimate of a significantly higher stationary population of closed conformation, coupled with faster rate of open → closed transition than its reverse process, dictates that the net conformational equilibrium would be swayed in favor of “closed” conformation. Together, the investigation quantitatively infers that although a potential substrate of cytochrome P450cam would, in principle, explore a diverse array of conformations of substrate-free protein, it would mostly encounter a “closed” or solvent-occluded conformation and hence would follow an induced-fit-based recognition process. Overall, the work reconciles multiple precedent crystallographic, spectroscopic investigations and establishes how a statistical elucidation of conformational heterogeneity in protein would provide crucial insights in the mechanism of potential substrate-recognition process.

Coherent Dynamics in Quantum Emitters under Dichromatic Excitation

We characterize the coherent dynamics of a two-level quantum emitter driven by a pair of symmetrically detuned phase-locked pulses. The promise of dichromatic excitation is to spectrally isolate the excitation laser from the quantum emission, enabling background-free photon extraction from the emitter. While excitation is not possible without spectral overlap between the exciting pulse and the quantum emitter transition for ideal two-level systems due to cancellation of the accumulated pulse area, we find that any additional interactions that interfere with cancellation of the accumulated pulse area may lead to a finite stationary population inversion. Our spectroscopic results of a solid-state two-level system show that, while coupling to lattice vibrations helps to improve the inversion efficiency up to 50% under symmetric driving, coherent population control and a larger amount of inversion are possible using asymmetric dichromatic excitation, which we achieve by adjusting the ratio of the intensities between the red- and blue-detuned pulses. Our measured results, supported by simulations using a real-time path-integral method, offer a new perspective toward realizing efficient, background-free photon generation and extraction.

Agglomeration economies, congestion diseconomies, and fertility dynamics in a two-region economy

Using a small, open, two-region economy model populated by two-period-lived overlapping generations, we analyze long-term agglomeration economy and congestion diseconomy effects of young worker concentration on migration and the overall fertility rate. When the migration-stability condition is satisfied, the distribution of young workers between regions is obtainable in each period for a predetermined population size. Results show that migration stability does not guarantee dynamic stability of the economy. The stationary population size stability depends on the model parameters and the initial population size. On a stable trajectory converging to the stationary equilibrium, the overall fertility rate might change non-monotonically with the population size of the economy because of interregional migration. In each period, interregional migration mitigates regional population changes caused by fertility differences on the stable path. Results show that the inter-regional migration-stability condition does not guarantee stability of the population dynamics of the economy.

The Incidence of Lymphoma in Beijing: Comparing Results from MIS-CASS (2019) and Beijing Cancer Registry (2017).

IntroductionThis study aimed to evaluate the performance of the Medical-Insurance-System-based Cancer Surveillance System (MIS-CASS) in estimating cancer incidence by comparing the results with the Beijing Cancer Registry (BCR), which is one of the highest-quality population-based cancer registries in China.MethodsUsing lymphoma as an example, we extracted relevant claims data from the administrative systems of medical insurance in Beijing (2012–2020) and estimated the most current lymphoma incidence in Beijing (2019) using a standard data processing procedure. The absolute number of new cases, crude incidence rate, and age-standardized incidence rate of lymphoma were compared with the latest data reported by the BCR (2017).ResultsBoth lymphoma incidence rates and age distribution of new cases estimated based on MIS-CASS were similar to the BCR data (crude incidence rate: 9.8/100,000 vs. 10.6/100,000). However, because MIS-CASS included more designated hospitals and covered a larger local stationary population irrespective of household registration (hukou), the absolute number of incident lymphoma cases identified by MIS-CASS was 39.1% higher than that reported by the BCR (2,002 vs. 1,439). ConclusionsThe MIS-CASS approach reflected the actual cancer burden in a more complete and timely manner as compared with the current BCR, providing new insights for improving cancer surveillance strategies in China.

How many species of angulate tortoises occur in Southern Africa? (Testudines: Testudinidae: Chersina)

AbstractUsing range‐wide sampling and 1,143 bp of mtDNA (cytochrome b gene) and 14 microsatellite loci, we examined genetic differentiation in the widely distributed Southern African angulate tortoise (Chersina angulata). We found evidence for two genealogical lineages that differ in both genetic marker systems and their preferred habitat conditions. According to a fossil‐calibrated molecular clock for all African tortoise lineages using 1,870 bp mitochondrial and 1,416 bp nuclear DNA, the two lineages of C. angulata diverged in the Pliocene (approx. 3.8 million years ago). Species distribution models reveal that the ranges of the two lineages shifted little since the Last Glacial Maximum, which is in agreement with the demographic population descriptors suggestive of stationary populations that did not experience expansion. One lineage occurs in the west, and the other in the south of the extant distribution range. In the geographic contact zone, the two lineages hybridize extensively, providing evidence for their conspecificity under the biological species concept. Each lineage could be recognized as a distinct subspecies, but the ill‐defined geographic origins of the type material of the available names prevent their identification with any taxon. With respect to the nuclear genomic markers, the western lineage shows further north‐south substructuring. A few genetically mismatched tortoises are interpreted as human translocations. Our study underlines that confiscated or captive angulate tortoises of unknown geographic provenance should not be released without prior genetic screening to avoid genetic pollution of wild populations.

On some stochastic properties of lives lived and left in non-stationary populations.

First, we revisit the "life lived equals life left" property for stationary populations and discuss it from a more general perspective. Specifically, we show that identically distributed random age and the remaining lifetime in stationary populations have the same distribution as the equilibrium distribution of the renewal theory. Then we consider specific non-stationary populations that are closed to migration and have a constant birth rate. We obtain some useful inequalities between random age and remaining lifetime for different instants of calendar time. We also discuss the aging properties of populations using different stochastic orders.

Nuptiality to regulate the commons? The case of the Don Cossacks (South Russia), 1867–1916

AbstractSustainability in the commons has been associated with the optimal net present value controlled by the harvest rate under stationary population. Population growth however disrupts this scheme. In traditional societies, fertility was regulated by age at marriage. In times of population growth and limited resources, economic sustainability then requires that age of marriage should be raised. In the case study of the Don Cossacks, 1867–1916, early marriage, which was an important marker of social cohesion, was too slow to increase when mortality declined, fuelling a population growth that threatened the agrarian economy: age at marriage then appears to be essential to the theory of the commons in traditional societies.

Contrasting demographic responses of toad populations to regionally synchronous pathogen (Batrachochytrium dendrobatidis) dynamics

Batrachochytrium dendrobatidis (Bd), a fungal pathogen that causes amphibian chytridiomycosis, has been implicated in population declines globally. To better understand how Bd affects survival and how threats vary spatially and temporally, we conducted long-term (range: 9–13 yrs) capture-recapture studies of boreal toads (Anaxyrus boreas) from three similar communities in western Montana. We also estimated temporal and spatial variation in population-level Bd prevalence among populations and the potential role of co-occurring Columbia spotted frogs (Rana luteiventris) in driving infection dynamics. Hierarchical models that accounted for detection uncertainty revealed Bd reduced apparent survival in one population that declined, was unassociated with survival in one stationary population, and was associated with increased survival in one population that is near extirpation. Despite different effects of Bd on hosts, pathogen prevalence was similar and synchronous across the populations separated by 111–176 km. Variation in Bd prevalence was driven partly by seasonal temperatures, but opposite the direction expected. Bd prevalence also decreased sharply over time across all populations, unrelated to trends in temperature, boreal toad survival, or infection dynamics of co-occurring Columbia spotted frogs. Toad Bd prevalence increased when frog abundance was high, consistent with an amplification effect. However, Bd prevalence of toads decreased as Bd prevalence of spotted frogs increased, consistent with a dilution effect. Our results reveal surprising variation in responses to Bd and show pathogen prevalence is not predictive of survival or population risk, and they illustrate the complexity in understanding disease dynamics across multiple populations.

Changes of cell permeability during Listeria monocytogenes persistence under nisin treatment

The study examined free radical production of Listeria monocytogenes under nisin stress by colorimetric cell proliferation assay, and used flow cytometry (FC) to investigate the persister population of L. monocytogenes since agar plating is limited in providing information on persister cells exposed to nisin. The stationary phase populations in spent medium or resuspended in fresh TSB medium were individually treated with 75 μg/ml nisin for 24 hr at 30°C. Intracellular and extracellular free radical production was detected in the resuspended group simultaneously, while free radicals were only detected within cells in the spent medium group during the nisin treatment, and FC indicated possible population differentiation from quadrants H1-1 (“dead region,”) H1-2 (“damaged region) and H1-3(“live region”). The change in cell permeability was different under the two conditions (spent medium vs. fresh medium) when facing exposure to nisin, indicating the effect of the environment on cell persistence under nisin stress. Practical applications The practical application of this work is an awareness of how the sensitivity of a food isolate of L. monocytogenes exposed to nisin as a food preservative, and survival of tested strains can be affected by the environment in generating a population of persistent cells. A nutrient rich environment appears to enhance the population of persister cells. This is an important consideration for the food industry trying to control L. monocytogenes in a nutrient rich environment such as food. In addition, FC can be used to rapidly assess the population of persister cells compared with dead cells and provide a useful tool in risk assessment of L. monocytogenes in a food where nisin is used as a preservative.

Glucose sensitizes the stationary and persistent population of Vibrio cholerae to ciprofloxacin.

The subject of analysis in this report was the antibiotic susceptibility of V. cholerae under glucose supplementation since the metabolites can significantly alter the antibiotic sensitivity of bacteria. Glucose could change the antibiotic susceptibility in a growth phase-dependent manner, however, the antibiotic susceptibility of exponentially growing cells was not affected in the presence of glucose. What has been shown is that the stationary phase cells which show higher antibiotic tolerance, could be sensitized to ciprofloxacin and ampicillin by glucose supplementation (tenfold sensitive). The glucose increases the respiration which in turn increases the metabolism and cell division rate. Furthermore, the addition of glucose could increase the susceptibility of persister cells to ciprofloxacin only. In general, the bacterial susceptibility can be increased by combining the antibiotics with glucose.

Demographic Approaches to the Study of Aging on Cell Cultures

Aging organisms die out in accordance with the “Gompertz law,” i.e., the probability of their death increases with age. Survival curve construction is the main tool for gerontologists to study aging and test antiaging drugs. The analysis of survival curves includes obtaining some indices characterizing aging of the population, for example, the average and maximum lifespan, the mortality rate, and the aging rate. Testing geroprotectors can be correctly performed only by obtaining such curves. The dying out of stationary cell populations—bacteria, yeast, and mammalian cell cultures—also occurs in accordance with the Gompertz equation. In this regard, it is reasonable to use the construction of survival curves and their analysis to study the “aging” of non-subcultured cell cultures and testing anti-aging drugs on them. We used this approach in our experiments, due to which we were able to detect the positive anti-aging effect of the Quinton Marine Plasma on stationary phase aging culture of Chinese hamster cells.

Mean first passage times reconstruct the slowest relaxations in potential energy landscapes of nanoclusters.

Relaxation modes are the collective modes in which all probability deviations from equilibrium states decay with the same relaxation rates. In contrast, a first passage time is the required time for arriving for the first time from one state to another. In this paper, we discuss how and why the slowest relaxation rates of relaxation modes are reconstructed from the first passage times. As an illustrative model, we use a continuous-time Markov state model of vacancy diffusion in KCl nanoclusters. Using this model, we reveal that all characteristics of the relaxations in KCl nanoclusters come from the fact that they are hybrids of two kinetically different regions of the fast surface and slow bulk diffusions. The origin of the different diffusivities turns out to come from the heterogeneity of the activation energies on the potential energy landscapes. We also develop a stationary population method to compute the mean first passage times as mean times required for pair annihilations of particle-hole pairs, which enables us to obtain the symmetric results of relaxation rates under the exchange of the sinks and the sources. With this symmetric method, we finally show why the slowest relaxation times can be reconstructed from the mean first passage times.