Steady-state Population Research Articles

Population dynamics of chemotrophs in anaerobic conditions where the metabolic energy acquisition per redox reaction is limited

We present a new model of microbial population growth that focuses on the acquisition of metabolic energy through chemosynthesis and how this depends on the concentration of resources and byproducts. Due to entropy effects, organisms extract the greater energy (i.e., they produce the greater amount of adenosine triphosphate) when they use resources that are abundant and generates byproducts that are rare. This effect, which we call the “abundant resource premium,” has been neglected in traditional models of microbial growth because the total metabolic energy acquisition is generally far greater than this premium. This term, however, cannot be neglected for many microbes, such as sulfate reducers, iron oxidizers, and methanogens, which live under conditions of low-energy availability. Our model showed qualitatively different behaviors from those observed in traditional microbial population growth models, such as the Monod model. For example, the steady-state population density was maximum at an intermediate resource-utilizing ability, suggesting that high substrate acquisition is not always advantageous for a microbial population when the availability of metabolic energy is low. We discuss possible implications for evolutionary and ecosystem sciences.

The Pure Effect of Social Preferences on Regional Location Choices: The Evolving Dynamics of Convergence to a Steady State Population Distribution

This paper tracks the consequences of individuals' desire to align their location with their social preferences. The social preference studied in the paper is distaste for relative deprivation, measured in a cardinal manner. Location is conceived as social space, with individuals choosing to relocate if, as a result, their relative deprivation will be reduced, holding their incomes constant. Conditions are provided under which the associated dynamics reaches a spatial steady state, the number of periods it takes to reach a steady state is specified, and light is shed on the robustness of the steady state outcome. By way of simulation it is shown that for large populations, a steady state of the relocation dynamics is almost always reached, typically in one period, and that cycles are more likely to occur when the populations' income distributions are more equal.

The Pure Effect of Social Preferences on Regional Location Choices: The Evolving Dynamics of Convergence to a Steady State Population Distribution

This paper tracks the consequences of individuals’ desire to align their location with their social preferences. The social preference studied in the paper is distaste for relative deprivation, measured in a cardinal manner. Location is conceived as social space, with individuals choosing to relocate if, as a result, their relative deprivation will be reduced, holding their incomes constant. Conditions are provided under which the associated dynamics reaches a spatial steady state, the number of periods it takes to reach a steady state is specified, and light is shed on the robustness of the steady state outcome. By way of simulation it is shown that for large populations, a steady state of the relocation dynamics is almost always reached, typically in one period, and that cycles are more likely to occur when the populations’ income distributions are more equal.

761. Age-Related Incidence of TB Infection Supporting Efficacy of BCG Vaccination

Background Mycobacterium tuberculosis (MTB) is a major, and potentially preventable, cause of morbidity and mortality worldwide. Bacillus Calmette-Guerin (BCG) remains the only licensed vaccine for TB, and while efficacy has been demonstrated in some populations, many uncertainties remain. Three BCG vaccination policies were implemented across bordering geographical regions in the South West of Ireland from 1972; neonatal vaccination (vaccinated region-a), vaccination of children aged 10–12 years (vaccinated region-b) and no vaccination (unvaccinated region-c). The aim of this study was to investigate the impact of BCG vaccination on incidence of MTB during the study period.MethodsSurveillance data were used to identify all M. tuberculosis complex (MTC) isolates from 2003 to 2016. Residential addresses for each case were geocoded using the Google Maps API. Case locations were spatially linked to 2011 census population data and to Local Health Offices (LHO) BCG coverage data for study regions a–c. The 13-year incidence of TB was calculated assuming a steady-state population. Using SatScan (v9.4.4), spatial clusters were identified at the small area level with the spatial scan statistic based on the discrete Poisson probability distribution.ResultsOf 638 MTC infections identified (621 MTB, 16 M. bovis, 1 M. africanum), 510 occurred in study regions a–c (median age 42 years (4 months–94 years), 65% male and 66% Irish born). The incidence of MTB was higher in the unvaccinated population, region-c 132/100,000 (95% CI 116–150) vs. vaccinated region-a 56/100,000 (95% CI 45–69) and region-b 44/100,000 (95% CI 29–63). A single high-risk cluster of 138 cases within a population of 46,000 was identified in unvaccinated region-c (relative risk 4.94 (95% CI 4–6). The year-on-year incidence rates in the 20- to 35-year-old age range suggested a decreasing risk consistent with a beneficial impact of vaccination policies.ConclusionPrevention and treatment of TB remains a significant challenge worldwide. Our study demonstrates significant differences in incidence of MTC infection in demographically similar populations based on BCG immunization policy and thus further supports efficacy of BCG for prevention of tuberculosis infection.Disclosures All authors: No reported disclosures.

Controllable radiation properties of a driven exciton-biexciton quantum dot couples to a graphene sheet

We investigate the radiation properties of a driven exciton-biexciton structure quantum dot placed close to a graphene sheet. The study of the Purcell factor then demonstrates the tunability of light-matter coupling, which in turn provides the possibility to control the steady-state populations. As the result, dipole transitions can be selectively enhanced and asymmetry in the resonance fluorescence can be observed. Meanwhile, both quadratures can exhibit two-mode squeezing at the Rabi sideband frequencies. A further study shows that although the increase in the environment temperature has a destructive influence on the population imbalance, squeezing occurs even at room temperature. Due to the flexibility in controlling the resonance fluorescence spectrum and producing two-mode squeezed states, our proposal would have potential applications in quantum information and other quantum research fields.

CLASP Facilitates Transitions between Cortical Microtubule Array Patterns.

Acentrosomal plant microtubule arrays form patterns at the cell cortex that influence cellular morphogenesis by templating the deposition of cell wall materials, but the molecular basis by which the microtubules form the cortical array patterns remains largely unknown. Loss of the Arabidopsis (Arabidopsis thaliana) microtubule-associated protein, CYTOPLASMIC LINKER ASSOCIATED PROTEIN (AtCLASP), results in cellular growth anisotropy defects in hypocotyl cells. We examined the microtubule array patterning in atclasp-1 null mutants and discovered a significant defect in the timing of transitions between array patterns but no substantive defect in the array patterns per se. Detailed analysis and computational modeling of the microtubule dynamics in two atclasp-1 fluorescent tubulin marker lines revealed marker-dependent effects on depolymerization and catastrophe frequency predicted to alter the steady-state microtubule population. Quantitative in vivo analysis of the underlying microtubule array architecture showed that AtCLASP is required to maintain the number of growing microtubule plus ends during transitions between array patterns. We propose that AtCLASP plays a critical role in cellular morphogenesis through actions on new microtubules that facilitate array transitions.

Stochastic Dynamics of the Latently Infected Cell Reservoir During HIV Infection.

The presence of cells latently infected with HIV is currently considered to be a major barrier to viral eradication within a patient. Here, we consider birth-death-immigration models for the latent cell population in a single patient, and present analytical results for the size of this population in the absence of treatment. We provide results both at steady state (viral set point), and during the non-equilibrium setting of early infection. We obtain semi-analytic results showing how latency-reversing drugs might be expected to affect the size of the latent pool over time. We also analyze the probability of rare mutant viral strains joining the latent cell population, allowing for steady-state and dynamic viral populations within the host.

The threat of Centaurs for terrestrial planets and their orbital evolution as impactors

Centaurs are solar system objects with orbits situated among the orbits of Jupiter and Neptune. Centaurs represent one of the sources of Near-Earth Objects. Thus, it is crucial to understand their orbital evolution which in some cases might end in collision with terrestrial planets and produce catastrophic events. We study the orbital evolution of the Centaurs toward the inner solar system, and estimate the number of close encounters and impacts with the terrestrial planets after the Late Heavy Bombardment assuming a steady state population of Centaurs. We also estimate the possible crater sizes. We compute the approximate amount of water released: on the Earth, which is about 0.00001 the total water present now. We also found sub-regions of the Centaurs where the possible impactors originate from. While crater sizes could extend up to hundreds of kilometers in diameter given the presently known population of Centaurs the majority of the craters would be less than about 10 km. For all the planets and an average impactor size of 12 km in diameter, the average impact frequency since the Late Heavy Bombardment is one every 1.9 Gyr for the Earth and 2.1 Gyr for Venus. For smaller bodies (e.g. > 1 km), the impact frequency is one every 14.4 Myr for the Earth, 13.1 Myr for Venus and, 46.3 for Mars, in the recent solar system. Only 53% of the Centaurs can enter into the terrestrial planet region and 7% can interact with terrestrial planets.

Pump wavelength dependence of ASE and SBS in single-frequency EYDFAs.

In this Letter, the pump wavelength dependence of the amplified spontaneous emission (ASE) and the threshold of stimulated Brillouin scattering (SBS) in a typical single-frequency continuous wave Er3+:Yb3+-codoped fiber amplifier is investigated numerically. The Er3+:Yb3+ system is modeled as coupled two- and three-level systems, linked by a Förster resonance energy transfer process and described by the corresponding rate equations. The evolution of the pump and signal power along the fiber is modeled by differential equations, taking into account the steady-state population densities. Since the absorption at 976nm can exceed the Yb3+-to-Er3+ energy transfer rate in high-power operation, unsaturated gain at around 1.0μm can generate excessive ASE. Off-peak pumping with commercially available pump diodes at 915 or 940nm spatially distributes the energy over a longer distance. For the studied amplifier configuration, energy transfer bottlenecking is prevented without the onset of SBS.

Radical Arene Addition vs Radical Reduction: Why Organometal Hydride Chain Reactions Stop and How To Make Them Go.

Nonideal kinetic chain analysis was used to examine the kinetic limitations of free-radical synthesis. Homolytic aromatic substitution (HAS: ArH + R• → ArR + H•) occurs in a chain-terminating side reaction to the tributyltin hydride ( SnH) reduction chain (RX + SnH + ( i•)cat. → RH + SnX). Kinetic modeling of premixed and slow reagent addition reactions have clarified the mechanisms of SM HAS, with the azo initiator ( iNN i) acting not only as radical source but also (as an H• acceptor) as the redox catalyst for aromatization, and/or as a postaddition oxidant. Refractory halides and other hitherto baffling anomalies may arise from the build up of ipso (rather than ortho)-cycloadduct radicals in the steady-state radical population. The implications of these findings for "tin-free" radical chains (and emerging photoredox methods) are considered via historical and recent examples of the effects of chain-degrading radical transfer (to substrate, product, solvent, initiator, and/or reagent ligands) on the reagent's chain.

Unraveling structural properties of Cu2O loaded on gC3N4 for enhanced photocatalytic hydrogen generation

In this study, we load Cu2O into gC3N4 via an ultrasonic reduction method. By doing so, the steady-state electron population is increased by 3 times. Due to the revealed critical role of Cu2O in enhancing the electron population in gC3N4, the structural features of the loaded Cu2O are studied with synchrotron x-ray absorption spectroscopy (XAS), including x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS). Results show that the Cu species are present in +1 oxidation state in the form of nano-sized Cu2O. Each Cu cation is approximately coordinated to 2 O anions with an average length of 1.85 Å. Loading 1 wt% of Cu2O into gC3N4 generates H2 with a rate of 7.53 μmol/g · h, which is more than 5-fold of bare gC3N4 (1.44 μmol/g · h), under visible light irradiation in the presence of methanol as holes scavenger. The examined Cu2O/gC3N4 shows appreciable stability within 5 cycles of H2 generation.

Earth's Minimoons: Opportunities for Science and Technology

(modified from published version) Twelve years ago the Catalina Sky Survey discovered Earth's first known natural geocentric object other than the Moon, a few-meter diameter asteroid designated 2006 RH120. Despite significant improvements in ground-based telescope and detector technology in the past decade the asteroid surveys have not discovered another temporarily-captured orbiter (TCO; colloquially known as minimoons). Within a few years the Large Synoptic Survey Telescope (LSST) will either begin to regularly detect TCOs or force a re-analysis of the creation and dynamical evolution of small asteroids in the inner solar system. The first studies of the provenance, properties, and dynamics of Earth's minimoons suggested that there should be a steady state population with about one 1- to 2-meter diameter captured objects at any time. That model was then improved and extended to include the population of temporarily-captured flybys (TCFs), objects that fail to make an entire revolution around Earth while energetically bound to the Earth-Moon system. Several different techniques for discovering TCOs have been considered but their small diameters, proximity, and rapid motion make them challenging targets for existing ground-based optical, meteor, and radar surveys. We expect that if the TCO population is confirmed, and new objects are frequently discovered, they can provide new opportunities for 1) studying the dynamics of the Earth-Moon system, 2) testing models of the production and dynamical evolution of small asteroids from the asteroid belt, 3) rapid and frequent low delta-v missions to multiple minimoons, and 4) evaluating in-situ resource utilization techniques on asteroidal material. Here we review the past decade of minimoon studies in preparation for capitalizing on the scientific and commercial opportunities of TCOs in the first decade of LSST operations.

Applications of He’s methods to the steady-state population balance equation in continuous flow systems

The population balance equation has numerous applications in physical and engineering sciences, where one of the phases is discrete in nature. Such applications include crystallization, bubble column reactors, bioreactors, microbial cell populations, aerosols, powders, polymers and more. This contribution presents a comprehensive investigation of the semi- analytical solutions of the population balance equation (PBE) for continuous flow particulate processes. The general PBE was analytically solved using homotopy perturbation method (HPM) and variational iteration method (VIM) for particulate processes where breakage, growth, aggregation, and simultaneous breakage and aggregation take place. These semi-analytical methods overcome the crucial difficulties of numerical discretization and stability that often characterize previous solutions of the PBEs. It was found that the series solutions converged exactly to available analytical steady-state solutions of the PBE using these two methods.

Pathogenesis of Alzheimer's Disease Examined Using a Modified Puri-Li Model that Incorporates Calcium Ion Homeostasis.

The Puri-Li kinetic model is modified to include neuronal calcium ion homeostasis to study the effect of calcium ions on the production of amyloid-β peptides (Aβ), microglia, and astroglia during the pathogenesis of Alzheimer's disease (AD). This is carried out by solving the modified Puri-Li model under steady-state conditions. The derived expressions show that the inclusion of calcium ions has altered the steady-state populations of Aβ, microglia, and astroglia. The calcium ions activate the synthesis of Aβ which in turn increases the calcium ions entering the cytoplasm of the neuronal cells, thus creating a positive loop. The study also shows that as AD progresses, the inclusion of calcium ions enhances the production of microglia and astroglia. Examination of the steady-state solutions of microglia and astroglia shows that equilibrium conditions are achieved by microglia and astroglia destroying neurons. These model results are in agreement with experimental findings, which show a feed back loop between calcium ion levels and Aβ; population increase in microglia, astroglia during AD; and microglia, astroglia acting as inflammatory cells producing toxins to destroy neurons during AD. Increased production of Aβ, microglia, and astroglia resulting from increased levels of calcium ions suggests that controlling the calcium ion levels could present a therapeutic strategy to combat AD.

Heat amplification and negative differential thermal conductance in a strongly coupled nonequilibrium spin-boson system

We investigate the nonequilibrium quantum heat transfer in a triangle-coupled spin-boson system within a three-terminal setup. By including the nonequilibrium noninteracting blip approximation approach combined with the full counting statistics, we analytically obtain the steady state populations and heat currents. The negative differential thermal conductance and giant heat amplification factor are clearly observed at strong qubit-bath coupling. %and the heat amplification is dramatically suppressed in the moderate coupling regime. Moreover, the strong interaction between the gating qubit and gating thermal bath is unraveled to be compulsory to exhibit these far-from equilibrium features.

Dissipation-induced dipole blockade and antiblockade in driven Rydberg systems

We study theoretically and experimentally the competing blockade and anti-blockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system's behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population's dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate equation model to the experimental observations in [E. A. Goldschmidt, et al., PRL 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drive.

Microwave Detection of Electron-Phonon Interactions in a Cavity-Coupled Double Quantum Dot.

Quantum confinement leads to the formation of discrete electronic states in quantum dots. Here we probe electron-phonon interactions in a suspended InAs nanowire double quantum dot (DQD) that is electric-dipole coupled to a microwave cavity. We apply a finite bias across the wire to drive a steady state population in the DQD excited state, enabling a direct measurement of the electron-phonon coupling strength at the DQD transition energy. The amplitude and phase response of the cavity field exhibit oscillations that are periodic in the DQD energy level detuning due to the phonon modes of the nanowire. The observed cavity phase shift is consistent with theory that predicts a renormalization of the cavity center frequency by coupling to phonons.

The distributional effects of a carbon tax on current and future generations

This paper uses a life cycle model to compare how different approaches for recycling carbon tax revenue affect the welfare of agents born in the future steady state versus agents alive when the policy is adopted. Our results demonstrate that the welfare consequences of a given policy vary substantially across these two groups. For agents born into the future steady state, the expected non-environmental welfare costs are minimized when carbon tax revenue is used to reduce an existing distortionary tax. In contrast, among the agents alive when the policy is adopted, recycling revenue through uniform, lump-sum rebates results in the largest welfare increase across the policies we examine. Moreover, we find that the regressivity or progressivity of a policy also differs within the living population versus the future steady state population. Overall, our results illustrate that estimates of the non-environmental welfare costs of carbon tax policies that are based on the long-run outcomes miss-represent the near-term consequences. Given the potential importance of these near-term effects on the political feasibility of a policy, our findings indicate that, when designing a carbon tax, policy makers must pay careful attention to not only the long-run outcomes, but also to the transitional welfare effects of the policy.

Dynamics of starvation and recovery predict extinction risk and both Damuth\u2019s law and Cope\u2019s rule

The eco-evolutionary dynamics of species are fundamentally linked to the energetic constraints of their constituent individuals. Of particular importance is the interplay between reproduction and the dynamics of starvation and recovery. To elucidate this interplay, here we introduce a nutritional state-structured model that incorporates two classes of consumers: nutritionally replete, reproducing consumers, and undernourished, nonreproducing consumers. We obtain strong constraints on starvation and recovery rates by deriving allometric scaling relationships and find that population dynamics are typically driven to a steady state. Moreover, these rates fall within a “refuge” in parameter space, where the probability of population extinction is minimized. We also show that our model provides a natural framework to predict steady state population abundances known as Damuth's law, and maximum mammalian body size. By determining the relative stability of an otherwise homogeneous population to a competing population with altered percent body fat, this framework provides a principled mechanism for a selective driver of Cope’s rule.

Prediction of bubble size and axial position distribution through hybridization of population balance modelling and dynamic gas disengagement

Bubble Column Reactors (BCRs) are suitable for multiphase fluid systems due to their low energy consumption, ease of fabrication and relatively high degree of mixing. When predicting the properties of the bubble population, it was shown in our previous study that the global Bubble Number Density Distribution (BNDD) could be determined through the coupling of Electrical Resistance Tomography (ERT) to the Dynamic Gas Disengagement (DGD) process. However, due to the low spatial resolution associated with the ERT, the local BNDD, bubble coalescence and breakage rates of the fluid dispersion, and the BCR hydrodynamic parameters could not be predicted.In the present paper, these limitations are addressed by hybridizing the steady-state Population Balance Model (PBM) with the DGD results. In the first stage of the hybridization, the PBM having the source terms of bubble coalescence and breakup rates was solved to simulate the bubble evolution process in a BCR of height 1.56m and diameter 0.29m designed with a porous tubular gas distributor. The PBM solution was utilized as an initial condition for a modelling of the unsteady state DGD process as an advection transport of mean bubble sizes under the influence of bubble expansion rates. The unsteady state PBM that models the DGD process was solved by the method of characteristics to obtain an analytical solution of the local transient disengaging gas volume. Accordingly, the inlet mean and standard deviation of bubble sizes parameters, the coalescence and breakage rates, and the local flux gradient parameter during DGD were adjusted to ensure the modelled local static and dynamic gas holdups during DGD process agree with the corresponding experimental measurements.Validation was achieved through comparison of the macro-properties that can be determined from the resolved BNDD. Such properties include the axial distributions of Sauter Mean Bubble Diameter (SMBD), gas holdups, and the volumetric gas-liquid mass transfer rates of the steady-state bubble population swarming. The comparison of predicted hydrodynamic parameters with two literature results yielded R-squares of 0.88 and 0.82, Chi-squares of 0.86 and 1.08 and f-statistics of 35.96 and 27.24 indicating good agreement. It is therefore proposed that hybridization of the PBM and DGD process yielded a high spatial prediction of the Size and Axial Distribution (SAD) of bubble dispersion and the bubble coalescence and breakage rates even though ERT offers a relatively low spatial resolution.