Effects Of Dispersal Research Articles

Analysis on a diffusive SIRS epidemic model with logistic source and saturated incidence rate

This paper provides the qualitative analysis on a diffusive SIRS epidemic model with logistic source and saturated incidence rate. We first establish the uniform boundedness of the parabolic system, and then explore the extinction/persistence of the infectious disease via the basic reproduction number. The effects of logistic source, dispersal, saturation, and spatial heterogeneity on asymptotic behaviors of the endemic equilibrium are also investigated. Our study show that the disease can not be controlled by limiting the dispersal rate and large saturation may cause the elimination of disease.

Controlling primary chain dispersity in network polymers: elucidating the effect of dispersity on degradation.

Although dispersity has been demonstrated to be instrumental in determining many polymer properties, current synthetic strategies predominantly focus on tailoring the dispersity of linear polymers. In contrast, controlling the primary chain dispersity in network polymers is much more challenging, in part due to the complex nature of the reactions, which has limited the exploration of properties and applications. Here, a one-step method to prepare networks with precisely tuned primary chain dispersity is presented. By using an acid-switchable chain transfer agent and a degradable crosslinker in PET-RAFT polymerization, the in situ crosslinking of the propagating polymer chains was achieved in a quantitative manner. The incorporation of a degradable crosslinker, not only enables the accurate quantification of the various primary chain dispersities, post-synthesis, but also allows the investigation and comparison of their respective degradation profiles. Notably, the highest dispersity networks resulted in a 40% increase in degradation time when compared to their lower dispersity analogues, demonstrating that primary chain dispersity has a substantial impact on the network degradation rate. Our experimental findings were further supported by simulations, which emphasized the importance of higher molecular weight polymer chains, found within the high dispersity materials, in extending the lifetime of the network. This methodology presents a new and promising avenue to precisely tune primary chain dispersity within networks and demonstrates that polymer dispersity is an important parameter to consider when designing degradable materials.

Drivers of contemporary lacustrine fish species richness in the glacial Lake Agassiz basin

AbstractAimBiological communities are the result of a stepwise spatiotemporal filtering process, driven by large‐scale historical and local contemporary determinants. The biogeographical pattern and species richness of North American fishes are predominantly determined by historical processes of past glaciations and postglacial dispersal and by contemporary environmental and ecological processes. We evaluated the effects of postglacial dispersal through glacial Lake Agassiz and habitat heterogeneity, represented by lake surface area, on contemporary freshwater fish species richness patterns of northwestern Ontario lakes.LocationNorthwestern Ontario, Canada.TaxonFreshwater fishes.MethodsApplying the theory of island biogeography and species–area curves, we examined the effects of isolation from the past dispersal corridor of glacial Lake Agassiz and habitat heterogeneity on species richness across 264 contemporary lakes. While controlling for correlations among the predictor variables, generalized linear models were constructed between species richness, as the response variable and the explanatory variables of lake elevation and surface area, and connection to the dispersal corridor.ResultsDifferential cover by glacial Lake Agassiz led to variation in fish species richness across contemporary lakes and it is higher in lakes that were covered by Lake Agassiz relative to basins remaining outside of the boundaries of the glacial lake. Lake surface area is the strongest predictor of species richness, while lake elevation is the strongest factor predicting isolation.Main ConclusionsHabitat heterogeneity and postglacial colonization have led to differences in fish richness within the same geographical region, which increases with lake surface area and decreases with elevation. These are likely driven by greater niche diversity facilitating the assembly of more diverse communities and isostatic rebound and fluctuating levels of Lake Agassiz isolating lakes at high elevations from the dispersal route earlier during the colonization process, respectively. These patterns underscore the importance of incorporating historical and environmental community determinants in biodiversity studies.

Polymer Brushes by Grafting to Reaction in Melt: New Insights into the Mechanism

AbstractUltrathin films of end‐tethered polymers, generally indicated as polymer brushes, have gained great interest for their ability to modify the surface interaction with the surrounding environment. One of the most common strategies to obtain polymer brushes is based on the reaction of end‐functional polymers with the substrate surface, in a process defined as grafting to. The two advantages of grafting to reactions are i) the functional polymer is prepared before the grafting reaction and therefore can be fully characterized and ii) the reaction has a self‐limiting nature, meaning that the number of grafted chains converges to a plateau value after a sufficiently long reaction time. The limit value of grafted chains is governed by the molecular weight of the employed polymer, thus allowing a fine control of the brush thickness. In this work, the origin of the self‐limiting nature of the grafting to reaction is discussed comparing theoretical models with experimental data. Furthermore, the kinetics of the process is discussed, considering both polymer diffusion and end‐group reactivity as the main drivers of the grafting to process. Finally, the effect of molecular weight dispersity on the brush characteristics is highlighted.

Effect of dispersal in two-patch environment with Richards growth on population dynamics

In this paper, we consider a two-patch model coupled by migration terms, where each patch follows a Richards law. First, we prove the global stability of the model. Second, in the case when the migration rate tends to infinity, the total carrying capacity is given, which in general is different from the sum of the two carrying capacities and depends on the parameters of the growth rate and also on the migration terms. Using the theory of singular perturbations, we give an approximation of the solutions of the system in this case. Finally, we determine the conditions under which fragmentation and migration can lead to a total equilibrium population which might be greater or smaller than the sum of two carrying capacities and we give a complete classification for all possible cases. The total equilibrium population formula for a large migration rate plays an important role in this classification. We show that this choice of local dynamics has an influence on the effect of dispersal. Comparing the dynamics of the total equilibrium population as a function of the migration rate with that of the logistic model, we obtain the same behavior. In particular, we have only three situations that the total equilibrium population can occur: it is always greater than the sum of two carrying capacities, always smaller, and a third case, where the effect of dispersal is beneficial for lower values of the migration rate and detrimental for the higher values. We end by examining the two-patch model where one growth rate is much larger than the second one, we compare the total equilibrium population with the sum of the two carrying capacities.

Pinoresinol stimulates keratinocyte proliferation and downregulates TNF-α secretion in peripheral blood mononuclear cells: An experimental in vitro study.

Natural coniferous resins are used in traditional medicine for the treatment of skin wounds. Coniferous wood resins ("callus" resin) are a mixture of abietic (resin) acids, lignans such as pinoresinol, and p-coumaric acid. The wound-healing properties of resins are thought to be related to their antimicrobial properties, but also to their effects on cell proliferation and inflammation. The purpose of this study was to identify and investigate the effects of novel aqueous dispersions of resin and its main components in the proliferation of human primary keratinocytes in vitroand in the expression of proinflammatory cytokines in human peripheral blood mononuclear cells. The proliferation studies were performed under low and high calcium conditions with or without added growth stimulators at the time points of 2and 6 days using AlamarBlue Cell Viability Reagent. The cytokine release assay was carried out by incubating the cells with the test articles for 18 h, after which the levels of tumor necrosis factor-α(TNF-α),interleukin-1β (IL-1β), IL-6, and IL-8 were measured in the supernatant by enzyme-linked immunosorbent assay. Resin and the purified lignan PINO, but not p-coumaric acid or abietic acid (industrial tall oil rosin), enhanced the proliferation of human keratinocytes in vitroand inhibited the expression of TNF-α, and to a lesser extent the expression of IL-1β in peripheral blood mononuclear cells. In this study, novel aqueous dispersions of spruce resin were used to investigate the effects of main resin components on keratinocyte proliferation and on the expression of key proinflammatory cytokines known to be associated with chronic wounds. The observations suggest that lignans, such as PINO, but not resin acids, are the components of resins that mediate the proliferative and TNF-α-suppressing effects. Lignans including PINO were identified as novel potential compounds in the treatment of chronic skin ulcers.

The interactive effects of environmental gradient and dispersal shape spatial phylogenetic patterns

IntroductionThe emergence and maintenance of biodiversity include interacting environmental conditions, organismal adaptation to such conditions, and dispersal. To understand and quantify such ecological, evolutionary, and spatial processes, observation and interpretation of phylogenetic relatedness across space (e.g., phylogenetic beta diversity) is arguably a way forward as such patterns contain signals from all the processes listed above. However, it remains challenging to extract information about complex eco-evolutionary and spatial processes from phylogenetic patterns.MethodsWe link environmental gradients and organismal dispersal with phylogenetic beta diversity using a trait-based and eco-evolutionary model of diversification along environmental gradients. The combined effect of the environment and dispersal leads to distinct phylogenetic patterns between subsets of species and across geographical distances.Results and discussionSteep environmental gradients combined with low dispersal lead to asymmetric phylogenies, a high phylogenetic beta diversity, and the phylogenetic diversity between communities increases linearly along the environmental gradient. High dispersal combined with a less steep environmental gradient leads to symmetric phylogenies, low phylogenetic beta diversity, and the phylogenetic diversity between communities along the gradient increases in a sigmoidal form. By disentangling the eco-evolutionary mechanisms that link such interacting environment and dispersal effects and community phylogenetic patterns, our results improve understanding of biodiversity in general and help interpretation of observed phylogenetic beta diversity.

Experimental study on methane explosion suppression by heptafluoropropane drived modified ABC powder

The accidental methane explosion accident will not only pose a serious threat to the safety of industrial processes, but also cause serious environmental pollution with excessive carbon emissions and greenhouse effect. Therefore, this paper has studied the inhibition effect of modified ABC powder driven by heptafluoropropane on methane explosion. Multiple methane explosion suppression experiments were carried out using a 3.2 L horizontal experimental pipeline under various working condition. The experimental results demonstrate that the modified ABC powder has a certain inhibitory effect on methane explosions, but the explosive suppression effect of the powder improves when heptafluoropropane is used as the driving gas. When 3∼4 % heptafluoropropane is used as the driving gas, the flame is obviously inhibited. The deformation degree of flame shape is the largest at 4 % concentration. The flame totally folds inward at this point, forming an uneven finger flame. When 4 % concentration of heptafluoropropane drives the powder, there is a critical value of the concentration of the powder, which is 0.06 g/L. According to the characterization results, the average particle size of the modified ABC powder is less than 5 µm. It has good dispersibility and pyrolysis effect and is not easy to agglomerate. Under the driving action of heptafluoropropane, the powder will form aerosol, which can fully contact and react with the flame. The inert gas around the powder will reduce the forward speed of the flame and ensure that the flame and powder can fully contact and react. The combination of the two has a good synergistic effect and can effectively inhibit methane explosion.

Inhibiting ice recrystallization by amyloid protein fibrils

Ice recrystallization is harmful to the quality of frozen foods and the cryopreservation of cells and biological tissues, requiring biocompatible materials with ice recrystallization inhibition (IRI) activity. Emerging studies have associated IRI activity with amphiphilic structures. We propose amphiphilic amyloid protein fibrils (APFs) may be IRI-active. APFs were prepared from whey protein isolate (WPI) in water (W-APFs) and in trifluoroethanol (TFE-APFs). W-APFs and TFE-APFs were more IRI-active than WPI over a concentration range of 2.5–10.0 mg/mL. Both APFs showed stronger IRI activity at pH 3.0 than at pH 5.0, 7.0, and 10.0, which was ascribed to the effect of water dispersibility and fibril length. The reduced IRI activity of the two APFs with increasing NaCl content was caused by fibril aggregation. Ice binding by APFs was absent or very weak. Ordered water was observed for the two APFs, which might be essential for IRI activity. Our findings may lead to the use of APFs as novel ice recrystallization inhibitors.

Effect of Micro-structural Dispersity of SiMo Ductile Iron on Thermal Cycling Performance

Effect of Micro-structural Dispersity of SiMo Ductile Iron on Thermal Cycling Performance

Synergistic effects of curcumin and gamma-oryzanol solid dispersions ameliorate muscle atrophy by upregulating Nrf2 and IGF1/Insulin-Akt-mTOR activities in middle-aged rats

• Curcumin mixed with gamma-oryzanol solid dispersions (GO-CURSD) on middle-aged rat’s muscles were tested. • Supplementation with GO-CURSD for 6 weeks ameliorated muscle atrophy. • GO-CURSD promoted anti-inflammatory and antioxidant activities through the Nrf2 pathway resulting in less muscle damage. • GO-CURSD ameliorated muscle atrophy by activating IGF1/Insulin-Akt-mTOR activity and down-regulating Atrogin-1 and MuRF-1 genes. Muscle atrophy is a reduction of muscle mass and size that occurs after the age of 30. The effects of the solid dispersions of curcumin (CURSD) and gamma-oryzanol (GOSD) were investigated on skeletal muscle of middle-aged Sprague-Dawley rats (12 months old) and compared to young rats (4 months old). A mixture of CURSD and GOSD supplements (GO-CURSD) increased antioxidant enzymes through the Nrf2 pathway which caused a reduction in lipid peroxidation and pro-inflammations, resulting in less muscle damage. The GO-CURSD increased IRS1-AKT-mTOR activity and suppressed Atrogin-1 and MuRF-1 genes, resulting in increased muscle mass and cross-sectional area. In addition, the GO-CURSD increased muscular glucose uptake and glycogen via IRS1-Akt up-regulated GLUT4 expression. These results suggest that the synergistic effect of CURSD and GOSD against age-related muscle atrophy regulated by increasing the antioxidant and anti-inflammatory activities, as well as improving muscle energy storage via the Nrf2 and IGF1/Insulin-Akt-mTOR signaling pathway.

A GAME WORTH THE CANDLE? META-ANALYSIS OF THE EFFECTS OF FORMALIZATION ON FIRM PERFORMANCE

Under what circumstances does firm formalization yield net benefits for previously informal firms? We systematically assessed 22 primary studies in a meta-analysis of African, Asian and Latin American firms. The studies are published between 2011 and 2021 and provide 1,372 performance and business practice estimates: 40 percent of the estimates show significantly positive and 54 percent insignificant effects. The FAT-PET analysis suggests a small positive effect of formalization on firm performance. We also employ a multivariate analysis: The overall genuine effect is modest. There is a positive role for information and time for effects to materialize. Notably, more rigorous designs and recent studies tend to identify smaller and more dispersed effects. The modest effects cast doubt about the capacity of formalization policies to improve business performances suggesting that policies might better focus on prioritizing business productivity and managerial capability over formalization. Yet, we need further experimenting and fine-tuning of policy approaches to precisely identify what could make the candle of formalization worth the effort. The current evidence supports theories arguing that the rational cost-benefit argument is an overly simplistic representation of the decision to formalize and that formalization is an uncertain decision affected by multiple and interrelated aspects.

The combined effects of dispersal and herbivores on stable states in coral reefs

The combined effects of dispersal and herbivores on stable states in coral reefs

Effect of Water Salt Composition on Oil Spill Dispersant Effectiveness Determined in Laboratory Conditions

Effect of Water Salt Composition on Oil Spill Dispersant Effectiveness Determined in Laboratory Conditions

Laboratory testing of dispersant effectiveness at high pressures

AbstractOil spills remain a serious environmental problem, and can have significant economic and ecological consequences. Despite the advantages, accidental deep‐sea oil releases during offshore exploration or production activities are of particular concern as the potential for such incidents increases significantly as we move to deeper waters. Dispersants are important mitigation tools as they have the capability to disperse the oil into a cloud of tiny oil droplets that can be readily degraded by hydrocarbon degraders if suitable environmental conditions prevail. In the case of an offshore incident, the dispersant is injected near the point of crude oil release so that dispersion is more effective. Given that our experience with subsea dispersant use is limited, the effect of pressure on the effectiveness of the dispersant has not been established, and hence, the composition and amount of dispersant to be injected has not been optimized. For typical surface oil spills, dispersant effectiveness is experimentally measured under laboratory conditions by the US‐Environmental Protection Agency (EPA) baffled flask test, which was later adapted as ASTM standard method F3251. Despite its extended use, this test cannot be used for testing dispersants at elevated pressures. In order to see whether pressure affects dispersant effectiveness, we developed a simple laboratory test protocol using a high‐pressure reactor (HPR). In addition, the effectiveness of five commercially available dispersants (COREXIT™ EC9500A, COREXIT™ EC9500B and COREXIT™ EC9527A, Marichem™, and Oiler 60) applied to a dead light crude oil has been determined at various pressures for the first time, and these values have been related to the standard baffled flask test (BFT) at atmospheric pressure. It is shown that pressure increase adversely affects dispersant effectiveness; however, the effect varies from a few percent to nearly a 50% decrease for a pressure increase of 100 bar depending on the particular dispersant used.

The Toxicity of Coated Silver Nanoparticles and Their Stabilizers towards Paracentrotus lividus Sea Urchin Embryos.

Surface modification of nanoparticles with different stabilizers is one of the most widely used methods to improve their stability and applicability. Silver nanoparticle (AgNPs) dispersions with biologically active stabilizers have great potential as plant protection products with synergetic antimicrobial properties and sufficient stability in terms of field application. The obtained AgNPs dispersions have the ability to enhance growth, increase yield and give better protection to various crops. At the same time, it is important to determine the fate, stability, and ecotoxicity of the applied nanosized products. The toxic effects of AgNPs dispersions and their constituents, organic stabilizers and additives, were evaluated using a phenotypic sea urchin embryo assay. Certain AgNPs dispersions with organic stabilizers demonstrated sufficient stability, even in seawater. The toxicity of the AgNPs decreased with the increasing tendency to agglomerate in seawater. Furthermore, the applied stabilizers were hazardous towards sea urchin embryos. They caused pronounced embryo abnormalities at 0.25-2.6 mg/L concentrations. AgNPs exhibited a lethal effect at concentrations that were equal to the MLC or exceeded the MEC of their stabilizers. Silver ions were more toxic towards sea urchin embryos than AgNPs.

THE EFFECT OF SiC DISPERSED SILICON CARBIDES ON THE QUALITY AND MICROHARDNESS OF Ni‒P-COATINGS AFTER CRYSTALLIZATION ANNEALING

The effect of SiC dispersed silicon carbides SiC additive (1.0 g/l) on formation of high (more than 1000HV) microhardness and defectiveness of the nickel-phosphorus coating of the steel parts used in critical assemblies and mechanisms at transportation of oil and mineral oil was evaluated. It is established, that regardless of SiC presence in the structure, the coating crystallizes with formation of identical microhardness level. However, the addition of SiC can drastically reduce the heat treatment time especially on parts with significant weight-size characteristics. The presence of defects in the coating – cracks and pore chains, was established by the standard method of wetting the inspected surface with an indicator solution. It has been shown that if the steel composition has less than 0.5% nickel, there are no defects on the surface of the coated parts both after crystallization annealing and during the long-term operation. If the nickel concentration is greater than 1.5%, cracking will occur in the nickel-phosphorus coating during heat treatment, despite the presence of the dispersive SiC additive in the composition. The revealed regularities of SiC dispersed silicon carbides effect on the microhardness value formed at crystallization annealing allow recommending their use in order to reduce the production process. The refined classification of steels, which nickel-phosphorus coatings are applied due to their tendency to defects, has revealed the main criterion – the content of nickel in the composition. It turned out that than lower the concentration of nickel is, then lower the risk of defect formation in the coating.

The effects of dispersal, herbivory, and competition on plant community assembly.

Dispersal is a key process in community assembly but is often considered separately from downstream assembly processes (e.g., competition, herbivory). However, dispersal varies by species and can interact with other assembly processes through establishment as species enter communities. Here, we sought to distinguish the role of dispersal in community assembly and its interaction with two biotic assembly processes: competition and herbivory. We used a tallgrass prairie restoration experiment that manipulated the competitive and herbivore environments while allowing for natural dispersal and establishment from a diverse regional species pool into areas of low diversity. Dispersal, competition, and herbivory all influenced local communities. By tracking the spread of four target species across the plots, we found interspecific and intraspecific differences in establishment patterns, with herbivores influencing the number of individuals present and the distances species moved. At the community level, only dispersal and competition significantly influenced alpha diversity, but all three processes additively influenced community composition. There was also evidence of herbivore-competition and herbivore-colonization trade-offs in our experiment. Some species that could tolerate herbivory were less likely to establish in competitive environments, while others that could tolerate herbivory were more likely to disperse greater distances. More work is needed to understand the contexts under which dispersal variation affects community assembly and its synergy with other processes.

Uncertainties and Radius Tracking in Flight-Path Angle Guidance for Aerogravity-Assist

This paper addresses the problem regarding the influence of random dispersions related to the environment and system on a flight-path angle guidance algorithm using lift modulation for aerogravity-assist maneuvers on hyperbolic trajectories. To compensate for the effects of dispersions and uncertainties, an original radius tracking guidance model is presented, with a formulation for both the temporal domain and the true anomaly domain. This algorithm allows a vehicle to successfully track a suboptimal trajectory planned before a mission. A case study involving a maneuver on a hyperbolic trajectory to Venus performed by a waverider, which is a spacecraft characterized by a high lift-to-drag ratio, is presented. An uncertainty and sensitivity analysis is used to evaluate the impacts of dispersions in the inputs on the main parameters and the performance characterizing the mission. The analysis provides an extensive range of cases that identify the density and thickness of the atmosphere as the most influential dispersed inputs. Adequately tuning the radius tracking guidance parameters enables the efficient attenuation and compensation of the perturbative effects of the uncertainties for obtaining trajectories that are close to the nominal trajectories, estimated before the mission in the absence of dispersions, in terms of the angular deflection and velocity magnitude variation. The presented model can be easily implemented for onboard guidance purposes.

Towards quantifying microbial dispersal in the environment.

Towards quantifying microbial dispersal in the environment.