The effects of crystal nucleation and growth on the viscosity of andesitic magmas are investigated at 1 atm. Pressure. The data are used to describe the rheological evolution of andesitic magmas and ...to derive empirical equations to model the crystallization dynamics. Viscosity experiments were performed at temperatures of 1473, 1483, and 1493 K with shear rates of 0.5 s−1 by using wide-gap concentric cylinder viscometry. We focused on eruptible magmas (i.e., crystal contents well-below ~50%) by following the time evolution of crystal nucleation and growth of a natural andesitic magma, while continuously monitoring the changes in viscosity. At near-equilibrium conditions, the basaltic-andesite contains 6, 13, and 25 area % crystals at 1493, 1483, and 1473 K, respectively, resulting in a viscosity increase of ca. 1 log unit. We show that the timescale of viscosity increase is mainly dictated by the delay time preceding crystallization and markedly decreases with increasing undercooling (from 22 to 42 K) and shear rates (from 0.1 to 1 s−1).
The plagioclase growth rates estimated from our data are in the order of ~3–5 × 10−6 cm/s, which is much faster than the rates estimated for crystallization in static conditions. We conclude that the effect of the shear rate must be taken into account in modelling magmatic and volcanic processes, especially when transient changes in viscosity need to be estimated. Our results are important for understanding the dynamics of lava flows where deformation plays a significant role in promoting crystallization.
•New viscosity data on dynamic basaltic-andesite magmas at shear rate of 0.5 s−1.•Increase in viscosity of ~1 log unit with increasing crystals content from 0 to 22 area% at 1473 K.•In undercooled systems, the delay time preceding crystallization decreases with undercoolingand shear rates.•Plagioclase growth rates in dynamic magmas are 2 to 3 orders of magnitude higher than the rates estimated for crystallization in static conditions.•Results have implications for the eruptive behavior and emplacement conditions of andesitic magmas and lavas.
•Methodology proposed to reflect effect of cold work on CGR model calculations for Type 316L SS.•Different crack tip strain rate equations adopted for different degrees of cold working.•Equation with ...explicit K dependence of CGR developed to assess BWR component integrity.•Developed equation applicable to evaluation of SCC CGRs in HAZ of pipe welds.
Stress corrosion cracking (SCC) is a critical issue for boiling water reactor (BWR) components, and their cold working is considered to be an accelerating factor for SCC crack growth rates (CGRs). However, no method has been proposed to quantitatively evaluate the SCC CGRs of cold worked stainless steels. In this study, the changes in material properties due to cold working were reflected in the input parameters of the Hashimoto-Koshiishi model, a mechanistic model of SCC growth based on the slip oxidation mechanism, to enable a quantitative evaluation of the SCC crack growth rate (CGR) of cold worked SSs. In addition, a simplified equation as a function of the yield strength of cold worked 316LSSs was developed for ease of practical use in the integrity assessment of components. The CGRs calculated by the model and/or the simplified equation were in good agreement with the experimentally obtained CGRs for cold worked SSs and the heat affected zone (HAZ) of Type 316L SSs.
The morphological evolution of organic crystals during crystallization depends on the face-specific growth rates. Classical growth rate models relate the face-specific growth rates to the crystal ...lattice, energy of stable facets, growth mechanism, and supersaturation. The complexities of these models have increased over time to account accurately for solution conditions, the structure of growth units, and their attachment rates. Such advanced growth rate models require several layers of computations to obtain attachment energies of facets, nucleation rates, kink density, and attachment rates. Among these, the most intensive and time-consuming computation is for attachment rates, which require molecular dynamic simulations. This substantially increases the overall computation time to predict the absolute growth rate for even one crystallization condition. Since it is nearly impossible to iterate such a growth rate model, optimization schemes cannot be implemented to identify solution conditions that favor specific crystal growth. To reduce the computational time for attachment rate calculations, we implement a group contribution method (GCM) that relates the properties of functional groups in a molecule to their attachment rates to the crystal lattice, thereby rapidly estimating the growth rates of organic crystals. The process of molecular attachment involves partial desolvation of a solvated molecule, referred to as a transition state, followed by total desolvation via spontaneous attachment to a crystal facet. The first step in GCM is to identify the equilibrium states of fully solvated and partially desolvated solute molecules. The degree of supersaturation dictates the extent of this equilibrium and, thereby, the activation barrier for the growth of crystals, according to transition state theory. Identifying this equilibrium phenomenon allows for capturing the functional-group-specific interactions that depend on molecular motion, which could be related to operating conditions such as temperature and pressure. The stochastic optimization technique with Monte-Carlo sampling allows an efficient optimization problem solution to obtain the group interaction parameters. The GCM approach is first validated for the estimation of growth rates of glutamic acid and L-histidine, and then extended to predict growth rates of alanine and glycine rapidly. The optimized parameters and GCM scheme can be used to estimate growth rates in other crystallization systems.
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•Group contribution method (GCM) is developed to estimate crystal growth rates.•Solvation-desolvation equilibrium provides group interaction parameters.•Interaction parameters are optimized using growth rates of glutamic acid and histidine.•Demonstrated GCM for rapid prediction of alanine and glycine growth rates.
PARADIGM TRANSFORMATION OF THE ECONOMIC CRISES MODELING Khalatur, Svitlana; Honcharenko, Oksana; Karamushka, Oleksandr ...
Fìnansovo-kreditna dìâlʹnìstʹ: problemi teorìì̈ ta praktiki (Online),
09/2022, Volume:
4, Issue:
45
Journal Article
Peer reviewed
Open access
In order to develop reasonable measures to counteract the destructive consequences of economic crises or to prevent them, it is important to build reasonable and adequate models of the emergence and ...course of crisis processes. The formal compliance of existing models with socio-economic processes during the crisis is often incomplete or cannot be adapted to other conditions, economies, and markets. Therefore, the article is devoted to the expediency and possibility of transformation of the existing paradigm of modeling economic crises.Modeling the interdependence of two basic indicators, which characterize the crisis in the economic development of European countries (GDP growth rates and employment growth rates), refuted the possibility of their mutual determination. The interdependence of the dynamics of GDP growth rates and employment growth rates for all studied objects without a shift in time, determined for the period 1996-2020 with a high level of reliability, is of the same type and made it possible to determine the range of their mutual changes. According to this range and the parameters of the codependencies of GDP growth rates and employment growth rates, eight clusters of countries were determined by the method of finding concentrations. The emergence of crisis processes coincides with specific parameters of the interdependent dynamics of GDP growth rates and employment growth rates but is not related to the internal division of Eurozone countries into clusters.The obtained results gave reason to put forward an alternative paradigm for modeling crisis processes, according to which economic crises arise as a result of the impact of random destructive events on systemic coincidences of potential periods of shifts in the contingent regularities of partial self-similar dynamics of economic processes. Within this paradigm, modeling of economic crises and forecasting their occurrence will be based on the study of self-similarity, dissipativeness and contingency of the dynamics of economic processes.
Abstract
Decommissioning the dingo barrier fence has been suggested to reduce destructive dingo control and encourage a free transfer of biota between environments in Australia. Yet the potential ...impacts that over a century of predator exclusion might have had on the population dynamics and developmental biology of prey populations has not been assessed. We here combine demographic data and both linear and geometric morphometrics to assess differences in populations among 166 red kangaroos (Osphranter rufus)—a primary prey species of the dingo—from two isolated populations on either side of the fence. We also quantified the differences in aboveground vegetation biomass for the last 10 years on either side of the fence. We found that the age structure and growth patterns, but not cranial shape, differed between the two kangaroo populations. In the population living with a higher density of dingoes, there were relatively fewer females and juveniles. These individuals were larger for a given age, despite what seems to be lower vegetation biomass. However, how much of this biomass represented kangaroo forage is uncertain and requires further on-site assessments. We also identified unexpected differences in the ontogenetic trajectories in relative pes length between the sexes for the whole sample, possibly associated with male competition or differential weight-bearing mechanics. We discuss potential mechanisms behind our findings and suggest that the impacts of contrasting predation pressures across the fence, for red kangaroos and other species, merit further investigation.
We show that one population of red kangaroos outside the dingo barrier fence has fewer females and joeys, and also grows up faster than a neighboring population that is protected by the fence. We argue that the impacts of contrasting predation pressures across the fence, for kangaroos and other prey, need further investigation.
Building on the entrepreneurial action and sustainable development literatures, we highlight how the current explanations of opportunity recognition, based on entrepreneurial knowledge and economic ...motivation, are insufficient for modeling the recognition of opportunities for sustainable development. Our model suggests that entrepreneurs are more likely to discover sustainable development opportunities the greater their knowledge of natural and communal environments become, the more they perceive that the natural and communal environment in which they live is threatened, and the greater their altruism toward others becomes. We propose that entrepreneurial knowledge plays a central role by moderating these effects.
Bivalve molluscs are a high quality animal protein source for humans, and the demand for farmed bivalves is increasing. Among the bivalve molluscs, the Portuguese oyster Crassostrea angulata, is one ...of the most popular species and is intensively farmed in warm water. In order to further increase the aquaculture yield of C. angulata through cost-effective farming practices, this study was conducted to evaluate the effects of stocking density, water depth and aquaculture gear on the aquaculture performance of C. angulata in the nursery and grow-out phases. The results of this study revealed that both stocking density and water depth affected the survival rate and growth rate of C. angulata in the nursery and grow-out phases. In the nursery phase, high stocking density reduced the survival rate, but was beneficial to the growth of C. angulata spats, while 1.5 m and 3 m were optimum for the survival and growth of C. angulata spats. In the grow-out phase, the use of lantern net/ rope culture, low stocking density with narrow substrate spacing and shallow water (1.5 m) were beneficial to the survival, growth and yeild of C. angulata. The results of this study can be used as a guide to further improve C. angulata aquaculture practices, and fill the knowledge gap on the effects of stocking density, water depth and aquaculture gear on C. angulata aquaculture.
•High stocking density reduced the survival of spats, but increased the growth.•Shallow water (1.5–3 m) favour the growth and survival of oyster spats.•Low stocking density and shallow water are best for oyster grow-out.•Lantern net is the best gear for C. angulata grow-out.
In coral reefs, dissolved organic matter (DOM) cycling is a critical process for sustaining ecosystem functioning. However, global and local stressors have caused persistent shifts from coral- to ...algae-dominated benthic communities. The influence of such phase shifts on DOM nature and its utilization by heterotrophic bacterioplankton remains poorly studied. Every second month for one year, we retrieved seawater samples enriched in DOM produced by coral- and algae-dominated benthic communities in a central Red Sea reef during a full annual cycle. Seawater incubations were conducted in the laboratory under in situ temperature and light conditions by inoculating enriched DOM samples with bacterial assemblages collected in the surrounding waters. Dissolved organic carbon (DOC) concentrations were higher in the warmer months (May–September) in both communities, resulting in higher specific growth rates and bacterial growth efficiencies (BGE). However, these high summer values were significantly enhanced in algal-DOM relative to coral-DOM, suggesting the potential for bacterioplankton biomass increase in reefs with algae replacing healthy coral cover under warmer conditions. The potential exacerbation of heterotrophic bacterial activity in the ongoing widespread regime shift from coral- to algae-dominated communities may have detrimental consequences for the overall health of tropical coral reefs.
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•Heterotrophic bacteria responses to coral- and algal-DOM changed seasonally.•DOC concentrations from both communities peaked during the warmer months.•Warmer months led to higher bacterial growth rates in algal-DOM.•Algal-DOM was processed more efficiently during the warmer months.
Modelling tourist expenditure at origin and destination Gómez-Déniz, Emilio; Pérez-Rodríguez, Jorge V; Boza-Chirino, José
Tourism economics : the business and finance of tourism and recreation,
05/2020, Volume:
26, Issue:
3
Journal Article
Peer reviewed
This article proposes a model of foreign tourist expenditure, based on expenditure in the country of origin (i.e. reservation of accommodation and transport) and on goods and services at the ...destination. The study focuses on two measures reflecting the two types of expenditure: the tourist budget share and the difference in growth rates between expenditure at origin and at destination. The random nature of each of these variables is taken into account. The tourist budget share is determined using a fractional response model, based on the beta distribution. This approach allows us to accommodate certain aspects of the empirical budget share distribution, such as skewness, and to represent the results as bounded between 0 and 1, but also to include covariates. The empirical analysis was conducted using data obtained by the Canary Islands Tourist Expenditure Survey, focusing on German and British tourists in particular. The results obtained show that the fractional regression model proposed represents the behaviour of the relevant variables reasonably well and surpasses the performance of the linear regression model.
•A field study evaluated Red Snapper growth after the Deepwater Horizon oil spill.•Pre- and post-spill vonBertalanffy growth curves were not significantly different.•Age-specific growth of the ...dominant ages declined significantly following the spill.•Environmental variables were unable to describe the significant growth variation.•Results have implications for population productivity in the short- and long-term.
The explosion of the Deepwater Horizon (DWH) oil platform in 2010 released more than 200 million gallons of crude oil into the northern Gulf of Mexico (GoM). Elevated levels of carcinogenic polycyclic aromatic hydrocarbons (PAHs) were abundant in the upper water column throughout the event. Previous research suggests that PAHs may have negatively affected fishes in the northern GoM. Our objective was to test whether crude oil contamination from the DWH oil spill was correlated with changes in growth rates in adult Red Snapper, Lutjanus campechanus. We fit von Bertalanffy growth curves and back-calculated length-at-age using data collected from 2011–2013 during long-line surveys in the northern GoM and on the West Florida Shelf. No significant variation in von Bertalanffy growth parameters existed among the catch years; a combined-years model gave L∞, k, and t0 values of 82.91, 0.20, and 0.43, respectively. No significant difference existed between pre- (back-calculated) and post-DWH growth curves. However, annual widths of the fourth, fifth, and sixth increments (the dominant cohorts in the population) declined significantly post-DWH (2010–2012) by 13%, 15%, and 22%, respectively, and were significantly smaller than the mean width of each respective increment in pre-spill years (2006–2009). While the DWH event was related temporally to growth declines in the dominant adult age groups, other environmental factors (winds, temperature, and river discharge) may also affect growth. Accordingly, meridional (V) and zonal (U) winds, sea level height anomalies (a proxy for water temperature variation), and Mississippi River discharge were compared to increment widths but none of the factors were strongly correlated with variation in age-specific growth increments (maximum Pearson’s r=0.47). Therefore, we are unable to reject the hypothesis that the DWH resulted in growth rate declines as opposed to climatic variation.
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