Assumption Of Homogeneity Research Articles

Homogenization assumptions for the two-scale analysis of first-order shear deformable shells

This contribution presents a multiscale approach for the analysis of shell structures using Reissner–Mindlin kinematics. A distinctive feature is that the thickness of the representative volume element (RVE) corresponds to the shell thickness. The main focus of this paper is on the choice of correct boundary conditions for the RVE. Three different types of boundary conditions, which fulfil the Hill–Mandel condition, are presented to bridge the two scales. A common feature is the application of zero-traction boundary conditions at the top and bottom surfaces of the RVE. Furthermore, an internal constraint is used to reduce the dependency of the stiffness components on the RVE size. The introduced boundary conditions differ mainly in the application of shear strains and their symmetry requirements on the RVE. The characteristic features are compared by means of linear-elastic benchmark tests. It is shown that the stress resultants and tangent stiffness components are obtained correctly. Moreover, the presented approach is verified using different macroscopic shell structures and different mesostructures. Both, linear and nonlinear small strain examples are compared to analytical values or full-scale solutions and demonstrate a wide applicability of the present formulation.

An independent framework-based evapotranspiration model (IFEM) for dual-source: From field to regional scale

The triangle/trapezoid framework model (TFM) is a widely used approach for mapping regional evapotranspiration (ET) based on thermal infrared remote sensing imagery. However, the homogeneity assumption for meteorological forcing and surface properties involved in TFM contradicts the characteristics of heterogeneous regions, leading to high uncertainty at regional scale, especially under energy-limited or strong advection conditions. Therefore, this study examined the linear relationship between soil moisture availability (ΛSM), evapotranspiration efficiency (ΛET) and radiation surface temperature (Trad), and developed an Independent Framework-based dual-source ET Model (IFEM) for heterogeneous regions. By fixing two key meteorological forcing variables, air temperature (Ta) and vapor pressure deficit (VPD), and three surface characteristic parameters, aerodynamic resistance (ra), albedo (α) and the ratio of soil heat flux to net radiation (Γ), the IFEM constructs a uniform fractional vegetation cover (fc)- Trad space. In this uniform fc-Trad space, isolines of ΛSM and ΛET are aligned with those of Trad, and an independent trapezoid framework is constructed for each pixel of RS images. It avoids the systematic bias caused by the distorted trapezoid space involved in traditional TFMs. The proposed model was applied in a hydrologically semi-enclosed irrigation area, the Hetao Irrigation District, with Landsat and MODIS datasets from 2016 to 2020 to evaluate its performance at the field and region scales. Firstly, the IFEM was capable of retrieving latent heat with a mean absolute error (MAE) of 34.43 W m−2 and a mean absolute percentage error (MAPE) of 8.68%, compared with the measurements from flux towers. Secondly, the IFEM reasonably separated the soil (MAPE = 21.33%) and canopy (MAPE = 14.33%) components from ET, compared with the soil evaporation observed by micro-lysimeters and the plant transpiration calculated by sap velocity upscaling technology. Thirdly, the IFEM showed high accuracy in estimating annual total ET with a percentage error range within ±3.0%, compared against the regional water balance calculations. Overall, the IFEM demonstrated high robustness and accuracy for field-scale and regional-scale applications, validating its potential as a reliable method for mapping regional ET in heterogeneous regions.

Space-time correlations of passive scalar in Kraichnan model

We consider the two-point, two-time (space-time) correlation of passive scalar R(r,τ) in the Kraichnan model under the assumption of homogeneity and isotropy. Using the fine-gird PDF method, we find that R(r,τ) satisfies a diffusion equation with constant diffusion coefficient determined by velocity variance and molecular diffusion. Its solution can be expressed in terms of the two-point, one time correlation of passive scalar, i.e., R(r,0). Moreover, the decorrelation of R^(k,τ), which is the Fourier transform of R(r,τ), is determined by R^(k,0) and a diffusion kernal.

Effect of resilience training on stress coping strategies among employees engaged in hard jobs during COVID-19 pandemic.

In recent years, the stress caused by the Covid-19 Pandemic has increased on the stress of working in difficult jobs, in this research resilience and coping styles focus on responding to stress. The present study aimed to examine the effect of resilience training on coping strategies during the COVID-19 pandemic by holding resilience-training sessions. This is a quasi-experimental study with a pretest-posttest control group design. The statistical population included all married personnel of Kavir Steel Complex, Aran and Bidgol County. In total, 30 couples were randomly selected and divided into case and control groups (n = 15 couples per group). In this study, Henderson and Milstein's resilience training package was used for resilience training; two basic assumptions of variance homogeneity of posttest error of coping strategies and homogeneity of regression line slope between pretests and posttests were examined. For data analyzing, we used SPSS Version 25. The results showed resilience training increased application of problem-oriented coping strategies (p < .01, SE = 1.88, Δx̄ = 10.19) and decreased application of emotion-oriented (p < .01, SE = 1.69, Δx̄ = 8.65) and avoidance (p < .01, SE = 1.86, Δx̄ = 4.15) coping strategies among the personnel. Moreover, the interaction effect of group and gender was only significant on emotion-oriented strategies at .05 (p < .05, F = 6.51). Analyzing the results showed that problem-oriented coping strategies, in contrast to avoidant and emotion-oriented strategies, positively controlled stress. The ability to deal with stressors is critical to daily functioning, adaptation, and mental and physical health. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Tackling local ecological homogeneity: Finding intraspecific trait variability in local populations of Mediterranean plants.

Local homogeneity, in ecology, is the often undisclosed assumption that variability within populations is negligible or mostly distributed evenly. In large areas, this can lead to the aggregation of different populations without regard for their unique needs and characteristics, such as drought sensitivity and functional trait distributions. Here, we discuss whether this assumption can be justified, and we hypothesize that discerning the source of variation between plasticity and adaptation could be a feasible approach to formulate an informed decision. We test this hypothesis on plants, resorting to a common garden experiment to determine the source of variation of several plant functional traits at a local scale (~60 km) of three wild species: Quercus ilex, Pistacia lentiscus, and Cistus salviifolius. Individuals of each species were sourced from three key sites chosen along a local aridity gradient. Our approach led to the rejection of the local homogeneity assumption for Q. ilex and C. salviifolius at this scale due to the adaptive divergence observed among neighboring populations. This case study provides evidence that addressing local homogeneity can highlight diverging populations in a relatively simple way. We conclude that gathering empirical evidence on intraspecific variability is a feasible approach that can provide researchers with solid bases to decide whether to adopt the local homogeneity assumption or not.

Growth Effect of Migrant Remittances and Human Capital: Panel Evidence from Sub-Saharan African Countries

Purpose: The aim of this study is to examine the growth effect of migrant remittances and human capital in sub-Saharan Africa (SSA) economies.&#x0D; &#x0D; Theoretical Framework: The study adopts the Cobb-Douglas production function of the AK model to examine the growth effect of migrant remittances and human capital in sub-Saharan Africa (SSA) economies.&#x0D; &#x0D; Design/Methodology: Data from 27 SSA countries for the period 2000-2020 was obtained from the World Development Indicator, a publication of the World Bank. The study variables include, real per capita income, migrant remittances, human capital, domestic investment, trade openness and inflation. The panel fully modified ordinary least square (PFMOLS) technique was deployed to analyse the study model.&#x0D; Findings: The study’s outcome showed that migrant remittances positively influence and cause growth while human capital has not contributed to growth in the SSA region.&#x0D; &#x0D; Research, Practical &amp; Social Implication: From the study findings, it is recommended that regional government should encourage the continuous inflow of migrant remittances to their countries and make conscious efforts in developing the level of human capital in their country via constant training, reducing or eradicating the number of school drop-out at all levels (primary, secondary, and tertiary).&#x0D; &#x0D; Originality/Value: In this study, the issue of migrant remittances, human capital and growth is re-examined by (i) considering a panel of similar economies, (ii) estimating Cobb-Douglas production function for the effect of migrant remittances via technology and human capital, (iii) adopting a robust technique (PFMOLS) that relax the assumption of homogeneity among parameters across economies and the exogeneity of migrant remittances.

Allometric model for height estimation of Alnus acuminata Kunth in agroecological zones of the high Andean tropics

The complexity in the management of field tools for recording dasometric information has led to the use of allometric equations that save time, work, and costs allowing the estimation of variables that are difficult to record, such as total height (TH). The objective of this research was to develop an allometric equation for the species Alnus acuminata in order to calculate TH from the diameter at breast height (DBH). At the Obonuco-AGROSAVIA Research Center in Pasto (Nariño), dasometric information was recorded for 75 months for 200 even-aged trees. Four models were evaluated: linear, polynomial, Mixed linear (random effect per tree age), and Mixed linear (random effect per tree). For the selection of the best model, the criteria were used with the lowest values ​​of Akaike (AIC) and Bayesian (BIC). The information was analyzed using the "Nonlinear Mixed-Effects Models" package, R software. The results revealed that A. acuminata had an 81% survival; the TH average was 7.4 ± 1.3 m; and the average DBH was 9.51 ± 2.23cm. The average annual increase of DBH was 1.5 cm year-1, and the TH was 1.18 m∙ per year-1. The mixed linear model confirmed the assumptions of normality, independence, and homogeneity of variances in addition of having good criteria in its predictive performance and efficiency through the equation TH=2.07+0.35*DBH+0.95*Age. This research contributes to the management of native species of the high tropics by designing an equation for the first vegetative growth phases of A. acuminata in high mountain agroecological zones.

Leveraging chemical heterogeneity in steels heat treated to retain metastable austenite

The assumption of chemical homogeneity simplifies heat treatment design, particularly for processes like quenching and partitioning (Q&P) aimed at retaining metastable phases in advanced high strength steels. However, real microstructures contain chemical heterogeneities (e.g., banding from solidification or phase partitioning); these effects on final microstructures are not well understood. To investigate the role of chemical heterogeneity, inter-band and intra-band chemical heterogeneities were measured across starting ferrite/pearlite microstructures to predictively model final Q&P microstructures produced by heat treatment. Two models were developed to investigate effects across chemical bands and within prior pearlite regions, supported by experimental measurements of solute distributions. These models quantify the impact of initial microstructural condition on final microstructures with heat treatment, are applicable to other alloys and heat treatments where retaining metastable phases and solute profiles is desirable, and could be used to intentionally design heat treatment processes to exploit chemical heterogeneities and create otherwise unobtainable microstructures.

Pspace-completeness of the temporal logic of sub-intervals and suffixes

In this paper, we prove Pspace-completeness of the finite satisfiability and model checking problems for the fragment of Halpern and Shoham interval logic with modality 〈E〉, for the “suffix” relation on pairs of intervals, and modality 〈D〉, for the “sub-interval” relation, under the homogeneity assumption. The result significantly improves the Expspace upper bound recently established for the same fragment, and proves the rather surprising fact that the complexity of the considered problems does not change when we add either the modality for suffixes (〈E〉) or, symmetrically, the modality for prefixes (〈B〉) to the logic of sub-intervals (featuring only 〈D〉).

Aging characterization and degradation of Nitrile Butadiene Rubber for viscoelastic damping applications

The aging and degradation of nitrile butadiene rubber (NBR) for viscoelastic damping applications is a critical issue for design engineers in ensuring the long-term service of mechanical systems. In this study, the aim was to characterize the aging of NBR and assess its impact on the damping characteristics of the material. The NBR material was allowed to age naturally under ambient conditions, with no load, and homogeneous and isotropic assumptions were made. The Fourier-transform infrared spectroscopy (FTIR) technique was utilized to identify alterations in the functional groups of NBR during the aging process. The complex properties of naturally aged NBR materials were compared to those of virgin NBR materials in the frequency and temperature domains using dynamic mechanical analysis (DMA) experiments. Mechanical tests were used to assess the hardness, elongation break, and failure stress of both virgin NBR and naturally aged NBR. An Obrest beam configuration with aluminum as the base material was employed in the experiments to examine the damping capacity of NBR. According to the results, NBR's damping ability declined with age, falling by 8% at the first resonance frequency and 34% at the third resonance frequency. The results of this study provide important insights into the aging and degradation of NBR for viscoelastic damping applications and will aid in the design and selection of materials for these applications.

Adaptive thresholding for iterative matrix completion with heterogeneous missing probability: H-AdaptiveImpute

Several low-rank matrix completion algorithms have been developed, which often employ thresholded singular value decomposition (SVD) iteratively. Their performance depends on the choice of thresholding tuning parameters and initial input matrix. In particular, the initialization of the non-convex optimization algorithms plays a pivotal role. However, they often use a zero matrix or a consistent low-rank matrix estimator under the simple homogeneous observation probability assumption as the initial input matrix. This paper proposes a non-convex low-rank matrix completion algorithm with an intelligent initial matrix under the heterogeneous observation probability structure. Specifically, the proposed algorithm iterates the thresholded SVD starting from a tailored initialization based on the estimator of the singular values and vectors of the underlying matrix. We show that the proposed initial estimator is consistent, and the adaptive thresholding tuning parameters are estimated using theoretically justified and data-driven procedures. The results of the numerical experiments show that the proposed algorithm performs well compared to the existing method.

Numerical simulation of the extrusion and layer deposition processes in 3D concrete printing with the Particle Finite Element Method

Abstract3D Concrete Printing (3DCP) is a rapidly evolving technology that allows for the efficient and accurate construction of complex concrete objects. In this paper, a numerical modelling approach is presented for the simulation of the printing process of cementitious materials, based on the homogeneous fluid assumption. To cope with the large deformations of the domain and the nonlinearity resulting from the use of a non-Newtonian rheological law, the Navier–Stokes equations are solved in the framework of the Particle Finite Element Method (PFEM). Furthermore, tailored solutions have been formulated and implemented for the time-dependent moving boundary conditions at the nozzle outlet and for the efficient handling of the inter-layer contact in the same PFEM framework. The overall computational cost is decreased by the implementation of an adaptive de-refinement technique, which drastically reduces the number of degrees of freedom in time. The proposed modelling approach is finally validated by simulating the printing process of six rectilinear layers and one multi-layer “wall”. The results show good agreement with the experimental data and provide valuable insights into the printing process, paving the way for the use of numerical modelling tools for the optimization of materials and processes in the field of 3D Concrete Printing.

The effective reproductive number: Modeling and prediction with application to the multi-wave Covid-19 pandemic

Classical compartmental models of infectious disease assume that spread occurs through a homogeneous population. This produces poor fits to real data, because individuals vary in their number of epidemiologically-relevant contacts, and hence in their ability to transmit disease. In particular, network theory suggests that super-spreading events tend to happen more often at the beginning of an epidemic, which is inconsistent with the homogeneity assumption. In this paper we argue that a flexible decay shape for the effective reproductive number (Rt) indexed by the susceptible fraction (St) is a theory-informed modeling choice, which better captures the progression of disease incidence over human populations. This, in turn, produces better retrospective fits, as well as more accurate prospective predictions of observed epidemic curves. We extend this framework to fit multi-wave epidemics, and to accommodate public health restrictions on mobility. We demonstrate the performance of this model by doing a prediction study over two years of the SARS-CoV2 pandemic.

Risk averse reproduction numbers improve resurgence detection.

The effective reproduction number R is a prominent statistic for inferring the transmissibility of infectious diseases and effectiveness of interventions. R purportedly provides an easy-to-interpret threshold for deducing whether an epidemic will grow (R>1) or decline (R<1). We posit that this interpretation can be misleading and statistically overconfident when applied to infections accumulated from groups featuring heterogeneous dynamics. These groups may be delineated by geography, infectiousness or sociodemographic factors. In these settings, R implicitly weights the dynamics of the groups by their number of circulating infections. We find that this weighting can cause delayed detection of outbreak resurgence and premature signalling of epidemic control because it underrepresents the risks from highly transmissible groups. Applying E-optimal experimental design theory, we develop a weighting algorithm to minimise these issues, yielding the risk averse reproduction number E. Using simulations, analytic approaches and real-world COVID-19 data stratified at the city and district level, we show that E meaningfully summarises transmission dynamics across groups, balancing bias from the averaging underlying R with variance from directly using local group estimates. An E>1generates timely resurgence signals (upweighting risky groups), while an E<1ensures local outbreaks are under control. We propose E as an alternative to R for informing policy and assessing transmissibility at large scales (e.g., state-wide or nationally), where R is commonly computed but well-mixed or homogeneity assumptions break down.

Episodes of regime transformation

This article provides a new conceptualization of regime transformation that allows scholars to address democratization and autocratization as related but obverse processes. We introduce a dataset that captures 680 episodes of regime transformation (ERT) from 1900 to 2019 and offers novel insights into regime change over the past 120 years. The ERT has three main advantages over other approaches. First, it avoids problematic assumptions of unit homogeneity and constant as well as symmetric effects. Second, it integrates key insights from qualitative studies by treating regime change as a gradual and uncertain process. Third, the ERT is based on a unified framework for studying regime transformation in either direction. The dataset differentiates between four broad types of regime transformation: liberalization in autocracies, democratic deepening in democracies, and autocratization in both democracies and autocracies (democratic and autocratic regression). It further distinguishes ten patterns with distinct outcomes, including standard depictions of regime change (i.e. democratic transition or breakdown). A minority (32%) of ERTs produce a regime transition, with the majority of episodes either ending before a transition takes place or not having the potential for such a transition (i.e. further democratization in democratic regimes or further autocratization in autocratic regimes). We also provide comparisons to other datasets, illustrative case studies to demonstrate face validity, and a discussion about how the ERT framework can be applied in peace research.

Multivariate effect of organic and inorganic fertilizer mixtures on growth of Lactuca sativa L.

The objective of this research was to evaluate the multivariate effect of organic and inorganic fertilizer mixtures on growth of Lactuca sativa L. For this purpose, a complete multivariate randomized design was performed, with 5 replicates in 20 parcels, to which the treatments were randomly distributed. The data on the number of leaves per plant and the height of lettuce was obtained at harvest in the study field where the experiment was conducted. The compliance with the basic assumptions of normality and multivariate homogeneity of the experimental residuals was significantly demonstrated, evidencing the adequacy of the model. Likewise, the levels of organic and inorganic fertilizers had significant effects on the number of leaves and height of the lettuce plant collectively and individually.

Numerical simulations of cavitating water jet by an improved cavitation model of compressible mixture flow with an emphasis on phase change effects

Focusing on cavitation phenomena caused by high-speed submerged water jets, this paper presents an improved cavitation model for a compressible fluid mixture based on a concise estimation of fluid compressibility that considers phase change effects. The homogeneous two-phase flow assumption is adopted, and the gas phase is assumed to consist of vapor and non-condensable components. Equations of state for a pure liquid and an ideal gas are employed to evaluate the compressibility of the liquid and non-condensable components, and the compressibility of the vapor is treated semi-empirically as a constant. The model is embedded in an unsteady Reynolds-averaged Navier–Stokes solver, with the realizable k-ε model employed to evaluate the eddy viscosity. The turbulent cavitating flow caused by an impulsively started submerged water jet is treated. The pattern of periodic cavitation cloud shedding is acceptably captured, and the mass flow rate coefficient and its fluctuation frequency evaluated by simulations agree with the experimental results well. The validity of the proposed method is confirmed. The results reveal that cavitation occurs when pin/Pin reaches 0.65 and fluid flow begins to pulsate. In the well-developed stage, the leading cavitation cloud and a subsequent cloud are successively shed downstream, and this process is repeated. The subsequent cloud catches the leading cloud, and they coalesce in the range x/d≈ 2–3. The pressure fluctuations concentrate in the range of x/d≈2–5 corresponding to the periodic shedding of cavitation clouds. The mass flow rate coefficient pulsates from 0.59–0.66 under the effect of cavitation.

Investigating the relationship between monetary policy, macro-prudential policy and credit risk in Indonesia banking industry

Using a novel panel data set we study the influence of monetary and macro-prudential policies on non-performing loans as a measure of credit risk in Indonesian banking industry from Q1 2010 to Q4 2022. The panel homogeneity assumption was verified through the utilization of the Chow and Roy-Zellner tests. The findings showed that the model was not homogenous, necessitating the use of the Pooled Mean Group (PMG) estimator. The results indicated that monetary and macro-prudential policies significantly impacted credit risk. Furthermore, tight monetary and macro-prudential policies increased and reduced credit risk in the long run, respectively. The findings also showed that a loosening monetary policy reduced credit risk in the short run. Therefore, higher authorities must establish effective monetary and macro-prudential policies to reduce the non-performing loan ratio and maintain credit risk in Indonesia's banking industry.

Relaxing parametric assumptions for non-linear Mendelian randomization using a doubly-ranked stratification method.

Non-linear Mendelian randomization is an extension to standard Mendelian randomization to explore the shape of the causal relationship between an exposure and outcome using an instrumental variable. A stratification approach to non-linear Mendelian randomization divides the population into strata and calculates separate instrumental variable estimates in each stratum. However, the standard implementation of stratification, referred to as the residual method, relies on strong parametric assumptions of linearity and homogeneity between the instrument and the exposure to form the strata. If these stratification assumptions are violated, the instrumental variable assumptions may be violated in the strata even if they are satisfied in the population, resulting in misleading estimates. We propose a new stratification method, referred to as the doubly-ranked method, that does not require strict parametric assumptions to create strata with different average levels of the exposure such that the instrumental variable assumptions are satisfied within the strata. Our simulation study indicates that the doubly-ranked method can obtain unbiased stratum-specific estimates and appropriate coverage rates even when the effect of the instrument on the exposure is non-linear or heterogeneous. Moreover, it can also provide unbiased estimates when the exposure is coarsened (that is, rounded, binned into categories, or truncated), a scenario that is common in applied practice and leads to substantial bias in the residual method. We applied the proposed doubly-ranked method to investigate the effect of alcohol intake on systolic blood pressure, and found evidence of a positive effect of alcohol intake, particularly at higher levels of alcohol consumption.

Social Entrepreneurship as a Family Resemblance Concept with Distinct Ethical Views

Almost 25 years after Dees’ article on the meaning of social entrepreneurship, conceptual controversy persists. Based on a qualitative analysis of 209 definitions of social entrepreneurship and respective academic articles, we argue that the concept follows a family resemblance structure and identify the 12 distinct attributes that comprehensively define it. Membership in social entrepreneurship is not defined by a case possessing a universally accepted set of criterial features but by carrying shared attributes with other cases. The family resemblance structure points to the persistent fallacy of using the same term to label different phenomena and cautions researchers against causal homogeneity assumptions among different conceptual subtypes. Assuming a descriptive stance, we shed light on how distinct ethical positions relate to different definitions of social entrepreneurship. Among the existing conceptual variety, we identify four prominent subtypes and find that ‘market-based’ conceptualizations relate to economism, the ‘social business’ subtype relates to rule utilitarian positions, ‘efficiency-driven’ definitions are associated with hedonistic act utilitarian views, and the ‘transformational impact’ subtype is akin to a eudemonic act utilitarian stance.