Steady-state Growth Research Articles

Fatigue crack propagation analysis in an aero-engine turbine disc using computational methods and spin test

This article presents a study on applying the fracture mechanics-based method to predict the fatigue crack growth (FCG) characteristics of the turbine disc in a turboshaft engine. According to the stress analysis results, the electric discharge machining (EDM) method introduced notches for initiating cracks of a specific size into the critical locations of the turbine disc. The FCG of these cracks under cyclic load was predicted utilising a three-dimensional (3D) numerical analysis method and a simplified rectangular plate model with relevant fracture mechanics properties. Meanwhile, the full-scale spin test was performed using a pre-flawed turbine disc under intentional loads at an isothermal temperature. After the test, the crack surface fractography and the quantitative fracture striation analysis revealed the practical crack propagation behaviour. There was a relatively small difference between the experimental results and the 3D finite element method, which indicated the good predictability of FEM for turbine disc crack growth. Furthermore, the rectangular plate models could predict the front stage of steady-state crack growth but were overall conservative due to their inability to precisely calculate the effects of crack growth and structure geometry on the stress intensity factor.

Factors involved in Economic Development and their Impact on State-Building in Malaysia

The successful history of poverty elimination and impressive economic development in Malaysia for the post-colonial period regarded a worth model for growth in developing world. The question raised in this achievement was; how economic development affected on the state-building in the country? Therefore, the motive of the study is to examine the determinants of economic development on state-building. Autoregressive distributed lag (ARDL) model employed to test economic factors affecting the state-building. The study covered data spanning from 1970-2017. The long-run co-integration in the model has confirmed, and econometric diagnostic tests are robust. The study findings show that human capital, oil rent, and per capita income, positively and significantly affect state-building in the long-run. In the short-run, human capital and oil revenue effects positively and significant. Population growth, democracy, inflation, and financial development have confirmed a negative and significant impact on state-building. Policy implication has highlighted the importance of human capital development, macroeconomic stability, and population growth in Malaysia's state-building. Demographic transition exerts a considerable negative effect on state-building in the long-run, affecting the economic health and steady-state growth. Financial development inserting a negative impact on state-building to promote development. The study recommended that the economic policymakers and relevant bureaucracies correct the fiscal deficit and ease domestic financial institutions into the credits based on the findings. Malaysia is facing a demographic threat in the long run due to the aging population and low fertility rate; therefore, it have to re-address the population policy.

Ahmed Galal and Nadeem Ul Haque (eds). Fiscal Sustainability in Emerging Markets: International Experience and Implications for Egypt. Cairo/ New York: The Egyptian Center for Economic Studies. 2006. ix+289 pages. Paperback. Price not given.

Fiscal sustainability is required to attain and maintain the long-run steady-state growth in emerging markets, to create fiscal space for rural and urban poverty, to safeguard financial stability, and to achieve the overall Millennium Development Goals. This can be done by providing financial support and by encouraging further research in this area. This book analyses the issues in the context of international experience and its implications for Egypt. It touches on issues of fiscal deficit and public debt sustainability, debt management, efficiency and equity of social expenditure, and public investment, the will and power to achieve civil service reform, and transparency and equitability of the budgetary process. It fills a gap in research.

Analysis of the Prospect of China's Cold-Chain Logistics Development

With the rising of China's fresh food e-commerce industry, the steady-state growth of the market scale, the improvement of the consuming ability, the reinforcement of the country's management of food safety, the increase of the requirement of the downstream application of cold chain logistics, traditional refrigerated transport can't meet the requirement of the market in various aspects such as organization, management, equipment, facilities, information services, etc. and the cold-chain transportation industry requires upgrade, which promotes China's cold-chain logistics transportation industry to enter a period of rapid development. This paper applies the PESTE model to analyze the differences of cold-chain logistics in China and in developed countries and the development status of China's cold-chain logistics, and uses the literature review to analyze the development prospect of China's cold-chain logistics in the future.

Does Okun’s Law Hold for China? Some Empirical Evidence

This paper seeks to estimate the applicability of Okun’s law to the situation in China between 1991 and 2020. A defining and most significant feature of this paper is that China’s unemployment rate has been proxied by youth unemployment and urban unemployment. The stochastic properties test reveals that all the three variables follow I(1) process. The paper uses this knowledge to build data generating process (DGP), which is an outstanding contribution to international research into the steady state growth. Many researchers have pointed out that the poor countries catch up faster and, consequently, their growth rate should have a trend component to it. The applied regression model has proxied the trend when estimating the operation of the Okun’s law. The inclusion of trend, strongly factual, is accounted for and reveals that Okun’s law is valid for China. Apart from the OLS estimator for testing the Okun’s law, the generalized method of moment estimator has also been used as another estimator with the first lag of both unemployment and GDP as instrumental variables. Empirical evidence supports the proposition that Okun’s law is indeed valid in the case of China contrary to the conclusion of some studies.

Coupling gene expression dynamics to cell size dynamics and cell cycle events: Exact and approximate solutions of the extended telegraph model

The standard model describing the fluctuations of mRNA numbers in single cells is the telegraph model which includes synthesis and degradation of mRNA, and switching of the gene between active and inactive states. While commonly used, this model does not describe how fluctuations are influenced by the cell cycle phase, cellular growth and division, and other crucial aspects of cellular biology. Here, we derive the analytical time-dependent solution of an extended telegraph model that explicitly considers the doubling of gene copy numbers upon DNA replication, dependence of the mRNA synthesis rate on cellular volume, gene dosage compensation, partitioning of molecules during cell division, cell-cycle duration variability, and cell-size control strategies. Based on the time-dependent solution, we obtain the analytical distributions of transcript numbers for lineage and population measurements in steady-state growth and also find a linear relation between the Fano factor of mRNA fluctuations and cell volume fluctuations. We show that generally the lineage and population distributions in steady-state growth cannot be accurately approximated by the steady-state solution of extrinsic noise models, i.e. a telegraph model with parameters drawn from probability distributions. This is because the mRNA lifetime is often not small enough compared to the cell cycle duration to erase the memoryof division and replication. Accurate approximations are possible when this memory is weak, e.g. for genes with bursty expression and for which there is sufficient gene dosage compensation when replication occurs.

Modeling Approach to Capture the Effect of High Frequency Flashing Light in Steady-State Microalgae Cultures

With the advent of efficient artificial light systems, the possibility of exploiting pulsed light (PL) in microalgal cultivation is gaining renewed attention. In this work, a model was developed to describeArthrospira maxima production in continuous cultivation systems, under both continuous and high-frequency pulsed light regimes. The model is based on the one originally developed by Camacho-Rubio, modified to link photosynthetic units activation to biomass growth, accounting also for maintenance. The modified model, calibrated in continuous light regime, was found to properly predict steady-state microalgal growth at different light intensities and residence times. The model was then validated on experimental data carried out under extreme PL conditions (high frequencies up to 3700 Hz and duty cycles as low as 0.01). Remarkably, it was able to account for the flashing light effect (FLE, i.e., increased biomass production with respect to continuous light supply) measured under such conditions and can therefore be a valuable tool to optimize the energetic efficiency of algal cultivation.

Aggregate and disaggregate impact of natural resources on economic performance: Role of green growth and human capital

A curse or blessing, natural resources remains a dilemma with diverse findings for both developed and developing economies. However, the disaggregated and aggregated impacts of natural resources have not yet been unearthed for high-income economies, i.e., the G-7 economies. This study is hence aimed to explore the aggregated and disaggregated impacts of natural resources on economic growth and the controlling role of carbon emissions, human capital, and green growth from 1990 to 2020. To obtain the coefficients of the selected regressors, the novel Method of Moments Quantile Regression (MMQR) approach is employed. From the empirical estimations, it is concluded that the availability of aggregated and disaggregated natural resource is negatively intertwined with economic development among the G-7 nations, thereby validating the existence of the “resource curse” hypothesis at both aggregated and disaggregated levels. This outcome is consequential and calls for immediate attention from the high authorities in the G-7 region. The member nations should work cooperatively to establish a stable regional market that can absorb the price volatility of natural resources and control the demand and supply mismatch of energy and related natural resources, which will help to attain steady-state economic growth. Additionally, the mining cost and mining-induced environmental costs need to be minimized through technological forwardness and scientific mining. The findings also unveil that green growth reduces economic development among the G-7 nations. This is justified, given that green growth requires more dependence on clean energy sources, which means less extraction and consumption of fossil fuels. Moreover, human capital development and CO2 emissions are boon for economic amelioration among the panel nations; however, CO2 emissions-induced development is highly discouraged considering the G-7 nation's green growth directory. However, it is speculated that the green growth agenda may exacerbate the region's resource curse dilemma. Therefore, the G-7 nations should cautiously estimate the trade-offs between green growth and a natural resource-induced curse.

Higher resistance and resilience of bacterial growth to drought in grasslands with historically lower precipitation

Climate change is expected to alter precipitation regimes, resulting in longer periods of drought and heavier precipitation events. Even though the direct effect of water availability on soil microbial processes is well documented, the influence of precipitation legacy on microbial resistance and resilience to drought remains unclear. Using soils from a natural mean annual precipitation (MAP) gradient (∼550–950 mm yr−1) equipped with long-term (>8 yr) rain-out shelters, we investigated how the history of precipitation influenced microbial ‘resistance’ (tolerance to drying) and ‘resilience’ (ability to recover growth rates following rewetting) to drought. We found that bacterial growth was more resistant and resilient to drought in sites with lower MAP. In contrast, the precipitation-reduction treatments had no detectable influence on microbial drought resistance or resilience. The microbial carbon-use efficiency immediately after rewetting was higher in soils from lower precipitation sites. In contrast, the steady-state microbial growth rates and respiration (under standardized moisture conditions) were consistent along the precipitation gradient. The variation in microbial drought resistance and resilience across the precipitation gradient was linked to the microbial community structure. Taken together, our results suggest that historical precipitation regimes – and the associated differences in exposure to drought – had selected for bacterial communities that were more resistant and resilient to drought.

Constrained Public Health Care Spending and Steady State in Health Outcomes in Nigeria

Health expenditure is described as expenses on health, which any government incurs for the maintenance and provision of healthcare services, for the good of the health system, society and the economy. The total government expenditure on health for Nigeria as for 1990, 2000, 2017, 2018 2020, and 2021 are N658.1million, N202.8million, N304billion, N340billion, N547billion and N427billion respectively. The belief is that this would improve the health of the citizenry, which can be translated into better human capital base with its multiplier effects on the health outcomes and status of the economy and as well as the economic growth and development. In modeling the effect of health expenditure on health outcome in Nigeria, the study used multiple regression analysis approach to captures the dynamics of annual health expenditure, cash expenditure on health, health insurance and health tax on health outcome (proxy by life expectancy and infant mortality) within the nation, using data set from World Development Indicator (WDI) from 1985 to 2020. The study found that private health expenditure as the major determinants to steady state growth in health outcome in Nigeria. The study revealed that public health expenditure shows a negative relationship with infant mortality and life expectancy in Nigeria due to constrained healthcare financing. This equally points to the fact that private sector (cash expenditure on health) is more efficient than the constrained public health budget allocations (public health expenditure). The implication of this finding is that private sector (cash expenditure on health) has greater influence on health outcomes especially in infant mortality and life expectancy. The economic implication of this finding is that health services will be obtained at a high cost in Nigeria due to constrained public health spending. That is to say that the principle of excludability is at work in Nigeria health sector thereby making achievement of social optimality in Nigerian health care services impossible. Following the finding of the study, therefore, government should endeavor that all the citizens benefit from health insurance irrespective status.

Flexible Power Point Tracking Using a Neural Network for Power Reserve Control in a Grid-Connected PV System

Renewable energy penetration in the global energy sector is in a state of steady growth. A major criterion imposed by the regulatory boards in the wake of electronic-driven power systems is frequency regulation capability. As more rooftop PV systems are under installation, the inertia response of the power utility system is descending. The PV systems are not equipped inherently with inertial or governor control for unseen frequency deviation scenarios. In the proposed method, inertial and droop frequency control is implemented by creating the necessary power reserve by the derated operation of the PV system. While, traditionally, PV systems operate in normal MPPT mode, a derated PV system follows a flexible power point tracking (FPPT) algorithm for creating virtual energy storage. The point of operation for the FPPT of the PV is determined by using a neural network block set available in MATLAB. For the verification of the controller, it is applied to a PV array in a modified IEEE-13 bus system modeled in the MATLAB/Simulink platform. The simulation results prove that when the proposed control is applied to the test network with renewable energy penetration, there is an improved system inertia response.

Experimental and modeling study of foam coarsening kinetics in porous media

The geometric confinement significantly affects the foam coarsening dynamics in porous media. We present the experimental and modeling studies of coarsening-induced foam structural evolution in a porous microfluidic chip. The findings are expected to shed light on predicting the foam structure in many applications, such as foam-assisted enhanced oil recovery process and CO2 geological sequestration. It is shown that, in porous media, small bubbles are constantly consumed by large bubbles due to inter-bubble gas diffusion until most bubbles grow to the pore or throat size. The coarsening of edge bubbles (bubbles contacting the boundary) dominates the foam coarsening process, showing a linear increase in the average area of edge bubbles with time in a steady-state growth state. A mass transfer model is proposed to fit the foam coarsening rate of edge bubbles, including critical parameters such as liquid film permeability, gas-liquid interfacial tension, the molar volume of the dispersed phase, and the polydispersity of bubble size distribution. We emphasize that, under the same experimental conditions, foams with a broader size distribution exhibits a faster coarsening rate due to higher capillary pressure differences among the bubbles as the mass transfer driving force.

Solvent-induced crack growth in poly(methyl methacrylate)/multiwalled carbon nanotube composites

Understanding the structural integrity of polymer composites in service conditions is of practical importance for the applications of polymer composites. In this work, we investigate the solvent-induced crack growth in poly(methyl methacrylate)/multiwalled carbon nanotube (PMMA/MWCNT) composites in respective organic solvents of 2-ethylhexyl alcohol (2 EA), cyclohexanol, and 1-butanol at different temperatures after being immersed in methanol at 50 °C for 25 min. The areal density of crack lengths and growth rate of a single crack in the PMMA/MWCNT composites increase with the immersion time and temperature for the solvents of 2 EA and cyclohexanol. The areal density of crack lengths in the PMMA/MWCNT composites immersed in 1-butanol is largest at 30 and 40 °C and smallest at 50 °C. The 1-butanol solvent causes the fastest, steady-state crack growth at 30 and 40 °C and the slowest crack growth at 50 °C. Increasing the fraction of MWCNTs reduces the areal density of crack lengths and the growth rate of a single crack in the healed and non-cracked areas. The crack growth is controlled by a thermally activated process. The crack growth rate is faster in the healed area than in the non-cracked area for the same composite and solvent. The activation energy for the motion of polymer chains associated with the single-crack growth in the non-cracked area is smaller than that for solvent-induced cracking because the interaction between cracks hinders crack growth.

Passivation of corrosion product layer on AM50 Mg by corrosion inhibitor

The influence of sodium dodecyl sulfate (SDS) on morphology and chemical composition of corrosion product layer formed on α-Mg matrix and cathodic Al-Mn intermetallic was systematically investigated by using FIB and TEM analysis for the first time to disclose the underlying inhibition mechanism. A porous corrosion bi-layer composed of crystalline MgO and Mg(OH) 2 was observed on both of α-Mg and Al-Mn intermetallic. It was found that a passive inner layer was deposited on α-Mg after immersion in SDS-containing NaCl solution, which can be ascribed to steady-state growth of magnesium and aluminum oxide under the protection of hydrophobic group of SDS. The inhibition mechanism of the inhibitor was mainly associated with formation of dense oxide layer on α-Mg matrix and preferential adsorption of SDS on the corrosion layer deposited on Al-Mn intermetallic.

Projecting the Impact of Rising Temperatures: The Role of Macroeconomic Dynamics

We use theory and empirics to distinguish between the impact of temperature on transition (temporary) and steady state (permanent) growth in output per capita. Standard economic theory suggests that the long-run growth rate of output per capita is determined entirely by the growth rate of total factor productivity (TFP). We find evidence suggesting that the level of temperature affects the level of TFP, but not the growth rate of TFP. This implies that a change in temperature will have a temporary, but not a permanent, impact on growth in output per capita. To highlight the quantitative importance of distinguishing between permanent and temporary changes in economic growth, we use our empirical estimates and theoretical framework to project the impacts of future increases in temperature from climate change. We find losses that are substantial, but smaller than those in the existing empirical literature that assumes a change in temperature permanently affects economic growth.

Consumption Structure Optimization Strategy for Scenic Spots Using the Deep Learning Model under Digital Economy.

The purpose is to find out the problems existing in the consumption economy structure of the scenic spots and to promote the rationalization of the consumption economy of the scenic spots. Based on the analysis of the applicability of the backpropagation neural network (BPNN) model, it uses BPNN to analyze the economic development level of Overseas Chinese Town East (OCT East). Firstly, the weight of each index is determined by the Analytic Hierarchy Process (AHP), and the expected value of the comprehensive evaluation is obtained. Secondly, to ensure the validity of the evaluation model for the development level of the tourism complex, the BPNN model is trained and tested to enable it to be applied to the evaluation of the economic development level of OCT East. The development level of OCT East from 2012 to 2021 is divided into three stages: high, higher, and lower. The development characteristics and existing problems of the OCT East are analyzed, and the optimization strategy of the consumption economy of the scenic spots is put forward in a targeted manner. The research results manifest, that from 2012 to 2021, the development level index of OCT East increased from 0.2457 to 0.5304, and it was in a state of steady growth. In 2019, the development level index reached 0.6497, and it was upgraded to “high-level,” but the average development level index of OCT East was only 0.5662, and there was a lot of room for improvement. According to the divided evaluation indicators, the development level of OCT East is evaluated. In 2012, the development level was low. From 2013 to 2018, it was at a high level, and from 2019 to 2021, it was a high level of development. By studying the Tourism Consumption Structure (TCS) of scenic spots in the OCT East, the research method of the consumption economic structure has been expanded. Therefore, it not only provides a reference for optimizing the consumption of scenic spots, but also contributes to the progress of the social tourism economy.

Scan strategies in EBM-printed IN718 and the physics of bulk 3D microstructure development

Three-dimensional (3D) characterization provides opportunities for understanding processing-structure relationships in additively manufactured (AM) materials. Bulk samples of Inconel 718 were fabricated via electron beam melting (EBM) in order to study microstructural development as a function of energy input and beam scan strategy. TriBeam tomography of bulk Inconel 718 microstructures built under steady-state growth conditions reveals the sensitivity of microstructure formation and evolution to machine process parameters. In this study, samples manufactured using a narrow range of energy input per unit build area result in varied grain morphologies and crystallographic textures. Using TRUCHAS, a thermal simulation software, the thermal history of bulk scan strategies was predicted, and combined with a calibrated microstructure-processing map to accurately predict bulk grain morphologies. The solidification parameters and the 3D measured nucleation density are used to predict the transition between columnar and equiaxed grain morphologies, providing a process map to guide AM parameter choices to locally control as-printed microstructure. A two-dimensional metric for characterizing bulk grain morphology was also found to agree well with predictions from the process map calibrated by 3D data. Combined with 3D tomography and thermal modelling, the physics of structure development were understood at a new level of detail with respect to the competing processes of grain nucleation and epitaxial growth.

Identifying supply and demand shocks in the South African Economy, 1960–2020

AbstractThis paper addresses the identification of supply and demand shocks in the South African economy over the 1960–2020 period, the relative importance of the two types of shock to fluctuations of growth and inflation from their steady‐state values, as well as the potential impact of the two types of shocks on the steady‐state growth and inflation values. Crucially, the paper examines the significance of three alternative identification strategies on the nature of supply and demand shocks and their impact on the economy: zero shock covariance in the presence of long‐run demand neutrality; non‐zero shock covariance in the presence of long‐run demand neutrality and long‐run demand non‐neutrality with zero shock covariance. Interest lies in which of the identification strategies provides shock decompositions that are theoretically coherent and congruent with the empirics of South African growth and inflation. Results support non‐zero shock covariance in the presence of long‐run demand neutrality identification. The analysis suggests that growth shocks in South Africa are dominated by supply shocks, and inflation shocks by demand shocks. Further, negative supply shocks lower steady state growth and raise steady‐state inflation, while positive demand shocks only raise steady‐state inflation and are growth neutral. South Africa appears relatively isolated from international productivity shocks.

Education policy and R&D-based growth in an overlapping-generations model

ABSTRACT We employ a research and development (R&D) based growth overlapping-generations model with endogenous education decision-making and the government’s education policy to examine how education policy and human capital accumulation influence R&D activities. According to our study, an increase in the government’s public education expenditure has an inverted U-shaped effect on the steady-state growth rate. Moreover, a tax rate level that maximizes the steady-state growth rate exists. At this tax rate level, the steady-state welfare level is also maximized.

Evaluation of prediction models for crack length of duplex 2205 stainless steel based on acoustic emission technology

Fatigue fracture is a common failure mode of steel structure, and it usually leads to steel structure failure. In this study, the fatigue damage of duplex 2205 stainless steel with different stress ratios was monitored based on acoustic emission (AE) technology. The fatigue crack growth length, stress intensity factor, fatigue crack growth rate, and the various characteristics of the count, amplitude, and average signal level (ASL) of AE parameters during the whole process were recorded. The results show that AE parameters count and amplitude can well characterize the three stages of fatigue crack initiation, steady-state growth and failure fracture. In the steady-state growth stage, the crack length prediction models based on single-factor and multi-factor of AE parameters suitable for different stress ratios were established and compared for the first time. The multi-factor model has the highest prediction accuracy and it can provide an effective basis for monitoring methods.