Theoretical Growth Model Research Articles

Social Capital, Government Expenditures, and Growth

Abstract This paper shows that social capital increases economic growth by raising government investment in human capital through better political incentives and selection. We provide empirical evidence that a greater share of output is spent on public education where social capital is higher, both across countries and across U.S. states. We develop a theoretical model of stochastic endogenous growth with imperfect political agency. Only some people correctly anticipate the future returns to current spending on public education. Greater social diffusion of information makes this knowledge more widespread among voters. As a result, social capital alleviates myopic political incentives to underinvest in human capital. It also helps voters select politicians who ensure high productivity in public education. Through this mechanism, we show that social capital raises the equilibrium growth rate of output and reduces its volatility.

Electrically driven amplification of terahertz acoustic waves in graphene

In graphene devices, the electronic drift velocity can easily exceed the speed of sound in the material at moderate current biases. Under these conditions, the electronic system can efficiently amplify acoustic phonons, leading to an exponential growth of sound waves in the direction of the carrier flow. Here, we show that such phonon amplification can significantly modify the electrical properties of graphene devices. We observe a superlinear growth of the resistivity in the direction of the carrier flow when the drift velocity exceeds the speed of sound — resulting in a sevenfold increase over a distance of 8 µm. The resistivity growth is observed at carrier densities away from the Dirac point and is enhanced at cryogenic temperatures. We develop a theoretical model for the resistivity growth due to the electrical amplification of acoustic phonons — reaching frequencies up to 2.2 THz — where the wavelength is controlled by gate-tunable transitions across the Fermi surface. These findings provide a route to on-chip high-frequency sound generation and detection in the THz frequency range.

Driving carbon emission reduction in China through green finance and green innovation: an endogenous growth perspective.

Discovering drivers of carbon dioxide (CO2) emissions is vital for the Chinese government to achieve carbon peak and carbon neutral. With this aim, a theoretical endogenous growth model capturing the mitigating effect of green finance and green innovation on carbon emissions is constructed in this study, which is further empirically examined using China's municipal-level panel data during 2010-2019. The main findings are as follows: First, there is theoretical and empirical evidence supporting that green finance and green innovation can inhibit carbon emissions. Second, the above inhibitory effects demonstrate clear regional disparities with significant effects only in eastern and central Chinese cities, which are moderated by environmental regulations and marketization levels, respectively. Third, in cities with high green finance, green finance plays a more significant role in reducing carbon emissions than green innovation, and the opposite is true in cities with low green finance. In addition, the robustness and endogeneity checks indicate that the results of this study are robust and reliable. These theoretical and empirical findings create profound implications for CO2 emission reduction by vigorously guiding funds to green finance and formulating scientific and effective environmental regulations to promote green innovation in China.

Residual cells and nutrient availability guide wound healing in bacterial biofilms.

Biofilms are multicellular heterogeneous bacterial communities characterized by social-like division of labor, and remarkable robustness with respect to external stresses. Increasingly often an analogy between biofilms and arguably more complex eukaryotic tissues is being drawn. One illustrative example of where this analogy can be practically useful is the process of wound healing. While it has been extensively studied in eukaryotic tissues, the mechanism of wound healing in biofilms is virtually unexplored. Combining experiments in Bacillus subtilis bacteria, a model organism for biofilm formation, and a lattice-based theoretical model of biofilm growth, we studied how biofilms recover after macroscopic damage. We suggest that nutrient gradients and the abundance of proliferating cells are key factors augmenting wound closure. Accordingly, in the model, cell quiescence, nutrient fluxes, and biomass represented by cells and self-secreted extracellular matrix are necessary to qualitatively recapitulate the experimental results for damage repair. One of the surprising experimental findings is that residual cells, persisting in a damaged area after removal of a part of the biofilm, prominently affect the healing process. Taken together, our results outline the important roles of nutrient gradients and residual cells on biomass regrowth on macroscopic scales of the whole biofilm. The proposed combined experiment-simulation framework opens the way to further investigate the possible relation between wound healing, cell signaling and cell phenotype alternation in the local microenvironment of the wound.

Theoretical models for large-sized crystal growth

An accurate cross scale model that can effectively transmit information is the key.

Comparing the Harrod-Domar, Solow and Ramsey growth models and their implications for economic policies

PurposeThe principal aim of this paper is to review three basic theoretical growth models, namely the Harrod-Domar model, the Solow model and the Ramsey model, and examine their implications for economic policies.Design/methodology/approachThe paper utilizes a positivist research framework that emphasizes the causal relationships between the variables in each of the three models. Mathematical methods are employed to formulate and examine the three models under study. Since the paper is theoretical, it does not use any empirical data although numerical illustrations are provided whenever they are appropriate.FindingsThe Harrod-Domar model explains why countries with high rates of saving may also enjoy high rate of economic growth. Both the Solow and Ramsey models can be used to explain the medium-income trap. The paper examines the impact of Covid shocks on the macroeconomy. While the growth rate can be recovered, it may not always possible to recover the output level.Research limitations/implicationsFor the Harrod-Domar model, the public spending decreases the private consumption at the period 1, but there is no change in the capital stock and hence the production in subsequent periods. For the Ramsey model with AK production function, both the private consumption and the outputs will be lowered. In both the Harrod-Domar and Ramsey models with Cobb-Douglas production function, if the debt is not high and the interest rate is sufficiently low, it is better to use public debt for production rather than for consumption. If the country borrows to recover the Total Factor Productivity after the Covid pandemic, both the Harrod-Domar and Ramsey models with Cobb-Douglas production function show that the rate of growth is higher for the year just after the pandemic but is the same as before the pandemic.Practical implicationsThe economy can recover the growth rate after a Covid shock, but the recovery process will generally take many periods.Social implicationsThis paper focuses on economic implications and does not aim to examine social implications of policy changes or Covid-type shock.Originality/valueThe paper provides a comparison of three basic growth models with respect to public spending, public debts and repayments and Covid-type shocks.

Theoretical one-dimensional porous media model for microbial growth on pore plugging and permeability evolution and its verification

ABSTRACT The growth, reproduction, and metabolic activities of microorganisms can lead to blockages within porous media, a phenomenon commonly observed in landfill engineering. Termed as microbial plugging, this phenomenon is significantly influenced by the inherent permeability characteristics of the system. In this study, we propose a simulation model based on the Monod equation to elucidate the clogging process caused by microorganisms in one-dimensional pore channels. Our primary focus is on the application of this model in landfill bioreactor systems. We demonstrate that microbial clogging in these systems is predominantly affected by factors such as the maximum environmental carrying capacity and pore size. These factors are directly influenced by the presence of solid waste within the landfill. By offering a theoretical foundation for mitigating microbial clogging in pore channels of landfill bioreactor systems, this research has the potential to contribute to the development of more efficient and effective waste management practices.

A Cost-Effectiveness Analysis of Pegcetacoplan for the Treatment of Geographic Atrophy

To evaluate the cost-effectiveness of the treatment of geography atrophy (GA) with intravitreal pegcetacoplan and to identify utility measurement surrogates. cost analysis based on data from a published study SUBJECTS: none; based on data from published sham control compared to 2 treatment groups in the index study METHODS: Costs were based on 2022 Medicare reimbursement data. Specific outcomes were extrapolated from the DERBY and OAKS trials. Assumptions were made for the lifetime analysis based on a theoretical logistic growth model of the atrophy. cost, cost-utility, cost per QALY, cost per area of GA (in US$) RESULTS: The cost to treat GA in every month (EM) and every other month (EOM) treatment groups over the 2 years as reported was $70,000 and $34,600, respectively. The cost per area of delaying GA for 2 years in all patients was $87,300/mm2 (EM) and $49,200/mm2 (EOM), and in initially extrafoveal patients, $53,900/mm2 (EM) and $32,100/mm2 (EOM). The cost per day of delaying GA for 2 years was $295 (EM) and $170 (EOM); the marginal cost (EM vs EOM) per RPE cell saved was $30. The modeled lifetime costs were $350,000 (EM) and $172,000 (EOM), or $309,000/mm2 (EM) and $180,000 (EOM) /mm2 . The modeled time to 95% atrophy at 13 years was delayed by 2.5 years (EM) and 2.1 years (EOM). The costs/QALY gained based on modeled visual loss with 95% atrophy were $706,000 (EM) and $397,000 (EOM). Treatment of GA with intravitreal pegcetacoplan EOM was more cost effective than EM. Treatment of extrafoveal lesions yielded greater utility compared to the treatment of the entire group. As atrophy progression approaches an upper limit, the marginal cost/benefit ratios increase.

Tissue Growth Model for Maintaining Tensional Homeostasis With Applications to Hypertension and Stented Artery

Abstract In this work, a theoretical growth model for maintaining a homeostatic mechanical environment was developed to capture the growth behavior of the artery and its association with its mechanical environment. The multiplicative decomposition approach was adopted to decompose the deformation matrix into an elastic term and a growth term. A growth factor relating to homeostatic stress was used to regulate the progressive changes in the arterial morphology. In addition, a growth coefficient was adopted to avoid unlimited growth. The arterial growth model was implemented in a commercial finite element software and tested in the cases of hypertension and stenting. Results have demonstrated that the arterial growth induced by hypertension can mitigate abnormal arterial stresses and restore the stress level in the artery back to its homeostasis. Following stenting, the arterial growth pattern was consistent with the distribution of the von Mises stresses in the artery. The arterial growth homogenized the stress distribution in the artery, except for the regions under the stent struts. The heterogeneous growth of the artery disrupted the alignment of the maximum principal stresses in the artery, elongated the stent, reduced the lumen area, and aggregated the tissue prolapse. It is expected that the growth model developed in this work could help to understand and regulate the chronic response of the tissue. Appropriate modeling of arterial growth in connection with tensional homeostasis provided insights for predicting alterations to the arterial mechanical environment, identifying biomechanical factors leading to restenosis, and designing therapeutic strategies to regulate the tissue adaptations.

Dynamic interactive characteristics between icicle growth and corona discharge on HVDC outdoor insulators during icing accretion

AbstractIn order to improve the stability and reliability of high voltage direct current (HVDC) transmission lines in cold regions, this article investigated the corona discharges and the icicle growth characteristics on outdoor insulators under DC voltages. The experiments were conducted at CIGELE laboratory at University of Quebec. The simulation model of corona discharges and the theoretical model of icicle growth were established. The dynamic process and interactive characteristics between the icicle growth and corona discharges under different HVDC voltages were obtained. The results showed that the discharge activity was strong and the cooling effect of ionic air was weak under negative DC voltage, resulting in a large number of bubbles inside the icicle. More negative ions were produced under negative DC voltage, which enhanced the polarisation of water droplets, leading to a greater density of ice beads outside the icicles. In addition, the longest icicles of each insulator under high humidity could bridge the shed gap. The accumulated charge and leakage current were higher under negative DC voltage, as well as the corona discharge at the top of the icicles lasted longer. Therefore, the negative DC corona discharge more significantly inhibited the growth of the icicle, resulting in a slower growth rate of the icicles.

SINE QUA NON: INFERRING KODJADERMEN-GUMELNIȚA-KARANOVO VI POPULATION DYNAMICS FROM AGGREGATED PROBABILITY DISTRIBUTIONS OF RADIOCARBON DATES

ABSTRACTPast human population dynamics play a key role in integrated models of understanding socio-ecological change over time. However, little analysis on this issue has been carried out for the prehistoric societies in the Lower Danube and Eastern Balkans area. Here, we use summed probability distributions of radiocarbon dates to investigate potential regional and local variation population dynamics. Our study adopts a formal model-testing approach to the fifth millennium BC archaeological radiocarbon record, performing a region-wide, comparative analysis of the demographic trajectories of the area along lower Danube River. We follow the current framework of theoretical models of population growth and perform global and regional significance and spatial permutation tests on the data. Specifically, we investigate whether populations on both sides of the Danube follow a logistic pattern of steady growth, followed by a major decline over time. Finally, our analysis of local-scale growth investigates whether considerable heterogeneity or homogeneity within the region may be observed over the time span considered here. The results show both similarities and differences in the population trends across the area. Our findings are showcased in relation to the cultural characteristics of the region’s 5th millennium BC societies, and future research directions are also suggested.

Economic Growth Models with Heterogeneous Discounting

A survey of theoretical economic growth models with agents having different subjective discount factors is proposed. The structure of equilibrium paths in such models, their dynamics and convergence to stationary equilibria, and the relationship with Pareto optimal paths are described. Models with socially determined discount factors in which time preferences are formed endogenously are discussed, and the basic difficulties associated with social choice in the case of heterogeneous discount factors are examined. The models presented in the paper shed light on internal mechanisms of a market economy that lead to the division of society into the rich and the poor.

Visualizing formation of high entropy alloy nanoparticles with liquid phase transmission electron microscopy.

High entropy alloy (HEA) nanoparticles hold promise as active and durable (electro)catalysts. Understanding their formation mechanism will enable rational control over composition and atomic arrangement of multimetallic catalytic surface sites to maximize their activity. While prior reports have attributed HEA nanoparticle formation to nucleation and growth, there is a dearth of detailed mechanistic investigations. Here we utilize liquid phase transmission electron microscopy (LPTEM), systematic synthesis, and mass spectrometry (MS) to demonstrate that HEA nanoparticles form by aggregation of metal cluster intermediates. AuAgCuPtPd HEA nanoparticles are synthesized by aqueous co-reduction of metal salts with sodium borohydride in the presence of thiolated polymer ligands. Varying the metal : ligand ratio during synthesis showed that alloyed HEA nanoparticles formed only above a threshold ligand concentration. Interestingly, stable single metal atoms and sub-nanometer clusters are observed by TEM and MS in the final HEA nanoparticle solution, suggesting nucleation and growth is not the dominant mechanism. Increasing supersaturation ratio increased particle size, which together with observations of stable single metal atoms and clusters, supported an aggregative growth mechanism. Direct real-time observation with LPTEM imaging showed aggregation of HEA nanoparticles during synthesis. Quantitative analyses of the nanoparticle growth kinetics and particle size distribution from LPTEM movies were consistent with a theoretical model for aggregative growth. Taken together, these results are consistent with a reaction mechanism involving rapid reduction of metal ions into sub-nanometer clusters followed by cluster aggregation driven by borohydride ion induced thiol ligand desorption. This work demonstrates the importance of cluster species as potential synthetic handles for rational control over HEA nanoparticle atomic structure.

Emotive and metacognitive processes in post-traumatic growth of University students

The purpose of the article was to find out the role of emotional and metacognitive processes in the post-traumatic growth of student youth. For this purpose, an online survey was conducted using the following methods: Emotion Regulation Questionnaire (ERQ), AAQ-II, Post Traumatic Growth Inventory (PTGI), The Changes in Outlook Questionnaire (CiOQ). The point-biserial correlation coefficient was used for the mathematical analysis of the data. As a result of the theoretical analysis, it was found that the prevailing theoretical models of posttraumatic growth are fundamentally cognitive. However, there are studies that have examined the relationship between PTG and metacognitive beliefs. A metacognitive way of thinking allows people to take a more critical stance on their cognitive capacities and can help facilitate PTG. It has also been found that emotivity as a linguistic embodiment of emotionality can play an important role in the development of PTG. The empirical study found that after 1 year of full-scale war in Ukraine, the average values of PTG indicators among the surveyed youth are quite high. Young people show positive changes in the perception of their own self, the emergence of new opportunities, an increase in personality strength, and a sense of inner integrity. We did not find a relationship between emotional expression and PTG. However, we did find a relationship between expression suppression and cognitive reappraisal, as well as significant relationships between cognitive reappraisal and PTG with all its components. These findings suggest that cognitive reappraisal can also be performed in relation to one's emotional reactions to traumatic events, helping young people to make sense of their traumatic experiences.

The effect of alloying elements in Ti-5Mo-5V-8Cr-3Al alloy on growth kinetics of TiB whiskers in boride layer

As one of the important ways to improve surface properties of Ti alloys, the boride layer prepared by the pack boriding is closely related to the growth and morphology of TiB whiskers in the boride layer, whereas the growth and morphology of TiB whiskers are significantly affected by alloying elements in the alloys. This work systematically explored the effect of alloying elements in β-type Ti-5Mo-5V-8Cr-3Al Ti alloy on growth kinetics of TiB whiskers and thickness of the boride layer using experiment and first-principles investigations. After boriding, an outer TiB2 layer and an inner TiB whisker + Ti layer are formed on Ti surface. TiB/β-Ti interface herein is non-coherent with the orientation relationships of (011)TiB//(1¯1¯ 0)β-Ti and [1¯ 00]TiB//[1¯ 11]β-Ti. Alloying elements segregated at the interface can increase diffusion energy barrier and slow down diffusion rate of active [B] atoms, and further reduce growth rate of TiB whiskers. Finally, a theoretical model for the boride layer growth on Ti surface was proposed.

Nueva ecuación dinámica de altura dominante e índice de sitio para Pinus chiapensis (Martínez) Andresen en Puebla y Veracruz, México

Introduction: Pinus chiapensis (Martínez) Andresen lacks in many areas of site index (SI) models to classify timber productivity. Objective: To develop a dynamic SI equation, using the generalized algebraic difference approach (GADA) to describe the dominant height growth pattern and classify the productivity of natural stands of P. chiapensis in Puebla and Veracruz, Mexico. Materials and methods: Four theoretical growth models were used to derive six equations in GADA, fitted to dominant height-age observations from stem analyses of 31 trees. Fitting was performed using the Dummy variable method, which is invariant to the base age; autocorrelation and heteroscedasticity were corrected. Results and discussion: Quantitative evaluation, graphical analysis of residuals and growth trends of equations allowed the selection of an equation derived from the Levakovic II model with higher predictive capacity. With this equation and a base age of 50 years, polymorphic SI curves with variable asymptotes were constructed to classify productivity into low, medium and high, corresponding to SI of 25, 32 and 39 m, respectively. The maximum mean annual increase for the SI of 32 m was 1.07 m∙yr-1 and occurred at 11.08 years. The equation exhibited better performance relative to a previously reported polymorphic equation. Conclusions: It is recommended to use the developed equation to predict dominant height growth and SI of P. chiapensis stands in Puebla and Veracruz, Mexico.

INFORMATION AS A RESOURCE IN THE DIGITAL ECONOMY ERA

The article examines the changing place of information in the digital technologies’ development context, the connection of information with digital and information capital. The methodology of the study includes general scientific methods of analysis and synthesis as well as the inductive method and the method of comparative analysis. Based on the analysis of modern domestic and foreign publications, we show that with the evolution of technologies, data collection and information processing are increasingly alienated from human beings and become the prerogative of digital computer systems. At the moment, there is no unity in the modern scientific literature in understanding the role of information in the production process. There are no unambiguous interpretations of the concepts of digital and information capital introduced into scientific circulation and its interrelation. In the research course, the author of this article clarified the concepts of digital and information capital and attempted to build a hierarchical relationship between digital, information capital and information. The paper substantiates the allocation of information as a separate factor of production, alienated from both human and physical capital. Inequality in access to information as a factor of production is the source of a new type of inequality: informational inequality. The results of the study can be used for developing theoretical models of economic growth and economic inequality as well as for justifying economic policy in the process of transition to the digital economy.

The kinetics of dissolution and cluster formation of fullerene in polar and low polar solutions

Fullerene and fullerene like nanostructures play a main role in various research areas. Theamount of investigations of fullerene C60 and C70 has grown up considerably due to their several unique properties [1-2, 6]. In this report we present theoretical models for cluster growth, the modeling of small angle neutron scattering curves, and the results of structural analysis (SANS) for polar solutions of these macromolecules. Investigation of kinetics of dissolution and complex formation are studied for C60/Benzene, C60/Toluene and C60/Nmethyl-2-pyrrolidone (NMP) solutions of various concentrations by UV-Vis spectrometry. We model the kinetics of simultaneously occurring processes in the solution via a system of basic kinetic equations and obtain the corresponding parameters dependence on preparation conditions. The investigation of structural properties of fullerene solution in CS2 was performed at the YuMO instrument of the IBR-2 reactor. The results are compared tomolecular dynamics simulations, and other research works

Damage spreading in quasi-brittle disordered solids: II. What the statistics of precursors teach us about compressive failure

We investigate numerically and theoretically the precursory intermittent activity characterizing the preliminary phase of damage accumulation prior to failure of quasi-brittle solids. We use a minimal but thermodynamically consistent model of damage growth and localization developed by Berthier et al. (2017) that accounts for both microstructural disorder and non-local interactions. Its numerical implementation permits performing a complete scaling description of the failure precursors. In particular, we show that their size, duration and spatial extent are related to each other by robust scaling laws and that these three quantities diverge close to failure. By developing a theoretical model of damage growth in disordered elasto-damageable specimen, we demonstrate that these scaling relations emerge from the physics of elastic manifolds driven in disordered media, while the divergence of these quantities close to failure is reminiscent of the loss of stability of the specimen at the localization threshold. Our study sorts out a long-standing debate on the nature of the compressive failure and the origin of the universal statistics of the precursors preceding it. Our analysis rules out a critical-point scenario in which the divergence of the precursors size close to failure is signature of a second-order phase transition governed by the microstructural disorder. Instead, we show that while the jerky evolution of damage prior to failure results from the presence of material disorder, the latter does not significantly change the nature of the localization process, which is an instability well described by standard bifurcation theory of homogeneous systems. Finally, we harness our detailed understanding of the precursory statistics to design a methodology to estimate the residual lifetime of a structure from the statistical analysis of precursors. This method relevant for structural health monitoring is shown to perform rather accurately on our data.

Theoretical models of void nucleation and growth for ductile metals under dynamic loading: A review

Void nucleation and growth under dynamic loading are essential for damage initiation and evolution in ductile metals. In the past few decades, the development of experimental techniques and simulation methods has helped to reveal a wealth of information about the nucleation and growth process from its microscopic aspects to macroscopic ones. Powerful and effective theoretical approaches have been developed based on this information and have helped in the analysis of the damage states of structures, thereby making an important contribution to the design of damage-resistant materials. This Review presents a brief overview of theoretical models related to the mechanisms of void nucleation and growth under dynamic loading. Classical work and recent research progress are summarized, together with discussion of some aspects deserving further study.