Constant Growth Rate Research Articles

Predicting the parabolic growth rate constant for high-temperature oxidation of steels using machine learning models

The parabolic growth rate constant (kp) of high-temperature oxidation of steels is predicted via a data analytics approach. Four machine learning models including Artificial Neural Networks, Random Forest, k-Nearest Neighbors, and Support Vector Regression are trained to establish the relations between the input features (composition and temperature) and the target value (kp). The models are evaluated by the indices: Mean Absolute Error, Mean Squared Error, Root Mean Squared Error and Coefficient of Determination. The steel composition regarding Cr and Ni content and the temperature were the most significant input features controlling the oxidation kinetics.

Gomperzt non-linear model for predicting growth performance of commercial broiler chickens

An experiment was conducted to estimate growth parameters for commercial broiler chickens in Indonesia. The data was collected from July 2021 to June 2022. A total of 1,570 samples consisting of four strains of broiler chickens were collected from 74 houses. The samples were daily weighed from 0 to 7 days of age, and they were weekly weighed from 1 to 5 weeks of age. A nonlinear Gompertz growth model was fitted to the observed body weights (BW). The results for five growth parameters were as follows: the asymptotic value (A) of the mature live weight ranged from 3.733 to 5.044 kg; the turning point of growth (B) ranged from 4.499 to 4.561; the value growth rate constant (K) ranged from 0.049 to 0.059 kg/week; Inflection points in ranged from 25.292 – 30.970 days, and 1.373 – 1.855 kg for inflection age (IA) and inflection weight (IW), respectively. The model was an excellent fit for the growth data in the commercial broiler with a low Akaike information criterion (AIC), and high coeffi-cient determination (R2).

Effects of boron addition on the high temperature oxidation of MoSi2 alloys

Boron containing MoSi2 is a promising material for applications at high temperature, but the oxidation mechanism is still unclear. In this work, the high temperature (1100 °C) oxidation of B doped MoSi2 in synthetic air has been investigated. A (boro)silicate layer is formed on the surface of the alloy, which features a mixture of amorphous SiO2 and cristobalite. After an initial transient period, the oxidation kinetics follows a parabolic growth rate law. The growth rate constant of the oxide layer is enhanced by the boron in the alloy by 90 % per at.% B. The increase in growth rate is associated with boron mitigating the formation of cristobalite thereby promoting the formation of amorphous SiO2.

Impact of monetary methods of economic regulation on fair pricing of shares in the Russian stock market

In the article, the author analyzes the Russian stock market, estimates the fair value of shares of domestic issuers and examines the impact on financial assets of the measures taken by the Central Bank of the Russian Federation within the framework of monetary policy. The fair value of securities is calculated on the basis of a constant dividend growth rate model, where the required return on equity is determined using the CAPM model. The results of the author’s comparative analysis of the fair value and market price of shares of Russian corporations show that securities on the Russian stock market are significantly undervalued. To eliminate the imbalances that have arisen in the financial market, the author suggests that the Central Bank of the Russian Federation implement a softer monetary policy, thus affecting the development of the domestic stock market and increasing the attractiveness of investments in securities of Russian corporations.

Atomic Layer Deposition of La2O3 Film with Precursor La(thd)3-DMEA

In this paper, a new precursor La(thd)3-DMEA (thd = 2,2,6,6-tetramethyl-3,5-heptanedione, DMEA = N,N′-dimethylethylenediamine) was synthesized and characterized with 1H-NMR and X-ray single crystal diffraction. The thermal properties of La(thd)3-DMEA were checked by thermogravimetric analysis (TGA), which confirmed that the volatility and suitability of La(thd)3-DMEA are suitable for atomic layer deposition (ALD). We studied the atomic layer deposition of La2O3 films on a SiO2 surface with La(thd)3-DMEA and O3 as precursors. Self-limiting deposition behaviors were found for the prepared films. The purity and surface morphology of the as-grown La2O3 films, which possessed a constant growth rate of ~0.4 Å/cycle at 250–280 °C, were confirmed by XPS, SEM, and AFM. The results show that La(thd)3-DMEA is a suitable precursor for the atomic layer deposition of La2O3 film.

Vortex-induced vibration forever even with high structural damping

This study investigates the effect of structural damping on vortex-induced vibration (VIV) of a circular cylinder when the mass ratio is below its critical value. It is confirmed by water-channel experiments and a reduced-order model (ROM) that the previously identified phenomenon of VIV forever, i.e. resonance oscillations at any reduced velocity, persists even with high structural damping. Of interest, the ROM results reveal that the wake mode for VIV forever is unstable with a constant positive growth rate with increasing reduced velocity, while the experimental results suggest that VIV forever is associated with a synchronisation between the non-stationary cylinder vibration frequency and the vortex-shedding frequency.

An efficient salt-thermo-carburizing method to prepare titanium carbide coating

Titanium carbide (TiC) coating was prepared by in-situ carbonization of titanium using a novel salt-thermo-carburizing (STC) method in molten CaCl2-CaC2. The effect of the concentration of CaC2, the temperature of the melt and the reaction duration on the composition, structure and thickness of the carbide coating were systematically investigated. The optimized immersion bath was CaCl2–2 wt% CaC2 at 900 °C. The thickness of the coating was increasing with the immersion time and it can reach 105 μm within 8 h. It was found that the growth kinetics of TiC coating follows a parabolic law in the temperature range of 850 to 900 °C, the obtained growth rate constants (k) is 1.43 × 10−15 at 850 °C, 68.38 × 10−15 at 875 °C, and 320.17 × 10−15 m2/s at 900 °C, respectively. In addition, the microhardness of the TiC coating obtained at 850 °C and 8 h is over 740 HV, which is more than five times that of the Ti substrate. This work offers a universal and facile method to prepare metallic carbide coating on the respective metal substrate.

Developing a metabolic model‐based fed‐batch feeding strategy for Pichia pastoris fermentation through fine‐tuning of the methanol utilization pathway

Pichia pastoris is a commonly used microbial host for recombinant protein production. It is mostly cultivated in fed-batch mode, in which the environment of the cell is continuously changing. Hence, it is vital to understand the influence of feeding strategy parameters on the intracellular reaction network to fine-tune bioreactor performance. This study used dynamic flux balance analysis (DFBA) integrated with transcriptomics data to simulate the recombinant P. pastoris (Muts ) growth during the induction phase for three fed-batch strategies, conducted at constant specific growth rates (μ-stat). The induction phase was split into equal time intervals, and the correlated reactions with protein yield were identified in the three fed-batch strategies using the Pearson correlation coefficient. Subsequently, principal component analysis (PCA) was applied to cluster induction phase time intervals and identify the role of correlated reactions on metabolic differentiation of time intervals. It was found that increasing fluxes through the methanol dissimilation pathway increased protein yield. By adding a methanol assimilation pathway inhibitor (HgCl2 ) to the shake flask medium growing on glycerol: methanol mixture (10%: 90%, v/v), the protein titre increased by 60%. As per DFBA, the higher the methanol to biomass flux ratio (Rmeoh/Δx ), the higher the protein yield. Finally, a novel feeding strategy was developed to increase the amount of Rmeoh/Δx compared to the three feeding strategies. The concentration of recombinant human growth hormone (rhGH), used as the model protein, increased by 16% compared to the optimal culture result obtained previously (800 mg L-1 to 928 mg L-1 ), while production yield improved by 85% (24.8 mg gDCW -1 to 46 mg gDCW -1 ).

Evaluation of geosynthetic interface friction at low normal stress: comparison between two different test procedures

The interface friction between geosynthetics has previously been extensively studied with reference to medium-high contact stresses. The interface strength at low contact stress is a less investigated chapter whose importance, however, is evident for the stability of geosynthetic landfill barriers during the construction stage and of the covering systems. The inclined plane is the most used laboratory test for measuring the geosynthetic interface friction at normal stresses as low as 5 kPa. This type of test, however, is not free from criticalities, due to the non-uniformity of the contact stresses induced by the inclination of the plane. Alternatively, it is possible to extrapolate the results of the classic direct shear test, which, however, generally cannot be performed at such low contact stress values. The paper compares data results provided by inclined plane tests and an experimental apparatus capable of performing horizontal shear tests at a vertical stress of 5 kPa. The peculiarity of this device is to guarantee a constant growth rate of the tangential stress equivalent to what happens with the inclined plane test. The good agreement of the interface strength data obtained for two different geosynthetic interfaces leads the way for possible future innovations and insights on the topic.

Grain growth inhibition by sluggish diffusion and Zener pinning in high‐entropy diboride ceramics

AbstractThis work reported the grain growth kinetics of high‐entropy diboride (HEB) and HEB‐SiC ceramics containing 10, 20, and 30 vol% SiC during heat treatment at 1800°C. The coarsening of HEB phase occurred in the four kinds of ceramics during heat treatment, especially in HEB ceramics. The kinetic analysis showed that the grain growth of HEB phase in HEB and HEB‐SiC ceramics is controlled by interface‐controlled kinetics and grain‐boundary pinning, respectively. The growth rate constant of HEB grains is lower than ZrB2, which is related to the low grain‐boundary energy and the sluggish diffusion effect in dynamics of high‐entropy materials. The growth rate of matrix phase in HEB‐SiC ceramics is similar to that in ZrB2–SiC ceramics, indicating that the pinning effect of the SiC second‐phase played the dominant role in inhibiting the grain growth of the high‐entropy matrix phase and disguised the sluggish diffusion effect. This study reveals that the grain growth inhibition through sluggish diffusion effect in a high‐entropy ceramic system may be magnified by the possible existence of segregated second‐phase particles located at the grain boundaries.

Reproductive biology of the Whitehead’s Broadbill (Calyptomena whiteheadi)

ABSTRACT Whitehead’s Broadbill, Calyptomena whiteheadi, an endemic species on the island of Borneo, has a declining population, raising the question of whether reproduction might be a factor limiting population growth. We studied breeding biology based on 52 nests in Kinabalu Park, Sabah, Malaysian Borneo in 2009–2020. Length of the egg-laying season was 99 days with a median of 22 March. Clutch size was typical of tropical songbirds at 2.0 ± 0.13 eggs (SE). Nest success was relatively high at 52%, and daily nest predation rate was relatively low at 0.013 ± 0.004 (SE). Concordantly, length of incubation and nestling periods were relatively long at 19.0 ± 0.26 d and 26.8 ± 0.3 d (SE), respectively. Similarly, the growth rate constants (K) for mass, wing length and tarsus length were slow at 0.252, 0.161 and 0.188, respectively. Slow growth might result in part from their frugivorous diet, as we show using seed traps, but they are reported to include insects in their diets and food provided to their young. Feeding effort, as reflected by the number of fruit seeds dropped below the nest, increased through the nestling period. Brooding effort of parents for nestlings was high on hatch day and decreased until Day 10–15 when it stopped. Food and parental care efforts do not seem to cause their slow growth. Ultimately, our study population has reproductive success that suggests it is not limiting population growth, but studies are needed in other locations to determine if it is a problem elsewhere.

Modeling and Operating Time Optimization of Layer Melt Crystallization and Sweating Processes

Improving the separation efficiency of the layer melt crystallization process is a key but difficult task. Herein, a comprehensive model involving both crystallization and sweating was proposed and used to optimize the operating time of crystallization and sweating processes. The crystallization process was modeled based on the relationship between differential and integral distribution coefficients under a constant layer growth rate. For the sweating process, an empirical sweating equation was employed to govern the sweating model, the parameters of which were determined experimentally using P-xylene as the model substance. The separation efficiency was then optimized by minimizing the operating time at a given product purity and yield. A sensitivity analysis showed that the crystallization and sweating times nonlinearly increase with increasing yield. After the yield exceeds 0.65, an increasing crystallization time is the dominant factor in improving the separation efficiency, while the sweating time and ratio even slightly decrease. The total operating time at low yield is U-shaped with the layer growth rate. The optimal layer growth rate decreases with increasing yield. This model provides guidance for determining the optimal operating parameters of layer melt crystallization and sweating processes.

Impact of Gd minor alloying on the crystallization kinetics of Pd40Ni40P20 bulk metallic glass

Minor alloying of metallic glasses is understood as a possible way to tune its properties and provides a study framework to the origin of their effects. Here, crystallization kinetics of Pd40Ni40P20 and minor-alloyed samples (Pd40Ni40P20)99Gd1 were studied using isothermal and isochronal calorimetry and the results were analyzed using the Johnson-Mehl-Avrami-Kolmogorov model. The addition of 1 at. % Gd into the primary alloy results in a substantial alteration of the crystallization kinetics. The Avrami exponent obtained directly from the calorimetric measurements varies from 2.5 for the ternary alloy to almost 4 for the minor-alloyed sample, indicating a change of the crystallization mechanism from a diffusion-controlled crystallization process with a constant nucleation rate and a gradually decreasing three-dimensional growth rate, to a transformation with a constant nucleation rate and a constant three-dimensional growth rate. TEM (transmission electron microscopy) microstructural analysis of the crystallized state indicates the formation of Pd-Gd-P areas, which might accelerate crystallization kinetics.

Confinement mechanism and compressive stress-strain behaviours of FRP-interlayer-steel confined concrete tubes

A fiber-reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) column is formed by bonding the FRP material and a concrete-filled steel tube (CFST) with the grouting material, and it can improve the corrosion resistance and bearing capacity of CFST columns and avoid the early cracking of the epoxy resin in FRP confined concrete-filled steel tubes (CCFT). However, there are few researches on the compressive behaviours of FISC columns and the dual confinement on core concrete from the FRP tube and steel tube has not been expounded clearly. In this paper, twelve FISC specimens were tested under axial compression. The ratio of FRP and steel confining indexes and the concrete strength were the main parameters and the loading conditions (core CFST loading and whole section loading) were included. Failure patterns, load–axial shortening curves, and the strain development were analysed. In addition, the confining stresses of the FRP tube and steel tube were obtained, and it was found that the confinement on concrete could be divided into three stages of the non-confinement stage, the steel-controlling stage, and the FRP-controlling stage. In the FRP-controlling stage, the FRP confining pressure increased at a constant growth rate while the steel confinement was gradually weakened owning to the restraints of the interlayer grouting material. Furthermore, by regarding the concrete and grouting material as a whole unity, the axial stress-strain model of the confined concrete-grouting was developed, and the proposed model can predict the compressive stress-strain behaviours of an FISC column with good accuracy and simplicity.

Comparison of sequential and joint nonlinear mixed effects modeling of tumor kinetics and survival following Durvalumab treatment in patients with metastatic urothelial carcinoma.

Standard endpoints such as objective response rate are usually poorly correlated with overall survival (OS) for treatment with immune checkpoint inhibitors. Longitudinal tumor size may serve as a more useful predictor of OS, and establishing a quantitative relationship between tumor kinetics (TK) and OS is a crucial step for successfully predicting OS based on limited tumor size measurements. This study aims to develop a population TK model in combination with a parametric survival model by sequential and joint modeling approaches to characterize durvalumab phase I/II data from patients with metastatic urothelial cancer, and to evaluate and compare the performance of the two modeling approaches in terms of parameter estimates, TK and survival predictions, and covariate identification. The tumor growth rate constant was estimated to be greater for patients with OS ≤ 16 weeks as compared to that for patients with OS > 16 weeks with the joint modeling approach (kg= 0.130 vs. 0.0551 week-1, p-value < 0.0001), but similar for both groups (kg = 0.0624 vs.0.0563 week-1, p-value = 0.37) with the sequential modeling approach. The predicted TK profiles by joint modeling appeared better aligned with clinical observations. Joint modeling also predicted OS more accurately than the sequential approach according to concordance index and Brier score. The sequential and joint modeling approaches were also compared using additional simulated datasets, and survival was predicted better by joint modeling in the case of a strong association between TK and OS. In conclusion, joint modeling enabled the establishment of a robust association between TK and OS and may represent a better choice for parametric survival analyses over the sequential approach.

Comparison of variational iteration and Adomian decomposition methods to solve growth, aggregation and aggregation-breakage equations

In this work, semi-analytical approaches such as the Adomian decomposition method (ADM), and variational iteration method (VIM) are examined to solve the aggregation, aggregation-breakage and pure growth equations in series forms. The analytical and truncated series solutions are compared for the number density and various moments. The solutions produced using ADM and VIM are mathematically equal in the pure growth case and provide closed-form solutions for constant growth rate. Additionally, Optimal variational iteration method (OVIM) is implemented to solve the growth and aggregation equations, which reduces the error compared to ADM and VIM to some extent but increases the computational cost. Furthermore, in this work, we provide the ADM and VIM formulations for the coupled aggregation-breakage model. Various test cases of each problem are taken to justify the efficiency and accuracy of the series approximated methods. These observations are shown numerically by comparing the finite term series solutions with the exact solutions of number density and moments.

Mutual independence of water and n-nonane nucleation at low temperatures.

The interaction of water with different substances in the earth's atmosphere lies at the heart of many processes that influence our climate. However, it is still unclear how different species interact with water on the molecular level and in which ways this interaction contributes to the water vapor phase transition. Here, we report the first measurements of water-nonane binary nucleation in the 50-110K temperature range, along with unary nucleation data of both. The time-dependent cluster size distribution in a uniform post-nozzle flow was measured by time-of-flight mass spectrometry coupled with single-photon ionization. From these data, we extract experimental rates and rate constants for both nucleation and cluster growth. The observed mass spectra of water/nonane clusters are not or only slightly affected by the introduction of the other vapor, and the formation of mixed clusters was not observed during nucleation of the mixed vapor. Additionally, the nucleation rate of either substance is not much affected by the presence (or absence) of the other species, i.e., the nucleation of water and nonane proceeds independently, indicating that hetero-molecular clusters do not play a role during nucleation. Only at the lowest temperature of our experiment (i.e., 51K) do the measurements suggest that interspecies interaction slows water cluster growth. The findings here are in contrast to our earlier work in which we showed that vapor components in other mixtures, e.g., CO2 and toluene/H2O, can interact to promote nucleation and cluster growth in a similar temperature range.

Fokker–Planck equation for the particle size distribution function in KJMA transformations

The Fokker–Planck (FP) equation has been derived for describing the temporal evolution of the particle size probability density function (PDF) for KJMA (Kolmogorov–Johnson–Mehl–Avrami) transformations. The classical case of transformations with constant rates of both nucleation and growth, in 3D space, has been treated. Integration of the equation shows that the PDF is given by the superposition of one-parameter gamma distributions with time-dependent mean size given by the KJMA theory. The asymptotic behavior of the FP solution offers a demonstration of the conjecture, previously proposed by Pineda et al. (2004), according to which the set of crystals formed at the same time are gamma-distributed, with the parameter depending on crystal birth time. Computer simulations of the transformation with constant nucleation and growth rates show that the temporal evolution of the PDF, in volume domain, is in good agreement with the Johnson–Mehl PDF. The approach based on the FP equation provides a particle size PDF that exhibits such behavior.

Taxing bitcoin: Incentivizing the difficulty adjustment mechanism to reduce electricity usage

This paper develops a model of the bitcoin market that views the bitcoin as a tradeable commodity whose supply is managed by the Bitcoin protocol. Miners utilize equipment and electricity to solve complex computational problems and the first miner to solve a problem is rewarded with bitcoins. The protocol adjusts the difficulty of the problem to target a constant growth rate in the supply of bitcoins over time. The model demonstrates that an increase (decrease) in the difficulty works in effect like a government’s placing an ad valorem tax (subsidy) on the price of a commodity. The rents that would have arisen from limiting supply, however, are wasted as electricity costs. It is shown that an actual tax on the price of the bitcoin can be used to displace the electricity costs. Using data from March 2014 to January 2019, it is estimated that the difficulty adjustment mechanism resulted in net welfare losses to the miners and buyers of bitcoins of 373.8 million USD. Average initial tax rates of 35% and 347.5% would have fully displaced the electricity costs and maximized their reduction, respectively.

A predator-prey model for the optimal control of fish harvesting through the imposition of a tax

This paper is devoted to the study of ecosystem based fisheries management. The model represents the interaction between prey and predator population with Holling II functional response consisting of different carrying capacities and constant intrinsic growth rates. We have considered the continuous harvesting of predator only. It is observed that if the intrinsic growth rate of predator population crosses a certain critical value, the system enters into Hopf bifurcation. Our observations indicate that tax, the management object in fisheries system play huge impacts on this system. The optimal harvesting policy is disposed by imposing a tax per unit of predator biomass. The optimal harvest strategy is determined using Pontryagin's maximum principle, which is subject to state equations and control limitations. The implications of tax are also examined. We have derived different bifurcations and global stability of the system. Finally, numerical simulations are used to back up the analytical results.