Initial Value Research Articles

대학 입학전형을 고려한 학업 성적의 변화 추이 및 영향요인 분석: 코로나-19 전후 비교

This study aims to examine the educational outcomes of college students by admission types, with a focus on the impact of COVID-19. For this purpose, we conducted a comparative analysis of academic progress and influencing factors among students admitted before and after the onset of the pandemic. Data from 1,074 students enrolled in 2018 and 1,136 students enrolled in 2020 were used. The results of a multi-group latent growth model analysis are as follows. First, irrespective of the admission year, students from both the 2018 and 2020 panels exhibited improvements in grades over the span of three semesters. Nonetheless, the 2020 group displayed a higher initial value and slope of academic progress compared to the 2018 panel. Second, among students admitted in 2018, those under regular-admission exhibited higher initial GPA compared to their early-admission counterparts. However, no such distinction by admission type was observed among students admitted in 2020. Furthermore, solely the 2020 panel demonstrated a positive impact of competency and extracurricular mileage on their initial GPAs. Finally, we provide a summary and discuss the implications of the study results.

Spherically symmetric evolution of self-gravitating massive fields

We are interested in the global dynamics of a massive scalar field evolving under its own gravitational field and, in this paper, we study spherically symmetric solutions to Einstein's field equations coupled with a Klein-Gordon equation with quadratic potential. For the initial value problem we establish a global existence theory when initial data are prescribed on a future light cone with vertex at the center of symmetry. A suitably generalized solution in Bondi coordinates is sought which has low regularity and possibly large but finite Bondi mass. A similar result was established first by Christodoulou for massless fields. In order to deal with massive fields, we must overcome several challenges and significantly modify Christodoulou's original method. First of all, we formulate the Einstein-Klein-Gordon system in spherical symmetry as a non-local and nonlinear hyperbolic equation and, by carefully investigating the global dynamical behavior of the massive field, we establish various estimates concerning the Einstein operator, the Hawking mass, and the Bondi mass, including novel positivity and monotonicity properties. Importantly, in addition to a regularization at the center of symmetry we find it necessary to also introduce a regularization at null infinity. We also establish new energy and decay estimates for, both, regularized and generalized solutions.

Directly Self-Starting Second-Order Explicit Integration Methods with Dissipation Control and Adjustable Bifurcation Points for Second-Order Initial Value Problems

This paper proposes a directly self-starting second-order [Formula: see text]-sub-step explicit method, within which the three novel members are developed and analyzed for demonstration. The novel explicit schemes can output second-order accelerations for general structures, which cannot be achieved for the directly self-starting single- and two-sub-step algorithms. Each explicit algorithm achieves controllable algorithmic dissipation and adjustable bifurcation points. As a result, the novel explicit algorithms impose two algorithmic parameters, [Formula: see text] and [Formula: see text], to control numerical dissipation and bifurcation point, respectively. The parameter [Formula: see text], denoting the spectral radius at the bifurcation point, controls numerical dissipation, whereas the parameter [Formula: see text], denoting the bifurcation point, adjusts the amount of dissipation imposed in the low-frequency range. This paper provides users with two recommended selections of [Formula: see text]. Apart from these desirable features, each novel explicit algorithm attains the maximum stability bound, [Formula: see text] where [Formula: see text] denotes the number of sub-steps. The four- and five-sub-step algorithms perform optimization to reduce numerical low-frequency dissipation. As the number of sub-steps increases, the novel explicit algorithms can have better numerical characteristics without an increase in the computational effort. Numerical examples are simulated to validate the performance and superiority of the novel explicit algorithms.

Optimal Impulse Control for Systems Deriven by Stochastic Delayed Differential Equations

In this paper we study the problem of optimal impulse control for stochastic systems with delay in the case when the value function of the impulse problem depends only on the initial data of the given process through its initial value (value at zero) and some weighted averages. A verification theorem for such impulse control problem is given. As an example the optimal stream of dividends with transaction costs is solved.

Research on optimization method for flyby observation mission adapted to satellite on-board computation

In this paper, the optimization problem of orbital transfer strategy for orbital flyby observation missions is studied. A hybrid optimization method is proposed, which is improved to make it more suitable for satellite on-board computing. This new algorithm is designed to solve the initial value sensitivity problem of the sequential quadratic programming algorithm (SQP). It is consisted of the depth-first search algorithm (DFS) and the SQP algorithm and thus has the characteristics of fast convergence, high reliability, and good robustness. With this method, the DFS with a large step size is calculated first, and then the optimal value in the calculation result is used as the initial value of the SQP algorithm for further optimization. This method can obtain the approximate optimal solution available in engineering. The numerical simulation of an orbital transfer optimization problem is set to verify the effectiveness of the new hybrid algorithm. The simulation results compared with the genetic algorithm (GA) show that the proposed hybrid algorithm can effectively reduce the on-board resource occupation when getting similar results and thus can meet the needs of satellite on-board computing.

Novel Approach for the Immobilization of Cellobiose Dehydrogenase in PEDOT:PSS Conductive Layer on Planar Gold Electrodes

Third-generation biosensors use enzymes capable of direct electron transfer (DET) to the sensor surface. They are of interest for continuous glucose monitoring in blood or interstitial fluid, but they are rarely investigated. One reason is the hindered DET of the enzymes to the metallic electrodes. In this publication, a novel method for the immobilization of cellobiose dehydrogenase (CDH) DET enzymes employing conductive poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) inks and a protective polyethylene glycol dimethacrylate (PEG-DMA) hydrogel layer on gold electrodes is reported. This layer stack showed a glucose-specific current response for voltages between −0.2 and 0.4 V in physiological PBS buffer, and enabled interference-less sensing in a solution of acetaminophen, ascorbic acid, dopamine, and uric acid at 0 V. A Michaelis–Menten fit led to a maximum current density (Imax) of 257 ± 7.9 nA/mm2 and a Michaelis–Menten constant (Km) of 28.4 ± 2.2 mM, with a dynamic range of 0.1–20 mM glucose and a limit of detection of 0.1 mM. After 16 h of continuous measurement of 20 mM glucose, the signal decreased to 60% of its initial value. Storage stability was successfully verified until up to 10 days. In summary, this paper shows a simplified approach for the fabrication of third-generation biosensors using CDH-PEDOT:PSS and PEG-DMA hydrogel inks.

Study on the Contribution of Groundwater Nitrogen Pollution Sources in a Typical Section of the Wei River in China

Aiming to assess the groundwater nitrogen pollution problem in a typical section of the Wei River in China, the contribution of groundwater nitrogen pollution sources in the region was studied. Using Hydrus-1D to implement the simulation process of substituting points for surfaces, we calculated the volume and nitrogen concentration of the water leaching out from the bottom of the encompassing aeration zone. The results of the Hydrus-1D simulation were input as initial values into the nitrogen migration and transformation numerical model constructed using Visual MODFLOW to integrate the simulation calculations between the surface, the aeration zone, and the aquifer system. In addition, the contribution rates of different groundwater nitrogen pollution sources were calculated using the equilibrium formula combined with the groundwater nitrogen test results. The simulation results showed that the groundwater nitrogen in the southern part of the Wei River comes from two main sources: vertical infiltration and river recharge. Specifically, ammonia nitrogen vertical infiltration and river recharge contribute 95.82% and 4.18%, respectively; nitrite nitrogen vertical infiltration and river recharge contribute 92.41% and 7.59%; and nitrate nitrogen vertical infiltration and river recharge contribute 94.26% and 5.74%. According to the simulation results, an increase in the intensity of surface water pollution control is required in the study area. It is also necessary to control the use of nitrogen fertiliser on farmland in the study area and improve the utilisation rate of nitrogen fertiliser to reduce the nitrogen pollution loads from these sources.

Deep learning models for monitoring landscape changes in a UNESCO Global Geopark

By identifying Earth heritage sites, UNESCO Global Geoparks (UGGps) have promoted geo-tourism and regional economic prosperity. However, commercial and tourism development has altered the natural contexts of these geoparks, diminishing their initial value. Before implementing land use policies, spatial landscape parameters should be monitored in multiple dimensions and in real time. This study aims to develop Bilateral Segmentation Network (BiSeNet) models employing an upgraded U-structured neural network in order to monitor land use/cover changes and landscape indicators in a Vietnamese UGGp. This network has proven effective at preserving input image data and restricting the loss of spatial information in decoding data. To demonstrate the utility of deep learning, eight trained BiSeNet models were evaluated against Maximum Likelihood, Support Vector Machine, and Random Forest. The trained BSN-Nadam model (128x128), with a precision of 94% and an information loss of 0.1, can become a valuable instrument for analyzing and monitoring monthly changes in land uses/covers once tourism activities have been rapidly expanded. Three tourist routes and 41 locations in the Dak Nong UGGp were monitored for 30 years using three landscape indices: Disjunct Core Area Density (DCAD), Total Edge Contrast Index (TECI), Shannon's Diversity Index (SHDI), based on the results of the model. As a result, 18 identified geo-sites in the Daknong Geopark have been influenced significantly by agricultural and tourist activities since 2010, making these sites less uniform and unsustainable management. It promptly alerts UNESCO management to the deterioration of geological sites caused by urbanization and tourist development.

Effective removal of Congo red from aqueous solutions using ethylenediamine-modified wheat straw as adsorbent

In this study, ethylenediamine (EDA)-modified wheat straw (EMWS) was prepared and used as an efficient adsorbent for removing Congo red (CR) from aqueous solutions. Adsorption of CR by EMWS was examined through static adsorption experiments to determine the effect of contact time, initial pH values, particle size of the adsorbent, solution concentration, and temperature. As pH ranged from 4.0 to 10.0, CR adsorption by the EMWS remained considerably elevated. The equilibrium adsorption capacity was determined to be 97.92 mg·g−1 for a CR concentration of 400 mg·L−1, pH of 4.0, temperature of 318 K, and EMWS dose of 2 g·L−1, which was found to be comparable to other materials used for CR adsorption. Following that, optimal conditions were used to conduct isothermal, kinetic, and thermodynamic studies. In the adsorption process of CR, the Freundlich isotherm model and the pseudo-second-order (PSO) kinetics provided the best fit, indicating the presence of both physisorption and chemisorption mechanisms. Electrostatic attraction and hydrogen bonding were primarily responsible for CR adsorption onto the EMWS. Based on thermodynamic investigations, the adsorption of CR on EMWS is determined to be spontaneous (ΔG < 0) and endothermic (ΔH = 60.83 kJ·mol−1), while also exhibiting an increase in disorder (ΔS = 289.9 J·mol−1·K−1). The elution was carried out using 0.20 M HCl, followed by washing the EMWS with water, resulting in no loss of functionality. This study suggests that EMWS possesses the potential to serve as a feasible and efficient adsorbent for CR removal in wastewater.

Effect of Initial pH on the Microbial Growth, Final pH Value, Crude Protein and Ash Level of Agaricus bisporus Cap and Stem in Submerged Fermentation

The aim of the study was to investigate the effect of submerged fermentation with Lactobacillus spp. on the nutritional composition of Agaricus bisporus cap and stem. Fresh A. bisporus was provided, and the cap and stem parts were separated and cut into small pieces. Afterward, distilled water (400 ml) and urea (8.4 g) were added to the mushroom parts (100 g) and placed in different fermentation flasks. The fermentation flasks containing mushroom caps or stems were divided into two groups, and the pH levels of the fermentation medium were adjusted to 6 and 7. Fermentation flasks were autoclaved at 121°C for 15 minutes and Lactobacillus spp. was inoculated to each flask at 1 ml (108 CFU/ml). A positive control group was formed by allocating one uninoculated flask for each replicate of each pH value. Fermentation flasks were incubated for 48 hours at 30°C. After fermentation, fermented and inoculated mushroom cap and stem were analyzed to determine the crude protein, ash content, Lactobacillus spp. count and pH value. Lactobacillus spp. count was higher (P=0.028) in the pH 6 group of mushroom cap and tended to be higher (P=0.078) in the pH 6 group of mushroom stems compared with the pH 7 group. Submerged fermentation decreased (P&lt;0.001) the ash content of the mushroom cap and stem in both pH values except the cap with pH 7 compared with the uninoculated mushroom. Similarly, the fermented mushroom cap and stem had lower (P&lt;0.01) final pH values in both initial pH values. Lactobacillus spp. increased (P&lt;0.001) the crude protein content of the mushroom cap with pH 6 but did not alter the crude protein content with pH 7. Besides, submerged fermentation decreased (P&lt;0.001) the crude protein content of mushroom stem with both pH values. The results indicate that submerged fermentation using Lactobacillus spp. can be used to improve the nutritional composition of mushroom caps with pH 6.

Conformable Granular Fractional Differentiability for Fuzzy Number Valued Functions

This paper deals with the utilization of the concept of the granular differentiability to establish a fractional derivative of the conformable type for fuzzy number valued functions. Subsequently, we introduce the notion of a conformable granular integral and provide evidence of its fundamental properties pertaining to differentiability and integrability through illustrative examples. Lastly, we delve into the discussion of the solution approach for the conformable granular initial value problem (CGIVP), as well as the solution of conformable granular differential equations (CGDEqs) associated with growth and decay.

Comprehensive evaluation of intrinsic safety of railway facilities and equipment based on improved cloud model-fuzzy Petri net

In order to achieve the goal of transforming China into a modernized railway powerhouse, a comprehensive evaluation model of intrinsic safety is constructed in this paper by focussing on the intrinsic safety of railway facilities and equipment. Firstly, the index system for evaluating the intrinsic safety of railway facilities and equipment is divided. Secondly, the fuzzy Petri net (FPN) model for intrinsic safety evaluation is constructed according to the fuzzy generative rules, and the similarity calculation method of the cloud model based on shape and distance is applied to derive the initial state value of the FPN model and carry out the calculation of fuzzy reasoning of the intrinsic safety. Finally, the comprehensive evaluation of intrinsic safety is carried out using the example of railroad facilities and equipment at one China Railway Group bureau’s station section. The results indicate that the intrinsic safety level of the station section falls into Class IV intrinsic safety, exhibiting a few vulnerabilities. However, the risk level is low, aligning with the findings of the actual research. Moreover, the evaluation results based on the FPN, the cloud model’s similarity calculation method and the suggested method are compared and analysed with the findings of the actual research. The comparative results demonstrate the accuracy and scientificity of the proposed method, providing a reference for enhancing the intrinsic safety of railway facilities and equipment.

Vesicoureteral reflux-stenosis: an approach to diagnosis and treatment

Vesicoureteral reflux-stenosis is a malformation of the urinary system in which reflux is combined with a narrowing of the distal ureter at the site of its confluence with the bladder. At the same time, the diameter of the lumen of the formed rigid section of the narrowed ureter is sufficient for the occurrence of reflux, but not enough for normal emptying of the upper urinary tract, which leads to the development of a reflux megaureter. Histologically, the wall of the narrowed ureter is characterized by the presence of fibrosis, atrophy of the submucosal layer and the absence of neuromuscular elements of the ureterovesical junction. Diagnosis of reflux stenosis should include mycological cystography and intravenous excretory urography, the results of which, in addition to reflux itself, often determine the “beak symptom” – narrowing in the distal ureter; cystoscopy, which reveals narrow ureteral mouths without peristalsis; computed tomography with contrast enhancement; ultrasound examination of the kidneys and ureters on a urethral catheter with a diuretic test – an increase in the volume of the upper urinary tract by more than 30% of the initial values indicates the presence of stenosis. To clarify kidney function, the study is supplemented with static nephroscintigraphy. The most preferable option is a staged surgical treatment – the narrowed distal ureter is bujured and a ureteral stent is installed for a period of 1 month. While maintaining reflux, according to the data of microvascular cystography, endoscopic plastic surgery of the ureteral mouth is performed. In case of ineffectiveness of minimally invasive interventions, they proceed to Cohen’s neoimplantation of the ureter with resection of the distal ureter and, if necessary, with straining of the enlarged ureter.

Large-eddy simulation of upwind-hill effects on wind-turbine wakes and power performance

The present study utilizes high-fidelity large-eddy simulation (LES) to examine the upwind-hill impacts on wind-turbine wakes and power performance. Both the LES and Reynolds-Averaged Navier–Stokes (RANS) show good agreement with the experimental results of average velocity, whereas the LES exhibits great improvements in predicting turbulence characteristics. In turbine simulations, the wake half-width shows different behaviors in the hill and flat cases. The Gaussian and cosine distributions are good representations of the unskewed profiles of velocity deficit, although some discrepancies are seen around the wake edges. However, the spanwise profiles of velocity deficit become skewed in some hill cases. The non-zero pressure gradient (NZPG) model is employed to predict the velocity deficit in the wakes of a hilltop-sited turbine, and a generalized condition is proposed so that the NZPG model can work in the scenario where the pressure gradients at the turbine location or in its near wakes are not zero. Appropriately assigning initial values for the NZPG model is important for its successful use. The presence of the upwind hill has an adverse influence on the power output of the hilltop-sited turbine. The installation of wind turbines in the valley region near upwind hills is not recommended due to the limited wind-energy resources and intense turbulence levels.

Design Method for Freeform Off-Axis Three-Mirror Anastigmat Optical Systems with a Large Field of View and Low Error Sensitivity

A freeform off-axis three-mirror anastigmat (TMA) optical system with a large field of view (FOV) can obtain target image information with a larger spatial range and more spatial details, which is a development trend within the realm of space optics. The optical aberration increases exponentially with the FOV, resulting in a significant increase in error sensitivity for large-FOV optical systems. To address this issue, a method for designing optical systems with a large FOV and low error sensitivity is proposed. The FOV is gradually expanded from a small initial value in equal-length increments until it reaches the full FOV. At each step, the error sensitivity is recalculated and controlled to a lesser extent than in the previous step. In this design process, the freeform surface is used to correct the aberration and obtain low error sensitivity. An optical system with a focal length of 1000 mm and an F-number of 10 is used as an example, and the FOV is enlarged from 5° × 1° to 20° × 4°. The design results show that the modulation transfer function (MTF) of the optical system can reach 0.45@50 lp/mm, and the average wavefront aberration is 0.029λ. After four rounds of FOV expansion and error sensitivity optimization, the error sensitivity is reduced by 37.27% compared to the initial system, which verifies the correctness and practicality of the method.

Numerical Solution of Fourth-order Initial Value Problems Using Novel Fourth-order Block Algorithm

In this paper, a one-step fourth-order block scheme for solving fourth order Initial Value Problems (IVPs) of Ordinary Differential Equations (ODE) is developed using interpolation and collocation techniques. The derived schemes contain two hybrid points which are chosen such that 0 &lt; w1 &lt; w2 &lt; 1 where w1 and w2 are defined as hybrid points. The characteristics of the developed schemes are analyzed. The obtained schemes are applied in block form to solve some fourth-order IVPs and the numerical results show the accuracy and effectiveness of the block scheme compared with some existing methods.

Further enhancement of surface mechanical properties of carburized 9310 steel by electropulsing-assisted ultrasonic surface rolling process

9310 carburized steel experiences significant wear and spalling problems when operating under high friction and heavy loads, which severely restricts its applications in the aviation industry. Therefore, it holds great significance to further enhance the surface mechanical properties of 9310 carburized steel through suitable surface strengthening technologies. The Electropulsing-Assisted Ultrasonic Surface Rolling Process (EP-USRP) has been successfully applied to carburized 9310 steel, yielding significant improvements in surface quality, hardness, friction and wear properties, and microstructure. Systematic investigations were conducted under varying EP-USRP parameters. Regarding the electric pulse parameters, it is observed that with the increase in output voltage, surface properties such as surface roughness and surface hardness tend to first optimize and then deteriorate. After applying EP-USRP with optimal parameters, the surface roughness of carburized 9310 steel was reduced to Ra 0.154 μm, a mere 5 % of its initial value. The surface hardness experienced a substantial increase, reaching 909.2 HV, representing a notable improvement of 29.9 % compared to the original sample, with a corresponding hardening depth of 1400 μm. Moreover, the wear amount of carburized 9310 steel witnessed a remarkable reduction to 11.8 % of its initial value, accompanied by a decrease in the coefficient of friction to 43.0 %. The enhancement of carburized 9310 steel through EP-USRP is attributed to two key mechanisms: deformation hardening induced by severe plastic deformation and microstructure strengthening resulting from strain-induced martensitic transformation. Among them, the severe plastic deformation mechanism is dominant, Through these mechanisms, the proportion of small-angle boundaries in carburized 9310 steel strengthened by EP-USRP increased. Additionally, the grain size of the surface layer decreased, and the content of retained austenite in the surface layer decreased, collectively contributing to significant improvements in surface properties, as well as friction and wear performance.

Stochastic dynamics of coral reef system with stage-structure for crown-of-thorns starfish

The outbreak of crown-of-thorns starfish (CoTS) is one of the most critical biological disturbances in coral reef systems and contributes greatly to the degradation of coral. Although many studies have focused on coral-CoTS interactions, there is no effective method for suppressing CoTS outbreaks in the long term, in part because of incomplete knowledge of their life cycle. In this paper, a stochastic system is formulated to characterize the interactions among coral, immature CoTS, and mature CoTS, where environmental noise is introduced into the growth of coral. The existence and uniqueness of a global positive solution with any given initial value are investigated, sufficient conditions are established for the extinction of CoTS, and the existence and uniqueness of a stable stationary distribution are explored by applying the Markov semigroup theory. In particular, by solving the Fokker–Planck equation, the approximate expression of the probability density function of the distribution around its quasi positive equilibrium is expounded under certain parametric restrictions. By employing Milstein’s higher-order method, numerical simulations are presented to validate the theoretical results. This study reveals that coral are more vulnerable and are more likely to go extinct in the presence of strong noise, while weak noise is more conducive to the existence of a stable stationary distribution, which implies the long-term persistence of coral and CoTS.

Large-area and high-performance SSZ-13 membranes for N2/CH4 separation

Separating N2 from CH4 is challenging but critical for the purification of unconventional natural gas. Herein, large-area and high-quality SSZ-13 membranes were reproducibly produced on the 50-cm-long tubular alumina supports for the N2/CH4 separation for the first time. The effects of test parameters such as pressure drop, temperature, feed flow rate, water vapor and hydrocarbon impurities on separation performance of the membrane were investigated. A mathematic model for concentration polarization (CP) index was established to evaluate the extent of CP. The CP can be released by decreasing feed pressure and increasing feed flow rate. Separation performance of semi-industrial-scale SSZ-13 membrane was superior to most small-area zeolite membranes. The membrane showed excellent stability in the presence of 5–10 % ethane and propane and saturated water vapor. Selectivity and permeance of the membrane can be restored to its initial values when the impurities are removed. The up-scaling and high-quality membranes have the great potentials for the industrial application in natural gas purification.

Enhancement of biohydrogen production by photo-fermentation of corn stover via visible light catalyzed titanium dioxide/activated carbon fiber

In this study, titanium dioxide/activated carbon fiber (TiO2/ACF) was synthesized by liquid-phase deposition method and the effect of TiO2/ACF on the performance of photo-fermentation biohydrogen production (PFHP) from corn stover under visible light catalysis was discussed. Results show the maximum cumulative hydrogen yield (CHY) obtained under the optimal conditions was 74.0 ± 1.3 mL/g TS with TiO2/ACF addition of 100 mg/L, which was twice that without TiO2/ACF addition (36.9 ± 1.0 mL/g TS). Initial pH value had the most significant effect on CHY. The addition of TiO2/ACF promoted the metabolic pathway of nitrogenase to reduce H+ produced by consuming acetic acid and butyric acid to hydrogen, and also shortened the photo-fermentation period. By scanning electron microscopy and X-ray diffraction analysis, the morphology and phase structure of TiO2/ACF after PFHP did not change significantly. This study laid the foundation for the reuse of TiO2 and its practical application in PFHP.