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排序方式: 共有517条查询结果,搜索用时 31 毫秒
81.
Ansari Saleh Ahmar Pawan Kumar Singh Nguyen Van Thanh Nguyen Viet Tinh Vo Minh Hieu 《计算机、材料和连续体(英文)》2022,70(1):523-534
The novel coronavirus has played a disastrous role in many countries worldwide. The outbreak became a major epidemic, engulfing the entire world in lockdown and it is now speculated that its economic impact might be worse than economic deceleration and decline. This paper identifies two different models to capture the trend of closing stock prices in Brazil (BVSP), Russia (IMOEX.ME), India (BSESN), and China (SSE), i.e., (BRIC) countries. We predict the stock prices for three daily time periods, so appropriate preparations can be undertaken to solve these issues. First, we compared the ARIMA, SutteARIMA and Holt-Winters (H-W) methods to determine the most effective model for predicting data. The stock closing price of BRIC country data was obtained from Yahoo Finance. That data dates from 01 November 2019 to 11 December 2020, then divided into two categories--training data and test data. Training data covers 01 November 2019 to 02 December 2020. Seven days (03 December 2020 to 11 December 2020) of data was tested to determine the accuracy of the models using training data as a reference. To measure the accuracy of the models, we obtained the means absolute percentage error (MAPE) and mean square error (MSE). Prediction model Holt-Winters was found to be the most suitable for forecasting the Brazil stock price (BVSP) while MAPE (0.50) and MSE (579272.65) with Holt-Winters (smaller than ARIMA and SutteARIMA), model SutteARIMA was found most appropriate to predict the stock prices of Russia (IMOEX.ME), India (BSESN), and China (SSE) when compared to ARIMA and Holt-Winters. MAPE and MSE with SutteARIMA: Russia (MAPE:0.7; MSE:940.20), India (MAPE:0.90; MSE:207271.16), and China (MAPE: 0.72; MSE: 786.28). Finally, Holt-Winters predicted the daily forecast values for the Brazil stock price (BVSP) (12 December to 14 December 2020 i.e., 115757.6, 116150.9 and 116544.1), while SutteARIMA predicted the daily forecast values of Russia stock prices (IMOEX.ME) (12 December to 14 December 2020 i.e., 3238.06, 3241.54 and 3245.01), India stock price (BSESN) (12 December to 14 December 2020 i.e.,. 45709.38, 45828.71 and 45948.05), and China stock price (SSE) (11 December to 13 December 2020 i.e., 3397.56, 3390.59 and 3383.61) for the three time periods. 相似文献
82.
Völcker N Klee D Höcker H Langefeld S 《Journal of materials science. Materials in medicine》2001,12(2):111-119
Surface modification techniques were employed in order to provide functionalized silicone rubber with enhanced cytocompatibility. Acrylic acid (AAc), methacrylic acid (MAAc) and glycidylmethacrylate (GMA) were graft-co-polymerized onto the surface of silicone induced by an argon plasma and thermal initiation. The polymerizations were carried out in solution, in the case of acrylic acid a vapor phase graft-co-polymerization subsequent to argon plasma activation was carried out as well. Human fibronectin (hFn), which acts as a cell adhesion mediator for fibroblasts, was immobilized by making use of the generated carboxylic or epoxy groups, respectively. Surface analysis was accomplished by means of X-ray photoelectron spectroscopy (XPS), infrared spectroscopy in attenuated total reflection mode (IR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle measurements using the Wilhelmy-plate method. The amount of immobilized active hFn was semiquantified by enzyme-linked immunosorbent assay (ELISA) using a structure-specific antibody against the cell-binding domain of hFn. In vitro testing showed a remarkable difference between surfaces exposing adsorbed-only and surfaces with covalently immobilized hFn. © 2001 Kluwer Academic Publishers 相似文献
83.
Christoph Weigel Valeriya Cherkasova Mathias Holz Hai Binh Phi Christian Görner Tenorio Björn Wilbertz Leonard Voßgrag Thomas Fröhlich Steffen Strehle 《Advanced Engineering Materials》2023,25(9):2201873
Ultralow expansion (ULE) glasses are of special interest for temperature stabilized systems for example in precision metrology. Nowadays, ULE materials are mainly used in macroscopic and less in micromechanical systems. Reasons for this are a lack of technologies for parallel fabricating high-quality released microstructures with a high accuracy. As a result, there is a high demand in transferring these materials into miniaturized application examples, realistic system modeling, and the investigation of microscopic material properties. Herein, a technological base for fabricating released micromechanical structures and systems with a structure height above 100 μm in ULE 7972 glass is established. Herein, the main fabrication parameters that are important for the system design and contribute thus to the introduction of titanium silicate as material for glass-based micromechanical systems are discussed. To study the mechanical properties in combination with respective simulation models, microcantilevers are used as basic mechanical elements to evaluate technological parameters and other impact factors. The implemented models allow to predict the micromechanical system properties with a deviation of only ±5% and can thus effectively support the micromechanical system design in an early stage of development. 相似文献
84.
With high upper critical fields, high temperature superconductors (HTSC) have been recognised as candidate materials for coil and magnet applications. High field devices, at one time or another, when operated close to their rated limits are often faced with instability problems which normally are electrical, magnetic or mechanical in nature. The determination of stability parameters, therefore, is of interest to the conductor designer which very much assists in the processing aspect of long length production of wires and tapes. Due to the morphology of the superconductor most HTSC devices made with Bi(Pb)—2223 precursor exist in tape form. Here the determination of stability parameters (for flux-jump and cryogenic stability) for multifilamentary Bi(Pb)—2223/Ag tapes are presented. Processing parameters such as intermediate deformation and filling factors have been found to play a crucial role, not only on the critical current density of the tapes but on the stability aspect in conductor design as well. 相似文献
85.
Drahomír Dvorský Jiří Kubásek Ilona Voňavková Dalibor Vojtěch 《Materials Science & Technology》2019,35(5):520-529
Rare earth elements are known to improve both mechanical and corrosion properties. However, it highly depends on the final microstructure conditions of prepared material. During extrusion, intermetallic phases may be redistributed, partially dissolved or on the contrary, precipitated. The knowledge of the impact of extrusion on the individual alloys is therefore essential for their application. In this work, three magnesium alloys (Mg-4Y-3RE, Mg-2Y-1Zn, Mg-3Nd-0.5Zn) were prepared by an extrusion process. Microstructure, mechanical and corrosion properties were compared with extruded pure Mg. The advantages and disadvantages of individual alloys are discussed. Based on the obtained results, the Mg-4Y-3RE alloy seems to exert the best mechanical and corrosion properties. Other materials were characterised with anisotropy of mechanical properties and much higher corrosion rate. 相似文献
86.
Container terminal operation and operations research - a classification and literature review 总被引:12,自引:11,他引:12
In the last four decades the container as an essential part of a unit-load-concept has achieved undoubted importance in international sea freight transportation. With ever increasing containerization the number of seaport container terminals and competition among them have become quite remarkable. Operations are nowadays unthinkable without effective and efficient use of information technology as well as appropriate optimization (operations research) methods. In this paper we describe and classify the main logistics processes and operations in container terminals and present a survey of methods for their optimization.
Correspondence to: Stefan Voß 相似文献
87.
This paper presents three dimensional (3D) finite element (FE) models of the low-impulse localised blast loading response of fibre-metal laminates (FMLs) based on an 2024-O aluminium alloy and a woven glass-fibre/polypropylene composite (GFPP). A vectorized user material subroutine (VUMAT) is developed to define the mechanical constitutive behaviour and Hashin’s 3D failure criteria incorporating strain-rate effects in the GFPP. In order to apply localised blast loading, a user subroutine VDLOAD is used to model the pressure distribution over the exposed area of the plate. These subroutines are implemented into the commercial finite element code ABAQUS/Explicit to model the deformation and failure mechanisms in FMLs. The FE models consider FMLs based on various stacking configurations. Both the transient and permanent displacements of the laminates are investigated. Good correlation is obtained between the measured experimental and numerical displacements, the panel deformations and failure modes. By using the validated models, parametric studies can be carried out to optimise the blast resistance of FMLs based on a range of stacking sequences and layer thicknesses. 相似文献
88.
In the field, aquifer remediation methods include pump and treat procedures based on hydraulic control systems. They are used to reduce the level of residual contamination present in the soil and soil pores of aquifers. Often, physical barriers are erected along the boundaries of the target (aquifer) site to reduce the leakage of the released soil contaminant to the surrounding regions. Physical barriers are expensive to build and dismantle. Alternatively, based on simple hydraulic principles, containment wells or image wells injecting clear water can be designed and built to provide hydraulic barriers along the contaminated site boundaries. For brevity, only one pattern of containment well system that is very effective is presented in detail. The study briefly reports about the method of erecting a hydraulic barrier around a contaminated region based on the simple hydraulic principle of images. During the clean-up period, hydraulic barriers can considerably reduce the leakage of the released contaminant from the target site to surrounding pristine regions. Containment wells facilitate the formation of hydraulic barriers. Hence, they control the movement of contaminants away from the site that is being remedied. However, these wells come into play, only when the pumping operation for cleaning up the site is active. After operation, they can be filled with soil to permit the natural ground water movement. They can also be used as monitoring wells. 相似文献
89.
In this paper an extension of Weibull theory by the introduction of a statistical length scale is presented. The classical Weibull strength theory is self-similar; a feature that can be illustrated by the fact that the strength dependence on structural size is a power law (a straight line on a double logarithmic graph). Therefore, the theory predicts unlimited strength for extremely small structures. In the paper, it is shown that such a behavior is a direct implication of the assumption that structural elements have independent random strengths. By the introduction of statistical dependence in the form of spatial autocorrelation, the size dependent strength becomes bounded at the small size extreme. The local random strength is phenomenologically modeled as a random field with a certain autocorrelation function. In such a model, the autocorrelation length plays the role of a statistical length scale. The focus is on small failure probabilities and the related probabilistic distributions of the strength of composites. The theoretical part is followed by applications in fiber bundle models, chains of fiber bundle models and the stochastic finite element method in the context of quasibrittle failure. 相似文献
90.