Student academic underachievement is a concern of paramount importance in Europe, where around 15% of the students in the last high school courses do not achieve the minimum knowledge academic requirement. In this paper, we propose a model based on a system of differential equations to study the dynamics of the students’ academic performance in the German region of the North Rhine-Westphalia. This approach is supported by the idea that both good and bad study habits, are a mixture of personal decisions and influence of classmates. This model allows us to forecast the student academic performance by means of confidence intervals over the next few years. 相似文献
The main purpose of this paper is to investigate the optimal replenishment lot size of supplier and optimal production rate of manufacturer under three levels of trade credit policy for supplier–manufacturer–retailer supply chain. The supplier provides a fixed credit period to settle the accounts to the manufacturer, while the manufacturer gives a fixed credit period to settle the account to the retailer and the retailer, in turn, also offers a credit period to each of its customers to settle the accounts. We assume that the supplier supplies the raw material to the manufacturer and sends back the defective raw materials to the outside supplier after completion of inspection at one lot with a sales price. The system always produces good items in the model. Also, we consider the idle times of supplier and manufacturer. Finally, numerical examples are provided to illustrate the behaviour and application of the model with graphical simulation. 相似文献
This paper presents a segment-based probabilistic approach to robustly recognize continuous sign language sentences. The recognition strategy is based on a two-layer conditional random field (CRF) model, where the lower layer processes the component channels and provides outputs to the upper layer for sign recognition. The continuously signed sentences are first segmented, and the sub-segments are labeled SIGN or ME (movement epenthesis) by a Bayesian network (BN) which fuses the outputs of independent CRF and support vector machine (SVM) classifiers. The sub-segments labeled as ME are discarded and the remaining SIGN sub-segments are merged and recognized by the two-layer CRF classifier; for this we have proposed a new algorithm based on the semi-Markov CRF decoding scheme. With eight signers, we obtained a recall rate of 95.7% and a precision of 96.6% for unseen samples from seen signers, and a recall rate of 86.6% and a precision of 89.9% for unseen signers. 相似文献
The effect of added solids on the rheology of oil in water emulsions was investigated. The range of the oil concentration, solids free basis, was (0-70%) and the solids volume fraction was (0-0.16). The solids mean diameter was 45 μm and it was about four times larger than the oil droplets. In the absence of added solids, non-Newtonian behaviour was observed for oil concentrations above 40%. The added solids increased the emulsion viscosity in a manner similar to the addition of solids to a homogeneous fluid. The rheological data of all the emulsion-solids mixtures investigated were correlated as relative viscosity versus solids volume fraction, where the relative viscosity is defined as the ratio of the emulsion-solids mixture viscosity to the solids-free emulsion viscosity. In the case of non-Newtonian systems, the emulsion-solids mixture viscosity and the solids-free emulsion viscosity were calculated at the same shear stress. The Barnea and Mizrahi viscosity correlation was found to fit the data well. 相似文献
Summary: A new technique, ultrasonically initiated in situ emulsion polymerization, was employed to prepare intercalated polystyrene/Na+‐MMT nanocomposites. FTIR, XRD, and TEM results confirm that the hydrophobic PS can easily intercalate into the galleries of hydrophilic montmorillonite via ultrasonically initiated in situ emulsion polymerization, taking advantages of the multi‐effects of ultrasonic irradiation, such as dispersion, pulverization, activation, and initiation. Properly reducing SDS concentration is beneficial to widen the d‐spacing between clay layers. However, the Na+‐MMT amount has little effect on the d‐spacing of nanocomposites. The glass transition temperature of nanocomposites increased as the percentage of clay increased, although the average molecular weight of PS decreased, and the decomposition temperature of the 1obtained nanocomposites moves to higher temperature.
TEM of PS/Na+‐MMT nanocomposite prepared by ultrasonically initiated in situ emulsion polymerization. 相似文献
An important part of network analysis is understanding community structures like topological clusters and attribute‐based groups. Standard approaches for showing communities using colour, shape, rectangular bounding boxes, convex hulls or force‐directed layout algorithms remain valuable, however our Group‐in‐a‐Box meta‐layouts add a fresh strategy for presenting community membership, internal structure and inter‐cluster relationships. This paper extends the basic Group‐in‐a‐Box meta‐layout, which uses a Treemap substrate of rectangular regions whose size is proportional to community size. When there are numerous inter‐community relationships, the proposed extensions help users view them more clearly: (1) the Croissant–Doughnut meta‐layout applies empirically determined rules for box arrangement to improve space utilization while still showing inter‐community relationships, and (2) the Force‐Directed layout arranges community boxes based on their aggregate ties at the cost of additional space. Our free and open source reference implementation in NodeXL includes heuristics to choose what we have found to be the preferable Group‐in‐a‐Box meta‐layout to show networks with varying numbers or sizes of communities. Case study examples, a pilot comparative user preference study (nine participants), and a readability measure‐based evaluation of 309 Twitter networks demonstrate the utility of the proposed meta‐layouts. 相似文献