查看更多>>摘要：This article investigates the blow-up behaviors for a porous medium equation with a superlinear source and local linear bound-ary dissipation.Making use of the concavity method,we establish sufficient conditions to guarantee the occurrence of the finite time blow-up phenomenon.Meanwhile,we show the existence of the finite time blow-up solutions for arbitrarily high initial energy.Finally,we de-rive the life span bounds(i.e.,the lower and upper bounds of the blow-up time).
查看更多>>摘要：The canonical transformation and Poisson theory of dynamical systems with exponential,power-law,and logarithmic non-standard Lagrangians are studied,respectively.The criterion equations of canonical transformation are established,and four basic forms of canonical transformations are given.The dynamic equations with non-standard Lagrangians admit Lie algebraic structure.From this,we es-tablish the Poisson theory,which makes it possible to find new conservation laws through known conserved quantities.Some examples are put forward to demonstrate the use of the theory and verify its effectiveness.
查看更多>>摘要：Estimating treatment effects has always been one of the hot issues in empirical research.It brings great challenges to estimating treatment effects because heterogeneity exists in the distribution of covariates between treated and controlled groups.Propensity score methods have been widely used to adjust for heterogeneity in observational studies.However,the propensity score is usually unknown and needs to be estimated.In this article,we propose a generalized single-index model to estimate the propensity score and use the propensity score residuals to reduce the estimation bias.The finite-sample performance of the proposed method is evaluated through simulation stud-ies.We use the proposed method to evaluate the policy of"Sunshine Running"and find that the physical test scores of college students par-ticipating in the"Sunshine Running"can be improved by 3.72 points.
查看更多>>摘要：The few-shot named entity recognition(NER)task aims to train a robust model in the source domain and transfer it to the target domain with very few annotated data.Currently,some approaches rely on the prototypical network for NER.However,these approaches often overlook the spatial relations in the span boundary matrix because entity words tend to depend more on adjacent words.We propose using a multidimensional convolution module to address this limitation to capture short-distance spatial dependencies.Additionally,we uti-lize an improved prototypical network and assign different weights to different samples that belong to the same class,thereby enhancing the performance of the few-shot NER task.Further experimental analysis demonstrates that our approach has significantly improved over baseline models across multiple datasets.
查看更多>>摘要：In recent years,self-supervised learning has achieved great success in areas such as computer vision and natural language pro-cessing because it can mine supervised signals from unlabeled data and reduce the reliance on manual labels.However,the currently gener-ated self-supervised signals are either neighbor discrimination or self-discrimination,and there is no model to integrate neighbor discrimi-nation and self-discrimination.Based on this,this paper proposes Fu-Rec that integrates neighbor-discrimination contrastive learning and self-discrimination contrastive learning,which consists of three modules:(1)neighbor-discrimination contrastive learning,(2)self-discrimination contrastive learning,and(3)recommendation module.The neighbor-discrimination contrastive learning and self-discrimination contrastive learning tasks are used as auxiliary tasks to assist the recommendation task.The Fu-Rec model effectively uti-lizes the respective advantages of neighbor-discrimination and self-discrimination to consider the information of the user's neighbors as well as the user and the item itself for the recommendation,which results in better performance of the recommendation module.Experi-mental results on several public datasets demonstrate the effectiveness of the Fu-Rec proposed in this paper.
查看更多>>摘要：Image semantic segmentation is an essential technique for studying human behavior through image data.This paper proposes an image semantic segmentation method for human behavior research.Firstly,an end-to-end convolutional neural network architecture is proposed,which consists of a depth-separable jump-connected fully convolutional network and a conditional random field network;then jump-connected convolution is used to classify each pixel in the image,and an image semantic segmentation method based on convolu-tional neural network is proposed;and then a conditional random field network is used to improve the effect of image segmentation of hu-man behavior and a linear modeling and nonlinear modeling method based on the semantic segmentation of conditional random field im-age is proposed.Finally,using the proposed image segmentation network,the input entrepreneurial image data is semantically segmented to obtain the contour features of the person;and the segmentation of the images in the medical field.The experimental results show that the image semantic segmentation method is effective.It is a new way to use image data to study human behavior and can be extended to other research areas.
查看更多>>摘要：Cracks,potholes,and other defects often occur on infrastructure such as bridges,among which cracks are one of the most fre-quent defects.They have diverse shapes and are difficult to detect.Traditional manual inspection methods are inefficient and have low ac-curacy,while automated inspection machines are bulky and inconvenient to carry and use.Based on the shortcomings of existing detection technologies,this paper proposes a portable structural surface crack detection system based on the Android platform using a portable hand-held image acquisition device.The system captures cracks on the structure's surface and obtains high-definition crack images.Then,these images are transmitted to portable smartphone terminals through Wi-Fi.Next,the image is pre-processed using weighted averaging,gray-scale linear transformation,and adaptive median filtering.Then,the improved Canny edge detection algorithm is applied to identify crack information,and the edge segmentation algorithm is used to determine the crack width.Finally,based on camera calibration,the pixels are converted into the length data required for actual measurement.The results show that the system is easy to operate,and it not only has crack storage and tracking functions,but also can effectively measure the crack width on the surface of components.The measurement ac-curacy of this system reaches the sub-pixel level,and in actual testing,compared with the crack width gauge,the maximum relative error does not exceed 6.25％.
查看更多>>摘要：In this work,porous biochar(MN-TRB750)was fabricated via direct pyrolysis of tea residue(TR)and Mg(NO3)2·6H2O(MN).The as-synthesized MN-TRB750 reached a specific surface area of 839.54 m2·g-1 and an average pore size of 3.75 nm with multi-level pore architecture.MN decreased TR's carbonization temperature and promoted the aromatics extent,pore structure for the frizzly flake-like bio-char.Rhodamine B(RhB)was chosen as the adsorbate to explore the removal performance of organic dyes in this study.The results indi-cated that the maximum adsorption capacity of RhB on MN-TRB750 at 20 ℃ is up to 809.0 mg·g-1 with isotherms fitted well to Freundlich and Dubinin-Radushkevic models.The adsorption kinetics followed pseudo-second-order and Elovich models with an equilibrium adsorp-tion capacity of 757.6 mg·g-1 as the initial concentration of RhB is 260 mg·L-1.High pore filling,hydrogen bond,π-π interaction deter-mined the adsorption of RhB onto MN-TRB850 through a multi-active center and exothermic chemical sorption process.
查看更多>>摘要：In order to improve the performance and service life of the Leningrader seal of the Stirling engine piston rod,interference,pre-load and friction coefficient were taken as influencing factors,and the curved surface response method was adopted to reduce the contact stress of sealing surface and von Mises stress of the sealing sleeve as the response index,with the optimization goal of reducing wear and extending life.The above three key parameters are analyzed and optimized,the influence of each parameter on the sealing performance and service life is obtained,and the best combination scheme of the three is determined.The results show that the interaction between pre-tightening force and interference fit has the greatest impact on contact stress.The interaction between interference fit and friction coeffi-cient has the most significant effect on von Mises stress.The optimized parameters can reduce the maximum contact stress and maximum von Mises stress of the sealing sleeve by 26.3％and 20.6％,respectively,under a media pressure of 5-9 MPa.Test bench verification shows that the leakage of the optimized sealing device in 12 h is reduced by 0.44 cc·min-1(1 cc=1 cm3).The wear rate of the sealing sleeve is 1.08％before optimization and 0.45％after optimization,indicating that the optimized parameters in this paper are effective.
NETL
NSTL
万方数据