Evaluation of Surface Roughness of Aluminum Alloy in Burnishing Process Based on Chaos Theory

Burnishing experiments with different burnishing parameters were performed on a computer numerical control milling machine to characterize the surface roughness of an aluminum alloy during burnishing.The chaos theory was employed to investigate the nonlinear features of the burnishing system.The experimental results show that the power spectrum is broadband and continuous,and the Lyapunov exponentλis positive,proving that burnishing has chaotic characteristics.The chaotic characteristic parameter,the correlation dimension D,is sensitive to the time behavior of the system and is used to establish the corresponding relationship with the surface roughness.The correlation dimension was the largest,when the surface roughness was the smallest.Furthermore,when the correlation dimension curve decreases,the roughness curve increases.The correlation dimension and surface roughness exhibit opposite variation trends.The higher the correlation dimension,the lower the surface roughness.The surface roughness of the aluminum alloy can be characterized online by calculating the correlation dimension during burnishing.

Motor Control Network Effective Connectivity in Regulating Muscle Force Output

Objective of the study: This study aimed at characterizing output features of the higher-order motor control centers (hoMCCs), including secondary (premotor cortex [Pre] and supplementary motor area [SMA]) and association (prefrontal cortex [PFC]) motor regions to the primary motor cortex (M1) during graded force tasks. It is well known that one of the major roles of the primary motor cortex (M1) is controlling motor output such as muscle force. However, it is unclear how the hoMCCs interact with M1 in regulating voluntary muscle contractions. Methods: fMRI data was acquired during graded force tasks and fMRI-based effective connectivity (EC) and muscle force analyses were performed to study the relationship between hoMCCs-M1 effective connectivity and voluntarily exerted handgrip force. Results: The results show that there is a consistent information flow from the hoMCCs to M1 under all force conditions, suggesting a hierarchical control mechanism in the brain in regulating voluntary muscle force. Only the premotor cortex exhibited a significant role in mediating the level of force production through its EC with M1 but that role diminished when the exerted force was high, suggesting perhaps a ceiling and/or fatigue effect on the EC. A flip in the direction of EC from the primary sensory cortex (S1) to the hoMCCs (PFC, SMA, and Pre) at lower force levels while at higher forces EC was observed from the hoMCCs to S1. Conclusion: The hoMCCs regulate M1 output to produce desired voluntary muscle force. Only the Pre-to-M1 connectivity strength directly correlates with the force level especially from low to moderate levels. The hoMCCs are involved in modulating higher force production likely by strengthening M1 output and downgrading inhibition from S1 to M1.

湖北神农架中亚热带山地落叶阔叶林25 ha动态监测样地群落物种组成与结构特征

神农架落叶阔叶林是中亚热带北缘山地保存较好的典型森林植被类型。为探究中亚热带落叶阔叶林的物种多样性维持机制和森林动态,中国科学院武汉植物园按照全球森林生物多样性监测网络(Forest Global Earth Observatory,ForestGEO)和中国森林生物多样性监测网络(Chinese Forest Biodiversity Monitoring Network,CForBio)的建设标准,于2022年在神农架南坡建设了一个25 ha的落叶阔叶林森林动态监测样地。本文基于样地内所有胸径≥1 cm的木本植物(不含竹、藤)调查数据,分析了其物种组成、植物区系特征、群落结构。结果表明:该样地海拔落差334 m,含木本植物149种(包含变种),61,054个独立个体(包括分枝共有97,664个体),隶属于44科79属,其中常绿和落叶树种分别为28种和121种;稀有种(<1株/ha)有44种(29.5%);有萌枝的个体占总个体数的26.8%,其物种数占样地物种总数的93.3%。样地科的分布以热带分布(19科,43.2%)占优势,属的分布以北温带分布(35属,44.3%)占优势。该群落乔木层以锐齿槲栎(Quercus aliena var.acutiserrata)和米心水青冈(Fagus engleriana)为优势种,其重要值分别占7.5%和6.6%。样地树种的平均胸径为7.71 cm,胸径≤10 cm的个体占优势(76.7%)。群落径级结构整体上呈倒“J”型,优势物种的径级结构主要呈现类倒“J”型和正态分布型。神农架中亚热带山地落叶阔叶林具有丰富的物种多样性,相较于纬度相近的样地,其物种多样性更高;植物区系多样;群落结构稳定,根萌比例高,物种更新良好。

Speckle-based interrogation system for quasi-distributed weak fiber Bragg gratings

A simple quasi-distributed fiber sensing interrogation system based on random speckles is proposed for weak fiber Bragg gratings(WFBGs) in this work. Without using tunable lasers or spectrometers, a piece of multimode fiber is applied to interrogate the WFBGs relying on the wavelength sensitivity of speckles. Instead of the CCD sensor, an InGaAs quadrant detector serves as the receiver to capture the fast-changing speckle patterns. A supervised deep learning algorithm of the multilayer perceptron architecture is implemented to process speckle data and to interrogate temperature changes or dynamic strains. The proposed demodulation system is experimentally demonstrated for WFBGs with 0.1% reflectivity.The experimental results demonstrate that the new system is capable of measuring temperature change with an accuracy of 1℃ and achieving dynamic frequency of 100 Hz. This speckle-based interrogation system paves a new way for distributed WFBGs sensing with a simple design.

微塑料:生物效应、分析和降解方法综述

微塑料(MPs)的出现引起了全球的广泛关注,它们遍布海洋和陆地的各个环境介质中,造成了严重的环境污染。微塑料通常被定义为粒径小于5 mm的塑料纤维、颗粒或者薄膜,可被生物吸收积累,产生生态风险和健康风险。实际上很多微塑料可达微米乃至纳米级别,肉眼是不可见的,因此也被形象地比作海洋中的“PM2.5”。作为目前学术界和社会各界争论的热点问题,本篇综述旨在系统地介绍环境中微塑料的来源与分布、生物效应以及分析鉴定方法,并重点介绍了微塑料污染的降解策略和研究成果,为今后微塑料降解方法的研究提供了参考。

Resonator fiber optic gyros with light time-division input and multiplexing output in clockwise and counterclockwise directions

A resonator fiber optic gyro with the light time-division input and multiplexing output(TDM-RFOG)in the clockwise(CW)and counterclockwise(CCW)directions is proposed.The light time-division input in the CW and CCW directions can effectively suppress the backscattering induced noise.The TDM-RFOG is implemented with the 2×2 Mach–Zehnder interferometer(MZI)optical switch.The response time of the fiber ring resonator is analyzed,and it is demonstrated by experiments that light time-division input in the CW and CCW directions can reduce the backscattering induced noise.The suppression effectiveness of backscattering induced noise in the TDM-RFOG is determined by the extinction ratio of the optical switch,so a closed loop is designed to adjust the phase shift difference between the two arms of the MZI optical switch to control the extinction ratio.The method using two arms of the MZI optical switch with twin 90°polarization-axis rotated splices is proposed to make the extinction ratio along both slow and fast axes greater than-70 d B.

Adaptive segmentation based on multi-classification model for dermoscopy images

Segmentation accuracy of dermoscopy images is important in the computer-aided diagnosis of skin cancer and a wide variety of segmentation methods for dermoscopy images have been developed. Considering that each method has its strengths and weaknesses, a novel adaptive segmentation framework based on multi-classification model is proposed for dermoscopy images. Firstly, five patterns of images are summarized according to the factors influencing segmentation. Then the matching relation is established between each image pattern and its optimal segmentationmethod. Next, the given image is classified into one of the five patterns by the multi-classification model based on BP neural network. Finaily, the optimal segmentation method for this image is selected according to the matching relation, and then the image is effectively segmented. Experiments show that the proposed method delivers better accuracy and more robust segmentation results compared with the other seven state-of-the-art methods.

Easy modeling of realistic trees from freehand sketches

Creating realistic 3D tree models in a convenient way is a challenge in game design and movie making due to diversification and occlusion of tree structures. Current sketch-based and imagebased approaches for fast tree modeling have limitations in effect and speed, and they generally include complex parameter adjustment, which brings difficulties to novices. In this paper, we present a simple method for quickly generating various 3D tree models from freehand sketches without parameter adjustment. On two input images, the user draws strokes representing the main branches and crown silhouettes of a tree. The system automatically produces a 3D tree at high speed. First, two 2D skeletons are built from strokes, and a 3D tree structure resembling the input sketches is built by branch retrieval from the 2D skeletons. Small branches are generated within the sketched 2D crown silhouettes based on self-similarity and angle restriction. This system is demonstrated on a variety of examples. It maintains the main features of a tree： the main branch structure and crown shape, and can be used as a convenient tool for tree simulation and design.