The magnetic gradient tensor systems using vector magnetic sensors are easily affected by single sensor error and sensor array misalignment, significantly affecting target localization accuracy. To address this problem, based on the differential measurement theory of magnetic gradient tensor, a vector sensor error model was established, and the single sensor errors were corrected using the total least square (TLS) ellipsoid fitting method. Besides, a misalignment error correction model for the sensor is obtained by constructing a rotation matrix for the magnetic sensor's three-axis orthogonal coordinate system transformation, and the tensor system can be aligned by performing the TLS estimation of the rotation angle. After calibration, the experimental results show that the outputs of each sensor have high coincidence and coaxiality. The root mean square error (RMSE) of the total magnetic intensity (TMI) is reduced to within 100 nT, and the RMSE of the tensor component is reduced to within 85 nT/m. Within a range of 5 m, the magnetic target positioning error is reduced to less than 25.1 cm. This technology can improve the measurement accuracy of the magnetic gradient tensor system with high stability and reliability.

The magnetic target location technology based on the principle of magnetic gradient tensor has broad engineering application prospects. However, commonly used target positioning methods are easily interfered with by the geomagnetic environment. We proposed a magnetic target nonlinear positioning method to achieve precise localization of magnetic objects. An ellipsoid fitting method based on the total least square algorithm is proposed to correct the measurement system's magnetic interference and array error. The results show that the algorithm can reduce the root mean square error of the total magnetic field strength by 93.05% to 0.1007 uT. The tensor components are all limited to 100 nT m-1. Then, a target positioning function is constructed with the magnetic moment information introduced as a constraint term, and the location of the magnetic target is optimally calculated using the Levenberg-Marquardt algorithm. The field experimental results indicate when the magnetic targets are located at (5,0,0) and (10,-5,0), the positioning errors are 5.11% and 6.62%. This technology can also achieve high-precision path tracking of magnetic targets.

又是新的一年. 计算机教育会有什么新的动向?《计算机教育》杂志又该有什么样的新作为?带着这样的憧憬和期待,作为一名编委,我也不由得思考良多. 我想,2022年,中国计算机教育界至少会出现这样一个新的行动. 首先要从中国政府友谊奖获得者约翰·爱德华·霍普克罗夫特(John E.Hopcroft)教授的不懈努力说起.许多读者大概也知道,霍普克罗夫特教授是1986年的ACM图灵奖获得者,按照我们常规的观念,他的科研一定是很厉害的,但从我和他渐交渐深的接触中却越来越发现,他对改进中国计算机本科教育的关注要远远超过对科研水平的关注.3年前,霍普克罗夫特先生见李克强总理时,特别强调改进本科教育的重要性,作为这个谈话的一个直接而具体的结果,就是在教育部支持下,霍普克罗夫特先生和北京大学高文教授一起张罗设立了"高校计算机专业优秀教师奖励计划",每年主要通过现场听课的方式,从几十所大学中遴选出一批在教学方面表现优秀的教师.此举的作用不仅仅是对教师的激励,同时还在于对高校教学工作的积极促进.

2022年4月21日,教育部召开新闻发布会,介绍了义务教育课程方案和课程标准修订情况."信息科技"首次作为义务教育中的一门独立的课程出现,体现了国家对信息科技在人类社会发展进程中作用的重视.《义务教育信息科技课程标准(2022年版)》(以下称《课标》)内容系统完整,内涵丰富,本文仅提供一点个人视角的理解.

"计算机领域本科教育教学改革试点工作"(简称"101计划")自2021年12月31日启动以来,以"改进"为宗旨,以"教什么、怎么教"为导向,以教材、教案和课堂为抓手,力图探索计算机领域高质量人才培养新模式.在全国33所高校500余位教师的共同努力下,该计划已经初步显现希望.以"改进"为宗旨开展教学质量提升尚无经验可循,学习与实践才能实现进步.

我们怎么备课,怎么上课? 40年前,备课是在一个备课笔记本上写写画画,上课是黑板+粉笔.没有"计算". 30年前,PPT出现,到20年前被人们普遍接受,备课多数就是写PPT,上课则是照PPT讲."计算"开始在教学中发挥作用. 互联网开始在中国出现大约是在30年前,大规模建设是在20年前,到人们真正感到网络无处不在,时时可用有用(不仅是基础设施,还包括网上信息的丰富程度),则是在10年前.对我们教学的最大支持可能就是获取各种资料,帮助备课的方便.这自然也是"计算"在发挥作用.

匹配,是人们社会生活中许多问题的一种抽象.例如高考录取,是考生与大学之间的匹配;学生毕业了找工作,是毕业生和用人单位之间的匹配;男女婚恋,自然也是一种匹配.这些匹配的形成过程,常常会在某种制度(包括法律法规、约定俗成的做法等)下进行.显然,这些匹配的结果如何(与制度很有关系),具有重大的社会意义.于是,匹配的制度设计就成为一个很有价值的问题.2012年诺贝尔经济学奖,就颁发给了两位在这方面作出突出贡献的学者.

人和人之间的关系,可以看成是一个网络,可以用图或有向图来描述,或者说用它们来建模.在本栏目第2期讨论一笔画问题时我们接触过图,在第4期谈连通问题时针对的也是图,而在第13期讨论网络最大流问题时采用的模型则是有向图.第21期谈选举,也用到了有向图.图和有向图是用算法求解问题中十分常见的一类模型.

本专栏上一期介绍的是分类问题中的算法,这一期讨论聚类. "分类"指的是要将一个未知类别的对象归到某个已知类别中."聚类"则是要将若干对象划分成几组,称每一组为一个类别. 在实际应用中,分类的类别是事先给定的,往往对应某种现实含义,如网购者可能分为"随性"和"理性"两个类别,人们大致也知道是什么意思.

谈到"对弈游戏",我们很容易马上想到的是各种棋艺.说到棋艺,简单的有对角棋,复杂的有象棋、围棋等.编写会下棋的计算机程序,几乎是计算机创始之初人们就有的追求.1958年,在中国的哈尔滨工业大学,曾经就研制出一台"能说话,会下棋"的模拟计算机(如图1).

The Sketch is a compact data structure useful for network measurements. However, to cope with the high speeds of the current data plane, it needs to be held in the small on-chip memory (SRAM). Therefore, the product of the counter size and the number of counters must be below a certain limit. With small counters, some will overflow. With large counters, the total number of counters will be small, but each counter will be shared by more flows, leading to poor accuracy. To address this issue, we propose a generic technique: self-adaptive counters (SEAD Counter). When the value of the counter is small, it works as a standard counter. When the value of the counter is large however, we increment it using a predefined probability, so as to represent this large value. Moreover, in the SEAD Counter, the probability decreases when the value increases. We show that this technique can significantly improve the accuracy of counters. This technique can be adapted to different circumstances. We theoretically analyze the improvements achieved by the SEAD Counter. We further show that our SEAD Counter can be extended to three typical sketches and Bloom filters. We conduct extensive experiments on three real datasets and one synthetic dataset. The experimental results show that, compared with the state-of-the-art, sketches using the SEAD Counter improve the accuracy by up to 13.6 times, while the Bloom filters using SEAD Counter can reduce the false positive rate by more than one order of magnitude.

The 360-degree video streaming system delivers a monocular panoramic video surrounding the user, and the user can change the viewing direction of mobile devices to see different parts of the video through the “viewport”. Due to the limited network bandwidth, playbacks of high-resolution 360-degree videos often suffer from rebuffering, while too much bandwidth is wasted in delivering those out-of-viewport parts that the user never watches. In this article, we present an Ensemble Prediction and Allocation based Streaming System, named as EPASS360, for delivering high Quality of Experience (QoE) 360-degree videos. The prediction model takes advantages of ensemble learning, providing high accuracy on the prediction of viewports. The allocation model divides a video into tiles, and allocates high resolution to tiles where a user's viewpoint may appear in the future by solving the QoE-aware optimization problem. Trace-driven emulation on real-world datasets shows that EPASS360 enhances the QoE in various scenarios compared to state-of-the-art streaming approaches. Experiments on the head-mounted device and the hand-held device over real-world Internet confirm the high user experience of EPASS360.

User profiles are not always visible in E-commerce scenarios, in which case the recommender systems can only summarize users' preferences through sessions of historical records. However, the items in a session might be irrelevant to users' preferences or become the disturbances for modelling the users' portraits, and thus degrade the performance of the recommender systems. In this paper, we propose the preferenceaware mask to capture user preferences over the items within the sessions, which adapts to the preference-irrelevant items within the sessions and provides explainable evidence for the recommendation. Evaluation over three real-world datasets verifies that MBTREC performs well on the new-item recommendation task, and outperforms several state-of-the-art recommender systems on the general metrics.

0 引? 言 计算思维谈了十多年了.如果于概念辨析的层面探讨,似乎还没有形成共识的"定义".事实上,并非任何事情都要先搞清楚定义才能展开内涵研究和实践,许多方向性的话题,本就不好下定义.然而,十多年没搞清楚定义,却还有人愿意继续谈,一定是这个词语后面蕴涵着某种比较广阔的人们觉得有价值的东西.于是,可以重点讨论或者展示些具体的做法和例子.是否属于计算思维的范畴,有些不同的看法也正常,重点是事情具体了,价值就容易判断.

由新冠肺炎疫情意外带来的一场大规模在线教学实践,不仅支撑了整个国家高等教育体系一学期的运转,其鼓舞人心的效果也引发了人们一些新的思考与憧憬.本文在指出这也是一场观念改变的实践基础上,针对在线教学的进一步作用及其发挥,提出了将重新定义什么叫"上了一门课"作为思想解放与教学实践改革的抓手.

This article provides an overview of the progress made on and the clinical applications of scaffolds in bone tissue engineering. After briefly introducing bone biology and fracture healing, the concept of bone tissue engineering and the requirements for bone scaffolds are described, followed by an examination of the materials, fabrication technologies, cell–surface interactions, and vascularization of bone scaffolds. Finally, current clinical applications of bone tissue engineering are summarized and the challenges in this field are discussed, along with possibilities for future research.

在高速公路网中有车流,在互联网上有信息流,在自来水管网中有水流,在公用电网中有电流,等等.但凡网络,大都和某种流联系在一起;网络的作用,就是要保障那些流的畅通.对网络中流的研究是具有普遍意义的主题.