Macroscopic Traversable Wormholes: Minimum Requirements

While wormholes are just as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. To allow for the possibility of interstellar travel, a macroscopic wormhole would need to maintain sufficiently low radial tidal forces. It is proposed in this paper that the assumption of zero tidal forces, i.e., the limiting case, is sufficient for overcoming the restrictions from quantum field theory. The feasibility of this approach is subsequently discussed by 1) introducing the additional conditions needed to ensure that the radial tidal forces can indeed be sufficiently low and 2) by viewing traversable wormholes as emergent phenomena, thereby increasing the likelihood of their existence.

Optimization of RDF link traversal based query execution

Aiming at the problem that only some types of SPARQL （ simple protocal and resource description framework query language） queries can be answered by using the current resource description framework link traversal based query execution （RDF-LTE） approach, this paper discusses how the execution order of the triple pattern affects the query results and cost based on concrete SPARQL queries, and analyzes two properties of the web of linked data, missing backward links and missing contingency solution. Then three heuristic principles for logic query plan optimization, namely, the filtered basic graph pattern （FBGP） principle, the triple pattern chain principle and the seed URIs principle, are proposed. The three principles contribute to decrease the intermediate solutions and increase the types of queries that can be answered. The effectiveness and feasibility of the proposed approach is evaluated. The experimental results show that more query results can be returned with less cost, thus enabling users to develop the full potential of the web of linked data.

An image encryption algorithm based on spatiotemporal chaos and middle order traversal of a binary tree

This paper proposes an image encryption algorithm based on spatiotemporal chaos and middle order traversal of a binary tree.Firstly,other programming software is used to perform the middle order traversal,and the plaintext image is sorted according to the middle order traversal sequence on the permutation.Secondly,the chaotic sequence is generated using the coupled map lattice to set the chaotic interference value.Finally,the XOR operation between the adjacent pixel values of the replacement image is completed to generate the ciphertext matrix.The simulation and experimental results show that the proposed algorithm can resist typical attacks and has good robustness.

An Improved Approach for Generating Test Cases during Model-Based Testing Using Tree Traversal Algorithm

During the model-based software testing process, test cases are generated from modeled requirements to conduct acceptance testing. However, existing approaches generate erroneous test cases, lack full coverage criteria and prototype tools. Therefore, the aim of this research is to develop an approach capable of reducing erroneous test case generation based on full coverage criteria and a prototype tool. The method employed was to develop a parser to extract information from the XMI file of a modeling diagram where a tree is constructed and a traversal operation executed on the nodes and edges to generate test cases. The results obtained from the proposed approach showed that 97.35% of the generated test cases were precise and comprehensive enough to conduct testing because 99.01% of all the nodes and edges were fully covered during the traversal operations.

Binary Tree’s Recursion Traversal Algorithm and Its Improvement

Binary tree is a very important data structure in computer science. Some major properties are discussed. Both recursive and non-recursive traversal methods of binary tree are discussed in detail. Some improvements in programming are proposed.

Network address translation traversal based on Bernoulli laws of large number in P2P streaming system

P2P streaming application must realize network address translation （NAT） traversal. To handle low success ratio of the existing NAT traversal algorithm, UPnP-STUN （UPUN） and port-mapping sample estimation （PMSE） algorithm are recommended in this paper. UPUN is the combination of UPnP and STUN, and PMSE utilizes port mapping samples added by symmetric NAT for different sessions to estimate regularity of port mapping of symmetric NAT, which takes advantage of the Bernoulli law of large numbers. Besides, for the situation that both peers are behind NAT, and to handle heavy relay server load when many inner peers want to communicate with each other, a peer auxiliary-relay （PAR） algorithm is presented. PAR lets outer peers with sufficient bandwidth act as relay servers to alleviate pressure of real server, which could avoid NAT traversal failure caused by single point failure of relay server. Finally, experiments show that the proposed algorithms could improve the success ratio significantly for NAT traversal in P2P streaming application as well as improve P2P streaming application applicability.

Recursive and Nonrecursive Traversal Algorithms for Dynamically Created Binary Trees

The modeling of dynamical systems from a time series implemented by our DSA program introduces binary trees of height D with all leaves on the same level, and the related subtrees of height L 〈 D. These are called e-trees and e-subtrees. The recursive and nonrecursive versions of the traversal algorithms for the trees with dynamically created nodes are discussed. The original nonrecursive algorithms that return the pointer to the next node in preorder, inorder and postorder traversals are presented. The space-time complexity analysis shows and the execution time measurements confirm that for these O（2D） algorithms, the recursive versions have approximately 10-25% better time constants. Still, the use of nonrecursive algorithms may be more appropriate in several occasions.

Exploration of Traversable Wormholes Sustained by an Extra Spatial Dimension

The main goal of this paper is to determine the effect of an extra dimension on a traversable wormhole. Here an earlier study by the author [Phys. Rev. D 98, 064041 (2018)] is extended in several significant ways. To begin with, the extra spatial dimension is assumed to be time dependent, while the redshift and shape functions, as well as the extra dimension, are functions of both r and l, the respective radial and extra coordinates;the last of these is therefore a function of r, l, and t. The main objective is to determine the conditions that allow the throat of the wormhole to be threaded with ordinary matter (by respecting the null energy condition) and that the same conditions lead to a violation of the null energy condition in the fifth dimension, which is therefore responsible for sustaining the wormhole. The dependence of the extra dimension on l and t is subject to additional conditions that are subsequently analyzed in this paper. Finally, the extra dimension may be extremely small or even curled up.

图计算体系结构和系统软件关键技术综述

图计算作为分析事物之间关联关系的重要工具,近年来已成为各国政府及公司争夺的关键技术.学术界和工业界在图计算体系结构和系统软件关键技术方面取得了一定进展.然而,现实场景图计算大多具有动态变化、应用需求复杂多样等特征.这给图计算在基础理论、体系架构和系统软件关键技术方面提出了新的需求,同时也带来了新的挑战.为应对这些挑战,科研人员提出了一系列图计算系统或图计算加速器,通过高性能计算、并行计算等技术来优化图计算过程.综述国内外图计算体系结构和系统软件关键技术的研究发展现状,对国内外研究的最新进展进行归纳、比较和分析,并结合国家发展战略和重大应用需求,选取与我国国计民生密切相关的领域,从典型应用分析总结图计算相关技术的行业进展.最后,就未来的技术挑战和研究方向进行展望.

星表探索漫游器地形通过风险的快速感知方法

星表漫游器是一类在地外行星表面执行探索、取样等任务的移动机器人,漫游器的高自主性、高可靠性依赖于其对自身周围地形环境的准确感知。针对漫游器自主导航对感知系统的要求,提出一种针对星表地形环境进行快速通过风险感知的方法。基于开源的星表地貌仿真系统生成逼真的虚拟数据集,同时考虑漫游器自身物理和运动学参数对地形通过风险的影响。实验结果表明:所提方法将单帧RGB图片的风险感知计算时间降低至0.1 s,相对于根据深度数据计算真实的通过风险,提出方法虽然略微损失了计算精度,但却带来计算速度的显著提升。基于神经网络的架构也赋予该方法处理跨尺度图像输入的能力,对不同分辨率的RGB图片输入都能保持较高的计算速度。

基于改进蚁群算法的农业机器人多田块路径规划方法与试验

[目的]针对丘陵地区因田块碎片化和障碍物影响农业机器人作业的情况,提出一种基于改进蚁群算法和A算法相结合的多田块路径规划方法。[方法]通过无人机构建农田遥感影像,利用栅格法对农田进行环境建模,再进行子区的划分与合并,在蚁群算法中引入区域启发函数,对不同区域内的移动代价作区分,通过人工增加最优路径中的信息素浓度并建立自适应信息素挥发系数,对信息素更新方法进行改进,以此求解作业子区间的最优遍历顺序,利用具有启发式搜索功能的A算法进行子区连接路径规划,最终实现多田块路径规划。[结果]MATLAB仿真试验结果表明,在子区数量为40时,采用改进蚁群算法进行规划的平均路径长度比传统的蚁群算法减少了3.19%,平均迭代收敛次数减少了79.5%;在路径遍历仿真试验中,农业机器人遍历路径覆盖率能达到100%,路径重复率为6.48%。利用农田无人机遥感影像和田间作业参数进行自然环境的仿真试验,进一步验证了该方法的有效性。[结论]本研究提出的方法能有效解决丘陵地区农业机器人多田块路径规划问题,可为丘陵地区农业机器人大面积作业提供路径参考与技术支持。

DYNAMIC TRAVERSAL CRITERION FOR GEOMETRIC FRACTALS

This paper presents a new generating criterion for self-similar geometric fractalsDynamic Traversal Criterion (DTC) and the principle to practice it. According to the principle,symbol shifting technique is put forward which can control the traversal symbols dynamically in recursive procession. The Dynamic Traversal Criterion inherits the mechanism for generating self-similar fractals from traditional way and creates more fractal images from one initiator and generator than Static traversal strategy.

“横向打通、纵向延伸”的课程教学改革探索——以计算机核心基础课程群为例

在新的产业发展和现代化建设环境下,知识与技术迭代加速、工作场域更加复杂。针对传统课程教学对学生横贯能力培养不足,与科技竞争和产业变革导致的复杂工作场域不够契合的问题,围绕产出导向,提出横纵贯通的课程教学改革思路。以计算机核心基础课程群教学改革为例,实施以课程目标达成为导向的螺旋递进式教学,有效衔接课程知识点与能力、品行的培养,引导学生在课程学习中持续提高知识应用能力和技能,激发学习动机,培育良好品行。在多维学习评价与反馈中不断提升学生的计算思维、系统思维等工程思维能力和团队合作、责任意识等品行。

数智时代学科图书核心出版社理论思辨与测定应用创新

对学科图书核心出版社的概念、功能作用和测定方法进行研究回顾和理论思辨,提出将现有笼统的核心出版社概念按其现实功用细化为出版图书、馆藏图书和引用图书三个核心出版社概念并分别定义,探索运用布拉德福定律和遍历法相结合的新分区方法兼顾核心出版社测定的统一性、客观性、合理性和多方面应用。在创新实践应用上,构造以核心出版社为引擎的多维综合数据,作为图书采选业务指导和馆员培训的参照蓝本;构建以核心出版社为中心的采选业务模式,推进图书馆藏重点采购与全面建设的协调发展;探索适宜的学科出版社特征构造与组合,促进图书智能采选模型从层次分析模型到机器学习模型的应用转型。

可抗穷举攻击的射频识别群组证明协议

针对孙达志等提出的群组证明协议进行重点分析,指出协议存在无法抗穷举攻击的安全缺陷,并在此基础上给出一个改进的协议。协议采用遍历取反运算对信息加密,遍历取反运算将根据加密参量自身汉明重量大小不同而进行对不同参量的取反操作,增加破解难度;协议将信息加密之后再发送,同时信息加密时确保多个参量攻击者无法知晓,以此来抵抗穷举攻击。从安全性角度分析协议,表明协议具有较好的安全性能;从仿真实验角度分析协议,表明协议具有计算量低的优势。

支持访问行为身份追踪的跨域密文共享方案

作为在云环境下被广泛应用的密文数据授权访问机制,密文策略属性基加密(ciphertext-policy attribute-based encryption,CP-ABE)具有细粒度、1对多和拥有者可控的特点.由于多个用户可能拥有相同属性集合,传统属性基加密机制难以追溯到滥用解密权限的恶意授权用户身份.虽然现有研究解决了恶意用户的特定解密权限滥用行为(白盒攻击与黑盒攻击)的身份追踪问题,但仍难以实现针对授权用户访问行为的身份追踪,这将导致潜在的安全风险和数据访问知情权合规性问题.为了在现实应用场景中实现密文数据访问行为身份追踪,方案基于密文策略属性基加密机制构造跨域密文共享方法,通过数字签名和交互式外包解密流程将可追踪密钥和授权用户访问行为绑定为访问请求,并利用区块链的不可篡改性实现访问请求的完整性保护.为了解决引入区块链所导致的访问行为身份追踪效率低下问题,方案引入加密倒排索引结构以优化区块遍历效率,并通过BLS签名和隐私集合交集思想实现索引查询的隐私保护.理论分析和实验验证表明所提方案是实用与高效的.

高速公路桥梁变宽段曲线横移架梁技术研究

在桥梁工程中,对于既处在曲线段又是变宽段的预制梁安装路段往往不可避免,此时一般采用架桥机常规直线横移轨道进行架梁铺设,随之带来的问题是需要令架桥机前、中支腿错位排布,如此一来施工的精度、难度都有所提升,并且存在一定的安全隐患。依托于江西宜遂高速公路桥梁某路段,提出了使用曲线横移轨道为架桥机在曲线变宽段进行架梁作业时平稳过渡到支腿错位分布提供条件,以达到缩短工期、保障安全和提高经济效益的目的。

基于相对强度算法和参数遍历试验的地震预测回溯性检验——以中国川滇地区为例

探索地震活动的时空分布对于地震风险评估,尤其是对于中国川滇地区这样的地震频发区和强震危险区而言具有重要意义。相对强度算法(RI)基于统计学理论,使用过去的地震强度评估预测同一地点的未来地震强度。其原理简单,已多次在国内外强震预测的实践应用中取得了良好的效果。目前,经过多年的发展完善,该方法的预测性能愈加突出。为了辅助川滇地区的地震活动性预测工作,文中使用相对强度算法(RI)和参数遍历试验(PTT)进行了全面的参数分析,深入研究了RI算法在中国川滇地区的适用性,结果表明:由于参数选择合理(包括网格大小、异常学习时间窗长度、预测时间窗起始时间和预测时间窗长度),RI和PTT的组合研究表现出了明显优于随机猜测的预测效果,揭示了川滇地震危险区地震预测的有效参数区间。相对强度算法能够对川滇地区的地震活动进行预测,文中成果丰富了地震危险区地震趋势预测的参考依据。

月球科研站关键区域智能选址及其典型环境要素分析

为服务未来国际月球科研站(ILRS)任务,搜索到符合科学目标和工程安全要求的探测区域,开展了着陆探测智能选址,以及着陆区典型要素和巡视可达性的综合分析。在着陆选址方面,基于1D-CNN选址模型在南极Scott M的西南侧遴选并划定了4个预选着陆区;针对着陆区关键要素,对实时光照和辐射、物理温度剖面、水冰赋存等环境特征进行了遥感探测与精细分析;针对巡视可达评估,采用顾及能量耗费的路径规划模型,评估预选着陆区中心点至潜在水冰点的巡视可达性。结果表明,预选着陆区均满足着陆适宜性,具有地形安全性高、供能高等特征。该研究的综合分析方法也可用于评估其他潜在着陆区的典型环境特征,为ILRS的着陆选址和科学目标巡视探测提供有益参考。

基于DFS的船舶配电网潮流计算

为提升船舶直流区域辐射型配电网潮流计算的效率与准确性,解决传统前推回代法在复杂网络和多节点情况下的计算问题。提出了一种改进的前推回代法,该方法融入深度遍历(DFS)策略,并优化了节点编号处理过程。通过DFS遍历网络,实现了节点的高效重新编号,并在节点数量较多时构建邻接矩阵,从而加速计算流程。计算结果显示,改进的前推回代法不仅加快了迭代速度,而且确保了计算误差精度。仿真案例中,与传统前推回代法相比,研究提出的方法在节点电压、支路电流和部分节点功率的计算误差上均有减少,同时,迭代次数保持不变的情况下,计算时间显著缩短。因此采用DFS结合节点编号优化的改进前推回代法,能够有效应对船舶配电网的复杂结构和多节点挑战,确保了潮流计算的高效性与准确性,为船舶电力系统的稳定运行提供了有力保障。该方法不仅提高了计算效率,还增强了船舶电力系统潮流分析的可靠性和实用性。