虚拟现实中的视觉系统与其实现技术

视觉系统是实现虚拟现实的关键部分。本文探讨了虚拟环境中视觉系统的设计思想，并介绍了现时流行的虚拟环境中视觉系统的实现方案。     

基于虚拟日志压缩的数据同步方案

在基于虚拟日志的数据同步中,当主库端存在对同一记录的频繁修改时,庞大的虚拟日志记录会影响整个数据同步效率。针对该问题,提出一种基于虚拟日志压缩的数据同步方案。虚拟日志压缩通过计算合并日志记录,只保留与数据同步相关的日志信息,从而减少网络数据流量,提高数据同步效率。实验结果表明,该方法适合广域网异构数据库的异步数据同步。     

A SIMD parallel trapezoid rasterization algorithm

An algorithm for the rasterization of trapezoids on the Connection Machine^TM (CM) is described. The input consists of an array of trapezoids, with two horizontal sides, arranged with one trapezoid per processor. (Unless otherwise indicated, “processor” should be taken to mean virtual processor.) Each trapezoid is converted to an edge record and the edge records are then distributed to enough processors so that each processor is responsible for one scanline of one trapezoid. Each processor computes a scan record for its scanline, and the scan records are then distributed to enough processors so that one processor is responsible for a single pixel. Final interpolation of position, and possibly shading information, is performed in parallel for all pixels thus created, and the pixels are then broadcast into a frame buffer array, with depth comparisons being performed at the receiving end to ensure that the nearest pixel appears in the array. The Connection Machine-specific features used by the algorithm are logarithmic time cumulative summing, general communication with comparisons for collision arbitration, and virtual processor sets. Performance is similar to that of good graphics workstations. The intended application is to display data already resident in the machine as the result of some previous computation, when a high-performance graphics workstation is not available.     

Running repeatable and controlled virtual routing experiments

This paper describes an approach to perform reproducible performance tests on virtual routers, comparing different virtual routing architectures, different software versions and configurations. The presented approach is based on VRKit, a software tool that allows to build pre‐configured bootable virtual router images with the desired characteristics. Design decisions are described, and some usage examples are presented, showing how the tool can be used for research on virtual routing, facilitating performance comparison of various virtual router implementations. Copyright © 2013 John Wiley & Sons, Ltd.     

A heuristic approach to output-only system identification under transient excitation

Output-only system identification is a very attractive technique for its implementation simplicity. However, it requires long records to validate the white-noise assumption of the excitation, mainly under transient forced vibration. Alternatively, free-vibration record segments can be selected before the identification process. This improves the accuracy, even using less data, but it requires human intervention or input recording. In the present paper, an approach is proposed for accurate system identification from short output-only records of vibration induced by transient excitation, without human intervention. The approach is based on a novel heuristic search algorithm to find free-vibration record segments, which is fully automatic and it handles the possibility of free-vibration absence. Tests with real-life data from Structural Health Monitoring (SHM) of a bridge showed that the free-vibration finding improves the accuracy of the modal parameter estimates up to ten times, as compared to using record segments starting at the response peak. The proposed approach drastically reduces the need to transmit large amounts of data, which impacts on hardware requirements of SHM implementations.     

Reducing object storage requirements in a multi-user environment

Many Smalltalk implementations store objects in a large file called a virtual image. Each user must have a copy of the virtual image to execute. Since the image can exceed a megabyte in size, considerable disk space is required to support such a system in a multi-user environment. In this paper, a method is described which can reduce storage requirements for systems which use generation scavenging as a memory reclamation technique. This method also improves the performance of the checkpoint operation and offline garbage-collection.     

Virtual reality in scientific visualization

The use of virtual environments in scientific visualization is discussed. Successful examples are surveyed in depth. Lessons about the usefulness and applicability of virtual environments to scientific visualization are drawn. Lessons learned from these applications for the development of virtual environments are also drawn. Difficulties in the application of virtual environments to scientific visualization are discussed. Problems encountered in virtual reality implementations of scientific visualization systems are briefly surveyed. Possible futures are briefly examined.     

面向显示界面工效研究的飞机座舱仿真系统

显示界面工效研究通常以时间和正确率为指标记录分析被试的操纵过程,显示界面需要一定的柔性,现有飞行模拟器无法满足上述需求. 将飞行员操纵飞机的过程分解为信息输入、信息处理、信息输出,记录信息输入、输出变化的时刻及事件,供后续分析研究. 为实现上述要求,明确仿真系统的功能需求、功能模块得出系统总体框架. 详细阐述系统仿真模块、虚拟仪表模块、视景模块、通信模块、数据管理模块的设计过程. 实现并测试仿真系统,结果表明该仿真系统能够记录被试的信息输入、输出变化的时间及状态,满足显示界面工效研究的需要. 为研究显示界面工效问题提供了一种新手段.     

Approximate entity extraction in temporal databases

We study the problem of efficiently extracting K entities, in a temporal database, which are most similar to a given search query. This problem is well studied in relational databases, where each entity is represented as a single record and there exist a variety of methods to define the similarity between a record and the search query. However, in temporal databases, each entity is represented as a sequence of historical records. How to properly define the similarity of each entity in the temporal database still remains an open problem. The main challenging is that, when a user issues a search query for an entity, he or she is prone to mix up information of the same entity at different time points. As a result, methods, which are used in relational databases based on record granularity, cannot work any further. Instead, we regard each entity as a set of “virtual records”, where attribute values of a “virtual record” can be from different records of the same entity. In this paper, we propose a novel evaluation model, based on which the similarity between each “virtual record” and the query can be effectively quantified, and the maximum similarity of its “virtual records” is taken as the similarity of an entity. For each entity, as the number of its “virtual records” is exponentially large, calculating the similarity of the entity is challenging. As a result, we further propose a Dominating Tree Algorithm (DTA), which is based on the bounding-pruning-refining strategy, to efficiently extract K entities with greatest similarities. We conduct extensive experiments on both real and synthetic datasets. The encouraging results show that our model for defining the similarity between each entity and the search query is effective, and the proposed DTA can perform at least two orders of magnitude improvement on the performance comparing with the naive approach.     

A processing algorithm for master—detail records in a relational database

Large numbers of data processing applications require processing of master records and their associated detail records. These relationships between master and detail files may be classified as one-to-many, zero-or-one-to-many and many-to-many. All are important to information systems, but database management system implementations differ widely in their ability to represent and process such relationships. Processing of zero-or-one-to-many relationships, in particular, is difficult in most relational databases. An obscure relational algebra operator, left outer join, that provides such a capability is described and its importance to master-detail processing is illustrated. An implementation of left outer join is presented for dBase III, a database management system providing some relational-like capability.     

SWI: A Semantic Web Interactive Gazetteer to support Linked Open Data

Current implementations of gazetteers, geographic directories that associate place names to geographic coordinates, cannot use semantics to answer complex queries (most gazetteers are just thesauri of place names), use domain ontologies for place name disambiguation, make their data sets available in the Semantic Web or support the use of Volunteered Geographic Information (VGI). A new generation of gazetteers has to tackle these problems. In this paper, we present a new architecture for gazetteers that uses VGI and Semantic Web tools, such as ontologies and Linked Open Data to overcome these limitations. We also present a gazetteer, the Semantic Web Interactive Gazetteer (SWI), implemented using this architecture, and show that it can be used to add absent geographic coordinates to biodiversity records. In our tests, we use this gazetteer to correct geographic data from a big sample (around 142,000 occurrence records of Amazonian specimens) from SpeciesLink, a big repository of biodiversity collection records from Brazil. The tests showed that the SWI Gazetteer was able to add geographic coordinates to around 30,000 records, increasing the records with coordinates from 30.29% to 57.5% of the total number of records in the sample (representing an increase of 90%).     

一种虚拟路由器的体系结构及实现

提出了一种虚拟路由器体系结构，并对其中的关键组成部件如虚拟协议栈模块、虚拟路由协议模块以及虚拟管理模块等功能和实现进行了描述，为了实现单一代码能够运行多个实例，使用封装技术修改了协议栈代码、路由协议代码和路由器中其它的功能模块代码，并以BSD4.3为基础实现了虚拟路由器原型。通过对原型的测试，表明提出的体系结构和实现方法能够达到预期效果，具有实际应用价值。     

TMS: A free-form text-management system

TMS (Text Management System) is a database management system that supports an access method based on both select and search queries. TMS provides support for variable-length records with pointer fields within the relation. Pointers can be used to support not only text but data from any media, such as graphics and images. An inverted index based on the variable-length record structure is used for speedy retrieval of records based on keywords. In this paper, the variable length record management of TMS and the keyword-based retrieval mechanism are described.     

LabVIEW中访问数据库的几种不同方法

本文分析了在LabVIEW中访问数据库的几种方法的优缺点。重点讨论了应用ADO技术,LabSQL,LabVIEWSQLToolkit访问数据库的方法,给出了新建数据表,新增数据、显示表中所有数据的具体实现细节。把数据库技术应用于虚拟仪器中,充分发挥了数据库的管理优势,大大扩展了虚拟仪器的功能。     

A virtual stack facility for mini-computer and microcomputer implementation of the finite element method

In this paper, the efficient implementation of the finite element method on mini-computers and microcomputers is considered. The main limitations of memory and address space are overcome and a software solution proposed with the use of a virtual stack facility which is implemented and tested. A new replacement algorithm for a virtual stack is presented and shown to be more efficient than other known implementations.     

基于虚拟化技术的动态污点分析

在现有的污点分析技术基础上,针对当前污点分析工具的记录不准确等缺陷,研究并实现了基于虚拟化技术的动态污点分析。结合虚拟化技术设计了动态污点分析框架,针对内存污点数据和硬盘污点数据分别设计了基于Hook技术的污点标记模型和Hash遍历的污点标记模型,依据Intel&AMD的指令编码格式对指令进行分类并依据指令类型设计污点传播策略,为解决信息记录冗余问题设计了基于指令筛选的污点记录策略。实验证明,该技术是有效的动态污点分析方法,可以很好地运用于模糊测试中的测试用例生成与漏洞检测。     

Formally specifying CARA in Java

A restricted dialect of Java is proposed as a language for writing formal specifications for reactive systems. Specifications written in this dialect have one Java class per system module. Each class uses static fields to record module state, uses synchronized static methods as entry points for services provided by the module, and communicates with other modules by method calls. Specifications written in this form are directly executable, can serve as a reference model for subsequent implementations, and can also be used as a target for formal verification techniques. Application of the method to construct an executable specification of the CARA (Computer-Assisted Resuscitation Algorithm) system is described.     

利用虚拟化平台进行内存泄露探测

文中利用虚拟机管理器,透明地记录应用程序对资源的申请、释放以及使用情况,提供了探测内存泄露的辅助信息.此机制首先不需要修改或重新编译源程序;其次,带来的性能损失很小.两者结合可以构建在线内存泄露探测和汇报机制.不仅如此,基于虚拟机环境的内存泄露探测还具备通用性,且不需要特殊的硬件支持.所有这些特性,是已有的解决方案所不能兼有的.实验结果表明:基于虚拟机环境的内存泄露探测机制具有实用性,性能损失也被控制在10%以内,能够运用在实际的生产环境中.     

三维虚拟校园漫游系统的研究与应用

虚拟校园是虚拟现实技术在数字化校园中的具体应用。本文主要研究了虚拟校园场景的漫游技术,重点研究了利用VIRTOOLS的交互功能进行虚拟校园漫游的实现方式。