A taxonomy for networked virtual environments

We discuss virtual environments in the context of how to distribute network communications, views, data, and processes while emphasizing those aspects critical to scaling environments. Systems that demand strong data consistency, causality, and reliable communications while supporting real-time interaction are not likely to scale very well. Furthermore, geographically dispersed systems require high-speed, multicast communication     

Learning method for identification of process dynamics

The dynamic behaviour of some parts of a process can be relatively easily used as part of a process model (the initial process model). Small perturbations are applied to the process input, and the initial process model can be updated by a learning procedure to give an updated process model, which should accurately match the process.     

Reality-based models for vibration feedback in virtual environments

Reality-based modeling of vibrations has been used to enhance the haptic display of virtual environments for impact events such as tapping, although the bandwidths of many haptic displays make it difficult to accurately replicate the measured vibrations. We propose modifying reality-based vibration parameters through a series of perceptual experiments with a haptic display. We created a vibration feedback model, a decaying sinusoidal waveform, by measuring the acceleration of the stylus of a three degree-of-freedom haptic display as a human user tapped it on several real materials. A series of perceptual experiments, where human users rated the realism of various parameter combinations, were performed to further enhance the realism of the vibration display for impact events. The results provided different parameters than those derived strictly from acceleration data. Additional experiments verified the effectiveness of these modified model parameters by showing that users could differentiate between materials in a virtual environment     

一种软件实现虚拟景深的方法

影视后期制作或图像合成中,动态实时改变显示画面的景深能进一步增强画面的真实感,但由于实时性要求较高,软件实现在处理速度方面容易产生瓶颈。为此,采用预处理的办法,分别对前景和背景进行低通滤波,得到前、背景各自的模拟帧序列,通过调节前景和背景帧序列的位置,模拟确定其各自的变焦程度,然后将前景和背景动态合成具有虚拟景深效果的画面。     

The effect of virtual surface stiffness on the haptic perception of detail

This brief presents a quantitative study of the effects of virtual surface stiffness in a simulated haptic environment on the haptic perception of detail. Specifically, the haptic perception of detail is characterized by identification, detection, and discrimination of round and square cross section ridges. Test results indicate that performance, measured as a percent correct score in the perception experiments, improves in a nonlinear fashion as the maximum level of virtual surface stiffness in the simulation increases. Further, test subjects appeared to reach a limit in their perception capabilities at maximum stiffness levels of 300 to 400 N/m, while the hardware was capable of 1000 N/m of maximum virtual surface stiffness. These results indicate that haptic interface hardware may be able to convey sufficient perceptual information to the user with relatively low levels of virtual surface stiffness.     

高对比度等离子体显示器驱动方法

提出了一种提高等离子体显示器(PDP)显示对比度的驱动方法，该方法以传统的寻址与显示分离(ADS)方式为基础，一场只需要一次全屏放电。在各子场的复位期，采用分别加在X和Y电极上的斜坡电压脉冲擦除壁电荷，斜坡电压脉冲末端的电位与X，Y电极在寻址期中被扫描到时所加电压一致，不仅提高了寻址的准确性，且有利于增大寻址电压动态范围并降低寻址电压。     

Quantitative analysis of visibility determinations for networked virtual environments

The Area-Of-Interest (AOI) model is a simple and popular technique used in many applications to determine the region which needs to be considered and processed for each entity (e.g., user). One example application is object visibility determination around user-representing avatars in virtual environments or networked games. There exist a number of variations of the AOI model and in our prior work we have demonstrated how object-oriented visibility determination is more suitable for networked virtual environments than conventional user-oriented visibility determination. Here we extend our work to study a unified and comprehensive analytical model that reveals fundamental properties about the different visibility determination techniques under a variety of virtual environment settings. We also present what the best operational scenarios are for each different approach. Although our discussion and analytical results are focused on the visibility domain, the arguments and conclusions can be extended to various applications or services where spatial attributes are required.     

虚拟现实中立体显示技术研究

阐述立体视觉及双目视差原理.采用双中心投影算法,介绍立体图像时生成的有关计算公式,详细描述OpenGL立体显示一个立方体的步骤,并借助红绿滤光眼镜观察生成的立体图像对.结果表明,采用双中心投影算法可以得到较好的立体效果,可广泛使用于建筑物和视景漫游等多种场合.     

A method for quantitative display of three-dimensional regional myocardial function

The DSR (dynamic spatial reconstructor), a multiple X-ray source scanner that generates stop action three-dimensional (3-D) images of a cylindrical volume, was used for quantitative imaging of left ventricular 3-D wall geometry and function in experimentally induced canine left ventricular myocardial infarction. Impaired regional myocardial function was induced by myocardial ischemia or infarction in four mongrel dogs by closed-chest occlusion of the proximal left anterior descending (LAD) coronary artery. At intervals of 6-14 weeks post occlusion, the dogs were scanned with the DSR during biatrial contrast injection. The 3-D shape, extent, and function of hypokinetic myocardium was measured from the DSR images utilizing measurement of the rate of local systolic wall thickening to detect regions of normal, ischemic, or scarred myocardium. The results were compared to scar size and anatomic distribution measured at postmortem examination. The anatomic extent and relationship of hypocontractile to normally contracting muscle was visualized by computer generated, pseudo 3-D shaded surface displays of the left ventricular chamber and by topographic projections of regional wall thickening rates onto a map of the left ventricular endocardial surface. The location of myocardial infarction and the surrounding zone of impaired function is clearly defined by this 3-D CT scanning procedure. The display method presented here provides both localization and quantification of the volume of ischemic and infarcted myocardium.     

Model-based speed identification for induction Machines in the whole operating range

A speed observer for induction machines without rotational transducers is presented. In contrast to known adaptive observer strategies, the proposed scheme uses-beside the conventional current difference-its integral and a new pair of stretch-turn operators not only to avoid the known instability region at braking but to obtain furthermore a constant gain. To ensure operation with very low stator frequencies, an elimination of parasitic dc components is presented additionally. Characteristics are explained and verified by measurements.     

A method for automatically finding multiple operating points in nonlinear circuits

A new algorithm based on a SPICE-like simulator that searches for multiple operating points automatically, with no user intervention required, is presented. This algorithm, which exploits the asymmetrical properties of nonlinear mappings that describe multistable circuits, has been implemented into a program which automatically finds multiple (in most cases, all) operating points of a circuit. In addition to finding multiple operating points, this method offers another feature: it is capable of detecting the stability of a particular operating point. Another useful feature of this method is that it allows the user to gauge how close a particular circuit is to possessing multiple operating points. For circuits known to possess multiple operating points, this method allows the user to specify which operating point is encountered first. Unlike other continuation methods, circuit element models are not modified; only augmenting resistors are required. Hence, this approach lends itself well as an "add-on" to existing circuit simulators. A number of circuit examples are given.     

虚拟化技术在网络操作系统教学中的应用研究

网络操作系统是高职网络技术专业的核心课程,其实验环境一般需要多台服务器组建,目前多采用虚拟化手段实现,但实验室中的计算机由于硬件性能限制,虚拟的主机数量较少,很多情况下无法满足实验要求。文中讨论如何利用企业级虚拟化和存储技术组建多机虚拟化系统,为实验室提供大量的虚拟主机,满足实验环境的需求。     

A new 3-D display method for 12-lead ECG

A new three-dimensional (3-D) 12-lead electrocardiogram (ECG) display method is presented which employs a 3-D rectangular coordinate system to display the 12-lead cardiac electric signals in two 3-D graphs. The 3-D graph consists of a temporal axis representing the time domain of the cardiac signals, a spatial axis representing the lead positions, and an amplitude axis representing the voltages of the cardiac signals. The six horizontal plane leads and the other six frontal plane leads were displayed in two 3-D graphs, respectively. The voltages of the cardiac signals were represented in rainbow-like colors. Cubic interpolation was employed to insert interconnecting points between neighboring leads on each plane and to smooth the surface of the 3-D ECG graphs. The 3-D ECG graphs of a normal subject, a patient with myocardial infarction, and a patient with left bundle branch block were presented in this paper. This new display method could not only be used as a complementary display method to the 12-lead ECG, but also provide physicians with an overall integral view about the spatial distribution of the cardiac signals.     

A mixed method for the simplification of large system dynamics

This correspondence presents a method for simplifying the dynamics of a large-order system using a combination of its Markov parameters and moments, in the light of the algorithm proposed recently by Lal and Mitra [4] for the technique of moment matching.     

Pseudo-haptics for rigid tool/soft surface interaction feedback in virtual environments

This paper proposes a novel pseudo-haptic soft surface stiffness simulation technique achieved by displaying the deformation of the soft surface and maneuvering an indenter avatar over a virtual soft surface by means of a touch-sensitive tablet. The visual feedback of the surface deformation and the alterations to the indenter avatar behavior produced by the proposed technique create the illusion of interaction with a hard inclusion embedded in the virtual soft surface. The proposed pseudo-haptics technique is validated with a series of experiments conducted by employing a tablet computer with an S-pen input and a tablet computer with a bare finger input. Tablet computers provide unique opportunities for presenting the pseudo-haptic (indenter avatar speed), haptic (contact reaction force from the device surface) and visual cues (surface information) at the same active point of interaction which facilitates information fusion. Hence, here, we evaluate the performance of tablet computers in identification of hard inclusions within virtual soft objects and compare it with the performance of a touchpad input device. A direct hand-soft surface interaction is used for benchmarking of this study. We found that compared with using a touchpad, both the sensitivity and the positive predictive value of the hard inclusion detection can be significantly improved by 33.3% and 13.9%, respectively, by employing tablet computers. Using tablet computers could produce results comparable to the direct hand-soft surface interaction in detecting hard inclusions in a soft object. The experimental results presented here confirm the potential of the proposed technique for conveying haptic information in rigid tool/soft surface interaction in virtual environments.     

A mixed-domain method for identification of quadratically nonlinearsystems

A new mixed-domain method for identifying Volterra transfer functions of a nonlinear system, which can be represented by a second-order truncated Volterra series, is presented in this paper. This method is built on a discrete mixed-domain Volterra model derived from analyzing both discrete time- and frequency-domain Volterra models of quadratically nonlinear systems. It is shown that the conventional discrete frequency-domain Volterra model can be derived from the discrete mixed-domain Volterra model by making certain approximations. In this sense, the frequency-domain model can be considered to be a cough version of the mixed-domain model and thus cannot outperform the mixed-domain model in terms of modeling capability. In addition, the new method is shown to be able to properly identify the Volterra transfer functions even when the output of the quadratically nonlinear system is aliased. Based on this insight, a new anti-aliasing frequency-domain method, which is immune from the output aliasing problem, is developed. The superiority of these new methods over the conventional method is demonstrated by using them to analyze known quadratically nonlinear systems     

A practical method for friction identification in hydraulic actuators

Friction in hydraulic actuators can be described using nonlinear, velocity dependent models. In this paper, the friction is described by an exponential Stribeck friction model. An iterative algorithm is presented to identify the friction model parameters. The method fits two lines on the experimental data relating steady-state velocities to actuator pressure differentials. The parameters of the fitted lines are obtained using an iterative optimization technique. Based on the obtained parameters, the original nonlinear friction model parameters are completely reconstructed. The proposed method is validated by building a simulation model for a valve-controlled hydraulic system in which the friction is modeled based on the method described here. The proposed method can be used in practical situations, whereby fast and reliable identification of major parameters of the friction in hydraulic actuators is needed with easy to obtained pressure measurements.     

The importance of the sense of touch in virtual and real environments

What would be worse, losing your sight or your sense of touch? Although touch (more generally, somesthesis) is commonly underrated, major somesthetic loss can't be adequately compensated for by sight. It results in catastrophic impairments of hand dexterity, haptic capabilities, walking, perception of limb position, and so on. Providing users with inadequate somesthetic feedback in virtual environments might impair their performance, just as major somesthetic loss does.     

Reliability and availability analysis of systems operating in multiple environments

This paper presents two newly developed stochastic models which can represent engineering systems operating in different types of environments. Laplace transforms of the state probabilities, system reliability and availability equations are developed. In addition, steady-state availability and mean-time-to-failure expressions are developed and their plots are shown.