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PubMed1998

Efficient dynamic constraints for animating articulated figures.

This paper presents an efficient dynamics-based computer animation system for simulating and controlling the motion of articulated figures. A non-trivial extension of Featherstone's O(n) recursive forward dynamics algorithm is derived which allows enforcing one or more constraints on the animated figures. We demonstrate how the constraint force evaluation algorithm we have developed makes it possible to simulate collisions between articulated figures, to compute the results of impulsive forces, to enforce joint limits, to model closed kinematic loops, and to robustly control motion at interactive rates. Particular care has been taken to make the algorithm not only fast, but also easy to implement and use. To better illustrate how the constraint force evaluation algorithm works, we provide pseudocode for its major components. Additionally, we analyze its computational complexity and finally we present examples demonstrating how our system has been used to generate interactive, physically correct complex motion with small user effort.

Acceleration↗
PubMed2002

Human motion planning based on recursive dynamics and optimal control techniques.

This paper presents an efficient optimal control and recursive dynamics-based computer animation system for simulating and controlling the motion of articulated figures. A quasi-Newton nonlinear programming technique (super-linear convergence) is implemented to solve minimum torque-based human motion-planning problems. The explicit analytical gradients needed in the dynamics are derived using a matrix exponential formulation and Lie algebra. Cubic spline functions are used to make the search space for an optimal solution finite. Based on our formulations, our method is well conditioned and robust, in addition to being computationally efficient. To better illustrate the efficiency of our method, we present results of natural looking and physically correct human motions for a variety of human motion tasks involving open and closed loop kinematic chains.

Algorithms↗
PubMed2002

Distant collaboration in drug discovery: the LINK3D project.

The work describes the development of novel software supporting synchronous distant collaboration between scientists involved in drug discovery and development projects. The program allows to visualize and share data as well as to interact in real time using standard intranets and Internet resources. Direct visualization of 2D and 3D molecular structures is supported and original tools for facilitating remote discussion have been integrated. The software is multiplatform (MS-Windows, SGI-IRIX, Linux), allowing for a seamless integration of heterogeneous working environments. The project aims to support collaboration both within and between academic and industrial institutions. Since confidentiality is very important in some scenarios, special attention has been paid to security aspects. The article presents the research carried out to gather the requirements of collaborative software in the field of drug discovery and development and describes the features of the first fully functional prototype obtained. Real-world testing activities carried out on this prototype in order to guarantee its adequacy in diverse environments are also described and discussed.

Computer Graphics↗
PubMed2004

Three dimensional virtual reality model of the normal female pelvic floor.

The anatomy of the pelvic floor is complex and difficult to visualize from conventional two-dimensional anatomy pictures. The goal of this project was to establish the methods necessary to develop a static three-dimensional virtual reality model of the normal female pelvic floor from high-resolution magnetic resonance imaging (MRI) scans. An asymptomatic nulliparous 23-year-old female with no urinary incontinence symptoms underwent a high-resolution pelvic floor MRI scan. Selected pelvic floor structures were manually segmented: bladder, urethra, vagina, uterus, cervix, levator ani, obturator externus, obturator internus, and pubic bone. With high-resolution scans, accurate segmentation of the structures was possible. The completed models were displayed on an ImmersaDesk Virtual Reality system and three clinicians verified their accuracy. Stereovision glasses were used to enhance the model while a receiver tracked head position. Three-dimensional virtual reality models of the female pelvic floor can enhance our understanding of anatomy and physiology of this complex part of the body. They can be used as tools for both research and teaching, facilitating improved treatment of pelvic floor pathologies.

Adult↗
PubMed2004

QSim, a program for NMR simulations.

We present QSim, a program for simulation of NMR experiments. Pulse sequences are implemented and analyzed in QSim using a mouse driven interface. QSim can handle almost any modern NMR experiment, using multiple channels, shaped pulses, mixing, decoupling, phase-cycling and pulsed field gradients. Any number of spins with any spin quantum number can, in theory, be used in simulations. Relaxation is accounted for during all steps of pulse sequences and relaxation interference effects are supported. Chemical kinetics between any numbers of states can be simulated. Both classical and quantum mechanical calculations can be performed. The result of a simulation can be presented either as magnetization as a function of time or as a processed spectrum.

Computer Graphics↗
PubMed2004

Impact of different software implementations on the performance of the Maxmin method for diverse subset selection.

Besides the choice of an automated software method for selecting 'maximally diverse' compounds from a large pool of molecules, it is the implementation of the algorithm that critically determines the usefulness of the approach. The speed of execution of two implementations of the Maxmin algorithm is compared for the selection of maximally diverse subsets of large compound collections. Different versions of the software are compared using various C compiler options and Java virtual machines. The analysis shows that the Maxmin algorithm can be implemented in both languages yielding sufficient speed of execution. For large compound libraries the Java version outperformes the C version. While the Java version selects the same compounds independent of the virtual machine used, the C version produces slightly different subsets depending on the compiler and on the optimization settings.

Algorithms↗
PubMed2000

Colour contrast sensitivity in cataract and pseudophakia.

PURPOSE: To study the influence of cataract on peripheral and central colour contrast sensitivity. METHODS: Peripheral and central colour contrast sensitivity was measured with a computer graphics system along the protan, deutan and tritan axes. Included were 30 patients with cataract divided into three sub-groups: cortical cataract, nuclear sclerosis and posterior subcapsular cataract. Colour contrast was measured before and after cataract operation. RESULTS: There were significant differences in peripheral colour contrast thresholds comparing the preoperative and postoperative results. This difference existed even in patients (n=19) with a pre-operative visual acuity > or = 0.5 (mean 0.6). The tritan axis was the one most affected by cataract. There was no significant difference between cataract sub-groups. Also, the central colour contrast sensitivity was affected by cataract. Again, the tritan axis was the most affected one. There was no significant difference between the cataract sub-groups. We also found large and significant differences in central colour contrast thresholds between normal subjects and postoperative values from the cataract group in all colour axes. The colour contrast sensitivity was poorer in pseudophakes than in normals. There was a difference between the three groups of different IOL material used (PMMA, acrylic and silicone). The difference was significant in the protan axis, the acrylic group having the best colour contrast sensitivity. CONCLUSION: Peripheral colour contrast sensitivity was affected by cataract, even when only moderately developed. This finding is of importance and should be considered when the method is used to study other eye diseases e.g. glaucoma. Central colour contrast sensitivity was also affected by cataract. The pseudophakes were found to have poorer colour contrast sensitivity than normals. The material in the IOL seemed to be of importance for colour contrast.

Acrylates↗
PubMed2002

Colour contrast sensitivity in ocular hypertension. A five-year prospective study.

PURPOSE: To evaluate a peripheral colour contrast sensitivity test as a tool for early diagnosis of glaucoma in a five-year prospective study. PATIENTS AND METHODS: Peripheral colour contrast sensitivity was measured with a computer graphics system developed by Arden et al. The test colours were varied along the protan, deutan and tritan colour confusion axes on a scale from 0 to 100 percentage units. Fifty-five ocular hypertensive (OH) patients examined with the colour contrast test, stereoscopic photography of the optic discs, and measurements of visual fields (Humphrey 24-2 glaucoma hemifield test (GHT)) in 1994, were re-examined after five years. RESULTS: Ten patients were 'outside normal limits' in the GHT at follow-up. This group of 10 patients did not differ in colour contrast thresholds at the test in 1994 from the 45 who were still 'normal' (or 'borderline') at follow-up. Neither were there proportionally more patients with GHT 'outside normal values' for the patients with high colour contrast thresholds (> 30% units) in 1994 regarding any of the three colour axes. As judged from patient files, 27 patients had developed glaucoma during follow-up. Although there were differences between these 27 glaucoma patients and the remaining OH group at the colour contrast test in 1994, these differences did not reach statistical significance for any of the colour axes (largest difference in the tritan axis: 6.2% units, P = 0.0745). At follow-up, however, there was a significant difference in colour contrast for the protan axis between the clinical glaucoma group and the OH group (6.7% units, P = 0.0105). CONCLUSION: The method used for colour contrast measurement did not reveal glaucomatous changes before conventional perimetry (Humphrey 24-2, GHT). Neither did it predict the patients who, in our clinic, subsequently developed glaucoma during a five-year period. A change over time in colour contrast in the protan axis for an OH patient may, however, indicate glaucoma development.

Color Perception↗
PubMed1995

Visual control of braking: a test of the tau hypothesis.

Deceleration during braking could be controlled by (a) using the time derivative of the relative rate of optical expansion, relative to a -0.5 margin value of tau-dot (D.N. Lee, 1976) or (b) computing the required deceleration from spatial variables (i.e., perceived distance, velocity, or object size). Participants viewed closed-loop displays of approach to an object and regulated their deceleration with a brake. The object appeared on a checkerboard ground surface (providing velocity, distance, and size information) or with no background (providing only optical expansion). Mean tau-dot during braking was -0.51, and estimates of the critical value of tau-dot based on brake adjustments were -0.44 and -0.52, close to the expected value. There were no overall effects of the ground surface or object size. The results are consistent with a tau-dot strategy, where the direction and magnitude of brake adjustments are regulated using tau-dot.

Acceleration↗
PubMed1994

Representational momentum for a spiral path.

When a ball is shot through a spiral tube at high speed, the ball emerges in a straight path tangent to the ball's point of departure from the tube. However, past research has shown that many Ss believe the ball follows a curved pathway. In the 3 experiments described in this article, a ball traveling through a spiral tube was animated on a computer graphics screen. Ss' memory distortions for positions of the ball along each of 3 pathways were measured using a representational momentum paradigm. Retention interval was varied across the 3 experiments. The results from the 3 experiments reported here replicate retention interval results previously reported for representational momentum effects, and they suggest that the representational pathway of a ball exiting a spiral tube is spiral in shape. These findings may shed some light on why people have demonstrated naiveté on the spiral tube problem in past research.

Humans↗
PubMed1996

Effect of type of practice in a computer-aided design environment in visualizing three-dimensional objects from two-dimensional orthographic projections.

The purpose of this study was to determine the effect of practice in manipulating 2- and 3-dimensional (D) wireframe images on a learner's ability to visualize 3-D objects. Practice, either rotational or not, consisted of visualizing 2- and 3-D objects generated by personal computer (PC)-based computer-assisted design software. Results indicated that participants in the rotation treatment group performed significantly better than those in either the nonrotation or control group on measures of spatial ability and 3-D visualization ability. Both treatment groups performed significantly better than the control group on measures of metacognition, effort, and worry. These results support a conclusion that spatial ability can be improved through practice that allows the learner to see the relationship between the 2-D and 3-D features of objects.

Adult↗
PubMed1989

Kinetic depth effect and identification of shape.

We introduce an objective shape-identification task for measuring the kinetic depth effect (KDE). A rigidly rotating surface consisting of hills and valleys on an otherwise flat ground was defined by 300 randomly positioned dots. On each trial, 1 of 53 shapes was presented; the observer's task was to identify the shape and its overall direction of rotation. Identification accuracy was an objective measure, with a low guessing base rate of the observer's perceptual ability to extract 3D structure from 2D motion via KDE. (1) Objective accuracy data were consistent with previously obtained subjective rating judgments of depth and coherence. (2) Along with motion cues, rotating real 3D dot-defined shapes inevitably produced a cue of changing dot density. By shortening dot lifetimes to control dot density, we showed that changing density was neither necessary nor sufficient to account for accuracy; motion alone sufficed. (3) Our shape task was solvable with motion cues from the 6 most relevant locations. We extracted the dots from these locations and used them in a simplified 2D direction-labeling motion task with 6 perceptually flat flow fields. Subjects' performance in the 2D and 3D tasks was equivalent, indicating that the information processing capacity of KDE is not unique. (4) Our proposed structure-from-motion algorithm for the shape task first finds relative minima and maxima of local velocity and then assigns 3D depths proportional to velocity.

Adult↗
PubMed2006

Smoking cues in a virtual world provoke craving in cigarette smokers.

Twenty smoking-deprived cigarette smokers participated in a study to test the ability of smoking cues within a virtual world to provoke self-reported craving to smoke. Participants were exposed to 2 virtual-reality simulations displayed on a computer monitor: a control environment not containing any intentional smoking stimuli and a cue-exposure environment containing smoking stimuli. At various points, participants rated their urge to smoke on a scale of 0-100. Results indicated that baseline urge ratings were equivalent in both conditions, but the maximum increase in urge ratings was significantly higher in the cue-exposure environment than in the control environment. This is comparable to what in vivo studies have reported, but with the advantage of simulating more naturalistic and complex settings in a controlled environment.

Adult↗
PubMed1999

Herbart's mathematical psychology.

J.F. Herbart (1824/1890b) provided a mathematical theory about how mental ideas (Vorstellungen) in consciousness at Time 1 (T1) could compete, possibly driving 1 or more Vorstellungen below a threshold of consciousness. At T1 a Vorstellung A could also fuse with another, B. If at a later T2, A resurfaced into consciousness, it could help B to re-resurface into consciousness. This article describes the historical and mathematical background of Herbart's theory, outlines the mathematical theory itself with the aid of computer graphics, and argues that the theory can be applied to the modern problem of predicting recognition latencies in short-term memory (Sternberg's task; Sternberg, 1966)

Germany↗
PubMedDate not supplied

Gene and protein structure of a beta-crystallin polypeptide in murine lens: relationship of exons and structural motifs.

A 23,000 molecular weight beta-crystallin (beta 23) of the murine eye lens is encoded in a 4.1 +/- 0.3-kilobase gene containing three introns. Each of the four exons seems to code for a separate structural motif of the protein, whose tertiary structure was predicted by an interactive computer graphics technique based on the crystallographic structure of bovine gamma II-crystallin. The first exon also encodes a hydrophobic N-terminal peptide resembling membrane anchor sequences of other proteins. Our results indicate structural homology among the beta- and gamma-crystallin polypeptides, and link gene structure with protein structure in this superfamily of lens proteins.

Amino Acid Sequence↗
PubMedDate not supplied

Structural and evolutionary analysis of HLA-D-region products.

The major histocompatibility complex (MHC)--HLA in man and H-2 in mouse--encodes two classes of cell-surface antigens involved in the immune response. The amino acid sequences have been determined for a number of these molecules. Class I antigens, typified by the HLA-ABC antigens, are composed of a 43,000-molecular weight (MW) glycosylated transmembrane polypeptide with three external domains (alpha 1, alpha 2 and alpha 3), of which the one nearest the membrane (alpha 3) is associated with a 12,000-MW nonglycosylated polypeptide, beta 2-microglobulin. The HLA-D-region or class II antigens, DR, DC and SB, are composed of two glycosylated transmembrane polypeptides, of MWs 34,000 (alpha-chain) and 28,000 (beta-chain). Both chains have two external domains which presumably associate with each other, alpha 2, beta 2 being membrane proximal and alpha 1, beta 1 N-terminal and membrane distal. All four membrane-proximal domains (class I alpha 3, beta 2-microglobulin, class II alpha 2 and beta 2) have amino acid sequences that show significant similarities with immunoglobulin constant-region domains. This, together with the similarly placed internal disulphide bonds, suggests they might have an immunoglobulin-like structure (Fig. 1). We have now used computer graphics techniques to predict a detailed three-dimensional structure for the membrane-proximal domains of the class II antigens (alpha 2 and beta 2) based on the known coordinates of immunoglobulin constant domains (Fig. 2). The transmembrane regions of class II antigens have been modelled as two alpha-helices packed together. The proposed structure accounts for conservation of amino acids and leads to evolutionary predictions.

Amino Acid Sequence↗
PubMed1994

The role of light scatter in the degradation of visual performance before and after Nd:YAG capsulotomy.

The aim of this study was to determine whether capsulotomy size influences visual performance. Snellen visual acuity and forward light scatter (light scattered towards the patient's retina, but out of the focussed retinal image) measurements using simple computer graphics based on van den Berg's technique were used to measure visual performance. Twelve patients were studied: 4 had small central capsulotomies through undilated pupils and 8 had wide capsulotomies through dilated pupils. The two groups were matched for age and pre-laser Snellen acuity. Following treatment, both groups had equal improvements in Snellen acuity. There was only a significant (p < 0.001) improvement in forward light scatter readings in the group who received wide capsulotomies. Measurements of forward light scatter are more sensitive than Snellen acuity testing in demonstrating loss of visual performance in patients with media opacities. It is recommended that pupils are dilated prior to Nd:YAG capsulotomy if forward light scatter from capsule remnants and the consequent glare disability are to be minimised.

Aged↗