Abstraction paradigms for computer graphics

In computer graphics we use techniques from different areas of mathematics. Mathematical models are used to simulate real-world objects, as well as natural phenomena. In order to understand these models and pose relevant problems in each particular field of this area, it is important to create levels of abstraction. These levels encapsulate common properties of the different models and allow us to have a global, conceptual view of the methods and techniques in each field. In this paper we study a paradigm for creating abstraction levels that can also be used to characterize more general problems in computational applied mathematics. We apply this paradigm to different areas of computer graphics: modeling, animation, illumination, color theory, image processing and human-computer interface.     

Neurological protection during cardiopulmonary bypass/deep hypothermia

OBJECTIVE: To determine if arthroscopic synovectomy in normal and inflamed joints had temporal or site-related effects on articular cartilage. STUDY DESIGN: Alterations in equine third carpal bone articular cartilage were studied at two time periods: groups 1 and 2 (6 weeks) and groups 3 and 4 (2 weeks) after synovectomy in normal (groups 2 and 4) and inflamed carpi (groups 1 and 3). ANIMAL POPULATION: 16 carpi from eight horses. METHODS: Biochemical and biomechanical properties of dorsal and palmar articular cartilage were determined by radioloabeling, proteoglycan (PG) extraction, chromatography, electrophoresis, and indentation testing. RESULTS: Synovectomy in inflamed joints produced the greatest concentration of newly synthesized PG in articular cartilage by 2 weeks. Synovectomy in normal joints produced significantly greater newly synthesized PG in articular cartilage by 6 weeks. Dorsal sites had greater newly synthesized and endogenous PG in some groups. Chromatographic profiles of newly synthesized PG demonstrated early and late PG peaks. Electrophoresis of late PG peak showed a toluidine blue-positive band that comigrated with human A1D1 PG monomer in the two groups with the most newly synthesized PG> This band was reactive with monoclonal antibody 1C6 specific for the hyaluronic acid-binding region of aggrecan. For the material properties evaluated, only Poisson's ratio was significantly decreased between groups as a function of time (6 weeks < 2 weeks). and this was most pronounced in the thicker dorsal sites. CONCLUSIONS: Synovectomy in inflamed joints produced site-specific, significantly greater responses in articular cartilage as compared with synovectomy in normal joints. CLINICAL RELEVANCE: Synovectomy may not be beneficial to the articular cartilage in inflamed joints.     

Dynamic strain aging and hydrogen-induced softening in alpha titanium

Compression tests were carried out on samples of commercial-purity titanium charged with up to 4.7 at. pct hydrogen. Strain rates of 10⁻³ to 1 s⁻¹ were employed and testing was limited to the α phase field at temperatures of 773 to 973 K. The dependences of the flow stress on strain, strain rate, and temperature were determined. A plateau or bulge appeared in the temperature and strain-rate dependences of the flow stress, and the work-hardening rate also showed peaks. Serrations were observed on some of the stress-strain curves. All these features indicated that dynamic strain aging (DSA) was occurring. Analysis of the results (together with data from other authors) indicates that there are three ranges of DSA behavior in this material within the experimentally investigated temperature range; these appear to be associated with the diffusion of iron, carbon, and oxygen, respectively. Alloying with hydrogen decreases the magnitude of the DSA attributable to these elements and displaces the phenomenon to higher temperatures and/or to lower strain rates. The dependence on strain rate and temperature of the relative softening attributable to hydrogen addition was determined. The results indicate that hydrogen-induced softening is related to the occurrence of DSA in this temperature range. Possible explanations for this relationship are discussed. O.N. SENKOV, on leave from the Institute of Solid State Physics, Russian Academy of Sciences, Moscow Region 142432, Russia     

Results of reconstructive surgery in renal hypertension]

A traumatic macular hole has never been seen immediately after the causal accident. We examined a case of macular hole within half an hour of the injury and photographed it within three hours. We comment on the genesis of traumatic macular edema.     

Experimental studies of the force to extrude a rate sensitive material

Distinctions are drawn between three mean strain rates in extrusion: those averaged over the accumulated strain, the distance travelled through the die, and the elapsed time. It is shown that when the strain rate varies, the mean strain rate based on strain is always the greatest, and the mean strain rate based on time the smallest. Three further mean strain rates are introduced, which are root mean power (RMP) values of the above strain rates. Conventional estimates of the extrusion pressure for frictionless, homogeneous flow are based on rate insensitive analyses and lead to pressures proportional to the mean strain rate based on time. When the rate sensitivity during flow is taken into account, the calculated pressure is shown to be a function of the RMP strain rate based on accumulated strain, which is considerably greater than the mean strain rate based on time. Experiments are described in which ice was extruded by the indirect process, leading to nearly frictionless, homogeneous flow. Extrusion ratios of 4, 9, 25, 81, and 144 were used. In the first series of experiments, the ram velocity was adjusted to give the samerate insensitive (i.e. time-based) mean strain rate for all the dies. In the second series of experiments, the ram velocity was adjusted to give the samerate sensitive (i.e. RMP) mean strain rate for all the dies. In all cases the extrusion pressure was proportional to the RMP strain rate and not to the time-based strain rate. The rate sensitivity correction factor is also described.     

Voiding pressure as it relates to outlet and/or sphincteric resistance

Electrically quantitated and controlled detrusor contraction can produce either minimal or excessive rise in intravesical pressure depending upon openness or occlusion of the bladder outlet. Higher rise in intravesical pressure thus does not imply stronger detrusor contraction but should be viewed as a reflection of the outflow resistance mechanism. Possible damaging hydrodynamic effect of sudden partial or complete functional occlusion of the bladder outlet by intermittent or sustained voluntary sphincter activity is illustrated.     

Screening for enzyme inhibitors by surface plasmon resonance combined with mass spectrometry

We have developed a novel strategy to identify enzyme inhibitors that interact directly with their enzyme targets. In the approach, an enzyme is immobilized on a sensor chip, and it is determined whether the immobilized enzyme is still active by incubation with model substrates and mass spectrometric analysis of the products. Putative inhibitors or mixtures containing putative inhibitors are then injected over the sensor chip for binding analysis with surface plasmon resonance. It is then tested whether the bound compounds inhibit the enzymatic activity by subsequent incubation with the model substrate and mass spectrometric analysis. If the bound compound inhibits the enzyme, the inhibitor is eluted from the enzyme and characterized by mass spectrometry. To test the strategy, it has been applied to the well-characterized interaction between trypsin and pure bovine pancreas trypsin inhibitor. Furthermore, fractions of plant extracts were screened for binding to and inhibition of carboxypeptidase B.     

Trainable Articulatory Control Models for Visual Speech Synthesis

This paper deals with the problem of modelling the dynamics of articulation for a parameterised talking head based on phonetic input. Four different models are implemented and trained to reproduce the articulatory patterns of a real speaker, based on a corpus of optical measurements. Two of the models, (Cohen-Massaro and Öhman) are based on coarticulation models from speech production theory and two are based on artificial neural networks, one of which is specially intended for streaming real-time applications. The different models are evaluated through comparison between predicted and measured trajectories, which shows that the Cohen-Massaro model produces trajectories that best matches the measurements. A perceptual intelligibility experiment is also carried out, where the four data-driven models are compared against a rule-based model as well as an audio-alone condition. Results show that all models give significantly increased speech intelligibility over the audio-alone case, with the rule-based model yielding highest intelligibility score.     

Variations in lipid composition and sound velocity in melon from the North Atlantic pilot whale,Globicephala melaena melaena

Nonpolar lipids and sound velocity at different distances from the skin surface within a sample of pilot whale melon were studied. Thin layer chromatography, sensitive radioisotopic methods, and an ultrasonic echo scanner were used. Wax esters had a maximum concentration at 11–12 cm from the skin surface. Non- and monoisovalero triglycerides both exhibited a minimum at 8–10 cm, whereas the diisovalero species increased steadily from the skin surface towards the center of the pilot whale head. A minimum of sound velocity, ca. 1340 m/s, was found at 9–11 cm, thus coinciding with a region rich in isovaleric acid esterified in wax and diisovalero triglycerides. These findings are compatible with predictions based on the known correlations between lipid structure and sound velocity. Consequently, additional evidence for refraction of sound in pilot whale melon is presented. This is important in understanding the system of echolocation of toothed whales.