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Biomedical subjects

R L Knoll

Publications and source records attributed to R L Knoll.

5 recordsLinked to original sources
PubMed1987

Soft intraocular lenses.

An in-depth review of the current status of soft intraocular lenses (IOLs) is presented. We have outlined the historical aspects of IOL development from polymethylmethacrylate material to newer soft polymers such as silicones and hydrogels. Chemical, physical, and biomaterial properties as well as the advantages and disadvantages of these materials and lenses are discussed. Clinical results from international investigators are presented, along with some thoughts about future trends in small incision cataract surgery and IOL substitutes.

Humans↗
PubMed1984

Perception, production, and imitation of time ratios by skilled musicians.

We have described our exploration of the judgment, production, and imitation of fractions of a beat by skilled musicians, illustrating our findings with data from violinist and conductor Paul Zukofsky. For small fractions we found systematic and substantial errors. In the judgment task small stimulus fractions are associated with names that are too large (overestimation). In both production and imitation tasks the fractions produced were too large (overproduction, overimitation). A summary of our findings and of the expectations they violate is provided in Figure 7. The temporal patterns we used are perhaps the simplest that qualify as rhythms, incorporating just a beat interval and a fraction. The phenomena we discovered in relation to these simple patterns, and their implications for underlying mechanisms, must be considered in attempts to understand the perception and production of more complex rhythms, as in actual music. We explored and rejected several plausible explanations for the overestimation and overproduction of small fractions. Although we have as yet no satisfactory explanations of the errors themselves, relations among the errors have powerful implications for human timing mechanisms. The relation between the errors in judgment and production requires us to reject a feedback model of production, in which a subject uses the same processes as in the judgment task to evaluate and adjust his performance in the production task. An explanation of the inconsistency between judgment and production seems most likely to lie in a change in time perception induced by the production task. Together with the existence of systematic errors in judgment, the equality of the errors in production and imitation argues that imitation is not accomplished by concatenating all the processes used in judgment and production. Our results are instead consistent with a model containing four internal transformation processes, in which judgment and production share no process, but do involve the same internal-fraction representation, and in which imitation shares one process with judgment and another with production.

Discrimination Learning↗
PubMed1980

Controlled microstructure of two stage polyhydroxyethyl methacrylate coatings on polyethylene terephthalate substrates for potential prosthetic applications.

Two types of polyethylene terephthalate (Dacron) substrates (USCI DeBakey Vasculour-D and USCI Sauvage filamentous) have been selectively coated with Poly-hydroxyethyl methacrylate (P-HEMA) in a two-stage process. Using scanning electon microscopy (SEM) techniques, the microstructural details of the fabrications were identified. The first stage of this process imparted a coating of P-HEMA having a heterogeneous macroporous structure and the second stage yielded an internal surface coating of hydrogel with a homogeneous microporous surface structure. The morphology on a colloidal level was controlled by adjustment of the cosolvent ratios holding other fabrication parameters constant. These microstructural features coupled with the chemical properties of the hydrogel suggest potential medical prosthetic applications. The results of initial canine carotid artery implantations indicate that an endothelial-like cell layer can be established within 21 days on the luminal surface of specific hydrogel impregnated Dacron knitted prosthetic materials. The chemical and morphological properties of a hydrogel impregnated Dacron prosthesis may present a blood flow surface which allows proper conditioning protein and cellular deposition leading to an accelerated endothelial development without the need to preclot the prosthesis wall.

Acrylates↗