PubMed Health⌕ Search

Biomedical subjects

R W Richards

Publications and source records attributed to R W Richards.

At least 19 recordsLinked to original sources
PubMed2003

Neutron-mapping polymer flow: scattering, flow visualization, and molecular theory.

Flows of complex fluids need to be understood at both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: Orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

Journal Article↗
PubMed2002

Surface visco-elastic moduli of a Langmuir film of a polystyrene-polydimethyl siloxane block copolymer at the air-ethyl benzoate interface.

Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier, but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry, the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration of 3.1 mg m(-2).

Journal Article↗
PubMed2002

Film thickness effects on the distribution of high-molecular-weight heterotelechelic polymers.

High-molecular-weight heterotelechelic deuteriopolystyrene, NDPSF, possessing an amine functional group at one end of the chain and a fluorocarbon group at the other was tethered to a silicon substrate by its amine functional group. These layers were coated with an unfunctionalised polystyrene matrix, HPS, such that the total film thickness covered a range from 2.2 to 9 times the radius of gyration of NDPSF. The detailed distribution of the polymers after annealing for times much greater than the reptation period of either of the components, was obtained using neutron reflectometry. No evidence for bridging of the two interfaces was found for the thicker films, but the finite concentration of the NDPSF polymer observed for the thinnest films may be due to bridging since the energy gain of the fluorocarbon end is just greater than the loss due to configurational entropy losses. A linear increase in the ellipsometric thickness of the excess of NDPSF at the substrate was discovered and we attribute this to the NDPSF slowly being leached out of the layer initially at the substrate followed by diffusion into the bulk of the film. The concentration profiles obtained are consistent with hindered relaxation of the large NDPSF molecules, when they are tethered at the substrate or at the vacuum surface.

Journal Article↗
PubMed2001

Subchronic cocaine produces training paradigm-dependent learning deficits in laboratory rats.

The effect of cocaine on spatial learning was investigated by exposing male Sprague-Dawley rats to 0, 20, or 40 mg/kg cocaine prior to and during training on a water maze task. Half the animals were pretrained on cued trials prior to hidden platform trials, while the remaining animals completed hidden platform trials immediately. Escape latencies for all animals improved with training, but pretrained animals located the hidden platform faster than untrained animals (P<.001). Pretraining also decreased the effect of cocaine. In pretrained animals, only the high dose of cocaine caused significant increases in escape latency (P<.001), while in the untrained group the lower dose of cocaine also caused a significant increase (P<.001). On working memory measures, cocaine affected both the pretrained (P<.01) and untrained (P<.001) groups. Dwell ratio measurements indicated unaffected reference memory in both pretrained (P<.001) and untrained (P<.001) animals, and no significant differences were detected among the treatment conditions in either group (P>.05). Thus, while cocaine did not abolish learning, the efficiency with which the task was learned was compromised. However, this effect was reduced by pretraining.

Animals↗
PubMed2001

Best practices in community-oriented health professions education: international exemplars.

INTRODUCTION: During 1998-2000, an international team of five researchers described nine innovative health professions education programmes as selected by The Network: Community Partnerships for Health through Innovative Education, Service, and Research. Each researcher visited one or two schools. Criteria for selection of these nine schools included commitment to multidisciplinary and community-based education, longitudinal community placements, formal linkages with government entities and a structured approach to community participation. The purpose of these descriptions was to identify key issues in designing and implementing community-based education. METHODOLOGY: Programmes in Chile, Cuba, Egypt, India, the Philippines, South Africa, Sudan, Sweden and the United States were visited. Before site visits were conducted, the researchers as a group agreed upon the elements to be described. Elements included overall institutional characteristics, curriculum, admissions practices, evaluation systems, research, service, community involvement, faculty development, postgraduate programmes and the school's relationship with government entities. Here I describe the common features of each of the nine programmes, their shared dilemmas and how each went about balancing the teaching of clinical competence and population perspectives. LESSONS LEARNED: Based upon an analysis of the cases, I present seven "lessons learned" as well as a discussion of programme development, institutionalization of reform and long-term implications for health professions education. The seven lessons are: (1) PBL and CBE are not seen as independent curricular reforms; (2) student activities are determined based upon sensitivity to locale; (3) health professionals need to work collaboratively; (4) there is a connection between personal health and population health issues; (5) population health interventions and treatment strategies need to be appropriate to local conditions; (6) graduates need to advocate for patients and the community in the public policy arena; and (7) organizational change takes a long time. CONCLUSIONS: Despite their differences, all nine exemplars are engaged in processes of organizational change. Schools are becoming more community-oriented and socially accountable, and all of these programmes have accepted two fundamental tenets: "take public money, give to the public" and "place matters".

Journal Article↗
PubMed1993

Community partnerships: educational linkages to increase the number of primary care practitioners.

The Community Partnerships initiative is focused on the creation of academic, non-hospital community health centers shaped by people and institutions at the local level. In our view, public policy-makers need such positive ideas and programs to support--things to be for rather than against. Incessant lamenting about the problems of the health care system will change the system less than will positive programs shaped and supported by the people whose needs they serve. All of us in medical education recognize the need for change in medical education. The Community Partnerships program represents one strategy for change that brings communities directly into the sphere of influence and enables them to enhance the relevance of the educational experience for health professions students.

Academic Medical Centers↗
PubMed1990

Bombesin improves rats' operant responding maintained by a differential-reinforcement-of-low-rates schedule of food reinforcement.

The present study examined rats' responding on a differential-reinforcement-of-low-rates schedule of food reinforcement following intraperitoneal injections of various doses of bombesin (4, 6, 8, 16, 32 micrograms/kg). Analyses indicated that only the 6 micrograms/kg dosage improved DRL responding. The findings are consistent with prior research examining bombesin's effect on operant behavior and support the notion that bombesin induces satiety rather than malaise.

Animals↗
PubMed1989

A collaboration between two innovative medical education programmes in Egypt and the United States.

In 1984, the Center for Educational Development at the University of Illinois at Chicago began to offer its Master of Health Professions Education leadership programme to 13 medical teachers on-site at Suez Canal University in Ismailia, Egypt. The central issue in this project was whether two institutions on different continents and representing different cultures could collaboratively develop and implement a relevant graduate programme. Of equal concern was whether the degree programme could be adapted to meet the needs of the teachers of a new innovative medical school in a developing country. The 13 doctors have now graduated. This paper describes the rationale for the enterprise, the planning phase of the project, the curriculum, problems that had to be overcome, and some indices of success.

Chicago↗
PubMed1987

Children's time perception as affected by order of stimulus presentation.

Two groups of 5- to 6-yr.-old children estimated the time required to view 15 color slides containing an assortment of familiar objects. In one group, the pictures appeared in categorical order. A second group viewed the same 15 slides in a random order. The results showed that, although picture-recall was similar for the two groups, children in the category group estimated significantly longer durations than subjects in the random condition. The findings were discussed in the context of Ornstein's 1969 storage size hypothesis.

Attention↗
PubMed1981

A comparison of signaled and unsignaled delay of reinforcement.

Pigeons were trained on either a variable-interval 60-second schedule, or on a schedule that differentially reinforced responses that were spaced at least 20 seconds apart. The birds were then exposed to several durations of reinforcement delay, with comparisons between signaled and unsignaled delays. Although unsignaled delays of 5 and 10 seconds produced large decreases in response rate, signaled delays of up to 10 seconds produced only moderate decreases in response rates. In addition, some subjects responded more rapidly with a .5 or 1.0 second duration of unsignaled delay than with immediate reinforcement. These response rate changes occurred regardless of whether the rate of reinforcement concomitantly decreased or increased.

Journal Article↗
PubMed1981

Preference for signaled versus unsignaled reinforcement delay in concurrent-chain schedules.

A concurrent-chain schedule was employed to examine pigeons' preferences for signaled versus unsignaled delay of reinforcement in which the delay durations ranged from zero to ten seconds. In general, pigeons preferred signaled delay over unsignaled delay especially when a variable-interval 30-second schedule operated in each initial link; when a variable-interval 90-second schedule operated in each initial link, these preferences tended toward indifference or were attenuated. In addition, prior training seemed to exert partial control over behavior. Responding in the terminal link was higher under signaled delay than unsignaled delay in a majority of the cases. Moreover, response rates under signaled delay remained fairly constant whereas responding under unsignaled delay was initially high, but decreased systematically with delay durations as short as 2.5 seconds. These results are consistent with a number of other studies demonstrating the significant role of a signal for impending positive stimuli.

Journal Article↗
PubMed1978

Ambulatory family practice experience as the primary and integrating clinical concept in a four-year undergraduate curriculum.

The Upper Peninsula Medical Education Program seeks to graduate primary care physicians who will practice in rural, underserved areas. The program has a unique curriculum that involves four years away from Michigan State University's main campus and is based on ambulatory outpatient experience in a family practice model office. All basic and clinical sciences are learned in this setting. Novel ways of organizing faculty and student time help facilitate this plan. A thorough evaluation system helps monitor student progress. Preliminary results are promising indications that the program is meeting its goals.

Community Health Centers↗