Squeeze-Film Flow in the Presence of a Thin Porous Bed, with Application to the Human Knee Joint

Motivated by the desire for a better understanding of the lubrication of the human knee joint, the squeeze-film flow of a thin layer of Newtonian fluid (representing the synovial fluid) filling the gap between a flat impermeable surface (representing the femoral condyles) and a flat thin porous bed (representing the articular cartilage) coating a stationary flat impermeable surface (representing the tibial plateau) is considered. As the impermeable surface approaches the porous bed under a prescribed constant load all of the fluid is squeezed out of the gap in a finite contact time. In the context of the knee, the size of this contact time suggests that when a person stands still for a short period of time their knees may be fluid lubricated, but that when they stand still for a longer period of time contact between the cartilage-coated surfaces may occur. The fluid particle paths are calculated, and the penetration depths of fluid particles into the porous bed are determined. In the context of the knee, these penetration depths provide a measure of how far into the cartilage nutrients are carried by the synovial fluid, and suggest that when a person stands still nutrients initially in the fluid layer penetrate only a relatively small distance into the cartilage. However, the model also suggests that the cumulative effect of repeated loading and unloading of the knees during physical activity such as walking or running may be sufficient to carry nutrients deep into the cartilage

Rooftop and ground standard temperatures: a comparison of physical differences

July 2000.Includes bibliographical references (pages 48-49).Accuracy and continuity of surface air temperature measurements are critical for many meteorological activities including short-term weather forecasting, warnings, and climate monitoring. In the United States and worldwide, most air temperature observations have historically been taken at a height of approximately 1.25 to 1.5 meters above the ground over a grass surface. In the last two decades, there has been a rapid expansion of nonfederal weather station networks to support state, regional and community needs. Many of these new weather stations are located on rooftops for reasons of security or convenience. Mixing these rooftop observations indiscriminately with observations from standard screen-height can pose significant issues for weather forecasting and verification, weather and climate analysis and climate applications such as energy demand planning and forecasting by large public utilities. This study establishes the physical mechanisms which cause a rooftop sensor to have a temperature bias relative to a nearby ground sensor. From a surface energy balance perspective, the physical characteristics of a surface are analyzed and related to temperature bias. This study identifies the surfaces and conditions leading to rooftop temperature bias in both maximum and minimum temperatures. These concepts are verified through both surface radiating temperature measurements and air temperature measurements contrasting roof and ground temperatures. Guidelines are then proposed to establish which roofs are unsuitable for temperature measurements and under what conditions a rooftop is vulnerable to temperature bias. Results indicate that overcast skies lead to small rooftop to ground differences in both surface radiating temperature and air temperature. Observations show differences of approximately 1 degree C or less in radiating temperature and less than 1 degree C in air temperature. An exception was observed where a wall effect led to more than a 2 degree C difference in air temperatures between roof and ground. Clear or partly cloudy skies allow larger rooftop temperature biases to develop. Roof to ground differences in surface radiating temperatures of up to 30 degrees C were observed. Although air temperature measurements were not made at all locations, observations show roof to ground differences of 3 degrees C for radiating temperature differences of 14 degrees C. The potential for even greater roof-ground air temperature differences exists at sites where radiating temperatures are further apart.Supported by the NOAA, National Weather Service, Office of Meteorology under grant NA67RJ0 152 Amend 21

Temperature data continuity with the automated surface observing system

Includes bibliographical references (pages 86-87).June 1996.To view the abstract, please see the full text of the document.This research was supported by the National Weather Service, Office of Meteorology, under NOAA grant #NA37RJ0202 - Item 9

A novel method of supplying nutrients permits predictable shoot growth and root: shoot ratios of pre-transplant bedding plants

BACKGROUND AND AIMS: Growth of bedding plants, in small peat plugs, relies on nutrients in the irrigation solution. The object of the study was to find a way of modifying the nutrient supply so that good-quality seedlings can be grown rapidly and yet have the high root : shoot ratios essential for efficient transplanting. METHODS: A new procedure was devised in which the concentrations of nutrients in the irrigation solution were modified during growth according to changing plant demand, instead of maintaining the same concentrations throughout growth. The new procedure depends on published algorithms for the dependence of growth rate and optimal plant nutrient concentrations on shoot dry weight Ws (g m–2), and on measuring evapotranspiration rates and shoot dry weights at weekly intervals. Pansy, Viola tricola ‘Universal plus yellow’ and petunia, Petunia hybrida ‘Multiflora light salmon vein’ were grown in four independent experiments with the expected optimum nutrient concentration and fractions of the optimum. Root and shoot weights were measured during growth. KEY RESULTS: For each level of nutrient supply Ws increased with time (t) in days, according to the equation {Delta}Ws/{Delta}t=K2Ws/(100+Ws) in which the growth rate coefficient (K2) remained approximately constant throughout growth. The value of K2 for the optimum treatment was defined by incoming radiation and temperature. The value of K2 for each sub-optimum treatment relative to that for the optimum treatment was logarithmically related to the sub-optimal nutrient supply. Provided the aerial environment was optimal, Rsb/Ro{approx}Wo/Wsb where R is the root : shoot ratio, W is the shoot dry weight, and sb and o indicate sub-optimum and optimum nutrient supplies, respectively. Sub-optimal nutrient concentrations also depressed shoot growth without appreciably affecting root growth when the aerial environment was non-limiting. CONCLUSION: The new procedure can predict the effects of nutrient supply, incoming radiation and temperature on the time course of shoot growth and the root : shoot ratio for a range of growing conditions

Snapshot of Colorado's climate during the 20th Century, A

June 1991.Prepared in conjunction with the Centennial Cooperative Weather Station Program held June 7-8, 1991 Colorado State University

Vibrational Stability of NLC Linac and Final Focus Components

Vertical vibration of linac components (accelerating structures, girders and quadrupoles) in the NLC has been studied experimentally and analytically. Effects such as structural resonances and vibration caused by cooling water both in accelerating structures and quadrupoles have been considered. Experimental data has been compared with analytical predictions and simulations using ANSYS. A design, incorporating the proper decoupling of structure vibrations from the linac quadrupoles, is being pursued.Comment: 3 pages, 8 figures presented at the LINAC 2002 conference, Gyeongju Kore

Effect of Cooling Water on Stability of NLC Linac Components

Vertical vibration of linac components (accelerating structures, girders and quadrupoles) in the NLC has been studied experimentally and analytically. Effects such as structural resonances and vibration caused by cooling water both in accelerating structures and quadrupoles have been considered. Experimental data has been compared with analytical predictions and simulations using ANSYS. A design, incorporating the proper decoupling of structure vibrations from the linac quadrupoles, is being pursued.Comment: 6 Pages 13 Figures Presented at The Nanobeam 2002 Workshop (Lausanne Switzerland