Transient heat transfer in Bénard convection

Experimental results are presented for a study of the effects of time-dependent heating on Bénard convection, where the fluids were 5cs (centistoke), 100cs and 500cs viscosity grades of silicone oil. Fluid layer depths were 0.00635 m, 0.01270 m and 0.01905 m. For each run the heat flux at the lower surface was approximately constant, and in the several runs a range of fluxes from 9.2 × 10²to 1.9 × 10⁷ (in dimensionless terms) was covered. The experiments were designed to examine the effects of different heating rates on the onset of convection, on the change of the Rayleigh number with time and on the development of motion. Observations were made from shadowgraph images, which were recorded photographically. As the heat flux at the lower surface is increased, the temperature difference required for the initiation of convection increases while the time to the onset of motion decreases. For the conditions of the present tests a “closed cell” pattern is the first to be observed, shortly after the onset of motion. This pattern does not appear in the steady-state system. Because of the “large” (greater than about 100) Prandtl number, specifying the time and the lower surface heat flux is sufficient to characterize the state of the fluid layer.     

Simple theory of stress-strain properties of filled polymers

By the use of simple models of filled plastics, approximate equations are derived for the elongation to break in the case of perfect adhesion between the phases and for the tensile strength in the case of no adhesion between the polymer and filler phases. By combining these equations with equations for the modulus (assuming Hookean behavior) all the stress–strain properties can be derived, including rough estimates of the impact strength, as a function of filler concentration. Among other things, the theory predicts a very rapid decrease in elongation to break as filler concentration increases, especially for the case of good adhesion. It is also predicted for the case of good adhesion that the tensile strength of a filled polymer can be greater than that of an unfilled polymer.     

Comparison of free α-tocopherol and α-tocopheryl acetate as sources of vitamin E in rats and humans

The uptake of α-tocopherol from 2R,4′R,8′R-α-tocopherol and 2R,4′R,8′R-α-tocopheryl acetate has been compared in rats and humans. The two forms of vitamin E were compared simultaneously in each subject (rat and human) by using a combination of deuterium-substitution and gas chromatography-mass spectrometry (GC-MS) to distinguish and measure the competitive uptake of α-tocopherol from an orally ingested mixture of the acetate and the free phenol forms. When rats were dosed in a manner analogous to that used in traditional bioassays, i.e., providing the two forms of vitamin E one daily in tocopherol-stripped corn oil for four successive days immediately prior to sacrifice, the net uptake of α-tocopherol from the free phenol form was only half that from the acetate. This result is consistent with the greater activity of the acetate that had been observed previously in bioassays. However, when the two forms of tocopherol were intubated into rats as a single dose mixed in with an aqueous bolus of standard laboratory diet, the amount of α-tocopherol taken up from the free form after 24 hr was very similar to that derived from the acetate. In five adult humans, competitive uptake studies of the two forms after a single dose taken with a meal showed that the amount of α-tocopherol from the free phenol form was equal to that from the acetate in plasma and red blood cells. These findings illustrate the value and potential of using deuterium-substituted α-tocopherol and GC-MS in evaluating the effectiveness of different forms of vitamin E in human studies. The results also stress the need for caution in using data obtained from animal bioassays when considering comparative human nutritional standards.     

Continual Process Improvement for ITIL Service Operations: A Lean Perspective

IT service management (ITSM) practitioners recognize the need for continuous improvement of IT services. Using a design science research approach, we develop a five – step process improvement framework for ITIL (Information Technology Infrastructure Library) service operations, based on the use of the Lean toolset. The proposed framework offers a structured approach for process improvement in practice and a basis for more systematic research.     

Participation rates in physics 12 in BC: Science teachers’ and students’ views

Abstract

In recent years, participation rates in the British Columbia (BC) provincial physics exams have been low, compared with chemistry and biology. A qualitative study employing questionnaire and interview methods sought the views of teachers and students of senior science courses on why this is the case. Data analysis revealed that students’ decisions about Physics 12 were influenced by their perceptions of the mathematical content of physics, the physics teachers’ personalities and teaching styles, the perceived difficulty of physics, and prior experience of physics. We conclude that enhancing student interest in taking physics at advanced high school levels may necessitate a wider, more articulated exposure to topics in physics, together with more careful attention to mathematical background and skills.     

The notch sensitivity of polymeric materials

Stress–strain tests were made on about five dozen polymeric materials using unnotched and notched specimens containing six different types of notches. Notches decrease the strength, but they decrease the elongation to break even more drastically in general. Notch sensitivity factors are defined for strength and for energy to fracture in such a manner that the greater the notch sensitivity factor, the greater is the effect of a notch relative to the unnotched material. The notch sensitivity factor for breaking (or yield) strength is not the same as the notch sensitivity factor for energy to fracture as measured by the area under the stress–strain curve. Brittle polymers and composites tend to have greater notch sensitivity factors for strength than ductile polymers. For brittle polymers, the notch sensitivity factor for energy to fracture tends to increase with the elongation to break of the unnotched polymer. Notches generally are more detrimental to ductile polymers than to brittle ones as far as the energy to fracture is concerned. For ductile polymers, the shape of the stress–strain curve is important in determining the sensitivity to notches. The ratio of the upper to lower yield strengths should be small for low notch sensitivity. It is desirable to have the breaking strength greater than the yield strength. Glass fibers and filler in ductile matrices increase the notch sensitivity for strength but decrease the sensitivity for energy to fracture relative to the unfilled polymer. Rubber–filled polymers have a reduced notch sensitivity for strength relative to the unfilled polymer, but the notch sensitivity for energy to fracture may be either increased or decreased, depending upon the system. The energy to fracture for notched specimens correlates better with Izod impact strength than does the energy to fracture for unnotched specimens. It is recommended that notched stress–strain specimens be routinely measured along with unnotched specimens.     

Scale errors in model tests on granular media with special reference to silo models

Theoretical solutions to silo problems are only given in a relatively few cases, mainly because of difficulties in formulating the constitutive equations for the silo medium. Wide use has therefore been made of model tests. In the present paper use is made of the centrifuge techniques to check the limitations of the method normally applied, in which model tests are performed neglecting the influence of volume forces.It is found that the single method can be used for materials normally considered to be non-cohesive, provided the model is not too small. This verifies Weber's assumptions for such models.The centrifuge method is recommended for cohesive materials, and an experimental technique for measuring pressure and visualizing flow patterns is described.     

Clinical assessment and treatment of insomnia.

Insomnia is characterized by problems initiating and maintaining sleep—problems that often go unrecognized by psychotherapists as well as physicians. This article addresses central questions related to the diagnosis, assessment, and treatment of this problem. Differential diagnosis is focused upon as well as the comorbidity with psychiatric and organic disorders. The Assessment of Insomnia section covers different subjective measures of sleep: sleep diaries, sleep questionnaires, and sleep interview. Additionally, central objective sleep measures are included. In the Treatment of Insomnia section, the 6 most common behavioral interventions are presented together with the most current pharmacological approaches. (PsycINFO Database Record (c) 2010 APA, all rights reserved)