Adolescent growth, development, and psychosocial aspects of sports participation: an overview

This chapter examines sports participation in the context of adolescent growth and development. Because the nature of sports participation is highly organized and competitive, it is imperative that parents, coaches, physicians, and other clinicians remember that they may be placing increased pressures on the adolescent to perform and practice. The authors review the impact of physical growth and psychosocial development and also describe how substance abuse, depression, and aggressive behavior may or may not be influenced by sports participation.     

Differential scanning calorimetric study of curing of acrylated epoxy resin with benzoyl peroxide

The curing reaction of the acrylated diglycidyl ether of bisphenol-A (DGEBA) with benzoyl peroxide has been investigated by differential scanning calorimetry at three different heating rates. The overall cure kinetics were found to be first-order, with Arrhenius parameters E=83 kJ mol^?1 and In A = 16.5 min^?1, independent of the scan rate, up to at least 90% conversion.     

Synthesis,characterization and curing of m-diethylaminophenol-formaldehyde resin

Polycondensation of m-diethylaminophenol with formaldehyde has been studied under various reaction conditions. The resins formed are fusible and soluble in common organic solvents. All the resin samples have been characterized by spectral studies, measurement of solution viscosity, estimation of M?ⁿ and by t.g.a. The curing of selected resin samples by hexamine has been studied both by measuring percentage of cured material as a function of time at different temperatures and by differential scanning calorimetry. The d.s.c. data have been analyzed by various methods to evaluate the gross kinetic parameters of the curing reactions.     

MESUREMENT OF SOLIDS CONCENTRATION PROFILE AROUND THE PERIPHERY OF AN IMMERSED TUBE IN A THREE-DIMENSIONAL GAS-FLUIDIZED BED

To adequately describe the heat transfer process at the surface of an immersed tube in a gas-fluidized bed, it is imperative to know the solids concentration at the tube surface. The knowledge of particle dynamics will also enable to establish the likely metal erosion and thus the heat exchanger life. However, determination of such parameters is not straightforward and here we describe the development of an image carrying fiber optic probe with a potential to generate such information. Using such a borescope in conjunction with a CCTV camera, TV monitor and video-cassette recorder, solids concentration profiles have been measured around the periphery of horizontal tubes (outside diameters 11 and 28 mm) immersed in an air-fluidized bed of 1.4 mm average diameter glass beads. In both the cases, it is found that the bulk bed voidage is considerably smaller than the voidage at the tube surface. The latter also varies with the location around the tube periphery. The smallest values are found for the downstream side, largest values for the equatorial sides, and intermediate values for the upstream side. These values are dependent on the fluidizing velocity and the tube diameter. Estimate are also given of the air film thickness at various locations between the tube and the particles.     

Calculation of thermal-gradient-induced stress birefringence in slab Lasers-I

A thorough analysis of the losses due to thermal-gradient-induced stresses in slab lasers is presented in which depolarization losses due to thermal-gradient-induced stresses are calculated properly by treating the changes in the dielectric impermeability tensor. In previous analyses of this problem, the approach in which the index of refraction is treated as a tensor quantity is only applicable in the limit of very small changes. Issues of how to correctly write the reduced-suffix forms of the tensors are also considered. Our formalism is then applied to an edge-pumped Yb:YAG slab laser. We consider straight-through propagation as an example of the formalism and indicate its application to the case of zigzag propagation.     

Synthesis,characterization and properties of ferroelectric rubidium hydrogen tartrate single crystals

Rubidium hydrogen tartrate single crystals were grown in silica hydrogel. Controlled reaction was employed between tartaric acid and rubidium chloride solutions by slow diffusion process in the gel medium. Colourless transparent crystals were grown at room temperature. The average density of crystals measured pyknometrically was 2·263 g cm⁻³. Thermal stability of the materials was studied. Chemical etching was employed to determine the perfection of these crystals.     

Influence of grain size variability on the strain rate dependence of the stress exponent in mixed-mode power law and diffusional creep

The relationship between the strain rate and the stress in power law and diffusional creep has usually been derived with the assumption that all the grains have the same size, which predicts a sharp transition from power law creep, with a stress exponent of about four to five, to diffusional creep, where the stress exponent is equal to one. We show that the use of distributed grain size can lead to a transition from power law to diffusional creep that is spread over several orders of magnitude in strain rate. The breadth of this transition depends on the standard deviation of the grain size probability density function. The experimental values for the stress exponent that are apparently greater than one, when measured over two or three orders of magnitude in strain rate, can result from a very gradual change in the stress exponent with the strain rate for a distributed grain size. Data sets from copper are compared to the model.     

An assessment of flow oriented schemes for reducing ‘false diffusion’

An important limiting factor in the accurate modelling of fluid flow problems is the numerical representation of the convection terms in the Navier-Stokes equations. This paper reviews several approaches used to approximate the convection terms and reduce the so-called false-diffusion errors, within the context of finite-difference and finite-volume methods. Numerical errors are characterized as those due to discretization of the differential terms and those due to the influence of the multidimensional nature of the flow. Necessary criteria are identified which a numerical scheme must satisfy, if it is to be a candidate, at least in terms of accuracy and practicality, for the successful solution of the Navier-Stokes equations. One of the criteria is the need of the scheme to account explicitly for the multidimensionality of the flow in the transport of scalar variables. All schemes except Raithby's SKEW approximation are deficient in this respect. However, the SKEW scheme does not satisfy some of the other criteria and does not always perform well. A new scheme called CUPID (Corner UPwInDing), which is based on the ideas of the SKEW scheme, yet obeys more of the criteria identified above, is described. The scheme is tested on a series of discriminating test problems which, the authors contend, demonstrate its potential for practical use in solving accurately the Navier-Stokes equations.     

Small-signal response of 1.3-/spl mu/m InAsP-InGaAsP quantum-well laser diodes obtained with a terahertz-bandwidth frequency comb

We describe an optical method to carry out small-signal frequency response measurements in laser diodes. This method uses a midinfrared tunable femtosecond optical parametric oscillator (OPO), whose frequency spectrum consists of a comb composed by the multiple harmonics of the 81-MHz repetition rate of the same intensity and extending over 2 THz. Tuning of the OPO allows selective generation of carriers in the different regions of the test laser active area without compromising the frequency bandwidth. The small-signal frequency response of the test laser is retrieved from the intensity changes in the frequency comb spectrum. We apply this method to investigate the small-signal frequency response of 1.3-/spl mu/m InAsP quantum-well (QW) lasers. The results of these experiments show that the intrinsic frequency bandwidth of these lasers is limited to less than 10 GHz as a result of state filling and related carrier escape out of the well. An analysis of the frequency response traces through a solution of a system of rate equations allows us to estimate the magnitude of the gain compression associated with this process.