Effect of Reynolds number and flow division on patterns of haemodynamic wall shear stress near branch points in the descending thoracic aorta

Atherosclerotic lesions are non-uniformly distributed at arterial bends and branch sites, suggesting an important role for haemodynamic factors, particularly wall shear stress (WSS), in their development. The pattern of lesions at aortic branch sites depends on age and species. Using computational flow simulations in an idealized model of an intercostal artery emerging perpendicularly from the thoracic aorta, we studied the effects of Reynolds number and flow division under steady conditions. Patterns of flow and WSS were strikingly dependent on these haemodynamic parameters. With increasing Reynolds number, WSS, normalized by the fully developed aortic value, was lowered at the sides of the ostium and increased upstream and downstream of it. Increasing flow into the side branch exacerbated these patterns and gave rise to a reversing flow region downstream of the ostium. Incorporation of more realistic geometric features had only minor effects and patterns of mean WSS under pulsatile conditions were similar to the steady flow results. Aspects of the observed WSS patterns correlate with, and may explain, some but not all of the lesion patterns in human, rabbit and mouse aortas.     

Toward shielding improvements in MRI gradients and other systems

A new method is described for reducing the shielding-error function in the ‘supershielding’ approach to designing MRI systems. The method is thus shown to lead to significantly better shielding and better control of eddy current effects associated with gradient coils. To illustrate this technique, a set of results for a z-gradient coil is presented. A generalization to non-standard geometries can be made in a straightforward manner with the new method. The usefulness of the relationship of all fringe-field quantities to the shielding-error function is emphasized. The formal limit of perfect shielding in a least-squares’ sense is shown for a simple strip-shield model along with a numerical eigenvalue study for comparison with the theoretical limit.     

Voluntary wheel running: a review and novel interpretation

One of the most difficult tasks for the practicing urologist is to counsel the patient in a decision for the optimal treatment for his localized prostate cancer. After providing the patient with contemporary and unbiased information and data, it is important to find the preferred treatment based on his age, the medical realities and, last but not least, the patient's personal preference. Radical prostatectomy, radiotherapy and observation are standard treatment options. TRUS-guided brachytherapy and cryosurgery are considered investigational treatment options since follow-up is inadequate to provide sufficiently precise outcome estimates. The literature does not provide clear-cut evidence for the superiority of any one treatment. The patient most likely to benefit from radical prostatectomy would have a relatively long life expectancy, no significant surgical risk factors and a preference to undergo surgery. The major advantage of radical prostatectomy is its potential for total removal of the cancer and cure in properly selected patients. Potential harm includes urinary incontinence and impotence. The patient most likely to benefit from radiation therapy would have a relatively long life expectancy, no significant risk factors for radiation toxicity and a preference for radiotherapy. The advantages of radiotherapy are that it has a potential for cure and it is well tolerated in the majority of men when the modern techniques are used. Potential harm includes radiation cystitis, proctitis and impotence, persisting severe complications are only seen in 1% of patients. The patient most likely to benefit from surveillance are those with a shorter life expectancy and/or a low grade tumour. Benefits are lack of treatment related morbidity with only marginal compromise of disease-specific survival at 5-10 years follow-up.     

Methods for stability and antioxidant measurement

A great variety of books and technical papers has been published dealing in detail with the basic chemistry of rancidity in fats and oils and the techniques which have been investigated as a means of determining the stability characteristics of fats and oils as well as the effectiveness of various agents, such as antioxidants, in improving those stability characteristics. This review of methods for stability and antioxidant measurement is intended to serve as a relatively brief outline of that particular area of fat and oil technology. Presented at the AOCS Short Course, “Processing Quality Control of Fats and Oils,” East Lansing, Mich., Aug. 29—Sept. 1, 1966.     

Tertiary butylhydroquinone as antioxidant for crude sunflower seed oil

This study indicates that crude sunflower seed oil is very susceptible to oxidation; thus prolonged storage should be avoided. Protection of the crude oil with a potent antioxidant such as tertiary butylhydroquinone (TBHQ) would seem both practical and beneficial. Discoloration which develops in the crude oil with or without TBHQ can be removed by proper selection of bleaching materials. Additional benefits to be derived from using TBHQ should be investigated by using test methods designed to study subtle flavor qualities of deodorized oils. Presented at the AOCS Meeting, Houston, May 1971.     

Antioxidants for food fats and oils

Types of antioxidants currently available for food fats and oils are listed, and theoretical and practical aspects of selecting the proper ones for various food uses are reviewed. Consideration is given to relative potencies, modes of application, regulations governing use, and some of the more prominent problems encountered in their commercial applications. A brief look is taken into future needs and possible developments with fat and oil antioxidants. One of seven papers presented in the symposium “Fats and Oils in Food Industry,” AOCS Meeting, Atlantic City, October 1971.     

Improved techniques for testing fats and oils by the oxygen bomb method

Summary The use of a dispersing agent to expand the surface area, thus providing an increase in reactivity of fats and oils under the conditions of the test, has been investigated. This dispersion technique permits the testing of a wider range of products, decreases the test time, and results in sharper end-points. These improvements should serve to increase the applicability of the Oxygen Bomb Method as a tool for oxidation studies and quality control in the food industry. A general comparison of the Oxygen Bomb Method with the AOM and Schaal Oven Method has been presented to illustrate the relationship between results obtained by these various methods. The dispersion technique has been combined with previously established bomb techniques, and procedures for testing a wide variety of fats, oils and food products by the Oxygen Bomb Method are suggested.     

On 2D elliptic discontinuous Galerkin methods

We discuss the discretization using discontinuous Galerkin (DG) formulation of an elliptic Poisson problem. Two commonly used DG schemes are investigated: the original average flux proposed by Bassi and Rebay (J. Comput. Phys. 1997; 131 :267) and the local discontinuous Galerkin (LDG) (SIAM J. Numer. Anal. 1998; 35 :2440–2463) scheme. In this paper we expand on previous expositions (Discontinuous Galerkin Methods: Theory, Computation and Applications. Springer: Berlin, 2000; 135–146; SIAM J. Sci. Comput. 2002; 24 (2):524–547; Int. J. Numer. Meth. Engng. 2003; 58 (2): 1119–1148) by adopting a matrix based notation with a view to highlighting the steps required in a numerical implementation of the DG method. Through consideration of standard C⁰‐type expansion bases, as opposed to elementally orthogonal expansions, with the matrix formulation we are able to apply static condensation techniques to improve efficiency of the direct solver when high order expansions are adopted. The use of C⁰‐type expansions also permits the direct enforcement of Dirichlet boundary conditions through a ‘lifting’ approach where the LDG flux does not require further stabilization. In our construction we also adopt a formulation of the continuous DG fluxes that permits a more general interpretation of their numerical implementation. In particular it allows us to determine the conditions under which the LDG method provides a near local stencil. Finally a study of the conditioning and the size of the null space of the matrix systems resulting from the DG discretization of the elliptic problem is undertaken. Copyright © 2005 John Wiley & Sons, Ltd.     

Theoretical and experimental studies of the effects of compressiveand tensile strain on the performance of InP-InGaAs multiquantum-welllasers

The authors have studied, both theoretically and experimentally, the effects of biaxial strain upon the performance characteristics of broad-area InP-InGaAsP-In_xGa_1-xAs (0.33⩽x ⩽0.73) separate confinement heterostructure multiquantum-well lasers. The theoretical calculations include the effects of strain on the bandstructure and the Auger recombination rates. A pronounced dependence of the threshold current density J_th upon x is observed. The lowest measured J_th is 589 A/cm² in an 800-μm laser with x=0.68. Also, internal quantum efficiencies as high as unity and loss coefficients as low as 5.6 cm^-1 have been measured for x=0.58