A high number of Internet shops makes it difficult for a customer to review manually all the available offers and select optimal outlets for shopping. A partial solution to the problem is brought by price comparators which produce price rankings from collected offers. However, their possibilities are limited to a comparison of offers for a single product requested by the customer. The issue we investigate in this paper is a multiple-item multiple-shop optimization problem, in which total expenses of a customer to buy a given set of items should be minimized over all available offers. In this paper, the Internet Shopping Optimization Problem (ISOP) is defined in a formal way and a proof of its strong NP-hardness is provided. We also describe polynomial time algorithms for special cases of the problem.

White and natural base oils are assessed as candidates for the formulation of ecological gear oils. They are compared to ‘classical’ mineral and polyalphaolefins‐based oils in scuffing four‐ball and gear tests. Four fully formulated gear oils were prepared by blending each base oil with the package of extreme pressure (EP) additives, an anti‐foam additive and an anti‐oxidant. It is shown that the resistance to scuffing of the white oil is comparable to the classical oils, but the natural (rapeseed) oil reduces resistance to scuffing, because the used EP additives may not be suited to the rapeseed ‘matrix’ producing adverse effects. Thus, rapeseed‐based gear oils can be used only for the lubrication of gears working under moderate load conditions. It is also indicated that, when comparing the mechanisms of tribochemical action of the EP additives in the four‐ball tribosystem and meshing teeth, care should be taken, because the conditions in the contact zones are different. Copyright © 2014 John Wiley & Sons, Ltd.

A surface gradient coil designed to obtain localized magnetic resonance spectroscopy of the heart in vivo is described. Images and 31P spectra from phantoms and both pig and dog hearts in vivo are shown. The coil was used in conjunction with a rf surface coil to obtain 31P spectra from transmural sections of the left ventricular wall of a dog heart in vivo to demonstrate differences between normal and ischemic tissue.

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