introduction lead-based shields are the most widely used attenuators in x-ray and gamma ray fields. the heavy weight, toxicity and corrosion of lead have led researchers towards the development of non-lead shields. materials and methods the purpose of this study was to design multi-layered shields for protection against x-rays and gamma rays in diagnostic radiology and nuclear medicine. in this...

1. Freehouse International Ltd., Gibraltar 2. StopTB, World Health Organization, Geneva, Switzerland 3. Department of Health, KwaZulu-Natal, Pietermaritzburg, South Africa 4. South African Centre for Epidemiological Modelling and Analysis, Stellenbosch, South Africa 5. Medical Research Council, Durban, South Africa 6. Academic Complex Business Unit, Inkosi Albert Luthuli Central Hospital, Natio...

• WILLARD P. GINGERICH, Ph.D., Provost and Vice President for Academic Affairs • KENNETH SUMNER, Ph.D., Acting Associate Provost for Academic Affairs • JOANNE COTE-BONANNO, Ph.D., Associate Provost for Academic Programs and Assessment • JAMES GERMAN, Ph.D., Associate Provost for Undergraduate Education • NICOLA SULLIVAN, M.B.A., Director of Administration • MARY COLON, M.A., Director, Academic ...

A series of crown ethers, 12-crown-4, 15-crown-5, 18-crown-6, and dibenzo-30-crown-10, are examined as a possible means of shifting the mobilities of peptide ions. In this approach, a crown ether is added to a solution containing a mixture of peptides and is electrosprayed into the gas phase in order to create distributions of peptide-crown complexes. The ion complexes have different mobilities...

We give a new combinatorial deenition of a sort of weak !-category originally devised by J. Baez and J. Dolan in nite dimensional cases. Our deenition is a mixture of both inductive and coinductive deenitions, and suitable for`computational category theory.'

The spatial organization of genes and chromosomes plays an important role in the regulation of several DNA processes. However, the principles and forces underlying this nonrandom organization are mostly unknown. Despite its small dimension, and thanks to new imaging and biochemical techniques, studies of the budding yeast nucleus have led to significant insights into chromosome arrangement and ...

Proteins that bind DNA so as to reduce its end-to-end length can be dissociated by application of force. The thermodynamics of this process are discussed, with special attention to the case of histones bound to DNA (i.e., a string of nucleosomes, or chromatin fiber). The histone octamer is predicted to be driven off chromatin fiber for tensions >2 piconewtons.