A Constraint Programming Approach to Extract the Maximum Number of Non-Overlapping Test Forms

This paper introduces a novel approach for extracting the maximum number of non-overlapping test forms from a large collection of overlapping test sections assembled from a given item bank. The approach involves solving maximum set packing problems (MSPs). A branch-and-bound MSP algorithm is developed along with techniques adapted from constraint programming to estimate lower and upper bounds on the optimal MSP solution. The algorithm is general and can be applied in other applications including combinatorial auctions. The results of computer simulations and experiments with an operational item bank are presented. An erratum to this article is available at .     

Ambient connections realising conformal Tractor holonomy

For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat ambient metric in the sense of Fefferman and Graham. Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse 9, 1090 Vienna, Austria Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany     

Heteroatom transfer to alkenes by N-protected-oxaziridines: new reaction pathways and products

N-Alkoxycarbonyl- and N-carboxamido-oxaziridines are shown to react with aromatic alkenes to give epoxide, aziridine or hydro-oxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydro-oxidation with promising levels of asymmetric induction.     

Environmental UV‐A and UV‐B Threshold Doses for Apoptosis and Necrosis in Humans Fibroblasts¶

Apoptosis involves a highly organized and programmed series of events aimed at maintaining genomic stability by eliminating defective host cells. The purpose of this study was to determine the threshold doses and environmental UV‐A and UV‐B exposure times necessary to produce apoptosis and necrosis in the normal cells of a human fibroblast cell line. Enviromental UV‐A and UV‐B doses were measured over a 6 year period with a four‐channel UV radiometer. The fibroblasts were irradiated once using an Oriel UV Solar Simulator with six doses of environmentally‐based UV. Doses corresponded to 0,11,19,23 and 45 min of average environmental UV‐A and UV‐B radiation at solar noon in Puerto Rico. The Annexin‐V binding method was used to differentiate between normal fibroblasts and apoptotic or necrotic fibroblasts. The threshold dose from apoptosis to necrosis was found between 24–28 kJ/m², which corresponded to 19 and 23 min of environmental UV‐A and UV‐B exposure. This study provides the first data that specify the environmental threshold doses of UV‐A and UV‐B at which human fibroblasts undergo apoptosis and necrosis. These results may provide valuable dose‐response thresholds for apoptosis and necrosis for future mechanistic studies and baseline data for skin cancer prevention programs.     

Total synthesis of (+)-zaragozic acid C

A total synthesis of (+)-zaragozic acid C is described. Key features of the synthesis are the use of a double Sharpless asymmetric dihydroxylation reaction of diene 6 to control stereochemistry at four contiguous stereocenters from C3 to C6; the introduction of the C1-side chain by reaction between the anion derived from the dithiane monosulfoxide 27 and the core aldehyde 12; a high yielding, acid-mediated simultaneous acetonide deprotection-dithiane removal-ketalization procedure leading exclusively to the 2, 8-dioxabicyclo[3.2.1]octane core 34; and a novel triple oxidation procedure allowing installation of the tricarboxylic acid.