Iterated nearest neighbors and finding minimal polytopes

We introduce a new method for finding several types of optimalk-point sets, minimizing perimeter, diameter, circumradius, and related measures, by testing sets of theO(k) nearest neighbors to each point. We argue that this is better in a number of ways than previous algorithms, which were based on high-order Voronoi diagrams. Our technique allows us for the first time to maintain minimal sets efficiently as new points are inserted, to generalize our algorithms to higher dimensions, to find minimal convexk-vertex polygons and polytopes, and to improve many previous results. We achieve many of our results via a new algorithm for finding rectilinear nearest neighbors in the plane in timeO(n logn+kn). We also demonstrate a related technique for finding minimum areak-point sets in the plane, based on testing sets of nearest vertical neighbors to each line segment determined by a pair of points. A generalization of this technique also allows us to find minimum volume and boundary measure sets in arbitrary dimensions. Portions of this paper were presented at the 3rd and 4th ACM-SIAM Symposia on Discrete Algorithms [17], [19]. This paper includes work done while Jeff Erickson was at the University of California at Irvine. David Eppstein's research was partially supported by NSF Grant CCR-9258335.     

DNA microarray technology used for studying foodborne pathogens and microbial habitats: minireview

Microarray analysis is an emerging technology that has the potential to become a leading trend in bacterial identification in food and feed improvement. The technology uses fluorescent-labeled probes amplified from bacterial samples that are then hybridized to thousands of DNA sequences immobilized on chemically modified glass slides. The whole gene or open reading frame(s) is represented by a polymerase chain reaction fragment of double-strand DNA, approximately 1000 base pair (bp) or 20-70 bp single-strand oligonucleotides. The technology can be used to identity bacteria and to study gene expression in complex microbial populations, such as those found in food and gastrointestinal tracts. Data generated by microarray analysis can be potentially used to improve the safety of our food supply as well as ensure the efficiency of animal feed conversion to human food, e.g., in meat and milk production by ruminants. This minireview addresses the use of microarray technology in bacterial identification and gene expression in different microbial systems and in habitats containing mixed populations of bacteria.     

Use of statistical design of experiments in the optimization of amide synthesis utilizing polystyrene-supported N-hydroxybenzotriazole resin

Two fields that routinely perform reaction optimization studies are chemical development (prior to scale-up) and medicinal or combinatorial chemistry (prior to analogue synthesis or library production). To date, the use of statistical design of experiments (DoE) in conjunction with automated synthesizers has been applied in process research to a greater extent than in the medicinal or combinatorial laboratories. We have applied DoE in conjunction with an automated synthesizer to optimize the synthesis of amides employing resin-bound N-hydroxybenzotriazole (PS-HOBt) active esters as intermediates. This methodology allowed the rapid development of an improved protocol for the parallel synthesis of amides by conversion of carboxylic acids to PS-HOBt esters followed by treatment with appropriate amines. Product isolation involved only simple filtration and evaporation.     

Acid-catalyzed oxygen-transfer reactions of ortho-alkenyldimethylbenzylamine oxides

Several ortho-alkenyldimethylbenzylamine oxides were found to rearrange in strong acid media to mixtures of aminophthalans and conjugated aminoketones     

Bach-flat asymptotically locally Euclidean metrics

We obtain a volume growth and curvature decay result for various classes of complete, noncompact Riemannian metrics in dimension 4; in particular our method applies to anti-self-dual or Kähler metrics with zero scalar curvature, and metrics with harmonic curvature. Similar results were obtained for Einstein metrics in [And89], [BKN89], [Tia90], but our analysis differs from the Einstein case in that (1) we consider more generally a fourth order system in the metric, and (2) we do not assume any pointwise Ricci curvature bound.     

Formation of nanooctahedra in molybdenum disulfide and molybdenum diselenide using pulsed laser vaporization

Pulsed laser vaporization has been used to produce nanooctahedra of MoS2 and MoSe2. The nanooctahedra primarily form in two- or three-layer nested octahedra, although nesting up to five layers has been observed. Tilting the TEM sample stage and mapping how the images of single particles transformed provided the evidence to verify their octahedral geometry. Analysis of 30 two- and three-layered octahedra showed that their outer edge lengths clustered at approximately 3.8 nm and approximately 5.1 nm, respectively. This discreet sizing and the high symmetry of these closed nanooctahedra represent the closest inorganic analogy yet to the carbon fullerenes. The geometrical implications for forming octahedra from these layered compounds are investigated by considering different atomic arrangements assuming either trigonal prismatic or octahedral coordination around the Mo atom and yields two possible configurations for the actual structure of the nanooctahedra. A preliminary survey of pulsed laser vaporization of other layered metal chalcogenides shows that these dichalcogenides differ in their tendency to form small closed layered fullerene-like structures. These materials can be ranked from highest tendency to lowest as follows: NbSe2, WS2, WSe2, SnS2, TaS2, GaS, ReS2, and MoTe2.     

A study of ion suppression effects in electrospray ionization from mobile phase additives and solid-phase extracts

Since the wide adoption of liquid chromatography/tandem mass spectrometry (LC/MS/MS), the ion suppression/enhancement phenomenon is the latest barrier to high-throughput analysis. This consequence of a nonoptimized analytical method can lead to adverse effects during quantitation (i.e. poor accuracy and precision). Previous papers have reported that ion suppression is a direct result of endogenous material present in biological samples. However, in the case of a solid-phase liquid chromatography/tandem mass spectrometry (SPE/LC/MS/MS) system, the measured result is the combination of several operating conditions and parameters. Little has been done to effectively monitor and/or choose optimized conditions for the complete sequence of extraction, clean up, separation and analysis. This paper describes a simple setup for quantification of ion suppression/enhancement. Several mobile phase additives, ion-pairing agents and SPE extracts were measured and compared against a standard reference. The results demonstrated that a clean up of plasma extracts based on ion exchange leads to minimal ion suppression/enhancement for the compounds that were investigated.     

C1 Coupling via bromine activation and tandem catalytic condensation and neutralization over CaO/zeolite composites

We demonstrate here an alternative scheme for C(1) coupling by way of methane bromination, followed by concurrent bromomethane condensation and quantitative HBr neutralization; regeneration of the metal oxide with O(2) with recovery of Br(2) completes the cycle.     

Observation of parity nonconservation in møller scattering

We report a measurement of the parity-violating asymmetry in fixed target electron-electron (M?ller) scattering: A(PV)=[-175+/-30(stat)+/-20(syst)] x 10(-9). This first direct observation of parity nonconservation in M?ller scattering leads to a measurement of the electron's weak charge at low energy Q(e)(W)=-0.053+/-0.011. This is consistent with the standard model expectation at the current level of precision: sin((2)theta(W)(M(Z))((-)MS)=0.2293+/-0.0024(stat)+/-0.0016(syst)+/-0.0006(theory).