Photochemistry of tetramethyl-4-pyrone in alcohol solvents

Irradiation of tetramethyl-4-pyrone in alcohol solvents leads to the formation of tetramethyl-2-pyrone and to a variety of cyclopent-2-enone and cyclopent-3-enone solvent adducts. The structure and mode of product formation is consistent with photochemical generation of a short-lived 2,6-bridged oxabicyclohexenyl zwitterion which undergoes sigmatropic rearrangement to a longer-lived epoxycyclopentenone. Although the zwitterion is efficiently trapped by methanol solvent, in less nucleophilic alcohol solvents it rearranges to the epoxycyclopentenone which isomerizes to the 2-pyrone or reacts with the alcohol solvent to form the observed solvent adducts.     

Trace quantitation of 4-hydroxy-2-nonenal in biological samples as its oxime-bis-tert.-butyldimethylsilyl derivative using 3-hydroxynonanal as an internal standard.

A gas chromatographic-mass spectrometric method for the determination of the lipid aldehyde 4-hydroxy-2-nonenal (4HNE) in trace quantities is described. The method utilizes the reaction of aldehydes with hydroxylamine leading to the formation of the oxime derivative. The aldehydes are recovered by octadecylsilyl solid-phase extraction and converted to the bis-tert.-butyldimethylsilyl derivatives for analysis using electron ionization. A novel 4HNE analogue, 3-hydroxynonanal, has been synthesized and is used as an internal standard. A limit of detection of approximately 1 pmol of 4 HNE in preparations of approximately 2.10(6) cells or 0.5 ml of whole blood, plasma or serum was observed. Standard addition analysis indicates that the method is accurate at these levels. Replicate analysis of the National Institutes of Standards and Technology Standard Reference Material SRM 909 indicates an average in-run precision of 8.1% and a between-run precision of 13.5% at an average concentration of 82.1 pmol/ml of reconstituted material.     

Use of transmitted color to calibrate the thickness of silicon samples

In preparing silicon-based semiconductors for transmission electron microscopy (TEM), it has been widely observed that a backlit silicon sample displays a series of colors in the thinnest regions. These colors results from absorption and optical interference of light within the silicon sample and depend upon the type of light source and the silicon sample thickness. These colors can range from deep red for thickness ≥5 μm, through orange and yellow in the thinner regions, to essentially colorless at the thinnest regions. In this work we present the first direct measurement of silicon color versus thickness and discuss the factors that influence this relationship.     

LowpT phenomena in A+A and p+A collisions at mid-rapidity

CERN experiment NA44 measures pion and kaon distributions atpT=0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at lowpT relative to p+Be, but less than observed at target rapidity. The lowpT behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.     

An antimicrobial sesterterpene from a Palauan sponge

An unidentified sponge from Palau contained the antimicrobial sesterpene $\text{1}$ that was identified by interpretation of spectral data and conversion into a degradation product of illimaquinone.     

Duct effects on the heave stability of plenum air cushions

Linear heave stability boundaries for a fun-duct-plenum air cushion suspension system are presented. These were obtained by using a quasi-static pressure-flow relationship for the fan, a finite element discretization for one dimensional unsteady duct flow, and a lumped capacitance model for the plenum. They indicate that even relatively short ducts can have a major effect at practical flow rates on the stability of cushion systems typically used for amphibious and overland operations. Some results obtained from a non-linear analysis, in which the method of characteristics was used for the duct flow, suggest that the linear approach should be adequate for practical stability calculations. Comparisons with lumped parameter models indicate that here the duct effect is associated primarily with the inertance of the air in the duct. It is also shown that for some operating conditions the duct-plenum system behaves as an Helmholtz resonator. Good agreement is obtained with an earlier transmission line analysis based on the wave equation.