Approaching a persistent favorskii zwitterion

2-Phenalanone has been synthesized via a double Curtius procedure and converted to the conjugate acid of 2-phenalenylium oxide, a potential persistent Favorskii zwitterion.     

Rapid determination of lead in biological tissues by microsampling-cup atomic absorption spectrometry

Lead can be determined in kidney, liver, and lung tissues by a rapid technique which does not require ashing or acid digestion of the sample. The tissue is homogenized with water, an aliquot of the homogenate is pipetted into a microsampling cup, and lead is determined directly by atomic absorption spectrometry. Calibration is by lead standards in a whole blood matrix. Results correlate well with those obtained by a wet-ashing procedure. The sensitivity (0.01 μg Pb g^-1 wet tissue) permits the analysis of typical tissues with good precision. The procedure is rapid, and its simplicity minimizes the risk of contamination by extraneous lead during sample preparation.     

25Mg (α, n)28Si and 26Mg(α, n)29Si as neutron sources in explosive neon burning

The yields of neutrons from the reaction ²⁵Mg(α, n)²⁸Si and of γ-rays from the reaction ²⁵Mg(α, nγ)²⁸Si have been measured as a function of bombarding energy over the range 1.8–6.3 MeV, and the yield of neutrons from ²⁶Mg(α, n)²⁹Si has been measured over the range 1.8–6.0 MeV. Cross sections for ^{25, 26}Mg(α, n)^{28, 29}Si were extracted from the data and compared with global statistical-model calculations. The agreement is very good. Thermonuclear reaction rates under stellar conditions appropriate for explosive neon burning are calculated and their significance for the nucleosynthesis of rare neutron-rich nuclei is discussed.     

Range of the screened coulomb interaction in electrolytes and double layer problems

It is shown that the range of the Coulomb interaction in unsymmetric electrolytes at large distances is determined not by the Debye screening length, but by a rather more complicated function of the density, which is evaluated explicitly.     

The orientation parameter for energy transfer in restricted geometries including block copolymer interfaces: a Monte Carlo study

We describe Monte Carlo simulations of resonance energy transfer (RET) experiments for immobile donor (D) and acceptor (A) dyes confined to planar, cylindrical, and spherical restricted geometries. We compare values of the quantum efficiency (PhiET) evaluated through consideration of individual donor-acceptor pairs, with values calculated assuming a pre-averaged value of the orientation parameter /kappa/2 = 0.476 appropriate for infinite three dimensional (3D) space. For dyes confined to restricted geometries where the length scale of the confining dimension is less than or equal to the F?rster radius R0, the coupling of the orientation parameter and the donor-acceptor distance becomes noticeable. Values of Phi(ET) obtained by proper consideration of the orientation parameter are smaller than those calculated using /kappa/2 = 0.476. We use this Monte Carlo method to reanalyze the fluoresce decay measured from dye-labeled poly(isoprene-b-methyl methacrylate) diblock copolymer with lamellar structure,(1) from which the interface thickness for PI-PMMA lamella can be retrieved. We found the retrieved interface thickness is sensitive to the choice of dipole orientation. If all dipoles in the confined polymer interface have a random orientation, the value of interface thickness was found to be 0.9 +/- 0.2 nm through consideration of individual dipole orientations. Assumption of /kappa/2 = 0.476 in the FRET calculations leads to a larger value of interface thickness (1.3 +/- 0.2 nm) due to the neglect of the coupling between dipole orientation and D-A distance for the dyes confined to lamellar interfaces.