The location of silver in frog epidermis after treatment by ranvier's method,and possible implication of the flask cells in transport

Summary Frog skin, bladder wall, and sciatic nerve were treated by Ranvier's silver nitrate method and subsequently fixed and sectioned for electron microscopy. In the epidermis of the skin, more silver is found deposited in the flask cells than elsewhere, especially as a sub-apical plaque in the neck of the flask, which appears after the skin has been flooded with silver nitrate for 5 minutes. Mitochondria rich cells in the bladder also accumulate more silver than the surrounding epithelial cells, but do not show such a distinct sub-apical plaque. In myelinated nerve fibres treated similarly, silver accumulates in the paranodal regions of the axon, and outside the axon at the node. It is suggested that silver may accumulate near a site of ion transport, due to structural specialisations not visible by standard electron microscope techniques, and that the flask cells may therefore be implicated in transport in the frog skin.     

Gel-phase P-NMR. A new analytical tool to evaluate solid phase oligonucleoside synthesis.

This paper shows Gel-phase ³¹P-NMR spectra of synthetic intermediates obtained during solid-phase oligonucleotide synthesis on polystyrene for the first time. We have demonstrated the application of this technique using the phosphotriester, H-phosphonate and phosphite triester approaches. The use of Gel-phase ³¹P-NMR for monitoring solid phase oligonucleotide synthesis is discussed.     

Conformational Isomers of Denatured and Unfolded Proteins: Methods of Production and Applications

Conformational isomers of denatured-unfolded proteins are rich in numbers and varied in shapes. They represent an opulent resource of biological molecules that have remained unexploited. The major obstacle in utilizing this untapped potential is that it is inherently difficult to isolate and characterize pure conformational isomers, not only because of the excessive large number, but also because of their instability and rapid inter-conversion. Our lab has developed a method for trapping selected conformational isomers of denatured proteins that are amenable to isolation, characterization and further applications. The method has potential usefulness, ranging from the comprehensive structural characterization of denatured proteins, to the elucidation of pathways of protein unfolding–folding, to the production of unlimited structurally defined non-native protein isomers for biomedical applications.     

Hierarchical Classification I: Single-Linkage Method

This is the first part of a survey of hierarchical clustering algorithms using joining methods: the Single-Linkage algorithm. Complete-Linkage and general algorithms defined by d(A_i, B) = = α,d(A_i, A_r)±α_sd(A_i, A_s)±βd(A_r, A_s) will be discussed in two subsequent papers.     

A Variation of the Method of Translation to Generate Bivariate and Multivariate Survival Distributions with Competing Risk or Reliability Applications

In the present paper, a variation of the methode of translation is discussed to generate bivariate or multivariate survival distributions starting a given bivariate or multivariate distribution which is not necessarily a life distribution. The new distribution has been called the dual of the given distribution. The duals of several bivariate and multivariate famílies of distributions are obtained, such as FRECHET'S , FARLIE -GUMBEL -MORGENSTERN'S , MARDIA'S and PLACKETT'S , among others. A necessary and sufficient condition is given for a bivariate distribution to be its own dual. Thus the present paper generates several survival distributions in addition to what are already available in the literature. These have important applications in competing risk theory or reliability of engineering systems.     

Estimation of Distances and Variances in Bookstein's Landmark Model

Planar random figures can be described by series of landmarks. Bookstein's model assumes that the landmarks result from independent individual fluctuations around fixed fictive landmark centres. The aim of this paper is to estimate the distances between the centers and the variances of fluctuations around them. Furthermore, two new shape variable estimators are suggested and compared with an estimator of Bookstein.     

A note on key factor analysis

Various aspects of a model for key factor analysis (Manly , 1977a) are discussed. Equations for estimating the parameters of the model are given. The jackknife method is suggested for obtaining standard errors for estimators. The case of circular populations (where the adults in one generation produce all the individuals alive at the start of the next, generation) is considered. A computer program is described. Varley et al.'s (1973) data on the winter moth is used for illustrative purposes.     

Determination of melatonin in Acyrthosiphon pisum aphids by liquid chromatography–tandem mass spectrometry

Melatonin is a hormone mainly involved in the regulation of circadian and seasonal rhythms in both invertebrates and vertebrates. Despite the identification of melatonin in many insects, its involvement in the insect seasonal response remains unclear. A liquid chromatography tandem mass spectrometry (LC–MS/MS) method has been developed for melatonin analysis in aphids (Acyrthosiphon pisum) for the first time. After comparing two different procedures and five extraction solvents, a sample preparation procedure with a mixture of methanol/water (50:50) was selected for melatonin extraction. The method was validated by analyzing melatonin recovery at three spiked concentrations (5, 50 and 100 pg/mg) and showed satisfactory recoveries (75–110%), and good repeatability, expressed as relative standard deviation (<10%). Limits of detection (LOD) and quantitation (LOQ) were 1 pg/mg and 5 pg/mg, respectively. Eight concentration levels were used for constructing the calibration curves which showed good linearity between LOQ and 200 times LOQ. The validated method was successfully applied to 26 aphid samples demonstrating its usefulness for melatonin determination in insects. This is -to our knowledge- the first identification of melatonin in aphids by LC–MS/MS.