Globally anisotropic high porosity silica aerogels

We discuss two methods by which high porosity silica aerogels can be engineered to exhibit global anisotropy. First, anisotropy can be introduced with axial strain (i.e. axial compression). In addition, intrinsic anisotropy can result during growth and drying stages and, suitably controlled, it can be correlated with preferential radial shrinkage in cylindrical samples. We have performed small angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We show that global anisotropy originating from either strain or shrinkage leads to optical birefringence and that optical cross-polarization studies are a useful characterization of the uniformity of the imposed global anisotropy.     

Sensitive solid-phase chemiluminescence microassay of thiols

A polysaccharide matrix binding a chemiluminescent thiol by a dithiol linkage is used to exchange with a thiol in the sample, and the chemiluminescence of the displaced thiol is measured. The detection limit is 5 picomole.     

Taxation,incentives, and risk sharing

The tendency for taxation to weaken incentives and induce inefficient behavior on the part of entrepreneurs is demonstrated with a simple example. Next the Mossin model is extended from a proportional to a progressive tax structure that closely approximates the one in place in the U.S.A. It is shown that increased progressivity causes the amount of wealth invested in the risky asset to decline rather than increase as is true with proportional taxes.     

Accrual capital gains taxation and the lock-in effect

The recent literature on capital gains taxation suggests that assets are sold sooner when taxes are assessed and paid continuously rather than at the time of sale. Our analysis tends to support this view, for this suggestion is valid if the asset value function is convex or if it is concave and there is full or partial-loss-offset.     

A differential scanning calorimetric study of phase transitions in polysubstitutedn-alkylammonium halides

A DSC investigation of severaln-alkylammonium salts is reported. The results of this investigation can be used to help decide which of several crystalline forms should be studied by X-ray diffraction for the best correlation between the liquid and solid states.

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Zusammenfassung Es wird über eine DSC-Untersuchung verschiedenern-Alkylammoniumsalze berichtet. Die Ergebnisse dieser Untersuchung können zur Entscheidung beitragen, welche von mehreren Kristallformen durch Röntgendiffraktion untersucht werden sollten um die beste Korrelation zwischen den flüssigen und festen Zuständen zu erzielen.

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Résumé On communique les résultats d'une étude par analyse calorimétrique différentielle (DSC) de divers sels den-alkylammonium. Les résultats de cette étude donnent des indications pour le choix des formes cristallines qui nécessitent d'être étudiées par diffraction des rayons X afin d'obtenir la meilleure corrélation entre les états liquides et solides.

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Visiting Professor of Chemistry, 1973–1974, Hebrew University, Jerusalem, Israel.

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This investigation was partially supported by the National Science Foundation. The hospitality of the Department of Inorganic and Analytical Chemistry of the Hebrew University is gratefully acknowledged. The authors thank Prof. I. Mayer and A. S. Kertes of the Hebrew University for suggesting this problem and for kindly furnishing samples of then-alkylammonium halides.