Catalysis of Organic Reactions. Part I: Enhancement of a Solid State Reaction by Proper Orientation within a Crystal. Part II. Micellar Effects on the Stereochemistry and Rate of Aqueous Solvolysis Reactions

Part I. The solid state rearrangement of methyl-p-dimethylaminobenzenesulfonate to the trimethylammoniumbenzenesulfonate zwitterion was studied by a combination of spectroscopic techniques. NMR, Field Desorption Mass Spectrometry, and X-Ray Crystallography were employed to determine the mechanism of this reaction. It was shown to be an intermolecular nucleophilic displacement whose rate is greatly enhanced by the crystallinity of the starting material. Part II. A study of the effects of micelles on the aqueous solvolysis of alkyl-p-trimethylammoniumbenzenesulfonates revealed that anionic micelles could change the rate and stereochemistry of the solvolysis reaction. The mechanism for the observed rate retardation and induced decrease in stereochemical integrity was probed and a unified mechanistic hypothesis is presented.</p

The synthesis, characterization and thermal chemistry of modified norbornenyl PMR endcaps

As part of a program to further the understanding of the polymerization of Nadic-Endcapped PMR systems, a series of model Norbornenyl-Imides has been synthesized and their thermal behavior explored. Their syntheses and characterizations as well as their rearrangement and polymerization chemistry are described. Monomer isomerization at temperatures as low as 125 C and oligomer formation at somewhat higher temperatures are observed. Approximate relative rates for competing isomerization pathways are established and some information is obtained about the details of oligomer formation. The relationship of this data to current PMR systems is briefly discussed

Focusing Vacuum Fluctuations II

The quantization of the scalar and electromagnetic fields in the presence of a parabolic mirror is further developed in the context of a geometric optics approximation. We extend results in a previous paper to more general geometries, and also correct an error in one section of that paper. We calculate the mean squared scalar and electric fields near the focal line of a parabolic cylindrical mirror. These quantities are found to grow as inverse powers of the distance from the focus. We give a combination of analytic and numerical results for the mean squared fields. In particular, we find that the mean squared electric field can be either negative or positive, depending upon the choice of parameters. The case of a negative mean squared electric field corresponds to a repulsive Van der Waals force on an atom near the focus, and to a region of negative energy density. Similarly, a positive value corresponds to an attractive force and a possibility of atom trapping in the vicinity of the focus.Comment: 26 pages, 15 figures; additional discussion added in Sects. IV and I

The Central Timna Valley Project: 5 Years of Ongoing Textile Research

In its initial five years of activity the Central Timna Valley Project has dedicated its efforts to the excavation of several Late Bronze and Iron Age sites (13th-9th centuries BC) in the southern Arabah Valley of Israel (fig. 1).1 The project, headed by Erez Ben-Yosef of Tel Aviv University, explores the ancient exploitation of copper ores at Timna; these were utilised for the production of copper ingots that were traded throughout the southern Levant and possibly the greater Mediterranean region. It is within the strata of several newly excavated sites that a few hundred individual textile, cordage and rope fragments were uncovered

Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

The spin-spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates

Spectral Dependence of Coherent Backscattering of Light in a Narrow-Resonance Atomic System

We report a combined theoretical and experimental study of the spectral and polarization dependence of near resonant radiation coherently backscattered from an ultracold gas of 85Rb atoms. Measurements in an approximately 6 MHz range about the 5s^{2}S_{1/2}- 5p^{2}P_{3/2}, F=3 - F'=4 hyperfine transition are compared with simulations based on a realistic model of the experimental atomic density distribution. In the simulations, the influence of heating of the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth, and other nonresonant hyperfine transitions are considered. Good agreement is found between the simulations and measurements.Comment: 10 pages, 12 figur

The Languages Spoken in the Water Body (or the Biological Role of Cyanobacterial Toxins)

Although intensification of toxic cyanobacterial blooms over the last decade is a matter of growing concern due to bloom impact on water quality, the biological role of most of the toxins produced is not known. In this critical review we focus primarily on the biological role of two toxins, microcystins and cylindrospermopsin, in inter- and intra-species communication and in nutrient acquisition. We examine the experimental evidence supporting some of the dogmas in the field and raise several open questions to be dealt with in future research. We do not discuss the health and environmental implications of toxin presence in the water body

Focusing Vacuum Fluctuations

The focusing of the vacuum modes of a quantized field by a parabolic mirror is investigated. We use a geometric optics approximation to calculate the energy density and mean squared field averages for scalar and electromagnetic fields near the focus. We find that these quantities grow as an inverse power of the distance to the focus. There is an attractive Casimir-Polder force on an atom which will draw it into the focus. Some estimates of the magnitude of the effects of this focusing indicate that it may be observable.Comment: 20 pages, 4 figures; typos corrected, two refs and some comments adde

Matter-field theory of the Casimir force

A matter-field theory of the Casimir force is formulated in which the electromagnetic field and collective modes of dielectric media are treated on an equal footing. In our theory, the Casimir force is attributed to zero-point energies of the combined matter-field modes. We analyze why some of the existing theories favor the interpretation of the Casimir force as originating from zero-point energies of the electromagnetic field and others from those of the matter.Comment: 12pages, 1 Postscript figur