Bright-Field Microscopy of Transparent Objects: A Ray Tracing Approach.

The formation of a bright-field microscopic image of a transparent phase object is described in terms of elementary geometrical optics. Our approach is based on the premise that the image replicates the intensity distribution (real or virtual) at the front focal plane of the objective. The task is therefore reduced to finding the change in intensity at the focal plane caused by the object.

Multinuclear nuclear magnetic resonance spectroscopic and high-performance liquid chromatographic characterization of silica, grafted with specifically deuterated 4-((propylamino)methyl)benzoic acid.

Specifically deuterated 4-((propylamino)methyl)benzoic acid-grafted silica (PAMBA-silica) was prepared by benzylation of propylamino-grafted silica (PA-silica) by either in situ reduction by sodium cyanoborodeuteride (NaCNBD3) of the Schiff base, formed by the reaction between PA-silica and 4-formylbenzoic acid, or by NaCNBD3 reduction of the isolated Schiff base. The PAMBA-silicas, which contain amine and carboxylic acid functionalities, were characterized by elemental analysis, (13)C, (29)Si, and (2)H solid state NMR, and HPLC. Solid state (13)C NMR revealed that PAMBA-silica prepared by the in situ method consists of di-benzylated, mono-benzylated, and unreacted amino-groups while PAMBA-silica prepared by the two-step synthesis consists of only mono-benzylated and unreacted amino-groups.

Uniform saturation of a strongly coupled spin system by two-frequency irradiation.

The theoretical basis of two-frequency saturation is given here in the framework of Provotorov theory. The parameters influencing the saturation efficiency are discussed and studied experimentally using a liquid-crystalline test system. It is shown that double-frequency irradiation can be extremely efficient when the irradiation frequencies are placed at opposite sides of the characteristic frequency of the spin system, and that the frequency separation in the double-frequency irradiation can be varied over a large range.

Stability and ring-shift tautomerization of cyclic anhydrides of benzenehexasulfonic acid.

Upon heating in a dry atmosphere, benzenehexasulfonic acid forms three cyclic anhydrides. Mono- and dianhydride do not hydrolyze readily due their flatter structures compared to the hydrolysis products. The trianhydride appears more to be reactive toward hydrolysis.

Magnetic resonance imaging of objects with dipolar-broadened spectra using soft excitation pulses.

Feasibility of acquiring high-resolution 3D NMR images of objects with dipolar-broadened spectra by using soft excitation pulses is experimentally demonstrated. The models are liquid-crystalline phantoms and a pencil eraser. The pulse sequence is a standard 3D gradient-echo sequence.

NMR implementation of a parallel search algorithm.

Recently it has been shown that the dynamics of a cluster of dipolar-coupled spins can be manipulated to store and process a large amount of information in a parallel way [Chem. Phys. Lett.