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.

Measurement of J-couplings between chemically equivalent nuclei using off-resonance decoupling.

The method of measuring J-couplings between chemically equivalent nuclei in isotopically/magnetically non-equivalent environment, based on off-resonance decoupling, is described. The approach uses intensities, rather than frequencies of the spectral peaks and, therefore, the accuracy of measurement is not limited by spectral resolution.

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.

Reversibility of dynamics and multiple-quantum coherences.

In spin systems, the decay of the Loschmidt echo in the time-reversal experiment (evolution-perturbation-time-reversed evolution) is linked to the generation of multiple-quantum (MQ) coherences. Unlimited growth of the MQ coherences leads to irreversibility of dynamics. In some cases, one can expect that the deviation of the Loschmidt echo and the second moment of the MQ intensities distribution are linear in time.

A model for membrane potential and intracellular ion distribution.

Most cells carry a negative electric charge. It produces a potential difference across the membrane, which regulates voltage-sensitive ion transport and ATP synthesis in mitochondria. The negative charge comes partly from an excess of negative ions in the cell interior (Donnan potential) and partly from ionized groups on the membrane (surface potential).