Applications of inverse gas chromatography in the study of liquid crystalline stationary phases

We describe measurements on a number of low-molar-mass and polymeric liquid crystals that contain the same mesogenic groups. Transition temperatures for the mesophases have been measured and the supercooled region of hexyloxycyanobiphenyl studied, revealing some differences from the stable mesophase. Activity coefficients and interaction parameters for a range of probes have been measured and allow us to determine the nature and origin of the thermodynamic interactions in the systems. A discussion of how this fundamental information can be used in designing more efficient stationary phases for analytical gas chromatography is also presented.     

The total synthesis of 13(R)- and 13(S)-dihydro-4-demethoxy-daunorubicin. Revision of stereochemistry of the microbial and mammalian reduction product of 4-demethoxydaunorubicin

The properties of 13(S)-dihydro-4-demethoxydaunorubicin, rather than the 13(R)-isomer, correspond to those of the microbial and mammalian reduction product of 4-demethoxydauno-rubicin.     

Raster-Elektronenmikroskopie- und Kleinwinkel-Lichtstreuungs-Untersuchungen der sphlirolithischen Filme von Polyathylenterephthalat

Ohne Zusammenfassung     

A discussion of causality and the Lorentz group

Zeeman (1964) has shown that the group of automorphisms for the relation of causality on Minkowski space is that generated by the orthochronous Poincaré (Halpern, 1968) group and dilatations. Here we prove that the group of automorphisms that preserve the time-like vectors of Minkowski space normwise is the complete Poincaré group. We prove that the timelike structure within the null cone of a single event does define the whole structure of Minkowski space. Further, it is shown that only inertial observers can use Minkowski space to describe space-time.     

Field-cycled PEDRI imaging of free radicals with detection at 450 mT

This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described.     

Hysteresis of charge tunneling in assemblies of carboxylic acid-modified gold nanoparticles

We report on charge transport measurements through laterally contacted assemblies of Au nanoparticles capped with 11-mercaptoundecanoic acid ligands. Both alternating- and direct-current data indicate that although the nanoparticles behave as electrically isolated metallic islands, there is a significant influence from the nanoparticle environment, indicating the existence of a slow reorganization process linked to charge transport. On the basis of the observation of temperature-dependent hysteresis of charge tunneling, we propose that this process is due to proton transfer between the carboxylic acid tails of the ligands.     

Quantum pathways for resonance energy transfer

A quantum electrodynamical calculation is presented that focuses individually on the two quantum pathways or time orderings for resonance energy transfer. Conventional mathematical procedures necessitate summing the quantum pathway amplitudes at an early stage in the calculations. Here it is shown, by the adoption of a different strategy that allows deferral of the amplitude summation, that it is possible to elicit key information regarding the relative significance of the two pathways and their distinct distance dependences. A special function integration method delivers equations that also afford new insights into the behavior of virtual photons. It is explicitly demonstrated that both time-ordered pathways are effective at short distances, while in the far field the dissipation of virtual traits favors one pathway. Hitherto unknown features are exhibited in the oblique asymptotic behavior of the time-ordered contributions and their quantum interference. Consistency with the rate equations of resonance energy transfer is demonstrated and results are presented graphically.     

Passive stabilization of a passively mode-locked laser by nonlinear absorption in indium phosphide

A diode-pumped Nd:KGd(WO4)2 laser mode locked by a saturable Bragg reflector (SBR) is passively stabilized to suppress Q-switched mode locking and to extend the parameter range of continuous-wave mode locking. An indium phosphide plate exhibiting two-photon absorption and free-carrier absorption is used for passive stabilization. The intracavity pulse energy for the onset of stable continuous-wave mode locking is reduced by a factor of 4 compared with the laser without stabilization. By increasing the modulation depth of the SBR, pulse shortening by 30% is achieved and bandwidth-limited 6.2-ps pulses are measured.     

Tracking regression and progression of atherosclerosis in human carotid arteries using high-resolution magnetic resonance imaging

BACKGROUND AND PURPOSE: Magnetic resonance imaging (MRI) can accurately and reproducibly measure the volume of atherosclerotic plaque in human carotid arteries. Atherosclerotic plaques may either progress or regress over time, depending on individual risk factors and treatment regimens. This study was designed to determine if regression or progression of human carotid atherosclerosis in patients receiving statin therapy over 24 months can be detected by high-resolution MRI. METHODS: In 11 subjects who had undergone unilateral carotid endarterectomy and were on statin therapy, volumes for total carotid artery, concentric wall (normal wall), eccentric wall (plaque), and lumen were quantified at 0, 16 and 24 months using a 1.5-T human imager equipped with 6-cm phased array coils. RESULTS: The interobserver mean coefficient of variation (CV) was lowest for the lumen volume (3.1%) and highest for the plaque volume (9.8%). The interscan mean CV was lowest for the total artery volume (3.2%) and highest for the plaque volume (9.9%). As much as 26% regression and 35% progression were observed in individual subject's carotid artery eccentric wall (plaque) volumes over time. Mean eccentric wall volume increased 5% by 16 months and 8% by 24 months. Mean total wall volume increased slightly at both 16 and 24 months (+1.2% and +1.8%). CONCLUSIONS: High-resolution MRI provides a noninvasive reproducible method of tracking changes in carotid atherosclerosis. This pilot study detected changes in individual subjects at both 16 and 24 months. MRI tracking of changes in atherosclerotic plaques should prove useful in assessing vascular disease risk and monitoring the efficacy of interventions designed to induce regression or retard progression.