Medical ultrasound imager based on time delay spectrometry

A reflection mode proof-of-concept medical ultrasound imager based on time delay spectrometry has been developed and tested. The system uses a broad band swept-frequency signal operating up to 10 MHz. Signal processing using a fast Fourier transform (FFT) permits extraction of range information. The imager has a higher signal-to-noise ratio than pulse-echo systems which allows high resolution at greater depths. The time delay spectrometry (TDS) spread spectrum operates at lower peak intensities than pulse-echo and permits more control of the spectral content and amplitude of the signal. At present, the system is non-real time which degrades in vivo imaging because of averaging over several cardiac cycles and tissue movement.     

Nucleophilic displacement of activated aryl triflates a new synthesis of oxindoles and arylacetic acids

2-Nitroaryl triflates undergo efficient base-catalyzed nucleophilic displacement by dimethyl malonate anion to yield dimethyl nitroarylmalonates, which subsequently are converted in high yields to nitroarylacetic acids and oxindoles.     

Enhanced thermal conductance at a copper-liquid helium interface in the presence of acoustic streaming

In a conventional Kapitza resistance experiment involving heat transfer across a copper surface into liquid helium, an acoustic streaming velocity field (at 10 MHz) was directed transverse to the surface normal. Ultrasound had no observable effect on the heat transfer to the superfluid phase (He-II), but in the normal fluid phase (He-I) the thermal conductance increased linearly with acoustic velocity amplitude, reaching a value 2.5 times the zero sound conductance for a sound velocity amplitude of 0.8 cm s^?1.     

Chloroindate(III) ionic liquids: recyclable media for Friedel-Crafts acylation reactions

Chloroindate(III) ionic liquids are versatile reaction media for Friedel-Crafts acylation reactions; the system is catalytic and totally recyclable, using an aqueous workup, with no leaching of the indium into the product phase.     

Use of acousto-optic techniques to detect subharmonic and cavitation activity

Observations were made of the diffraction patterns produced by the acousto-optic effect in superfluid helium and in methanol for both cylindrical and plane wave sound fields. Thresholds for the subharmonic of order $\text{1}\text{2}$ and transient cavitation were determined by observation of abrupt changes in the diffraction patterns. The onset of the subharmonic produced additional diffracted signals in a stable diffraction pattern while onset of cavitation completely disrupted the diffraction pattern.     

Variable temperature H NMR studies on Grubbs catalysts

Variable temperature ¹H NMR studies were conducted to investigate whether steric congestion is influencing the structural rigidity of (IMesH₂)(PCy₃)(Cl)₂RuCHPh (IMesH₂ = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) in solution. It was shown that both mesityl ligands rotate at about the same rate around the N-Mesityl bonds in the IMesH₂ ligand and that changing the solvent does not significantly alter this rotation. It was found that the increased steric congestion in (IMesH₂)(PCy₃)(Cl)₂RuCHPh compared to (PCy₃)₂(Cl)₂RuCHPh does affect the rates of rotation around the C_alkylidene-Ph bonds. Unusual chemical shift positions were also observed in the low temperature ¹H NMR spectrum for the aromatic proton signals for (IMesH₂)(PCy₃)(Cl)₂RuCHPh and (PCy₃)₂(Cl)₂RuCHPh.     

The energetics of tetrahydrocarbazole aromatization over Pd(111): a computational analysis

The carbazole moiety is a component of many important pharmaceuticals including anticancer and anti-HIV agents and is commonly utilized in the production of modern polymeric materials with novel photophysical and electronic properties. Simple carbazoles are generally produced via the aromatization of the respective tetrahydrocarbazole (THCZ). In this work, density functional theory calculations are used to model the reaction pathway of tetrahydrocarbazole aromatization over Pd(111). The geometry of each of the intermediate surface species has been determined and how each structure interacts with the metal surface addressed. The reaction energies and barriers of each of the elementary surface reactions have also been calculated, and a detailed analysis of the energetic trends performed. Our calculations have shown that the surface intermediates remain fixed to the surface via the aromatic ring in a manner similar to that of THCZ. Moreover, the aliphatic ring becomes progressively more planer with the dissociation of each subsequent hydrogen atom. Analysis of the reaction energy profile has revealed that the trend in reaction barriers is determined by the two factors: (i) the strength of the dissociating ring-H bond and (ii) the subsequent gain in energy due to the geometric relaxation of the aliphatic ring.     

Redox control of meso-zinc(II) ferrocenylporphyrin based fluorescence switches

The efficient on/off switching of fluorescence from thienyl- and phenyl-substituted porphyrin-ferrocene dyads is achieved through redox control of excited-state electron-transfer quenching.