Magnetic resonance studies of jets in a gas–solid fluidised bed

Magnetic resonance imaging (MRI) has been used to study the behaviour of jets at the distributor of a 50 mm diameter fluidised bed of 0.5 mm diameter poppy seeds. Two perforated-plate distributors were examined, containing either 10 or 14 holes, each 1 mm diameter. Ultra-fast MR imaging was able to show the transient nature of the upper parts of the jets, where discrete bubbles are formed. Imaging in 3D showed that the central jets were the longest for flow rates below minimum fluidisation. Above minimum fluidisation, the outer jets, nearest the wall of the fluidised bed, arched inward towards the central axis. In this latter case, interpretation of the time-averaged 3D image required the use of ultra-fast MR imaging to identify the approximate height above the distributor at which discrete bubbles were formed. The apparently continuous void extending along the central axis above this height in the time-averaged 3D image was thus identified, using ultra-fast MR imaging, as representing the averaged paths of released bubbles. Time-averaged MR velocity mapping was also used to identify dead zones of stationary particles resting on the distributor between the jets. The dead zones could be observed when the superficial velocity of the gas approached minimum fluidisation, but they were smaller than those observed at lower gas superficial velocity. Comparable images of a single jet through 1.2 mm diameter poppy seeds from MRI and electrical capacitance volume tomography (ECVT) are also demonstrated.     

Beauveria bassiana ATCC 7159 Containsan L-Specific a-Amino Acid Benzamidase

Summary.  Biotransformation of a series of racemic N-benzoyl α-amino acids by the fungus Beauveria bassiana ATCC 7159 results in isolation of the corresponding D-amino acid benzamides in high enantiomeric purity and yield. Received December 20, 1999. Accepted January 21, 2000     

A low-dimensional dynamical system to describe low-frequency fluctuations in a semiconductor laser with optical feedback

We derive a low-dimensional dynamical system to describe a semiconductor laser with optical feedback. This model captures many features from the original time delayed dynamical system and explains the origin of the low-frequency instability observed in the time-delayed equation.     

Binding affinity of alkynes and alkenes to low-coordinate iron

We report the synthesis, spectroscopy, and structural characterization of iron-alkyne and -alkene complexes of the type L(Me)Fe(ligand) [L(Me) = bulky beta-diketiminate, ligand = HCCPh, EtCCEt, CH2CHPh, EtCHCHEt, HCC(p-C6H4OCH3), HCC(p-C6H4CF3)]. The neutral ligand exchanges rapidly at room temperature, and the equilibrium constants have been measured or estimated. The binding affinity toward the low-coordinate Fe follows the trend HCCPh > EtCCEt > CH2CHPh > EtCHCHEt approximately PPh3 > benzene > N2. This trend is consistent with a model in which pi back-bonding from the formally Fe(I) center is the dominant interaction in determining the relative binding affinities. In nitrogenase, alkynes are reduced while alkenes are unreactive, and this work suggests that the different binding affinities to low-coordinate Fe might explain the differential activity of the enzyme toward these two substrates.     

Alkyl isomerisation in three-coordinate iron(II) complexes

The tertiary to iso-butyl isomerisation of three-coordinate iron(II) diketiminate complexes is reported and a hydride intermediate is proposed on the basis of exchange experiments.     

Design and development in self-reference differential scanning calorimetry

An intermediate range (50–1000°C) self-referencing differential scanning calorimeter (SR-DSC) has been built and its performance evaluated. The SR-DSC measures heat flow across a heat flow metal plate, and any changes to the heat flow caused by a thermal transition occurring in a centrally placed sample is monitored by a temperature difference across the plate. The criteria for high sensitivity are that the circular plate should be as thin as possible and have a low thermal conductivity. The best sensitivity conducive with robust behaviour was achieved with an inconel thermal plate of uniform thickness, 75 m, this gave reproducible results, and the enthalpy of the thermal transition was proportional to sample mass. Calorimeter sensitivity decreased with increasing temperature and a sloped baseline was observed. Both of these effects can be corrected mathematically. An example of the use of the SR-DSC in polymer characterisation was limited to a study of the physical ageing of PET.This revised version was published online in November 2005 with corrections to the Cover Date.Paper was read at the TAC2001 Conference in Liverpool.     

Solution-phase parallel synthesis of substituted benzimidazoles

A solution-phase parallel synthesis of o-phenylenediamines is described. These intermediates were then subsequently converted to benzimidazole scaffolds (three-point diversity) in excellent purities and yields. High-throughput purification of this multistep synthetic sequence was accomplished using polymer-bound scavengers and reagents and liquid-liquid extraction protocols.     

Signatures of resonance superfluidity in a quantum Fermi gas

We predict a direct and observable signature of the superfluid phase in a quantum Fermi gas, in a temperature regime already accessible in current experiments. We apply the theory of resonance superfluidity to a gas confined in a harmonic potential and demonstrate that a significant increase in density will be observed in the vicinity of the trap center.