DRYING GRANULAR POROUS MEDIA: GRAVITATIONAL EFFECTS IN THE ISENTHALPIC REGIME AND THE ROLE OF DIFFUSION MODELS

In this paper we have examined the influence of gravity on the moisture transport process during the isenthalpic drying period, and we have considered the use of diffusion models both to predict saturation pro- files and to extract apparent diffusivities from experi- mental data. For granular or unconsolidated porous media, the one-dimensional moisture transport process can be characterized by two dimensionless groups that account for capillary forces, gravitational forces and viscous forces. Detailed numerical solutions of the saturation transport equation indicate under what circumstances the diffusion model can be used with confidence, and under what circumstances the diffusion model can be used to predict saturation profiles even though it is an incorrect representation of the moisture transport process. In addition to exploring the predictive capabilities of the diffusion model, we have     

The Polymorphism of C.I. Pigment Yellow 5

Department of Physics Brunei University Uxbridge Middlesex UB8 3PH By interpretation of X-ray diffraction patterns it has been found that C. I. Pigment Yellow 5 (α-[1-hydroxy-ethylidene\acetanilide-α-azo-\2′;-nitrobenzene]) is dimorphic, both forms being available commercially. The single-crystal data and X-ray powder pattern are reported for one form (termed α) and the powder pattern has been indexed from the single-crystal unit cell dimensions. The second form (β) has only been obtained as a powder, and the powder pattern is reported. This form changes to the α-form by recrystallisation from toluene.     

Ultrafast response of As-implanted GaAs photoconductors

The photoconductive response of an optoelectronic switch fabricated from GaAs implanted with arsenic ions is measured to have a duration as short as 0.7 ps and a relaxation time as fast as 0.5 ps. The switching efficiency and relaxation time of the photoswitches using the As-implanted GaAs substrates are determined to be comparable to photoconductive devices employing GaAs grown by low-temperature molecular-beam epitaxy (LT-GaAs). For high dc-bias values, persistent photocurrent tails from transient leakage currents are found to be very prominent in bulk GaAs devices that were implanted with 10¹⁶ cm^-2 arsenic ions at 200 keV. This behavior has been determined to arise from substrate leakage current underneath the thin implanted layer, which recrystallizes and exhibits, as does LT-GaAs, arsenic-precipitate formation after annealing. In order to reduce this leakage current, multiple ion dosages with various implantation energies have been implemented. An epitaxial GaAs layer has also been implanted with arsenic ions, isolated from its semi-insulating substrate, and bonded onto a fused silica wafer in order to verify that the persistent tail response from the photoconductive switches was not actually due to the implanted region of the GaAs     

A new type of methylamine oxidase: the sole oxidase produced during growth of Sporobolomyces albo-rubescens on primary alkylamines

Under conditions known to separate methylamine oxidase from benzylamine oxidase in other yeast strains, only a single oxidase could be detected in Sporobolomyces albo-rubescens. This occurred irrespective of whether methylamine or n-butylamine was the nitrogen source for growth. The oxidase did not attack benzylamine. It was concluded that this organism can only produce a methylamine oxidase. The enzyme was purified to 90% homogeneity and found to have properties significantly different from the methylamine oxidases previously characterised. It lost only 40% of its activity in 30 min at 45 degrees C, whereas methylamine oxidases previously described had half-lives of from 2 to 9 min at 45 degrees C. It showed also a lower activity with short chain 1-aminoalkanes and a higher activity with longer chain 1-aminoalkanes than other methylamine oxidases, and had a significantly smaller subunit molecular weight (57,000 compared with 80,000).     

Defensive Spiroketals from Asceles glaber (Phasmatodea): Absolute Configuration and Effects on Ants and Mosquitoes

Insects are the largest and most diverse group of organisms on earth, with over 1,000,000 species identified to date. Stick insects (“walkingsticks” or “phasmids”, Order Phasmatodea) are known for and name-derived from their camouflage that acts as a primary line of defense from predation. However, many species also possess a potent chemical defense spray. Recently we discovered that the spray of Asceles glaber contains spiroketals [a confirmed major component: (2S,6R)-(?)(E)-2-methyl-1,7-dioxaspiro[5.5]undecane, and a tentatively identified minor component: 2-ethyl-1,6-dioxaspiro[4.5]decane] and glucose. In this paper, we: 1) illustrate the identification of spiroketals and glucose in the defense spray of A. glaber by using Nuclear Magnetic Resonance (NMR), Gas Chromatography/Mass Spectrometry (GC/MS), and comparison with a synthetic reference sample; 2) provide the elucidation of the absolute configuration of the major spiroketal in that defense spray; and 3) demonstrate the effect of this compound and its enantiomer on both fire ants (Solenopsis invicta) and mosquitoes (Aedes aegypti).     

Alkyldimethylpyrazines in the Defensive Spray of <Emphasis Type="Italic">Phyllium westwoodii</Emphasis>: A First for Order Phasmatodea

Phyllium westwoodii is a phasmid insect (Order Phasmatodea) belonging to the Family Phylliidae (leaf insects). These rather large and ornate creatures are known for their morphological resemblance to plant leaves for camouflage. Pyrazines are a common class of compounds used or produced by a wide variety of organisms, even humans. When an individual of P. westwoodii is disturbed, it sprays an opaque liquid from a pair of prothoracic glands, which are utilized by other phasmid species for defense. The current study has found that this liquid contains glucose and a mixture of 3-isobutyl-2,5-dimethylpyrazine, 2,5-dimethyl-3-(2-methylbutyl)pyrazine, and 2,5-dimethyl-3-(3-methylbutyl)pyrazine. This is the first report of pyrazines found in the defensive gland spray of phasmid insects, and the first chemical analysis of glandular material from family Phylliidae.