Soft-laser scanning densitometry performed on a 35-mm slide illustrating SDS-PAGE separation of adenovirion polypeptides

Virion polypeptides (35 S), methionine-labeled and purified by CsCl gradient centrifugation, were separated by SDS-gel electrophoresis. Analysis of their band pattern was performed by scanning the images of the SDS-gels shown on a 35-mm slide. The densitometric tracings revealed the presence of 17 protein bands, although only 15 of them were visible to the naked eye. The high sensitivity and resolving capacities of the soft-laser scanning densitometer enabled us to detect trace amounts of protein bands separated in SDS-gels and to obtain a resolution compatible to that of electrophoresis. Fourfold electronic amplification of the densitometric tracings, produced by a computer, generated new information regarding the pattern of the electrophoregram. The facility to amplify peaks of importance is particularly advantageous when faint or overlapping protein bands revealed on a gel are assessed.     

Detection and assessment of citrus tristeza virus antigens by computer-aided scanning densitometry

Citrus tristeza virus (CTV) extracted from Etrog citron (C.medica L.) was immunoprecipitated. The immunoprecipitate was fractionated by SDS-PAGE and western blotted onto nitrocellulose. The CTV antigens were determined by immunoblot analysis using rabbit anti-CTV IgG, and the protein-band pattern exhibited on the nitrocellulose was assessed by soft-laser scanning densitometry. The densitometric tracing revealed the presence of bands that were not visible to the naked eye. Using the superimposition mode of the instrument, it was also revealed that the protein-band patterns of different CTV samples were not identical. Computer-aided soft-laser scanning densitometry proved to be a powerful approach in the detection and assessment of protein bands revealed on nitrocellulose immunoblots, which we were previously unable to do employing conventional methods.     

Degradation of parathion methyl on field-sprayed apples and stored apples

Residue levels of parathion methyl on field-sprayed Granny-Smith apples were studied. The pesticide was applied according to producer recommendations. Apples received a single spraying at a rate of 40 g active ingredient/100 L. Residues were determined with a simple gas chromatographic method. Recovery of parathion methyl was 88-108%, and the limit of determination was 0.002 mg/kg. Decomposition of parathion methyl was studied in apples remaining on trees after spraying and in apples harvested and stored under ambient-temperature, refrigerated-room, and controlled-atmosphere conditions. During post harvest storage, parathion methyl degrades more slowly than on apples remaining on the trees. Best-fit curves were determined, and kinetic equations, rate constants, and half-lives were calculated. Half-lives found were 8 days for apples on trees, 45 days for apples stored at ambient conditions, 68 days for apples stored in controlled-atmosphere room, and 62 days for apples stored in a refrigerated room. Under storage conditions, levels of parathion methyl residues need a long time to become lower than the legal limit (0.2 mg/kg).     

Dark channels in resonant tunneling transport through artificial atoms

We investigate sequential tunneling through a multilevel quantum dot confining multiple electrons in the regime where several channels are available for transport within the bias window. By analyzing solutions to the master equations of the reduced density matrix, we give general conditions on when the presence of a second transport channel in the bias window quenches transport through the quantum dot. These conditions are in terms of distinct tunneling anisotropies which may aid in explaining the occurrence of negative differential conductance in quantum dots in the nonlinear regime.     

The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Optimal intervention policies for a multidimensional simple epidemic process

We consider a deterministic simple epidemic process in which the susceptibles are exposed to n+1 diseases. It is assumed that one disease is relatively harmless while the others cause serious symptoms. Policies for introducing infection by the harmless disease are considered and, under a suitable cost structure, the optimal policy that minimises the future cost for every initial state is found. For the corresponding stochastic model, the optimal policy is found by implementing a suitable dynamic programming algorithm, and is compared numerically with the optimal policy for the deterministic model.     

Effect of storage temperature on degradation of methidathion in fortified orange and peach juices

The effect of storage temperature on methidathion degradation in orange and peach juices was studied. The insecticide was aseptically added to packed orange and peach juices, which were stored at 40, 15, and 0 degrees C. Samples were taken at regular intervals and examined for residues of methidathion. Residues were determined with a simple gas chromatographic method; recoveries of methidathion from orange and peach juices ranged from 88.1 to 110% for both juices, and the limits of determination were 0.004 and 0.003 mg/kg, respectively. The experimental data were used to evaluate rate constants, half-lives, and times required to reach legal maximum residue limits, and activation energies for the decomposition of methidathion in orange and peach juices. Storage of fruit juices in refrigerated rooms greatly extended the half-life of methidathion beyond that of methidathion in samples stored at higher temperatures. Half-life values for methidathion in orange and peach juices, respectively, were 4.1 and 3.8 days for storage at 40 degrees C, 115 and 113 days for storage at 15 degrees C, and 330 and 385 days for storage at 0 degrees C. Activation energies for methidathion degradation in orange and peach juices were 22.6 and 21.7 kcal/mol, respectively.     

Electron impact mass spectra of penitrem A,some derivatives and its analogues

The mass spectra of penitrems A-E and some derivatives of penitrem A have been measured. Fragmentation pathways have been confirmed by use of the linked scan (B/E) technique and are consistent with the formulation of the compounds as analogues of paspalinine.     

Observations on the electron impact induced fragmentation of methyl and phenyl 4,6-O-Benzylideneglucopyranosides

The structure of some rearrangement ions in the electron impact induced fragmentation of methyl 4,6-O-benzylidene-2,3-di-O-methyl-α-D -glucopyranoside and phenyl 4,6-O-benzylidene-2,3-di-O-methyl-β-D -glucopyranoside have been investigated using high resolution, deuterium labelling and linked scan (B,E) techniques. Shifts of methoxyl groups from C-2 and C-3 to C-1 have been confirmed.     

Hydrocolloid interferences in the determination of pectin by the carbazole method.

In the colorimetric determination of pectin by the carbazole method, some of the interfering compounds have been identified but the possible interference of different hydrocolloids is not known. Several hydrocolloids are currently used in the preparation of imitation and adulterated orange juice for cloud stabilization. Hydrocolloids studied were gum arabic, carboxylmethyl cellulose, sodium alginate, carrageenan, guar gum, and xanthan. The effects of these hydrocolloids on the carbazole method for pectin determination was studied. Procedures are proposed for the correct use of the carbazole method for pectin determination in the presence of extraneous hydrocolloids.