Measurement of alpha-amylase activity in white wheat flour,milled malt,and microbial enzyme preparations,using the Ceralpha assay: collaborative study

This study was conducted to evaluate the method performance of a rapid procedure for the measurement of alpha-amylase activity in flours and microbial enzyme preparations. Samples were milled (if necessary) to pass a 0.5 mm sieve and then extracted with a buffer/salt solution, and the extracts were clarified and diluted. Aliquots of diluted extract (containing alpha-amylase) were incubated with substrate mixture under defined conditions of pH, temperature, and time. The substrate used was nonreducing end-blocked p-nitrophenyl maltoheptaoside (BPNPG7) in the presence of excess quantities of thermostable alpha-glucosidase. The blocking group in BPNPG7 prevents hydrolysis of this substrate by exo-acting enzymes such as amyloglucosidase, alpha-glucosidase, and beta-amylase. When the substrate is cleaved by endo-acting alpha-amylase, the nitrophenyl oligosaccharide is immediately and completely hydrolyzed to p-nitrophenol and free glucose by the excess quantities of alpha-glucosidase present in the substrate mixture. The reaction is terminated, and the phenolate color developed by the addition of an alkaline solution is measured at 400 nm. Amylase activity is expressed in terms of Ceralpha units; 1 unit is defined as the amount of enzyme required to release 1 micromol p-nitrophenyl (in the presence of excess quantities of alpha-glucosidase) in 1 min at 40 degrees C. In the present study, 15 laboratories analyzed 16 samples as blind duplicates. The analyzed samples were white wheat flour, white wheat flour to which fungal alpha-amylase had been added, milled malt, and fungal and bacterial enzyme preparations. Repeatability relative standard deviations ranged from 1.4 to 14.4%, and reproducibility relative standard deviations ranged from 5.0 to 16.7%.     

Studies on the effect of equi-biaxial stretching on the exfoliation of nanoclays in polyethylene terephthalate

TEM image analyses of PET nanocomposites were done to study the effect of equi-biaxial stretching and stretch ratio on the exfoliation and other tactoid properties. Though XRD spectra did not show any evidence of exfoliation, TEM image analysis revealed 10% exfoliation of clay platelets in the unstretched sheets. Stretching further improved the exfoliation as the concentration of thinner tactoids in the matrix increased due to stretching. Stretching also caused an increase in the concentration of longer tactoids and tactoids having higher aspect ratio, the reason for which was assumed to be due to the slippage of the platelets while stretching. It was found that stretch ratio affected the nanocomposite properties as increase in stretch ratio improved the exfoliation of clay platelets. Equi-biaxial stretching imparted preferential orientation of the tactoids in the matrix. Dynamic mechanical and barrier property measurements confirmed the observations made by the TEM image analysis.     

CuD in burnout V

The neutral diatomic molecule, CuD, with rotational excitation temperature of 0.23 eV, has been positively identified in the Burnout V apparatus. The molecule CD has also been observed by replacing portions of the copper, Burnout V liner material with carbon. The dependence of the molecular spectral radiance on combinations of carbon, copper and niobium, a material of minimal sputtering characteristics, and their location in the liner, lead one to believe that the molecules are produced by energetic Cu and C (?3 keV) bombardment of deuterium occluded in the liner material.     

Control of a coupled map lattice model for vortex shedding in the wake of a cylinder

The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns, vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle map.     

The development of information storage materials — How microscopy can help?

The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.     

The effect of varying carboxylate ligation on the electronic environment of N2O(x) (x = 1-3) nonheme iron: a DFT analysis

Mononuclear nonheme iron oxygenase (MNO) enzymes contain a subclass of metalloproteins capable of catalyzing the O(2)-dependent hydroxylation of unactivated substrates at a ferrous ion center coordinated to a highly conserved His-His-Glu/Asp motif. These enzymes, which utilize additional reducing equivalents obtained from the decarboxylation of a coordinated α-ketoglutarate (αKG) cofactor, do not readily interact with O(2) in the absence of αKG binding. Density functional theory calculations with the B3LYP functional were performed to gain insight into the electrochemical behavior of three sets of Fe(II/III) complexes containing a core N, N, O facial binding motif in which the number of carboxylate ligands was systematically altered, to provide one, two (cis) or three (fac) labile sites. The calculated trend in Fe(II/III) reduction potentials was observed to parallel that observed in cyclic voltammetry experiments, showing a decrease in potential (stabilized oxidized state) with increasing carboxylate ligation. This trend does not appear to be the result of differential charge on the metal complex. Changes in the redox-active molecular orbital (RAMO) energy due to covalent effects dominate across the series of complexes when chloride is modeled as the labile ligand, with the π anti-bonding nature of the RAMO being an important factor. With water molecules as the labile ligands, however, a much steeper redox dependence on the number of carboxylate ligands is observed and this effect seems to be largely electrostatic in origin. Differential relaxation of the occupied molecular orbitals in the ferric complexes appears to contribute to the redox trend as well. Finally, these observations are placed in the context of MNO enzyme mechanisms.