Observation of the loss of the hydroxyapatite sixfold symmetry in a human fetal tooth enamel crystal

A deviation from the hydroxyapatite hexagonal symmetry of a human tooth enamel crystal observed by high-resolution electron microscopy is reported. This symmetry deviation is characterized by: (1) ‘preferential’ planes that can be indexed as (100) with an intensity that differs from the (300) and the other {100} hexagonal equivalent planes; and (2) streaking of higher order reflections in the optical diffractogram of the image of the crystal. Computer simulations show that similar ‘preferential’ planes can also be observed at specific crystal tilt angles (and/or beam tilt and/or objective aperture misalignment) and at crystal thickness/microscope defocus values in images of hydroxyapatite crystals observed along the [0001] or [] zone axes. The streaking of higher order reflections in the optical diffractogram is related to a deformation of the crystal itself and does indeed show a symmetry deviation of the crystal under observation.     

Calibration of a wide-field frequency-domain fluorescence lifetime microscopy system using light emitting diodes as light sources

High brightness light emitting diodes are an inexpensive and versatile light source for wide‐field frequency‐domain fluorescence lifetime imaging microscopy. In this paper a full calibration of an LED based fluorescence lifetime imaging microscopy system is presented for the first time. A radio‐frequency generator was used for simultaneous modulation of light emitting diode (LED) intensity and the gain of an intensified charge coupled device (CCD) camera. A homodyne detection scheme was employed to measure the demodulation and phase shift of the emitted fluorescence, from which phase and modulation lifetimes were determined at each image pixel. The system was characterized both in terms of its sensitivity to measure short lifetimes (500 ps to 4 ns), and its capability to distinguish image features with small lifetime differences. Calibration measurements were performed in quenched solutions containing Rhodamine 6G dye and the results compared to several independent measurements performed with other measurement methodologies, including time correlated single photon counting, time gated detection, and acousto optical modulator (AOM) based modulation of excitation sources. Results are presented from measurements and simulations. The effects of limited signal‐to‐noise ratios, baseline drifts and calibration errors are discussed in detail. The implications of limited modulation bandwidth of high brightness, large area LED devices (～40 MHz for devices used here) are presented. The results show that phase lifetime measurements are robust down to sub ns levels, whereas modulation lifetimes are prone to errors even at large signal‐to‐noise ratios. Strategies for optimizing measurement fidelity are discussed. Application of the fluorescence lifetime imaging microscopy system is illustrated with examples from studies of molecular mixing in microfluidic devices and targeted drug delivery research.     

Sensitivity analysis of pulse-frequency-modulated control using a linearized model†

The paper discusses the sensitivity of pulse-frequency modulated (PFM) control systems with respect to changes in the plant and controller parameters. The investigations of the sensitivity behaviour of non-linear PFM control systems are carried out using a linearized approach for the PFM controller, as proposed by Frank and Dillmann. The goal of this paper is to study the effectiveness of this method as applied to the investigation of an unstable plant. The sensitivity functions of the PFM system and the corresponding continuous equivalent systems are evaluated by considering parameter changes in the actual plant. The limitations of this method are pointed out.     

INCORPORATION OF MINCED TROUT (ONCORHYNCHUS MYKISS) INTO EGG-BASED NOODLES

Recovering minced fish from fish frames following filleting operations is a common way to increase fish muscle yield as well as fully utilize aquatic food resources. Therefore, it is important to develop new and feasible applications for minced fish that will add value to fishery products. In this study, washed minced trout (Oncorhynchus mykiss) was incorporated at 10 and 20% flour replacement level into a conventional egg noodle formulation. Textural attributes (by TPA) of cooked noodles were evaluated. In addition, textural, functional and sensory attributes of fried noodles, a snack food item, were also evaluated. Visual color (CIE )‐Lab of fresh noodles containing minced trout was less red and yellow than the control and the overall difference in color (ΔE) increased as the level of minced trout increased. Noodles incorporating 10% minced trout had cooked texture profiles similar to the control; however, there were significant decreases in hardness, gumminess and chewiness in the cooked noodles containing 20% minced trout. For the fried noodles, adding fish tended to reduce the yellow color and yielded a product with texture profiles similar to the control at a 10% substitution level. The experimental and control products were acceptable. Product preference was evenly divided between the control fried noodle and the noodle containing 10% minced trout.     

Thermal Decomposition of Some Substituted Barium Titanyl Oxalates and Its Effect on the Semiconducting Properties of the Doped Materials

Thermal analysis has been performed on BaTiO(C₂O₄)₂.4H₂O, Ba_0.6Sr_0.4TiO(C₂O₄)₂.4H₂O, Sr(TiO(C₂O₄)₂.4H₂O, Ba_0.9Pb_0.1TiO(C₂O₄)₂.4H₂O, and BaTi_0.9Zr_0.1O(C₂O₄)₂.4H₂O. It was observed that the strontium compound decomposes differently than the others. Previous investigators have proposed conflicting mechanisms for the pyrolysis of the barium salt and these results are discussed in comparison with this work. The electrical resistivity and temperature coefficient of fired lanthanum-doped materials were found to vary with the calcination temperature. Maximum conductivity was observed in samples calcined at 900°C whereas maximum positive temperature coefficient was observed for materials calcined at 1050°C. Particle sizes of the calcined material were compared with grain sizes in the fired pieces and correlated with the electrical properties. A cursory examination was made on the effects of fabrication pressure, 1.25 to 15 tsi, on the electrical conductivity. Both the conductivity and positive temperature coefficient were found to increase with decreasing fabrication pressure.     

A Microcomputer Interactive Graphics Software for Design of Steel Trusses

Current advances in microcomputer technology provide the tools to use interactive graphics in the development of efficient computer programs. The use of computer graphics facilitates the definition of complicated engineering models, and permits a clear display of the results. In this paper, an educational microcomputer software package, TRUSS-AD, is described to demonstrate the effectiveness of applying interactive computer graphics in solving structural engineering design problems. TRUSS-AD allows the user to: (1) define a truss geometry and loading conditions graphically; (2) analyze and design the truss in an interactive mode; and (3) display all results in a concise and clear graphical representation. The stiffness method is used in the analysis process. The design can be performed by using either the "Load and Resistance Factor Design" or the "Allowable Stress Design" methods. The software is written using the basic language for IBM or compatible personal computers.     

EFFECT OF GROWTH TEMPERATURE AND MEDIA ON INACTIVATION OF LISTERIA MONOCYTOGENES BY CHLORINE

The objective of this study was to determine the effect of growth environment on the susceptibility of Listeria monocytogenes to inactivation by hypochlorite sanitizer. Cells were grown in tryptic soy broth (TSB) at 35, 21, and 6°C and in 1:15 dilution of TSB (low nutrient medium, LNM) at 35°C. Late exponential phase cells were harvested, washed, and exposed to a 1 ppm sodium hypochlorite solution for periods up to 5 min. After 30 s exposure, cells grown at 35°C in TSB were reduced in number by 2.1 ± .3, at 21°C, 3.1 ± .3 and at 6°C, 3.4 ± .3 log units. After 30 s exposure to 5 ppm free chlorine cells grown at 35°C in TSB were reduced in number by 5.2 ± .2 and in LNM by 3.1 ± .1 log units. These data demonstrate that growth environment has a significant effect on chlorine inactivation of L. monocytogenes.     

EFFECT OF PARTICLE SIZE AND SAMPLE SIZE ON LIPID STABILITY OF MILLED FLAXSEED (Linum usitatissimum L.)

Experiments were conducted to determine the effect of sample size and particle size on lipid oxidation of milled flaxseed. An initial experiment showed that most of the lipid oxidation detected in milled flaxseed samples occurred on the surface that was exposed to the air during storage. In a subsequent experiment, milled flaxseed at 100, 200 and 300 g were stored in the dark in rectangular pans for 8, 24 and 48 days at 50C. Lipid oxidation, as determined by surface lipid content, peroxide value and α-linolenic acid content, was lower in the 300 g samples than in the 100 g samples of milled flaxseed. Large versus small samples had less apparent lipid oxidation because of their inherently lower surface to volume ratio. In a third experiment, oxidation was lower in lipid extracted from coarse ( > 600 µm) than fine particles ( < 600 µm), after 48 days of storage.

PRACTICAL APPLICATIONS

This research has practical applications to the flaxseed milling and food industries. These results show that assessment of lipid oxidation in milled flaxseed needs to consider sample size (collection). Milled flaxseed oxidized predominantly at the sample surface where a polymerized layer of flaxseed particles formed over time. Relatively little oxidation occurred in the interior of the sample. Thus, sampling from the surface or interior of a milled flaxseed sample will end in different results and conclusions. Similarly, results will vary with surface : interior ratio of milled flaxseed. Food manufacturers may want to discard the top layer of milled flaxseed that has been exposed to air. Lipid oxidation was less with coarse than fine particles. Thus it would be prudent not to use milled flaxseed with a finer particle size than is necessary for acceptable end-use quality.     

NaF-KF-K2NbF7 Fused Salt Temperature-Solubility Diagram

Freezing and eutectic temperatures were determined for the NaF-KF-K₂NbF₇ ternary system and the NaF-K₂NbF₇, KFK₂NbF₇, and NaF-KF binary systems. The compound KF-K₂NbF₇ freezes congruently at 770°C; eutectics occur at 708° and 724°C for high- and low-K₂NbF₇ mixtures, respectively. The NaF-K₂NbF₇ eutectic freezes at 658°C. The ternary system has two eutectics, a high-KF mixture and a high-K₂NbF₇ mixture, which occur at 663° and 652°C, respectively.