Tailoring the I/V characteristics of a superlattice tunnel diode

We demonstrate the exploitation of the precise growth control afforded by molecular beam epitaxy (MBE) to realise the design of a superlattice tunnel diode with a large negative differential resistance (NDR) feature (peak-to-valley ratio of 2.5:1) at room temperature.     

Effect of Microstructural Parameters on the Relative Densities of Metal Foams

A detailed quantitative microstructural analyses of primarily open cell FeCrAlY and 314 stainless steel metal foams with different relative densities and pores per inch (p.p.i.) were undertaken in the present investigation to determine the effect of microstructural parameters on the relative densities of metal foams. Several elements of the microstructure, such as major and minor cell sizes, cell areas and perimeters, ligament dimensions, cell shapes, and area fractions of closed and open cells, were measured. The cross-sections of the foam ligaments showed numerous pores, and their circularity factors and average sizes were determined. The area fractions of the open cells and ligaments decreased, whereas that of the closed cells increased linearly with increasing relative density. The relative densities and p.p.i. were not significantly dependent on cell size, cell perimeter, and ligament dimensions within the limits of experimental scatter. A phenomenological model is proposed to rationalize the present microstructural observations.     

Cluster mean-field theory accurately predicts statistical properties of large-scale DNA methylation patterns

The accurate establishment and maintenance of DNA methylation patterns is vital for mammalian development and disruption to these processes causes human disease. Our understanding of DNA methylation mechanisms has been facilitated by mathematical modelling, particularly stochastic simulations. Megabase-scale variation in DNA methylation patterns is observed in development, cancer and ageing and the mechanisms generating these patterns are little understood. However, the computational cost of stochastic simulations prevents them from modelling such large genomic regions. Here, we test the utility of three different mean-field models to predict summary statistics associated with large-scale DNA methylation patterns. By comparison to stochastic simulations, we show that a cluster mean-field model accurately predicts the statistical properties of steady-state DNA methylation patterns, including the mean and variance of methylation levels calculated across a system of CpG sites, as well as the covariance and correlation of methylation levels between neighbouring sites. We also demonstrate that a cluster mean-field model can be used within an approximate Bayesian computation framework to accurately infer model parameters from data. As mean-field models can be solved numerically in a few seconds, our work demonstrates their utility for understanding the processes underpinning large-scale DNA methylation patterns.     

Changes in the ultrastructure and texture of prawn muscle (Macrobrachuim rosenbergii) during cold storage

Changes in the ultrastructure and proteolytic activity of prawn muscle were determined during storage at 5 °C, in order to better understand changes in physical and sensory texture measurements. Progressive deterioration of myofibril structure was observed during refrigeration of prawn for 14 d. The loss of density and order in Z-line alignment was first detected after 3 d of storage. Progressive disruption of Z-line, I-bands and M-lines was observed after 4-6 d of storage. Muscle degradation included pronounced disruption of the mitochondria as revealed by swollen cristae, loss of cristae material, and membrane breakage. Along with ultrastructural changes, decreased shear force values and mean textures scores were measured. An initial shear force value of 18.21 N/g decreased to 14.50, 12.46, and 10.79 N/g on days 3, 6, and 14, respectively. Mean texture scores indicated that prawn muscle maintained firm texture during 0-3 d of storage, and became soft during 4-6 d of storage. After 6 d of storage, the prawn texture was very soft. Increased deterioration of the muscle ultrastructure coincided with the increase of proteolytic microorganisms and salt soluble muscle proteins found by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is concluded that the weakening of the ultrastructure is related to proteolytic activity and results in a more soft texture in prawns.     

Numerical validation of the new track equations for static problems

This paper presents a numerical validation of the new equations for the rail-tie structure, derived recently by Kerr and Zarembski [Acta Mech. 40, 253–276 (1981)], for the track response in the lateral plane. Equations of this type are needed for the analysis of track buckling and lateral track dynamics. This is achieved by comparing the results based on the new equations with those of a finite-element analysis, for a 24 m (80 ft) long rail-tie structure. The comparison revealed very close agreement for the lateral deflections and bending moments, for a wide range of rail and tie spacings currently in use, which includes narrow and wide gauge tracks. The effect of the boundaries, where the rail-tie structure experiences a discontinuity, was found to be negligibly small. The findings show that the new equations are suitable for the analysis of cross-tie tracks in the lateral plane. They also confirm that, for tracks with stiff fasteners, the use of the standard beam bending equation with a ‘substitute’ track bending stiffness is of questionable validity.     

Florida DOT Project-Level Bridge Management Models

The Florida Department of Transportation (FDOT) is in the process of implementing Pontis, a Bridge Management System, to provide decision support to engineers in the headquarters and district offices as they make routine policy, programming, and budgeting decisions regarding the preservation and improvement of the state’s bridges. As part of this effort, an ongoing research program is underway to adapt the system to FDOT needs as well as to advance the state of the art in several areas important to the Department. Most of the research results are organized around a new project-level decision support framework that complements and builds on Pontis’ existing network-level analysis. Specific new models include accident risk and user cost due to roadway width and alignment deficiencies; user cost of load capacity and vertical clearance restrictions, and moveable bridge openings; project-level prediction models for bridge element condition and costs; and prediction of economics of scale and scoping possibilities. The new models are built into a highly graphical spreadsheet model for decision support use.     

Detection of naturally expressed receptors for gastrin-releasing peptide and tachykinins using cyanine 3-labelled neuropeptides

Peptides labelled with the fluorophore cyanine 3 were used to study naturally expressed neuropeptide receptors by confocal microscopy in continuous cell lines, primary cultures, and unfixed tissue. Swiss 3T3 fibroblasts bound cyanine 3-gastrin-releasing peptide at 4 degrees C, and internalized the peptide after 10 min at 37 degrees C. Internalization was specific, since it was blocked by incubation with unlabelled peptide. Primary cultures of myenteric neurons of the guinea pig incubated with cyanine 3-substance P at 4 degrees C had specific surface labelling. After 30 s at 37 degrees C, the peptide was internalized into vesicles in both the soma and neurites. Direct observation of live neurons showed movement of fluorescent vesicles to a perinuclear region after 30 min. Endocytosis was associated with a loss of surface binding sites. Unfixed whole mounts of guinea pig and rat ileum were incubated with cyanine 3-neurokinin A at 4 degrees C. After 5 min at 37 degrees C, Cy3-neurokinin A was specifically internalized in neurons and smooth muscle cells. After 30 min, a perinuclear labelling occurred in some cells. Labelling in rat neurons was diminished by the NK3-R antagonist SR142801. Thus, cyanine 3-neuropeptides are valuable tools to study expression and endocytosis of naturally expressed receptors.     

Reactivity of trypsin in reverse micelles: pH-effects on the W0 versus enzyme activity profiles

We have adapted the new MxA gene-induction bioassay to measure neutralizing antibodies to interferon-beta1b (IFN-beta1b, the active ingredient in Betaseron) in sera from patients treated with Betaseron. This antibody assay has been validated to quantify neutralizing titers of 1:20 and above, with a precision of +/- 0.20 in log10. We have used this MxA gene-induction antibody assay to reinvestigate serum samples from multiple sclerosis (MS) patients treated with Betaseron. The titers measured were closely comparable to those obtained in antiviral assays. Data obtained by both methods show that neutralizing antibodies may appear and subsequently disappear over time in the sera of some patients treated with Betaseron. Sera from some patients contain binding antibodies to IFN-beta1b. It was shown that binding antibody titers do not correlate quantitatively or qualitatively with neutralizing antibody titers, and indeed, a number of patients develop high levels of binding antibodies but never form measurable levels of neutralizing antibodies.     

Intrathyroidal parathyroid glands can be a cause of failed cervical exploration for hyperparathyroidism

BACKGROUND: The incidence of intrathyroidal parathyroid glands remains controversial. The purpose of this study was to determine the incidence in a series of patients with hyperparathyroidism. METHODS: Three hundred nine patients underwent parathyroidectomy. Patients were divided into two groups: uniglandular disease versus hyperplasia. RESULTS: Eighteen of 309 patients (6%) had abnormal intrathyroidal parathyroid glands. The incidence was 3% (7 of 222) in patients with uniglandular disease versus 15% (11 of 73) in those with hyperplasia. With a mean follow-up of 54 months, 12 patients are eucalcemic, 5 have persistent hypocalcemia, and 1 has recurrent hypercalcemia. There were no recurrent laryngeal nerve injuries. CONCLUSIONS: These data suggest that an intrathyroidal adenoma is an uncommon cause of failure, whereas abnormal intrathyroidal parathyroid tissue may be a more common cause of failure in patients with hyperplasia.