Delta-1 negatively regulates the transition from prehypertrophic to hypertrophic chondrocytes during cartilage formation

Endochondral bone development begins with the formation of a cartilage template. Chondrocytes within this template undergo a progressive program of maturation from proliferative to prehypertrophic chondrocytes to hypertrophic chondrocytes. The progression of cells through these steps of differentiation must be carefully controlled to ensure coordinated growth. Because the Delta/Notch signaling system is known to regulate cell fate choices, we sought to determine if these molecules might be involved in the progressive cell fate decisions that chondocytes undergo. Here we demonstrate in the chick that Delta/Notch signaling negatively regulates progression from the prehypertrophic to hypertrophic state of differentiation. Delta-1 is expressed specifically in the hypertrophic chondrocytes while Notch-2 is expressed in chondrocytes at all stages. Misexpression of Delta-1 using a replication-competent retrovirus blocks chondrocyte maturation. Prehypertrophic cells form normally but do not undergo differentiation to hypertrophic cells, resulting in shortened skeletal elements that lack ossification. We conclude that Delta-1 acts during chondrogenesis to inhibit the transition from prehypertrophic chondrocytes to hypertrophic chondrocytes, thus defining a novel mechanism for the regulation of the chondrocyte maturation program. In addition, these results reveal a new role for Delta/Notch signaling in regulating the progression to a terminally differentiated state.     

POCl3 diffusion for industrial Si solar cell emitter formation

POCl₃ diffusion is currently the de facto standard method for industrial n-type emitter fabrication. In this study, we present the impact of the following processing parameters on emitter formation and electrical performance: deposition gas flow ratio, drive-in temperature and duration, drive-in O₂ flow rate, and thermal oxidation temperature. By showing their influence on the emitter doping profile and recombination activity, we provide an overall strategy for improving industrial POCl₃ tube diffused emitters.     

Dynamic light scattering from polymer gels: spring-rotor model

Dynamic light scattering behaviour in the form of periodic oscillating correlation functions has been found from measurements on both physically and chemically crosslinked hydrogels. The former were aqueous methyl cellulose at the thermal gelation temperature and the latter were poly(N,N-dimethylacrylamide-co-methyl methacrylate-co-ethylene dimethacrylate) at swelling equilibrium in water. In order to explain the oscillating behaviour, a spring-rotor model is proposed in which the molecular motions inside a gel are modelled as vibrations of springs having various frequencies. These frequencies are equivalent to the rotational frequencies when the free rotor theory was used to process the oscillating correlation functions by a modified CONTIN computer program. The validity of this model is supported by experimental data in three ways. (1) The model fits the experimental data almost perfectly. (2) The main peak positions of the obtained frequency distribution are not affected by the scattering angle. (3) For the chemically crosslinked hydrogels differing only in content of ethylene dimethacrylate, the mean vibrational frequency of the gel spring is higher the shorter the spring, i.e. the lower the average molecular mass between crosslinks. © 1998 SCI     

The impact of workplace change on occupational health and safety: A study of four manufacturing plants

This article examines the relationship between changes in the management of work organization and occupational health and safety (OHS) in four manufacturing companies in Australia between 1988 and 1995. The period is one in which the Australian manufacturing sector faced considerable change as it grappled with the pressures of global competition. Government policies as well as industry initiatives created an environment favoring the development of a “new workplace culture” in manufacturing enterprises. The greater levels of employee involvement and responsibility in many manufacturing workplaces suggested that the employees would gain a greater direct control over their work environment and the hazards inherent in that environment. The study suggests that three factors appear to mediate the translation of management practices from work organization and involvement over production matters to OHS. These are: changes in the management of people, including employee involvement and team working practices; the role and influence of OHS experts in shaping the priorities and methods used to manage OHS; and the degree and extent of union involvement in decisions within the organization. © 1998 John Wiley & Sons, Inc.     

A pseudo first order rate model for the adsorption of an organic adsorbate in aqueous solution

Five low rank, coal‐based adsorbents, i.e. coal, grus, two chars, and an activated carbon were used to adsorb a low molecular weight organic compound from aqueous solution. The rates of adsorption were found to conform to pseudo first order kinetics with good correlation (r² greater than 0.996). This kinetic model was used to calculate pseudo first order rate constants (k₁^′ min ⁻¹) and relative rate constants (rate constant/unit mass of adsorbent, k₁^″ min⁻¹ g⁻¹) for the adsorption process. Rate properties have been explained in terms of both a diffusion and chemically controlled rate determining step. Rate constants for the five adsorbents vary as expected on the basis of their physical properties, that is slowest for grus (compressed coal) and fastest for the activated carbon. © 1999 Society of Chemical Industry     

Determination of the Bingham parameters of an electrorheological fluid in an axial flow concentric-cylinder rheometer

Electrorheological (ER) fluids are fluids that undergo changes in their rheological properties in the presence of an applied electrical field. The change in the flow properties with an applied electrical field has led to their being investigated for use as ‘smart’ lubricants. The Bingham model is currently used to describe the behaviour of these fluids. In this work, the Bingham model parameters of a commercially available ER fluid are obtained using an axial flow concentric-cylinder rheometer. Two methods are used to determine these parameters. One is the Weissenberg (—Rabinowitsch) method applied to thin annular slits, to obtain corrected stress—strain rate information. The other method involves directly fitting the velocity—pressure curve data to the axial flow rate equation of a Bingham fluid through concentric cylinders. The results obtained by these two methods differ by as much as 49.4 and 63.5% for the yield stress and viscosity, respectively. It is observed for this ER fluid that the yield stress increases according to a power law relationship with the applied electrical field. The viscosity appears to decrease linearly with an increase in the applied electrical field.     

The determination of monomers and oligomers from polyester-based can coatings into foodstuffs over extended storage periods

The polymeric coating used in metal packaging such as cans for foods and beverages may contain residual amounts of monomers used in the production of the coating, as well as unreacted linear and cyclic oligomers. Traditionally, although designed for use with plastic food contact materials, food simulants have been used to determine the migration of monomers from coatings into foodstuffs. More recently, food simulants have also been used to determine oligomeric species migrating from can coatings. In the work reported here, the migration of both monomers and oligomers from polyester-based can coatings into food simulants and foodstuffs, some of which were towards the end of their shelf-life, is compared. The concentrations of monomers and selected oligomers in canned foods at the end of their shelf life were found to be significantly lower than those in food simulants, which in turn was lower than those in the extraction solvent acetonitrile.     

High-resolution ab initio three-dimensional x-ray diffraction microscopy

Coherent x-ray diffraction microscopy is a method of imaging nonperiodic isolated objects at resolutions limited, in principle, by only the wavelength and largest scattering angles recorded. We demonstrate x-ray diffraction imaging with high resolution in all three dimensions, as determined by a quantitative analysis of the reconstructed volume images. These images are retrieved from the three-dimensional diffraction data using no a priori knowledge about the shape or composition of the object, which has never before been demonstrated on a nonperiodic object. We also construct two-dimensional images of thick objects with greatly increased depth of focus (without loss of transverse spatial resolution). These methods can be used to image biological and materials science samples at high resolution with x-ray undulator radiation and establishes the techniques to be used in atomic-resolution ultrafast imaging at x-ray free-electron laser sources.     

The turbulent burning velocity of iso-octane/air mixtures

Turbulent burning velocities of iso-octane air mixtures have been measured for expanding flame kernels within a turbulent combustion bomb. High speed schlieren images were used to derive turbulent burning velocity. Turbulent velocity measurements were made at u′ = 0.5, 1.0, 2.0, 4.0, 6.0 m/s, equivalence ratios of 0.8, 1.0, 1.2, 1.4 and pressures of P = 0.1, 0.5, 1.0 MPa. The turbulent burning velocity was found to increase with time and radius from ignition, this was attributed to turbulent flame development. The turbulent burning velocity increased with increasing rms turbulent velocity, and with pressure; although differences were found in the magnitude of this increase for different turbulent velocities. Generally, raising the equivalence ratio resulted in enhanced turbulent burning velocity, excepting measurements made at the lowest turbulent velocity. The results obtained in this study have been compared with those evaluated for a number turbulent burning velocity correlations and the differences are discussed.     

The role of nanoscale architecture in supramolecular templating of biomimetic hydroxyapatite mineralization

Understanding and mimicking the hierarchical structure of mineralized tissue is a challenge in the field of biomineralization and is important for the development of scaffolds to guide bone regeneration. Bone is a remarkable tissue with an organic matrix comprised of aligned collagen bundles embedded with nanometer-sized inorganic hydroxyapatite (HAP) crystals that exhibit orientation on the macroscale. Hybrid organic-inorganic structures mimic the composition of mineralized tissue for functional bone scaffolds, but the relationship between morphology of the organic matrix and orientation of mineral is poorly understood. Herein the mineralization of supramolecular peptide amphiphile templates, that are designed to vary in nanoscale morphology by altering the amino acid sequence, is reported. It is found that 1D cylindrical nanostructures direct the growth of oriented HAP crystals, while flatter nanostructures fail to guide the orientation found in biological systems. The geometric constraints associated with the morphology of the nanostructures may effectively control HAP nucleation and growth. Additionally, the mineralization of macroscopically aligned bundles of the nanoscale assemblies to create hierarchically ordered scaffolds is explored. Again, it is found that only aligned gel templates of cylindrical nanostructures lead to hierarchical control over hydroxyapatite orientation across multiple length scales as found in bone.