Mathematical model of the movement of layers of metal during the rotary rolling of semifinished products made of hypereutectic silumins

A mathematical model has been constructed to describe the kinematics of the movement of metal on the surface of semifinished products made of hypereutectic silumin alloys as they undergo rotary rolling. The model is based on the dependence of the pitch of the helical lines of metal flow on the deformation ε of the product and the feed angle α. The pitch is minimal when ε = 50–55%, regardless of the feed angle α. The degree of deformation ε = 50–55% is optimum for ensuring that the unit number of cycles in which the semifinished product is loaded by the work rolls is such as to produce a fine-grained structure and maximize the ductility characteristics of hypereutectic silumins. __________ Translated from Metallurg, No. 6, pp. 57–59, June, 2006.     

Nucleation of solidification in liquid droplets

Analytical and numerical methods have been developed to analyze the solidification kinetics of a mass of liquid droplets dispersed in a fluid or solid matrix using classical nucleation theory. The resulting analytical expressions and numerical calculations can be compared directly with calorimetric measurements of the droplet solidification exotherms to obtain information about the nucleation mechanism. With increasing contact angle at the solid-liquid-matrix triple point, the solidification onset, peak, and end temperatures and exothermic peak height all decrease sharply and the droplet solidification exotherms become broader. Decreasing either the droplet radius or the number of potential catalytic nucleation sites produces a similar but smaller effect. Distributions in droplet radius, contact angle, and nucleation sites have no effect on the solidification peak temperature, but the droplet solidification exotherms become broader and more symmetric. The solidification onset temperature is independent of cooling rate in the calorimeter, but the solidification peak and end temperatures decrease and the exothermic peak height increases with increasing cooling rate. Predicted droplet solidification exotherms are in excellent agreement with detailed experimental measurements on 10-nm-radius Cd droplets embedded in a solid Al matrix. Analytical predictions give best-fit values of 43 deg and 430 for the contact angle and the number of potential catalytic nucleation sites per droplet, respectively; numerical predictions give best-fit values of 43 deg and 750 for the contact angle and the number of potential catalytic nucleation sites per droplet, respectively.     

Multiple intracellular signals coordinate structural dynamics in the sea urchin egg cortex at fertilization

Fertilization of the sea urchin egg is accompanied by a sequence of structural changes in the egg cortex that include exocytosis, endocytosis, and microvillar growth. This architectural reorganization is coordinated by two intracellular signals: a rapid, transient rise in cyto-solic free calcium and a slower, longer lasting increase in cytoplasmic pH. In this report we provide ultrastructural views of these events in quick-frozen eggs and discuss their relationship to the calcium and pH signals.     

Materials technology for aerospace applications

Modern helicopter design depends on the successful combination of materials to fulfil a very wide range of critical functions. In the past few years demands from the aerospace industry have caused considerable enhancement in the favourable properties of both polymer based materials and metals. These are discussed in connection with the progressive technical evolution of helicopters and other advanced technological products from the Westland Group.     

Modelling and analysis of 3-D arrangements of particles by point processes with examples of application to biological data obtained by confocal scanning light microscopy

Within the concept of point processes, a review is presented of quantities which can be used in studies of three-dimensional (3-D) aggregates of particles. Suitable characteristics and estimators are given for both unmarked and marked point processes. To demonstrate the feasibility of such quantitative approaches, an application in histology, dealing with 3-D arrangements of cell nuclei in rat liver, is described. Using a confocal scanning light microscope, 3-D images are recorded and image analysis used to obtain the coordinates of the centroid, together with the volume and DNA content, of each cell nucleus. Examples of results are given, using both unmarked and marked point processes. In the latter case, cell type, nuclear volume and ploidy group are suitable marks.     

Comparison of nutrient cycling in a surface-flow constructed wetland and in a facultative pond treating secondary effluent.

There is a growing interest in the possibilities offered by combinations of waste stabilisation ponds (WSP) and constructed wetlands (CW). The purpose of our study was to compare treatment performances and nutrient cycling in a surface-flow wetland (SFW) and in a WSP treating secondary effluent. In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of the wastewater treatment plant and their performance monitored while both were active under the same conditions. The SFW was planted with Phragmites australis and Eichhornia crassipes, while in the WSP development of algae was spontaneous. Performance efficiency was monitored by means of evaluation of physical and chemical parameters in water, by measurement of plant productivity and by analysis of N and P contents in biomass. The SFW with macrophytes proved more efficient in decreasing the suspended solids (64.6%), settleable solids (91.8%), organic N (59.3%), total N (38%), COD (67.2%) and BOD5 (72.1%) than the WSP. The WSP with algae was more efficient in treatment of ammonia nitrogen (48.9%) and ortho-phosphate (43.9%). The results of this study provide data that are of help in optimising combinations of SFW and WSP.     

Architecture and algorithms for tracking football players with multiple cameras

A system architecture and method for tracking people is presented for a sports application. The system input is video data from static cameras with overlapping fields-of-view at a football stadium. The output is the real-world, real-time positions of football players during a match. The system comprises two processing stages, operating on data from first a single camera and then multiple cameras. The organisation of processing is designed to achieve sufficient synchronisation between cameras, using a request-response pattern, invoked by the second stage multi-camera tracker. The single-view processing includes change detection against an adaptive background and image-plane tracking to improve the reliability of measurements of occluded players. The multiview process uses Kalman trackers to model the player position and velocity, to which the multiple measurements input from the single-view stage are associated. Results are demonstrated on real data.     

Crystal growth of selected II–VI semiconducting alloys by directional solidification: Part I Ground-based experiments

A series of Hg_0.84Zn_0.16 Te crystal ingots have been grown from pseudobinary melts by the Bridgmam–Stockbarger type directional solidification using a Marshall Space Flight Center/Space Science Laboratory heat-pipe furnace and the ground control experiment laboratory furnace of the crystal growth furnace which was flown on the first United States Microgravity Mission. A number of translation rates and a series of hot- and cold-zone temperatures were employed to assess the influence of growth parameters on the crystal properties for the purpose of optimizing the in-flight growth conditions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Artefactual cleavage of E coli H-NS by OmpT

In the bacterium Escherichia coli, H-NS-(H1, H1a) is a heat-stable protein with a molecular mass of 15.5 kDa involved in nucleoid organisation and gene regulation linked to certain signal transduction pathways. We have shown that, following addition of preparations of everted inner membrane vesicles, heat-stable cleavage products of approximately 10 kDa of H-NS are formed in vitro from newly synthesised, radio-labelled H-NS and from purified H-NS. The 15.5 kDa protein and its cleavage products were also recovered from a minicell system. These results raised the possibility that cleavage of H-NS is physiologically significant. However, the cleavage of H-NS observed appears to occur during cell breakage and to depend on the method of protein extraction and the presence of the outer membrane protease, OmpT. Nevertheless, the results indicate that H-NS may contain at least two separate domains with cleavage occurring between these domains at a preferred OmpT site. Failure to take account of H-NS cleavage in sample preparation and analysis can lead to serious underestimation of H-NS levels.