Segregation band formation in Al-Si die castings

Banded defects are often found in high-pressure die castings. These bands can contain segregation, porosity, and/or tears, and changing casting conditions and alloy are known to change the position and make-up of the bands. Due to the complex, dynamic nature of the high-pressure die-casting (HPDC) process, it is very difficult to study the effect of individual parameters on band formation. In the work presented here, bands of segregation similar to those found in cold-chamber HPDC aluminum alloys were found in laboratory gravity die castings. Samples were cast with a range of fraction solids from 0 to 0.3 and the effect of die temperature and external solid fraction on segregation bands was investigated. The results are considered with reference to the theological properties of the filling semisolid metal and a formation mechanism for bands is proposed by considering flow past a solidifying immobile wall layer.

Capsule and fimbria interaction in Klebsiella pneumoniae

The capsular polysaccharide and type I fimbriae are two of the major surface-located virulence properties associated with the pathogenesis of Klebsiella pneumoniae. The capsule is an elaborate polysaccharide matrix that encases the entire cell surface and provides resistance against many host defense mechanisms. In contrast, type 1 fimbriae are thin adhesive thread-like surface organelles that can extend beyond the capsular matrix and mediate D-mannose-sensitive adhesion to host epithelial cells. These fimbriae are archetypical and consist of a major building block protein (FimA) that comprises the bulk of the organelle and a tip-located adhesin (FimH). It is assumed that the extended major-subunit protein structure permits the FimH adhesin to function independently of the presence of a capsule. In this study, we have employed a defined set of K. pneumoniae capsulated and noncapsulated strains to show that the function of type I fimbriae is actually impeded by the concomitant expression of a polysaccharide capsule. Capsule expression had significant effects on two parameters commonly used to define FimH function, namely, yeast cell agglutination and biofilm formation. Our data suggest that this effect is not due to transcriptional/translational changes in fimbrial gene/protein expression but rather the result of direct physical interference. This was further demonstrated by the fact that we could restore fimbrial function by inhibiting capsule synthesis. It remains to be determined whether the expression of these very different surface components occurs simply via random events of phase variation or in a coordinated manner in response to specific environmental cues.

Control of ordered structure and morphology of large-pore periodic mesoporous organosilicas by inorganic salt

Highly ordered rodlike periodic mesoporous organosilicas (PMO) were successfully synthesized using 1.2-bis(trimethoxysilyl)ethane as an precursor and triblock copolymer P123 as a template at low acid concentration and in the presence of inorganic salts (KCl). The role of acid and salt as well as the effects of synthesis temperature and reactant mole ratio in the control of morphology and the formation of ordered mesostructure was systematically examined. It was found that the addition of inorganic salt can dramatically expand the range of the synthesis parameters to produce highly ordered PMO structure and improve the quality of PMO materials. The morphology of PMOs was significantly dependent on the induction time for precipitation. The uniform PMO rods can only be synthesized in a narrow range of acid and salt concentrations. The results also show that the optimized salt concentration (I M) and low acidity (0.167 M) were beneficial to the formation of not only highly ordered mesostructure but also rodlike morphology. Increasing acidity resulted in fast hydrolysis reaction and short rod or plate-like particles. Highly ordered rod can also be prepared at low temperature (35 degrees C) with high salt amount (1.5 M) or high temperature (45 degrees C) with low salt amount (0.5 M). Optimum reactant molar composition at 40 degrees C is 0.035P123:8KCl:1.34HCI:444H(2)O:1.0bis(trimethoxysilyl)ethane. Lower or higher SiO2/PI23 ratio led to the formation of uniform meso-macropores or pore-blocking effect. (c) 2005 Elsevier Inc. All rights reserved.

Long wave generation by the shoaling and breaking of transient wave groups on a beach

This paper presents new laboratory data on the generation of long waves by the shoaling and breaking of transient-focused short-wave groups. Direct offshore radiation of long waves from the breakpoint is shown experimentally for the first time. High spatial resolution enables identification of the relationship between the spatial gradients of the short-wave envelope and the long-wave surface. This relationship is consistent with radiation stress theory even well inside the surf zone and appears as a result of the strong nonlinear forcing associated with the transient group. In shallow water, the change in depth across the group leads to asymmetry in the forcing which generates significant dynamic setup in front of the group during shoaling. Strong amplification of the incident dynamic setup occurs after short-wave breaking. The data show the radiation of a transient long wave dominated by a pulse of positive elevation, preceded and followed by weaker trailing waves with negative elevation. The instantaneous cross-shore structure of the long wave shows the mechanics of the reflection process and the formation of a transient node in the inner surf zone. The wave run-up and relative amplitude of the radiated and incident long waves suggests significant modification of the incident bound wave in the inner surf zone and, the dominance of long waves generated by the breaking process. It is proposed that these conditions occur when the primary short waves and bound wave are not shallow water waves at the breakpoint. A simple criterion is given to determine these conditions, which generally occur for the important case of storm waves.

Structure and activity in assessing antioxidant activity in vitro and in vivo:a critical appraisal illustrated with the flavonoids

Structure–activity relationships are indispensable to identify the most optimal antioxidants. The advantages of in vitro over in vivo experiments for obtaining these relationships are, that the structure is better defined in vitro, since less metabolism takes place. It is also the case that the concentration, a parameter that is directly linked to activity, is more accurately controlled. Moreover, the reactions that occur in vivo, including feed-back mechanisms, are often too multi-faceted and diverse to be compensated for during the assessment of a single structure–activity relationship. Pitfalls of in vitro antioxidant research include: (i) by definition, antioxidants are not stable and substantial amounts of oxidation products are formed and (ii) during the scavenging of reactive species, reaction products of the antioxidants accumulate. Another problem is that the maintenance of a defined concentration of antioxidants is subject to processes such as oxidation and the formation of reaction products during the actual antioxidant reaction, as well as the compartmentalization of the antioxidant and the reactive species in the in vitro test system. So determinations of in vitro structure-activity relationships are subject to many competing variables and they should always be evaluated critically. (c) 2005 Published by Elsevier B.V.

The spatial patterns of beta-amyloid (Abeta) deposits and neurofibrillary tangles (NFT) in late-onset sporadic Alzheimer's disease

The spatial patterns of beta-amyloid (Abeta) deposits and neurofibrillary tangles (NFT) were studied in areas of the cerebral cortex in 16 patients with the late-onset, sporadic form of Alzheimer’s disease (AD). Diffuse, primitive, and classic Abeta deposits and NFT were aggregated into clusters; the clusters being regularly distributed parallel to the pia mater in many areas. In a significant proportion of regions, the sizes of the regularly distributed clusters approximated to those of the cells of origin of the cortico-cortical projections. The diffuse and primitive Abeta deposits exhibited a similar range of spatial patterns but the classic Abeta deposits occurred less frequently in large clusters >6400microm. In addition, the NFT often occurred in larger regularly distributed clusters than the Abeta deposits. The location, size, and distribution of the clusters of Abeta deposits and NFT supports the hypothesis that AD is a 'disconnection syndrome' in which degeneration of specific cortico-cortical and cortico-hippocampal pathways results in synaptic disconnection and the formation of clusters of NFT and Abeta deposits.

The influence of nutrient supply and cell density on the growth and survival of intervertebral disc cells in 3D culture

The adult human intervertebral disc (IVD) is normally avascular. Changes to the extracellular matrix in degenerative disc disease may promote vascularisation and subsequently alter cell nutrition and disc homeostasis. This study examines the influence of cell density and the presence of glucose and serum on the proliferation and survival of IVD cells in 3D culture. Bovine nucleus pulposus (NP) cells were seeded at a range of cell densities (1.25 × 10(5)-10(6) cells/mL) and cultured in alginate beads under standard culture conditions (with 3.15 g/L glucose and 10 % serum), or without glucose and/or 20% serum. Cell proliferation, apoptosis and cell senescence were examined after 8 days in culture. Under standard culture conditions, NP cell proliferation and cluster formation was inversely related to cell seeding density, whilst the number of apoptotic cells and enucleated "ghost" cells was positively correlated to cell seeding density. Increasing serum levels from 10% to 20% was associated with increased cluster size and also an increased prevalence of apoptotic cells within clusters. Omitting glucose produced even larger clusters and also more apoptotic and senescent cells. These studies demonstrate that NP cell growth and survival are influenced both by cell density and the availability of serum or nutrients, such as glucose. The observation of clustered, senescent, apoptotic or "ghost" cells in vitro suggests that environmental factors may influence the formation of these phenotypes that have been previously reported in vivo. Hence this study has implications for both our understanding of degenerative disc disease and also cell-based therapy using cells cultured in vitro.

Industry evolution and cross-sectoral skill transfers:a comparative analysis of the video game industry in Japan, the United States, and the United Kingdom

In this paper we explore the interrelationship between technological progress and the formation of industry-specific skills by analysing the evolution of the video-game industry in three countries: Japan, the United States, and the United Kingdom. We argue that the cross-sectoral transfer of skills occurs differently depending on national contexts, such as the social legitimacy and strength of preexisting industries, the socioeconomic status of entrepreneurs or pioneer firms in an emerging industry, and the sociocultural cohesiveness between the preexisting and emerging industries. Each country draws on a different set of creative resources, which results in a unique trajectory. Whereas Japan's video-game industry emerged out of corporate sponsorships in arcades, toys, and consumer electronics industries and drew skills from the comic book and animated-film sectors, the video-game industry in the United States evolved from arcades and personal computers. In the United Kingdom the video-game industry developed bottom-up, through a process of skills formation in the youth culture of 'bedroom coders' that nurtured self-taught programmers in their teens throughout the country.

The influence of serum, glucose and oxygen on intervertebral disc cell growth in vitro:implications for degenerative disc disease

The avascular nature of the human intervertebral disc (IVD) is thought to play a major role in disc pathophysiology by limiting nutrient supply to resident IVD cells. In the human IVD, the central IVD cells at maturity are normally chondrocytic in phenotype. However, abnormal cell phenotypes have been associated with degenerative disc diseases, including cell proliferation and cluster formation, cell death, stellate morphologies, and cell senescence. Therefore, we have examined the relative influence of possible blood-borne factors on the growth characteristics of IVD cells in vitro.

S100A4 downregulates filopodia formation through increased dynamic instability

Cell migration requires the initial formation of cell protrusions, lamellipodia and/or filopodia, the attachment of the leading lamella to extracellular cues and the formation and efficient recycling of focal contacts at the leading edge. The small calcium binding EF-hand protein S100A4 has been shown to promote cell motility but the direct molecular mechanisms responsible remain to be elucidated. In this work, we provide new evidences indicating that elevated levels of S100A4 affect the stability of filopodia and prevent the maturation of focal complexes. Increasing the levels of S100A4 in a rat mammary benign tumor derived cell line results in acquired cellular migration on the wound healing scratch assay. At the cellular levels, we found that high levels of S100A4 induce the formation of many nascent filopodia, but that only a very small and limited number of those can stably adhere and mature, as opposed to control cells, which generate fewer protrusions but are able to maintain these into more mature projections. This observation was paralleled by the fact that S100A4 overexpressing cells were unable to establish stable focal adhesions. Using different truncated forms of the S100A4 proteins that are unable to bind to myosin IIA, our data suggests that this newly identified functions of S100A4 is myosin-dependent, providing new understanding on the regulatory functions of S100A4 on cellular migration.

The retromer coat complex coordinates endosomal sorting and dynein-mediated transport, with carrier recognition by the trans-Golgi network

Early endosome-to-trans-Golgi network (TGN) transport is organized by the retromer complex. Consisting of cargo-selective and membrane-bound subcomplexes, retromer coordinates sorting with membrane deformation and carrier formation. Here, we describe four mammalian retromers whose membrane-bound subcomplexes contain specific combinations of the sorting nexins (SNX), SNX1, SNX2, SNX5, and SNX6. We establish that retromer requires a dynamic spatial organization of the endosomal network, which is regulated through association of SNX5/SNX6 with the p150(glued) component of dynactin, an activator of the minus-end directed microtubule motor dynein; an association further defined through genetic studies in C. elegans. Finally, we also establish that the spatial organization of the retromer pathway is mediated through the association of SNX1 with the proposed TGN-localized tether Rab6-interacting protein-1. These interactions describe fundamental steps in retromer-mediated transport and establish that the spatial organization of the retromer network is a critical element required for efficient retromer-mediated sorting.

Effect of osmotic and matrix potential on Saprolegnia diclina and S. ferax

Growth of biomass and sporulation of pathogenic and non-pathogenic Saprolegnia species was markedly decreased at reduced water potentials. Oogonium and zoosporangium formation were more sensitive to reduced osmotic and matrix potentials than growth in biomass. Although little difference was observed between the effects of matrix and osmotic potentials, the Saprolegnia species investigated responded differently to those solutes utilized in control of osmotic potential. Biomas, oogonium and zoosporangium formation were greater in the presence of reduced osmotic potentials mediated by mannitol than equivalent potentials mediated by potassium chloride. Endogenous potassium levels varied little with reduced matrix or osmotic potentials. Conversly, mannitol content of colonies exposed to reduced osmotic potentials mediated by mannitol initailly increased while endogenous amino acid levels were observed to rise in response to moderately reduced water potentials. Sensitivity of Saprolegnia species to reduced potantials and effects on substrate colonization are discussed in the light of these observations.

Study on the pyrolytic behaviour of xylan-based hemicellulose using TG-FTIR and Py-GC-FTIR

Two sets of experiments, categorized as TG–FTIR and Py–GC–FTIR, are employed to investigate the mechanism of the hemicellulose pyrolysis and the formation of main gaseous and bio-oil products. The “sharp mass loss stage” and the corresponding evolution of the volatile products are examined by the TG–FTIR graphs at the heating rate of 3–80 K/min. A pyrolysis unit, composed of fluidized bed reactor, carbon filter, vapour condensing system and gas storage, is employed to investigate the products of the hemicellulose pyrolysis under different temperatures (400–690 °C) at the feeding flow rate of 600 l/h. The effects of temperature on the condensable products are examined thoroughly. The possible routes for the formation of the products are systematically proposed from the primary decomposition of the three types of unit (xylan, O-acetylxylan and 4-O-methylglucuronic acid) and the secondary reactions of the fragments. It is found that the formation of CO is enhanced with elevated temperature, while slight change is observed for the yield of CO2 which is the predominant products in the gaseous mixture.

Studies of the metabolism and the toxicity of N-Methylformamide and related amides

The hepatotoxicity of the industrial solvent and investigational anti-tumour agent N-methylformamide (NMF, HOCNHCH3) and several structural analogues was assessed in mice. NMF and its ethyl analogue (NEF) were equipotent hepatotoxins causing extensive centrilobular necrosis and damage to the gall bladder. Pretreatment of mice with SKF525A did not influence the toxicity of these N-alkylformamides. Replacement of the formyl hydrogen of NMF with deuterium or methyl significantly reduced its hepatotoxicity. An in vitro model for the study of the toxicity and metabolism of N-alkylformamides was developed using isolated mouse hepatocytes. The cytotoxicity of NMF in vitro was concentration-dependent with maximal toxicity being achieved at concentrations of 5mM or above. The cytotoxic potential of related amides correlated well with their in vivo hepatotoxic potential. Pretreatment of mice with buthionine sulphoximine (BSO), which depleted hepatocytic levels of glutathione to 15% of control values, exacerbated the cytotoxicity of NMF towards the hepatocytes. NMF (1mM or above), incubated with isolated mouse hepatocytes, depleted intracellular glutathione levels to 26% of control values within 4h. Depletion of glutathione was quantitatively matched by the formation of a carbamoylating metabolite. Metabolism was dependent on the concentration of NMF and was drastically reduced in incubations of hepatocytes isolated from mice pretreated with BSO. The carbamoylating metabolite, S-(N-methylcarbamoyl)-glutathione (SMG), was identified in vitro using FAB-MS. The generation of SMG was subject to a large primary H/D kinetic isotope effect when the formyl hydrogen was replaced with deuterium. Likewise, glutathione depletion and metabolite formation were reduced or abolished by the deuteration or methylation of the formyl moiety of NMF. NEF, like NMF, depleted hepatocytic glutathione levels and was metabolised to a carbamoylating metabolite. Radioactivity derived from 14C-NMF and 14C-NEF, labelled in the alkyl moieties, was found to be irreversibly associated with microsomal protein on incubation in vitro. Binding was dependent on the presence of NADPH and was mostly abolished in the presence of reduced glutathione. SKF525A failed to influence the binding.

Palaeozoic volcanogenic mineral deposits at Parys Mountain, Avoca, and S.E. Canada: a comparative study. Available in 2 volumes.

The sulphide mineralisation at Avoca and Parys Mountain is intimately related to volcanism and is of volcanogenic sedimentary type. The associated volcanics are predominantly pyroclastics of rhyodacitic composition and of Upper Ordovician age. They were erupted from discrete small volcanic centres, products of single local volcanic events, whose spatial distribution was related to fractures in the sialic basement of the paratectonic Caledonides of the British Isles. These fractures resulted in linear controls on volcanic, plutonic and tectonic features; they are the result of predominantly strikeslip stresses generated in this part of the European plate during closure of the Iapetus ocean. The mineralisation, predominantly pyritic, consists of a siliceous footwall zone containing bedded and cross-cutting sulphides and an overlying non-siliceous zone of bedded sulphides which may show vertical zoning of metal ratios. The sulphides are associated with chert and iron formation and have been affected by slumping. Mineralisation developed near the vents during intense fumarolic activity accompanying strong volcanism; at Parys Mountain, fumarolic activity commenced prior to, and continued after, the rnain volcanic event. Comparison with similar deposits in Newfoundland and at Bathurst, in the Canadian Appalachians, shows that mineralisation can be associated with any discrete pulse of acid magmatism in shallow subaqueous conditions. Local features of the sulphides and associated sediments are similar, although in more distal deposits (with respect to a volcanic centre) footwall alteration and mineralisation are less well developed. The nature of the basement and the presence or absence of earlier volcanics are not critical, although establishment of a local tensional regime at the time of ore formation may be important. The volcanics hosting mineralisation are rhyodacitic pyroclastics, generally related to a small centre and representing a single episode of volcanism.