Etude de l'effet du brassage électromagnétique sur les microstructures d'alliages cuivreux

In order to eliminate internal and surface defects, which appear in the ingots during continuous casting of metallic alloys, homogeneous and fine structures are often required. Therefore, when the adjunction of inoculant substances is not possible, the electromagnetic stirring (EMS) process is used during solidification. It consists to create convective mouvements in the liquid part of the casting, by the action of an electromagnetic field. A fine equiaxed grain structure can then be observed. The main goal of this research is to study the effect of the EMS process on grain structures for two industrial copper-base alloys : C97 (Cu-1%Ni-1%Pb-0.2%P) and BZ4 (Cu-4%Zn- 4%Sn-4%Pb). In particular, it included the determination of the optimal experimental parameters to obtain a grain refinement, the characterization of their effect on the solidification and the understanding of the physical mechanisms driving grain refinement. For that purpose, a Bridgman type furnace was modified in order to add an electromagnetic stirring device. Indeed, as the industrial continuous casting process is rigid and complex, the investigations were easier to carry out on the Bridgman installation, enabling us to define the influence of each experimental parameter : power of the induction, casting speed, coil position, temperature of the liquid and composition of the alloy. This experimental study was completed by the numerical simulation of the experimental conditions. The analysis of the structures, refined or not, showed that the dominant factors concerning the capacity of EMS to refine the structure, are the position of the inductor with respect to the liquidus, and the permeability of the mushy zone of the alloy. The more permeable the alloy is near the liquidus the more effective is the grain refinement. Concerning the position of the inductor, in-situ temperature measurements clearly revealed the local reheating of the liquid induced by convection. To correctly refine the low concentration alloy (C97), this local reheating must be brought on the position close to the dendrite position. During EMS-induced grain refinement, fragmentation of the dendrite arms by remelting and their survival in the melt are prevalent. Remelting can occur only if the "hot" liquid penetrates the mushy zone. Thus, the concept of permeability according to the model of Karman-Cozeny was used in simulation in order to characterize the penetration of the liquid in the mushy zone. From these results, a criterion of remelting, based on Flemings model of macrosegregation, was adapted and applied to our case. This criterion shows that remelting takes place if the velocity of the interdendritic liquid is lager than the speed of the isotherms. The velocity of the interdendritic liquid was calculated by numerical simulation for both alloys, under various experimental conditions. These results confirmed the importance to bring the inductor closer to the position of the liquidus to remelt dendrites, in particular in the case of the C97 alloy, which proves to be much more difficult to refine than the BZ4 alloy. Lastly, survival of the fragments was also studied. It depends on the casting conditions (casting speed and thermal gradient) and on the composition of the alloy. From the differences in composition of both alloys, it could be shown that the survival of dendrites fragments is improved during the solidification of the BZ4 alloy, compared with the C97 alloy

Final Thoughts

I’ve always loved trains; the sound of a locomotive’s air horn piercing the night is as calming to me as a glass of wine. Rail, in my opinion, is the only civilized way to travel, with none of the stress and acrimony that comes from driving or flying. The United States pioneered the art of train travel well over a century ago, and by the 1930s possessed the finest rail infrastructure on Earth—including a vast matrix of streetcars and “inter-urbans” that delivered you practically at your doorstep. Of course, the civility of rail travel was sacrificed after World War II for the holy motor car, which flattered our American individualist ego and— let’s face it—proved awfully convenient for getting around

Emergence of the American elm as a cultural and urban design element in nineteenth-century New England

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1999.Includes bibliographical references (leaves 214-228).This dissertation is a cultural history of the American elm. It explores the transformation of a native tree into a major icon of New England culture in the nineteenth century-both as a multi valanced symbol of New England life, and a defining element in the spatial design of its villages, towns and cities. Drawing from a wide range of source material-traveler's records, local histories, town and municipal records and contemporary newspaper accounts-the study traces the forces and events which made the elm a ubiquitous feature of the Yankee scene, and a core element in the identity and image of the region. The historical narrative begins with a description of the tree in the pre-European era, and explains how cultural disturbance by both native Americans and colonists amplified the elm's presence in the landscape. Subsequent chapters examine the tree first as a solitary or totemic artifact in the landscape, and then as a element which, following a region-wide "village improvement movement" in the 1840s, was planted in vast numbers in villages, towns and cities. The totemic elm endowed Yankee space with meaning, as a civic centerpiece, a relic of antiquity, or a monument to specific historical events or persons. Planted en masse as a street tree, elms changed the quality of that space itself, transforming the appearance of the common landscape, and forging one of the most powerful images of place in American history-the elm-tossed New England town. The study culminates by examining the symbolic and spatial significance of the tree in the urban context, and argues that city elms were perceived by nineteenth-century observers as a mechanism of synthesis between rus and urbe. Long before the Olmsted park, planting elms on city streets placed the elusive ideal of a "pastoral city" within reach. As Charles Dickens observed of New Haven in his American Notes (1842), city elms brought about "a kind of compromise between town and country; as if each had met the other half-way, and shaken hands upon it." In conclusion, the seminal influence of New England on American culture at large is considered, a factor which eventually made the elm a national icon, and "Elm Street" an American institution.by Thomas J. Campanella.Ph.D

An evolutionary approach to modelling the thermo-mechanical behaviour of unsaturated soils

A new data mining approach is presented for modelling of the stress-strain and volume change behaviour of unsaturated soils considering temperature effects. The proposed approach is based on the evolutionary polynomial regression (EPR), which unlike some other data mining techniques, generates a transparent and structured representation of the behaviour of systems directly from raw experimental (or field) data. The proposed methodology can operate on large quantities of data in order to capture nonlinear and complex relationships between contributing variables. The developed models allow the user to gain a clear insight into the behaviour of the system. Unsaturated triaxial test data from literature was used for development and verification of EPR models. The developed models were also used (in a coupled manner) to produce the entire stress path of triaxial tests. Comparison of the EPR model predictions with the experimental data revealed the robustness and capability of the proposed methodology in capturing and reproducing the constitutive thermo-mechanical behaviour of unsaturated soils. More importantly, the capability of the developed models in accurately generalising the predictions to unseen data cases was illustrated. The results of a sensitivity analysis showed that the models developed from data are able to capture and represent the physical aspects of the unsaturated soil behaviour accurately. The merits and advantages of the proposed methodology are also discussed

CXCL10 Can Inhibit Endothelial Cell Proliferation Independently of CXCR3

CXCL10 (or Interferon-inducible protein of 10 kDa, IP-10) is an interferon-inducible chemokine with potent chemotactic activity on activated effector T cells and other leukocytes expressing its high affinity G protein-coupled receptor CXCR3. CXCL10 is also active on other cell types, including endothelial cells and fibroblasts. The mechanisms through which CXCL10 mediates its effects on non-leukocytes is not fully understood. In this study, we focus on the anti-proliferative effect of CXCL10 on endothelial cells, and demonstrate that CXCL10 can inhibit endothelial cell proliferation in vitro independently of CXCR3. Four main findings support this conclusion. First, primary mouse endothelial cells isolated from CXCR3-deficient mice were inhibited by CXCL10 as efficiently as wildtype endothelial cells. We also note that the proposed alternative splice form CXCR3-B, which is thought to mediate CXCL10's angiostatic activity, does not exist in mice based on published mouse CXCR3 genomic sequences as an in-frame stop codon would terminate the proposed CXCR3-B splice variant in mice. Second, we demonstrate that human umbilical vein endothelial cells and human lung microvascular endothelial cells that were inhibited by CXL10 did not express CXCR3 by FACS analysis. Third, two different neutralizing CXCR3 antibodies did not inhibit the anti-proliferative effect of CXCL10. Finally, fourth, utilizing a panel of CXCL10 mutants, we show that the ability to inhibit endothelial cell proliferation correlates with CXCL10's glycosaminoglycan binding affinity and not with its CXCR3 binding and signaling. Thus, using a very defined system, we show that CXCL10 can inhibit endothelial cell proliferation through a CXCR3-independent mechanism

In vitro growth environment produces lipidomic and electron transport chain abnormalities in mitochondria from non-tumorigenic astrocytes and brain tumours

The mitochondrial lipidome influences ETC (electron transport chain) and cellular bioenergetic efficiency. Brain tumours are largely dependent on glycolysis for energy due to defects in mitochondria and oxidative phosphorylation. In the present study, we used shotgun lipidomics to compare the lipidome in highly purified mitochondria isolated from normal brain, from brain tumour tissue, from cultured tumour cells and from non-tumorigenic astrocytes. The tumours included the CT-2A astrocytoma and an EPEN (ependymoblastoma), both syngeneic with the C57BL/6J (B6) mouse strain. The mitochondrial lipidome in cultured CT-2A and EPEN tumour cells were compared with those in cultured astrocytes and in solid tumours grown in vivo. Major differences were found between normal tissue and tumour tissue and between in vivo and in vitro growth environments for the content or composition of ethanolamine glycerophospholipids, phosphatidylglycerol and cardiolipin. The mitochondrial lipid abnormalities in solid tumours and in cultured cells were associated with reductions in multiple ETC activities, especially Complex I. The in vitro growth environment produced lipid and ETC abnormalities in cultured non-tumorigenic astrocytes that were similar to those associated with tumorigenicity. It appears that the culture environment obscures the boundaries of the Crabtree and the Warburg effects. These results indicate that in vitro growth environments can produce abnormalities in mitochondrial lipids and ETC activities, thus contributing to a dependency on glycolysis for ATP production

Expression and Localization of Mitochondrial Ferritin mRNA in Alzheimer's Disease Cerebral Cortex

Mitochondrial ferritin (MtF) has been identified as a novel ferritin encoded by an intron-lacking gene with specific mitochondrial localization located on chromosome 5q23.1. MtF has been associated with neurodegenerative disorders such as Friedreich ataxia and restless leg syndrome. However, little information is available about MtF in Alzheimer's disease (AD). In this study, therefore, we investigated the expression and localization of MtF messenger RNA (mRNA) in the cerebral cortex of AD and control cases using real-time polymerase chain reaction (PCR) as well as in situ hybridization histochemistry. We also examined protein expression using western-blot assay. In addition, we used in vitro methods to further explore the effect of oxidative stress and β-amyloid peptide (Aβ) on MtF expression. To do this we examined MtF mRNA and protein expression changes in the human neuroblastoma cell line, IMR-32, after treatment with Aβ, H2O2, or both. The neuroprotective effect of MtF on oxidative stress induced by H2O2 was measured by MTT assay. The in situ hybridization studies revealed that MtF mRNA was detected mainly in neurons to a lesser degree in glial cells in the cerebral cortex. The staining intensity and the number of positive cells were increased in the cerebral cortex of AD patients. Real-time PCR and western-blot confirmed that MtF expression levels in the cerebral cortex were significantly higher in AD cases than that in control cases at both the mRNA and the protein level. Cell culture experiments demonstrated that the expression of both MtF mRNA and protein were increased by treatment with H2O2 or a combination of Aβ and H2O2, but not with Aβ alone. Finally, MtF expression showed a significant neuroprotective effect against H2O2-induced oxidative stress (p<0.05). The present study suggests that MtF is involved in the pathology of AD and may play a neuroprotective role against oxidative stress