bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of base metal microstructure on microstructural development in aluminium based alloy friction stir welds
Authors: Attallah M. M. , Davis C. L. , Strangwood M.
Published: June 2007

The formation of ‘onion rings’ during friction stir welding of many aluminium based alloys has previously been related to the process parameters (forward and rotational tool motion). The ‘onion rings’ have also been observed to contain fine and coarse grain bands and particle rich and particle poor bands. However, the influence of variations in the base metal microstructure on the presence of the ‘onion rings’ has not been investigated and is the subject of this paper. 2xxx and 5xxx sheet materials in various tempers prepared by both direct chill and continuous casting have been characterised through thickness using optical and electron microscopy. Stereological studies of the intermetallic particle distributions in the base metal and the welds were carried out. The relationship between the banding of constituent particles (e.g. Alx(Fe, Mn)ySiz and MgxSi in AA5xxx and the Al2CuMg or Al2Cu in AA2xxx) along the rolling direction and the formation of the ‘onion rings’ structure and the banded grain structure was investigated. Within the range of welding parameters investigated, it was found that base materials with clear banding of the intermetallic particles showed a defined ‘onion rings’ structure with a banded grain and particle structure, whereas similar area fractions of intermetallic particles randomly distributed in the base metal did not give clear ‘onion rings’ on friction stir welding. The intermetallic particle distribution had a greater effect on the ‘onion ring’ formation than variations in the processing parameters.
Effect of process parameter on mechanical properties of friction stir welded tailored blanks from aluminium alloy 6181-T4
Authors: Sheikhi S. , dos Santos J. F.
Published: June 2007

Tailor welded blanks (TWBs) are produced by joining at least two sheets of dissimilar gauge and/or properties to achieve a lighter blank of desired stiffness and strength. In this way, the properties of the blank may be tailored to meet the design requirements of a panel. As in steel structures, cost and weight can be saved when using the TWB concept for aluminium. However, use of aluminium is a concern in the automotive industry because of well documented weldability and reproducibility problems, since relatively minor changes in welding parameters may affect the quality of the weld. Friction stir welding offers an attractive alternative to conventional fusion welding methods because of the excellent properties (particularly ductility), reproducibility, robustness and surface finish obtained. However, the working envelope for friction stir welded tailored blanks has yet to be fully explored. In the present study TWBs of the alloy 6181-T4 in a thickness combination 1 to 2 mm have been produced. The influence of welding parameters and welding tools on the weld quality and mechanical properties has been determined. Satisfactory surface finish with no detrimental effects to the mechanical properties has been observed. Weld efficiencies >90% have been consistently achieved.
Model for predicting heat generation and temperature in friction stir welding from the material properties
Authors: Colegrove P. A. , Shercliff H. R. , Zettler R.
Published: June 2007

This paper describes a simple numerical model for predicting the heat generation in friction stir welding (FSW) from the material hot deformation and thermal properties, the process parameters, and the tool and plate dimensions. The model idealises the deformation zone as a two-dimensional axisymmetric problem, but allowance is made for the effect of translation by averaging the three-dimensional temperature distribution around the tool in the real weld. The model successfully predicts the weld temperature field and has been applied with minimal recalibration to aerospace aluminium alloys 2024, 7449 and 6013, which span a wide range of strength. The conditions under the tool are presented as novel maps of flow stress against temperature and strain rate, giving insight into the relationship between material properties and optimum welding conditions. This highlights the need in FSW for experimental high strain rate tests close to the solidus temperature. The model is used to illustrate the optimisation of process conditions such as rotation speed in a given alloy and to demonstrate the sensitivity to key parameters such as contact radius under the shoulder, and the choice of stick or slip conditions. The aim of the model is to provide a predictive capability for FSW temperature fields directly from the material properties and weld conditions, without recourse to complex computational fluid dynamics (CFD) software. This will enable simpler integration with models for prediction of, for example, the weld microstructure and properties.
In situ neutron diffraction measurements of temperature and stresses during friction stir welding of 6061-T6 aluminium alloy
Authors: Woo W. , Feng Z. , Wang X.-L. , Brown D. W. , Clausen B. , An K. , Choo H. , Hubbard C. R. , David S. A.
Published: June 2007

The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the lattice spacing changes measured by neutron diffraction. The deep penetration capability of neutrons made it possible for the first time to obtain the temperature and thermal stresses inside a friction stir weld.
Friction stir welding of single crystal aluminium
Authors: Fonda R. W. , Wert J. A. , Reynolds A. P. , Tang W.
Published: June 2007

Friction stir welds were prepared in different orientations in an aluminium single crystal. The welds were quenched to preserve the microstructure surrounding the tool and then electron backscattered diffraction was used to reveal the generation of grain boundaries and the evolution of crystallographic texture around the tool in each weld. The extent of both dynamic recrystallisation and conventional recrystallisation varied considerably as a function of weld orientation. As the base plate begins to interact with the deformation field surrounding the tool, regions of the single crystal rotate to new crystal orientations, producing new grain boundaries in the process. These refined grains develop a {112}<110> texture closer to the tool. Large conventionally recrystallised grains sometimes form in the outer regions of the refined grain structure, but become ever more deformed as they approach the tool until they are indistinguishable from the surrounding material.
Process response parameter relationships in aluminium alloy friction stir welds
Authors: Long T. , Tang W. , Reynolds A. P.
Published: June 2007

In the present paper, an attempt has been made to link friction stir welding (FSW) process control and response variables. Substantial similarities among the relationships between torque, nugget grain size, x axis force and tool rotation rate have been elucidated for three different aluminium alloys. Comparison of the experimental work to results from process simulation indicates that in each case a temperature limit is reached above some critical value of tool rotation rate. A simple method of estimating the strain and strain rate in friction stir welds is presented. The flow stress during FSW is calculated from measured torque values and analysed with respect to aluminium alloy flow stresses measured in standard, high temperature torsion and tensile tests. Results indicate that perhaps either sticking friction conditions are not always applicable during FSW (on all or part of the tool) or that, above a critical tool rotation rate, intermittently lubricated contact is present due to local melting in the weld process zone.
Grain growth phenomena in friction stir welded 1100 Al during post-weld heat treatment
Authors: Sato Y. S. , Watanabe H. , Kokawa H.
Published: June 2007

Grain growth phenomena during post-weld heat treatment (PWHT) were examined in friction stir (FS) welded 1100 Al. The FS welds were produced at rotational speeds between 550 and 3600 rev min−1. The FS weld produced at the lower rotational speed had the finer equiaxed grain structure containing feature of the more deformed microstructure in the as welded state. It was found that the regions having more deformed microstructure in the as welded state experienced abnormal grain growth more preferentially in the stir zone during PWHT. The stir zone exposed to higher temperature during FSW was more stable at higher PWHT temperatures. When the weld was heated for a long time at a temperature that was high enough for the abnormal grain growth, the stir zone produced at the lower rotational speed had the smaller grown grains. The present study suggested that the abnormal grain growth of the stir zone during PWHT had similar features of primary recrystallisation.
Effect of rotational material flow on temperature distribution in friction stir welds
Authors: Simar A. , Pardoen T. , de Meester B.
Published: June 2007

A finite element pseudosteady state thermal model takes the mechanical power as input data while distributing the total power input between surface and volume heat sources. A simple model for the material flow around the tool has been developed in order to take heat convection into account based on the shape of the thermomechanically affected zone. The model is assessed for a large number of different welding parameters. Special attention is given to the type of contact at the tool/workpiece interface, i.e. sliding, sticking or both and at the workpiece backing plate interface. The rotational material flow creates asymmetry in the temperature distribution between the two sides of the weld.
Effect of initial temper on mechanical properties of friction stir welded Al-2024 alloy
Authors: Dixit V. , Mishra R. S. , Lederich R. J. , Talwar R.
Published: June 2007

The microstructural evolution and resultant mechanical properties during the friction stir welding (FSW) of precipitation strengthened aluminium alloys depend on initial temper as well as FSW process parameters. Al-2024 alloy under two different initial tempers, T3 and T8, was used in the present study. FSW bead-on-plate runs were performed at different values of process parameters (tool rotation rate and tool traverse speed). Microstructure and mechanical properties of the nugget region and heat affected zone (HAZ) were evaluated. Differential scanning calorimetry (DSC) revealed that in the nugget region, presence of Guinier–Preston–Bagaryatskii (GPB) zone results from the partial dissolution of Al2CuMg phase. The microstructure and tensile properties were found to be independent of the initial temper of the material in the nugget region. In the HAZ region, tensile properties increased at higher heat index values for T3 condition, and decreased monotonically for T8 condition.
Torque based weld power model for friction stir welding
Authors: Pew J. W. , Nelson T. W. , Sorensen C. D.
Published: June 2007

For decades, models have been developed for predicting the size of the weld nugget and heat affected zones in fusion welded structures. The basis for these models is the welding heat input, which is fairly well understood for most arc welding processes. However, this traditional approach is not as straightforward for friction stir welding (FSW). To date, no definitive relationship exists to quantify the heat input for FSW. An important step to establish a heat input model is to identify how FSW process parameters affect weld power. This study details the relationship between FSW process parameters and torque for three different aluminium alloys: 7075, 5083 and 2024. A quantitative weld power and heat input model is created from the torque input. The heat input model shows that decreasing the spindle speed or increasing the feedrate significantly decreases the heat input at low feedrates. At high feedrates, the feedrate and spindle speed have little effect on the heat input. Process parameter v. heat input trends are verified by measurements of the weld heat affected zones. In addition, this study outlines and validates the use of a variable spindle speed test for determining torque over a broad range of parameters. The variable spindle speed test provided significant improvements over previous methods of determining torque because this new method enabled the torque to be modelled over a broad range of parameters using a minimum number of welds. The methods described in this study can be easily used to develop torque models for different alloys and materials.
Modelling of residual stresses and property distributions in friction stir welds of aluminium alloy 6061-T6
Authors: Feng Z. , Wang X.-L. , David S. A. , Sklad P. S.
Published: June 2007

An integrated thermal–metallurgical–mechanical model is used to analyse and provide insights into the formation of the residual stress and the changes in microstructure and property of Al6061-T6 friction stir welds. The simulations were conducted by means of a three-dimensional finite element model that accounts for the phenomena of frictional heating, weld microstructure and strength changes due to dissolution and reprecipitation of the hardening precipitate particles, and the mechanical workpiece/tool contact during the friction stir welding (FSW) process. The model predictions were confirmed by experimental measurement data from previous studies. For the friction stir welds investigated, it was found that the residual stress distribution is strongly dependent on the welding process parameters and the degree of material softening caused by welding. The recovery of material strength from natural aging does not increase the residual stress in the weld. The failure of friction stir weld under tensile load is controlled by the combination of the reduction in strength and the residual stresses in the heat affected zone (HAZ).
Terminology in friction stir welding
Authors: Threadgill P. L.
Published: June 2007

In an attempt to avoid confusion and duplication, TWI proposed an initial basic terminology at an early stage of the development of friction stir welding (FSW). This terminology has since been revised and extended in consultation with licensees and other interested parties, to the form summarised in this paper. A definitive standard on FSW is being prepared by Working Group B1 of Commission III of the International Institute of Welding, and it is expected that this will be adopted as an ISO standard.
Distinct roles of integrins α6 and α4 in homing of fetal liver hematopoietic stem and progenitor cells
Authors: Qian Hong , Georges-Labouesse Elisabeth , Nyström Alexander , Domogatskaya Anna , Tryggvason Karl , Jacobsen Sten Eirik W. , Ekblom Marja
Published: June 2007

Homing of hematopoietic stem cells (HSCs) into the bone marrow (BM) is a prerequisite for establishment of hematopoiesis during development and following transplantation. However, the molecular interactions that control homing of HSCs, in particular, of fetal HSCs, are not well understood. Herein, we studied the role of the α6 and α4 integrin receptors for homing and engraftment of fetal liver (FL) HSCs and hematopoietic progenitor cells (HPCs) to adult BM by using integrin α6 gene–deleted mice and function-blocking antibodies. Both integrins were ubiquitously expressed in FL Lin−Sca-1+Kit+ (LSK) cells. Deletion of integrin α6 receptor or inhibition by a function-blocking antibody inhibited FL LSK cell adhesion to its extracellular ligands, laminins-411 and -511 in vitro, and significantly reduced homing of HPCs to BM. In contrast, the anti-integrin α6 antibody did not inhibit BM homing of HSCs. In agreement with this, integrin α6 gene–deleted FL HSCs did not display any homing or engraftment defect compared with wild-type littermates. In contrast, inhibition of integrin α4 receptor by a function-blocking antibody virtually abrogated homing of both FL HSCs and HPCs to BM, indicating distinct functions for integrin α6 and α4 receptors during homing of fetal HSCs and HPCs.
Cerebellar gene expression profiles of mouse models for Rett syndrome reveal novel MeCP2 targets
Authors: Jordan ChaRandle , Li Hong Hua , Kwan Helen C , Francke Uta
Published: June 2007

Background

MeCP2, methyl-CpG-binding protein 2, binds to methylated cytosines at CpG dinucleotides, as well as to unmethylated DNA, and affects chromatin condensation.MECP2mutations in females lead to Rett syndrome, a neurological disorder characterized by developmental stagnation and regression, loss of purposeful hand movements and speech, stereotypic hand movements, deceleration of brain growth, autonomic dysfunction and seizures. Most mutations occurde novoduring spermatogenesis. Located at Xq28,MECP2is subject to X inactivation, and affected females are mosaic. Rare hemizygous males suffer from a severe congenital encephalopathy.

Methods

To identify the pathways mis-regulated by MeCP2 deficiency, microarray-based global gene expression studies were carried out in cerebellum ofMecp2mutant mice. We compared transcript levels in mutant/wildtype male sibs of two different MeCP2-deficient mouse models at 2, 4 and 8 weeks of age. Increased transcript levels were evaluated by real-time quantitative RT-PCR. Chromatin immunoprecipitation assays were used to documentin vivoMeCP2 binding to promoter regions of candidate target genes.

Results

Of several hundred genes with altered expression levels in the mutants, twice as many were increased than decreased, and only 27 were differentially expressed at more than one time point. The number of misregulated genes was 30% lower in mice with the exon 3 deletion (Mecp2tm1.1Jae) than in mice with the larger deletion (Mecp2tm1.1Bird). Between the mutants, few genes overlapped at each time point. Real-time quantitative RT-PCR assays validated increased transcript levels for four genes:Irak1, interleukin-1 receptor-associated kinase 1;Fxyd1, phospholemman, associated with Na, K-ATPase;Reln, encoding an extracellular signaling molecule essential for neuronal lamination and synaptic plasticity; andGtl2/Meg3, an imprinted maternally expressed non-translated RNA that serves as a host gene for C/D box snoRNAs and microRNAs. Chromatin immunoprecipitation assays documentedin vivoMeCP2 binding to promoter regions ofFxyd1, Reln, andGtl2.

Conclusion

Transcriptional profiling of cerebellum failed to detect significant global changes inMecp2-mutant mice. Increased transcript levels ofIrak1, Fxyd1, Reln, andGtl2may contribute to the neuronal dysfunction in MeCP2-deficient mice and individuals with Rett syndrome. Our data provide testable hypotheses for future studies of the regulatory or signaling pathways that these genes act on.
Elevated expression of VEGFR-3 in lymphatic endothelial cells from lymphangiomas
Authors: Norgall Susanne , Papoutsi Maria , Rössler Jochen , Schweigerer Lothar , Wilting Jörg , Weich Herbert A
Published: June 2007

Background

Lymphangiomas are neoplasias of childhood. Their etiology is unknown and a causal therapy does not exist. The recent discovery of highly specific markers for lymphatic endothelial cells (LECs) has permitted their isolation and characterization, but expression levels and stability of molecular markers on LECs from healthy and lymphangioma tissues have not been studied yet. We addressed this problem by profiling LECs from normal dermis and two children suffering from lymphangioma, and also compared them with blood endothelial cells (BECs) from umbilical vein, aorta and myometrial microvessels.

Methods

Lymphangioma tissue samples were obtained from two young patients suffering from lymphangioma in the axillary and upper arm region. Initially isolated with anti-CD31 (PECAM-1) antibodies, the cells were separated by FACS sorting and magnetic beads using anti-podoplanin and/or LYVE-1 antibodies. Characterization was performed by FACS analysis, immunofluorescence staining, ELISA and micro-array gene analysis.

Results

LECs from foreskin and lymphangioma had an almost identical pattern of lymphendothelial markers such as podoplanin, Prox1, reelin, cMaf and integrin-α1 and -α9. However, LYVE-1 was down-regulated and VEGFR-2 and R-3 were up-regulated in lymphangiomas. Prox1 was constantly expressed in LECs but not in any of the BECs.

Conclusion

LECs from different sources express slightly variable molecular markers, but can always be distinguished from BECs by their Prox1 expression. High levels of VEGFR-3 and -2 seem to contribute to the etiology of lymphangiomas.
Study on roles of anaplerotic pathways in glutamate overproduction of Corynebacterium glutamicum by metabolic flux analysis
Authors: Shirai Tomokazu , Fujimura Koki , Furusawa Chikara , Nagahisa Keisuke , Shioya Suteaki , Shimizu Hiroshi
Published: June 2007

Background

Corynebacterium glutamicum has several anaplerotic pathways (anaplerosis), which are essential for the productions of amino acids, such as lysine and glutamate. It is still not clear how flux changes in anaplerotic pathways happen when glutamate production is induced by triggers, such as biotin depletion and the addition of the detergent material, Tween 40. In this study, we quantitatively analyzed which anaplerotic pathway flux most markedly changes the glutamate overproduction induced by Tween 40 addition.

Results

We performed a metabolic flux analysis (MFA) with [1-13C]- and [U-13C]-labeled glucose in the glutamate production phase of C. glutamicum, based on the analysis of the time courses of 13C incorporation into proteinogenic amino acids by gas chromatography-mass spectrometry (GC-MS). The flux from phosphoenolpyruvate (PEP) to oxaloacetate (Oxa) catalyzed by phosphoenolpyruvate carboxylase (PEPc) was active in the growth phase not producing glutamate, whereas that from pyruvate to Oxa catalyzed by pyruvate carboxylase (Pc) was inactive. In the glutamate overproduction phase induced by the addition of the detergent material Tween 40, the reaction catalyzed by Pc also became active in addition to the reaction catalyzed by PEPc.

Conclusion

It was clarified by a quantitative 13C MFA that the reaction catalyzed by Pc is most markedly increased, whereas other fluxes of PEPc and PEPck remain constant in the glutamate overproduction induced by Tween 40. This result is consistent with the previous results obtained in a comparative study on the glutamate productions of genetically recombinant Pc- and PEPc-overexpressing strains. The importance of a specific reaction in an anaplerotic pathway was elucidated at a metabolic level by MFA.
Genome position and gene amplification
Authors: Gajduskova Pavla , Snijders Antoine M , Kwek Serena , Roydasgupta Ritu , Fridlyand Jane , Tokuyasu Taku , Pinkel Daniel , Albertson Donna G
Published: June 2007

Background

Amplifications, regions of focal high-level copy number change, lead to overexpression of oncogenes or drug resistance genes in tumors. Their presence is often associated with poor prognosis; however, the use of amplification as a mechanism for overexpression of a particular gene in tumors varies. To investigate the influence of genome position on propensity to amplify, we integrated a mutant form of the gene encoding dihydrofolate reductase into different positions in the human genome, challenged cells with methotrexate and then studied the genomic alterations arising in drug resistant cells.

Results

We observed site-specific differences in methotrexate sensitivity, amplicon organization and amplification frequency. One site was uniquely associated with a significantly enhanced propensity to amplify and recurrent amplicon boundaries, possibly implicating a rare folate-sensitive fragile site in initiating amplification. Hierarchical clustering of gene expression patterns and subsequent gene enrichment analysis revealed two clusters differing significantly in expression of MYC target genes independent of integration site.

Conclusion

These studies suggest that genome context together with the particular challenges to genome stability experienced during the progression to cancer contribute to the propensity to amplify a specific oncogene or drug resistance gene, whereas the overall functional response to drug (or other) challenge may be independent of the genomic location of an oncogene.
Molecular mechanisms of thrombin-induced interleukin-8 (IL-8/CXCL8) expression in THP-1-derived and primary human macrophages
Authors: Zheng Lei , Martins-Green Manuela
Published: June 2007

Under normal conditions, macrophages provide essential innate immune surveillance in tissues. These cells also play key functions during wound healing and in pathological conditions. When macrophages are exposed to thrombin, an enzyme released from leaky blood vessels, they are stimulated to produce inflammatory cytokines, which are critical for wound healing and can also facilitate tumor growth and invasion. Using antibody cytokine arrays, we identified IL-8/CXCL8, a chemokine that plays important functions in inflammation and angiogenesis and consequently in healing and tumor development, as one of the cytokines that is highly stimulated in macrophages by thrombin. Here, we investigated the signal transduction mechanism by which thrombin stimulates IL-8/CXCL8 expression in THP-1-derived and primary human macrophags. We show that JNK is a crucial mediator of the thrombin signaling pathways in macrophages, and the activation of JNK is dependent on stimulation of the Rho small GTPase. The thrombin-induced Rho/JNK cascade is a novel signaling cascade for IL-8/CXCL8 transcription activation. Understanding the molecular mechanism by which thrombin controls the expression of inflammatory cytokines in macrophages can lead to therapeutic interventions, which can provide better management of healing, inflammation, and tumorigenesis.
MHC Class II levels and intracellular localization in human dendritic cells are regulated by calmodulin kinase II
Authors: Herrmann Tara L , Agrawal Reitu S , Connolly Sean F , McCaffrey Ramona L , Schlomann Jamie , Kusner David J
Published: June 2007

Dendritic cells (DC) are professional APC, which activate the adaptive immune response. A Ca2+-calmodulin (CaM)-CaM kinase II (CaMKII) pathway regulates maturation and MHC Class II antigen presentation in human DC. The objective of this study was to characterize the mechanisms by which CaMKII modulates the levels and subcellular distribution of MHC Class II molecules. Inhibition of CaMKII via the highly specific, autoinhibitory peptide derived from the enzyme’s regulatory domain resulted in rapid (60 min) and sustained (24 h) reduction of MHC Class II levels in antigen-stimulated, primary, human DC. The initial depletion of intracellular and cell surface MHC Class II was associated with its enhanced lysosomal trafficking and increased activity of specific proteases in the absence of effects on other transmembrane proteins (CD1b and CD34) or a detectable change in lysosomal degradation of exogenous protein. Inhibition of CaMKII also resulted in significant reductions in the level and stability of MHC Class II mRNA and the levels and nucleocytosolic localization of its major transcriptional regulator CIITA. These data support a model in which CaMKII regulates the levels and localization of MHC Class II protein in human DC via transcriptional, post-transcriptional, and post-translational mechanisms. These pathways are likely important to the physiologic regulation of MHC Class II as well as to its dysregulation in disease states associated with altered CaMKII function.
Cross-talk between Toll-like receptors 5 and 9 on activation of human immune responses
Authors: Merlo Andrea , Calcaterra Claudia , Mènard Sylvie , Balsari Andrea
Published: June 2007

The recognition of pathogen-associated molecular patterns by TLRs triggers the activation of innate and adaptive immune responses. Flagellin, the agonist of TLR5, is expressed by prokaryotes and eukaryotes, and DNA sequences containing unmethylated CpG dinucleotides, agonists of TLR9, are present essentially in prokaryotes. To test the potential modulating effects of simultaneous activation of different TLRs on the immune response, we compared the outcomes in different immune cell copartments induced by triggering TLR5 and TLR9 individually and in combination. PBMCs, monocytes, and monocyte-derived DC (MoDC) secreted high levels of IL-10 in response to flagellin, whereas oligodeoxynucleotides (ODN) containing the CpG sequence (CpG-ODN), synthetic ligands of TLR9, did not induce IL-10 secretion in any of the three cell types but synergized with flagellin in this induction. In contrast, PBMC production of IFN-α induced by CpG-ODN was strongly inhibited by flagellin. Conversely, CpG-ODN did not enhance the up-regulation of activation markers in MoDC induced to mature in the presence of flagellin. Flagellin-matured, but not CpG-ODN-matured, MoDC stimulated the expansion of allogeneic CD4+CD25+ T cells, and the extent of expansion induced by MoDC, matured in the presence of flagellin and CpG-ODN, was similar to that induced by flagellin-matured MoDC. Moreover, flagellin and CpG-ODN differentially affected NK-mediated cytotoxicity, and flagellin completely abrogated the NK-mediated immune response induced by CpG-ODN stimulation. Together, these results suggest that flagellin inhibits the TLR9-induced cell activation and cytokine production, which favor Th1-type immune responses, possibly because the signals evoked by flagellin to indicate the presence of extracellular pathogens must favor a Th2-polarized response. Thus, TLR5 and TLR9, alerted by the presence of microorganisms, influence each other to mount the more efficient and appropriate immune response to contain the infection of a specific pathogen.
Mechanism of the nongenomic effects of estrogen on intestinal myeloperoxidase activity following trauma-hemorrhage: up-regulation of the PI-3K/Akt pathway
Authors: Yu Huang-Ping , Hsieh Ya-Ching , Suzuki Takao , Choudhry Mashkoor A , Schwacha Martin G , Bland Kirby I , Chaudry Irshad H
Published: June 2007

As studies indicate that genomic and nongenomic pathways are involved in mediating the salutary effects of 17β-estradiol (E2) following trauma-hemorrhage, we examined if the nongenomic effects of E2 on attenuation of intestinal injury after trauma-hemorrhage involve the PI-3K/Akt pathway. Male Sprague-Dawley rats (∼300 g body weight) underwent trauma-hemorrhage (mean blood pressure 40 mmHg for 90 min), followed by resuscitation. E2 conjugated to BSA (E2-BSA; 1 mg/Kg E2), with or without an estrogen receptor antagonist (ICI 182,780), a PI-3K inhibitor (Wortmannin), or vehicle, was injected i.v. during resuscitation. At 2 h after trauma-hemorrhage or sham operation, intestinal myeloperoxidase (MPO) activity, ICAM-1, cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-3, and IL-6 levels were measured (n=6 rats/group). Intestinal PI-3K, phosphorylation of Akt (p-Akt), and Akt protein expressions were also determined. One-way ANOVA and Tukey’s test were used for statistical analysis. The results indicated that trauma-hemorrhage increased intestinal MPO activity and ICAM-1, CINC-1, CINC-3, and IL-6 levels. These parameters were improved significantly in the E2- or E2-BSA-treated rats subjected to trauma-hemorrhage. Although trauma-hemorrhage decreased intestinal PI-3K and p-Akt protein expressions, E2 or E2-BSA treatment following trauma-hemorrhage prevented such decreases in intestinal PI-3K and p-Akt protein expressions. Coadministration of ICI 182,780 or Wortmannin abolished the beneficial effects of E2-BSA on attenuation of intestinal injury following trauma-hemorrhage. Thus, the PI-3K/Akt pathway plays a critical role in mediating the nongenomic, salutary effects of E2 on attenuation of shock-induced intestinal tissue damage.
Reduction of friction torque in vane pump by smoothing cam ring surface
Authors: Inaguma Y , Hibi A
Published: June 2007

This work deals with the influence of surface roughness of cam contours on friction torque in a hydraulic balanced vane pump and it is verified that smoothing the surface of the cam contour can reduce friction torque. In the vane pump, the friction torque arising from the friction between a cam contour and vane tips is significant.

In this article, first, the values of the coefficient of friction between the vane tip and its sliding surfaces were measured by using cylindrical test rings with various kinds of surface roughness. Then the torque characteristics of vane pumps having cam ring contours with various values of surface roughness were measured and their results compared with the results of an analysis of the coefficient of friction investigated using test rings. As a result, the friction torque caused by the friction between the cam contour and the vane tip was reduced by lessening the surface roughness of the cam contour, resulting in an improvement of the mechanical efficiency. The coefficient of friction measured by using the test rings could be applied to the actual vane pumps.
Design and analysis of a new singularity-free three-prismatic-revolute-cylindrical translational parallel manipulator
Authors: Xu Q , Li Y
Published: June 2007

A new three-prismatic-revolute-cylindrical (three-PRC) translational parallel manipulator (TPM) with orthogonally arranged fixed actuators is proposed in this paper. The mobility of the manipulator is analysed via screw theory. The inverse kinematics, forward kinematics, and velocity analyses are performed and the singularities and isotropic configurations are identified afterwards. Moreover, the mechanism design rules producing a singularity-free manipulator have been generated. Under different cases of physical constraints subject to mechanical joints, the reachable workspace of the manipulator is geometrically determined and compared. In particular, it is illustrated that the manipulator has a regular shape workspace with a maximum cuboid defined as the usable workspace inscribed and one isotropic configuration involved. Furthermore, to obtain a large usable workspace, the architecture design of a three-PRC TPM is carried out and the singularity property within the usable workspace is verified. Simulation results show that there are no singular configuration within the workspace, which reveal the validity of design rules for a singularity-free three-PRC TPM.
Techniques for optimizing parameters of negative stiffness
Authors: Park S-T , Luu T-T
Published: June 2007

Passive isolation systems based on springs are often used to resist vibration due to their low cost and reliability. The basic principle of these systems is that they try to decrease the natural frequency as low as possible. Stiffness of the overall spring system must be low to make the isolator achieve the low natural frequency. An approach to obtain the low dynamic stiffness is the combination of a negative stiffness system and a common isolator. There are, however, a lot of negative stiffness systems, and selecting the best one is difficult. In this paper, mathematical analyses are used to determine the best system that is then applied to construct a vertical isolator of the anti-vibration table.
A study of micro-electro discharge machining electrode wear
Authors: Pham D T , Ivanov A , Bigot S , Popov K , Dimov S
Published: June 2007

This paper studies the influence of factors contributing to electrode wear during the micro-electro discharge machining (EDM) process. The paper proposes a method for calculating the volumetric wear ratio based only on geometrical information obtained from the process. The objective of the work is to investigate the suitability of micro-EDM electrode wear compensation methods. Electrode shape deformation and random variations in the volumetric wear are studied as two main factors affecting the applicability of wear compensation methods as well as indicating the accuracy achievable with micro-EDM. EDM drilling and EDM milling are regarded as separate processes as they require different approaches in investigating and implementing the results of the study.
Rapid calculation of the pressures and clearances in rough, rolling-sliding elastohydrodynamically lubricated contacts. Part 2: General, non-sinusoidal roughness
Authors: Hooke C J , Li K Y , Morales-Espejel G
Published: June 2007

Part 1 of this paper [1] described how the behaviour of low amplitude, sinusoidal roughness in elastohydrodynamically lubricated (EHL) contacts could be characterized by three complex quantities: attenuation of original profile, amplitude of complementary wave and its wave number and decay rate. This second part outlines how these results can be used to estimate, rapidly, the clearances and pressures in any rough EHL contact. The method is applied to a number of contacts for which accurate experimental results are available and it is shown that the process gives close estimates of the clearance and pressure distributions where the amplitude of the attenuated roughness is less than 50 per cent of the clearance and good indication of the behaviour of rougher surfaces.
Branch identification and motion domain analysis of Stephenson type six-bar linkages
Authors: Tsai C-C , Wang L-C T
Published: June 2007

A general approach for branch identification and motion domain analysis of Stephenson type six-bar linkages is presented. By applying the Sturm theorem to the input-output polynomial equation, the dead-centre positions of the linkage are first evaluated and classified into two groups in order to discriminate the upper and lower bounds of the motion domains. The circuits of the linkage are then identified by matching the dead centres to the branches, which are attributed in accordance with the case where the input is assigned to a joint within the four-bar chain. Finally, the branches and motion domains of the more complicated case where the input is given through one of the uncoupled joints within the five-bar chain, are identified by mapping the circuits onto the domain of the specified input joint. This approach does not rely on the coupler curve of the constituent four-link mechanism. This is also suitable for computer implementation and can be systematically applied to all types of Stephenson linkages, regardless of the types of joints and the selection of input-output pair.
On the torque generated in a servo valve torque motor using permanent magnets
Authors: Urata E
Published: June 2007

This paper describes a theory and experiments for the conversion of electric current to mechanical torque by a torque motor in servo valves. The feature of the torque motor treated in this paper is the use of a permanent magnet. These kinds of torque motors are most commonly used in modern servo valves. For this type of torque motor, the theory developed by Merritt is most notable among fluid power engineers and scientists. However, his theory does not agree very well with experiments because he ignored the magnetic reluctance and leakage flux of permanent magnets. This paper corrects these points and offers some formulae that agree well with experiments.
The atomic-scale finite-element modelling of single-walled carbon nanotubes
Authors: Ding H , Chen S-J , Cheng K
Published: June 2007

In this paper, an atomic-scale finite-element (AFE) model is proposed for single-walled carbon nanotubes (SWCNTs), which are considered to behave like space-frame structures when subjected to loadings. To create the AFE models, three-dimensional beam elements are used to model the bonds between carbon atoms as loading-carrying elements, while the nodes are placed at the locations of carbon atoms to connect the loading-carrying elements. The material properties of beam elements can be determined by using a linkage between molecular and continuum mechanics.

In order to evaluate the AFE model and its performance, the influence of tube wall thickness on Young's modulus of SWCNTs is investigated. It is found that the selection of wall thickness significantly affects the magnitude of the Young's modulus. For the values of wall thickness used in this study, the obtained values of Young's modulus agree well with the corresponding theoretical results. Furthermore, the results also illustrate that Young's modulus is inversely proportional to the wall thickness. The presented results demonstrate that the proposed AFE model can be used as a valuable tool for studying the mechanical behaviour of carbon nanotubes.
Computation of a modified Haigh-Goodman diagram for damage tolerant design for infinite fatigue life
Authors: Gänser H-P , Leitgeb A , Glinsner K , Eichlseder W
Published: June 2007

A method for constructing a modified Haigh-Goodman diagram for flawed components is proposed based on the approximation by El Haddad for the crack growth threshold diagram, taking into account the influence of the stress ratio on the fatigue limit of the unflawed material as well as on the linear-elastic crack growth threshold. The modified Haigh diagram uses a minimum of easily obtainable material parameters and permits an easy application of damage tolerant design concepts when dimensioning for infinite fatigue life.
A novel high-performance low-NOx fuel-rich/fuel-lean two-stage combustion gas and steam turbine system for power and heat generation
Authors: Yamamoto T , Lior N , Furuhata T , Arai N
Published: June 2007

This paper proposes, describes, and analyses a novel high temperature and performance reheat gas turbine (GT) cogeneration system. This newly proposed system employing two-stage fuel-rich and fuel-lean combustion system is named as the ‘Fuel Rich-Lean Combustion Reheat GT Cogeneration System’ (RLCC). Energy and exergy analyses (the latter mainly to evaluate and demonstrate the reduction in exergy loss of this combustion process compared with conventional single-stage and fuel lean-lean combustion) of the proposed cogeneration system were performed and compared with a conventional cogeneration system. The proposed RLCC system is predicted to have an overall power generation efficiency of up to 53.0 per cent (low heating value (LHV) basis), exergy efficiency up to 61.9 per cent, and specific power up to 524.3 kJ/kg. Compared with a conventional cogeneration (CGC) system, its energy utilization efficiency was as high as 95.0 percent, 4.0 percentage points higher than that of the CGC system, the overall power generation efficiency was higher by 6.2 percentage points, and the exergy efficiency was higher by 7.8 percentage points, and the overall power-based NO x emissions was reduced by up to 34.0 per cent.
Reaction thrust of submerged water jets
Authors: Yang Y. S. , Nie S. L. , Zhu Y. Q. , Li Y. P. , Huang G. H.
Published: June 2007

Reaction thrusts of submerged water jets for different cylindrical nozzles are investigated numerically and experimentally. Simplified models of the pressure distribution on the interior walls of high-pressure chambers, the reaction thrust of water jets and the thrust coefficients are all established on the basis of the general characteristics of the isobaric surface near the inlet of the nozzle, respectively. Simulation studies on the reaction thrust are also conducted through a commercial computational fluid dynamics (CFD) software package called FLUENT. In particular, the effects of the inlet conditions as well as the nozzle dimensions on the reaction thrust of the water jet are addressed. Comparison analyses are also performed on the results of the simplified models, the CFD simulation and the experiments. It is concluded from the results that: (a) the model results and the CFD simulation results are in excellent agreement with the experimental results; (b) the nozzle diameter and the inlet conditions exert a significant influence on the reaction thrust of the water jet; and (c) the reaction thrust coefficient is almost a constant, ranging from 1.1 to 1.3. The related conclusions are extended to the study of the water hydraulic flapper-nozzle a servo valve.
Investigation on the oil supply system of a scroll compressor
Authors: Cui M. M. , Sauls J
Published: June 2007

A numerical model is developed for the complete oil supply system of a scroll compressor. The system includes oil sump, pickup tube, oil gallery, bearings, and associated oil feed holes, vent, and port. There are two fluids, oil and gas, inside the system. The flow is numerically simulated as a heterogeneous Eulerian-Eulerian turbulent multi-phase flow. The investigation covers the entire working process of the scroll compressor from dry-start to steady state. Two design parameters, initial oil sump depth and viscosity, are studied comparatively. The detailed oil-gas flow inside the oil supply system is characterized by the field quantities. The physical mechanisms controlling oil supply rate are defined. The oil supply rate and the bearing prime time (the time after which oil is flowing through a bearing) are obtained. The results can be used to design and optimize the oil supply system to improve the reliability and efficiency of scroll compressors.
Optimization of a regenerative gas-turbine cogeneration system based on a new exergetic performance criterion: Exergetic performance coefficient
Authors: Ust Y , Sahin B , Yilmaz T
Published: June 2007

A performance analysis and an optimization based on a new exergetic performance criterion named exergetic performance coefficient (EPC) have been carried out for an irreversible regenerative gas-turbine cogeneration system. The EPC objective function defined as the total exergy output per unit loss rate of availability is taken as the optimization criterion. The design parameters and performances under optimal conditions have been investigated and the results obtained are compared with those obtained using the alternative criteria given in the literature. It is shown that for the regenerative gas-turbine cogeneration system, a design based on the maximum EPC conditions is more advantageous from the viewpoint of entropy generation rate, exergy efficiency, and investment cost.
Application of computational fluid dynamics to performance analysis of a Francis hydraulic turbine
Authors: Oh H. W. , Yoon E. S.
Published: June 2007

Hydrodynamic performance analysis of a Francis turbine with medium/high specific speed of 1.4 has been accomplished using the validated commercial computational fluid dynamics (CFD) code. Predicted results by the CFD code adopted in the present study are in fairly good agreement with measured data over the entire operating conditions. The prediction method presented herein can be used efficiently as a reliable tool for the practical design and performance analysis of Francis hydraulic turbines.
Reciprocating thermocompressor performance with non-ideal component characteristics
Authors: Edwards M. J. , Peterson R. B.
Published: June 2007

Using heat to compress a gas can have many technological uses including power generation and heat-activated cooling. A model is presented here for a reciprocating, displacer-based thermocompressor. The model is based upon expressions derived from mass and energy conservation for each component of the system through each part of the cycle. It also incorporates features not found in previous works, such as specified regenerator effectiveness and component dead volumes. In order to form a thermodynamic cycle, work is generated from an ideal isothermal expansion of the compressed gas. The model shows that Carnot efficiency is achieved from the ideal work-generating cycle for a regenerator with unity effectiveness. However, for non-ideal conditions, thermal efficiency is highly sensitive to the regenerator performance. For example, assuming zero dead volume in the system, for a temperature ratio of 2 and a pressure ratio of 1.4, a regenerator effectiveness of 0.9 corresponds to a thermal efficiency of only 44 per cent of the Carnot efficiency. Dead volume also adversely impacts performance, with cold space dead volume being the most critical.