bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Hormones in the Induction of Iron Deficiency Responses in Arabidopsis Roots
Authors: Schmidt Wolfgang , Tittel Julia , Schikora Adam
Published: July 2002

In “strategy I” plants, several alterations in root physiology and morphology are induced by Fe deficiency, although the mechanisms by which low Fe levels are translated into reactions aimed at alleviating Fe shortage are largely unknown. To prove whether changes in hormone concentration or sensitivity are involved in the adaptation to suboptimal Fe availability, we tested 45 mutants of Arabidopsis defective in hormone metabolism and/or root hair formation for their ability to increase Fe(III) chelate reductase activity and to initiate the formation and enlargement of root hairs. Activity staining for ferric chelate reductase revealed that all mutants were responsive to Fe deficiency, suggesting that hormones are not necessary for the induction. Treatment of wild-type plants with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid caused the development of root hairs in locations normally occupied by non-hair cells, but did not stimulate ferric reductase activity. Ectopic root hairs were also formed in −Fe roots, suggesting a role for ethylene in the morphological responses to Fe deficiency. Ultrastructural analysis of rhizodermal cells indicated that neither Fe deficiency nor 1-aminocyclopropane-1-carboxylic acid treatment caused transfer-cell-like alterations in Arabidopsis roots. Our data indicate that the morphological and physiological components of the Fe stress syndrome are regulated separately.
Role of Magnesium Chelatase Activity in the Early Steps of the Tetrapyrrole Biosynthetic Pathway
Authors: Papenbrock Jutta , Mock Hans-Peter , Tanaka Ryouichi , Kruse Elisabeth , Grimm Bernhard
Published: July 2002

Magnesium-protoporphyrin IX chelatase (Mg-chelatase) is located at the branchpoint of tetrapyrrole biosynthesis, at which point protoporphyrin IX is distributed for the synthesis of chlorophyll and heme. We investigated the regulatory contribution of Mg-chelatase to the flow of metabolites. In plants, the enzyme complex consists of three subunits, designated CHL D, CHL I, and CHL H. Transgenic tobacco (Nicotiana tabacum) plants expressing antisense RNA for the Mg-chelatase subunit CHL H were analyzed to elucidate further the role of Mg-chelatase in the distribution of protoporphyrin IX into the branched tetrapyrrolic pathway. The transgenic plants displayed a reduced growth rate and chlorophyll deficiency. Both phenotypical properties were correlated with lower Mg-chelatase activity. Unexpectedly, less protoporphyrin IX and heme accumulated, and a decrease in 5-aminolevulinate (ALA)-synthesizing capacity and ALA dehydratase activity paralleled the progressive reduction in Mg-chelatase activity in the transformants compared with control plants. The reduced activities of the early enzymatic steps corresponded with lower levels of transcripts encoding glutamyl-tRNA reductase and ALA-dehydratase. The decreased expression and activities of early enzymes in the pathway could be explained by a feedback-controlled mechanism in response to lower Mg-chelatase activity. We discuss intercompartmental signaling that synchronizes the activities of the first steps in tetrapyrrolic metabolism with the late steps for the synthesis of end products.
Elicitation of Suspension-Cultured Tomato Cells Triggers the Formation of Phosphatidic Acid and Diacylglycerol Pyrophosphate
Authors: van der Luit Arnold H. , Piatti Titus , van Doorn Aveline , Musgrave Alan , Felix Georg , Boller Thomas , Munnik Teun
Published: July 2002

Phosphatidic acid (PA) and its phosphorylated derivative diacylglycerol pyrophosphate (DGPP) are lipid molecules that have been implicated in plant cell signaling. In this study we report the rapid but transient accumulation of PA and DGPP in suspension-cultured tomato (Lycopersicon esculentum) cells treated with the general elicitors,N,N′,N",N‴-tetraacetylchitotetraose, xylanase, and the flagellin-derived peptide flg22. To determine whether PA originated from the activation of phospholipase D or from the phosphorylation of diacylglycerol (DAG) by DAG kinase, a strategy involving differential radiolabeling with [32P]orthophosphate was used. DAG kinase was found to be the dominant producer of PA that was subsequently metabolized to DGPP. A minor but significant role for phospholipase D could only be detected when xylanase was used as elicitor. Since PA formation was correlated with the high turnover of polyphosphoinositides, we hypothesize that elicitor treatment activates phospholipase C to produce DAG, which in turn acts as substrate for DAG kinase. The potential roles of PA and DGPP in plant defense signaling are discussed.
Regulation of Transcript Levels of a Potato Gibberellin 20-Oxidase Gene by Light and Phytochrome B
Authors: Jackson Stephen D. , James Pat E. , Carrera Esther , Prat Salomé , Thomas Brian
Published: July 2002

Up to three gibberellin (GA) 20-oxidase genes have now been cloned from several species including Arabidopsis, bean (Phaseolus vulgaris), and potato (Solanum tuberosum). In each case the GA 20-oxidase genes exhibit different patterns of tissue expression. We have performed extensive northern analysis on one of the potato GA 20-oxidase genes (StGA20ox1), which is the only one that shows significant transcript levels in leaves. We show that levels ofStGA20ox1 transcript are elevated in transgenic antisense plants that have reduced levels of phytochrome B (PHYB) compared with wild-type plants, implicating PHYB in the control of GA biosynthesis. We show that StGA20ox1 transcript levels vary in leaves of different age throughout the plant and cycle throughout the day, furthermore they are up-regulated by light and down-regulated in the dark. The degree of the response to the light-on signal is similar in potato plants deficient in phytochrome A or PHYB and wild-type plants. The induction ofStGA20ox1 by blue light raises the possibility that a blue light receptor may be involved in the control of this gene by light.
Analysis of Oxidative Stress and Wound-Inducible Dinor Isoprostanes F1 (Phytoprostanes F1) in Plants
Authors: Imbusch Ruth , Mueller Martin J.
Published: July 2002

Isoprostanes F2 are arachidonate autoxidation products in mammals that have been shown to be induced during several human disorders associated with enhanced free-radical generation. Isoprostanes F2 represent not only extremely reliable markers of oxidative stress in vivo, but they also exert potent biological effects. Therefore, it has been postulated that isoprostanoids are mediators of oxidant injury in vivo. Higher plants, however, do not synthesize arachidonic acid or isoprostanes. Here we show that a series of isoprostane F2 analogs termed phytoprostanes F1 (previously dinor isoprostanes F1) are formed by an analogous pathway from α-linolenate in plants. High-performance liquid chromatography and gas chromatography-mass spectrometry methods using [18O]3phytoprostanes F1 as internal standard have been developed to quantify phytoprostanes F1. In fresh peppermint (Mentha piperita) leaves, phytoprostanes F1 were found in free form (76 ng/g of dry weight) and at about 150-fold higher levels esterified in lipids. It is notable that these levels of phytoprostanes F1 are more than two orders of magnitude higher than the basal levels of isoprostanes F2 in mammalian tissues. Furthermore, wounding, as well as butyl hydroperoxide or cupric acetate stress triggered a dramatic increase of free and esterified phytoprostanes F1. Thus phytoprostanes F1 may represent a sensitive measure of oxidative damage in plants similar to isoprostanes in mammals. However, one of the most exciting issues to be clarified is the possibility that linolenate-derived phytoprostanes F1 exert biological activities in plants and/or animals.
Mechanism of Arsenate Resistance in the Ericoid Mycorrhizal Fungus Hymenoscyphus ericae
Authors: Sharples Jade M. , Meharg Andrew A. , Chambers Susan M. , Cairney John W.G.
Published: July 2002

Arsenate resistance is exhibited by the ericoid mycorrhizal fungusHymenoscyphus ericae collected from As-contaminated mine soils. To investigate the mechanism of arsenate resistance, uptake kinetics for arsenate (H2AsO4  −), arsenite (H3AsO3), and phosphate (H2PO4  −) were determined in both arsenate-resistant and -non-resistant H. ericae. The uptake kinetics of H2AsO4  −, H3AsO3, and H2PO4  − in both resistant and non-resistant isolates were similar. The presence of 5.0 μm H2PO4  − repressed uptake of H2AsO4  − and exposure to 0.75 mm H2AsO4  −repressed H2PO4  − uptake in bothH. ericae. Mine site H. ericaedemonstrated an enhanced As efflux mechanism in comparison with non-resistant H. ericae and lost approximately 90% of preloaded cellular As (1-h uptake of 0.22 μmol g−1 dry weight h−1 H2AsO4  −) over a 5-h period in comparison with non-resistant H. ericae, which lost 40% of their total absorbed H2AsO4  −. As lost from the fungal tissue was in the form of H3AsO3. The results of the present study demonstrate an enhanced H3AsO3 efflux system operating in mine siteH. ericae as a mechanism for H2AsO4  − resistance. The ecological significance of this mechanism of arsenate resistance is discussed.
Sequences Downstream of the Translation Initiation Codon Are Important Determinants of Translation Efficiency in Chloroplasts
Authors: Kuroda Hiroshi , Maliga Pal
Published: July 2002

The objective of this study was to determine if mRNA sequences downstream of the translation initiation codon are important for translation of plastid mRNAs. We have employed a transgenic approach, measuring accumulation of the neomycin phosphotransferase (NPTII) reporter enzyme translationally fused with 14 N-terminal amino acids encoded in the rbcL or atpB plastid genes. NPTII accumulation from wild-type and mutant rbcLand atpB segments was compared. We report that silent mutations in the rbcL segment reduced NPTII accumulation 35-fold. In contrast, mutations in the atpB mRNA reduced NPTII accumulation only moderately from approximately 7% (w/w) to approximately 4% (w/w) of the total soluble cellular protein, indicating that the importance of sequences downstream of the translation initiation codon are dependent on the individual mRNA. Information provided here will facilitate transgene design for high-level expression of recombinant proteins in chloroplasts by translational fusion with the N-terminal segment of highly expressed plastid genes or by introduction of silent mutations in the N-terminal part of the coding region.
Salicylic Acid and Ethylene Pathways Are Differentially Activated in Melon Cotyledons by Active or Heat-Denatured Cellulase fromTrichoderma longibrachiatum
Authors: Martinez Christelle , Blanc Frédéric , Le Claire Emilie , Besnard Olivier , Nicole Michel , Baccou Jean-Claude
Published: July 2002

Infiltration of cellulase (EC 3.2.1.4) from Trichoderma longibrachiatum into melon (Cucumis melo) cotyledons induced several key defense mechanisms and hypersensitive reaction-like symptoms. An oxidative burst was observed 3 hours after treatment and was followed by activation of ethylene and salicylic acid (SA) signaling pathways leading to marked induction of peroxidase and chitinase activities. The treatment of cotyledons by heat-denatured cellulase also led to some induction of peroxidase and chitinase activities, but the oxidative burst and SA production were not observed. Co-infiltration of aminoethoxyvinil-glycine (an ethylene inhibitor) with the active cellulase did not affect the high increase of peroxidase and chitinase activities. In contrast, co-infiltration of aminoethoxyvinil-glycine with the denatured enzyme blocked peroxidase and chitinase activities. Our data suggest that the SA pathway (induced by the cellulase activity) and ethylene pathway (induced by heat-denatured and active protein) together coordinate the activation of defense mechanisms. We found a partial interaction between both signaling pathways since SA caused an inhibition of the ethylene production and a decrease in peroxidase activity when co-infiltrated with denatured cellulase. Treatments with active or denatured cellulase caused a reduction in powdery mildew (Sphaerotheca fuliginea) disease.
Biotechnology in agriculture
Authors: Saba Anna , Rosati Simona , Vassallo Marco
Published: July 2002

This paper presents the findings of an empirical work on attitudes towards the application of the gene technology to food production in Italy. It focuses on the importance of perception of risks, benefits and uncertainty in determining general attitude to foods produced by genetic engineering. Also, the role of general attitudes and perceived moral obligation in influencing the expectation of consuming foods produced by gene technology was analysed. A mail survey was organised and 434 subjects completed the questionnaires. The results revealed that more people had unfavourable attitudes towards the application of genetic engineering to food production than favourable. More people indicated low benefits than high, more people reported high risks than low risks. Also, more people agreed that there is high uncertainty about potential consequences by genetic engineering than certainty. The findings of regression analyses showed that the perception of benefits outweighed perception of risks in the impact on general attitudes towards the applications of genetic engineering to food production, whereas the perception of uncertainty contributed marginally to the prediction of attitudes. General attitudes appeared to be an important determinant of the expectation of consuming food produced by genetic engineering.
A measure of the learning organization
Authors: Hill Rosemary
Published: July 2002

Suggests that there are many dilemmas facing the aspiring learning organization and true commitment to its principles is a way of integrating the false dichotomy of “concern for the task” versus “concern for the people”. Each organization’s journey in learning endeavour will be different. How to understand, release and apply the powerful pragmatism of the learning organization is the key to success. Begins by exploring some key concepts based on action research and studies into the learning organization. Describes a model of learning culture, an associated learning culture survey and how this translates into a flexible programme of organizational development. Concludes by considering how this methodology may be posited as a useful investigation, analysis and measurement tool within an overall framework of organizational development.
Organisational politics: the missing discipline of management?
Authors: Butcher David , Clarke Martin
Published: July 2002

Traditional approaches to the management of change are failing to produce lasting benefit and are more likely to engender demotivation and feelings of insecurity than tightly integrated and focused strategy implementation. These traditional approaches seldom take full account of the positive role of political fluency in the effective management of such change. This paper examines this political dimension for a collection of senior managers implementing change following two intensive public management development programmes. The findings show that managing political agendas was central to their success in making things happen and therefore postulates whether political awareness should be taught as a mainstream management discipline.
Why kick the “L” out of “LEarning”? The development of students’ employability skills through part‐time working
Authors: Davies Lloyd
Published: July 2002

Research shows that, in general, graduate applicants seeking their first career jobs do not possess the personal, transferable and employability skills which employers require, and Dearing has recommended that most HE students should undertake work experience to remedy this limitation. This article describes the Working for Skills project run by Leeds Metropolitan University and several major local employers. Some 20 “skills and attributes”, identified primarily from independent research projects, are presented to students in a workfile. The workfile addresses two principal areas: experiential learning, and the use of (principally) work experience to grow the identified skills and attributes. A simple model of experiential learning is presented to help students to analyse their work experiences and build awareness of the identified skills and attributes. The article also reports on pilot trials, student feedback and discusses some of the problems associated with this type of material.
Robots and landmines
Authors: Trevelyan James
Published: July 2002

There is a widespread belief that the global land‐mine problem can be solved using a combination of advanced robotics, sophisticated sensors and powerful computing devices. Recent research results suggest that this confidence is misplaced. There is little likelihood of sensing improvements in the short‐term and all the proposed robotic solutions are too expensive to be practical for humanitarian demining operations in countries like Angola, Afghanistan and Cambodia. However, simple equipment improvements and low‐cost robotic devices might provide some useful improvements in safety and cost‐effectiveness in the short‐ to medium‐term. Reviews contributions in robotics and sensing technology, and proposes some practical directions for future work.
Adaptability potentials for buildings and infrastructure in sustainable cities
Authors: Kincaid David
Published: July 2002

A significant shift in the demand for buildings is under way due to IT innovations, new working practices and tightening of the environmental agenda. This is both reducing the extent and altering the nature of the demand for space. The paper explores how existing buildings may be adapted to support new needs and how new buildings may be designed to support a variety of uses and functions. It concludes that a degree of physical redundancy, use ambiguity and flexibility, within a permissive and dynamic regulatory system, could lead to a more adaptable and sustainable future for facilities, buildings and infrastructure.
On adaptive remeshing techniques for crack simulation problems
Authors: Koenke C. , Harte R. , Krätzig W.B. , Rosenstein O.
Published: July 2002

The simulation of fracture processes for discrete crack propagation is well established for linear‐elastic cracking problems. Applying finite element techniques for the numerical formulation, at every incremental macro‐crack step the element mesh has to be adapted such that the crack path remains independent of the initial mesh. The accuracy of the obtained results has to be controlled by suitable error estimators and error indicators. Considering the dependence of the predicted crack path on the precision of the displacement and stress computation, quality measures for the computed results are recommended. In this research the use of the Babuska/Rheinboldt error indicator in combination with linear‐elastic crack propagation problems is demonstrated. Based on this error measure an adaptive mesh refinement technique is developed. In comparison with classical discrete crack propagation simulations the advantages of the new concept can be clearly observed.
Shape representation and contact detection for discrete element simulations of arbitrary geometries
Authors: Hogue Caroline
Published: July 2002

When simulating the behaviour of granular assemblies and multi‐body systems using a discrete element analysis, the shape representation of the bodies and the contact detection algorithm greatly influence the flexibility, accuracy and efficiency of the simulation. Several geometrical shape descriptors of two and three dimensional arbitrary rigid bodies are reviewed and a flexible 3‐D descriptor introduced. The aim is to identify appropriate shape descriptors which allow a variety of types of bodies to be investigated while ensuring accurate and efficient detection of inter‐particle contacts. Polygons/polyhedrons, and continuous and discrete function representations are examined. The investigation favours discrete representations due to their efficiency and flexibility, but illustrates the elegance and efficiency of using a continuous function representation, e.g. a superquadric, to generate the discrete representation and simplify the contact detection process.
Norfolk and Norwich Central Library: the emerging phoenix
Authors: Hammond Hilary
Published: July 2002

Describes the aftermath and losses incurred by the fire which destroyed the Norfolk and Norwich Central Library in 1994. Discusses the short, medium and long‐term decisions which had to be taken on the road to recovery. Discusses recommendations for future fire protection of libraries and also insurance issues. Presents the basic specifications, new technology and funding required for a new Norfolk Library.
Competences in management development: challenging the myths
Authors: Jubb Richard , Robotham David
Published: July 2002

The use of competences has proved to be perhaps the major growth area in management development during the last ten years. An increasing number of organizations have looked to competence‐based training as the solution to enhancing the performance of their managers. But there remain several fundamental weaknesses that supporters of competences have yet to counter adequately. Identifies and challenges the dominant myths behind the competence approach, the suggestion being that it is perhaps time to stop and evaluate the usefulness of competence‐based training in more depth.
Exploring Dynamic Group Processes with GAIA – Groups of Adaptive Inferencing Agents
Authors: Sedbrook Tod
Published: July 2002

Applies a computer model GAIA (Groups of Adaptive Inferencing Agents) to simulate the lifecycle of artificial groups directed by agendas which specify varying strategies for collective problem solving. Within GAIA, groups of artificial agents dynamically learn and interact by proposing, combining and testing inductive hypotheses in the form of genetic building blocks. Agents share and combine building block solutions to evolve decision trees to respond to environmental inputs. Effects of agendas which emphasize stages of conservative and liberal problem solving strategies over a group’s lifecycle were simulated. Conservative strategies emphasize consensus and collective memories within groups. Liberal strategies emphasize challenges to collective memory and individual agent predictions. Agendas which vary from conservative to liberal resulted in the poor group solutions. Significantly better group solutions were produced by an agenda varying from liberal to conservative and back to liberal (L‐C‐L). The L‐C‐L agenda focuses on critical evaluation and rewards for individual contribution in the beginning and ending lifecycle stages and provides a middle stage of collective exploration.
A successive approximation method for solving multi‐objective fuzzy optimization problems
Authors: Zhang B.X. , Chung B.T.F. , Lee Edward T.
Published: July 2002

An efficient method utilizing a “max‐pro” optimum scheme for solving the “max‐min” decision function in a fuzzy optimization environment. The proposed method significantly simplifies the “max‐min” optimum solving problem, especially in the case when the number of objectives and constraints is large. Presents illustrative examples. The technique may also have valuable applications in solving general optimization problems with a piecewise‐smoothed objective function.
On being an elephant in the age of oblivion
Authors: Corbett J. Martin
Published: July 2002

In their review of research on organisational memory, Walsh and Ungson argue that the extant representations of the concept are fragmented and underdeveloped. It is argued that this is due, at least in part, to the dominance of psychological models of memory based on the individual which are employed by organisational memory system designers. In this article it is argued that the development of a more social psychological theory of memory not only helps us understand the roots of the present confusion surrounding the concept of organisational memory, but it also enables the development of a more coherent theoretical model to guide research on the transformational effects of computer‐based information systems on organisational memory.
Characteristic‐based‐split (CBS) algorithm for incompressible flow problems with heat transfer
Authors: Massarotti N. , Nithiarasu P. , Zienkiewicz O.C.
Published: July 2002

In our earlier papers we have presented a general algorithm for the solution of both compressible and incompressible Navier‐Stokes equations. The objective of the present work is to show the performance of this algorithm when it is used to solve thermal flow problems. Both natural and forced convection and transient problems are considered in this study. The semi‐implicit form of the algorithm has been used to deal with a variety of these problems.
Disaster response: risk, vulnerability and resilience
Authors: Paton Douglas , Smith Leigh , Violanti John
Published: July 2002

The assumption of an automatic link between disaster exposure and pathological outcomes is increasingly being questioned. Recognition of the possibility of positive reactions and growth outcomes in this context necessitates the development of alternative models and, in particular, the accommodation of the resilience construct in research and intervention agenda. Reviews possible vulnerability and resilience factors and adopts a risk management framework to outline its potential for modelling the complex relationships between these variables and both growth and distress outcomes. Resilience and vulnerability is discussed at dispositional, cognitive and organisational levels. The paradigm developed here focuses attention on facilitating recovery and growth in professionals for whom disaster work and its consequences is an occupational reality.
Total Quality Management Applied to Engineering Education
Authors: Jaraiedi Majid , Ritz David
Published: July 2002

A methodology demonstration using Quality Function Deployment (QFD) as a
tool to explore some key elements of higher education. QFD is most
commonly applied in industrial settings where products are manufactured.
This research applies QFD to a service, specifically engineering
education. The goal of this research is, therefore, twofold. While
exploring the quality of engineering education in a university setting,
a new application of QFD was tried and tested. Considering the
university students as the primary customers, the results of a nominal
group technique session, along with interviews of faculty members and
administrators were used to define “the voice of the customer”. QFD
procedures and forms were used to analyse and scrutinize the specific
areas of advising and teaching within the university. Recommendations
were devised which range from a comprehensive instructor‐training
programme to self‐help and mentor programmes by student groups.
Developing market‐driven product strategies
Authors: Cravens David W. , Piercy Nigel F. , Prentice Ashley
Published: July 2002

Successful companies encounter unique competitive challenges. However, there are several product strategy initiatives that are relevant to all organizations seeking to develop market‐driven strategies. Key initiatives include the leveraging the business design, recognizing the growth mandate, developing market vision, achieving a capabilities/value match, exploring strategic relationships, building strong brands, brand leveraging, and recognizing the advantages of proactive cannibalization. We propose a product strategy agenda for review by executives in identifying which initiatives should be assessed relative to the needs of their organization.
A review of process planning techniques in layered manufacturing
Authors: Kulkarni Prashant , Marsan Anne , Dutta Debasish
Published: July 2002

Layered manufacturing (LM) is emerging as a new manufacturing technology that can enhance the scope of manufacturing. One of the essential tasks in LM is process planning. This paper defines, conceptualizes and reviews the literature in this emerging area. The paper concludes with future projections on the possible directions of research in this area.
Curing characteristics of acrylic photopolymer used in stereolithography process
Authors: Fuh J.Y.H. , Chew S.
Published: July 2002

Rapid prototypes formed using stereolithography (SL) method have to undergo post‐curing to increase their strength and rigidity. This study attempts to reduce, if not eliminate, post‐cure distortion by characterising curing behaviours. Curing (both heat and UV initiated) characteristics of an acrylic‐based photopolymer under actual fabrication conditions were studied using Raman spectroscopy as well as differential scanning calorimetry (DSC) and differential scanning photo‐calorimetry (DSP). Specimens of single photopolymer lines were created using a SL machine. Raman spectroscopy was used to quantify the curing percentage at different areas on the cross‐section of these lines. Curing percentages before and after post‐curing were also obtained from the experiments. Difference in percentage of post‐curing gave an indication of the distortions faced. It was found that uncured and partially cured resins trapped within the photopolymer resulted in inhomogeneity of curing in the specimens causing shrinkage and distortion.
Behavioral research into heuristics and bias as an academic pursuit
Authors: Hardin William
Published: July 2002

Behavioral research is an accepted research paradigm in business disciplines outside of finance including management, marketing and accounting. This paper looks at these disciplines and proposes goals for increasing acceptance of this form of research in real estate. Primary goals include investigation of actual heuristic use, concentration on expert decision makers, either as a group or in comparison to novices, incorporation of additional theory advocating functional heuristics, incorporation of real estate specific theory and identifying both theoretically and empirically when, why and how heuristic use may bias the decision process.
High and low oxygen affinity conformations of T state hemoglobin
Authors: Bruno Stefano , Bonaccio Maria , Bettati Stefano , Rivetti Claudio , Viappiani Cristiano , Abbruzzetti Stefania , Mozzarelli Andrea
Published: July 2002

To understand the interplay between tertiary and quaternary transitions associated with hemoglobin function and regulation, oxygen binding curves were obtained for hemoglobin A fixed in the T quaternary state by encapsulation in wet porous silica gels. At pH 7.0 and 15°C, the oxygen pressure at half saturation (p50) was measured to be 12.4 ± 0.2 and 139 ± 4 torr for hemoglobin gels prepared in the absence and presence of the strong allosteric effectors inositol hexaphosphate and bezafibrate, respectively. Both values are in excellent agreement with those found for the binding of the first oxygen to hemoglobin in solution under similar experimental conditions. The corresponding Hill coefficients of hemoglobin gels were 0.94 ± 0.02 and 0.93 ± 0.03, indicating, in the frame of the Monod, Wyman, and Changeux model, that high and low oxygen‐affinity tertiary T‐state conformations have been isolated in a pure form. The values, slightly lower than unity, reflect the different oxygen affinity of α‐ and β‐hemes. Significantly, hemoglobin encapsulated in the presence of the weak effector phosphate led to gels that show intermediate oxygen affinity and Hill coefficients of 0.7 to 0.8. The heterogeneous oxygen binding results from the presence of a mixture of the high and low oxygen‐affinity T states. The Bohr effect was measured for hemoglobin gels containing the pure conformations and found to be more pronounced for the high‐affinity T state and almost absent for the low‐affinity T state. These findings indicate that the functional properties of the T quaternary state result from the contribution of two distinct, interconverting conformations, characterized by a 10‐fold difference in oxygen affinity and a different extent of tertiary Bohr effect. The very small degree of T‐state cooperativity observed in solution and in the crystalline state might arise from a ligand‐induced perturbation of the distribution between the high‐ and low‐affinity T‐state conformations.
Total chemical synthesis of human matrix Gla protein
Authors: Hackeng Tilman M. , Rosing Jan , Spronk Henri M.H. , Vermeer Cees
Published: July 2002

Human matrix Gla protein (MGP) is a vitamin K–dependent extracellular matrix protein that binds Ca2+ ions and that is involved in the prevention of vascular calcification. MGP is a 10.6‐kD protein (84 amino acids) containing five γ‐carboxyglutamic acid (Gla) residues and one disulfide bond. Studies of the mechanism by which MGP prevents calcification of the arterial media are hampered by the low solubility of the protein (<10 μg/mL). Because of solubility problems, processing of a recombinantly expressed MGP‐fusion protein chimera to obtain MGP was unsuccessful. Here we describe the total chemical synthesis of MGP by tBoc solid‐phase peptide synthesis (SPPS) and native chemical ligation. Peptide Tyr1‐Ala53 was synthesized on a derivatized resin yielding a C‐terminal thioester group. Peptide Cys54‐Lys84 was synthesized on Lys‐PAM resin yielding a C‐terminal carboxylic acid. Subsequent native chemical ligation of the two peptides resulted in the formation of a native peptide bond between Ala53 and Cys54. Folding of the 1–84‐polypeptide chain in 3 M guanidine (pH 8) resulted in a decrease of molecular mass from 10,605 to 10,603 (ESI‐MS), representing the loss of two protons because of the formation of the Cys54‐Cys60 internal disulfide bond. Like native MGP, synthetic MGP had the same low solubility when brought into aqueous buffer solutions with physiological salt concentrations, confirming its native like structure. However, the solubility of MGP markedly increased in borate buffer at pH 7.4 in the absence of sodium chloride. Ca2+‐binding to MGP was confirmed by analytical HPLC, on which the retention time of MGP was reduced in the presence of CaCl2. Circular dichroism studies revealed a sharp increase in α‐helicity at 0.2 mM CaCl2 that may explain the Ca2+‐dependent shift in high‐pressure liquid chromatography (HPLC)‐retention time of MGP. In conclusion, facile and efficient chemical synthesis in combination with native chemical ligation yielded MGP preparations that can aid in unraveling the mechanism by which MGP prevents vascular calcification.
Influence of pre‐exercise muscle glycogen content on exercise‐induced transcriptional regulation of metabolic genes
Authors: Pilegaard Henriette , Keller Charlotte , Steensberg Adam , Wulff Helge Jørn , Klarlund Pedersen Bente , Saltin Bengt , Neufer P. Darrell
Published: July 2002

Transcription of metabolic genes is transiently induced during recovery from exercise in skeletal muscle of humans. To determine whether pre‐exercise muscle glycogen content influences the magnitude and/or duration of this adaptive response, six male subjects performed one‐legged cycling exercise to lower muscle glycogen content in one leg and then, the following day, completed 2.5 h low intensity two‐legged cycling exercise. Nuclei and mRNA were isolated from biopsies obtained from the vastus lateralis muscle of the control and reduced glycogen (pre‐exercise glycogen = 609 ± 47 and 337 ± 33 mmol kg−1 dry weight, respectively) legs before and after 0, 2 and 5 h of recovery. Exercise induced a significant (P < 0.05) increase (2‐ to 3‐fold) in transcription of the pyruvate dehydrogenase kinase 4 (PDK4) and uncoupling protein 3 (UCP3) genes in the reduced glycogen leg only. Although PDK4, lipoprotein lipase (LPL) and hexokinase II (HKII) mRNA were elevated in the reduced glycogen leg before exercise, no consistent difference was found between the two legs in response to exercise. In a second study, six subjects completed two trials (separated by 2 weeks) consisting of 3 h of two‐legged knee extensor exercise with either control (398 ± 52 mmol kg−1 dry weight) or low (240 ± 38 mmol kg−1 dry weight) pre‐exercise muscle glycogen. Exercise induced a significantly greater increase in PDK4 transcription in the low glycogen (> 6‐fold) than in the control (< 3‐fold) trial. Induction of PDK4 and UCP3 mRNA in response to exercise was also signficantly higher in the low glycogen (11.4‐ and 3.5‐fold, respectively) than in the control (5.0‐ and 1.7‐fold, respectively) trial. These data indicate that low muscle glycogen content enhances the transcriptional activation of some metabolic genes in response to exercise, raising the possibility that signalling mechanisms sensitive to glycogen content and/or FFA availability may be linked to the transcriptional control of exercise‐responsive genes.
A Study of Process-Induced Residual Stress in PBGA Packages
Authors: Wu Zhu , Lu Jian , Guo Yifan
Published: July 2002

Process-induced residual stresses can play a significant role in the reliability of electronic components and packages. In this paper, a practical method is developed to determine residual stresses for electronic packaging. In this method, blind holes are drilled into the specimens and relationships are established, between the released surface displacements and the corresponding residual stress, by introducing a set of calibration coefficients. A multilayer 3D-FEM model is established to determine the relevant calibration coefficients. This methodology, which combines moire´ interferometry and the incremental hole drilling method, can provide an accurate determination of residual stresses in materials and structures by precisely controlled incremental blind-hole drilling and an accurate determination of the surface in-plane displacement fields in the hole drilling region. The methodology is implemented by investigating the residual stress in the Plastic Ball Grid Array (PBGA) packages. The tensile residual stresses are determined in both the plastic molding compound and the glass/epoxy laminate chip carrier. The method is accurate, simple, convenient, and practical. More applications, in residual stress determinations and in process evaluations in electronic packaging, are anticipated. [S1043-7398(00)00103-1]
LGA Connectors: An Automated Design Technique for a Shrinking Design Space
Authors: Deshpande A. , Subbarayan G.
Published: July 2002

The ever-increasing demand for higher-density interconnection between a multi-chip module and the printed circuit board has resulted in the emergence of Land-Grid Array (LGA) connectors as an alternative to the traditional pin and socket area-array connectors. The design of high-density land-grid array connectors involves trade-off between conflicting performance requirements on the normal force, wipe, bulk resistance, contact resistance, stress, contact z-dimensional thickness, and z-compression. These stringent design requirements have significantly shrunk the space of viable designs and have necessitated automated search procedures for finding designs that satisfy the design requirements. In this paper, such an automated design procedure based on nonlinear optimization techniques is presented. The design procedure includes a general shape representation scheme based on B-spline curves and a set of programs for carrying out automated nonlinear elastic-plastic-contact finite element analysis (for a given shape) using a commercial finite element code. This automated analysis procedure is coupled with a nonlinear optimization code to carryout optimal design of LGA connectors. The design of LGA connectors is mathematically formulated as an optimization problem and nine different design cases (with representative dimensions and material) are solved to determine the influence of initial design and optimization problem formulation. It is shown that better solutions (with less stress) result if both the width and the thickness of the contacts are allowed to vary. In general, the choice of initial design strongly influences the optimal solution. A triply-curved symmetric contact shape is shown to produce the least stress of three possible common LGA shape designs. [S1043-7398(00)00403-5]
Interface Properties Due to Microslip From Vibration Measurement
Authors: Sherif H. A. , Abu Omar T. M.
Published: July 2002

A method of measuring contact stiffness and friction damping at interacting plane surfaces of a mechanical system comprised of two sub-structures in dry contact is presented. The method is based on the measurement of displacement ratio of the contacting sub-structures as a function of frequency due to light impulse excitation at a single point on any of the two sub-structures. The theoretical analysis depends on a very simple model of a two-degree-of-freedom system with elastic coupling. The effects of applied normal loads, and contact configuration on the interface parameters are shown. The theoretical and experimental analyses show that the interface properties for the flat-on-flat surfaces of the two contacting sub-structures can be determined from the measured peak amplitude and peak frequency of the microslip in the frequency domain.
Design and Operation of a Droplet Deposition System for Freeform Fabrication of Metal Parts
Authors: Tseng A. A. , Lee M. H. , Zhao B.
Published: July 2002

A droplet generator has been designed and built to make wax and tin alloy droplets for freeform fabrication. The linear stability theory of liquid jets for forming droplets is first reviewed. The analytical formula for predicting droplet size and breakup length at optimal conditions are then developed. The suitability of the formulas to be used for the present droplet deposition system is studied by comparing its prediction with the more accurate numerical results and previously published experimental data. Only the suitable formulation is adopted for the design and operation of the droplet generator system. Experiments have been conducted at a wide range of operating conditions including different nozzle sizes, jet velocities, and frequencies. Good agreements are found between the predictions based on the adopted analytical formulation and the experimental results. It has been found that using the present design and procedure recommended, the droplet sizes can be controlled having a size deviation of less than 3 percent and the shape variation of the deposited layer can be managed within 3 percent of its deposited width.
Measurement of Critical Velocities for Fluidelastic Instability Using Vibration Control
Authors: Caillaud S. , de Langre E. , Piteau P.
Published: July 2002

Fluidelastic effects may be responsible for instabilities of heat exchanger tubes when the fluid flow reaches the critical velocity. The fluidelastic phenomenon is usually studied on experimental mock-ups, which may display only one critical velocity. In this paper, a method based on active vibration control is proposed in order to derive several critical velocities for fluidelastic instability corresponding to several different values of damping, which is artificially varied on the same mock-up. Experimental tests are performed on a flexible tube equipped with piezoelectric actuators in a rigid array under air-water cross-flow. It is shown that the reduced critical velocities thus obtained fit well in a classical stability map. [S0739-3717(00)01603-2]
Tensile Strengths for Laser-Fabricated Parts and Similarity Parameters for Rapid Manufacturing
Authors: Kahlen Franz-Josef , Kar Aravinda
Published: July 2002

This paper presents a set of process parameter selection rules to deposit a good metal part. A CO2 laser is used to melt metal powder to achieve layer by layer deposition for fabricating three-dimensional parts. Dimensionless numbers characterizing this powder deposition process are identified using Buckingham’s Π-Theorem. These dimensionless numbers are used to identify a range of values for the process parameters, such as the laser power, spot diameter, speed of the xyz stage and powder flow rate, to achieve good quality layers for different materials. The yield and ultimate strengths are examined for parts fabricated with stainless steel 304 (SS 304) powder under three different processing conditions. These stresses are correlated to the operating conditions and physical dimensions of the deposit through the dimensionless similarity parameters. Experimental data indicate that the yield strength of the part is close to the value of standard sample (250 MPa, same as wrought stainless steel SS304). It is also observed that the direction of maximum yield strength is oriented very close to the dominant direction of material solidification. The ultimate strength is found to be considerably less than the ultimate strength of wrought SS 304 (540 MPa) which may be due to the residual stresses generated in the part.
A New Algorithm Based on Two Extra-Sensors for Real-Time Computation of the Actual Configuration of the Generalized Stewart-Gough Manipulator
Authors: Parenti-Castelli Vincenzo , Di Gregorio Raffaele
Published: July 2002

It is well known that the direct position analysis of fully-parallel manipulators provides more than one solution, i.e., more than one configuration of the mechanism is possible for a given set of the actuated variables of motion. Extra information is, thus, necessary to find the actual configuration of the manipulator. This paper presents a new algorithm for the real-time computation of the actual configuration of the generalized Stewart-Gough manipulator, also known as 6-6 fully-parallel manipulator with general geometry. The proposed algorithm makes use of two extra rotary sensors in addition to five out of the six sensors normally implemented in the servosystems of the manipulator. A one-to-one correspondence between the sensor measurements and the manipulator configuration is provided. With respect to other algorithms recently presented in the literature, the proposed method greatly reduces the computational burden. Finally a case study shows the effectiveness of the proposed procedure. [S1050-0472(00)01703-7]
Fatigue Damage Mechanisms of Bridging Fibers in Titanium Metal Matrix Composites1
Authors: Tamin M. N. , Ghonem H.
Published: July 2002

This paper investigates the fatigue damage mechanisms of SiC fibers bridging a fatigue crack in unidirectional reinforced titanium matrix composites. For this purpose, an experimental/computational fiber fracture model is developed on the basis of the occurrence of two damage events taking place along a bridging fiber. These events are the time-dependent evolution of axial stresses and the simultaneous strength degradation of the fiber due to cyclic-related damage processes. The stress evolution in a fiber is calculated using the finite element method employing a cylinder model of a fiber embedded in a cracked matrix phase. The model considers the visco-plastic behavior of the matrix phase at elevated temperature loadings. The failure strength of the as-received SiC fiber are determined through a series of monotonic tension, residual fatigue strength and fatigue-life tests performed on SiC fibers at different temperatures. In order to take into account the notch-like effects resulting from the presence of fiber coating cracks and possible deflection of fiber/matrix interfacial cracks, the fatigue strength of the as-received SiC fiber was modified using elastic stress localization. The resulting fatigue strength of bridging fibers was found to be about 56 percent less than the corresponding strength of as-received fibers. The fiber stress evolution curve and the modified fatigue strength curve were then combined to predict the life of bridging fibers. Results of the model are compared with those obtained experimentally for bridging fibers in SiC/Timetal-21S composite subjected to load conditions including low and high loading frequency at 500 and 650°C. [S0094-4289(00)01804-1]