bluuebunny/crossref_metadata_2025 huggingface dataset:
Wildlife and human use of buffer-zone areas in a wildlife sanctuary
Authors: Jotikapukkana Sukanda , Berg Åke , Pattanavibool Anak
Published: October 2010

Context. Buffer zones are supposed to serve the dual purpose of ‘extension buffering’, or an extension of core habitat areas, and ‘socio buffering’ to provide goods and services to humans; however, few studies have evaluated both human use of buffer zones and the occurrence of wildlife. Aims. The aim of the present study was to quantify the effects of human disturbance on wildlife by recording the use of the 4-km-wide buffer zone of Huai Kha Kaeng Wildlife Sanctuary (HKKWS), Thailand, by humans and domestic animals. Methods. Occurrence of signs of large mammals were recorded along 37 transects and relationships among distance to settlements, human activities, occurrence of domestic animals and different wildlife species were analysed. Key results. In total, 210 interviewed respondents from adjacent villages all used the buffer zone, and the transect survey revealed that a large proportion of the plots (71%) were used by humans and/or domestic animals. The frequency of human use decreased linearly with distance from the buffers-zone edge, whereas the use by cattle decreased rapidly at a distance of 2000 m from the buffer-zone edge. In general, the HKKWS buffer zone was a suitable habitat for several wildlife species. Sambar deer and banteng occurred in >25% of the plots. The proportion of plots with signs of sambar deer, banteng and elephant was negatively associated with the proportion of plots with signs of domestic animals, whereas the proportion of plots with signs of common muntjac was negatively associated with the proportion of plots with signs of human activities. Conclusions. The results from the present study suggest that the 4-km buffer zone in HKKWS reduces the impact of both humans and domestic animals. Implications. The size of human populations, restrictions for grazing domestic animals and habitat quality are suggested to be factors of importance for establishment of well designed buffer zones.
Single-particle cryoelectron microscopy analysis reveals the HIV-1 spike as a tripod structure
Authors: Wu Shang-Rung , Löving Robin , Lindqvist Birgitta , Hebert Hans , Koeck Philip J. B. , Sjöberg Mathilda , Garoff Henrik
Published: October 2010

The HIV-1 spike is a trimer of the transmembrane gp41 and the peripheral gp120 subunit pair. It is activated for virus–cell membrane fusion by binding sequentially to CD4 and to a chemokine receptor. Here we have studied the structural transition of the trimeric spike during the activation process. We solubilized and isolated unliganded and CD4-bound spikes from virus-like particles and used cryoelectron microscopy to reconstruct their 3D structures. In order to increase the yield and stability of the spike, we used an endodomain deleted and gp120-gp41 disulfide-linked variant. The unliganded spike displayed a hollow cage-like structure where the gp120-gp41 protomeric units formed a roof and bottom, and separated lobes and legs on the sides. The tripod structure was verified by fitting the recent atomic core structure of gp120 with intact N- and C-terminal ends into the spike density map. This defined the lobe as gp120 core, showed that the legs contained the polypeptide termini, and suggested the deleted variable loops V1/V2 and V3 to occupy the roof and gp41 the bottom. CD4 binding shifted the roof density peripherally and condensed the bottom density centrally. Fitting with a V3 containing gp120 core suggested that the V1/V2 loops in the roof were displaced laterally and the V3 lifted up, while the core and leg were kept in place. The loop displacements probably prepared the spike for coreceptor interaction and roof opening so that a new fusion-active gp41 structure, assembled at the center of the cage bottom, could reach the target membrane.
Highly episodic fire and erosion regime over the past 2,000 y in the Siskiyou Mountains, Oregon
Authors: Colombaroli Daniele , Gavin Daniel G.
Published: October 2010

Fire is a primary mode of natural disturbance in the forests of the Pacific Northwest. Increased fuel loads following fire suppression and the occurrence of several large and severe fires have led to the perception that in many areas there is a greatly increased risk of high-severity fire compared with presettlement forests. To reconstruct the variability of the fire regime in the Siskiyou Mountains, Oregon, we analyzed a 10-m, 2,000-y sediment core for charcoal, pollen, and sedimentological data. The record reveals a highly episodic pattern of fire in which 77% of the 68 charcoal peaks before Euro-American settlement cluster within nine distinct periods marked by a 15-y mean interval. The 11 largest charcoal peaks are significantly related to decadal-scale drought periods and are followed by pulses of minerogenic sediment suggestive of rapid sediment delivery. After logging in the 1950s, sediment load was increased fourfold compared with that from the most severe presettlement fire. Less severe fires, marked by smaller charcoal peaks and no sediment pulses, are not correlated significantly with drought periods. Pollen indicators of closed forests are consistent with fire-free periods of sufficient length to maintain dense forest and indicate a fire-triggered switch to more open conditions during the Medieval Climatic Anomaly. Our results indicate that over millennia fire was more episodic than revealed by nearby shorter tree-ring records and that recent severe fires have precedents during earlier drought episodes but also that sediment loads resulting from logging and road building have no precedent in earlier fire events.
Homolog of tocopherol
C
methyltransferases catalyzes
N
methylation in anticancer alkaloid biosynthesis
Authors: Liscombe David K. , Usera Aimee R. , O’Connor Sarah E.
Published: October 2010

Madagascar periwinkle (
Catharanthus roseus
) is the sole source of the anticancer drugs vinblastine and vincristine, bisindole alkaloids derived from the dimerization of the terpenoid indole alkaloids vindoline and catharanthine. Full elucidation of the biosynthetic pathways of these compounds is a prerequisite for metabolic engineering efforts that will improve production of these costly molecules. However, despite the medical and commercial importance of these natural products, the biosynthetic pathways remain poorly understood. Here we report the identification and characterization of a
C. roseus
cDNA encoding an
S
-adenosyl-L-methionine-dependent
N
methyltransferase that catalyzes a nitrogen methylation involved in vindoline biosynthesis. Recombinant enzyme produced in
Escherichia coli
is highly substrate specific, displaying a strict requirement for a 2,3-dihydro bond in the aspidosperma skeleton. The corresponding gene transcript is induced in methyl jasmonate-elicited seedlings, along with the other known vindoline biosynthetic transcripts. Intriguingly, this unique
N
methyltransferase is most similar at the amino acid level to the plastidic γ-tocopherol
C
methyltransferases of vitamin E biosynthesis, suggesting an evolutionary link between these two functionally disparate methyltransferases.
Single amino acid change alters the ability to specify male or female organ identity
Authors: Airoldi Chiara A. , Bergonzi Sara , Davies Brendan
Published: October 2010

The molecular mechanisms underlying the developmental processes that shape living organisms provide a basis to understand the evolution of biological complexity. Gene duplication allows biological functions to become separated, leading to increased complexity through subfunctionalization. Recently, the relative contributions to morphological evolution of changes to the regulatory and/or coding regions of duplicated genes have been the subject of debate. Duplication generated multiple copies of the MADS-box transcription factor genes that play essential roles in specifying organ identity in the flower, making this evolutionary novelty a good model to investigate the nature of the changes necessary to drive subfunctionalization. Here, we show that naturally occurring variation at a single amino acid in a MADS-box transcription factor switches its ability to specify male and female reproductive organs by altering its repertoire of protein–protein interactions. However, these different developmental fates are only manifest because of an underlying variation in the expression pattern of interacting proteins. This shows that the morphological outcomes of changes to protein sequence and gene expression must be interpreted in the context of the wider regulatory network. It also suggests an explanation for the surprisingly widespread duplications of some of the floral transcription factors.
Retinoic acid regulates bone morphogenic protein signal duration by promoting the degradation of phosphorylated Smad1
Authors: Sheng Nengyin , Xie Zhihui , Wang Chen , Bai Ge , Zhang Kejing , Zhu Qingqing , Song Jianguo , Guillemot Francois , Chen Ye-Guang , Lin Anning , Jing Naihe
Published: October 2010

The proper function of the bone morphogenic protein (BMP) pathway during embryonic development and organ maintenance requires its communication with other signaling pathways. Unlike the well-documented regulation of the BMP pathway by FGF/MAPK and Wnt/GSK3 signals, cross-talk between BMP/Smad and retinoic acid (RA)/RA receptor (RAR) pathways is poorly understood. Here, we show that RA represses BMP signal duration by reducing the level of phosphorylated Smad1 (pSmad1). Through its nuclear receptor-mediated transcription, RA enhances the interaction between pSmad1 and its ubiquitin E3 ligases, thereby promoting pSmad1 ubiquitination and proteasomal degradation. This regulation depends on the RA-increased Gadd45 expression and MAPK activation. During the neural development in chicken embryo, the RA/RAR pathway also suppresses BMP signaling to antagonize BMP-regulated proliferation and differentiation of neural progenitor cells. Furthermore, this cross-talk between RA and BMP pathways is involved in the proper patterning of dorsal neural tube of chicken embryo. Our results reveal a mechanism by which RA suppresses BMP signaling through regulation of pSmad1 stability.
Engineering of a synthetic electron conduit in living cells
Authors: Jensen Heather M. , Albers Aaron E. , Malley Konstantin R. , Londer Yuri Y. , Cohen Bruce E. , Helms Brett A. , Weigele Peter , Groves Jay T. , Ajo-Franklin Caroline M.
Published: October 2010

Engineering efficient, directional electronic communication between living and nonliving systems has the potential to combine the unique characteristics of both materials for advanced biotechnological applications. However, the cell membrane is designed by nature to be an insulator, restricting the flow of charged species; therefore, introducing a biocompatible pathway for transferring electrons across the membrane without disrupting the cell is a significant challenge. Here we describe a genetic strategy to move intracellular electrons to an inorganic extracellular acceptor along a molecularly defined route. To do so, we reconstitute a portion of the extracellular electron transfer chain of
Shewanella oneidensis
MR-1 into the model microbe
Escherichia coli
. This engineered
E. coli
can reduce metal ions and solid metal oxides ∼8× and ∼4× faster than its parental strain. We also find that metal oxide reduction is more efficient when the extracellular electron acceptor has nanoscale dimensions. This work demonstrates that a genetic cassette can create a conduit for electronic communication from living cells to inorganic materials, and it highlights the importance of matching the size scale of the protein donors to inorganic acceptors.
Skeletal development in sloths and the evolution of mammalian vertebral patterning
Authors: Hautier Lionel , Weisbecker Vera , Sánchez-Villagra Marcelo R. , Goswami Anjali , Asher Robert J.
Published: October 2010

Mammals show a very low level of variation in vertebral count, particularly in the neck. Phenotypes exhibited at various stages during the development of the axial skeleton may play a key role in testing mechanisms recently proposed to explain this conservatism. Here, we provide osteogenetic data that identify developmental criteria with which to recognize cervical vs. noncervical vertebrae in mammals. Except for sloths, all mammals show the late ossification of the caudal-most centra in the neck after other centra and neural arches. In sloths with 8–10 ribless neck vertebrae, the caudal-most neck centra ossify early, matching the pattern observed in cranial thoracic vertebrae of other mammals. Accordingly, we interpret the ribless neck vertebrae of three-toed sloths caudal to V7 as thoracic based on our developmental criterion. Applied to the unusual vertebral phenotype of long-necked sloths, these data support the interpretation that elements of the axial skeleton with origins from distinct mesodermal tissues have repatterned over the course of evolution.
Adaptation and extinction in experimentally fragmented landscapes
Authors: Fakheran Sima , Paul-Victor Cloé , Heichinger Christian , Schmid Bernhard , Grossniklaus Ueli , Turnbull Lindsay A.
Published: October 2010

Competition and disturbance are potent ecological forces that shape evolutionary trajectories. These forces typically work in opposition: when disturbance is infrequent, densities are high and competition is intense. In contrast, frequent disturbance creates a low-density environment in which competition is weak and good dispersal essential. We exploited recent advances in genomic research to quantify the response to selection by these powerful ecological forces at the phenotypic and molecular genetic level in experimental landscapes. We grew the annual plant
Arabidopsis thaliana
in discrete patches embedded in a hostile matrix and varied the number and size of patches and the intensity of disturbance, by creating both static and dynamic landscapes. In static landscapes all patches were undisturbed, whereas in dynamic landscapes all patches were destroyed in each generation, forcing seeds to disperse to new locations. We measured the resulting changes in phenotypic, genetic, and genotypic diversity after five generations of selection. Simulations revealed that the observed loss of genetic diversity dwarfed that expected under drift, with dramatic diversity loss, particularly from dynamic landscapes. In line with ecological theory, static landscapes favored good competitors; however, competitive ability was linked to growth rate and not, as expected, to seed mass. In dynamic landscapes, there was strong selection for increased dispersal ability in the form of increased inflorescence height and reduced seed mass. The most competitive genotypes were almost eliminated from highly disturbed landscapes, raising concern over the impact of increased levels of human-induced disturbance in natural landscapes.
Müllerian inhibiting substance preferentially inhibits stem/progenitors in human ovarian cancer cell lines compared with chemotherapeutics
Authors: Wei Xiaolong , Dombkowski David , Meirelles Katia , Pieretti-Vanmarcke Rafael , Szotek Paul P. , Chang Henry L. , Preffer Frederic I. , Mueller Peter R. , Teixeira Jose , MacLaughlin David T. , Donahoe Patricia K.
Published: October 2010

Cancer stem cells are proposed to be tumor-initiating cells capable of tumorigenesis, recurrence, metastasis, and drug resistance, and, like somatic stem cells, are thought to be capable of unlimited self-renewal and, when stimulated, proliferation and differentiation. Here we select cells by expression of a panel of markers to enrich for a population with stem cell-like characteristics. A panel of eight was initially selected from 95 human cell surface antigens as each was shared among human ovarian primary cancers, ovarian cancer cell lines, and normal fimbria. A total of 150 combinations of markers were reduced to a panel of three—CD44, CD24, and Epcam—which selected, in three ovarian cancer cell lines, those cells which best formed colonies. Cells expressing CD44, CD24, and Epcam exhibited stem cell characteristics of shorter tumor-free intervals in vivo after limiting dilution, and enhanced migration in invasion assays in vitro. Also, doxorubicin, cisplatin, and paclitaxel increased this enriched population which, conversely, was significantly inhibited by Müllerian inhibiting substance (MIS) or the MIS mimetic SP600125. These findings demonstrate that flow cytometry can be used to detect a population which shows differential drug sensitivity, and imply that treatment of patients can be individualized to target both stem/progenitor cell enriched and nonenriched subpopulations. The findings also suggest that this population, amenable to isolation by flow cytometry, can be used to screen for novel treatment paradigms, including biologic agents such as MIS, which will improve outcomes for patients with ovarian cancer.
Crystal structure of Spot 14, a modulator of fatty acid synthesis
Authors: Colbert Christopher L. , Kim Chai-Wan , Moon Young-Ah , Henry Lisa , Palnitkar Maya , McKean William B. , Fitzgerald Kevin , Deisenhofer Johann , Horton Jay D. , Kwon Hyock Joo
Published: October 2010

Spot 14 (S14) is a protein that is abundantly expressed in lipogenic tissues and is regulated in a manner similar to other enzymes involved in fatty acid synthesis. Deletion of S14 in mice decreased lipid synthesis in lactating mammary tissue, but the mechanism of S14’s action is unknown. Here we present the crystal structure of S14 to 2.65 Å and biochemical data showing that S14 can form heterodimers with MIG12. MIG12 modulates fatty acid synthesis by inducing the polymerization and activity of acetyl-CoA carboxylase, the first committed enzymatic reaction in the fatty acid synthesis pathway. Coexpression of S14 and MIG12 leads to heterodimers and reduced acetyl-CoA carboxylase polymerization and activity. The structure of S14 suggests a mechanism whereby heterodimer formation with MIG12 attenuates the ability of MIG12 to activate ACC.
Mental models and human reasoning
Authors: Johnson-Laird Philip N.
Published: October 2010

To be rational is to be able to reason. Thirty years ago psychologists believed that human reasoning depended on formal rules of inference akin to those of a logical calculus. This hypothesis ran into difficulties, which led to an alternative view: reasoning depends on envisaging the possibilities consistent with the starting point—a perception of the world, a set of assertions, a memory, or some mixture of them. We construct mental models of each distinct possibility and derive a conclusion from them. The theory predicts systematic errors in our reasoning, and the evidence corroborates this prediction. Yet, our ability to use counterexamples to refute invalid inferences provides a foundation for rationality. On this account, reasoning is a simulation of the world fleshed out with our knowledge, not a formal rearrangement of the logical skeletons of sentences.
High-performance continuous-wave room temperature 4.0-μm quantum cascade lasers with single-facet optical emission exceeding 2 W
Authors: Lyakh A. , Maulini R. , Tsekoun A. , Go R. , Von der Porten S. , Pflügl C. , Diehl L. , Capasso Federico , Patel C. Kumar N.
Published: October 2010

A strain-balanced, AlInAs/InGaAs/InP quantum cascade laser structure, designed for light emission at 4.0 μm using nonresonant extraction design approach, was grown by molecular beam epitaxy. Laser devices were processed in buried heterostructure geometry. An air-cooled laser system incorporating a 10-mm × 11.5-μm laser with antireflection-coated front facet and high-reflection-coated back facet delivered over 2 W of single-ended optical power in a collimated beam. Maximum continuous-wave room temperature wall plug efficiency of 5.0% was demonstrated for a high-reflection-coated 3.65-mm × 8.7-μm laser mounted on an aluminum nitride submount.
GRIP1 and 2 regulate activity-dependent AMPA receptor recycling via exocyst complex interactions
Authors: Mao Lifang , Takamiya Kogo , Thomas Gareth , Lin Da-Ting , Huganir Richard L.
Published: October 2010

PSD-95/SAP90/DLG/ZO-1 (PDZ) domain-mediated protein–protein interactions play important roles in regulating AMPA receptor trafficking and neuronal plasticity. GRIP1 and GRIP2 are homologous multi-PDZ domain-containing proteins that bind to the C-termini of AMPA-R GluA2 and GluA3 subunits. Previous attempts to determine the cellular roles of GRIP1 and GRIP2 in neurons have been complicated by nonspecific reagents, and by the embryonic lethality of conventional GRIP1 KO mice. To circumvent these issues we developed a conditional targeted deletion strategy to knock out GRIP1 in postnatal neurons derived from GRIP2 KO mice. Loss of GRIP1 and 2 did not affect normal AMPA-R steady-state trafficking and endocytosis, but strikingly impaired activity-dependent AMPA-R recycling. This previously uncharacterized role for GRIP1 appears to be mediated by novel interactions with the cellular trafficking machinery via the exocyst protein complex. Indeed, disruption of GRIP1-exocyst binding caused a strikingly similar deficit in AMPA-R recycling. Together these findings reveal a previously unidentified role for AMPA-R-GRIP1-exocyst protein complexes in activity-dependent AMPA-R trafficking.
Genetic reduction of striatal-enriched tyrosine phosphatase (STEP) reverses cognitive and cellular deficits in an Alzheimer’s disease mouse model
Authors: Zhang Yongfang , Kurup Pradeep , Xu Jian , Carty Nikisha , Fernandez Stephanie M. , Nygaard Haakon B. , Pittenger Christopher , Greengard Paul , Strittmatter Stephen M. , Nairn Angus C. , Lombroso Paul J.
Published: October 2010

Alzheimer's disease (AD) is a progressive and incurable neurodegenerative disorder. Early in the pathophysiology of AD, synaptic function is disrupted by soluble Aβ oligomers, possibly through Aβ-mediated internalization of NMDA receptors. Striatal-enriched phosphatase (STEP) is a tyrosine phosphatase that regulates the internalization of NMDA receptors. Recent work shows that STEP is elevated in the prefrontal cortex of human AD patients and in animal models of AD. Here, we use genetic manipulations to reduce STEP activity in a triple transgenic AD mouse model and show that a decrease in STEP levels reverses cognitive and cellular deficits observed in these mice. Our results suggest that STEP inhibitors may prove therapeutic for this devastating disorder.
Push-and-pull regulation of the fusion pore by synaptotagmin-7
Authors: Segovia Margarita , Alés Eva , Montes María Angeles , Bonifas Imelda , Jemal Imane , Lindau Manfred , Maximov Anton , Südhof Thomas C. , Alvarez de Toledo Guillermo
Published: October 2010

In chromaffin cells, Ca
2+
binding to synaptotagmin-1 and -7 triggers exocytosis by promoting fusion pore opening and fusion pore expansion. Synaptotagmins contain two C2 domains that both bind Ca
2+
and contribute to exocytosis; however, it remains unknown whether the C2 domains act similarly or differentially to promote opening and expansion of fusion pores. Here, we use patch amperometry measurements in WT and synaptotagmin-7–mutant chromaffin cells to analyze the role of Ca
2+
binding to the two synaptotagmin-7 C2 domains in exocytosis. We show that, surprisingly, Ca
2+
binding to the C2A domain suffices to trigger fusion pore opening but that the resulting fusion pores are unstable and collapse, causing a dramatic increase in kiss-and-run fusion events. Thus, synaptotagmin-7 controls fusion pore dynamics during exocytosis via a push-and-pull mechanism in which Ca
2+
binding to both C2 domains promotes fusion pore opening, but the C2B domain is selectively essential for continuous expansion of an otherwise unstable fusion pore.
Role of the hippocampus in remembering the past and imagining the future
Authors: Squire Larry R. , van der Horst Anna S. , McDuff Susan G. R. , Frascino Jennifer C. , Hopkins Ramona O. , Mauldin Kristin N.
Published: October 2010

It has been proposed that a core network of brain regions, including the hippocampus, supports both past remembering and future imagining. We investigated the importance of the hippocampus for these functions. Five patients with bilateral hippocampal damage and one patient with large medial temporal lobe lesions were tested for their ability to recount autobiographical episodes from the remote past, the recent past, and to imagine plausible episodes in the near future. The patients with hippocampal damage had intact remote autobiographical memory, modestly impaired recent memory, and an intact ability to imagine the future. The patient with large medial temporal lobe lesions had intact remote memory, markedly impaired recent memory, and also had an intact ability to imagine the future. The findings suggest that the capacity for imagining the future, like the capacity for remembering the remote past, is independent of the hippocampus.
The surface protein HvgA mediates group B streptococcus hypervirulence and meningeal tropism in neonates
Authors: Tazi Asmaa , Disson Olivier , Bellais Samuel , Bouaboud Abdelouhab , Dmytruk Nicolas , Dramsi Shaynoor , Mistou Michel-Yves , Khun Huot , Mechler Charlotte , Tardieux Isabelle , Trieu-Cuot Patrick , Lecuit Marc , Poyart Claire
Published: October 2010

Streptococcus agalactiae (group B streptococcus; GBS) is a normal constituent of the intestinal microflora and the major cause of human neonatal meningitis. A single clone, GBS ST-17, is strongly associated with a deadly form of the infection called late-onset disease (LOD), which is characterized by meningitis in infants after the first week of life. The pathophysiology of LOD remains poorly understood, but our epidemiological and histopathological results point to an oral route of infection. Here, we identify a novel ST-17–specific surface-anchored protein that we call hypervirulent GBS adhesin (HvgA), and demonstrate that its expression is required for GBS hypervirulence. GBS strains that express HvgA adhered more efficiently to intestinal epithelial cells, choroid plexus epithelial cells, and microvascular endothelial cells that constitute the blood–brain barrier (BBB), than did strains that do not express HvgA. Heterologous expression of HvgA in nonadhesive bacteria conferred the ability to adhere to intestinal barrier and BBB-constituting cells. In orally inoculated mice, HvgA was required for intestinal colonization and translocation across the intestinal barrier and the BBB, leading to meningitis. In conclusion, HvgA is a critical virulence trait of GBS in the neonatal context and stands as a promising target for the development of novel diagnostic and antibacterial strategies.
STAT6-mediated displacement of polycomb by trithorax complex establishes long-term maintenance of GATA3 expression in T helper type 2 cells
Authors: Onodera Atsushi , Yamashita Masakatsu , Endo Yusuke , Kuwahara Makoto , Tofukuji Soichi , Hosokawa Hiroyuki , Kanai Akinori , Suzuki Yutaka , Nakayama Toshinori
Published: October 2010

Polycomb group (PcG) and trithorax group (TrxG) complexes exert opposing effects on the maintenance of the transcriptional status of the developmentally regulated Hox genes. In this study, we show that activation of STAT6 induces displacement of the PcG complex by the TrxG complex at the upstream region of the gene encoding GATA3, a transcription factor essential for T helper type 2 (Th2) cell differentiation. Once Th2 cells differentiate, TrxG complex associated with the TrxG component Menin binds to the whole GATA3 gene locus, and this binding is required for the long-term maintenance of expression of GATA3 and Th2 cytokine. Thus, STAT6-mediated displacement of PcG by the TrxG complex establishes subsequent STAT6-independent maintenance of GATA3 expression in Th2 cells via the recruitment of the Menin–TrxG complex.
The effects of metal vapour in arc welding
Authors: Murphy Anthony B
Published: October 2010

Metal vapour is formed in arc welding processes by the evaporation of molten metal in the weld pool, and in the case of gas–metal arc welding, in the wire electrode and droplets. The presence of metal vapour can have a major influence on the properties of the arc and the size and shape of the weld pool. Previous experimental and computational works on the production and transport of metal vapour in welding arcs, in particular those relevant to gas–metal arc welding and gas–tungsten arc welding, are reviewed. The influence of metal vapour on the thermodynamic, transport and radiative properties of plasmas is discussed. The effect of metal vapour on the distributions of temperature, current density and heat flux in arcs is examined in terms of these thermophysical properties. Different approaches to treating diffusion of metal vapour in plasmas, and the production of vapour from molten metal, are compared. The production of welding fume by the nucleation and subsequent condensation of metal vapour is considered. Recommendations are presented about subjects requiring further investigation, and the requirements for accurate computational modelling of welding arcs.
Plasma diagnostics in gas metal arc welding by optical emission spectroscopy
Authors: Valensi F , Pellerin S , Boutaghane A , Dzierzega K , Zielinska S , Pellerin N , Briand F
Published: October 2010

The plasma column in a metal inert gas welding process is investigated by optical emission spectroscopy and high-speed imaging. The concentration and repartition of iron vapours are measured and correlated with the plasma and electrode geometric configuration. Plasma temperatures and electron densities are also measured for each studied position in the plasma. The temperatures are calculated using two different methods, allowing validation of the local thermodynamic equilibrium state of the plasma. The results show a maximum temperature of 12 500 K in the upper part of the arc, away from the arc axis. The iron concentration reaches a maximum of 0.3% close to the anode and strongly decreases along both the vertical and radial directions.

The plasma thermophysical properties, calculated from this plasma composition, are then discussed regarding the metal transfer mode.
Spectroscopic investigation of the high-current phase of a pulsed GMAW process
Authors: Rouffet M E , Wendt M , Goett G , Kozakov R , Schoepp H , Weltmann K D , Uhrlandt D
Published: October 2010

While metal vapours have an important impact on the efficiency of the pulsed gas metal arc welding process, only a few papers are focused on this effect. In this paper, methods based on emission spectroscopy are performed to improve the understanding of the physical phenomena occurring during the high-current pulse. Boltzmann plots applied to iron lines, the Stark broadening of the 696.5 nm argon line and composition calculations assuming local thermodynamic equilibrium are used to determine characteristic parameters of the plasma. It is observed that the central part of the arc is composed mainly of iron. The percentage of iron increases quickly at the beginning of the high-current pulse, and slowly decreases when the central part broadens. During the high-current phase the temperature profile has a minimum value of around 8000 K at the axis of the arc while the argon envelope of the central part reaches temperatures of approximately 13.000 K. The high percentage of iron and the high radiation of the plasma at the centre can explain the measured shape of the temperature profile.
Study of the welding gas influence on a controlled short-arc GMAW process by optical emission spectroscopy
Authors: Wilhelm G , Gött G , Schöpp H , Uhrlandt D
Published: October 2010

The controlled short-arc processes, variants of the gas metal arc welding (GMAW) process, which have recently been developed, are used to reduce the heat input into the workpiece. Such a process with a wire feeding speed which varies periodically, using a steel wire and a steel workpiece to produce bead-on-plate welds has been investigated. As welding gases CO2 and a mixture of Ar and O2 have been used. Depending on the gas, the properties of the plasma change, and as a consequence the weldseams themselves also differ distinctly. Optical emission spectroscopy has been applied to analyse the plasma. The radial profiles of the emission coefficients of an iron line and an argon line or an atomic oxygen line, respectively, have been determined. These profiles indicate the establishment of a metal vapour arc core which has a broader profile under CO2 but is more focused in the centre for argon. The measured iron line emission was near to its norm maximum in the case of CO2. From this fact, temperatures around 8000 K and a metal vapour molar fraction above 75% in the arc centre could be roughly estimated for this case. Estimations of the electrical conductivity and the arc field indicate that the current path must include not only the metal vapour arc core but also outer hot regions dominated by welding gas properties in the case of argon.
Measurement of atomic Stark parameters of many Mn I and Fe I spectral lines using GMAW process
Authors: Zielinska S , Pellerin S , Dzierzega K , Valensi F , Musiol K , Briand F
Published: October 2010

The particular character of the welding arc working in pure argon, whose emission spectrum consists of many spectral lines strongly broadened by the Stark effect, has allowed measurement, sometimes for the first time, of the Stark parameters of 15 Mn I and 10 Fe I atomic spectral lines, and determination of the dependence on temperature of normalized Stark broadening in N
e = 1023 m−3 of the 542.4 nm atomic iron line. These results show that special properties of the MIG plasma may be useful in this domain because composition of the wire-electrode may be easily adapted to the needs of an experiment.
Calculation of diffusion coefficients in air–metal thermal plasmas
Authors: Cressault Y , Gleizes A
Published: October 2010

This paper presents the combined diffusion coefficients of metal vapours (silver, copper and iron) in air thermal plasmas for temperatures ranging from 300 to 30 000 K. The theory used to calculate these coefficients is remembered and validated by comparison with the literature values in several cases such as Ar–He, Ar–Cu and N2–O2 mixtures. The results are discussed showing the influences of the metal concentration, of the vapour nature and of the pressure. The results show rather similar behaviour for the three metals. The maximum values of the combined ordinary diffusion coefficient in the evolution with temperature are obtained for temperature around 10 000 K but this peak is shifted to the highest temperatures when the metal proportion increases. Another result shows that the diffusion coefficient decreases when pressure increases.
Radiative emission from air thermal plasmas with vapour of Cu or W
Authors: Aubrecht V , Bartlova M , Coufal O
Published: October 2010

This paper deals with the net emission coefficients of radiation of air thermal plasmas with admixtures of copper and tungsten as a function of the plasma temperature up to 25 000 K and the arc radius (0.01 to 10 cm) at various pressures. The net emission coefficients are calculated for various equilibrium compositions (mole fractions of Cu and W) of the plasma. Calculations take into account continuum and line radiations, and special attention has also been paid to the fraction of radiation that is below a threshold of 120 nm. From the results it follows that the presence of metallic vapour increases the net emission coefficients even at low temperatures below 10 000 K.
Modelling of gas–metal arc welding taking into account metal vapour
Authors: Schnick M , Fuessel U , Hertel M , Haessler M , Spille-Kohoff A , Murphy A B
Published: October 2010

The most advanced numerical models of gas–metal arc welding (GMAW) neglect vaporization of metal, and assume an argon atmosphere for the arc region, as is also common practice for models of gas–tungsten arc welding (GTAW). These models predict temperatures above 20 000 K and a temperature distribution similar to GTAW arcs. However, spectroscopic temperature measurements in GMAW arcs demonstrate much lower arc temperatures. In contrast to measurements of GTAW arcs, they have shown the presence of a central local minimum of the radial temperature distribution.

This paper presents a GMAW model that takes into account metal vapour and that is able to predict the local central minimum in the radial distributions of temperature and electric current density. The influence of different values for the net radiative emission coefficient of iron vapour, which vary by up to a factor of hundred, is examined. It is shown that these net emission coefficients cause differences in the magnitudes, but not in the overall trends, of the radial distribution of temperature and current density. Further, the influence of the metal vaporization rate is investigated. We present evidence that, for higher vaporization rates, the central flow velocity inside the arc is decreased and can even change direction so that it is directed from the workpiece towards the wire, although the outer plasma flow is still directed towards the workpiece. In support of this thesis, we have attempted to reproduce the measurements of Zielińskaet alfor spray-transfer mode GMAW numerically, and have obtained reasonable agreement.
Time-dependent calculations of molten pool formation and thermal plasma with metal vapour in gas tungsten arc welding
Authors: Tanaka M , Yamamoto K , Tashiro S , Nakata K , Yamamoto E , Yamazaki K , Suzuki K , Murphy A B , Lowke J J
Published: October 2010

A gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode. The whole region of GTA atmosphere including the tungsten cathode, the arc plasma and the anode was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of the shielding gas and metal vapour. The transient two-dimensional distributions of temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the molten pool as a function of time for a 150 A arc current at atmospheric pressure, both for helium and argon gases. It was shown that the thermal plasma in the GTA was influenced by iron vapour from the molten pool surface and that the concentration of iron vapour in the plasma was dependent on the temperature of the molten pool.

GTA on high sulfur stainless steel was calculated to discuss the differences between a low sulfur and a high sulfur stainless steel anode. Helium was selected as the shielding gas because a helium GTA produces more metal vapour than an argon GTA. In the GTA on a high sulfur stainless steel anode, iron vapour and current path were constricted. Radiative emission density in the GTA on high sulfur stainless steel was also concentrated in the centre area of the arc plasma together with the iron vapour although the temperature distributions were almost the same as that in the case of a low sulfur stainless steel anode.
Modelling of metal vapour in pulsed TIG including influence of self-absorption
Authors: Iwao Toru , Mori Yusuke , Okubo Masato , Sakai Tadashi , Tashiro Shinichi , Tanaka Manabu , Yumoto Motoshige
Published: October 2010

Pulsed TIG (tungsten inert gas) welding is used to improve the stability and speed of arc welding, and to allow greater control over the heat input to the weld. The temperature and the radiation power density of the pulsed arc vary as a function of time, as does the distribution of metal vapour, and its effects on the arc. A self-consistent two-dimensional model of the arc and electrodes is used to calculate the properties of the arc as a function of time. Self-absorption of radiation is treated by two methods, one taking into account absorption of radiation only within the control volume of emission, and the other taking into account absorption throughout the plasma. The relation between metal vapour and radiation power density is analysed by calculating the iron vapour distribution. The results show that the transport of iron vapour is strongly affected by the fast convective flow during the peak current period. During the base current period, the region containing a low concentration of metal vapour expands because of the low convective flow. The iron vapour distribution does not closely follow the current pulses. The temperature, iron vapour and radiation power density distributions depend on the self-absorption model used. The temperature distribution becomes broader when self-absorption of radiation from all directions is considered.
Numerical analysis of the influence of splitter-plate erosion on an air arc in the quenching chamber of a low-voltage circuit breaker
Authors: Yang Fei , Rong Mingzhe , Wu Yi , Murphy Anthony B , Pei Jun , Wang Liqiang , Liu Zengchao , Liu Yiying
Published: October 2010

The influence of metal vapour on the arc behaviour during the arc-splitting process in the quenching chamber of a low-voltage circuit breaker is investigated numerically. A three-dimensional magnetohydrodynamic model of air arc plasma, taking into account the production of metal vapour from erosion of an iron splitter plate, is developed. An equation describing conservation of the iron vapour mass is added to the standard mass, momentum and energy conservation equations. The influence of the iron vapour on the thermodynamic and transport properties of the gas mixture is considered. The arc voltage, distributions of temperature, gas flow and mass fraction of iron vapour in the arc chamber are calculated. The formation of new arc roots on the splitter plate is examined. The simulation results indicate that this is strongly influenced by the presence of iron vapour from the splitter plate, due to the increased electrical conductivity in the arc root formation region. The consequences of this are dramatic. The presence of metal vapour causes the arc to attach first to the cathode side of the splitter plate, and electromagnetic forces then cause the arc on this side to move more rapidly than the arc on the anode side. The opposite occurs if metal vapour is neglected. High-speed photography of arc motion is used to confirm the arc motion predicted in the presence of metal vapour. Further, the calculated arc voltage taking into account metal vapour is lower than that calculated neglecting metal vapour, because of the increased electrical conductivity, and agrees much better with the measured voltage.
Numerical analysis of fume formation mechanism in arc welding
Authors: Tashiro Shinichi , Zeniya Tasuku , Yamamoto Kentaro , Tanaka Manabu , Nakata Kazuhiro , Murphy Anthony B , Yamamoto Eri , Yamazaki Kei , Suzuki Keiichi
Published: October 2010

In order to clarify the fume formation mechanism in arc welding, a quantitative investigation based on the knowledge of interaction among the electrode, arc and weld pool is indispensable. A fume formation model consisting of a heterogeneous condensation model, a homogeneous nucleation model and a coagulation model has been developed and coupled with the GTA or GMA welding model. A series of processes from evaporation of metal vapour to fume formation from the metal vapour was totally investigated by employing this simulation model. The aim of this paper is to visualize the fume formation process and clarify the fume formation mechanism theoretically through a numerical analysis. Furthermore, the reliability of the simulation model was also evaluated through a comparison of the simulation result with the experimental result. As a result, it was found that the size of the secondary particles consisting of small particles with a size of several tens of nanometres reached 300 nm at maximum and the secondary particle was in a U-shaped chain form in helium GTA welding. Furthermore, it was also clarified that most part of the fume was produced in the downstream region of the arc originating from the metal vapour evaporated mainly from the droplet in argon GMA welding. The fume was constituted by particles with a size of several tens of nanometres and had similar characteristics to that of GTA welding. On the other hand, if the metal transfer becomes unstable and the metal vapour near the droplet diffuses directly towards the surroundings of the arc not getting into the plasma flow, the size of the particles reaches several hundred nanometres.
High mobility and low operating voltage ZnGaO and ZnGaLiO transistors with spin-coated Al2O3 as gate dielectric
Authors: Xia D X , Xu J B
Published: October 2010

Spin-coated alumina serving as a gate dielectric in thin film transistors shows interesting dielectric properties for low-voltage applications, despite a moderate capacitance. With Ga singly doped and Ga, Li co-doped ZnO as the active channel layers, typical mobilities of 4.7 cm2 V−1 s−1 and 2.1 cm2 V−1 s−1 are achieved, respectively. At a given gate bias, the operation current is much smaller than the previously reported values in low-voltage thin film transistors, primarily relying on the giant-capacitive dielectric. The reported devices combine advantages of high mobility, low power consumption, low cost and ease of fabrication. In addition to the transparent nature of both the dielectric and semiconducting active channels, the superior electrical properties of the devices may provide a new avenue for future transparent electronics.
Far-field x-ray phase contrast imaging has no detailed information on the object
Authors: Kohn V G , Argunova T S , Je J H
Published: October 2010

We show that x-ray phase contrast images of some objects with a small cross-section diameter d satisfy a condition for a far-field approximation d ≪ r
1 where r
1 = (λz)1/2, λ is the x-ray wavelength, z is the distance from the object to the detector. In this case the size of the image does not match the size of the object contrary to the edge detection technique. Moreover, the structure of the central fringes of the image is universal, i.e. it is independent of the object cross-section structure. Therefore, these images have no detailed information on the object.
Preparation of core–shell Fe3O4/SiO2 microspheres as adsorbents for purification of DNA
Authors: Gai Ligang , Li Zhili , Hou Yunhua , Jiang Haihui , Han Xiaoyun , Ma Wanyong
Published: October 2010

Nearly monodisperse core–shell Fe3O4/SiO2 microspheres have been prepared via a glycol reduction method followed by a modified Stöber process. The thickness of the silica shells can be tuned in the range 33–53 nm by varying the amount of tetraethyl silicate (TEOS) during syntheses. The magnetic composite microspheres were characterized with XRD, XPS, FTIR, TEM, ICP–OES and VSM, and further tested as adsorbents for purification of plasmid DNA from Escherichia coli DH5α cells. The magnetic purification of plasmid DNA leads to satisfying integrity, yield and purity in comparison with those isolated by the traditional phenol–chloroform extraction.
Determination of the entropy change using the acoustic detection technique in the investigation of the magnetocaloric effect
Authors: Soffner M E , Mansanares A M , Gandra F C G , Coelho A A , Gama S , Carvalho A Magnus G , Pires M J M , Guimarães A O , Silva E C da
Published: October 2010

In this paper we demonstrate the use of the acoustic detection as an alternative way to determine the entropy variation, ΔS

T
, a parameter normally used to characterize the magnetocaloric effect. The measurements were performed for a Gd sample in the 252–316 K temperature range for magnetic fields from zero up to 50 kOe. The reversible adiabatic curves were built in a T versus H diagram, and specific heat data obtained at zero-magnetic field were employed to assign the entropy values of each curve. Subsequently, the entropy was plotted as a function of temperature for fixed magnetic fields, and therefore the isothermal entropy variation, ΔS

T
, was found as a function of the temperature for several magnetic field steps.