bluuebunny/crossref_metadata_2025 huggingface dataset:
The x-ray calibration facility of the laser integration line in the 0.9–10 keV range: The high energy x-ray source and some applications
Authors: Hubert S. , Dubois J. L. , Gontier D. , Lidove G. , Reverdin C. , Soullié G. , Stemmler P. , Villette B.
Published: May 2010

The laser integration line (LIL) located at CEA-CESTA is equipped with x-ray plasma diagnostics using different kinds of x-ray components such as filters, mirrors, crystals, detectors, and cameras. The CEA-DAM of Arpajon is currently developing x-ray calibration methods and carrying out absolute calibration of LIL x-ray photodetectors. To guarantee LIL measurements, detectors such as x-ray cameras must be regularly calibrated close to the facility. A new x-ray facility is currently available to perform these absolute x-ray calibrations. This paper presents the x-ray tube based high energy x-ray source delivering x-ray energies ranging from 0.9 to 10 keV by means of an anode barrel. The purpose of this source is mainly to calibrate LIL x-ray cameras but it can also be used to measure x-ray filter transmission of plasma diagnostics. Different x-ray absolute calibrations such as x-ray streak and framing camera yields, x-ray charge-coupled device quantum efficiencies, and x-ray filter transmissions are presented in this paper. A x-ray flat photocathode detector sensitivity calibration recently performed for a CEA Z-pinch facility is also presented.
A high frequency GaN Lamb-wave sensor device
Authors: Pantazis A. K. , Gizeli E. , Konstantinidis G.
Published: May 2010

Lamb-wave devices are characterized by high sensitivity to surface perturbations due to acoustic energy confinement in a thin piezoelectric membrane. In this paper, a Lamb-wave delay line device based on a single crystalline GaN membrane is presented. The observed operating frequency of 178.82 MHz was found to be in excellent agreement with numerical analysis predictions. The device as a chemical sensor was evaluated during the application of various concentrations of glycerol on the device surface; its ability to operate as a biosensor was also assessed during the detection of the specific binding of a protein (IgG) to the device surface.
Defect reduction in silicon nanoparticles by low-temperature vacuum annealing
Authors: Niesar S. , Stegner A. R. , Pereira R. N. , Hoeb M. , Wiggers H. , Brandt M. S. , Stutzmann M.
Published: May 2010

Using electron paramagnetic resonance, we find that vacuum annealing at 200 °C leads to a significant reduction in the silicon dangling bond (Si-db) defect density in silicon nanoparticles (Si-NPs). The best improvement of the Si-db density by a factor of 10 is obtained when the vacuum annealing is combined with an etching step in hydrofluoric acid (HF), whereas HF etching alone only removes the Si-dbs at the Si/SiO2 interface. The reduction in the Si-db defect density is confirmed by photothermal deflection spectroscopy and photoconductivity measurements on thin Si-NPs films.
Electrode dependence of resistive switching in Mn-doped ZnO: Filamentary versus interfacial mechanisms
Authors: Peng H. Y. , Li G. P. , Ye J. Y. , Wei Z. P. , Zhang Z. , Wang D. D. , Xing G. Z. , Wu T.
Published: May 2010

We carry out a comparative study on resistive switching in Mn-doped ZnO thin films; samples grown on Pt and Si show unipolar and bipolar switching behaviors, respectively. Fittings of the current-voltage curves and area dependence of the device resistance reveal the filamentary conduction in Pt/Mn:ZnO/Pt. On the other hand, the interfacial effect dominates in Pt/Mn:ZnO/Si, and its low resistance state exponentially relaxes toward the high resistance state in contrast to the good data retention in Pt/Mn:ZnO/Pt. Our results suggest that selecting electrodes dictates the resistive switching mechanism presumably by affecting the migration dynamics of oxygen vacancies.
Nanoelectromechanical torsion switch of low operation voltage for nonvolatile memory application
Authors: Xiang Wenfeng , Lee Chengkuo
Published: May 2010

Nanoelectromechanical torsion switches are fabricated by using focused ion beam milling on silicon-on-insulator substrate. The device layer thickness of the substrate is 220 nm. A 9 μm long and 1.5 μm wide suspended silicon cantilever is mechanically connected to peripheral silicon device layer via a silicon torsion spring with the length of 2.4 μm and width of 530 nm. After hydrofluoric-acid vapor releasing, the silicon cantilever shows downward deflection. The pull-in voltage is about 5.5 V and the ratio of current measured at the ON/OFF states is over 1000. Moreover, the simulated data of pull-in voltage of torsion switch is in agreement with the experimental result, which will contribute to design of an optimal nanoelectromechanical torsion switch with a driven voltage as low as 1.2 V. According to the preliminary results, this torsion switch with low driven voltage has a great potential for high density non-volatile memory application.
Current-induced switching of magnetic vortex core in ferromagnetic elliptical disks
Authors: Yamada Keisuke , Kasai Shinya , Nakatani Yoshinobu , Kobayashi Kensuke , Ono Teruo
Published: May 2010

We report the experimental observation and micromagnetics simulation of the current-induced switching of the magnetic vortex core in ferromagnetic elliptical disks. We found that the critical current density required for the core switching depends on the relative alignment between the current direction and the elliptical axes of the disk. The micromagnetics simulation results qualitatively reproduce the experimental findings, suggesting that the vortex core displacement induced by the current plays a significant role for the core switching rather than the core velocity.
Static properties of polymer melts in two dimensions
Authors: Meyer H. , Wittmer J. P. , Kreer T. , Johner A. , Baschnagel J.
Published: May 2010

Self-avoiding polymers in strictly two-dimensional (d=2) melts are investigated by means of molecular dynamics simulation of a standard bead-spring model with chain lengths ranging up to N=2048. The chains adopt compact configurations of typical size R(N)∼Nν with ν=1/d. The precise measurement of various distributions of internal chain distances allows a direct test of the contact exponents Θ0=3/8, Θ1=1/2, and Θ2=3/4 predicted by Duplantier. Due to the segregation of the chains the ratio of end-to-end distance Re(N) and gyration radius Rg(N) becomes Re2(N)/Rg2(N)≈5.3<6 for N⪢100 and the chains are more spherical than Gaussian phantom chains. The second Legendre polynomial P2(s) of the bond vectors decays as P2(s)∼1/s1+νΘ2, thus measuring the return probability of the chain after s steps. The irregular chain contours are shown to be characterized by a perimeter length L(N)∼R(N)dp of fractal line dimension dp=d−Θ2=5/4. In agreement with the generalized Porod scattering of compact objects with fractal contour, the Kratky representation of the intramolecular structure factor F(q) reveals a strong nonmonotonous behavior with qdF(q)∼1/(qR(N))Θ2 in the intermediate regime of the wave vector q. This may allow to confirm the predicted contour fractality in a real experiment.
Tunnel magnetoresistance properties and film structures of double MgO barrier magnetic tunnel junctions
Authors: Gan H. D. , Ikeda S. , Shiga W. , Hayakawa J. , Miura K. , Yamamoto H. , Hasegawa H. , Matsukura F. , Ohkubo T. , Hono K. , Ohno H.
Published: May 2010

The authors fabricated double MgO barrier magnetic tunnel junctions (MTJs) with 3-nm-thick Co40Fe40B20 free layer. When annealed at 350 °C, tunnel magnetoresistance (TMR) ratio at room temperature was 130%, much lower than that (297%) of single MgO barrier MTJs processed and annealed under the same condition. The middle CoFeB free layer sandwiched between the two MgO barriers was found to be mostly amorphous. Replacement of the Co40Fe40B20 free layer by a highly oriented Co50Fe50 layer and a composite Co50Fe50/Co40Fe40B20 layer led to the enhanced TMR ratios up to 165% and 212% at annealing temperature of 350 °C, respectively.
Electrical current flow at conductive nanowires formed in GaN thin films by a dislocation template technique
Authors: Amma Shin-ichi , Tokumoto Yuki , Edagawa Keiichi , Shibata Naoya , Mizoguchi Teruyasu , Yamamoto Takahisa , Ikuhara Yuichi
Published: May 2010

Conductive nanowires were fabricated in GaN thin film by selectively doping of Al along threading dislocations. Electrical current flow localized at the nanowires was directly measured by a contact mode atomic force microscope. The current flow at the nanowires was considered to be Frenkel–Poole emission mode, suggesting the existence of the deep acceptor level along the nanowires as a possible cause of the current flow. The results obtained in this study show the possibility for fabricating nanowires using pipe-diffusion at dislocations in solid thin films.
Efficient approximation of the cluster size distribution in binary condensation
Authors: van Putten Dennis S. , Sidin Ryan S. R. , Hagmeijer Rob
Published: May 2010

We propose a computationally efficient method for the calculation of the binary cluster size distribution. This method is based on the phase path analysis algorithm, which was originally derived for single-component condensation. We extend this method by constructing the binary general dynamic equation, which introduces clusters at a point in two component n1,n2-space. The location of this source point is determined by the Gibbs free energy of formation and the impingement rates of the two constituents. The resulting model describes the binary cluster size distribution along a line in n1,n2-space. The solution of the binary general dynamic equation is compared with the solution of formally exact binary Becker–Döring equations for a typical nucleation pulse experiment. The results show good agreement for the cluster composition and size and the integral properties of the size distribution.
Transport properties of LaTiO3/SrTiO3 heterostructures
Authors: Ohtsuka R. , Matvejeff M. , Nishio K. , Takahashi R. , Lippmaa M.
Published: May 2010

Resistivity measurements show that SrTiO3/LaTiO3/SrTiO3 heterostructures remain metallic even for single unit cell LaTiO3 layers. Hall resistances of all heterostructures are nonlinear functions of the applied field. The Hall data is analyzed in terms of a two-layer model, indicating that a low-mobility layer exists at the LaTiO3/SrTiO3 interface, while carriers with mobilities approaching 10 000 cm2/V s are present deep in the SrTiO3 substrate.
Cyclotron resonance of two-dimensional electron system affected by neighboring quantum dot layer
Authors: Takehana K. , Imanaka Y. , Takamasu T. , Henini M.
Published: May 2010

We have investigated the cyclotron resonance (CR) in a two-dimensional electron system (2DES) separated by a thin barrier layer from InAs self-assembled quantum dots (QDs). Two absorption peaks of CR of the 2DES were clearly observed, indicating coexistence of free electrons with high mobility and trapped electrons within local potential minima caused by the neighboring QDs. The CR of the trapped electrons changes its intensity, corresponding to the charge state of the QDs. This is the first optical measurements to show that the charge state of the QDs affects on the 2DES in the role as a floating gate.
An Agent-Based Heuristic Method for Generating Land-Use Plans in Urban Planning
Authors: Arentze Theo A , Borgers Aloys W J , Ma Linda , Timmermans Harry J P
Published: May 2010

Land-use models are a well-established component of planning support systems to support urban planning for and with a local community. Existing models are based on either land-suitability analysis or facility-network performance analysis, reflecting two major approaches in modelling for spatial planning—land-use-allocation or land-use-change modelling, and location-allocation modelling. In this study, we propose an agent-based approach to combine methods from both approaches in a single system. We argue and illustrate in a case study that the integrated model is better able to account for a difference in nature between area-type land uses (for example, housing, industry, nature), on the one hand, and facility-type land uses (for example, retailing, schools, medical services), on the other. The model is able to generate a limited set of different land-use-plan alternatives by systematically varying macrocharacteristics of facility networks. The results of a case study suggest that the model generates meaningful sets of land-use-plan alternatives in reasonable computation time.
Understanding gay men's sex venues as sites for sexual health promotion
Authors: Smith Anthony M. A. , Grierson Jeffrey W. , von Doussa Henry
Published: May 2010

Background: Despite being understood as sites for the potential spread of sexually transmissible infections, we know remarkably little about how men spend their time when they visit sex venues. The present paper aims to describe the nature of men’s visits to sex venues in terms of where they arrived from, their use of alcohol and other drugs before and while at the venue, their expenditure of time in a range of activities at the venue, and their awareness of sexual health promotion materials at the venue. Methods: Telephone interviews were conducted with 219 men completed within 2 days of them being recruited as they left a sex venue. Results: The majority of men arrived from home or work and had not consumed alcohol or drugs in the 4 h before the visit. The visit lasted 201 min on average and time spent in particular sites or activities within venues varied somewhat with respect to the demographic and behavioural characteristics of the men. Most men reported seeing posters or pamphlets dealing with sexual health. Conclusion: Understanding how men use such venues should allow more effective health promotion in those venues.
Do women use dental dams? Safer sex practices of lesbians and other women who have sex with women
Authors: Richters Juliet , Prestage Garrett , Schneider Karen , Clayton Stevie
Published: May 2010

Dental dams are distributed and promoted in some safer sex campaigns for use in oral sex. However, whether and how often dams are used for sex between Australian women remains unknown. We investigated the use of dental dams for sex by lesbians and other women who have sex with women, and the relationship between dam use and sexual risk for this group. In 2004, a self-completion questionnaire was distributed to women attending the Sydney Gay and Lesbian Mardi Gras Fair Day and lesbian community venues and health services in Sydney (n = 543). Among the 330 women who had had oral sex with a woman in the previous 6 months, 9.7% had used a dental dam and 2.1% had used one ‘often’. There was little evidence of dam use for prevention of sexually transmissible infections. Although women who practised rimming (oral–anal contact) or had fetish sex involving blood were more likely to have used a dam, dam use was not significantly more common among women who had more partners, or had casual or group sex. Some women avoided oral sex during menstruation or had oral sex with a tampon in place. Latex gloves and condoms were used by more women and more often than dams.
Australian men's sexual practices in saunas, sex clubs and other male sex on premises venues
Authors: Lyons Anthony , Smith Anthony M. A. , Grierson Jeffrey W. , von Doussa Henry
Published: May 2010

Background: Sex on premises venues (SOPVs) where men have sex with men have been implicated in the spread of sexually transmissible infections, but few studies have described men’s sexual encounters in SOPVs, particularly the degree to which men from different backgrounds engage in risky sexual practices. Methods: Interviewer administered surveys were conducted with 186 Australian men who have sex with men (MSM) within 48 h of visiting an SOPV. They reported their sexual practices, the characteristics of their partners and other circumstances surrounding their sexual encounters. Results: All analyses were based on the number of sexual encounters (n = 430). Oral sex was the most common practice, occurring in 74.9% of encounters, followed by massage, frottage or kissing (53.7%), solo or mutual masturbation (36.3%), and anal sex (32.1%). Multivariate analyses revealed age as a significant factor for having protected anal sex (P = 0.001), insertive anal sex (P = 0.004) and receptive anal sex (P < 0.001). These practices were more frequent in encounters among younger men, while masturbation (P = 0.03) was more frequent among older men. When men’s sexual partners were affected by alcohol, encounters were less likely to involve unprotected anal intercourse (P = 0.006) and more likely to involve massage, frottage or kissing (P = 0.009). Men disclosed their HIV status in only 7.7% of encounters. Conclusions: With the likelihood of risky sexual practices varying according to background, results from this study should be used to guide interventions aiming to promote safer sex in SOPVs.
Turbulent kinetic energy during wildfires in the north central and north-eastern US
Authors: Heilman Warren E. , Bian Xindi
Published: May 2010

The suite of operational fire-weather indices available for assessing the atmospheric potential for extreme fire behaviour typically does not include indices that account for atmospheric boundary-layer turbulence or wind gustiness that can increase the erratic behaviour of fires. As a first step in testing the feasibility of using a quantitative measure of turbulence as a stand-alone fire-weather index or as a component of a fire-weather index, simulations of the spatial and temporal patterns of turbulent kinetic energy during major recent wildfire events in the western Great Lakes and north-eastern US regions were performed. Simulation results indicate that the larger wildfires in these regions of the US were associated with episodes of significant boundary-layer ambient turbulence. Case studies of the largest recent wildfires to occur in these regions indicate that the periods of most rapid fire growth were generally coincident with occurrences of the product of the Haines Index and near-surface turbulent kinetic energy exceeding a value of 15 m2 s–2, a threshold indicative of a highly turbulent boundary layer beneath unstable and dry atmospheric layers, which is a condition that can be conducive to erratic fire behaviour.
Beyond wildfire: perspectives of climate, managed fire and policy in the USA
Authors: Kolden Crystal A. , Brown Timothy J.
Published: May 2010

Climate–wildfire relationships have been widely addressed by the scientific community over the last two decades; however, the role of climate in managed fire in the US (i.e. prescribed fire and wildland fire use) has not yet been addressed. We hypothesised that if climate is an important component of managed fire, the fire community would already be aware of this and using climate information in order to mitigate risks associated with managed fires. We conducted 223 surveys with fire managers to ascertain how climate information is utilised in managed-fire decision-making. We found that wildland fire use managers consider climate to be an important aspect of managed fire and use various types of climate information, but prescribed-fire managers do not generally consider climate or use climate information in their planning activities. Survey responses also indicate a lack of agency training on climate information and decision-support tools. This is partly attributed to obstacles in US fire policy that inhibit widespread utilisation of climate information. We suggest these results are indicative of a broader conflict in US wildfire policy, which does not directly address climate despite two decades of scientific research showing climate plays a key role in wildfire regimes.
Flammability descriptors of fine dead fuels resulting from two mechanical treatments in shrubland: a comparative laboratory study
Authors: Marino Eva , Madrigal Javier , Guijarro Mercedes , Hernando Carmen , Díez Carmen , Fernández Cristina
Published: May 2010

Mechanical treatments are traditionally used to modify the fuel complex in shrubland, but information about their actual effectiveness in reducing the risk of wildfire initiation is scarce. The effects of two mechanical fuel treatments (shrub clearing with crushing and manual removal) on flammability in a shrubland community in north-western Spain were compared. Three months after treatment, laboratory tests using a point-ignition source were conducted on the fine dead fuels to analyse the effect of type of treatment and fuel moisture content (FMC) under two conditions: (1) flaming; or (2) glowing+wind ignition source. Fuel load effect within each treatment was also studied. Time-to-ignition, flaming duration, number of burnt sides of the sample and fuel consumption ratio were assessed. Logistic models were developed to assess ignition and sustained combustion probabilities. Type of treatment and FMC significantly affected flammability under both experimental conditions tested. Slow smouldering was observed in fuels subjected to shrub clearing and removal, whereas crushing fuels were rapidly burnt with flaming phase combustion. In general, shrub clearing and removal appeared to be more effective in reducing wildfire hazard in these shrubland communities.
Convective heat transfer in fire spread through fine fuel beds
Authors: Anderson W. R. , Catchpole E. A. , Butler B. W.
Published: May 2010

An extensive set of wind-tunnel fires was burned to investigate convective heat transfer ahead of a steadily progressing fire front moving across a porous fuel bed. The effects of fuel and environmental variables on the gas temperature profile and the ‘surface wind speed’ (gas velocity at the fuel bed surface) are reported. In non-zero winds, the temperature of the air near the fuel bed surface decays exponentially with distance from the fire front. In zero winds, the temperature decreases rapidly within a very short distance of the flame front, then decays slowly thereafter. The maximum air temperature decreases as the free stream wind speed, packing ratio and fuel moisture content increase. The characteristic distance of the exponential decay increases strongly with the free stream wind speed and decreases with the packing ratio and surface area-to-volume ratio of the fuel. The surface wind speed depends strongly on the free stream wind speed, and to a lesser extent on packing ratio, fuel bed depth and fuel moisture content. There are three general regimes for the surface flow: (1) a constant velocity flow of approximately half the free stream flow, far from the flame front; (2) an intermediate zone of minimum flow characterised by low or reversed flow; and (3) a region near the flame front where the velocity rises rapidly almost to the free stream velocity. The boundaries between the three regions move further from the flame front with increasing wind speed, in a way which is only slightly affected by fuel geometry.
Spatial variation of trends in wildfire and summer drought in British Columbia, Canada, 1920 - 2000
Authors: Meyn Andrea , Schmidtlein Sebastian , Taylor Stephen W. , Girardin Martin P. , Thonicke Kirsten , Cramer Wolfgang
Published: May 2010

Owing to large climatic and orographic variation, British Columbia covers a variety of ecosystems extending from temperate rainforests on the Pacific coast to boreal forests in the north-east. The aim of this study is to investigate the spatial variation of trends in wildfire activity and their relationship to summer drought for the entire province of British Columbia. Time series of annual wildfire extent and occurrence, summer self-calibrating Palmer Drought Severity Index and summer Aridity Index were derived from spatially explicit data. Sixteen landscape regions according to the provincial Biogeoclimatic Ecosystem Classification system served as spatial reference. The regional series for 1920–2000 were subjected to trend analysis. Correlations between area burned and summer drought were assessed and tested for significance. The observed decrease in wildfire activity is significantly related to wetter summers with the strength of the relationship considerably varying between British Columbia’s landscapes. Our results suggest that aggregated statistics for large regions with complex topography and climate can hide the spatial variation in direction and strength of changes and may accordingly obscure the relationship between fire and drought. Based on high-spatial-resolution data, our study is the first to provide a differentiated picture for British Columbia.
Spliceosome discards intermediates via the DEAH box ATPase Prp43p
Authors: Mayas Rabiah M. , Maita Hiroshi , Semlow Daniel R. , Staley Jonathan P.
Published: May 2010

To promote fidelity in nuclear pre-mRNA splicing, the spliceosome rejects and discards suboptimal substrates that have engaged the spliceosome. Whereas DExD/H box ATPases have been implicated in rejecting suboptimal substrates, the mechanism for discarding suboptimal substrates has remained obscure. Corroborating evidence that suboptimal, mutated lariat intermediates can be exported to the cytoplasm for turnover, we have found that the ribosome can translate mutated lariat intermediates. By glycerol gradient analysis, we have found that the spliceosome can dissociate mutated lariat intermediates in vivo in a manner that requires the DEAH box ATPase Prp43p. Through an in vitro assay, we demonstrate that Prp43p promotes the discard of suboptimal and optimal 5′ exon and lariat intermediates indiscriminately. Finally, we demonstrate a requirement for Prp43p in repressing splicing at a cryptic splice site. We propose a model for the fidelity of exon ligation in which the DEAH box ATPase Prp22p slows the flow of suboptimal intermediates through exon ligation and Prp43p generally promotes discard of intermediates, thereby establishing a pathway for turnover of stalled intermediates. Because Prp43p also promotes spliceosome disassembly after exon ligation, this work establishes a parallel between the discard of suboptimal intermediates and the dissociation of a genuine excised intron product.
Actin, microtubules, and vimentin intermediate filaments cooperate for elongation of invadopodia
Authors: Schoumacher Marie , Goldman Robert D. , Louvard Daniel , Vignjevic Danijela M.
Published: May 2010

Invasive cancer cells are believed to breach the basement membrane (BM) using specialized protrusions called invadopodia. We found that the crossing of a native BM is a three-stage process: invadopodia indeed form and perforate the BM, elongate into mature invadopodia, and then guide the cell toward the stromal compartment. We studied the remodeling of cytoskeleton networks during invadopodia formation and elongation using ultrastructural analysis, spatial distribution of molecular markers, and RNA interference silencing of protein expression. We show that formation of invadopodia requires only the actin cytoskeleton and filopodia- and lamellipodia-associated proteins. In contrast, elongation of invadopodia is mostly dependent on filopodial actin machinery. Moreover, intact microtubules and vimentin intermediate filament networks are required for further growth. We propose that invadopodia form by assembly of dendritic/diagonal and bundled actin networks and then mature by elongation of actin bundles, followed by the entry of microtubules and vimentin filaments. These findings provide a link between the epithelial to mesenchymal transition and BM transmigration.
Suspended Animation Extends Survival Limits ofCaenorhabditis elegansandSaccharomyces cerevisiaeat Low Temperature
Authors: Chan Kin , Goldmark Jesse P. , Roth Mark B.
Published: May 2010

The orderly progression through the cell division cycle is of paramount importance to all organisms, as improper progression through the cycle could result in defects with grave consequences. Previously, our lab has shown that model eukaryotes such as Saccharomyces cerevisiae, Caenorhabditis elegans, and Danio rerio all retain high viability after prolonged arrest in a state of anoxia-induced suspended animation, implying that in such a state, progression through the cell division cycle is reversibly arrested in an orderly manner. Here, we show that S. cerevisiae (both wild-type and several cold-sensitive strains) and C. elegans embryos exhibit a dramatic decrease in viability that is associated with dysregulation of the cell cycle when exposed to low temperatures. Further, we find that when the yeast or worms are first transitioned into a state of anoxia-induced suspended animation before cold exposure, the associated cold-induced viability defects are largely abrogated. We present evidence that by imposing an anoxia-induced reversible arrest of the cell cycle, the cells are prevented from engaging in aberrant cell cycle events in the cold, thus allowing the organisms to avoid the lethality that would have occurred in a cold, oxygenated environment.
TBC-2 Regulates RAB-5/RAB-7-mediated Endosomal Trafficking inCaenorhabditis elegans
Authors: Chotard Laëtitia , Mishra Ashwini K. , Sylvain Marc-André , Tuck Simon , Lambright David G. , Rocheleau Christian E.
Published: May 2010

During endosome maturation the early endosomal Rab5 GTPase is replaced with the late endosomal Rab7 GTPase. It has been proposed that active Rab5 can recruit and activate Rab7, which in turn could inactivate and remove Rab5. However, many of the Rab5 and Rab7 regulators that mediate endosome maturation are not known. Here, we identify Caenorhabditis elegans TBC-2, a conserved putative Rab GTPase-activating protein (GAP), as a regulator of endosome to lysosome trafficking in several tissues. We show that tbc-2 mutant animals accumulate enormous RAB-7–positive late endosomes in the intestine containing refractile material. RAB-5, RAB-7, and components of the homotypic fusion and vacuole protein sorting (HOPS) complex, a RAB-7 effector/putative guanine nucleotide exchange factor (GEF), are required for the tbc-2(−) intestinal phenotype. Expression of activated RAB-5 Q78L in the intestine phenocopies the tbc-2(−) large late endosome phenotype in a RAB-7 and HOPS complex-dependent manner. TBC-2 requires the catalytic arginine-finger for function in vivo and displays the strongest GAP activity on RAB-5 in vitro. However, TBC-2 colocalizes primarily with RAB-7 on late endosomes and requires RAB-7 for membrane localization. Our data suggest that TBC-2 functions on late endosomes to inactivate RAB-5 during endosome maturation.
Free Edges in Epithelial Cell Sheets Stimulate Epidermal Growth Factor Receptor Signaling
Authors: Block Ethan R. , Tolino Michael A. , Lozano Jennifer S. , Lathrop Kira L. , Sullenberger Rebecca S. , Mazie Abigail R. , Klarlund Jes K.
Published: May 2010

The ability of epithelia to migrate and cover wounds is essential to maintaining their functions as physical barriers. Wounding induces many cues that may affect the transition to motility, including the immediate mechanical perturbation, release of material from broken cells, new interactions with adjacent extracellular matrix, and breakdown of physical separation of ligands from their receptors. Depending on the exact nature of wounds, some cues may be present only transiently or insignificantly. In many epithelia, activation of the epidermal growth factor receptor (EGFR) is a central event in induction of motility, and we find that its continuous activation is required for progression of healing of wounds in sheets of corneal epithelial cells. Here, we examine the hypothesis that edges, which are universally and continuously present in wounds, are a cue. Using a novel culture model we find that their presence is sufficient to cause activation of the EGFR and increased motility of cells in the absence of other cues. Edges that are bordered by agarose do not induce activation of the EGFR, indicating that activation is not due to loss of any specific type of cell–cell interaction but rather due to loss of physical constraints.
MiR-322/424 and -503 Are Induced during Muscle Differentiation and Promote Cell Cycle Quiescence and Differentiation by Down-Regulation of Cdc25A
Authors: Sarkar Sukumar , Dey Bijan K. , Dutta Anindya
Published: May 2010

Induction of a G1 phase cell cycle arrest, caused primarily by the inhibition of cyclin-dependent-kinase 2 (cdk2), is a critical step in the differentiation of myoblasts into myotubes. Here, we report that two microRNAs, miR-322/424 and miR-503, are induced and promote cdk2 inhibition during myogenesis. These microRNAs down-regulate Cdc25A, the phosphatase responsible for removing inhibitory phosphorylation of cdk2, both in myoblasts differentiating into myotubes and in nonmuscle cells. Cdc25A is down-regulated during muscle differentiation by multiple pathways: action of these two microRNAs, proteasomal degradation of Cdc25A protein and transcriptional repression. Overexpression of Cdc25A or of cdk2 with mutations on T14 and Y15 (cdk2-AF), so that it cannot be inhibited by phosphorylation, decreases differentiation and differentiation-induced cell cycle quiescence. Introduction of miR-322/424 and miR-503 in heterologous cancer cells induces G1 arrest, which is also attenuated by overexpression of the cdk2-AF mutant. Until now Cdc25A and the inhibitory phosphorylation on T14 and Y15 of cdk2 have only been implicated in the intra-S phase checkpoint pathway after DNA damage. Our results reveal an unexpected role of Cdc25A down-regulation and the inhibitory phosphorylation of cdk2 T14 and Y15 in cell cycle quiescence during muscle differentiation and implicate two muscle differentiation-induced microRNAs in the process.
P38 Mitogen-activated Protein Kinase Activity Is Required during Mitosis for Timely Satisfaction of the Mitotic Checkpoint But Not for the Fidelity of Chromosome Segregation
Authors: Lee Kyunghee , Kenny Alison E. , Rieder Conly L.
Published: May 2010

Although p38 activity is reported to be required as cells enter mitosis for proper spindle assembly and checkpoint function, its role during the division process remains controversial in lieu of direct data. We therefore conducted live cell studies to determine the effect on mitosis of inhibiting or depleting p38. We found that in the absence of p38 activity the duration of mitosis is prolonged by ∼40% in nontransformed human RPE-1, ∼80% in PtK2 (rat kangaroo), and ∼25% in mouse cells, and this prolongation leads to an elevated mitotic index. However, under this condition chromatid segregation and cytokinesis are normal. Using Mad2/YFP-expressing cells, we show the prolongation of mitosis in the absence of p38 activity is directly due to a delay in satisfying the mitotic checkpoint. Inhibiting p38 did not affect the rate of chromosome motion; however, it did lead to the formation of significantly (10%) longer metaphase spindles. From these data we conclude that normal p38 activity is required for the timely stable attachment of all kinetochores to spindle microtubules, but not for the fidelity of the mitotic process. We speculate that p38 activity promotes timely checkpoint satisfaction by indirectly influencing those motor proteins (e.g., Klp10, Klp67A) involved in regulating the dynamics of kinetochore microtubule ends.
Jack of All Trades: Cramp Shipbuilding, Mixed Production, and the Limits of Flexible Specialization in American Warship Construction, 1940–1945
Authors: Heinrich Thomas B
Published: May 2010

Naval shipbuilding was one of the most ambitious industrial undertakings of World War II. A marginal business, in 1939 employing only twelve shipyards, it expanded over the course of the war into a massive network of shipbuilding firms, engineering works, steel mills, and specialty producers that built the world's largest fleet. At its peak in 1944, warship building employed one million shipyard workers, a million others in collateral industries, and consumed one-fifth of the nation's steel output in the construction of aircraft carriers, battleships, cruisers, destroyers, and thousands of smaller combatants.
Infection Processes and Involvement of Defense-Related Genes in the Expression of Resistance in Cultivars of Subterranean Clover (Trifolium subterraneum) to Phytophthora clandestina
Authors: Ma X. , Li Hua , Sivasithamparam K. , Barbetti M. J.
Published: May 2010

Studies on infection processes and gene expression were done to determine differential responses of cultivars of Trifolium subterraneum resistant and susceptible to infection by races of Phytophthora clandestina. In the infection process study, one race was inoculated onto the roots of T. subterraneum cvs. Woogenellup and Junee (compatible or incompatible interactions, respectively). There were no differences in relation to the processes of cyst attachment, germination, and hyphal penetration. There were, however, major differences in infection progression observed post-penetration between compatible and incompatible interactions. In susceptible cv. Woogenellup, hyphae grew into the vascular bundles and produced intercellular antheridia and oogonia in the cortex and stele by 4 days postinoculation (dpi), oospores in the cortex and stele by 8 dpi, when sporangia were evident on the surface of the root. Infected taproots were discolored. Early destruction of taproots prevented emergence of lateral roots. Roots of resistant cv. Junee showed no oospores or sporangia and no disease at 8 dpi. In the gene expression studies, two races of P. clandestina were inoculated onto three cultivars of T. subterraneum. Results showed that three genes known to be associated with plant defense against plant pathogens were differentially expressed in the roots during compatible and incompatible interactions. Phenylalanine ammonia lyase and chalcone synthase genes were activated 4 h postinoculation (hpi) and cytochrome P450 trans-cinnamic acid 4-monooxygenase gene was activated 8 hpi in the incompatible interactions in cvs. Denmark and Junee following inoculation with Race 177. In contrast, in compatible interactions in cv. Woogenellup, there were no significant changes in the activation of these three genes following inoculation, indicating that these three genes were associated with the expression of resistance to Race 177 of the pathogen by the host. To confirm this result, in the second test, cv. Woogenellup was challenged by Race 000 of P. clandestina. In this incompatible interaction, cv. Woogenellup was resistant and expressed highly all three genes in the manner similar to the incompatible interactions observed in the first test.
Host Range and Complete Genome Sequence of Cucurbit chlorotic yellows virus, a New Member of the Genus Crinivirus
Authors: Okuda Mitsuru , Okazaki Shinichiro , Yamasaki Shuichi , Okuda Shiori , Sugiyama Mitsuhiro
Published: May 2010

Cucurbit chlorotic yellows virus (CCYV) causes chlorotic yellows on cucumber (Cucumis sativus) and melon (Cucumis melo) and is transmitted by Bemisia tabaci biotype B and Q whiteflies. To characterize the host range of CCYV, 21 cucurbitaceous and 12 other plant species were inoculated using whitefly vectors. All tested Cucumis spp. except Cucumis anguria and Cucumis zeyheri were systemically infected with CCYV, although infection rates varied among species. Citrullus lanatus, Cucurbita pepo, and Luffa cylindrica were susceptible to CCYV; however, the infection rates were low and symptoms were unclear. In addition to the cucurbitaceous plants, Beta vulgaris, Chenopodium amaranticolor, Chenopodium quinoa, Spinacia oleracea, Lactuca sativa, Datura stramonium, and Nicotiana benthamiana were also systemically infected by CCYV. Complete RNA1 and RNA2 were reverse-transcribed, cloned, and sequenced. CCYV RNA1 was found to be 8,607 nucleotides (nt) long and contained four open reading frames (ORFs). The first ORF spanned methyltransferase and RNA helicase domains followed by an RNA-dependent RNA polymerase domain, presumably translated by a +1 ribosomal frameshift. CCYV RNA2 was found to be 8,041 nt long and contained eight ORFs, including the hallmark gene array of the family Closteroviridae. Phylogenetic analysis demonstrated that CCYV was genetically close to Lettuce chlorosis virus, Bean yellow disorder virus, and Cucurbit yellow stunting disorder virus. Amino acid sequence similarities of representative proteins with these viruses indicated that CCYV should be classified as a distinct crinivirus species.
Guangdong and Florida Populations of ‘Candidatus Liberibacter asiaticus’ Distinguished by a Genomic Locus with Short Tandem Repeats
Authors: Chen J. , Deng X. , Sun X. , Jones D. , Irey M. , Civerolo E.
Published: May 2010

Huanglongbing (HLB) (yellow shoot disease) is a highly destructive disease that threatens citrus production worldwide. The disease was first observed in Guangdong, P.R. China, over 100 years ago, and was found in Florida, United States, in 2005. ‘Candidatus Liberibacter asiaticus’ has been associated with HLB in many citrus-growing regions around the world, including Guangdong and Florida. The global epidemiology of HLB, as well as management of the disease, relies on knowledge of ‘Ca. L. asiaticus’ populations in different geographical regions around the world. In this study, we identified a genetic marker containing small tandem repeats in the genome of ‘Ca. L. asiaticus’ and comparatively analyzed the tandem repeat numbers (TRNs) in ‘Ca. L. asiaticus’ populations from Guangdong and Florida. Analyses of TRNs showed that the bacterial population in Guangdong was different from that in Florida. The Guangdong population consisted predominately of strains with a TRN of 7 (TRN7) at a frequency of 47.6%. The Florida population consisted predominately of strains with a TRN of 5 (TRN5) at a frequency of 84.4%. TRNs ranged from 3 to 16. The apparent absence of TRNs of 9, 10, 11, and 12 separated the bacterial strains into two groups: TRNs < 10 (TRN<10) and TRNs > 10 (TRN>10). In Florida, TRN<10 strains (103/109, or 94.5%) were widely distributed in all HLB-affected counties. TRN>10 strains (6/109, or 5.5%) were found in central Florida. This is the first report documenting the differentiation of ‘Ca. L. asiaticus’ populations between Asia and North America and the possible presence of two differentially distributed genotypes of ‘Ca. L. asiaticus’ in Florida.
Ectopic Expression of the Rice Lumazine Synthase Gene Contributes to Defense Responses in Transgenic Tobacco
Authors: Wu Tingquan , Guo An , Zhao Yanying , Wang Xiaomeng , Wang Ying , Zhao Dan , Li Xiaojie , Ren Haiying , Dong Hansong
Published: May 2010

Lumazine synthase (LS) catalyzes the penultimate reaction in the multistep riboflavin biosynthesis pathway, which is involved in plant defenses. Plant defenses are often subject to synergistic effects of jasmonic acid and ethylene whereas LS is a regulator of jasmonic acid signal transduction. However, little is known about whether the enzyme contributes to defense responses. To study the role of LS in plant pathogen defenses, we generated transgenic tobacco expressing the rice (Oryza sativa) LS gene, OsLS. OsLS was cloned and found to have strong identity with its homologues in higher plants and less homology to microbial orthologues. The OsLS protein localized to chloroplasts in three OsLS-expressing transgenic tobacco (LSETT) lines characterized as enhanced in growth and defense. Compared with control plants, LSETT had higher content of both riboflavin and the cofactors flavin mononucleotide and flavin adenine dinucleotide. In LSETT, jasmonic acid and ethylene were elevated, the expression of defense-related genes was induced, levels of resistance to pathogens were enhanced, and resistance was effective to viral, bacterial, and oomycete pathogens. Extents of OsLS expression correlated with increases in flavin, jasmonic acid, and ethylene content, and correlated with increases in resistance levels, suggesting a role for OsLS in defense responses.
Canopy and litter ant assemblages share similar climate–species density relationships
Authors: Weiser Michael D. , Sanders Nathan J. , Agosti Donat , Andersen Alan N. , Ellison Aaron M. , Fisher Brian L. , Gibb Heloise , Gotelli Nicholas J. , Gove Aaron D. , Gross Kevin , Guénard Benoit , Janda Milan , Kaspari Michael , Lessard Jean-Philippe , Longino John T. , Majer Jonathan D. , Menke Sean B. , McGlynn Terrence P. , Parr Catherine L. , Philpott Stacy M. , Retana Javier , Suarez Andrew V. , Vasconcelos Heraldo L. , Yanoviak Stephen P. , Dunn Robert R.
Published: May 2010

Tropical forest canopies house most of the globe's diversity, yet little is known about global patterns and drivers of canopy diversity. Here, we present models of ant species density, using climate, abundance and habitat (i.e. canopy versus litter) as predictors. Ant species density is positively associated with temperature and precipitation, and negatively (or non-significantly) associated with two metrics of seasonality, precipitation seasonality and temperature range. Ant species density was significantly higher in canopy samples, but this difference disappeared once abundance was considered. Thus, apparent differences in species density between canopy and litter samples are probably owing to differences in abundance–diversity relationships, and not differences in climate–diversity relationships. Thus, it appears that canopy and litter ant assemblages share a common abundance–diversity relationship influenced by similar but not identical climatic drivers.
What do fish make of mirror images?
Authors: Desjardins Julie K. , Fernald Russell D.
Published: May 2010

Fish act aggressively towards their mirror image suggesting that they consider it another individual, whereas in some mammals behavioural response to mirrors may be an evidence of self-recognition. Since fish cannot self-recognize, we asked whether they could distinguish between fighting a mirror image and fighting a real fish. We compared molecular, physiological and behavioural responses in each condition and found large differences in brain gene expression levels. Although neither levels of aggressive behaviour nor circulating androgens differed between these conditions, males fighting a mirror image had higher immediate early gene (IEG) expression in brain areas homologous to the amygdala and hippocampus than controls. Since amygdalar responses are associated with fear and fear conditioning in other species, higher levels of brain activation when fighting a mirror suggest fish experience fear in response to fights with a mirror image. Clearly, the fish recognize something unusual about the mirror image and the differential brain response may reflect a cognitive distinction.
Cell size is positively correlated between different tissues in passerine birds and amphibians, but not necessarily in mammals
Authors: Kozłowski J. , Czarnołęski M. , François-Krassowska A. , Maciak S. , Pis T.
Published: May 2010

We examined cell size correlations between tissues, and cell size to body mass relationships in passerine birds, amphibians and mammals. The size correlated highly between all cell types in birds and amphibians; mammalian tissues clustered by size correlation in three tissue groups. Erythrocyte size correlated well with the volume of other cell types in birds and amphibians, but poorly in mammals. In birds, body mass correlated positively with the size of all cell types including erythrocytes, and in mammals only with the sizes of some cell types. Size of mammalian erythrocytes correlated with body mass only within the most taxonomically uniform group of species (rodents and lagomorphs). Cell volume increased with body mass of birds and mammals to less than 0.3 power, indicating that body size evolved mostly by changes in cell number. Our evidence suggests that epigenetic mechanisms determining cell size relationships in tissues are conservative in birds and amphibians, but less stringent in mammals. The patterns of cell size to body mass relationships we obtained challenge some key assumptions of fractal and cellular models used by allometric theory to explain mass-scaling of metabolism. We suggest that the assumptions in both models are not universal, and that such models need reformulation.