1,977 research outputs found
Selenium uptake, translocation and speciation in wheat supplied with selenate or selenite
Selenite can be a dominant form of selenium (Se) in aerobic soils; however, unlike selenate, the mechanism of selenite uptake by plants remains unclear. Uptake, translocation and Se speciation in wheat (Triticum aestivum) supplied with selenate or selenite, or both, were investigated in hydroponic experiments. The kinetics of selenite influx was determined in short-term (30 min) experiments. Selenium speciation in the water-extractable fraction of roots and shoots was determined by HPLC-ICPMS. Plants absorbed similar amounts of Se within 1 d when supplied with selenite or selenate. Selenate and selenite uptake were enhanced in sulphur-starved and phosphorus-starved plants, respectively. Phosphate markedly increased K-m of the selenite influx. Selenate and selenite uptake were both metabolically dependent. Selenite was rapidly converted to organic forms in roots, with limited translocation to shoots. Selenomethionine, selenomethionine Se-oxide, Se-methyl-selenocysteine and several other unidentified Se species were detected in the root extracts and xylem sap from selenite-treated plants. Selenate was highly mobile in xylem transport, but little was assimilated to organic forms in 1 d. The presence of selenite decreased selenate uptake and xylem transport. Selenite uptake is an active process likely mediated, at least partly, by phosphate transporters. Selenite and selenate differ greatly in the ease of assimilation and xylem transport
Incorporation of calcium in glasses: a key to understand the vitrification of sewage sludge
The quantity of sewage sludge generated daily by wastewater treatment plants represents a major environmental problem and a financial burden for plant operators. Valorization strategies focusing on reusing sewage sludge as a raw material are currently developed. Vitrification can help us reduce the volume of waste and binds the components in the structure of chemically stable glasses and glassāceramics. In this study, the vitrification of sewage sludge inside a basaltic rock has been simulated by producing glasses and a glassāceramic from basalt enriched in calcium that lie between the stability fields of pyroxene and melilite in the system CaOāMgOāSiO2āAl2O3. CaO addition causes the oxidation of the melt at above the liquidus, increases the crystallization temperature, decreases the melting temperature and improves the microhardness of the glasses Glassāceramic processes improves the properties of the Caādoped basalt glass. The microhardness of the glass (8.2 GPa) and the glassāceramic (8.6 GPa) and leaching tests (in the ppb range) place both the glass and the glassāceramics at the high end of the mechanical properties and chemical resistance of ceramic tiles for the building industry
Integrating Delphi methodology to some classical concepts of the Boston consulting group framework: arctic maritime technology BCG Delphi foresightāa pilot study from Finland
Measurement of the hadronic photon structure function F_{2}^{Ī³} at LEP2
The hadronic structure function of the photon F_{2}^{Ī³} (x, QĀ²) is measured as a function of Bjorken x and of the photon virtuality QĀ² using deep-inelastic scattering data taken by the OPAL detector at LEP at eāŗeā» centre-of-mass energies from 183 to 209 GeV. Previous OPAL measurements of the x dependence of F_{2}^{Ī³} are extended to an average QĀ² of ćQĀ²ć=780 GeVĀ² using data in the kinematic range 0.15<x<0.98. The QĀ² evolution of F_{2}^{Ī³} is studied for 12.1<ćQĀ²ć<780 GeVĀ² using three ranges of x. As predicted by QCD, the data show positive scaling violations in F_{2}^{Ī³} with F_{2}^{Ī³} (QĀ²)/Ī± = (0.08Ā±0.02āŗā°Ā·ā°āµ_ā.āā) + (0.13Ā±0.01āŗā°Ā·ā°Ā¹_ā.āā) lnQĀ², where QĀ² is in GeVĀ², for the central x region 0.10ā0.60. Several parameterisations of F_{2}^{Ī³} are in qualitative agreement with the measurements whereas the quark-parton model prediction fails to describe the data
Measurement of the charm structure function F_{2,c)^{Ī³} of the photon at LEP
The production of charm quarks is studied in deep-inelastic electronāphoton scattering using data recorded by the OPAL detector at LEP at nominal eāŗeā» centre-of-mass energies from 183 to 209 GeV. The charm quarks have been identified by full reconstruction of charged D* mesons using their decays into Dā°Ļ with the Dā° observed in two decay modes with charged particle final states, KĻ and KĻĻĻ. The cross-section Ļ^{D*} for production of charged D* in the reaction eāŗeā»āeāŗeā»D*Ī§ is measured in a restricted kinematical region using two bins in Bjorken x, 0.00140.1 the perturbative QCD calculation at next-to-leading order agrees perfectly with the measured cross-section. For x<0.1 the measured cross-section is 43.8Ā±14.3Ā±6.3Ā±2.8 pb with a next-to-leading order prediction of 17.0āŗĀ²Ā·ā¹_ā.ā pb
Phosphorylation of Puma modulates its apoptotic function by regulating protein stability
Puma is a potent BH3-only protein that antagonises anti-apoptotic Bcl-2 proteins, promotes Bax/Bak activation and has an essential role in multiple apoptotic models. Puma expression is normally kept very low, but can be induced by several transcription factors including p53, p73, E2F1 and FOXO3a, whereby it can induce an apoptotic response. As Puma can to bind and inactivate all anti-apoptotic members of the Bcl-2 family, its activity must be tightly controlled. We report here, for the first time, evidence that Puma is subject to post-translational control through phosphorylation. We show that Puma is phosphorylated at multiple sites, with the major site of phosphorylation being serine 10. Replacing serine 10 with alanine causes reduced Puma turnover and enhanced cell death. Interestingly, Puma turnover occurs through the proteasome, and substitution of serine 10 causes elevated Puma levels independently of macroautophagy, Bcl-2 family member binding, caspase activity and apoptotic death. We conclude, therefore, that phosphorylation of Puma at serine 10 promotes Puma turnover, represses Puma's cell death potential and promotes cell survival. Owing to the highly pro-apoptotic nature of Puma, these studies highlight an important additional regulatory step in the determination of cellular life or death
Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy
Our Galaxy is thought to have undergone an active evolutionary history
dominated by star formation, the accretion of cold gas, and, in particular,
mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of
these interactions in the form of stellar streams, substructures, and
chemically distinct stellar components. The impact of dwarf galaxy mergers on
the content and morphology of the Galactic disk is still being explored. Recent
studies have identified kinematically distinct stellar substructures and moving
groups, which may have extragalactic origin. However, there is mounting
evidence that stellar overdensities at the outer disk/halo interface could have
been caused by the interaction of a dwarf galaxy with the disk. Here we report
detailed spectroscopic analysis of 14 stars drawn from two stellar
overdensities, each lying about 5 kiloparsecs above and below the Galactic
plane - locations suggestive of association with the stellar halo. However, we
find that the chemical compositions of these stars are almost identical, both
within and between these groups, and closely match the abundance patterns of
the Milky Way disk stars. This study hence provides compelling evidence that
these stars originate from the disk and the overdensities they are part of were
created by tidal interactions of the disk with passing or merging dwarf
galaxies.Comment: accepted for publication in Natur
Measurement of triple gauge boson couplings from WāŗWā» production at LEP energies up to 189 GeV
A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pbā»Ā¹. After combining with our previous measurements at centre-of-mass energies of 161ā183 GeV we obtain Īŗ = 0.97_{-0.16}^{+0.20}, g_{1}^{z} = 0.991_{-0.057}^{+0.060} and Ī» = -0.110_{-0.055}^{+0.058}, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their Standard Model values. These results are consistent with the Standard Model expectations
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
Grouping of tooth surfaces by susceptibility to caries: a study in 5ā16 year-old children
BACKGROUND: The decline in caries has slowed and this may be indicative of variation in the susceptibility of differing teeth to caries. This study tests the hypothesis that in children, there are groups of tooth sites that exhibit differences in caries susceptibility. METHODS: Probit analysis of caries data collected from a 4-year longitudinal study of 20,000 schoolchildren aged between 5 and 16 years in 10 differing locations in the United States. RESULTS: The development of dental caries within the mouth followed a fixed hierarchy indicating that tooth surfaces show variation in caries susceptibility. Certain teeth and tooth sites have similar susceptibilities and can be grouped, the sizes of the groups vary. The most susceptible group consists of six tooth surfaces: the buccal pits and occlusal fissured surfaces of the first molar teeth. The second group consisted of 12 sites on the second molar and premolar teeth. The group formed by the least susceptible sites included the largest number of tooth surfaces and consists of the majority of the lower anterior teeth and canines. CONCLUSION: Variation in the caries susceptibility of tooth surfaces exists. Surfaces can be grouped according to caries susceptibility. An effect that reduces the cariogenic challenge of one of the sites within a group is likely to affect all the other sites within the particular group
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