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Träfflista för sökning "WFRF:(Chen L. C.) srt2:(2000-2004)"

Sökning: WFRF:(Chen L. C.) > (2000-2004)

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1.
  • Ahrens, J., et al. (författare)
  • Observation of high energy atmospheric neutrinos with the Antarctic muon and neutrino detector array
  • 2002
  • Ingår i: Physical Review D. - : American Physical Society. - 1550-7998 .- 1550-2368. ; 66:1, s. 120051-1200520
  • Tidskriftsartikel (refereegranskat)abstract
    • The Antarctic muon and neutrino detector array (AMANDA) began collecting data with ten strings in 1997. Results from the first year of operation are presented. Neutrinos coming through the Earth from the Northern Hemisphere are identified by secondary muons moving upward through the array. Cosmic rays in the atmosphere generate a background of downward moving muons, which are about 106 times more abundant than the upward moving muons. Over 130 days of exposure, we observed a total of about 300 neutrino events. In the same period, a background of 1.05 × 109 cosmic ray muon events was recorded. The observed neutrino flux is consistent with atmospheric neutrino predictions. Monte Carlo simulations indicate that 90% of these events lie in the energy range 66 GeV to 3.4 TeV. The observation of atmospheric neutrinos consistent with expectations establishes AMANDA-B10 as a working neutrino telescope.
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2.
  • Andres, E., et al. (författare)
  • Selected recent results from AMANDA
  • 2001
  • Ingår i: ICHEP 2000. Proceedings of the 30th International Conference on High Energy Physics. - : World Scientific. ; , s. 965-968
  • Konferensbidrag (refereegranskat)abstract
    • We present a selection of results based on data taken in 1997 with the 302-PMT Antarctic Muon and Neutrino Detector Array-B10 ("AMANDA-B10") array. Atmospheric neutrinos created in the northern hemisphere are observed indirectly through their charged current interactions which produce relativistic, Cherenkov-light-emitting upgoing muons in the South Pole ice cap. The reconstructed angular distribution of these events is in good agreement with expectation and demonstrates the viability of this ice-based device as a neutrino telescope. Studies of nearly vertical upgoing muons limit the available parameter space for WIMP dark matter under the assumption that WIMPS are trapped in the earth's gravitational potential well and annihilate with one another near the earth's center.
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3.
  • Abt, I, et al. (författare)
  • Measurement of the b(b)over-bar production cross section in 920 GeV fixed-target proton-nucleus collisions
  • 2003
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 26:3, s. 345-355
  • Tidskriftsartikel (refereegranskat)abstract
    • Using the HERA-B detector, the b (b) over bar production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The b (b) over bar production was tagged via inclusive bottom quark decays into J/psi by exploiting the longitudinal separation of J/psi --> l(+)l(-) decay vertices from the primary proton-nucleus interaction. Both e(+)e(-) and mu(+)mu(-) channels have been reconstructed and the combined analysis yields the cross section sigma(b (b) over bar) = 32(-12)(+14)(stat) (+6)(-7)(sys) nb/nucleon.
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4.
  • Ahmed, M., et al. (författare)
  • Search for the lepton-family-number nonconserving decay μ +→e +γ
  • 2002
  • Ingår i: Physical Review D. - : American Physical Society. - 1550-7998 .- 1550-2368. ; 65:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The MEGA experiment, which searched for the muon- and electron-number violating decay μ +→e + γ, is described. The spectrometer system, the calibrations, the data taking procedures, the data analysis, and the sensitivity of the experiment are discussed. The most stringent upper limit on the branching ratio, B(μ + →e + γ)<1.2×10 -11 with 90% confidence, is derived from a likelihood analysis.
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5.
  • Andrés, E., et al. (författare)
  • Observation of high-energy neutrinos using Čerenkov detectors embedded deep in Antarctic ice
  • 2001
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 410:6827, s. 441-443
  • Tidskriftsartikel (refereegranskat)abstract
    • Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions. The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova2, as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water3,4 or ice5. Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations1.
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6.
  • Andrés, E., et al. (författare)
  • Recent results from AMANDA
  • 2001
  • Ingår i: International Journal of Modern Physics A. - 0217-751X .- 1793-656X. ; 16:1C, s. 1013-1015
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results based on data taken in 1997 with the 302-PMT Antarctic Muon and Neutrino Detector Array-B10 ("AMANDA-B10") array. Atmospheric neutrinos created in the northern hemisphere are observed indirectly through their charged current interactions which produce relativistic, Cherenkov-light-emitting upgoing muons in the South Pole ice cap. The reconstructed angular distribution of these events is in good agreement with expectation and demonstrates the viability of this ice-based device as a neutrino telescope.
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7.
  • Karle, A., et al. (författare)
  • Observation of high energy atmospheric neutrinos with AMANDA
  • 2000
  • Ingår i: AIP Conference Proceedings. - : American Institute of Physics (AIP). ; , s. 823-827
  • Konferensbidrag (refereegranskat)abstract
    • In 1997 the Antarctic Muon and Neutrino Detector Array (AMANDA) started operating with 10 strings. In an analysis of data taken during the first year of operation 188 atmospheric neutrino candidates were found. Their zenith angle distribution agrees with expectations based on Monte Carlo simulations. A preliminary upper limit is given on a diffuse flux of high energy neutrinos of astrophysical origin.
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8.
  • Wiebusch, C., et al. (författare)
  • Results from AMANDA
  • 2002
  • Ingår i: Modern Physics Letters A. - : Institution of Electrical Engineers (IEE). - 0217-7323 .- 1793-6632. ; 17:31, s. 2019-2037
  • Tidskriftsartikel (refereegranskat)abstract
    • The Antarctic Muon and Neutrino Detector Array (AMANDA) is a high-energy neutrino telescope operating at the geographic South Pole. It is a lattice of photomultiplier tubes buried deep in the polar ice. The primary goal of this detector is to discover astrophysical sources of high energy neutrinos. We describe the detector methods of operation and present results from the AMANDA-B10 prototype. We demonstrate the improved sensitivity of the current AMANDA-II detector. We conclude with an outlook to the envisioned sensitivity of the future IceCube detector.
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9.
  • Abt, I, et al. (författare)
  • Inclusive V-0 production cross sections from 920 GeV fixed target proton-nucleus collisions
  • 2003
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 29:2, s. 181-190
  • Tidskriftsartikel (refereegranskat)abstract
    • Inclusive differential cross sections dsigma(pA)/dx(F) and dsigma(pA)/dp(t)(2) for the production of K-S(0), Lambda, and (&ULambda;) over bar particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to roots = 41.6 GeV in the proton-nucleon system. The ratios of differential cross sections dsigma(pA)(K-S(0))/dsigma(pA)(Lambda) and dsigma(pA)((&ULambda;) over bar)/dsigma(pA) (Lambda) are measured to be 6.2 +/- 0.5 and 0.66 +/- 0.07, respectively, for x(F) approximate to -0.06. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions da,Ald t also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections sigma(pA) on the atomic mass A of the target material is discussed, and the deduced cross sections per nucleon sigma(pN) are compared with results obtained at other energies.
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10.
  • Ahrens, J., et al. (författare)
  • Results from the Antarctic muon and nuetrino detector array
  • 2003
  • Ingår i: Nuclear physics B, Proceedings supplements. - : Elsevier. - 0920-5632 .- 1873-3832. ; 118, s. 371-379
  • Tidskriftsartikel (refereegranskat)abstract
    • We show new results from both the older and newer incarnations of AMANDA (AMANDA-B10 and AMANDA-II, respectively). These results demonstrate that AMANDA is a functioning, multipurpose detector with significant physics and astrophysics reach. They include a new higher-statistics measurement of the atmospheric muon neutrino flux and preliminary results from searches for a variety of sources of ultrahigh energy neutrinos: generic point sources, gamma-ray bursters and diffuse sources producing muons in the detector, and diffuse sources producing electromagnetic or hadronic showers in or near the detector.
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11.
  • Ahrens, J., et al. (författare)
  • Search for supernova neutrino bursts with the AMANDA detector
  • 2001
  • Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 16:4, s. 345-359
  • Tidskriftsartikel (refereegranskat)abstract
    • The core collapse of a massive star in the Milky Way will produce a neutrino burst, intense enough to be detected by existing underground detectors. The AMANDA neutrino telescope located deep in the South Pole ice can detect MeV neutrinos by a collective rate increase in all photo-multipliers on top of dark noise. The main source of light comes from positrons produced in the CC reaction of anti-electron neutrinos on free protons ve + p → e+ + n. This paper describes the first supernova search performed on the full sets of data taken during 1997 and 1998 (215 days of live time) with 302 of the detector's optical modules. No candidate events resulted from this search. The performance of the detector is calculated, yielding a 70% coverage of the galaxy with one background fake per year with 90% efficiency for the detector configuration under study. An upper limit at the 90% c.l. on the rate of stellar collapses in the Milky Way is derived, yielding 4.3 events per year. A trigger algorithm is presented and its performance estimated. Possible improvements of the detector hardware are reviewed.
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12.
  • Imanishi, T., et al. (författare)
  • Integrative annotation of 21,037 human genes validated by full-length cDNA clones
  • 2004
  • Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 2:6, s. 856-875
  • Tidskriftsartikel (refereegranskat)abstract
    • The human genome sequence defines our inherent biological potential; the realization of the biology encoded therein requires knowledge of the function of each gene. Currently, our knowledge in this area is still limited. Several lines of investigation have been used to elucidate the structure and function of the genes in the human genome. Even so, gene prediction remains a difficult task, as the varieties of transcripts of a gene may vary to a great extent. We thus performed an exhaustive integrative characterization of 41,118 full-length cDNAs that capture the gene transcripts as complete functional cassettes, providing an unequivocal report of structural and functional diversity at the gene level. Our international collaboration has validated 21,037 human gene candidates by analysis of high-quality full-length cDNA clones through curation using unified criteria. This led to the identification of 5,155 new gene candidates. It also manifested the most reliable way to control the quality of the cDNA clones. We have developed a human gene database, called the H-Invitational Database (H-InvDB; http://www.h-invitational.jp/). It provides the following: integrative annotation of human genes, description of gene structures, details of novel alternative splicing isoforms, non-protein-coding RNAs, functional domains, subcellular localizations, metabolic pathways, predictions of protein three-dimensional structure, mapping of known single nucleotide polymorphisms (SNPs), identification of polymorphic microsatellite repeats within human genes, and comparative results with mouse full-length cDNAs. The H-InvDB analysis has shown that up to 4% of the human genome sequence (National Center for Biotechnology Information build 34 assembly) may contain misassembled or missing regions. We found that 6.5% of the human gene candidates (1,377 loci) did not have a good protein-coding open reading frame, of which 296 loci are strong candidates for non-protein-coding RNA genes. In addition, among 72,027 uniquely mapped SNPs and insertions/deletions localized within human genes, 13,215 nonsynonymous SNPs, 315 nonsense SNPs, and 452 indels occurred in coding regions. Together with 25 polymorphic microsatellite repeats present in coding regions, they may alter protein structure, causing phenotypic effects or resulting in disease. The H-InvDB platform represents a substantial contribution to resources needed for the exploration of human biology and pathology.
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13.
  • Ahrens, J., et al. (författare)
  • Limits to the muon flux from WIMP annihilation in the center of the Earth with the AMANDA detector
  • 2002
  • Ingår i: Physical Review D. - : American Physical Society. - 1550-7998 .- 1550-2368. ; 66:3, s. 032006-
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for nearly vertical up-going muon-neutrinos from neutralino annihilations in the center of the Earth has been performed with the AMANDA-B10 neutrino detector. The data collected in 130.1 days of live time in 1997, ∼10 9 events, have been analyzed for this search. No excess over the expected atmospheric neutrino background has been observed. An upper limit at 90% confidence level has been obtained on the annihilation rate of neutralinos in the center of the Earth, as well as the corresponding muon flux limit, both as a function of the neutralino mass in the range 100 GeV-5000 GeV. © 2002 The American Physical Society.
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14.
  • Ahrens, J., et al. (författare)
  • Search for Extraterrestrial Point Sources of Neutrinos with AMANDA-II
  • 2004
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 92:7, s. 711021-711025
  • Tidskriftsartikel (refereegranskat)abstract
    • The results of a search for point sources of high energy neutrinos in the northern hemisphere were presented using AMANDA-II data collected in the year 2000. The results included the flux limits on several active-galactic-nuclei blazars, microquasars, magnetars, and other candidate neutrino sources. A search for excesses above a random background of cosmic ray induced atmospheric neutrinos and misreconstructed downgoing cosmic-rays muons, which revealed no statistically significant neutrino point sources was also presented. It was shown that AMANDA-II had achieved the sensitivity required to probe known TeV γ-ray sources such as the blazar Markarian 501 in its 1997 flaring state at a level where neutrino and γ-ray fluxes were equal.
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15.
  • Ahrens, J., et al. (författare)
  • Search for neutrino-induced cascades with the AMANDA detector
  • 2003
  • Ingår i: Physical Review D. - : American Physical Society (APS). - 1550-7998 .- 1550-2368. ; 67:1, s. 012003-
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on a search for electromagnetic and/or hadronic showers (cascades) induced by a diffuse flux of neutrinos with energies between 5 TeV and 300 TeV from extraterrestrial sources. Cascades may be produced by matter interactions of all flavors of neutrinos, and contained cascades have better energy resolution and afford better background rejection than throughgoing νμ-induced muons. Data taken in 1997 with the AMANDA detector were searched for events with a high-energy cascadelike signature. The observed events are consistent with expected backgrounds from atmospheric neutrinos and catastrophic energy losses from atmospheric muons. Effective volumes for all flavors of neutrinos, which allow the calculation of limits for any neutrino flux model, are presented. The limit on cascades from a diffuse flux of νe+ νμ + ντ+ ν̄e + ν̄μ+ ν̄τ is E2(dΦ/dE)<9.8×10-6 GeV cm-2 s-1 sr-1, assuming a neutrino flavor flux ratio of 1:1:1 at the detector. The limit on cascades from a diffuse flux of νe+ν̄e is E2(dΦ/dE)<6. 5×10-6 GeV cm-2 s-1 sr-1, independent of the assumed neutrino flavor flux ratio. © 2003 The American Physical Society.
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16.
  • Alcorn, J, et al. (författare)
  • Basic instrumentation for Hall A at Jefferson Lab
  • 2004
  • Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 522:3, s. 294-346
  • Tidskriftsartikel (refereegranskat)abstract
    • The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved.
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17.
  • Kowalski, Marek, et al. (författare)
  • Physics results from the AMANDA neutrino detector
  • 2001
  • Ingår i: Proceedings of Science. - 1824-8039. ; HEP2001
  • Tidskriftsartikel (refereegranskat)abstract
    • In the winter season of 2000, the AMANDA (Antarctic Muon And NeutrinoDetector Array) detector was completed to its nal state. We report on major physicsresults obtained from the AMANDA-B10 detector, as well as initial results of the fullAMANDA-II detector.
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18.
  • Ahrens, J., et al. (författare)
  • Initial results from AMANDA
  • 2001
  • Ingår i: 21st Rencontres de Moriond Workshop on Very High-Energy Phenomena in the Universe.
  • Konferensbidrag (refereegranskat)
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19.
  • Ahrens, J., et al. (författare)
  • Results from AMANDA
  • 2001
  • Ingår i: Proceedings, 9th International Workshop, Venice, Italy, March 6-9, 2001. Vol. 1, 2. ; , s. 569-580
  • Konferensbidrag (refereegranskat)
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20.
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21.
  • Bai, X., et al. (författare)
  • Status of the Neutrino Telescope AMANDA : Monopoles and WIMPS
  • 2001
  • Ingår i: Dark Matter in Astro- and Particle Physics. - Berlin, Heidelberg : Springer. - 9783642626081 ; , s. 699-706
  • Konferensbidrag (refereegranskat)abstract
    • The neutrino telescope AMANDA has been set up at the geographical South Pole as first step to a neutrino telescope of the scale of one cubic kilometer, which is the canonical size for a detector sensitive to neutrinos from Active Galactic Nuclei (AGN), Gamma Ray Bursts (GRB) and Topological Defects (TD). The location and depth in which the detector is installed is given by the requirement to detect neutrinos by the Cherenkov light produced by their reaction products and to keep the background due to atmospheric muons as small as possible. However, a detector optimized for this purpose is also capable to detect the bright Cherenkov light from relativistic Monopoles and neutrino signals from regions with high gravitational potential, where WIMPS are accumulated and possibly annihilate. Both hypothetical particles might contribute to the amount of dark matter. Therefore here a report about the status of the experiment (autumn 2000) and about the status of the search for these particles with the AMANDA B10 sub-detector is given.
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22.
  • Edsjö, Joakim, et al. (författare)
  • WIMP searches with AMANDA-B10
  • 2001
  • Ingår i: The Identification Of Dark Matter. - : World Scientific. - 9789810246020 ; , s. 499-505
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)
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23.
  • Niessen, Peter, et al. (författare)
  • Recent results from the amanda experiment
  • 2003
  • Ingår i: Proceedings of 38th Rencontres de Moriond on Electroweak Interactions and Unified Theories 15-22 Mar 2003. Les Arcs, France.
  • Konferensbidrag (refereegranskat)abstract
    • AMANDA (Antarctic Muon And Neutrino Detector Array) is a neutrino telescope built under the southern polar icecap and its scope is to explore the possibility to detect high energy cosmic neutrinos. This should generate insight into the powerful celestial objects where acceleration mechanisms can bring up to 10 20   eV. We describe the achievements and results from the AMANDA-B10 prototype and the preliminary results from the current AMANDA-II detector which show dramatic increase in sensitivity.
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24.
  • Wijesooriya, K, et al. (författare)
  • Polarization measurements in high-energy deuteron photodisintegration
  • 2001
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 86:14, s. 2975-2979
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of the recoil proton polarization for the d(γ⃗,p⃗)n reaction at θc.m. = 90° for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization py vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(γ,p)ncross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.
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25.
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26.
  • Gayou, O, et al. (författare)
  • Measurement of G(Ep)/G(Mp) in (e)over-right-arrowp -> e(p)over-right-arrow to Q(2)=5.6 GeV2
  • 2002
  • Ingår i: Physical Review Letters. - 1079-7114. ; 88:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The ratio of the electric and magnetic form factors of the proton G(Ep)/G(Mp), which is an image of its charge and magnetization distributions, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic (e) over right arrowp --> e (p) over right arrow reaction. The new data presented span the range 3.5 < Q(2) < 5.6 GeV2 and are well described by a linear Q(2) fit. Also, the ratio rootQ(2) F-2p/F-1p reaches a constant value above Q(2) = 2 GeV2.
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27.
  • Schulte, EC, et al. (författare)
  • High energy angular distribution measurements of the exclusive deuteron photodisintegration reaction
  • 2002
  • Ingår i: Physical Review C (Nuclear Physics). - : American Physical Society. - 0556-2813 .- 1089-490X. ; 66:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E-gamma=2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.
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28.
  • Ma, C. B., et al. (författare)
  • Great framework variation of polymers in the manganese(II) maleate/alpha,alpha' - Diimine system : Syntheses, structures, and magneto-structural correlation
  • 2003
  • Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :15, s. 2872-2879
  • Tidskriftsartikel (refereegranskat)abstract
    • Three novel manganese(II) coordination polymers, [Mn (maleate)(phen)](n) (1; phen = 1,10-phenanthroline), [Mn-(maleate)(phen)](n).nH(2)O (2), and [Mn(maleate)(bpy)](n) (3; bpy = 2,2'-bipyridine), have been synthesized by treatment of Mn2+ with maleic acid with participation of chelate diimine ligands, and have been identified by single-crystal, X-ray diffraction to have either one-dimensional (1D) zigzag chain structures (1 and 2) or a two-dimensional (2D) sinuous layer structure (3). Each maleate dianion coordinates to three Mn centers, in different bridging modes (syn-anti in 1 and 2, syn-syn and anti-anti in 3). These compounds represent an interesting example of structural topology variation from 1D to 2D mediated by chemically similar auxiliary chelate ligands. Variable-temperature magnetic susceptibility measurements show weak anti-ferromagnetic exchange interactions between the adjacent Mn-II ions, with J = -0.06 cm(-1) (2) and J = -1.3 cm(-1), zJ' = -0.27 cm(-1) (3). The differences in the magnitudes of these coupling interactions agree well with the nature of the carb oxylate-bridging coordination of maleate.
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29.
  • Huang, D. G., et al. (författare)
  • Synthesis, structural characterizations and magnetic properties of a series of mono-, di- and polynuclear manganese pyridinecarboxylate compounds
  • 2004
  • Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :7, s. 1454-1464
  • Tidskriftsartikel (refereegranskat)abstract
    • Seven new manganese(II, III, IV) pyridinecarboxylate compounds (Et4N)[MnCl2(pic)(2)] (1, Hpic = picolinic acid) [MnCl(Pic)(2)(H2O)].H2O (2), [MnCl(pic)(H2O)2](n) (3), [Mn(Pic)(2)](n) (4), [MnCl(pic)](n) (5), [MnCl2(4-C5H4NHCOO)](n) (6) and [Mn2O2(pic)(4)] (7) were synthesized and structurally characterized. The picolinate ligand coordinates to the Mn ion forming a chelating five-membered ring which constructs diverse architectures by various bridging modes, such as mu-Cl, mu(1,1)(-) and mu(1,3)-carboxylate bridges (syn-syn and syn-anti modes). The interaction between the pyridyl rings is discussed, displaying a face-to-face pi-pi stacking for complex 6 and a T-shaped C-H...pi attraction for complex 4. Complex 3 has an infinite zigzag chain structure in which two neighboring Mn ions are linked by a carboxylate bridge in a syn-anti mode. In complex 4, the Mn(pic)(2) fragments are joined to each other by double mu(1,1)-carboxylate bridges, forming a 2D layer structure. Complex 5 contains Mn4O4 square subunits which are connected by double mu-Cl bridges to form a grid-like 2D structure. The isonicotinate complex 6 has a zigzag chain structure containing mixed double mu-Cl and mu(1,3)-carboxylate bridges in a syn-syn mode. Protonation at the pyridyl-N position was found and identified by the IR and magnetic properties of 6. The participation of an oxidizing agent like MnO4- leads to complexes containing higher valent manganese (1, 2 and 7). The IR spectra of these complexes are discussed and found to be consistent with the structural features. The magnetic properties of complexes 4, 5 and 6 have been investigated. Antiferromagnetic coupling interactions were observed and satisfactory fitting results were obtained with J values ranging from -0.63 cm(-1) to -2.35 cm(-1). The magnetic parameters of these complexes, together with the parameters of other Mn complexes with comparable structures, are compared and discussed based on the bridging modes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).
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30.
  • Huang, D. U., et al. (författare)
  • Synthesis, structural characterization and magnetic properties of 2-pyrazinecarboxylate manganese compounds Mn(pyz)(2)(H2O)(4) and MnCl(pyz)(H2O) (n) (pyz=2-pyrazinecarboxylate)
  • 2003
  • Ingår i: Inorganica Chimica Acta. - 0020-1693 .- 1873-3255. ; 353, s. 284-291
  • Tidskriftsartikel (refereegranskat)abstract
    • Two pyz complexes [Mn(pyz)(2)(H2O)(4)] (1) and [MnCl(pyz)(H2O)] (2) have been synthesized and structurally characterized. Complex 1 contains an eight-coordinate Mn(II) ion with square anti-prismatic geometry. The extensive intermolecular hydrogen-bonding interactions of O-carboxyl...H-O-aqua correlate the complex molecules, forming 2D polymeric layer structure. The structure of complex 2 contains 1D Mn/pyz chains, which link to each other by double mu(2)-Cl bridges to form 2D layer with Mn...Mn distance of 3.664 Angstrom. Hydrogen-bonding interactions of O-carboxyl...H-O-aqua are found between the layers to correlate the 2D layers to form a 3D framework. In addition, the variable temperature magnetic susceptibilities of complex 2 were measured and weak ferromagnetic exchange interactions between the neighboring magnetic species were found with J = 0.42 cm(-1).
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31.
  • Wijesooriya, K, et al. (författare)
  • Polarization measurements in neutral pion photoproduction
  • 2002
  • Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of the recoil proton polarization for the H-1((γ) over right arrow,(p) over right arrow)pi(0) reaction for theta(c.m.)(pi) = 60degrees-135degrees and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region.
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32.
  • Chen, C. N., et al. (författare)
  • Aggregate manganese Schiff base moieties by terephthalate or acetate : Dinuclear manganese and trinuclear mixed metal Mn-2/Na complexes
  • 2003
  • Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:11, s. 3540-3548
  • Tidskriftsartikel (refereegranskat)abstract
    • A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn-2(mu-phth)(CH3OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn-2(mu-phth)(CH3OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn-2(mu-phth)(CH3OH)(H2O) (3), and (salen)(2)Mn-2(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH3OH)(NO3) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H{Mn2Na(salpn)(2)(mu-OAc)(2)(H2O)(2)}(OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. H-1 NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/0.12V has been assigned to the redox of Mn-2(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.
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33.
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34.
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35.
  • Ma, C. B., et al. (författare)
  • Structural transformation mediated by o-, m-, and p-phthalates from two to three dimensions for manganese/phthalate/4,4 '-bpy complexes (4,4 '-bpy=4,4 '-bipyridine)
  • 2003
  • Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1144-0546 .- 1369-9261. ; 27:5, s. 890-894
  • Tidskriftsartikel (refereegranskat)abstract
    • Three isomers of o-, m-, and p-phthalate are used to link together Mn centres, resulting in [Mn(phth)(H2O)(x)](n) moieties ( phth = phthalate dianion) with single-chain, double-chain and sheet structures, respectively, which predetermine the extended structures derived from the crosslinkage of 4,4'-bipyridine, and show the influence of isomerism of the phthalate on topological changes of the final polymers from two dimensional (2D) single-layer, double-layer to 3D network architectures. These structural changes in topology are correlated with the differences in the magnetic and optical properties of the polymers.
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36.
  • Carpten, JD, et al. (författare)
  • HRPT2, encoding parafibromin, is mutated in hyperparathyroidism-jaw tumor syndrome
  • 2002
  • Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 32:4, s. 676-680
  • Tidskriftsartikel (refereegranskat)abstract
    • We report here the identification of a gene associated with the hyperparathyroidism-jaw tumor (HPT-JT) syndrome. A single locus associated with HPT-JT (HRPT2) was previously mapped to chromosomal region 1q25-q32. We refined this region to a critical interval of 12 cM by genotyping in 26 affected kindreds. Using a positional candidate approach, we identified thirteen different heterozygous, germline, inactivating mutations in a single gene in fourteen families with HPT-JT. The proposed role of HRPT2 as a tumor suppressor was supported by mutation screening in 48 parathyroid adenomas with cystic features, which identified three somatic inactivating mutations, all located in exon 1. None of these mutations were detected in normal controls, and all were predicted to cause deficient or impaired protein function. HRPT2 is a ubiquitously expressed, evolutionarily conserved gene encoding a predicted protein of 531 amino acids, for which we propose the name parafibromin. Our findings suggest that HRPT2 is a tumor-suppressor gene, the inactivation of which is directly involved in predisposition to HPT-JT and in development of some sporadic parathyroid tumors.
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37.
  • Gao, Y. L., et al. (författare)
  • Crystal structure and electrochemical behavior of copper complex with 6-hydroxymethyl-substituted tris(2-pyridylmethyl) amine, CuCl(C19H20N4O) ClO4
  • 2004
  • Ingår i: Chinese journal of structural chemistry. - 0254-5861. ; 23:11, s. 1262-1265
  • Tidskriftsartikel (refereegranskat)abstract
    • A Cu(II) complex [CuCl(C19H20N40)]ClO4 1 containing hydroxymethyl substituted TPA (TPA = tris(2-pyridylmethyl)amine) was prepared. It crystallizes in monoclinic, space group P2(1)/c with a = 11.7628(2), b = 13.0083(3), c = 15.11280(10) Angstrom, beta = 108.724(2)degrees, V = 2190.09(7) Angstrom(3), M-r = 518.83, Z = 4, T = 293 (2) K, D-c = 1.574 g/cm(3), mu = 1.280 mm(-1), F(000) = 1060 and S = 1.085. The final R = 0.0543 and wR = 0.1433 for 2693 observed reflections with I >2sigma(I). The penta-coordinated copper (H) complex. assumes an approximate square pyramidal geometry. Cyclic voltammetry measurement of the complex showed a quasi-reversible Cu-II/Cu-I redox couple with E-1/2 -0.467 v and DeltaE = 68 mv.
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38.
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39.
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40.
  • Dai, X W, et al. (författare)
  • Pyrolysis of waste tires in a circulating fluidized-bed reactor
  • 2001
  • Ingår i: Energy. - 0360-5442 .- 1873-6785. ; 26:4, s. 385-399
  • Tidskriftsartikel (refereegranskat)abstract
    • Using a circulating fluidized bed (CFB) as the main reactor, an integrated process development unit was operated aiming at the pyrolysis of waste tires. The main chemical processes in the CFB can be divided into two zones corresponding to pyrolysis and secondary reactions. The pyrolysis of tire powder was carried out at various pyrolysis temperatures, particle sizes of tire powder and feed positions. The effects of temperature, residence time and heating rate on pyrolysis were analyzed based on the experimental data. The main trends are that (1) a long residence time contributes to secondary reactions and (2) lower temperature and heating rate favor carbonization, which reduces the oil yield. Analysis of the pyrolytic oil shows that the predominant components are aromatics, followed by alkanes, non-hydrocarbons and asphalt.
  •  
41.
  • Desmyter, L., et al. (författare)
  • Expression of the human ferritin light chain in a frataxin mutant yeast affects ageing and cell death
  • 2004
  • Ingår i: Experimental Gerontology. - : Elsevier BV. - 0531-5565. ; 39:5, s. 707-715
  • Tidskriftsartikel (refereegranskat)abstract
    • Ferritin is one of the major eukaryotic proteins involved in regulating iron metabolism and maintaining iron homeostasis. However, Saccaromyces cerevisiae is an exception, possessing no ferritin and using other means to store excess iron. The only potential iron storage protein identified in yeast so far is the homologue of human frataxin (YFH1p). In this study, we found that dysfunction of yeast frataxin shortens mean lifespan by 49% compared to the WT control. Interestingly, the human ferritin L gene can, at least partially, complement the function of yeast frataxin, extending lifespan and protecting cells from death induced by oxidative stress or excess iron. Our findings indicate that ferritin L can perform functions in yeast that are similar to its functions in mammals, and suggest that common mechanisms may exist for preventing iron and oxidative damage in single- and multi-cellular eukaryotic organisms. Clearly, elucidation of the function of human ferritin in yeast would help in gaining a better understanding the molecular basis of iron storage diseases
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42.
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43.
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44.
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45.
  • Fujise, O, et al. (författare)
  • Clonal distribution of natural competence in Actinobacillus actinomycetemcomitans.
  • 2004
  • Ingår i: Oral Microbiology and Immunology. - : Wiley. - 0902-0055 .- 1399-302X. ; 19:5, s. 340-342
  • Tidskriftsartikel (refereegranskat)abstract
    • The competence for natural transformation was investigated in 67 Actinobacillus actinomycetemcomitans strains. The transformation assays were performed with both cloned DNA fragments and chromosomal markers of A. actinomycetemcomitans. Competence was found in 12 of 18 serotype a strains, 0 of 21 serotype b strains, 0 of 14 serotype c strains, 3 of 6 serotype d strains, 3 of 4 serotype e strains, 0 of 3 serotype f strains, and 0 of 1 nonserotypeable strain. The transformation frequencies varied from 5 x 10(-3) to 4 x 10(-6) (median 1.5 x 10(-4)). The distribution pattern of natural competence is concordant with the major clonal lineages of A. actinomycetemcomitans. Serotype a strains are predominantly competent for transformation, while serotypes b and c strains are apparently non-competent.
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46.
  • Hoieggen, A., et al. (författare)
  • The impact of serum uric acid on cardiovascular outcomes in the LIFE study
  • 2004
  • Ingår i: Kidney Int. - 0085-2538. ; 65:3, s. 1041-9
  • Tidskriftsartikel (refereegranskat)abstract
    • BACKGROUND: The Losartan Intervention For Endpoint reduction in hypertension (LIFE) study demonstrated the superiority of a losartan-based regimen over atenolol-based regimen for reduction of cardiovascular (CV) morbidity and mortality. It has been suggested that the LIFE study results may be related to the effects of losartan on serum uric acid (SUA). SUA has been proposed as an independent risk factor for CV morbidity and death. METHODS: Cox regression analysis was used to assess relationship of SUA and treatment regimens with the LIFE primary composite outcome (CV death, fatal or nonfatal myocardial infarction, fatal or nonfatal stroke). RESULTS: Baseline SUA was significantly associated with increased CV events [hazard ratio (HR) 1.024 (95% CI 1.017-1.032) per 10 micromol/L, P < 0.0001] in the entire study population. The association was significant in women [HR = 1.025 (1.013-1.037), P < 0.0001], but not in men [HR = 1.009 (0.998-1.019), P= 0.108]. After adjustment for Framingham risk score (FRS), SUA was no longer significant in the entire study population [HR = 1.006 (0.998-1.014), P= 0.122] or in men [HR = 1.006 (0.995-1.017), P= 0.291], but was significant in women [HR = 1.013 (1-1.025), P= 0.0457]. The baseline-to-end-of-study increase in SUA (standard deviation, SD) was greater (P < 0.0001) in atenolol-treated subjects (44.4 +/- 72.5 micromol/L) than in losartan-treated subjects (17.0 +/- 69.8 micromol/L). SUA as a time-varying covariate was strongly associated with events (P < 0.0001) in the entire population. The contribution of SUA to the treatment effect of losartan on the primary composite end point was 29% (14%-107%), P= 0.004. The association between time-varying SUA and increased CV risk tended to be stronger in women (P < 0.0001) than in men (P= 0.0658), although the gender-outcome interaction was not significant (P= 0.079). CONCLUSION: The increase in SUA over 4.8 years in the LIFE study was attenuated by losartan compared with atenolol treatment, appearing to explain 29% of the treatment effect on the primary composite end point. The association between SUA and events was stronger in women than in men with or without adjustment of FRS.
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47.
  • Lazdina, U, et al. (författare)
  • Humoral and CD4(+) T helper (Th) cell responses to the hepatitis C virus non-structural 3 (NS3) protein: NS3 primes Th1-like responses more effectively as a DNA-based immunogen than as a recombinant protein
  • 2001
  • Ingår i: The Journal of general virology. - : Microbiology Society. - 0022-1317 .- 1465-2099. ; 82:Pt 6, s. 1299-1308
  • Tidskriftsartikel (refereegranskat)abstract
    • The non-structural 3 (NS3) protein is one of the most conserved proteins of hepatitis C virus, and T helper 1 (Th1)-like responses to NS3 in humans correlate with clearance of infection. Several studies have proposed that DNA-based immunizations are highly immunogenic and prime Th1-like responses, although few head-to-head comparisons with exogenous protein immunizations have been described. A full-length NS3/NS4A gene was cloned in eukaryotic vectors with expression directed to different subcellular compartments. Inbred mice were immunized twice in regenerating tibialis anterior (TA) muscles with either plasmid DNA or recombinant NS3 (rNS3). After two 100 μg DNA immunizations, specific antibody titres of up to 12960 were detected at week 5, dominated by IgG2a and IgG2b. NS3-specific CD4+ T cell responses in DNA-immunized mice peaked at day 13, as measured by proliferation and IL-2 and IFN-γ production. Mice immunized with 1–10 μg rNS3 without adjuvant developed antibody titres comparable to those of the DNA-immunized mice, but dominated instead by IgG1. CD4+ T cell responses in these mice showed peaks of IL-2 response at day 3 and IL-6 and IFN-γ responses at day 6. With adjuvant, rNS3 was around 10-fold more immunogenic with respect to speed and magnitude of the immune responses. Thus, immunization with rNS3 in adjuvant is superior to DNA immunization with respect to kinetics and quantity in priming specific antibodies and CD4+ T cells. However, as a DNA immunogen, NS3 elicits stronger Th1-like immune responses, whereas rNS3 primes a mixed Th1/Th2-like response regardless of the route, dose or adjuvant.
  •  
48.
  • Linderson, Maj-Lena, et al. (författare)
  • Statistical downscaling and scenario construction of precipitation in Scania, southern Sweden
  • 2004
  • Ingår i: Nordic Hydrology. - 0029-1277. ; 35:3, s. 261-278
  • Tidskriftsartikel (refereegranskat)abstract
    • Statistical downscaling models for precipitation in Scania, southern Sweden, have been developed and applied to calculate the changes in the future Scanian precipitation climate due to projected changes in the atmospheric composition. The models are based on multiple linear regression, linking large-scale predictors at monthly time resolution to regional statistics of daily precipitation on a monthly basis. To account for spatial precipitation variability within the area, the precipitation statistics were derived for different regions in Scania. The final downscaling models, developed for different regions and seasons, use atmospheric circulation, large-scale humidity and precipitation as predictors. Among the precipitation statistics examined, only the models for estimating the mean precipitation and the frequency of wet days were skilful. Based on the Canadian Global Circulation Model 1 (CGCM1), a future scenario of these two statistics was created. The downscaled scenario shows a significant increase of the annual mean precipitation by about 10% and a slight decrease in the frequency of wet days, indicating an increase in the precipitation amounts as well as in the precipitation intensity. The main increase of precipitation amounts and intensity occur during winter, while the summer precipitation amounts decrease slightly. The seasonal changes found in precipitation are likely attributed to changes in the westerly flow of the atmospheric circulation.
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