Showing papers by "Paul Scherrer Institute published in 2009"
University of Gothenburg1, University College Cork2, Paul Scherrer Institute3, Weizmann Institute of Science4, Chalmers University of Technology5, Norwegian Meteorological Institute6, University of Antwerp7, Carnegie Mellon University8, University of Lyon9, Centre national de la recherche scientifique10, University of California, Berkeley11, University of York12, Leibniz Institute for Neurobiology13, University of Mainz14, University of Florida15, University of Colorado Boulder16, Forschungszentrum Jülich17, Ghent University18, University of Manchester19, Aix-Marseille University20, California Institute of Technology21
TL;DR: In this article, an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and analytical techniques used to determine the chemical composition of SOA is presented.
Abstract: Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.
3,324 citations
University of Colorado Boulder1, Carnegie Mellon University2, Paul Scherrer Institute3, University at Albany, SUNY4, University of California, Berkeley5, Swiss Federal Laboratories for Materials Science and Technology6, University of California, Davis7, State University of New York System8, University of Eastern Finland9, Finnish Meteorological Institute10, University of Helsinki11, Stockholm University12, Texas A&M University13, Max Planck Society14, University of Tokyo15, University of New Hampshire16, National Oceanic and Atmospheric Administration17
TL;DR: A unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state is presented, which can serve as a basis for improving parameterizations in regional and global models.
Abstract: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
3,104 citations
TL;DR: The results reveal a spin-momentum locked Dirac cone carrying a non-trivial Berry’s phase that is nearly 100 per cent spin-polarized, which exhibits a tunable topological fermion density in the vicinity of the Kramers point and can be driven to the long-sought topological spin transport regime.
Abstract: Helical Dirac fermions—charge carriers that behave as massless relativistic particles with an intrinsic angular momentum (spin) locked to its translational momentum—are proposed to be the key to realizing fundamentally new phenomena in condensed matter physics. Prominent examples include the anomalous quantization of magneto-electric coupling, half-fermion states that are their own antiparticle, and charge fractionalization in a Bose– Einstein condensate, all of which are not possible with conventional Dirac fermions of the graphene variety. Helical Dirac fermions have so far remained elusive owing to the lack of necessary spin-sensitive measurements and because such fermions are forbidden to exist in conventional materials harbouring relativistic electrons, such as graphene or bismuth. It has recently
been proposed that helical Dirac fermions may exist at the edges of certain types of topologically ordered insulators—materials with a bulk insulating gap of spin–orbit origin and surface states protected against scattering by time-reversal symmetry—and that their peculiar properties may be accessed provided the insulator is tuned into the so-called topological transport regime. However, helical Dirac fermions have not been observed in existing topological insulators. Here we report the realization and characterization of a tunable topological insulator in a bismuthbased class of material by combining spin-imaging and
momentum-resolved spectroscopies, bulk charge compensation,
Hall transport measurements and surface quantum control. Our
results reveal a spin-momentum locked Dirac cone carrying a nontrivial
Berry’s phase that is nearly 100 per cent spin-polarized,
which exhibits a tunable topological fermion density in the vicinity
of the Kramers point and can be driven to the long-sought
topological spin transport regime. The observed topological nodal
state is shown to be protected even up to 300 K. Our demonstration
of room-temperature topological order and non-trivial spintexture
in stoichiometric Bi_2Se_3.M_x (M_x indicates surface doping
or gating control) paves the way for future graphene-like studies of
topological insulators, and applications of the observed spinpolarized
edge channels in spintronic and computing technologies
possibly at room temperature.
1,685 citations
TL;DR: Using Mott polarimetry, it is demonstrated that topological quantum numbers are completely determined from spin texture–imaging measurements and the origin of its topological order and unusual chiral properties are identified.
Abstract: A topologically ordered material is characterized by a rare quantum organization of electrons that evades the conventional spontaneously broken symmetry–based classification of condensed matter. Exotic spin-transport phenomena, such as the dissipationless quantum spin Hall effect, have been speculated to originate from a topological order whose identification requires a spin-sensitive measurement, which does not exist to this date in any system. Using Mott polarimetry, we probed the spin degrees of freedom and demonstrated that topological quantum numbers are completely determined from spin texture–imaging measurements. Applying this method to Sb and Bi1–xSbx, we identified the origin of its topological order and unusual chiral properties. These results taken together constitute the first observation of surface electrons collectively carrying a topological quantum Berry's phase and definite spin chirality, which are the key electronic properties component for realizing topological quantum computing bits with intrinsic spin Hall–like topological phenomena.
926 citations
TL;DR: It is directly shown that Bi2Te3 is a large spin-orbit-induced indirect bulk band gap semiconductor whose surface is characterized by a single topological spin-Dirac cone, and it is demonstrated that the dynamics of spin- Dirac fermions can be controlled through systematic Mn doping.
Abstract: We show that the strongly spin-orbit coupled materials Bi_2Te_3 and Sb_2Te_3 and their derivatives belong to the Z_2 topological-insulator class. Using a combination of first-principles theoretical calculations and photoemission spectroscopy, we directly show that Bi_2Te_3 is a large spin-orbit-induced indirect bulk band gap (δ∼150 meV) semiconductor whose surface is characterized by a single topological spin-Dirac cone. The electronic structure of self-doped Sb_2Te_3 exhibits similar Z_2 topological properties. We demonstrate that the dynamics of spin-Dirac fermions can be controlled through systematic Mn doping, making these materials classes potentially suitable for topological device applications.
840 citations
TL;DR: This paper describes the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.
Abstract: National user facilities such as the NIST Center for Neutron Research (NCNR) require a significant base of software to treat the data produced by their specialized measurement instruments. There is no universally accepted and used data treatment package for the reduction, visualization, and analysis of inelastic neutron scattering data. However, we believe that the software development approach adopted at the NCNR has some key characteristics that have resulted in a successful software package called DAVE (the Data Analysis and Visualization Environment). It is developed using a high level scientific programming language, and it has been widely adopted in the United States and abroad. In this paper we describe the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.
805 citations
University of Leicester1, Centre national de la recherche scientifique2, Cooperative Institute for Research in Environmental Sciences3, Earth System Research Laboratory4, Norwegian Institute for Air Research5, United Kingdom Department for Environment, Food and Rural Affairs6, Japan Agency for Marine-Earth Science and Technology7, International Institute for Applied Systems Analysis8, Danish Meteorological Institute9, Paul Scherrer Institute10, ETH Zurich11, University of California, Irvine12, University of Leeds13, Aristotle University of Thessaloniki14, École Polytechnique Fédérale de Lausanne15, Geophysical Fluid Dynamics Laboratory16, National Center for Atmospheric Research17, Stockholm University18, Swiss Federal Laboratories for Materials Science and Technology19, Forschungszentrum Jülich20, University of Oslo21, Max Planck Society22, University of Helsinki23, Joseph Fourier University24, Blaise Pascal University25, University of York26, University of Toulouse27, University of Urbino28, University of Manchester29, National University of Ireland, Galway30, University of Edinburgh31, Heidelberg University32, University of East Anglia33, Weizmann Institute of Science34, Chalmers University of Technology35, Norwegian Meteorological Institute36, Energy Research Centre of the Netherlands37, University of Stuttgart38, VU University Amsterdam39
TL;DR: A review of the state of scientific understanding in relation to global and regional air quality is outlined in this article, in terms of emissions, processing and transport of trace gases and aerosols.
760 citations
TL;DR: Structural and biochemical data reveal the molecular basis of the EB1-SxIP interaction and explain its negative regulation by phosphorylation and establish a general "microtubule tip localization signal" (MtLS) and delineate a unifying mechanism for this subcellular protein targeting process.
617 citations
TL;DR: A new reconstruction procedure that retrieves both the specimen's image and the illumination profile was recently demonstrated with hard X-ray data and is presented in greater details to illustrate its practical applicability with a visible light dataset.
616 citations
TL;DR: A fast, powerful and stable filter based on combined wavelet and Fourier analysis for the elimination of horizontal or vertical stripes in images is presented and compared with other types of destriping filters.
Abstract: A fast, powerful and stable filter based on combined wavelet and Fourier analysis for the elimination of horizontal or vertical stripes in images is presented and compared with other types of destriping filters. Strict separation between artifacts and original features allowing both, suppression of the unwanted structures and high degree of preservation of the original image information is endeavoured. The results are validated by visual assessments, as well as by quantitative estimation of the image energy loss. The capabilities and the performance of the filter are tested on a number of case studies related to applications in tomographic imaging. The case studies include (i) suppression of waterfall artifacts in electron microscopy images based on focussed ion beam nanotomography, (ii) removal of different types of ring artifacts in synchrotron based X-ray microtomography and (iii) suppression of horizontal stripe artifacts from phase projections in grating interferometry.
570 citations
TL;DR: These results resolve a long-standing issue about the population mechanism of quintet states in iron(II)-based complexes, which are identified as a simple 1MLCT→3 MLCT→5T cascade from the initially excited state.
Abstract: X-ray absorption spectroscopy is a powerful probe of molecular structure, but it has previously been too slow to track the earliest dynamics after photoexcitation. We investigated the ultrafast formation of the lowest quintet state of aqueous iron(II) tris(bipyridine) upon excitation of the singlet metal-to-ligand-charge-transfer ( 1 MLCT) state by femtosecond optical pump/x-ray probe techniques based on x-ray absorption near-edge structure (XANES). By recording the intensity of a characteristic XANES feature as a function of laser pump/x-ray probe time delay, we find that the quintet state is populated in about 150 femtoseconds. The quintet state is further evidenced by its full XANES spectrum recorded at a 300-femtosecond time delay. These results resolve a long-standing issue about the population mechanism of quintet states in iron(II)-based complexes, which we identify as a simple 1 MLCT→ 3 MLCT→ 5 T cascade from the initially excited state. The time scale of the 3 MLCT→ 5 T relaxation corresponds to the period of the iron-nitrogen stretch vibration.
ETH Zurich1, University of Colorado Boulder2, Universidad Autónoma del Estado de Morelos3, Paul Scherrer Institute4, University of Reading5, University of Wisconsin-Madison6, Texas A&M University7, Montana State University8, Saint Louis University9, Brookhaven National Laboratory10, Pacific Northwest National Laboratory11, University of Arkansas12, University of Nevada, Reno13, Massachusetts Institute of Technology14
TL;DR: In this article, an analysis of high resolution OA spectra was performed at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation.
Abstract: . Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation. Mass concentrations, diurnal cycles, and size distributions of inorganic and organic species are similar to results from the CENICA supersite in April 2003 with organic aerosol (OA) comprising about half of the fine PM mass. Positive Matrix Factorization (PMF) analysis of the high resolution OA spectra identified three major components: chemically-reduced urban primary emissions (hydrocarbon-like OA, HOA), oxygenated OA (OOA, mostly secondary OA or SOA), and biomass burning OA (BBOA) that correlates with levoglucosan and acetonitrile. BBOA includes several very large plumes from regional fires and likely also some refuse burning. A fourth OA component is a small local nitrogen-containing reduced OA component (LOA) which accounts for 9% of the OA mass but one third of the organic nitrogen, likely as amines. OOA accounts for almost half of the OA on average, consistent with previous observations. OA apportionment results from PMF-AMS are compared to the PM2.5 chemical mass balance of organic molecular markers (CMB-OMM, from GC/MS analysis of filters). Results from both methods are overall consistent. Both assign the major components of OA to primary urban, biomass burning/woodsmoke, and secondary sources at similar magnitudes. The 2006 Mexico City emissions inventory underestimates the urban primary PM2.5 emissions by a factor of ~4, and it is ~16 times lower than afternoon concentrations when secondary species are included. Additionally, the forest fire contribution is at least an order-of-magnitude larger than in the inventory.
University of Cambridge1, Monash University2, Centre national de la recherche scientifique3, University of Bonn4, Harish-Chandra Research Institute5, University of Paris6, University of Turin7, Center for Theoretical Studies, University of Miami8, KEK9, University of Barcelona10, Spanish National Research Council11, University of Montpellier12, CERN13, Stanford University14, University of Edinburgh15, Fermilab16, ETH Zurich17, University of Southampton18, University of Zaragoza19, University of Würzburg20, Moscow State University21, Durham University22, Sapienza University of Rome23, Paul Scherrer Institute24
TL;DR: Extensions of the conventions of the first SLHA are proposed to include various generalisations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavour, as well as the simplest next-to-minimal model.
University of Montana1, California Institute of Technology2, Paul Scherrer Institute3, University of Colorado Boulder4, National Center for Atmospheric Research5, United States Forest Service6, University of Miami7, University of Hawaii8, National Oceanic and Atmospheric Administration9, Arizona State University10
TL;DR: The first detailed field measurements of biomass burning (BB) emissions in the Northern Hemisphere tropics as part of the MILAGRO project were made by two instrumented aircraft were the National Center for Atmospheric Research C-130 and a University of Montana/US Forest Service Twin Otter.
Abstract: . In March 2006 two instrumented aircraft made the first detailed field measurements of biomass burning (BB) emissions in the Northern Hemisphere tropics as part of the MILAGRO project. The aircraft were the National Center for Atmospheric Research C-130 and a University of Montana/US Forest Service Twin Otter. The initial emissions of up to 49 trace gas or particle species were measured from 20 deforestation and crop residue fires on the Yucatan peninsula. This included two trace gases useful as indicators of BB (HCN and acetonitrile) and several rarely, or never before, measured species: OH, peroxyacetic acid, propanoic acid, hydrogen peroxide, methane sulfonic acid, and sulfuric acid. Crop residue fires emitted more organic acids and ammonia than deforestation fires, but the emissions from the main fire types were otherwise fairly similar. The Yucatan fires emitted unusually high amounts of SO2 and particle chloride, likely due to a strong marine influence on this peninsula. As smoke from one fire aged, the ratio ΔO3/ΔCO increased to ~15% in 1×107 molecules/cm3) that were likely caused in part by high initial HONO (~10% of NOy). Thus, more research is needed to understand critical post emission processes for the second-largest trace gas source on Earth. It is estimated that ~44 Tg of biomass burned in the Yucatan in the spring of 2006. Mexican BB (including Yucatan BB) and urban emissions from the Mexico City area can both influence the March-May air quality in much of Mexico and the US.
TL;DR: Semiconductor photodiodes were developed in the early 'Forties approximately at the time when the photomultiplier tube became a commercial product (RCA 1939) as mentioned in this paper.
Abstract: Semiconductor photodiodes were developed in the early `Forties approximately at the time when the photomultiplier tube became a commercial product (RCA 1939) Only in recent years, with the invention of the Geiger-mode avalanche photodiodes, have the semiconductor photo detectors reached sensitivity comparable to that of photomultiplier tubes The evolution started in the `Sixties with the p-i-n (PIN) photodiode, a very successful device, which is still used in many detectors for high energy physics and a large number of other applications like radiation detection and medical imaging The next step was the development of the avalanche photodiode (APD) leading to a substantial reduction of noise but not yet achieving single photon response The weakest light flashes that can be detected by the PIN diode need to contain several hundreds of photons An improvement of the sensitivity by 2 orders of magnitude was achieved by the development of the avalanche photodiode, a device with internal gain At the end of the millennium, the semiconductor detectors evolved with the Geiger-mode avalanche photodiode into highly sensitive devices, which have an internal gain comparable to the gain of photomultiplier tubes and a response to single photons A review of the semiconductor photo detector design and development, the properties and problems, some applications and a speculative outlook on the future evolution will be presented
TL;DR: Characterization of PILATUS single-photon-counting X-ray detector modules regarding charge sharing, energy resolution and rate capability is presented and the performance of the detector was tested with surface diffraction experiments at the synchrotron.
Abstract: PILATUS is a silicon hybrid pixel detector system, operating in single-photon-counting mode, that has been developed at the Paul Scherrer Institut for the needs of macromolecular crystallography at the Swiss Light Source (SLS). A calibrated PILATUS module has been characterized with monochromatic synchrotron radiation. The influence of charge sharing on the count rate and the overall energy resolution of the detector were investigated. The dead-time of the system was determined using the attenuated direct synchrotron beam. A single module detector was also tested in surface diffraction experiments at the SLS, whereby its performance regarding fluorescence suppression and saturation tolerance were evaluated, and have shown to greatly improve the sensitivity, reliability and speed of surface diffraction data acquisition.
University of Helsinki1, Finnish Meteorological Institute2, Paul Scherrer Institute3, National Research Council4, Stockholm University5, Norwegian Meteorological Institute6, National University of Ireland, Galway7, Max Planck Society8, Leibniz Association9, Royal Netherlands Meteorological Institute10, Met Office11, Centre national de la recherche scientifique12, University of Grenoble13, ETH Zurich14, University of Manchester15, University of the Aegean16, Foundation for Research & Technology – Hellas17, Norwegian Institute for Air Research18, Lund University19, University of Aveiro20, International Institute for Applied Systems Analysis21, University of Warsaw22, University of São Paulo23, University of Birmingham24, University of Gothenburg25, North-West University26, University of Copenhagen27, University of East Anglia28, Blaise Pascal University29, University of Lyon30, University of Mainz31, Karlsruhe Institute of Technology32, Peking University33, University of Tartu34, University of Crete35, Hungarian Academy of Sciences36, University of Oslo37, University of Eastern Finland38, The Energy and Resources Institute39, Deutscher Wetterdienst40, University of Leeds41, Hebrew University of Jerusalem42, University of Clermont-Ferrand43, Chalmers University of Technology44
TL;DR: The European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI) as mentioned in this paper was the first project to study aerosol processes fron nano to global scale and their effects on climate and air quality.
Abstract: In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.
TL;DR: In this article, a comparative study of conductive, free-standing, binder-free flexible films made from three different types of commercial carbon nanotubes (CNTs) was carried out.
01 Aug 2009-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The PILATUS hybrid pixel detector as discussed by the authors combines silicon sensors with CMOS processing chips by a 2D micro bump-bonding interconnection technology developed at the Paul Scherrer Institute.
Abstract: The hybrid pixel technology combines silicon sensors with CMOS-processing chips by a 2D micro bump-bonding interconnection technology developed at Paul Scherrer Institute [C. Broennimann, E.F. Eikenberry, B. Henrich, R. Horisberger, G. Huelsen, E. Pohl, B. Schmitt, C. Schulze-Briese, M. Suzuki, T. Tomizaki, H. Toyokawa, A. Wagner. J. Synchrotron Rad. 13 (2005) 120 [1] ; T. Rohe, C. Broennimann, F. Glaus, J. Gobrecht, S. Heising, M. Horisberger, R. Horisberger, H.C. Kaestl, J. Lehmann, S. Streuli, Nucl. Instr. and Meth. Phys. Res. A 565 (2006) 303 [2] ]. PILATUS hybrid pixel detectors like other instruments [X. Llopart, M. Campell, R. Dinapoli, D. San Segundo, E. Pernigotti. IEEE Trans. Nucl. Sci. 49 (2002) 2279 [3] ; N. Boudet, J.-F. Berar, L. Blanquart, P. Breugon, B. Caillot, J.-C. Clemens, I. Koudobine, P. Delpierre, C. Mouget, R. Potheau, I. Valin, Nucl. Instr. and Meth. Phys. Res. A 510 (2003) 41 [4] ] are operating in the so-called “single photon counting mode”: Every X-ray quantum is directly converted into an electrical signal and counted by the detector system. Several prototype detectors in various geometries were produced, tested and established at different synchrotron beamlines worldwide. We explain the technology and present some recent highlights from various fields of applications.
TL;DR: In this paper, the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mossbauer spectroscopy on the series LaO(1-x)F(x)FeAs.
Abstract: The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates, heavy fermions and organic superconductors. Here superconductivity is often found close to a quantum critical point where long-range antiferromagnetic order is gradually suppressed as a function of a control parameter, for example charge-carrier doping or pressure. It is believed that dynamic spin fluctuations associated with this quantum critical behaviour are crucial for the mechanism of superconductivity. Recently, high-temperature superconductivity has been discovered in iron pnictides, providing a new class of unconventional superconductors. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state and superconductivity is induced on charge-carrier doping. In this Letter the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mossbauer spectroscopy on the series LaO(1-x)F(x)FeAs. We find a discontinuous first-order-like change of the Neel temperature, the superconducting transition temperature and the respective order parameters. Our results strongly question the relevance of quantum critical behaviour in iron pnictides and prove a strong coupling of the structural orthorhombic distortion and the magnetic order both disappearing at the phase boundary to the superconducting state.
TL;DR: In this article, a high-resolution Time-Of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was used to characterize the volatilities of different chemical species in ambient aerosols.
Abstract: . The volatilities of different chemical species in ambient aerosols are important but remain poorly characterized. The coupling of a recently developed rapid temperature-stepping thermodenuder (TD, operated in the range 54–230°C) with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) during field studies in two polluted megacities has enabled the first direct characterization of chemically-resolved urban particle volatility. Measurements in Riverside, CA and Mexico City are generally consistent and show ambient nitrate as having the highest volatility of any AMS standard aerosol species while sulfate showed the lowest volatility. Total organic aerosol (OA) showed volatility intermediate between nitrate and sulfate, with an evaporation rate of 0.6%·K−1 near ambient temperature, although OA dominates the residual species at the highest temperatures. Different types of OA were characterized with marker ions, diurnal cycles, and positive matrix factorization (PMF) and show significant differences in volatility. Reduced hydrocarbon-like OA (HOA, a surrogate for primary OA, POA), oxygenated OA (OOA, a surrogate for secondary OA, SOA), and biomass-burning OA (BBOA) separated with PMF were all determined to be semi-volatile. The most aged OOA-1 and its dominant ion, CO2+, consistently exhibited the lowest volatility, with HOA, BBOA, and associated ions for each among the highest. The similar or higher volatility of HOA/POA compared to OOA/SOA contradicts the current representations of OA volatility in most atmospheric models and has important implications for aerosol growth and lifetime. A new technique using the AMS background signal was demonstrated to quantify the fraction of species up to four orders-of-magnitude less volatile than those detectable in the MS mode, which for OA represent ~5% of the non-refractory (NR) OA signal. Our results strongly imply that all OA types should be considered semivolatile in models. The study in Riverside identified organosulfur species (e.g. CH3HSO3+ ion, likely from methanesulfonic acid), while both studies identified ions indicative of amines (e.g. C5H12N+) with very different volatility behaviors than inorganic-dominated ions. The oxygen-to-carbon ratio of OA in each ambient study was shown to increase both with TD temperature and from morning to afternoon, while the hydrogen-to-carbon ratio showed the opposite trend.
TL;DR: In this article, a new approach, TDMAinv, was proposed to represent the inverted GF-PDF as a piecewise linear function, where the convergence of the inversion is robust and independent of the initial guess.
TL;DR: In this article, the chemical composition of secondary organic aerosol (SOA) particles, formed by the dark ozonolysis of α-pinene, was characterized by a high-resolution time-of-flight aerosol mass spectrometer.
Abstract: . The chemical composition of secondary organic aerosol (SOA) particles, formed by the dark ozonolysis of α-pinene, was characterized by a high-resolution time-of-flight aerosol mass spectrometer. The experiments were conducted using a continuous-flow chamber, allowing the particle mass loading and chemical composition to be maintained for several days. The organic portion of the particle mass loading was varied from 0.5 to >140 μg/m3 by adjusting the concentration of reacted α-pinene from 0.9 to 91.1 ppbv. The mass spectra of the organic material changed with loading. For loadings below 5 μg/m3 the unit-mass-resolution m/z 44 (CO2+) signal intensity exceeded that of m/z 43 (predominantly C2H3O+), suggesting more oxygenated organic material at lower loadings. The composition varied more for lower loadings (0.5 to 15 μg/m3) compared to higher loadings (15 to >140 μg/m3). The high-resolution mass spectra showed that from >140 to 0.5 μg/m3 the mass percentage of fragments containing carbon and oxygen (CxHyOz+) monotonically increased from 48% to 54%. Correspondingly, the mass percentage of fragments representing CxHy+ decreased from 52% to 46%, and the atomic oxygen-to-carbon ratio increased from 0.29 to 0.45. The atomic ratios were accurately parameterized by a four-product basis set of decadal volatility (viz. 0.1, 1.0, 10, 100 μg/m3) employing products having empirical formulas of C1H1.32O0.48, C1H1.36O0.39, C1H1.57O0.24, and C1H1.76O0.14. These findings suggest considerable caution is warranted in the extrapolation of laboratory results that were obtained under conditions of relatively high loading (i.e., >15 μg/m3) to modeling applications relevant to the atmosphere, for which loadings of 0.1 to 20 μg/m3 are typical. For the lowest loadings, the particle mass spectra resembled observations reported in the literature for some atmospheric particles.
TL;DR: It is concluded that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source, indicating a tight coupling in the plants-soil system and the importance of plant metabolism for soil CO(2) fluxes.
Abstract: Soil respiration is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere. Here, we tested the hypothesis that photosynthesis affects the diurnal pattern of grassland soil-respired CO(2) and its C isotope composition (delta(13)C(SR)). A combined shading and pulse-labelling experiment was carried out in a mountain grassland. delta(13)C(SR) was monitored at a high time resolution with a tunable diode laser absorption spectrometer. In unlabelled plots a diurnal pattern of delta(13)C(SR) was observed, which was not explained by soil temperature, moisture or flux rates and contained a component that was also independent of assimilate supply. In labelled plots delta(13)C(SR) reflected a rapid transfer and respiratory use of freshly plant-assimilated C and a diurnal shift in the predominant respiratory C source from recent (i.e. at least 1 d old) to fresh (i.e. photoassimilates produced on the same day). We conclude that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source. These findings indicate a tight coupling in the plant-soil system and the importance of plant metabolism for soil CO(2) fluxes.
University of Oslo1, Earth System Research Laboratory2, Cooperative Institute for Research in Environmental Sciences3, Norwegian Meteorological Institute4, International Institute for Applied Systems Analysis5, Met Office6, University of Cambridge7, German Aerospace Center8, Max Planck Society9, Centre national de la recherche scientifique10, University of Leicester11, Paul Scherrer Institute12, Goddard Institute for Space Studies13, Royal Netherlands Meteorological Institute14, Urbana University15
TL;DR: In this paper, the authors present progress in their understanding of processes of importance for climate-chemistry interactions, and their contributions to changes in atmospheric composition and climate forcing, and identify several areas where climate change can affect the tropospheric oxidation process and the chemical composition.
TL;DR: In this paper, the effect of different dopants including niobium, iron, tungsten and zirconium oxide on the low-temperature activity of MnOx-CeO2 catalysts for the selective catalytic reduction (SCR) of NOx with ammonia has been studied with coated cordierite monoliths in model gas experiments.
Abstract: The effect of different dopants including niobium, iron, tungsten and zirconium oxide on the low-temperature activity of MnOx–CeO2 catalysts for the selective catalytic reduction (SCR) of NOx with ammonia has been studied with coated cordierite monoliths in model gas experiments. A clearly higher activity and particularly superior nitrogen selectivity was obtained with the niobium-doped catalyst in comparison with the MnOx–CeO2 reference system. At 200 °C, the DeNOx was 80% while the N2 selectivity reached more than 96%. In contrast, a decrease of the SCR activity was observed when iron, zirconium or tungsten oxides were added to MnOx–CeO2. However, the addition of niobium oxide did not improve the resistance of the catalyst against SO2 poisoning. A strong and irreversible deactivation occurred after exposure to SO2.
TL;DR: The results point to an electronic reconstruction in the LaAlO3 overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the Berezinskii-Kosterlitz-Thouless type.
Abstract: The conducting interface of ${\mathrm{LaAlO}}_{3}/{\mathrm{SrTiO}}_{3}$ heterostructures has been studied by hard x-ray photoelectron spectroscopy. From the Ti $2p$ signal and its angle dependence we derive that the thickness of the electron gas is much smaller than the probing depth of 4 nm and that the carrier densities vary with increasing number of ${\mathrm{LaAlO}}_{3}$ overlayers. Our results point to an electronic reconstruction in the ${\mathrm{LaAlO}}_{3}$ overlayer as the driving mechanism for the conducting interface and corroborate the recent interpretation of the superconducting ground state as being of the Berezinskii-Kosterlitz-Thouless type.
TL;DR: With target definition, dose prescription and normal organ tolerance levels similar to passive-scattering based PT series, complication-free, tumor control and survival rates are at present comparable.
Abstract: Purpose To evaluate effectiveness and safety of spot-scanning-based proton radiotherapy (PT) in skull-base chordomas and chondrosarcomas. Methods and Materials Between October 1998 and November 2005, 64 patients with skull-base chordomas ( n = 42) and chondrosarcomas ( n = 22) were treated at Paul Scherrer Institute with PT using spot-scanning technique. Median total dose for chordomas was 73.5 Gy(RBE) and 68.4 Gy(RBE) for chondrosarcomas at 1.8–2.0 Gy(RBE) dose per fraction. Local control (LC), disease specific survival (DSS), and overall survival (OS) rates were calculated. Toxicity was assessed according to CTCAE, v. 3.0. Results Mean follow-up period was 38 months (range, 14–92 months). Five patients with chordoma and one patient with chondrosarcoma experienced local recurrence. Actuarial 5-year LC rates were 81% for chordomas and 94% for chondrosarcomas. Brainstem compression at the time of PT ( p = 0.007) and gross tumor volume >25 mL ( p = 0.03) were associated with lower LC rates. Five years rates of DSS and OS were 81% and 62% for chordomas and 100% and 91% for chondrosarcomas, respectively. High-grade late toxicity consisted of one patient with Grade 3 and one patient with Grade 4 unilateral optic neuropathy, and two patients with Grade 3 central nervous system necrosis. No patient experienced brainstem toxicity. Actuarial 5-year freedom from high-grade toxicity was 94%. Conclusions Our data indicate safety and efficacy of spot-scanning based PT for skull-base chordomas and chondrosarcomas. With target definition, dose prescription and normal organ tolerance levels similar to passive-scattering based PT series, complication-free, tumor control and survival rates are at present comparable.
TL;DR: In this article, the authors used a chemical box model to simulate secondary organic aerosol (SOA) formation from anthropogenic and biogenic VOCs in different plumes using recently reported dependencies of SOA yields on VOC/NOx ratios.
Abstract: [1] We present measurements of organic aerosol (OA) in urban plumes from Houston and Dallas/Fort Worth as well as in industrial plumes in the Houston area during TexAQS-2006. Consistent with the TexAQS-2000 study, measurements show greater amount of aerosol mass downwind of the industrial centers compared to urban areas. This is likely due to higher emission and processing of volatile organic compounds (VOCs) from the industrial sources along the Houston ship channel. Comparisons of the current measurements with observations from the northeastern (NE) United States indicate that the observed ratios of the enhancement above background in OA, ΔOA, to the enhancement above background in CO, ΔCO, downwind of urban centers of Houston and Dallas/Fort Worth are within a factor of 2 of the same values in plumes from urban areas in the NE United States. In the ship channel plumes, ΔOA/ΔCO exceeds that in the urban areas by factors ranging from 1.5 to 7. We use a chemical box model to simulate secondary organic aerosol (SOA) formation from anthropogenic and biogenic VOCs in different plumes using recently reported dependencies of SOA yields on VOC/NOx ratios. Modeled SOA to CO enhancement ratios are within a factor of 2 of measurements. The increase in SOA from biogenic VOCs (BVOCs) predicted by the chemical box model as well as by a separate analysis using a Lagrangian particle dispersion model (FLEXPART) is <0.7 μg per standard m3 (sm−3). We find no evidence for a substantial influence of BVOCs on OA formation in our measurements in Houston area.
TL;DR: A new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve is presented and the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.
Abstract: Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.