Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions

We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10−5 is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions

Verminderung der Emission von Schadgasen und Feinstaeuben durch Trockensorption und filternde Entstauber hinter Verbrennungsanlagen Schlussbericht

With 22 refs., 9 tabs., 42 figs.Copy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Atomically Resolved Characterization of Optically Driven Ligand Reconfiguration on Nanoparticle Catalyst Surfaces

Dynamic ligand layers on nanoparticle surfaces could prove to be critically important to enhance the functionality of individual materials. Such capabilities could complement the properties of the inorganic component to provide multifunctionality or the ability to be remotely actuated. Peptide-based ligands have demonstrated the ability to be remotely responsive to structural changes when adsorbed to nanoparticle surfaces via incorporation of photoswitches into their molecular structure. In this contribution, direct spectroscopic evidence of the remote actuation of a photoswitchable peptide adsorbed onto Au nanoparticles is demonstrated using X-ray absorption fine structure spectroscopic methods. From this analysis, Au–X (X = C or N) coordination numbers confirm the changes before and after photoswitching in the surface ligand conformation, which was correlated directly to variations in the catalytic application of the materials for nitrophenol reduction processes. In addition, the catalytic application of the materials was demonstrated to be significantly sensitive to the structure of the nitrophenol substrate used in the reaction, suggesting that changes in the reactivity are likely based upon the peptide conformation and substrate structure. Such results confirm that surface ligands can be remotely reconfigured on nanoparticle surfaces, providing pathways to apply such capabilities to a variety of applications beyond catalysis ranging from drug delivery to sensing

Z-Contrast Enhancement in Au-Pt Nanocatalysts by Correlative X-ray Absorption Spectroscopy and Electron Microscopy: Implications for Composition Determination

The properties of bimetallic nanoparticles (BNPs) vary widely as a function of their composition and size distributions. X-ray absorption line structure analysis is commonly used to characterize their structure, but its application to elements that are close to each other in the periodic table is hampered by poor Z-contrast. We trained an artificial neural network to recognize the partial coordination numbers in AuPt NPs synthesized via peptide templating using their X-ray absorption near-edge structure spectra. This approach, combined with scanning transmission electron microscopy analysis, revealed unique details of this prototype catalytic system that has different forms of heterogeneities at both the intra- and inter-particle levels. Our method based on the enhancement of Z-contrast of metal species will have implications for compositional studies of BNPs

Transition from SU(2)_L x SU(2)_R x U(1)_B_-_L representation to SU(2)_L x U(1)_#UPSILON# by q-deformation and the corresponding classical breaking term of chiral U(2)

The minimal Standard Model exhibits a nontrivial chiral U(2) symmetry if the VEV and the hypercharge splitting #DELTA#=(y_R"u-y_R"d)/2 of right-handed leptons (quarks) in a family vanish and Q=T_0+Y independently in each helicity sector. As a generalization, we start with SU(2)_L x SU(2)_R x U(1)_(_B_-_L_) and introduce #DELTA# as a continuous parameter which is a measure of explicit symmetry breakdown. Values 0#<=##DELTA##<=#1/2 take the neutral generator of the isospin-1/2 representation to the singlet representation, i.e. 'deformes' the LR representation into the minimal Standard one. The corresponding classical O(3)-breaking term is a magnetic field perpendicular to the x_3-axis. A simple mapping on the fundamental Drinfeld-Jimbo q-deformed SU(2) representation is given. (orig.)Available from TIB Hannover: RA 2999(94-129) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Light absorption by brown carbon over the South-East Atlantic Ocean

International audienceBiomass burning emissions often contain brown carbon (BrC), which represents a large family of light-absorbing organics that are chemically complex, thus making it difficult to estimate their absorption of incoming solar radiation, resulting in large uncertainties in the estimation of the global direct radiative effect of aerosols. Here we investigate the contribution of BrC to the total light absorption of biomass burning aerosols over the South-East Atlantic Ocean with different optical models, utilizing a suite of airborne measurements from the ORACLES 2018 campaign. An effective refractive index of black carbon (BC), meBC=1.95+ikeBC, that characterizes the absorptivity of all absorbing components at 660 nm wavelength was introduced to facilitate the attribution of absorption at shorter wavelengths, i.e. 470 nm. Most values of the imaginary part of the effective refractive index, keBC, were larger than those commonly used for BC from biomass burning emissions, suggesting contributions from absorbers besides BC at 660 nm. The TEM-EDX single-particle analysis further suggests that these long-wavelength absorbers might include iron oxides, as iron is found to be present only when large values of keBC are derived. Using this effective BC refractive index, we find that the contribution of BrC to the total absorption at 470 nm (RBrC,470) ranges from ∼8 %-22 %, with the organic aerosol mass absorption coefficient (MACOA,470) at this wavelength ranging from 0.30±0.27 to 0.68±0.08 m2 g-1. The core-shell model yielded much higher estimates of MACOA,470 and RBrC,470 than homogeneous mixing models, underscoring the importance of model treatment. Absorption attribution using the Bruggeman mixing Mie model suggests a minor BrC contribution of 4 % at 530 nm, while its removal would triple the BrC contribution to the total absorption at 470 nm obtained using the AAE (absorption Ångström exponent) attribution method. Thus, it is recommended that the application of any optical properties-based attribution method use absorption coefficients at the longest possible wavelength to minimize the influence of BrC and to account for potential contributions from other absorbing materials

Deep-inelastic final states in a space-time description of shower development and hadronization

We extend a quantum kinetic approach to the description of hadronic showers in space, time and momentum space to deep-inelastic ep collisions, with particular reference to experiments at HERA. We follow the history of hard scattering events back to the initial hadronic state and forward to the formation of colour-singlet pre-hadronic clusters and their decays into hadrons. The time evolution of the space-like initial-state shower and the time-like secondary partons are treated similarly, and cluster formation is treated using a spatial criterion motivated by confinement and a non-perturbative model for hadronization. We calculate the time evolution of particle distributions in rapidity, transverse and longitudinal space. We also compare the transverse hadronic energy flow and the distribution of observed hadronic masses with experimental data from HERA, finding encouraging results, and discuss the background to large-rapidity-gap events. The techniques developed in this paper may be applied in the future to more complicated processes such as eA, pp, pA and AA collisions. (orig.)Available from TIB Hannover: RA 2999(96-088) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Neutral Higgs-boson pair production at hadron colliders: QCD corrections

Neutral Higgs-boson pair production provides the possibility of studying the trilinear Higgs couplings at future high-energy colliders. We present the QCD corrections to the gluon-initiated processes in the limit of a heavy top quark in the loops and the Drell-Yan-like pair production of scalar and pseudoscalar Higgs particles. The pp cross sections are discussed for LHC energies within the standard model and its minimal supersymmetric extension. The QCD corrections are large, enhancing the total cross sections significantly. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(98-028) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Charmonium at finite temperature

We study charmonium correlators and spectral functions at finite temperature within the quenched approximation using isotropic lattices with lattice spacing a"-"1=4.86 GeV and 9.72 GeV. Although we observe some medium modifications of the ground state charmonium spectral function above deconfinement, we find that ground state charmonia (J/#psi# and #eta#_c) exist in the deconfined phase at least up to temperatures as high as 1.5T_c. P-wave charmonia (#chi#_c) on the other hand are dissociated already at 1.12T_c. (orig.)Available from TIB Hannover: RA 2999(03-119) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

New particle formation in the remote marine boundary layer

Marine low clouds play an important role in the climate system, and their properties are sensitive to cloud condensation nuclei concentrations. While new particle formation represents a major source of cloud condensation nuclei globally, the prevailing view is that new particle formation rarely occurs in remote marine boundary layer over open oceans. Here we present evidence of the regular and frequent occurrence of new particle formation in the upper part of remote marine boundary layer following cold front passages. The new particle formation is facilitated by a combination of efficient removal of existing particles by precipitation, cold air temperatures, vertical transport of reactive gases from the ocean surface, and high actinic fluxes in a broken cloud field. The newly formed particles subsequently grow and contribute substantially to cloud condensation nuclei in the remote marine boundary layer and thereby impact marine low clouds