An experimental setup combining a highly sensitive detector for reaction products with a mass-selected cluster source and a low-temperature STM for advanced nanocatalysis measurements

We report on a home-built detector for catalytic reaction measurements offering good gas isolation from the surrounding ultrahigh vacuum components, high sensitivity for reaction products and a fast response time of 10 ms enabling dynamic studies correlated to reactant gas pulses. The device is mounted in ultrahigh vacuum and combined with a low-temperature scanning tunneling microscope and a source for the deposition of mass-selected clusters. This combination allows for a direct correlation between surface morphology and catalytic properties of model catalysts. The performances of the new detector are illustrated by measurements on two model systems. Thermal desorption spectroscopy of CO carried out on morphologically well characterized Pt on TiO₂(110)-(1 × 1) reveals several desorption features, which can be attributed to different surface sites. Catalytic CO oxidation performed by alternatingly pulsing isotopic CO and O₂ on a Pt film on yttria stabilized zirconia reveals the CO or O rich temperature regimes. The CO₂ production rate correlated with either one of the reactants can perfectly be reproduced by a kinetic reaction model giving access to the respective adsorption energies.     

Sooting turbulent jet flame: characterization and quantitative soot measurements

Computational fluid dynamics (CFD) modelers require high-quality experimental data sets for validation of their numerical tools. Preferred features for numerical simulations of a sooting, turbulent test case flame are simplicity (no pilot flame), well-defined boundary conditions, and sufficient soot production. This paper proposes a non-premixed C₂H₄/air turbulent jet flame to fill this role and presents an extensive database for soot model validation.     

Absolute frequency measurements of wavelength standards 532 nm, 543 nm, 633 nm and 1540 nm

This paper describes the results of absolute frequency measurements of primary wavelength standards 633 nm, 543 nm, 532 nm, (iodine stabilized) and 1540 nm (acetylene stabilized) in CMI. The values obtained with Menlo Systems femtosecond frequency comb in CMI are compared with previous measurements of the same standards in BIPM, BEV and MPQ. Measured sub-Doppler linewidths and relative intensities of several hyperfine spectral components of iodine molecule are also presented.     

A mid-infrared scanned-wavelength laser absorption sensor for carbon monoxide and temperature measurements from 900 to 4000 K

Mid-infrared laser absorption sensors based on quantum cascade laser (QCL) technology offer the potential for high-sensitivity, selective, and high-speed measurements of temperature and concentration for species of interest in high-temperature environments, such as those found in combustion devices. A new mid-infrared QCL absorption sensor for carbon monoxide and temperature measurements has been developed near the intensity peak of the CO fundamental band at 4.6 μm, providing orders-of-magnitude greater sensitivity than the overtone bands accessible with telecommunications lasers. The sensor is capable of probing the R(9), R(10), R(17), and R(18) transitions of the CO fundamental ro-vibrational band which are located at frequencies where H₂O and CO₂ spectral interference is minimal. Temperature measurements are made via scanned-wavelength two-line ratio techniques using either the R(9) and R(17) or the R(10) and R(18) line pairs. The high-speed (1–2 kHz) scanned-wavelength sensor is demonstrated in room-temperature gas cell measurements of CO and, to demonstrate the potential of the sensor for high-temperature thermometry, in shock-heated gases containing CO for a very wide range of temperature (950–3500 K) near 1 atm. To our knowledge, these measurements represent the first use of QCL-based absorption sensor for thermometry at elevated combustion-like temperatures. The high-temperature measurements of CO mole fraction and temperature agree with the post-reflected-shock conditions within ±1.5% and ±1.2% (1σ deviation), respectively.     

Methane analyzer based on TDL’s for measurements in the lower stratosphere: design and laboratory tests

This paper describes a tunable diode laser spectrometer for the in situ measurement of methane by high-resolution absorption spectroscopy of roto-vibrational lines, using a distributed feedback laser emitting in the near infrared (1.65 μm) and a multi-pass cell, with a two-tone detection scheme. The instrument was designed to be installed on the high-altitude aircraft M55 Geophysica, for high-sensitivity and high-temporal-resolution measurement of CH₄, both as a greenhouse gas and as a tracer of air-mass motion. The instrument-design criteria to achieve the compactness, low weight, and ruggedness necessary for automatic operation on an unpressurized high-altitude aircraft are reported. Results of the laboratory testing are also shown and discussed. Received: 1 April 2002 / Revised version: 28 May 2002 / Published online: 12 September 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/313-7597, E-mail: damato@scintec.it     

Simultaneous measurement of liquid water film thickness and vapor temperature using near-infrared tunable diode laser spectroscopy

A fiber-based multiplexed tunable diode-laser absorption sensor with three near-infrared distributed-feedback diode lasers at ∼1.4 μm is used for simultaneous nonintrusive measurements of liquid water film thickness and vapor-phase temperature. Water film thicknesses are derived from broad-band absorption determined at two fixed wavelengths while gas-phase temperature above the film is obtained via two-line thermometry using the fast wavelength tuning with line-integrating absorption. Probing the liquid film at two wavelengths with significantly different liquid-phase absorption cross sections allows discriminating against additional signal losses due to surface fowling, reflection, and beam steering. The technique is demonstrated for liquid layers of defined thicknesses and in time-resolved measurements of evaporating films.     

Mode decomposition and source localization performance for the short vertical array in shallow water

I.IntroductionWhentheMFPl1-5]andMMPI6-111forsourcelocalizationaresuccessfulinboththeoryandpractice,onepayattentiontoapplythenewlocalizationmethodtotheengineeringproject.Therealizableproblemsaretoshortenthelengthofverticalarrayandtodecreasethenumberofhydrophones.ItiswellknownforMMPthatthelengthofarraymustcoverstheelitirewatercolunm,andthenumberofhydrophonesmustbelargerthanorat1eastequaltothenUmberofmodesexcitedbyasourceinshallowwater,i.e.themodesmustbeadequatelysampledbyaverticalarray.Rece…     

Interaction of binary cuprates with oxygen and water vapor at temperatures of 200–400°C

Interaction of binary cuprates with oxygen and water vapor at T = 200–400°C has been studied. It has been established that only compounds containing oxygen vacancy chains in their structure can absorb oxygen and moisture from annealing atmosphere. Absorption of oxygen brings about decrease in the lattice parameters while embedding of OH^? groups leads to their growth. In contrast to YBa₂Cu₃O _y , binary cuprates do not undergo phase transitions in interaction with the atmosphere. Saturation with water and formation of oxyhydroxides is followed by their hydrolytic decomposition involving formation of simpler oxides and hydroxides.     

Fluorescence spectroscopy of 1,2,4-trimethylbenzene at high temperatures and pressures: application to temperature measurements

Fluorescence of the S₁→S₀ transition of 1,2,4-trimethylbenzene vapour after laser excitation at 266 nm was investigated in a heated cell. Experiments were performed for temperature between 350 and 900 K, at pressure between 0.1 and 3.0 MPa and for oxygen molar fraction between 0 and 21%. The absorption cross section was found to reduce by about 20% between 350 and 900 K. 1,2,4-trimethylbenzene fluorescence exponentially decreased by three orders of magnitude as temperature increased. A similar behaviour was observed with pressure, although fluorescence reduced only by a factor of 2.5 between 0.1 and 3.0 MPa. Additionally, Stern–Volmer plots were found to be linear for temperatures between 450 and 750 K. Using the dependence of 1,2,4-trimethylbenzene fluorescence on temperature, potential use of this molecule for temperature measurements in turbulent flows is suggested.     

Implications of causality for quantum biology – I: topology change

A framework for describing the causal, topology changing, evolution of interacting biomolecules is developed. The quantum dynamical manifold equations (QDMEs) derived from this framework can be related to the causality restrictions implied by a finite speed of light and to Planck's constant to set a transition frequency scale. The QDMEs imply conserved stress-energy, angular-momentum and Noether currents. The functional whose extremisation leads to this result provides a causal, time-dependent, non-equilibrium generalisation of the Hohenberg–Kohn theorem. The system of dynamical equations derived from this functional and the currents J derived from the QDMEs are shown to be causal and consistent with the first and second laws of thermodynamics. This has the potential of allowing living systems to be quantum mechanically distinguished from non-living ones.     

Temperature-related performance of Yb^3＋：YAG disc lasers and optimum design for diamond cooling

In this paper the temperature-related performances of the Yb^3＋：YAG disc laser has been investigated based on quasi-three level rate equation model. A compact diamond window cooling scheme also has been demonstrated. In this cooling scheme, laser disc is placed between two thin discs of single crystal synthetic diamond, the heat transfer from Yb^3＋：YAG to the diamond, in the direction of the optical axis, and then rapidly conducted radically outward through the diamond to the cooling water at the circumference of the diamond/Yb^3＋ ：YAG assembly. Simulation results show that increasing the thickness of the diamond and the overlap-length （between diamond and water） decreases the disc temperature. Therefore a 0.3-0.5 mm thick diamond window with the overlap-length of 1.5 2.0 mm will provide acceptable cost effective cooling, e.g., with a pump intensity of 15 kW/cm^2 and repetitive rate of 10 Hz, to keep the maximum temperature of the lasing disc below a reasonable value （310K）, the heat exchange coefficient of water should be about 3000 W/m^2K.     

Influence of post-grown Li-rich and Li-poor vapor transport equilibration on composition, OH− absorption and optical-damage threshold of Mg (5 mol%) : LiNbO3 crystals

Li-rich (Li-poor) vapor transport equilibration (VTE) treatments on a number of Z-cut 0.47 mm thick congruent MgO (5 mol% in melt) : LiNbO₃ crystals were carried out at 1100°C over different durations ranging in 1–172 (40–395) h. Neutron activation analysis shows that neither Li-rich nor Li-poor VTE-induced Mg and Nb loss from the crystal occurred. The Li₂O content in the crystal was measured as a function of VTE duration by the gravimetric method. The Li-rich/Li-poor VTE effects on OH⁻ absorption were studied in comparison with the as-grown crystal. The study shows that the Li-rich VTE results in OH⁻ absorption band annihilation. After further oxidation treatment the band reemerges and peaks at the same wavenumber as that of the as-grown crystal (∼3535.6 cm⁻¹), showing that the MgO concentration in the Li-rich VTE crystal is still above the optical-damage threshold. The Li-poor VTE causes OH⁻ band shift to 3486.3–3491.6 cm⁻¹, indicating that the MgO concentration in all Li-poor VTE crystals is all below the optical-damage threshold. Further successive Li-rich VTE and oxidation treatments on the Li-poor VTE-treated crystal lead the band to shift back to 3535.6 cm⁻¹, showing that the post Li-rich VTE brought the Li-poor VTE-treated crystal above the optical-damage threshold again. It is found that the peaking position, band width, peaking absorption and band area of the absorption at ∼3486 cm⁻¹ all increase monotonously with the decrease of the Li₂O content arising from prolonged Li-poor VTE, and quantitative relationships to the Li₂O content are established for the latter two parameters. The VTE effects on the OH⁻ absorption are conducted with the VTE-induced OH⁻ content alteration and charge redistribution.     

Faddeev–Jackiw canonical path integral quantization for a general scenario,its proper vertices and generating functionals

We generalize the Faddeev–Jackiw canonical path integral quantization for the scenario of a Jacobian with J=1 to that for the general scenario of non-unit Jacobian, give the representation of the quantum transition amplitude with symplectic variables and obtain the generating functionals of the Green function and connected Green function. We deduce the unified expression of the symplectic field variable functions in terms of the Green function or the connected Green function with external sources. Furthermore, we generally get generating functionals of the general proper vertices of any n-points cases under the conditions of considering and not considering Grassmann variables, respectively; they are regular and are the simplest forms relative to the usual field theory.     

Soft processes at the LHC,II: soft–hard factorisation breaking and gap survival

We calculate the probability that the rapidity gaps in diffractive processes survive both eikonal and enhanced rescattering. We present arguments that enhanced rescattering, which violates soft–hard factorisation, is not very strong. Accounting for NLO effects, there is no reason to expect that the black-disc regime is reached at the LHC. We discuss the predictions for the survival of the rapidity gaps for exclusive Higgs production at the LHC.     

Structure,stability and energetics of ionic arsenic–water complexes

The structure, stability and energetics of ionic arsenic–water complexes [As³⁺–nH₂O (n?=?1–5) and As⁵⁺–nH₂O (n?=?3–5)] have been studied in detail using the MP2 method. Both the trivalent and pentavalent ionic states of arsenic were considered. The change in binding energy of the complexes with increasing number of water molecules was investigated. For both complexes involving trivalent and pentavalent arsenic, highly intense modes are observed in the high-frequency region. The structure and symmetry of the complexes with increasing number of water molecules is discussed. The charge transfer in these complexes is illustrated with the help of the natural electron configuration. Both donation and back-donation processes involving the orbitals of oxygen and arsenic are analysed to explain the charge transfer.     

Definition and extraction of characterization parameters for pyrocarbon by chemical vapor infiltration based on 0 0 2 lattice fringe images

Some quantification methods were developed for microstructure characterization of pyrocarbon (PyC) in carbon/carbon (C/C) composites fabricated by chemical vapor infiltration. Firstly, the feature parameters were strictly defined based on 002 lattice fringe images in high-resolution transmission electron microscopy. They were illustrated with the diagram. Image analysis was adopted to measure or calculate the feature parameters of describing individual fringe or expressing the relationship between fringes. An improved comprehensive parameter, crystallinity factor, was introduced to indicate the crystallization of PyC. Then, judgment rules of microcrystal units were considered from three aspects: interlayer spacing, stacked position, and parallelism between layers. The latter two were analyzed by drawing geometrical figures. Finally, the extracted parameters were displayed in statistical histograms, and also compared with the measurements from manual observation, X-ray diffraction, and selected area electron diffraction. The results were in general agreement. The developed algorithms were performed automatically by the computer. They are especially applicable to analyze the microstructure evolution of C/C composites in graphitization process. The extracted feature parameters supply the basis for studying mechanism of graphitization and interfacial structure of PyC.     

Materials,technologies, and circuit concepts for nanocrossbar-based bipolar RRAM

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO₂, WO₃, GeSe, SiO₂ and MSQ thin films were integrated into nanojunctions of 100×100 nm². The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10¹⁰ bit.     

Incoherent broad-band cavity-enhanced absorption spectroscopy for simultaneous trace measurements of NO2 and NO3 with a LED source

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NO _x , SO _x , CO, and CO₂. We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) set-up which uses a LED emitting around 625 nm for the simultaneous detection of NO₂ and NO₃. The LED light transmitted through a high-finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO₂ reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO₂ and NO₃ concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400 s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2×10⁻¹⁰ cm⁻¹, which corresponds to detection limits of 600 pptv for NO₂ and 2 pptv for NO₃. This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.