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The Spaceborne Imaging Radar-C, X-Band Synthetic Aperture Radar (SIR-C/X-SAR) was launched on space shuttle Endeavour at 7:05 AM EDT, Saturday, April 9, 1994. Soon after launch, the radars were activated and began around the clock operations which lasted for the next 10 days.
An apparatus for measuring the W-band (75-110GHz) complex permittivity of dielectrics at 1000 °C was developed. This apparatus allows for measurements at approximately twice the temperature of previously published high temperature free-space measurement systems while maintaining similar precision. Challenges were addressed related to high temperature measurements, including temperature uniformity, the accuracy of temperature measurements, and preventing temperature related changes to mm-wave measurement systems. The details of complex permittivity extraction from the measured S-parameters are discussed. Sources of error related to permittivity measurement and mathematical models were identified and are discussed in detail herein. Thermally-cycled, mm-wave absorbing, aluminum nitride ceramic composites containing varying levels of molybdenum additives were measured over the range of 25-1000 °C. These measurements were compared to the same composites before thermal cycling. It was found that ceramic composites are largely stable after thermal cycling in terms of dielectric properties despite the presence of visible surface modifications.
The first observation of the decays Λ$^0_b$ → $χ$ c1 $pK$ - and Λ$^0_b$ → $χ$ c2 $pK$ - is reported using a data sample corresponding to an integrated luminosity of 3.0 fb -1 , collected by the LHCb experiment in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: $$\frac{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}=0.242 ± 0.014 ± 0.013 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→J/ψpK^-)}= 0.248 ± 0.020 ± 0.014 ± 0.009$$ $$\frac{\mathscr{B}(Λ^0_b→Χ_{c2}pK^-)}{\mathscr{B}(Λ^0_b→Χ_{c1}pK^-)}= 1.02 ± 0.10 ± 0.02 ± 0.05$$ where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the $Χ_{c1}$ → $Jψγ$ and $Χ_{c2}$ → $Jψγ$ decays. Using both decay modes, the mass of the Λ$^0_b$ baryon is also measured to be $m$ Λ$^0_b$ = 5619.44 ± 0.28 ± 0.26 MeV/$c$ 2 , where the first and second uncertainties are statistical and systematic, respectively.
This paper is an erratum to a previous paper (EPJC 73 (2013) 2531) published by C. Adolph et al. (The COMPASS Collaboration) using a data sample taken in 2004. In the course of the ongoing analysis of the more recent 2006 data sample, and following some additional hints we identified a problem in the analysis of the 2004 data presented in EPJC 73 (2013) 2531. The acceptance correction for the 2004 data sample did not properly account for the use of semi-inclusive triggers on top of the inclusive triggers.
The high catalytic reactivity of homoleptic tris(alkyl) lanthanum La{C(SiHMe2)3}3 is highlighted by C–O bond cleavage in the hydroboration of esters and epoxides at room temperature. The catalytic hydroboration tolerates functionality typically susceptible to insertion, reduction, or cleavage reactions. Turnover numbers (TON) up to 10 000 are observed for aliphatic esters. Finally, Lanthanum hydrides, generated by reactions with pinacolborane, are competent for reduction of ketones but are inert toward esters. Instead, catalytic reduction of esters requires activation of the lanthanum hydride by pinacolborane.
New experimental data on the distributions of silver (Ag), bismuth (Bi), and antimony (Sb) between liquid iron-silicate slag and liquid copper metal in equilibrium with tridymite in the Cu-Fe-O-Si system at T = 1250 °C and 1300 °C (1523 K and 1573 K) have been obtained. The experimental methodology involved high-temperature equilibration, rapid quenching of the equilibrated phases, followed by direct measurement of the equilibrium phases with electron probe X-ray microanalysis (EPMA) for measurement of major element concentrations and laser ablation inductively coupled plasma mass spectrometry (LAICPMS) for the measurement of minor element concentrations. The 4-point test approach was employed to confirm the achievement of chemical equilibrium in the current study. Open-system equilibration on quartz substrates in controlled gas atmospheres (CO/CO{sub 2}/Ar) and closed-system equilibration in sealed quartz ampoules were used. The new experimental data resolve significant discrepancies found in previous studies and can be used as input for the development of thermodynamic databases for copper-making processes.
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In contrast to the adage “Models are to be used, not believed”, combustion kinetics models have been intended to be predictive in nature. Theoretical chemical kinetics is now understood to provide a firm foundation for the reaction parameters, thereby facilitating predictive simulations of chemical reactivity, even in regimes that are poorly characterized by chemical kinetic and/or combustion experiments. In this study, we describe a theory-informed kinetics model (ThInK) for small molecule combustion chemistry (H 2 and C 1 – C 3 species) that is based on the prodigious use of theoretical predictions for reaction rate coefficients, thermochemistry, and transport parameters. The distinct features of this kinetics model, which was developed over the course of several decades, are illustrated through simulations of flame propagation and auto-ignition.
The pyrolysis of C 2 –C 4 linear perfluoroalkanes was investigated using laser schlieren densitometry (LS) in a diaphragmless shock tube. Mixtures of 1, 2, and 4% perfluoroethane (PFE), perfluoropropane (PFP), and perfluorobutane (PFB) in excess krypton were shock-heated to 1400–2500 K at pressures of 60, 120, and 240 Torr. The initiation step for all perfluoroalkanes involved carbon–carbon bond fission. The rate constants for unimolecular decomposition were computed using microcanonical rate theory, and these rate constants were combined into a detailed chemical kinetic mechanism. For PFE and PFP, there was one dissociation channel, while PFB dissociated via two competing bond-fission reactions. The perfluoroalkyl radicals subsequently recombined or underwent further unimolecular decomposition. In conclusion, the kinetic model accurately simulated the density gradient profiles of all perfluoroalkanes.
The stability of palladium supported on ceria (Pd/CeO 2 ) was studied during liquid flow transfer hydrogenation using primary and secondary alcohols as hydrogen donors. For primary alcohols, the ceria support was reduced to cerium hydroxy carbonate within 14 h and was a contributing factor toward catalyst deactivation. For secondary alcohols, cerium hydroxy carbonate was not observed during the same time period and the catalyst was stable upon prolonged reaction. Regeneration through oxidation/reduction does not restore initial activity likely due to irreversible catalyst restructuring. Lastly, a deactivation mechanism involving C–C scission of acyl and carboxylate intermediates is proposed.
Enantioselective hydrogenation of C═C bonds is foundational to asymmetric synthesis, yet its adaptation to electrochemical methods has been limited by challenges in achieving chemoselectivity versus the hydrogen evolution reaction (HER). In this article, we present a modular electrochemical strategy that merges chiral nickel catalysis with a cobaltocene-derived proton-coupled electron transfer (PCET) mediator to enable the asymmetric hydrogenation of α,β-unsaturated carbonyl compounds. Under optimized conditions, a range of substrates featuring diverse amide functionalities and substitution patterns are hydrogenated in high yields (up to 95%) and enantioselectivities (up to 98% ee). The results described highlight the potential benefits of mediator-assisted, fixed-potential electrocatalysis in selective, stereocontrolled hydrogenation under mild conditions.
Reduction of the aluminum iodide AlI 2 Ar i Pr8 ( 1 ; Ar i Pr8 = C 6 H-2,6-(C 6 H 2 -2,4,6-Pr i 3 ) 2 -3,5-Pr i 2 ) with 5% w/w Na/NaCl in hexanes gave a dark red solution from which the monomeric alanediyl : AlAr i Pr8 ( 2 ) was isolated in ca. 28% yield as yellow-orange crystals. Compounds 1 and 2 were characterized by X-ray crystallography, electronic and NMR spectroscopy, and theoretical calculations. The Al atom in 2 is one-coordinate, and the compound displays two absorptions in its electronic spectrum at 354 and 455 nm. It reacts with H 2 under ambient conditions to give the aluminum hydride {AlH(μ-H)Ar i Pr8 } 2 , probably via a weakly bound dimer of 2 as an intermediate.
Land-based carbon removals, specifically afforestation/reforestation and bioenergy with carbon capture and storage (BECCS), vary widely in 1.5 °C and 2 °C scenarios generated by integrated assessment models. Because underlying drivers are difficult to assess, we use a well-known integrated assessment model, GCAM, to demonstrate that land-based carbon removals are sensitive to the strength and scope of land-based mitigation policies. We find that while cumulative afforestation/reforestation and BECCS deployment are inversely related, they are both typically part of cost-effective mitigation pathways, with forestry options deployed earlier. While the CO 2 removal intensity (removal per unit land) of BECCS is typically higher than afforestation/reforestation over long time horizons, the BECCS removal intensity is sensitive to feedstock and technology choices whereas the afforestation/reforestation removal intensity is sensitive to land policy choices. Finally, we find a generally positive relationship between agricultural prices and removal effectiveness of land-based mitigation, suggesting that some trade-offs may be difficult to avoid.
Carbon dioxide-assisted coupling of methane offers an approach to chemically upgrade two greenhouse gases and components of natural gas to produce ethylene and syngas. Prior research on this reaction has concentrated efforts on catalyst discovery, which has indicated that composites comprised of both reducible and basic oxides are especially promising. There is a need for detailed characterization of these bifunctional oxide systems to provide a more fundamental understanding of the active sites and their roles in the reaction. We studied the dependence of physical and electronic properties of Ca-modified ZnO materials on Ca content via X-ray photoelectron and absorption spectroscopies, electron microscopy, and infrared spectroscopic temperature-programmed desorption (IR-TPD). It was found that introduction of only 0.6 mol% Ca onto a ZnO surface is necessary to induce significant improvement in the catalytic production of C 2 species: C 2 selectivity increases from 5% on un-modified ZnO to 58%, at similar conversions. Evidence presented shows that this selectivity increase results from the formation of an interface between the basic CaO and reducible ZnO phases. Furthermore, the basicity of these interface sites correlates directly with catalytic activity over a wide composition range, and this relationship indicates that moderate CO 2 adsorption strength is optimal for CH 4 coupling. These results demonstrate, for the first time to our knowledge, a volcano-type relationship between CO 2 -assisted CH 4 coupling activity and catalyst surface basicity, which can inform further catalyst development.
We propose to measure the γ-ray emission probability from excited states above 5 MeV including giant resonance of {sup 16}O and {sup 12}C as a function of excitation energy in 1-MeV step. Here, we measure both the excitation energy (E{sub x}=5-30MeV) at the forward scattering angles (0°-3°) of the {sup 16}O, {sup 12}C (p, p’) reaction using Grand-Raiden Spectrometer and the energy of γ-rays (E{sub γ}) using an array of NaI(Tl) counters. The purpose of the experiment is to provide the basic and important information not only for the γ-ray production from primary neutral-current neutrino-oxygen (-carbon) interactions but also for that from the secondary hadronic (neutron-oxygen and -carbon) interactions.
Here, environmental metal pollution is a growing health risk to flora and fauna. It is therefore important to fully elucidate metal detoxification pathways. Phytochelatin synthase (PCS), an enzyme involved in the biosynthesis of phytochelatins (PCs), plays an important role in cadmium detoxification. The PCS and PCs are however not restricted to plants, but are also present in some lower metazoans. The model nematode Caenorhabditis elegans , for example, contains a fully functional phytochelatin synthase and phytochelatin pathway. By means of a transgenic nematode strain expressing a pcs -1 promoter-tagged GFP ( pcs -1::GFP) and a pcs -1 specific qPCR assay, further evidence is presented that the expression of the C. elegans phytochelatin synthase gene (pcs-1) is transcriptionally non-responsive to a chronic (48 h) insult of high levels of zinc (500 μM) or acute (3 h) exposures to high levels of cadmium (300 μM). However, the accumulation of cadmium, but not zinc, is dependent on the pcs -1 status of the nematode. Synchrotron based X-ray fluorescence imaging uncovered that the cadmium body burden increased significantly in the pcs -1(tm1748) knockout allele. Taken together, this suggests that whilst the transcription of pcs -1 may not be mediated by an exposure zinc or cadmium, it is nevertheless an integral part of the cadmium detoxification pathway in C. elegans .
Theoretical transition energies and absorption oscillator strengths for the c{sub 4}{sup ′1}Σ{sub u}{sup +} (v′ = 0–2, 5, 7, 8) − X{sup 1}Σ{sub g}{sup +}(v{sup ′′}=0--14) and c{sub 5}{sup ′1}Σ{sub u}{sup +} (v′ = 0, 2) − X{sup 1}Σ{sub g}{sup +} (v″ = 0–14) Rydberg bands, and b{sup ′1}Σ{sub u}{sup +} (v′ = 0–9, 11, 12, 14–19, 21, 22) − X{sup 1}Σ{sub g}{sup +} (v″ = 0–14) valence bands of molecular nitrogen are reported. The strong interaction between {sup 1}Σ{sub u}{sup +} states has been dealt with through a vibronic interaction matrix. As a consequence of the Rydberg-valence interaction, irregularities in the vibrational structure of the above band systems are observed. Good agreement is found with the scarce high-resolution data that are available for oscillator strengths. The new band oscillator strengths reported here may be useful for a reliable interpretation of the spectra from atmospheres of the Earth, Titan, and Triton, where N{sub 2} is the mayor constituent.
Absorption spectra recorded on the high-resolution Fourier transform spectrometer at Kitt Peak National Observatory/National Solar Observatory were used to measure individual line strengths of the nu(2) and nu(4) bands of (C-12)H4 and (C-13)H4. The measurements were used to obtain expressions that could be used to correctly predict individual line strengths through five orders of magnitude of absorption strength and high values of J-prime. Transition strengths were modeled using the dyad formalism of two interacting bands and a seven-term second-order dipole-moment expansion. The successful fitting of these data indicates that the method can be used to model measurements of 2- to 5-percent precision even at high values of J. For remote sensing applications, the present prediction of the dyad spectrum represents a substantial improvement.