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31.
Andrew M. Poitras Sadie E. Knight Mark W. Bezpalko Bruce M. Foxman Christine M. Thomas 《Angewandte Chemie (International ed. in English)》2018,57(6):1497-1500
Addition of H2 across the cobalt–phosphorus bond of (PPP)CoPMe3 ( 3 ) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP?) donor. The chlorophosphine CoII complex (PPClP)CoCl2 ( 2 ) can be generated through coordination of the chlorophosphine ligand (PPClP, 1 ) to CoCl2. Subsequent reduction of 2 with KC8 in the presence of PMe3 generates (PPP)CoPMe3 ( 3 ), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H2 to complex 3 cleanly affords (PPHP)Co(H)PMe3 ( 4 ), in which H2 has ultimately been added across the metal–phosphorus bond. Complex 4 was characterized spectroscopically and using computational methods to predict its geometry. 相似文献
32.
33.
Ice VI is a hydrogen bond disordered crystal over its known region of stability. In this work, we predict that ice VI will transform into a hydrogen bond ordered phase near 108 K, and have identified the likely low-temperature phase as ferroelectric (space group Cc) with an antiferroelectric structure (space group P2(1)2(1)2(1)) close by in energy. Electronic density functional theory calculations provide input to our calculations, which are extended to cells large enough for statistical simulations by using graph invariants. A significant decrease in the configurational entropy is predicted as hydrogen bonds exhibit partial order above the transition, provided that the hydrogen bonds can equilibrate on an experimental time scale. Conversely, partial disorder is predicted at temperatures below the transition. Although some evidence for ordering of ice VI has been observed in experiments, a low-temperature proton ordered phase has not been identified experimentally. 相似文献
34.
The existence of an ice Ih/XI proton-ordering transition to a low-temperature ferroelectric phase has sparked considerable debate in the literature. Electronic density functional theory calculations, extended using graph invariants, confirm that a transition to a low-temperature ferroelectric phase should occur. The predicted transition at 98 K is in qualitative agreement with the observed transition at 72 K, and the low-temperature phase is the ferroelectric phase determined in diffraction experiments. The theoretical methods used to predict the phase transition are validated by comparing their prediction to the well-characterized ice VII/VIII proton-ordering transition. 相似文献
35.
Remington PJ Knight JS Hanna D Rowley C 《The Journal of the Acoustical Society of America》2005,117(1):68-78
A prototype hybrid system consisting of active and passive components for controlling far-field locomotive exhaust noise has been designed, assembled, and tested on a locomotive. The system consisted of a resistive passive silencer for controlling high-frequency broadband noise and a feedforward multiple-input, multiple-output active control system for suppressing low-frequency tonal noise. The active system used ten roof-mounted bandpass speaker enclosures with 2-12-in. speakers per enclosure as actuators, eight roof-mounted electret microphones as residual sensors, and an optical tachometer that sensed locomotive engine speed as a reference sensor. The system was installed on a passenger locomotive and tested in an operating rail yard. Details of the system are described and the near-field and far-field noise reductions are compared against the design goal. 相似文献
36.
We describe the fabrication and characterization of a free-standing silica glass membrane waveguide formed using fiber fabrication processes. The membrane has a thickness of 0.6 microm and a width of 60 microm and is many meters long. The optical attenuation is measured as 0.4 dB/m. Such attenuation outperforms that of conventional planar waveguides by several orders of magnitude. 相似文献
37.
Kylstra NJ Worthington RA Patel A Knight PL Vazquez De Aldana JR Roso L 《Physical review letters》2000,85(9):1835-1838
An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations. 相似文献
38.
We describe the use of tapered hollow-core photonic crystal fibres for delivery and compression of ultrashort optical pulses. We demonstrate delivery of transform-limited pulses with less than 100 fs pulse length and above 50 nJ energy through 8 m of fibre, in a single transverse mode. 相似文献
39.
Aequationes mathematicae - 相似文献
40.
D.J.E. Knight F. Minardi P. De Natale P. Laporta 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(3):211-216
A good frequency standard is required at 1083 nm for measurements on the fine structure of helium and of the fine structure
constant. Several milliwatts of CW frequency-doubled light offers the prospect of stabilisation to a Doppler-free hyperfine
transition in molecular iodine. The 1083 nm emission of an extended-cavity DBR diode laser has been amplified using an ytterbium-doped
fibre amplifier, and applied to a type-I phase matched Mg:LiNbO3 crystal in a high-Q fundamental-resonant cavity for frequency doubling. The amplifier gain at 1083 nm under typical operating conditions was
13.8 dB, with a coherent output power up to 63 mW, limited by the maximum signal input power. The doubling cavity Q was , and about 70% of the incident power was coupled in. The maximum 2nd-harmonic conversion efficiency exceeded 20% and provided
an output power of 3.7 mW for making continuous frequency scans of up to 600 MHz in the green. An optical spectrum analyser
at 541.5 nm showed fringes of 4.6 MHz full width half maximum, close to the instrumental width.
Received: 25 February 1998 / Revised and Accepted: 28 May 1998 相似文献