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41.
42.
We report the precise transfer of radio-frequency signals by use of the pulse repetition frequency of mode-locked laser sources at 1.5 microm transmitting through a fiber network. The passive transfer instability through a 6.9-km fiber is below 3 x 10(-14) at 1 s, which is comparable with the optical carrier-frequency transfer of a narrow-linewidth cw laser. The instability of the measurement system is below 7 x 10(-15) at 1 s. It is noted that the pulsed mode of operation offers almost an order-of-magnitude improvement in stability at 1 s over that with a sinusoidal amplitude modulation on an optical carrier. 相似文献
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44.
R.J. Jones W.-Y. Cheng K.W. Holman L. Chen J.L. Hall J. Ye 《Applied physics. B, Lasers and optics》2002,74(6):597-601
The absolute frequency of the length standard at 514.67 nm based on the molecular iodine (127
I
2) transition of the P(13) 43-0 component a3 is measured using a self-referenced femtosecond optical comb. This frequency-based technique improves measurement precision
more than 100 times compared with previous wavelength-based results. Power- and pressure-related frequency shifts have been
carefully studied. The measured absolute frequency is 71.8±1.5 kHz higher than the internationally accepted value of 582490603.37±0.15 MHz,
adopted by the Comité International des Poids et Mesures (CIPM) in 1997.
Received: 7 March 2002 / Published online: 24 April 2002 相似文献
45.
D.F. Holman M.L. Chaudhry B.R.K. Kashyap 《European Journal of Operational Research》1983,13(2):142-145
In the present paper we consider the service system MX/G/∞ characterized by an infinite number of servers anda general service time distribution. The customers arrive at the system in groups of size X, which is a random variable, the time between group arrivals being exponentially distributed. Using simple probability arguments, we obtain probability generating functions (p.g.f.'s) of the number of busy servers at time t and the number that depart by time t. Several other properties of these random variables are also discussed. 相似文献
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48.
Cichewicz RH Kenyon VA Whitman S Morales NM Arguello JF Holman TR Crews P 《Journal of the American Chemical Society》2004,126(45):14910-14920
The selective inhibition of human 15-lipoxygenase (15-hLO) could serve as a promising therapeutic target for the prevention of atherosclerosis. A screening of marine sponges revealed that crude extracts of Psammocinia sp. exhibited potent 15-hLO inhibitory activity. Bioassay-guided fractionation led to the isolation of chromarols A-E (8-12) as potent and selective inhibitors of 15-hLO. An additional 22 structurally related compounds, including meroditerpenes from the same Psammocinia sp. (3, 4, 13-16) and our pure compound repository (17, 18), commercially available tocopherols (19-24), and synthetic chromanes (25-32), were evaluated for their ability to inhibit human lipoxygenases. The 6-hydroxychromane moiety found in chromarols A-D was identified as essential for the selective redox inhibition of 15-hLO. Furthermore, the oxidized form of the 6-hydroxychromane could be reduced by ascorbate, suggesting a potential regeneration pathway for these inhibitors in the body. This pharmacophore represents a promising paradigm for the development of a unique class of recyclable 15-hLO redox inhibitors for the treatment of atherosclerosis. 相似文献
49.
Ivana Brekalo David E. Deliz Prof. Leonard J. Barbour Prof. Michael D. Ward Prof. Tomislav Friščić Prof. K. Travis Holman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(5):2013-2018
Guanidinium organosulfonates (GSs) are a large and well-explored archetypal family of hydrogen-bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4-benzenedisulfonate ( p -G2BDS ). p -G2BDS is obtained from its acetone solvate, AcMe@ G2BDS , by single-crystal-to-single-crystal (SC-SC) desolvation, and exhibits a Type I low-temperature/pressure N2 sorption isotherm (SABET=408.7(2) m2 g−1, 77 K). SC-SC sorption of N2, CO2, Xe, and AcMe by p -G2BDS is explored under various conditions and X-ray diffraction provides a measurement of the high-pressure, room temperature Xe and CO2 sorption isotherms. Though p -G2BDS is formally metastable relative to the “collapsed”, nonporous polymorph, np -G2BDS , a sample of p -G2BDS survived for almost two decades under ambient conditions. np -G2BDS reverts to zCO2@ p -G2BDS or yXe@ p -G2BDS (y,z=variable) when pressure of CO2 or Xe, respectively, is applied. 相似文献
50.
Thin films of semiconductor nanocrystals with tunable optical properties are promising materials for new device applications, but progress has been slow for group IV materials. We report absorption measurements near the absorption edge of thin films of germanium nanocrystals synthesized in a plasma and impacted onto substrates. Band gaps extracted from the absorption data vary from the near‐bulk value of 0.73 eV for 9.0 nm nanocrystals to over 1.0 eV for 4.7 nm nanocrystals. These values are comparable to those reported for isolated, non‐interacting germanium nanocrystals, indicating minimal loss of quantum confinement upon dense film formation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献