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21.
M. John Plater Mark R. St. J. Foreman Janet M. S. Skakle 《Journal of chemical crystallography》2000,30(8):535-537
The synthesis and molecular structure of the title compound are reported. The metal ion has a distorted octahedral geometry and is coordinated by two cis thiocyanate nitrogens, two trans pyridine nitrogens and two cis pyridazine nitrogens. The structure has an orthorhombic space group Pbcn with a = 12.9376(6) Å, b = 13.4312(7) Å, c = 18.8992(9) Å, V = 3284.1(3) Å3, and Z = 8. 相似文献
22.
Matthew Foreman 《Advances in Mathematics》2009,222(2):565-2687
Since the work of Godel and Cohen many questions in infinite combinatorics have been shown to be independent of the usual axioms for mathematics, Zermelo Frankel Set Theory with the Axiom of Choice (ZFC). Attempts to strengthen the axioms to settle these problems have converged on a system of principles collectively known as Large Cardinal Axioms.These principles are linearly ordered in terms of consistency strength. As far as is currently known, all natural independent combinatorial statements are equiconsistent with some large cardinal axiom. The standard techniques for showing this use forcing in one direction and inner model theory in the other direction.The conspicuous open problems that remain are suspected to involve combinatorial principles much stronger than the large cardinals for which there is a current fine-structural inner model theory for.The main results in this paper show that many standard constructions give objects with combinatorial properties that are, in turn, strong enough to show the existence of models with large cardinals are larger than any cardinal for which there is a standard inner model theory. 相似文献
23.
Two mode-locked femtosecond fiber lasers, connected via a 7 km fiber link, are synchronized to an rms timing jitter of 19 fs, observed over the entire Nyquist bandwidth (half of the 93 MHz repetition frequency). This result is achieved in two steps. First, active cancellation of the fiber-transmission noise reduces timing jitter caused by path length fluctuations to a record level of 16 fs. Second, using a wide bandwidth interactivity actuator, the slave laser is synchronized to the incoming stable pulse train from the reference laser to within 10 fs. These results are confirmed by an optical cross-correlation measurement performed independently of the feedback loop operated in the microwave domain. 相似文献
24.
Repulsive potentials between about 0.2 eV and 20 eV are determined for interactions of oxygen atoms with the noble gas atoms and with H2, N2, O2, NO, CO, CO2 and H2O molecules from incomplete total scattering cross sections. Good agreement with theory is obtained for the noble gases. The potentials for the interaction with molecules obtained by assuming spherically symmetric potentials are compared with the same potentials computed by averaging the cross sections for different orientations of the molecules. By introducing reduced variables, the problem of finding two isotropic potential parameters is simplified to a search for one, the other being determined by a least-squares constraint. 相似文献
25.
Cross sections for the 111, 110, 212, and 211 rotational states and for total beam attenuation of H2CO were measured using a beam maser spectrometer. Significant inelastic scattering in the forward direction was obtained for He and CF3H. Significant inelastic contributions were not observed using H2 as a scattering gas. Observed cross sections for the 111 state are larger than those for the 110 state. The relations of the present cross sections to various models for obtaining a low excitation temperature for the 111-110 doublet of formaldehyde in interstellar space is discussed. 相似文献
26.
J. K. Foreman 《Mikrochimica acta》1956,44(10):1481-1487
Summary The analysis of gases by theKrogh technique of entrapping a bubble under glycerol and exposing it to selective absorbents has been examined to assess its value as a means of determining quantitatively oxygen, carbon dioxide, carbon monoxide and hydrogen in volumes of sample of the microlitre order. The method, after modifications to accommodate for non-specificity of the absorption reagents, has given satisfactory performance, and it possesses the additional advantage of simplicity of apparatus.
The author wishes to thank Mr.F. J. Woodman who initiated this work, and Mr.I. Waide for technical co-operation. This paper is published by permission of the Managing Director, United Kingdom Atomic Energy Authority (Industrial Group). 相似文献
Zusammenfassung Das gasanalytische Verfahren vonKrogh, wonach eine Gasblase in Glycerin eingeschlossen und unter dem Mikroskop der Einwirkung selektiver Absorptionsmittel ausgesetzt wird, wurde geprüft, um seine Eignung zur quantitativen Bestimmung von Sauerstoff, Kohlendioxyd, Kohlenmonoxyd und Wasserstoff in Proben der Größenordnung von Mikrolitern festzustellen. Das Verfahren wurde modifiziert, um es der Verwendung nicht spezifischer Absorptionsreagenzien anzupassen, und läßt sich nun in befriedigender Form durchführen. Es bietet den zusätzlichen Vorteil der Einfachheit in apparativer Hinsicht.
Résumé La technique d'analyse de gaz deKrogh qui consiste à emprisonner une bulle de gaz sous du glycerol et à l'exposer à des réactifs absorbants sélectifs a été éprouvée pour le dosage de l'oxygène, du gaz carbonique, de l'oxyde de carbone et de l'hydrogène sur des échantillons dont le volume est de l'ordre de grandeur du microlitre. La méthode a fourni des résultats satisfaisants après certaines modifications destinées à tenir compte de la non spécificité des réactifs absorbants; elle présente l'avantage complémentaire de la simplicité de l'appareillage mis en oeuvre.
The author wishes to thank Mr.F. J. Woodman who initiated this work, and Mr.I. Waide for technical co-operation. This paper is published by permission of the Managing Director, United Kingdom Atomic Energy Authority (Industrial Group). 相似文献
27.
K. W. Foreman A. T. Phillips J. B. Rosen K. A. Dill 《Journal of computational chemistry》1999,20(14):1527-1532
We provide some tests of the convex global underestimator (CGU) algorithm, which aims to find global minima on funnel-shaped energy landscapes. We use two different potential functions—the reduced Lennard–Jones cluster potential, and the modified Sun protein folding potential, to compare the CGU algorithm with the simplest versions of the traditional trajectory-based search methods, simulated annealing (SA), and Monte Carlo (MC). For both potentials, the CGU reaches energies lower on the landscapes than both SA and MC, even when SA and MC are given the same number of starting points as in a full CGU run or when all methods are given the same amount of computer time. The CGU consistently finds the global minima of the Lennard–Jones potential for all cases with up to at least n=30 degrees of freedom. Finding the global or near-global minimum in the CGU method requires polynomial time [scaling between O(n3) and O(n4)], on average. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1527–1532, 1999 相似文献
28.
James D. Scott Linda Chalker-Scott Alynda Empie Foreman Michael D'Angelo 《Photochemistry and photobiology》1999,70(3):308-313
Abstract The ability to avoid or tolerate UVB radiation (290–320 nm) probably reduces the quality of phytoplankton as food for zooplankton. Ultraviolet avoidance forces motile algae lower in the water column, reducing net primary productivity. Production of UV-absorbing compounds as a tolerance mechanism takes carbon and energy away from cell growth; these compounds are also less useful as food for herbivores. We assessed the food quality of UVB-irradiated Chlamydomonas reinhardtii Dang, by analysis of cohort life tables for the herbivore Daphnia pulex Leydig. Algal cultures were grown under fluorescent lights interspersed with UV bulbs (20°C, 16 h light: 8 h dark) and covered with either cellulose acetate (+UVB) or Mylar D (-UVB). After a 7 day UVB exposure, carotenoid levels of C. reinhardtii were significantly greater than in unexposed cultures; there were no significant differences in chlorophyll, lipid, protein or nonstructural carbohydrate levels. After an initial decrease in growth rate, UVB-exposed algae recovered and final growth rates of both cultures were similar after 7 days. Daphnia neonates were raised under optimal conditions (20°C, 16 h light:8 h dark) and fed either UVB-irradiated or control algae. Daphnia fed UVB-irradiated algae had significantly increased mortality, decreased growth rate at the time of first clutch production, delayed release of the first clutch and decreased overall fecundity (P < 0.05). Daphnia were also less efficient at clearing UVB-irradiated algae from the water column (17% removal in 18 h) when compared with Daphnia that grazed upon nonirradiated algae (85% removal in 18 h). These data suggest that even though UVB-irradiated algal populations can recover from their initial decline, their predators may not be able to utilize them as an effective food source. Therefore, the impacts of UVB radiation within 相似文献
29.
We demonstrate a new experimental approach for flexible femtosecond pulse generation in the mid-IR by use of difference-frequency generation from two tightly synchronized Ti:sapphire lasers. The resultant mid-IR pulse train can be easily tuned, with an adjustable repetition frequency up to 100 MHz, a pulse energy of approximately 1.5 x 10(-13) J, and an intensity noise similar to that of the Ti:sapphire. Rapid switching of the mid-IR wavelength and programmable amplitude modulation are achieved by precision setting of the time delay between two original pulses. 相似文献
30.
Foreman BA 《Physical review letters》2000,84(11):2505-2508
A theory of optical anisotropy for zinc-blende semiconductors in an electric field is derived by extending the formalism of Luttinger and Kohn [Phys. Rev. 97, 869 (1955)] to higher order. This resolves a recent controversy over the correct form of the Hamiltonian for the degenerate valence bands. 相似文献