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排序方式: 共有211条查询结果,搜索用时 31 毫秒
51.
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Spatial and temporal variations of the inherent and apparent optical properties in a shallow coastal lake 总被引:2,自引:0,他引:2
Bracchini L Dattilo AM Falcucci M Loiselle SA Hull V Arena C Rossi C 《Journal of photochemistry and photobiology. B, Biology》2005,80(3):161-177
Apparent and inherent optical properties in the coastal lagoon of Fogliano were measured in three seasonal surveys in 2002. Irradiance data from in situ measurements of ultraviolet and visible wavebands permitted to estimate the related attenuation coefficients. Laboratory extinction measurements on filtered (0.22 microm) and unfiltered water samples were also performed. The integrated approach between in situ and laboratory measurements allowed the determination of the role of the suspended and dissolved matter in the attenuation and extinction of ultraviolet and visible radiation within the water column. As noted, the impact of the suspended and dissolved matter on the lake optical quality was influenced by wind resuspension of particulate matter: the relative role of dissolved matter in the absorption of UV and visible radiation was prevailing at low wind velocity conditions (less than 2.2 m s(-1)), while at high wind velocities (3.9 m s(-1)), particulate matter resuspension strongly influenced the attenuation and the extinction measurements. The extinction in the analyzed wavelengths of filtered and unfiltered water samples and the in situ irradiance measurements allowed us to define new optical parameters and important correlations with limnological and classical optical measurements. By sampling at high spatial resolution (18 stations in 4 km2), it was possible to evidence a spatial gradient of the optical and limnological properties, these distributions showed a consistent pattern in all three surveys, and were important for the characterization of the chromophoric dissolved organic matter that was estimated with the spectral slope of the extinction curve spectra. A relatively higher spectral slope was found in the southern basin with respect to the northern, where the maximum values of the attenuation coefficients and limnological parameters were found. These results suggest different sources of dissolved organic matter and/or a different level of photobleaching. 相似文献
54.
Cheng X Canavan HE Stein MJ Hull JR Kweskin SJ Wagner MS Somorjai GA Castner DG Ratner BD 《Langmuir : the ACS journal of surfaces and colloids》2005,21(17):7833-7841
Surface-immobilized poly(N-isopropyl acrylamide) (pNIPAM) is currently used for a wide variety of biosensor and biomaterial applications. A thorough characterization of the surface properties of pNIPAM thin films will benefit those applications. In this work, we present analysis of a plasma-polymerized NIPAM (ppNIPAM) coating by multiple surface analytical techniques, including time-of-flight secondary-ion mass spectrometry (ToF-SIMS), contact angle measurement, atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. ToF-SIMS data show that the plasma-deposited NIPAM polymer on the substrate is cross-linked with a good retention of the monomer integrity. Contact angle results confirm the thermoresponsive nature of the film as observed by a change of surface wettability as a function of temperature. Topographic and force-distance curve measurements by AFM further demonstrate that the grafted film shrinks or swells depending on the temperature of the aqueous environment. A clear transition of the elastic modulus is observed at 31-32 degrees C. The change of the surface wettability and mechanical properties vs temperature are attributed to different conformations taken by the polymer, which is reflected on the outmost surface as distinct side chain groups orienting outward at different temperatures as measured by SFG. The results suggest that a ppNIPAM thin film on a substrate experiences similar mechanical and chemical changes to pNIPAM bulk polymers in solution. The SFG result provides evidence supporting the current theory of the lower critical solution temperature (LCST) behavior of pNIPAM. 相似文献
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Derek Hull 《Macromolecular Symposia》1986,1(1):139-150
The ability of polymer-based fibre reinforced composite materials to absorb energy when subjected to high stress depends on the micromechanics of deformation and fracture of the individual laminae and the interaction between laminae. The micromechanismsdepend on the properties of the matrix, fibres and fibre-matrix interface. The capacity of material to absorb energy is important in many applications and particular reference is made to the response of structures to impact. 相似文献
57.
J.M. Tarascon J.V. Waszczak G.W. Hull F.J. DiSalvo L.D. Blitzer 《Solid State Communications》1983,47(12):973-979
New ternary molybdenum chalcogenides HgxMo6S8 (0 < x < 1) have been synthesized and investigated for their structural, magnetic, and superconducting behavior. These new phases prepared at low temperature by reaction of mercury with Mo6S8 (obtained from oxidation of Cu2Mo6S8 by iodine) have been characterized by x-ray diffraction, static Faraday susceptibility, and superconducting transition temperature studies. HgMo6S8 crystallizes in the rhombohedral space group , has a paramagnetic, temperature dependent susceptibility, and superconducts at 8.1K. As the mercury content decreases, a continuous decrease in Tc from 8.1K to 1.7K for x=0 (Mo6S8) is observed. 相似文献
58.
A one- and a two-dimensional INADEQUATE NMR experiment afforded one-bond 13C13C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1). 13C13C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1). 相似文献
59.
The 500 MHz 1H NMR spectra of somatostatin and the precursor, di-S3,14-acetamidomethyl dihydrosomatostatin, in dimethyl sulphoxide solution have been assigned. Chemical shifts, coupling constants and NH shifts vs temperature coefficients are tabulated. The data are consistent with a stable β-turn/β-sheet conformation for the precurso, while somatostatin itself appears to be more conformationally mobile, with an average conformation significantly different from that in aqueous solution. 相似文献
60.
Atomic absorption spectrophotometry, differential scanning calorimetry, differential thermal analysis, thermogravimetric analysis, and infrared spectroscopy, combined with oxidizable carbon determinations and pollen counting, were applied in the paleoecological study of lacustrine sediments taken from some lakes in Northern Ireland. Details of the techniques, and the methods of sampling and sample preparation are described, and the results discussed. Such studies reveal valuable information on past environments. 相似文献