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41.
Spectroradiometers using photodiode array detectors (PDAs) are increasingly applied for airborne and ground-based atmospheric measurements of spectral actinic flux densities due to their high time resolution (less than one second). However they have limited sensitivity of ultraviolet (UV) radiation for wavelengths less than about 305 nm. This results in uncertainties of ozone photolysis frequencies derived from spectral actinic flux density measurements using PDA spectrometers. To overcome this limitation a parameterization method is introduced which extrapolates the data towards the wavelength range of limited sensitivity of the PDA spectrometers (less than about 305 nm). The parameterization is based on radiative transfer simulations and is valid for measurements in the lower troposphere. The components of the suggested parameterization are the lower threshold wavelength of the PDA spectrometer, the slant ozone column (ratio of the total ozone column and the cosine of the solar zenith angle), and the ambient temperature. Tests of the parameterization with simulated actinic flux density spectra have revealed an uncertainty of the derived ozone photolysis frequency of ±5%. Field comparisons of the parameterization results with independent measurements of the ozone photolysis frequency were within ±10% for solar zenith angles less than 70^∘. Finally the parameterization was applied to airborne measurements to emphasize the advantage of high time resolution of PDA spectrometers to study ozone photolysis frequency fields in inhomogeneous cloud condtitions. 相似文献
42.
Several source parameters (source dimensions, slip, particle velocity, static and dynamic stress drop) are determined for the moderate-size October 27th, 2004 (MW = 5.8), and the large August 30th, 1986 (MW = 7.1) and March 4th, 1977 (MW = 7.4) Vrancea (Romania) intermediate-depth earthquakes. For this purpose, the empirical Green's functions method of Irikura [e.g. Irikura, K. (1983). Semi-Empirical Estimation of Strong Ground Motions during Large Earthquakes. Bull. Dis. Prev. Res. Inst., Kyoto Univ., 33, Part 2, No. 298, 63–104., Irikura, K. (1986). Prediction of strong acceleration motions using empirical Green's function, in Proceedings of the 7th Japan earthquake engineering symposium, 151–156., Irikura, K. (1999). Techniques for the simulation of strong ground motion and deterministic seismic hazard analysis, in Proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering: integrated training in earthquake risk reduction practices, Kefallinia, 453–554.] is used to generate synthetic time series from recordings of smaller events (with 4 ≤ MW ≤ 5) in order to estimate several parameters characterizing the so-called strong motion generation area, which is defined as an extended area with homogeneous slip and rise time and, for crustal earthquakes, corresponds to an asperity of about 100 bar stress release [Miyake, H., T. Iwata and K. Irikura (2003). Source characterization for broadband ground-motion simulation: Kinematic heterogeneous source model and strong motion generation area. Bull. Seism. Soc. Am., 93, 2531–2545.] The parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and MSK intensity pattern inversion for the 1977 event using a genetic algorithm. The strong motion recordings of the analyzed Vrancea earthquakes as well as the MSK intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas, which corresponds to small asperities with high stress drops (300–1200 bar) and high particle velocities (3–5 m/s). These results imply a very efficient high-frequency radiation, which has to be taken into account for strong ground motion prediction, and indicate that the intermediate-depth Vrancea earthquakes are inherently different from crustal events. 相似文献
43.
Many natural porous geological rock formations, as well as engineered porous structures, have fractal properties, i.e., they
are self-similar over several length scales. While there have been many experimental and theoretical studies on how to quantify
a fractal porous medium and on how to determine its fractal dimension, the numerical generation of a fractal pore structure
with predefined statistical and scaling properties is somewhat scarcer. In the present paper a new numerical method for generating
a three-dimensional porous medium with any desired probability density function (PDF) and autocorrelation function (ACF) is
presented. The well-known Turning Bands Method (TBM) is modified to generate three-dimensional synthetic isotropic and anisotropic
porous media with a Gaussian PDF and exponential-decay ACF. Porous media with other PDF's and ACF's are constructed with a
nonlinear, iterative PDF and ACF transformation, whereby the arbitrary PDF is converted to an equivalent Gaussian PDF which
is then simulated with the classical TBM. Employing a new method for the estimation of the surface area for a given porosity,
the fractal dimensions of the surface area of the synthetic porous media generated in this way are then measured by classical
fractal perimeter/area relationships. Different 3D porous media are simulated by varying the porosity and the correlation
structure of the random field. The performance of the simulations is evaluated by checking the ensemble statistics, the mean,
variance and ACF of the simulated random field. For a porous medium with Gaussian PDF, an average fractal dimension of approximately
2.76 is obtained which is in the range of values of actually measured fractal dimensions of molecular surfaces. For a porous
medium with a non-Gaussian quadratic PDF the calculated fractal dimension appears to be consistently higher and averages 2.82.
The results also show that the fractal dimension is neither strongly dependent of the porosity nor of the degree of anisotropy
assumed. 相似文献
44.
45.
Rainer Altherr Manfred Schliestedt Martin Okrusch Eberhard Seidel Hans Kreuzer Wilhelm Harre Heinz Lenz Immo Wendt Günther A. Wagner 《Contributions to Mineralogy and Petrology》1979,70(3):245-255
Polymetamorphic rocks of Sifnos (Greece) have been investigated by Rb-Sr, K-Ar, and fission track methods. Critical mineral assemblages from the northern and southernmost parts of Sifnos include jadeite+quartz+3T phengite, and omphacite+garnet +3T phengite, whereas the central part is characterized by the assemblage albite+chlorite+epidote+2M
1 phengite.K-Ar and Rb-Sr dates on phengites (predominantly 3T) of the best preserved high P/itTmetamorphic rocks from northern Sifnos gave concordant ages around 42 m.y., indicating a Late Lutetian age for the high P/T metamorphism. Phengites (2M
1+3T) of less preserved high P/T assemblages yielded K-Ar dates between 48 and 41 m.y. but generally lower Rb-Sr dates. The higher K-Ar dates are interpreted as being elevated by excess argon.K-Ar and Rb-Sr ages on 2M
1 phengites from central Sifnos vary between 24 and 21 m.y. These ages date a second, greenschist-facies metamorphism which overprinted the earlier high-pressure metamorphic rocks. 相似文献
46.
Vorgestellt wird cine Algizidtestvariante, die es erlaubt, unter laboratoriumsmäßig standardisierten Bedingungen ein repräsentatives Sortiment von Vertretern aus den Gruppen der Cyanophyceen, Diatomeen sowie monadaler, kokkaler und ulotrichaler Chlorophyceen zur Überprüfung der Wirksamkeit neu entwiekelter Substanzen einzusetzen. Die Testergebnisse liegen bereits nach 10 bzw. 24 h vor. Die elf Algenreinkulturstämme werden asynchron in Suspensionen bei 30 °C unter Dauerlicht kultiviert. Die Überprüfung der Wirksamkeit der Herbizide Amitrol, Paraquat, Atrazin, Fenuron und 2,4-D-Säure sowie der Algizide Quartolan, Cumasina ,,aktiv“ und Dimanin A zeigte, daß sich der als Bezugsorganismus eingesetzte Reinkulturstamm der Species Chlorella vulgaris (A 6) in seiner Empfindlichkeit gegenüber algiziden Substanzen als repräsentativ für einen großen Teil der übrigen Testorganismen erwies. Abweichungen in der Algizidempfindlichkeit einzelner Vertreter haben ihre Ursache vorwiegend in physiologischen und anatomisehen Besonderheiten bzw. im jeweiligen Volumen-Oberflächenverhältnis und der Bildung von Coenobien. Deshalb kann ein Test mit den ausgewählten Organismen in kurzer Zeit eine umfassende Aussage über den Wirkungsgrad algizider Substanzen ermöglichen. 相似文献
47.
48.
From wind profile and wave measurements performed during the JONSWAP II experiment, relations between the dimensionless profile slope and the significant wave height are derived. It is shown that the wind profile is distorted by the waves especially in the vicinity of the water surface. The wave influence on the profile seems to be restricted to heights below about three wave heights. Above this level, the dimensionless profile slope is an approximately constant value corresponding to a drag coefficient of about 1.15 × 10–3. 相似文献
49.
Hong Kong is a hyper-dense city with 7×106 people living in an area of 1100km2. One way to improve the livability of compacted and congested cities like Hong Kong is through the provision of urban parks,
an aspect that has largely been under-researched. This study focuses on how users perceive and utilize various facilities
in the Kowloon Park. The findings revealed that the Kowloon Park is one of the most preferred parks in Hong Kong for both
local residents and tourists. Users were quite satisfied with the park’s facilities. Notably, the most important component
of an urban park is its greenery. This is followed by water elements, seating places, and facilities for various recreational
activities. The improvements users would like to see in urban parks include good design and management, meeting users’ needs,
overcoming barriers to use, and providing a high quality and varied experience for different groups in the community. The
findings of this study provide a good basis to address park management issues from the users’ perspective. In particular,
parks should provide easy access, encourage optimum usage and enable complimentary improvements to the environment.
Foundation item: Under the auspices of the Germany-Hong Kong Joint Research Scheme (No.GER/99-00/01) and the Faculty Research
Grant of the Hong Kong Baptist University (No.FRG/00-01/I-38)
Biography: WONG Koon-kwai (1950—), male, a native of Guangdong Province, Ph.D., associate professor, specialized in the analysis
of human-environment interaction. E-mail: kenwong@hkbu.edu.hk 相似文献
50.
Yannick Garcin Annett Junginger Daniel Melnick Daniel O. Olago Manfred R. Strecker Martin H. Trauth 《Quaternary Science Reviews》2009,28(9-10):911-925
The Late Pleistocene to Middle Holocene African Humid Period (AHP) was characterized by dramatic hydrologic fluctuations in the tropics. A better knowledge of the timing, spatial extent, and magnitude of these hydrological fluctuations is essential to decipher the climate-forcing mechanisms that controlled them. The Suguta Valley (2°N, northern Kenya Rift) has recorded extreme environmental changes during the AHP. Extensive outcrops of lacustrine sediments, ubiquitous wave-cut notches, shorelines, and broad terrace treads along the valley margins are the vestiges of Lake Suguta, which once filled an 80 km long and 20 km wide volcano–tectonic depression. Lake Suguta was deep between 16.5 and 8.5 cal ka BP. During its maximum highstand, it attained a water depth of ca 300 m, a surface area of ca 2150 km2, and a volume of ca 390 km3. The spatial distribution of lake sediments, the elevation of palaeo-shorelines, and other geomorphic evidences suggest that palaeo-Lake Suguta had an overflow towards the Turkana basin to the north. After 8.5 cal ka BP, Lake Suguta abruptly disappeared. A comparison of the Lake Suguta water-level curve with other reconstructed water levels from the northern part of the East African Rift System shows that local insolation, which is dominated by precessional cycles, may have controlled the timing of lake highstands in this region. Our data show that changes of lake levels close to the Equator seem to be driven by fluctuations of spring insolation, while fluctuations north of the Equator are apparently related to variations in summer insolation. However, since these inferred timings of lake-level changes are mostly based on the radiocarbon dating of carbonate shells, which may have been affected by a local age reservoir, alternative dating methods are needed to support this regional synthesis. Between 12.7 and 11.8 cal ka BP, approximately during the Northern Hemisphere high-latitude Younger Dryas, the water level of Lake Suguta fell by ca 50 m, suggesting that remote influences also affected local hydrology. 相似文献