Urban albedo as a function of the urban structure — A two-dimensional numerical simulation   总被引：4，自引：0，他引：4  

Masaru Aida  Kiyoshi Gotoh 《Boundary-Layer Meteorology》1982,23(4):415-424

Urban albedo change as a function of urban geometrical structure has been examined by using a two-dimensional urban block-canyon array model. The complex multiple reflections of incident photons in the urban canyon are simulated by using a Monte-Carlo method. The photons are tracked until they leave the canyon or are completely absorbed. In the model, the direct and diffuse components of incident solar radiation are introduced and the specular and isotropic reflection characteristics are considered for the relevant urban surfaces. The result shows that the urban albedo decreases as the urban irregularity increases as indicated by the model experiment of Aida (1982). The dependence of albedo on the incident solar zenith angle observed in the experiment is also confirmed for various urban models.As an application, some actual urban structures in the Marunouchi area in Tokyo are examined. Urban planning for absorption and reflection of solar radiation in urban areas is also discussed based on the analysis of the change in albedo with canyon dimensions and solar zenith angle.  相似文献   

A new fracture criterion for brittle rocks     

Kiyoshi Seya  Isao Suzuki 《Tectonophysics》1980,64(3-4)

A general form of a “fracture function” for isotropic brittle materials is expressed in terms of the three invariants of the stress tensor. The coefficients in the function are determined by use of the small number of experimental data under specific conditions. This function is applicable to an estimate of the fracture condition of brittle rocks under a general stress state i.e., σ₁ ≠ σ₂ ≠ σ₃. The application of this function is attempted for the data of three brittle rocks i.e., Dunham dolomite, Mizuho trachyte, and Westerly granite, reported by previous workers. For the first two, this criterion gives a good estimation of the effect of the intermediate principal stress σ₂ on failure. For the last, the fracture strength at high confining pressure is estimated by use of the several data obtained under very low confining pressures, and the agreement with experimental data is also satisfactory.  相似文献   

Spectroscopic Studies of the Solar Corona – V. Physical Properties of Coronal Structures     

Singh  Jagdev  Sakurai  Takashi  Ichimoto  Kiyoshi  Muneer  S. 《Solar physics》2003,212(2):343-359

Spectra around the 6374 Å [Fex] and 7892 Å [Fexi] emission lines were obtained simultaneously with the 25-cm coronagraph at Norikura Observatory covering an area of 200 ×500 of the solar corona. The line width, peak intensity and line-of-sight velocity for both the lines were computed using Gaussian fits to the observed line profiles at each location (4 ×4 ) of the observed coronal region. The line-width measurements show that in steady coronal structures the FWHM of the 6374 Å emission line increases with height above the limb with an average value of 1.02 mÅ arc sec^–1. The FWHM of the 7892 Å line also increases with height but at a smaller average value of 0.55 mÅ arc sec^–1. These observations agree well with our earlier results obtained from observations of the red, green, and infrared emission lines that variation of the FWHM of the coronal emission lines with height in steady coronal structures depends on plasma temperatures they represent. The FWHM gradient is negative for high-temperature emission lines, positive for relatively low-temperature lines and smaller for emission lines in the intermediate temperature range. Such a behaviour in the variation of the FWHM of coronal emission lines with height above the limb suggests that it may not always be possible to interpret an increase in the FWHM of emission line with height as an increase in the nonthermal velocity, and hence rules out the existence of waves in steady coronal structures.  相似文献   

Effects of deposit feeder Stichopus japonicus on algal bloom and organic matter contents of bottom sediments of the enclosed sea   总被引：4，自引：0，他引：4  

Michio K  Kengo K  Yasunori K  Hitoshi M  Takayuki Y  Hideaki Y  Hiroshi S 《Marine pollution bulletin》2003,47(1-6):118-125

Algae growing in an enclosed sea may inhibit eutrophication because they absorb nutrients in the water. However, dead algae often cause anaerobic conditions in the water just above and on sediment after they are deposited on the bottom. We found that Stichopus japonicus inhibited the anaerobic processes coupling water sulfite production in sediment. The present study investigates whether S. japonicus inhibits algal flourish and influences sediment properties such as organic matter contents. Aquarium experiments were carried out at Komatsushima port in Tokushima Prefecture, western Japan. The aquaria used in the experiments were supplied with water directly from the adjacent sea (6 L/min), laid with sand of 10 cm depths, and lighted at 12 h intervals. Six aquaria each containing a sea cucumber from Komatsushima port and six aquaria without any were used in the experiments. Water temperature ranged between 9 and 15 degrees C during December 2000 and April 2001. Salinity ranged between 32 per thousand and 34 per thousand. Algae began to cover the bottom of the aquaria without S. japonicus after 2 weeks, whereas no growth was evident in the aquaria containing sea cucumbers. Chlorophyll a concentration in the surface sediment of the aquaria with S. japonicus (6.1+/-3.6 microg/g, mean S.D.+/-standard deviation) was significantly lower than that without it (60+/-17 microg/g, U-test, p<0.05). Phaeophytin concentration in the surface sediment of the aquaria with S. japonicus (0.9+/-0.09 microg/g) was also significantly lower than that without it (4.5+/-1.0 microg/g, U-test, p<0.05). TOC concentration in the surface sediment of the aquaria with S. japonicus (2.6+/-1.3 microg/g) was slightly lower than that without it (4.0+/-1.2 microg/g). These results showed that algal biomass and organic matter concentration of the bottom were decreased in the presence of S. japonicus. Therefore, S. japonicus inhibits algal bloom and decrease the contents of organic matter deposited on the bottom of enclosed sea areas.  相似文献   

Interstadial coral reef terraces and relative sea-level changes during marine oxygen isotope stages 3–4, Kikai Island, central Ryukyus, Japan     

Keiichi Sasaki  Akio Omura  Kazuo Murakami  Natsume Sagawa  Toru Nakamori 《Quaternary International》2004,120(1):51

Coral reef terraces are one of the best recorders of relative sea-level changes during the last glacial cycle. Thus far, knowledge of relative sea-level record based on coral reefs during the marine Oxygen Isotope Stage (OIS) 3 has been limited to studies of the Huon Peninsula, Papua New Guinea. High-precision a α-spectrometric ²³⁰Th/²³⁴U dating demonstrated an offlapping sequence of five coral reef complexes, ages of which are 66, 64, 62, 55 and 52 ka, in the northern part of Kikai Island, central Ryukyus of Japan. Interstadial reefs, characterized by deepening-upward sequences of coral assemblages, recorded three hemicycles from transgression to highstand at 52, 62, and 66 ka, during which these reefs were drowned. These highstands in the relative sea-level record can be correlated with the eustatic record reconstructed from the Huon reef terraces and with the interstadials 14, 18, and 19 of the GISP 2 oxygen isotope record. This consistency confirms the Huon sea-level record of OIS 3 and implies that the eustatic sea level responded to the millennial-scale climate changes even during the glacial period of OIS 4.  相似文献   

Electrical Structure in Marine Tectonic Settings     

Kiyoshi Baba 《Surveys in Geophysics》2005,26(6):701-731

This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations, (2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle. The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab) are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent. Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity patterns in the depth range of 60–200 km.  相似文献   

The 1998 Hida Mountain, Central Honshu, Japan, earthquake swarm: Double-difference event relocation, frequency–magnitude distribution and Coulomb stress changes     

Bogdan Enescu  Kiyoshi Ito   《Tectonophysics》2005,409(1-4):147-157

By using the double-difference relocation technique, we have determined the fine structure of seismicity during the 1998 Hida Mountain earthquake swarm. The distribution of seismic activity defines two main directions (N–S and E–W) that probably correspond to the regional stress pattern. The detailed structure of seismicity reveals intense spatio-temporal clustering and earthquake lineations. Each cluster of events contains a mainshock and subsequent aftershock activity that decays according to the Omori law. The seismicity and the b-value temporal and spatial patterns reflect the evolution of the static stress changes during the earthquake swarm. About 80% of the swarm's best-relocated events occur in regions of increased ΔCFF. The smaller value of b found in the northern part of the swarm region and a larger b-value observed to the south, for the same period of time, could be well explained by the static stress changes caused by the larger events of the sequence. We argue that the state of stress in the crust is the main factor that controls the variation of b-value.  相似文献   

Stray-light correction in magnetograph observations using the maximum entropy method     

Chae  Jongchul  Yun  Hong Sik  Sakurai  Takashi  Ichimoto  Kiyoshi 《Solar physics》1998,183(2):245-261

We have developed a method of stray-light correction which is applicable to filter-based magnetograph observations. Stray-light-corrected Stokes images are obtained by performing the deconvolution of observed Stokes images by the point spread function which is determined from the Stokes I image. For image deconvolution, the maximum entropy principle is used to guarantee that intensity should be positive and polarization degrees should be less than unity. We present an iterative algorithm for the maximum entropy method, which seeks the solution in Fourier space and thus accomplishes fast convergence. We find that our method is effective in correcting stray light which has a spread angle greater than the full width at half maximum of the point spread function. We also discuss the effect of stray light on magnetograph calibration.  相似文献   

Seismic stratigraphy and structural characteristics of back-arc rifts on the Izu-Ogasawara Arc     

Fumitoshi  Murakami 《Island Arc》1996,5(1):25-42

Abstract Seven back-arc rifts are recognized in the Izu-Ogasawara Arc, namely, the Hachijo, the Aogashima, the Myojin, the Sumisu, the Torishima, the Sofu and the Nishinoshima Rifts from north to south. The acoustic stratigraphy is divided into three units (Units A, B and C) based on the seismic reflection profiles crossing the rifts. The structure of the rifts systematically changes from a half-graben type to a full graben type in the back-arc rifts from the Hachijo Rift to the Torishima Rift. The Hachijo and the Aogashima Rifts have a structure of half-graben, and the Myojin Rift has both structural characteristics of a half-graben and a full graben. The Sumisu and the Torishima Rifts are an asymmetric full graben. The Sofu and the Nishinoshima Rifts have different structural characteristics from the remaining rifts, from the Hachijo Rift to the Torishima Rift. The boundary faults in the back-arc rifts from the Hachijo to the Torishima Rifts cut to Unit B. Unit B correlates with volcaniclastic sediments during pre-rift volcanism between 4 and 2 Ma. The pre-rift volcanism was probably widespread on the northern Izu-Ogasawara Arc as is the present arc volcanism. These factors suggest that the beginning of rifting is dated at some time after 2 Ma. The developing process of the rift consists of three stages; (i) a sag stage in the crust at the location of the large offset boundary fault; (ii) a stage of half-graben formation; (iii) a stage of full graben formation. The offset of the boundary faults becomes larger from the Hachijo Rift to the Torishima Rift and the east-west width of the rifts also widens to the south. This is presumably because the Hachijo Rift is an earlier rifting stage than the Sumisu and the Torishima Rifts. The more primitive structure in the rifting stage from the Torishima Rift to the Hachijo Rift is probably caused by the propagation of rifting from south to north. The structural difference between the rifts in the northern part and the Sofu and the Nishinoshima Rifts seems to be due to structural differences in the crust between the northern and the southern parts from the tectonic gap.  相似文献   

High temperature creep of single crystal gadolinium gallium garnet     

Zichao Wang  Shun-ichiro Karato  Kiyoshi Fujino 《Physics and Chemistry of Minerals》1996,23(2):73-80

High temperature creep of single crystal gadolinium gallium garnet (GGG) was studied in the temperature range of 1723–1853 K (0.86–0.94 T_m, T_m: melting temperature) and strain rate from 9 · 10^?7 s^?1 to 2 · 10^?5 s^?1. The compression tests were made along the 〈100〉 and 〈111〉 orientations. We have performed both constant strain-rate and stress-dip tests. For the 〈100〉 orientation, deformation occurs via the 〈111〉 slip systems. For the 〈111〉 orientation, both the 〈100〉 {010} and the 〈111〉 slip systems can be activated. GGG garnet is very strong under these conditions: σ/μ=(1–3)×10^?3 (σ: creep strength, μ: shear modulus). The creep behavior is characterized by a power law with stress exponent n=2.9–3.3 and high activation energies E^*=612–743 kJ/mol (E^*～45×RT_m, at zero stress which decrease with the increase of stress). Stress-dip tests suggest a small internal stress (σ_i/σ～0.62; σ_i: internal stress, σ: applied stress) compared to other materials. These results suggest that the high creep strength of GGG is mainly due to difficulty of dislocation glide rather than dislocation climb.  相似文献