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161.
K. Giannopoulou M. Santamouris I. Livada C. Georgakis Y. Caouris 《Pure and Applied Geophysics》2010,167(11):1433-1449
The present paper investigates the impact of canyon geometry on the temperature regime and nocturnal heat island development
in the very dense urban area of Athens, Greece. Detailed measurements of air temperature have been carried out within three
deep urban canyons of different aspect ratios (H/W = 3, 2.1 and 1.7) during the night period of the summer and autumn of 2007. An analysis was carried out to investigate the
relative impact of the canyon geometry, the undisturbed wind velocity, ambient temperature, and cloud cover on the development
of a nocturnal heat island. A clear increase of the median, maximum and minimum values of the cooling rates has been observed
for decreasing aspect ratios. Under low ambient temperatures, high wind speeds correspond to a substantial rise of the cooling
rate in the urban canyons mainly because of the increased convective losses. On the contrary, cooling rates decrease substantially
under high-undisturbed wind speeds and ambient temperatures because of the important convective gains. The impact of cloud
cover was found to be important as cloudy skies cause a substantial decrease of the cooling rates in the urban canyons. Comparisons
were performed between the temperature data collected in the three studied urban canyons and temperatures recorded in an urban
as well as a suburban open space station. 相似文献
162.
Contribution to diffuse gamma-rays in the Galactic Centre region from unresolved millisecond pulsars
W. Wang Z. J. Jiang K. S. Cheng 《Monthly notices of the Royal Astronomical Society》2005,358(1):263-269
Diffuse gamma-rays in the Galactic Centre region have been studied. We propose that there exists a population of millisecond pulsars in the Galactic Centre, which emit GeV gamma-rays through synchrotron-curvature radiation as predicted by outer gap models. These GeV gamma-rays from unresolved millisecond pulsars probably contribute to the diffuse gamma-ray spectrum detected by EGRET which displays a break at a few GeV. We have used a Monte Carlo method to obtain simulated samples of millisecond pulsars in the Galactic Centre region covered by EGRET (∼ 15) according to the different period and magnetic field distributions from observed millisecond pulsars in the Galactic field and globular clusters, and superposed their synchrotron-curvature spectra to derive the total GeV flux. Our simulated results suggest that there probably exist about 6000 unresolved millisecond pulsars in the region of angular resolution of EGRET, the emissions of which could contribute significantly to the observed diffuse gamma-rays in the Galactic Centre. 相似文献
163.
Meysam Fadaee I. Anastasopoulos G. Gazetas M.K. Jafari M. Kamalian 《地震工程与工程振动(英文版)》2013,12(3):473-486
When seismic thrust faults emerge on the ground surface,they are particularly damaging to buildings,bridges and lifelines that lie on the rupture path.To protect a structure founded on a rigid raft,a thick diaphragm-type soil bentonite wall(SBW) is installed in front of and near the foundation,at sufficient depth to intercept the propagating fault rupture.Extensive numerical analyses,verified against reduced–scale(1 g) split box physical model tests,reveal that such a wall,thanks to its high deformability and low shear resistance,"absorbs" the compressive thrust of the fault and forces the rupture to deviate upwards along its length.As a consequence,the foundation is left essentially intact.The effectiveness of SBW is demonstrated to depend on the exact location of the emerging fault and the magnitude of the fault offset.When the latter is large,the unprotected foundation experiences intolerable rigid-body rotation even if the foundation structural distress is not substantial. 相似文献
164.
Observed polarization ellipses for fundamental-mode surface waves observed at a digital station in Hawaii deviate from those expected for isotropic models of crust and mantle structure for that region. The anomalous motion occurs as rotations of the ellipse about all three axes in a cartesian corrdinate system. The largest and most consistent deviations occur as anomalous slopes of the ellipse about the horizontal axis transverse to the direction of propagation.The observed orientations and magnitudes of these angles can be explained by models of the upper mantle which contain olivine for which thea-axis dips significantly from the horizontal and which includes a sufficiently thick sedimentary layer (1 km) and a thicker than normal oceanic crust (15 km). The ellipses are also generally inclined from great circle paths about the vertical axis and are tilted about the axis aligned with the propagation direction. Both angles are small and difficult to measure, but the inclination angles are consistent with a model of the upper mantle in which thea-axis of olivine is preferentially oriented in an east-west direction. 相似文献
165.
Possible orbits for the motion of a region in the gravitational field of the central body of the galaxy NGC 4151 are presented.
The region is manifest through its line emission, observed in the red wing of the Hα, Pβ, and other broad lines. We carried out a computer selection of all Keplerian orbits for which the measured radial velocities
of the emission-line region could be observed. We used radial-velocity data obtained by us at the Fesenkov Astrophysical Institute,
as well as data from the literature. The computation results can be used to determine the mass range for the central body
of NGC 4151 that provides the best agreement with the observational data: (61–65)× 106
M
⊙. Suitably designed monitoring of active galactic nuclei can be used to verify these results, and to carry out similar analyses
for other Seyfert galaxies. 相似文献
166.
The gravitational instability of an infinite homogenous rotating plasma through a porous medium in the presence of a uniform magnetic field with finite electrical and thermal conductivities has been studied. With the help of relevant linearized perturbation equations of the problem, a general dispersion relation is obtained, which is further reduced for the special cases of rotation, parallel and perpendicular to the megnetic field acting in the vertical direction. Longitudinal and transverse modes of propagation are discussed separately. It is found that the joint effect of various parameters is simply to modify the Jeans's condition of instability. The effect of finite electrical conductivity is to remove the effect of magnetic field where as the effect of thermal conductivity is to replace the adiabatic velocity of sound by the isothermal one. Rotation has its effect only along the magnetic field in the transverse mode of propagation for an inviscid plasma, thereby stabilizing the system. Porosity reduces the effect of both, the magnetic field and the rotation, in the transverse mode of propagation in both the cases of rotation. The effect of viscosity is to remove the rotational effects parallel to the magnetic field in the transverse mode of propagation. 相似文献
167.
K. Schneider-Carius 《Pure and Applied Geophysics》1949,15(3-4):236-241
Ohne Zusammenfassung 相似文献
168.
It is known for over two decades now that the rotation of the photospheric magnetic fields determined by two different methods
of correlation analysis leads to two vastly differing rotation laws - one the differential and the other rigid rotation. Snodgrass
and Smith (2001) reexamining this puzzle show that the averaging of the correlation amplitudes can tilt the final profile
in favour of rigid rotation whenever the contribution of the rigidly rotating large-scale magnetic structures (the plumes)
to the correlation dominates over that of the differentially rotating small-scale and mesoscale features. We present arguments
to show that the large-scale unipolar structures in latitudes >40 deg, which also show rigid rotation (Stenflo, 1989), are
formed mainly from the intranetwork magnetic elements (abbreviated as IN elements). We then estimate the anchor depths of
the various surface magnetic elements as locations of the Sun's internal plasma layers that rotate at the same rate as the
flux elements, using the rotation rates of the internal plasma layers given by helioseismology. We infer that the anchor depths
of the flux broken off from the decay of sunspot active regions (the small-scale and mesoscale features that constitute the
plumes) are located in the shallow layers close to the solar surface. From a similar comparison with helioseismic rotation
rates we infer that the rigid rotation of the large-scale unipolar regions in high latitudes could only be coming from plasma
layers at a radial distance of about 0.66–0.68 R
⊙ from the Sun's centre. Using Stenflo's (1991) ‘balloon man’ analogy, we interpret these layers as the source of the magnetic
flux of the IN elements. If so, the IN flux elements seem to constitute a fundamental component of solar magnetism. 相似文献
169.
Merging rates for compact binaries (double neutron stars or black holes) are calculated based on modern concepts of binary star evolution. It is found that the first laser interferometers, with rms sensitivities of 10-21 at a frequency of 100 Hz, can detect 10-700 black holes and only 1 neutron star coalescences in a 1-year integration time. The implications of evolutionary effects for the cosmological origin of gamma ray bursts are also discussed. 相似文献
170.
There is a need to bridge theory and practice for incorporating parameter uncertainty in geostatistical simulation modeling workflows. Simulation workflows are a standard practice in natural resource and recovery modeling, but the incorporation of multivariate parameter uncertainty into those workflows is challenging. However, the objectives can be met without considerable extra effort and programming. The sampling distributions of statistics comprise the core theoretical notion with the addition of the spatial degrees of freedom to account for the redundancy in the spatially correlated data. Prior parameter uncertainty is estimated from multivariate spatial resampling. Simulation-based transfer of prior parameter uncertainty results in posterior distributions which are updated by data conditioning and the model domain extents and configuration. The results are theoretically tractable and practical to achieve, providing realistic assessments of uncertainty by accounting for large-scale parameter uncertainty, which is often the most important component impacting a project. A simulation-based multivariate workflow demonstrates joint modeling of intrinsic shale properties and uncertainty in estimated ultimate recovery in a shale gas project. The multivariate workflow accounts for joint prior parameter uncertainty given the current well locations and results in posterior estimates on global distributions of all modeled properties. This is achieved by transferring the joint prior parameter uncertainty through conditional simulations. 相似文献