Constitutive modelling of state-dependent behaviour of unsaturated soils: an overview     

Ng  C. W. W.  Zhou  C.  Chiu  C. F. 《Acta Geotechnica》2020,15(10):2705-2725

An unsaturated soil is a three-phase material that is ubiquitous on the earth’s surface. The fully saturated and completely dry states are just two limiting conditions of an unsaturated soil. The state and properties of unsaturated soils can change significantly with external loads, weather conditions and groundwater level. Proper modelling of the state-dependent behaviour of unsaturated soils is crucial for analysing the performance of almost all civil engineering structures. So far, there are many unsaturated soil models and several relevant review papers in the literature. None of the existing review papers, however, focused on the state dependency of unsaturated soil behaviour. Moreover, some aspects of soil behaviour have not been reviewed, including small strain stiffness, dilatancy and stress-dependence of water retention curve. In the current review paper, the state dependency of unsaturated soil behaviour is reviewed, with a particular attention to the three missing parts. The review is carried out in a unified and relatively simple constitutive framework, which adopts a three-by-three compliance matrix to link incremental volumetric strain, deviator strain and degree of saturation to incremental mean net stress, deviator stress and suction. All of the nine variables in the proposed three-by-three compliance matrix have clear physical meanings and can be measured through compression, shearing and water retention tests. Theoretical models based on other constitutive stress variables can be also converted to this framework by matrix transformation.

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National policy of watershed management and flood mitigation after the 921 Chi-Chi earthquake in Taiwan     

Yong-Jun Lin  Yuan-Hsiou Chang  Yih-Chi Tan  Hong-Yuan Lee  Yu-Jia Chiu 《Natural Hazards》2011,56(3):709-731

Registering a 7.3 magnitude on the Richter scale, the 921 Chi-Chi Earthquake that struck central Taiwan on September 21, 1999 left the island nation with fragile soils, frequent floods, and debris flow, further weakening homeland resources. Taiwan’s dense population had forced its residents to use mountain hills for agriculture and development. The 92-Flood in 2004, which incurred vast monetary losses and human casualties, caused the government to rethink its strategy for land use. In order to use land in a more efficient and in an eco-friendly manner, the Council for Economic Planning and Development, Executive Yuan of the Taiwanese government proposed the “Land Recovery Strategy and Action Plan” in 2006. Its core concept was aimed at “respecting, and adapting to, nature.” To achieve this goal, a hillside watershed management and flood mitigation policy was proposed. Factors of safety, economy, and ecology were included in the policy. Both strategies and practical measures to be implemented were organized in a chart for better understanding and for reference by other countries with similar conditions.  相似文献   

Laboratory Simulation of Magnetospheric Plasma Shocks     

R. Presura  V. V. Ivanov  Y. Sentoku  V. I. Sotnikov  P. J. Laca  N. Le Galloudec  A. Kemp  R. Mancini  H. Ruhl  A. L. Astanovitskiy  T. E. Cowan  T. Ditmire  C. Chiu  W. Horton  P. Valanju  S. Keely 《Astrophysics and Space Science》2005,298(1-2):299-303

An experimental simulation of planetary magnetospheres is being developed to investigate the formation of collisionless shocks and their effects. Two experimental situations are considered. In both, the solar wind is simulated by laser ablation plasmas. In one case, the “solar wind” flows across the magnetic field of a high-current discharge. In the other, a transverse magnetic field is embedded in the plasma flow, which interacts with a conductive obstacle. The ablation plasma is created using the “Tomcat” laser, currently emitting 5 J in a 6 ns pulse at 1 μm wavelength and irradiance above 10¹³ W/cm². The “Zebra” z-pinch generator, with load current up to 1 MA and voltage up to 3.5 MV produces the magnetic fields. Hydrodynamic modeling is used to estimate the plasma parameters achievable at the front of the plasma flow and to optimize the experiment design. Particle-in-cell simulations reveal details of the interaction of the “solar wind” with an external magnetic field, including flow collimation and heating effects at the stopping point. Hybrid simulations show the formation of a bow shock at the interaction of a magnetized plasma flow with a conductor. The plasma density and the embedded field have characteristic spatial modulations in the shock region, with abrupt jumps and fine structure on the skin depth scale.  相似文献   

The GLARE Survey – II. Faint z≈ 6 Lyα line emitters in the HUDF     

Elizabeth R. Stanway †  rew J. Bunker  Karl Glazebrook  Roberto G. Abraham  James Rhoads  Sangeeta Malhotra  David Crampton  Matthew Colless  Kuenley Chiu 《Monthly notices of the Royal Astronomical Society》2007,376(2):727-738

The galaxy population at   z ≈ 6  has been the subject of intense study in recent years, culminating in the Hubble Ultra Deep Field (HUDF) – the deepest imaging survey yet. A large number of high-redshift galaxy candidates have been identified within the HUDF, but until now analysis of their properties has been hampered by the difficulty of obtaining spectroscopic redshifts for these faint galaxies. Our 'Gemini Lyman-Alpha at Reionization Era' (GLARE) project has been designed to undertake spectroscopic follow-up of faint  ( z ' < 28.5)  i '-drop galaxies at   z ≈ 6  in the HUDF. In a previous paper we presented preliminary results from the first 7.5 h of data from GLARE. In this paper we detail the complete survey. We have now obtained 36 h of spectroscopy on a single GMOS slitmask from Gemini-South, with a spectral resolution of  λ/Δλ_FWHM≈ 1000  . We identify five strong Lyα emitters at   z > 5.5  , and a further nine possible line emitters with detections at lower significance. We also place tight constraints on the equivalent width of Lyα emission for a further ten i '-drop galaxies and examine the equivalent width distribution of this faint spectroscopic sample of   z ≈ 6  galaxies. We find that the fraction of galaxies with little or no emission is similar to that at   z ≈ 3  , but that the   z ≈ 6  population has a tail of sources with high rest-frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass function.  相似文献   

Using a hybrid genetic algorithm–simulated annealing algorithm for fuzzy programming of reservoir operation     

Yu‐Chen Chiu  Li‐Chiu Chang  Fi‐John Chang 《水文研究》2007,21(23):3162-3172

We present a novel approach for optimizing reservoir operation through fuzzy programming and a hybrid evolution algorithm, i.e. genetic algorithm (GA) with simulated annealing (SA). In the analysis, objectives and constraints of reservoir operation are transformed by fuzzy programming for searching the optimal degree of satisfaction. In the hybrid search procedure, the GA provides a global search and the SA algorithm provides local search. This approach was investigated to search the optimizing operation scheme of Shihmen Reservoir in Taiwan. Monthly inflow data for three years reflecting different hydrological conditions and a consecutive 10‐year period were used. Comparisons were made with the existing M‐5 reservoir operation rules. The results demonstrate that: (1) fuzzy programming could effectively formulate the reservoir operation scheme into degree of satisfaction α among the users and constraints; (2) the hybrid GA‐SA performed much better than the current M‐5 operating rules. Analysis also found the hybrid GA‐SA conducts parallel analyses that increase the probability of finding an optimal solution while reducing computation time for reservoir operation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

The stellar mass density at z≈ 6 from Spitzer imaging of i'-drop galaxies     

Laurence P. Eyles  rew J. Bunker  Richard S. Ellis  Mark Lacy  Elizabeth R. Stanway  Daniel P. Stark  Kuenley Chiu 《Monthly notices of the Royal Astronomical Society》2007,374(3):910-930

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The optical and near-infrared properties of 2837 quasars in the United Kingdom Infrared Telescope Infrared Deep Sky Survey     

Kuenley Chiu  Gordon T. Richards  Paul C. Hewett  Natasha Maddox 《Monthly notices of the Royal Astronomical Society》2007,375(4):1180-1188

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Enforced self‐organizing map neural networks for river flood forecasting     

Fi‐John Chang  Li‐Chiu Chang  Yan‐Shiang Wang 《水文研究》2007,21(6):741-749

Self‐organizing maps (SOMs) have been successfully accepted widely in science and engineering problems; not only are their results unbiased, but they can also be visualized. In this study, we propose an enforced SOM (ESOM) coupled with a linear regression output layer for flood forecasting. The ESOM re‐executes a few extra training patterns, e.g. the peak flow, as recycling input data increases the mapping space of peak flow in the topological structure of SOM, and the weighted sum of the extended output layer of the network improves the accuracy of forecasting peak flow. We have investigated an ESOM neural network by using the flood data of the Da‐Chia River, Taiwan, and evaluated its performance based on the results obtained from a commonly used back‐propagation neural network. The results demonstrate that the ESOM neural network has great efficiency for clustering, especially for the peak flow, and super capability of modelling the flood forecast. The topology maps created from the ESOM are interesting and informative. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Global distribution of thermospheric heat sources: EUV absorption and joule dissipation     

B.K. Ching  Y.T. Chiu 《Planetary and Space Science》1973,21(10):1633-1646

The global distribution and temporal variations of thermospheric heating due to Joule dissipation of measured ionospheric electric fields are computed. It is shown that the volume Joule dissipation rate at high and middle latitude is similar in magnitude and altitudinal profile to the global solar EUV absorption rate discussed in the previous papers. Thus, Joule dissipation contributes significantly towards reconciling the quantitatively known sources of thermospheric heat input and that required to maintain the normal thermosphere. The combined heat source due to EUV absorption and Joule dissipation varies with the annual cycle in a manner closely resembling that of the thermospheric density.  相似文献   

Theory of solar radio pulsation     

Y. T. Chiu 《Solar physics》1970,13(2):420-443

We show that the observed modulation of some coronal microwave, X-ray and Type III emission into pulses of 10 sec intervals is a consequence of the stimulation of electron cyclotron waves propagated in the whistler mode in dipole-like bipolar regions of dimension 0.2 R . Assuming that a power law spectrum of 10 keV electrons with a slope similar to solar flare protons can be trapped in a bipolar region, we show that whistlers can be generated by pitch angle instability. The resultant 10 sec bounce motion of whistler wave trains leads to enhanced, modulated emission in microwave and X-ray frequencies by pitch angle scattering of MeV electrons, and to modulated Type III emission by scattering with coherent plasma waves. A direct prediction of the theory is the existence of sympathetic pulsations at two sources a fraction of a solar radius apart. A second test of the theory is that modulated Type III emission should show strong polarization.This work was conducted under U.S. Air Force Space and Missile Systems Organization (SAMSO) Contract No. F04701-69-C-0066.  相似文献