A study of long-term climate change in a simple seasonal nonlinear climate model     

R Q Lin  H Kreiss  W J Kuang  L Y Leung 《Climate Dynamics》1991,6(1):35-41

Solar radiation cycles, earth-orbital changes, and continental drift drive long to very long term (10³–10⁶ years) climatic changes. Lin and North used the stationary solutions of a simple energy balance model (EBM) to study the equilibrium climatic stages. In this paper, we study time dependent solutions and, in particular, transition processes. We make use of two time scales: a seasonal cycle (fast variation) and a long term time change (slow variation). Variations over short time scales are solved using a Fourier transform in time and long term variations are studied using a 4th order Runge-Kutta method. The energy balance equation is a parabolic type equation and it is well posed. Climate changes depend mainly on external forcing and the state of the climate is determined by the slow time scale forcing. In other words, transitions from one climate stage (snow-covered) to another (snow-free) at bifurcation points are monotonic, despite 20% to 50% shortperiod random fluctuations in the solar energy. This smooth transition is especially noticeable when the land bands lie close to the north pole (70° N to 90° N) or at high latitudes (50° N to 75° N).Now at Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD 20723, USA  相似文献   

Simplified mechanical subgrade model for dynamic response analysis of shallow foundations     

Toyoaki Nogami  Ming Biu Leung 《地震工程与结构动力学》1990,19(7):1041-1055

Baranov proposed an approach for the treatment of the subgrade in the dynamic response analysis of a rigid foundation which is partially embedded. The approach is based on a Winkler approximation together with wave equation solutions developed for simplified conditions. The paper extends and modifies Baranov's approach so as to be applicable to surface foundation problems, by introducing an internal coupling mechanism. Closed form expressions are presented for the steady state harmonic responses of a massless rigid footing and an elastic beam on the surface of the presented subgrade model. These expressions can accommodate the inhomogeneity of the subgrade in a straightforward manner. The model is found to perform well in reproducing the continuous subgrade medium behaviour. The dynamic responses of structures are often highly dependent on the subgrade modelling and therefore great caution is needed in modelling the subgrade.  相似文献   

Changes to the groundwater system, from 1888 to present, in a highly-urbanized coastal area in Hong Kong, China   总被引：3，自引：1，他引：2  

Jiu Jimmy Jiao  Chi-man Leung  Guoping Ding 《Hydrogeology Journal》2008,16(8):1527-1539

Historical groundwater levels in a coastal region of Hong Kong Island (China) were reviewed and compared with data collected recently to reveal changes to the groundwater regime over the last century. The coastal springs and seeps have disappeared and the lower boundary of the seepage zone has moved uphill. Groundwater was found to be flowing upward along the boundary of natural slopes and urbanized areas. Artesian flows were commonly noted in the deep piezometers in the lower urbanized areas. Moreover, an overall rise in water levels in a 10-year period was observed in the urbanized areas, except in areas with good drainage. Extensive urbanization since the 1950s has included large-scale land reclamation, deep foundations of high-rise buildings, an underground transport system, water mains and horizontal drains in slopes; the effect has been a slow but gradual increase in the water level of the hillslope groundwater system. Further urbanization activities such as the westward extension of the underground transport system and new major drainage systems in the slopes, should be assessed for possible further changes to the groundwater system. The results presented here may serve as reference for other highly-urbanized coastal areas in the world.  相似文献   

The impacts of economic structure on China’s carbon dioxide emissions: an analysis with reference to other East Asian economies     

Tin Fai Kwok  Xiao Liu  Yee Leung 《Climate Policy》2018,18(10):1235-1245

A change in economic structure influences the total energy consumption as well as CO₂ emissions of a country, given the inherent difference in levels of energy intensity and energy fuel mix of different economic sectors. Its significance has been recognized in recent literature on China’s emission mitigation which could arguably raise China’s mitigation potential and thus the possibility of keeping the 2-degree trajectory on track. This article utilizes the past trend of economic structural change of five East Asian developed economies to project the energy consumption and CO₂ emissions of China in the coming decades. A special delineation of the economic sector is made, putting private consumption together with the three typical economic production sectors, to resolve the mismatch between the statistical data of energy consumption and economic production, in that residential energy consumption is typically merged into the tertiary sector, although it does not directly correspond to gross domestic product (GDP) output. Results suggest that the level of CO₂ emissions would be lower if China followed a development pathway emphasizing the development of the tertiary sector and continuously shrinking her secondary sector, making it possible for China to contribute more to global carbon mitigation. The impact from the rise of private consumption would be relatively insignificant compared to deindustrialization. In addition to continuous improvement in technology, economic structural change, which reduces carbon emission intensity, would be essential for China to be able to achieve the carbon emission level pledged in the Paris Agreement.

Key policy insights

• For China, significant economic structural reform, particularly deindustrialization, is necessary to achieve the goal of ‘peak emission by 2030’.

• Any additional contribution from China to the global effort to maintain a 2-degree trajectory would be limited – from a ‘fair-contribution’ perspective based on share of population or GDP – because the implied mitigation targets would be almost impossible to achieve.

• If developing countries follow the pathway of developed economies, particularly in developing energy-intensive industries, energy consumption and CO₂ emissions would significantly increase, reducing the possibility of keeping global temperature rise within the 2-degree Celsius benchmark.

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The influence of radiation pressure on equipotential surfaces in high-temperature binary systems     

Hong-Nan Zhou  Kam-Ching Leung 《Astrophysics and Space Science》1988,141(2):257-270

In this paper we considered the effect of the radiation pressure from both components of the high-temperature binary systems in terms of a modified Roche potential. Usually, the parameters of radiation pressures ₁, ₂ can be written as a function of radiiR, effective temperatureT _eff , and massM of components. The simulation calculation shows that the positions of saddle pointsL ₁ ,L ₂ ,L ₃ and shape of critical surface are changed with radiation pressure factors ₁, ₂. Consequently, use of the conventional critical Roche model to estimate value of radii and mass ratios may be completely unwarranted if effective temperature of both componentsT _eff 30 000 K.These conclusions are applied to Wolf-Rayet binary systems V444 Cygni,v ₂ Velorum, and O-type binary system Y Cygni. The modified critical potentials are calculated and discussed.  相似文献   

Hybrid Finite-Discrete Element Simulation of the EDZ Formation and Mechanical Sealing Process Around a Microtunnel in Opalinus Clay     

Andrea Lisjak  Bryan S. A. Tatone  Omid K. Mahabadi  Giovanni Grasselli  Paul Marschall  George W. Lanyon  Rémi de la Vaissière  Hua Shao  Helen Leung  Christophe Nussbaum 《Rock Mechanics and Rock Engineering》2016,49(5):1849-1873

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The effect of carbon tax on carbon emission abatement and GDP: a case study     

Xiao Liu  Yee Leung  Yuan Xu  Linda Chor Wing Yung 《Journal of Geographical Systems》2017,19(4):399-414

Carbon tax has been advocated as an effective economic instrument for the abatement of CO₂ emission by various countries, including China, the world’s biggest carbon emission country. However, carbon emission abatement cannot be done while ignoring the impact on economic growth. A delicate balance needs to be achieved between the two to find an appropriate pathway for sustainable development. This paper applies a multi-objective optimization approach to analyze the impact of levying carbon tax on the energy-intensive sectors of Guangdong province in China under the constraint of emission reduction target. This approach allows us to evaluate carbon emission minimization while maximizing GDP. For policy analysis, we construct five scenarios for evaluation and optimal choice. The results of the analysis show that a lower initial carbon tax rate is not necessarily better, and that a carbon tax is an effective means to reduce CO₂ emissions while maintaining a certain level of GDP growth.  相似文献   

Spatio-temporal variations in the diversity and abundance of commercially important Decapoda and Stomatopoda in subtropical Hong Kong waters     

Karen K.Y. Lui  Jasmine S.S. Ng  Kenneth M.Y. Leung   《Estuarine, Coastal and Shelf Science》2007,72(4):635-647

In subtropical Hong Kong, western waters (WW) are strongly influenced by the freshwater input from the Pearl River estuary, especially during summer monsoon, whereas eastern waters (EW) are predominantly influenced by oceanic currents throughout the year. Such hydrographical differences may lead to spatio-temporal differences in biodiversity of benthic communities. This study investigated the diversity and abundance of commercially important decapods and stomatopods in EW (i.e. Tolo Harbour and Channel) and WW (i.e. Tuen Mun and Lantau Island) of Hong Kong using monthly trawl surveys (August 2003–May 2005). In total, 22 decapod and nine stomatopod species were recorded. The penaeid Metapenaeopsis sp. and stomatopod Oratosquillina interrupta were the most abundant and dominant crustaceans in EW and WW, respectively. Both univariate and multivariate analyses showed that WW supported significantly higher abundance, biomass and diversity of crustaceans than EW, although there were significant between-site and within-site variations in community structure. Higher abundance and biomass of crustaceans were recorded in summer than winter. Such spatio-temporal variations could be explained by differences in the hydrography, environmental conditions and anthropogenic impacts between the two areas. Temporal patterns in the abundance–biomass comparison curves and negative W-statistics suggest that the communities have been highly disturbed in both areas, probably due to anthropogenic activities such as bottom trawling and marine pollution.  相似文献   

Survival, growth, metallothionein and glycogen levels of Nucella lapillus (L.) exposed to subchronic cadmium stress: the influence of nutritional state and prey type     

Leung KM  Furness RW 《Marine environmental research》2001,52(2):173-194

Dogwhelks Nucella lapillus feed mainly on mussels and barnacles, and may experience periods of starvation. We report effects of nutritional state and prey type on the survival, growth, cadmium (Cd) accumulation, metallothionein (MT) induction and glycogen stores in N. lapillus exposed to Cd in water. Adult dogwhelks, with similar shell length (30.0+/-1.5 mm), were either starved or fed to satiation with barnacles Semibalanus balanoides, mussels Mytilus edulis or Cd-dosed M. edulis, and kept in filtered natural seawater (< 0.01 microg Cd 1(-1)) or Cd-contaminated (400 microg Cd 1(-1)) seawater for 80 days. Mortality and individual growth rate were determined. Cd, MT and glycogen were measured in different tissues. Prolonged starvation and exposure to Cd significantly reduced the survivorship of N. lapillus, but feeding could help dogwhelks to combat Cd toxicity and minimise mortality. Extended starvation also caused tissue wastage, leading to higher concentrations of Cd and MT in tissues, whereas fed animals increased in weight and had lower Cd and MT concentrations because of the tissue dilution effect. Prey type significantly affected growth rate of dogwhelks and indirectly influenced Cd accumulation, MT induction and glycogen stores. Eating mussels promoted better growth and higher glycogen reserves than eating barnacles. Individual growth rate decreased with increasing Cd accumulation. Cd-exposed survivors grew faster and consumed more than control animals, implying that these survivors may have better fitness and greater tolerance to Cd toxicity. The use of growth, condition index, MT and glycogen as biomarkers of environmental pollution are discussed. These results indicate a need to incorporate biological data including growth (or at least condition index) and prey type into biomonitoring programmes to allow sound interpretation.  相似文献   

Behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic   总被引：2，自引：0，他引：2  

Ng SL  Leung S 《Marine environmental research》2003,56(5):555-567

A series of land-based surveys were conducted at two vantage points of known dolphin abundance in Hong Kong. The purpose of this study was to determine the behavioral response of Indo-Pacific humpback dolphin (Sousa chinensis) to vessel traffic. Results indicated that dolphins dove for a longer duration in areas of heavy vessel traffic or when there was the presence of an oncoming vessel. Dependent upon the type of vessel and the relative distance, dolphins might flee, continue their ongoing activity, perform a new activity, or approach the vessel. Whilst slow-moving vessels appeared not to cause immediate stress on the dolphin community, fast-moving vessels often cause disruption of behavior and social life. In order to ensure a better environment for the animals, we suggest that proactive conservation measures such as the creation of a marine park, rules and regulations for dolphin watching activities, and regional control of vessel speed should be implemented.  相似文献