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    Recent progress of coastal aeolian research in China

    2011-08-15 00:52:52YuXiangDong
    Sciences in Cold and Arid Regions 2011年6期

    YuXiang Dong

    1. School of Geography and Planning, Sun Yat-sen University, Guangzhou, Guangdong 510275, China

    2. Guangdong Key Laboratory for Urbanization and Geo-simulation, Guangzhou, Guangdong 510275, China

    Recent progress of coastal aeolian research in China

    YuXiang Dong1,2*

    1. School of Geography and Planning, Sun Yat-sen University, Guangzhou, Guangdong 510275, China

    2. Guangdong Key Laboratory for Urbanization and Geo-simulation, Guangzhou, Guangdong 510275, China

    Recent progress of coastal aeolian research in China is reviewed and summarized. Topics considered include coastal dune type,distribution, formation and evolution, characteristics of modern and ancient sediments, and observations of sand transport of coastal aeolian dunes in China. Following international trends in aeolian research, research directions for the near future in China are suggested which focus on observation and modeling of coastal aeolian transport processes, the relationship between coastal aeolian processes and global change, a surfzone-beach-dune interaction model, and the problem of coastal aeolian damages in China.

    China; coastal aeolian; research progress

    1. Introduction

    Coastal aeolian research in China, initiated and promoted since 1980s, has been made significant progress in terms of research scope and depth, especially in the study of type and formation of coastal aeolian dunes, coastal aeolian sediments, and observation of coastal aeolian sand movement.This paper outlines and summarizes the main progress and achievements in coastal aeolian research in China during the recent past, and identifies research areas worthy of special attention in the near future.

    2. Types and formation models of coastal aeolian dunes

    2.1. Types and distribution of coastal aeolian dunes in China

    Coastal dunes in China are of diverse types. Extensive investigations of coastal dune type have been conducted in the main regions of occurrence, including the coasts of the Yellow Sea and the Bohai Sea (Fu and Sha, 1994; Fuet al.,1997; Dong, 2000); the Changli coast in Hebei Province(Gao, 1983; Liet al., 1987; Wang and Zhu, 1987; Zenget al.,2003; Qiet al., 2004), the Shandong peninsula coast (Liet al., 1985); the northern Jiaodong peninsula coast (Zhang and Yang, 1992; Zhang, 1995); the Changle coast in Fujian Province (Zhang, 1994; Chenet al., 1995; Zhang and Li,1995; Chen and Zhu, 1996), Haitan Island in Fujian Province (Chen, 1994); Pingtan Island in Fujian Province (Sun,1995); the Huilai coast in Guangdong Province (Wang,1996); the Zhanjiang coast in Guangdong Province (Yang,1996); the northeast coast of Hainan Island (Wu Z and Wu KG, 1987); the South China coast (Wuet al., 1995a,b); and the Taiwan coast (Shihet al., 1992, 1993, 1994).

    Research reviews of all of the above work (Wuet al.,1995b; Fuet al., 1997; Dong, 2000) show that the basic types of coastal dunes in China include embryonic foredune,crescent foredune, transverse ridge, coppice dune, parabolic dune, incipient sand ridge, crescent dune, transverse ridge,longitudinal dune ridge, climbing dune, coast sand sheet,wind-eroded residual dune, and wind-scoured trough. These can be classed into two major groups (foredunes and back shore dunes), and three developmental stages (incipient dune,stable dune, and unstable dune, respectively). The spatial distribution of coastal dunes in China is extensive but sporadic. Their distribution terrains are diversified but are mostly concentrated in the river-mouth regions, and they differ greatly in their type and size. The main reason for this is the influence of monsoon climate. During winter and spring the climate of the coastal zone in China is arid, with strong and persistent winds that provide a necessary condition for the development of aeolian landforms. Coastal dunes in China do not appear to follow zonal distribution laws. Rather, they are scattered along the coast from northern temperate sub-humid regions to southern sub-tropics and tropic humid regions in China.

    2.2. Formation and evolution model of coastal aeolian dunes in China

    Coastal aeolian dune formation in China is less significantly controlled by precipitation, and instead depends on wind regimes, sand sources, and the synchronous occurrence of dry season and monsoon (Liet al., 1989). In this regard,Wang and Zhu (1987) suggested that the formation conditions of large-scale coastal dunes are: (1) abundant coastal sandy deposits; (2) strong onshore winds with relatively constant direction; and (3) gently sloping coastal slopes with a moderate tidal range. Wu Z and Wu KG (1987) also pointed out that the main factors affecting the formation and development of coastal dunes are wind regime, sand sources,and the terrain where dunes form. Strong wind provides the dynamic force for sand movement, and an abundant sand source provides the material basis for the formation of aeolian dunes. Large-scale coastal aeolian dune systems in China mostly develop on both sides of fluvial outfalls, such as the northern Changli coast at the mouth of the Luanhe River in Hebei Province, and the Changle coast to the south of the ocean outfall of the Mingjiang River in Fujian Province.These represent the largest-scale and most typical coastal aeolian dune areas in China (Wu Z and Wu KG, 1990).

    The formation of coastal dunes is controlled by geomorphic setting, the coastal wind conditions, and the availability of sand. Different coastal zones have therefore generated different dune formation models. The coastal dunes on the South China coast are formed under the action of onshore winds. Here, the foredune acts as a springboard to help landward transport of beach sands, which form into aggraded transverse dunes, crescent dunes, parabolic dunes, and longitudinal dunes that comprise the main body of high coastal dunes. Reduction in wind force landward allows development of sand sheets at the rear of the dunefield (Wuet al., 1995a; Chen and Zhu, 1996).

    The coastal dunes on the northern coasts of the Bohai Sea and the Yellow Sea follow one of three development patterns (Fuet al., 1997). First, on the open coastal plain with abundant sediment sources, a sequence of forms extending from the sea inland typically follows a pattern of:foredune zone → aggraded transverse sand ridge → insequent sand ridge → coppice dune zone → flat sand sheet.Second, the development sequence on open tableland coast and small bay plain coast with adequate sand sources is:foredune → longitudinal dune ridge or parabolic dune or undulating sandy land with coppice dunes → high dunes or dune chains → aeolian flat sand sheets. Third, on a sand beach at a cape bay, the aeolian forms are arranged from the sea to the inland in a sequence of foredunes, longitudinal dune ridges, or undulatory sandy land with small dunes →high parabolic dunes or dune chains → inclined mountain-slope aeolian sand land.

    Age determinations of coastal aeolian dune formation in China by the ESR method show that most coastal aeolian sands are younger than about 7×105years (Yeet al., 1995).A series of developmental events has been identified. The period of 20,000-12,000 yrs B.P. was a period of significant development for coastal dunes; 12,000-2,500 yrs B.P. was a period of decline, and 2,500 yrs B.P. to the present has been another growth and expansion period. These fluctuations in coastal aeolian dune development are consistent with global environmental changes (Chenet al., 1991). Modern coastal dunes formed in the past few thousand years, such as those on the Changli coast in Hebei Province, are believed to have formed under dry-cold climatic conditions during the old period of the Holocene (Wang and Zhu, 1987), and they originated about 2,000-35,000 yrs B.P. (Liet al., 1987).Coastal dunes on the South China coast were also the products of dry-cold climate, and formed since the mid-Holocene(Wuet al., 1995a, b), especially in the past 3,000 years. For example, coastal aeolian dunes on the northeast coast of Hainan Island were formed from about 3,000 years ago to the present (Wu Z and Wu KG, 1987); coastal dunes at the mouth of the Mingjiang River were formed after 2,470 yrs B.P. (Chen and Zhu, 1996); and coastal dunes at Xitouxia in the southeastern part of Xiamen Island started to be formed in the Sui and Tang dynasties, about 1,500 years ago (Yanget al., 2002). Meanwhile, research on coastal aeolian environmental change in different coastal regions has been conducted (Liet al., 2009; Liaoet al., 2009).

    3. Characteristics of coastal aeolian sediments in China

    3.1. Modern sediments

    In view of significant differences in grain size, surface texture, and depositional structures between coastal aeolian sand and beach sand (Chen and Li, 1984), studies of modern coastal aeolian sediments in China have mainly focused on the grain-size characteristics of coastal dune sand, the surface texture of quartz sands, and depositional structures generated by aeolian processes (Zhou, 1979; Cai AZ and Cai YE, 1983; Chenet al., 1987; Liet al., 1987; Wu Z and Wu KG, 1987; Fu and Sha, 1993, 1994; Wuet al., 1995a, b;Wang, 1996; Dong, 2002, 2003; Zenget al., 2003; Qiet al.,2004; Donget al., 2008a, b, c, d).

    Research results of grain-size characteristics of coastal aeolian dune in China show that coastal dune sands are not entirely composed of well-sorted fine sands. Grain-size parameters also show a marked regional difference, and change with dune type and scale as well as distance from shoreline (Dong, 2002; Donget al., 2008a, b, c, d). The distribution model of grain size on coastal transverse ridge and barchan was studied (Donget al., 2008a, b, c), and it was found that human activity could influence the change of sand grain-size characteristics over coastal aeolian dunes(Donget al., 2008d). In contrast to beach sands, coastal dune sands in China generally contain silts, which are characterized by fine composition, positive skewness and narrow kurtosis,etc. However, they are very difficult to distinguish from each other by the scatter diagram of grain-size parameters and the factorial analysis method. This is because China’s coast has obvious monsoon climatic features, the sandy coastal areas are geologically very young, the duration of wind action is limited, and windblown sand movement has a narrow zone of action due to the disturbance of water and gravity. However, coastal aeolian dune sands and beach sands do exhibit some differences. For example, the grain size consists of coastal dune sands that show no evident changes in the vertical sequence and horizontal direction,while beach sands tend to show large changes. Beach sands have higher shell and organic matter contents than do coastal dune sands, and their sorting is generally poorer than in coastal dune sands. The surfaces of coastal dune quartz grains have better developed saucer-shaped pits and convolute pieces than beach sand, and the cumulative distribution curves of beach sand tend to be bimodal, while that of coastal dune sand is mostly unimodal (Fu and Sha, 1993).

    From scanning electron microscope observations, Wuet al.(1995c) summarized the surface texture characteristics of quartz grains in coastal dune sands of China: (1) sand grain surfaces typically have aeolian environmental characteristics such as saucer-shaped pits, crescent impact pits, rounded particles, mechanical pitting, SiO2depositional layers, and cracks; (2) there are underwater-impact V-shaped pits indicating sea-beach environment, chemical corrosion grooves,and pits (including directional triangular pits), the edges of which have experienced different degrees of abrasion and rounding due to sand transportation by winds; and (3) the surface texture characteristics representing these two environments often occur on the surface of the same quartz grain in the forms of superimposition or paragenesis.

    Since coastal dune sands mainly originate from beaches,they have aeolian characteristics and also inherit and modify the beach sand characteristics. The surface texture characteristics of quartz grains are believed to be the most important marks to judge the sedimentary environments under any climatic conditions. But from comparative study of surface textures of quartz grains in northern and southern China’s coastal dunes, Chenet al.(1987) suggested that from north to south the mechanical marks on quartz grain surfaces change from strong to weak, while the chemical marks change from weak to strong. This shows that comparisons of the reconstruction of ancient sedimentation environments by using quartz grains can only be made in the same climatic zone; it is very difficult to make such comparisons in different climate zones.

    Observations from trenches and natural profiles reveal that coastal aeolian dune bedding in China mainly includes the following types: large-scale, high-angle tabular or wedge cross-bedding, low-angle tabular cross-bedding, wedge bedding, and parallel bedding (Liet al., 1987; Zenget al., 2003;Qiet al., 2004). In addition, some special coastal environments have preserved thick topset beds and various penecontemporaneous deformation structures (Wu Z and Wu KG,1987, 1990). Penecontemporaneous deformation structures are important depositional structural features of coastal dunes. They commonly include the shear plane formed by collapse, contorted bedding, brecciated structure, curled bedding formed by differential loading, and root pipes formed by plants. The main reason for this is that humidity is high in coastal zones, so as wet sands slide down the slip face they tend to cause a massive slip and collapse and therefore cannot form sand flow. As a result, massive sands mix with bioclastics to form breccia; interlayer shear forms shear planes and drag folds (contorted bedding), and under water saturation conditions they form convolute beddings.

    3.2. Ancient sands

    Earlier studies of ancient coastal aeolian sands in China mainly focused on coastal dune rock and old red sands.Since the 1980s, coastal dune rock has been found at many sites along the South China coast. However, due to similarities in shape and composition with beach rock, there has been disagreement about the genesis of this material. Some scholars argued that it was "elevated beach rock". The cements contain rarely found flower-like Mg-, Na-, and K-bearing aragonite crystals, Fe-bearing sparry calcites,and micro-palaeobiologic species. The beach eco-environmental characteristics reflected by this composition, as well as the crustal surface with hole washouts,suggest that it is beach sedimentary rock and should not be regarded as aeolianite. The "elevated beach rock" was thought to have reached its present elevation through lifting due to intense, deep-seated tectonic activity and strong earthquakes (Yuanet al., 1989).

    Alternatively, some scientists (Zhaoet al., 1988, 1989;Wanget al., 1990; Wanget al., 1997; Wang and Wu, 1999)have suggested that the distribution of sites, elevation,grain size and composition of deposits, grain shapes,chemical composition, and biological characteristics demonstrate that coastal dune rock is quite different in origin from beach rock. They argue that dune rock was formed of coastal dune sand, through cementation induced by atmospheric precipitation, and they also suggest some concrete indicators of origin. Beach rock forms in the inter-tidal zone, through deposition and cementation under the action of seawater (tidal flows and waves). In contrast,coastal dune rock forms in the tidal zone from windblown sand and precipitation-induced cementation, and therefore should have distinct aeolian geomorphic features, such as climbing slope deposition structures.

    Quartz grains in coastal dune rocks are generally well sorted and rounded, and their surfaces have textures such as saucer-shaped pits and crescent impact pits that are indicative of aeolian origin. They also have large-scale, high-angle cross bedding and deformation structures such as curled bedding and collapse structure and calcareous root pipes(formed by plant roots). Dune rock cement is granular,low-Mg calcite, and cemented structures include crescent contact adhesion and gravity-suspended adhesion, which are typical atmospheric freshwater seepage adhesive features.Beach rocks lack all of these characteristics (Wu Z and Wu KG, 1990).

    Reconstruction of ancient coastal dune shapes from bedding types has received significant attention. Yeet al.(1985)roughly defined some ancient dune types in terms of bedding types of dune rocks in Shidao Island of Xisha archipelago of Hainan Province, including crescent dunes, transverse dunes, longitudinal dunes (include seif dunes, whaleback dunes), dome dunes, and their spatial distribution. Zhaoet al. (1988) identified three classes of sand ridge of dune rock and obtained their distribution, shapes, scales, and elevations on the Putian Houshijing coast in Fujian Province.Based on the shapes and sedimentary structures, the ancient dune types and ancient wind directions were reconstructed,and they are thought to be vegetated dunes and wind shadow dunes that were formed by beach deposits under the actions of prevailing northwest monsoon winds during the late mid-Holocene. From this it can be seen that the ancient and present wind directions do not show significant change in this region.

    A brownish-red or yellowish-brown, semi-cemented,medium to fine sand deposit is referred to as "old red sand"in China. This material is discontinuously distributed in South China’s coastal regions to the south of Pingtan Island of Fujian Province, the Shandong peninsula, and Zhoushan Island. In recent years much work has been done on the origins and ages of old red sand. Some scholars believe that old red sand is a type of near-source beach deposit, but others think it is aeolian in origin, and there is also debate as to whether it formed under conditions of high sea level or low sea level. Zhanget al.(1985) suggested that old red sand is a near-source, rapidly deposited coastal sediment, and it is a product of long-term oxidation under the hot and humid climatic conditions of South China. Wu (Wu Z and Wu KG,1990; Wuet al., 1994; Wu, 1996; Wu and Wang, 1997) argued that old red sand is an aeolian sand deposited during the low sea level stage of the last glacial period, and afterward it experienced reddening in the relatively high sea-level environment under hot and humid climatic conditions during the sub-interglacial and postglacial periods.Therefore, its depositional characteristics and spatial distribution cannot be used as an indicator of sea level change,neoteric movement, or seismic activity. Some scholars support the view that old red sand is aeolian (Liet al., 1989;Wang, 1997; Chenet al., 1998; Zenget al., 1999).

    4. Characteristics of coastal aeolian sand movement in China

    In recent years, studies have been conducted on the processes and characteristics of aeolian sand movement in coastal China, such as the field observation of aeolian sand flow structure at the Changli coast in Hebei Province (Donget al., 2008e, f, g, 2009a) and the Changle coast in Fujian Province (Chen and He, 1997), and observations of coastal dune migration on the Beihai coast in Guangxi Province(Fan, 1996) and the Changli coast (Hu and Gu, 1996).

    4.1. Threshold wind velocity of sand movement and aeolian sand flow structure

    Observations of aeolian sand movement on the Changle coast in Fujian Province (Chen and He, 1997) showed that beach sand grain size and moisture content are important factors for the initiation of sand particle movement by wind.The threshold wind velocity for the beach sand at the south bank of the Mingjiang River mouth is 6-7 m/s. Under the same conditions, the threshold wind velocity for dune sand movement is significantly lower. However, the threshold wind velocities for the initiation of coastal dune sand movement are much higher than those of inland desert sand of similar grain size, because the coastal dune sand has relatively higher moisture content and stronger inter-particle adhesive forces.

    Measurements of coastal dune sand movement on the Changle coast in Fujian Province (Chen and He, 1997) show that the distribution of sand transport with height follows an exponential relation. It is believed that the structure of aeolian sand flow in the coastal zone is roughly similar to that in inland desert regions. Differences include that the mean sand concentration during transport in coastal systems occurs at a slightly higher height than in inland deserts, and that the transport rate is significantly smaller in the coastal zone, due to the influences of coastal environmental factors.

    The results of field observations at the Changli coast in Hebei Province (Donget al., 2008e, f) also showed that the basic characteristics of the structure of aeolian sand flow at the crest of the coastal transverse ridge can be summarized as the decrease in mass of sand materials transported by wind with height, and this coincides with an exponential distribution, especially within a 0-40-cm height over the dune surface. The correlation coefficient of the exponential function relation reached 0.995 or more. However, with increase in height above the dune surface, the relation between the two incurred some changes. The sand transport rate at the 20-60-cm height decreased in a power function law with height, while the sand transport rate at the 40-60-cm height increased in a polynomial function law.This was caused by the difference of sand size and its form of movement within the different heights, and was affected by the sand composition in this region, which is dominated by medium sand and relatively coarse sand particles.

    Donget al.(2008g, 2009a) observed the influence of wind velocity and sand transport rate on the structure of aeolian sand flow on the coastal transverse ridge. They showed that with the change of wind velocity and sand transport rate, the structure of aeolian sand flow also changes. These changes were closely related to the limit of wind-transported sand grain size and the composition of sand grain size in the wind-sand flow. The varying forms of movement of different sizes of sands in the aeolian sand flow represent different vertical distribution models, which leads to change of the structure of aeolian sand flow. This is further discussed in the next section.

    4.2. Vertical distribution of different grain size groups in aeolian sand flow

    Research has explained the change of sand grain size composition at different heights in aeolian sand flow on aeolian sand dunes. Observations on the Changli coast(Donget al., 2008f) showed that at 0-10-cm, 10-40-cm, and 40-60-cm heights the medium sand contents correspondingly gradually decreased from the ground surface upward,became stable, and then gradually increased upward. The fine sand showed an opposite change. The particle-size composition of sand materials in the aeolian sand flow at the 0-10-cm height was dominated by medium sand; at the 10-40-cm height it was dominated by both medium sand and fine sand; and at the 40-60-cm height it was dominated by medium sand. The mean particle size gradually became fine and stable, and then became coarse. Therefore, the vertical variation of sand particle size in the aeolian sand flow was not the same as the general view: the higher the height of the airflow layer, the finer the sand particles it contains and the coarser the sand particles in the near-surface airflow layer.

    On the basis of data from field observations and wind tunnel experiments (Donget al., 2009), the vertical distribution models of sand transport rate of different grain size groups in coastal aeolian sand flow over coastal dune are different. The vertical distribution of coarse sands could be expressed by a typical power function, but the vertical distribution of the sand transport rate of medium sands and fine sands could be typically expressed by an exponential function. The reasons for the difference in vertical distribution models of sands in different grain size groups in aeolian sand flow are the height of distribution of sands of different grain size groups and their form of movement in aeolian sand flow. Coarse sand particles are mainly distributed near the surface of dunes. Normally, turbulent flow plays a leading role in the movement of sands at low heights over dunes.The influence of turbulent flow in the near-surface layer makes most of the coarse sand particles move in the manner of surface creep, and the distribution model of sand transport rate of coarse particles with height satisfies the negative power relation. In comparison, fine sands and medium sands mostly move in the manner of saltation, and the vertical distribution of sand transport rate of saltation particles follows an exponential decrease function. The change of wind velocity and sand transport rate in aeolian sand flow will lead to a change of vertical distribution models of the different grain size groups (Dong and Ma, 2008, 2009b). Field measurement results show that the changes of models of vertical distribution of medium sands and fine sands in wind-sand flow at the different sites over coastal dune are not essentially different; there is only some different in the extent of change (Donget al., 2010).

    4.3. Migration rates of coastal dunes in China

    Hu and Gu (1996) investigated morphological changes and migration rates of coastal dunes on the Changli coast in Hebei Province by the fixed site observation method, and they measured cross-sectional changes in coastal dunes and their migration rates. By comparing undisturbed coastal dunes with those used for sand-surfing, they assessed migration rates under human disturbance and undisturbed conditions. Based on observations obtained from October 1991 to April 1994, they found that the height of natural coastal dunes increased from 18.77 m to 22.95 m, an increase of 4.18 m. In contrast, the heights of two sand-surfing dunes increased by 0.87 m and 0.47 m. During the same period,the cross-sectional area of the natural dune increased from 1,736.7 m2to 1,861.7 m2, while the sand-surfing dunes experienced negative change. These dunes continuously moved landward under the actions of onshore winds. During the observation period, the landward slope base of natural coastal dune migrated 11.10 m, while the two sand-surfing dunes migrated 7.63 m and 1.33 m, respectively. Dune crests also migrated landward; during the observation period the crest of the natural coastal dune migrated 10.8 m, while the crest of the natural coastal dune migrated 1.0-2.0 m/yr.These observations are typical of the migration rates of coastal dunes in the region. However, migration rates differ greatly between regions in China. Observations of dune migration rates on the Beihai coast in Guangxi Province during the period from April 1992 to July 1995 gave a mean annual migration rate of 12.64 m, and during the observation period the sand dune area enlarged about twofold (Fan,1996).

    5. Prospects for coastal aeolian research in China

    Coastal aeolian research in China was initiated in the 1980s. Although substantial results have been achieved and blanks in this research field have begun to be filled, there is a clear gap as compared with other countries because our study of this subject was initiated comparatively late (Dong,2001, 2006, 2007). In view of this, special attention should be paid to the following aspects in future studies of coastal aeolian phenomena in China.

    Observation and modeling of coastal aeolian sediment transport is a fundamental component of advancing under-standing of this subject. There is a clear need for observation and modeling that is representative of the coastal zones of China. Systematic observation and simulation are required to understand China’s coastal dune assemblages and types,airflow movement patterns over typical dune surfaces, sand flow structures, transport rates and dune migration rates, and the influences of wind speed, vegetation cover, surface moisture content, and topographic slope on the sand transport rate. Such studies will contribute to a better understanding of the dynamic processes and internal mechanisms of coastal aeolian movement in coastal zones of China.

    Coastal aeolian landforms themselves have highly variable adaptability and persistence, and their formation can be strongly influenced by global change. Considering the increasing concern in regard to global environmental change,research on the relation between global changes and coastal aeolian processes and landform development is an important subject for future work. In the context of research on the aeolian processes over coastal dunes, research on surfzone-beach-dune interaction models will hopefully provide a macroscopic explanation of coastal dune origination and the evolution mechanisms, which is essential to understand the regional differences of coastal dune type and size and related issues, and is one of the most important aspects of coastal aeolian research(Dong, 2010).

    Owing to the great practical value of coastal sand lands in terms of coastal protection, economic use, tourism, culture, and education, the human development and utilization of coastal sand lands has never ceased. Irrational use of coastal sand lands in some regions has resulted in disastrous consequences; therefore, research into the dynamics and control of coastal aeolian processes is essential.

    This work is supported by the National Natural Science Foundation of China (Nos. 40571019, 40971007).

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    10.3724/SP.J.1226.2011.00543

    *Correspondence to: Dr. YuXiang Dong, Professor of School of Geography and Planning, Sun Yat-sen University, Guangzhou,Guangdong 510275, China. Tel: +86-20-84112396; Email: eesdyx@mail.sysu.edu.cn

    16 June 2011 Accepted: 13 September 2011

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