• 全国中文核心期刊
  • 中国科技核心期刊
  • 美国工程索引(EI)收录期刊

2011 Vol. 22, No. 1

Display Method:
Distribution charateristics of hillslope curvature and its effects on hydological processes:A real-world test
LIU Jin-tao, FENG De-zeng, CHEN Xi, WU Ji-chun, GU Wei-ming
2011, 22(1): 1-6.
Abstract:
Hillslope curvature includes the characters e.g.divergent/convergent and convex/concave etc.These characters are second-order topographic parameters contrasted to slope and length of hillslope.In this study,a 10 m×10 m DEM dataset was created using the 1:10000 elevation contour maps for the Jiangwan catchment of Tiaoxi River, on the Taihu basin.The curvature distribution within hillslopes can thus be studied.The averaged profile and plan curvature for the catchment are found to be -4.62×10-4 and 3.49×10-4,respectively,indicating the catchment is overall convergent and divergent.Through dividing of the catchment into two types of hillslopes headwater and side-slope,we find that the headwater hillslope is generally convergent,while the sideslope hillslope tends to be more divergent.Divergent,convergent,convex and concave are coexisting within an individual hillslope.A total of ninety soil moisture samples were taken from the Hemuqiao sub-catchment.Soil moisture contents and corresponding curvatures were analyzed.It is shown that the concave or convergent hillslopes are always with higher soil moisture values, while convex or divergent hillslopes with lower ones.Soil moisture contents decline with the increase of elevations.
Spatial and temporal variation of insoluble particles in precipitation at alpine and rural sites on the Urumqi River valley in Tianshan Mountains of China
DONG Zhi-wen, LI Zhong-qin
2011, 22(1): 7-14.
Abstract:
Chemical and environmental significance of insoluble particles in precipitation are studied using methods of parameter comparison and correlation analysis at alpine and rural sites on the Urumqi river valley in Tianshan Mountains.The HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory)model is also employed to examine the transport process of air mass and insoluble particles in this region.Results show that the concentration,the size distribution and the chemical constitutes of dust particles in precipitation all exhibit significant seasonality at both sites.The dust concentration increases in winter and spring seasons and decreases during summer and autumn periods,showing a negative correlation with seasonal changes in precipitation.This indicates the significant influence of Asian dust storm in the river valley.The volume-size distribution reveals that large-sized particles are found in winter and spring seasons,while,small-sized one appears to be in summers and autumns.The seasonal variation in chemical constitutes of dust particles indicates that both regional atmospheric environment and human activities of Central Asia may have influence on the formation of regional precipitation.
Analysis of pan evaporation changes in the Huaihe River basin
RONG Yan-shu, ZHOU Yun, WANG Wen
2011, 22(1): 15-22.
Abstract:
Long-term observational records from the Huaihe River basin show that the evaporation rate from open pans of water has been steadily decreasing over the past 50 years.Traditionally,the Huaihe River valley is seen as the transition zone dividing the arid north from the tropical south in China.Due to its geographic location,studying of pan evaporation changes in the basin would be important to understanding the basin's water cycle and water resources conditions,especially in a changing climate.In this study,the pan evaporation change in the past 50 years is investigated using the observed pan evaporation,temperature,surface wind speed,sunshine duration,relative humidity,air pressure and rainfall from the China Meteorological Information Centre,as well as the monthly mean cloud amount data of UK Climatic Research Unit (CRU)and the NCEP/NCAR re-analysis data.The result confirms the pan evaporation in the basin has undergone a significant downward trend change over the past 50 years.The most pan evaporation occurs in springs and summers,and thus showing a strongest downward trend.Regionally,the greatest pan evapora-tion and the related downward trend change are found to be in the basin east and south.The study on the cause of decreased pan evaporation reveals that the downward trend change might be the result of the decreasing in surface wind speeds and sunshine duration,as well as the increasing in relative humidity and precipitation.The increase of both relative and specific humidity in the troposphere can result in an increase of surface relative humidity,cloud amount and precipitation,and thus weakening the intensity of solar radiation and shortening the sunshine duration.Such a process will eventually cause the reduction in pan evaporation.
Measurements and modeling of canopy interception in the Gongga Mountain subalpine succession forest
SUN Xiang-yang, WANG Gen-xu, LI Wei, LIU Guang-sheng, LIN yun
2011, 22(1): 23-29.
Abstract:
Gross rainfall,throughfall and stemflow were measured during the growing seasons of two tree species of Abies afbri and Populus purdomii in 2008 and 2009 in a subalpine succession forest on the Gongga Mountain. Throughfall (the net precipitation under the two tree species),steamflow and canopy interception are analyzed.In addition,the applicability of the Gash model (1995)is examined using the measurement.The model requires only a limited amount input and uses the Penman-Monteith equation for evapotranspiration estimation.The capacity of the canopy storage is calculated using the Preira method in the model.The results show that the throughfall can account for 76.4% and 77.0% of gross rainfall in 2008 and 2009,respectively,while the stemflow is too small to contribute the gross rainfall,and the remaining is intercepted by canopies.The amount of gross rainfall is found to be the main influential factor on the interception process compared to the rainfall duration and intensity.Simulations of canopy interceptions agree well with the observed values for the two growing seasons.For example,the values of simulated and observed interceptions are respectively 125.6 mm and 126.1 mm for the growing season of 2008,which illustrates that the applicability of the Gash model in this region.
Application of Valiantzas approach to estimating reference evapotranspiration in China
PAN Yun, GONG Hui-li, LI Xiao-juan, ZHU Lin, ZHANG Jing
2011, 22(1): 30-37.
Abstract:
A Penman-Valiantzas model is developed based on the Valiantzas approach for estimating reference evapo-transpiration in China without wind speed data.Besides,the Hargreaves radiation equation is used for deriving a Pen-man-Valiantzas-Hargreaves model,in which only the relative humidity and the air temperature are required as the model input.The two new models are tested with the CLIMWAT database of UN Food and Agriculture Organization (FAO).A total of 156 Chinese stations are extracted from the database,which contain long-term monthly mean val-ues of climatic parameters.The result shows that the correlation coefficients between reference evapotranspirations cal-culated by the two models and the FAO Penman-Menteith model are 96.64% and 93.44%,respectively.The corre-sponding values of the root mean square error are 0.32 mm/d and 0.43 mm/d,respectively.These two new models can produce a more accurate reference evapotranspiration than that obtained by other two widely used models (Priest-ley-Taylor and Hargreaves).The Penman-Valiantzas model is further tested using the long-term measurement observed at the Yanqing Station in Beijing.The result of a 20-year monthly simulation reveals that the correlation coefficients between reference evapotranspirations calculated by the Penman-Valiantzas model and the FAO Penman-Menteith model as well as observed by the pan observation at the station are 97.84% and 86.38%,respectively.The daily simulation of reference evapotranspiration using the Penman-Valiantzas-Hargreaves model has also been improved. Our results demonstrate the applicability of the two new models in China in the absence of the wind speed and sun-shine hour data date.
Crop water demand in China under the SRA1B emissions scenario
CONG Zhen-tao, YAO Ben-zhi, NI Guang-heng
2011, 22(1): 38-43.
Abstract:
Projections of the crop demand under future climate scenarios would help us to understand the potential influence of climate change on food safety and water resources.Using the United Nations Food & Agriculture Organization (FAO)modified Penman-Monteith equation and the output from the Model for interdisciplinary Research on Climate (MIROC3.2)for the SRA1B emissions scenario,the reference evapotranspiration (ET0)can be calculated for China for the next 50 years.Using the FAO crop coefficients and the K-ppen climate classification system,the crop coefficient can thus be determined for every calculation unit.The estimation of crop water demands is achieved using ET0 and the crop coefficient,and the corresponding irrigation water requirement can also be worked out by matching the effective precipitation with the crop water demand.The result shows that on average,China's ET0 could increase by about 8%,and so does for the crop water demand and the irrigation water requirement.Over the northeast region, this increase in irrigation water requirement could reach above 10%,and the increase over South China is also significant.The upward trends in water demands are mainly due to the increase in future temperatures,which can result in an increase of ET0 values.The matter could be further complicated by the reduction of the projected precipitation for the northeast and south regions of China.However,the projected increase in precipitation over the north region could moderate the issue of water demands.
Risk analysis of synchronous-asynchronous encounter probability of rich-poor precipitation in the Middle Route of South-to-North Water
KANG Ling, HE Xiao-cong
2011, 22(1): 44-50.
Abstract:
One of the major risk factors in managing water resources in the middle route project of South-to-North Water diversion will be due to spatial and temporal variations in precipitation.This is because the synchronous-asyn-chronous encounter probability of rich-poor precipitation can be different at the source area of water and at the receiving area of water.In this study,a risk analysis model is developed using a combined approach based on the copula function and Bayesian networks.The copula function is used to establish the joint probability distribution and to calculate the conditional probability among the areas of source water and receiving water.The Bayesian network is applied to analyzing the synchronous-asynchronous encounter risk.Using the risk analysis model,a risk analysis is conducted to determine the lease favorable distribution of the synchronous-asynchronous encounter probability of rich-poor precipitation at different locations.The result shows that the risk probability is less than 25% for water transfer to four receiving areas.Our risk analysis model is simple and practicable,and can provide a new tool for conducting the multi-variate analysis of hydrological risks.
Impacts of climate and land-use change on water resources in a watershed:A case study on the Trent River basin in North Carolina,USA
WANG Yun-qi, QI Shi, SUN Ge, Steve G McNulty
2011, 22(1): 51-58.
Abstract:
The distributed precipitation-runoff modeling system (PRMS)will support the study on the impacts of climate change and land-use change on water resources in a watershed.Modeling results show that the PRMS model performs satisfactorily for simulating water yield,as indicated by an overall Nash-Sutcliffe simulation efficiency over 0.8. The reduced scales of HRU (Hydrological Response Units)delineation show a better model-fit efficiency to some extend about 7%.The 71 HRUs delineation can result in the best overall performance of the modeling system.The order of land-use and climate change sensitivity to evapotranspiration and water yield is given as follows:precipitation > urban land-use > temperature > crop and grasses.The water yield has greatly larger changes than the evapotranspiration under land-use and climate changes.It is predicted that the annual evapotranspiration will increase 5.64-201.29 mm,and the water yield will increase about 160 mm or decrease about 180 mm under the scenarios of land-use change corresponding with the climate change.
Estimation of soil moisture in summer by active microwave remote sensing for the Maqu area at the upper reaches of the Yellow River
TIAN Hui, WEN Jun, SHI Xiao-kang, WANG Xin, LIU Rong, ZHANG Jing-hui, LÜ Shao-ning
2011, 22(1): 59-66.
Abstract:
The estimation of soil moisture in summer of 2009 is carried out using the ENVISAT-1/ASAR VV polarization data for the Maqu area at the upper reaches of the Yellow River.The geometrical optics model (GOM)is used to compute backscattering coefficients.The effect of surface short grasses on the estimation can be eliminated from the total microwave backscatters using a semi-empirical water-cloud model.The latter is calibrated using measurements collected synchronously from the regional soil moisture network.The result shows that the root mean square error of the remotely sensed soil moisture is less than 0.02 m3/m3,while the R2 (coefficient of determination)is greater than 0.86.A high value of 0.4 m3/m3 is obtained in the summer soil moisture average,indicating that the Maqu area might serve as an important source water area for the Yellow River.However,a significant heterogeneity is present in the spatial distribution of soil moisture due to the influence of terrains.The spatial correlation distance of 500 m to 1000 m is found for the soil moisture in mountainous regions,while that in flat regions is greater than 2000 m.Our result demonstrates the applicability of using remote sensing techniques for soil moisture retrieval at the regional scale.
Bias error induced by concentration gradients in the measurement of sediment-laden flows
SHI Jian, GUO Bo, GONG Fu-yuan, HE Xiao-gang, LI Dan-xun
2011, 22(1): 67-74.
Abstract:
The presence of concentration gradients shifts the effective location of the reported mean velocity away from the sampling bin's center in sediment-laden flow measurement with particle tracking velocimetry.Under typical velocity and concentration profiles for open channel flows,the bias error proves to be constantly less than zero,leading to an underestimate of the actual velocity.The error is closely related to three variables which are the relative location of the flow,the size of the sampling bin,and the suspension index of the sediment particles.Numerical analysis shows that the magnitude of the error follows a first-decrease-then-increase pattern from the bottom to the water surface along the vertical.
Nutrient exchange across sediment-water interface in wetlands
GU Xiao-zhi, ZHANG Lei, BAI Xiang, SHEN Qiu-shi, WANG Zhao-de, FAN Cheng-xin
2011, 22(1): 75-83.
Abstract:
In order to reducing benthic nutrients release,we investigate the effectiveness of three physical amelioration measures (fine sand covered,sediment loosened,and reed planting)on the diffusive flux from sediment-overlying water.An in-situ sampling technique (Peeper)was employed to obtain the vertical distribution of nutrient elements and diffusive fluxes on the Nansi Lake in China.The results show that in the case of all three amelioration measures,the sediment water content and porosity have increased by 91% and 54% compared to the Control Treatment,respectively.The nutrient profiles NH4+ and PO43- in pore water on the sediment-water interface exhibit a nearly exponential increase with depth with a concentration maximum being at the 8 cm depth.The contents of NH4+, PO43- and NO3- decrease significantly in pore water after reed planting.With all three amelioration measures,the proportion of NH4Cl-extractable PO43- to the total content of PO43- in sediments is found to be decreased in upmost sediments,whereas those of bicarbonate dithionite (BD)BD-extractable PO43- are increased as the result of amelioration measures.Such result is enhanced by reed planting.The diffusive flux across the sediment-water interface could be calculated using the Fick's First Law of diffusion.It is found that the diffusive fluxes of NH4+and PO43- have been reduced from 57.47~72.19 μg/(m2·d)and 2.55~3.21μg/(m2·d)to -95.54~-130.94 μg/(m2·d)and 1.50~2.05 μg/(m2·d)after sediment loosened.The measure of surface sediment loosening can decrease the diffusive fluxes of NH4+,PO43- from surface sediments.The measure is thus recommended as one of the effective controls towards the internal nutrient load reduction in lakes.
Comparison study on the conditions for incipient motion of cohesionless sediment based on the concept of equivalent grain size
NIE Rui-hua, WANG Tao, HUANG Er, LIU Xing-nian
2011, 22(1): 84-88.
Abstract:
A uniform expression is presented to describe the incipient motion of nonuniform sediment based on the concept of equivalent grain size.Using eight formulas,a comparison study is conducted to explore the issues of hiding and exposure and the aspects of sediment sorting due to heterogeneity.Results show that the hiding and exposure effect is well described in the modeling of nonuniform sediment transport by all eight formulas.Coarse sediment is usually underrepresented by its equivalent particle size,which can artificially ease the condition for incipient motion of coarse sediment.The opposite is true for fine sediment.However,there are still some differences among the formulas,mainly in dealing with the hiding effect of fine sediment.Different formulas use different feature sizes to simulate the hiding and exposure effect of nonuniform sediment.Among those,HAN Qi-wei,ZHANG Qi-wei and LIU Xingnian formulas can better handle the sorting function for sediment incipient motion.For fine sediment,the performance of Egiazaroff,Hayashi and QIN Rong-yu formulas is less satisfactory due to clear-water scouring.
Phosphorous adsorption characteristics of upper layer sediments in the water level fluctuating zone of Three Gorges Reservoir area
CAO Lin, JI Fang-ying, LIN Mao, LI Si, WANG Tu-jin
2011, 22(1): 89-96.
Abstract:
The upper layer sediment in the water level fluctuating zone of Three Gorges Reservoir area (TGRA)is studied through an analysis of phosphorous forms and adsorption isotherm curves in the fluctuating zone with wet-drycycles.The result shows that the total phosphorous (TP)content for August would be higher than of May in the over-lying water,while the lowest value is found in November.The max adsorption quantity of phosphorus and the max buffer capacity of soil of sediments increase while their equilibrium phosphorus concentration and reactive desorbed phosphorus drop when sediments alternated from the submerged state to the exposed state,which indicates that phos-phorous fixing strengthens whereas phosphorous releasing weakens in the exposed sediments in summer.Moreover,in the course of being submerged for the first time,sediments phosphorous show an alternation from a source to a sink. During the initial stage of impoundment of Three Gorges Reservoir,phosphorous is being accumulated in the sediment.This phosphorous-enriched upper sediment layer in the water level fluctuating zone will be washed away with reservoir sluicing in the following year.
3D numerical modeling of wind-driven flow in the high salinity Aibi Lake
HAN Long-xi, LONG Dong-yan, LI Hong-jing, ZHANG De-min, ZHANG Peng
2011, 22(1): 97-103.
Abstract:
According to the hydrodynamic characteristics of high salinity lake,a three-dimensional (3D)hydrodynamic numerical model is designed to simulate the dynamic in Aibi Lake which is a high salinity lake in northwest China.Selecting typical wind fields,we apply this model to simulate the formation process of wind driven flow and 3D spatial distribution characteristics of hydrodynamic parameters.The study result shows that the formation process of wind driven flow can be divided into three stages:The flow direction is consistent with wind direction,the flow direction deviates from the wind direction in the transitional stage and the current ultimately forms a circulation stable stage.When the flow field is on steady state,the flow direction in most of the waters are in consistent with the wind direction while there are several small scale circulations in central.The bottom current in central is opposite to the surface one with a compensation current character.Overall,the horizontal velocity from the surface to the bottom is decreasing.The inshore velocity is greater than the central one.It shows that the distribution characteristics of hydro-dynamic parameters in high salinity lake are similar to that of fresh water.Increased water salinity has no effect on the structure of lake circulation.
Upstream contributions to the chromophoric dissolved organic matter in the Taihu Lake during summer rainy seasons
FENG Long-qing, LIU Ming-liang, ZHANG Yun-lin, YIN Yan, SHI Zhi-qiang, LIU Xiao-han
2011, 22(1): 104-111.
Abstract:
The spectral absorption and the three-dimensional fluorescence of chromophoric dissolved organic matter (CDOM)in three rivers (Zhihugang,Dapukou,and Changdougang)located upstream of the Taihu Lake are deter-mined.Such an upstream contribution to CDOM in the lake during the summer rainy season of 2008 is analyzed.It is found that the Zhihugang River has the highest CDOM absorption value,and followed by Dapukou.The lowest CDOM value is found in the Changdougang River.This result indicates that the allochthonous pollutant of the north river up-stream of the Taihu Lake contributes the most CDOM in the lake.Our results also show that the mean value of (4.76±0.79)m-1 is found for the absorption coefficient of CDOM at 355 nm in the three rivers,which is significantly lar-ger than that of (3.62±0.84)m-1 in the Taihu open water.Furthermore,CDOM absorption decreases gradually from the upstream of rivers to the river mouths,and to the Taihu Lake.It is thus clear that the three rivers are the major sources of allochthonous pollutants in the Taihu Lake during summer rainy seasons.In addition,the parallel factor analysis of the three-dimensional CDOM fluorescent excitation-emission matrix spectra reveals the presence of four fluorescent components.The component 1 and component 2 can be characterized as the protein-like fluorescence,and the rests are the humic-like fluorescence.The intensity of the latter decreases gradually from the river mouth to the open water of the lake,and the opposite is true for the protein-like fluorescence intensity.This analysis shows that the humic-like fluorescent dissolved organic matter in the Taihu comes mainly from the upstream rivers.
Quantitative study of the damping effect of buffer strips with different slopes on runoff and pollutant removal efficiency
WU Jian-qiang
2011, 22(1): 112-117.
Abstract:
Using the constructed buffer strip experimental site and the hydrometric devices in the Dongfeng Port of Shanghai,a quantitative study is conducted to investigate the damping effect of buffer strips with different slopes on runoff and the pollutant removal efficiency of nitrogen (N)and phosphorous (P)from agricultural lands.The result shows that for a similar configuration of vegetation structure,the gentler the slope gradient is in relation to the damping effect of buffer strips,the slower the runoff moves,and the greater the hydraulic permeability is.For example,on a 19-m long buffer strip with a 2% slope,there will be a delay of 7.3 minutes for runoff starting to flow out of the strip compared to that with a 5% slope.The two slope configurations can lead to a ratio of 1:1.74 with respect to the seep-age water.The improvement in the pollutant removal efficiency of N and P would be more significant in comparison with the damping effect on runoff when the slope gradient increases.For instances,on the buffer strips with 2%, 3%,4% and 5% slopes,the improvement ratio of the two elements are 2.32,2.15,1.82 and 1.64,respectively. The gentler the slope gradient is in relation to the pollutant removal efficiency of N and P,the greater the total efficiency and unit area improvements will be.For example,on the buffer strips with 2% and 5% slopes,the two im-provement ratios are found to be 1.56 and 1.66,respectively.The buffer strip with a 2% slope would have the high-est pollutant removal efficiency of total nitrogen (TN),ammonia nitrogen (NH3-N)and total phosphorous (TP), which are 0.661、0.672 and 0.044 g/m2,respectively.
Estimating submarine groundwater discharge to the Jiulong River estuary using Ra isotopes
GUO Zhan-rong, HUANG Lei, YUAN Xiao-jie, LIU Hua-tai, LI Kai-pei
2011, 22(1): 118-125.
Abstract:
A mass balance model of naturally-occurring short-lived and long-lived radium isotopes (224 Ra and 226 Ra) for the Jiulong River Estuary is developed to estimate the submarine groundwater discharge (SGD)to the estuary.All likely source and sink terms are considered in the model establishment.The source terms for Ra include river dis-charge,desorption from riverine suspended particles,desorption from resuspended particles,diffusion from subtidal sediments,and input from open sea and SGD.Ra can also be removed through radioactive decay and with ebb tide. The modeling result shows that up to 41.9% to 56.9% of the total Ra input can be attributed to the contribution of submarine groundwater in the estuary,and this has to be sustained by a discharge of 1.65×108 to 1.83×108 m3/d in groundwater input.Such groundwater amounts can be four times that of river discharge in the estuary.Assuming that fresh groundwater can account for 10% of the total amount of groundwater,then the model calculated inorganic nutri-ent fluxes are 4.61×106 mol/d for dissolved inorganic nitrogen (DIN),0.22×106 mol/d for dissolved inorganic phosphate (DIP),and 6.94×106 mol/d for dissolved inorganic silicon (DSi),respectively.And such inorganic nutrient fluxes are 23%,28% and 77% of that delivered by river discharge in the estuary,respectively.The result suggests that a considerable amount of nutrients in the Jiulong River Estuary is coming from the contribution of SGD.The latter itself is also significant in relation to the total river discharge in the estuary.Nutrients contributed by SGD could potentially cause environmental concerns of estuary and coastal marine eutrophication.Such an environmental issue must be considered in the future management plan.
Advances in water ecosystem service study and its key supporting technologies
ZHANG Cheng, YAN Deng-hua, HAO Cai-lian, QIN Tian-ling, WANG Ling-he
2011, 22(1): 126-134.
Abstract:
As for key supporting technologies,studies on coordination between economic development and ecology conservation have attracted extensive attention in the assessment of ecosystem functions and ecosystem services.The study is especially relevant to the issues of water quality degradation and the deterioration of ecosystem functioning.In this study,certain hot issues on the subject including function identification,assessment method and driving mecha-nism are addressed.The concept of water ecosystem services in its broad and narrow sense is discussed.As the result,a board and narrow sense concept in water ecosystem service,the double-function identification method and research models are proposed.The study also reviews key supporting technologies for the subject including observational prototype technologies,coupled eco-hydrological models,and multidimensional analyses.The study highlights the major shortcomings of current research,e.g.,weak connotation and function identification,imperfect assessment methods,untapped key supported technologies,and unsatisfactory results from technology application.Finally,the future prospects for the subject are presented.
Review of methods for measuring greenhouse gas flux from the air-water interface of reservoirs
ZHAO Yan, ZENG Yuan, WU Bing-fang, CHEN Yong-bo, WANG Qiang, YUAN Chao
2011, 22(1): 135-146.
Abstract:
Carbon dioxide (CO2)and methane (CH4)produced during decomposition of organic matter (OM)in reservoirs are emitted from the air-water interface either by diffusion or ebullition.The static-chamber,gradient descent,invert funnel,TDLAS (Tunable Diode Laser Absorption Spectroscopy)and eddy covariance are commonly used methods for measuring CO2 and CH4 fluxes from the air-water interface of reservoirs in abroad.In this study,we review the principle and application of above mentioned methods,their pros and cons,as well as applicability limitations.Factors affecting the emission of greenhouse gases from reservoirs are analyzed from the perspective of water, terrestrial and climatic environment.Prospects of the application of remote sensing technologies for monitoring green-house gas emissions from reservoirs are presented.Using remote sensing technologies and surface measuring methods can be complementary to each other in both time and space.Our study provides a valuable reference for monitoring greenhouse gas emissions from reservoirs in China.
2011, 22(1): 147-150.
Abstract: