Statistical distribution of depth-integrated local horizontal momentum for second-order random ocean waves in finite water depth

Based on the second-order random wave solutions of water wave equations in finite water depth, statistical distributions of the depth- integrated local horizontal momentum components are derived by use of the characteristic function expansion method. The parameters involved in the distributions can be all determined by the water depth and the wave-number spectrum of ocean waves. As an illustrative example, a fully developed wind-generated sea is considered and the parameters are calculated for typical wind speeds and water depths by means of the Donelan and Pierson spectrum. The effects of nonlinearity and water depth on the distributions are also investigated.

Outer wave number spectrum and statistical distribution of apparent wave number vector

Based on the ray theory and Longuet-Higgins's linear,model of sea waves, the joint distribution of wave envelope and apparent wave number vector is established. From the joint distribution, we define a new concept, namely the outer wave number spectrum, to describe the outer characteristics of ocean waves. The analytical form of the outer wave number spectrum, the probability distributions of the apparent wave number vector and its components are then derived. The outer wave number spectrum is compared with the inner wave number spectrum for the average status of wind-wave development corresponding to a peakness factor P = 3. Discussions on the similarity and difference between the outer wave number spectrum and inner one are also presented in the paper. (C) 2002 Elsevier Science Ltd. All rights reserved.

Statistical distribution of wave-surface elevation for second-order random directional ocean waves in finite water depth

Based on the second-order random wave solutions of water wave equations in finite water depth, a statistical distribution of the wave-surface elevation is derived by using the characteristic function expansion method. It is found that the distribution, after normalization of the wave-surface elevation, depends only on two parameters. One parameter describes the small mean bias of the surface produced by the second-order wave-wave interactions. Another one is approximately proportional to the skewness of the distribution. Both of these two parameters can be determined by the water depth and the wave-number spectrum of ocean waves. As an illustrative example, we consider a fully developed wind-generated sea and the parameters are calculated for various wind speeds and water depths by using Donelan and Pierson spectrum. It is also found that, for deep water, the dimensionless distribution reduces to the third-order Gram-Charlier series obtained by Longuet-Higgins [J. Fluid Mech. 17 (1963) 459]. The newly proposed distribution is compared with the data of Bitner [Appl. Ocean Res. 2 (1980) 63], Gaussian distribution and the fourth-order Gram-Charlier series, and found our distribution gives a more reasonable fit to the data. (C) 2002 Elsevier Science B.V. All rights reserved.

Statistical distribution of nonlinear random wave height

A statistical model of random wave is developed using Stokes wave theory of water wave dynamics. A new nonlinear probability distribution function of wave height is presented. The results indicate that wave steepness not only could be a parameter of the distribution function of wave height but also could reflect the degree of wave height distribution deviation from the Rayleigh distribution. The new wave height distribution overcomes the problem of Rayleigh distribution that the prediction of big wave is overestimated and the general wave is underestimated. The prediction of small probability wave height value of new distribution is also smaller than that of Rayleigh distribution. Wave height data taken from East China Normal University are used to verify the new distribution. The results indicate that the new distribution fits the measurements much better than the Rayleigh distribution.

笼形水簇和溶解甲烷之间平均力势能的约束型分子动力学计算及其在天然气水合物成核研究中的意义

That the dodecahedral water cluster (DWC) can adsorb dissolved methane molecules, an important phenomenon related to the hydrate nucleation study, has been observed through molecular dynamics simulations, but it has not been explained satisfactorily [Guang-Jun Guo; Yi-Gang Zhang; Hua Liu. J. Phys. Chem. C, 2007, 111, 2595]. In order to explain this phenomenon by using the potential of mean force (PMF) between the DWC and the dissolved methane, we perform several series of constrained molecular dynamics simulations in the methane-water system. The distance between the center of DWC and the methane molecule is constrained from 5 Å to 18 Å by adding 0.2 Å every time. For each fixed distance, we perform 20 independent simulations to improve the statistical precision. We first get the constraint force between the DWC and the dissolved methane in each simulation and then calculate the PMF by integrating these forces. Subsequently, the radial distribution function (RDF) is obtained from the PMF through an equation of statistical mechanics. The results show that the RDF has a sharp peak at about 6.2 Å, successfully explaining why the DWC adsorbs dissolved methane molecules. The preferential binding coefficient is a positive value (=2.05±0.5), indicates that the DWC tends to adsorb dissolved methane rather than water molecules in methane aqueous solutions. The curve of PMF for the DWC encaging a methane almost coincides that for the empty DWC, meaning that it is the DWC rather than the encaged methane who could adsorb dissolved methane molecules. By comparing the curves of PMF for different directions of the DWC relative to the dissolved methane, we find that it is the cage face rather than the cage edge or vertex that plays an essential role when the DWC adsorbing dissolved methane. This research sheds light on the driving force for the methane adsorption, and it is helpful in understanding the nucleation process of methane hydrate.

电离层参量M(3000)F2和hmF2的经验正交函数方法建模研究

The ionospheric parameter M(3000)F2 (the so-called transmission factor or the propagation factor) is important not only in practical applications such as frequency planning for radio-communication but also in ionospheric modeling. This parameter is strongly anti-correlated with the ionospheric F2-layer peak height hmF2，a parameter often used as a key anchor point in some widely used empirical models of the ionospheric electron density profile (e.g., in IRI and NeQuick models). Since hmF2 is not easy to obtain from measurements and M(3000)F2 can be routinely scaled from ionograms recorded by ionosonde/digisonde stations distributed globally and its data has been accumulated for a long history, usually the value of hmF2 is calculated from M(3000)F2 using the empirical formula connecting them. In practice, CCIR M(3000)F2 model is widely used to obtain M(3000)F2 value. However, recently some authors found that the CCIR M(3000)F2 model has remarkable discrepancies with the measured M(3000)F2, especially in low-latitude and equatorial regions. For this reason, the International Reference Ionosphere (IRI) research community proposes to improve or update the currently used CCIR M(3000)F2 model. Any efforts toward the improvement and updating of the current M(3000)F2 model or newly development of a global hmF2 model are encouraged. In this dissertation, an effort is made to construct the empirical models of M(3000)F2 and hmF2 based on the empirical orthogonal function (EOF) analysis combined with regression analysis method. The main results are as follows: 1. A single station model is constructed using monthly median hourly values of M(3000)F2 data observed at Wuhan Ionospheric Observatory during the years of 1957–1991 and compared with the IRI model. The result shows that EOF method is possible to use only a few orders of EOF components to represent most of the variance of the original data set. It is a powerful method for ionospheric modeling. 2. Using the values of M(3000)F2 observed by ionosondes distributed globally, data at grids uniformly distributed globally were obtained by using the Kriging interpolation method. Then the gridded data were decomposed into EOF components using two different coordinates: (1) geographical longitude and latitude; (2) modified dip (Modip) and local time. Based on the EOF decompositions of the gridded data under these two coordinates systems, two types of the global M(3000)F2 model are constructed. Statistical analysis showed that the two types of the constructed M(3000)F2 model have better agreement with the observational M(3000)F2 than the M(3000)F2 model currently used by IRI. The constructed models can represent the global variations of M(3000)F2 better. 3. The hmF2 data used to construct the hmF2 model were converted from the observed M(3000)F2 based on the empirical formula connecting them. We also constructed two types of the global hmF2 model using the similar method of modeling M(3000)F2. Statistical analysis showed that the prediction of our models is more accurate than the model of IRI. This demonstrated that using EOF analysis method to construct global model of hmF2 directly is feasible. The results in this thesis indicate that the modeling technique based on EOF expansion combined with regression analysis is very promising when used to construct the global models of M(3000)F2 and hmF2. It is worthwhile to investigate further and has the potential to be used to the global modeling of other ionospheric parameters.

太阳耀斑和日食期间电离层行为的统计和模拟研究

The ionosphere is the ionized component of the Earth's upper atmosphere. Solar EUV radiation is the source of ionospheric ionization. Thus the ionosphere is affected strongly by the variations in solar radiation. Solar flares and solar eclipses can induce remarkable short time changes in solar radiation: the solar radiation would increase suddenly during solar flares and decrease significantly during solar eclipses. Solar flare and eclipse events not only affect directly the photochemical processes, but also affect the dynamic processes, and even affect the neutral atmosphere, which is strongly coupled with the ionosphere. The study on the ionospheric response to solar flares and eclipses can advance our knowledge on the ionosphere and its photochemical and dynamic processes and help us to evaluate the ionospheric parameters (such as ion loss coefficients). In addition, the study on the ionospheric responses to solar flares and eclipses is an important part of the ionospheric space weather, which can provide guides for space weather monitoring. This thesis devotes to the study on the ionospheric responses to solar flares and solar eclipses. I have developed two models to simulate the variations of solar EUV radiation during solar flares and solar eclipses, and involved in developing a 2D mid- and low-latitude ionospheric model. On the basis of some observed data and the ionospheric model, I study the temporal and spatial variations of the ionosphere during solar flares and eclipses, and investigate the influences of solar activity, solar zenith angle, neutral gas density, and magnetic dip angle on the ionospheric responses to solar flares and solar eclipses. The main points of my works and results are summarized as follows. 1. The ionospheric response to the X17.2 solar flare on October 28, 2003 was modeled via using a one-dimension theoretical ionospheric model. The simulated variation of TEC is in accordance with the observations, though there are some differences in the amplitude of the variation. Then I carried out a series of simulations to explore the local time and seasonal dependences of the ionospheric responses to solar flares. These calculations show that the ionospheric responses are largely related with the solar zenith angle (SZA). During the daytime (small SZA), most of the increases in electron density occur at altitudes below 300 km with a peak at around 115 km; whereas around sunrise and sunset (SZA>90°), the strongest ionospheric responses occur at much higher altitudes. The TEC increases slower at sunrise than at sunset, which is caused by the difference in the evolution of SZA at sunrise and sunset: SZA decreases with time at sunrise and increase with time at sunset. The ionospheric response is largest in summer and smallest in winter, which is also related to the seasonal difference of SZA. 2. Based on the observations from the ionosondes in Europe and the ionospheric model, I investigated the differences of the ionosphere responses to solar eclipses between the E-layer and F1-layer. Both the observation and simulation show that the decrease in foF1 due to the solar eclipses is larger than that in foE. This effect is due to that the F1 region locates at the transition height between the atomic ion layer and the molecular ion layer. With the revised model of solar radiation during solar flares, our model calculates the radiations from both the inside and outside of photosphere. Large discrepancy can be found between the observations and the calculations with an unrevised model, while the calculations with the revised model consist with the observations. 3. I also explore the effects of the F2-layer height, local time, solar cycle, and magnetic dip angle on the ionospheric responses to solar eclipses via using an ionospheric model and study on the solar zenith angle and the dip dependences by analyzing the data derived from 23 ionosonde stations during seven eclipse events. Both the measured and simulated results show that these factors have significant effect on the ionospheric response. The larger F2-layer height causes the smaller decrease in foF2, which is because that the electron density response decreases with height. The larger dip results in the smaller eclipse effect on the F2 layer, because the larger dip would cause the more diffusion from the top ionosphere which can make up for the plasma loss. The foF2 response is largest at midday and decreases with the increasing SZA. The foF2 response is larger at high solar activity than at low solar activity. The simulated results show that the local time and solar activity discrepancy of the eclipse effect mainly attribute to the difference of the background neutral gas density. 4. I carried out a statistical study on the latitudinal dependence of the ionospheric response to solar eclipses and modeled this latitudinal dependence by the ionospheric model. Both the observations and simulations show that the foF2 and TEC responses have the same latitudinal dependence: the eclipse effects on foF2 and TEC are smaller at low latitudes than at middle latitudes; at the middle latitudes (>40°), the eclipse effect decreases with increasing latitude. In addition, the simulated results show the change in electron temperature at the heights of above 300 km of low latitudes is much smaller than that at the same heights of middle latitudes. This is due to the smaller decrease in photoelectron production rate at its conjugate low heights. 5. By analyzing the observed data during the October 3, 2005 solar eclipse, I find some significant disturbances in the conjugate region of the eclipse region, including a decrease in Te, an increase in foF2 and TEC, and an uprising in hmF2. I also simulated the ionosphere behavior during this eclipse using a mid-low latitude ionospheric model. The simulations reproduce the measured ionospheric disturbances mentioned above in the conjugated hemisphere. The simulations show that the great loss of arriving photoelectron heat from the eclipse region is the principal driving source for the disturbances in the conjugate hemisphere.

地震P-S波时差耦合作用的斜坡崩滑效应研究

China locates between the circum-Pacific and the Mediterranean-Himalayan seismic belt. The seismic activities in our country are very frequent and so are the collapses and slides of slope triggered by earthquakes. Many collapses and slides of slope take place mainly in the west of China with many earthquakes and mountains, especially in Sichuan and Yunnan Provinces. When a strong earthquake happening, the damage especially in mountains area caused by geological hazards it triggered such as rock collapses, landslides and debris flows is heavier than that it caused directly. A conclusion which the number of lives lost caused by geological hazards triggered by a strong earthquake in mountains area often accounts for a half even more of the total one induced by the strong earthquake can be made by consulting the statistical loss of several representative earthquakes. As a result, geological hazards such as collapses and slides of slope triggered by strong earthquakes attract wide attention for their great costs. Based on field geological investigation, engineering geological exploration and material data analysis, chief conclusions have been drawn after systematic research on formation mechanism, key inducing factors, dynamic characteristics of geological hazards such as collapses and slides of slope triggered by strong earthquakes by means of engineering geomechanics comprehensive analysis, finite difference numerical simulation test, in-lab dynamic triaxial shear test of rock, discrete element numerical simulation. Based on research on a great number of collapses and landslides triggered by Wenchuan and Xiaonanhai Earthquake, two-set methods, i.e. the method for original topography recovering based on factors such as lithology and elevation comparing and the method for reconstructing collapsing and sliding process of slope based on characteristics of seism tectonic zone, structural fissure, diameter spatial distribution of slope debris mass, propagation direction and mechanical property of seismic wave, have been gotten. What is more, types, formation mechanism and dynamic characteristics of collapses and slides of slope induced by strong earthquakes are discussed comprehensively. Firstly, collapsed and slided accumulative mass is in a state of heavily even more broken. Secondly, dynamic process of slope collapsing and sliding consists of almost four stages, i.e. broken, thrown, crushed and river blocked. Thirdly, classified according to failure forms, there are usually four types which are made up of collapsing, land sliding, land sliding-debris flowing and vibrating liquefaction. Finally, as for key inducing factors in slope collapsing and sliding, they often include characteristics of seism tectonic belts, structure and construction of rock mass, terrain and physiognomy, weathering degree of rock mass and mechanical functions of seismic waves. Based on microscopic study on initial fracturing of slope caused by seismic effect, combined with two change trends which include ratio of vertical vs. horizontal peak ground acceleration corresponding to epicentral distance and enlarging effect of peak ground acceleration along slope, key inducing factor of initial slope fracturing in various area with different epicentral distance is obtained. In near-field area, i.e. epicentral distance being less than 30 km, tensile strength of rock mass is a key intrinsic factor inducing initial fracturing of slope undergoing seismic effect whereas shear strength of rock mass is the one when epicentral distance is more than 30 km. In the latter circumstance, research by means of finite difference numerical simulation test and in-lab dynamic triaxial shear test of rock shows that initial fracture begins always in the place of slope shoulder. The fact that fracture strain and shear strength which are proportional to buried depth of rock mass in the place of slope shoulder are less than other place and peak ground acceleration is enlarged in the place causes prior failure at slope shoulder. Key extrinsic factors inducing dynamic fracture of slope at different distances to epicenter have been obtained through discrete element numerical simulation on the total process of collapsing and sliding of slope triggered by Wenchuan Earthquake. Research shows that combined action of P and S seismic waves is the key factor inducing collapsing and sliding of slope at a distance less than 64 km to initial epicenter along earthquake-triggering structure. What is more, vertical tensile action of P seismic wave plays a leading role near epicenter, whereas vertical shear action of S seismic wave plays a leading role gradually with epicentral distance increasing in this range. On the other hand, single action of P seismic wave becomes the key factor inducing collapsing and sliding of slope at a distance between 64 km and 216 km to initial epicenter. Horizontal tensile action of P seismic wave becomes the key factor gradually from combined action between vertical and horizontal tensile action of P seismic wave with epicentral distance increasing in this distance range. In addition, initial failure triggered by strong earthquakes begins almost in the place of slope shoulder. However, initial failure beginning from toe of slope relates probably with gradient and rock occurrence. Finally, starting time of initial failure in slope increases usually with epicentral distance. It is perhaps that the starting time increasing is a result of attenuating of seismic wave from epicenter along earthquake-triggering structure. It is of great theoretical and practical significance for us to construct towns and infrastructure in fragile geological environment along seism tectonic belts and conduct risk management on earthquake-triggered geological hazards by referring to above conclusions.

电离层垂直TEC映射函数的实验观测与统计特性

When used in the determining the total electron content (TEC), which may be the most important ionospheric parameter, the worldwide GPS observation brings a revolutionary change in the ionospheric science. There are three steps in the data processing to retrieve GPS TEC: (1) to estimate slant TEC from the measurements of GPS signals; (2) to map the slant TEC into vertical; and (3) to interpolate the vertical TEC into grid points. In this scientific dissertation we focus our attention on the second step, the mapping theory and method to convert slant TEC into vertical. This is conventionally done by multiplying on the slant TEC a mapping function which is usually determined by certain models of electron density profile. Study of the vertical TEC mapping function is of significance in GPS TEC measurement. This paper first reviews briefly the three steps in GPS TEC mapping process. Then we compare the vertical TEC mapping function which were respectively calculated from the electron density profiles of the ionospheric model and retrieved from the observation of worldwide GPS TEC. We also perform the statistical analysis on the observational mapping functions. The main works and results are as follows: 1. We calculated the vertical TEC mapping functions for both SLM and Chapman models, and discussed the modulation of the ionosphere height to the mapping functions. We use two simple models, single layer model (SLM) and Chapman models, of the ionospheric electron density profiles to calculate the vertical TEC mapping function. In the case of the SLM, we discuss the control of the ionospheric altitude, i.e., the layer height hipp, to the mapping function. We find that the mapping function decreases rapidly as hipp increases. For the Chapman model we study also the control mapping function by both ionospheric altitude indicated by the peak electron density height hmF2, and the scale height, H, which present the thickness of the ionosphere. It is also found that the mapping function decreases rapidly as hmF2 increases. and it also decreases as H increases. 2. Then we estimate the mapping functions from the GPS observations and compare them with those calculated from the electron density models. We first, proposed a new method to estimate the mapping functions from GPS TEC data. This method is then used to retrieve the observational mapping function from both the slant TEC (TECS) provided by International GPS Service (IGS）and vertical TEC provide by JPL Global Ionospheric Maps (GIMs). Then we compare the observational mapping function with those calculated from the electron density models, SLM and Chapman. We find that the values of the observational mapping functions are much smaller than that from the model mapping functions, when the zenith angle is large enough. We attribute this to the effect of the plasmasphere which is above about 1000 km. 3. We statistically analyze the observational mapping functions and reveal their climatological changes. Observational mapping functions during 1999-2007 are used in our statistics. The main results are as follows. (1) The observational mapping functions decrease obviously with the decrement of the solar activity which is represented by the F10.7 index; (2) In annual variations of the observational mapping functions, the semiannual component is found at low-latitudes, and the remarkable seasonal variations at mid- and high-latitudes. (3) The diurnal variation of the observational mapping functions is that they are large in daytime and small at night, they become extremely small in the early morning before sunrise. (4) The observational mapping functions change with latitudes that they are smaller at lower latitudes and larger at higher. All of the above variations of the observational mapping functions are explained by the existence of the plasmasphere, which changes more slowly with time and more rapidly with latitude than the ionosphere does . In summary, our study on the vertical TEC mapping function imply that the ionosphere height has a modulative effect on the mapping function. We first propose the concept of the 'observational mapping functions' , and provide a new method to calculate them. This is important in improving the TEC mapping. It may also possible to retrieving the plasmaspheric information from GPS observations.

内蒙古草地植被群落生物量的梯度特征研究

Relationship between biology and environment is always the theme of ecology. Transect is becoming one of the important methods in studies on relationship between global change and terrestrial ecosystems, especially for analysis of its driving factors. Inner Mongolia Grassland is the most important in China Grassland Transect brought forward by Yu GR. In this study, changes in grassland community biomass along gradients of weather conditions in Inner Mongolia was researched by the method of transect. Methods of regression about biomass were also compared. The transect was set from Eerguna county to Alashan county (38° 07' 35" ~50° 12' 20" N, 101° 55' 25" -120° 20' 46" E) in Inner Mongolia, China. The sample sites were mainly chosen along the gradient of grassland type, meadow steppe-* typical steppe-*desert steppe-*steppification desert-^desert. The study was carried out when grassland community biomass got the peak in August or September, 2003 and 2004. And data of 49 sample sites was gotten, which included biomass, mean annual temperature, annual precipitation, accumulated temperature above zero, annual hours of sunshine and other statistical and descriptive data. The aboveground biomass was harvested, and the belowground biomass was obtained by coring (30 cm deep). Then all the biomass samples were dried within (80 + 5) °C in oven and weighted. The conclusion is as follows: 1) From the northeast to the southwest in Inner Mongolia, along the gradient of grassland type, meadow steppe-*typical steppe-*desert steppe-*steppification desert-* desert, the cover degree of vegetation community reduces. 2) By unitary regression analysis, biomass is negatively correlated with mean annual temperature, s^CTC accumulated temperature, ^10°C accumulated temperature and annual hours of sunshine, among which mean annual temperature is crucial, and positively with mean annual precipitation and mean annual relative humidity, and the correlation coefficient between biomass and mean annual relative humidity is higher. Altitude doesn't act on it evidently. Result of multiple regression analysis indicates that as the primary restrictive factor, precipitation affects biomass through complicated way on large scale, and its impaction is certainly important. Along the gradient of grassland type, total biomass reduces. The proportion of aboveground biomass to total biomass reduces and then increases after desert steppe. The trend of below ground biomass's proportion to total biomass is adverse to that of aboveground biomass. 3) Precipitation is not always the only driving factor along the transect for below-/aboveground biomass ratio of different vegetation type composed by different species, and distribution of temperature and precipitation is more important, which is much different among climatic regions, so that the trend of below-/aboveground biomass ratio along the grassland transect may change much through the circumscription of semiarid region and arid region. 4) Among reproductive allocation of aboveground biomass, only the proportion of stem in total biomass notably correlates to the given parameters. Stem/leaf biomass ratio decreases when longitude and latitude increase, caloric variables decrease, and variables about water increase from desert to meadow steppe. The change trends are good modeled by logarithm or binomial equations. 5) 0'-10 cm belowground biomass highly correlates to environmental parameters, whose proportion to total biomass changes most distinctly and increases along the gradient from the west to the east. The deeper belowground biomass responses to the environmental change on the adverse trend but not so sensitively as the surface layer. Because the change value of 0~10 cm belowground biomass is always more than that of below 10 cm along the gradient, the deference between them is balanced by aboveground biomass's change by the resource allocation equilibrium hypothesis.

Peak identification for PCDD/Fs in environmental samples at different temperature programs

A method has been developed for peak recognition of 136 polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at different temperature programs. Their retention behaviours are predicted on the basis of an identification database of retention values (A, B) of gas chromatography. By the retention times of C-13 labelled 2,3,7,8-substituted PCDD/F internal standards, the retentions of all PCDDs and PCDFs can be calculated. After comparison with the retentions of practical environmental samples, the predicted values have been proved to be very accurate. (C) 2000 Elsevier Science Ltd. All rights reserved.

Computer-assisted automatic peak recognition and result evaluation for analysis of chlorinated hydrocarbons in environmental samples

A data manipulation method has been developed for automatic peak recognition and result evaluation in the analysis of organic chlorinated hydrocarbons with dual-column gas chromatography. Based on the retention times of two internal standards, pentachlorotoluene and decachlorobiphenyl, the retention times of chlorinated hydrocarbons can be calibrated automatically and accurately. It is very convenient to identify the peaks by comparing the retention times of samples with the calibrated retention times calculated from the relative retention indices of standards. Meanwhile, with a suggested two-step evaluation method the evaluation coefficients and the suitable quantitative results of each component can be automatically achieved for practical samples in an analytical system using two columns with different polarities and two internal standards. (C) 2002 Elsevier Science B.V. All rights reserved.

认知电位时空模式研究

This report mainly focused on methodology of spatiotemporal patterns (STP) of cognitive potentials or event-related potentials (ERP). The representation of STP of brain wave is an important issue in the research of neural assemblies. This paper described methods of parametric 3D head or brain modeling and its corresponding interpolation for functional imaging based on brain waves. The 3D interpolation method is an extension of cortical imaging technique. It can be used with transformed domain features of brain wave on realistic head or brain models. The simulating results suggests that it is a better method in comparison with the global nearest neighbor technique. A stable and definite STP of brainwave referred as microstate may become basic element for comprehending sophisticated cognitive processes. Fuzzy c-mean algorithm was applied to segmentation STPs of ERP into microstates and corresponding membership functions. The optimal microstate number was estimated with both the trends of objective function against increasing clustering number and the decorrelation technique base don microstate shape similarity. Comparable spatial patterns may occur at different moments in time with fuzzy indices and thus the serial processing limit generated from behavioral methods has been break through. High-resolution frequency domain analysis was carried out with multivariate autoregressive model. Bases on a 3D interpolation mentioned above, visualization of dynamical coordination of cerebral network was realized with magnitude-squared partial coherence. Those technique illustrated with multichannel ERP of 9 subjects when they undertook Strop task. Stroop effects involves several regions during post-perception stage with technique of statistical parameter mapping based F-test [SPM(F)]. As SPM(F) suggested task effects occurred within 100 ms after stimuli presentation involved several sensory regions, it may reflect the top-down processing effect.

Improved performance of comprehensive two-dimensional HPLC separation of traditional Chinese medicines by using a silica monolithic column and normalization of peak heights

Performance of comprehensive two-dimensional liquid chromatography system is greatly improved than we reported previously by using a silica monolithic column as for the second dimensional separation. Due to the increase of the elution speed on the second dimensional monolithic column, the first dimensional column efficiency and analysis rate can be greatly improved as comparing with conventionally second dimensional column. The developed system was applied to analysis of methanol extraction of two umbelliferae herbs Ligusticum chuanxiong Hort. and Angelica sinensis (Oliv.) Diels by using CN column as for the first dimensional separation and a silica monolithic ODS column for the second dimensional separation, and the obtained three-dimensional chromatograms were treated by normalization of peak heights with the value of the highest peak or setting a certain value using a software written in-house. It was observed that much more peaks for low-abundant components in TCM extract can clearly be detected here than we reported before, due to the large difference for the amount of components in TCMs' extract. With the above improvements in separation performance and data treatment, totally about 120 components in methanol extraction of Rhizoma chuanxiong and 100 in A. sinensis were separated with UV detection within 130 min. This result meant that both the number of peaks detected increase twice but the analysis time decease twice if comparing with the previously reported result. (c) 2005 Published by Elsevier B.V.