首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
This work evaluates objective functions for multiresponse non-linear modeling using computersimulations.Tests are performed under a variety of signal-to-noise ratios and noise variance-covariancestructures.The standard error of prediction for the model parameters,computed from 50 trials,is usedfor performance comparisons.The full rank and rank-deficient problems are considered.For the fullrank problem one model was investigated,a first-order two-step consecutive reaction model,and twoobjective functions were considered,the total sum of squares and the determinant criterion.Nodistinction could be made between the two objective functions for this model.For the rank-deficient case two models were investigated,a first-order two-step consecutive reactionas in the full rank case,and a pH titration model described by the Henderson-Hasselbalch equation.Three objective functions were investigated for the rank-deficient case,the total sum of squares,aweighted total sum of squares and the determinant criterion.The total sum of squares was found toperform poorly under all conditions tested compared to the weighted total sum of squares and thedeterminant criterion.The determinant criterion was found to perform much better than the other twocriteria when the data have a combination of a low signal-to-noise ratio and high variance-covariancenoise structure.  相似文献   

2.
A program for the potentiometric determination of the protonation constants of mononuclear polyproticsubstances is described.A maximum of twelve parameters can be determined simultaneously,includingup to six protonation constants,four electrode calibration parameters,the protolysis constant of thesolvent and the titrant concentration.Optimization is carried out by using the non-simplifiedNewton-Raphson method,which is potentiated by the Marquardt algorithm and a distance speeding-upcoefficient.A direct search method is also used to improve the initial set of values.Variances arecalculated very accurately,since the real Hessian function is used.Statistical weights and ionic strengthcorrections are also considered,The program has been tested by using simulated titration curves ofpolyprotic acids with close constants.  相似文献   

3.
  相似文献   

4.
A new regression method for non-linear near-infrared spectroscopic data is proposed.The technique isbased on a model which is linear in the principal components and simple functions(squares and products)of them.Added variable plots are used to determine which squares and products to incorporate into themodel.The regression coefficients are estimated by a Stein estimate which shrinks towards the estimatedetermined by the first several principal components and the selected non-linear terms.The technique isnot computationally intensive and is appropriate for routine predictions of chemical concentrations.Themethod is tested on three data sets and in all cases gives more accurate predictions than does linearprincipal components regression.  相似文献   

5.
?ngstr?m-Prescott equation (AP) is the algorithm recommended by the Food and Agriculture Organization (FAO) of the United Nations for calculating the surface solar radiation (R_s) to support the estimation of crop evapotranspiration.Thus,the a_s and b_s coefficients in the AP are vital.This study aims to obtain coefficients a_s and b_s in the AP,which are optimized for China’s comprehensive agricultural divisions.The average monthly solar radiation and relative sunshine duration data at 121 stations from 1957–2016 were collected.Using data from 1957 to 2010,we calculated the monthly a_s and b_s coefficients for each subregion by least-squares regression.Then,taking the observation values of R_s from 2011 to 2016 as the true values,we estimated and compared the relative accuracy of R_s calculated using the regression values of coefficients a_s and b_s and that calculated with the FAO recommended coefficients.The monthly coefficients,a_s and b_s,of each subregion are significantly different,both temporally and spatially,from the FAO recommended coefficients.The relative error range (0–54%) of R_s calculated via the regression values of the a_s and b_s coefficients is better than the relative error range (0–77%) of R_s calculated using the FAO suggested coefficients.The station-mean relative error was reduced by 1%to 6%.However,the regression values of the a_s and b_s coefficients performed worse in certain months and agricultural subregions during verification.Therefore,we selected the a_s and b_s coefficients with the minimum R_(s )estimation error as the final coefficients and constructed a coefficient recommendation table for 36 agricultural production and management subregions in China.These coefficient recommendations enrich the case study of coefficient calibration for the AP in China and can improve the accuracy of calculating R_s and crop evapotranspiration based on existing data.  相似文献   

6.
Based on the daily precipitation data of 27 meteorological stations from 1960 to 2009 in the Huaihe River Basin, spatio-temporal trend and statistical distribution of extreme precipitation events in this area are analyzed. Annual maximum series (AM) and peak over threshold series (POT) are selected to simulate the probability distribution of extreme precipitation. The results show that positive trend of annual maximum precipitation is detected at most of used stations, only a small number of stations are found to depict a negative trend during the past five decades, and none of the positive or negative trend is significant. The maximum precipitation event almost occurred in the flooding period during the 1960s and 1970s. By the L-moments method, the parameters of three extreme distributions, i.e., Generalized extreme value distribution (GEV), Generalized Pareto distribution (GP) and Gamma distribution are estimated. From the results of goodness of fit test and Kolmogorov-Smirnov (K-S) test, AM series can be better fitted by GEV model and POT series can be better fitted by GP model. By the comparison of the precipitation amounts under different return levels, it can be found that the values obtained from POT series are a little larger than the values from AM series, and they can better simulate the observed values in the Huaihe River Basin.  相似文献   

7.
A simple algorithm for deconvolution and regression of shot-noise-limited data is illustrated in this paper.The algorithm is easily adapted to almost any model and converges to the global optimum.Multiple-component spectrum regression,spectrum deconvolution and smoothing examples are used to illustratethe algorithm.The algorithm and a method for determining uncertainties in the parameters based on theFisher information matrix are given and illustrated with three examples.An experimental example ofspectrograph grating order compensation of a diode array solar spectroradiometer is given to illustratethe use of this technique in environmental analysis.The major advantages of the EM algorithm are foundto be its stability,simplicity,conservation of data magnitude and guaranteed convergence.  相似文献   

8.
A TEST OF SIGNIFICANCE FOR PARTIAL LEAST SQUARES REGRESSION   总被引：1，自引：0，他引：1  
Partial least squares (PLS) regression is a commonly used statistical technique for performingmultivariate calibration, especially in situations where there are more variables than samples. Choosingthe number of factors to include in a model is a decision that all users of PLS must make, but iscomplicated by the large number of empirical tests available. In most instances predictive ability is themost desired property of a PLS model and so interest has centred on making this choice based on aninternal validation process. A popular approach is the calculation of a cross-validated r~2 to gauge howmuch variance in the dependent variable can be explained from leave-one-out predictions. Using MonteCarlo simulations for different sizes of data set, the influence of chance effects on the cross-validationprocess is investigated. The results are presented as tables of critical values which are compared againstthe values of cross-validated r~2 obtained from the user's own data set. This gives a formal test forpredictive ability of a PLS model with a given number of dimensions.  相似文献   

9.
Nowadays, Southwestern Romania faces a large-scale aridization of the climate, revealed by the rise of temperatures and the decline of the amount of precipitations, with negative effects visible, among others, in the desiccation of forest vegetation. The present study means to identify the changes that occurred, quality-wise, in the past two decades(1990–2011) in forest vegetation in Southwestern Romania, and to establish the link between those changes and extant thermal stress in the region, whose particular features are high average annual and seasonal temperatures. In order to capture the evolution in time of climate aridization, a first step consisted in using climate data, the temperature and precipitation parameters from three weather stations; these parameters were analyzed both individually and as aridity indexes(De Martonne and UNEP). In order to quantify the changes in forest vegetation, NDVI indexes were used and analyzed, starting off from Landsat satellite images, acquired at three distinct moments in time, 1990, 2000 and 2011. In order to identify the link between the changes of NDVI index values and regional thermal stress, a yardstick of climate changes, statistical correlations were established between the peak values of average annual temperatures, represented in space, and negative changes in the NDVI index, as revealed by the change-detection analysis. The results obtained indicated there is an obvious(statistically significant) connection between thermal stress and the desiccation(degradation) of forest species in the analyzed area, with false acacia(Robinia Pseudoacacia) the main species to be impacted.  相似文献   

10.
The methods PARAFAC and three-way PLS are compared with respect to their ability to predictreversed-phase retention values.Special attention is paid to simple validatory tools,the meaning and useof which are explained.The simple validatory tools consist of percentages of explained variation in the training set and thosethat can be calculated with the use of markers.These markers are special(reference)solutes,the retentionvalues of which are used to gain information about a new object for which predictions are wanted.Different validatory tools can be calculated with the use of these marker retention values:percentagesof used variation and mean sum of squared residuals after applying the model to these marker retentionvalues.The validatory tools are evaluated on their power to estimate their test set counterparts:thepercentages of explained variation in the test set and mean sum of squared prediction errors in the test set.Two different data sets from reversed-phase chromatography are used to evaluate the validatory tools.The first data set has a high signal-to-noise ratio and is measured under the same measurementconditions.The second data set has a low signal-to-noise ratio and is measured under differentmeasurement conditions.Some of the simple validatory tools seem to have relevance to their test setcounterparts,even in the case of the second data set.  相似文献   

11.
High-performance liquid chromatography with diode array detection(HPLC-DAD)is used tocharacterize mixtures from chlorophyll α degradation experiments.Overlapping chromatographic peaksare resolved by means of the heuristic evolving latent projections(HELP)method.The HELP methodis a self-modelling curve resolution method.No assumptions are made about spectral and/orchromatographic peak shape.In the first step the method establishes the real noise level in the data byuse of the so-called zero-component regions.This information is used to reveal selective chromatographicinformation and the number of chemical species at every retention time in unresolved chromatographicpeaks.Utilising the selective chromatographic regions in combination with the zero-concentrationwindows,unique resolution into concentration profiles and spectra of the pure chemical species isaccomplished.HPLC-DAD data from six chlorophyll a degradation experiments were analysed.Consistent results were obtained even with very similar spectra for six or seven overlapping chemicalcomponents.  相似文献   

12.
A method is presented by which it is possible to estimate the initial rate of chemical reactions when theexperimental conditions are varied according to a response surface design.The method is intended as acomplementary method for analysing data obtained from experiments in synthetic chemistry when theobjective is to optimize the yield of the reaction.Data obtained by simulations have been used to develop the method.From the simulated reactions itis shown that sequential analysis of the chemical yield of the reaction makes it possible to estimate modelswhich describe how the parameters of the response surface of the yield vary over time.The derivativesof these time functions of the response surface parameters can be used to define a rate function whichdescribes how the variations in the experimental conditions influence the rate of the reaction.It is shown how such rate functions can be used to afford reasonable estimates of the initial rates ofthe reaction.The initial reaction rates thus estimated can be used to determine the kinetic order of thereactants and also to provide estimates of the activation energy of the reaction.A thorough discussion of how canonical analysis of the rate function may assist in the elucidation ofreaction mechanisms is given.  相似文献   

13.
Palaeoflood hydrology study is a leading subject in global change study. Through field investigation in the upper reaches of Hanjiang River, palaeoflood slackwater deposits(SWD) were found in the bedrock gorges of the Yunxi reach. The results of field observation, laboratory analysis including particle-size distribution and magnetic susceptibility, and comparison with modern flood deposits, the SWD were identified as the most typical Holocene palaeoflood deposits of the Hanjiang River. By using stratigraphic correlation and OSL dating method, the palaeoflood event was dated to be 3200–2800 a BP at the turn from the middle to late Holocene. According to the palaeoflood peak stage and hydraulic parameters, the peak discharges of the palaeoflood were reconstructed as 48,830–51,710 m3/s by using the slope-area method. At same time, the flood peak discharges of 1983, 2005 and 2010 severe floods were reconstructed with the same method and hydraulic parameters in the same cross section. The error between the reconstructed and gauged discharges was 1.99%–4.21%. This showed that the reconstructed palaeoflood peak discharges were reliable. The flood peak discharge-frequency relationship at 10,000-year time scale was established by a combination of the gauged flood, historical flood and palaeoflood hydrological data. These results are very important for hydraulic engineering and flood mitigation on the Hanjiang River.  相似文献   

14.
Seasonal variation of stable isotopes in precipitation of Kathmandu Valley on the southern slope of Himalaya was carried out to understand the controlling mechanism of amount and temperature effect on the basis of one year stable isotope data from 2010 to 2011. Highly depleted isotope values in major rainy period are obtained just after the onset of precipitation in summer, which accounts for "amount effect" due to saturation isotopic compositions in high moisture condition, whereas, the higher values in winter are indicative to regional vapors (temperature effect) recycling of various sources. An abrupt depletion of isotope values in mid-June, indicates the onset date of monsoon precipitation, by the replacement of winter air mass with southern monsoon. Thus, precipitation isotopes are a tool revealing the onset date of summer monsoon and temporal features of variability, in local and regional monsoons precipitations. A comparison of long term monthly values of δ 18 O, temperature, and precipitation with GNIP δ 18 O data shows the temporal variations of stable isotopes are mostly controlled by amount and temperature effects. During summer monsoon, the amount effects are stronger for high values of precipitation (R=0.7) and altitude effect appears for low moisture in late rainy season, thus from December to June (winter to pre-monsoon) the controlling features of isotopes remains under the temperature effect. A temporal rate of temperature effect is derived as 0.04‰ per year which indicates a dry signal of atmospheric condition and a temperature relation δ 18 O=(0.371±0.08)T+(0.156±0.05) is obtained from this analysis. The meteoric water lines of Kathmandu before and after monsoon onset of 2011, are found as δD=(4.36±0.3)δ 18 O+(15.66±1.2) and δD=(6.91±0.2)δ 18 O (7.92±2.26) from lab samples result, and δD=9.2δ 18 O+11.725 and δD=8.53δ 18 O+16.65 from GNIP data, which lacks the consistency both for slopes and intercepts values for the study period. The mean lapse rate values of δ 18 O and δD from GNIP data are obtained as 0.002‰/m and 0.015 ‰/m, which indicate the altitudinal effects in regional precipitation of the southern slope of Himalayas. This study estimates new stable isotopes data in recent precipitation using simple methodology which can be important for regional precipitation monitoring systems, environmental change and paleo-climatic studies.  相似文献   

15.
It is shown that the presence of 31-35 commonly measured volatile organic compounds(VOCs)inground water can be detected with small error rates by using screening methods which analyze for a subsetof such VOCs.A study of selected data sets indicates that analytical determinations of only from twoto eight VOCs will suffice to detect 95% of all VOC hits.It is also shown that a serially optimal algorithmfor selecting the VOCs for screening is very nearly as accurate as a globally optimal algorithm and mucheasier to implement.These conclusions are supported by empirical evidence from two drinking-water datasets and one hazardous waste site data set.Additional research areas are also outlined.  相似文献   

16.
Crop potential productivity is a key index of scientifically appraising crop production and land population-supporting capacity. This study firstly simulated the potential and waterlimited yield of summer maize in the Beijing-Tianjin-Hebei (BTH) region using WOFOST model with meteorological data of 40 years, and then analyzed yield gaps between the actual and potential yield based on statistical data at county level. The potential and water-limited yield of summer maize in the BTH region is 6854–8789 kg/hm2 and 6434–8741 kg/hm2, and the weighted average for whole region is 7861 kg/hm2 and 7185 kg/hm2, respectively. The simulated yields gradually decrease from northeast to southwest with changes in climatic conditions particularly temperature and precipitation. Annual variation of potential yield is higher in the central and southern parts than the northeastern part. Compared to potential yield, the water-limited yield has higher coefficient of variation (CV), because of precipitation effects. The actual yield of summer maize was 2537–8730 kg/hm2, regionally averaged at 5582 kg/hm2, about 70% of the potential yield, implying that the region has room to increase the yield by improving crop management and irrigation systems.  相似文献   

17.
长江口拦门沙河段潮滩表层沉积物分布特征(英文)   总被引：2，自引：0，他引：2  
Sediment samples with high spatial resolution (432 samples in total) and flow data were collected on the tidal flats in the mouth-bar region of the Yangtze Estuary. The data was collected in July 2005, July 2006 and May 2007. The samples were analyzed with a particle sizer, resulting in the sediment distribution. The grain sizes and related parameters were analyzed. The results were presented in a ternary diagram. The sediment mainly consisted of sand, silty sand, sandy silt, sand-silt-clay, silt and clayey silt. And sand skeletons and clay matrices were found. At Nanhui Shoal, silt skeletons could be identified as well. Furthermore, the results were discussed per shoal. Although some depth dependencies were found per shoal, no general relation was found. The results are as follows: sediment located at these tidal flats of the Yangtze Estuary was mainly composed of sand, silty sand and silt. The median grain size in sediment was relatively complex with a range from 2.5 φ to 8 φ. The distributions of sorting coefficients ranging from 1 to 2 were in agreement with median sizes. It was suggested that sediment of the tidal flats was coarser and better sorted or finer and worse sorted. The skewness in sediment distribution varied from 0.1 to 0.8. In addition, the distributions of sorting coefficient and skewness in sediment at Chongming Eastern Shoal, Hengsha Eastern Shoal and Jiuduan Shoal were of similar characteristics because there were closely positive correlated relationships among these parameters. However, due to the location difference between Nanhui Southern Shoal and Eastern Shoal, the values of sorting coefficient and skewness had relatively large distinctions. The tracks of sediment transport could be described based on the distributions of sediment, which might reveal sediment transport controlled by two dominant hydrodynamic factors of current and wave. It was appreciable that coarser sediment with lower sorted coefficient was affected by dominant ebb current action and intense wave action resulted from rapidly dissipated wave energy. Moreover, due to the effects of obstructed branches, guided current and broken wave actions of the Deep Water Channel Project, grain-size in sediment located at two sides of the groyne was of uneven distribution characteristics.  相似文献   

18.
A multivariate statistical analysis was performed by combining metal and anion data found in particulatematter from the atmosphere of Sant Adrià de Besòs(Barcelona)with SO_2,total suspended particle andsmoke values as well as with some meteorological measurements.Factor analysis allowed us in a previous work to recognize some emissor sources(soil,traffic,NO_x-SO_2,fuel oil,sea,incineration)by means of the analysis of some metals and anions.In the presentwork some meteorological data(temperature,humidity and sunshine),the concentration of SO_2 andvalues of total suspended particles and smoke were introduced into the correlation matrix in order tostudy their contribution to the identification of emissor sources.It was found that a decrease in temperature is in accordance with an increase in the presence of tracersfrom traffic emissions;chloride and humidity have a close correlation:SO_2 and sulphates come from thesame source;and oxidation from NO_x and SO_2 to nitrate and sulphate is higher with a decrease in thepercentage of sunshine.  相似文献   

19.
Window factor analysis(WFA)is a self-modeling chemometric technique for obtaining the concentrationprofiles of components from evolutionary processes such as chromotography,titrations and reactionkinetics.By specifying the‘window’,i.e.the region along the evolutionary axis indigenous to acomponent,the concentration profile of the component can be obtained without recourse to anyinformation concerning the other components.Mathematical expressions required to perform suchcomputations are derived.The method is applied to the investigation of copper(Ⅱ)complexation withethylenediaminetetraacetate(EDTA)by recording and factor analyzing the ultraviolet spectra of aqueoussolutions containing a fixed amount of the disodium salt of EDTA and varying amounts of CuCl_2.Evidence for four different species of EDTA is obtained.Clues concerning the stoichiometry of thespecies are garnered from the concentration profiles.  相似文献   

20.
Data of the hydrolysis of adenosine 5'-triphosphate have been re-evaluated using a computer program thatnumerically integrates the differential rate equations within a routine that optimizes rate coefficients givena suitable model and concentration versus time data. The model is tested by calculation of Hamilton R-values, the Fisher F-statistic, a sensitivity analysis,the standard errors on the rate coefficients and by constructing contour maps of the objective functionversus two rate coefficients. An optimization using only phosphate concentration data cannot distinguish between a model in whichadenosine 5'-monophosphate is formed predominantly directly with a molecule of pyrophosphate, andone in which it is formed via adenosine 5'-diphosphate. A more accurate set of rate coefficients iscalculated from existing data and the relative importance of the two paths determined.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号