不同比例尺DEM提取地面坡度的精度研究——以在黄土丘陵沟壑区的试验为例

以陕北绥德县韭园沟流域为试验样区 ,采用高精度 1∶ 1万 DEM所提取的坡度为准值 ,应用多层面复合分析和比较分析的方法 ,研究该地区 1∶ 5万 DEM提取地面坡度的误差特征与纠正方法。试验结果显示 ,所获得的不同空间尺度下 DEM所提取坡度值的转换图谱 ,可对 1∶ 5万 DEM计算的地面坡度统计值进行有效修正。该成果对于 DEM数据在水土保持领域若干应用标准的制定 ,提供了重要的理论依据与技术路线

L1-Norm-Based 2DPCA

In this paper, we first present a simple but effective L1-norm-based two-dimensional principal component analysis (2DPCA). Traditional L2-norm-based least squares criterion is sensitive to outliers, while the newly proposed L1-norm 2DPCA is robust. Experimental results demonstrate its advantages.

Quantifying intrinsic specificity: A potential complement to affinity in drug screening

We report here the investigation of a novel description of specificity in protein-ligand binding based on energy landscape theory. We define a new term, intrinsic specificity ratio (ISR), which describes the level of discrimination in binding free energies of the native basin for a protein-ligand complex from the weaker binding states of the same ligand. We discuss the relationship between the intrinsic specificity we defined here and the conventional definition of specificity. In a docking study of molecules with the enzyme COX-2, we demonstrate a statistical correspondence between ISR value and geometrical shapes of the small molecules binding to COX-2. We further observe that the known selective (nonselective) inhibitors of COX-2 have higher (lower) ISR values. We suggest that intrinsic specificity ratio may be a useful new criterion and a complement to affinity in drug screening and in searching for potential drug lead compounds.

Optimal specificity and function for flexible biomolecular recognition

Biomolecular associations often accompanied by large conformational changes, sometimes folding and unfolding. By exploring an exactly solvable model, we constructed the free energy landscape and established a general framework for studying the biomolecular flexible binding process. We derived an optimal criterion for the specificity and function for flexible biomolecular binding where the binding and conformational folding are coupled.

Optimal specificity and function for flexible biomolecular recognition

Biomolecular associations often accompanied by large conformational changes, sometimes folding and unfolding. By exploring an exactly solvable model, we constructed the free energy landscape and established a general framework for studying the biomolecular flexible binding process. We derived an optimal criterion for the specificity and function for flexible biomolecular binding where the binding and conformational folding are coupled.

Quantifying robustness and dissipation cost of yeast cell cycle network: The funneled energy landscape perspectives

We study the origin of robustness of yeast cell cycle cellular network through uncovering its underlying energy landscape. This is realized from the information of the steady-state probabilities by solving a discrete set of kinetic master equations for the network. We discovered that the potential landscape of yeast cell cycle network is funneled toward the global minimum, G1 state. The ratio of the energy gap between G1 and average versus roughness of the landscape termed as robustness ratio ( RR) becomes a quantitative measure of the robustness and stability for the network. The funneled landscape is quite robust against random perturbations from the inherent wiring or connections of the network. There exists a global phase transition between the more sensitive response or less self-degradation phase leading to underlying funneled global landscape with large RR, and insensitive response or more self-degradation phase leading to shallower underlying landscape of the network with small RR. Furthermore, we show that the more robust landscape also leads to less dissipation cost of the network. Least dissipation and robust landscape might be a realization of Darwinian principle of natural selection at cellular network level. It may provide an optimal criterion for network wiring connections and design.

Funneled landscape leads to robustness of cellular networks: MAPK signal transduction

We uncover the underlying potential energy landscape for a cellular network. We find that the potential energy landscape of the mitogen-activated protein-kinase signal transduction network is funneled toward the global minimum. The funneled landscape is quite robust against random perturbations. This naturally explains robustness from a physical point of view. The ratio of slope versus roughness of the landscape becomes a quantitative measure of robustness of the network. Funneled landscape is a realization of the Darwinian principle of natural selection at the cellular network level. It provides an optimal criterion for network connections and design. Our approach is general and can be applied to other cellular networks.

Independence of the brittle-ductile transition from the rubber particle size for impact-modified poly(vinyl chloride)

A series of acrylic impact modifiers (AIMS) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle-ductile transition of impact-modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 degrees C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle-ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2-341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle-ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle-ductile transition for the PVC/AIM blends.

Temperature dependence of the distribution of the first passage time: Results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Go-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T-opt*. The optimal folding temperature T-opt* is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T-opt* and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T-opt* and start to diverge when the temperature is lower than T-opt*. The distribution of FPT is close to a log-normal-like distribution at T* greater than or equal to T-opt*. At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.

A double logarithmic method for studying the adsorption effects in an irreversible electrochemical process

The adsorption of an electroinactive product greatly influences an irreversible electrochemical reaction in three ways, including self-block, self-inhibition, and self-acceleration, and changes not only the heterogeneous electron-transfer rate constant but also the modified formal potential and electron-transfer coefficient of the electrochemical reaction. In order to study these adsorption effects, a double logarithmic method was suggested to be used in processing the potential-controlled thin layer spectroelectrochemical data. The result shows three types of double logarithmic plots for three kinds of adsorption effects. These double logarithmic plots can be a diagnostic criterion of the adsorption effects and enable us to determine some thermodynamic and kinetic parameters. The combination of nonlinear regression with double logarithmic method is a convenient way to examine the suggested mechanism and to extract more information from the limited experimental data. Some examples are given to test the theoretical results. (C) 1999 The Electrochemical Society. S0013-4651(98)05-012-5. All rights reserved.

Controlling factors for the occurrence of heteroepitaxy of polyethylene on highly oriented isotactic polypropylene

The controlling factors for the epitaxial crystallization of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) substrates have been studied in detail by means of transmission electron microscopy and electron diffraction. The results obtained in this work indicate that the crystallization process must be considered in the investigation of epitaxial growth of polymers on polymeric substrates, because of the unique morphological and crystallization characteristics of polymers. Crystallization rate has an important effect on the epitaxial crystallization of polymers. Higher rates result in the formation of thicker epitaxial layers. Isothermal crystallization temperature is another factor affecting epitaxial growth of polymers. Lower temperatures are favorable to epitaxial crystallization of polymers. There exists a critical epitaxial temperature at given experimental conditions, above which no epitaxial growth occurs at all. The influence of crystal dimensions of both the substrates and the deposited polymers on epitaxial growth confirms that secondary nucleation is an important controlling factor for the occurrence of epitaxial crystallization in polymers. The requirement satisfying the secondary nucleation criterion is that the substrate crystal dimension in the matching direction must be greater than the crystal thickness of the deposited polymer. Once the requirement of the secondary nucleation is satisfied, subsequent epitaxial growth is based on the lamellar growth habit of the deposited polymer itself. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone). V: Estimation of temperature distribution during cure process

A numerical method to estimate temperature distribution during the cure of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based composite is suggested. The effect of the temperature distribution on the selection of cure cycle is evaluated using a suggested alternation criterion. The effect of varying heating rate and thickness on the temperature distribution, viscosity distribution and distribution of the extent of cure reaction are discussed based on the combination of the here-established temperature distribution model and the previously established curing kinetics model and chemorheological model. It is found that, for a thin composite (<=10mm) and low heating rate (<=2.5K/min), the effect of temperature distribution on cure cycle and on the processing window for pressure application can be neglected. Low heating rate is of benefit to reduce the temperature gradient. The processing window for pressure application becomes narrower with increasing thicknesses of composite sheets. The validity of the temperature distribution model and the modified processing window is evaluated through the characterization of mechanical and physical properties of E-PEK-based composite fabricated according to different temperature distribution conditions.

Toughening mechanism of polymer blends: Influence of voiding ability of dispersed-phase particles

The parameters which effect the cavitation strain of polymer blends toughened with a shear yield mechanism have been studied by analysis of the stress acted on the equatorial plane of dispersed-phase particles. As a result, the cavitation strain of polymer blends depends on the Young's modulus and the Poisson's ratio of the dispersed-phase particles and the matrix and also on the break stress of dispersed-phase particles. We tried to provide a criterion for selecting the materials used as dispersed-phase particles which can effectively enhance the toughness of polymer blends. (C) 1996 John Wiley & Sons, Inc.

KALMAN FILTERING FOR RESOLUTION OF OVERLAPPING LINES IN INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION-SPECTROMETRY

A Kalman filter was developed for resolving overlapping lines in inductively coupled plasma atomic emission spectrometry (ICP-AES) and evaluated experimentally with the determination of La in the presence of Ho, and Cu in the presence of Pr. The whiteness of the innovation sequence for an optimal filter was explored to be the criterion for the correction of the wavelength positioning errors which may occur in spectral scans. Under the conditions of the medium-resolution spectrometer and 1.5 pm step size in scans, the filter effectively resolved the Cu/Pr line pair having a small peak separation of 4.8 pm. For the La/Ho line pair with a peak distance of 9.8 pm, an unbiased estimate for La concentration was still obtained even when the signal-to-background ratio was down to 0.048. Favourable detection limits for real samples were achieved. Unstructured backgrounds were modeled theoretically and all spectral scans therefore did not require the correction for solvent.

EVALUATION OF THE RELIABILITY OF KALMAN FILTERING RESULTS IN INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION-SPECTROMETRY

This paper deals with the evaluation of the reliability of the analytical results obtained by Kalman filtering. Two criteria for evaluation were compared: one is based on the autocorrelation analysis of the innovation sequence, the so-called NAC criterion; the other is the innovations number, which actually is the autocorrelation coefficient of the innovation sequence at the initial wavelength. Both criteria allow compensation for the wavelength positioning errors in spectral scans, but there exists a difference in the way they work. The NAC criterion can provide information about the reliability of an individual result, which is very useful for the indication of unmodelled emissions, while the innovations number should be incorporated with the normalization of the innovations or seek the help of the sequence itself for the same purpose. The major limitation of the NAC criterion is that it does not allow the theoretical modelling of continuous backgrounds, which, however, is convenient in practical analysis and can be taken with the innovations number criterion.