Evaluation of Taylor dispersion injections: determining kinetic/affinity interaction constants and diffusion coefficients in label-free biosensing

In label-free biomolecular interaction analysis, a standard injection provides an injection of uniform analyte concentration. An alternative approach exploiting Taylor dispersion produces a continuous analyte titration allowing a full analyte dose response to be recorded in a single injection. The enhanced biophysical characterization that is possible with this new technique is demonstrated using a commercially available surface plasmon resonance-based biosensor. A kinetic interaction model was fitted locally to Taylor dispersion curves for estimation of the analyte diffusion coefficient in addition to affinity/kinetic constants. Statistical confidence in the measured parameters from a single Taylor dispersion injection was comparable to that obtained for global analysis of multiple standard injections. The affinity constants for multisite interactions were resolved with acceptable confidence limits. Importantly, a single analyte injection could be treated as a high-resolution real-time affinity isotherm and was demonstrated using the complex two-site interaction of warfarin with human serum albumin. In all three model interactions tested, the kinetic/affinity constants compared favorably with those obtained from standard kinetic analysis and the estimates of analyte diffusion coefficients were in good agreement with the expected values.     

Modeling Taylor dispersion injections: determination of kinetic/affinity interaction constants and diffusion coefficients in label-free biosensing

A new method based on Taylor dispersion has been developed that enables an analyte gradient to be titrated over a ligand-coated surface for kinetic/affinity analysis of interactions from a minimal number of injections. Taylor dispersion injections generate concentration ranges in excess of four orders of magnitude and enable the analyte diffusion coefficient to be reliably estimated as a fitted parameter when fitting binding interaction models. A numerical model based on finite element analysis, Monte Carlo simulations, and statistical profiling were used to compare the Taylor dispersion method with standard fixed concentration injections in terms of parameter correlation, linearity of parameter error space, and global versus local model fitting. A dramatic decrease in parameter correlations was observed for TDi curves relative to curves from standard fixed concentration injections when surface saturation was achieved. In FCI the binding progress is recorded with respect to injection time, whereas in TDi the second time dependency encoded in the analyte gradient increases resolving power. This greatly lowers the dependence of all parameters on each other and on experimental interferences. When model parameters were fitted locally, the performance of TDis remained comparable to global model fitting, whereas fixed concentration binding response curves yielded unreliable parameter estimates.     

Matrix solid-phase dispersion as a valuable tool for extracting contaminants from foodstuffs

This review updates our knowledge on matrix solid-phase dispersion (MSPD), a sample treatment procedure that is increasingly used for extracting/purifying contaminants from a variety of solid, semi-solid, viscous, and liquid foodstuffs. MSPD is primarily used because of its flexibility, selectivity, and the possibility of performing extraction and cleanup in one step, this resulting in drastically shortening of the analysis time and low consumption of toxic and expensive solvents. Technical developments and parameters influencing the extraction yield and selectivity are examined and discussed. Experimental results for the analysis of pesticides, veterinary drugs, persistent environmental chemicals, naturally occurring toxicants, and surfactants in food are reviewed.     

麦秸秆/高密度聚乙烯（HDPE）复合材料中纤维分散性的描述模型

麦秸秆纤维作为一种重要生物质资源已被广泛应用于热塑性复合材料中。纤维在复合材料中的分散性是影响复合材料力学性能的重要因素之一,而目前对其定量化的描述和分析方法仍存在一定不足。本研究基于实验获得的纤维尺寸的统计分布规律,利用随机生成算法模拟纤维在复合材料中的分布;构建描述纤维分散性的指标:分散度,单个纤维数和接触纤维数;统计分析纤维含量、纤维大小对分散性指标影响。结果表明单个纤维数随纤维含量增加而增加,但其增量随纤维含量的增加而降低,降低规律符合三次函数。纤维接触数随纤维含量增加,增加规律符合二次函数,亦符合理论估计。纤维大小影响单个纤维数和接触纤维数的增加幅度,但不影响单个纤维数的百分比。分散度随纤维含量的增加呈线性下降规律。纤维分散性的定量化描述为进一步的复合材料性能分析和建模提供了量化指标。     

Integrating ecological features of species in spatial pattern analysis of a plant community

Objective: This empirical study was designed to explore the role of ecological features of species in the spatial patterning of a grassland community. Location: Banks of the river Rhône in France. Material and Methods: First, we explored the spatial pattern of 29 species recorded in the community using spatial autocorrelation analysis of species cover values. Second, we then explored the relationship between the patterns found and a set of life attributes that characterized the ecological features of species for resource foraging or dispersion. Finally, we explored the spatial relationship of groups of species that shared the same ecological features using cross‐correlation analysis. Results: We found a significant relationship between the spatial pattern and life attributes of the species highlighting three groups of species: (1) species characterized as competitors, reproducing by runner clonal organs and forming large, dense patches; (2) species characterized as competitive‐rud‐erals, dispersing exclusively by seed production and forming small periodic patches; and (3) species classified as CSR, characterized by rosette morphology and short rhizomes as clonal organs without any significant spatial autocorrelation. Spatial segregation was found between group 1 and group 2 up to 14 m; no significant cross‐correlation between groups 1 and 3 between 0 and 3.5 m, and association between groups 2 and 3 up to 14 m. Conclusions: These results helped to understand how species attributes (relative to stature or dispersion abilities); external factors (such as disturbance) and biotic processes (competition) interplay in structuring the plant community under study in space.     

Modelling Heterogeneous Dispersion in Marginal Models for Longitudinal Proportional Data

Continuous proportional data is common in biomedical research, e.g., the pre‐post therapy percent change in certain physiological and molecular variables such as glomerular filtration rate, certain gene expression level, or telomere length. As shown in (Song and Tan, 2000) such data requires methods beyond the common generalised linear models. However, the original marginal simplex model of (Song and Tan, 2000) for such longitudinal continuous proportional data assumes a constant dispersion parameter. This assumption of dispersion homogeneity is imposed mainly for mathematical convenience and may be violated in some situations. For example, the dispersion may vary in terms of drug treatment cohorts or follow‐up times. This paper extends their original model so that the heterogeneity of the dispersion parameter can be assessed and accounted for in order to conduct a proper statistical inference for the model parameters. A simulation study is given to demonstrate that statistical inference can be seriously affected by mistakenly assuming a varying dispersion parameter to be constant in the application of the available GEEs method. In addition, residual analysis is developed for checking various assumptions made in the modelling process, e.g., assumptions on error distribution. The methods are illustrated with the same eye surgery data in (Song and Tan, 2000) for ease of comparison. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A simple parameter of dispersion index that serves as an adjunct to karyotype asymmetry

In order to refine the measure of karyotype asymmetry a new chromosomal parameter of dispersion index is proposed that has the potential to decipher even the minor karyotypic variations, thus permitting further evolutionary gradations to the karyotype asymmetry classes of Stebbins. The higher the dispersion index, the more specialized would be the karyotype. The dispersion index takes into account the variance lor gradual change in chromosome size within a complementvis-a-vis variance for the position of centromere in a karyotypic totality. The dispersion index is calculated as the proportionate measure of centromeric gradient to the coefficient of variation for chromosome length; wherin centromeric gradient = length of median short arm — length of median chromosome. Thus, the three most important karyotypic criteriaviz., differences in: absolute chromosome size, position of centromere and relative chromosome size, are all covered in the proposed parameter. The effectiveness of dispersion index has been tested on a plant taxa,Papaver L., where karyomorphological details, nuclear DNA content, and morphotaxonomic parameters have been amply elucidated from an evolutionary stand point. It is hoped that dispersion index would find immense utility in delimiting species interrelationships particularly in the closely related taxa, when applied in conjunction with other systematic parameters.     

Matrix solid phase dispersion (MSPD)

A review of the many uses of matrix solid phase dispersion (MSPD) in the extraction and analysis of a variety of compounds from a range of samples is provided. Matrix solid phase dispersion (MSPD) has found particular application as a somewhat generic analytical process for the preparation, extraction and fractionation of solid, semi-solid and/or highly viscous biological samples. Its simplicity and flexibility contribute to it being chosen over more classical methods for these purposes. MSPD is based on several simple principles of chemistry and physics, involving forces applied to the sample by mechanical blending to produce complete sample disruption and the interactions of the sample matrix with a solid support bonded-phase (SPE) or the surface chemistry of other solid support materials. These principles are discussed as are the factors to be considered in conducting a MSPD extraction.     

Apparent Diffusivity and Taylor Dispersion of Water and Solutes in Capillary Beds

A physical theory explaining the anisotropic dispersion of water and solutes in biological tissues is introduced based on the phenomena of Taylor dispersion, in which highly diffusive solutes cycle between flowing and stagnant regions in the tissue, enhancing dispersion in the direction of microvascular flow. An effective diffusion equation is derived, for which the coefficient of dispersion in the axial direction (direction of capillary orientation) depends on the molecular diffusion coefficient, tissue perfusion, and vessel density. This analysis provides a homogenization that represents three-dimensional transport in capillary beds as an effectively one-dimensional phenomenon. The derived dispersion equation may be used to simulate the transport of solutes in tissues, such as in pharmacokinetic modeling. In addition, the analysis provides a physically based hypothesis for explaining dispersion anisotropy observed in diffusion-weighted imaging (DWI) and diffusion-tensor magnetic resonance imaging (DTMRI) and suggests the means of obtaining quantitative functional information on capillary vessel density from measurements of dispersion coefficients. It is shown that a failure to account for flow-mediated dispersion in vascular tissues may lead to misinterpretations of imaging data and significant overestimates of directional bias in molecular diffusivity in biological tissues. Measurement of the ratio of axial to transverse diffusivity may be combined with an independent measurement of perfusion to provide an estimate of capillary vessel density in the tissue.     

Calibration-free concentration analysis for an analyte prone to self-association

Calibration-free concentration analysis (CFCA) based on surface plasmon resonance uses the diffusion coefficient of an analyte to determine the concentration of that analyte in a bulk solution. In general, CFCA is avoided when investigating analytes prone to self-association, as the heterogeneous diffusion coefficient results in a loss of precision. The derivation for self-association of the analyte was presented here. By using the diffusion coefficient for the monomeric state, CFCA provides the lowest possible concentration even though the analyte is self-associated.     

On prediction of optical properties of two- and multiphase nanocomposites for nanomedicine

The theory of optical properties of nanoparticles is considered with the aid of dispersion relations, which are based on the Kramers-Kronig analysis. It is shown that one can utilize rather general dispersion relations, which hold for liquid matrices that contain nanoparticles. Wiener bounds incorporating the Kramers-Kronig analysis are utilized in assessment of the complex permittivity of a nanoparticle.     

A test of normalization methods for marine sediment,including a new post-extraction normalization (PEN) technique

Chemical analyses of sediment are used for assessing the ability of sediment to support a healthy benthos (sediment quality) and for determining contaminant source and dispersion in aquatic systems. Total sediment analysis is used for sediment quality assessment, whereas source identification and dispersion requires normalised contaminant data. Normalized contaminant data are obtained by physical fractionation (size-normalization) of the sediment and analyses of a constant size fraction (usually the 62.5 m fraction), whereas elemental normalization uses the total sediment analysis normalized to a conservative element. Elemental normalization is preferable, as it is cheaper and less time consuming than size-normalization techniques. In addition, some contaminants associated with oxides and oxyhydroxides in the coarse fraction are excluded in fine fraction analyses. Five techniques used to normalize sedimentary contaminant data were tested in the current study, including a new post-extraction normalization method where total sediment data are normalized to the residue after digestion, on the assumption that this fraction acts as a diluent only. Results of the tests indicated that simple normalization to the mud fraction provides useful dispersion information, but that the post-extraction normalization method produced a superior indication of source. Limited source and dispersion information was gleamed from the elemental-normalization (Al, Fe) approach, whereas the size-normalization technique provided the clearest indication of source and dispersion. Simple mud normalization and post-extraction normaliaation methods should be considered because only one analysis provides sediment quality, as well as source and dispersion information. However, for detailed information on source and dispersion, size normalization is recommended.     

在上树时间序列过程中,油松毛虫越冬幼虫扩散型变化的趋势分析

本文在测定油松毛虫越冬幼虫静态空间格局及其抽样技术研究的基础上,为了进一步揭示越冬幼虫在上树时序过程中扩散或聚集的变化趋势,本研究从越冬幼虫上树开始到结束,随着幼虫由树下逐渐向树上转移,分别以株为单元,轮为单元和枝为单元进行了3种抽样的调查,通过测定其种群聚集度指标,根据Mont Lloyd(1967)给出的判断法,并在此基础上应用谐波分析法来研究越冬幼虫种群与其环境之间所表现的种的特性反应和行为。     

Process optimization and characterization of poloxamer solid dispersions of a poorly water-soluble drug

The objective of the present investigation was to improve the dissolution rate of Rofecoxib (RXB), a poorly water-soluble drug by solid dispersion technique using a water-soluble carrier, Poloxamer 188 (PXM). The melting method was used to prepare solid dispersions. A 3² full factorial design approach was used for optimization wherein the temperature to which the melt-drug mixture cooled (X ₁) and the drug-to-polymer ratio (X ₂) were selected as independent variables and the time required for 90% drug dissolution (t₉₀) was selected as the dependent variable. Multiple linear regression analysis revealed that for obtaining higher dissolution of RXB from PXM solid dispersions, a low level ofX ₁ and a high level ofX ₂ were suitable. The differential scanning calorimetry and x-ray diffraction studies demonstrated that enhanced dissolution of RXB from solid dispersion might be due to a decrease in the crystallinity of RXB and PXM and dissolution of RXB in molten PXM during solid dispersion preparation. In conclusion, dissolution enhancement of RXB was obtained by preparing its solid dispersions in PXM using melting technique. The use of a factorial design approach helped in identifying the critical factors in the preparation and formulation of solid dispersion. Published: April 13, 2007     

Synthesis and characterization of a stable dispersion of multifunctional Gd2O3:Er,Yb in polyvinyl alcohol

A stable dispersion of multifunctional Gd₂O₃:Er,Yb phosphor in polyvinyl alcohol (PVA) was synthesized by varying the concentration of Yb³⁺ ions. It had a strong ultraviolet–visible‐near infrared (UV–vis) upconversion emission and applications in temperature and magnetic field sensors (e.g., nano‐heaters), as well as potential use in bioleveling and bioimaging. Stability of the dispersion was found to strongly depend on the mixing process of the powder in the polymer solution. Spherical shaped nanoparticles in cubic phase of ~ 43 nm diameter were synthesized and characterized by X‐ray diffraction; results were confirmed by scanning electron microscopy (SEM). Fourier transform infrared sspectroscopy (FT‐IR) and thermal analysis supported the presence of PVA. NIR pumping produced strong UC emission bands in the red and green regions extending up to very high UV (240 nm). This method provides an alternative for synthesizing a highly UC‐efficient non‐agglomerated pure transparent dispersion from various efficient phosphors for biological applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of methods for extraction of bacteria from soil

Abstract Several methods for dispersion of soil were tested for possible use in procedures for extraction of bacteria. Physical cell damage on cells and efficiency in extraction of indigenous cells from soil, were investigated. Cell damage by the dispersion methods was investigated by measuring the physical cell integrity and viability of pure cultures of Escherichia coli and Bacillus subtilis , as well as soil bacteria extracted from soil, when dispersed in slurries of γ-sterilized soil. Separation of bacteria and soil particles on the basis of buoyant density was conducted with the nonionic density gradient medium Nycodenz. When slurries of γ-sterilized soil with added pure cultured cells were centrifuged (10000 × g ) over cushions of Nycodenz (1.3 g ml⁻¹), practically all the added cells were recovered in a layer on top of the cushion. This proves that a reversible attachment and cosedimentation is not an important phenomenon in this procedure. The efficiency of the different dispersion methods for the extraction of indigenous soil bacteria, was assessed after separation of dislodged and attached soil bacteria. This separation was done either on the basis of sedimentation rate by low speed centrifugation, or buoyant density by Nycodenz density gradient centrifugation. The physical dispersion by ultrasonic treatment and chemical dispersion by the use of a chelating agent together with a detergent, were inferior to physical dispersion either by Waring blender (for large volumes) or a rotating rubber pestle treatment (for smaller volumes). The physical dispersion did not appear to be destructive to the cells tested.     

Two-stage recovery of S-adenosylmethionine using supported liquid membranes with strip dispersion

We report the selective recovery of S-adenosylmethionine (SAM) from fermentation broths using a two-stage supported liquid membrane system with strip dispersion (SLM-SD). The system utilized two MiniModule^® hollow-fiber membrane modules as microporous supports and an organic membrane solution consisting of the extractants of sodium di-2-ethylhexyl sulfosuccinate (AOT), di-(2-ethylhexyl)phosphoric acid (DEHPA), and trioctylphosphine oxide (TOPO) in the solvent n-octanol. SAM was extracted in the first membrane module. Methionine (Met) was captured by the first stripping solution and further purified in the second membrane module. pH values in the feed phase and the first and second stripping solutions, extractant concentrations, NaCl concentration, and the SAM acceptor in the first stripping solution were optimized. Strip dispersion mixing speed, pressure differences across the membranes, and flow rates of the feed and strip dispersion phases were investigated experimentally. The optimal extractant concentrations were: AOT 2.78 wt%, DEHPA 27.0 wt%, and TOPO 1.61 wt%. The optimal pH values in the feed phase and the first and second stripping solution were 3.0, 2.5, and 1.0, respectively. SAM extraction efficiency of 98.7%, SAM recovery efficiency of 91.8% and Met removal efficiency of 85.4% were achieved within 5 h. Finally, the mass transfer analysis indicated that the mass transfer resistances from the extraction reaction and the membrane phase were predominant.     

Stochastic analysis of the relationships between saturated hydraulic conductivity variance and solute dispersion in heterogeneous soils

The effect of three‐dimensional heterogeneity of saturated hydraulic conductivity on the vertical transport of solutes in soils is examined by means of controlled numerical experiments. Saturated hydraulic conductivity, an important transport parameter that controls the dispersion of pollutants in heterogeneous soils, is assumed to be composed of a homogeneous mean value and a perturbation caused by the vertical variability of soil properties, producing a stochastic process in the mean flow direction. The spatial heterogeneity of porous soils is characterized by the variance and correlation scale of the saturated hydraulic conductivity in the transport domain. Numerical experiments are carried out to evaluate the extent of contaminant dispersion in Hawaiian Oxic soils when uncertainty exists as a result of the spatial heterogeneity of saturated hydraulic conductivity. Statistical analysis of the saturated hydraulic conductivity measurements on undisturbed soil cores from two locations in Hawaiian Oxic soils indicated two different soils with the same mean and different variances. The partial differential equations describing three‐dimensional transient flow and solute transport in soils with a random conductivity field were solved to evaluate the effect of these two variance levels on the transport of a contaminant plume originating from the surface. The significance of the variance on the spatial and temporal distribution of tracer concentrations is demonstrated using solute breakthrough curves at various depths in the soil profile. The longitudinal macrodispersivity resulting from tracer spreading in the heterogeneous soils with a finite local dispersivity is also analyzed. The analysis shows a similar solute dispersion behavior for the two variances. However, there is an overall reduction in the dispersion of solutes resulting from a uniform velocity field with the same mean. Macrodispersivity values in heterogeneous soils are proportional to the variance at smaller travel distances but converge to the same value at larger travel distances.     

表征心室复极不一致有效参数的仿真研究

建立了从心内膜到心外膜的一维心肌几何模型,采用心肌双域模型建立心电电位的仿真模型,通过改变缺血程度构造不同的心室复极不一致状态,利用有限差分法求解控制方程,模拟了心电兴奋在心室复极不一致状态下形成的心电电位,并从中提取QT离散度和兴奋恢复间期(activation-recovery interval,ARI)离散度。分析结果显示：缺血区与正常区电位的QT间期没有明显差异,QT离散度接近于零,不能有效地表征心室肌复极不一致;缺血区ARI明显区别于正常区,ARI离散度与缺血程度有很好的对应关系,可以用来表征心室复极不一致。     

P波离散度对房颤消融术后复发的预测价值

目的:探讨P波离散度对心房颤动(房颤)导管消融术后复发的预测价值。方法:连续收集经导管消融的房颤患者120例,根据是否复发分为复发组与对照组,分别测定和比较两组术后心电图最大P波时限(Pmax)及最小P波时限(Pmin)并计算P波离散度(Pd)。结果:房颤消融术后,53例病人复发,复发组最大P波时限(132±23mm VS 102±25mm)及P波离散度(33±9mm VS 29±10mm)均显著高于非复发组,差异有统计学意义(P0.05)。结论:P波离散度可用于辅助预测房颤导管消融术后是否复发。