Improved protein recovery in reversed-phase liquid chromatography by the use of ultrahigh pressures

The effect that elevated pressure used in ultrahigh-pressure liquid chromatography (UHPLC) has on protein recovery was investigated. Specifically, protein carryover ("ghosting") and recovery were examined. Four model proteins (ribonuclease A, ovalbumin, myoglobin, BSA) were separated by gradient RPLC at both conventional (160 bar) and ultrahigh pressures (>1500 bar). A custom gradient UHPLC system was used to generate conventional pressures on 5-microm diameter reversed-phase supports and ultrahigh pressures on identical 1.4-microm supports. The results indicate that, by increasing the pressure, protein carryover from run to run is reduced and in some cases eliminated above a certain threshold pressure for the model proteins studied. Further work indicates that recovery was enhanced for each of the proteins studied, even approaching 100% for certain proteins.     

Modelling the compression behavior of ground tire rubber

The purpose of this paper was to study elastomer powder from crushed used tires (CUTs). In particular, the behavior of the green density of elastomeric powder was analyzed by varying compaction pressure. In the Anglo‐saxon bibliography, this powder is known as ground tire rubber: ground tire rubber (GTR). The density of the tyre was made using a hydrostatic balance, the analysis of grain size using cribbing sieves, and the measures of compression parameters by means of a Universal Testing Machine. The main goal was to obtain a behavior model of ground tire rubber along different compaction pressures. This model was used to predict optimum compaction pressures in order to achieve the highest density. This was the first step to obtain recycled products when sintering processes are applied, evidently if thermal compression was used as a manufacturing process. This established model predicted the evolution of green density versus compaction pressures very accurately.     

Vapor-liquid equilibria for the ternary system N2 + CO2 +n-C4H10 at 250 and 270 K1

The system studied was nitrogen + carbon dioxide +n-butane at 250 and 270 K and at pressures from 1.5 to 14 MPa. The Peng-Robinson equation was used to model the results, since it is the most widely accepted equation of state in the gas processing industry. In general, the predictions are most accurate at low and moderate pressures and poorest at high pressures, especially near the critical region.     

Adsorption of chlorinated hydrocarbon vapors onto soil in the presence of water

Chlorinated solvents partition readily into the vapor-phase in unsaturated soils. Sorption from the vapor-phase affects both transport and recovery. The Brunauer-Emmett-Teller (BET) isotherm has been used to model adsorption of chlorinated solvent vapors; however, the BET equation is not accurate above reduced vapor pressures (p/p(sat)) of 0.35. New measurements of chlorinated alkane sorption have been used with a modified BET equation (MBET) to model the adsorption isotherms for five solvents. The MBET equation was found to fit experimental data accurately, especially at high reduced vapor pressures. The capacity of sandy loam soil to adsorb organic vapors decreased with increasing water content, probably due to less soil surface available for sorption. This effect is most evident at reduced vapor pressures greater than 0.5. Adsorption is related to distribution of excess surface energy, the number of molecular layers of water sorbed at the surface, and solute polarity. Results suggest that water films contain areas of high interfacial energy that interact with solute molecules via induced electrostatic forces.     

Experimentelle und theoretische Untersuchungen zu Hochdruck-Sicherheitsventilen – Auslegung und Design unterstützt durch numerische Rechenmethoden (CFD)

High-pressure safety valves with set pressures of more than 200 bar are required in industry, e.g. for polyethylene and synthesis gas applications. They are presently sized according to ISO 4126-1. Only equations for ideal gases are presented there, and there are no indications as to how the real gas factor and the adiabatic exponent for real gases are to be calculated. For this reason, an equation for the critical mass flow rate of a real gas through a nozzle was derived and compared with the model according to EN-ISO 4126-1 and with experimental data. It is recommended that the current ISO-standard be supplemented by the nozzle flow model for real gases. The first numerical calculations (ANSYS-CFX) show that the discharge coefficient for a high pressure safety valve measured at moderate pressures can be extrapolated to very high pressures if it is used in conjunction with the nozzle flow model for real gases. However, this numerical result must yet be validated for further valve types by experiment. For this purpose, BASF has set up a high pressure valve test facility in Ludwigshafen.     

Navier-Stokes simulation of flow through a highly contoured subsonic diffuser

The flow through a highly offset subsonic diffuser with cross-sectional profiles that varied from rectangular at the duct entrance to circular a t the engine face was numerically simulated. A multizonal approach combined with a two-grid topology was used to represent both the internal and external flow fields, and an implicit, approximately-factored, partially flux-split finite-difference algorithm was used to solve the three-dimensional thin-layer Navier-Stokes equations. The computed static pressures along the inlet wall and total pressures on the engine face were compared with experimental data. In addition, the overall flow field within the duct was examined in detail. Good agreement is shown between experiment and computations, with the limiting factor being the lack of a reliable turbulence model for internal flow problems.     

Microplane finite element analysis of tube‐squash test of concrete with shear angles up to 70°

Finite element analysis of the response of concrete structures to impact events such as missile penetration, explosive driving of anchors, blast, ground shock or seismic loading, requires knowledge of the stress–strain relations for concrete for finite strain at high pressures. A novel type of material test achieving very large shear angles of concrete at very large pressures, called the tube‐squash test, can be used to calibrate a concrete model taking into account plastic deformation at extreme pressures. A finite element analysis of such a test is performed by using a finite strain generalization of microplane models for concrete and steel. The results obtained are in good agreement with those previously obtained with a simplified method of analysis. Thus, they provide a validation of the microplane model, which is shown to be capable of reproducing the response of concrete not only for small strains at small pressures, which is predominantly brittle, but also for high pressures and large finite strains, which is predominantly frictional plastic. Copyright © 2001 John Wiley & Sons, Ltd.     

Compaction Properties of Powders: The Relationship Between Compression Cycle Hysteresis Areas and Maximally Applied Punch Pressures

The consolidation behaviors of various pharmaceutical solids were characterized by investigating the relationship between the calculated hysteresis areas and the maximally applied punch pressures. An Instron universal testing apparatus and an instrumented die were used to generate compression cycle profiles at various maximally applied punch pressures for the materials studied. Based on the profiles obtained, hysteresis areas were calculated for the materials studied as a function of maximally applied punch pressures. Furthermore, model profiles describing the plastic and brittle fracture processes were utilized to derive mathematical relationships between the calculated hysteresis cycle areas and the maximally applied punch pressures. The mathematical relationships derived indicate that a linear relationship between hysteresis areas and maximally applied punch pressures exists for plastic materials, whereas for brittle materials the hysteresis areas are related to the square of the maximally applied punch pressures. Experimental data obtained support the mathematical relationships derived. The goodness of fit to the models derived is used to rank order the consolidation mechanism of various drugs and pharmaceutical excipients.     

输液管线中的地震动水压力及其影响因素

强烈地震作用可使地上输液管线中的液体产生较大的动水压力。基于模态叠加原理及地震反应谱理论，考虑流体可压缩性及管弹性，建立了输液管线地震动水压力的计算模型。根据流体所处边界条件的不同，给出两种典型工况下，管流地震动水压力的计算公式，并与依据附加质量模型计算所得的结果进行了比较。比较结果表明：管线长度对管流地震动水压力有显著的影响，对长管道而言，以附加质量模型求得的的地震动水压力高于考虑流体可压缩性时求得的地震动水压力，而对于短管道，情况刚好相反。另外，场地类型及管流所处工况对管流地震动水压力也有显著的影响，软土场地上的管理道。其内部流体地震动水压力明显高于硬土场地上的动水压力。     

Modelling and state estimation for a two-dimensional moving boundary problem

The five-spot waterflooding problem has been modelled as a two-dimensional moving boundary problem with a sharp interface separating the water and oil regions. The Galerkin method was used to solve for the shape and movement of the interface, as well as for the pressures in the reservoir. Having obtained a working model, the extended Kalman filter was then used to estimate the interfacial position when using corrupted pressure measurements from a single sensor in the field.     

A discrete element model of concrete under high triaxial loading

A numerical model based on a three dimensional Discrete Element Method (DEM) has been used to study the behavior of concrete under high-confining pressures (up to 650 MPa). At this range of pressures, irreversible compaction of the material occurs and needs to be considered. Within the discontinuous nature of the model, a local constitutive law has been developed to reproduce this phenomenon quantitatively. Local parameters to be used in this constitutive law are identified by simulating reference uniaxial and triaxial experimental tests in compression. Once these parameters have been obtained, the model is used to predict the response of concrete sample for triaxial compressive tests at different levels of confinement. Beyond the macroscopic volumetric and stress–strain response, the model gives interesting insights on the local evolution of the nature of the interaction forces between the discrete elements. The computational implementation has been carried out in the discrete element and open source code YADE (http://yade-dem.org[20]).     

Thermodynamics and nucleation of bubbles in normal and superfluid liquid helium-4 at negative pressures

We report on a theoretical investigation of liquid helium-4 at negative pressures. For normal liquid helium we estimate the thermodynamic functions for negative pressure via extrapolation of measurements made for positive pressures. We determine the free energy as a function of density and temperature and find the location of the liquid-vapor spinodal. The results of these calculations are used to construct a temperature-dependent density-functional scheme to describe the inhomogeneous liquid. This density functional is then applied to calculate the rate at which bubbles nucleate in the liquid at negative pressures. We include a discussion of the properties of the superfluid phase based on the use of Landau's quasi-particle model.     

Strain localisation modelling and pore pressure in saturated sand samples

Dynamic strain localisation theory together with a multiphase material model is used to simulate shear band dominated processes in fully saturated sand samples. The fluid-saturated medium is viewed as multi-phase continuum consisting of a solid skeleton and pores filled by fluids. The governing equations are based on the general framework of averaging theories. A generalised plasticity constitutive model for fully saturated soils is adopted in the computational process. Both samples of medium-loose and dense sands are studied. Negative water pressures, which are important in localisation phenomena of fully saturated dilatant geomaterials, are obtained for dense sands, while positive water pressures result for medium-loose sands.     

低层坡屋面群体建筑表面风压的数值模拟

结合低层民房风荷载及抗风性能的研究,基于Reynolds时均N-S方程,采用由标准k-e湍流模型扩展的RNG k-e模型,对一幢低层双坡屋面单体房屋和由六幢该类房屋组成的群体建筑的周围风场及表面风压进行了数值模拟。数值模拟采用具有良好适应性的四面体单元进行计算区域的网格划分,顶点中心格式的有限容积法进行控制微分方程的离散,SIMPLE压力校正迭代算法实现对非线性离散化方程的求解。在单体计算结果和风洞试验结果有较好吻合的前提下,重点获得了群体效应下低层双坡屋面房屋表面风压的分布规律和特征。     

A method for measuring vapor pressures of low-volatility organic aerosol compounds using a thermal desorption particle beam mass spectrometer

A temperature-programmed thermal desorption method for measuring vapor pressures of low-volatility organic aerosol compounds has been developed. The technique employs a thermal desorption particle beam mass spectrometer we have recently developed for real-time composition analysis of organic aerosols. Particles are size selected using a differential mobility analyzer, sampled into a high-vacuum chamber as an aerodynamically focused beam, collected by impaction on a cryogenically cooled surface, slowly vaporized by resistive heating, and analyzed in a quadrupole mass spectrometer. A simple evaporation model developed from the kinetic theory of gases is used to calculate compound vapor pressures over the temperature range of evaporation. The data are fit to a Clausius-Clapeyron equation to obtain a relationship between vapor pressure and temperature and to determine the heat of vaporization. The technique has been evaluated using C13-C18 monocarboxylic and C6-C8 dicarboxylic acids, which have vapor pressures at 25 degrees C of approximately 10(-4) - 10(-6) Pa, but less volatile compounds can also be analyzed. The method is relatively simple and rapid and yields vapor pressures and heats of vaporization that are in good agreement with literature values. The technique will be used to generate a new database of vapor pressures for low-volatility atmospheric organic compounds.     

A mechanism of formation of gas-liquid systems

A mathematical model is constructed for the process of formation of a disperse liquid-gas bubble system as a result of evolution of dissolved gas due to changes in the external pressure. The model is implemented numerically for chlorine and air and is used to explain the difference in the rates of bubble growth at small and large excess pressures.     

建筑表面风压的三维数值模拟

本文采用数值模拟方法预测由近地三维流动风引起的建筑物的表面风压。文中运用一种扩展的ｋ－ε紊流封闭模型，导得了稳态流动风的统一形式的控制微分方程。采用控制容积法对微分方程作了离散，ＳＩＭＰＬＥＣ压力校正迭代算法实现了非线性离散化方程的求解。实例计算与分析比较表明，本文的模拟方法改善了对建筑物侧风面和顶面风压值的预测     

非高斯风压峰值因子估计:基于矩的转换过程法的对比研究

建筑围护结构抗风设计需要准确估计非高斯风压极值或者峰值因子。对于非高斯风压峰值因子估计,常用的基于矩的转换过程法有Hermite多项式模型（HPM）、Johnson转换模型（JTM）及平移广义对数正态分布（SGLD）模型。极值通常由母本概率密度函数（PDF）的尾部决定,现阶段对于三种模型基于相同前四阶矩预测的非高斯母本PDF尾部的差别尚不清楚,自然,对于这三种模型预测的极值或者峰值因子的差别尚无答案。为了探明三种模型的异同,从而提供一定的选取原则,该文就三种方法对非高斯风压峰值因子估计效果进行了系统的对比研究。首先从理论上对比了三种方法预测得到的母本PDF的差异和估计的峰值因子差别;其次,选用长时距风洞试验风压数据检验了三种方法对非高斯风压峰值因子的估计效果。结果表明在三种模型都适用的偏度和峰度组合范围内,HPM对非高斯风压峰值因子估计结果相比SGLD模型和JTM模型估计结果更准确。     

Modeling of multiphase flow with phase change in porous media – a case study

A general numerical model developed to simulate the time‐dependent changes of moisture content, temperature and pore pressures is proposed for a porous material. The model is based on a coupled heat and mass transfer mathematical formulation. The model’s validation is conducted using experimental data for concrete. The gravimetric technique is used to obtain the experimental data on moisture content in cylinders made up of fully saturated concrete exposed to drying. Further to demonstrate the applicability of the model, it is also studied the moisture migration, temperature development and thermal stresses in a concrete element exposed to fire. The obtained results indicate that during fire, several degradation phenomena are taking place at the same time. Thermal stresses developed by the temperature differential, especially when temperature‐dependent material properties are taken into the account, along with the increase of pore pressures, may contribute to structural failure.     

Research on visco-elastic-plastic creep model of artificially frozen soil under high confining pressures

The triaxial creep experiment of artificially frozen soil in deep alluvium was performed by a self-developed machine of triaxial creep frozen soil. After analyzing the experiment results, applying parabolic yield criterion for improved viscoplasticity in the Nishihara model, a new creep constitutive model was established for describing frozen-soil's creep characteristics under high confining pressures. The secondary development tools and data interface had been used to add the visco-elastic-plastic creep constitutive model to standard ADINA FEM. Numerical simulation of the shaft well excavation process and field measurement displacements of frozen wall were performed in the mine; and the results showed that the visco-elastic-plastic creep constitutive model was suitable and reasonable. This constitutive model could be significance for the frozen soil structure long-term stability analysing and the displacement forecasting.