Effect of Hydrodynamic Interaction on Flow-induced Polymer Translocation Through a Nanotube

We investigated the effect of hydrodynamic interaction(HI) on flow-induced polymer translocation through a nanotube by Brownian dynamics simulations. Whether there is HI in the simulation system is separately controlled by using different diffusion tensors. It is found that HI has no effect on critical velocity flux for long polymer chains due to the competition between more drag force and the hindrance of chain stretching from HI, however, HI broadens the transition interval. In addition, for flow-induced polymer translocation with HI, the critical velocity flux firstly slowly decreases with the increase of chain length and then becomes identical to that of it without HI, that is, the critical velocity flux is independent of chain length. At the same time, HI also accelerates the translocation process and makes the relative variation amplitude of single bead translocation time smaller. In fact, HI can enhance the intrachain cooperativity to make the whole chain obtain more drag force from fluid field and hinder chain stretching, both of which play an important role in translocation process.     

Differential magnetic catch and release: experimental parameters for controlled separation of magnetic nanoparticles

Differential magnetic catch and release (DMCR) has been used as a method for the purification and separation of magnetic nanoparticles. DMCR separates nanoparticles in the mobile phase by magnetic trapping of magnetic nanoparticles against the wall of an open tubular capillary wrapped between two narrowly spaced electromagnetic poles. Using Au and CoFe(2)O(4) nanoparticles as model systems, the loading capacity of the 250 μm diameter capillary is determined to be ～130 μg, and is scalable to higher quantities with larger bore capillary. Peak resolution in DMCR is externally controlled by selection of the release time (R(t)) at which the magnetic flux density is removed, however, longer capture times are shown to reduce the capture yield. In addition, the magnetic nanoparticle capture yields are observed to depend on the nanoparticle diameter, mobile phase viscosity and velocity, and applied magnetic flux. Using these optimized parameters, three samples of CoFe(2)O(4) nanoparticles whose diameters are different by less than 10 nm are separated with excellent resolution and capture yield, demonstrating the capability of DMCR for separation and purification of magnetic nanoparticles.     

离子液体捕集二氧化碳非平衡热力学研究方法学探讨

介绍了应用非平衡热力学研究离子液体捕集二氧化碳（CO2）动力学的思路，分析了其成功应用需解决三大关键科学难题，即可靠的热力学模型，界面传递速率描述以及准确的通量数据．其中，准确通量数据的获得需要可靠的实验动力学数据和离子液体捕集CO2过程传递面积的有效考察．在此基础上系统地总结了该三大关键科学问题最新的研究进展和分析后续开展的工作，并对离子液体捕集二氧化碳非平衡热力学研究提出展望．     

Effects of Nozzle Length and Process Parameters on Highly Constricted Oxygen Plasma Cutting Arc

The influence of nozzle length and two process parameters (arc current, mass flow rate) on the plasma cutting arc is investigated. Modeling results show that nozzle length and these two process parameters have essential effects on plasma arc characteristics. Long nozzle torch can provide high velocity plasma jet with high heat flux. Both arc voltage and chamber pressure increase with the nozzle length. High arc current increases plasma velocity and temperature, enhances heat flux and augments chamber pressure and thus, the shock wave. Strong mass flow has pinch effect on plasma arc inside the torch, enhances the arc voltage and power, therefore increases plasma velocity, temperature and heat flux.     

Thermal conduction in molecular chains: non-Markovian effects

We study the effect of non-Markovian reservoirs on the heat conduction properties of short to intermediate size molecular chains. Using classical molecular dynamics simulations, we show that the distance dependence of the heat current is determined not only by the molecular properties, rather it is also critically influenced by the spectral properties of the heat baths, for both harmonic and anharmonic molecular chains. For highly correlated reservoirs the current of an anharmonic chain may exceed the flux of the corresponding harmonic system. Our numerical results are accompanied by a simple single-mode heat conduction model that can capture the intricate distance dependence obtained numerically.     

Characterization of the Converging Jet Region in a Triple Torch Plasma Reactor

Enthalpy probe measurements were taken of the converging plasma plume in a triple torch plasma reactor and related to substrate heat flux measurements. Results show excellent entrainment of process gases injected into the converging plasma plume by way of the central injection probe. At lower pressures (40 kPa), the plasma volume is equivalent to at least a 3 cm diameter, 4 cm long cylinder, with relatively uniform temperature, velocity, and substrate heat flux profiles when compared to a typical dc arc jet. Converging plasma plume size, substrate heat flux, and enthalpy profiles are also shown to be a strong function of applied system power. Substrate heat flux measurements show smaller radial gradients than enthalpy probe measurements, because of the high radial velocity component of gases above the substrate boundary layer. Enthalpy probe measurements were also conducted for diamond deposition conditions and approximate temperature and velocity profiles obtained. Problems with the uniform gas mixture assumption prohibited more accurate measurements. Reproducibility of enthalpy measurement results was shown with an average standard deviation of 11.8% for the velocity and 7.6% for the temperature measurements.     

Neural network approach for modeling the performance of reverse osmosis membrane desalting

A neural network-based modeling approach with back-propagation and support vector regression algorithms was investigated as a mean of developing data-driven models for forecasting reverse osmosis (RO) plant performance and for potential use for operational diagnostics. The concept of plant “short-term memory” time-interval was introduced to capture the time-variability of plant performance since both a state of the plant model and standard time-series analyses for both flux decline and salt passage did not result in realistic predictive horizons for practical purposes. Past information of normalized permeate flux and salt passage were introduced as unique input variables along with process operating parameters to capture short-term plant performance variability. Sequential models, where the time-variation within each forecasting time-interval was also taken as input information, and marching forecasting models, where target values were predicted at fixed future times from past plant information, were developed. Models were trained, with normalized permeate flux and salt passage, for various model architectures, memory time-intervals and forecasting times using both back-propagation and support vector regression approaches. State of the plant models (without forecasting) were able to describe the relatively small permeate flux variations but were unable to capture salt passage trends (for any present time condition) since unsteady state phenomena could not be properly described without plant memory information. Forecasting of plant performance, with both sequential and marching models, yielded good predictive accuracy for short-term memory time-intervals in the range of 8–24 h for permeate flux and salt passage for forecasting times up to 24 h. Current work is ongoing to extend the approach for longer time scales and to incorporate data-driven forecasting models of RO plant into control strategies and process diagnostics.     

Flux improvement by Dean vortices: ultrafiltration of colloidal suspensions and macromolecular solutions

Coiled and straight hollow-fibre modules have been built and tested; the permeate flux obtained in ultrafiltration with these two geometries is compared for two feeds: a colloidal bentonite suspension and a dextran solution. In the case of colloidal suspensions, the secondary flows induced by the coiled geometry allow fouling to be reduced and the permeate flux is multiplied by a factor of up to 2. An empirical relationship is proposed to express the limiting flux of permeate as a function of both the velocity and some geometrical parameters of the coiled modules. Analogous results are obtained during the ultrafiltration of dextran. It is also shown that under certain conditions almost no deposit was formed; the permeate flux under these conditions is three times higher for coiled modules than for straight ones. For a given energy expenditure and ultrafiltration process, the gain in permeate flux can reach a factor of 1.8.     

Identification of the laminar-turbulent transition process in a plasma plume

This paper illustrates the complete dynamics of the laminar-turbulent transition process in a plasma plume using a simple measurement of the magnation-point heat flux correlated with acoustic, optical, and voltage drop fluctuations. In the laminar flow regime a steady jet is produced and the heat fluxes are accurately predicted hr laminar correlations. The initial stage of transition is characterized by the formation of axisymmetric structures and velocity fluctuations which increase the heat flux over laminar correlations. This is followed by a rapid decrease in heat flux as the vortex structures become more intense and rapidly entrain external air into the plume. The plume oscillations (acoustical and voltage drop) become most intense and are identical in frequency at the point of minimum heat flux. The transition is complete which the transition to small-scale turbulence in the exiting boundary layer which results in dec reased entrainment and increased heat flux.     

膜吸收-再生循环技术捕集CO_2操作性能及其参数优化研究

采用N-甲基二乙醇胺(MDEA)+哌嗪(PZ)复合溶液作为捕集CO2吸收剂,研究了膜吸收-再生循环装置的操作性能,考察了气液流量、吸收剂浓度和再生电压等因素对捕集率和传质通量的影响,采用正交实验方法,优化操作条件,确定最佳操作方案。结果表明,气体流量对捕集率的影响明显大于液体流量的影响;气体流量增大对传质通量影响不明显;吸收剂浓度的增大使传质通量迅速增大,但大于一定值时通量不再增大;正交实验得出最佳操作条件为液体流量110 mL/min、气体流量0.65 L/min、吸收剂总浓度2.5 mol/L和再生电压210 V,捕集率大于95%,传质通量维持在5.86×10-4mol/(m2.s)。     

Asymmetry of Monomer Unit Arrangements in Multicomponent Polymers

The concept of “flux” is proposed for quantitatively describing the manner in which the relative concentrations of three chain ends remain at a steady state in a terpolymerization. The flux is a measure of the net rate of transition from one chain end to another. If a terpolymerization remains at a steady state with respect to the relative concentrations of the three chain ends, then the flux must be either zero or some finite number which is independent of the choice of chain ends used to calculate it. It is a necessary and sufficient condition for Ham's concept of sequence reversibility to be true that the flux be zero. The flux calculated for many systems using reactivity ratio data is quite near zero. However, the calculations necessarily share the imprecision of reactivity ratio data. Ter-polymer sequence distribution data, if available, could be used in a proposed method of calculating flux.     

Ribonucleotides and RNA Promote Peptide Chain Growth

All known forms of life use RNA‐mediated polypeptide synthesis to produce the proteins encoded in their genes. Because the principal parts of the translational machinery consist of RNA, it is likely that peptide synthesis was achieved early in the prebiotic evolution of an RNA‐dominated molecular world. How RNA attracted amino acids and then induced peptide formation in the absence of enzymes has been unclear. Herein, we show that covalent capture of an amino acid as a phosphoramidate favors peptide formation. Peptide coupling is a robust process that occurs with different condensation agents. Kinetics show that covalent capture can accelerate chain growth over oligomerization of the free amino acid by at least one order of magnitude, so that there is no need for enzymatic catalysis for peptide synthesis to begin. Peptide chain growth was also observed on phosphate‐terminated RNA strands. Peptide coupling promoted by ribonucleotides or ribonucleotide residues may have been an important transitional form of peptide synthesis that set in when amino acids were first captured by RNA.     

Reversibility of fouling formed in activated sludge filtration

This paper investigates the reversibility of membrane fouling by activated sludge in a membrane bioreactor equipped with a 0.1 μm pore ceramic membrane. The membrane was submitted to a series of tests in which the permeate flux, the transmembrane pressure (TMP) or the circulation velocity were successively varied in cycles by step increments or decreases. When the permeate flux is set below the critical flux, the TMP remains stable and fouling is reversible. On the contrary, when the critical flux is exceeded, the TMP increases and does not stabilize, as in dead-end filtration. The fouling formed is partly irreversible when the flux is lowered again. When the TMP is first increased up to 400 kPa and then decreased back at constant velocity, no hysteresis is found on the flux–TMP graph, showing that fouling is reversible in this case. Velocity cycles were performed by first lowering the velocity from 5 to 1 m/s and raising it again to 5 m/s. In this case again, the fouling induced by reducing the velocity was found to be reversible. However, when the same pressure and velocity cycle tests were performed with activated sludge collected in the aeration tank of a classical wastewater treatment plant, fouling was found to be partly irreversible, showing that the cake formed in the absence of shearing is much more cohesive. In the final part of the paper, we tested a hydrodynamic method of fouling control consisting in alternating short periods of filtration (1–4 s) and short periods of washing (1 or 2 s) at low TMP and high velocity. This method yielded to a 20% permeate flux increase with a 10% reduction in hydraulic energy consumption for classical plant activated sludge.     

Impact of ultrafiltration operating conditions on membrane irreversible fouling

The main limitation of the ultrafiltration (UF) process identified in drinking water treatment is membrane fouling. Although adsorption of natural organic matter (NOM) is known to cause irreversible fouling, operating conditions also impact the degree of irreversible fouling. This study examined the impact of several operating parameters on fouling including flux, concentrate velocity in hollow fibers, backwash frequency, and transmembrane pressure. A hydrophilic cellulose derivative membrane and a hydrophobic acrylic polymer membrane were used to conduct these tests. Pilot testing showed that when short-term reversible fouling was limited during a filtration cycle by increasing the concentrate velocity, reducing the flux, and increasing the backwash frequency, the evolution of the membrane toward irreversible fouling could be controlled. It appeared that operating parameters should be adjusted to maintain the increase of transmembrane pressure below a certain limit, determined to be approximately 0.85 to 1.0 bar for the tested UF membrane, in order to minimize the rate of irreversible fouling. This threshold for transmembrane pressure was confirmed empirically by compiling data from over 36 pilot studies. Other testing results demonstrated that hydraulic backwash effectiveness decreased as the transmembrane pressure applied in the previous filtration cycle increased. Backwash efficiency in terms of membrane flux recovery after hydraulic backwash was reduced by 50% when the transmembrane pressure was increased from 0.4 bar to 1.4 bar.     

拉伸分子动力学方法研究聚乙烯单链的力学行为

采用拉伸分子动力学方法(steered molecular dynamics,SMD)研究一端固定的聚乙烯单链(singlepolyethylene chain)在被拉伸过程中的力学性质.在拉伸过程中发现平均拉力〈f〉受拉伸速度v的影响,当v<0.05 nm/ps时,〈f〉在250 pN附近会出现一个拉力平台.聚乙烯单链各部分的形状因子在拉伸过程中表现出一定的规律性,总是头部和尾部的形状因子〈δh〉、〈tδ〉先增加然后才是中间部分〈δm〉增加.如果按顺序再释放被拉开的聚乙烯单链,就会出现力学回滞现象,这与Kellermayer等的力学回滞曲线实验是一致的.力学回滞曲线面积表示耗散能〈Ed〉,与速度v满足方程〈Ed〉=a+b×e-cv,而且在v<0.005 nm/ps和v>0.005 nm/ps两个速度区域有不同的特性.〈Ed〉在不同的分子热运动温度区域,也表现出不同的规律性,当温度T>220 K时,〈Ed〉随着温度T的升高而减小,这与Pegoretti等的实验一致,当T<220 K时〈Ed〉随着温度T的升高而增加.     

Analysis of the slip effect on the permeate flux in membrane ultrafiltration

A method for predicting the mass transfer coefficient as well as the limiting permeate flux in membrane ultrafiltration has been found, based upon the boundary-layer theory which takes into account the slip velocity on the membrane surface. The theory presupposes the existence of a slip flow on a porous membrane surface, especially for the limiting permeate-flux operations. Further, the slip velocity increases with the size of the pores of the membrane, with feed velocity and also with feed concentration. The theory also showed that the permeate flux increases with the increase of the slip velocity. A considerable improvement in theoretical prediction of the permeate flux is expected if the slip flow effect is taken into consideration.     

Concentrating the extract of traditional Chinese medicine by direct contact membrane distillation

This study applies direct contact membrane distillation (DCMD) to concentrating the extract of traditional Chinese medicine (TCM). The trans-membrane flux under various operation conditions was measured in real-time during concentration process. By decoupling the factors affecting the trans-membrane flux decline, it was found that the observed flux decline throughout the process could be attributed to the membrane fouling, the reduction of water vapor pressure and the increase of transport resistance at feed side. Analysis of the combined factors was given to show in detail the mechanism of flux decline. Factors that may affect the flux level, such as feed velocity, feed temperature and pretreatment were experimentally examined. Gas bubbling or sparging was introduced into DCMD system for reducing membrane fouling, and it was found that both gas–liquid two-phase flow at the feed side and gas back-washing within membrane module are effective ways to control membrane fouling.     

3种阴离子交换色谱固定相捕获细胞培养上清液中红细胞生成素的效果比较（英文）

Affinity and ion exchange conventional chromatography have been used to capture erythropoietin(EPO)from mammalian cell culture supernatant.Currently,chromatographic adsorbent perfusion is available,however a limited number of applications have been found in the literature.In this work,three anion exchange chromatographic supports(gel,membrane and monolithic)were evaluated in the capture step of the recombinant erythropoietin purification process.The influences of load and flow rate on each support performance were analyzed.Also the purity of the EPO molecules was determined.A productivity analysis,as a decision tool for larger scale implementation,was done.As a conclusion,the evaluated supports are technically suitable to capture EPO with adequate recovery and good purity.However,the monolithic column admits high operating velocity,showing the highest adsorption capacity and productivity.     

Comparison among three anion exchange chromatographic supports to capture erythropoietin from cell culture supernatant Lourdes

Affinity and ion exchange conventional chromatography have been used to capture erythropoietin (EPO) from mammalian cell culture supernatant. Currently, chromatographic adsorbent perfusion is available, however a limited number of applications have been found in the literature. In this work, three anion exchange chromatographic supports (gel, membrane and monolithic) were evaluated in the capture step of the recombinant erythropoietin purification process. The influences of load and flow rate on each support performance were analyzed. Also the purity of the EPO molecules was determined. A productivity analysis, as a decision tool for larger scale implementation, was done. As a conclusion, the evaluated supports are technically suitable to capture EPO with adequate recovery and good purity. However, the monolithic column admits high operating velocity, showing the highest adsorption capacity and productivity.