Elongation flow studies of DNA as a function of temperature

The response of T4‐phage DNA molecules to an elongational flow field was monitored by flow‐induced birefringence as a function of temperature. The flow‐induced birefringence observed in this study was localized in the pure elongational flow area with a critical strain rate, indicating that the birefringence was attributed to a coil–stretch transition of DNA molecules. The slight decrease in the birefringence intensity with increases in temperature to 40°C was explained by a thermal‐activation process. At temperatures above 50°C, flow‐induced birefringence decreased remarkably, and no birefringence was observed at temperatures above 60°C. After the flow experiments, ambient temperature was reduced back to room temperature, and flow experiments at room temperature were performed again. Flow‐induced birefringence was recovered almost completely in samples for which the first flow measurements were made at temperatures below 53°C. Irreversible changes were observed for samples for which the first flow experiments were performed at temperatures above 55°C. The temperature dependence of UV‐absorption spectra revealed that the double‐strand DNA helix began to partially untwine at a temperature over 50°C, and duplexes became almost completely untwined at a temperature over 55°C. A comparison of electrophoresis patterns for untwined molecules showed that flow‐induced scission of DNA molecules occurred in a sample solution in flow experiments performed at 65°C, while no molecular weight reduction was observed in the sample solution at 55°C. In this article, this difference between the untwined DNA molecules is discussed on the basis of the thermally activated bond scission (TABS) model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1357–1365, 2002     

Inception and termination of the core‐annular flow pattern for oil‐water downflow through a vertical pipe

Different flow patterns for lube oil–water and for kerosene‐water downflow through a vertical glass tube have been analyzed with the help of flow visualization. Core‐annular flow is the dominant flow regime, with oil forming the core, and water is forming the wall film. When the velocities are increased, transition to slug flow and transition to dispersed flow are found. The waves found during the transition to slug flow depend on oil viscosity: axisymmetric bamboo waves are seen in kerosene‐water downflow and the waves are asymmetric in case of lube oil–water flow where they have a cork‐screw shape. Based on the experimental observations, simple mathematical models have been proposed for predicting the flow pattern transition curves. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Moisture diffusion in epoxy systems

The moisture diffusion process of an epoxy system is studied as a function of epoxy‐amine stoichiometry and the resulting microstructure. Differences in diffusion behavior are related to the relative importance of diffusion through the low‐density and high‐density microstructural phases for different stoichiometries. Also, changes in saturation level with stoichiometry are explained by competing effects of free volume versus the content of the low‐density phase. Increasing the humidity level causes a corresponding increase in saturation level, while increasing the temperature causes more pronounced non‐Fickian behavior. The effects of absorbed moisture on the thermomechanical properties of the epoxies are also investigated. Reductions in the glass transition temperature, T_g, and moisture‐induced swelling strains are measured after exposure of samples to the three conditioning environments. Moisture‐induced swelling strains increase with increasing moisture content. The reductions in T_g range from 5 to 20°C and are generally larger for amine‐rich samples than for epoxy‐rich and stoichiometric samples. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 787–798, 1999     

Counter‐ion‐specific helix formation of poly(γ‐methyl L‐glutamate) derivatives containing sulfonate group in aqueous alcohols

Charged polypeptides containing sulfonate groups were prepared by transesterification of poly(γ‐methyl L ‐glutamate) with isethionic acid. The coil–helix transition of the sulfonated polypeptides was investigated in aqueous alcohols. Marked counter‐ion specificity was observed for helix formation: Li⁺ < Na⁺ < Cs⁺ ≦ Rb⁺ ≦ K⁺; this was different to that for poly(L ‐glutamate) (PLG): Cs⁺ ? K⁺ < Li⁺ < Na⁺. Specific helix stabilization by counter‐ion mixing, which has been found for the PLG system, was not observed for the sulfonated polypeptides. The counter‐ion‐ and solvent‐specific helix formation is discussed and compared with that in PLG. © 2001 Society of Chemical Industry     

Urea‐induced conformational changes of chitosan molecules and the shift of break point of Mark–Houwink equation by increasing urea concentration

Chitosan solutions of the same 83% degree of deacetylation (DD) but different weight average molecular weights (M_ws) (78–914 kDa) in 0.01M HCl containing different concentrations of urea (0–6M) were prepared. Intrinsic viscosity ([η]) and weight average molecular weight (M_w) of chitosan were measured with a capillary viscometer and light scattering, respectively. Mark–Houwink exponent a was used as the parameter of conformational index. The Mark–Houwink exponent a increased with increasing concentrations of urea. When solutions contained 0, 2, 3, 4, and 6M urea, the value of a increased from 0.715 to 0.839, 0.894, 1.000, and 1.060, respectively. This indicates the occurrence of urea‐induced conformational transitions of chitosans. The break point shifted from 223 kDa in solutions containing no urea to 280 kDa in 2M urea solutions, to 362 kDa in 4M urea solutions and further to 481 kDa in 6M urea solutions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 452–457, 2000     

Higher‐Order Human Telomeric G‐Quadruplex DNA Metalloenzymes Enhance Enantioselectivity in the Diels–Alder Reaction

Short human telomeric (HT) DNA sequences form single G‐quadruplex (G₄) units and exhibit structure‐based stereocontrol for a series of reactions. However, for more biologically relevant higher‐order HT G₄‐DNAs (beyond a single G₄ unit), the catalytic performances are unknown. Here, we found that higher‐order HT G₄‐DNA copper metalloenzymes (two or three G₄ units) afford remarkably higher enantioselectivity (>90 % ee) and a five‐ to sixfold rate increase, compared to a single G₄ unit, for the Diels–Alder reaction. Electron paramagnetic resonance (EPR) and enzymatic kinetic studies revealed that the distinct catalytic function between single and higher‐order G₄‐DNA copper metalloenzymes can be attributed to different Cu^II coordination environments and substrate specificity. Our finding suggests that, like protein enzymes and ribozymes, higher‐order structural organization is crucial for G₄‐DNA‐based catalysis.     

Hydrodynamics and mass transfer of gas–liquid flow in a falling film microreactor

In this article, flow pattern of liquid film and flooding phenomena of a falling film microreactor (FFMR) were investigated using high‐speed CCD camera. Three flow regimes were identified as “corner rivulet flow,” “falling film flow with dry patches,” and “complete falling film flow” when liquid flow rate increased gradually. Besides liquid film flow in microchannels, a flooding presented as the flow of liquid along the side wall of gas chamber in FFMR was found at high liquid flow rate. Moreover, the flooding could be initiated at lower flow rate with the reduction of the depth of the gas chamber. CO₂ absorption was then investigated under the complete falling flow regime in FFMR, where the effects of liquid viscosity and surface tension on mass transfer were demonstrated. The experimental results indicate that k_L is in the range of 5.83 to 13.4 × 10^?5 m s^?1 and an empirical correlation was proposed to predict k_L in FFMR. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Hydrodynamic modeling on the external liquid–solid wetting efficiency in a trickling flow reactor

A three‐region model was proposed, which considers the bed cross section being composed of a stagnant liquid region, a liquid film region, and a rivulet flow region. To estimate the fractions of the three regions, the fraction of film flow was evaluated first, by transforming the complex trickling flow texture into pure liquid film flow. Through the measurements of liquid holdup and pressure drop for the film flow, a relationship between relative permeability and gas saturation was established, and from which the fraction of film flow region was obtained. It shows packing size is most important to the faction of rivulet flow. The external wetting efficiency of the packing was correlated as the sum of two‐third power of the liquid film fraction and the rivulet flow fraction, besides, a correlation based on Reynolds and Galileo numbers of the two phases in the form of was proposed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 283–294, 2013     

Study of cryostructuring of polymer systems. XIX. On the nature of intermolecular links in the cryogels of locust bean gum

In this study of freeze–thaw‐induced gelation of aqueous locust bean gum (LBG) solutions we found that gel formation proceeded through at least two kinetic stages. Initially, rather weak spongy cryostructurates were formed as a result of freezing the system, but their strength and thermostability (fusion temperature) could be increased considerably by means of thawing out the system sufficiently slowly. Preparation of LBG cryogels in the presence of chaotropic (urea) and anti‐chaotropic (sodium sulfate) substances showed that the major mechanism responsible for stabilization of junction zones in these gel materials was hydrogen bonding. Therefore, use of the agents facilitating formation of hydrogen bonds enabled the gelation of LBG solutions without the need for synergistic polymers or cryogenic treatments. © 2000 Society of Chemical Industry     

Trajectory modeling of gas–liquid flow in microchannels with stochastic differential equation and optical measurement

The numbering‐up of microchannel reactors definitely faces great challenge in uniformly distributing fluid flow in every channel, especially for multiphase systems. A model of stochastic differential equations (SDEs) is proposed based on the experimental data recorded by a long‐term optical measurement to well quantify the stochastic trajectories of gas bubbles and liquid slugs in parallel microchannels interconnected with two dichotomic distributors. The expectation and variance of each subflow rate are derived explicitly from the SDEs associated with the Fokker–Planck equation and solved numerically. A bifurcation in the trajectory is found using the original model, then a modification on interactions of feedback and crosstalk is introduced, the evolutions of subflow rates calculated by the modified model match well with experimental results. The established methodology is helpful for characterizing the flow uniformity and numbering‐up the microchannel reactors of multiphase system. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4028–4034, 2015     

Study of cryostructuration of polymer systems. XVI. Freeze–thaw‐induced effects in the low concentration systems amylopectin–water

Studies of the freeze–thaw behavior of low‐concentrated (0.01–0.25 g/dL) water solutions and dilute pastes (0.5–1.0 g/dL) of maize starch amylopectin showed that cryogenic treatment of these systems resulted in the formation of precipitated matter, whose yield and thermal characteristics (melting temperature and enthalpy) depended on the initial polymer concentration and conditions of freezing, frozen storage, and thawing. Research of the kinetic features of these cryoprecipitation events revealed at least two stages for this process: (i) a rapid stage, when the precipitation of virtually all of the dissolved polysaccharide occurred while the system was freezing, and (ii) a slower stage, the rate of which was mainly dependent on the thawing regimes or duration of the sample storage frozen at subzero temperatures. Cryoprecipitation phenomena were observed to be most extensive at temperatures 1–2° below the melting point of the frozen system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1740–1748, 2000     

Liquid‐bridge flow in the channel of helical string and its application to gas–liquid contacting process

To solve the problems of the traditional packings, such as high pressure drop, mal‐distribution and short liquid residence time, a helical flow structured packings was proposed. Two different flow patterns, liquid‐bridge flow and liquid‐drop flow were identified when the width of the channel of the helical string was adjusted. Moreover, the characteristics of the helical liquid‐bridge flow including maximum liquid loading, mean thickness of liquid film, mean residence time and effective specific surface area, were examined. And the separation efficiency was studied by the lab‐scale distillation column. In comparison, the effective specific surface area of the helical flow type packings is almost as large as the traditional B1‐350Y structured packings, but with thinner liquid film, longer liquid residence time and finally higher separation efficiency. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3360–3368, 2018     

Turbulent mixing in the confined swirling flow of a multi‐inlet vortex reactor

Turbulent mixing in the confined swirling flow of a multi‐inlet vortex reactor (MIVR) was investigated using planar laser induced fluorescence (PLIF). The investigated Reynolds numbers based on the bulk inlet velocity ranged from 3290 to 8225, and the Schmidt number of the passive scalar was 1250. Measurements were taken in the MIVR at three different heights (¼, ½, and ¾ planes). The mixing characteristics and performance of the MIVR were investigated using instantaneous PLIF fields and pointwise statistics such as mixture fraction mean, variance, and one‐point concentration probability density function. It was found that the scalar is stretched along velocity streamlines, forming a spiral mixing pattern in the free‐vortex region. In the forced‐vortex region, mixing intensifies as the turbulent fluctuations increase significantly there. The mixing mechanisms in the MIVR were revealed by identifying specific segregation zones. At Re = 8225 the mixing in the free‐vortex region was dominated by both large‐scale structures and turbulent diffusion, while in the forced‐vortex region mixing is dominated by turbulent diffusion. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2409–2419, 2017     

Simulations of solid–liquid scalar transfer for a spherical particle in laminar and turbulent flow

Scalar transfer from a solid sphere to a surrounding liquid has been studied numerically. The simulation procedure involves full hydrodynamic resolution of the solid–liquid interaction and the flow (laminar and turbulent) of the carrier fluid by means of the lattice‐Boltzmann method. Scalar transport is solved with a finite volume method on coupled overlapping domains (COD): an outer domain discretized with a cubic grid and a shell around the solid sphere with a spherical grid with fine spacing in the radial direction. The shell is needed given the thin scalar boundary layer around the sphere that is the result of high Schmidt numbers (up to Sc = 1000). After assessing the COD approach for laminar benchmark cases, it is applied to a sphere moving through homogeneous isotropic turbulence with the sphere radius larger (by typically a factor of 10) than the Kolmogorov length scale so that it experiences an inhomogeneous hydrodynamic environment. This translates in pronounced scalar concentration variations and transfer rates over the sphere's surface. Overall scalar‐transfer coefficients are compared to those derived from classical Sherwood number correlations. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1202–1215, 2014     

Finite pointset method for simulation of the liquid–liquid flow field in an extractor

Finite pointset method (FPM) is applied for the simulation of the single- and two-phase flow field in a rotating disc contactor (RDC) type extraction column. FPM is a numerical method to solve fluid dynamic equations. This is a Lagrangian and meshfree particle method, where the particles move with fluid velocity and carry all information necessary for solving fluid dynamic quantities. The simulations are validated by single- and two-phase 2D particle image velocimetry (PIV) measurements. In addition, the results are compared to simulations of the commercial CFD code Fluent. The results show that FPM can predict the one- and two-phase flow field in the RDC, whereas the predicted velocities are in good agreement with the experimental ones. FPM also bears comparison with the results of the commercial CFD code Fluent.     

Identification of the flow structures and regime transition in gas–solid fluidized beds through moment analysis

Using statistic parameters of solids holdup signals, a moment consistency data processing method (MCDPM) was proposed. Experiments were carried out using FCC particles of 76 μm under different operating conditions, and MCDPM was used to successfully obtain solids holdups of the dense and dilute phases and the phase fractions over five fluidization regimes, bubbling (BFB), turbulent (TFB), circulating turbulent (CTFB), high‐density circulating (HDCFB), and circulating (CFB) fluidized bed systems. In BFB, TFB, and CTFB regimes, only dense phase fraction decreased with increasing air velocity, while the transition from HDCFB to CFB experienced appreciable change in the solids holdup of the dense phase. From the low‐velocity to the high‐velocity regimes, both the solids holdup and the fraction of the dense phase experienced a drastic decrease, suggesting that this transition corresponded to a profound change in flow structure and further suggesting that CTFB is in reality still a TFB. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1479–1490, 2013     

Acoustic characteristics of PMMA in the steady stress–strain state investigated by coherent Brillouin scattering method

The acoustic properties of PMMA poly(methyl methacrylate) deformed by tensile stress were investigated by the coherent Brillouin scattering method. The ultrasonic velocities of PMMA in steady stress–strain states were measured in the frequency range of 100 MHz to 1 GHz. The ultrasonic velocities decreased with increasing strain, and the ratio of the decrease increased with increasing strain rate. This result indicates that the crazing residues still remain in the steady stress–strain states, and the amount of the residues depends upon the strain rate. The velocity dispersion was observed around 400 MHz for virgin and deformed PMMA and reproduced with a single relaxation process. The relaxation process is assigned to the γ‐relaxation according to the dispersion map for methyl group relaxation in PMMA. The relaxation frequency and strength were independent of the applied stress and strain. The viscoelastic and plastic deformations have little effect on the γ‐relaxation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 978–986, 2000     

On the correlation equations of liquid and solid 13C‐NMR,thermomechanical analysis,Tg, and network strength in polycondensation resins

Wide‐scope mathematical relationships have been established between the ¹³C‐NMR of liquid polycondensation resins, such as urea–formaldehyde and phenol–formaldehyde resins, and the strength of the network formed by the same resin when hardened under well‐defined conditions, the thermomechanical analysis deflection, the number average molecular mass and the number of degrees of freedom of the average polymer segment between crosslinking nodes in the hardened resin network, the resin network glass transition temperature, its solid‐phase ¹³C‐NMR proton‐rotating frame spin‐lattice relaxation time, and the homogeneous and heterogeneous polymer segment/polymer segment interfacial interaction energy calculated by molecular mechanics. These mathematical relationships allow the calculation of any of these parameters from any of the techniques listed, provided that all of the systems are used under well‐defined conditions. Under different conditions, the values of the numerical coefficients involved change; and, whereas the equations are still valid, a different set of coefficients needs to be recalculated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1703–1709, 1999