Experimental study of dielectrophoresis and liquid dielectrophoresis mechanisms for particle capture in a droplet

This work presents a microfluidic system that can transport, concentrate, and capture particles in a controllable droplet. Dielectrophoresis (DEP), a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field, is used to manipulate particles. Liquid dielectrophoresis (LDEP), a phenomenon in which a liquid moves toward regions of high electric field strength under a non-uniform electric field, is used to manipulate the fluid. In this study, a mechanism of droplet creation presented in a previous work that uses DEP and LDEP is improved. A driving electrode with a DEP gap is used to prevent beads from getting stuck at the interface between air and liquid, which is actuated with an AC signal of 200 V(pp) at a frequency of 100 kHz. DEP theory is used to calculate the DEP force in the liquid, and LDEP theory is used to analyze the influence of the DEP gap. The increment of the actuation voltage due to the electrode with a DEP gap is calculated. A set of microwell electrodes is used to capture a bead using DEP force, which is actuated with an AC signal of 20 V(pp) at a frequency of 5 MHz. A simulation is carried out to investigate the dimensions of the DEP gap and microwell electrodes. Experiments are performed to demonstrate the creation of a 100-nL droplet and the capture of individual 10-μm polystyrene latex beads in the droplet.     

N‐Linked Glycans of Chloroviruses Sharing a Core Architecture without Precedent

N‐glycosylation is a fundamental modification of proteins and exists in the three domains of life and in some viruses, including the chloroviruses, for which a new type of core N‐glycan is herein described. This N‐glycan core structure, common to all chloroviruses, is a pentasaccharide with a β‐glucose linked to an asparagine residue which is not located in the typical sequon N‐X‐T/S. The glucose is linked to a terminal xylose unit and a hyperbranched fucose, which is in turn substituted with a terminal galactose and a second xylose residue. The third position of the fucose unit is always linked to a rhamnose, which is a semiconserved element because its absolute configuration is virus‐dependent. Additional decorations occur on this core N‐glycan and represent a molecular signature for each chlorovirus.     

Electrophoresis of a rigid sphere in a Carreau fluid normal to a large charged disk

The electrophoresis of a rigid sphere in a Carreau fluid normal to a large disk is analyzed theoretically under the conditions of low surface potential and weak applied electric field. Previous analyses are extended to the case where a disk can be charged, and a more realistic electrostatic force formula is applied. We show that the qualitative behavior of a sphere depends largely on its distance from a disk, the thickness of double layer, and the nature of a fluid. In general, the presence of a disk has the effect of increasing the conventional hydrodynamic drag on a sphere, and a decrease in the thickness of the double layer surrounding a sphere has the effect of enhancing the shear-thinning effect. However, this might not be the case if a sphere is uncharged and a disk is charged, where the osmotic pressure field and the induced charge on the sphere surface can be significant. The shear-thinning effect is important only if the thickness of double layer is sufficiently thick. This result can play a significant role in practice such as in electrophoretic deposition, where the deposition electrode is charged and the fluid medium is usually of shearing-thinning nature.     

Information-theoretic approach to kinetic-energy functionals: the nearly uniform electron gas

We strengthen the connection between information theory and quantum mechanical systems using a recently developed dequantization procedure which results in a decomposition of the kinetic energy as the sum of a classical term and a purely quantum term. For the nearly uniform electron gas, we thereby approximate the noninteracting kinetic energy as the sum of the Thomas-Fermi term, which is exact for the uniform electron gas, and the Weizsäcker term, which is proportional to the Fisher information. Electron correlation is included via a nonlocal analytical expression which is a functional of the (N-1)-conditional probability density. This expression is evaluated via a statistically rigorous Monte-Carlo procedure to obtain the correlation energy as a functional of the electron density. We show that this functional is well aproximated by a term which is proportional to the Shannon entropy. Thus the kinetic energy is expressed as the standard Thomas-Fermi term plus terms which are proportional to two of the cornerstones of information theory: the Fisher information, which is a measure of localization, and the Shannon entropy, which is a measure of delocalization.     

Hybrid genetic algorithm–tabu search approach for optimising multilayer optical coatings

Constructing multilayer optical coatings (MOCs) is a difficult large-scale optimisation problem due to the enormous size of the search space. In the present paper, a new approach for designing MOCs is presented using genetic algorithms (GAs) and tabu search (TS). In this approach, it is not necessary to specify how many layers will be present in a design, only a maximum needs to be defined. As it is generally recognised that the existence of specific repeating blocks is beneficial for a design, a specific GA representation of a design is used which promotes the occurrence of repeating blocks. Solutions found by GAs are improved by a new refinement method, based on TS, a global optimisation method which is loosely based on artificial intelligence. The improvements are demonstrated by creating a visible transmitting/infrared reflecting filter with a wide variety of materials.     

Monte Carlo estimation of kinetic parameters in polymerization reactions

A general method for estimating kinetic parameters in polymerization reactions using Monte Carlo simulation to represent the models of the reactions is developed. From a statistical point of view, the procedure is a Bayesian one in which a posterior probability density surface (PPDS) is calculated for points on a grid in the parameter space. A smoothing function is fitted to the PPDS, then a posterior probability region, which is similar to a confidence region, is calculated for the parameters. An application to a relatively trivial example, the Mayo–Lewis copolymerization model is shown in detail. Many other potential applications are suggested.     

Surface-tension-driven instabilities of a pure liquid layer evaporating into an inert gas

A theoretical model of the evaporation of a pure liquid layer is developed. We focus on the influence of an inert gaseous component, in addition to vapor, on surface-tension-driven Bénard instabilities. It is assumed that the gas phase is perfectly mixed at some distance from the liquid-gas interface (given composition, pressure, and temperature). If this distance is not much larger than the liquid layer thickness, it is shown that a reduction of the full two-layer problem to a one-layer problem is possible, provided the evaporation rate is not too large. An analytical expression is given for the corresponding dimensionless heat transfer coefficient (a generalized, wavenumber-dependent Biot number) at the evaporating interface. The approach is validated through a comparison with a direct numerical resolution of the full two-layer problem.     

Optimization of asymmetric permeation in heterogeneous composite membranes

Asymmetric permeation in two-phase composite membranes with heterogeneous structures represented by a one-dimensional distribution of composition is treated theoretically on the basis of an irreversible thermodynamic transport equation. It is assumed that the permeability of one of the component phases is a monotone function of the activity of permeant while that of the other phase is constant, and that the permeability of the composite membrane is given by the volume average of the resistance coefficient, which is the inverse of permeability. Under these assumptions, it is shown that the optimal membrane which maximizes the degree of asymmetric permeation reduces to a binary laminate membrane. The condition for constructing the optimal laminate membrane is obtained explicitly. Conversely a condition on a desirable membrane component which realizes an arbitrary degree of asymmetric permeation is presented. These results can be applied to the optimal design of a membrane valve which is a chemical analog of a diode. © 1993 John Wiley & Sons, Inc.     

Coulometric sensors,the application of a sensor-actuator system for long-term stability in chemical sensing

We present a new type of chemical transducer, the coulometric sensor. This sensor is in fact an integrated sensor-actuator system that is able to measure the concentration of acids and bases by means of coulometric titration. An ISFET is used as the sensor to monitor the pH changes induced by the actuator, which is a gold electrode that fits closely around the ISFET's gate area. Coulometry is an absolute method and therefore the output of the new sensor is only determined by its dimensions and is not subject to changes in offset and sensitivity of the indicator electrode. It is thus expected that the operation of the sensor will be stable for a long time, so that only a one-time calibration is needed. As a first example of this new class of chemical transducers, a carbon dioxide sensor is presented. It is shown that the stability is some orders of magnitude better than that for a ‘classical” potentiometric sensor.     

Pretransitional electro-optic response of 6CB liquid crystal in the isotropic phase

In this work, the electro-optic response of a 6CB liquid crystal layer is studied using a sensitive differential technique. The layer is held at a temperature just above the nematic to isotropic phase transition. Transverse magnetic (p) polarized light incident on the cell is coupled to guided modes in the liquid crystal layer using prism coupling. The modes manifest themselves as sharp dips in the reflectivity as the angle of incidence is scanned. When a low frequency sinusoidal voltage is applied to the cell, the resonant mode shapes and excitation angles are altered at a frequency which is twice that of the applied field, resulting in a modulation of the reflectivity for a given angle of incidence. By synchronous observation of the modulated signal, a differential signal is recorded. Comparing the data with modelling generated from multilayer optics theory, two effects are then quantified. The first of these is an induced birefringence, varying quadratically with applied voltage, which is well understood and can be expressed in terms of Landau-de Gennes theory. The second is a field induced perturbation in the imaginary part of the optical permittivity, δε_i, which implies a modification of the light scattering properties of the liquid crystal. The measurement of the latter effect is, as far as we know, a novel one, being only made possible by the remarkable sensitivity of the synchronous differential technique.     

论化学反应动力学中的稳态假设

对单分子气相反应undemann机理提出了一个不用稳态假设的动力学新表述，并指出经典表述中的稳态假设是主观硬性加上的，缺少了一个条件。当反应气体压强变小时，经典表述中虽然应用稳态假设，但实际上是高活性中间产物的近似，并不真正存在稳态。稳态假设的适用性有两种不同的近似本质，一是平衡态近似或真稳态，另一是高活性中间产物近似，应予分辨。过去文献中往往把两者混在一起，这会导致得不到一般性结论，或所得一般性结论会有错误。文中也讨论了在复杂反应中真稳态的存在，而平衡态和真稳态的建立，都需经过一个初期瞬间过程，而高活性中间产物近似没有初期瞬间过程，因为不是一个形成稳态的过程。     

Facile Electrochemical Hydrogenation and Chlorination of Glassy Carbon to Produce Highly Reactive and Uniform Surfaces for Stable Anchoring of Thiolated Molecules

Carbon is a highly adaptable family of materials and is one of the most chemically stable materials known, providing a remarkable platform for the development of tunable molecular interfaces. Herein, we report a two‐step process for the electrochemical hydrogenation of glassy carbon followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The carbon surface at each stage of the process is characterized by AFM, SEM, Raman, attenuated total reflectance (ATR) FTIR, X‐ray photoelectron spectroscopy (XPS), and electroanalytical techniques. Electrochemical chlorination of hydrogen‐terminated surfaces is achieved in just 5 min at room temperature with hydrochloric acid, and chemical chlorination is performed with phosphorus pentachloride at 50 °C over a three‐hour period. A more controlled and uniform surface is obtained using the electrochemical approach, as chemical chlorination is observed to damage the glassy carbon surface. A ferrocene‐labeled alkylthiol is used as a model system to demonstrate the genericity and potential application of the highly reactive chlorinated surface formed, and the methodology is optimized. This process is then applied to thiolated DNA, and the functionality of the immobilized DNA probe is demonstrated. XPS reveals the covalent bond formed to be a C?S bond. The thermal stability of the thiolated molecules anchored on the glassy carbon is evaluated, and is found to be far superior to that on gold surfaces. This is the first report on the electrochemical hydrogenation and electrochemical chlorination of a glassy carbon surface, and this facile process can be applied to the highly stable functionalization of carbon surfaces with a plethora of diverse molecules, finding widespread applications.     

Theoretical study of the ruthenium-catalyzed cyclocotrimerization of alkynes with isocyanates and iothiocyanates: cemoselective formation of pyridine-2-one and thiopyrane-2-imine

The cyclocotrimerization of acetylene with isocyanate HNCO and isothiocyanate HNCS, mediated by CpRuCl, is theoretically investigated on the basis of DFT/B3LYP calculations. By these means, the experimental result can be rationalized as to why, with HNCO, a nitrogen-heterocycle is formed, but with HNCS a sulfur-heterocycle is formed. According to the proposed mechanism, the key reaction step is the addition of a double bond to a metallacyclopentatriene formed by oxidative coupling of two acetylene ligands coordinated to CpRuCl, giving a bicyclic carbene intermediate. This double-bond-addition is initiated by eta1 attack at the ruthenium center, and it is just the attacking atom that is going to be incorporated into the cycle. Thus, the chemoselectivity originates from the fact that, for HNCO, N attack is preferred over O, but for HNCS, S attack is preferred over N. The onward reaction is a reductive elimination to give a coordinatively unsaturated metallaheteronorbornene intermediate finally rearranging to a ligated heterocycle. Completion of the cycles is achieved by an exothermic displacement of the respective heterocyclic product by two acetylene molecules which regenerates the bisacetylene complex.     

Moving of a nonhomogeneous, porous floc normal to a rigid plate

The boundary effect on the moving of a porous, nonhomogeneous, spherical floc normal to a rigid plate is analyzed theoretically for the case of low to medium Reynolds number. In particular, the drag force acting on the floc under various conditions is evaluated. A two-layer structure is adopted to simulate the nonhomogeneous nature of a floc. We show that if a floc is away from the plate, the streamlines surrounding the floc are distorted, but the degree of distortion becomes less significant if the floc is near the plate. The modified drag coefficient of a porous floc is orders of magnitude smaller than that of the corresponding rigid particle. For a fixed volume-averaged permeability, the effect of the presence of the plate on the behavior of a nonhomogeneous floc is more significant than that of a homogeneous floc, and this effect depends largely on the structure of a floc. The nonhomogeneous structure of a floc leads to a positive deviation from a Stokes-law-like correlation in the modified drag coefficient, and the smaller the volume-averaged permeability of a floc the greater the deviation. The presence of the plate has the effect of reducing this deviation. The nonhomogeneous structure of a floc on its modified drag coefficient is pronounced when it is close to a boundary.     

Automated precolumn derivatization device to determine neurotransmitter and other amino acids by reversed-phase high-performance liquid chromatography

A device to derivatize amino acids with o-phthaldialdehyde, which is directly connected to high-performance liquid chromatographic equipment is described. Its principle is that a sample (10-500 microliters) is mixed with a reagent (containing o-phthaldialdehyde, 2-mercaptoethanol and sodium hydrogen carbonate buffer), using a peristaltic pump. This mixture is pumped into a loop of a pneumatically controlled injection valve at atmospheric pressure. When the derivatization is complete the valve switches, so that the sample is applied to a column and the amino acid derivatives are separated with a gradient of methanol-phosphate buffers. The reproducibility is such that brain perfusates or tissue extracts can be analyzed for the amino acid transmitter content and no internal standard is necessary. The major advantages of the present device are that it produces thorough mixing of reagent and sample, so that a high and constant degree of derivatization occurs (thus producing high sensitivity; less than 0.1 pmol can be detected) and its low cost.     

Design and fabrication of 2 kHz nematic liquid crystal variable retarder with reflection mode

ABSTRACT

This study proposes a simple method of designing a high-speed liquid crystal variable retarder (LCVR) with reflection mode. First, a series of simple formulas is provided for analysing the effects of tilt incidence and birefringence of the liquid crystal on the phase retardation and response time of the LCVR. Then, a reflective LCVR is fabricated to validate the theoretical analysis. Measured results show that the response speed can reach 2.7 kHz with a phase retardation of 1 λ. Furthermore, the theoretical curve is close to the measured curve while the incident angle is less than 10°. However, the theoretical and measured values show a considerable difference under a large incident angle. This problem is discussed, and a modified method is given. This work is helpful for the design and fabrication of high-speed LCVR.     

Effect of a charged boundary on electrophoresis in a Carreau fluid: a sphere at an arbitrary position in a spherical cavity

The influence of a charged boundary on the electrophoretic behavior of an entity in a non-Newtonian fluid is studied by considering a sphere at an arbitrary position in a spherical cavity filled with a Carreau fluid under the conditions of low surface potential and weak applied electric field. The dependence of the mobility of a sphere on its position in a cavity, the size of a cavity, the thickness of a double layer, and the nature of a fluid is investigated. In addition to the fact that the effect of shear-thinning is advantageous to the movement of a sphere, several other interesting results are also observed. For instance, if an uncharged sphere is in a positively charged cavity, where the electroosmotic flow and the induced charge on the sphere surface play a role, the effect of shear-thinning is important only if the thickness of the double layer is either sufficiently thin or sufficiently thick. However, this might not be the case if a positively charged sphere is in an uncharged cavity.     

On the path-dependence of the open-cell voltage of a galvanic cell involving a ternary or multinary compound with multiple mobile ionic species under multiple chemical potential gradients

It is well known that the open-cell voltage (U) of a galvanic cell involving a binary compound, or a multinary compound with a single kind of mobile ionic species, is a state property under a gradient of chemical potential of the mobile component. It is not so transparent, however, whether U is still a state property when involving a ternary or multinary compound with two or more kinds of mobile ions under multiple chemical potential gradients of those mobile components. We clarify this issue with a multinary oxide that conducts oxide ions, protons and electron holes and is exposed to the chemical potential gradients of both water and oxygen. We show that U is path- and history-dependent, and manifests itself along the diffusion paths of the two mobile components H and O under given boundary conditions.     

Intrinsic field theory of chemical reactions

An intrinsic principle of least action is presented for the intrinsic dynamism of chemical reactions. Then, as the stationary trajectory, a meta-IRC (intrinsic reaction coordinate) draws a geodesic curve in a rigged Riemannian space. This establishes a geodesic law for the intrinsic dynamism. Moreover, a diagrammatic perturbation theory is formulated for the intrinsic dynamism, and a dynamical interaction between a chemically reacting system and a background system is investigated. Then, the structural stability of the system is discussed using a new concept of the dynamical potential field. An example is given in order to elucidate the present theory.Dedicated to Prof. Hermann Hartmann on the occasion of his 65th birthday.