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.     

Dominant representations and a markaracter table for a group of finite order

Summary The concept of markaracter is proposed to discuss marks and characters for a group of finite order on a common basis. Thus, we consider a non-redundant set of dominant subgroups and a non-redundant set of dominant representations (SDR), where coset representations concerning cyclic subgroups are named dominant representations (DRs). The numbers of fixed points corresponding to each DR are collected to form a row vecter called a dominant markaracter (mark-character). Such dominant markaracters for the SDR are collected as a markaracter table. The markaracter table is related to a subdominant markaracter table of its subgroup so that the corresponding row of the former table is constructed from the latter. The data of the markaracter table are in turn used to construct a character table of the group, after each character is regarded as a markaracter and transformed into a multiplicity vector. The concept of orbit index is proposed to classify multiplicity vectors; thus, the orbit index of each DR is proved to be equal to one, while that corresonding to an irreducible representation is equal to zero.     

Measuring the electrophoretic mobility of concentrated suspensions in nonaqueous media

We present a new method of measuring the electrophoretic mobility of a particle in a concentrated suspension. The method is used to measure the electrophoretic mobility of PMMA particles (diameter 10 microm) suspended in a mixture of liquid hydrocarbons. The particle volume fraction of the suspension is varied from 0 up to 0.30 and the resulting variation of the electrophoretic mobility is discussed. The suspending liquid is such that its refractive index is very close to that of the particles. Thus the suspension is almost transparent and it is possible to follow through a microscope the motion of one particle. The suspension is subjected to a low-frequency electric field (0.5 Hz). The cell containing the suspension is mounted on a piezoelectric crystal. The displacement that compensates for the particle motion (when the particle image is steady) is determined.     

Popularising Chemistry in Secondary Schools——through the development of Scientific and Technological Literacy for All

While chemistry is popular for children of primary school age,its popularity drops dramatically in secondary schools,A potential solution to address this is to recognise the need for greater relevance-relevance to the curriculum,to the needs of society and,in the eyes of the students.The paper tries to puts forward a rethink of the philosophy for school chemistry education,based on the underlying belief that chemistry education is an integral part of education.The target is labelled scientific and technological literacy for all (STL),STL rejects the notion that chemistry is taught solely to acquire tha abilities to be a scientist and supports the vision of a single curriculum goal,applicable to all students.Besides being a philosophy,STL is also a teaching approach.This approach is to initiate the teaching of chemistry topics,starting from a carefully chosen society perspective and to introduce the conceptual learning on a need-to-know basis.A limitatioin is the professional development of teachers,Suggestion for overcoming this involve workshop on materials development.Aconcern is expressed in cases where teachers make use of ready-made teaching materials(a common practice),without first gaining an understanding and an appreciation of the intended philosophy related to these materials.     

On the choice of gaussian 4f functions for use in calculations on transition metal compounds

One uncontracted 4f gaussian function is found to perform well as a polarization function at the SCF level When correlation is included, it is found that a two-gaussian fit to a Slater 4f function is much superior to a single gaussian, but that a three-term GTO fit is only slightly better than the two-term GTO 4f.     

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.     

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.     

Recombination of ions of a dense ion plasma in a fluorine atmosphere

A new effect leading to the slowing of recombination in a weakly nonideal ion plasma is considered. The solvation of ions is included in the explanation of the results from studying a gas discharge afterglow in a fluorine atmosphere. It is shown that recombination in such a system is slowed in comparison to the standard relationships for ideal plasma. The formation and composition of cluster ions in such a medium are considered. The relationship between the variation in the kinetics of recombination and the course of the process according to a complicated mechanism with the intermediate formation of metastable cluster pairs is established. A quantitative model is built and a formula allowing us to describe the recombination rate over a wide range of parameters of the medium is obtained. It is shown that the proposed model is in good agreement with the experimental data.     

Linear analysis of pattern formation in nematics in oblique magnetic fields

The dynamics of nematic director field reorientation in non-Freedericksz geometries, after a magnetic field H is applied at an oblique angle relatively to the initial homogeneous director n 0 ( H not normal to n 0), is studied considering a magnetic reorientation driven by hydrodynamic instabilities (with backflow). This study is carried out for bounded samples between two parallel plates with planar boundary conditions and with rigid anchoring. Linear stability and wave vector selection analysis predict that, when the angle of the magnetic to the initial director field is increased, for a given magnetic field intensity, two transitions from a homogeneous to a transient distorted director field reorientation can occur: a transition at a first critical angle to an aperiodic distorted director field and a transition at a second critical angle to a periodic distorted director field. It is shown that the periodic mode is cut off at a higher reduced field when the magnetic field acts away from the normal direction.     

Use of molecular properties in the one-dimensional model of nonadiabatic transitions

A systematic analysis of a diabatization method proposed in a recent publication is presented for the one-dimensional linear model of nonadiabatic transitions, and the method is extended to the exponential model. The asymptotic behavior of molecular properties is studied, and the usefulness of simple properties like the kinetic energy and multipole moments is examined in detail. The method is easy to use, and provides a reliable a posteriori procedure to deal with the existence of strong radial couplings between adiabatic states, when a program to calculate the radial couplings exactly is not available.     

Gravity-induced convective flow in microfluidic systems: electrochemical characterization and application to enzyme-linked immunosorbent assay tests

A way of using gravity flow to induce a linear convection within a microfluidic system is presented. It is shown and mathematically supported that tilting a 1 cm long covered microchannel is enough to generate flow rates up to 1000 nL.min(-1), which represents a linear velocity of 2.4 mm.s(-1). This paper also presents a method to monitor the microfluidic events occurring in a covered microchannel when a difference of pressure is applied to force a solution to flow in said covered microchannel, thanks to electrodes inserted in the microfluidic device. Gravity-induced flow monitored electrochemically is applied to the performance of a parallel-microchannel enzyme-linked immunosorbent assay (ELISA) of the thyroid-stimulating hormone (TSH) with electrochemical detection. A simple method for generating and monitoring fluid flows is described, which can, for instance, be used for controlling parallel assays in microsystems.     

Protocol for uncertainty assessment of half-lives

The apparent tendency to underestimate the uncertainty of experimentally determined half-life values of radionuclides is discussed. It is argued that the uncertainty derived from a least-squares analysis of a decay curve is prone to error. As it is quite common for a series of activity measurement results to be autocorrelated, the prerequisite of randomness of data for common statistical tests to apply is not fulfilled. In this work, an alternative data analysis method is applied that leads to a more realistic uncertainty budget. The uncertainty components are being subdivided in three categories according to the relative frequency at which they occur, an appropriate uncertainty propagation formula applied and then the total uncertainty obtained from an independent sum. An attempt is made to apply the protocol to problematic cases in literature, yet it is clear that the reporting is usually incomplete for a full uncertainty analysis. Suggestions are made for a concise but more complete reporting style, for the sake of traceability.     

Spectrophotometric Evidence for the Formation of a Mixed Bismuth-Phosphorus Heteropoly Acid

Abstract

Spectrophotometric evidence is presented to show that bismuth interacts with phosphate and molybdate in acid solution to form a mixed bismuth-phosphorus heteropoly acid. The complex is similar to 12-molybdophosphoric acid by virtue of its degree of dissociation in both concentrated and dilute acid solutions. The complex is more stable than 12-molybdophosphoric acid because it is formed when bismuth is added to a solution of 12-molybdophosphoric acid. The proposed bismuth-phosphorus compound is reduced much more readily to a heteropoly blue than is 12-molybdophosphoric acid, a fact that has contributed to a false belief that the bismuth may have been acting catalytically in the reduction of 12-molybdophosphoric acid.     

Heterogeneous proton-bound dimers with a high dipole moment monomer: how could we experimentally observe these anomalous ionic hydrogen bonds?

Electronic structure calculations (CBS-QB3 and G3MP2) have been used to predict a suitable method to experimentally observe the anomalous structure which is predicted to exist in a proton-bound dimer with a high dipole moment monomer. The enthalpy associated with forming the proton-bound dimer from its protonated and neutral monomers is shown to be linearly related to the difference in proton affinities which has been observed experimentally. However, unlike previous experimental studies, the linear correlation is not predicted to depend strongly, if at all, on whether the basic sites are C=O, C=N, or O(H) n-donor bases. Thermochemical measurements, then, are probably not the best method to distinguish between the structures of heterogeneous proton-bound dimers. It has been shown that a suitable method to experimentally observe the anomalous structure of proton-bound dimers containing a high dipole moment monomer (or very polar monomer) is by spectroscopic measurement. The O-H+-O asymmetric stretch is probably not the best infrared band to try to correlate with structure. The best band to observe is one which is in a region of the spectrum not masked by other absorptions and is also sensitive to the proximity of the binding proton. For example, it is shown that the methanol-free O-H stretch is very sensitive to the O-H+ bond distance for a series of heterogeneous proton-bound dimers containing methanol. It is predicted that the free O-H stretch of the methanol/acetonitrile proton-bound dimer is more closely related to the O-H stretch in protonated methanol than the O-H stretch in neutral methanol. Observations of these bands should confirm that the proton is closer to methanol in the methanol/acetonitrile proton-bound dimer despite acetonitrile having a higher proton affinity.     

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.     

Raman hyperspectral imaging applied to chemical co-localization in diluted samples of perylene-doped nanotubes

Raman imaging is known to be an efficient tool to localize different chemical species in a sample. Nevertheless, the signature of a minor compound is hard to retrieve in a dense heterogeneous sample. This paper aims at demonstrating that Raman imaging used in a hyperspectral configuration is still a very efficient tool to extract the signature of traces in heterogeneous samples, if the sample is diluted. It opens the way to study chemical co-localization in the case of minor compounds. This possibility is illustrated in the case of perylene-doped single-wall nanotubes (SWNTs).     

Core model calculation of the electric field gradient: Projection operator formalism with application to NH3

A core model approach to the calculation of deuteron quadrupole coupling constants is investigated using NH₃ as an example. First the deuteron quadrupole coupling constant is calculated from a CNDO wave function. This result is subsequently improved by recomputing the N—D bond orbital by means of a variational calculation using the CNDO function to construct a core potential for the bond Hamiltonian. In order to simplify integrations a single-center basis is chosen to represent the variational wave function. A projection operator formalism is used as a computational scheme to maintain orthogonality of the bond orbital to core orbitals. Excellent agreement with experiment is obtained. The procedure is applicable to more complicated molecules.