Use Of Electric Fields Research Articles

Pseudo-coulmetric loading in capillary electrophoresis DNA sequencing

While injection volumes in capillary electrophoresis are typically in the nanoliter range, it is difficult to physically prepare and manipulate samples much smaller than a microliter. As a result, only a small fraction of the analyte contained with the sample volume is transferred to the capillary. This problem is particularly acute in DNA sequencing applications, where on-column stacking is difficult and where the sequencing sample is relatively expensive to prepare. We report a method that transfers 75% of the DNA contained within a 3 μl sample onto a capillary for DNA sequencing. This method relies on the use of very low ionic strength formamide to resuspend the DNA after an ethanol precipitation. The use of low ionic strength formamide achieves two tasks. First, it produces a very high resistance sample, which increases the voltage drop across the sample and decreases the field across the capillary. This electric field manipulation ensures that DNA fragments do not migrate down the capillary during the loading process, allowing long injection periods without excessive band-broadening. Second, the low ionic strength of the formamide increases the transference number of the DNA; more of the current passing through the injection tip of the capillary is carried by DNA fragments. In the limit of complete elimination of impurity ions from the loading solvent, current passing through the sample is carried only by DNA fragments and loading becomes a coulometric process.

Cylindrical conductive particles in the proximity of an electrode affected by a high-intensity electric field

The electrostatics of cylindrical conductive particles between parallel plane electrodes is a research topic related to the development of various technologies which make use of electric fields for processing of granular materials. A program based on the boundary-element method was employed in order to compute the charge acquired by conductive cylinders and the force acting on them, while in contact with or in the proximity of an electrode, affected by a uniform field. The calculations shown that the field intensification generated by these particles is a function of their charge, of their dimensions and of their position with respect to an electrode of similar or opposite polarity. The basic experimental set-up consisted of two horizontally disposed parallel-plate electrodes, in air at atmospheric pressure. In some experiments, the upper electrode was substituted by a matrix of corona-emitting points, in order to evidence the peculiarities of particle behaviour in an ionized field. Conductive cylinders (diameters: 0.5–1.5 mm, lengths: 2–20 mm) were placed on the bottom electrode. The dielectric strength of air gaps containing single conductive particles was found to decrease in the presence of space charge. Mobile cylindrical particles were proved to be more harmful than the fixed ones.

Electric field induced gas permeation change at the interface of ferroelectrics and electrode.

Shape-selective catalysis and efficient separation of gases have been achieved with A-order pores of zeolite, such as ZSM-5 (Young et al., 1982). Highly selective catalysts have recently been obtained by synthesizing mesoporous siliceous materials with 2.5 to 10 nm pores (Kresge et al., 1992; Tanev et al., 1994). Techniques for controlling flow rates of gases and liquids with micro switching valves have also been developed (Emmer et al., 1992; Shoji and Esashi, 1994), where the gas feed is precisely controlled by opening and shutting an aperture driven by a stack-type piezoelectric actuator. If the aperture size is reduced to molecular dimensions, more efficient separation and catalysis are possible, as by use of electric fields one can directly change the space which is the key in functions of separation and catalysis by porous materials. Piezoelectric action has been utilized at the soft solid-solid interface of a piezoelectric polymer (Seto, 1995). Further, we devised an apparatus in which electrostatic force was utilized at the solid-solid interface of ferroelectric ceramics sandwiched in between two electrodes. The microaperture was fabricated at the interface by means of a vapor deposition technique. The microaperture is changed by the electrostatic force generated under the imposed electric field. This paper reports the measurement of field-induced permeation change at the microaperture and its dependence on gas type

Nerve regeneration

The regeneration of nerve is a brilliant example of plasticity within the nervous system. Axonal sprouts form within a few hours of nerve injury and grow vigorously over long distances. Nonetheless, recovery from nerve injury, such as that seen after laceration of distal motor-sensory nerve, is often incomplete. A variety of approaches to enhance peripheral nerve regeneration are currently being pursued. They include the use of electric fields, treatment with neurotrophic factors and Schwann cell manipulation.

Use of electric fields to study nuclear spin conversion in molecules. Application to CH 3F

The ortho-para nuclear spin conversion rate of gaseous 13CH 3F molecules subjected to an external electric field has been calculated in the framework of intramolecular state mixing. Results are given for the mixing induced by the magnetic dipole-dipole interaction between the molecular nuclei. It is found that the Stark shift of the rotational levels can speed up the conversion rate by a few orders of magnitude at gas pressures appropriate to the experiment. Measurements of this effect will provide information about the role of state mixing in the conversion and the type of intramolecular interaction involved.

Second-order polarizability of donor—acceptor substituted oligothiophenes: substituent variation and conjugation length dependence

Second-order polarizabilities and excited state dipole moments of a number of donor—acceptor substituted α-oligothiophenes have been investigated by use of electric field induced second harmonic generation (EFISH), solvatochromism and electrooptical absorption measurements (EOAM). The experimental results reveal that oligothiophenes are very effective conjugation units offering substantial enhancement of the second-order polarizability with increasing chain length.

Photoconductivity Studies of Titanyl Phthaloc yanine

Abstract Recently, a new polymorph of TiOPc with characteristic XRD peaks at 2θ = 9.5 and 27.3° has been identified as having a quantum efficiency of carrier generation in the infrared approaching unity. In this paper, we will discuss the use of electric field induced fluorescence quenching technique in investigating the photoconductivity of this highly sensitive form of TiOPc. Linear correlation found between electric field induced fluorescence quenching and carrier generation in this material indicates that the photogeneration involves the field assisted dissociation of the first excited singlet state which is typical of other phthalocyanines. However, the highly sensitive TiOPc exhibits a smaller overall field dependence of carrier generation and an efficient carrier generation is “switched on” at much lower applied fields. Furthermore photoconductive and fluorescence responses are humidity dependent indicating that water plays an important role in the photogeneration processes.

Use of an electric field to alter membrane morphology in a polysulfone-polyvinylpyrrolidone blend

An inherent characteristic of many polymer-based systems used in membrane manufacture is the tendency to form numerous defects such as macrovoids and pinholes. Such defects are manifested as large scale surface pores. In this research note we discuss the potential use of electric fields to influence the mechanisms by which these defects are formed during the precipitation step in the wet-cast phase-inversion process for polymeric membrane formation. Several electrical field phenomena including surface-induced-polarization, electrohydrodynamic convection, and enhanced transport can potentially be used to alter polymeric membrane morphology if the time scale for these electric field effects is short enough. We report preliminary experimental results corresponding to the formation of tubular membranes from a polysulfone-polyvinylpyrrolidone blend in a N,N-dimethylacetamide solution precipitated in water under the influence of an a.c. electric field. This study suggests that the electric field effects can be operative on the short time scale of membrane formation. Based upon the statistically significant differences in the frequency distribution of defect number versus defect area which were obtained, the results indicate that the presence of a 2.2 kV/cm a.c. electric field decreases the average number density of defects while increasing the total defect area. These results suggest that further experiments with more sophisticated equipment would permit the electric field effects to be optimized in order to reduce the number and the size of the surface defects.

Immobilization osteoporosis in paraplegia.

The pathophysiology of osteoporosis as it relates to immobilization or disuse osteoporosis in paraplegics is briefly reviewed. The physiology of bone formation and resorption is discussed, and the influence of piezoelectric forces on bone integrity and the consequences of the loss of this effect in paraplegics is addressed. When bone is stressed, negative charges accumulate on the side from which the stress is applied and positive charges accumulate on the opposite side. Presumably the collagenous component of bone plays the major role in the generation of electrical potentials. Another mechanism important in the generation of electrical potentials is created by liquid planes streaming past solid planes. Diminished forces acting on bone, as in paraplegia, are translated into changes in the activity of bone remodeling units which can be assessed by histomorphic and histoenzymatic techniques. Other biochemical and endocrine consequences of immobilization involve increased serum calcium, decreased serum parathyroid hormone (PTH), and decreased dihydroxy-vitamin D synthesis. Urinary hydroxyproline and calcium excretion are increased, as is stool calcium. The bone loss that follows immobilization may produce an increased susceptibility to fractures involving long bones more than the spinal column, and is due more to decreased bone formation than to accelerated bone resorption. The treatment of immobilization osteoporosis primarily involves early remobilization, but other treatments, including the use of electrical fields and the administration of bisphosphonates, calcitonin, and a growth hormone are being actively investigated.

Electric field mediated transfer of enzymes into human oocytes

In an attempt to develop a simple, atraumatic technique of introducing macromolecules and enzymes into human oocytes, we have investigated the use of electric field mediated transfer. Eighty-seven percent of human oocytes showed cytochemical evidence for the transfer of the enzyme horseradish peroxidase (HRP). The cell viability after this procedure was 89% as determined by the vital dye rhodamine-123. This study demonstrates that the enzyme HRP can be transferred into human oocytes using the electric field mediated method. Functional activity of the enzyme was maintained after this transfer.

Temperature Dependence and Dispersion of the Rotatory Power of a Ferroelectric Liquid Crystal in the SI* Phase

Abstract High resolution rotatory power measurements have been carried out in the vicinity of the SA-SI* phase transition of 1-ethoxycarbonylethyl (S)-4-(4′-decyloxy-2′-hydroxybenzylidene)aminocinnamate (DOHBAECEC). A remarkable rotatory dispersion has been observed in the visible range, together with a decrease in light transmission due to the selective reflection phenomenon. This effect has allowed us to measure the helical pitch in the SI* phase and, in conjunction with the optical activity, to obtain the temperature dependence of the tilt angle. This indirect method, which has been recently described in the literature, provides the tilt data on the unperturbed helicoidal phase and thus avoids the problems connected with the use of electric fields. The tilt results present a behaviour similar to the case of a SA-SC* transition and can be accounted for within the framework of a mean-field model.

Electrophoresis of Cytoplasmic Molecules Through Gap Junctions by Externally Applied Electric Fields.

External electric fields are efficiently conducted into the cytoplasmic interior of extended chains of cells that are electrotonically coupled by gap junctions. For chains of cells or tissues that are much longer than their electrical length constant, the cytoplasmic electric field within the center of the ensemble is identical in magnitude to the externally applied field. Over a period of time, this internal electric field should cause a intercellular redistribution of charged molecules that are permeant to gap junctions, within the coupled tissue. This prediction was confirmed experimentally by observing the directed migration of 6-carboxyfluorescein (negatively charged) within the electrotonically coupled lateral giant neurons of a crayfish nerve cord under the influence of externally applied DC electric fields. To determine whether such redistributions could occur in developing epithelial tissues, hydra were exposed to DC electric fields, after charged fluorescent dyes had been loaded into their ectoderm. In this electrotonically coupled tissue, the fluorescent dyes also underwent an electrophoretic redistribution in response to externally applied fields. To facilitate the future use of electric fields as an experimental means to redistribute intracellular constituents in developing tissues, mathematical relationships are presented that predict the time course and steady-state concentration profiles of molecules under-going intercellular electrophoresis.

Use of Electric Fields in Solvent Extraction: A Review and Prospectus

Abstract Electric fields have been used in applications related to solvent extraction for nearly seventy years, primarily to break aqueous-in-organic emulsions. It was not until about twenty years ago that the use of electric fields was contemplated as a means of driving and controlling extraction processes. The initial ideas revolved around droplet formation from charged nozzles and have led to development of several designs for continuous contacting devices. Electric field driven devices are not used to any signific an text entin industry, but recent results in this area, some of which are described in this paper, suggest that this technique may produce systems that are an order of magnitude more effective than present day machines.

Liquid/vapour phase separation in 4He using electric fields

In space, a replacement must be found for gravity to physically control and, in certain instances, contain cryogenic liquids. A programme has been started at the Jet Propulsion Laboratory to study the use of electric field generated forces to establish the required orienting effects. We present measurements which show that it is possible to apply strong enough electric fields to a liquid/vapour interface of 4He to obtain an orienting force comparable to gravity. Our measurements span the temperature range 1.7–4.2 K and demonstrate the applicability of Pashen's law for maximum attainable field before breakdown occurs. Some advantages of the electric field separator as opposed to passive surface tension devices are identified.

Quadratic nonlinear properties of N-(4-nitrophenyl)-L-prolinol and of a newly engineered molecular compound N-(4-nitrophenyl)-N-methylaminoacetonitrile: a comparative study

A new molecular engineering strategy is proposed that favors the packing of charge-transfer conjugated molecules to enhance their crystalline quadratic nonlinear efficiency. A highly polar substituent is grafted to an achiral molecule at a position remote from the donor–acceptor π-electron conjugated system. Dipolar interaction forces will act mainly toward the antiparallel coupling of local dipoles, while the remaining nonlinear portion of the molecule is freed, under other influences, to set up a noncentrosymmetric and possibly optimal structure. Among other 4-nitroanilinelike compounds, N-(4-nitrophenyl)-N-methylaminoacetonitrile (NPAN) exemplifies this new approach and is shown to have a powder second-harmonic generation efficiency of the same order as that of N-(4-nitrophenyl)-L-prolinol (NPP), i.e., more than 2 orders of magnitude above that of urea. The nonlinearity of both molecules (vector part of the β tensor projected along the dipole moment) has been measured by use of electric-field induced second-harmonic (EFISH) generation in solution at 1.06 μm. The nonlinearity of the NPAN molecule is roughly half that of NPP, but the transparency range of NPAN is significantly increased toward the UV compared with that of NPP. Two theoretical models, based, respectively, on a finite-field perturbation of the Hartree–Fock equations and on a sum-over-states expansion of tensor β both at a semiempirical level of approximation, are used to compute the coefficients of the first-order hyperpolarizability of NPP and NPAN. A two-level quantum model is used to account for frequency dispersion, and theoretical crystalline coefficients are obtained from an oriented-gas description of the crystal. Theoretical molecular polarizabilities are in satisfactory agreement with the EFISH experimental results. The experimental crystalline nonlinearity of NPP is also well accounted for by calculations, while the optimized nonlinear coefficient dZYY of crystalline NPAN is predicted to be of the order of 140 × 10−9 esu, coming close to that of NPP.

Membrane fouling prevention in crossflow microfiltration by the use of electric fields

From an analysis of fluid velocity and electric field profiles the trajectory of particles through crossflow microfiltration units has been calculated. A tubular geometry filter leads to the most effective use of electrical power, when it is used as an aid to prevent membrane fouling. Results for plate, tubular and mutitube filters are given. Some experimental data from a tubular filter are presented, which demonstrate typical effects of the important parameters.

Use of electric fields to monitor the dynamical aspect of cell behavior in tissue culture.

Mammalian cells can be cultured and therefore studied in vitro. Normally, the cells' morphology and other static properties are observed with the aid of a light microscope. A method is described here that allows observation of the dynamical aspects of cultured cells. Mammalian fibroblasts are cultured in polystyrene dishes that contain evaporated gold electrodes. As the cells attach to the electrodes, their presence and their motion is directly reflected in the measured impedance.

Preparation of asymmetric charged membrane by electric field method.

A new method for a preparation of asymmetric charged polymer membranes by use of electric field is successfully applied to a system composed of acrylamide and methacrylic acid. The membrane obtained under +7000V has considerable asymmetry in the charge distribution of its vertical crosssection and in the membrane potential. A possible application of the method is inferred.

Electric field-mediated cell fusion

The use of electrical fields to guide, hold and fuse cells is described. The electrical fusion process consists of two steps: the cells are collected to form pearl-chains between Pt electrodes by the action of dielectrophoresis, then a brief DC pulse is applied, such that the breakdown voltage of the membranes is briefly exceeded and cell-to-cell juncture of the membranes occurs around the pore formed by the pulse. Giant fused cells (diameter up to 100 m) can be formed by the electrically mediated fusion of mouse 3T3 fibroblast cells, provided that pronase is added just before field application.

Enhancement of electron beam denitrization process by means of electric field

Abstract A novel way of denitrization and desulphurization of flue gas, “Electron Beam Method”, consist of two stage processes. The first one is a radiochemical process in which NO x and SO x are rapidly converted into solid aerosol particles by the irradiation of a high energy electron beam. NH 3 is added to the gas in this process. The second one is a collection process of these converted particles, which performed in an electrostatic precipitator located downstream. The authors discovered that this electrostatic precipitation can be made inside the irradiation chamber itself by applying a d.c. electric field. A further investigation revealed that the radiochemical process of denitrization is enhanced by application of the electric field. The electric field accelerated greatly the reaction rate once it exceeded 2.2 kV/cm, and the increment of the reaction rate became proportional to the 5th power of the increment of the field strength. This leads to an expectation that the high initial and running costs of the electron beam source—the major obstacles against the electron beam method in spite of its many advantages—may be greatly reduced by the use of electric field.