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Frontiers of mechanical engineering (2020). doi:10.1007/s11465-019-0582-6, Published by Springer, Heidelberg, Secaucus, N.J.

Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs.

The topology of variable polarity (VP) arc welding power supply is composed of a first inverting stage responsible for the adjustment of output current amplitude and a second inverting stage used for the commutation of output current polarity. A reverse voltage generating (RVG) circuit is proposed, which could be applied in the second inverting stage of a VP arc welding power supply to generate a stable reverse voltage with fixed amplitude during the commutation procedure and to make the commutation rate of output current more rapidly. First, a basic circuit unit is designed to illustrate the operating principle of the RVG circuit. Then, the Pspice simulations for the comparison between the RVG circuit and the conventional RC resonant circuit in the half-bridge applications of second inverting stage are carried out to illustrate the superiority of RVG circuit. Finally, an experimental prototype of VP arc welding power supply is established to test and verify the proposed RVG circuit. The experimental waveforms of output current and voltage demonstrate that the RVG circuit is effective and suitable for generating a stable reverse voltage with fixed amplitude, and realizing a rapid commutation of the output current polarity in VP arc welding power supply.

White etching crack (WEC) early bearing failures occur when the rolling contact is subjected to a so-called additional load such as an electrical current flowing through the bearing, in addition to the pure rolling load (pHz). Tests on rolling bearings showed that a low electrical direct current flow, such as that resulting from electrostatic charges, can lead to WEC failures in oil-lubricated roller bearings and greased ball bearings.The WEC formation in the performed tests was dependent on the current, electrical polarity, load type (rotating or stationary ring load), and bearing load. A black oxidation of the WEC critical bearing ring led to a significant increase in lifetime. Based on the findings, the failure hypothesis “cathodic WEC fatigue” for electrical direct current-initiated WEC failures was established.

Electric field strength and polarity in electrospinning processes and their effect on process dynamics and the physical properties of as-spun fibers is studied. Using a solution of the neutral polymer such as poly(methyl methacrylate) (PMMA) we explored the electrospun jet motion issued from a Taylor cone. We focused on the straight jet section up to the incipient stage of the bending instability and on the radius of the disk of the fibers deposited on the collecting electrode. A new correlation formula using dimensionless parameters was found, characterizing the effect of the electric field on the length of the straight jet, L&tilde, E~E&tilde, 0.55. This correlation was found to be valid when the spinneret was either negatively or positively charged and the electrode grounded. The fiber deposition radius was found to be independent of the electric field strength and polarity. When the spinneret was negatively charged, L&tilde, E was longer, the as-spun fibers were wider. The positively charged setup resulted in fibers with enhanced mechanical properties and higher crystallinity. This work demonstrates that often-overlooked electrical polarity and field strength parameters influence the dynamics of fiber electrospinning, which is crucial for designing polymer fiber properties and optimizing their collection.

The vast majority of techniques to study the physiology of the nervous system involve inserting probes into the brain for stimulation, recording, or sampling. Research is increasingly uncovering the fine microstructure of the brain, each of its regions with dedicated functions. Accurate knowledge of the placement of probes interrogating these regions is critical. We have developed a customizable concentric marking electrode (CME) consisting of an iron core within a 125 μm-stainless steel (SS) sheath for co-localization of targeted regions in the brain. We used a dielectric layer stack of SiO2, Al2O3, SiO2 to electrically encapsulate the iron core and minimize exposure area to avoid significant increases in inflammatory response triggered by the probes. The CME can record multi-neuronal extracellular firing patterns. Appropriate electrical polarity of the iron and SS components controls the deposition of iron microdeposits on brain tissue. We show that in vivo labels by this method can be as small as 100 μm, visible via noninvasive magnetic resonance imaging (MRI) as well as post-mortem histology, and illustrate how deposit size can be tuned by varying stimulus parameters. We targeted the CA3 area of the hippocampus in adult rats and demonstrate that iron microdeposits are remarkably stable and persist up to 10 months post-deposition. Using a single probe for recording and marking avoids inaccuracies with re-insertion of separate probes and utilizes iron microdeposits as valuable fiducial markers in vivo and ex vivo.

We study the energy landscape of the negatively charged protein bovine serum albumin adsorbed on a negatively charged silica surface at pH 7. We use fully atomistic molecular dynamics (MD) and steered MD (SMD) to probe the energy of adsorption and the pathway for the surface diffusion of the protein and its associated activation energy. We find an adsorption energy ∼1.2 eV, which implies that adsorption is irreversible even on experimental time scales of hours. In contrast, the activation energy for surface diffusion is ∼0.4 eV so that it is observable on the MD simulation time scale of 100 ns. This analysis paves the way for a more detailed understanding of how a protein layer forms on biomaterial surfaces, even when the protein and surface share the same electrical polarity.

A novel method is proposed for non-contact measurement of static electricity distribution on a surface using focused ultrasound to excite movement of the charge. The focused ultrasound is generated by controlling individually the phases of 285 airborne ultrasound transducers, and it was demonstrated local excitation could be measured. An electric field is induced by local excitation of a charged object. The electric field intensity and phase are related to the surface potential and electrical polarity of the object, respectively. It is possible to measure static electricity distribution over an entire object surface by scanning the position of the focused ultrasound.

Nonpolar resistive switching (RS), a combination of bipolar and unipolar RS, is demonstrated for the first time in a single nanowire (NW) system. Exploiting Ag@TiO2 core–shell (CS) NWs synthesized by postgrowth shell formation, the switching mode is controlled by adjusting the current compliance effectively, tailoring the electrical polarity response. We demonstrate ON/OFF ratios of 105 and 107 for bipolar and unipolar modes, respectively. In the bipolar regime, retention times could be controlled up to 103 s, and in the unipolar mode, >106 s was recorded. We show how the unique dual-mode switching behavior is enabled by the defect-rich polycrystalline material structure of the TiO2 shell and the interaction between the Ag core and the Ag electrodes. These results provide a foundation for engineering nonpolar RS behaviors for memory storage and neuromorphic applications in CSNW structures.

The generally rhizotoxic ion Al3+ often enhances root growth at low concentrations. The hypothesis that Al3+ enhances growth by relieving H+ toxicity was tested with wheat seedlings (Triticum aestivum L.). Growth enhancement by Al3+ only occurred under acidic conditions that reduced root elongation. Al3+ increased cell membrane electrical polarity and stimulated H+ extrusion. Previous investigations have shown that Al3+ decreases solute leakage at low p H and that the alleviation of H+ toxicity by cations appears to be a general phenomenon with effectiveness dependent upon charge (C3+ >C2+ >Cl+ ). Alleviation of one cation toxicity by another toxic cation appears to be reciprocal so that Al3+ toxicity is relieved by H+ . It has been argued previously that this latter phenomenon accounts for the apparent toxicity of ALOH2+ and Al(OH)+2 . Reduction of cell-surface electrical potential by the ameliorative cation may reduce the cell-surface activity of the toxic cation.

Properties of methyl orange (MO) degradation and their dependence on experimental parameters such as electrical polarity, pulse frequency, the material, and thickness of the discharge electrode, as well as electrode gap distance were investigated in a laboratory scale pulsed corona discharge system. The MO degradation and H2O2 generation were significantly enhanced by positive polarity than negative polarity because of the numerous micro-discharges that were generated by the space charge effect induced by positive polarity. The increase of pulse frequency reduced the MO degradation even though it enhanced the number of streamers produced. An electrode material having low electrical and thermal conductivities resulted in more MO degradation. The smaller the curvature radius of the discharge electrode, the more efficient the MO degradation was. The number of electrode needles and the electrode gap distance also affected MO degradation during the discharge process.

A process of creating controlled silver nanostructures using atomic force microscope technique is reported. The nanostructures are grown on both the silica surface and silica–indium-tin-oxide interface of a silver salt impregnated mesoporous silica film, deposited on indium tin oxide coated glass substrate. Voltage is applied between a conductive atomic force microscope tip and the indium tin oxide substrate to create the silver nanostructures. The possibility of switching the positions of the nanostructures between the silica film surface and the film–indium-tin-oxide interface, by reversing the electrical polarity of the tip, is demonstrated. It is also shown that the conductive channels can be created through the silica layer provided that the created metallic nanostructures are large enough to grow inside the film volume from one side to the other. The electrical conductivity of the film can be locally changed in a reversible manner by applying successively negative and positive voltages to the tip.

Microtubules (MTs) are macromolecular structures consisting of tubulin heterodimers and present in almost every eukaryotic cell. MTs fulfill all conditions for generation of electromagnetic field and are electrically polar due to the electrical polarity of a tubulin heterodimer. The calculated static electric dipole moment of about 1000 Debye makes them capable of being aligned parallel to the applied electromagnetic field direction. In the present study, the tubulin heterodimers were extracted and purified from the rat brains. MTs were obtained by polymerization in vitro. Samples of microtubules were adsorbed in the absence and in the presence of electromagnetic fields with radio frequency of 900 Hz. Our results demonstrate the effect of electromagnetic field with 900 Hz frequency to change the structure of MTs. In this paper, a related patent was used that will help to better understand the studied subject.

Calcium phosphate powders (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, and tetracalcium phosphate) were electrically polarized by an applied dc voltage. Thermally stimulated depolarization current measurements confirmed that each calcium phosphate powder exhibited surface charges after polarization treatment. The surface adsorption of simvastatin on each powder was investigated. We observed a difference in adsorption between polarized and non-polarized powders. This difference in adsorption is due to the electrostatic force between the polarized surface and the open-ring form of simvastatin, which has a larger electrical polarity than its closed-ring form.

Polar tweed was discovered in mechanically stressed LaAlO3. Local patches of strained material (diameter ca. 5 μm) form interwoven patterns seen in birefringence images, Piezo-Force Microscopy (PFM) and Resonant Piezoelectric Spectroscopy (RPS). PFM and RPS observations prove unequivocally that electrical polarity exists inside the tweed patterns of LaAlO3. The local piezoelectric effect varies greatly within the tweed patterns and reaches magnitudes similar to quartz. The patterns were mapped by the shift of the Eg soft-mode frequency by Raman spectroscopy.

This article reports the piezoelectric moduli of wood d 31, d 32, and d 36. The piezoelectric moduli of wood d 31 and d 32 have not been previously reported, although there has been much research on the d 14 and d 25 moduli of wood. The moduli d 31, d 32, and d 36 were measured carefully because their absolute values were considerably smaller than those of d 14 and d 25. For Softwoods, d 36 values were mostly negative, whereas the values for hardwoods had either positive or negative values. The other moduli, d 31 and d 32, were a mixture of positive and negative values in softwoods and hardwoods. The existence of d 31 and d 32 suggests the presence of an electrical polarity of the cellulose crystal in the fiber direction of the wood. The polarities of d 31 and d 32 became clear from wood in the outer part of the trunk, where the crystallinity of cellulose is large and the alignment of the crystals becomes parallel to the fiber direction.

In recent years, multielement films have been required for high-performance cutting tools. In this paper, a Y-shaped filtered-arc-deposition (Y-FAD) system with two vacuum-arc sources was developed. First, an optimum magnetic coil arrangement was experimentally established to transport two plasma beams through the Y-shaped duct at the same time. Since the two plasma beams have the same electrical polarity, they naturally tend to repel each other. Therefore, in the second step, the two plasma beams were combined into one plasma beam through a mixer part by vibrating the plasma beams with a laterally oscillating magnetic field. Third, the electrical bias applied to the duct was optimized to obtain a higher transportation rate of plasma and deposition rate. After these design developments and tuning, titanium-aluminum (Ti-Al) film with a combined deposition pattern was finally obtained with Al and Ti cathodes. The controllability of the composition ratio by the arc current was verified.

Forest rings are large, circular features in boreal forests that commonly exceed [Formula: see text] in diameter and are visible on aerial photographs. A detailed study of redox conditions and spontaneous potential (SP) was carried out over a forest ring that overlies an [Formula: see text] accumulation. Studies included drilling, monitoring well installation, and downhole SP using both polarizing and nonpolarizing electrodes. Also measured were redox potential of groundwater and soils, concentrations of sulfur species in groundwater, and headspace concentrations of redox-sensitive gases in monitoring wells. The results show positive SP anomalies in the shallow subsurface and near-horizontal, negative-inward redox gradients in the water-saturated overburden at theedges of the ring. SP anomalies are spatially correlated with redox gradients, suggesting that the two are related. The SP anomalies may be produced in response to redox gradients as redox-active ions and polar molecules spontaneously align with the negative poles toward the oxidizing end of the gradient, i.e., toward their more electronegative neighbors. This orientation of dipoles imparts a macroscopic electrical polarity to the redox gradient and results in the observed positive electrical anomaly inside the forest ring. Ongoing oxidation reactions occurring around the periphery of the forest ring maintain strong [Formula: see text] concentration gradients, which result in an outward steady-state diffusive flux of [Formula: see text]. Electromigration of redox-active ions in the redox-induced electrical field may also contribute to maintenance of the redox gradient.

An innovative texturing technique, high repetitive rate YAG laser-induced discharge texturing (LIDT), has been developed. The principle is a laser pulse synchronized with electrical pulse radiates on one of two electrodes, a plasma plume appears, that serves as discharge channel and the breakdown may occur between the electrodes far below the breakdown threshold. If the roll and a conical metal rod are the two electrodes, with the rotating of roll and the moving of laser set and conical metal rod along the axial of the roll, the deterministic or the random crater patterns are obtained on the roll surface by a serial laser-induced discharge. The experiments were carried out in different current discharge waveforms, media and electrical polarities on several materials. The results show that crater morphology is mainly determined by electrical polarity and medium. Simple explanations of the result are suggested.

One of the most interesting questions about Titan is the possibility of finding evidence of electrical activity that could lead to some chemical transformations of its nitrogen and methane rich atmosphere. Following the proposal by Navarro-Gonzalez and Ramirez, (Navarro-Gonzalez, R., Ramirez, S.I., Corona discharge of Titan’s troposphere, Adv. Space Res. 19 (7), 1121–1133, 1997.) on the likelihood of the presence of electrical discharges developing in Titan’s low atmosphere, we present here the energy yields of 24 hydrocarbons and six nitriles synthesized by positive and negative corona discharges from mixtures of methane and nitrogen at 298 K. We have investigated the effect of the methane mixing ratio (0.02–0.1), gas pressure (100–1000 mbar), the electrical polarity of the corona discharge and the design of the reactor on the energy yields of the identified gas-phase organic products. Our results show that the synthesis of molecules containing 2 or 3 carbon atoms is slightly favoured by an initial gas pressure of 1000 mbar. Ethane and methanenitrile have the highest energy yields at a methane mixing ratio of 0.05. These molecules could be the precursors of heavier hydrocarbons and nitriles identified in our experiments at higher exposure times. Saturated hydrocarbons and nitriles have higher energy yields in positive corona discharge. We present and discuss these results in the frame of the Cassini–Huygens mission.

Microtubules form a fundamental organization structure in the cytoskeleton of the cell. Electrical polarity and high deformability at low stress are important physical properties of microtubules. I...

The correspondence of the state of alignment of macromolecules in biomimetic materials and natural tissues is demonstrated by investigating a mechanism of electrical polarity formation: An in vitro grown biomimetic FAp/gelatin composite is investigated for its polar properties by second harmonic (SHGM) and scanning pyroelectric microscopy (SPEM). Hexagonal prismatic seed crystals formed in gelatin gels represent a monodomain polar state, due to aligned mineralized gelatin molecules. Later growth stages, showing dumbbell morphologies, develop into a bipolar state because of surface recognition by gelatin functionality: A reversal of the polar alignment of macromolecules, thus, takes place close to that basal plane of the seed. In natural hard tissues (teeth and bone investigated by SPEM) and the biomimetic FAp/gelatin composite, we find a surprising analogy in view of growth-induced states of polarity: The development of polarity in vivo and in vitro can be explained by a Markov-type mechanism of molecular recognition during the attachment of macromolecules.

It was shown earlier [E. Kovacs, T. Savopol, A. Dinu, The polar behavior of frog photoreceptors, Biochim. Biophys. Acta, 1273 (1995) 217–222] that intact photoreceptor rod outer segments (ROS) are permanent dipoles, their polarity being, very probably, related to the dark current which flows along the cell in dark-adapted, living specimens [R.D. Penn, W.A. Hagins, S. Yoshikami, Dark current and photocurrent in retinal rods, Biophys. J. 10 (1970) 380–412; J.L. Schnapf, Dependence of the single photon response on longitudinal position of absorbtion in toad rod outer segment, J. Physiol. 343 (1983) 147–158] The light induced change in the dark current (the `photocurrent') is the electrophysiological response of the photoreceptor cell to the light stimulus, being large enough to account for the visual system's ability to detect single photons in the rod outer segments [R.D. Penn, W.A. Hagins, Kinetics of the photocurrent of retinal rods, Biophys. J. 12 (1972) 1073–1094]. The dark current is maintained by cell metabolism and is present only in freshly isolated, dark-adapted, living cells. If the cell polarity is related to the charge accumulation due to the dark current, it must also depend on cell metabolism. In order to check if the observed cell polarity is dependent indeed on cell energy, the sensitivity of photoreceptor orientation ability to Na+/K+-ATP-ase inhibitor, ouabaine was tested. It was found that photoreceptor rods loose their electrical polarity in the presence of ouabaine. That means that cell polarity is dependent on functioning of the membrane ion pumps, which provide a continuous flow of the dark current along the cell. Computerized videomicroscopy catching of photoreceptor cells orientation patterns in static electric fields thus seems to be a possible test for structural and functional integrity of photoreceptor cells to be used before performing elaborated microelectrophysiological measurements.

The regulation of chromosome separation during mitosis is not fully understood yet. Microtubules forming mitotic spindles are targets of treatment strategies which are aimed at (i) the triggering of the apoptosis or (ii) the interruption of uncontrolled cell division. Despite these facts, only few physical models relating to the dynamics of mitotic spindles exist up to now. In this paper, we present the first electromechanical model which enables calculation of the electromagnetic field coupled to acoustic vibrations of the mitotic spindle. This electromagnetic field originates from the electrical polarity of microtubules which form the mitotic spindle. The model is based on the approximation of resonantly vibrating microtubules by a network of oscillating electric dipoles. Our computational results predict the existence of a rapidly changing electric field which is generated by either driven or endogenous vibrations of the mitotic spindle. For certain values of parameters, the intensity of the electric field and its gradient reach values which may exert a not-inconsiderable force on chromosomes which are aligned in the spindle midzone. Our model may describe possible mechanisms of the effects of ultra-short electrical and mechanical pulses on dividing cells--a strategy used in novel methods for cancer treatment.

Mercury, a 2-TW inductive voltage adder located at the Naval Research Laboratory in Washington, DC, had previously been converted from negative to positive polarity output by rotating each of the cells[1]. Positive polarity was needed to field an ion-beam diode.[2] However, rotating the cells takes about 2 to 3 weeks and is very labor intensive. So, when we next needed to operate in positive polarity, we considered two options to quickly turnaround Mercury to positive polarity; reverse charging the Marx and fielding a vacuum convolute. Charging the Marx with the opposite polarity is the simplest way to operate Mercury in positive polarity. However, because the breakdown and flashover strengths of the components are lowered when the polarity is reversed in this way, it is required to limit the Marx charge to 2/3 of its normal charging voltage to prevent failures. This limits the maximum output voltage, with the existing center conductor, to about 4.5 MV. An alternative approach we considered was to operate in negative polarity but to field a vacuum convolute inside our large diameter load chamber. Simulations and field calculations showed that this approach could work and the maximum output would be about 6 MV. We chose to operate Mercury in positive polarity by reverse charging the Marx and successfully operated an ion diode at a lower power level. To improve the pulse shape, we modified the self-breaking PFL water switch hardware. After this and a few other changes, Mercury can now be switched to a reliable and repeatable positive polarity mode in days instead of weeks, although at a lower than maximum power level. Details and results will be presented.

Magnetic‐field penetration is characterized in a current conducting plasma between planar electrodes used as a plasma opening switch [G. G. Spanjers, E. J. Yadlowsky, R. C. Hazelton, and J. J. Moschella, J. Appl. Phys. 77, 3657 (1995)]. The experiment is performed in a regime where Hall effects [Amnon Fruchtman, Phys. Fluids B 3, 1908 (1991)] are predicted to describe the current channel migration. Measurements of the magnetic‐field penetration in two cases with opposite electrical polarity indicate that the Hall effects are not the dominate process. A one‐dimensional resistive magnetohydrodynamic model is used to show that current channels in agreement with those measured can be predicted through a coupling of a plasma snowplow motion with resistive diffusion.

The frictional properties of freshly cleaved (010) surfaces of the ferroelectric TriGlycine Sulfate (TGS) were investigated by combined scanning and friction force microscopy under ambient conditions. A frictional contrast could be observed between domains with different electrical polarity, as well as between terraces inside individual domains which are separated by steps of half of the unit-cell height or an odd multiple of this value. The latter contrast mechanism originates from the arrangement of the molecules at the surface which is chemically homogeneous, but structurally rotated by 180° between different terraces. The resulting asymmetric surface potential gives rise to a frictional anisotropy in different directions that can be detected by the force microscope, as well as to a change of the frictional force between forward and backward scan direction.

The effect of high-voltage electric fields on the degradation of penicillin G has been studied in the context of the electrostatically enhanced solvent extraction of penicillin from whole broths. Eight parameters (voltage, penicillin G concentration, pH, presence of whole broth material, electrical polarity, solvent exposure, joule heating and residence time) were studied.

We have imposed steady DC electric fields over developing gastrula and neurula stage axolotls, Ambystoma mexicanum. These applied voltages were meant to confound cues provided by endogenous currents and fields that we have measured and believe to be controls of pattern and morphogenesis during early development. Applied voltages in the physiological range (25–75 mV/mm) cause severe disruption of development when imposed over neurulae whose orientation within the field is random or fixed. In the latter case, developmental defects are more likely to occur at that end of the neurula (rostral or caudal) that faces the cathode, or negative pole, of the applied field. In neurulae whose orientation within the field was fixed, the lowest magnitude producing developmental abnormality was between 5 and 25 mV/mm. Physiological measurement of the embryonic transepithelial potential (TEP) when perturbed by artificially applied voltages demonstrates that ectoderm facing the cathode is hyperpolarized, while ectoderm facing the anode is depolarized at all fields strengths tested. These data show that the electrical polarity of embryonic ectoderm is predictably disrupted by applied voltages. Though applied voltages exert this same effect on the ectoderm of gastrulae, exposure only during gastrulation does not lead to developmental abnormality. This observation demonstrates that the applied electric field does not harm the embryo in some non-specific way and further emphasizes the stages of neurulation as those most sensitive to artificially applied or endogenous voltages. These data strongly support the notion the polarized natural voltages within amphibian embryos are controls of their emerging pattern. © 1994 Wiley-Liss, Inc.

Summary form only given. The Cornell University COBRA pulser is a nominal 1 MA, 1 MV machine, capable of driving upto 8 wire cylindrical Z pinches. COBRA operates normally in negative polarity, with the driving capacitors charged negative with respect to machine ground. This in turn normally establishes the polarity of the array to be negative with respect to the grounded return conductors that are symmetrically located outside of the array radius. A bolt-on convolute can be arranged to establish the negative array potential described above. This will be referred to as the "negative polarity" configuration, and in this case the electric field lines terminate on the wires of the array, a condition favorable for generating electron field emission. If a section of the convolute is rotated, then one end of the array is attached to machine ground, and one end of each of the return conductors, still outside the radius of the array, is connected to the negative machine potential. The electric field lines in this configuration originate on the wires of the array, and this is referred to as the "positive polarity" configuration. Data were collected on 8-wire 12.5 in aluminum Z-pinches in both polarities. Time dependent X-ray signals were measured using diodes and diamond detectors. A 6 ns pulsed laser was used as a back lighter to obtain images that were time-stepped through the evolution of the pinch. Pinches in positive polarity showed an increase in the power and total energy of the soft X-rays, and a decrease in the power and total energy of the emitted hard X-rays as compared to negative polarity pinches. Initial observations indicated that the pinch column in positive polarity began to form earlier than in negative polarity, and the structure of the imploding material was shown to be drastically different for the two polarity configurations

Summary form only given. We present here the results of a series of experiments comparing the operation of an X-pinch in positive and negative polarity. Of particular interest are the X-ray yield, timing, radiating spot size, and the number of radiating spots in a given X-pinch. Conventionally, an X-pinch is operated in negative polarity resulting in electric field lines that terminate on the wires. This choice of polarity for the generator is due to the fact that breakdown in these machines is easier to prevent when they are operated in negative polarity. Previous experiments involving single wire explosions at low current (1-5 kA) have shown that more energy can be deposited in the wire cores when they are driven in positive as opposed to negative polarity. These results raised the question of what happens when pinch-type experiments are driven in positive polarity. Recently, it has become possible to use the 450 kA XP pulser at Cornell to drive X-pinches in positive polarity. The positive polarity condition is established by inserting a convolute before the load and this results in electric field lines that originate on the wires of the X-pinch. This arrangement added complexity and inductance to the positive polarity shots, making it difficult to directly compare results from positive and negative shots. More recently, the entire pulser was switched to positive polarity. This allows a more direct comparison between positive and negative polarity X-pinch operation

Using arguments based on both electronic structure calculations and ionic radii, we propose that interfacial charges contribute to the ionic part of the lattice mismatch. As a result, the Si‐terminated 6H–SiC(0001) surface is a superior substrate for GaN to the C‐terminated surface. This viewpoint unifies (i) the Sasaki–Matsuoka proposal that substrate quality depends on electrical polarity and (ii) the conventional viewpoint that the best substrate has zero lattice mismatch with the film deposited on it.

The polar organisation is characteristic to the living cell and disappears with the cell functional decay. Here we report experimental evidence that frog retinal photoreceptor rod cell shows a polar distribution of the electrical charge and of free cytosolic Ca(2+) along its length. Retinal rod cells were loaded with Calcium sensitive dye (Green 1) and examined under fluorescence microscopy coupled with an image analysis system. In addition, suspension of rod cells was placed in direct current electric field for electrical polarity assessment. Both polar Ca(2+) and electrical charge distribution can be objectively measured and quantified providing thus a fine test for cell viability. Such a test is required in checking the functional integrity of photoreceptors used in rentinal transplant.

The high current regime of a magnetron-type discharge has been investigated. The discharge uses a permanent magnet as a cold cathode which emits secondary electrons while the chamber wall or a grounded electrode serves as the anode. As the discharge voltage is increased, the magnet develops cathode spots, which are short duration arcs that provide copious electrons to increase the discharge current dramatically. Short (1 μs), high current (200 A) and high voltage (750 V) discharge pulses are produced in a relaxation instability between the plasma and a charging capacitor. Spots are also observed on a negatively biased plane Langmuir probe. The probe current pulses are as large as those on the magnet, implying that the high discharge current does not depend on the cathode surface area but on the properties of the spots. The fast current pulses produce large inductive voltages, which can reverse the electrical polarity of the magnet and temporarily operate it as an anode. The discharge current may also osci...

During microwave heating, temperature distribution controls the product safety in pasteurization and sterilization. It also ensures that the desired quality of the food is reached. Microwave heating uniformity is controlled by a number of interacting factors such as the composition of the food and the package, the geometry of the food and the microwave field created inside the food. The type of electrical polarity of the oven fields is of large importance to the coupling of microwave oven energy fields (TE and TM volume cavity modes) to the food and the resulting temperature distribution. Different types of cavity modes will give large differences in corner- and edge overheating, an important problem in microwave heating of foods, as illustrated by advanced three-dimensional numerical simulations and by infrared thermographic measurements.

Bipolar resistive switching (RS) behavior was observed in epitaxially deposited TiO2−δ/La2/3Sr1/3MnO3 stacks. An intermediate initial state of this device demonstrated that the original resistive state would switch to either the higher or the lower state, depending only on the electrical polarity of the initial measurement. As the analogue intermediate states were obtained by device fabrication, the direct observation of these switching states was possible, knowing the microscopic physical origin of the RS effect. Based on x-ray photoelectron spectroscopy analysis, an understanding of this interesting phenomenon was proposed, well supporting the oxygen vacancy formation and recombination mechanism.

Weak externally applied electric currents changed the natural electrical pattern surrounding cells from tobacco (Nicotiana tabacum L.) suspension cultures. The artificial currents were applied transversely to short filaments of cells placed between a microelectrode lose to the filament surface and a large platinum electrode some distance away. The natural current patterns before and after electrical treatment were measured with a vibrating probe. Significant effects were confined to the cell adjacent to the microelectrode. Currents with densities of 100 μA · cm(-2) at the cell surface applied for 10 min or 3 μA · cm(-2) for several hours caused a localized increase in the natural current entering the part of the cell which had been nearest the positive electrode. There was no corresponding local increase in current leaving from the opposite side of the cell. Instead, the extra current appeared to leave over a relatively large area. The overall effect was a tendency for the cell to repolarize transversely with a greater proportion of its transcellular currents flowing in the direction of the current applied. The effect was measurable for several hours after the external current was discontinued and may be evidence for a natural mechanism by which neighbouring cells entrain one another's polarities during differentiation. The effect of external currents on cells growing in a 2,4-dichlorophenoxyacetic acid (2,4-D) medium (which suppresses differentiation) was qualitatively the same as on cells in an indole-3-acetic acid medium (which promotes differentiation). If anything, the response was greater in 2,4-D, implying that the disruptive effect of 2,4-D on cell and tissue polarization is not a consequence of it preventing cells sensing the transcellular currents of their neighbours.

A system and method to map a biological tissue of alternating electrical polarity having a boundary between a depolarized portion and a polarized portion is provided. The system includes a computer, a transducer probe, and a receiver. The transducer probe is in communication with the computer and configured to transmit acoustic waves at a frequency through the biological tissue of alternating electrical polarity. The receiver is in communication with the computer and operable to detect a variation in an electrical activity at approximately the frequency of the acoustic waves. The computer creates a display of at least a portion of the variation in the electrical activity at approximately the frequency of the acoustic waves.