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DC power supply has become the driving source for some essential modern applications. Thereby, DC power conditioning has become a significant issue for engineers. Typically used rectifiers associated with a bridge structure is nonlinear in nature. Thereby, the current at input side of the rectifier contains harmonics, which also flow through the power line. The presence of harmonics causes several interruptions and reduce power quality. In this regard, a new close loop SEPIC controlled rectifier is proposed in this paper. The conventional scheme is arranged with a rectifier connected to a DC-DC converter, which is an open loop system. Consequently, such system cannot regulate voltage at load varying condition. The proposed SEPIC controlled rectifier can regulate voltage under load varying condition for a wide range. Additionally, the performance in terms of total harmonic distortion (THD) of input current and power factor at AC side are also within satisfactory range for the closed loop configuration. The controlled rectifier has four operating phases associated with switching states and input voltage polarity. The close loop configuration also incorporates a current and a voltage loop at the feedback path. The comparative studies have been performed among the proposed closed loop construction, the open-loop structure as well as the conventional construction. The effectiveness of the proposed controlled rectifier is verified in terms of THD and input power factor considering the results obtained from simulation.

The electrically induced resistance changes in lithium-doped zinc oxide (ZnO:Li) film sandwiched between metal electrodes (Ag and fluorine doped SnO 2 (FTO)) are analyzed by electrical transport measurements. The bipolar resistance switching and inversed bipolar resistance switching with respect to voltage polarity are observed and characterized for Ag/ZnO:Li/FTO structure.

As large as 4607 cm−1 gain coefficient in two beam coupling experiment was obtained by introducing PVK:C60 film to ZnSe assisted liquid crystal system. As short as 5.0 ms holographic recording time was reached when probing the grating formation process, showing great potential in real time applications. Systematical two beam coupling and grating probing experiments were performed in studying the mechanism behind the high photorefractive (PR) performance. Unusual energy transfer direction change and gain coefficient fluctuation were observed when the voltage polarity and incidence side were altered in the related two wave coupling experiments.

This paper concerns the studies on streamer propagation in mineral oil, synthetic ester and natural ester at standard lightning impulse inception voltage in small point-plane gaps. The inception voltages of both polarities were measured using step method and then analysed statistically. Simultaneously, streamer characteristics such as shape, emitted light and propagation velocity were compared between the liquids tested. The obtained results showed that the inception voltages were close to each other for all the three liquids tested. Concerning streamer characteristics, it was seen that the spatial shapes of the streamers were similar taking into consideration the given voltage polarity. The same may be said about the propagation velocities, indicating that the velocities of the positive streamers were twice as high as the negative ones. In the case of registered time courses of emitted light, the frequencies of the light pulses corresponding to the propagation of the streamers in both esters were a little bit higher than the pulses emitted by the streamers, which developed in mineral oil. In general, in all three liquids the streamers at inception voltages developed as so-called `stopping length' streamers.

Plasma technology is a highly promising and advantageous technology for liquid processing. In air in-contact with water, plasma produces highly reactive species (ions, electrons, radicals, photons, etc) that diffuse into the water volume and initiate physical and chemical phenomena of interest, e.g. organic and inorganic pollutant degradation. In this study, we investigate the influence of basic parameters, such as voltage polarity, voltage amplitude, plasma lifetime, and air-gap distance, on the properties of a discharge in air in-contact with deionized water. Specifically, we analyze the electrical characteristics, the plasma behaviour at the water surface, water acidity and conductivity, and the decoloration rate of a standard organic dye (methylene blue). The concentration of the main reactive oxygen and nitrogen species produced in water is also reported. Compared to positive polarity conditions, the negative polarity voltages enhance the decolaration rate of methylene blue. For instance, under negative polarity voltages and while applying 4 and 6 kV, the decoloration rate is relatively low (

A new hybrid Cuk converter with wide step-up and step-down conversion ratio and reverse output voltage polarity relative to the input voltage is presented in this paper. Compared to the classical Cuk converter, in step-up mode, the novel converter exhibits a wider range of the voltage conversion ratio with the same duty cycle. The DC equations are derived, the static characteristics are depicted, then stresses of devices are evaluated. The converter is simulated and experimentally tested in order to confirm the feasibility of the proposed hybrid Cuk converter.

In this paper, the discharge frequency was measured for two types of cylindrical cavities at DC voltage. One was surrounded by polyethylene (PE), while the upper surface of the other was metallic. It is found that the partial discharge (PD) frequency was independent on voltage polarity for the former sample, while for the latter one the discharge frequency in the case with positive voltage application was larger than that with negative voltage. In order to explain experimental results, a PD simulation model was constructed based on surface charge decay. In terms of it, the dynamic distributions of surface charges during PD sequences were obtained, which took place in the two types of cavities. In the cavity with one metallic surface, positive charges landed on the lower surface of the cavity when the positive voltage was applied, and the polarity of surface charges would be reversed if the voltage polarity varied. Due to the slower decay rate of negative surface charges, discharge frequency in the case with positive voltage was higher than that with negative voltage application. However, as for the cavity embedded in the solid insulation, there was no such law because positive and negative charges always accumulated on both surfaces regardless of voltage polarity.

This paper describes experimental studies on streamer propagation in synthetic ester and mineral oil under lightning impulse voltage. These studies are concentrated around the small electrode gaps (15 and 20 mm) of the point-plane electrode arrangement. The spatial shapes of the developing streamers, oscillograms of light emitted and propagation velocities were analyzed and compared. Two streamer propagation modes were observed during the studies performed. Slow 2nd mode streamers developed below the so-called acceleration voltage while fast 3rd mode streamers developed at acceleration voltage and above. Independently of the liquid used the registered streamers shapes corresponding to a given voltage polarity were identical. Concerning the light oscillograms, higher frequencies of light pulses were observed in the case of synthetic ester. A significant difference between both the considered liquids was however noticed in the threshold value of the testing voltage at which the 3rd mode streamers appeared. Fast positive streamers started to develop in synthetic ester at lower testing voltage (of about 26 kV for 20 mm gap and 20 kV for 15 mm gap) than in the case of mineral oil. For negative polarity of lightning impulse, within the applied testing voltages, 3rd mode streamers were observed only in synthetic ester. For both electrode gaps acceleration voltage for negative polarity was 2.2 of estimated inception voltage. This allowed forming the conclusion that synthetic esters have a lower ability of preventing the development of fast and energetic streamers, even at small (15 and 20 mm) electrode gaps.

In this study, investigation of the unipolar resistive switching (RS) of InGaZnO film indicates that the reset voltage polarity can strongly affect the RS region. The dependence of the RS characteristics on the top electrode (Pt, Al, or Cu) was investigated. Asymmetrical electrodes (Cu/InGaZnO/Al) were chosen and the dependence of the RS parameters (e.g., high and low resistance states, set and reset voltages) on these two diverse electrodes can provide two indicators to trace the location of the RS region. The RS region is usually located near the anode when the applied set and reset voltages have the same polarity. In comparison, when the reset voltage has the opposite polarity to the set voltage, the RS region prefers to be located near the anode of the reset process rather than the cathode (which is used as the anode in the set process), indicating the movement of the RS region during the reset process. With the aid of joule heating, oxygen ions can overcome the energy barrier during the reset process under small voltage, resulting in the CFs restructuring and having the inverse shape, which is responsible for the drift mechanism of the RS region.

The active-forced-commutated (AFC) bridge employs a symmetrical thyristor-bridge with auxiliary self-commutated full-bridge chain-link (FB-CL) circuit to assist its soft transition and forced commutation. This combination can form a thyristor based voltage source converter (VSC) with significantly reduced on-state losses and dc-fault blocking capability. Due to the full topological symmetry of the AFC-bridge, either current direction or dc-link voltage polarity can be reversed for power flow reversal as for the full-bridge modular multilevel converter (FB-MMC). Thus, the AFC-bridge is compatible with both line-commutated-converter (LCC) and VSC terminals in a multi-terminal high voltage direct current (MT-HVDC) network. This paper investigates its front-to-front (F2F) dc-dc application for matching the regional dc grids in a LCC and VSC hybrid HVDC network. Simulation studies are carried out to demonstrate its potentials as a high efficiency multi-functional solution for dc-dc conversion.

This paper gives a detailed analysis about the causes of the voltage distortion caused by dead time in dual active bridge (DAB) DC-DC converter. The zero-crossing point of the equivalent leakage inductor's current is the definitive factor for various voltage distortion phenomena, which is determined by dead time and phase-shift ratios. Based on the switching characterization of DAB in dual-phase-shift scheme, a comprehensive summary of dead-time effect is acquired, including voltage polarity reversal, voltage sag and duty-cycle abnormity. At the same time, the causes of these phenomena are analyzed in detail. Considering all kinds of voltage distortion phenomena will affect the transmission power and other issues, a special operation mode defined as recessive-dead-time mode is obtained. In recessive-dead-time mode, the dead-time effect can be avoided by reasonable parameter-setting, thus, the voltage distortion will not occur. Finally, experimental results verify the theoretical analysis.

We demonstrate the coexistence of the unipolar and bipolar switching behaviors in a single oxide resistive device composed of Pt-CuO0.8-W structure and we reveal the switching mechanism by the comprehensive analyses of both unipolar and bipolar switching behaviors. The observations suggest that the RESET (turning OFF) mechanism of unipolar and bipolar switching modes can be explained by a unified scheme. The results also elucidate that the SET (turning ON) process in bipolar mode is originated from by the drift of ions though charged vacancies, while the SET process in unipolar mode is explained by electron tunneling through vacancies. The proposed model successfully explains the observations of resistive switching of our device regardless of input voltage polarity and, more importantly, we propose a way to selectively choose one specific operation mode.

The effect control voltage polarity has on the diffraction characteristics of photonic structures formed in polymer dispersed liquid crystals (PDLCs) is discussed. The possibility of controlling these characteristics with an alternating electric field is demonstrated.

The nanopore sensor can detect cancer-derived nucleic acid biomarkers such as microRNAs (miRNAs), providing a noninvasive tool potentially useful in medical diagnostics. However, the nanopore-based detection of these biomarkers remains confounded by the presence of numerous other nucleic acid species found in biofluid extracts. Their nonspecific interactions with the nanopore inevitably contaminate the target signals, reducing the detection accuracy. Here we report a novel method that utilizes a polycationic peptide-PNA probe as the carrier for selective miRNA detection in the nucleic acid mixture. The cationic probe hybridized with microRNA forms a dipole complex, which can be captured by the pore using a voltage polarity that is opposite the polarity used to capture negatively charged nucleic acids. As a result, nontarget species are driven away from the pore opening, and the target miRNA can be detected accurately without interference. In addition, we demonstrate that the PNA probe enables accurate discrimination of miRNAs with single-nucleotide difference. This highly sensitive and selective nanodielectrophoresis approach can be applied to the detection of clinically relevant nucleic acid fragments in complex samples.

Recently, non-contact radio-frequency (RF) methods have shown promising potential to be used as a complement to the IEC 60270 standard method for the detection and localization of partial discharge (PD) in high voltage insulation. This paper reports the results of an experimental investigation on the characteristic of partial discharge in an air gap using the (RF) method combined with the high-frequency current transformer (HFCT) method. The experiments were carried out under DC and AC high voltages and the effect of voltage polarity, voltage magnitude, and locations of the RF sensor relative to the PD source were examined. Analysis of the measured signals was carried out to classify both the frequency content of the discharge and its duration. The results show that the emitted electromagnetic signals from the AC discharge typically has its energy focused within two dominant frequency bands, while those of the DC discharge showed one dominant frequency band. The results indicate that the location of the RF sensor relative to the PD source had significant influence on the magnitude of measured PD signals.

The switch mode power conversion circuits buck, boost, and buck-boost incorporate a power inductor as an energy storage device. If the power inductor in these fundamental circuits is replaced with a transmission line, new power conversion circuits will emerge. By introducing microwave properties, such as propagation delay and characteristic impedance, new functions may be feasible in the area of power conversion. Examples of such functions could be inverting and noninverting voltage polarity abilities or circuits, which share switch components between multiple output voltages reducing the number of semiconductors needed. Alternatively, the buck-boost power converter circuit may give rise to new high-efficiency radio circuits in the area of microwave technology.

ThefilamentarygrowthandswitchingmechanismofSiOx-basedresistiveswitchingrandomaccessmemorieshavebeeninvestigated. In test structures with two devices connected in series, it has been found that the applied voltage in the first electroforming sweep equally stressed the SiOx in both devices. Therefore, it is concluded that a conducting filament (CF) grows in both devices. The resistance switching is induced by the rupture and recovery in a weak spot of the CF. The weak spot formation is a random process in the CF and could be anywhere along the CF. Once the weak spot is established, the rupture and recovery is localized in that particular region and independent of applied voltage polarity.

We demonstrate strong, analog, reversible, and nonvolatile memcapacitance in a Si-based MOS (metal-oxide-semiconductor) memcapacitor with an ITO (In-Sn-O)/HfOx/Si structure. Both accumulation and depletion capacitances change sequentially and reversibly upon repeating voltage application with respect to voltage polarity. This memcapacitance is thought to be induced by oxygen ions' migration between ITO and HfOx layers, which changes the HfOx permittivity and the depletion states in Si and ITO. The Si-based memcapacitor has potential to be applied to the gate stack of the MOS field-effect-transistor for nonvolatile memory and synaptic transistors through modulating drain current determined by the capacitance change of the MOS gate stack.

This paper explores the influence of air pressure, temperature and humidity on the switching impulse (SI) flashover performance of different types of clean and dry insulators at different high altitude sites of 2820 m to 5050 m along the Qinghai-Tibet Railway, the highest elevation railway in the world. Seven types of insulators are used in the flashover tests: one is a composite insulator, two are glass insulators and four are porcelain insulators. At the test sites, the ambient temperature varies between 6.7 degC to 28.5 degC and the absolute humidity is between 4.11 g/m3 to 9.69 g/m3. The test results show that the 50% switching impulse flashover voltage of different types of insulators at high altitude sites is independent of the materials and sheds of insulators but has a multi-factor non-linear relation with the shortest arc distance, the dry air pressure, the absolute humidity and the ambient temperature. The relative flashover voltage decreased with the ambient temperature is dependent on the voltage polarity, with 0.152% to 0.165% /degC for negative SI and 0.099% to 0.108% /degC for positive SI at the ambient temperature of from 6.7 degC to 28.5 degC. The relative flashover voltage increased with the absolute humidity and is dependent on the air pressure. The higher the altitude is, the more the influence is of the absolute humidity on the flashover voltage of insulators.

On the basis of a self-consistent solution of the Schrodinger and Poisson equations, the features of the tunnel-current hysteresis in w-GaN/AlGaN(0001) double-barrier structures are investigated. It is shown that the hysteresis loop depends on the mutual orientation of external and internal fields in the well and is wider at the voltage polarity when these fields compensate each other. Within the framework of the single-resonance approximation, a tunnel-current model in the double-barrier structure is developed, and the relation between the hysteresis-loop parameters and resonant states is found. It is established that the hysteresis loop can be relatively wide (∼4 V) even in geometrically symmetric structures with the participation of two resonances. In asymmetrical structures, the change in the growth-surface type results in enhancement or suppression of the hysteresis loop depending on the alternation of nonequivalent barriers.

Breakdown and corona are investigated in clean and dust-polluted rod-rod air gaps varying gap length, rod radius and voltage polarity. It is shown that similar to previous results under impulse voltages, dust pollution can significantly reduce the DC breakdown voltage values of such gaps which depends upon electrode radius, gap length and voltage polarity. These factors should therefore be considered prior to the design and application of air insulation in desert regions, where sand and dust storms can occur frequently. Possible mechanisms which control the observed behaviour are explained in detail.

Curvature of Selemion, C, exhibited a quite definite relationship to the charge, Q. There was an almost perfect linear relationship between them, as long as the applied voltage to Selemion was higher than Vth, which was a threshold voltage in need for the induction of redox reaction 2Ag + 1 2 O2 ↔ Ag2O. At Vth or above, a larger quantity of charge was given to the Selemion owing to the reaction. Although such a linear relationship slightly worsened, once the voltage polarity was reversed, Q versus C still maintained a certain definite relationship. Therefore, it was speculated that the Selemion bending curvature was still controllable through the control of charge (or current). Besides charge (or current), the existence of water inside Selemion was an essential factor for the induction of its bending. Because Selemion is an electrically insulating material, quite indifferently to the applied voltage, and the water contained in Selemion created ions, and Selemion must have been converted into a semi-conductive material that could respond to the applied voltage.

Nanopore fabrication by controlled breakdown (CBD) overcomes many of the challenges of traditional nanofabrication techniques, by reliably forming solid-state nanopores sub-2 nm in size in a low-cost and scalable way for nucleic acid analysis applications. Herein, the breakdown kinetics of thin dielectric membranes immersed in a liquid environment are investigated in order to gain deeper insights into the mechanism of solid-state nanopore formation by high electric fields. For various fabrication conditions, we demonstrate that nanopore fabrication time is Weibull-distributed, in support of the hypothesis that the fabrication mechanism is a stochastic process governed by the probability of forming a connected path across the membrane (i.e. a weakest-link problem). Additionally, we explore the roles that various ions and solvents play in breakdown kinetics, revealing that asymmetric pH conditions across the membrane can significantly affect nanopore fabrication time for a given voltage polarity. These results, characterizing the stochasticity of the nanopore fabrication process and highlighting the parameters affecting it, should assist researchers interested in exploiting the potential of CBD for nanofluidic channel fabrication, while also offering guidance towards the conceivable manufacturing of solid-state nanopore-based technologies for DNA sequencing applications.

This paper is a first step towards the evaluation of the life and reliability of HVDC cable systems in the presence of voltage polarity reversals. It combines a physical-phenomenological life model for HVDC cables subjected to voltage polarity with a recently-developed life model for HVDC cables subjected to load cycles. Under some meaningful approximations, a quite powerful model that accounts both for load cycles and voltage polarity reversal is eventually attained. Such model can be applied in order to predict the life of HVDC cables subjected to voltage polarity reversal tests with load cycles superimposed, performed in line with CIGRE Recommendations after Electra 189, 2000. By doing so, results in agreement with the experience gained by Terna (the Italian TSO) in testing HVDC cables - in particular MIND cables - are attained.

The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined.

The basic characteristics of reset discharges related to a wall voltage and a priming effect were investigated under a conventional ramp driving scheme. The reset discharges could be minimized by controlling the wall voltage which is determined by pre-reset conditions. Accordingly, the current study presents a simple pre-reset condition for minimizing the reset discharge. Essentially, it is not only to reduce the duration of reset discharges but also to reduce the intensity of light emissions when the wall voltage polarity is opposite to the external voltage polarity.

Evaluation of insulation strength for lightning surge that actually enters into substations is important in estimating insulation reliability of gas-insulated equipment. The standard lightning impulse voltage (1.2/50 µs) is used for factory tests. However, the actual lightning surge waveforms in substations are complex and are usually superimposed with various oscillations. Insulation characteristics of SF6 gas as a function of such complex voltages have not been sufficiently clarified. This paper deals with gap breakdown characteristics in SF6 gas under submicrosecond pulses. Breakdown voltages are lower under a polarity reversal condition than under a monopolarity condition. The cause of this difference is discussed while observing discharge propagation using an image converter camera. The electrode size effect is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 18–25, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10246

A theoretical model of the contact metal topography of a photoconductive cell and a thermal model of an optoelectronic switch of the voltage polarity are considered. Expressions for photo and thermal emf of photoconductive cells with arbitrary contact metal topographies and distributions of the illumination and temperature at the cell surface are obtained. The regularities of minimization of parasitic emf of photoconductive cells are revealed. An optoelectronic switch of the voltage polarity with low levels of temperature (

This paper describes the molecular alignment behavior of polymer networks with switching of a ferroelectric liquid crystal (FLC) in a molecularly aligned FLC/polymer composite film. The polymer alignment in the composite film, which was slowly formed by photopolymerization-induced phase separation of a heated nematic-phase solution of FLC and monomers, was observed by polarization Raman spectral microscopy. Raman peak intensities originating from the polymers were changed with those from the FLC, when the applied voltage polarity was changed. The trace patterns of the Raman peak intensity with in-plane rotation of the composite film indicated that the formed flexible polymers can follow FLC molecular switching.

We investigate translocation of linear and circular double-stranded DNA molecules through solid state nanopores where each molecule is recaptured and re-translocated many times. Single molecules can be recaptured by switching voltage polarity for hundreds or even thousands of times. The large number of recapture events allows statistics on the translocation of individual molecules. Surprisingly, we observe that recaptured DNA molecules do not translocate in a linear head-to-tail fashion, but instead translocate as a folded blob where multiple parts of the DNA molecule simultaneously translocate through the pore in parallel. This folding is observed through the presence of up to 13 DNA double strands from the same molecule simultaneously inside the pore, as well as many smaller fold numbers occurring during the course of a translocation event. The strong folding is particularly prominent when the molecule is recaptured at short time scales, i.e. shorter than its characteristic time to relax to its equilibrium configuration. At longer recapture times, both the amount of folding and the mean duration of translocation approach the values observed in non-recapture experiments. The data shows that the translocation time of a molecule depends on the molecule’s conformation at the start of the translocation process, with extended molecules having a longer translocation time. The observations can be attributed to a high-density non-equilibrium DNA configuration that arises in the close vicinity of the nanopore immediately after translocation, which dissipates on a time scale given by the Zimm relaxation time.

This paper presents the results of the studies concerning propagation of the streamers in natural and synthetic ester under lightning impulse 1.2/50 μs at inception voltage. The results are presented in the form of comparison with the results obtained for mineral oil at the same conditions. For the different interelectrode gaps changed from 5 to 20 mm, the inception voltage and propagation velocity were measured and analyzed. Additionally, the oscillograms of light emitted during discharge development under inception voltage and shapes of discharge forms recorded photographically for all three dielectric liquids, were compared. The obtained results showed that at the inception voltage both the light courses and shapes of discharge forms are very similar in all three cases, depending on voltage polarity. Identical values are also observed in the case of propagation velocity of the streamers and in the case of inception voltages determined statistically using maximum likelihood method.

Pt/TiO2/Pt/Ti memristive devices were electrically formed to either the ON or OFF state using voltages of the same polarity but with different amplitudes. The forming step dictated the subsequent switching behaviour. A qualitative model based on the creation and migration of oxygen vacancies was proposed to explain the experimental results.

To better understand the mechanisms of creation and rupture of conductive filaments in resistive switching devices such as Cu/TaOx/Pt, with Cu and Pt being the active and inert electrodes, respectively, a device with limited supply of active metal electrode has been manufactured and electrically characterized. The limited supply of active metal has been realized by depositing a thin (delta) Cu layer (δ-Cu), 6 nm and 12 nm thick, on TaOx, resulting in a Pt/δ-Cu/TaOx/Pt device structure. The limited active metal supply i) has a direct impact on the onresistance (Ron) of the Cu bridge, and leads, after several conventional set-reset cycles, to ii) pulsating behavior, when device turns on and off repeatedly, to iii) symmetric switching behavior with respect to applied voltage polarity, when the device can be set and reset both at positive and negative bias, and to iv) volatile switching behavior.

This paper reports on systematic measurements of voltage-time curves of a 25/70-mm coaxial-cylinder SF6 gap. Tests were carried out with 0.5/50-μs and 1.2/50-μs voltage impulses, for SF6 pressures in the range 0.1–0.3 MPa. Times to breakdown were measured in the range of 0.2–7.0 μs, paying due attention to the random nature of breakdown delay and its principle components, namely the statistical and formative time lags. Gas pressure, voltage polarity and field concentration due to the presence of spherical particle attached to the high-voltage electrode were systematically investigated with respect to their effects on breakdown delays. The results of this study could be significant from the point of view of the insulation coordination of gas-insulated systems.

Current induced resistance changes were investigated in magnetic tunnel junctions with ultrathin Al-Ox barriers. The nonuniformity of the insulator induced a strong coupling between the two magnetic electrodes and no magnetoresistance. However, the current-voltage (I–V) characteristics at low bias voltages were consistent with a tunnellike behavior. At larger bias voltages, they showed an abrupt change of slope that was reversible for an opposite voltage polarity. The resistance versus current (R–I) curves exhibited reversible resistance changes that reached over 100%. We interpret this as controlled electromigration in local nanoconstrictions of the barrier.

A new working principle for electrochemical micropump with the gas termination time as short as 100 microseconds is presented. It is based on water electrolysis with a fast change of voltage polarity. A simple electrochemical micropump is designed to demonstrate this pumping principle. The device consists of a working chamber with metallic electrodes, inlet and outlet diffusers, and channels for liquid. The chamber and the channels are filled with the electrolyte that plays a role of the pumped liquid. The pump was tested in different regimes. One of these regimes related to formation and termination of short-lived microbubbles is especially promising. Long time stability of the electrodes is demonstrated.

In this paper, a novel repetitive frequency voltage booster (named repetitive Fitch booster by the authors) based on magnetic switches and Fitch generators is proposed. The principle of operation is to charge capacitors in parallel when magnetic switches (MSs) are unsaturated and reverse voltage polarity of every other capacitor when MSs saturate. With the principle, circuit topology of a 4-stage repetitive Fitch booster (RFB) is presented. Simulation as well as experiment shows its feasibility in boosting voltage and compressing rise-time. In simulation, the input voltage of 100 V is boosted to 372 V, while test stand yields output voltage with frequency of 1 kHz, amplitude of 19 kV with each capacitor charged to about 5.6 kV, and rise-time compression from 7.3 μs to 700 ns. Meanwhile, calculations show that the 4-stage RFB effectively reduces core volume by about half, from 1093.5 cm(3) to 585.2 cm(3). Furthermore, design rules are proposed so that topologies of RFBs with stages other than four can be conveniently derived. As an example, an 8-stage RFB is proposed and verified with circuit simulation, which shows an output voltage of 759 V with the input voltage of 100 V.

Deep levels measured by Photo-Induced Current Transient Spectroscopy (PICTS) are interpreted taking into account different bulk and surface properties of semi-insulating crystals, results of directly measured isothermal transients and types of observed deep levels determined from the measurements with different voltage polarity. The principal interest is focused on the temperature interval 250–450 K where peaks related to the deep levels causing semiinsulating properties are observed in the PICTS spectra. Majority of deep levels observed in various samples may be ascribed to the EL2, EL3, EL4, HL1 and HL9 levels. Maxima exhibiting inverse polarity in PICTS spectra are not related to EL2 or HL1.

Responsivity and thermionic dark current are studied in asymmetric stepped GaAs/AlGaAs multiquantum well infrared detectors with a single bound state. Although attributed to different transport properties, both the photoexcited and the thermally emitted carriers exhibit asymmetric transport properties with respect to the voltage polarity. The experimental characteristics are explained by the minibands-quasi continuum energy structure above the barrier.

We show that bias polarity can greatly accelerate device failure in GST- based (GeSbTe) PCM devices, and trace this effect to elemental segregation, initially driven by bias across the melt but then enhanced during the crystallization process. Implications include device, pulse, and materials design for high endurance.

This paper is an experimental study of a pulsed filamentary plasma discharge inside liquid water in pin-to-plane electrode configuration. Time-resolved electrical and imaging diagnostics have been performed. The initiation and the propagation of the discharge have been studied for several experimental parameters. The propagation is continuous and is followed by reilluminations at low water conductivity. The measured propagation velocity of the plasma discharge is 30 km s−1for the secondary positive mode. This velocity was found to be surprisingly constant whatever the experimental parameters and especially as a function of the water conductivity.

The influence of the voltage polarity and also the thickness and material of the upper electrode on the electroforming and breakdown of a thin-film MIM system has been investigated. It is shown that the processes in the insulator in the breakdown and forming have the same nature. On the basis of the experimental results it is concluded that the main factors which distinguish the forming from the breakdown are the magnitude of the energy deposition on the formation of a discharge channel in the insulator and the nature of the gas release from the discharge channel. These determine the geometrical sizes and morphology of the defects formed in the MIM system under the influence of the voltage and are in the one case formed channels and in the other breakdown channels.

Controlling the contents of liposomes and vesicles is essential for their use in medicine, biotechnology, and basic research. Cargos such as proteins, DNA, and RNA are of growing interest for therapeutic applications as well as for fundamental studies of cellular organization and function, but controlled encapsulation and mixing of biomolecules within vesicles has been a challenge. Recently, micro fluidic encapsulation has been shown to efficiently load arbitrary solutions of biomolecules into unilamellar vesicles. This method utilizes a piezo-electrically driven liquid jet to deform a planar bilayer and form a vesicle, with the fluid vortex formed by the jet mixing the solution in the jet with the surrounding solution. Here, we describe the equipment and protocol used for loading mixtures within unilamellar vesicles by microfluidic encapsulation, and we measure the encapsulated fraction to be 79 ± 5% using a falling vesicle technique. Additionally, we find that the presence of a continuous flow from the nozzle and changes in actuation voltage polarity do not significantly affect the encapsulated fraction. These results help to guide current applications and future development of this microfluidic encapsulation technique for forming and loading unilamellar vesicles.

The non-Fermi-liquid system ${\text{YbCu}}_{5\ensuremath{-}x}{\text{Al}}_{x}$ $(x=1.3\char21{}1.75)$ has been investigated in heterocontact as well as homocontact arrangement in magnetic fields up to 22.5 T. The observed differential resistance $[dV/dI(V)]$ characteristics reveal asymmetry in heterocontact arrangement and do not agree with the model of thermal contact heating, at least close to zero-bias voltage. In the case of a heterocontact arrangement we have observed a maximum at only one voltage polarity at about 1.3 mV (for $x=1.5$) and this asymmetry is suppressed in an applied magnetic field. We show that such behavior is connected with the non-Fermi-liquid state of the studied system.