Negative DC Research Articles

Inactivation of Dermatophytes Causing Onychomycosis and Its Therapy Using Non-Thermal Plasma.

Onychomycosis is one of the most common nail disorders. Its current treatment is not satisfactorily effective and often causes adverse side effects. This study aims to determine the optimal conditions for non-thermal plasma (NTP) inactivation of the most common dermatophytes in vitro and to apply it in patient`s therapy. The in vitro exposure to NTP produced by negative DC corona discharge caused full inactivation of Trichophyton spp. if applied during the early growth phases. This effect decreased to negligible inactivation with the exposure applied six days after inoculation. In a group of 40 patients with onychomycosis, NTP therapy was combined with nail plate abrasion and refreshment (NPAR) or treatment with antimycotics. The cohort included 17 patients treated with NPAR combined with NTP, 11 patients treated with antimycotics and NTP, and 12 patients treated with NPAR alone. The combination of NPAR and NTP resulted in clinical cure in more than 70% of patients. The synergistic effect of NPAR and NTP caused 85.7% improvement of mycological cure confirmed by negative microscopy and culture of the affected nail plate. We conclude that NTP can significantly improve the treatment of onychomycosis.

Relaxation of competing electromechanical couplings in murine artery

Piezoelectricity and pyroelectricity in biological tissues, which originate from oriented fibrous proteins with a polar axis, have long been suggested to play important roles in physiological functions. The possible manipulation of their polarity by external mechanisms, however, remains unsettled. We revisit this problem here using piezoresponse force microscopy (PFM) as the tool and the intima layer of murine artery as a model system. By carefully examining first and second harmonic piezoresponses at both selected points and through spatial mapping, we establish that electromechanical coupling probed by PFM is predominantly piezoelectric in the intima layer, while the quadratic effect makes only minor contributions. More importantly, we observe competition between the linear and quadratic effects after removal of DC biases applied to the sample surface, revealing not only interesting relaxation dynamics, but also highly asymmetric piezoresponse. Positive DC rotates dipoles in tropoelastin monomers away with reduced alignment, while negative DC aligns dipoles more leading to enhanced piezoresponse. The electric manipulation of biological polarity is thus demonstrated, with the relaxation time constant determined on the order of 0.1 s, much slower than classical ferroelectrics.

Comparison of breakdown voltage of vegetable olive with mineral oil, natural and synthetic ester liquids under DC voltage

This paper deals with a comparative study of the negative and positive DC breakdown voltages of different insulating liquids namely two natural esters (an extra virgin olive oil (OO) without additive and rapeseed oil), two synthetic ester fluids (a methyleolate obtained by transesterification of olive oil and tetraester), and a naphthenic mineral oil (MO); an oils mixture namely 80% OO + 20% MO is also investigated. Statistical analysis of the experimental data is also performed. The obtained results are also compared with those obtained in our previous work under AC and lightning impulse voltages. It is observed that the negative and positive DC breakdown voltages of natural esters are higher than those of mineral oil. On the other hand, the DC breakdown voltage of (80% OO + 20 % MO) mixture shows comparable behavior to that of mineral oil. The DC negative breakdown voltages are higher than the positive ones in the tested liquids. It is also shown that the DC breakdown voltage values of the investigated liquids generally obey the normal distribution.

Investigation on the performance of thermally aged natural ester fluid impregnated pressboard material

This paper reports the key findings from an experimental study carried out on thermally aged natural ester fluid impregnated pressboard (EOIP) material. The results show that the surface discharge inception voltage (SDIV) with thermally aged EOIP material is higher under negative DC voltage compared with positive DC and AC voltage. The SDIV increases with AC voltage frequency and a minimal reduction in voltage was observed under harmonic AC voltages with different total harmonic distortion (THD). The rate of change in voltage due to ripple content in DC voltage affects the SDIV of EOIP material, initiating discharges at lower voltages. The UHF signals radiated during the surface discharge process have a bandwidth in the range 0.9 to 2 GHz. Surface potential variation studies indicated the formation of high trap sites and trap density due to thermal aging. A reduction in the oxidation onset temperature and the activation energy of thermal decomposition were observed with thermally aged EOIP material. A pyrolysis study showed high composition of levoglucosan and acidic residue with the thermally aged specimen, which reduces its degree of polymerization. Impedance spectroscopic analysis indicates a non-Debye type of relaxation with thermally aged EOIP material. The mobility and charge transfer characteristics were also inferred from the modulus spectroscopy which showed less change for thermally aged pressboard material.

Classification and comparison of AC and DC partial discharges by pulse waveform analysis

This study aims to classify and compare AC and DC partial discharge (PD) based on PD pulse waveform analysis. To achieve this goal, we designed a testbed that enables precise measurements of individual PD pulses. The testbed is used for collecting data from four different types of PDs including cavity, surface, corona, and floating potential discharges generated by individual PD source samples. All samples were examined under AC, positive DC, and negative DC electrical stresses, through which we captured thousands of PD pulses. We classify the waveforms of each PD type into representative groups associated to their discharge mechanisms. The statistical data of the measured pulses are utilized to identify the differences between AC and DC PDs while the clustered patterns of PD amplitude versus their temporal characteristics serve as a means to classify the types of PDs under AC and DC electrical stresses.

Discontinuous Space Vector Modulation Schemes for Modular Multilevel Converters

In this article, a new, simple, and generalized discontinuous pulse width modulation (PWM)-based submodule capacitor voltage balancing approach is proposed and generated within the carrier-based PWM for modular multilevel converters (MMCs). In this scheme, different variants of zero-sequence voltage (ZSV) component is injected into the pulse width modulator so that each arm of the MMC is virtually clamped to positive or negative dc bus during a specific interval to achieve discontinuous modulation. A simple approach based on the location of the voltage vector mapping to a two-level space-vector diagram is presented to determine various ZSV components. The effectiveness of the proposed scheme with a voltage balancing algorithm is demonstrated through PLECS simulations and experimentally verified using a hardware-in-the-loop-based system. The performance of MMC with different ZSV injections is holistically evaluated to determine the best possible sequence over a wide range of modulation index.

Improving the surface insulating performance of epoxy resin/Al 2 O 3 composite materials by extending chain of liquid epoxy resin with Me‐THPA

Basin-type insulators are made by epoxy resin composite materials. Curing defects are easily formed in basin-type insulators, and degrade their insulating performances. High curing exothermic rates of epoxy resin composite materials have deemed as the main cause of curing defects formation. In this study, methyl tetrahydrophthalic anhydride (Me-THPA) was used to extend the molecular chain of liquid epoxy resin to prepare epoxy resin composite materials with low curing exothermic rates. Curing exothermic properties, molecular weight distribution, curing stress, microstructures, and surface flashover characteristics of the composite materials were investigated. The results showed that chain-extended epoxy resin had low curing exothermic rates. The curing stress of the chain-extended epoxy resin composite materials was small. The curing defects forming in the composite materials were inhibited. Negative DC surface flashover characteristics of these composite materials were improved. Furthermore, variation of functional groups of the composite materials was studied before and after surface flashover tests. Results showed that the content of carbon–oxygen single bonds (–C–O) in the chain-extended epoxy resin composite materials was observed to decrease. The –C–O bonds also affect the voltage withstand capability of the epoxy resin composite materials.

New insight into the association between bile infection and clinically relevant pancreatic fistula in patients undergoing pancreatoduodenectomy.

The association between bacterial infection and clinically relevant postoperative pancreatic fistula (CR-POPF) after pancreatoduodenectomy (PD) has not been fully elucidated. Microbiological data for intraoperative bile culture (BC) and drain culture on postoperative day 4 (DC) were collected. The study population was classified into the following three groups: P1 (positive BC and DC), P2 (positive BC and negative DC), and N (negative BC). A total of 209 patients (P1: 38, P2: 72, and N: 99) who underwent PD between May 2013 and May 2018 met the inclusion criteria of the study. The rate of CR-POPF was significantly higher in the P1 group (34.2%) than in the P2 (12.5%; P=.007) and N groups (14.1%; P=.008). Between P1 and P2 groups, a significant difference was observed in the proportion of Enterococcus faecalis grown in BC (42.1% vs 4.2%; P<.001). Multivariable logistic regression analysis showed that the presence of E faecalis in bile was independently associated with CR-POPF. The detection of both bile and postoperative abdominal fluid infections can be more accurate in predicting CR-POPF. Furthermore, the presence of E faecalis in bile may serve as a novel surrogate marker for CR-POPF.

Study of the Development of Negative DC Corona Discharges on the Basis of Visible Digital Images

The noncontact diagnosis methods of discharge plasma include spectrum, electromagnetic wave, ultraviolet image, and high-speed nanosecond image analyses, but there are few studies on the visible image diagnosis method. With the development of digital cameras, the number of pixels in a visible image is far greater than that of ultraviolet, infrared, and high-speed cameras; the image contains a considerable amount of discharge spatial information and provides a new solution for plasma diagnosis. We obtained visible digital images of short gap negative dc coronas with the corresponding oscilloscope current signals under the experimental conditions of atmospheric pressure and room temperature. Two colorimetric indicators ( RGB and HSI ) were proposed to study the colorimetry features of discharge images, of which the analysis was correlated with the amplitude and frequency of oscilloscope current signals. The result shows that the hue value of the overall image region is positively related to the pulse amplitude, while the intensity value corresponds to the pulse frequency. The stage division based on the hue value is better than that based on current pulses, which shows that the Trichel stage can be further subdivided. In addition, we observed that the anode discharge begins earlier than the formation of pulseless glow, and we illustrated that anode discharge played an important role in the formation of pulseless glow and spark breakdown. Briefly, the discharge image corresponds well with the results of traditional detection methods and provides a new perspective for the corona discharge study, deserving further research.

Optimum Electrical and Dielectric Performance of Multi-Walled Carbon Nanotubes Doped Disposed Transformer Oil

This paper intends to prepare a nanofluid sample by suspending Multi-walled Carbon Nanotubes (MWCNTs) at 0.005g/L concentration and analyze the behavior of electrical and dielectric properties based on the International Electrotechnical Commision test method. In order to validate the effectiveness of MWCNT nanofluid, alternating current breakdown voltage (BDV), negative polarity lightning impulse (LI), dielectric permittivity, dissipation factor (DF), DC resistivity and Raman structural measurement are executed accordingly. In the following, an analysis of the statistical distribution using the two-parameter Weibull distribution law of BDV and LI are evaluated at four experimental conditions to predict the probability of breakdown occurring at different percentages. Based on the observation, the MWCNT filler has a substantial effect in improving the BDV and LI characteristics of disposed mineral oil. The permittivity, DF and resistivity performance of MWCNT nanofluid from 25 °C to 90 °C also produces comparable and reliable performance as a fresh transformer oil. As for Raman structure, the revolution of transformer oil by doping MWCNT does not disrupt the original chemical structure of mineral oil. Hence, this study proves the improvement of the electrical and the behavior of dielectric properties and chemical structure of nanofluid, providing a huge contribution towards the development of insulating materials for transformer application.

Understanding the impact of gamma irradiation of epoxy titania nanocomposites on surface and bulk charge characteristics

Epoxy titania nanocomposites were prepared under optimum process conditions through shear mixing of titania nanoparticles in to epoxy resin, for its potential application as insulant in nuclear power plants and space applications. The complex intrinsic nature of properties, its characteristic variation due to ageing of nanocomposite insulating material upon its continuous exposure to gamma irradiation, and their charge trap and space charge characteristics are explored. Surface potential variation studies were carried out under DC voltage. In the present study, the charge trap performance was assessed under switching impulse voltage. It is observed that surface potential decay and shallow trap formation are high with gamma irradiated specimen. In addition, the potential decay is high under switching impulse voltage compared to DC voltage. Also, the trap depth formed is less under switching impulse voltage compared to DC voltage and it is high under negative DC voltage. The space charge analysis through Pulsed electro acoustic (PEA) studies has shown increase in accumulation of space charge and enhancement of electric field with increase in dosage of gamma-irradiation. Polarity reversal tests have revealed that the electric field enhancement is high before reversal of polarity, irrespective of level of gamma irradiation dosage. The direct correlation between characteristic variation in trap depth values with the gamma irradiated specimen and its contact angle was observed.

Electrostatic precipitator for fine and ultrafine particle removal from indoor air environments

An electrostatic precipitator was evaluated to reduce nanometric and micron-sized particles in indoor air environments. This process consists in a negative air ionizer assisted by a parallel-plate collector. The ionization stage contained four or eight corona needles, which were supplied by a negative high-voltage DC. The collection stage was designed in a plate-to-plate configuration, of which the plates are alternately connected to a high-voltage DC supply and the ground. Fractional efficiency (expressed in number) was investigated using NaCl ultrafine particles and atmospheric aerosol according to different geometric, environmental and operating parameters (concentration, relative humidity, collector and ionizer voltage, collector length, number of needles, and airflow rates). The results are discussed according to particle size. Under optimized conditions (eight needles, 20 cm collector length, −7 kV ionization voltage, 5 kV collection voltage, 1 m/s air velocity), the process revealed high performance levels. The efficiency of particles of 10–25 nm in diameter was 94%, between 30 and 300 nm the efficiency was 99%, while in the most penetrating particle size, the efficiency was 96%, with an ozone concentration at the outlet of the process less than 5 ppbv. This process generated a very low ozone concentration, which is an essential challenge for indoor air treatment. The results confirmed the existence of the partial charging regime for particles less than a few tens of nanometers for which the efficiency was lower. For these particles, the collection conditions (collection time and voltage) had no influence on the efficiency. For larger particles, both the parameters of the charging phase (ion concentration, charging time) and the parameters of the collection phase (collection time and voltage) had a significant influence on the collection efficiency.

Novel flexible HVDC transmission converter station topology with DC fault blocking capability

The conventional half-bridge submodule (HBSM)-based multilevel modular converter (MMC) cannot block DC faults. To solve this problem, a novel flexible overhead-line high-voltage direct current (HVDC) transmission converter station topology is proposed in this study, which provides DC fault blocking capability. By adding blocking submodules (SMs) onto the positive and negative DC buses of a conventional HBSM converter station, a rapid fault current blocking can be achieved in the case of a DC bus short circuit. The DC fault blocking principle of the proposed topology and the rapid fault blocking capability of the blocking SM are analyzed. The quantity of required major components is also calculated. In addition, the IGBT, the system loss and the control complexity quantities are comprehensively compared with those of existing topologies. The validity of the proposed topology is demonstrated based on simulation and experimental studies.

Study of the Characteristics of DC Multineedle-to-Water Plasma-Activated Water and Its Germination Inhibition Efficiency: The Effect of Discharge Mode and Gas Flow

In this article, a negative dc multineedle-to-water discharge device was designed to generate plasma-activated water (PAW) with a total volume of 580 mL. The physicochemical properties of PAW were investigated. The results showed that the products concentration of PAW and its acidity were not continuously increased by adding the applied voltage. When it turned from pulse corona discharge to DC glow-like discharge (−19.5 to −20.5 kV), the corresponding value decreased with the increase of the applied voltage. This decrease was attributed to the fact that the differences in the discharge figure had an effect on the reactions of transient species with N x O y in different discharge modes. In addition, by comparing the product concentrations of PAW in different gas conditions, we discovered that the gas flow would lead to a decrease of active species in PAW and its inactivation. Although the gas flow took away the N x O y diffused in the discharge chamber and formed microbubbles in the gas-washing bottle, which benefitted for increasing the absorption area with water, this process also took away NO out of the discharge area, which decreased its reaction with transient species such as OH, O2−, and O to form HNO2 and HNO3 directly. Finally, the germination inhibition rate (GIR) of penicillium spores was calculated to estimate the inactivation efficiency of PAW. The maximum GIR was 71.5% when the applied voltage was −19.5 kV (corona discharge) and the gas flow rate was 0 L/h.

Effect on Resistive Switching by Inserting TiO&lt;sub&gt;x&lt;/sub&gt; Thin Layer in SiO&lt;sub&gt;x&lt;/sub&gt;: Ag-Based Memristor

An approach to design a memristor by inserting a TiOx thin layer in Pt-Ag/SiOx:Ag/TiOx/P++-Si memristor in order to exhibit analog resistive switching has been proposed. The device shows continuous resistance change under positive and negative DC sweeping bias, and the device conductance can also be modulated by consecutive potentiating and depressing pulse programming. These primitive results are beneficial to realize the learning and computing in such kind of memristor devices. High-resolution transmission electron microscopy observations demonstrate a clear interface between the thin layers of Ag nanoclusters embedded SiOx and the amorphous TiOx. The I-V analysis of Pt-Ag/SiOx:Ag/TiOx/P++-Si memristor confirms that the presence of TiOx thin layer controls the formation/rupture of Ag-filament across the Pt-Ag and P++-Si electrodes, realizing the gradual conductance modulation, which is essential to emulate the bio-synaptic characteristics.

± 180° Discontinuous PWM for Single-Phase PWM Converter of High-Speed Railway Propulsion System

As high-capacity alternating current/direct current (ac/dc) power conversion systems, single-phase pulse-width modulation (PWM) converters used in high-speed railway propulsion systems adopt high-voltage Insulated-Gate Bipolar Transistors (IGBTs) as switching elements. Due to their high breakdown voltage characteristics, the switching dynamics are inferior to those of low-voltage IGBTs and switching losses are more dominant than conduction losses despite operating at relatively low switching frequencies of hundreds to several kHz. To solve this problem, this paper proposes ± 180° discontinuous PWM (DPWM) suitable for a single-phase circuit. With the simple addition of offset voltages, the proposed DPWM method can be implemented easily and switching losses can be reduced by half by clamping the switching legs of the H-bridge converter to the positive or negative dc rail during every half cycle. In addition, temperature deviation between the power stacks can be minimized by using selective application of clamping modes. The validity and effectiveness of the proposed DPWM are verified through simulations and experiments of a prototype converter.

Electrification of Sonoluminescing Single Bubble.

The charge of microbubbles in water is considered to be negative at the liquid-bubble interface. We investigated, for the first time, the charge of a single bubble sonoluminescence (SBSL bubble) that exhibits spatiotemporally stable light emission. When negative DC voltage was applied, the SBSL bubble was attracted to a hot electrode. Conversely, the SBSL bubble was repelled by the hot electrode when positive DC voltage was applied. The translation of the SBSL bubble under an electric field suggests that it is positively charged, and the bubble moved to an equilibrium position to balance the primary Bjerknes force and the electrostatic force. The amount of bubble translation under an electric field depended on the elapsed time of sonoluminescence, suggesting that the products generated inside the SBSL bubble affect the mechanism of bubble charging. Furthermore, we measured the electric field effects on bubble expansion and contraction by a light scattering technique. Applying a positive voltage decreased the maximum bubble diameter and also the intensity of the SBSL. Conversely, applying a negative voltage increased the maximum bubble diameter and also the intensity of the SBSL. The present study revealed that a SBSL bubble is positively charged.

The pulsed mode of negative DC corona in nitrogen at atmosphere pressure: Comparison with Trichel pulses in air

The pulsed mode of negative DC corona discharge in nitrogen at atmosphere pressure is investigated in needle–plate electrodes and compared with Trichel pulses in air. Current/voltage waveforms and time-resolved discharge pictures are recorded experimentally. It is found that the pulsed mode only appears in the presence of a large ballast resistor. The slope of pulsed mode time-averaged voltage–current curve is negative, in contrast to that of Trichel pulses. A transition of slope from negative to positive is tracked by increasing the oxygen fraction. The development of pulse discharge in nitrogen can be divided into three stages: (1) current raising stage, (2) current falling stage, and (3) charging stage. At stage 1, the current raises and forms a peak. The leading edge lasts for dozens of nanoseconds, similar to that of Trichel pulses in air. At stage 2, the voltage decreases monotonically, where a second hump can appear in the current waveform. Through intensified charge coupled device (ICCD) pictures and fluid model simulation, the hump is attributed to the further development of temporal glow discharge. The relative value and occurrence time of this hump are shown to be affected by a parallel capacitor, the space between electrodes, and the applied source voltage. At stage 3, the current remains constant, combined with a rise of gap voltage. Meanwhile, the stray capacitor is charged, which is analyzed by an equivalent circuit model. Through this experiment and simulation, we further clarify the mechanisms of pulses in nitrogen and differences between pulses in nitrogen and Trichel pulses in air.

Synaptic learning and memory functions in SiO2:Ag/TiO2 based memristor devices

In this study, a TiO2 thin layer is deliberately inserted in the Pt–Ag/SiO2:Ag/p++-Si memristor to achieve enhanced resistive switching performance in terms of retention and cyclic endurance characteristics. The memristor device exhibits a bidirectional analog switching behavior corresponding to a wide dynamic range of synaptic weight modulation as potentiation and depression under the consecutive positive or negative DC bias sweeps and pulse trains. Moreover, the learning and memory functions, including paired-pulse facilitation and pulse repetition-induced short-term memory to long-term memory transition, are also demonstrated. The relation of the memory stability to the repeated input pulse stimulus and the device conductance with time have also been revealed by the stretched exponential relaxation model. It is shown that the conductance of our newly fabricated Pt–Ag/SiO2:Ag/TiO2/p++-Si memristor device can be modulated by successive Ag-filament growth and dissolution in the SiO2:Ag/TiO2 bilayer oxide structure, which is essential for potential applications in memory devices and artificial neural systems.

Ionic wind produced by a DC needle-to-plate corona discharge with a gap of 15 mm

The goal of the present study is to better understand the electrohydrodynamic (EHD) phenomena occurring in 15 mm gap point-to-plate corona discharges supplied by positive and negative DC voltages, and to link them to the discharge regime. For that, discharge current measurements have been conducted and a 20 kHz Particle Image Velocimetry system has been used to characterize the ionic wind produced by the discharges. The main results are as follows: (a) the Townsend’s law can always correctly interpolate the experimental I–V characteristics of a negative corona, even in presence of Trichel pulses, (b) in the case of a positive streamer discharge, the current does not follow the Townsend’s law as it evolves in Vk with k = 4 in the present study, (c) Indeed, the discharge current becomes higher than the Townsend’s law when the glow-to-streamer regime transition occurs, (d) the ionic wind is unsteady, more especially in the case of a positive corona for which it seems that its velocity is pulsed at the same frequency than the streamer one, (e) when the positive high voltage is switched on, a strong streamer occurs at the end of the voltage rising (t = 25 µs for +6 kV), resulting in an over-velocity region upstream the head of the ionic wind jet that progresses in quiescent air toward the plate, (f) the topology of the time-averaged ionic wind is fully different compared to the one observed in a previous study where the gap was equal to 25 mm, (g) in the case of a negative corona, the ionic wind velocity is nearly constant in the electrode gap, (h) in the case of the positive corona, the results are even more surprising since the velocity is minimum at the tip and increases when one approaches the grounded plate, indicating that there is a significant space charge remained by the streamers in the second half of the inter-electrode region, (i) generally speaking, this study highlights that the spatio-temporal characteristics of the EHD force and the resulting ionic wind depend on the distribution of the space charge between both electrodes, the latter being linked to the voltage polarity, the discharge regime and the electrode gap.