Breakdown Effects Research Articles

Manchado de mandarina Satsuma ‘Okitsu’: descripción anatómica, efecto de factores ambientales y manejo postcosecha

En la cáscara de mandarina Satsuma ‘Okitsu’ se detectó en Uruguay un manchado durante la postcosecha, ocasionando en algunos años importantes pérdidas. En este trabajo se estudió el daño a nivel micro y macroscópico, su asociación con factores ambientales previos a la cosecha y el efecto del desverdizado y encerado de frutos sobre su incidencia y severidad. A partir de los 15 días de almacenamiento, se visualizó entre las glándulas de aceite una zona irregular de color pardo. Luego de 15 días de mostrador, en las zonas con síntomas más severos, se observó colapso de células subepidérmicas, avanzando hacia el parénquima subyacente y en algunos casos hacia la epidermis, sin afectar a la cutícula. En los dos primeros años evaluados, la incidencia de frutos manchados fue de 17 % y 7 % respectivamente, mientras que en los dos últimos no se registraron frutos afectados. La mayor incidencia se asoció a un período de mayor temperatura máxima, menor humedad relativa y menores precipitaciones durante los 10 días previos a la cosecha. El desverdizado no afectó la incidencia de frutos manchados a los 30 días de almacenamiento + 15 de vida de mostrador, mientras que el encerado de frutos la disminuyó en más de un 50 %. Los resultados sugieren que las condiciones ambientales precosecha favorables a la deshidratación de frutos y/o las condiciones postcosecha que no logren evitar la pérdida de agua, promueven el manchado de los frutos de mandarina Satsuma ‘Okitsu’.

Screening white-rot fungi for bioremediation potential of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Ligninolytic fungi contain a number of representative strains consisting of mainly white-rot fungi (WRF) that produce lignin-modifying enzymes (LME) such as laccases and manganese peroxidases. Lignin-modifying enzymes are multipurpose enzymes which have potential for application in various fields such as, for example, bioremediation and biomass conversion. Because of the non-specific nature of these enzymes, they are also capable of biodegradation and removal of xenobiotic pollutants. In this study we used a tiered screening process where we screened over 70 Vietnamese WRF fungal isolates for LME activity and subsequently for the ability to breakdown the dioxin TCDD. After the initial screening we selected four fungal strains, which belong to the order of Polyporales, which excreted high laccase enzyme levels. The most active fungus being isolate FMD21, a species of Rigidoporus, which was isolated from a forest in the South of Vietnam and which produced both laccase and manganese peroxidase. In the optimized PDSRb medium, FMD21 laccase levels reaced activities of 238800 U/L after 10 days while MnP activity showed the highest activity at day 4 of aproximately 40 U/L. 2,3,7,8-TCDD, which is the most toxic dioxin congener, is a persistent organic pollutant of which few organisms are known that break it down. After the final screening, FMD21 was the only fungus capable of degrading TCDD and was able to reach a breakdown percentage of 73% after 28 days culture with a start concentration of 0.5 pg TEQ/μL TCDD. Co-cultivation experiments of up to three fungi were performed to test for a synergistic breakdown effect of TCDD but such an effect was not observed. FMD21 is a fungus that shows a potential to be used as a bioremediation agent to clean up dioxin contamination in the environment.

Optimization of triboelectric nanogenerator load characteristics considering the air breakdown effect

Working in the ambient environment, the behavior of triboelectric nanogenerator (TENG) is inevitably limited by the air breakdown phenomenon. In this paper, the load characteristics of TENG considering the air breakdown effect are systematically studied. The maximum retainable surface charge density varies with resistive loads, and a saturation state is seen during the capacitive charging process in the TENG due to the air breakdown effect. The optimization criterion to maximize the TENG output was also investigated with the consideration of air breakdown effect. Through theoretical analysis and experimental verification, this work provides a solid criterion to guide the TENG design and operational process.

Theoretical and experimental research on a high efficiency X-band klystron-like RBWO

In this paper, we study an X-band klystron-like relativistic backward wave oscillator (RBWO) with a pre-modulation cavity, modulation ridge, drift tube in the slow wave structure (SWS) and extraction cavity in both theoretical and experiment. PIC simulations show that the conversion efficiency can be up to 62% with output power of 3.0 GW. In experiment, when the diode voltage is 660 kV, and the diode current is 6.4 kA, the output power is 1.9 GW, and the conversion efficiency is 45%(±5%). And we find that the conversion efficiency mainly suffers from the breakdown in the extraction cavity and the plasma from the cylindrical collector. To suppress the breakdown and plasma effect, the breakdown electric field threshold in RF structures(especially in the extraction cavity) had better be larger than 700 kV/cm. Moreover, the distance between the position where the electrons are collected and the end of extraction cavity should be larger than 20 mm in case of the cylindrical collector.

Effects of Mechanical Load and Ionizing Radiation on Glass

This paper develops an approach to investigation of a solid as an integral system whose fundamental properties are determined by the energetics of its structure. Addressing the subject from a unified viewpoint, we consider the formation, accumulation, and transformations of defects in silicate and aluminophosphate glasses, which emit electromagnetic waves in a wide frequency range as a result of cracking. It has been shown that electron irradiation causes spontaneous electrical discharges, whose magnitude depends on the electron energy and irradiation time. The discharges occur at surface defects. Brush discharges develop in a layer where charged particles are distributed. In a thin layer of a charged dielectric, we observe a breakdown effect. The electrical discharge concentrates at surface defects, which can be produced in advance. A discharge can be initiated by approaching a grounded metallic tip to a charged surface even some time after irradiation. A discharge, mechanical loading, cooling, or heating of glass is accompanied by not only a light burst but also electromagnetic emission (EME), which correlates well with a polymorphic transformation process, thermoluminescence, etc. Thus, the release of accumulated energy from unirradiated and irradiated inorganic glasses on heating and cooling is accompanied by pulsed EME, whose intensity depends on the energy stored in the material.

Plasma effects of the directional coupler for high-power microwave measurements

The directional coupler is an important online power measurement device based on coupling principles. It is widely used for real-time monitoring of the performance of high-power microwave devices. However, insufficient power handling capacity limits further applications of the coupler in higher-pulsed energy measurements. From a theoretical and numerical analysis, the plasma effects of breakdown on the coupler are investigated. The plasma is found to break the fixed phase relationship between the coupling holes and eventually the directivity of the coupler. As the plasma density increases, the isolation of the coupler decreases rapidly, and thus, a negative power flux in the secondary rectangular waveguide increases gradually. Simultaneously, the positive power flux fluctuates and even terminates ahead of the microwave pulse in the main circular waveguide. The conclusions provide a good interpretation of the experimental phenomena.

Investigation on the surface flashover of high gain SI‐GaAs PCSS

AbstractThe GaAs photoconductive semiconductor switch (PCSS) is generally recognized currently as a leading power electronic device for its unique advantages. A major limitation of PCSS has been its surprisingly low voltage threshold for the surface flashover found when PCSS works at the high gain mode. In this paper, the surface flashover of high gain PCSS is studied by experiments. We propose that the non‐uniform distribution of the surface field that resulted from the photo‐activated charge domain (PACD) and the gas desorption is the key cause of such reducing of the SF field. SF6 ambient dielectric is efficient in increasing the surface field, and the experiment results show that the PCSS we developed could resist a voltage as high as 20 kV/cm when the ambient dielectric is 3 atmospheric SF6. This conclusion has the practical application of significance to improve the performance of the high gain PCSS, which is severely limited by the premature breakdown effects.

Parity-violating hybridization in heavy Weyl semimetals

We introduce a simple model to describe the formation of heavy Weyl semimetals in non-centrosymmetric heavy fermion compounds under the influence of a parity-mixing, onsite hybridization. A key aspect of interaction-driven heavy Weyl semimetals is the development of surface Kondo breakdown, which is expected to give rise to a temperature-dependent re-configuration of the Fermi arcs and the Weyl cyclotron orbits which connect them via the chiral bulk states. Our theory predicts a strong temperature dependent transformation in the quantum oscillations at low temperatures. In addition to the effects of surface Kondo breakdown, the renormalization effects in heavy Weyl semimetals will appear in a variety of thermodynamic and transport measurements.

Increasing the Operation Voltage of Integrated Solid-State Diodes through Nanostructured Porous Silicon Technology

Here, we report on the use of nanostructured porous-silicon (PS) technology as an alternative to standard field-plates technology to increase the operation voltage of silicon-based integrated solid-state devices. As a case study, we show that integration of nanostructured porous silicon in the high-field regions of a solid-state diode allows a significant increase of the breakdown voltage (VBR> 65V) to be achieved with respect to a reference diode (VBR=25V) under reverse-bias operation. On the other hand, the electrical characteristics of the diode under forward-bias operation are not affected from the presence of nanostructured PS. We argue that the nanocrystalline nature of PS reduces the mean-free path of charge carriers accelerated in high-field regions of the diode reducing, in turn, carrier velocity developed for a given applied voltage under reverse-bias operation. A standard n+/p diode with size varying between 1 and 10 um is used as a reference in this work. Under reverse-bias operation, a depletion zone establishes across the np junction, with an intense electric field developing across the depletion zone at high reverse bias. The electric field has higher intensity in correspondence of the curved edges of the junction with respect flat central regions, due to the thinner depletion zone of the former. Therefore, charge carriers are highly accelerated in the curved regions of the np junctions giving rise to breakdown effects. Electrical measurements of the current-voltage curves of the diodes shows that: i) Ron in forward biasing is of a few tens to hundreds Ohm, depending on the size of the diodes; ii) the breakdown voltage VBD is of about 25 V. The reference diode was modified through electrochemical conversion of p-type silicon to nanostructured porous-silicon in correspondence of the curved regions of the np junction. This allows the mean-free path of charge carriers in correspondence of the curved regions of the diode to be shorted and, in turn, carrier velocity developed at high electric field to be reduced under reverse-bias operation. Electrical measurements of the I-V curves of diodes modified with nanostructured PS highlight that: i) electrical characteristics of the diode in forward biasing are not affected by the presence of the PS layer (e.g. Ron changes of a few percent with respect to that of the reference diode); ii) the breakdown voltage of the diode in reverse biasing is increased to more than 65 V (i.e. a factor about 3). TO further verify our experimental findings, we carried out failure analysis through emission microscopy (EMMI). EMMI analysis of both reference and PS-modified diodes clearly shows that in the reference diode avalanche breakdown starts around 25V in correspondence of the curved regions of the n+/p junction; conversely, no breakdown effects are evident in the same regions for the diode modified with nanostructured porous silicon, which actually occurs above 65 V in other regions of the diode where PS was not produced, thus corroborating our hypothesis the presence of PS reduce the charge carrier velocity, increasing, in turn, the breakdown voltage.

Microparticle manipulation using femtosecond photonic nanojet-assisted laser cavitation.

We report the effect of laser cavitation in water initiated by femtosecond pulses confined into subwavelength volume of photonic nanojet of spherical microparticles. The effect of nanoscale optical breakdown was employed for controllable and nondestructive micromanipulation of silica microspheres. We combine this technique with optical trapping for cyclic particle movements and estimate a peak velocity and an acceleration acquired by microspheres propelled by nanojet cavitation. Our study provides a strategy for nondestructive optical micromanipulation, cavitation-assisted drug delivery, and laser energy transduction in microdevices.

Temperature measurements in confined swirling spray flames by vibrational coherent anti-stokes Raman spectroscopy

A gas turbine model combustor for swirling spray flames has been operated at atmospheric pressure with n-hexane, n-dodecane and kerosene Jet A-1. Temperature measurements were performed using single-shot broadband shifted vibrational coherent anti-Stokes Raman spectroscopy (SV-CARS). Series of 1200 single-shot measurements were performed at different radial and vertical locations in the flames from which the temperature distributions were deduced. In regions with high droplet load a significant number of CARS spectra were discarded due to large signal background from laser-induced breakdown effects. Results from the flames burning different fuels were compared and revealed considerable differences in the temperature profiles. The temperature measurements are part of a comprehensive research program that aims at the design of alternative fuels for aero engines and stationary gas turbines. In addition to the experimental characterization of the spray flames, the datasets are used for the validation and improvement of computational models.

Effect of electron avalanche breakdown on a high-purity semi-insulating 4H-SiC photoconductive semiconductor switch under intrinsic absorption.

High-power photoconductive semiconductor switching devices were fabricated from a high-purity, semi-insulating 4H-SiC wafer. A highly n-doped GaN subcontact layer was inserted between the contact metal and the high-resistivity SiC wafer. The minimum ON-state resistance of the device was less than 1ohm when the energy of a 355nm laser was 10.5mJ with a bias voltage of 6kV. The maximum device lifetime is 3151 pulses, after which the device completely fails. The failure mechanisms are determined using several analysis methods. Under a strong electric field, the failure mechanism differs for the two electrodes. Near the edge of the anode electrode, the switch is damaged due to the thermal stress caused by impact ionization. At the edge of the cathode electrode, the electrode erosion is the main reason for the failure to operate for long periods of time. These two different damage mechanisms are both important factors influencing the device performance. The electron avalanche breakdown at the edge of the anode electrode causes the formation of cracks between the electrodes, which is the root cause of the switch failure.

ELECTRICAL SOLUTION OF THE DIELECTRIC AND ITS INFLUENCE ON FLAME EMISSION WITH ELECTROMAGNETIC FIELD

Studies have been carried out on the effect of an electric breakdown of a dielectric on flame suppression by an electric field of high voltage. In the course of research in the event of electric breakdown of air, the quenching efficiency was reduced to zero. This effect occurs due to the drop in electrical tension between the electrodes. The electrical breakdown in dielectrics when extinguishing a flame is due to the presence of a certain number of ions and electrons, which under the action of the electric field move to the anode. It is established that the electrical strength of the material exerts the greatest influence on the outcome of experimental studies on extinguishing a fire by an electromagnetic field. Therefore, increasing the values of the electrical strength of the material (dielectric), it is possible to exclude the possibility of electrical breakdown. If glass and electrotechnical porcelain are used as dielectrics on electrodes, the boundaries of the investigation flame process by an electric field of high tension will expand. Studies have shown that an electric breakdown has a negative effect on flame suppression by an electric field of high tension. The probability of electrical breakdown is influenced by such parameters as: the distance between the electrodes (the probability of breakdown increases with decreasing distance), atmospheric pressure, air humidity (the probability of electric breakdown decreases with decreasing air humidity), the strength of the material (with an increase in the strength of the material, the probability of breakdown decreases ) and voltage at the electrodes (with increasing voltage, the probability of breakdown increases). In the course of the research it was established that an increase in the electrical strength of the electrodes will allow to conduct studies with a voltage of up to 20,000 kV without the occurrence of electrical breakdown.

Improvement of the electrical disintegration of coal sample with different concentrations of NaCl solution

The application of high-voltage electrical pulse (HVEP) technology to the improvement of pore structure of coal has achieved encouraging results. However, the very high breakdown voltage of some kinds of coal seriously affects the application of HVEP technology. In this study, the relationship between the concentration of NaCl solution and the breakdown voltage of coal sample was studied by improving the electrical breakdown effects of Linhua anthracite coal and Hongliu bituminous coal with different concentrations of NaCl solution, and a negative exponential relationship was established. The results indicate that the breakdown voltages of coal samples decrease with the increase of the concentration of NaCl solution, but there is a limit to the magnitude of the decrease. Additionally, nuclear magnetic resonance (NMR) and X-ray photoelectron spectrometer (XPS) were adopted in this study to investigate variations in pore structure and functional groups before and after the electrical breakdown. The NMR analysis demonstrates that the electrical breakdown mainly improves the number of mesopores and macropores and enhances the connectivity between them, thus providing a smoother channel for gas extraction. The XPS analysis reveals that a new oxidation reaction appears where the current flows through, which promotes gas desorption from surfaces of coal samples.

Water Quantity-Based Quality Measurement of Transformer Oil Using Polymer Optical Fiber as Sensor

Measurement of transformer oil quality plays an important role in health condition monitoring of a transformer. The breakdown voltage of transformer oil is influenced by both water content and temperature variation. Therefore, accurate assessment of water content in transformer oil and variation of breakdown voltage due to change in temperature are essential for health condition monitoring of a transformer. It helps to estimate the life expectancy of a transformer. This paper presents a polymer optical fiber sensor based instrumentation system (POFSBIS) to measure the water content in transformer oil of a transformer. Furthermore, the POFSBIS is also used to detect the effect of transformer oil breakdown under controlled laboratory environment. Ultraviolet visual spectrophotometer has been employed to study the changing temperature effect and voltage breakdown effect on transformer oil. The instrumentation system measures the water content in transformer oil as well as provides the online information about the breakdown occurrence in transformer oil which helps to prevent the catastrophic losses of a transformer.

A comprehensive study of cryogenic cooled millimeter-wave frequency multipliers based on GaAs Schottky-barrier varactors

AbstractThe benefit of cryogenic cooling on the performance of millimeter-wave GaAs Schottky-barrier varactor-based frequency multipliers has been studied. For this purpose, a dedicated compact model of a GaAs Schottky-barrier varactor using a triple-anode diode stack has been developed for use with a commercial RF and microwave CAD tool. The model implements critical physical phenomena such as thermionic-field emission current transport at cryogenic temperatures, temperature dependent mobility, reverse breakdown, self-heating, and high-field velocity saturation effects. A parallel conduction model is employed in order to include the effect of barrier inhomogeneities which is known to cause deviation from the expected I--V characteristics at cryogenic temperatures. The developed model is shown to accurately fit the I--V --T dataset from 25 to 295 K measured on the varactor diode stack. Harmonic balance simulations using the model are used to predict the efficiency of a millimeter-wave balanced doubler from room to cryogenic temperatures. The estimation is verified experimentally using a 188 GHz balanced doubler cooled down to 77 K. The model has been further verified down to 14 K using a 78 GHz balanced doubler.

Quantifying contributions of slaking and mechanical breakdown of soil aggregates to splash erosion for different soils from the Loess plateau of China

The information of aggregate disintegration mechanisms during splash erosion is scant. This study was conducted to quantify contributions of the mechanisms of aggregate disintegration to splash erosion. Six soils with five soil textures were used. Soil aggregate stability was determined by the Le Bissonnais (LB) method. Deionized water was used to simulate the combined effect of slaking and mechanical disaggregation, while ethanol was used to estimate the sole contribution of the mechanical breakdown. Simulated rainfall with intensity of 60 mm h−1 was applied at five fall heights (0.5 m, 1 m, 1.5 m, 2 m and 2.5 m) to achieve different levels of rainfall kinetic energy. The results indicated that slaking caused the most severe aggregate breakdown, and followed by mechanical breakdown, while chemical dispersion in slow wetting with deionized water was the weakest breakdown mechanism. The splash erosion rates due to the effects of slaking and mechanical breakdown increased with an increase in rainfall kinetic energy. The contributions of the slaking (mechanical breakdown) to splash erosion decreased (increased) as rainfall kinetic energy increased. The contribution of mechanical breakdown had a power function relation with rainfall kinetic energy, and had the most significant correlation with RSI (relative slaking index)/RMI (relative mechanical breakdown index). A power and a linear function could be used to describe the relationships between the contributions of mechanical breakdown with rainfall kinetic energy and RSI/RMI, respectively, which could be used to estimate the contribution of mechanical breakdown. The results of this research would be helpful to improving the soil erosion prediction models.

Separation of cancer cells using vortical microfluidic flows.

Label-free separation of viable cancer cells using vortical microfluidic flows has been introduced as a feasible cell collection method in oncological studies. Besides the clinical importance, the physics of particle interactions with the vortex that forms in a wall-confined geometry of a microchannel is a relatively new area of fluid dynamics. In our previous work [Haddadi and Di Carlo, J. Fluid. Mech. 811, 436-467 (2017)], we have introduced distinct aspects of inertial flow of dilute suspensions over cavities in a microchannel such as breakdown of the separatrix and formation of stable limit cycle orbits for finite size polystyrene particles. In this work, we extend our experiments to address the engineering-physics of cancer cell entrapment in microfluidic cavities. We begin by studying the effects of the channel width and device height on the morphology of the vortex, which has not been discussed in our previous work. The stable limit cycle orbits of finite size cancer cells are then presented. We demonstrate effects of the separatrix breakdown and the limit cycle formation on the operation of the cancer cell separation platform. By studying the flow of dilute cell suspensions over the cavities, we further develop the notion of the cavity capacity and the relative rate of cell accumulation as optimization criteria which connect the device geometry with the flow. Finally, we discuss the proper placement of multiple cavities inside a microchannel for improved cell entrapment.

Localized Corrosion: Passive Film Breakdown vs Pit Growth Stability: Part II. A Model for Critical Pitting Temperature

Potentiostatic temperature-scanned experiments were performed on 316L stainless steel and revealed that both the measured values of critical pitting temperature (CPT) and their distribution ranges increased with the decrease of the aggressiveness of exposure conditions. Previous models for CPT cannot explain these observations, so a model for CPT is proposed based on criteria for pit growth stability with added effects of the passive film breakdown. The criterion for pit stability is assumed to be the maintenance of a critical pit solution concentration at the pit surface, which requires the maximum pit dissolution current density to be equal to or greater than the diffusion current density associated with this critical concentration. The resulting model can explain many observations of nature of the CPT. The CPT is shown not to be a single-valued critical value; instead, it is a statistically distributed value based on the detailed behavior of many pitting events. For potentiostatic measurements, the measured CPT is just the temperature at which the first stable pit forms. The commonly recognized and tightly distributed CPT is determined from the perspective of pit growth stability and it represents the temperature with the highest probability to form the first stable pit.

Growth Mechanism of Self-Assembled TixWyO Nanotubes Fabricated by TiW Alloy Anodization

Nanostructures, such as nanodots and nanorods, have been fabricated by the anodization process with an aid of anodic aluminum oxide (AAO) for several decades. However, tubular nanostructures have not been reported by using an AAO-assistant anodization technology until now. In this study, we successfully synthesized self-organized TixWyO nanotubes with cap structures for the first time by using a two-step anodization process from Al-coated TiW alloy layers. The TixWyO nanotubes were observed only in the shaped pores of AAO with large enough pore size, and otherwise the nanostructures would become solid rods due to the aggregation of TixWyO. The wall of nanotubes was ∼30% inside the pores and the other ∼70% penetrated into the AAO template. Furthermore, no tubular nanostructures were found unless the percentage of W element in TiW alloys is larger than 50%, attributing to the formation of a void by oxygen bubbles arising from the oxidation reaction of tungsten metal. Besides, the height of the nanotubes is limited by an electric field of 0.82 GV/m due to the dielectric breakdown effect. Finally, a bottom-up growth mechanism at the oxide/metal interface is proposed, based on the observation of the cap structure on the top of the tubular architecture.