Breakdown Phenomena Research Articles

P‐2: Nitrogen Behaviors in PEALD‐Grown SiO2 Films Using N2O Plasma Reactant and Its Application in ALD‐IZO TFTs

We studied nitrogen (N) behaviors in plasma‐enhanced atomic layer deposition (PEALD)‐grown silicon dioxide (SiO2) using nitrous oxide (N2O) plasma reactant. The gradually improved breakdown phenomenon is attributed to N contents. However, although increase in the N contents, excess plasma power is degraded electrical characteristics. For applications of the SiO2 films using N2O plasma reactant, we fabricated indium‐zinc oxide top‐gate thin film transistors with SiO2 gate insulator (G.I). The stable both transfer characteristics and instability results are originated from decrease in oxygen vacancy in active layer by N2O plasma treatment during the G.I deposition.

Temporal evolution of failure avalanches of the fiber bundle model on complex networks.

We investigate how the interplay of the topology of the network of load transmitting connections and the amount of disorder of the strength of the connected elements determines the temporal evolution of failure cascades driven by the redistribution of load following local failure events. We use the fiber bundle model of materials' breakdown assigning fibers to the sites of a square lattice, which is then randomly rewired using the Watts-Strogatz technique. Gradually increasing the rewiring probability, we demonstrate that the bundle undergoes a transition from the localized to the mean field universality class of breakdown phenomena. Computer simulations revealed that both the size and the duration of failure cascades are power law distributed on all network topologies with a crossover between two regimes of different exponents. The temporal evolution of cascades is described by a parabolic profile with a right handed asymmetry, which implies that cascades start slowly, then accelerate, and eventually stop suddenly. The degree of asymmetry proved to be characteristic of the network topology gradually decreasing with increasing rewiring probability. Reducing the variance of fibers' strength, the exponents of the size and the duration distribution of cascades increase in the localized regime of the failure process, while the localized to mean field transition becomes more abrupt. The consistency of the results is supported by a scaling analysis relating the characteristic exponents of the statistics and dynamics of cascades.

Multi view interferometric tomography measurements of convective phenomena in a differentially-heated nanofluid layer

ABSTRACT Three-dimensional reconstructions of thermal field in a differentially heated cylindrical cavity with dilute concentrations of nanofluids as the working medium have been reported. Experiments have been conducted in a specially designed tomography cell filled with dilute concentrations of Al2O3 nanofluids with ethylene glycol dimethacrylate (EGD) as the basefluid. The two horizontal walls of the cell have been differentially heated to apply the temperature potential across the fluid layer. Multiple projection data in the form of interferometric images have been recorded at every 20° view angle by slowly turning the cell over the range of 0 to 360°. The two-dimensional temperature fields retrieved through the quantitative analysis of interferometric images recorded at various view angles have been used to reconstruct the complete three-dimensional temperature field at select horizontal planes of the fluid layer. Iterative multiplicative algebraic reconstruction technique (MART) has been employed for tomography reconstructions. Based on the tomography reconstructions, possible fluid movement in the test cavity and the strong dependence of convective field on varying nanofluid concentrations and cavity temperature differences have been explained. Distribution of local temperature fields near the cavity wall surfaces revealed the phenomena of breakdown of large length scale fluid structures into multiple roll-like patterns with increasing concentration of nanoparticles. The distribution of the local Nusselt number, on select horizontal planes near the top and bottom wall surfaces of the cavity, highlighted the possible role of nanoparticles enhancing the heat transfer rates. An overall energy balance in the cavity was also to be seen based on the reconstructions of the local profiles of Nusselt numbers.

Influence of Area and Volume Effect on Dielectric Behaviour of the Mineral Oil-Based Nanofluids

Transformer oil is conventionally used as an insulating liquid for the purpose of insulation and cooling in power transformers. The rise in the power demand has put stress on the existing insulation system used for power transmission. Nanotechnology provides an advanced approach to upgrade the conventional insulation system by producing nano-oil with enhanced dielectric characteristics. The aim of the study is to present the influence of area volume effect on the dielectric performance of mineral oil and its nanofluids. In this paper, nanofluids are prepared by dispersing two different concentrations of SiO2 nanoparticles in base transformer oil using a two-step method. The effect of area and volume is investigated on nanofluids in the laboratory using coaxial electrode configurations under different test conditions. The AC breakdown voltage and maximum electric stress is determined for the pure oil and nanofluids. The results show that the addition of SiO2 nanoparticles significantly improves the dielectric characteristics of transformer oil. Moreover, the breakdown phenomenon is also discussed to analyze the effect of nanoparticle, stressed area, and stressed volume on the dielectric strength of insulating oil. Nanofluids could be an alternative to mineral oil.

High-voltage SiC power devices for improved energy efficiency.

Silicon carbide (SiC) power devices significantly outperform the well-established silicon (Si) devices in terms of high breakdown voltage, low power loss, and fast switching. This review briefly introduces the major features of SiC power devices and then presents research works on breakdown phenomena in SiC pn junctions and related discussion which takes into account the energy band structure. Next, recent progress in SiC metal-oxide-semiconductor field effect transistors, which are the most important unipolar devices, is described with an emphasis on the improvement of channel mobility at the SiO2/SiC interface. The development of SiC bipolar devices such as pin diodes and insulated gate bipolar transistors, which are promising for ultrahigh-voltage (>10 kV) applications, are introduced and the effect of carrier lifetime enhancement is demonstrated. The current status of mass production and how SiC power devices can contribute to energy saving are also described.

FLOW ANALYSIS ON DELTA WING – A REVIEW

Many aircraft, like fighters and bombers, are delta-winged aircraft. These aircraft have the characteristics of producing a greater lift at very small angles of attack even at very low Reynold’s number. Highly swept-wing aircraft experience greater lift due to the generation of the leading-edge vortex at a high angle of attack flight. The phenomena of vortex breakdown are noticed which leads to the reduction of the vortex lift and leads to the instability of the aircraft. This paper deals with an analysis of the flow on the delta wing with the existing literature and compares its benefits over the conventional wings using experimental and computational methods. The critical angles, pressure, and velocity variations are observed along with chord and spanwise locations.

Parapatric Genetic Lineages Persist in a Multiply Introduced Non-native Bush-Cricket

To understand colonization success of an invasive species we need to know the origin of the founders, where and when they were introduced, and how they spread from the introduction site(s) through the landscape. Admixture of different genetic lineages from multiple introductions is generally hypothesized to be beneficial to invasive species thanks to adaptive variation and heterozygosity-fitness correlations. In this study, population genetic and landscape data was gathered for Roesel’s bush-cricket,Roeseliana roeseliia small bush-cricket common in central and eastern Europe that currently is expanding its range in northern Europe. We examined how colonization history and landscape structure affect the spread of the species and its population genetic structure, as a consequence of multiple introductions. Using comprehensive information of the species ecology and dispersal, together with genetic structure inferred from samples from 29 locations in central Sweden (we employed data published by Preuss et al., 2015), we found that two parapatric founding lineages have coexisted with very little gene flow during a long time span. An isolation-by-distance pattern and a decrease of genetic diversity toward marginal areas were more pronounced in the lineage situated in forest dominated landscapes. Our findings are in strong contrast to the hypothesis that different genetic lineages will admix when introduced to the same area. The presence of the separate lineages decades after introduction and without physical barriers for gene flow shows that some mechanism prevents them from admixture. One possibility is that the lineages with different genetic setups have adapted independently to local conditions and their admixture resulted in loss of locally adapted genotypes and hybrid offspring, less viable than the respective ancestral genotypes. However, an alternative post-mating reproductive barrier and hybrid breakdown phenomenon should also be considered. Our data indicate that besides landscape characteristics, human transportation of agricultural goods may play an important role for the overall spatial genetic pattern of the species in the study area by aiding the spread of the species.

Flashover Voltage of Epoxy FRP Insulators with Different Surface Roughness and Groove under Nanosecond Pulses in SF6

In order to further improve the insulation performance of fiber reinforce plastic (FRP) materials used in electromagnetic pulse (EMP) simulators, the flashover characteristics of FRP materials with different surface roughness and groove, i.e., those who are easily achieved and have a prominent effect, are investigated in 0.1 MPa SF6 under nanosecond pulse voltage with a rise time of 20–30 ns. The experimental results show that surfaces with different roughness have no significant influence on the flashover voltages of the FRP insulators, and both the convex grooves made of FRP and the convex grooves with nylon rings inlaid to form projections can improve the surface flashover voltage of epoxy FRP insulators under nanosecond pulse, in which the effect of the former surface is more obvious. For the insulators with convex grooves made of FRP, it is found that the root of the FRP protrusions breaks down after a number of shots with the occurrence of carbonization channels and spots, which is nonexistent for the nylon projections. Combined with the test results of surface characteristics, the surface roughness and the secondary electron emission yield (SEEY) are not key factors of flashover characteristics in SF6 under nanosecond pulse, arguably due to the fact that the energy needed for an incident electron to ionize an SF6 molecule is lower than that to excite two secondary electrons. Hence, the flashover performance cannot be improved by adjusting the surface roughness, and the flashover channel is principally governed by the macroscopic distribution of electrical field which can be changed by the convex groove. Breakdown phenomena of FRP protrusions indicate that the bulk insulation performance of resin FRP is weaker compared to pure resin because of its composite structure, as well as the impurities and voids introduced in the manufacturing process. The results are instructive for the design of FRP insulation structures in the compact EMP simulator.

Avalanche Photodiodes With Composite Charge-Layers for Low Dark Current, High-Speed, and High-Power Performance

In this work, a novel In_0.52Al_0.48As based top-illuminated avalanche photodiode (APD) is demonstrated. By combining the composite charge-layer design with a special p-side up etched mesa structure to zero the electric (E)-field at the periphery of this APD's multiplication (M-) layer, the edge breakdown phenomenon can be eliminated. This in turn leads to the simultaneous high-speed, high-saturation-power, high responsivity, and low-dark current performance characteristics of our APDs, which are essential for high-performance coherent receiver applications. The demonstrated device, with its simple top-illuminated structure exhibits a wide optical-to-electrical (O-E) bandwidth (21 GHz), high responsivity (5.5 A/W at 0.9 V_br), and saturation current as high as 8 mA with a large active diameter of 24 μm for easy optical alignment. Furthermore, the nonlinear driving of a wavelength sweeping laser in the self-heterodyne beating setup can generate an optical pulse train like waveform, providing an effective optical modulation depth of up to 158%, which leads to a maximum photo-generated RF power (at 10 GHz) from our APD as high as +5.5 dBm. The excellent performance of our demonstrated APDs opens up new possibilities for the next generation of coherent receivers.

Newton’s Third Law in the Framework of Special Relativity for Charged Bodies Part 2: Preliminary Analysis of a Nano Relativistic Motor

(1) Background: In a recent paper discussing Newton’s third law in the framework of special relativity for charged bodies, it was suggested that one can construct a practical relativistic motor provided high enough charge and current densities are available. As on the macroscopic scale charge density is limited by the phenomena of dielectric breakdown, it was suggested to take advantage of the high charge densities which are available on the microscopic scale. (2) Methods: We use standard physical theories such as Maxwell electrodynamics and quantum mechanics, supplemented by tools from vector analysis and numerics. (3) Results: We show that a hydrogen atom either in the ground state or excited state will not produce a relativistic engine effect, but by breaking the symmetry or putting the electron in a wave packet state may produce relativistic motor effect. (4) Conclusions: A highly localized wave packet will produce a strong relativistic motor effect. The preliminary analysis of the current paper suggests new promising directions of research both theoretical and experimental.

Influence of Blade Lean on Performance and Shock Wave/Tip Leakage Flow Interaction in a Transonic Compressor Rotor

Blade lean has been extensively used in axial compressor stators to control flow separations, but its influence mechanism on transonic compressor rotors remains to be revealed. The aim of this study is to numerically explore the influence of blade lean on the performance and shock wave/tip leakage flow interaction in a transonic compressor rotor. The effects of leaned pattern (positively lean and negatively lean), leaned angle and leaned height were studied. Results showed that, compared with baseline configuration, the efficiency and total pressure ratio of the entire constant rotating speed line of positively leaned rotor were both decreased. The absolute value of peak efficiency was reduced by as much as 4.34% at 20° lean angle, whereas the maximum reduction of peak total pressure ratio was 0.1 at 20° lean angle. The tip leakage flow streamlines of baseline transonic rotor can be divided into two parts, i.e., the primary vortex and secondary vortex which arises after the shock. Due to shock/tip leakage vortex interaction, the primary vortex enlarged and low-momentum region showed up after the shock; under near stall (NS) condition, tip leakage vortex breakdown occurred after interacting with shock. As positively leaned angle increased, the shock and the shock/tip leakage vortex interaction point moved upstream. In addition, the phenomenon of tip leakage vortex breakdown was enhanced. For negatively leaned rotors, as negatively leaned angle increased, the peak efficiency and total pressure ratio showed a tendency of first increasing and then decreasing. At 5° leaned angle, the peak efficiency was increased by 0.8% at most, and the maximum increment of total pressure ratio was 0.05 at 5° leaned angle. Besides, the loading of blade tip reduced and the loading moved toward trailing edge, resulting in the downstream movements of primary vortex, shock front and shock/tip leakage vortex interaction location. The results may help to improve the near tip flow field of transonic compressor rotor with leaned blade technology.

Shape Anisotropy Effect on Magnetic Domain Wall Dynamics in Nanowires Under Thermal Gradient

We investigate the magnetic-domain wall (DW) dynamics in uniaxial/biaxial-nanowires under a thermal gradient (TG). The findings reveal that the DW propagates toward the hotter region in both nanowires. In uniaxial-nanowire, the DW propagates accompanying a rotation of the DW-plane. In biaxial nanowire, DW propagates in the hotter region, and the so-called Walker breakdown phenomenon is observed. The main physics of such DW dynamics is the magnonic angular momentum transfer to the DW. The hard (shape) anisotropy exists in biaxial-nanowire, which contributes an additional torque; hence DW speed is larger than that in uniaxial-nanowire. But rotational speed is lower initially as hard anisotropy suppresses the DW-rotation. After certain TG, DW-plane overcomes the hard anisotropy; thus, the rotational speed increases again. DW dynamics show a decreasing trend with the damping since the magnon propagation length decreases. Therefore, the above findings might be useful to realize the spintronics (i.e., fast racetrack memory) devices.

Envisioning the financial and psychological hardships of cancer.

Cancer is one of the leading causes of premature death and disability worldwide. With the progress of the health-care system, the cost of cancer treatment is also rising. Poor households suffer disproportionately from the financial burden of cancer treatment, which has pushed many households into poverty. Thus, cancer poses an economic burden for individuals, families, societies, and governments because of the prolonged medical costs, out-of-pocket expenditures, loss of productivity, and premature deaths. Moreover, the psychological breakdown phenomenon and social implications of cancer play a vital role in dealing with cancer patients. The psychological effect of battling with cancer falls not only on the patient but also on the caregivers and family members. With these backgrounds, an attempt is made in this review paper to highlight the implications of cancer on financial and psychological aspects.

Review on Laser Interaction in Confined Regime: Discussion about the Plasma Source Term for Laser Shock Applications and Simulations

This review proposes to summarize the development of laser shock applications in a confined regime, mainly laser shock peening, over the past 50 years since its discovery. We especially focus on the relative importance of the source term, which is directly linked to plasma pressure. Discussions are conducted regarding the experimental setups, experimental results, models and numerical simulations. Confined plasmas are described and their specific properties are compared with those of well-known plasmas. Some comprehensive keys are provided to help understand the behavior of these confined plasmas during their interaction with laser light to reach very high pressures that are fundamental for laser shock applications. Breakdown phenomena, which limit pressure generation, are also presented and discussed. A historical review was conducted on experimental data, such as pressure, temperature, and density. Available experimental setups used to characterize the plasma pressure are also discussed, and improvements in metrology developed in recent years are presented. Furthermore, analytical and numerical models based on these experiments and their improvements, are also reviewed, and the case of aluminum alloys is studied through multiple works. Finally, this review outlines necessary future improvements that expected by the laser shock community to improve the estimation of the source term.

Dielectric Strength of Polymeric Solid–Solid Interfaces under Dry-Mate and Wet-Mate Conditions

One of the most important causes of insulation system failure is the breakdown of the interface between two solid dielectrics; understanding the mechanisms governing this breakdown phenomenon is therefore critical. To that end, investigating and reviewing the practical limitations of the electrical breakdown strength of solid–solid interfaces present in insulating components is the primary objective of this work. The published literature from experimental and theoretical studies carried out in order to scrutinize the effects of the presence of solid–solid interfaces is investigated and discussed, considering macro, micro, and nano-scale characteristics. The reviewed literature suggests that solid–solid interfaces in accessories have non-uniform distributions of electrical fields within them in comparison to cables, where the distribution is mostly radial and symmetrical. Many agree that the elastic modulus (elasticity), radial/tangential pressure, surface smoothness/roughness, and dielectric strength of the ambient environment are the main parameters determining the tangential AC breakdown strength of solid–solid interfaces.

Algorithm of the Automated Scientific Research System for Studying the Drying Process of Multicomponent Polymers

One of the main quality problems of products made of polymer materials is the excessive moisture content in the feedstock. Earlier developments of the authors show the possibility of controlling and eliminating this factor by the method of preliminary acclimatization and drying of the material. Automation of drying of raw materials for polymer packaging at the enterprise cannot be developed and implemented without preliminary research of the drying process, development of recommendations for the organization of an automated control system. The issue of drying multicomponent and composite materials in the finished mixture remains open today. (Research purpose) The research purpose is developing an algorithm for automating scientific research of the high-frequency drying process of multicomponent polymer materials. (Materials and methods) The article presents the existing automated systems for scientific research of high-frequency processing and their methodology, based on previously stated controlled parameters. The article describes the approach and the algorithm for an automated system of scientific research of the drying process of a multicomponent polymer mixture. A new temperature parameter controlled in the volume of the heated polymer was proposed. The depth of the controlled layer was selected according to the described methodology. (Results and discussion) The system was protected from breakdown phenomena, which limits the current consumption in automatic mode in accordance with the characteristics of industrial equipment (0.9 amperes). The automatization of control system was made using the studied law of changing the power of a high-frequency generator on the rotation angle of the regulator. (Conclusions) The developed system of automated scientific research made it possible to conduct a series of experiments, the results of which, after final processing, will be presented to the scientific community in the near future.

Development of Microchip Laser for Ophthalmic Therapy Application

We have recently developed a several milli-joule, sub-nanosecond laser source for ophthalmic therapy application which allows to lower a laser breakdown threshold, less than half, and more stably/effectively yield the breakdown phenomenon compared to that based on conventionally employed source, implying the developed source has a potential to realize more minimally invasive ophthalmic treatment for secondary cataract. For further laser performance, the use of a photonic crystal device as an output coupler of the laser source has been also demonstrated. With this system, pulse width shortening and polarization control of the laser output could be achieved simultaneously. This paper presents these recent ophthalmic laser developments.

Mathematical Modeling of the Phenomenon of Space-Charge Breakdown in the Galvanostatic Mode in the Section of the Electromembrane Desalination Channel.

One of the ways to increase the efficiency of the desalination process in membrane systems is to use intensive current modes. Recently, the phenomenon of space-charge breakdown was theoretically described for desalination under intensive current modes. The space-charge breakdown is a decrease in the magnitude and size of the extended space charge regions (SCRs) of opposite signs, formed at the cation- and anion-exchange membranes in the desalination channel, when they approach each other. Therefore, this phenomenon negatively affects the intensity of electroconvection and the efficiency of mass transfer in membrane systems. We report the results of the first theoretical analysis of the space-charge breakdown in the galvanostatic electric mode, which is generally used in the research and operation of membrane systems. For this purpose, a one-dimensional model of the ion transfer of the electrolyte solution in the section of the desalination channel at the direct current is developed. The regularities of changes in the extended SCRs in the galvanostatic mode are determined. A relation is obtained for the onset time of the space-charge breakdown, which makes it possible to determine the parameters of the effective operation of the membrane system.

Microparticle‐initiated electron emission and subsequent gas breakdown

AbstractMicroparticle‐initiated breakdown phenomena in gas gap have obtained extensive research interest and micro‐gap discharge is convinced to play a key role. To illustrate this, this paper focused on microparticle‐initiated electron emission and subsequent gas breakdown process in a nitrogen gap. Analytic results of the electric field distribution between the charged microparticle and electrode surface are obtained by using the image method first. Results indicate that for the typical microparticles (R < 20 μm) from electrode erosion, when the micro‐gap distance h is lower than 2 μm, the maximum enhanced field strength could exceed 3 × 107 V/m. Based on this, a two‐dimensional axis‐symmetry numerical model is calculated by using the particle‐in‐cell coupling with Monte Carlo method and the charged microparticle is positioned near anode and cathode separately. In both cases, the local enhanced electron emission between microparticle and electrode surface is the key to initiate the final gas breakdown. The breakdown near cathode is electron‐dominated, which could accomplish in several nanoseconds. The breakdown near anode is ion‐dominated, which needs stronger field enhancement factor or longer breakdown time and would be harder to occur in reality.

Experimental research on falling film flow and heat transfer characteristics outside the vertical tube

• Flow and heat transfer characteristics of falling film are studied experimentally. • The experimental data show large differences with values of existing correlations. • Correlations of heat transfer coefficient and dry burning condition are developed. • The study provides a reference for the research on evaporator of MVR. The falling film flow has attracted much attention recently due to its advantages of low temperature difference, low flow rate, high heat transfer coefficient and high heat flux density. In this paper, a series of experiments were carried out to investigate the falling film flow and heat transfer characteristics outside the vertical tube based on the established experimental system. Flow patterns, the trend of heat transfer coefficients along the tube as well as the falling film breakdown phenomenon were described. Two new correlations were obtained to predict the heat transfer coefficient and falling film dry burning based on experimental data, and the maximum deviation between the experimental data and predicted values were −13.36% and 16.81%, respectively. The new correlations can provide a reference for the design of the heater in the Mechanical vapor recompression systems.