Modeling and Simulations of Electrical Breakdown and Thermal Failure in Zinc Oxide and Titanium Dioxide for High-Voltage Dielectric Applications

The development of transmission lines with higher energy storage capabilities is an important goal for compact pulsed power systems. In this context, ceramic dielectrics are promising candidates from the standpoint of high dielectric constants and breakdown strength. Though such materials look promising, their breakdown response characteristics have not been well studied, nor adequately understood. The electrical response of dielectrics also seems to depend on the internal structure and its granularity. For example, the breakdown strength of nano-crystalline insulators such as titania and zinc oxide have been observed to depend on the internal grain size. In general, the hold-off voltage increases monotonically with decreases in grain sizes. For example, nano-crystalline TiO2 exhibits higher breakdown strength as compared to micron size TiO2. In this dissertation, time-dependent, two-dimensional simulations based on random Voronoi networks have been developed to study the electrical breakdown and thermal failure in ceramic dielectrics in ZnO varistors in response to high-voltage pulsing. Our simulations allow for dynamic predictions of internal failures and to track the progression of hot-spots and thermal stresses in samples. The focus is on internal grain-size variations and relative disorder. Our results predict that parameters such as the device hold-off voltage, the average internal temperature, and average dissipated energy density, and applied pulse-durations would be higher with more uniform grains. Furthermore, scaling down the average grain size offers similar advantages. Finally, it is shown that for the situations studied, the principle failure mechanism arises from internal localized melting, while thermal stresses are well below the thresholds for cracking. In addition, the somewhat surprising observation of lower breakdown fields for TiO2 under pulsed conditions as compared to quasi-DC biasing, was studied. Our simulation results indicated that electrical breakdown of TiO2 under multiple pulsed conditions can occur at lower voltages as compared to quasi-DC biasing. We hypothesize that the lower breakdown voltages observed in TiO2 under pulsed conditions, is a direct rise-time effect, coupled with cumulative detrapping. Finally, the role of granular dielectrics having non-linear, voltage-dependent capacitances on pulse rise-time sharpening was also probed and has been discussed

The tribological properties of zinc borate ultrafine powder as a lubricant additive in sunflower oil

This paper presents an investigation on the tribological properties of zinc borate ultrafine powder employed as a lubricant additive in sunflower oil. The stable dispersions of 0.5 wt%, 1 wt% and 2 wt% zinc borate ultrafine powder in sunflower oil were achieved by using an ultrasonic homogeniser. Both a 4-ball tester and a pin-on-disc tester were employed to evaluate the anti-wear and friction reduction capabilities of zinc borate ultrafine powder. Tribo-films with dark colour were generated on the worn surfaces and showed a good contrast with the substrate. The worn surface with different morphologies reflected as the colour alterations on the worn surface were observed when different lubricants were applied. The morphology and elemental analysis of the worn surfaces were studied using atomic force microscopy (AFM) and scanning electronic microscopy (SEM). Mechanical properties of the tribo-films and substrates were studied with a nano-indentation tester. Test results suggest that tribo-films generated on the worn surface have a relatively low hardness compared with the steel substrate. The substrates on the worn surfaces lubricated in sunflower oil with the powder demonstrated higher hardness than that of the substrate lubricated with pure sunflower oil due to the possible tribo-chemical reaction between the zinc borate additive and substrate. The combination of sunflower oil with 0.5% zinc borate ultrafine powder has delivered the most balanced performance in friction and wear reduction. This study has demonstrated the possibility of application of this industrially applicable solid lubricant additive (zinc borate) with a decomposable vegetable based lubricant oil.Peer reviewedFinal Accepted Versio

Smooth Muscle-specific Expression of Calcium-independent Phospholipase A2 (iPLA2 ) Participates in the Initiation and Early Progression of Vascular Inflammation and Neointima Formation

Background: The role of iPLA 2 β as a regulator of inflammatory signaling and neointima formation is unknown. Result: Smooth muscle-specific expression of iPLA 2 β exacerbates proinflammatory cytokine production, macrophage infiltration, and neointima formation. Conclusion: Smooth muscle-specific iPLA 2 β participates in the initiation and early progression of vascular inflammation and neointima formation. Significance: iPLA 2 β may represent a novel therapeutic target for attenuating vascular inflammation and restenosis

NaSn2(PO4)3 submicro-particles for high performance Na/Li mixed-ion battery anodes

NaSn2(PO4)3 has open framework, high ionic conductivity, low working potential, high theoretical capacity more than twice of graphite. However, its commercial application is limited by its low electrical conductivity and rapid capacity fading. To overcome this challenge, we synthesize NaSn2(PO4)3 submicro-particles (around 100–300 nm in size) by hydrothermally assisted pyrolysis reactions. The synthesized NaSn2(PO4)3 anode for Na/Li mixed-ion batteries delivers an ultrahigh initial discharge capacities, excellent rate performance and superior cycling stability. This design provides a promising pathway for developing high performance mixed-ion batteries

第665回 千葉医学会例会・第18回 佐藤外科例会 6.

Estimates of Diptychus maculatus divergence times obtained with BEASTv1.8.0. (DOCX 86 kb

Smooth-Muscle BMAL1 Participates in Blood Pressure Circadian Rhythm Regulation

As the central pacemaker, the suprachiasmatic nucleus (SCN) has long been considered the primary regulator of blood pressure circadian rhythm; however, this dogma has been challenged by the discovery that each of the clock genes present in the SCN is also expressed and functions in peripheral tissues. The involvement and contribution of these peripheral clock genes in the circadian rhythm of blood pressure remains uncertain. Here, we demonstrate that selective deletion of the circadian clock transcriptional activator aryl hydrocarbon receptor nuclear translocator-like (Bmal1) from smooth muscle, but not from cardiomyocytes, compromised blood pressure circadian rhythm and decreased blood pressure without affecting SCN-controlled locomotor activity in murine models. In mesenteric arteries, BMAL1 bound to the promoter of and activated the transcription of Rho-kinase 2 (Rock2), and Bmal1 deletion abolished the time-of-day variations in response to agonist-induced vasoconstriction, myosin phosphorylation, and ROCK2 activation. Together, these data indicate that peripheral inputs contribute to the daily control of vasoconstriction and blood pressure and suggest that clock gene expression outside of the SCN should be further evaluated to elucidate pathogenic mechanisms of diseases involving blood pressure circadian rhythm disruption

A Study of Tribological Properties of Water-Based Ceria Nanofluids

This is an Accepted Manuscript of an article published by Taylor & Francis in Tribology Transactions on 10 January 2013, available online: http://www.tandfonline.com/doi/abs/10.1080/10402004.2012.748948.This paper presents an investigation on the potential tribological properties of the water-based cerium dioxide nanofluids. The nanofluids with different nanoparticle concentrations were prepared in a materials laboratory. A stable dispersion of nanoparticles in the fluids was achieved with an appropriate percentage of surfactant sorbitan monostearate. The stability of particle dispersion was studied using a Zeta-potential measuring device. Additive conglomerate size in the nanofluids was measured using Dynamic Light Scattering (DLS) device. It has been observed that the dispersibility of nanoparticles played an important role in the frictional properties of the nanofluids. The tribological properties of the water-based nanofluids were evaluated using a Pin-on-disc tester under different loading conditions. A significant improvement on tribological properties of the water-based cerium dioxide nanofluids was observed. The worn surfaces of the contact elements were characterised using SEM and a Nano-tester. According to the test results, the significant reductions of the friction coefficient and the anti-wear property of water-based cerium dioxide nanofluids are attributed to the deposition of nanoparticles on worn contact surfaces.Peer reviewe

Influences of nanoparticle zinc oxide on acutely isolated rat hippocampal CA3 pyramidal neurons

Original article can be found at : http://www.sciencedirect.com/ Copyright ElsevierThe effects of zinc oxide nanoparticles (nano-ZnO) on the properties of voltage-dependent sodium, potassium currents and evoked action potentials were studied in acutely isolated rat hippocampal CA3 pyramidal neurons at postnatal ages of 10–14 days rats using the whole-cell patch-clamp technique. The results indicated that: (1) in the present of final concentration of 10−4 g/ml nano-ZnO, the current–voltage curve of sodium current (INa) was decreased, and the peak amplitudes of INa were increased considerably from −50 to +20 mV (p < 0.05). Meanwhile, the inactivation and the recovery from inactivation of INa were also promoted by the nano-ZnO solution (10−4 g/ml) (p < 0.01). However, the steady-state activation curve of INa was not shifted by the nano-ZnO. (2) The amplitudes of transient outward potassium current (IA) were increased by the nano-ZnO solution (10−4 g/ml), while the current–voltage curve of delayed rectifier potassium current (IK) was significantly increased from +20 to +90 mV (p < 0.05). However, it is apparent that the nano-ZnO solution did not shift the steady-state activation curve of IA and IK, and neither had significant effects on the inactivation and the recovery from inactivation of IA. (3) Peak amplitude and overshoot of the evoked single action potential were increased and half-width was diminished in the presence of the 10−4 g/ml nano-ZnO solution (p < 0.05). Simultaneously, a prolonged depolarizing current injection enhanced (p < 0.05) repetitive firing evoked firing rate. These results suggested that 10−4 g/ml nano-ZnO solution can lead to an enhancement in the current amplitudes of INa and IK by increasing the opening number of sodium channels, delaying rectifier potassium channels, and enhancing the excitability of neurons, which lead to Na+ influx and the accumulation of intracellular Na+, as well as K+ efflux plus the loss of cytoplasmic K+. These may disturb the ionic homeostasis and the physiological functions of neurons.Peer reviewe