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It is known that titanium (Ti) implant surfaces exhibit poor antibacterial properties and osteogenesis. In this study, chitosan particles loaded with aspirin, amoxicillin or aspirin + amoxicillin were synthesized and coated onto implant surfaces. In addition to analysing the surface characteristics of the modified Ti surfaces, the effects of the modified Ti surfaces on the adhesion and viability of rat bone marrow-derived stem cells (rBMSCs) were evaluated. The metabolic activities of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) biofilms on the modified Ti surfaces were also measured in vitro. Moreover, S. aureus was tested for its antibacterial effect by coating it in vivo. Using water as the droplet medium, the contact angles of the modified Ti surfaces increased from 44.12 ± 1.75° to 58.37 ± 4.15°. In comparison to those of the other groups tested, significant increases in rBMSC adhesion and proliferation were observed in the presence of aspirin + amoxicillin-loaded microspheres, whereas a significant reduction in the metabolic level of biofilms was observed in the presence of aspirin + amoxicillin-loaded microspheres both in vitro and in vivo. Aspirin and amoxicillin could be used in combination to coat implant surfaces to mitigate bacterial activities and promote osteogenesis. [ABSTRACT FROM AUTHOR]

This study is the first to investigate the process of osteoclast (OCL) differentiation, its potential functions, and the associated mRNA and signalling pathways in embryonic palatal bone. Our findings suggest that OCLs are involved in bone remodelling, bone marrow cavity formation, and blood vessel formation in embryonic palatal bone. We observed TRAP-positive OCLs at embryonic day 16.5 (E16.5), E17.5, and E18.5 at the palatal process of the palate (PPP) and posterior and anterior parts of the palatal process of the maxilla (PPMXP and PPMXA, respectively), with OCL differentiation starting 2 days prior to TRAP positivity. By comparing the key periods of OCL differentiation between PPMX and PPP (E14.5, E15.5, and E16.5) using RNA-seq data of the palates, we found that the PI3K-AKT and MAPK signalling pathways were sequentially enriched, which may play critical roles in OCL survival and differentiation. Csf1r, Tnfrsff11a, Ctsk, Fos, Tyrobp, Fcgr3, and Spi1 were significantly upregulated, while Pik3r3, Tgfbr1, and Mapk3k7 were significantly downregulated, in both PPMX and PPP. Interestingly, Tnfrsff11b was upregulated in PPMX but downregulated in PPP, which may regulate the timing of OCL appearance. These results contribute to the limited knowledge regarding mRNA-specific steps in OCL differentiation in the embryonic palatal bone. [ABSTRACT FROM AUTHOR]

This study is the first to investigate the process of osteoclast (OCL) differentiation, its potential functions, and the associated mRNA and signalling pathways in embryonic palatal bone. Our findings suggest that OCLs are involved in bone remodelling, bone marrow cavity formation, and blood vessel formation in embryonic palatal bone. We observed TRAP-positive OCLs at embryonic day 16.5 (E16.5), E17.5, and E18.5 at the palatal process of the palate (PPP) and posterior and anterior parts of the palatal process of the maxilla (PPMXP and PPMXA, respectively), with OCL differentiation starting 2 days prior to TRAP positivity. By comparing the key periods of OCL differentiation between PPMX and PPP (E14.5, E15.5, and E16.5) using RNA-seq data of the palates, we found that the PI3K-AKT and MAPK signalling pathways were sequentially enriched, which may play critical roles in OCL survival and differentiation. Csf1r, Tnfrsff11a, Ctsk, Fos, Tyrobp, Fcgr3, and Spi1 were significantly upregulated, while Pik3r3, Tgfbr1, and Mapk3k7 were significantly downregulated, in both PPMX and PPP. Interestingly, Tnfrsff11b was upregulated in PPMX but downregulated in PPP, which may regulate the timing of OCL appearance. These results contribute to the limited knowledge regarding mRNA-specific steps in OCL differentiation in the embryonic palatal bone. [ABSTRACT FROM AUTHOR]

Background: Tooth regeneration depends on the longevity of the dental epithelial lamina. However, the exact mechanism of dental lamina regression has not yet been clarified. To explore the role of the Sonic hedgehog (Shh) signaling pathway in regression process of the rudimentary successional dental lamina (RSDL) in mice, we orally administered a single dose of a Shh signaling pathway inhibitor to pregnant mice between embryonic day 13.0 (E13.0) and E17.0. Results: We observed that the Shh signaling pathway inhibitor effectively inhibited the expression of Shh signaling pathway components and revitalized RSDL during E15.0–E17.0 by promoting cell proliferation. In addition, mRNA‐seq, reverse transcription plus polymerase chain reaction (RT‐qPCR), and immunohistochemical analyses indicated that diphyodontic dentition formation might be related to FGF signal up‐regulation and the Sostdc1‐Wnt negative feedback loop. Conclusions: Overall, our results indicated that the Shh signaling pathway may play an initial role in preventing further development of mouse RSDL in a time‐dependent manner. Key Findings: RSDL, Shh signal, tooth regeneration, Wnt/β‐catenin, mouse molar. [ABSTRACT FROM AUTHOR]

Hard palate consists anteriorly of the palatal process of the maxilla (ppmx) and posteriorly of the palatal process of the palatine (ppp). Currently, palatal osteogenesis is receiving increasing attention. This is the first study to provide an overview of the osteogenesis process of the mouse hard palate. We found that the period in which avascular mesenchymal condensation becomes a vascularized bone structure corresponds to embryonic day (E) 14.5 to E16.5 in the hard palate. The ppmx and ppp differ remarkably in morphology and molecular respects during osteogenesis. Osteoclasts in the ppmx and ppp are heterogeneous. There was a multinucleated giant osteoclast on the bone surface at the lateral‐nasal side of the ppmx, while osteoclasts in the ppp were more abundant and adjacent to blood vessels but were smaller and had fewer nuclei. In addition, bone remodeling in the hard palate was asymmetric and exclusively occurred on the nasal side of the hard palate at E18.5. During angiogenesis, CD31‐positive endothelial cells were initially localized in the surrounding of palatal mesenchymal condensation and then invaded the condensation in a sprouting fashion. At the transcriptome level, we found 78 differentially expressed genes related to osteogenesis and angiogenesis between the ppmx and ppp. Fifty‐five related genes were up/downregulated from E14.5 to E16.5. Here, we described the morphogenesis and the heterogeneity in the osteogenic and angiogenic genes profiles of the ppmx and ppp, which are significant for subsequent studies of normal and abnormal subjects. [ABSTRACT FROM AUTHOR]

Both atmospheric pressure dielectric barrier discharge (AP-DBD) deposition and direct fluorination are effective methods to modify the surface electrical properties of polymer insulation. To investigate the surface charge decay properties of Al 2 O 3 -filled epoxy resin (ER) prepared by AP-DBD and direct fluorination treatments, before and after drying, samples were studied under various treatment parameters. The experimental results show that charge decay rates for AP-DBD and fluorinated samples are more than 90% after 5 days in ambient air. The corresponding bulk and surface resistivity is reduced when the charge decay rate increases. After a longer time, the surface charge on the fluorinated samples decays faster than those on the AP-DBD samples before drying. The hydrophilicity of the fluorinated samples significantly affects the surface charge decay after drying. After 100 days of storage, the decay rates for the fluorinated samples decrease with increased storage time (less than 9% after 100 days) while for AP-DBD treated samples the decay rates exceed 24%. The surface resistivity of the AP-DBD samples is always lower than that of the fluorinated ones. Therefore, for a long storage time, AP-DBD treatment may provide a better solution to the surface charge decay of ER than direct fluorination treatment, after drying. [ABSTRACT FROM AUTHOR]

The phenomenon of surface flashover in vacuum is a common problem in vacuum insulation systems. Although the theory of secondary electron emission avalanche is widely accepted, the developing process of vacuum surface flashover is not very clear and it needs to be further studied. The surface discharge process was diagnosed by spectral and mass spectrum analysis in this paper. The surface flashover was initiated by a microsecond pulse with a rise time of 500 ns and a full width at half maximum of 8 μs. Optical diagnostic methods were used to obtain the luminous properties of several polymeric materials. The time-domain optical signal was measured by a photomultiplier tube with wavelength range of 300–650 nm. The spectrograph was used to detect the optical emission from the surface discharge. The outgassing characteristics in the flashover were also measured by mass spectrometer connected to the vacuum experiment chamber. The results show that the optical signal appears before flashover and the light intensity reaches its maximum at about 80 ns after the flashover occurs. The optical emission spectrum is mainly in range of 400–800 nm, and C 2 , H and Cu spectrum lines were detected in polymeric materials. The results of mass spectrum measurement show that the outgassing of polymeric materials in surface flashover includes the desorbed gases and decomposed gases of insulation materials. It is consistent between the results of emission spectrum and mass spectrum. [ABSTRACT FROM AUTHOR]

Surface flashover characteristics of insulation materials in vacuum are key factors to determine the behavior of high voltage electrical equipment. Although the surface flashover in vacuum has been investigated for decades, the surface insulation properties of polymeric materials after repeated surface discharges have shown little attention by researchers. In order to investigate the aging characteristics of polymeric materials caused by repeated flashovers in vacuum, several typical materials were used to flashover by microsecond pulses. The flashover voltages were obtained for polytetrafluoroethylene, polymethylmethacrylate and polyamide for thousands of flashovers. The surface morphology of samples was observed after different numbers of flashovers. The trap parameter distribution was obtained by the isothermal surface potential decay method. To analyze the flashover voltage change with discharge times, the Weibull distribution was used to determine the conditioning and degradation effects in repeated discharge experiments. The results show that the morphology near the cathode triple junction and deep traps together affect the subsequent flashover voltage. The conditioning and degradation phenomena often coexist in the aging process of polymers and affect the surface insulation properties. This study could provide a reference for the type selection, design, and modification of insulation materials in vacuum. [ABSTRACT FROM AUTHOR]

The surface charge accumulation on polymers can reduce the insulation performance of the materials and even cause surface flashover. The characteristics of surface charge accumulation and dissipation for epoxy resin (EP) exposed to various nanosecond pulse voltage parameters (i.e. pulse rise time, pulse width and voltage amplitude) are investigated. The results show that the fractional decay of surface charge increases with pulse rise time and decreases with pulse width and voltage amplitude. However, abnormal dissipation phenomenon appears when the pulse voltage reaches 9 kV. Analysis suggests that the abnormal dissipation phenomenon can be attributed to surface charge transport primarily along the surface. Furthermore, the surface charge fractional decay is less than 30% for a dissipation time of 30 min under different nanosecond pulse voltage parameters. In addition, the method of atmospheric pressure plasma jet (APPJ) is utilized to deposit SiCxHyOz thin film on the surface of epoxy resin (EP) samples. It is found that the fractional decay of surface charge for treated EP samples is promoted approximately by an average of 90%. The trap density distribution indicates that the shallow traps that are formed by APPJ treatment result in a decrease in the trap energy level. [ABSTRACT FROM AUTHOR]

Surface modification of polytetrafluoroethylene (PTFE) is performed by nitrogen ion implantation for improving the PTFE surface flashover voltage in vacuum. In this paper, nitrogen ions are produced by an electron cyclotron resonance ion source. The properties of the samples are investigated with X-ray photoelectron spectroscopy, electrometer, microhardness tester, surface potential measurement, and surface flashover system. The Stopping and Range of Ions in Matter software is used to simulate the ion implantation. Experimental results show that the surface flashover voltage of treated samples improves remarkably and increases with the injection energy. After ion implantation, the content of fluorine in the treated samples decreases, and the content of oxygen increases. The surface conductivity increases from $1.15\times 10^{{-15}}$ to 1.36 10−13 S/m, the surface potential decreases faster, and the trap density and energy increase with the implantation energy. The process of electron avalanche and the accumulation of surface charges have been suppressed, thus hindering the development of flashover and improving the surface flashover voltage. [ABSTRACT FROM AUTHOR]

The free metal particles pollution has been a severe problem affecting the safety operation of gas insulated transmission lines (GIL) system and causes insulation failure. In this paper, a facile insulation film deposition method by using atmospheric pressure dielectric barrier discharge (AP-DBD) plasma was introduced. The SiOx film was deposited on copper surface to improve the lift-off voltage of metal particles. The film composition, surface morphology and film thickness based on the plasma deposition time were well studied. The results showed that deposited film was composed with Si- O-Si group, Si-OH group along with small amount of inorganic groups (CH2 and CH3). The oxidation degree and film thickness were enhanced when plasma treatment time was longer. The theoretical model of particle lift-off voltage was calculated before and after surface coating. After the electrode covered with SiOx insulation film, the lifting voltage of metal particles improved by about 38%, which agreed well with the prediction value. Our results proved that SiOx film deposited by AP-DBD was a very effective method for lift-off voltage improvement. [ABSTRACT FROM AUTHOR]

This work presents experimental results on different discharge modes for microsecond-pulse gliding discharges and their transition, and then analyzes the effect of the gap distance and flow rate on the discharge modes. The current amplitude, energy consumption per pulse and voltage range are used to reflect some discharge characteristics of discharge modes. The results show that there are three discharge modes for microsecond-pulse gliding discharges, i.e. the corona, diffuse and spark. Among the three modes, the values of the amplitude of the discharge current and the energy consumption per pulse for corona mode are lowest, then the diffuse mode and spark mode accordingly. When the gap spacing is smaller than 5 mm, there is no diffuse mode, and the corona discharges directly transit to spark discharges with the increase of the voltage. When the gap spacing is or more than 5 mm, the corona-diffuse-spark mode transition with the increase of the voltage is observed. The voltage range for diffuse discharge increases with the gap spacing. Moreover, when the flow rate increases, the ignition voltage for spark discharges increases, but the ignition voltage for diffuse discharges slightly changes, resulting in the voltage range for diffuse discharges increases. Therefore, diffuse mode is more likely to be obtained in a large gap with a relatively high flow rate. [ABSTRACT FROM AUTHOR]

Long-time partial discharge (PD) is regarded as one of the main reasons for the insulation failure of high-voltage cables. In this work, we report on the application of atmospheric pressure plasma to deposit siloxane film on copper to avoid PDs. The dielectric barrier discharge (DBD) plasma is driven by AC power supply, with tetraethoxysilane (TEOS), argon, and oxygen mixture as the source gas. The effect of oxygen gas flow rate on the thin film surface morphology, chemical composition, and electrical properties is studied systematically. Our results show that the stability of the plasma deteriorated, when the oxygen flow rate exceeded 10 sccm. The addition of oxygen in the source gas induced a high oxidation level of deposited thin film. The chemical composition of thin film was in the form of SiOx ( x = 1.9) with 10 sccm oxygen compared to SiOx ( x = 1.2), when deposited in the absence of oxygen. Additionally, the optimal thin film with good stability was obtained with the surface resistivity 1.1 × 1011 Ω, when deposited in the absence of oxygen. The corresponding relative permittivity of the deposited thin film is 2.9. The simulation results demonstrated that the electric field distortion was weaken after the film deposition, which reduced the probability of PD to occur. [ABSTRACT FROM AUTHOR]

In this paper, an atmospheric-pressure dielectric barrier discharge is used to modify the surface of the epoxy material and enhance the dissipation of surface charge to reduce the accumulation of surface charge. In the experiments, atmospheric-pressure air dielectric barrier discharge is driven by a microsecond pulse generator. Surface properties of epoxy before and after the plasma treatment are characterized by water contact angle, surface potential, and surface/volume conductivity measurements. Atomic force microscope and X-ray photoelectron spectroscopy are used to investigate the changes of the morphology and the chemical composition of the epoxy surface. Experimental results indicate that the surface of epoxy is etched by the plasma and the increase of the surface roughness enhances the surface insulation ability. The O radicals in plasma and the carbonyl groups formed on the surface make the surface charge trap shallower, change the epoxy surface composition then increase the surface conductivity and accelerate surface charge dissipation. When the epoxy is treated for an appropriate time, the epoxy surface insulation performance will be enhanced obviously and the surface charge dissipation will be accelerated. [ABSTRACT FROM PUBLISHER]

The audible noise (AN) production mechanism caused by corona discharge in ultrahigh voltage transmission lines is less understood. The study on sound pressure characteristic is necessary to obtain the inherent relation between AN and corona discharge. In this paper, the experimental research on single-point direct current (dc) corona discharge was evolved and the time-domain sound pressure waveform was obtained using capacitor microphone. The experiment results show that the dc corona discharge comprises multiple subsequent discharge pulses. The discharge voltage and the electrode polarity have a direct effect on the rising time and pulsed width of the single current pulse. The waveform of sound pressure produced by single discharge is a bipolar microsecond pulse, which lags behind the current pulse in time domain. The time delay is propagation time of sound signal from the discharge spot to the measurement spot. Based on the corona discharge characteristic in dc voltage, the experiment platform for nanosecond pulsed discharge was built to obtain the relation between discharge parameter and sound parameter. The characteristics of sound pressure in different discharge conditions were analyzed. The study results indicate that the sound pressure produced by pulsed discharge is similar with that produced by corona discharge. The experiment platform for pulsed discharge can be used to research the AN production mechanism by dc corona discharge. [ABSTRACT FROM AUTHOR]

Hydrophilic modification of polymethyl methacrylate (PMMA) surface is performed by atmospheric pressure plasma jet (APPJ) in Ar gas for improving the PMMA surface flashover performance in vacuum. In the experiments, APPJ is driven by a microsecond-duration pulsed generator, which has voltages of 0-30 kV, a rise time of 300 ns and a full width at half maximum of 2μs. Characteristics of the APPJ are analyzed according to its voltage and current waveform, discharge image and optical emission spectrum. Furthermore, surface properties of the PMMA surface before and after the treatment are characterized by water contact angle measurements and morphology observations. Results show that the main species of the plasma jet are composed of N2, Ar, OH, and O, among which such polar groups as OH and O enhance the hydrophilic property of the PMMA surface. The water contact angle decreases from 68° to a minimum value (16°) after the treatment. In addition, all the surface flashover voltages in vacuum for the PMMA samples treated by APPJ are higher than those for the untreated PMMA samples. [ABSTRACT FROM AUTHOR]

This paper describes experimental studies of the dependence of the X-ray intensity on the anode material in nanosecond high-voltage discharges. The discharges were generated by two nanosecond-pulse generators in atmospheric air with a highly inhomogeneous electric field by a tube-plate gap. The output pulse of the first generator (repetitive pulse generator) has a rise time of about 15 ns and a full width at half maximum of 30-40 ns. The output of the second generator (single pulse generator) has a rise time of about 0.3 ns and a full width at half maximum of 1 ns. The electrical characteristics and the X-ray emission of nanosecond-pulse discharge in atmospheric air are studied by the measurement of voltage-current waveforms, discharge images, X-ray count and dose. Our experimental results showed that the anode material rarely affects electrical characteristics, but it can significantly affect the X-ray density. Comparing the density of X-rays, it was shown that the highest x-rays density occurred in the diffuse discharge in repetitive pulse mode, then the spark discharge with a small air gap, and then the corona discharge with a large air gap, in which the X-ray density was the lowest. Therefore, it could be confirmed that the bremsstrahlung at the anode contributes to the X-ray emission from nanosecond-pulse discharges. [ABSTRACT FROM AUTHOR]

Gliding discharges can generate nonthermal plasma at atmospheric pressure. Therefore, they are widely used in plasma-assisted ignition and combustion. In this paper, the gliding discharge sustained by a resonant ac power supply was obtained with a pin-to-pin electrode geometry, and the characteristics of such discharge were investigated through its voltage–current and discharge images. Inceptive, nonstable, and stable stages involved in this gliding discharge were studied. Experimental results showed that the discharge was first ignited by a spark with a current peak of tens of amperes and soon turned into a stable stage, where the discharge respectively behaved in repetitive spark mode with a current peak of several amperes in a small gap and glowlike mode with a current peak of several microamperes in a relatively large gap spacing. Under a certain situation, a nonstable discharge was observed, which changed from a spark discharge to a glowlike discharge after some time. In addition, both the discharge stability and the breakdown voltage were influenced by the air flow. The discharge became unstable when the air flow exceeded 3 L/min. [ABSTRACT FROM PUBLISHER]

Atmospheric-pressure gas discharge driven by high voltage pulses with fast rise-time and short duration has attracted significant attention for various plasma applications. In this paper, discharges were generated in a highly non-uniform electric field by point-plane gaps in open air by four repetitive nanosecond-pulse generators with repetition rate up to 1 kHz. The rise time of generators was 25 (generator #1), 15 (generator #2), 3 (generator #3), and 0.2 ns (generator #4) and a full width at half maximum was 40, 30-40, 5, and 1 ns, respectively. The experimental results show that there were typical discharge fashions, i.e., corona, diffuse, spark, or arc modes. The variables affecting the discharge characteristics, including the gap spacing and applied pulse parameters, were investigated. Especially, the diffuse discharges were investigated and discussed. With generator #1 at voltage 70-120 kV, characteristics of measured x-rays on the discharge modes were studied, and it indicates that counts of x-rays in a diffuse discharge are up to a peak value under the experimental conditions. With amplitude of voltage pulses in incident wave up to 18 (generator #3) and 12.5 kV (generator #4), runaway electron beam in low pressure helium, nitrogen, and air in a pulse-periodic mode of discharge with repetition rate up to 1 kHz was obtained. Electron beam was registered behind a thin foil in a pressure range from several to tens of Torr. X-ray radiation was obtained in a wide range of pressures, as well as at atmospheric pressure of helium, nitrogen, and air. Voltage pulses of positive and negative polarities were used. Generation of runaway electrons with pulses of positive polarity appeared because of reflected voltage pulses of reverse polarity. [ABSTRACT FROM AUTHOR]

Pulsed power can provide instantaneously high power density to generate atmospheric nonthermal plasma in open air. In this paper, using two power supplies including a \(\mu \) s-pulse generator with a rise time of 300 ns and a pulsewidth of 5 \(\mu \) s and a ns-pulse generator of a rise time of 70 ns and a pulsewidth of 100 ns, pulsed gliding discharges are created with point-to-point electrodes in open air. Discharge images with these two generators under different flow rates are presented for a brief comparison of \(\mu \) s- and ns-pulse gliding discharges in air flow. [ABSTRACT FROM PUBLISHER]

Front Cover: A facile strategy by using atmospheric pressure dielectric barrier discharge (AP‐DBD) with tetraethoxysilane (TEOS)/Ar/O2 as the source gas is employed for siloxane film deposition (upper). The composition of deposited siloxane film can be tuned by oxygen content in the working gas. The deposited siloxane film shows good stability and high surface resistivity, and reduces the odds of partial discharge, which is promising for power transmission application (below). Further details can be found in the article by Ruixue Wang et al. on 1600248. [ABSTRACT FROM AUTHOR]

Nanosecond pulsed discharges have various discharge modes, such as corona, diffuse discharge, spark or arc. A dense diffuse discharge is particularly desirable for various applications at atmospheric pressure. In this paper, a magnetic-compression pulse generator was used to produce repetitive positive nanosecond pulses for excitation of a diffuse discharge. The output pulse of the generator had a rise time of about 25 ns and a full width at half maximum of 40 ns. Electrical characteristics of the diffuse discharge were studied by measuring its voltage and current waveforms, as well as images of the discharge. The conduction current was calculated by the measured voltage and current, which was a true discharge current. The experimental results show that a stable diffuse discharge could be obtained at atmospheric pressure, and the conduction current was unipolar and had similar amplitude of several amperes under our experimental condition, which has the similar amplitude with the displacement current. Furthermore, the air gap spacing and pulse repetition frequency (PRF) affected the intensity and mode transition of the diffuse discharge. The conduction current increased with the PRF but decreased with the air gap spacing. Therefore, the diffuse discharge was likely available under some conditions of proper air gap, high PRF with positive pulse. [ABSTRACT FROM AUTHOR]

The relation of desorbed gases and surface discharge in vacuum is a complex problem without reliable theory. The vacuum experimental platform of direct current and nanosecond pulse source was built, and the quadrupole mass spectrometer connected to vacuum cavity was used to analysis the out-gassing characteristics of insulation materials. Then the vacuum surface discharge experiments were done and the desorbed gases were measured in the process. By comparing the mass spectrum before discharges with ones after discharges, we obtained the out-gassing composition of several insulation materials. Meanwhile we analyzed the probable sources of different gases. Main gas components generated by vacuum surface flashover included H2O, N2, H2, O2, hydrocarbon fragment, CO, CO2 and sometimes high polymer fragment. C2H2 appeared in gas components when the filamentary discharge channel was formed between two electrodes. The results show that the high polymer surface may decompose and the dissolved gases may be extracted besides gas desorption in discharges. The discharge pattern has direct effect on their out-gassing characteristics. We'll thoroughly research their relation in subsequent work. [ABSTRACT FROM AUTHOR]

Microstack insulators were developed to satisfy application demands for pulsed power system high performance and miniaturization. Using a high temperature lamination method, we manufactured two types of microstack insulators from interleaved layers of brass and polyimide (PI) and from stainless steel and fluorinated ethylene propylene (FEP). The surface state and vacuum out-gassing characteristics of these microstack insulator samples were measured. Then using a nanosecond (10 ns/30 ns) pulse source with a Marx generator and a single coaxial pulse-forming line, the vacuum surface flashover characteristics of samples were tested. The results show that flashover takes place during the rising period of the voltage, and the maximum vacuum flashover field intensity for microstack insulator samples is close to 180 kV/cm. Based on the preceding work, the high frequency dielectric constants of microstack insulators were also measured using an impedance analyzer. The results show that microstack insulators have better high frequency dielectric performance than conventional insulation materials [ABSTRACT FROM AUTHOR]