Increase Of Pulse Repetition Frequency Research Articles

Stability of trimethylsilyl acetate-based plasma polymers towards atmospheric and water environments

In the present work, SiOxCyHz coatings were prepared in capacitively coupled RF glow discharge from gaseous mixture of trimethylsilyl acetate (TMSAc) monomer and oxygen. Properties of thin solid films prepared using continuous wave (CW) plasma and pulsed wave (PW) plasma were examined, including long–term stability in contact with air and water environments. The presented study proves that it is possible to prepare organosilicon coatings showing properties in a wide range from soft organic polymeric structures to materials similar to SiO2 with Martens hardness of 4 GPa. The content of carbon species in organosilicon structure and water contact angle (WCA) decreased with increasing oxygen ratio from 7.7 % to 75.0 %. The water contact angle of TMSAc-based coatings prepared in CW mode decreased from 95° to 76°. The application of pulsed mode using an oxygen ratio of 50 % and pulse repetition frequencies in the range of 0.33 Hz to 300 Hz led to materials with hydrophobic character (WCA in range of 86°–94°) with increased content of CHx and Si-CH3 structures in comparison to CW mode. This study proves that the aging mechanism significantly depends on deposition parameters. The increase of oxygen ratio, as well as the increase of pulse repetition frequency, led to the higher resistance towards the atmospheric environment. On the other side, organosilicon coatings prepared in CW mode using high oxygen ratios (50–75 %) showed significant delamination after immersion in water. However, the use of PW plasma for the preparation of SiOxCyHz thin films significantly improved the stability of resulting materials under water environment.

Nanosecond pulsed plasma assisted dry reforming of CH4: The effect of plasma operating parameters

Dry reforming is a promising approach to converting CH4 and CO2 (i.e., two common greenhouse gases) into clean fuels and valuable chemicals. Non-thermal plasma, acting as an alternative to the traditional reforming processes, achieves considerable gas conversion with low energy consumption under mild operating conditions. In this study, CH4 and CO2 were converted to syngas (i.e., H2 and CO) in a nanosecond pulsed dielectric barrier discharge plasma at a total gas flow rate of 50 sccm. Through evaluating the effects of electrical parameters on reforming performance, the experimental results showed that CH4 and CO2 conversions increased with the increase of pulse repetition frequency owing to the increased energy injection. Shorter rise and fall times resulted in better CH4 and CO2 conversions and higher energy conversion efficiencies, due to the rapid acceleration of electrons in a shorter discharge time. In the case where the optimal pulse peak width was 150 ns, the secondary discharge was improved because of the charge accumulation in the primary discharge, thereby increasing the CH4 and CO2 conversions. Among all experiments, when the pulse repetition frequency was 10 kHz and the discharge power was 55.7 W, the maximum conversions of CH4 and CO2 were 39.6% and 22.9%, respectively, while the total energy conversion efficiencies of the syngas and all detected products were 5.0% and 7.1%, respectively. Furthermore, an optical emission spectroscopy was used to characterize the active species formed during the reforming process.

Behaviour of aqueous sulfamethizole solution and temperature effects in cold plasma oxidation treatment

The increase in volume and variety of pharmaceuticals found in natural water bodies has become an increasingly serious environmental problem. The implementation of cold plasma technology, specifically gas-phase pulsed corona discharge (PCD), for sulfamethizole abatement was studied in the present work. It was observed that sulfamethizole is easily oxidized by PCD. The flow rate and pH of the solution have no significant effect on the oxidation. Treatment at low pulse repetition frequency is preferable from the energy efficiency point of view but is more time-consuming. The maximum energy efficiency was around 120 g/kWh at half-life and around 50 g/kWh at the end of the treatment. Increasing the solution temperature from room temperature to 50 °C led to a significant reaction retardation of the process and decrease in energy efficiency. The pseudo-first order reaction rate constant (k1) grows with increase in pulse repetition frequency and does not depend on pH. By contrast, decreasing frequency leads to a reduction of the second order reaction rate constant (k2). At elevated temperature of 50 °C, the k1, k2 values decrease 2 and 2.9 times at 50 pps and 500 pps respectively. Lower temperature of 10 °C had no effect on oxidation efficiency compared with room temperature.

Model of bit error rate for laser communication based on superconducting nanowire single photon detector

The high-speed deep space communication is one of the key technologies for deep space exploration. Laser communication system equipped with sensitivity of single photon will improve existing deep space communication speed. However, laser communication at single photon level needs to consider not only the effect of transmission environment, but also the performance of used single photon detector and the photon number distribution. As a new single photon detector, superconducting nanowire single photon detector (SNSPD) outperforms the traditional semiconducting SPDs at near infrared wavelengths, and has high detection efficiency, low dark count rate, low timing jitter, high counting rate, etc. The SNSPD can be used for detecting single photons efficiently, rapidly and accurately. In this paper, we introduce the system detection efficiency and dark count rate of SNSPD based on the photoelectric detecting model without considering the effect of atmospheric turbulence, establish the mathematical model of bit error, and put forward the formula of system bit error rate. What should be emphasized is that the bit error rate is an important parameter for measuring the performance of laser communication system. Error is partly from background thermal radiation and circuit electromagnetic interference; in addition, error appears when photons reach the surface of device without being absorbed to successfully produce resistance area or photons are absorbed but there occurs no response. As a result, the calculation of bit error rate includes the whole process of photoelectric conversion. In order to analyze how to affect the size of system bit error rate, first we simulate two factors of the formula, i.e., light intensity and laser pulse repetition frequency. The results show that the light intensity has the greatest influence on error bit rate. With the light intensity increasing from 0.01 to 1000 photon/pulse, the error bit rate significantly decreases from 10-1 to 10-7 level. The influence of laser pulse repetition frequency is restricted by the light intensity, which declines with the increase of pulse repetition frequency. Then we measure the error bit rate experimentally, which validates the simulation model. However, when increasing light intensity or speed, experimental bit error rate is about 10-4 times higher than simulation result. The reason may be that the insufficiency of actual communication modulation extinction ratio of optical signal to the background noise through optical fiber increases the dark count rate. The above model and experimental results could be the foundation of high-speed deep space laser communication such as moon-earth and Mars-earth based on SNSPD.

X-ray generation in repetitive pulsed discharge in atmospheric air with a point-to-plane gap

Research on the characteristics of X-ray emission in repetitive pulsed discharge is associated with the behavior of runaway electrons and the mechanism of nanosecond pulsed discharge. In the experiments, X-ray emission in the repetitive pulsed discharge with a rise time of ～15 ns and an FWHM of 30-40 ns in atmospheric air is directly measured by a detection system consisting of NaI scintillator and a photomultiplier tube, and the energy range of the X-ray detector is demonstrated to be between 10 and 130 keV. Results show that main part of the energy of X-ray is from 20 keV to 90 keV, and a little X-ray with an the energy of less than 20 keV or more than 90 keV is detected. X-ray emission increases with the increase of pulse repetition frequency, and it has a peak value with the variation of air gap spacing. There is a maximum value of X-ray emission when the nanosecond discharge appears in a diffuse mode.

Influence of various instrument settings on the flow information derived from the power mode

To evaluate the factors influencing flow information displayed by the power operating mode, color Doppler flow mapping was used to image the flow in an in vitro left heart pulse duplicator system. The effect of changing one instrument setting, such as pulse repetition frequency, color filter and frame rate while keeping all other instrumental settings constant, was noted on the displayed flow areas. The flow areas derived using power and velocity modes were also compared. An increase in pulse repetition frequency and color filter decreased the flow areas significantly, and a flow area increase occurred with a decrease in frame rate. No significant difference was observed between the flow areas derived using the two operating modes. Like the velocity mode, the power mode display is also influenced by instrument settings. Although low velocity flows are better delineated using this mode, however, no significant difference occurred in the flow areas measured by this mode and velocity mode. Further studies need to be conducted to address its potential applications in the clinical setting and in quantitation.

Laser diode pumped solid state laser for laser fusion reactor driver.

The most promising alternative to flashlamp pumping of high power solid-state laser driver for inertial confinement fusion reactor is the rapidly growing semiconductor laser (also called laser diode). It has inherently high efficiency, long lifetime (over three years at 10 Hz) and small thermal load to the laser material. The latter will enable an increase in pulse repetition frequency. It is shown that for laser fusion reactor driver a LD pumped MJ 0.35 p m regenerative solid-state laser with an overall efficiency of 10 % can be designed. It may be capable to operate at 4 Hz and 10 Hz with the laser material of Nd : glass and Nd SiO2 (or Nd : YAG), respectively.