Search

In this work, a fluid/Monte Carlo collision (fluid/MCC) hybrid model is developed based on the framework of multi-physics analysis of plasma sources. This hybrid model could be highly accurate in predicting the nonequilibrium phenomena in capacitively coupled plasmas and meanwhile avoid the limitation caused by the computational cost. Benchmarking against the well-established particle-in-cell/MCC (PIC/MCC) method and comparison with experimental data have been presented both in electropositive N2 discharges and electronegative O2 discharges. The results indicate that in N2 discharges, the ion density evolves from a uniform distribution to an edge-high profile as power increases. Besides, the electron energy distribution function (EEDF) at the bulk center exhibits a ‘hole’ at about 3 eV, and the ‘hole’ becomes less obvious at the radial edge, because more low energy electrons are generated there. In O2 discharges, the EEDF exhibits a Druyvesteyn-like distribution in the bulk region, and it evolves to a Maxwellian distribution in the sheath, indicating the dominant influence of the electric field heating there. The results obtained by the hybrid model agree well with those calculated by the PIC/MCC method, as well as those measured by double probe, except for a slight discrepancy in absolute values. The qualitative agreement achieved in this work validates the potential of this hybrid model as an effective tool in the deep understanding of plasma properties, as well as in the improvement of plasma processing.

Based on particle-in-cell and test-particle simulations, an α- to γ-mode transition of the electron power absorption dynamics is found to be induced as a function of an externally applied transverse magnetic field in low pressure capacitively coupled radio frequency discharges operated in argon. This transition is caused by the increased magnetic confinement of energetic ion-induced secondary electrons (γ-electrons) at higher magnetic fields. If a transverse magnetic field is applied, γ-electrons, that are accelerated to high energies by the sheath electric field, are confined in the vicinity of the sheath. Due to their gyromotions they are returned periodically to the adjacent sheath and interact repetitively with the sheath electric field. Such confined γ-electrons are, thus, effectively multiplied by ionization collisions in the vicinity of the sheath, thereby resulting in a significant enhancement of the local ionization rate and the plasma density. In such cases, the energy coupling efficiency of γ-electrons is greatly enhanced, implying that the discharge operates in a magnetized γ-mode. Moreover, the effects of the magnetic field on ion properties and ionization dynamics at different driving frequencies and operating pressures are studied.

An enhanced electron heating mechanism based on a resonance between the cyclotron motion of electrons and radio frequency (rf) electric field in the plasma bulk is reported in weakly magnetized capacitively coupled argon plasmas at low pressure. When the electron cyclotron frequency coincides with the applied power source frequency, the bulk electrons can continuously acquire energy from the background electric field within certain rf periods during the cyclotron motion, inducing overall distinct increase of excitation rate and electron temperature in the plasma bulk. This enhanced electron heating effect has been examined by a combination of kinetic particle simulations, experimental measurements, and an analytical model, and the dynamics of electrons are revealed at resonant conditions.

An electron heating mechanism based on a resonance between the cyclotron motion of electrons and the radio frequency sheath oscillations is reported in weakly magnetized capacitively coupled plasmas at low pressure. If half of the electron cyclotron period coincides with the radio frequency period, then electrons will coherently collide with the expanding sheath and gain substantial energy, which enhances the plasma density. A relation between the magnetic field and the driving frequency is found to characterize this resonance effect and the kinetics of electrons are revealed at resonance conditions for various driving frequencies.

The mechanism of resonance heating between the gyrating electrons and the oscillating sheath induced by a small transverse magnetic field in low-pressure capacitively coupled plasmas is investigated. The gyrating electrons will coherently collide with the expanding sheath if the electron gyro-frequency coincides with half the driving frequency. These electrons will gain substantial energy from collision-less heating, which strongly enhances the electron power absorption and the plasma density at a constant driving voltage. The electron kinetics is revealed at resonant conditions by particle simulations. Our numerical results demonstrate that the relation between the magnetic field and the driving frequency determines this resonance effect. Besides, it is found that the operating pressure, electrode gap, and driving voltage all strongly affect this electron resonance mechanism. The resonance effect is more pronounced at the conditions of low pressure, large gap, and high voltage.

Plasma parameters (electron density, electron temperature and relative light intensity) often follow an unstable state at the initial pulse stage in pulsed radio frequency discharges. For instance, the electron temperature and the excitation rate often experience overshoot phenomena within a short time after the pulsed power is turned on, while the electron density first shows a sharp increase and then continues to increase more slowly before reaching a stable value within a relatively longer time. A systematic interpretation of the evolution of plasma parameters in synchronized dual-level radio frequency pulsing capacitively coupled plasmas is reported based on 1D3V particle-in-cell simulations with Monte Carlo Collisions in argon. The low electron density and rapid sheath expansion accompanied by a strong electric field in the bulk, are found to be of great importance for the overshoot of the electron temperature and excitation rate. In addition, a time-varying ambipolar electric field develops at the initial pulse stage, which compresses the plasma bulk toward the discharge center, contributing to a sharp increase of the plasma density.

New colorimetric and fluorometric fluoride ion probe, anthra[1,9-cd]pyrazol- 6(2H)-one (1), was synthesized by one-step condensation. The probe 1 shows F−-selective color change from colorless to pink and appearance of red fluorescence. The fluorescence quantum yield of free probe 1 in DMSO was calculated to be 0.03. After addition of 15 equiv. of F−, its fluorescence quantum yield can be increased to 0.37. The analytical detection limit for F− was 2.8 × 10− 7 M. 1H NMR analysis and DFT calculation show that the F−-induced colorimetric and fluorometric responses of 1 are driven by deprotonation process.

The mechanism of nonlinear oscillations in symmetric capacitively coupled plasmas is studied by the particle-in-cell/Monte Carlo collisions approach. A physical origin of this nonlinear phenomenon is identified by spatiotemporal kinetic analysis of electron dynamics. It is found that multi-beams of high-energy electrons are stimulated at the sheath expansion phase, following with reversed electric field filaments. The instantaneous absence of the quasi-neutrality in the vicinity of the sheaths is responsible for the observed phenomenon. In addition, a simple theoretical model is introduced to qualitatively illustrate the numerical findings. Our simulations demonstrate that the frequency and intensity of this nonlinearity are very sensitive to the plasma density, sheath velocity, and sheath thickness. More nonlinear oscillations could be stimulated at the condition of high density and high sheath velocity, while a large sheath thickness normally induces large-amplitude oscillations. A simple relation of pressure and gap distance for nonlinear sheath oscillations has been built.

The electrical asymmetry effect combined with the magnetic asymmetry effect in a geometrically symmetric argon discharge is investigated using a one-dimensional particle-in-cell simulation with a Monte Carlo collision model. Both the asymmetry effects can induce an asymmetric plasma response with a consequent dc self-bias. It is found that these two asymmetry effects work independently of each other to some extent, which greatly enhances the flexibility for controlling the ion properties of interest, e.g. ion flux Γi and mean ion energy E i at electrodes on the weak magnetic field side. On one hand, Γi can be modulated by tuning the gradient of the magnetic field, while the angle distribution on electrodes remains approximately unaffected for a fixed phase angle θ on the weak magnetic field side with a small shift in ion energy peak. On the other hand, E i can be modulated by adjusting θ, while Γi only slightly fluctuates at a fixed gradient of magnetic field. Besides, the confinement effect of magnetic field on electron motion induces enhanced ionization rate and plasma density near the sheath edge on the strong magnetic field side.

Particle-in-cell/Monte Carlo collision (PIC/MCC) simulations are performed to investigate the asymmetric secondary electron emission (SEE) effects when electrons strike two different material electrodes in low pressure capacitively coupled plasmas (CCPs). To describe the electron-surface interactions, a realistic model, considering the primary electron impact energy and angle, as well as the corresponding surface property-dependent secondary electron yields, is employed in PIC/MCC simulations. In this model, three kinds of electrons emitted from the surface are considered: (i) elastically reflected electrons, (ii) inelastically backscattered electrons, and (iii) electron induced secondary electrons (SEs, i.e., delta-electrons). Here, we examined the effects of electron-surface interactions on the ionization dynamics and plasma characteristics of an argon discharge. The discharge is driven by a voltage source of 13.56MHz with amplitudes in the range of 200-2000V. The grounded electrode material is copper (Cu) for all cases, while the powered electrode material is either Cu or silicon dioxide (SiO2). The simulations reveal that the electron impact-induced SEE is an essential process at low pressures, especially at high voltages. Different electrode materials result in an asymmetric response of SEE. Depending on the instantaneous local sheath potential and the phase of the SEE, these SEs either are reflected by the opposite sheath or strike the electrode surface, where they can induce delta-electrons upon their residual energies. It is shown that highly energetic delta-electrons contribute significantly to the ionization rate and a self-bias forms when the powered electrode material is assumed to be made of SiO2. Complex dynamics is observed due to the multiple electron-surface interaction processes and asymmetric yields of SEs in CCPs.

A high-performance bandgap reference voltage source design method is proposed in this paper, according to the shortcomings of traditional bandgap reference voltage source. This method combined CSMC 0.35μm CMOS process with Aether software technology, enabling to improve the bandgap reference source op amp performance and take into account accuracy and stability of the system. From the experimental results: this bandgap reference voltage source output voltage has changed about 63 mV when the temperature varied from to , and the line regulator is 0.4mV/V when the power supply voltage varied from 3.2V to 3.3V. This system has advantages of high accuracy and good stability.

By using the waveform measurements and the least square method, the duration of transient level, and the duration of transient decreasing segment of aircraft DC transient signal are evaluated precisely. The evaluation courses and some technical problems are discussed in detail, the uncertainty analysis both of the durations are presented. Some test results have proved the effectiveness and practicability of the method. It could be applied to the characteristic and performance evaluation of aircraft DC transient signal waveform generators.

Water eutrophication has become one of the most serious problems in Chaohu Lake problem in recent years, and understanding the mechanisms of water eutrophication in Western Chaohu Lake will help for prevention and remediation of water eutrophication. In this paper, we selected 6 routine sampling sites in the water area of Chaohu Lake. TP, TN, CODMn and Chl-a are chosen to describe the eutrophication of the Study area. The influencing factors and major mechanisms of water eutrophication were discussed. The reasons of eutrophication changes in Western Chaohu Lake are very complicated; consist of the suitable natural condition, the built of Yuxi Gate, the deteriorated watershed ecological environment and a great amount of pollutants discharged. The treatment and control of the industrial and domestic wastewater from Hefei City are essential to the treatment. More attention should be paid to the treatment of non-point pollution.

In this study, we describe the presence of CRP2 (cysteine- and glycine-rich protein 2) and CRIP2 (cysteine-rich intestinal protein 2), which are members of group 2 LIM proteins, in rat olfactory precursor cells by reverse transcription polymerase chain reaction. We have developed polyclonal antibodies against CRP2 and CRIP2 individually. Specificity of the antibodies was demonstrated by Western blot analysis, using CRP2 and CRIP2 transfected cells. No cross-reactivity was observed between the antibodies. Furthermore, we used the antibodies to determine the expression and localization of CRP2 and CRIP2 in olfactory precursor cells by Western blot analysis and immunofluorescence staining. Our results demonstrated that in undifferentiated olfactory precursor cells CRP2 was distributed both in the nucleus and the cytoplasm, whereas CRIP2 was predominantly localized in the cytoplasm. While the olfactory precursor cells differentiated into end cells, only the expression of CRIP2 would be detected. The function of these LIM proteins in olfactory precursor cells warrants further study.

A combination of ultrasonic and low concentration iron (3 mgL(-1)) of Fenton process (US/Fenton) has been used to treat wastewater containing Acid black 1 (AB1). The results show that the oxidation power of low concentration iron of Fenton could be significantly enhanced by ultrasonic irradiation. The degradation of AB1 in aqueous solution by US/Fenton can receive better results compared with either Fenton oxidation or ultrasonic alone. Many operational parameters, such as ultrasonic power density, the pH value, the Fe(2+) dosage, the H(2)O(2) dosage, AB1 concentration and the temperature, affecting the degradation efficiency were investigated. Also, the effects of various inorganic anions (such as Cl(-), NO(3)(-), CO(3)(2-), etc.) on the oxidation efficiency of US/Fenton were studied. Under the given test conditions, 98.83% degradation efficiency was achieved after 30 min reaction by US/Fenton. The effect of various inorganic anions was in the following decreasing order: SO(3)(2-)CH(3)COO(-)Cl(-)CO(3)(2-)HCO(3)(-)SO(4)(2-)NO(3)(-). The results show that the US/Fenton can be an effective technology for the treatment of organic dyes in wastewater.

(Pt–NbPO x )/multi-walled carbon nanotubes (MWCNTs) with different NbPO x MWCNTs were prepared by a simple microwave irradiation method. The (Pt–NbPO x )/MWCNTs catalyst was characterized, and the kinetics toward oxygen reduction reaction (ORR) was determined, compared with that of Pt/MWCNTs catalyst. It was found that 10 wt% NbPO x was the best loading in terms of current density. The number of exchange electrons for the ORR was found to be close to four on both (Pt–NbPO x )/MWCNTs and Pt/MWCNTs.

Sn(IV) doped and nano-sized TiO 2 immobilized on active carbon (AC) (Sn(IV)/TiO 2 /AC) were prepared by the sol–gel and dip-calcination method. An azo dye, Orange G (OG), was used as a model compound to study its photocatalytic activity in a fluidized bed photoreactor. The addition of Sn(IV) on TiO 2 could greatly improve the activity of TiO 2 , and the optimal amount of tin was 2.5 at.%. The effects of calcination temperature, pH value, the initial hydrogen peroxide concentration ([H 2 O 2 ] 0 ), the catalyst amount ([TiO 2 ]), the initial OG concentration ([dye] 0 ) and co-existing negative ions on the photocatalytic activity of Sn(IV)/TiO 2 /AC were studied. The optimal conditions were as follows: pH 2.00, [H 2 O 2 ] 0 = 1.5mL/L, [dye] 0 = 50 mg/L, [TiO 2 ] = 12.5 g/L, when the 300 W high pressure mercury light was used as the light source. Under these conditions, the degradation efficiency of OG reached 99.1% after 60 min reaction. The kinetics of the OG degradation was also analyzed. The results showed that the kinetics of this reaction fit the Langmiur–Hinshelwood kinetics model well and the absorption of OG on the Sn(IV)/TiO 2 /AC surface was the controlling step in the whole degradation process. In addition, the catalyst, liquid and gas were separated effectively, and the integrative process of reaction and separation was achieved during the experiment.

There exist large accumulations of natural genetic diversifications under the natural and artificial selections on the flower among the Chinese tree peony cultivars incited by ornamental and medicinal uses in the past over 1500 years in China. Paeonia suffruticosa `Xiao Ci Wei' is a unique Chinese tree peony cultivar possessing special bicolored petals with tubular tip structure (Paeoniaceae). This natural mutant is not only a unique ornamental, but also a valuable material for scientific researches in Evodevotics.

In inductively coupled plasma sources, discharge transitions from electrostatic mode (E mode) to electromagnetic mode (H mode) and from H mode to E mode occur. In previous studies, only a few works paid attention to the effects of the impedance matching network. Cunge et al. [Plasma Sources Sci. Technol. 8, 576 (1999)] investigated the E-H and H-E mode transitions under two different impedance matching situations, but no physical mechanism or interpretation was presented. This issue is remained to be systematically and quantitatively investigated, and the underlying mechanism to be unveiled. In this paper, the effects of the impedance matching network were experimentally studied in electropositive argon gas by varying the series capacitance in an inversely L-shaped matching network. The positive and negative feedback regions are established according to the effect of varying the series capacitance on the output power of the rf power supply. It was found that under the same experimental parameters, the dis...