Optical Properties of Neutral and Charged Low Band Gap Alternating Copolyfluorenes： TD-DFT Investigation

Electronic structure and optical properties of neutral and charged low band gap alternating copolyfluorenes （Green 1, which is based on alternating repeating units consisting of alkyl-substituted fluorene and a thiophene-[1,2,5]thiadiazolo-[3,4]quinoxaline-thiophene （T-TDQ-T） unit were investigated theoretically with time-dependent density functional theory （TD-DFT） method, and their excited state properties were further analyzed with 2D site and 3D cube representations. For neutral Green 1, the band gap, binding energy, exciton binding energy, and nuclear relaxation energy were obtained. The transition dipole moments of neutral and charged Green 1 are compared using 3D transition density, which reveals the orientation and strength of transition dipole moments. The charge redistribution of neutral and charged Green 1 upon excitation are displayed and compared with 3D charge difference density. The electron-hole coherences of neutral and charged Green 1 upon excitation are investigated with 2D site representation （transition density matrix）. The excited state properties of neutral Green 1 calculated with TD-DFT method are compared with that calculated with ZINDO method, which reveals the importance of electron-electron interaction （in TD-DFT） in the excited state properties.

Coagulation behavior of polyaluminum chloride: Effects of pH and coagulant dosage

Coagulation mechanisms of polyaluminum chloride(PACl) at various dosages were studied using a conventional jar test at different final and initial pH values during treating kaolin suspension. The optimal final pH and dosages for PACl were obtained based on residual turbidity and zeta potential of flocs. The coagulation zones at various PACl dosages and solution p H values were developed and compared with those of alum. It is found that the optimal mechanism under acidic condition is charge neutralization, while alkaline condition will facilitate the coagulation of PACl. Both charge neutralization coagulation and sweep coagulation can achieve high coagulation efficiency under the alkaline condition ranging from final p H 7.0 to 10.0. Stabilization, charge neutralization destabilization, restabilization and sweep zones occur successively with increasing PACl dosages with the final p H values fixed at 7.0 and 8.0, but restabilization zone disappears at final p H 10.0. When the final p H is not controlled and consequently decreases with increasing PACl dosage, no typical sweep zone can be observed and the coagulant efficiency decreases at high PACl dosage. It seems that the final pH is more meaningful than the initial p H for coagulation. Charge neutralization coagulation efficiency is dominated by zeta potential of flocs and PACl precipitates. The charge neutralization and sweep coagulation zones of PACl are broader in the ranges of coagulant dosage and p H than those of alum. The results are helpful for us to treat water and wastewater using PACl and to understand the coagulation process of PACl.

Effects of Slow-Mixing on the Coagulation Performance of Polyaluminum Chloride （PACI）

Conventional jar tests and on-line size monitoring were used to investigate the effects of slow-mixing intensity and duration on residual turbidity and floc size during charge neutralization coagulation and sweep floc- culation with polyaluminum chloride. The compensatory effect of slow-mixing on coagulation performance fol- low!ng inadequate_or excessive rapid-mi_xing was also examined. It is found that slowTmixing intensity has a more marked positive ettect on charge neutralization coas;ulatlon tlaan on sweep tlocculatlon. llle optimal root-mean- square velocity gradient, G, for slow-mixing is 15 s-＇ for both coagulation mechanisms, and charge neutralization coagulation requires a longer slow-mixing duration. The optimal slow-mixing duration, based on residual turbidity,is longer than the time to tbrm the largest mean Ilocs. The optimal product of G and mixing duration, GT, lbr slow-mixing during charge neutralization coagulation （13500） are higher than that during sweep flocculation （4500） and both are less than the range of values recommended by the American Water Works Association （24000-84000）.The optimal GT value under various slow-mixing conditions increases with G. Appropriate extension＇of slow-mixing duration during charge neutralization coagulation can improve coagulation performance after an inadequate or excessive rapid-mixing duration, but during sweep flocculation, appropriate shortening of slow-mixing duration after an excessive rapid-mixing or appropriate extension of slow-mixing duration after an inadequate rapid-mixing is favorable.

Mixed ion and electron transport theory and application in solid oxide conductors

Mixed ions and electron conductors(MIECs)are an important family of electrocatalysts for electrochemical devices,such as reversible solid oxide cells,rechargeable metal-air batteries,and oxygen transport membranes.Concurrent ionic and electronic transports in these materials play a key role in electrocatalytic activity.An in-depth fundamental understanding of the transport phenomena is critically needed to develop better MIECs.In this brief review,we introduced generic ionic and electronic transport theory based on irreversible thermodynamics and applied it to practical oxide-based materials with oxygen vacancies and electrons/holes as the predominant defects.Two oxide systems,namely CeO_(2)-based and La CrO_(3)-based materials,are selected as case studies to illustrate the utility of the transport theory in predicting oxygen partial pressure distribution across MIECs,electrochemical electronic/ionic leakage currents,and the effects of external load current on the leakage currents.

Effect of Low Energy Electron Exposure on Ion Scattering Spectroscopy

The effect of low energy electron (LEE) exposure on ISS, including on the sputter peak and scatter peak as well as on ion neutralization, has been investigated for different samples. Some new results are discussed.

Ion-focused propagation of a relativistic electron beam in the self-generated plasma in atmosphere

It is known that ion-focused regime(IFR)can effectively suppress expansion of a relativistic electron beam(REB).Using the particle-in-cell Monte Carlo collision(PIC-MCC)method,we numerically investigate the propagation of an REB in neutral gas.The results demonstrate that the beam body is charge neutralization and a stable IFR can be established.As a result,the beam transverse dimensions and longitudinal velocities keep close to the initial parameters.We also calculate the charge and current neutralization factors of the REB.Combined with envelope equations,we obtain the variations of beam envelopes,which agree well with the PIC simulations.However,both the energy loss and instabilities of the REB may lead to a low transport efficiency during long-range propagation.It is proved that decreasing the initial pulse length of the REB can avoid the influence of electron avalanche.Using parts of REB pulses to build a long-distance IFR in advance can improve the beam quality of subsequent pulses.Further,a long-distance IFR may contribute to the implementation of long-range propagation of the REB in space environment.

Impact of Updraft on Neutralized Charge Rate by Lightning in Thunderstorms:A Simulation Case Study

The rate of neutralized charge by lightning（RNCL） is an important parameter indicating the intensity of lightning activity.The total charging rate（CR）,the CR of one kind of polarity（e.g.,negative） charge（CROP）,and the outflow rate of charge on precipitation（ORCP） are proposed as key factors impacting RNCL,based on the principle of conservation of one kind of polarity charge in a thunderstorm.In this paper,the impacts of updraft on CR and CROP are analyzed by using a 3D cloud resolution model for a strong storm that occurred in Beijing on 6 September 2008.The results show that updraft both promotes and inhibits RNCL at the same time.（1） Updraft always has a positive influence on CR.The correlation coefficient between the updraft volume and CR can reach 0.96.Strengthening of the updraft facilitates strengthening of RNCL through this positive influence.（2） Strengthening of the updraft also promotes reinforcement of CROP.The correlation coefficient between the updraft volume and CROP is high（about0.9）,but this promotion restrains the strengthening of RNCL because the strengthening of CROP will,most of the time,inhibit the increasing of RNCL.（3） Additionally,increasing of ORCP depresses the strengthening of RNCL.In terms of magnitude,the peak of ORCP is equal to the peak of CR.Because precipitation mainly appears after the lightning activity finishes,the depression effect of ORCP on RNCL can be ignored during the active lightning period.

New neutralization method for measuring the secondary electron yield of insulative material

Purpose The limitation of the traditional bias neutralization method is proved,and a new neutralization method is proposed to measure the secondary electron yield of insulating materials.Method While measuring the secondary electron yield of an insulating sample using the bias neutralization method,the region of an insulating sample irradiated by an electron beam may not be neutralized,because electrons enforced by the bias are not returned to the proper location.The above-mentioned phenomenon is verified by a simulation.To achieve proper neutralization,we propose a method of moving the electron beam to irradiate the metal sample stage without applying a bias voltage,which generates many low-energy electrons around the insulating sample.Those electrons are automatically attracted to the positively charged region of the insulating sample surface and rejected if enough electrons accumulated on the surface.Result and conclusion The limitation of neutralization of bias voltage was verified by simulation,and the new neutralization method was proved to be effective through experiments.

Insight into the underlying competitive mechanism for the shift of the charge neutrality point in a trilayer-graphene field-effect transistor

Layer-number modulation in graphene has become a recent focus of research due to the superior degree of freedom that can be achieved in terms of magic-angle,wettability,superconductivity,and superlattices.However,the intrinsic transport of multilayer graphene is indistinguishable in atmospheric adsorbates and supporting environment,and its underlying charge transfer mechanism has not yet been thoroughly determined.In this study,a shift in the charge neutrality point of trilayer graphene(TLG)is demonstrated to be regulated by three governing factors:oxygen gas(O_(2)),water molecules(H_(2)O),and thermally activated electrons.Absorbed O_(2) induces a high work function in semimetallic TLG,while H_(2)O is not an evident dopant but can strengthen binding against O_(2) desorption.A simplified model is developed to elucidate the competitive mechanism and charge transfer among these two dopants(O_(2),H_(2)O)and thermal electrons,and the model is demonstrated by work function regulation and Bader charge transfer based on density functional theory calculations.This study provides a strategy to explore transport modulation of multilayer graphene in the fields of ballistic transport and low power consumption of graphene field-effect transistors.

Discharge mode and particle transport in radio frequency capacitively coupled Ar/O_(2) plasma discharges

Simulations are conducted on capacitively coupled Ar/O_(2)mixed gas discharges employing a one-dimensional fluid coupled with an electron Monte Carlo(MC)model.The research explores the impact of different O_(2)ratio and pressures on the discharge characteristics of Ar/O_(2)plasma.At a fixed Ar/O_(2)gas ratio,with the increasing pressure,higher ion densities,as well as a slight increase in electron density in the bulk region can be observed.The discharge remains dominated by the drift-ambipolar(DA)mode,and the flux of O(3P)at the electrode increases with the increasing pressure due to higher background gas density,while the fluxes of O(1D)and Ardecrease due to the pronounced loss rate.With the increasing proportion of O_(2),a change in the dominant discharge mode from a mode to DA mode can be detected,and the O_(2)-associated charged particle densities are significantly increased.However,Ar+density shows a trend of increasing and then decreasing,while for neutral fluxes at the electrode,Arflux decreases,and O(3P)flux increases with the reduced Ar gas proportion,while trends in O(1D)flux show slight differences.The evolution of the densities of the charged particle and the neutral fluxes under different discharge parameters are discussed in detail using the ionization characteristics as well as the transport properties.Hopefully,more comprehensive understanding of Ar/O_(2)discharge characteristics in this work will provide a valuable reference for the industry.

Study on the pre-chopper in CSNS LEBT

Physical designing of the pre-chopper in CSNS LEBT is carried out, which includes the deflecting voltage, the length and the width of the deflecting plates, and the gap between the deflecting plates. The most outstanding feature of the design is that both the gap and the width vary with the beam envelope size. So both the requried deflecting voltage and the loaded capacitance are lowered. In order to avoid destruction of the space charge neutralization by the pre-chopper in the whole LEBT, an electron-trapping electrode is arranged to confine the electrostatic field of the pre-chopper to the local area. To examine the reliability of the pre-chopping design in CSNS LEBT, a similar pre-chopping design in ADS RFQ LEBT is set up and an experiment on the pre-chopper is prepared. 3-dimensional simulations are carried out to determine the loaded capacitance and the applied voltage of the electron-trapping electrode.

Effects of cerium incorporation on the catalytic oxidation of benzene over flame-made perovskite La_(1-x)Ce_xMnO_3 catalysts

Perovskite-type La1-xCexMnO3 （x= 0-10%） catalysts were prepared by flame spray pyrolysis and their activities during the catalytic oxidation of benzene were examined over the temperature range of 100-450 ℃. The structural properties and reducibility of these materials were also characterized by X-ray diffraction （XRD）, N2 adsorption/desorption, H2 temperature-programmed reduction （H2-TPR） and X-ray photoelectron spectroscopy （XPS）. The incorporation of Ce was found to improve the benzene oxidation activity, and the perovskite in which x was 0.1 exhibited the highest activity. Phase composition and surface elemental analyses indicated that non-stoichiometric compounds were present. The incorporation of Ce had a negligible effect on the specific surface area of the perovskites and hence this factor has little impact on the catalytic activity. Introduction of Ce^4＋ resulted in modification of the chemical states of both B-site ions and oxygen species and facilitated the reducibility of the perovskite. The surface Mn^4＋/Mn^3＋ ratio was increased as a result of Ce^4＋ substitution, while a decrease in the surface-adsorbed O/lattice O （Oads/Olatt） ratio was observed. The relationship between the surface elemental ratios and catalytic activity was established to allow a better understanding of the process by which benzene is oxidized over perovskites.

Hydrolysis of polyaluminum chloride prior to coagulation:Effects on coagulation behavior and implications for improving coagulation performance

The effects of polyaluminum chloride（PACl） hydrolysis prior to coagulation on both the coagulation zone and coagulation performance of a kaolin suspension were investigated by a novel jar test named the ＂reversed coagulation test＂.The tests showed that PACl hydrolysis prior to coagulation decreased the performance of charge neutralization coagulation in the case of short-time slow mixing（10 min;G = 15 sec-1） and increased the optimal dosage for charge neutralization and sweep coagulation.Moreover,the hydrolysis time had insignificant effects on the size and zeta potential of PACl precipitates and the residual turbidity of the raw water.However,PACl hydrolysis prior to coagulation and the size of PACl precipitates had a negligible effect on the performance of sweep coagulation.The results imply that,in practice,preparing a PACl solution with deionized water,rather than tap water or the outlet water from a wastewater treatment unit,can significantly save PACl consumption and improve the performance of charge neutralization coagulation,while preparing the PACl solution with tap or outlet water would not affect the performance of sweep coagulation.In addition,the optimal rapid mixing intensity appears to be determined by a balance between the degree of coagulant hydrolysis before contacting the primary particles and the average size of flocs in the rapid mixing period.These results provide new insights into the role of PACl hydrolysis and will be useful for improving coagulation efficiency.

Demulsification performance and mechanism of oil droplets by electrocoagulation: Role of surfactant

Surfactants are widely used to improve the solubility of oil in water in petrochemical,making it more difficult to remove oil–water emulsions during the water treatment process.Electrocoagulation(EC) is an appropriate method for treating oily wastewater and destabilizing emulsions. However, the demulsification mechanism of oil–water droplets emulsified by surfactants with different charges have not been investigated systematically. The demulsification performance of electrocoagulation on emulsions wastewater containing cationic,non-ionic, and anionic surfactants was studied. The results showed that the removal rate of total organic carbon(TOC) in oily wastewater with anionic surfactant by EC reached92.98% ± 0.40% at a current density of 1 mA/cm^(2), while that of the non-ionic surfactant was 84.88% ± 0.63%. The characterization of flocs showed that EC has the highest coagulation and demulsification of oil droplets with a negative charge on the surface(-70.50 ± 10.25mV), which indicated that the charge neutralization of oil droplets was beneficial for the destabilization of the formed oily flocs. However, when the zeta potential of the oil droplets reached 75.50 ± 1.25 mV, the TOC removal efficiency was only 11.80% ± 1.43%. The TOC removal could achieve 33.23% ± 3.21% when the current density improved from 1 mA/cm^(2)to 10 mA/cm^(2). The enhanced removal was due to the sweep coagulation rather than charge neutralization. This study provides a fundamental basis for the electrochemical treatment of oily wastewater.