: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

/pdf/electrical-and-mechanical-characteristics-of-surface-ac-1mbx9840kz.pdf

Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control

The triboelectric nanogenerator (TENG) is a new type of energy generator first demonstrated in 2012. TENGs have shown potential as power sources for electronic devices and as sensors for detecting mechanical and chemical stimuli. To date, studies on TENGs have focused primarily on optimizing the systems and circuit designs or exploring possible applications. Even though triboelectricity is highly related to the material properties, studies on materials and material designs have been relatively less investigated. This review article introduces recent progress in TENGs, by focusing on materials and material designs to improve the electrical output and sensing performance. This article discusses the current technological issues and the future challenges in materials for TENG. The development of materials for a technology that uses the movement of the human body to provide power has been reviewed by scientists in South Korea. A triboelectric nanogenerator converts mechanical energy into electricity by harnessing the fact that two surfaces rubbing against one another can become electrically charged. This is known as the triboelectric effect. One exciting use for these nanogenerators is in wearable electronics, where the motion of the body provides the power. Unyong Jeong and colleagues from Pohang University of Science and Technology have reviewed recent progress in material advances in the four main elements of a triboelectric nanogenerator: the charge-generating layer, the charge-trapping layer, the charge-collecting layer, and the charge-storage layer. These improvements all aim to increase the electrical output of such devices. Over the last decade, triboelectric nanogenerator (TENG) has been verified to be an effective way of converting daily mechanical energy into electric power or detecting various stimuli in the external environment. To promote the material researches in TENG, we introduce recent progresses in materials and material designs to improve the power generation and sensing performance. Also, we discuss on the future challenges and suggest possible approaches to solve the challenges.

/pdf/material-aspects-of-triboelectric-energy-generation-and-2j8tumglpy.pdf

Material aspects of triboelectric energy generation and sensors

https://iopscience.iop.org/article/10.1088/0963-0252/25/6/063001/pdf

Dynamics of near-surface electric discharges and mechanisms of their interaction with the airflow

Space charge formation in polymeric materials can cause some serious concern in real operation, because it has significant influence on the performance of polymers. For example, space charge in some insulating materials can severely distort the electric field, even lead to materials degradation. On the contrary, in the case of its applications, space charge stored in electrets can greatly improve their properties. It is therefore important to understand trapped charge distribution in materials as it is considered to be a novel indicator for effective evaluation of aging status and electric withstanding strength of insulating materials. In this paper, a model based on isothermal surface potential decay (ISPD) is proposed to study the distribution of trapped charges by considering the physical mechanism of the detrapping process. By measuring the ISPD characteristics of polymeric materials and fitting the data according to the assumption of shallow and deep traps, the distribution of trapped charges is obtained, which may be related to the change of aggregation structure of polymers. In order to verify the model, it is used to analyze different ISPD decay curves of polypropylene (PP) and low density polyethylene (LDPE), as well as the ISPD data of PP electrets with/without pressure expanding treatment. The results show that the proposed ISPD model is effective and convenient. Two peaks are observed on the curve of the trapped charge density versus the trap level. The obtained distribution of the trapped charges in polymers can reveal the different nature of electron/hole traps and the different transportation behavior of hole/electron carriers, i.e., the electron-type traps show an inter-chain character while the character of hole-type traps is intra-chain. In addition, the distribution of trapped charge is further related to aggregation structure of PP and LDPE, as well as PP electrets with/without pressure expanding treatment.

The energy distribution of trapped charges in polymers based on isothermal surface potential decay model

Surface breakdown of dielectric window seriously limits the generation and transmission of high-power microwave (HPM), which blocks the development of microwave technology. Some research discusses that periodic rectangular grooves on the dielectric window perpendicular to microwave electric field can improve the threshold of breakdown greatly in a certain power range. For further understanding the mechanism, the simulation model of electrons movement in grooves is built in this paper. The physical process of rectangular grooves suppression breakdown has been discussed, and the movement trajectory of multipactor electron in grooves is obtained. The results indicate that the multipactor can be suppressed on the grooves side.

Multipactor simulation of grooved dielectric window surface

The silicone rubber(SR) insulated cable joint contains a composite interface between cross-linked polyethylene(XLPE) and SR, which is the weak component of the joint. Conductivity is an important factor affecting the tangential electric field in XLPE/SR interface of HVDC cables by changing the potential distribution in the insulation. Considering that the cable joint consists of two kinds of insulation, the relationship between their conductivity ratio coefficient and tangential electric field of interface is primarily calculated. It is found that reducing the difference of conductivity between XLPE and SR can keep the tangential field strength of the interface at a relative low level. In addition, considering the nonlinear conductivity of the insulation, the tangential electric field of the interface under DC superposition switching impulse voltage is calculated. The results show that the tangential field strength of the interface is the largest when DC superposition positive switching overvoltage at low temperature, which makes the probability of discharge and breakdown in the joint to be highest. And maximum tangential field strength of the interface is larger under DC superimposed both positive and negative switching impulse voltage than that of the steady-state at higher temperature.

Influence of Conductivity on Tangential Electric Field of Composite Interface of HVDC Cable Joint

Due to the excellent properties, C4F7N/CO2 mixture is the most concerned eco-friendly SF6 alternative gas. For a better understanding of the surface discharge characteristics, the surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages is investigated in this work. The morphology of the surface discharge is obtained by an optical method and a dust figure method. The structure of the surface discharge is established, which from the outside to the inside consists of electron cloud, streamer, streamer stem, and leader. The propagation pattern of the surface discharge in C4F7N/CO2 mixture under negative impulse follows the stepwise expansion pattern. The structure of the surface discharge in C4F7N/CO2 mixtures with different ratios and SF6 has no obvious difference, and the propagation pattern is also the same. The results of this work can help to better understand the surface discharge phenomenon and the insulation characteristics of C4F7N/CO2 mixture.

Surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages

Ultra-high-frequency (UHF) method has been applied to detect and localize partial discharge (PD) in air-insulated substation (AIS). The localization accuracy is closely dependent on the configuration of antenna array. This paper presents a PD localization error simulation method. Assuming that the estimated time difference of arrival (TDOA) error is normally distributed, the mean value and standard derivation of localization error for numerous positions in AIS are calculated with a Monte Carlo method. Then the localization error of square, Y shape, triangle and diamond arrays are compared, and the factors influence the localization error are analyzed. Since the optimal orientation is easily to be recognized and with minor distance error, the diamond array is more suitable for PD localization in AIS. Experiments are conducted for square and diamond arrays to calculate the localization error, and confirm the effectiveness of proposed simulation method.

UHF antenna configuration optimization for partial discharge source localization in air-insulated substation

Since increasingly more cables are adopted in distribution line, more hybrid cable-OHL lines are used in distribution network. Due to the difference of impedance and admittance of hybrid line compared with pure OHL, the energy redistribution is affected during line re-energization. This presentation focuses on the transient overvoltage during line re-energization with the use of EMT -type program. Firstly, due to the randomness of closing timings of circuit breaker, statistical distribution of reclosing overvoltage is studied. It is found that most severe overvoltage appears when cable share is 20%. Moreover, the most severe overvoltage can reach up to more than 3p.u, and its dominant frequency is 20.67 kHz. Furthermore, the influence of source network on the characteristic of reclosing overvoltage is studied as well. This work has reference value on insulation coordination and reclosing strategy in hybrid cable-OHL line.

Junbo Deng

Papers

Multipactor simulation of grooved dielectric window surface

Influence of Conductivity on Tangential Electric Field of Composite Interface of HVDC Cable Joint

Surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages

UHF antenna configuration optimization for partial discharge source localization in air-insulated substation

Analysis of Statistical and Frequency Characteristics of Transient Overvoltage of Hybrid Cable-OHL Lines