: 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

Silicone oil is a promising alternative insulating liquid especially for the sites where fireproofing and environment protection must be considered. In this paper, the chemical and dielectric performance of silicone oil-paper composite insulation system under thermal aging is discussed. Two kinds of oil-paper systems are tested: mineral oil and silicone oil (Shin-Etsu Chemical KF-96-20 Lower viscosity fluid). In this study, mineral oil is used as the comparison sample. The accelerated aging process is at 140C in nitrogen. Aging samples with the aging duration of 250 hours, 500 hours and 750 hours and 1000 hours are tested. Experimental results indicate that the silicone oil has much lower acidity content and dielectric loss compared to the mineral oil. New mineral has a little higher AC breakdown voltage compared to silicone oil. For both silicone oil and mineral oil, with the increase of impurities such as water and solid particles during the aging process, the AC breakdown voltage decreases slightly. Acidic materials generated during aging process have little influence on the AC breakdown voltage. Different from the mineral oil whose impulse breakdown voltage decreases significantly with the increase of aging time, however, the silicone oil's negative impulse breakdown voltage of different aging time almost keeps the same.

Dielectric performance of silicone oil-paper composite insulation system under thermal aging

The degradation of oil-paper caused by thermal aging seriously affects the lifetime of power equipment such as transformers. In order to investigate the relationship between partial discharge (PD) and degradation of oil-paper insulation, PD characteristics and trap parameters of the paper are measured. In this work, we fabricate oil-paper model with cavity discharge, and the adopted oil-immersed paper specimens with different degree of polymerization (DP) are achieved by thermally accelerated aging to simulate transformers with different operation time. For each sample, the phase resolved partial discharge (PRPD) spectrogram is recorded. The trap parameters such as density and energy of different aged paper specimen are obtained by thermally stimulated depolarization current (TSDC) method. Furthermore, the microstructure of each paper specimen is observed by scanning electron microscope (SEM). Experimental results show two levels of trap existing on the surface of oil-paper: shallow (0.10–0.59 eV) and relatively deep (0.60–0.90 eV) energy level. Further analysis illustrates that thermally aging makes the trap energy deeper. It is considered that the change of PD and trap characteristics is of great significance for insulation condition assessment, and the trap parameter is promising to be new characteristic for aged paper insulation.

Partial discharge characteristics and trap parameters analysis of oil-paper after thermal aging

In recent years, molecular simulation technology, as the third mothed besides experiment and analysis, has been widely used in various fields. In the field of high voltage, molecular simulation is widely used in oilpaper and polymer insulation characteristics analysis, pyrolysis analysis and so on. In this paper, in order to clarify the electric aging mechanism of cross-linked polyethylene(XLPE), a simple XLPE molecular model is established with the ORCA package and the basic sets 3–21G, 6–31G and 6–311G(d, p) are utilized to optimize and get the most stable structure. We have chosen the band length, band gap and charge transfer within the molecule to characterize the XLPE molecule's status under electric field. The results show that the structural parameters and energy of the molecule present linear changes with electric strength. Especially, the band gap presents a downward trend, which means the insulation property of the material has decreased with the electric strength increases. These phenomena reveal the aging mechanism of XLPE molecule under electric field conditions, which is of great significance to the status evaluation of XLPE cable.

Insulation property analysis of cross-linked polyethylene based on density functional theory

The accumulated charge on insulator surface is an important factor to trigger surface flashover. A surface charge experimental setup as well as measurement system under high gas pressure is built. An active electrostatic probe (Trek 3455ET, Model 341B) is used to measure surface potential distribution on a downsized cone-type spacer in SF 6 /N 2 mixtures of different pressure under DC voltage. The actual charge density distribution is computed by the charge inverse algorithm, which considers the impact of the probe. The surface charge distribution shows similar shape at different pressure, including the homo-charges presenting a symmetrical distribution and a streak-like distribution. For the home-charges presenting a symmetrical distribution, they come from surface conductivity. For the streak-like distribution, they are located between central and grounded electrode. These charges come from the ionization of SF 6 due to the local electrical field concentrated.

Junbo Deng

Papers

Dielectric performance of silicone oil-paper composite insulation system under thermal aging

Partial discharge characteristics and trap parameters analysis of oil-paper after thermal aging

Insulation property analysis of cross-linked polyethylene based on density functional theory

Surface Charge Accumulation Behavior on GIL Spacer Under DC Voltages in SF 6 /N 2 Mixtures

Algorithm for fast calculating the energization overvoltages along a power cable based on modal theory and numerical inverse Laplace transform