: 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

For identifying electron and hole traps in polymeric materials, we combine the isothermal relaxation current theory and surface potential decay together and present a model called isothermal surface potential decay (ISPD). A non-contact measurement setup is specially designed, which features that energy distribution of electron or hole-type traps can be discriminated with negative or positive corona charging, respectively. By measuring the ISPD characteristics of low-density polyethylene and polypropylene films, their trap distributions are obtained, revealing the different semi-crystalline morphology of these two materials. The results we obtained may imply the essentially distinct nature of electron/hole traps: inter-chain for electron-type traps and intra-chain for hole-type traps, which is in agreement with other researchers' molecular modeling results.

Identification of electron and hole trap based on isothermal surface potential decay model

During the field service of composite insulators, high temperature vulcanized (HTV) silicone rubber (SIR) material used for insulator’s sheath and sheds is gradually aging, and thus how to effectively evaluate its aging state has become an inevitable issue. In this paper, artificially corona-aged and naturally site-aged SIR materials are employed as samples, and their properties such as hydrophobicity, leakage current, trap density/energy level, surface microstructure and chemical composition are investigated for comparative study. With the increasing of corona aging intensity, the contact angle of SIR samples drops gradually and recovers more slowly. The hydrophobicity of site-aged insulators also declines, from HC1 for 2-year service to HC5 for 15-year service. The leakage current of corona-aged and site-aged samples both increase with aging, which indicates that aging induces the increase of surface conductivity of SIR material. The peak trap density of corona-aged and site-aged samples increases with the aging duration or service duration remarkably. The changes of these properties are attributed to the changes of micro-structures and compositions in the surface layer of SIR. The scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analysis results reflect that a hardened inorganic silica-like (SiO2) layer with many polar chemical groups and distributed micro-pores is formed on the surface of SIR material after corona aging. Because of this silica-like layer, the hydrophobicity decreases while surface conductivity and trap density of SIR material increases. Besides the traditional properties like hydrophobicity and surface conductivity, the trap density is expected to be a novel parameter for effective evaluation of aging state of HTV silicone rubber material.

Aging characterization of high temperature vulcanized silicone rubber housing material used for outdoor insulation

Effects of surface roughness on surface charge accumulation characteristics and surface flashover performance of alumina-filled epoxy resin spacers

The regulation mechanism of SiC/epoxy coatings on surface charge behavior and flashover performance of epoxy/alumina spacers

https://iopscience.iop.org/article/10.1088/1361-6463/ab6d1a/pdf

Junbo Deng

Papers

Identification of electron and hole trap based on isothermal surface potential decay model

Aging characterization of high temperature vulcanized silicone rubber housing material used for outdoor insulation

Effects of surface roughness on surface charge accumulation characteristics and surface flashover performance of alumina-filled epoxy resin spacers

The regulation mechanism of SiC/epoxy coatings on surface charge behavior and flashover performance of epoxy/alumina spacers

Surface charge transport behavior and flashover mechanism on alumina/epoxy spacers coated by SiC/epoxy composites with varied SiC particle size