Superhumps in a Peculiar SU UMa-Type Dwarf Nova ER Ursae Majoris

We report the photometry of a peculiar SU UMa-type dwarf nova - ER UMa for ten nights during 1998 December and 1999 March covering a complete rise to the supermaximum and a normal outburst cycle. Superhumps have been found during the rise to the superoutburst. A negative superhump appeared in Dec.22 light curve, while the superhump on the next night became positive and had large amplitude and distinct waveform from that of the previous night. In the normal outburst we captured, superhumps with larger or smaller amplitudes seem to always exist, although it is not necessarily true for every normal outburst. These results show great resemblance with V1159 Ori (Patterson et al. 1995). It is more likely that superhumps occasionally exist at essentially all phases of the eruption cycles of ER UMa stars, which should be considered in modeling.Comment: 4 pages, 5 figures, Accepted by ApJ Letter

Surface charging on HVDC spacers considering time-varying effect of temperature and electric fields

The dynamic behavior of surface charging on spacers in DC-GILs can be influenced by multi-factors including the non-uniform distributed electric field as well as the time-varying temperature gradient. In this paper, the time-varying effect of surface charging phenomenon on spacers is studied and a time-varying mathematical model is established, based on the influence of temperature and electric field on the ion mobility at the gas phase and the bulk conductivity in the solid phase. The results verify that the bulk conductivity can be greatly influenced by temperature, which leads to an increase in the surface charge density on the spacer. This allows the surface charge accumulation to stabilize more quickly. However, the ion mobility from the gas phase is less affected by temperature. When the non-uniform distributed electric field changes from 1.3 to 6.4 kV/mm, ion mobility is less influenced and the surface charge density on the spacer varies slightly. In this case, the effects of the non-uniformly distributed electric field in surface charge density variation is much smaller and can be ignored

A Review of Knowledge-Based Defect Identification via PRPD Patterns in High Voltage Apparatus

Partial discharge (PD) as one of well-known signatures of defects in the insulation system of high voltage equipment has been studied over eight decades. It is of a great interest to power grid operators and owners to identify and distinguish local weak spots in insulation system of the key components of power system by using the obtained PD information to make timely decision thus to avoid any unexpected failures in the system. This article reviews the research progress of PD in high voltage apparatus, including motors and generators, cables, transformers and gas insulated equipment, with attempts to assess the severity of different types of PD initiating defects as well as key PD features that can be selected for classifying defects. Experimental and on-site test results for each type of discharge and defect associated are summarized and discussed. Also, development of these defects during operation of equipment caused by changes in physical and chemical parameters of defect and/or insulation, and its impact on phase-resolved PD pattern variation are thoroughly explained. It is expected that this paper can provide a comprehensive guideline for PD data analysis of available PD information extracted by conventional PD acquisition instruments for both engineers and asset managers of high voltage apparatus

Photometry and Spectroscopy of KS Ursae Majoris during Superoutburst

We report photometric and spectroscopic observations of the SU UMa-type dwarf novae, KS Ursae Majoris, during its 2003 February superoutburst. Modulations with a period of $0.07017\pm0.00021$ day, which is 3.3% larger than the orbital period, have been found during the superoutburst and may be positive superhumps. A maximum trough-to-peak amplitude of around 0.3 magnitude is determined for this superhump. The spectra show broad, absorption-line profiles. The lines display blue and red troughs which alternate in depth. The radial velocity curve of the absorption wings of H$\beta$ has an amplitude of $40\pm11$ km s$^{-1}$ and a phase offset of $0.12\pm0.03$. The $\gamma$ velocity of the binary is $3\pm9$ km s$^{-1}$ and varies on an order of 50 km s$^{-1}$ from day to day. From another clear evidence for a precessing eccentric disk, we obtain a solution to an eccentric outer disk consistent with theoretical works, which demonstrates the validity of the relation between superhumps and tidal effects. The inner part of the disk is also eccentric as evidenced by asymmetric and symmetric wings in the lines. Therefore, the whole disk is eccentric and the variation of $\gamma$ velocity and the evolutionary asymmetric line profiles could be criterions for an precessing eccentric accretion disk.Comment: 12 pages, 8 figures, accpeted for publication in A

A Directly Numerical Algorithm for a Backward Time-Fractional Diffusion Equation Based on the Finite Element Method

We study a backward problem for a time-fractional diffusion equation, which is formulated into a regularized optimization problem. After solving a sequence of well-posed direct problems by the finite element method, a directly numerical algorithm is proposed for solving the regularized optimization problem. In order to obtain a reasonable regularization solution, we utilize the discrepancy principle with decreasing geometric sequence to choose regularization parameters. One- and two-dimensional examples are given to verify the efficiency and stability of the proposed method

Determination of Dopamine in the Presence of Ascorbic Acid using Poly (Acridine red) Modified Glassy Carbon Electrode

Poly (acridine red) modified glassy carbon electrode was used for the detection of dopamine in the presence of ascorbic acid in a pH 7.4 phosphate buffer solutions (PBS) by cyclic voltammetry and differential pulse voltammetry. The major difficulty of the overlapped oxidation potential of ascorbic acid could be overcome through the distinct attractive ability of poly (acridine red) film to cationic dopamine and anionic ascorbic acid. The results showed that the dopamine anodic peak current and the concentration of dopamine had a linear relationship in the range of 1.0×10-7 ~ 1.0×10-4 mol dm-3. The detection limit (S/N=3) obtained by differential pulse voltammetry was 1.0×10-9 mol dm-3. The relative standard deviation of 10 successive scans was 2.07 % for 1.0×10-6 mol dm-3 DA. Ascorbic acid had hardly interference with the determination of dopamine. The proposed method exhibits good recovery and reproducibility

Protocol for electrocatalytic hydrogenation of 5-hydroxymethylfurfural using H and flow cells

Summary: Recently, there has been a growing interest in using sustainable energy to decrease lignin monomers to generate high-value-added products. Here, we present a protocol for electrocatalytic hydrogenation of 5-hydroxymethylfurfural. We describe steps for catalyst preparation, performing electrocatalytic experiments, high-performance liquid chromatography analysis, and in situ infrared reflection-absorption spectroscopy testing. The synthesized catalyst used in this reaction exhibits enhanced selectivity and Faradaic efficiency in NaClO4 solution.For complete details on the use and execution of this protocol, please refer to Zhang et al.1 : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics