电力变压器微水在线测量的先进方法

研究了测量变压器油-纸绝缘的电力变压器中水含最的新方法.微水的扩散和平衡是和潜在的水分有关.比较了测量变压器内纸绝缘中水含量的各种方法.微水平衡图的常规应用会导致错误的结果,因此,创建了改成以微水吸收量和相关材料老化参数的微水平衡图.使用变压器油中的相对湿度来绘制微水平衡图先进的表示法,产生了比较好的效果.此外,按变压器油和绝缘材料中的活跃的水分来确定湿度,能提供方便、精确和连续的测量,并且直接反映变压器油-纸绝缘中的水分的破坏性潜力.这些均可在在线系统中显示出来.     

Multi-scale structuring for thermoplastic-metal contour joints of hollow profiles

In contrast to common and classical joining technologies for composite/metal hybrid structures such as bonding and riveting, profile and contour joints offer a promising potential for novel lightweight hybrid structures. Contour joints with form locking elements on multiple scale levels enable to pass very high loads into rod- and tube-shaped fibre reinforced structures and promise high degrees of material utilization for the composite part. This paper demonstrates the advantage of multi-scale structured load introduction elements. First the intrinsic manufacturing process, whereas the thermoplastic tape braided preform is simultaneously consolidated and formed into the metallic load introduction element is shown. Numerical investigations on the macro- and generic microscale demonstrate the potential to trigger cohesive or adhesive failure by appropriate designed form locking elements. The extensive experimental investigation of meso-, macro- or combined-structured tubular specimen shows the beneficial effect of multi-scale structuring to increase the joining strength. Concluding advises for the contour joints’ design are given.     

Electrical and Electrochemical Characteristics of Withania somnifera Leaf Extract Incorporation Sodium Alginate Polymer Film for Energy Storage Applications

The current investigation addresses the alternating current electrical properties, electrochemical characteristics on biopolymer as Withania somnifera leaf extract incorporated sodium alginate [WLISA] polymer film prepared by solution casting method. Some crystallinity along with the amorphous nature of sodium alginate emerged due to the incorporation of Withania somnifera leaf extract [WSLE]. Two absorption maximum (λ_max) were obtained for both WLISA and WSLE samples in the UV–Vis spectrum. The blue, green, and red emission of WSLE and weak blue emission of WLISA are studied by PL analysis. The more amount of strain that occurred in crystallization provides broaden peak in X-ray diffraction pattern. With aid of guluronic and mannuronic acids in sodium alginate making hydroxyl bond formation with leaf extract due to the cross-linking process can be analyzed from Fourier transform infrared spectroscopy. The EDAX analysis showed the chemical composition of WSLE. At room temperature, the prepared 5 ml leaf extract WLISA film has demonstrated the highest ionic conductivity in the typical value of 2.80?×?10^–6 S/Cm. The electrochemical window of the prepared polymer film is in the range of ? 0.4 to 0.4 V suggesting that used as an electrolyte for supercapacitor applications.

     

Pigment Epithelium-Derived Factor (PEDF) Receptors Are Involved in Survival of Retinal Neurons

The demise of retinal ganglion cells (RGCs) is characteristic of diseases of the retina such as glaucoma and diabetic or ischemic retinopathies. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted protein that mediates neuroprotection and inhibition of angiogenesis in the retina. We have studied expression and regulation of two of several receptors for PEDF, patatin-like phospholipase 2 gene product/PEDF-R and laminin receptor (LR), in serum-starved RGC under normoxia and hypoxia and investigated their involvement in the survival of retinal neuronal cells. We show that PEDF-R and LR are co-expressed in RGC and R28 retinal precursor cells. Expression of both receptors was enhanced in the presence of complex secretions from retinal glial (Müller) cells and upregulated by VEGF and under hypoxic conditions. PEDF-R- and LR-knocked-down cells demonstrated a markedly attenuated expression of anti-apoptotic Bcl-2 family members (Bcl-2, Bcl-xL) and neuroprotective mediators (PEDF, VEGF, BDNF) suggesting that both PEDF-R and LR mediate pro-survival effects of PEDF on RGC. While this study does not provide evidence for a differential survival-promoting influence of either PEDF-R or LR, it nevertheless highlights the importance of both PEDF receptors for the viability of retinal neurons.     

Single Sampling Point Detection of Frequency Modulated Terahertz Waves

We present single sampling point detection of the amplitude and phase of frequency modulated continuous wave terahertz radiation. Employing a conventional photomixing setup with a precise wavelength control allows for rapid scan rates in the kHz regime. Two application examples demonstrate the potential of this approach for real time monitoring of samples’ thicknesses and transmittances.     

Discrete Terahertz Beam Steering with an Electrically Controlled Liquid Crystal Device

We present an electronic beam switching/steering device for operation at THz frequencies. The propagation direction of the THz beam is switched via electronic manipulation of the refractive index of a liquid crystal. The design of the steering device and the parameters of the liquid crystal are described and angle-dependent THz-TDS measurements of the beam steering are reported. This device is able to deflect the propagation direction of the THz beam by 6.3?°. This particular device approach offers a viable option for beam steering/switching in various THz applications including fiber switches, scanning imagers, and free-space communication systems in which the detector or emitter is in motion.     

Terahertz quasi-time-domain spectroscopy imaging

We demonstrate terahertz (THz) imaging with a quasi-time-domain spectrometer. This type of THz system is inexpensive, compact, and relatively easy to set up. Beating the simultaneously emitted equidistant modes of a compact diode laser allows for analysis of samples at multiple frequencies with a single measurement. Thus, this technique merges the potential of terahertz time-domain spectrometers with the simplicity of continuous wave lasers. Multiple imaging applications and stability issues are discussed.     

Microstructural Analysis of Reballed Tin-Lead,Lead-Free,and Mixed Ball Grid Array Assemblies Under Temperature Cycling Test

In this study, ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (SAC305) solder balls were reballed with Sn-37Pb solder balls. Three different reballing methods were used. The non-reballed lead-free BGAs were assembled with SAC305 and Sn-37Pb solder pastes to form the lead-free and mixed assemblies. The reballed Sn-Pb BGAs were assembled with Sn-37Pb solder paste to form the reballed Sn-Pb assemblies. All assemblies were subjected to a temperature cycling test with a temperature range of −55°C to 125°C. For the same component type, the reballed BGA assemblies showed similar temperature cycling reliability regardless of the reballing methods. However, the temperature cycling reliability of the reballed assemblies was worse than that of the mixed and the lead-free assemblies. The mean cycles-to-failure of the mixed assemblies was larger than or equal to that of the lead-free assemblies. Failure analysis revealed that the failure site in reballed Sn-Pb assemblies was located in the bulk solder at the component side regardless of the component type and the reballing method, indicating that the reballing method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the lead-free assemblies, i.e., in the bulk solder at the component side. The microstructure differences between the tin-lead, lead-free, and mixed assemblies are also discussed in detail.     

Aspects of reproducibility and stability for partial cure of epoxy matrix resin

Partial cure of thermosets is a promising approach to enhance manufacturing possibilities of reinforced and unreinforced polymers. If partial cure is taken into consideration as a genuine process parameter, novel manufacturing technologies can be developed by exploiting the specific properties of incomplete polymer networks. A main concern in this context is to control the kinetic reaction avoiding inhomogeneous or instable degrees of cure. Based on a combination of numerical simulations and experiments, a methodology is presented that enables a systematic assessment of the reproducibility and stability of partial cure. Special attention is paid to the interaction of thermal boundary conditions and the cure kinetic of thick samples as well as the storability of partially cured resin under different conditions. Guidelines for cure cycle selection, mold design, and storage are derived. The possibility to use complex multistep cure schedules and extended storage periods is demonstrated for an unmodified noninhibited epoxy resin. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48342.