Electric field and space charge measurements in thick powerr cable isulation - [Feature Article]

This paper describes the evolution of electric field and space charge in high voltage AC and DC cable polymeric insulation, followed using the thermal step method.     

In situ spectral monitoring of mRNA translation in embryonic stem cells during differentiation in vitro

Raman microspectroscopy was used to determine biochemical markers during the differentiation of embryonic murine stem cells (mES) in vitro. Such markers are useful to determine the differentiation status of ES cells cultured on biomaterials. Raman spectra of mES cells as undifferentiated, spontaneously differentiated (4 days), and differentiated cells via formation of embryoid bodies (16, 20 days) were analyzed. Unsupervised hierarchical cluster analysis and principal component analysis were used to determine biochemical differences between mES cells in various states of differentiation. The undifferentiated cells were characterized by high scores of the first principal component (PC1, 49% variance). Similarity between the PC1 loading and the Raman spectrum of RNA indicated a high concentration of RNA in mES cells compared to differentiated cells. The ratio between the peak areas of RNA and proteins was used as a measure of mRNA translation. Using the same peak area ratio, it was possible to differentiate even between mES as undifferentiated and in early stages of differentiation (4 days). These findings were correlated with biological studies reporting high levels of nontranslated mRNA during early embryonic development. Therefore, the RNA translation obtained from the Raman spectra can be used as marker of differentiation state of mES cells.     

Spectral depth profiling of arbitrary surfaces by thermal emission decay-Fourier transform infrared spectroscopy

We report a new spectroscopic technique that combines step-scanning Fourier transform infrared spectroscopy with opto-thermal transient emission radiometry (OTTER) in order to provide near-surface depth-resolved spectra in the range 700-1800 cm(-1). It works nondestructively, without contact, with samples of arbitrary shape and size, without requiring prior preparation. The depth of surface probed depends on the thermal diffusivity of the sample; for organic materials it is approximately 10 microm. With homogeneous samples, absolute absorption coefficients can be measured. With two-layered samples, the technique proved able to distinguish between the spectral properties of the top layer and the substrate and to estimate the thickness of the top layer. We present a theoretical analysis with the main design features of the instrumentation and software, together with studies of homogeneous and layered samples, to validate the methods and illustrate the potential of the technique for practical applications.     

Progress in Raman spectroscopy in the fields of tissue engineering, diagnostics and toxicological testing

This review summarises progress in Raman spectroscopy and its application in diagnostics, toxicological testing and tissue engineering. Applications of Raman spectroscopy in cell biology are in the early stages of development, however, recent publications have demonstrated its utilisation as a diagnostic and development tool with the key advantage that investigations of living cells can be performed non-invasively. Some of the research highlighted here demonstrates the ability of Raman spectroscopy to accurately characterise cancer cells and distinguish between similar cell types. Many groups have used Raman spectroscopy to study tissues, but recently increased effort has gone into single cell analysis of cell lines; the advantages being that cell lines offer ease of handling and increased reproducibility over tissue studies and primary cells. The main goals of bio-Raman spectroscopy at this stage are twofold. Firstly, the aim is to further develop the diagnostic ability of Raman spectroscopy so it can be implemented in a clinical environment, producing accurate and rapid diagnoses. Secondly, the aim is to optimise the technique as a research tool for the non-invasive real time investigation of cell/material interactions in the fields of tissue engineering and toxicology testing.     

The effect of water treeing on the electric field distribution ofXLPE. Consequences for the dielectric strength

This paper describes the influence of water trees on dielectric properties of flat samples cut from a HV crosslinked polyethylene (XLPE) cable insulation. In order to obtain experimental results in a short period of time, we used accelerated aging conditions of voltage and frequency as well as different techniques for producing a multitude of artificial water tree inception points. The average value of the water tree permittivity and a law for the time-dependence of permittivity inside the treed degraded areas were deduced from measurements of capacitance and water tree lengths. On the basis of the experimental knowledge of permittivity and water tree length, we determined with analytical numerical methods, the distribution of the electric field for different shapes of treed regions. Because of the increase in length and permittivity of the water tree, the electric field in front of the degraded area is amplified, which is an important factor of risk leading to the electric breakdown     

Experimental Study of the Corona Discharge in a Modified Coaxial Wire-Cylinder Electrostatic Precipitator

Coaxial wire-cylinder electrode arrangements are widely used for the electrostatic precipitation of dust particles contained in flue gases. The aim of this paper was to evaluate a new design, which was expected to increase the particle collection efficiency. The collector electrode of the several models under study consisted of a cylinder with alternate small- and large-diameter sections. In a first set of experiments, the current–voltage characteristics of each model were compared with those obtained for a standard wire-cylinder electrode arrangement, at both polarities of the high-voltage supply, and for three values of the inlet airflow rate, namely, 0, 4.5, and 6 $hbox{dm}^{3}/hbox{min}$, with the corresponding air velocities in the large-diameter sections being 0, 6.0, and 8.0 cm/s. A second set of experiments showed that the current density distribution inside the models depends on the geometry of the electrode system but is roughly the same at 4.5 and 6 $hbox{dm}^{3}/hbox{min}$. The particle collection efficiency of the different models was evaluated in a third set of experiments, performed with 2-g samples of starch powder, under various operating conditions. Data analysis revealed that the modified precipitators have higher efficiency than the standard model. As expected, for a given geometry of the electrode arrangement, the efficiency was found be lower at higher inlet airflow rates. These findings could serve in the design of new industrial electrostatic precipitators.      

The effect of poly[styrene‐b‐(ethylene‐co‐butylene)‐ b‐styrene] on dielectric,thermal, and morphological characteristics of polypropylene/silica nanocomposites

The effect of poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) copolymer on the thermal and dielectric properties of polypropylene (PP)—nanosilica (NS) composites in relation with morphological aspects revealed by atomic force microscopy (AFM) was investigated in this article. SEBS hindered the crystallization process of PP in PP/NS composites, leading to a smaller degree of crystallinity and lower perfection of crystalline structure. Broader lamellar thickness distribution was obtained in nanocomposites containing SEBS. Almost two times higher dielectric loss as compared to PP reference and two relaxation processes were detected in ε_r ^′′(f) curves of nanocomposites. The first peak, in the same frequency domain as for the references, was assigned to α‐relaxation of polymer components together with interfacial polarization. The relaxation time follows the Arrhenius law with an activation energy of 80–90 kJ/mol. For the second process, the temperature dependence of the relaxation times obeyed the VFT equation. The dielectric changes following the incorporation of SEBS support its tendency to hinder the motional processes in PP, in accordance with DSC results. A smooth transition from a phase rich in SEBS to one containing mainly PP was detected in the AFM image of the composite with the larger amount of SEBS, emphasizing the good compatibility at the PP/SEBS interface. POLYM. ENG. SCI., 53:2081–2092, 2013. © 2013 Society of Plastics Engineers     

Study of space charge accumulation in polyolefins submitted to acstress

The aim of the present study was to follow space charge formation under ac field (50 Hz) in polyolefins. The thermal step method was used, and charge accumulation was observed in crosslinked polyethylene (XLPE), very low density polyethylene (VLDPE), isotactic polypropylene (PP) and a PE /PP copolymer, the temperature varying from 45 to 90°C. It was found that the amount of charge accumulated under ac conditions may reach a maximum value at a given temperature, while the highest space charge was found in the polyolefin with the lowest crystallinity ratio. The conduction current characteristics of XLPE specimens show the existence of traps in the polymer at a level deeper than the potential barrier electrode/dielectric, explaining the accumulation of injected charge in the material. The injection and conduction mechanisms observed were interpreted by Schottky and Poole-Frenkel processes and used to explain the maximum accumulation of charge occurring at certain temperatures     

Thermal step method for space charge measurements under applied dcfield

The thermal step method (TSM) is a nondestructive technique which measures the distribution of the electric field and space charge density across solid insulating materials. This work first reviews the principle and the basic equations of the TSM when used on a short circuited flat insulating structure (film or plate). An evolution of the method, which allows the determination of space charge distribution in an insulator while submitted to an external dc field, is then described. The fundamentals, the experimental setup and the validation of this technique on flat samples and on power cables are presented and discussed