Organic Contaminants in Crosslinked Polyethylene for Demanding High Voltage Applications

Oxidation or chemical aging of polyethylene may occur before, during or even after the extrusion process used to produce crosslinked polyethylene (XLPE), creating oxidized particles referred to as organic contaminants. XLPE is a common insulating material used for e.g. high voltage cables. Not much work is published on the effect of organic contaminants on electrical degradation such as electrical treeing and water treeing. This work aims to examine the effects of organic contaminants with different degrees of oxidation on in particular electrical treeing. These contaminants were introduced in XLPE samples made for electrical treeing measurements. Instead of using a commonly used needle-needle or needle-plane configuration, a wire-plane configuration was used for all test samples. The electrical tree initiation and propagation was examined with a method developed at Chalmers University of Technology. As found in the literature, the organic contaminants are known to have increasing conductivity and permittivity depending on the degree of oxidation. These properties could create local field enhancements in the material. Also the morphology of the material might be affected when contaminants are inserted. A combination of these factors might influence the electrical performance of the insulation. As this was the first time organic contaminants were introduced into the wire-plane test method, a wide variety of tests were performed such as wet and dry aging, AC tests and DC tests. From these tests a number of observations were made, giving support to a set of possible conclusions for these topics

Topographical Impact on Space Charge Injection, Accumulation and Breakdown in Polymeric HVDC Cable Interfaces

Extruded HVDC cable systems feature a variety of interface types, for which physio-chemical properties will depend on the type of application. Such applications can be joints, terminations or the cable itself, all introducing different material combinations and manufacturing methods. To ensure beyond 40 years of faultless cable system operation, the interface’s design and quality control procedures are essential. Interfacial control requires detailed knowledge on how measurable physio-chemical properties of polymer surfaces relate to their electrical performance, through features such as localized electric field strength, space charge injection and breakdown strength. This work aims to expand such understanding by assessing polymer surfaces created with different, industrialized preparation methods, featuring different degrees of surface roughness. Surface preparation was carried out on real HVDC cable prototypes, from which cable peelings were extracted, ensuring replication of the material’s bulk and interfacial natures into the small-scale tests. Also, DC breakdown tests on medium voltage cables revealed strong impact of surface roughness, pinpointing the need for an accurate roughness evaluation.\ua0While chemical characterization assessed certain features brought about in the preparation, physical assessments such as optical profilometry quantified the surfaces’ topographies. It was found that, the topography, featuring micro and sub micrometer geometrical variation, could be readily adopted in a mesoscopic modelling approach. Thereby, the geometric impact on local quantities of field strength, charge density and injection current density was estimated. Also, a set of roughness enhanced charge injection equations were derived for charge injection types such as Schottky, Fowler-Nordheim and hopping injection mechanisms. Such equations, featuring surface specific field (β) parameters, were employed in a one-dimensional bipolar charge transport model. Through careful model calibration against the results of space charge measurements, the parameters for roughness enhanced charge injection, together with parameters for charge transport, trapping, detrapping and recombination, were estimated. This calibration verified roughness enhanced injection and generated a description of the density of states in the material’s bulk. Furthermore, DC breakdown tests performed on the cable peelings for establishing the relationship between surface roughness and breakdown strength. An adopted multi-scale simulation approach, based on the calibrated parameter set, estimated local field strength, charge density and other quantities in the surface domain.\ua0Conclusively, surface topography causes a local redistribution of the electric field, in turn locally increasing charge injection due to its strong field dependency at the rough asperities. Ultimately, coinciding high field strength and high charge density, at repeated positions along the surface, yields a lower breakdown strength. Such knowledge allows for tailoring the methodologies of surface preparation and quality control in HVDC cable systems, and other HV apparatuses. Control over mesoscopic surface effects will allow engineers to design ever more advanced and long-lasting HV components, meeting humanity’s renewable energy transmission needs for decades to come

A missing high-spin molecule in the family of cyano-bridged heptanuclear heterometal complexes, [(LCuII)6FeIII(CN)6]3+, and its CoIII and CrIII analogues, accompanied in the crystal by a novel octameric water cluster

Three isostructural cyano-bridged heptanuclear complexes, [{CuII(saldmen)(H2O)}6{MIII(CN)6}](ClO4)3$\cdotp$8H2O (M = FeIII 2; CoIII, 3; CrIII 4), have been obtained by reacting the binuclear copper(II) complex, [Cu2(saldmen)2(mu-H2O)(H2O)2](ClO4)2$\cdotp$2H2O 1, with K3[Co(CN)6], K4[Fe(CN)6], and, respectively, K3[Cr(CN)6] (Hsaldmen is the Schiff base resulted from the condensation of salicylaldehyde with N,N-dimethylethylenediamine). A unique octameric water cluster, with bicyclo[2,2,2]octane-like structure, is sandwiched between the heptanuclear cations in 2, 3 and 4. The cryomagnetic investigations of compounds 2 and 4 reveal ferromagnetic couplings of the central FeIII or CrIII ions with the CuII ions (JCuFe = +0.87 cm-1, JCuCr = +30.4 cm-1). The intramolecular Cu-Cu exchange interaction in 3, across the diamagnetic cobalt(III) ion, is -0.3 cm-1. The solid-state1H-NMR spectra of compounds 2 and 3 have been investigated

Employing transposon mutagenesis to investigate foot-and-mouth disease virus replication

Probing the molecular interactions within the foot-and-mouth disease virus (FMDV) RNA replication complex has been restricted in part to the lack of suitable reagents. Random insertional mutagenesis has proven an excellent method to reveal domains of proteins essential for viral replication as well as locations that can tolerate small genetic insertions. Such insertion sites can be subsequently adapted by the incorporation of commonly used epitope tags and so facilitate their detection with commercial available reagents. In this study, we use random transposon-mediated mutagenesis to produce a library of 15 nucleotide insertions in the FMDV nonstructural polyprotein. Using a replicon-based assay we isolated multiple replication-competent as well as replication-defective insertions. We have adapted the replication competent insertion sites for the successful incorporation of epitope tags within FMDV non-structural proteins, for the use in a variety of downstream assays. Additionally, we show that replication of some of the replication-defective insertion mutants can be rescued by co-transfection of a 'helper' replicon, demonstrating a novel use of random mutagenesis to identify inter-genomic trans-complementation. Both the epitope tags and replication-defective insertions identified here will be valuable tools for probing interactions within picornaviral replication complexes

Peregrinus Sum, Studies in History of Hungarian-Dutch Cultural Relations in Honour of Ferenc Postma on the Occasion of His 70th Birthday: Szerkesztette Margriet Gosker, Monok István, Budapest-Amsterdam, 2015, 292 lap

Peregrinus Sum, Studies in History of Hungarian-Dutch Cultural Relations in Honour of Ferenc Postma on the Occasion of His 70th Birthday - recenzi

Identification of pre-leukaemic haematopoietic stem cells in acute leukaemia.

In acute myeloid leukaemia (AML), the cell of origin, nature and biological consequences of initiating lesions, and order of subsequent mutations remain poorly understood, as AML is typically diagnosed without observation of a pre-leukaemic phase. Here, highly purified haematopoietic stem cells (HSCs), progenitor and mature cell fractions from the blood of AML patients were found to contain recurrent DNMT3A mutations (DNMT3A(mut)) at high allele frequency, but without coincident NPM1 mutations (NPM1c) present in AML blasts. DNMT3A(mut)-bearing HSCs showed a multilineage repopulation advantage over non-mutated HSCs in xenografts, establishing their identity as pre-leukaemic HSCs. Pre-leukaemic HSCs were found in remission samples, indicating that they survive chemotherapy. Therefore DNMT3A(mut) arises early in AML evolution, probably in HSCs, leading to a clonally expanded pool of pre-leukaemic HSCs from which AML evolves. Our findings provide a paradigm for the detection and treatment of pre-leukaemic clones before the acquisition of additional genetic lesions engenders greater therapeutic resistance

Measures of functional, real-world communication for aphasia: a critical review

Purpose: Aphasia is a language impairment caused by acquired brain damage such as stroke. For successful rehabilitation, a thorough understanding of naturalistic, real-world communication is imperative, as this is the behaviour speech and language therapy (SLT) ultimately aims to improve. In the field of aphasiology, there currently is a lack of consensus about the way in which communication should be measured. Underlying this is a fundamental lack of agreement over what real-world communication entails and how it should be defined. Method: In this critical review, we review the instruments that are currently used to quantify functional, real-world communication in people with aphasia (PWA). Each measure is checked against a newly proposed, comprehensive, theoretical framework of situated language use, which defines communication as: (1) interactive, (2) multimodal, and (3) based on context (common ground). Results: The instrument that best fits the theoretical definition of situated language use and allows for the quantification of communicative ability is the Scenario Test. Conclusions: This article provides a start in a more systematic and theoretically founded approach to the study and measurement of functional, real-world communication in aphasia. More work is needed to develop an instrument that can quantify communicative ability across different aphasia types and severities