Background: Brain metastasis is a leading cause of cancer mortality and affects 20-40% of all cancer patients. The BBB is responsible for isolation and protection of the brain parenchyma from many diagnostic and therapeutic agents. New molecular agents that target tumour-associated VCAM-1 expression on the brain endothelium show improvements in the early diagnosis of brain metastasis. The vascular endothelium of the CNS plays an important role in the maintenance of the brain microenvironment and possibly aids the extravasation of tumour cells via expression of CAMs. Aims: Using the breast carcinoma-derived 4T1 cell line, syngeneic to BALB/c mice, this work aimed (i) to determine the level of colocalisation between VCAM-1 expression at sites of brain metastasis and the presence of VCAM-MPIO-induced hypointensities in MR datasets; (ii) to describe the normal developmental characteristics of the intracardial BALB/c-4T1 brain metastatic model in the absence of overt inflammation; (iii) to test the effects of an adenovirus-induced systemic inflammatory challenge on metastatic uptake and development in the brain. Results: The level of correspondence of VCAM-MPIO-derived hypointensities with VCAM-1 expression at the tumour site was found to be dependent on the size of metastasis. An improved method for detection of VCAM-MPIO hypointensities using an automated method has been presented. Tumours were found to develop preferentially on venous rather than arteriolar blood vessels, and showed greater and lesser abundance in different anatomical brain regions. Adenovirus injection was found to cause an upregulation of a range of peripheral pro-inflammatory cytokines, and expression of VCAM-1 on cerebral vasculature, preferentially on arteriolar blood vessels. Both pre- and post-treatment with adenovirus caused a two-fold reduction in tumour numbers and altered developmental characteristics of established tumours, although no significant differences were observed in VCAM-MPIO hypointensities in MR datasets. Conclusions: The development of molecular MRI approaches to target VCAM-1 expression at the site of brain metastases has improved the sensitivity of tumour detection. 4T1-GFP metastasis to the brain is specific both to anatomical sites and to regions of the vascular bed, suggesting differences in vascular morphology and/or signalling dynamics in these locations. The changes in tumour number and morphology as a result of systemic inflammation suggest an anti-tumour effect of adenoviral treatment and, given the role of the systemic immune system and its importance in the development of immunotherapies, possible future directions for research.

This project investigates the moisture barrier properties of bio-based polymers and ways of improving them. The first section addresses the effect of crystallinity on the water permeability of poly(lactic acid) (PLA). The second section investigates PLA/talc composites and PLA/ montmorillonite nanocomposites. The third section is focused on a new polymer, polybutylene succinate (PBS), and its nanocomposites with montmorillonite. In the first section, the water vapour transmission rates (WVTR) through samples of polylactic acid of different crystallinities have been measured. Three different grades of commercial PLA were used with different ratios of L-lactide and D-lactide to give a range of crystallinities from 0 to 50%. Sheets of PLA were prepared by melt compounding followed by compression moulding and annealing at different temperatures and for different times to give the range of crystallinities required. Crystallinity was measured by differential scanning calorimetry (DSC) and the morphology of the samples was observed under crossed polars in a transmitted light microscope. Water vapour transmission rates through the films were measured at 38°C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased linearly with increasing crystallinity of the PLA from 0 to 50%. The results are discussed in terms of the effect of crystallinity on solubility and shown to fit the tortuous path model. The model was also successfully used to explain published data on water permeability of polyethylene terephthalate. In the second section, a series of PLA/talc composites and PLA/ montmorillonite nanocomposites were prepared by melt compounding followed by compression moulding. The morphologies of the composites were investigated using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) and it was found that the fillers were well dispersed in the polymer matrix. The average aspect ratio of the compounded talc was found to be 8, and that of the nanoclay was found to be 50. Water vapour transmission rates (WVTR) through the films were measured at 38°C and at a relative humidity of 90%. It was found that the measured values of WVTR decreased with increasing filler content and the results gave good agreement with predictions from the Nielsen tortuous path model. In the third section, PBS/ montmorillonite nanocomposites were prepared by melt compounding followed by compression moulding. The melting and crystallisation behaviour of the pure PBS samples were investigated using differential scanning calorimetry (DSC) and cross polarised optical microscopy. A slight decrease of the degree of crystallinity was found in PBS containing 5% nanoclay. The morphology of the composites was investigated using transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD) and it was confirmed that that composite structures were intercalated. Water vapour transmission rates (WVTR) through the PBS sheets were measured using a MOCON Permatran-W®398. The measured values of WVTR decreased with increasing nanoclay content. However, the experimental values were all higher than the values predicted by the Nielsen tortuosity model. This result shows that in the case of PBS, which is a highly crystalline polymer, the nanoclay is not as well dispersed and is not as effective in reducing water vapour permeability as in the case of PLA.

Vascular, especially cerebrovascular, dysfunction may be a critical factor in ageing and dementia. Cerebrovascular impairment due to risk factors such as ageing, stroke, smoking, diabetes and cerebral hypoperfusion has a deterious impact on the normal supply of basic nutrients such as oxygen and glucose to the brain; their absence leads inevitably to neuronal death. The cerebral white matter lesions found in most forms of dementia are reportedly the result of chronic cerebral hypoperfusion. However the temporal and spatial evolution of damage remains unclear. Furthermore, any decrease in the integrity of the blood-brain barrier (BBB) has been hypothesised to be a precocious attack on white matter. The “milieu interieure” the most protected in the body, namely the extracellular fluid of the brain, is no longer maintained homeostatically. The cumulation of these various pathophysiological processes alters cerebral function and it has been postulated that, in the most extreme instances, the outcome of this cascade of nefarious events leads to dementia. This thesis examines the supposition that chronic cerebral hypoperfusion could be responsible for the time-related development of white and grey matter pathology and investigates the relationships between the disturbances in the integrity of the BBB and white matter pathology. Three studies addressed these aims. In the first, chronic cerebral hypoperfusion, induced in male Wistar rats by bilateral common carotid artery occlusion (BCCAo), was chosen as the model to study changes in axons, myelin, perikarya as well as microglial activation. The groups of rats that underwent BCCAo were examined at three hours as well as three, seven, 14 and 28 days after the induction of chronic cerebral hypoperfusion. The microscopic examination revealed that, after three hours post BCCAo, damage was detected only in axons and myelin. In contrast, no visible pathology to the neuronal perikarya or enhancement of activated microglia (compared to the sham group) was observable. Injury in both white and grey matter and enhancement of activated microglia was observed from three days post BCCAo and increased with time post BCCAo. The most severe damage to the white and grey matter and enhancement of microglial activation was detected at seven days post BCCAo. These results would indicate that white matter damage precedes grey matter pathology and the enhancement of activated microglia. In the second study, the integrity of the BBB at three hours (when only white matter pathology was found according to the results of the first study) and seven days post BCCAo (when more severe damage to the white and grey matter was shown) was assessed by the use of MRI on T1-weighted image acquisitions with gadolinium as a tracer for BBB permeability. White matter integrity was measured by MTR maps from MTI acquisitions in four brain structures (corpus callosum, caudatoputamen, the external and internal capsules). No differences in white matter integrity were detected between the BCCAo and sham group at three hours and seven days. No differences in signal enhancement of gadolinium were detected three hours post BCCAo. However, a significant signal enhancement of gadolinium was detected at seven days post BCCAo in the caudatoputamen and in the external capsule. Furthermore, immunohistochemistry revealed a significant enhancement of activated microglia seven days post BCCAo compared to the sham group. This functional and immunohistochemical finding, when taken together, might indicate that chronic cerebral hypoperfusion is not in itself responsible for BBB permeability. Rather, the damage to the white matter caused by cerebral hypoperfusion may be responsible for the dysfunction of the BBB over time. Another point of interest was the evidence that the enhancement of activated microglia may play a critical role in the increased permeability of the BBB. The final study in this thesis aimed to investigate the possible pathway and proteins potentially implicated in white matter damage and BBB permeability. To address this question, protein levels and the expression of genes involved in the apoptotic and nonapoptotic hypoxic pathways were compared to the sham groups (at three hours and seven days after BCCAo), in three brain structures (cortex, corpus callosum and caudatoputamen). The levels of HIF-1α, MMP-2, Caspase-3 and VEGF were unchanged compared to the sham group after BCCAo. However, VEGF mRNA expression was found to be significantly different to the sham group seven days post BCCAo in all the three structures examined. An overexpression of HIF-1α and a significant level of Caspase-3 would indicate the activation of the apoptotic pathway. However, neither of these criteria were met and these negative results suggest that the apoptotic pathway is not implicated in the mechanisms that lead to white matter pathology after cerebral hypoperfusion. Finally, the significant expression of VEGF mRNA, compared to the sham group seven days post BCCAo, may contribute to the time-relate increased permeability of the BBB. The results presented within this thesis provide a body of evidence to support the hypothesis that chronic cerebral hypoperfusion is - at least – causal to the damage to different components of the white matter which precedes either early ischaemic changes to the perikarya or enhancement of activated microglia following BCCAo. The increased permeability of the BBB, which can be related to the significant over-expression of VEGF mRNA (compared to the sham group seven days post BCCAo), does not appear to be primarily responsible for white matter pathology, because the MRI investigations indicated that BBB integrity was not affected after three hours of BCCAo. The increased permeability of the BBB, observed seven days post BCCAo with MRI, seems to be the consequence of increased brain damage; thereafter, there is a time-dependent relationship between increasing BBB permeability and increasing brain pathology. Overall, the studies reported herein, strengthen the initial working hypothesis. The conclusion – and direction for future studies – would be that minimising white matter pathology and protecting components of the BBB represent potential targets to decrease then incidence of neuropsychological function or to obtund the cerebral dysfunction in patients who suffer from chronic cerebral hypoperfusion.

Lacunar strokes account for approximately a quarter of all ischaemic strokes and traditionally are thought to result from occlusion of a small deep perforating arteriole in the brain. Lacunar infarcts can be up to 2cm in diameter and are found in deep brain structures such as the thalamus and internal capsule. Despite their prevalence and specific accompanying clinical syndromes, the cause of lacunar stroke and its associated vascular pathology remain unclear. Many hypotheses as to the cause exist, which fall broadly into two categories; firstly, a direct occlusion via emboli or thrombus usually from a cardiac or large artery source, microatheroma (intrinsic lenticulostriate occlusion) or macroatheroma (parent artery occlusion) all operating primarily via ischaemia. Secondly, there could be an indirect occlusion resulting from vasospasm, endothelial dysfunction or other forms of endovascular damage (e.g. inflammation). Therefore the question of whether the resulting lesions are truly “ischaemic” or actually arise secondary to an alternative process is still under debate. To clarify the chain of pathological events ultimately resulting in lacunar stroke, in this thesis I firstly undertook a systematic assessment of human lacunar stroke pathology literature to determine the information currently available and the quality of these studies (including terminology). The majority of these studies were performed in patients who had died long after their stroke making it difficult to determine the early changes, and there were few patients with a clinically verified lacunar syndrome. Therefore I adopted alternative approaches. In this thesis, I systematically looked for all potential experimental models of lacunar stroke and identified what appears at present to be the most pertinent - the spontaneous pathology of the stroke-prone spontaneously hypertensive rat (SHRSP). However, the cerebral pathology described in this model to date is biased towards end stage pathology, with little information concerning the microvasculature (as opposed to the brain parenchyma) and confounding by use of salt to exacerbate pathology. Therefore, the aim of the experimental work in this thesis was to assess pathological changes within the cerebral vasculature and brain parenchyma of the SHRSP across a variety of ages (particularly young pre-hypertensive animals) and to look at the effects of salt loading on both the SHRSP and its parent strain (the Wistar Kyoto rat - WKY). Three related studies (qualitative and quantitative histology, immunohistochemistry and a microarray study of gene expression confirmed by quantitative PCR), revealed that the presence of inflammation (via significant changes in gene expression in the acute phase response pathway and increased immunostaining of activated microglia and astrocytes) plus alterations in vascular tone regulation, (via genetic alteration of the nitric oxide signaling pathway probably secondary to abnormal oxidative state), impaired structural integrity of the blood brain barrier (histological evidence of endothelial dysfunction and significantly decreased Claudin-5 staining) and reduced plasma oncotic potential (reduced albumin gene expression) are all present in the native SHRSP at 5 weeks of age, i.e. well before the onset of hypertension and without exposure to high levels of salt. We also confirmed previous findings of vessel remodelling at older ages likely as a secondary response to hypertension (thickened arteriolar smooth muscle, increased smooth muscle actin immunostaining). Furthermore, we found not only that salt exacerbated the changes see in the SHRSP at 21 weeks, but also that the control animals (WKY) exposed to a high salt intake developed features of cerebral microvascular pathology independently of hypertension (e.g. white matter vacuolation and significant changes in myelin basic protein expression). In conclusion, via the assessment of the most pertinent experimental model of lacunar stroke currently available, this thesis has provided two very important pieces of evidence: firstly that cerebral small vessel disease is primarily caused by a non-ischaemic mechanism and that any thrombotic vessel lesions occur as secondary end stage pathology; secondly that these features are not simply the consequence of exposure to raised blood pressure but occur secondary to abnormal endothelial integrity, inflammation, abnormal oxidative pathways influencing regulation of vascular tone and low plasma oncotic pressure. Patients with an innate susceptibility to increased blood brain barrier permeability and/or chronic inflammation could therefore have a higher risk of developing small vessel disease pathology and ultimately lacunar stroke and other features of small vessel disease. Research, addressing whether lacunar stroke patients should be treated differently to those with atherothromboembolic stroke is urgently needed.

Purpose of this paper: The purpose of this paper is to provide an overview of the factors that enable or aggravate the implementation of a GSCM strategy for textile and fashion companies. Moreover, it shall be investigated how textile and fashion companies perceive their incentives of implementing GSCM and what their organizational responses regarding the perceived barriers and enablers look like. Design/methodology/approach: The report combines a literature study on previous research in the field of supply chain management, Green Supply Chain Management and the drivers and barriers of implementing a GSCM strategy, with an empirical study consisting of an online survey, a semi-structured interview and two case studies that are based on literature review. In order to analyze the survey results, a method to calculate a company’s GSCM incentive score has been developed. Findings: The factors that have been identified as the strongest or most important ones by many companies of the survey, as well as the interviewee and the case studies are supplier collaboration, the lack of supplier commitment, customer demand for more sustainability, customer desire for lower prices and top management commitment. Some companies also perceived the alignment of their company’s strategy as strong GSCM enabler. However, the calculation shows that the overall incentive score of most participants is in the neutral level; meaning that they in total perceive neither significant incentives nor barriers to implement GSCM. With mostly internal enablers and external barriers, more than half of the survey participants can be categorized as Agenda Setters. Research limitations: Due to the low response rate, the sample size of this study is very small. Moreover, the results strongly depend on the personal opinion and experiences of the interviewee and the individual situations of the companies. This means that the results of this study give an indication, but are not generalizable. Therefore, another study with a different sampling method and a larger sample size is needed. Practical implications: The outcomes of this study show that GSCM concerns every aspect of a supply chain. A company that wants to engage in GSCM needs to have good relationships with and control over its suppliers in order to ensure that they fulfill the sustainability requirements, and deal with pressure from NGOs. Additionally, the company needs to balance customer demands for low prices and sustainability, expect some (one-time) investments and sacrifice short-term profit in order to ensure sustainable production. Originality/value: This report identifies the most important GSCM barriers and enablers for textile companies. By evaluating how companies within the textile and fashion sector perceive their incentives of implementing GSCM and investigating their organizational behavior towards barriers and enablers of GSCM, this study indicates what the current situation in the textile industry looks like; shows where improvements are necessary and gives insight for companies that aim to engage in green practices. The development of the so called GSCM incentive score; a method to calculate a company’s perceived incentives to implement a GSCM strategy, can be useful for future studies within this field.

Bakgrund: Personcentrerad omvårdnad är beroende av kommunikationen mellan vårdgivare och vårdsökande person. Andelen utlandsfödda i Sverige och övriga världen ökar samtidigt som denna grupp rapporteras ha sämre tillgång till hälso- och sjukvård och sämre hälsa än icke utlandsfödda. Därför står hälso- och sjukvården inför stora utmaningar. Syfte: Att beskriva vårdsökande personers erfarenheter av att kommunicera med vårdpersonal då gemensamt modersmål saknas. Metod: En litteraturöversikt bestående av 14 artiklar skrivna med kvalitativ metod som söktes fram i databaserna Cinahl och PsycINFO. Analys utfördes induktivt och utmynnade i fyra kategorier. Resultat: Språkbarriärer inverkar på vårdens kvalitet och individens tillgång till vård. Kommunikation i vårdmötet upplevs som svårare än annan kommunikation och kan leda till att vårdsökande personer sluter sig gentemot vårdpersonal. Empatiskt bemötande, tålamod och intresse från vårdpersonal förbättrade upplevelsen. Informell tolk användes till följd av okunskap om att professionell tolk tillhandahölls. Slutsats: Vårdens tillgänglighet för personer som upplever språkbarriärer måste öka. Vårdpersonal bör anpassa sitt språk och försäkra sig om att vårdsökande personer förstår. Vården måste bli bättre på att informera om och bistå med lämpliga tolkar – val av tolk ska utgå från personens önskemål. Vidare forskning kan göras för att hitta fler sätt att arbeta personcentrerat trots språkbarriärer. / Background: Person-centered care is dependent on communication between healthcare provider and patient. The proportion of foreign-born in Sweden and the rest of the world increases. A group with less access to healthcare and poorer health than non-foreign-born. This presents major challenges to healthcare. Objective: To describe patient´s experiences of communicating with healthcare professionals in the absence of a common mother tongue. Methods: A literature review consisting of 14 articles with a qualitative approach that were retrieved from the databases CINAHL and PsycINFO. Analysis was made using an inductive approach resulting in four categories. Results: Language barriers affect quality of, and access to care. Communication in healthcare was perceived as more difficult than other communication and might lead to patients distancing themselves from healthcare professionals. Empathy, patience and interest from healthcare professionals improves patient´s experience. Informal interpreters are often used due to a lack of knowledge regarding professional interpreters. Conclusions: Healthcare availability for persons experiencing language barriers needs to increase. Professionals need to adapt their language and ensure that patients understand. Healthcare professionals must inform patients about, and assist with appropriate interpreters based on the person’s preferences. Further research may identify alternate ways to work person-centered despite language barriers.

The trace elements zinc and copper are essential components of many enzymes, some of which are of importance for the development and function of the central nervous system. Deficiency of the metals has been shown to lead to malformations and to the loss of myelin in animals. Earlier reports of zinc concentrations in the cerebrospinal fluid are few and the results variable. In multiple sclerosis and in epilepsy therapy with phenytoin there are varying reports of changes in serum concentrations of zinc and copper. A method was developed for the determination of zinc in cerebrospinal fluid by flame atomic absorption spectrophotometry utilizing a pulse nebulizer technique. Zinc and copper in serum were determined by flame atomic absorption spectrophotometry with conti nous aspiration. The normal concentrations of zinc in cerebrospi nal fluid was 0.16_+0.03 micromoles per litre (mean +_ S.D.). The zinc concentrations were correlated with protein and albumin concentrations in the cerebrospinal fluid but not with the serum zinc levels. In the patients with increased protein concentrations in the cerebrospinal fluid or with subarachnoid haemorrhage increased zinc levels were found. In 50 patients with multiple sclerosis lower serum concentrations of zinc were found compared to age and sex matched controls. In younger patients low serum levels of copper were also observed. There was no correlation between zinc and protein parameters in the cerebrospinal fluid of multiple sclerosis patients. In untreated epileptic males low serum zinc concentrations were observed. During the first 72 hours of phenytoin therapy increased serum concentrations of zinc and copper were found. during long-term therapy with phenytoin alone or in combination with other antiepileptic drugs there was an increased serum concentration of copper and ceruloplasmin but no change in zinc concentration compared with controls. / <p>Diss. Umeå, Umeå universitet, 1982, härtill 4 uppsatser</p> / digitalisering@umu

Lower k and low-leakage silicon carbonitride (SiCxNy ) films were fabricated using single precursor by using radio-frequency (RF) plasma-enhanced chemical vapor deposition (PECVD). We explored precursors with (1) cyclic-carbon-containing structures, (2) higher C/Si ratio, (3) multiple vinyl groups, as well as (4) the incorporation of porogen for developing low-k SiCxNy films as etch-stop/diffusion barrier (ES/DB) layer for copper interconnects in this study. SiCxNy films with k values between 3.0 and 3.5 were fabricated at T≦ 200 o C, and k~4.0-4.5 at 300-400 °C. Precursors with vinyl groups yielded SiCxNy films with low leakage, excellent optical transmittance and high mechanical strength due to the formation of cross-linked Si-(CH2)n-Si linkages.

Thesis (MScEng (Civil Engineering)--University of Stellenbosch, 2007. / The introduction of toughened glass into the construction industry has had several significant consequences. For the first time, glass panels can be used without continuous edge supports, and as a result can be used as load-bearing element. An excellent and very common example of the use of glass as structural element is a freestanding glass balustrade. During an undergraduate investigation, a number of impact tests were performed on continuous supported freestanding glass balustrade panels at the University of Stellenbosch [6]. It was observed that none of the balustrade panels complied with the guidelines for impact loading stipulated in the SABS [7] loading standards. The failure to meet the loading requirements highlighted the need to investigate the design of glass balustrades. This thesis describes the investigation undertaken to determine the static- and dynamic loading capacity of freestanding glass balustrades. Following a review of South African and international design standards, the static- and dynamic material properties of toughened glass was established by means of a laboratory test series. The laboratory test series consisted of both a destructive laboratory test series and finite element analysis, the outcome of which determined the static- and dynamic material properties of toughened glass. The series also included the influence of different connection types. A second phase employed the identified material properties of toughened glass to determine the loading capacity of full-scale balustrades. Using finite elements each balustrade set-up was loaded as required by the relevant South African loading standards. The finite element analyses identified which balustrade set-ups could resist the required imposed loads. Finally, a second laboratory test series was undertaken, the aim of which was to verify the finite element results. The successful resistance of the tested balustrade set-ups confirmed the finite element model. Recommendation to the existing design- and loading standards are made based on the results of the thesis.

Η παρούσα διπλωματική εργασία πραγματεύεται την επίδραση που επιφέρουν στην τάση διάσπασης διακένου αέρα, διάφορα μονωτικά φύλλα (διαφράγματα) τοποθετούμενα κάθετα προς τον κεντρικό άξονα μεταξύ της διάταξης των ηλεκτροδίων του διακένου και σε διαφορετικές θέσεις μεταξύ της απόστασης αυτών. Η διερεύνηση της επίδρασης των διαφραγμάτων στην διηλεκτρική συμπεριφορά των διακένων είναι γνωστή γενικά και ως το Φαινόμενο του Διαφράγματος (Barrier Effect). Η διάταξη που χρησιμοποιήθηκε για την εκπόνηση της παρούσας εργασίας ήταν διάκενο αέρα ακίδας-πλάκας μήκους 6 cm, και στο ενδιάμεσο των ηλεκτροδίων τοποθετήθηκε το διάφραγμα (Σχήμα 1). Σχήμα 1) Διάταξη διακένου ακίδας-πλακάς με διάφραγμα. Χρησιμοποιήθηκαν 3 διαφορετικά υλικά ως διαφράγματα, ως προς το πάχος τους, με αποτέλεσμα τα σύνθετα διάκενα αέρα-διηλεκτρικού που προκύπτουν να είναι τα εξής: 1) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,2 mm. 2) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,19 mm. 3) Διάκενο αέρα “ακίδας-πλάκας” με διάφραγμα πάχους 0,125 mm. Η καταπόνηση του κάθε σύνθετου διακένου αέρα-διηλεκτρικού έγινε με θετικές κρουστικές τάσεις χειρισμών υπό ατμοσφαιρική πίεση. Για το διάκενο αέρα “ακίδας-πλάκας” μήκους 6 cm με διαφράγματα polyfilm πάχους 0,125 mm και 0,19 mm, διερευνήθηκε η συμπεριφορά αυτών για τρείς διαφορετικές θέσεις ξ=x/D, του διαφράγματος στο διάκενο (x=1, x=2, x=3) και με δύο διαφορετικές περιπτώσεις καταπόνησης για την κάθε θέση ξ του διαφράγματος στο διάκενο. Στην πρώτη περίπτωση το διάφραγμα διατηρήθηκε το ίδιο για κάθε στάθμη τάσεως καταπόνησης του και στη δεύτερη άλλαζε για κάθε στάθμη. Για το διάκενο αέρα “ακίδας-πλάκας” με διαφράγματα τύπου nomex πάχους 0,2 mm, διερευνήθηκε η συμπεριφορά του για έξι διαφορετικές θέσεις ξ του διαφράγματος στο διάκενο. / The aim of this thesis is to investigate the effect of different insulation materials (barriers) into the breakdown voltage of air-gaps, created by two electrodes. The barrier is placed between these electrodes and crosses their central axes perpendicularly, at various locations along this axes. The system used for this work was an air-gap ‘’needle-plate’’, which had a width of 6cm and a barrier placed between the electrodes (figure1). Figure 1) Schematic diagram of ‘’needle-plate’’ air gap with barrier. There were 3 barriers used,of different thicknesses. The resulting air-dielectric gaps formed are as follows: 1) needle plate air-gap, with a 2mm thick barrier. 2) needle plate air-gap, with a 0,19 mm thick barrier. 3) needle plate air-gap, with a 0,125 mm thick barrier. The stress of each air-dielectric gap composite was accomplished using positively impulsed voltage, at atmospheric pressure. In the 6cm wide air gap of the needle plate, a polyfilm barrier was used with a thickness of 0.125 or 0.19mm. The barrier was placed at three different positions between the plates (ξ=x/d; x=1,2,3). At each location, two cases were investigated: 1) the same barrier was kept still and a voltage of various levels was applied and 2) the barrier was varied at each different level of voltage applied. The behaviour/response/efficiency of the air gap needle plate, having a nomex type barrier of 0.2 mm thickness, was investigated, when the barrier was placed at 6 different locations, ξ, between the electrodes.