The material properties of low stress silicon nitride make it a possible replacement material for beryllium in X-ray windows. In this study, X-ray windows made of LPCVD deposited low stress silicon nitride are fabricated and characterized. The Young's modulus of the LPCVD low stress silicon nitride are characterized and found to be 226±23 GPa. The residual stress is characterized using two different methods and is found to be 127±25 MPa and 141±0.28 MPa. Two support structure geometries for the low stress silicon nitride X-ray windows are used. X-ray windows with thicknesses of 100 nm and 200 nm are suspended on a silicon rib support structure. A freestanding circular geometry is used for a 600 nm thick X-ray window. The 100 nm and 200 nm thick low stress silicon nitride X-ray windows with a silicon support structure are burst tested, cycling tested and leak rate tested. The average burst pressure for the 100 and 200 nm films on a silicon support structure are 1.4 atm and 2.2 atm respectively. Both 100 nm and 200 nm windows are able to withstand a difference in pressure of 1 atm for over 100 cycles with a leak rate of less than 10-10 mbar-L/s.The low stress silicon nitride with 100 nm and 200 nm thicknesses, the 600 nm freestanding low stress silicon nitride windows and freestanding 8 micron thick beryllium windows are mechanical shock resistance tested. The support structure low stress silicon nitride and beryllium windows are tested with an applied vacuum. The freestanding 600 nm thick low stress silicon nitride windows burst at 0.4 atm and are therefore mechanical shock wave tested without an applied vacuum. The support structure low stress silicon nitride windows fractured when subjected to an acceleration of roughly 5,000 g. The 8 micron thick beryllium windows are subjected to accelerations of over 30,000 g without fracturing. A quasistatic model is used to show that for low stress silicon nitride with a freestanding circular geometry, an acceleration of 106 g is required to have the same order of magnitude of stress caused by a pressure differential of 1 atm. Low stress silicon nitride can act as a replacement for beryllium in X-ray windows, but the support geometry, residual stress, and strength of the material need to be optimized.

No description available.

<p>Opisani&nbsp; su&nbsp; detalji&nbsp; konstrukcije&nbsp; novog&nbsp; izvora&nbsp; plazme, u impulsnom režimu, konstruisanog za&nbsp; potrebe ekscitacija linija berilijuma u&nbsp; prisustvu berilijumske&nbsp; pra&scaron;ine.&nbsp; Konstrukcija&nbsp; izvora&nbsp; je ostvarena&nbsp; na&nbsp; takav&nbsp; način&nbsp; da&nbsp; je&nbsp; sprečeno prodiranje&nbsp; čestica&nbsp; pra&scaron;ine&nbsp; u&nbsp; atmosferu&nbsp; laboratorije.&nbsp; Opisane&nbsp; su&nbsp; dodatne&nbsp; 2&nbsp; cevi&nbsp; za pražnjenje&nbsp; konstruisane&nbsp; od&nbsp; Al2O3 i&nbsp; SiO 2 . Pronađeni&nbsp; su&nbsp; i&nbsp; opisani&nbsp; optimalni&nbsp; uslovi&nbsp; za&nbsp; rad<br />izvora&nbsp; plazme.&nbsp; Vrednosti&nbsp; elektronske&nbsp; koncentracije,&nbsp; određene&nbsp; nakon&nbsp; maksimuma<br />struje,&nbsp; kori&scaron;ćenjem&nbsp; vodonikove&nbsp; balmer&nbsp; beta linije,&nbsp; kreću&nbsp; se&nbsp; u&nbsp; opsegu&nbsp; 1,16-9,2&nbsp; ∙10<br />22&nbsp; m -3 . Elektronska temperatura je određena&nbsp; na&nbsp; osnovu relativnih&nbsp; intenziteta&nbsp; linija&nbsp; dva&nbsp; uzastopna jonizaciona&nbsp; stanja&nbsp; istog&nbsp; elementa&nbsp; i&nbsp; kreće&nbsp; se&nbsp; u opsegu&nbsp; 10&nbsp; 500-15&nbsp; 500&nbsp; K.&nbsp; Prikazane&nbsp; su snimljene&nbsp; linije&nbsp; berilijuma,&nbsp; osim&nbsp; rezonantnih. Dato&nbsp; je&nbsp; poređenje&nbsp; snimljenih&nbsp; linija&nbsp; sa postojećim&nbsp; teorisjkim&nbsp; podacima.&nbsp; Dve&nbsp; linije berilijuma&nbsp; koje&nbsp; se&nbsp; pojavljuju&nbsp; sa&nbsp; zabranjenom komponentom su prikazane prvi put. Pokazano je&nbsp; da&nbsp; postoji&nbsp; tipičan&nbsp; trend&nbsp; zavisnosti&nbsp; odnosa dozvoljene&nbsp; i&nbsp; zabranjene&nbsp; komponente,&nbsp; kao&nbsp; i rastojanja&nbsp; između&nbsp; položaja&nbsp; maksimuma intenziteta ove dve komponente, od elektronske koncentracije,&nbsp; koji&nbsp; se&nbsp; javlja&nbsp; kod&nbsp; linija&nbsp; sa zabranjenim&nbsp; komponentama,&nbsp;&nbsp;&nbsp; &scaron;to&nbsp; govori&nbsp; o<br />mogućnosti ove linije za primenu u dijagnostici plazme.</p> / <p>Construction&nbsp; details&nbsp; of&nbsp; new&nbsp; plasma&nbsp; source,&nbsp; running in pulsed regime,&nbsp; for beryllium spectral line&nbsp; studies,&nbsp; in&nbsp; the&nbsp; presence&nbsp; of&nbsp; beryllium&nbsp; dust particles are presented.&nbsp; The construction of the source&nbsp; was&nbsp; realised&nbsp; in&nbsp; such&nbsp; a&nbsp; way&nbsp; that&nbsp; it prevented&nbsp; the&nbsp; ingress&nbsp; of&nbsp; dust&nbsp; particles&nbsp; into&nbsp; the laboratory&nbsp; atmospher.&nbsp; Construction&nbsp; details&nbsp; and<br />testing&nbsp; of&nbsp; BeO&nbsp; discharge&nbsp; tube&nbsp; in&nbsp; comparison with&nbsp; SiO2 and&nbsp; Al2O3 discharge&nbsp; tubes&nbsp; are&nbsp; presented,&nbsp; also.&nbsp; Optimal&nbsp; conditions&nbsp; for&nbsp; plasma source operation&nbsp; and beryllium line studies are found.&nbsp; The&nbsp; electron&nbsp; density&nbsp; measured&nbsp; after discharge current maximum is determined from&nbsp; the peak separation of the hydrogen Balmer beta<br />spectral&nbsp; line,&nbsp; and&nbsp; the&nbsp; electron&nbsp; temperature&nbsp; is&nbsp; determined&nbsp; from&nbsp; the&nbsp; ratios&nbsp; of&nbsp; the&nbsp; relative&nbsp; intensities&nbsp; of&nbsp; Be&nbsp; spectral&nbsp; lines&nbsp; emitted&nbsp; from successive&nbsp; ionized&nbsp; stages&nbsp; of&nbsp; atoms.&nbsp; Maximum values&nbsp; of&nbsp; electron&nbsp; density&nbsp; and&nbsp; temperature&nbsp; are measured&nbsp; to&nbsp; be&nbsp; 9.3∙1022 m -3 and&nbsp; 16&nbsp; 800&nbsp; K, respectively.&nbsp; The&nbsp; recorded&nbsp; spectral&nbsp; lines&nbsp; of beryllium,&nbsp; other&nbsp; then&nbsp; resonant&nbsp; lines,&nbsp; are&nbsp; presented. The lines&nbsp; with forbidden component are&nbsp; described&nbsp; for&nbsp; the&nbsp; first&nbsp; time.&nbsp; The&nbsp; functional dependence of the wavelength separation range and&nbsp; peak&nbsp; intensity&nbsp; ratio&nbsp; of&nbsp; these&nbsp; lines&nbsp; upon<br />electron&nbsp; number&nbsp; density&nbsp; suggests&nbsp; the&nbsp; complex profile of the forbidden and allowed line, which can be used for diagnostics of low-temperature beryllium containing plasmas.</p>

This study investigates the photoluminescence (PL), cathodoluminescence (CL), radioluminescence (RL) and ionoluminescence (IL) of natural and synthetic minerals. The natural minerals (fluorapatite, leucophanite, meliphanite and zircon) are mostly from Ilímaussaq Alkaline Complex in South Greenland, Langesundsfjord in Norway and from different localities within Scotland. Synthetic fluorapatite (manufactured as part of the present study) and zircon doped with rare earth elements (REE) were used to compare single and multidoped materials. This study has shown that many of the generally accepted applications of luminescence are not as straightforward as often suggested by the current literature. For example, the study demonstrates how site distribution of REE, based on luminescence, is greatly affected by the dopant level and structural changes, and that different conclusions can be drawn on the same sample depending on method applied. Furthermore, it is clearly demonstrated that using luminescence as a tool for quantitative trace element determination is not going to be a standard technique in the near future if ever. The two main findings supporting this conclusion are the non-linear intensity decrease between different REE activators in the same sample and a large variation between activators at the concentration at which self-quenching starts. In contrast to the general perception that luminescence related to REE is mostly independent of the host, this study has shown a strong interaction between host and REE activators. This conclusion is supported by the change in the activator’s coordination polyhedron observed with single-crystal and powder X-ray diffraction combined with full chemical characterisation. When combining the weak interaction between some REE with the strong host interaction this study has shown the potential for designing new types of colour tuneable and “white light” LEDs based on natural minerals. This study also reveals that zircon doped with Gd³⁺ and Eu³⁺ can potentially have quantum-cutting properties.

The Round Top laccolith is considered to be one of the youngest laccoliths in a series of five known as the Sierra Blanca peaks, located in Hudspeth county, Texas. The laccolith is anomalous within the region in that it is peraluminous and enriched in HREEs, F, and U, and is comprised of intermingled discrete packages of various rhyolite types. The laccolith rhyolite varies in color from gray, purple, red, and tan, which combine locally to form distinct geometric mottled textures. The general composition of the rhyolite is 48-52% potassium feldspar, 28-30% quartz, 8-14% plagioclase feldspar, 4-5% annite biotite, 2-3% magnetite-hematite, 1% zircon, and 1% trace phases. The morphology of the trace phases suggests quenching of a late-stage volatile-rich vapor phase at the time of the laccolith formation. The rhyolite displays a wide array of unique mineralogical characteristics indicative to rapid emplacement and metastable crystallization conditions, including three-part quartz phenocrysts, hourglass sector-zoned potassium feldspars, and late-stage anhedral zircons. Unique accessory and trace phases include cassiterite, cerianite-(Ce), changbaiite, columbite, cryolite, tantalite, thorite, yttrofluorite, yttrocerite, and two unidentified minerals named (W) and (X). Initial alteration of the laccolith by high temperature volatile-rich vapor during the late stages of crystallization caused the partial dissolution of the feldspars and quartz. Subsequent quenching of this high temperature vapor phase produced the abundant interstitial, and pore filling REE-fluorides common to the laccolith. The variation in rhyolite color and the presence of the mottled textures are a direct result of partial oxidation of the laccolith by secondary fluids. The oxidizing fluids migrated within the laccolith along an extensive fracture network, altering the adjacent wallrock by oxidizing magnetite phenocrysts to hematite. The gray, purple, and red rhyolite types reflect an increase in turbidity caused by hematitic inclusions primarily within the pore spaces of the potassium feldspar portions of the groundmass. The tan rhyolite is locally restricted to the base of the laccolith and has been subjected to an intense degree of alteration independent of the other rhyolite types, primarily indicated by the conversion of feldspars to clay. Petrographic, microbeam, and geochemical studies have determined little variation in REE concentration between the three rhyolites of similar alteration intensity, but have indicated a depletion in LREEs within the more altered tan rhyolite. The average REE+Y content for the rhyolites sampled (n=11) ranges between 249 ppm and 518 ppm. The REE+Y concentrations between rhyolite samples of the same type show some variation, possibly indicating a correlation between alteration and REE+Y abundance and/or innate heterogeneity in the vapor phase during the initial laccolith formation. The magma emplaced at Round Top underwent a prolonged evolutionary process of fractionation/differentiation as evident by the unusual mineral assemblage and geochemical enrichment associated with the laccolith (e.g. extremely negative europium anomaly, and the positive La/Yb correlation). Future exploration for Round Top style REE-deposits should center within long-lived, tectonically active and complex regions where laccoliths are likely to exist. Specifically, exploration should focus on identifying the youngest laccolith in a felsic series, as this is the most likely to contain the greatest abundance of incompatible elements within the laccolithic group. The early alteration of feldspars by the high temperature vapor phase was crucial in the development of the REE+Y enrichment at Round Top. The feldspar dissolution provided abundant open pore space that was subsequently filled by the REE-fluorides. Thus, exploration should additionally seek laccoliths that have undergone a similar early alteration process, and expand to potential laccolith groups not yet exposed by erosional processes. / text

This thesis develops a better knowledge of the extent and timing of glaciations in southern Argentina throughout the Quaternary. It provides a detailed understanding of successive major glacial outlet lobes in the Lago Pueyrredón valley. The glacial and glaciofluvial deposits in the valley, as elsewhere in the region, are extremely well-preserved and reflect punctuated glacial advances between ~ 1.1 Ma and ~ 17 ka. Several intermediate glaciations are undated, constrained by the limited time frame of radiocarbon age dating, the limited potential volcanic sites for K-Ar or 40Ar/39Ar age dating, and erosion and exhumation problems associated with cosmogenic-nuclide surface exposure ages on moraines. This thesis provides a new chronology for the mid-Quaternary glaciations based on methodological advances in cosmogenic-nuclide surface exposure age dating. This is done by deriving ages from glacial outwash terrace sediment and demonstrating their reliability. The work shows that for younger (i.e., last glacial) moraines, well-constrained ages can be derived from the common-practice of dating large boulders on the moraine surface. However, on older moraines, the ages so-derived become considerably scattered. This is interpreted to be caused primarily by boulder exhumation as a consequence of moraine erosion, resulting in shorter residence of some boulders at the surface relative to the moraine formation date. By contrast, glacial outwash surfaces in this area, if carefully chosen, can be shown to have undergone little aggradation or erosion, and thus have had long and consistent surface exposure since formation. Provided these surfaces can be stratigraphically linked with the glacial limits, they can provide good surface exposure ages. This has been convincingly confirmed in one location by a sequence of ages obtained from a 10Be concentration depth-profile which demonstrate the surface stability and lack of inherited nuclides. Using these methods, cosmogenic 10Be and 26Al surface exposure ages indicate successive major advances occurred at ~ 1.2 Ma, ~ 600 ka, ~ 260 ka and ~27 – 17.5 ka. These are correlated with global marine and ice core records.

No description available.

Worldwide, peatlands cover an area of 4.106 km2 . Plant primary production dominated over organic matter decomposition and enabled organic matter to accumulate during the last 11 000 years. Peatlands represent a reservoir of atmospheric carbon and they are a useful scientific tool for reconstructions of historical atmospheric pollution. The first part of the thesis focuses on peatlands as a dynamic carbon reservoir under predicted climate change that would influence carbon cycling and emissions of greenhouse gases into the atmosphere. Three methodological approaches were used - a mesocosm laboratory incubation, a transplant experiment and in situ gas flux measurements. The laboratory incubation studied the response of peat samples from temperate (Velké Dářko, Czech Republic) and boreal (Stor Åmyran, Sweden) zone to a temperature increase, water table decrease and their combination. Today, the warmer site exhibits ~14 times higher CH4 production potential than the colder site (28 mg m-2 hr-1 at VD, and 2 mg m-2 hr-1 at SA). Both sites respond differently to temperature increases. Changes in methane production were up to 9 fold due to different temperatures. A gradual decrease of water table level from 2 to 14 cm below the peat surface had a much stronger effect, VD exhibited a decrease in methane...

A contaminação de equipamentos e materiais hospitalares por microrganismos potencialmente infecciosos e altamente resistentes aos antibióticos incitam grupos de pesquisa e industrias ao redor do mundo a produzir novos materiais, e que estes possuam propriedades capazes de inibir ou eliminar (quase que completamente) a permanência desses patógenos sobre sua superfície. O objetivo deste trabalho foi avaliar a citotoxicidade da liga níquel-berílio quando em contato com as cepas bacterianas de Staphylococcus aureus (ATCC 25932), Staphylococcus epidermidis (ATCC 12228), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (amostra clínica) e Escherichia coli (ATCC 11775), após diferentes períodos de incubação, e em contato com a linhagem celular NCTC Clone 929, célula de tecido conectivo de camundongo. Para realização destes ensaios, foram confeccionados corpos de prova da liga níquel-berílio, com aproximadamente 10,0 mm e diâmetro e 3,0 mm de espessura. Para metodologia de citotoxicidade as células bacterianas preparou-se um inóculo bacteriano de 109 Unidades Formadoras de Colônia por mililitro. Para cada bactéria, um inóculo bacteriano foi preparado e deste, 40 &#956l foram aplicados em um swab estéril e espalhado no corpo de prova, onde foram introduzidos em placas de Petri, deixados a temperatura 20°C, por diferentes períodos de exposição (1, 3, 6, 9, 12, 18, 24 e 72 horas). Este teste foi realizado em triplicata. Após cada período de tempo, os corpos de prova eram pressionados contra o meio de cultura Agar Mueller-Hinton, em dez diferentes pontos da placa. O método de difusão em Agar foi utilizado para verificar a citotoxicidade da liga níquel-berílio à linhagem celular NCTC clone 929. Os resultados obtidos demonstram uma maior resistência a liga níquel-berílio das bactérias gram-positivas (S. aureus e S. epidermidis) quando comparadas com as gram-negativas (P. aeruginosa, K. pneumonia e E. coli). Destas últimas citadas, a E. coli foi a única que sobreviveu até a sexta hora de exposição, quando em contato de uma hora com o corpo de prova. Todavia, os S. aureus e S. epidermidis foram capazes de resistir até a décima segunda hora em contato com a liga níquel-berílio. Contudo, a partir deste período de incubação, nem mesmo os estafilococos toleraram a presença desses íons. Quando analisados os resultados de citotoxicidade, a liga não apresentou qualquer efeito citotóxico as células NCTC clone 929, sendo classificadas como índice de zona (IZ) zero. Os dados obtidos demonstram que a liga possui propriedades antibacteriana contra as células bacterianas testadas e que não possui nenhum efeito tóxico à linhagem celular NCTC clone 929. Além disso, a liga NiBe mostrou-se mais citotóxica contra as bactérias gram-negativas. / The contamination of equipment and hospital supplies for potentially infectious microorganisms and highly resistant to antibiotics encourage research groups and industries around the world to produce new materiais, and they have properties able to inhibit or eliminate (almost completely) to stay these pathogens on its surface. The objective of this study was to evaluate the cytotoxicity of nickel-beryllium alloy when in contact with the bacterial strains of Staphylococcus aureus (ATCC 25932), Staphylococcus epidermidis (ATCC 12228), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (clinical sample) and Escherichia coli (ATCC 11775), after different periods of incubation, and in contact with the cell line NCTC Clone 929, connective tissue of mouse cell. For these assays were prepared coupons of nickel-beryllium alloy, with approximately 10.0 mm and diameter and 3.0 mm thick. For cytotoxicity methodology bacterial cells prepared in a bacterial inoculum of 109 Colony-Forming Units per milliliter. For each bacterium, a bacterial inoculum was prepared and this, 40 &#956l were applied in a sterile swab and spread in the coupons, which were introduced in Petri dishes left at 20°C temperature, for different exposure times (1, 3, 6, 9, 12, 18, 24 and 72 hours). This test was performed in triplicate. After each time period, the samples were pressed against the culture medium Mueller-Hinton Agar at ten different points of the plate. The agar diffusion method was used to assess the cytotoxicity of nickel-beryllium alloy to clone cell line NCTC 929. The results show a greater resistance to nickel-beryllium alloy of gram-positive bacteria (S. aureus and S. epidermidis) compared to gram-negative (Pseudomonas aeruginosa, K. pneumoniae and E. coli). Of the latter mentioned, E. coli was the only one that survived until the sixth hour of exposure when contact an hour with the alloy. However, S. aureus and S. epidermidis were able to hold out until the twelfth time in contact with nickel-beryllium alloy. However, from this incubation period, even staphylococci tolerated the presence of these ions. When analyzed the results of cytotoxicity, the alloy showed no cytotoxic effect the NCTC clone 929 cells, are classified as zone index (IZ) zero. The data obtained show that the alloy possesses antibacterial properties against the tested bacterial cells and has no toxic effect on the cell line NCTC clone 929. Furthermore, \'Ni\'\'Be\' alloy was more cytotoxic against gram-negative bacteria.

LE 8B PRODUIT DANS LE COEUR DU SOLEIL A TRAVERS LA REACTION 7BE(P,) 8B EST LA SOURCE MAJEURE SINON UNIQUE DES NEUTRINOS DE HAUTES ENERGIES DETECTES DANS LA PLUPART DES EXPERIENCES DE DETECTION DES NEUTRINOS SOLAIRES, EXCEPTE GALLEX ET SAGE. CES EXPERIENCES ONT TOUTES MESURE UN FLUX DE NEUTRINOS INFERIEUR A CELUI PREDIT PAR LES MODELES SOLAIRES. PLUSIEURS EXPLICATIONS ONT ALORS ETE INVOQUEES POUR TENTER DE COMPRENDRE CE DEFICIT MAIS TOUTES NECESSITENT UNE CONNAISSANCE PRECISE DE LA VALEUR DE LA SECTION EFFICACE DE LA REACTION 7BE(P,) 8B, PUISQUE LE FLUX DES NEUTRINOS DU 8B EST DIRECTEMENT PROPORTIONNEL A CETTE DERNIERE. LA MESURE DIRECTE DE LA SECTION EFFICACE DE CETTE REACTION A L'ENERGIE SOLAIRE EST IMPOSSIBLE A CAUSE DE SA TRES FAIBLE VALEUR (DE L'ORDRE DU FEMTOBARN). POUR CONTOURNER CE PROBLEME, LES SECTIONS EFFICACES SONT MESUREES A PLUS HAUTE ENERGIE PUIS EXTRAPOLEES A L'ENERGIE SOLAIRE EN UTILISANT UNE DEPENDANCE EN ENERGIE THEORIQUE. LES SIX DETERMINATIONS EXPERIMENTALES PRECEDENTES DE LA SECTION EFFICACE SE DIVISAIENT EN DEUX GROUPES BIEN DISTINCTS PRESENTANT DES ECARTS DE L'ORDRE DE 30%, CE QUI IMPLIQUAIT UNE INCERTITUDE DU MEME ORDRE SUR LE FLUX DES NEUTRINOS DE HAUTES ENERGIES. REMESURER AVEC UNE MEILLEURE PRECISION LA SECTION EFFICACE DE CETTE REACTION EST DONC APPARU TRES IMPORTANT. DANS UN PREMIER TEMPS, NOUS AVONS EFFECTUE DES MESURES DIRECTES DE LA SECTION EFFICACE DE CETTE REACTION DANS LA GAMME D'ENERGIE COMPRISE ENTRE 0.35 ET 1.4 MEV (CM). CES EXPERIENCES ONT FAIT L'OBJET D'UNE MESURE PRECISE DE CHACUN DES PARAMETRES INTERVENANT DANS LA DETERMINATION DE LA SECTION EFFICACE. DANS UN SECOND TEMPS, NOUS AVONS ENTREPRIS DES MESURES DE LA SECTION EFFICACE AUPRES DE L'ACCELERATEUR PAPAP, A 185.8 KEV, 134.7 KEV ET 111.7 KEV, L'ENERGIE DANS LE CENTRE DE MASSE LA PLUS BASSE JAMAIS ATTEINTE A CE JOUR. LES RESULTATS SONT EN EXCELLENT ACCORD AVEC CEUX OBTENUS A PLUS HAUTES ENERGIES. LA VALEUR TROUVEE POUR LE FACTEUR ASTROPHYSIQUE S 1 7(0), PAR L'EXTRAPOLATION DE NOS DONNEES EST EGALE A 19.21.3 EV-B, CE QUI ENTRAINE UNE REDUCTION SENSIBLE DE L'INCERTITUDE SUR LE FLUX DES NEUTRINOS DE HAUTE ENERGIE DU 8B.