576 resultados para Grinding (comminution)


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This work attempts to bring critical insights into the electromagnetic shielding efficiency in polymeric nanocomposites with respect to the particle size of magnetic nanoparticles added along with or without a conductive inclusion. To gain insight, various Ni-Fe (NixFe1-x; x = 10, 20, 40; Ni: nickel, Fe: iron) alloys were prepared by a vacuum arc melting process and different particle sizes were then achieved by a controlled grinding process for different time scales. Poly(vinylidene fluoride), PVDF based composites involving different particle sizes of the Ni-Fe alloy were prepared with or without multiwall carbon nanotubes (MWNTs) by a wet grinding approach. The Ni-Fe particles were thoroughly characterized with respect to their microstructure and magnetization; and the electromagnetic (EM) shielding efficiency (SE) of the resulting composites was obtained from the scattering parameters using a vector network analyzer in a broad range of frequencies. The saturation magnetization of Ni-Fe nanoparticles and the bulk electrical conductivity of PVDF/Ni-Fe composites scaled with increasing particle size of NiFe. Interestingly, the PVDF/Ni-Fe/MWNT composites showed a different trend where the bulk electrical conductivity and SE scaled with decreasing particle size of the Ni-Fe alloy. A total SE of similar to 35 dB was achieved with 50 wt% of Ni60Fe40 and 3 wt% MWNTs. More interestingly, the PVDF/Ni-Fe composites shielded the EM waves mostly by reflection whereas, the PVDF/Ni-Fe/MWNT shielded mostly by absorption. A minimum reflection loss of similar to 58 dB was achieved in the PVDF/Ni-Fe/MWNT composites in the X-band (8-12 GHz) for a particular size of Ni-Fe alloy nanoparticles. This study brings new insights into the EM shielding efficiency in PVDF/magnetic nanoparticle based composites in the presence and absence of conducting inclusion.

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The objective of the present study is to assess the capabilities of a recently developed mechanism-based model for inelastic deformation and damage in structural ceramics. In addition to conventional lattice plasticity, the model accounts for microcrack growth and coalescence as well as granular flow following comminution. The assessment is made through a coupled experimental/computational study of the indentation response of a commercial armor ceramic. The experiments include examinations of subsurface damage zones along with measurements of residual surface profiles and residual near-surface stresses. Extensive finite element computations are conducted in parallel. Comparisons between experiment and simulation indicate that the most discriminating metric in the assessment is the spatial extent of subsurface damage following indentation. Residual stresses provide additional validation. In contrast, surface profiles of indents are dictated largely by lattice plasticity and thus provide minimal additional insight into the inelastic deformation resulting from microcracking or granular flow. A satisfactory level of correlation is obtained using property values that are either measured directly or estimated from physically based arguments, without undue reliance on adjustable (nonphysical) parameters. © 2011 The American Ceramic Society.

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For fully three decades there has been an almost steady decline in Maryland's oyster production... are alarmed for its future. Reasons for decline, data supplied,importance of brood oysters and clutch replenishment. Problems of warm weather and bacterial activity as well as tongs grinding the bottom. Conflicts in canning of early season oysters and late season crops like tomatoes. (PDF contains 16 pages)

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Techniques are described for preparing acetate peels of sectioned valves of ocean quahogs, Arctica islandica, for age determinations. The respective sequence of preparation begins by sectioning left valves oriented to include a single hinge tooth, bleaching to remove the heavy periostracum, embedding the valves in an epoxy resin, grinding and polishing the embedments to a high luster, etching the exposed cut valve surfaces, and applying sheet acetate with acetone. Annuli are clearly defined relative to growth increments in the peel preparations for all sizes and ages of ocean quahogs. (PDF file contains12 pages.)

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O objeto de estudo foi o preparo e a administração de medicamentos por cateter pela enfermagem em pacientes que recebem nutrição enteral. O objetivo geral foi investigar o padrão de preparo e administração dos medicamentos por cateter em pacientes que recebem nutrição enteral concomitante. Os objetivos específicos foram apresentar o perfil dos medicamentos preparados e administrados de acordo com a possibilidade de serem administrados por cateter enteral e avaliar o tipo e a freqüência de erros que ocorrem no preparo e administração de medicamentos por cateter. Tratou-se de uma pesquisa com desenho transversal de natureza observacional, sem modelo de intervenção. Foi desenvolvida em um hospital do Rio de Janeiro onde foram observados técnicos de enfermagem preparando e administrando medicamentos por cateter na Unidade de Terapia Intensiva. Foram observadas 350 doses de medicamentos sendo preparados e administrados. Os grupos de medicamentos prevalentes foram os que agem no Sistema Cardiovascular Renal com 164 doses (46,80%), seguido pelos que agem no Sistema Respiratório e Sangue com 12,85% e 12,56% respectivamente. Foram encontrados 19 medicamentos diferentes do primeiro grupo, dois no segundo e cinco no terceiro. As categorias de erro no preparo foram trituração, diluição e misturas. Encontrou-se uma taxa média de 67,71% no preparo de medicamentos. Comprimidos simples foram preparados errados em 72,54% das doses, e todos os comprimidos revestidos e de liberação prolongada foram triturados indevidamente entre sólidos a categoria de erro prevalente foi trituração com 45,47%, preparar misturando medicamentos foi um erro encontrado em quase 40% das doses de medicamentos sólidos. A trituração insuficiente ocorreu em 73,33% das doses de ácido fólico, do cloridrato de amiodarona (58,97%) e bromoprida (50,00%). A mistura com outros medicamentos ocorreu em 66,66% das doses de bromoprida, de besilato de anlodipina (53,33%), bamifilina (43,47%), ácido fólico (40,00%) e ácido acetilsalicílico (33,33%). Os erros na administração foram ausência de pausa e manejo indevido do cateter. A taxa média de erros na administração foi de 32,64%, distribuídas entre 17,14% para pausa e 48,14% para manejo do cateter. A ausência de lavagem do cateter antes foi o erro mais comum e o mais incomum foi não lavar o cateter após a administração. Os medicamentos mais envolvidos em erros na administração foram: cloridrato de amiodarona (n=39), captopril (n=33), cloridrato de hidralazina (n=7), levotiroxina sódica (n=7). Com relação à lavagem dos cateteres antes, ela não ocorreu em 330 doses de medicamentos. O preparo e administração inadequados de medicamentos podem levar à perdas na biodisponibilidade, diminuição do nível sérico e riscos de intoxicações para o paciente. Preparar e administrar medicamentos são procedimentos comuns, porém apresentou altas taxas de erros, o que talvez reflita pouco conhecimento desses profissionais sobre as boas práticas da terapia medicamentosa. Constata-se a necessidade de maior investimento de todos os profissionais envolvidos, médicos, enfermeiros e farmacêuticos nas questões que envolvam a segurança com medicamentos assim como repensar o processo de trabalho da enfermagem.

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Shockwave lithotripsy is a noninvasive medical procedure wherein shockwaves are repeatedly focused at the location of kidney stones in order to pulverize them. Stone comminution is thought to be the product of two mechanisms: the propagation of stress waves within the stone and cavitation erosion. However, the latter mechanism has also been implicated in vascular injury. In the present work, shock-induced bubble collapse is studied in order to understand the role that it might play in inducing vascular injury. A high-order accurate, shock- and interface-capturing numerical scheme is developed to simulate the three-dimensional collapse of the bubble in both the free-field and inside a vessel phantom. The primary contributions of the numerical study are the characterization of the shock-bubble and shock-bubble-vessel interactions across a large parameter space that includes clinical shockwave lithotripsy pressure amplitudes, problem geometry and tissue viscoelasticity, and the subsequent correlation of these interactions to vascular injury. Specifically, measurements of the vessel wall pressures and displacements, as well as the finite strains in the fluid surrounding the bubble, are utilized with available experiments in tissue to evaluate damage potential. Estimates are made of the smallest injurious bubbles in the microvasculature during both the collapse and jetting phases of the bubble's life cycle. The present results suggest that bubbles larger than 1 μm in diameter could rupture blood vessels under clinical SWL conditions.

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[ES]Este trabajo pretende analizar la influencia que tiene la longitud de corte elegida y el filtro empleado en la medida de la rugosidad. Se realizan medidas de rugosidad en tres probetas que han sido sometidas a diferentes procesos de fabricación (fresado, rectificado y electroerosión). Además, se utilizan tres instrumentos diferentes para la medición. Tras realizar las medidas, se comparan los resultados y se extraen las conclusiones

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散粒磨料研磨与固着磨料研磨是光学研磨加工过程中的两种主要手段,但两者材料去除的机制不同。目前针对高功率固体激光装置中的主要工作物质——磷酸盐激光钕玻璃的亚表面缺陷(SSD)研究相对较少,因此在实验的基础上,通过系统地研究固着磨料对磷酸盐激光钕玻璃的研磨工艺过程,分析了多种因素,如磨料粒径、载荷大小、机床转速,以及结合剂材料与冷却液等对钕玻璃亚表面缺陷形成的影响,并与散粒磨料研磨工艺所产生的亚表面缺陷进行了比较,对关键工艺参数进行定量,为高质量钕玻璃制造工艺的选型以及进一步优化亚表面缺陷提供了重要的参考数据。

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We present a destructive method for detecting and measuring subsurface damage of Nd-doped phosphate glasses. An instrument based on the dimple method - a destructive method - was developed. Subsurface damage depth produced in each fabrication procedure was obtained. We extend the surface roughness-subsurface damage relation to Nd-doped phosphate glasses. The constant ratio of subsurface damage and surface roughness was obtained as well. We also analyse the relation of abrasive size and subsurface damage experimentally. From a measurement of the surface roughness or abrasive size, one can obtain an accurate estimate of the damage layer thickness that must be eliminated by polishing or subsequent grinding operations. (C) 2007 Elsevier GmbH. All rights reserved.

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系统地研究了光学研磨过程中,磨料粒径、载荷大小以及机床转速对钕玻璃表面及亚表面损伤的影响。结果表明,机床转速和载荷基本不改变材料表面粗糙度,而较大载荷或较低机床转速产生较大的亚表面缺陷,表面粗糙度和亚表面缺陷缺陷深度基本与最大磨料粒径呈正比,载荷增倍使亚表面缺陷与表面粗糙度的常数比值增加0.05。研究结果为钕玻璃加工工艺改进提供了参考依据。

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[ES]Cada vez más industrias como las aeronáuticas o espaciales buscan nuevos materiales con excelentes propiedades hoy en día. Sin embargo, estos materiales suelen presentar hándicaps como por ejemplo su maquinabilidad. Mediante este TFG, se estudiará el rectificado de uno de estos materiales, el Inconel 718. Para conseguir los objetivos, este TFG se elaborará en varias etapas. Primero es necesario conocer las propiedades del Inconel 718 y analizarlas. Tras esto, se realizará el mismo proceso con el proceso de rectificado, haciendo hincapié en el desgaste de muelas; para finalmente, encontrar soluciones y alternativas que optimicen el proceso de rectificado. La ejecución de este TFG permitirá comprender y minimizar el desgaste de las muelas durante el proceso de rectificado.

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Schinus terebinthifolius Raddi (Anacardiaceae) é uma espécie nativa da América do Sul com grande distribuição geográfica e muito comum em áreas de restinga. Sua grande plasticidade ecológica e boa interação biótica a torna espécie-chave na restauração de ambientes, porém, sua dominância pode estar relacionada à liberação de compostos alelopáticos. O objetivo do estudo foi avaliar o potencial alelopático dos extratos aquosos e óleos essenciais de folhas de Schinus terebinthifolius nas diferentes estações do ano sobre espécies-alvo nativas da restinga (Cereus fernambucensis, Erythroxylum ovalofolium, Pilosocereus arrabidae), uma espécie agrícola (Lactuca sativa) e nela própria (autoalelopatia). Para isso, suas folhas foram coletadas sazonalmente na restinga de Massambaba para o preparo dos extratos aquosos e extração dos óleos essenciais. Os extratos aquosos foram obtidos através da secagem das folhas a 60 C, trituração em liquidificador, diluição em água destilada e filtração, obtendo as concentrações de 5, 10, 15 e 20%. As extrações dos óleos foram realizadas através da hidrodestilação de 300 g de folhas frescas. A análise da composição dos óleos essenciais foi realizada através de cromatografia gasosa utilizando fibra SPME. O efeito fitotóxico foi avaliado nas espécies-alvo através da porcentagem de germinação, velocidade de germinação, crescimento aéreo e radicular, condutividade elétrica e massa seca. O efeito alelopático dos extratos aquosos foi observado em todas as espécies-alvo, principalmente sobre as espécies nativas. Esse efeito variou nas estações do ano de forma dose-dependente e espécie-específica. Os óleos essenciais de S. terebinthifolius também foram capazes de inibir a germinação e crescimento das espécies-alvo, e, da mesma forma que os extratos aquosos, esses efeitos variaram nas estações do ano e para cada espécie. Sugere-se que essas diferenças estejam relacionadas às fenofases de S. terebinthifolius e condições ambientais da restinga. Esse efeito fitotóxico, se comprovado em campo, pode restringir a utilização de S. terebinthifolius na restauração de ambientes.

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Abrasion by hard particles is responsible for wear in many practical situations, but can also be used constructively in grinding and polishing processes. A brief overview of abrasion is presented, followed by an historical survey of polishing and a discussion of laboratory abrasion test methods.

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Feeding habits of many animals have been used widely in animal classifications. This is so, because the type of diet an organism requires demands structural specialisation which will utilise the available resource. Many animals may however have many structural modifications to enable them to be described as omnivourous or generalised feeders such as H. empodisma and H. riponianus (GREENWOOD 1960) which may show varying degrees of structural and adaptational intermediacy between two trophic groups. Generally, however, the diet of many animals including fish changes as the animal grow larger. The change in structural modifications is usually correlated with changes in the diet. In fishes the change may involve change from tricuspid to biscuspid and finally to unicuspid type of teeth. The degree of modification in the structure depends on the diet, thus Haplochromis that feeds on soft tissues of snails only requires modifications in oral dentition while Haplochromis that feeds on both soft tissues and shells of snails require modification in the lower pharyngeal bone for grinding purposes. Other modifications connected with food utilisation may be located in the alimentary canal. (I) The fish species that are commercially exploited are Protopterus aethiopicus, Clarias mossambicus, Tilapia esculenta, Tilapia amphimelas and Tilapia hybrids. The other fish species present in the lake but not commercially exploited are: Gnathonemus sp. Alestes sp. Labeo sp., Barbus paludinoses, Barbus jacksoni, Barbus lineomaculatus, Barbus regersi, Leptogrlanis sp., Schilbe sp., Haplochromis spp. and Hemihaplochromis sp. (2) Protopterus sp. and Clarias sp. are mostly caught with hooks on long lines. There has been a steady increase in number of hooks on the lake. Since the stocks of Protopterus and C/arias in the lake have a limit, we should control the number of hooks used by each of the fishermen in order to avoid overharvesting. (3) All the previous studies on Lake Kitangiri fisheries suggested the use of gill nets with mesh size greater than 88.9 mm in order to avoid the capture of immature Ti/apia spp. But if the fishermen are to obtain economic gains from the fishery, the optimum mesh size for use is 88.9 -101.6 mm. (4) The gillnet is a passive gear with very beneficial selective characteristics. Unfortunately the drive-in fishery which exists on Lake Kitangiri more or less destroys the gillnet selectivity characteristics. It is therefore recommended that the beating of water with poles be discouraged and stopped. (5) There is need for provision of stable fishing canoes to replace the unstable bottle palm dug-out canoes which are currently being used and which are very risky to operate. (6) The fish processing facilities on Lake Kitangiri are still inadequate. Most of the fish is sun dried, Since sun drying is very difficult during the rainy season, most fishermen carry out intensive fishing during the dry season, Concentrating most of the fishing effort in anyone season instead of spreading evenly this effort over the whole year could damage the age structure of the exploitable stocks. (7) There are considerable fluctuations in the volume of water of the lake. The feasibility of regulating the water loss through the effluent Sibiti river should be investigated by the Water Development Department. (8) Damming the Sibiti river is an expensive undertaking and therefore, the Rural Development Bank of Tanzania should be asked to assess the economic feasibility of such a project.

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We investigate the relation between the thickness of sapphire substrates and the extraction efficiency of LED. The increasing about 5% was observed in the simulations and experiments when the sapphire thickness changed from 100um to 200um. But the output power increasing is inconspicuous when the thickness is more than 200um. The structure on bottom face of sapphire substrates can enhance the extraction efficiency of GaN-based LED, too. The difference of output power between the flip-chip LED with smooth bottom surface and the LED with roughness bottom surface is about 50%, where only a common sapphire grinding process is used. But for those LEDs grown on patterned sapphire substrate the difference is only about 10%. Another kind of periodic pattern on the bottom of sapphire is fabricated by the dry etch method, and the output of the back-etched LEDs is improved about 50% than a common. case.