360 research outputs found

    Load carrying capacity of a heterogeneous surface bearing

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    It has been shown before that liquids can slip at a solid boundary, which prompted the idea that parallel-surfaces bearings can be achieved just by alternating slip and non-slip regions in the direction of fluid flow. The amount of slip at the wall depends on the surface tension at the liquidā€“solid interface, which in turn depends on the chemical state of the surface and its roughness. In the present study a heterogeneous surface was obtained by coating half of a circular glass disc with a coating repellant to glycerol. A rotating glass disc was placed at a known/calibrated distance and the gap was filled with glycerol. With the mobile surface moving from the direction of slip to non-slip region it can be theoretically shown that a pressure build up can be achieved. The pressure gradient in the two regions is constant, similar to that in a Rayleigh step bearing, with the maximum pressure at the separation line. The heterogeneous disc was placed on a holder supported by a load cell thus the force generated by this pressure increase can be measured accurately. Tests were carried out at different sliding speeds and gaps and the load carried was measured and subsequently compared with theoretical calculations. This allowed the slip coefficient to be evaluated

    The behaviour of lubricated EHD contacts subjected to vibrations

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    Machine components containing contacts working in elastohydrodynamic (EHD) conditions are often subjected to vibrations. These may be originated from the mechanism or machine the contact is part of, the surrounding environment and within the contact itself. The influence of vibrations upon the behaviour of elastohydrodynamic films has been studied experimentally in a number of papers, but a comprehensive study of the effect of the parameters of the oscillatory motion upon the film thickness has not been carried out yet. In this study the authors evaluate the effect of the frequency of the oscillatory motion upon the EHD film thickness. Optical interferometry is used to measure lubricant film thickness in a ball-on-flat disc arrangement. A high ā€“ speed camera records the interferometric images for later analysis and conversion into film thickness maps. The disc runs at a constant angular velocity while the ball is driven by the traction forces developed in the EHD film. In steady state conditions, this would ensure pure rolling conditions, however in the present investigation the ball is subjected to harmonic vibrations in a direction perpendicular to the plane of the film. The contact under study is lubricated by basic oils and the temperature is kept at a constant value of 60Ā°C. The aim of this paper is to understand how vibrations influence the lubricant film formation

    Effect of a Fatty Acid Additive on the Kinetic Friction and Stiction of Confined Liquid Lubricants

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    Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.Apresentamos neste texto parte das produƧƵes de pesquisa que acompanhou a construĆ§Ć£o de corpos inseridos num Centro de AtenĆ§Ć£o Psicossocial para Ɓlcool e outras Drogas, em cidade do nordeste brasileiro, focando de modo mais acentuado em arranjos de masculinidades. Especial atenĆ§Ć£o Ć© dada Ć  tensĆ£o entre normalizaĆ§Ć£o de corpos e tentativas de (re)existĆŖncias. A argumentaĆ§Ć£o se desenvolve no campo da saĆŗde pĆŗblica, em particular o da saĆŗde mental, e alicerƧada nos estudos de gĆŖnero e sexualidade. A produĆ§Ć£o de dados se valeu de observaƧƵes registradas em diĆ”rio de campo, acompanhamento itinerante, composiĆ§Ć£o de um coletivo de pesquisa, entrevistas, grupos focais em que, dentre outras coisas, se discutia trechos de diĆ”rios de campo, rodas de conversa e oficinas com profissionais e usuĆ”ri*s. A aposta metodolĆ³gica foi a de forjar um modo de narrar coletivo que agenciasse experimentaĆ§Ć£o e desaprendizagens corporais, junto a modos de produzir cuidado em saĆŗde e de fazer pesquisa.The paper presents part of the research productions that accompanied the construction of bodies inserted in a Psychosocial Care Center for Alcohol and Other Drugs (CAPS-AD) of a city in the northern region of Brasil, focusing more sharply on masculinities arrangements. Special attention is given to the tension between normalized bodies and attempts at resistance and (re) exist. The argument is in the field of public health, particularly mental health, and rooted in gender and sexuality studies. The data production methodology made use of observations recorded in a diary, itinerant follow-up of a collective of research, interviews, focus groups where, among other things, was discussed diary topics, conversation circles and workshops. The attempt was to produce a way of collective narrating strategy, combining up experience and body (un)learn well as ways of producing health care and doing research

    An analytical approach for prediction of elastohydrodynamic friction with inlet shear heating and starvation

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    An analytical friction model is presented, predicting the coefficient of friction in elastohydrodynamic (EHD) contacts. Three fully formulated SAE 75W-90 axle lubricants are examined. The effect of inlet shear heating (ISH) and starvation is accounted for in the developed friction model. The film thickness and the predicted friction are compared with experimental measurements obtained through optical interferometry and use of a mini traction machine. The results indicate the significant contribution of ISH and starvation on both the film thickness and coefficient of friction. A strong interaction between those two phenomena is also demonstrated, along with their individual and combined contribution on the EHD friction

    The synergetic effects of surface texturing and MoDDP additive applied to ball-on-disk friction subject to both flooded and starved lubrication conditions

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    This paper reports a novel work on the synergetic effects of microscale surface texturing and lubricant friction modifier additive of molybdenum dialkyldithiophosphate (MoDDP) subject to both flooded and starved lubrication conditions. The experiments were performed on reciprocating ball-on-disk friction in GTL8 base oil with and without MoDDP. In the flooded lubrication condition, the test results demonstrated that the presence of the MoDDP additive contributed to lower friction coefficients, and also more pronounced effect of surface textures on friction than in the case of the bare base oil. In the starved lubrication experiments, textured and texture-free surfaces in the oils with and without MoDDP additive were tested until an abrupt rising of friction coefficient was detected. The results showed that the magnitude of friction coefficient before terminating each test was the almost same for various tests, while the endurance time in different test conditions was significantly different. The textured surface exhibited longer endurance time than the texture-free surface, especially when the MoDDP additive was used. The mechanism of the synergetic effects of surface textures and MoDDP additive has been discussed based on the experimental observations in the following sections. This study provides a new idea for the application of surface texture in boundary lubrication when lubricant additive is contained in the lubricating oils

    Antifungal Activity of Microbial Secondary Metabolites

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    Secondary metabolites are well known for their ability to impede other microorganisms. Reanalysis of a screen of natural products using the Caenorhabditis elegans-Candida albicans infection model identified twelve microbial secondary metabolites capable of conferring an increase in survival to infected nematodes. In this screen, the two compound treatments conferring the highest survival rates were members of the epipolythiodioxopiperazine (ETP) family of fungal secondary metabolites, acetylgliotoxin and a derivative of hyalodendrin. The abundance of fungal secondary metabolites indentified in this screen prompted further studies investigating the interaction between opportunistic pathogenic fungi and Aspergillus fumigatus, because of the ability of the fungus to produce a plethora of secondary metabolites, including the well studied ETP gliotoxin. We found that cell-free supernatant of A. fumigatus was able to inhibit the growth of Candida albicans through the production of a secreted product. Comparative studies between a wild-type and an A. fumigatus Ī”gliP strain unable to synthesize gliotoxin demonstrate that this secondary metabolite is the major factor responsible for the inhibition. Although toxic to organisms, gliotoxin conferred an increase in survival to C. albicans-infected C. elegans in a dose dependent manner. As A. fumigatus produces gliotoxin in vivo, we propose that in addition to being a virulence factor, gliotoxin may also provide an advantage to A. fumigatus when infecting a host that harbors other opportunistic fungi

    Genes Differentially Expressed in Conidia and Hyphae of Aspergillus fumigatus upon Exposure to Human Neutrophils

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    Aspergillus fumigatus is the most common etiologic agent of invasive aspergillosis in immunocompromised patients. Several studies have addressed the mechanism involved in host defense but only few have investigated the pathogen's response to attack by the host cells. To our knowledge, this is the first study that investigates the genes differentially expressed in conidia vs hyphae of A. fumigatus in response to neutrophils from healthy donors as well as from those with chronic granulomatous disease (CGD) which are defective in the production of reactive oxygen species.Transcriptional profiles of conidia and hyphae exposed to neutrophils, either from normal donors or from CGD patients, were obtained by using the genome-wide microarray. Upon exposure to either normal or CGD neutrophils, 244 genes were up-regulated in conidia but not in hyphae. Several of these genes are involved in the degradation of fatty acids, peroxisome function and the glyoxylate cycle which suggests that conidia exposed to neutrophils reprogram their metabolism to adjust to the host environment. In addition, the mRNA levels of four genes encoding proteins putatively involved in iron/copper assimilation were found to be higher in conidia and hyphae exposed to normal neutrophils compared to those exposed to CGD neutrophils. Deletants in several of the differentially expressed genes showed phenotypes related to the proposed functions, i.e. deletants of genes involved in fatty acid catabolism showed defective growth on fatty acids and the deletants of iron/copper assimilation showed higher sensitivity to the oxidative agent menadione. None of these deletants, however, showed reduced resistance to neutrophil attack.This work reveals the complex response of the fungus to leukocytes, one of the major host factors involved in antifungal defense, and identifies fungal genes that may be involved in establishing or prolonging infections in humans
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