Apparent stress-strain relationships in experimental equipment where magnetorheological fluids operate under compression mode

Abstract: This paper presents an experimental investigation of two different magnetorheological ( MR) fluids, namely, water-based and hydrocarbon-based MR fluids in compression mode under various applied currents. Finite element method magnetics was used to predict the magnetic field distribution inside the MR fluids generated by a coil. A test rig was constructed where the MR fluid was sandwiched between two flat surfaces. During the compression, the upper surface was moved towards the lower surface in a vertical direction. Stress-strain relationships were obtained for arrangements of equipment where each type of fluid was involved, using compression test equipment. The apparent compressive stress was found to be increased with the increase in magnetic field strength. In addition, the apparent compressive stress of the water-based MR fluid showed a response to the compressive strain of greater magnitude. However, during the compression process, the hydrocarbon-based MR fluid appeared to show a unique behaviour where an abrupt pressure drop was discovered in a region where the apparent compressive stress would be expected to increase steadily. The conclusion is drawn that the apparent compressive stress of MR fluids is influenced strongly by the nature of the carrier fluid and by the magnitude of the applied current

Meningoencefalite chagásica em AIDS simulando metástases cerebrais: relato de caso

A case of Chagas' meningoencephalitis in a 47 year-old patient with AIDS is presented. The diagnosis was established by examination of the cerebrospinal fluid which showed the presence of Trypanosoma cruzi. CT-scan revealed multiple cerebral lesions which only became evident by contrast administration. A second CT after 13 days showed a severe evolution with displacement of the midline structures leading to the patient's death. This case, as well as other case reports published, has shown the fulminant evolution of Chagas' meningoencephalitis in AIDS patients and the importance of cerebrospinal fluid examination for the diagnosis.Apresentamos um caso de meningoencefalite chagásica em paciente de 47 anos com AIDS. O diagnóstico foi feito pelo encontro do Trypanosoma cruzi no LCR. A tomografia de crânio mostrou múltiplas lesões cerebrais que se tornaram evidentes apenas na fase com contraste. Uma segunda tomografia após 13 dias mostrou evolução tipo tumoral com intenso efeito de massa e acentuado desvio de estruturas da linha média, levando o paciente ao óbito. Este caso e outros da literatura mostram a evolução fulminante da meningoencefalite chagásica em pacientes com AIDS e a importância do exame de LCR para o diagnóstico.Escola Paulista de Medicina Department of NeurologyHospital Albert Einstein Division of NeuroimagingUNIFESP, EPM, Department of NeurologySciEL

The performance of magnetorheological fluid in squeeze mode

Abstract: In magnetorheological (MR) fluid, the rheological properties can be changed in a controlled way, the changes being reversible and dependent on the strength of the magnetic field. The fluids have potentially beneficial applications when placed in various geometrical arrangements. The squeeze mode is a geometrical arrangement where two flat parallel solid surfaces, facing each other, are pushed towards each other by an external force operating at right angles to the surfaces. The liquid initially in the gap between them is free to move away from this increasingly small gap, and it does so by flowing parallel to the surfaces, and collecting in a region where it is no longer in the gap between them. The performance of an MR fluid in compression ( squeeze) mode has been studied with the magnetic field being generated by a coil carrying different magnitudes of DC electrical current. A test rig was designed to perform this operation with the flat surfaces being horizontal and being pushed together in a vertical direction and the liquid being forced to move in all directions in a horizontal plane. The rig operated by decreasing the size of the gap at a constant rate. For each trial the current in the coil was kept constant and the instantaneous compressive force was recorded. When plotting compressive stress against compressive strain for each trial, the slope of the curve was found to be larger in general when the current was larger. This was an expected result; however, the behaviour is more complicated than this. For a significant range of values of compressive strain, the slope falls to zero, so that the compressive stress shows no increase during this period while the compressive strain continues to increase. The details of this behaviour are strongly dependent on the initial size of the ga

External validation of the preoperative Karakiewicz nomogram in a large multicentre series of patients with renal cell carcinoma

To perform a formal external validation of the preoperative Karakiewicz nomogram (KN) for the prediction of cancer-specific survival (CSS) using a large series of surgically treated patients diagnosed with organ-confined or metastatic renal cell carcinoma (RCC).Patient population originated from a series of retrospectively gathered cases that underwent radical or partial nephrectomy between years 1995 and 2007 for suspicion of kidney cancer. The original Cox coefficients were used to generate the predicted risk of CSS at 1, 2, 5, and 10 years following surgery and compared to the observed risk of CSS in the current population. External validation was quantified using measures of predictive accuracy, defined as model discrimination and calibration.A total of 3,374 patients were identified. Relative to the original development cohort, the current sample population had a larger proportion of patients with localized (40.0 vs. 26.3 \%, P < 0.001) and non-metastatic (92.2 vs. 88.1 \%, P = 0.03) disease at presentation. Model discrimination for the prediction of CSS was 87.8 \% (95 \% CI, 84.4-91.4) at 1 year, 87.0 \% (95 \% CI, 84.4-89.5) at 2 years, 84.7 \% (95 \% CI, 82.3-87.1) at 5 years, and 85.9 \% (95 \% CI, 83.2-88.6) at 10 years. The relationship between predicted and observed CSS risk was adequate in the calibration plot.The use of the KN for the prediction of CSS in patients diagnosed with renal cell carcinoma was validated in the current study. In consequence, this tool may be recommended for routine clinical counseling in patients with various stages of RCC in the preoperative setting