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Pressure Load (pressure + load)
Selected AbstractsEngineering investigations on the potentiality of the thermoformability of HDPE charged by wood flours in the thermoforming partPOLYMER ENGINEERING & SCIENCE, Issue 8 2009F. Erchiqui A dynamic finite element method is used to analyze the thermoformability of composites containing wood and a thermoplastic matrix for five different proportions of wood flour. Linear viscoelastic properties can be obtained by small amplitude oscillatory shear tests and the viscoelastic behavior is characterized using the Lodge model. To account for enclosed gas volume, which inflates the thermoplastic composite membrane, a thermodynamic approach is used to express the external work in terms of a closed volume. Pressure load is deduced by thermodynamic law using the Redlich,Kwong gas equation. The Lagrangian method together with the assumption of membrane theory is used in the finite element implementation. In addition, the influence of air flow on thickness and stress and the energy required to form a thin polymeric part in the thermoforming process are analyzed for five different proportions of wood flour in the HDPE material. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Neostigmine and pilocarpine attenuated tumour necrosis factor , expression and cardiac hypertrophy in the heart with pressure overloadEXPERIMENTAL PHYSIOLOGY, Issue 1 2008Jessica Freeling The inflammatory cytokine tumour necrosis factor , (TNF,) is known to be a major factor contributing to cardiac remodelling and dysfunction. Parasympathetic nervous system cholinergic function can inhibit TNF, expression during systemic infection. In the present study, we tested the effects of a cholinesterase inhibitor, neostigmine, and a muscarinic cholinergic agonist, pilocarpine, on cardiac hypertrophy and TNF, levels during pressure overload. Rats with transverse aortic constriction exhibited elevated TNF, protein levels in the heart, increased heart weight to body weight ratios (an index of cardiac hypertrophy) and decreased left ventricular diastolic function. Two weeks of infusion with neostigmine (6 ,g kg,1 day,1) or pilocarpine (0.3 mg kg,1 day,1) significantly reduced cardiac hypertrophy, reduced TNF, levels and elevated interleukin-10 levels in heart tissues, and improved ventricular function in rats with transverse aortic constriction. Neither of these treatments significantly changed ventricular pressure load. Furthermore, in primary cultured neonatal cardiac cells, treatment with pilocarpine attenuated adrenergic agonist phenylephrine-induced increased TNF, expression and [3H]leucine (a marker of protein synthesis) incorporation in the cells. Collectively, both cholinergic agents decreased TNF, levels and attenuated cardiac hypertrophy. Since both agents potentially enhanced cholinergic function, the anti-inflammatory action may be involved in the cardioprotective effect of the treatments with these agents. [source] Constitutive model for quasi-static deformation of metallic sandwich coresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2004Zhenyu Xue Abstract All-metal sandwich construction holds promise for significant improvements in stiffness, strength and blast resistance for built-up plate structures. Analysis of the performance of sandwich plates under various loads, static and dynamic, requires modelling of face sheets and core with some fidelity. While it is possible to model full geometric details of the core for a few selected problems, this is unnecessary and unrealistic for larger complex structures under general loadings. In this paper, a continuum constitutive model is proposed as an alternative means of modelling the core. The constitutive model falls within the framework of a compressible rate-independent, anisotropic elastic,plastic solid. The general form of the model is presented, along with algorithmic aspects of its implementation in a finite element code, and selected problems are solved which benchmark the code against existing codes for limiting cases and which illustrate features specific to compressible cores. Three core geometries (pyramidal truss, folded plate, and square honeycomb) are considered in some detail. The validity of the approach is established by comparing numerical finite element simulations using the model with those obtained by a full three-dimensional meshing of the core geometry for each of the three types of cores for a clamped sandwich plate subject to uniform pressure load. Limitations of the model are also discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] Die shape design optimization of sheet metal stamping process using meshfree methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001Nam Ho Kim Abstract A die shape design sensitivity analysis (DSA) and optimization for a sheet metal stamping process is proposed based on a Lagrangian formulation. A hyperelasticity-based elastoplastic material model is used for the constitutive relation that includes a large deformation effect. The contact condition between a workpiece and a rigid die is imposed through the penalty method with a modified Coulomb friction model. The domain of the workpiece is discretized by a meshfree method. A continuum-based DSA with respect to the rigid die shape parameter is formulated using a design velocity concept. The die shape perturbation has an effect on structural performance through the contact variational form. The effect of the deformation-dependent pressure load to the design sensitivity is discussed. It is shown that the design sensitivity equation uses the same tangent stiffness matrix as the response analysis. The linear design sensitivity equation is solved at each converged load step without the need of iteration, which is quite efficient in computation. The accuracy of sensitivity information is compared to that of the finite difference method with an excellent agreement. A die shape design optimization problem is solved to obtain the desired shape of the workpiece to minimize spring-back effect and to show the feasibility of the proposed method. Copyright © 2001 John Wiley & Sons, Ltd. [source] Surrogate model-based strategy for cryogenic cavitation model validation and sensitivity evaluationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2008Tushar Goel Abstract The study of cavitation dynamics in cryogenic environment has critical implications for the performance and safety of liquid rocket engines, but there is no established method to estimate cavitation-induced loads. To help develop such a computational capability, we employ a multiple-surrogate model-based approach to aid in the model validation and calibration process of a transport-based, homogeneous cryogenic cavitation model. We assess the role of empirical parameters in the cavitation model and uncertainties in material properties via global sensitivity analysis coupled with multiple surrogates including polynomial response surface, radial basis neural network, kriging, and a predicted residual sum of squares-based weighted average surrogate model. The global sensitivity analysis results indicate that the performance of cavitation model is more sensitive to the changes in model parameters than to uncertainties in material properties. Although the impact of uncertainty in temperature-dependent vapor pressure on the predictions seems significant, uncertainty in latent heat influences only temperature field. The influence of wall heat transfer on pressure load is insignificant. We find that slower onset of vapor condensation leads to deviation of the predictions from the experiments. The recalibrated model parameters rectify the importance of evaporation source terms, resulting in significant improvements in pressure predictions. The model parameters need to be adjusted for different fluids, but for a given fluid, they help capture the essential fluid physics with different geometry and operating conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] OIL POLYMERISATION AND FLUID EXPULSION FROM LOW TEMPERATURE, LOW MATURITY, OVERPRESSURED SEDIMENTSJOURNAL OF PETROLEUM GEOLOGY, Issue 3 2008D. D. J. Antia A mechanism for hydrocarbon expulsion from low temperature (T = <20 , 150° C), low maturity (Ro=<0.6), overpressured sediments (clays, shales and enclosed sands) with active hydrocarbon concentration and/or generation is outlined. Low temperature polymerisation of light hydrocarbons (e.g. biogenic methane) is considered to be a potential source for some oils found in association with hydrates (resulting from fluidisation discharges from overpressured zones), and some oils found in shales displaying suppression of vitrinite reflectance. It is observed that low temperature polymerisation will increase the potential pressure load retained within an overpressured zone and increase the overall volume of gas/fluids discharged on pressure release. Field observations, including measured recharge volumes and the fluid discharge volumes through a chimney from an overpressured zone, have been used to produce a triple porosity, poroelastic fluidisation expulsion model which links the discharge volume to pressure loading. The model predicts that expulsion from an active pressure mound will be cyclic and episodic. Published geochemical results from seismic chimneys in the Lower Congo Basin have been reinterpreted using the model to demonstrate that expulsion through a chimney is episodic, and to identify overpressured zones where the dominant fluid is oil and others where the overpressured zone contains both oil and gas. It is suggested that some of the oil in these overpressured zones, currently interpreted as thermogenic, may be derived from the polymerisation of biogenic gas. [source] Left ventricular mass in hypertensive patients with mild-to-moderate reduction of renal functionNEPHROLOGY, Issue 2 2010GIOVANNI CERASOLA ABSTRACT: Aim: Left ventricular hypertrophy (LVH) is an independent predictor of cardiovascular (CV) morbidity and mortality. The aim of the present study was to evaluate the relationship between LV mass and mild-to-moderate renal dysfunction in a group of non-diabetic hypertensives, free of CV diseases, participating in the Renal Dysfunction in Hypertension (REDHY) study. Methods: Patients with diabetes, a body mass index (BMI) of more than 35 kg/m2, secondary hypertension, CV diseases and a glomerular filtration rate (GFR) of less than 30 mL/min per 1.73 m2 were excluded. The final sample included 455 patients, who underwent echocardiographic examination and ambulatory blood pressure monitoring. Results: There was a significant trend for a stepwise increase in LV mass, indexed by both body surface area (LVMI) and height elevated to 2.7 (LVMH2.7), with the declining renal function, that remained statistically significant after correction for potential confounders. The prevalence of LVH, defined either as LVMI of 125 g/m2 or more or as LVMH2.7 of 51 g/m2.7 or more, was higher in subjects with lower values of GFR than in those with normal renal function (P < 0.001 in both cases). The multiple regression analysis confirmed that the inverse association between GFR and LVM was independent of confounding factors. Conclusion: The present study confirms the high prevalence of LVH in patients with mild or moderate renal dysfunction. In the patients studied (all with a GFR of 30 mL/min per 1.73 m2), the association between LVM and GFR was independent of potential confounders, including 24 h blood pressure load. Taking into account the negative prognostic impact of LVH, further studies focusing on a deeper comprehension of the mechanisms underlying the development of LVH in chronic kidney disease patients are needed. [source] RHYTHMIC AND IRREGULAR MOVEMENT OF THE FIRST MOLAR WHILE EATING FOODS WITH DIFFERENT TEXTURESJOURNAL OF TEXTURE STUDIES, Issue 3 2000MICHIKO TOGASHI ABSTRACT The three-dimensional movement of a tooth, any tooth, while naturally eating, was measured by an apparatus developed in our laboratory. The movement of the first molar on the usually used side is reported here. The mastication movements are divided into two parts, namely the rhythmical chewing period during which there are mastication pressure loads on the molar and the irregularly pulsated moving period in preparation for the swallowing followed by the rhythmical one during which there is no more pressure on it. The amplitudes of the up and down movements of the molar are 10,22mm for the rhythmical chewing period which are bigger than those for the irregularly moving period. The rhythmical chewing periods are distributed around 10,40 s depending on 14 kinds of food texture, and also on the size of the food, in a fairly similar manner for the participants. The period is longer for tough foods and bigger samples. The irregularly pulsated moving periods are widely distributed, 2,45s, and depend both on the food texture and on the participant. The irregular moving periods are longer for foods which scatter in the mouth or adhere to the teeth when chewing. The ingestion difficulty of the food was divided into two groups. One is where it is difficult to break down the food with the teeth and the other is where it is difficult to prepare for swallowing. [source] | ||||||||||