A critical reassessment of elastic unloading in sharp instrumented indentation experiments and the extraction of mechanical properties

This work examines the extraction of mechanical properties from instrumented indentation P-h(s) curves via extensive three-dimensional finite element analyses for pyramidal tips in a wide range of solids under frictional and frictionless contact conditions. Since the topography of the imprint changes with the level of pile-up or sink-in, a relationship is identified between correction factor beta in the elastic equation for the unloading indentation stage and the amount of surface deformation effects. It is shown that the presumption of a constant beta significantly affects mechanical property extractions. Consequently, a new best-fit function is found for the correlation between penetration depth ratios h(e)/h(max), h(r)/h(max) and n, circumventing the need for the assumption of a constant value for beta, made in our prior investigation [Acta Mater. 53 (2005) pp. 3545-3561]. Simulations under frictional contact conditions provide sensible boundaries for the influence of friction on both h(e)/h(max) and h(r)/h(max). Friction is essentially found to induce an overestimation in the inferred n. Instrumented indentation experiments are also performed in three archetypal metallic materials exhibiting distinctly different contact responses. Mechanical property extractions are finally demonstrated in each of these materials.

Discrete approximation to the global spectrum of the tangent operator for flow past a circular cylinder

This paper deals with the calculation of the discrete approximation to the full spectrum for the tangent operator for the stability problem of the symmetric flow past a circular cylinder. It is also concerned with the localization of the Hopf bifurcation in laminar flow past a cylinder, when the stationary solution loses stability and often becomes periodic in time. The main problem is to determine the critical Reynolds number for which a pair of eigenvalues crosses the imaginary axis. We thus present a divergence-free method, based on a decoupling of the vector of velocities in the saddle-point system from the vector of pressures, allowing the computation of eigenvalues, from which we can deduce the fundamental frequency of the time-periodic solution. The calculation showed that stability is lost through a symmetry-breaking Hopf bifurcation and that the critical Reynolds number is in agreement with the value presented in reported computations. (c) 2007 IMACS. Published by Elsevier B.V. All rights reserved.

On Seliger and Whitham`s variational principle for hydrodynamic systems from the point of view of `fictitious particles`

FAPESP, the Sao Paulo State Research Foundation[04/04611-5]

A comparison of the critical impeller speed for solids suspension in a bench-scale and a pilot-scale mechanical flotation cell

This paper compares the critical impeller speed results for 6 L Denver and Wemco bench-scale flotation cells with findings from a study by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2007. Evaluation of solids suspension in a pilot-scale mechanical flotation cell: the critical impeller speed. Minerals Engineering 20,233-240; Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621-629] conducted in a 125 L Batequip flotation cell. Understanding solids suspension has become increasingly important due to dramatic increases in flotation cell sizes. The critical impeller speed is commonly used to indicate the effectiveness of solids suspension. The minerals used in this study were apatite, quartz and hematite. The critical impeller speed was found to be strongly dependent on particle size, solids density and air flow rate, with solids concentration having a lesser influence. Liquid viscosity was found to have a negligible effect. The general Zwietering-type critical impeller speed correlation developed by Van der Westhuizen and Deglon [Van der Westhuizen, A.P., Deglon, D.A., 2008. Solids suspension in a pilot scale mechanical flotation cell: a critical impeller speed correlation. Minerals Engineering 21, 621-629] was found to be applicable to all three flotation machines. The exponents for particle size, solids concentration and liquid viscosity were equivalent for all three cells. The exponent for solids density was found to be less significant than that obtained by the previous authors, and to be consistent with values reported in the general literature for stirred tanks. Finally, a new dimensionless critical impeller speed correlation is proposed where the particle size is divided by the impeller diameter. This modified equation generally predicts the experimental measurements well, with most predictions within 10% of the experimental. (C) 2009 Elsevier Ltd. All rights reserved.

Fixed-point DSP implementation of nonlinear H(infinity) controller for large gap electromagnetic suspension system

Electromagnetic suspension systems are inherently nonlinear and often face hardware limitation when digitally controlled. The main contributions of this paper are: the design of a nonlinear H(infinity) controller. including dynamic weighting functions, applied to a large gap electromagnetic suspension system and the presentation of a procedure to implement this controller on a fixed-point DSP, through a methodology able to translate a floating-point algorithm into a fixed-point algorithm by using l(infinity) norm minimization due to conversion error. Experimental results are also presented, in which the performance of the nonlinear controller is evaluated specifically in the initial suspension phase. (C) 2009 Elsevier Ltd. All rights reserved.

Measuring Hydraulic Conductivity to Wilting Point Using Polymer Tensiometers in an Evaporation Experiment

The polymer tensiometer is a novel instrument to measure soil water pressure heads from saturation to permanent wilting conditions. We used tensiometers of this type in an experiment to determine the hydraulic properties of evaporating soil samples in the laboratory. Relative errors in the hydraulic conductivity function in the wet part were high due to the relatively low accuracy of the pressure transducers, resulting in a large uncertainty in the hydraulic gradient and therefore in the calculated hydraulic conductivity. In the dry part, the error related to this accuracy was on the same order of magnitude as the error related to balance accuracy. Therefore, the method can be assumed adequate for measuring soil hydraulic properties except under very wet conditions. In our experiments, relative error and bias increased significantly at pressure heads less negative than -1 m.

Can native vegetation recover after slash pine cultivation in the Brazilian Savanna?

There is a widespread view that forest plantations with exotic species are green deserts, unable to sustain biodiversity. Few studies have demonstrated, however, that planted stands of exotic trees have a greater negative effect on the plant diversity of savanna vegetation. We compared the native woody flora under four stands of slash pine of about 45 years old with four stands where the previously existing native Cerrado vegetation was preserved and protected from disturbances for the same period, has changed into dense vegetation - the ""cerradao"", at Assis municipality, Sao Paulo State, Brazil. Aiming at understanding the potential ecological filters driving these communities, we assessed air and soil humidity, light availability and classified the native species on the basis of shade tolerance, dispersal syndrome and biomes in which they occur (Atlantic Forest or Cerrado). We recorded an average of 70 (+/- 13) species under pine stands and 54 (+/- 16) species in cerradao. Of the total of 136 species recorded, 78 occurred in both habitats, eight were exclusive to the ""cerradao"" (shade tolerant and also occurring in forest ecosystems) and 18 were recorded only under pine stands (82% heliophytic, exclusive to the Cerrado biome). Among the functional attributes and abiotic variables analyzed, only light availability explained the floristic differences found. Since richness was higher under pine, we refuted the hypothesis that exotic species constrain the establishment of the native species richness in the understory. On the other hand, the dark environment under the closed-canopy of the ""cerradao"" acts as a filter inhibiting the establishment of typical Cerrado species. Since pine stands, if managed in long cycle, maintain a reasonable pool of Cerrado endemic species in the understory pine plantations may be a good starting point for savanna restoration. (C) 2011 Elsevier B.V. All rights reserved.

Relationship between Rheological Properties and One-Step W/O/W Multiple Emulsion Formation

Formation of a normal (not temporary) W/O/W multiple emulsion via the one-step method as a result of the simultaneous occurrence of catastrophic and transitional phase inversion processes has been recently reported. Critical features of this process include the emulsification temperature (corresponding to the ultralow surface tension point), the use of a specific nonionic surfactant blend and the surfactant blend/oil phase ratio, and the addition of the surfactant blend to the oil phase. The purpose of this study was to investigate physicochemical properties in an effort to gain a mechanistic understanding of the formation of these emulsions. Bulk, surface, and interfacial theological properties of adsorbed nonionic surfactant (CremophorRH40 and Span80) films were investigated under conditions known to affect W/O/W emulsion formation. Bulk viscosity results demonstrated that CremophorRH40 has a higher mobility in oil compared than in water, explaining the significance of the solvent phase. In addition, the bulk viscosity profile of aqueous solutions containing CremophorRH40 indicated a phase transition at around 78 +/- 2 degrees C, which is in agreement with cubic phase formation in the Winsor III region. The similarity in the interfacial elasticity values of CremophorRH40 and Span80 indicated that canola oil has a major effect on surface activity, showing the significance of vegetable oil. The highest interfacial shear elasticity and viscosity were observed when both surfactants were added to the oil phase, indicating the importance of the microstructural arrangement. CremophorRH40/Span80 complexes tended to desorb from the solution/solution interface with increasing temperature, indicating surfactant phase formation as is theoretically predicted in the Winsor III region. Together these interfacial and bulk rheology data demonstrate that one-step W/O/W emulsions form as a result of the simultaneous occurrence of phase-transition processes in the Winsor III region and explain the critical formulation and processing parameters necessary to achieve the formation of these normal W/O/W emulsions.

Tests for the hysteresis hypothesis in Brazilian industrialized exports: A threshold cointegration analysis

This paper examines the hysteresis hypothesis in the Brazilian industrialized exports using a time series analysis. This hypothesis finds an empirical representation into the nonlinear adjustments of the exported quantity to relative price changes. Thus, the threshold cointegration analysis proposed by Balke and Fomby [Balke, N.S. and Fomby, T.B. Threshold Cointegration. International Economic Review, 1997; 38; 627-645.] was used for estimating models with asymmetric adjustment of the error correction term. Amongst sixteen industrial sectors selected, there was evidence of nonlinearities in the residuals of long-run relationships of supply or demand for exports in nine of them. These nonlinearities represent asymmetric and/or discontinuous responses of exports to different representative measures of real exchange rates, in addition to other components of long-run demand or supply equations. (C) 2007 Elsevier B.V. All rights reserved.

A comparison of methods to identify open-lung PEEP

Purpose: Many methods exist in the literature for identifying PEEP to set in ARDS patients following a lung recruitment maneuver (RM). We compared ten published parameters for setting PEEP following a RM. Methods: Lung injury was induced by bilateral lung lavage in 14 female Dorset sheep, yielding a PaO(2) 100-150 mmHg at F(I)O(2) 1.0 and PEEP 5 cmH(2)O. A quasi-static P-V curve was then performed using the supersyringe method; PEEP was set to 20 cmH(2)O and a RM performed with pressure control ventilation (inspiratory pressure set to 40-50 cmH(2)O), until PaO(2) + PaCO(2) > 400 mmHg. Following the RM, a decremental PEEP trial was performed. The PEEP was decreased in 1 cmH(2)O steps every 5 min until 15 cmH(2)O was reached. Parameters measured during the decremental PEEP trial were compared with parameters obtained from the P-V curve. Results: For setting PEEP, maximum dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), and minimum shunt calculated during the decremental PEEP trial, and the lower Pflex and point of maximal compliance increase on the inflation limb of the P-V curve (Pmci,i) were statistically indistinguishable. The PEEP value obtained using the deflation upper Pflex and the point of maximal compliance decrease on the deflation limb were significantly higher, and the true inflection point on the inflation limb and minimum PaCO(2) were significantly lower than the other variables. Conclusion: In this animal model of ARDS, dynamic tidal respiratory compliance, maximum PaO(2), maximum PaO(2) + PaCO(2), minimum shunt, inflation lower Pflex and Pmci,i yield similar values for PEEP following a recruitment maneuver.

Meta-analysis of infrapopliteal angioplasty for chronic critical limb ischemia

Background: Percutaneous transluminal angioplasty has been used with increasing frequency in the treatment of infrainguinal arterial occlusive disease. This meta-analysis aimed to assess the middle-term outcomes after crural angioplasty in patients with chronic critical limb ischemia and compare results with a meta-analysis of popliteal-to-distal vein bypass graft. Methods: Data were retrieved from 30 articles published from 1990 through 2006 (63% of articles published between 2000 and 2006). All studies used survival analysis, reported a 12-month cumulative rate of patency or limb salvage, and included at least 15 infrapopliteal angioplasties. The outcome measures were immediate technical success, primary and secondary patency, limb salvage, and patient survival. Data from life-tables, survival curves, and texts were used. Results. The pooled estimate of success was 89.0% +/- 2.2% for immediate technical result. Results at 1 and 36 months were 77.4% +/- 4.1% and 48.6% +/- 8.0% for primary patency, 83.3% +/- 1.4% and 62.9% +/- 11.0% for secondary patency, 93.4% +/- 2.3% and 82.4% +/- 3.4% for limb salvage, and 98.3% +/- 0.7% and 68.4% +/- 5.5% for patient survival, respectively. Studies with >75% of the limbs with tissue loss fared worse than their respective comparative subgroup for technical success and patency but not for limb salvage or survival. No publication bias was detected. Conclusion: The technical success and subsequent durability of crural angioplasty are limited compared with bypass surgery, but the clinical benefit is acceptable because limb salvage rates are equivalent to bypass surgery. Further studies are necessary to determine the proper role of infrapopliteal angioplasty.

Fluid Resuscitation With Isotonic or Hypertonic Saline Solution Avoids Intraneural Calcium Influx After Traumatic Brain Injury Associated With Hemorrhagic Shock

Background: Calcium is one of the triggers involved in ischemic neuronal death. Because hypotension is a strong predictor of outcome in traumatic brain injury (TBI), we tested the hypothesis that early fluid resuscitation blunts calcium influx in hemorrhagic shock associated to TBI. Methods: Fifteen ketamine-halothane anesthetized mongrel dogs (18.7 kg +/- 1.4 kg) underwent unilateral cryogenic brain injury. Blood was shed in 5 minutes to a target mean arterial pressure of 40 mm Hg to 45 mm Hg and maintained at these levels for 20 minutes (shed blood volume = 26 mL/kg +/- 7 mL/kg). Animals were then randomized into three groups: CT (controls, no fluid resuscitation), HS (7.5% NaCl, 4 mL/kg, in 5 minutes), and LR (lactate Ringer`s, 33 mL/kg, in 15 minutes). Twenty minutes later, a craniotomy was performed and cerebral biopsies were obtained next to the lesion (""clinical penumbra"") and from the corresponding contralateral side (""lesion`s mirror"") to determine intracellular calcium by fluorescence signals of Fura-2-loaded cells. Results: Controls remained hypotensive and in a low-flow state, whereas fluid resuscitation improved hemodynamic profile. There was a significant increase in intracellular calcium in the injured hemisphere in CT (1035 nM +/- 782 nM), compared with both HS (457 nM +/- 149 nM, p = 0.028) and LR (392 nM +/- 178 nM, p = 0.017), with no differences between HS and LR (p = 0.38). Intracellular calcium at the contralateral, uninjured hemisphere was 438 nM +/- 192 nM in CT, 510 nM +/- 196 nM in HS, and 311 nM +/- 51 nM in LR, with no significant differences between them. Conclusion: Both small volume hypertonic saline and large volume lactated Ringer`s blunts calcium influx in early stages of TBI associated to hemorrhagic shock. No fluid resuscitation strategy promotes calcium influx and further neural damage.

Preferential use of nonreversed vein grafts in above-knee femoropopliteal bypasses for critical ischemia: Midterm outcome

We evaluated nonreversed vein grafts in above-knee bypasses for chronic critical limb ischemia in a retrospective study with intention-to-treat analysis in patients who underwent above-knee bypass grafting. During a 4-year period, 51 patients (men, 32; women, 19; mean age 66 years) with 53 critically ischemic lower extremities underwent above-knee femoropopliteal bypass grafting. The follow-up evaluation consisted of clinical examination, assessment of the ankle- brachial systolic blood pressure index, and, whenever necessary, duplex scanning. Three ( 5.7%) deaths occurred within 30 days, two from myocardial infarction and one from an undetermined cause. The 2-year cumulative success rate was 82.5 +/- 9.6% for primary patency, 84.6 +/- 8.9% for secondary patency, 90.1 +/- 7.3% for tertiary patency, 86.9 +/- 7.6% for limb salvage, 77.7 +/- 8.4% for survival, 68.0 +/- 11.1% for composite patency, and 68.4 +/- 9.3% for amputation- free survival; the corresponding estimates for vein grafts alone were 86.6 +/- 9.2%, 88.9 +/- 8.6%, 89.0 +/- 8.5%, 88.1 +/- 8.1%, 81.1 +/- 9.1, 76.8 +/- 11.1%, and 72.6 +/- 10.2%. Three prosthetic grafts failed and were replaced with an arm vein graft. Nonreversed vein bypass grafts in above- knee revascularization of critically ischemic limbs are justified.

Neutrophils recruitment during sepsis: Critical points and crossroads

The mechanisms that initiate an inflammatory systemic response to a bacterial infection lead to a high mortality and constitute the first cause of death in Critical Care Units (ICU`s). Sepsis is a poorly understood disease and despite life support techniques and the administration of antibiotics, not much more can be done to improve its diagnosis and treatment. The present article has as main objective to discuss the role of neutrophils recruitment in sepsis, dissecting the molecular mechanisms implicated in this complex process and its importance to the pathogenesis of this outstanding cause of death.