Energy-entropy-momentum time integration methods for coupled smooth dissipative problems

Esta tesis aborda la formulación, análisis e implementación de métodos numéricos de integración temporal para la solución de sistemas disipativos suaves de dimensión finita o infinita de manera que su estructura continua sea conservada. Se entiende por dichos sistemas aquellos que involucran acoplamiento termo-mecánico y/o efectos disipativos internos modelados por variables internas que siguen leyes continuas, de modo que su evolución es considerada suave. La dinámica de estos sistemas está gobernada por las leyes de la termodinámica y simetrías, las cuales constituyen la estructura que se pretende conservar de forma discreta. Para ello, los sistemas disipativos se describen geométricamente mediante estructuras metriplécticas que identifican claramente las partes reversible e irreversible de la evolución del sistema. Así, usando una de estas estructuras conocida por las siglas (en inglés) de GENERIC, la estructura disipativa de los sistemas es identificada del mismo modo que lo es la Hamiltoniana para sistemas conservativos. Con esto, métodos (EEM) con precisión de segundo orden que conservan la energía, producen entropía y conservan los impulsos lineal y angular son formulados mediante el uso del operador derivada discreta introducido para asegurar la conservación de la Hamiltoniana y las simetrías de sistemas conservativos. Siguiendo estas directrices, se formulan dos tipos de métodos EEM basados en el uso de la temperatura o de la entropía como variable de estado termodinámica, lo que presenta importantes implicaciones que se discuten a lo largo de esta tesis. Entre las cuales cabe destacar que las condiciones de contorno de Dirichlet son naturalmente impuestas con la formulación basada en la temperatura. Por último, se validan dichos métodos y se comprueban sus mejores prestaciones en términos de la estabilidad y robustez en comparación con métodos estándar. This dissertation is concerned with the formulation, analysis and implementation of structure-preserving time integration methods for the solution of the initial(-boundary) value problems describing the dynamics of smooth dissipative systems, either finite- or infinite-dimensional ones. Such systems are understood as those involving thermo-mechanical coupling and/or internal dissipative effects modeled by internal state variables considered to be smooth in the sense that their evolutions follow continuos laws. The dynamics of such systems are ruled by the laws of thermodynamics and symmetries which constitutes the structure meant to be preserved in the numerical setting. For that, dissipative systems are geometrically described by metriplectic structures which clearly identify the reversible and irreversible parts of their dynamical evolution. In particular, the framework known by the acronym GENERIC is used to reveal the systems' dissipative structure in the same way as the Hamiltonian is for conserving systems. Given that, energy-preserving, entropy-producing and momentum-preserving (EEM) second-order accurate methods are formulated using the discrete derivative operator that enabled the formulation of Energy-Momentum methods ensuring the preservation of the Hamiltonian and symmetries for conservative systems. Following these guidelines, two kind of EEM methods are formulated in terms of entropy and temperature as a thermodynamical state variable, involving important implications discussed throughout the dissertation. Remarkably, the formulation in temperature becomes central to accommodate Dirichlet boundary conditions. EEM methods are finally validated and proved to exhibit enhanced numerical stability and robustness properties compared to standard ones.

Relationship between residual stresses and mechanical behavior in ceramic composites

En este trabajo, materiales de tipo alúmina/Y-TZP (ZrO2 tetragonal, estabilizada con 3 mol. % Y2O3), como sistema cerámico popular por sus mejoradas propiedades mecánicas en comparación con las cerámicas de alúmina puras, han sido estudiados en términos de propiedades mecánicas y tensiones residuales. El novedoso método de colado en cinta, consistente en el apilamiento de cintas de cerámica verde a temperatura ambiente y el uso de bajas presiones, se ha escogido para la presente investigación con el fin de poder aprovechar al máximo el futuro desarrollo de materiales laminados de alúmina-óxido de circonio. Se han determinado las propiedades de los materiales obtenidos por este nuevo método de procesamiento comparándolas con las de los materiales obtenidos por “slip casting”, con el fin de analizar si el método propuesto afecta a la microestructura y, por tanto, a las propiedades mecánicas y tensiones residuales propias de estos materiales. Para analizar la idoneidad del proceso de fabricación, utilizado para evitar la presencia de discontinuidades en las intercaras entre las láminas así como otros fenómenos que puedan interferir con las propiedades mecánicas, se estudiaron materiales cerámicos con la misma composición en cintas. Por otra parte también se analizó el efecto de la adición de óxido de circonio sobre la aparición de tensiónes residuales en cerámicas Al2O3/Y-TZP, teniendo en cuenta su notable influencia sobre las propiedades microestructurales y mecánicas de los materiales, así como el requisito de co-sinterización de capas con diferentes materiales compuestos en materiales laminados. La caracterización del material incluye la determinación de la densidad, el análisis de la microestructura, la obtención de las propiedades mecánicas (módulo de elasticidad, dureza, resistencia a la flexión y tenacidad de fractura) así como de las tensiones residuales. En combinación con otros métodos de medida tradicionales, la nanoindentación también se empleó como una técnica adicional para la medida del módulo de elasticidad y de la dureza. Por otro lado, diferentes técnicas de difracción con neutrones, tanto las basadas en longitud de onda constante (CW) como en tiempo de vuelo (TOF), han sido empleadas para la medición fiable de la deformación residual a través del grosor en muestras a granel. Las tensiones residuales fueron determinadas con elevada precisión, aplicando además métodos de análisis apropiados, como por ejemplo el refinamiento de Rietveld. Las diferentes fases en cerámicas sinterizadas, especialmente las de zirconia, se examinaron con detalle mediante el análisis de Rietveld, teniendo en cuenta el complicado polimorfismo del Óxido de Zirconio (ZrO2) así como las posibles transformaciones de fase durante el proceso de fabricación. Los efectos del contenido de Y-TZP en combinación con el nuevo método de procesamiento sobre la microestructura, el rendimiento mecánico y las tensiones residuales de los materiales estudiados (Al2O3/Y-TZP) se resumen en el presente trabajo. Finalmente, los mecanismos de endurecimiento, especialmente los relacionados con las tensiones residuales, son igualmente discutidos. In present work, Alumina/Y-TZP (tetragonal ZrO2 stabilized with 3 mol% Y2O3) materials, as an popular ceramic system with improved mechanical properties compared with the pure alumina ceramics, have been studied in terms of mechanical properties and residual stresses. The novel tape casting method, which involved the stacking of green ceramics tapes at room temperature and using low pressures, is selected for manufacturing and investigation, in order to take full advantage of the future development of alumina-zirconia laminated materials. Features of materials obtained by the new processing method are determined and compared with those of materials obtained by conventional slip casting in a plaster mold, in order to study whether the proposed method of processing affects microstructure and thereby the mechanical properties and residual stresses characteristics of materials. To analyse the adequacy of the manufacturing process used to avoid the presence of discontinuities at the interfaces between the sheets and other phenomena that interfere with the mechanical properties, ceramic materials with the same composition in tapes were investigated. Moreover, the effect of addition of zirconia on residual stress development of Al2O3/Y-TZP ceramics were taken into investigations, considering its significantly influence on the microstructure and mechanical properties of materials as well as the requirement of co-sintering of layers with different composites in laminated materials. The characterization includes density, microstructure, mechanical properties (elastic modulus, hardness, flexure strength and fracture toughness) and residual stresses. Except of the traditional measurement methods, nanoindentation technique was also used as an additional measurement of the elastic modulus and hardness. Neutron diffraction, both the constant-wavelength (CW) and time-of-flight (TOF) neutron diffraction techniques, has been used for reliable through-thickness residual strain measurement in bulk samples. Residual stresses were precisely determined combined with appropriate analysis methods, e.g. the Rietveld refinement. The phase compositions in sintered ceramics especially the ones of zirconia were accurately examined by Rietveld analysis, considering the complex polymorph of ZrO2 and the possible phase transformation during manufacturing process. Effects of Y-TZP content and the new processing method on the microstructure, mechanical performance and residual stresses were finally summarized in present studied Al2O3/Y-TZP materials. The toughening mechanisms, especially the residual stresses related toughening, were theoretically discussed.

Nonlinear normal modes in mechanical systems: concept and computation with numerical continuation

The purpose of this Project is, first and foremost, to disclose the topic of nonlinear vibrations and oscillations in mechanical systems and, namely, nonlinear normal modes NNMs to a greater audience of researchers and technicians. To do so, first of all, the dynamical behavior and properties of nonlinear mechanical systems is outlined from the analysis of a pair of exemplary models with the harmonic balanced method. The conclusions drawn are contrasted with the Linear Vibration Theory. Then, it is argued how the nonlinear normal modes could, in spite of their limitations, predict the frequency response of a mechanical system. After discussing those introductory concepts, I present a Matlab package called 'NNMcont' developed by a group of researchers from the University of Liege. This package allows the analysis of nonlinear normal modes of vibration in a range of mechanical systems as extensions of the linear modes. This package relies on numerical methods and a 'continuation algorithm' for the computation of the nonlinear normal modes of a conservative mechanical system. In order to prove its functionality, a two degrees of freedom mechanical system with elastic nonlinearities is analized. This model comprises a mass suspended on a foundation by means of a spring-viscous damper mechanism -analogous to a very simplified model of most suspended structures and machines- that has attached a mass damper as a passive vibration control system. The results of the computation are displayed on frequency energy plots showing the NNMs branches along with modal curves and time-series plots for each normal mode. Finally, a critical analysis of the results obtained is carried out with an eye on devising what they can tell the researcher about the dynamical properties of the system.

Mechanical and chemical unfolding of a single protein: A comparison

Is the mechanical unraveling of protein domains by atomic force microscopy (AFM) just a technological feat or a true measurement of their unfolding? By engineering a protein made of tandem repeats of identical Ig modules, we were able to get explicit AFM data on the unfolding rate of a single protein domain that can be accurately extrapolated to zero force. We compare this with chemical unfolding rates for untethered modules extrapolated to 0 M denaturant. The unfolding rates obtained by the two methods are the same. Furthermore, the transition state for unfolding appears at the same position on the folding pathway when assessed by either method. These results indicate that mechanical unfolding of a single protein by AFM does indeed reflect the same event that is observed in traditional unfolding experiments. The way is now open for the extensive use of AFM to measure folding reactions at the single-molecule level. Single-molecule AFM recordings have the added advantage that they define the reaction coordinate and expose rare unfolding events that cannot be observed in the absence of chemical denaturants.

Solid-state synthesis and mechanical unfolding of polymers of T4 lysozyme

Recent advances in single molecule manipulation methods offer a novel approach to investigating the protein folding problem. These studies usually are done on molecules that are naturally organized as linear arrays of globular domains. To extend these techniques to study proteins that normally exist as monomers, we have developed a method of synthesizing polymers of protein molecules in the solid state. By introducing cysteines at locations where bacteriophage T4 lysozyme molecules contact each other in a crystal and taking advantage of the alignment provided by the lattice, we have obtained polymers of defined polarity up to 25 molecules long that retain enzymatic activity. These polymers then were manipulated mechanically by using a modified scanning force microscope to characterize the force-induced reversible unfolding of the individual lysozyme molecules. This approach should be general and adaptable to many other proteins with known crystal structures. For T4 lysozyme, the force required to unfold the monomers was 64 ± 16 pN at the pulling speed used. Refolding occurred within 1 sec of relaxation with an efficiency close to 100%. Analysis of the force versus extension curves suggests that the mechanical unfolding transition follows a two-state model. The unfolding forces determined in 1 M guanidine hydrochloride indicate that in these conditions the activation barrier for unfolding is reduced by 2 kcal/mol.

Flexible ruthenium oxide-activated carbon cloth composites prepared by simple electrodeposition methods

This work focuses on the preparation of flexible ruthenium oxide containing activated carbon cloth by electrodeposition. Different electrodeposition methods have been used, including chronoamperometry, chronopotentiometry and cyclic voltammetry. The electrochemical properties of the obtained materials have been measured. The results show that the potentiostatic method allows preparing composites with higher specific capacitance than the pristine activated carbon cloth. The capacitance values measured by cyclic voltammetry at 10 mV s−1 and 1 V of potential window were up to 160 and 180 F g−1. This means an improvement of 82% and 100% with respect to the capacitance of the pristine activated carbon cloth. This excellent capacitance enhancement is attributed to the small particle size (4–5 nm) and the three-dimensional nanoporous network of the ruthenium oxide film which allows reaching very high degree of oxide utilization without blocking the pore structure of the activated carbon cloth. In addition, the electrodes maintain the mechanical properties of the carbon cloth and can be useful for flexible devices.

Ventilated Stone Veneer: Mechanical Behaviour, Calculation Methodologies, Major Pathologies and Existing Tests

The increase of building pathologies related to the use of stone materials and the use of ventilated stone veneers, requires the reformulation of design concepts in building façades and also the reformulation of the architectural project. The aim of this paper is to identify, analyze and evaluate synthetically building pathologies in stone ventilated façades in order to obtain the main technical conditions to be considered in the architectural design, by interpreting its mechanical behavior and capabilities to prevent such pathologies and to ensure the proper features during the building lifetime. The methodology is based on both laboratory stone tests and in situ tests about construction systems, by analyzing physical and mechanical behavior of the outer layer in relation to other building requirements. The results imply the need of proper sizing, specific quality control and practical application of calculation methods, to control high concentration pressures in ventilated façades by reaching appropriate project solutions. In conclusion, the research about different pathologies of stone ventilated façades, the study of their mechanical behavior, their anchorage and their connection with their constructive aspects, will help to improve the construction quality of the stone ventilated façade in buildings and to enhance the use of natural stone in modern architecture.

Short structured feedback training is equivalent to a mechanical feedback device in two-rescuer BLS: a randomised simulation study.

BACKGROUND Resuscitation guidelines encourage the use of cardiopulmonary resuscitation (CPR) feedback devices implying better outcomes after sudden cardiac arrest. Whether effective continuous feedback could also be given verbally by a second rescuer ("human feedback") has not been investigated yet. We, therefore, compared the effect of human feedback to a CPR feedback device. METHODS In an open, prospective, randomised, controlled trial, we compared CPR performance of three groups of medical students in a two-rescuer scenario. Group "sCPR" was taught standard BLS without continuous feedback, serving as control. Group "mfCPR" was taught BLS with mechanical audio-visual feedback (HeartStart MRx with Q-CPR-Technology™). Group "hfCPR" was taught standard BLS with human feedback. Afterwards, 326 medical students performed two-rescuer BLS on a manikin for 8 min. CPR quality parameters, such as "effective compression ratio" (ECR: compressions with correct hand position, depth and complete decompression multiplied by flow-time fraction), and other compression, ventilation and time-related parameters were assessed for all groups. RESULTS ECR was comparable between the hfCPR and the mfCPR group (0.33 vs. 0.35, p = 0.435). The hfCPR group needed less time until starting chest compressions (2 vs. 8 s, p < 0.001) and showed fewer incorrect decompressions (26 vs. 33 %, p = 0.044). On the other hand, absolute hands-off time was higher in the hfCPR group (67 vs. 60 s, p = 0.021). CONCLUSIONS The quality of CPR with human feedback or by using a mechanical audio-visual feedback device was similar. Further studies should investigate whether extended human feedback training could further increase CPR quality at comparable costs for training.

Profiles of automotive suppliers industries - engineered mechanical components.

National Highway Traffic Safety Administration, Office of Research and Development, Washington, D.C.

An investigation of simultaneous motions as treated in the methods-time measurement system; a progress report.

Mode of access: Internet.

Graphical and mechanical computation,

"Embodies a course given by the writer for a number of years in the mathematical laboratory of the Massachusetts Institute of Technology."

Structural and mechanical properties of nanostructured granular alumina catalysts

Granular gamma-Al2O3 support and 8 wt % CuO/gamma-Al2O3 catalyst were synthesized by a sol-gel granulation method. The pore structure, crush strength, hardness, and elasticity of these sol-gel-derived catalysts were studied and compared with similar commercial catalysts prepared by non-sol-gel methods. Alumina and CuO-coated alumina granular particles prepared by different methods have different macro- and microstructure. The sol-gel-derived granular gamma-alumina and CuO-coated gamma-alumina granular particles have a structure defined by compact packing of uniform, nanosized gamma-alumina crystallites. They are characterized by a more uniform pore size distribution and larger surface area as compared to similar commercial samples with a structure defined by packing of aggregates consisting of nonuniform gamma-alumina crystallites. Because of the differences in the macro- and microstructure, the sol-gel-derived granular samples offer higher crush strength and greater hardness than the commercial samples.

Australian and New Zealand practice in intensive care (ANZPIC II: The spectrum of practice in the diagnosis and management of pneumonia in patients requiring mechanical ventilation

This study of ventilated patients investigated current clinical practice in 476 episodes of pneumonia (48% community-acquired pneumonia, 24% hospital-acquired pneumonia, 28% ventilator-associated pneumonia) using a prospective survey in 14 intensive care units (ICUs) within Australia and New Zealand. Diagnostic methods and confidence, disease severity, microbiology and antibiotic use were assessed. All pneumonia types had similar mortality (community-acquired pneumonia 33%, hospital-acquired pneumonia 37% and ventilator-associated pneumonia 24%, P = 0.15) with no inter-hospital differences (P = 0.08-0.91). Bronchoscopy was performed in 26%, its use predicted by admission hospital (one tertiary: OR 9.98, CI 95% 5.11-19.49, P < 0.001; one regional: OR 629, CI 95% 3.24-12.20, P < 0.001), clinical signs of consolidation (OR 3.72, CI 95% 2.09-662, P < 0.001) and diagnostic confidence (OR 2.19, CI 95% 1.29-3.72, P = 0.004). Bronchoscopy did not predict outcome (P = 0.11) or appropriate antibiotic selection (P = 0.69). Inappropriate antibiotic prescription was similar for all pneumonia types (11-13%, P = 0.12) and hospitals (0-16%, P = 0.25). Blood cultures were taken in 51% of cases. For community-acquired pneumonia, 70% received a third generation cephalosporin and 65% a macrolide. Third generation cephalosporins were less frequently used for mild infections (OR 0.38, CI 95% 0.16-0.90, P = 0.03), hospital-acquired pneumonia (OR 0.40, CI 95% 0.23-0.72, P < 0.01), ventilator-associated pneumonia (OR 0.04, CI 95% 0.02-0.13, P < 0.001), suspected aspiration (OR 0.20, CI 95% 0.04-0.92, P = 0.04), in one regional (OR 0.26, CI 95% 0.07-0.97, P = 0.05) and one tertiary hospital (OR 0.14, CI 95% 0.03-0.73, P = 0.02) but were more commonly used in older patients (OR 1.02, CI 95% 1.01-1.03, P = 0.01). There is practice variability in bronchoscopy and antibiotic use for pneumonia in Australian and New Zealand ICUs without significant impact on patient outcome, as the prevalence of inappropriate antibiotic prescription is low. There are opportunities for improving microbiological diagnostic work-up for isolation of aetiological pathogens.

Mechanical stimulation alters pleiotrophin and aggrecan expression by human intervertebral disc cells and influences their capacity to stimulate endothelial migration

Study Design. The influence of mechanical load on pleiotrophin (PTM) and aggrecan expression by intervertebral disc (IVD) cells, and the effects of disc cell conditioned medium on endothelial cell migration was investigated. Objective. To examine possible interactions of mechanical loads and known pro- and antiangiogenic factors, which may regulate disc angiogenesis during degeneration. Summary of Background Data. Pleiotrophin expression can be influenced by mechanical stimulation and has been associated with disc vascularization. Disc aggrecan inhibits endothelial cell migration, suggesting an antiangiogenic role. A possible interplay between these factors is unknown. Methods. The influence of the respective predominant load (cyclic strain for anulus fibrosus and hydrostatic pressure for nucleus pulposus cells) on PTN and aggrecan expression by IVD cells was determined by real-time RT-PCR and Western blotting (PTN only). The effects of IVD cell conditioned medium on endothelial cell migration were analyzed in a bioassay using human microvascular endothelial (HMEC-1) cells. Results. Application of both mechanical loads resulted in significant alterations of gene expression of PTN (+67%, P = 0.004 in anulus cells; +29%, P = 0.03 in nucleus cells) and aggrecan (+42%, P = 0.03 in anulus cells, -25%, P = 0.03 in nucleus cells). These effects depended on the cell type, the applied load, and timescale. Conditioned media of nucleus pulposus cells enhanced HMEC-1 migration, but this effect was diminished after 2.5 MPa hydrostatic pressure, when aggrecan expression was diminished, but not 0.25 MPa, when expression levels were unchanged. Conclusion. Mechanical loading influences PTN expression by human IVD cells. Conditioned media from nucleus pulposus cell cultures stimulated HMEC-1 endothelial cell migration. This study demonstrates that the influence of mechanical loads on vascularization of the human IVD is likely to be complex and does not correlate simply with altered expression of known pro- and antiangiogenic factors.