GENERATION, MECHANICAL AND STATISTICAL ANALYSIS, AND FEM SIMULATION OF FRACTURE OF REPEATABLE RANDOM ROUGH SURFACES

Natural weathering and wear of structural materials in service nearly always generate surface roughness, and follow the Central Limit Theorem prediction for surface topology. This study couples experimental and statistical theory, and FEM to extend knowledge of life of materials from initial service surface conditions through surface damage accumulation. Statistical moments and other parameters were correlated with fracture locations probability (H/N), versus auto correlation length, and depth. As the surface grows to a full Gaussian, H/N increases its dependence on profile’s Average and RMS Roughness, and derived parameters. This dependence shows an asymptotic limit behavior that approaches agreeably Griffith’s crack criterion, though with multiple pit locations. Importantly, a Transitional Region was observed, below which the probable location of fracture is uncorrelated to the parameters studied. This is because introduced roughness is insufficient to compete with impurities, internal and external manufacturing flaws, and scratches, due to handling and machining, on the samples

Nariai--Bertotti--Robinson spacetimes as a building material for one-way wormholes with horizons, but without singularity

We discuss the problem of wormholes from the viewpoint of gluing together two Reissner--Nordstr\"om-type universes while putting between them a segment of the Nariai-type world (in both cases there are also present electromagnetic fields as well as the cosmological constant). Such a toy wormhole represents an example of one-way topological communication free from causal paradoxes, though involving a travel to next spacetime sheet since one has to cross at least a pair of horizons through which the spacetimes' junction occurs. We also consider the use of thin shells in these constructions. Such a ``material'' for wormholes we choose taking into account specific properties of the Nariai--Bertotti--Robinson spacetimes.Comment: 5 pages, a talk delivered at the 11th Marcel Grossmann Meeting (2006

Moisture Performance Criteria for UK Dwellings

The new ventilation regulations in England and Wales have introduced performance criteria for the control of mould. The UK Government\'s Building Regulations Research Programme has funded University College London (UCL) to investigate the extent to which these are the most appropriate criteria for thecontrol of mould in UK dwellings. This paper reports on the plans for this study which involve both field and laboratory related work. Some initial early work has already been undertaken and the paper summarises the progress to date. This initial work is based on analysis of data from a national study of England\'s Home Energy Efficiency scheme (Warm Front). Surveys were undertaken of dwellings and households participating in the scheme in five urban areas. Half-hourly living room and main bedroom temperatures and relative humidity measurements were recorded for two to four weeks (in the heating season) in approximately 1600 dwellings. This data is being analysed to investigate the typical relativehumidities that exist in UK dwellings and also any relationship that exists between these levels and the mould growth that was recorded

Preliminary Results on the Use of Machine Learning for Advance Controls of a Dielectric Elastomer Actuator

Undergraduate Applie

Estudio de factores asociados a preeclampsia y su relación con hipertension postparto

Determinar si los factores: prematuridad del recién nacido, antecedentes de trastornos hipertensivos, obesidad y diabetes pregestacional o gestacional; asociados a preeclampsia, están relacionados con Hipertensión postparto. Materiales y Métodos. 60 pacientes preeclámpticas que dieron a luz en el Hospital Belén de Trujillo fueron incluidas en este estudio de cohortes prospectivo. Se obtuvieron sus datos como edad, severidad de la preeclampsia, exposición o no a factores como: recién nacido prematuro, antecedente de preeclampsia / historia familiar de hipertensión arterial, obesidad y diabetes pregestacional o gestacional. Luego se evaluaron los niveles de presión arterial en el puerperio. Resultados. La edad promedio de la serie total fue 27,95 ± 7,973 años (rango: 15 - 45 años). La frecuencia de preeclampsia leve fue 2 (11,8%) y 15 (88,2%) casos, y de preeclampsia severa fue 28 (65,1%) y 15 (34,9%) casos, para los grupos expuestos y no expuesto respectivamente (p < 0,05). El grupo de pacientes preeclámpticas con factores asociados presentó una mayor frecuencia de hipertensión postparto comparada con aquellas preeclámpticas sin factores asociados (70,6% vs 29,4% respectivamente; p = 0,045). Conclusiones. Las gestantes preeclámpticas que padecieron además con alguno de los cuatro factores asociados investigados, tuvieron 2,4 veces más riesgo de padecer hipertensión postparto, respecto del grupo no expuesto.To determine if the factors: prematurity of the newborn, history of hypertensive disorders, obesity and pregestational or gestational diabetes; associated with preeclampsia, are related to Postpartum hypertension. Materials and Methods. 60 preeclamptic patients who deliver at the Hospital Belén de Trujillo were included in this propective cohort study. We obtained data such as age, severity of preeclampsia, exposure to factors such as: preterm newborn, preeclampsia history / family history of hypertension, obesity and pregestational or gestational diabetes. Blood pressure levels were then evaluated in the Postpartum period. Results. The mean age of the total series was 27,95 ± 7,973 years (range: 15 - 45 years). The frequency of mild preeclampsia was 2 (11,8%) and 15 (88,2%) cases, and severe preeclampsia was 28 (65,1%) and 15 (34,9%) cases, for the groups exposed and not exposed respectively (p < 0,05). The group of preeclamptic patients with associated factors presented a highr frequency of Postpartum hypertension compared to preeclamptic without associated factors (70,6% vs 29,4% respectively; p = 0,045) Conclusion. Preeclamptic women who suffered from any of the four associated factors investigated were 2.4 times more likely to suffer from postpartum hypertension than the nonexposed group.

Early prediction of fracture in bodies bounded by random rough surfaces

Under certain loading conditions, surfaces topography coupled with materials degree of brittleness can significantly compromise the mechanical performance of structures. The foregoing remains valid even if roughness is intentionally introduced for engineering reasons. In either case, stress can concentrate. The case of the stress concentration in surfaces having randomly distributed pits is a problem that, although being very practical, yet it remains unsolved. The complexity of a random configuration renders difficult the problem of analytically finding relationships between surface parameters and markers indicative of mechanical failure. Another difficulty is the reproducibility of replicates of specimens possessing random rough surfaces, for destructive testing followed by statistical analysis. An experimental technique to produce highly controlled replicates of random rough surfaces (including modeling of degradation growth) was developed. This method was used to experimentally and statistically study the effects on fracture of early randomly degraded surfaces of poly methyl methacrylate (PMMA) versus topographical parameters. Growth of degradation was assumed to go from an engineering surface to one whose heights are normally distributed. (Early stage of degradation is meant to be that level of roughness which is in the neighborhood of the critical flaw size for a given material). Among other findings, it was found that neither stress nor strain alone can be used to predict fracture at this early stage of degradation. However, fracture location was found to be strongly correlated to the ratio of the root-mean square roughness (RMS) to auto correlation length (ACL), above some RMS threshold. This correlation decreases as the material becomes less brittle (i.e., decrease of Young’s modulus or increase of percent of elongation). Simultaneously, a boundary value problem involving traction-free random rough surfaces was solved using a perturbation method, assuming elastic and isotropic conditions. For small RMS/ACL ratio, the solution for the RMS stress concentration factor, kt was found to be: kt = 1 + 2*SQRT(2)*(RMS/ACL), which agrees very well with the experimental work. Finally, a generalization of stress concentration factor formulas for several geometrical configurations and loading conditions into the Modified Inglis Formula was proposed. Finite element analysis was carried out and comparison was made with both experimental and analytical results. Applications of these results are broad. In surface engineering, for example, our analytical solution can be coupled with Fick’s Law to find critical conditions under which a film could become unstable to random roughness. Additionally, in design and maintenance of surfaces in service, it can be used to preliminarily assess how stress concentrates in surfaces where well defined notches cannot be used as an approximation

Decision-Making Processes of Residents in Preservation, Thermal Comfort, and Energy Efficiency in Heritage Buildings: A Pilot Study in Mexico City

With building construction representing one of the largest sectors responsible for the use of natural resources, retrofitting existing heritage buildings becomes a necessity, albeit a challenging one. The emergence of specific guidance on retrofitting heritage buildings has unveiled more than never the need to understand how residents negotiate, thermal comfort, energy efficiency, and heritage conservation decisions. The paper reports the complexity of the decision-making process of residents of heritage buildings in the Historic Centre of Mexico City regarding energy efficiency, intending to improve thermal comfort and reduce energy consumption while preserving heritage values. The study involved in-depth semi-structured interviews with users of heritage buildings that were thematically analysed, complemented by the monitoring of internal environmental conditions and system dynamics analysis. The results show that although the residents perceived the buildings’ temperature as poor, passive thermal comfort actions (e.g., wearing more clothes and closing windows) were preferred against invasive retrofitting solutions for thermal comfort due to residents’ resistance to a potential loss in the buildings’ values and the high cost of changes. The degree of change necessary for maintenance, renovation, and actions for improving the thermal comfort of a heritage building is related to values and to their preservation for future generations. The users’ changes were limited to small-scale interventions in floors and ceilings while avoiding touching what they consider essential to preserve and protect (i.e., social and cultural values). Integrating the user into the decision-making process would enhance the long-term continuity and sustainability of retrofitting policies and guidelines, thus avoiding losing heritage-built stock

Centralización del bombeo hidraulico en el campo lago agrío

El presente trabajo tiene como finalidad la construcción de dos estaciones de bombeo hidráulico centralizadas, la primera será instalada en la estación de producción central y la otra en la estación de producción norte, del campo Lago Agrio propiedad de Petroecuador ,ya que existe el espacio físico y la infraestructura necesaria para su construcción. La construcción de este sistema centralizado se lo propone como solución al problema energético por el cual atraviesa el sistema de bombeo hidráulico actual.(UNIHIDRAULIC). Para el diseño del Sistema Centralizado se tomo en consideración condiciones actuales, condiciones criticas y condiciones futuras del yacimiento,que pudieren afectar a dicho sistema. El sistema centralizado va a tener capacidad de generar suficiente energía,y esta a su vez va a ser suministrada a las bombas de subsuelo de los pozos que producen mediante bombeo hidráulico y estas van a trabajar a su máxima eficiencia,y como consecuencia se tendrá un considerable incremento de producción,aproximadamente 670 Bls de petróleo. Con el objeto de optimizar la circulación de fluido motriz, también se diseño bombas pistón(parte del sistema) para que se bajen en algunos pozos que tienen condiciones para su instalación y están trabajando con bomba jet,es decir que se va remplazar bombas jet por pistón ,debido a que estas son mas eficientes(consumen menos fluido motriz y sacan el mismo volumen de fluido). Con la ejecución de este sistema también, se lograra disminuir los costos de supervisión y mantenimiento, ya que se tendrá solo dos bombas funcionando en superficie ubicadas en un solo lugar

Design factors affecting the passive release of tracer gas for ventilation measurements

The ventilation rate is an important parameter for assessing indoor air quality and energy efficiency. In occupied buildings, ventilation measurements utilising passive methods are preferable to active methods due to their simplicity and less intrusive nature. The perfluorocarbon tracer method can be used to measure long-term ventilation rates for this purpose. This method requires the passive release of a tracer gas which is often a liquid chemical diffusing out of a vial. The tracer gas emission rate is a key parameter of the vial design as if it is too low, the sampler will not be able to detect the tracer gas. If the emission rate is too high, the sampler can become saturated. Both scenarios will lead to inaccurate ventilation results. There is wide variability in vial design but little information about the relative impact of each design factor. Thus, the aim of this study was to compare the emission rate of a common tracer gas, perfluoromethylcyclohexane, using different vials designs i.e. capping styles, septa materials, and fill levels. Samples were kept in an incubator and gravimetric analysis was carried out using a semi-microbalance (resolution: 0.01 mg). The results demonstrate that the emission rate is significantly affected by capping style but not by fill level