201,582 research outputs found
Non-contact measurement techniques to study the microsized particle adhesion phenomenon
No full textAirborne microsized particles are generated by artificial activity and natural sources. Due to their characteristics, these airborne particles are highly volatile and can cover thousands of kilometers according to weather conditions (in particular, wind intensity and humidity). As a result, these microsized particles could contaminate engineering systems determining their operation and performance modification. Phenomena such as photovoltaic panel soiling or gas turbine fouling are two of the most detrimental effects generated by the interaction between airborne particles and the relevant surfaces of the system. The present work proposes a set of non-contact measurement methodologies to study the adhesion phenomenon. The non-contact techniques are devoted to studying the deposited layer without altering the deposits. Image and video analysis have been used to show how the deposit can be studied in detail. Stationary and rotating facilities have been employed to show the applicability and the related constraints to the non-contact measurement techniques
Acrylamide removal from heated foods
No full textThe possibility to remove acrylamide from foods by exploiting its chemical physical properties was studied. Commercial biscuits and potato chips were subjected to vacuum treatments at different combinations of pressure, temperature and time. Results showed that acrylamide removal was achieved only in samples previously hydrated at water activity values higher than 0.83, and that, a maximum of acrylamide removal was obtained between 5 and 15 min of vacuum treatment at 6.67 Pa and 60 °C. By applying these process conditions, it was possible to remove 43% and 18% acrylamide from the biscuits and the potato chips, respectively. It was hypothesised that the vacuum treatment could favour acrylamide formation by promoting the decarboxylation of the Schiff base, a key intermediate of acrylamide formation. Although further research is needed to find out for each food category the process conditions that can maximise acrylamide removal while minimising its formation as well as to evaluate the effects on the sensory properties, this technology would represent a promising and alternative strategy to mitigation interventions aimed at reducing acrylamide levels in foods. © 2009 Elsevier Ltd. All rights reserved
Sebastian von Einsiedel, David M. Malone, Suman Pradhan (dir.). -Nepal in Transition, From People’s War to Fragile Peace, 2012
No full textAnnoussamy David. Sebastian von Einsiedel, David M. Malone, Suman Pradhan (dir.). -Nepal in Transition, From People’s War to Fragile Peace, 2012. In: Revue internationale de droit comparé. Vol. 65 N°1,2013. pp. 219-221
Sebastian von Einsiedel, David M. Malone, Suman Pradhan (dir.). -Nepal in Transition, From People’s War to Fragile Peace, 2012
No full textAnnoussamy David. Sebastian von Einsiedel, David M. Malone, Suman Pradhan (dir.). -Nepal in Transition, From People’s War to Fragile Peace, 2012. In: Revue internationale de droit comparé. Vol. 65 N°1,2013. pp. 219-221
The role of coping strategies and resilience in the perception of well-being among school-aged children
No full textSeveral studies showed that individuals perceiving themselves as resilient are more likely to experience a sense of well-being. However, few studies assessed how coping styles chosen and used by children in facing daily difficulties can be associated with resilience and, consequently, with perceived well-being in this age group. The present study investigated the role played by coping strategies and resilience in the perception of well-being among school-aged children. A total of 335 children (188 boys), attending the 4th and 5th grade of primary school (M = 10 years; SD = 7 months), participated in the study and were asked to complete self-report questionnaires on the target constructs. Correlation analyses confirmed a significant association between the perception of well-being and resilience. In addition, resilience and well-being were positively related to adaptive coping strategies, and negatively associated with maladaptive strategies. Mediation analyses revealed that resilience partially mediates the relationship between internalizing coping strategies and perception of well-being. Therefore, to promote well-being and resilience in primary school, guiding children towards the use of adaptive coping strategies and discouraging dysfunctional strategies could prove effective
Motion planning under uncertainty: application to an unmanned helicopter
No full textA methodology is presented in this work for intelligent motion planning in an
uncertain environment using a non-local sensor, like a radar sensor, that allows the
sensing of the environment non-locally. This methodology is applied to an unmanned
helicopter navigating a cluttered urban environment. It is shown that the problem of
motion planning in a uncertain environment, under certain assumptions, can be posed as
the adaptive optimal control of an uncertain Markov Decision Process, characterized by a
known, control dependent system, and an unknown, control independent environment.
The strategy for motion planning then reduces to computing the control policy based on
the current estimate of the environment, also known as the "certainty equivalence
principle" in the adaptive control literature. The methodology allows the inclusion of a
non-local sensor into the problem formulation, which significantly accelerates the
convergence of the estimation and planning algorithms. Further, the motion planning and
estimation problems possess special structure which can be exploited to reduce the
computational burden of the associated algorithms significately. As a result of the
methodology developed for motion planning in this thesis, an unmanned helicopter is
able to navigate through a partially known model of the Texas A&M campus
DESIGN OF AN INNOVATIVE EXPERIMENTAL RIG FOR THE STUDY OF DEPOSITION PHENOMENA IN AXIAL COMPRESSORS
No full textCompressor fouling is one of the main causes of gas turbine performance degradation. Fouling is promoted by micrometric particles of industrial pollutants in the air and unfavorable environmental conditions (fog, rain, humidity). Airborne particles ingested in heavy-duty gas turbines deposit on the compressor blades and sidewalls, increasing the surface roughness and changing the shape of the profile. This work aims to design a subsonic wind tunnel to study the gas turbine fouling phenomenon. Lump-parameter analysis and two- and three-dimensional fluid dynamics simulations support the design. Simulations were needed to optimize the blade cascade and identify particular fluid dynamic phenomena, such as separation, stagnation point, and vortex. In addition, great attention was devoted to the thermo-hygrometric conditions responsible for the capillarity forces. All these factors strongly influence the compressor cascade performance and the contamination rate. Particle concentration, number, and size are specified to perform a quantitative analysis of the particle impact on the blade surface and a qualitative analysis of the impact zones. As a result, realistic impact conditions of industrial relevance are reproduced in the wind tunnel in order to forecast the adhesion rate, the areas of the compressor airfoils impacted by particles, and thus the performance losses over the operation
An innovative approach towards fouling modeling: Microscale deposition pattern and its effect on the flow field
No full textSolid particle ingestion is one of the main compressor degradation mechanisms for both heavy-duty and aero-propulsion gas turbines. Particles impacting the inner surfaces of the machine can stick there forming deposits. The presence of such deposits reflects on the reduction in performance of the machinery. Over last years, several methods have been developed in order to study the problem from the numerical standpoint. Examples of these techniques are the mesh morphing approach and the added-roughness-and-thickness method. In this work, an innovative procedure is proposed in order to evaluate the losses and the variation in the fluid flow due to the deposits. Particularly, an algorithm capable of determining the microscale deposition pattern has been developed. By using this methodology, a comprehensive analysis of the variation of the performance of the compressor over time can be carried out. The deposition severity and the subsequent roughness variation can be kept into account in a very detailed and precise fashion. Furthermore, this approach overcomes the difficulties that may arise by using a mesh morphing technique. The computational grid is not modified and thus its quality is retained, without re-meshing requirements, even for large deposits. The local roughness variation is accounted for without extra-effort. The procedure developed, shown here in deposition problems, can be easily extended to erosion or even icing problems. The only parameter to be changed is the model that takes care of the particle-wall interaction, using an erosion rather than an icing law
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