Stability of switched linear differential systems

We study the stability of switched systems where the dynamic modes are described by systems of higher-order linear differential equations not necessarily sharing the same state space. Concatenability of trajectories at the switching instants is specified by gluing conditions, i.e. algebraic conditions on the trajectories and their derivatives at the switching instant. We provide sufficient conditions for stability based on LMIs for systems with general gluing conditions. We also analyse the role of positive-realness in providing sufficient polynomial-algebraic conditions for stability of two-modes switched systems with special gluing conditions

Development of dynamic calibration methods for POGO pressure transducers

Two dynamic pressure sources are described for the calibration of pogo pressure transducers used to measure oscillatory pressures generated in the propulsion system of the space shuttle. Rotation of a mercury-filled tube in a vertical plane at frequencies below 5 Hz generates sinusoidal pressures up to 48 kPa, peak-to-peak; vibrating the same mercury-filled tube sinusoidally in the vertical plane extends the frequency response from 5 Hz to 100 Hz at pressures up to 140 kPa, peak-to-peak. The sinusoidal pressure fluctuations can be generated by both methods in the presence of high pressures (bias) up to 55 MPa. Calibration procedures are given in detail for the use of both sources. The dynamic performance of selected transducers was evaluated using these procedures; the results of these calibrations are presented. Calibrations made with the two sources near 5 Hz agree to within 3% of each other

A dynamic pressure source for the calibration of pressure transducers

A dynamic pressure source is described for producing sinusoidally varying pressures of up to 34 kPa zero to peak, over the frequency range of approximately 50 Hz to 2 kHz. The source is intended for the dynamic calibration of pressure transducers. The transducer to be calibrated is mounted near the base of the thick walled aluminum tube forming the vessel so that the pressure sensitive element is in contact with the liquid in the tube. A section of the tube is filled with small steel balls to damp the motion of the 10-St dimethyl siloxane working fluid in order to extend the useful frquency range to higher frequencies than would be provided by an undamped system. The dynamic response of six transducers provided by the sponsor was evaluated using the pressure sources; the results of these calibrations are given

Impaction of spray droplets on leaves: influence of formulation and leaf character on shatter, bounce and adhesion

This paper combines experimental data with simple mathematical models to investigate the influence of spray formulation type and leaf character (wettability) on shatter, bounce and adhesion of droplets impacting with cotton, rice and wheat leaves. Impaction criteria that allow for different angles of the leaf surface and the droplet impact trajectory are presented; their predictions are based on whether combinations of droplet size and velocity lie above or below bounce and shatter boundaries. In the experimental component, real leaves are used, with all their inherent natural variability. Further, commercial agricultural spray nozzles are employed, resulting in a range of droplet characteristics. Given this natural variability, there is broad agreement between the data and predictions. As predicted, the shatter of droplets was found to increase as droplet size and velocity increased, and the surface became harder to wet. Bouncing of droplets occurred most frequently on hard to wet surfaces with high surface tension mixtures. On the other hand, a number of small droplets with low impact velocity were observed to bounce when predicted to lie well within the adhering regime. We believe this discrepancy between the predictions and experimental data could be due to air layer effects that were not taken into account in the current bounce equations. Other discrepancies between experiment and theory are thought to be due to the current assumption of a dry impact surface, whereas, in practice, the leaf surfaces became increasingly covered with fluid throughout the spray test runs.Comment: 19 pages, 6 figures, accepted for publication by Experiments in Fluid

Mercury removal in wastewater by iron oxide nanoparticles

Mercury is one of the persistent pollutants in wastewater; it is becoming a severe environmental and public health problem, this is why nowadays its removal is an obligation. Iron oxide nanoparticles are receiving much attention due to their properties, such as: great biocompatibility, ease of separation, high relation of surface-area to volume, surface modifiability, reusability, excellent magnetic properties and relative low cost. In this experiment, Fe3O4 and γ-Fe2O3 nanoparticles were synthesized using iron salts and NaOH as precipitation agents, and Aloe Vera as stabilizing agent; then these nanoparticles were characterized by three different measurements: first, using a Zetasizer Nano ZS for their size estimation, secondly UV-visible spectroscopy which showed the existence of resonance of plasmon at λmax∼360 nm, and lastly by Scanning Electron Microscopy (SEM) to determine nanoparticles form. The results of this characterization showed that the obtained Iron oxides nanoparticles have a narrow size distribution (∼100nm). Mercury removal of 70% approximately was confirmed by atomic absorption spectroscopy measurements

Model ab initio study of charge carrier solvation and large polaron formation on conjugated carbon chains

Using long C_{N}H_{2} conjugated carbon chains with the polyynic structure as prototypical examples of one-dimensional (1D) semiconductors, we discuss self-localization of excess charge carriers into 1D large polarons in the presence of the interaction with a surrounding polar solvent. The solvation mechanism of self-trapping is different from the polaron formation due to coupling with bond-length modulations of the underlying atomic lattice well-known in conjugated polymers. Model ab initio computations employing the hybrid B3LYP density functional in conjunction with the polarizable continuum model are carried out demonstrating the formation of both electron- and hole-polarons. Polarons can emerge entirely due to solvation but even larger degrees of charge localization occur when accompanied by atomic displacements

Comparative environmental assessment of two materials suited to central tower CSP technology

Compatibility of containment materials with molten salt thermal storage media is a significant technical challenge for Concentrating Solar Power plants. Metal alloys in contact with molten salt must have a specific behavior, mechanical properties and resistance to degradation processes that allow them to operate at temperatures above 500 °C, being both respectful to the environment. Firstly, this study presents two types of specific materials to operate at raised temperatures in Concentrating Solar Power plants, particularly the central tower technology. The materials are AISI 347H stainless steel and the Ni-based alloy HRSA INCONEL 617. Then, a Life Cycle Assessment shows the influence and contribution to different impact categories from the elements that compose both metals, demonstrating that materials that provide better mechanical properties could have environmental shortcomings. This paper aims to contribute to an improved understanding of the environmental implications of these materials and which is the best choice in terms of sustainability. The results showed better environmental behavior in the AISI 347H case against INCONEL 617.Publicad

Life Cycle Assessment of heat transfer fluids in parabolic trough concentrating solar power technology

The majority of parabolic trough concentrating solar power plants consist of an indirect system where the heat transfer fluid (typically synthetic oil) exchanges energy with a secondary circuit which is connected to the power cycle. Synthetic oil has a technical limitation by the maximum operating temperature. This results in the search for new fluids. On the other hand, with the aim of having energy when there is no sun shining, it has increased the use of thermal storage. Thermal energy storage systems are composed of molten salts and presents higher operating temperatures than synthetic oil. Thus, direct systems, in which thermal storage and heat transfer fluid are unified and normally molten salts, emerge to improve the power cycle performance. To determine the future potential of direct systems, this paper evaluates the environmental damage of two types of molten salts and synthetic oil in order to decide whether the use of salts is better than synthetic oil, from an environmental point of view by using the Life Cycle Assessment (LCA) techniques. LCA results showed greater impacts in the syntheticoil case than the molten saltsPublicad

Influence of elemental composition in environmental impacts of steel

The environmental behavior of four steels was analyzed. In the operation phase of concentrating solar power plants, steels withstand high temperature because of its contact with molten salts. Hence, choosing the steel type for the molten salt tanks remains a great challenge. In the cold tank, carbon steel is usually used although an approach with low chromium content steel is being studied for these applications. Likewise, in high temperature applications, such as hot store tank, austenitic stainless steel is the most frequent choice. However, ferritic steel is being considered as a promising material in these applications. As many researchers studied the steel technical properties without considering their environmental damages, this work aimed to introduce the environmental aspects into the material choice by using the life cycle assessment technique. On one hand, the results showed the environmental adequacy of carbon steel against low chromium content steel. On the other hand, the results obtained in those steels suitable in high temperature application revealed significant environmental benefits from the ferritic steel instead of the austenitic steel