A hierarchical controller for miniature VTOL UAVs: Design and stability analysis using singular perturbation theory

This paper presents the design and the stability analysis of a hierarchical controller for unmanned aerial vehicles (UAV), using singular perturbation theory. Position and attitude control laws are successively designed by considering a time-scale separation between the translational dynamics and the orientation dynamics of a six degrees of freedom vertical take-off and landing (VTOL) UAV model. For the design of the position controller, we consider the case where the linear velocity of the vehicle is not measured. A partial state feedback control law is proposed, based on the introduction of a virtual state into the translational dynamics of the system. Results from simulation and from experiments on a miniature quadrirotor UAV are provided to illustrate the performance of the proposed control scheme.     

Characterization and reduction of noise in Mo/Au transition edge sensors

We measured noise in a variety of Mo/Au transition-edge sensor (TES) X-ray calorimeters. We investigated the relationship between the noise, bias, and the superconducting phase transition in the TESs. Our square TES calorimeters have achieved very good energy resolutions (2.4 eV at 1.5 keV) but their resolutions have been limited by broadband white excess noise generated by the TES when it is biased in the phase transition. We have recently fabricated Mo/Cu TESs with interdigitated normal metal bars deposited on top of the bilayer. The new TES calorimeters have demonstrated little or no excess noise in the phase transition. These results point the way to development of TES calorimeters with higher energy resolution.     

Effect of synthesis methods for mesoporous zirconia on its structural and textural properties

Zirconia was synthesized by sol–gel and post-hydrothermal treatment under autogenous pressure in order to study the effect of synthesis methods on its structural and textural properties. On the basis of thermal analysis, in situ X-ray diffraction and Raman spectroscopy techniques, the synthesis processes exhibit similar thermal behavior and zirconia phase transformation. The effect of in situ calcination temperature on the crystallization behavior, crystal phase transition, and crystallite size analysis was studied. The results obtained revealed that amorphous zirconia transformed into tetragonal phase above 400 °C and thermally stabilized up to 700 °C. A biphasic mixture of tetragonal and monoclinic zirconia was formed at 750 °C. Activation energy of sintering due to grain growth mechanism predicted that the zirconia phase transformation is due to the increase in the crystallite size of tetragonal phase above its critical size. The post-hydrothermal treatment resulted in the formation of high surface area mesoporous zirconia (213 m² g^?1). Upon increasing the calcination temperature, a pronounced decrease in the specific surface area of zirconia samples due to sintering process and phase transformation.     

Traffic-aware auto-configuration protocol for service oriented low-power and lossy networks in IoT

Wireless Networks - Many diversified services can be offered by smart objects, referred to herein by nodes, in low-power and lossy networks (LLNs) contributing to the Internet of Things (IoT). A...     

Some Remarks on Hydrogen Trapping

A model for the pressure-dependent diffusion and accumulation of hydrogen ahead of a decohesive intergranular crack front is developed. In the model, the pressure dependency of the diffusion is incorporated into the activation energy of an Arrhenius form of the material diffusivity along high-diffusivity grain boundaries. A key feature of the model is the ability to describe the trapping of hydrogen ahead of a decohesive crack front, which is observed in laboratory experiments.     

Comparison of Neural and Conventional Approaches to Mode Choice Analysis

This paper describes a new approach to behavioral mode choice modeling using neurofuzzy models. The new approach combines the learning ability of artificial neural networks and the transparent nature of fuzzy logic. The approach is found to be highly adaptive and efficient in investigating nonlinear relationships among different variables. In addition, the approach only selects the variables that significantly influence the mode choice and displays the stored knowledge in terms of fuzzy linguistic rules. This allows the modal decision-making process to be examined and understood in great detail. The neurofuzzy model is tested on the U.S. freight transport market using information on individual shipper and individual shipments. Shipments are disaggregated at the five-digit Standard Transportation Commodity Code level. Results obtained from this exercise are compared with similar results obtained from the conventional logit mode choice model and the standard back-propagation artificial neural network. The advantages of using the neurofuzzy approach are described.     

A coupled discrete element-finite difference model of selective laser sintering

Selective laser sintering (SLS) is an additive manufacturing technology whereby one can 3D print parts out of a powdered material. However, in order to produce defect free parts of sufficient strength, the process parameters (laser power, scan speed, powder layer thickness, etc.) must be carefully optimized depending on material, part geometry, and desired final part characteristics. Computational methods are very useful in the quick optimization of such parameters without the need to run numerous costly experiments. Most published models of this process involve continuum-based techniques, which require the homogenization of the powder bed and thus do not capture the stochastic nature of this process. Thus, the aim of this research is to produce a reduced order computational model of the SLS process which combines the essential physics with fast computation times. In this work the authors propose a coupled discrete element-finite difference model of this process. The powder particles are modeled as discrete, thermally and mechanically interacting spheres. The solid, underneath substrate is modeled via the finite difference method. The model is validated against experimental results in the literature and three-dimensional simulations are presented.     

Improving Design Coordination for Building Projects. I: Information Model

Detailed design of building projects is a complex multidisciplinary process highly dependent upon effective aggregation of individual designs to produce a coherent set of final design documents. Throughout the detailed design process, changes are frequently introduced and need to be properly managed among the various members of the design team. This paper presents an information model for storing design information, recording design rationale, and managing design changes. The proposed model is built around a central library of generalized building components that can be used to describe a complete building project hierarchy. Each component allows the designer to store desired performance criteria and related design rationale. Each component is also sensitive to its own changes and automatically communicates such changes to affected parties through preset communication paths. The model, as such, provides improved design coordination and control over changes, thus helping to increase the consistency and productivity of the overall design process. Conceptual details of the model are described in this paper, and model implementation into a collaborative design system is presented in a companion paper.