Modal analysis of UH-60A instrumented rotor blades

The dynamic characteristics of instrumented and production UH-60A Black Hawk main rotor blades were measured, and the results were validated with NASTRAN finite element models. The blades tested included pressure and strain-gage instrumented blades, which are part of the NASA Airloads Flight Research Phase of the Modern Technology Rotor Program. The dynamic similarity of the blades was required for accurate data collection in this program. Therefore, a nonrotating blade modal analysis was performed on the first 10 free-free modes to measure blade similarities. The results showed small differences between the modal frequencies of instrumented and production blades and a close correlation with the NASTRAN models. This type of modal testing and analysis is recommended as a standard procedure for future instrumented blade flight testing

COMBINING QUANTITATIVE AND QUALITATIVE APPROACHES TO RURAL DEVELOPMENT ANALYSIS: THE CASE OF AGRICULTURAL INTENSIFICATION IN LEBANON

While peripheral rural regions in Lebanon face typical problems of lagging development and economic marginalisation, they have not been regarded as a priority for policy-makers, and significant disparities between these and other regions have emerged as a result. Local extensionists have encouraged technological innovation as a means to improving farmers’ livelihoods, and this has led to increasing input use and an intensification of agricultural production. This paper applies contrasting quantitative and qualitative methodologies to analyse the effects of such changes at the level of the overall economy of Lebanon and also to explore the impacts on rural households. A Computable General Equilibrium (CGE) model explores several simulation scenarios in which agricultural output increases due to intensification in the use of intermediate inputs. The results are evaluated at local level through the use of qualitative case-study analysis carried out in the Hermel region of northeast Lebanon. Quantitative simulations indicate that, while intensification has a positive effect overall on the Lebanese economy, the effects on rural households and the income of farmers are negative; the case-study demonstrates that, at local level, agricultural trade liberalisation, increased agricultural output and greater volatility of commodity prices has resulted in farmers opting for lower input use and more secure market forms of production.Community/Rural/Urban Development,

Finite element modeling of laser assisted friction stir welding of carbon steels for enhanced sustainability of welded joints

Part of: Seliger, Günther (Ed.): Innovative solutions : proceedings / 11th Global Conference on Sustainable Manufacturing, Berlin, Germany, 23rd - 25th September, 2013. - Berlin: Universitätsverlag der TU Berlin, 2013. - ISBN 978-3-7983-2609-5 (online). - http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-40276. - pp. 247-251.In Friction stir welding (FSW) of carbon steels, process parameters must be set to avoid defects such as warm holes. Proper selection of process parameters also affects the final grain microstructure and phase transformations and, ultimately, the weld’s mechanical properties. Process parameters, including laserassisted heating, of AISI 1045 carbon steel were investigated via a 3D finite element method (FEM) model. The laser action was modeled as heat source with constant flux. The simulation findings favorably agree with experiments reported in the literature and suggesting that with laser-assisted-FSW welding can be performed at higher traverse speeds (400 vs. 100 mm/min) while maintaining defect free weld. Also, evolved phase transformations are predicted across the weld geometry as time progresses. Such findings will help in the prediction of sound welding parameters and in estimating the mechanical properties of the various regions of the weld leading to more sustainable joints

Adaptive Mesh Refinement for Coupled Elliptic-Hyperbolic Systems

We present a modification to the Berger and Oliger adaptive mesh refinement algorithm designed to solve systems of coupled, non-linear, hyperbolic and elliptic partial differential equations. Such systems typically arise during constrained evolution of the field equations of general relativity. The novel aspect of this algorithm is a technique of "extrapolation and delayed solution" used to deal with the non-local nature of the solution of the elliptic equations, driven by dynamical sources, within the usual Berger and Oliger time-stepping framework. We show empirical results demonstrating the effectiveness of this technique in axisymmetric gravitational collapse simulations. We also describe several other details of the code, including truncation error estimation using a self-shadow hierarchy, and the refinement-boundary interpolation operators that are used to help suppress spurious high-frequency solution components ("noise").Comment: 31 pages, 15 figures; replaced with published versio

Evaluation of Three Rapid Tests for Diagnosis of P. Falciparum and P. Vivax Malaria in Colombia.

The diagnostic capacity of three malaria rapid diagnostic tests (RDTs), NOW-Malaria-ICT, OptiMAL-IT, and Paracheck-Pf, was evaluated against expert microscopy in Colombia. We tested 896 patients, of whom microscopy confirmed 139 P. falciparum, 279 P. vivax, and 13 mixed P.f/P.v infections and 465 negatives. Paracheck-Pf and NOW-malaria-ICT were more accurate in detecting P. falciparum (sensitivities 90.8% and 90.1%, respectively) in comparison with Optimal-IT (83.6%). NOW showed an acceptable Pf detection rate at low densities (< 500/microL), but resulted in a higher proportion of false positives. For P. vivax diagnosis, Optimal-IT had a higher sensitivity than NOW (91.0% and 81.4%, respectively). The choice between the two Pf/Pv detecting RDTs balances P. falciparum and P. vivax detection rates. Considering some degree of P. falciparum overtreatment and failure to detect all P. vivax cases as more acceptable than missing some cases of P. falciparum, we recommend careful implementation of NOW-malaria-ICT in areas where microscopy is lacking. The price is however still a constraint

Particle Creation in the Marginally Bound, Self Similar Collapse of Inhomogeneous Dust

We consider the evaporation of the (shell focusing) naked singularity formed during the self-similar collapse of a marginally bound inhomogeneous dust cloud, in the geometric optics approximation. We show that, neglecting the back reaction of the spacetime, the radiation on \scrip tends to infinity as the Cauchy Horizon is approached. Two consequences can be expected from this result: (a) that the back reaction of spacetime will be large and eventually halt the formation of a naked singularity thus preserving the Cosmic Censorship Hypothesis and (b) matter attempting to collapse into a naked singularity will radiate away energy at an intense rate, thereby possibly providing experimental signatures of quantum effects in curved spacetimes.Comment: 18 pages, 4 figures. Version to appear in Nucl. Phys.

Scaling of curvature in sub-critical gravitational collapse

We perform numerical simulations of the gravitational collapse of a spherically symmetric scalar field. For those data that just barely do not form black holes we find the maximum curvature at the position of the central observer. We find a scaling relation between this maximum curvature and distance from the critical solution. The scaling relation is analogous to that found by Choptuik for black hole mass for those data that do collapse to form black holes. We also find a periodic wiggle in the scaling exponent.Comment: Revtex, 2 figures, Discussion modified, to appear in Phys. Rev.

Dynamics of false vacuum bubbles: beyond the thin shell approximation

We numerically study the dynamics of false vacuum bubbles which are inside an almost flat background; we assumed spherical symmetry and the size of the bubble is smaller than the size of the background horizon. According to the thin shell approximation and the null energy condition, if the bubble is outside of a Schwarzschild black hole, unless we assume Farhi-Guth-Guven tunneling, expanding and inflating solutions are impossible. In this paper, we extend our method to beyond the thin shell approximation: we include the dynamics of fields and assume that the transition layer between a true vacuum and a false vacuum has non-zero thickness. If a shell has sufficiently low energy, as expected from the thin shell approximation, it collapses (Type 1). However, if the shell has sufficiently large energy, it tends to expand. Here, via the field dynamics, field values of inside of the shell slowly roll down to the true vacuum and hence the shell does not inflate (Type 2). If we add sufficient exotic matters to regularize the curvature near the shell, inflation may be possible without assuming Farhi-Guth-Guven tunneling. In this case, a wormhole is dynamically generated around the shell (Type 3). By tuning our simulation parameters, we could find transitions between Type 1 and Type 2, as well as between Type 2 and Type 3. Between Type 2 and Type 3, we could find another class of solutions (Type 4). Finally, we discuss the generation of a bubble universe and the violation of unitarity. We conclude that the existence of a certain combination of exotic matter fields violates unitarity.Comment: 40 pages, 41 figure

Scale invariance and critical gravitational collapse

We examine ways to write the Choptuik critical solution as the evolution of scale invariant variables. It is shown that a system of scale invariant variables proposed by one of the authors does not evolve periodically in the Choptuik critical solution. We find a different system, based on maximal slicing. This system does evolve periodically, and may generalize to the case of axisymmetry or of no symmetry at all.Comment: 7 pages, 3 figures, Revtex, discussion modified to clarify presentatio