Phase doppler measurements: system set-up optimization for characterization of a diesel nozzle

A commercial phase Doppler system was set up, optimized and used to measure the time resolved characteristics of the droplets inside a diesel spray. The purpose of this work was to understand exactly the influence of each system parameter, and to find the best setup enabling measurements in the spray zones that are densest and closest to the injector. Parametric studies were performed to gain an understanding of the particle density limits of the system and their dependence on the system parameters. Then the diesel spray produced by a single-hole injector was measured, with the fuel pressure ranging from 300 to 1300 bar and gas density in the test chamber ranging from ambient conditions to 40 kg/m³. The optic parameters (beam waist size, lenses focal length) were chosen to the best expected values allowed by the optical stand-off of the spray enclosure. The receiver slit width, which was found to have a dramatic effect on the detection of droplets during the injection main period, was tested in the range from 100 μm to 25 μm. Tests were carried out with two different slit lengths, namely 1 mm and 50 μm, with results indicating minimal effect on performance. PMT voltage (gain) was held to a moderately low value between 400 and 500 V and the laser power between 400 and 800 mW in the green line. An optimum burst threshold was found to obtain the best quality data regardless of signal background level, which varies greatly in high-density pulsed sprays. In the end, a set of results from the complete nozzle characterization in various conditions is presented in order to show the practical application of the optimization study and to provide some means of appreciating the results accuracy. The results obtained were also used to show that the gas-jet theory can be used to predict if PDPA measurement are possible in a given experimental situation.     

Analytical study on the mode III stress fields due to blunt notches with cracks

This work presents an analytical study on the stress fields induced by cracks nucleated at the tip of radiused notches under antiplane shear and torsion loadings. Closed‐form solutions for both shallow and deep notches are derived leveraging a combination of proper curvilinear coordinate systems and the complex potential method for antiplane elasticity. Based on the exact stress field solutions, convenient expressions for the stress intensity factors are derived. The accuracy of all the analytical formulations is verified by comparison with the results from a bulk of numerical analyses.     

Guidelines for the Integration of Autonomous UAS into the Global ATM

The growing social and economic interest in new unmanned aircraft systems (UASs) applications demands that UASs operate beyond the segregated airspace they are currently able to fly. However, UAS operations in non-segregated airspace should be regulated by aeronautical authorities before UASs can share airspace with manned aircraft. It has been a challenge for regulatory authorities to define these regulations because they do not understand the topic well. In addition, there is no consensus in the academic community regarding UAS concepts, such as taxonomy and features. This study proposes guidelines that could support UAS regulations for the future integration of autonomous UASs into the Global Air Traffic Management System (GATM). These guidelines are based on three viewpoints: the aircraft, the piloting autonomous system (PAS) and the integration of autonomous UASs into non-segregated airspace. We recommend that the UAS concept should be based on genuine aeronautical precepts, which would be directly applied, without terminology or conceptual adaptations, for the integration of these aircraft into airspace according to the GATM paradigm.     

Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale

Magnetic Resonance Materials in Physics, Biology and Medicine - An initiative to design and build magnetic resonance imaging (MRI) and spectroscopy (MRS) instruments at 14 T and beyond to...     

Scattering and radiation analysis of cavity-backed microstrip patch antennae with anisotropic slabs via a variational formulation

Abstract

In this paper we examine an arbitrarily shaped cavity-backed microstrip patch antenna with a very general anisotropic grounded slab. We apply a hybrid finite-element-boundary-integral method. We use the finite-element method to solve the Helmholtz equation in the interior of the micro-strip antenna and use the boundary-integral method, together with the dyadic Green function approach, to determine the fields exterior to the microstrip patch antenna. We couple the two methods at the interface plane by enforcing the field continuity conditions. Several numerical results are presented demonstrating the validity, efficiency and capability of this technique.     

Nickel Sensitivity Is Associated with GH-IGF1 Axis Impairment and Pituitary Abnormalities on MRI in Overweight and Obese Subjects

Nickel (Ni) is a ubiquitous metal, the exposure of which is implied in the development of contact dermatitis (nickel allergic contact dermatitis (Ni-ACD)) and Systemic Ni Allergy Syndrome (SNAS), very common among overweight/obese patients. Preclinical studies have linked Ni exposure to abnormal production/release of Growth Hormone (GH), and we previously found an association between Ni-ACD/SNAS and GH-Insulin-like growth factor 1 (IGF1) axis dysregulation in obese individuals, altogether suggesting a role for this metal as a pituitary disruptor. We herein aimed to directly evaluate the pituitary gland in overweight/obese patients with signs/symptoms suggestive of Ni allergy, exploring the link with GH secretion; 859 subjects with overweight/obesity and suspected of Ni allergy underwent Ni patch tests. Among these, 106 were also suspected of GH deficiency (GHD) and underwent dynamic testing as well as magnetic resonance imaging for routine follow up of benign diseases or following GHD diagnosis. We report that subjects with Ni allergies show a greater GH-IGF1 axis impairment, a higher prevalence of Empty Sella (ES), a reduced pituitary volume and a higher normalized T2 pituitary intensity compared to nonallergic ones. We hypothesize that Ni may be detrimental to the pituitary gland, through increased inflammation, thus contributing to GH-IGF1 axis dysregulation.     

MatCarloRe: An integrated FT and Monte Carlo Simulink tool for the reliability assessment of dynamic fault tree

With the aim of a more effective representation of reliability assessment for real industry, in the last years concepts like dynamic fault trees (DFT) have gained the interest of many researchers and engineers (dealing with problems concerning safety management, design and development of new products, decision analysis and project management, maintenance of industrial plant, etc.). With the increased computational power of modern calculators is possible to achieve results with low modeling efforts and calculating time. Supported by the strong mathematical basis of state space models, the DFT technique has increased its popularity. Nevertheless, DFT analysis of real application has been more likely based on a specific case to case resolution procedure that often requires a great effort in terms of modeling by the human operator. Moreover, limitations like the state space explosion for increasing number of components, the constrain of using exponential distribution for all kind of basic events constituting any analyzed system and the ineffectiveness of modularization for DFT which exhibit dynamic gates at top levels without incurring in calculation and methodological errors are faces of these methodologies. In this paper we present a high level modeling framework that exceeds all these limitations, based on Monte Carlo simulation. It makes use of traditional DFT systemic modeling procedure and by replicating the true casual nature of the system can produce relevant results with low effort in term of modeling and computational time. A Simulink library that integrates Monte Carlo and FT methodologies for the calculation of DFT reliability has been developed, revealing new insights about the meaning of spare gates.     

Comparison of the Methods for the Determination of Surface Acidity of Solid Catalysts

The concept of surface acidity was originally introduced with the aim of justifying the presence of some substances formed in catalytic chemical reactions, not as a consequence of suppositions about the nature of surface-active sites of solid catalysts. The formation of such substances in some reactions (e.g., cracking, isomerization, or polymerization) can be better explained by admitting the formation of reaction intermediates having the structure of a carbonium ion, which can be formed by interaction between the reacting substance (hydrocarbon) and an acid center. As an example, in the cracking of alkylaromatics catalyzed by decationated zeolites, the following reaction mechanism is generally accepted:     

Electromagnetic wave propagation in rectangular waveguides filled with Omega-medium

A time-harmonic electromagnetic plane wave propagating in a uniaxial bianisotropic medium, the so-called Omega medium, is considered. Plane waves are identified together with their dispersion equations with the help of an appropriate coordinate system. The plane wave solution is then used to study in a rigorous way the coupled-mode equations satisfied by the electromagnetic field in a rectangular waveguide filled with such a material and bounded by perfect electrically conducting walls. The features of this approach are demonstrated and an application to rectangular waveguides is discussed. Numerical results are also presented as a function of the material parameters.