THE SENSITIVITY OF 2D COMPRESSOR INCIDENCE RANGE TO IN-SERVICE GEOMETRIC VARIATION

The loss mechanisms which control 2D incidence range are discussed with an emphasis on determining which real in-service geometric variations will have the largest impact. For the majority of engine compressor blades (Minlet>0.55) both the negative and positive incidence limits are controlled by supersonic patches. It is shown that these patches are highly sensitive to the geometric variations close to, and around the leading edge. The variations used in this study were measured from newly manufactured as well as ex-service blades. Over most the high pressure compressor considered, it was shown that manufacture variations dominated. The first part of the paper shows that, despite large geometric variations (~10% of leading edge thickness), the incidence range responded in a linear way. The result of this is that the geometric variations have little effect on the mean incidence range of a row of blades. In the second part of the paper a region of the design space is identified where non-linear behavior can result in a 10% reduction in positive incidence range. The mechanism for this is reported and design guidelines for its avoidance offered. In the final part of the paper, the linear behavior at negative incidence and the transonic nature of the flow is exploited to design a robust asymmetric leading edge with a 5% increase in incidence range.

Computer generated holograms for carbon nanotube arrays.

Multiwalled carbon nanotubes are highly diffractive structures in the optical regime. Their metallic character and large scattering cross-section allow their usage as diffractive elements in Fraunhofer holograms. This work elaborates some important features of the far field diffraction patterns produced from periodic arrays of nanotubes. A theoretical approach for the interaction of arrays of nanotubes with light is presented and a computer generated hologram is calculated by means of periodical patterns. Based on the results, fabrication of carbon nanotube arrays (in holographic patterns) was performed. Experimentally measured diffraction patterns were in good agreement with the calculations.

Self-similar organization of arrays of individual carbon nanotubes and carbon nanotube micropillars

It is well-known that carbon nanotube (CNT) growth from a dense arrangement of catalyst nanoparticles creates a vertically aligned CNT forest. CNT forests offer attractive anisotropic mechanical, thermal, and electrical properties, and their anisotropic structure is enabled by the self-organization of a large number of CNTs. This process is governed by individual CNT diameter, spacing, and the CNT-to-CNT interaction. However, little information is known about the self-organization of CNTs within a forest. Insight into the self-organization is, however, essential for tailoring the properties of the CNT forests for applications such as electrical interconnects, thermal interfaces, dry adhesives and energy storage. We demonstrate that arrays of CNT micropillars having micron-scale diameters organize in a similar manner as individual CNTs within a forest. For example, as previously demonstrated for individual CNTs within a forest, entanglement of small-diameter CNT micropillars during the initial stage of growth creates a film of entwined pillars. This layer enables coordinated subsequent growth of the pillars in the vertical direction, in a case where isolated pillars would not grow in a self-supporting fashion. Finally, we provide a detailed overview of the self-organization as a function of the diameter, length and spacing of the CNT pillars. This study, which is applicable to many one-dimensional nanostructured films, demonstrates guidelines for tailoring the self-organization which can enable control of the collective mechanical, electrical and interfacial properties of the films. © 2009 Elsevier B.V. All rights reserved.

Rank-preserving geometric means of positive semi-definite matrices

The generalization of the geometric mean of positive scalars to positive definite matrices has attracted considerable attention since the seminal work of Ando. The paper generalizes this framework of matrix means by proposing the definition of a rank-preserving mean for two or an arbitrary number of positive semi-definite matrices of fixed rank. The proposed mean is shown to be geometric in that it satisfies all the expected properties of a rank-preserving geometric mean. The work is motivated by operations on low-rank approximations of positive definite matrices in high-dimensional spaces.© 2012 Elsevier Inc. All rights reserved.

Riemannian metric and geometric mean for positive semidefinite matrices of fixed rank

This paper introduces a new metric and mean on the set of positive semidefinite matrices of fixed-rank. The proposed metric is derived from a well-chosen Riemannian quotient geometry that generalizes the reductive geometry of the positive cone and the associated natural metric. The resulting Riemannian space has strong geometrical properties: it is geodesically complete, and the metric is invariant with respect to all transformations that preserve angles (orthogonal transformations, scalings, and pseudoinversion). A meaningful approximation of the associated Riemannian distance is proposed, that can be efficiently numerically computed via a simple algorithm based on SVD. The induced mean preserves the rank, possesses the most desirable characteristics of a geometric mean, and is easy to compute. © 2009 Society for Industrial and Applied Mathematics.

Geometric optimization methods for independent component analysis applied on gene expression data

DNA microarrays provide a huge amount of data and require therefore dimensionality reduction methods to extract meaningful biological information. Independent Component Analysis (ICA) was proposed by several authors as an interesting means. Unfortunately, experimental data are usually of poor quality- because of noise, outliers and lack of samples. Robustness to these hurdles will thus be a key feature for an ICA algorithm. This paper identifies a robust contrast function and proposes a new ICA algorithm. © 2007 IEEE.

Cell proliferation tracking using graphene sensor arrays

The development of a novel label-free graphene sensor array is presented. Detection is based on modification of graphene FET devices and specifically monitoring the change in composition of the nutritive components in culturing medium. Micro-dispensing of Escherichia coli in medium shows feasibility of accurate positioning over each sensor while still allowing cell proliferation. Graphene FET device fabrication, sample dosing, and initial electrical characterisation have been completed and show a promising approach to reducing the sample size and lead time for diagnostic and drug development protocols through a label-free and reusable sensor array fabricated with standard and scalable microfabrication technologies. Copyright © 2012 Ronan Daly et al.

Geometric perspectives on MDO and MDO architectures

Two main perspectives have been developed within the Multidisciplinary Design Optimization (MDO) literature for classifying and comparing MDO architectures: a numerical point of view and a formulation/data flow point of view. Although significant work has been done here, these perspectives have not provided much in the way of a priori information or predictive power about architecture performance. In this report, we outline a new perspective, called the geometric perspective, which we believe will be able to provide such predictive power. Using tools from differential geometry, we take several prominent architectures and describe mathematically how each constructs the space through which it moves. We then consider how the architecture moves through the space which it has constructed. Taken together, these investigations show how each architecture relates to the original feasible design manifold, how the architectures relate to each other, and how each architecture deals with the design coupling inherent to the original system. This in turn lays the groundwork for further theoretical comparisons between and analyses of MDO architectures and their behaviour using tools and techniques derived from differential geometry. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Novel field emission from graphene sheets supported by CNTs arrays

A good quality graphene is transferred onto honeycomb-like CNTs arrays with inner supporting CNTs. The efficient field emission is demonstrated due to a high aspect ratio protrusions and graphene crack edges. A high efficient current density about 1.2 mA/cm2 at threshold electric field of 7.8 V/μm with a turn-on electric field of 1.8 V/μm at the current density of 10 μA/cm2 is observed due to high localized electric field. Stable field emission is tested in a vacuum chamber. The results are of significance to the development of Graphene based field emitters. © 2013 IEEE.

Instantaneous frequency and bandwidth estimation using filterbank arrays

Accurate estimation of the instantaneous frequency of speech resonances is a hard problem mainly due to phase discontinuities in the speech signal associated with excitation instants. We review a variety of approaches for enhanced frequency and bandwidth estimation in the time-domain and propose a new cognitively motivated approach using filterbank arrays. We show that by filtering speech resonances using filters of different center frequency, bandwidth and shape, the ambiguity in instantaneous frequency estimation associated with amplitude envelope minima and phase discontinuities can be significantly reduced. The novel estimators are shown to perform well on synthetic speech signals with frequency and bandwidth micro-modulations (i.e., modulations within a pitch period), as well as on real speech signals. Filterbank arrays, when applied to frequency and bandwidth modulation index estimation, are shown to reduce the estimation error variance by 85% and 70% respectively. © 2013 IEEE.

Dry oxidation and vacuum annealing treatments for tuning the wetting properties of carbon nanotube arrays.

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.(1,2) These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.(2) Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.(3-5) The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

Reversible tuning of the wettability of carbon nanotube arrays: the effect of ultraviolet/ozone and vacuum pyrolysis treatments.

Among diverse types of synthetic materials, arrays of vertically aligned carbon nanotubes have attracted the most attention, mainly because of their exceptional mechanical, electrical, optical, and thermal properties. However, their wetting properties are yet to be understood. In this present study, oxygenated surface functional groups have been identified as a vital factor in controlling the wetting properties of carbon nanotube arrays. The results presented herein indeed show that a combination of ultraviolet/ozone and vacuum pyrolysis treatments can be used to vary the surface concentration of these functional groups such that the carbon nanotube array can be repeatedly switched between hydrophilic and hydrophobic.

Effect of dry oxidation on the performance of carbon nanotube arrays electrochemical capacitors

In this study, the effect of dry oxidation on the electrochemical properties of carbon nanotube arrays is investigated. Oxygenated surface functional groups were introduced to the arrays by oxygen plasma treatment, where their surface concentrations were varied by controlling the exposure time. The finding presented herein shows an augmentation of nearly thirty times in term of specific capacitance when the arrays are oxidized. Similar behavior is also observed in the non-aqueous electrolytes where the specific capacitance of the oxidized carbon nanotube arrays is measured more than three times higher than that of the pristine ones. However, overexposure to oxygen plasma treatment reverses this effect. At such high oxidation level, the damage to the graphitic structure becomes more pronounced such that the capacitive behavior of the arrays is overshadowed by their resistive behavior. These findings are important for further development of carbon nanotube based electrochemical capacitors. © 2012 Materials Research Society.

Deterministic cold cathode electron emission from carbon nanofibre arrays.

The ability to accurately design carbon nanofibre (CN) field emitters with predictable electron emission characteristics will enable their use as electron sources in various applications such as microwave amplifiers, electron microscopy, parallel beam electron lithography and advanced Xray sources. Here, highly uniform CN arrays of controlled diameter, pitch and length were fabricated using plasma enhanced chemical vapour deposition and their individual emission characteristics and field enhancement factors were probed using scanning anode field emission mapping. For a pitch of 10 µm and a CN length of 5 µm, the directly measured enhancement factors of individual CNs was 242, which was in excellent agreement with conventional geometry estimates (240). We show here direct empirical evidence that in regular arrays of vertically aligned CNs the overall enhancement factor is reduced when the pitch between emitters is less than half the emitter height, in accordance to our electrostatic simulations. Individual emitters showed narrow Gaussian-like field enhancement distributions, in excellent agreement with electric field simulations.