Challenges in Developing a Bessel-Beam Based Ultrafast Ablation Probe

Instruments and Experimental Techniques - With its elongated depth of focus, Bessel beams offer rapid and high aspect ratio ablation capability, in contrast to Gaussian beam counterparts. In this...     

Flow-Boundary Effects on Critical Submergence of Intake Pipe

In this study, the effects of intake-pipe blockage and location of impervious boundaries on critical submergence of an intake pipe are presented. Experiments were conducted on a horizontal intake pipe sited in a dead-end canal flow. Theoretical results and available experimental data are compared. It is shown that, as the distance between the intake-pipe entrance and the dead end gets smaller than the critical submergence depth, the deviation between theoretical and experimental results increases. A potential flow solution still gives acceptable results when this distance is smaller than the critical submergence, but it overpredicts by about 80% when the distance between the intake-pipe entrance becomes much smaller than the critical submergence depth.     

Identification of structural non-linearities using describing functions and the Sherman–Morrison method

In this study, a new method for type and parametric identification of a non-linear element in an otherwise linear structure is introduced. This work is an extension of a previous study in which a method was developed to localize non-linearity in multi-degree of freedom systems and to identify type and parameters of the non-linear element when it is located at a ground connection of the system. The method uses a describing function approach for representing the non-linearity in the structure. The describing function contains only the first harmonic terms. The Sherman–Morrison matrix inversion method is used in the present study to put the response expression in a form where the non-linearity term can be isolated. Using measured responses one can calculate the value of the describing function representation of the non-linear element and thus perform the identification. This new method can be used for type and parametric identification of a non-linear element between any two coordinates of the system. Case studies are given to demonstrate the applicability of the method.     

Formability of Ultrafine-Grained Interstitial-Free Steels

The stretch formability of ultrafine-grained (UFG) interstitial-free steel (IF-steel) produced by equal-channel angular extrusion/pressing (ECAE/P) via various strain paths was investigated with a miniaturized Erichsen test. A coarse-grained (CG) sample demonstrated high formability with an Erichsen index (EI) of 4.5 mm. Grain refinement by ECAE decreased the formability, but increased the required punch load (F _EI) depending on the applied strain paths. The EI values were 0.35, 2.90, and 3.91 mm for 8A-, 8Bc-, and 8C-processed samples, respectively. Decrease in the biaxial stretch formability was attributed to the limited strain-hardening capacity of the UFG microstructure. Also, the grain morphology of the UFG microstructure was found to be very influential on stretch formability. Heavily elongated grain morphology in the 8A-processed microstructure resulted in the lowest formability due to the increased cracking tendency through elongated grain boundaries. However, the UFG microstructures with equiaxed grains obtained after 8C and 8Bc ECAE resulted in better formability compared to 8A. The UFG microstructure reduced the roughness (orange peel effect) of the free surface of the biaxial stretched samples by decreasing the non-uniform grain flow leading to the so-called orange peel effect. It should be noted that the strength and ductility values gained from uniaxial tensile tests are not comparable directly to the EI and F _EI values determined from the Erichsen tests. Finally, it is important to emphasize that the UFG microstructure produced by a suitable strain path leading to equiaxed grains below 1 μm could be highly deformed even under multiaxial stress conditions.     

Concatenation of space‐time block codes and turbo trellis coded modulation (ST‐TTCM) over Rician fading channels with imperfect phase

In this paper, the performance of space time‐turbo trellis coded modulation (ST‐TTCM) is evaluated over Rician and Rayleigh fading channels with imperfect phase. We modify Baum–Welch (BW) algorithm to estimate the fading and phase jitter parameters for multi‐antenna configurations. Thus, we assume that the channel parameters change slower than carrier frequency. We know that, at high data rate transmissions over wireless fading channels, space–time block codes (STBC) provide the maximal possible diversity advantage. Here, the combined effects of the amplitude and the phase of the received signal are considered, each one modelled by Rician and Tikhonov distributions, respectively. We investigate space time‐turbo trellis coded modulation (ST‐TTCM) for 8‐PSK for several Rician factor K and phase distortion factor η. Thus, our results reflect the degradations both due to the effects of the fading on the amplitude and phase noise of the received signal while the channel parameters are estimated by BW algorithm. Copyright © 2004 John Wiley & Sons, Ltd.     

Out of Context: NMDA Receptor Antagonism in the Avian 'Prefrontal Cortex' Impairs Context Processing in a Conditional Discrimination Task.

Processing of context information is implicated in prefrontal functions as response selection or attention. N-methyl-D-aspartate (NMDA) receptors in the mammalian prefrontal cortex (PFC) and in the nidopallium caudolaterale (NCL) of birds, the avian functional equivalent of the PFC, are involved in learning, which also requires processing of context. The authors investigated the role of NMDA receptors in the pigeon (Columba livia) NCL for context processing and response selection in a simultaneous-matching-to-sample task with 2 trial types, requiring either processing of context information, delivered by a conditional stimulus (context dependent), or only recall of a stimulus-response association (fixed response). The competitive NMDA antagonist DL-2-amino-5-phosphonovaleric acid impaired performance only in context-dependent trials. Therefore, NMDA receptors in the avian PFC participate in response selection requiring context processing rather than in response selection per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of deflection amplification factor in steel moment‐resisting frames

Steel moment‐resisting frames (SMRFs) are the most common type of structural systems used in steel structures. The first step of structural design for SMRFs starts with the selection of the structural sections on the basis of story drift limitation. ASCE 7 (2010) requires that the inelastic story drifts be obtained by multiplying the deflections determined by elastic analysis under design earthquake forces with a deflection amplification factor (C_d). For special moment‐resisting frames, C_d is given as 5.5 in ASCE 7 (2010). Lower C_d values will increase the overall inelastic response of the structure. On the other hand, the inelastic response of the structure is expected to be less severe when designed for higher C_d values. The performance objective is that the structure should sustain the inelastic deformation demand imposed due to design earthquake ground motions. This study aims at investigating the inelastic seismic response that low‐rise, medium‐rise and high‐rise SMRFs can experience under design earthquake ground motions and maximum considered earthquake (MCE) level ground motions and evaluating the deflection amplification factors (C_d) for SMRFs in a rational way. For this purpose, nonlinear dynamic time history and pushover analyses will be carried out on SMRFs with 4, 9 and 20 stories. The results indicate that the current practice for computing the inelastic story drifts for SMRFs is rational and the frames designed complying with the current code requirements can sustain the inelastic deformations imposed during design earthquake ground motions when seismically designed and detailed. Copyright © 2013 John Wiley & Sons, Ltd.     

A review: Fibre metal laminates,background, bonding types and applied test methods

During the past decades, increasing demand in aircraft industry for high-performance, lightweight structures have stimulated a strong trend towards the development of refined models for fibre-metal laminates (FMLs). Fibre metal laminates are hybrid composite materials built up from interlacing layers of thin metals and fibre reinforced adhesives. The most commercially available fibre metal laminates (FMLs) are ARALL (Aramid Reinforced Aluminium Laminate), based on aramid fibres, GLARE (Glass Reinforced Aluminium Laminate), based on high strength glass fibres and CARALL (Carbon Reinforced Aluminium Laminate), based on carbon fibres. Taking advantage of the hybrid nature from their two key constituents: metals (mostly aluminium) and fibre-reinforced laminate, these composites offer several advantages such as better damage tolerance to fatigue crack growth and impact damage especially for aircraft applications. Metallic layers and fibre reinforced laminate can be bonded by classical techniques, i.e. mechanically and adhesively. Adhesively bonded fibre metal laminates have been shown to be far more fatigue resistant than equivalent mechanically bonded structures.     

Node pacing for small optical RAM-buffered packet-switching networks

One of the difficulties with optical packet switched (OPS) networks is buffering optical packets in the network. The only available solution that can currently be used for buffering in the optical domain is using long fiber lines called fiber delay lines (FDLs), which have severe limitations. Moreover, the research on optical RAM presently being done is not expected to achieve a large capacity soon. However, the burstiness of Internet traffic causes high packet drop rates and low utilization in very small buffered OPS networks. We therefore propose a new node-based pacing algorithm for decreasing burstiness. We show that by applying some simple pacing at the edge or core backbone nodes, the performance of very small optical RAM buffered core OPS networks with variable-length packets can be notably increased.     

Weighted averaging for denoising with overcomplete dictionaries.

We consider the scenario where additive, independent, and identically distributed (i.i.d) noise in an image is removed using an overcomplete set of linear transforms and thresholding. Rather than the standard approach, where one obtains the denoised signal by ad hoc averaging of the denoised estimates provided by denoising with each of the transforms, we formulate the optimal combination as a conditional linear estimation problem and solve it for optimal estimates. Our approach is independent of the utilized transforms and the thresholding scheme, and as we illustrate using oracle-based denoisers, it extends established work by exploiting a separate degree of freedom that is, in general, not reachable using previous techniques. Our derivation of the optimal estimates specifically relies on the assumption that the utilized transforms provide sparse decompositions. At the same time, our work is robust as it does not require any assumptions about image statistics beyond sparsity. Unlike existing work, which tries to devise ever more sophisticated transforms and thresholding algorithms to deal with the myriad types of image singularities, our work uses basic tools to obtain very high performance on singularities by taking better advantage of the sparsity that surrounds them. With well-established transforms, we obtain results that are competitive with state-of-the-art methods.