bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasticity in the brainstem vagal circuits controlling gastric motor function triggered by corticotropin releasing factor
Authors: Browning Kirsteen N. , Babic Tanja , Toti Luca , Holmes Gregory M. , Coleman F. Holly , Travagli R. Alberto
Published: August 2014

Key points

The prototypical stress hormone, corticotropin releasing factor (CRF), and the prototypical anti‐stressor hormone, oxytocin (OXT), are known to modulate brainstem neurocircuits involved in visceral reflexes.

We demonstrated recently that the brainstem neurocircuits through which OXT exerts its actions are modulated by vagal afferent fibres; however, it is unknown whether the OXT‐induced modulation of brainstem vagal neurocircuits is also regulated differentially by CRF.

Here we elucidate the cellular mechanisms and the effects on gastric tone of OXT following exposure of vagal brainstem neurones to CRF and report that CRF induces short‐term plastic changes in OXT‐sensitive vagal neurocircuits.

The results presented may represent a possible mechanism through which stress alters the central regulation of gastrointestinal functions and may reflect the vagal dysregulation occurring as a consequence of stress‐exacerbated functional dyspepsia.

Stress impairs gastric emptying, reduces stomach compliance and induces early satiety via vagal actions. We have shown recently that the ability of the anti‐stress neuropeptide oxytocin (OXT) to modulate vagal brainstem circuits undergoes short‐term plasticity via alterations in cAMP levels subsequent to vagal afferent fibre‐dependent activation of metabotropic glutamate receptors. The aim of the present study was to test the hypothesis that the OXT‐induced gastric response undergoes plastic changes in the presence of the prototypical stress hormone, corticotropin releasing factor (CRF). Whole cell patch clamp recordings showed that CRF increased inhibitory GABAergic synaptic transmission to identified corpus‐projecting dorsal motor nucleus of the vagus (DMV) neurones. In naive brainstem slices, OXT perfusion had no effect on inhibitory synaptic transmission; following exposure to CRF (and recovery from its actions), however, re‐application of OXT inhibited GABAergic transmission in the majority of neurones tested. This uncovering of the OXT response was antagonized by pretreatment with protein kinase A or adenylate cyclase inhibitors, H89 and di‐deoxyadenosine, respectively, indicating a cAMP‐mediated mechanism. In naive animals, OXT microinjection in the dorsal vagal complex induced a NO‐mediated corpus relaxation. Following CRF pretreatment, however, microinjection of OXT attenuated or, at times reversed, the gastric relaxation which was insensitive to l‐NAME but was antagonized by pretreatment with a VIP antagonist. Immunohistochemical analyses of vagal motoneurones showed an increased number of oxytocin receptors present on GABAergic terminals of CRF‐treated or stressed vs. naive rats. These results indicate that CRF alters vagal inhibitory circuits that uncover the ability of OXT to modulate GABAergic currents and modifies the gastric corpus motility response to OXT.
Different fixational eye movements mediate the prevention and the reversal of visual fading
Authors: McCamy Michael B. , Macknik Stephen L. , Martinez‐Conde Susana
Published: August 2014

Key points

Fixational eye movements (microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different fixational eye movements influence this process is a matter of debate.

Previous studies confounded the reversal of fading (where vision is restored after fading) with its prevention (where fading is blocked before it happens). We found that, whereas microsaccades are most important to reversing fading, both microsaccades and drift help to prevent it.

Drift's contribution to preventing fading is potentially larger than that of microsaccades, but microsaccades prevent fading with higher efficacy than drift.

Microsaccades prevent foveal and peripheral fading in an equivalent fashion, and microsaccadic efficacy does not depend on microsaccade size, number, or direction; further, faster drift may prevent fading better than slower drift.

These combined findings help reconcile the long‐standing controversy concerning the roles of microsaccades and drift in visibility during fixation.

Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long‐standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation.
Determination of cable parameters in skeletal muscle fibres during repetitive firing of action potentials
Authors: Riisager Anders , Duehmke Rudy , Nielsen Ole Bækgaard , Huang Christopher L. , Pedersen Thomas Holm
Published: August 2014

Key points

Current methods for determination of the resting membrane conductance in active, action potential‐firing muscle fibres are based on the assumptions that the volume and the cytosolic composition of the fibres remain constant during activity.

Here, we present a microelectrode‐based method that without such assumptions measures a range of cable parameters including the resting membrane conductance together with action potential characteristics of individual fibres during intermittent action potential firing.

The method can be used to study the role of activity‐induced regulation of the resting membrane conductance for action potential excitation and propagation in active muscles.

Recent studies in rat muscle fibres show that repetitive firing of action potentials causes changes in fibre resting membrane conductance (Gm) that reflect regulation of ClC‐1 Cl− and KATP K+ ion channels. Methodologically, these findings were obtained by inserting two microelectrodes at close proximity in the same fibres enabling measurements of fibre input resistance (Rin) in between action potential trains. Since the fibre length constant (λ) could not be determined, however, the calculation of Gm relied on the assumptions that the specific cytosolic resistivity (Ri) and muscle fibre volume remained constant during the repeated action potential firing. Here we present a three‐microelectrode technique that enables determinations of multiple cable parameters in action potential‐firing fibres including Rin and λ as well as waveform and conduction velocities of fully propagating action potentials. It is shown that in both rat and mouse extensor digitorum longus (EDL) fibres, action potential firing leads to substantial changes in both muscle fibre volume and Ri. The analysis also showed, however, that regardless of these changes, rat and mouse EDL fibres both exhibited initial decreases in Gm that were eventually followed by a ∼3‐fold, fully reversible increase in Gm after the firing of 1450–1800 action potentials. Using this three‐electrode method we further show that the latter rise in Gm was closely associated with excitation failures and loss of action potential signal above −20 mV.
The Effects of Vane Showerhead Injection Angle and Film Compound Angle on Nozzle Endwall Cooling (Phantom Cooling)
Authors: Zhang Luzeng , Yin Juan , Koo Moon Hee
Published: August 2014

The effects of airfoil showerhead (SH) injection angle and film-cooling hole compound angle on nozzle endwall cooling (second order film-cooling effects, also called "phantom cooling") were experimentally investigated in a scaled linear cascade. The test cascade was built based on a typical industrial gas turbine nozzle vane. Endwall surface phantom cooling film effectiveness measurements were made using a computerized pressure sensitive paint (PSP) technique. Nitrogen gas was used to simulate cooling flow as well as a tracer gas to indicate oxygen concentration such that film effectiveness can be obtained by the mass transfer analogy. Two separate nozzle test models were fabricated, which have the same number and size of film-cooling holes but different configurations. One had a SH angle of 45 deg and no compound angles on the pressure and suction side (SS) film holes. The other had a 30 deg SH angle and 30 deg compound angles on the pressure and SS film-cooling holes. Nitrogen gas (cooling air) was fed through nozzle vanes, and measurements were conducted on the endwall surface between the two airfoils where no direct film cooling was applied. Six cooling mass flow ratios (MFRs, blowing ratios) were studied, and local (phantom) film effectiveness distributions were measured. Film effectiveness distributions were pitchwise averaged for comparison. Phantom cooling on the endwall by the SS film injections was found to be insignificant, but phantom cooling on the endwall by the pressure side (PS) airfoil film injections noticeably helped the endwall cooling (phantom cooling) and was a strong function of the MFR. It was concluded that reducing the SH angle and introducing a compound angle on the PS injections would enhance the endwall surface phantom cooling, particularly for a higher MFR.
Quantitative Computational Fluid Dynamics Analyses of Particle Deposition on a Transonic Axial Compressor Blade—Part I: Particle Zones Impact
Authors: Suman Alessio , Kurz Rainer , Aldi Nicola , Morini Mirko , Brun Klaus , Pinelli Michele , Ruggero Spina Pier
Published: August 2014

Solid particle ingestion is one of the principal degradation mechanisms in the turbine and compressor sections of gas turbines. In particular, in industrial applications, the microparticles that are not captured by the air filtration system cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which areas of the compressor airfoils are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separate from the continuous phase. Then, the NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase treatment have been validated against the experimental and numerical data available in literature. The number of particles, sizes, and concentrations are specified in order to perform a quantitative analysis of the particle impact on the blade surface. The results show that microparticles tend to follow the flow by impacting at full span with a higher impact concentration on the pressure side (PS). The suction side (SS) is affected only by the impact of the smaller particles (up to 1 μm). Particular fluid dynamic phenomena, such as separation, stagnation point, and tip leakage vortex, strongly influence the impact location of the particles.
Quantitative Computational Fluid Dynamic Analyses of Particle Deposition on a Transonic Axial Compressor Blade—Part II: Impact Kinematics and Particle Sticking Analysis
Authors: Suman Alessio , Morini Mirko , Kurz Rainer , Aldi Nicola , Brun Klaus , Pinelli Michele , Ruggero Spina Pier
Published: August 2014

In heavy-duty gas turbines, the microparticles that are not captured by the air filtration system can cause fouling and, consequently, a performance drop of the compressor. This paper presents three-dimensional numerical simulations of the microparticle ingestion (0 μm–2 μm) on an axial compressor rotor carried out by means of a commercial computational fluid dynamic (CFD) code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The NASA Rotor 37 is considered as a case study for the numerical investigation. The compressor rotor numerical model and the discrete phase model were previously validated by the authors in the first part of this work. The kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface of an axial transonic compressor are shown. The blade zones affected by particle impact were extensively analyzed and reported in the first part of this work, forming the starting point for the analyses shown in this paper. The kinematic analysis showed a high tendency of particle adhesion on the suction side (SS), especially for the particles with a diameter equal to 0.25 μm. Fluid dynamic phenomena and airfoil shape play a key role regarding particle impact velocity and angle. This work has the goal of combining, for the first time, the kinematic characteristics of particle impact on the blade with fouling phenomenon by the use of a quantity called sticking probability (SP) adopted from literature. From these analyses, some guidelines for a proper management of the power plant (in terms of filtration and washing strategies) are highlighted.
Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry—Part I: Compressor Performance Analysis
Authors: Ubben Stefan , Niehuis Reinhard
Published: August 2014

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency as long as the diffuser passage is broad enough with respect to the clearance height. The flow phenomena responsible for this detected performance behavior are exposed in Part II, where the results of detailed measurements with pressure probes at diffuser exit and particle image velocimetry (PIV) measurements conducted inside the diffuser channel are discussed. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”
Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part II—Detailed Flow Analysis
Authors: Ubben Stefan , Niehuis Reinhard
Published: August 2014

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. In Part I it was shown that an one-sided diffuser clearance is able to contribute to an increase in flow range, stall margin, pressure ratio, and efficiency. In order to reveal the relevant flow phenomena, in Part II the results of detailed measurements of the pressure distribution at diffuser exit and particle image velocimetry (PIV) measurements inside the diffuser channel performed at three clearance configurations and three diffuser angles at a fixed radial gap are discussed. It was found that, for defined diffuser configurations, the clearance flow amplifies the diffuser throat vortex capable to reduce the loading of the highly loaded vane pressure side and to support a more homogenous diffuser flow. It turned out that the co-action of the geometry parameter diffuser vane angle and diffuser clearance height is of particular importance. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”
The Dual Mechanisms and Implementations of Stability Enhancement With Discrete Tip Injection in Axial Flow Compressors
Authors: Li Jichao , Lin Feng , Tong Zhiting , Nie Chaoqun , Chen Jingyi
Published: August 2014

The mechanisms and implementation scheme of discrete tip air injection are studied in this paper. A map that summarized the routes to stall is then proposed. It is argued that there exists a critical tip clearance ratio that separates two different routes to stall, which infers that the stability enhancement can also be based on two different mechanisms. A summation of tip injection test data in the literatures demonstrates that this is actually the case. For each compressor, there are two trends in the curve of stall margin improvement (SMI) versus injected momentum ratio, which is separated by a demarcation ratio of injected momentum. A series of tests are done in a low-speed compressor to show that the micro injection, wherein the injected momentum ratio is less than the demarcation ratio, can only act on the tip leakage flow (TLF) and thus provide small SMI by weakening the self-induced unsteadiness of the tip leakage flow (UTLF), while in contrast the macro injection can provide much larger SMI by acting on the main flow, decreasing the inlet angle-of-attack and thus unloading the blade tip. Based on these findings, a novel detecting-actuating scheme is designed and implemented onto a low-speed axial compressor. A cross-correlation coefficient is used to detect the UTLF in the prestall process way before stall inception and then to guide the opening of proportional electromagnetic valves. The injected flow rate can be smoothly varied to cover both micro- and macro-injection, which saves energy when the compressor is stable, and provides protection when it is needed. The same principle is applied to a high-speed compressor with a recirculation injection and the preliminary test results are very encouraging.
X-Ray Diffraction Analysis of Kraft Lignins and Lignin-Derived Carbon Nanofibers
Authors: Goudarzi Azadeh , Lin Li-Ting , Ko Frank K.
Published: August 2014

Lignin is a renewable material and it is abundantly available as low priced industrial residue. Lignin-based carbon fibers are economically attractive and sustainable. In addition, remarkably oxidized molecule of the lignin decreases the required time and temperature of the thermostabilization process compared to other carbon fiber precursors such as polyacrylonitrile (PAN); and thus, decreases the processing cost of carbon fiber production. The fraction 4 of softwood Kraft lignin (SKL-F4) was previously shown to be spinnable via electrospinning to produce carbon nanofibers. In this paper, we characterized different Kraft lignin powders through X-ray diffraction (XRD) analysis to measure the mean size of the ordered domains in different fractionations of softwood and hardwood samples. According to our results, SKL-F4 has largest ordered domains among SKLs and highest hydroxyl content according to Fourier transform infrared (FTIR) analysis. In addition, variations in the XRD patterns during carbon nanofiber formation were studied and the peak for (101) plane in graphite was observed in the carbon nanofiber carbonized at 1000 °C.
Effect of Pad Reinforcement on the Plastic Limit Load for Nozzle Connection of Cylindrical Vessel
Authors: Skopinsky V. N. , Berkov N. A. , Vozhov R. A.
Published: August 2014

The objective of this paper is the further investigation of the shell intersection problem. The pad reinforced nozzle connections of the cylindrical vessel under internal and external loads are investigated using elastic–plastic analysis and the stress analysis in intersecting shells (SAIS) special-purpose computer program. The method for determining the plastic limit load based on the maximum criterion of the rate of the change of the relative plastic work and program module LOAD_PL for its realization are presented. The results of comparisons with the twice elastic-slope (TES) method were considered for determining the plastic limit load using known experimental data for models of a pad reinforced cylindrical vessel with a radial nozzle under a transverse force. The results of a parametric study of unreinforced and pad reinforced vessel models with a nozzle under internal pressure, in-plane moment, and out-plane moment loadings are discussed.
A Method of Finding Biologically Inspired Guidelines for Environmentally Benign Design and Manufacturing
Authors: Reap John , Bras Bert
Published: August 2014

Fundamental characteristics identified via observation of the inherently sustainable biosphere can inform and guide environmentally benign design and manufacturing (EBDM). In support of this premise, this paper identifies characteristics, extracts biological principles, translates them into guidelines for EBDM, and briefly reports on their application in situations of engineering interest. It outlines and illustrates the use of constant comparative method (CCM) to identify and extract fundamental biosphere characteristics from biology and ecology literature. Then, it translates these biological principles into general guidelines with associated metrics. To illustrate the efficacy of this approach, bio-inspired metrics are used for the purposes of assessing micro/nanoscale self-cleaning surfaces and designing a carpet tile recycling network. These efforts suggest that learning the phenomena responsible for the biosphere's inherent sustainability can yield insight into EBDM.
Link-Based Performance Optimization of Spatial Mechanisms
Authors: Yihun Yimesker , Bosworth Ken W. , Perez-Gracia Alba
Published: August 2014

In the design of spatial linkages, the finite-position kinematics is fully specified by the position of the joint axes, i.e., a set of lines in space. However, most of the tasks have additional requirements regarding motion smoothness, obstacle avoidance, force transmission, or physical dimensions, to name a few. Many of these additional performance requirements are fully or partially independent of the kinematic task and can be fulfilled using a link-based optimization after the set of joint axes has been defined. This work presents a methodology to optimize the links of spatial mechanisms that have been synthesized for a kinematic task, so that additional requirements can be satisfied. It is based on considering the links as anchored to sliding points on the set of joint axes, and making the additional requirements a function of the location of the link relative to the two joints that it connects. The optimization of this function is performed using a hybrid algorithm, including a genetic algorithm (GA) and a gradient-based minimization solver. The combination of the kinematic synthesis together with the link optimization developed here allows the designer to interactively monitor, control, and adjust objectives and constraints, to yield practical solutions to realistic spatial mechanism design problems.
A Mechanistic Study on the Inhibition of Zinc Behavior During Laser Welding of Galvanized Steel
Authors: Zhang Yi , Li Qingfu , Xu Lei , Duan Linyong
Published: August 2014

The characteristics of zinc behavior that the zinc layer is vaporized and ionized during laser welding of galvanized steel are closely related to the stability of the molten pool, and the weld keyhole formation, easily leading to weld defects such as pores, splashes, cave, and incomplete fusion. In this paper, an experimental platform was built based on a multichannel spectrum signal acquisition to study spectral characteristics of zinc, plasma temperature, electron density, and bremsstrahlung absorption in laser welding of galvanized steel with the copper addition. The results show that, due to the formation of a copper–zinc solid solution during the laser welding of galvanized steel, the zinc content in the welding joints increased significantly. Meanwhile, by adding an appropriate amount of copper powder, the temperature and oscillation amplitude of the plasma plume during the laser welding of galvanized steel decreased significantly. Further, the inverse bremsstrahlung radiation absorption coefficient decreased, and there was less attenuation of the laser energy when passed through the plasma plume outside the keyhole. Therefore, the method implemented here improved the utilization of laser energy during welding.
Flexible Mechanical Joint as Human Exoskeleton Using Low-Melting-Point Alloy
Authors: Deng Yueguang , Liu Jing
Published: August 2014

A flexible mechanical joint for human exoskeleton based on low-melting-point alloy is proposed for the first time. With the liquid–solid phase change capability, this unique joint can easily switch between its flexible and rigid states. Such mechanism allows the fabricated human exoskeleton arm to conveniently and effectively perform the powerful lifting action. Conceptual investigations disclosed that metal-based mechanical joints provided excellent moving flexibility and large loading capacity. Comparative measurements demonstrated that the phase change joint responded much faster and could support heavier loads than that of the conventional paraffin-based joint. This method opens a soft mechanical joint for human exoskeleton in future civilian use.
Enhancing Structural Damage Identification Robustness to Noise and Damping With Integrated Bistable and Adaptive Piezoelectric Circuitry
Authors: Kim Jinki , Harne R. L. , Wang K. W.
Published: August 2014

The accurate and reliable identification of damage in modern engineered structures is essential for timely corrective measures. Vibration-based damage prediction has been studied extensively by virtue of its global damage detection ability and simplicity in practical implementation. However, due to noise and damping influences, the accuracy of this method is inhibited when direct peak detection (DPD) is utilized to determine resonant frequency shifts. This research investigates an alternative method to detect frequency shifts caused by structural damage based on the utilization of strongly nonlinear bifurcation phenomena in bistable electrical circuits coupled with piezoelectric transducers integrated with the structure. It is shown that frequency shift predictions by the proposed approach are significantly less susceptible to error than DPD when realistic noise and damping levels distort the shifting resonance peaks. As implemented alongside adaptive piezoelectric circuitry with tunable inductance, the new method yields damage location and severity identification that is significantly more robust and accurate than results obtained following the DPD approach.
Dynamic Analysis of a High-Speed Rotor-Ball Bearing System Under Elastohydrodynamic Lubrication
Authors: Zhang Yu-Yan , Wang Xiao-Li , Zhang Xiao-Qing , Yan Xiao-Liang
Published: August 2014

The nonlinear dynamic behaviors of a high-speed rotor-ball bearing system under elastohydrodynamic lubrication (EHL) are investigated. First, the numerical curve fittings for stiffness and damping coefficients of lubricated contacts between rolling elements and races are undertaken, and then the fitted formulae are introduced to the equations of motion of the rotor-ball bearing system to investigate its nonlinear characteristics. Furthermore, the time responses, power spectra, phase trajectories, orbit plots, and bifurcation diagrams for cases of ignoring and considering the lubrication condition in bearings are inspected and compared. The results indicate that, when lubrication is taken into account, the amplitudes of vibration displacements and velocities of the rotor system increase, and the appearance of different regions of periodic, quasi-periodic, and chaotic behavior is strongly dependent on the speed and load.
Modeling of Multisample Nanoplacing
Authors: Landolsi Fakhreddine , Ghorbel Fathi H.
Published: August 2014

Recently, we proposed a new probe-based manipulation technique, namely, vibrational nanoplacing, which reduces the requirements on the substrate flatness. The new manipulation scheme relies on adhesion forces to capture a sample at the nanoscale and transport it. The sample is then released using dynamic oscillations of the probe. In the present paper, we analyze the generalization of the proposed approach to multisamples and investigate selective release.
Searching and Localizing a Radio Target by an Unmanned Flying Vehicle Using Bootstrap Filtering
Authors: Saghafi Fariborz , Esmailifar Sayyed Majid
Published: August 2014

In this article, an algorithm has been developed to search and localize a radio target in a marine area. This algorithm consists of two main parts, estimation and guidance. In the estimation part, bootstrap filtering has been employed to extract the target states from measurements. Although, by utilizing bootstrap filter, the target states can be estimated without requiring special maneuvers, exploiting proper guidance law to maximize the information gain can significantly enhance the localization performance. For evaluating the developed algorithm, an accurate simulation software with six degrees of freedom mathematical model including autopilot is used. Obtained statistical results from different simulation runs for both stationary and moving targets are presented to demonstrate the performance of the developed algorithm.
Adaptive Semi-Active Suspension of Quarter-Vehicle With Magnetorheological Damper
Authors: El Majdoub K. , Ghani D. , Giri F. , Chaoui F. Z.
Published: August 2014

This paper addresses the problem of controlling quarter-vehicle semi-active suspension systems. Presently, the suspension system involves a magnetorheological (MR) damper featuring hysteretic behavior captured through the Bouc–Wen model. The control objective is to regulate well the chassis vertical position despite the road irregularities. The difficulty of the control problem lies in the nonlinearity of the system model, the uncertainty of some parameters and the inaccessibility to measurements of the hysteresis internal state variable. The control design is performed using Lyapunov control design tools; it includes an observer providing online estimates of the hysteresis internal state and an adaptive state-feedback regulator. The adaptive controller, obtained by combining the state observer and the state-feedback regulator, is formally shown to meet the desired control objectives. This theoretical result is confirmed by several simulations. The latter illustrate the performances of the present adaptive controller and compare them with those of earlier control approaches and those of the passive suspension.
Fabrication of Anodic Aluminum Oxide Template and Copper Nanowire Surface Fastener
Authors: Teshima Hiromasa , Kojima Kohei , Ju Yang
Published: August 2014

Through-hole anodic aluminum oxide (AAO) was fabricated by two steps anodization method. The pore diameter of the AAO was 40 nm. Cu nanowire array was prepared using the fabricated AAO as a template by electrochemical deposition. The mechanical and electrical performances of Cu nanowire surface fastener (NSF) were realized by the interconnection of Cu nanowire arrays. The shear and normal bonding strengths for the Cu NSF with 40 nm diameter nanowires were 3.38 × 10−3 and 2.46 × 10−3 N/cm2, respectively, and the parasitic resistance of it was approximately 22.5 Ω · cm2.
Compliant Cellular Materials With Elliptical Holes for Extremely High Positive and Negative Poisson's Ratios
Authors: Lee Jaehong , Kim Kwangwon , Ju Jaehyung , Kim Doo-Man
Published: August 2014

Cellular materials' two important properties—structure and mechanism—can be selectively used for materials design; in particular, they are used to determine the modulus and yield strain. The objective of this study is to gain a better understanding of these two properties and to explore the synthesis of compliant cellular materials (CCMs) with compliant porous structures (CPSs) generated from modified hexagonal honeycombs. An in-plane constitutive CCM model with CPSs of elliptical holes is constructed using the strain energy method, which uses the deformation of hinges around holes and the rotation of links. A finite element (FE) based simulation is conducted to validate the analytical model. The moduli and yield strains of the CCMs with an aluminum alloy are about 4.42 GPa and 0.57% in one direction and about 2.14 MPa and 20.9% in the other direction. CCMs have extremely high positive and negative Poisson's ratios (NPRs) (νxy* ∼ ±40) due to the large rotation of the link member in the transverse direction caused by an input displacement in the longitudinal direction. A parametric study of CCMs with varying flexure hinge geometries using different porous shapes shows that the hinge shape can control the yield strength and strain but does not affect Poisson's ratio which is mainly influenced by rotation of the link members. The synthesized CPSs can also be used to design a new CCM with a Poisson's ratio of zero using a puzzle-piece CPS assembly. This paper demonstrates that compliant mesostructures can be used for next generation materials design in tailoring mechanical properties such as moduli, strength, strain, and Poisson's ratios.
Investigation and Prediction of Steam-Induced Stall-Margin Reduction in Two Transonic Rotor Fans
Authors: Gannon Anthony J. , Hobson Garth V. , Hedges Collin R. , Descovich Gregory L.
Published: August 2014

An investigation into the behavior of two transonic compressor rotors operating at near-stall conditions while ingesting hot-steam was undertaken. This type of inlet flow was similar to that experienced by naval aircraft during steam catapult launches and has had the potential to adversely affect engine performance. The research was divided into three broad areas: experimental, theoretical and numerical. The first area, experimental, used the Naval Postgraduate School's transonic compressor rig. The rig was modified to introduce hot steam into the inlet flow during testing. Two rotor-only tests were completed; one with an unswept rotor and the other with a forward swept rotor. The experimental program yielded two sets of results. The first recorded data on the operational behavior of a transonic compressor ingesting a super-heated steam and air mixture, notably the quantification of the stall margin (SM) reduction. The second data set captured transient measurements of the inlet flow gas properties. The transient inlet data were then used in the second research area; a theoretical analysis based on a thermodynamic model of the inlet flow. Prior to this investigation, little information was available for higher temperature steam–air mixtures of this type. The analysis used certain simplifying assumptions to perform a fundamental of the inflow which yielded the inlet flow transient changes of specific heat capacities, gas constants, and, therefore, sonic velocities. Using these transient inlet properties, the third area of the investigation was performed, developing a numerical model. A fully transient simulation over the time period of an ingestion event would not be practical due to the large computational requirements needed. A quasi-transient method with large intermediate time steps was developed. The method is presented and was found to be reasonable at predicting the stall-margin reduction when compared to the available experimental results. These results would have potential use in design applications and for evaluating existing compressor steam ingestion tolerance.
Evaluation of Cutting Forces During Single Pass Microtrenching of Poly (Methyl Methacrylate)
Authors: James Thomas P. , Eckman Nathaniel B. , Sagar Amrit , Saigal Anil
Published: August 2014

Research was conducted to evaluate a microtrenching process to create microchannels on the surface of poly (methyl methacrylate) (PMMA) for applications in tissue engineering. Experiments with a trenching tool included an exaggerated cutting edge radius (48 μm) to study the impact of a highly negative effective rake angle on forces during single pass microtrenching at subradius cutting conditions. During microtrenching, forces were measured by dynamometer and compared to a finite element (FE) model using an elastic-perfectly plastic material model for an undeformed chip thickness from 9 to 64 μm. During experiments, cutting was first observed when the ratio of undeformed chip thickness to cutting edge radius was 0.33. Measured and predicted values of thrust force exceeded cutting force up to an undeformed chip thickness equivalent to the cutting edge radius. The FE model predicted a linear trend in cutting force with feed (r = 0.99) and was substantiated by linear regression of experimental data (r = 0.99). However, at lower values of feed the model overestimated force, with a maximum difference of 42% at a feed of 22 μm. Thrust force was also predicted to be linear (r = 0.99), but at greater feed the experiments indicated a nonlinear decline in thrust force, resulting in a maximum difference of 27% at 64 μm. Finally, an analysis of nodal velocity plots from the FE model revealed a material stagnation zone developed along the cutting edge, rising from the workpiece surface in proportion to feed and then remaining fixed at 63 deg (stagnation angle) for all feeds greater than 35 μm. While the application of an elastic-perfectly plastic material model for PMMA was sufficient to predict microtrenching forces by the FE method, differences between predicted and measured thrust forces at greater undeformed chip thickness implies a more complex rheological model may add value.
Performance Degradation Assessment for Bearing Based on Ensemble Empirical Mode Decomposition and Gaussian Mixture Model
Authors: Hong Sheng , Wang Baoqing , Li Guoqi , Hong Qian
Published: August 2014

This paper proposes a novel performance degradation assessment method for bearing based on ensemble empirical mode decomposition (EEMD), and Gaussian mixture model (GMM). EEMD is applied to preprocess the nonstationary vibration signals and get the feature space. GMM is utilized to approximate the density distribution of the lower-dimensional feature space processed by principal component analysis (PCA). The confidence value (CV) is calculated based on the overlap between the distribution of the baseline feature space and that of the testing feature space to indicate the performance of the bearing. The experiment results demonstrate the effectiveness of the proposed method.
On the Use of Spectral Averaging of Acoustic Emission Signals for Bearing Fault Diagnostics
Authors: Van Hecke Brandon , He David , Qu Yongzhi
Published: August 2014

For years, vibration analysis has been the industry standard for bearing fault diagnosis. However, due to the various advantages over vibration based techniques, the quantification of acoustic emission (AE) for bearing health diagnosis has been an area of interest for recent years. Additionally, most AE based methodologies to date utilize data mining technologies. Presented in this paper is a new approach, combining a heterodyne based frequency reduction technique, time synchronous resampling, and spectral averaging to process AE signals and compute condition indicators (CIs) for bearing fault diagnostics. First, the heterodyne based frequency reduction technique allows the AE signal frequency to be down shifted from several MHz to less than 50 kHz, which approaches that of vibration based methodologies. Next, the sampled AE signals are band pass filtered to retain the useful information related to the bearing defects. Last, a trigger signal is utilized to time synchronously resample the AE signals to allow the calculation of a spectral average and the extraction and evaluation of CIs for bearing fault diagnosis. The technique presented in this paper is validated using the AE signals of seeded fault steel bearings on a bearing test rig. Presented is an effective AE based approach validated to diagnose all four fault types: inner race, outer race, ball, and cage. Moreover, the effectiveness of the presented approach is established through the comparison of both AE and vibration data.
Unintentionally doped semi-insulating GaN with a low dislocation density grown by metalorganic chemical vapor deposition
Authors: He Xiaoguang , Zhao Degang , Jiang Desheng , Zhu Jianjun , Chen Ping , Liu Zongshun , Le Lingcong , Yang Jing , Li Xiaojing , Zhang Shuming , Yang Hui
Published: August 2014

Unintentionally doped semi-insulating GaN films possessing a low dislocation density are grown via metalorganic vapor phase epitaxy on a sapphire substrate. The obtained electrical resistivity reaches 4.8 × .a8 Ω·cm, and the full width at half maximum of the x-ray diffraction rocking curves of the (002) and (102) planes is as low as 201.6 and 378.0 arcsec, respectively. The GaN films are grown at low pressure (LP) to introduce residual carbon and to compensate background donors. The dislocation density in these samples is significantly reduced by using a low V/III ratio in the initial epitaxial growth stage. It is also found that the resistivity of the LP-grown samples decrease when the residual carbon concentration is excessive, which is attributed to the self-compensation of carbon impurities. Therefore, the carbon concentration of LP-grown GaN should be carefully modulated to maintain its high resistivity.
Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session
Authors: Callewaert Chris , De Maeseneire Evelyn , Kerckhof Frederiek-Maarten , Verliefde Arne , Van de Wiele Tom , Boon Nico
Published: August 2014

Clothing textiles protect our human body against external factors. These textiles are not sterile and can harbor high bacterial counts as sweat and bacteria are transmitted from the skin. We investigated the microbial growth and odor development in cotton and synthetic clothing fabrics. T-shirts were collected from 26 healthy individuals after an intensive bicycle spinning session and incubated for 28 h before analysis. A trained odor panel determined significant differences between polyester versus cotton fabrics for the hedonic value, the intensity, and five qualitative odor characteristics. The polyester T-shirts smelled significantly less pleasant and more intense, compared to the cotton T-shirts. A dissimilar bacterial growth was found in cotton versus synthetic clothing textiles. Micrococci were isolated in almost all synthetic shirts and were detected almost solely on synthetic shirts by means of denaturing gradient gel electrophoresis fingerprinting. A selective enrichment of micrococci in an
in vitro
growth experiment confirmed the presence of these species on polyester. Staphylococci were abundant on both cotton and synthetic fabrics. Corynebacteria were not enriched on any textile type. This research found that the composition of clothing fibers promotes differential growth of textile microbes and, as such, determines possible malodor generation.
Strain Diversity of CTX-M-Producing Enterobacteriaceae in Individual Pigs: Insights into the Dynamics of Shedding during the Production Cycle
Authors: Hansen Katrine Hartung , Bortolaia Valeria , Damborg Peter , Guardabassi Luca
Published: August 2014

The aim of this study was to evaluate the population dynamics of CTX-M-producing
Enterobacteriaceae
in individual pigs on a farm positive for CTX-M-14-producing
Escherichia coli
. Fecal samples were collected once around the farrowing time from five sows and four times along the production cycle from two of their respective offspring. Multiple colonies per sample were isolated on cefotaxime-supplemented MacConkey agar with or without prior enrichment, resulting in 98 isolates identified by matrix-assisted laser desorption ionization–time of flight mass spectrometry and tested for
bla
CTX-M
. CTX-M-positive isolates (
n
= 86) were typed by pulsed-field gel electrophoresis (PFGE). Plasmids harboring
bla
CTX-M
were characterized in 22 representative isolates by replicon typing and restriction fragment length polymorphism. Based on the PFGE results, all individuals shed unrelated CTX-M-14-producing
E. coli
strains during the course of life. Concomitant shedding of CTX-M-2/97-producing
Proteus mirabilis
or
Providencia rettgeri
was observed in two sows and two offspring. At least two genetically unrelated CTX-M-producing
E. coli
strains were isolated from approximately one-fourth of the samples, with remarkable differences between isolates obtained by enrichment and direct plating. A clear decrease in strain diversity was observed after weaning. Dissemination of
bla
CTX-M-14
within the farm was attributed to horizontal transfer of an IncK plasmid that did not carry additional resistance genes and persisted in the absence of antimicrobial selective pressure. Assessment of strain diversity was shown to be influenced by the production stage from which samples were collected, as well as by the isolation method, providing useful information for the design and interpretation of future epidemiological studies of CTX-M-producing
Enterobacteriaceae
in pig farms.