bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Forcing Parameters of Film Cooling Effectiveness
Authors: Babaee Hessam , Acharya Sumanta , Wan Xiaoliang
Published: October 2013

An optimization strategy is described that combines high-fidelity simulations with response surface construction, and is applied to pulsed film cooling for turbine blades. The response surface is constructed for the film cooling effectiveness as a function of duty cycle, in the range of DC between 0.05 and 1, and pulsation frequency St in the range of 0.2–2, using a pseudospectral projection method. The jet is fully modulated and the blowing ratio, when the jet is on, is 1.5 in all cases. Overall 73 direct numerical simulations (DNS) using spectral element method were performed to sample the film cooling effectiveness on a Clenshaw–Curtis grid in the design space. The geometry includes a 35-degree delivery tube and a plenum. It is observed that in the parameter space explored a global optimum exists, and in the present study, the best film cooling effectiveness is found at DC = 0.14 and St = 1.03. In the same range of DC and St, four other local optimums were found. The physical mechanisms leading to the forcing parameters of the global optimum are explored and ingestion of the crossflow into the delivery tube is observed to play an important role in this process. The gradient-based optimization algorithms are argued to be unsuitable for the current problem due to the nonconvexity of the objective function.
An Experimental Study of Mist/Air Film Cooling on a Flat Plate With Application to Gas Turbine Airfoils—Part I: Heat Transfer
Authors: Zhao Lei , Wang Ting
Published: October 2013

Film cooling is a cooling technique widely used in high-performance gas turbines to protect the turbine airfoils from being damaged by hot flue gases. Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments in this study. A small amount of tiny water droplets (7 wt. %) with an average diameter about 5 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facility is specifically built for this unique experiment. A phase Doppler particle analyzer (PDPA) system is employed to measure the droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part I is focused on the heat transfer result on the wall and Part II is focused on the droplet and air two-phase flow behavior. Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. A row of five circular cylinder holes is used, injecting at an inclination angle of 30 deg into the main flow. For the 0.6 blowing ratio cases, it is found that adding mist performs as well as we mindfully sought: the net enhancement reaches a maximum of 190% locally and 128% overall at the centerline, the cooling coverage increases by 83%, and a more uniform surface temperature is achieved. The latter is critical for reducing wall thermal stresses. When the blowing ratio increases from 0.6 to 1.4, both the cooling coverage and net enhancement are reduced to below 60%. Therefore, it is more beneficial to choose a relatively low blowing ratio to keep the coolant film attached to the surface when applying the mist cooling. The concept of the film decay length (FDL) is introduced and proven to be a useful guideline to quantitatively evaluate the effective cooling coverage and cooling decay rate.
The Performance of Diamond-Like Carbon Coated Drills in Thermally Assisted Drilling of Ti-6Al-4V
Authors: Bhowmick S. , Alpas A. T.
Published: October 2013

Drilling performances of diamond-like carbon coatings incorporating W (W-DLC) deposited on high-speed steel tools were evaluated when drilling Ti-6Al-4V at 25 °C and under thermally assisted machining (TAM) conditions at 400 °C. Dry drilling using W-DLC coated drills caused immediate tool failure as a result of titanium adhesion. The tool lives improved for TAM drilling using W-DLC when the Ti-6Al-4V was placed (with dry surface) in a cooling bath at −80 °C and resulted in low and uniform drilling torques as well as good surface finish. The low coefficient of friction (COF) of W-DLC against Ti-6Al-4V observed under TAM conditions was attributed to the formation of W oxide layers at the tool surface, as determined by Raman spectroscopy. Introducing a cooling bath was necessary in order to restrict the temperature rise in the workpiece that caused rapid tool wear above 500 °C during drilling operations and also to prevent adhesion with minimal built-up edge (BUE) formation during drilling. The TAM performance of W-DLC coated drills was shown to be similar to that of WC-Co drills used in conventional flooded drilling.
Finite Element Modeling of Cutting Force and Chip Formation During Thermally Assisted Machining of Ti6Al4V Alloy
Authors: Xi Yao , Bermingham Michael , Wang Gui , Dargusch Matthew
Published: October 2013

The improvement in machinability during thermally assisted turning of the Ti-6Al-4V alloy has been investigated using finite element modeling. A 2D thermally assisted turning model was developed and validated by comparing the simulation results with experimental results. The effect of workpiece temperature on the cutting force and chip formation process was examined. The predicted cutting forces and chip morphologies from the simulation strongly correlated with the experimental results. It was observed from the simulation that the chip forms after the coalescence of two deformed regions in the shear band and that the cyclic cutting forces are strongly related to this chip formation process.
Influence of Preheating on Chip Segmentation and Microstructure in Orthogonal Machining of Ti6Al4V
Authors: Joshi Shashikant , Tewari Asim , Joshi Suhas
Published: October 2013

Chip segmentation due to shear localization during machining of titanium alloys affects cutting forces and their machinability. Despite several studies on modeling and understanding influence of chip segmentation, little is known about the effect of preheating on it. This work therefore, involves orthogonal machining of Ti6Al4V alloy under preheating between 100 °C and 350 °C to investigate chip segmentation, shear band configuration, and microstructure of machined surfaces, through optical and scanning electron microscopy of chips and chip roots. Conceptual models of chip segment formation have been evolved. Shear band formation appears to be the dominant mechanism of chip segmentation up to 260 °C preheating, however at 350 °C, extent of fracture along the shear plane increases. The preheating increases spacing between shear bands in chips, reduces shear band thickness from 21 μm at 100 °C to 8 μm at 350 °C, and ultimately reduces cutting forces fluctuation, and compressive residual stresses in the machined surfaces.
Operational Space Formulation and Analysis for Rovers
Authors: Hirschkorn Martin , Kövecses József
Published: October 2013

Many techniques have been developed for analyzing and evaluating mechanical systems for the purpose of improving design and control, such as the operational space formulation. It has been been shown to be a useful tool when working with robotic manipulators, but has not been extended to consider rovers. Rovers are fundamentally different due to the wheel-ground contact, that does not exist for fixed-base systems. In this paper, several different aspects of the operations space formulation, inertial properties, control, multi-arm systems, redundancy, and unactuated coordinates are investigated in the context of rovers. By considering a different interpretation of the operational space of a rover, several sets of generalized coordinates were chosen to represent the movement of two example rovers. Simulations were performed to demonstrate how these choices of generalized coordinates can be used to analyze various characteristics of the rovers and can improve the behavior for certain maneuvers, such as wheel walking.
Alternative Criterion for Investigation of Pitchfork Bifurcations of Limit Cycle in Relay Feedback Systems
Authors: Xu Huidong , Wen Guilin
Published: October 2013

Relay feedback systems are strongly nonlinear due to their switching properties. Some nonlinear properties of relay feedback systems have been verified to be preferable to modern control engineering, whereas others might drive the system to be more complex or even unpredictable. An alternative criterion is proposed to investigate the pitchfork bifurcations of the limit cycle of relay feedback systems in this paper. The proposed critical criterion is explicitly formulated by the coefficients of the characteristic polynomial equation instead of the eigenvalues of the Jacobian matrix. It is more convenient and efficient for detecting the existence of this type of bifurcation than the classical critical criterion. Numerical simulations show the pitchfork bifurcation behaviors in relay feedback systems and demonstrate that the proposed criterion is a general and exact analytic method for determining pitchfork bifurcations in maps.
Numerical Modeling of Heat Distribution in the Electron Beam Melting® of Ti-6Al-4V
Authors: Jamshidinia Mahdi , Kong Fanrong , Kovacevic Radovan
Published: October 2013

Electron beam melting® (EBM) is one of the fastest growing additive manufacturing processes capable of building parts with complex geometries, made predominantly of Ti-alloys. Providing an understanding of the effects of process parameters on the heat distribution in a specimen built by EBM®, could be the preliminary step toward the microstructural and consequently mechanical properties control. Numerical modeling is a useful tool for the optimization of processing parameters, because it decreases the level of required experimentation and significantly saves on time and cost. So far, a few numerical models are developed to investigate the effects of EBM® process parameters on the heat distribution and molten pool geometry. All of the numerical models have ignored the material convection inside the molten pool that affects the real presentation of the temperature distribution and the geometry of molten pool. In this study, a moving electron beam heat source and temperature dependent properties of Ti-6Al-4V were used in order to provide a 3D thermal-fluid flow model of EBM®. The influence of process parameters including electron beam scanning speed, electron beam current, and the powder bed density were studied. Also, the effects of flow convection in temperature distribution and molten pool geometry were investigated by comparing a pure-thermal with the developed thermal-fluid flow model. According to the results, the negative temperature coefficient of surface tension in Ti-6Al-4V was responsible for the formation of an outward flow in the molten pool. Also, results showed that ignoring the material convection inside the molten pool resulted in the formation of a molten pool with narrower width and shorter length, while it had a deeper penetration and higher maximum temperature in the molten pool. Increasing the powder bed density was accompanied with an increase in the thermal conductivity of the powder bed that resulted in a reduction in the molten pool width on the powder bed top surface. Experimental measurements of molten pool width and depth are performed to validate the numerical model.
Stick-Slip Effect in a Vibration-Driven System With Dry Friction: Sliding Bifurcations and Optimization
Authors: Fang Hongbin , Xu Jian
Published: October 2013

Vibration-driven systems can move progressively in resistive media owing to periodic motions of internal masses. In consideration of the external dry friction forces, the system is piecewise smooth and has been shown to exhibit different types of stick-slip motions. In this paper, a vibration-driven system with Coulomb dry friction is investigated in terms of sliding bifurcation. A two-parameter bifurcation problem is theoretically analyzed and the corresponding bifurcation diagram is presented, where branches of the bifurcation are derived in view of classical mechanics. The results show that these sliding bifurcations organize different types of transitions between slip and sticking motions in this system. The bifurcation diagram and the predicted stick-slip transitions are verified through numerical simulations. Considering the effects of physical parameters on average steady-state velocity and utilizing the sticking feature of the system, optimization of the system is performed. Better performance of the system with no backward motion and higher average steady-state velocity can be achieved, based on the proposed optimization procedures.
Neural Dynamics and Newton–Raphson Iteration for Nonlinear Optimization
Authors: Guo Dongsheng , Zhang Yunong
Published: October 2013

In this paper, a special type of neural dynamics (ND) is generalized and investigated for time-varying and static scalar-valued nonlinear optimization. In addition, for comparative purpose, the gradient-based neural dynamics (or termed gradient dynamics (GD)) is studied for nonlinear optimization. Moreover, for possible digital hardware realization, discrete-time ND (DTND) models are developed. With the linear activation function used and with the step size being 1, the DTND model reduces to Newton–Raphson iteration (NRI) for solving the static nonlinear optimization problems. That is, the well-known NRI method can be viewed as a special case of the DTND model. Besides, the geometric representation of the ND models is given for time-varying nonlinear optimization. Numerical results demonstrate the efficacy and advantages of the proposed ND models for time-varying and static nonlinear optimization.
Optimal Posture and Supporting Hand Force Prediction for Common Automotive Assembly One-Handed Tasks
Authors: Howard Bradley , Yang James , Ozsoy Burak
Published: October 2013

People often complete tasks using one hand for the task and one hand for support. These one-handed support tasks can be found in many different types of jobs, such as automotive assembly jobs. Optimization-based posture prediction has proven to be a valid tool in predicting the postures necessary to complete the tasks, but the related external support forces have been prescribed and not predicted. This paper presents a method in which the optimal posture and related supporting hand forces can be predicted simultaneously using optimization and stability analysis techniques. Postures are evaluated using a physics-based human performance measure (HPM) while external forces are assessed using stability analysis. The physics-based performance measures are based on joint torque. Stability is analyzed using criteria based on a 3D zero moment point (ZMP). The human model used in the prediction contains 56 degrees of freedom and is based on a 50th percentile female in stature. Tasks based on common automotive assembly one-handed tasks found in literature are considered as examples to test the proposed method. Overall, the predicted supporting hand forces have good correlation with experimentally measured forces.
Demand Management of Distributed Energy Loads Based on Genetic Algorithm Optimization
Authors: Li Jiaming , Platt Glenn , James Geoff
Published: October 2013

Management of a very large number of distributed energy resources, energy loads, and generators, is a hot research topic. Such energy demand management techniques enable appliances to control and defer their electricity consumption when price soars and can be used to cope with the unpredictability of the energy market or provide response when supply is strained by demand. We consider a multi-agent system comprising multiple energy loads, each with a dedicated controller. This paper introduces our latest research in self-organization of coordinated behavior of multiple agents. Energy resource agents (RAs) coordinate with each other to achieve a balance between the overall consumption by the multi-agent collective and the stress on the community. In order to reduce the overall communication load while permitting efficient coordinated responses, information exchange is through indirect communications between RAs and a broker agent (BA). This gives a decentralized coordination approach that does not rely on intensive computation by a central processor. The algorithm presented here can coordinate different types of loads by controlling their set-points. The coordination strategy is optimized by a genetic algorithm (GA) and a fast coordination convergence has been achieved.
Computing the Branches, Singularity Trace, and Critical Points of Single Degree-of-Freedom, Closed-Loop Linkages
Authors: Myszka David H. , Murray Andrew P. , Wampler Charles W.
Published: October 2013

This paper considers single degree-of-freedom (DOF), closed-loop linkages with a designated input angle and one design parameter. For a fixed value of the design parameter, a linkage has input singularities, that is, turning points with respect to the input angle, which break the motion curve into branches. Motion of the linkage along each branch can be driven monotonically from the input. As the design parameter changes, the number of branches and their connections, in short the topology of the motion curve, may change at certain critical points. Allowing the design parameter to vary, the singularities form a curve called the critical curve, whose projection is the singularity trace. Many critical points are the singularities of the critical curve with respect to the design parameter. The critical points have succinct geometric interpretations as transition linkages. This paper presents a general method to compute the singularity trace and its critical points. As an example, the method is used on a Stephenson III linkage, and a range of the design parameter is found where the input angle is able to rotate more than one revolution between singularities. This characteristic is associated with critical points that appear as cusps on the singularity trace.
Adaptive Redundant Inertial Measurement Unit/Global Positioning System Integration Filter Structure for Fault Tolerant Navigation
Authors: Yun Cho Seong , Keun Lee Hyung , Gook Park Chan
Published: October 2013

This paper proposes a new adaptive filter structure containing two subfilters, a fault detection and isolation (FDI) filter, and a main-filter for redundant inertial measurement unit (RIMU)/global positioning system (GPS) integrated navigation system tolerant toward faults of inertial sensors. The purpose of subfilters is compensation of sensor level bias (SLB) of the RIMU during in-flight alignment for successful FDI processing. Also, that of the main-filter is providing of error compensated navigation solution based on the good FDI result. To achieve these purposes, two coordinate frames, sub-body frame (SBF) and master-body frame (MBF), are defined first. Then, two different error models for the RIMU are formulated in the SBF for sensor level compensation and in the MBF for module level compensation, respectively. Based on the formulated error models, an adaptive filter structure is designed. Some numerical simulations are performed to validate the performance of the proposed adaptive filter structure.
Spring Parameters Design for the New Hydraulic Actuated Quadruped Robot
Authors: Chen Xianbao , Gao Feng , Qi Chenkun , Tian Xinghua , Zhang Jiaqi
Published: October 2013

More and more state-of-the-art robots have employed hydraulic actuating systems. It has a high power-to-weight ratio. Robots with these actuators can bear more payloads and achieve highly dynamic performance. However, the energy consumption is also very high and the system is very complicated comparing to the electronic motor actuated robot. A lot of research has been done to save the energy. Among which the application of springs is one of the most commonly used methods. This paper presents another use of the spring to save the energy by reducing the hydraulic system pressure of a newly built robot called the “Baby Elephant.” The configuration of the spring is designed according to the leg mechanism. The spring gives an assist force in the stance phase of the leg and exerts a passive payload in the swing phase. The maximum cylinder force is then reduced so as to bring down the pump pressure. The energy to be saved depends on how much the hydraulic pressure can be reduced. In this paper, the Baby Elephant is briefly introduced, the design of the springs on saving the energy are described. Simulations and experiments are carried out to confirm the effect.
Ultrasonic Cavitation Peening of Stainless Steel and Nickel Alloy
Authors: Gao Yibo , Wu Benxin , Liu Ze , Zhou Yun , Shen Ninggang , Ding Hongtao
Published: October 2013

Ultrasonic cavitation peening is a peening process utilizing the high pressure induced by ultrasonic cavitation in liquids (typically water). In this paper, ultrasonic cavitation peening on stainless steel and nickel alloy has been studied. The workpiece surface microhardness, the microhardness variation at different depths, the workpiece surface profile, roughness, and morphology have been measured or observed. It has been found that for the studied situations, ultrasonic cavitation peening (at a sufficiently high horn vibration amplitude) can obviously enhance the workpiece surface hardness without significantly increasing the surface roughness. Under the investigated conditions, a surface layer of more than around 50 μm has been hardened under a horn vibration amplitude of ∼20 μm.
Thermal Performance of a Water-Cooled Microchannel Heat Sink With Grooves and Obstacles
Authors: Xie Yonghui , Shen Zhongyang , Zhang Di , Lan Jibing
Published: October 2013

With the rapid development of microelectromechanical systems (MEMS) in IT industry, the heat flux in microchannel has reached a high level which demands preferable cooling technology. Water cooling has become a favor cooling approach in electronic microdevices due to better thermal performance than air cooling method. In the present paper, thermal performance in microchannels with grooves and obstacles are investigated numerically. The height and width of the rectangular microchannel are 200 and 50 μm, respectively. As a simple modification of dimple/protrusion, the groove/obstacle diameter is 100 μm and the depth is 20 μm. Different arrangements of grooves and obstacles are considered on Reynolds range of 100–900. The numerical results show that groove/obstacle structure is effective for cooling enhancement in microchannel. Among the cases in this research, the normalized Nusselt number Nu/Nu0 is within the range of 1.446–26.19, while the pressure penalty f/f0 has a much larger range from 0.86 to 110.18 depending on specific orientation. Field synergy analysis and performance evaluation plot are adopted to discuss the mechanism of heat transfer enhancement and energy saving performance integrating the pumping performance. From the viewpoint of energy saving, groove on single surface (case 1) has the best performance. Furthermore, performances of grooved microchannels are compared with that of dimpled microchannels which were discussed in the author’s previous research. The results indicate grooved microchannels have larger range of both Nu/Nu0 and f/f0 and some grooved cases possess high TP than dimpled microchannels.
Extension of Generalized Plasticity Model for Thermocyclic Loading
Authors: Sobotka J. C. , Dodds R. H.
Published: October 2013

This work extends the generalized plasticity model for structural metals under cyclic loading proposed by Lubliner et al. (1993, “A New Model of Generalized Plasticity and its Numerical Implementation,” Int. J. Solids Struct., 22, pp. 3171–3184) to incorporate temperature-dependence into the elastic-plastic response. Proposed flow equations satisfy the Clausius–Duhem inequality through a thermodynamically consistent energy functional and retain key aspects of conventional plasticity models: Mises yield surface, normal plastic flow, and additive decomposition of strain. Uniaxial specialization of the 3D rate equations leads to a simple graphical method to estimate model properties. The 3D integration scheme based on backward Euler discretization leads to a scalar quadratic expression to determine the plastic strain rate multiplier and has a symmetric algorithmic tangent matrix. Both properties of the integration lead to a computationally efficient implementation especially suited to large-scale, finite element analyses. In comparison studies using experimental data from a Cottrell–Stokes test, the modified rate equations for the generalized plasticity model capture a thermally activated increase in the flow stress.
Features of Vortex-Induced Vibration in Oscillatory Flow
Authors: Fu Shixiao , Wang Jungao , Baarholm Rolf , Wu Jie , Larsen C. M.
Published: October 2013

Vortex-induced vibration (VIV) in oscillatory flow is experimentally investigated in the ocean basin. The test flexible cylinder was forced to harmonically oscillate in various combinations of amplitude and period with Keulegan-Carpenter (KC) number between 26 and 178 in three different maximum reduced velocities, URmax=4, URmax=6.5, and URmax=7.9 separately. VIV responses at cross-flow (CF) direction are investigated using modal decomposition and wavelet transformation. The results show that VIV in oscillatory flow is quite different from that in steady flow; features, such as intermittent VIV, hysteresis, amplitude modulation, and mode transition (time sharing) are observed. Moreover, a VIV developing process including “building-up,” “lock-in,” and “dying-out” in oscillatory flow, is further proposed and analyzed.
Mobility/Impedance Methods: A Guide for Application
Authors: Booker J. F.
Published: October 2013

Mobility and impedance methods provide extremely efficient and robust journal orbit/trajectory calculation through use of bearing characteristics stored (at least conceptually) in the form of widely-available “maps.” These inversely-related methods are widely used for design optimization and for dynamic system analysis, both of which are often computationally intensive. All concepts and data sources necessary for straightforward application to both rotating and reciprocating machinery are identified and presented in some detail in this brief note.
A Novel Damping Device for Broadband Attenuation of Low-Frequency Combustion Pulsations in Gas Turbines
Authors: Bothien Mirko R. , Noiray Nicolas , Schuermans Bruno
Published: October 2013

Damping of thermoacoustically induced pressure pulsations in combustion chambers is a major focus of gas turbine operation. Conventional Helmholtz resonators are an excellent means to attenuate thermoacoustic instabilities in gas turbines. Usually, however, the damping optimum is in a narrow frequency band at one operating condition. The work presented here deals with a modification of the basic Helmholtz resonator design overcoming this drawback. It consists of a damper body housing multiple volumes that are connected to each other. Adequate adjustment of the governing parameters results in a broadband damping characteristic for low frequencies. In this way, changes in operating conditions and engine-to-engine variations involving shifts in the combustion pulsation frequency can conveniently be addressed. Genetic algorithms and optimization strategies are used to derive these parameters in a multidimensional parameter space. The novel damper concept is described in more detail and compared with cold-flow experiments. In order to validate the performance under realistic conditions, the new broadband dampers were implemented in a full-scale test engine. Pulsation amplitudes could be reduced by more than 80%. In addition, it is shown that, due to sophisticated damper placement in the engine, two unstable modes can be addressed simultaneously. Application of the damper concept allowed a considerable increase of the engine operating range, thereby reducing NOx emissions by 55%. Predictions obtained with the physics-based model excellently agree with experimental results for all tested damper geometries, bias flows, excitation amplitudes, and most importantly with the measurements in the engine.
Computational Framework for Determining Patient-Specific Total Knee Arthroplasty Loading
Authors: Lundberg Hannah J. , Wimmer Markus A.
Published: October 2013

The purpose of this work is to describe a computational framework for predicting total knee arthroplasty loads which are necessary for accurate preclinical testing of implant designs. Inputs required include patient knee joint kinematics, and implant type, size, and physiological alignment. Computational models used in the framework include the calculation of knee joint kinematics and kinetics, prediction of the contact path, a model to determine muscle forces, and a force model to obtain parametric solutions for implant forces. The resulting knee implant forces have been validated in two studies, and in both the model accurately predicted differences in knee joint loading. To date, implant contact forces have been predicted for 35 patients with four different implant types. Forces have been calculated for walking, chair, and stair activities.
Application of a Homogeneous Balance Method to Exact Solutions of Nonlinear Fractional Evolution Equations
Authors: Jafari H. , Tajadodi H. , Baleanu D.
Published: October 2013

The fractional Fan subequation method of the fractional Riccati equation is applied to construct the exact solutions of some nonlinear fractional evolution equations. In this paper, a powerful algorithm is developed for the exact solutions of the modified equal width equation, the Fisher equation, the nonlinear Telegraph equation, and the Cahn–Allen equation of fractional order. Fractional derivatives are described in the sense of the modified Riemann–Liouville derivative. Some relevant examples are investigated.
Control of Fractional-Order Systems Using Chatter-Free Sliding Mode Approach
Authors: Pourmahmood Aghababa Mohammad
Published: October 2013

The problem of stabilization of nonlinear fractional systems in spite of system uncertainties is investigated in this paper. First, a proper fractional derivative type sliding manifold with desired stability and convergence properties is designed. Then, the fractional stability theory is adopted to derive a robust sliding control law to force the system trajectories to attain the proposed sliding manifold and remain on it evermore. The existence of the sliding motion is mathematically proven. Furthermore, the sign function in the control input, which is responsible to the being of harmful chattering, is transferred into the fractional derivative of the control input. Therefore, the resulted control input becomes smooth and free of the chattering. Some numerical simulations are presented to illustrate the efficient performance of the proposed chattering-free fractional variable structure controller.
Energy Considerations for Mechanical Fractional-Order Elements
Authors: Lorenzo Carl F. , Hartley Tom T.
Published: October 2013

This paper considers the energy aspects of fractional-order elements defined by the equation: force is proportional to the fractional-order derivative of displacement, with order varying from zero to two. In contrast to the typically conservative assumption of classical physics that leads to the potential and kinetic energy expressions, a number of important nonconservative differences are exposed. Firstly, the considerations must be time-based rather than displacement or momentum based variables. Time based equations for energy behavior of fractional elements are presented and example applications are considered. The effect of fractional order on the energy input and energy return of these systems is shown. Importantly, it is shown that the history, or initialization, has a significant effect on energy response. Finally, compact expressions for the work or energy, are developed.
Electron Beam Additive Manufacturing of Titanium Components: Properties and Performance
Authors: Edwards P. , O'Conner A. , Ramulu M.
Published: October 2013

This research evaluates the fatigue properties of Ti-6Al-4V specimens and components produced by Electron Beam additive manufacturing. It was found that the fatigue performance of specimens produced by additive manufacturing is significantly lower than that of wrought material due to defects such as porosity and surface roughness. However, evaluation of an actual component subjected to design fatigue loads did not result in premature failure as anticipated by specimen testing. Metallography, residual stress, static strength and elongation, fracture toughness, crack growth, and the effect of post processing operations such as machining and peening on fatigue performance were also evaluated.
Transport of Dynamic Biochemical Signals in Steady Flow in a Shallow Y-Shaped Microfluidic Channel: Effect of Transverse Diffusion and Longitudinal Dispersion
Authors: Li Yong-Jiang , Li Yizeng , Cao Tun , Qin Kai-Rong
Published: October 2013

Dynamic biochemical signal control is important in in vitro cell studies. This work analyzes the transportation of dynamic biochemical signals in steady and mixing flow in a shallow, Y-shaped microfluidic channel. The characteristics of transportation of different signals are investigated, and the combined effect of transverse diffusion and longitudinal dispersion is studied. A method is presented to control the widths of two steady flows in the mixing channel from two inlets. The transfer function and the cutoff frequency of the mixing channel as a transmission system are presented by analytically solving the governing equations for the time-dependent Taylor–Aris dispersion and molecular diffusion. The amplitude and phase spectra show that the mixing Y-shaped microfluidic channel acts as a low-pass filter due to the longitudinal dispersion. With transverse molecular diffusion, the magnitudes of the output dynamic signal are reduced compared to those without transverse molecular diffusion. The inverse problem of signal transportation for signal control is also solved and analyzed.
Effect of Pre-Stress on the Dynamic Tensile Behavior of the TMJ Disc
Authors: Lomakin J. , Sprouse P. A. , Detamore M. S. , Gehrke S. H.
Published: October 2013

Previous dynamic analyses of the temporomandibular joint (TMJ) disc have not included a true preload, i.e., a step stress or strain beyond the initial tare load. However, due to the highly nonlinear stress-strain response of the TMJ disc, we hypothesized that the dynamic mechanical properties would greatly depend on the preload, which could then, in part, account for the large variation in the tensile stiffnesses reported for the TMJ disc in the literature. This study is the first to report the dynamic mechanical properties as a function of prestress. As hypothesized, the storage modulus (E′) of the disc varied by a factor of 25 in the mediolateral direction and a factor of 200 in the anteroposterior direction, depending on the prestress. Multiple constant strain rate sweeps were extracted and superimposed via strain-rate frequency superposition (SRFS), which demonstrated that the strain rate amplitude and strain rate were both important factors in determining the TMJ disc material properties, which is an effect not typically seen with synthetic materials. The presented analysis demonstrated, for the first time, the applicability of viscoelastic models, previously applied to synthetic polymer materials, to a complex hierarchical biomaterial such as the TMJ disc, providing a uniquely comprehensive way to capture the viscoelastic response of biological materials. Finally, we emphasize that the use of a preload, preferably which falls within the linear region of the stress-strain curve, is critical to provide reproducible results for tensile analysis of musculoskeletal tissues. Therefore, we recommend that future dynamic mechanical analyses of the TMJ disc be performed at a controlled prestress corresponding to a strain range of 5–10%.
Development of a Hip Joint Model for Finite Volume Simulations
Authors: Cardiff P. , Karač A. , FitzPatrick D. , Flavin R. , Ivanković A.
Published: October 2013

This paper establishes a procedure for numerical analysis of a hip joint using the finite volume method. Patient-specific hip joint geometry is segmented directly from computed tomography and magnetic resonance imaging datasets and the resulting bone surfaces are processed into a form suitable for volume meshing. A high resolution continuum tetrahedral mesh has been generated, where a sandwich model approach is adopted; the bones are represented as a stiffer cortical shells surrounding more flexible cancellous cores. Cartilage is included as a uniform thickness extruded layer and the effect of layer thickness is investigated. To realistically position the bones, gait analysis has been performed giving the 3D positions of the bones for the full gait cycle. Three phases of the gait cycle are examined using a finite volume based custom structural contact solver implemented in open-source software OpenFOAM.
Linear- and Nonlinear-Electromyographic Analysis of Supracutaneous Vibration Stimuli of the Forearm Using Diverse Frequencies and Considering Skin Physiological Properties
Authors: Ko Chang-Yong , Chang Yunhee , Kim Sol-Bi , Kim Shinki , Kim Gyoosuk , Ryu Jeicheong , Mun Musung
Published: October 2013

Numerous studies have reported the efficacy of vibration in sensory feedback or substitution devices for users of myoelectric hand prostheses. Although most myoelectric hand prostheses are presently manipulated by a surface electromyogram (sEMG), only a few studies have been conducted on the effect of vibration on an sEMG. This study aimed to determine whether vibration stimulation affects the linear and nonlinear properties of surface electromyography (sEMG) considering the skin properties. The vibration stimuli, with frequencies ranging from 37 to 258 Hz, were applied to the proximal part of the arms of the eight female and seven male subjects. The skinfold thickness, hardness, and vibration threshold at the stimuli loci were measured. The root mean square (rms) and fractal dimension (DF) of the sEMG were measured at a distance of 1 cm in the upward direction from the stimuli loci. Above 223 Hz there were no differences between the rms of the genders in between the vibration stimuli (p > 0.05). Moreover, no differences were observed between the DF of the genders for any frequency (p > 0.05). Above 149 Hz, there were correlations between the rms and the skin hardness in the females. Otherwise, no correlations were observed between the rms and DF and the skin properties in both genders for most of the frequencies (all p > 0.05). These results suggest that vibration stimuli affect the linear properties of the sEMG, but not the nonlinear properties.
A Nitinol Based Flexor Tendon Fixation Device: Gapping and Tensile Strength Measurements in Cadaver Flexor Tendon
Authors: Reese Shawn P. , Kubiak Erik N.
Published: October 2013

In this study, a new nitinol based fixation device was investigated for use in repairing severed digital flexor tendons. The device, composed of superelastic nitinol, is tubular in shape with inward facing tines for gripping tissue. Its cellular structure was designed such that it has a large effective Poisson's ratio, which facilitates a “finger trap” effect. This allows for reduced tendon compression during a resting state (to permit vascular perfusion) and increased compression during loading (to drive the tines into the tissue for gripping). To test the feasibility of using this device for flexor tendon repair, it was tested on cadaver flexor digitorum profundus tendons. The tendons were excised, cut in the region corresponding to a zone II laceration, and repaired using the device. The device was easy to install and did not prevent the tendon from bending. Constant strain rate tensile testing revealed a mean tensile strength of 57.6 ± 7.7 N, with a force of 53.2 ± 7.8 N at a 2 mm gap. This exceeds the suggested primary repair strength of 45 N, which has been proposed as the necessary strength for enabling early mobilization. Although considerable future studies will be needed to determine the suitability of the new repair device for clinical use, this study demonstrates the feasibility of utilizing a tubular, nitinol repair device for flexor tendon fixation.
Microbial Biotransformation of Gentiopicroside by the Endophytic Fungus Penicillium crustosum 2T01Y01
Authors: Zeng Wen-Liang , Li Wan-Kui , Han Han , Tao Yan-Yan , Yang Li , Wang Zheng-Tao , Chen Kai-Xian
Published: October 2013

Endophytic fungi are symbiotic with plants and possess multienzyme systems showing promising metabolite potency with region selectivity and stereoselectivity. The aim of this study was to use these special microorganisms as an
in vitro
model to mimic the potential mammalian metabolites of a natural iridoid gentiopicroside (GPS, compound 1). The fungi isolated from a medicinal plant,
Dendrobium candidum
Wall. ex Lindl., were screened for their biotransformation abilities with GPS as the substrate, and one strain with high converting potency was identified as
Penicillium crustosum
2T01Y01 on the basis of the sequence of the internal transcribed spacer of the ribosomal DNA region. Upon the optimized incubation of
P. crustosum
2T01Y01 with the substrate, seven deglycosylated metabolites were detected by ultraperformance liquid chromatography/quadrupole time of flight mass spectrometry (UPLC/Q-TOF MS). Preparative-scale biotransformation with whole cells of the endophytic fungus resulted in the production of five metabolites, including three novel ones, 5α-(hydroxymethyl)-6β-methyl-3,4,5,6-tetrahydropyrano[3,4-
c
]pyran-1(8
H
)-one (compound 2), (
Z
)-4-(1-hydroxybut-3-en-2-yl)-5,6-dihydropyran-2-one (compound 3), and (
E
)-4-(1-hydroxybut-3-en-2-yl)-5,6-dihydropyran-2-one (compound 4), along with two known ones, 5α-(hydroxymethyl)-6β-methyl-1
H
,3
H
-5,6-dihydropyrano[3,4-
c
]pyran-1(3
H
)-one (compound 5) and 5α-(hydroxymethyl)-6α-methyl-5,6-dihydropyrano[3,4-
c
]pyran-1(3
H
)-one (compound 6), aided by nuclear magnetic resonance and high-resolution mass spectral analyses. The other two metabolites were tentatively identified by online UPLC/Q-TOF MS as 5-hydroxymethyl-5,6-dihydroisochromen-1-one (compound 7) and 5-hydroxymethyl-3,4,5,6-tetrahydroisochromen-1-one (compound 8), and compound 8 is a new metabolite. To test the metabolic mechanism, the β-glucosidase activity of the fungus
P. crustosum
2T01Y01 was assayed with ρ-nitrophenyl-β-
d
-glucopyranoside as a probe substrate, and the pathway of GPS biotransformation by strain 2T01Y01 is proposed. In addition, the hepatoprotective activities of GPS and metabolite compounds 2, 5, and 6 against human hepatocyte line HL-7702 injury induced by hydrogen peroxide were evaluated.
Toxicity of Bioactive and Probiotic Marine Bacteria and Their Secondary Metabolites in Artemia sp. and Caenorhabditis elegans as Eukaryotic Model Organisms
Authors: Neu Anna Katrin , Månsson Maria , Gram Lone , Prol-García María J.
Published: October 2013

We have previously reported that some strains belonging to the marine
Actinobacteria
class, the
Pseudoalteromonas
genus, the
Roseobacter
clade, and the
Photobacteriaceae
and
Vibrionaceae
families produce both antibacterial and antivirulence compounds, and these organisms are interesting from an applied point of view as fish probiotics or as a source of pharmaceutical compounds. The application of either organisms or compounds requires that they do not cause any side effects, such as toxicity in eukaryotic organisms. The purpose of this study was to determine whether these bacteria or their compounds have any toxic side effects in the eukaryotic organisms
Artemia
sp. and
Caenorhabditis elegans
.
Arthrobacter davidanieli
WX-11,
Pseudoalteromonas luteoviolacea
S4060,
P. piscicida
S2049,
P. rubra
S2471,
Photobacterium halotolerans
S2753, and
Vibrio coralliilyticus
S2052 were lethal to either or both model eukaryotes. The toxicity of
P. luteoviolacea
S4060 could be related to the production of the antibacterial compound pentabromopseudilin, while the adverse effect observed in the presence of
P. halotolerans
S2753 and
V. coralliilyticus
S2052 could not be explained by the production of holomycin nor andrimid, the respective antibiotic compounds in these organisms. In contrast, the tropodithietic acid (TDA)-producing bacteria
Phaeobacter inhibens
DSM17395 and
Ruegeria mobilis
F1926 and TDA itself had no adverse effect on the target organisms. These results reaffirm TDA-producing
Roseobacter
bacteria as a promising group to be used as probiotics in aquaculture, whereas
Actinobacteria
,
Pseudoalteromonas
,
Photobacteriaceae
, and
Vibrionaceae
should be used with caution.
Synthetic Promoters Functional in Francisella novicida and Escherichia coli
Authors: McWhinnie Ralph L. , Nano Francis E.
Published: October 2013

In this work, we describe the identification of synthetic, controllable promoters that function in the bacterial pathogen
Francisella novicida
, a model facultative intracellular pathogen. Synthetic DNA fragments consisting of the tetracycline operator (
tetO
) flanked by a random nucleotide sequence were inserted into a
Francisella novicida
shuttle plasmid upstream of a promoterless artificial operon containing the reporter genes
cat
and
lacZ
. Fragments able to promote transcription were selected for based on their ability to drive expression of the
cat
gene, conferring chloramphenicol resistance. Promoters of various strengths were found, many of which were repressed in the presence of the tetracycline repressor (TetR) and promoted transcription only in the presence of the TetR inducer anhydrotetracycline. A subset of both constitutive and inducible synthetic promoters were characterized to find their induction ratios and to identify their transcription start sites. In cases where
tetO
was located between or downstream of the −10 and −35 regions of the promoter, control by TetR was observed. If the
tetO
region was upstream of the −35 region by more than 9 bp, it did not confer TetR control. We found that three of three promoters isolated in
F. novicida
functioned at a comparable level in
E. coli
; however, none of the 10 promoters isolated in
E. coli
functioned at a significant level in
F. novicida
. Our results allowed us to isolate minimal
F. novicida
promoters of 47 and 48 bp in length.