bluuebunny/crossref_metadata_2025 huggingface dataset:
Spontaneous glutamatergic activity induces a BDNF‐dependent potentiation of GABAergic synapses in the newborn rat hippocampus
Authors: Kuczewski Nicola , Langlois Anais , Fiorentino Hervé , Bonnet Stéphanie , Marissal Thomas , Diabira Diabe , Ferrand Nadine , Porcher Christophe , Gaiarsa Jean‐Luc
Published: September 2008

Spontaneous ongoing synaptic activity is thought to play an instructive role in the maturation of the neuronal circuits. However the type of synaptic activity involved and how this activity is translated into structural and functional changes is not fully understood. Here we show that ongoing glutamatergic synaptic activity triggers a long‐lasting potentiation of γ‐aminobutyric acid (GABA) mediated synaptic activity (LLPGABA‐A) in the developing rat hippocampus. LLPGABA‐A induction requires (i) the activation of AMPA receptors and L‐type voltage‐dependent calcium channels, (ii) the release of endogenous brain‐derived neurotrophic factor (BDNF), and (iii) the activation of postsynaptic tropomyosin‐related kinase receptors B (TrkB). We found that spontaneous glutamatergic activity is required to maintain a high level of native BDNF in the newborn rat hippocampus and that application of exogenous BDNF induced LLPGABA‐A in the absence of glutamatergic activity. These results suggest that ongoing glutamatergic synaptic activity plays a pivotal role in the functional maturation of hippocampal GABAergic synapses by means of a cascade involving BDNF release and downstream signalling through postsynaptic TrkB receptor activation.
Calcium‐permeable presynaptic AMPA receptors in cerebellar molecular layer interneurones
Authors: Rossi Bénédicte , Maton Gilliane , Collin Thibault
Published: September 2008

Axons of cerebellar molecular layer interneurones (MLIs) bear ionotropic glutamate receptors. Here, we show that these receptors elicit cytosolic [Ca2+] transients in axonal varicosities following glutamate spillover induced by stimulation of parallel fibres (PFs). A spatial profile analysis indicates that these transients occur at the same locations when induced by PF stimulation or trains of action potentials. They are not affected by the NMDAR antagonist AP‐V, but are abolished by the AMPAR inhibitor GYKI‐53655. Mimicking glutamate spillover by a puff of AMPA triggers axonal [Ca2+]itransients even in the presence of TTX. Addition of specific voltage‐dependent Ca2+channel (VDCC) blockers such as ω‐AGAIVA and ω‐conotoxin GVIA or broad range inhibitors such as Cd2+did not significantly inhibit the signal indicating the involvement of Ca2+‐permeable AMPARs. This hypothesis is further supported by the finding that the subunit specific AMPAR antagonist IEM‐1460 blocks 75% of the signal. Bath application of AMPA increases the frequency and mean peak amplitude of GABAergic mIPSCs, an effect that is blocked by philanthotoxin‐433 (PhTx) and reinforced by facilitating concentrations of ryanodine. By contrast, a high concentration of ryanodine or dantrolene reduced the effects of AMPA on mIPSCs. Single‐cell RT‐PCR experiments show that all GluR1–4 subunits are potentially expressed in MLI. Taken together, the results suggest that Ca2+‐permeable AMPARs are colocalized with VDCCs in axonal varicosities and can be activated by glutamate spillover through PF stimulation. The AMPAR‐mediated Ca2+signal is amplified by Ca2+‐induced Ca2+release from intracellular stores, leading to GABA release by MLIs.
Depletion of calcium stores regulates calcium influx and signal transmission in rod photoreceptors
Authors: Szikra Tamas , Cusato Karen , Thoreson Wallace B. , Barabas Peter , Bartoletti Theodore M. , Krizaj David
Published: September 2008

Tonic synapses are specialized for sustained calcium entry and transmitter release, allowing them to operate in a graded fashion over a wide dynamic range. We identified a novel plasma membrane calcium entry mechanism that extends the range of rod photoreceptor signalling into light‐adapted conditions. The mechanism, which shares molecular and physiological characteristics with store‐operated calcium entry (SOCE), is required to maintain baseline [Ca2+]i in rod inner segments and synaptic terminals. Sustained Ca2+ entry into rod cytosol is augmented by store depletion, blocked by La3+ and Gd3+ and suppressed by organic antagonists MRS‐1845 and SKF‐96365. Store depletion and the subsequent Ca2+ influx directly stimulated exocytosis in terminals of light‐adapted rods loaded with the activity‐dependent dye FM1–43. Moreover, SOCE blockers suppressed rod‐mediated synaptic inputs to horizontal cells without affecting presynaptic voltage‐operated Ca2+ entry. Silencing of TRPC1 expression with small interference RNA disrupted SOCE in rods, but had no effect on cone Ca2+ signalling. Rods were immunopositive for TRPC1 whereas cone inner segments immunostained with TRPC6 channel antibodies. Thus, SOCE modulates Ca2+ homeostasis and light‐evoked neurotransmission at the rod photoreceptor synapse mediated by TRPC1.
Differential dependence of store‐operated and excitation‐coupled Ca2+ entry in skeletal muscle on STIM1 and Orai1
Authors: Lyfenko Alla D. , Dirksen Robert T.
Published: September 2008

In non‐excitable cells, agonist‐induced depletion of intracellular Ca2+ stores triggers Ca2+ influx via a process termed store‐operated Ca2+ entry (SOCE). In T‐lymphocytes, stromal interaction molecule 1 (STIM1) acts as the intra‐store Ca2+ sensor and Orai1 functions as the Ca2+‐permeable SOCE channel activated by STIM1 following store depletion. Two functionally distinct Ca2+ entry pathways exist in skeletal muscle; one activated by store depletion (SOCE) and a second by sustained/repetitive depolarization that does not require store depletion (excitation‐coupled Ca2+ entry, ECCE). However, the role of STIM1 and Orai1 in coordinating SOCE and ECCE activity in skeletal muscle and whether these two Ca2+ entry pathways represent distinct molecular entities or two different activation mechanisms of the same channel complex is unknown. Here we address these issues using siRNA‐mediated STIM1 knockdown, dominant‐negative Orai1, and permeation‐defective Orai1 to determine the role of STIM1 and Orai1 in store‐operated and excitation‐coupled Ca2+ entry in skeletal myotubes. SOCE and ECCE activity were quantified from both intracellular Ca2+ measurements and Mn2+ quench assays. We found that STIM1 siRNA reduced STIM1 protein by more than 90% and abolished SOCE activity, while expression of siRNA‐resistant hSTIM1 fully restored SOCE. SOCE was also abolished by dominant‐negative Orai1 (E106Q) and markedly reduced by expression of a permeation‐defective Orai1 (E190Q). In contrast, ECCE was unaffected by STIM1 knockdown, E106Q expression or E190Q expression. These results are the first to demonstrate that SOCE in skeletal muscle requires both STIM1 and Orai1 and that SOCE and ECCE represent two distinct molecular entities.
Comparison of the myoplasmic calcium transient elicited by an action potential in intact fibres of mdx and normal mice
Authors: Hollingworth Stephen , Zeiger Ulrike , Baylor Stephen M.
Published: September 2008

The myoplasmic free [Ca2+] transient elicited by an action potential (Δ[Ca2+]) was compared in fast‐twitch fibres of mdx (dystrophin null) and normal mice. Methods were used that maximized the likelihood that any detected differences apply in vivo. Small bundles of fibres were manually dissected from extensor digitorum longus muscles of 7‐ to 14‐week‐old mice. One fibre within a bundle was microinjected with furaptra, a low‐affinity rapidly responding fluorescent calcium indicator. A fibre was accepted for study if it gave a stable, all‐or‐nothing fluorescence response to an external shock. In 18 normal fibres, the peak amplitude and the full‐duration at half‐maximum (FDHM) of Δ[Ca2+] were 18.4 ± 0.5 μm and 4.9 ± 0.2 ms, respectively (mean ±s.e.m.; 16°C). In 13 mdx fibres, the corresponding values were 14.5 ± 0.6 μm and 4.7 ± 0.2 ms. The difference in amplitude is statistically highly significant (P= 0.0001; two‐tailed t test), whereas the difference in FDHM is not (P= 0.3). A multi‐compartment computer model was used to estimate the amplitude and time course of the sarcoplasmic reticulum (SR) calcium release flux underlying Δ[Ca2+]. Estimates were made based on several differing assumptions: (i) that the resting myoplasmic free Ca2+ concentration ([Ca2+]R) and the total concentration of parvalbumin ([ParvT]) are the same in mdx and normal fibres, (ii) that [Ca2+]R is larger in mdx fibres, (iii) that [ParvT] is smaller in mdx fibres, and (iv) that [Ca2+]R is larger and [ParvT] is smaller in mdx fibres. According to the simulations, the 21% smaller amplitude of Δ[Ca2+] in mdx fibres in combination with the unchanged FDHM of Δ[Ca2+] is consistent with mdx fibres having a ∼25% smaller flux amplitude, a 6–23% larger FDHM of the flux, and a 9–20% smaller total amount of released Ca2+ than normal fibres. The changes in flux are probably due to a change in the gating of the SR Ca2+‐release channels and/or in their single channel flux. The link between these changes and the absence of dystrophin remains to be elucidated.
Simulation of Laser-Induced Incandescence Measurements in an Anisotropically Scattering Aerosol Through Backward Monte Carlo
Authors: Daun K. J. , Thomson K. A. , Liu F.
Published: September 2008

Laser-induced incandescence (LII) measurements carried out in aerosols having a large particle volume fraction must be corrected to account for extinction between the energized aerosol particles and the detector, called signal trapping. While standard correction techniques have been developed for signal trapping by absorption, the effect of scattering on LII measurements requires further investigation, particularly the case of highly anisotropic scattering and along a path of relatively large optical thickness. This paper examines this phenomenon in an aerosol containing highly aggregated soot particles by simulating LII signals using a backward Monte Carlo analysis; these signals are then used to recover the soot particle temperature and soot volume fraction. The results show that inscattered radiation is a substantial component of the LII signal under high soot loading conditions, which can strongly influence properties derived from these measurements. Correction techniques based on Bouguer’s law are shown to be effective in mitigating the effect of scatter on the LII signals.
Magnetohydrodynamic Mixed-Convective Flow and Heat and Mass Transfer Past a Vertical Plate in a Porous Medium With Constant Wall Suction
Authors: Makinde O. D. , Sibanda P.
Published: September 2008

The problem of steady laminar hydromagnetic heat transfer by mixed convection flow over a vertical plate embedded in a uniform porous medium in the presence of a uniform normal magnetic field is studied. Convective heat transfer through porous media has wide applications in engineering problems such as in high temperature heat exchangers and in insulation problems. We construct solutions for the free convection boundary-layer flow equations using an Adomian–Padé approximation method that in the recent past has proven to be an able alternative to the traditional numerical techniques. The effects of the various flow parameters such as the Eckert, Hartmann, and Schmidt numbers on the skin friction coefficient and the concentration, velocity, and temperature profiles are discussed and presented graphically. A comparison of our results with those obtained using traditional numerical methods in earlier studies is made, and the results show an excellent agreement. The results demonstrate the reliability and the efficiency of the Adomian–Padé method in an unbounded domain.
Extraordinary Coherent Thermal Emission From SiC Due to Coupled Resonant Cavities
Authors: Dahan Nir , Niv Avi , Biener Gabriel , Gorodetski Yuri , Kleiner Vladimir , Hasman Erez
Published: September 2008

In high temperature and vacuum applications, when heat transfer is predominantly by radiation, the material’s surface texture is of substantial importance. Several micro- and nanostructure designs have been proposed to enhance a material’s emissivity and its radiative coherence, as control of thermal emission is of crucial concern in the design of infrared sources, optical filters, and sensing devices. In this research, an extraordinary coherent thermal emission from an anisotropic microstructure is experimentally and theoretically presented. The enhanced coherency is due to coherent coupling between resonant cavities obtained by surface standing waves, wherein each cavity supports a localized field that is attributed to coupled surface phonon polaritons. We show that it is possible to obtain a polarized quasimonochromatic thermal source from a SiC microstructure with a high quality factor of 600 at the resonant frequency of the cavity and a spatial coherence length of 716 wavelengths, which corresponds to an angular divergence of 1.4mrad. In the experimental results, we measured a quality factor of 200 and a spatial coherence length of 143 wavelengths. We attribute the deviation in the experimental results to imperfections in the fabrication of the high quality factor cavities.
Competing Dynamic Solutions in a Parametrically Excited Pendulum: Attractor Robustness and Basin Integrity
Authors: Lenci Stefano , Rega Giuseppe
Published: September 2008

The competing solutions of a planar pendulum parametrically excited by the vertical motion of the pivot are investigated in terms of both attractor robustness and basin integrity. Two different measures are considered to highlight how the integrity of the system is modified by changing the amplitude of the excitation. Various attractors, both in-well and out-of-well, are considered, and the integrity profiles of each of them are determined. A detailed discussion of the interaction and mutual erosion of the various attractors is performed by clarifying the role of the two complementary measures, and the most relevant characteristics of the erosion profiles are interpreted in terms of the underlying topological mechanisms involving local or global bifurcations.
Efficient Treatment of Gyroscopic Bodies in the Recursive Solution of Multibody Dynamics Equations
Authors: Tong Martin M.
Published: September 2008

This paper presents an efficient treatment of gyroscopic bodies in the recursive solution of the dynamics of an N-body system. The bodies of interest include the reaction wheels in satellites, wheels on a car, and flywheels in machines. More specifically, these bodies have diagonal inertia tensors. They spin about one of its principal axes, with the moment of inertia along the transverse axes identical. Their center of mass lies on the spin axis. Current recursive solution methods treat these bodies identically as any other body in the system. The proposition here is that a body with gyroscopic children can be collectively treated as a composite body in the recursive solution process. It will be shown that this proposition improves the recursive solution speed to the order(N−m) where m is the number of gyroscopic bodies in the system. A satellite with three reaction wheels is used to illustrate the proposition.
The Generalized-α Scheme as a Linear Multistep Integrator: Toward a General Mechatronic Simulator
Authors: Brüls Olivier , Arnold Martin
Published: September 2008

This paper presents a consistent formulation of the generalized-α time integration scheme for mechanical and mechatronic systems. The algorithm can deal with a nonconstant mass matrix, controller dynamics, and kinematic constraints. The theoretical background relies on the analogy with linear multistep formulas, which leads to elegant results related to consistency, order conditions for constant and variable step-size methods, as well as global convergence. Those results are illustrated for a controlled spring-mass system, and the method is also applied for the simulation of a vehicle semi-active suspension.
A Simple and Efficient Numerical Method for Dynamic Interaction Analysis of a High-Speed Train and Railway Structure During an Earthquake
Authors: Tanabe M. , Matsumoto N. , Wakui H. , Sogabe M. , Okuda H. , Tanabe Y.
Published: September 2008

In this paper, a simple and efficient numerical method to solve for the dynamic interaction of a high-speed train and railway structure during an earthquake is given. The motion of the train is modeled in multibody dynamics with nonlinear springs and dampers used to connect components. An efficient mechanical model for contact dynamics between the wheel and rail during an earthquake is presented. The railway structure is modeled with various finite elements. A nonlinear spring element based on a trilinear elastic-plastic material model is given for the concrete railway structure during an earthquake. A substructure model where a train runs repeatedly has been devised to obtain an approximated combined motion of the long train with many cars connected and the railway structure during an earthquake. A modal method has been developed to solve large-scale nonlinear equations of motion of the train and railway structure effectively. Based on the present method, a computer program DIASTARS for the dynamic interaction analysis of a Shinkansen train (high-speed train in Japan) and the railway structure during an earthquake has been developed. Numerical examples are demonstrated.
Increasing the Efficiency of Energy Scavengers by Magnets
Authors: Shahruz S. M.
Published: September 2008

In this paper, a methodology for designing efficient energy scavengers is proposed. The scavenger consists of a cantilever beam on which piezoelectric films and a mass are mounted. The mass at the tip of the beam is known as the proof mass and the device is called either an energy scavenger or a beam-mass system. The proof mass is a permanent magnet, where in its vicinity attracting permanent magnets are placed. When a scavenger is mounted on a vibration source, the cantilever beam would vibrate. Due to the vibration of the beam, the piezoelectric films generate electric charge. The generated charge is proportional to the amplitude of vibration of the tip of the beam. It is shown that when the magnets have appropriate strengths and are placed appropriately, the vibration of the tip of the beam can be amplified, thereby the scavenger efficiency is increased. Examples are given throughout the paper.
Large-Scale Pulsation Detection by Means of Temperature Measurements
Authors: Silin N. , Masson V. , Rauschert A.
Published: September 2008

In the present work we explore the potential of time-resolved temperature measurements to obtain information on large-scale pulsations in a rod bundle geometry with axial flow. Large-scale flow pulsation is the phenomenon that dominates the turbulent mixing between the subchannels of rod bundles, which explains why it is of great importance for the design or assessment of nuclear fuel elements. The objective of the present work is to determine the characteristics of large-scale pulsations that can be used for the verification or validation of computational fluid dynamics code results. The method proposed is to generate a temperature gradient across the location of flow pulsations and to measure the time-varying temperature field downstream. Pulsation characteristic times, lengths, and traveling speed have been obtained. This study has been performed in a rod bundle similar to a nuclear fuel assembly and the results obtained are in good agreement with previous works on similar geometries. The technique can be applied to obtain additional large-scale structure information in test sections designed for thermal measurements, in situations where convection is dominated by these structures.
Definition and Evaluation of Mean Beam Lengths for Applications in Multidimensional Radiative Heat Transfer: A Mathematically Self-Consistent Approach
Authors: Yuen Walter W.
Published: September 2008

A set of mathematically self-consistent definitions of mean beam length is introduced to account for surface-surface, surface-volume, and volume-volume radiative exchanges in general three-dimensional inhomogeneous medium. Based on these definitions, the generic exchange factor (GEF) formulated by the recently introduced multiple-absorption-coefficient-zonal-method (MACZM) can be written in an equivalent one-dimensional form. The functional behavior of the proposed mean beam lengths is shown to be readily correlated by either simple algebraic relations or neural network based correlations. They can be implemented directly with MACZM in general computational code to account for the radiation effect in complex three-dimensional systems. In addition, these definitions of mean beam length can also be used to assess the accuracy of the conventional mean beam length concept currently used by the practicing engineering community.
The
Limiting Radius for Freezing a Tumor During Percutaneous
Cryoablation
Authors: Nakayama Akira , Kuwahara Yusuke , Iwata Kansei , Kawamura Masafumi
Published: September 2008

The freezing front in a tumor during percutaneous cryoablation therapy was traced both analytically and numerically exploiting a bioheat equation. It has been shown that there exists a limiting size of the tumor, which one single cryoprobe can freeze at the maximum. The freezing front moves radially outward from the cryoprobe and reaches the end, where the heat from the surrounding tissue to the frozen tissue balances with the heat being absorbed by the cryoprobe. An excellent agreement between the analytical and numerical results has been achieved for the time required to freeze the tumor using the cryoprobe of a single needle. An analytical expression for estimating the limiting radius has been derived to give useful information for cryotherapy treatment plans.
Demonstration of Heat Transfer Enhancement Using Ferromagnetic Particle Laden Fluid and Switched Magnetic Fields
Authors: Murray Mark M.
Published: September 2008

A convective heat transfer enhancement technique and the experimental methods used to quantify the improvement in heat transfer and subsequent differential pressure are introduced. The enhancement technique employed time varying magnetic fields produced in a pipe to cause the ferromagnetic particles of a particle laden fluid (mineral oil and iron filings) to be attracted to and released from a heated pipe wall. The ferromagnetic particles acted not only to advect heat from the pipe wall into the bulk fluid but they also significantly modified the flow field, disrupted the boundary layer, allowed cooler fluid to reach the high temperature pipe wall, increased thermal energy transfer directly to the fluid, and contributed to the overall improvement in heat transfer rate. The experimental method utilized to quantify an increased effectiveness of convective heat transfer used an apparatus designed to replicate an internally cooled fin, whose surface temperature was measured with an IR camera. These temperature measurements were utilized to calculate the convective heat transfer coefficient (h) of the fluid within the pipe. The enhancement technique demonstrated a 267% increase in heat transfer coefficient with only a corresponding 48% increase in flow differential pressure for an electromagnetic switching frequency of 2 Hz. It is also found that there were optimum magnetic field switching frequencies for both enhancement and differential pressure magnitudes.
Monitoring the Lubrication Condition of Rolling Element Bearings Using the Acoustic Emission Technique
Authors: Fan Yibo Edward , Shi Zhanqun , Harris Georgina , Gu Fengshou , Ball Andrew
Published: September 2008

Lubrication condition strongly influences the behaviour and operational life of a rolling element bearing. This paper presented an experimental investigation of rolling element bearings with no lubricant and with grease-lubricant containing contaminants using the acoustic emission (AE) technique. High frequency sampling and data streaming technology were applied in the measurement of AE, instead of traditionally measured AE parameters such as the counts, events, and peak amplitude of the signal etc. By processing the AE signals with frequency domain analysis technology, the no lubricant and containing contaminants conditions can be clearly discriminated. This result proved that the frequency domain AE signal processing technique is a suitable method for monitoring the lubrication condition in rolling element bearings.
Computational and Neuro-Fuzzy Study of the Effect of Small Objects on the Flow and Thermal Fields of Bluff Bodies
Authors: Abdel Gawad Ahmed F.
Published: September 2008

The aim of the present study is to find computationally the optimum parameters that affect the drag reduction of bluff bodies using a small object (obstacle). These parameters include the size of the obstacle as well as the gap between the obstacle and the bluff body. Two- and three-dimensional bodies were investigated in turbulent flow fields. The research was focused on the cases of the rectangular-section obstacle. Four values of the obstacle size were studied, namely: 4%, 10%, 35%, and 100% of the size of the bluff body. The effect of the obstacle on the thermal field of the two-dimensional body was also studied. Comparisons were carried out with the available experimental measurements. A proposed neuro-fuzzy approach was used to predict the drag reduction of the entire system. Results showed that system drag reductions up to 62% (two-dimensional flows) and 48% (three-dimensional flows) can be obtained. Also, enhancement of the body cooling up to 75% (two-dimensional flows) may be achieved. Generally, useful comments and suggestions are stated.
Thermoelastic Stability of Imperfect Functionally Graded Plates Based on the Third Order Shear Deformation Theory
Authors: Samsam Shariat B. , Eslami M. R. , Bagri A.
Published: September 2008

Thermal buckling analysis of rectangular functionally graded plates with initial geometric imperfections is presented in this paper. It is assumed that the non-homogeneous mechanical properties vary linearly through the thickness of the plate. The plate is assumed to be under various types of thermal loadings, such as the uniform temperature rise and nonlinear temperature gradient through the thickness. A double-sine function for the geometric imperfection along the x and y-directions is considered. The equilibrium equations are derived using the third order shear deformation plate theory. Using a suitable method, equilibrium equations are reduced from 5 to 2 equations. The corresponding stability equations are established. Using these equations accompanied by the compatibility equation yield to the buckling loads in a closed form solution for each loading case. The results are compared with the known data in the literature.
Parametric Study of Installed Fogging Systems Using CFD Model
Authors: Hain Y. , Litinetski V. , Litinetsky A.
Published: September 2008

Water fogging of inlet air has become widely acceptable for gas turbine power augmentation. Fogging systems are generally designed for a specific set of conditions called the design point. As a rule, the design point is specified to provide the maximum capacity of the fogging system at extreme ambient temperatures, when gas turbine power output is maximally decreased. Since the extreme ambient conditions rarely occur, the fogging system primarily operates at partial loads, when only a part of the installed cooling stages is in operation. At partial loads the fogging system does not provide uniform fogging of the inlet air, which could result in insufficient fog evaporation, less air-cooling and entrainment of non-evaporated water into the compressor. Prolonged operation at such off-design conditions requires careful tuning of the system in order to maximize cooling efficiency and eliminate a possible impact on gas turbine maintenance. This requires clear understanding of conceptual features of thin droplets evaporation and fog cloud behavior inside gas turbine inlet ducts. To this purpose, computational fluid dynamics (CFD) analysis was used. A CFD model is described, which comprises a straight duct equipped with fog nozzles operating in conditions similar to field conditions at design point, as well as, at partial load operation of the fogging system. The study focused on problems, which are critical in design and operation of real fogging systems, namely: single droplet, mono- and poly-fraction fog evaporation; influence of flow turbulent intensity; fog cloud shape and dimensions; polyfraction fog evaporation in the wide range of ambient conditions; over-spray and under-spray operation of the fogging system. The study results were helpful in the tuning of the installed fogging systems to site specific ambient conditions that provided efficient cooling with safe compressor operation. These results should be useful to both designers and operators of the fogging systems.
CDT Analysis is Used as a Condition Monitoring Parameter to Study the Tribological Behavior of Bearing Lubricant Under Different Operating Pressure
Authors: Browne R. Edwin , Ramachandran K. P. , De Silva A. K. M. , Harrison D. K.
Published: September 2008

The deceleration and running down operation of any rotating system when analysed would lead to useful input function for condition monitoring. When the power supply to any rotor system is cut off, total momentum gained through the sustained operation will dissipate and the system will come to halt. The time elapsed between the power cutoff and the complete stop of the system is defined as CDT (Coast Down Time). The tribological behaviour could be effectively monitored through this parameter (CDT), which has been conducted on a horizontal rotor system with a full journal bearing at different speed and lubrication pressures. The characteristics are compared with steady state vibration in order to emphasize the potential benefit of using CDT as a useful diagnostic parameter for condition monitoring.
FEM Simulation of the Whole Circle of Aluminum Hot Extrusion Using Circular Dies With Different Extrusion Angle
Authors: Lontos A. , Bouzakis K.-D. , Demosthenous G. , Baldoukas A.
Published: September 2008

On of the most typical forming processes used for the production of long, straight semi-finished products in the form of various section geometries is extrusion. Hot extrusion is a thermo-mechanical process whish involves complicated interactions between process parameters, tooling and deforming material /1,2/. In the present paper, FEM simulation is performed in the aluminum extrusion using circular dies with different geometries in order to extract quantitative simulating results regarding various forming parameters. Most specifically the parameters that are investigated are the die design-geometry, the process parameters (i.e. ram speed, container temperature, billet temperature) and the product quality (i.e. extruded shape, surface condition). The finite element modeling is based on 3D simulation tools using the DEFORM 3D software /3–5/. The used work piece is the aluminum AA6061 in cylindrical form with a diameter of 14 mm. The used material for the extrusion die is the hot work steel AISI H13. The geometry of the die is circular with a variation in die angle. The container and the billet temperature will vary from 450 to 550 degrees, and the mandrel (ram) speed will be at the range of 2 mm/sec. On the basis of simulating results such as pressure distribution on the extrusion die, effective stresses on the billet and product quality, new and improve die geometry will be introduced. Although the simulation problem is an axisymmetric one the authors decide to proceed with 3D FEM simulation in order to examine and verify the 3D simulating results. This paper is the first part of a further research project in which more complicated die geometries will be used as simulating and experimental specimens. In addition to simulating results, experimental results will be presented in the next few months.
Primary Resonance of a Vehicle Suspension System With Nonlinear Stiffness and Nonlinear Damping
Authors: Li Shaohua , Yang Shaopu
Published: September 2008

In this work, primary resonance of a single-degree-of-freedom (SDOF) vehicle suspension system with nonlinear stiffness and nonlinear damping under multi-frequency excitations is investigated. The primary resonance equation is obtained by average method, and then the system’s bifurcation behaviors are studied by singularity theory. In addition, the effect of changing physical model parameters on the system’s primary resonance is studied.
Exponential Stability of Discrete Time Delay Systems With Nonlinear Perturbations
Authors: Stojanovic S. B. , Debeljkovic D. Lj.
Published: September 2008

This paper gives sufficient condition for the exponential stability of discrete delay systems with nonlinear perturbations. This new, delay–dependent condition is derived using approach based on Lyapunov’s direct method. A numerical example has been working out to show the applicability of results derived.
Design of a Fuzzy Controller for an Underwater Vehicle Aiming at a Stationary Target
Authors: Azarsina Farhood , Sayyaadi Hassan
Published: September 2008

In this paper, on the basis of a robust algorithm for the analysis of the 6 DOF motion of an underwater vehicle in calm water, after presenting the dynamics model and simulating motion, the model is put in the closed loop control to perform a controlled mission. The mission is defined as to navigate the submarine toward a desired point in the vertical plane. In performing the mission, the least time and of course the least position error with respect to the target point is aimed. The designed controller based on fuzzy logic and thus adapted to the human patterns for navigation, with a simple structure, performs the mission accurately. The intelligent structure of the fuzzy controller, results in a spectacular capability in target finding; such that by the increase of mission duration, the submarine, which never completely stops in this modeling, reaches the target point multiple times. Several simulations of the controlled motion, changing the coordinates of target point, proved the controller effectiveness.
Failure Analysis of LDPE Compressor Bolts
Authors: Al-Shahrani Saeed Y. , Ahmed Shahreer
Published: September 2008

In Low Density Polyethylene (LDPE) plant, the ethylene gas is compressed up to a pressure of 3000 bar. This is achieved by compressing the ethylene gas using two stages as primary [18 °C (64.4 °F), 1700 bar] and secondary [90 °C (194 °F), 3000 bar] stage compressors. The studs under investigation were used to clamp the flange of the suction and discharge valves to the cylinder head (Studs from the Flanges of 1st Stage - Secondary Hyper Compressor). Six cylinders are present in each stage and 6 studs are used to fix each flange on the suction or discharge valve to the cylinder head. The material used to fabricate these studs was B7 and the threads were produced by rolling. In the 1st stage cylinders frequent failures of studs started within two months of operation. Since the start up about 11 studs from different location have been failed. A metallographic examination using optical and scanning electron microscopy as well as energy dispersive spectrometry (EDS) revealed that the failure was due to fatigue.
Fatigue Life Prediction of Optimum Hollowness of Hollow Cylindrical Rollers in Pure Rolling Contact
Authors: Abu-Jadayil Wisam M. , Flugrad Donald R. , Qamhiyah Abir Z.
Published: September 2008

Fatigue life investigations have been made for cylindrical hollow rollers in pure rolling contact. In addition to normal loading, the rollers have been subjected to tangential loading of 1/3rd the normal load value. Sufficient coefficient of friction has been used to ensure no slipping occurs. Two main models were built with different hollowness percentages to investigate the hollowness percentage that gives the longest fatigue life. The first model consists of two cylindrical rollers of same size, while the second model consists of two rollers of different sizes. Two cases have been studied, when both rollers are hollow and when only one roller is hollow. The stress distribution in the roller body and the resulting deformation has been investigated using the finite element package, ABAQUS. Then the Ioannides-Harris (IH) theory was used to predict the fatigue life of the hollow rollers in pure rolling contact. Investigations have been made for five different materials, CVD 52100, Carburized steel, VIMVAR M50, M50NiL and Induction-hardened steel. It has been found that the optimum hollowness percentage with the longest fatigue life ranges between 50% and 70%. Many factors affect the optimum hollowness percentage, like the kind of the material used for the cylindrical roller, whether the rollers in contact are of the same size or different size and whether the hollow roller is in contact with another hollow roller or in contact with solid roller. At the optimum hollowness percentage, the roller can live hundred times the life of solid roller. So, as the endurance limit of the material increases, as the fatigue life of the rollers increases too. It has been found that cylindrical roller in contact with another identical sized roller has shorter fatigue life than the cylindrical roller in contact with a bigger roller. That might be related to increase the flexibility of the system that acts as a spring mass system and to the increase of the contact surface area. In case of identical sized models, the longest fatigue life achieved was two hollow rollers of 50% percentage of hollowness. When only one roller is hollow, the optimum shifts to 70% percentage of hollowness. For the non identical sized rollers, the optimum is around 50% but when one roller only is hollow, the fatigue life is longer. That might be related to optimum flexibility that gives the longest fatigue life. If the flexibility of the system is very high, the fatigue life of the roller is reduced because of the effect of the bending stresses.
Engineering Development of an Instrument Panel Concept Using a Unified FE Modeling Approach
Authors: Danesh Sararoudi Mehdi , Shamsaei Nima , Darijani Hossein , Naghdabadi Reza
Published: September 2008

In today’s global economy, the automotive design engineer’s responsibilities are made more complex by the differences between regulatory requirements of the various global markets. This paper compares instrument panel head impact requirements of FMVSS 201 with its European counterparts, ECE 21. The behavior during a head impact test has been studied. Due to the gravity of the cockpit module, the sag has been analyzed to simulate shipping, loading, and assembly conditions. The interior parts of the vehicle cabin are exposed to temperature variations due to radiation effect of sun ray or freezing temperature in winter. Plastic parts appear to be more thermally susceptible than steel parts in temperature variations. The key issue was minimizing thermal deformation while developing the IP. The cockpit design engineers have gained an understanding of the factors involved in ensuring that their design fully meets the requirements of the subject regulations. CAE simulations performed which are repetitive processes and a unified FE modeling approach has handled analyses by different codes.
Stress Analysis of Three-Unit All-Ceramic Dental Bridges Using FEM
Authors: Biria M. J. , Shamsaei Nima , Farahmand Farzam , Eslami A. G. Reza
Published: September 2008

Mechanical fracture is a common cause of failure for 3-unit dental bridges, particularly, the all-ceramic structures. The purpose of the present study was to evaluate the effect of convergence angles of the abutments on the distribution of the mechanical stresses, within the prosthesis and at the restoration-abutments interface of a 3-unit all-ceramic bridge. The 3-D geometrical data of the second premolar and first and second molar teeth were obtained using ATOS scanner system and utilized for reconstruction of a surface model of the 3-unit bridge in I-Deas as solid modeler software. This was then transferred to MSC/Nastran software for mesh generation and finite element analysis. Two FE models were developed with different convergence angles, including 171900 and 168700 tetrahedral solid four-node elements. The models were subjected to two different prosthesis material and three different load cases. Therefore, twelve cases were analyzed and compared. Aforementioned comparing indicated that the maximum tensile stresses occur on the gingival surface of the second premolar retainer, and at the tooth/restoration interface on the marginal distal surface of the second molar. The peak tensile stress was relatively lower for the model with the higher convergence angles but the difference was not significant. Changing the prosthesis material from IE2 to Dicor decreased the stresses within the prosthesis; however, the safety factor was still higher for IE2 due to its higher mechanical strength. The load condition found to have an important role in the mechanical stresses observed.
Machines on the Basis of Variable Structure Mechanisms (VSM)
Authors: Abdraimov Samudin , Abdraimova Nazira Samudinovna
Published: September 2008

The new type of mechanisms — the variable structure mechanisms (VSM) possess a unique possibility of rapid and practically instantaneous transformation of the motion law of actuating link under influence of insignificant non-force displacement of one of the kinematical elements without breaking up the entire kinematical chain. The main feature of VSM is in its ability to fulfill two and more laws of motion by output link. The change of motion law for lever mechanisms occurs without disruption in the kinematical chain and thus enables to expend less effort and time. Whereas the couplings, brakes and other power impact elements control the block of interacting mechanisms till now, this results in disruption of entire kinematical chain. A considerable part of power will be required to put these elements into action. This results in decrease of machine efficiency and, especially, extremely influences the machine parts’ durability. The variable structure mechanisms (VSM) exclude such supplementary operative power consumption elements.
New Generation of Multi Connected Systems of Flexible Automation and the Ways of Strategic Control of Them
Authors: Darovskih Vladimir Dmitrievich
Published: September 2008

Principles are opened and solved problems of technology, designing and control at transformation of discrete processes of the automated machine-building manufacture to continuous streams on its output with an opportunity of achievement by actual productivity of a level technological therefore technological mechanisms of new generation in which by means of multi connected structure technological machines and robots, control systems and information monitoring, the control and designing, diagnostics and restoration of working capacity are flexibly incorporated are created and solved problems of strategy of control through system likelihood opportunities.
Elastoplastic Stress Study in Thick-Walled Spherical Vessels Considering Finite Deformation
Authors: Darijani Hossein , Naghdabadi Reza , Shamsaei Nima , Danesh Sararoudi Mehdi
Published: September 2008

An exact elasto-plastic analytical solution for large-strained internal pressurized thick-walled spherical vessels made of elastic-linear and nonlinear hardening material is derived in this paper. This solution is based on the notion of finite strains, the deformation theory of Hencky and the yield criteria of von Mises and Tresca. Nolinear elastic solution of an axisymetric boundary value problem is used as a basis to generate its inelastic solution, whereas the Hyper-elastic constitutive equation is invoked to represent the material response in the elastic region. This method treats the material parameters as field variables. Their distributions are obtained in an iterative manner using Nuber’s rule. Obtained Results for stress distribution using the present method shown are in excellent agreement with only analytical result which has been determined in the case of isochoric volume.
Assessment of a Design Method for Composite Over-Wrapped Pressure Vessels for Hydrogen Storage
Authors: Brusa Eugenio G. M. , Nobile Matteo
Published: September 2008

Present work deals with over-wrapped composite pressure vessels, for hydrogen storage, with inner metallic liner, reinforced by outer carbon-epoxy laminate. It is built by filament winding and includes hoop and helical layers. A design procedure is assessed, by including: a preliminary netting analysis, a definition of composite layers, according to the theory of composite laminates, and further refined by FEM. Numerical model investigates material strength at burst pressure, computes auto-frettage pressure for liner and predicts fatigue life, in low cycle range. An industrial prototype was used as test case for the implementation and the preliminary validation of the proposed approach, by performing an optimization of the final layout of the whole over-wrapped composite vessel.
A Multi-Level Approach for the Mechanical Design of Cluster Mills for Cold Rolling of Thin Steel Products
Authors: Brusa Eugenio G. M. , Lemma Luca
Published: September 2008

So-called “cluster mills” for cold rolling are currently preferred to prevent strip faults, as the back-up rolls present on the work rolls assure the stiffness required to avoid bending. An effective prediction of dynamic behaviour using an analytical approach is more difficult than for 2 and 4-high mills. The aim of this paper is to find models to simulate operating conditions in cluster mills. Two typical test cases such as Sendzimir and Z-mill are used to detect relevant aspects of dynamics on the experimental signatures, acquired in service. A multi-level approach, based on a core mill model and on some additional models, is proposed to investigate second order approximation problems. Co-simulation with the core model is avoided, as it takes too long. Phenomena, models, available tools and implementation issues are systematically analysed, while a preliminary experimental validation of results, based on available industrial mills, is discussed.
Stress Analysis of Bearing Metal and Research of Testing Method for Fatigue Strength
Authors: Yu A. M. , Wang C. T.
Published: September 2008

A newly-developed fatigue-testing machine for small bushes has been developed in accordance with ISO/DP7905/4, which can be used to test the fatigue strength of the bushes coated with bearing metal. The formulae of evaluating the normal stresses and displacements in two-material curved beams, in this paper, are established to determine the relationship among testing load, radial deformation of guage dia and normal stress for the bushes. An experimental set-up for the bush stress and deformation measurements is especially designed to achieve the anticipated loading conditions. A numerical example involving a bush consisting of two materials is used to demonstrate the capability of the model for predicting normal stresses and radial displacements. Being checked with the FEM analysis and electrical method measured shows that theoretical formulae fully meet the precision prescribed.
Prediction of Residual Stresses and Buckling Distortion in Welding of a Thin Wall Aluminum Butt Joint
Authors: Yazdanparast Sanaz , Asle Zaeem Mohsen , Rajabi Iraj
Published: September 2008

In this paper, global welding buckling distortion of a thin wall aluminum butt joint is investigated. To determine longitudinal residual stresses, a thermo-elastoplastic model is employed; analysis of thermal model and elastic-viscoplastic (Anand) model are decoupled. By using birth and death element method and time dependent model, molten puddle motion (speed of welding) is modeled. Three dimensional nonlinear-transient heat flow analysis has been used to obtain temperature distribution. By applying thermal results and using three dimensional Anand elastic-viscoplastic model, stress and deformation distributions are obtained. Residual stresses are applied on a structural model and by using eigenvalue methods, global buckling instability of butt welded joint is determined. The result of buckling investigation in the numerical model is compared with the result of an experiment.