bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Static and Dynamic Characteristics of Liquid Annular Convergent-Tapered Damper Seals With Honeycomb Roughness Pattern
Authors: Kaneko Satoru , Ikeda Takashi , Saito Takuro , Ito Shin
Published: June 2003

Honeycomb damper seals with convergent-tapered clearance have been proposed to improve static and dynamic characteristics of liquid annular seals employed in pumps. Their characteristics are experimentally investigated and compared to those for a conventional straight (no taper) annular seal with smooth surface and a straight damper seal with identical honeycomb pattern in seal stator. Three convergent-tapered honeycomb damper seals are used in the test, and have different inlet clearance (maximum clearance) and almost the same outlet clearance (minimum clearance). Their outlet clearance is almost the same as the clearance of the straight smooth seal and is slightly smaller than the clearance of the straight damper seal. Experimental results show that the convergent-tapered damper seals as well as the straight damper seal have lower leakage flow rate and cross-coupled stiffness coefficients, and larger main damping coefficients than the straight smooth seal, resulting in larger effective damping coefficients. These results are mainly due to surface roughness in the seal stator such as a honeycomb pattern used in the present analysis. The convergent-tapered damper seals also have larger main stiffness coefficients than the straight smooth and damper seals, which is mainly due to the convergent-tapered clearance and yields larger radial reaction force for a small concentric whirling motion. Consequently, the convergent-tapered damper seals have better seal characteristics than the conventional straight smooth seal and the straight damper seal with the same roughness pattern from the viewpoints of decreasing the leakage and improving the rotor stability capacity.
Pad Soaking Effect on Interfacial Fluid Pressure Measurements During CMP
Authors: Ng Sum Huan , Hight Robert , Zhou Chunhong , Yoon Inho , Danyluk Steven
Published: June 2003

Prior work has shown that there exist a sub-ambient fluid pressure at the interface between a rigid flat and the polishing pad during chemical mechanical polishing (CMP). This sub-ambient fluid pressure can have a significant impact on the polishing process since its magnitude may be similar to the applied load, depending on conditions. Further results have shown that there is a relationship between pad soaking time and the magnitude of this sub-ambient fluid pressure. This paper addresses measurements of the pad soaking time versus the magnitude of the sub-ambient interfacial fluid pressure. Experiments utilized a Rodel IC1000 polishing pad made of foamed polyurethane with average void size of 30 to 50 microns. Pad soaking tests indicated that the weight of the pad increased with soaking time due to water absorption. There is a high rate of water absorption initially before the pad becomes saturated and the mass of the pad stabilizes. It is also observed that the pad material is impermeable to water and most of the water penetrated only the topmost layer of voids in the material. These experiments suggest that the water progressively “softens” the top layers of the pad during the soaking and causes the sub-ambient fluid pressure to increase in magnitude. A model of the sub-ambient fluid pressure increasing as the elastic modulus of the pad decreases is also suggested.
Compressible Stokes Flow in Thin Films
Authors: van Odyck D. E. A. , Venner C. H.
Published: June 2003

A multigrid numerical solution algorithm has been developed for the laminar (Stokes) flow of a compressible medium in a thin film. The solver has been applied to two model problems each representative of lubrication problems in a specific way. For both problems the solutions of the Stokes equations are compared with the solutions of the Reynolds equation. The configurations of both model problems were chosen such that based on the ratio film thickness to contact length (H/L) the difference between the Reynolds and the Stokes solutions will be very small, so the geometry of the gap itself does not lead to a significant cross film dependence of the pressure. It is shown that in this situation the compressibility can still lead to a cross-film pressure dependence which is predicted by the Stokes solution and not by the Reynolds solution. The results demonstrate that limitations exist to the validity of the Reynolds equation related to the compressibility of the medium.
Tribological Properties of Polyoxymethylene Composites Against Aluminum
Authors: Kurokawa Masaya , Uchiyama Yoshitaka , Iwai Tomoaki , Nagai Susumu
Published: June 2003

Tribological properties of several kinds of polyoxymethylene (POM) composites were evaluated for the purpose of developing a polymeric tribomaterial especially suited for mating with aluminum parts having low surface hardness. POM composites containing small amounts of silicon carbide (SiC), POM/SiC; those containing a small amount of calcium octacosanonoate besides SiC, POM/SiC/Ca-OCA; and the one blended with 24 wt % of polytetrafluoroethylene, POM/PTFE(24); were injection-molded into pin specimens and their tribological properties were tested by means of a pin-on-disk type wear apparatus using an aluminum (A5056) mating disk in comparison with a 303 stainless steel (SUS303) disk. Evaluation was focused on observation of the sliding surfaces of the pin specimens and the mating disks by a scanning electron microscope and an optical microscope together with the measurement of surface roughness. In the case of mating against a SUS303 disk having high surface hardness, all pin specimens did not roughen the disk surfaces even after long time of rubbing. Only POM/PTFE(24) composite obviously made a transfer film on the disk surface, while the other composites made an extremely thin one on it. POM/SiC(0.1)/Ca-OCA(1) composite, containing SiC 0.1 wt. % and Ca-OCA 1 wt. %, was found to show the lowest coefficient of friction and the lowest wear rate forming extremely thin transfer film on the mating disk. On the other hand, against an A5056 disk which has lower surface hardness than that of SUS303 disk, unfilled POM and POM composites except POM/SiC(0.1)/Ca-OCA(1) composite roughened the disk surfaces. However, the sliding surface of the A5056 disk rubbed with POM/SiC(0.1)/Ca-OCA(1) composite was significantly smoother and that of the pin specimen was also quite smooth in comparison with other pin specimens. Further, when each POM composite was rubbed against the A5056 disk, formation of transfer film was not obvious on the disk surfaces. For POM/SiC(0.1)/Ca-OCA(1) composite, the wear rate was the lowest of all POM composites, and the coefficient of friction was as low level as 60 percent of that of unfilled POM, but slightly higher than that of POM/PTFE(24) composite. For POM/SiC(0.1)/Ca-OCA(1) composite, the nucleating effect of SiC and Ca-OCA, which accelerated the crystallization of POM during its injection molding to form a matrix containing fine spherulites, must have resulted in increasing the toughness of the matrix and lowering the wear rate. Also, the lubricant effect of Ca-OCA should have lowered the coefficient of friction of the same matrix for rubbing against aluminum mating disk. POM/SiC(0.1)/Ca-OCA(1) composite was concluded as an excellent tribomaterial for mating with aluminum parts.
An Investigation of Slider Vibrations in Near Contact Recording Using a Digital Laser Doppler Vibrometer
Authors: Yonemura Shinji , Zhou Lin , Talke Frank E.
Published: June 2003

At a flying height of 10 nanometers, contacts between slider and disk are likely to occur, and control of contact-induced slider vibrations is an important design consideration. In this study, slider vibrations during contact are investigated using a digital laser Doppler vibrometer (LDV). The noise level of the digital interferometer is compared with that of a conventional analog LDV. In addition, acoustic emission (AE) sensors are used to evaluate the contact behavior of the slider. A comparison of AE and LDV data is performed. The results show that the noise level of the digital LDV is lower than that of the analog LDV, and that suspension sway mode vibrations and torsion mode vibrations are excited during contact as a function of the skew angle.
New Evaluation Method on Gear Dynamics Using Continuous and Discrete Wavelet Transforms
Authors: Ohue Yuji , Yoshida Akira
Published: June 2003

The aim of this study is to propose a new evaluation method of gear dynamics using the continuous and discrete wavelet transforms. The wavelet transform (WT) is a method for the time-frequency analysis of signals. In order to evaluate the difference in the gear dynamics due to the gear materials, which are sintered and steel ones, the dynamic characteristics of gears were measured using a power circulating gear testing machine. The gear dynamics were analyzed in a time-frequency domain by the continuous and discrete WTs. The new evaluation method using the WTs proposed in this paper was more useful compared with the conventional one to investigate the damping characteristic and the dynamic condition of the gear equipment.
Nonlinear Parameter Estimation in Rotor-Bearing System Using Volterra Series and Method of Harmonic Probing
Authors: Chatterjee Animesh , Vyas Nalinaksh S.
Published: June 2003

Volterra series provides a structured analytical platform for modeling and identification of nonlinear systems. The series has been widely used in nonparametric identification through higher order frequency response functions or FRFs. A parametric identification procedure based on recursive evaluation of response harmonic amplitude series is presented here. The procedure is experimentally investigated for a rotor-bearing system supported in rolling element bearings. The estimates of nonlinear bearing stiffness obtained from experimentation have been compared with analytical values and experimental results of previous works.
Vibration of Flex Circuits in Hard Disk Drives
Authors: Wickert J. A.
Published: June 2003

A flex circuit connects the stationary electronic components in a hard disk drive to the rotating arm that carries the read/write heads and positions them above data tracks on the disk. Flex circuits are conventionally formed as a laminate of polyimide substrate, adhesive, and copper conductors. Deformation of a flex circuit is discussed in the context of the following stages: the initial unstressed shape, configurations in which stresses set and relax in response to elevated temperature, equilibrium, and small amplitude vibration. The model involves displacements of the flex circuit in the directions tangent and normal to the local equilibrium shape, and those motions couple with the arm’s dynamics. Nonlinearity associated with finite curvature, partial elastic springback, and the arm’s geometry and inertia properties are incorporated within the vibration model to predict system-level natural frequencies, mode shapes, and coupling factors between the circuit and the arm. Laboratory measurements using noncontact laser interferometry validate the model with respect to the circuit’s shape, stiffness, restoring moment, and natural frequencies. The primary degrees of freedom for optimizing flex circuit design are the thicknesses of the individual layers within the circuit, free length, and the locations and slopes of the circuit’s attachment points to the arm and electronics block. The model’s predictions and trends developed from a case study in free length are discussed with a view toward reducing coupling between the circuit and arm in certain vibration modes.
Nonlinear Dynamic Analysis of a Rotor Shaft System With Viscoelastically Supported Bearings
Authors: Shabaneh Nabeel , Zu Jean W.
Published: June 2003

This research investigates the dynamic analysis of a single-rotor shaft system with nonlinear elastic bearings at the ends mounted on viscoelastic suspension. Timoshenko shaft model is utilized to incorporate the flexibility of the shaft; the rotor is considered to be rigid and located at the mid-span of the shaft. A nonlinear bearing pedestal model is assumed which has a cubic nonlinear spring and linear damping characteristics. The viscoelastic supports are modeled using Kelvin-Voigt model. Free and forced vibration is investigated based on the direct multiple scales method of one-to-one frequency-to-amplitude relationship using third order perturbation expansion. The results of the nonlinear analysis show that a limiting value of the internal damping coefficient of the shaft exists where the trend of the frequency-response curve switches. Also, the primary resonance peak shifts to higher frequencies with the increase of the bearing nonlinear elastic characteristics, but with a flattened curve and hence lower peak values. A jump phenomenon takes place for high values of the bearing nonlinear elastic characteristics.
Investigation of the Sound Transmission into an Advanced Grid-Stiffened Structure
Authors: Vipperman Jeffrey S. , Li Deyu , Avdeev Ilya , Lane Steven A.
Published: June 2003

The noise transmission behavior of an advanced grid-stiffened (AGS) composite structure has been investigated by combining numerical and experimental methods. Structural-acoustic coupling was found to be light, permitting separate analysis of the structure and acoustic cavity. Finite element analysis permitted the resonant frequencies of acoustic cavity and structure to be calculated, which play an important role for noise transmission through the structure. Acoustic mode shapes permitted internal coincidence frequencies to be estimated and provided insight into modal pressure distributions, when considering payload location. Experimental structural and acoustic modal analysis permitted the resonant frequencies and damping ratios for the structure and cavity to be determined, which in turn were used to corroborate the FEA model. Finally, direct measurement of the noise transmission was performed based on noise reduction spectrum (NRS), which is calculated from spatial averages of the RMS acoustic pressures inside and outside of the shell. It was found that the NRS was dominated by acoustic resonances, which were marked by sharp dips in the NRS curve. Internal coincidence of the axial wavenumbers was also found to be a significant mechanism for noise transmission. External coincidence and ring frequencies were found to provide less of an impact on the overall NRS for the structure.
Optimal Stiffener Design for Interior Sound Reduction Using a Topology Optimization Based Approach
Authors: Luo Jianhui , Gea Hae Chang
Published: June 2003

A topology optimization based approach is proposed to study the optimal configuration of stiffeners for the interior sound reduction. Since our design target is aimed at reducing the low frequency noise, a coupled acoustic-structural conservative system without damping effect is considered. Modal analysis method is used to evaluate the interior sound level for this coupled system. To formulate the topology optimization problem, a recently introduced Microstructure-based Design Domain Method (MDDM) is employed. Using the MDDM, the optimal stiffener configurations problem is treated as a material distribution problem and sensitivity analysis of the coupled system is derived analytically. The norm of acoustic excitation is used as the indicator of the interior sound level. The optimal stiffener design is obtained by solving this topology optimization problem using a sequential convex approximation method. Examples of acoustic box under single frequency excitation and a band of low frequency excitations are presented and discussed.
Theory on Pitch Noise and Its Application
Authors: Nakajima Yukio
Published: June 2003

A theory on pitch noise of a tire has been developed based on the assumption that noise is approximated by a series of Dirac delta-function. The proposed theory predicts the existence of special lug shapes where tire noise becomes almost zero. In addition a tire noise simulation system is developed based on this theory to predict tire noise from CAD data. The prediction of overall noise of various tires with practical patterns is verified to be in good agreement with the measurement.
Closed-Form Exact Solution to H∞ Optimization of Dynamic Vibration Absorbers (Application to Different Transfer Functions and Damping Systems)
Authors: Asami Toshihiko , Nishihara Osamu
Published: June 2003

H ∞ optimization of the dynamic vibration absorbers is a classical optimization problem, and has been already solved more than 50 years ago. It is a well-known solution, but we know this solution is only an approximate one. Recently, one of the authors has proposed a new method for attaining the H∞ optimization of the absorber in linear systems. The new method enables us to obtain the exact algebraic solution of the H∞ optimization problem of the absorber. In this paper, we first apply this method to the design optimization of a viscous damped (Voigt type) absorber and a hysteretic damped absorber attached to undamped primary systems. For each absorber, six different transfer functions are taken here as performance indices to vibration suppression or isolation. As a result, we found the closed-form exact solutions to all transfer functions. The solutions obtained here are then compared with those of the approximate ones. Finally, we present the closed-form exact solutions to the hysteretic damped absorber attached to damped primary systems.
Vibration Control of a Traveling Suspended System Using Wave Absorbing Control
Authors: Saigo M. , Tani K. , Usui H.
Published: June 2003

This paper describes vibration control of a suspended system using a wave absorbing method. Here, we treat a system that accepts a traveling command. This system is called a traveling system. In the previous paper, we treated a system that performs only the vibration control, where the support of the suspended system moves only for vibration control and eventually settles at the original position. This system is called a nontraveling system. In a traveling system, the support moves both for traveling and for vibration control. We present a new control strategy for these two different aims by applying the vibration control method developed in the previous paper. A traveling multiple-pendulum system and a traveling wire-and-load system are treated. The wire-and-load system has a small rigid pendulum between the support and the wire. The vibration control is performed by monitoring this small rigid pendulum. The wire-and-load system is extended to a model crane system that has a motor system to roll up and down the suspended mass like a real crane. The same program with different parameter values controls these three systems. Both numerical simulation and experiment have been conducted, and the developed control method has been shown to be quite effective.
A Stochastic Model for Simulation and Diagnostics of Rolling Element Bearings With Localized Faults
Authors: Antoni J. , Randall R. B.
Published: June 2003

This paper addresses the stochastic modeling of the vibration signal produced by localized faults in rolling element bearings and its use for diagnostic purposes. The aim is essentially to provide a better understanding of the recognized “envelope analysis” technique as classically used in the diagnostics of rolling element bearings, and incidentally give theoretical proofs for the specific features of envelope spectra as obtained from experimental data. The proposed model may also prove useful for simulation purposes. First, the excitation force generated by a defect is modeled as a random point process and its spectral signature is derived analytically. Then its transmission through the bearing is investigated in detail in order to find the spectral characteristics of the resulting vibration signal. The analysis finally gives sound justification for “squared” envelope analysis and the type of spectral indicators that should be used with it.
Active Vibration Suppression With Time Delayed Feedback
Authors: Sipahi Rifat , Olgac Nejat
Published: June 2003

Various active vibration suppression techniques, which use feedback control, are implemented on the structures. In real application, time delay can not be avoided especially in the feedback line of the actively controlled systems. The effects of the delay have to be thoroughly understood from the perspective of system stability and the performance of the controlled system. Often used control laws are developed without taking the delay into account. They fulfill the design requirements when free of delay. As unavoidable delay appears, however, the performance of the control changes. This work addresses the stability analysis of such dynamics as the control law remains unchanged but carries the effect of feedback time-delay, which can be varied. For this stability analysis along the delay axis, we follow up a recent methodology of the authors, the Direct Method (DM), which offers a unique and unprecedented treatment of a general class of linear time invariant time delayed systems (LTI-TDS). We discuss the underlying features and the highlights of the method briefly. Over an example vibration suppression setting we declare the stability intervals of the dynamics in time delay space using the DM. Having assessed the stability, we then look at the frequency response characteristics of the system as performance indications.
Dynamic Stiffness Formulation and Its Application for a Combined Beam and a Two Degree-of-Freedom System
Authors: Banerjee J. R.
Published: June 2003

This paper is concerned with the dynamic stiffness formulation and its application for a Bernoulli-Euler beam carrying a two degree-of-freedom spring-mass system. The effect of a two degree-of-freedom system kinematically connected to the beam is represented exactly by replacing it with equivalent stiffness coefficients, which are added to the appropriate stiffness coefficients of the bare beam. Numerical examples whose results are obtained by applying the Wittrick-Williams algorithm to the total dynamic stiffness matrix are given and compared with published results. Applications of the theory include the free vibration analysis of frameworks carrying two degree-of-freedom spring-mass systems.
Determining Stability Boundaries Using Gyroscopic Eigenfunctions
Authors: Renshaw Anthony A.
Published: June 2003

By taking advantage of modal decoupling and reduction of order, we derive a simplified procedure for applying the method of multiple scales to determine the stability boundaries of parametrically excited, gyroscopic systems. The analytic advantages of the procedure are illustrated with three examples.
Effect of Damping on Asymmetric Systems
Authors: Gallina Paolo
Published: June 2003

This paper addresses the phenomenon of the destabilizing effect of slight damping on asymmetric linear systems. Previous works had showed that the destabilizing effect, regarded for a long time as a “paradox,” depends upon the ratio of the damping coefficients. This work extends those results to n-dof systems. In fact, conditions for a general asymmetric n-dof slightly damped system to be stable are obtained. Also, a useful sufficient condition is carried out. This practical design tool gives optimum damping ratios and takes into consideration the parameter uncertainties as well. The solution is based on the eigenvalue sensitivity analysis. Moreover, a formal physical explanation of the destabilizing effect of damping is given. Eventually, the theory is validated by means of a simple example.
The Effect of Actuator and Sensor Placement on the Active Control of Rotor Unbalance
Authors: Johnson Marty E. , Nascimento Luiz P. , Kasarda Mary , Fuller Chris R.
Published: June 2003

This paper investigates both theoretically and experimentally the effect of the location and number of sensors and magnetic bearing actuators on both global and local vibration reduction along a rotor using a feedforward control scheme. Theoretical approaches developed for the active control of beams have been shown to be useful as simplified models for the rotor scenario. This paper also introduces the time-domain LMS feedforward control strategy, used widely in the active control of sound and vibration, as an alternative control methodology to the frequency-domain feedforward approaches commonly presented in the literature. Results are presented showing that for any case where the same number of actuators and error sensors are used there can be frequencies at which large increases in vibration away from the error sensors can occur. It is also shown that using a larger number of error sensors than actuators results in better global reduction of vibration but decreased local reduction. Overall, the study demonstrated that an analysis of actuator and sensor locations when feedforward control schemes are used is necessary to ensure that harmful increased vibrations do not occur at frequencies away from rotor-bearing natural frequencies or at points along the rotor not monitored by error sensors.
Bayesian Model Screening for the Identification of Nonlinear Mechanical Structures
Authors: Kerschen Gae¨tan , Golinval Jean-Claude , Hemez Franc¸ois M.
Published: June 2003

The development of techniques for identification and updating of nonlinear mechanical structures has received increasing attention in recent years. In practical situations, there is not necessarily a priori knowledge about the nonlinearity. This suggests the need for strategies that allow inference of useful information from the data. The present study proposes an algorithm based on a Bayesian inference approach for giving insight into the form of the nonlinearity. A family of parametric models is defined to represent the nonlinear response of a system and the selection algorithm estimates the likelihood that each member of the family is appropriate. The (unknown) probability density function of the family of models is explored using a simple variant of the Markov Chain Monte Carlo sampling technique. This technique offers the advantage that the nature of the underlying statistical distribution need not be assumed a priori. Enough samples are drawn to guarantee that the empirical distribution approximates the true but unknown distribution to the desired level of accuracy. It provides an indication of which models are the most appropriate to represent the nonlinearity and their respective goodness-of-fit to the data. The methodology is illustrated using two examples, one of which comes from experimental data.
Rotor Isolation for Vibration and Noise Reduction
Authors: Brungart Timothy A. , Riggs Eric T.
Published: June 2003

A technique for reducing the vibration and noise from marine propulsors is examined theoretically and demonstrated experimentally. A single layer of elastomer is incorporated into a rotor to form a rotating vibration isolation mount. The mount isolates the rotor hub and shaft from the unsteady forces generated on the blades due to their interaction with circumferentially non-uniform, time-averaged inflow and turbulence. This results in reduced vibration and noise. Nonrotating isolated rotor transmissibility is well predicted with a simple lumped parameter rotor model for frequencies below the first bending mode of the blades. Tests performed under operational (i.e., rotating) conditions have shown that rotor isolation provides a reduction of up to 15 dB in transmissibility compared to an identical rotor without isolation.
Torsional Vibration Analysis of Complicated Multi-Branched Shafting Systems by Modal Synthesis Method
Authors: Zou Chun-Ping , Chen Duan-Shi , Hua Hong-Xing
Published: June 2003

The torsional vibration calculations of the complicated multi-branched system with rigid connection and flexible connections made up of elastic-coupling parts are very difficult to perform using conventional methods. In this paper, a modal synthesis method of torsional vibration analysis for the system is proposed. This approach is an improved method of Hurty’s fixed-interface and Hou’s free-interface modal synthesis methods. Because of the introduction of flexible substructure, the improved modal synthesis method can effectively treat the complicated system in which there exists a rigid connection and a flexible connection that is formed by an elastic-coupling part. When the calculation is performed, the complicated multi-branched system is divided into several substructures that are analyzed by FEM (finite element method) except the special elastic-coupling part that is defined as flexible substructure and treated individually. The efficiency of modal synthesis is improved by choosing suitable number of lower-frequency modes in modal synthesis. As an example of an application of this method, the analysis of torsional vibration of a cam-type engine shafting system is carried out both numerically and experimentally. The results show that the above kind of multi-branched shafting system can be analyzed effectively by the proposed method.
Spectrum of High-Frequency Acoustic Noise in Inviscid Liquid-Linear Approximation for Spherical Waves
Authors: Likhterov L. , Berman A.
Published: June 2003

The high-frequency asymptotics of the acoustic noise spectrum is considered for the case of spherically symmetric waves propagating in an unbounded inviscid liquid. Using the Kirkwood and Bethe hypothesis regarding kinetic enthalpy, the Euler equations, the equation of state in the Tait’s form and following linearization allow the kinetic enthalpy and “reduced” pressure to be obtained. The Fourier transform yields the spectral density of acoustic energy which proves to be inversely proportional to the square frequency and decreases approximately by 6 decibels per octave with increase of a frequency.
Robust Control of a 2D Acoustic Enclosure*
Authors: Pota Hemanshu R. , Petersen Ian R. , Kelkar Atul G.
Published: June 2003

This paper reports experimental results in the application of feedback control of acoustic noise in a 2D enclosure. It is shown that the feedback control of 2D enclosures poses peculiar problems compared to simple 1D ducts. The chief among them are the need for explicit budgeting of uncertainties and dealing with high model orders. This paper demonstrates a practical way to design controllers for such systems using minimax LQG methods. It is shown that an important step in the controller design is the proper choice of a weighting function. The results presented in this paper are impressive and they can be further improved by proper choice of actuator and sensor placements.
Effect of Thrust Magnetic Bearing on Stability and Bifurcation of a Flexible Rotor Active Magnetic Bearing System
Authors: Ho Y. S. , Liu H. , Yu L.
Published: June 2003

This paper is concerned with the effect of a thrust active magnetic bearing (TAMB) on the stability and bifurcation of an active magnetic bearing rotor system (AMBRS). The shaft is flexible and modeled by using the finite element method that can take the effects of inertia and shear into consideration. The model is reduced by a component mode synthesis method, which can conveniently account for nonlinear magnetic forces and moments of the bearing. Then the system equations are obtained by combining the equations of the reduced mechanical system and the equations of the decentralized PID controllers. This study focuses on the influence of nonlinearities on the stability and bifurcation of T periodic motion of the AMBRS subjected to the influences of both journal and thrust active magnetic bearings and mass eccentricity simultaneously. In the stability analysis, only periodic motion is investigated. The periodic motions and their stability margins are obtained by using shooting method and path-following technique. The local stability and bifurcation behaviors of periodic motions are obtained by using Floquet theory. The results indicate that the TAMB and mass eccentricity have great influence on nonlinear stability and bifurcation of the T periodic motion of system, cause the spillover of system nonlinear dynamics and degradation of stability and bifurcation of T periodic motion. Therefore, sufficient attention should be paid to these factors in the analysis and design of a flexible rotor system equipped with both journal and thrust magnetic bearings in order to ensure system reliability.
Study on the Dynamics of a Rotor in a Maneuvering Aircraft
Authors: Lin Fusheng , Meng Guang
Published: June 2003

This paper shows how the dynamics of a rotor in a maneuvering aircraft changes according to the operation of the aircraft. The mathematical model of an unbalanced rotor system located in the maneuvering aircraft is derived. The dynamic characteristics of the rotor running at a constant angular speed or a constant acceleration are studied under the assumptions that the aircraft maneuvers only in a vertical plane and that the pitching angle and the flight path inclination of the aircraft are equal. The effects of gravity and unbalance parameter are considered. The results show that the unbalanced response of a rotor in an aircraft is obviously influenced by the aircraft’s flying status.
Control of Self-Excited Vibration of a Rotor System With Active Gas Bearings
Authors: Qiu Jinhao , Tani Junji , Kwon Taekyu
Published: June 2003

This paper presents an experimental study on the active control of self-excited vibrations in a rotor-bearing system supported on a pair of externally pressurized thrust bearings in the axial direction and on actively controlled journal gas bearings in the radial direction. The active journal gas bearings used are of the tilting-pad type with one traditional passive pad and two active pads with embedded piezoelectric actuators. Feedback control systems are constructed with gap sensors for measuring the vibration of the rotor, embedded piezoelectric actuators, and PID controllers. The experimental results show that the self-excited vibration can be effectively suppressed with the designed feedback control system, if the gains of the PID controllers are properly tuned.
A Dynamic Model of a Contacting Mechanical Seal for Down-Hole Tools1
Authors: Xiong Shunhe , Salant Richard F.
Published: June 2003

A dynamic model of a contacting mechanical seal for down-hole tools, operating in the mixed lubrication regime, has been constructed. Two dynamic cases are examined: the behavior of the seal after it is subjected to a nonequilibrium initial condition and the behavior of the seal as it tracks axial runout of the rotating face. In both cases the seal experiences much larger leakage and inflow (incursion) rates than under steady-state conditions, although in the former case the duration of the increased rates is very short.
Watching a Protein as it Functions with 150-ps Time-Resolved X-ray Crystallography
Authors: Schotte Friedrich , Lim Manho , Jackson Timothy A. , Smirnov Aleksandr V. , Soman Jayashree , Olson John S. , Phillips George N. , Wulff Michael , Anfinrud Philip A.
Published: June 2003

We report picosecond time-resolved x-ray diffraction from the myoglobin (Mb) mutant in which Leu
29
is replaced by Phe (L29Fmutant). The frame-by-frame structural evolution, resolved to 1.8 angstroms, allows one to literally “watch” the protein as it executes its function. Time-resolved mid-infrared spectroscopy of flash-photolyzed L29F MbCO revealed a short-lived CO intermediate whose 140-ps lifetime is shorter than that found in wild-type protein by a factor of 1000. The electron density maps of the protein unveil transient conformational changes far more dramatic than the structural differences between the carboxy and deoxy states and depict the correlated side-chain motion responsible for rapidly sweeping CO away from its primary docking site.
Myocyte Adrenoceptor Signaling Pathways
Authors: Xiang Yang , Kobilka Brian K.
Published: June 2003

Adrenoceptors (ARs), members of the G protein–coupled receptor superfamily, form the interface between the sympathetic nervous system and the cardiovascular system, with integral roles in the rapid regulation of myocardial function. However, in heart failure, chronic catecholamine stimulation of adrenoceptors has been linked to pathologic cardiac remodeling, including myocyte apoptosis and hypertrophy. In cardiac myocytes, activation of AR subtypes results in coupling to different G proteins and induction of specific signaling pathways, which is partly regulated by the subtype-specific distribution of receptors in plasma membrane compartments containing distinct complexes of signaling molecules. The Connections Maps of the Adrenergic and Myocyte Adrenergic Signaling Pathways bring into focus the specific signaling pathways of individual AR subtypes and their relevant functions in vivo.
TRB3: A
tribbles
Homolog That Inhibits Akt/PKB Activation by Insulin in Liver
Authors: Du Keyong , Herzig Stephan , Kulkarni Rohit N. , Montminy Marc
Published: June 2003

Insulin resistance is a major hallmark in the development of type II diabetes, which is characterized by the failure of insulin to promote glucose uptake in muscle and to suppress glucose production in liver. The serine-threonine kinase Akt (PKB) is a principal target of insulin signaling that inhibits hepatic glucose output when glucose is available from food. Here we show that TRB3, a mammalian homolog of
Drosophila tribbles
, functions as a negative modulator of Akt. TRB3 expression is induced in liver under fasting conditions, and TRB3 disrupts insulin signaling by binding directly to Akt and blocking activation of the kinase. Amounts of TRB3 RNA and protein were increased in livers of
db/db
diabetic mice compared with those in wild-type mice. Hepatic overexpression of TRB3 in amounts comparable to those in
db/db
mice promoted hyperglycemia and glucose intolerance. Our results suggest that, by interfering with Akt activation, TRB3 contributes to insulin resistance in individuals with susceptibility to type II diabetes.
Reversal and Stabilization of Synaptic Modifications in a Developing Visual System
Authors: Zhou Qiang , Tao Huizhong W. , Poo Mu-ming
Published: June 2003

Persistent synaptic modifications are essential for experience-dependent refinement of developing circuits. However, in the developing
Xenopus
retinotectal system, activity-induced synaptic modifications were quickly reversed either by subsequent spontaneous activity in the tectum or by exposure to random visual inputs. This reversal depended on the burst spiking and activation of the
N
-methyl-D-aspartate subtype of glutamate receptors. Stabilization of synaptic modifications can be achieved by an appropriately spaced pattern of induction stimuli. These findings underscore the vulnerable nature of activity-induced synaptic modifications in vivo and suggest a temporal constraint on the pattern of visual inputs for effective induction of stable synaptic modifications.
Kin Selection in Cooperative Alliances of Carrion Crows
Authors: Baglione Vittorio , Canestrari Daniela , Marcos José M. , Ekman Jan
Published: June 2003

In most cooperative vertebrates, delayed natal dispersal is the mechanism that leads to the formation of kin societies. Under this condition, the possibility that kin-based cooperative breeding is an unselected consequence of dispersal patterns can never be ruled out because helpers can only help their relatives. Here we show that a population of carrion crows (
Corvus corone corone
) fully fits the central prediction of kin selection theory that cooperative breeding should arise among relatives. On their territory, resident breeders are aided not only by nonbreeding retained offspring but also by immigrants (mainly males), with whom they share matings. Philopatry cannot account, however, for the high degree of genetic relatedness found between breeders and immigrants of the same sex that cooperate at a nest, indicating that crows actively choose to breed cooperatively with their relatives.
Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999
Authors: Nemani Ramakrishna R. , Keeling Charles D. , Hashimoto Hirofumi , Jolly William M. , Piper Stephen C. , Tucker Compton J. , Myneni Ranga B. , Running Steven W.
Published: June 2003

Recent climatic changes have enhanced plant growth in northern mid-latitudes and high latitudes. However, a comprehensive analysis of the impact of global climatic changes on vegetation productivity has not before been expressed in the context of variable limiting factors to plant growth. We present a global investigation of vegetation responses to climatic changes by analyzing 18 years (1982 to 1999) of both climatic data and satellite observations of vegetation activity. Our results indicate that global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally. The largest increase was in tropical ecosystems. Amazon rain forests accounted for 42% of the global increase in net primary production, owing mainly to decreased cloud cover and the resulting increase in solar radiation.
Morphs, Dispersal Behavior, Genetic Similarity, and the Evolution of Cooperation
Authors: Sinervo Barry , Clobert Jean
Published: June 2003

Genetic similarity owing to kin relationship is often invoked to explain the evolution of social cooperation. In this study, male color morphs of side-blotched lizards settle nonrandomly with respect to genetic similarity. Blue morphs tend to settle in close proximity to other blue morphs with high genetic similarity. Blue neighbors have three times the average fitness of blue males lacking such neighbors. Conversely, genetically similar males depress fitness of the orange morph. Moreover, orange males are hyperdispersed with respect to genetic similarity. Pedigree and dispersal data show that genetically similar blue neighbors are not kin. Instead, conditions for the evolution of dispersal and cooperation are promoted by an emergent property of the morph locus that increases genetic similarity within morphs: genome-wide correlational selection links many traits to the morph locus, including settlement behavior.
Femtosecond Phase-Coherent Two-Dimensional Spectroscopy
Authors: Tian Peifang , Keusters Dorine , Suzaki Yoshifumi , Warren Warren S.
Published: June 2003

Femtosecond phase-coherent two-dimensional (2D) spectroscopy has been experimentally demonstrated as the direct optical analog of 2D nuclear magnetic resonance. An acousto-optic pulse shaper created a collinear three-pulse sequence with well-controlled and variable interpulse delays and phases,which interacted with a model atomic system of rubidium vapor. The desired nonlinear polarization was selected by phase cycling (coadding experimental results obtained with different interpulse phases). This method may enhance our ability to probe the femtosecond structural dynamics of macromolecules.
In-Depth View of Structure, Activity, and Evolution of Rice Chromosome 10
Authors:   The Rice Chromosome 10 Sequencing Consortium
Published: June 2003

Rice is the world's most important food crop and a model for cereal research. At 430 megabases in size, its genome is the most compact of the cereals. We report the sequence of chromosome 10, the smallest of the 12rice chromosomes (22.4 megabases), which contains 3471 genes. Chromosome 10 contains considerable heterochromatin with an enrichment of repetitive elements on 10S and an enrichment of expressed genes on 10L. Multiple insertions from organellar genomes were detected. Collinearity was apparent between rice chromosome 10 and sorghum and maize. Comparison between the draft and finished sequence demonstrates the importance of finished sequence.
Inhibited and Uninhibited Infants "Grown Up": Adult Amygdalar Response to Novelty
Authors: Schwartz Carl E. , Wright Christopher I. , Shin Lisa M. , Kagan Jerome , Rauch Scott L.
Published: June 2003

Infants with an inhibited temperament tend to develop into children who avoid people, objects, and situations that are novel or unfamiliar, whereas uninhibited children spontaneously approach novel persons, objects, and situations. Behavioral and physiological features of these two temperamental categories are moderately stable from infancy into early adolescence and have been hypothesized to be due, in part, to variation in amygdalar responses to novelty. We found that adults who had been categorized in the second year of life as inhibited, compared with those previously categorized as uninhibited, showed greater functional MRI signal response within the amygdala to novel versus familiar faces.
Oscillatory Thermomechanical Instability of an Ultrathin Catalyst
Authors: Cirak Fehmi , Cisternas Jaime E. , Cuitiño Alberto M. , Ertl Gerhard , Holmes Philip , Kevrekidis Ioannis G. , Ortiz Michael , Rotermund Harm Hinrich , Schunack Michael , Wolff Janpeter
Published: June 2003

Because of the small thermal capacity of ultrathin (∼200 nanometers) metal single crystals, it is possible to explore the coupling of catalytic and thermal action at low pressures. We analyzed a chemothermomechanical instability in this regime, in which catalytic reaction kinetics interact with heat transfer and mechanical buckling to create oscillations. These interacting components are separated and explored through experimentation, mathematical modeling, and scientific computation, and an explanation of the phenomenon emerges from their synthesis.
Nota Bene: Bewitching, Bewildered, Believable
Authors: Lavine Marc
Published: June 2003

The Science of Harry Potter
How Magic Really Works. Roger Highfield. Viking, New York, 2002. 344 pp. $23.95, C$34.99. ISBN 0-670-03153-4. Headline, London, £12.99. ISBN 0-7553-1150-7. Paper, Penguin, New York, 2003. $14, C$21. ISBN 0-14-200355-7. Headline, London, £6.99. ISBN 0-7553-1151-5.

Highfield uses elements from the Harry Potter series to discuss modern science, and vice versa.
Dimples on Nanocrystalline Fracture Surfaces As Evidence for Shear Plane Formation
Authors: Hasnaoui A. , Van Swygenhoven H. , Derlet P. M.
Published: June 2003

Tensile experiments of fully dense nanocrystalline structures with a mean grain size of less than 100 nanometers demonstrate a considerable increase in hardness but a remarkable drop in elongation-to-failure, indicating brittle behavior. However, dimple structures are often observed at the fracture surface, indicating some type of ductile fracture mechanism. Guided by large-scale atomistic simulations, we propose that these dimple structures result from local shear planes formed around clustered grains that, because of their particular misorientation, cannot participate in the grain boundary accommodation processes necessary to sustain plastic deformation. This raises the expectation that general high-angle grain boundaries are necessary for good ductility.
Single Neurons in the Monkey Hippocampus and Learning of New Associations
Authors: Wirth Sylvia , Yanike Marianna , Frank Loren M. , Smith Anne C. , Brown Emery N. , Suzuki Wendy A.
Published: June 2003

The medial temporal lobe is crucial for the ability to learn and retain new declarative memories. This form of memory includes the ability to quickly establish novel associations between unrelated items. To better understand the patterns of neural activity during associative memory formation, we recorded the activity of hippocampal neurons of macaque monkeys as they learned new associations. Hippocampal neurons signaled learning by changing their stimulus-selective response properties. This change in the pattern of selective neural activity occurred before, at the same time as, or after learning, which suggests that these neurons are involved in the initial formation of new associative memories.