bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotordynamic Coefficients for Stepped Labyrinth Gas Seals
Authors: Scharrer J. K.
Published: October 2009

The basic equations are derived for compressible flow in a stepped labyrinth gas seal. The flow is assumed to be completely turbulent in the circumferential direction where the friction factor is determined by the Blasius relation. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equations. The first order equations are solved by a separation of variables solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients. The results of this analysis are presented in the form of a parametric study, since there are no known experimental data for the rotordynamic coefficients of stepped labyrinth gas seals. The parametric study investigates the relative rotordynamic stability of convergent, straight and divergent stepped labyrinth gas seals. The results show that, generally, the divergent seal is more stable, rotordynamically, than the straight or convergent seals. The results also show that the teeth-on-stator seals are not always more stable, rotordynamically, then the teeth-on-rotor seals as was shown by experiment by Childs and Scharrer (1986b) for a 15 tooth seal.
Large Bearing Numbers and Stationary Reynolds Roughness
Authors: Greengard C.
Published: October 2009

The nature of Reynolds roughness for wide bearings with large bearing numbers and short wavelength stationary roughness is investigated. It is shown that the White and the To̸nder formulas both apply to the compressible Reynolds equation. However, they apply in different physical regimes—the limiting averaged pressure distribution depends upon the relative sizes of the bearing number and the roughness frequency. Asymptotic expansion methods and numerical calculations are used to find the pressure distributions for different relationships between the bearing number and the roughness frequency.
Equilibrium and Associated Load Distribution in Ball and Roller Bearings Loaded in Five Degrees of Freedom While Neglecting Friction—Part I: General Theory and Application to Ball Bearings
Authors: de Mul J. M. , Vree J. M. , Maas D. A.
Published: October 2009

A new, general and consistent mathematical model of highly modular character is presented for calculation of the equilibrium and associated load distribution in rolling element bearings. The bearings may be loaded and displaced in five degrees of freedom. High speed rolling element loading is considered, internal friction is neglected, the material is assumed linearly elastic and the bearing rings are modelled as rigid except for local contact deformation. Either classical Hertzian contact analysis or modern non-Hertzian contact analysis of sophisticated or approximate character is used as applicable. The bearing stiffness matrix is computed analytically and used internally in the iterative bearing equilibrium calculation; its final values may be used for other purposes such as (rotor) dynamics analysis. In Part I, the general theory and application to ball bearings is presented. In Part II, application of the general theory to roller bearings and an experimental verification are presented.
A Theory for the Lubrication of Layered Liquid Crystals
Authors: Tichy J. A. , Rhim Y.
Published: October 2009

Layered liquid crystals hold promise as advanced lubricants. These materials have been exhaustively studied from a fundamental continuum mechanics perspective. Recent studies from a lubrication perspective have involved measurements of behavior in rheological instruments and in elastohydrodynamic test rigs. The present study is an effort to adapt the basic theory to the lubrication geometry. A permeation parameter is seen to determine the nature of flow process and the layer structure. Problems are solved for limiting cases when this parameter is small or large. In the former case a modified Reynolds equation can be obtained. The liquid crystal lubricant may enhance the load carry significantly relative to an equivalent viscous liquid.
Internal Stresses in Elastohydrodynamic Lubrication of Rolling/Sliding Contacts
Authors: Sadeghi Farshid , Sui Ping C.
Published: October 2009

The internal stress distribution in elastohydrodynamic lubrication of rolling/sliding line contact was obtained. The technique involves the full EHD solution and the use of Lagrangian quadrature to obtain the internal stress distributions in the x, y, z-directions and the shear stress distribution as a function of the normal pressure and the friction force. The principal stresses and the maximum shear stress were calculated for dimensionless loads ranging from (2.0452 × 10−5) to (1.3 × 10−4) and dimensionless velocity of 10−10 to 10−11 for slip ratios ranging from 0 to pure sliding condition.
Squeeze and Entraining Motion in Nonconformal Line Contacts. Part I—Hydrodynamic Lubrication
Authors: Lee Rong-Tsong , Hamrock B. J.
Published: October 2009

An analytical solution to the problem of combined entraining and normal squeeze motion in nonconformal line contacts hydrodynamically lubricated with an isoviscous, incompressible lubricant has been obtained without any limitations on dimensionless load, dimensionless entraining velocity, and dimensionless velocity parameter. The dimensionless load and entraining velocity are fixed for a complete range of operating parameters for both normal approach and separation. Results show that the lubrication of the outlet boundary and the location of the maximum pressure move upstream into the inlet region as the central film thickness decreases or the dimensionless velocity parameter increases from negative (normal approach) to positive (normal separation). All the dynamic performance parameters relating to the steady-state bearing performance parameters have been found to be functions of only the dimensionless velocity parameter with constant load and entraining velocity. The dimensionless velocity parameter significantly influenced those dynamic performance parameters. The results of this study will be used as the initial guess for the elastohydrodynamic lubrication of nonconformal line contacts.
New Formulation for Lubrication With Non-Newtonian Fluids
Authors: Najji B. , Bou-Said B. , Berthe D.
Published: October 2009

A global method for the solution of thermohydrodynamic problems is proposed for the analysis of lubricated contacts with non-newtonian fluids. A set of algebraic equations is obtained after introducing the weak form of the energy equation and a modified generalized equation for thin fluid flows. This last equation represents a new formulation for lubrication with non-newtonian fluids. The establishment of this equation is presented below along with several tests including explicit and implicit rheological laws with some comments on the effect of the different parameters which occur in the study.
Hydrodynamic Analysis and Fluid-Solid Interaction Effects on the Behavior of a Compliant Wall (Thick) Journal Bearing. Part 1: Theory
Authors: Braun M. J. , Dougherty J. D.
Published: October 2009

In the first part of this two part paper we have introduced a new hybrid model for the solution of the compliant wall bearing problem. A cylindrical three dimensional finite element model (FEM) for an axisymmetric body, subjected to nonaxisymmetric loading has been combined with a finite difference model (FDM) for the solution of the fluid pressure Reynolds equation. The latter equation handles both axial misalignment and the working fluid variable properties. The pressures were expressed as continuous Fourier series along the circumference and provided the nodal forces for the loading the compliant liner. The method of solution is an iterative procedure which combines the FEM and the FDM algorithms to yield the deformation of the liner and the bearing pressure map.
Squeeze and Entraining Motion in Nonconformal Line Contacts. Part II—Elastohydrodynamic Lubrication
Authors: Lee Rong-Tsong , Hamrock B. J.
Published: October 2009

A fast numerical approach to the solution of elastohydrodynamic lubrication (EHL) of line contacts in combined entraining and normal squeeze motion is developed. The initial conditions for the pressure profile, the central normal squeeze velocity, and the location of the outlet boundary at any specified dimensionless load and dimensionless entraining velocity were obtained from the hydrodynamic lubrication study in Lee and Hamrock (1988). The pressure and film thickness were obtained by solving the transient Reynolds, elasticity, rheology, and time-dependent central squeeze velocity equations. The squeeze effect on this transient EHL problem has been proved in that the maximum peak pressure was always higher than the maximum pressure calculated at the steady-state condition. The needle-shaped pressure profile during the transient process produced a dimpled shape near the center of the contacts. In general, the maximum peak pressure increased with increasing dimensionless load, decreasing dimensionless entraining velocity, and increasing dimensionless materials parameter. The dynamic performance parameters were plotted and are a function not only of the dimensionless velocity parameter (as described in Lee and Hamrock, (1988)), but also of the dimensionless load, the dimensionless entraining velocity, and the dimensionless materials parameter. The major factor causing the pressure gradient to be infinity during the transient process was the viscosity. A non-Newtonian fluid is suggested to execute the problem for high load and low entraining velocity.
Gyroscopic and Support Effects on the Steady-State Response of a Noncontacting Flexibly Mounted Rotor Mechanical Face Seal
Authors: Green I.
Published: October 2009

The dynamic behavior of a noncontacting rotary mechanical face seal is analyzed. A closed-form solution is presented for the response of a flexibly mounted rotor to forcing misalignments which normally exist due to manufacturing and assembly tolerances. The relative misalignment between the rotor and the stator, which is the most important seal parameter, has been found to be time dependent with a cyclically varying magnitude. The relative response is minimum when support stiffness and damping are minimum. The gyroscopic couple is shown to have a direct effect on the dynamic response. This effect is enhanced at high speeds, and depending on the ratio between the transverse and polar moments of inertia, it can either decrease or increase the dynamic response. Its effect is most beneficial to seal performance when the rotor is a “short disk.” A numerical example demonstrates that a flexibly-mounted rotor seal outperforms a flexibly mounted stator seal with regard to the total relative misalignment, the critical stator misalignment, and the critical speed.
Geometric Effects on Eddy Current Bearing Performance
Authors: Tichy J. A. , Connor K. A.
Published: October 2009

The properties of magnetic bearings, particularly those based on repulsive forces due to eddy currents, are determined by a complex mixture of electrical and mechanical length and time scales. A perturbation solution for the magnetic field structure based on careful ordering of these parameters has permitted the effects of realistic gap geometries to be analyzed. The load capacity of eddy current journal bearings is found to be somewhat larger than previously predicted in an earlier paper which used magnetic fields based on constant gap size. The present results may be of interest to those concerned with calculating eddy currents in conventional attractive magnetic bearings.
Roughness-Induced Shear- and Squeeze-Film Effects in Magnetic Recording—Part I: Analysis
Authors: Bhushan Bharat , To̸nder Kristian
Published: October 2009

General analyses are developed to predict the role of surface roughness, rarefaction effects, and various operating parameters in thin-film gas lubrication. Both shear- and squeeze-film effects are considered. The squeeze-film analysis is developed for transient and periodic motions. The analyses are based on average flow (roughness) factors. The results are presented in terms of Knudsen number, h/σ (film thickness/standard deviations of composite roughness) and roughness-orientation parameters. The appropriate analyses presented in this paper are simple and can be applied to magnetic recording and other applications to provide design guidelines.
A Computerized Expert System for Tribological Failure Diagnosis
Authors: Tallian T. E.
Published: October 2009

A micro-computer supported, rule-based expert system for failure diagnosis of tribo-components is described. Included is a brief review of AI tools and system organization methods used. The system, as implemented, encompasses: (a) observation of the machine or device containing the tribo-components; (b) identification of component failure modes by visual appearance comparison with photographic standards, and (c) reverse-engineering of the component selection for the application. Not implemented, but defined are: laboratory and advanced analytic diagnostic methods. The system consists of interactive screen-dialogs, augmented by engineering computation routines and followed by the generation of formatted diagnostic and corrective action reports.
Friction-Induced Thermo-Mechanical Cracking in a Coated Medium With a Near Surface Cavity
Authors: Chen T. Y. , Ju F. D.
Published: October 2009

This paper deals with the problem of an asperity-excited thermo-mechanical field in a medium with a thin surface layer and a near surface void defect. The solutions for the temperature distribution and stress state in the vicinity of the void are obtained. Numerical results are obtained using the material properties of Stellite III for both the coating and the substrate. The parametric effects of material properties in the coating and the substrate are considered by varying the corresponding property in the coating or the substrate. The stress field solutions of the coated medium with a cavity are compared with the solutions for a single material with a cavity. In the case of the single material with a cavity, while the thermal stress is much larger than the thermal stress of the no cavity case, the principal directions of the thermal stress are not significantly changed. However, for the case of a coated medium with a cavity, not only is the thermal stress much larger than that of the no cavity case, but also the principal directions of the thermal stress are changed. The principal directions of the thermal stress field depend on both the material properties and the ligament thickness (thickness between the wear surface and the top edge of the cavity). When the angle of the principal directions becomes larger, shear delamination will initiate at the coating/substrate interface.
Thermally Induced Seizures of Journal Bearings
Authors: Dufrane K. F. , Kannel J. W.
Published: October 2009

The paper presents a simple theory for predicting seizure times for journal bearings. Under conditions of insufficient lubrication when bearing friction is high, seizure is predicted to occur in less than 20 seconds of operation. Insufficient lubrication can occur during bearing start-up, application of unusual loads, or as a result of an interruption of the lubricant supply system. Three examples where bearing seizure has been observed are discussed and the actual times to seize are compared with theoretical predictions. The actual seizure times are slightly less than predicted by theory, which is probably the result of bearing imperfections or uneven loading not considered in the theory.
Elasto-Plastic Finite Element Analyses of Two-Dimensional Rolling and Sliding Contact Deformation of Bearing Steel
Authors: Kumar A. M. , Hahn G. T. , Bhargava V. , Rubin C.
Published: October 2009

In the past, the mechanics of repeated rolling and sliding contact could only be treated for the idealized, elastic-perfectly-plastic (and isotropic) cyclic materials behavior, albeit approximately. They have not proven useful because the real cyclic plastic behavior of contacting materials is anything but perfectly plastic or isotropic. Using finite element methods, the authors have developed techniques for treating elastic-linear-kinematic hardening-plastic (ELKP) behavior, an idealization that comes much closer to the behavior of low, medium, and high hardness steels. In an earlier paper, the authors have examined rolling and sliding on rail steel, which is much softer than hardened bearing steel and displays quite different ELKP properties. The present paper offers the first results for repeated rolling and sliding for high strength bearing steel ELKP behavior and material properties.
Friction-Induced Thermal Influences in Elastic Contact Between Spherical Asperities
Authors: Ting Bond-Yen , Winer W. O.
Published: October 2009

The friction-induced thermal energy at the contacting surface increases the contact temperature which changes the material properties and produces thermal stresses in the body. Plastic yielding of the contacting bodies resulting from the combined thermal and isothermal effects is investigated. An associated wear mechanism controlled by plastic deformation is introduced, and a wear control approach is presented.
A Double Scale Analysis Approach of the Reynolds Roughness Comments and Application to the Journal Bearing
Authors: Bayada G. , Faure J. B.
Published: October 2009

This paper describes a theoretical analysis that can be used to study every periodic roughness pattern effects when Reynolds equation is valid. Numerical results using this new “averaged” equation point out the field of application of the method, particularly with respect to the roughness wavelength.
A Spectral Approach to the Analysis of Rough Surfaces
Authors: Moalic H. , Fitzpatrick J. A. , Torrance A. A.
Published: October 2009

A brief summary of the methods commonly used for the analysis of rough surfaces and the errors associated with these techniques is given. A frequency domain digital differentiator is shown to reduce the bias errors for estimates of the properties of slopes and curvatures for a sample spacing determined by the profilometer probe size. A comparison of this “spectral” approach with finite difference methods for calculating slope and curvature characteristics for a ground surface show substantial underestimates for the latter methods.
Wear Resistance of Laser Treated Partially Stabilized Zirconia
Authors: Aronov V. , Benetatos M.
Published: October 2009

The laser beam treatment of magnesia partially stabilized zirconia (Mg-PSZ) sample surfaces has shown a considerable improvement in their wear resistance and surface hardness. The laser beam treated surfaces exhibited higher wear resistance than either ground untreated or ground and laser treated ceramic surfaces. There are optimum combination of the laser treatment process parameters (laser power and exposure characteristics) that resulted in the minimum wear rate or the maximum surface hardness. There was no correlation found between the wear rate and the surface hardness. There were two wear mechanisms operational, namely, surface fracture and surface polishing. The treatment of the ceramic surfaces reduced the fracture component of the wear rate. The laser treatment effect on the polishing process was not detected. The increase in the wear resistance and the surface hardness of the laser beam treated surfaces were due to the thermally induced phase transformations resulted in the formation of the compressive stress field on the surface and altering the surface structure.
Static and Dynamic Characteristics of Turbulent Annular Eccentric Seals: Effect of Convergent-Tapered Geometry and Variable Fluid Properties
Authors: Simon F. , Frene J.
Published: October 2009

The static and dynamic characteristics of annular plain seals were investigated theoretically in the turbulent flow regime. The turbulence model which uses the nonlinear analysis developed by Elrod and Ng has been improved for Reynolds numbers higher than 100,000 to include cryogenic application. In addition, velocity boundary conditions have been reexamined. The two-dimensional Reynolds equation was solved numerically considering the swirl effect and the pressure drop due to axial acceleration of liquid at the inlet of the seal. Integration of the pressure distribution defines the reaction force developed by the seal and the corresponding rotordynamic coefficients. The solution applies for taper geometry of eccentric seal and variable fluid properties.
Predicting the Coefficient of Friction in Sliding-Rolling Contacts
Authors: Li Yufeng , Seireg Ali
Published: October 2009

This paper deals with the development of a dimensionless empirical formula for calculating the coefficient of friction in sliding-rolling steel on steel contacts under different operating conditions in the thermal regime. The effect of lubrication, surface roughness, and surface coating on friction are considered. The formula shows excellent correlation with the experimental tests conducted by many investigators and provides a unified relationship for all the published data.
Approximate Design of Statically Loaded Cylindrical Journal Bearings
Authors: San Andres Luis A.
Published: October 2009

This technical note presents an approximate solution for the fluid film forces and design coefficents for statically loaded cylindrical journal bearings. The solution is an improved correction to the infinitely long journal bearing model. The formulas derived are of extreme simplicity and the results are excellent for most practical journal bearing configurations.
Dry Friction of Silicon Carbide and Silicon Nitride Against Metals: The Effect of Humidity and Oxide Films
Authors: Demizu K. , Ishigaki H. , Wadabayashi R.
Published: October 2009

Friction experiments were conducted with a reciprocating friction test apparatus to determine the effect of humidity and oxide films on the friction characteristics of ceramics slid against pure metals. The friction coefficients of silicon carbide were not affected very much by varying humidity or metals. On the other hand, the friction coefficients of nitride were affected by both humidity and the type of metal. Some of these metals showed high friction coefficients in high humid air. Preexisting thick oxide layers, which had formed on metal surfaces before sliding, caused an increase in the friction coefficients in an environment of 50 percent relative humidity (RH) air. The friction coefficients of silicon nitride to metal contacts were strongly affected by the oxidation of the metal surfaces, and those in 90 percent RH air correlated well with the Gibbs free energy of formation of the lowest metal oxide.
A Numerical Analysis for the Transient EHL Process of a Cam-Tappet Pair in I. C. Engine
Authors: Ai Xiaolan , Yu Haiqing
Published: October 2009

The transient elastohydrodynamic lubrication (EHL) process of cam-tappet pair in I. C. engine is analyzed with a full numerical method. The variations of pressure distribution and film profile as a function of rotation angle of cam shaft provide useful information in evaluating lubrication conditions as well as analyzing failures of contacting surfaces. Results show that the segment in cam contour from φ = 30 to φ = 110 deg is a difficult lubrication range, and surface failure may occur first in this range. This statement was confirmed by preliminary exprimental work conducted in a testing rig.
Theoretical Condition for the Cxy=Cyx Relation in Fluid Film Journal Bearings
Authors: Kato T. , Hori Y.
Published: October 2009

A computer program for calculating dynamic coefficients of journal bearings is necessary in designing fluid film journal bearings and an accuracy of the program is sometimes checked by the relation that the cross terms of linear damping coefficients of journal bearings are equal to each other, namely “Cxy = Cyx”. However, the condition for this relation has not been clear. This paper shows that the relation “Cxy = Cyx” holds in any type of finite width journal bearing when these are calculated under the following condition: (I) The governing Reynolds equation is linear in pressure or regarded as linear in numerical calculations; (II) Film thickness is given by h = c (1 + κcosθ); and (III) Boundary condition is homogeneous such as p=0 or dp/dn=0, where n denotes a normal to the boundary.
Static Characteristics of the Regular and Reversible Rotation Type Herringbone Grooved Journal Bearing
Authors: Kawabata Nobuyoshi , Ozawa Yasumi , Kamaya Shuji , Miyake Yutaka
Published: October 2009

A new type herringbone grooved journal bearing, which produces an oil film bearing pressure with a shaft or bearing rotation in either direction, is proposed in this paper. A numerical analysis of the bearing parameters using the narrow groove theory and the Gu¨mbel condition confirmed that the load capacity of this bearing and the radial load component (related to stability) do not differ greatly from those of a conventional bearing. The values of the bearing parameters which give maximum load capacity, and the values of the load capacity and its direction angle are also determined numerically for the case of either grooved member or smooth member rotation.
A Fundamental Tribological Study of Ti/Al2O3 Contact in Sliding Wear
Authors: Hong H. , Winer W. O.
Published: October 2009

The tribological properties of titanium in sliding contact with single crystal Al2O3 were studied to investigate wear mechanism associated with tribo-chemical reaction due to friction heating. Oxidational wear was observed. A theoretical approach to predict the wear rate of titanium was also studied.
A Flexible Rectangular Plate on an Elastic Layer: Large Area Contact
Authors: Dempsey J. P. , Li Hui
Published: October 2009

The unbonded frictionless receding contact problem of a symmetrically loaded thin rectangular plate resting on an elastic layer is solved in this paper. The contact is assumed to be tensionless. The problem is transformed into the solution of three coupled two-dimensional singular integral equations. The possible contact pressure singularities along the plate edges and at the corners are treated using adaptive discretization. The contact regions are found iteratively since the problem is nonlinear. Contact regions and numerical values of displacements and contact pressures are presented to illustrate the influences of uplift, layer depth, aspect ratio, stiffness ratio, Poisson’s ratio, and other quantities.
A General Model for Microelastohydrodynamic Lubrication and Its Full Numerical Solution
Authors: Ai Xiaolan , Zheng Linqing
Published: October 2009

A general transient model for microelastohydrodynamic lubrication with Eyring fluid was established in this paper to describe the basic processes involved in thin film lubrication with rough surfaces, namely the process of a single asperity when it passes through the macro-EHL contact with or without sliding, and the process for a pair of asperities when they collide under macro-EHL pressure ambient. The solution of this model was performed by a relaxation iteration method that had been found to be simple and effective. Results showed some physical features that were previously unknown, and provided information to unlock the mysteries of several important failure mechanisms in lubricated concentrated contacts.
Investigations on Large Turbine Bearings Working Under Transitional Conditions Between Laminar and Turbulent Flow
Authors: Hopf G. , Schu¨ler D.
Published: October 2009

The report deals with investigations on large turbine bearings, a tilting pad bearing, and an elliptical bearing. In special cases, the maximum babbitt temperatures show a sudden leap, caused by a slight change of the operating conditions. According to the test results, the temperatures do not change within the whole bearing, but only in a region near the minimum gap width. As proved by comparative theoretical investigations, the reason for this temperature leap is a local transition between laminar and turbulent flow, changing the thermal conductivity within the oil film to a high degree. Thus, the consideration of thermal diffusion in the energy equation is essential for precalculating this phenomenon. As a consequence of locally high surface temperatures, considerably large thermoelastic deformations are observed at both test bearings. For this reason the comparative calculations are based upon measured gap width profiles.
Growth of the Shell/Transverse Defect in Rails
Authors: Yu Maria Min-Hui , Keer L. M.
Published: October 2009

An approximate analysis of the shell/transverse defect growth in steel rails during use is presented. A general solution for a single subsurface crack is presented first. A simpler approach, which considers the transverse defect alone, is examined as well. Residual stresses are included by introducing their stress distributions mechanically. A proposed mixed-mode loading growth law is used for fatigue life calculations and the crack length versus life curves are obtained. The life of the shell/transverse defect is found to be much shorter than that of the single transverse defect.
Some Effects of Lubricant Composition and Tappet Rotation on Cam/Tappet Friction
Authors: Willermet P. A. , Pieprzak J.
Published: October 2009

A cam/tappet friction rig was constructed from a 1.6 L Ford valve train. The head casting and the camshaft were shortened so that only two journal bearings remained. Only one of the two remaining cam/tappet contacts was used as a frictional contact. All other contacts were equipped with rolling element bearings so that essentially all the turning torque came from cam/tappet friction and valve spring forces. The rig, together with a data acquisition/wave form analyzer system and a computer, was capable of measuring instantaneous torque with an angular resolution of less than one degree, and reducing the data to provide calculated values for parameters such as the friction coefficient. The experimental data were compared with results from a cam/tappet friction model to assist in interpretation. The data and model illustrated that lubricant composition and tappet rotation have important effects not only on overall friction, but also on the shape of friction versus cam angle curves.
Self-Loading Slider Dynamics for Noncontact Start Stop Operation With Negative Pressure Air-Lubricated Slider Bearing in Magnetic Disk Storage
Authors: Tagawa N. , Hashimoto M.
Published: October 2009

This paper proposes self-loading flying head slider mechanisms to be used for information storage on magnetic disk media under noncontact start/stop mode conditions. The mechanisms consist of a zero-load negative pressure air-lubricated slider bearing, a slider suspension mechanism, and a twin-structure piezoelectric actuator as the head loading mechanism. Experimental research was carried out on fundamental flying characteristics for the slider. The dynamics of a self-loading/unloading negative pressure air-lubricated slider bearing were successfully studied in detail with a laser Doppler vibrometer. No intermittent contact between head and disk was observed in either the self-load or unload cases. A theoretical study on the self-loading phenomenon was carried out, and its conclusions were in good agreement with the experimental results. This suggests the feasibility of achieving a high head/disk interface reliability and, in particular, of overcoming problems regarding stiction and tribology between head and disk.
Tangential Compliance of Rough Elastic Bodies in Contact
Authors: Raoof M. , Hobbs R. E.
Published: October 2009

A simple method is presented for determining the tangential force-displacement relationship between two elastically identical generally curved bodies when the tangential force is not directed along either of the principal axes of the contact patch. It is shown that with one suitable assumption the desired solution of the general problem can be derived using the available closed form solutions for the particular cases where the tangential force is directed along one or other of the principal axes of contact. The analysis was motivated by a study of wire rope behavior, but has potential applications in several other fields.
Micro-Elastohydrodynamic Lubrication of Circumferentially Finished Rollers: The Influence of Temperature and Roughness
Authors: Barragan de Ling FdM. , Evans H. P. , Snidle R. W.
Published: October 2009

The paper describes a full elastohydrodynamic lubrication analysis for circumferentially grooved rollers. Isothermal conditions are assumed and the form of the grooves is sinusoidal. Results are presented which show the effect of both temperature (i.e., lubricant viscosity) and amplitude of the roughness upon the distribution of pressure and the film thickness. The operating conditions used in the analysis are representative of those found in disk machine experiments that have been used to simulate scuffing failure of gears.
Structural Insight into Nascent Polypeptide Chain–Mediated Translational Stalling
Authors: Seidelt Birgit , Innis C. Axel , Wilson Daniel N. , Gartmann Marco , Armache Jean-Paul , Villa Elizabeth , Trabuco Leonardo G. , Becker Thomas , Mielke Thorsten , Schulten Klaus , Steitz Thomas A. , Beckmann Roland
Published: October 2009

Nascent Chains Revealed

Detailed analysis of protein translation and translocation across membranes requires the identification and structural analysis of intermediates involved in these processes (see the Perspective by

Kampmann and Blobel

).

Seidelt
et al.

(p.
1412
, published online 29 October) report the visualization by cryo-electron microscopy of a nascent polypeptide chain in the tunnel of the ribosome at 5.8 angstroms. This resolution allows analysis of the conformation and distinct contacts of the nascent chain within the ribosomal tunnel, which suggests a mechanism by which translational stalling is induced by this peptide. Protein translocation across cellular membranes involves the Sec61 protein, a component of a protein-conducting channel. Whether Sec61 acts as a monomer or as an oligomer during protein translocation has been unclear.

Becker
et al.

(p.
1369
, published online 29 October) describe active yeast and mammalian ribosome-Sec61 structures that show the Sec61 complex interacting with the ribosome and a nascent secretory protein signal sequence. The analysis unambiguously reveals that the active protein-conducting channel is a single Sec61 copy with its central pore serving as conduit for the nascent polypeptide.
A Simple Cipher Governs DNA Recognition by TAL Effectors
Authors: Moscou Matthew J. , Bogdanove Adam J.
Published: October 2009

TAL Order

Xanthomonas
bacteria attack their plant hosts by delivering their own transcription-activator–like (TAL) proteins into the plant cell nucleus and alter the plant's gene regulation (see the Perspective by

Voytas and Joung

).
Moscou and Bogdanove
(p.
1501
, published online 29 October: see the cover) and

Boch
et al.

(p.
1509
, published online 29 October) have now discovered how the similar but not identical repeats in the TAL proteins encode the specificity needed for the proteins to find their targets. Each repeat is specific for one DNA base pair, a specificity encoded by hypervariable amino acid positions. Combining several repeats with different amino acids in the hypervariable positions allowed the production of new effectors that targeted new DNA sites.
Should we enhance animals?
Authors: Chan S
Published: October 2009

Much bioethical discussion has been devoted to the subject of human enhancement through various technological means such as genetic modification. Although many of the same technologies could be, indeed in many cases already have been, applied to non-human animals, there has been very little consideration of the concept of “animal enhancement”, at least not in those specific terms. This paper addresses the notion of animal enhancement and the ethical issues surrounding it. A definition of animal enhancement is proposed that provides a framework within which to consider these issues; and it is argued that if human enhancement can be considered to be a moral obligation, so too can animal enhancement.
Telecare and self-management: opportunity to change the paradigm?
Authors: Schermer M
Published: October 2009

Telecare, the provision of care through remote interaction enabled by information and communication technology, is quickly developing. Integration with other technological developments is to be expected and will create systems that enable more intense, continuous and unobtrusive monitoring of health, and more personalised feedback and instructions. One of the goals of telecare is enhancing the independence and self-management of patients. In this article three degrees of self-management are described and a distinction is made between compliant and concordant forms of self-management. It is argued that telecare merely promotes forms of self-management in which compliance to medical instructions is central. Technological developments and normative policy considerations may enforce this trend to implement an interpretation of self-management in which compliance to a strict medical regime is prominent. Against this, a plea is made for developing telecare systems that incorporate concordant and collaborative forms of self-management, in which the patient’s own perspective is empowered.
THE VLASOV CONTINUUM LIMIT FOR THE CLASSICAL MICROCANONICAL ENSEMBLE
Authors: KIESSLING MICHAEL K.-H.
Published: October 2009

For classical Hamiltonian N-body systems with mildly regular pair interaction potential (in particular, [Formula: see text] integrability is required), it is shown that when N → ∞ in a fixed bounded domain Λ ⊂ ℝ3, with energy [Formula: see text] scaling as [Formula: see text], then Boltzmann's ergodic ensemble entropy [Formula: see text] has the asymptotic expansion SΛ(N,N2ε) = - N ln N + sΛ(ε) N + o(N). Here, the N ln N term is combinatorial in origin and independent of the rescaled Hamiltonian, while sΛ(ε) is the system-specific Boltzmann entropy per particle, i.e. –sΛ(ε) is the minimum of Boltzmann's H function for a perfect gas of energy ε subjected to a combination of externally and self-generated fields. It is also shown that any limit point of the n-point marginal ensemble measures is a linear convex superposition of n-fold products of the H-function-minimizing one-point functions. The proofs are direct, in the sense that (a) the map [Formula: see text] is studied rather than its inverse [Formula: see text]; (b) no regularization of the microcanonical measure [Formula: see text] is invoked, and (c) no detour via the canonical ensemble. The proofs hold irrespective of whether microcanonical and canonical ensembles are equivalent or not.
STABILITY ANALYSIS OF A CLASS OF GENERAL PERIODIC NEURAL NETWORKS WITH DELAYS AND IMPULSES
Authors: ZHAO YONG , XIA YONGHUI , LU QISHAO
Published: October 2009

Based on the inequality analysis, matrix theory and spectral theory, a class of general periodic neural networks with delays and impulses is studied. Some sufficient conditions are established for the existence and globally exponential stability of a unique periodic solution. Furthermore, the results are applied to some typical impulsive neural network systems as special cases, with a real-life example to show feasibility of our results.
ROBUST LOCATION AND SPREAD MEASURES FOR NONPARAMETRIC PROBABILITY DENSITY FUNCTION ESTIMATION
Authors: LÓPEZ-RUBIO EZEQUIEL
Published: October 2009

Robustness against outliers is a desirable property of any unsupervised learning scheme. In particular, probability density estimators benefit from incorporating this feature. A possible strategy to achieve this goal is to substitute the sample mean and the sample covariance matrix by more robust location and spread estimators. Here we use the L1-median to develop a nonparametric probability density function (PDF) estimator. We prove its most relevant properties, and we show its performance in density estimation and classification applications.
BURSTING NEAR BAUTIN BIFURCATION IN A NEURAL NETWORK WITH DELAY COUPLING
Authors: SONG ZIGEN , XU JIAN
Published: October 2009

Bursting behavior is one of the most important firing activities of neural system and plays an important role in signal encoding and transmission. In the present paper, a neural network with delay coupling is modeled to investigate the generation mechanism of bursting behavior. The Andronov-Hopf bifurcation is firstly studied and then the degenerated Andronov-Hopf bifurcation, namely Bautin bifurcation, is analyzed with the external input varying. Classifying dynamics in the neighborhood of the Bautin bifurcation, we obtain the bifurcation sets where the supercritical/subcritical Andronov-Hopf, or the fold limit cycle bifurcation may happen in the system under consideration. For a periodic disturbance occurring in the neighborhood of the Bautin bifurcation, it is seen that the Andronov-Hopf bifurcation and fold limit cycle bifurcation may lead to the transition from quiescent state to firing activities. Complex bursting phenomena, including Hopf/Hopf bursting, Hopf/Fold cycle bursting, SubHopf/Hopf bursting and SubHopf/Fold cycle bursting are found in the firing area. The results show that the dynamical properties of different burstings are related to the dynamical behaviors derived from the bifurcations of the system. Finally, it is seen that the bursting disappears but the periodic spiking appears in the delayed neural network for large values of delay.
IMPROVING NEURAL NETWORKS PREDICTION ACCURACY USING PARTICLE SWARM OPTIMIZATION COMBINER
Authors: ELRAGAL HASSAN M.
Published: October 2009

This paper proposes a technique to improve Artificial Neural Network (ANN) prediction accuracy using Particle Swarm Optimization (PSO) combiner. A hybrid system consists of two stages with the first stage containing two ANNs. The first ANN predictor is a multi-layer feed-forward network trained with error back-propagation and the second predictor is a functional link network. These two predictors are combined in the second stage using PSO combiner in a linear and non-linear fashion. The proposed method is applied to problem of predicting daily natural gas consumption. The performance of ANN predictors and combination methods are tested on real data from four different gas utilities. The experimental results show that the proposed particle swarm optimization combiners results in more accurate prediction compared to using single ANN predictor. Prediction accuracy improvement of the proposed PSO combiners have been shown using hypothesis testing.
A REVIEW OF DESIGN PATTERN MINING TECHNIQUES
Authors: DONG JING , ZHAO YAJING , PENG TU
Published: October 2009

The quality of a software system highly depends on its architectural design. High quality software systems typically apply expert design experience which has been captured as design patterns. As demonstrated solutions to recurring problems, design patterns help to reuse expert experience in software system design. They have been extensively applied in the industry. Mining the instances of design patterns from the source code of software systems can assist in the understanding of the systems and the process of re-engineering them. More importantly, it also helps to trace back to the original design decisions, which are typically missing in legacy systems. This paper presents a review on current techniques and tools for mining design patterns from source code or design of software systems. We classify different approaches and analyze their results in a comparative study. We also examine the disparity of the discovery results of different approaches and analyze possible reasons with some insight.
"DATA TEMPERATURE" IN MINIMUM FREE ENERGIES FOR PARAMETER LEARNING OF BAYESIAN NETWORKS
Authors: ISOZAKI TAKASHI , KATO NORIJI , UENO MAOMI
Published: October 2009

Maximum likelihood method for estimating parameters of Bayesian networks (BNs) is efficient and accurate for large samples. However, the method suffers from overfitting when the sample size is small. Bayesian methods, which are effective to avoid overfitting, present difficulties for determining optimal hyperparameters of prior distributions with good balance between theoretical and practical points of view when no prior knowledge is available.

As described in this paper, we propose an alternative estimation method of the parameters on BNs. The method uses a principle, rooted in thermodynamics, of minimizing free energy (MFE). We define internal energies, entropies, and temperature, which constitute free energies. Especially for temperature, we propose a "data temperature" assumption and some explicit models. This approach can treat the maximum likelihood principle and the maximum entropy principle in a unified manner of the MFE principle. For assessments of classification accuracy, our method shows higher accuracy than that obtained using the Bayesian method with normally recommended hyperparameters. Moreover, our method exhibits robustness for the choice of introduced hyperparameters.
A NEW LINEAR GENETIC PROGRAMMING APPROACH BASED ON STRAIGHT LINE PROGRAMS: SOME THEORETICAL AND EXPERIMENTAL ASPECTS
Authors: ALONSO CÉSAR L. , MONTAÑA JOSÉ LUIS , PUENTE JORGE , BORGES CRUZ ENRIQUE
Published: October 2009

Tree encodings of programs are well known for their representative power and are used very often in Genetic Programming. In this paper we experiment with a new data structure, named straight line program (slp), to represent computer programs. The main features of this structure are described, new recombination operators for GP related to slp's are introduced and a study of the Vapnik-Chervonenkis dimension of families of slp's is done. Experiments have been performed on symbolic regression problems. Results are encouraging and suggest that the GP approach based on slp's consistently outperforms conventional GP based on tree structured representations.
MOMENTUM ENTANGLEMENT OF PHOTON–EXCITON
Authors: NGUYEN GIANG D. , VAN T. T. T. , NGO V. THANH , VIET N. A.
Published: October 2009

We studied the entanglement of a photon and an exciton in semiconductors. Our model shows a superhigh degree of entanglement between the exciton and the emitted photon, higher than that between the atom and the photon.11 We obtained the simple analytical formulas for both R and K which are the specific parameters of the entanglement. We also investigated the dependence of entanglement on the main parameters of the exciton in semiconductors. These results are in a good agreement with previous works.
VON NEUMANN AND LUDERS POSTULATES AND QUANTUM INFORMATION THEORY
Authors: KHRENNIKOV ANDREI
Published: October 2009

This note is devoted to some foundational aspects of quantum mechanics (QM) related to quantum information (QI), especially quantum teleportation and "one way quantum computing." We emphasize the role of the projection postulate (determining post-measurement states) in QI and the difference between its Lüders and von Neumann versions. As is well-known, these postulates differ in the case of observables with degenerate spectra. Such observables are important in operations with entangled states: any measurement on one subsystem is represented by an observable with degenerate spectrum in the Hilbert space of a composite system. Some QI schemes (e.g. quantum teleportation and "one way quantum computing") are based on the use of Lüders postulate. The formal application of von Neumann postulate can block these QI schemes. In this note, we present a list of natural conditions under which von Neumann's description of measurements via refinement implies Lüders projection postulate.