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COLD SPRAY TANTALUM COATING Researchers at the University of Wisconsin-Madison are using a new coating technology to produce a hardworking material that can withstand the harsh conditions inside a fusion [...]

The spectral analysis of surface waves (SASW) method is a nondestructive testing method of pavements based on the dispersive characteristic of seismic surface waves. The method can provide the thickness and stiffness of pavement layers. One of the more complex aspects of the SASW method is an iterative process to estimate the pavement parameters, called the inversion procedure. In this paper, the feasibility of completely automating the inversion process and substituting it with artificial neural network (ANN) models was explored. A number of different ANN models were developed using various ANN training strategies. To improve the performance of some ANN models, a sequential modeling technique was implemented. In the sequential modeling, some pavement parameters are estimated first from an initial set of ANN models, which is then the input to subsequent ANN models to estimate other parameters of interest. Furthermore, the performance of the ANN models was evaluated using a number of well-characterized pavement sections. The results illustrated that ANN models could estimate the upper layers' parameters so well that they could replace the inversion process. The ANN models for other layers were capable of generating robust initial estimates for a well-constrained formal inversion that can be readily automated. DOI: 10.1061/(ASCE)0899-1561(2009)21:12(722) CE Database subject headings: Neural networks; Pavements; Surface waves; Automation.

To investigate the complex hydrological, morphodynamic, and environmental processes in watersheds, a physically-based integrated two-dimensional (2D) surface and three-dimensional (3D) subsurface model for flow, soil erosion and transport, and contaminant transport in the surface-subsurface system is presented in this paper. The model simulates the rainfall-induced surface flow by solving the depth-averaged 2D diffusion wave equation and the variably-saturated subsurface flow by solving the 3D mixed-form Richards equation. The surface and subsurface flow equations are coupled using the continuity conditions of pressure and exchange flux at the ground surface. The model uses the concept of nonequilibrium in the depth-averaged 2D simulation of nonuniform total-load sediment transport in upland fields, considering detachments by rainsplash and hydraulic erosion driven by surface flow. The integrated 2D surface and 3D subsurface contaminant transport model takes into account the contaminant changes due to sediment sorption and desorption, as well as exchanges between surface and subsurface domains due to infiltration, diffusion, and bed change. The model applies the same set of surface equations of flow, sediment, and contaminant transport for describing both upland areas and streams, so that no special treatments are required at their interface. The established model has been evaluated by comparisons with published experimental, numerical, and analytical data and then applied in an agricultural watershed. The model is suitable for wetland areas and agricultural watersheds in which streams are not very narrow and deep, and meanwhile a relatively fine mesh that can distinguish the streams is preferred. DOI: 10.1061/(ASCE)HY. 1943-7900.0000116 CE Database subject headings: Numerical models; Integrated systems; Rainfall; Infiltration; Overland flow; Subsurface flow; Erosion; Pollution; Sorption; Watersheds.

Through experiments using two-dimensional particle-image velocimetry (PIV), this paper examines the nature of transition in a separation bubble and manipulations of the resultant breakdown to turbulence through passive means of control. An airfoil was used that provides minimal variation in the separation location over a wide operating range, with various two-dimensional modifications made to the surface for the purpose of manipulating the transition process. The study was conducted under low-freestream-turbulence conditions over a flow Reynolds number range of 28,000-101,000 based on airfoil chord. The spatial nature of the measurements has allowed identification of the dominant flow structures associated with transition in the separated shear layer and the manipulations introduced by the surface modifications. The Kelvin--Helmholtz (K-H) instability is identified as the dominant transition mechanism in the separated shear layer, leading to the roll-up of spanwise vorticity and subsequent breakdown into small-scale turbulence. Similarities with planar free-shear layers are noted, including the frequency of maximum amplification rate for the K-H instability and the vortex-pairing phenomenon initiated by a subharmonic instability. In some cases, secondary pairing events are observed and result in a laminar intervortex region consisting of freestream fluid entrained toward the surface due to the strong circulation of the large-scale vortices. Results of the surface-modification study show that different physical mechanisms can be manipulated to affect the separation, transition, and reattachment processes over the airfoil. These manipulations are also shown to affect the boundary-layer losses observed downstream of reattachment, with all surface-indentation configurations providing decreased losses at the three lowest Reynolds numbers and three of the five configurations providing decreased losses at the highest Reynolds number. The primary mechanisms that provide these manipulations include: suppression of the vortex-pairing phenomenon, which reduces both the shear-layer thickness and the levels of small-scale turbulence; the promotion of smaller-scale turbulence, resulting from the disturbances generated upstream of separation, which provides quicker transition and shorter separation bubbles; the elimination of the separation bubble with transition occurring in an attached boundary layer; and physical disturbance, downstream of separation, of the growing instability waves to manipulate the vortical structures and cause quicker reattachment. [DOI: 10.1115/1.2978997]

Approximate closed-form equations are derived for normal and tangential contact forces of rough surfaces in dry friction. Using an extension of the Greenwood and Tripp (1970, Proc, Inst. Mech. Eng., 185, pp. 625-633) model, in which the derivations permit asperity shoulder-to-shoulder contact and viscoelastic asperity behavior, mathematical formulae are derived for normal and tangential components of the contact force that depend not only on the proximity of the two surfaces but also the rate of approach and relative sliding. A statistical approach is forwarded in which dependence of the asperity tangential contact force on relative tangential velocity of two asperities can be cast as corrective factors in the mathematical description of tangential force. In this regard two corrective coefficients are derived: force directionality corrective coefficient and force-velocity directionality corrective coefficient. The results show that for a moderate to high load ranges the contact force can be analytically described to within 20% accuracy of that from a numerical integration of the contact equations, well below the uncertainties due to surface profile measurement. [DOI: 10.1115/1.2736730] Keywords: kinetic friction, viscoelastic contact model, rough surfaces

This paper proves that a generalized Hertz pressure (the product of Hertz square root and an even polynomial of degree 2n with respect to coordinates) applied over elastic half-space boundary generates a polynomial normal displacement of degree 2n + 2. Polynomial surface coefficients are combinations of elliptical integrals. The equation of rigid punch surface generating this pressure is derived, as well as the conditions in which an elliptical contact occurs. For second order surfaces, n = 0, these results yield all Hertz formulas, whereas new formulas are derived for contact parameters between fourth, sixth, and eight order surfaces. [DOI: 10.1115/1.2345420] Keywords: elliptic contact, generalized Hertz pressure, high order surfaces, polynomial normal displacement

Instead of a general consideration of the fractal dimension (D) and the topothesy (G *) as two invariants in the fractal analysis of surface asperities, these two roughness parameters in the present study are varied by changing the mean separation (d *) of two contact surfaces. The relationship between the fractal dimension and the mean separation is found first. By equating the structure functions developed in two different ways, the relationship among the scaling coefficient in the power spectrum function, the fractal dimension, and topothesy of asperity heights can be established. The variation of topothesy can be determined when the fractal dimension and the scaling coefficient have been obtained from the experimental results of the number of contact spots and the power spectrum function at different mean separations. A numerical scheme is developed in this study to determine the convergent values of fractal dimension and topothesy corresponding to a given mean separation. The theoretical results of the contact spot number predicted by the present model show good agreement with the reported experimental results. Both the fractal dimension and the topothesy are elevated by increasing the mean separation. Significant differences in the contact load or the total contact area are shown between the models of constant D and G * and variable D and G * as the mean separation is reduced to smaller values. [DOI: 10.1115/1.2197839] Keywords: roughness, fractal dimension, topothesy

For several decades, asperities of nominally flat rough surfaces were considered to be points higher than their immediate neighbors. Recently, it has been recognized that this model is incorrect. To address the issue, a new multiple-point asperity model, called the n-point asperity model, is introduced in this paper In the new model asperities are composed of n neighboring sampled points with n-2 middle points being above a certain level. When the separation between two surfaces decreases, new asperities with higher number of sample points, n, will come into existence. Based on the above model the height and curvature of n-point asperities are defined and their distributions are found. The model is developed for Gaussian surfaces and for the general case of an autocorrelation function (ACF). As a case study, the exponential ACF is applied to the new model, which is shown to produce remarkably good agreement with measurements from real and simulated surfaces. [DOI: 10.1115/1.2194915]

For ductile solids with periodic microstructures (e.g., honeycombs, fiber-reinforced composites, cellular solids) which are loaded primarily in compression, their ultimate failure is related to the onset of a buckling mode. Consequently, for periodic solids of infinite extent, one can define as the onset of failure the first occurrence of a bifurcation in the fundamental solution, for which all cells deform identically. By following all possible loading paths in strain or stress space, one can construct onset-of-failure surfaces for finitely strained, rate-independent solids with arbitrary microstructures. The calculations required are based on a Bloch wave analysis on the deformed unit cell. The presentation of the general theory is followed by the description of a numerical algorithm which reduces the size of stability matrices by an order of magnitude, thus improving the computational efficiency for the case of continuum unit cells. The theory is subsequently applied to porous and particle-reinforced hyperelastic solids with circular inclusions of variable stiffness. The corresponding failure surfaces in strain-space, the wavelength of the instabilities, and their dependence on micro-geometry and macroscopic loading conditions are presented and discussed. [DOI: 10.1115/1.2126695]

An efficient algorithm for isometry-invariant matching of surfaces is presented. The key idea is computing the minimum-distortion mapping between two surfaces. For this purpose, we introduce the generalized multidimensional scaling, a computationally efficient continuous optimization algorithm for finding the least distortion embedding of one surface into another. The generalized multidimensional scaling algorithm allows for both full and partial surface matching. As an example, it is applied to the problem of expression-invariant three-dimensional face recognition. Gromov-Hausdorff distance | isometric embedding | iterative-closest-point | partial embedding

Turbulent boundary-layer measurements have been carried out on flat surfaces coated with two different new generation marine antifoulings. The coatings were applied on 2.1-m-long test sections that were fitted in a 2.1-m-long flat plate setup. The measurements were carried out in two different recirculating water tunnels by means of two-component laser Doppler velocimetry and were compared with measurements of a smooth steel reference surface and a surface covered with sand grit. Both coatings exhibited an increase in frictional resistance compared to the reference surface, but the increase was significantly smaller for the Foul(ing) Release coatings than for the Tin-free SPC coating. The coatings did not significantly affect the boundary-layer thickness. When expressed in inner variables, the coatings did not have an effect on the turbulence intensity profiles, but when expressed in outer variables, the coatings affected the near-wall turbulence intensities. [DOI: 10.1115/1.1891148]

The meshing clearance of the helical surfaces under the condition of conjugation is studied in depth in this paper, which is significant to industrial practice as well as scholastic field. A general conjugation criterion for making clearance of the meshed helical surfaces is clearly defined for the first time, which states that the rotation angle of return stroke caused by clearance for all the points in the tooth surface must be identical. Based on this criterion, it is shown that the commonly adopted uniform clearance is not reasonable for all the meshed helical surfaces. For traditional involute helical surfaces, it is intrinsically correct to adopt the uniform clearance. However, for the helical surfaces with complex transverse tooth profiles, such as those applied to the twin screw compressors, it is unreasonable and harmful to do so due to violation of the conjugation criterion, leading to a severe local contact in the tooth surfaces and higher noise level and, hence, damaging the performance of the helical surfaces in application. As a general principle, the 'uniform rotation angle' clearance distribution is a unique one, satisfying the conjugation criterion.

The stiction forces that exist in microelectromechanical systems (MEMS) are characterized by surface energy and surface roughness. To simulate this contact condition, a three-dimensional fractal surface geometry and an adhesive contact model for a single asperity are used together to create a numerical adhesive rough surface solution methodology. This novel method of solution determines the characteristic adhesive contact type for each individual asperity uniquely at the time of load and area integration. Such a simulation more accurately represents the physics of the asperity-based contact. Numerical results for the adherence force are presented as a function of surface topography, interface compliance, and the work of adhesion for a MEMS interface. The magnitude of the force required to separate an adhesive rough surface interface is given in relation to a polysilicon system.

The focus in this paper is to automatically design the air-bearing surface (ABS) considering the randomness of its geometry as an uncertainty of design variables. Designs determined by the conventional optimization could only provide a low level of confidence in practical products due to the existence of uncertainties in either engineering simulations or manufacturing processes. This calls for a reliability-based approach to the design optimization, which increases product or process quality by addressing randomness or stochastic properties of design problems. In this study, a probabilistic design problem is formulated considering the reliability analysis which is employed to estimate how the fabrication tolerances of individual slider parameters affect the final flying attitude tolerances. The proposed approach first solves the deterministic optimization problem. Beginning with this solution, the reliability-based design optimization (RBDO) is continued with the probabilistic constraints affected by the random variables. Probabilistic constraints overriding the constraints of the deterministic optimization attempt to drive the design to a reliability solution with a minimum increase in the objective. The simulation results of the probabilistic design are directly compared with the values of the initial design and the results of the deterministic optimum design, respectively. In order to show the effectiveness of the proposed approach, the reliability analyses by the Monte Carlo simulation are carried out. And the results demonstrate how efficient the proposed approach is, considering the enormous computation time of the reliability analysis.

The Greenwood and Williamson (1966) model is an elegant and often-cited paradigm for predicting the load-displacement behavior of contacting rough surfaces given the height distribution of the contacting asperities. By use of an inverse technique and available load-displacement data, this work provides an alternative method to determine the asperity distribution directly from topographic measurement and subsequent data reduction. This method produces distributions that are consistent with the Greenwood and Williamson representation of the load-displacement data and demonstrates how the asperity height distribution can evolve with loading. Keywords: Rough Surface, Asperity, Contact, Inverse Methods

The bifurcation structure of viscous flow in curved square ducts is studied numerically and the stability of solutions on various solution branches is examined extensively. The solution structure of the flow is determined using the Euler-Newton continuation, the arc-length continuation, and the local parameterization continuation scheme. Test function and branch switch technique are used to monitor the bifurcation points in each continuation step and to switch branches. Up to 6 solution branches are found for the case of a flow in the curved square channel within the parameter range under consideration. Among them, three are new. The flow patterns on various bifurcation branches are also examined. A direct transient calculation is made to determine the stability of various solution branches. The results indicate that, within the scope of the present work, at given set of parameter values, the arbitrary initial disturbances lead all solutions to the same state. In addition to stable steady two-vortex solutions and temporally periodic solutions, intermittent and chaotic oscillations are discovered within a certain region of the parameter space. Temporal intermittency that is periodic for certain time intervals manifests itself by bursts of aperiodic oscillations of finite duration. After the burst, a new periodic phase starts, and so on. The intermittency serves as one of the routes for the onset of chaos. The results show that the chaotic flow in the curved channel develops through the intermittency. The chaotic oscillations appear when the number of bursts becomes large. The calculations also show that transient solutions on various bifurcation branches oscillate chaotically about the common equilibrium states at a high value of the dynamic parameter. [DOI: 10.1115/1.1412457]

Highly unsteady three-dimensional flows in curved pipes with significant variation of flow geometry and flow parameters are studied. Using improvements in computational efficiency, detailed knowledge concerning flow structures is obtained. The numerical solutions of the Navier-Stokes equations have been obtained with a variation of the projection method, and the numerical method was enhanced by new algorithms derived from the physics of the flow. These enhancements include a prediction of the flow unsteady pressure gradient based on fluid acceleration and global pressure field corrections based on mass flow. This new method yields an order of magnitude improvement in the calculation's efficiency, allowing the study of complex flow problems. Numerical flow simulations for oscillating flow cycles show that the curved pipe flows have a significant inviscid-like nature at high values of the frequency parameter. The shape of the velocity profiles is strongly influenced by the frequency parameter, whereas the influence of variations on the pipe cross-sectional area is shown to be rather weak. For large values of the frequency parameter the flow history strongly influences the low mass flow part of the cycle leading to highly unusual velocity profiles. The wall shear stress is studied for all the flows calculated. Our results show that wall shear stress is sensitive to area constrictions, the frequency parameter, as well as the shape of the entrance profile. [DOI: 10.1115/1.1400748]

The possibility of magnetoelastic SH-waves in a semi-infinite perfectly conducting medium having a superficial layer was examined. Basic equations such as Maxwell's equations established the electromagnetic boundary conditions. Numerical solutions were presented for the propagation of magnetoelastic Love waves. Results indicated that the magnetic field may cause such waves, even when they are absent in the purely elastic case.

A two-dimensional circular annulus was examined as a method of providing the scientific foundation for guided wave techniques in detecting radial cracks in annular structures. Data showed that guided circumferential waves were dispersive. The dispersion equation derived depended on the shape and not the size of the annulus. The dispersion curves of the annulus can be estimated by that of a flat plane with the same thickness. The solution to a solid disk cannot be obtained by shrinking the inner diameter of an annulus to zero.

Dynamic fracture criteria were proposed for subsonic crack growth along bimaterial surfaces. These criteria, namely, exponential crack profile growth criterion and vectorial crack-face displacement criterion, were based on the premise that crack-face displacements at a point behind the crack tip increase with instantaneous crack-tip velocity. This assumption established a generalized relationship between the dynamic energy release rate and the instantaneous crack-tip velocity.

The steady-state motion of a line mechanical/heat source over the surface of a half space was analyzed using an asymptotic solution based on thermoelastodynamic theory. Expressions for the surface temperature, displacement and stress were obtained by two-sided Laplace transform and exact asymptotic inversions. Results show that thermal parameters significantly affect the constantly moving source.

The most efficient bed-material surface sampling procedure involves the removal of a sufficiently large volume of sediment, application of sieve analysis and the interpretation of results using frequency distribution by weight or volume. On the other hand, a photographic method will only be of limited use and will require an exhaustive effort to achieve desired results. However, results brought about by such a method can be useful provided that some areas are emphasized.

This paper describes the floating characteristics of squeeze-film gas bearings with a vibration absorber. This bearing uses a piezoelectric actuator directly attached to a counterweight to impart oscillations to a bearing surface and, therefore, can generate a squeeze-film between the bearing and the guideway surfaces. Furthermore, in this squeeze bearing, a vibration absorber is inserted between a counterweight and a carried object to reduce the vibrational amplitude of the carried object and improve the motion accuracy. The effects of the vibration absorber on the floating characteristics are discussed theoretically and experimentally. It was found that the material of the vibration absorber greatly affected the floating characteristics, and the absorber made of silicone rubber was very effective to reduce the vibrational amplitude of the carried object.

The lubrication of isotropic rough surfaces has been studied numerically, and the flow factors given in the so-called Average Flow Model have been calculated. Both pressure flow and shear flow are considered. The flow factors are calculated from a small bearing part, and it is shown that the flow in the interior of this subarea is nearly unaffected by the bearing part's boundary conditions. The surface roughness is generated numerically, and the Reynolds equation is solved by the finite element method. The method used for calculating the flow factors can be used for different roughness patterns.

A new pressure-shear plate impact experiment is described for measuring the friction between two sliding surfaces at high temperature. Additionally, the techniques developed for this experiment extend the capability of the general pressure-shear experiment so that the shear strength of materials can be measured at high temperatures.

When hard rough surfaces slide repeatedly on softer half-spaces, systems of protective residual stresses may be developed in the near surface layers of the softer material which enable loads sufficiently large to cause plastic deformation in the early cycles of loading to be accommodated purely elastically in the later stages of component life. This is the process of shakedown and limits on the intensity of the allowable Hertzian pressures consistent with the eventual cessation of plastic deformation for uniform half-spaces are now well established. In this paper, we produce shakedown maps for coated or treated surfaces, choosing principally to carry out the numerical calculations on a system which models the behavior of ceramic coatings on steel substrates. In addition to the relative hardnesses of coating and the substrate, important system parameters are shown to be the normalized thickness of the coating and the strength or integrity of the bond at the interface between the coating and substrate. It is quite possible for the production of a coating of less than the critical thickness, or one displaying poor adhesion, to reduce the shakedown performance to lower values than would be the case for an unprotected surface. Design curves are produced which illustrate how the improvement in shakedown performance of such coated surfaces varies with the normalized depth of coating and the strength of the interlayer bond.

Static and dynamic characteristics of an externally pressurized porous annular thrust gas bearing (PATGB), which has a thin restricted surface layer, are investigated by numerical analysis and experiment. In the analysis, it is assumed that the fluid flow obeys Darcy's law in the porous material, restricted with Darcy's restrictor (Darcy-Darcy model) or orifice restrictor (Darcy-Orifice model) in the surface layer. From experimental investigation, it is found that the theoretical results calculated by the Darcy-Darcy model agree with the experimental data better than those of the Darcy-Orifice model. Based on the Darcy-Darcy model, the unique relationships among the design parameters, which can provide the maximum damping ratio, were derived as functions of feeding parameter under the conditions of allowable static stiffness and the local minimum dynamic stiffness. Considering the dimensionless mass of the body supported by the bearing, an optimal design method is proposed to maximize the damping ratio at the natural frequency, while maintaining the required stiffness in the low frequency region.

A numerical simulation technique for calculating the pressure distribution and the deformed geometry of an elastic half-space which has a hard surface layer in contact with a rigid indenter with a rough surface is presented. In order to reduce the computing time, the Conjugate Gradient Method (CGM) is applied to solve a set of linear equations for unknown pressures. In each iteration of the CGM, the Fast Fourier Transform (FFT) is used for the task of multiplying a direction vector by an influence coefficient matrix. An FFT-based scheme for evaluating subsurface stresses in the layer and the substrate is also presented. As an example, the pressure distribution and the deformed geometry of a steel surface coated with a TiN layer in contact with a rigid rough indenter are calculated. The subsurface stresses are also compared with von Mises yield criterion to investigate the deformation mode at the asperity contacts. The results show that the limit of elastic contact is highly dependent on the layer thickness and the surface roughness.

Elastic contact between a rigid plane and a halfspace whose surface height is described by a bandwidth-limited Fourier series is considered. The surface normal displacements and contact pressures are found by a numerical technique that exploits the structure of the Fast Fourier Transform (FFT) and an exact result in linear elasticity. The multiscale nature of rough surface contact is implicit to the method, and features such as contact agglomeration and asperity interaction - a source of difficulty for asperity-based models - evolve naturally. Both two-dimensional (2-D) and three-dimensional (3-D) contact are handled with equal ease. Finally, the implementation is simple, compact, and fast.

A homogenization method has been recently developed to optimize the topology of a structure. This method will suggest a structural topology, but the results will be in finite element form. Most engineering applications, however, require smooth structures, whether the faces of the structures be planar or curved. Given the topology of a three-dimensional structure as suggested by the homogenization method, an algorithm is developed to interpret the structure and generate a smooth, manufacturable surface representation of the structure. Structures designed by the homogenization method can be quite complex and traditional manufacturing techniques may not be well suited for constructing them. Layered manufacturing is adopted for producing such structures and it is shown how to generate the necessary data for this novel manufacturing technique from the surface model of the structure. Some steps of the algorithm require designer inputs. Examples are given which demonstrates this algorithm.

In this study, several blends of BPA polycarbonate and acrylonitrile/butadiene/styrene (ABS) resins having different gloss levels and microscopic surface roughness values were injection molded over a range of injection rates. Changes in surface appearance were monitored by visual observation, optical microscopy, and electron microscopy. The onset of unstable flow was marked by the development of regularly spaced surface patches on the molded parts. The surface irregularities were found to be strikingly similar to those produced by dragging crosslinked rubbers across hard surfaces. It was observed that blends having higher surface roughness values had lower coefficients of friction and exhibited unstable flow at lower stresses than compositions with smoother surfaces. The data were used to quantify the rheological parameters and surface characteristics defining an acceptable molding envelope for these materials., INTRODUCTION During the last several years, many end users have made a strong effort to substitute unpainted engineering thermoplastics for painted resins in appearance parts. Pressure for this change has [...]

A three-dimensional method derived from the Mindlin point force model is developed to analyze arbitrary planar cracks in a half-space. The differential crack-opening displacement replaces the dislocation's vectors to generate a singular integral equation defined by the opening's gradients. The method allows the conversion of integrals over the source elements into line integrals, which eases numerical analysis.

In this article we generalize the concept of Bezier curves to curved spaces, and illustrate this generalization with an application in kinematics. We show how De Casteljau's algorithm for constructing Bezier curves can be extended in a natural way to Riemannian manifolds. We then consider a special class of Riemannian manifold, the Lie groups. Because of their group structure Lie groups admit an elegant, efficient recursive algorithm for constructing Bezier curves. Spatial displacements of a rigid body also form a Lie group, and can therefore be interpolated (in the Bezier sense) using this recursive algorithm. We apply this alogorithm to the kinematic problem of trajectory generation or motion interpolation for a moving rigid body. The orientation trajectory of motions generated in this way have the important property of being invariant with respect to choices of inertial and body-fixed reference frames.

In this paper we study Computer Aided Geometric Design (CAGD) and Manufacturing (CAM) of developable surfaces. We develop a direct representation of developable surfaces in terms of plane geometry. It uses control planes to determine a surface which is a Bezier or a B-spline interpolation of the control planes. In the Bezier case, a de Casteljau type construction method is presented for geometric design of developable Bezier surfaces. In the B-spline case, de Boor type construction for the geometric design of the developable surface and Boehm type knot insertion algorithm are presented. In the area of manufacturing or fabrication of developable surfaces, we present simple methods for both development of a surface into a plane and bending of a flat plane into a desired developable surface. The approach presented uses plane and line geometries and eliminates the need for solving differential equations of Riccatti type used in previous methods. The results are illustrated using an example generated by a CAD/CAM system implemented based on the theory presented.

Transient correlations for laminar aiding mixed convection over a vertical thermal surface include correlations for local and mean heat transfer rates and shear stresses. The correlations are valid over a range of Prandtl numbers. The values obtained from the correlations do not differ by more than 3% over the entire mixed convection range. The correlations are valid for use in the natural, mixed and forced convection regimes.

Analysis of the heat transfer for a heated, upward facing surface impacted by liquid droplets of diameters ranging from 2.3 mm to 3.8 mm and drop frequencies from 2 to 15 droplets per second yielded adjusted critical heat flux values ranging between 100 W and 320 W per square centimeter. The maximum heat flux occurred at a wall superheat temperature of 24 degrees Celsius. The film thickness produced by droplet impact on the surface influences heat flux limits.

The continuity equation and Navier-Stokes equations derived from a non-orthogonal helical coordinate system are solved by the Galerkin finite-element method in an attempt to study the torsion effect on the fully developed laminar flow in the helical square duct. Since high-order terms of curvature and torsion are considered, the approach is also applicable to the problems with finite curvature and torsion. The interaction effects of curvature, torsion, and the inclined angle of the cross section on the secondary flow, axial velocity, and friction factor in the helical square duct are presented. The results show that the torsion has more pronounced effect on the secondary flow rather than the axial flow. In addition, unlike the flow in the toroidal square duct, Dean's instability of the secondary flow, which occurs near the outer wall in the helical square duct, can be avoided due to the effects of torsion and/or inclined angle. In such cases, a decrease of the friction factor is observed. However, as the pressure gradient decreases to a small value, the friction factor for the toroidal square duct is also applicable to the helical square duct.

A study was done on the configurations of adsorbed hard spheres after diffusion in a gravitational field using computer simulations. It was shown that the reduced relative surface coverage for polystyrene particles is constant and equal to the random sequential adsorption jamming limit value for radii not larger than 1 micrometer. The shape of the radial distribution function confirms the closer packing of large radii which is also equivalent to large gravitational forces.

A study was conducted on the standard slope method, Clauser chart method and the standard and modified Bradshaw methods. The standard slope wall similarity method can compute drag reducing flows while statistically compensating experimental data scattering. The standard slope method, however, cannot accurately determine the linear region amplitude and central location. A new approach was also developed for small upward shift approximation.

Arc repressor forms a homodimer in which the subunits intertwine to create a single globular domain. To obtain Arc sequences that fold preferentially as heterodimers, variants with surface patches of excess positive or negative charge were designed. Several but not all oppositely charged sequence pairs showed preferential heterodimer formation. In the most successful design pair, [Alpha] helix B of one subunit contained glutamic acids at positions 43, 46, 47, 48, and 50, whereas the other subunit contained lysines or arginines at these positions. A continuum electrostatic model captures many features of the experimental results and suggests that the most successful designs include elements of both positive and negative design. Arc repressor | continuum electrostatics | heterodimer | negative design | protein stability

A numerical simulation technique based on elastic asperity deformation is presented to analyze real surface contact and pressure distributions in sliding wear. The calculations have been applied to experimentally produced surfaces whose topography has been determined using an atomic force microscope. A variational approach is applied to minimize the stored energy in the contact, which determines contact area without additional iteration. Two-dimensional FIR digital filter techniques are used and an FFT procedure is used to improve the efficiency of the filter implementation. The model is used to obtain the pressure distribution, real contact area, and the distribution of real contact area under sliding conditions either parallel or perpendicular to the grinding lay. The calculated results of real contact stress at different stages of wear are given. The calculated and experimental results suggest that the stress distribution of real contact follows an exponential function. The contact stress distribution index [Beta] governs the stress distribution form and reflects the performance of the frictional components in sliding wear. The proportion of plastic contact deformation [Psi] is also related to [Beta]; therefore, reflecting the frictional property in sliding wear. The experimental and calculated results show that the smaller frictional coefficient and more homogeneous distribution of stress occur when the sliding direction is parallel rather than perpendicular to the grinding-lay direction. [DOI: 10.1115/1.1326441]

Thermal and tangential momentum accommodation coefficients have been obtained for [N.sub.2] colliding with various surfaces of relevance to the disk-drive air bearing using molecular beam scattering techniques. Analysis of the velocity and angular distributions of scattered species indicates that [N.sub.2] is essentially fully accommodated at the relevant surfaces for energies characteristic of room temperature gas.

Researchers at the U.S. Department of Energy's Brookhaven National Laboratory, Upton, N.Y., in collaboration with scientists at the European Synchrotron Radiation Facility (ESRF), France, and Bar-Ilan University, Israel, discovered that [...]

Researchers at Brown University, Providence, R.I., created nanoscale surfaces for implanted materials that mimic the contours of natural skin. The surfaces attract skin cells that, over time, build a natural [...]

Studies reveal that the number of atomic bounce increases when focussed atoms bounce on a curved trampoline surface, with the bounces limited only by scattering. The trampoline used is a small mirror and the atoms are initially collected by a magnetooptical map which compresses the atoms. Probe laser beams study the atomic bouncing along with a photodiode that detects atomic fluorescence.

A study on critical heat flux in modern equipment was conducted to obtain critical heat flux data for near-saturated and sub-cooled flow in a curved, rectangular channel subjected only to concave heating using a long, thick heater. The same test matrix, which included a broad range of velocity, was repeated for a straight channel to gauge the enhancement for which curvature is responsible. Flow visualization tests were also performed to obtain insights into the mechanisms responsible for the enhancement indicated in the data.