bluuebunny/crossref_metadata_2025 huggingface dataset:
A Hierarchical Decomposition Scheme for the Topological Synthesis of Articulated Gear Mechanisms
Authors: Chen D.-Z. , Liu C.-P.
Published: February 2008

An efficient methodology for the topological synthesis of articulated gear mechanisms (AGMs) is presented. A hierarchical model is developed to represent the structural topology of an AGM in which sub-systems in the bottom level are used as design primitives. By a proposed partition algorithm, design specifications are decomposed along the model to determine the attributes of the sub-systems in each level. The decomposition results in a composition polynomial that symbolically reveals all structural compositions of desired mechanisms. With the polynomial and the database of design primitives, the number of admissible mechanisms for a given design specification can be derived and all possible graph representations can be efficiently enumerated. Two 3-dof examples are presented for illustration.
Effect of Involute Tip Relief on Dynamic Response of Spur Gear Pairs
Authors: Kahraman A. , Blankenship G. W.
Published: February 2008

The influence of gear tooth flank modifications in the form of linear involute tip relief on the torsional vibration behavior of a spur gear pair is investigated by using an experimental test stand. Measured dynamic transmission error (DTE) values are compared and a family of forced response curves is presented. Guidelines for the design of quiet spur gear sets are also given.
Singularities of a Manipulator With Offset Wrist
Authors: Williams R. L.
Published: February 2008

The singularities of manipulators with offset wrists are difficult to enumerate. This article presents a numerical study to illuminate singularity problems when using an offset wrist with an articulated regional arm. Ironically, the regional manipulator singularity problem is worsened when using a singularity-free offset wrist. No wrist singularities exist (they are forced by design to lie outside of joint limits). However, the existing regional arm singularities become skewed from the well-known singular configurations of common manipulators. The wrist offset also skews the well-known wrist singularities (though they hopefully still lie outside of joint limits, their locations are no longer easily determined). Thus, a zero-offset singularity-free wrist is preferable with regard to overall manipulator singularities.
A Methodology for the Configuration Synthesis of Machining Centers with Automatic Tool Changer
Authors: Chen F.-C. , Yan H.-S.
Published: February 2008

The purpose of this paper is to present a design methodology for the configuration synthesis of machining centers with automatic tool changer to meet the required topology and motion characteristics. According to the concept of coordinate system, graph theory, generalization, specialization, and motion synthesis, this design methodology is proposed and computerized, and the machining centers with automatic tool changer up to eight links are synthesized. As the result, for the machining centers with drum type tool magazine, the numbers of configurations of machining centers with 6, 7, and 8 links are 2, 13, and 20, respectively. Similarly, for the machining centers with linear type tool magazine, the numbers of configurations of machining centers with 5, 6, 7, and 8 links are 1, 5, 20, and 60, respectively. Furthermore, this work provides a systematic approach for synthesizing spatial open-type mechanisms with topology and motion requirements.
Approximately Arc-Length Parametrized C3 Quintic Interpolatory Splines
Authors: Wang F.-C. , Wright P. K. , Barsky B. A. , Yang D. C. H.
Published: February 2008

A quasi-global interpolation method that fits a quintic spline curve to a set of designated data points is described in this paper. The resultant curve has several important features. First, the curve is smooth with C3 continuity and has no unwanted oscillations. Second, the generated quintic spline is “optimally” parametrized; that is, the curve is parametrized very closely to its arc length. In addition, with the interpolation method, straight line segments can be preserved to generate a quintic spline of hybrid curve segments. The properties of C3 continuity and the “near arc length” parametrization have direct applications to trajectory planning in robotics and the development of new types of machine tool controllers for high speed and precision machining. The encapsulation of straight line segments enhances the capability for the shape designers to design more complicated shapes, including free form curves and straight line segments in a uniform way.
Design of Spherical 4R Mechanisms: Function Generation for the Entire Motion Cycle
Authors: Farhang K. , Zargar Y. S.
Published: February 2008

Spherical 4R mechanisms are studied for which the crank is relatively smaller than the remaining links. The theory of small-crank mechanisms is applied to obtain approximate descriptions for the follower angular displacement in terms of the input crank angle. The follower angle is presumed to comprise a mean and a perturbational motion. This results in an approximate expression in which the follower displacement is given as a linear combination of simple harmonic functions of the first and second harmonics of the crank angle. The approximate equations are utilized for synthesis of spherical 4R mechanisms for function generation. In contrast to the conventional design procedures, the use of the approximate equations allows the synthesis of spherical mechanisms in which a prescribed function is satisfied for the entire motion of the mechanism. In addition to design examples, sample error charts are provided to assist the designer in ascertaining feasible ranges for design and corresponding orders of error.
Dynamic Loads in the Three-Lobe Supercharger
Authors: Mimmi G. C. , Pennacchi P. E.
Published: February 2008

In previous papers the authors have analyzed the functioning of the three lobe supercharger. This analysis was made possible by a complete analytical model of the rotors. The dynamic transformation of the chambers occupied by the fluid allows us to point out specific problems regarding trapped volumes and to design special devices to avoid these problems. As a result it is possible to simulate the performance of the compressor and to propose an analytical model in order to determine the dynamic loads on the rotors. The topic of this paper is the comparison between the performances achieved by helical and spur rotors, with particular attention to the loads, force and moment, acting on the rotors.
On the Influence of Friction in the Calculation of Conical Disk Springs
Authors: Curti G. , Montanini R.
Published: February 2008

An analytical solution is proposed by the authors in order to take into account the effects of friction in the calculation of conical disk springs. The new formulation allows a more accurate estimate of the load corresponding to a given displacement, but it implies the knowledge of the friction coefficient f between the spring and the supporting surfaces. The reported numerical examples show that, disregarding friction effects, the maximum error committed in the evaluation of the load is in the range 2–5%, with f = 0.14 (average friction coefficient value determined experimentally on commercial conical disk springs with different geometry). Comparison with both experimental and finite element calculations show a very good agreement of the analytical prediction.
Investigation of Torsion Springs by Considering the Friction and the End Effect
Authors: Wu M. H. , Hsu W.
Published: February 2008

In this study, the nonlinearity in moment and angular displacement of torsion springs is studied analytically and experimentally. It is shown that the inclined angles at both ends have direct effects on the nonlinearity of a constant-pitch torsion spring. Also, an algorithm for determining the friction between the spring coils in close-wound torsion springs is proposed. From the comparison to experimental data, it is found that the spring rates are different at forward and backward strokes. The dynamic equations for the close-wound torsion spring is also derived by considering the friction between the spring coils, and two different natural frequencies are found in simulation.
A New Semianalytical Algorithm for Calculating Diffuse Plane View Factors
Authors: Mavroulakis A. , Trombe A.
Published: February 2008

A new semianalytical algorithm for calculating diffuse plane view factors which is based on an extension of Nusselt’s sphere method is presented. For simple cases of view factor calculations where exact solutions exist, the accuracy of the algorithm is tested and compared with the accuracy of others.
Transient Thermal Effects of Radiant Energy in Translucent Materials
Authors: Siegel R.
Published: February 2008

When a solid or stationary fluid is translucent, energy can be transferred internally by radiation in addition to heat conduction. Since radiant propagation is very rapid, it can provide energy within a material more quickly than diffusion by heat conduction. Radiation emitted in a hot material can also be distributed rapidly in the interior. The result is that transient temperature responses including radiation can be significantly different from those by conduction alone. This is important for evaluating the thermal performance of translucent materials that are at elevated temperatures, are in high temperature surroundings, or are subjected to large incident radiation. Detailed transient solutions are necessary to examine heat transfer for forming and tempering of glass windows, evaluating ceramic components and thermal protection coatings, studying highly backscattering heat shields for atmospheric reentry, porous ceramic insulation systems, ignition and flame spread for translucent plastics, removal of ice layers, and other scientific and engineering applications involving heating and forming of optical materials. Radiation effects have been studied less for transients than for steady state because of the additional mathematical and computational complexities, but an appreciable literature has gradually developed. This paper will review the applications, types of conditions, and geometries that have been studied. Results from the literature are used to illustrate typical radiation effects on transient temperatures, and comparisons are made of transient measurements with numerical solutions.
Numerical Simulations of Heat Transfer in Taylor-Couette Flow
Authors: Kedia R. , Hunt M. L. , Colonius T.
Published: February 2008

Numerical simulations have been performed to study the effects of the gravitational and the centrifugal potentials on the stability of heated, incompressible Taylor-Couette flow. The flow is confined between two differentially heated, concentric cylinders, and the inner cylinder is allowed to rotate. The Navier-Stokes equations and the coupled energy equation are solved using a spectral method. To validate the code, comparisons are made with existing linear stability analysis and with experiments. The code is used to calculate the local and average heat transfer coefficients for a fixed Reynolds number (Re = 100) and a range of Grashof numbers. The investigation is primarily restricted to radius ratios 0.5 and 0.7 for fluids with Prandtl number of about 0.7. The variation of the local coefficients of heat transfer on the cylinder surface is investigated, and maps showing different stable states of the flow are presented. Results are also presented in terms of the equivalent conductivity, and show that heat transfer decreases with Grashof number in axisymmetric Taylor vortex flow regime, and increases with Grashof number after the flow becomes nonaxisymmetric.
Prediction of Milling Force Coefficients From Orthogonal Cutting Data
Authors: Budak E. , Altintas¸ Y. , Armarego E. J. A.
Published: February 2008

The mechanistic and unified mechanics of cutting approaches to the prediction of forces in milling operations are briefly described and compared. The mechanistic approach is shown to depend on milling force coefficients determined from milling tests for each cutter geometry. By contrast the unified mechanics of cutting approach relies on an experimentally determined orthogonal cutting data base (i.e., shear angle, friction coefficient and shear stress), incorporating the tool geometrical variables, and milling models based on a generic oblique cutting analysis. It is shown that the milling force coefficients for all force components and cutter geometrical designs can be predicted from an orthogonal cutting data base and the generic oblique cutting analysis for use in the predictive mechanistic milling models. This method eliminates the need for the experimental calibration of each milling cutter geometry for the mechanistic approach to force prediction and can be applied to more complex cutter designs. This method of milling force coefficient prediction has been experimentally verified when milling Ti6Al4V titanium alloy for a range of chatter, eccentricity and run-out free cutting conditions and cutter geometrical specifications.
On the Mechanism of Fluid Transport Across the Grinding Zone
Authors: Chang C. C. , Wang S. H. , Szeri A. Z.
Published: February 2008

By considering both hydrodynamic pressure and ram pressure effects on flow through a porous wheel, we construct here a predictive model for calculating the flow-rate of the cooling fluid through the grinding zone. The hydrodynamic pressure is computed by means of a modified Reynolds equation, with upstream boundary conditions supplied by the ram pressure. To find the tangential velocity, the radial velocity, the depth of penetration of the fluid into the wheel, and the flow rate through the grinding zone, we solve momentum and continuity equations for flow through porous media. An empirical correlation for permeability, containing two dimensionless parameters, is employed to provide correction for wheel surface roughness, yielding theoretical results that show good agreement with experimental data for both conventional and creep feed grinding.
Statistical Analysis of the Effects of Feed, Speed, and Wear on Hole Quality in Drilling
Authors: Furness R. J. , Wu C. L. , Ulsoy A. G.
Published: February 2008

A statistical analysis of hole quality in drilling was performed. Using standard twist drills, holes were drilled dry in hot rolled steel. The effects of feed and speed on the hole quality features of oversize, out-of-roundness, location error, angularity error, and taper were examined using a full factorial analysis of variance. The effects of workpiece surface condition, geometrical variation among drills, and drill wear were qualitatively observed. The results showed that feed and speed have a relatively small effect on the measured hole quality features. With the exception of hole location error, the hole quality was not predictably or significantly affected by the cutting conditions. Although these results were not expected, they have the important positive implication that production rates may be increased without sacrificing hole quality. The drilling feeds and speeds would be constrained by factors other than hole quality, such as drill wear, drill breakage, or force, torque, and power limits.
Modeling and Calibration of a Structured-light Optical CMM via Skewed Frame Representation
Authors: Che Chenggang , Ni Jun
Published: February 2008

A new tetrahedron-target-based approach is presented for the extrinsic calibration of a non-contact “light-striping” (structured light) optical coordinate measuring machine (CMM). The procedure makes automated on-line calibration possible. The system modeling is based on a unique skewed frame representation without the use of pin-hole camera model assumption. It is demonstrated that the extrinsic calibration matrix can be decomposed into two classes of transformations, one homogeneous and the other nonhomogeneous. The nonhomogeneous transformation between a Cartesian world frame and the non-Cartesian skewed sensor frame is studied. The sensitivity of the dimensional deformation on the two skew angles is simulated. Experimental studies show that a micron level calibration accuracy can be achieved.
A New Method to Leak Test Piping Joints
Authors: Jensen R. A. , Agnone A. M.
Published: February 2008

A new device to leak test piping joints is described. The test is done external to the unpressurized pipe while the joints are easily accessible. Typically it would be done before burial of the pipe and completion of the entire system. It is adaptable to metal or plastic piping systems and a variety of joint types. The device was tested on butt fusion welds in polyethylene piping, a type of pipe commonly used in the distribution systems of natural gas utilities. Test results show that the device is as reliable as a standard soap bubble test, or a pressure test, both of which require the system to be hermetically sealed and pressurized. A trained mechanic can do this test in the field in about 20 minutes.
Nesting of Complex 2-D Parts Within Irregular Boundaries
Authors: Lamousin H. J. , Waggenspack W. N. , Dobson G. T.
Published: February 2008

An algorithm is outlined for the nesting of complex parts onto resources with irregular boundaries. The algorithm adapts Albano and Sapuppo’s technique for nesting irregular profiles on rectangular resources using a novel placement procedure. Several techniques for improving computational efficiency are also described, including complex profile simplification using a modified convex hull strategy. The enhanced algorithm is applied to the nesting of irregular parts on both rectangular resources and within irregular shaped part voids as applied to the offshore platform and ship building industry.
Effects of Welding Conditions on Molten Drop Geometry in Arc Welding
Authors: Joo Tong M. , Yoo Choong D. , Lee Tae S.
Published: February 2008

The precise geometry of the molten drop attached to the electrode has substantial influence on the metal transfer. The geometry of the drop is a function of various parameters including the welding current and voltage, composition of shielding gas, electrode extension and material properties of the electrode. A new approach is proposed to enable an improved description of the molten drop drop in equilibrium. Among various forces which influence the profile of the static pendant drop, the surface tension, gravity and electromagnetic forces are considered to formulate the energy of the molten drop system. The present formulation leads to a numerical scheme, which is based on discretizing the volume of the drop with appropriate slabs. By minimizing the energy of the molten drop system, the proper shape of the drop is calculated. Explicit effects of a number of welding conditions parameters are evaluated. These include the welding current, molten drop volume and arc covered area. The model predictions are shown to be in satisfactory agreement with the available experimental data. These comparison exercises give credence to the robustness and accuracy of the present methodology.
Application of Reynolds Stress Modeling to Engine Flow Calculations
Authors: Lebre`re L. , Buffat M. , Le Penven L. , Dillies B.
Published: February 2008

To improve the prediction of turbulence inside internal combustion engines, a Reynolds stress turbulence model is implemented in the Kiva-II code. After a rapid description of the Launder-Reece-Rodi model (noted LRR), two validation test cases (the plane channel flow and the flow over a backward facing step) are presented. The advantages of a second order closure and the shortcomings of the LRR model are then analyzed. Finally, a simulation of an intake and compression stroke using both the standard k – ε model and the LRR model is described. As a precise knowledge of the velocity and turbulent fields near TDC is necessary for the prediction of the mixing and the combustion processes, we have analyzed the influence of the turbulence model on the flow field. Results are compared with experimental data and show a strong influence of the turbulence model even on the mean flow, especially at the end of the compression stroke (TDC).
Transient Gas-Liquid Flow in Upward Sloping Pipes, Approaching the Wavy-to-Slug Flow Transition
Authors: Grolman Eric , Fortuin Jan M. H.
Published: February 2008

A model is presented for transient, cocurrent gas-liquid pipe flow in the stratified-smooth and stratified-wavy flow regimes. It is based on the equations of continuity and motion in the direction of flow and results in two hyperbolic partial differential equations, which are solved numerically using the combined methods of lines (Schiesser, 1991) and characteristics (Stoker, 1957). In wavy gas-liquid pipe flow, three different interfacial areas and corresponding shear stresses are identified. Three friction-factor correlations were derived on the basis of an extensive set of 2500 steady-state measurements. The transient behavior of inclined gas-liquid pipe flow is successfully simulated and compares well with the results obtained from on-line measurements, right up to the onset of slug flow.
Study of Unsteady Orifice Flow Characteristics in Hydraulic Oil Lines
Authors: Washio Seiichi , Takahashi Satoshi , Yu Yonguang , Yamaguchi Satoshi
Published: February 2008

A technique to measure fluctuating differential pressures with high fidelity has been developed first. When applied to detecting differential pressures generated by an accelerated or decelerated liquid column, the technique turned out to be effective in finding unsteady flow rates. An experimental study has been carried out on periodically changing hydraulic oil flows through an orifice. The results support the validity of the traditional standpoint that characteristics of an unsteady orifice flow can be approximately represented by those of a steady-state one. When inspected in detail, however, a net pressure loss across an orifice in a periodical flow is delayed against a change of the flow rate. The resulting relation between the pressure loss and the flow rate describes a loop with a counter-clockwise hysteresis and a nonlinear twist along the steady-state one. Pressure recovery in a pulsating orifice flow varies with the flow rate almost along the steady-state relation, which is confirmed when the change is not fast.
Exploring a Three-Equation R–k–ε Turbulence Model
Authors: Goldberg U. C.
Published: February 2008

A low Reynolds number extension of the k–ε model is proposed and evaluated. This version has the following attributes: (a) it does not involve wall distance or normal-to-wall directionality; (b) it enforces time scale realisability by preventing it from falling below the Kolmogorov (dissipative eddy) scale, (ν/ε)1/2; (c) it employs a simple wall boundary condition for ε. The current approach requires an additional transport equation for the undamped eddy viscosity, R, thus the resulting model is of the three-equation variety. Since wall distance is not used, the proposed model is applicable to arbitrary flow topologies. Predictions using this model are compared with experimental data of several flow cases, with encouraging results.
An Investigation of Turbulent Taylor-Couette Flow Using Laser Doppler Velocimetry in a Refractive Index Matched Facility
Authors: Parker J. , Merati P.
Published: February 2008

Turbulent Taylor-Couette flow in an annulus formed by two concentric cylinders with dead end walls was investigated with Laser Doppler Velocimetry (LDV). The test apparatus was designed to provide refractive index matching between the annulus and a working fluid of aqueous sodium iodide. LDV was used to measure the three components of mean velocity and turbulence intensity, concentrating on end wall effects. The flow Taylor and Reynolds numbers were T = 2.107 × 109 and Re = 73,440, respectively. Vector plots of radial-axial component velocities and contour plots of component velocities and turbulence intensities reveal the Taylor vortex flow structure at this high Taylor number.
Computation of Unsteady Separated Flow Fields Using Anisotropic Vorticity Elements
Authors: Huyer S. A. , Grant J. R.
Published: February 2008

A novel computational methodology to compute two-dimensional unsteady separated flow fields using a vorticity based formulation is presented. Unlike traditional vortex methods, the elements used in this method are designed to take advantage of the natural anisotropy of most external flows. These vortex elements are disjoint and of compact support. The vorticity is uniform over rectangular elements whose initial thickness is set by a diffusion length scale. The elements are a mathematical construction which enables the vorticity of the flow to be created and followed numerically, and the Biot-Savart integral to be performed. This integral specifies the associated velocity field. Since the vorticity of a single element is of finite extent, the velocity associated with an element is given by a nonsingular expression. Viscous diffusion effects are modeled using random walk and the advection term is computed by transporting the vorticity elements with the local velocity field. Consequently, this Lagrangian mesh continually evolves through time. Since pressure does not explicitly appear in the formulation, surface pressures are computed using a stagnation enthalpy formulation. These elements are used to compute vorticity production, accumulation, transport and viscous diffusion mechanisms for unsteady separated flow fields past a pitching airfoil. Dynamic stall vortex initiation and development were examined and compared with existing experimental data. Surface pressure data and integrated force coefficient data were found to be in excellent agreement with experimental data. Effects of geometry were provided with baseline calculations of the unsteady flow past an impulsively started cylinder. Both qualitative and quantitative comparisons with experimental data for equivalent test conditions establish the applicability of this approach to depict unsteady separated flow fields.
Laminar Natural Convection Flow Over a Vertical Backward-Facing Step
Authors: Abu-Mulaweh H. I. , Armaly B. F. , Chen T. S.
Published: February 2008

Measurements and predictions of laminar boundary-layer air flow in natural convection over a vertical two-dimensional backward-facing step are reported. The upstream and downstream walls and the step itself were heated to a uniform and constant temperature. The experiment was carried out for the ranges of step heights 3.5 mm ≤ s ≤ 9 mm, temperature differences of 5.8°C ≤ ΔT ≤ 23°C between the heated wall and the free stream (corresponding to 2.238 × 107 < Grxi < 8.877 × 107), and reference velocities of 0.24 m/s ≤ u* ≤ 0.47 m/s. Laser-Doppler velocimeter and cold-wire anemometer were utilized to measure, respectively, the velocity and the temperature distributions simultaneously. Flow visualization was also performed to determine the reattachment length. Measurements compare favorably with predictions. These results reveal that the step height significantly affects the velocity and temperature distributions, the friction coefficient, and the rate of heat transfer downstream of the backward-facing step.
Nonlinear Aspects of High Heat Flux Nucleate Boiling Heat Transfer
Authors: Sadasivan P. , Unal C. , Nelson R.
Published: February 2008

This paper deals with potential nonlinear effects in nucleate boiling systems as a result of the behavior of individual nucleation sites on the heater surface. This requires detailed microscopic modeling of the surface. A computational model has been formulated for this purpose. The model addresses the three-dimensional transient conduction heat transfer process within the problem domain comprised of the macrolayer and heater. Hydrodynamic effects are represented through boundary conditions. Individual nucleation sites are activated or deactivated depending on the thermal conditions that prevail at the site. The model has been used to examine the behavior of sites on a realistic heater surface. The results indicate that significant spatial and temporal temperature variations can occur on the surface, and that thermal interactions among sites can result in some sites operating intermittently. Surface-averaged temperatures show nonlinear period-doubling behavior. A chaotic case was found. Qualitative comparisons are made to both local instantaneous temperature measurements and recent experiments that showed chaotic behavior. We believe that such nonlinear behavior is one of the reasons that mechanistic predictive capabilities for the boiling process have remained elusive.
A Control Volume Approach for Investigating Forces on a Departing Bubble Under Subcooled Flow Boiling
Authors: Kandlikar S. G. , Stumm B. J.
Published: February 2008

This paper presents the theoretical and experimental work conducted on nucleating vapor bubbles in subcooled flow boiling of water at atmospheric pressure and 60°C in a 3 mm × 50 mm × 400 mm long rectangular channel. A new model is developed for analyzing forces acting on the vapor bubble under pseudo-static conditions corresponding to the thermally controlled region of bubble growth. The model considers two separate control volumes for the front and rear regions of the bubble. The forces due to surface tension, buoyancy, drag, pressure difference, and momentum changes are considered, and the effects of different upstream and downstream contact angles are included. These angles and the departure bubble diameters are measured from the top and the side views of bubbles recorded on a video camera through a microscope. The new model and the experimental study confirm that the bubble removal in flow boiling for small diameter bubbles investigated in this study (less than 500 μm) is initiated at the front edge of the bubble through a sweep-removal mechanism. Previous models available in the literature consider a force balance on the entire bubble, and are therefore unable to address the effect of a significant reduction in the component of the surface tension force in the flow direction at the leading edge caused by an increase in the upstream contact angle.
Measurement of Cyclic Biaxial Elastoplastic Stresses at Notch Roots
Authors: Yang C. H. , Sharpe W. N.
Published: February 2008

A straightforward procedure is demonstrated for measuring local cyclic elastoplastic biaxial stresses at notch roots. First, the biaxial cyclic strains are measured over short gage lengths (150 or 200 micrometers) with a laser-based strain measuring system. Then, cyclic stresses are computed from those measured strains by using an elastoplastic constitutive model. The material selected for this study is HY-80 steel which has a fine grain size and is isotropic. Double-notched specimens were prepared with two different notch geometries: a U-shaped notch with a 4.76 mm radius and a V-shaped notch with a 1.0 mm radius. Two thicknesses, 2.54 and 12.7 mm, were tested for each notch geometry to produce four different amounts of notch constraint. The results of cyclic biaxial strain measurements show good reproducibility. Stress computations based on two different constitutive models were used to compute stresses for the first cycle and a stable cycle. One of the constitutive models is the classical J2flow theory and the other is a two-surface cyclic plasticity model. The results computed using these two models show good agreement with each other. The measured stresses show the effect of constraint on the elastoplastic behavior at notch roots under cyclic loading conditions.
Rotation of a Cylinder in a Casing at Zero Reynolds Number
Authors: Wang C. Y.
Published: February 2008

A finite solid cylinder rotates inside a larger, fluid-filled cylindrical casing. The Stokes equation is solved by an efficient method using domain decomposition, eigenfunction expansion, and collection. The resistive torque is found as a function of the geometric parameters. The torque due to the rotation of a finite cylinder in an infinite fluid is extrapolated.
On the Inverse Problem of Rectangular Plates Subjected to Elastic Impact, Part II: Experimental Verification and Further Applications
Authors: Yen Ching-Shih , Wu Enboa
Published: February 2008

Experimental verification of the method developed in Part 1 to identify both the impact location and the force history from strain responses on a rectangular plate was performed. Results showed the validity of the method in a real impact event. Also, a method was developed to further identify the initial velocity and the mass of an impactor by which a transverse impact was induced. This was accomplished by solving algebraic equations obtained from the assumption that the lateral displacements of both the impactor and the plate at the impact point were coincident during the contact period. Moreover, the inverse problem using incomplete response signals as the given data was investigated. A procedure to temporarily reconstruct the lost portions of the recorded signals was first presented, and the identification problem could then be solved by similar methods as that used for the complete response signals. Experimental verification was also performed. The agreement between the measured and the identified results was very satisfactory.
Free Vibration of a Class of Homogeneous Isotropic Solids
Authors: Young P. G. , Dickinson S. M.
Published: February 2008

A Ritz approach, with simple polynomials as trial functions, is used to obtain the natural frequencies of vibration of a class of solids. Each solid is modeled by means of a segment which is described in terms of Cartesian coordinates and is bounded by the yz, zx, and xy orthogonal coordinate planes as well as by a fourth curved surface, which is defined by a polynomial expression in the coordinates x, y, and z. By exploiting symmetry, a number of three-dimensional solids previously considered in the open literature are treated, including a sphere, a cylinder and a parallelepiped. The versatility of the approach is then demonstrated by considering several solids of greater geometric complexity, including an ellipsoid, an elliptical cylinder, and a cone.
Anisotropic Yield Surfaces Based on Elastic Projection Operators
Authors: Schreyer H. L. , Zuo Q. H.
Published: February 2008

Although most materials are anisotropic to some extent, most yield surfaces are either chosen to be isotropic or to be a smooth anisotropic surface with no connection to the elastic anisotropic features. Here, the elastic projection operators obtained from the spectral decomposition of the elasticity tensor are used to define anisotropic yield surfaces with a yield surface defined for each of the projection operators. The advantages of the approach are (1) plastic deformation modes are associated with the elastic anisotropic behavior, (2) the spectral decomposition of the tangent tensor is readily available for a bifurcation analysis, (3) the composite yield surface has vertices which are thought to be important for predicting plastic buckling, and (4) the contributions to plastic deformations from each yield surface are uncoupled. The result is a theory that is actually quite simple but yet reflects some of the observed features for materials to yield in specific modes.
Quantum Gases
Authors: Bloch Immanuel
Published: February 2008

Ultracold quantum gases are proving to be a powerful model system for strongly interacting electronic many-body systems. This Perspective explores how such atomic ensembles can help to unravel some of the outstanding open questions in the field.
Proton Radiography of Inertial Fusion Implosions
Authors: Rygg J. R. , Séguin F. H. , Li C. K. , Frenje J. A. , Manuel M. J.-E. , Petrasso R. D. , Betti R. , Delettrez J. A. , Gotchev O. V. , Knauer J. P. , Meyerhofer D. D. , Marshall F. J. , Stoeckl C. , Theobald W.
Published: February 2008

A distinctive way of quantitatively imaging inertial fusion implosions has resulted in the characterization of two different types of electromagnetic configurations and in the measurement of the temporal evolution of capsule size and areal density. Radiography with a pulsed, monoenergetic, isotropic proton source reveals field structures through deflection of proton trajectories, and areal densities are quantified through the energy lost by protons while traversing the plasma. The two field structures consist of (i) many radial filaments with complex striations and bifurcations, permeating the entire field of view, of magnetic field magnitude 60 tesla and (ii) a coherent, centrally directed electric field of order 10
9
volts per meter, seen in proximity to the capsule surface. Although the mechanism for generating these fields is unclear, their effect on implosion dynamics is potentially consequential.
Ceramide Triggers Budding of Exosome Vesicles into Multivesicular Endosomes
Authors: Trajkovic Katarina , Hsu Chieh , Chiantia Salvatore , Rajendran Lawrence , Wenzel Dirk , Wieland Felix , Schwille Petra , Brügger Britta , Simons Mikael
Published: February 2008

Intraluminal vesicles of multivesicular endosomes are either sorted for cargo degradation into lysosomes or secreted as exosomes into the extracellular milieu. The mechanisms underlying the sorting of membrane into the different populations of intraluminal vesicles are unknown. Here, we find that cargo is segregated into distinct subdomains on the endosomal membrane and that the transfer of exosome-associated domains into the lumen of the endosome did not depend on the function of the ESCRT (endosomal sorting complex required for transport) machinery, but required the sphingolipid ceramide. Purified exosomes were enriched in ceramide, and the release of exosomes was reduced after the inhibition of neutral sphingomyelinases. These results establish a pathway in intraendosomal membrane transport and exosome formation.
Deeply Inverted Electron-Hole Recombination in a Luminescent Antibody-Stilbene Complex
Authors: Debler Erik W. , Kaufmann Gunnar F. , Meijler Michael M. , Heine Andreas , Mee Jenny M. , Pljevaljčić Goran , Di Bilio Angel J. , Schultz Peter G. , Millar David P. , Janda Kim D. , Wilson Ian A. , Gray Harry B. , Lerner Richard A.
Published: February 2008

The blue-emissive antibody EP2-19G2 that has been elicited against
trans
-stilbene has unprecedented ability to produce bright luminescence and has been used as a biosensor in various applications. We show that the prolonged luminescence is not stilbene fluorescence. Instead, the emissive species is a charge-transfer excited complex of an anionic stilbene and a cationic, parallel π-stacked tryptophan. Upon charge recombination, this complex generates exceptionally bright blue light. Complex formation is enabled by a deeply penetrating ligand-binding pocket, which in turn results from a noncanonical interface between the two variable domains of the antibody.
Membrane Proteins of the Endoplasmic Reticulum Induce High-Curvature Tubules
Authors: Hu Junjie , Shibata Yoko , Voss Christiane , Shemesh Tom , Li Zongli , Coughlin Margaret , Kozlov Michael M. , Rapoport Tom A. , Prinz William A.
Published: February 2008

The tubular structure of the endoplasmic reticulum (ER) appears to be generated by integral membrane proteins, the reticulons and a protein family consisting of DP1 in mammals and Yop1p in yeast. Here, individual members of these families were found to be sufficient to generate membrane tubules. When we purified yeast Yop1p and incorporated it into proteoliposomes, narrow tubules (∼15 to 17 nanometers in diameter) were generated. Tubule formation occurred with different lipids; required essentially only the central portion of the protein, including its two long hydrophobic segments; and was prevented by mutations that affected tubule formation in vivo. Tubules were also formed by reconstituted purified yeast Rtn1p. Tubules made in vitro were narrower than normal ER tubules, due to a higher concentration of tubule-inducing proteins. The shape and oligomerization of the “morphogenic” proteins could explain the formation of the tubular ER.
Supersolidity
Authors: Chan M. H. W.
Published: February 2008

The observation of nonclassical rotational inertia (NCRI) by the torsional oscillator in 2004 gave rise to a renaissance in the study of solid helium-4. Recent theoretical and experimental studies found evidence that disorder in the solid plays a key role in enabling superfluidity. A recent experiment found a marked increase in the shear modulus that shares the same temperature and helium-3 impurity concentration dependence as that of NCRI. This correlation indicates that the onset of superfluidity requires the pinning and stiffening of the dislocation network by helium-3.
Efficacy of SPK-843, a Novel Polyene Antifungal, in a Murine Model of Systemic Cryptococcosis
Authors: Kakeya Hiroshi , Miyazaki Yoshitsugu , Senda Hisato , Kobayashi Tsutomu , Seki Masafumi , Izumikawa Koichi , Yamamoto Yoshihiro , Yanagihara Kazunori , Tashiro Takayoshi , Kohno Shigeru
Published: February 2008

SPK-843, a new polyene antifungal, possessed efficacy in a murine model of systemic infection caused by
Cryptococcus neoformans
. The administration of 4.0 mg/kg SPK-843 led to better survival prolongation and fungal reduction than those observed with the administration of 0.7 mg/kg amphotericin B and 80 mg/kg fluconazole (
P
< 0.001), without histopathological renal changes.
Timing of Specimen Collection for Blood Cultures from Febrile Patients with Bacteremia
Authors: Riedel Stefan , Bourbeau Paul , Swartz Brandi , Brecher Steven , Carroll Karen C. , Stamper Paul D. , Dunne W. Michael , McCardle Timothy , Walk Nathan , Fiebelkorn Kristin , Sewell David , Richter Sandra S. , Beekmann Susan , Doern Gary V.
Published: February 2008

Bloodstream infections are an important cause of morbidity and mortality. Physician orders for blood cultures often specify that blood specimens be collected at or around the time of a temperature elevation, presumably as a means of enhancing the likelihood of detecting significant bacteremia. In a multicenter study, which utilized retrospective patient chart reviews as a means of collecting data, we evaluated the timing of blood culture collection in relation to temperature elevations in 1,436 patients with bacteremia and fungemia. The likelihood of documenting bloodstream infections was not significantly enhanced by collecting blood specimens for culture at the time that patients experienced temperature spikes. A subset analysis based on patient age, gender, white blood cell count and specific cause of bacteremia generally also failed to reveal any associations.
RNase-Resistant Virus-Like Particles Containing Long Chimeric RNA Sequences Produced by Two-Plasmid Coexpression System
Authors: Wei Yuxiang , Yang Changmei , Wei Baojun , Huang Jie , Wang Lunan , Meng Shuang , Zhang Rui , Li Jinming
Published: February 2008

RNase-resistant, noninfectious virus-like particles containing exogenous RNA sequences (armored RNA) are good candidates as RNA controls and standards in RNA virus detection. However, the length of RNA packaged in the virus-like particles with high efficiency is usually less than 500 bases. In this study, we describe a method for producing armored L-RNA. Armored L-RNA is a complex of MS2 bacteriophage coat protein and RNA produced in
Escherichia coli
by the induction of a two-plasmid coexpression system in which the coat protein and maturase are expressed from one plasmid and the target RNA sequence with modified MS2 stem-loop (pac site) is transcribed from another plasmid. A 3V armored L-RNA of 2,248 bases containing six gene fragments—hepatitis C virus, severe acute respiratory syndrome coronavirus (SARS-CoV1, SARS-CoV2, and SARS-CoV3), avian influenza virus matrix gene (M300), and H5N1 avian influenza virus (HA300)—was successfully expressed by the two-plasmid coexpression system and was demonstrated to have all of the characteristics of armored RNA. We evaluated the 3V armored L-RNA as a calibrator for multiple virus assays. We used the WHO International Standard for HCV RNA (NIBSC 96/790) to calibrate the chimeric armored L-RNA, which was diluted by 10-fold serial dilutions to obtain samples containing 10
6
to 10
2
copies. In conclusion, the approach we used for armored L-RNA preparation is practical and could reduce the labor and cost of quality control in multiplex RNA virus assays. Furthermore, we can assign the chimeric armored RNA with an international unit for quantitative detection.
Coronavirus Infection Modulates the Unfolded Protein Response and Mediates Sustained Translational Repression
Authors: Bechill John , Chen Zhongbin , Brewer Joseph W. , Baker Susan C.
Published: February 2008

During coronavirus replication, viral proteins induce the formation of endoplasmic reticulum (ER)-derived double-membrane vesicles for RNA synthesis, and viral structural proteins assemble virions at the ER-Golgi intermediate compartment. We hypothesized that the association and intense utilization of the ER during viral replication would induce the cellular unfolded protein response (UPR), a signal transduction cascade that acts to modulate translation, membrane biosynthesis, and the levels of ER chaperones. Here, we report that infection by the murine coronavirus mouse hepatitis virus (MHV) triggers the proximal UPR transducers, as revealed by monitoring the IRE1-mediated splicing of XBP-1 mRNA and the cleavage of ATF6α. However, we detected minimal downstream induction of UPR target genes, including ERdj4, ER degradation-enhancing α-mannosidase-like protein, and p58
IPK
, or expression of UPR reporter constructs. Translation initiation factor eIF2α is highly phosphorylated during MHV infection, and translation of cellular mRNAs is attenuated. Furthermore, we found that the critical homeostasis regulator GADD34, which recruits protein phosphatase 1 to dephosphorylate eIF2α during the recovery phase of the UPR, is not expressed during MHV infection. These results suggest that MHV modifies the UPR by impeding the induction of UPR-responsive genes, thereby favoring a sustained shutdown of the synthesis of host cell proteins while the translation of viral proteins escalates. The role of this modified response and its potential relevance to viral mechanisms for the evasion of innate defense signaling pathways during coronavirus replication are discussed.
Dominant Negative Inhibition of Human Immunodeficiency Virus Particle Production by the Nonmyristoylated Form of Gag
Authors: Kawada Shigeo , Goto Toshiyuki , Haraguchi Hiyori , Ono Akira , Morikawa Yuko
Published: February 2008

Myristoylation of human immunodeficiency virus (HIV) Gag protein is essential for membrane targeting of Gag and production of viral particles. We show here that coexpression of wild-type and nonmyristoylated forms of HIV Gag resulted in severe inhibition of viral particle production, indicating that the nonmyristoylated counterpart had a dominant negative effect on particle release. When coexpressed, the nonmyristoylated Gag partially incorporated into membrane and lipid raft fractions, likely through coassembly with the wild-type Gag. The membrane and raft associations of the wild-type Gag appeared unaffected, and yet particle production was severely impaired. When viral particles produced from the coexpressing cells were analyzed, the wild-type Gag was more abundant than the nonmyristoylated Gag. Confocal microscopy showed that both forms of Gag were diffusely distributed in the cytoplasm of coexpressing cells but that a portion of the wild-type Gag population was accumulated in EEA1- and CD63-positive endosomes. The intracellular accumulation of Gag was more frequently observed at late time points. The Gag accumulation was also observed on the cell surface protrusion. Electron microscopy of the coexpressing cells revealed budding arrest phenotypes, including the occurrence of interconnected virions on the plasma membrane, and intracellular budding. We also show that the inhibition of particle production and the Gag accumulation to endosomes were suppressed when the nucleocapsid (NC) domain was deleted from the nonmyristoylated Gag, although the NC-deleted Gag was still capable of coassembly. Overall, our data indicate that coassembly with the nonmyristoylated Gag impairs HIV particle release, a phenomenon that may involve NC-mediated Gag-Gag interaction.