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This paper examines applicability and limitations of simplified models of elastic cylindrical shells for carbon nanotubes. The simplified models examined here include Donnell equations and simplified Flugge equations characterized by an uncoupled single equation for radial deflection. These simplified elastic shell equations are used to study static buckling and free vibration of carbon nanotubes, with detailed comparison to exact Flugge equations of cylindrical shells. It is shown that all three elastic shell models are in excellent agreement (with relative errors less than 5%) with recent molecular dynamics simulations for radial breathing vibration modes of carbon nanotubes, while reasonable agreements for various buckling problems have been reported previously for Donnell equations. For general cases of buckling and vibration, the results show that the simplified Flugge model, which retains mathematical simplicity of Donnell model, is consistently in better agreement with exact Flugge equations than Donnell model, and has a significantly enlarged range of applicability for carbon nanotubes. In particular, the simplified Flugge model is applicable for carbon nanotubes (with relative errors around 10% or less) in almost all cases of physical interest, including some important cases in which Donnell model results in much larger errors. These results are significant for further application of elastic shell models to carbon nanotubes because simplified shell models, characterized by a single uncoupled equation for radial deflection, are particularly useful for multiwall carbon nanotubes of large number of layers.

The difference equations governing the rotation of a segmented rod under axial force is formulated. The stability boundaries are found to be highly dependent on the number of links, the rotation rate and the compressive force. For a large number of links, the result approaches to that of the continuous elastic rod through some fractional power. The analysis is applicable to segmented drill shafts.

Blood flow in small curved tubes is modeled by the two-fluid model where a relatively cell-free fluid layer envelops a fluid core of higher viscosity. The parameters in the model are successfully curve fitted to experimental data for straight tubes. The curved tube equations are then solved by perturbation theory. It was found that curvature in general lowers the tube resistance, but increases the shear stress near the inside wall

This paper presents the Ritz method for buckling analysis of rectangular plates with an internal line hinge. The Ritz method involves the domain decomposition method to cater for the discontinuity of slope at the hinge line. The correctness of the Ritz formulation and solutions is confirmed by the exact solutions derived using the Levy method for plates with two opposite sides simply supported. Based on the Ritz method, buckling factors are generated for rectangular plates of various aspect ratios, hinge locations, and support and loading conditions. DOI: 10.1061/(ASCE)0733-9399(2003) 129:6(683) CE Database subject headings: Buckling; Plates; Hinges.

The viscous flow in a curved tube with partial slip on the boundary occurs in many practical situations. The problem is formulated in curved tube coordinates and solved by perturbation for small curvature. The mutual interaction of slip, curvature, and inertia causes changes in the axial flow, surface shear, and secondary flow. It is found that the net flow increases with increased slip and decreased Reynolds numbers.

Presented herein are exact stability criteria for Euler columns under intermediate and end concentrated axial loads. The stability criteria cover all combinations of classical boundary conditions, arbitrary location of the intermediate concentrated load, and ratios of the magnitude of the intermediate load to the end load. Also included is the buckling problem of a new class of Euler columns where one segment is in tension while the other segment in compression. CE Database subject headings: Columns; Buckling; Axial loads; Stability criteria.

Cutting test specimens from molded plaques is commonly used in mechanical testing. The mechanical properties of these cut specimens may be affected by cutting process as it could introduce extrinsic [...]

In this study, a high fuel utilization approach for polymer electrolyte fuel cells (PEFC) is proposed and studied experimentally. This approach uses an ultra-low hydrogen stoichiometry supply (i.e., ξa = 1.02) meanwhile sustaining stable cell performance. Systematic experiments showed the feasibility of high fuel utilization approach under different pressures and hydrogen/air inlet humidification conditions. It is indicated that the fuel cell is able to provide stable performance at a real fuel stoichiometry ξa = 1.02 under high-current density operation. For all the tests at ξa/ξc = 1.5/2.0 or 1.02/2.0, there exist unstable operation regimes typically in low power conditions. The instability as a result of flooding is affected mainly by air stoichiometry and less by fuel stoichiometry. [ABSTRACT FROM AUTHOR]

The radially symmetric, steady, slow viscous slip flow through a curved duct of rectangular cross section is studied. The Stokes equation is solved using eigenfunction expansions and Navier's slip condition. As slip is increased, the location of the maximum velocity moves from near center to the outer wall. The minimum velocity occurs at the inside corners. It is found that both slip and curvature promote the flow rate but not necessarily the mean velocity. [DOI: 10.1115/1.1445142]

This paper is concerned with the determination of the funicular shapes of submerged arches. A universal set of curves is generated, from which the shapes of funicular arches under hydrostatic forces may be extracted. The method of extraction of the funicular arch shape depends on the specified design parameters such as the water depth, arch height, and arch span. More importantly, this study shows that depending on the specification of the design parameters, there may not exist any funicular arch solution or there may be occasions in which there could be more than one funicular arch solution for the problem. DOI: 10.1061/(ASCE)0733-9445(2002)128:2(266) CE Database keywords: Arches; Hydrostatic pressure; Structural design.

Yijian Huang is Assistant Member (E-mail: eugene@fhcrc.org) and C. Y. Wang is Associate Member (E-mail: cywang@fhcrc.org), Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109. This research was partially supported by the National Institutes of Health funds A129168, AG15026, and CA53996. The authors thank Professor Victor DeGruttola for providing the AIDS data analyzed in Section 6.2. They also gratefully acknowledge insightful and constructive comments from the reviewers, which led to improvement in the presentation., ********** KEY WORDS: Conditional score; Corrected score; Estimating equation; Generalized linear model; Instrumental Variable; Measurement error; Nonparametric correction; Parametric correction; Replication data. We propose consistent functional methods for logistic regression [...]

Onset of convection in a fluid-saturated porous layer above a solid layer heated by constant flux is discussed. Thermoconvective stability of a porous layer over a solid layer is important in ocean floor hydrothermal systems and thermal insulation problems. The critical Rayleigh number for the porous layer increases with solid-layer thickness. That is the reverse of the case for constant-temperature heating. Topics include the impermeable top and constant-pressure top cases. Results are compared to those of R. McKibbin et al., 1983.

The torsion of a compound bar is studied by eigenfunction expansion and collocation. The bar has a regular polygonal cross section bonded with a circular core of different material. It is found that the torque is insensitive to the core size when the latter is less than 0.2 of the maximum dimension. Otherwise, the torque is highly dependent on the core size ratio and the shear moduli ratio of the two materials. The results obtained should be useful in the design of torsion members.

A study on dendritic alloy solidification was conducted to investigate the grain structural development and columnar-to-equiaxed transition during directional dendritic solidification using the NH4Cl-H2O model alloy. The experiment is the first phase of a continuing effort to ultimately model and simulate the columnar-to-equiaxed transition in the presence of crystal sedimentation and melt convection using a multiphase model developed by two researchers in a previous study.

Research is conducted to examine the thermal conductivity of composite materials. The process involves the development of closed-form solutions of the thermal effect of a composite with a single thin fiber. Numerical results for a composite containing an infinite staggered array of thin strips is then presented. Results reveal that stagger may be used to increase or decrease conducting without changing the amount of materials in the composite.