Search

This is an analytical study on Stokes flow through a tube of which the wall is patterned with periodic transverse grooves filled with an inviscid gas. In one period of the pattern, the fluid flows through an annular groove and an annular rib subject to no-shear and no-slip boundary conditions, respectively. The fluid may penetrate the groove to a certain depth, so there is an abrupt change in the cross section of flow through the two regions. The problem is solved by the method of domain decomposition and eigenfunction expansions, where the coefficients of the expansion series are determined by matching velocities, stress, and pressure on the domain interface. The effective slip length and pressure distributions are examined as functions of the geometrical parameters (tube radius, depth of fluid penetration into grooves, and no-shear area fraction of the wall). Particular attention is paid to the limiting case of flow through annular fins on a no-shear wall. Results are generated for the streamlines, resistance, and pressure drop due to the fins. It is found that the wall condition, whether no-shear or no-slip, will be immaterial when the fin interval is smaller than a certain threshold depending on the orifice ratio. [DOI: 10.1115/1.4002654]

The vibration of a free standing column under its own weight is studied. An intermediate support increases the fundamental frequency. The optimum location for the support is determined for clamped-free, pinned-free, and sliding-free columns. The problem is integrated by a simple accurate initial value method. Approximate and exact relations are also found. [DOI: 10.1115/1.4001511] Keywords: column, vibration, heavy, support

An infinite beam attached to an elastic foundation is buckled by an axial force. The beam is weakened by one or more joints or partial cracks. The governing equations are solved analytically and an exact nonlinear characteristic equation gives the buckling criterion. It is found that the buckling force depends on the foundation stiffness and the rotational resistance of the joints. The buckling modes are complex, and may be either antisymmetric or symmetric. DOI: 10.1061/(ASCE)EM.1943-7889.0000097 CE Database subject headings: Buckling; Beams; Elastic foundation; Joints. Author keywords: Buckling; Beam; Elastic foundation; Joint.

The authors analyzed data from the Women's Health Initiative (WHI) Calcium and Vitamin D Supplementation Trial (CAD) to learn more about factors affecting adherence to clinical trial study pills (both active and placebo). Most participants (36,282 postmenopausal women aged 50-79 years) enrolled in CaD 1 year after joining either a hormone trial or the dietary modification trial of WHI. The WHI researchers measured adherence to study pills by weighing the amount of remaining pills at an annual study visit; adherence was primarily defined as taking [greater than or equal to] 80% of the pills. The authors in this study examined a number of behavioral, demographic, procedural, and treatment variables for association with study pill adherence. They found that relatively simple procedures (ie, phone contact early in the study [4 weeks post randomization] and direct social contact) later in the trial may improve adherence. Also, at baseline, past pill-use experiences, personal supplement use, and relevant symptoms may be predictive of adherence in a supplement trial. Index Terms: adherence, calcium supplementation, clinical trial, women, In the Women's Health Initiative (WHI) Calcium and Vitamin D Supplementation Trial (CAD), an intention-to-treat analysis showed that active treatment did not significantly reduce hip fracture, which was the primary [...]

The flow through a symmetric, lens-shaped duct is solved by accurate Ritz and perturbation methods. The flow rate (resistance) is found for various thickness ratios. The flow rate is much better than friction factor-Reynolds number product as an index for duct flows, especially for the lens duct studied in this paper. The results are also important for the torsion of lens-shaped bars.

The buckling of a column affected by both an internal hinge and an elastic foundation is studied analytically. It is found that the elastic foundation raises the buckling force, but nonlinearly. The optimum locations for the hinge are determined.

In most publications on vibration of annular plates, the natural frequencies are only presented for inner radius as small as one-tenth of its outer radius, but there are hardly any results presented for cores smaller than this inner radius value. This is attributed to severe scaling problems upon using numerical techniques to obtain the fundamental frequency of plates when the inner radius becomes very small. This study aims to solve this class of plate vibration problem where the annular plates are thick and their core radii are much less than one-tenth of the outer radius. The analysis involved using the Mindlin plate theory so as to allow for the effects of transverse shear deformation and rotary inertia and the truncation of the terms in the Bessel functions defining the characteristic equations in order to overcome the scaling problem. Eventually, the fundamental frequency of a thick annular plate could be deduced as finite or zero when the inner radius approaches zero. DOI: 10.1061/(ASCE)0733-9399(2007)133:5(597) CE Database subject headings: Vibration; Plates; Frequency.

Missing covariate data are common in epidemiologic studies and disease prevention trials. In this article regression parameter estimation in the Cox proportional hazards model is considered when certain covariates are observed for all study subjects and other covariate data are collected only for a subset. The article presents both simple weighted and kernel-assisted fully augmented weighted estimators that use the partially incomplete data nonparametrically. We use nonparametric methods to estimate selection probabilities in the simple weighted estimating functions. We also use nonparametric kernel smoothing techniques to estimate certain conditional expectations in fully augmented weighted estimating functions. The proposed methods are nonparametric in the sense that they require neither a model for the missing-data mechanism nor specification of the conditional distribution of missing covariates given observed covariates. These estimators allow the missing-data mechanism to depend on outcome variables and observed covariates, and they are applicable to various cohort sampling procedures, including case-cohort and nested case-control designs. We show that the simple and the kernel-assisted fully augmented weighted estimators are typically consistent and asymptotically normal. Moreover, the proposed estimators are more efficient than the simple weighted estimator with the inverse of true selection probability as weight. They also correct the bias of estimates from analysis of the complete data alone when the missing-data mechanism depends on outcome variables. In addition, when covariates are time-independent, certain simple weighted estimators are shown to be asymptotically equivalent to the kernel-assisted fully augmented weighted estimators. Moderate sample size performance of the estimators is examined via simulation and by application to two real datasets. KEY WORDS: Case-cohort; Kernel smoother; Missing covariate data; Nested case-control; Nonparametric method; Weighted estimating equation.

The slow film flow down a doubly periodic bumpy surface is studied for the first time. Perturbations on the primary variables and the complex boundary conditions lead to a system of successive equations. The secondary flow and the free surface shape depend on the wavelength of the bumps and a surface tension-inclination parameter There exists an optimum aspect ratio of the protuberances for maximal flow rate. [DOI: 10.1115/1.2060730]

The buckling problem of a column weakened at an interior location is studied for the first time. The weakness is modeled by a rotationally restrained junction. Exact buckling load values are obtained for the weakened column with various end conditions. Depending on the end conditions of the column, the buckling loads show sensitivity (and insensitivity) to junction location and rotational stiffness. The optimum location of the junction could be at the midpoint, at the ends, or somewhere in between. CE Database subject headings: Buckling; Columns; Joints.