BackgroundWe surveyed HIV patients with late-stage disease in southern Vietnam to determine if barriers to access and service quality resulted in late HIV testing and delays from initial diagnosis to entry into HIV care.Methodology196 adult patients at public HIV clinics with CD4 counts less than 250 cells/mm3 completed a standardized questionnaire. We used multivariate analysis to determine risk factors for delayed entry into care, defined as >3 months time from diagnosis to registration.ResultsCommon reasons for delayed testing were feeling healthy (71%), fear of stigma and discrimination in the community (43%), time conflicts with work or school (31%), did not want to know if infected (30%), and fear of lack of confidentiality (27%). Forty-five percent of participants delayed entry into care with a median CD4 count of 65 cells/mm3. The most common reasons for delayed entry were feeling healthy (51%), fear of stigma and discrimination in the community (41%), time conflicts with work or school (33%), and fear of lack of confidentiality (26%). Independent predictors for delayed entry were feeling healthy (aOR 3.7, 95% CI 1.5–9.1), first positive HIV test at other site (aOR 2.9, CI 1.2–7.1), history of injection drug use (IDU) (aOR 2.9, 95% CI 1.1–7.9), work/school conflicts (aOR 4.3, 95% CI 1.7–10.8), prior registration at another clinic (aOR 77.4, 95% CI 8.6–697), detention or imprisonment (aOR 10.3, 95% CI 1.8–58.2), and perceived distance to clinic (aOR 3.7, 95% CI 1.0–13.7).ConclusionDelayed entry into HIV care in Vietnam is common and poses a significant challenge to preventing AIDS and opportunistic infections, decreasing mortality, and reducing HIV transmission. Improved linkages between testing and care are needed, particularly for patients who feel healthy, as well as incarcerated and drug-using populations who may face structural and social barriers to accessing care.

Buckling and postbuckling behaviors of toroidal shell segment reinforced by single-walled carbon nanotubes, surrounded by an elastic medium, exposed to a thermal environment and subjected to uniform external pressure are investigated in this paper. Carbon nanotubes are reinforced into matrix phase by uniform distribution or functionally graded distribution along the thickness direction. Material properties of constituents are assumed to be temperature dependent, and the effective properties of carbon nanotube reinforced composite are estimated by extended mixture rule through a micromechanical model. Governing equations for toroidal shell segments are based on the classical thin shell theory taking into account geometrical nonlinearity, surrounding elastic medium, and varying degree of tangential constraints of edges. Three-term solution of deflection and stress function are assumed to satisfy simply supported boundary condition, and Galerkin method is applied to derive nonlinear load–deflection relation from which buckling loads and postbuckling equilibrium paths are determined. Analysis shows that tangential edge restraints have significant effects on nonlinear buckling of carbon nanotube reinforced composite toroidal shell segments. In addition, the effects of carbon nanotube volume fraction, distribution types, geometrical ratios, elastic foundation, and thermal environments on the buckling and postbuckling behaviors of carbon nanotube reinforced composite toroidal shell segments are analyzed and discussed.

Buckling and postbuckling behavior of carbon nanotube‐reinforced composite (CNTRC) cylindrical shells with tangentially restrained edges exposed to preexisting temperature conditions and subjected to uniform external pressure are presented in this analytical study. Three temperature conditions considered are that uniform temperature rise, through‐the‐thickness temperature gradient, and in‐plane linear temperature distribution. Carbon nanotubes (CNTs) are reinforced into matrix phase through uniform or functionally graded distributions. The properties of CNTs and matrix are assumed to be temperature‐dependent and effective moduli of CNTRC are determined according to extended rule of mixture. Governing equations are based on the classical shell theory taking into account Von Karman‐Donnell nonlinearity and elasticity of tangential constraints of edges. Multi‐term solutions of deflection and stress function are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to derive closed‐form expression of nonlinear pressure‐deflection relation from which critical buckling pressures and postbuckling paths are determined. A variety of numerical examples are given and interesting remarks are achieved. Due to practical situations of boundary edges and various temperature conditions, this paper aims to analyze separate and combined influences of tangential edge constraints and preexisting temperatures on thermomechanical postbuckling behavior of pressure‐loaded nanocomposite cylindrical shells.

Cylindrical shells are usually buckled under complex and combined loading conditions. This article presents an analytical approach to investigate the buckling and postbuckling behaviors of cylindrical shells reinforced by single-walled carbon nanotubes, surrounded by an elastic medium, exposed to thermal environments, and subjected to combined axial compression and lateral pressure loads. Carbon nanotubes (CNTs) are imbedded into matrix phase by uniform distribution or functionally graded distribution along the thickness direction. The properties of constituents are assumed to be temperature dependent, and effective properties of CNT-reinforced composite (CNTRC) are determined by an extended rule of mixture. Governing equations are based on the classical shell theory (CST) taking von Karman–Donnell nonlinearity and surrounding elastic foundations into consideration. Three-term form of deflection is assumed to satisfy simply supported boundary conditions, and Galerkin method is applied to obtain nonlinear load–deflection relations from which buckling loads and postbuckling equilibrium paths are determined. Numerical examples are carried out to show the effects of CNT volume fraction, distribution types, thermal environments, preexisting nondestabilizing lateral pressure and axial compression loads, and elastic medium on the buckling and postbuckling behaviors of CNTRC cylindrical shells.

Buckling and postbuckling behavior of thin composite cylindrical shells reinforced by carbon nanotubes (CNTs), surrounded by elastic media and exposed to uniform temperature rise, are investigated in this article. CNTs are reinforced into isotropic matrix phase through uniform distribution or functionally graded distributions across the thickness direction. Material properties are assumed to be temperature dependent, and effective elastic moduli of CNT-reinforced composite are determined according to extended rule of mixture. Formulations are based on the classical thin shell theory taking Von Karman–Donnell nonlinearity, surrounding elastic media and elastic constraints of boundary edges into consideration. Multi-term solutions of deflection and stress function are assumed to satisfy simply supported boundary condition, and Galerkin method is applied to obtain nonlinear relation of thermal load and deflection. An iteration algorithm is used to determine buckling temperatures and postbuckling paths. Numerical examples are given to analyze the effects of volume fraction and distribution type of CNTs, geometrical parameters, degree of tangential edge constraint, buckling mode, and surrounding elastic media on the buckling temperatures and postbuckling strength of thermally loaded nanocomposite cylindrical shells.