Edward C. Smith

Stigma, Culture, and HIV and AIDS in the Western Cape, South Africa: An Application of the PEN-3 Cultural Model for Community-Based Research:

HIV- and AIDS-related stigma has been reported to be a major factor contributing to the spread of HIV. In this study, the authors explore the meaning of stigma and its impact on HIV and AIDS in South African families and health care centers. They conducted focus group and key informant interviews among African and Colored populations in Khayelitsha, Gugulethu, and Mitchell’s Plain in the Western Cape province. The audio-recorded interviews were transcribed and coded using NVivo. Using the PEN-3 cultural model, the authors analyzed results showing that participants’ shared experiences ranged from positive/nonstigmatizing, to existential/ unique to the contexts, to negative/stigmatizing. Families and health care centers were found to have both positive nonstigmatizing values and negative stigmatizing characteristics in addressing HIV/AIDS-related stigma. The authors conclude that a culture-centered analysis, relative to identity, is central to understanding the nature and contexts of HIV/AIDS-related stigma in South Africa.

FORMULATION AND EVALUATION OF AN ANALYTICAL MODEL FOR COMPOSITE BOX-BEAMS

A direct method for determining the effective elastic stiffnesses and deformation behavior of composite box-beam (BB) structures is developed analytically, validated, and demonstrated. The BB walls are modeled as orthotropic-ply laminated plates, so that the elastic properties vary both through the thickness and around the BB contour; deformation is described in terms of extension, bending, twisting, shearing, and torsion-related out-of-plane warping. Numerical results for several BB configurations are presented in tables and graphs and compared with experimental data and FEM computations (Stemple and Lee, 1989): good general agreement is obtained for cross-ply, antisymmetric, and symmetric layups, except for symmetric layups with ply orientation angles theta greater than 30 deg. Both out-of-plane warping and transverse shear coupling are found to have significant effects on BB elastic response.

Health Wise South Africa: Development of a Life Skills Curriculum for Young Adults

Abstract The purpose of this paper is to describe the development of an international collaborative effort that aims to reduce risky behavior (e.g., substance use, risky sexual behavior) that leads to outcomes such as HIV/AIDs, pregnancy, and addictions among a sample of South African youth. Because many of these risky behaviors occur in free time, a major part of the effort was leisure education to promote positive use of free time. The program described has been pilot tested and is currently underway as a larger-scale, randomized trial in the Province of the Western Cape in South Africa. This paper describes the conceptualization and revision of the HealthWise curriculum, working with the Western Cape Education Department, and the on-going randomized trial.

Characterization and Modeling of the Low Strain Amplitude and Frequency Dependent Behavior of Elastomeric Damper Materials

The low-strain (0.1 to 20%) amplitude behavior of elastomeric materials in simple shear was investigated both experimentally and analytically. Amplitudes, temperatures (-40° to 150°F), and frequencies (0.01 to lOHz) were chosen to represent the working range of typical helicopter damper applications. A nonlinear model was developed to capture the combined amplitude and frequency dependence. The model extends the nonlinear Anelastic Displacement Fields (ADF) approach to include friction-type elements. These elements operate in parallel with the original ADF model. This configuration is shown to improve the performance of the ADF model over the amplitude and frequency range of interest. Experimental tests (single frequency harmonic) were conducted at several frequencies and amplitudes to support model characterization. The current model and a baseline nonlinear model (which does not include friction-type elements) were characterized using linearized material complex modulus data. The current model captures observed material behavior more accurately than the baseline model. Additional single- and dual-frequency harmonic data (nonlinear stress time-histories) was then used to validate the current model. The model accurately represents the material behavior for these loading conditions. Experimental investigations were further expanded to examine the influence of temperature and static precompression.

Induced-shear piezoelectric actuators for rotor blade trailing edge flaps

Much of the current rotorcraft research is focused on improving performance by reducing unwanted helicopter noise and vibration. One of the most promising active rotorcraft vibration control systems is an active trailing edge flap. In this paper, an induced-shear piezoelectric tube actuator is used in conjunction with a simple lever–cusp hinge amplification device to generate a useful combination of trailing edge flap deflections and hinge moments. A finite-element model of the actuator tube and trailing edge flap (including aerodynamic and inertial loading) was used to guide the design of the actuator–flap system. A full-scale induced shear tube actuator flap system was fabricated and bench top testing was conducted to validate the analysis. Hinge moments corresponding to various rotor speeds were applied to the actuator using mechanical springs. The testing demonstrated that for an applied electric field of 3 kV cm−1, the tube actuator deflected a representative full-scale 12 inch flap ±2.8° at 0 rpm and ±1.4° for a hinge moment simulating a 400 rpm condition. The per cent error between the predicted and experimental full-scale flap deflections ranged from 4% (low rpm) to 12.5% (large rpm). Increasing the electric field to 4 kV cm−1 results in ±2.5° flap deflection at a rotation speed of 400 rpm, according to the design analysis. A trade study was conducted to compare the performance of the piezoelectric tube actuator to the state of the art in trailing edge flap actuators and indicated that the induced-shear tube actuator shows promise as a trailing edge flap actuator.

Localization of a Breathing Crack Using Super-Harmonic Signals due to System Nonlinearity

In this paper, a new damage detection technique able to identify the location of a breathing crack in an isotropic rod, relying only on real-time measurements, is proposed. The detection algorithm exploits the phase information associated with the superharmonic components produced, in the Fourier spectrum, by the nonlinear dynamic response of this kind of defect under the influence of an external dynamic excitation. The validity of the proposed algorithmforaweaklynonlinearsystemissupportedbyananalyticalsolutionforacrackedbeamobtainedthrough the harmonic balance approach. A numerical investigation is conducted by means of a finite element model of an isotropic beam integrating nonlinear contactelements in the damaged area and solved for the steady-state response. Threedifferentpostprocessingapproaches,incorporatingtheproposeddamagedetectionalgorithm,areformulated andcomparedtoassessthecapabilityofthecurrentmethodology.Resultsfromthecrackedbeammodelclearlyshow thegenerationofthesuperharmonicsasaresultofthenonlineardynamicbehaviorofthebreathingcrack.Thephase associated with the superharmonic components is then processed through the detection algorithm and the predicted location is compared with the actual position of the defect to assess the performances of the methodology.

Ultrasonic De-Icing of Wind-Tunnel Impact Icing

Ultrasonic excitation has proven to provide ice-interface transverse shear stresses exceeding the adhesion strength of freezer ice to various metals, promoting instantaneous ice delamination. Wind-tunnel impact ice presents challenges that are not encountered when removing freezer ice. The low-power, nonthermal ultrasonic de-icing concept is investigated under impact-icing conditions in an icing wind tunnel. In this research effort, ultrasonic actuator disks excite isotropic plates and airfoil-shaped structures that are representative of helicopter leading-edge protection-cap shapes. Off-the-shelf ultrasonic actuators are used to create ice-interface shear stresses sufficient to promote instantaneous ice delamination of thin layers of impact ice (less than 3 mm thick). A steel plate of 30.48 cm x 30.48 cm x 1 mm was actuated by three lead zirconate titanate disks excited at their ultrasonic radial mode. The ultrasonic vibration introduced transverse shear stresses that prevented ice formation on top of the actuator locations for a fraction of the power required with electrothermal systems used in helicopter rotor blades (0.18 W/cm 2 vs 3.8 W/cm 2 ). Experiments also showed ice delamination in areas of the plates where transverse shear stresses were concentrated. As ice thicknesses reached a critical value of approximately 1.2 mm, ice debonded from those steel-plate areas. A model of the three disk actuated steel plate was created and correlated with experimental results observed during impact-icing test experiments. Both, the predicted ultrasonic modes of the system and the ice-shedding areas agreed with experimental results. In addition, a second set of experiments involving NACA 0012 airfoil-shaped structures were conducted. Actuators located on the top and bottom surfaces of the leading-edge cap were actuated with an input power as low as 200 W (32 kHz ultrasonic mode). Thin layers of ice (less than 2 mm thick) constantly delaminated from the leading edge of the airfoil on those regions where stress concentrations were predicted.

Coupled Torsion-Lateral Stability of a Shaft-Disk System Driven Through a Universal Joint

Understanding the instability phenomena of rotor-shaft and driveline systems incorporating universal joints is becoming increasingly important because of the trend towards light-weight, high-speed supercritical designs. In this paper, a nondimensional, periodic, linear time-varying model with torsional and lateral degrees-of-freedom is developed for a rotor shaft-disk assembly supported on a flexible bearing and driven through a U-joint. The stability of this system is investigated utilizing Floquet theory. It is shown that the interaction between torsional and lateral dynamics results in new regions of parametric instability that have not been addressed in previous investigations. The presence of load inertia and misalignment causes dynamic coupling of the torsion and lateral modes, which can result in torsion-lateral instability for shaft speeds near the sum-type combinations of the torsion and lateral natural frequencies. The effect of angular misalignment, static load-torque, load-inertia, lateral frequency split, and auxiliary damping on the stability of the system is studied over a range of shaft operating speeds. Other than avoiding the unstable operating frequencies, the effectiveness of using auxiliary lateral viscous damping as a means of stabilizing the system is investigated. Finally, a closed-form technique based on perturbation expansions is derived to determine the auxiliary damping necessary to stabilize the system for the least stable case (worst case). ©2002 ASME

Thermomechanical modeling of elastomeric materials

A thermomechanical model for elastomeric materials is formulated using the method of anelastic displacement fields. The single anelastic field modeling methodology is presented in detail, including nonlinear finite element formulation. Numerical simulations using room temperature material properties and a classical Arrhenius temperature shift function relationship are presented. Material self-heating predictions are compared to experimental data. The results indicate that the model accurately captures material self-heating, as well as low-temperature stiffening and high-temperature softening effects. Simulations using an increased material shear thickness show the ability of the model to predict increased local temperatures and strains. Use of multiple anelastic fields improves the ability to capture material behavior over a broad range of temperatures and frequencies.

Air and ground resonance of helicopters with elastically tailored composite rotor blades

The aeromechanical stability, including air resonance in hover, air resonance in forward flight, and ground resonance, of a helicopter with elastically tailored composite rotor blades is investigated. Five soft-inplane hingeless rotor configurations, featuring elastic pitch-lag, pitch-flap and extension-torsion couplings, are analyzed. Elastic couplings introduced through tailored composite blade spars can have a powerful effect on both air and ground resonance behavior. Elastic pitch-flap couplings (positive and negative) strongly affect body, rotor and dynamic inflow modes. Air resonance stability is diminished by elastic pitch-flap couplings in hover and forwrad flight. Negative pitch-lag elastic coupling has a stabilizing effect on the regressive lag mode in hover and forward flight. The negative pitch-lag coupling has a detrimental effect on ground resonance stability. Extension-torsion elastic coupling (blade pitch decreases due to tension) decreases regressive lag mode stability in both airborne and ground contact conditions. Increasing thrust levels has a beneficial influence on ground resonance stability for rotors with pitch-flap and extension-torsion coupling and is only marginally effective in improving stability of rotors with pitch-lag coupling.