Introducing a level-set based shape and topology optimization method for the wear of composite materials with geometric constraints

The wear of materials continues to be a limiting factor in the lifetime and performance of mechanical systems with sliding surfaces. As the demand for low wear materials grows so does the need for models and methods to systematically optimize tribological systems. Elastic foundation models offer a simplified framework to study the wear of multimaterial composites subject to abrasive sliding. Previously, the evolving wear profile has been shown to converge to a steady-state that is characterized by a time-independent elliptic equation. In this article, the steady-state formulation is generalized and integrated with shape optimization to improve the wear performance of bi-material composites. Both macroscopic structures and periodic material microstructures are considered. Several common tribological objectives for systems undergoing wear are identified and mathematically formalized with shape derivatives. These include (i) achieving a planar wear surface from multimaterial composites and (ii) minimizing the run-in volume of material lost before steady-state wear is achieved. A level-set based topology optimization algorithm that incorporates a novel constraint on the level-set function is presented. In particular, a new scheme is developed to update material interfaces; the scheme (i) conveniently enforces volume constraints at each iteration, (ii) controls the complexity of design features using perimeter penalization, and (iii) nucleates holes or inclusions with the topological gradient. The broad applicability of the proposed formulation for problems beyond wear is discussed, especially for problems where convenient control of the complexity of geometric features is desired.     

A rapid spectroscopic method for quantification of P57 in Hoodia gordonii raw material

The feasibility of quantifying the perceived active ingredient (P57) in Hoodia gordonii raw material using Fourier transform near- and mid-infrared spectroscopy combined with chemometric techniques was investigated. The concentration of P57 (a triterpene glycoside) was determined in 146 plant samples with liquid chromatography coupled to mass spectrometry and these values were used to develop a calibration model based on the partial least squares projections to latent structures (PLS) and orthogonal projections to latent structures (O-PLS) regression algorithms. The performance of each calibration model was evaluated according to the root mean square error of prediction (RMSEP) and correlation coefficient (R²). The PLS model with 2nd derivative pre-processing predicted P57 content based on the FT-NIR spectra with the best accuracy and a correlation coefficient (R²) value of 0.9629 and the lowest RMSEP of 0.03%. These results demonstrated that FT-NIR spectroscopy can be used to rapidly quantify P57 in H. gordonii raw material with high accuracy.     

Relationships between process effects and treating time for waterborne preservative systems

Timber from different Eucalyptus species were subjected to different vacuum and vacuum/pressure treatments involving water as a treating medium. It was found that a vacuum period of five minutes gave the most time effective absorption rate. This is recommended to be used as the initial vacuum period for the vacuum/pressure treatments under the conditions of this study. The time to reach the maximum applied pressure inside the treating cylinder, as well as the pressure period required for an absorption of 200 kg/m³, were highly dependent on the applied pressure, yielding a very steep negative correlation between the variables, (i.e. the higher the applied pressure, the more time effective the treatment). The relationship between pressure absorption and time was found to be positive and curvilinear with absorption rate decreasing progressively as the absorption increased. This became more pronounced as the applied pressure was decreased. Lowering the pressure pump capacity had very little effect on the above results.     

Process and technology challenges in swift-starting virtual teams

Virtual teams often face tight schedules and a need to start quickly and perform instantly. The goal of our study was to enhance understanding of the challenges faced by such teams. We used time–interaction–performance theory as the framework for following the processes and functions within virtual teams working on a systems development task. Our study provided a detailed examination of the group process, applied to virtual teams working under time pressure. The challenges faced by virtual teams in such settings showed that teams must work to enhance their effectiveness in multiple dimensions.     

Equilibrium slag losses in ferrovanadium production

Ferrovanadium is sometimes produced from V₂O₃ in electric arc furnaces, using aluminum as a reductant. The CaO fluxes the alumina, which forms during reduction of the vanadium oxide. Incomplete reduction of vanadium oxide from the slag is a significant cause of vanadium losses. To quantify factors that can affect the equilibrium vanadium loss, the vanadium oxide activity coefficient was measured experimentally for different slag compositions. Hydrogen-water mixtures were used to control the partial oxygen pressure (approximately 10⁻¹³ atm) ove CaO-Al₂O₃ slags contained in vanadium crucibles at 1700 °C; gas-phase mass transfer was controlled by jetting the gas mixture onto the slag surface. Manipulation of the redox conditions at a single slag composition and temperature showed that, as expected, the vanadium is present in the trivalent state in the slag. The slag basicity (CaO-Al₂O₃ ratio) was found to have a very strong effect on the activity coefficient of VO_1.5, with clear implications for the effect of plant practice on vanadium loss. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Immunohistochemical evaluation after Sr-enriched biphasic ceramic implantation in rabbits femoral neck: comparison of seven different bone conditions

Strontium (Sr) has shown effectiveness for stimulating bone remodeling. Nevertheless, the exact therapeutic values are not established yet. Authors hypothesized that local application of Sr-enriched ceramics would enhance bone remodeling in constant osteoporosis of rabbits’ femoral neck bone. Seven different bone conditions were analyzed: ten healthy rabbits composed a control group, while other twenty underwent ovariectomy and were divided into three groups. Bone defect was filled with hydroxyapatite 30% (HAP) and tricalcium phosphate 70% (TCP) granules in 7 rabbits, 5% of Sr-enriched HAP/TCP granules in 7, but sham defect was left unfilled in 6 rabbits. Bone samples were obtained from operated and non-operated legs 12 weeks after surgery and analyzed by histomorphometry and immunohistochemistry (IMH). Mean trabecular bone area in control group was 0.393 mm2, in HAP/TCP – 0.226 mm2, in HAP/TCP/Sr – 0.234 mm2 and after sham surgery – 0.242 mm2. IMH revealed that HAP/TCP/Sr induced most noticeable increase of nuclear factor kappa beta 105 (NFkB 105), osteoprotegerin (OPG), osteocalcin (OC), bone morphogenetic protein 2/4 (BMP 2/4), collagen type 1α (COL-1α), interleukin 1 (IL-1) with comparison to intact leg; NFkB 105 and OPG rather than pure HAP/TCP or sham bone. We concluded that Sr-enriched biomaterials induce higher potential to improve bone regeneration than pure bioceramics in constant osteoporosis of femoral neck bone. Further studies on bigger osteoporotic animals using Sr-substituted orthopedic implants for femoral neck fixation should be performed to confirm valuable role in local treatment of osteoporotic femoral neck fractures in humans.

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Managing strategic contradictions in hybrid teams

It has become a common practice to organize work teams to include members in multiple geographic locations. In contrast to co-located teams and purely virtual teams, these ‘hybrid’ teams combine face-to-face communication with computer-mediated interaction. In this paper, we report a qualitative study of management practices in three hybrid teams in one organization. We adopt the theoretical approach of strategic contradiction, in which apparently contradictory pairs of elements can be managed by attending to their possible synergies or clarifying their distinctions so as to make balanced trade-offs over time. Our data reveal four sets of paradoxical frames in hybrid teams: remoteness–closeness, cultural uniformity–cultural diversity, rationality–emotionality, and control–empowerment. In referencing these paradoxical frames, teams engaged in three cognitive processes: (a) integrating to produce synergies between opposing tensions, (b) differentiating to clarify distinctions between opposing tensions and to balance trade-offs over time, and (c) polarizing to remove tensions between opposing elements by using one element to reduce the effects of another. Both integrating and differentiating processes were found to be instrumental to sustaining contradictions as interdependent dualities, whereas polarizing processes were found to preserve contradictions as dualisms. Our findings advance the understanding of managing strategic contradictions by showing how managers influence cognitive processes that paradoxically emphasize remoteness and closeness, cultural uniformity and cultural diversity, rationality and emotionality, and control and empowerment.     

Measuring the refractive state of an eye based on the intensity of the retinal reflex

When examining the fundus of the eye with an ophthalmoscope, the intensity of the retinal reflex depends on the refractive state of the eye. In this study, application of this phenomenon for measuring the refractive state of the eye is demonstrated. First, a calibration curve relating the intensity of the retinal reflex and the refractive state was obtained using a model eye. Next, the intensity of the retinal reflex was measured while subjects were viewing a checker-board pattern, the distance of which was varied within the range from 0.17 to 1 m. Further, the relation between the refractive state and the optical power of the stimulus could be determined based on the measured light intensity and the calibration curve. Generally, the measured refractive state increased with the optical power of the stimulus. However, blinking and fluctuations in accommodation had undesired effects on the results.     

Evaluation of the physical and antimicrobial properties of silver doped hydroxyapatite depending on the preparation method

In the present study, the effect of the preparation method on the physical and antibacterial properties of silver doped hydroxyapatite (HAp/Ag) samples was investigated. HAp/Ag with 0.1–5 % of silver was prepared using two different modified wet chemical precipitation methods. A comparison of thermal stability and thermodynamical properties indicated that the thermal stability and sintering temperature of HAp/Ag were higher than those of pure hydroxyapatite if Ca(NO₃)₂·4H₂O, AgNO₃, NH₄OH and (NH₄)₂HPO₄ were used as raw materials. Phase composition and silver release were determined by XRD and ICP-MS. The study showed that, after 50 h in simulated body fluid 0.8–1.8 % of silver of the total silver amount was released from compact HAp/Ag scaffolds, and release kinetics strongly depended on the HAp/Ag preparation method. In vitro antibacterial activity of samples from each method against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa was approved. Results showed that, in the case of using Ca(OH)₂, H₃PO₄ and AgNO₃ as raw materials for HAp/Ag synthesis, higher antibacterial activity towards both bacterial strains could be obtained.