Mechanical characterization and modeling stress relaxation behavior of acrylic–polyurethane-based graft-interpenetrating polymer networks

The stress relaxation behavior of acrylic–polyurethane (PU)-based graft-interpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been studied computationally, numerical modeling of IPN systems is still in its infancy. A three-dimensional FEM model was developed using the Generalized Maxwell model and four-term Prony series constants, which were extracted from the stress relaxation experiments. With four terms in the Prony series, a good match was observed between experimental observations and results from the FEM model.     

Speech intelligibility measured with shortened versions of Callsign Acquisition Test (CAT)

The Callsign Acquisition Test (CAT) is a new speech intelligibility test developed by the Human Research and Engineering Directorate of the U.S. Army Research Laboratory (ARL-HRED). CAT uses the phonetic alphabet and digit stimuli combined together to form 126 test items.

Objective

The purpose of this study was to assess the reliability of data collected with shorter versions of CAT.

Design

A total of 5 shorter versions of the original list (CAT-120, CAT-60, CAT-40, CAT-30, and CAT-24) were formed and evaluated using 19 participants. Each of the subsets of CAT was presented in pink noise at signal-to-noise ratios (SNRs) of −6 dB and −9 dB.

Results

Results showed that shortened CAT lists have the capability of providing the same predictive power as the full CAT with good test-retest reliability.

Conclusions

Under the experimental conditions of this study, any of the shorter versions of the CAT can be utilized in place of the full version to reduce testing times with no effect on predictive power.     

Supporting command and control training functions in the emergency management domain using cognitive systems engineering

The design and implementation of MERMAIDS, a computer-based training system in the domain of emergency command and control, is described. The research investigates the use of cognitive systems engineering and information management tools for modelling and representing training knowledge of emergency system operators. We propose a decision-centric human-computer interface as a new method of supporting computer-based modelling in the domain of emergency systems. Several interacting themes in information management relevant to emergency response planning are discussed.     

Reliability-based life cycle costing

Given the system life cycle and the number of hours the system is in operation in a year, a discounted life cycle cost of using the system during its life cycle is obtained under an uncertain system design parameter (its failure distribution).     

Approaches to life cycle cost analysis with system availability constraints — A review

Life Cycle Costing (LCC) has attracted growing attention as a tool for choosing between designs of operational facilities and between modes of operating them. Since failures, repairs, and replacements are major contributors to life cycle costs, it has become apparent that eliability, vailability, and aintainability (RAM) modeling techniques should be incorporated into LCC modeling. A variety of approaches to combining these techniques have appeared in the technical literature. This paper is a state-of-the art review of the literature pertaining to availability-based life cycle cost analysis.     

Availability-based life cycle cost model: A simulation approach

Life Cycle Costing (LCC) has become a popular technique for studying operating facility designs prior to their construction. However, many such designs have operating characteristics that are marked by uncertainty. In particular, component failure rates and repair/replacement rates are uncertain. Thus, downtimes and maintenance costs are similarly uncertain. These various costs and uncertainties must be balanced if intelligent cost-based design decisions are to be made. This paper developes a model of Life Cycle Cost which integrates various availability parameters of reliability and maintainability. A simulation algorithm is presented as the appropriate tool for studying life cycle cost of a plant design.     

Application of RAMCOST-II simulation model to space suit (kit-inventory) during a mission

RAM ( eliability, vailability, and aintainability) parameters have been known to be a predominant factor in inventory planning of perishable items. However, the existing models have been developed and applied in piece-wise cases. In this paper, we discuss a system application of RAM factors in planning space suit inventory during extra-vehicular activities (EVA) for a space mission. The model is implemented in the RAMCOST-II Simulation environment. RAMCOST-II is a logistics-based simulation platform which integrates RAM factors and life cycle ing during a design.     

Desiccant solar air conditioning in tropical climates: I—Dynamic experimental and numerical studies of silicagel and activated alumina

This paper presents a dynamic study of moist air dehumidification in view of its use in an air conditioning process by evaporative cooling in tropical climates. A special device has been built to study dehumidification of tropical-like inlet air, through a fixed compact bed of silicagel and activated alumina. The compact desiccant storage is composed of two parallel beds to reduce the pressure drop. A good agreement is obtained for our experiment, and the computed amount of cycled water from the numerical model in the adiabatic process. This analytical model is used to simulate a complete air conditioning open cycle operating with hot and humid air.     

Forest governance and REDD+ in Central Africa: towards a participatory model to increase stakeholder involvement in carbon markets

Forests play a significant role in the global carbon budget, and can help to mitigate climate change impacts. Tropical forests which experience high rates of deforestation and forest degradation are particularly important, as they are the most active in winter. Based on academic research into global environmental policies in Central Africa, this study finds that REDD+ policies can succeed when there is a carbon market mechanism that increases participation by developing countries, with better integration of forest management and community forestry. Incentives should be based on an appropriate baseline, accurate carbon stocks and fluxes estimation, a suitable silvicultural system and regular monitoring.     

A quantitative impact of fingerprint distortion on recognition performance

Two goals of this study are to determine the extent of fingerprint distortion on recognition performance and establish if varying levels of distortion in acquired fingerprints linearly impact recognition performance. The first goal was achieved by determining the performance metrics: false accept and reject rates, equal error rates and detection trade-off curves for six categories of fingerprints of 201 individuals acquired under one normal and five other varying degrees of distortion. The second goal was achieved by first determining if a relationship exists between genuine scores and levels of distortion from the p-value, and second establishing a linear relationship equation using regression analysis. The results reveal that the increase in fingerprint distortion linearly impacts the recognition performance. The results of this study are beneficial to the academia, where theoretically sound fingerprint algorithms robust to distortions are yet to be designed for the secure use of fingerprint biometrics.