In many mechanical systems, the tendency of sliding components to intermittently stick and slip leads to undesirable performance, vibration, and control behaviors. Computer simulations of mechanical systems with friction are difficult because of the strongly nonlinear behavior of the friction force near zero sliding velocity. In this paper, two improved friction models are proposed. One model is based on the force-balance method and the other model uses a spring-damper during sticking. The models are tested on hundreds of lumped mass-spring-damper systems with time-varying excitation and normal contact forces for both one-dimensional and two-dimensional stick-slip motions on a planar surface. Piece-wise continuous analytical solutions are compared with solutions using other published force-balance and spring-damper friction models. A method has been developed to set the size of the velocity window for Karnopp’s friction model. The extensive test results show that the new force-balance algorithm gives much lower sticking velocity errors compared to the original method and that the new spring-damper algorithm exhibits no spikes at the beginning of sticking. Weibull distributions of the sticking velocity errors enable maximum errors to be estimated a priori., Technical papers, Published. Received February 03, 2000; Revised August 17, 2000.
Proceedings from the 23rd Annual ACM Conference on Innovation and Technology in Computer Science Education. Computer science and technology education should provide not only a strong theoretical foundation, but also problem solving, and communication and teamwork skills to prepare the students for careers. Including projects in curricula is a norm in many disciplines. However, projects are generally individual or based on small teams (two to five members). This paper presents my approach to teaching a capstone undergraduate computer technology course at the British Columbia Institute of Technology (BCIT) in the Computer System Technology (CST) Program in which a large class of students (maximum 22), organized into small teams work together and apply Agile software development practices to design, implement, integrate and test a large project. This model provides students with unique learning opportunities and experiences, as well as improving their soft skills, engagement and motivation., Peer reviewed, Conference paper, Published.
Gene recruitment or cooption occurs when a gene, which may be part of an existing gene regulatory network (GRN), comes under the control of a new regulatory system. Such re-arrangement of pre-existing networks is likely more common for increasing genomic complexity than the creation of new genes. Using evolutionary computations (EC), we investigate how cooption affects the evolvability, outgrowth and robustness of GRNs. We use a data-driven model of insect segmentation, for the fruit fly Drosophila, and evaluate fitness by robustness to maternal variability—a major constraint in biological development. We compare two mechanisms of gene cooption: a simpler one with gene Introduction and Withdrawal operators; and one in which GRN elements can be altered by transposon infection. Starting from a minimal 2-gene network, insufficient for fitting the Drosophila gene expression patterns, we find a general trend of coopting available genes into the GRN, in order to better fit the data. With the transposon mechanism, we find co-evolutionary oscillations between genes and their transposons. These oscillations may offer a new technique in EC for overcoming premature convergence. Finally, we comment on how a differential equations (in contrast to Boolean) approach is necessary for addressing realistic continuous variation in biochemical parameters., Peer-reviewed article, Published. Received 29 September 2012; Accepted 13 November 2012.
Biological development depends on the coordinated expression of genes in time and space. Developmental genes have extensive cis-regulatory regions which control their expression. These regions are organized in a modular manner, with different modules controlling expression at different times and locations. Both how modularity evolved and what function it serves are open questions. We present a computational model for the cis-regulation of the hunchback (hb) gene in the fruit fly (Drosophila). We simulate evolution (using an evolutionary computation approach from computer science) to find the optimal cis-regulatory arrangements for fitting experimental hb expression patterns. We find that the cis-regulatory region tends to readily evolve modularity. These cis-regulatory modules (CRMs) do not tend to control single spatial domains, but show a multi-CRM/multi-domain correspondence. We find that the CRM-domain correspondence seen in Drosophila evolves with a high probability in our model, supporting the biological relevance of the approach. The partial redundancy resulting from multi-CRM control may confer some biological robustness against corruption of regulatory sequences. The technique developed on hb could readily be applied to other multi-CRM developmental genes., Peer-reviewed article, Published.
To improve the efficiency of enzymatic hemicellulose removal from bamboo pre-hydrolysis kraft pulp, mechanical refining was conducted prior to enzyme treatment. Refining significantly improved the subsequent hemicellulose removal efficiency by xylanase treatment. Results showed that when PFI refining was followed by 3 h xylanase treatment, the xylan content of the bamboo pre-hydrolysis kraft pulp (after first stage oxygen delignification) could be decreased to 2.72% (w/w). After bleaching of enzyme treated pulp, the alpha-cellulose content was 93.4% (w/w) while the xylan content was only 2.38%. The effect of refining on fibre properties was investigated in terms of freeness, water retention value, fibre length and fibrillation characteristics. The brightness, reactivity and viscosity were also determined to characterize the quality of final pulp. Results demonstrated the feasibility of combining refining and xylanase treatment to produce high quality bamboo dissolving pulp., Peer-reviewed article, Published. Received 1 September 2016; Revised 9 October 2016; Accepted 12 October 2016; Available online 24 October 2016.
9th International Conference on Indoor Air Quality, Ventilation & Energy Conservation (IAQVEC), October 23-26, 2016, Songdo, South Korea. This project studied the relative humidity and indoor temperature variations in three houses in the pacific coastal climates. The houses have been monitored for one month in each four different seasons under different size of occupants, temperature variation and living conditions. These three houses represent different air tightness, number of occupants and floor size. The temperature and RH data loggers are used in every room in each house to better understand which rooms in a certain living conditions are more susceptible to moisture related problems. In addition, three existing models (European Indoor Class Model, ASHRAE 160P simple and intermediate models) are used to generate the indoor humidity level and the calculated values are compared to the measured field data., Conference paper, Published.
Proceedings of Rehabilitation Engineering and Assistive Technology Society of North America Annual Conference 2011. The FreeWheel™ wheelchair attachment was developed to overcome the burden that front casters pose to manual wheelchairs., Conference paper, Published.
Background: During pretreatment, hemicellulose is removed from biomass via proton-catalyzed hydrolysis to produce soluble poly- and mono-saccharides. Many kinetic models have been proposed but the dependence of rate on proton concentration is not well-defined; autohydrolysis and dilute-acid hydrolysis models apply very different treatments despite having similar chemistries. In this work, evolution of proton concentration is examined during both autohydrolysis and dilute-acid hydrolysis of hemicellulose from green bamboo. An approximate mathematical model, or “toy model”, to describe proton concentration based upon conservation of mass and charge during deacetylation and ash neutralization coupled with a number of competing equilibria, was derived. The model was qualitatively compared to experiments where pH was measured as a function of time, temperature, and initial acid level. Proton evolution was also examined at room temperature to decouple the effect of ash neutralization from deacetylation.
Results: The toy model predicts the existence of a steady-state proton concentration dictated by equilibrium constants, initial acetyl groups, and initial added acid. At room temperature, it was found that pH remains essentially constant both at low initial pH and autohydrolysis conditions. Acid is likely in excess of the neutralization potential of the ash, in the former case, and the kinetics of neutralization become exceedingly small in the latter case due to the low proton concentration. Finally, when the hydrolysis reaction proceeded at elevated temperatures, one case of non-monotonic behavior in which the pH initially increased, and then decreased at longer times, was found. This is likely due to the difference in rates between neutralization and deacetylation.
Conclusions: The model and experimental work demonstrate that the evolution of proton concentration during hydrolysis follows complex behavior that depends upon the acetyl group and ash content of biomass, initial acid levels and temperature. In the limit of excess added acid, pH varies very weakly with time. Below this limit, complex schemes are found primarily related to the selectivity of deacetylation in comparison to neutralization. These findings indicate that a more rigorous approach to models of hemicellulose hydrolysis is needed. Improved models will lead to more efficient acid utilization and facilitate process scale-up., Peer-reviewed article, Published. Received: 23 July 2016 ; Accepted: 22 September 2016 ; Published: 21 October 2016.
There is a continuous dynamic heat, air and moisture (HAM) interaction between the indoor environment, building envelope and mechanical systems. In spite of these interdependences, the current indoor, building envelope and energy analysis tools are used independently. In this paper a holistic HAM model that integrates building envelope enclosures, indoor environment, HVAC systems, and indoor heat and moisture generation mechanisms, and solves simultaneously for the respective design parameters is developed. The model is benchmarked with internationally published test cases that require simultaneous prediction of indoor environmental conditions, building envelope moisture performance and energy efficiency of a building., Peer reviewed article, Published. Received 26 February 2009, Accepted 11 March 2010, Available online 16 April 2010.
In spite of the progress in developing methods and tools to support sustainable building design, there is still a lack of a formal approach to bridge the "no man’s land” gap between the traditional building engineering disciplines, and between these and the architecture, to achieve the level of building integration required for sustainability. This paper presents an integration framework that aims at facilitating the inclusion of life-cycle considerations in the design process from the outset, so that materials and systems are selected not only from environmentally friendly resources, but most importantly, to match service life performance expectations. The framework describes an iterative methodology to evaluate these expectations in practice, which is based on an understanding and modeling of the dynamics of the built environment to which materials, components, and systems are exposed. Quantitative methods and test protocols can be incorporated into the framework for assessing function-performance aspects of alternative solutions. Due to its complexity stemming from its inherent exposure to variable environmental loads and its multi-functionality, the framework focuses on addressing the life cycle of the building enclosure system. It is expected that the organization of the underlying principles of building life-cycle performance described in this paper will become a knowledge core that will facilitate a more integrated treatment of buildings in research, education, and practice., Peer reviewed, Peer reviewed article, Received 29 October 2010 ; Revised 13 January 2011 ; Accepted 18 January 2011 ; Available online 27 January 2011., Life-cycle, Service life, Building science, Building enclosure, Building integration
Proceedings of IEEE EPEC’08 Conference, Vancouver, Oct 2008. This paper describes a major research initiative by British Columbia Institute of Technology for the construction of an Intelligent Micro Grid on its campus in Burnaby, BC, Canada., Conference paper, Published.