High capacity photonic integrated switching circuits

As the demand for high-capacity data transfer keeps increasing in high performance computing and in a broader range of system area networking environments; reconfiguring the strained networks at ever faster speeds with larger volumes of traffic has become a huge challenge. Formidable bottlenecks appear at the physical layer of these switched interconnects due to its energy consumption and footprint. The energy consumption of the highly sophisticated but increasingly unwieldy electronic switching systems is growing rapidly with line rate, and their designs are already being constrained by heat and power management issues. The routing of multi-Terabit/second data using optical techniques has been targeted by leading international industrial and academic research labs. So far the work has relied largely on discrete components which are bulky and incurconsiderable networking complexity. The integration of the most promising architectures is required in a way which fully leverages the advantages of photonic technologies. Photonic integration technologies offer the promise of low power consumption and reduced footprint. In particular, photonic integrated semiconductor optical amplifier (SOA) gate-based circuits have received much attention as a potential solution. SOA gates exhibit multi-terahertz bandwidths and can be switched from a high-gain state to a high-loss state within a nanosecond using low-voltage electronics. In addition, in contrast to the electronic switching systems, their energy consumption does not rise with line rate. This dissertation will discuss, through the use of different kind of materials and integration technologies, that photonic integrated SOA-based optoelectronic switches can be scalable in either connectivity or data capacity and are poised to become a key technology for very high-speed applications. In Chapter 2, the optical switching background with the drawbacks of optical switches using electronic cores is discussed. The current optical technologies for switching are reviewed with special attention given to the SOA-based switches. Chapter 3 discusses the first demonstrations using quantum dot (QD) material to develop scalable and compact switching matrices operating in the 1.55µm telecommunication window. In Chapter 4, the capacity limitations of scalable quantum well (QW) SOA-based multistage switches is assessed through experimental studies for the first time. In Chapter 5 theoretical analysis on the dependence of data integrity as ultrahigh line-rate and number of monolithically integrated SOA-stages increases is discussed. Chapter 6 presents some designs for the next generation of large scale photonic integrated interconnects. A 16x16 switch architecture is described from its blocking properties to the new miniaturized elements proposed. Finally, Chapter 7 presents several recommendations for future work, along with some concluding remark

Understanding the effects of e-business on business processes, a simulation approach

This thesis defines a new approach to the analysis of the effect of e-business on business processes, utilising simulation as evaluation tool. This research was focused on answering five research questions about the suitability of simulation in this context, the role of static modelling and generic business processes, the identification of patterns for e-business activities and how to operationalise these patterns into components in simulation software, as well as how to use these components. Requirements for modelling of e-business processes were identified and documented. Pilot cases studies proved the potential of simulation for studying e-business processes (Feasibility). Generic e-business activities were derived and classified from the literature and case studies in order to fill gaps identified in existent process models. Re-usable simulation components are proposed as a result of the unique combination of simulation and e-activities in order to make simulation modelling of e-business easier. The components were tested in industrial case studies and quasi-experiments with end users for feasibility, usability and usefulness. Results show that the components' approach is feasible, that having re-usable components promotes a better analysis, (usefulness) and that it is easy to build models using the components (usability). The theoretical novelty of this research resides in bringing together three areas of study: ebusiness, simulation and business processes to analyse e-business implementations. The research contributes to the knowledge of components and re-use theory in simulation by proposing a new approach to component development, operationalisation and analysis of the degree of granularity required for these components. From a practical point of view, this research provides companies with an easier and more complete way of analysing e-business processes, breaking the barrier for the use of simulation, speeding up model building of eprocesses and getting a better understanding of the dynamics of e-processes. Future work in the area will include extending the component approach to supply chains and inter-company transactions.This thesis defines a new approach to the analysis of the effect of e-business on business processes, utilising simulation as evaluation tool. This research was focused on answering five research questions about the suitability of simulation in this context, the role of static modelling and generic business processes, the identification of patterns for e-business activities and how to operationalise these patterns into components in simulation software, as well as how to use these components. Requirements for modelling of e-business processes were identified and documented. Pilot cases studies proved the potential of simulation for studying e-business processes (Feasibility). Generic e-business activities were derived and classified from the literature and case studies in order to fill gaps identified in existent process models. Re-usable simulation components are proposed as a result of the unique combination of simulation and e-activities in order to make simulation modelling of e-business easier. The components were tested in industrial case studies and quasi-experiments with end users for feasibility, usability and usefulness. Results show that the components' approach is feasible, that having re-usable components promotes a better analysis, (usefulness) and that it is easy to build models using the components (usability). The theoretical novelty of this research resides in bringing together three areas of study: ebusiness, simulation and business processes to analyse e-business implementations. The research contributes to the knowledge of components and re-use theory in simulation by proposing a new approach to component development, operationalisation and analysis of the degree of granularity required for these components. From a practical point of view, this research provides companies with an easier and more complete way of analysing e-business processes, breaking the barrier for the use of simulation, speeding up model building of eprocesses and getting a better understanding of the dynamics of e-processes. Future work in the area will include extending the component approach to supply chains and inter-company transactions

Tropical forest remnants as shelters of avian diversity within a tourism development matrix in Yucatan Peninsula, Mexico

Tropical forests have undergone extensive transformation because of increasing tourism development, in addition to historic clearing for agricultural and cattle grazing activities. Altogether, these activities have had an important effect on bird diversity, reducing the habitat available to many species. In this study, the role of tropical forest remnants located between different land use types was evaluated for species diversity, composition, and distribution of the bird community at Akumal region in Quintana Roo, Mexico. Point counts were used to quantify the avifauna by habitat, and Shannon´s and Simpson´s diversity index were used to determine bird diversity. Additionally, bird species were classified according to seasonality and trophic guild by type of habitat. A total of 160 species and 50 families was recorded, of which 100 species were permanent residents, 47 winter visitors and 11 transients. Mature tropical forest and tropical forest remnants had higher species richness than those of modified environments. This study supports the importance of tropical forest remnants as shelters for bird species in landscapes with tourism developments, and the relevance of these remnants to maintaining high bird diversity

Using Transcriptomes as Mutant Phenotypes Reveals Functional Regions of a Mediator Subunit in Caenorhabditis elegans

Although transcriptomes have recently been used as phenotypes with which to perform epistasis analyses, they are not yet used to study intragenic function/structure relationships. We developed a theoretical framework to study allelic series using transcriptomic phenotypes. As a proof-of-concept, we apply our methods to an allelic series of dpy-22, a highly pleiotropic Caenorhabditis elegans gene orthologous to the human gene MED12, which encodes a subunit of the Mediator complex. Our methods identify functional units within dpy-22 that modulate Mediator activity upon various genetic programs, including the Wnt and Ras modules

A Hybrid System Of Enterprise Resource Planning (ERP) And Informality

One of the current research trends in Enterprise Resource Planning (ERP) involves examining the critical factors for its successful implementation. However, there is limited beyond system implementation, focusing on flexibly of ERP to respond to changes in business. Therefore, this study explores a combination system, involving an ERP system and informality, which focus on providing a company with efficient and flexible performance simultaneously. The paper aims to understand the constraints of using a single ERP system, and to define a new system corresponding to these problems, which is achieved by studying four Chinese companies operating in different industries. The study reveals that an ERP with pre-determined business activities cannot react promptly to unanticipated changes in a business. Incorporating informality into an ERP can react to different situations by using different procedures that are based on the practical knowledge of frontline employees

ENTREPRENEURIAL FAILURE AND RESILIENCE: A CONTINUOUS INTERPLAY BETWEEN RIGIDITY AND FLEXIBILITY

Resilience studies are increasingly relevant to understand business processes. This study aimed to explore how entrepreneurs in Mexico recovered from situations of business failure. Which key factors did move en­trepreneurs to move forward with their ventures rather than desisting after a failure event? Through a qua­litative study that utilized focus groups with entrepreneurs that had faced entrepreneurial failure, discourses, and repre­sen­tations around the failure experience were analyzed. Findings suggested that entrepreneurs lied in a con­tinuum between resilience and resistance, depending on their access assets such as entrepreneurial networks, ecosystems, and pool of knowledge as antecedents of resistance and resilience. The study shed light in the understanding of the role communities surrounding entrepreneurs played in their trajectory, failure, and even­tual recovery

The application of simulation to product service systems:A review (WIP)

One innovative strategy among product manufacturers is to compete through the delivery of services to their clients. The range of advanced services provided by these manufacturers are underpinned by a system known as product-service systems (PSS). Based on a literature review, a description of a PSS with its dynamic behaviour is provided. Three PSS modelling and simulation methods (system dynamics, discrete event simulation and agent based simulation) and the nature of their application in the context of PSS are identified and discussed. Results indicate DES as the mostly used simulation approach accounting for over 50% papers reviewed due to its ability to model the dynamic behaviour of PSS over time. Previous and current research have focused on the design and in-service phase of PSS lifecycle phase. The choice of specific simulation method is dependent on the objectives intended, which include optimization of design configuration during the design and development phase and performance evaluation and optimization of resource utilization during the in-service phase of a PSS lifecycle. An area for further research is the application of simulation as a tool for cost analysis and cost estimation

Improved predictions of the geographic distribution of invasive plants using climatic niche models

"Climatic niche models for invasive plants are usually constructed with occurrence records taken from literature and collections. Because these data neither discriminate among life-cycle stages of plants (adult or juvenile) nor the origin of individuals (naturally established or man-planted), the resulting models may mispredict the distribution ranges of these species. We propose that more accurate predictions could be obtained by modelling climatic niches with data of naturally established individuals, particularly with occurrence records of juvenile plants because this would restrict the predictions of models to those sites where climatic conditions allow the recruitment of the species. To test this proposal, we focused on the Peruvian peppertree (Schinus molle), a South American species that has largely invaded Mexico. Three climatic niche models were constructed for this species using high-resolution dataset gathered in the field. The first model included all occurrence records, irrespective of the life-cycle stage or origin of peppertrees (generalized niche model). The second model only included occurrence records of naturally established mature individuals (adult niche model), while the third model was constructed with occurrence records of naturally established juvenile plants (regeneration niche model). When models were compared, the generalized climatic niche model predicted the presence of peppertrees in sites located farther beyond the climatic thresholds that naturally established individuals can tolerate, suggesting that human activities influence the distribution of this invasive species. The adult and regeneration climatic niche models concurred in their predictions about the distribution of peppertrees, suggesting that naturally established adult trees only occur in sites where climatic conditions allow the recruitment of juvenile stages. These results support the proposal that climatic niches of invasive plants should be modelled with data of naturally established individuals because this improves the accuracy of predictions about their distribution ranges.