387 research outputs found
Cycle Double Covers and Integer Flows
My research focuses on two famous problems in graph theory, namely the cycle double cover conjecture and the integer flows conjectures. This kind of problem is undoubtedly one of the major catalysts in the tremendous development of graph theory. It was observed by Tutte that the Four color problem can be formulated in terms of integer flows, as well as cycle covers. Since then, the topics of integer flows and cycle covers have always been in the main line of graph theory research. This dissertation provides several partial results on these two classes of problems
Flexible and Stretchable Electronics
Flexible and stretchable electronics are receiving tremendous attention as future electronics due to their flexibility and light weight, especially as applications in wearable electronics. Flexible electronics are usually fabricated on heat sensitive flexible substrates such as plastic, fabric or even paper, while stretchable electronics are usually fabricated from an elastomeric substrate to survive large deformation in their practical application. Therefore, successful fabrication of flexible electronics needs low temperature processable novel materials and a particular processing development because traditional materials and processes are not compatible with flexible/stretchable electronics. Huge technical challenges and opportunities surround these dramatic changes from the perspective of new material design and processing, new fabrication techniques, large deformation mechanics, new application development and so on. Here, we invited talented researchers to join us in this new vital field that holds the potential to reshape our future life, by contributing their words of wisdom from their particular perspective
Modelling, simulation and control of photovoltaic converter systems
The thesis follows the development of an advanced solar photovoltaic power conversion
system from first principles. It is divided into five parts.
The first section shows the development of a circuit-based simulation model of a
photovoltaic (PV) cell within the 'SABER' simulator environment. Although simulation models
for photovoltaic cells are available these are usually application specific, mathematically intensive
and not suited to the development of power electronics. The model derived within the thesis is
a circuit-based model that makes use of a series of current/voltage data sets taken from an actual
cell in order to define the relationships between the cell double-exponential model parameters and
the environmental parameters of temperature and irradiance. Resulting expressions define a
'black box' model, and the power electronics designer may simply specify values of temperature
and irradiance to the model, and the simulated electrical connections to the cell provide the
appropriate I/V characteristic.
The second section deals with the development of a simulation model of an advanced PVaware
DC-DC converter system. This differs from the conventional in that by using an embedded
maximum power tracking system within a conventional linear feedback control arrangement it
addresses the problem of loads which may not require the level of power available at the
maximum power point, but is also able to drive loads which consistently require a maximum
power feed such as a grid-coupled inverter.
The third section details a low-power implementation of the above system in hardware.
This shows the viability of the new, fast embedded maximum power tracking system and also the
advantages of the system in terms of speed and response time over conventional systems.
The fourth section builds upon the simulation model developed in the second section by
adding an inverter allowing AC loads (including a utility) to be driven. The complete system is
simulated and a set of results obtained showing that the system is a usable one.
The final section describes the construction and analysis of a complete system in hardware
(c. 500W) and identifies the suitability of the system to appropriate applications
Mechanistic studies of high temperature reactions of hydrocarbons
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