572 research outputs found
Development and application of the vinylepoxide – dihydrofuran rearrangement
The vinylepoxide - diliydrofuran rearrangement offers a route to substituted 2,3- dihydrofurans with a high degree of diastereoselectivity. The rearrangement proceeds via an ylide-type intermediate arising from the thermolysis of a carbon-carbon epoxide bond. This thesis discusses work aimed at developing the rearrangement, introducing asymmetric control, and application of the dihydrofuran products in target molecule synthesis. Synthesis of the vinylepoxide rearrangement precursors is described, and development of the rearrangement to achieve a moderate scale rearrangement process is discussed. Alternative rearrangement technologies are also explored. Asymmetric induction into the rearrangement was approached by the use of chiral auxiliaries and in particular C2 symmetric amines. A novel synthesis of (S,S)-2,5-diphenylpyrrolidine and (S,S)-2,6-diphenylpiperidine is reported. High degrees of enantiomeric purity were achieved through the application of an effective oxazaborolidine catalyst in the reduction of dibenzoylethane and dibenzoylpropane. Use of this chiral reduction catalyst on further diketones is described. Application of the dihydrofuran products in the synthesis of several 2,6-disubstituted- 3,7-dioxabicyclo[3.3.0]octanes. These compounds, commonly termed furofuran lignans exhibit a wide range of biological properties. The dihydrofuran products were combined with a range of dimethylacetals, in a one pot synthesis, with high degrees of stereocontrol, by a Noyori type transacetalisation. Further derivatisation of these bicyclic compounds was accomplished and is discussed.Finally, with the vinylepoxide - dihydrofuran rearrangement established a preliminary exploration of the related vinylaziridine - 2-pyrroline rearrangement is reported
Edge Dominating Sets and Vertex Covers
Bipartite graphs with equal edge domination number and maximum matching cardinality are characterized. These two parameters are used to develop bounds on the vertex cover and total vertex cover numbers of graphs and a resulting chain of vertex covering, edge domination, and matching parameters is explored. In addition, the total vertex cover number is compared to the total domination number of trees and grid graphs
China and the Fifth Estate: Net Delusion or Democratic Potential?
Arguably, liberal democratic societies are seeing the emergence of a ‘Fifth Estate’ that is being enabled by the Internet. This new organizational form is comparable to, but potentially more powerful than, the Fourth Estate, which developed as a significant force in an earlier period with an independent press and other mass media. While the significance of the press and the Internet to democratic governance is questioned in all societies, there is particular skepticism of their relevance outside the most liberal democratic regimes, which have a relatively free press and more pluralistic political systems, such as in North America and West Europe. Nevertheless, there have been vivid examples of where networked individuals have appeared to assert greater communicative power in the politics of governance, the media and everyday life, even in non-liberal democratic regimes, such as Hong Kong, and in some cases, China. This potential points to the need for more systematic empirical research in a wider variety of economic and political settings worldwide, particularly in states in which the Internet might offer a potential for more democratic governance and greater accountability of government controlled media. This paper examines cases in which networked individuals in China used the Internet to hold governmental and press institutions more accountable. The cases provide support for the relevance of the Fifth Estate concept in China, and also illuminates the process – showing how the Internet can be used to empower networked individuals in more autocratic regimes
Development of sampling efficiency and internal noise in motion detection and discrimination in school-aged children
AbstractThe aim of this study was to use an equivalent noise paradigm to investigate the development and maturation of motion perception, and how the underlying limitations of sampling efficiency and internal noise effect motion detection and direction discrimination in school-aged children (5–14years) and adults. Contrast energy thresholds of a 2c/deg sinusoidal grating drifting at 1.0 or 6.0Hz were measured as a function of added dynamic noise in three tasks: detection of a drifting grating; detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Compared to the ideal observer, in both children and adults, the performance for all tasks was limited by reduced sampling efficiency and internal noise. However, the thresholds for discrimination of motion direction and detection of moving gratings show very different developmental profiles. Motion direction discrimination continues to improve after the age of 14years due to an increase in sampling efficiency that differs with speed. Motion detection and summation were already mature at the age of 5years, and internal noise was the same for all tasks. These findings were confirmed in a 1-year follow-up study on a group of children from the initial study. The results support suggestions that the detection of a moving pattern and discriminating motion direction are processed by different systems that may develop at different rates
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Application of Advanced Reservoir Characterization, Simulation and Production Optimization Strategies to Maximize Recovery in Slope and Basin Clastic Reservoirs, West Texas (Delaware Basin)
The objective of this Class III project is to demonstrate that detailed reservoir characterization of slope and basin elastic reservoirs in sandstones of the Delaware Mountain Group in the Delaware Basin of West Texas and New Mexico is a cost-effective way to recover oil more economically through geologically based field development. The project is focused on East Ford, a Delaware Mountain Group field that produces from the upper Bell Canyon Formation (Ramsey sandstone). The field, discovered in 1960, is operated by Orla Petco, Inc., as the East Ford unit. A CO2 flood is being conducted in the unit, and this flood is the Phase 2 demonstration for the project. Reservoir characterization was conducted using logs and pressure and production information from the East Ford unit, supplemented by Bell Canyon outcrop data and information from the nearby Geraldine Ford field. Characterization was enhanced this year by recovery of a core from the Ramsey reservoir interval in the EFU 41R well. Ramsey sandstones are interpreted as having been deposited in a basin-floor setting in a channel-levee system with attached lobes. Overbank splays are interpreted as being the main area of sand storage outside of the channels. Porosity and permeability of the reservoir sandstones are controlled by calcite cement that can be concentrated in layers ranging from 5 to 40 cm in thickness. These laterally extensive calcite-cemented layers form significant vertical permeability baffles in some areas of the reservoir.Bureau of Economic Geolog
CMOS SPAD-based image sensor for single photon counting and time of flight imaging
The facility to capture the arrival of a single photon, is the fundamental limit to the detection of quantised
electromagnetic radiation. An image sensor capable of capturing a picture with this ultimate optical and
temporal precision is the pinnacle of photo-sensing. The creation of high spatial resolution, single photon
sensitive, and time-resolved image sensors in complementary metal oxide semiconductor (CMOS) technology
offers numerous benefits in a wide field of applications. These CMOS devices will be suitable to replace high
sensitivity charge-coupled device (CCD) technology (electron-multiplied or electron bombarded) with
significantly lower cost and comparable performance in low light or high speed scenarios. For example, with
temporal resolution in the order of nano and picoseconds, detailed three-dimensional (3D) pictures can be
formed by measuring the time of flight (TOF) of a light pulse. High frame rate imaging of single photons can
yield new capabilities in super-resolution microscopy. Also, the imaging of quantum effects such as the
entanglement of photons may be realised.
The goal of this research project is the development of such an image sensor by exploiting single photon
avalanche diodes (SPAD) in advanced imaging-specific 130nm front side illuminated (FSI) CMOS technology.
SPADs have three key combined advantages over other imaging technologies: single photon sensitivity,
picosecond temporal resolution and the facility to be integrated in standard CMOS technology. Analogue
techniques are employed to create an efficient and compact imager that is scalable to mega-pixel arrays. A
SPAD-based image sensor is described with 320 by 240 pixels at a pitch of 8μm and an optical efficiency or
fill-factor of 26.8%. Each pixel comprises a SPAD with a hybrid analogue counting and memory circuit that
makes novel use of a low-power charge transfer amplifier. Global shutter single photon counting images are
captured. These exhibit photon shot noise limited statistics with unprecedented low input-referred noise at an
equivalent of 0.06 electrons.
The CMOS image sensor (CIS) trends of shrinking pixels, increasing array sizes, decreasing read noise, fast
readout and oversampled image formation are projected towards the formation of binary single photon imagers
or quanta image sensors (QIS). In a binary digital image capture mode, the image sensor offers a look-ahead to
the properties and performance of future QISs with 20,000 binary frames per second readout with a bit error
rate of 1.7 x 10-3. The bit density, or cumulative binary intensity, against exposure performance of this image
sensor is in the shape of the famous Hurter and Driffield densitometry curves of photographic film.
Oversampled time-gated binary image capture is demonstrated, capturing 3D TOF images with 3.8cm
precision in a 60cm range
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