9,864 research outputs found
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Lost and Found: the Bristlecone Pine Collection
No full textThis item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring Research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
A study of the ring opening metathesis polymerization of polycyclic aromatic monomers and cyclopentenes with well defined initiators
No full textThis thesis describes studies into the ring opening metathesis polymerisation (ROMP) of polycyclic aromatic monomers and cyclopentenes. Chapter 1 reviews general aspects of ring opening metathesis polymerisation of relevance to the themes of this thesis. Chapter 2 describes the synthesis of polycyclic aromatic monomers, the endo and the exo Diels-Alder adducts of acenaphthylene and cyclopentadiene. Chapter 3 reports a study on the polymerisation of these monomers using well defined initiators and classical catalyst systems. Chapter 4 describes the synthesis of a substituted cyclopentene. Chapter 5 reports an investigation of polymerisation of cyclopentene using a variety of well defined initiators of general formula M(=NAr)(- OR)(_2)(=CHR) where M=Mo or W. Chapter 6 presents a study on the polymerisation of a substituted cyclopentene, 4-methylcyclopentene, using a series of well defined initiators, and the characterisations of the polymers obtained using infrared, (^1)H, and (^13)C n.m.r. spectroscopy, differential scanning calorimetry, and gel permeation chromatography and an analysis of detailed microstructure with respect to meso/racemic configurations in the polymer chain. Finally, Chapter 7 summarises the conclusions and makes some suggestions for future work
Numerical modelling of optical micro-cavity ring resonators for WDM networks
No full textAugmenting the level of integration for a lower cost and enhancing the performance of the
optical devices have turned out to be the focus of many research studies in the last few
decades. Many distinct approaches have been proposed in a significant number of researches
in order to meet these demands. Optical planar waveguides stand as one of vital employed
approach in many studies. Although, their low propagation loss, and low dispersion, they
suffers from high power losses at sharp bends. For this reason, large radius of curvature is
required in order to achieve high efficiency and compromise the high level of integration. For
the purpose of this research, in this thesis different ways to improve the performance of
optical microcavity ring resonators (MRRs) have been thoroughly investigated and new
configurations have been proposed.
The Multiresolution Time Domain (MRTD) technique was further developed and employed throughout this thesis as the main numerical modelling technique. The MRTD algorithm is
used as a computer code. This code is developed and enhanced using self built Compaq
Visual Fortran code. Creating the structure and Post-processing the obtained data is carried
out using self built MATLAB code. The truncating layers used to surround the computational
domain were Uniaxial Perfectly Matched Layers (UPML). The accuracy of this approach is
demonstrated via the excellent agreement between the results obtained in literature using
FDTD method and the results of MRTD.
This thesis has focused on showing numerical efficiency of MRTD where the mesh size
allowed or the total number of computed points is about half that used with FDTD.
Furthermore, the MRR geometry parameters such as coupling gap size, microring radius of curvature, and waveguide width have been thoroughly studied in order to predict and
optimise the device performance.
This thesis also presents the model analysis results of a parallel-cascaded double-microcavity
ring resonator (PDMRR). The analysis is mainly focus on the extraction of the resonant
modes where the effect of different parameters of the structure on transmitted and coupled
power is investigated.
Also, accurate analysis of 2D coupled microcavity ring resonator based on slotted
waveguides (SMRR) has been thoroughly carried out for the purpose of designing optical
waveguide delay lines based on slotted ring resonator (SCROW).
The SCROW presented in this thesis are newly designed to function according to the
variation of the resonance coupling efficiency of a slotted ring resonators embedded between two parallel waveguides.
The slot of the structures is filled with SiO2 and Air that cause the coupling efficiency to vary
which in turn control both the group velocity and delay time of SCROW structures results
from the changing the properties of the bent slotted waveguide modes which strongly
depends on the slot’s position.
Significant improvements on the quality factor and greater delay time have been achieved by
introducing sub-wavelength-low-index slot into conventional waveguide
Effect of confinement on the decay of vortex ring
No full textThe effect of confinement on the decay of vortex ring is studied computationally using Lattice Boltzmann Method. An Initial vortex ring, introduced inside a wall bounded cubical domain, is let to evolve and its decay is noted in terms of maximum vorticity at the core and the total kinetic energy inside the domain. The study shows distinct regimes of decay in all cases of confinement ratios(ratio of vortex ring diameter to length of the cubical domain)
Ring Rotterdam als lab voor een integrale aanpak
No full textHet ministerie van IenW heeft de Leerstoel Gebiedsontwikkeling en de Vereniging Deltametropool gevraagd de mogelijkheden te verkennen voor een toekomstbestendige (her)ontwikkeling van de Ring Rotterdam en omgeving. Welke ontwerp- en sturingsaanpak hoort daarbij? “Niet de wil, maar de systematiek staat duurzame verstedelijking in de weg.”Urban Development ManagementPractice Chair Urban Area Developmen
Volcanic cooling signal in tree ring temperature records for the past millennium
No full textThe authors acknowledge the National Science Foundation for funding much of the research presented herein. RW's Scottish work is currently funded through the UK Leverhulme Trust and Natural Environment Research Council (NERC) projects, “RELiC: Reconstructing 8000 years of Environmental and Landscape change in the Cairngorms (F/00 268/BG)” and “SCOT2K: Reconstructing 2000 years of Scottish climate from tree rings (NE/K003097/1).”Tree rings are an important proxy for understanding the timing and environmental consequences of volcanic eruptions as they are precisely dated at annual resolution and, particularly in tree line regions of the world, sensitive to cold extremes that can result from climatically significant volcanic episodes. Volcanic signals have been detected in ring widths and by the presence of frost-damaged rings, yet are often most clearly and quantitatively represented within maximum latewood density series. Ring width and density reconstructions provide quantitative information for inferring the variability and sensitivity of the Earth's climate system on local to hemispheric scales. After a century of dendrochronological science, there is no evidence, as recently theorized, that volcanic or other adverse events cause such severely cold conditions near latitudinal tree line that rings might be missing in all trees at a given site in a volcanic year (stand-wide missing rings), resulting in misdating of the chronology. Rather, there is a clear indication of precise dating and development of rings in at least some trees at any given site, even under adverse cold conditions, based on both actual tree ring observations and modeling analyses. The muted evidence for volcanic cooling in large-scale temperature reconstructions based at least partly on ring widths reflects several factors that are completely unrelated to any misdating. These include biological persistence of such records, as well as varying spatial patterns of response of the climate system to volcanic events, such that regional cooling, particularly for ring widths rather than density, can be masked in the large-scale reconstruction average.Peer reviewe
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A Machine Learning Approach To Analyzing The Relationship Between Temperatures And Multi-Proxy Tree-Ring Records
No full textMachine learning (ML) is a widely unexplored field in dendroclimatology, but it is a powerful tool that might improve the accuracy of climate reconstructions. In this paper, different ML algorithms are compared to climate reconstruction from tree-ring proxies. The algorithms considered are multiple linear regression (MLR), artificial neural networks (ANN), model trees (MT), bagging of model trees (BMT), and random forests of regression trees (RF). April-May mean temperature at a Quercus robur stand in Slovenia is predicted with mean vessel area (MVA, correlation coefficient with April-May mean temperature, r = 0.70, p 0.05 (ns)) chronologies. The predictive performance of ML algorithms was estimated by 3-fold cross-validation repeated 100 times. In both spring and summer temperature models, BMT performed best respectively in 62% and 52% of the 100 repetitions. The second-best method was ANN. Although BMT gave the best validation results, the differences in the models' performances were minor. We therefore recommend always comparing different ML regression techniques and selecting the optimal one for applications in dendroclimatology.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Statistical Significance and Reproducibility of Tree-Ring Response Functions
No full textThis paper is concerned with the overall significance and reproducibility of the response function. A test of significance is devised which is based on the Binomial distribution. Combined with other tests, the method is then used to compare two different response functions to examine the reproducibility of climate-chronology response. Two approaches are used: the first compares two response functions covering the same period from the same site, based on independent chronologies of the same species; the second compares the response of a single chronology over two equal non-overlapping time periods. The results suggest that the response in the examples used is statistically reproducible on a site, and statistically stable over periods of time.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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Tom Landry, 70th birthday party, part 1
No full textVideo of part 1 of "an evening of sport and spirit" in honor of Tom Landry's 70th birthday party. This segment features former U.S. Secretary of Education and Drug Czar Bill Bennett, and Dallas Cowboys Ring of Honor recipients. Cynthia Clawson performs the Star-Spangled Banner. The DFW Mass Choir (directed by Rev. Dr. Armond W. Brown) also performs. Former Cowboys player Tony Dorsett was present, as was Randy White. The event was recorded live, and this video includes the playing of videos at the event not seen on this recording. The host also announces silent auction logistics and raffle winners, and this recording ends as he introduces Louise Mandrell
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