Revealing Carrier-Envelope Phase through Frequency Mixing and Interference in Frequency Resolved Optical Gating

We demonstrate that full temporal characterisation of few-cycle electromagnetic pulses, including retrieval of the carrier envelope phase (CEP), can be directly obtained from Frequency Resolved Optical Gating (FROG) techniques in which the interference between non-linear frequency mixing processes is resolved. We derive a framework for this scheme, defined Real Domain-FROG (ReD-FROG), as applied to the cases of interference between sum and difference frequency components and between fundamental and sum/difference frequency components. A successful numerical demonstration of ReD-FROG as applied to the case of a self-referenced measurement is provided. A proof-of-principle experiment is performed in which the CEP of a single-cycle THz pulse is accurately obtained and demonstrates the possibility for THz detection beyond the bandwidth limitations of electro-optic sampling.Comment: 7 pages, 4 figures. To be submitted for publication in Optics Express, January 201

Educational Sociology: Its Province and Possibilities

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River, tidal and wind interactions in a deltaic estuarine system

The balance between river and marine influences is important in governing landscape sustainability in river deltas. River- and atmospherically driven sea level variability, sediment loading, and estuary-ocean exchange in the Mississippi River delta are examined in this study. Subtidal estuarine sea level variability in the Breton Sound estuary was driven by a combination of remote atmospheric forcing outside the estuary over the continental shelf and controlled river inputs through a gated diversion structure at the estuary head. The highly-frictional deltaic landscape acted as a low-pass filter to coastal fluctuations near the estuary mouth. When substantial quantities river water were discharged into the estuary, upper estuary sea levels responded to a combination of river and atmospheric forcing, while sea levels in the lower estuary responded only to coastal forcing. Annual sediment loading into Breton Sound through a Mississippi River diversion was approximately 1 × 105 metric tons yr-1. Four pulsed, high-discharge diversions were conducted during the study, and sediment loading across each pulse was highly variable and was greatest during rising limbs of Mississippi River floods. Overland flow was induced when diversion discharge exceeded 100 m3 s-1. These results indicate timing and magnitude of diversion events are both important factors governing marsh sediment deposition in river diversion receiving basins. Sediment inputs measured during this study were negligible compared to historical loading through crevasses in the region. An investigation of estuary-shelf exchanges through Barataria Pass revealed that tidal exchange accounted for approximately 80% of the observed flow variability. Two dominant vertical subtidal exchange modes were identified. A barotropic mode, which accounted for most of the flow variance, was most coherent with cross-shelf wind stress. A second mode resembling baroclinic estuarine circulation recurred over fortnightly timescales, apparently in response to variations in tidal stirring. The baroclinic mode also appeared to be modulated by variability in freshwater inputs to the estuary. These findings provide a greater understanding of the physical dynamics that govern landscape sustainability in microtidal river delta

Electron Impact Studies on Halogen Containing Molecules

The work described in this thesis has been divided into three sections, namely: 1. "The Latent Heat of Sublimation of Carbon and the Heat of Dissociation of Nitrogen." 2. "The Mass Spectra of Camphor and Some of its Halogen Derivatives." 3. "Electron Impact Studies on some Chlorinated Benzaldehydes." In Section 1 a study of the ionization and dissoc-riation of the molecules CX4 (X = F,Cl,Br); CHX3, CH2X2, CH3X (X = Cl,Br) and NH3 was undertaken. Appearance potentials of some of the positive ions produced under electron bombardment were obtained for each compound, while a suitable method was devised for the generation of some of the corresponding free radicals and the measure-sment of their ionization potentials. Dissociation processes were then selected to account for the formation of each ion. Combination of the experimental data in the appropriate equations then gave a series of bond dissoc-siation energies from which the heat of atomization of each compound was obtained. Substitution of this heat of atomization in a suitable thermochemical cycle then all:owed a value for the latent heat of carbon (Lc) or the heat of dissociation of nitrogen, D(N2), to be estimated. Prom the results it was concluded that Lc = 7.386 eV., and D(N2) = 9.756 eV. are most likely to be correct. In Section 2, the "Cracking Patterns" of camphor, alpha-bromo-, alpha-chloro-, beta-bromo-, beta-iodo-, alpha:alpha-dibromo- and alpha:beta-dibromo camphors are recorded. An attempt was then made to explain the occurrence of the principal peaks of each spectrum in terms of the current theories of the origin of mass spectra and to interpret the differences in the spectra of the seven compounds with the variation in molecular structure. This has been fulfilled with some modicum of success. Plausible mechanisms, based on such generalizations as facile allylic bond fission, ready elimination of CO and the occurrence of rearrange:ments promoted by the relative stabilities of the fragment ions, have been proposed for the production of the more prominent ions observed. It is emphasized that the results of the present work can only give an indication rather than a conclusive proof of the behaviour of the camphor skeleton under electron impact. In Section 3, the appearance and ionization potentials of some of the ions produced in the electron impact induced dissociation of o-, m- and p- chlorobenzalde-:hydes are recorded. The dissociation energies of the bond between CHO and the aromatic nucleus, D(Ar-CHO), was measured in each case, and compared with that of benzaldehyde itself. It was then possible to interpret the results in terms of the Inductive and Conjugative effects of the substituent chlorine atom. The dissociation energies of the corresponding bond in the molecule ion, D(Ar+-CHO), were also obtained. The relationship between D(Ar-CHO) and D(Ar+-CHO) was discussed, resulting in the tentative proposal that a benzaldehyde type molecule ion may undergo ring expansion to give an ionized derivative of tropone

Random Matrices with Correlated Elements: A Model for Disorder with Interactions

The complicated interactions in presence of disorder lead to a correlated randomization of states. The Hamiltonian as a result behaves like a multi-parametric random matrix with correlated elements. We show that the eigenvalue correlations of these matrices can be described by the single parametric Brownian ensembles. The analogy helps us to reveal many important features of the level-statistics in interacting systems e.g. a critical point behavior different from that of non-interacting systems, the possibility of extended states even in one dimension and a universal formulation of level correlations.Comment: 19 Pages, No Figures, Major Changes to Explain the Mathematical Detail

Asymmetric Diels-Alder Reactions of Acylnitroso Compounds

The Diels-Alder cycloaddition reactions of a small selection of transient C-nitroso compounds (two achiral and one chiral) were carried out with the unsymmetrically substituted, conjugated diene (E)-penta-1,3-diene 111 (piperylene). The aim of these experiments was to study the regiochemistry and any associated asymmetric induction of the cycloadducts. Acetohydroxamic acid 182d was oxidized, with periodate, in the presence of (E)-penta-1,3-diene 111 at

Experimental investigations of excited-state dynamics in conjugated polymers using time-resolved laser spectroscopy

In this thesis, time-resolved laser spectroscopy has been used to advance the understanding of the excited-state dynamics in a variety of conjugated polymers and related systems. The properties of electron-phonon coupling in the conjugated polymer ladder-type methyl-substituted poly(para-phenylene) have been investigated using steady-state and picosecond fluorescence spectroscopy, with results demonstrating the thermal population of low energy stretching modes of the polymer backbone in the excited-state after thermalisation. Polarised measurements are used to demonstrate a fundamental relationship between the vibrational mode of the polymer through which fluorescence occurs and the corresponding fluorescence polarisation. Time-resolved measurements confirmed that the electron-phonon coupling in the polymer does not influence the fluorescence lifetime, with observations to the contrary attributed to the presence of an underlying defect state. Picosecond fluorescence spectroscopy has also been used to investigate the properties of intramolecular energy transfer between different monomer subunits in the conjugated copolymer Super Yellow. The photoluminescence quantum yield of the copolymer was measured and its relatively high value was attributed to the effect of the aforementioned energy transfer. Femtosecond pump-probe spectroscopy has been used to identify and characterise the properties of interchain exciton formation in ladder-type methyl-substituted poly(para-phenylene). This process was observed to occur with a time period of 1ps, which was attributed to the time required for a singlet exciton to become delocalised over adjacent polymer chains. Finally, delocalised polaron generation in blends of the regio-regular polythiophene poly(3-dodecylthiophene-2,5-diyl) with the electron acceptor [6,6]-phenyl-C61-butyric acid methyl ester was investigated using femtosecond pump-probe spectroscopy. Both the rate and yield of delocalised polaron formation were shown to be dependent on excitation energy, with the dissociation of geminate polaron-pairs making a substantial contribution to the yield. This latter observation is significant, as the geminate recombination of polaron-pairs constitutes a fundamental and inherent loss of potential delocalised polarons in this system

The Application of Non-Axisymmetric Endwall Contouring in a 1½ Stage, Rotating Turbine

Today gas turbines are a crucial part of the global power generation and aviation industries. Small improvements to the efficiencies of individual components within the gas flow path can, over time, lead to dramatic cost savings for the operator and at the same time improve on the amount of carbon dioxide gas emissions to the environment. One such technology is the reduction of secondary flow losses in individual blade rows within the compressor or turbine section of the gas turbine through the use of non-axisymmetric endwall contouring. By introducing subtle geometrical features onto the endwall it has been shown to be possible to improve the efficiency of individual blade rows by between 1 and 2%. Few studies of these non-axisymmetric endwalls have been performed outside of the two dimensional cascade and computational domain, in addition these endwalls have been designed and tested to improve the performance of blade rows at a single design point with the off design performance having been ignored. The work presented here is aimed at investigating the use of such endwalls in a rotating blade row both at design and off-design conditions and in the presence of an upstream blade row. To this end a 1½ stage, low speed, turbine test rig has been refurbished and a new set of blades was designed to accommodate the profile of the Durham cascade at the hub. The Durham cascade is a de facto industry test case for non-axisymmetric endwall applications and therefore a generic, cascade proven, endwall design is available from the literature. The design of this new blade set is unique in that it is openly available. The results include steady-state 5-hole pressure probe measurements between blade rows and computational fluid dynamics solutions to provide detailed analysis of the flow quality found within the turbine. These results are reproduced for a turbine with annular or reference endwalls and one with the generic P2 endwall design obtained from the Durham cascade. Experimentally a 1.5% improvement in mixed out stage efficiency at the design condition has been found with a positive trend with increasing load. Additionally the rotor exit flows are show to be generally more uniform in the presence of profiled endwalls. The rotor torque is however reduced by as much as 3.5% and the improved flow uniformity does not always translate into a improved performance in the downstream row. Insight into the overall performance and fluid mechanics of the generic non-axisymmetric endwall at a variety of load conditions has been gained and an analysis of the parameters commonly used in optimising these endwalls is discussed with Cske being clearly shown to be the superior parameter in this case. CFD evidence suggests that while the cross passage pressure gradient is reduced by endwall profiling the extent of the effect of the change in hub endwalls reaches as far as the tip. The mechanism by which the overall loss is reduced appears to be a through a change in the relative strengths of the suction and pressure side horseshoe vortices and through the delayed migration of the passage cross flow, this change the relationship of these two vortex structures; dispersing the vortex structures as they leave the row and reducing the potential for mixing losses downstream

Improving Search Ranking Using a Composite Scoring Approach

In this thesis, the improvement to relevance in computerized search results is studied. Information search tools return ranked lists of documents ordered by the relevance of the documents to the user supplied search. Using a small number of words and phrases to represent complex ideas and concepts causes user search queries to be information sparse. This sparsity challenges search tools to locate relevant documents for users. A review of the challenges to information searches helps to identify the problems and offer suggestions in improving current information search tools. Using the suggestions put forth by the Strategic Workshop on Information Retrieval in Lorne (SWIRL), a composite scoring approach (Composite Scorer) is developed. The Composite Scorer considers various aspects of information needs to improve the ranked results of search by returning records relevant to the user’s information need. The Florida Fusion Center (FFC), a local law enforcement agency has a need for a more effective information search tool. Daily, the agency processes large amounts of police reports typically written as text documents. Current information search methods require inordinate amounts of time and skill to identify relevant police reports from their large collection of police reports. An experiment conducted by FFC investigators contrasted the composite scoring approach against a common search scoring approach (TF/IDF). In the experiment, police investigators used a custom-built software interface to conduct several use case scenarios for searching for related documents to various criminal investigations. Those expert users then evaluated the results of the top ten ranked documents returned from both search scorers to measure the relevance to the user of the returned documents. The evaluations were collected and measurements used to evaluate the performance of the two scorers. A search with many irrelevant documents has a cost to the users in both time and potentially in unsolved crimes. A cost function contrasted the difference in cost between the two scoring methods for the use cases. Mean Average Precision (MAP) is a common method used to evaluate the performance of ranked list search results. MAP was computed for both scoring methods to provide a numeric value representing the accuracy of each scorer at returning relevant documents in the top-ten documents of a ranked list of search results. The purpose of this study is to determine if a composite scoring approach to ranked lists, that considers multiple aspects of a user’s search, can improve the quality of search, returning greater numbers of relevant documents during an information search. This research contributes to the understanding of composite scoring methods to improve search results. Understanding the value of composite scoring methods allows researchers to evaluate, explore and possibly extend the approach, incorporating other information aspects such as word and document meaning