• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 15
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 35
  • 6
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

The detection and characterisation of extrasolar planets

Leigh, Christopher January 2004 (has links)
Since the discovery of 51 Pegasi b in 1995, continued observations have indirectly identified over 110 planetary objects. These Jupiter-mass objects cause their host star to "wobble" slightly about the common centre-of-mass of the system, which is detectable as radial motion in high-precision Doppler spectroscopy. Of the known planets, approximately 20% are found to orbit within 0.1 AU of the star, whilst the transit of HD209458 has inferred the gas-giant nature of these close-in extrasolar giant planets (CEGPs). The discovery of CEGPs has produced a wave of speculative theory as to the exact nature of these objects, and how they came to exist so close to their parent star. Our spectroscopic technique provides a method of achieving the direct detection of a CEGP atmosphere, the results of which will allow us to test emerging models that aim to predict the atmospheric nature of CEGPs and may provide additional information on the orbital inclination and mass of the planet. We start with a historical review of the field of extrasolar planets, followed by an introduction to the fundamental concepts which underpin the reflection of starlight from a planet's surface. We then investigate the prospects of detecting such a reflection, before detailing the technique we have devised and applied here to two known CEGP hosts. In the first instance, r Bootis, we combined observations at the 4.2-m William Herschel telescope in 1998, 1999 and 2000. The dataset comprised 893 high-resolution échelle spectra with a total integration time of 75hr 32min spanning 17 nights. We establish an upper limit on the planet's geometric albedo p < 0.39 (at the 99.9% significance level) at the most probable orbital inclination i ~ 36 deg, assuming a grey albedo, a Venus-like phase function and a planetary radius Rp - 1.2RJup. Although a weak candidate signal appears near to the most probable radial velocity amplitude, its statistical significance is insufficient for us to claim a detection with any confidence. In the second instance, HD75289, 4 nights of VLT(UT2)/UVES observations were secured in 2003 Jan, yielding 684 high-resolution spectra with a total integration time of 26 hours. We establish an upper limit on the planet's geometric albedo p < 0.12 (to the 99.9% significance level) at the most probable orbital inclination i ~/= 60 deg, assuming a grey albedo, a Venus-like phase function and a planetary radius Rp = 1.6RJup. In both cases, we are able to rule out some combinations of the predicted planetary radius and atmospheric albedo models with high, reflective cloud decks.
22

An Empirical Assessment of the 2004 EU Merger Policy Reform

Duso, Tomaso, Gugler, Klaus, Szücs, Florian 21 November 2013 (has links) (PDF)
Based on a database of 368 merger cases scrutinized by the European Commission (EC) between 1990 and 2007, we evaluate the economic impact of the change in European merger legislation in 2004. We propose a general framework to assess merger policy effectiveness, focusing on four different policy dimensions: 1) predictability, 2) decision errors, 3) reversion of anti-competitive rents, and 4) deterrence. We compare the results before and after the reform, finding that the "more economic approach" resulted in improved ex-ante predictability of decisions and a reduction of the frequency of type I errors. Merger policy enforcement deters anti-competitive mergers without over-deterring pro-competitive transactions. Yet, the policy shift away from prohibitions, which are effective as a policy tool and as a deterrence mechanism, does not seem to be well grounded. (authors' abstract)
23

Is the event study methodology useful for merger analysis? A comparison of stock market and accounting data

Duso, Tomaso, Gugler, Klaus, Yurtoglu, Burcin B. 21 January 2010 (has links) (PDF)
This paper presents empirical evidence about the ability of event studies to capture mergers' ex-post profitability as measured by accounting data. We use a sample of large horizontal concentrations during the period 1990-2002 involving 482 firms either as merging firms or competitors, and contrast a measure of the mergers' profitability based on stock market event studies with one based on balance sheet profit data. We show that using a long window around the announcement date (25 or 50 days before the event) increases the ability to capture the ex-post merger effect: the pairwise correlation coefficient is positive and highly significant.
24

A Functional Approach to Memory-Safe Operating Systems

Leslie, Rebekah 01 January 2011 (has links)
Purely functional languages--with static type systems and dynamic memory management using garbage collection--are a known tool for helping programmers to reduce the number of memory errors in programs. By using such languages, we can establish correctness properties relating to memory-safety through our choice of implementation language alone. Unfortunately, the language characteristics that make purely functional languages safe also make them more difficult to apply in a low-level domain like operating systems construction. The low-level features that support the kinds of hardware manipulations required by operating systems are not typically available in memory-safe languages with garbage collection. Those that are provided may have the ability to violate memory- and type-safety, destroying the guarantees that motivate using such languages in the first place. This work demonstrates that it is possible to bridge the gap between the requirements of operating system implementations and the features of purely functional languages without sacrificing type- and memory-safety. In particular, we show that this can be achieved by isolating the potentially unsafe memory operations required by operating systems in an abstraction layer that is well integrated with a purely functional language. The salient features of this abstraction layer are that the operations it exposes are memory-safe and yet sufficiently expressive to support the implementation of realistic operating systems. The abstraction layer enables systems programmers to perform all of the low-level tasks necessary in an OS implementation, such as manipulating an MMU and executing user-level programs, without compromising the static memory-safety guarantees of programming in a purely functional language. A specific contribution of this work is an analysis of memory-safety for the abstraction layer by formalizing a meaning for memory-safety in the presence of virtual-memory using a novel application of noninterference security policies. In addition, we evaluate the expressiveness of the abstraction layer by implementing the L4 microkernel API, which has a flexible set of virtual memory management operations.
25

The dynamics of suspended particles in a seasonally stratified coastal sea

Cross, Jaimie January 2013 (has links)
A comprehensive investigation into the relationship between physical forcing and sus- pended particles in the shallow shelf region of the Western English Channel has been conducted, in order to evaluate the temporal dynamics of suspended particle populations. Measurements were taken across tidal cycles and seasons at station L4, part of the Western Channel Observatory (WCO), using the combination of a free-fall microstructure profiler and holographic imaging. Confirmation that L4 is weakly stratified is given, and that the formation of the seasonal thermocline is substantially altered by the spring-neap cy- cle. Stratification is variable and prone to periodic and partial erosion from atmospheric forcing during any point in any season. L4 undergoes moderate turbulent dissipation, principally as a result of tidal forcing. Typically, values of ε do not exceed 10−4 W kg−1 . L4 also exhibits tidal asymmetry, chiefly in response to stratification which, albeit weak, is frequently able to suppress turbulence when generated from the sea bed. The potential energy anomaly is small at L4, as expected for a weakly-stratified environment. Maxi- mum values in summer were shown to not exceed 50 J m−3 . Values of bed stress, τ0 , are rarely greater than around 0.18 N m−2 . Nonetheless, the critical erosion threshold falls below this, and is therefore smaller than that observed in similar locations around the UK. Seasonality in the amount of material resuspended from the seabed is important at L4. The presence of certain biological particles strongly influence particle size and may also determine if a given particle is lifted from the bed. Particles ≥ 200 μm are relatively rare, the site is dominated by particles smaller than this value in line with many other UK sites. Under certain conditions the theoretical maximum limit of particle size, the Kolmogorov length scale, does not hold and many examples of occasions when this threshold is exceeded are shown. This may generate important consequences in subsequent work undertaken at this site and other temperate shelf locations globally, particularly as these results indicate that maximum particle size appears to be governed less by the size of the local turbulent eddies and more by the presence of biological particles. This is another key seasonal component to particle dynamics in the Western English Channel. Phytoplankton populations are readily advected into and out of the L4 site, calling into question the current sampling strategy of the WCO to rely exclusively upon point measurements. Small increases in atmospheric forcing have the ability to rapidly disperse patches of phytoplankton, possibly to the point of cell mortality. Traditional sampling techniques for assessing zooplankton density have been shown to radically underestimate the number of animals present at L4, which will increase error estimates on current ecosystem models.
26

Characterisation of organic materials for photovoltaic devices

Lewis, Andrew J. January 2006 (has links)
This thesis presents an investigation into a wide range of potential materials for organic photovoltaic (PV) devices. A variety of optical techniques are used to define physical parameters for each material such as the photoluminescence quantum yield (PLQY), absorption coefficient and exciton diffusion length. Electrical characterisation is used to determine the optimal structure for devices fabricated with these materials. A number of novel materials are presented in this thesis. These include new polymers, both soluble and precursor, and a relatively new class of material, the conjugated dendrimer. These are highly configurable branching molecular structures that enable fine tuning of material properties. Work on polymers presented in this thesis investigates how such materials can be improved by testing the effect of small changes to their molecular structure. One of these changes had significant effects upon the overall material characteristics. The introduction of a dipole across a polymer successfully created a charge separating material without the need for an extra species such as C60 to be present. The introduction of the conjugated dendrimer to PV applications allows significant scope for molecular engineering. Dendrimers enable tight control over certain aspects of the molecular properties. Small changes can be made such as colour tuning or solubility that enable optimisation to be performed on the molecular level, rather than on device structure. Such changes produced significantly higher internal quantum efficiencies (> 90%) than typical polymer devices and offer the prospect of power conversion efficiencies in excess of 10%. Time-resolved luminescence (TRL) spectroscopy was used to characterise the behaviour of photogenerated excitons within organic films. The investigation of exciton diffusion length was performed upon two polymers, each utilising two different time-resolved methods; diffusion to a quencher and exciton-exciton annihilation. It was found that diffusion in polythiophene films is anisotropic and the photoluminescence lifetime is dependent upon film thickness. This is explained by the formation of self-ordered microstructures during the spin coating process. Data modelling was performed which took into account both the thickness variation and the interaction of excitons with a quenching interface producing a much more realistic approach than previously published work.
27

Material and device design for organic optoelectronics

Levell, Jack William January 2011 (has links)
This thesis describes investigations into the photophysical properties of luminescent materials and their application in optoelectronic devices such as light emitting diodes and photodetectors. The materials used were all solution processable because of the interest in low cost processing of organics. I have investigated the photophysics of 1,4,5,8,9,12-hexamethyltriphenylene, a triphenylene derivative which has its luminescence enhanced by the addition of methyl groups. These groups change the planar shape of the triphenylene molecule into a twisted one, changing the symmetry of the molecule and increasing its dipole moment in absorption and emission by ~4 fold. This increased its rate of radiative deexcitation by ~20 times. In addition, the twisted shape of the molecule prevents intermolecular interactions and concentration effects from affecting the luminescence. This results in an efficient solid-state photoluminescence quantum yield of 31%. This thesis also includes an investigation into phosphorescent polymer dendrimers, designed to have suitable viscosities in solution for inkjet printed OLED applications. A photophysical study of the intra-chain aggregation effects on the luminescence was undertaken in both homopolymers and copolymers with high energy gap spacer units. Using double dendrons to increase the steric protection of the luminescent cores, the best homopolymers achieved 12.1% external quantum efficiency (39.3 cd/A) at 100 cd/m² brightness and the best co-polymer achieved 14.7% EQE (48.3 cd/A) at 100 cd/m². This compares favourably with 11.8% EQE for the best phosphorescent polymer and 16% for the best solution processed dendrimer OLED previously reported. Finally I have applied a solution processed enhancement layer to silicon photodiodes to enhance their ultraviolet response. Using a blend of materials to give favourable absorption and emission properties, 61% external quantum efficiency was achieved at 200 nm, which is better than the 20-30% typical for vacuum deposited lumogen enhancement layers used commercially.
28

Implementace protokolu ACP do operačního systému L4 / Implementation of the ACP protocol into L4 operating system

Kolarík, Tomáš January 2012 (has links)
This thesis deals with the implementation of ACP protocol which serves to manage the access for operation system based on L4 microkernel. The theoretical part of the thesis deals with methods of access management in computer networks. It focuses primarily on AAA systems which make access management possible. Furthermore it describes in detail the ACP protocol, the types of messages and their feedback. The next theoretical part is dedicated to operation systems and in particular to their architecture and services. Then we get a closer look at L4 microkernel family, their philosophy and properties. We continue with a detailed description of the L4 application interface and its ways of expansion. The practical section deals with the implemented concept of system for ACP protocol support in computers. General concept is then applied in real implementation of ACP protocol into the L4 operation system environment based on the L4 platform. To assist, I also included a detailed tutorial explaining the modeling and compilation of software for this platform. At this point we describe the methods used at the implementation and the description of particular modules and features. The end of the thesis concludes the information about the ways of testing and the implementation properties.
29

Dynamics of interplay between third-party interveners and national factions in civil war peace negotiations : case studies on Cambodia and El Salvador

Lee, Sung Yong January 2011 (has links)
This thesis examines the processes of the peace negotiations in Cambodia (1987-1993) and El Salvador (1989-1993) in order to address the following question: What does the interplay between the national factions and the external interveners in peace negotiations tell us about their chances of achieving their goals? By using the concept of ‘interplay,’ this study reinterprets the negotiation processes as the negotiating actors’ exchanges of strategic moves. In particular, it explores how the negotiating actors’ attitudes towards the core negotiation issues changed in the two cases and how the changes affected their counterparts’ negotiating strategies. There are two aspects to the findings of this thesis, one descriptive and the other explanatory. First, this study has investigated the characteristics of the negotiating actors’ strategies and the pattern of the interplay between them. As for the interveners’ strategies, this thesis finds that impartial third parties generally employ diplomatic intervention methods, while advocate states enjoy a wider range of options. In addition, national factions’ behaviour is generally affected by three factors: their fundamental goals, the domestic resources under their control, and the incentives or pressure from external interveners. It is also observed that the stronger the intervention becomes, the more that national factions’ provisional strategies are inclined to be receptive towards the intervention. Nevertheless, the national factions rarely fully accepted proposals that they deemed harmful to the achievement of their fundamental goals. Second, based on the descriptive findings, this thesis highlights the importance of mutual understanding between national factions and external interveners. The case studies of Cambodia and El Salvador show that the effectiveness of a particular intervention depends not so much on the type of method employed but on the context in which it is applied. An intervention is more likely to be effective when it is used in a way that national factions can understand and is supported by the consistently strong attention of external interveners. In addition, it is observed that actors’ ethnocentric perceptions on core concepts of conflict and negotiation as well as their lack of an effective communication capability are some of the common causes of the misunderstandings that arise during negotiation processes.
30

Corporate social responsibility and gambling industry : an exploratory study

Leung, Cheng Han January 2014 (has links)
Corporate Social Responsibility (CSR) is one important response to the increasing amounts of criticism levelled at corporations. A number of studies have focused on CSR in a range of industries; however, some contentious industries, e.g. the gambling industry, remain unexplored. Mobilizing CSR in a novel setting not only enhances the knowledge of CSR and gambling, but also provides an overview of this industry itself. This thesis attempts to investigate three questions: to what extent does the gambling industry disclose CSR-related data, how is CSR understood in this industry and why does the gambling industry engage in CSR? This thesis provides a general overview of the international gambling industry and an in-depth investigation of Macao's gambling industry. The research design of the thesis employs mixed methods: content analysis and semi-structured interviews. The principal research is based on 49 interviews. This thesis advances three main arguments. First, it will be argued that there are relatively low volumes of Corporate Social Disclosure (CSD) and Responsible Gambling (RG) disclosure in the international gambling industry, which can be viewed as a legitimising strategy. Second, in Macao's gambling industry, it is argued that organisations in this industry tend to place a greater emphasis on positive social impacts, while obscuring such negative impacts as gambling addiction and health-related issues. Third, this thesis holds that organisations in Macao's gambling industry engage symbolically, rather than substantively, with CSR and RG in order to manage stakeholders' perceptions in an attempt to gain different sources of legitimacy and in turn to enhance its economic interests. In conclusion, the gambling industry does not entirely conform to the institutional environment, which poses a challenge to the organisational legitimacy literature. This thesis introduces a necessary caution into the discussions about the extent of CSD, CSR, and RG in this industry more generally.

Page generated in 0.033 seconds