5,179 research outputs found
The AdS5 x S5 string and the one-loop correction to the circular Wilson loop.
No full textLa tesi tratta della correzione ad un loop al Wilson loop circolare nella rappresentazione totalmente simmetrica di rango K. La corrispondenza AdS/CFT reinterpreta tale quantità come funzione di partizione della stringa di tipo IIB in AdS5xS5.ope
Science, Engineering and Technology Research Funding Policy in Ireland 1995-2008: A Policy Document Analysis
No full textIn the period 1995 to 2008 there has been an increased level of government funding for research and development in higher education institutions in Ireland.
This thesis analyses the evolving theoretical literature on the production of knowledge, and traces how models of research and innovation have evolved in the contemporary period. Four models are discussed: (i) linear model, (ii) national systems of innovation, (iii) mode-2 science, and (iv) triple helix.
The thesis presents a detailed analysis of a series of public documents produced in Ireland in the period, and discusses how each one relates to the theoretical background. Some of these relationships are explicit, where documents cite key authors and the models as discussed in the theoretical literature. Some of the relationships are implicit, where the manner in which the process of research and development is described implies that certain models are being assumed.
The thesis subsequently discusses the results of this analysis, where it seems that the Irish policy literature is moving away from an engagement with at least some of these theoretical models, towards a very operationalised implementation strategy. This is epitomised by the development of the Strategy for Science Technology and Innovation.
The thesis finally makes a number of recommendations for policy makers, advising the more detailed study and analysis of Ireland’s own national system of innovation, and the prioritisation of the use of research funding to build up capabilities in identified areas of this system that are weak
Fluorescence in ultraviolet active binaries: the case of FF Aquarii
No full textThe eclipsing binary FF Aquarii (FF Aqr) consists of a small hot star of uncertain type and a red giant. An Hα feature varies from absorption during eclipse to maximum emission during hot star transit. We have obtained simultaneous differential photometry in BVRI bands and Hα spectroscopy in 1998 that covered an entire orbit with some overlap. A binary star model was used with our light-curve, radial velocity and Hα data to refine stellar and orbital parameters. A new ephemeris indicates that the period has increased or is longer than previously thought. A physically simple algorithm is developed that generates properly blended spectral line profiles of binaries with arbitrary combinations of surface emission and absorption line regions. Although there is no radiative transfer, the algorithm can accommodate modest geometrical intricacy. For now, all line broadening in the model is rotational. The algorithm has now been incorporated within the general Wilson-Devinney binary star model, and we used it to model FF Aqr\u27s photospheric iron profile. It also is used to generate templates that illustrate problems with FF Aqr\u27s strongly time-dependent Hα emission profiles, which appear to be blends of features from the photosphere and from above the photosphere. The dominant broadening mechanism should be rotation for individual line components. Absorption profiles were generated by the model and fit to the observations to yield a red star radius ~6.9 Rsolar, which then requires i~ 76°. Our light-curve models have five spots with temperatures ~1000 K cooler than the surrounding photosphere. Hα emission was modelled on the red star surface, centred at the substellar point to simulate a fluorescent chromosphere. Additional emission is seen outside our modelled profiles. The origins of this excess emission may be corotating prominences, winds, or coronal mass ejections, all of which could affect the orbit period
The Aresys FF-SAR Service for Cryosat-2 at ESA GPOD
No full textThe Fully-Focused SAR (FF-SAR) processing, introduced in Egido and Smith (2016) allows obtaining a maximum resolution of 0.5 m in the along-track direction. It provides significant benefits for inland water altimetry investigations allowing the successful investigation of very small rivers and canals (Kleinherenbrink, 2020) that are typically harder to be analysed by using unfocused Delay-Doppler SAR (DD-SAR) data (about 300 m resolution in the along-track direction).In its development, two major limitations were associated with the FF-SAR processing: 1) the presence of evenly spaced high sidelobes in the Point Target Response (PTR) due to the closed-loop burst mode implemented in Sentinel-3 & Cryosat-2 altimeter payloads, used for initial FF-SAR investigations, and 2) the heavy computational burden with respect to the unfocused DD-SAR processing. The first limitation can be overcome by designing the radar system differently adopting an open-loop transmission scheme as, for instance, the one implemented in the altimeter payload of the Sentinel-6 Michael Freilich mission, launched on 21 November 2020. The second limitation has been addressed in research works following Egido and Smith (2016) indicating that an improvement in terms of computational burden can be achieved by adopting algorithms in the frequency domain (Guccione et al., 2018).Being the role of FF-SAR for future inland water altimetry well understood, along with the possibility to see it implemented with reduced drawbacks during the Sentinel-6 Michael Freilich mission, a collaboration has started between the ESA GPOD Team, already hosting the successful SARvatore services portfolio for unfocused SAR & SARin altimetry, and Aresys. Aresys has developed a generic FF-SAR prototype processor, that is able to process data acquisition from different instruments and exploiting the frequency-domain Omega-K algorithm (Guccione et al., 2018 & Scagliola et al., 2018). The Aresys's FFSAR prototype processor for CryoSat-2 allows users to process, on line and on demand, low-level CryoSat FBR products in SAR mode up to FF-SAR Level-1 products with self-customized options. Additionally a wide set of processing parameters is configurable, allowing as an example to select the along-track resolution or to obtain FFSAR multilooked waveforms at the desired posting rate. The collaboration led to the creation of a new service for the processing of CryoSat Baseline D data in FF-SAR mode. Users will be able to select the following options: 1) range oversampling factor, 2) bandwidth factor (responsible for the along-track resolution value) and 3) multilook posting rate (1Hz-500Hz). Geophysical corrections and L2 estimates from both a threshold peak retracker and an ALES-like subwaveform retracker are part of the output package. In preliminary open ocean analyses, very good results on SSH noise have been obtained by the ALES-like subwaveform retracker.In this presentation, the Aresys FF-SAR prototype processor is described and the outcome of some preliminary validation activities, performed by a group of altimetry researchers, is reported. The service is scheduled to open to all GPOD/SARvatore users in the first semester of 2021. Future evolutions should include the extension of the service to Sentinel-3 and Sentinel-6 data.Astrodynamics & Space Mission
Combining macros and SAT planning
No full textPlanning based on propositional satisfiability is a powerful approach for computing makespan-optimal plans. However, it is usually slower then heuristic-based sub-optimal approaches. In this work we propose MacroSatPlan; a SatPlan based planner which exploits macros extracted by Macro-FF and uses a predictive model of the optimal solution length that is constructed by WEKA, a commonly used toolkit of machine learning algorithms
The Devil's altar? : crime and the early modern public house
No full textWas the early modern public house really such a dangerous place, as Puritan preachers (and many historians) suggested? This article discusses offences by publicans and patrons. It argues that the evidence for crime needs to be carefully contextualised and that taverns could stabilise as well as threaten the social order
Flexible time–space network formulation and hybrid metaheuristic for conflict-free and energy-efficient path planning of automated guided vehicles
No full textOperations of Automated Guided Vehicles (AGVs) are desired to be more energy-efficient while maintaining high transport productivity, motivated by the green production requirements. This paper investigates a new energy-efficient planning problem for determining conflict-free paths of the AGVs in its transport roadmap. In this problem, the vehicle path and transport time in the roadmap are jointly optimized, based on a flexible time–space network (FTSN). We provide the mathematical problem formulation of the energy-efficient path planning problem. The resulting optimization problem is proved to be a non-convex mixed-integer nonlinear programming which is computationally intractable. We further propose a hybrid metaheuristic that integrates the genetic algorithm and estimation of the distribution algorithm to improve its computational efficiency. Numerical results show the effectiveness of the developed algorithm based on the FTSN framework, compared to the existing metaheuristics, the conventional path planning method, and a commercial solver. The proposed method has a wide application in improving energy use of material handling, providing a guiding significance on promoting cleaner production of flexible manufacturing systems.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport Engineering and Logistic
Optimal Configuration of Omega-Kappa FF-SAR Processing for Specular and Non-Specular Targets in Altimetric Data: The Sentinel-6 Michael Freilich Study Case
No full textIn this study, the full-focusing (FF) algorithm is reviewed with the objective of optimizing it for processing data from different types of surfaces probed in altimetry. In particular, this work aims to provide a set of optimal FF processing parameters for the Sentinel-6 Michael Freilich (S6-MF) mission. The S6-MF satellite carries an advanced radar altimeter offering a wide range of potential FF-based applications which are just beginning to be explored and require prior optimization of this processing. In S6-MF, the Synthetic Aperture Radar (SAR) altimeter acquisitions are known to be aliased in the along-track direction. Depending on the target, aliasing can be tolerated or may be a severe impairment to provide the level of performance expected from FF processing. Another key aspect to consider in this optimization study is the unprecedented resolution of the FF processing, which results in a higher posting rate than the standard SAR processing. This work investigates the relationship between posting rate and noise levels and provides recommendations for optimal algorithm configurations in various scenarios, including transponder, open ocean, and specular targets like sea-ice and inland water scenes. The Omega–Kappa (WK) algorithm, which has demonstrated superior CPU efficiency compared to the back-projection (BP) algorithm, is considered for this study. But, unlike BP, it operates in the Doppler frequency domain, necessitating further precise spectral and time domain settings. Based on the results of this work, real case studies using S6-MF acquisitions are presented. We first compare S6-MF FF radargrams with Sentinel-1 (S1) images to showcase the potential of optimally configured FF processing. For highly specular surfaces such as sea-ice, distinct techniques are employed for lead signature identification. S1 relies on image-based lineic reconstruction, while S6-MF utilizes phase coherency of focalized pulses for lead detection. The study also delves into two-dimensional wave spectra derived from the amplitude modulation of image/radargrams, with a focus on a coastal example. This case is especially intriguing, as it vividly illustrates different sea states characterized by varying spectral peak positions over time.Astrodynamics & Space Mission
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