169,727 research outputs found
Thermal profiles and improved confinement accessibility in RFX-mod and TCV
No full textHumans do not live by bread alone. Physically we are puny creatures with limited prowess, but with unlimited dreams. In the last few decades humankind reached the Moon (1969) and
built airports over the sea (1994), but 925 million people are still under- or malnourished (2010). To follow his dream to ensure every human being the same adequate quality of life, humankind needs energy. The long-term world energy scenarios (50-80 years) foresee the need for reliable, sustainable and environmental friendly sources of energy. Thermonuclear fusion is one of the main actors in the energetic basket, it offers the possibility to produce large supplies of energy at relatively low costs reducing the impact on the environment. In fact, thermonuclear fusion represents a promising chance to generate energy without the emission of carbon dioxide and the production of long living radioactive wastes. Moreover, the raw materials used as fuel in the fusion reactions, deuterium and tritium, are easily available on Earth. This chance motivates the efforts on the controlled thermonuclear fusion research. Anyway, the development of nuclear fusion as an energy source is one of the most complex scientific and technical tasks ever undertaken for non-military purposes. The nuclear fusion obtained by magnetic confinement of plasma emerged in the latest years as the most promising concept to menage the power produced by fusion reactions. The studies developed in that direction, since the fifties, yielded more and more encouraging results and important breakthroughs both in physics and technology and inspired the ITER project. This experimental reactor could give, in the next few decades, the definitive answers to many questions on the scientific and technological feasibility of a fusion reactor. One of the major concerns in magnetic confinement fusion research is the quest for the best
plasma performance, which is intimately linked to two main issues: plasma confinement and boundary conditions. Both, incidentally, are connected to plasma stability. The link between confinement and boundary conditions is very strong and found many evidences. For example in the tokamak (the magnetic confinement configuration main line) the quest for a mild plasma-wall interaction a controlled recycling led to the discovery of an ameliorated operating mode with high performance. As a matter of fact, H-mode was discovered in
ASDEX the first diverted device. In RFPs (an alternative magnetic confinement configuration) a spontaneous transition to an ameliorated plasma state, the QSH state, is due to a reduced chaos obtained with an accurate control of the magnetic boundary conditions. In turn, the access to the QSH state led to a favorable edge topology characterized by better boundary conditions. The onset of the QSH state induces an edge helical ripple which reduce the plasma wall interaction. My research activity, reported in this thesis work, focused on the accessibility conditions and characterization of improved confinement regimes in TCV tokamak and RFX-mod RFP devices. In RFX-mod my research activity focused on the study and the characterization of electron temperature profiles. Temperature is one of the key parameters that qualifies fusion plasma performance and, in RFX-mod plasmas, it is mainly determined by three quantities: plasma current, electron density and plasma magnetic state. Through a large statistical analysis the temperature profile variations were investigated and related to the main macroscopic and operational plasma parameters. This analysis resulted in scaling laws for central temperature, external temperature and temperature gradient. Some further analysis was dedicated to a distinctive feature: the appearance of transport and thermal barriers which result in better plasma performance. The formation of an Internal Transport Barrier (eITB) is triggered by the growth of a dominant MHD tearing mode which, in turn, leads to a reduced magnetic chaos
in the plasma core. Starting from previous analysis, these eITBs were investigated and their influence of the whole temperature profile addressed. Besides the established phenomena related to eITBs, the occasional appearance of extremely high gradients in the external region of the plasma column was observed. Some general observations and a first speculation on the physical mechanism leading to their formation will be presented. The work ends up in a wide and general picture which tries to clear up the physics governing the temperature profile
modifications and proposes possible operations to trigger them. Present day tokamaks high performance scenarios rely on the possibility to access the high confinement mode (H-mode). Transition from the standard confinement mode (L-mode) to the H-mode is typically achieved when the external input power exceeds a threshold. This power threshold is found to strongly depend on plasma density, toroidal magnetic field and plasma size, but many experiments have shown this power threshold to also depend on plasma shape and configuration geometry. My activity at TCV aimed at the study of such dependence, in particular the influence of X-point location on H-mode power threshold was investigated. During a two months stay in 2011, a series of experiments was dedicated to such a study. Significant variations in the power threshold due to a reduction of the X-point height has been documented, in agreement with the scaling observed in other machines. Moreover, the well-established non-monotonic density dependence of the H-mode power threshold has
been measured and recorded. In this thesis work the analysis procedure followed to the TCV experimental campaign is reported
PO-1658 Inverse Consistency Error for quantifying uncertainty in DIR: validation on three different sites
No full textOD26 - Inverse consistency error as a validation metric for deformable image registration: preliminary implementation research
No full textThe aim of this work is to develop a novel automatic voxel-based quantitative measurement approach to evaluate the registration accuracy of a Deformable Image Registration (DIR) algorithm in clinical practice. As the Inverse Consistency Error (ICE) can be computed directly from the deformation vector field (DVF) generated by the Treatment Planning System (TPS), it appears to be a valid surrogate of standard quality assurance metrics to assess the spatial error in the registration process
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
MO-03.8 - INVERSE CONSISTENCY ERROR AS A VALIDATION METRIC FOR DEFORMABLE IMAGE REGISTRATION: IMPLEMENTATION RESEARCH WITH DIFFERENT COMPUTATIONAL PHANTOMS
No full textThis work aims to apply the Inverse Consistency Error (ICE) metric on deformable vector fields (DVFs) to evaluate the deformable image registration (DIR) spatial uncertainties in the context of dose warping applications
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 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.Electronic InstrumentationMicroelectronic
A ±25A Versatile Shunt-Based Current Sensor with 10kHz Bandwidth and ±0.25% Gain Error from -40°C to 85°C Using 2-Current Calibration
No full textAccurate current sensing is critical in many industrial applications, such as battery management and motor control. Precise shunt-based current sensors have been reported with gain errors of less than 1% over the industrial temperature range (-40°C to 85°C) [1]–[4]. However, since they are intended for coulomb counting, their bandwidth is limited to a few tens of Hz, making them unsuitable for battery impedance or motor-current sensing. This paper presents a current sensor with a wide (10kHz) bandwidth and a tunable temperature compensation scheme (TCS), which allows it to be flexibly used with different types of shunts while maintaining high accuracy. A low-cost room-temperature calibration scheme is proposed to optimize gain flatness over temperature by exploiting the shunt's self-heating at large currents. Over the industrial temperature range and a ±25A current range, it achieves state-of-the-art gain error (±0.25%) with both low-cost PCB and stable metal-alloy shunts.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.Electronic InstrumentationMicroelectronic
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