170,125 research outputs found
Eccentric Anomaly Synchronism and Regularised Dynamics for Continuum Interplanetary Orbital Uncertainty Propagation
No full textUncertainty propagation features many of modern orbital dynamics-related engineering analyses. A solid understanding of how inaccurate measurements affect the subsequent phases of a mission is a crucial task to ensure its safety and success. Typical techniques to assess how uncertain phenomena impact the development of a mission all rely on Monte Carlo-based approaches for the interplanetary space and make use of a Cartesian formulation of the dynamics, so that high-fidelity models can be straightforwardly used. The proposed work studies how the regularisation of the dynamics' formulation, and in particular the choices made for the independent variable in the numerical integration, allow to drastically reduce the chaotic nature of the orbital motion for uncertainty propagation. A simple regularisation approach, commonly known as Kustaanheimo-Stiefel, uses an eccentric anomaly-like independent integration variable. A sample-based study on clouds of initial conditions propagated with this formulation is proposed, which immediately introduces strong evidence of a statistical continuum-like non-chaotic behaviour of the propagated cloud. The scattering effect of close approaches on the propagated uncertainty can also be modelled in a more predictable way, where exponential divergence replaces the apparent chaos that characterises the Cartesian dynamics and, more in general, any orbital description centred on the concept of physical time
GPU-based Augmented Trajectory Propagation: Orbital Regularization Interface and NVIDIA CUDA Tensor Core Performance
No full text
GPU-based high-precision orbital propagation of large sets of initial conditions through Picard–Chebyshev augmentation
No full textThe orbital propagation of large sets of initial conditions under high accuracy requirements is currently a bottleneck in the development of space missions, e.g. for planetary protection compliance analyses. The proposed approach can include any force source in the dynamical model through efficient Picard–Chebyshev (PC) numerical simulations. A two-level augmentation of the integration scheme is proposed, to run an arbitrary number of simulations within the same algorithm call, fully exploiting high performance and GPU (Graphics Processing Units) computing facilities. The performances obtained with implementation in C and NVIDIA® CUDA® programming languages are shown, on a test case taken from the optimization of a Solar Orbiter-like first resonant phase with Venus
Surfing Chaotic Perturbations in Interplanetary Multi-Flyby Trajectories: Augmented Picard-Chebyshev Integration for Parallel and GPU Computing Architectures
No full textThe computational intensity of the trajectory design problem severely affects the development time of any space mission, both in its preliminary phase and in the consequent optimization. This paper presents a formulation of the design problem that can account for any force source in the dynamical model through efficient Picard-Chebyshev numerical simulations. A two-level augmentation of the integration scheme is proposed, to run an arbitrary number of simulations within the same algorithm call, fully exploiting high performance and GPU computing facilities. The performances obtained with implementation in C and NVIDIA® CUDA® programming languages are shown, highlighting possible use cases and paradigms for the efficient use of GPU computing architectures
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
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
- …
