169,911 research outputs found
Probabilistic estimation of turbidity current risk for offshore developments under changing climate conditions
No full textRecent advances in direct monitoring of submarine canyons activity suggest that metocean events can prime or ultimately trigger turbidity currents at sub-annual to centennial frequencies, challenging the paradigm that such highly destructive flows typically result from infrequent submarine landslides. Here we present a methodology aimed to link information on nearshore circulation and sediment resuspension events such as floods, tides and storms to the downslope evolution of turbidity flows, applied to cyclone-triggered turbidity currents affecting a deep-sea gas development offshore northern Mozambique. We evaluate seabed current velocities at the canyon heads derived from a 10,000 year long synthetic cyclone database consistent with expected future climate conditions. We couple the results for each event to a dedicated 1D turbidity current numerical model accounting for multiple grain-sizes, water entrainment and detrainment, overspill and spatial variations of the channel width and seabed gradient. The 1000’s of individual modelled events allow a statistically consistent estimation of the return period of turbidity currents at different control points along the canyons, and provide an estimation of flow structure, density and velocity necessary to evaluate the risk for offshore developments. Results are validated by the analysis of core samples, seabed morphology and dedicated 3D modelling of critical events
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
Impact of dumping operations at a canyon head on turbidity current geohazard: insights from a project development
No full textIn the framework of a liquified natural gas (LNG) project developmenti, 16 million m3 of sediment will be dumped at the head of a submarine canyon. We investigate the ability of spring tides an monsoon storms to resuspend the dumped sediment and trigger turbidity currents (TCs) along the canyon. An integrated modelling is developed and validated against in-situ measurements to describe the dispersion of the dumped sediment, its subsequent erosion due to macro-tidal and storm-induced currents, the triggering and down-canyon evolution of TCs. Our results show that TCs can ben triggered by both energetic spring tides and extreme storms after the dumping, indicating a pontential yearly frequency of these flows. However, the first TCs can erode most of the fine-grained sediments, cleaning the canyon of the fuel for successive events. If confirmed by surveys of tidal erosion, these findings imply a limited risk of damage for the planned subsea infrastructures
Vertical and Lateral Changes in Facies, Bed Thickness, and Grain Size in Submarine Channels from an Ultra-High Resolution Dataset, Western Niger Delta Slope: Implications for Turbidity Current Stratification
No full textModern seafloor and shallow subsurface studies offer a high-resolution view into the morphology, architecture, and evolution of submarine channels. In addition to architecture derived from seismic data, lithologic and age calibration are needed to constrain the evolution of submarine channels and the properties of the flows that sculpt them. Near-seafloor seismic and core data from the western Niger Delta slope allow for the quantification of lateral and vertical changes in facies, bed thickness, and grain size in a well-constrained channel system. The dataset consists of a 3D seismic volume, high-resolution 2D seismic profiles, 21 sediment cores, and more than 500 grain-size analyses.
Core and seismic data reveal that the channel axis consists of thick-bedded, amalgamated, coarse-grained sands. Channel margin deposits are thin-bedded and heterolithic, and show a pronounced decrease in bed thickness and grain size with increasing distance above and away from the channel thalweg. Margin deposits exist in ‘scallops’ that correspond to bends of an older, more sinuous channel. While individual scallops are disconnected from each other, beds can be correlated over hundreds of meters between cores within the same scallop.
Multiple core transects across the channel demonstrate a rapid decrease in bed thickness and deposition rate (calculated from radiocarbon ages) with increasing height above channel thalweg. Grain size distributions obtained with a laser particle-size analyzer also show a strong fining with height above thalweg. These trends reflect the stratification of grain size and sediment concentration in channelized turbidity currents. Simple theoretical concentration and grain-size profiles match the observed trends, providing constraints for numerical and rule-based modeling approaches.
Although facies models for submarine channels often assume quasi-horizontal fill with rapid lateral facies changes, this dataset suggests that there is a significant difference in elevation between coeval axis and margin deposits. The relationships between grain size, bed thickness, and height above channel thalweg can be used to estimate location of deposition relative to the base of the time-equivalent geomorphic channel when only limited data (e.g., core or outcrop) is available
A 3D model for Deep-Water Reservoirs Coupling a Depth Averaged Theory for Turbidity Currents Flowing in Meandering Channels and Vertical Channel Trajectories
No full textMitomycin 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
Trichoscopy findings of frontal fibrosing alopecia on the eyebrows: A study of 151 cases
No full textBackground: Eyebrow loss (madarosis) is a frequent sign of frontal fibrosing alopecia (FFA), and it can be the first sign of the disease. Objective: To describe trichoscopy findings of FFA on the eyebrows. Methods: The analysis included 151 women with histologically proven diagnosis of FFA and eyebrow loss. Trichoscopy of the eyebrow area was performed with either a FotoFinder videodermatoscope or handheld dermoscope DermLite II pro. Results: The most frequent signs on trichoscopy were yellow dots (92.7%), multiple pinpoint dots (79.5%), short thin hairs/vellus (76.2%), black dots (66.2%), and dystrophic hairs (60.9%). Tapering hairs were found in 21 (13.9%) patients and dystrophic hairs in 92 (60.9%) patients. Limitations: Inner limitations of a case series (there was no comparison with healthy control individuals or patients with other hair disorders) and lack of histologic correlation to the trichoscopy findings. Conclusions: Although FFA is a scarring alopecia, the most common trichoscopy signs found in the eyebrows are usually related to noncicatricial alopecia. Therefore, in most cases, trichoscopy of the eyebrows does not resemble the trichoscopy of FFA on the scalp. Black dots, dystrophic hairs, and broken hairs are frequent signs. Occasionally, tapered hairs can be present on the eyebrows in FFA, leading to misdiagnosis of alopecia areata
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
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