169,718 research outputs found
Evaluation of bulk carbonate delta C-13 data from Triassic hemipelagites and the initial composition of carbonate mud
No full textBulk carbonate samples of hemipelagic limestone–marl alternations from the
Middle and Upper Triassic of Italy are analysed for their isotopic
compositions. Middle Triassic samples are representative of the Livinallongo
Formation of the Dolomites, while Upper Triassic hemipelagites were sampled
in the Pignola 2 section, within the Calcari con Selce Formation of the
Southern Apennines in Southern Italy. Triassic hemipelagites occur either as
nodular limestones with chert nodules or as plane-bedded limestone–marl
alternations which are locally silicified. In the Middle Triassic Livinallongo
Formation, diagenetic alteration primarily affected the stable isotopic
composition of sediment surrounding carbonate nodules, whereas the latter
show almost pristine compositions. Diagenesis lowered the carbon and oxygen
isotope values of bulk carbonate and introduced a strong correlation between
d13C and d18O values. In the Middle Triassic successions of the Dolomites,
bulk carbonate of nodular limestone facies is most commonly unaltered,
whereas carbonate of the plane-bedded facies is uniformly affected by
diagenetic alteration. In contrast to carbonate nodules, plane-bedded facies
often show compaction features. Although both types of pelagic carbonate
rocks show very similar petrographic characteristics, scanning electron
microscopy studies reveal that nodular limestone consists of micrite (< 5 lm
in diameter), whereas samples of the plane-bedded facies are composed of
calcite crystals ca 10 lm in size showing pitted, polished surfaces. These
observations suggest that nodular and plane-bedded facies underwent
different diagenetic pathways determined by the prevailing mineralogy of
the precursor sediment, i.e. probably high-Mg calcite in the nodular facies and
aragonite in the case of the plane-bedded facies. Similar to Middle Triassic
nodular facies, Upper Triassic nodular limestones of the Lagonegro Basin are
also characterized by uncorrelated d13C and d18O values and exhibit small, less
than 5 lm size, crystals. The alternation of calcitic and aragonitic precursors in
the Middle Triassic of the Dolomites is thought to mirror rapid changes in the
type of carbonate production of adjacent platforms. Bioturbation and
dissolution of metastable carbonate grains played a key role during early
lithification of nodular limestone beds, whereby early stabilization recorded
the carbon isotopic composition of sea water. The bulk carbonate d13C values
of Middle and Upper Triassic hemipelagites from Italy agree with those of
Tethyan low-Mg calcite shells of articulate brachiopods, confirming that
Triassic hemipelagites retained the primary carbon isotopic composition of the
bottom sea water. A trend of increasing d13C from the Late Anisian to the Early Carnian, partly seen in the data set presented here, is also recognized in
successions from tropical palaeolatitudes elsewhere. The carbon isotopic
composition of Middle and Upper Triassic nodular hemipelagic limestones
can thus be used for chemostratigraphic correlation and palaeoenvironmental
studies
Triassic and Jurassic calcareous nannofossils of the Pizzo Mondello section: a SEM study.
No full textPizzo Mondello is a 500 m thick pelagic-hemipelagic succession cropping out in Sicily, consisting of a nodular cherty limestone facies association of late Carnian to late Norian age. The uppermost portion was attributed to the Rhaetian and is represented by the plane-bedded Portella Gebbia Limestone. The section has been proposed as stratotype for the base of the Norian stage. The calcareous nannofossil content of limestones was studied with Scanning Electron Microscope (SEM) in two portions of the Pizzo Mondello section, one within “La Cava” that encompasses all proposed horizons for the base of the Norian, and one within the Portella Gebbia Limestone in the uppermost part of the section.
Calcareous nannofossil assemblages of the first portion display a low diversity, being constituted exclusively by calcispheres, that may constitute up to 40% of the sediment volume. Species richness increases in the upper portion. Initially, samples are dominated by Prinsiosphaera triassica, a nannolith of unknown taxonomic affinity. Rare calcareous dinocysts (Thoracosphaera cf. geometrica) and coccoliths are present in few samples. Uppermost samples are still dominated by "calcispheres" comparable to Thoracosphaera, but also yield a variety of coccoliths and nannoliths.
Calcareous nannofossil biohorizons was calibrated with conodont and radiolarian biostratigraphy. On this basis of this integrated work, specimens attribuited to cf. Thoracosphaera, observed in the lower portion of the section, are late Carnian to early Norian, while samples dominated by Prinsiosphaera, with rare Thoracosphaera and coccoliths are Rhaetian. The calcareous nannofossil assemblage of the uppermost samples, along with radiolarians and the absence of conodonts, point to a Jurassic age (Pliensbachian) for the uppermost Portella Gebbia Limestone at Pizzo Mondello. In conclusion, the age of the uppermost part of the Pizzo Mondello section is Jurassic, i.e., younger than previously thought. Calcareous nannofossils are present from the base of section and exhibit a significant taxonomic diversity, thus providing an auxiliary biostratigraphic frame for the Rhaetian - Jurassic interval in this area
Bio-chronostratigraphic calibration of the Upper Carnian-Lower Norian magnetostratigraphic scale at Pizzo Mondello (Sicani Mountains, Sicily)
No full textPizzo Mondello section is known since 15 years because
of the continuous Late Triassic pelagic record of great
significance for the establishment of an integrated chronostratigraphy
of the Late Triassic (Gullo et al. 1996;
Muttoni et al. 2001, 2004).
During the last 4 years, Pizzo Mondello section has been
studied in detail to provide a new and high resolution integrated
bio-chronostratigraphy for the calibration of the
magnetostratigraphy and chemostratigraphy proposed by
Muttoni et al. (2001, 2004), and now it is one of the GSSP
candidates for the definition of the base of the Norian.
The lowest 143 m of the Cherty Limestone, straddling the
C/N boundary have been studied in detail. The preliminary
data of the ongoing research have been presented in all the
meetings of the STS from Albuquerque 2007 and here we
summarize the final results.
The key correlation to the standard marine Triassic Scale
is provided by the ammonoids. They are relatively rare,
however the available collections document the Upper
Carnian Discotropites plinii and Gonionotites italicus
Subzones, from meter 15 to meter 80 from the base of the
section. The following 15 meters are poor in ammonoids,
while higher up the lower part of the Lower Norian Guembelites
jandianus Zone is documented by Dimorphites cf.
n. sp.1 of Krystyn, 1980.
Conodonts are very abundant and have a great potential
as practical tool for global correlations. The abundance
of specimens at Pizzo Mondello gave the opportunity to
point out clear relationships among the five most widespread
Upper Camian/Lower Norian conodont genera
(Paragondolella, Carnepigondolella, Metapolygnathus,
Epigondolella and Norigondolella) and to identify trends
of the generic turnovers (Mazza et al. 2010). The two biomarkers
so far proposed as possible marker events for the
GSSP were the FAD of E. quadrata (sample FNP88A) and
the FAD of M. communisti (sample NA35). However, the
FAD of E. quadrata occurs within the Gonionotites italicus
Subzone, while the FAD of M. communisti is on its top.
Halobiids are extremely common in the Cherty Limestone
and they have also a great potential for large scale correlations.
Nine species of Halobia have been recognized:
Halobia carnica, H. lenticularis, H. simplex, H. superba,
H. cf. rugosa, H. radiata, H. austriaca, H. styriaca and H.
mediterranea. The best possible marker for the base of the
Norian is the first occurrence of Halobia austriaca, that is
recorded in the middle of the interval between the record
of the Gonionotites italicus Subzone and the Guembelites
jandianus Zone.
Radiolarians were found in few samples but with high
diversity assemblages. In the upper Gonionotites italicus
Subzone to the Guembelites jandianus Zone there is an
overlap of species previously considered Late Carnian
with species usually regarded as Early Norian. About 4 m
above the FAD of E. quadrata, in the Gonionotites italicus
Subzone, the first assemblage with Capnuchosphaera
deweveri Kozur & Mostler, Capnuchosphaera tricornis
De Wever, Kahlerosphaera norica Kozur & Mock and
Xiphothecaella longa Kozur & Mock, usually referred to
Early Norian, occurs.
These integrated bio-chronostratigraphic studies lead to
identify some possible GSSP marker events especially on
conodonts and halobiids, which occur in the upper part of
magnetozone PM 4n, within PM 4r and in the lower part
of PM 5n.
Possibly the most suitable magnetostratigraphic event to
recognize the basal Norian is the base of magnetozone
PM 5n, as already suggested by Krystyn et al. 2002 and
Muttoni et al. 2004
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
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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