309,003 research outputs found
Biometric study of late Oligocene larger benthic Foraminifera (Lepidocyclinidae and Nummulitidae) from the Qom Formation, Central Iran (Tajar-Kuh section)
No full textThe Oligocene strata of the Qom Formation from the Tajar-Kuh section, Central Iran, are rich in various Larger Benthic Foraminifera (LBF). Morphometric studies of the internal features of the LBF tests were carried out based on matrix-free specimens from seven samples. The LBF assemblage studied in 24 populations mainly contains representatives of two nummulitid (the reticulate Nummulites bormidiensis Tellini, 1888, only in the lower three samples, and the radiate Nummulites kecskemetii Less, 1991 in all samples) and of two lepidocyclinid lineages. Of the latter, Nephrolepidina praemarginata (R. Douvillé, 1908) occurs in all the samples, whereas Eulepidina formosoides H. Douvillé, 1925 is present in the lower six samples. In the upper sample, the slightly more advanced Eulepidina ex. interc. formosoides H. Douvillé, 1925 et dilatata (Michelotti, 1861) is recorded. Due to the very similar taxonomic composition of the Tajar-Kuh section with their coeval faunas of the Mediterranean, the age was evaluated in the frame of the Western Tethyan Oligo-Miocene shallow benthic zonation (SBZ). Although the presence of E. formosoides suggests late Rupelian (SBZ 22A Zone) age, the occurrence of Heterostegina assilinoides, N. kecskemetii, N. bormidiensis, and Planolinderina sp. preferably represents the SBZ 22B Zone of the early Chattian. Based on the obtained results, at least the lower six samples can indicate the very basal part of the Chattian. More advanced Eulepidina from the uppermost sample suggests a slightly younger but still early Chattian age
A MONOTYPIC STAND OF NEOCALAMITES IRANENSIS N. SP. FROM THE CARNIAN PLUVIAL EPISODE (LATE TRIASSIC) OF THE AGHDARBAND AREA, NE IRAN (TURAN PLATE)
No full textThe Aghdarband Basin in the Kopeh-Dagh Range (NE Iran) is one of the most important areas for unraveling the evolution of the Turan plate (southern margin of Eurasia) during the last phase of the closure of the Paleotethys and to reconstruct the history of the Cimmerian blocks just before their collision with Eurasia during the early Late Triassic. The youngest sediments affected by the Early Cimmerian orogeny are those of the Upper Triassic Miankuhi Formation, which covers unconformably the Upper Triassic (lower Carnian) marine beds of the Sina Formation by an interval of continental facies including local conglomerates, cross-bedded sandstones, mudstone layers, silty shales, an up to one-meter thick coal layer with plant remains, and shales. The plant assemblages represent a relatively wide variety of different forms (sphenophytes, ginkgophytes, conifers, and incertis sedis), documenting wetlands with lush vegetation typical of warm and humid environments. In this study, we describe a plant fossil assemblage from the base of the Miankuhi Fm., dominated by roots and vegetative organs of Neocalamites iranensis n. sp., with few plant fossils of uncertain botanical affinity. Palynological investigations of the basal part of the Miankuhi Formation confirm a latest early Carnian to late Carnian age for this interval and reveal, for the first time, a clear link between this plant-bearing bed, and a time of global environmental changes, the Carnian Pluvial Episode. This is the first report of the Carnian Pluvial Episode in the Turan plate (southern margin of Eurasia) and Iran
Quarantined Cc-stretched Formic Acid: Molecular Work-out In (self) Isolation
No full textVibrational spectra of small molecules effectively probe the underlying potential energy hypersurface, which can be tested when combined with accurate anharmonic calculations.\footnote{P. R. Franke, J. F. Stanton, G. E. Douberly, \textit{J. Phys. Chem. A} \textbf{2021}, \textit{125}, 1301--1324; J. M. Bowman, T. Carrington, H.-D. Meyer, \textit{Mol. Phys.} \textbf{2008}, \textit{106}, 2145--2182.} Particularly suited for a performance test of quantum chemical gas phase calculations are spectra recorded in a supersonic expansion, as significant rotational cooling is achieved while the molecules or molecular clusters remain isolated in the gas phase. One of the smallest reference systems for such a benchmarking study is the formic acid monomer with its --torsional isomerism.\footnote{D. P. Tew, W. Mizukami, \textit{J. Phys. Chem. A} \textbf{2016}, \textit{120}, 9815--9828; F. Richter, P. Carbonni\`{e}re, \textit{J. Chem. Phys.} \textbf{2018}, \textit{148}, 064303; A. Nejad, E. L. Sibert III, \textit{J. Chem. Phys.} \textbf{2021}, \textit{154}, 064301.} Recently, new vibrational reference data on the stretching vibrations of all four H/D isotopologues of the higher-energy -conformer were provided the combination of Raman jet spectroscopy with thermal excitation.\footnote{A. Nejad , M. A. Suhm, K. A. E. Meyer, \textit{Phys. Chem. Chem. Phys.} \textbf{2020}, \textit{22}, 25492--25501.} Another very interesting carboxylic acid for such a study is the smallest acetylenic acid, HCC-COOH, whose - and -rotamers will be discussed in this contribution. Of particular interest are two almost isoenergetic -fundamentals of different symmetry which are shown to be a particularly useful benchmarking target, but also the dimers of the CC-stretched formic acid prove to be an insightful reference system for benchmarking.\footnote{K. A. E. Meyer, A. Nejad, \textit{Phys. Chem. Chem. Phys.} \textbf{2021}, \textit{23}, 17208--17223.
New Jet-cooled Vibrational Spectroscopic Benchmark Data Of The Cyclic Dimer And Trimer Of Formic Acid
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Using well-established FTIR and Raman jet spectroscopic set-ups, the gas phase vibrational database of the cyclic formic acid dimer, (FF), has been reviewed and updated for the slow fingerprint vibrations [below 1500\,{\wn}] of the main and its three symmetrically deuterated isotopologues.\footnote{A. Nejad, K. A. E. Meyer, F. Kollipost, Z. Xue, M. A. Suhm , \textit{J. Chem. Phys.} \textbf{2021}, \textit{155}, 224301 and A. Nejad, PhD thesis, submitted (2022).}
Experimental benchmarks validate the popular second-order vibrational perturbation theory approach in combination with high-level [hybrid] force fields which is shown to provide accurate predictions for moderate excitations of the intermolecular van der Waals\footnote{A. Nejad, M. A. Suhm , \textit{J. Indian Inst. Sci.} \textbf{2020}, \textit{100}, 5.} and intramolecular fingerprint vibrations of (FF).
The new and extended benchmark-quality database of (FF) is particularly useful to guide recent efforts\footnote{C. Qu, J. M. Bowman, \textit{Phys. Chem. Chem. Phys.} \textbf{2019}, \textit{21}, 3397 and A. M. Santa Dar\'{i}a, G. Avila, E. M\'{a}tyus, \textit{Phys. Chem. Chem. Phys.} \textbf{2021}, \textit{23}, 6526.%
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to accurately model the 24-dimensional vibrational dynamics of this prototypical model system in a `bottom-up' approach.
As a byproduct, the number of assigned vibrational fundamentals [and selected overtone bands] of the vacuum-isolated formic acid trimer, F(FF), has been drastically increased. Since the polar dimer, FF, is a fragment of the trimer, the experimentally validated theoretical description of F(FF) promises to provide reliable spectral predictions for future gas phase spectroscopic searches of FF
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
Structural control on magmatism in intraplate collisional settings: extinct example from NE Iran and current analogues
No full textVolcanic activity focuses along plate boundaries. However, large volcanoes are also found in intraplate settings. For these volcanoes, geodynamic processes responsible for magma generation and structural controls on magma rise and extrusion need to be evaluated. We merge original (field and remote sensing) and available (geodetic, geophysical, and petrological) data to consider the tectono-magmatic relationships of three large intraplate volcanoes in the E-Anatolian-Iranian plateau; Sar’akhor (NE Iran), Damavand (Central Alborz) and Ararat (E Anatolia). In NE Iran, a Miocene-Pliocene NW-trending compression activated E-W dextral faults to the NW of Sar’akhor and N-S sinistral faults to the SE, creating an extruding wedge to the west of this volcano. Since Quaternary, NE-trending
compression inverted fault movement, hindering further block extrusion and volcanism terminated. The adakitic composition of the Sar’akhor rocks suggests post-collisional melting of oceanic slab and/or mafic lower crust, possibly triggered by an asthenospheric rise after slab break-off or intramantle delamination. For the active Damavand and Ararat volcanoes, available data suggest magma generation due to rising hot asthenosphere, following lithospheric delamination or slab break-off in a transtensional environment. The features common to Sar’akhor, Damavand and Ararat allow proposing a model, where transtension focuses the rise of magma in intraplate settings overlying hot asthenosphere produced by delamination or slab break-off
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
CC-stretched formic acid: isomerisation, dimerisation, and carboxylic acid complexation
No full textThe cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer. Two near-isoenergetic trans -fundamentals of different symmetry (CCO bend and OH torsion) prove to be a sensitive benchmarking target, as their energetic order is susceptible to the choice of electronic structure method, basis set size, and inclusion of vibrational anharmonicity. For the infrared- and Raman-active CO stretching fundamentals of the cyclic ( C 2h ) trans -propiolic acid dimer, resonance couplings are found that in part extend to the C s -symmetric heterodimer of trans -propiolic and trans -formic acid. Exploratory vibrational perturbation theory (VPT2) calculations show that all perturbing states involve displacements of the OH moieties located on the doubly hydrogen bonded ring. The comparison of the infrared spectra of the propiolic acid dimer and its heterodimer with formic acid to that of several other carboxylic acid dimers from the literature reveals a notable similarity regarding a non-fundamental dimer band around 1800 cm −1 , which in most cases is so far unassigned. VPT2 calculations and a simple harmonic model suggest an assignment to a combination vibration of the symmetric and antisymmetric OH torsion.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer.The cis – trans -isomerism of the propiolic acid monomer (HCC–COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis -rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans -conformer. Two near-isoenergetic trans -fundamentals of different symmetry (CCO bend and OH torsion) prove to be a sensitive benchmarking target, as their energetic order is susceptible to the choice of electronic structure method, basis set size, and inclusion of vibrational anharmonicity. For the infrared- and Raman-active CO stretching fundamentals of the cyclic ( C 2h ) trans -propiolic acid dimer, resonance couplings are found that in part extend to the C s -symmetric heterodimer of trans -propiolic and trans -formic acid. Exploratory vibrational perturbation theory (VPT2) calculations show that all perturbing states involve displacements of the OH moieties located on the doubly hydrogen bonded ring. The comparison of the infrared spectra of the propiolic acid dimer and its heterodimer with formic acid to that of several other carboxylic acid dimers from the literature reveals a notable similarity regarding a non-fundamental dimer band around 1800 cm −1 , which in most cases is so far unassigned. VPT2 calculations and a simple harmonic model suggest an assignment to a combination vibration of the symmetric and antisymmetric OH torsion
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