Search results for "Leo"
showing 10 items of 8768 documents
Más allá de los dinosaurios: nuevas perspectivas para el patrimonio paleontológico de La Rioja
2018
El patrimonio paleontológico en nuestro país ha sido objeto de discusión entre científicos y legisladores desde su controvertida consideración dentro del patrimonio histórico en la Ley 16/1985, de 25 de junio, del Patrimonio Histórico Español. Así, tanto el patrimonio inmueble (yacimientos) como el mueble (ejemplares ex situ alojados en museos, colecciones y exposiciones locales) se gestionaron durante años bajo esta norma hasta su inclusión, en el año 2007, en la nueva Ley 42/2007, de 13 de diciembre, de Patrimonio Natural y Biodiversidad. Fil: García Ortiz de Landaluce, Esperanza. Universidad de la Rioja; España Fil: Díaz Martínez, Ignacio. Consejo Nacional de Investigaciones Científicas …
The influence of decision-making in tree ring-based climate reconstructions.
2021
Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in…
Cave bear occupation in Schwabenreith Cave, Austria, during the early last glacial: constraints from 230 Th/U‐dated speleothems
2019
The cave bear was a prominent member of the Upper Pleistocene fauna in Eurasia. While breakthroughs were recently achieved with respect to its phylogeny using ancient DNA techniques, it is still challenging to date cave bear fossils beyond the radiocarbon age range. Without an accurate and precise chronological framework, however, key questions regarding the palaeoecology cannot be addressed, such as the extent to which large climate swings during the last glacial affected the habitat and possibly even conditioned the final extinction of this mammal. Key to constraining the age of cave bear fossils older than the lower limit of radiocarbon dating is to date interlayered speleothems using 23…
Theoretical and experimental studies of the neutron rich fission product yields at intermediate energies
2012
A new method to measure the fission product independent yields employing the ion guide technique and a Penning trap as a precision mass filter, which allows an unambiguous identification of the nuclides is presented. The method was used to determine the independent yields in the proton-induced fission of 232 Th and 238 U at 25 MeV. The data were analyzed with the consistent model for description of the fission product formation cross section at the projectile energies up to 100 MeV. Pre-compound nucleon emission is described with the two-component exciton model using Monte Carlo method. Decay of excited compound nuclei is treated within time-dependent statistical model with inclusion of the…
Two-neutron correlations at small relative momenta in ^40Ar + ^197Au collisions at 60 MeV/nucleon
2000
Two-neutron correlation functions are measured in the 40Ar + 197Au reaction at 60 MeV/nucleon to study the space-time characteristics of neutron emitting sources. The source temperatures and velocities are deduced by fitting the single-neutron energy spectra with a three-source model. A comparison of the correlation data with the predictions of the model of moving sources and with the dynamical Landau-Vlasov model suggests the relevance of a multisource description. Particular care has been paid to the influence of the relative source abundance on the shape of the correlation function.
Origin of Enzymatic Kinetic Isotope Effects in Human Purine Nucleoside Phosphorylase
2017
Here we report a study of the effect of heavy isotope labeling on the reaction catalyzed by human purine nucleoside phosphorylase (hPNP) to elucidate the origin of its catalytic effect and of the enzymatic kinetic isotope effect (EKIE). Using quantum mechanical and molecular mechanical (QM/MM) molecular dynamics (MD) simulations, we study the mechanism of the hPNP enzyme and the dynamic effects by means of the calculation of the recrossing transmission coefficient. A free energy surface (FES), as a function of both a chemical and an environmental coordinate, is obtained to show the role of the environment on the chemical reaction. Analysis of reactive and nonreactive trajectories allows us …
Dynamics of the excited-state hydrogen transfer in a (dG)·(dC) homopolymer: intrinsic photostability of DNA
2018
Multiscale molecular dynamics simulations reveal out-of-plane distortions that favour DNA photostability. A novel photostability mechanism involving four proton transfers and triggered by a nearby Na+ ion is also unveiled.
First moments of the nucleon generalized parton distributions from lattice QCD
2012
We report on our lattice calculations of the nucleon's generalized parton distributions (GPDs), concentrating on their first moments for the case of N_f=2. Due to recent progress on the numerical side we are able to present results for the generalized form factors at pion masses as low as 260 MeV. We perform a fit to one-loop covariant baryon chiral perturbation theory with encouraging results.
Sensitive Assays by Nucleophile-Induced Rearrangement of Photoactivated Diarylethenes.
2018
Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure−reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes’ intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalyti…
Nucleophilic iodonium interactions (NIIs) in 2-coordinate iodine(i) and silver(i) complexes
2021
The generality of nucleophilic iodonium interactions (NIIs) has been demonstrated by preparing a range of silver(i) and iodonium (I+) complexes and studying their 15N NMR chemical shifts, with the first example of a NII-complex involving a 2-coordinate silver(i) complex being confirmed by X-ray crystallography, and its nucleophilicity studied by DFT calculations.