Semiempirical Modeling of Reset Transitions in Unipolar Resistive-Switching based Memristors

We have measured the transition process from the high to low resistivity states, i.e., the reset process of resistive switching based memristors based on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for their electrical characteristics. When the characteristic curves are plotted in the current-voltage (I-V) domain a high variability is observed. In spite of that, when the same curves are plotted in the charge-flux domain (Q-phi), they can be described by a simple model containing only three parameters: the charge (Qrst) and the flux (rst) at the reset point, and an exponent, n, relating the charge and the flux before the reset transition. The three parameters can be easily extracted from the Q-phi plots. There is a strong correlation between these three parameters, the origin of which is still under study

Charged-current inclusive neutrino cross sections in the SuperScaling model including quasielastic, pion production and meson-exchange contributions

Charged current inclusive neutrino-nucleus cross sections are evaluated using the superscaling model for quasielastic scattering and its extension to the pion production region. The contribution of two-particle-two-hole vector meson-exchange current excitations is also considered within a fully relativistic model tested against electron scattering data. The results are compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE experiments. For experiments where $\langle E_\nu \rangle \sim 0.8$ GeV, the three mechanisms considered in this work provide good agreement with the data. However, when the neutrino energy is larger, effects from beyond the $\Delta$ also appear to be playing a role. The results show that processes induced by two-body currents play a minor role at the kinematics considered.Comment: 10 pages, 7 figure

EmC-ICDSST 2019: 5th International Conference on Decision Support System Technology - ICDSST 2019 & EURO Mini Conference 2019 on "Decision Support Systems: Main Developments & Future Trends"

info:eu-repo/semantics/publishedVersio

Chronological control and centennial-scale climatic subdivisions of the Last Glacial Termination in the western Mediterranean region

The Last Glacial Termination is marked by changing environmental conditions affected by abrupt and rapid climate oscillations, such as Heinrich Stadial 1 (HS1), which is characterized by extremely low sea surface temperatures (SST) and significant changes in northern hemisphere terrestrial landscape (e.g., vegetation) and human dispersion. Previous studies show that overall cold/dry conditions occurred during HS1, but the lack of high-resolution records precludes whether climate was stable or instead characterized by instability. A high-resolution paleoclimatic record from the Padul wetland (southern Iberian Peninsula), supported by a high-resolution chronology and contrasted with other records from southern Europe and the Mediterranean region, shows 1) that the age boundaries of HS1 in this area occurred at similar to 18.0 kyr BP (median age = 17,970 cal yr BP; mean age = 18,030 +/- 330 cal yr BP) and similar to 15.2 kyr BP (median age = 15,210 cal yr BP; mean age = 15,200 +/- 420 cal yr BP) and 2) that climate during HS1 was non-stationary and centennial-scale variability in moisture is superimposed on this overall cold climatic period. In this study, we improve the pollen sampling resolution with respect to previous studies on the same Padul-15-05 sedimentary core and suggest a novel subdivision of HS1 in 7 sub-phases, including: i) 3 sub-phases (a.1-a.3) during an arid early phase (HS1a; similar to 18.4-17.2 kyr BP), ii) a relatively humid middle phase (HS1b; similar to 17.2-16.9 kyr BP), and iii) 3 sub-phases (c.1-c.3) during an arid late phase (HS1c; similar to 16.9-15.7 kyr BP). This climatic subdivision is regionally supported by SST oscillations from the Mediterranean Sea, suggesting a strong land-sea coupling. A cyclostratigraphic analysis of pollen data between 20 and 11 kyr BP indicates that the climate variability and the proposed subdivisions characterized by similar to 2000 and similar to 800-yr periodicities could be related to solar forcing controlling climate in this area. (C) 2021 Elsevier Ltd. All rights reserved.Peer reviewe

Meson-exchange currents and quasielastic predictions for charged-current neutrino-12C scattering in the superscaling approach

We evaluate and discuss the impact of meson-exchange currents (MECs) on charged-current quasielastic neutrino cross sections. We consider the nuclear transverse response arising from two-particle two-hole states excited by the action of electromagnetic, purely isovector meson-exchange currents in a fully relativistic framework based on the work by the Torino Collaboration [A. D. Pace, M. Nardi, W. M. Alberico, T. W. Donnelly, and A. Molinari, Nucl. Phys. A726, 303 (2003)]. An accurate parametrization of this MEC response as a function of the momentum and energy transfers involved is presented. Results of neutrino-nucleus cross sections using this MEC parametrization together with a recent scaling approach for the one-particle one-hole contributions (named SuSAv2) are compared with experimental data (MiniBooNE, MINERvA, NOMAD and T2K Collaborations).Comment: 16 pages, 19 figure

The Holocene Cedrus pollen record from Sierra Nevada (S Spain), a proxy for climate change in N Africa

Comprehending the effects of climate variability and disturbance on forested ecosystems is paramount to successfully managing forest environments under future climate scenarios (e.g., global warming, aridi-fication increase). Changes in fossil pollen abundance in sedimentary archives record past vegetation dynamics at regional scales, mainly related to climate changes and, in the last few millennia, to human impact. Pollen records can thus provide long databases with information on how the environment reacted to climate change before the historical record. In this study, we synthesized fossil pollen data from seven sites from the Sierra Nevada in southern Spain to investigate the response of forests in the western Mediterranean area to millennial-scale climate changes and to human impact during the Holocene. In particular, here we focused on Cedrus pollen abundances, which most-likely originated from Northern Africa and were carried to Sierra Nevada by wind. Cedrus pollen has received little attention in the Iberian Peninsula palynological records, for it occurs in low concentrations and has an African source, and thus this article explores the potential to reconstruct its past history and climate. Although Cedrus abundances are generally lower than 1% in the studied pollen samples, a comparison with North African (Moroccan) Cedrus pollen records shows similar trends at long- and short-term time-scales. Therefore, this record could be used as a proxy for changes in this forest species in North Africa. As observed in the Sierra Nevada synthetic record, the increasing trend of Cedrus pollen during the Middle and Late Holocene closely correlates with decreasing summer insolation. This would have produced overall cooler annual temperatures in Northern Africa (Middle Atlas and Rif Mountains) as well as lower summer evaporation, benefiting the growth of this cool-adapted montane tree species while increasing available moisture during the summer, which is critical for this water-demanding species. Millennial-scale variability also characterizes the Sierra Nevada Cedrus synthetic pollen record. Cedrus abundance oscillations co-vary with well-known millennial-scale climatic variability that controlled cedar abundance and altitudinal distribution in montane areas of N Africa. (C) 2020 Elsevier Ltd. All rights reserved.Peer reviewe

Millennial-scale cyclical environment and climate variability during the Holocene in the western Mediterranean region deduced from a new multi-proxy analysis from the Padul record (Sierra Nevada, Spain)

A high-resolution multi-proxy approach, integrating pollen, inorganic and organic geochemical and sedimentological analyses, has been carried out on the Holocene section of the Padul sedimentary record in the southern Iberian Peninsula reconstructing vegetation, environment and climate throughout the last ~ 11.6 cal kyr BP in the western Mediterranean. The study of the entire Holocene allows us to determine the significant climate shift that occurred during the middle-to-late Holocene transition. The highest occurrence of deciduous forest in the Padul area from ~ 9.5 to 7.6 cal kyr BP represents the Holocene humidity optimum probably due to enhanced winter precipitation during a phase of highest seasonal anomaly and maximum summer insolation. Locally, insolation maxima induced high evaporation, counterbalancing the effect of relatively high precipitation, and triggered very low water table in Padul and the deposition of peat sediments. A transitional environmental change towards more regional aridity occurred from ~ 7.6 to 4.7 cal kyr BP and then aridification enhanced in the late Holocene most likely related to decreasing summer insolation. This translated into higher water levels and a sedimentary change at ~ 4.7 cal kyr BP in the Padul wetland, probably related to reduced evaporation during summer in response to decreased in seasonality. Millennial-scale variability is superimposed on the Holocene long-term trends. The Mediterranean forest regional climate proxy studied here shows significant cold-arid events around ~ 9.6, 8.5, 7.5, 6.5 and 5.4 cal kyr BP with cyclical periodicities (~1100 and 2100 yr) during the early and middle Holocene. A change is observed in the periodicity of these cold-arid events towards ~1430 yr in the late Holocene, with forest declines around ~ 4.7–4, 2.7 and 1.3 cal kyr BP. The comparison between the Padul-15-05 data with published North Atlantic and Mediterranean paleoclimate records suggests common triggers for the observed climate variability, with the early and middle Holocene forest declines at least partially controlled by external forcing (i.e. solar activity) and the late Holocene variability associated with internal mechanisms (oceanic-atmospheric)

Sliding window multi-curve resolution: application to gas chromatography - ion mobility spectrometry

Blind source separation (BSS) techniques aim to extract a set of source signals from a measured mixture in an unsupervised manner. In the chemical instrumentation domain source signals typically refer to time-varying analyte concentrations, while the measured mixture is the set of observed spectra. Several techniques exist to perform BSS on ion mobility spectrometry, being simple-to-use interactive self-modelling mixture analysis (SIMPLISMA) and multivariate curve resolution (MCR) the most commonly used. The addition of a multi-capillary gas chromatography column using the ion mobility spectrometer as detector has been proposed in the past to increase chemical resolution. Short chromatography times lead to high levels of co-elution, and ion mobility spectra are key to resolve them. For the first time, BSS techniques are used to deconvolve samples of the gas chromatography-ion mobility spectrometry tandem. We propose a method to extract spectra and concentration profiles based on the application of MCR in a sliding window. Our results provide clear concentration profiles and pure spectra, resolving peaks that were not detected by the conventional use of MCR. The proposed technique could also be applied to other hyphenated instruments with similar strong co-elutions

Climatic control on the Holocene hydrology of a playa-lake system in the western Mediterranean

Evaporitic lakes such as playa-lakes are characteristic of many arid regions and are unique environments with respect to fauna and flora, while being very vulnerable to climate and environmental fluctuations and threatened by the current global change scenario. Water balance oscillations in these systems can trigger the precipitation or dissolution of different evaporitic minerals, negatively impacting local biodiversity and economic activities. Here, we study the sedimentary record of a small saline pond from a playa-lake complex in southwestern Iberia in order to reconstruct the paleohydrological evolution of this area and assess potential anthropogenic disturbances. The different proxies studied in the-11.9 ky old sedimentary record of the Laguna de la Ballestera suggest that the greatest lake extension and the highest water levels occurred during the Early Holocene, pointing to the wettest period of the record. Climate transitioned towards more arid conditions during the Middle Holocene, and even more dramatically during the Late Holocene. In this last stage the wetland surface and the water level largely diminished and gypsum precipitation gradually increased pointing towards a negative precipitation/ evapotranspiration balance and lowest water levels. Summer desiccation likely occurred under this scenario, especially after-1.0-0.9 cal ky BP coeval with the Medieval Climate Anomaly, when gypsum content started to rise abruptly. However, this significant gypsum precipitation was only associated with a massive drop in the siliciclastic content and scarce carbonates (dolomite and calcite) during the last-400 years. This evidence suggests a shift from a (semi) permanent to a temporal/seasonal hydrological regime. The environmental evolution of this wetland responded to the general climatic evolution of the western Mediterranean during the Holocene, being mostly controlled by changes in insolation. Our data also show that the environmental response of the studied wetland to natural climate variations was only significantly disturbed by human activities since the 20th century, especially in the second half of the century, deduced by abrupt fluctuations in the siliciclastic, gypsum and organic content in the sediments, as well as by the enhanced sedimentary accumulation rates, probably as a response to changes in the hydroperiod of the lake and in the catchment land use.Peer reviewe

Paleohydrological dynamics in the Western Mediterranean during the last glacial cycle

The transitional regions between the low and high latitudes of the Northern Hemisphere are highly vulnerable to future climate change yet most of the current climate models usually diverge in their projections. To better understand the dynamics in these regions, the reconstruction of past hydrological fluctuations and precipitation patterns is of paramount importance to accurately constrain present and future climate scenarios. In this study, we investigated paleohydrological dynamics in the western Mediterranean region, a transitional zone between low-mid latitudes and Atlantic - Mediterranean realms. We reconstruct precipitation and moisture source changes during the last -35 ka in order to propose the potential mechanisms driving these oscillations. To do so, we use hydrogen isotopes from sedimentary leaf waxes, more specifically the C31 n-alkane homologue, and a precipitation proxy based on previously published pollen data from a sedimentary core (Padul-15-05) in southern Iberia (Padul wetland -37-N). With this combination we disentangle the coupled effect of precipitation amount and source on the hydrogen isotopic signature of the studied C31 n-alkane record. Our results show three main periods characterized by different precipitation patterns. Low precipitation, mainly linked to a significant contribution from an isotopically-enriched Mediterranean precipitation source, occurred from -30 to -15.5 ka BP and during the last -5 ka, whereas enhanced precipitation with a predominant isotopically-depleted Atlantic precipitation source prevailed from -15.5 to -5 ka BP. This latter stage is here defined as the Western Mediterranean Humid Period (WMHP). In addition, some occasional millennial-scale opposite precipitation patterns can be observed during these climatically distinct periods. These changes in the source of precipitation were likely coupled to a shift in the main rainy season from winter, when Atlantic precipitation prevailed, to late winter-early spring, when the contribution of Mediterranean moisture is higher. Comparison between the studied mid-latitude terrestrial Padul-15-05 core and a low-latitude marine record offshore of northwestern Africa shows clear long-term synchronous responses of both western Mediterranean precipitation and western African monsoon systems to northern Hemisphere atmospheric dynamics, ultimately controlled by orbital forcing and ice-sheets fluctuations.Peer reviewe