The role of excitons and trions on electron spin polarization in quantum wells

We have studied the time evolution of the electron spin polarization under continuous photoexcitation in remotely n-doped semiconductor quantum wells. The doped region allows us to get the necessary excess of free electrons to form trions. We have considered electron resonant photoexcitation at free, exciton and trion electron energy levels. Also, we have studied the relative effect of photoexcitation energy density and doping concentration. In order to obtain the two-dimensional density evolution of the different species, we have performed dynamic calculations through the matrix density formalism. Our results indicate that photoexcitation of free electron level leads to a higher spin polarization. Also, we have found that increasing the photoexcitation energy or diminishing the doping enhances spin polarization.Comment: 30 pages, 11 figures, 1 tabl

Improving the signal detection accuracy of functional Magnetic Resonance Imaging

Available online 12 April 2018A major drawback of functional Magnetic Resonance Imaging (fMRI) concerns the lack of detection accuracy of the measured signal. Although this limitation stems in part from the neuro-vascular nature of the fMRI signal, it also reflects particular methodological decisions in the fMRI data analysis pathway. Here we show that the signal detection accuracy of fMRI is affected by the specific way in which whole-brain volumes are created from individually acquired brain slices, and by the method of statistically extracting signals from the sampled data. To address these limitations, we propose a new framework for fMRI data analysis. The new framework creates whole-brain volumes from individual brain slices that are all acquired at the same point in time relative to a presented stimulus. These whole-brain volumes contain minimal temporal distortions, and are available at a high temporal resolution. In addition, statistical signal extraction occurred on the basis of a non-standard time point-by-time point approach. We evaluated the detection accuracy of the extracted signal in the standard and new framework with simulated and real-world fMRI data. The new slice-based data-analytic framework yields greatly improved signal detection accuracy of fMRI signals.See https://github.com/iamnielsjanssen/slice-based for a full analysis script using the Slice-Based method. This work was supported by The Spanish Ministry of Economy and Competitiveness (RYC2011-08433 and PSI2013-46334 to NJ)

Trion dynamics in coupled double quantum wells. Electron density effects

We have studied the coherent dynamics of injected electrons when they are either free or bounded both in excitons and in trions (charged excitons). We have considered a remotely doped asymmetric double quantum well where an excess of free electrons and the direct created excitons generate trions. We have used the matrix density formalism to analyze the electron dynamics for different concentration of the three species. Calculations show a significant modification of the free electron inter-sublevel oscillations cWe have studied the coherent dynamics of injected electrons when they are aused by electrons bound in excitons and trions. Based on the present calculations we propose a method to detect trions through the emitted electromagnetic radiation or the current density.Comment: 14 pages, 13 figure

Designing the physical metallurgy of a bainitic microalloyed steel with a dilatometer

During the past decade, medium carbon microalloyed steels have become increasingly important in the automotive sector. These steels are especially suitable for automobile components such as connecting rods, crankshafts and wheel hubs. Their mechanical properties are generally adequate in most cases although their toughnesses are consistently low. High toughness can be obtained in medium carbon microalloyed bainitic steel (38MnV7) after a careful control of the chemistry and heat thermal treatment. An specific chemical composition of a 38MnV7 steel has been developed, providing impact energies after Charpy-V tests at room temperature as high as 40J (the steel in bainitic state). Present work is oriented to an optimization of the above chemical composition by control of the Transformation Time Temperature (TTT) curves as well as the Precipitation Time Temperatures (PTT) curves of the present microallying elements. To attain this purpose six different casting were prepared, ranging the chemical composition as follows %C: 0.35-0.46, %Mn: 1.33-1.84, %V: 0.066-0.14% and %Ti: 0.010- 0.025. To appropriate design the thermal cycle, TTT curves were determined for each steel at two austenitization conditions, in order to promote fine and large initial grain sizes.. PTT curves were determined by the stress relaxation technique, a method which can be also be used to derive recrystrallization kinetics. All curves, TTT and PTT curves where derived by using a quenching dilatometer Bahr DIL805A/D. While the TTT curves were obtained in a classical way, the relaxation test consist in sample austenization followed by cooling down to the testing temperature. After a short stabilization period of 10s, samples are deformed to different strain levels and then relaxed, i.e. deformation is kept constant and the variation of the stress with the time is recorded. The different deformation levels are selected to evaluate the effect of deformation on precipitation characteristics. The relaxation curves under these conditions gave information about the kinetics of precipitation when there is no plastic deformation and, thus, generation of dislocations involved. Results are finally discussed in terms of the chemical composition, initial microstructure and precipitates interaction.Peer Reviewe

Temporal stimulated intersubband emission of photoexcited electrons

We have studied the transient evolution of electrons distributed over two levels in a wide quantum well, with the two levels below the optical phonon energy, after an ultrafast interband excitation and cascade emission of optical phonons. If electrons are distributed near the top of the passive region, a temporal negative absorption appears to be dominant in the intersubband response. This is due to the effective broadening of the upper level state under the optical phonon emission. We have then considered the amplification of the ground mode in a THz waveguide with a multiquantum well placed at the center of the cavity. A huge increase of the probe signal is obtained, which permits the temporal stimulated emission regime of the photoexcited electrons in the THz spectral region.Comment: 5 pages, 5 figures, brief repor

Functional connectivity of the hippocampus and its subfields in resting-state networks

First published: 30 March 2021Many neuroimaging studies have shown that the hippocampus participates in a resting-state network called the default mode network. However, how the hippocampus connects to the default mode network, whether the hippocampus connects to other resting-state networks and how the different hippocampal subfields take part in resting-state networks remains poorly understood. Here, we examined these issues using the high spatial-resolution 7T resting-state fMRI dataset from the Human Connectome Project. We used data-driven techniques that relied on spatially-restricted Independent Component Analysis, Dual Regression and linear mixed-effect group-analyses based on participant-specific brain morphology. The results revealed two main activity hotspots inside the hippocampus. The first hotspot was located in an anterior location and was correlated with the somatomotor network. This network was subserved by co-activity in the CA1, CA3, CA4 and Dentate Gyrus fields. In addition, there was an activity hotspot that extended from middle to posterior locations along the hippocampal long-axis and correlated with the default mode network. This network reflected activity in the Subiculum, CA4 and Dentate Gyrus fields. These results show how different sections of the hippocampus participate in two known resting-state networks and how these two resting-state networks depend on different configurations of hippocampal subfield co-activity.Agencia Canaria de Investigación, Innovación y Sociedad de la Información; Ministerio de Ciencia, Innovación y Universidades, Grant/Award Number: PSI2017-84933- P, PSI2017-91955- EXP and TEC2016-80063- C3- 2- R; NIH Blueprint for Neuroscience Research, Grant/Award Number: 1U54MH091657; McDonnell Center for Systems Neuroscience; European Social Fund (ESF

Population genetic structure and colonization sequence of Drosophila subobscura in the Canaries and Madeira Atlantic islands as inferred by autosomal, sex-linked and mtDNA traits

The genetic structure In Atlantic Islands and continental populations of Drosophila subobscura has been studied using autosomal and sex-linked allozymes and ml tochondrial DNA (mtDNA) haplotypes. From the data it Is deduced that whereas the Canary Islands have long been isolated, the neighboring island of Madeira has been subjected to continuous migration from the mainland. In addition, sex-linked allo zymes and mtDNA data show a large divergence between the geologically younger western Islands of the Canarian Archipelago and the older central ones, finding strong founder effects In the former. Divergence rates of sex-linked and mltochon drlal genes relative to autosomlc loci several times higher than expected under neutrality have been explained by differential migration between sexes. The Ca narian Archipelago colonization fits in well with a stepping-stone model of a direc tional east-west migration that parallels the geological origin of these Islands.info:eu-repo/semantics/publishedVersio

Semantic parafoveal processing in natural reading: Insight from fixation-related potentials & eye movements

First published: 23 December 2021Prior research suggests that we may access the meaning of parafoveal words during reading. We explored how semantic-plausibility parafoveal processing takes place in natural reading through the co-registration of eye movements (EM) and fixation-related potentials (FRPs), using the boundary paradigm. We replicated previous evidence of semantic parafoveal processing from highly controlled reading situations, extending their findings to more ecologically valid reading scenarios. Additionally, and exploring the time-course of plausibility preview effects, we found distinct but complementary evidence from EM and FRPs measures. FRPs measures, showing a different trend than EM evidence, revealed that plausibility preview effects may be long-lasting. We highlight the importance of a co-registration set-up in ecologically valid scenarios to disentangle the mechanisms related to semantic-plausibility parafoveal processing.Ministerio de Ciencia e Innovación, Grant/Award Number: PID2020-118487GB- I00; Ministerio de Economía, Industria y Competitividad, Gobierno de España, Grant/Award Number: BES-2017- 08179