8,822 research outputs found
Anomalous Hall conductivity control in MnNiN antiperovskite by epitaxial strain along the kagome plane
Antiferromagnetic manganese-based nitride antiperovskites, such as MnNiN,
hold a triangular frustrated magnetic ordering over their kagome lattice formed
by the Mn atoms along the (111)-plane. As such, frustration imposes a
non-trivial interplay between the symmetric and asymmetric magnetic
interactions, which can only reach equilibrium in a noncollinear magnetic
configuration. Consequently, the associated electronic interactions and their
possible tuning by external constraints, such as applied epitaxial strain, play
a crucial role in defining the microscopic and macroscopic properties of such
topological condensed matter systems. Thus, in the present work, we explored
and explained the effect of the epitaxial strain imposed within the
(111)-plane, in which the magnetic and crystallographic symmetry operations are
kept fixed, and only the magnitude of the ionic and electronic interactions are
tuned. We found a linear shifting in the energy of the band structure and a
linear increase/decrease of the available states near the Fermi level with the
applied strain. Concretely, the compression strain reduces the Mn-Mn distances
in the (111) kagome plane but linearly increases the separation between the
stacked kagome lattices and the available states near the Fermi level. Despite
the linear controlling of the available states across the Fermi energy, the
anomalous Hall conductivity shows a non-linear behavior where the
conductivity nearly vanishes for tensile strain. On the other
hand, fetches a maximum increase of 26\% about the unstrained
structure for a compression value close to 1.5\%.This behavior found an
explanation in the non-divergent Berry curvature within the kagome plane, which
is increased for constraining but significantly reduced for expansion strain
values..
Pesquisa participativa em melhoramento de mandioca: uma experiência no Semi-Árido do Nordeste do Brasil.
Este trabalho teve por objetivos provar conjuntamente com agricultores, extensionistas e pesquisadores uma metodologia complementar, denominada de pesquisa participativa em melhoramento de mandioca, que aplicada a clones em etapas avançadas de avaliação, incremente a possibilidade de serem adotados pelos produtores, bem como estabelecer uma retroalimentação entre estes segmentos que permita identificar os principais critérios de seleção utilizados pelos produtores do semi-árido para a adoção de novas cultivares de mandioca. O trabalho foi desenvolvido em quatro locais do semi-árido dos Estados da Bahia (Itaberaba), Pernambuco (Petrolina e Araripina) e Ceara (Quixadá), em parceria com a EBDA,IPA e EPACE. Iniciou-se com um diagnostico, seguido do planejamento e implantação das provas participativas, avaliação e retro informação. Foram estabelecidas dezessete provas participativas, nos anos de 1993/94, com nove clones selecionados para as condições semi-áridas. Como resultados principais traçou-se o perfil de uma variedade ideal para o semi-árido, baseado nos critérios de seleção estabelecidos pelos produtores dessa região, formou-se um glossário sobre a terminologia agrícola local do produtor de mandioca e adaptou-se um livro de campo gerado no CIAT, as características consideradas importantes pelos produtores de mandioca do semi-árido.bitstream/item/81301/1/Pesquisa-Participativa-Wania-Fukuda-Documentos-73-1997.pd
Source identification for mobile devices, based on wavelet transforms combined with sensor imperfections
One of the most relevant applications of digital image forensics is to accurately identify the device used for taking a given set of images, a problem called source identification. This paper studies recent developments in the field and proposes the mixture of two techniques (Sensor Imperfections and Wavelet Transforms) to get better source identification of images generated with mobile devices. Our results show that Sensor Imperfections and Wavelet Transforms can jointly serve as good forensic features to help trace the source camera of images produced by mobile phones. Furthermore, the model proposed here can also determine with high precision both the brand and model of the device
First joint observations of space weather events over Mexico
Abstract. The Mexican Space Weather Service (SCiESMEX in Spanish) and National Space Weather Laboratory (LANCE in Spanish) were organized in 2014 and in 2016, respectively, to provide space weather monitoring and alerts, as well as scientific research in Mexico. In this work, we presenttheresultsofthefirstjointobservationsoftwoevents (22 June and 29 September 2015) with our local network of instruments and their related products. This network includes the MEXART radio telescope (solar flare and radio burst), the Compact Astronomical Low-frequency, Low-cost Instrument for Spectroscopy in Transportable Observatories (CALLISTO)attheMEXARTstation(solarradioburst),the Mexico City Cosmic Ray Observatory (cosmic ray fluxes), GPS receiver networks (ionospheric disturbances), and the Teoloyucan Geomagnetic Observatory (geomagnetic field). The observations show that we detected significant space weather effects over the Mexican territory: geomagnetic and ionospheric disturbances (22 June 2015), variations in cosmicrayfluxes,andalsoradiocommunications’interferences (29September2015).Theeffectsoftheseperturbationswere registered,forthefirsttime,usingspaceweatherproductsby SCiESMEX:totalelectroncontent(TEC)maps,regionalgeomagneticindexKmex,radiospectrographsoflowfrequency, and cosmic ray fluxes. These results prove the importance of
monitoring space weather phenomena in the region and the need to strengthening the instrumentation network
First observations of oblique ionospheric sounding chirp signal in Mexico
The results of the first experiment of oblique ionospheric sounding (OIS) chirp signal reception in Mexico are
reported. Maximal and Lowest Observed Frequencies variations were studied under the quiet Space Weather
conditions. The diurnal ionospheric variations by OIS signal confirm the results based on GNSS data in the
Mexican region. The best HF radio propagation conditions along the considered path are during morning and
daytime hours. The multi-hop propagation is frequent. The interlayer propagation modes are present at nighttime
Discovery of the Optical Transient of the Gamma Ray Burst 990308
The optical transient of the faint Gamma Ray Burst 990308 was detected by the
QUEST camera on the Venezuelan 1-m Schmidt telescope starting 3.28 hours after
the burst. Our photometry gives , , , and for times ranging from 3.28 to 3.47
hours after the burst. The colors correspond to a spectral slope of close to
. Within the standard synchrotron fireball model,
this requires that the external medium be less dense than , the
electrons contain of the shock energy, and the magnetic field energy
must be less than 24% of the energy in the electrons for normal interstellar or
circumstellar densities. We also report upper limits of at 132 s
(with LOTIS), from 132-1029s (with LOTIS), at 28.2 min
(with Super-LOTIS), and a 8.5 GHz flux of at 110 days (with the
Very Large Array). WIYN 3.5-m and Keck 10-m telescopes reveal this location to
be empty of any host galaxy to and . The lack of a host
galaxy likely implies that it is either substantially subluminous or more
distant than a red shift of .Comment: ApJ Lett submitted, 5 pages, 2 figures, no space for 12 coauthor
Electrostatic potential and valence modulation in La0.7Sr0.3MnO3 thin films
The Mn valence in thin film La0.7Sr0.3MnO3 was studied as a function of film thickness in the range of 1–16 unit cells with a combination of non-destructive bulk and surface sensitive X-ray absorption spectroscopy techniques. Using a layer-by-layer valence model, it was found that while the bulk averaged valence hovers around its expected value of 3.3, a significant deviation occurs within several unit cells of the surface and interface. These results were supported by first principles calculations. The surface valence increases to up to Mn3.7+, whereas the interface valence reduces down to Mn2.5+. The change in valence from the expected bulk value is consistent with charge redistribution due to the polar discontinuity at the film-substrate interface. The comparison with theory employed here illustrates how this layer-by-layer valence evolves with film thickness and allows for a deeper understanding of the microscopic mechanisms at play in this effect. These results offer insight on how the two-dimensional electron gas is created in thin film oxide alloys and how the magnetic ordering is reduced with dimensionality
Analysis of immunization time, amplitude, and adverse events of seven different vaccines against SARS-CoV-2 across four different countries
Background: Scarce information exists in relation to the comparison of seroconversion and adverse events following immunization (AEFI) with different SARS-CoV-2 vaccines. Our aim was to correlate the magnitude of the antibody response to vaccination with previous clinical conditions and AEFI. Methods: A multicentric comparative study where SARS-CoV-2 spike 1-2 IgG antibodies IgG titers were measured at baseline, 21-28 days after the first and second dose (when applicable) of the following vaccines: BNT162b2 mRNA, mRNA-1273, Gam-COVID-Vac, Coronavac, ChAdOx1-S, Ad5-nCoV and Ad26.COV2. Mixed model and Poisson generalized linear models were performed. Results: We recruited 1867 individuals [52 (SD 16.8) years old, 52% men]. All vaccines enhanced anti-S1 and anti-S2 IgG antibodies over time (p<0.01). The highest increase after the first and second dose was observed in mRNA-1273 (p<0.001). There was an effect of previous SARS-CoV-2 infection; and an interaction of age with previous SARS-CoV-2 infection, Gam-COVID-Vac and ChAdOx1-S (p<0.01). There was a negative correlation of Severe or Systemic AEFI (AEs) of naïve SARS-CoV-2 subjects with age and sex (p<0.001); a positive interaction between the delta of antibodies with Gam-COVID-Vac (p=0.002). Coronavac, Gam-COVID-Vac and ChAdOx1-S had less AEs compared to BNT162b (p<0.01). mRNA-1273 had the highest number of AEFIs. The delta of the antibodies showed an association with AEFIs in previously infected individuals (p<0.001). Conclusions: The magnitude of seroconversion is predicted by age, vaccine type and SARS-CoV-2 exposure. AEs are correlated with age, sex, and vaccine type. The delta of the antibody response only correlates with AEs in patients previously exposed to SARS-CoV-2. Registration number: ClinicalTrials.gov, identifier NCT05228912
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