Stomatal control of water use in olive tree leaves

Little is known about the strategies used by olive trees to overcome the long dry periods typical of the areas where they are cropped. This makes it difficult to optimize the water supply in orchards. To study the control of water consumption by olive trees, measurements of leaf water potential (Ψ) and stomatal conductance to H2O (g) were made on 26-year-old Manzanillo olive trees under three irrigation treatments. The first treatment provided enough water to cover the crop water demand, the next treatment supplied one third of that rate, and the final treatment was no irrigation at all, typical of dry-farming conditions. Under conditions of high vapour pressure deficit of the air (D(a)), the olive trees prevented excessive water loss by closing their stomata. Leaves of the current year showed better stomatal control than did the 1-year-old leaves. The upper-bound functional relationships between g and D(a) and photon flux density (I(P)) were obtained by boundary-line analysis, based on a technique of non-linear least squares. Maximum values of g were observed at relatively low levels of I(p), from about 500 μmol m-2 s-1, and a proportional decrease in g with increasing D(a) was also found, at least for values of up to approximately 3.5 kPa. Higher values of g were observed in the morning than in the afternoon, for similar levels of I(P) and D(a). Unirrigated olive trees recovered quickly after the dry season, showing values of Ψ and g similar to those of irrigated trees after just two days.Peer Reviewe

Carbon stars in the X-shooter Spectral Library

We provide a new collection of spectra of 35 carbon stars obtained with the ESO/VLT X-shooter instrument as part of the X-shooter Spectral Library project. The spectra extend from 0.3$\mu$m to 2.4$\mu$m with a resolving power above $\sim$ 8000. The sample contains stars with a broad range of (J-K) color and pulsation properties located in the Milky Way and the Magellanic Clouds. We show that the distribution of spectral properties of carbon stars at a given (J-K) color becomes bimodal (in our sample) when (J-K) is larger than about 1.5. We describe the two families of spectra that emerge, characterized by the presence or absence of the absorption feature at 1.53$\mu$m, generally associated with HCN and C$_2$H$_2$. This feature appears essentially only in large-amplitude variables, though not in all observations. Associated spectral signatures that we interpret as the result of veiling by circumstellar matter, indicate that the 1.53$\mu$m feature might point to episodes of dust production in carbon-rich Miras.Comment: 29 pages, 21 figures, 9 tables, Accepted for publication in A&

Resistive switching and charge transport mechanisms in ITO/ZnO/p-Si devices

[EN] The resistive switching properties of ITO/ZnO/p-Si devices have been studied, which present well-defined resistance states with more than five orders of magnitude difference in current. Both the high resistance state (HRS) and the low resistance state (LRS) were induced by either sweeping or pulsing the voltage, observing some differences in the HRS. Finally, the charge transport mechanisms dominating the pristine, HRS, and LRS states have been analyzed in depth, and the obtained structural parameters suggest a partial re-oxidation of the conductive nanofilaments and a reduction of the effective conductive area.This work was financially supported by the Spanish Ministry of Economy and Competitiveness (Project Nos. TEC2012-38540-C02-01 and TEC2016-76849-C2-1-R). O.B. also acknowledges the subprogram "Ayudas para Contratos Predoctorales para la Formacion de Doctores" of the Spanish Ministry of Economy and Competitiveness for economical support. X.P., C.L., and C.G. are grateful to C. Frilay for his expertise in the maintenance of the sputtering kit used for the growth of the ZnO films.Blázquez, O.; Frieiro, J.; López-Vidrier, J.; Guillaume, C.; Portier, X.; Labbé, C.; Sanchis Kilders, P.... (2018). Resistive switching and charge transport mechanisms in ITO/ZnO/p-Si devices. Applied Physics Letters. 113(18):1-6. https://doi.org/10.1063/1.50469111611318I. G. Baek , M. S. Lee , S. Sco , M. J. Lee , D. H. Seo , D.S. Suh , J. C. Park , S. O. Park , H. S. Kim , I. K. Yoo , U.I. Chung , and J. T. Moon , in IEDM Technical Digest. IEEE International Electron Devices Meeting, 2004 ( IEEE, 2004), pp. 587–590.Waser, R., & Aono, M. (2007). Nanoionics-based resistive switching memories. Nature Materials, 6(11), 833-840. doi:10.1038/nmat2023Kaeriyama, S., Sakamoto, T., Sunamura, H., Mizuno, M., Kawaura, H., Hasegawa, T., … Aono, M. (2005). A nonvolatile programmable solid-electrolyte nanometer switch. 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M., Panda, D., Tsai, T.-L., Lin, C.-A., Wei, K.-H., & Tseng, T.-Y. (2015). Enhancing the memory window of AZO/ZnO/ITO transparent resistive switching devices by modulating the oxygen vacancy concentration of the top electrode. Journal of Materials Science, 50(21), 6961-6969. doi:10.1007/s10853-015-9247-ySimanjuntak, F. M., Prasad, O. K., Panda, D., Lin, C.-A., Tsai, T.-L., Wei, K.-H., & Tseng, T.-Y. (2016). Impacts of Co doping on ZnO transparent switching memory device characteristics. Applied Physics Letters, 108(18), 183506. doi:10.1063/1.4948598Simanjuntak, F. M., Panda, D., Tsai, T.-L., Lin, C.-A., Wei, K.-H., & Tseng, T.-Y. (2015). Enhanced switching uniformity in AZO/ZnO1−x/ITO transparent resistive memory devices by bipolar double forming. Applied Physics Letters, 107(3), 033505. doi:10.1063/1.4927284Liu, Q., Guan, W., Long, S., Jia, R., Liu, M., & Chen, J. (2008). Resistive switching memory effect of ZrO[sub 2] films with Zr[sup +] implanted. Applied Physics Letters, 92(1), 012117. doi:10.1063/1.2832660Shuai, Y., Zhou, S., Bürger, D., Helm, M., & Schmidt, H. (2011). Nonvolatile bipolar resistive switching in Au/BiFeO3/Pt. Journal of Applied Physics, 109(12), 124117. doi:10.1063/1.3601113Chen, J.-Y., Hsin, C.-L., Huang, C.-W., Chiu, C.-H., Huang, Y.-T., Lin, S.-J., … Chen, L.-J. (2013). Dynamic Evolution of Conducting Nanofilament in Resistive Switching Memories. Nano Letters, 13(8), 3671-3677. doi:10.1021/nl4015638Hubbard, W. A., Kerelsky, A., Jasmin, G., White, E. R., Lodico, J., Mecklenburg, M., & Regan, B. C. (2015). Nanofilament Formation and Regeneration During Cu/Al2O3 Resistive Memory Switching. Nano Letters, 15(6), 3983-3987. doi:10.1021/acs.nanolett.5b00901Liu, Q., Sun, J., Lv, H., Long, S., Yin, K., Wan, N., … Liu, M. (2012). Real-Time Observation on Dynamic Growth/Dissolution of Conductive Filaments in Oxide-Electrolyte-Based ReRAM. 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Modulation of the electroluminescence emission from ZnO/Si NCs/p-Si light-emitting devices via pulsed excitation

In this work, the electroluminescence (EL) emission of zinc oxide (ZnO)/Si nanocrystals (NCs)-based light-emitting devices was studied under pulsed electrical excitation. Both Si NCs and deep-level ZnO defects were found to contribute to the observed EL. Symmetric square voltage pulses (50-μs period) were found to notably enhance EL emission by about one order of magnitude. In addition, the control of the pulse parameters (accumulation and inversion times) was found to modify the emission lineshape, long inversion times (i.e., short accumulation times) suppressing ZnO defects contribution. The EL results were discussed in terms of the recombination dynamics taking place within the ZnO/Si NCs heterostructure, suggesting the excitation mechanism of the luminescent centers via a combination of electron impact, bipolar injection, and sequential carrier injection within their respective conduction regimes

Light-activated electroforming in ITO/ZnO/p-Si resistive switching devices

We report on light-activated electroforming of ZnO/p-Si heterojunction memristors with transparent indium tin oxide as the top electrode. Light-generated electron-hole pairs in the p-type substrate are separated by the external electric field and electrons are injected into the active ZnO layer. The additional application of voltage pulses allows achieving different resistance states that end up in the realization of the low resistance state (LRS). This process requires much less voltage compared to dark conditions, thus avoiding undesired current overshoots and achieving a self-compliant device. The transport mechanisms governing each resistance state are studied and discussed. An evolution from an electrode-limited to a space charge-limited transport is observed along the electroforming process before reaching the LRS, which is ascribed to the progressive formation of conductive paths that consequently induce the growth of conductive nanofilaments through the ZnO layer. This work was financially supported by the Spanish Ministry of Economy and Competitiveness (Project Nos. TEC2012-38540-C02-01 and TEC2016-76849-C2-1-R). O.B. also acknowledges the subprogram "Ayudas para Contratos Predoctorales para la Formación de-Doctores" from the Spanish Ministry of Economy and Competitiveness for economical support. J.L.F. acknowledges the subprogram "Ayudas para la Formación de Profesorado Universitario" (No. FPU16/06257) from the Spanish Ministry of Education, Culture and Sports for economical support. X.P., C.L., and C.G. are grateful to C. Frilay for his expertise in the maintenance of the sputtering setup used for the growth of the ZnO films

Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters

Bisectors of the HARPS cross-correlation function (CCF) can discern between planetary radial-velocity (RV) signals and spurious RV signals from stellar magnetic activity variations. However, little is known about the effects of the stellar atmosphere on CCF bisectors or how these effects vary with spectral type and luminosity class. Here we investigate the variations in the shapes of HARPS CCF bisectors across the HR diagram in order to relate these to the basic stellar parameters, surface gravity and temperature. We use archive spectra of 67 well studied stars observed with HARPS and extract mean CCF bisectors. We derive previously defined bisector measures (BIS, v_bot, c_b) and we define and derive a new measure called the CCF Bisector Span (CBS) from the minimum radius of curvature on direct fits to the CCF bisector. We show that the bisector measures correlate differently, and non-linearly with log g and T_eff. The resulting correlations allow for the estimation of log g and T_eff from the bisector measures. We compare our results with 3D stellar atmosphere models and show that we can reproduce the shape of the CCF bisector for the Sun.Comment: 13 pages, 20 figures. Accepted by A&

Correlación entre el diagnóstico de depresión y la sintomatología presentada en pacientes de atención primaria

La depresión mayor es una enfermedad crónica con una alta prevalencia que cursa habitualmente de manera episó- dica, con una duración media del episodio de 16 semanas. No se han encontrado análisis que evalúen la concordancia entre la aparición de los mismos y la evolución del episodio. El objetivo de este estudio es analizar la concordancia entre la evolución sintomática (aparición, mantenimiento, remisión de los diversos síntomas) y la evolución del diagnóstico de depresión mayor (aparición, mantenimiento y remisión) en una cohorte de personas con y sin diagnóstico de depresión mayor. Se realizó un estudio de cohortes prospectivo a un año de seguimiento en el que se entrevistó a una muestra aleatoria de 741 sujetos que acudían a consultas de atención primaria, se elaboró el diagnóstico de depresión según criterios del DSM-IV y se analizó la sintomatología que presentaba. Estos sujetos fueron re-evaluados a los 6 meses y 12 meses. El estado de ánimo deprimido, la disminución del interés o anhedonia y los síntomas relacionados con el sueño (insomnio o hipersomnia), la agitación, el sentimiento de culpa y la fatiga o pérdida de energía son concordantes con el diagnóstico. El resto de los síntomas muestran una evolución independiente de la evolución del diagnóstico. En Atención Primaria, es importante conocer qué síntomas son claves en la evolución del diagnóstico con la finalidad de conseguir la remisión total de la depresión y evitar mantenimiento de sintomatología residual que puede dar lugar a pródromos

Stellar population and the origin of intra-cluster stars around brightest cluster galaxies: the case of NGC 3311

Context. We investigate the stellar population and the origin of diffuse light around brightest cluster galaxies. Aims. We study the stellar population of the dynamically hot stellar halo of NGC 3311, the brightest galaxy in the Hydra I cluster, and that of photometric substructures in the diffuse light to constrain the origin of these components. Methods. We analyze absorption lines in medium-resolution, long-slit spectra in the wavelength range 4800-5800 angstrom obtained with FORS2 at the Very Large Telescope. We measure the equivalent width of Lick indices out to 20 kpc from the center of NGC 3311 and fit them with stellar population models that account for the [alpha/Fe] overabundance. Results. Stars in the dynamically hot halo of NGC 3311 are old (age > 13 Gyr), metal-poor ([Z/H] ~ -0.35), and alpha-enhanced ([alpha/Fe] ~ 0.48). Together with the high velocity dispersion, these measurements indicate that the stars in the halo were accreted from the outskirts of other early-type galaxies, with a possible contribution from dwarf galaxies. We identify a region in the halo of NGC 3311 associated with a photometric substructure where the stellar population is even more metal-poor ([Z/H] ~ -0.73). In this region, our measurements are consistent with a composite stellar population superposed along the line of sight, consisting of stars from the dynamically hot halo of NGC 3311 and stars stripped from dwarf galaxies. The latter component contributes < 28% to the local surface brightness. Conclusions. The build-up of diffuse light around NGC 3311 is on-going. Based on the observed stellar population properties, the dominant part of these stars may have come from the outskirts of bright early-type galaxies, while stars from stripped dwarf galaxies are presently being added.Comment: 8 pages, 4 figures. Accepted for publication in Astronomy & Astrophysic