Micropropagación de Ulmus minor y U. minor x U. pumila a partir de ramets de 4 años de edad

As part of the Spanish breeding programme against Dutch elm disease, investigations were undertaken on reproduction of Ulmus minor by means of tissue culture. Microshoots were obtained from nodal segments, collected from terminal twigs of 4-year-old ramets of selected clones of this species and of U. minor x U. pumila, and cultured on a modified Murashige & Skoog medium containing 6-Benzylaminopurine (BA). When subcultured, the microshoots or nodal segments excised from these, formed new shoots, their maximum numbers per explant (1.94 to 2) being obtained with the hybrid clone M-TC2 on media containing 3.5 to 8.8 μM BA. The number of microshoots obtained was highest with subcultures of the whole shoot, e.g. 6.9 times superior to control, against 1.5 with nodal segments of VJR1 in presence of 8.8 μM BA. The addition of 0.5 to 5.3 μM indole-acetic acid of α-naphthaleneacetic acid to the medium induced the highest percentage of root formation from the shoots. Both shoot and root formation varied greatly among clones.En el presente trabajo se describen los trabajos sobre reproducción de Ulmus minor mediante las técnicas de cultivo de tejidos, llevados a cabo en el marco del Programa de Mejora Genética Español de los Olmos Frente a la Grafiosis. Brotes obtenidos a partir de segmentos nodales de ramillos terminales de ramets de 4 años de edad, pertenecientes a clones seleccionados de esta especie y de U. minor x U. pumila, fueron cultivados en el medio de Murashige & Skoog modificado conteniendo 6-Bencilaminopurina (BA). Una vez subcultivados los brotes enteros o los segmentos nodales obtenidos a partir del material vegetal in vitro, se originaron nuevos brotes, y fue el clon híbrido MTC2 el que proporcionó un mayor número por explanto (1,94 a 2) sobre medio conteniendo 3,5 a 8,8 μM BA. El número de brotes obtenidos fue mayor cuando todo el brote fue subcultivado, e.g. 6,9 veces superior al control, frente a 1,5 con segmentos nodales de V-JR1 en presencia de 8,8 μM BA. La adición de 0,5 a 5,3 mm de ácido indolacético o α-naftalenacético al medio, provocó el mayor porcentaje de formación de raíz en los brotes. Tanto la formación de brotes como la formación de raíz fue muy variable entre clones

DNA/Histone Ratio in Different Regions of Polytene Chromosomes in the Embryo Suspensor Cells of Phaseolus Coccineus

SUMMARYThe DNA/histone ratio was calculated through Feulgen/fast green absorption in different regions of polytene chromosomes in Phaseolus coccineus embryo suspensor cells. A great variability of ratios, related with the structural characteristics of DNA in the different regions, has been found. This seems to indicate that complexes of histone with DNA may depend on changes in DNA metabolic activity. In one and the same cell, and even in one and the same chromosome, different chromosome segments have different DNA/histone ratios.These findings are discussed in relation to some characteristics of polytene chromosomes in Phaseolus suspensor cells

Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet

The electric (E) field control of magnetic properties opens the prospects of an alternative to magnetic field or electric current activation to control magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have proven to be particularly sensitive to the influence of an E-field due to the interfacial origin of their anisotropy. In these systems, E-field effects have been recently applied to assist magnetization switching and control domain wall (DW) velocity. Here we report on two new applications of the E-field in a similar material : controlling DW nucleation and stopping DW propagation at the edge of the electrode

Near-Perfect Correlation of the Resistance Components of Mesoscopic Samples at the Quantum Hall Regime

We study the four-terminal resistance fluctuations of mesoscopic samples near the transition between the $\nu=2$ and the $\nu=1$ quantum Hall states. We observe near-perfect correlations between the fluctuations of the longitudinal and Hall components of the resistance. These correlated fluctuations appear in a magnetic-field range for which the two-terminal resistance of the samples is quantized. We discuss these findings in light of edge-state transport models of the quantum Hall effect. We also show that our results lead to an ambiguity in the determination of the width of quantum Hall transitions.Comment: As publishe

Lagged and instantaneous dynamical influences related to brain structural connectivity

Contemporary neuroimaging methods can shed light on the basis of human neural and cognitive specializations, with important implications for neuroscience and medicine. Different MRI acquisitions provide different brain networks at the macroscale; whilst diffusion-weighted MRI (dMRI) provides a structural connectivity (SC) coincident with the bundles of parallel fibers between brain areas, functional MRI (fMRI) accounts for the variations in the blood-oxygenation-level-dependent T2* signal, providing functional connectivity (FC).Understanding the precise relation between FC and SC, that is, between brain dynamics and structure, is still a challenge for neuroscience. To investigate this problem, we acquired data at rest and built the corresponding SC (with matrix elements corresponding to the fiber number between brain areas) to be compared with FC connectivity matrices obtained by 3 different methods: directed dependencies by an exploratory version of structural equation modeling (eSEM), linear correlations (C) and partial correlations (PC). We also considered the possibility of using lagged correlations in time series; so, we compared a lagged version of eSEM and Granger causality (GC). Our results were two-fold: firstly, eSEM performance in correlating with SC was comparable to those obtained from C and PC, but eSEM (not C nor PC) provides information about directionality of the functional interactions. Second, interactions on a time scale much smaller than the sampling time, captured by instantaneous connectivity methods, are much more related to SC than slow directed influences captured by the lagged analysis. Indeed the performance in correlating with SC was much worse for GC and for the lagged version of eSEM. We expect these results to supply further insights to the interplay between SC and functional patterns, an important issue in the study of brain physiology and function.Comment: Accepted and published in Frontiers in Psychology in its current form. 27 pages, 1 table, 5 figures, 2 suppl. figure

Dynamics of a millimeter size drop exposed to MHz-frequency surface acoustic wave in the underlying solid substrate

We present an experimental, theoretical, and computational study of the spreading of a millimetric silicon oil drop under the excitation of a surface acoustic wave (SAW), traveling in the underlying solid substrate. Our theoretical model, formulated within the long wave approach, dynamically captures the interplay between fluid dynamics and acoustic driving forces, emphasizing Eckart streaming as the dominant mechanism over Schlichting and Rayleigh streaming due to drop thickness. Following an initial deformation phase to accommodate acoustic stress, the drop accelerates to a sustained translation at nearly constant speed, leaving behind a thin wetting layer. This speed is sustained by the quasi-steady shape of the drop's main body, influenced by SAW attenuation. Notably, SAW attenuation becomes significant once the wave reaches the main body of the drop, with weaker effects observed under the air and the micron-thick liquid trail left behind the drop. The translating drop's speed is found to be dependent on the drop size, as well as on the SAW intensity. The drop's steady shape and speed are further informed by analytical consideration of a simplified traveling wave type model, that clarifies contributions from different physical effects. The theoretical results show qualitative and sometimes even quantitative agreement with the experiments, particularly regarding drop height and traveling speed

The nature of domain walls in ultrathin ferromagnets revealed by scanning nanomagnetometry

The recent observation of current-induced domain wall (DW) motion with large velocity in ultrathin magnetic wires has opened new opportunities for spintronic devices. However, there is still no consensus on the underlying mechanisms of DW motion. Key to this debate is the DW structure, which can be of Bloch or N\'eel type, and dramatically affects the efficiency of the different proposed mechanisms. To date, most experiments aiming to address this question have relied on deducing the DW structure and chirality from its motion under additional in-plane applied fields, which is indirect and involves strong assumptions on its dynamics. Here we introduce a general method enabling direct, in situ, determination of the DW structure in ultrathin ferromagnets. It relies on local measurements of the stray field distribution above the DW using a scanning nanomagnetometer based on the Nitrogen-Vacancy defect in diamond. We first apply the method to a Ta/Co40Fe40B20(1 nm)/MgO magnetic wire and find clear signature of pure Bloch DWs. In contrast, we observe left-handed N\'eel DWs in a Pt/Co(0.6 nm)/AlOx wire, providing direct evidence for the presence of a sizable Dzyaloshinskii-Moriya interaction (DMI) at the Pt/Co interface. This method offers a new path for exploring interfacial DMI in ultrathin ferromagnets and elucidating the physics of DW motion under current.Comment: Main text and Supplementary Information, 33 pages and 12 figure

Comparison of Navier-Stokes simulations with long-wave theory: Study of wetting and dewetting

The classical long-wave theory (also known as lubrication approximation) applied to fluid spreading or retracting on a solid substrate is derived under a set of assumptions, typically including small slopes and negligible inertial effects. In this work, we compare the results obtained by using the long-wave model and by simulating directly the full two-phase Navier-Stokes equations employing a volume-of-fluid method. In order to isolate the influence of the small slope assumption inherent in the long-wave theory, we present a quantitative comparison between the two methods in the regime where inertial effects and the influence of gas phase are negligible. The flow geometries that we consider include wetting and dewetting drops within a broad range of equilibrium contact angles in planar and axisymmetric geometries, as well as liquid rings. For perfectly wetting spreading drops we find good quantitative agreement between the models, with both of them following rather closely Tanner's law. For partially wetting drops, while in general we find good agreement between the two models for small equilibrium contact angles, we also uncover differences which are particularly evident in the initial stages of evolution, for retracting drops, and when additional azimuthal curvature is considered. The contracting rings are also found to evolve differently for the two models, with the main difference being that the evolution occurs on the faster time scale when the long-wave model is considered, although the ring shapes are very similar between the two models.Fil: Mahady, K.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados UnidosFil: Afkhami, S.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados UnidosFil: Diez, Javier Alberto. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Fisica Arroyo Seco; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tandil; ArgentinaFil: Kondic, L.. New Jersey Institute of Technology. Department of Mathematical Sciences; Estados Unido