Influence of M-phase chromatin on the anisotropy of microtubule asters

In many eukaryotic cells going through M-phase, a bipolar spindle is formed by microtubules nucleated from centrosomes. These microtubules, in addition to being "captured" by kinetochores, may be stabilized by chromatin in two different ways: short-range stabilization effects may affect microtubules in close contact with the chromatin, while long-range stabilization effects may "guide" microtubule growth towards the chromatin (e.g., by introducing a diffusive gradient of an enzymatic activity that affects microtubule assembly). Here, we use both meiotic and mitotic extracts from Xenopus laevis eggs to study microtubule aster formation and microtubule dynamics in the presence of chromatin. In "low-speed" meiotic extracts, in the presence of salmon sperm chromatin, we find that short-range stabilization effects lead to a strong anisotropy of the microtubule asters. Analysis of the dynamic parameters of microtubule growth show that this anisotropy arises from a decrease in the catastrophe frequency, an increase in the rescue frequency and a decrease in the growth velocity. In this system we also find evidence for long-range "guidance" effects, which lead to a weak anisotropy of the asters. Statistically relevant results on these long-range effects are obtained in "high-speed" mitotic extracts in the presence of artificially constructed chromatin stripes. We find that aster anisotropy is biased in the direction of the chromatin and that the catastrophe frequency is reduced in its vicinity. In this system we also find a surprising dependence of the catastrophe and the rescue frequencies on the length of microtubules nucleated from centrosomes: the catastrophe frequency increase and the rescue frequency decreases with microtubule length

Anomalous precursor diamagnetism at low reduced magnetic fields and the role of Tc inhomogeneities in the superconductors Pb55In45 and underdoped La1.9Sr0.1CuO4

The magnetic field dependence of the magnetization was measured above the superconducting transition in a high-Tc underdoped cuprate La1.9Sr0.1CuO4 and in a low-Tc alloy (Pb55In45). Near the superconducting transition [typically for (T-Tc)/Tc<0.05] and under low applied magnetic field amplitudes [typically for H/Hc2(0)<0.01, where Hc2(0) is the corresponding upper critical field extrapolated to T=0 K] the magnetization of both samples presents a diamagnetic contribution much larger than the one predicted by the Gaussian Ginzburg-Landau (GGL) approach for superconducting fluctuations. These anomalies have been already observed in cuprate compounds by various groups and attributed to intrinsic effects associated with the own nature of these high-Tc superconductors. However, we will see here that our results in both high and low-Tc superconductors may be explained quantitatively, and consistently with the GGL behavior observed at higher fields, by just taking into account the presence in the samples of an uniform distribution of Tc inhomogeneities. These Tc inhomogeneities, which may be in turn associated with stoichiometric inhomogeneities, were estimated from independent measurements of the temperature dependence of the field-cooled magnetic susceptibility under low applied magnetic fields.Comment: 25 pages, including 6 figures and 1 table. Typos corrected. Compacte

Magnetism of two-dimensional defects in Pd: stacking faults, twin boundaries and surfaces

Careful first-principles density functional calculations reveal the importance of hexagonal versus cubic stacking of closed packed planes of Pd as far as local magnetic properties are concerned. We find that, contrary to the stable face centered cubic phase, which is paramagnetic, the hexagonal close-packed phase of Pd is ferromagnetic with a magnetic moment of 0.35 $\mu_{B}$/atom. Our results show that two-dimensional defects with local hcp stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd structure, increase the magnetic susceptibility. The (111) surface also increases the magnetic susceptibility and it becomes ferromagnetic in combination with an individual stacking fault or twin boundary close to it. On the contrary, we find that the (100) surface decreases the tendency to ferromagnetism. The results are consistent with the magnetic moment recently observed in small Pd nanoparticles, with a large surface area and a high concentration of two-dimensional stacking defects.Comment: 8 pages, 10 figure

Nilpotent subgroups of the group of fibre homotopy equivalences

Let $\xi=(E,p,B,F)$ be a Hurewicz fibration. In this paper we study the space \Cal L_G(\xi) consisting of fibre homotopy self equivalences of $\xi$ inducing by restriction to the fibre a self homotopy equivalence of $F$ belonging to the group $G$. We give in particular conditions implying that \pi_1(\Cal L_G(\xi)) is finitely generated or that \Cal L_1(\xi) has the same rational homotopy type as $\operatorname{aut}_1(F)$

Autonomía y orientación en el Espacio Europeo de Educación Superior mediante el portafolio y la tutoría

En el nuevo rol del profesor y del estudiante universitario, según el cual el primero asume funciones de guía, orientador, asesor y facilitador de recursos para el aprendizaje activo del segundo, se le da más importancia al aprendizaje que a la enseñanza. En este trabajo mostramos la percepción que tienen 290 estudiantes de distintas especialidades de Magisterio y Fisioterapia sobre el uso del portafolios y de la tutoría como elementos de interés para los procesos de innovación docente (Espacio Europeo de Educación Superior). Para tal fin se ha pasado un cuestionario, efectuándose un análisis descriptivo y comparativo, obteniendo evidencias de interés

Unconditional security at a low cost

By simulating four quantum key distribution (QKD) experiments and analyzing one decoy-state QKD experiment, we compare two data post-processing schemes based on security against individual attack by L\"{u}tkenhaus, and unconditional security analysis by Gottesman-Lo-L\"{u}tkenhaus-Preskill. Our results show that these two schemes yield close performances. Since the Holy Grail of QKD is its unconditional security, we conclude that one is better off considering unconditional security, rather than restricting to individual attacks.Comment: Accepted by International Conference on Quantum Foundation and Technology: Frontier and Future 2006 (ICQFT'06

Teratogenic, oxidative stress and behavioural outcomes of three fungicides of natural origin (Equisetum arvense, mimosa tenuiflora, thymol) on zebrafish (danio rerio)

The improper use of synthetic fungicides has raised public concerns related to environmental pollution and animal health. Over the years, plant-derived antifungals have been investigated as safer alternatives, although little scientific evidence of its neurodevelopmental effects exist. The main objective of this study was to explore the effects of three alternative natural extracts (Equisetum arvense, Mimosa tenuiflora, Thymol) with antifungal properties during the early development of zebrafish by evaluating different teratogenic, oxidative stress and behavioural outcomes. Following the determination of the 96 h-LC50, exposure to sublethal concentrations showed the safety profile of both E. arvense and M. tenuiflora. However, following 96-h exposure to Thymol, increased lethality, pericardial oedema, yolk and eye deformations, and decreased body length were observed. The reduced and oxidized glutathione (GSH:GSSG) ratio was increased, and the glutathione-s-transferase activity in the group exposed to the highest Thymol concentration. Overall, these results support a more reducing environment associated with possible effects at the cellular proliferation level. In addition, the disruption of behavioural states (fear-and anxiety-like disorders) were noted, pointing to alterations in the c-Jun N-terminal kinase developmental signalling pathway, although further studies are required to explore this rationale. Notwithstanding, the results provide direct evidence of the teratogenic effects of Thymol, which might have consequences for non-target species.This research was funded by European Investment Funds by FEDER/COMPETE/POCI– Operational Competitiveness and Internationalization Programme, under the project POCI-01–0145-FEDER-006958 and National Funds by FCT—“Fundação para a Ciência e a Tecnologia”, under the project UIBD/04033/2020 and under the PhD grant number SFRH/BD/144904/2019