On the Non-existence of 3-Dimensional Tiling in the Lee Metric

AbstractWe prove that there does not exist a tiling with Lee spheres of radius at least 2 in the 3-dimensional Euclidean space. In particular, this result verifies a conjecture of Golomb and Welch forn=3

Current-induced two-level fluctuations in pseudo spin-valves (Co/Cu/Co) nanostructures

Two-level fluctuations of the magnetization state of pseudo spin-valve pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires (~40 nm in diameter, 6000 nm in length) are triggered by spin-polarized currents of 10^7 A/cm^2 at room temperature. The statistical properties of the residence times in the parallel and antiparallel magnetization states reveal two effects with qualitatively different dependences on current intensity. The current appears to have the effect of a field determined as the bias field required to equalize these times. The bias field changes sign when the current polarity is reversed. At this field, the effect of a current density of 10^7 A/cm^2 is to lower the mean time for switching down to the microsecond range. This effect is independent of the sign of the current and is interpreted in terms of an effective temperature for the magnetization.Comment: 4 pages, 5 figures, revised version, to be published in Phys. Rev. Let

Spin-dependent transport in cluster-assemblednanostructures: influence of cluster size and matrix material

Abstract.: Spin-dependent transport in granular metallic nanostructures has been investigated by means of a thermoelectric measurement. Cobalt clusters of well-defined size (〈n〉 = 15-600) embedded in copper and silver matrices show magnetic field responses of up to several hundred percent at low temperature. The experimental observations are attributed to spin mixing. The influence of cluster size and matrix are discusse

In vitro and in vivo behaviour of paclitaxel loaded lipid nanocapsules

International audienc

Le diagnostic architectural : un outil d’évaluation des sapinières dépérissantes

En région méditerranéenne, le sapin pectiné se trouve dans la limite sud de son aire de répartition et depuis 2003, des dépérissements sont observés dans le département de l’Aude et dans la région Provence-Alpes-Côte d’Azur. Ce constat préoccupe les forestiers et pose de façon cruciale la question du diagnostic de l’état de santé des arbres. Comment ne pas confondre vieillissement et dépérissement ? Quel est l’état normal, ou arbre de référence, d’un sapin ? Peut-on pronostiquer le caractère passager ou inéluctable d’un dépérissement ? La méthode d’analyse architecturale des arbres (ou méthode ARCHI) appliquée au sapin répond à ces interrogations. En reconstituant la dynamique de développement depuis la plantule jusqu’à la sénescence, elle nous renseigne sur l’ontogénèse du sapin. C’est en se référant à cette séquence que la méthode ARCHI peut prendre en compte les deux composantes d’un dépérissement, à savoir : les symptômes de dégradation des houppiers, c'est-à-dire les écarts à la normale, et les processus de résilience, c'est-à-dire les retours à la normale (ou à un état proche de la normale). Cinq états sont ainsi définis : l’état normal (arbre sain), les écarts à la normale (arbres stressés), les retours à la normale (arbres résilients et descentes de cimes) et les points de non-retour à la normale (arbres en dépérissement irréversible). Après simplification du protocole d’observation sur le terrain, une clef de détermination des types architecturaux est proposée aux gestionnaires forestiers. Les perspectives offertes par la méthode ARCHI sont passées en revue, de même que ses limites

Thermally driven spin injection from a ferromagnet into a non-magnetic metal

Creating, manipulating and detecting spin polarized carriers are the key elements of spin based electronics. Most practical devices use a perpendicular geometry in which the spin currents, describing the transport of spin angular momentum, are accompanied by charge currents. In recent years, new sources of pure spin currents, i.e., without charge currents, have been demonstrated and applied. In this paper, we demonstrate a conceptually new source of pure spin current driven by the flow of heat across a ferromagnetic/non-magnetic metal (FM/NM) interface. This spin current is generated because the Seebeck coefficient, which describes the generation of a voltage as a result of a temperature gradient, is spin dependent in a ferromagnet. For a detailed study of this new source of spins, it is measured in a non-local lateral geometry. We developed a 3D model that describes the heat, charge and spin transport in this geometry which allows us to quantify this process. We obtain a spin Seebeck coefficient for Permalloy of -3.8 microvolt/Kelvin demonstrating that thermally driven spin injection is a feasible alternative for electrical spin injection in, for example, spin transfer torque experiments

Seebeck Effect in Magnetic Tunnel Junctions

Creating temperature gradients in magnetic nanostructures has resulted in a new research direction, i.e., the combination of magneto- and thermoelectric effects. Here, we demonstrate the observation of one important effect of this class: the magneto-Seebeck effect. It is observed when a magnetic configuration changes the charge based Seebeck coefficient. In particular, the Seebeck coefficient changes during the transition from a parallel to an antiparallel magnetic configuration in a tunnel junction. In that respect, it is the analog to the tunneling magnetoresistance. The Seebeck coefficients in parallel and antiparallel configuration are in the order of the voltages known from the charge-Seebeck effect. The size and sign of the effect can be controlled by the composition of the electrodes' atomic layers adjacent to the barrier and the temperature. Experimentally, we realized 8.8 % magneto-Seebeck effect, which results from a voltage change of about -8.7 {\mu}V/K from the antiparallel to the parallel direction close to the predicted value of -12.1 {\mu}V/K.Comment: 16 pages, 7 figures, 2 table

Diverse and productive source of biopolymer inspiration: marine collagens

Marine biodiversity is expressed through the huge variety of vertebrate and invertebrate species inhabiting intertidal to deep-sea environments. The extraordinary variety of â forms and functionsâ  exhibited by marine animals suggests they are a promising source of bioactive molecules and provides potential inspiration for different biomimetic approaches. This diversity is familiar to biologists and has led to intensive investigation of metabolites, polysaccharides, and other compounds. However, marine collagens are less well-known. This review will provide detailed insight into the diversity of collagens present in marine species in terms of their genetics, structure, properties, and physiology. In the last part of the review the focus will be on the most common marine collagen sources and on the latest advances in the development of innovative materials exploiting, or inspired by, marine collagens.The authors are grateful for the financial support from European Union, under the scope of European Regional Development Fund((ERDF) through the POCTEP project 0687_NOVOMAR_1_P and Structured Project NORTE-01- 0145-FEDER-000021 and from the Portuguese Foundation for Science and Technology (FCT), under the scope of the BiogenInk project (M-ERA-NET2/0022/2016) and from the European Cooperation in Science & Technology program (EU COST). Grant title: “Stem cells of marine/aquatic inverte brates: from basic research to innovative applications” (MARISTEM). MSR acknowledges FCT for the Ph.D. scholarship (PD/BD/143091/2018)

Negatively Charged Excitons and Photoluminescence in Asymmetric Quantum Well

We study photoluminescence (PL) of charged excitons ($X^-$) in narrow asymmetric quantum wells in high magnetic fields B. The binding of all $X^-$ states strongly depends on the separation $\delta$ of electron and hole layers. The most sensitive is the ``bright'' singlet, whose binding energy decreases quickly with increasing $\delta$ even at relatively small B. As a result, the value of B at which the singlet--triplet crossing occurs in the $X^-$ spectrum also depends on $\delta$ and decreases from 35 T in a symmetric 10 nm GaAs well to 16 T for $\delta=0.5$ nm. Since the critical values of $\delta$ at which different $X^-$ states unbind are surprisingly small compared to the well width, the observation of strongly bound $X^-$ states in an experimental PL spectrum implies virtually no layer displacement in the sample. This casts doubt on the interpretation of PL spectra of heterojunctions in terms of $X^-$ recombination