Self-similar magnetoresistance of Fibonacci ultrathin magnetic films

We study numerically the magnetic properties (magnetization and magnetoresistance) of ultra-thin magnetic films (Fe/Cr) grown following the Fibonacci sequence. We use a phenomenological model which includes Zeeman, cubic anisotropy, bilinear and biquadratic exchange energies. Our physical parameters are based on experimental data recently reported, which contain biquadratic exchange coupling with magnitude comparable to the bilinear exchange coupling. When biquadratic exchange coupling is sufficiently large a striking self-similar pattern emerges.Comment: 5 pages, 5 EPS figures, REVTeX, accepted for publication in Phys. Rev.

In vivo recordings of brain activity using organic transistors.

In vivo electrophysiological recordings of neuronal circuits are necessary for diagnostic purposes and for brain-machine interfaces. Organic electronic devices constitute a promising candidate because of their mechanical flexibility and biocompatibility. Here we demonstrate the engineering of an organic electrochemical transistor embedded in an ultrathin organic film designed to record electrophysiological signals on the surface of the brain. The device, tested in vivo on epileptiform discharges, displayed superior signal-to-noise ratio due to local amplification compared with surface electrodes. The organic transistor was able to record on the surface low-amplitude brain activities, which were poorly resolved with surface electrodes. This study introduces a new class of biocompatible, highly flexible devices for recording brain activity with superior signal-to-noise ratio that hold great promise for medical applications

Hidden chromosomal abnormalities in pleuropulmonary blastomas identified by multiplex FISH

BACKGROUND: Pleuropulmonary blastoma (PPB) is a rare childhood dysontogenetic intrathoracic neoplasm associated with an unfavourable clinical behaviour. CASES PRESENTATION: We report pathological and cytogenetic findings in two cases of PPB at initial diagnosis and recurrence. Both tumors were classified as type III pneumoblastoma and histological findings were similar at diagnosis and relapse. In both cases, conventional cytogenetic techniques revealed complex numerical and structural chromosomal abnormalities. Molecular cytogenetic analysis (interphase/metaphase FISH and multicolor FISH) identified accurately chromosomal aberrations. In one case, TP53 gene deletion was detected on metaphase FISH. To date, only few cytogenetic data have been published about PPB. CONCLUSION: The PPB genetic profile remains to be established and compared to others embryonal neoplasia. Our cytogenetic data are discussed reviewing cytogenetics PPBs published cases, illustrating the contribution of multicolor FISH in order to identify pathogenetically important recurrent aberrations in PPB

Phase-amplitude coupled persistent theta and gamma oscillations in rat primary motor cortex in vitro

In vivo, theta (4-7 Hz) and gamma (30-80 Hz) neuronal network oscillations are known to coexist and display phase-amplitude coupling (PAC). However, in vitro, these oscillations have for many years been studied in isolation. Using an improved brain slice preparation technique we have, using co-application of carbachol (10 μM) and kainic acid (150 nM), elicited simultaneous theta (6.6 ± 0.1 Hz) and gamma (36.6 ± 0.4 Hz) oscillations in rodent primary motor cortex (M1). Each oscillation showed greatest power in layer V. Using a variety of time series analyses we detected significant cross-frequency coupling 74% of slice preparations. Differences were observed in the pharmacological profile of each oscillation. Thus, gamma oscillations were reduced by the GABAA receptor antagonists, gabazine (250 nM and 2 μM), and picrotoxin (50 μM) and augmented by AMPA receptor antagonism with SYM2206 (20 μM). In contrast, theta oscillatory power was increased by gabazine, picrotoxin and SYM2206. GABAB receptor blockade with CGP55845 (5 μM) increased both theta and gamma power, and similar effects were seen with diazepam, zolpidem, MK801 and a series of metabotropic glutamate receptor antagonists. Oscillatory activity at both frequencies was reduced by the gap junction blocker carbenoxolone (200 μM) and by atropine (5 μM). These data show theta and gamma oscillations in layer V of rat M1 in vitro are cross-frequency coupled, and are mechanistically distinct. The development of an in vitro model of phase-amplitude coupled oscillations will facilitate further mechanistic investigation of the generation and modulation of coupled activity in mammalian cortex

Micro-connectomics: probing the organization of neuronal networks at the cellular scale.

Defining the organizational principles of neuronal networks at the cellular scale, or micro-connectomics, is a key challenge of modern neuroscience. In this Review, we focus on graph theoretical parameters of micro-connectome topology, often informed by economical principles that conceptually originated with Ramón y Cajal's conservation laws. First, we summarize results from studies in intact small organisms and in samples from larger nervous systems. We then evaluate the evidence for an economical trade-off between biological cost and functional value in the organization of neuronal networks. Various results suggest that many aspects of neuronal network organization are indeed the outcome of competition between these two fundamental selection pressures.This work was supported by the National Institute of Health Research (NIHR) Cambridge Biomedical Research Centre.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the Nature Publishing Group

Phonon excitations in quasicrystals

Contains fulltext : 28029___.PDF (publisher's version ) (Open Access

Study of the Global Thermal Hysteresis in D-BCCD with Elastic Neutron Scattering

We have studied, with elastic neutron scattering, the temperature dependence on heating and on cooling of the wave vector of the modulation in the two incommensurate phases (INC1 and INC2) of fully deuterated betaine calcium chloride dihydrate (D-BCCD). A large (2-3 K) global hysteresis appears in these two phases up to $T_i$. Moreover, the study of the higher order satellites intensities suggests the non-sinusoidal character of the modulation below $T_{i}$-20 K. These phenomena could be the experimental signature of the “complete Devil's staircase” regime.Nous avons étudié par diffusion élastique de neutrons la dépendance en température au refroidissement et au chauffage du vecteur d'onde de la modulation dans les deux phases incommensurables (INC1 et INC2) du chlorure de bétaine et de calcium di-hydraté complètement deutéré (D-BCCD). Une large (2-3 K) hystérésis globale apparaît dans ces deux phases, et ce jusqu'à $T_i$. De plus, l'étude des intensités des satellites d'ordre supérieur suggère le caractère non sinusoïdal de la modulation en dessous de $T_i$-20 K. Ces phénomènes pourraient être la signature expérimentale du régime de type “escalier du Diable complet”

Inelastic neutron scattering investigation of low temperature phase transition in Rb2_2ZnCl4_4 and K2_2ZnCl4_4

Inelastic scattering of neutrons has revealed soft optic modes at the T point ${1}/{2}({\bf b}^*+{\bf c}^*)$ of the Brillouin zone both in Rb$_2$ZnCl$_4$ and K$_2$ZnCl$_4$ which are responsible for the phase transition from the ferroelectric to the lowest temperature phase of these materials. Moreover, in K$_2$ZnCl$_4$ near the T point a minimum on the soft optic branch in the direction $(\mu{\bf b}^*+ ({1}/{2}){\bf c}^*)$ has been found which confirms the existence of a new incommensurate phase recently discovered by Gesi. The origin of this incommensurate phase is discussed from a phenomenological point of view and formulae for elastic constants are derived describing their behaviour near transition into incommensurate phase.Des mesures de diffusion inélastique des neutrons ont mis en évidence l'existence d'un mode optique mou au point T$({1}/{2}({\bf b}^*+{\bf c}^*))$ de la zone de Brillouin responsable de la transition de la phase ferroélectrique vers la phase basse température dans les deux composés Rb$_2$ZnCl$_4$ and K$_2$ZnCl$_4$. Pour K$_2$ZnCl$_4$ on montre que la branche optique molle présente un minimum au voisinage de T dans la direction $(\mu{\bf b}^*+ ({1}/{2}){\bf c}^*)$, ce qui confirme l'existence de la nouvelle phase incommensurable récemment trouvée par Gesi. L'origine de cette phase est discutée sur la base d'un modèle phénoménologique dont on dérive aussi les formules des constantes élastiques et leur comportement au voisinage de la transition vers la phase incommensurable

Compare raman study of the phase transitions in K2ZnCl4 and Rb2ZnCl4, Rb2ZnBr4, K2SeO4

The Raman spectra of K2ZnCl4 single crystals have been measured over the temperature range covering the successive phase transitions at Ti = 553 K, TL = 403 K down to 10 K. An amplitude mode is detected below T i. Evidence for a new phase below T0 is given by the observation of a soft phonon mode. The measured temperature dependence of the birefringence clearly confirms the existence of this low temperature phase in K2ZnCl 4 and Rb2ZnBr4 at T0 = 175 K and 107 K respectively. It is shown that group theoretical considerations applied to experimental Raman data of Rb2ZnCl4 are not sufficient to assign the space group of this low temperature phase in K2ZnCl4, Rb2ZnCl 4 and Rb2ZnBr4. The mechanism of the transition from the paraelectric phase to the incommensurate phase is discussed for the four compounds K2SeO4, K2ZnCl4, Rb2ZnCl4 and Rb2ZnBr4 on the basis of Raman and neutron data obtained in the vicinity of Ti ; the possibility of a crossover between a displacive regime and an order disorder regime is emphasized.Les spectres de diffusion Raman de monocristaux de K2ZnCl 4 ont été étudiés dans un domaine de température qui comprend les températures de transition de phase successives de ce composé (Ti = 553 K, TL = 403 K), et qui s'étend jusqu'à 10 K. Un mode d'amplitude est observé dans la phase incommensurable (T < Ti). Une nouvelle phase est détectée par l'observation d'un mode mou pour T < T0 . Des mesures de biréfringence faites en fonction de la température confirment l'existence de cette phase basse température dans K2ZnCl4 et Rb2ZnBr 4 et permettent de déterminer le point de transition T0 (T 0 = 175 K et 107 K pour K2ZnCl4 et Rb2ZnBr 4 respectivement). Des arguments de théorie des groupes sont appliqués aux résultats Raman obtenus pour T < T0 et ne sont pas suffisants pour faire une attribution certaine du groupe d'espace de la phase basse température observée dans K2ZnCl4, Rb2ZnCl 4, Rb2ZnBr4. Le mécanisme de la transition de la phase para-électrique vers la phase incommensurable est discuté sur la base des résultats obtenus au voisinage de Ti par diffusion inélastique cohérente de neutrons et de la lumière