Two-photon exchange and normal spin asymmetries in the A4 experiment

The A4 Collaboration at the MAMI facility has measured, at backward angles and at Q2 = 0.23 (GeV/c)2 and Q2 = 0.35 (GeV/c)2, the asymmetry in the elastic and quasielastic scattering of normally polarized electrons on hydrogen and deuterium, respectively. Some preliminary results will be presented

New membership determination and proper motions of NGC 1817. Parametric and non-parametric approach

We have calculated proper motions and re-evaluated the membership probabilities of 810 stars in the area of two NGC objects, NGC 1817 and NGC 1807. We have obtained absolute proper motions from 25 plates in the reference system of the Tycho-2 Catalogue. The plates have a maximum epoch difference of 81 years; and they were taken with the double astrograph at Zo-Se station of Shanghai Observatory, which has an aperture of 40 cm and a plate scale of 30 arcsec/mm. The average proper motion precision is 1.55 mas/yr. These proper motions are used to determine the membership probabilities of stars in the region, based on there being only one very extended physical cluster: NGC 1817. With that aim, we have applied and compared parametric and non-parametric approaches to cluster/field segregation. We have obtained a list of 169 probable member stars.Comment: 11 pages, 8 figures, A&A in pres

uvby-Hbeta CCD photometry and membership segregation of the open cluster NGC 2548; Gaps in the Main Sequence of open clusters

Deep CCD photometry in the uvby-Hbeta intermediate-band system is presented for the cluster NGC 2548 (M 48). A complete membership analysis based on astrometric and photometric criteria is applied. The photometric analysis of a selected sample of stars yields a reddening value of E(b-y)=0.06\pm0.03, a distance modulus of V_0-M_V=9.3\pm0.5 (725 pc) and a metallicity of [Fe/H]= -0.24\pm0.27. Through isochrone fitting we find an age of log t = 8.6\pm0.1 (400 Myr). Our optical photometry and JHK from 2MASS are combined to derive effective temperatures of cluster member stars. The effective temperature distribution along the main sequence of the cluster shows several gaps. A test to study the significance of these gaps in the main sequence of the HR diagram has been applied. The method is also applied to several other open clusters (Pleiades, Hyades, NGC 1817 and M 67) to construct a sequence of metallicities and ages. The comparison of the results of each cluster gives four gaps with high significance (one of them, centred at 4900 K, has not been previously reported).Comment: 11 pages, 8 figures, A&A in press. Corrected typos on Table

Attracting dynamics of frontal cortex ensembles during memory-guided decision-making.

A common theoretical view is that attractor-like properties of neuronal dynamics underlie cognitive processing. However, although often proposed theoretically, direct experimental support for the convergence of neural activity to stable population patterns as a signature of attracting states has been sparse so far, especially in higher cortical areas. Combining state space reconstruction theorems and statistical learning techniques, we were able to resolve details of anterior cingulate cortex (ACC) multiple single-unit activity (MSUA) ensemble dynamics during a higher cognitive task which were not accessible previously. The approach worked by constructing high-dimensional state spaces from delays of the original single-unit firing rate variables and the interactions among them, which were then statistically analyzed using kernel methods. We observed cognitive-epoch-specific neural ensemble states in ACC which were stable across many trials (in the sense of being predictive) and depended on behavioral performance. More interestingly, attracting properties of these cognitively defined ensemble states became apparent in high-dimensional expansions of the MSUA spaces due to a proper unfolding of the neural activity flow, with properties common across different animals. These results therefore suggest that ACC networks may process different subcomponents of higher cognitive tasks by transiting among different attracting states

The extended halo of NGC 2682 (M 67) from Gaia DR2

Context: NGC 2682 is a nearby open cluster, approximately 3.5 Gyr old. Dynamically, most open clusters should dissolve on shorter timescales, of ~ 1 Gyr. Having survived until now, NGC 2682 was likely much more massive in the past, and is bound to have an interesting dynamical history. Aims: We investigate the spatial distribution of NGC 2682 stars to constrain its dynamical evolution, especially focusing on the marginally bound stars in the cluster outskirts. Methods: We use Gaia DR2 data to identify NGC 2682 members up to a distance of ~150 pc (10 degrees). Two methods (Clusterix and UPMASK) are applied to this end. We estimate distances to obtain three-dimensional stellar positions using a Bayesian approach to parallax inversion, with an appropriate prior for star clusters. We calculate the orbit of NGC 2682 using the GRAVPOT16 software. Results: The cluster extends up to 200 arcmin (50 pc) which implies that its size is at least twice as previously believed. This exceeds the cluster Hill sphere based on the Galactic potential at the distance of NGC 2682. Conclusions: The extra-tidal stars in NGC 2682 may originate from external perturbations such as disk shocking or dynamical evaporation from two-body relaxation. The former origin is plausible given the orbit of NGC 2682, which crossed the Galactic disk ~40 Myr ago.Comment: 9 pages, 5 figures, accepted for publication on A&

Estimació de construccions compromeses per la presència de coves en el litoral del sud i llevant de Mallorca mitjançant l’ús de Sistemes d’Informació Geogràfica (SIGs)

[cat] S’exposen els resultats estimats de l’extensió de construccions (habitatges) i infraestructures construïdes sobre quatre cavitats càrstiques a la franja litoral del Sud i Llevant de Mallorca a partir de l’ús de Sistemes d’Informació Geogràfica (SIGs). L’estudi s’ha basat en l’anàlisi cartogràfic en el que s’ha contrastat la cartografia existent del recorregut de les coves, el mapa topogràfic digital a escala 1/5.000, diverses col·leccions de fotografies aèries i la cartografia digital del cadastre. La informació manejada es troba disponible al visor cartogràfic del Servei d’Informació Territorial de les Illes Balears S.A. i es pot visualitzar a qualsevol programa de SIG. La cartografia corresponent al recorregut de les cavitats es troba a les publicacions de la revista Endins, també disponibles a internet. Els resultat es una estimació dels metres quadrats construïts sobre les coves. D’aquesta manera s’ofereix una informació que podria esser una eina de consulta per a la presa de decisions i contribuir a la sostenibilitat de la zona costanera d’acord amb una concepció integrada de les àrees costeres i marines.[eng] This work exposes the estimated results of the built area (homes and infrastructures) above four karstic caves located at the coastal fringe in the South and East of the Mallorca Island using Geographical Information Systems (GIS). The study has been based on the analysis of the cartography of the path/extension of the caves, 1/5.000 scale topographic maps, many collections of digital aerial photography and the cartography of the cadastre. The information managed is available in the map viewer of the Geographical Information Service of the Balearic Islands and can be displayed in any GIS program. Cartography of the paths of the caves are in the issues of Endins Journal, also available in internet. The result is an estimation of the square meters built above the caves. In this way, we offer a kind of information that could be a decision support tool to contribute to the sustainability of the coastal zone according with the concept of integrity of coastal and marine areas

Can we identify non-stationary dynamics of trial-to-trial variability?"

Identifying sources of the apparent variability in non-stationary scenarios is a fundamental problem in many biological data analysis settings. For instance, neurophysiological responses to the same task often vary from each repetition of the same experiment (trial) to the next. The origin and functional role of this observed variability is one of the fundamental questions in neuroscience. The nature of such trial-to-trial dynamics however remains largely elusive to current data analysis approaches. A range of strategies have been proposed in modalities such as electro-encephalography but gaining a fundamental insight into latent sources of trial-to-trial variability in neural recordings is still a major challenge. In this paper, we present a proof-of-concept study to the analysis of trial-to-trial variability dynamics founded on non-autonomous dynamical systems. At this initial stage, we evaluate the capacity of a simple statistic based on the behaviour of trajectories in classification settings, the trajectory coherence, in order to identify trial-to-trial dynamics. First, we derive the conditions leading to observable changes in datasets generated by a compact dynamical system (the Duffing equation). This canonical system plays the role of a ubiquitous model of non-stationary supervised classification problems. Second, we estimate the coherence of class-trajectories in empirically reconstructed space of system states. We show how this analysis can discern variations attributable to non-autonomous deterministic processes from stochastic fluctuations. The analyses are benchmarked using simulated and two different real datasets which have been shown to exhibit attractor dynamics. As an illustrative example, we focused on the analysis of the rat's frontal cortex ensemble dynamics during a decision-making task. Results suggest that, in line with recent hypotheses, rather than internal noise, it is the deterministic trend which most likely underlies the observed trial-to-trial variability. Thus, the empirical tool developed within this study potentially allows us to infer the source of variability in in-vivo neural recordings

Amphetamine Exerts Dose-Dependent Changes in Prefrontal Cortex Attractor Dynamics during Working Memory

Modulation of neural activity by monoamine neurotransmitters is thought to play an essential role in shaping computational neurodynamics in the neocortex, especially in prefrontal regions. Computational theories propose that monoamines may exert bidirectional (concentration-dependent) effects on cognition by altering prefrontal cortical attractor dynamics according to an inverted U-shaped function. To date, this hypothesis has not been addressed directly, in part because of the absence of appropriate statistical methods required to assess attractor-like behavior in vivo. The present study used a combination of advanced multivariate statistical, time series analysis, and machine learning methods to assess dynamic changes in network activity from multiple single-unit recordings from the medial prefrontal cortex (mPFC) of rats while the animals performed a foraging task guided by working memory after pretreatment with different doses of d-amphetamine (AMPH), which increases monoamine efflux in the mPFC. A dose-dependent, bidirectional effect of AMPH on neural dynamics in the mPFC was observed. Specifically, a 1.0 mg/kg dose of AMPH accentuated separation between task-epoch-specific population states and convergence toward these states. In contrast, a 3.3 mg/kg dose diminished separation and convergence toward task-epoch-specific population states, which was paralleled by deficits in cognitive performance. These results support the computationally derived hypothesis that moderate increases in monoamine efflux would enhance attractor stability, whereas high frontal monoamine levels would severely diminish it. Furthermore, they are consistent with the proposed inverted U-shaped and concentration-dependent modulation of cortical efficiency by monoamines

Proper motions and membership probabilities of stars in the region of globular cluster NGC 6809

NGC 6809 is a luminous metal-poor halo globular cluster that is relatively easy to study due to its proximity and low concentration. Because of its high Galactic latitude (b = -23deg), interstellar reddening and contamination is not very high. We aim to determine the relative proper motion and membership probability of the stars in the wide area of globular cluster NGC 6809. To target cluster members reliably during spectroscopic surveys and both spatial and radial distributions in the cluster outskirts without including field stars, a good proper motion and membership probability catalogue of NGC 6809 is required.The archival data of two epochs with a time-base line of 7.1 years have been collected with Wide Field Imager (WFI) mounted on the 2.2m MPG/ESO telescope. The CCD images of both epochs have been reduced using the astrometric techniques as described in Anderson et al. (2006). The calibrated UBVI magnitudes have been derived using Stetson's secondary standard stars. We derived the relative proper motion and membership probabilities for \sim 12600 stars in the field of globular cluster NGC 6809. The measurement error in proper motions for the stars of V \sim 17 mag is 2.0 mas/yr, gradually increasing up to \sim 3 mas/yr at V = 20 mag. We also provide the membership probability for the published different types of sources in NGC 6809. An electronic catalogue with proper motion and membership probability for the stars will be available to the astronomical community.Comment: Accepted for publication in The A&A. 11 pages. 11 figures,5 Table

Spontaneous synchronization to speech reveals neural mechanisms facilitating language learning

We introduce a deceptively simple behavioral task that robustly identifies two qualitatively different groups within the general population. When presented with an isochronous train of random syllables, some listeners are compelled to align their own concurrent syllable production with the perceived rate, whereas others remain impervious to the external rhythm. Using both neurophysiological and structural imaging approaches, we show group differences with clear consequences for speech processing and language learning. When listening passively to speech, high synchronizers show increased brain-to-stimulus synchronization over frontal areas, and this localized pattern correlates with precise microstructural differences in the white matter pathways connecting frontal to auditory regions. Finally, the data expose a mechanism that underpins performance on an ecologically relevant word-learning task. We suggest that this task will help to better understand and characterize individual performance in speech processing and language learning