Relationships between diatoms and the environment in Spanish reservoirs

Diatoms are very useful environmental indicators in limnological and paleolimnological studies. Spanish reservoirs offer a valuable opportunity for the study of relationships between diatoms and environmental conditions, since these ecosystems are abundant in this country and the patterns of their regional limnology are well established. We report the results from a study carried out on diatom communities in 40 reservoirs from several Spanish water basins. More than 200 diatom taxa were found. A canonical correspondence analysis was applied to the abundance data of the most common taxa and the main physical and chemical variables. This analysis showed that mineralisation (conductivity and alkalinity) was the most important environmental factor explaining diatom distribution, while trophic state was the second most important. These results are similar to those in previous studies on phytoplankton in Spanish reservoirs. Conductivity and alkalinity optima of the selected taxa allow us to consider these taxa as good indicators of water mineral content in similar ecosystems.Las diatomeas son indicadores ambientales muy útiles en estudios limnológicos y paleolimnológicos. En España los embalses ofrecen una gran oportunidad para el estudio de las relaciones entre las diatomeas y las condiciones ambientales, ya que son ecosistemas muy abundantes y las principales características de su limnología regional están bien estudiadas. Se presentan aquí los resultados de un estudio sobre las comunidades de diatomeas efectuado en 40 embalses de diversas cuencas hidrográficas españolas. En ellos se encontraron más de 200 taxones de diatomeas. Se efectuó un análisis de correspondencias canónicas con los datos de abundancia de los taxones más frecuentes y las principales variables físico-químicas. Este análisis muestra que el factor con mayor influencia sobre las comunidades de diatomeas es la mineralización (conductividad y alcalinidad), y en segundo lugar el grado trófico. Estos resultados son similares a estudios previos sobre el fitoplancton de embalses españoles. Los valores de los óptimos respecto a la conductividad y alcalinidad de los principales taxones, permiten considerar dichos taxones como buenos indicadores del contenido mineral del agua en ecosistemas similares

Semi-Automated Identification of Motor Units Concurrently Recorded in High-Density Surface and Intramuscular Electromyography

: An increasing focus on extending automated surface electromyography (EMG) decomposition algorithms to operate under non-stationary conditions requires rigorous and robust validation. However, relevant benchmarks derived manually from iEMG are laborsome to obtain and this is further exacerbated by the need to consider multiple contraction conditions. This work demonstrates a semi-automatic technique for extracting motor units (MUs) whose activities are present in concurrently recorded high-density surface EMG (HD-sEMG) and intramuscular EMG (iEMG) during isometric contractions. We leverage existing automatic surface decomposition algorithms for initial identification of active MUs. Resulting spike times are then used to identify (trigger) the sources that are concurrently detectable in iEMG. We demonstrate this technique on recordings targeting the extensor carpi radialis brevis in five human subjects. This dataset consists of 117 trials across different force levels and wrist angles, from which the presented method yielded a set of 367 high-confidence decompositions. Thus, our approach effectively alleviates the overhead of manual decomposition as it efficiently produces reliable benchmarks under different conditions.Clinical Relevance- We present an efficient method for obtaining high-quality in-vivo decomposition particularly useful in the verification of new surface decomposition approaches

Optimal Motor Unit Subset Selection for Accurate Motor Intention Decoding: Towards Dexterous Real-Time Interfacing

Objective: Motor unit (MU) discharge timings encode human motor intentions to the finest degree. Whilst tapping into such information can bring significant gains to a range of applications, current approaches to MU decoding from surface signals do not scale well with the demands of dexterous human-machine interfacing (HMI). To optimize the forward estimation accuracy and time-efficiency of such systems, we propose the inclusion of task-wise initialization and MU subset selection. Methods: Offline analyses were conducted on data recorded from 11 non-disabled subjects. Task-wise decomposition was applied to identify MUs from high-density surface electromyography (HD-sEMG) pertaining to 18 wrist/forearm motor tasks. The activities of a selected subset of MUs were extracted from test data and used for forward estimation of intended motor tasks and joint kinematics. To that end, various combinations of subset selection and estimation algorithms (both regression and classification-based) were tested for a range of subset sizes. Results: The mutual information-based minimum Redundancy Maximum Relevance (mRMR-MI) criterion retained MUs with the highest predicative power. When the portion of tracked MUs was reduced down to 25%, the regression performance decreased only by 3% (R2=0.79) while classification accuracy dropped by 2.7% (accuracy = 74%) when kernel-based estimators were considered. Conclusion and Significance: Careful selection of tracked MUs can optimize the efficiency of MU-driven interfacing. In particular, prioritization of MUs exhibiting strong nonlinear relationships with target motions is best leveraged by kernel-based estimators. Hence, this frees resources for more robust and adaptive MU decoding techniques to be implemented in future

Polar coherent states in bilayer graphene under a constant uniform magnetic field

Symmetries associated with the Hamiltonian describing bilayer graphene subjected to a constant magnetic field perpendicular to the plane of the bilayer are calculated using polar coordinates. These symmetries are then applied to explain some fundamental properties, such as the spectrum and the integer pseudo-spin character of the eigenfunctions. The probability and current densities of the bilayer Hamiltonian have also been calculated in polar coordinates and shown to be gauge invariant and scalar under generalized rotations. We also define appropriate coherent states of this system as eigenfunctions, with complex eigenvalues, of a suitable chose annihilation operator. In this framework, symmetries are also useful to show the meaning of the complex eigenvalue in terms of expected values. The local current density of these coherent states is shown to exhibit a kind of radial component interference effect, something that has gone unnoticed until now. Some of these results that have just been exposed are graphically illustrated throughout the manuscript

Spectrum generating algebra for the continuous spectrum of a free particle in Lobachevski space

In this paper, we construct a Spectrum Generating Algebra (SGA) for a quantum system with purely continuous spectrum: the quantum free particle in a Lobachevski space with constant negative curvature. The SGA contains the geometrical symmetry algebra of the system plus a subalgebra of operators that give the spectrum of the system and connects the eigenfunctions of the Hamiltonian among themselves. In our case, the geometrical symmetry algebra is $\frak{so}(3,1)$ and the SGA is $\frak{so}(4,2)$. We start with a representation of $\frak{so}(4,2)$ by functions on a realization of the Lobachevski space given by a two sheeted hyperboloid, where the Lie algebra commutators are the usual Poisson-Dirac brackets. Then, introduce a quantized version of the representation in which functions are replaced by operators on a Hilbert space and Poisson-Dirac brackets by commutators. Eigenfunctions of the Hamiltonian are given and "naive" ladder operators are identified. The previously defined "naive" ladder operators shift the eigenvalues by a complex number so that an alternative approach is necessary. This is obtained by a non self-adjoint function of a linear combination of the ladder operators which gives the correct relation among the eigenfunctions of the Hamiltonian. We give an eigenfunction expansion of functions over the upper sheet of two sheeted hyperboloid in terms of the eigenfunctions of the Hamiltonian.Comment: 23 page

Cyanobacteria distribution and abundance in the Spanish water reservoirs during thermal stratification

A study of the distribution and abundance of Cyanobacteria in 47 Spanish water reservoirs revealed a significant correlation between these algae and total phosphorus in the water. Cyanobacteria distribution was related to the N:P ratio, and they were scarce when the atomic ratio of total inorganic N / total P exceeded 50. The N:P ratio was influenced by the geology of the catchment, and it was lower in the solute-poor waters of western Iberian Peninsula, where Cyanobacteria were more abundant (mainly the Nostocales). Therefore, this area would be more prone to present problems derived from Cyanobacteria proliferation than the eastern part of Spain. In the studied reservoirs we have recorded 45 taxa of Cyanobacteria, many of which can produce toxins. A comparison of our results with those of previous studies served to conclude that Cyanobacteria have increased both in biomass and species number in Spanish reservoirs.El estudio de la distribución y abundancia de Cianobacterias en 47 embalses españoles reveló una correlación significativa entre estas algas y la concentración de fósforo total en el agua. La distribución de Cianobacterias estuvo relacionada con el cociente N:P, siendo generalmente poco abundantes cuando la relación atómica N inorgánico total / P total fue superior a 50. La relación N:P en el agua está influenciada por la geología de la cuenca, y fue menor en las aguas menos mineralizadas del oeste de la Península Ibérica, donde las cianobacterias fueron más abundantes (especialmente las nostocales). Por lo tanto, esta zona de la península Ibérica sería más propensa a sufrir problemas relacionados con la proliferación de Cianobacterias que la zona este de España. En los embalses estudiados hemos encontrado 45 taxones de Cianobacterias, muchas de las cuales pueden producir toxinas. La comparación de nuestros resultados con estudios realizados previamente sirvió para concluir que en los embalses españoles se ha producido un aumento del número de especies y de la biomasa de Cianobacterias

Disease Activity and Progression in Multiple Sclerosis: New Evidences and Future Perspectives

Multiple sclerosis (MS) is a chronic, debilitating, autoimmune-mediated, inflammatory disease of the central nervous system (CNS), in which a combination of inflammation, demyelination and axonal degeneration takes place with extreme highly interpersonal variability [...]

Fermi-LAT Observations of High- and Intermediate-Velocity Clouds: Tracing Cosmic Rays in the Halo of the Milky Way

It is widely accepted that cosmic rays (CRs) up to at least PeV energies are Galactic in origin. Accelerated particles are injected into the interstellar medium where they propagate to the farthest reaches of the Milky Way, including a surrounding halo. The composition of CRs coming to the solar system can be measured directly and has been used to infer the details of CR propagation that are extrapolated to the whole Galaxy. In contrast, indirect methods, such as observations of gamma-ray emission from CR interactions with interstellar gas, have been employed to directly probe the CR densities in distant locations throughout the Galactic plane. In this article we use 73 months of data from the Fermi Large Area Telescope in the energy range between 300 MeV and 10 GeV to search for gamma-ray emission produced by CR interactions in several high- and intermediate-velocity clouds located at up to ~ 7 kpc above the Galactic plane. We achieve the first detection of intermediate-velocity clouds in gamma rays and set upper limits on the emission from the remaining targets, thereby tracing the distribution of CR nuclei in the halo for the first time. We find that the gamma-ray emissivity per H atom decreases with increasing distance from the plane at 97.5% confidence level. This corroborates the notion that CRs at the relevant energies originate in the Galactic disk. The emissivity of the upper intermediate-velocity Arch hints at a 50% decline of CR densities within 2 kpc from the plane. We compare our results to predictions of CR propagation models.Comment: Accepted for publication in the Astrophysical Journa