374 research outputs found
Construction of direction selectivity in V1: from simple to complex cells
Despite detailed knowledge about the anatomy and physiology of the primary visual cortex (V1), the immense number of feed-forward and recurrent connections onto a given V1 neuron make it difficult to understand how the physiological details relate to a given neuron’s functional properties. Here, we focus on a well-known functional property of many V1 complex cells: phase-invariant direction selectivity (DS). While the energy model explains its construction at the conceptual level, it remains unclear how the mathematical operations described in this model are implemented by cortical circuits. To understand how DS of complex cells is constructed in cortex, we apply a nonlinear modeling framework to extracellular data from macaque V1. We use a modification of spike-triggered covariance (STC) analysis to identify multiple biologically plausible "spatiotemporal features" that either excite or suppress a cell. We demonstrate that these features represent the true inputs to the neuron more accurately, and the resulting nonlinear model compactly describes how these inputs are combined to result in the functional properties of the cell. In a population of 59 neurons, we find that both simple and complex V1 cells are selective to combinations of excitatory and suppressive motion features. Because the strength of DS and simple/complex classification is well predicted by our models, we can use simulations with inputs matching thalamic and simple cells to assess how individual model components contribute to these measures. Our results unify experimental observations regarding the construction of DS from thalamic feed-forward inputs to V1: based on the differences between excitatory and inhibitory inputs, they suggest a connectivity diagram for simple and complex cells that sheds light on the mechanism underlying the DS of cortical cells. More generally, they illustrate how stage-wise nonlinear combination of multiple features gives rise to the processing of more abstract visual information
Investigating Dimensions of Trust in Public Discussions of Diabetes Led by Certified Diabetes Educators
The givens of âtrustâ and âcredibilityâ are often glossed over in research concerning the efficacy of community-based approaches to health issues. This research focuses on one type of community intervention aimed at increasing citizensâ interest in acting to address diabetes: a series of community discussions led by Certified Diabetes Educators (CDEs). We take a critical discourse analysis approach to answering several questions including: How does the discourse between CDEs and participants work to establish or hinder the CDEsâ credibility
Dynamik der atmosphĂ€rischen Grenzschicht ĂŒber der Stadt â erste Ergebnisse der Wind-LIDAR-Messungen am Leipziger Institut fĂŒr Meteorologie
Seit 2015 gibt es Doppler-LIDAR-Messungen der Windgeschwindigkeit ĂŒber Leipzig. Diese Messungen werden zum einen vom HALO Photonics Streamline Doppler-LIDAR am Leipziger Institut fĂŒr TroposphĂ€renforschung (TROPOS) sowie vom Leosphere Windcube 8 Doppler-LIDAR am Leipziger Institut fĂŒr Meteorologie (LIM) aufgenommen. In dieser Arbeit werden insbesondere die Daten des Windcubes bezĂŒglich der horizontalen Windgeschwindigkeit, der Windrichtung und der TurbulenzintensitĂ€t bis in eine Höhe von ca. 500 m ausgewertet. Der Vergleich mit dem HALO Photonics Streamline Doppler-LIDAR zeigt gute Korrelationen zwischen beiden GerĂ€ten. Die Ergebnisse beinhalten unter anderem eine gute Ăbereinstimmung mit der Ekman-Theorie. Auch die erhöhte Rauhigkeit der StadtflĂ€che gegenĂŒber dem lĂ€ndlichen Raum wird in der Auswertung deutlich. Es wurde ein Verfahren getestet, das es erlaubt, den turbulenten Diffusionskoeffizienten und die aerodynamische RauhigkeitslĂ€nge aus den Messwerten abzuleiten und erste AbschĂ€tzungen dieser GröĂen vorzunehmen. Diese Arbeit legt nahe, den Einsatz der Fernerkundungsmessung zur Bestimmung der urbanen Grenzschichtdynamik fortzusetzen und wenn möglich zu erweitern.Since 2015 Doppler-LIDAR measurements above Leipzig are available. The Leibniz Institute for Tropospheric Research (TROPOS) operates a HALO Photonics Streamline Doppler-LIDAR while the Institute of Meteorology Leipzig uses a Leosphere Windcube 8 Doppler-LIDAR. In this study mainly meausrements of the Windcube for horizontal wind velocity, wind direction and turbulence intensity below 500 m are evaluated. The comparison to the HALO Photonics Streamline LIDAR shows good correlations between both devices. Among others, the results include good agreements with the Ekman theory. Additionally
the increased roughness of the city surface compared to rural areas becomes apparent. A way to determine characteristic quantities like the turbulent diffusion coefficient and the aerodynamic roughness length is described and initial estimations were conducted. This study suggests to continue and if possible expand such remote sensing measurements for analyses of urban boundary layer dynamics
Animal production in different integrated crop-livestock systems in a lowland of Southern Brazil.
To achieve higher lowland use efficiency in Brazilian Southern, a region commonly used for rice production, the livestock activity during the winter period (in succession to summer crops) is a sustainable alternative..
Observation of the hyperfine transition in lithium-like Bismuth : Towards a test of QED in strong magnetic fields
We performed a laser spectroscopic determination of the hyperfine
splitting (HFS) of Li-like and repeated the measurement
of the HFS of H-like . Both ion species were
subsequently stored in the Experimental Storage Ring at the GSI
Helmholtzzentrum f\"ur Schwerionenforschung Darmstadt and cooled with an
electron cooler at a velocity of . Pulsed laser excitation of
the hyperfine-transition was performed in anticollinear and collinear
geometry for and , respectively, and
observed by fluorescence detection. We obtain for , different from the literature
value, and for .
These values provide experimental evidence that a specific difference between
the two splitting energies can be used to test QED calculations in the
strongest static magnetic fields available in the laboratory independent of
nuclear structure effects. The experimental result is in excellent agreement
with the theoretical prediction and confirms the sum of the Dirac term and the
relativistic interelectronic-interaction correction at a level of 0.5%
confirming the importance of accounting for the Breit interaction.Comment: 5 pages, 2 figure
Implementation of different integrated crop-livestock systems in lowlands of Southern Brazil: an animal production approach.
The introduction of integrated crop-livestock systems (ICLS) is an alternative to rice monoculture in lowlands of Southern Brazil..
Braided racks, Hurwitz actions and Nichols algebras with many cubic relations
We classify Nichols algebras of irreducible Yetter-Drinfeld modules over
groups such that the underlying rack is braided and the homogeneous component
of degree three of the Nichols algebra satisfies a given inequality. This
assumption turns out to be equivalent to a factorization assumption on the
Hilbert series. Besides the known Nichols algebras we obtain a new example. Our
method is based on a combinatorial invariant of the Hurwitz orbits with respect
to the action of the braid group on three strands.Comment: v2: 35 pages, 6 tables, 14 figure
Treatment of backscattering in a gas of interacting fermions confined to a one-dimensional harmonic atom trap
An asymptotically exact many body theory for spin polarized interacting
fermions in a one-dimensional harmonic atom trap is developed using the
bosonization method and including backward scattering. In contrast to the
Luttinger model, backscattering in the trap generates one-particle potentials
which must be diagonalized simultaneously with the two-body interactions.
Inclusion of backscattering becomes necessary because backscattering is the
dominant interaction process between confined identical one-dimensional
fermions. The bosonization method is applied to the calculation of one-particle
matrix elements at zero temperature. A detailed discussion of the validity of
the results from bosonization is given, including a comparison with direct
numerical diagonalization in fermionic Hilbert space. A model for the
interaction coefficients is developed along the lines of the Luttinger model
with only one coupling constant . With these results, particle densities,
the Wigner function, and the central pair correlation function are calculated
and displayed for large fermion numbers. It is shown how interactions modify
these quantities. The anomalous dimension of the pair correlation function in
the center of the trap is also discussed and found to be in accord with the
Luttinger model.Comment: 19 pages, 5 figures, journal-ref adde
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