Action Potential Onset Dynamics and the Response Speed of Neuronal Populations

The result of computational operations performed at the single cell level are coded into sequences of action potentials (APs). In the cerebral cortex, due to its columnar organization, large number of neurons are involved in any individual processing task. It is therefore important to understand how the properties of coding at the level of neuronal populations are determined by the dynamics of single neuron AP generation. Here we analyze how the AP generating mechanism determines the speed with which an ensemble of neurons can represent transient stochastic input signals. We analyze a generalization of the $\theta$-neuron, the normal form of the dynamics of Type-I excitable membranes. Using a novel sparse matrix representation of the Fokker-Planck equation, which describes the ensemble dynamics, we calculate the transmission functions for small modulations of the mean current and noise noise amplitude. In the high-frequency limit the transmission function decays as $\omega^{-\gamma}$, where $\gamma$ surprisingly depends on the phase $\theta_{s}$ at which APs are emitted. In a physiologically plausible regime up to 1kHz the typical response speed is, however, independent of the high-frequency limit and is set by the rapidness of the AP onset, as revealed by the full transmission function. In this regime modulations of the noise amplitude can be transmitted faithfully up to much higher frequencies than modulations in the mean input current. We finally show that the linear response approach used is valid for a large regime of stimulus amplitudes.Comment: Submitted to the Journal of Computational Neuroscienc

Gardner's deformations of the N=2 supersymmetric a=4-KdV equation

We prove that P.Mathieu's Open problem on constructing Gardner's deformation for the N=2 supersymmetric a=4-Korteweg-de Vries equation has no supersymmetry invariant solutions, whenever it is assumed that they retract to Gardner's deformation of the scalar KdV equation under the component reduction. At the same time, we propose a two-step scheme for the recursive production of the integrals of motion for the N=2, a=4-SKdV. First, we find a new Gardner's deformation of the Kaup-Boussinesq equation, which is contained in the bosonic limit of the super-hierarchy. This yields the recurrence relation between the Hamiltonians of the limit, whence we determine the bosonic super-Hamiltonians of the full N=2, a=4-SKdV hierarchy. Our method is applicable towards the solution of Gardner's deformation problems for other supersymmetric KdV-type systems.Comment: Extended version of the talks given by A.V.K. at 8th International conference `Symmetry in Nonlinear Mathematical Physics' (June 20-27, 2009, Kiev, Ukraine) and 9th International workshop `Supersymmetry and Quantum Symmetries' (July 29 - August 3, 2009, JINR, Dubna, Russia); 22 page

Large-scale albuminuria screen for nephropathy models in chemically induced mouse mutants

Background/Aim: Phenotype-driven screening of a great pool of randomly mutant mice and subsequent selection of animals showing symptoms equivalent to human kidney diseases may result in the generation of novel suitable models for the study of the pathomechanisms and the identification of genes involved in kidney dysfunction. Methods: We carried out a large-scale analysis of ethylnitrosourea (ENU)-induced mouse mutants for albuminuria by using qualitative SDS-polyacrylamide gel electrophoresis. Results: The primary albuminuria screen preceded the comprehensive phenotypic mutation analysis in a part of the mice of the Munich ENU project to avoid loss of mutant animals as a consequence of prolonged suffering from severe nephropathy. The primary screen detected six confirmed phenotypic variants in 2,011 G1 animals screened for dominant mutations and no variant in 48 G3 pedigrees screened for recessive mutations. Further breeding experiments resulted in two lines showing a low phenotypic penetrance of albuminuria. The secondary albuminuria screen was carried out in mutant lines which were established in the Munich ENU project without preceding primary albuminuria analysis. Two lines showing increased plasma urea levels were chosen to clarify if severe kidney lesions are involved in the abnormal phenotype. This analysis revealed severe albuminuria in mice which are affected by a recessive mutation leading to increased plasma urea and cholesterol levels. Conclusion: Thus, the phenotypic selection of ENU-induced mutants according to the parameter proteinuria in principle demonstrates the feasibility to identify nephropathy phenotypes in ENU-mutagenized mice. Copyright (C) 2005 S. Karger AG, Basel

Expanding the Family of Grassmannian Kernels: An Embedding Perspective

Modeling videos and image-sets as linear subspaces has proven beneficial for many visual recognition tasks. However, it also incurs challenges arising from the fact that linear subspaces do not obey Euclidean geometry, but lie on a special type of Riemannian manifolds known as Grassmannian. To leverage the techniques developed for Euclidean spaces (e.g, support vector machines) with subspaces, several recent studies have proposed to embed the Grassmannian into a Hilbert space by making use of a positive definite kernel. Unfortunately, only two Grassmannian kernels are known, none of which -as we will show- is universal, which limits their ability to approximate a target function arbitrarily well. Here, we introduce several positive definite Grassmannian kernels, including universal ones, and demonstrate their superiority over previously-known kernels in various tasks, such as classification, clustering, sparse coding and hashing

Redox reactions with empirical potentials: Atomistic battery discharge simulations

Batteries are pivotal components in overcoming some of today's greatest technological challenges. Yet to date there is no self-consistent atomistic description of a complete battery. We take first steps toward modeling of a battery as a whole microscopically. Our focus lies on phenomena occurring at the electrode-electrolyte interface which are not easily studied with other methods. We use the redox split-charge equilibration (redoxSQE) method that assigns a discrete ionization state to each atom. Along with exchanging partial charges across bonds, atoms can swap integer charges. With redoxSQE we study the discharge behavior of a nano-battery, and demonstrate that this reproduces the generic properties of a macroscopic battery qualitatively. Examples are the dependence of the battery's capacity on temperature and discharge rate, as well as performance degradation upon recharge.Comment: 14 pages, 10 figure

Discovery of a Hot Symbiotic Star in the Cold Antarctic Sky: Symbiotics Are Outliers in SkyMapper uvgriz Photometry

Using near-ultraviolet flux excess and variability from the SkyMapper Southern Sky Survey11 as novel diagnostics to search for symbiotic stars?cool giants accreting onto compact objects, typically white dwarfs (WDs), we report that Hen 3-1768 (≡ASAS J195948?8252.7) is a symbiotic star. It may be an optimal target for continuous monitoring by Antarctic telescopes; at a decl. of −82877, it is now the closest known symbiotic to either geographic pole, and the only known symbiotic more southern than the Small Magellanic Cloud (Belczyński et al. 2000; Akras et al. 2019, ApJS, in press). Figure 1 shows that Hen 3-1768 produced unambiguous emission from Raman O vi 6830,7088 Å, He ii 4686 Å, and other transitions, proving that it is a symbiotic star (e.g., Shore et al. 2014). Comparing to Pickles (1998) template spectra, we preliminarily constrained the giant donor´s spectral type to between K4 and K7, making Hen 3-1768 one of the dozen or so yellow symbiotics with stellar-type infrared (IR) colors currently known (e.g., Baella et al. 2016). The 2MASS IR colors (J − H)0 = 0.82 and (H − Ks)0 = 0.21 (Skrutskie et al. 2006; de-reddened by total Galactic extinction12 ) are consistent with this conclusion (see Figure 1 in Baella et al. 2016).Fil: Lucy, Adrian B.. Columbia University; Estados UnidosFil: Sokoloski, J. L.. Columbia University; Estados UnidosFil: Nuñez, Natalia Edith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Wolf, C.. Research School Of Astronomy And Astrophysics, Anu; AustraliaFil: Bohlsen, T.. Mirranook Observatory,; AustraliaFil: Luna, Gerardo Juan Manuel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin