1,911 research outputs found
Neural Connectivity with Hidden Gaussian Graphical State-Model
The noninvasive procedures for neural connectivity are under questioning.
Theoretical models sustain that the electromagnetic field registered at
external sensors is elicited by currents at neural space. Nevertheless, what we
observe at the sensor space is a superposition of projected fields, from the
whole gray-matter. This is the reason for a major pitfall of noninvasive
Electrophysiology methods: distorted reconstruction of neural activity and its
connectivity or leakage. It has been proven that current methods produce
incorrect connectomes. Somewhat related to the incorrect connectivity
modelling, they disregard either Systems Theory and Bayesian Information
Theory. We introduce a new formalism that attains for it, Hidden Gaussian
Graphical State-Model (HIGGS). A neural Gaussian Graphical Model (GGM) hidden
by the observation equation of Magneto-encephalographic (MEEG) signals. HIGGS
is equivalent to a frequency domain Linear State Space Model (LSSM) but with
sparse connectivity prior. The mathematical contribution here is the theory for
high-dimensional and frequency-domain HIGGS solvers. We demonstrate that HIGGS
can attenuate the leakage effect in the most critical case: the distortion EEG
signal due to head volume conduction heterogeneities. Its application in EEG is
illustrated with retrieved connectivity patterns from human Steady State Visual
Evoked Potentials (SSVEP). We provide for the first time confirmatory evidence
for noninvasive procedures of neural connectivity: concurrent EEG and
Electrocorticography (ECoG) recordings on monkey. Open source packages are
freely available online, to reproduce the results presented in this paper and
to analyze external MEEG databases
Boundary K-matrices for the XYZ, XXZ AND XXX spin chains
The general solutions for the factorization equations of the reflection
matrices for the eight vertex and six vertex models (XYZ, XXZ
and XXX chains) are found. The associated integrable magnetic Hamiltonians are
explicitly derived, finding families dependig on several continuous as well as
discrete parameters.Comment: 13 page
An atlas of Calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering the
region around the 8498, 8542, 8662 Calcium triplet (CaT) lines. The sample
comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst
and 6 normal galaxies. The spectra pertain to the inner ~300 pc in radius, and
thus sample the central kinematics and stellar populations of active galaxies.
The data are used to measure stellar velocity dispersions (sigma_star) both
with cross-correlation and direct fitting methods. These measurements are found
to be in good agreement with each-other and with those in previous studies for
objects in common. The CaT equivalent width is also measured. We find average
values and sample dispersions of W_CaT of 4.6+/-2.0, 7.0 and 7.7+/-1.0
angstrons for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We
further present an atlas of [SIII]\lambda 9069 emission line profiles for a
subset of 40 galaxies. These data are analyzed in a companion paper which
addresses the connection between stellar and Narrow Line Region kinematics, the
behaviour of the CaT equivalent width as a function of sigma_star, activity
type and stellar population properties.Comment: 18 pages, 10 figures, accepted for publication in MNRA
Deconvolution analysis for classifying gastric adenocarcinoma patients based on differential scanning calorimetry serum thermograms
Recently, differential scanning calorimetry (DSC) has been acknowledged as a novel tool for diagnosing and monitoring several diseases. This highly sensitive technique has been traditionally used to study thermally induced protein folding/unfolding transitions. In previous research papers, DSC profiles from blood samples of patients were analyzed and they exhibited marked differences in the thermal denaturation profile. Thus, we investigated the use of this novel technology in blood serum samples from 25 healthy subjects and 30 patients with gastric adenocarcinoma (GAC) at different stages of tumor development with a new multiparametric approach. The analysis of the calorimetric profiles of blood serum from GAC patients allowed us to discriminate three stages of cancer development (I to III) from those of healthy individuals. After a multiparametric analysis, a classification of blood serum DSC parameters from patients with GAC is proposed. Certain parameters exhibited significant differences (P < 0.05) and allowed the discrimination of healthy subjects/patients from patients at different tumor stages. The results of this work validate DSC as a novel technique for GAC patient classification and staging, and offer new graphical tools and value ranges for the acquired parameters in order to discriminate healthy from diseased subjects with increased disease burden
Boundary K-Matrices for the Six Vertex and the n(2n-1) A_{n-1} Vertex Models
Boundary conditions compatible with integrability are obtained for two
dimensional models by solving the factorizability equations for the reflection
matrices . For the six vertex model the general solution
depending on four arbitrary parameters is found. For the models all
diagonal solutions are found. The associated integrable magnetic Hamiltonians
are explicitly derived.Comment: 9 pages,latex, LPTHE-PAR 92-4
A novel and chemoselective process of N-alkylation of aromatic nitrogen compounds using quaternary ammonium salts as starting material
Artículo Internacional Open AccesThe process of N-alkylation of several pyrroles, indoles, and derivative heterocycles is herein described, using quaternary ammonium salts as the source of an alkylating agent. These reactions were carried out on several heterocyclic rings with triethylbenzylammonium chloride or tetradecyltrimethyl ammonium bromide and an NaOH solution at 50%, leading to a chemoselective N-alkylated product and an average yield of 73%. This is an alternative process to the traditional benzylation and methylation of N-heterocycles with direct handling of alkyl halides.CONACYT, Secretaría de Investigación y Estudios Avanzados de la UAE
Mossy fiber plasticity and enhanced hippocampal excitability, without hippocampal cell loss or altered neurogenesis, in an animal model of prolonged febrile seizures.
Seizures induced by fever (febrile seizures) are the most frequent seizures affecting infants and children; however, their impact on the developing hippocampal formation is not completely understood. Such understanding is highly important because of the potential relationship of prolonged febrile seizures to temporal lobe epilepsy. Using an immature rat model, we have previously demonstrated that prolonged experimental febrile seizures render the hippocampus hyperexcitable throughout life. Here we examined whether (1) neuronal loss, (2) altered neurogenesis, or (3) mossy fiber sprouting, all implicated in epileptogenesis in both animal models and humans, were involved in the generation of a pro-epileptic, hyperexcitable hippocampus by these seizures. The results demonstrated that prolonged experimental febrile seizures did not result in appreciable loss of any vulnerable hippocampal cell population, though causing strikingly enhanced sensitivity to hippocampal excitants later in life. In addition, experimental febrile seizures on postnatal day 10 did not enhance proliferation of granule cells, whereas seizures generated by kainic acid during the same developmental age increased neurogenesis in the immature hippocampus. However, prolonged febrile seizures resulted in long-term axonal reorganization in the immature hippocampal formation: Mossy fiber densities in granule cell- and molecular layers were significantly increased by 3 months (but not 10 days) after the seizures. Thus, the data indicate that prolonged febrile seizures influence connectivity of the immature hippocampus long-term, and this process requires neither significant neuronal loss nor altered neurogenesis. In addition, the temporal course of the augmented mossy fiber invasion of the granule cell and molecular layers suggests that it is a consequence, rather than the cause, of the hyperexcitable hippocampal network resulting from these seizures
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