Entropy-based parametric estimation of spike train statistics

We consider the evolution of a network of neurons, focusing on the asymptotic behavior of spikes dynamics instead of membrane potential dynamics. The spike response is not sought as a deterministic response in this context, but as a conditional probability : "Reading out the code" consists of inferring such a probability. This probability is computed from empirical raster plots, by using the framework of thermodynamic formalism in ergodic theory. This gives us a parametric statistical model where the probability has the form of a Gibbs distribution. In this respect, this approach generalizes the seminal and profound work of Schneidman and collaborators. A minimal presentation of the formalism is reviewed here, while a general algorithmic estimation method is proposed yielding fast convergent implementations. It is also made explicit how several spike observables (entropy, rate, synchronizations, correlations) are given in closed-form from the parametric estimation. This paradigm does not only allow us to estimate the spike statistics, given a design choice, but also to compare different models, thus answering comparative questions about the neural code such as : "are correlations (or time synchrony or a given set of spike patterns, ..) significant with respect to rate coding only ?" A numerical validation of the method is proposed and the perspectives regarding spike-train code analysis are also discussed.Comment: 37 pages, 8 figures, submitte

Non-radial Oscillation Modes of Compact Stars with a Crust

Oscillation modes of isolated compact stars can, in principle, be a fingerprint of the equation of state (EoS) of dense matter. We study the non-radial high-frequency l=2 spheroidal modes of neutron stars and strange quark stars, adopting a two-component model (core and crust) for these two types of stars. Using perturbed fluid equations in the relativistic Cowling approximation, we explore the effect of a strangelet or hadronic crust on the oscillation modes of strange stars. The results differ from the case of neutron stars with a crust. In comparison to fluid-only configurations, we find that a solid crust on top of a neutron star increases the p-mode frequency slightly with little effect on the f-mode frequency, whereas for strange stars, a strangelet crust on top of a quark core significantly increases the f-mode frequency with little effect on the p-mode frequency.Comment: 10 pages, 6 figure

Analysis of the Effectiveness of the F-15E Risk Management During Peacetime Operations

Human factors are causal or contributory in 80% of Class A mishaps in the Air Force. Risk management tools are used throughout the service in every aircraft to help mitigate the risk of those human factors occurring. The F-15E Strike Eagle community was selected for analysis on the effectiveness of its risk management program but the data was comprised on Class A mishaps from Accident Investigation Boards since 2000 between the F-15 (all models), F-16 (all models), and F-22. Cases were selected if there were human factors root causes or contributory. A fault tree analysis coupled with the Department of Defense\u27s Human Factors Analysis and Classification System guidelines were used to determine the underlying factors which lead to a degradation in the aircrew\u27s ability to avoid catastrophes resulting in the loss of aircraft or life. These results were compared with existing risk management programs in the form of unit worksheet assessments. This study found all risk management programs within the F-15E community to be effective but inadequate for addressing the risk factors and a new assessment tool was developed to properly manage risk to aircrew. Finally, the F-15E training program was found to be contributory to managing risk to aircrew through its proficiency and currency annual program and requirements

Dissipative Dynamics of Collisionless Nonlinear Alfven Wave Trains

The nonlinear dynamics of collisionless Alfven trains, including resonant particle effects is studied using the kinetic nonlinear Schroedinger (KNLS) equation model. Numerical solutions of the KNLS reveal the dynamics of Alfven waves to be sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. The combined effects of both wave nonlinearity and Landau damping result in the evolutionary formation of stationaryOA S- and arc-polarized directional and rotational discontinuities. These waveforms are freqently observed in the interplanetary plasma.Comment: REVTeX, 6 pages (including 5 figures). This and other papers may be found at http://sdphpd.ucsd.edu/~medvedev/papers.htm

Solitary lift : redesigning the base and tilter modules to meet customer needs

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 21).A theoretical investigation towards the redesign of the base and the tilting module of the Solitary Lift prototype improved the machine with a weight reduction of 5.731bs. Besides lighter weight, the other criteria used to measure improvement were speed, ease of use, and durability. In these areas this iteration of the prototype increased the speed to raise the tilter by 25 seconds, replaced a complicated locking mechanism with a familiar sleeve lock found on folding tables, and considered the substitution of plastic materials for aluminum in the structure.by Elliot B. Vasquez.S.B

Las Arterias Circunflejas Femorales en el Triángulo Femoral

Galdames, IS (Suazo Galdames, Ivan). Univ Talca, Fac Ciencias Salud, Talca, ChileIt is important to identify the origin and distribution of the circumflex femoral arteries (CFA) at the time of vascular reconstructive surgery. The femoral triangle contents in 92 lower extremities of formolized adult male cadavers of different ethnic groups, were dissected uncovering the femoral artery (FA) and its branches originating at the level of the femoral triangle. The origin of each CFA was identified determining the origin type and location. The medial circumflex femoral artery (MCFA) originated from the FA in 43 cases (46.7%); from the profunda femoris artery (PFA) in 41 cases (44.6%); from a common trunk formed by the PFA and CFA in 7 cases (7.6%), and in one case (1.1%) from the lateral circumflex femoral artery (LCFA). In 75 cases (81.5%) the MCFA was most proximal than the LCFA, and in 9 cases (9.8%) it originated at the same level. The LCFA originated at the PFA in 68 cases (73.9%); from the FA in 17 cases (18.5%); from a common trunk formed by the PFA and CFA in 7 cases (7.6%). The origin of the LCFA was considered regardless, whether the descending branch originated therein or from the FA. Considering the presence of a number of important elements it is essential to identify the precise origin of the arteries and its eventual variations in procedures carried out in that area

Características Estereológicas del Hígado de Rata (Rattus norvergicus) sometidas a Menopausia Inducida por Ovariectomía

Trujillo, E (reprint author), Univ Talca, Univ La Frontera, Lircay S-N, Talca, Chile.During menopause, hormonal changes such as decreased estradiol and increased follicle stimulating and luteinizing hormones occur. In premenopausal women fibrosis and hepatic steatosis is less than in postmenopausal women and improves when hormone replacement therapy is administered. The aim of this study was to determine quantitative aspects of the liver of rats undergoing an experimental model of ovariectomy-induced menopause. We used 10 Sprague-Dawley (Rattus norvergicus) healthy adults. The rats were weighed and divided into two groups (bilateral oophorectomy = Group Ovx and control = Group Sham). The animals were sacrificed at 60 days and the liver removed, obtaining a piece of each liver. Five cuts were made of 4 microns and stained with HE. We analyzed five fields per slide. M42 test was used. Stereo logical parameters considered were as follows: Nv, Vv, Sv and total number (Tn) of hepatocytes and sinusoids. The average weight of Ovx and Sham group was 300.8 g and 285.8 g, respectively. The Nv of hepatocytes of rats subjected to sham surgery (CS) and Ovx (CO) was 6.89 and 7.70 x 10(5)/mm(3) x 10(5)/mm(3), respectively. The Vv of CS and CO hepatocytes was 71.92% and 80.48%, respectively. SV and CO, CS hepatocytes was 260.61mm(2)/mm(3) and 273.64 mm(2)/mm(3), respectively. The average volume of CS livers was 8.40 mm(3) and hepatocyte Tn averaged 5.79 x 10(6). The average volume was 9.28 mm(3) CO livers and Tn of 7.15 x 10(6). Regarding the sinusoids, the Nv in the liver CS and CO was 2.81 x 10(5)/mm(3) and 2.64 x 10(5)/mm(3), respectively. The Vv of sinusoids in CS and CO was 16.74% and 16.46%, respectively. The sinusoids in rats Sv CS and CO was 49.40 mm(2)/mm(3) and 45.21 mm(2)/mm(3), respectively. The sinusoids Tn CS and CO averaged 2.37 x 10(6) and 2.45 x 10(6), respectively. The lack of estrogen can cause fibrosis and hepatic steatosis as noted by other authors, but also changes in the organization and the proportion of the components of the liver, factors to consider during diagnosis and prognosis of liver disorders

Insectos de la "una de gato" (Uncaria guianenesis y U. tomentosa : Rubiaceae), planta medical de la Amazonia peruana

Two species of #Rubiaceae$ known as "una de gato", vernaculate name, are medicinal plants very used in the Peruvian Amazonia. Its excessive exploitation in the natural environment has made its cultivation necessary. Different species of phytophagous insects have been observed on "una de gato" in an experimental plantation in Iquitos, Peru. (Résumé d'auteur