Period-two cycles in a feed-forward layered neural network model with symmetric sequence processing

The effects of dominant sequential interactions are investigated in an exactly solvable feed-forward layered neural network model of binary units and patterns near saturation in which the interaction consists of a Hebbian part and a symmetric sequential term. Phase diagrams of stationary states are obtained and a new phase of cyclic correlated states of period two is found for a weak Hebbian term, independently of the number of condensed patterns $c$.Comment: 8 pages and 5 figure

Symmetric sequence processing in a recurrent neural network model with a synchronous dynamics

The synchronous dynamics and the stationary states of a recurrent attractor neural network model with competing synapses between symmetric sequence processing and Hebbian pattern reconstruction is studied in this work allowing for the presence of a self-interaction for each unit. Phase diagrams of stationary states are obtained exhibiting phases of retrieval, symmetric and period-two cyclic states as well as correlated and frozen-in states, in the absence of noise. The frozen-in states are destabilised by synaptic noise and well separated regions of correlated and cyclic states are obtained. Excitatory or inhibitory self-interactions yield enlarged phases of fixed-point or cyclic behaviour.Comment: Accepted for publication in Journal of Physics A: Mathematical and Theoretica

Optical Pointing Sensor

The optical pointing sensor provides a means of directly measuring the relative positions of JPL s Formation Control Testbed (FCT) vehicles without communication. This innovation is a steerable infrared (IR) rangefinder that gives measurements in terms of range and bearing to a passive retroreflector

Validation of Collision Detection and Avoidance Methods for Urban Air Mobility through Simulation

Urban Air Mobility is a new concept of regional aviation that has been growing in popularity as a solution to the issue of ever-increasing ground traffic. Electric vehicles with vertical take-off and landing capabilities are being developed by numerous market companies as a result of the push toward environmentally sustainable aviation. The next stage in the eVTOL development process would be to define the concept of operation of these conceptual aircraft and then to integrate them with the existing airspace once they are airborne. In addition to coordinating with conventional air traffic and other Urban Air Mobility (UAM) vehicles, collision avoidance with uncooperative airspace users has to be addressed. Birds and drones of all sizes could be dangerous for these low-flying aircraft. Innovative collision detection and avoidance techniques need to be employed due to the uncooperative nature of these airspace users and different performance characteristics of urban air mobility vehicles compared to classical fixed-wing aircraft. The aim of this study is to validate one such system by means of fast-time solutions. This system uses a decision tree and safety envelopes to prevent collisions with non-cooperative airspace members. The system is designed to work with different aircraft configurations used for Urban Air Mobility (UAM) operations. Various scenarios are modelled by varying intruder type, location, flight path among others. Changes in flight time and closest point of approach are assessed to evaluate the system with regard to safety and efficiency

Experimental Evaluation of Bird Strikes in Urban Air Mobility

Advanced mobility concepts such as Urban Air Mobility are emerging in full swing. In that concept, a safe and efficient aviation transportation system will use highly automated aircraft that will transport passengers or cargo at low altitudes within and between metropolitan regions. To accomplish these missions, new types of aircraft which are sometimes known as air taxis are being developed. A successful integration of these aircraft into existing airspace is complicated and needs to take into account various aspects. One of these is the risk of wildlife strikes which is predicted to be higher in case of air taxis. The proposed operational cruising altitude of air taxis is lower resulting in higher probability of collision as these are the altitudes where birds typically fly. Additionally, air taxis are smaller in size and have lower certification requirements compared to conventional aircraft. As a result, the severity of damaging bird strikes is higher. To assess the risk and formulate suitable regulations, an extensive analysis is required providing more quantitative insight into the bird strike challenge. Therefore, a theoretical model of bird strike to quantify the impact force by considering different bird and aircraft related parameters was developed previously. This paper aims to validate this theoretical model experimentally. It presents a methodology for implementing an experimental setup, allowing for the theoretical impact force model to be fully validated. A test matrix containing seven test cases, nine test scenarios and 135 iterations is formulated to conduct the bird strike experiment and the influencing parameters are considered for theoretical model verification. The paper closes with the presentation of the experimental results for validating the theoretical model which indicate 92.89 % conformance of experimental results with the theoretical model

Comparing extractions of Sivers functions

A comparison is given of the various recently published extractions of the Sivers functions from the HERMES and COMPASS data on single-transverse spin asymmetries in semi-inclusive deeply inelastic scattering.Comment: Contribution to the proceedings of "The International Workshop on Transverse Polarisation Phenomena in Hard Processes" (Transversity 2005), Villa Olmo (Como), 7-10th. September 200

Femmes au masculin : Jane Dieulafoy et Marc de Montifaud

Les photographies issues d\u27une collection unique en son genre, celle de la bibliothèque Marguerite Durand, nous convient à une traversée en pointillé de cent cinquante ans d\u27histoire des femmes, des années 1860 aux années MLF. Portraits, photographies d\u27art ou documentaires révèlent quelques-unes des grandes aventures collectives de la vie des femmes, celles du travail, des arts et de leurs mobilisations pour leur libération. Ce parcours en images met en lumière la double perspective de la collection depuis sa création : rendre visibles les femmes présentes dans l\u27espace public, actives dans des domaines traditionnellement réservés aux hommes et archiver les témoignages de leurs combats, encore inachevés. Restituer ces multiples regards invite à une écriture du passé qui accorde à l\u27émancipation des femmes toute son importance, décisive dans la conquête de l\u27égalité et de liberté de tous.

IDO2 in Immunomodulation and Autoimmune Disease.

IDO2 is a relative of IDO1 implicated in tryptophan catabolism and immune modulation but its specific contributions to normal physiology and pathophysiology are not known. Evolutionary genetic studies suggest that IDO2 has a unique function ancestral to IDO1. In mice, IDO2 gene deletion does not appreciably affect embryonic development or hematopoiesis, but it leads to defects in allergic or autoimmune responses and in the ability of IDO1 to influence the generation of T regulatory cells. Gene expression studies indicate that IDO2 is a basally and more narrowly expressed gene than IDO1 and that IDO2 is uniquely regulated by AhR, which serves as a physiological receptor for the tryptophan catabolite kynurenine. In the established KRN transgenic mouse model of rheumatoid arthritis, where IDO1 gene deletion has no effect, IDO2 deletion selectively blunts responses to autoantigen but has no effect on responses to neoantigen challenge. In human populations, natural variations in IDO2 gene sequence that attenuate enzymatic activity have been reported to influence brain cancer control and adaptive immune responses to the IDO2 protein itself, consistent with the concept that IDO2 is involved in shaping immune tolerance in human beings. Biochemical and pharmacological studies provide further evidence of differences in IDO2 enzymology and function relative to IDO1. We suggest that IDO2 may act in a distinct manner from IDO1 as a set-point for tolerance to altered-self antigens along the self-non-self continuum where immune challenges from cancer and autoimmunity may arise

Rabi Oscillations at Exceptional Points in Microwave Billiards

We experimentally investigated the decay behavior with time t of resonances near and at exceptional points, where two complex eigenvalues and also the associated eigenfunctions coalesce. The measurements were performed with a dissipative microwave billiard, whose shape depends on two parameters. The t^2-dependence predicted at the exceptional point on the basis of a two-state matrix model could be verified. Outside the exceptional point the predicted Rabi oscillations, also called quantum echoes in this context, were detected. To our knowledge this is the first time that quantum echoes related to exceptional points were observed experimentally.Comment: 10 pages, 3 figure

Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies

We have analyzed Chandra archival observations of the Antennae galaxies to study the distribution and physical properties of its hot interstellar gas. Eleven distinct diffuse X-ray emission regions are selected according to their underlying interstellar structures and star formation activity. The X-ray spectra of these regions are used to determine their thermal energy contents and cooling timescales. Young star clusters in these regions are also identified and their photometric measurements are compared to evolutionary stellar population synthesis models to assess their masses and ages. The cluster properties are then used to determine the stellar wind and supernova energies injected into the ISM. Comparisons between the thermal energy in the hot ISM and the expected stellar energy input show that young star clusters are sufficient to power the X-ray-emitting gas in some, but not all, active star formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the ISM, but the yield of hot interstellar gas is not directly proportional to the cluster mass. Finally, there exist diffuse X-ray emission regions which do not show active star formation or massive young star clusters. These regions may be powered by field stars or low-mass clusters formed within the last ~100 Myr.Comment: 36 pages, 6 figures, 8 tables, 2 appendices, to appear in the Astrophysical Journal, April 20 issu