A physical model suggests that hip-localized balance sense in birds improves state estimation in perching: implications for bipedal robots

In addition to a vestibular system, birds uniquely have a balance-sensing organ within the pelvis, called the lumbosacral organ (LSO). The LSO is well developed in terrestrial birds, possibly to facilitate balance control in perching and terrestrial locomotion. No previous studies have quantified the functional benefits of the LSO for balance. We suggest two main benefits of hip-localized balance sense: reduced sensorimotor delay and improved estimation of foot-ground acceleration. We used system identification to test the hypothesis that hip-localized balance sense improves estimates of foot acceleration compared to a head-localized sense, due to closer proximity to the feet. We built a physical model of a standing guinea fowl perched on a platform, and used 3D accelerometers at the hip and head to replicate balance sense by the LSO and vestibular systems. The horizontal platform was attached to the end effector of a 6 DOF robotic arm, allowing us to apply perturbations to the platform analogous to motions of a compliant branch. We also compared state estimation between models with low and high neck stiffness. Cross-correlations revealed that foot-to-hip sensing delays were shorter than foot-to-head, as expected. We used multi-variable output error state-space (MOESP) system identification to estimate foot-ground acceleration as a function of hip- and head-localized sensing, individually and combined. Hip-localized sensors alone provided the best state estimates, which were not improved when fused with head-localized sensors. However, estimates from head-localized sensors improved with higher neck stiffness. Our findings support the hypothesis that hip-localized balance sense improves the speed and accuracy of foot state estimation compared to head-localized sense. The findings also suggest a role of neck muscles for active sensing for balance control: increased neck stiffness through muscle co-contraction can improve the utility of vestibular signals. Our engineering approach provides, to our knowledge, the first quantitative evidence for functional benefits of the LSO balance sense in birds. The findings support notions of control modularity in birds, with preferential vestibular sense for head stability and gaze, and LSO for body balance control,respectively. The findings also suggest advantages for distributed and active sensing for agile locomotion in compliant bipedal robots

An optimization model for metabolic pathways

This article is available open access through the publisher’s website through the link below. Copyright @ The Author 2009.Motivation: Different mathematical methods have emerged in the post-genomic era to determine metabolic pathways. These methods can be divided into stoichiometric methods and path finding methods. In this paper we detail a novel optimization model, based upon integer linear programming, to determine metabolic pathways. Our model links reaction stoichiometry with path finding in a single approach. We test the ability of our model to determine 40 annotated Escherichia coli metabolic pathways. We show that our model is able to determine 36 of these 40 pathways in a computationally effective manner. Contact: [email protected] Supplementary information: Supplementary data are available at Bioinformatics online (http://bioinformatics.oxfordjournals.org/cgi/content/full/btp441/DC1)

Sur quelques Cystoidées cités par les Drs. J. Almera et M.Faura dans l'Ordovicien de Barcelone

Con motivo de la elaboración del Mapa Geológico de Cataluña a escala 1:40.000, subvencionado por la Excma. Diputación Provincial de Barcelona, a partir de 1886, dirigida por el Dr. J. Almera con la colaboración del Dr. M. Faura i Sans, fueron recogidos numerosos fósiles paleozoicos en la Provincia de Barcelona, entre los cuales figuraban algunos ejemplares de Cystoideos que fueron clasificados como Echinosphaerites cf. balticus EICHW., por Barrois (1891), procedentes de las localidades de Montcada, El Papiol, Gracia y Aiguafreda, actualmente inaccesibles en su mayor parte. Estos ejemplares estuvieron depositados en el Museo Geológico del Seminano Conciliar de Barcelona hasta 1918, en que fueron trasladados al Museo Geológico Municipal en el Parque de la Ciudadela.Dentro de nuestro plan de estudio y revisión de los Cystoideos de España hemos considerado necesario proceder a la revisión de estos fósiles, estudiados hace más de 70 años y que últimamente hemos podido localizar en las colecciones de los dos Museos mencionados, pues todo parecía indicar que su clasificación no era correcta, ya que últimamente se ha podido comprobar que la especie Heliocrinites (Echinosphaerites) balticus (EIcHw.), no existe en nuestra Peninsula.Todos los ejemplares revisados son placas aisladas de Cystoideos, conservadas como moldes externos sobre pizarras, por haberse disuelto las placas posteriormente a su fosilización.Uno de los ejemplares pertenece a las colecciones del Seminario Conciliar, procede de Montcada, ya fue determinado por Almera como Echinosphaerites sp; posteriormente como Oocystis? por el Dr. Via Boada, y se trata realmente del molde externo de una placa de Caryocrinites (=Oocystis) aff. europaeus QUENSTEDT.Los demás ejemplares proceden de las colecciones del Museo Municipal de Barcelona, y son también Caryocrinites, aunque aparecían en las etiquetas como Echinosphaerites aff. balticus. Probablemente corresponden al Caryocrinites rugatus (FORBES).Por lo que se refiere al nivel estratigráfico en que fueron recogidos los ejemplares, parece ser más bien Ashgill en vez de Caradoc

The Rise of the AGB in the Galactic Halo: Mg Isotopic Ratios and High Precision Elemental Abundances in M71 Giants

High-resolution (R ≈ 100,000), high signal-to-noise spectra of M71 giants have been obtained with High Resolution Echelle Spectrometer at the Keck I telescope in order to measure their Mg isotopic ratios, as well as elemental abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Ni, Zr, and La. We demonstrate that M71 has two populations, the first having weak CN, normal O, Na, Mg, and Al, and a low ratio of ^(26)Mg/Mg (~4%) consistent with models of galactic chemical evolution with no contribution from asymptotic giant branch (AGB) stars. The Galactic halo could have been formed from the dissolution of globular clusters prior to their intermediate-mass stars reaching the AGB. The second population has enhanced Na and Al accompanied by lower O and by higher ^(26)Mg/Mg (~8%), consistent with models which do incorporate ejecta from AGB stars via normal stellar winds. All the M71 giants have identical [Fe/H], [Si/Fe], [Ca/Fe], [Ti/Fe], and [Ni/Fe] to within σ = 0.04 dex (10%). We therefore infer that the timescale for formation of the first generation of stars we see today in this globular cluster must be sufficiently short to avoid a contribution from AGB stars, i.e., less than ~0.3 Gyr. Furthermore, the Mg isotopic ratios in the second M71 population, combined with their elemental abundances for the light elements, demonstrate that the difference must be the result of adding in the ejecta of intermediate-mass AGB stars. Finally, we suggest that the low amplitude of the abundance variations of the light elements within M71 is due to a combination of its low mass and its relatively high Fe-metallicity

IRFM T_(eff) calibrations for cluster and field giants in the Vilnius, Geneva, RI_(C) and DDO photometric systems

Based on a large sample of disk and halo giant stars for which accurate effective temperatures derived through the InfraRed Flux Method (IRFM) exist, a calibration of the temperature scale in the Vilnius, Geneva, RI_(C) and DDO photometric systems is performed. We provide calibration formulae for the metallicity-dependent T_(eff) vs. color relations as well as grids of intrinsic colors and compare them with other calibrations. Photometry, atmospheric parameters and reddening corrections for the stars of the sample have been updated with respect to the original sources to reduce the dispersion of the fits. Application of our results to Arcturus leads to an effective temperature in excellent agreement with the value derived from its angular diameter and integrated flux. The effects of gravity on these T(_eff) vs. color relations are also explored by taking into account our previous results for dwarf stars

Branching Deregulation and Merger Optimality

The U.S. banking industry has been characterized by intense merger activity in the absence of economies of scale and scope. We claim that the loosening of geographic constraints on U.S. banks is responsible for this consolidation process, irrespective of value-maximizing motives. We demonstrate this by putting forward a theoretical model of banking competition and studying banks’ strategic responses to geographic deregulation. We show that even in the absence of economies of scale and scope, bank mergers represent an optimal response. Also, we show that the consolidation process is characterized by merger waves and that some equilibrium mergers are not profitable per se -they yield losses- but become profitable as the waves of mergers unfold.Banking Competition, Deregulation, Mergers

Effect of Antioxidants in Cathepsin B Release by HIV Infected Macrophages

During HIV infection of macrophages, the lysosomal protein cathepsin B is released and induces neurotoxicity. Also, the levels of cathepsin B are increased in plasma and post-mortem brain tissue of patients with HIV-associated dementia. Oxidative damage is increased in HIV- infected patients, while antioxidants are decreased in HIV-associated dementia. Dimethyl fumarate (DMF), an antioxidant, has been reported to decrease HIV replication and neurotoxicity caused by HIV-infected macrophages. Since HIV also increases cathepsin B, we hypothesize that DMF will also reduce cathepsin B release from HIV-infected macrophages. Monocyte-derived macrophages (MDM) were isolated from healthy donors and inoculated with HIV-1ADA. After removal of infection, MDM were treated with DMF at different concentrations (15, 30, and 60 µM) until day 12 post-infection, changing and collecting media every three days. HIV-1p24 and cathepsin B levels were assessed from HIV-infected MDM supernatants at the end of cultures using ELISA. Results indicate that DMF reduced HIV-1 replication and cathepsin B secretion from HIV-infected macrophages, in a concentration-dependent manner, in comparison with vehicle (DMSO)-treated controls. However, cathepsin B secretion was not affected by HIV infection in vehicle-treated controls. In conclusion, DMSO may have had an unexpected effect in cathepsin B secretion in our experiments, and this could explain why cathepsin B secretion was not affected by HIV infection. Future experiments will include an untreated control group to determine if DMSO vehicle is having an effect in cathepsin B secretion. This will lead us to determine the role of DMF in cathepsin B secretion from HIV-infected macrophages