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

Transfer of Sulfur from IscS to IscU during Fe/S Cluster Assembly

The cysteine desulfurase enzymes NifS and IscS provide sulfur for the biosynthesis of Fe/S proteins. NifU and IscU have been proposed to serve as template or scaffold proteins in the initial Fe/S cluster assembly events, but the mechanism of sulfur transfer from NifS or IscS to NifU or IscU has not been elucidated. We have employed [35S]cysteine radiotracer studies to monitor sulfur transfer between IscS and IscU from Escherichia coli and have used direct binding measurements to investigate interactions between the proteins. IscS catalyzed transfer of 35S from [35S]cysteine to IscU in the absence of additional thiol reagents, suggesting that transfer can occur directly and without involvement of an intermediate carrier. Surface plasmon resonance studies and isothermal titration calorimetry measurements further revealed that IscU binds to IscS with high affinity (Kd ~2 µM) in support of a direct transfer mechanism. Transfer was inhibited by treatment of IscU with iodoacetamide, and 35S was released by reducing reagents, suggesting that transfer of persulfide sulfur occurs to cysteinyl groups of IscU. A deletion mutant of IscS lacking C-terminal residues 376-413 (IscSDelta 376-413) displayed cysteine desulfurase activity similar to the full-length protein but exhibited lower binding affinity for IscU, decreased ability to transfer 35S to IscU, and reduced activity in assays of Fe/S cluster assembly on IscU. The findings with IscSDelta 376-413 provide additional support for a mechanism of sulfur transfer involving a direct interaction between IscS and IscU and suggest that the C-terminal region of IscS may be important for binding IscU

PAM4 Transmitter and Receiver Equalizers Optimization for High-Speed Serial Links

As the telecommunications markets evolves, the demand of faster data transfers and processing continue to increase. In order to confront this demand, the peripheral component interconnect express (PCIe) has been increasing the data rates from PCIe Gen 1(4 Gb/s) to PCIe Gen 5(32 Gb/s). This evolution has brought new challenges due to the high-speed interconnections effects which can cause data loss and intersymbol interference. Under these conditions the traditional non return to zero modulation (NRZ) scheme became a bottle neck due to bandwidth limitations in the high-speed interconnects. The pulse amplitude modulation 4-level (PAM4) scheme is been implemented in next generation of PCIe (PCIe6) doubling the data rate without increasing the channel bandwidth. However, while PAM4 solve the bandwidth problem it also brings new challenges in post silicon equalization. Tuning the transmitter (Tx) and receiver (Rx) across different interconnect channels can be a very time-consuming task due to multiple equalizers implemented in the serializer/deserializer (SerDes). Typical current industrial practices for SerDes equalizers tuning require massive lab measurements, since they are based on exhaustive enumeration methods, making the equalization process too lengthy and practically prohibitive under current silicon time-to-market commitments. In this master’s dissertation a numerical method is proposed to optimize the transmitter and receiver equalizers of a PCIe6 link. The experimental results, tested in a MATLAB simulation environment, demonstrate the effectiveness of the proposed approach by delivering optimal PAM4 eye diagrams margins while significantly reducing the jitter.ITESO, A.C

Singularidad centro-foco en R3

En este articulo se estudian las singularidades de campos vectoriales X en el origen de R3 (con coordenadas (x1, x2, x3)) tales que DX(0) = - bx2 --+ bx1 --+ AX3 --. ax1 ax2 . ax3 b, A f O. La conducta de estas singularidades corresponde alcentrojoco en R3 con un eje hiperbólico. El conjunto de gérmenes de tales campos vectoriales es un conjunto estratificado, cuyas estratas son conjuntos localmente cerrados y de codimensión creciente en el espacio de gérmenes de singularidades en R3. Además estas singularidades son localmente C° estables y se bifurcan a n-parámetros colapsando n-cilindros concéntricos invariantes, es decir. una bifurcación de Hopf cilindrar generalizada

Diurnal variation of non-specular meteor trails

We present results of simulated radar observations of meteor trails in an effort to show how non-specular meteor trails are expected to vary as a function of a number of key atmospheric, ionospheric and meteoroid parameters. This paper identifies which geophysical sources effect the variability in non-specular trail radar observations, and provides an approach that uses some of these parameter dependencies to determine meteoroid and atmospheric properties based upon the radar meteor observations. The numerical model used follows meteor evolution from ablation and ionization to head echo plasma generation and through formation of field aligned irregularities (FAI). Our main finding is that non-specular meteor trail duration is highly sensitive to the presence of lower thermospheric winds or electric fields and the background ionospheric electron density. In an effort to make key predictions we present the first results of how the same meteoroid is expected to produce dramatically different meteor trails as a function of location and local time. For example, we show that mid-latitude trail durations are often shorter lasting than equatorial trail observations because of the difference in mid-latitude wind speed and equatorial drift speed. The simulated trails also account for observations showing that equatorial nighttime non-specular meteor trails last significantly longer and are observed more often than daytime trails