Spatiotemporal symmetries in the disynaptic canal-neck projection

The vestibular system in almost all vertebrates, and in particular in humans, controls balance by employing a set of six semicircular canals, three in each inner ear, to detect angular accelerations of the head in three mutually orthogonal coordinate planes. Signals from the canals are transmitted to eight (groups of) neck motoneurons, which activate the eight corresponding muscle groups. These signals may be either excitatory or inhibitory, depending on the direction of head acceleration. McCollum and Boyle have observed that in the cat the relevant network of neurons possesses octahedral symmetry, a structure that they deduce from the known innervation patterns (connections) from canals to muscles. We rederive the octahedral symmetry from mathematical features of the probable network architecture, and model the movement of the head in response to the activation patterns of the muscles concerned. We assume that connections between neck muscles can be modeled by a “coupled cell network,” a system of coupled ODEs whose variables correspond to the eight muscles, and that this network also has octahedral symmetry. The network and its symmetries imply that these ODEs must be equivariant under a suitable action of the octahedral group. It is observed that muscle motoneurons form natural “push-pull pairs” in which, for given movements of the head, one neuron produces an excitatory signal, whereas the other produces an inhibitory signal. By incorporating this feature into the mathematics in a natural way, we are led to a model in which the octahedral group acts by signed permutations on muscle motoneurons. We show that with the appropriate group actions, there are six possible spatiotemporal patterns of time-periodic states that can arise by Hopf bifurcation from an equilibrium representing an immobile head. Here we use results of Ashwin and Podvigina. Counting conjugate states, whose physiological interpretations can have significantly different features, there are 15 patterns of periodic oscillation, not counting left-right reflections or time-reversals as being different. We interpret these patterns as motions of the head, and note that all six types of pattern appear to correspond to natural head motions

Pattern Competition in the Photorefractive Semiconductors

We analytically study the photorefractive Gunn effect in n-GaAs subjected to two external laser beams which form a moving interference pattern (MIP) in the semiconductor. When the intensity of the spatially independent part of the MIP, denoted by $I_0$, is small, the system has a periodic domain train (PDT), consistent with the results of linear stability analysis. When $I_0$ is large, the space-charge field induced by the MIP will compete with the PDT and result in complex dynamics, including driven chaos via quasiperiodic route

Spin-Valley Kondo Effect in Multi-electron Silicon Quantum Dots

We study the spin-valley Kondo effect of a silicon quantum dot occupied by $\mathcal{N}$ electrons, with $\mathcal{N}$ up to four. We show that the Kondo resonance appears in the $\mathcal{N}=1,2,3$ Coulomb blockade regimes, but not in the $\mathcal{N}=4$ one, in contrast to the spin-1/2 Kondo effect, which only occurs at $\mathcal{N}=$ odd. Assuming large orbital level spacings, the energy states of the dot can be simply characterized by fourfold spin-valley degrees of freedom. The density of states (DOS) is obtained as a function of temperature and applied magnetic field using a finite-U equation-of-motion approach. The structure in the DOS can be detected in transport experiments. The Kondo resonance is split by the Zeeman splitting and valley splitting for double- and triple-electron Si dots, in a similar fashion to single-electron ones. The peak structure and splitting patterns are much richer for the spin-valley Kondo effect than for the pure spin Kondo effect.Comment: 8 pages, 4 figures, in PRB format. This paper is a sequel to the paper published in Phys. Rev. B 75, 195345 (2007

The Damping of Panels by Thick Layers of Elastic Porous Media

In this paper a technique is presented for calculating the response of a panel to a line force input when loaded by both a finite‐depth layer of elastic porous material and a heavy fluid. Damping theories normally require that an attached damping layer be thin compared to the flexural wavelength in the base panel. Here this requirement is avoided by allowing explicitly for wave propagation within the damping layer. Specifically, the porous damping layer is modeled using a theory derived by Biot that allows for the existence of two dilatational waves and a transverse wave. Conditions required to couple the porous medium to the panel and an adjacent fluid will be discussed. A formal solution for the plate response may be obtained easily in the wavenumber domain. Although it is not possible to obtain the spatial response analytically in this instance, it will be shown that under practical circumstances the required inversion integral may be evaluated efficiently and “exactly” by using the fast Fourier transform algorithm. Results will be given illustrating the damping potential of thick layers of porous materials

Sound Transmission through Stiffened Double-Panel Structures Lined with Elastic Porous Materials

This paper presents transmission loss prediction models for a periodically stiffened panel and and stiffened double panel structures using the periodic structure theory. The inter-panel cavity in the double-panels structures can be modelled as being separated by an airspace or filled with an elastic porous layer in various configurations. The acoustic behavior of the elastic porous layer is described by a theory capable of accounting fully for multi-dimensional wave propagation in such materials. The predicted transmission loss of a single stiffened panel is compared with the measured data

HBV Testing and Vaccinations among Asian and Pacific Islander Patients: Understanding the Impact of the San Francisco Hepatitis B Free Campaign on Physician Awareness

Background and Significance: One in 12 Asian and Pacific Islanders (APIs) are infected with hepatitis B (HBV). APIs represent one-third of the population in San Francisco. San Francisco Hep B Free (SFHBF), a citywide collaboration, works to educate physicians and the community on the importance of hepatitis B among APIs through increasing awareness, education and the availability of screening and vaccinations. The purpose of this paper was to qualitatively assess the perceived impact of SFHBF on the awareness and attitudes of physicians regarding screening and vaccination of APIs. Methods: Twenty physicians (n=20) participated in key informant interviews about HBV awareness and involvement with SFHBF. The questions focused on physician attitudes and practice towards HBV screening, vaccination and follow-up care, communication with patients about HBV, and awareness and effectiveness of the SFHBF outreach efforts. Results: Findings highlighted SFHBF’s impact on physicians’ sensitivity and awareness. Overall, physicians were increasing their HBV screening and vaccination rates among their API patients. Physicians noted the need for continual support to prioritize HBV screening and vaccination among their API patients. Conclusion: The findings of this study are important for understanding the impact of public health campaigns on physician attitudes and practices regarding HBV education, screening, and vaccinations among their API patients

Clustering Approach to Quantify Long-Term Spatio-Temporal Interactions in Epileptic Intracranial Electroencephalography

Abnormal dynamical coupling between brain structures is believed to be primarily responsible for the generation of epileptic seizures and their propagation. In this study, we attempt to identify the spatio-temporal interactions of an epileptic brain using a previously proposed nonlinear dependency measure. Using a clustering model, we determine the average spatial mappings in an epileptic brain at different stages of a complex partial seizure. Results involving 8 seizures from 2 epileptic patients suggest that there may be a fixed pattern associated with regional spatio-temporal dynamics during the interictal to pre-post-ictal transition

Changing Attitudes towards Hepatitis B among Asian Americans: From Saving Face to Getting Serious

Background: Asian Americans have the highest prevalence of hepatitis B virus (HBV) in the US. The San Francisco Hep B Free (SFHBF) campaign aimed to increase awareness and access to HBV education and services among Asian Americans in San Francisco. Purpose: We sought to examine attitudes and knowledge among Asian Americans regarding HBV at baseline (2009) and benefits of the SFHBF outreach campaign four years later (2013). Methods: Four focus groups were conducted (n=45) in 2009, followed by in-depth interviews (n=40) in 2013. Results: In 2009, many participants were misinformed about HBV symptoms and transmission. They also reported stigma associated with HBV, which hindered Asian Americans from discussing the disease and seeking services. The 2013 interviews revealed that SFHBF had contributed towards awareness of HBV screenings and vaccinations, and also instilled acute seriousness that HBV could affect them directly. Conclusion: The in-depth interviews conducted in 2013 illustrated that there was less concern about “saving face,” but a shift to a level of seriousness associated with HBV. Future efforts among Asian Americans should continue to focus on self-efficacy regarding HBV prevention, including screening and vaccination

Global Optimization of Plug-In Hybrid Vehicle Design and Allocation to Minimize Life Cycle Greenhouse Gas Emissions

We pose a reformulated model for optimal design and allocation of conventional (CV), hybrid electric (HEV), and plug-in hybrid electric (PHEV) vehicles to obtain global solutions that minimize life cycle greenhouse gas (GHG) emissions of the fleet. The reformulation is a twice-differentiable, factorable, nonconvex mixed-integer nonlinear programming (MINLP) model that can be solved globally using a convexification-based branch-and-reduce algorithm. We compare results to a randomized multistart local-search approach for the original formulation and find that local-search algorithms locate global solutions in 59% of trials for the two-segment case and 18% of trials for the three-segment case. The results indicate that minimum GHG emissions are achieved with a mix of PHEVs sized for 25-45 miles of electric travel. Larger battery packs allow longer travel on electrical energy, but production and weight of underutilized batteries result in higher GHG emissions. Under the current average U.S. grid mix, PHEVs offer a nearly 50% reduction in life cycle GHG emissions relative to equivalent conventional vehicles and about 5% improvement over HEVs when driven on the standard urban driving cycle. Optimal allocation of different PHEVs to different drivers turns out to be of second order importance for minimizing net life cycle GHGs