FTC of hidden Markov process with application to resource allocation in air operation

This paper investigates the feedback control of hidden Markov process(HMP) in the face of loss of some observation processes.The control action facilitates or impedes some particular transitions from an inferred current state in the attempt to maximize the probability that the HMP is driven to a desirable absorbing state.This control problem is motivated by the need for judicious resource allocation to win an air operation involving two opposing forces.The effectiveness of a receding horizon control scheme based on the inferred discrete state is examined.Tolerance to loss of sensors that help determine the state of the air operation is achieved through a decentralized scheme that estimates a continuous state from measurements of linear models with additive noise.The discrete state of the HMP is identified using three well-known detection schemes.The sub-optimal control policy based on the detected state is implemented on-line in a closed-loop,where the air operation is simulated as a stochastic process with SimEvents,and the measurement process is simulated for a range of single sensor loss rates.     

UNC-6/netrin and its receptor UNC-5 locally exclude presynaptic components from dendrites

Polarity is an essential feature of many cell types, including neurons that receive information from local inputs within their dendrites and propagate nerve impulses to distant targets through a single axon. It is generally believed that intrinsic structural differences between axons and dendrites dictate the polarized localization of axonal and dendritic proteins. However, whether extracellular cues also instruct this process in vivo has not been explored. Here we show that the axon guidance cue UNC-6/netrin and its receptor UNC-5 act throughout development to exclude synaptic vesicle and active zone proteins from the dendrite of the Caenorhabditis elegans motor neuron DA9, which is proximal to a source of UNC-6/netrin. In unc-6/netrin and unc-5 loss-of-function mutants, presynaptic components mislocalize to the DA9 dendrite. In addition, ectopically expressed UNC-6/netrin, acting through UNC-5, is sufficient to exclude endogenous synapses from adjacent subcellular domains within the DA9 axon. Furthermore, this anti-synaptogenic activity is interchangeable with that of LIN-44/Wnt despite being transduced through different receptors, suggesting that extracellular cues such as netrin and Wnts not only guide axon navigation but also regulate the polarized accumulation of presynaptic components through local exclusion.     

Improper ferroelectricity in perovskite oxide artificial superlattices

Ferroelectric thin films and superlattices are currently the subject of intensive research because of the interest they raise for technological applications and also because their properties are of fundamental scientific importance. Ferroelectric superlattices allow the tuning of the ferroelectric properties while maintaining perfect crystal structure and a coherent strain, even throughout relatively thick samples. This tuning is achieved in practice by adjusting both the strain, to enhance the polarization, and the composition, to interpolate between the properties of the combined compounds. Here we show that superlattices with very short periods possess a new form of interface coupling, based on rotational distortions, which gives rise to 'improper' ferroelectricity. These observations suggest an approach, based on interface engineering, to produce artificial materials with unique properties. By considering ferroelectric/paraelectric PbTiO3/SrTiO3 multilayers, we first show from first principles that the ground-state of the system is not purely ferroelectric but also primarily involves antiferrodistortive rotations of the oxygen atoms in a way compatible with improper ferroelectricity. We then demonstrate experimentally that, in contrast to pure PbTiO3 and SrTiO3 compounds, the multilayer system indeed behaves like a prototypical improper ferroelectric and exhibits a very large dielectric constant of epsilon(r) approximately 600, which is also fairly temperature-independent. This behaviour, of practical interest for technological applications, is distinct from that of normal ferroelectrics, for which the dielectric constant is typically large but strongly evolves around the phase transition temperature and also differs from that of previously known improper ferroelectrics that exhibit a temperature-independent but small dielectric constant only.     

A common mass scale for satellite galaxies of the Milky Way

The Milky Way has at least twenty-three known satellite galaxies that shine with luminosities ranging from about a thousand to a billion times that of the Sun. Half of these galaxies were discovered in the past few years in the Sloan Digital Sky Survey, and they are among the least luminous galaxies in the known Universe. A determination of the mass of these galaxies provides a test of galaxy formation at the smallest scales and probes the nature of the dark matter that dominates the mass density of the Universe. Here we use new measurements of the velocities of the stars in these galaxies to show that they are consistent with them having a common mass of about 10(7) within their central 300 parsecs. This result demonstrates that the faintest of the Milky Way satellites are the most dark-matter-dominated galaxies known, and could be a hint of a new scale in galaxy formation or a characteristic scale for the clustering of dark matter.     

On Modeling Bio-Scaffolds: Structural and Fluid Transport Characterization Based on 3-D Imaging Data

Bio-scaffolds which are most commonly open celled porous structures are increasingly used for tissue engineering and regenerative medicine. A number of studies have shown that the bulk properties of such irregular structures are poorly modeled using idealized unit cell approaches. The paper therefore uses novel image based meshing techniques to explore both fluid flow and bulk structural properties of a bone scaffold, as accurate modeling of bio-scaffolds with non-uniform cellular structures is very important for the development of optimal scaffolds for tissue engineering application. In this study, a porous hydroxyapatite/tricalcium phosphate (HA/TCP) bone scaffold has been scanned in a Micro-CT scanner, and converted into a volumetric mesh using image processing software developed by the authors. The resulting mesh was then exported to commercial FEA and CFD solvers for analysis. Initial FEA and CFD studies have shown promising results and have highlighted the importance of accurate modeling to understand how microstructures influence the mechanical property of the scaffold, and to analyze flow regimes through the sample. The work highlights the potential use of image based meshing for the ad hoc characterization of scaffolds as well as for assisting in the design of scaffolds with tailored strength, stiffness, and transport properties.     

Safety Analysis of the Eco-Approach and Departure Application at a Signalized Corridor

Various intelligent transportation systems and strategies for reducing vehicle fuel consumption and emissions have been developed. Energy and emissions could be reduced with the compromise of travel time in some environment-focused Connected Vehicle(CV) applications, which highlighted performance measures in terms of mobility and sustainability. Nevertheless, few studies have focused on safety assessment of such CV applications. In this study, a CV-based eco-driving application, namely, Eco-Approach and Departure(EAD), is selected as an example. A microscopic safety analysis tool, Surrogate Safety Assessment Model(SSAM), is utilized to assess the safety influence of EAD application in multiple scenarios. Further analysis is performed from two perspectives:(1) application users, i.e., EAD-equipped vehicles versus unequipped vehicles; and(2) traffic operators, i.e., overall traffic performance with and without the introduction of EAD. For each perspective, conflict statistics(e.g., frequency, time-to-collision distribution), overall and by type, are analyzed. Results indicate EAD is beneficial in improving the safety performance of equipped vehicles. The influence of EAD on overall traffic is scenario dependent, and a high penetration rate shows positive effects on network-wide safety benefits for most scenarios.     

The NCBI dbGaP database of genotypes and phenotypes

The National Center for Biotechnology Information has created the dbGaP public repository for individual-level phenotype, exposure, genotype and sequence data and the associations between them. dbGaP assigns stable, unique identifiers to studies and subsets of information from those studies, including documents, individual phenotypic variables, tables of trait data, sets of genotype data, computed phenotype-genotype associations, and groups of study subjects who have given similar consents for use of their data.     

Systematic meta-analyses of Alzheimer disease genetic association studies: the AlzGene database

The past decade has witnessed hundreds of reports declaring or refuting genetic association with putative Alzheimer disease susceptibility genes. This wealth of information has become increasingly difficult to follow, much less interpret. We have created a publicly available, continuously updated database that comprehensively catalogs all genetic association studies in the field of Alzheimer disease (http://www.alzgene.org). We performed systematic meta-analyses for each polymorphism with available genotype data in at least three case-control samples. In addition to identifying the epsilon4 allele of APOE and related effects, we pinpointed over a dozen potential Alzheimer disease susceptibility genes (ACE, CHRNB2, CST3, ESR1, GAPDHS, IDE, MTHFR, NCSTN, PRNP, PSEN1, TF, TFAM and TNF) with statistically significant allelic summary odds ratios (ranging from 1.11-1.38 for risk alleles and 0.92-0.67 for protective alleles). Our database provides a powerful tool for deciphering the genetics of Alzheimer disease, and it serves as a potential model for tracking the most viable gene candidates in other genetically complex diseases.