10,394 research outputs found
Second fundamental form of the Prym map in the ramified case
In this paper we study the second fundamental form of the Prym map in the ramified case .
We give an expression of it in terms of the second fundamental form of the
Torelli map of the covering curves. We use this expression to give an upper
bound for the dimension of a germ of a totally geodesic submanifold, and hence
of a Shimura subvariety of , contained in the
Prym locus.Comment: To appear in Galois Covers, Grothendieck-Teichmueller Theory and
Dessins d'Enfants - Interactions between Geometry, Topology, Number Theory
and Algebra. Springer Proceedings in Mathematics & Statistics. arXiv admin
note: text overlap with arXiv:1711.0342
Single-species fragmentation: the role of density-dependent feedbacks
Internal feedbacks are commonly present in biological populations and can
play a crucial role in the emergence of collective behavior. We consider a
generalization of Fisher-KPP equation to describe the temporal evolution of the
distribution of a single-species population. This equation includes the
elementary processes of random motion, reproduction and, importantly, nonlocal
interspecific competition, which introduces a spatial scale of interaction.
Furthermore, we take into account feedback mechanisms in diffusion and growth
processes, mimicked through density-dependencies controlled by exponents
and , respectively. These feedbacks include, for instance, anomalous
diffusion, reaction to overcrowding or to rarefaction of the population, as
well as Allee-like effects. We report that, depending on the dynamics in place,
the population can self-organize splitting into disconnected sub-populations,
in the absence of environment constraints. Through extensive numerical
simulations, we investigate the temporal evolution and stationary features of
the population distribution in the one-dimensional case. We discuss the crucial
role that density-dependency has on pattern formation, particularly on
fragmentation, which can bring important consequences to processes such as
epidemic spread and speciation
Anharmonicity and self-similarity of the free energy landscape of protein G
The near-native free energy landscape of protein G is investigated through
0.4 microseconds-long atomistic molecular dynamics simulations in explicit
solvent. A theoretical and computational framework is used to assess the
time-dependence of salient thermodynamical features. While the quasi-harmonic
character of the free energy is found to degrade in a few ns, the slow modes
display a very mild dependence on the trajectory duration. This property
originates from a striking self-similarity of the free energy landscape
embodied by the consistency of the principal directions of the local minima,
where the system dwells for several ns, and of the virtual jumps connecting
them.Comment: revtex, 6 pages, 5 figure
Semi-autonomous Intersection Collision Avoidance through Job-shop Scheduling
In this paper, we design a supervisor to prevent vehicle collisions at
intersections. An intersection is modeled as an area containing multiple
conflict points where vehicle paths cross in the future. At every time step,
the supervisor determines whether there will be more than one vehicle in the
vicinity of a conflict point at the same time. If there is, then an impending
collision is detected, and the supervisor overrides the drivers to avoid
collision. A major challenge in the design of a supervisor as opposed to an
autonomous vehicle controller is to verify whether future collisions will occur
based on the current drivers choices. This verification problem is particularly
hard due to the large number of vehicles often involved in intersection
collision, to the multitude of conflict points, and to the vehicles dynamics.
In order to solve the verification problem, we translate the problem to a
job-shop scheduling problem that yields equivalent answers. The job-shop
scheduling problem can, in turn, be transformed into a mixed-integer linear
program when the vehicle dynamics are first-order dynamics, and can thus be
solved by using a commercial solver.Comment: Submitted to Hybrid Systems: Computation and Control (HSCC) 201
Optimized Large-Scale CMB Likelihood And Quadratic Maximum Likelihood Power Spectrum Estimation
We revisit the problem of exact CMB likelihood and power spectrum estimation
with the goal of minimizing computational cost through linear compression. This
idea was originally proposed for CMB purposes by Tegmark et al.\ (1997), and
here we develop it into a fully working computational framework for large-scale
polarization analysis, adopting \WMAP\ as a worked example. We compare five
different linear bases (pixel space, harmonic space, noise covariance
eigenvectors, signal-to-noise covariance eigenvectors and signal-plus-noise
covariance eigenvectors) in terms of compression efficiency, and find that the
computationally most efficient basis is the signal-to-noise eigenvector basis,
which is closely related to the Karhunen-Loeve and Principal Component
transforms, in agreement with previous suggestions. For this basis, the
information in 6836 unmasked \WMAP\ sky map pixels can be compressed into a
smaller set of 3102 modes, with a maximum error increase of any single
multipole of 3.8\% at , and a maximum shift in the mean values of a
joint distribution of an amplitude--tilt model of 0.006. This
compression reduces the computational cost of a single likelihood evaluation by
a factor of 5, from 38 to 7.5 CPU seconds, and it also results in a more robust
likelihood by implicitly regularizing nearly degenerate modes. Finally, we use
the same compression framework to formulate a numerically stable and
computationally efficient variation of the Quadratic Maximum Likelihood
implementation that requires less than 3 GB of memory and 2 CPU minutes per
iteration for , rendering low- QML CMB power spectrum
analysis fully tractable on a standard laptop.Comment: 13 pages, 13 figures, accepted by ApJ
Orbital dynamics of "smart dust" devices with solar radiation pressure and drag
This paper investigates how perturbations due to asymmetric solar radiation pressure, in the presence of Earth shadow, and atmospheric drag can be balanced to obtain long-lived Earth centred orbits for swarms of micro-scale 'smart dust' devices, without the use of active control. The secular variation of Keplerian elements is expressed analytically through an averaging technique. Families of solutions are then identified where Sun-synchronous apse-line precession is achieved passively to maintain asymmetric solar radiation pressure. The long-term orbit evolution is characterized by librational motion, progressively decaying due to the non-conservative effect of atmospheric drag. Long-lived orbits can then be designed through the interaction of energy gain from asymmetric solar radiation pressure and energy dissipation due to drag. In this way, the usual short drag lifetime of such high area-to-mass spacecraft can be greatly extended (and indeed selected). In addition, the effect of atmospheric drag can be exploited to ensure the rapid end-of-life decay of such devices, thus preventing long-lived orbit debris
Sites for Gamma-ray Astronomy in Argentina
We have searched for possible sites in Argentina for the installation of
large air Cherenkov telescope arrays and water Cherenkov systems. At present
seven candidates are identified at altitudes from 2500 to 4500 m. The highest
sites are located at the Northwest of the country, in La Puna. Sites at 2500
and 3100 m are located in the West at El Leoncito Observatory, with excellent
infrastructure. A description of these candidate sites is presented with
emphasis on infrastructure and climatology.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
Dietary patterns of early childhood and maternal socioeconomic status in a unique prospective sample from a randomized controlled trial of Prenatal DHA Supplementation
A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author's publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.Background
Dietary habits established in early childhood and maternal socioeconomic status (SES) are important, complex, interrelated factors that influence a child’s growth and development. The aim of this study was to define the major dietary patterns in a cohort of young US children, construct a maternal SES index, and evaluate their associations.
Methods
The diets of 190 children from a randomized, controlled trial of prenatal supplementation of docosahexaenoic acid (DHA) were recorded at 6-mo intervals from 2-4.5 years by 24-h dietary recall. Hierarchical cluster analysis of age-adjusted, average daily intake of 24 food and beverage groups was used to categorize diet. Unrotated factor analysis generated an SES score from maternal race, ethnicity, age, education, and neighborhood income.
Results
We identified two major dietary patterns: “Prudent” and “Western.” The 85 (45%) children with a Prudent diet consumed more whole grains, fruit, yogurt and low-fat milk, green and non-starchy vegetables, and nuts and seeds. Conversely, those with a Western diet had greater intake of red meat, discretionary fat and condiments, sweet beverages, refined grains, French fries and potato chips, eggs, starchy vegetables, processed meats, chicken and seafood, and whole-fat milk. Compared to a Western diet, a Prudent diet was associated with one standard deviation higher maternal SES (95% CI: 0.80 to 1.30).
Conclusions
We found two major dietary patterns of young US children and defined a single, continuous axis of maternal SES that differed strongly between groups. This is an important first step to investigate how child diet, SES, and prenatal DHA supplementation interact to influence health outcomes.
Trial registration
NCT00266825. Prospectively registered on December 15, 2005
Electronic supplementary material
The online version of this article (doi:10.1186/s12887-016-0729-0) contains supplementary material, which is available to authorized users
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