24,349 research outputs found
Automatic collision avoidance of ships
One of the key elements in automatic simulation of ship manoeuvring in confined waterways is route finding and collision avoidance. This paper presents a new practical method of automatic trajectory planning and collision avoidance based on an artificial potential field and speed vector. Collision prevention regulations and international navigational rules have been incorporated into the algorithm. The algorithm is fairly straightforward and simple to implement, but has been shown to be effective in finding safe paths for all ships concerned in complex situations. The method has been applied to some typical test cases and the results are very encouraging
Demographic Dividends, Human Capital, and Saving.
The objective of this paper is to provide new evidence about the development effects of changes in population age structure and human and physical capital. This extends our previous work by developing and employing a more comprehensive model of demographic dividends. In addition, we extend earlier analysis about the quantity-quality tradeoff using newly available NTA data for 39 countries, in contrast to the nineteen with the necessary data in our 2010 study. This permits a more detailed analysis, treating public expenditures and private expenditures separately, and considering the role of per capita income as well as fertility and child dependency in relation to human capital spending. The analysis is used in a simulation with realistic demography to show how human capital investment has varied in relation to the changing demography from 1950 to the present, and how it might be expected to change over the rest of this century. These new estimates are then used in a more comprehensive model that incorporates both human and physical capital. The analysis provides estimates of the first and second demographic dividends and how they are affected by speed of fertility decline. The timing of the effects is documented and the relative importance of investment in physical and human capital is assessed. This improves our understanding of the economic implications of the demographic dividend and particularly the “second demographic dividend”
Instanton solutions mediating tunneling between the degenerate vacua in curved space
We investigate the instanton solution between the degenerate vacua in curved
space. We show that there exist -symmetric solutions not only in de
Sitter but also in both flat and anti-de Sitter space. The geometry of the new
type of solutions is finite and preserves the symmetry. The nontrivial
solution corresponding to the tunneling is possible only if gravity is taken
into account. The numerical solutions as well as the analytic computations
using the thin-wall approximation are presented. We expect that these solutions
do not have any negative mode as in the instanton solution.Comment: Some typos are corrected and references are added with respect to the
published version. 17pages, 11fi
Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy
We present a new method to characterize unresolved point sources (PSs),
generalizing traditional template fits to account for non-Poissonian photon
statistics. We apply this method to Fermi Large Area Telescope gamma-ray data
to characterize PS populations at high latitudes and in the Inner Galaxy. We
find that PSs (resolved and unresolved) account for ~50% of the total
extragalactic gamma-ray background in the energy range ~1.9 to 11.9 GeV. Within
10 of the Galactic Center with , we find that ~5-10%
of the flux can be accounted for by a population of unresolved PSs, distributed
consistently with the observed ~GeV gamma-ray excess in this region. The excess
is fully absorbed by such a population, in preference to dark-matter
annihilation. The inferred source population is dominated by near-threshold
sources, which may be detectable in future searches.Comment: 7+22 pages, 4+18 figures; v2, minor changes, new Pass 8 data analyzed
(conclusions unchanged); v3, PRL version, substantive improvements and
additional checks (conclusion unchanged
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Polymorphic Aβ42 fibrils adopt similar secondary structure but differ in cross-strand side chain stacking interactions within the same β-sheet.
Formation of polymorphic amyloid fibrils is a common feature in neurodegenerative diseases involving protein aggregation. In Alzheimer's disease, different fibril structures may be associated with different clinical sub-types. Structural basis of fibril polymorphism is thus important for understanding the role of amyloid fibrils in the pathogenesis and progression of these diseases. Here we studied two types of Aβ42 fibrils prepared under quiescent and agitated conditions. Quiescent Aβ42 fibrils adopt a long and twisted morphology, while agitated fibrils are short and straight, forming large bundles via lateral association. EPR studies of these two types of Aβ42 fibrils show that the secondary structure is similar in both fibril polymorphs. At the same time, agitated Aβ42 fibrils show stronger interactions between spin labels across the full range of the Aβ42 sequence, suggesting a more tightly packed structure. Our data suggest that cross-strand side chain packing interactions within the same β-sheet may play a critical role in the formation of polymorphic fibrils
Dyadosphere formed in gravitational collapse
We first recall the concept of Dyadosphere (electron-positron-photon plasma
around a formed black holes) and its motivation, and recall on (i) the Dirac
process: annihilation of electron-positron pairs to photons; (ii) the
Breit-Wheeler process: production of electron-positron pairs by photons with
the energy larger than electron-positron mass threshold; the
Sauter-Euler-Heisenberg effective Lagrangian and rate for the process of
electron-positron production in a constant electric field. We present a general
formula for the pair-production rate in the semi-classical treatment of quantum
mechanical tunneling. We also present in the Quantum Electro-Dynamics
framework, the calculations of the Schwinger rate and effective Lagrangian for
constant electromagnetic fields. We give a review on the electron-positron
plasma oscillation in constant electric fields, and its interaction with
photons leading to energy and number equipartition of photons, electrons and
positrons. The possibility of creating an overcritical field in astrophysical
condition is pointed out. We present the discussions and calculations on (i)
energy extraction from gravitational collapse; (ii) the formation of
Dyadosphere in gravitational collapsing process, and (iii) its hydrodynamical
expansion in Reissner Nordstr\"om geometry. We calculate the spectrum and flux
of photon radiation at the point of transparency, and make predictions for
short Gamma-Ray Bursts.Comment: 29 pages and 34 figure
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