38,562 research outputs found
On the type species of Aubignyna and a description of A. hamblensis, a new microforaminifer from temperate shallow waters
The genus Aubignyna Margerel, 1970 (type A. mariei) was originally described from the upper Pliocene of NW France. Examination and re-illustration of topotypes of A. mariei Margerel, 1970, the holotype of Buccella planidorso Atkinson, 1969 (from the Recent of Cardigan Bay, Wales) and syntypes of Rotalia perlucida Heron-Allen and Earland, 1913 (from the Clare Island Survey, western Ireland) shows them to be conspecific. Consequently, the type-species of Aubignyna becomes R. perlucida, for which a lectotype is chosen. A new species of microforaminifera formally described here is assigned to Aubignyna and shown to occur in a wide range of intertidal - shallow subtidal, brackish - normal marine estuaries and lagoons in Europe and North America
Situational reasoning for road driving in an urban environment
Robot navigation in urban environments requires situational reasoning.
Given the complexity of the environment and the behavior specified by traffic
rules, it is necessary to recognize the current situation to impose the correct
traffic rules. In an attempt to manage the complexity of the situational reasoning
subsystem, this paper describes a finite state machine model to govern the situational
reasoning process. The logic state machine and its interaction with the
planning system are discussed. The approach was implemented on Alice, Team
Caltech’s entry into the 2007 DARPA Urban Challenge. Results from the qualifying
rounds are discussed. The approach is validated and the shortcomings of
the implementation are identified
Polarization Structures in the Thomson-Scattered Emission Lines in Active Galactic Nuclei
A line photon incident in an electron-scattering medium is transferred in a
diffusive way both in real space and in frequency space, and the mean number of
scatterings changes as the wavelength shifts from the line center. This leads
to the profile broadening and polarization dependence on the wavelength shift
as a function of the Thomson optical depth . We find that the
polarization of the Thomson-scattered emission lines has a dip around the line
center when does not exceed a few. Various structures such as the
polarization flip are also seen. An application to an ionized halo component
surrounding the broad emission line region in active galactic nuclei is
considered and it is found that the polarization structures may still persist.
Brief discussions on observational implications are given.Comment: 14 pages, 3 figures, accepted for publication in ApJ Letter
Machine Assisted Proof of ARMv7 Instruction Level Isolation Properties
In this paper, we formally verify security properties of the ARMv7 Instruction Set Architecture (ISA) for user mode executions.
To obtain guarantees that arbitrary (and unknown) user processes are able to run isolated from privileged software and other user processes, instruction level noninterference and integrity properties are provided, along with proofs that transitions to privileged modes can only occur in a controlled manner.
This work establishes a main requirement for operating system and hypervisor verification, as demonstrated for the PROSPER separation kernel. The proof is performed in the HOL4 theorem prover, taking the Cambridge model of ARM as basis.
To this end, a proof tool has been developed, which assists the verification of relational state predicates semi-automatically
Memory-Controlled Diffusion
Memory effects require for their incorporation into random-walk models an
extension of the conventional equations. The linear Fokker-Planck equation for
the probability density is generalized to include non-linear and
non-local spatial-temporal memory effects. The realization of the memory
kernels are restricted due the conservation of the basic quantity . A
general criteria is given for the existence of stationary solutions. In case
the memory kernel depends on polynomially the transport is prevented. Owing
to the delay effects a finite amount of particles remains localized and the
further transport is terminated. For diffusion with non-linear memory effects
we find an exact solution in the long-time limit. Although the mean square
displacement shows diffusive behavior, higher order cumulants exhibits
differences to diffusion and they depend on the memory strength
Migration and proliferation dichotomy in tumor cell invasion
We propose a two-component reaction-transport model for the
migration-proliferation dichotomy in the spreading of tumor cells. By using a
continuous time random walk (CTRW) we formulate a system of the balance
equations for the cancer cells of two phenotypes with random switching between
cell proliferation and migration. The transport process is formulated in terms
of the CTRW with an arbitrary waiting time distribution law. Proliferation is
modeled by a standard logistic growth. We apply hyperbolic scaling and
Hamilton-Jacobi formalism to determine the overall rate of tumor cell invasion.
In particular, we take into account both normal diffusion and anomalous
transport (subdiffusion) in order to show that the standard diffusion
approximation for migration leads to overestimation of the overall cancer
spreading rate.Comment: 9 page
Velocity fluctuations of noisy reaction fronts propagating into a metastable state: testing theory in stochastic simulations
The position of a reaction front, propagating into a metastable state,
fluctuates because of the shot noise of reactions and diffusion. A recent
theory [B. Meerson, P.V. Sasorov, and Y. Kaplan, Phys. Rev. E 84, 011147
(2011)] gave a closed analytic expression for the front diffusion coefficient
in the weak noise limit. Here we test this theory in stochastic simulations
involving reacting and diffusing particles on a one-dimensional lattice. We
also investigate a small noise-induced systematic shift of the front velocity
compared to the prediction from the spatially continuous deterministic
reaction-diffusion equation.Comment: 5 pages, 5 figure
Dynamical Effects from Asteroid Belts for Planetary Systems
The orbital evolution and stability of planetary systems with interaction
from the belts is studied using the standard phase-plane analysis. In addition
to the fixed point which corresponds to the Keplerian orbit, there are other
fixed points around the inner and outer edges of the belt. Our results show
that for the planets, the probability to move stably around the inner edge is
larger than the one to move around the outer edge. It is also interesting that
there is a limit cycle of semi-attractor for a particular case. Applying our
results to the Solar System, we find that our results could provide a natural
mechanism to do the orbit rearrangement for the larger Kuiper Belt Objects and
thus successfully explain the absence of these objects beyond 50 AU.Comment: accepted by International Journal of Bifurcation and Chaos in Aug.
2003, AAS Latex, 27 pages with 6 color figure
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