5,423 research outputs found
Conjugacy of one-dimensional one-sided cellular automata is undecidable
Two cellular automata are strongly conjugate if there exists a
shift-commuting conjugacy between them. We prove that the following two sets of
pairs of one-dimensional one-sided cellular automata over a full shift
are recursively inseparable: (i) pairs where has strictly larger
topological entropy than , and (ii) pairs that are strongly conjugate and
have zero topological entropy.
Because there is no factor map from a lower entropy system to a higher
entropy one, and there is no embedding of a higher entropy system into a lower
entropy system, we also get as corollaries that the following decision problems
are undecidable: Given two one-dimensional one-sided cellular automata and
over a full shift: Are and conjugate? Is a factor of ? Is
a subsystem of ? All of these are undecidable in both strong and weak
variants (whether the homomorphism is required to commute with the shift or
not, respectively). It also immediately follows that these results hold for
one-dimensional two-sided cellular automata.Comment: 12 pages, 2 figures, accepted for SOFSEM 201
Adiabatic CMB perturbations in pre-big bang string cosmology
We consider the pre-big bang scenario with a massive axion field which starts
to dominate energy density when oscillating in an instanton-induced potential
and subsequently reheats the universe as it decays into photons, thus creating
adiabatic CMB perturbations. We find that the fluctuations in the axion field
can give rise to a nearly flat spectrum of adiabatic perturbations with a
spectral tilt in the range .Comment: 15 pages, 1 figure; Version to appear in Nucl.Phys.B. Figure
improved, discussion and one reference adde
LET-99 functions in the astral furrowing pathway, where it is required for myosin enrichment in the contractile ring.
The anaphase spindle determines the position of the cytokinesis furrow, such that the contractile ring assembles in an equatorial zone between the two spindle poles. Contractile ring formation is mediated by RhoA activation at the equator by the centralspindlin complex and midzone microtubules. Astral microtubules also inhibit RhoA accumulation at the poles. In the Caenorhabditis elegans one-cell embryo, the astral microtubule-dependent pathway requires anillin, NOP-1, and LET-99. LET-99 is well characterized for generating the asymmetric cortical localization of the Gα-dependent force-generating complex that positions the spindle during asymmetric division. However, whether the role of LET-99 in cytokinesis is specific to asymmetric division and whether it acts through Gα to promote furrowing are unclear. Here we show that LET-99 contributes to furrowing in both asymmetrically and symmetrically dividing cells, independent of its function in spindle positioning and Gα regulation. LET-99 acts in a pathway parallel to anillin and is required for myosin enrichment into the contractile ring. These and other results suggest a positive feedback model in which LET-99 localizes to the presumptive cleavage furrow in response to the spindle and myosin. Once positioned there, LET-99 enhances myosin accumulation to promote furrowing in both symmetrically and asymmetrically dividing cells
Searching for a holographic connection between dark energy and the low-l CMB multipoles
We consider the angular power spectrum in a finite universe with different
boundary conditions and perform a fit to the CMB, LSS and supernova data. A
finite universe could be the consequence of a holographic constraint, giving
rise to an effective IR cutoff at the future event horizon. In such a model
there is a cosmic duality relating the dark energy equation of state and the
power spectrum, which shows a suppression and oscillatory behaviour that is
found to describe the low l features extremely well. However, much of the
discussion here will also apply if we actually live inside an expanding bubble
that describes our universe. The best fit to the CMB and LSS data turns out to
be better than in the standard Lambda-CDM model, but when combined with the
supernova data, the holographic model becomes disfavored. We speculate on the
possible implications.Comment: 16 pages, 5 figures, to appear in JCA
On the Complexity of Limit Sets of Cellular Automata Associated with Probability Measures
We study the notion of limit sets of cellular automata associated with
probability measures (mu-limit sets). This notion was introduced by P. Kurka
and A. Maass. It is a refinement of the classical notion of omega-limit sets
dealing with the typical long term behavior of cellular automata. It focuses on
the words whose probability of appearance does not tend to 0 as time tends to
infinity (the persistent words). In this paper, we give a characterisation of
the persistent language for non sensible cellular automata associated with
Bernouilli measures. We also study the computational complexity of these
languages. We show that the persistent language can be non-recursive. But our
main result is that the set of quasi-nilpotent cellular automata (those with a
single configuration in their mu-limit set) is neither recursively enumerable
nor co-recursively enumerable
Reference-Plane Invariant Method for Measuring Electromagnetic Parameters of Materials
This paper presents a simple and effective wideband method for the
determination of material properties, such as the complex index of refraction
and the complex permittivity and permeability. The method is explicit
(non-iterative) and reference-plane invariant: it uses a certain combination of
scattering parameters in conjunction with group-velocity data. This technique
can be used to characterize both dielectric and magnetic materials. The
proposed method is verified experimentally within a frequency range between 2
to 18 GHz on polytetrafluoroethylene and polyvinylchloride samples. A
comprehensive error and stability analysis reveals that, similar to other
methods based on transmission/reflection measurement, the uncertainties are
larger at low frequencies and at the Fabry-Perot resonances.Comment: 12 pages, 21 figure
Mars Atmospheric and Climatic Survey System
Before Mars can be explored by humans, its extreme climate and environment must be investigated. This can be achieved through the deployment of weather station probes capable of measuring Martian air temperature, atmospheric pressure, relative humidity, and wind speed. The Mars Atmospheric and Climatic Survey System (MACSS) aims to collect this data, allowing predictive models of global climate patterns on Mars to be developed. These models will aid NASA in providing the needed knowledge to prepare for long-term exposure to the conditions on Mars.
The probes are compact and lightweight; they have been designed to withstand Mars’ harsh environment: extreme temperatures, statically-charged dust particles, a thin atmosphere, and intense solar radiation. Considerations of deployment were also made, with the size and weight of each probe allowing for them to be deployed as-needed and as accessories in future missions rather than simultaneously in a single mission.
With regards to components, solar panels are to supply the probes with primary power. Data would be collected by sensors and stored on a solid-state drive. A low-gain antenna would establish communication between the probes, NASA’s Deep Space Network, and Mars’ rovers and orbiters. This data can then be evaluated on Earth, allowing models of Martian climate to be formed. In order to demonstrate the feasibility of MACSS, a mockup was designed, simulating data collection in real time with Earth-equivalent components. With continued collaboration, MACSS and its probes can be further optimized for deployment to and longevity on Mars.https://scholarscompass.vcu.edu/capstone/1202/thumbnail.jp
On Scars
On Scars is a personal essay written about the varying perspectives of scars and my personal fascination with them. I was inspired by my own body\u27s scars and how people typically react to seeing them. I want readers to develop a deeper understanding about scars as a bodily phenomenon as well as an emotional representation beyond the stereotypes impressed by Western culture
The Role of Educational Experiences on the Development of Knowledge, Skills, and Dispositions of Successful Entrepreneurs in Hawai‘i.
Ed.D. Thesis. University of Hawaiʻi at Mānoa 2017
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