1,463 research outputs found
Signal Transmission Across Tile Assemblies: 3D Static Tiles Simulate Active Self-Assembly by 2D Signal-Passing Tiles
The 2-Handed Assembly Model (2HAM) is a tile-based self-assembly model in
which, typically beginning from single tiles, arbitrarily large aggregations of
static tiles combine in pairs to form structures. The Signal-passing Tile
Assembly Model (STAM) is an extension of the 2HAM in which the tiles are
dynamically changing components which are able to alter their binding domains
as they bind together. For our first result, we demonstrate useful techniques
and transformations for converting an arbitrarily complex STAM tile set
into an STAM tile set where every tile has a constant, low amount of
complexity, in terms of the number and types of ``signals'' they can send, with
a trade off in scale factor.
Using these simplifications, we prove that for each temperature
there exists a 3D tile set in the 2HAM which is intrinsically universal for the
class of all 2D STAM systems at temperature (where the STAM does
not make use of the STAM's power of glue deactivation and assembly breaking, as
the tile components of the 2HAM are static and unable to change or break
bonds). This means that there is a single tile set in the 3D 2HAM which
can, for an arbitrarily complex STAM system , be configured with a
single input configuration which causes to exactly simulate at a scale
factor dependent upon . Furthermore, this simulation uses only two planes of
the third dimension. This implies that there exists a 3D tile set at
temperature in the 2HAM which is intrinsically universal for the class of
all 2D STAM systems at temperature . Moreover, we show that for each
temperature there exists an STAM tile set which is intrinsically
universal for the class of all 2D STAM systems at temperature ,
including the case where .Comment: A condensed version of this paper will appear in a special issue of
Natural Computing for papers from DNA 19. This full version contains proofs
not seen in the published versio
Performance of the neutron polarimeter NPOL3 for high resolution measurements
We describe the neutron polarimeter NPOL3 for the measurement of polarization
transfer observables with a typical high resolution of 300 keV
at 200 MeV.
The NPOL3 system consists of three planes of neutron detectors.
The first two planes for neutron polarization analysis are made of 20 sets of
one-dimensional position-sensitive plastic scintillation counters with a size
of 100 cm 10 cm 5 cm, and they cover the area of 100
100 .
The last plane for detecting doubly scattered neutrons or recoiled protons is
made of the two-dimensional position-sensitive liquid scintillation counter
with a size of 100 cm 100 cm 10 cm.
The effective analyzing powers and double scattering
efficiencies were measured by using the three kinds
of polarized neutrons from the , , and reactions at = 198 MeV.
The performance of NPOL3 defined as
are similar to that of the
Indiana Neutron POLarimeter (INPOL) by taking into account for the counter
configuration difference between these two neutron polarimeters.Comment: 28 pages, 18 figures, submitted to Nucl. Instrum. Methods Phys. Res.
Linac modeling for external beam radiotherapy quality assurance using a dedicated 2D pixelated detector
International audienceQuality assurance is a key issue in intensity modulated radiotherapy. Errors can occur in the dose delivery process induces significant differences between the planned treatment and the delivered one. In this context, the Medical Application Physics group of the LPSC is developing TraDeRa (Transparent Detector for Radiotherapy), a 2D pixelated matrix of ionization chambers located upstream to the patient. The signal map obtained with TraDeRa has to be processed to provide medical observables to quantify the quality of the treatment delivery. This relies on accurate Monte Carlo simulations benchmarked with measurements performed under a linear accelerator (Linac).The work described in this paper lies in the optimization of the Linac head simulation and the development of an innovative Monte Carlo/measurements comparison method to perform an accurate enough model of the X-ray production device. An optimized parametrization of the particles transport allowed an increase of the simulation efficiency by a factor 3. The characteristics of an electron beam of a reference Linac were matched with the simulation results by using dose deposition of the created X-ray beam in a water tank. Two parameters are particularly critical: the nominal energy of the electrons and the radial distribution of impact on the target. The innovative method was able to provide within minutes those two parameters for any Linac, achieving, for example, a 10 keV precision on the energy determination for a 6 MV operating Linac
A New Approach to Background Subtraction in Low-Energy Neutrino Experiments
We discuss a new method to extract neutrino signals in low energy
experiments. In this scheme the symmetric nature of most backgrounds allows for
direct cancellation from data. The application of this technique to the Palo
Verde reactor neutrino oscillation experiment allowed us to reduce the
measurement errors on the anti-neutrino flux from % to %. We
expect this method to substantially improve the data quality in future low
background experiments such as KamLAND and LENS.Comment: 7 pages, 2 figure
Fast preparation route to high-performances textured Sr-doped Ca 3 Co 4 O 9 thermoelectric materials through precursor powder modification
This work presents a short and very efficientmethod to produce high performance textured Ca3Co4O9thermoelectric materials through initial powders modifica-tion. Microstructure has shown good grain orientation, andlow porosity while slightly lower grain sizes were obtained insamples prepared from attrition milled powders. All samplesshow the high density of around 96% of the theoretical value.These similar characteristics are reflected in, approximately,the same electrical resistivity and Seebeck coefficient valuesfor both types of samples. However, in spite of similar powerfactor (PF) at low temperatures, it is slightly higher at hightemperature for the attrition milled samples. On the otherhand, the processing time reduction (from 38 to 2 h) whenusing attrition milled precursors, leads to lower mechanicalproperties in these samples. All these data clearly point out tothe similar characteristics of both kinds of samples, with adrastic processing time decrease when using attrition milledprecursors, which is of the main economic importance whenconsidering their industrial production
EDGE: The shape of dark matter haloes in the faintest galaxies
Collisionless Dark Matter Only (DMO) structure formation simulations predict
that Dark Matter (DM) haloes are prolate in their centres and triaxial towards
their outskirts. The addition of gas condensation transforms the central DM
shape to be rounder and more oblate. It is not clear, however, whether such
shape transformations occur in `ultra-faint' dwarfs, which have extremely low
baryon fractions. We present the first study of the shape and velocity
anisotropy of ultra-faint dwarf galaxies that have gas mass fractions of
. These dwarfs are drawn from the
Engineering Dwarfs at Galaxy formation's Edge (EDGE) project, using high
resolution simulations that allow us to resolve DM halo shapes within the half
light radius (pc). We show that gas-poor ultra-faints (M; ) retain
their pristine prolate DM halo shape even when gas, star formation and feedback
are included. This could provide a new and robust test of DM models. By
contrast, gas-rich ultra-faints (M;
) become rounder and more oblate within half
light radii. Finally, we find that most of our simulated dwarfs have
significant radial velocity anisotropy that rises to at
. The one exception is a dwarf that forms a rotating
gas/stellar disc because of a planar, major merger. Such strong anisotropy
should be taken into account when building mass models of gas-poor
ultra-faints.Comment: 16 pages and 11 figures (excluding appendices), accepted by MNRA
Predicting Neutron Production from Cosmic-ray Muons
Fast neutrons from cosmic-ray muons are an important background to
underground low energy experiments. The estimate of such background is often
hampered by the difficulty of measuring and calculating neutron production with
sufficient accuracy. Indeed substantial disagreement exists between the
different analytical calculations performed so far, while data reported by
different experiments is not always consistent. We discuss a new unified
approach to estimate the neutron yield, the energy spectrum, the multiplicity
and the angular distribution from cosmic muons using the Monte Carlo simulation
package FLUKA and show that it gives a good description of most of the existing
measurements once the appropriate corrections have been applied.Comment: 8 pages, 7 figure
EDGE: the puzzling ellipticity of Eridanus II's star cluster and its implications for dark matter at the heart of an ultra-faint dwarf
The Eridanus II (EriII) 'ultra-faint' dwarf has a large () and
low mass () star cluster (SC) offset from its
centre by in projection. Its size and offset are naturally
explained if EriII has a central dark matter core, but such a core may be
challenging to explain in a CDM cosmology. In this paper, we revisit
the survival and evolution of EriII's SC, focussing for the first time on its
puzzlingly large ellipticity (). We perform a suite of
960 direct -body simulations of SCs, orbiting within a range of spherical
background potentials fit to ultra-faint dwarf (UFD) galaxy simulations. We
find only two scenarios that come close to explaining EriII's SC. In the first,
EriII has a low density dark matter core (of size and
density ). In this
model, the high ellipticity of EriII's SC is set at birth, with the lack of
tidal forces in the core allowing its ellipticity to remain frozen in for long
times. In the second, EriII's SC orbits in a partial core, with its high
ellipticity owing to its imminent tidal destruction. However, this latter model
struggles to reproduce the large size of EriII's SC, and it predicts
substantial tidal tails around EriII's SC that should have already been seen in
the data. This leads us to favour the cored model. We discuss potential caveats
to these findings, and the implications of the cored model for galaxy formation
and the nature of dark matter.Comment: 16 pages, 12 figures + appendices. Published with MNRAS. Comments
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The discovery of an M4+T8.5 binary system
The original article can be found at: http://www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14620.xWe report the discovery of a T8.5 dwarf, which is a companion to the M4 dwarf Wolf 940. [Please see original online abstract for complete version with correct notation]Peer reviewe
A fiber injection unit for the Keck Planet Imager and Characterizer (KPIC)
Coupling a high-contrast imaging instrument to a high-resolution spectrograph has the potential to enable the most detailed characterization of exoplanet atmospheres, including spin measurements and Doppler mapping. The high-contrast imaging system serves as a spatial filter to separate the light from the star and the planet while the high-resolution spectrograph acts as a spectral filter, which differentiates between features in the stellar and planetary spectra. The Keck Planet Imager and Characterizer (KPIC) located downstream from the current W. M. Keck II adaptive optics (AO) system will contain a fiber injection unit (FIU) combining a high-contrast imaging system and a fiber feed to Keck’s high resolution infrared spectrograph NIRSPEC. Resolved thermal emission from known young giant exoplanets will be injected into a single-mode fiber linked to NIRSPEC, thereby allowing the spectral characterization of their atmospheres. Moreover, the resolution of NIRSPEC (R = 37,500) is high enough to enable spin measurements and Doppler imaging of atmospheric weather phenomenon. The module will be integrated and tested at Caltech before being transferred to Keck in 2018
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