268 research outputs found
The Desert Home or the Adventures of a Lost Family in the Wilderness
https://commons.und.edu/settler-literature/1033/thumbnail.jp
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When the path is never shortest: a reality check on shortest path biocomputation
Shortest path problems are a touchstone for evaluating the computing
performance and functional range of novel computing substrates. Much has been
published in recent years regarding the use of biocomputers to solve minimal
path problems such as route optimisation and labyrinth navigation, but their
outputs are typically difficult to reproduce and somewhat abstract in nature,
suggesting that both experimental design and analysis in the field require
standardising. This chapter details laboratory experimental data which probe
the path finding process in two single-celled protistic model organisms,
Physarum polycephalum and Paramecium caudatum, comprising a shortest path
problem and labyrinth navigation, respectively. The results presented
illustrate several of the key difficulties that are encountered in categorising
biological behaviours in the language of computing, including biological
variability, non-halting operations and adverse reactions to experimental
stimuli. It is concluded that neither organism examined are able to efficiently
or reproducibly solve shortest path problems in the specific experimental
conditions that were tested. Data presented are contextualised with biological
theory and design principles for maximising the usefulness of experimental
biocomputer prototypes.Comment: To appear in: Adamatzky, A (Ed.) Shortest path solvers. From software
to wetware. Springer, 201
Navigating Digital Ethics for Rural Research : Guidelines and recommendations for researchers and administrators of social media groups
This document was produced as a deliverable of the research project âNavigating Digital Ethics for Rural Research: Guidelines and recommendations for researchers and administrators of social media groupsâ (DigiEthics). Digiethics is a transdisciplinary project seeking to advance digital ethics by co-designing guidelines for engaging Facebook groups. This project was funded by the by the British Academy Early Career Research Network Scotland Hub Seed Fund 2023. This document is available online with background information at: https://www.hutton.ac.uk/research/ projects/digiethics-navigating-digital-ethics-rural-research If you have read/used this document and you have any comments or feedback you would like to share with us, we would love to hear from you. Please contact [email protected] PD
Evolved star water maser cloud size determined by star size
Cool, evolved stars undergo copious mass loss but the details of how the
matter is returned to the ISM are still under debate. We investigated the
structure and evolution of the wind at 5 to 50 stellar radii from Asymptotic
Giant Branch and Red Supergiant stars. 22-GHz water masers around seven evolved
stars were imaged using MERLIN, at sub-AU resolution. Each source was observed
at between 2 and 7 epochs (several stellar periods). We compared our results
with long-term Pushchino single dish monitoring. The 22-GHz emission is located
in ~spherical, thick, unevenly filled shells. The outflow velocity doubles
between the inner and outer shell limits. Water maser clumps could be matched
at successive epochs separated by <2 years for AGB stars, or at least 5 years
for RSG. This is much shorter than the decades taken for the wind to cross the
maser shell, and comparison with spectral monitoring shows that some features
fade and reappear. In 5 sources, most of the matched features brighten or dim
in concert from one epoch to the next. One cloud in W Hya was caught in the act
of passing in front of a background cloud leading to 50-fold, transient
amplification. The masing clouds are 1-2 orders of magnitude denser than the
wind average and contain a substantial fraction of the mass loss in this
region, with a filling factor <1%. The RSG clouds are ~10x bigger than those
round the AGB stars. Proper motions are dominated by expansion, with no
systematic rotation. The maser clouds survive for decades (the shell crossing
time) but the masers are not always beamed in our direction. Radiative effects
cause changes in flux density throughout the maser shells on short timescales.
Cloud size is proportional to parent star size; clouds have a similar radius to
the star in the 22-GHz maser shell. Stellar properties such as convection cells
must determine the clumping scale.Comment: Accepted by A&A 2012 July 10 Main text 29 pages, 62 figures Appendix
44 pages, 23 figure
HRC-I/Chandra X-ray observations towards sigma Orionis
Aims: We investigated the X-ray emission from young stars and brown dwarfs in
the sigma Orionis cluster (tau~3 Ma, d~385 pc) and its relation to mass,
presence of circumstellar discs, and separation to the cluster centre by taking
advantage of the superb spatial resolution of the Chandra X-ray Observatory.
Methods: We used public HRC-I/Chandra data from a 97.6 ks pointing towards the
cluster centre and complemented them with X-ray data from IPC/Einstein,
HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and
infrared photometry and spectroscopy from the literature and public catalogues.
On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and
searched for short-term variability. We also looked for long-term variability
by comparing with previous X-ray observations. Results: Among the 107 detected
X-ray sources, there were 70 cluster stars with known signposts of youth, two
young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two
galaxies with optical-infrared counterpart. The remaining sources had
extragalactic nature. Based on a robust Poisson-chi^2 analysis, nine cluster
stars displayed flares or rotational modulation during the HRC-I observations,
while other eight stars and one brown dwarf showed long-term X-ray flux
variations. We constructed a cluster X-ray luminosity function from O9.5 (~18
Msol) to M6.5 (~0.06 Msol). We found: a tendency of early-type stars in
multiple systems or with spectroscopic peculiarities to display X-ray emission,
that the two detected brown dwarfs and the least-massive star are among the
sigma Orionis objects with the highest L_X/L_J ratios, and that a large
fraction of known classical T Tauri stars in the cluster are absent in this and
other X-ray surveys. We concluded that dozens X-ray sigma Orionis stars and
brown dwarfs are still to be detected [abridged].Comment: A&A, in pres
Slime mould: The fundamental mechanisms of biological cognition
© 2018 Elsevier B.V. The slime mould Physarum polycephalum has been used in developing unconventional computing devices for in which the slime mould played a role of a sensing, actuating, and computing device. These devices treated the slime mould as an active living substrate, yet it is a self-consistent living creature which evolved over millions of years and occupied most parts of the world, but in any case, that living entity did not own true cognition, just automated biochemical mechanisms. To ârehabilitateâ slime mould from the rank of a purely living electronics element to a âcreature of thoughtsâ we are analyzing the cognitive potential of P. polycephalum. We base our theory of minimal cognition of the slime mould on a bottom-up approach, from the biological and biophysical nature of the slime mould and its regulatory systems using frameworks such as Lyon's biogenic cognition, Muller, di Primio-LengelerĆ modifiable pathways, Bateson's âpatterns that connectâ framework, Maturana's autopoietic network, or proto-consciousness and Morgan's Canon
Towards a Physarum learning chip
Networks of protoplasmic tubes of organism Physarum polycehpalum are macro-scale structures which optimally span multiple food sources to avoid repellents yet maximize coverage of attractants. When data are presented by configurations of attractants and behaviour of the slime mould is tuned by a range of repellents, the organism preforms computation. It maps given data configuration into a protoplasmic network. To discover physical means of programming the slime mould computers we explore conductivity of the protoplasmic tubes; proposing that the network connectivity of protoplasmic tubes shows pathway-dependent plasticity. To demonstrate this we encourage the slime mould to span a grid of electrodes and apply AC stimuli to the network. Learning and weighted connections within a grid of electrodes is produced using negative and positive voltage stimulation of the network at desired nodes; low frequency (10 Hz) sinusoidal (0.5 V peak-to-peak) voltage increases connectivity between stimulated electrodes while decreasing connectivity elsewhere, high frequency (1000 Hz) sinusoidal (2.5 V peak-to-peak) voltage stimulation decreases network connectivity between stimulated electrodes. We corroborate in a particle model. This phenomenon may be used for computation in the same way that neural networks process information and has the potential to shed light on the dynamics of learning and information processing in non-neural metazoan somatic cell networks
Intermediate to low-mass stellar content of Westerlund 1
We have analysed near-infrared NTT/SofI observations of the starburst cluster
Westerlund 1, which is among the most massive young clusters in the Milky Way.
A comparison of colour-magnitude diagrams with theoretical main-sequence and
pre-main sequence evolutionary tracks yields improved extinction and distance
estimates of A_Ks = 1.13+-0.03 mag and d = 3.55+-0.17 kpc (DM = 12.75+-0.10
mag). The pre-main sequence population is best fit by a Palla & Stahler
isochrone for an age of 3.2 Myr, while the main sequence population is in
agreement with a cluster age of 3 to 5 Myr. An analysis of the structural
parameters of the cluster yields that the half-mass radius of the cluster
population increases towards lower mass, indicative of the presence of mass
segregation. The cluster is clearly elongated with an eccentricity of 0.20 for
stars with masses between 10 and 32 Msun, and 0.15 for stars with masses in the
range 3 to 10 Msun. We derive the slope of the stellar mass function for stars
with masses between 3.4 and 27 Msun. In an annulus with radii between 0.75 and
1.5 pc from the cluster centre, we obtain a slope of Gamma = -1.3. Closer in,
the mass function of Westerlund 1 is shallower with Gamma = -0.6. The
extrapolation of the mass function for stars with masses from 0.08 to 120 Msun
yields an initial total stellar mass of ~52,000 Msun, and a present-day mass of
20,000 to 45,000 Msun (about 10 times the stellar mass of the Orion Nebula
Cluster, and 2 to 4 times the mass of the NGC 3603 young cluster), indicating
that Westerlund 1 is the most massive starburst cluster identified to date in
the Milky Way.Comment: 15 pages, jpg figures, uses aa.cls and graphicx, accepted for
publication in A&
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