5,842 research outputs found
THE UNSYSTEMATIC SURVIVAL OF SYSTEMS: THE PARASITE, THE JOKER AND THE BRICOLEUR IN MICHEL SERRES AND CLAUDE LEVI-STRAUSS
With our increasing reliance on systems from information theory to economics, it is important to understand how systems are constructed, how they break down and how they preserve themselves. The philosopher Michel Serres in his work The Parasite showed how systems can never preserve their order in a pure manner; they always involve noise and lost signals. He explores this by employing the idea of parasitism from biology. But the problem remains of how systems maintain themselves in the face of parasitism. This paper will explore the concept of bricolage conceived by structural anthropologist Claude Levi-Strauss in his seminal work The Savage Mind. This concept can be found within a single ambiguous quotation by Serres in The Parasite, but remains undeveloped. This article will therefore develop these connections between bricolage and parasitism, and show how bricolage is important to the adaptation of any system to change
Comparison of |Q|=1 and |Q|=2 gauge-field configurations on the lattice four-torus
It is known that exactly self-dual gauge-field configurations with
topological charge |Q|=1 cannot exist on the untwisted continuum 4-torus. We
explore the manifestation of this remarkable fact on the lattice 4-torus for
SU(3) using advanced techniques for controlling lattice discretization errors,
extending earlier work of De Forcrand et. al. for SU(2). We identify three
distinct signals for the instability of |Q|=1 configurations, and show that
these manifest themselves early in the cooling process, long before the
would-be instanton has shrunk to a size comparable to the lattice
discretization threshold. These signals do not appear for our |Q|=2
configurations. This indicates that these signals reflect the truly global
nature of the instability, rather than local discretization effects.
Monte-Carlo generated SU(3) gauge field configurations are cooled to the
self-dual limit using an O(a^4)-improved gauge action chosen to have small but
positive O(a^6) errors. This choice prevents lattice discretization errors from
destroying instantons provided their size exceeds the dislocation threshold of
the cooling algorithm. Lattice discretization errors are evaluated by comparing
the O(a^4)-improved gauge-field action with an O(a^4)-improved action
constructed from the square of an O(a^4)-improved lattice field-strength
tensor, thus having different O(a^6) discretization errors. The number of
action-density peaks, the instanton size and the topological charge of
configurations is monitored. We observe a fluctuation in the total topological
charge of |Q|=1 configurations, and demonstrate that the onset of this unusual
behavior corresponds with the disappearance of multiple-peaks in the action
density. At the same time discretization errors are minimal.Comment: 12 pages, 9 figures, submitted to Phys. Rev.
Navigability Analysis of Natural Terrains with Fuzzy Elevation Maps from Ground-based 3D Range Scans
Mobile robot navigation through natural terrains is a challenging issue with applications such as planetary exploration or search and rescue. This paper proposes navigability assessment of natural terrains scanned from ground-based 3D laser rangefinders. A continuous model of the terrain is obtained as a fuzzy elevation map (FEM). Based on this model, the proposed solution incorporates terrain navigability both in terms of uncertainties of the 3D input data and slope of the fuzzy surface. Moreover, the paper discusses the application of this method for local path planning. For this purpose, the Bug algorithm has been adapted to compute local paths on the navigable region of the FEM. The method has been applied to actual 3D point clouds on two different experimental sites.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech.
This work was partially supported by the Spanish CICYT project DPI 2011-22443 and the Andalusian project PE-2010 TEP-6101
Molecular mechanism of Gαi activation by non-GPCR proteins with a Gα-Binding and Activating motif
Heterotrimeric G proteins are quintessential signalling switches activated by nucleotide exchange on Gα. Although activation is predominantly carried out by G-protein-coupled receptors (GPCRs), non-receptor guanine-nucleotide exchange factors (GEFs) have emerged as critical signalling molecules and therapeutic targets. Here we characterize the molecular mechanism of G-protein activation by a family of non-receptor GEFs containing a Gα-binding and -activating (GBA) motif. We combine NMR spectroscopy, computational modelling and biochemistry to map changes in Gα caused by binding of GBA proteins with residue-level resolution. We find that the GBA motif binds to the SwitchII/α3 cleft of Gα and induces changes in the G-1/P-loop and G-2 boxes (involved in phosphate binding), but not in the G-4/G-5 boxes (guanine binding). Our findings reveal that G-protein-binding and activation mechanisms are fundamentally different between GBA proteins and GPCRs, and that GEF-mediated perturbation of nucleotide phosphate binding is sufficient for Gα activation
Supportingâelectrolyteâfree electrochemical methoxymethylation of alcohols using a 3Dâprinted electrosynthesis continuous flow cell system
We describe the development of a novel lowâcost smallâfootprint 3Dâprinted electrosynthesis continuous flow cell system that was designed and adapted to fit a commercially available Electrasyn 2.0. The utility and effectiveness of the combined flow/electrochemistry system over the batch process was demonstrated in the development of an improved and supportingâelectrolyteâfree version of our anodic methoxymethylation of alcohols
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Transcriptome-pathology correlation identifies interplay between TDP-43 and the expression of its kinase CK1E in sporadic ALS.
Sporadic amyotrophic lateral sclerosis (sALS) is the most common form of ALS, however, the molecular mechanisms underlying cellular damage and motor neuron degeneration remain elusive. To identify molecular signatures of sALS we performed genome-wide expression profiling in laser capture microdissection-enriched surviving motor neurons (MNs) from lumbar spinal cords of sALS patients with rostral onset and caudal progression. After correcting for immunological background, we discover a highly specific gene expression signature for sALS that is associated with phosphorylated TDP-43 (pTDP-43) pathology. Transcriptome-pathology correlation identified casein kinase 1Δ (CSNK1E) mRNA as tightly correlated to levels of pTDP-43 in sALS patients. Enhanced crosslinking and immunoprecipitation in human sALS patient- and healthy control-derived frontal cortex, revealed that TDP-43 binds directly to and regulates the expression of CSNK1E mRNA. Additionally, we were able to show that pTDP-43 itself binds RNA. CK1E, the protein product of CSNK1E, in turn interacts with TDP-43 and promotes cytoplasmic accumulation of pTDP-43 in human stem-cell-derived MNs. Pathological TDP-43 phosphorylation is therefore, reciprocally regulated by CK1E activity and TDP-43 RNA binding. Our framework of transcriptome-pathology correlations identifies candidate genes with relevance to novel mechanisms of neurodegeneration
MIRA: Mental Imagery for Robotic Affordances
Humans form mental images of 3D scenes to support counterfactual imagination,
planning, and motor control. Our abilities to predict the appearance and
affordance of the scene from previously unobserved viewpoints aid us in
performing manipulation tasks (e.g., 6-DoF kitting) with a level of ease that
is currently out of reach for existing robot learning frameworks. In this work,
we aim to build artificial systems that can analogously plan actions on top of
imagined images. To this end, we introduce Mental Imagery for Robotic
Affordances (MIRA), an action reasoning framework that optimizes actions with
novel-view synthesis and affordance prediction in the loop. Given a set of 2D
RGB images, MIRA builds a consistent 3D scene representation, through which we
synthesize novel orthographic views amenable to pixel-wise affordances
prediction for action optimization. We illustrate how this optimization process
enables us to generalize to unseen out-of-plane rotations for 6-DoF robotic
manipulation tasks given a limited number of demonstrations, paving the way
toward machines that autonomously learn to understand the world around them for
planning actions.Comment: CoRL 2022, webpage: https://yenchenlin.me/mir
Eta bound states in nuclei: a probe of flavour-singlet dynamics
We argue that eta bound states in nuclei are sensitive to the singlet
component in the eta. The bigger the singlet component, the more attraction and
the greater the binding. Thus, measurements of eta bound states will yield new
information about axial U(1) dynamics and glue in mesons. Eta - etaprime mixing
plays an important role in understanding the value of the eta-nucleon
scattering length.Comment: 8 pages, version to appear in PL
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