3,467 research outputs found
On-surface and Subsurface Adsorption of Oxygen on Stepped Ag(210) and Ag(410) Surfaces
The adsorption of atomic oxygen and its inclusion into subsurface sites on
Ag(210) and Ag(410) surfaces have been investigated using density functional
theory. We find that--in the absence of adatoms on the first metal
layer--subsurface adsorption results in strong lattice distortion which makes
it energetically unfavoured. However subsurface sites are significantly
stabilised when a sufficient amount of O adatoms is present on the surface. At
high enough O coverage on the Ag(210) surface the mixed on-surface + subsurface
O adsorption is energetically favoured with respect to the on-surface only
adsorption. Instead, on the Ag(410) surface, at the coverage we have considered
(3/8 ML), the existence of stable terrace sites makes the subsurface O
incorporation less favourable. These findings are compatible with the results
of recent HREEL experiments which have actually motivated this work.Comment: 8 pages, 4 figures and 1 tabl
First week is editorial, second week is algorithmic : platform gatekeepers and the platformization of music curation
This article investigates the logics that underpin music curation, and particularly the work of music curators, working at digital music streaming platforms. Based on ethnographic research that combines participant observation and a set of interviews with key informants, the article questions the relationship between algorithmic and human curation and the specific workings of music curation as a form of platform gatekeeping. We argue that music streaming platforms in combining proprietary algorithms and human curators constitute the \u201cnew gatekeepers\u201d in an industry previously dominated by human intermediaries such as radio programmers, journalists, and other experts. The article suggests understanding this gatekeeping activity as a form of \u201calgo-torial power\u201d that has the ability to set the \u201clistening agendas\u201d of global music consumers. While the power of traditional gatekeepers was mainly of an editorial nature, albeit data had some relevance in orienting their choices, the power of platform gatekepeers is an editorial power \u201caugmented\u201d and enhanced by algorithms and big data. Platform gatekeepers have more data, more tools to manage and to make sense of these data, and thus more power than their predecessors. Platformization of music curation then consists of a data-intense gatekeeping activity, based on different mixes of algo-torial logics, that produces new regimes of visibility. This makes the platform capitalistic model potentially more efficient than industrial capitalism in transforming audience attention into data and data into commodities
Topological invariants in interacting Quantum Spin Hall: a Cluster Perturbation Theory approach
Using Cluster Perturbation Theory we calculate Green's functions,
quasi-particle energies and topological invariants for interacting electrons on
a 2-D honeycomb lattice, with intrinsic spin-orbit coupling and on-site e-e
interaction. This allows to define the parameter range (Hubbard U vs spin-orbit
coupling) where the 2D system behaves as a trivial insulator or Quantum Spin
Hall insulator. This behavior is confirmed by the existence of gapless
quasi-particle states in honeycomb ribbons. We have discussed the importance of
the cluster symmetry and the effects of the lack of full translation symmetry
typical of CPT and of most Quantum Cluster approaches. Comments on the limits
of applicability of the method are also provided.Comment: 7 pages, 7 figures: discussion improved, one figure added, references
updated. Matches version published in New J. Phy
Parietal maps of visual signals for bodily action planning
The posterior parietal cortex (PPC) has long been understood as a high-level integrative station for computing motor commands for the body based on sensory (i.e., mostly tactile and visual) input from the outside world. In the last decade, accumulating evidence has shown that the parietal areas not only extract the pragmatic features of manipulable objects, but also subserve sensorimotor processing of others’ actions. A paradigmatic case is that of the anterior intraparietal area (AIP), which encodes the identity of observed manipulative actions that afford potential motor actions the observer could perform in response to them. On these bases, we propose an AIP manipulative action-based template of the general planning functions of the PPC and review existing evidence supporting the extension of this model to other PPC regions and to a wider set of actions: defensive and locomotor actions. In our model, a hallmark of PPC functioning is the processing of information about the physical and social world to encode potential bodily actions appropriate for the current context. We further extend the model to actions performed with man-made objects (e.g., tools) and artifacts, because they become integral parts of the subject’s body schema and motor repertoire. Finally, we conclude that existing evidence supports a generally conserved neural circuitry that transforms integrated sensory signals into the variety of bodily actions that primates are capable of preparing and performing to interact with their physical and social world
Chronic neural probe for simultaneous recording of single-unit, multi-unit, and local field potential activity from multiple brain sites
Drug resistant focal epilepsy can be treated by resecting the epileptic focus
requiring a precise focus localization using stereoelectroencephalography
(SEEG) probes. As commercial SEEG probes offer only a limited spatial
resolution, probes of higher channel count and design freedom enabling the
incorporation of macro and microelectrodes would help increasing spatial
resolution and thus open new perspectives for investigating mechanisms
underlying focal epilepsy and its treatment. This work describes a new
fabrication process for SEEG probes with materials and dimensions similar to
clinical probes enabling recording single neuron activity at high spatial
resolution. Polyimide is used as a biocompatible flexible substrate into which
platinum electrodes and leads are...
The resulting probe features match those of clinically approved devices.
Tests in saline solution confirmed the probe stability and functionality.
Probes were implanted into the brain of one monkey (Macaca mulatta), trained to
perform different motor tasks. Suitable configurations including up to 128
electrode sites allow the recording of task-related neuronal signals. Probes
with 32 and 64 electrode sites were implanted in the posterior parietal cortex.
Local field potentials and multi-unit activity were recorded as early as one
hour after implantation. Stable single-unit activity was achieved for up to 26
days after implantation of a 64-channel probe. All recorded signals showed
modulation during task execution. With the novel probes it is possible to
record stable biologically relevant data over a time span exceeding the usual
time needed for epileptic focus localization in human patients. This is the
first time that single units are recorded along cylindrical polyimide probes
chronically implanted 22 mm deep into the brain of a monkey, which suggests the
potential usefulness of this probe for human applications
Evaluation of an automatic gas chromatographic system for the identification of bacterial infective agents
The potential clinical application of gas chromatography to
microbial identifcation was evaluated. A completely automated
system, the MIS (Microbial Identification System; Hewlett-
Packard) can analyse and identify pure strains by comparison of
their cellular fatty acids patterns (C9-C20) with the reference
parameters stored in a library. Three hundred and sixty-seven
strains were tested, comparing the gas chromatographic results
with those obtained by the traditional microbiological methods in
the bacteriology laboratory of our Institute. A standardized
extractive procedure was followed to obtain the fatty acid methyl
esters (FAMEs), but some modifications to the recommended
procedure were introduced in the bacterial growth procedures:
colonies harvested not only from the recommended growth media but
also from selective media routinely used in the bacteriology
laboratory were successfully examined. These modifications did not
influence the results but improved the ease for the user; good
agreement with the comparison method was observed as far as
identifications of genus and species are concerned for 238 cases.
The major advantages of this computerized system are a reduction
in the time required to obtain the final results, the elimination of
human errors by using the autosampler and a better inter-laboratory
comparability of results owing to a higher degree of objectivity. On
the other hand, the limited throughput of MIS (only 40 samples in
24 h) prevents its use in a large routine laboratory; this technology
is appropriate in emergency cases, in taxonomic studies and as a
confirmatory method
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