943 research outputs found
Generalized Density-Functional Tight-Binding Repulsive Potentials from Unsupervised Machine Learning
We combine the approximate density-functional tight-binding (DFTB) method with unsupervised machine learning. This allows us to improve transferability and accuracy, make use of large quantum chemical data sets for the parametrization, and efficiently automatize the parametrization process of DFTB. For this purpose, generalized pair-potentials are introduced, where the chemical environment is included during the learning process, leading to more specific effective two-body potentials. We train on energies and forces of equilibrium and nonequilibrium structures of 2100 molecules, and test on ∼130 000 organic molecules containing O, N, C, H, and F atoms. Atomization energies of the reference method can be reproduced within an error of ∼2.6 kcal/mol, indicating drastic improvement over standard DFTB
A search for edge-on galaxy lenses in the CFHT Legacy Survey
[ABRIDGED] The new generation of wide field optical imaging like the Canada
France Hawaii Telescope Legacy Survey (CFHTLS) enables discoveries of all types
of gravitational lenses present in the sky. The Strong Lensing Legacy Survey
(SL2S) project has started an inventory, respectively for clusters or groups of
galaxies lenses, and for Einstein rings around distant massive ellipticals.
Here we attempt to extend this inventory by finding lensing events produced by
massive edge-on disk galaxies which remains a poorly documented class of
lenses. We implement and test an automated search procedure of edge-on galaxy
lenses in the CFHTLS Wide fields with magnitude 18Comment: several major edits, 8 pages, A&A accepte
Quantum point contact on graphite surface
The conductance through a quantum point contact created by a sharp and hard
metal tip on the graphite surface has features which to our knowledge have not
been encountered so far in metal contacts or in nanowires. In this paper we
first investigate these features which emerge from the strongly directional
bonding and electronic structure of graphite, and provide a theoretical
understanding for the electronic conduction through quantum point contacts. Our
study involves the molecular-dynamics simulations to reveal the variation of
interlayer distances and atomic structure at the proximity of the contact that
evolves by the tip pressing toward the surface. The effects of the elastic
deformation on the electronic structure, state density at the Fermi level, and
crystal potential are analyzed by performing self-consistent-field
pseudopotential calculations within the local-density approximation. It is
found that the metallicity of graphite increases under the uniaxial compressive
strain perpendicular to the basal plane. The quantum point contact is modeled
by a constriction with a realistic potential. The conductance is calculated by
representing the current transporting states in Laue representation, and the
variation of conductance with the evolution of contact is explained by taking
the characteristic features of graphite into account. It is shown that the
sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev.
B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12
LoRattle - An Exploratory Game with a Purpose Using LoRa and IoT
The Internet of Things (IoT) is opening new possibilities
for sensing, monitoring and actuating in urban environments. They sup port a shift to a hybrid network of humans and things collaborating in
production, transmission and processing of data through low-cost and
low power devices connected via long-range (LoRa) wide area networks
(WAN). This paper describes a 2-player duel game based on IoT con trollers and LoRa radio communication protocol. Here we report on the
main evaluation dimensions of this new design space for games, namely:
(i) game usability (SUS) leading to an above average score; (ii) affective
states of the players (SAM) depicting pleasant and engaging gameplay,
while players retain control; (iii) radio coverage perception (RCP) show ing that most participants did not change their perception of the radio
distance after playing. Finally, we discuss the findings and propose future
interactive applications to take advantage of this design space.info:eu-repo/semantics/publishedVersio
Hamlet and the fall of the Berlin wall : the myth of interventionist Shakespeare performance
The critical reception of Heiner Müller’s 1990 Hamlet/Maschine at the Deutsches Theater in East Berlin epitomizes a trend of crediting GDR Shakespeare performance with political influence. Drawing on rehearsal notes and reviews, Oliver challenges the interventionist Shakespeare myth, contrasting the Deutsches Theater’s political involvement with the impact of its Hamlet production on events surrounding the fall of the Berlin Wall. Shakespeare’s capacity for political intervention at this point was limited by theater practitioners’ reliance on public funding, their close relationships with governmental authority, and an underlying distrust of the masses. Ultimately, GDR artists proved useful to the 1989 protest movement because they occupied a unique position at the interface of dissidence and power
The Gas Content in Galactic Disks: Correlation with Kinematics
We consider the relationship between the total HI mass in late-type galaxies
and the kinematic properties of their disks. The mass for galaxies with
a wide variety of properties, from dwarf dIrr galaxies with active star
formation to giant low-brightness galaxies, is shown to correlate with the
product ( is the rotational velocity, and is the radial
photometric disks scale length), which characterizes the specific angular
momentum of the disk. This relationship, along with the anticorrelation between
the relative mass of HI in a galaxy and , can be explained in terms of the
previously made assumption that the gas density in the disks of most galaxies
is maintained at a level close to the threshold (marginal) stability of a
gaseous layer to local gravitational perturbations. In this case, the
regulation mechanism of the star formation rate associated with the growth of
local gravitational instability in the gaseous layer must play a crucial role
in the evolution of the gas content in the galactic disk.Comment: revised version to appear in Astronomy Letters, 8 pages, 5 EPS
figure
Observational Evidence Against Long-Lived Spiral Arms in Galaxies
We test whether the spiral patterns apparent in many large disk galaxies
should be thought of as dynamical features that are stationary in a co-rotating
frame for > t_{dyn}, as implied by the density wave approach for explaining
spiral arms. If such spiral arms have enhanced star formation (SF),
observational tracers for different stages of the SF sequence should show a
spatial ordering, from up-stream to downstream in the corotating frame: dense
HI, CO, tracing molecular hydrogen gas, 24 micron emission tracing enshrouded
SF and UV emission tracing unobscured young stars. We argue that such a spatial
ordering should be reflected in the angular cross-correlation (CC, in polar
coordinates) using all azimuthal positions among pairs of these tracers; the
peak of the CC should be offset from zero, in different directions inside and
outside the corotation radius. Recent spiral SF simulations by Dobbs & Pringle,
show explicitly that for the case of a stationary spiral arm potential such
angular offsets between gas and young stars of differing ages should be
observable as cross-correlation offsets. We calculate the angular
cross-correlations for different observational SF sequence tracers in 12 nearby
spiral galaxies, drawing on a data set with high quality maps of the neutral
gas HI, THINGS), molecular gas (CO, HERACLES) along with 24 micron emission
(Spitzer, SINGS); we include FUV images (GALEX) and 3.6 m emission
(Spitzer, IRAC) for some galaxies, tracing aging stars and longer timescales.
In none of the resulting tracer cross-correlations for this sample do we find
systematic angular offsets, which would be expected for a stationary dynamical
spiral pattern of well-defined pattern speed. This result indicates that spiral
density waves in their simplest form are not an important aspect of explaining
spirals in large disk galaxies.Comment: 13 pages, 16 figure
Microstructural degradation of Ti-45Al-8Nb alloy during the fabrication process by electron beam melting
Toward A Brain-Based Theory of Beauty
We wanted to learn whether activity in the same area(s) of the brain correlate with the experience of beauty derived from different sources. 21 subjects took part in a brain-scanning experiment using functional magnetic resonance imaging. Prior to the experiment, they viewed pictures of paintings and listened to musical excerpts, both of which they rated on a scale of 1-9, with 9 being the most beautiful. This allowed us to select three sets of stimuli-beautiful, indifferent and ugly-which subjects viewed and heard in the scanner, and rated at the end of each presentation. The results of a conjunction analysis of brain activity showed that, of the several areas that were active with each type of stimulus, only one cortical area, located in the medial orbito-frontal cortex (mOFC), was active during the experience of musical and visual beauty, with the activity produced by the experience of beauty derived from either source overlapping almost completely within it. The strength of activation in this part of the mOFC was proportional to the strength of the declared intensity of the experience of beauty. We conclude that, as far as activity in the brain is concerned, there is a faculty of beauty that is not dependent on the modality through which it is conveyed but which can be activated by at least two sources-musical and visual-and probably by other sources as well. This has led us to formulate a brain-based theory of beauty
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