1,006 research outputs found
Permutation-invariant distance between atomic configurations
We present a permutation-invariant distance between atomic configurations,
defined through a functional representation of atomic positions. This distance
enables to directly compare different atomic environments with an arbitrary
number of particles, without going through a space of reduced dimensionality
(i.e. fingerprints) as an intermediate step. Moreover, this distance is
naturally invariant through permutations of atoms, avoiding the time consuming
associated minimization required by other common criteria (like the Root Mean
Square Distance). Finally, the invariance through global rotations is accounted
for by a minimization procedure in the space of rotations solved by Monte Carlo
simulated annealing. A formal framework is also introduced, showing that the
distance we propose verifies the property of a metric on the space of atomic
configurations. Two examples of applications are proposed. The first one
consists in evaluating faithfulness of some fingerprints (or descriptors), i.e.
their capacity to represent the structural information of a configuration. The
second application concerns structural analysis, where our distance proves to
be efficient in discriminating different local structures and even classifying
their degree of similarity
Surface-induced near-field scaling in the Knudsen layer of a rarefied gas
We report on experiments performed within the Knudsen boundary layer of a
low-pressure gas. The non-invasive probe we use is a suspended
nano-electro-mechanical string (NEMS), which interacts with He gas at
cryogenic temperatures. When the pressure is decreased, a reduction of the
damping force below molecular friction had been first reported in
Phys. Rev. Lett. Vol 113, 136101 (2014) and never reproduced since. We
demonstrate that this effect is independent of geometry, but dependent on
temperature. Within the framework of kinetic theory, this reduction is
interpreted as a rarefaction phenomenon, carried through the boundary layer by
a deviation from the usual Maxwell-Boltzmann equilibrium distribution induced
by surface scattering. Adsorbed atoms are shown to play a key role in the
process, which explains why room temperature data fail to reproduce it.Comment: Article plus supplementary materia
Representation of Indigenous peoples in climate change reporting
This article examines how newspapers reporting on climate change have covered and framed Indigenous peoples. Focusing on eight newspapers in Canada, the USA, Australia, and New Zealand, we examine articles published from 1995 to 2015, and analyze them using content and framing analyses. The impacts of climate change are portrayed as having severe ecological, sociocultural, and health/safety impacts for Indigenous peoples, who are often framed as victims and “harbingers” of climate change. There is a strong focus on stories reporting on the Arctic. The lack of substantive discussion of colonialism or marginalization in the reviewed stories limits media portrayal of the structural roots of vulnerability, rendering climate change as a problem for, rather than of society. Indigenous and traditional knowledge is widely discussed, but principally as a means of corroborating scientific knowledge, or in accordance with romanticized portrayals of Indigenous peoples. Widespread disparities in the volume, content, and framing of coverage are also observed across the four nations
Sur l'équation indéterminée en nombres entiers différents de zéro, quand est fractionnaire et sur une équation analogue plus générale
On the thermodynamic limit of form factors in the massless XXZ Heisenberg chain
We consider the problem of computing form factors of the massless XXZ
Heisenberg spin-1/2 chain in a magnetic field in the (thermodynamic) limit
where the size M of the chain becomes large. For that purpose, we take the
particular example of the matrix element of the third component of spin between
the ground state and an excited state with one particle and one hole located at
the opposite ends of the Fermi interval (umklapp-type term). We exhibit its
power-law decrease in terms of the size of the chain M, and compute the
corresponding exponent and amplitude. As a consequence, we show that this form
factor is directly related to the amplitude of the leading oscillating term in
the long-distance asymptotic expansion of the two-point correlation function of
the third component of spin.Comment: 28 page
Large distance asymptotic behavior of the emptiness formation probability of the XXZ spin-1/2 Heisenberg chain
Using its multiple integral representation, we compute the large distance
asymptotic behavior of the emptiness formation probability of the XXZ spin-1/2
Heisenberg chain in the massless regime.Comment: LPENSL-TH-10, 8 page
Domain wall partition functions and KP
We observe that the partition function of the six vertex model on a finite
square lattice with domain wall boundary conditions is (a restriction of) a KP
tau function and express it as an expectation value of charged free fermions
(up to an overall normalization).Comment: 16 pages, LaTeX2
The R-matrix structure of the Euler-Calogero-Moser model
We construct the -matrix for the generalization of the Calogero-Moser
system introduced by Gibbons and Hermsen. By reduction procedures we obtain the
-matrix for the Euler-Calogero-Moser model and for the standard
Calogero-Moser model.Comment: 7 page
Computation of dynamical correlation functions of Heisenberg chains in a field
We compute the momentum- and frequency-dependent longitudinal spin structure
factor for the one-dimensional spin-1/2 Heisenberg spin chain in a
magnetic field, using exact determinant representations for form factors on the
lattice. Multiparticle contributions are computed numerically throughout the
Brillouin zone, yielding saturation of the sum rule to high precision.Comment: 4 pages, 14 figure
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