391 research outputs found
Ab Initio Electron-Phonon Interactions Using Atomic Orbital Wavefunctions
The interaction between electrons and lattice vibrations determines key
physical properties of materials, including their electrical and heat
transport, excited electron dynamics, phase transitions, and superconductivity.
We present a new ab initio method that employs atomic orbital (AO)
wavefunctions to compute the electron-phonon (e-ph) interactions in materials
and interpolate the e-ph coupling matrix elements to fine Brillouin zone grids.
We detail the numerical implementation of such AO-based e-ph calculations, and
benchmark them against direct density functional theory calculations and
Wannier function (WF) interpolation. The key advantages of AOs over WFs for
e-ph calculations are outlined. Since AOs are fixed basis functions associated
with the atoms, they circumvent the need to generate a material-specific
localized basis set with a trial-and-error approach, as is needed in WFs.
Therefore, AOs are ideal to compute e-ph interactions in chemically and
structurally complex materials for which WFs are challenging to generate, and
are also promising for high-throughput materials discovery. While our results
focus on AOs, the formalism we present generalizes e-ph calculations to
arbitrary localized basis sets, with WFs recovered as a special case
PASSATA - Object oriented numerical simulation software for adaptive optics
We present the last version of the PyrAmid Simulator Software for Adaptive
opTics Arcetri (PASSATA), an IDL and CUDA based object oriented software
developed in the Adaptive Optics group of the Arcetri observatory for
Monte-Carlo end-to-end adaptive optics simulations. The original aim of this
software was to evaluate the performance of a single conjugate adaptive optics
system for ground based telescope with a pyramid wavefront sensor. After some
years of development, the current version of PASSATA is able to simulate
several adaptive optics systems: single conjugate, multi conjugate and ground
layer, with Shack Hartmann and Pyramid wavefront sensors. It can simulate from
8m to 40m class telescopes, with diffraction limited and resolved sources at
finite or infinite distance from the pupil. The main advantages of this
software are the versatility given by the object oriented approach and the
speed given by the CUDA implementation of the most computational demanding
routines. We describe the software with its last developments and present some
examples of application.Comment: 9 pages, 2 figures, 3 tables. SPIE conference Astronomical Telescopes
and Instrumentation, 26 June - 01 July 2016, Edinburgh, Scotland, United
Kingdo
Infinite impulse response modal filtering in visible adaptive optics
Diffraction limited resolution adaptive optics (AO) correction in visible
wavelengths requires a high performance control. In this paper we investigate
infinite impulse response filters that optimize the wavefront correction: we
tested these algorithms through full numerical simulations of a
single-conjugate AO system comprising an adaptive secondary mirror with 1127
actuators and a pyramid wavefront sensor (WFS). The actual practicability of
the algorithms depends on both robustness and knowledge of the real system:
errors in the system model may even worsen the performance. In particular we
checked the robustness of the algorithms in different conditions, proving that
the proposed method can reject both disturbance and calibration errors
Charge Transport in Organic Molecular Semiconductors from First Principles: The Band-Like Hole Mobility in Naphthalene Crystal
Predicting charge transport in organic molecular crystals is notoriously
challenging. Carrier mobility calculations in organic semiconductors are
dominated by quantum chemistry methods based on charge hopping, which are
laborious and only moderately accurate. We compute from first principles the
electron-phonon scattering and the phonon-limited hole mobility of naphthalene
crystal in the framework of ab initio band theory. Our calculations combine GW
electronic bandstructures, ab initio electron-phonon scattering, and the
Boltzmann transport equation. The calculated hole mobility is in very good
agreement with experiment between 100300 K, and we can predict its
temperature dependence with high accuracy. We show that scattering between
inter-molecular phonons and holes regulates the mobility, though
intra-molecular phonons possess the strongest coupling with holes. We revisit
the common belief that only rigid molecular motions affect carrier dynamics in
organic molecular crystals. Our work provides a quantitative and rigorous
framework to compute charge transport in organic crystals, and is a first step
toward reconciling band theory and carrier hopping computational methods.Comment: 7 pages, 4 figures, Accepted by Phys. Rev.
Joint Image and 3D Shape Part Representation in Large Collections for Object Blending
We propose a new approach to perform object shape retrieval from images, it can handle the
shape of the part of the object and combine parts from different sources to find a different 3D shape. Our
method creates a common representation for images and 3D models that enables mixing elements from
both kinds of inputs. Our approach automatically extracts the desired part and its 3D shape from each source
without the need of annotations. There are many applications to combining parts from images and 3D models,
for example, performing smart online catalogue searches by selecting the parts that we are looking for from
images or 3D models and retrieve a 3D shape that has the desired arrangement of parts. Our approach is
capable of obtaining the shape of the parts of an object from an image in the wild, independently of the pose
of the object and without the need of annotations of any kind
Leydig Cell Tumour and Mature Ovarian Teratoma: Rare Androgen-Secreting Ovarian Tumours in Postmenopausal Women
Androgen-secreting ovarian tumours are extremely rare accounting for <5% of all ovarian neoplasms. They are more frequent in postmenopausal women and should be suspected in the case of a rapid onset of androgenic symptoms. We report 4 cases of postmenopausal women who presented with signs of virilisation. All patients revealed increased serum levels of testosterone, normal dehydroepiandrosterone-sulfate and negative pelvic ultrasound for adnexal masses. An androgen-secreting ovarian tumour was suspected and all of them were submitted to bilateral oophorectomy. Histology confirmed the diagnosis of Leydig cell tumours in 3 patients and mature teratoma in 1. A successful response to surgery, which includes a decline in serum androgen levels and signs of hyperandrogenism, was observed in our patients. This case series demonstrates that androgen-secreting ovarian neoplasms may not be detectable by imaging studies, but should be considered in the differential diagnosis of all postmenopausal women with signs of hyperandrogenism.info:eu-repo/semantics/publishedVersio
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