848 research outputs found
The Impact of Molecular Polarization on the Electronic Properties of Molecular Semiconductors
In a molecular semiconductor, the carrier is dressed with a polarization
cloud that we treat as a quantum field of Frenkel excitons coupled to it. The
consequences of the existence of this electronic polaron on the dynamics of an
extra charge in a material like pentacene can thus be evaluated.Comment: 7 pages, 1 figure, LaTe
Polarization effects in the channel of an organic field-effect transistor
We present the results of our calculation of the effects of dynamical
coupling of a charge-carrier to the electronic polarization and the
field-induced lattice displacements at the gate-interface of an organic
field-effect transistor (OFET). We find that these interactions reduce the
effective bandwidth of the charge-carrier in the quasi-two dimensional channel
of a pentacene transistor by a factor of two from its bulk value when the gate
is a high-permittivity dielectric such as
while this reduction essentially vanishes using a polymer gate-insulator. These
results demonstrate that carrier mass renormalization triggers the dielectric
effects on the mobility reported recently in OFETs.Comment: 19 pages, 3 figure
Supersolid phase with cold polar molecules on a triangular lattice
We study a system of heteronuclear molecules on a triangular lattice and
analyze the potential of this system for the experimental realization of a
supersolid phase. The ground state phase diagram contains superfluid, solid and
supersolid phases. At finite temperatures and strong interactions there is an
additional emulsion region, in contrast to similar models with short-range
interactions. We derive the maximal critical temperature and the
corresponding entropy for supersolidity and find feasible
experimental conditions for its realization.Comment: 4 pages, 4 figure
Few Shot Learning in Histopathological Images:Reducing the Need of Labeled Data on Biological Datasets
Although deep learning pathology diagnostic algorithms are proving comparable results with human experts in a wide variety of tasks, they still require a huge amount of well annotated data for training. Generating such extensive and well labelled datasets is time consuming and is not feasible for certain tasks and so, most of the medical datasets available are scarce in images and therefore, not enough for training. In this work we validate that the use of few shot learning techniques can transfer knowledge from a well defined source domain from Colon tissue into a more generic domain composed by Colon, Lung and Breast tissue by using very few training images. Our results show that our few-shot approach is able to obtain a balanced accuracy (BAC) of 90% with just 60 training images, even for the Lung and Breast tissues that were not present on the training set. This outperforms the finetune transfer learning approach that obtains 73% BAC with 60 images and requires 600 images to get up to 81% BAC.This study has received funding from the European
Union’s Horizon 2020 research and innovation programme
under grant agreement No. 732111 (PICCOLO project)
DSR as an explanation of cosmological structure
Deformed special relativity (DSR) is one of the possible realizations of a
varying speed of light (VSL). It deforms the usual quadratic dispersion
relations so that the speed of light becomes energy dependent, with preferred
frames avoided by postulating a non-linear representation of the Lorentz group.
The theory may be used to induce a varying speed of sound capable of generating
(near) scale-invariant density fluctuations, as discussed in a recent Letter.
We identify the non-linear representation of the Lorentz group that leads to
scale-invariance, finding a universal result. We also examine the higher order
field theory that could be set up to represent it
On A Cosmological Invariant as an Observational Probe in the Early Universe
k-essence scalar field models are usually taken to have lagrangians of the
form with some general function of
. Under certain conditions this lagrangian
in the context of the early universe can take the form of that of an oscillator
with time dependent frequency. The Ermakov invariant for a time dependent
oscillator in a cosmological scenario then leads to an invariant quadratic form
involving the Hubble parameter and the logarithm of the scale factor. In
principle, this invariant can lead to further observational probes for the
early universe. Moreover, if such an invariant can be observationally verified
then the presence of dark energy will also be indirectly confirmed.Comment: 4 pages, Revte
The four fixed points of scale invariant single field cosmological models
We introduce a new set of flow parameters to describe the time dependence of
the equation of state and the speed of sound in single field cosmological
models. A scale invariant power spectrum is produced if these flow parameters
satisfy specific dynamical equations. We analyze the flow of these parameters
and find four types of fixed points that encompass all known single field
models. Moreover, near each fixed point we uncover new models where the scale
invariance of the power spectrum relies on having simultaneously time varying
speed of sound and equation of state. We describe several distinctive new
models and discuss constraints from strong coupling and superluminality.Comment: 24 pages, 6 figure
Near Scale Invariance with Modified Dispersion Relations
We describe a novel mechanism to seed a nearly scale invariant spectrum of
adiabatic perturbations during a non-inflationary stage. It relies on a
modified dispersion relation that contains higher powers of the spatial
momentum of matter perturbations. We implement this idea in the context of a
massless scalar field in an otherwise perfectly homogeneous universe. The
couplings of the field to background scalars and tensors give rise to the
required modification of its dispersion relation, and the couplings of the
scalar to matter result in an adiabatic primordial spectrum. This work is meant
to explicitly illustrate that it is possible to seed nearly scale invariant
primordial spectra without inflation, within a conventional expansion history.Comment: 7 pages and no figures. Uses RevTeX
Dark Matter and Dark Energy
I briefly review our current understanding of dark matter and dark energy.
The first part of this paper focusses on issues pertaining to dark matter
including observational evidence for its existence, current constraints and the
`abundance of substructure' and `cuspy core' issues which arise in CDM. I also
briefly describe MOND. The second part of this review focusses on dark energy.
In this part I discuss the significance of the cosmological constant problem
which leads to a predicted value of the cosmological constant which is almost
times larger than the observed value \la/8\pi G \simeq
10^{-47}GeV. Setting \la to this small value ensures that the
acceleration of the universe is a fairly recent phenomenon giving rise to the
`cosmic coincidence' conundrum according to which we live during a special
epoch when the density in matter and \la are almost equal. Anthropic
arguments are briefly discussed but more emphasis is placed upon dynamical dark
energy models in which the equation of state is time dependent. These include
Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model
independent methods to determine the cosmic equation of state and the
Statefinder diagnostic are also discussed. The Statefinder has the attractive
property \atridot/a H^3 = 1 for LCDM, which is helpful for differentiating
between LCDM and rival dark energy models. The review ends with a brief
discussion of the fate of the universe in dark energy models.Comment: 40 pages, 11 figures, Lectures presented at the Second Aegean Summer
School on the Early Universe, Syros, Greece, September 2003, New References
added Final version to appear in the Proceeding
Spinors, Inflation, and Non-Singular Cyclic Cosmologies
We consider toy cosmological models in which a classical, homogeneous, spinor
field provides a dominant or sub-dominant contribution to the energy-momentum
tensor of a flat Friedmann-Robertson-Walker universe. We find that, if such a
field were to exist, appropriate choices of the spinor self-interaction would
generate a rich variety of behaviors, quite different from their widely studied
scalar field counterparts. We first discuss solutions that incorporate a stage
of cosmic inflation and estimate the primordial spectrum of density
perturbations seeded during such a stage. Inflation driven by a spinor field
turns out to be unappealing as it leads to a blue spectrum of perturbations and
requires considerable fine-tuning of parameters. We next find that, for simple,
quartic spinor self-interactions, non-singular cyclic cosmologies exist with
reasonable parameter choices. These solutions might eventually be incorporated
into a successful past- and future-eternal cosmological model free of
singularities. In an Appendix, we discuss the classical treatment of spinors
and argue that certain quantum systems might be approximated in terms of such
fields.Comment: 12 two-column pages, 3 figures; uses RevTeX
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