7,420 research outputs found
Simple factorization of unitary transformations
We demonstrate a method for general linear optical networks that allows one
to factorize any SU() matrix in terms of two SU( blocks coupled by an
SU(2) entangling beam splitter. The process can be recursively continued in an
efficient way, ending in a tidy arrangement of SU(2) transformations. The
method hinges only on a linear relationship between input and output states,
and can thus be applied to a variety of scenarios, such as microwaves,
acoustics, and quantum fields.Comment: 5 pages, 4 figures. Comments welcome
Geomorphology and surface geology of Mount St. Helens volcano
Acknowledgments This work has been supported by SAGES (Scottish Alliance for Geosciences Environment and Society) Small Grants Scheme and the Jack Kleinman Grant for Volcano Research to travel to the US and perform fieldwork necessary for the realization and interpretation of the map. Thanks to the Associate Editor, Prof. Knight and the reviewers Dr. Heike Apps, Mr. Adolfo Quesada and Dr. Guido Ventura for their constructive comments and suggestions. Thanks to Alexa Van Eaton, J. J. Major and R. Waitt for their suggestions and Corrado Palucci for fieldwork assistance.Peer reviewedPublisher PD
The Tiered Radio Extragalactic Continuum Simulation (T-RECS)
We present the Tiered Radio Extragalactic Continuum Simulation (T-RECS): a
new simulation of the radio sky in continuum, over the 150 MHz-20 GHz range.
T-RECS models two main populations of radio galaxies: Active Galactic Nuclei
(AGNs) and Star-Forming Galaxies (SFGs), and corresponding sub-populations. Our
model also includes polarized emission over the full frequency range, which has
been characterised statistically for each population using the available
information. We model the clustering properties in terms of probability
distributions of hosting halo masses, and use lightcones extracted from a
high-resolution cosmological simulation to determine the positions of haloes.
This limits the sky area for the simulations including clustering to a 25deg2
field of view. We compare luminosity functions, number counts in total
intensity and polarization, and clustering properties of our outputs to
up-to-date compilations of data and find a very good agreement. We deliver a
set of simulated catalogues, as well as the code to produce them, which can be
used for simulating observations and predicting results from deep radio surveys
with existing and forthcoming radio facilities, such as the Square Kilometre
Array (SKA).Comment: 20 pages, 11 figures, accepted by MNRA
Finite dimensional corrections to mean field in a short-range p-spin glassy model
In this work we discuss a short range version of the -spin model. The
model is provided with a parameter that allows to control the crossover with
the mean field behaviour. We detect a discrepancy between the perturbative
approach and numerical simulation. We attribute it to non-perturbative effects
due to the finite probability that each particular realization of the disorder
allows for the formation of regions where the system is less frustrated and
locally freezes at a higher temperature.Comment: 18 pages, 5 figures, submitted to Phys Rev
Irreversible thermodynamics of open chemical networks I: Emergent cycles and broken conservation laws
In this and a companion paper we outline a general framework for the
thermodynamic description of open chemical reaction networks, with special
regard to metabolic networks regulating cellular physiology and biochemical
functions. We first introduce closed networks "in a box", whose thermodynamics
is subjected to strict physical constraints: the mass-action law, elementarity
of processes, and detailed balance. We further digress on the role of solvents
and on the seemingly unacknowledged property of network independence of free
energy landscapes. We then open the system by assuming that the concentrations
of certain substrate species (the chemostats) are fixed, whether because
promptly regulated by the environment via contact with reservoirs, or because
nearly constant in a time window. As a result, the system is driven out of
equilibrium. A rich algebraic and topological structure ensues in the network
of internal species: Emergent irreversible cycles are associated to
nonvanishing affinities, whose symmetries are dictated by the breakage of
conservation laws. These central results are resumed in the relation between the number of fundamental affinities , that of broken
conservation laws and the number of chemostats . We decompose the
steady state entropy production rate in terms of fundamental fluxes and
affinities in the spirit of Schnakenberg's theory of network thermodynamics,
paving the way for the forthcoming treatment of the linear regime, of
efficiency and tight coupling, of free energy transduction and of thermodynamic
constraints for network reconstruction.Comment: 18 page
High performance bilayer-graphene Terahertz detectors
We report bilayer-graphene field effect transistors operating as THz
broadband photodetectors based on plasma-waves excitation. By employing
wide-gate geometries or buried gate configurations, we achieve a responsivity
and a noise equivalent power in the 0.29-0.38 THz range, in photovoltage and photocurrent mode.
The potential of this technology for scalability to higher frequencies and the
development of flexible devices makes our approach competitive for a future
generation of THz detection systems.Comment: 8 pages, 5 figures. Submitted to Applied Physics Letter
Meaningful characterisation of perturbative theoretical uncertainties
We consider the problem of assigning a meaningful degree of belief to
uncertainty estimates of perturbative series. We analyse the assumptions which
are implicit in the conventional estimates made using renormalisation scale
variations. We then formulate a Bayesian model that, given equivalent initial
hypotheses, allows one to characterise a perturbative theoretical uncertainty
in a rigorous way in terms of a credibility interval for the remainder of the
series. We compare its outcome to the conventional uncertainty estimates in the
simple case of the calculation of QCD corrections to the e+e- -> hadrons
process. We find comparable results, but with important conceptual differences.
This work represents a first step in the direction of a more comprehensive and
rigorous handling of theoretical uncertainties in perturbative calculations
used in high energy phenomenology.Comment: 28 pages, 5 figures. Language modified in order to make it more
'bayesian'. No change in results. Version published in JHE
The dramatic size evolution of elliptical galaxies and the quasar feedback
Observations have evidenced that passively evolving massive galaxies at high
redshift are much more compact than local galaxies with the same stellar mass.
We argue that the observed strong evolution in size is directly related to the
quasar feedback, which removes huge amounts of cold gas from the central
regions in a Salpeter time, inducing an expansion of the stellar distribution.
The new equilibrium configuration, with a size increased by a factor >~ 3, is
attained after ~ 40 dynamical times, corresponding to ~ 2 Gyr. This means that
massive galaxies observed at z >~ 1 will settle on the Fundamental Plane by z ~
0.8-1. In less massive galaxies (M_star <~ 2 10^10 M_sun), the nuclear feedback
is subdominant, and the mass loss is mainly due to stellar winds. In this case,
the mass loss timescale is longer than the dynamical time and results in
adiabatic expansion that may increase the effective radius by a factor of up to
~ 2 in 10 Gyr, although a growth by a factor of ~ 1.6 occurs within the first
0.5 Gyr. Since observations are focused on relatively old galaxies, with ages
>~ 1 Gyr, the evolution for smaller galaxies is more difficult to perceive.
Significant evolution of velocity dispersion is predicted for both small and
large galaxies.Comment: 4 pages, 2 figures, uses REVTeX4 + emulateapj.cls and apjfonts.sty.
Accepted by ApJ
Role of fetal MRI in the evaluation of isolated and non-isolated corpus callosum dysgenesis: results of a cross-sectional study
PURPOSE:
The aims of this study were to characterize isolated and non-isolated forms of corpus callosum dysgenesis (CCD) at fetal magnetic resonance imaging (MRI) and to identify early predictors of associated anomalies.
METHODS:
We retrospectively analyzed 104 fetuses with CCD undergoing MRI between 2006 and 2016. Corpus callosum, cavum septi pellucidi, biometry, presence of ventriculomegaly, gyration anomalies, cranio-encephalic abnormalities and body malformations were evaluated. Results of genetic tests were also recorded.
RESULTS:
At MRI, isolated CCD was 26.9%, the rest being associated to other abnormalities. In the isolated group, median gestational age at MRI was lower in complete agenesis than in hypoplasia (22 vs 28 weeks). In the group with additional findings, cortical dysplasia was the most frequently associated feature (P = 0.008), with a more frequent occurrence in complete agenesis (70%) versus other forms; mesial frontal lobes were more often involved than other cortical regions (P = 0.006), with polymicrogyria as the most frequent cortical malformation (40%). Multivariate analysis confirmed the association between complete agenesis and cortical dysplasia (odds ratio = 7.29, 95% confidence interval 1.51-35.21).
CONCLUSIONS:
CCD is often complicated by other intra-cranial and extra-cranial findings (cortical dysplasias as the most prevalent) that significantly affect the postnatal prognosis. The present study showed CCD with associated anomalies as more frequent than isolated (73.1%). In isolated forms, severe ventriculomegaly was a reliable herald of future appearance of associated features
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