671 research outputs found
Reduction of deltaic channel mobility by tidal action under rising relative sea level
As Holocene river deltas continue to experience sea-level rise, sediment carried by distributary channels counteracts delta-plain drowning. Many deltas worldwide are subject to tidal action, which strongly affects the morphology of distributary channels and could also influence their mobility. Here we show, through physical laboratory experiments, that distributary-channel mobility can be dramatically reduced in systems affected by tides in comparison to an identical system with no tides, and that the mobility of distributary channels decreases as the ratio of tidal to fluvial energy increases. This effect occurs even if new accommodation space is created by rising relative sea level. By analyzing synthetic stratigraphy derived from both digital elevation data and time-lapse photography, we show also that the reduction of channel mobility in tidal deltas increases channel stacking and connectivity in the stratigraphic record
Authenticity of Ecuadorian Commercial Honeys
Control of honey frauds is needed in Ecuador to protect bee keepers and consumers because simple syrups and new syrups with eucalyptus are sold as genuine honeys. Authenticity of Ecuadorian commercial honeys was tested with a vortex emulsion consisting on one volume of honey:water (1:1) dilution, and two volumes of diethyl ether. This method allows a separation of phases in one minute to discriminate genuine honeys that form three phase and fake honeys that form two phases; 34 of the 42 honeys analyzed from five provinces of Ecuador were genuine. This was confirmed with 1H NMR spectra of honey dilutions in deuterated water with an enhanced amino acid region with signals for proline, phenylalanine and tyrosine. Classic quality indicators were also tested with this method (sugars, HMF), indicators of fermentation (ethanol, acetic acid), and residues of citric acid used in the syrup manufacture. One of the honeys gave a false positive for genuine, being an admixture of genuine honey with added syrup, evident for the high sucrose. Sensory analysis was the final confirmation to recognize the honey groups studied here, namely honey produced in combs by Apis mellifera, fake honey, and honey produced in cerumen pots by Geotrigona, Melipona, and Scaptotrigona. Chloroform extractions of honey were also done to search lipophilic additives in NMR spectra. This is a valuable contribution to protect honey consumers, and to develop the beekeeping industry in Ecuador
Vascular remodeling after endovascular treatment: quantitative analysis of medical images with a focus on aorta
In the last years, the convergence of advanced imaging techniques and endovascular procedures
has revolutionized the practice of vascular surgery. However, regardless the anatomical
district, several complications still occur after endovascular treatment and the impact of endovascular
repair on vessel morphology remains unclear. Starting from this background, the
aim of this thesis is to ll the gaps in the eld of vessel remodeling after endovascular procedure.
Main focus of the work will be the repair of the aorta and, in particular thoracic and
thoracoabdominal treatments. Furthermore an investigation of the impact of endovascular
repair on femoro-popliteal arterial segment will be reported in the present work. Analyses of
medical images will been conducted to extract anatomical geometric features and to compare
the changes in morphology before treatment and during follow-up.
After illustrating in detail the aims and the outline of the dissertation in Chapter 1, Chapter
2 will concern the anatomy and the physiology of the aorta along with the main aortic
pathologies and the related surgical treatments. Subsequently, an overview of the medical
image techniques for segmentation and vessel geometric quantication will be provided.
Chapter 3 will introduce the concept of remodeling of the aorta after endovascular procedure.
In particular, two types of aortic remodeling will be considered. On one side remodeling can
be seen as the shrinkage of the aneurysmal sac or false lumen thrombosis. On the other side,
aortic remodeling could be seen as the changes in the aortic morphology following endograft
placement which could lead to complications.
Chapter 4 will illustrate a study regarding the analysis of medical images to measure the geometrical
changes in the pathological aorta during follow-up in patients with thoracoabdominal
aortic aneurysms treated with endovascular procedure using a novel uncovered device, the Cardiatis
Multilayer Flow Modulator.
Chapter 5 will focus on the geometrical remodeling of the aortic arch and descending aorta in
patients who underwent hybrid arch treatment to treat thoracic aneurysms. The goal of the
work is to develop a pipeline for the processing of pre-operative and post-operative Computed
Tomography images in order to detect the changes in the aortic arch physiological curvature
due to endograft insertion.
Chapter 6 will focuse on the use of 3D printing technology as valuable tool to support patient's
follow-up. In particular, we report a case of a patient originally treated with endovascular
procedure for type B aortic dissection and which experimented several complications during
follow-up. 3D printing technology is used to show the remodeling of the aortic vasculature
during time.
Chapter 7 will concern patient-specic nite element simulations of aortic endovascular procedure.
In particular, starting from a clinical case where complication developed during followup,
the predictive value of computational simulations will be shown.
Chapter 8 will illustrate a study concerning the evaluation of morphological changes of the
femoro-popliteal arterial segment due to limb exion in patients undergoing endovascular
treatment of popliteal artery aneurysms
The Classical Solution for the Bosonic String in the Presence of Three D-branes Rotated by Arbitrary SO(4) Elements
We consider the classical instantonic contribution to the open string
configuration associated with three D-branes with relative rotation matrices in
SO(4) which corresponds to the computation of the classical part of the
correlator of three non Abelian twist fields. We write the classical solution
as a sum of a product of two hypergeometric functions. Differently from all the
previous cases with three D-branes, the solution is not holomorphic and
suggests that the classical bosonic string knows when the configuration may be
supersymmetric. We show how this configuration reduces to the standard Abelian
twist field computation. From the phenomenological point of view, the Yukawa
couplings between chiral matter at the intersection in this configuration are
more suppressed with respect to the factorized case in the literature.Comment: 41 pages, 8 figure
2D fermion on the strip with boundary defects as a CFT with excited spin fields
We consider a two-dimensional fermion on the strip in the presence of an arbitrary number of zero-dimensional boundary changing defects. We show that the theory is still conformal with time dependent stress-energy tensor and that the allowed defects can be understood as excited spin fields. Finally we compute correlation functions involving these excited spin fields without using bosonization
Field migration rates of tidal meanders recapitulate fluvial morphodynamics
The majority of tidal channels display marked meandering features.
Despite their importance in oil-reservoir formation and
tidal landscape morphology, questions remain on whether tidalmeander
dynamics could be understood in terms of fluvial processes
and theory. Key differences suggest otherwise, like the
periodic reversal of landscape-forming tidal flows and the widely
accepted empirical notion that tidal meanders are stable landscape
features, in stark contrast with their migrating fluvial counterparts.
On the contrary, here we show that, once properly
normalized, observed migration rates of tidal and fluvial meanders
are remarkably similar. Key to normalization is the role of
tidal channel width that responds to the strong spatial gradients
of landscape-forming flow rates and tidal prisms. We find that
migration dynamics of tidal meanders agree with nonlinear theories
for river meander evolution. Our results challenge the conventional
view of tidal channels as stable landscape features and
suggest that meandering tidal channels recapitulate many fluvial
counterparts owing to large gradients of tidal prisms across meander
wavelengths
Experimental delta evolution in tidal environments: Morphologic response to relative sea\u2010level rise and net deposition
Tide-influenced deltas are among the largest depositional features on Earth and are ecologically and economically im-portant as they support large populations. However, the continued rise in relative sea level threatens the sustainability of these land-scapes and calls for new insights on their morphological response. While field studies of ancient deposits allow for insight into deltaevolution during times of eustatic adjustment, tide-influenced deltas are notoriously hard to identify in the rock record. We present asuite of physical experiments aimed at investigating the morphological response of tide-influenced deltas subject to relative sea-levelrise. We show that increasing relative tidal energy changes the response of the delta because tides effectively act to remove fluviallydeposited sediment from the delta topset. This leads to enhanced transgression, which we quantify via a new methodology for com-paring shoreline transgression rates based on the concept of a\u2018transgression anomaly\u2019relative to a simple reference case. We alsoshow that stronger tidal forcing can create composite deltas where distinct land-forming processes dominate different areas of thedelta plain, shaping characteristic morphological features. The net effect of tidal action is to enhance seaward transfer of bedloadsediment, resulting in greater shoreline transgression compared to identical, yet purely fluvial, deltaic systems that exhibit static oreven regressive shorelines
On the Origin of Divergences in Time-Dependent Orbifolds
We consider time-dependent orbifolds in String Theory and we show that
divergences are not associated with a gravitational backreaction since they
appear in the open string sector too. They are related to the non existence of
the underlying effective field theory as in several cases fourth and higher
order contact terms do not exist. Since contact terms may arise from the
exchange of string massive states, we investigate and show that some three
points amplitudes with one massive state in the open string sector are
divergent on the time-dependent orbifolds. To check that divergences are
associated with the existence of a discrete zero eigenvalue of the Laplacian of
the subspace with vanishing volume, we construct the Generalized Null Boost
Orbifold where this phenomenon can be turned on and off.Comment: 43 page
HyperPCA: a Powerful Tool to Extract Elemental Maps from Noisy Data Obtained in LIBS Mapping of Materials
Laser-induced breakdown spectroscopy is a preferred technique for fast and
direct multi-elemental mapping of samples under ambient pressure, without any
limitation on the targeted element. However, LIBS mapping data have two
peculiarities: an intrinsically low signal-to-noise ratio due to single-shot
measurements, and a high dimensionality due to the high number of spectra
acquired for imaging. This is all the truer as lateral resolution gets higher:
in this case, the ablation spot diameter is reduced, as well as the ablated
mass and the emission signal, while the number of spectra for a given surface
increases. Therefore, efficient extraction of physico-chemical information from
a noisy and large dataset is a major issue. Multivariate approaches were
introduced by several authors as a means to cope with such data, particularly
Principal Component Analysis. Yet, PCA is known to present theoretical
constraints for the consistent reconstruction of the dataset, and has therefore
limitations to efficient interpretation of LIBS mapping data. In this paper, we
introduce HyperPCA, a new analysis tool for hyperspectral images based on a
sparse representation of the data using Discrete Wavelet Transform and
kernel-based sparse PCA to reduce the impact of noise on the data and to
consistently reconstruct the spectroscopic signal, with a particular emphasis
on LIBS data. The method is first illustrated using simulated LIBS mapping
datasets to emphasize its performances with highly noisy and/or highly
interfered spectra. Comparisons to standard PCA and to traditional univariate
data analyses are provided. Finally, it is used to process real data in two
cases that clearly illustrate the potential of the proposed algorithm. We show
that the method presents advantages both in quantity and quality of the
information recovered, thus improving the physico-chemical characterisation of
analysed surfaces.Comment: 20 pages, 8 pages of supplementary materia
- …