2,088 research outputs found
Nonsurgical repair of the ascending aorta: why less is more
Objective: Advanced endovascular options for acute and chronic pathology of the ascending aorta are emerging; however, several problems with stent grafts placed in the ascending aorta have been identified in patients unsuitable for surgical repair, such as migration and erosion at aorta interface. Method: Among the six cases analysed in this report, three were treated with a stent graft in the ascending aorta to manage chronic dissection in the proximal aorta; dimensions of those stent grafts varied between 34 and 45 mm in diameter, and from 77 to 100 mm in length. Three patients, matched by age, sex and their nature of pathology, were subjected to the focal closure of a single communicating entry by the use of an occluding device (Amplatzer ASD and PFO occluders between 14 and 18 mm disc diameter) with similar Charlson comorbidity score. Results: Both conceptually different nonsurgical management strategies were technically feasible; however, with stent grafts, an early or delayed erosion to full re-dissection was documented with stent grafts, in contrast to complete seal, with an induced remodelling and a long-term survival after the successful placing of coils and occluder devices. Moreover, aortic root motion was not impaired by the focal occlusion of a communication with an occluder, while free motion was impeded after stent graft placement. Conclusions: The intriguing observation in our small series was that stent grafts placed in the ascending aorta portends the risk of an either early (post-procedural) or delayed migration and erosion of aortic tissues at the landing site or biological interface between 12 and 16 months after the procedure, a phenomenon not seen with the use of focal occluding devices up to 5 years of follow-up. Obviously, the focal approach avoids the erosion of the aortic wall as the result of minimal interaction with the biological interface, such as a diseased aortic wall. Potential explanations may be related to a reduced motion of the aortic root after the placement of stent graft in the ascending aorta, whereas the free motion of aortic root was preserved with an occluder. The causality of erosion may however not be fully understood, as besides the stiffness and radial force of the stent graft, other factors such as the induced inflammatory reactions of aortic tissue and local adhesions within the chest may also play a role. With stent grafts failing to portend long-term success, they may still have a role as a temporizing solution for elective surgical conversion. Larger datasets from registries are needed to further explore this evolving field of interventions to the ascending aorta
Interparticle Potential up to Next-to-leading Order for Gravitational, Electrical, and Dilatonic Forces
Long-range forces up to next-to-leading order are computed in the framework
of the Einstein-Maxwell-dilaton system by means of a semiclassical approach to
gravity. As has been recently shown, this approach is effective if one of the
masses under consideration is significantly greater than all the energies
involved in the system. Further, we obtain the condition for the equilibrium of
charged masses in the system.Comment: 19 pages, 19 figures, RevTeX4.1. Revised version, Title change
A complex network based model for detecting isolated communities in water distribution networks
2013-2014 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Estimation of divergence times for major lineages of galliform birds: Evidence from complete mitochondrial genome sequences
Determining an absolute timescale for avian evolutionary history has been recently challenged by the relaxed molecular clock methods, that rates of molecular evolution can vary significantly among organisms. In this study, we used relaxed molecular clocks to date the divergence of major lineages of Galliformes based on complete mitochondrial genomes. A nucleotide dataset of 13 concatenated protein-coding genes from 22 species of Galliformes was used to investigate the evolutionary divergences within the group. Using Gallus bravardi, Schaubortyx and Gallinuloides fossils ascalibration points, divergence times analyses were performed with four relaxed molecular clock methods as follows: (1) Bayesian method of Multidivtime; (2) Bayesian Markov chain Monte Carlo (MCMC) analysis of the Bayesian evolutionary analysis by sampling trees (BEAST); (3) local rate minimum deformation method (LRMD) of TREEFINDER; and (4) nonparametric rate smoothing (NPRS) of TREEFINDER. The various relaxed clock methods all indicated that (1) Megapodiidae originated in theLate Cretaceous; (2) Numididae, Phasianidae, Arborophilinae and Coturnicinae originated in the Eocene of Palaeogene; (3) Pavoninae and Gallininae originated at the Eocene-Oligocene boundary; (4) Phasianinae and Meleagridinae originated in the Oligocene; (5) divergence times estimation among most genera of Phasianidae were much older than those of the previous studies. Our results might provide a more likely time scale for evolutionary history of the galliform birds
Van der Waals epitaxy of Bi2Se3 on Si(111) vicinal surface: An approach to prepare high-quality thin films of topological insulator
Epitaxial growth of topological insulator Bi2Se3 thin films on nominally flat
and vicinal Si(111) substrates is studied. In order to achieve planner growth
front and better quality epifilms, a two-step growth method is adopted for the
van der Waal epitaxy of Bi2Se3 to proceed. By employing vicinal Si(111)
substrate surfaces, the in-pane growth rate anisotropy of Bi2Se3 is explored to
achieve single crystalline Bi2Se3 epifilms, in which threading defects and
twins are effectively suppressed. Optimization of the growth parameters has
resulted in vicinal Bi2Se3 films showing a carrier mobility of ~ 2000 cm2V-1s-1
and the background doping of ~ 3 x 1018 cm-3 of the as-grown layers. Such
samples not only show relatively high magnetoresistance but also a linear
dependence on magnetic field.Comment: 18 pages, 4 figure
Electronic and Magnetic Properties of Partially-Open Carbon Nanotubes
On the basis of the spin-polarized density functional theory calculations, we
demonstrate that partially-open carbon nanotubes (CNTs) observed in recent
experiments have rich electronic and magnetic properties which depend on the
degree of the opening. A partially-open armchair CNT is converted from a metal
to a semiconductor, and then to a spin-polarized semiconductor by increasing
the length of the opening on the wall. Spin-polarized states become
increasingly more stable than nonmagnetic states as the length of the opening
is further increased. In addition, external electric fields or chemical
modifications are usable to control the electronic and magnetic properties of
the system. We show that half-metallicity may be achieved and the spin current
may be controlled by external electric fields or by asymmetric
functionalization of the edges of the opening. Our findings suggest that
partially-open CNTs may offer unique opportunities for the future development
of nanoscale electronics and spintronics.Comment: 6 figures, to appear in J. Am. Chem. So
Complex zeros of real ergodic eigenfunctions
We determine the limit distribution (as ) of complex
zeros for holomorphic continuations \phi_{\lambda}^{\C} to Grauert tubes of
real eigenfunctions of the Laplacian on a real analytic compact Riemannian
manifold with ergodic geodesic flow. If is an
ergodic sequence of eigenfunctions, we prove the weak limit formula
\frac{1}{\lambda_j} [Z_{\phi_{j_k}^{\C}}] \to \frac{i}{\pi} \bar{\partial}
{\partial} |\xi|_g, where [Z_{\phi_{j_k}^{\C}}] is the current of
integration over the complex zeros and where is with respect
to the adapted complex structure of Lempert-Sz\"oke and Guillemin-Stenzel.Comment: Added some examples and references. Also added a new Corollary, and
corrected some typo
Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions
We investigate the optical properties of edge-functionalized graphene
nanosystems, focusing on the formation of junctions and charge transfer
excitons. We consider a class of graphene structures which combine the main
electronic features of graphene with the wide tunability of large polycyclic
aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we
show that, upon convenient choice of functional groups, low energy excitations
with remarkable charge transfer character and large oscillator strength are
obtained. These properties can be further modulated through an appropriate
width variation, thus spanning a wide range in the low-energy region of the
UV-Vis spectra. Our results are relevant in view of designing all-graphene
optoelectronic nanodevices, which take advantage of the versatility of
molecular functionalization, together with the stability and the electronic
properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres
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