1,514 research outputs found
Fosfatos naturais reativos: resultados obtidos no sul do Brasil.
bitstream/item/84108/1/CNPT-BOL.-PESQ.-4-00.pd
Stationary Entangled Radiation from Micromechanical Motion
Mechanical systems facilitate the development of a new generation of hybrid
quantum technology comprising electrical, optical, atomic and acoustic degrees
of freedom. Entanglement is the essential resource that defines this new
paradigm of quantum enabled devices. Continuous variable (CV) entangled fields,
known as Einstein-Podolsky-Rosen (EPR) states, are spatially separated two-mode
squeezed states that can be used to implement quantum teleportation and quantum
communication. In the optical domain, EPR states are typically generated using
nondegenerate optical amplifiers and at microwave frequencies Josephson
circuits can serve as a nonlinear medium. It is an outstanding goal to
deterministically generate and distribute entangled states with a mechanical
oscillator. Here we observe stationary emission of path-entangled microwave
radiation from a parametrically driven 30 micrometer long silicon nanostring
oscillator, squeezing the joint field operators of two thermal modes by
3.40(37) dB below the vacuum level. This mechanical system correlates up to 50
photons/s/Hz giving rise to a quantum discord that is robust with respect to
microwave noise. Such generalized quantum correlations of separable states are
important for quantum enhanced detection and provide direct evidence for the
non-classical nature of the mechanical oscillator without directly measuring
its state. This noninvasive measurement scheme allows to infer information
about otherwise inaccessible objects with potential implications in sensing,
open system dynamics and fundamental tests of quantum gravity. In the near
future, similar on-chip devices can be used to entangle subsystems on vastly
different energy scales such as microwave and optical photons.Comment: 13 pages, 5 figure
In vitro haemodynamic testing of Amplatzer plugs for paravalvular leak occlusion after Transcather Aortic Valve Implantation
Objective: We aimed to in-vitro test Amplatzer devices (Amplatzer Vascular Plug II and Amplatzer Vascular Plug III, SJM St. Paul, MN) in closing PVL generated by transcatheter balloon expandable aortic valve prosthesis in order to quantify the effective treatment of PVL. Background: Transcatheter aortic valve replacement (TAVI) procedures represent the treatment of choice for high risk patients. Despite evolving technologies paravalvular leak (PVL) is still a major unaddressed issue. This severe complication significantly impair long-term survival. Percutaneous treatment of this complication is usually performed with the implantation of not specifically designed and not approved vascular devices. Methods: A 23mm Sapien XT (Edwards Lifesciences, Irvine, CA) was implanted in a rubber aortic root and a semi-elliptical shape PVL was created. The vascular occluder devices were implanted in the PVL and hemodynamic performance was tested in a pulse duplicator according to international standard ISO 5840-3:2013. Different type of comparison tests together with high speed camera recording allowed us to define the global efficiency of the occluders and their interaction with the transcatheter prosthesis. Results: The results revealed that the use of vascular plugs was not per se sufficient to produce an effective or substantial reduction of PVL with a maximum efficiency inferior of 50%. Recorded video showed clearly that the vascular plug always interfered with the leaflet of the prosthetic valve. Conclusions: Current used devices do not guarantee effective treatment of PVL and may otherwise compromise the structural integrity of the prosthetic valve implanted. Specific designed devices are required
In Vitro and Ex Vivo Hemodynamic Testing of an Innovative Occluder for Paravalvular Leak After Transcather Aortic Valve Implantation
This study aims at achieving a proof-of-concept for a novel device designed to occlude the orifices that may form between transcatheter valves and host tissues after TAVI. The device effect on the performance of a SAPIEN XT with a paravalvular gap was assessed into an in vitro and ex vivo pulse duplicator. The in vitro tests were performed complying with the standard international regulations, measuring the trasvalvular pressure and regurgitant volumes with and without the paravalvular gap, and with the occluder correctly positioned into the gap. In the second series of tests, the leakage reduction due to the presence of the occluder was assessed for the same setup, into a beating swine heart. The occluder implantation decreased the regurgitant fraction of about 50% for the in vitro assessment and 75% for the ex vivo test, under rest operating conditions. These results suggest that suitably designed occluders can lead to important benefit in the PVL treatment
In vitro assessment of pacing as therapy for aortic regurgitation
Background and objective Clinical evaluation of pacing therapy in mitigating the aortic insufficiency after transchateter aortic valve implantation often gives contradictory outcomes. This study presents an in vitro investigation aimed at clarifying the effect of pacing on paravalvular leakage. Methods A series of in vitro tests reproducing the heart operating changes clinically obtained by pacing was carried out in a 26 mm Edwards Sapien XT prosthesis with mild paravalvular leakage. The effect of pacing on the regurgitant volumes per cycle and per minute was quantified, and the energy and power consumed by the left ventricle were calculated. Results Results indicate that though pacing results in some reduction in the total regurgitation per cycle, the volume of fluid regurgitating per minute increases substantially, causing overload of left ventricle. Conclusions Our tests indicate no effective haemodynamic benefit from pacing, suggesting a prudential clinical use of this therapy for the treatment of postoperative aortic regurgitation
Some remarks on the spectral functions of the Abelian Higgs Model
We consider the unitary Abelian Higgs model and investigate its spectral
functions at one-loop order. This analysis allows to disentangle what is
physical and what is not at the level of the elementary particle propagators,
in conjunction with the Nielsen identities. We highlight the role of the
tadpole graphs and the gauge choices to get sensible results. We also introduce
an Abelian Curci-Ferrari action coupled to a scalar field to model a massive
photon which, like the non-Abelian Curci-Ferarri model, is left invariant by a
modified non-nilpotent BRST symmetry. We clearly illustrate its non-unitary
nature directly from the spectral function viewpoint. This provides a
functional analogue of the Ojima observation in the canonical formalism: there
are ghost states with nonzero norm in the BRST-invariant states of the
Curci-Ferrari model.Comment: 32 pages, 12 figure
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