46,060 research outputs found
Computational Fluid Dynamic Studies of Vortex Amplifier Design for the Nuclear Industry—I. Steady-State Conditions
In this study the effects of changes to the geometry of a vortex amplifier are investigated using computational fluid dynamics (CFD) techniques, in the context of glovebox operations for the nuclear industry. These investigations were required because of anomalous behavior identified when, for operational reasons, a long-established vortex amplifier design was reduced in scale. The aims were (i) to simulate both the anomalous back-flow into the glovebox through the vortex amplifier supply ports, and the precessing vortex core in the amplifier outlet, then (ii) to determine which of the various simulated geometries would best alleviate the supply port back-flow anomaly. Various changes to the geometry of the vortex amplifier were proposed; smoke and air tests were then used to identify a subset of these geometries for subsequent simulation using CFD techniques. Having verified the mesh resolution was sufficient to reproduce the required effects, the code was then validated by comparing the results of the steady-state simulations with the experimental data. The problem is challenging in terms of the range of geometrical and dynamic scales encountered, with consequent impact on mesh quality and turbulence modeling. The anomalous nonaxisymmetric reverse flow in the supply ports of the vortex amplifier has been captured and the mixing in both the chamber and the precessing vortex core has also been successfully reproduced. Finally, by simulating changes to the supply ports that could not be reproduced experimentally at an equivalent cost, the geometry most likely to alleviate the back-flow anomaly has been identified
Fast and efficient transport of large ion clouds
The manipulation of trapped charged particles by electric fields is an
accurate, robust and reliable technique for many applications or experiments in
high-precision spectroscopy. The transfer of the ion sample between multiple
traps allows the use of a tailored environment in quantum information, cold
chemistry, or frequency metrology experiments. In this article, we
experimentally study the transport of ion clouds of up to 50 000 ions. The
design of the trap makes ions very sensitive to any mismatch between the
assumed electric potential and the actual local one. Nevertheless, we show that
being fast (100 s to transfer over more than 20 mm) increases the
transport efficiency to values higher than 90 %, even with a large number of
ions. For clouds of less than 2000 ions, a 100 % transfer efficiency is
observed
Energy Loss from Reconnection with a Vortex Mesh
Experiments in superfluid 4He show that at low temperatures, energy
dissipation from moving vortices is many orders of magnitude larger than
expected from mutual friction. Here we investigate other mechanisms for energy
loss by a computational study of a vortex that moves through and reconnects
with a mesh of small vortices pinned to the container wall. We find that such
reconnections enhance energy loss from the moving vortex by a factor of up to
100 beyond that with no mesh. The enhancement occurs through two different
mechanisms, both involving the Kelvin oscillations generated along the vortex
by the reconnections. At relatively high temperatures the Kelvin waves increase
the vortex motion, leading to more energy loss through mutual friction. As the
temperature decreases, the vortex oscillations generate additional reconnection
events between the moving vortex and the wall, which decrease the energy of the
moving vortex by transfering portions of its length to the pinned mesh on the
wall.Comment: 9 pages, 10 figure
Anaesthetic challenging in microsurgical flap reconstruction: a systematic review
Background: Anaesthetic management for microvascular reconstructive surgery is challenging and clearly
affects the risk of major complications such as flap hypo-perfusion.
In this systematic review we explore recent (last 7 years) clinical evidences related to perioperative management and anaesthetic controversy of patients undergoing microvascular reconstructive surgery, especially focused on head and neck surgery with free flaps (FF) and breast reconstructive surgery with deep inferior epigastric perforator flap (DIEP-flap).
Methods: A literature search of published clinical studies between 2011 and 2018 was conducted, yielding a total of 4307 papers. Only 150 were eligible, according inclusion and exclusion criteria.
Results: 62 studies were selected for this review and categorized in 3 groups: preoperative-intraoperative- postoperative anaesthetic management and areas of controversy for patients undergoing head and neck surgery with FF and breast reconstructive surgery with DIEP-flap.
Discussion: Anaesthetic management for flap reconstructive surgery remains an open field of interest with limited evidences regarding a standard care. Main components of research currently are: the need to join standard multidisciplinary enhanced recovery pathways, as well as the necessity to develop a standard intraoperative management. In theatre, the recent hemodynamic parameter “Hypotension Probability Indicator” (HPI) is promising: the advantage to predict a drop in the mean arterial pressure can be more effective than a fluid therapy titrated to maintain SVV less than 13%. Prospective studies are necessary to clarify
CIS-lunar space infrastructure lunar technologies: Executive summary
Technologies necessary for the creation of a cis-Lunar infrastructure, namely: (1) automation and robotics; (2) life support systems; (3) fluid management; (4) propulsion; and (5) rotating technologies, are explored. The technological focal point is on the development of automated and robotic systems for the implementation of a Lunar Oasis produced by Automation and Robotics (LOAR). Under direction from the NASA Office of Exploration, automation and robotics were extensively utilized as an initiating stage in the return to the Moon. A pair of autonomous rovers, modular in design and built from interchangeable and specialized components, is proposed. Utilizing a buddy system, these rovers will be able to support each other and to enhance their individual capabilities. One rover primarily explores and maps while the second rover tests the feasibility of various materials-processing techniques. The automated missions emphasize availability and potential uses of Lunar resources, and the deployment and operations of the LOAR program. An experimental bio-volume is put into place as the precursor to a Lunar environmentally controlled life support system. The bio-volume will determine the reproduction, growth and production characteristics of various life forms housed on the Lunar surface. Physicochemical regenerative technologies and stored resources will be used to buffer biological disturbances of the bio-volume environment. The in situ Lunar resources will be both tested and used within this bio-volume. Second phase development on the Lunar surface calls for manned operations. Repairs and re-configuration of the initial framework will ensue. An autonomously-initiated manned Lunar oasis can become an essential component of the United States space program
Cavitation inception of a van der Waals fluid at a sack-wall obstacle
Cavitation in a liquid moving past a constraint is numerically investigated
by means of a free-energy lattice Boltzmann simulation based on the van der
Waals equation of state. The fluid is streamed past an obstacle and, depending
on the pressure drop between inlet and outlet, vapor formation underneath the
corner of the sack-wall is observed. The circumstances of cavitation formation
are investigated and it is found that the local bulk pressure and mean stress
are insufficient to explain the phenomenon. Results obtained in this study
strongly suggest that the viscous stress, interfacial contributions to the
local pressure, and the Laplace pressure are relevant to the opening of a vapor
cavity. This can be described by a generalization of Joseph's criterion that
includes these contributions. A macroscopic investigation measuring mass flow
rate behavior and discharge coefficient was also performed. As theoretically
predicted, mass flow rate increases linearly with the square root of the
pressure drop. However, when cavitation occurs, the mass flow growth rate is
reduced and eventually it collapses into a choked flow state. In the cavitating
regime, as theoretically predicted and experimentally verified, the discharge
coefficient grows with the Nurick cavitation number
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