140 research outputs found
Study of heat and mass transfer applications in the field of engineering by using OpenFOAM
The aim of the project is to study OpenFOAM software and establish a well-based guide of standard and complex heat and mass transfer applications in engineering. OpenFOAM is a free, open source CFD software package. By being open, OpenFOAM offers users complete freedom to customise and extend its existing functionality. On the other hand, OpenFOAM offers a quick start user guide and there also is little available documentation and several examples. Thus, the project intends to: - Prepare an introductory and complete user guide to OpenFOAM with solved standard heat and mass transfer applications to the beginners, specially bachelor students ‐ Numerical simulation of complex heat and mass transfer applications in engineering with OpenFOAM in two‐ and three‐dimensional problems ‐ Practice in developing engineering projects by combining technical work with economic and environmental aspectsThe main tasks to be carried out in this project will be to: - Edit problems solved with OpenFOAM including explanations and detailed considerations in order to prepare a guide for new learners, specially bachelor students - Work in the study and analysis of heat and mass transfer simulations involving real engineering problems - Determine feasibility of the engineering project to be carried out - Study the socio-economics aspects in fluid dynamics applications solved by numerical simulation and fields of interest - Results analysi
The impact of red giant/AGB winds on AGN jet propagation
Dense stellar winds may mass-load the jets of active galactic nuclei,
although it is unclear what are the time and spatial scales in which the mixing
takes place. We study the first steps of the interaction between jets and
stellar winds, and also the scales at which the stellar wind may mix with the
jet and mass-load it. We present a detailed two-dimensional simulation,
including thermal cooling, of a bubble formed by the wind of a star. We also
study the first interaction of the wind bubble with the jet using a
three-dimensional simulation in which the star enters the jet. Stability
analysis is carried out for the shocked wind structure, to evaluate the
distances over which the jet-dragged wind, which forms a tail, can propagate
without mixing with the jet flow. The two-dimensional simulations point at
quick wind bubble expansion and fragmentation after about one bubble shock
crossing time. Three-dimensional simulations and stability analysis point at
local mixing in the case of strong perturbations and relatively small density
ratios between the jet and the jet dragged-wind, and to a possibly more stable
shocked wind structure at the phase of maximum tail mass flux. Analytical
estimates also indicate that very early stages of the star jet-penetration time
may be also relevant for mass loading. The combination of these and previous
results from the literature suggest highly unstable interaction structures and
efficient wind-jet flow mixing on the scale of the jet interaction height,
possibly producing strong inhomogeneities within the jet. In addition, the
initial wind bubble shocked by the jet leads to a transient, large interaction
surface. The interaction structure can be a source of significant non-thermal
emission.Comment: Accepted for publication in Astronomy & Astrophysic
Anomalous momentum diffusion in a dissipative many-body system
Decoherence is ubiquitous in quantum physics, from the conceptual foundations
to quantum information processing or quantum technologies, where it is a threat
that must be countered. While decoherence has been extensively studied for
simple, well-isolated systems such as single atoms or ions, much less is known
for many-body systems where inter-particle correlations and interactions can
drastically alter the dissipative dynamics. Here we report an experimental
study of how spontaneous emission destroys the spatial coherence of a gas of
strongly interacting bosons in an optical lattice. Instead of the standard
momentum diffusion expected for independent atoms, we observe an anomalous
sub-diffusive expansion, associated with a universal slowing down of the decoherence dynamics. This algebraic decay reflects the
emergence of slowly-relaxing many-body states, akin to sub-radiant states of
many excited emitters. These results, supported by theoretical predictions,
provide an important benchmark in the understanding of open many-body systems.Comment: Supplementary material available as ancillary fil
Large-scale emission in FR I jets
The termination structures of the jets of Fanaroff & Riley galaxies are
observed to produce extended non-thermal emission in a wide frequency range.
The study of these structures can provide valuable insights on the conditions
for particle acceleration and radiation at the shock fronts.We have studied the
thermal and non-thermal emission that can be expected from the jet termination
regions of Fanaroff & Riley type I sources. The broadband emission from these
galaxies has been recently extended to include the high-energy gamma-ray
domain, owing to the Fermi detection of Cen A lobes. Exploring the physics
behind the jet/medium interactions in FRI can provide valuable insights on the
conditions for particle acceleration and radiation in the jet termination
shocks. Making use of the results of a fully relativistic numerical simulation
code of the evolution of a FRI jet we model the expected radiative output and
predict spectra and lightcurves of both thermal and non-thermal emission at
different source ages.Comment: Proceedings of the High Energy Phenomena in Relativistic Outflows III
conferenc
Non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
Binaries hosting a massive star and a non-accreting pulsar are powerful
non-thermal emitters due to the interaction of the pulsar and the stellar wind.
The winds of massive stars are thought to be inhomogeneous, which could have an
impact on the non-thermal emission. We study numerically the impact of the
presence of inhomogeneities or clumps in the stellar wind on the high-energy
non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. We
compute the trajectories and physical properties of the streamlines in the
shocked pulsar wind without clumps, with a small clump, and with a large one.
This information is used to compute the synchrotron and inverse Compton
emission from the non-thermal populations, accounting also for the effect of
gamma-ray absorption through pair creation. A specific study is done for PSR
B1259-63/LS2883. When stellar wind clumps perturb the two-wind interaction
region, the associated non-thermal radiation in the X-ray band,of synchrotron
origin, and in the GeV-TeV band, of inverse Compton origin, is affected by
several effects: (i) strong changes in the the plasma velocity direction that
result in Doppler boosting factor variations, (ii) strengthening of the
magnetic field that mainly enhances the synchrotron radiation, (iii)
strengthening of the pulsar wind kinetic energy dissipation at the shock,
potentially available for particle acceleration, and (iv) changes in the rate
of adiabatic losses that affect the lower energy part of the non-thermal
particle population. The radiation above 100 GeV detected, presumably, during
the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be
roughly reproduced assuming that the crossing of the disc is modeled as the
encounter with a large inhomogeneity.Comment: 13 pages, 12 figures, submitted to A&
Clouds and red giants interacting with the base of AGN jets
Extragalactic jets are formed close to supermassive black-holes in the center
of galaxies. Large amounts of gas, dust, and stars cluster in the galaxy
nucleus, and interactions between this ambient material and the jet base should
be frequent, having dynamical as well as radiative consequences. This work
studies the dynamical interaction of an obstacle, a clump of matter or the
atmosphere of an evolved star, with the innermost region of an extragalactic
jet. Jet mass-loading and the high-energy outcome of this interaction are
briefly discussed. Relativistic hydrodynamical simulations with axial symmetry
have been carried out for homogeneous and inhomogeneous obstacles inside a
relativistic jet. These obstacles may represent a medium inhomogeneity or the
disrupted atmosphere of a red giant star. Once inside the jet, an homogeneous
obstacle expands and gets disrupted after few dynamical timescales, whereas in
the inhomogeneous case, a solid core can smoothen the process, with the
obstacle mass-loss dominated by a dense and narrow tail pointing in the
direction of the jet. In either case, matter is expected to accelerate and
eventually get incorporated to the jet. Particles can be accelerated in the
interaction region, and produce variable gamma-rays in the ambient matter,
magnetic and photon fields. The presence of matter clumps or red giants into
the base of an extragalactic jet likely implies significant jet mass-loading
and slowing down. Fast flare-like gamma-ray events, and some level of
persistent emission, are expected due to these interactions.Comment: 13 pages, 15 Figures, accepted for publication in Astronomy and
Astrophysic
Energy use and energy efficiency, the way to reduce energy consumption in university buildings
The Technical University of Catalonia (UPC) has been developing since 1996 a number of actions
and strategies to reduce the energy consumption of its 96 buildings.
From the collaboration agreement signed in 2006 with the Catalan Institute of Energy (ICAEN),
UPC has agreed to develop measures to encourage energy savings and enhance energy efficiency on
its own buildings, distributed over ten campuses.
One of the first actions carried out was the implementation of the Resource Consumption Efficiency
Plan (PECR), which culminated in 29 energy audits carried out on different types of buildings:
schools, sports facilities, libraries and administration buildings and services. These were performed
by Technical Architecture and Building Engineering students as a Final Degree Project.Peer ReviewedPostprint (published version
Simulations of an inhomogeneous stellar wind interacting with a pulsar wind in a binary system
Binary systems containing a massive star and a non-accreting pulsar present
strong interaction between the stellar and the pulsar winds. The properties of
this interaction, which largely determine the non-thermal radiation in these
systems, strongly depend on the structure of the stellar wind, which can be
clumpy or strongly anisotropic, as in Be stars. We study numerically the
influence of inhomogeneities in the stellar wind on the structure of the
two-wind interaction region. We carried out for the first time axisymmetric,
relativistic hydrodynamical simulations, with Lorentz factors of ~6 and
accounting for the impact of instabilities, to study the impact in the two-wind
interaction structure of an over-dense region of the stellar wind. We also
followed the evolution of this over-dense region or clump as it faces the
impact of the pulsar wind. For typical system parameters, and adopting a
stellar wind inhomogeneity with a density contrast >~10, clumps with radii of a
few percent of the binary size can significantly perturb the two-wind
interaction region, pushing the two-wind interface to <~40% of the initial
distance to the pulsar. After it is shocked, the inhomogeneity quickly expands
and is disrupted when it reaches the smallest distance to the pulsar. It
eventually fragments, being advected away from the binary system. The whole
interaction region is quite unstable, and the shocked pulsar wind can strongly
change under small perturbations. We confirm the sensitive nature of the
two-wind interaction structure to perturbations, in particular when the stellar
wind is inhomogeneous. For realistic over-dense regions of the stellar wind,
the interaction region may shrink by a factor of a few, with the shocked flow
presenting a complex spatial and temporal pattern. This can lead to strong
variations in the non-thermal radiation.Comment: This version matches the published version. The appendix at the end
of the article appears as on-line material in the journa
Preparation and characterization of a supramolecular hydrogel made of phospholipids and oleic acid with a high water content
A hydrogel formed with phospholipids and fatty acids would be of great interest in the medical field due to the biological relevance that these molecules have in living organisms. However, the tendency of phospholipid mixtures to form vesicular or micellar aggregates at high water content hinders the formation of this type of hydrogel. In this study, a highly hydrated hydrogel (95% water) was formed with hydrogenated phosphatidylcholine and oleic acid. The preparation method involved a freeze-heating cycle of the aqueous lipid mixture, favouring the supramolecular aggregation of these molecules into a microscopic spongy morphology. Confocal fluorescence imaging showed that the microstructure of the hydrogel is made from the aggregation of giant multilamellar vesicles (5-20 μm diameter) while transmission electron microscopy revealed the existence of nanosized unilamellar vesicles (150 nm diameter) coexisting with lipid lamellae. Despite this type of aggregation, X-ray scattering experiments performed on the hydrogel show almost no correlation between lipid membranes. In terms of rheological properties, the material shows a prevalent elastic behaviour and low structural strength, a consequence of non-covalent interactions. With such properties and composition, this structured but easily deformable material might become a useful tool for biomedical applications
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