Examinando por Autor "Lozano, Carlos"

Mostrando 1 - 13 de 13

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Analytic adjoint solutions for the 2-D incompressible Euler equations using the Green's function approach
(Cambridge University Press, 2022-06-13) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
The Green's function approach of Giles and Pierce (J. Fluid Mech., vol. 426, 2001, pp. 327–345) is used to build the lift and drag based analytic adjoint solutions for the two-dimensional incompressible Euler equations around irrotational base flows. The drag-based adjoint solution turns out to have a very simple closed form in terms of the flow variables and is smooth throughout the flow domain, while the lift-based solution is singular at rear stagnation points and sharp trailing edges owing to the Kutta condition. This singularity is propagated to the whole dividing streamline (which includes the incoming stagnation streamline and the wall) upstream of the rear singularity (trailing edge or rear stagnation point) by the sensitivity of the Kutta condition to changes in the stagnation pressure.
Acceso Abierto
Can Halophilic and Psychrophilic Microorganisms Modify the Freezing/Melting Curve of Cold Salty Solutions? Implications for Mars Habitability
(Mary Ann Liebert Publishers, 2020-09-15) García Descalzo, L.; Gil Lozano, C.; Muñoz Iglesias, V.; Prieto Ballesteros, O.; Azua Bustos, A.; Fairén, Alberto G.; European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO); European Commission (EC); Agencia Estatal de Investigación (AEI); García Descalzo, L. [0000-0002-0083-6786]; Gil Lozano, C. [0000-0003-3500-2850]; Muñoz Iglesias, V. [0000-0002-1159-9093]; Prieto Ballesteros, O. [0000-0002-2278-1210]; Azua Bustos, A. [0000-0002-2278-1210]; Fairén, A. G. [0000-0002-2938-6010]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present the hypothesis that microorganisms can change the freezing/melting curve of cold salty solutions by protein expression, as it is known that proteins can affect the liquid-to-ice transition, an ability that could be of ecological advantage for organisms on Earth and on Mars. We tested our hypothesis by identifying a suitable candidate, the well-known psycrophile and halotolerant bacteriaRhodococcussp. JG3, and analyzing its response in culture conditions that included specific hygroscopic salts relevant to Mars-that is, highly concentrated magnesium perchlorate solutions of 20 wt % and 50 wt % Mg(ClO4)(2)at both end members of the eutectic concentration (44 wt %)-and subfreezing temperatures (263 K and 253 K). Using a combination of techniques of molecular microbiology and aqueous geochemistry, we evaluated the potential roles of proteins over- or underexpressed as important players in different mechanisms for the adaptability of life to cold environments. We recorded the changes observed by micro-differential scanning calorimetry. Unfortunately,Rhodococcussp. JG3 did not show our hypothesized effect on the melting characteristics of cold Mg-perchlorate solutions. However, the question remains as to whether our novel hypothesis that halophilic/psychrophilic bacteria or archaea can alter the freezing/melting curve of salt solutions could be validated. The null result obtained after analyzing just one case lays the foundation to continue the search for proteins produced by microorganisms that thrive in very cold, high-saline solutions, which would involve testing different microorganisms with different salt components. The immediate implications for the habitability of Mars are discussed.
Acceso Abierto
Constraining the preservation of organic compounds in Mars analog nontronites after exposure to acid and alkaline fluids.
(Nature Research Journals, 2020-09-15) Gil Lozano, C.; Fairén, Alberto G.; Muñoz Iglesias, V.; Fernández Sampedro, M.; Prieto Ballesteros, O.; Gago Duport, L.; Losa Adams, E.; Carrizo, D.; Bishop, J. L.; Fornaro, T.; Mateo Martí, Eva; European Research Council (ERC); Agencia Estatal de Investigación (AEI); European Commission (EC); 0000-0002-5536-2565; 0000-0003-1932-7591; 0000-0002-1159-9093; 0000-0003-3500-2850; 0000-0002-2278-1210; 0000-0002-2646-5995; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as "treated nontronites") under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditions.
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Detection of Potential Lipid Biomarkers in Oxidative Environments by Raman Spectroscopy and Implications for the ExoMars 2020-Raman Laser Spectrometer Instrument Performance.
(Mary Ann Liebert Publishers, 2020-03-02) Carrizo, D.; Muñoz Iglesias, V.; Fernández Sampedro, M.; Gil Lozano, C.; Sánchez García, L.; Prieto Ballesteros, O.; Medina, J.; Rull, F.; Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); Fernández Sampedro, M. [0000-0003-1932-7591]; Lozano, C. G. [0000-0003-3500-2850]; Muñoz Iglesias, V. [0000-0002-1159-9093]; Sánchez García, L. [0000-0002-7444-1242]; Prieto Ballesteros, O. [0000-0002-2278-1210]; Carrizo, D. [0000-0003-1568-4591]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The aim of the European Space Agency's ExoMars rover mission is to search for potential traces of present or past life in the swallow subsurface (2 m depth) of Mars. The ExoMars rover mission relies on a suite of analytical instruments envisioned to identify organic compounds with biological value (biomarkers) associated with a mineralogical matrix in a highly oxidative environment. We investigated the feasibility of detecting basic organics (linear and branched lipid molecules) with Raman laser spectroscopy, an instrument onboard the ExoMars rover, when exposed to oxidant conditions. We compared the detectability of six lipid molecules (alkanes, alkanols, fatty acid, and isoprenoid) before and after an oxidation treatment (15 days with hydrogen peroxide), with and without mineral matrix support (amorphous silica rich vs. iron rich). Raman and infrared spectrometry was combined with gas chromatography-mass spectrometry to determine detection limits and technical constrains. We observed different spectral responses to degradation depending on the lipid molecule and mineral substrate, with the silica-rich material showing better preservation of organic signals. These findings will contribute to the interpretation of Raman laser spectroscopy results on cores from the ExoMars rover landing site, the hydrated silica-enriched delta fan on Cogoon Vallis (Oxia Planum).
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Entropy and adjoint methods
(Springer Link, 2019-11-11) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
Aerodynamic drag can be partially approximated by the entropy flux across fluid domain boundaries with a formula due to Oswatitsch. In this paper, we build the adjoint solution that corresponds to this representation of the drag and investigate its relation to the entropy variables, which are linked to the integrated residual of the entropy transport equation. For inviscid isentropic flows, the resulting adjoint variables are identical to the entropy variables, an observation originally due to Fidkowski and Roe, while for non-isentropic flows there is a significant difference that is explicitly demonstrated with analytic solutions in the shocked quasi-1D case. Both approaches are also investigated for viscous and inviscid flows in two and three dimensions, where the adjoint equations and boundary conditions are derived. The application of both approaches to mesh adaptation is investigated, with especial emphasis on inviscid flows with shocks.
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Entropy production by implicit Runge–Kutta schemes
(Springer Link, 2019-01-23) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
This paper follows up on the author’s recent paper “Entropy Production by Explicit Runge–Kutta schemes” (Lozano in J Sci Comput 76(1):521–564, 2018. https://doi.org/10.1007/s10915-017-0627-0), where a formula for the production of entropy by fully discrete schemes with explicit Runge–Kutta time integrators was presented. In this paper, the focus is on implicit Runge–Kutta schemes, for which the fully discrete numerical entropy evolution scheme is derived and tested.
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Exact inviscid drag-adjoint solution for subcritical flows
(Aerospace Research Central, 2021-09-25) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
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Explaining the lack of mesh convergence of inviscid adjoint solutions near solid walls for subcritical flows
(Multidisciplinary Digital Publishing Institute (MDPI), 2023-04-24) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
Numerical solutions to the adjoint Euler equations have been found to diverge with mesh refinement near walls for a variety of flow conditions and geometry configurations. The issue is reviewed, and an explanation is provided by comparing a numerical incompressible adjoint solution with an analytic adjoint solution, showing that the anomaly observed in numerical computations is caused by a divergence of the analytic solution at the wall. The singularity causing this divergence is of the same type as the well-known singularity along the incoming stagnation streamline, and both originate at the adjoint singularity at the trailing edge. The argument is extended to cover the fully compressible case, in subcritical flow conditions, by presenting an analytic solution that follows the same structure as the incompressible one.
Acceso Abierto
Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars
(Nature Research Journals, 2020-11-05) Azua Bustos, A.; Fairén, Alberto G.; González Silva, C.; Carrizo, D.; Fernández Martínez, M. A.; Arenas Fajardo, C.; Fernández Sampedro, M.; Gil Lozano, C.; Sánchez García, L.; Ascaso, C.; Wierzchos, J.; Rampe, E. B.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Sánchez García, L. [0000-0002-7444-1242]; Lozano, C. G. [0000-0003-3500-2850]; Fernández Sampedro, M. [0000-0003-1932-7591]
The modern Martian surface is unlikely to be habitable due to its extreme aridity among other environmental factors. This is the reason why the hyperarid core of the Atacama Desert has been studied as an analog for the habitability of Mars for more than 50 years. Here we report a layer enriched in smectites located just 30 cm below the surface of the hyperarid core of the Atacama. We discovered the clay-rich layer to be wet (a phenomenon never observed before in this region), keeping a high and constant relative humidity of 78% (aw 0.780), and completely isolated from the changing and extremely dry subaerial conditions characteristic of the Atacama. The smectite-rich layer is inhabited by at least 30 halophilic species of metabolically active bacteria and archaea, unveiling a previously unreported habitat for microbial life under the surface of the driest place on Earth. The discovery of a diverse microbial community in smectite-rich subsurface layers in the hyperarid core of the Atacama, and the collection of biosignatures we have identified within the clays, suggest that similar shallow clay deposits on Mars may contain biosignatures easily reachable by current rovers and landers.
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Long-lasting habitable periods in Gale crater constrained by glauconitic clays
(Springer Link, 2021-06-28) Losa Adams, E.; Gil Lozano, C.; Fairén, Alberto G.; Bishop, J. L.; Rampe, E. B.; Gago Duport, L.; European Research Council (ERC); Xunta de Galicia
In situ investigations by the Mars Science Laboratory Curiosity rover have confirmed the presence of an ancient lake that existed in Gale crater for up to 10 million years. The lake was filled with sediments that eventually converted to a compacted sandstone. However, it remains unclear whether the infilling of the lake was the result of background sedimentation processes or represents punctual flooding events in a largely isolated lake. Here, we used the X-ray diffraction data obtained with the Chemistry and Mineralogy instrument onboard the Curiosity rover to characterize the degree of disorder of clay minerals in the Murray formation at Gale crater. Our analysis shows that they are structurally and compositionally related to glauconitic clays, which are a sensitive proxy of quiescent conditions in liquid bodies for extended periods of time. Such results provide evidence of long periods of extremely low sedimentation in an ancient brackish lake on Mars, the signature of an aqueous regime with slow evaporation at low temperatures. More in general, the identification of lacustrine glauconitic clays on Mars provides a key parameter in the characterization of aqueous Martian palaeoenvironments that may once have harboured life.
Acceso Abierto
Shock equations and jump conditions for the 2D adjoint euler equations
(Multidisciplinary Digital Publishing Institute (MDPI), 2023-03-10) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
This paper considers the formulation of the adjoint problem in two dimensions when there are shocks in the flow solution. For typical cost functions, the adjoint variables are continuous at shocks, wherein they have to obey an internal boundary condition, but their derivatives may be discontinuous. The derivation of the adjoint shock equations is reviewed and detailed predictions for the behavior of the gradients of the adjoint variables at shocks are obtained as jump conditions for the normal adjoint gradients in terms of the tangent gradients. Several numerical computations on a very fine mesh are used to illustrate the behavior of numerical adjoint solutions at shocks.
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Singularity and mesh divergence of inviscid adjoint solutions at solid walls
(Elsevier, 2023-09-15) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
The mesh divergence problem occurring at subsonic and transonic speeds with the adjoint Euler equations is reviewed. By examining a recently derived analytic adjoint solution, it is shown that the explanation is that the adjoint solution is singular at the wall. The wall singularity is caused by the adjoint singularity at the trailing edge, but not in the way it was previously conjectured.
Restringido
Watch your adjoints! Lack of mesh convergence in inviscid adjoint solutions
(Aerospace Research Central, 2019-08-05) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)
It has been long known that 2D and 3D inviscid adjoint solutions are generically singular at sharp trailing edges. In this paper, a concurrent effect is described by which wall boundary values of 2D and 3D inviscid continuous and discrete adjoint solutions based on lift and drag are strongly mesh dependent and do not converge as the mesh is refined. Various numerical tests are performed to characterize the problem. Lift-based adjoint solutions are found to be affected for any flow condition, whereas drag-based adjoint solutions are affected for transonic lifting flows. A (laminar) viscous case is examined as well, but no comparable behavior is found, which suggests that the issue is exclusive to inviscid flows. It is argued that this behavior is caused by the trailing edge adjoint singularity.