1,429 research outputs found
Promising Impregnated Mn-based Oxygen Carriers for Chemical Looping Combustion of Gaseous Fuels
Promising impregnated oxygen carriers, based on copper and iron, have been previously developed for CLC with gaseous fuels (CH4, syngas, LHC). Recently, because of its low cost and environmental compatibility, Mn-based oxygen carriers are now being considered as an attractive option for chemical-looping combustion (CLC) applications. In this work, a screening of different commercial supports in fluidizable particle size for impregnated Mn-based materials has been carried out. Different oxygen carriers have been prepared by incipient impregnation on ZrO2, and CaAl2O4, and evaluated with respect to their mechanical resistance, fuel gas reactivity and fluidization properties such as agglomeration and attrition rate. In a first step, particles showing high enough crushing strength values were selected for the reactivity investigation. The redox reactivity was evaluated through TGA experiments at suitable temperatures for the CLC process (i.e. 850-950 °C) using H2, CO and CH4. Multi cycle redox analysis and full physical and chemical characterization was also performed. In a second step, materials with high enough reactivity were prepared for fluidized bed evaluation. A batch fluidized bed installation with continuous gaseous fuel feed was used to analyze the product gas distribution during reduction and oxidation reactions at different operation temperatures, and agglomeration and attrition behavior of the selected materials. Results showed that an oxygen carrier impregnated using ZrO2 as support, had high enough reactivity and low attrition rate. Therefore, this material can be selected as a candidate for the development of CLC with syngas with promising results
Dynamics and thermodynamics of the spherical frustrated Blume-Emery-Griffiths model
We introduce a spherical version of the frustrated Blume-Emery-Griffiths
model and solve exactly the statics and the Langevin dynamics for zero
particle-particle coupling (K=0). In this case the model exhibits an
equilibrium transition from a disordered to a spin glass phase which is always
continuous for nonzero temperature. The same phase diagram results from the
study of the dynamics. Furthermore, we notice the existence of a nonequilibrium
time regime in a region of the disordered phase, characterized by aging as
occurs in the spin glass phase. Due to a finite equilibration time, the system
displays in this region the pattern of interrupted aging.Comment: 19 pages, 8 figure
Spin and density overlaps in the frustrated Ising lattice gas
We perform large scale simulations of the frustrated Ising lattice gas, a
three-dimensional lattice model of a structural glass, using the parallel
tempering technique. We evaluate the spin and density overlap distributions,
and the corresponding non-linear susceptibilities, as a function of the
chemical potential. We then evaluate the relaxation functions of the spin and
density self-overlap, and study the behavior of the relaxation times. The
results suggest that the spin variables undergo a transition very similar to
the one of the Ising spin glass, while the density variables do not show any
sign of transition at the same chemical potential. It may be that the density
variables undergo a transition at a higher chemical potential, inside the phase
where the spins are frozen.Comment: 7 pages, 10 figure
Bibliometric analysis on the use of natural fibers in construction materials
Received: February 2nd, 2021 ; Accepted: August 3rd, 2021 ; Published: August 30th, 2021 ; Correspondence: [email protected] to the increasing interest of the population in the sustainability theme, there was
a consequent growth in publications related to the theme in the area of civil construction. Agroindustrial waste has become an environmental problem, and with that natural fibers have found
space in the reuse of waste due to its characteristics and possibilities of improving the mechanical
properties of its products. In order to achieve sustainable construction demand, along with the
need to reuse waste, studies have begun to analyze the application of natural fibers in construction
materials. The documents provided by the Web of Science (WOS) database through research
carried out with the search for the terms ‘Natural Fibers’ and ‘Building materials’ restricted to
the period 2010–2020 in the main WOS collection. The institutions involved with the
publications, the countries of origin of the documents, the year of publication, the keywords used
by the authors and the number of citations for each document were analyzed using bibliometrics
in the VOSVIEWER (VOS) software. The result of the analysis shows an increase in documents
related to the theme over the years, and that the countries with the most studies in the area are
China (16), USA (14) and Brazil (11), respectively. The results presented after analysis of the
keywords show that natural fiber (61 occurrences), mechanical properties (44 occurrences) and
composites (31 occurrences) are the words with the highest occurrence among the analyzed
documents. The present study shows the growth of research related to the theme, in addition to
discriminating countries, institutions and authors, which allows monitoring the scientific
expansion of the theme and guiding future studies
Drought impact on forest carbon dynamics and fluxes in Amazonia
In 2005 and 2010 the Amazon basin experienced two strong droughts, driven by shifts in the tropical hydrological regime possibly associated with global climate change, as predicted by some global models. Tree mortality increased after the 2005 drought, and regional atmospheric inversion modelling showed basin-wide decreases in CO2 uptake in 2010 compared with 2011 (ref. 5). But the response of tropical forest carbon cycling to these droughts is not fully understood and there has been no detailed multi-site investigation in situ. Here we use several years of data from a network of thirteen 1-ha forest plots spread throughout South America, where each component of net primary production (NPP), autotrophic respiration and heterotrophic respiration is measured separately, to develop a better mechanistic understanding of the impact of the 2010 drought on the Amazon forest. We find that total NPP remained constant throughout the drought. However, towards the end of the drought, autotrophic respiration, especially in roots and stems, declined significantly compared with measurements in 2009 made in the absence of drought, with extended decreases in autotrophic respiration in the three driest plots. In the year after the drought, total NPP remained constant but the allocation of carbon shifted towards canopy NPP and away from fine-root NPP. Both leaf-level and plot-level measurements indicate that severe drought suppresses photosynthesis. Scaling these measurements to the entire Amazon basin with rainfall data, we estimate that drought suppressed Amazon-wide photosynthesis in 2010 by 0.38 petagrams of carbon (0.23-0.53 petagrams of carbon). Overall, we find that during this drought, instead of reducing total NPP, trees prioritized growth by reducing autotrophic respiration that was unrelated to growth. This suggests that trees decrease investment in tissue maintenance and defence, in line with eco-evolutionary theories that trees are competitively disadvantaged in the absence of growth. We propose that weakened maintenance and defence investment may, in turn, cause the increase in post-drought tree mortality observed at our plots.Gordon and Betty Moore FoundationNatural Environment Research Council (NERC)EU FP7 Amazalert (282664) projectEU FP7GEOCARBON (283080) projectNational Council for Scientific and Technological Development (CNPq, Brazil)ARC - fellowship awardERC - Advanced Investigator AwardRoyal Society - Wolfson Research Merit AwardJackson FoundationJohn Fell Fun
Non-vacuum Solutions of Bianchi Type VI_0 Universe in f(R) Gravity
In this paper, we solve the field equations in metric f(R) gravity for
Bianchi type VI_0 spacetime and discuss evolution of the expanding universe. We
find two types of non-vacuum solutions by taking isotropic and anisotropic
fluids as the source of matter and dark energy. The physical behavior of these
solutions is analyzed and compared in the future evolution with the help of
some physical and geometrical parameters. It is concluded that in the presence
of isotropic fluid, the model has singularity at and represents
continuously expanding shearing universe currently entering into phantom phase.
In anisotropic fluid, the model has no initial singularity and exhibits the
uniform accelerating expansion. However, the spacetime does not achieve
isotropy as in both of these solutions.Comment: 20 pages, 5 figures, accepted for publication in Astrophys. Space Sc
Large-scale collective motion of RFGC galaxies
We processed the data about radial velocities and HI linewidths for 1678 flat
edge-on spirals from the Revised Flat Galaxy Catalogue. We obtained the
parameters of the multipole components of large-scale velocity field of
collective non-Hubble galaxy motion as well as the parameters of the
generalized Tully-Fisher relationship in the "HI line width - linear diameter"
version. All the calculations were performed independently in the framework of
three models, where the multipole decomposition of the galaxy velocity field
was limited to a dipole, quadrupole and octopole terms respectively. We showed
that both the quadrupole and the octopole components are statistically
significant.
On the basis of the compiled list of peculiar velocities of 1623 galaxies we
obtained the estimations of cosmological parameters Omega_m and sigma_8. This
estimation is obtained in both graphical form and as a constraint of the value
S_8=sigma_8(Omega_m/0.3)^0.35 = 0.91 +/- 0.05.Comment: Accepted for publication in Astrophysics and Space Scienc
Cosmic Acceleration in Brans-Dicke Cosmology
We consider Brans-Dicke theory with a self-interacting potential in Einstein
conformal frame. We show that an accelerating expansion is possible in a
spatially flat universe for large values of the Brans-Dicke parameter
consistent with local gravity experiments.Comment: 10 Pages, 3 figures, To appear in General Relativity and Gravitatio
Large-scale collective motion of RFGC galaxies in curved space-time
We consider large-scale collective motion of flat edge-on spiral galaxies
from the Revised Flat Galaxy Catalogue (RFGC) taking into account the curvature
of space-time in the Local Universe at the scale 100 Mpc/h. We analyse how the
relativistic model of collective motion should be modified to provide the best
possible values of parameters, the effects that impact these parameters and
ways to mitigate them. Evolution of galactic diameters, selection effects, and
difference between isophotal and angular diameter distances are inadequate to
explain this impact. At the same time, measurement error in HI line widths and
angular diameters can easily provide such an impact. This is illustrated in a
toy model, which allows analytical consideration, and then in the full model
using Monte Carlo simulations. The resulting velocity field is very close to
that provided by the non-relativistic model of motion. The obtained bulk flow
velocity is consistent with {\Lambda}CDM cosmology.Comment: 10 pages, 3 figures, 2 table
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