855 research outputs found
CMB statistical anisotropy from noncommutative gravitational waves
No full textPrimordial statistical anisotropy is a key indicator to investigate early Universe models and has been probed by the cosmic microwave background (CMB) anisotropies. In this paper, we examine tensor-mode CMB fluctuations generated from anisotropic gravitational waves, parametrised by Ph(k) = Ph((0))(k) [ 1 + ∑LM fL(k) gLM YLM (hat k)], where Ph((0))(k) is the usual scale-invariant power spectrum. Such anisotropic tensor fluctuations may arise from an inflationary model with noncommutativity of fields. It is verified that in this model, an isotropic component and a quadrupole asymmetry with f(0)(k) = f(2)(k) propto k(-2) are created and hence highly red-tilted off-diagonal components arise in the CMB power spectra, namely l(2) = l(1) ± 2 in TT, TE, EE and BB, and l(2) = l(1) ± 1 in TB and EB. We find that B-mode polarisation is more sensitive to such signals than temperature and E-mode polarisation due to the smallness of large-scale cosmic variance and we can potentially measure g(00) = 30 and g(2)M = 58 at 68% CL in a cosmic-variance-limited experiment. Such a level of signal may be measured in a PRISM like experiment, while the instrumental noise contaminates it in the Planck experiment. These results imply that it is impossible to measure the noncommutative parameter if it is small enough for the perturbative treatment to be valid. Our formalism and methodology for dealing with the CMB tensor statistical anisotropy are general and straightforwardly applicable to other early Universe models
The two faces of mimetic Horndeski gravity: Disformal transformations and Lagrange multiplier
No full textWe show that very general scalar-tensor theories of gravity (including, e.g., Horndeski models) are generically invariant under disformal transformations. However there is a special subset, when the transformation is not invertible, that yields new equations of motion which are a generalization of the so-called "mimetic" dark matter theory recently introduced by Chamsedinne and Mukhanov. These conclusions hold true irrespective of whether the scalar field in the action of the assumed scalar-tensor theory of gravity is the same or different than the scalar field involved in the transformation. The new equations of motion for our general mimetic theory can also be derived from an action containing an additional Lagrange multiplier field. The general mimetic scalar-tensor theory has the same number of derivatives in the equations of motion as the original scalar-tensor theory. As an application we show that the simplest mimetic scalar-tensor model is able to mimic the cosmological background of a flat FLRW model with a barotropic perfect fluid with any constant equation of state
Cosmological perturbations in mimetic Horndeski gravity
No full textWe study linear scalar perturbations around a flat FLRW background in mimetic Horndeski gravity. In the absence of matter, we show that the Newtonian potential satisfies a second-order differential equation with no spatial derivatives. This implies that the sound speed for scalar perturbations is exactly zero on this background. We also show that in mimetic G(3) theories the sound speed is equally zero. We obtain the equation of motion for the comoving curvature perturbation (first order differential equation) and solve it to find that the comoving curvature perturbation is constant on all scales in mimetic Horndeski gravity. We find solutions for the Newtonian potential evolution equation in two simple models. Finally we show that the sound speed is zero on all backgrounds and therefore the system does not have any wave-like scalar degrees of freedom
CMB constraints on running non-Gaussianity
No full textWe develop a complete set of tools for CMB forecasting, simulation and estimation of primordial running bispectra, arising from a variety of curvaton and single-field (DBI) models of Inflation. We validate our pipeline using mock CMB running non-Gaussianity
realizations and test it on real data by obtaining experimental constraints on the f_NL running spectral index, n_NG, using WMAP 9-year data. Our final bounds (68% C.L.) read −0.6 < n_NG < 1.4, −0.3 < n_NG < 1.2, −1.1 < n_NG < 0.7 for the single-field curvaton,
two-field curvaton and DBI scenarios, respectively. We show forecasts and discuss potential
improvements on these bounds, using Planck and future CMB surveys
Large-scale structure in mimetic Horndeski gravity
No full textIn this paper, we propose to use the mimetic Horndeski model as a model for the dark universe. Both cold dark matter (CDM) and dark energy (DE) phenomena are described by a single component, the mimetic field. In linear theory, we show that this component effectively behaves like a perfect fluid with zero sound speed and clusters on all scales. For the simpler mimetic cubic Horndeski model, if the background expansion history is chosen to be identical to a perfect fluid DE (PFDE) then the mimetic model predicts the same power spectrum of the Newtonian potential as the PFDE model with zero sound speed. In particular, if the background is chosen to be the same as that of LCDM, then also in this case the power spectrum of the Newtonian potential in the mimetic model becomes indistinguishable from the power spectrum in LCDM on linear scales. A different conclusion may be found in the case of non-adiabatic perturbations. We also discuss the distinguishability, using power spectrum measurements from LCDM N-body simulations as a proxy for future observations, between these mimetic models and other popular models of DE. For instance, we find that if the background has an equation of state equal to ‐0.95 then we will be able to distinguish the mimetic model from the PFDE model with unity sound speed. On the other hand, it will be hard to do this distinction with respect to the LCDM model
Living with ghosts in Hořava-Lifshitz gravity
No full textWe consider the branch of the projectable Hořava-Lifshitz model which exhibits ghost instabilities in the low energy limit. It turns out that, due to the Lorentz violating structure of the model and to the presence of a finite strong coupling scale, the vacuum decay rate into photons is tiny in a wide range of phenomenologically acceptable parameters. The strong coupling scale, understood as a cutoff on ghosts’ spatial momenta, can be raised up to Λ ∼ 10 TeV. At lower momenta, the projectable Hořava-Lifshitz gravity is equivalent to General Relativity supplemented by a fluid with a small positive sound speed squared (10−42 ≲) cs^2 ≲ 10−20, that could be a promising candidate for the Dark Matter. Despite these advantages, the unavoidable presence of the strong coupling obscures the implementation of the original Hořava’s proposal on quantum gravity. Apart from the Hořava-Lifshitz model, conclusions of the present work hold also for the mimetic matter scenario, where the analogue of the projectability condition is achieved by a non-invertible conformal transformation of the metric
A comparative life cycle assessment of centralised and decentralised wood pellets production for residential heating
No full textRecently, wood pellets have become a reliable and clean renewable fuel for residential heating, replacing fossil fuels and reducing greenhouse gas emissions. Wood pellets are normally produced in industrial pellet plants (centralised production), but decentralised small-scale local production also occurs. This study applies Life Cycle Assessment (LCA) to quantify and compare the environmental profile of one centralised and two decentralised alternatives for wood pellet production for residential heating in Portugal: (1) industrial wood pellets production (centralised), (2) wood pellets production at sawmills (decentralised) and (3) wood pellets production at households (decentralised). System boundaries include the stages of forest management, wood pellet production, wood pellet distribution and wood pellet energetic conversion. The impact results show that industrial pellet production ranks as the worst alternative, while pellet production at households has the best environmental profile for all the impact categories under study. However, the environmental impacts of pellet production at the sawmill do not differ greatly from those of the pellet production at households; they are 14 to 16% higher for global warming and fossil resources scarcity and 0.3 to 3% higher for the remaining impact categories. The worst environmental performance of the industrial pellet production alternative is mainly due to high electricity and diesel consumption during wood pellet production and the use of logging residues to generate heat for drying biomass feedstock. A sensitivity analysis was performed to evaluate the influence of changing the distance travelled during the transport of packed pellets to stores and sawdust to households. The results show changes in the environmental performance ranking, highlighting that for short distances, both decentralised alternatives can be more sustainable from an environmental perspective than the centralised alternative, but for larger distances, the pellet production at households should be avoided
Aplicabilidade do reactor MBBR no tratamento de efluentes vínicos
No full textMestrado em Gestão Ambiental, Materiais e Valorização de ResíduosO presente trabalho pretendeu analisar a aplicabilidade do reactor do tipo
Moving Bed Biofilm Reactor (MBBR) no tratamento de efluentes vínicos.
A natureza dos efluentes provenientes das adegas depende da região e do
tipo de vinho processado e, para além disso, a sua quantidade e a qualidade
variam significativamente ao longo do ano.
Os principais objectivos deste trabalho foram analisar a aplicabilidade do
reactor MBBR no tratamento de efluentes vínicos a operar com um tempo de
retenção hidráulico de 24 horas, comparar o desempenho de reactores quando
são utilizados meios de enchimento com características diferentes, comparar o
desempenho de reactores com e sem recirculação de lamas e analisar o
comportamento hidráulico deste tipo de reactores com e sem a presença de
biomassa.
Foram realizados ensaios em cinco reactores à escala laboratorial, em que
quatro deles tinham enchimento, dos quais dois operaram com recirculação de
lamas e os outros dois sem recirculação. O quinto reactor simulou um reactor
de lamas activadas convencional com recirculação de lamas. Utilizaram-se
dois tipos de enchimento, o Bioflow 9 e o Bioflow 40.
Os modelos de escoamento hidráulico dos diferentes reactores foram
determinados recorrendo a ensaios de tracer com e sem a presença de
biomassa. Os ensaios efectuados demonstraram que os reactores que
possuem enchimento têm comportamentos hidráulicos idênticos, sendo ambos
caracterizados por modelos de mistura perfeita com zonas mortas e a
percentagem de zonas mortas diminui nos ensaios realizados com biomassa
(35-36% de zonas mortas para 10-12% de zonas mortas), concluindo-se que o
grau de mistura melhora com a existência de biomassa. O reactor de lamas
activadas foi caracterizado, em ambos os ensaios, pelo modelo de mistura
perfeita com zonas mortas e curto-circuito, havendo uma ligeira alteração dos
parâmetros quando o reactor opera com biomassa (28% de zonas mortas, 9%
de curto-circuito para 26% de zonas mortas e 10% de curto-circuito).
No presente estudo verificou-se que as condições limite de operação dos
reactores foram alcançadas para um TRH de 24 h, 50% da altura do reactor
com enchimento Bioflow 9 e o CQOalimentação = 8000 mg.L-1 (8,0. kgCQO.m-3.d-
1). Nestas condições o efluente tratado apresentou um CQOsolúvel = 1500 mg.L-1
correspondente a uma percentagem de remoção de CQO de 81%.
Verificou-se também que para todos os reactores e em todas as condições
operatórias testadas até à carga orgânica 6,5 kgCQO.m-3.d-1, a percentagem
de remoção de CQO foi superior a 90%. Os resultados mais elevados
registaram-se na carga 6,0 kgCQO.m-3.d-1, com valores próximos de 98%. Os
valores de CQOsolúvel do efluente tratado nos diferentes reactores não
ultrapassaram os 150 mg.L-1 até à carga 6,0 kgCQO.m-3.d-1, verificando-se um
aumento significativo em cargas superiores.
Concluiu-se que a recirculação de biomassa suspensa não exerce efeitos
positivos na eficiência dos reactores, no entanto durante o período de arranque
diminui significativamente o tempo de estabilização dos mesmos.
ABSTRACT: The present study intended to evaluate the applicability of a MBBR reactor for
the treatment of winery wastewaters.
The wastewater originated in wine cellars strongly depends on the region and
the type of wine processed and also its quantity and quality changes
substantially during the year.
The aims of this experimental study were to analyse the applicability of a
MBBR reactor for the winery wastewater treatment operating with a hydraulic
retention time of 24 hours, to compare the performance of reactors when
different packing bed materials were used, to compare the performance of
reactors with and without sludge recycling, and finally to examine the hydraulic
behaviour of each reactor with and without biomass.
Experiments were conducted with five lab-scale reactors where four had
packing material, two operating with sludge recycling, two without it and a fifth
reactor simulated a conventional activated sludge system. Two types of carrier
elements were used, the Bioflow 9 and the Bioflow 40.
The hydraulic flow models for the five reactors were determined recoursing to
experimental studies with tracer elements in the presence and in the absence
of biomass.
Tracer studies demonstrated that the reactors filled with carrier elements had
identical flow models and behaved as complete mixing reactors with dead
spaces. The fraction of dead spaces decreases in experiments with biomass
(35-36% of dead spaces to 10-12% of dead spaces), concluding that the
degree of mixture improves in the presence of biomass. The activated sludge
flow model was characterized, in both cases, as complete mixing reactor with
dead spaces and short-circuiting with a slightly difference on the parameters in
the presence of biomass (28% of dead spaces, 9% of short-circuiting to 26% of
dead spaces and 10% of short-circuiting).
In the present study it was verified that the limit operation conditions of the
reactors were reached for a HRT of 24 h, 50% of the reactor volume packed
with Bioflow 9 and a CODfeed= 8000 mg.L-1 (8,0 kgCOD.m-3.d-1). At this
operational conditions the treated wastewater had a CODsoluble = 1500 mg.L-1
corresponding to a COD removal rate of 81%.
It was also verified that for all the reactors and in all the operation conditions up
to the organic load applied of 6,5 kgCOD.m-3.d-1, the COD removal rate was
higher than 90%. The highest results were obtained at an organic load of 6,0
kgCOD.m-3.d-1 with values near 98%.
The COD soluble values of the treated winery wastewater in the different
reactors didn’t exceed 150 mg.L-1 up to an organic load of 6,0 kgCOD.m-3.d-1,
and for higher loads a significant increase was verified.
The sludge recycling doesn’t affect in a positive way the efficiency of the
reactors, although during the start-up phase the reduction of the stabilization
time was significant
Planck 2018 results: IX. Constraints on primordial non-Gaussianity
No full textCSIC, MINECO, JA, and RES (Spain); ERC and PRACE (EU) (...)Akrami, Y., Arroja, F., Ashdown, M., Aumont, J., Baccigalupi, C., Ballardini, M., Banday, A.J., Barreiro, R.B., Bartolo, N., Basak, S., Benabed, K., Bernard, J.-P., Bersanelli, M., Bielewicz, P., Bond, J.R., Borrill, J., Bouchet, F.R., Bucher, M., Burigana, C., Butler, R.C., Calabrese, E., Cardoso, J.-F., Casaponsa, B., Challinor, A., Chiang, H.C., Colombo, L.P.L., Combet, C., Crill, B.P., Cuttaia, F., De Bernardis, P., De Rosa, A., De Zotti, G., Delabrouille, J., Delouis, J.-M., Di Valentino, E., Diego, J.M., Doré, O., Douspis, M., Ducout, A., Dupac, X., Dusini, S., Efstathiou, G., Elsner, F., Enßlin, T.A., Eriksen, H.K., Fantaye, Y., Fergusson, J., Fernandez-Cobos, R., Finelli, F., Frailis, M., Fraisse, A.A., Franceschi, E., Frolov, A., Galeotta, S., Galli, S., Ganga, K., Génova-Santos, R.T., Gerbino, M., González-Nuevo, J., Górski, K.M., Gratton, S., Gruppuso, A., Gudmundsson, J.E., Hamann, J., Handley, W., Hansen, F.K., Herranz, D., Hivon, E., Huang, Z., Jaffe, A.H., Jones, W.C., Jung, G., Keihänen, E., Keskitalo, R., Kiiveri, K., Kim, J., Krachmalnicoff, N., Kunz, M., Kurki-Suonio, H., Lamarre, J.-M., Lasenby, A., Lattanzi, M., Lawrence, C.R., Le Jeune, M., Levrier, F., Lewis, A., Liguori, M., Lilje, P.B., Lindholm, V., López-Caniego, M., Ma, Y.-Z., Maciás-Pérez, J.F., Maggio, G., Maino, D., Mandolesi, N., Marcos-Caballero, A., Maris, M., Martin, P.G., Martínez-González, E., Matarrese, S., Mauri, N., McEwen, J.D., Meerburg, P.D., Meinhold, P.R., Melchiorri, A., Mennella, A., Migliaccio, M., Miville-Deschênes, M.-A., Molinari, D., Moneti, A., Montier, L., Morgante, G., Moss, A., Münchmeyer, M., Natoli, P., Oppizzi, F., Pagano, L., Paoletti, D., Partridge, B., Patanchon, G., Perrotta, F., Pettorino, V., Piacentini, F., Polenta, G., Puget, J.-L., Rachen, J.P., Racine, B., Reinecke, M., Remazeilles, M., Renzi, A., Rocha, G., Rubiño-Martín, J.A., Ruiz-Granados, B., Salvati, L., Savelainen, M., Scott, D., Shellard, E.P.S., Shiraishi, M., Sirignano, C., Sirri, G., Smith, K., Spencer, L.D., Stanco, L., Sunyaev, R., Suur-Uski, A.-S., Tauber, J.A., Tavagnacco, D., Tenti, M., Toffolatti, L., Tomasi, M., Trombetti, T., Valiviita, J., Van Tent, B., Vielva, P., Villa, F., Vittorio, N., Wandelt, B.D., Wehus, I.K., Zacchei, A., Zonca, A
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