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Now showing items 1 - 16 of 93934

  • The cycle of biodiesel production from Crambe abyssinica in Portugal

    Costa, E.   Almeida, M. F.   Alvim-Ferraz, C.   Dias, J. M.  

    Biodiesel is usually produced from edible oils which compete with the food market. Crambe abyssinica is a non-food crop referred as having high potential for biodiesel production. An entire cycle of seeding, harvesting, oil extraction and biodiesel production was performed with Crambe; probably, the first study carried out with this specie in Portugal aiming to evaluate its full viability. Biodiesel was produced from crude and refined oil of Crambe seeds cultivated (oil content of 26 +/- 4 wt.%) and the results were compared to those obtained using a commercial oil originated from Brazil, where most studies are found. Biodiesel produced from the oil extracted from the Portuguese seeds showed good quality fulfilling almost all the requirements settled by EN 14214. The viscosity (5.80 mm(2) s(-1)) and the cold filter plugging point (7 degrees C), which are mostly associated with the oil's nature, were close to the limits, indicating the need for blending at an industrial scale. Anyway, the biodiesel produced with the refined oil showed the highest quality, due to the lower level of contaminants. The high oxidation stability (16 h) of the biodiesel produced from seeds cultivated in Portugal can be argued as an advantage for this product. The study shows that Crambe oil might be a promising complementary alternative to the conventional edible oils used for biodiesel production.
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  • Tetra and pentaquarks from the molecular perspective

    Oset, E.   Wang, En   Xie, J.J.   Geng, L.S.   Debastiani, V.R.   Dias, J. M.   Liang, W. H.   Wrońska, A.   Magiera, A.   Przygoda, W.  

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  • Understanding close-lying exotic charmonia states within QCD sum rules

    Martinez Torres, A.   Khemchandani, K. P.   Dias, J. M.   Navarra, F. S.   Nielsen, M.  

    Motivated by the experimental findings of some new exotic states decaying into channels like J/psi phi, we investigate the formation of resonances/bound states in the Ds*(D) over bars* system using QCD sum rules. To do this we start with a current of the type vector times vector and use spin projectors to separate the spin 0, 1 and 2 contributions to the correlation function. We find three states with isospin 0, nearly spin degenerate, with a mass around 4.1 GeV. We have also investigated the decay of these states to J/psi phi and provide the corresponding partial widths. Such information should be useful for experimental studies in future. (C) 2017 Elsevier B.V. All rights reserved.
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  • The radiative decay D-0 -> (K)over-bar*(0)gamma with vector meson dominance

    Dias, J. M.   Debastiani, V. R.   Xie, Ju-Jun   Oset, E.  

    Motivated by the experimental measurements of D-0 radiative decay modes, we have proposed a model to study the D-0 -> (K) over bar*(0)gamma decay, by establishing a link with D-0 -> (K) over bar*(0) V (V =3D rho(0), omega) decays through the vector meson dominance hypothesis. In order to do this properly, we have used the Lagrangians from the local hidden gauge symmetry approach to account for V gamma conversion. As a result, we have found the branching ratio B[D-0 -> (K) over bar*(0)gamma]=3D(1.55-3.44)x10(-4), which is in fair agreement with the experimental values reported by the Belle and BaBar collaborations.
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  • Influence of upwelling on SST trends in La Guajira system

    Santos, F.   Gomez-Gesteira, M.   Varela, R.   Ruiz-Ochoa, M.   Dias, J. M.  

    La Guajira upwelling system has shown a moderate cooling (similar to-0.05 degrees C dec(-1)) over the period 1982-2014 for the months with strong upwelling (JFM). This contrasts with the general warming observed for most of the Caribbean region (similar to 0.25 degrees C dec(-1)) over the same period. Cooling is in good agreement with the upwelling increase (similar to 0.04 m(2)s(-1)dec(-1)) observed in the region during winter months, although the position of the peaks in upwelling and SST trends does not coincide exactly due to the presence of the Caribbean Coastal Undercurrent.
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  • Global and regional evolution of sea surface temperature under climate change

    Ruela, R.   Sousa, M. C.   deCastro, M.   Dias, J. M.  

    Sea surface temperature (SST) has important local and remote influence on global climate through the distribution and transport of heat and moisture, which in turn affect precipitation and air temperature patterns across the globe. Thus, this work aims to assess the worldwide regionalization of the SST evolution for the 21st century under the influence of climate change by means of: 1) division of the worldwide SST data in regions applying a K-means cluster procedure and validation of the most suitable CMIP5 models by a comparative analysis with SST data from Era-Interim reanalysis; 2) calculation of SST trends along the 21st century and assessment of future SST differences between RCP 4.5 and RCP 8.5 greenhouse gas emission scenarios and historical SST data. Global climate model (GCM) projections show a SST warming worldwide although with different intensity depending on the region. Northern Hemisphere regions present a higher seasonal thermal amplitude comparing with equivalent regions in the Southern Hemisphere. Northern Hemisphere has also a higher annual SST increment than clusters in the Southern Hemisphere, independently of the future time period and climate scenario. The Northern Sub-Tropical cluster (STRN) shows the highest significant increment (4.34 degrees C on RCP 8.5). Under the RCP 4.5 climate scenario, SST trends from 1975 to 2100 range from 0.075 degrees C dec(-1) at South Polar cluster (PRS) to 0.21 degrees C dec(-1) at STRN cluster. Relatively to RCP 8.5 climatic scenario, SST trends change from 0.13 degrees C dec(-1) at PRS cluster to 0.36 degrees C dec(-1) at the North Polar cluster (PRN).
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  • A QCD sum rule calculation of the X-+/-(5568) -> B-s(0)pi(+/-) decay width

    Dias, J. M.   Khemchandani, K. P.   Martinez Torres, A.   Nielsen, M.   Zanetti, C. M.  

    To understand the nature of the X(5568), recently observed in the mass spectrum of the B-s(0)pi(+/-) system by the D0 Collaboration, we have investigated, in a previous work, a scalar tetraquark (diquak-antidiquark) structure for it, within the two-point QCD sum rules method. We found that it is possible to obtain a stable value of the mass compatible with the D0 result, although a rigorous QCD sum rule constrained analysis led to a higher value of mass. As a continuation of our investigation, we calculate the width of the tetraquark state with same quark content as X(5568), to the channel B-s(0)pi(+/-), using the three-point QCD sum rule. We obtain a value of (20.4 +/- 8.7) MeV for the mass similar to 5568 MeV, which is compatible with the experimental value of 21.9 +/- 6.4(sta)(-2.5)(+5.0)(syst) MeV/c(2). We find that the decay width to B-s(0)pi(+/-) does not alter much for a higher mass state. (C) 2016 Published by Elsevier B.V.
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  • X, Y and Z States

    Nielsen, M.   Albuquerque, R. M.   Dias, J. M.   Khemchandani, K. P.   Martinez Torres, A.   Navarra, F. S.   Zanetti, C. M.  

    Many new states in the charmonium mass region were recently discovered by BaBar, Belle, CLEO-c, CDF, DO, BESIII, LHCb and CMS Collaborations. We use the QCD Sum Rule approach to study the possible structure of some of these states.
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  • f(1)(1285) decays into a(0)(980) pi(0),f(0)(980) pi(0) and isospin breaking

    Aceti, F.   Dias, J. M.   Oset, E.  

    We evaluate the decay width for the processes f1(1285). p 0 a0(980) and f1(1285). p 0 f0(980) taking into account that all three resonances are dynamically generated from the meson- meson interaction, the f1(1285) from K* _ K - c. c. and the a0(980), f0(980) from p., K _ K and pp, K _ K, respectively. We use a triangular mechanism similar to that of.(1405). pp., which provides a decay width for f1(1285). p 0 a0(980) with a branching fraction of the order of 30%, in agreement with experiment. At the same time we evaluate the decay width for the isospin- forbidden f1(1285). p 0 f0(980), which appears when we consider different masses for the charged and neutral kaons, and show that it is much more suppressed than in the.(1405). pp. case, but gives rise to a narrow shape of the p + p- distribution similar to the one found in the eta(1405) -> pi pi eta decay.
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  • Relation Between Tcc,bb and Xc,b from QCD

    Dias, J. M.   Narison, S.   Navarra, F. S.   Nielsen, M.   Richard, J. M.  

    We use double ratio of QCD (spectral) sum rules, to study the ratio masses of T-cc and X(3872) structures, assuming that they are described respectively by the DD* and D (D) over bar* molecular currents. In this approach and within our approximation, we found that the masses of these two states are almost degenerated. In addition, if the observed Belle resonance X(3872) is a D (D) over bar* molecule, then the DD* molecule should exists with approximately the same mass. We have studied an extension for the case including bottom quark. In this situation, our results indicates the same conclusion.
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  • decay width in QCD sum rules

    Dias, J. M.   Navarra, F. S.   Nielsen, M.   Zanetti, C. M.  

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  • Prediction of a Z(c)(4000) state and relationship with the claimed Z(c)(4025)

    Aceti, F.   Bayar, M.   Dias, J. M.   Oset, E.  

    After discussing the OZI suppression of one light meson exchange in the interaction of with isospin I = 1 , we study the contribution of the two-pion exchange to the interaction and the exchange of heavy vectors, J/psi for diagonal transitions and D-* for transitions of to J/psi rho. We find these latter mechanisms to be weak, but enough to barely bind the system in J = 2 with a mass around 4000 MeV, while the effect of the two-pion exchange is a net attraction, though weaker than that from heavy-vector exchange. We discuss this state and try to relate it to the Z (c) (4025) state, above the threshold, claimed in an experiment at BES from an enhancement of the distribution close to threshold. Together with the results from a recent reanalysis of the BES experiment showing that it is compatible with a J = 2 state below threshold around 3990 MeV, we conclude that the BES experiment could show the existence of the state that we find in our approach.
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  • as a mixed charmonium-tetraquark state

    Dias, J. M.   Albuquerque, R. M.   Nielsen, M.   Zanetti, C. M.  

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  • An ultra-high gain and efficient amplifier based on Raman amplification in plasma

    Vieux, G.   Cipiccia, S.   Grant, D. W.   Lemos, N.   Grant, P.   Ciocarlan, C.   Ersfeld, B.   Hur, M. S.   Lepipas, P.   Manahan, G. G.   Raj, G.   Gil, D. Reboredo   Subiel, A.   Welsh, G. H.   Wiggins, S. M.   Yoffe, S. R.   Farmer, J. P.   Aniculaesei, C.   Brunetti, E.   Yang, X.   Heathcote, R.   Nersisyan, G.   Lewis, C. L. S.   Pukhov, A.   Dias, J. M.   Jaroszynski, D. A.  

    Raman amplification arising from the excitation of a density echelon in plasma could lead to amplifiers that significantly exceed current power limits of conventional laser media. Here we show that 1-100 J pump pulses can amplify picojoule seed pulses to nearly joule level. The extremely high gain also leads to significant amplification of backscattered radiation from "noise", arising from stochastic plasma fluctuations that competes with externally injected seed pulses, which are amplified to similar levels at the highest pump energies. The pump energy is scattered into the seed at an oblique angle with 14 J sr(-1), and net gains of more than eight orders of magnitude. The maximum gain coefficient, of 180 cm(-1), exceeds high-power solid-state amplifying media by orders of magnitude. The observation of a minimum of 640 J sr(-1) directly backscattered from noise, corresponding to approximate to 10% of the pump energy in the observation solid angle, implies potential overall efficiencies greater than 10%.
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  • Relation between Tcc,bb and Xc,b from QCD

    Dias, J. M.   Narison, S.   Navarra, F. S.   Nielsen, M.   Richard, J. -M.  

    We have studied, using double ratio of QCD (spectral) sum rules, the ratio between the masses of T(cc) and X(3872) assuming that they are respectively described by the D - D* and D - (D) over bar* molecular currents. We found (within our approximation) that the masses of these two states are almost degenerate. Since the pion exchange interaction between these mesons is exactly the same, we conclude that if the observed X(3872) meson is a D (D) over bar* + c.c. molecule, then the DD* molecule should also exist with approximately the same mass. An extension of the analysis to the b-quark case leads to the same conclusion. We also study the SU(3) breakings for the T(QQ)(s)/T(QQ) mass ratios. Motivated by the recent Belle observation of two Z(b) states, we revise our determination of X(b) by combining results from exponential and FESR sum rules. (C) 2011 Elsevier B.V. All rights reserved.
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  • Forward directed ion acceleration in a LWFA with ionization-induced injection

    Lemos, N.   Martins, J. L.   Dias, J. M.   Marsh, K. A.   Pak, A.   Joshi, C.  

    In this work we present an experimental study where energetic ions were produced in an underdense 2.5 x 10(19) cm(-3) plasma created by a 50 fs Ti:Sapphire laser with 5 TWs of power. The plasma comprises 95% He and 5% N-2 gases. Ionization-induced trapping of nitrogen K-shell electrons in the laser-induced wakefield generates an electron beam with a mean energy of 40 MeV and similar to 1 nC of charge. Some of the helium ions at the wake-vacuum interface are accelerated with a measured minimum ion energy of He1+ ions of 1.2 MeV and He2+ ions of 4 MeV. The physics of the interaction is studied with 2D particle-in-cell simulations. These reveal the formation of an ion filament on the axis of the plasma due to space charge attraction of the wakefield-accelerated high-charge electron bunch. Some of these high-energy electrons escape the plasma to form a sheath at the plasma vacuum boundary that accelerates some of the ions in the filament in the forward direction. Electrons with energy less than the sheath potential cannot escape and return to the plasma boundary in a vortex-like motion. This in turn produces a time-varying azimuthal magnetic field, which generates a longitudinal electric field at the interface that further accelerates and collimates the ions.
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