469 research outputs found
Probing the infrared quark mass from highly excited baryons
We argue that three-quark excited states naturally group into quartets, split
into two parity doublets, and that the mass splittings between these parity
partners decrease higher up in the baryon spectrum. This decreasing mass
difference can be used to probe the running quark mass in the mid-infrared
power-law regime. A measurement of masses of high-partial wave Delta*
resonances should be sufficient to unambiguously establish the approximate
degeneracy. We test this concept with the first computation of excited high-j
baryon masses in a chirally invariant quark model.Comment: 4 pages, 4 figures. submitted to Phys Rev Letter
Using highly excited baryons to catch the quark mass
Chiral symmetry in QCD can be simultaneously in Wigner and Goldstone modes,
depending on the part of the spectrum examined. The transition regime between
both, exploiting for example the onset of parity doubling in the high baryon
spectrum, can be used to probe the running quark mass in the mid-IR power-law
regime. In passing we also argue that three-quark states naturally group into
same-flavor quartets, split into two parity doublets, all splittings decreasing
high in the spectrum. We propose that a measurement of masses of high-partial
wave Delta* resonances should be sufficient to unambiguously establish the
approximate degeneracy and see the quark mass running. We test these concepts
with the first computation of the spectrum of high-J excited baryons in a
chiral-invariant quark model.Comment: 6 pages, 9 figures, To appear in the proceedings of the 19th
International IUPAP Conference on Few-Body Problems in Physics; added
acknowledgment, hyphenized author nam
Time evolution of the behaviour of Brazilian legislative Representatives using a complex network approach
The follow up of Representative behavior after elections is imperative for a
democratic Representative system, at the very least to punish betrayal with no
re-election. Our goal was to show how to follow Representatives' and how to
show behavior in real situations and observe trends in political crises
including the onset of game changing political instabilities. We used
correlation and correlation distance matrices of Brazilian Representative votes
during four presidential terms. Re-ordering these matrices with Minimal
Spanning Trees displays the dynamical formation of clusters for the sixteen
year period, which includes one Presidential impeachment. The reordered
matrices, colored by correlation strength and by the parties clearly show the
origin of observed clusters and their evolution over time. When large clusters
provide government support cluster breaks, political instability arises, which
could lead to an impeachment, a trend we observed three years before the
Brazilian President was impeached. We believe this method could be applied to
foresee other political storms.Comment: 11 pages, 4 Figure
On the distribution of an effective channel estimator for multi-cell massive MIMO
Accurate channel estimation is of utmost importance for massive MIMO systems to provide significant improvements in spectral and energy efficiency. In this work, we present a study on the distribution of a simple but yet effective and practical channel estimator for multi-cell massive MIMO systems suffering from pilot-contamination. The proposed channel estimator performs well under moderate to aggressive pilot contamination scenarios without previous knowledge of the inter-cell large-scale channel coefficients and noise power, asymptotically approximating the performance of the linear MMSE estimator as the number of antennas increases. We prove that the distribution of the proposed channel estimator can be accurately approximated by the circularly-symmetric complex normal distribution, when the number of antennas, M, deployed at the base station is greater than 10
Resistência genética de clones de cajueiro anão precoce às principais fitomoléstias.
No processo seletivo de clones de cajueiro anão precoce, diversos atributos têm sido considerados. Entretanto, o uso da resistência genética a doenças ainda e pouco conhecida e explorada. Este trabalho se propos determinar a variabilidade genética e identificar genótipos resistentes de cajueiro anão precoce quanto a antracnose (Colletotrichum gloeosporioides), ao mofo preto (Pilgeriella anacardium) e a mancha-angular (Septoria anacardil), as doenças mais importantes da cultura no Brasil. Os coeficientes de determinação genotÃpica foram de 80,72%, 85,20% e 74,92% para a antracnose, mofo-preto e mancha-angular, respectivamente. Os clones que demonstraram maior grau de resistência foram CAP 14, CAP 17, CAP 05 e CAP 07, para a antracnose; CAP 08, CAP 17 e CAP 11, para o mofo-preto e CAP 02, CAP 05 e CAP 03, para a mancha-angular. Verificou-se que entre os clones comerciais, o CCP 06 apresentou maior resistência a antracnose e ao mofo-preto, enquanto que os clones CCP 76 e CCP 1001 foram mais suscetÃveis ao mofo-preto e o CCP 09 a antracnose. Os resultados indicam ampla variabilidade genética entre os clones, para todas as doenças avaliadas, possibilitando progresso genético por meio de seleção fenotÃpica.bitstream/CNPAT-2010/5486/1/Bp-034.pd
Evaluation of the chemical additive effect on asphaltene aggregation in dead oils: a comparative study between ultraviolet–visible and near-infrared-laser light scattering techniques
Asphaltenes flocculate as a consequence of changes in the temperature, pressure, or composition. This flocculation can result in several oil production problems. The application of chemical additives (inhibitors or dispersants) is a well-known way to control asphaltene flocculation. Ultraviolet-visible (UV-vis) spectroscopy is the most common analytical technique that has been applied to study the effectiveness of chemical additives in keeping asphaltene particles dispersed into crude oils. However, this technique requires being performed in diluted solutions, which can interfere significantly in the aggregation phenomena. The objective of this work was to evaluate the effect of three chemical additives, 4-dodecyl benzenesulfonic acid (DBSA) and two commercial products (CO and C1), on the asphaltene aggregation behavior of two Brazilian crude oils, using near-infrared (NIR)-laser (lambda = 1550 nm) scattering measurements. This is a new methodology developed to study the aggregation kinetics and settling of asphaltenes around its n-heptane flocculation onset. The NIR-laser scattering method offers the possibility to work with samples at a higher crude oil concentration, being more representative of real systems. The results obtained were compared to those determined with the traditional UV-vis method (lambda = 850 nm) and showed qualitatively similar trends. Settling measurements suggest that the stabilization provided by the additives can occur by slowing both formation and growing of asphaltene particles and delaying the phase separation process. DBSA was more effective in keeping the asphaltene particles dispersed in solution and prevented them from settling at lower concentrations when compared to commercial products, for both crude oils studied. It was demonstrated that the methodology developed using NIR-laser scattering was more accurate and sensitive.Asphaltenes flocculate as a consequence of changes in the temperature, pressure, or composition. This flocculation can result in several oil production problems. The application of chemical additives (inhibitors or dispersants) is a well-known way to cont29528132822sem informaçãosem informaçãoThe authors acknowledge Petrobras for their financial suppor
Reação de clones comerciais de cajueiro anão à antracnose e ao mofo preto.
A expansao da cultura do cajueiro depende, fundamentalmente, da adocao de modernas tecnicas de producao, colheita e utilizacao de seus produtos. Evidentemente, o uso de clones de cajueiro anao representa um consenso generalizado dentro deste novo enfoque empresarial da cultura.bitstream/CNPAT-2010/11951/1/Ct-012.pd
Channel estimation for massive MIMO TDD systems assuming pilot contamination and frequency selective fading
Channel estimation is crucial for massive multiple-input multiple-output (MIMO) systems to scale up multi-user MIMO, providing significant improvement in spectral and energy efficiency. In this paper, we present a simple and practical channel estimator for multipath multi-cell massive MIMO time division duplex systems with pilot contamination, which poses significant challenges to channel estimation. The proposed estimator addresses performance under moderate to strong pilot contamination without previous knowledge of the inter-cell large-scale fading coefficients and noise power. Additionally, we derive and assess an approximate analytical mean square error (MSE) expression for the proposed channel estimator. We show through simulations that the proposed estimator performs asymptotically as well as the minimum MSE estimator with respect to the number of antennas and multipath coefficients
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