776 research outputs found
Universal geometrical scaling of the elliptic flow
The presence of scaling variables in experimental observables provide very
valuable indications of the dynamics underlying a given physical process. In
the last years, the search for geometric scaling, that is the presence of a
scaling variable which encodes all geometrical information of the collision as
well as other external quantities as the total energy, has been very active.
This is motivated, in part, for being one of the genuine predictions of the
Color Glass Condensate formalism for saturation of partonic densities. Here we
extend these previous findings to the case of experimental data on elliptic
flow. We find an excellent scaling for all centralities and energies, from RHIC
to LHC, with a simple generalization of the scaling previously found for other
observables and systems. Interestingly the case of the photons, difficult to
reconcile in most formalisms, nicely fit the scaling curve. We discuss the
possible interpretations of this finding in terms of initial or final state
effects.Comment: 6 pages, 4 figures, accepted for publication in Phys Rev
Limiting fragmentation in heavy-ion collisions and percolation of strings
The observed limiting fragmentation of charged particle distributions in
heavy ion collisions is difficult to explain as it does not apply to the proton
spectrum itself. On the other hand, string percolation provides a mechanism to
regenerate fast particles, eventually compensating the rapidity shift (energy
loss) of the nucleons. However a delicate energy-momentum compensation is
required, and in our framework we see no reason for limiting fragmentation to
be exact. A prediction, based on percolation arguments, is given for the
charged particle density in the full rapidity interval at LHC energy .Comment: 9 pages, 2 figures (2 eps files), late
On Hierarchy and Equivalence of Relativistic Equations for Massive Fields
A non-canonical correspondence of the complete sets of solutions to the Dirac
and Klein-Gordon free equations in Minkowski space-time is established. This
allows for a novel viewpoint on the relationship of relativistic equations for
different spins and on the origin of spinor transformations. In particular,
starting from a solution to the Dirac equation, one obtains a chain of other
solutions to both Dirac and Klein-Gordon equations. A comparison with the
massless case is performed, and examples of non-trivial singular solutions are
presented. A generalization to Riemannian space-time and inclusion of
interactions are briefly discussed.Comment: 7 pages, twocolumn. Problem of construction the hierarchy of
solutions in the massive case reformulate
Infanticide in Chimpanzees: Taphonomic Case Studies from Gombe
Objectives
We present a study of skeletal damage to four chimpanzee (Pan troglodytes) infanticide victims from Gombe National Park, Tanzania. Skeletal analysis may provide insight into the adaptive significance of infanticide by examining whether nutritional benefits sufficiently explain infanticidal behavior. The nutritional hypothesis would be supported if bone survivorship rates and skeletal damage patterns are comparable to those of monkey prey. If not, other explanations, such as the resource competition hypothesis, should be considered. Methods
Taphonomic assessment of two chimpanzee infants included description of breakage and surface modification, data on MNE, %MNE, and bone survivorship. Two additional infants were assessed qualitatively. The data were compared to published information on monkey prey. We also undertook a review of published infanticide cases. Results
The cases were intercommunity infanticides (one male and three female infants) committed by males. Attackers partially consumed two of the victims. Damage to all four infants included puncture marks and compression fractures to the cranium, crenulated breaks to long bones, and incipient fractures on ribs. Compared to monkey prey, the chimpanzee infants had an abundance of vertebrae and hand/foot bones. Conclusions
The cases described here suggest that chimpanzees may not always completely consume infanticide victims, while reports on chimpanzee predation indicated that complete consumption of monkey prey usually occurred. Infanticidal chimpanzees undoubtedly gain nutritional benefits when they consume dead infants, but this benefit may not sufficiently explain infanticide in this species. Continued study of infanticidal and hunting behavior, including skeletal analysis, is likely to be of interest
Nuclear like effects in proton-proton collisions at high energy
We show that several effects considered nuclear effects are not nuclear in
the sense that they do not only occur in nucleus-nucleus and hadron-nucleus
collisions but, as well, they are present in hadron-hadron (proton-proton)
collisions. The matter creation mechanism in hh, hA and AA collisions is always
the same. The pT suppression of particles produced in large multiplicity events
compared to low multiplicity events, the elliptic flow and the Cronin effect
are predicted to occur in pp collisions at LHC energies as a consequence of the
obtained high density partonic medium
Percolation Effects in Very High Energy Cosmic Rays
Most QCD models of high energy collisions predict that the inelasticity
is an increasing function of the energy. We argue that, due to percolation of
strings, this behaviour will change and, at GeV, the
inelasticity will start to decrease with the energy. This has straightforward
consequences in high energy cosmic ray physics: 1) the relative depth of the
shower maximum grows faster with energy above the knee; 2) the energy
measurements of ground array experiments at GZK energies could be
overestimated.Comment: Correction of equation (19) and figures 3 and 4. 4 pages, 4 figure
Efeito de diferentes períodos de alagamento no desenvolvimento de Brachiaria brizantha cv. marandu.
O objetivo do presente trabalho foi avaliar a resposta da Brachiaria brizantha cv Marandu a diferentes períodos de alagamento O experimento foi conduzido em casa-de-vegetação nas dependências da Embrapa Pecuária Sudeste, São Carlos, com delineamento de blocos completos ao acaso, em esquema fatorial 5x2, e quatro repetições. Os tratamentos foram constituídos por 5 períodos de alagamento: zero, cinco, dez, quinze e vinte dias de alagamento, e 2 épocas de coleta: a primeira foi realizada ao final do Período de alagamento e a segunda após 15 dias de rebrota. No experimento conduzido não houve efeito significativo do alagamento sobre a taxa de alongamento foliar (P>0,05), sendo seu resultado inverso ao esperado. Observouse que a percentagem de raízes foi maior para as plantas que não sofreram alagamento e menor nas plantas que permaneceram por 20 dias com lâmina d?água. Concluiu-se que períodos de 20 dias de alagamento restringem o desenvolvimento do sistema radicular da espécie de Brachiaria brizantha cv. Marandu
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