7,491 research outputs found
A characterization of the scientific impact of Brazilian institutions
In this paper we studied the research activity of Brazilian Institutions for
all sciences and also their performance in the area of physics between 1945 and
December 2008. All the data come from the Web of Science database for this
period. The analysis of the experimental data shows that, within a nonextensive
thermostatistical formalism, the Tsallis \emph{q}-exponential distribution
can constitute a new characterization of the research impact for
Brazilian Institutions. The data examined in the present survey can be fitted
successfully by applying a universal curve namely, with for {\it all} the available citations
, being an "effective temperature". The present analysis ultimately
suggests that via the "effective temperature" , we can provide a new
performance metric for the impact level of the research activity in Brazil,
taking into account the number of the publications and their citations. This
new performance metric takes into account the "quantity" (number of
publications) and the "quality" (number of citations) for different Brazilian
Institutions. In addition we analyzed the research performance of Brazil to
show how the scientific research activity changes with time, for instance
between 1945 to 1985, then during the period 1986-1990, 1991-1995, and so on
until the present. Finally, this work intends to show a new methodology that
can be used to analyze and compare institutions within a given country.Comment: 7 pages, 5 figure
Nature of the X(5568) : a critical Laplace sum rule analysis at N2LO
We scrutinize recent QCD spectral sum rules (QSSR) results to lowest order
(LO) predicting the masses of the BK molecule and (su)\bar(bd) four-quark
states. We improve these results by adding NLO and N2LO corrections to the PT
contributions giving a more precise meaning on the b-quark mass definition used
in the analysis. We extract our optimal predictions using Laplace sum rule
(LSR) within the standard stability criteria versus the changes of the external
free parameters (\tau-sum rule variable, t_c continuum threshold and
subtraction constant \mu). The smallness of the higher order PT corrections
justifies (a posteriori) the LO order results + the uses of the ambiguous heavy
quark mass to that order. However, our predicted spectra in the range (5173\sim
5226) MeV, summarized in Table 7, for exotic hadrons built with four different
flavours (buds), do not support some previous interpretations of the D0
candidate[1], X(5568), as a pure molecule or a four-quark state. If
experimentally confirmed, it could result from their mixing with an angle: sin
2\theta\approx 0.15. One can also scan the region (2327~ 2444) MeV (where the
D*_{s0}(2317) might be a good candidate) and the one (5173~ 5226) MeV for
detecting these (cuds) and (buds) unmixed exotic hadrons (if any) via,
eventually, their radiative or \pi+hadrons decays.Comment: Version matching with the publised version : some references added
and updated, comments added, misprint corrected (51 pages, 66 figures, 7
tables
Weak interactions and quasi-stable particle energy loss
We discuss the interplay between electromagnetic energy loss and weak
interactions in the context of quasistable particle particle propagation
through materials. As specific examples, we consider staus, where weak
interactions may play a role, and taus, where they don't.Comment: 4 pages, 4 figures, to appear in the proceedings of the Second
Workshop on TeV Particle Astrophysics (August 2006, Madison, WI
Anisotropic Lifshitz Point at
We present the critical exponents , and
for an -axial Lifshitz point at second order in an expansion.
We introduced a constraint involving the loop momenta along the -dimensional
subspace in order to perform two- and three-loop integrals. The results are
valid in the range . The case corresponds to the usual
Ising-like critical behavior.Comment: 10 pages, Revte
A Chemical and Enzymatic Approach to Study Site-Specific Sumoylation.
A variety of cellular pathways are regulated by protein modifications with ubiquitin-family proteins. SUMO, the Small Ubiquitin-like MOdifier, is covalently attached to lysine on target proteins via a cascade reaction catalyzed by E1, E2, and E3 enzymes. A major barrier to understanding the diverse regulatory roles of SUMO has been a lack of suitable methods to identify protein sumoylation sites. Here we developed a mass-spectrometry (MS) based approach combining chemical and enzymatic modifications to identify sumoylation sites. We applied this method to analyze the auto-sumoylation of the E1 enzyme in vitro and compared it to the GG-remnant method using Smt3-I96R as a substrate. We further examined the effect of smt3-I96R mutation in vivo and performed a proteome-wide analysis of protein sumoylation sites in Saccharomyces cerevisiae. To validate these findings, we confirmed several sumoylation sites of Aos1 and Uba2 in vivo. Together, these results demonstrate that our chemical and enzymatic method for identifying protein sumoylation sites provides a useful tool and that a combination of methods allows a detailed analysis of protein sumoylation sites
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