3,183 research outputs found
Petrographical and geochemical signatures of the Granja paragneisses (NW Ceará, Brasil)
The Granja Granulitic Complex
(GCC) constitutes a NE–SW
trending high-grade
metamorphic belt occupying the
western sector of the Médio
Coreaú Domain (NW Ceará,
Brasil) (Figs. 1 and 2).
According to the published data,
the GCC represents a segment
of the Paleoproterozoic
basement intensely reworked
during the Brasiliano Orogeny.
Lithologically, the GCC is mainly
composed of garnet-sillimanite
migmatitic paragneisses,
enclosing discontinuous lenses
of mafic granulites and
enderbites.
At outcrop scale, the GCC
gneisses are well-foliated fineto
medium-grained grey rocks
showing a stromatic layering
parallel to the main regional
fabric (Fig. 3). The occurrence of
lenses of leucocratic quartzfeldspathic
material interlayered
with the host paragneisses
indicates that these rocks
reached partial melting
conditions during the Brasiliano
orogenic event (≈ 600 Ma).
Petrographically, the gneisses
are characterized by the
presence of mineral
assemblages dominated by
garnet, sillimanite and biotite
with moderate amounts of
quartz, plagioclase, cordierite
and K-feldspar (Figs. 4a-b).
Twelve whole-rock samples
were analyzed for major and
trace elements. As shown in
Graph 1, all the analyzed
samples plot in the sedimentary
field. Their REE patterns closely
resemble those of PAAS (PostArchean
average Australian
Shale) confirming the
sedimentary origin of the
paragneiss protoliths (Graph 2).
Geochemical data also suggest
that these sediments derived
from source areas of felsic to
intermediate composition and
were deposited in a tectonically
active continental margin
(Graphs 3 and 4)
Rheological behavior of thermoreversible k-carrageenan/nanosilica gels
The rheological behavior of silica/κ-carrageenan nanocomposites has been investigated as a function of silica particle size and load. The addition
of silica nanoparticles was observed to invariably impair the gelation process, as viewed by the reduction of gel strength and decrease of gelation
and melting temperatures. This weakening effect is seen, for the lowest particle size, to become slightly more marked as silica concentration (or
load) is increased and at the lowest load as particle size is increased. These results suggest that, under these conditions, the particles act as physical
barriers to polysaccharide chain aggregation and, hence, gelation. However, for larger particle sizes and higher loads, gel strength does not weaken
with size or concentration but, rather, becomes relatively stronger for intermediate particles sizes, or remains unchanged for the largest particles, as
a function of load. This indicates that larger particles in higher number do not seem to increasingly disrupt the gel, as expected, but rather promote
the formation of stable gel network of intermediate strength. The possibility of this being caused by the larger negative surface charge found for
the larger particles is discussed. This may impede further approximation of neighboring particles thus leaving enough inter-particle space for gel
formation, taking advantage of a high local polysaccharide concentration due to the higher total space occupied by large particles at higher loads.FCT - PTDC/QUI/67712/2006FEDE
The Problem of Large Leptonic Mixing
Unlike in the quark sector where simple permutation symmetries can
generate the general features of quark masses and mixings, we find it
impossible (under conditions of hierarchy for the charged leptons and without
considering the see-saw mechanism or a more elaborate extension of the SM) to
guarantee large leptonic mixing angles with any general symmetry or
transformation of only known particles. If such symmetries exist, they must be
realized in more extended scenarios.Comment: RevTeX, 4 pages, no figure
Matching gauge theory and string theory in a decoupling limit of AdS/CFT
We identify a regime of the AdS/CFT correspondence in which we can
quantitatively match N=4 super Yang-Mills (SYM) for small 't Hooft coupling
with weakly coupled type IIB string theory on AdS_5 x S^5. We approach this
regime by taking the same decoupling limit on both sides of the correspondence.
On the gauge theory side only the states in the SU(2) sector survive, and in
the planar limit the Hamiltonian is given by the XXX_{1/2} Heisenberg spin
chain. On the string theory side we show that the decoupling limit corresponds
to a non-relativistic limit. In this limit some of the bosonic modes and all of
the fermionic modes of the string become infinitely heavy and decouple. We
first take the decoupling limit of the string sigma-model classically. This
enables us to identify a semi-classical regime with semi-classical string
states even though we are in a regime corresponding to small 't Hooft coupling.
We furthermore analyze the quantum corrections that enter in taking the limit.
From this we infer that gauge theory and string theory match, both in terms
of the action and the spectrum, for the leading part and the first correction
away from the semi-classical regime. Finally we consider the implications for
the hitherto unexplained matching of the one-loop contribution to the energy of
certain gauge theory and string theory states, and we explain how our results
give a firm basis for the matching of the Hagedorn temperature in
hep-th/0608115.Comment: 29 pages, 1 figure. v2: Version published in JHEP, section 4 improve
Industry/University collaboration in product focussed Å“nological research in Portugal - the SOGRAPE / UCP ESB partnership 1995 - 1998
A innovative model of collaboration between a wine company and a university research
group is presented. A protocol was established as a response to the perceived need to, on the part of the university, (i) focus research on specific scientific bottlenecks which would have a real impact in the producing industry and, on the part of the company, (ii) to have access to
the scientific capacity to conduct in-depth studies to approach specific technical challenges. A closely managed programme was jointly established and the major characteristics are presented here together with the main results obtained during the first 2 and a half years of operation
Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments
Seismology of stars is strongly developing. To address this question we have
formed an international collaboration OPAC to perform specific experimental
measurements, compare opacity calculations and improve the opacity calculations
in the stellar codes [1]. We consider the following opacity codes: SCO,
CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large
differences for Fe and Ni in equivalent conditions of envelopes of type II
supernova precursors, temperatures between 15 and 40 eV and densities of a few
mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar
results and differ from OP ones for the lower temperatures and for spectral
interval values [3]. In this work we discuss the role of Configuration
Interaction (CI) and the influence of the number of used configurations. We
present and include in the opacity code comparisons new HULLAC-v9 calculations
[5, 6] that include full CI. To illustrate the importance of this effect we
compare different CI approximations (modes) available in HULLAC-v9 [7]. These
results are compared to previous predictions and to experimental data.
Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and
Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences
201
Kinky D-branes and straight strings of open string tachyon effective theory
In this letter we construct the kink D1-brane super D-helix solution and its
T-dual the D2-brane supertube using the effective action of non-BPS tachyonic
D-branes . In the limit of zero angular momentum, both types of solutions
collapse to zero radius, giving rise respectively to a degenerate string
configuration corresponding to a particle travelling with the speed of light
and to a static straight string configuration. These solutions share all the
properties of fundamental strings and do not have the pathological behavior of
other solutions previously found in this context. A short discussion on the
``generalized gauge transformations'' suggested by Sen is used to justify the
validity of our approach.Comment: 10 pages, latex, typos corrected and references adde
Flavor Changing Neutral Currents involving Heavy Quarks with Four Generations
We study various FCNC involving heavy quarks in the Standard Model (SM) with
a sequential fourth generation. After imposing , and constraints, we find can be enhanced by an order of magnitude to ,
while decays can reach , which are orders of magnitude
higher than in SM. However,these rates are still not observable for the near
future.With the era of LHC approaching, we focus on FCNC decays involving
fourth generation and quarks. We calculate the rates for
loop induced FCNC decays , as well as
t^\prime\to tZ,\tH, tg, t\gamma. If is of order , tree level decay would dominate, posing a challenge
since -tagging is less effective. For ,
would tend to dominate, while could also open for heavier
, leading to thepossibility of quadruple- signals via . The FCNC decays could still dominate if
is just above 200 GeV. For the case of , ingeneral would be dominant, hence it behaves like a heavy top. For both and
, except for the intriguing light case, FCNC decays are in the
range, and are quite detectable at the LHC.For a possible
future ILC, we find the associated production of FCNC ,
are below sensitivity, while
and can be better probed.Tevatron Run-II can still probe the
lighter or scenario. LHC would either discover the fourth generation
and measure the FCNC rates, or rule out the fourth generation conclusively.Comment: 31 pages, 15 eps figures, version to appear in JHE
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