68 research outputs found
Parallel Evolution of Quasi-separatrix Layers and Active Region Upflows
Persistent plasma upflows were observed with Hinode's EUV Imaging
Spectrometer (EIS) at the edges of active region (AR) 10978 as it crossed the
solar disk. We analyze the evolution of the photospheric magnetic and velocity
fields of the AR, model its coronal magnetic field, and compute the location of
magnetic null-points and quasi-sepratrix layers (QSLs) searching for the origin
of EIS upflows. Magnetic reconnection at the computed null points cannot
explain all of the observed EIS upflow regions. However, EIS upflows and QSLs
are found to evolve in parallel, both temporarily and spatially. Sections of
two sets of QSLs, called outer and inner, are found associated to EIS upflow
streams having different characteristics. The reconnection process in the outer
QSLs is forced by a large-scale photospheric flow pattern which is present in
the AR for several days. We propose a scenario in which upflows are observed
provided a large enough asymmetry in plasma pressure exists between the
pre-reconnection loops and for as long as a photospheric forcing is at work. A
similar mechanism operates in the inner QSLs, in this case, it is forced by the
emergence and evolution of the bipoles between the two main AR polarities. Our
findings provide strong support to the results from previous individual case
studies investigating the role of magnetic reconnection at QSLs as the origin
of the upflowing plasma. Furthermore, we propose that persistent reconnection
along QSLs does not only drive the EIS upflows, but it is also responsible for
a continuous metric radio noise-storm observed in AR 10978 along its disk
transit by the Nan\c{c}ay Radio Heliograph.Comment: 29 pages, 10 figure
Efficiency Maximization of a Jet Pump for an Hydraulic Artificial Lift System
In science and engineering, mathematical modeling serves as a tool to understand processes and systems acting as a testing bed for several hypotheses. The selection of a specific model, as well as its variables and parameters, depends on the nature of the system under analysis and the acceptable simplifying assumptions. Therefore, it must allow for a good fit between both the hypothesis and the available data. Opposite to other design approaches based on experimental data or/and complex models, this work presents a simpler numerical design method for efficiency maximization of an Hydraulic Jet Pump (HJP) for oil-well extraction process, considering its hydraulic and geometric parameters. The design process consists in setting and solving a constrained non-linear optimization problem by taking into account the hydraulic model of the HJP in terms four design variables: throat area, nozzle area, injection flow, and injection pressure to the oil-well. The objective function of this case aims to maximize the HJP's efficiency avoiding to approach cavitation condition as well fulfilling technical constraints. A numerical technique, Differential Evolution Algorithm (DEA), has been implemented to solve the optimization problem. The proposed methodology leads to a solution set by considering only commercial geometries and feasible operating conditions for the HJP, which facilitates its practical implementation. A set of ten oil-wells with land production data, operating in the southeaster of Mexico, is used to compare and validate several Jet pump designs, i. e., through comparison with actual oil-well's operation condition.Peer Reviewe
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE
In this small note we are concerned with the solution of Forward-Backward
Stochastic Differential Equations (FBSDE) with drivers that grow quadratically
in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem
is a comparison result that allows comparing componentwise the signs of the
control processes of two different qgFBSDE. As a byproduct one obtains
conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio
Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at , 2.76 and 7 TeV
Measurements of the sphericity of primary charged particles in minimum bias
proton--proton collisions at , 2.76 and 7 TeV with the ALICE
detector at the LHC are presented. The observable is linearized to be collinear
safe and is measured in the plane perpendicular to the beam direction using
primary charged tracks with GeV/c in . The
mean sphericity as a function of the charged particle multiplicity at
mid-rapidity () is reported for events with different
scales ("soft" and "hard") defined by the transverse momentum of the leading
particle. In addition, the mean charged particle transverse momentum versus
multiplicity is presented for the different event classes, and the sphericity
distributions in bins of multiplicity are presented. The data are compared with
calculations of standard Monte Carlo event generators. The transverse
sphericity is found to grow with multiplicity at all collision energies, with a
steeper rise at low , whereas the event generators show the
opposite tendency. The combined study of the sphericity and the mean with multiplicity indicates that most of the tested event generators
produce events with higher multiplicity by generating more back-to-back jets
resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with
tune PERUGIA-2011 exhibits a noticeable improvement in describing the data,
compared to the other tested generators.Comment: 21 pages, 9 captioned figures, 3 tables, authors from page 16,
published version, figures from
http://aliceinfo.cern.ch/ArtSubmission/node/308
Centrality dependence of charged particle production at large transverse momentum in Pb-Pb collisions at TeV
The inclusive transverse momentum () distributions of primary
charged particles are measured in the pseudo-rapidity range as a
function of event centrality in Pb-Pb collisions at
TeV with ALICE at the LHC. The data are presented in the range
GeV/ for nine centrality intervals from 70-80% to 0-5%.
The Pb-Pb spectra are presented in terms of the nuclear modification factor
using a pp reference spectrum measured at the same collision
energy. We observe that the suppression of high- particles strongly
depends on event centrality. In central collisions (0-5%) the yield is most
suppressed with at -7 GeV/. Above
GeV/, there is a significant rise in the nuclear modification
factor, which reaches for GeV/. In
peripheral collisions (70-80%), the suppression is weaker with almost independently of . The measured nuclear
modification factors are compared to other measurements and model calculations.Comment: 17 pages, 4 captioned figures, 2 tables, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/284
Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at TeV
The elliptic, , triangular, , and quadrangular, , azimuthal
anisotropic flow coefficients are measured for unidentified charged particles,
pions and (anti-)protons in Pb-Pb collisions at TeV
with the ALICE detector at the Large Hadron Collider. Results obtained with the
event plane and four-particle cumulant methods are reported for the
pseudo-rapidity range at different collision centralities and as a
function of transverse momentum, , out to GeV/.
The observed non-zero elliptic and triangular flow depends only weakly on
transverse momentum for GeV/. The small dependence
of the difference between elliptic flow results obtained from the event plane
and four-particle cumulant methods suggests a common origin of flow
fluctuations up to GeV/. The magnitude of the (anti-)proton
elliptic and triangular flow is larger than that of pions out to at least
GeV/ indicating that the particle type dependence persists out
to high .Comment: 16 pages, 5 captioned figures, authors from page 11, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/186
Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at TeV
The effect of event background fluctuations on charged particle jet
reconstruction in Pb-Pb collisions at TeV has been
measured with the ALICE experiment. The main sources of non-statistical
fluctuations are characterized based purely on experimental data with an
unbiased method, as well as by using single high particles and
simulated jets embedded into real Pb-Pb events and reconstructed with the
anti- jet finder. The influence of a low transverse momentum cut-off
on particles used in the jet reconstruction is quantified by varying the
minimum track between 0.15 GeV/ and 2 GeV/. For embedded jets
reconstructed from charged particles with GeV/, the
uncertainty in the reconstructed jet transverse momentum due to the heavy-ion
background is measured to be 11.3 GeV/ (standard deviation) for the 10% most
central Pb-Pb collisions, slightly larger than the value of 11.0 GeV/
measured using the unbiased method. For a higher particle transverse momentum
threshold of 2 GeV/, which will generate a stronger bias towards hard
fragmentation in the jet finding process, the standard deviation of the
fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0
GeV/ for the 10% most central events. A non-Gaussian tail of the momentum
uncertainty is observed and its impact on the reconstructed jet spectrum is
evaluated for varying particle momentum thresholds, by folding the measured
fluctuations with steeply falling spectra.Comment: 21 pages, 5 captioned figures, 3 tables, authors from page 16,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/350
Pion, kaon, and proton production in central Pb-Pb Collisions at TeV
In this Letter we report the first results on , K, p and
production at mid-rapidity () in
central Pb-Pb collisions at = 2.76 TeV, measured by the
ALICE experiment at the LHC. The distributions and yields are
compared to previous results at = 200 GeV and expectations
from hydrodynamic and thermal models. The spectral shapes indicate a strong
increase of the radial flow velocity with , which in
hydrodynamic models is expected as a consequence of the increasing particle
density. While the ratio is in line with predictions from the
thermal model, the ratio is found to be lower by a factor of
about 1.5. This deviation from thermal model expectations is still to be
understood.Comment: 15 pages, 2 captioned figures, 1 table, authors from page 10,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/286
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