1,794 research outputs found
Increasing the dimension of linear systems solved by classical or quantum binary optimization: A new method to solve large linear equation systems
Recently, binary optimization has become an attractive research topic due to
the development of quantum computing and specialized classical systems inspired
by quantum computing. These hardware systems promise to speed up the
computation significantly. In this work, we propose a new method to solve
linear systems written as a binary optimization problem. The procedure solves
the problem efficiently and allows it to handle large linear systems. Our
approach is founded on the geometry of the original linear problem and
resembles the gradient conjugate method. The conjugated directions used can
significantly improve the algorithm's convergence rate. We also show that a
partial knowledge of the intrinsic geometry of the problem can divide the
original problem into independent sub-problems of smaller dimensions. These
sub-problems can then be solved using quantum or classical solvers. Although
determining the geometry of the problem has an additional computational cost,
it can substantially improve the performance of our method compared to previous
implementations.Comment: 12 pages, 10 figure
Eutrophication and macroalgal blooms in temperate and tropical coastal waters: Nutrient enrichment experiments with Ulva spp.
Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low- to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ15N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.Fil: Teichberg, Mirta. Leibniz Center For Tropical Marine Research; AlemaniaFil: Fox, Sophia E.. Marine Biological Laboratory; Estados UnidosFil: Olsen, Ylva S.. Bangor University; Reino UnidoFil: Valiela, Ivan. Marine Biological Laboratory; Estados UnidosFil: Martinetto, Paulina Maria del Rosario. Universidad Nacional de Mar del Plata; ArgentinaFil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Muto, Elizabeti Yuriko. Universidade de Sao Paulo; BrasilFil: Petti, Monica A.V.. Universidade de Sao Paulo; BrasilFil: Corbisier, Thaïs N.. Universidade de Sao Paulo; BrasilFil: Soto-Jiménez, Martín. Universidad Nacional Autónoma de México; MéxicoFil: Páez-Osuna, Federico. Universidad Nacional Autónoma de México; MéxicoFil: Castro, Paula. University Of Coimbra; BrasilFil: Freitas, Helena. University Of Coimbra; BrasilFil: Zitelli, Andreina. Università Iuav Di Venezia; ItaliaFil: Cardinaletti, Massimo. Gruppo Veritas; ItaliaFil: Tagliapietra, Davide. Consiglio Nazionale delle Ricerche; Itali
How close can one approach the Dirac point in graphene experimentally?
The above question is frequently asked by theorists who are interested in
graphene as a model system, especially in context of relativistic quantum
physics. We offer an experimental answer by describing electron transport in
suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with
the onset of Landau quantization occurring in fields below 5 mT. The observed
charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state
with a few charge carriers per entire micron-scale device. Above liquid helium
temperatures, the electronic properties of such devices are intrinsic, being
governed by thermal excitations only. This yields that the Dirac point can be
approached within 1 meV, a limit currently set by the remaining charge
inhomogeneity. No sign of an insulating state is observed down to 1 K, which
establishes the upper limit on a possible bandgap
Supermassive black holes at high redshifts
MeV blazars are the most luminous persistent sources in the Universe and emit
most of their energy in the MeV band. These objects display very large jet
powers and accretion luminosities and are known to host black holes with a mass
often exceeding . An MeV survey, performed by a new generation
MeV telescope which will bridge the entire energy and sensitivity gap between
the current generation of hard X-ray and gamma-ray instruments, will detect
1000 MeV blazars up to a redshift of . Here we show that this would
allow us: 1) to probe the formation and growth mechanisms of supermassive black
holes at high redshifts, 2) to pinpoint the location of the emission region in
powerful blazars, 3) to determine how accretion and black hole spin interplay
to power the jet.Comment: 7 pages, 4 figure. Submitted to the Astro2020 call for Science White
Paper
A Genome-Wide Analysis of Promoter-Mediated Phenotypic Noise in Escherichia coli
Gene expression is subject to random perturbations that lead to fluctuations in the rate of protein production. As a consequence, for any given protein, genetically identical organisms living in a constant environment will contain different amounts of that particular protein, resulting in different phenotypes. This phenomenon is known as “phenotypic noise.” In bacterial systems, previous studies have shown that, for specific genes, both transcriptional and translational processes affect phenotypic noise. Here, we focus on how the promoter regions of genes affect noise and ask whether levels of promoter-mediated noise are correlated with genes' functional attributes, using data for over 60% of all promoters in Escherichia coli. We find that essential genes and genes with a high degree of evolutionary conservation have promoters that confer low levels of noise. We also find that the level of noise cannot be attributed to the evolutionary time that different genes have spent in the genome of E. coli. In contrast to previous results in eukaryotes, we find no association between promoter-mediated noise and gene expression plasticity. These results are consistent with the hypothesis that, in bacteria, natural selection can act to reduce gene expression noise and that some of this noise is controlled through the sequence of the promoter region alon
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
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
Effective Rheology of Bubbles Moving in a Capillary Tube
We calculate the average volumetric flux versus pressure drop of bubbles
moving in a single capillary tube with varying diameter, finding a square-root
relation from mapping the flow equations onto that of a driven overdamped
pendulum. The calculation is based on a derivation of the equation of motion of
a bubble train from considering the capillary forces and the entropy production
associated with the viscous flow. We also calculate the configurational
probability of the positions of the bubbles.Comment: 4 pages, 1 figur
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