1,377 research outputs found
Hadron Systematics and Emergent Diquarks
We briefly review a variety of theoretical and phenomenological indications
for the probable importance of powerful diquark correlations in hadronic
physics. We demonstrate that the bulk of light hadron spectroscopy can be
organized using three simple hypotheses: Regge-Chew-Frautschi mass formulae,
feebleness of spin-orbit forces, and energetic distinctions among a few
different diquark configurations. Those hypotheses can be implemented in a
semi-classical model of color flux tubes, extrapolated down from large orbital
angular momentum . We discuss refinements of the model to include the
effects of tunneling, mass loading, and internal excitations. We also discern
effects of diquark correlations in observed patterns of baryon decays. Many
predictions and suggestions for further work appear.Comment: 18 pages, 11 figures. Talk by FW at a workshop at Schloss Ringberg,
October 2005. To appear in the Proceeding
Anomalous Currents on Closed Surfaces: Extended Proximity, Partial Quantization, and Qubits
Motivated by the surface of topological insulators, the Dirac anomaly's
discontinuous dependence on sign of the mass, , is investigated on
closed topologies when mass terms are weak or only partially cover the surface.
It is found that, unlike the massive Dirac theory on an infinite plane, there
is a smoothly decreasing current when the mass region is not infinite; also, a
massive finite region fails to exhibit a Hall current edge--exerting an
extended proximity effect, which can, however, be uniformly small--and
oppositely orientated Hall phases are fully quantized while accompanied by
diffuse chiral modes. Examples are computed using Dirac energy eigenstates on a
flat torus (genus one topology) and closed cap cylinder (genus zero topology)
for various mass-term geometries. Finally, from the resulting the properties of
the surface spectra, a potential application for a flux-charge qubit is
presented.Comment: 22 pages, 13 figures. References and focus updated. Added effective
action arguments. Same text as published versio
Continuation of Nesterov's Smoothing for Regression with Structured Sparsity in High-Dimensional Neuroimaging
Predictive models can be used on high-dimensional brain images for diagnosis
of a clinical condition. Spatial regularization through structured sparsity
offers new perspectives in this context and reduces the risk of overfitting the
model while providing interpretable neuroimaging signatures by forcing the
solution to adhere to domain-specific constraints. Total Variation (TV)
enforces spatial smoothness of the solution while segmenting predictive regions
from the background. We consider the problem of minimizing the sum of a smooth
convex loss, a non-smooth convex penalty (whose proximal operator is known) and
a wide range of possible complex, non-smooth convex structured penalties such
as TV or overlapping group Lasso. Existing solvers are either limited in the
functions they can minimize or in their practical capacity to scale to
high-dimensional imaging data. Nesterov's smoothing technique can be used to
minimize a large number of non-smooth convex structured penalties but
reasonable precision requires a small smoothing parameter, which slows down the
convergence speed. To benefit from the versatility of Nesterov's smoothing
technique, we propose a first order continuation algorithm, CONESTA, which
automatically generates a sequence of decreasing smoothing parameters. The
generated sequence maintains the optimal convergence speed towards any globally
desired precision. Our main contributions are: To propose an expression of the
duality gap to probe the current distance to the global optimum in order to
adapt the smoothing parameter and the convergence speed. We provide a
convergence rate, which is an improvement over classical proximal gradient
smoothing methods. We demonstrate on both simulated and high-dimensional
structural neuroimaging data that CONESTA significantly outperforms many
state-of-the-art solvers in regard to convergence speed and precision.Comment: 11 pages, 6 figures, accepted in IEEE TMI, IEEE Transactions on
Medical Imaging 201
Two Nucleon-States in a Chiral Quark-Diquark Model
We study the ground and first excited states of nucleons in a chiral
quark-diquark model. We include two quark-diquark channels of the
scalar-isoscalar and axial-vector-isovector types for the nucleon states. The
diquark correlation violating the spin-flavor SU(4) symmetry allows to
treat the two quark-diquark channels independently. Hence the two states appear
as the superpositions of the two quark-diquark channels; one is the nucleon and
the other is a state which does not appear in the SU(4) quark models.
With a reasonable choice of model parameters, the mass of the excited state
appears at around 1.5 GeV, which we identify with the Roper resonance N(1440).Comment: 11 pages, 5 figures. Errors are corrected. Conclusions are not
affecte
Pore-scale processes in tertiary low salinity waterflooding in a carbonate rock: Micro-dispersions, water film growth, and wettability change
HYPOTHESIS: The wettability change from oil-wet towards more water-wet conditions by injecting diluted brine can improve oil recovery from reservoir rocks, known as low salinity waterflooding. We investigated the underlying pore-scale mechanisms of this process to determine if improved recovery was associated with a change in local contact angle, and if additional displacement was facilitated by the formation of micro-dispersions of water in oil and water film swelling. EXPERIMENTS: X-ray imaging and high-pressure and temperature flow apparatus were used to investigate and compare high and low salinity waterflooding in a carbonate rock sample. The sample was placed in contact with crude oil to obtain an initial wetting state found in hydrocarbon reservoirs. High salinity brine was then injected at increasing flow rates followed by low salinity brine injection using the same procedure. FINDINGS: Development of water micro-droplets within the oil phase and detachment of oil layers from the rock surface were observed after low salinity waterflooding. During high salinity waterflooding, contact angles showed insignificant changes from the initial value of 115°, while the mean curvature and local capillary pressure values remained negative, consistent with oil-wet conditions. However, with low salinity, the decrease in contact angle to 102° and the shift in the mean curvature and capillary pressure to positive values indicate a wettability change. Overall, our analysis captured the in situ mechanisms and processes associated with the low salinity effect and ultimate increase in oil recovery
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