704 research outputs found
Self-organization in systems of self-propelled particles
We investigate a discrete model consisting of self-propelled particles that
obey simple interaction rules. We show that this model can self-organize and
exhibit coherent localized solutions in one- and in two-dimensions.In
one-dimension, the self-organized solution is a localized flock of finite
extent in which the density abruptly drops to zero at the edges.In
two-dimensions, we focus on the vortex solution in which the particles rotate
around a common center and show that this solution can be obtained from random
initial conditions, even in the absence of a confining boundary. Furthermore,
we develop a continuum version of our discrete model and demonstrate that the
agreement between the discrete and the continuum model is excellent.Comment: 4 pages, 5 figure
Core-scale geophysical and hydromechanical analysis of seabed sediments affected by CO2 venting
Safe offshore Carbon Capture Utilization and Storage (CCUS) includes monitoring of the subseafloor, to identify and assess potential CO2 leaks from the geological reservoir through seal bypass structures. We simulated CO2-leaking through shallow marine sediments of the North Sea, using two gravity core samples from ∼1 and ∼2.1 m below seafloor. Both samples were subjected to brine−CO2 flow-through, with continuous monitoring of their transport, elastic and mechanical properties, using electrical resistivity, permeability, P-wave velocity and attenuation, and axial strains. We used the collected geophysical data to calibrate a resistivity-saturation model based on Archie’s law extended for clay content, and a rock physics for the elastic properties. The P-wave attributes detected the presence of CO2 in the sediment, but failed in providing accurate estimates of the CO2 saturation. Our results estimate porosities of 0.44 and 0.54, a background permeability of ∼10−15 and ∼10-17 m2, and maximum CO2 saturation of 18 % and 10 % (±5 %), for the sandier (shallower) and muddier (deeper) sample, respectively. The finer-grained sample likely suffered some degree of gas-induced fracturing, exhibiting an effective CO2 permeability increase sharper than the coarser-grained sample. Our core-scale multidisciplinary experiment contributes to improve the general interpretation of shallow sub-seafloor gas distribution and migration patterns
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Activation of α7 nicotinic receptors improves phencyclidine-induced deficits in cognitive tasks in rats: Implications for therapy of cognitive dysfunction in schizophrenia
YesRationale: Nicotinic α7 acetylcholine receptors (nAChRs) have been highlighted as a target for cognitive enhancement in schizophrenia. Aim: To investigate whether the deficits induced by sub-chronic phencyclidine (PCP) in reversal learning and novel object recognition could be attenuated by the selective α7 nAChR full agonist, PNU-282987. Methods: Adult female hooded-Lister rats received sub-chronic PCP (2 mg/kg) or vehicle i.p. twice daily for seven days, followed by 7-days washout. In cohort 1, PCP-treated rats then received PNU-282987 (5, 10, 20 mg/kg; s.c.) or vehicle and were tested in the reversal learning task. In cohort 2, PCP-treated rats received PNU-282987 (10 mg/kg; s.c.) or saline for 15 days and were tested in the novel object recognition test on day 1 and on day 15, to test for tolerance. Results: Sub-chronic PCP produced significant deficits in both cognitive tasks (P<0.01-0.001). PNU-282987 attenuated the PCP-induced deficits in reversal learning at 10 mg/kg (P<0.01) and 20 mg/kg (P<0.001), and in novel object recognition at 10 mg/kg on day 1 (P<0.01) and on day 15 (P<0.001). Conclusions: These data show that PNU-282987 has efficacy to reverse PCP-induced deficits in two paradigms of relevance to schizophrenia. Results further suggest that 15 day daily dosing of PNU-282987 (10 mg/kg s.c.) does not cause tolerance in rat. This study suggests that activation of α7 nAChRs, may represent a suitable strategy for improving cognitive deficits of relevance to schizophrenia.SL McLean was supported by a joint University of Bradford–GSK postgraduate studentship
Controlling spatiotemporal chaos in oscillatory reaction-diffusion systems by time-delay autosynchronization
Diffusion-induced turbulence in spatially extended oscillatory media near a
supercritical Hopf bifurcation can be controlled by applying global time-delay
autosynchronization. We consider the complex Ginzburg-Landau equation in the
Benjamin-Feir unstable regime and analytically investigate the stability of
uniform oscillations depending on the feedback parameters. We show that a
noninvasive stabilization of uniform oscillations is not possible in this type
of systems. The synchronization diagram in the plane spanned by the feedback
parameters is derived. Numerical simulations confirm the analytical results and
give additional information on the spatiotemporal dynamics of the system close
to complete synchronization.Comment: 19 pages, 10 figures submitted to Physica
Fredholm Modules on P.C.F. Self-Similar Fractals and their Conformal Geometry
The aim of the present work is to show how, using the differential calculus
associated to Dirichlet forms, it is possible to construct Fredholm modules on
post critically finite fractals by regular harmonic structures. The modules are
d-summable, the summability exponent d coinciding with the spectral dimension
of the generalized laplacian operator associated with the regular harmonic
structures. The characteristic tools of the noncommutative infinitesimal
calculus allow to define a d-energy functional which is shown to be a
self-similar conformal invariant.Comment: 16 page
Correlation between voxel based morphometry and manual volumetry in magnetic resonance images of the human brain
This is a comparative study between manual volumetry (MV) and voxel based morphometry (VBM) as methods of evaluating the volume of brain structures in magnetic resonance images. The volumes of the hippocampus and the amygdala of 16 panic disorder patients and 16 healthy controls measured through MV were correlated with the volumes of gray matter estimated by optimized modulated VBM. The chosen structures are composed almost exclusively of gray matter. Using a 4 mm Gaussian filter, statistically significant clusters were found bilaterally in the hippocampus and in the right amygdala in the statistical parametric map correlating with the respective manual volume. With the conventional 12 mm filter,a significant correlation was found only for the right hippocampus. Therefore,narrowfilters increase the sensitivity of the correlation procedure, especially when small brain structures are analyzed. The two techniques seem to consistently measure structural volume.Trata-se de estudo comparativo entre a volumetria manual(VM) e a morfometria baseada no vóxel (MBV), como métodos de avaliação do volume de estruturas cerebrais. Os volumes do hipocampo e da amídala de 16 pacientes de pânico e 16 controles sadios medidos através da VM foram correlacionados com os volumes de matéria cinzenta estimados pela MBV.As estruturas escolhidas são constituídas quase exclusivamente de matéria cinzenta. Utilizando um filtro Gaussiano de 4 mm, encontram-se, bilateralmente, aglomerados significativos de correlação nas duas estruturas no mapa estatístico paramétrico, correspondendo ao respectivo volume manual. Com o filtro convencional de 12 mm, apenas uma correlação significativa foi encontrada no hipocampo direito. Portanto, filtros estreitos aumentam a sensibilidade do procedimento de correlação,especialmente quando estruturas pequenas são analisadas. Ambas as técnicas parecem medir consistentemente o volume estrutural.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)(FAEPA) Hospital das Clínicas da FMRPUSP - Fundação de Apoio ao Ensino, Pesquisa e Asssistênci
All Inequalities for the Relative Entropy
The relative entropy of two n-party quantum states is an important quantity
exhibiting, for example, the extent to which the two states are different. The
relative entropy of the states formed by reducing two n-party to a smaller
number of parties is always less than or equal to the relative entropy of
the two original n-party states. This is the monotonicity of relative entropy.
Using techniques from convex geometry, we prove that monotonicity under
restrictions is the only general inequality satisfied by relative entropies. In
doing so we make a connection to secret sharing schemes with general access
structures.
A suprising outcome is that the structure of allowed relative entropy values
of subsets of multiparty states is much simpler than the structure of allowed
entropy values. And the structure of allowed relative entropy values (unlike
that of entropies) is the same for classical probability distributions and
quantum states.Comment: 15 pages, 3 embedded eps figure
Asymptotic Scaling of the Diffusion Coefficient of Fluctuating "Pulled" Fronts
We present a (heuristic) theoretical derivation for the scaling of the
diffusion coefficient for fluctuating ``pulled'' fronts. In agreement
with earlier numerical simulations, we find that as ,
approaches zero as , where is the average number of particles per
correlation volume in the stable phase of the front. This behaviour of
stems from the shape fluctuations at the very tip of the front, and is
independent of the microscopic model.Comment: Some minor algebra corrected, to appear in Rapid Comm., Phys. Rev.
Strong duality in conic linear programming: facial reduction and extended duals
The facial reduction algorithm of Borwein and Wolkowicz and the extended dual
of Ramana provide a strong dual for the conic linear program in the absence of any constraint qualification. The facial
reduction algorithm solves a sequence of auxiliary optimization problems to
obtain such a dual. Ramana's dual is applicable when (P) is a semidefinite
program (SDP) and is an explicit SDP itself. Ramana, Tuncel, and Wolkowicz
showed that these approaches are closely related; in particular, they proved
the correctness of Ramana's dual using certificates from a facial reduction
algorithm.
Here we give a clear and self-contained exposition of facial reduction, of
extended duals, and generalize Ramana's dual:
-- we state a simple facial reduction algorithm and prove its correctness;
and
-- building on this algorithm we construct a family of extended duals when
is a {\em nice} cone. This class of cones includes the semidefinite cone
and other important cones.Comment: A previous version of this paper appeared as "A simple derivation of
a facial reduction algorithm and extended dual systems", technical report,
Columbia University, 2000, available from
http://www.unc.edu/~pataki/papers/fr.pdf Jonfest, a conference in honor of
Jonathan Borwein's 60th birthday, 201
Water waves generated by a moving bottom
Tsunamis are often generated by a moving sea bottom. This paper deals with
the case where the tsunami source is an earthquake. The linearized water-wave
equations are solved analytically for various sea bottom motions. Numerical
results based on the analytical solutions are shown for the free-surface
profiles, the horizontal and vertical velocities as well as the bottom
pressure.Comment: 41 pages, 13 figures. Accepted for publication in a book: "Tsunami
and Nonlinear Waves", Kundu, Anjan (Editor), Springer 2007, Approx. 325 p.,
170 illus., Hardcover, ISBN: 978-3-540-71255-8, available: May 200
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