Feedback-induced stationary localized patterns in networks of diffusively coupled bistable elements

Effects of feedbacks on self-organization phenomena in networks of diffusively coupled bistable elements are investigated. For regular trees, an approximate analytical theory for localized stationary patterns under application of global feedbacks is constructed. Using it, properties of such patterns in different parts of the parameter space are discussed. Numerical investigations are performed for large random Erdös-Rényi and scale-free networks. In both kinds of systems, localized stationary activation patterns have been observed. The active nodes in such a pattern form a subnetwork, whose size decreases as the feedback intensity is increased. For strong feedbacks, active subnetworks are organized as trees. Additionally, local feedbacks affecting only the nodes with high degrees (i.e., hubs) or the periphery nodes are considered

Self-Organized Stationary Patterns in Networks of Bistable Chemical Reactions

Experiments with networks of discrete reactive bistable electrochemical elements organized in regular and nonregular tree networks are presented to confirm an alternative to the Turing mechanism for the formation of self-organized stationary patterns. The results show that the pattern formation can be described by the identification of domains that can be activated individually or in combinations. The method also enabled the localization of chemical reactions to network substructures and the identification of critical sites whose activation results in complete activation of the system. Although the experiments were performed with a specific nickel electrodissolution system, they reproduced all the salient dynamic behavior of a general network model with a single nonlinearity parameter. Thus, the considered pattern-formation mechanism is very robust, and similar behavior can be expected in other natural or engineered networked systems that exhibit, at least locally, a treelike structure

Gapless color superconductivity

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 155-164).In this thesis, we propose and investigate the "Gapless Color-Flavor Locked" (gCFL) phase, a possible new phase of dense and cold quark matter. At high enough densities, quarks interact with each other and form pairs similarly to electrons in superconductors. This phenomenon in the case of quark matter is called Color Superconductivity. Color superconducting matter must be electrically and color neutral, because otherwise there are huge energy costs, due to the charges. At asymptotically high densities, equal numbers of up, down, and strange quarks make the system neutral, all the quarks pair, and the quark matter is in the Color-Flavor-Locked phase. At intermediate densities however, the strange quark mass changes the number densities of the quarks and this makes the CFL phase unstable. The gCFL phase emerges as a result of the strange quark mass effect and the neutrality conditions. The gCFL phase has gapless modes and non-zero electron density, unlike CFL. These new properties of gCFL have significant astrophysical implications. The interior of neutron stars might have densities at the regime where gCFL dominates. If this is the case, we argue that gCFL will change significantly the cooling of such a star, keeping it hot, even for late times. Also in this thesis we explore the rest of the phase diagram of neutral quark matter at high density as a function of temperature and strange quark mass. We investigate how zero temperature superconducting phases evolve if we heat the system. We derive the phase diagram of dense quark matter using a Nambu-Jona- Lasinio (NJL) model, that might be a good guide for understanding the QCD phase diagram.by Christoforos N. Kouvaris.Ph.D

Green synthesis and characterization of silver nanoparticles produced using 'Arbutus Unedo' leaf extract

Metallic nanoparticles have received great attention from chemists, physicists, biologists and engineers who wish to use them for the development of a new generation of nanodevices. In the present study silver nanoparticles were synthesized from aqueous silver nitrate through a simple and eco-friendly route using leaf broth of Arbutus unedo, which acted as a reductant and stabilizer simultaneously. The aqueous silver ions when exposed to the leaf broth were reduced and stabilized over long periods of time resulting in the green synthesis of surface functionalized silver nanoparticles. The bio-reduced silver nanoparticles were appropriately characterized. The results revealed the formation of single crystalline Ag nanoparticles with a narrow size distribution for each sample. The particles, although discrete, were predominately coated with the organic leaf extract forming small aggregates, which makes them stable over long time periods and highly appropriate for coatings or biotechnology applications.Publicad

Gapless phases of color-superconducting matter

We discuss gapless color superconductivity for neutral quark matter in beta equilibrium at zero as well as at nonzero temperature. Basic properties of gapless superconductors are reviewed. The current progress and the remaining problems in the understanding of the phase diagram of strange quark matter are discussed.Comment: 8 pages, 2 figures. Plenary talk at Strangeness in Quark Matter 2004 (SQM2004), Cape Town, South Africa, 15-20 September 2004. Minor correction

Spectral properties of the Laplacian of multiplex networks.

One of the more challenging tasks in the understanding of dynamical properties of models on top of complex networks is to capture the precise role of multiplex topologies. In a recent paper, Gómez et al. [ Phys. Rev. Lett. 110 028701 (2013)], some of the authors proposed a framework for the study of diffusion processes in such networks. Here, we extend the previous framework to deal with general configurations in several layers of networks and analyze the behavior of the spectrum of the Laplacian of the full multiplex. We derive an interesting decoupling of the problem that allow us to unravel the role played by the interconnections of the multiplex in the dynamical processes on top of them. Capitalizing on this decoupling we perform an asymptotic analysis that allow us to derive analytical expressions for the full spectrum of eigenvalues. This spectrum is used to gain insight into physical phenomena on top of multiplex, specifically, diffusion processes and synchronizability

Zero Sound in Neutron Stars with Dense Quark Matter under Strong Magnetic Fields

We study a neutron star with a quark matter core under extremely strong magnetic fields. We investigate the possibility of an Urca process as a mechanism for the cooling of such a star. We found that apart from very particular cases, the Urca process cannot occur. We also study the stability of zero sound modes under the same conditions. We derive limits for the coupling constant of an effective theory, in order the zero sound to be undamped. We show that zero sound modes can help kinematically to facilitate a cooling process

Dark Matter Interference

We study different patterns of interference in WIMP-nuclei elastic scattering that can accommodate the DAMA and CoGeNT experiments via an isospin violating ratio $f_n/f_p=-0.71$. We study interference between the following pairs of mediators: Z and Z', Z' and Higgs, and two Higgs fields. We show under what conditions interference works. We also demonstrate that in the case of the two Higgs interference, an explanation of the DAMA/CoGeNT is consistent with Electroweak Baryogenesis scenarios based on two Higgs doublet models proposed in the past.Comment: 14 pages, 2 figures, references and appendix added, match with the published versio

Scalar Bilepton Dark Matter

In this work we show that 3-3-1 model with right-handed neutrinos has a natural weakly interacting massive particle (WIMP) dark mater candidate. It is a complex scalar with mass of order of some hundreds of GeV which carries two units of lepton number, a scalar bilepton. This makes it a very peculiar WIMP, very distinct from Supersymmetric or Extra-dimension candidates. Besides, although we have to make some reasonable assumptions concerning the several parameters in the model, no fine tunning is required in order to get the correct dark matter abundance. We also analyze the prospects for WIMP direct detection by considering recent and projected sensitivities for WIMP-nucleon elastic cross section from CDMS and XENON Collaborations.Comment: 21 pages, 8 figures, uses iopart.cls, same text as published version with a small different arrangement of figure

Asymmetric Origin for Gravitino Relic Density in the Hybrid Gravity-Gauge Mediated Supersymmetry Breaking

We propose the hybrid gravity-gauge mediated supersymmetry breaking where the gravitino mass is about several GeV. The strong constraints on supersymmetry viable parameter space from the CMS and ATLAS experiments at the LHC can be relaxed due to the heavy colored supersymmetric particles, and it is consistent with null results in the dark matter (DM) direct search experiments such as XENON100. In particular, the possible maximal flavor and CP violations from the relatively small gravity mediation may naturally account for the recent LHCb anomaly. In addition, because the gravitino mass is around the asymmetric DM mass, we propose the asymmetric origin of the gravitino relic density and solve the cosmological coincident problem on the DM and baryon densities \Omega_{\rm DM}:\Omega_{B}\approx 5:1. The gravitino relic density arises from asymmetric metastable particle (AMP) late decay. However, we show that there is no AMP candidate in the minimal supersymmetric Standard Model (SM) due to the robust gaugino/Higgsino mediated wash-out effects. Interestingly, AMP can be realized in the well motivated supersymmetric SMs with vector-like particles or continuous U(1)_R symmetry. Especially, the lightest CP-even Higgs boson mass can be lifted in the supersymmetric SMs with vector-like particles.Comment: RevTex4, 21 pages, 1 figure, minor corrections, JHEP versio