17,185 research outputs found
Localized modes and bistable scattering in nonlinear network junctions
We study the properties of junctions created by crossing of N identical
branches of linear discrete networks. We reveal that for N>2 such a junction
creates a topological defect and supports two types of spatially localized
modes. We analyze the wave scattering by the junction defect and demonstrate
nonzero reflection for any set of parameters. If the junction is nonlinear, it
is possible to achieve the maximum transmission for any frequency by tuning the
intensity of the scattering wave. In addition, near the maximum transmission
the system shows the bistable behaviour.Comment: 5 pages, 7 figures, submitted to Physical Review
Prediction of narrow and resonances with hidden charm above 4 GeV
The interaction between various charmed mesons and charmed baryons are
studied within the framework of the coupled channel unitary approach with the
local hidden gauge formalism. Several meson-baryon dynamically generated narrow
and resonances with hidden charm are predicted with mass
above 4 GeV and width smaller than 100 MeV. The predicted new resonances
definitely cannot be accommodated by quark models with three constituent quarks
and can be looked for at the forthcoming PANDA/FAIR experiments.Comment: 4 pages, 3 figure
Fano resonance in quadratic waveguide arrays
We study resonant light scattering in arrays of channel optical waveguides
where tunable quadratic nonlinearity is introduced as nonlinear defects by
periodic poling of single (or several) waveguides in the array. We describe
novel features of wave scattering that can be observed in this structure and
show that it is a good candidate for the first observation of Fano resonance in
nonlinear optics.Comment: 3 pages, 3 figures, submitted to Optics Letters, slightly revise
Cultivation and anaerobic digestion of Scenedesmus spp. grown in a pilot-scale open raceway
Digestibility of a micro-algal mixture was evaluated by mesophilic anaerobic digestion in continuously-stirred tank reactors. The culture consisted primarily of Scenedesmus spp. continuously cultivated over a 6-month period in a 100 m2 raceway reactor instrumented to record pH, dissolved oxygen and temperature. The raceway received supplementary carbon in the form of flue gas from a diesel boiler (10% CO2) injected into a 1-m deep sump to control pH in the range 7.8–8.0. Dilution was optimised to biomass productivity and gave values of 10–15 and 20–25 g total suspended solids (TSS) m? 2 day? 1 in winter (December–February) and spring (April–May), respectively. The culture for the anaerobic digestion trial was harvested in February by centrifugation to give an algal paste containing 4.3% volatile solids (VS). Semi-continuous digestion at organic loading rates of 2.00, 2.75 and 3.50 g VS l? 1 day? 1 gave volumetric biogas productions of ~ 0.66, ~ 0.83 and ~ 0.99 l l? 1 day? 1, respectively. Specific methane yield ranged from 0.13 to 0.14 l CH4 g? 1 VSadded with biogas methane content ~ 62%. Overall the digestion process was stable, but only ~ 30% VS destruction was achieved indicating low biodegradability, due to the short retention times and the recalcitrant nature of this type of biomas
The decay of the and resonances in the hidden gauge formalism
Using recent results obtained within the hidden gauge formalism for vector
mesons, in which the and resonances are dynamically
generated resonances from the interaction, we evaluate the
radiative decay of these resonances into . We obtain results for
the width in good agreement with the experimental data for the
state and a width about a factor five smaller for the resonance,
which would agree with preliminary results from the Belle collaboration,
hinting at an order of magnitude smaller width for this resonance than for the
.Comment: 7 pages, 9 figures, proof of gauge invariance adde
Justifications-on-demand as a device to promote shifts of attention associated with relational thinking in elementary arithmetic
Student responses to arithmetical questions that can be solved by using arithmetical structure can serve to reveal the extent and nature of relational, as opposed to computational thinking. Here, student responses to probes which require them to justify-on-demand are analysed using a conceptual framework which highlights distinctions between different forms of attention. We analyse a number of actions observed in students in terms of forms of attention and shifts between them: in the short-term (in the moment), medium-term (over several tasks), and long-term (over a year). The main factors conditioning students´ attention and its movement are identified and some didactical consequences are proposed
Comments on the dispersion relation method to vector-vector interaction
We study in detail the method proposed recently to study the vector-vector
interaction using the method and dispersion relations, which concludes
that, while for , one finds bound states, in the case of , where the
interaction is also attractive and much stronger, no bound state is found. In
that work, approximations are done for and and a subtracted dispersion
relation for is used, with subtractions made up to a polynomial of second
degree in , matching the expression to at threshold. We
study this in detail for the interaction and to see the
convergence of the method we make an extra subtraction matching at
threshold up to . We show that the method cannot be used
to extrapolate the results down to 1270 MeV where the resonance
appears, due to the artificial singularity stemming from the "on shell"
factorization of the exchange potential. In addition, we explore the
same method but folding this interaction with the mass distribution of the
, and we show that the singularity disappears and the method allows one
to extrapolate to low energies, where both the and
expansions lead to a zero of , at
about the same energy where a realistic approach produces a bound state. Even
then, the method generates a large that we discuss is
unphysical.Comment: 8 pages, 10 figures, 1 tabl
Hundreds of Low-Mass Active Galaxies in the Galaxy And Mass Assembly (GAMA) Survey
We present an entirely new sample of 388 low-mass galaxies () that have spectroscopic signatures indicating the presence of
massive black holes (BHs) in the form of active galactic nuclei (AGNs) or tidal
disruption events (TDEs). Of these, 70 have stellar masses in the dwarf galaxy
regime with . We identify the
active galaxies by analyzing optical spectra of a parent sample of 23,000
low-mass emission-line galaxies in the Galaxy and Mass Assembly (GAMA) Survey
Data Release 4, and employing four different diagnostics based on narrow
emission line ratios and the detection of high-ionization coronal lines. We
find that 47 of the 388 low-mass active galaxies exhibit broad H in
their spectra, corresponding to virial BH masses in the range with a median BH mass of . Our sample extends to higher redshifts () than previous samples of AGNs in low-mass/dwarf galaxies based
on Sloan Digital Sky Survey spectroscopy, which can be attributed to the
spectroscopic limit of GAMA being magnitudes deeper. Moreover, our
multi-diagnostic approach has revealed low-mass active galaxies spanning a wide
range of properties, from blue star-forming dwarfs to luminous "miniquasars"
powered by low-mass BHs. As such, this work has implications for BH seeding and
AGN feedback at low masses.Comment: Accepted for publication in The Astrophysical Journa
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