817 research outputs found
Evolution equation for a model of surface relaxation in complex networks
In this paper we derive analytically the evolution equation of the interface
for a model of surface growth with relaxation to the minimum (SRM) in complex
networks. We were inspired by the disagreement between the scaling results of
the steady state of the fluctuations between the discrete SRM model and the
Edward-Wilkinson process found in scale-free networks with degree distribution
for [Pastore y Piontti {\it et al.},
Phys. Rev. E {\bf 76}, 046117 (2007)]. Even though for Euclidean lattices the
evolution equation is linear, we find that in complex heterogeneous networks
non-linear terms appear due to the heterogeneity and the lack of symmetry of
the network; they produce a logarithmic divergency of the saturation roughness
with the system size as found by Pastore y Piontti {\it et al.} for .Comment: 9 pages, 2 figure
Consensus formation on coevolving networks: groups' formation and structure
We study the effect of adaptivity on a social model of opinion dynamics and
consensus formation. We analyze how the adaptivity of the network of contacts
between agents to the underlying social dynamics affects the size and
topological properties of groups and the convergence time to the stable final
state. We find that, while on static networks these properties are determined
by percolation phenomena, on adaptive networks the rewiring process leads to
different behaviors: Adaptive rewiring fosters group formation by enhancing
communication between agents of similar opinion, though it also makes possible
the division of clusters. We show how the convergence time is determined by the
characteristic time of link rearrangement. We finally investigate how the
adaptivity yields nontrivial correlations between the internal topology and the
size of the groups of agreeing agents.Comment: 10 pages, 3 figures,to appear in a special proceedings issue of J.
Phys. A covering the "Complex Networks: from Biology to Information
Technology" conference (Pula, Italy, 2007
No trace of a single-degenerate companion in late spectra of SNe 2011fe and 2014J
Left-over, ablated material from a possible non-degenerate companion can
reveal itself after about one year in spectra of Type Ia SNe (SNe Ia). We have
searched for such material in spectra of SN 2011fe (at 294 days after the
explosion) and for SN 2014J (315 days past explosion). The observations are
compared with numerical models simulating the expected line emission. The
spectral lines sought for are H-alpha, [O I] 6300 and [Ca II] 7291,7324, and
the expected width of these lines is about 1000 km/s. No signs of these lines
can be traced in any of the two supernovae. When systematic uncertainties are
included, the limits on hydrogen-rich ablated gas in SNe 2011fe and 2014J are
0.003 M_sun and 0.0085 M_sun, respectively, where the limit for SN 2014J is the
second lowest ever, and the limit for SN 2011fe is a revision of a previous
limit. Limits are also put on helium-rich ablated gas. These limits are used,
in conjunction with other data, to argue that these supernovae can stem from
double-degenerate systems, or from single-degenerate systems with a spun
up/spun down super-Chandrasekhar white dwarf. For SN 2011fe, other types of
hydrogen-rich donors can likely be ruled out, whereas for SN 2014J a
main-sequence donor system with large intrinsic separation is still possible.
Helium-rich donor systems cannot be ruled out for any of the two supernovae,
but the expected short delay time for such progenitors makes this possibility
less likely, especially for SN 2011fe. The broad [Ni II] 7378 emission in SN
2014J is redshifted by about +1300 km/s, as opposed to the known blueshift of
roughly -1100 km/s for SN 2011fe. [Fe II] 7155 is also redshifted in SN 2014J.
SN 2014J belongs to a minority of SNe Ia that both have a nebular redshift of
[Fe II] 7155 and [Ni II] 7378, and a slow decline of the Si II 6355 absorption
trough just after B-band maximum.Comment: 13 pages, submitted to A&
Consensus formation on adaptive networks
The structure of a network can significantly influence the properties of the
dynamical processes which take place on them. While many studies have been
devoted to this influence, much less attention has been devoted to the
interplay and feedback mechanisms between dynamical processes and network
topology on adaptive networks. Adaptive rewiring of links can happen in real
life systems such as acquaintance networks where people are more likely to
maintain a social connection if their views and values are similar. In our
study, we consider different variants of a model for consensus formation. Our
investigations reveal that the adaptation of the network topology fosters
cluster formation by enhancing communication between agents of similar opinion,
though it also promotes the division of these clusters. The temporal behavior
is also strongly affected by adaptivity: while, on static networks, it is
influenced by percolation properties, on adaptive networks, both the early and
late time evolution of the system are determined by the rewiring process. The
investigation of a variant of the model reveals that the scenarios of
transitions between consensus and polarized states are more robust on adaptive
networks.Comment: 11 pages, 14 figure
Fisher Waves and Front Roughening in a Two-Species Invasion Model with Preemptive Competition
We study front propagation when an invading species competes with a resident;
we assume nearest-neighbor preemptive competition for resources in an
individual-based, two-dimensional lattice model. The asymptotic front velocity
exhibits power-law dependence on the difference between the two species' clonal
propagation rates (key ecological parameters). The mean-field approximation
behaves similarly, but the power law's exponent slightly differs from the
individual-based model's result. We also study roughening of the front, using
the framework of non-equilibrium interface growth. Our analysis indicates that
initially flat, linear invading fronts exhibit Kardar-Parisi-Zhang (KPZ)
roughening in one transverse dimension. Further, this finding implies, and is
also confirmed by simulations, that the temporal correction to the asymptotic
front velocity is of .Comment: 8 pages, 5 figures; Papers on related work can be found at
http://www.rpi.edu/~korniss/Researc
Polyethylene imine-based receptor immobilization for label free bioassays
Polyethylene imine (PEI) based immobilization of antibodies is described and the concept is proved on the
label free assay of C-Reactive Protein (CRP). This novel immobilization method is composed of a hyperbranched
PEI layer which was deposited at a high pH (9.5) on the sensor surface. The free amino groups
of PEI were derivatized with neutravidin by Biotin N-hydroxysuccinimide ester and the biotinylated
anti-CRP antibody immobilized on this layer. Direct binding assay of recombinant CRP was successfully
performed in the low μg/ml concentrations using a label free optical waveguide biosensor
Supernova 1998bw - The final phases
The probable association with GRB 980425 immediately put SN 1998bw at the
forefront of supernova research. Here, we present revised late-time BVRI light
curves of the supernova, based on template images taken at the VLT. To follow
the supernova to the very last observable phases we have used HST/STIS. Deep
images taken in June and November 2000 are compared to images taken in August
2001. The identification of the supernova is firmly established. This allows us
to measure the light curve to about 1000 days past explosion. The main features
are a rapid decline up to more than 500 days after explosion, with no sign of
complete positron trapping from the Cobolt-56 decay. Thereafter, the light
curve flattens out significantly. One possible explanation is powering by more
long lived radioactive isotopes, if they are abundantly formed in this
energetic supernova.Comment: 13 pages, 5 figures, A&A, In pres
Circumstellar Na I and Ca II lines of type Ia supernovae in symbiotic scenario
Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is
studied for the case, when supernova explodes in a binary system with a red
giant. The model suggests a spherically-symmetric wind and takes into account
ionization and heating of the wind by X-rays from the shock wave and by
gamma-quanta of ^{56}Ni radioactive decay. For the wind density typical of the
red giant the expected optical depth of the wind in Na I lines turnes out too
low (\tau<0.001}) to detect the absorption. For the same wind densities the
predicted optical depth of Ca II 3934 \AA is sufficient for the detection
(\tau>0.1). I conclude that the absorption lines detected in SN 2006X cannot
form in the red giant wind; they are rather related to clouds at distances
larger than the dust evaporation radius (r>10^{17} cm). From the absence in SN
2006X of Ca II absorption lines not related with the similar Na I components I
derive the upper limit of the mass loss rate by the wind with velocity u:
\dot{M}<10^{-8}(u/10 km/s) M_{\odot} yr^{-1}.Comment: 10 pages, 6 figures, Astronomy Letters (accepted
Search for broad absorption lines in spectra of stars in the field of supernova remnant RX J0852.0-4622 (Vela Jr.)
Supernova remnant (SNR) RX J0852.0-4622 is one of the youngest and is most
likely the closest among known galactic supernova remnants (SNRs). It was
detected in X-rays, the 44Ti gamma-line, and radio. We obtain and analyze
medium-resolution spectra of 14 stars in the direction towards the SNR RX
J0852.0-4622 in an attempt to detect broad absorption lines of unshocked ejecta
against background stars. Spectral synthesis is performed for all the stars in
the wavelength range of 3740-4020AA to extract the broad absorption lines of Ca
II related to the SNR RX J0852.0-4622. We do not detect any broad absorption
line and place a 3-sigma upper limit on the relative depths of <0.04 for the
broad Ca II absorption produced by the SNR. We detect narrow low and high
velocity absorption components of Ca II. High velocity |V(LSR)|=100-140 km/s
components are attributed to radiative shocks in clouds engulfed by the old
Vela SNR. The upper limit to the absorption line strength combined with the
width and flux of the 44Ti gamma-ray line 1.16 MeV lead us to conclude that SNR
RX J0852.0-4622 was probably produced by an energetic SN Ic explosion.Comment: 9 pages, 8 figures, accepted in A&
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