2,380 research outputs found
Predicting the epidemic threshold of the susceptible-infected-recovered model
Researchers have developed several theoretical methods for predicting
epidemic thresholds, including the mean-field like (MFL) method, the quenched
mean-field (QMF) method, and the dynamical message passing (DMP) method. When
these methods are applied to predict epidemic threshold they often produce
differing results and their relative levels of accuracy are still unknown. We
systematically analyze these two issues---relationships among differing results
and levels of accuracy---by studying the susceptible-infected-recovered (SIR)
model on uncorrelated configuration networks and a group of 56 real-world
networks. In uncorrelated configuration networks the MFL and DMP methods yield
identical predictions that are larger and more accurate than the prediction
generated by the QMF method. When compared to the 56 real-world networks, the
epidemic threshold obtained by the DMP method is closer to the actual epidemic
threshold because it incorporates full network topology information and some
dynamical correlations. We find that in some scenarios---such as networks with
positive degree-degree correlations, with an eigenvector localized on the high
-core nodes, or with a high level of clustering---the epidemic threshold
predicted by the MFL method, which uses the degree distribution as the only
input parameter, performs better than the other two methods. We also find that
the performances of the three predictions are irregular versus modularity
Suppressing disease spreading by using information diffusion on multiplex networks
Although there is always an interplay between the dynamics of information
diffusion and disease spreading, the empirical research on the systemic
coevolution mechanisms connecting these two spreading dynamics is still
lacking. Here we investigate the coevolution mechanisms and dynamics between
information and disease spreading by utilizing real data and a proposed
spreading model on multiplex network. Our empirical analysis finds asymmetrical
interactions between the information and disease spreading dynamics. Our
results obtained from both the theoretical framework and extensive stochastic
numerical simulations suggest that an information outbreak can be triggered in
a communication network by its own spreading dynamics or by a disease outbreak
on a contact network, but that the disease threshold is not affected by
information spreading. Our key finding is that there is an optimal information
transmission rate that markedly suppresses the disease spreading. We find that
the time evolution of the dynamics in the proposed model qualitatively agrees
with the real-world spreading processes at the optimal information transmission
rate.Comment: 11 pages, 8 figure
Raman and Infra-red properties and layer dependence of the phonon dispersions in multi-layered graphene
The symmetry group analysis is applied to classify the phonon modes of
-stacked graphene layers (NSGL's) with AB- and AA-stacking, particularly
their infra-red and Raman properties. The dispersions of various phonon modes
are calculated in a multi-layer vibrational model, which is generalized from
the lattice vibrational potentials of graphene to including the inter-layer
interactions in NSGL's. The experimentally reported red shift phenomena in the
layer number dependence of the intra-layer optical C-C stretching mode
frequencies are interpreted. An interesting low frequency inter-layer optical
mode is revealed to be Raman or Infra-red active in even or odd NSGL's
respectively. Its frequency shift is sensitive to the layer number and
saturated at about 10 layers.Comment: enlarged versio
Ground state and glass transition of the RNA secondary structure
RNA molecules form a sequence-specific self-pairing pattern at low
temperatures. We analyze this problem using a random pairing energy model as
well as a random sequence model that includes a base stacking energy in favor
of helix propagation. The free energy cost for separating a chain into two
equal halves offers a quantitative measure of sequence specific pairing. In the
low temperature glass phase, this quantity grows quadratically with the
logarithm of the chain length, but it switches to a linear behavior of entropic
origin in the high temperature molten phase. Transition between the two phases
is continuous, with characteristics that resemble those of a disordered elastic
manifold in two dimensions. For designed sequences, however, a power-law
distribution of pairing energies on a coarse-grained level may be more
appropriate. Extreme value statistics arguments then predict a power-law growth
of the free energy cost to break a chain, in agreement with numerical
simulations. Interestingly, the distribution of pairing distances in the ground
state secondary structure follows a remarkable power-law with an exponent -4/3,
independent of the specific assumptions for the base pairing energies
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Unsaturated Ligands Seed an Order to Disorder Transition in Mixed Ligand Shells of CdSe/CdS Quantum Dots.
A phase transition within the ligand shell of core/shell quantum dots is studied in the prototypical system of colloidal CdSe/CdS quantum dots with a ligand shell composed of bound oleate (OA) and octadecylphosphonate (ODPA). The ligand shell composition is tuned using a ligand exchange procedure and quantified through proton NMR spectroscopy. Temperature-dependent photoluminescence spectroscopy reveals a signature of a phase transition within the organic ligand shell. Surprisingly, the ligand order to disorder phase transition triggers an abrupt increase in the photoluminescence quantum yield (PLQY) and full-width at half-maximum (FWHM) with increasing temperature. The temperature and width of the phase transition show a clear dependence on ligand shell composition, such that QDs with higher ODPA fractions have sharper phase transitions that occur at higher temperatures. In order to gain a molecular understanding of the changes in ligand ordering, Fourier transform infrared and vibrational sum frequency generation spectroscopies are performed. These measurements confirm that an order/disorder transition in the ligand shell tracks with the photoluminescence changes that accompany the ligand phase transition. The phase transition is simulated through a lattice model that suggests that the ligand shell is well-mixed and does not have completely segregated domains of OA and ODPA. Furthermore, we show that the unsaturated chains of OA seed disorder within the ligand shell
Computational investigation of static multipole polarizabilities and sum rules for ground-state hydrogen-like ions
High precision multipole polarizabilities, for
of the ground state of the hydrogen isoelectronic series are obtained from
the Dirac equation using the B-spline method with Notre Dame boundary
conditions. Compact analytic expressions for the polarizabilities as a function
of with a relative accuracy of 10 up to are determined by
fitting to the calculated polarizabilities. The oscillator strengths satisfy
the sum rules for all multipoles from
to . The dispersion coefficients for the long-range H-H and H-He
interactions are given.Comment: 8 figures, 8 table
Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state
Recent observations strongly suggest that the millisecond pulsar binary PSR
J1023+0038 has developed an accretion disk since 2013 June. We present a
multi-wavelength analysis of PSR J1023+0038, which reveals that 1) its
gamma-rays suddenly brightened within a few days in June/July 2013 and has
remained at a high gamma-ray state for several months; 2) both UV and X-ray
fluxes have increased by roughly an order of magnitude, and 3) the spectral
energy distribution has changed significantly after the gamma-ray sudden flux
change. Time variabilities associated with UV and X-rays are on the order of
100-500 seconds and 50-100 seconds, respectively. Our model suggests that a
newly formed accretion disk due to the sudden increase of the stellar wind
could explain the changes of all these observed features. The increase of UV is
emitted from the disk, and a new component in gamma-rays is produced by inverse
Compton scattering between the new UV component and pulsar wind. The increase
of X-rays results from the enhancement of injection pulsar wind energy into the
intra-binary shock due to the increase of the stellar wind. We also predict
that the radio pulses may be blocked by the evaporated winds from the disk and
the pulsar is still powered by rotation.Comment: 8 pages, 3 figures; accepted for publication in Ap
Random RNA under tension
The Laessig-Wiese (LW) field theory for the freezing transition of random RNA
secondary structures is generalized to the situation of an external force. We
find a second-order phase transition at a critical applied force f = f_c. For f
f_c, the extension L as a function of
pulling force f scales as (f-f_c)^(1/gamma-1). The exponent gamma is calculated
in an epsilon-expansion: At 1-loop order gamma = epsilon/2 = 1/2, equivalent to
the disorder-free case. 2-loop results yielding gamma = 0.6 are briefly
mentioned. Using a locking argument, we speculate that this result extends to
the strong-disorder phase.Comment: 6 pages, 10 figures. v2: corrected typos, discussion on locking
argument improve
Efficient community-based control strategies in adaptive networks
Most researches on adaptive networks mainly concentrate on the properties of
steady state, but neglect transient dynamics. In this study, we pay attention
to the emergence of community structures in transient process and the effects
of community-based control strategies on epidemic spreading. First, by
normalizing modularity , we investigate the evolution of community
structures during the transient process, and find that very strong community
structures are induced by rewiring mechanism in the early stage of epidemic
spreading, which remarkably delays the outbreaks of epidemic. Then we study the
effects of control strategies started from different stages on the prevalence.
Both immunization and quarantine strategies indicate that it is not "the
earlier, the better" for the implementing of control measures. And the optimal
control effect is obtained if control measures can be efficiently implemented
in the period of strong community structure. For immunization strategy,
immunizing the S nodes on SI links and immunizing S nodes randomly have similar
control effects. Yet for quarantine strategy, quarantining the I nodes on SI
links can yield far better effects than quarantining I nodes randomly. More
significantly, community-based quarantine strategy plays more efficient
performance than community-based immunization strategy. This study may shed new
lights on the forecast and the prevention of epidemic among human population.Comment: 5 pages, 5 figure
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