988 research outputs found
Quantifying discrepancies in opinion spectra from online and offline networks
Online social media such as Twitter are widely used for mining public
opinions and sentiments on various issues and topics. The sheer volume of the
data generated and the eager adoption by the online-savvy public are helping to
raise the profile of online media as a convenient source of news and public
opinions on social and political issues as well. Due to the uncontrollable
biases in the population who heavily use the media, however, it is often
difficult to measure how accurately the online sphere reflects the offline
world at large, undermining the usefulness of online media. One way of
identifying and overcoming the online-offline discrepancies is to apply a
common analytical and modeling framework to comparable data sets from online
and offline sources and cross-analyzing the patterns found therein. In this
paper we study the political spectra constructed from Twitter and from
legislators' voting records as an example to demonstrate the potential limits
of online media as the source for accurate public opinion mining.Comment: 10 pages, 4 figure
Crossover from Endogenous to Exogenous Activity in Open-Source Software Development
We have investigated the origin of fluctuations in the aggregated behaviour
of an open-source software community. In a recent series of papers, de Menezes
and co-workers have shown how to separate internal dynamics from external
fluctuations by capturing the simultaneous activity of many system's
components. In spite of software development being a planned activity, the
analysis of fluctuations reveals how external driving forces can be only
observed at weekly and higher time scales. Hourly and higher change frequencies
mostly relate to internal maintenance activities. There is a crossover from
endogenous to exogenous activity depending on the average number of file
changes. This new evidence suggests that software development is a
non-homogeneous design activity where stronger efforts focus in a few project
files. The crossover can be explained with a Langevin equation associated to
the cascading process, where changes to any file trigger additional changes to
its neighbours in the software network. In addition, analysis of fluctuations
enables us to detect whether a software system can be decomposed in several
subsystems with different development dynamics.Comment: 7 pages, 4 figures, submitted to Europhysics Letter
Clustering properties of a generalised critical Euclidean network
Many real-world networks exhibit scale-free feature, have a small diameter
and a high clustering tendency. We have studied the properties of a growing
network, which has all these features, in which an incoming node is connected
to its th predecessor of degree with a link of length using a
probability proportional to . For , the
network is scale free at with the degree distribution and as in the Barab\'asi-Albert model (). We find a phase boundary in the plane along which
the network is scale-free. Interestingly, we find scale-free behaviour even for
for where the existence of a new universality class
is indicated from the behaviour of the degree distribution and the clustering
coefficients. The network has a small diameter in the entire scale-free region.
The clustering coefficients emulate the behaviour of most real networks for
increasing negative values of on the phase boundary.Comment: 4 pages REVTEX, 4 figure
Drive level dependency in quartz resonators
AbstractCommon piezoelectric resonators such as quartz resonators have a very high Q and ultra stable resonant frequency. However, due to small material nonlinearities in the quartz crystal, the resonator is drive level dependent, that is, the resonator level of activity and its frequency are dependent on the driving, or excitation, voltage. The size of these resonators will be reduced to one fourth of their current sizes in the next few years, but the electrical power which is applied will not be reduced as much. Hence, the applied power to resonator size ratio will be larger, and the drive level dependency may play a role in the resonator designs.We study this phenomenon using the Lagrangian nonlinear stress equations of motion and Piola–Kirchhoff stress tensor of the second kind. Solutions are obtained using COMSOL for the AT-cut, BT-cut, SC-cut and other doubly rotated cut quartz resonators and the results compared well with experimental data. The phenomenon of the drive level dependence is discussed in terms of the voltage drive, electric field, power density and current density. It is found that the drive level dependency is best described in terms of the power density. Experimental results for the AT-, BT- and SC-cut resonators in comparison with our model results are presented. Results for new doubly rotated cuts are presented. The effects of spurious modes, quality factor and air damping on DLD are presented
Self Consistent Expansion for the Molecular Beam Epitaxy Equation
Motivated by a controversy over the correct results derived from the dynamic
renormalization group (DRG) analysis of the non linear molecular beam epitaxy
(MBE) equation, a self-consistent expansion (SCE) for the non linear MBE theory
is considered. The scaling exponents are obtained for spatially correlated
noise of the general form . I find a lower critical dimension , above, which the linear MBE solution appears. Below the
lower critical dimension a r-dependent strong-coupling solution is found. These
results help to resolve the controversy over the correct exponents that
describe non linear MBE, using a reliable method that proved itself in the past
by predicting reasonable results for the Kardar-Parisi-Zhang (KPZ) system,
where DRG failed to do so.Comment: 16 page
Modeling the Internet's Large-Scale Topology
Network generators that capture the Internet's large-scale topology are
crucial for the development of efficient routing protocols and modeling
Internet traffic. Our ability to design realistic generators is limited by the
incomplete understanding of the fundamental driving forces that affect the
Internet's evolution. By combining the most extensive data on the time
evolution, topology and physical layout of the Internet, we identify the
universal mechanisms that shape the Internet's router and autonomous system
level topology. We find that the physical layout of nodes form a fractal set,
determined by population density patterns around the globe. The placement of
links is driven by competition between preferential attachment and linear
distance dependence, a marked departure from the currently employed exponential
laws. The universal parameters that we extract significantly restrict the class
of potentially correct Internet models, and indicate that the networks created
by all available topology generators are significantly different from the
Internet
An Application Of An Artificial Neural Network Investment System To Predict Takeover Targets
Artificial neural networks are a robust, effective complement to traditional statistical methods in financial applications. They can incorporate qualitative and quantitative information, and recognize underlying patterns and trends in large, complex data sets. This paper applies a neural network model to identify potential acquisition targets. The model incorporates various factors based on acquisition theories suggested in the literature. The resulting neural network model exhibits a highly successful prediction rate and a portfolio of predicted target stocks identified by the network substantially outperformed the market
Diffusive Capture Process on Complex Networks
We study the dynamical properties of a diffusing lamb captured by a diffusing
lion on the complex networks with various sizes of . We find that the life
time and the survival probability becomes finite on scale-free networks with degree exponent
. However, for has a long-living tail on
tree-structured scale-free networks and decays exponentially on looped
scale-free networks. It suggests that the second moment of degree distribution
kn(k)n(k)\sim k^{-\sigma}\gamma<3n(k)k\approx k_{max}n(k)n(k)\sim k^2P(k)N_{tot}, which
causes the dependent behavior of and $.Comment: 9 pages, 6 figure
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