134 research outputs found
The Opportunistic Transmission of Wireless Worms between Mobile Devices
The ubiquity of portable wireless-enabled computing and communications
devices has stimulated the emergence of malicious codes (wireless worms) that
are capable of spreading between spatially proximal devices. The potential
exists for worms to be opportunistically transmitted between devices as they
move around, so human mobility patterns will have an impact on epidemic spread.
The scenario we address in this paper is proximity attacks from fleetingly
in-contact wireless devices with short-range communication range, such as
Bluetooth-enabled smart phones. An individual-based model of mobile devices is
introduced and the effect of population characteristics and device behaviour on
the outbreak dynamics is investigated. We show through extensive simulations
that in the above scenario the resulting mass-action epidemic models remain
applicable provided the contact rate is derived consistently from the
underlying mobility model. The model gives useful analytical expressions
against which more refined simulations of worm spread can be developed and
tested.Comment: Submitted for publicatio
Quantum Monte Carlo Analysis of Exchange and Correlation in the Strongly Inhomogeneous Electron Gas
We use variational quantum Monte Carlo to calculate the density-functional
exchange-correlation hole n_{xc}, the exchange-correlation energy density
e_{xc}, and the total exchange-correlation energy E_{xc}, of several electron
gas systems in which strong density inhomogeneities are induced by a
cosine-wave potential. We compare our results with the local density
approximation and the generalized gradient approximation. It is found that the
nonlocal contributions to e_{xc} contain an energetically significant
component, the magnitude, shape, and sign of which are controlled by the
Laplacian of the electron density.Comment: 4 pages, 3 figure
A Ternary Lattice Boltzmann Model for Amphiphilic Fluids
A lattice Boltzmann model for amphiphilic fluid dynamics is presented. It is
a ternary model, in that it conserves mass separately for each chemical species
present (water, oil, amphiphile), and it maintains an orientational degree of
freedom for the amphiphilic species. Moreover, it models fluid interactions at
the microscopic level by introducing self-consistent forces between the
particles, rather than by positing a Landau free energy functional. This
combination of characteristics fills an important need in the hierarchy of
models currently available for amphiphilic fluid dynamics, enabling efficient
computer simulation and furnishing new theoretical insight. Several
computational results obtained from this model are presented and compared to
existing lattice-gas model results. In particular, it is noted that lamellar
structures, which are precluded by the Peierls instability in two-dimensional
systems with kinetic fluctuations, are not observed in lattice-gas models, but
are easily found in the corresponding lattice Boltzmann models. This points out
a striking difference in the phenomenology accessible to each type of model.Comment: 12 pages, 6 figures included with graphic
Light trapping and guidance in plasmonic nanocrystals
We illustrate the possibility of light trapping and funneling in periodic
arrays of metallic nanoparticles. A controllable minimum in the transmission
spectra of such constructs arises from a collective plasmon resonance
phenomenon, where an incident plane wave sharply localizes in the vertical
direction, remaining delocalized in the direction parallel to the crystal
plane. Using hybrid arrays of different structures or different materials, we
apply the trapping effect to structure the eigen-mode spectrum, introduce
overlapping resonances, and hence direct the light in space in a
wavelength-sensitive fashion
Worm Epidemics in Wireless Adhoc Networks
A dramatic increase in the number of computing devices with wireless
communication capability has resulted in the emergence of a new class of
computer worms which specifically target such devices. The most striking
feature of these worms is that they do not require Internet connectivity for
their propagation but can spread directly from device to device using a
short-range radio communication technology, such as WiFi or Bluetooth. In this
paper, we develop a new model for epidemic spreading of these worms and
investigate their spreading in wireless ad hoc networks via extensive Monte
Carlo simulations. Our studies show that the threshold behaviour and dynamics
of worm epidemics in these networks are greatly affected by a combination of
spatial and temporal correlations which characterize these networks, and are
significantly different from the previously studied epidemics in the Internet
Reducing congestion in obstructed highways with traffic data dissemination using adhoc vehicular networks
Vehicle-to-vehicle communications can be used effectively for intelligent transport systems (ITSs) and location-aware services. The ability to disseminate information in an ad hoc fashion allows pertinent information to propagate faster through a network. In the realm of ITS, the ability to spread warning information faster and further is of great advantage to receivers. In this paper we propose and present a message-dissemination procedure that uses vehicular wireless protocols to influence vehicular flow, reducing congestion in road networks. The computational experiments we present show how a car-following model and lane-change algorithm can be adapted to “react” to the reception of information. This model also illustrates the advantages of coupling together with vehicular flow modelling tools and network simulation tools
Automatic trust calculation for service-oriented systems
Among various service providers providing identical or similar services with varying quality of service, trust is
essential for service consumers to find the right one. Manually assigning feedback costs much time and suffers from several
drawbacks. Only automatic trust calculation is feasible for large-scale service-oriented applications. Therefore an automatic
method of trust calculation is proposed. To make the calculation accurate, the Kalman filter is adopted to filter out malicious
non-trust quality criterion (NTQC) values instead of malicious trust values. To offer higher detection accuracy, it is further
improved by considering the relationship between NTQC values and variances. Since dishonest or inaccurate values can still
influence trust values, the similarity between consumers is used to weight data from other consumers. As existing models
only used the Euclidean function and ignored others, a collection of distance functions is modified to calculate the similarity.
Finally, experiments are carried out to access the robustness of the proposed model. The results show that the improved
algorithm can offer higher detection accuracy, and it was discovered that another equation outperformed the Euclidean function
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