7,160 research outputs found
Directed Multicut with linearly ordered terminals
Motivated by an application in network security, we investigate the following
"linear" case of Directed Mutlicut. Let be a directed graph which includes
some distinguished vertices . What is the size of the
smallest edge cut which eliminates all paths from to for all ? We show that this problem is fixed-parameter tractable when parametrized in
the cutset size via an algorithm running in time.Comment: 12 pages, 1 figur
Transport Mean Free Path for Magneto-Transverse Light Diffusion
We derive an expression for the transport mean free path
associated with magneto-transverse light diffusion for a random collection of
Faraday-active
Mie scatterers. This expression relates the magneto-transverse diffusion in
multiple scattering directly to the magneto-transverse scattering of a single
scatterer.Comment: 5 pages, 1 figure, Latex, accepted for publication in Europhysics
Letter
CAPD: A Context-Aware, Policy-Driven Framework for Secure and Resilient IoBT Operations
The Internet of Battlefield Things (IoBT) will advance the operational
effectiveness of infantry units. However, this requires autonomous assets such
as sensors, drones, combat equipment, and uncrewed vehicles to collaborate,
securely share information, and be resilient to adversary attacks in contested
multi-domain operations. CAPD addresses this problem by providing a
context-aware, policy-driven framework supporting data and knowledge exchange
among autonomous entities in a battlespace. We propose an IoBT ontology that
facilitates controlled information sharing to enable semantic interoperability
between systems. Its key contributions include providing a knowledge graph with
a shared semantic schema, integration with background knowledge, efficient
mechanisms for enforcing data consistency and drawing inferences, and
supporting attribute-based access control. The sensors in the IoBT provide data
that create populated knowledge graphs based on the ontology. This paper
describes using CAPD to detect and mitigate adversary actions. CAPD enables
situational awareness using reasoning over the sensed data and SPARQL queries.
For example, adversaries can cause sensor failure or hijacking and disrupt the
tactical networks to degrade video surveillance. In such instances, CAPD uses
an ontology-based reasoner to see how alternative approaches can still support
the mission. Depending on bandwidth availability, the reasoner initiates the
creation of a reduced frame rate grayscale video by active transcoding or
transmits only still images. This ability to reason over the mission sensed
environment and attack context permits the autonomous IoBT system to exhibit
resilience in contested conditions
Coherent backscattering of light by atoms in the saturated regime
We present the first calculation of coherent backscattering with inelastic
scattering by saturated atoms. We consider the scattering of a
quasi-monochromatic laser pulse by two distant atoms in free space. By
restricting ourselves to scattering of two photons, we employ a perturbative
approach, valid up to second order in the incident laser intensity. The
backscattering enhancement factor is found to be smaller than two (after
excluding single scattering), indicating a loss of coherence between the doubly
scattered light emitted by both atoms. Since the undetected photon carries
information about the path of the detected photon, the coherence loss can be
explained by a which-path argument, in analogy with a double-slit experiment.Comment: 16 pages, 10 figure
Hanle effect in coherent backscattering
We study the shape of the coherent backscattering (CBS) cone obtained when
resonant light illuminates a thick cloud of laser-cooled rubidium atoms in
presence of a homogenous magnetic field. We observe new magnetic
field-dependent anisotropies in the CBS signal. We show that the observed
behavior is due to the modification of the atomic radiation pattern by the
magnetic field (Hanle effect in the excited state).Comment: 4 pages, 3 figure
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