69,409 research outputs found
Service quality measurements for IPv6 inter-networks
Measurement-based performance evaluation of
network traffic is becoming very important, especially for
networks trying to provide differentiated levels of service quality to the different application flows. The non-identical response of flows to the different types of network-imposed performance degradation raises the need for ubiquitous measurement mechanisms, able to measure numerous performance properties, and being equally applicable to different applications and transports. This paper presents a new measurement mechanism, facilitated by the steady introduction of IPv6 in network nodes and hosts, which exploits native features of the protocol to provide support for performance measurements at the network (IP) layer. IPv6 Extension Headers have been used to carry the
triggers involving the measurement activity and the
measurement data in-line with the payload data itself, providing a high level of probability that the behaviour of the real user traffic flows is observed. End-to-end one-way delay, jitter, loss, and throughput have been measured for applications operating on top of both reliable and unreliable transports, over different-capacity
IPv6 network configurations. We conclude that this
technique could form the basis for future Internet measurements that can be dynamically deployed where and when required in a multi-service IP environment
Extraordinary nonlinear plasmonics in graphene nanoislands
Nonlinear optical processes rely on the intrinsically weak interactions
between photons enabled by their coupling with matter. Unfortunately, many
applications in nonlinear optics are severely hindered by the small response of
conventional materials. Metallic nanostructures partially alleviate this
situation, as the large light enhancement associated with their localized
plasmons amplifies their nonlinear response to record high levels. Graphene
hosts long-lived, electrically tunable plasmons that also interact strongly
with light. Here we show that the nonlinear polarizabilities of graphene
nanoislands can be electrically tuned to surpass by several orders of magnitude
those of metal nanoparticles of similar size. This extraordinary behavior
extends over the visible and near-infrared for islands consisting of hundreds
of carbon atoms doped with moderate carrier densities. Our quantum-mechanical
simulations of the plasmon-enhanced optical response of nanographene reveal
this material as an ideal platform for the development of electrically tunable
nonlinear optical nanodevices.Comment: 16 pages, 12 figures, 54 reference
Matrix Product Density Operators: Renormalization Fixed Points and Boundary Theories
We consider the tensors generating matrix product states and density
operators in a spin chain. For pure states, we revise the renormalization
procedure introduced by F. Verstraete et al. in 2005 and characterize the
tensors corresponding to the fixed points. We relate them to the states
possessing zero correlation length, saturation of the area law, as well as to
those which generate ground states of local and commuting Hamiltonians. For
mixed states, we introduce the concept of renormalization fixed points and
characterize the corresponding tensors. We also relate them to concepts like
finite correlation length, saturation of the area law, as well as to those
which generate Gibbs states of local and commuting Hamiltonians. One of the
main result of this work is that the resulting fixed points can be associated
to the boundary theories of two-dimensional topological states, through the
bulk-boundary correspondence introduced by Cirac et al. in 2011.Comment: 63 pages, Annals of Physics (2016). Accepted versio
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