8,393 research outputs found
Data Aggregation and Packet Bundling of Uplink Small Packets for Monitoring Applications in LTE
In cellular massive Machine-Type Communications (MTC), a device can transmit
directly to the base station (BS) or through an aggregator (intermediate node).
While direct device-BS communication has recently been in the focus of 5G/3GPP
research and standardization efforts, the use of aggregators remains a less
explored topic. In this paper we analyze the deployment scenarios in which
aggregators can perform cellular access on behalf of multiple MTC devices. We
study the effect of packet bundling at the aggregator, which alleviates
overhead and resource waste when sending small packets. The aggregators give
rise to a tradeoff between access congestion and resource starvation and we
show that packet bundling can minimize resource starvation, especially for
smaller numbers of aggregators. Under the limitations of the considered model,
we investigate the optimal settings of the network parameters, in terms of
number of aggregators and packet-bundle size. Our results show that, in
general, data aggregation can benefit the uplink massive MTC in LTE, by
reducing the signalling overhead.Comment: to appear in IEEE Networ
Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes
We measure the conductivity spectra of thin films comprising bundled
single-walled carbon nanotubes (CNTs) of different average lengths in the
frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed
temperature-induced changes in the terahertz conductivity spectra are shown to
depend strongly on the average CNT length, with a conductivity around 1 THz
that increases/decreases as the temperature increases for short/long tubes.
This behaviour originates from the temperature dependence of the electron
scattering rate, which we obtain from Drude fits of the measured conductivity
in the range 0.3-2 THz for 10 m length CNTs. This increasing scattering
rate with temperature results in a subsequent broadening of the observed THz
conductivity peak at higher temperatures and a shift to lower frequencies for
increasing CNT length. Finally, we show that the change in conductivity with
temperature depends not only on tube length, but also varies with tube density.
We record the effective conductivities of composite films comprising mixtures
of WS nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1
THz, finding that the conductivity increases/decreases for low/high density
films as the temperature increases. This effect arises due to the density
dependence of the effective length of conducting pathways in the composite
films, which again leads to a shift and temperature dependent broadening of the
THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8
figures. Supplementary material: 5 pages, 6 figure
Finite Size Polyelectrolyte Bundles at Thermodynamic Equilibrium
We present the results of extensive computer simulations performed on
solutions of monodisperse charged rod-like polyelectrolytes in the presence of
trivalent counterions. To overcome energy barriers we used a combination of
parallel tempering and hybrid Monte Carlo techniques. Our results show that for
small values of the electrostatic interaction the solution mostly consists of
dispersed single rods. The potential of mean force between the polyelectrolyte
monomers yields an attractive interaction at short distances. For a range of
larger values of the Bjerrum length, we find finite size polyelectrolyte
bundles at thermodynamic equilibrium. Further increase of the Bjerrum length
eventually leads to phase separation and precipitation. We discuss the origin
of the observed thermodynamic stability of the finite size aggregates
Disease spread through animal movements: a static and temporal network analysis of pig trade in Germany
Background: Animal trade plays an important role for the spread of infectious
diseases in livestock populations. As a case study, we consider pig trade in
Germany, where trade actors (agricultural premises) form a complex network. The
central question is how infectious diseases can potentially spread within the
system of trade contacts. We address this question by analyzing the underlying
network of animal movements.
Methodology/Findings: The considered pig trade dataset spans several years
and is analyzed with respect to its potential to spread infectious diseases.
Focusing on measurements of network-topological properties, we avoid the usage
of external parameters, since these properties are independent of specific
pathogens. They are on the contrary of great importance for understanding any
general spreading process on this particular network. We analyze the system
using different network models, which include varying amounts of information:
(i) static network, (ii) network as a time series of uncorrelated snapshots,
(iii) temporal network, where causality is explicitly taken into account.
Findings: Our approach provides a general framework for a
topological-temporal characterization of livestock trade networks. We find that
a static network view captures many relevant aspects of the trade system, and
premises can be classified into two clearly defined risk classes. Moreover, our
results allow for an efficient allocation strategy for intervention measures
using centrality measures. Data on trade volume does barely alter the results
and is therefore of secondary importance. Although a static network description
yields useful results, the temporal resolution of data plays an outstanding
role for an in-depth understanding of spreading processes. This applies in
particular for an accurate calculation of the maximum outbreak size.Comment: main text 33 pages, 17 figures, supporting information 7 pages, 7
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