67 research outputs found
Occupation time statistics of the random acceleration model
The random acceleration model is one of the simplest non-Markovian stochastic
systems and has been widely studied in connection with applications in physics
and mathematics. However, the occupation time and related properties are
non-trivial and not yet completely understood. In this paper we consider the
occupation time of the one-dimensional random acceleration model on the
positive half-axis. We calculate the first two moments of analytically
and also study the statistics of with Monte Carlo simulations. One goal
of our work was to ascertain whether the occupation time and the time
at which the maximum of the process is attained are statistically
equivalent. For regular Brownian motion the distributions of and
coincide and are given by L\'evy's arcsine law. We show that for randomly
accelerated motion the distributions of and are quite similar but
not identical. This conclusion follows from the exact results for the moments
of the distributions and is also consistent with our Monte Carlo simulations.Comment: 10 pages, 4 figure
Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul
[EN] The bandwidth demands in mobile communication systems are growing exponentially day by day as the number of users has increased drastically over the last five years. This mobile data explosion, together with the fixed service limitations, requires a new approach to support this increase in bandwidth demand. Solutions based on lower-frequency microwave wireless systems may be able to meet the bandwidth demand in a short term. However, with the small-cell mass deployment requiring total capacities of 1 Gb/s/km2, scalable, multigigabit backhaul systems are required. Millimeter-wave technology fits nicely into these new backhaul scenarios as it provides extended bandwidth for high-capacity links and adaptive throughput rate, which allows efficient and flexible deployment. Besides these advantages, millimeter-wave solutions become even more attractive when the cost of backhaul solutions and the cost of spectrum licenses are factored in. Compared to the cost of laying fiber to a cell base station, which is the only other scalable solution, the millimeter-wave solution becomes the most appropriate approach.The research leading to these results received funding from the European Commission's seventh Framework Programme under grant agreement 288267.Vilar Mateo, R.; Czarny, R.; Lee, ML.; Loiseaux, B.; Sypek, M.; Makowski, M.; Martel, C.... (2014). Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul. IEEE Microwave Magazine. 15(4):121-130. https://doi.org/10.1109/MMM.2014.2308769S12113015
Structural modeling of the flagellum MS ring protein FliF reveals similarities to the type III secretion system and sporulation complex
The flagellum is a large proteinaceous organelle found at the surface of many bacteria,
whose primary role is to allow motility through the rotation of a long extracellular
filament. It is an essential virulence factor in many pathogenic species, and is also a
priming component in the formation of antibiotic-resistant biofilms. The flagellum
consists of the export apparatus on the cytosolic side; the basal body and rotor, spanning
the bacterial membrane(s) and periplasm; and the hook-filament, that protrudes away
from the bacterial surface. Formation of the basal body MS ring region, constituted of
multiple copies of the protein FliF, is one of the initial steps of flagellum assembly.
However, the precise architecture of FliF is poorly understood. Here, I report a
bioinformatics analysis of the FliF sequence from various bacterial species, suggesting
that its periplasmic region is composed of three globular domains. The first two are
homologous to that of the type III secretion system injectisome proteins SctJ, and the
third possesses a similar fold to that of the sporulation complex component SpoIIIAG.
I also describe that Chlamydia possesses an unusual FliF protein, lacking part of
the SctJ homology domain and the SpoIIIAG-like domain, and fused to the rotor
component FliG at its C-terminus. Finally, I have combined the sequence analysis of
FliF with the EM map of the MS ring, to propose the first atomic model for the FliF
oligomer, suggesting that FliF is structurally akin to a fusion of the two injectisome
components SctJ and SctD. These results further define the relationship between the
flagellum, injectisome and sporulation complex, and will facilitate future structural
characterization of the flagellum basal body
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