428 research outputs found
Probing massive neutrinos with the Minkowski functionals of large-scale structure
Massive neutrinos suppress the growth of structure under their free-streaming
scales. The effect is most prominent on small scales where the widely-used
two-point statistics can no longer capture the full information. In this work,
we study the signatures massive neutrinos leave on large-scale structure (LSS)
as revealed by its morphological properties, which are fully described by
Minkowski functionals (MFs), and quantify the constraints on the summed
neutrino mass from the MFs, by using publicly available N-body
simulations. We find the MFs provide important complementary information, and
give tighter constraints on than the power spectrum. Specifically,
depending on whether massive neutrinos are included in the density field (the
`m' field) or not (the `cb' field), we find the constraint on from
the MFs with a smoothing scale of Mpc is or times better
than that from the power spectrum. When the MFs are combined with the power
spectrum, they can improve the constraint on from the latter by a
factor of 63 for the `m' field and 5 for the `cb' field. Notably, when the `m'
field is used, the constraint on from the MFs can reach eV
with a volume of , while the combination of the MFs and
power spectrum can tighten this constraint to be eV, a
significance on detecting the minimum sum of the neutrino masses. For the `m'
field, we also find the and degeneracy is broken with the
MFs, leading to stronger constraints on all 6 cosmological parameters
considered in this work than the power spectrum.Comment: Accepted for publication in JCAP. Changes from the first version: add
figure 10, and minor text revisions. Matches accepted version. 33 pages, 10
figures, 2 table
Implementation of an Internet-based remote controller with guaranteed exponential stabilization
International audienceAn Internet-based remote control system is designed and implemented. The communication is based on the Master-Slave structure. The Master PC communicates with the Slave from about 40km away by UDP protocol. In order to guarantee the Master and Slave clocks to be synchronized, the NTP (Network Time Protocol) is used in both sides. The packets are sent together with time-stamps. The controller design (Master) relies on a remote observer that achieves a state prediction of the application (Slave), despite the variable communication delays. The Slave comprises a PC and a robot Miabot of Merlin company. Internet-based remote systems are subject to variable time delays (including communication and data-sampling delays). We have continuously tested the RTT (round-triptime) between the two PCs in the day-time and night-time by the protocol ICMP (Internet Control Message). From these tests, an evaluation of the maximal time delay is obtained. The structure allows one to guarantee an exponential stabilization performance, which is proven via a Lyapunov-Krassovski functional technique and involves the estimated delay upperbound. This means that the guaranteed decay rate is computed (via some LMI optimization) in relation to some maximal value of the communication delays. Of course, for greater delay values, the performance cannot be guaranteed anymore and an alternative solution has to be considered. In our system, we give a command for the robot to stop until the communication comes back to a sufficient quality
Superconducting traction transformer
An ongoing project to develop HTS traction transformers for the Chinese Fuxing high-speed train is demonstrating that the high-power density can be reached using high-temperature superconductors
(HTS). The findings are spectacular: the existing 6.5 MVA traction transformers can be replaced with drop-in superconducting transformers, achieving targets of less than 3 tons transformer system weight and 99.5 % efficiency compared to 6 tons and 95 % in the existing devices. The key to achieving these impressive figures is minimizing the AC loss of the HTS windings. New high-performance
wire, high current HTS Roebel conductor, high aspect-ratio windings, and flux diverters placed at the winding ends all contribute to reducing the electrical loss to less than 2 kW
Output control with Internet-in-the-loop : An event-driven realization
International audienceThis work is devoted to the remote feedback control of a linear process with "Internet in the loop". In such a networked control situation, variable and unpredictable delays arise, which may decrease the global performance or destabilize the system. Our aim is to obtain the best performance despite the variation of the network QoS (quality of service). The considered application is based on a Master-Slave structure. The Slave is a light mobile robot, that receives the control data and sends its sampled position via a UDP protocol. A Master computer realizes the remote control, based on a remote observer and a state feedback. The global strategy is without buffers. The packets are time-stamped so the Master detects the variable time delays (the network QoS). This information is used to adapt its observer/controller gains and guarantee the best possible performances. The design of this gain scheduling strategy relies on Lyapunov-Krasovskii functionals with an LMI optimization which guarantees the stability even with packet losses. Experimental results are provided
The effects of peculiar velocities on the morphological properties of large-scale structure
It is known that the large-scale structure (LSS) mapped by a galaxy redshift
survey is subject to distortions by galaxies' peculiar velocities. Besides the
signatures generated in common N-point statistics, such as the anisotropy in
the galaxy 2-point correlation function, the peculiar velocities also induce
distinct features in LSS's morphological properties, which are fully described
by four Minkowski functionals (MFs), i.e., the volume, surface area, integrated
mean curvature and Euler characteristic (or genus). In this work, by using
large suite of N-body simulations, we present and analyze these important
features in the MFs of LSS on both (quasi-)linear and non-linear scales, with a
focus on the latter. We also find the MFs can give competitive constraints on
cosmological parameters compared to the power spectrum, probablly due to the
non-linear information contained. For galaxy number density similar to the DESI
BGS galaxies, the constraint on from the MFs with one smoothing
scale can be better by than from the power spectrum. These findings
are important for the cosmological applications of MFs of LSS, and probablly
open up a new avenue for studying the peculiar velocity field itself.Comment: 6 pages, 3 figures, accepted by PR
Networked control and observation for Master-Slave systems
2009, 350 p. 110 illus., Hardcover. ISBN: 978-0-387-85594-3This chapter concerns the design of a remote control loop constituted by a Slave system (with computing and energy limitations) and a Master computer, communicating via an Internet connection. In such a situation, the communication cost is reduced but the Quality of Service of the Internet connection is not guaranteed. In particular, when the Slave dynamics are expected to be fast enough, the network induces perturbations (delays, jitters, packet dropouts and sampling) that may damage the performance. Here, the proposed solution relies on a delay-dependent, state-feedback control, computed by the Master on the basis of an observer. This last estimates the present Slave's state from its past sampled outputs, despite the various delays. Then, the computing task is concentrated in the Master. The theoretical results are based on the Lyapunov-Krasovskii functional and the approach of LMI, which guarantee the stabilization performance with respect to the expected maximum delay of the connection. Two strategies are applied: one is a constant controller/observer gain strategy, which takes into account a fixed upperbound for the communication delay. The second strategy aims at improving the performance by adapting the gains to the available network QoS (here, with two possible upperbounds)
Delay dependent stability analysis of interval time-delay systems
International audienceWe consider interval time-varying delay systems. The time-delay interval is divided into several zones and the systems switch among the different zones. Based on Lyapunov-Krasovskii functional methods and on linear matrix inequality (LMI) techniques, exponential stability is exploited for every time-delay zone. The global stability of the switched system is guaranteed if some minimum average dwell time conditions are satisfied. Numerical examples and comparisons with other works show that the methods enlarge the value of the maximum upper-bound of allowable time-delays
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