289 research outputs found
Energy Efficient and Reliable Wireless Sensor Networks - An Extension to IEEE 802.15.4e
Collecting sensor data in industrial environments from up to some tenth of
battery powered sensor nodes with sampling rates up to 100Hz requires energy
aware protocols, which avoid collisions and long listening phases. The IEEE
802.15.4 standard focuses on energy aware wireless sensor networks (WSNs) and
the Task Group 4e has published an amendment to fulfill up to 100 sensor value
transmissions per second per sensor node (Low Latency Deterministic Network
(LLDN) mode) to satisfy demands of factory automation. To improve the
reliability of the data collection in the star topology of the LLDN mode, we
propose a relay strategy, which can be performed within the LLDN schedule.
Furthermore we propose an extension of the star topology to collect data from
two-hop sensor nodes. The proposed Retransmission Mode enables power savings in
the sensor node of more than 33%, while reducing the packet loss by up to 50%.
To reach this performance, an optimum spatial distribution is necessary, which
is discussed in detail
Raman and XPS analyses of pristine and annealed N-doped double-walled carbon nanotubes
N-doped single/multi-walled carbon nanotubes (CNTs) were studied for long
time from synthesis to properties. However, the stability of N in the CNT
lattice still needs further developments. In this work, to obtain more stable
N-doped CNTs, concentric double-walled (DW) CNTs with more N were synthesized
using benzylamine as C and N source. In order to test the stability of N-doped
DWCNTs, high-temperature annealing in vacuum was performed. By XPS and Raman
spectroscopic measurements, we found that the N-doped DWCNTs are still stable
under 1500 \,^{\circ}\mathrm{C}: the graphitic N does not change at all, the
molecular N is partly removed, and the pyridinic N ratio greatly increases by
more than two times. The reason could be that the N atoms from the surrounded
N-contained materials combine into the CNT lattice during the annealing.
Compared with the undoped DWCNTs, no Raman frequency shift was observed for the
RBM, the G-band, and the G'-band of the N-doped DWCNTs.Comment: 6 pages, 5 figure
Probing many-body dynamics on a 51-atom quantum simulator
Controllable, coherent many-body systems can provide insights into the
fundamental properties of quantum matter, enable the realization of new quantum
phases and could ultimately lead to computational systems that outperform
existing computers based on classical approaches. Here we demonstrate a method
for creating controlled many-body quantum matter that combines
deterministically prepared, reconfigurable arrays of individually trapped cold
atoms with strong, coherent interactions enabled by excitation to Rydberg
states. We realize a programmable Ising-type quantum spin model with tunable
interactions and system sizes of up to 51 qubits. Within this model, we observe
phase transitions into spatially ordered states that break various discrete
symmetries, verify the high-fidelity preparation of these states and
investigate the dynamics across the phase transition in large arrays of atoms.
In particular, we observe robust manybody dynamics corresponding to persistent
oscillations of the order after a rapid quantum quench that results from a
sudden transition across the phase boundary. Our method provides a way of
exploring many-body phenomena on a programmable quantum simulator and could
enable realizations of new quantum algorithms.Comment: 17 pages, 13 figure
Quantum Kibble-Zurek mechanism and critical dynamics on a programmable Rydberg simulator
Quantum phase transitions (QPTs) involve transformations between different
states of matter that are driven by quantum fluctuations. These fluctuations
play a dominant role in the quantum critical region surrounding the transition
point, where the dynamics are governed by the universal properties associated
with the QPT. While time-dependent phenomena associated with classical,
thermally driven phase transitions have been extensively studied in systems
ranging from the early universe to Bose Einstein Condensates, understanding
critical real-time dynamics in isolated, non-equilibrium quantum systems is an
outstanding challenge. Here, we use a Rydberg atom quantum simulator with
programmable interactions to study the quantum critical dynamics associated
with several distinct QPTs. By studying the growth of spatial correlations
while crossing the QPT, we experimentally verify the quantum Kibble-Zurek
mechanism (QKZM) for an Ising-type QPT, explore scaling universality, and
observe corrections beyond QKZM predictions. This approach is subsequently used
to measure the critical exponents associated with chiral clock models,
providing new insights into exotic systems that have not been understood
previously, and opening the door for precision studies of critical phenomena,
simulations of lattice gauge theories and applications to quantum optimization
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