4,300 research outputs found
Wireless industrial monitoring and control networks: the journey so far and the road ahead
While traditional wired communication technologies have played a crucial role in industrial monitoring and control networks over the past few decades, they are increasingly proving to be inadequate to meet the highly dynamic and stringent demands of todayâs industrial applications, primarily due to the very rigid nature of wired infrastructures. Wireless technology, however, through its increased pervasiveness, has the potential to revolutionize the industry, not only by mitigating the problems faced by wired solutions, but also by introducing a completely new class of applications. While present day wireless technologies made some preliminary inroads in the monitoring domain, they still have severe limitations especially when real-time, reliable distributed control operations are concerned. This article provides the reader with an overview of existing wireless technologies commonly used in the monitoring and control industry. It highlights the pros and cons of each technology and assesses the degree to which each technology is able to meet the stringent demands of industrial monitoring and control networks. Additionally, it summarizes mechanisms proposed by academia, especially serving critical applications by addressing the real-time and reliability requirements of industrial process automation. The article also describes certain key research problems from the physical layer communication for sensor networks and the wireless networking perspective that have yet to be addressed to allow the successful use of wireless technologies in industrial monitoring and control networks
Single-molecule stochastic resonance
Stochastic resonance (SR) is a well known phenomenon in dynamical systems. It
consists of the amplification and optimization of the response of a system
assisted by stochastic noise. Here we carry out the first experimental study of
SR in single DNA hairpins which exhibit cooperatively folding/unfolding
transitions under the action of an applied oscillating mechanical force with
optical tweezers. By varying the frequency of the force oscillation, we
investigated the folding/unfolding kinetics of DNA hairpins in a periodically
driven bistable free-energy potential. We measured several SR quantifiers under
varied conditions of the experimental setup such as trap stiffness and length
of the molecular handles used for single-molecule manipulation. We find that
the signal-to-noise ratio (SNR) of the spectral density of measured
fluctuations in molecular extension of the DNA hairpins is a good quantifier of
the SR. The frequency dependence of the SNR exhibits a peak at a frequency
value given by the resonance matching condition. Finally, we carried out
experiments in short hairpins that show how SR might be useful to enhance the
detection of conformational molecular transitions of low SNR.Comment: 11 pages, 7 figures, supplementary material
(http://prx.aps.org/epaps/PRX/v2/i3/e031012/prx-supp.pdf
Periodically-driven quantum systems: Effective Hamiltonians and engineered gauge fields
Driving a quantum system periodically in time can profoundly alter its
long-time dynamics and trigger topological order. Such schemes are particularly
promising for generating non-trivial energy bands and gauge structures in
quantum-matter systems. Here, we develop a general formalism that captures the
essential features ruling the dynamics: the effective Hamiltonian, but also the
effects related to the initial phase of the modulation and the micro-motion.
This framework allows for the identification of driving schemes, based on
general N-step modulations, which lead to configurations relevant for quantum
simulation. In particular, we explore methods to generate synthetic spin-orbit
couplings and magnetic fields in cold-atom setups.Comment: 25 pages, 6 figures, includes Appendices (A-K). An erroneous factor
of two has been corrected in the last term of Eq. C10 (Appendix C); this typo
had no impact on the rest of the articl
Area spectral efficiency of soft-decision spaceâtimeâfrequency shift-keying-aided slow-frequency-hopping multiple access
Slow-frequency-hopping multiple access (SFHMA) can provide inherent frequency diversity and beneficially randomize the effects of cochannel interference. It may also be advantageously combined with our novel space-timeâfrequency shift keying (STFSK) scheme. The proposed systemâs area spectral efficiency is investigated in various cellular frequency reuse structures. Furthermore, it is compared to both classic Gaussian minimum shift keying (GMSK)-aided SFHMA and GMSK-assisted time- division/frequency-division multiple access (TD/FDMA). The more sophisticated third-generation wideband code-division multiple access (WCDMA) and the fourth-generation Long Term Evolution (LTE) systems were also included in our comparisons. We demonstrate that the area spectral efficiency of the STFSK-aided SFHMA system is higher than the GMSK-aided SFHMA and TD/FDMA systems, as well as WCDMA, but it is only 60% of the LTE system
Survey on wireless technology trade-offs for the industrial internet of things
Aside from vast deployment cost reduction, Industrial Wireless Sensor and Actuator Networks (IWSAN) introduce a new level of industrial connectivity. Wireless connection of sensors and actuators in industrial environments not only enables wireless monitoring and actuation, it also enables coordination of production stages, connecting mobile robots and autonomous transport vehicles, as well as localization and tracking of assets. All these opportunities already inspired the development of many wireless technologies in an effort to fully enable Industry 4.0. However, different technologies significantly differ in performance and capabilities, none being capable of supporting all industrial use cases. When designing a network solution, one must be aware of the capabilities and the trade-offs that prospective technologies have. This paper evaluates the technologies potentially suitable for IWSAN solutions covering an entire industrial site with limited infrastructure cost and discusses their trade-offs in an effort to provide information for choosing the most suitable technology for the use case of interest. The comparative discussion presented in this paper aims to enable engineers to choose the most suitable wireless technology for their specific IWSAN deployment
Revisiting multi-channel communication to mitigate interference and link dynamics in wireless sensor networks
Multichannel communication has been proposed as alternative to adaptive (single-channel) routing protocols for mitigating the impact of interference and link dynamics in wireless sensor networks. While several studies have advocated features of both techniques (not without running up against contradicting arguments) a comprehensive study that aligns these results is still lacking. This paper aims at filling this gap. We present an experimental test bed setup used to perform extensive measurements for both single-channel and multichannel communication. We first analyze single-channel and multichannel communication over a single-hop in terms of packet reception ratio, maximum burst loss, temporal correlation of losses, and loss correlations across channels. Results show that multichannel communication with channel hopping significantly reduces link burstiness and packet loss correlation. For multi-hop networks, multi-channel communication and adaptive routing show similar end-to-end reliability in dense topologies, while multichannel communication can outperform adaptive routing in sparse networks with bursty links
Adiabatic two-qubit gates in capacitively coupled quantum dot hybrid qubits
The ability to tune qubits to flat points in their energy dispersions ("sweet
spots") is an important tool for mitigating the effects of charge noise and
dephasing in solid-state devices. However, the number of derivatives that must
be simultaneously set to zero grows exponentially with the number of coupled
qubits, making the task untenable for as few as two qubits. This is a
particular problem for adiabatic gates, due to their slower speeds. Here, we
propose an adiabatic two-qubit gate for quantum dot hybrid qubits, based on the
tunable, electrostatic coupling between distinct charge configurations. We
confirm the absence of a conventional sweet spot, but show that controlled-Z
(CZ) gates can nonetheless be optimized to have fidelities of 99% for a
typical level of quasistatic charge noise (1
eV). We then develop the concept of a dynamical sweet spot (DSS), for
which the time-averaged energy derivatives are set to zero, and identify a
simple pulse sequence that achieves an approximate DSS for a CZ gate, with a
5 improvement in the fidelity. We observe that the results depend on
the number of tunable parameters in the pulse sequence, and speculate that a
more elaborate sequence could potentially attain a true DSS.Comment: 14 pages, 9 figure
Universal High-Frequency Behavior of Periodically Driven Systems: from Dynamical Stabilization to Floquet Engineering
We give a general overview of the high-frequency regime in periodically
driven systems and identify three distinct classes of driving protocols in
which the infinite-frequency Floquet Hamiltonian is not equal to the
time-averaged Hamiltonian. These classes cover systems, such as the Kapitza
pendulum, the Harper-Hofstadter model of neutral atoms in a magnetic field, the
Haldane Floquet Chern insulator and others. In all setups considered, we
discuss both the infinite-frequency limit and the leading finite-frequency
corrections to the Floquet Hamiltonian. We provide a short overview of Floquet
theory focusing on the gauge structure associated with the choice of
stroboscopic frame and the differences between stroboscopic and
non-stroboscopic dynamics. In the latter case one has to work with dressed
operators representing observables and a dressed density matrix. We also
comment on the application of Floquet Theory to systems described by static
Hamiltonians with well-separated energy scales and, in particular, discuss
parallels between the inverse-frequency expansion and the Schrieffer-Wolff
transformation extending the latter to driven systems.Comment: 84 pages, 25 figures, 4 appendice
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