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Internet of Energy Harvesting Cognitive Radios
No full textThe Internet of Things (IoT) offers enhanced connectivity so that any system, being, or process can be reached from anywhere at any time by perpetual surveillance, which results in very large and complex data sets, i.e., Big Data. Despite numerous advantages, IoT technology comes with some unavoidable drawbacks. Considering the number of devices to be added to the current electromagnetic spectrum, it is a fact that wireless communications will severely suffer and eventually become inoperable. Furthermore, as wireless devices are equipped with limited capacity batteries, frequent replenishments and/or maintenance will be needed. However, this is neither practical nor achievable due to the excessive number of devices envisioned by the IoT paradigm. Here, the unification of Energy Harvesting (EH) and Cognitive Radio (CR) stands highly promising to alleviate the current drawbacks, enabling more efficient data generation, acquisition, and analysis. This chapter outlines a new vision, namely Internet of Energy Harvesting Cognitive Radios (IoEH-CRs), to take the IoT-enabled Big Data paradigm a step further. It discusses the basics of the EH-assisted spectrum-aware communications and their implications for the IoT, as well as the challenges posed by the unification of these techniques. An operational framework together with node and network architectures is also presented
Experimental investigation of large-scale non-decaying rotating turbulence
No full textCopyright © ETC 2013 - 14th European Turbulence Conference.All rights reserved. Laboratory experiments on rotating turbulence have been conducted to explore the formation of columnar vortices in a forced steady-state environment. Forcing was achieved by means of co-rotating impellers situated at the top and bottom surfaces of a large cylindrical tank of height 2 m and diameter 2 m. As the impellers rotated the fluid, the turbulence generated, characterized by the root mean squared (rms) velocity |u|, was controlled using symmetrically located baffles on the inner walls of the tank. By varying the rms velocity |u| and bulk rotation rate Ω, the flow was investigated over a range of in-plane Rossby numbers, |u|/2Ωl. 2D Particle image velocimetry (PIV) was carried out for a plane normal to the axis of rotation at the center of the tank, and was utilized to compute velocity fields and streamlines which revealed the emergence of columnar eddies, as is often seen in decaying experiments on rotating turbulence. PIV results were used to deduce the parameters affecting the structure, frequency of occurrence and life cycle of these columns. The tendency of columns to be predominantly cyclonic and the effect of columns on bulk rotation rate were also analyzed
Introduction to the Special Section on Learning-Based Modeling, Management, and Control for Computer and Communication Networks
No full textOff-wall boundary conditions for bounded turbulent flow simulations
No full textWe investigated the possibility of modeling off-wall boundary conditions for bounded turbulent flows. Such boundary conditions circumvent the need to resolve the buffer layer near the wall by providing conditions directly above it for the overlying flow. Our objective is to model the effect of the buffer layer on the overlying flow as an off-wall, Dirichlet boundary condition for the flow variables. We selected the plane at y+ ≈ 100 as our off-wall boundary, since this plane can be interpreted as a notional interface between the buffer and logarithmic regions. We tested different boundary conditions on channel flow with increasing levels of abstraction/modeling, starting from exact, time-resolved conditions from a previous DNS, all the way to a reduced-order model obtained from minimal flow units of a transitional boundary layer
Tents, Chairs, Tacos, Kites, and Rods: Shapes and Plasmonic Properties of Singly Twinned Magnesium Nanoparticles
No full textNanostructures of some metals can sustain light-driven electron oscillations called localized surface plasmon resonances, or LSPRs, that give rise to absorption, scattering, and local electric field enhancement. Their resonant frequency is dictated by the nanoparticle (NP) shape and size, fueling much research geared toward discovery and control of new structures. LSPR properties also depend on composition; traditional, rare, and expensive noble metals (Ag, Au) are increasingly eclipsed by earth-abundant alternatives, with Mg being an exciting candidate capable of sustaining resonances across the ultraviolet, visible, and near-infrared spectral ranges. Here, we report numerical predictions and experimental verifications of a set of shapes based on Mg NPs displaying various twinning patterns including (101¯ 1), (101¯ 2), (101¯ 3), and (112¯ 1), that create tent-, chair-, taco-, and kite-shaped NPs, respectively. These are strikingly different from what is obtained for typical plasmonic metals because Mg crystallizes in a hexagonal close packed structure, as opposed to the cubic Al, Cu, Ag, and Au. A numerical survey of the optical response of the various structures, as well as the effect of size and aspect ratio, reveals their rich array of resonances, which are supported by single-particle optical scattering experiments. Further, corresponding numerical and experimental studies of the near-field plasmon distribution via scanning transmission electron microscopy electron-energy loss spectroscopy unravels a mode nature and distribution that are unlike those of either hexagonal plates or cylindrical rods. These NPs, made from earth-abundant Mg, provide interesting ways to control light at the nanoscale across the ultraviolet, visible, and near-infrared spectral ranges
Tracking bridge tilt behaviour using sensor fusion techniques
No full textThe resilience of the built environment to extreme weather events is fundamental for the day-to-day operation of our transport network, with scour representing one of the biggest threats to bridges built over flowing water. Condition monitoring of the bridge using a structural health monitoring system enhances resilience by reducing the time needed to return the bridge to normal use by providing timely information on structural condition and safety. The work presented in this report discusses use of rotational measurements in structural health monitoring. Traditionally tiltmeters (which can be a form of DC accelerometer) are used to measure rotation but are known to be affected by dynamic movements, while gyroscopes react quickly to dynamic motion but drift over time. This review will introduce gyroscopes as a complementary sensor for accelerometer rotational measurements and use sensor fusion techniques to combine the measurements from both sensors to get an optimised rotational result. This method was trialled on a laboratory scaled model, before the system was installed on an in-service single-span skewed railway bridge. The rotational measurements were compared against rotation measurements obtained using a vision-based measurement system to confirm the validity of the results. An introduction to gyroscopes, field test measurement results with the sensors and their correlation with the vision-based measurement results are presented in this article
Combining phonon accuracy with high transferability in Gaussian approximation potential models.
No full textMachine learning driven interatomic potentials, including Gaussian approximation potential (GAP) models, are emerging tools for atomistic simulations. Here, we address the methodological question of how one can fit GAP models that accurately predict vibrational properties in specific regions of configuration space while retaining flexibility and transferability to others. We use an adaptive regularization of the GAP fit that scales with the absolute force magnitude on any given atom, thereby exploring the Bayesian interpretation of GAP regularization as an "expected error" and its impact on the prediction of physical properties for a material of interest. The approach enables excellent predictions of phonon modes (to within 0.1 THz-0.2 THz) for structurally diverse silicon allotropes, and it can be coupled with existing fitting databases for high transferability across different regions of configuration space, which we demonstrate for liquid and amorphous silicon. These findings and workflows are expected to be useful for GAP-driven materials modeling more generally
Improving Motorway Mobility and Environmental Performance via Vehicle Trajectory Data-Based Control
No full text© 2013 IEEE. High cost and relatively low reliability of stationary sensors hinder the wide spread of advanced motorway traffic control measures. In this research, we propose a vehicle trajectory data based variable speed limit (VSL) controller to improve mobility and environmental performance of motorways. First, a model based estimator is designed to estimate traffic states using data directly derived from probe vehicle with spacing measurement equipment (PVSMEs). Extended kalman filter (EKF) and METANET model are employed as the data assimilation tool and the process model for the estimator, respectively. Next, we incorporate the estimator with a model predictive control (MPC) to realize optimal VSL control. Finally, a 3.2km stretch in Auckland, New Zealand is selected and simulated to evaluate the proposed VSL under various PVSME penetration rates and traffic scenarios. The simulation results reveal that the PVSME-based VSL controller offers an effective solution to improve mobility and environmental performance of motorways. With an increase in PVSME penetration rates, the mobility and environmental benefits of the PVSME-based VSL increase
A Transition Metric in Polar Co-ordinates for MLSE of a Complex Modulated DML
No full textWe propose a metric for MLSE-Viterbi differential decoding of complex modulation of directly modulated lasers (CM-DML) that reports SNR gains of 1.8 dB at BER=10-3 on a simulated PAM4 signal with a typical linewidth enhancement factor α =
On the bi-stable nature of turbulent premixed bluff-body stabilized flames at elevated pressure and near lean blow-off
No full textThis study considers turbulent premixed bluff-body stabilized flames at elevated pressures. Specifically, the lean blow-off (LBO) limit of such flames is determined for a range of bulk velocities (5 U 50m/s) and operating pressures up to 3 bar. Two key observations emerge from this stability assessment. The first is that considering elevated pressure leads to two stability regimes: one at atmospheric conditions and those with elevated pressure and U & 20m/s (regime-a), and another at elevated pressures with U . 20m/s (regime-b). The second observation is that within these regimes, LBO limits are insensitive to pressure. Flames in regime-a (S-flames) are found to be more stable than those in regime-b (U-flames). Advanced image-based diagnostics were employed to understand reasons for this difference in stability. Flow field measurements indicate that U-flames are associated with an outer recirculation zone (ORZ) that formed as pressure increased but receded from the burner as U surpassed 20m/s. PLIF images of CH2O and OH demonstrated that the ORZ interacts with U-flames such that their downstream regions are prevented from collapsing to the inner recirculation zone (IRZ). Furthermore, analysis of the OH-PLIF images indicate that U-flames possess larger turbulent consumption rates, helping them form large IRZs and rendering them more susceptible to influence from the ORZ. Results of highspeed OH∗ imaging demonstrate that LBO events differ between U- and Sflames. Namely, while S-flames collapse to their IRZs during LBO, U-flames lift off from the burner, depleting their anchoring regions of reactions and hot products. Losing back-support in this region is what ultimately reduces the stability of U-flames. Finally, the reason U-flames lift off from the burner during LBO is elucidated by joint flow-flame measurements. Specifically, the anchoring regions of U-flames reside in regions of large axial velocity, which likely stems from their enhanced burning rates