824,941 research outputs found
Mobility power flow analysis of an L-shaped plate structure subjected to acoustic excitation
An analytical investigation based on the Mobility Power Flow method is presented for the determination of the vibrational response and power flow for two coupled flat plate structures in an L-shaped configuration, subjected to acoustical excitation. The principle of the mobility power flow method consists of dividing the global structure into a series of subsystems coupled together using mobility functions. Each separate subsystem is analyzed independently to determine the structural mobility functions for the junction and excitation locations. The mobility functions, together with the characteristics of the junction between the subsystems, are then used to determine the response of the global structure and the power flow. In the coupled plate structure considered here, mobility power flow expressions are derived for excitation by an incident acoustic plane wave. In this case, the forces (acoustic pressures) acting on the structure are dependent on the response of the structure because of the scattered pressure component. The interaction between the structure and the fluid leads to the derivation of a corrected mode shape for the plates' normal surface velocity and also for the structure mobility functions. The determination of the scattered pressure components in the expressions for the power flow represents an additional component in the power flow balance for the source plate and the receiver plate. This component represents the radiated acoustical power from the plate structure
Experimental Study on Low Power Wide Area Networks (LPWAN) for Mobile Internet of Things
In the past decade, we have witnessed explosive growth in the number of
low-power embedded and Internet-connected devices, reinforcing the new
paradigm, Internet of Things (IoT). The low power wide area network (LPWAN),
due to its long-range, low-power and low-cost communication capability, is
actively considered by academia and industry as the future wireless
communication standard for IoT. However, despite the increasing popularity of
`mobile IoT', little is known about the suitability of LPWAN for those mobile
IoT applications in which nodes have varying degrees of mobility. To fill this
knowledge gap, in this paper, we conduct an experimental study to evaluate,
analyze, and characterize LPWAN in both indoor and outdoor mobile environments.
Our experimental results indicate that the performance of LPWAN is surprisingly
susceptible to mobility, even to minor human mobility, and the effect of
mobility significantly escalates as the distance to the gateway increases.
These results call for development of new mobility-aware LPWAN protocols to
support mobile IoT.Comment: To appear at 2017 IEEE 85th Vehicular Technology Conference (VTC'17
Spring
Mobile Unmanned Aerial Vehicles (UAVs) for Energy-Efficient Internet of Things Communications
In this paper, the efficient deployment and mobility of multiple unmanned
aerial vehicles (UAVs), used as aerial base stations to collect data from
ground Internet of Things (IoT) devices, is investigated. In particular, to
enable reliable uplink communications for IoT devices with a minimum total
transmit power, a novel framework is proposed for jointly optimizing the
three-dimensional (3D) placement and mobility of the UAVs, device-UAV
association, and uplink power control. First, given the locations of active IoT
devices at each time instant, the optimal UAVs' locations and associations are
determined. Next, to dynamically serve the IoT devices in a time-varying
network, the optimal mobility patterns of the UAVs are analyzed. To this end,
based on the activation process of the IoT devices, the time instances at which
the UAVs must update their locations are derived. Moreover, the optimal 3D
trajectory of each UAV is obtained in a way that the total energy used for the
mobility of the UAVs is minimized while serving the IoT devices. Simulation
results show that, using the proposed approach, the total transmit power of the
IoT devices is reduced by 45% compared to a case in which stationary aerial
base stations are deployed. In addition, the proposed approach can yield a
maximum of 28% enhanced system reliability compared to the stationary case. The
results also reveal an inherent tradeoff between the number of update times,
the mobility of the UAVs, and the transmit power of the IoT devices. In
essence, a higher number of updates can lead to lower transmit powers for the
IoT devices at the cost of an increased mobility for the UAVs.Comment: Accepted in IEEE Transactions on Wireless Communications, Sept. 201
Evolution of mobility governance in Flanders: opening up for bottom-up initiatives or suffering from lock-in?
Mobility policy in Flanders lacks a clear discourse on implementing the policy objectives for 2020 and beyond. Though mobility planning can show success stories, mobility problems seem to aggravate. For supra local mobility projects in Flanders the executive power often lies with deconcentrated administrations at the level of the province, this is e.g. the case for public transportation and major roads, where province boundaries impede public transport projects across borders. For local mobility plans, the local administration and council have the power. But as these local mobility plans have highly formalised procedures, they tend to be rigid frameworks or administrations and risk to be suffering from lock-in. There is a need for new dynamics in mobility policy in reference to present developments. Here bottom-up or outside-in initiatives can be regarded as the key to real change. To that end radical changes in the organisation and mobility planning itself are necessary to meet these new inititiaves from the bottum-up and outside-in. Next to hardware and software approaches or innovations to turn mobility planning more sustainable, we additionally propose in this paper an âorgwareâ solution, demonstrated in some case studies. In these cases key actors of bottom-up projects and their associations with other actors are visualised. Furthermore barriers and potentials for implementation are formulated leading onto recommendations for further research in order to improve the implementation of the policy objectives
Scattering Mechanism in Modulation-Doped Shallow Two-Dimensional Electron Gases
We report on a systematic investigation of the dominant scattering mechanism
in shallow two-dimensional electron gases (2DEGs) formed in modulation-doped
GaAs/Al_{x}Ga_{1-x}As heterostructures. The power-law exponent of the electron
mobility versus density, mu \propto n^{alpha}, is extracted as a function of
the 2DEG's depth. When shallower than 130 nm from the surface, the power-law
exponent of the 2DEG, as well as the mobility, drops from alpha \simeq 1.65
(130 nm deep) to alpha \simeq 1.3 (60 nm deep). Our results for shallow 2DEGs
are consistent with theoretical expectations for scattering by remote dopants,
in contrast to the mobility-limiting background charged impurities of deeper
heterostructures.Comment: 4 pages, 3 figures, modified version as accepted in AP
Impact of Mobility on MIMO Green Wireless Systems
This paper studies the impact of mobility on the power consumption of
wireless networks. With increasing mobility, we show that the network should
dedicate a non negligible fraction of the useful rate to estimate the different
degrees of freedom. In order to keep the rate constant, we quantify the
increase of power required for several cases of interest. In the case of a
point to point MIMO link, we calculate the minimum transmit power required for
a target rate and outage probability as a function of the coherence time and
the number of antennas. Interestingly, the results show that there is an
optimal number of antennas to be used for a given coherence time and power
consumption. This provides a lower bound limit on the minimum power required
for maintaining a green network.Comment: Accepted for EUSIPCO conference. 5 page
Mobility of Power-law and Carreau Fluids through Fibrous Media
The flow of generalized Newtonian fluids with a rate-dependent viscosity
through fibrous media is studied with a focus on developing relationships for
evaluating the effective fluid mobility. Three different methods have been used
here: i) a numerical solution of the Cauchy momentum equation with the Carreau
or power-law constitutive equations for pressure-driven flow in a fiber bed
consisting of a periodic array of cylindrical fibers, ii) an analytical
solution for a unit cell model representing the flow characteristics of a
periodic fibrous medium, and iii) a scaling analysis of characteristic bulk
parameters such as the effective shear rate, the effective viscosity,
geometrical parameters of the system, and the fluid rheology. Our scaling
analysis yields simple expressions for evaluating the transverse mobility
functions for each model, which can be used for a wide range of medium porosity
and fluid rheological parameters. While the dimensionless mobility is, in
general, a function of the Carreau number and the medium porosity, our results
show that for porosities less than , the dimensionless
mobility becomes independent of the Carreau number and the mobility function
exhibits power-law characteristics as a result of high shear rates at the pore
scale. We derive a suitable criterion for determining the flow regime and the
transition from a constant viscosity Newtonian response to a power-law regime
in terms of a new Carreau number rescaled with a dimensionless function which
incorporates the medium porosity and the arrangement of fibers
Influence of Charge Carrier Mobility on the Performance of Organic Solar Cells
The power conversion efficiency of organic solar cells based on
donor--acceptor blends is governed by an interplay of polaron pair dissociation
and bimolecular polaron recombination. Both processes are strongly dependent on
the charge carrier mobility, the dissociation increasing with faster charge
transport, with raised recombination losses at the same time. Using a
macroscopic effective medium simulation, we calculate the optimum charge
carrier mobility for the highest power conversion efficiency, for the first
time accounting for injection barriers and a reduced Langevin-type
recombination. An enhancement of the charge carrier mobility from
m/Vs for state of the art polymer:fullerene solar cells to about
m/Vs, which yields the maximum efficiency, corresponds to an
improvement of only about 20% for the given parameter set.Comment: 3 pages, 4 figure
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