AROMA: Automatic Generation of Radio Maps for Localization Systems

WLAN localization has become an active research field recently. Due to the wide WLAN deployment, WLAN localization provides ubiquitous coverage and adds to the value of the wireless network by providing the location of its users without using any additional hardware. However, WLAN localization systems usually require constructing a radio map, which is a major barrier of WLAN localization systems' deployment. The radio map stores information about the signal strength from different signal strength streams at selected locations in the site of interest. Typical construction of a radio map involves measurements and calibrations making it a tedious and time-consuming operation. In this paper, we present the AROMA system that automatically constructs accurate active and passive radio maps for both device-based and device-free WLAN localization systems. AROMA has three main goals: high accuracy, low computational requirements, and minimum user overhead. To achieve high accuracy, AROMA uses 3D ray tracing enhanced with the uniform theory of diffraction (UTD) to model the electric field behavior and the human shadowing effect. AROMA also automates a number of routine tasks, such as importing building models and automatic sampling of the area of interest, to reduce the user's overhead. Finally, AROMA uses a number of optimization techniques to reduce the computational requirements. We present our system architecture and describe the details of its different components that allow AROMA to achieve its goals. We evaluate AROMA in two different testbeds. Our experiments show that the predicted signal strength differs from the measurements by a maximum average absolute error of 3.18 dBm achieving a maximum localization error of 2.44m for both the device-based and device-free cases.Comment: 14 pages, 17 figure

Methodology Options for Hydrogen Safety Analysis

Master's thesis in Risk ManagementThe development of applications using hydrogen as a clean energy carrier has increased in recent years. Hydrogen is versatile and can be used in a wide range of applications. Hydrogen is already being widely used as a chemical feedstock for producing fertilizers and petrochemicals. Hydrogen can be used to power vehicles and generate heat and electricity. A prerequisite for commercial applications of hydrogen is to ensure that the risk associated with its production, storage, transport and use is at least not significantly higher than that of existing fuels. Hydrogen is not inherently more dangerous than other conventional fuels, but it has quite different properties, namely very low ignition energy, wide flammability range, high laminar burning velocity and high buoyancy. Consequence analysis is a critical part of any Quantitative Risk Assessment (QRA), which is used to predict the physical effects of the accidental release of flammable materials. A wide range of consequence analysis tools exist, ranging from simple integral tools based on empirical correlations to sophisticated three-dimensional Computational Fluid Dynamics (CFD) tools. Integral tools are easy to use and require less computational time; however, they take limited account of the influence of obstacles on the flow. Whereas CFD tools are more complex and require longer computational time (typically hours or day) and more skills, but they can predict the effect of complex geometries on the flow. Despite the intrinsic differences, CFD tools and integral tools are considered to perform the same task in consequences analysis. Uncertainties are always part of any consequence analysis, especially for emerging applications. Thus, it is important to understand the underlying assumptions and inherent limitations of the available tools, as well as the expected level of accuracy in the results for different types of hazardous scenarios. This study examines and compares the results predicted by the CFD tool (FLACS) and integral tools (FRED, PHAST and EFFECTS) which are used in hydrogen safety studies. The focus is to show where the tools predict similar results and where their results deviate strongly. It includes a description of the physical models used in FLACS, FRED, PHAST and EFFECTS for release modelling of hydrogen gas leak through an orifice from a pressurized storage tank. Release and dispersion simulations are carried out in each of FRED, EFFECTS, PHAST and FLACS for 81 hypothetical hydrogen gas release scenarios in open flat terrain. Then, sensitivity analysis is performed with variations in input parameters such as orifice size, wind speed, release direction, atmospheric stability class and surface roughness length to study their effect on the dispersion of the gas cloud. Finally, dispersion simulations are carried out in FLACS for hydrogen gas release from a dispenser in a refuelling gas station and its corresponding release scenario in open flat terrain to study the effect of obstacles on the dispersion of the gas cloud. A comparison tool was developed using the results produced by the four tools for 72 hydrogen gas release scenarios. The comparison includes the mass flow rate, the downwind distances to lower flammability limit (LFL) and half of lower flammability limit (½ LFL), and the amount of flammable mass between upper and lower flammability limits. The results showed that FLACS, FRED, EFFECTS and PHAST predicted almost the same mass flow rates for hydrogen gas released at 5 bar and 25 bar; however, FLACS predicted higher mass flow rates compared to the other tools for hydrogen gas released at 350 bar. The results of the dispersion simulations conclude that EFFECTS is not recommended for hydrogen safety studies due to the large discrepancies in the results when compared to FLACS, FRED and PHAST. FLACS predicted longer downwind distances to LFL and ½ LFL, and larger amount of flammable mass for most of the considered release scenarios; however, the results need to be compared against experimental results as it is not possible to recommend the use of one tool over the other based only on the results of this study. Hydrogen buoyancy does not prevent the formation of a large flammable cloud. The common argument is that a release of hydrogen gas in an unconfined area will rise and disperse relatively quickly upon release; however, this is not always the case. Hydrogen buoyancy is only valid outside the part of dispersion which is controlled by the jet momentum. From the results, a higher initial pressure produces a jet with higher momentum and the buoyancy force takes longer to dominate the flow. Also, hydrogen gas releases near the ground, tend to deflect towards the ground and cling to it because of an effect known as the Coandă effect. The results showed that this effect increases with the increase in wind speed. Obstacles in the path of the gas cloud help in decreasing the jet momentum and allow the buoyancy to have more effect; however, a large flammable cloud can still be formed

Isothermal and kinetic screening of methyl red and methyl orange dyes adsorption from water by Delonix regia biochar-sulfur oxide (DRB-SO)

Abstract In this study, Delonix regia seed pods (DRSPs) as a locally available material were refluxed in 90% H2SO4 to yield a novel D. regia seed pods biochar-sulfur oxide (DRB-SO). FTIR, BET, BJH, SEM, EDX, XRD, DSC and TGA were applied to investigate the characterizations of the prepared DRB-SO. Various adsorption parameters like pH effect, dye concentration effect, adsorbent dose, reaction time isotherm and kinetic study were carried out to explain the process of adsorption of methyl orange (MO) and methyl red (MR) onto DRB-SO. Langmuir's adsorption model perfectly explained the adsorption process onto the surface of DRB-SO as a monolayer. The maximum adsorption efficiency of DRB-SO was (98%) and (99.6%) for MO and MR respectively which attained after 150 min with an adsorbent dose of 0.75 g/L. The pseudo-second-order kinetic model best explained the process of adsorption of MO and MR dyes by DRB-SO. The highest observed adsorption amount was as high as 144.9 mg/g for MO dye and 285.7 mg/g for MR dye, comparable with other reported materials based on activated carbon materials. All of the outcomes signposted a prodigious perspective of the fabricated biochar composite material in wastewater treatment. Using the regenerating DRB-SO through an acid–base regeneration process, six cycles of adsorption/desorption were examined. Over the course of the cycles, there was a minor decrease in the adsorption and desorption processes. Also, it was revealed what the most plausible mechanism was for DRB-SO to absorb the ions of the MO and MR dyes

Tracking Chronically Recorded Single-Units in Cortically Controlled Brain Machine Interfaces*

Abstract-Multiple single-units recorded from chronicallyimplanted microelectrode arrays frequently exhibit variability in their spike waveform features and firing characteristics, making it challenging to ascertain the identity of recorded neurons across days. In this study, we present a fast and efficient algorithm that tracks multiple single-units, recorded in a nonhuman primate performing brain control of a robotic arm, across days based on features extracted from units' average waveforms. Furthermore, the algorithm does not require long recording duration to perform the analysis and can be applied at the start of each recording session without requiring the subject to be engaged in a behavioral task. The algorithm achieves a classification accuracy of up to 92% compared to experts' manual tracking