Pasan Hettiarachchi

Pasan Hettiarachchi
Uppsala University | UU · Department of Medical Sciences

Doctor of Philosophy

About

39
Publications
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130
Citations

Publications

Publications (39)
Preprint
BACKGROUND There is increasing recognition of the need for more comprehensive surveillance data, including information on physical activity of all intensities, sedentary behavior, and sleep. However, meeting this need poses significant challenges for current surveillance systems, which are mainly reliant on self-report. OBJECTIVE The primary objec...
Article
Full-text available
Background: There is increasing recognition of the need for more comprehensive surveillance data, including information on physical activity of all intensities, sedentary behavior, and sleep. However, meeting this need poses significant challenges for current surveillance systems, which are mainly reliant on self-report. Objective: The primary o...
Article
Full-text available
Body postural allocation during daily life is important for health, and can be assessed with thigh-worn accelerometers. An algorithm based on sedentary bouts from the proprietary ActivePAL software can detect lying down from a single thigh-worn accelerometer using rotations of the thigh. However, it is not usable across brands of accelerometers. Th...
Article
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This work presents the first simultaneous X‐ray measurement and high‐speed video observation of the propagation of a lightning leader producing X‐rays. As a result, the three‐dimensional leader distance from the X‐ray measurement and, for the first time, the conditions of the preexisting channel during the leader propagation were observed. Although...
Article
Full-text available
We present observations of X-rays from laboratory sparks created in the air at atmospheric pressure by applying an impulse voltage with long (250 µs) rise-time. X-ray production in 35 and 46 cm gaps for three different electrode configurations was studied. The results demonstrate, for the first time, the production of X-rays in gaps subjected to sw...
Article
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We report the occurrence of X-rays at ground level due to cloud-to-ground flashes of upward-initiated lightning from Gaisberg Tower, in Austria, which is located at an altitude of 1300 m. This is the first observation of X-ray emissions from upward lightning from a tower top located at high altitude. Measurements were carried out using scintillatio...
Article
Full-text available
The energy deposited from X-rays generated by 1 m long laboratory sparks in air created by 950 kV negative lightning impulses on scintillated detectors was measured. Assuming the X-ray energy detected in such sparks results from the accumulation of multiple photons at the detector having a certain energy distribution, an experiment was designed in...
Article
This paper presents the characteristics of the electric fields produced by the first and the subsequent return strokes observed in positive ground flashes in Sweden. Fifty one positive ground flashes containing 60 return strokes recorded during 2014 summer thunderstorms were analyzed. In our analysis, only 12% of the cases were multiple-stroke whil...
Conference Paper
Full-text available
It is an ungainly tough exercise to devise experiments under the laboratory conditions to study how Surge Protective Devices (SPDs) behave against the lightning induced transient voltages. Therefore, this study is carried out to model a Matlab based SPD module to replace actual SPDs to conduct diverse simulations against the real life induced volta...
Article
Full-text available
In this study, electromagnetic field radiation bursts known as chaotic pulse trains (CPTs) and regular pulse trains (RPTs) generated by lightning flashes were analyzed. Through a numerical analysis it was found that a typical CPT could be generated by superimposing several RPTs onto each other. It is suggested that the chaotic pulse trains are crea...
Article
This paper presents the characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analysed in detail the electric field changes occurring just before the first return stroke in 51 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses (having the sam...
Conference Paper
Full-text available
Variation of fractal dimension of long laboratory sparks were studied using high speed video recordings and still images. Four sparks were selected for the study, including both positive and negative polarities in lightning and switching impulses. Temporal and spatial variation of fractal dimension was studied. It was found that the fractal dimensi...
Article
In this experimental work, the influence of the grounded anode geometry is studied on the X-ray production from the laboratory sparks in air at atmospheric pressure when a negative impulse voltage is applied to a high voltage rod which served as a cathode. The result shows that the smaller the diameter of the anode, the higher the energy of X-ray b...
Article
Full-text available
Long air gap electrical discharges are of particular interest among scientists and engineers working on high voltage techniques and lightning research. In the present work we report experimental results obtained while testing a long rod-plane air gap with positive switching-like voltage impulses to study the velocity and tortuous progression of the...
Article
Full-text available
This paper presents the characteristics of the preliminary breakdown pulses (PBP) in 51 positive ground flashes recorded during 2014 summer thunderstorms in Sweden. Electric field measurements were conducted remotely using a broadband antenna system (up to 100 MHz) for a recording length of 1 s with 200 ms trigger time. In the analysis, PBP trains...
Article
The formation of bead lightning, where the lightning channel appears to break up into luminous fragments, is still an object of speculation. Here we report similar observations in laboratory discharges. Analysis of time resolved photographs shows that the discharge channel exhibits a ‘bead pattern’ in the decaying stage of the discharge and the occ...
Article
Full-text available
In this study, the electric field signatures of negative ground flashes pertinent to the Swedish thunderstorms were recorded simultaneously during the summer of 2014 using wide (up to 100 MHz) and narrow (at 3 MHz and 30 MHz as central frequencies) bandwidth antenna systems. The electric field signatures were recorded for a time duration of 250 ms....
Conference Paper
Compared to negative ground flashes, not much is known about the characteristics of leaders in positive ground flashes. This paper presents some characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analyzed in detail the electric field changes produced by 50 positive ground flashes during 20...
Conference Paper
Full-text available
— In this study, Electric field sensed by the wide band and narrow band (3MHz and 30MHz) antenna systems recorded simultaneously, have been analysed. The measurement was carried out during the summer 2014. Although, the electric field produced by lightning was recorded for 250ms, field radiation by the preliminary breakdown (PB) process has only be...
Conference Paper
This paper presents a preliminary observation of lightning signature at 2400 MHz. We believe this is the first time such observation was made in such frequency band. One positive ground discharge and one cloud discharge waveforms have been selected from a collection of waveforms recorded using fast and slow broadband antenna systems. In addition, w...
Chapter
The goal of this chapter is to provide a summary of the basic concepts of electro- magnetic theory as a complement to the subject matter, most of which is related to electromagnetism, discussed in this book. The chapter covers only the concepts that are necessary to understand the electromagnetics of lightning flashes.
Conference Paper
An automated, remote rainfall gauging system is developed to monitor the rainfall in five remote areas from one base station. The automated rain gauge stations (ARGSs) were installed at five selected locations in Sri Lanka. Two replica base stations are going to be installed at the department of meteorology, and national building research organizat...

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Project (1)
Project
Establish the behavior of lightning down conductors under transient conditions under different earth profiles and study the SPD performances against the induced voltages due to CG and CC flashers.