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| 3. |
- Ahmad, Mohd Riduan, et al.
(författare)
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Preliminary Observations of Lightning Signature At 2400 MHz in Sweden Thunderstorm
- 2012
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Konferensbidrag (refereegranskat)abstract
- 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, waveforms recorded directly from 2400 MHz whip antenna associated with the selected ground and cloud discharges waveforms were observed. The measurements were carried out in Uppsala, Sweden in July 2012. We discovered a possible lightning signature at 2400 MHz with the existence of bursts of pulses happened to occur simultaneously with preliminary breakdown, negative return stroke and cloud pulses. These bursts of pulses possibly interfered in some ways with the transmitted bits leading to higher recorded error bits during the thunderstorm.
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| 4. |
- Arevalo, Liliana, et al.
(författare)
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Attachment process of the discharge of competing grounded electrodes - Experimental observations and modeling
- 2021
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Ingår i: 2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium On Lightning Protection (SIPDA). - : IEEE. - 9781665423465
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Konferensbidrag (refereegranskat)abstract
- The lightning attachment discharge process theory is based on studies of the physics of the discharge obtained from high voltage laboratory tests. The process of propagation of positive and negative discharges has been studied independently and then the gathered information has been used to understand and explain the lightning attachment development. In this paper, an experimental set-up is built to describe the dynamic behavior of positive and negative discharges. Electrodes of different dimensions placed at different distances are used as grounded electrodes and a high voltage electrode is subject to negative switching impulses. Test results allow to identify different stages of the dynamic process of attachment of the discharge between a downward negative discharge and a positive upward leader discharge. The principles of physics of discharge for positive and negative polarities are used to model the laboratory test measurements. The model can reproduce in an accurate manner majority of the dynamic processes of the discharge. In addition, statistical results of the effect of nearby and competing upward discharges is obtained.
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- Arevalo, Liliana, et al.
(författare)
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The leader propagation velocity in long air gaps
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - : IEEE. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- Experimental measurements of long gap discharges and its interpretation are the base of engineering equations and complex models to design clearance distances, lightning protection systems, among others. Parameters like leader propagation velocity, average electric field of the leader channel, stability electric field of the streamer region, etc. are derived from experimental measurements for rod-plane arrangements. However, in high voltage engineering geometries are not only rod-plane arrangements but also rounded electrode geometries. Experimental measurements of sphere - plane arrangements are presented in this paper. Attention is given to the velocity of propagation of the leader. The velocity of propagation of the leader is compared for two different applied voltage conditions, such as overvoltage and non-overvoltage. Experimental observations indicate that the velocity of the leader does not have a linear relationship with the increment of the applied voltage, as described by other authors for rod-plane arrangements. By means of a model based on the physics of the discharge, it is observed that the velocity of propagation of the leader depends on the injected charge to the leader channel. The injected charge depends on the background electric field, the potential at the leader tip, the steepness of the applied voltage waveform, among other parameters.
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| 6. |
- Baharudin, Zikri Abadi, et al.
(författare)
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Electric field changes generated by preliminary breakdown pulse for positive lightning ground flashes in Sweden
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This is the new study of the electric field changes generated by the preliminary breakdown for positive cloud-to-ground flashes which concerning on the association of slow field changes in preliminary breakdown process. In this study, a 107 positive cloud-to-ground lightning flashes recorded from the total of 14 thunderstorms generated by the whole flash were examined. The electric fields were measured with nanosecond resolution by using the slow electric field, fast electric field and narrowband radiation field at 3 and 30 MHz signals simultaneously. Our result shows that there is a pre-starting time, i.e. the duration between the first preliminary breakdown pulse and slow field changes starting point, which is found to be after the first preliminary breakdown pulse. The pre-starting time has the arithmetic mean – 3.0 ms and geometric mean – 1.8 ms, ranging from 0.3 to 21.7 ms. This study is consistent with the latest finding for the slow field changes in negative ground flashes where the slow field changes never start before the preliminary breakdown process.
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| 7. |
- Baharudin, Zikri Abadi, et al.
(författare)
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On the characteristics of positive lightning ground flashes in Sweden
- 2016
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Ingår i: Journal of Atmospheric and Solar-Terrestrial Physics. - : Elsevier BV. - 1364-6826 .- 1879-1824. ; 138, s. 106-111
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Tidskriftsartikel (refereegranskat)abstract
- In this study the stroke characteristics of positive cloud-to-ground flashes in Sweden were obtained from the electric field records measured from 14 thunderstorms. The electric fields were measured with nanosecond resolution. Together with the fast and the slow electric field records, the narrowband radiation field at 3 and 30 MHz signals were also measured simultaneously. Out of a total of 107 flashes, 30 flashes had two strokes, 7 had three strokes and 3 flashes had four strokes. The arithmetic and geometric means of the interstroke intervals were found to be 116 and 70 ms, respectively. The arithmetic and geometric mean ratio between the peak electric field of the Subsequent Return Stroke (SRS) and the first Return Stroke (RS) were 0.48 and 0.36, respectively. Of the 40 positive multiple-stroke ground flashes, 5% have at least one SRS with field peak higher than the first RS. The percentage of SRS with field peaks greater than the first RS was 6%. In our best of our knowledge, this is the first time a large sample of positive return strokes in Sweden was analysed. It was found to be statistically more significant than the previous studies.
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| 8. |
- Blodgett, Joanna M., et al.
(författare)
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Device-measured physical activity and cardiometabolic health : the Prospective Physical Activity, Sitting, and Sleep (ProPASS) consortium
- 2023
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Ingår i: European Heart Journal. - 0195-668X .- 1522-9645.
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Tidskriftsartikel (refereegranskat)abstract
- Background and Aims: Physical inactivity, sedentary behaviour (SB), and inadequate sleep are key behavioural risk factors of cardiometabolic diseases. Each behaviour is mainly considered in isolation, despite clear behavioural and biological interdependencies. The aim of this study was to investigate associations of five-part movement compositions with adiposity and cardiometabolic biomarkers.Methods: Cross-sectional data from six studies (n = 15 253 participants; five countries) from the Prospective Physical Activity, Sitting and Sleep consortium were analysed. Device-measured time spent in sleep, SB, standing, light-intensity physical activity (LIPA), and moderate-vigorous physical activity (MVPA) made up the composition. Outcomes included body mass index (BMI), waist circumference, HDL cholesterol, total:HDL cholesterol ratio, triglycerides, and glycated haemoglobin (HbA1c). Compositional linear regression examined associations between compositions and outcomes, including modelling time reallocation between behaviours.Results: The average daily composition of the sample (age: 53.7 ± 9.7 years; 54.7% female) was 7.7 h sleeping, 10.4 h sedentary, 3.1 h standing, 1.5 h LIPA, and 1.3 h MVPA. A greater MVPA proportion and smaller SB proportion were associated with better outcomes. Reallocating time from SB, standing, LIPA, or sleep into MVPA resulted in better scores across all outcomes. For example, replacing 30 min of SB, sleep, standing, or LIPA with MVPA was associated with −0.63 (95% confidence interval −0.48, −0.79), −0.43 (−0.25, −0.59), −0.40 (−0.25, −0.56), and −0.15 (0.05, −0.34) kg/m2 lower BMI, respectively. Greater relative standing time was beneficial, whereas sleep had a detrimental association when replacing LIPA/MVPA and positive association when replacing SB. The minimal displacement of any behaviour into MVPA for improved cardiometabolic health ranged from 3.8 (HbA1c) to 12.7 (triglycerides) min/day.Conclusions: Compositional data analyses revealed a distinct hierarchy of behaviours. Moderate-vigorous physical activity demonstrated the strongest, most time-efficient protective associations with cardiometabolic outcomes. Theoretical benefits from reallocating SB into sleep, standing, or LIPA required substantial changes in daily activity.
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| 9. |
- Chandimal, A. P. L., et al.
(författare)
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Impedance Behavior of Earth Enhancing Compound Under Lightning Transient Conditions
- 2018
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Ingår i: 2018 34th international conference on lightning protection (ICLP 2018). - New York : IEEE. - 9781538666357
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Konferensbidrag (refereegranskat)abstract
- This study was aimed at finding the performance of commercially available earth enhancing compound (EEC) under lightning conditions. Further to that, this is an extension of a previous study conducted by the same authors referring to the same EEC. The selected material seems to perform impressively under lightning conditions passing considerably large current values. The prepared EEC mixture and the setup was tested under dry conditions and exhibited low dynamic impedance characteristics for lightning impulse voltages. Ten-stage Marx-generator was used for the experiment, and due to high conductive nature of the material, HV supply between the sample was unable to increase more than few kV. Thus the 12 cm gap inside the material was complemented with an external air gap of 90 cm. The study was a comparison between "air-gap breakdown" and "air-gap plus material-gap breakdown". The results confirmed a low impedance characteristic for the selected EEC and suggested a very low electric field inside the material gap. An approximate value for the impedance of the test setup was calculated from the collected data. A time window was selected during the steady current discharge appeared just after the point of current peak and the impedance curves for both experiments were compared at a previously defined point at the time axis. The impedance value for EEC setup was estimated to be in the region of 1 - 2 Omega.
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