Short Gap Research Articles

Discharge Characteristics of Short Air Gap and Insulation Surface Under Flame Conditions

An experimental study was conducted to investigate the discharge characteristics of short air gap and insulation surface under flame conditions. The influence of ac electric field on flame and the mechanism leading to the reduction of breakdown voltage under flame conditions are analyzed. Results show that under the ac electric field, the flame is deflected to the high voltage electrode, and compared with normal conditions (without flame), the breakdown voltage of the short air gap and the insulation surface is decreased by 74.4% and 70%, respectively. Besides, arc levitation appears at high probability under the flame conditions. Furthermore, the decrease of the breakdown voltage of short air gap and the flashover voltage of insulation surface under the flame conditions are mainly due to the increase of the air conductivity and the decrease of the air density. For the insulating dielectric, the change of the flashover path is also one of the main reasons for the decrease of the flashover voltage.

The tactile detection threshold changes when a visual stimulus is presented with a short temporal gap.

[Purpose] The interaction between the visual and tactile modalities influences on different levels from neural activity, perception, higher cognition to behavior. The aim of this study was to examine how a visual stimulus influences tactile sensitivity depending on temporal asynchrony. [Subjects and Methods] In total, 15 participants took part in this study. They were required to perform a two-alternative forced-choice task regarding whether a tactile pulse was felt. The individual participants’ tactile thresholds were estimated using a repetitive stepwise method. Visual stimuli were simultaneously presented with various temporal gaps (0 ms, ± 50 ms, ± 100 ms, and ± 300 ms), whereas no visual stimulus was presented in the tactile only condition. The tactile thresholds in eight conditions were compared using analysis of variance. [Results] Of the participants, 53.5% showed the most sensitive tactile threshold when presented with a visual stimulus with a short temporal gap, especially when the visual stimulus preceded the tactile one by 50 ms. [Conclusion] The preceding visual stimulus facilitates the perceptual sensitivity of the tactile sensation. Providing sensory stimuli in a multisensory mode benefits perceptual encoding. A pre-attentional mechanism led by a particular sensory modality might work as a perceptual advantage for another modality.

Differential research impact in cancer practice guidelines’ evidence base: lessons from ESMO, NICE and SIGN

BackgroundThis is an appraisal of the impact of cited research evidence underpinning the development of cancer clinical practice guidelines (CPGs) by the professional bodies of the European Society for Medical Oncology (ESMO), the National Institute for Health and Care Excellence (NICE) and the Scottish Intercollegiate Guidelines Network (SIGN).MethodsA total of 101 CPGs were identified from ESMO, NICE and SIGN websites across 13 cancer sites. Their 9486 cited references were downloaded from the Web of Science Clarivate Group database, analysed on Excel (2016) using Visual Basic Application macros and imported onto SPSS (V.24.0) for statistical tests.ResultsESMO CPGs mostly cited research from Western Europe, while the NICE and SIGN ones from the UK, Canada, Australia and Scandinavian countries. The ESMO CPGs cited more recent and basic research (eg, drugs treatment), in comparison with NICE and SIGN CPGs where older and more clinical research (eg, surgery) papers were referenced. This chronological difference in the evidence base is also in line with that ESMO has a shorter gap between the publication of the research and its citation on the CPGs. It was demonstrated that ESMO CPGs report more chemotherapy research, while the NICE and SIGN CPGs report more surgery, with the results being statistically significant.ConclusionsWe showed that ESMO, NICE and SIGN differ in their evidence base of CPGs. Healthcare professionals should be aware of this heterogeneity in effective decision-making of tailored treatments to patients, irrespective of geographic location across Europe.

AI-Based Malicious Network Traffic Detection in VANETs

Inherent unreliability of wireless communications may have crucial consequences when safety-critical C-ITS applications enabled by VANETs are concerned. Although natural sources of packet losses in VANETs such as network traffic congestion are handled by decentralized congestion control (DCC), losses caused by malicious interference need to be controlled too. For example, jamming DoS attacks on CAMs may endanger vehicular safety, and first and foremost are to be detected in real time. Our first goal is to discuss key literature on jamming modeling in VANETs and revisit some existing detection methods. Our second goal is to present and evaluate our own recent results on how to address the real-time jamming detection problem in V2X safety-critical scenarios with the use of AI. We conclude that our hybrid jamming detector, which combines statistical network traffic analysis with data mining methods, allows the achievement of acceptable performance even when random jitter accompanies the generation of CAMs, which complicates the analysis of the reasons for their losses in VANETs. The use case of the study is a challenging platooning C-ITS application, where V2X-enabled vehicles move together at highway speeds with short inter-vehicle gaps.

Creeping discharges features propagating in air at atmospheric pressure on various materials under positive lightning impulse voltage – part 2: modelling and computation of discharges’ parameters

In this paper, the propagation mechanism of creeping discharges up to flashover for short air gaps is examined and described on various materials based on laboratory de-noised data (namely current, voltage and captured images). The main parameters considered for investigating the development of creeping discharges and their characteristics deal with the measurement, modelling and calculation of (i) their final/stopping length and morphology, (ii) their propagation velocity and (iii) the electric field distribution including the maximal magnitude ( E max ) and the geometric coefficient ( β ) estimation. The obtained results evidenced that both length and velocity of discharges are emphasised for polyamide-based materials (namely PA6/50 and PA66/50) whereas their ignition remains inhibited for filled cycloaliphatic epoxy resin (FCEP) and ethylene propylene diene monomere (EPDM) surfaces. As the electric field is concerned, both analytical and numerical models are developed and their results are compared and discussed. It has been shown that the presence of a polymer acts as a barrier when being incorporated between an electrodes gap whose dielectric strength depends strongly on the used material. Moreover, the FCEP barrier, in comparison to other materials, exhibits a marked dielectric reinforcement and an enhanced stability of the system making it suitable to provide a better protection to high-voltage equipment against discharges effects.

The Studies of a Vacuum Gap Breakdown after High-Current Arc Interruption with Increasing the Voltage

Vacuum-gap breakdown has been studied after high-current arc interruption with a subsequent increase in the transient recovery voltage across a gap. The effects of factors, such as the rate of the rise in the transient voltage, the potential of the shield that surrounds a discharge gap, and the arc burning time, have been determined. It has been revealed that opening the contacts earlier leads to the formation of an anode spot, which is the source of electrode material vapors into the discharge gap after current zero moment. Under the conditions of increasing voltage, this fact results in the breakdown. Too late opening leads to the breakdown of a short gap due to the high electric fields.

Dynamic phase alignment of ongoing auditory cortex oscillations

Neural oscillations can synchronize to external rhythmic stimuli, as for example in speech and music. While previous studies have mainly focused on elucidating the fundamental concept of neural entrainment, less is known about the time course of entrainment. In this human electroencephalography (EEG) study, we unravel the temporal evolution of neural entrainment by contrasting short and long periods of rhythmic stimulation. Listeners had to detect short silent gaps that were systematically distributed with respect to the phase of a 3 Hz frequency-modulated tone. We found that gap detection performance was modulated by the stimulus stream with a consistent stimulus phase across participants for short and long stimulation. Electrophysiological analysis confirmed neural entrainment effects at 3 Hz and the 6 Hz harmonic for both short and long stimulation lengths. 3 Hz source level analysis revealed that longer stimulation resulted in a phase shift of a participant's neural phase relative to the stimulus phase. Phase coupling increased over the first second of stimulation, but no effects for phase coupling strength were observed over time. The dynamic evolution of phase alignment suggests that the brain attunes to external rhythmic stimulation by adapting the brain's internal representation of incoming environmental stimuli.

Measurement of sliding friction coefficient of micro-line patterned surfaces on ice

Although the sliding friction of patterned surfaces on ice has been investigated for over a century, physical analysis still needs to be improved. In this study, we investigate the friction coefficient on ice by changing the experimental conditions of temperature, gap between line patterns (20 μm and 200 μm), and sliding direction. In the temperature region of −17.7 °C < T <−2.5 °C, a longer gap (200 μm) patterned surface has a lower friction coefficient for both parallel and perpendicular sliding directions at the same temperatures. Interestingly, a lower friction coefficient is found when the sliding direction is perpendicular to the micro-structure patterns at T < −7.6 °C for gap = 20 μm and at T < −9.9 °C for gap = 200 μm. To understand this interesting phenomenon, a theoretical model is derived by modifying the model from the study by Oksanen and Keinonen. Based on this modified model, the surface with a shorter gap (20 μm) makes fewer contacts and the pattern direction determines the water layer elongation at each contact. This validates that friction on ice can be controlled using a micro-structure pattern and moreover suggests a method for finding an optimized micro-structured surface for reducing friction on ice.

On transition from diffuse mode to the constricted one with high-current cathode spot in overvoltage open discharge in D2

So called “open discharges” in a narrow gap between the solid cathode and grid anode are widely used for generation of the pulsed high-current electron beams with energy up to 100 keV. The need to get high-energy e-beams leads to the necessity in using of strong overvoltage of the short gas gap with the reduced electric field of the order of 105 Td or higher. The discharge under strong overvoltage is unstable and tends to transit into high-current regime with low voltage. In the case of the open discharge in D2 at low pressure (about 0.5-2 Torr) and powered by stepwise voltage with amplitude up to 25 kV we revealed that this discharge exhibits two diffuse regimes which follow one by one and finally transits into the constricted mode with formation of high-current spots on the cathode. The physical properties of these gas discharge regimes have been explored in detail with the usage of the fast multi-frame camera synchronized with the current and voltage of discharge. Our findings promote more insight into physics of the overvoltage open discharge generating the e-beams with energy up to 25 keV.

Evolution of the shape of a high-current and moderate energy electron beam at its propagation through D2 at low pressure

The paper presents the experimental data on the time-spatial evolution of electron beam that is formed and propagates in a dielectric tube of large volume filled with D2 at low pressure of 1-2 Torr. The e-beam is generated by gas discharge in a short gap powered by the stepwise high voltage with amplitude up to 25 kV. Initially, this discharge appears in a strongly over-voltage regime which is unstable and eventually (in several hundreds of ns) transits into abnormal glow discharge at the voltage about of 1.5 - 2.5 kV and the current amplitude of several hundreds of Amps. The every of the mentioned discharge regimes generates the e-beam with energy up to 25 and 2.5 keV respectively. The ability of the over-voltage gap to generate the high- and low-energy e-beams happening one by one can be of great interest for many applications. The features in spatial structures of high-energy and low-energy e-beams in the course of their propagation over long distance through deuterium at low pressure are revealed and discussed.

Vocalizing during gaps in anthropogenic noise is an uncommon trait for enhancing communication in songbirds

Mounting evidence suggests that anthropogenic noise neg-atively impacts many wildlife species, including songbirds. One mechanism by which noise affects songbirds may be through acoustic obstruction to their systems of vocal communication. However, many species increase the amplitude or pitch of their vocalizations, which may partially mitigate the impact of high noise levels. When the amplitude of anthropogenic noise varies over time, such as near a moderate-use highway, short gaps between noise events may also provide an important oppor- tunity for communication. But, whether songbirds adjust vocalization rates rapidly to avoid overlap with noise is unknown for most species. We used acoustic playback to expose song- birds to simulated road noise during the dawn chorus in oth- erwise quiet habitats. We measured vocalization rates under ambient conditions and during quiet gaps embedded within playback of road noise to assess whether a community of songbirds, and nineteen individual species, vocalize more reg- ularly during noise gaps. There were no significant differences in community-wide acoustic output. Species-specific analysis revealed that only four species altered their vocal rates during quiet gaps in noise, but that the direction of the effect varied by species. Point count results revealed that birds generally remained on site for the duration of the experiment, suggesting that abandonment of noisy locations was unlikely to confound our results. In sum, increasing vocal output during short gaps in noise occurred in only a handful of species, perhaps con- tributing to the limited number of species that are found within noisy habitats.

Vocalizing during gaps in anthropogenic noise is an uncommon trait for enhancing communication in songbirds

Abstract Mounting evidence suggests that anthropogenic noise negatively impacts many wildlife species, including songbirds. One mechanism by which noise affects songbirds may be through acoustic obstruction to their systems of vocal communication. However, many species increase the amplitude or pitch of their vocalizations, which may partially mitigate the impact of high noise levels. When the amplitude of anthropogenic noise varies over time, such as near a moderate-use highway, short gaps between noise events may also provide an important opportunity for communication. But, whether songbirds adjust vocalization rates rapidly to avoid overlap with noise is unknown for most species. We used acoustic playback to expose songbirds to simulated road noise during the dawn chorus in otherwise quiet habitats. We measured vocalization rates under ambient conditions and during quiet gaps embedded within playback of road noise to assess whether a community of songbirds, and nineteen individual species, vocalize more regularly during noise gaps. There were no significant differences in community-wide acoustic output. Species-specific analysis revealed that only four species altered their vocal rates during quiet gaps in noise, but that the direction of the effect varied by species. Point count results revealed that birds generally remained on site for the duration of the experiment, suggesting that abandonment of noisy locations was unlikely to confound our results. In sum, increasing vocal output during short gaps in noise occurred in only a handful of species, perhaps contributing to the limited number of species that are found within noisy habitats.

Fabrication, properties and cytotoxicity evaluation of degradable poly(trimethylene carbonate-co-lactide) for the use as nerve guidance channels

Strategies to improve healing of damaged nerves include the application of specialized nerve guides, which hold the promise for allowing reanastomosis of the severed or damaged fibers. Studies have demonstrated that the use of a slowly degradable polymeric nerve guide can improve the nature and rate of nerve regeneration across a short gap in small nerves. The objective of this study was to characterize a biodegradable nerve guide based on poly(trimethylene carbonate-co-lactide) for peripheral nerve regeneration and to evaluate its cytotoxicity. The obtained copolymer films were incubated in two different media (distilled water and simulated body fluid), and while the degradation process appeared, pH and ion conductivity changes of solutions were monitored as well as mass loss of the samples. Additionally, mechanical tests (tensile strength, elongation at break and Young’s modulus parameters) before and after different time points were carried out. To evaluate cytotoxicity biological test were done on fibroblasts cells (NIH 3T3). Cell metabolic activity was determined using Alamar Blue reagent and their morphology was observed under fluorescence microscopy. The growth of pH in both media were mostly caused by steadily degradation of carbonate units into alkaline diols. The growth of ion conductivity value at the beginning of the incubation process was associated with the releasing of free ions to the solution. The mechanical parameters decreased with the progress of degradation process. Ringer’s fluid, as more aggressive, caused higher decrease in mechanical properties. The measured contact angles showed good surface wettability. Both surfaces, the top and the bottom, had similar hydrophilicity. Moreover, activity of fibroblasts cells were similar on both sides as well as on the reference TCPS. Good adhesion of NIH 3T3 cells to the surface suggests that the hydrophilic polymers promote colonization of fibroblasts cells on their surface. Biological studies have shown that used cells are very sensitive to surface topography which they colonize and cell viability was higher at the bottom surface, which has a slightly higher average roughness Ra. Thus, fibroblasts cell preferred colonizing rougher than smoother surfaces. Fabricated films does not affect negatively, namely, toxic on cell cultures and forms substrate with favourable surface properties. This was confirmed by the Alamar Blue tests and microscopic observations.

Breakdown in short rod-plane air gaps under positive lightning impulse stress

Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100 mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.

Breakdown in short rod-plane air gaps under positive lightning impulse stress

<p>Prediction of withstand voltages in air-insulated systems are made on the basis of empirical models that are not sufficiently accurate for complex geometries. Better understanding of the spatiotemporal development of electrical discharges is necessary to improve the present models. Discharges in lightning impulse stressed 20–100mm rod-plane gaps are examined using a highspeed camera, photo-multiplier tubes (PMTs) and a highbandwidth current measurement system. The images and measurements of gaps larger than 20mm show a fast initial streamer discharge with a current rise time of some tens of ns, followed by a dark period of a few μs and a propagation of a slower leader-type channel leading to breakdown. The breakdown mechanisms in the shortest gaps are faster and geometry dependent, probably occuring by heating of initial streamer channels. Different light filters used with the PMTs indicate that all parts of the leader-type discharge development emit light over a spectrum from UV to IR. The initial discharges emit low amounts of warm light and IR compared to the leader-type channel. Finally, it is suggested that empirical breakdown voltage prediction models should be interpreted in light of the leader-type breakdown mechanism.</p>

Tracheoesophageal fistula in sibilings - A rare occurence

Introduction Esophageal atresia is one of the most common congenital malformations occurring in 1 in every 2000-4000 live births. Previously considered to be a fatal condition, it has now become an eminently treatable condition with survival limited only by the presence or absence of major cardiac malformations. For the majority of families, the condition is unique to one child which in itself is challenging. It is extremely rare to affect more than one sibling in any family. The risk of recurrence is 0.5-2% and rises to 20% if another sibling is affected. Case description We report on two siblings, born two years apart with Type C TOF who were treated at King Hamad University Hospital, Bahrain. The first sibling was born with a short gap esophageal atresia with a distal fistula and repaired shortly after birth in another institution. The second sibling was born with a more challenging long gap esophageal atresia also with a distal fistula. The fistula was ligated on the second day of life and a gastrostomy tube put in place for feeding; repair of the atresia took place 2 months later. Both patients underwent serial dilatations to overcome strictures but are both tolerating oral diets. The third sibling in the family was unaffected with TOF or any VACTREL association. Conclusion The etiology of TOF is multifactorial with genetic, environmental and unknown components. There were no known environmental factors which could have contributed to this rare occurrence, but the only factor of significance is consanguinity of the parents who are first cousins. On the other hand, genetic factors are responsible for 12% of cases, these are classified as Chromosomal mutations, Syndromic or Isolated. These siblings do not fall into any of the mentioned categories and it is therefore speculated that this occurrence is due to a sporadic mutation. Take-home message Esophageal atresia with or without fistula is a fairly common condition encountered by paediatric surgeons on a daily basis. Despite increased experience and advancements in management of complex cases, the etiology remains a mystery. Future research should focus on more in-depth genetic studies on the impact of co-sanguinity on sibling TOFs.

Modeling heat dominated electric breakdown in air, with adaptivity to electron or ion time scales

We model heat dominated electrical breakdown in air in a short planar gap. We couple the discharge dynamics in fluid approximation with the hydrodynamic motion of the air heated by the discharge. To be computationally efficient, we derive a reduced model on the ion time scale, and we switch between the full model on the electron time scale and the reduced model. We observe an ion pulse reaching the cathode, releasing electrons by secondary emission, and these electrons create another ion pulse. These cycles of ion pulses might lead to electrical breakdown. This breakdown is driven by Ohmic heating, thermal shocks and induced pressure waves, rather than by the streamer mechanism of local field enhancement at the streamer tip.

Short and long gap peripheral nerve repair with magnesium metal filaments

A current clinical challenge is to replace autografts for repair of injury gaps in peripheral nerves, which can occur due to trauma or surgical interruption. Biodegradable metallic magnesium filaments, placed inside hollow nerve conduits, could support nerve repair by providing contact guidance support for axonal regeneration. This was tested by repairing sciatic nerves of adult rats with single magnesium filaments placed inside poly(caprolactone) nerve conduits. Controls were empty conduits, conduits containing titanium filaments and/or isografts from donor rats. With a nerve gap of 6 mm and 6 weeks post-repair, magnesium filaments had partially resorbed. Regenerating cells had attached to the filaments and axons were observed in distal stumps in all animals. Axon parameters were improved with magnesium compared to conduits alone or conduits with single titanium filaments. With a longer gap of 15 mm and 16 weeks post-repair, functional parameters were improved with isografts, but not with magnesium filaments or empty conduits. Magnesium filaments were completely resorbed and no evidence of scarring was seen. While axon outgrowth was not improved with the longer gap, histological measures of the tissues were improved with magnesium compared to empty conduits. Therefore, the use of magnesium filaments is promising because they are biocompatible and improve aspects of nerve regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3148-3158, 2017.

Unstable Leader Inception Criteria of Atmospheric Discharges

In the literature, there are different criteria to represent the formation of a leader channel in short and long gap discharges. Due to the complexity of the physics of the heating phenomena, and the limitations of the computational resources, a simplified criterion for the minimum amount of electrical charge required to incept an unstable leader has recently been used for modeling long gap discharges and lightning attachments. The criterion is based on the assumption that the total energy of the streamer is used to heat up the gas, among other principles. However, from a physics point of view, energy can also be transferred to other molecular processes, such as rotation, translation, and vibrational excitation. In this paper, the leader inception mechanism was studied based on fundamental particle physics and the energy balance of the gas media. The heating process of the plasma is evaluated with a detailed two-dimensional self-consistent model. The model is able to represent the streamer propagation, dark period, and unsuccessful leaders that may occur prior to the heating of the channel. The main processes that participate in heating the gas are identified within the model, indicating that impact ionization and detachment are the leading sources of energy injection, and that recombination is responsible for loss of electrons and limiting the energy. The model was applied to a well-known experiment for long air gaps under positive switching impulses reported in the literature, and used to validate models for lightning attachments and long gap discharges. Results indicate that the streamer–leader transition depends on the amount of energy transferred to the heating process. The minimum electric charge required for leader inception varies with the gap geometry, the background electric field, the reduction of electric field due to the space charge, the energy expended on the vibrational relation, and the environmental conditions, among others.

Esophageal Atresia with Tracheo-Esophageal Fistula Presenting Beyond 7 Days.

Aim: To describe our experience of neonates with esophageal atresia with tracheo-esophageal fistula (EA with TEF) who presented after a week. Design: Retrospective study of the patients of EA with TEF who presented after a week. Study Setting: Department of Pediatric Surgery, Government Medical College Nagpur. Study Duration: Eight years. Materials and Methods: Demographic information, hematological, biochemical and radiological data were obtained from the patients' medical records. The gap between two ends of the esophagus, nature of upper pouch and lower esophagus were noted intra-operatively. Outcome in terms of mortality and surgical complications were noted. In operated group, babies who survived were compared with non-survivors with respect to various preoperative variables. Results: Of 52 patients, 27 babies expired during initial stabilisation period before surgery. The causes of mortality were severe pneumonitis and septicemia. One baby had associated cyanotic heart disease. Twenty-five patients with mean age of 8.28±1.21 days underwent surgery. Nearly two-third of them were male. All of them were born at full-term with mean birth weight of 2.47±0. 12 kg. More than 80% were previously hospitalised and nearly 70% babies were given feeds before present hospitalization. Mean Downe’s score for respiratory distress was 5.8±1.49. All patients were positive for septic profile. Associated congenital anomalies were present in ten patients. Intra-operatively, two ends of esophagus were either approximating or have short gap in 24 patients. All patients had well developed, thick and muscular upper oesophageal pouch. Lower esophagus at fistula was thin but dilated in 18 patients while thin and narrowed in 7 patients. However, esophageal anastomosis was possible with ease without any tension in all except one patient. There were 15 deaths in our study (13 due to pneumonitis and 2 during follow up due to aspiration). Three survivors required anti-reflux surgery. Comparison of preoperative variables of survivors and non-survivors showed a significant difference with respect to the variables like feedings, abdominal girth, immature band cells to neutrophil ratio and nature of pharyngeal or endotracheal aspirate. Conclusions: Late presentations in EA with TEF are associated with high mortality but less anastomotic complications after surgery. Preoperative factors like feedings, abdominal distension, immature band cells to neutrophil ratio and bilious pharyngeal or endotracheal aspirate are associated with high mortality.