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Strictures caused by esophageal cancer can narrow down the esophageal lumen, leading to dysphagia. Palliation of dysphagia has driven the development of a robotic soft esophagus (RoSE), which provides a novel in vitro platform for esophageal stent testing and food viscosity studies. In RoSE, peristaltic wave generation and control were done in an open-loop manner since the conduit lacked visibility and embedded sensing capability. Hence, in this work, RoSE version 2.0 (RoSEv2.0) is designed with embedded time of flight (TOF) and pressure sensors to measure conduit displacement and air pressure, respectively, for modeling and control. Model predictive control (MPC) of RoSEv2.0 is implemented to govern the peristalsis and air pressure profile autonomously. The implemented MPC used sparse identification of nonlinear dynamics with control (SINDYC) models to estimate the future states of ROSEv2.0. The dynamic models are discovered from the TOF and pressure sensor data. Peristalsis waves of speed 20 mm $\cdot$ s $ ^{-1}$ , wavelength 75 mm, and amplitudes 5, 7.5, and 10 mm were successfully generated by the MPC. Additionally, RoSEv2.0 with the MPC was employed to perform stent migration testing with various food boluses consistencies. The major contribution claimed in this article is the application of SINDYC-based MPC to solve the closed-loop control problem of RoSE for achieving desired peristaltic waves. [ABSTRACT FROM AUTHOR]

Soft actuators are compliant structures that are generally made of elastomers and generates large deformation. The behavior of these structures cannot be estimated accurately using infinitesimal strain theories. The objective of soft robotics applications is the controlled large deformation of these structures. In this article, we propose an analytical model for a pneu-net soft actuator. The model is based on the Euler–Bernoulli finite strain hyperelastic thin cantilever beam theory. The deformation of the air chambers is modeled using finite strain membrane theory. The analytical model is developed for two different states of the actuator: 1) free space; and 2) when the actuator was subjected to tip contact. The proposed theoretical model predicts the deformation and force characteristics of the actuator for the grasping state. The theoretical formulation of the developed model is different from previously developed infinitesimal strain models for the actuator, as it considers the axial stretch and forces applied to the actuator. In addition, it can be theoretically implemented on similar structured actuators for various applications. The theoretically calculated deformation and force characteristics of different actuators are compared with the finite element (FE) model and experimental characteristics. The results suggest that the proposed model can predict the actuator deformation and force characteristics as accurately as the FE model, but the computation time of the proposed model is less than 1% that of the FE model. The proposed model is further implemented on a three-finger gripper to predict the air pressure required for a stable grasp of different objects and is validated experimentally. [ABSTRACT FROM AUTHOR]

An increased dc-link voltage and fast-switching semiconductors constitute new challenges on the insulation system of low-voltage electrical machines, especially in automotive applications. During the design process, the different components of the insulation system can be tested according to IEC 60034-18-41. This industrial standard prescribes certain test voltages for type-I insulation systems based on empirical values. However, important ambient influence factors such as humidity and air pressure are not considered. Therefore, this work focuses on the influence of ambient conditions on the insulation strength of low-voltage electrical machines. Partial discharge tests are performed on specimens representing the interturn insulation which is usually regarded to be the weakest part of the insulation system. To represent the electrical stress during inverter operation, a bipolar test voltage is applied. The results of the measurements show that the standard is not applicable for the studied conditions in this work. It is concluded that the humidity and especially the ambient pressure have to be considered. The standard method using safety factors to calculate the test voltage is discussed. The method is extended to consider ambient conditions which are not covered by the standard. [ABSTRACT FROM AUTHOR]

Dry air is promising as an alternative insulation medium for SF6 gas in high-voltage equipment. Since its dielectric strength is about one-third of that of SF6 gas, one of the most effective ways to apply dry air to high-voltage gas-insulated switchgears (GISs) is to further increase gas pressure. In this article, impulse breakdown strength of dry air at high pressure under quasi-uniform electric field is measured. Furthermore, the probability distribution of breakdown voltage is predicted using the volume-time theory in consideration of initial electron generation probability in gas gap and field electron emission from an electrode. The predicted distribution of breakdown voltage by the volume-time theory is in line with the experimental results. [ABSTRACT FROM AUTHOR]

Corona discharges get accelerated at low air pressure conditions leading to severe aging of the polymeric housing material, eventually causing the failure of the insulator. In this article, the effect of ac corona on different silicone rubber (SiR) micro- and nanocomposite samples at low pressure is studied. Micro alumina trihydrate (ATH), nano-titanium dioxide (TiO2), and nano-silica are used as filler materials in varying concentrations. This article compares the filler materials for nanocomposite preparation based on their performance in low-pressure conditions. It is observed that the decrease in pressure results in increased corona discharges and loss of hydrophobicity in the samples. The formation of carboxylic acid is evident from the Fourier transform infrared spectroscopy (FTIR) for the treated samples. The performance of silica nanocomposite with 5 wt% loading is better than the silica nanocomposite with 3 wt% loading. Crack width, surface roughness, and physicochemical changes were significantly reduced in silicone dioxide filled SiR (SSR5%) when compared to other silica and TiO2-filled samples at low pressure. The SiR samples filled with 5 wt% nano-silica perform better in terms of resisting corona-induced degradation at low pressure. [ABSTRACT FROM AUTHOR]

The effect of axial magnetic field on glow discharge parameters at low pressure is studied in this article. First, Paschen’s law under axial magnetic field is modified. The results show that under the same conditions, the magnetic field will increase the breakdown voltage of glow discharge. The experimental results are consistent with the theoretical analysis, but the experimental value is higher than the theoretical value. Second, the physical model of parallel field glow discharge is established, and the plasma density of glow discharge under different pressure, discharge spacing, and magnetic field is studied. The results show that the plasma density increases with the increase in magnetic field at low pressure; at high pressure, the larger the magnetic field, the smaller the plasma density. At the same position, the plasma density increases with the increase in discharge spacing in weak magnetic field, and it decreases with the increase in discharge spacing in strong magnetic field. When the surface area of the magnet is only 20% of the surface area of the anode and cathode, the radial nonuniformity of the magnetic field makes the plasma density reach the maximum when the radial $r =0$. [ABSTRACT FROM AUTHOR]

The article presents an investigation of the effect of radio frequency (RF) field (Wi-Fi signal) on electrical discharges produced by high-voltage (HV) pulses of different time duration applied between two pin electrodes in ambient air at atmospheric pressure. In the course of the work, electrical characterization was carried out, namely, the measurement and analysis of the breakdown voltage and the energy of single and multiple discharges with a duration from 500 ns to 200 $\mu \text{s}$ in the presence, as well as without external influence, of RF radiation with a power of 30 W at a frequency of 2.45 GHz. The study results showed that the energy of the discharges remained unchanged in all cases; the breakdown voltage of the primary pulse was unchanged as well, whereas the amplitude of subsequent pulses in the packet for the case of multiple pulses dropped by half. Despite this fact, under current experimental conditions, a potential ignition risk of electric breakdown is still highly improbable. This result is of interest for the installation of wireless sensors in flammable environments. [ABSTRACT FROM AUTHOR]

This study aims to simplify the driving system of pneumatic soft robots by developing a lightweight and small-sized multimode flow control valve (MMFCV). It can be embedded in robots as the components, and thus it requires no conventional valves with large size and heavy mass, which significantly reduced the volume and mass of the driving system. The valve is comprised of an input port, an output port, a positive port, and a negative port. By designing the connection of these ports to the actuators, the MMFCV can work in three different modes: one-direction delay mode, delay deflating mode, and double-port control mode. The pressure output characteristics of the MMFCV are modeled, and the validity is verified through experiments. In addition, a robot that comprised of two radial expansion modules, one axial expansion module, and four MMFCVs are fabricated, and the body is driven by the air pressure from the air supply through only one tube. The results of the pipe crawling experiments demonstrate that the MMFCV with multimode increased the flexibility of circuit and time sequence of the air flow, which can reduce the number of the tubes from the air supply to the robot. As a result, it reduced the load pulled by the tubes, and prevented the mission failure from the risk of entanglement of the tubes. [ABSTRACT FROM AUTHOR]

A comprehensive study of developing a novel printing system using a low-cost open-source printer for fully 3-D printing frequency-selective surface is presented in this article. The novel printing setup employs a low-cost printer to print a plastic-based filament and a conductive silver ink paste simultaneously. As there were no printers available in the market for this application, the open-source fused filament fabrication (FFF) printer was modified to accommodate two extruders mounted on the same extruder carriage. Techcon TS250 air pressure dispenser was employed for the extrusion of silver ink. Extension pieces for the extruder carriage were also 3-D printed using a fused deposition modeling (FDM) printer to reduce the production costs. A bandstop FSS comprising of square loop elements was designed to demonstrate the full fabrication. The FSS operated at a central frequency of 2.55 GHz and provided a good angle of response with wide bandwidths. Surface profiles of the printed FSS and substrate demonstrate the reliable fabrication of the FSS design. This full 3-D printing method provides an economical, eco-friendly, swift, reliable, and viable substitute for the fabrication of FSS designs that could be highly customized in terms of fabricating 3-D FSS designs with reliable performances. The designs can be printed and deployed to reduce the drop in signal within an enclosed environment. [ABSTRACT FROM AUTHOR]

Common materials used in dielectric mirrors are inorganic and rigid such that their optical properties cannot be modified. Here, we developed a method to fabricate a dielectric mirror with free-standing flexible layers that can be actuated by applying an electrostatic force or air pressure between the top and bottom ones. The membranes are sequentially compressed by reducing the structure reflectance by eliminating the air layers, where reflectance is the total electromagnetic power reflected divided in the incident one. A potential bias is applied between the layers of up to 30 V and an actuation time is shown to be less than 4.1 ms, recorded with a camera at 240 frames/s. Mirrors with length and width of up to $230~\mu \text{m}$ each were achieved with three polymer/air layers. The polymer free-standing layers thickness ranged from 840 to 1240 nm and the air gaps from 140 to 400 nm. The small gaps and the large length of the mirrors allow fast actuation with relatively low voltages. The mirrors can be designed to reflect specific colors of the visual spectrum with potential application for color reflective displays. [ABSTRACT FROM AUTHOR]

More-electric-aircrafts (MEAs) are heading towards larger power, higher voltage, and more optimum architectures, it is extremely important to understand partial discharge (PD) behaviors under the challenging aeronautical power systems. PD under the pressure of 1–101 kPa and frequency of 50–1000 Hz is studied to emulate the practical situation with the consideration of insulation defects from electric machine windings. The high frequency current transformer (HFCT) is specifically employed to pick up partial discharge signals. Experimental results indicate that PD inception voltage (PDIV) decreases almost linearly with air pressure. As to the discharge amplitude, it increases first and then decreases as air pressure dropping. The highest discharge repetition rate and the number of discharges appear at 30 kPa. High frequency doubles the number of discharges without affecting PD amplitude. Low air pressure causes the phase shift and phase width of the phase-resolved partial discharge (PRPD) to increase, and the trend also is accelerated by high frequency. This experimental approach is beneficial to provide prerequisite knowledge in characterizing PD and assessing its potential adverse impact on the aeronautical power system and consequently contribute to optimizing the insulation design for MEA. [ABSTRACT FROM AUTHOR]

Thanks to their continuously deformable features, soft bending actuators, including pneumatic and electric actuators, are increasingly used in continuum robots. Further development, however, is limited by the complexity of the multicavity structure in pneumatic actuators and the instability of the electromechanical coupling in dielectric elastomer actuators. In this article, by combining the advantages of the two actuation techniques, a novel hybrid electro-pneumatic bending actuator is proposed that is capable of bending with significantly reduced complexity and improved stability. A timing control method is proposed that enables rapid and significant bending. A low voltage is used for bending guidance with air-pressure concurrently to produce a large bending stroke. The results of experiments indicate that, with increasing air pressure, the bending angle varies in three different stages. These stages are (I) a low-pressure guidance stage, (II) an instability induction stage, and (III) a stable deformation stage. By harnessing the instability at stage II, the driving voltage can be substantially reduced to avoid electric breakdown. By studying the effect of prestretch on bending, the controllability of the bending deformation is improved. The simulation is also used to verify the control method and predict the development path of soft robots. [ABSTRACT FROM AUTHOR]

Although much work has been done and significant progress has been made on partial discharges (PD) measurement and detection techniques, this is not the case for PD modeling. Four types of internal PD modeling, in sequential order from first to last developed, are three-capacitance (abc), induced charge concept (ICC), finite element analysis (FEA), and Multiphysics models. The abc model is too simple to provide an understanding of the physical phenomena affecting PD. In contrast, Multiphysics models are immature. Multiphysics models require a high number of physical parameters that need to be experimentally determined, which is not a trivial task. Moreover, adjusting the physical parameters to achieve a good agreement between simulation results and measurement results for a specific geometry and dimension may not work for other geometries and dimensions. The FEA model, a relatively recent model, and the ICC model, which fall between the abc and Multiphysics models in terms of modeling complexity, can partly explain mechanisms and physical phenomena associated with internal PD. However, to the best of our knowledge, there is only one paper comparing ICC and FEA models for a case study; thus, further research is needed to elucidate various aspects of these two models. In this paper, 1) an improved ICC and a FEA capable of describing phenomena occurring during PD are developed, 2) both developed models are coded and implemented either in MATLAB or in COMSOL Multiphysics linked with MATLAB, and their simulation results are compared and analyzed, and 3) the influence of different parameters including void shape, void size, and void air pressure on PD parameters are studied. [ABSTRACT FROM AUTHOR]

A dielectric barrier discharge (DBD) in atmospheric pressure air was excited by a high-voltage pulse power supply. Capacitors with different capacitance were connected in the discharge circuit and their effects on discharge power calculation were evaluated. The average power deposited into the discharge were calculated by three different methods: 1) Lissajous figure; 2) product of voltage and current; and 3) watt-hour meter. Further studies showed that the capacitor with 10 nF was suitable for power calculation. At applied voltage of 9 kV, discharge power calculated by three methods were similar (around 25–27 W). However, with the increase of applied voltage, the discharge power obtained by product of voltage and current was far beyond the real value. Lissajous method has proven more appreciable for discharge power calculation in a pulsed plasma at high voltage. This study provides a practical guide for power calculation in a pulsed-driven DBD system. [ABSTRACT FROM AUTHOR]

Using the Global Navigation Satellite System (GNSS) differenced total electron content (dTEC) series, the traveling ionosphere disturbances (TIDs) of 22 typhoons registered in Taiwan/Japan between 2013 and 2016 were studied. The horizontal speed of the first TID during a typhoon landing can be estimated by a two-station method with the ionosphere anomaly indicator in total electron count units (TECUs) (|dTEC| ≥ 0.15 TECU). The horizontal speed of the TIDs was from 155 to 210 m/s and with an average speed of 168.70 m/s. The estimated TID speeds of Typhoons Soudelor (205.93 m/s) and Megi (158.47 m/s) are not consistent with each other, even though they had very similar trajectories when cross through Taiwan Island. Moreover, the propagation velocity of the typhoon ionospheric anomaly showed a significant positive correlation (r = 0.78 , α = 0.05) with the change rate of the typhoon central air pressure and a negative correlation (r = −0.52 , α = 0.05) with the central pressure before landing. Gravity waves were generated by land friction, terrain blocking, and strong wind shear transport energy into the atmosphere from the near surface to the mesosphere and thermosphere, which is the main cause of ionosphere disturbances during typhoon landing. [ABSTRACT FROM AUTHOR]

The article is the continuation of the work devoted to the numerical study of processes in the single-phase ac plasma torch operating at low current (up to 10A RMS). The main attention is paid to the analysis of the flow pattern and the behavior of gasdynamic parameters. The effects of flow acceleration and rarefaction of near axial arc core are shown. The effects of the transformation of gasdynamic structures typical for cold flow (e.g., vortex behind the back step), as well as the appearance of new structures (e.g., vortexes in the jet periphery), are demonstrated and discussed. An explanation is given for the effect of the increase of the arc voltage drop with the increase of the flow rate of supplied air, associated with the increase of the medium electric resistance. The presented results are in accordance with the experimental data on the voltage drop in a conventional ac plasma torch. [ABSTRACT FROM AUTHOR]

Air breakdown in sub- and supersonic flows induced by the subcritical streamer discharge and the effect of the initiator shape on breakdown conditions are studied. Experiments with varying the electric field strength and air pressure show that the ability of electromagnetic vibrators to initiate air breakdown has a resonant character. Placing a small electromagnetic vibrator in a microwave beam allows one to initiate air breakdown with a field strength in the microwave beam which is significantly smaller than the critical breakdown strength. The dependencies of the critical intensity of the electric field on the pressure and location of the initiator are reported. The dependence of the field amplification coefficient at the vibrator edge on the screen dimensions is presented at different lengths and widths of the screen. [ABSTRACT FROM AUTHOR]

The atmospheric pressure multicorona plasmas and plasma-activated water (PAW) have been used to improve the germination and growth of rat-tailed radish seeds (Raphanus sativus var. caudutrus). The multicorona plasmas at 30 kV were used to treat the seeds for 2 and 4 min. The PAW activated by multicorona plasmas (for 1, 5, and 10 min) was then used to soak the plasma-treated seeds for 4 h. The plasma-treated seeds were watered with PAW daily for 7 days. The nonactivated tap water (NAW) was used to soak and water the plasma-treated seeds as a control group. The germination rate, stem length, and the dry weight of all plasma-treated groups are greater than those in the control group. All measurements were increased with increasing PAW times. The highest germination rate of 92% was found in the seeds exposed to plasma for 2 and 4 min with watering 10-min PAW. This germination rate was higher than that in the control group by 10%. This was because the reactive species in plasma and PAW could stimulate the germination rate by increasing water absorption. The highest stem length of 74.76 mm/seedling and dry weight of 14.66 mg/seedling were found in the seeds exposed by plasma for 4 min with watering 10-min PAW. These measurements were higher than those in the control group by 78.42% and 21.66%, respectively. This was because the increase of water absorption and reactive nitrogen species in PAW could stimulate seedling growth. From the observed results, it can be concluded that the increase in plasma treatment times and PAW activated by plasma treatment times on seeds led to a positive effect on seedling growth. Therefore, the atmospheric pressure multicorona plasma and PAW can be considered as an environmentally friendly and innovative tool to enhance the germination and growth of rat-tailed radish seeds. [ABSTRACT FROM AUTHOR]

In order to study the effect of surface morphology of dielectric materials on features of dielectric barrier discharge (DBD) in air at atmospheric pressure (AP), electrical characteristics and optical emission spectrum are obtained in a 2-mm air gap with quartz glass and ceramic used as the dielectric layer (the capacitance of the used dielectrics is similar). The transition of discharge mode is observed for different dielectric material and surface morphology. Results show that with varying dielectric material and surface morphology, air atmospheric pressure dielectric barrier discharge (APDBD) presents three discharge modes, including a filamentary mode, a homogeneous mode, and a mixed mode of them. Further investigation reveals that the homogenous mode is in a Townsend discharge regime, which is realized in a proper surface morphology of 96% Al2O3 ceramic. Moreover, optical emission spectrum is obtained, which mainly consists of atomic lines of nitrogen and molecular bands originating from the second positive system of N2($\text{C}^{3}\Pi _{\mathrm {u}}\to \text{B}^{3}\Pi _{\mathrm {g}}$). From N2($\text{C}^{3}\Pi _{\mathrm {u}}\to \text{B}^{3}\Pi _{\mathrm {g}}$), molecular vibrational temperature is investigated as a function of surface roughness ($R_{\mathrm {a}}$) of the different dielectric materials. Result reveals that there is a minimal vibrational temperature when the discharge is in the homogeneous mode. With quartz glass used as the dielectric, the vibrational temperature decreases first and then increases with increasing $R_{\mathrm {a}}$. The minimum value appears at $R_{\mathrm {a}}$ of 215 nm. Besides, the discharge current is the most concentrated in time, and the discharge looks the most homogeneous under this circumstance. [ABSTRACT FROM AUTHOR]

Pressure wave therapy is widespread for multiple purposes, from cell metabolism stimulation to tendons, ligaments, muscles, and bones pathologies treatment. However, in the literature, there are no quantitative metrological data related to pressure wave devices. On the contrary, it would be extremely important to have more information on the provided therapeutic signal, which could also be exploited as input for a finite-element model able to foresee the pressure wave propagation inside the tissues. The authors investigated three different versions of the same device in terms of force applied to the tissue. The results show high variability of the pulses intensities (up to 25%), highlighting a nonuniformity of the treatment (in particular at low frequencies and high compressed air pressure). Moreover, the dependence from different parameters (i.e., pulse frequency, pressure, opening time of the solenoid valve for the compressed air pushing the bullet) was investigated. It was found that the lower the frequency and the higher the opening time of the valve, the higher the force applied to the tissue. An estimation of energy density was done; sometimes the limit values provided by pressure wave therapy guidelines (i.e., DIGEST and ISMST) are exceeded, in particular for soft tissues. [ABSTRACT FROM AUTHOR]

A new method based on the charge simulation technique is proposed for computing the electric field in a short uniform field gap with space charge and without space charge of avalanches growing in the gap. The self-space-charge field of the avalanche is evaluated to result in field enhancement ahead of the avalanche due to electrons at its head and behind the avalanche due to positive ions in its wake. Also, a criterion is proposed for calculating the breakdown voltage and time-to-breakdown when the primary avalanche crosses the gap. The criterion is based on self-recurrence of the avalanche by secondary processes, and the most dominant one is the photoemission at the cathode. The condition of transition of the primary avalanche to anode- and cathode-directed streamers is formulated where the avalanche is chocked by its self-space-charge field. The number of electrons starting avalanche chains forming the streamers is evaluated in the gas ahead and behind the primary avalanche by photoionization and at the cathode by photoemitted electrons. The present computed values of the breakdown voltage of air at different pressures and N2 at atmospheric pressure as well as the time-to-breakdown in air at atmospheric pressure agree satisfactory with those recorded experimentally. The computed temporal variation of the size of the primary avalanche as influenced by its self-space-charge field agrees with that reported in the literature at different $E/N$ values. The computed current waveforms of the primary avalanche and its successor chains agree reasonably with those measured and those calculated using a finite-element method. [ABSTRACT FROM AUTHOR]

The effect of Al electrode erosion and its influence on plasma temperature and ambient pressure in a closed air vessel due to fault arcing are investigated theoretically with a magnetic-hydrodynamic model for fault arc developed with various energy transport mechanisms considered. The results show that the increased radiation due to Al vapor dominates the cooling of central plasma at low currents, while the mass transfer is more important at high currents. Inversely, the influence of increased electrical conductivity is relatively weak. The visualized simulation of energy transport suggests that the pressure rise is seriously affected by Al vapor due to the changeless of heat transport processes of fault arc. The chemical reaction involving Al vapor offers a more dominant positive contribution to pressure rise in contrast to mass transfer, whereas the negative contribution of increased radiation due to Al vapor to pressure rise is greater than the increased electrical conductivity. [ABSTRACT FROM AUTHOR]

Breakdown voltage (BDV) is calculated for two electrode structures, namely, sphere and donut gaps, operating in air at atmospheric pressure. The calculation is based on the streamer BD criterion. COMSOL software package is used for field analysis and calculation of critical number of electrons by assessing integrals of the efficient ionization coefficient along field lines. Thus, also lengths of critical avalanches that can propagate from both electrodes were obtained. First, simulations were performed for sphere gaps at conditions standardized by IEEE to derive critical number of electrons for highly reliable experimental data. It was shown that these numbers deviate greatly from the widely accepted 108 number, and that clear tendencies for the deviations exist depending on the gap to sphere diameter ratio. This assisted us in the second part of this work, which is a description of a spark gap (SG) formed by two donuts. Such gaps are compact and can serve as closing switches, and as a crude HV measurement means. Experimental results and comparison to calculated BDVs are reported. These two examples illustrate a simple and effective method of BDV calculation in arbitrary geometries with weakly nonuniform field for well-characterized gases at moderate pressures; it can be used with industry-standard software in HV practice. [ABSTRACT FROM AUTHOR]

This article aims to develop a semi-noncontact stress-sensing system using a laser-generated ultrasound (LGU) wave assisted by candle soot nanoparticle (CSNP) composite. While the acoustoelastic effect is commonly targeted to measure the stress level, efforts to combine it with the LGU wave signal have been lacking due to weak signal intensity. In this study, the CSNP-based transducer is designed to potentiate the photoacoustic energy conversion. To demonstrate the wave propagation with the designed parameters, a numerical simulation was first conducted. The experimental results showed that a laser intensity of 6.5 mJ/cm2 was enough to generate the subsurface longitudinal (SSL) wave from the CSNP composite transducer. The normal beam projection is the most effective wave-generation method, exhibiting the highest signal magnitude compared with inclined projection cases. Finally, the laser-assisted stress-sensing system was assessed by increasing the internal pressure of an air tank. The sensitivity of the developed sensor system was estimated to be 0.296 ns/MPa, showing a correlation of 0.983 with the theoretical prediction. The proposed sensing system can be used to monitor the structural integrity of nuclear power plants. [ABSTRACT FROM AUTHOR]

Objective: Investigation of pain-related brain processing in animal models is often performed with unspecific stimuli that are not representative of clinically relevant pain phenomena such as punctate hyperalgesia or pressure pain. In order to explore cerebral processing of mechanically evoked pain with functional Magnetic Resonance Imaging (fMRI), a MRI-compatible spatially- and strength-specific mechanical stimulator incorporating either von-Frey filaments or an air-puff system was developed. With this device, mechanical stimuli can be applied to various aspects on the rat hind paw (HP). Methods: The mechanical stimulator consists of an electro-pneumatic unit connected to the part delivering the mechanical stimulation (MS) via a non-magnetic spring for punctate MS (using a von-Frey filament) or via a Lure-lock unit for pressure pain (air-puffs). The strengths of stimuli were calibrated against the delivered air pressure and weight exerted on a pressure pad or in vivo. BOLD fMRI was performed in a 9.4T MRI scanner during calibrated MS at increasing air pressure. Results: We observed a linear relationship between air pressure and force. These calibrations provided quantitative, adjustable, precise and reproducible sub- and supra-threshold MS. Changes in brain activation were investigated up to a force of 154 g using von-Frey filaments, while the maximum force was 30.9 g for air-puffs. Stimulation demonstrated a significant difference between the two types of MS. Unilateral suprathreshold MS induced strong bilateral brain activation in the areas related to pain processing for both types of MS. However, the patterns of brain activity in subcortical areas evoked by von-Frey MS were different from that evoked by air-puffs. Conclusion: The precise delivery of calibrated and reproducible punctate and static MS allows for the specific assessment of clinically relevant supra-spinal correlates of pain-related processes using BOLD fMRI. Significance: A novel device for clinically relevant MS in BOLD fMRI pain studies in rats, providing results that may be directly translated to human pain research. [ABSTRACT FROM AUTHOR]

Slider/disk contact, which will lead to lubricant depletion, is likely to occur due to the nano spacing between slider and disk. To understand the mechanism of lubricant depletion under contact, a molecular dynamics model is developed in this article. The effects of air bearing pressure, the contact force, and the disk velocity on the penetration depth of the slider and the depletion volume of lubricant is studied. The results show that higher contact force and smaller air bearing pressure cause deeper penetration depth, which leads to a larger amount of lubricant depletion. The effect of disk velocity on lubricant depletion can be neglected at a high contact force. In order to effectively reduce lubricant transfer and lubricant depletion, high air bearing pressure should be suggested and slider/disk contact should be avoided. [ABSTRACT FROM AUTHOR]

The possibilities of creating a homogeneous discharge in air of atmospheric pressure between a flat metallic electrode covered by a dielectric barrier and water surface are demonstrated. In the experiments, the discharge was initiated in the gas gaps by applying unipolar voltage pulses with fronts of ~15 ns and duration of ~100 ns. It was found that the discharge mode was affected by the pulse repetition rate. Its critical magnitude corresponding to the appearance of a homogeneous discharge was reduced from 500 to 50 s−1 if the length of the air gap was increased from 1 to 4 mm. The lifetime of a homogeneous discharge mode was affected by the total duration of the discharge. Thus, it was about several tens of seconds at a pulse repetition frequency of 100 s−1 and it reduced at increased frequencies. It is suggested that the transition from homogeneous to inhomogeneous modes is associated with local overheating of the gas due to significant energy dissipation in the discharge volume. [ABSTRACT FROM AUTHOR]

The inclusion of a barometer in a wearable fall detector has been shown to improve the detection accuracy by measuring the altitude change associated with a fall event. However, the barometer is a power-hungry sensor, and the sensing power of barometer can be the dominant power consumption source in a wearable fall detector. In this study, we propose a triggering method that reduces barometer power consumption and prolongs the battery life. This approach utilizes a hermetically sealed and waterproof enclosure, with a small inlet covered by a semi-permeable membrane (SPM) to delay the time at which equilibrium between the internal and external pressures is reached, allowing the barometer to be woken from an idle low-power mode and capture the rising air pressure caused by the decrease in altitude during the fall. Two alternative signal processing methods were applied to the pressure waveform to detect the rising pressure pattern, a differential moving average filter (DMAF) and a Kalman filter (KF). The proposed fall detector was evaluated with data collected from a laboratory-based trial and a free-living trial, in which the barometric pressure data, recorded in open-air, were passed through a mathematical model of the leaky enclosure and the SPM assembly. The results show that the proposed fall detector with a 3.7 V, 140 mAh lithium-polymer battery provides a long battery life (DMAF 447 days, KF 444 days) while not compromising the sensitivity (DMAF 91.8%, KF 91.9%), specificity (DMAF 95.2% and KF 95.5%), or the false alarm rate (DMAF 0.035 alarms/hour and KF 0.064 alarms/hour). [ABSTRACT FROM AUTHOR]

Pressure, temperature and humidity are the basic parameters of air, which affect the average mobility of ions in it. In this paper a series of the average mobilities of ions in corona discharge in air at different pressures, temperatures and humidities are measured using an apparatus for generating parallel plane ion flow field in a climatic test cabinet. The pressure, relative humidity, and temperature is from 80 to 110 kPa, 20 to 85%, and −10 to 40°C, respectively. The variation of the average mobility of ions in corona discharge in air, with respect to pressure, humidity and temperature, is discussed and calculated from the fundamental mobility equation. [ABSTRACT FROM AUTHOR]

Atmospheric pressure loading plays a crucial role in precise space geodesy, thus its omission, especially the nontidal loading (ANTL) part, leads to the inconsistency between solutions based on the microwave [Global Navigation Satellite Systems (GNSS)] and optical [satellite laser ranging (SLR)] observations. SLR observations are performed only during the cloudless conditions coincident with high values of air pressure that deforms the earth’s crust downward. The systematic shift of the estimated SLR station coordinates, which arises from the ANTL omission, is called the Blue-Sky effect. The offset is related to the long-term averaging of ANTL for SLR observations which are provided in sparse intervals, unlike GNSS, which observes continuously. Based on the ANTL model applied on SLR observations to GNSS, we determined the values of the Blue-Sky effect. The largest values of the Blue-Sky effect are observed for the inland stations, i.e., 2.3, 2.1, 2.0, and 1.9 mm for Svetloe, Potsdam, Baikonur, and Altay, respectively. We also investigate the impact of the omission of ANTL corrections on geodetic parameters, i.e., earth rotation parameters, geocenter motion, precise GNSS orbits, as well as on the global SLR network. The negligence of ANTL causes a systematic effect on geocenter coordinates with the amplitude of the annual signal at the level of 1.9 mm for the Z-component. The omission of ANTL corrections causes also a systematic shift of the multi-GNSS orbit constellation with the amplitude of the annual signal at the level of 2.7 mm for the Z-component. [ABSTRACT FROM AUTHOR]

In this paper, a closed-form mathematic equation that governs gas ingression of hermetic packages is derived from first principles and applied to moist air and water vapor ingression conditions. The equation models internal gas partial pressure change as a function of time, external conditions, and package characteristics. The equation provides the theoretical basis for direct comparisons of ingression behaviors of different gases into hermetic packages. Comparing the rates of internal air pressure increase due to air ingression and water vapor partial pressure buildup due to water vapor ingression, the authors theorize that vacuum decay may present a greater challenge to the performance of microelectromechanical systems (MEMS) devices within hermetic packages than that of water vapor content induced corrosion failures. This paper also examines gas ingression of hermetic enclosures with multiple layers of seals. [ABSTRACT FROM AUTHOR]

Determined from leader velocity, leader channel length is an important parameter in gas discharge calculations which helps in studying the voltage drop from the electrode and the electric field distribution in the gap. For comprehensive air-gap discharge studies, a pressure-adjustable test platform including an artificial climate chamber and a Mach–Zehnder laser interferometer was used. Discharge current waveforms, interference images, and luminescence images at air pressures ranging from 0.3 to 2 atm were obtained. A discharge initiates several stems simultaneously and the leader channels form significant branches during the discharge. At lower pressures, fewer stems formed simultaneously in the early discharge, but there were more main leader channels before gap breakdown. The reverse occurred at higher pressures. From recorded data, which was verified using high-speed cameras, the total discharge current was found distributed over several leader channels. The relationship between leader velocity and current is analyzed considering the branching, and a power-law function between the positive leader velocity and current is found. [ABSTRACT FROM AUTHOR]

The specific heat ratio of air is the key parameter in describing the hypersonic flow field. The existing search tables of its values indexed by temperature and air pressure are not suitable for hypersonic flow field calculation. Therefore, theoretical calculations of the hypersonic flow field set the specific heat ratio of air at a constant value resulting in large calculation errors in general. In this paper, a 2-D search table for the specific heat ratio of air based on velocity and height as search variables is proposed for hypersonic flow field calculations to replace the invalid temperature–pressure specific heat ratio of air. Taking the calculation of the stagnation temperature of the hypersonic flow field as an example, the theoretical calculation results and the measured data of the RAM-C hypersonic flight experiment are compared and discussed. A comparison of results shows that the proposed 2-D search table meets the computational requirements for hypersonic flow field calculations and provides a fast and accurate query database for the specific heat ratio of air and related parameters. [ABSTRACT FROM AUTHOR]

This paper proposes an all-in-one system for hyperloop that conducts propulsion, levitation, and guidance. Currently demand on high-speed long-distance transportation is increasing, so that hyperloop is getting attention and studied hard globally. Hyperloop is a new innovative transportation in which a levitated subsonic speed train travels through a vacuum cylindrical tube. Hyperloop needs functions of propulsion, levitation, and guidance for its service, and many devices are necessary for those functions. In the tube, a constrained space, many devices make the entire system complicated, and the size of the vehicle and tube are increased. Therefore, the costs of maintenance, manufacture, and construction are increased and control of each device becomes very difficult. But a non-symmetric double-sided linear induction motor (NSDLIM), the subject of this paper, is an all-in-one system that could conduct all functions. In this paper, the concept of NSDLIM was introduced and its possibility was suggested. Requirements of NSDLIM were investigated considering very high acceleration, velocity, and low air pressure. An NSDLIM model was designed and analyzed by using the finite-element method. Then, NSDLIM parameters that affect performance were investigated and adjusted to improve performance. The derived model performance was shown, and its possibility was considered. [ABSTRACT FROM AUTHOR]

The bare conductor in switchgear constitutes complicated air gaps, and their AC withstand characteristic will obviously affect switchgear insulation performance. In this paper, AC withstand tests of various types of air gap were carried out. The air gap samples were rod-plane air gap and 4 typical types of air gap from the bus chamber of 40.5 kV metal-enclosed switchgear. The samples were tested in climate chamber where high altitude environment was simulated. And correction of withstand voltage for switchgear air gaps at low air pressure were conducted. Test results indicate that, the withstand characteristic of 4 typical types of air gap in switchgear are different from that of rod-plane air gap. The relationship between withstand voltage Uw and air gap distance d is nonlinear. The influencing characteristic exponent n of air pressure on Uw is related with air gap type. Linearity value m and air pressure index n are independent to some degree. An equation was proposed to express the relationship of Uw with air gap distance d and altitude H, and this equation can be used to calculate the safety distance of air gaps in switchgear under low air pressure situations. The results are significant for the design and selection of switch devices. [ABSTRACT FROM PUBLISHER]

Most of the UHV transmission lines passed the high altitude and high humidity area. It was necessary to study the influence of air pressure and humidity on characteristics of flashover along the insulation surfaces. In the three-electrode arrangement, the characteristics of streamer propagation in air alone and along the silicone rubber surface were measured at Shenzhen, Kunming, and Yangbajing, respectively. The data of the streamer ?stability? propagation field and velocity were measured at the different air pressure and humidity. Empirical equations were presented expressing the effects of the air pressure and humidity on the streamer ?stability? propagation field and velocity. Furthermore, the variation of the streamer ?stability? propagation field and velocity with air pressure and humidity was analysed. The test results showed that the streamer stability propagation field was in proportion to air pressure or humidity. Under the same electric field, the streamer propagation velocity was in inverse proportion to air pressure or humidity. Therefore, it was easier for streamer propagation in the lower air pressure or humidity. Furthermore, the effect of the humidity and air pressure on stability fields of streamer propagation along silicone rubber surface was larger than that in air alone. [ABSTRACT FROM AUTHOR]

Results of experimental and computational study of the dynamics and structure of atmospheric-pressure air plasma jets formed by barrier discharge in a thin dielectric tube are presented. Formation of plasma bullet-guided streamers, moving along the jet with velocity varying in the range (1–3) $\times 10^{{\mathrm {7}}}$ cm \text{s}^{{\mathrm {-1}}} , is observed. Simulation, for conditions of the experiment, gives the streamer radius, velocity, and propagation length in reasonable agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A new tape–head design with surface cavities is presented as an alternative to the conventional skiving-edge flat-profile head design. The new head design is referred to as the vacuum head, inspired by the sub-ambient air pressure that develops in the surface cavities during operation. Two prototype head modules, a writer and a reader, were fabricated by modifying commercial tape–head modules and are compared with unmodified reference modules. A finite-element model is presented to simulate the head–tape interface and aid in the surface topography design of the vacuum head prototypes. The modeling results correspond qualitatively with experimental data from interferometer measurements of the shape of tape as it passes over the vacuum heads. The vacuum heads are operated successfully in data read/write experiments, with a slightly reduced signal-to-noise ratio performance compared with the reference heads. An indirect measure of head friction is obtained from tape velocity spectra that show a much reduced friction-induced compressional wave tape resonance for the vacuum modules compared with that for the reference modules. The results presented in this paper show that the new vacuum head design is a promising candidate for future heads with low friction, enabling the use of very smooth media for reduced magnetic spacing and increased areal densities. [ABSTRACT FROM PUBLISHER]

Air pressure affects the electrical performance of polluted insulator. The dc pollution flashover process of 7-unit XP-160 insulator string under low air pressure was presented by laboratory tests in this paper. During the tests, the flashover voltage and the critical flashover current were measured. Also, based on the insight of insulator flashover process, the length of discharge path, the arc propagation velocity and arc radius under different air pressure were investigated and measured. The research results indicate that, the position of arcing point is stochastic and multipoint arcing phenomenon exists. Surface arc will levitate and develop into air-gap arc under low air pressure. The length of discharge path is related to air pressure and pollution degree, and it is always shorter than the total creepage of insulator string. The leakage current, the arc shape and arc propagation velocity, are also related to air pressure. In this study, it was measured that the arc radius (ra) varied from 1.5 to 3.5 mm, and the characteristic exponent describing the influence of air pressure on arc radius (m) varied from -0.35 to -0.65. The research results are of some significance for revealing the mechanism of flashover and discharge performance of arcs. [ABSTRACT FROM AUTHOR]

This paper introduces a new configuration in the compressed air production, which aims for a more efficient energy layout and innovative air network control and feeding. The target is achieved by applying a real-time earliest-deadline-first (EDF) scheduling technique to the management of the air production and delivery, seen as an energy service. The control action in a closed loop is applied to the activation/deactivation of valves, delivering air to networks operating at different pressure levels. The new configuration deals with a single compressor, which has a fixed speed and is electrically driven, and a centralized type of production, which is an alternative and is more efficient to a decentralized one. A set of suitably controlled valves intercepts air at the desired pressure level and feeds the networks while their operation guarantees that each pressure level is kept inside safe ranges. The algorithm integrates with a previous work. Future developments are also anticipated. [ABSTRACT FROM AUTHOR]

Pressure is an important factor for the effect of the medium in the process of the electrical explosion of wire in air. In this paper, the electrical explosions of copper and aluminum wires at different air pressures in the range of subatmospheric pressure were investigated with pulsed voltage in a submicrosecond time scale. Based on the measurements of the current and voltage in wire explosion with a current monitor and a high-voltage probe, respectively, the deposited energy in the stages of melting, liquid state, and vaporization was calculated by mathematical methods. The effect of air pressure on deposited energy in the three stages mentioned above was analyzed by experiments and calculation. The results show that the breakdown field strength varied with air pressure, and plays a vital role in energy deposition and the time of duration in the vaporization stage. In addition, the exothermic reaction of Al microparticles and surrounding air also has an important effect on the energy deposition in the vaporization stage. The deposited energy in the electrical explosion of copper and aluminum wire is higher at the higher air pressure, particularly after the beginning of vaporization. [ABSTRACT FROM PUBLISHER]

The air breakdown driven by the high-power microwave radiated from the circular waveguide is investigated using the 2-D fluid model. We focus on the case of the air pressure higher than 100 torr, and therefore neglect the electron diffusion loss to the wall in the fluid model. A proper numerical scheme for the finite-difference time-domain method is developed to solve the fluid model. The results show that the air breakdown mainly occurs near the dielectric window due to the high electric field, and the generated nonuniform plasma causes significant attenuation in the radiated field. The wave reflection by the air plasma, far larger than the plasma absorbtion, attenuates the transmitted power significantly at low pressures, while at high pressures, the plasma absorbtion plays a major role in the transmitted power loss. The accuracy of the fluid model is validated by comparing with the reported experimental results. [ABSTRACT FROM AUTHOR]

The corona discharge process in a point-plane structure has been simulated using the 3-D particle-in-cell code VORPAL. The motivation behind these simulations was to understand how the corona needle worked in the gas switch, and to look for the methods to improve the stability of the gas switch by achieving a steady corona discharge. The influences of three parameters on ionization region were investigated, the needle size, the gas pressure, and the voltage applied across the electrodes. The needle size varied from 0.05 to 0.25 mm, the air pressure varied from 1.0 to 3.0 atm and the applied voltage varied from 1.2 to 2.3 kV. The voltage polarity was also changed. From the simulations, we obtained the electric field distribution, the distribution of the ionization region, and the current–voltage characteristic. All these parameters have an effect on the corona. Different voltage polarity would result in a different corona shape. Unlike the voltage polarity, the needle size, the air pressure, and the applied voltage have no effect on the shape of the corona. However, with an increase in needle size, or applied voltage, the corona size will also increase, while the corona size will decrease when the air pressure increases. The degree of influence is different; that of the applied voltage is the highest followed by the needle size, while that of the air pressure is the lowest. [ABSTRACT FROM AUTHOR]

We study the plasma discharge initiated by microwave radiation with stochastically jumping phase (MWRSJP) in a coaxial waveguide at the optimal mode of the beam-plasma generator. Present results continue the line of the previous research. In this paper, the conditions of a microwave discharge ignition, its stable maintenance in air by MWRSJP, and the pressure range at which required power is minimal are found. We also experimentally examine optical characteristics of the discharge plasma in a wide range of air pressure. In general, the research aims to develop a new type of sources of optical radiation. [ABSTRACT FROM PUBLISHER]

The Wells turbine is a bidirectional air turbine which operates efficiently over a restricted range of air flow. The optimization of its efficiency requires control of rotational velocity in order to maintain the ratio between airflow and tip speed within the high efficiency range. This paper introduces two generator control strategies that optimize the power take-off efficiency for low inertia turbine systems in which instantaneous control of the turbine air flow to tip speed ratio is a realistic goal. The first control strategy requires measurement of turbine rotational speed and air chamber pressure, and the second strategy removes the requirement for air pressure measurement. The implementation issues associated with this level of control are examined and the simulation results are validated in an experimental test rig. [ABSTRACT FROM AUTHOR]

This paper examines the direct current (DC) icing flashover performance of typical DC porcelain, glass, and composite insulators in a complex environment of high altitude, icing, and pollution. The effects of the insulator string length, ice thickness, pollution level, freezing water conductivity, air pressure, and arrangement of insulator strings on the DC icing flashover performance are analyzed, and the correction formula for the DC icing flashover voltage is obtained. The DC flashover process of ice-covered insulators at high altitude is classified into dynamic changes of surface arcs, air-gap arcs, and residual resistance of the ice layer, as observed through a high-speed camera, and a DC flashover circuit model explaining the flashover performance for ice-covered insulators at high altitude is established. [ABSTRACT FROM PUBLISHER]

A six-stage gas switch developed for linear transformer drivers is presented in this paper. The switch features an easy-handling structure consisting of stackable cylindrical insulators and brimmed toroidal electrodes. Following an electrode conditioning procedure, the switch and one of its gaps undergo self-breakdown tests by which normal distribution parameters of the self-breakdown voltage at each experimental air pressure are determined. Assuming that all gaps are the same, the switch's voltage with a 50% self-breakdown probability is predicted as the summed voltage of six gaps which individually have a 10.9% self-breakdown probability of voltage being calculated by using the experimentally determined normal function. The calculated result is 7–14 kV higher than the measured voltage because of a nonuniform voltage distribution which is later confirmed by using unequal gaps. For a more uniform voltage distribution, electrodes are revised to suppress corona discharge, and this revision has finally increased the switch hold-off voltage by 4–6 kV, which is the same as a resistive divider. [ABSTRACT FROM PUBLISHER]

The development of a three-electrode trigatron gap with the trigger electrode inside the main electrode is discussed in this paper. Two models of the operation mechanism are proposed to explain the breakdown in the trigatron gap. In addition, a mathematical model was proposed to calculate the breakdown time based on the theoretical analysis. The influence of different parameters on the breakdown time is discussed. Some characteristics in dry air have been experimentally determined such as the influence of the air pressure and the influence of the undervoltage ratio on the spark gap operation. The experimental results show that the operating voltage range between 0.5 and 0.7 might be reasonable. Then, the experimental results and analysis demonstrate that there are three regions divided by two inflection points, and the corresponding values of the undervoltage ratio are threshold values presenting different breakdown processes. [ABSTRACT FROM PUBLISHER]

This paper studies the air bearing features on discrete track media by very small mesh size. The mesh size is only 5 nm, and it allows to study the air bearing characteristics of a small square pad flying on discrete track media with sub-micrometer groove pitch. The air bearing spikes and the flying height loss are calculated and discussed. It is observed that the air bearing spikes exist mainly on discrete track media with groove pitches of micrometer level. When the groove pitch is smaller than 0.3 \mum, the air bearing cannot “see” the grooves clearly, and the air bearing pressure profile is smooth generally. For groove pitch of micrometer level, the surface with a larger groove pitch provides a stronger air bearing force, if the groove depth and the groove ratio are fixed. For sub-micrometer groove pitches, the air bearing force is approximately independent of the pitch size. [ABSTRACT FROM AUTHOR]

Although current technique of photoplethysmography (PPG) is a popular noninvasive method of waveform contour analysis in assessing arterial stiffness, data obtained are frequently affected by various environmental and physiological factors. We proposed an easily operable air pressure sensing system (APSS) for radial arterial signal capturing. Totally, 108 subjects (young, the aged with or without diabetes) were recruited from July 2009 to May 2010. Arterial waveform signals from the wrist were obtained and analyzed using Hilbert–Huang transformation (HHT). Through ensemble empirical mode decomposition (EEMD), the signals were decomposed into eight intrinsic mode functions (IMF1–8) of which IMF5 was found to be the desired signal with a discernible diastolic peak. The results showed significant differences in reflection index (RI) and stiffness index (SI) from the young subjects and those from the aged participants with or without diabetes. Significant differences in RI and SI were also noted between subjects with well-controlled diabetes and those without. Good reproducibility and correlation were demonstrated. In conclusion, the present study proposed the application of radial arterial signal capturing subsystem and HHT in acquiring more reliable data on RI and SI compared with the conventional PPG method. [ABSTRACT FROM AUTHOR]