scholarly journals The Nanosecond Impulsive Breakdown Characteristics of Air, N2 and CO2 in a Sub-mm Gap

Plasma ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 12-29
Author(s):  
Ting Liu ◽  
Igor Timoshkin ◽  
Mark P. Wilson ◽  
Martin J. Given ◽  
Scott J. MacGregor
Keyword(s):  
Breakdown Voltage ◽  
Rise Time ◽  
Breakdown Field ◽  
Number Density ◽  
Electrode Gap ◽  
Scaling Relationships ◽  
Wide Range ◽  
Gas Pressures

The present paper investigates the breakdown characteristics—breakdown voltage, with breakdown occurring on the rising edge of the applied HV impulses, and time to breakdown—for gases of significance that are present in the atmosphere: air, N2 and CO2. These breakdown characteristics have been obtained in a 100 µm gap between an HV needle and plane ground electrode, when stressed with sub-µs impulses of both polarities, with a rise time up to ~50 ns. The scaling relationships between the reduced breakdown field Etip/N and the product of the gas number density and inter-electrode gap, Nd, were obtained for all tested gases over a wide range of Nd values, from ~1020 m−2 to ~1025 m−2. The breakdown field-time to breakdown characteristics obtained at different gas pressures are presented as scaling relationships of Etip/N, Nd, and Ntbr for each gas, and compared with data from the literature.

Combining First-Principles and Data Modeling for the Accurate Prediction of the Refractive Index of Organic Polymers

2017 ◽  
Author(s):  
Mohammad Atif Faiz Afzal ◽  
Chong Cheng ◽  
Johannes Hachmann
Keyword(s):  
First Principles ◽  
Data Modeling ◽  
Accurate Prediction ◽  
Index Of Refraction ◽  
Structure Theory ◽  
Organic Polymers ◽  
Number Density ◽  
Lorenz Equation ◽  
In Silico Studies ◽  
Wide Range

Organic materials with a high index of refraction (RI) are attracting considerable interest due to their potential application in optic and optoelectronic devices. However, most of these applications require an RI value of 1.7 or larger, while typical carbon-based polymers only exhibit values in the range of 1.3–1.5. This paper introduces an efficient computational protocol for the accurate prediction of RI values in polymers to facilitate in silico studies that an guide the discovery and design of next-generation high-RI materials. Our protocol is based on the Lorentz-Lorenz equation and is parametrized by the polarizability and number density values of a given candidate compound. In the proposed scheme, we compute the former using first-principles electronic structure theory and the latter using an approximation based on van der Waals volumes. The critical parameter in the number density approximation is the packing fraction of the bulk polymer, for which we have devised a machine learning model. We demonstrate the performance of the proposed RI protocol by testing its predictions against the experimentally known RI values of 112 optical polymers. Our approach to combine first-principles and data modeling emerges as both a successful and highly economical path to determining the RI values for a wide range of organic polymers.

scholarly journals Influence from cosmological uncertainties on galaxy number count at faint limit

2015 ◽  
Vol 30 (28) ◽  
pp. 1550139
Author(s):  
Keji Shen ◽  
Qiang Zhang ◽  
Xin-He Meng
Keyword(s):  
Galaxy Evolution ◽  
Number Density ◽  
Number Count ◽  
Density Prediction ◽  
Evolution Pattern ◽  
Wide Range ◽  
Different Types ◽  
Physical Cosmology ◽  
Cosmology Observations ◽  
Near Future

Counting galaxy number density with wide range sky surveys has been well adopted in researches focusing on revealing evolution pattern of different types of galaxies. As understood intuitively the astrophysics environment physics is intimately affected by cosmology priors with theoretical estimation or vice versa, or simply stating that the astrophysics effect couples the corresponding cosmology observations or the way backwards. In this paper, we try to quantify the influence on galaxy number density prediction at faint luminosity limit from the uncertainties in cosmology, and how much the uncertainties blur the detection of galaxy evolution, with the hope that this trying may indeed help for precise and physical cosmology study in near future or vice versa.

Harmonic Coefficients of Engine Torque Curves

1943 ◽  
Vol 10 (1) ◽  
pp. A33-A48
Author(s):  
Frederic P. Porter
Keyword(s):  
Diesel Engines ◽  
Combined Effects ◽  
Connecting Rod ◽  
Engine Torque ◽  
Wide Range ◽  
Inertia Forces ◽  
Gas Pressures

Abstract Engine torque curves depend upon the combined effects of gas pressures, inertia forces, and weights. Tables for the harmonic coefficients of the torque due to inertia and weight effects are given for a wide range of crank-to-connecting-rod ratios. Families of indicator diagrams, representative of various types of engines, are shown and tables of the harmonic coefficients of the resulting torques are given. The types of engines considered are two-cycle gas, semi-Diesel, single-acting Diesel, double-acting Diesel, two-shaft opposed-piston Diesel, and four-cycle gasoline and Diesel engines.

scholarly journals A Computational Survey of Semiconductors for Power Electronics

2019 ◽  
Author(s):  
Prashun Gorai ◽  
Robert McKinney ◽  
Nancy Haegel ◽  
Andriy Zakutayev ◽  
Vladan Stevanovic
Keyword(s):  
Thermal Conductivity ◽  
Power Electronics ◽  
Figure Of Merit ◽  
Large Scale ◽  
Lattice Thermal Conductivity ◽  
Consumer Products ◽  
Breakdown Field ◽  
Experimental Investigations ◽  
Wide Range ◽  
Screening Parameter

Power electronics (PE) are used to control and convert electrical energy in a wide range of applications from consumer products to large-scale industrial equipment. While Si-based power devices account for the vast majority of the market, wide band gap semiconductors such as SiC, GaN, and Ga2O3 are starting to gain ground. However, these emerging materials face challenges due to either non-negligible defect densities, or high synthesis and processing costs, or poor thermal properties. Here, we report on a broad computational survey aimed to identify promising materials for future power electronic devices beyond SiC, GaN, and Ga2O3. We consider 863 oxides, sulfides, nitrides, carbides, silicides, and borides that are reported in the crystallographic database and exhibit finite calculated band gaps. We utilize ab initio methods in conjunction with models for intrinsic carrier mobility, and critical breakdown field to compute the widely used Baliga figure of merit. We also compute the lattice thermal conductivity as a screening parameter. In addition to correctly identifying known PE materials, our survey has revealed a number of promising candidates exhibiting the desirable combination of high figure of merit and high lattice thermal conductivity, which we propose for further experimental investigations.

scholarly journals Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model

2014 ◽  
Vol 14 (23) ◽  
pp. 13013-13022 ◽  
Author(s):  
D. M. Murphy
Keyword(s):  
Temperature Dependence ◽  
Low Temperatures ◽  
Ice Crystals ◽  
Strong Increase ◽  
Number Density ◽  
Dimensional Model ◽  
One Dimensional ◽  
Slow Growth Rate ◽  
Wide Range ◽  
The One

Abstract. A parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possible small spread in the homogeneous freezing threshold due to varying particle composition is identified as a sensitive nucleation parameter. In a parcel model, the slow growth rate of ice crystals at low temperatures inherently leads to a strong increase in ice number density at low temperatures. This temperature dependence is not observed. The model temperature dependence occurs for a wide range of assumptions and for either homogeneous or, less strongly, heterogeneous freezing. However, the parcel model also shows that random temperature fluctuations result in an extremely wide range of ice number densities. A one-dimensional model is used to show that the rare temperature trajectories resulting in the lowest number densities are disproportionately important. Low number density ice crystals sediment and influence a large volume of air. When such fall streaks are included, the ice number becomes less sensitive to the details of nucleation than it is in a parcel model. The one-dimensional simulations have a more realistic temperature dependence than the parcel mode. The one-dimensional model also produces layers with vertical dimensions of meters even if the temperature forcing has a much broader vertical wavelength. Unlike warm clouds, cirrus clouds are frequently surrounded by supersaturated air. Sedimentation through supersaturated air increases the importance of any process that produces small numbers of ice crystals. This paper emphasizes the relatively rare temperature trajectories that produce the fewest crystals. Other processes are heterogeneous nucleation, sedimentation from the very bottom of clouds, annealing of disordered to hexagonal ice, and entrainment.

scholarly journals On the observed energy of runaway electron beams in air

2011 ◽  
Vol 29 (4) ◽  
pp. 425-435 ◽  
Author(s):  
G.A. Mesyats ◽  
A.G. Reutova ◽  
K.A. Sharypov ◽  
V.G. Shpak ◽  
S.A. Shunailov ◽  
...  
Keyword(s):  
Electric Field ◽  
Runaway Electron ◽  
Electron Beams ◽  
Beam Current ◽  
Acceleration Of Particles ◽  
Runaway Electrons ◽  
Electrode Gap ◽  
Cathode Voltage ◽  
Wide Range ◽  
Widespread Belief

AbstractExperiments with an air electrode gap have been performed where the current/charge of a picosecond beam of runaway electrons was measured over a wide range (up to four orders of magnitude) downstream of the absorbing foil filters. Measurements and calculations have made it possible to refer the beam current to the rise time of the accelerating voltage pulse to within picoseconds. It has been shown that, in contrast to a widespread belief, the runaway electron energies achieved are no greater than those corresponding to the mode of free acceleration of electrons in a nonstationary, highly nonuniform electric field induced by the cathode voltage. The experimental data agree with predictions of a numerical model that describes free acceleration of particles. It has been confirmed that the magnitude of the critical electric field that is necessary for electrons to go into the mode of continuous acceleration of electrons in atmospheric air corresponds to classical notions.

BREAKDOWN OF A RADIO-FREQUENCY DISCHARGE IN THE PRESENCE OF A SUPERIMPOSED d-c. FIELD

1965 ◽  
Vol 43 (8) ◽  
pp. 1543-1551 ◽  
Author(s):  
S. N. Sen ◽  
B. Bhattacharjee
Keyword(s):  
Radio Frequency ◽  
Breakdown Voltage ◽  
Experimental Results ◽  
Breakdown Field ◽  
Theoretical Expression ◽  
Rare Gases ◽  
Field Frequency ◽  
Radio Frequency Field ◽  
Frequency Field ◽  
Positive Ions

Breakdown voltages have been determined in the case of some rare gases (He, Ne, A) and oxygen at a constant pressure (10 mm Hg) when excited simultaneously by a radio-frequency field (frequency 10 Mc/sec) and a variable d-c. field. It is found in all cases that the breakdown voltage is higher when both the fields are present than when the gases are excited by the radio-frequency field alone and the breakdown voltage gradually increases with the increase of the applied d-c. field. The variation of breakdown field with d-c. field is of the same nature in all of the gases studied. A theoretical expression for the breakdown voltage in the presence of both the r-f. and d-c. fields has been deduced from the theory of electrical discharge by Kihara (1952) together with the expression of equivalent length as deduced by Varnerin and Brown (1950). The theoretical expression cannot explain satisfactorily the experimental results, and the rate of rise of breakdown voltage in the d-c. field as obtained from theory is smaller than that obtained from experimental results. The discrepancy has been ascribed partly to the uncertainty in the values of the numerical constants introduced by Kihara and also to the increase of diffusion caused by the presence of positive ions—a factor which has not been taken into consideration in the present treatment.

4H-SiC Bipolar Junction Transistors with a Current Gain of 108

2008 ◽  
Vol 600-603 ◽  
pp. 1159-1162 ◽  
Author(s):  
Q. Jon Zhang ◽  
Charlotte Jonas ◽  
Albert A. Burk ◽  
Craig Capell ◽  
Jonathan Young ◽  
...  
Keyword(s):  
High Temperatures ◽  
Breakdown Voltage ◽  
Current Gain ◽  
Bipolar Junction Transistors ◽  
High Current ◽  
Emitter Current ◽  
Wide Range ◽  
Operating Temperatures ◽  
A Current

4H-SiC BJTs with a common emitter current gain (b) of 108 at 25°C have been demonstrated. The high current gain was accomplished by using a base as thin as 0.25 μm. The current gain decreases at high temperatures but is still greater than 40 at 300°C. The device demonstrates an open emitter breakdown voltage (BVCBO) of 1150 V, and an open base breakdown voltage (BVCEO) of 250 V. A low specific on-resistance of 3.6 mW-cm2 at 25°C was achieved. The BJTs have shown blocking capabilities over a wide range of operating temperatures up to 300°C.

scholarly journals Measurement of Some Argon Plasma Parameters Glow Discharge Under Axial Magnetic Field

2019 ◽  
Vol 7 (4) ◽  
pp. 158-166
Author(s):  
Pshtiwan M.A. Karim ◽  
Diyar S. Mayi ◽  
Shamo Kh. Al-Hakary
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Glow Discharge ◽  
Electron Temperature ◽  
Breakdown Voltage ◽  
Axial Magnetic Field ◽  
Argon Plasma ◽  
Emission Lines ◽  
Plasma Parameters ◽  
Gas Pressures

This paper investigates the characteristics some of argon plasma parameters of glow discharge under axial magnetic field. The DC power supply of range (0-6000) V is used as a breakdown voltage to obtain the discharge of argon gas. The discharge voltage-current (V-I) characteristic curves and Paschen’s curves as well as the electrical conductivity were studied with the presents of magnetic field confinement at different gas pressures. The magnetic field up to 25 mT was obtained using four coils of radius 6 cm and 320 turn by passing A.C current up to 5 Amperes. Spectroscopic measurements are employed for purpose of estimating two main plasma parameters electron temperature (Te) and electron density (ne). Emission spectra from positive column (PC) zone of the discharge have been studies at different values of magnetic field and pressures at constant discharge currents of 1.5 mA. Electron temperature (Te) and its density are calculated from the ratio of the intensity of two emission lines of the same lower energy levels. Experimental results show the abnormal glow region characteristics (positive resistance). Breakdown voltage versus pressure curves near the curves of paschen and decrease as magnetic field increases due to magnetic field confinement of plasma charged particles. Also the electrical conductivity increases due to enhancing magnetic field at different gas pressures. Both temperature density of electron and the intensities of two selected emission lines decrease with increasing pressure due decreasing of mean free path of electron. Electron density increase according to enhancing magnetic field, while the intensity of emitting lines tends to decrease.

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