The impulse breakdown voltage and time-lag characteristics of long gaps in air II. The negative discharge

1964 ◽  
Vol 256 (1069) ◽  
pp. 213-234 ◽  
Keyword(s):  
Wave Front ◽  
Breakdown Voltage ◽  
Breakdown Strength ◽  
Time Lag ◽  
Time Lags ◽  
Impulse Wave ◽  
Time Resolved ◽  
Wide Range ◽  
Negative Impulse ◽  
Long Time

Oscillographic measurement and time-resolved photographic recording have been used to examine the breakdown of rod/rod, rod/sphere and rod/plane gaps with long-duration negative impulse potentials of up to 1 MV crest. As in the positive discharge, the breakdown process is found often to cease for considerable periods on the impulse wave tail. Breakdown then occurs after a long time lag for gaps composed of rod cathodes and rod or small sphere anodes. Where the anode is large, no long time lags are observed. Measurement of the variation of breakdown strength with time during the impulse duration has been made by the superimposition of a second impulse upon the first, following a controllable delay. The results show a minimum probability of breakdown initiation after 15 μs of the applied impulse, and a subsequent slow recovery. It is suggested that this confirms the effect of the initial corona phase in causing space charge fouling of the gap. The breakdown voltage of rod/rod gaps is shown to decrease by up to 30 % when the impulse wave front is reduced from 0.50 to 0.06 μs. The breakdown strength with negative impulses is thus less than with positive impulses for wave fronts faster than 0.20 μs. For the wave form 0.50/2000 μs, the breakdown voltage is found to depend more critically upon the dimensions of the earthed electrode than is the case with positive impulses. The breakdown voltage for a rod/25 cm sphere gap is 73 % greater than for a rod/rod gap, yet also 15 % greater than for a rod/plane gap. For gap lengths between 25 and 65 cm, the breakdown voltage of the rod/plane gap is found to increase with decreasing wave front duration. The variation of the negative impulse corona with rate of potential rise and with crest voltage is examined photographically. Many of the observed variations of breakdown voltage and time-lag characteristics can be accounted for in terms of the impulse corona phase. The time-resolved photography of the negative discharge over a wide range of conditions suggests that in the range of gap lengths investigated the formation of the positive leader rather than the negative leader is the necessary forerunner of sparkover.

The impulse breakdown voltage and time-lag characteristics of long gaps in air I. The positive discharge

1964 ◽  
Vol 256 (1069) ◽  
pp. 185-212 ◽  
Keyword(s):  
Space Charge ◽  
Wave Front ◽  
Breakdown Voltage ◽  
Breakdown Strength ◽  
Electrical Breakdown ◽  
Time Lag ◽  
Short Wave ◽  
Time Lags ◽  
Long Time ◽  
Statistical Time

The electrical breakdown of rod/rod, rod/sphere and rod/plane gaps in the atmosphere has been examined oscillographically and photographically. Positive polarity impulse potentials of crest value up to 1 MV, of wave-front variable between 0.06 and 2.0 μs and of wave tail 2 ms were used. It has been found that the lack of a sharply defined breakdown potential was due to the existence of long time lags quite distinct from the shorter times to breakdown observed with the conventional short wave-tail impulse. A ‘ dead-time ’ of low probability of breakdown on the wave tail separated the two classes of breakdown. The breakdown voltage of a rod/rod gap has been found to be dependent upon the wave front of the impulse. An accompanying photographic examination of the initial corona phase of breakdown also revealed a variation with the impulse voltage wave front. It is shown that these results were consistent with the electric field distortion arising from space charge. The corona phase of breakdown was responsible for this space charge. The statistical behaviour of long gap breakdown was due to random variations in the corona phase. The effect of the statistical time lag in the production of initiatory electrons upon the corona phase is discussed. A rotating-mirror camera of f/1.0 aperture and a technique for controlled suppression of the breakdown enabled the growth of the discharge with time to be studied in some detail. It was shown that the positive leader either preceded or was coincident with the negative leader, depending upon the gap arrangement. It is concluded that the establishment of the leader at the high-tension electrode is the criterion for breakdown. The role of the earthed cathode in aiding this leader development was dependent upon its size and geometry. For cathodes of small dimensions the occurrence of a negative corona phase increased the anode electric gradient; for large cathodes the surface charge induced by the anode corona discharge became important. The variation of breakdown strength with gap geometry is accountable in these terms.

Non-Gaussian probability distributions of solar wind fluctuations

1994 ◽  
Vol 12 (12) ◽  
pp. 1127-1138 ◽  
Author(s):  
E. Marsch ◽  
C. Y. Tu
Keyword(s):  
Solar Wind ◽  
Probability Distributions ◽  
Time Lag ◽  
Small Scale ◽  
Time Lags ◽  
Mhd Turbulence ◽  
Theoretical Concepts ◽  
Fluid Turbulence ◽  
Long Time ◽  
Non Gaussian

Abstract. The probability distributions of field differences ∆x(τ)=x(t+τ)-x(t), where the variable x(t) may denote any solar wind scalar field or vector field component at time t, have been calculated from time series of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is found that for comparatively long time lag τ, ranging from a few hours to 1 day, the differences are normally distributed according to a Gaussian. For shorter time lags, of less than ten minutes, significant changes in shape are observed. The distributions are often spikier and narrower than the equivalent Gaussian distribution with the same standard deviation, and they are enhanced for large, reduced for intermediate and enhanced for very small values of ∆x. This result is in accordance with fluid observations and numerical simulations. Hence statistical properties are dominated at small scale τ by large fluctuation amplitudes that are sparsely distributed, which is direct evidence for spatial intermittency of the fluctuations. This is in agreement with results from earlier analyses of the structure functions of ∆x. The non-Gaussian features are differently developed for the various types of fluctuations. The relevance of these observations to the interpretation and understanding of the nature of solar wind magnetohydrodynamic (MHD) turbulence is pointed out, and contact is made with existing theoretical concepts of intermittency in fluid turbulence.

scholarly journals The relationship between meteorological variables and sporadic cases of Legionnaires' disease in residents of England and Wales

2014 ◽  
Vol 142 (11) ◽  
pp. 2352-2359 ◽  
Author(s):  
K. D. HALSBY ◽  
C. A. JOSEPH ◽  
J. V. LEE ◽  
P. WILKINSON
Keyword(s):  
Conditional Logistic Regression ◽  
Time Lag ◽  
Time Lags ◽  
England And Wales ◽  
Long Time ◽  
Sporadic Cases ◽  
Risk Of Disease ◽  
Legionnaires Disease ◽  
Short Time ◽  
The Relationship

SUMMARYWe studied the timing of occurrence of 1676 sporadic, community-acquired cases of Legionnaires' disease in England and Wales between 1993 and 2008, in relation to temperature, relative humidity, rainfall, windspeed and ultraviolet light using a fixed-stratum case-crossover approach. The analysis was conducted using conditional logistic regression, with consideration of appropriate lag periods. There was evidence of an association between the risk of Legionnaires' disease and temperature with an apparently long time lag of 1–9 weeks [odds of disease at 95thvs. 75th centiles: 3·91, 95% confidence interval (CI) 2·06–7·40], and with rainfall at short time lags (of 2–10 days) (odds of disease at 75thvs.50th centiles: 1·78, 95% CI 1·50–2·13). There was some evidence that the risk of disease in relation to high temperatures was greater at high relative humidities. A higher risk of Legionnaires' disease may be indicated by preceding periods of warmer wetter weather.

scholarly journals Preparation of Three Types of Transformer Oil-Based Nanofluids and Comparative Study on the Effect of Nanoparticle Concentrations on Insulating Property of Transformer Oil

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Qi Wang ◽  
Muhammad Rafiq ◽  
Yuzhen Lv ◽  
Chengrong Li ◽  
Kai Yi
Keyword(s):  
Thermal Properties ◽  
Comparative Study ◽  
Breakdown Voltage ◽  
Breakdown Strength ◽  
Transformer Oil ◽  
Standard Methods ◽  
Maximum Value ◽  
Negative Impulse ◽  
The Difference

Nanofluids have the potential to become the alternatives of conventional transformer oil for their exquisite electrical and thermal properties. Three kinds of nanoparticles with distinct conductivities, namely, nonconductive nanoparticle Al2O3, conductive nanoparticle Fe3O4, and semiconductive nanoparticle TiO2, with different concentrations from 5% to 40% w/v were selected and suspended into transformer oil to develop nanofluids. The lightening impulse breakdown strengths of the oil samples with and without nanoparticles were measured according to IEC standard methods. The positive impulse breakdown strength indicated that breakdown strength is first increased up to the maximum value at certain concentration and then starts decreasing. The results of negative impulse breakdown manifested that the breakdown voltages of nanofluids with different concentrations were less than the breakdown voltage of pure transformer oil. Different effect mechanisms of dielectric and conductive nanoparticles were also used to describe the difference among three prepared nanofluids.

scholarly journals Synchronization of Independent Neural Ensembles in Human EEG during Choice Tasks

2019 ◽  
Vol 9 (12) ◽  
pp. 132
Author(s):  
Alexander Zaleshin ◽  
Galina Merzhanova
Keyword(s):  
Time Lag ◽  
Individual Characteristics ◽  
Situational Factors ◽  
Time Lags ◽  
Risk Averse ◽  
Behavioral Experiments ◽  
Neural Ensembles ◽  
Long Time ◽  
Beta Rhythms ◽  
Alpha Beta

During behavioral experiments, humans placed in a situation of having to choose between a more valuable but risky reward and a less valuable but guaranteed reward make their decisions in accordance with external situational factors and individual characteristics, such as inclination to risk or caution. In such situations, humans can be divided into “risk-inclined” and “risk-averse” (or “cautious”) subjects. In this work, characteristics of EEG rhythms, such as phase–phase relationships and time lags between rhythms, were studied in pairs of alpha–beta and theta–beta rhythms. Phase difference can also be expressed as a time lag. It has been suggested that statistically significant time lags between rhythms are due to the combined neural activity of anatomically separate, independent (in activation/inhibition processes) ensembles. The extents of synchronicity between rhythms were compared as percentages between risk-inclined and risk-averse subjects. The results showed that synchronicity in response to stimuli was more often observed in pairs of alpha–beta rhythms of risk-averse subjects compared with risk-inclined subjects during the choice of a more valuable but less probable reward. In addition, significant differences in the percentage ratio of alpha and beta rhythms were revealed between (i) cases of synchronization without long time lags and (ii) cases with long time lags between rhythms (from 0.08 to 0.1 s).

scholarly journals Flame Transfer Functions and Dynamics of a Closely Confined Premixed Bluff Body Stabilised Flame With Swirl

2020 ◽  
Author(s):  
Håkon T. Nygård ◽  
Nicholas A. Worth
Keyword(s):  
Time Scales ◽  
Equivalence Ratio ◽  
Bluff Body ◽  
Transfer Functions ◽  
Time Lag ◽  
Operating Conditions ◽  
Flame Height ◽  
Time Lags ◽  
Temporal Shift ◽  
Wide Range

Abstract The Flame Transfer Function (FTF) and flame dynamics of a single, highly swirled, closely confined, premixed flame is studied over a wide range of operating conditions at a fixed perturbation level at the dump plane. The equivalence ratio and bulk velocity are varied in order to examine the important ratio of flame height to velocity in scaling the flame response function. The enclosure geometry is kept constant, and therefore due to the close confinement and varying flame height, strong flame-wall interactions are present for some operating conditions. The effect of these interactions on the FTF due to changes in the “relative” or “effective confinement” of the flame can therefore be studied. When the equivalence ratio is sufficiently high, and therefore the effective confinement sufficiently small, modulations, or dips, in the gain and phase of the FTF are observed, due to interference of the perturbations created at the swirler and at the dump plane. Due to the small length scales and relatively high velocities in the current configuration, the dip is at a high frequency and spans a wide range of frequencies compared to similar studies which have previously identified similar phenomena. It is also observed that when the equivalence ratio was decreased, increasing the effective confinement, a critical point is reached where the modulations are suppressed. This is linked to a temporal shift in the heat release rate at the downstream location where the flame impinges on the combustion chamber walls during the oscillation cycle. The shift causes a decrease in the expected level of interference, demonstrating that the effective confinement is an important parameter to consider for the nature of the FTF response. Additionally, a Distributed Time Lag (DTL) model with two distinct time lags, capturing the swirler perturbations and the perturbations at the inlet, is successfully applied to the FTFs. The model provides a simple way to accurately capture the two dominant time scales in the problem without the need of prior knowledge of the cause of the perturbations, and a simple expression to recreate the complex valued FTF. In addition the model also provides insight into the time scales of the problem, demonstrating in the current work that time scales recovered from the DTL analysis are offset from simple Strouhal number scaling, due to the effects of increasing effective confinement.

Long Short-Term Memory

1997 ◽  
Vol 9 (8) ◽  
pp. 1735-1780 ◽  
Author(s):  
Sepp Hochreiter ◽  
Jürgen Schmidhuber
Keyword(s):  
Short Term Memory ◽  
Constant Error ◽  
Time Lag ◽  
Back Propagation ◽  
Time Lags ◽  
Short Term ◽  
Time Step ◽  
Term Memory ◽  
Long Time ◽  
Long Short Term Memory

Learning to store information over extended time intervals by recurrent backpropagation takes a very long time, mostly because of insufficient, decaying error backflow. We briefly review Hochreiter's (1991) analysis of this problem, then address it by introducing a novel, efficient, gradient based method called long short-term memory (LSTM). Truncating the gradient where this does not do harm, LSTM can learn to bridge minimal time lags in excess of 1000 discrete-time steps by enforcing constant error flow through constant error carousels within special units. Multiplicative gate units learn to open and close access to the constant error flow. LSTM is local in space and time; its computational complexity per time step and weight is O. 1. Our experiments with artificial data involve local, distributed, real-valued, and noisy pattern representations. In comparisons with real-time recurrent learning, back propagation through time, recurrent cascade correlation, Elman nets, and neural sequence chunking, LSTM leads to many more successful runs, and learns much faster. LSTM also solves complex, artificial long-time-lag tasks that have never been solved by previous recurrent network algorithms.

scholarly journals Flame Transfer Functions and Dynamics of a Closely Confined Premixed Body Stabilised Flame with Swirl

2021 ◽  
Author(s):  
Håkon Tormodsen Nygård ◽  
Nicholas Worth
Keyword(s):  
Transfer Functions ◽  
Time Lag ◽  
Operating Conditions ◽  
Flame Height ◽  
Time Lags ◽  
Simple Method ◽  
Temporal Shift ◽  
High Frequencies ◽  
Flame Dynamics ◽  
Wide Range

Abstract The Flame Transfer Function (FTF) and flame dynamics of a highly swirled, closely confined, premixed flame is studied over a wide range of equivalence ratios and bulk velocities at a fixed perturbation level at the dump plane. The operating conditions are varied to examine the ratio of flame height to velocity in scaling the FTF. The enclosure geometry is kept constant, resulting in strong flame-wall interactions for some operating conditions due to varying flame height. The resulting effect on the FTF due to changes in the "effective flame confinement" can therefore be studied. For sufficiently high equivalence ratio, and the resulting sufficiently small effective confinement, modulations of the FTF are observed due to interference of the perturbations created at the swirler and at the dump plane. The small length scales and high velocities results in modulations centered at high frequencies and spanning a wide range of frequencies compared to previous studies of similar phenomena. A critical point was reached for increasing effective confinement, where the modulations are suppressed. This is linked to a temporal shift in the heat release rate where the flame impinges on the combustion chamber walls. The shift reduced the expected level of interference, demonstrating effective confinement is important for the FTF response. Additionally, a Distributed Time Lag (DTL) model with two time lags is successfully applied to the FTFs, providing a simple method to capture the two dominant time scales in the problem, recreate the FTF and examine the effect of effective confinement.

The Problem of Identifying and Modeling the Relationship between Monetary Factor and Inflation in the Russian Economy

2008 ◽  
pp. 61-76
Author(s):  
A. Porshakov ◽  
A. Ponomarenko
Keyword(s):  
Money Supply ◽  
Money Demand ◽  
Russian Economy ◽  
Long Run ◽  
Complex Approach ◽  
Wide Range ◽  
Long Time ◽  
The Relationship ◽  
Supply Side Factors

The role of monetary factor in generating inflationary processes in Russia has stimulated various debates in social and scientific circles for a relatively long time. The authors show that identification of the specificity of relationship between money and inflation requires a complex approach based on statistical modeling and involving a wide range of indicators relevant for the price changes in the economy. As a result a model of inflation for Russia implying the decomposition of inflation dynamics into demand-side and supply-side factors is suggested. The main conclusion drawn is that during the recent years the volume of inflationary pressures in the Russian economy has been determined by the deviation of money supply from money demand, rather than by money supply alone. At the same time, monetary factor has a long-run spread over time impact on inflation.

Reduction of carbon impurities in aluminium nitride from time-resolved chemical vapour deposition using trimethylaluminum

2020 ◽  
Author(s):  
Polla Rouf ◽  
Pitsiri Sukkaew ◽  
Lars Ojamäe ◽  
Henrik Pedersen
Keyword(s):  
Chemical Vapour Deposition ◽  
Vapour Deposition ◽  
Chemical Vapour ◽  
Aluminium Nitride ◽  
Methyl Groups ◽  
Time Resolved ◽  
Thermally Induced ◽  
Light Emitting ◽  
Carbon Impurities ◽  
Wide Range

<p>Aluminium nitride (AlN) is a semiconductor with a wide range of applications from light emitting diodes to high frequency transistors. Electronic grade AlN is routinely deposited at 1000 °C by chemical vapour deposition (CVD) using trimethylaluminium (TMA) and NH<sub>3</sub> while low temperature CVD routes to high quality AlN are scarce and suffer from high levels of carbon impurities in the film. We report on an ALD-like CVD approach with time-resolved precursor supply where thermally induced desorption of methyl groups from the AlN surface is enhanced by the addition of an extra pulse, H<sub>2</sub>, N<sub>2</sub> or Ar between the TMA and NH<sub>3</sub> pulses. The enhanced desorption allowed deposition of AlN films with carbon content of 1 at. % at 480 °C. Kinetic- and quantum chemical modelling suggest that the extra pulse between TMA and NH<sub>3</sub> prevents re-adsorption of desorbing methyl groups terminating the AlN surface after the TMA pulse. </p>

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