Steepness Of Front Research Articles

Characteristics of winter lightning current on Japan Sea Coast

Long-term observation of winter lightning has been conducted on the Japan Sea Coast since 1978. From various kinds of observations, the results of lightning current measurement by an automatic lightning current recording system are reported. It is shown that winter lightning current has wide variations in its waveform, but the frequency distribution of the front duration, the tail duration, and the front steepness can be approximated by a logarithmic normal distribution. Positive polarity lightning current tends to have much longer front and tail duration than negative lightning current. The ratio of the positive to the negative polarity is one to two in winter lightning, which is much higher than that of summer lightning. The cumulative frequency distribution of the winter lightning current peak agrees with that of the summer lightning current. The fractional distribution was proposed for winter lightning protection design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigations of factors influencing the current density distribution of a large cross section electron beam

Investigations are presented of the initial phase of operation of multi-edge cathodes for large-aperture electron guns. The influence of the form and amplitude of the supply voltage on the spatial distribution of the electron beam current density is shown. It was demonstrated that whilst the voltage is rising the cathode plasma is generated by the groups of operating edges and has a spot structure. An approximate analytical dependence between the number of operating edges and the voltage applied to the gun electrodes was determined. Quantitative results illustrating the dependence of the current distribution uniformity on the steepness of the voltage pulse front were obtained.

Simulation of phosphate transport in soil columns. II. Simulation results

Phosphate (P) transport in vertical soil columns was simulated, assuming steady-state flow. The retention of P in soil was modeled assuming two mechanisms for the reaction, i.e., adsorption and precipitation. In a companion paper we showed that P displaces in a travelling wave like fashion for a homogeneous soil column and exhibits a relatively sharp front for total P when parameter values as determined in laboratory experiments are used. Reasonable changes in the flow velocity, the volumetric water fraction at which drainage occurs, and the diffusion/dispersion coefficient have only minor effects on the front steepness. Of the chemical parameters notably a change in the precipitation kinetics has a large effect on the front shape. In case the lower bound concentration c e below which no precipitation occurs is increased, the double front that is intrinsic to distinguishing two sorption processes may start to spread out. For large enough values of c e the downstream part of the front, which is affected only by adsorption, moves faster than the upstream part, which is also retarded by precipitation. A criterion when such front splitting occurs is presented and depends on the chemistry parameters. When the inflow of P is discontinuous, the concentration front is highly variable in time, but the total-P front responds only slightly on the variation of c in time. Also for layered soils steep P-fronts were simulated. For layered soils the front depth depends on the properties of different layers situated upstream, while the shape mostly depends on the layer properties where the front is situated. Discontinuation of P-applications leads to a perturbation of the front shape. In that case, as well as when a homogeneous uptake of P by crops following discontinuation is simulated, mobile P (dissolved and adsorbed reversibly) decreases rapidly. Discontinuation of P-input and intensive cropping may significantly limit P-leaching.

An attempt to reconstruct the lithotriptor shock wave pulse in kidney: Possible temperature effects

Based on measurements carried out in water in two lithotriptor systems, the authors have made an attempt to reconstruct numerically amplitudes and shapes of shock wave pulses penetrating into kidney which differ from those in water. The difference between these pulses and those observed in water was analyzed and was also demonstrated experimentally. The amplitude and the steepness of the reconstructed pulse front were shown to be much lower than in water depending on the distance of the kidney stone from the patient's body surface. For a distance equal to 4 cm, the shock wave pulse amplitude of 40 MPa in water was estimated to decrease in the kidney by a factor of about two and the steepness of the positive shock pulse front to decrease several times. The analysis was carried out by considering the possible changes of absorption and attenuation in tissues which increase in an unknown way with the wave amplitude. It was shown that the temperature elevation caused by the increase of nonlinear high amplitude absorption is limited due to a corresponding increase in attenuation of the shock wave penetrating soft tissues. The temperature elevation was estimated on the basis of this work to be at most 1.8 times that one estimated in the case of two considered lithotripsy systems when assuming small amplitude absorption and attenuation coefficients.

Analytical traveling wave solutions for transport with nonlinear and nonequilibrium adsorption

Transport was modeled for a soil with dual porosity, or with chemical nonequilibrium, assuming first‐order kinetics. The equilibrium sorption equation in the immobile region is nonlinear. Two equilibrium equations for sorption were considered, that is, the Langmuir and the Van Bemmelen‐Freundlich equations. The sorption equation in the mobile region is assumed to be linear. Analytical solutions were obtained that describe the traveling wave displacement found for initial resident concentrations that are smaller than the feed concentration and for infinite displacement times, neglecting the coupled effects of dispersion and nonequilibrium conditions. These waves travel with a fixed shape and a fixed velocity through the homogeneous flow domain. Besides expressions for the front shape, expressions for the front thickness and the front position were also presented. Differences with respect to the linear sorption case are the smaller front thickness and the non‐Fickian type of displacement. The non‐Fickian behavior is intrinsic to the traveling wave assumption as the front does not spread with the square root of time. The analytical solutions obtained for the equilibrium and for the nonequilibrium situations are mathematically equivalent. Only the effective diffusion/dispersion coefficient needs to be adapted to account for nonequilibrium effects, as for linear dual‐porosity models. Apart from early time behavior, the traveling wave solutions agree well with numerical approximations. The front steepness depends sensitively on the degree of nonlinearity. The sensitivity on the dispersion coefficient and first‐order rate coefficient may be large but depends on which mechanism controls front spreading.

Carbonation in a 36 year old, in-situ concrete

Thermogravimetric analysis (TGA) of drillings at 5mm depth intervals from a 36 year old in-situ concrete provided information on the steepness on the carbonation front for indoor and outdoor exposure. TGA results for indoor exposure suggested that the cement gel was fully carbonated to a depth of 45mm but calcium hydroxide was present from 25mm and increased to a maximum at a depth of 65mm: a gradient covering 40mm. For outdoor exposure the gradient extended over only 10mm. Phenolphthalein measurements identified the first drill sample containing calcium hydroxide and showed neutralization depths of 26 and 38mm for indoor and outdoor exposure respectively. The phenolphtalein results and the TGA data for complete carbonation indicated that outdoor exposure was more severe but TGA data for the deepest penetration of carbon dioxide suggested the reverse. It was recommended that service life studies of reinforced concrete structures should consider the steepness of the carbonation front.

Computation of Transmission Line Transients Including Corona Effects

Surges propagating on an overhead power transmission line are attenuated and distorted by a number of factors. Corona is probably the most significant one of all these factors for surges with sufficiently high crest values and steepness of fronts. A good understanding of the effect of corona is thus important in overvoltage protection and insulation coordination. The effect of corona on wave propagation has been under investigation with a long history. However, a satisfactory approach to include it quantitatively in the calculations of transmission line transients is still not available due to the intricacy of the mutual effect of corona and surges. Empirical formulas are still being used widely in the calculations for insulation designs and other purposes. Corona effect on travelling waves is attributed to the power loss and change in capacitance during corona. Early studies considered only one of these two aspects. Recent efforts have been made to combine both of them. This is achieved in this paper by simulating a non-linear capacitor having the same charge-voltage characteristics as the line in corona. From the point of view of the algorithms for the computation of transmission line transients, recent progress has been made in two directions. The first one is to solve numerically either the telegraphers' equations or the wave equation that describes the wave propagation on transmission lines. The finite different method is commonly used in this methodology. Convergence, stability, and efficiency are important here.

Prediction of Occurrences of Steep and High Waves in Deep Water

Estimates for encounter probabilities of occurrence of steep and high waves in deep water for given sea states by using two different parametric models for the joint distribution of crest front steepness and wave height are presented. The parametric models are fitted to the same data set, with data from a zero‐downcross analysis of wave data obtained from measurements at sea on the Norwegian continental shelf. The probability of occurrence of waves with different crest front steepness are estimated with each parametric model for a family of JONSWAP spectra. An example is given where the probabilities of occurrence of “extreme waves,” which are considered to be critical to capsizing of smaller vessels, are estimated with one parametric model for sea states described by significant wave height and mean zero‐crossing period.

Steepness and asymmetry of extreme waves and the highest waves in deep water

Traditional wave steepness s=H/L does not define steep asymmetric waves in a random sea uniquey. Three additional parameters characterising single zero-downcross waves in a time series are crest front steepness, vertical asymmetry factor and horizontal asymmetry factor. Results for steepness and asymmetry from zero-downcross analysis of wave data obtained from full scale measurements in deep water on the Norwegian continental shelf in 58 time series are presented. The analysis demonstrates clearly the asymmetry of both “extreme waves” and the highest waves. The period and height of the highest waves are also given together with their correlation to spectral parameters. The measured maximum wave heights are also compared with predicted values of maximum wave heights showing good agreement.

Measurement and Analysis of Near-Classical Thermal Transport in One-Micron Laser-Irradiated Spherical Plasmas

Solid spherical layered targets have been uniformly illuminated at irradiances of ${10}^{14}$ to ${10}^{15}$ W/${\mathrm{cm}}^{2}$. Extensive diagnostics including time-resolved x-ray emission and optical probing were used to determine the plasma ablation rate and the plasma blowoff conditions. Comparisons with hydrodynamic simulations show that the thermal conduction is well characterized by a flux limit ${f}_{e}=0.08\ifmmode\pm\else\textpm\fi{}0.02$, with a steep temperature gradient. The steepness of the heat front was confirmed with time-resolved spectroscopy.

Parametric modelling of joint probability density distributions for steepness and asymmetry in deep water waves

Traditional wave steepness s = H/ L does not define steep asymmetric waves uniquely. Three additional parameters characterising single zero-downcross waves in a time series are crest front steepness, vertical asymmetry factor and horizontal asymmetry factor. Parametric models for joint probability density distributions for deep water waves are presented. The joint distributions are for crest front steepness-wave height, vertical asymmetry factor-wave height, total wave steepness-wave height and wave height-wave period. The parametric models are estimated from zero-downcross analysis of wave data obtained from measurements at sea on the Norwegian continental shelf. The results of the analysis presented here can be used in the estimation of the probabilities of occurrence of steep asymmetric waves and breaking waves in deep water. Thus the results are useful for the practical naval architect and ocean engineer who are considering unusual events in the sea, the associated accidents or responses and the probability of occurrence of such events.

Rarefaction shock wave near the critical liquid–vapour point

The existence of a rarefaction shock wave or negative shock wave in a substance whose unperturbed state is close to the thermodynamic critical liquid–vapour point has been demonstrated experimentally. Its evolution and propagation velocity in a shock tube with Freon-13 as the test substance are described. It is shown that the steepness of the wave front does not diminish as the wave evolves. An equation is derived that describes the evolution of long-wave perturbations near the critical point.

Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado

Research Article| February 01, 1981 Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado STEVEN G. VICK STEVEN G. VICK 1Dames & Moore, Salt Lake City, Utah 84111 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1981) 92 (2): 75–84. https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation STEVEN G. VICK; Morphology and the role of landsliding in formation of some rock glaciers in the Mosquito Range, Colorado. GSA Bulletin 1981;; 92 (2): 75–84. doi: https://doi.org/10.1130/0016-7606(1981)92<75:MATROL>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Some 23 rock glaciers have been identified in the central portion of the Mosquito Range. Surface features and characteristic forms correlate well with those reported for rock glaciers in Alaska and elsewhere in Colorado, New Mexico, and Utah. On the basis of air-photo interpretation, about two-thirds of the rock glaciers are lobate in form, and one-third are tongue-shaped. Only 5 of the 23 rock glaciers are believed to be active.A detailed stability analysis of two rock glaciers in Iowa Gulch indicates that landsliding of unstable morainal deposits played a major role in their formation. Landslide debris provided loading necessary to initiate ice creep in frozen till on the lower valley slopes. Ice creep continued, eventually bringing the rock glaciers to their present form. With the supply of landslide debris exhausted and with insufficient ice wedging and rock exposure to generate large talus cones, stresses generated by the superincumbent load were reduced by creep-induced spreading, and motion ceased. Internal ice, in the form of both interstitial ice and ice layers, still remains.Techniques developed to evaluate activity of rock glaciers in Alaska have been applied to the two rock glaciers in Iowa Gulch. These techniques, based principally on steepness and form of the rock glacier front as well as on calculated values of basal shear stress, indicate both rock glaciers to be inactive. Re-survey of a mining claim corner and inspection of a shaft show that no movement has occurred over the period of record and that the rock glaciers are indeed inactive, substantiating the usefulness and validity of the above-described techniques for assessment of rock glacier activity elsewhere. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

WAVE-WAVE INTERACTIONS, CURRENT-WAVE INTERACTIONS AND RESULTING EXTREME WAVES AND BREAKING WAVES

The influence of an opposing current on highly non-linear transient breaking waves in deep water is described quantitatively from experiments. 3 new parameters that describe crest front steepness and wave asymmetry are introduced. Further, joint probability density distributions are obtained from an analysis of field data containing nearly 25000 storm waves. Thus, a tool is provided from which estimates for probabilities for occurrences of steep breaking waves in deep water, may be obtained.

Disintegration of brittle powders in load waves

The existing methods of studying the shock-wave disintegration of brittle powders, e.g., of abrasive and refractory materials, are based on their physicochemical investigation after the application of load. Only one load parameter is employed in these studies, viz., maximum pressure in the load wave, determined by measurement or calculation [1-3]. Because of this, powders produced in different investigations by the application of an explosive load to a starting material under the same shock compression pressures may differ widely in their crystal structure characteristics (magnitude of crystal lattice distortions, density of structural defects, etc.), particle size distribution, phase composition, strength, abrasive ability, and the like. The cause of such differences may reside in the use of impulses of various shapes, varying substantially in front steepness and duration.

Diffusion with discontinuous swelling III. Type II diffusion as a particular solution of conventional diffusion equation

Very often a non-solvent diffuses into a glassy polymer with a steep concentration profile proceeding at an almost constant rate v yielding a weight gain proportional to time. Such a diffusion is called type II diffusion in order to distinguish it from the more usual “Fickian” diffusion proceeding without such a constant concentration front and yielding, at least in the beginning, a weight gain proportional to the square root of time. It turns out that the conventional diffusion equation without any special new term but with a diffusion coefficient rapidly increasing with concentration has a series of solutions representing exactly such type II diffusion with v as a completely free parameter which determines the steepness of concentration front. With the usual boundary conditions and infinite medium the diffusion coefficient has to become infinite at the highest penetrant concentration. This case can be considered as an extreme limit which is approached to a high degree in an actual experiment. The finite sample thickness, however, requires only a very large but not an infinite diffusion coefficient. Hence type II diffusion is only a special case of possible diffusion processes compatible with the conventional diffusion equation without any need for new terms if only the diffusion coefficient increases sufficiently fast with penetrant concentration.

Application of the implicit method to surges in open channels

A technique is proposed by which continuous numerical computation of flows with surges in open channels can be handled with an implicit formulation. The one‐dimensional gradually varied flow equations of continuity and momentum are written in finite difference form for the point (I + ½, J + θ) in the x, t plane, where I is the distance counter, J is the time counter, and θ is a weighting parameter that is varied from 0.5 to 1.0. A computer program was written to solve the problem in which the discharge hydrograph is given at the upstream end of a channel and a stage‐discharge relationship is specified at the downstream end. This program was applied to different flow situations in laboratory channels and natural rivers. It was found that θ = 0.5 produced results with a steep wave front but with considerable numerical instability. The use of θ = 1.0 gave results with considerable diffusion of the wave front. The use of θ = 0.60 produced results that had a steep wave front and only a minor degree of numerical instability. This value of θ resulted in good agreement between calculated and measured hydrographs at the downstream end of the channel in most applications. However, the optimum value of θ depends on channel friction and the steepness of the wave front.

Characteristics of the transient responses of transistorized differential bioelectric signal amplifiers.

1. Because of the difference between the polarization potentials at different points of the specimen under investigation, step signals with a large amplitude (attaining tens of millivolts), which are commensurable with the emitter junction voltage, may arrive at the input of the measuring channel when the electrode branches are switched. 2. After they are supplied to the input of a transistorized differential RC-amplifier, these signals block the channel. The duration of this blocking increases with the time constant of the channel. For instance, in switching electrocardiograph branches, this leads to a loss of 10–20 cardiocycles. 3. The unbalances of the arms of the first amplifier stage, which are difficult to eliminate, are the causes of the slow establishment of operating conditions in transistorized differential RC-amplifiers. They produce a slowly damped (with the time constant c/gcc) underswing in the transient response of this stage. 4. The best way of eliminating this disadvantage is to use a channel without capacitors that is provided with a polarization potential compensator. 5. In the presence of RC-junctions, the effect of a large time constant c/gcc can be reduced by balancing the stages and maintaining a symmetric structure along the entire channel. 6. Since it is impossible to maintain the balance over a long period of time, the most efficient method of reducing the pulling is to transfer the first capacitive junction to the output of the first amplifier stage and introduce at this place a “damping” circuit, which would secure a short capacitor charging time. 7. The time characteristics could be improved by using a branch switching system, which would reduce the front steepness of the step perturbation signals. 8. Any measure aiming at a reduction of the capacitances of the coupling capacitors, and also maintaining the time constant of the channel tends to reduce the time necessary for the establishment of the operating conditions.

Effect or Preceding Bias Voltage on Switching-Surge Operation of Spill Gaps and Lightning Arresters

Line-dropping tests on the Southern California Edison Company system showed that previously encountered spill-gap operation was not caused by extremely high switching-surge voltages, but by abnornally low sparkover of bushing-mounted gaps. In some cases lightning arresters also operated at abnormally low switching-surge voltages. Laboratory tests showed that a nonuniform gap field and trapped charges on the adjacent porcelain surface rendered spill-gap sparkover susceptible to wave front steepness and, particularly, to preceding voltages of opposite polarity. A gap located remotely from porcelain surfaces was found to be relatively free from these effects.

Protection of station equipment against lightning

Protection of station equipment against lightning over-voltages is usually effected, by voltage-limiting devices such as spark-gaps or surge diverters. When there is appreciable separation between two items of equipment a protective device located near one may not be effective in limiting the voltage at the other to a safe value. The paper is in two parts: in Part 1 the factors determining the most suitable location for the device and its range of protection are investigated, and it is shown that, except for terminal stations involving only one overhead line, the most effective position as on the equipment nearest the overhead line. It is also shown that the range of protection which determines whether more than one protective device is desirable is very dependent on the steepness of front of the over-voltage. The steepness is dependent on the attenuation due to corona during the passage of the over-voltage along the overhead line; this question is examined in Part 2.