Pulse Events Research Articles

Surface pulses in the lower St. Lawrence Estuary

Temperature, salinity, sea level and meteorological data from the ‘couplage entre les processus physiques et biogéochimiques’ (COUPPB) study of 1990 were examined to determine the forcing of fresh water pulses in the lower St. Lawrence Estuary. Anchor stations, during and after the passage of a pulse event, indicated that profound changes occurred in the hydrography at the head of the Laurentian Channel. A factor analysis of rotated eigenmodes of surface temperature and salinity indicated three co‐varying groups ‐ the first, on the north shore of the river, the second, on the south slope of the Laurentian Channel and the third in the middle of the estuary. A multivariate regression was used to relate salinity and temperature variations to forcing variates. It was found that sea level elevation and local winds accurately predicted fluctuations on the north shore. Salinity and temperature fluctuations on the south shore were best explained by propagation. In the middle of the estuary, salinity fluctuations were only weakly explained by propagation while temperature fluctuations could not be predicted by any of the forcing variates.

Pulsatile urea excretion in gulf toadfish (Opsanus beta): evidence for activation of a specific facilitated diffusion transport system.

When toadfish are made ureotelic by a crowding/confinement protocol, they excrete approximately 90 % of their urea nitrogen (urea-N) production in large, irregular pulses (1-2 pulses per day) from the gill region. We investigated three hypotheses as to the mechanism of pulsatile excretion: (i) the presence of an active reabsorptive 'back-transport' mechanism that is periodically inhibited to allow urea-N excretion to occur; (ii) the periodic occurrence of a generalized, non-specific increase in gill permeability; and (iii) the presence of a specific facilitated diffusion transport system that is periodically activated. Exposure of toadfish during non-pulse periods to treatments designed to block a 'back-transport' mechanism (Na+-free sea water or the urea analogues 30 mmol l-1 thiourea or 30 mmol l-1 acetamide in the external water) did not stimulate a leakage of urea-N, thereby opposing the first hypothesis. The second hypothesis was opposed by several results. Neither injection of the potent branchial vasodilator L-isoprenaline (10(-5) mol l-1) nor infusion of NH4Cl, the latter at levels known to stimulate urea-N efflux in perfused gills, had any effect on urea-N excretion. Furthermore, during natural pulse events, when the normally very low gill permeability to urea (3x10(-7) cm s-1) increased at least 35-fold, there was no accompanying increase in permeability to either 3H2O (1.5x10(-5) cm s-1) or the paracellular marker [14C]PEG-4000 (10(-8) cm s-1). However [14C]thiourea permeability (1.5x10(-7) cm s-1) increased approximately fivefold, in support of the third hypothesis. Furthermore, when 30 mmol l-1 urea was placed in the external water, a concentration (60 000 micromol-N l-1) approximately three times that of blood (20 000 micromol-N l-1), each efflux pulse event (measured with [14C]urea) was accompanied by a net uptake, such that blood urea-N levels rose rather than fell. A proportional 1:1 relationship between influx per unit external concentration and efflux per unit internal (i.e. plasma) concentration indicated a fully bidirectional transport system. The simultaneous presence of 60 mmol l-1 thiourea in the external water inhibited the influx component by 73 %, further supporting this conclusion. These data, together with recent molecular, morphological and endocrinological evidence, strongly suggest that pulsatile urea-N excretion is caused by the periodic activation of a facilitated urea transporter in the gills, similar to the vasopressin-regulated urea transporter in the mammalian kidney.

Decrease in ac surface partial discharges on an insulator with backing electrode by use of a hollow electrode

Alternating-current surface partial discharges (PDs) in air from the triple junction (TJ) of a cylindrical insulator with a backing electrode were decreased by use of a hollow electrode. The voltage applied was varied over a range from 1 to 1.5 times the PD initiation voltage (Vpd). The thickness of the insulator was varied over a range from 2 mm to 7.5 mm. For applied voltages of 1.2 × (Vpd) and 7.5 mm thickness, the combined magnitude of the PD pulses for the hollow electrode was about 80% smaller than that for the nonhollow electrode; the total number of pulse events was 40% to 50% smaller than for the nonhollow electrode; and PD pulses stronger than approximately 7 × 10−11 C were suppressed significantly. Calculation of the electric field around the TJ suggested that the generation and propagation of the PD pulse resulted from an increase in potential and strength of the vertical field component on the surface of the insulator near the TJ. It was observed from powder figures that the propagation of PDs on the hollow insulator kept their length about 50% shorter than on the nonhollow insulator. © 1998 Scripta Technica, Inc. Electr Eng Jpn, 121(3): 1–8, 1997

Determination of high spatial resolution argon isotope variations in metamorphic biotites

The circumstances of preservation of relict metamorphic minerals and fabrics which have subsequently been involved in later metamorphic cycles remain enigmatic because the kinetic parameters are not well understood. Textures and chemistry cannot always give direct information on the conditions attained in the successive events. We show in this study that 40 Ar 39 Ar laser studies can, in contrast, provide thermal history determinations and successfully discriminate between geological models. Two samples have been examined from the Seconda Zona Diorito Kinzigitica (IIDK) of the Sesia Zone, Italian Alps. A unit which preserves relict Hercynian metamorphic assemblages and is now located structurally above rocks which preserve Alpine eclogite and greenschist facies assemblages. The circumstances of this preservation remain controversial, with proposed models falling into two main categories. One hypothesis advocates that the IIDK was juxtaposed into its present position late in the Alpine orogeny and experienced no significant heating event. Alternatively the IIDK has been in its present position for the duration of the Alpine orogenic cycle and has been exposed to high temperatures but due to sluggish reaction kinetics, it failed to reequilibrate and develop Alpine metamorphic minerals. A high spatial resolution 40 Ar 39 Ar study using the ultraviolet laser ablation microprobe (UVLAMP) technique was undertaken with the aims of reassessing the metamorphic history of the IIDK and investigating the behavior of argon within the unit during its thermal evolution. 128 analyses have been obtained from ten profiles, between 60 and 275 μm long, across biotite grains which show apparent ages ranging from 514 to 161 Ma within individual crystals. These apparent age variations are systematic according to location in the grain, with the oldest ages at the grain edges and the youngest in the cores. These apparent age variations can not be explained by chemical alteration and require diffusion of excess argon into the grains. The age profiles show a remarkable fit to theoretically derived curves for volume diffusion of argon. Time integrated diffusion values obtained for the profiles fall between 2 × 10 −6 cm −6 and 5 × 10 -6 cm 2; this variation is interpreted as being due to spatial and temporal fluctuations in the availability of argon from the grain boundary network. Diffusion, and hence profile development, initiated at different times within the biotites, consequently producing the range of time integrated diffusion values. The temperatures at which the profiles developed have been estimated using published biotite diffusion parameters to model possible thermal histories. Using the assumptions of either a short thermal pulse event or continuous cooling from high temperatures, the models suggest that the profiles developed at temperatures less than 300°C. Possible geological models are proposed which document the thermal and excess argon history of the IIDK from the Hercynian through to the Alpine orogeny. The study shows the key role of detailed argon isotope studies in assessing the thermal evolution of rocks with relict metamorphic assemblages.

Pulsatile urea excretion in the toadfish (Opsanus beta) is due to a pulsatile excretion mechanism, not a pulsatile production mechanism

When subjected to a crowding/confinement protocol in the laboratory, toadfish become facultatively ureotelic, excreting approximately 90 % of their nitrogenous waste as urea-nitrogen (urea-N). The great majority of this excretion occurs via large, irregular pulses from the head region which occur on average once per day, with a duration of 3 h or less. Pulses measured chemically by the appearance of urea-N in the external water were identical to those measured by assaying [14C]urea appearance in the water from the blood plasma. Individual toadfish maintained plasma urea concentrations over widely differing ranges (6600­39 890 µmol-N l-1). However, independent of absolute levels, both [14C]urea and total urea were distributed at ratios close to unity between the blood plasma and the water compartments of liver and white muscle. At times of pulsatile excretion, plasma urea concentration fell sharply. These decreases, distributed throughout the tissues of the whole body, closely matched the sizes of the measured excretion pulses. Between pulses, plasma urea concentration increased steadily at a much slower rate; the rate of rise, when distributed throughout the tissues of the whole body, corresponded to the time-averaged excretion rate over the whole day. Infusion of a typical pulse amount of urea immediately after the end of a natural pulse event raised plasma urea concentration slightly above the pre-pulse level, but did not induce another pulse event. Plasma cortisol levels declined by approximately 60 % over the 4 h period prior to a natural pulse event and then rose quickly again once the pulse had occurred. These results indicate that urea pulses are due to activation of an excretion mechanism that rapidly clears urea from the blood plasma, thereby lowering stores throughout the whole body. Metabolic production of urea is continuous and is not responsible for pulsatile excretion. The pulse event is not triggered by a specific plasma urea threshold, but may involve the hypothalamo­interrenal axis.

Improved Signal-to-noise Ratio in Glow Discharge Ion Trap Mass Spectrometryvia Pulsed Discharge Operation

An improvement in the S/N ratio is reported for the analysis of trace elements in brass by glow discharge ion trap mass spectrometry. This was achieved by synchronizing the pulsed discharge voltage with the ion injection and acquisition events; ‘on’ during ion injection and ‘off’ during data acquisition. Two modes of operation were evaluated: (1) a high duty cycle pulse, which allowed a continuous injection over the duration of the pulse; and (2) a low duty cycle pulse with multiple data gates, which allowed gated injections of ions at selected regions of the pulse profile. The latter afforded a means of selective ion injection since discharge and residual gas species are formed at different times in the pulse event than analyte ions. Improvements in S/N ratios greater than 40-fold were observed, primarily due to a reduction in background and background noise after the discharge was extinguished. Evidence is presented which suggests that electrons emanating from the ion source are the precursors of most of the noise. Detection limits for various elements were 0.2–0.5 ppm.

Modeling and interpreting element ratios in water and sediments: A sensitivity analysis of post‐Chernobyl Ru : Cs ratios

When elements are simultaneously added to lakes, experimentally or by accident, their ratios in the water phase and in bottom sediments can change with time due to differential partitioning between solution and suspended particles or sediments. A number of equations are developed to show the change of ratio with time in water and sediments assuming simultaneous pulse inputs followed by a range of combinations of loss processes from solution (i.e. hydraulic losses, sorption to particles followed by settling, and diffusion into the sediments). The pattern of events is discussed both for pulse events with specific limiting assumptions and for combined continuous and pulse inputs. The models show that elemental ratios in sediments are generally less sensitive indicators of differential partitioning than are elemental ratios in water. For lakes with long residence times, the long‐term elemental ratio in the sediments does not differ from that in the initial spike to the water column, but for short residence times, it is directly dependent on the ratio of either partition or diffusion coefficients.The models are used to interpret Ru : Cs ratios measured in the water and sediments of Esthwaite Water subsequent to the pulse input of Chernobyl fallout. The ratios can be explained by assuming nuclides were lost either by flushing and sorption or by flushing, sorption, and diffusion. The process combination of flushing and diffusion is incompatible with the observed constant ratios.

Determination of naturalα-radionuclides related to millisecond order lives in environmental samples using the time interval analysis (TIA) method

The time files due to radioactive decay events were analyzed for the selective extraction of successive alpha-decay pulse events in millisecond orders, such as216Po (145 ms, thorium series),217At (32.3 ms, neptunium series), and215Po (1.78 ms, actinium series) after respective preceding parents decay, using a multiple time interval analysis (TIA-MTA) technique from both theoretical and experimental viewpoints. In the theoretical treatments, the detection sensitivities of each correlated event in natural decay series was compared with more generalized conditions. It was noteworthy that the evaluated detection sensitivity had increased proportionally with shorter half-lives in the following order:214Po>215Po>217At>216Po.

On the inclusion of trace materials into massive coral skeletons. 1. Materials occurring in the environment in short pulses

Trace materials included in coral skeletons during growth provide three distinct types of proxy environmental record; long-term (years to decades), annual and short-term or “pulse” records. Long-term records are not likely to be affected by skeletal growth mechanisms because these mechanisms operate at annual or shorter time scales. However, annual and pulse records will be affected by annual cycles in skeletal density and extension rate, and by mechanisms which control the time and position in which new skeleton is added. Numerical models of skeletal growth in Porites (Taylor et al., 1993) are extended and used to examine the effect of growth mechanisms upon pulse inclusions. The results suggest that useful proxy records can be recovered by optical measurements of lines which can be seen, or which can be made visible, in a section sawn along a skeletal growth axis. The results suggest that it will be difficult to recover records of pulse events from measurements of the concentration of trace material in the skeleton. Overall, the results reinforce recent suggestions that understanding of coral skeletal growth mechanisms is fundamental to recovery of reliable proxy environmental records from massive corals.

On the HEMP environment for protective relays

An assessment of the transient environment for protective relays produced by high-altitude electromagnetic pulse (HEMP) events is presented in this paper. Several mechanisms for coupling of HEMP to relay terminals are used to develop estimates of possible HEMP threats to relays. These predicted relay responses to HEMP events are compared to measured data on a solid state based relay's impulse strength. >

Time resolved energy spectrum of the axial ion beam generated in plasma focus discharges

The energy spectrum of the deuteron beam along the electrode axis (0 degrees ) in a plasma focus discharge has been determined with a time of flight (TOF) method and with a differential filter method in the ion energy interval E=0.3-9 MeV. The ion TOF method is applied to single-ion pulse events with an ion emission time t(E) that is only weakly dependent on the ion energy E for E>0.3 MeV. The correlation of the ion beam intensity with the filling pressure, the neutron yield and the hard X-ray intensity is also reported

Measurements of 222Rn in Air Using a Flow-Through Lucas Cell and Multiple Time Analysis of Recorded Pulse Events

Measurements of 222Rn in Air Using a Flow-Through Lucas Cell and Multiple Time Analysis of Recorded Pulse Events

Measurements of 222Rn in Air Using a Flow-Through Lucas Cell and Multiple Time Analysis of Recorded Pulse Events

A multiple time analysis technique has successfully been applied for measurements of environmental levels of 220Rn using a flow-through Lucas radon detector. The method is based on selective alpha counting of the short-lived nuclide 216Po. Owing to its short half-life (0.145 s), the alpha particle emitted at the decay of a 220Rn atom will, within a fraction of a second, be followed by an alpha particle from the decay of 216Po. By measuring the time interval between successive alpha counts followed by a multiple time analysis, the 216Po activity and thereby the 220Rn activity can be calculated. The method applied to a commercial instrument with a 160 ml Lucas cell as detector shows that a mean 220Rn air concentration of less than 20 Bq.m-3 can easily be determined even if the 22Rn air concentration is 10 times higher and varies. At lower 222Rn levels a 220Rn concentration less than 1 Bq.m-3 can be assessed using this technique. The method will be described together with some examples of its practical use.

Measuring techniques for environmental levels of radon-220 in air using flow-through Lucas cell and multiple time analysis of recorded pulse events

Measuring techniques for environmental levels of radon-220 in air using flow-through Lucas cell and multiple time analysis of recorded pulse events

Impacts of a nominal nuclear electromagnetic pulse on electric power systems: a probabilistic approach

Since 1983, the US Department of Energy has been actively pursuing a research program to assess the potential effects of one or more electromagnetic pulse (EMP) events on the nation's electric energy supply. A nominal EMP environment suitable for assessing geographically large systems has been used to provide an indication of EMP effects on electric power systems. It was found that a single high-altitude burst, significantly disturbs the geomagnetic field, could cause significant load and generation loss, but permanent damage would be isolated. Multiple bursts would increase the disturbance. Nevertheless, based on the effects of a nominal EMP environment, a long-term blackout is not expected since major components such as power transformers are not likely to be damaged.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the prediction of the mode-partitioning floor in injection lasers with multiple side modes at 2 and 10 Gb/s

An analytical method is presented for estimating the error-rate floor to be expected in a digital transmission system using an injection laser. A computer model of the laser, including Langevin noise sources and with random sequences of signal pulses, is used to find the probability of the main-mode average power during an ON pulse being less than 0.5 times normal average power during an ON pulse event. With sufficient fiber dispersion, this constitutes a useful estimate of the mode-partitioning floor. Three methods are included for determining the floor: (1) direct calculation using a single Monte Carlo run; (2) extrapolation to floors in the 10/sup -10/ region of a series of Monte Carlo runs for different laser modal loss differences ( Delta alpha ); and (3) extrapolation of a single Monte Carlo run to low error-rate floors using a new analytical expression with parameters derived from the Monte Carlo run. In order to avoid a serious error-rate floor at 2 or 10 Gb/s, it is found that Delta alpha must be about 10 or 30-35 cm/sup -1/, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

地震動尾部に現れるパルス状震動の繰り返し

The Waseda bore-hole seismometer array, Tokyo, occasionally records periodic repetition of seismic pulses in coda part of seismic waves. Each pulse looks like a Ricker wavelet of several to ten second duration and of repetition intervals for about 10-20 and 50-60 sec. Total duration of the ground motion of this type reaches 5 minites. Obervation at other stations seems to suggest that such coda pulses of our interest could be observed in a considerably wide area in and around Tokyo Metropolis. Seismological analyses of the records and numerical tests of wave propagation prove that a possible mechanism of the present pulse events is generation of local surface waves and multiple horizontal reflection of them between underground boundaries. The main reflector may be located at the outer rim of the thick sedimentary basin. Further conclusion must be made after precise location of the reflectors, using dense array newtwork data and information of local underground structures. From the engineering point of view, repetition of seismic pulses as above may affect seismic vibration of artificial structures. Large artificial structures of long period and low damping factor might undergo additional vibration by the pulses, if the characteristic periods fit the interval of the pulses.

Solar microwave bursts recorded at 2.84 GHz with millisecond time resolution

A millisecond recorder for solar observation at 2.84 GHz was put to work in 1981. From April 1981 to September 1982 it recorded 250‘spike pulse events’, which are here listed together with information on the associated solar flares, hard X-ray bursts and radio bursts. In defining these spike events, particular attention has been paid to ensure the reliability of the recorded data. Statistical analysis of the data has given some interesting results. The spike pulses have shorter duration and higher flux density than were previously known, and the basic units of the spike pulse events are single spike pulses crowded together forming separate clusters. Many spike pulses observed are not yet resolved at 1 ms. Fast spike pulse events are closely correlated with complex magnetic field regions, and are often accompanied by hard X-ray bursts and fast drifting radio bursts. Some such events showed no correspondence with the radio bursts at the same frequency, 2.84 GHz, but corresponded to those occurring at dm and short cm wavelengths. Some theoretical investigations of the spike phonomena have been carried out, the details of which will be discussed elsewhere.

New Toxicological Approaches for Establishing Safer Water Quality Criteria

The most common form of entry of xenobiotics into the aquatic environment is by intermittent pulse. Some pulse discharges result directly from man’s agricultural and industrial activities such as periodic applications of larvicides and industrial spills. Others are more indirect and are associated with naturally occurring periodic events such as the spring run-off of contaminated melt waters and the spring or fall turnover of previously separated water bodies. All of these can result in a short-term exposure of aquatic organisms to compounds that are not present on a day-to-day basis. The most sensitive indicators of toxicant impact to fish are usually reproduction and embryo/larval survival, both of which are often closely associated in time with pulse events. The majority of toxicological research, however, is done under conditions of continuous toxicant exposure using juvenile/adult animals. Accordingly, most water quality criteria are derived from data obtained during continuous exposure experiments. Based on recent work, it is felt that intermittent exposure of fish to low levels of pesticides such as methoxychlor may be partly responsible for the decline of fish populations. It is recommended that future research include work on the effects of pulse administered xenobiotics on fish, using the embryo/larval life stages for determining acute effects, and undertaking life-cycle studies to assess chronic effects. Since differences in toxicity can be extremely large between species at the embryo/larval life stages, two methodologies are suggested. The first is to predetermine selected "target" species of value, and establish water quality criteria based on that species. The second more flexible approach is to experimentally determine species application factors using embryo/larval fish, life-cycle studies and "type" toxicants. If species-specific impact can be predicted from "type" toxicants, water quality criteria can be established based on the most sensitive or most valuable indicator species, depending on the type and level of protection desired. These criteria would be based on temporal as well as concentration values, and would raise the level of realistic protection.

Forest turnover and the dynamics of bole wood litter in subalpine balsam fir forest

A chronosequence of three stands of balsam fir was sampled in 1974 and 1982; during these 8 years, recruitment was absent so mortality alone accounted for an 18–30% decrease in live tree density. In a mature 78-year-old stand, the mass of bole wood on the forest floor was 1.4 kg•m−2 compared with an estimated aboveground live and dead bole biomass of 17.2 kg•m−2. During 5 years of repetitive sampling, annual bole input to the forest floor was episodic and variable in time and space, ranging from 3 to 365 g•m−2•year−1. A mass balance model was used to characterize the changes in wood litter on the forest floor. If most of the live trees die within a short period of time, bole input would occur in a pulse event and cause a peak in wood litter mass, which would then decline over time (and with stand maturation) as decomposition prevails. The assumption of steady-state conditions for wood litter is not valid; rather the mass of wood litter will wax and wane through time. Over a landscape, spatial patterns in the abundance of wood litter reflect a stand's history; old mature stands would have little wood litter while young regenerating stands would have large amounts. A maximum value for wood litter would be found in a stand located immediately behind a fir wave. Natural disturbances from wind and avalanches lead to contrasting patterns with high and low wood litter values, respectively. About 41% of forest turnover in the balsam fir zone is initiated from natural disturbance and fir waves.