Positive Surge Research Articles

The Luteinizing Hormone Surge Is Preceded by an Estrogen-Induced Increase of Hypothalamic Progesterone in Ovariectomized and Adrenalectomized Rats

As circulating estrogen levels rise on the afternoon of proestrus, they stimulate the hypothalamo-pituitary axis. This estrogen positive feedback is pivotal to stimulate the luteinizing hormone (LH) surge required for ovulation and luteinization of ovarian follicles. In addition to estrogen, pre-LH surge progesterone is critical for an LH surge as was demonstrated by blocking progesterone synthesis. In ovariectomized (OVX) rats treated with trilostane, a blocker of the enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD) that catalyzes the conversion of pregnenolone to progesterone, estrogen did not induce an LH surge. Further, estrogen induced an LH surge in OVX and adrenalectomized (ADX) rats, indicating that the source of progesterone was neither the ovary nor adrenal gland. This estrogen-only LH surge was inhibited by pretreatment with trilostane, indicating that although the adrenal gland and ovary were not necessary for positive feedback, progesterone synthesis was critical for estrogen-induced positive feedback in an OVX/ADX rat. This suggested that the LH surge is dependent on the pre-LH surge synthesis of progesterone. Estrogen-induced progesterone receptors in the hypothalamus are vital for the LH surge, so a potential location for progesterone synthesis is the hypothalamus. OVX/ADX female rats were treated with 17β-estradiol (50 µg) and progesterone levels were assayed by RIA. Progesterone levels were elevated in hypothalamic tissue following estrogen treatment. No increases in tissue progesterone levels were found in parietal cortex, cerebellum, medulla, pituitary or plasma. Additionally, male rats that do not have an estrogen positive feedback-induced LH surge were examined. Castrated/ADX male rats had no increase in hypothalamic progesterone levels after estrogen treatment. Together, these data strongly suggest that estrogen enhances neuroprogesterone synthesis in the hypothalamus that is involved in the positive feedback regulating the LH surge.

Comparison of travelling ionospheric disturbance measurements with thermosphere/ionosphere model results

Abstract. Comparisons of modeled and measured responses of the ionosphere to the passage of atmospheric gravity waves are made for data recorded by an ionosonde located at Almaty (76°55' E, 43°15' N) from June 2000 until May 2001. Temporal variations of the altitude (hmF) and electron content (NmF) of the F-layer peak are used for comparisons. A significant part of the observations showed well-defined wave structures on the hmF, NmF and other parameter variations observed throughout the entire nights. Both the modeling study and measurements showed that, as the F-layer is lifted by the positive surge in gravity wave, the electron content at the F-layer peak decreases, with the slab thickness being increased as well. Subsequently, the opposite happens as hmF falls below its equilibrium value. Some discrepancy between the model and experimental results related to the phase difference between hmF and NmF variations is revealed.Key words. Ionosphere (ionosphere-atmosphere interaction, ionospheric disturbances)

Night Irrigation Reduction for Water Saving in Medium-Sized Systems

In many medium-sized irrigation systems water is wasted during the night because demand is low and supply is not reduced accordingly. A hydrodynamic model was applied, using MIKE 11 as a software tool, to simulate abrupt discharge changes and their travel times along small irrigation canals. Filling and emptying of the canal were also analyzed. The model was calibrated with data of a field experiment that included startup, positive, and negative surges. A technique was developed to take into account the considerable water losses in the canal. Performance indicators efficiency, adequacy, equity, and dependability, proposed by Molden and Gates in 1990, were redefined using the concept of usefully delivered discharge. The newly defined indicators were consequently used to find the gate operation scenario that meets optimally the target day and night discharges. It was found that it is feasible to implement night delivery reduction. The calibrated model was used to develop guidelines for the operation of the canal with daily flow variation, resulting in considerable water savings during the night.

Recent evolution of sea-level extremes at Trieste (Northern Adriatic)

The evolution of sea-level extremes at Trieste (Northern Adriatic) is analysed for the 1939–2001 period by studying the occurrence of positive and negative surges and positive and negative anomalies of observed sea level. Marked interannual and multiannual fluctuations are recognized, which can be related to the observed changes in the atmospheric pressure and wind regimes that affected the Adriatic region in the period of interest. Over the period under study, weak and moderate surges of both signs do not exhibit a clear trend, while the frequency of both strong positive and negative surges tends to decrease. Weak and moderate positive sea-level anomalies become more frequent, while all negative anomalies tend to exhibit a negative trend, because of the superposition of the general mean sea-level rise on the surge evolution. One consequence is that the frequency of strong positive anomalies, among which flood events, appears to be almost stable. The role of the anomalous behaviour of sea-level extremes observed in the winters 1989–1993, as a consequence of persisting atmospheric pressure anomalies, is also investigated.

Comparison of several one-step home urinary luteinizing hormone detection test kits to OvuQuick®

Objective: To compare clinical accuracy and ease of use for several of the new rapid one-step home urinary LH detection kits compared with the preexisting OvuQuick brand LH detection kit (designated as the standard).Design: Prospective cohort study.Setting: University-based infertility clinic.Patient(s): All women undergoing intrauterine inseminations at the clinic, regardless of infertility diagnosis, were offered enrollment during a 28-month study period.Intervention(s): Each participant was supplied three one-step test kits (OvuQuick One-Step, ClearPlan Easy, and SureStep) in addition to a multistep OvuQuick test kit and instructed to run the tests in parallel on the same urine sample and to record the results. Urine testing was performed every 12 hours, beginning 3 days before the anticipated onset of an LH surge, and continued with the one-step kits every 12 hours for 48 hours after the surge was first detected by OvuQuick. Subjects also completed questionnaires evaluating the use of each test kit.Main Outcome Measure(s): Correlation of LH surge detection by one-step kits in comparison to surge detection by OvuQuick. Satisfaction and ease of use questionnaires.Result(s): Sixty-three volunteers returned useable data, from which 81 evaluable cycles were analyzed. The majority of patients found the newer one-step kits to be easier to use and less time consuming than OvuQuick. The three one-step kits detected the LH surge within ± one testing period (±12 hours) of detection by OvuQuick 68%–84% of the time. OvuQuick One-Step, with modified instructions allowing for an equal color intensity in the test and reference areas, had the highest correlation with OvuQuick (84%). However, with a study power (α = 0.05, β = 0.10) sufficient to detect a 10% difference between Ovuquick and each one-step kit, all one-step kits were statistically equivalent to each other. There was no cycle in which a one-step kit detected a positive LH surge but OvuQuick did not.Conclusion(s): One-step urinary LH kits are easier for patients to use than a multistep home urinary LH kit and have reasonable correlation with the multistep kit when used clinically for timing artificial inseminations.

Surges, atmospheric pressure and wind change and flooding probability on the Atlantic coast of France

A statistical study of hourly tide-gauge records at Saint-Gildas, Saint-Nazaire, Port Tudy, Brest, Le Conquet and Roscoff, as well of three-hourly wind and air pressure records at Belle Ile and Ouessant over the last 50 years, has made possible the definition of the main meteorological factors which are associated with the development of positive or negative surges. Recent changes in these meteorological factors indicate that atmospheric depressions and strong surge winds are becoming less frequent and that the ongoing trends of climate variability show a decrease in the frequency and hence the gravity of coastal flooding. However the highest sea surges of the last decades did not occur at the time of spring high tide. There is a significant statistical probability that coastal flooding reaching higher elevations than in the recent past may occur in the near future, in spite of the improvement of climatic trends. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS surge / wind / climate variability / flooding probability / French Atlantic coast

Les surcotes à Brest depuis un siècle : analyse des paramètres météorologiques influents à l'échelle locale

Positive and negative sea surges are short periods events among the most extreme oceanic phenomena due to the climatic variability. A phenomenological study of hourly tide-gauge records at Brest, at local scale, allow to show strong relation between evolutions of pressure, wind speed and direction and positives sea surges. Pressure is often prevailing for weak intensities of positive sea surges, whereas wind speed is the most important parameter during highest events. Their duration seems to be controlled by wind direction, without neglecting two others parameters.

Air Influence on Hydraulic Transients on Fluid System With Air Valves

A study is made on the pressure surges on a fluid system with air valves. The effects of the presence and distribution of air on the system response are studied. Several distinct pressure transient characteristics were observed through this investigation. Investigations showed that air valves with high inflow characteristics installed at peak locations of a fluid system with entrapped air may reduce the magnitude of the extreme negative pressure surges. However, for near zero air entrainment levels, air valves with higher outflow characteristics tend to result in higher positive pressure surges. The effectiveness of the air valves installed for the purpose of surge protection depends not only on the physical configuration of the fluid system, the physical properties of the pipeline and the fluid, but significantly also on the characteristics of the air valves and the distribution of air in the system. The results of the investigations in the present work were confirmed through field observations and measurements.

Numerical study on the effects of air valve characteristics on pressure surges during pump trip in pumping systems with air entrainment

An improved numerical model and computational method are proposed here for the study of the effects of air valve characteristics on pressure surges during pump trip in fluid systems with air entrainment. Numerical experiments have shown that air valves with higher inflow characteristics installed at peak locations of a fluid system may reduce the magnitude of the extreme negative pressure surges. However, for near zero air entrainment levels in the fluid system, air valves with higher outflow characteristics tend to result in higher positive pressure surges

Hindcast of a storm surge induced by local real wind fields in the Venice Lagoon

This paper investigates the effects of the wind blowing over the Venice Lagoon on both water level and circulation patterns. This has been carried out using a finite element hydrodynamic model coupled, for the first time, with experimental wind stress fields obtained from measurement of the horizontal and vertical wind components. A spatially variable wind field is used to compute the wind stress directly from the velocity fluctuations. The hindcast concerns a case of strong northeasterly wind (Bora) which occurred from the 22nd to the 24th December 1994. Results are discussed both in terms of the spatial pattern of the storm surge levels and of the water exchanges with the open sea through the three lagoon inlets. There is an area of set-down in the north of the lagoon and of one of set-up in the south. At the centre of the lagoon, the effects of the storm surge are small. Results show that the set-down and set-up peaks occur in opposition of phase with the tide. In the south, this is related to the bottom friction term which enhances or reduces the magnitude of the storm surge elevation, whereas in the north the mechanisms of nonlinear interaction between tide and storm surge are less clear. Also, a positive surge difference is found between the western and the eastern lagoon, and between the water levels close to the inlets and the open sea, the latter triggering the sea-lagoon water exchanges. Analysis of the discharges through inlets and ideal transects (which divide the lagoon into three parts) shows that the spatial and temporal behaviors of the storm surge in the south and in the north of the lagoon are almost independent. During the entire period under study, the sea water inflow through the northern inlet was continuous and considerable compared with the outflow through the central and southern inlets. Interesting circulation patterns are found in the northern lagoon, whilst water dynamics in the southern lagoon are essentially driven by the outflow at the meridional inlet. Comparison of these results with the hindcast obtained using spatially constant wind stress fields shows the importance of the wind spatial gradients in determining the storm surge level patterns.

Tide‐surge interaction in the Gulf of Suez, Egypt

A two‐dimensional, nonlinear, vertically integrated model for the Gulf of Suez, Egypt, was used to simulate the interaction between tides and the surge heights resulting from a 15 m/s storm blowing from the northwestern direction for 24 hours. The results show that the predominant surges as well as the envelope of the tide plus surge curve are all negative throughout the whole area of the Gulf of Suez and increasing northward. It was shown that, although in principle, the shallow Gulf of Suez can support and propagate positive storm surges, they do not occur, mainly because the winds from the prevailing weather systems are conducive to generate negative surges. Since the tidal range in the Gulf of Suez is small, even the combined water level from the surge and tide remains mostly negative.

Effects of an atmospheric gravity wave on the midlatitude ionospheric F layer

A modeling study of the atmospheric response to a single short burst of enhanced ion convection at high latitudes, undertaken using the Sheffield/University College London/Space Environment Laboratory coupled ionosphere/thermosphere model, has revealed a large‐scale atmospheric gravity wave (AGW) moving equatorward from a source in the dawn sector auroral zone. The wave propagates to midlatitudes, perturbing the ionosphere and creating a traveling ionospheric disturbance. Analysis of the interaction between the thermosphere and ionosphere during the passage of the AGW at midlatitudes is undertaken and reveals a complex height‐dependent response. At lower altitudes the field‐aligned velocity of the ions follows closely the field‐aligned wind. Above the F peak, diffusion processes become important and the field‐aligned ion velocity shows fluctuations which exceed those in the wind. Changes in NmF2 and hmF2, during the interaction, are due to redistribution of plasma alone with changes in production and loss insignificant. As the F layer is lifted by the positive surge in the gravity wave, NmF2 decreases, due to a divergence in the ion flux, itself caused by the combination of a divergent neutral wind and an increase in the effects of diffusion with altitude. The slab thickness also increases. Subsequently, the opposite happens as hmF2 falls below its equilibrium value.

Electroluminescence in epoxy insulation

Electroluminescence (EL) in transparent epoxy subjected to repetitive voltage surges has been investigated. The effect of surge voltage magnitude, repetition rate, and polarity on the magnitude and number of light pulses emitted was studied. Using a needle-plane electrode geometry, the light inception stress was determined to be approximately 200 kV/mm for both positive and negative voltage surges. As the peak voltage of a surge increased, the number of light pulses increased exponentially. More light pulses were emitted under negative surges than under positive ones, and more were detected on the leading edge than the trailing edge of a negative surge, whereas the reverse occurred under a positive surge. As the surge repetition rate was increased, the amount of EL per surge decreased. Finally, there was no change of the spectral composition of EL with either polarity or magnitude of the applied surge. The results suggest that the detected EL may be due to single photons. The observed EL response is attributed to the creation and depletion of trapped space charges.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Puncture breakdown characteristics of protected rubber insulating gloves

The results of puncture breakdown tests on rubber gloves are presented. A positive polarity switching surge voltage (275/2500 mu s) or a 60 H alternating voltage was applied to the glove to cause breakdown. The effect of mechanical pressure on glove breakdown behavior and the influence of using a leather protector were investigated. It was found that protected gloves are more likely to break down at a position other than where the needle electrode has been placed. In both AC and switching surge breakdown tests, the standard deviation in breakdown voltage for protected samples was greater than that of the nonprotected samples by 25%. Under AC conditions, with mechanical stress applied, a bare glove will break down at a voltage which is approximately 22% below the nonstressed condition. A protected glove which is mechanically stressed will break down at a value 12.75% below the nonstressed condition. It is suggested that the results obtained will help to determine the operating limits and reliability of the glove insulation. >

OVARIAN SENSITIVITY TO GONADOTROPHINS IN PATIENTS WITH PCO IS UNAFFECTED BY SUPPRESSION OF LH

Infertile women with oligomenorrhoea and elevated LH concentrations (presumed polycystic ovary disease, PCO) were treated with exogenous gonadotrophins, HMG and HCG, for induction of follicular growth and ovulation, respectively. This was effected in the absence or presence of a gonadotrophin releasing hormone analogue (GnRH-A) to suppress basal LH and the positive feedback surge of LH. Analyses of the duration of HMG therapy required to attain the degree of stimulation for HCG to be administered showed no difference between those with and without LH suppression. Analyses of the ultrasound estimations of rates of follicle growth and continued recruitment during the course of HMG also failed to show any effect of LH suppression. These data show that the high sensitivity of these patients to HMG is not related to the circulating LH concentrations.

Rapid inhibitory effects of an LHRH agonist implant on the oestrogen-induced LH surge and the induction of a defective luteal phase after an agonist-induced ovulation in the macaque

Three experiments were performed to evaluate in detail pituitary--ovarian function during the first 21 days after treatment with a luteinizing hormone releasing hormone (LHRH) agonist implant. First, six adult macaques with normal menstrual cycles received an LHRH agonist implant during the late luteal or early follicular phase. To investigate the rapidly of effects on pituitary responsiveness the macaques were treated with 50 micrograms LHRH at the time of implant (day 0) and at days 4, 10 and 21. Effects on serum LH and FSH were determined on basal samples and at 30 and 60 min. At 4 days, LH and FSH were elevated as a result of the implant and no further response to LHRH challenge was observed. By 10 days, LH had returned to the pretreatment range but was unresponsive to the LHRH challenge; by 21 days, LH was lower than the pretreatment range and again LHRH failed to induce a significant response. Serum FSH concentrations also declined during treatment, but in contrast to LH, a significant response to LHRH was observed on day 10. Secondly, the ability to respond to an oestrogen provocation test was examined in six macaques with normal menstrual cycles treated with the LHRH agonist implant during the late luteal or early follicular phase and 7 days later with 50 micrograms/kg oestradiol benzoate in oil s.c. to induce an LH/FSH surge. In control animals, oestrogen treatment resulted in a positive feedback surge, reaching a maximum at 48 h post-injection. In contrast, agonist-treated animals showed complete abolition of the expected increase in LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of the oestrogen-induced LH surge in the ovariectomized common marmoset (Callithrix jacchus) by an LHRH antagonist

Six long-term ovariectomized adult marmoset monkeys were treated at 0 h with 35 micrograms oestradiol benzoate s.c. to induce an LH surge. They were also treated with detirelix (an LHRH antagonist) at 0 h, 12 h and 24 h (Exp. 1), or at 0 h and 24 h (Exp. 2) at a dose of 300 micrograms/kg s.c., or received the detirelix vehicle alone at 0 h, 12 h and 24 h (Exp. 3). All animals received the three treatments, with at least 4 weeks between experiments. Blood samples were collected at 0 h and at 6-12 h intervals for 72 h after oestradiol for the determination of plasma LH by bioassay. In control animals, oestrogen treatment resulted in a decline in plasma LH from 30.0 +/- 5.8 at 0 h to 12.8 +/- 2.6 ng/ml at 6 h (negative feedback), followed by a positive feedback surge, reaching a maximum of 148.0 +/- 34.6 ng/ml at 24 h. Values then declined to pretreatment levels by 56 h. In contrast, antagonist-treated animals showed complete abolition of the expected increase at 24 h, the low levels of the negative feedback phase being maintained for 36-72 h. These results show that hypothalamic LHRH release is essential during the oestrogen-induced LH surge, and that a direct oestrogen-induced component at the pituitary level is not expressed in the absence of LHRH in the marmoset.

Measurements of Mixed Transient Flows

Laboratory experiments were carried out to observe the mechanism of transition between free‐surface flow and pressurized flow conditions in a circular pipe. Filling or pressurization of a pipe is typically accomplished by a positive surge moving toward the free‐surface flow region. Under certain conditions airwater interaction during pressurization can produce water hammer pressures. Draining or depressurization also produces a shock surface, i.e. a negative surge, that moves toward the pressurized zone. Unlike the positive surge, the negative surge produces negative pressure in the pressurized zone. Some aspects of the transition between positive and negative surges were also studied.

Storm surges in the Arabian Gulf

The storm surge phenomenon in the Arabian Gulf, including the Strait of Hormuz, is discussed with particular emphasis on the development of mathematical models for prediction purposes. The Gulf is mainly influenced by extra-tropical weather systems, whereas the region south of the Strait of Hormuz is affected by tropical cyclones. The west-to-east directed extra-tropical cyclone tracks and the generally east-to-west directed tropical cyclone tracks converge near the Strait of Hormuz. A meso-scale weather system that deserves special attention in prescribing the meteorological forcing functions is the so-called ‘winter Shamal’. A two-dimensional numerical model is developed to study the storm surges in the Arabian Gulf. The results show that the Gulf is subject to major negative and positive storm surges. Strong winds associated with the Shamal system, coupled with atmospheric pressure gradients, topography and tidal effects, can give rise to water level deviations of several meters. Storm surges observed during the period 17–19 January 1973 show that negative values in the 0.5 to 1.0m range were widespread in the Gulf.

The role of "beta-endorphin & beta-lipotropin" on the gonadotropin regulation in the mechanism of human ovulation

The aim of this study is to elucidate the role of "beta-endorphin (beta-End) & beta-lipotropin (beta-LPH)" on the regulation of gonadotropin (Gn) secretion. We investigated the relationships between immunoreactive beta-End plus beta-LPH and Gn in peripheral plasma of normal menstruating women, 1) during periovulatory period, especially at the time of Gn surge, 2) at the estrogen induced Gn surge (positive feedback) and 3) at the time of hypoxic stress. Plasma concentrations of beta-End plus beta-LPH were measured as immunoreactive beta-End (i-beta-End) by RIA after extraction with Sep-Pak C18. First, we assessed pulsatile Gn secretions during periovulatory period in 19 normal women every 10 minutes for 4 hours, some women were at the time of Gn surge in its ascending limb, plateau of the peak, and descending limb of the surge. Meanwhile, circadian variations of plasma i-beta-End levels of these subjects were assessed at 4 hours' interval on the same day. In two subjects, on the day before the onset of LH surge, significantly low (p less than 0.05) basal and peak levels of i-beta-End were observed, although the basic patterns of circadian rhythm were preserved. Secondly, changes of plasma i-beta-End levels during estrogen (estradiol benzoate 1mg i.m.) induced positive feedback tests were evaluated in 16 normal women and 6 hypothalamic amenorrheic women by daily blood sampling. In normal subjects, small but significant increases (p less than 0.05) of plasma i-beta-End were observed when Gn showed initial decreases at 48 hours after injection. Subsequently at 72 hours, however, plasma i-beta-End decreased precipitously at the time of Gn surge. On the other hand, in hypothalamic amenorrheic women who were devoid of Gn surge, no significant changes of plasma i-beta-End levels were observed. The transient decreases of plasma i-beta-End just prior to the Gn surge support the idea that i-beta-End exerts tonic inhibition on the onset of Gn surge and the disappearance of its inhibition might trigger the positive Gn surge. And it was also suggested that release mechanisms of both i-beta-End and Gn are impaired in hypothalamic amenorrhea. Thirdly, in acute hypoxic stress experiment, 5 normal female volunteers were placed in hypobaric (500 mbar) condition in which oxygen supply is a half of atmosphere, simultaneous blood samplings of Gn, prolactin and i-beta-End were performed every 15 minutes for 3 hours.(ABSTRACT TRUNCATED AT 400 WORDS)