Maximum Instantaneous Value Research Articles

Experimental Study on the Behavior of Aluminum Fuse Element Inside 24 kV, 50 kA High-Voltage Fuses

High-voltage fuses are found in most electrical installations, where they are used for overcurrent protection and are the pieces of equipment providing the highest degree of protection for the lowest initial cost. This article focuses on the behavior of high-voltage fuses containing a fuse element entirely made of aluminum. We made high-power linear electrical circuits for experiments on these fuses under the most severe operating conditions. The article presents the construction details of the fuse element and its features, as well as various arc extinguishing media. The heating behavior and time–current characteristics were studied in comparison with fuses made of copper. We obtained the maximum instantaneous value of the current reached during interruption for a 24 kV, 50 kA, 50 A fuse, as well as the value of the minimum breaking current.

Measured Analysis on Surface Deformation and Influence of Cutter Torque for Twin Shield Tunnelling in Silty Sand

In this study, the field measurement was conducted on the twin shield tunnelling in a shield section of Hangzhou Metro Line 6, where the surface deformation caused by twin shield tunnelling in the silty sand was obtained. The surface deformation law and the applicability of the twin‐line Peck formula in the silt area were analyzed. The relationship between the cutterhead torque and the surface deformation in the silty sand was identified. Furthermore, the differences in surface deformation of twin shield tunnelling in the Hangzhou soft soil area were discussed. The results show that the settlement process caused by twin shield tunnelling in silty sand is faster than that of soft soil and has no rebound phenomenon. The twin‐line Peck formula is suitable in silty sand, but the prediction of the latter line using this formula is slightly deviated because of the secondary disturbance effect. Due to the secondary disturbance of the soil caused by the construction of the latter line, the soil loss rate of the latter line is higher than that of the former line. Therefore, the reference ratio of the soil loss rate of the latter line and the former line is given. Furthermore, the cutterhead torque of the shield machine was found to be associated with the maximum instantaneous value of the surface deformation.

Non-stationary convective heat transfer in an air synthetic impinging jet. Experiment and numerical simulation

An unsteady local heat transfer in an air synthetic non-steady-state jet impingement onto a flat plate with a variation of the Reynolds number, nozzle-to-plate distance and pulses frequency is experimentally and numerically studied. Measurements of the averaged and pulsating heat transfer at the stagnation point are conducted using a heat flux sensor. The axisymmetric URANS method and the Reynolds stress model are used for numerical simulations. For local values of heat transfer, zones with the maximum instantaneous value of heat flux and heat transfer coefficient are identified. The heat transfer increases at relatively low nozzle-to-plate distances (H/d ≤ 4). The heat transfer decreases at high distance from the orifice and target surface. An increase in the Reynolds number causes reduction of heat transfer.

Évaluation préliminaire de l’utilisation de détecteurs individuels portatifs de peroxyde d’hydrogène au sein d’une unité de préparation centralisée de médicaments cytotoxiques

For 1 year, our unit has been equipped with portable H₂O₂ Dräger detectors contributing to protect the staff from a possible exposure to this odourless and toxic gas. This work shows the current available data about H₂O₂ toxicity, describes the organization of the implementation and the analysis of the values measured over 12 months. Data about H₂O₂ toxicity have been obtained through a literature review. The measured values are presented in instantaneous value and occupational exposure limit (OEL) over 8 h. Over six technicians, the average percentage, of detected values superior to zero reached 1.06% in August. The detected maximum instantaneous value reached 2.2 ppm in May. These isolated exposures have little incidence when related to the 8-h exposure with an occupational exposure limit (OEL) of 0.072 ppm over 12 months. The implementation of this tool has allowed to highlight a technical problem of the sterilization airlock that could be resolved. This measuring device of H₂O₂ concentration in the air in real time allows to secure everyday working conditions and to alert the staff of a possible technical failure. However, literature data regarding chronic toxicity are limited and restrict the analysis of the measured values.

Suspended sediment transport in a highly erodible catchment: The River Isábena (Southern Pyrenees)

Understanding and quantifying sediment load is important in catchments draining highly erodible materials that eventually contribute to siltation of downstream reservoirs. Within this context, the suspended sediment transport and its temporal dynamics have been studied in the River Isábena (445 km 2, south-central Pyrenees, Ebro basin) by means of direct sampling and turbidity recording during a 3-year dry period. The average flood-suspended sediment concentration was 8 g l − 1 , with maximum instantaneous values above 350 g l − 1 . The high scatter between discharge and suspended sediment concentrations (up to five orders of magnitude) has not permitted the use of rating curve methods to estimate the total load. Interpolation techniques yielded a mean annual sediment load of 184,253 t y − 1 for the study period, with a specific yield of 414 t km − 2 y − 1 . This value resembles those reported for small torrents in nearby mountainous environments and is the result of the high connectivity between the badland source areas and stream courses, a fact that maximises sediment conveyance through the catchment. Floods dominated the sediment transport and yield. However, sediment transport was more constant through time than that observed in Mediterranean counterparts; this can be attributed to the role of base flows that entrain fine sediment temporarily stored in the channel and force the river to carry high sediment concentrations (i.e., generally in the order of 0.5 g l − 1 ), even under minimum flow conditions.

Seasonal and diurnal patterns in leaf gas exchange of Eucalyptusglobulus trees growing in Portugal

Gas exchange of adult leaves of Eucalyptusglobulus Labill. trees growing in Portugal was monitored during weekly periods between September 1982 and August 1983. Photosynthetic carbon assimilation rates and leaf water use efficiency were highest (maximum instantaneous values, ca. 12 μmol CO2 m−2 s−1 and ca. 7 mmol CO2 mol H2O−1, respectively) in the spring, somewhat reduced in the winter, and strongly depressed by the middle of the summer, when severe drought conditions prevailed. Diurnal patterns of variation in stomatal conductance and net photosynthesis rates showed a marked seasonal variation. With the transition from winter to spring and summer, as the environmental conditions became warmer and drier, there was an increasing tendency for a midday depression in gas exchange rates as well as a decreasing capacity in the afternoon for recovery to the same net photosynthesis rates measured in the morning. Midday depression in gas exchange and stomatal conductance occurred in leaves positioned both vertically and horizontally inside the measurement cuvettes. Leaf dark respiratory rates also changed with the season; the temperature necessary to evoke similar rates increased with the transition from winter to summer.

SEASONAL VARIATION OF SOLAR UV‐RADIATION AT A HIGH MOUNTAIN STATION

Abstract— At the high mountain station Jungfraujoch (3576 m), the maximum daily totals for erythemal dose (GER), UV‐A radiation (GUVA) and global radiation (G) are 29 Sunburn Units d−1, l.7 MJ m−2d−1 and 37 MJ m−2 d−1. The maximum instantaneous values at solar noon in midsummer are 4.2 Sunburn Unit h−1, 53 W m−2 and 1110 W m−2. A significantly nonlinear relation between GER and G results from the influence of the irradiated ozone mass on the UV‐B erythemal dose. In contrast, GUVA and G are linearly proportional, which can be seen from the diurnal and seasonal courses of the ratios GER/G and GUVA/G AND from their dependence on the optical air mass. UV‐A radiation flux is less attenuated by cloudiness than is global radiation. This effect is masked for the erythemal dose by variations in the ozone concentration. Due to seasonal ozone layer thickness and effective pathlength variations, the ratio GER/G shows a significant asymmetry. At the autumn equinox it is about 16% higher than at the spring equinox.

Quantitative transcutaneous measurements of blood flow in carotid artery by means of pulse and continuous wave Doppler methods.

<h2>Abstract</h2> The authors present results of quantitative measurements of blood <i>in vivo</i> in the carotid artery of man. The Doppler pulse technique was used after being previously verified for steady state flows in tubes and for pulsating flows in a canine aorta where the electromagnetic method was also used for comparison. An ultrasonic probe with two transducers was adapted for determination of the angle of the ultrasonic beam in relation to the vessel allowing the measurement of the vessel diameter which was also determined by means of the ultrasonographic <i>B</i>-mode technique. By means of the Doppler pulse method profiles of the blood velocity in the carotid artery were determined as a function of time. The continous wave Doppler technique together with the zero-crossing system and spectral analysis were also used for making measurements. The flow velocity and the shape of the flow curve with time obtained with the above techniques showed good agreement. The measured flow rate in the carotid artery amounted to <i>Q</i>_M = 1.61/min (maximum instantaneous value) and <i>Q</i>₀ - 0.531/min (mean time value).

Short-circuits of A-C. Generators — II

At the mid-winter convention of the A. I. E. E. in February, 1924, the writer presented a paper on the maximum instantaneous values of the currents delivered by alternating-current generators under different short-circuit conditions. A summarized table was given for the maximum values of the short-circuit currents for different winding combinations of an ideal generator on the basis of a constant field flux, and that the short-circuit occurs at the instant the axis of the field winding coincides with the axis of the particular portion of the armature winding under consideration.

Short circuits of alternating-current generators

In this paper, the author presents a physical conception and simple non-mathematical analysis of the short-circuit phenomena of alternating-current generators. Formulas are developed for the maximum instantaneous values of the armature and field short-circuit currents delivered by both single and polyphase generators, which are equipped with and without damper windings.

Short Circuits of Alternating-Current Generators

In this paper, the author presents a physical conception and simple non-mathematical analysis of the short-circuit phenomena of alternating-current generators. Formulas are developed for the maximum instantaneous values of the armature and field short-circuit currents delivered by both single and polyphase generators, which are equipped with and without damper windings. A similar analysis covering the rate of decay and the sustained values of the short-circuit currents will be presented in the near future.

Short-Circuits of A-C. Generators-II

At the mid-winter convention of the A. I. E. E. in February, 1924, the writer presented a paper on the maximum instantaneous values of the currents delivered by alternating-current generators under different short-circuit conditions. A summarized table was given for the maximum values of the short-circuit currents for different winding combinations of an ideal generator on the basis of a constant field flux, and that the short-circuit occurs at the instant the axis of the field winding coincides with the axis of the particular portion of the armature winding under consideration. In the present paper, a similar analysis is given for the magnitude and variation of magnitude of the short-circuit currents during the transient period, that is, during the time the currents vary from the maximum to the sustained values.