Oceanographic and behavioural assumptions in models of the fate of coral and coral reef fish larvae

A predictive model of the fate of coral reef fish larvae in a reef system is proposed that combines the oceanographic processes of advection and turbulent diffusion with the biological process of horizontal swimming controlled by olfactory and auditory cues within the timescales of larval development. In the model, auditory cues resulted in swimming towards the reefs when within hearing distance of the reef, whereas olfactory cues resulted in the larvae swimming towards the natal reef in open waters by swimming against the concentration gradients in the smell plume emanating from the natal reef. The model suggested that the self-seeding rate may be quite large, at least 20% for the larvae of rapidly developing reef fish species, which contrasted with a self-seeding rate less than 2% for non-swimming coral larvae. The predicted self-recruitment rate of reefs was sensitive to a number of parameters, such as the time at which the fish larvae reach post-flexion, the pelagic larval duration of the larvae, the horizontal turbulent diffusion coefficient in reefal waters and the horizontal swimming behaviour of the fish larvae in response to auditory and olfactory cues, for which better field data are needed. Thus, the model suggested that high self-seeding rates for reef fish are possible, even in areas where the ‘sticky water’ effect is minimal and in the absence of long-term trapping in oceanic fronts and/or large-scale oceanic eddies or filaments that are often argued to facilitate the return of the larvae after long periods of drifting at sea.     

Current equalization in SPWM FACTS controllers at lowest switchingrates

This paper shows that sinusoidal pulsewidth modulation (SPWM) flexible AC transmission system (FACTS) controllers can be synthesized by employing the phase-shifted triangle carrier technique to multiconverters at a switching rate of only three pulses. The options of parallel, series and series/parallel module connections are examined for current equalization. This paper presents simulation and experimental results     

Multimodular multilevel converters with input/output linearity

Multilevel converters constitute the key technology of power electronics to reach the high power ratings required by controllers of flexible AC transmission systems (FACTS). This paper shows that the sinusoidal pulsewidth modulation (SPWM) technique, as applied to multilevel converters, inherently requires a high switching rate. The paper then presents a strategy based on multiple modules of multilevel converters which operate with the lowest possible switching loss (each gate-turn-off thyristor (GTO) switches ON and OFF only once during the modulation period), while maintaining the high gain-bandwidth product of linear amplifiers to handle fast feedbacks, which FACTS controllers must be capable of, in order to carry out dynamic performance enhancement     

谷物纤维及粉尘阴燃实验研究

以麦麸纤维及粉尘为试样.在圆筒形实验装置中进行了顺风向阴燃传播实验,利用热电偶测量阴燃平均传播速度,气体成分分析仪测量阴燃特征气体组分,研究了通风量、试样松散密度、试样中粉尘含量对阴燃传播速度的影响.研究表明:在通风量较低的情形下,谷物粉尘也容易发生阴燃,阴燃早期主要特征气体为CO、CO2,阴燃速度与通风量成正比,与试样松散密度成反比,通风量达到一定值时,阴燃极易发展为有焰燃烧.     

UPFC using multiconverter operated by phase-shifted trianglecarrier SPWM strategy

The acronym UPFC covers Ggugyi's unified power flow controller and Akagi and Fujita's unified power flow conditioner. This paper describes one method of meeting high MVA specifications by using multiple modules of two-level three-phase power converter modules controlled by the phase-shifted triangle carrier technique of the sinusoidal pulsewidth modulation (SPWM) strategy. Two conceptual designs are presented. The first is the gate-turn-off (GTO)-SPWM-UPFC at the lowest switching rate, f_c/f_m=3, to minimize GTO switching loss. The design is based on applying the fundamentals of SPWM theory to overcome unbalances arising from sideband harmonic interferences. The second is the insulated gate bipolar transistor (IGBT)-SPWM-UPFC, at f_c/f_m=12 or higher, in which SPWM theory assures that direct paralleling of the modules is free of current unbalance. A laboratory UPFC based on six modules of three-phase 5-kVA size IGBT power converters operating at the baseline condition of dual unity displacement factor at the sending end and the receiving end has been implemented     

Unified power flow controller (UPFC) based on chopper stabilizeddiode-clamped multilevel converters

As the diode-clamped, multilevel converter has been found to have attractive features for STATCOM application, there is interest in extending it to UPFC application by using multilevel converters as the series and the shunt converters. Unfortunately, as is demonstrated in this paper, the DC voltages at their DC links, are inherently unstable. Faced with this impasse, a solution is sought in a system of local feedback controlled Class B choppers to equalize the DC. A laboratory experimental model establishes the feasibility of the proposal. Digital simulations show that current ratings in the choppers need be only 10% of the current ratings in the converters. The chopper cost is estimated as 1% of the cost of the multilevel converters     

The trigger detector for APEX: An array of position-sensitive NaI(Tl) detectors for the imaging of positrons from heavy-ion collisions

We describe a 24-element position-sensitive cylindrical NaI(Tl) detector which allows positron imaging with an on-axis position resolution of 3 cm FWHM and annihilation radiation energy resolution of 13% FWHM. Two such detectors will provide the trigger for the APEX experiment at Argonne National Laboratory, which is exploring anomalous positron and electron production observed in heavy-ion collisions.     

Effect of nonisentropic processes on transition from combustion to detonation in combustible mixtures

The problem of spontaneous combustion of a compressible reacting gas in a wall boundary layer behind a single shock wave in a tube with an adiabatic wall is examined. The possibility of leading spontaneous combustion of the gas in the boundary layer compared with spontaneous combustion in the flow core is shown in an approximation of a one-stage chemical reaction. Explosion in the boundary layer occurs locally, and in the vicinity of the exploding gas particle there is a finite gradient of the spontaneous-combustion induction time. The calculated velocity of the spontaneous-combustion (spontaneous-flame) wave is close to the local sound velocity, which indicates the possibility of the generation of a strong blast wave. With consideration of the nonadiabatic character of the wall, the investigated effect is manifested as a result of multiple compression of the reacting mixture by shock waves or simple compression waves, as well as for a wall made of a material with a low thermal conductivity.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 3, pp. 29–36, May–June, 1995.     

Microprocessor-implemented SPWM for multiconverters withphase-shifted triangle carriers

This paper reports on research aimed at achieving computer control of power electronic converters for high-power applications. Hitherto, in motor-drives applications, the 4-Timer Method has been adequate in approximating the sinusoidal pulsewidth modulation (SPWM) strategy for microprocessor control. This paper shows that the ideas of the 4-Timer Method can be extended, with modifications, to the multimodule arrays of converters which will be required to meet high megavoltampere ratings. Simulation and experimental results have shown that the resultant 7-Timer Method can implement the linear SPWM strategy for multiconverters     

Recycling light metals from end-of-life vehicle

The amount of aluminum used in cars and light trucks is growing steadily. However, without new developments in aluminum recycling technologies, sheet from automotive aluminum could eventually flood all current markets for recycled aluminum. This article summarizes the use of light metals and different alloys in transportation applications, the current auto recycling system, and new developments in the sorting of light metals by the metal recycling industry and by Huron Valley Steel Corporation, the world’s largest non-ferrous scrap sorter. For more information, contact A. Gesing, Huron Valley Steel Corporation, 41000 Huron River Drive, Belleville, Michigan 48111; (734) 697-6313; fax (734) 697-3420; e-mail gesinga@hvsc.net.