An integrated off-on line approach for increasing stability and effectiveness of automated controlled systems based on pump dependability—case study: Offshore industry

Automated controlled systems are vulnerable to faults. Faults can be amplified by the closed loop control systems and they can develop into malfunction of the loop. A control loop failure will easily cause production stop or malfunction at a petrochemical plant. A way to achieve a stable and effective automated system is to enhance equipment dependability. This paper presents a standard methodology for the analysis and improvement of pump performance to enhance total operational effectiveness and stability in offshore industry based on dependability. Furthermore, it is shown how a reliability–safety analysis can be conducted through equipment dependability indicators to facilitate the mitigation of hazard frequency in a plant. The main idea is to employ principle component analysis (PCA) and importance analysis (IA) to provide insight on the pumps performance. The pumps of offshore industries are considered according to OREDA classification. The approach identifies the critical pump and their fault through which the major hazards could initiate in the process. At first PCA is used for assessing the performance of the pumps and ranking them. IA is then performed for the worst pump which could have most impact on the overall system effectiveness to classify their components based on the component criticality measures (CCM). The analysis of the classified components can ferret out the leading causes and common-cause events to pave a way toward improving pump performance through design optimization and online fault detection which ultimately enhance overall operational effectiveness.     

Reversed sex change by widowed males in polygynous and protogynous fishes: female removal experiments in the field

Sex change, either protogyny (female to male) or protandry (male to female), is well known among fishes, but evidence of bidirectional sex change or reversed sex change in natural populations is still very limited. This is the first report on female removal experiments for polygnous and protogynous fish species to induce reversed sex change in the widowed males in the field. We removed all of the females and juveniles from the territories of dominant males in the cleaner wrasse Labroides dimidiatus (Labridae) and the rusty angelfish Centropyge ferrugata (Pomacanthidae) on the coral reefs of Okinawa. In both species, if new females or juveniles did not immigrate into the territories of the widowed males, some of them emigrated to form male–male pairs. When a male–male pair formed, the smaller, subordinate partner began to perform female sexual behaviours (n = 4 in L. dimidiatus; n = 2 in C. ferrugata) and, finally, released eggs (n = 1, respectively). Thus, the reversed sex change occurred in the widowed males according to the change of their social status. These results suggest that such female removal experiments will contribute to the discovery of reversed sex change in the field also in other polygnous and protogynous species.     

Standing crops and vertical distribution of four groups of marine planktonic ciliates in relation to phytoplankton chlorophyll a

Standing crops and the vertical distribution of four groups of ciliates, autotrophic naked ciliates (ANC), heterotrophic naked ciliates (HNC ), mixotrophic naked ciliates (MNC) and loricated ciliates (LC ), were analysed in relation to phytoplankton chlorophyll a in the western Pacific. Data were gathered from the upper 60 to 200 m of water in the subarctic North Pacific in spring, in the subtropical North Pacific in spring, in Toyama Bay in summer, off eastern Australia in spring and off Sanriku in spring and fall. Of the four groups, the standing crop of HNC (cells l⁻¹) showed the highest correlation to phytoplankton chloro- phyll a [CHL, μg l⁻¹; r=0.66, n=365 (HNC=490 ×CHL ^0.653)]. Depths of the maximum layers of HNC and MNC were usually shallower than that of chlorophyll a, while those of ANC and LC occurred frequently beneath the chlorophyll maximum layer. This indicates that these four ciliate groups are substantially different from each other, and that each group holds a different ecological position in the marine microbial food web. Received: 27 October 1997 / Accepted: 27 June 1998