Syarif Hidayat

Spatial and temporal distribution of lightning activity around Java

Cloud-to-ground lightning flashes on and around the island of Java, Indonesia, in the tropical maritime continent region, were observed continuously by a magnetic direction-finder network for lightning location from December 1994 to January 1996. The annual ground flash density, estimated by correcting the raw data by using the detection efficiency of the network, ranged from less than 2 to about 16 flashes/y/km 2 on the island. The average annual ground flash density over the entire island was 3.2 flashes/y/km 2 , as opposed to 0.24 flashes/y/km 2 on the Indian Ocean about 100 km south of the island. The majority of the flashes on the land occurred during November to April in the rainy season. In the dry season, lightning was active only in the western part of the island. The amount of monthly precipitation over the island was related to the monthly number of ground flashes, but the ratio of the precipitation to the ground flash density differed from season to season, from 4 × 10 8 kg/flash in the rainy season to 1.3 × 10 9 kg/flash for other months. The ratio observed in the rainy season is equal to that for the break period in the rainy season observed at Darwin, Australia, in the same maritime continent region. The annual ratio for the entire island was 6 × 10 8 kg/flash. The diurnal variation of the lightning activity averaged over the island in the set season showed a single peak in the afternoon with the peak time of about 1530 LT, similar to those reported for land stations in the tropics. The diurnal variation over the ocean had a peak in the early morning, showing the same characteristic observed in the western Pacific. The diurnal variation of the lightning activity on the sea of offshore regions around Java showed an almost out-of-phase pattern to the variation on the land, indicating the influence of the land-sea effect.

Diurnal variation of lightning characteristics around Java Island

The diurnal variation of lightning activity on and around Java Island, Indonesia, is examined by using the observation results from a magnetic direction finder network. The magnetic direction finder network has four direction finders on Java Island and has been operating since 1994. Lightning is active during the rainy season, usually from October to May. The highest ground flash density on Java Island was 16 flashes per km2 per year. The diurnal variation of the lightning activity over land shows its peak at around 1500 LT. There is a small peak in the early morning around 0300–0500 LT over the sea, several hours prior to the reported peak times of the cold cloudiness, an indicator of deep convection observed from meteorological satellites. Existence of close sea-land interaction related to the activity of deep convection in this area is suggested from the diurnal variations in the lightning activity. The diurnal variation is also found in the peak currents of negative first return strokes over land, medians from 25 kA around noon to 30 kA around midnight. The lightning activity over the ocean does not show such diurnal variation and delivers currents of higher amplitudes with a median of 36 kA.

Integrating Web Server Applications With LDAP Authentication: Case Study on Human Resources Information System of UI

Lightweight directory access protocol (LDAP) accomodates the need of high level of security, single sign-on, and centralized user management. This protocol offers security services and integrated directory with capability of storage management user information in a directory. Therefore at the same time the user can determine application, service, server to be accessed, and user privileges. In this paper, we explain our experience in implementing the authentication mechanism for our human resources information system Web server application by taking identification of user information from LDAP server using LDAP authentication method. We also show the result and performance analyses on the access speed in using LDAP method

Lightning Discharges on Land and on Sea in Indonesia

To investigate lightning on land and on sea in Indonesia, an observation using a lightning detection network has been carried out on the Java Island (Indonesia), employing a lightning detection network with four MDF stations. Analysis on the collected data revealed high lightning flash density around the Java Island, especially during the rainy season. The highest annual flash density on the Java Island was 16 flashes per km2 per year. Lightning discharges around Java exhibits a diurnal variation, where the activity mostly takes place on the island in the afternoon. A smaller peak of activity, especially in the rainy season, takes place in the early morning offshore. The median of the lightning current amplitudes in this area is around 26 kA, close to the result of direct measurement. The analysis also shows that discharges on the sea bring larger currents than those on the land. Storms on the land tend to deliver more number of strokes with higher maximum flash rates in smaller coverage areas than those occur on the sea

Observation of Lightning Discharges in Indonesia by Lightning Detection Network

A real-time lightning location network started to operate in Indonesia in mid 1995 and began providing reliable data in the end of the same year. The network consists of 8 signal receiving stations and works using the Time-Of-Arrival (TOA) technique. Area covered by the network includes: Java Island, Bali Island, Southern part of Sumatra Island, Southern part of Kalimantan Island, and Southern part of Sulawesi Island. The present work reports on the lightning stroke density obtained by the TOA network for 5 consecutive years from 1996 to 2000 on the Java Island. Maps of the lightning stroke density and its annual variations are presented. Further, monthly variation of the detected lightning strokes is also discussed. Lightning activity on the Island shows a consistent high density. The spatial and temporal distribution of lightning activity on the Island as reported by Hidayat and Ishii are confirmed. The density obtained using the present network is comparable to that reported by Hidayat and Ishii. On the other hand, the current amplitude is almost two-fold higher with an increasing tendency from 1995 to 1999

Hydrogen production in microbial reverse-electrodialysis electrolysis cells using a substrate without buffer solution

The aim of this work was to use substrate without buffer solution in a microbial reverse-electrodialysis electrolysis cell (MREC) for hydrogen production under continuous flow condition (10 cell pairs of RED stacks, HRT=5, 7.5, and 15h). Decreasing in the HRT (increasing in the organic matter) made cell current stable and increased. Hydrogen gas was produced at a rate of 0.61m(3)-H2/m(3)-Van/d in H-MREC, with a COD removal efficiency of 81% (1.55g/L/d) and a Coulombic efficiency of 41%. This MREC system without buffer solution could successfully produce hydrogen gas at a consistent rate.

Lightning characteristics and performance of distribution system around Jakarta

A real-time lightning location network started to operate in Indonesia in mid 1995 and began providing reliable data in the end of the same year. The network consists of 8 signal receiving stations and works using the time-of-arrival (TOA) technique. The present paper reports on lightning characteristics observed by the LPATS-III network for 5 consecutive years from 1996 to 2000 on the Java Island, Indonesia. Performance of the MV distribution system in Jakarta recorded for the same period is analyzed in relation to the lightning activity. Lightning activity on the Island shows a consistent high density. The spatial and temporal distribution of lightning activity on the Island as reported by Hidayat and Ishii are confirmed. OH line outages and temporary outages dominate the performance of MV distribution line in Jakarta. Both types of outage exhibit strong correlation with lightning activity. The performances of OH lines and cable for Jakarta distribution system are estimated to be 36.2 and 24.6 outages per 100 km per year, respectively.

Performance of a continuous flow microbial reverse-electrodialysis electrolysis cell using a non-buffered substrate and catholyte effluent addition

A continuous flow microbial reverse-electrodialysis electrolysis cell (MREC) was operated under non-buffered substrate with various flow rates of catholyte effluent into anode chamber to investigate the effects on the hydrogen gas production. Adding the catholyte effluent to the anolyte influent resulted in increased salt concentration in the anolyte influent. The increasing anolyte influent salt concentration to 0.23M resulted in improved hydrogen gas production, Coulombic recovery, yield, and hydrogen production rate to 25±1.4mL, 83±5%, 1.49±0.15mol-H2/mole-COD, 0.91±0.03m3-H2/m3-Van/day, respectively. These improvements were attributed to the neutral pH rather than increase in anolyte conductivity as there was no significant improvement in the reactor performance when the NaCl was directly added to the reactor. These results show that addition of catholyte effluent into the anode chamber improved the MREC performance.

Lightning protection system on overhead distribution line using Multi Chamber Arrester

New innovation on arrester technology has been made by appearance of Multi Chamber Arrester (MCA). This kind of arrester has basic principle similar to previous technology which use air gap and air pressure in chamber as its technology. MCA has a function to protect overhead line from lightning. For instance, 20 kV medium voltage overhead line.

Design technology in wireless mesh network system for eruption disaster mitigation of Merapi volcano

Indonesia is one country in the world that has the biggest natural disaster risk. That is because the position of Indonesia which is located at the confluence of three plaques Indo-Australian, Eurasian and Philippines. One of the disasters that often occur is the eruption of a volcano that is indeed one of the most active volcanoes in the world located in Indonesia called Merapi volcano. Currently, monitoring a volcano still rely on measurements on site and remote monitoring using camera and outposts near Merapi volcano. It is becoming less effective due to the efficiency and effectiveness of the key staple of disaster mitigation process. This paper provides a new approach to monitor the state of the Merapi based on ambient temperature in Merapi using wireless mesh network system based on Zigbee modules, effectiveness and reliability found in volcano monitoring which the level of reliability of a particular node at a distance of 200m and can perform data transmission when multiple nodes are damaged and the data is sent successfully.