Low Correlation Sequences over the QAM Constellation

This paper presents the first concerted look at low correlation sequence families over QAM constellations of size M^2=4^m and their potential applicability as spreading sequences in a CDMA setting. Five constructions are presented, and it is shown how such sequence families have the ability to transport a larger amount of data as well as enable variable-rate signalling on the reverse link. Canonical family CQ has period N, normalized maximum-correlation parameter theta_max bounded above by A sqrt(N), where 'A' ranges from 1.8 in the 16-QAM case to 3.0 for large M. In a CDMA setting, each user is enabled to transfer 2m bits of data per period of the spreading sequence which can be increased to 3m bits of data by halving the size of the sequence family. The technique used to construct CQ is easily extended to produce larger sequence families and an example is provided. Selected family SQ has a lower value of theta_max but permits only (m+1)-bit data modulation. The interleaved 16-QAM sequence family IQ has theta_max <= sqrt(2) sqrt(N) and supports 3-bit data modulation. The remaining two families are over a quadrature-PAM (Q-PAM) subset of size 2M of the M^2-QAM constellation. Family P has a lower value of theta_max in comparison with Family SQ, while still permitting (m+1)-bit data modulation. Interleaved family IP, over the 8-ary Q-PAM constellation, permits 3-bit data modulation and interestingly, achieves the Welch lower bound on theta_max.Comment: 21 pages, 3 figures. To appear in IEEE Transactions on Information Theory in February 200

Coral reef fish abundance and diversity of seagrass beds in Kavaratti atoll, Lakshadweep, India

The community organization of coral reef fishes in the seagrass sub-habitat of Kavaratti toll, Lakshadweep, India was studied during the period from January 1991 to June 1992. Twenty-seven families represented by 65 species were recorded by the visual censes method. The community diversity for families and species was 2.49 and 3.14 respectively. Juveniles and sub-adults of the most adult reef fish, which inhabit other sub-habitats, were recorded here. The high species diversity in the seagrass beds is due to their roles as nurseries, shelter and foraging grounds for many species. Labridae, Chaetodontidae, Acanthuridae and Mullidae were the most speciose families. Ocurrence of siganids was highly seasonal. The cover that seagrass canopy provides conceals many species and perhaps influenced counts. The occurrence of balistids could be related to the presence of interstitial and patches and abundant invertebrate food. Scorpaenids subsisted on abundant invertebrates and juveniles fishes. High counts and pronounced variations make seagrass beds unstable habitats. However, monsoon assemblages were relatively stable perhaps due to lack of excessive new recruits and a habitat shift by most species

Studies on some aspects of biology and ecology of coral reef fishes of Lakshadweep with observations on other coral reef ecosystems in the seas around India

The prelude for this study was an investigation conducted by me in 1988 - '89 on the bionomics of three marine ornamental fishes from Lakshadweep which emboided results of research mainly concerning biological aspects of feeding and reproduction. Motivated by the richness of reef fishes, their fascinating relationships evident from casual observations and from the basics obtained previously, it was considered desirable to undertake investigations on a broader scale which might open up a nearly dormant field of fisheries science in India

Enabling Context-Based Learning with KPortal Webspace Technology

Recognizing the importance of context-based learning and the general lack of technology applications in the design and development of the ideal and formal curricula, this paper describes an experimental system at a large public university. The authors describe the creation of a contextual environment for introducing concepts related to information security to undergraduate business students using the KPortal (Knowledge Portals) webspace technology that supports dynamic content gathered from various sources automatically. The KPortal webspace rated highly on the various attributes of effective contexts and the characteristics of technologies that enable context-based learning. The flexibility provided by the webspace permitted the authors to develop adaptable environments in which the students could connect well with rather abstract concepts. The overall intervention was designed to examine if a limited portion of the course could be supported by technology and next phases of the research will broaden its use to semester-length curriculum

Habitat distribution and species diversity of coral reef fishes in the reefslope of the Kavaratti atoll, Lakshadweep, India

Habitat distribution and species diversity of coral reef fishes in the reef slope of Kavaratti atoll was studied by the visual census method during January 1991 to June 1992. Twenty seven families represented by 121 species, the highest for any sub-habitat of the atoll were recorded. The community diversity, also the highest both for families and species was 3.32 and 4.45 respectively. Family assemblages were not stable between censuses and pre-monsoon, mon- soon and post-monsoon seasons. Labridae, Chaetodontidae, Balistidae, Pomacentridae and Acanthuridae were the most specious families. Low abundance of coral feeders indicated unhealthy reef condition. While dominance of some surgeonfish indicated availability of al- gal food, balistids provided clues for topographic complexity

Community organization of reef fishes in the live coral sub-habitat of Kavaratti atoll, Lakshadweep, India

Data on the community organization of coral reef fishes of Kavaratti atoll, Lakshadweep, India were collected during the period January 1991 to June 1992. Species were enumerated by visual census on the live coral sub-habitat for frequency of occurrence, abundance, composition, diversity, evenness and seasonal variation in community parameters. As the live coral zone was composed of a single species of ramose coral (Acropora formosa), only 14 families and 39 species of reef fishes made use of this zone, the community diversity being 1.84 and 3.16. Chaetodontids, labrids and pomacentrids were comparatively more abundant. Varying habitats of chaetodontids explain their restricted distribution. Live coral does not seem to be a preferred habitat of labrids. The occurrence of epinephelids was influenced by readily available prey. Most species among live coral were resident, variations resulted from factors affecting new recruits rather than habitat shifts

Community organization of coral reef fishes in the rubble sub-habitat of Kavaratti Atoll, Lakshadweep, India

A visual census of the coral reef fishes, conducted during January 1991 to June 1992, indicated the occurrence of 64 species belonging to fifteen families in the rubble sub-habitat of Kavaratti A toll (Lat. 10°33'N; Long. 7Z038'E) in Lakshadweep. The community diversity for families and species was 2.68 and 3.58 respectively. Family assemblages were not stable during different seasons. Labridae and pomacentridae made use of the rubble zone efficiently. Pomacentrids were characteristically site attached but varied in relative abundance. Rhinecanthus aculeatus among balistids depended on rubble for food and nesting sites. The occurrence of chaetodontids was due to their flexible feeding habits, in the absence of coral cover. Availability of food strongly determined the distribution of the surgeonfish, Acanthurus triostegus. The abundant turf algae harbored by rubble attracted schools of sub-adult herbivores resulting in variations

Occurrence of juvenile fishes on the seagrass beds of Kavaratti Atoll, Lakshadweep, India

In the atolls of Lakshadweep, juveniles of Acanthuridae and Labridae were most abundant on seagrass beds, the former during pre-monsoon and postmonsoon periods and the latter in pre-monsoon. Schooling species showed variable recruitment. Non-schooling species were rare. Peak settlement was observed during pre-monsoon and post-monsoon seasons. Continuous occurrence of juveniles in different size ranges confirms the continuous spawning habits. Chaetodontids and holocentrids occurred consistently round the year. Seasonality in occurrence was most pronounced in Carangidae and Siganidae, but not so in Apogonidae, Lutjanidae and Mullidae. Seasonal abundance of juveniles was influenced by summer peaks, timing and magnitude of settlement, adult spawning and local migrations. Abundance of larvae increased with salinity. Juvenile abundance, independent of environmental parameters seemed to be controlled by seasons, tides and currents. Lunar phases and abundance of juveniles were found to be co-related

Reproductive biology of some common coral reef fishes of the Indian EEZ

The reproductive biology of some common coral reef fishes from the Lakshadweep ( 8" to 12"N and 71" 45' to 73"45'E) and the Gulf of Mannar (8"48' to 9"14'N and 799' to 79O14'E) in the Indian EEZ during January 1991 to June 1992 is reported. Protogyny was prominent in labrids, while other species either matured synchronously or differentially, with males maturing earlier or later than females. Sex-ratio indicated that females were dominant in most species. Fecundity estimates varied greatly, from 700 to 2,25,850 ova per female. Whenever the environment is favourable the coral reef fish spawn on a daily, weekly, fortnightly and monthly basis. Total fecundity per year, therefore, is presumably very high. Most species appeared to be perennial spawners, some showed small breaks, while very few indicated biannual spawning. Continuous occurrence of juveniles in different size ranges confirmed the continuous spawning habits. Spawning activity was minimum during monsoon seasons, evidently an adaptation to tide over adverse environmental conditions prevailing at that time lest the eggs and larvae are transported far and wide. This was corroborated by peak settlement during pre-monsoon and post-monsoon seasons