Frequency of occurrence

A climatology of the Great Plains low-level jet (LLJ) is developed from 2 yr of research rawinsonde data obtained up to eight times per day at a site in north-central Oklahoma. These data have better height and time resolution than earlier studies, and show that jets are stronger than previously reported and that the heights of maximum wind speed are closer to the ground. LLJs are present in 47% of the warm season soundings and 45% of the cold season soundings. More than 50% of the LLJs have wind maxima below 500 m above ground level (AGL). Because the 404-MHz radar profiler network in the central United States has its first data points at 500 m AGL, it is likely to miss some LLJ events and will have inadequate vertical resolution of LLJ wind structure.Previous studies have identified LLJs on the basis of a wind speed profile criterion. This criterion fails to separate the classical southerly LLJs from the less frequent northerly jets, which differ in both structure and evolution. Classical southerly jets are more frequent; they occur year round, with the highest frequency in the summer and at night. Southerly LLJ wind speed maxima are most frequently found at 300-600 m AGL, and peak speeds, typically between 15 and 21 m s1, are attained at 0200 CST. The height of the wind speed maximum varies little during nighttime-a period when surface-based inversions grow in depth but generally remain below the jet. Winds at the nose of the southerly jets exhibit a distinct diurnal clockwise turning in wind direction and an oscillation in speed.Northerly jets occur year round. They are generally associated with cold air outbreaks and are found in the cold air behind southward-moving cold fronts. In winter, their frequency of occurrence rivals that of the southerly jets. Their occurrence, however, is less dependent on time of day, with a weak daytime maximum. They are more variable in the heights of their wind speed maxima, are associated more frequently with elevated frontal inversions, and do not exhibit a clockwise turning with time. The heights of the jet speed maxima are found to increase with distance behind the surface cold front.

Tropical ecosystems have a great organismal diversity. However, the trophic relations of many components are poorly understood and this is particularly the case for caecilian amphibians. We analysed spatial and temporal aspects of the diet of a caecilian (Ichthyophis cf. kohtaoensis) at a field site in North-eastern Thailand (Mekong valley, Khemmarat District, Ubon Ratchathani Province). This is the first study to include both aquatic larvae and terrestrial adult stages of any caecilian. Larval I. cf. kohtaoensis feed exclusively on aquatic invertebrates (e.g., dragonfly larvae, water beetles and clam shrimps). A comparison of potential prey taxa available indicates that larval I. cf. kohtaoensis prefer benthic prey. Terrestrial I. cf. kohtaoensis consume mostly soil invertebrates such as megascolecid earthworms, ants and termites (soil ecosystem engineers). Numerically and in terms of their frequency of occurrence, these major prey groups varied strongly between seasons. Scarabaeid beetle larvae, oribatid and mesostigmatid mites and occasionally microhylid frogs were also recorded in the diet. During ontogeny, I. cf. kohtaoensis move from an aquatic to terrestrial existence. Despite this, accompanying changes in trophic position are superficial because both stages are carnivorous generalists. In this regard, they are more similar to salamanders than frogs with biphasic life history cycles.

Reports of key MIS issues based on the perceptions of senior IS executives appear periodically in the MIS literature. In this article, we provide another perspective on key MIS issues by examining published MIS articles. A content analysis of MIS articles appearing between 1989 and ...

The winter diet and foraging range of gentoo penguins, Pygoscelis papua, were studied at Kidney Cove, Falkland Islands. The mean wet mass of the 56 stomach-content samples collected from May to October was 32.7±47.4 g. The diet consisted generally of cephalopods, crustaceans and fish, as well as two other molluscs. Among the six cephalopod species identified, the commercially fished Patagonian squid, Loligo gahi, had the highest abundance and was also the main prey by reconstituted mass (53% of the total reconstituted mass). Lobster krill, Munida gregaria, one of five species of crustaceans, was the most abundant prey species by frequency of occurrence and by number (68% and 60%, respectively). Rock cod, Patagonotothen ramsayi, accounted for the majority of the fish diet with 34% of the total reconstituted mass. Most prey species identified in the winter diet were also abundant diet components during the breeding season. However, the known biology of the prey species and their rate of digestion indicated that, in winter, adults may forage further offshore than during the breeding season. This assumption was supported by the results obtained from two birds satellite-tracked during the study period. Both birds remained mainly in inshore waters and returned frequently ashore, but one penguin foraged up to 276 km from the coast. The differences in the foraging behaviour of the two birds were reflected in significant differences with regard to time spent underwater, distance travelled per day and calculated travelling speed. Furthermore, the progress of cohorts of L. gahi over the winter is consistent with results from life-cycle studies in this region and suggests that birds have been foraging in the feeding grounds of L. gahi.

On the basis of the lexical corpus created by Amano and Kondo (2000), using theAsahi newspaper, the present study provides frequencies of occurrence for units of Japanese phonemes, morae, and syllables. Among the five vowels, /a/ (23.42%), /i/ (21.54%), /u/ (23.47%), and /o/ (20.63%) showed similar frequency rates, whereas /e/ (10.94%) was less frequent. Among the 12 consonants, /k/ (17.24%), /t/ (15.53%), and /r/ (13.11%) were used often, whereas /p/ (0.60%) and /b/ (2.43%) appeared far less frequently. Among the contracted sounds, /sj/ (36.44%) showed the highest frequency, whereas /mj/ (0.27%) rarely appeared. Among the five long vowels, /ar/ (34.4%) was used most frequently, whereas /ur/ (12.11%) was not used so often. The special sound /n/ appeared very frequently in Japanese. The syllable combination /k/+V+/n/ (19.91%) appeared most frequently among syllabic combinations with the nasal /n/. The geminate (or voiceless obstruent) /q/, when placed before the four consonants /p/, /t/, /k/, and /s/, appeared 98.87% of the time, but the remaining 1.13% did not follow the definition. The special sounds /r/, /n/, and /q/ seem to appear very frequently in Japanese, suggesting that they are notspecial in terms of frequency counts. The present study further calculated frequencies for the 33 newly and officially listed morae/syllables, which are used particularly for describing alphabetic loanwords. In addition, the top 20 bi-mora frequency combinations are reported. Files of frequency indexes may be downloaded from the Psychonomic Society Web archive athttp://www.psychonomic.org/archive/.