Men who have sex with men: a comparison of a probability sample survey and a community based study

We compared characteristics of men who have sex with men (MSM) in a probability sample survey with a community based study in London. The majority of men in both surveys reported male sex partner(s) in the last year but MSM recruited through the population based survey had lower levels of HIV risk behaviour, reported fewer sexually transmitted infections and HIV testing than those recruited from gay venues. Community samples are likely to overestimate levels of risk behaviour among all MSM

Fish response to the annual flooding regime in the Kavango River along the Angola/Namibia border

The results of the first seasonal survey of the fish of the Kavango River floodplain along the Angola/Namibia border are reported. The river experiences peak flooding from February through June, with the 375-km long floodplain extending up to 5 km across. The floodplain was sampled five times in 1992 by seine, fish traps and rotenone. The data indicated a pronounced structural and functional response of the fish community in relation to the alternating flood and drought conditions in the river. Catch per unit effort and diversity were highest during months of peak flooding (May and June), and lowest during the month of least flow (November). The reproductive strategies of K-selected piscivorous cichlids and tigerfish were in advance of flooding. Many r-selected invertivores, especially cyprinids, were in relative synchrony with flooding and the stimulation of littoral zone plant growth, while other invertivores lagged the cyprinids. Herbivores had lowest relative abundance during peak flooding; this seemingly inverse relationship with the invertivores should not be interpreted as replacement, but rather the swamping of the system with young-of-the-year r-selected invertivores. The data support the Flood Pulse Concept, which hypothesizes that flooding is the major “driver” of productivity in lowland or floodplain rivers.Keywords: behaviour, floodplain fishery, migration, Okavango Delta, r-/K-selection, subsistence fisheryAfrican Journal of Marine Science 2001, 23: 449–46

Learning about sex: Results from Natsal 2000.

11-13 September 2002

Meal size is a critical driver of weight gain in early childhood

Larger serving sizes and more frequent eating episodes have been implicated in the rising prevalence of obesity at a population level. This study examines the relative contributions of meal size and frequency to weight gain in a large sample of British children. Using 3-day diet diaries from 1939 children aged 21 months from the Gemini twin cohort, we assessed prospective associations between meal size, meal frequency and weight gain from two to five years. Separate longitudinal analyses demonstrated that every 10 kcal increase in meal size was associated with 1.5 g/wk or 4% (p = 0.005) faster growth rate, while meal frequency was not independently associated with growth (β = 0.3 g/wk p = 0.20). Including both meal parameters in the model strengthened associations (meal size: β = 2.6 g/wk, p < 0.001; meal frequency: β = 1.0 g/wk, p = 0.001). Taken together, the implication is that meal size promotes faster growth regardless of frequency, but meal frequency has a significant effect only if meal size is assumed to be held constant. Clearer advice on meal size and frequency, especially advice on appropriate meal size, may help prevent excess weight gain

Optimal Gersgorin-Style Estimation Of The Largest Singular Value, Ii

In estimating the largest singular value in the class of matrices equiradial with a given n-by-n complex matrix A, it was proved that it is attained at one of n(n - 1) sparse nonnegative matrices (see C.R. Johnson, J.M. Penna and T. Szulc, Optimal Gersgorin-style estimation of the largest singular value; Electronic Journal of Linear Algebra Algebra Appl., 25: 48-59, 2011). Next, some circumstances were identified under which the set of possible optimizers of the largest singular value can be further narrowed (see C.R. Johnson, T. Szulc and D. Wojtera-Tyrakowska, Optimal Gersgorin-style estimation of the largest singular value, Electronic Journal of Linear Algebra Algebra Appl., 25: 48-59, 2011). Here the cardinality of the mentioned set for n-by-n matrices is further reduced. It is shown that the largest singular value, in the class of matrices equiradial with a given n-by-n complex matrix, is attained at one of n (n - 1) /2 sparse nonnegative matrices. Finally, an inequality between the spectral radius of a 3-by-3 nonnegative matrix X and the spectral radius of a modification of X is also proposed