Problematic Internet Use Among University Students in Jamaica.

The prevalence of problematic Internet use (PIU) and its associated negative outcomes among college students has been heavily researched in developed countries. However, despite the increased accessibility of the Internet and indicators which may suggest PIU in developing countries such as Jamaica, PIU in this context remains grossly understudied. This study surveyed 277 Jamaican university students and found evidence of PIU, with younger respondents (ages 18-23) at risk. The findings also indicate that the predictors of PIU in this sample are depressive symptomatology, avoidant-attachment, and low social connectedness (R 2 = .208, F[7, 269] = 10.112, p < .001). Findings from the current study highlight that problematic Internet use is of concern in this developing context and warrants further exploration.

Bisexual branching processes in a genetic context: the extinction problem for Y-linked genes.

In this paper the inheritance of a Y-linked gene with alleles R and r in a population with both females and males is modelled using a two-type bisexual branching process. It is assumed that the reproductive distribution associated with the R allele can differ from the associated with the r allele and that females prefer to mate with a male having the R allele rather than with a male with the r allele. Under these assumptions, we provide some conditions for the extinction and/or survival of both alleles in the population. These conditions depend on the magnitudes of the average number of females and males per mating unit. Moreover, the almost sure extinction of the r allele is independent of the behaviour of the R allele. On the other hand, the survival of the R allele with positive probability may depend strongly on the reproductive behaviour of the other allele. Theoretical results are illustrated by means of simulated examples and some open problems are proposed to the reader as conjectures.

A reconsideration of Galton's problem (using a two-sex population).

The main purposes of this paper are to promote and expound the bisexual Galton-Watson branching process as a relevant model for the consideration of Francis Galton's problem regarding the extinction of surnames of "men of note." A scheme for adapting the bisexual process to consider Galton's problem is introduced. A necessary and sufficient condition for the certain extinction of a male-induced property in a two-sex species is presented. An approach for calculating the extinction of a male-generated characteristic in the two-sex species is proposed. That approach is then used to find the probability of the extinction of surnames in a bisexual population for Alfred Lotka's data based on an United States Census. Finally, these results are then compared with the classic extinction probabilities (from Lotka) associated with the traditional Galton-Watson branching process using asexual reproduction.

The derivation and verification of a non-stationary, optimal smoothing filter for nuclear medicine image data.

A non-stationary optimal smoothing filter for digital nuclear medicine image data, degraded by Poisson noise, has been derived and applied to temporal simulated and clinical gated blood pool study (GBPS) data. The derived filter is automatically calculated from a large group (library) of similar GBPS which are representative of all studies acquired according to the same protocol in a defined patient population (the ensemble). The filter is designed to minimize the mean-square difference between the filtered data and the true image values; it provides an optimal trade-off between noise reduction and signal degradation for members of the ensemble. The filter is evaluated using a computer simulated ensemble of GBPS. Libraries of Poisson-degraded and non-degraded studies were generated. Libraries of up to 400 Poisson-degraded simulated studies were used to estimate optimal temporal filters that, when applied to Poisson-degraded members of the ensemble not included in the libraries, reduced the mean-square error in the raw data by 65%. When the non-degraded studies were used instead to compute the optimal filter values, the corresponding reduction in the error was 83%. Libraries of previously acquired clinical GBPS were then used to estimate optimal temporal filters for an ensemble of similarly acquired studies. These filters were subsequently applied to studies of 13 patients (not in the original libraries) who received multiple sequential repeat studies. Comparisons of both the filtered and raw data to averages of the repeat studies demonstrated that optimal filters calculated from 400 and 800 clinical studies reduced the mean-square error in the clinical data by 56% and 63% respectively.

How to see in the dark: photon noise in vision and nuclear medicine.

This paper is concerned with the construction of optimal filters for smoothing the photon noise that arises under low-light conditions in vision and under low-dose or short-exposure conditions in nuclear medicine. In the case of vision, the paper explores the hypothesis that the retina functions as an optimal filter. The consequences of this hypothesis for light adaptation are studied. In the case of nuclear medicine, a method for constructing optimal filters is introduced, and the method is tested by computer simulation.

Nuclear resonant scattering of gamma rays--a new technique for in vivo measurement of body iron stores.

A technique for the measurement of body iron utilising nuclear resonant scattering of gamma rays has been developed. 847 keV photons emitted from a gaseous 56MnCl2 source are resonantly scattered from 56Fe present in the body. Measurement is made using large volume Ge(Li) detectors. The spatial uniformity of activation, the sensitivity of the detection system and the limits of detection have been investigated. Measurements were made on a liver phantom. The resonance scattering technique permits determination of normal levels of Fe in the liver with a radiation dose of 2 rem.