Inferring landscape effects on gene flow: a new model selection framework.

Populations in fragmented landscapes experience reduced gene flow, lose genetic diversity over time and ultimately face greater extinction risk. Improving connectivity in fragmented landscapes is now a major focus of conservation biology. Designing effective wildlife corridors for this purpose, however, requires an accurate understanding of how landscapes shape gene flow. The preponderance of landscape resistance models generated to date, however, is subjectively parameterized based on expert opinion or proxy measures of gene flow. While the relatively few studies that use genetic data are more rigorous, frameworks they employ frequently yield models only weakly related to the observed patterns of genetic isolation. Here, we describe a new framework that uses expert opinion as a starting point. By systematically varying each model parameter, we sought to either validate the assumptions of expert opinion, or identify a peak of support for a new model more highly related to genetic isolation. This approach also accounts for interactions between variables, allows for nonlinear responses and excludes variables that reduce model performance. We demonstrate its utility on a population of mountain goats inhabiting a fragmented landscape in the Cascade Range, Washington.

Self-noise problems in hearing aids.

A study has been carried out to determine the extent to which the self-noise of a hearing aid constitutes a problem for aid users. A survey of hearing aid users was carried out followed by a laboratory study. None of the 75 hearing aid users seen during the survey complained of being troubled by self-noise and none of the subjects investigated at the Institute of Sound and Vibration Research was able to hear any self-noise at normal aid settings when listened for in a sound proofed room. Tests confirmed that aid noise becomes audible only when the noise level in any 1/3 octave band rises above the threshold for a pure tone at the centre of that band, and typical equivalent input noise levels indicate that audible self-noise is caused by gain being applied over a frequency band where the aid user has negligible or no hearing loss, as is likely in the case of persons with 'ski-slope' hearing loss. It is suggested that anyone else complaining of problems with self-noise is probably mistaking external background noise for self-noise of the aid.

Binaural hearing aids for high-frequency hearing loss.

A recent study has examined the differences between certain monaural and binaural frequency responses as used in hearing aids for persons with high-frequency (often noise induced) hearing loss, in terms of both speech discrimination score and subjective rating methods. Slight variations in speech discrimination score resulted from changing the frequency response of a monaurally fitted aid while subjective preferences favoured an aid with adaptive low-frequency gain regulation for more severe high-frequency losses. A much more pronounced improvement, was however found for a binaural fitting of the preferred aid, resulting in increased discrimination score and subjective ratings of sound quality, speech clarity and overall impression. A binaural fitting of a subjectively preferred monaural hearing aid produced speech discrimination scores which were at least as good as, if not better than, those obtained from the optimum monoaural fitting. These findings are thought to have important implications for the fitting of hearing aids.

Women at the top.

Management has long been male dominated, but recently women have been entering the field in increasing numbers. This influx has required the management establishment to think and behave in new ways.

Selecting a computerized billing system--a dynamic process.

This case study of the procedures used by the College of Physicians and Surgeons of Columbia University in selecting a computerized billing service provides a model for other institutions with similar needs for evaluating billing systems.

Sound levels from personal cassette players.

Techniques have been devised whereby the levels at which users of personal cassette players listen to tape-recorded sounds through lightweight headphones may be measured and expressed in terms of free-field equivalent continuous A-weighted sound pressure levels. Data have been obtained on over 60 users of such devices who variously listened, in laboratory and field conditions, to music and speech against quiet and noisy backgrounds. The results have been interpreted in terms of noise exposure. Comparison with damage risk criteria indicates that 5% of the sample are listening in such a manner that habitual use would constitute a damage risk to hearing.

Damage risk from personal cassette players.

Studies of the listening habits of personal cassette player users have been carried out in both Southampton and Turin. The results have been compared with other researches carried out independently in London and Nottingham. Patterns of noise exposure have been examined and estimates of hearing damage risk hypothesised. Habitual users of such devices could suffer adverse effects and should be aware of the symptoms associated with temporary threshold shifts in hearing.