Suchergebnisse

1. What is ultrasound? -- The discovery of animal ultrasound -- The properties of ultrasound -- 2. Methods of detection and analysis -- Ultrasonic microphones -- Cathode-ray oscilloscopes -- Tape-recording and analysis -- Bat detectors -- 3. Bats -- The biology of bats -- The echo-location signals of bats -- Short-pulse echo-location in Megachiroptera -- Frequency sweep pulses in Microchiroptera -- Constant frequencies in Microchiroptera -- Mixed signals in Microchiroptera -- Sound production and emission in Microchiroptera -- Frequency-sweep bats -- Constant frequency bats -- Nose-leaves -- Hearing in the Microchiroptera -- Other senses and social use of ultrasound in Microchiroptera -- 4. Countermeasures by insects -- Noctuidae -- The evasive behaviour of noctuid moths -- Acoustic sensitivity of the tympanic organ -- Directionality -- Central co-ordination -- Arctiidae, Notodontidae and Ctenuchidae -- Pyralididae -- Sphingidae -- Geometridae -- Neuroptera -- Evolution -- 5. The songs of bush crickets (Tettigoniidae) -- The physics of strigilation in general -- The mechanism of sound production in tettigoniids -- The ultrasonic songs of tettigoniids -- The acoustic behaviour of tettigoniids -- The ability of tettigoniids to hear ultrasonic sounds -- Some further considerations -- 6. Other insects -- Gryllidae, crickets -- Gryllotalpidae, mole crickets -- Acrididae, grasshoppers and locusts -- Insects of other groups -- 7. Ultrasound in rodents -- The ultrasonic calls of infant rodents -- The physical characteristics of the calls -- The motivation for the emission of ultrasonic calls by infant rodents -- The role of infant distress calls in adult-young relationships -- Ultrasound and aggressive behaviour -- Rats -- Other myomorph rodents -- Social significance -- Ultrasound and mating behaviour -- Mice -- Rats -- Other myomorph rodents -- Social significance -- Other situations involving ultrasound emission in rodents -- The mechanism of ultrasound production in rodents -- The ability of rodents to hear high frequency sounds -- 8. Other vertebrate groups -- Birds -- Cetacea -- The sounds of odontocetes -- The site of sound production -- The ear of odontocetes -- Hearing in odontocetes -- Evidence for echo-location in odontocetes -- Other marine mammals -- Insectivora -- 9. Review and speculations -- Appendix Some formulae summarizing the rules of echo-location -- References -- Indexes.

This article argues that the prevailing discourses of transitions and of social exclusion are no longer adequate to describe or explain the experiences of a substantial minority of young people. Reporting on a study of 800 16–19-year-olds, it is argued that an extensively diversified market in post-16 options produces instability and dislocation. Some young people are able to normalize these experiences of serial short-life engagements with courses and jobs into emergent new subjectivities, constructed around highly interdependent modes of studentship, employment and consumption. For others (the poorest students, those with special needs, some racialized groups) these subjectivities are not available.