Background speech, but not speech-shaped noise, disrupted working memory span in 5-year-old children. These results support the idea that background speech engages domain-general cognitive processes used during the recall of known objects in a way that speech-shaped noise does not.

Spectral degradation reduces access to the acoustics of spoken language and compromises how learners break into its structure. We hypothesised that spectral degradation disrupts word segmentation, but that listeners can exploit other cues to restore detection of words. Normal-hearing adults were familiarised to artificial speech that was unprocessed or spectrally degraded by noise-band vocoding into 16 or 8 spectral channels. The monotonic speech stream was pause-free (Experiment 1), interspersed with isolated words (Experiment 2), or slowed by 33% (Experiment 3). Participants were tested on segmentation of familiar vs. novel syllable sequences and on recognition of individual syllables. As expected, vocoding hindered both word segmentation and syllable recognition. The addition of isolated words, but not slowed speech, improved segmentation. We conclude that syllable recognition is necessary but not sufficient for successful word segmentation, and that isolated words can facilitate listeners’ access to the structure of acoustically degraded speech.

A S reported in a previous note, 1 experiments have been carried out with the cyclotron in this institute to investigate the cross section for fission in thorium and uranium produced by impact of deuterons with different energies. The fission outputs were determined by collecting the radioactive fragments on aluminum foils facing the targets and screened from the deuteron beam. Because of the difficulty of estimating the number of fission processes from the /^-radioactivity of these foils, a considerable uncertainty, however, was involved in the determination of the absolute value of the fission cross section.In continued experiments, this uncertainty has been reduced by a calibrating procedure in which two thin uranium targets were exposed to neutron impact. One of the targets was placed in a small ionization chamber and the number of fission particles emitted from this target counted by a linear amplifier. The fission particles from the second target were collected on a thin lead foil; the distance between the two targets was sufficiently small to ensure that the neutron intensity was very nearly the same. By measuring the activity of the collecting foil with the same counting arrangement as in the experiments with deuterons, the ratio between the foil activity and the number of fission particles emitted during the irradiation could thus be determined.Instead of the preliminary value of 0.5 • 10~2 6 cm 2 given in the previous note, the measurements thus calibrated gave now the value (2.2 ±1) • 10 -26 cm 2 for the fission cross section in uranium at 9-Mev deuteron energy. The results found for the variation of the cross section with deuteron energy and the ratio between the cross sections in thorium and uranium given in the note remain, of course, unaltered. From the value 0.7 for the last ratio, which agrees with the independent determination by Krishnan and Banks, 2 we obtain in consequence, (1.5±0.7)« 10~2 6 cm 2 for the fission cross section in thorium at 9-Mev deuteron energy.Details of the experiments are described in a paper in print in the Communications of the Copenhagen Academy of Sciences where, also, a description of the cyclotron has just been published. 3 1 I N a paper by Foster Evans on "Electric fields produced by cosmic rays," 1 the conductivity of interstellar space has been computed on the assumption that electrons are scattered by neutral atoms with a collision radius of 10~8 cm. He assumes that there are two neutral atoms, one ion and one electron per cm 3 and that the electron temperature is 10,000°K. For these conditions the collision radius for a collision between an electron and a positive ion 2 is 50X10 -8 cm so that the scattering by neutral atoms is entirely negligible. The mean free path is about 5 X10 12 cm and not 10 15 cm as estimated by Evans.The resistivity is given by the equation for an ionized gas 2 where R is resistivity in ohm-centimeters, T e is electron temperature and N + is the number of ions per cm 3 . The above numerical values give the resistivity of interstellar spa...

The nature of the pressure against density curve at constant temperature is investigated by the methods of the grand canonical ensemble for a system of identical molecules between which only short range forces act. It is shown that, except for surface effects, the total energy, entropy, etc., are proportional to the number of molecules in the system. The pressure is proven to be a non-decreasing function of the density which may have regions of constancy as a function of the density. This shows rather clearly the impossibility for any analytic equation of the Van der Waals* type being able to give a satisfactory account of condensation without ad hoc assumptions. I T should be possible to understand the isothermal change of a vapor into a liquid in terms of the forces acting between the molecules. Since this change takes place for nearly every system of molecules, one would expect that the detailed nature of the forces is not important. Only such general considerations should enter, as whether the forces are attractive or repulsive, and their behavior for large distances of separation of the molecules.We shall show for a system of molecules of one species between which only short range forces act that: (a) the pressure is a monotonically increasing function of the density at constant temperature, although there may be regions in which the pressure is independent of the density; (b) the energy, entropy, free energy, etc., are approximately proportional to the number of molecules present. It is only in the asymptotic approximation for a large number of molecules and where the dimensions of the space containing the molecules are large compared to the range of the molecular forces that (a) and (b) hold. The neglected terms may be regarded as giving rise to surface effects. It should not be implied that short range forces are necessary for (a) and (b), although we have been able to show that (a) and (b) are true only for this case.The grand canonical ensemble will be used for the statistical description of the system because of its elegance and convenience. We will furthermore consider the system to obey the laws of classical mechanics. This has been shown by Kahn and Uhlenbeck 1 not to be an essential restriction. The appearance of Planck's constant in our equation is for dimensional purposes. It has no quantum mechanical implications.The partition function of a classical grand canonical ensemble with generic phases isIn terms of the function, \f/> the pressure, average number of particles in the system, and the mean square fluctuations in the number of particles are:<[iV-(i\0 Av ]%= -fid**/da*.Equations (2) and (3) do not insure the existence of an equation of state. For a general \p the pressure is not necessarily a function of the temperature and particle density only. To investigate the conditions under which an equation of state exists we write 0 = ln V. (5) 1 B. Kahn and G. E. Uhlenbeck, Physica 5, 399 (1938). 63