Observation of audio-frequency edge magnetoplasmons in the classical two-dimensional electron gas

The electric admittance of a two-dimensional electron gas on liquid helium measured at audio frequencies ¿ is observed to oscillate as a function of magnetic field at strong magnetic fields. The oscillations can be attributed to the propagation of very-low-frequency (¿t~10-6, t scattering time; ¿/¿c~10-8, ¿c cyclotron frequency) edge magnetoplasmons. The directly determined dispersion relation agrees with theory and quantitatively with measurements in the collisionless regime (¿t»1). The attenuation, theoretically obtained by incorporating the screening in a simple local-capacitance model, agrees well with experiments

Single electron magneto-conductivity of a nondegenerate 2D electron system in a quantizing magnetic field

We study transport properties of a non-degenerate two-dimensional system of non-interacting electrons in the presence of a quantizing magnetic field and a short-range disorder potential. We show that the low-frequency magnetoconductivity displays a strongly asymmetric peak at a nonzero frequency. The shape of the peak is restored from the calculated 14 spectral moments, the asymptotic form of its high-frequency tail, and the scaling behavior of the conductivity for omega -> 0. We also calculate 10 spectral moments of the cyclotron resonance absorption peak and restore the corresponding (non-singular) frequency dependence using the continuous fraction expansion. Both expansions converge rapidly with increasing number of included moments, and give numerically accurate results throughout the region of interest. We discuss the possibility of experimental observation of the predicted effects for electrons on helium.Comment: RevTeX 3.0, 14 pages, 8 eps figures included with eps

Living for the weekend: youth identities in northeast England

Consumption and consumerism are now accepted as key contexts for the construction of youth identities in de-industrialized Britain. This article uses empirical evidence from interviews with young people to suggest that claims of `new community' are overstated, traditional forms of friendship are receding, and increasingly atomized and instrumental youth identities are now being culturally constituted and reproduced by the pressures and anxieties created by enforced adaptation to consumer capitalism. Analysis of the data opens up the possibility of a critical rather than a celebratory exploration of the wider theoretical implications of this process

Pelvis morphology suggests that early Mesozoic birds were too heavy to contact incubate their egg

Numerous new fossils have driven an interest in reproduction of early birds, but direct evidence remains elusive. No Mesozoic avian eggs can be unambiguously assigned to a species, which hampers our understanding of the evolution of contact incubation, which is a defining feature of extant birds. Compared to living species, eggs of Mesozoic birds are relatively small, but whether the eggs of Mesozoic birds could actually have borne the weight of a breeding adult has not yet been investigated. We estimated maximal egg breadth for a range of Mesozoic avian taxa from the width of the pelvic canal defined by the pubic symphysis. Known elongation ratios of Mesozoic bird eggs allowed us to predict egg mass and hence the load mass an egg could endure before cracking. These values were compared to the predicted body masses of the adult birds based on skeletal remains. Based on 21 fossil species, we show that for nonornithothoracine birds body mass was 187% of the load mass of the eggs. For Enantiornithes, body mass was 127% greater than the egg load mass, but some early Cretaceous ornithuromorphs were 179% heavier than their eggs could support. Our indirect approach provides the best evidence yet that early birds could not have sat on their eggs without running the risk of causing damage. We suggest that contact incubation evolved comparatively late in birds

Building a tuberculosis-free world: The Lancet Commission on tuberculosis

___Key messages___ The Commission recommends five priority investments to achieve a tuberculosis-free world within a generation. These investments are designed to fulfil the mandate of the UN High Level Meeting on tuberculosis. In addition, they answer

Temperature dependence of propagation and damping of nonresonant edge magnetoplasmons for electrons on liquid helium

Very low frequency edge magnetoplasmons (EMP's) for electrons on liquid helium are investigated in the nonresonant regime from current-voltage phase shift measurements for temperatures of 1.57 K and 1.93 K. At these temperatures the mobilities, and therefore the zero field phase shifts, differ by about a factor of three. The phase shift in the EMP regime is the same within 10 %. This confirms the theoretically predicted temperature independence of the EMP dispersion

Numerical calculations on edge magnetoplasmons for electrons on helium with inhomogeneous density and capacitance profiles

The transmission line model to describe the AC-response of electrons on helium in a magnetic field has been extended by introducing inhomogeneous electron density and capacitance profiles at the edge. The transmission line equations were solved numerically for mobility values corresponding to t=1.8 K. The results yield an oscillatory response as a function of magnetic field, in agreement with experimental observations and are attributed to damped edge magnetoplasmons (EMP's)