In response to acute exposure to moderate high-altitude hypoxia, mammals increase their blood hemoglobin concentration very rapidly by reducing their plasma volume. This phenomenon is caused not only by a redistribution of the body fluid volumes but also by a suppression of voluntary sodium and water intake as well as an inhibition of renal tubular sodium reabsorption with natriuresis and diuresis. This article reviews the role of the peripheral arterial chemoreceptors within the framework of the reflex mechanisms that might cause the changes in sodium and water metabolism in acute arterial hypoxia. The evidence that the peripheral arterial chemoreceptors do also influence sodium and water homeostasis in normoxia is presented. The interrelations between carotid body structure and arterial chemoreceptor reflex effects on the one hand and primary systemic hypertension on the other are discussed.

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We study the irregular wave functions of a highly excited hydrogen atom in a uniform magnetic field. The "scarring" of wave functions by periodic orbits is quantitatively investigated. The shape of unperturbed scars is in good agreement with recent semiclassical predictions.PACS numbers: 32.60.+i, 03.65.Sq, 05.45.+bIn quantum mechanics all information about the system under consideration is contained in its Green's function G(r',r,£), For integrable systems both the wave functions {%,} and the structure of the spectrum {E n } are well understood and conventional semiclassical methods approximate their exact solutions rather well, at least for short de Broglie wavelengths. Unfortunately, the appearance of chaotic motion in nonintegrable systems prevents the applicability of these methods and our general knowledge about quantum systems possessing classically chaotic dynamics is still fragmentary. Most of the progress achieved concerns the structure of the eigenvalue spectra, which have been studied in detail during the last few years (for reviews see, e.g., Refs. 1 and 2, and for the particular problem of a hydrogen atom in a magnetic field, Refs. 3 and 4). Our knowledge of generic properties of the associated wave functions is by far not as well developed. Recently Bogomolny 5 derived an expression for the wave functions using the semiclassical expansion of the Green's function in terms of classical trajectories as derived by Gutzwiller. 6 In this theory the wave function consists of an average, which is given by the projection of the classical microcanonical distribution on the coordinate space (the so-called "semiclassical eigenfunction hypothesis" 7 ), and of strongly energy-dependent contributions localized around the closed classical paths (the so-called "scars" 8 ). In this way he was able to explain many of the finer details observed in the highly excited eigenfunctions of the quantized stadium billiard. 5 ' 8,9 In a recent paper Berry extended these ideas to a phase-space approach. 10 So far studies on wave functions of "realistic" ergodic systems (smooth potentials) were only qualitative. 11 In this Letter we report a quantitative approach to wavefunction scarring. The physical system under consideration is the hydrogen atom in a uniform magnetic field, which is known to be chaotic around the ionization threshold. 3 The Hamiltonian of a hydrogen atom in a uniform magnetic field B is given by (in atomic units) 3if-^-+ V7 2 (* 2 +J> 2 >.(2) ToThe z axis is chosen as the direction of the magnetic field B, which is measured in units of Z?o~2.35xl0 5 T, B^yBn. Because of scaling properties 3 the classical dynamics depend only on the scaled energy e, which is a combination of the energy E and the field strength y, e-Ey~2 /3 . Here we will study the Hamiltonian (2) in semiparabolic coordinates (ju,v,0), which (after separating the motion) transform (2) into h _£l±£L_ €^2+v 2 )+ l_ ifl 4 v 2 +v 2^2Analogous transformations can be applied to the Schrodinger equation, which for constant scaled energy e reads ...

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