White-light promoted degradation of leucopterin and related pteridines dissolved in seawater, with evidence for involvement of complexation from major divalent cations of seawater

The photochemical instability of several related pteridines in seawater was investigated by aseptic incubation of solutions at 20–22°C under illumination from cool-white light of intensity 6 kerg cm⁻² sec⁻¹, and the chemical changes were spectrophotometrically monitored. All the pteridines showed markedly accelerated degradation from this illumination relative to their behaviour in total darkness.Pterin and lumazine were degraded very slowly with zero-order reaction kinetics, while the other pteridines photolysed rapidly (according to first-order kinetics) with decomposition rates increasing in the order dioxylumazine (2,4,6,7-tetrahydroxypteridine) < leucopterin < isoxanthopterin < xanthopterin < oxylumazine (2,4,6-trihydroxypteridine). Excepting leucopterin and dioxylumazine, the photolysis rates were attributable to the pH of seawater and not its salt content; this was also the case with oxylumazine which required the salt content of seawater for decomposition in darkness. Leucopterin and dioxylumazine (both 6,7-dihydroxylated pteridines) gave evidence of complexation with the major divalent cations (Ca²⁺, Mg²⁺) of seawater, by virtue of which their photolytic degradation rates were enhanced to magnitudes obtained in pH-10 buffer without seawater. It is proposed that such complexation produces structural forms of these pteridines analogous to their normal ionic forms at pH 10–12.The photolysis of the 6-hydroxylated pteridines (xanthopterin, oxylumazine) proceeded via intermediate formation of their corresponding 7-hydroxylated derivatives (leucopterin, dioxylumazine).     

The eruption of a quiescent prominence as observed in UV lines

We compare observations of an eruptive and a quiescent prominence in order to better understand the energetic processes in an eruptive prominence. Observations of an eruptive prominence were obtained in H, several UV emission lines (1215–1640 Å), and coronal white light at approximately 19:00 UT on September 20, 1980. The data we present shows the development of the eruption in the H and UV emission lines and is compared with the intensities from similar observations of a quiescent prominence. While the event is coincident with some coronal changes, above 1.2 and up to 1.5 solar radii, it does not result in a true coronal mass ejection event.The comparison between the eruptive and quiescent prominences reveals several differences which suggest that the activation consists not only of a mechanical movement of material, but also changes in the temperature of the prominence plasma. Some prominence material that does not seem to participate in the large scale prominence motion is heated during the eruptive event. Most of this material is heated to transition zone temperatures with almost no cool core (i.e., no or very little H emission). The behavior indicates that there are structures that are first cool and then heat up to transition zone temperatures (apparently remaining stable for some time at these temperatures). Since this is an unstable temperature region for prominence type structures the energy transport that allows this is not understood and presents an interesting theoretical problem.Member of the Carrera del Investigador, CONICET, Argentina, presently at The University of Alabama in Huntsville.     

China's population: an alternative perspective

The author presents a selection of cartograms designed to illustrate aspects of the demography of China. Topics covered include population growth, density, regional variations in fertility, and age distribution. A discussion of the advantages of using cartograms (maps drawn proportional to a given variable) as opposed to conventional, area-based maps, is included.     

The homologous flare events in solar active regions

This paper consists of two parts. We first discuss recent general results on the study of properties of flare homology, and their relevance to the physical interpretation of the flare phenomenon at large. We devote particular attention to the discovery of homologous flares which occur in rapid succession, within a few minutes of each other in many cases. We name these kind of flares rafales. These flares signal the existence of several episodes of energy release within the same magnetic configuration. We also show the existence of particular sites in the solar atmosphere which have peculiar characteristics in terms of solar rotation, and where recurrent flaring may take place over and over again in different solar rotations. This indicates that the disturbance causing the emergence of activity is deep seated, below the solar photosphere. Finally, in the second part, we discuss an extensive set of observations of two homologous flares of a rafale, stressing the dynamic aspects of the observations, particularly the presence of peaks in the vertical component of the velocity field. These results are shown to be in agreement with studies of filament activations and the surging arches which are observed before the flash phase of solar flares.     

Application of a new evolutionary model for stellar populations to photometric maps of M32

We have developed a new model of evolutionary synthesis of stellar population, from a working cyclical approximation to a general solution for the mass and time dependence of the birth function of stars. The general solution enables us to introduce a functionG(t): the ratio of gas injected into a defined region to that which forms stars in the same time interval, at timet. This function, by relating directly the output of dying stars with the formation of the next generation, allows us to make analytical approximations (in the absence of more accurate numerical information) to the macroscopic evolution of stellar populations in a well-defined zone of a galaxy.The model has been initially applied to 4 zones of the dwarf elliptical M32 (NGC 221) where, usingU, B, V from the literature, and our own photometric maps inJ andK, we obtained the following results: (a) Star formation in the most recent 10⁸ years is lower by a factor 3–4 in a zone 68 arc sec (200 pc) from the nucleus than in the nuclear zone. (b) The metallicity appears to be a little lower in a zone diametrically away from the parent galaxy M31 than in a zone towards M31 at the same galactocentric distance (c) TheM/L ratio is a factor 2 higher at 200 pc from the nucleus towards M31, than in the nuclear zone. (d) A high concentration of mass is evident in the nuclear zone. (e) The estimated age of all the zones is of the same order,1.5×10¹⁰ yr.     

Radiometry of near-earth asteroids

We report 10 micrometers infrared photometry for 22 Aten, Apollo, and Amor asteroids. Thermal models are used to derive the corresponding radiometric albedos and diameters. Several of these asteroids appear to have surfaces of relatively high thermal inertia due to the exposure of bare rock or a coarse regolith. The Apollo asteroid 3103, 1982 BB, is recognized as class E. The Jupiter-crossing Amor asteroid 3552, 1983 SA, is confirmed as class D, but low albedos remain rare for near-Earth asteroids.     

Period distributions in pulsating and binary stars

We analyze the hypothesis of quantization in bands for the angular momenta of binary systems and for the maount of actionA _c in stable and pulsating stars. This parameter isA _c=Mv _eff R _eff, where the effective velocity corresponds to the kinetic energy in the stellar interior and the effective radius corresponds to the potential energyGM ²/R _eff. Analogous parameters can be defined for a pulsating star withm=M where is the rate of the massm participating in the oscillation to the total massM andv _osc,R _osc the effective velocity and oscillation radius.From an elementary dimensional analysis one has thetA _c (energy x time) (period)^1/3 independently ifA _c corresponds to the angular momentum in a binary system, or to the oscillation in a pulsating star or the inner energy and its time-scaleP _eff in a stable star.From evolving stellar models one has that P _effP _eff(solar)1.22 hr a near-invariant for the Main Sequence and for the range of masses 0.6M <M<1.6M .With this one can give scalesn _k=kn ₁ withk integers andn ₁=(P/P ₁)^1/3 withP ₁=P _eff1.22 hr. In these scales proportional toA _c, one sees that the periods in binary and pulsating stars are clustered in discrete unitsn ₁,n ₂,n ₃, etc.This can be seen in pulsating Scuti, Cephei, RR Lyrae, W Virginis, Cephei, semi-regular variables, and Miras and in binary stars as cataclysmic binaries, W Ursa Majoris, Algols, and Lyrae with the corresponding subgroups in all these materials. Phase functions (n _k) in RR Lyrae and Cephei are also associated with discrete levelsn _k.the suggested scenario is that the potential energies and the amounts of actionE _p(t), A_c(t) are indeed time-dependent, but the stars remain more time in determinated most proble states. The Main Sequence itself is an example of this. These most probable states in binary systems, or pulsating or stable stars, must be associated with velocities sub-multiplesc/ _F , given by the velocity of light and the fine structure constant.Additional tests for such a hypothesis are suggested when the sufficient amount of observational data are available. They can made with oscillation velocities in pulsating stars and velocity differences of pairs of galaxies.     

Magnetoacoustic-gravity surface waves

The linearized theory for the parallel propagation of magnetoacoustic-gravity surface waves is developed for an interface of a horizontal magnetic field above a field-free medium. The media either side of the interface are taken to be isothermal. The dispersion relation is obtained for the case of a constant Alfvén speed. In the absence of gravity the interface may support one or two surface modes, determined by the relative temperatures and magnetism of the two media. The effect of gravity on the modes is examined and dispersion diagrams and eigenfunctions are given. In the usual - k _x diagnostic diagram, the domain of evanescence is shown to be divided into two distinct regions determining whether a given mode will have a decaying or growing vertical velocity component. In the absence of a magnetic field the transcendental dispersion relation may be rewritten as a polynomial. This polynomial possesses two acceptable solutions only one of which may exist in any given circumstances (depending on the ratio of the densities). If the gas density within the field exceeds that in the field-free medium, then the f-mode may propagate. The f-mode exists in a restricted band of horizontal wavenumber and only when the field-free medium is warmer than the magnetic atmosphere. An analytical form for the wave speed of the f-mode is obtained for small values of the Alfvén speed. It is shown that the f-mode is related to the fast magnetoacoustic surface wave, merging into that mode at short wavelengths.