Comment on the Guzmán-Bianchi type-VII h solutions

It is shown that the recently presented Brans-Dicke-Bianchi type-VII _h perfect fluid solutions by Guzmán (1989) are nothing but the solutions given already by us in our previous paper (Lorenz-Petzold, 1984).     

Comments on the comment on Jordan-Brans-Dicke universes

The principal objections to our paper on Jordan-Brans-Dicke Bianchi-type universes are misleading. The intended solutions assume a power-law form, only in the limit of very large times. Although this is the only one for which we wrote down explicit solutions. The physical point of view behind our paper was to extend the re-scaling method, developed by one of us, to anisotropic universes in general and not to make a detailed study of each of the possible solutions that could be obtained through this process.     

Comments on the BDT-FRW perfect fluid solutions

It is shown that the BDT-FRW perfect fluid solutions given some years ago by Chauvet and Obregón (1979) are identical to the solutions first given by Jordan (1955) and later by Brill (1962).     

Comments on the BDT-FRW solutions with a cosmological constant

Some critical comments are made on the power-law solutions recently given by Pimentel (1985) on the basis of the Brans-Dicke field equations for Friedmann-Robertson-Walker space-times.     

Comments on homogeneous and inhomogeneous Bianchi type-VI0 solutions

We show that the solutions obtained by Lorenz-Petzold (1982) are special cases of the solutions given by us (1985b). We also show that the observations made by Lorenz-Petzold (1985a) about the solution given by Roy and Narain (1985a) are not correct.     

Comments on the application of power series solutions to problems in celestial mechanics

The author relates his experiences in utilizing the power series method to generate trajectories for orbital and sub-orbital vehicles and for then-body problem.     

The frequency of meteorite falls: Comments on two conflicting solutions to the problem

Abstract— Recent estimates of the current rate of meteorite falls have been derived from camera network observations and from the statistics of the recovery of small fragments in Roosevelt County, New Mexico. The results are discordant. The integrated sky coverage for the camera data is an order of magnitude greater than the long exposure over small areas in New Mexico, yet the number of inferred events is comparable. We examine potential problems and find no effects other than random ones to bias the camera data. New data on the total number of suitable fireballs indicate that the flux from the camera network is already close to the upper limit imposed by the count of over 700 fireballs. By contrast, the calibration of the decay time for small fragments in New Mexico appears insecure and could account for a factor-of-three discrepancy. The large area of a typical strewn field relative to the small search areas is also a serious problem that remains uncalibrated. There are problems with the application of either the camera results or the New Mexico data to the statistics of recoveries in Antarctica since the Antarctic search areas are not free from the strewn-field problem. Since there is no evidence for a substantial change in the infall rate in intervals less than the ages of the collecting surfaces, we believe the camera network flux data remain the best estimate for the arrival rate of small meteorites on Earth.     

A comment on the ARP QSO's

Statistical arguments for the reality of physical associations between a class of QSO's and certain peculiar galaxies are now sufficiently convincing to require an explanation for the nature of the associations. If the associations are indeed real, the objects were probably liberated by tidal encounters between galaxies, rather than by explosive ejection.     

Comments on the moon's magnetism

Various lines of evidence indicate that permanent magnetization of lunar rocks, acquired during the early history of the Moon, is responsible for the weak (tens of gammas) and patchy magnetic field found at the surface of the Moon. It would be necessary to invoke a core dynamo (with all its important implications) in order to account for the inducing fieldB of not less than 10³ in which lunar rocks acquired their stable permanent magnetization if no other source ofB can be found. In this connection we point out that the magnetic effects of high-velocity meteoroid impacts have not yet been ruled out. Indeed, according to rough calculations these effects might not be negligible and detailed studies would be worth carrying out. Shock waves followed by rarefaction waves would spread out into the body of the Moon from the area of impact, first demagnetizing any material shock-heated above the Curie temperature and then, as the material cools rapidly during the passage of the rarefaction wave, re-magnetizing the material to an intensity determined by the background fieldB. The main source ofB would be the pulse of electric current generated by magneto-hydrodynamic interaction between the electrically-conducting ejecta from the explosion and the weak ambient interplanetary magnetic field.This impact dynamo hypothesis also has possible implications concerning the magnetism of meteorites.     

A comment on the insolation at Mercury

E. Van Hemelrijck and J. Vercheval [Icarus48, 167–179 (1981)] presented calculations of the insolation at Mercury and Venus which neglect the finite angular size of the Sun. To determine the temperature structure in the subsurface a more accurate calculation is needed, especially at longitudes ±90° on Mercury, where the Sun takes 18 days to rise or set. These calculations are presented here.     

Comments on the origin of Mercury

Mercury is not only highly refractory, but remarkably small. Both properties may have been affected by planetesimal scattering and collisions, as well as by solar activity.     

Comments on the Bilderberg Continuum Atmosphere

The Bilderberg Continuum Atmosphere fails to reproduce the observed limb-darkening throughout the range of wavelengths 4500 Å<< 25 000 Å. The temperature-pressure diagram for the deep layers of this model is a curve which is flatter than the relation predicted from the mixing length theory. A modification of the Bilderberg Continuum Atmosphere that improves representation of the observations and theoretical results is proposed.The work described here was supported in part by Contract N(onr)-1224(19) with the Office of Naval Research.     

Comments on the so-called Maunder minimum

Arguments are presented in favour of the operation of the 11-yr cycle during the Maunder minimum and before it. The laws of differential rotation (1642–1644 and 1899–1901) before the low cycle are shown to differ insignificantly. It is suggested that the Maunder minimum was a result of the 600-yr cycle effect (during its epoch of minimum) on the 80–90 yr cycle.     

A comment on ‘A comment on the damping of magnetohydrodynamic waves’ by Bibhas R. De

We point out that in the case of sunspots, when Coulomb collisions are included, the reduction in lundqvist number due to anisotropic conductivity is several orders of magnitude less than the reduction estimated by De. This result suggests that, contrary to De's conclusion, sunspot conditions do permit efficient MHD wave propagation.     

A comment on the damping of magneto-hydrodynamic waves

It is shown that a revision is necessary in the commonly used expression for the damping scalelength of a magnetohydrodynamic wave in a plasma when the plasma exhibits anisotropic conductivity. The consequence of this revision may be quite drastic in some astrophysical situations.     

Comments on the mechanism for the spicule support

A one-dimensional model of nonviscous gas in isothermal flow is considered, using the theory of Abramovich (1976). A mechanism of spicule flow is proposed which successfully explains the observed spicule height. The model further predicts inhomogeneities in the magnetic field topology, and in the direction and magnitude of the velocity flow.     

Comments on the proton whistler generation process

The problem of the propagation of an electromagnetic wave originating for instance in a lightning flash through the ionospheric medium is analysed in order to understand the formation at high ionospheric altitudes of the so-called proton whistler. It is shown that the accessibility of the hydrodynamic (or kinetic) proton resonance at the satellite altitude requires that a mode conversion process must take place slightly above the transition region separating the one ion (O⁺) from the two ion (O⁺ + H⁺) component plasmas. Moreover, the transformation conditions in the wave conversion region imply that the magnetic field should be (almost) perpendicular to the density gradient. Otherwise, the incident electromagnetic wave will never reach the satellite altitude in the frequency range of the proton whistler. However, some former proton whistler theories have postulated that the signal is the result of simple ionospheric propagation effects, in contradiction with the above results. These former proton whistler theories are reviewed and it is shown that the basic flaw in these theories lies in that the incident electromagnetic wave has been supposed from the beginning to have reached the high ionospheric altitudes where is located the satellite without being influenced by the lower ionospheric layers. Some various aspects, like the high variability of the wave electric to magnetic field ratio and the harmonics bands as observed by Injun are analysed in the light of the obtained results. Finally, numerical solutions of the wave dispersion relation for both the fast hydrodynamic mode (the extraordinary mode) and the slow ion kinetic mode are presented which shows that a coupling process between the two modes may take place at various frequencies between the O⁺ and the H⁺ gyrofrequencies.     

Comments on the observability of coronal variations

We discuss the observable variability of spectral lines in the soft X-ray and XUV region. Rapid variability of coronal emission, both in flaring and non-flaring structures has been reported and is particularly prominent when high spatial resolution is available. Examination of the ionization and recombination time-scales for the formation and removal of ions with prominent solar emission lines shows that, even though ionization equilibrium generally prevails, the observable variability time-scales are often limited by these atomic processes, independent of the physical process which is causing the change in the solar atmosphere. Rapid heating can lead to an initial freezing-in of abundances of some ions; observations of at least one low- and one high-excitation line from such an ion would permit studies of the time evolution of the emission measure and temperature. In a very limited number of cases, rapid cooling leads to freezing-in of the abundance of an ion and observations of a low-excitation line of this ion will not yield accurate information about the thermal evolution. Thus, future observations of Mgx 609 Å should be augmented by simultaneous observation at another wavelength, such as 63 Å. In addition, with the ability to produce images in isolated spectral lines it becomes possible to select those for which rapid variability is observable, such asOvii, rather than lines which were selected on the basis of previous hardware constraints, such asOvii.