Comparative effect of viscous dissipation on heat transfer in mixed convection flow: UWT and UHF cases

The effect of viscous dissipation on mixed convection flow about a rotating sphere with a prescribed uniform surface heat flux (UHF) has been investigated analytically. Merk's type of series expansions is used to obtain the heat transfer rate and the skin-friction coefficients. The results are presented for Pr=1;B=0, 1; ^*0, 0.5, 1 and various values of the dissipation parameter Ec^* at various angular positions. As in the case of uniform wall temperature (UWT), the heat transfer rate decreases with viscous dissipation. It is also observed that for an equivalence viscous dissipation effect, heating by UHF yields larger Nusselt number than heating by UWT.     

Astrometric investigation with the Tautenburg Schmidt telescope

The observations and the plate reduction technique for the determination of positions and absolute proper motions which is used in Potsdam are described. Recent results have shown that an accuracy of about 0 _. 1 for positions and 0 _. ⁷ cent _. ^–1 for proper motions can be achieved both for bright (8^m–12^m) and faint (16^m–18^m) stars. Three astrometric programmes using the Tautenburg plates are presented.     

Expansions of the negative powers of mutual distances between bodies

The negative powers of the mutual distance ^– between two bodies are developed into series converging at any moment but that of collision. On the base of these expansions the series have been constructed representing ^– in the perturbation theory of celestial mechanics. In the general case, including intersecting orbits, the terms are quasi-periodic functions of the time. In the case of non-intersecting orbits the expansion is a double Fourier series in the mean anomalies. All the expansions have a literal form with respect to osculating elements.     

Decametric survey of discrete sources in the northern sky

The region of the celestial sphere between declinations =52°.3 and =59° and right ascensions =1^h and =19^h has been surveyed with the UTR-2 radiotelescope. The results of the survey are presented.The catalogue contains the positions and flux densities of 313 radio-sources detected at 10, 12.6, 14.7, 16.7, 20, and 25 MHz.     

Spectral analysis of Hα, Hβ, and Hγ lines of a white-light flare (3B/X6.1) on October 27, 1991

We have analyzed time series of H, H, and H line profiles taken from a 3B/X6.1 flare which occurred on October 27, 1991 in active region NOAA 6891. Each set of the spectra was taken simultaneously for the first 10 min of the flare event with a low and non-uniform time resolution of 10–40 s. A total of 22 sets of H, H, and H were scanned by a PDS with absolute intensity calibration to derive the dynamics and energetics of material in the flare region. Our results are as follows: (1) The Balmer line emitting region is accelerated downward to about 50 km s^-1 for the first 50 s and then is decelerated to about 10 km s^-1 for the next 150 s. (2) The radial velocity peak precedes the Balmer line intensity peak by about 40 s. (3) The total energy radiated from these Balmer lines is estimated to be 4.9 × 10²⁹ erg.     

Ultraviolet spectral reflectance properties of common planetary minerals

Ultraviolet spectral reflectance properties (200-400 nm) of a large number of minerals known or presumed to exist on the surfaces of Mars, the Moon, and asteroids, and in many meteorites, were investigated. Ultraviolet reflectance spectra (200-400 nm) of these minerals range from slightly blue-sloped (reflectance decreasing toward longer wavelengths) to strongly red-sloped (reflectance increasing toward longer wavelengths). Most exhibit one or two absorption features that are attributable to FeO charge transfers involving Fe³⁺ or Fe²⁺. The UV region is a very sensitive indicator of the presence of even trace amounts (<0.01 wt%) of Fe³⁺ and Fe²⁺. The major Fe³⁺O absorption band occurs at shorter wavelengths (∼210-230 nm), and is more intense than the major Fe²⁺O absorption band (∼250-270 nm). Ti-bearing minerals, such as ilmenite, rutile and anatase exhibit UV absorption bands attributable to Ti⁴⁺O charge transfers. While the positions of metal-O charge transfer bands sometimes differ for different minerals, the variation is often not diagnostic enough to permit unique mineral identification. However, iron oxides and oxyhydroxides can generally be distinguished from Fe-bearing silicates in the 200-400 nm region on the basis of absorption band positions. Within a given mineral group (e.g., low-calcium pyroxene, olivine, plagioclase feldspar), changes in Fe²⁺ or Fe³⁺ abundance do not appear to result in a measurable change in absorption band minima positions. Absorption band positions can vary as a function of grain size, however, and this variation is likely due to band saturation effects. The intensity of metal-O charge transfers means that some minerals will exhibit saturated UV absorption bands even for fine-grained (<45 μm) powders. In cases where absorption bands are not saturated (e.g., Fe²⁺O bands in some plagioclase feldspars and pyroxenes), changes in Fe²⁺ content do not appear to cause variations in band position. In other minerals (e.g., olivine), changes in band positions are correlated with compositional and/or grain size variations, but this is likely due to increasing band saturation rather than compositional variations. Overall, we find that the UV spectral region is sensitive to different mineral properties than longer wavelength regions, and thus offers the potential to provide complementary capabilities and unique opportunities for planetary remote sensing.     

Solar activity in the past and the problem of solar dynamo

We study a new indirect index, or proxy data, of the solar activity - the intensity of luminescence of the microzones of cave flowstones. This index is in anticorrelation with the index deposition rate of ¹⁴C and in direct correlation with the solar activity as in thermoluminescent time series of sediment cores. Luminescence time series was obtained for long time intervals with different time resolution (from 5 years per pixel to 5 pixels per year). In such time series the long minima of Maunder and Spoerer, the Medieval maximum and other well known long lasting minima and maxima as well as some new ones can be seen. The very good resolution permits to study the general statistical properties of past solar activity. Some of the results obtained refer to the problem of the mechanism of solar magnetic field generation.     

Analytical developments of rigid Mars nutation and tide generating potential series

In this paper, series of rigid Mars nutations for the angular momentum axis, the rotation axis and the figure axis, as well as series of rigid Mars tide generating potential (TGP) are computed. The method used is based on the calculation of the forces produced by the external bodies on the rigid Mars. We have included the direct effect of the sun, Phobos and Deimos. We have also included the indirect effects associated with these bodies and planets of the Solar System which are given at the level of the ephemerides. For the nutation series, with a truncation level of 0.1mas (milliarcsecond), related to the present-day precision of the Martian precession constant, 24 terms in longitudes (*****) and 10 terms in obliquity (*****) are computed. The value of the dynamical flattening used is H _D=(C–A)/C=0.00536, derived from the value p _a=–7576±35mas/yr for the precession rate. Our results show a perfect agreement with those of Bouquillon and Souchay (1996) to the truncation level of Bouquillon and Souchary (1mas). For the TGP series, we have set the truncation level to 10^–6m²/s² which corresponds to an effect on the vertical acceleration on Mars surface of about 10^–12m/s²=0.1nanogal (1nanogal=10^–11m/s². With this truncation level, 134 terms are computed.     

Detection and discrimination of sulfate minerals using reflectance spectroscopy

A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance-compositional-structural relations for this group of minerals. Sulfates exhibit diverse spectral properties, and absorption-band assignments have been developed for the 0.3-26 μm range. Sulfate absorption features can be related to the presence of transition elements, OH, H₂O, and SO₄ groups. The number, wavelength position, and intensity of these bands are a function of both composition and structure. Cation substitutions can affect the wavelength positions of all major absorption bands. Hydroxo-bridged Fe³⁺ results in absorption bands in the 0.43, 0.5, and 0.9 μm regions, while the presence of Fe²⁺ results in absorption features in the 0.9-1.2 μm interval. Fundamental SO bending and stretching vibration absorption bands occur in the 8-10, 13-18, and 19-24 μm regions (1000-1250, 550-770, and 420-530 cm⁻¹). The most intense combinations and overtones of these fundamentals are found in the 4-5 μm (2000-2500 cm⁻¹) region. Absorption features seen in the 1.7-1.85 μm interval are attributable to HOH/OH bending and translation/rotation combinations, while bands in the 2.1-2.7 μm regions can be attributed to H₂O- and OH-combinations as well as overtones of SO bending fundamentals. OH- and H₂O-bearing sulfate spectra are fundamentally different from each other at wavelengths below ∼6 μm. Changes in H₂O/OH content can shift SO band positions due to change in bond lengths and structural rearrangement. Differences in absorption band wavelength positions enable discrimination of all the sulfate minerals used in this study in a number of wavelength intervals. Of the major absorption band regions, the 4-5 μm region seems best for identifying and discriminating sulfates in the presence of other major rock-forming minerals.     

Tentative identification of the diffuse interstellar absorption bands and of a diffuse interstellar doublet line

The four diffuse interstellar absorption bands at 4430, 4760, 4890, and 6180 and the two diffuse lines at 5780 and 5797 are interpreted as belonging to pre-ionization transitions in H^– and O^–, respectively. In both cases the identifications are supported by extrapolations of wave numbers of resonance lines along isoelectronic sequences.In the H^– case the hypothesis as to the origin of the bands is supported by quantum-mechanical results byHerzenberg andMandl (1963) as to the positions of resonances in collisions between neutral hydrogen atoms and free electrons. The relatively large intensities of the forbidden transitions indicate that the extent of the ion in its excited states may be very large as compared to ordinary atomic dimensions. In the O^– case the relative doublet separation, as extrapolated along the isoelectronic sequence, is used for the identification of the doublet.     

The dynamics of the ring nebula surrounding the LBV candidate He 3-519

High spatial and spectral resolution observations of the ring nebula surrounding the LBV candidate He 3-519 are presented. The data were obtained at the AAT with the UCL echelle spectrograph and cover the H and [N II] emission lines for two slit positions. The nebular motions are clearly resolved and have a total velocity spread of -40 to +100 km s^–1. The shell shows some deviations from spherical symmetry but overall is expanding at 61 km s^–1 and has an ionized mass of 2 M. The nebular parameters are found to be similar to those of the AG Car nebula, suggesting that it resulted from a bulk ejection of material 2 × 10⁴ yr ago.     

On the solving of the Hill's differential equation through the method of operational calculus

Using a method previously applied to the treatment of the Mathieu differential equation, we solve the Hill's differential equation of lunar theory through the way of operational calculus, which avoids the cumbersome infinite determinants of the classical procedure. The one-sided Laplace transformation changes it into a difference equation with an infinite number of terms and variable coefficients. When its first member is divided by a suitable factor, this difference equation is the image of an integral equation of the Volterra type which is equivalent to the initial Hill's differential equation. Solution of this Volterra integral equation is unique and it is the general solution of the Hill's differential equation. This solution is a series in the powers of a small dimensionless parameter ² which appears as a factor in the second member of the Hill's differential equation. We reduce it to the sum of its terms of degree 12 with respect to which is the precision usually required in a lunar theory and we write down effectively the coefficients of the terms in ², ( ²)² and the coefficient of the term in ( ²)³ which depends upon the initial valuey(0) of the Hill's differential equation.     

New C13N14 search regions in the solar spectrum

Ten new rotational line positions, due to the (0,0) red C¹³N¹⁴ band, are calculated to fall squarely within continuum regions 1–2 Å wide in the near infrared solar spectrum, , 10 990–11 630. Precision observations of the isotopic line strengths in this spectral region, albeit difficult, should resolve the present ambiguity in the blue-violet observations of whether or not the solar C¹²/C¹³ ratio is equal to or larger than the terrestrial ratio.     

Some calculations bearing on the heating and cooling of quiescent prominences

We discuss the evolution of pulses of heat both along and perpendicular to magnetic fields threading quiescent prominences. We show that while heating of prominence material can take place on a time scale of the order 10³ s (of the same order as the observed winking of H light from prominences and also of the same order as the dynamical Alfvén time scale across a prominence sheet) individual flux tubes are effectively thermally insulated from neighboring tubes, since the transverse (to the ambient supporting magnetic field) heat conduction time scale is of order 10⁴ yr. The exact solution to the one-dimensional parallel heat conduction problem is shown to differ significantly from the approximate solution reported by Ioshpa (1965). We also suggest that uneven heating of a quiescent prominence by the surrounding solar corona may be a contributory mechanism for surges and/or the observed winking phenomenon - both of which are recorded in many quiescent prominences. The signature of such a temperature pulse would be a sharp (10³ s) brightening of continuum radiation with a correlated decrease in the free-bound emission, followed by a slow (10⁴ s) recovery of both to their pre-heat pulse levels.     

Solar activity in the last millennium recorded in the δ18O profile of planktonic foraminifera of a shallow water Ionian Sea core

In this paper we present the ¹⁸O profile of Globigerinoides ruber measured in the GT90/3 shallow water Ionian sea core, dated with high precision. The ¹⁸O profile covers the period 1200–1900 AD, with a resolution of 3.87 years. This long record of 700 years of ¹⁸O allows us to identify the imprint of the solar cycle in a climatic record. In fact, the spectral analysis of the time series performed with different methods shows a dominant periodicity of about 11 years with an amplitude of 0.07. The signal is in opposition to the sunspot number cycle. This component is identified at a high significance level by Monte Carlo Singular Spectrum Analysis (MC-SSA).     

The 3410 Å band of the PH molecule in the solar photospheric spectrum

Some weak unidentified solar photospheric lines in the wavelength range: (3400–3465) Å may be due to PH lines of the (0, 0) band of the PH(A ³ _i - X ^{3 -})system. These faint PH molecular lines have resulted an excitation temperature of the order of 4500 K. Using experimental lifetime data for PH in the A ³ _i state, an absorption oscillator strength f ₀₀ = 0.0075 is derived for the 3410 Å band of the PH (A ³ _i - X ^{3 -})system. Accurate line positions, oscillator strength and transition probability for the 4.4 fundamental rotation-vibration band of the PH molecule are obtained. A comparison of positions of some lines of the 4.4 band with those obtained on new tracings of high resolution solar spectra shows many coincidences with weak solar lines.     

Mass effects in the problem of three bodies

This is a study of the dynamical behavior of three point masses moving under their mutual gravitational attraction in a plane. The initial positions and velocities are identical for all cases studied and only the masses of the participating bodies change in the series of numerical experiments. In this way the effect of the coupling terms in the differential equations of motion are investigated. The motion in all 125 cases begins with an interplay between the three bodies, followed by temporary ejections or by an eventual escape. The total mass of the system is kept constant while the massratios change from 1 to 5. The initial velocities being zero, the total energy is negative in all cases.Approximately 74% of the cases disintegrated (i.e. two bodies formed a binary and the third body escaped) in less than 140 time units, 47% in less than 50 time units and 10% ended in escape in less than 10 time units. Considering three stars with total mass 12M , initially placed at 3, 4 and 5 parsec distances (or three galaxies with mass 2.4×10¹² M , initially placed 30, 40 and 50 kpc apart), the unit of time (approximately the crossing time) becomes 1.5×10⁷ y (3.2×10⁷ y). The average time of disintegration was found to be of the order of 10⁹ y. The average semi-major axis of the binaries left behind after disintegration was 0.7 parsec and the average value of the eccentricity was 0.76. The effect of the masses on the escapes was established and it was found that the bodynot with the smallest mass escaped in 13% of the disintegrated cases. The cases which did not disintegrate in 150 time units were analyzed in detail and the time of their eventual escape was estimated.The numerical results are tabulated regarding escape time, ejection period, total energy, escape energy, terminal velocity, semi-major axis, and eccentricity.The evolution of triple systems is followed from interplays through ejections to escapes and the orbital parameters for the separation of these classes are estimated.     

Spectral characteristics of solar S bursts

Observations of the solar radio spectrum have been made with high time and frequency resolution. Spectra were recorded over six 3-MHz bands between 30 and 82 MHz. The receivers used were capable of time and frequency resolutions of 1 ms and 2 kHz, respectively. A large number of radio bursts exhibiting a variety of find spectral structure were recorded.The bursts, referred to here as S bursts, were observed throughout the 30–82 MHz frequency range but were most numerous in the 33–44 MHz band and were very rare at 80 MHz. On a dynamic spectrum the bursts appeared as narrow sloping lines with the centre frequency of each burst decreasing with time. The rate of frequency drift was about 1/3 that of type III bursts. Most bursts were observed over only a limited frequency range (< 5 MHz) but some drifted for more than 10 MHz. The durations measured at a single frequency and the instantaneous bandwidths of S bursts were small; t = 49 ± 34 ms and f = 123 ± 56 kHz for bursts observed near 40 MHz. A significant number had t 20 ms. Flux densities of S burst sources were estimated to fall in the range 10²³-5 × 10²¹ Wm^–1 Hz^–1.A small proportion (1–2%) of bursts showed a fine structure in which the burst source apparently only emitted at discrete, regularly spaced frequencies causing the spectrogram to exhibit a series of bands or fringes. The fringe spacing increased with wave frequency and was f - 90 kHz for fringes near 40 MHz. The bandwidths of fringes was narrow, often less than 30 kHz and in some cases down to 10–15 kHz.New address: Astronomy Program, University of Maryland, College Park, MD, U.S.A.     

The clustering of Lα absorption lines in the QSO spectra

For nine published high-resolution QSO spectra a correlation analysis of their L forest lines has been performed. The two-point correlation functions show some quasi-periodic structure of magnitude ||0.3. Their characteristic separation along the line-of-sight amounts to s ₀=3×10^–3 or to s ₀=5×10^–3 for =1 and 0.2, respectively. Especially the distribution of nearest neighbouring line positions in two close QSO pairs allows for the interpretation that the absorption clouds lie in sheet-like structures as predicted by the pancake theory. The correlation data contain some hints on metal absorbers within the forest of unidentified lines.     

Uv Line Profiles of Biv from a 10-Ps Krf-Laser-Produced Plasma

We use a KrF laser that generates pulses up to 8 × 10¹⁴ watt/cm² when focused onto a boron nitride target. We measured the line profile of the near UV, n = 0, n = 2 transitions of helium-like boron and we studied the triplet 1s2p³P-1s2s³S at 2825.85 (J = 1), 2821.68 (J = 2) and 2824.57 (J = 0) Å, at various positions from the target surface, in order to correlate details of this profile with the presence of self-generated magnetic fields and/or dynamic turbulence among other processes. We fitted the measured profiles to a 0-D model, that includes, Stark, Doppler, Zeeman and instrumental broadening. The effect of the magnetic field was included using an intermediate field calculations. Preliminary results of these measurements are presented and discussed.