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  • 1
    Electronic Resource
    Electronic Resource
    Influence of growth velocity and temperature gradient on the encapsulation of B lymphoblasts
    Amsterdam : Elsevier
    Cryobiology 25 (1988), S. 529 
    Details
    ISSN: 0011-2240
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0011-2240(88)90356-2
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  • 2
    Electronic Resource
    Electronic Resource
    A Search for Warm Neutral Gas Associated with the Giant HII Region NGC 604 (2000)
    Springer
    Astrophysics and space science 272 (2000), S. 15-22 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The characteristics of the halo gas and its interaction with the galactic disk in spiral galaxies are poorly known; this is particularly true for the warm neutral gas associated with HVCs and galactic chimneys. The detection of absorption features such as the NaI D or the CaII (H,K)lines is instrumental to study its detailed physical properties but requires very long integration times. In this work very deep optical spectra of NGC 604, the brightest giant HII region among the nearby spirals, are presented. The detection of two absorption components at LSR velocities -255 km/s and −20 km/s respectively, is reported; the first component is associated with the HII region. The inferred line width after deconvolution is 155 km/s; this large width is produced by the blending of the multiple absorption components produced by the diverse sources of internal motion (expanding shells and general turbulence). The radial velocity of the CaII absorption is slightly larger than the measured in the HII emission lines suggesting a possible flow of gas into the halo above the young star cluster. The large ratio x = W λ (NaID_2)/W λ (CaIIK) = 0.7indicates the probable presence of shocks which release Ca from the dust grains into the gas phase. The lower velocity component most likely trace galactic gas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002664700505
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  • 3
    Electronic Resource
    Electronic Resource
    Chemical etching of GaAs with a novel low energy ion beam source : A low damage process for device fabrication
    Amsterdam : Elsevier
    Vacuum 44 (1993), S. 257-261 
    Details
    ISSN: 0042-207X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0042-207X(93)90165-7
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  • 4
    Electronic Resource
    Electronic Resource
    Solar enhancements at 1.2 mm wavelength (1971)
    Springer
    Solar physics 16 (1971), S. 87-102 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solar observations through the atmospheric pass-band centred at 250 GHz have been made in the form of isophote maps. These show chromospheric features which have higher brightness temperatures than the mean disc temperature by up to 10%. Examination of corresponding maps at lower frequencies and also of Caii and Hα spectroheliograms reveals that the hot areas lie above photospheric active regions, and are regular features of the chromospheric millimetric emission having stable structure and duration of several weeks. Less frequently observed variable enhancements are also described, and linked with the formation of the stable active regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154504
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  • 5
    Electronic Resource
    Electronic Resource
    Studies of the solar chromosphere from millimetre and sub-millimetre observations (1973)
    Springer
    Solar physics 29 (1973), S. 25-39 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spectroheliograms were obtained in bands centred at 1.2 mm, 0.8 mm and 0.4 mm wavelength during 1969 and 1971. In order to obtain photometrically valid data, a specialized set of reduction techniques was employed, obviating the effects of severe differential attenuation across the disc by atmospheric water vapour and of emission noise from the atmosphere, before taking out the instrumental spread functions of the telescope and detector. Comparison of our maps with those of other observers at 3 mm and 8.6 mm wavelength suggests that the chromospheric brightness temperature increments above active regions show a monotonic increase with increasing height above the photosphere over the normal increase in brightness temperature in the quiet chromosphere. Within the limit of angular resolution of 3′ available, no evidence was recorded of normal limb brightening in our three passbands but the presence of isophotes at 50% of the central disc temperature consistently circumscribing the optical limb implies a narrow spike of sub-millimetre brightening close to the limb.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153437
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  • 6
    Electronic Resource
    Electronic Resource
    Studies of the solar chromosphere from millimetre and sub-millimetre observations (1973)
    Springer
    Solar physics 31 (1973), S. 319-338 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A compilation of brightness temperature data in the millimetre and sub-millimetre wavelength ranges is used to obtain an empirical relation T B = Cλ n between brightness temperature and wavelength, valid between 1 mm and 1 cm. An analytically soluble model, giving electron temperatures and densities between 1500 km and 4000 km above the photosphere is derived from this relationship, and eclipse data of Thomas and Athay, of the emission at the head of the Balmer continuum. Although this over-simplified model lacks precision in the height co-ordinate, it allows a scale height of around 1000 km for electrons to be deduced, and supplies a convincing test for the absence of hydrostatic equilibrium throughout the region. A more comprehensive and reliable though still simplified numerical model is then presented, being a modification of previous models accounting only for millimetre data. It shows marked departure from UV derived models in this region, and an explanation for the discrepancy is proposed in terms of thermal inhomogeneities on the scale of the chromospheric supergranulation. The stratified model is then geometrically modified to account for observed centrelimb profiles of the Sun measured throughout the sub-millimetre and millimetre region. The scale of any roughness thus introduced is related to the notable lack of millimetric limb brightening, and observational tests for that scale are suggested here. A qualitative picture of this part of the chromosphere is proposed, consistent with existing observations in the millimetre, visible and UV regions of the spectrum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152810
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  • 7
    Electronic Resource
    Electronic Resource
    The local interstellar medium: A test-bed for the galactic ISM (1989)
    Springer
    Astrophysics and space science 156 (1989), S. 243-249 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We outline a method to explore the column density of the Local Interstellar Medium (LISM) using absorptions in the resonance H and K lines of Mgii. The intrinsic strengths of these lines in the temperature and density conditions prevailing in warm clouds (T eff〈104 K) in the LISM allows them to be used to explore many lines of sight where lines such a NaD and Caii H and K are too weak, but where Lα is saturated. The number of measurable lines-of-sight is greatly enhanced by using cool stars as the background emitters, but this implies reliable separation of the LISM components from stellar chromospheric selfabsorptions. We explain how to do this, and how to use a combination of column density and radial velocity data to measure the spatial extent and the physical parameters of the single cloud in which the Sun is embedded. This proves to be an oblate spheroid, of characteristic diameter 8 pc, withT eff ∼ 104 K,n(Hi) of 0.1 cm−3 and a mass 〈5M ⊙, streaming in the LSR from a point 1″=4°,B″=+16° with velocity equal to 16 km s−1, and is surrounded by the much hotter lower density ionized gas of the local supernova bubble.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646373
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  • 8
    Electronic Resource
    Electronic Resource
    Differential efficiency of massive star formation in NGC 628 (1989)
    Springer
    Astrophysics and space science 156 (1989), S. 289-293 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The efficiency ratio of massive star formation in the arms of the spiral NGC 628 to that in the interarm region has been determined from the sizes and positions of itsHii regions following the method described in Cepa and Beckman (1989a, b). The variation of this relative star formation efficiency with radius shows a very similar behaviour for each of the three arms of this galaxy with a minimum at 100 arc sec from the centre, which can be identified with the corotation radius distances at which the arms show bifurcations or sudden changes in their pitch angles. This result, together with the higher star formation efficiency in the arms than that in the interarm zones, is evidence supporting the hypothesis that the spiral arms of NGC 628 are driven by a density wave which triggers the star formation according to the spiral density wave theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646380
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  • 9
    Electronic Resource
    Electronic Resource
    A photometric study of the double ring structure of NGC 4736 (1989)
    Springer
    Astrophysics and space science 156 (1989), S. 301-313 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this study we present photometric results for the galaxy NGC 4736: infrared and visible profiles. After a careful correction for the extinction within the galaxy based on measured neutral gas surface densities, we interpret the profiles in the individual bands and in colour indices, in terms of the radial distribution of stellar populations. We pick out the behaviour of the two rings, an inner ring some 40–50 arc sec from the nucleus, and an outer ring some 300 arc sec away. We show how the photometry allows us to make tentative physical inferences about the nature of these two structures, showing that the inner ring is connected with an outflow of gas observed via itsHii regions, and is probably the result of an axisymmetric starburst, while the outer ring is a site of star formation which appears to be further from the centre than the typical resonant structures associated with a density wave.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646382
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  • 10
    Electronic Resource
    Electronic Resource
    Application of a new evolutionary model for stellar populations to photometric maps of M32 (1989)
    Springer
    Astrophysics and space science 157 (1989), S. 89-101 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00637315
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