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  • 1
    Electronic Resource
    Electronic Resource
    Physical mapping of 4S RNA genes on chloroplast DNA of Spirodela oligorhiza (1981)
    Springer
    Current genetics 4 (1981), S. 187-190 
    Details
    ISSN: 1432-0983
    Keywords: Chloroplast DNA ; Spirodela oligorhiza ; 4S RNA ; Physical map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have determined the position of Spirodela oligorhiza chloroplast 4S RNA genes on the restriction fragment map of cp DNA, using purified in vitro[32P]-labeled 4S RNA. The overall organization of these genes is very similar to the organization of tRNAs on spinach cp DNA (Driesel et al. 1979).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00420497
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular cloning and characterization of the chloroplast ribosomal RNA genes from Spirodela oligorhiza (1983)
    Springer
    Current genetics 7 (1983), S. 7-12 
    Details
    ISSN: 1432-0983
    Keywords: Chloroplast DNA ; Spirodela oligorhiza ; Ribosomal RNA genes ; Physical map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The organization of the chloroplast ribosomal RNA genes in Spirodela oligorhiza has been determined. We have therefore characterized two cloned BamHI fragments containing the genes for the large and small rRNA genes, and two PstI fragments, each containing one of the two large, invertedly repeated regions of chloroplast DNA. Characterization was performed by restriction endonuclease mapping, DNA/RNA hybridization and electronmicroscopic R-loop analysis. The results show that the rRNA genes are present in the order 16S, 23S, 4.5S and 5S. The 16S (1.5 kb) and 23S (2.9 kb) rRNA genes are separated by a spacer of 2.25 kb. There appears to be a close resemblance between the organization of the chloroplast rRNA genes in Spirodela oligorhiza and other higher plants so far examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365674
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  • 3
    Electronic Resource
    Electronic Resource
    Transcription of ribosomal DNA in chloroplasts of Spirodela oligorhizaa (1984)
    Springer
    Current genetics 9 (1984), S. 91-97 
    Details
    ISSN: 1432-0983
    Keywords: Chloroplast DNA ; Spirodela oligorhiza ; Ribosomal RNA genes ; Transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The genes for the two large ribosomal RNAs (16S and 23S) and for the 4.5S rRNA in Spirodela oligorhiza chloroplast DNA are transcribed as one large, 7,000 nucleotides long precursor rRNA. Using S1-nuclease mapping, we have determined that the transcript ends 135 nucleotides 3′ distal of the 4.5S rRNA gene. 5S rRNA therefore, is most likely transcribed separately. Northern blotting of chloroplast RNA with distinct probes derived from the rDNA region reveals RNAs, which can be described as intermediates in the processing of the large precursor. With these findings a pathway for the maturation of this precursor is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396209
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  • 4
    Electronic Resource
    Electronic Resource
    Repeated sequences on mitochondrial DNA ofSpirodela oligorhiza (1985)
    Springer
    Plant molecular biology 4 (1985), S. 219-224 
    Details
    ISSN: 1573-5028
    Keywords: plant mitochondrial DNA ; repeated sequence ; Spirodela oligorhiza
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mitochondrial DNA ofSpirodela oligorhiza (duck weed) was analyzed with restriction enzymes. The genome size appears to be at least 250 kbp. Four different PstI fragments were cloned. These four clones contain a sequence which is reiterated about 100-fold on theSpirodela mitochondrial DNA. Hybridization analysis showed that a similar sequence is present onZea mays mitochondrial DNA, although much less reiterated here. The presence of these reiterated sequences might contribute to the physical heterogeneity of plant mitochondrial DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02418239
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  • 5
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    The Optical Counterpart to Gamma-Ray Burst GRB 970228 Observed Using the Hubble Space Telescope (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Although more than 2,000 astronomical gamma-ray bursts (GRBS) have been detected, and numerous models proposed to explain their occurrence, they have remained enigmatic owing to the lack of an obvious counterpart at other wavelengths. The recent ground-based detection of a transient optical source in the vicinity of GRB970228 may therefore have provided a breakthrough. The optical counterpart appears to be embedded in an extended source which, if a galaxy, as has been suggested would lend weight to those models that place GRBs at cosmological distances. Here we report, observations using the Hubble Space Telescope of the transient counterpart and extended source 26 and 39 days after the initial gamma-ray outburst. We find that the counterpart has faded since the initial detection (and continues to fade), but the extended source exhibits no significant change in brightness between the two dates of the observations reported here. The size and apparent constancy of the extended source imply that it is extragalactic, but its faintness makes a definitive statement about its nature difficult. Nevertheless, the decay profile of the transient source is consistent with a popular impulsive-fireball model13, which assumes a merger between two neutron stars in a distant galaxy.
    Keywords: Space Radiation
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  • 6
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    The Radio-to-X-Ray Spectrum of GRB 970508 on 1997 May 21.0 UT (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We have reconstructed the spectrum of the afterglow of GRB 970508 on 1997 May 21.0 UT (12.1 days after the gamma-ray burst) on the basis of observations spanning the X-ray-to-radio range. The low-frequency power-law index of the spectrum, alpha = 0.44 +/- 0.07 (F(sub nu) proportional to nu(exp alpha)), is in agreement with the expected value alpha = 1/3 for optically thin synchrotron radiation. The 1.4 GHz emission is self-absorbed. We infer constraints on the break frequencies nu(sub c) and nu(sub m) on 1997 May 21.0 UT from a spectral transition from F(sub nu) approx. nu(exp -0.6) to F(sub nu) approx. nu(exp -1.1) in the optical passband around 1.4 days. A model of an adiabatically expanding, blast wave emitting synchrotron radiation, in which a significant fraction of the electrons cool rapidly, provides a successful and consistent description of the afterglow observations over nine decades in frequency, ranging in time from trigger until several months later.
    Keywords: Space Radiation
    Type: Astrophysical Journal; 500; L97-L100
    Format: text
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  • 7
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    The Decay of Optical Emission from the gamma-Ray Burst GRB970228 (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The origin of gamma-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray and optical wavelengths coincident with the location of the gamma-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity, the latter having been tentatively identified as a high-redshift galaxy. This would seem to favour models that place gamma-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of approximately 40, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model, but the subsequent decrease in the rate of fading may prove harder to explain.
    Keywords: Space Radiation
    Type: NASA-TM-112889 , NAS 1.15:112889 , Letters to Nature; 387; 479-481
    Format: application/pdf
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  • 8
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    Radio and Optical Follow-Up Observations and Improved IPN Position of GRB 970111 (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We report on Westerbork 840 MHz, 1.4 and 5 GHz radio observations of the improved IPN-WFC error box of the gamma ray burst GRB 970111, between 26.4 hours and 120 days after the event onset. In the approximately 16 sq arcmin area defined by the IPN (BATSE and Ulysses) annulus and the published refined BeppoSAX Wide Field Camera (WFC) error box we detected no steady sources brighter than 0.56 mJy (4sigma), and no varying radio emission, down to 1.0 mJy (4sigma). We also report on B, V, R and I band observations of the error box with the 4.2 m William Herschel Telescope at La Palma. Subject headings: gamma rays: bursts - gamma rays: individual (GRB 9701 1 1)
    Keywords: Space Radiation
    Type: Astrophysical Journal
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  • 9
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    Two Variable Radio Sources Near the Position of GRB 940301 (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We report on the results of a search for a radio counterpart to the strong gamma-ray burst GRB 940301. Observations with the Westerbork Synthesis Radio Telescope of the Compton Telescope error box region of GRB 940301 began on March 4, 1994, at 21 cm and April 2, 1994, at 92 cm. No flux density variations were detected at 92 cm above S= 10 mJy (5 (sigma)) within a period of 1 to 4 months after the burst. However, when we compared the field with Westerbork Northern Sky Survey data, taken two years prior to GRB 940301, we found two radio sources with significantly increased flux densities. These sources, only 17 min. apart, are located at the 2.3 and 2.6(sigma) Compton Telescope confidence contours. Their separation from the Inter Planetary Network annulus virtually excludes association with GRB 940301. Further observations in January 1996 reveal that the sources continued to change in flux density. The relatively large flux density variations at 92 cm, compared to those at higher frequencies, and the inverted spectra in the frequency range from 325-38O MHz make the sources somewhat unusual. Because the sources were already detected at 5 GHz in 1986 most, if not all, of the radio emission is probably associated with activity in Active Galactic Nuclei in distant galaxies.
    Keywords: Space Radiation
    Type: Astronomy and Astrophysics; 321; 229-235
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  • 10
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    The Decay of Optical Emission Form the Gamma-Ray Burst GRB 970228 (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The origin of gamma-ray bursts has been one of the great unsolved mysteries in high-energy astrophysics for almost 30 years. The recent discovery of fading sources at X-ray and optical wave-lengths coincident with the location of the gamma-ray burst GRB970228 therefore provides an unprecedented opportunity to probe the nature of these high-energy events. The optical counterpart appears to be a transient point source embedded in a region of extended nebulosity, the latter having been tentatively identified as a high-redshift galaxy. This would seem to favour models that place gamma-ray bursts at cosmological distances, although a range of mechanisms for producing the bursts is still allowed. A crucial piece of information for distinguishing between such models is how the brightness of the optical counterpart evolves with time. Here we re-evaluate the existing photometry of the optical counterpart of GRB970228 to construct an optical light curve for the transient event. We find that between 21 hours and six days after the burst, the R-band brightness decreased by a factor of approx. 50, with any subsequent decrease in brightness occurring at a much slower rate. As the point source faded, it also became redder. The initial behaviour of the source appears to be consistent with the 'fireball' model, in which the burst results from the merger of two neutron stars, but the subsequent decrease in the rate of fading may prove harder to explain. The gamma-ray burst of 28 February 1997, detected with the Gamma-Ray Burst Monitor on board the BeppoSAX satellite, and located with an approx. 3 feet radius position with the Wide Field Camera on the same satellite, was the first for which a fading X-ray and optical counterpart were discovered. The optical Counterpart was discovered from a comparison of V- and I-band images taken with the William Herschel Telescope (WHT) on February 28.99 UT, and the Isaac Newton Telescope (INT; V band) and the WHT (I band) on March 8.8 uT.
    Keywords: Space Radiation
    Type: Nature; 1
    Format: text
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