352 research outputs found
Differences in the Morphological Characteristics of the Land Races of the Soft and Emmer Wheat in Relation to the Modern Varieties
For the organic farmers there is important question which varieties of wheat are right for organic farming in Less Favoured Areas. Modern varieties of wheat are bred in the conditions of conventional (high imput) farming. That is why the organic farmers asked about the suitability of land
races of soft wheat (Triticum aestivum L.) or different species like emmer wheat grown in the past (Triticum dicoccum SCHUEBL). The paper results from the study of fourty land races, two intermediate and ten modern varieties of soft wheat in comparison to ten land races of emmer wheat at two locations in the Czech Republic. We evaluated tuft shape, length of plant, length and width of flag leaf, length and density of spike and awnedness. The
modern varieties of soft wheat are characterised by a high level of uniformity. Their tuft shape is erect or semi-erect and length of plant is 60-70 cm, it does not rise the weed competitiveness. On the other hand, they have a medium or long flag leaf whose width is narrow or medium. Length of spike is medium or long. On the other hand, emmer wheat land races have the same tuft shape as forgoing modern varieties. Length of plant (89-119 cm) is the positive aspect of the weed competitiveness. Their flag leaf is narrow, but it is compesated by its length. The spike is shorter than the spike of modern varieties of soft wheat, but it is effectivelly compensated by an increased
density. Intermediate wheat land races are characterised by looselly spreading tuft shape which puts the weeds down, but on the other hand, it favours the mildew because of the microclimate of soil. Its flag leaf is very short and narrow. Length of spike is medium and it is lax dense. The group of land races of soft wheat is characterised by a high diversity. The tuft shape is most frequently semi-erect. The length of plant varies from 60 to 120 cm, it
usually ranges from 90 to 110 cm. Flag leaf is usually long or very long, but its width is very narrow or narrow. The spike is often long, but lax dense. Some of the evaluated varieties of landraces are proved to be suitable for organic farming from the point of view of the morphological characteristics
The Radio Recovery of SN 1970G: The Continuing Radio Evolution of SN 1970G
Using the Very Large Array, we have detected radio emission from the site of
SN 1970G in the Sc galaxy M101. These observations are 31 years after the
supernova event, making SN 1970G the longest monitored radio supernova. With
flux densities of 0.12 +/- 0.020 mJy at 6 cm and 0.16 +/- 0.015 mJy at 20 cm,
the spectral index of -0.24 +/- 0.20 appears to have flattened somewhat when
compared with the previously reported value of -0.56 +/- 0.11, taken in 1990.
The radio emission at 20 cm has decayed since the 1990 observations with a
power-law index of beta_20cm = -0.28 +/- 0.13. We discuss the radio properties
of this source and compare them to those of other Type II radio supernovae.Comment: 11 pages, 1 table and 2 figures; To appear in Astrophysical Journal
Letter
Radio Detection of SN 1986E in NGC 4302
Radio observations of SN 1986E have shown a clear detection of emission at 6
cm wavelength about 8 months after optical discovery. Combined with a number of
new upper limits and a study of the possible models, it appears that SN 1986E
was probably a fairly normal Type IIL supernova, somewhat similar to SN 1980K,
with radio emission at roughly expected levels. This detection continues the
correlation between radio detection and late time optical emission.Comment: 14 pages, LaTeX (AASTeX), 2 PostScript figures, to appear in ApJ
(Letters
Radio emission from SNe and young SNRs
Study of radio supernovae (RSNe), the earliest stages of supernova remnant (SNR) formation, over the past 20 years includes two dozen detected objects and more than 100 upper limits. From this work we are able to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. More speculatively, it may be possible to provide distance estimates to RSNe
Radio Emission from SN 2001gd in NGC 5033
We present the results of monitoring the radio emission from the Type IIb
supernova SN 2001gd between 2002 February 8 and 2002 October 28. Most of the
data were obtained using the Very Large Array at the five wavelengths of
1.3 cm (22.4 GHz), 2.0 cm (14.9 GHz), 3.6 cm (8.44 GHz), 6.2
cm (4.86 GHz), and 21 cm (1.4 GHz). Observations were also made with Giant
Meterwave Radio Telescope at 21 cm (1.4 GHz). The object was
discovered optically well after maximum light, making any determination of the
early radio evolution difficult. However, subsequent observations indicate that
the radio emission has evolved regularly in both time and frequency and is well
described by the SN shock/circumstellar medium interaction model.Comment: 16 pages 2 figures to appear in Astrophysical Journa
Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution
New observations of SN 1980K made with the VLA at 20 and 6 cm from 1994 April
through 1996 October show that the supernova (SN) has undergone a significant
change in its radio emission evolution, dropping by a factor of ~2 below the
flux density S \propto t^{-0.73} power-law decline with time t observed
earlier. However, although S at all observed frequencies has decreased
significantly, its current spectral index of \alpha= -0.42\pm0.15 (S \propto
\nu^{+\alpha}) is consistent with the previous spectral index of
\alpha=-0.60_{-0.07}^{+0.04}.
It is suggested that this decrease in emission may be due to the SN shock
entering a new region of the circumstellar material which has a lower density
than that expected for a constant speed (w), constant mass-loss rate (Mdot)
wind from the progenitor. If such an interpretation is correct, the difference
in wind and shock speeds appears to indicate a significant evolution in the
mass-loss history of the SN progenitor ~10^4 years before explosion, with a
change in circumstellar density (\propto Mdot/w) occurring over a time span of
\lesssim 4 kyr. Such features could be explained in terms of a fast
``blue-loop'' evolutionary phase of a relatively massive pre-SN progenitor
star. If so, we may, for the first time, provide a stringent constraint on the
mass of the SN progenitor based solely on the SN's radio emission.Comment: 22 pages, 3 figures, to appear in Ap
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