ALBERT

Notes: The use of anther culture in breeding winter wheat.II. Production of new doubled haploid lines of winter wheat with 1AL—1RS-translocationA total of 4472 anhers was cultured from 8 F1 populations of winter wheat with the 1AL—1RS wheat-rye translocation cultivar ‘Amigo’ as one of the crossing arents. When averaged over all populations a frequency of embruoid formation of 10% and of regeneration efficiency of green plants of 1% were observed. In addition to the 45 green regenerated plants, 93 albinos were obtained. 44% of the green plantlets had 21 chromosome in root tips and 29% were spontaneous diploids. Multiple peroxidases were used a biochemical markers in the subsequent characterization of the homogeneous breeding material. The electrophoretic patterns showed that 16 doubled haploids without rye chromosome segments were produced. In addition the features of dh0- plants showed, that several of the new 1AL—1RS-translocation lines were awnless.

Notes: Plane-wave ray tracing has been performed through 2-D random media with Gaussian and exponential autocorrelation functions of the slowness perturbations. The standard deviation is ɛ, correlation length a and propagation distance L; computations have been performed for ɛ= 1 and 3 per cent and for L/a= 2.5 to 60. Up to L/a= 5 or 10, regular focusing and defocusing of the rays is observed. Then, irregular behaviour develops, apparently without foci, but with increasing deviations q from the straight rays of a homogeneous medium. Two neighbouring rays at the top of a rectangular cross-section usually arrive far from each other at the bottom, and rays can even turn. The standard deviation σ of q, normalized by L, is approximately σ/L=ɛ(L/a)1/2.From the traveltimes of the rays at the bottom of the cross-section, the first arrivals were determined and compared with the first arrivals according to the Huygens method of Podvin & Lecomte (1991). Both ray tracing and the Huygens method are high-frequency methods, but their traveltimes do not always agree. The reason is that the Huygens method gives first arrivals including diffractions around the slow parts of the structure, whereas ray tracing, in the sense of initial-value ray tracing, gives only transmitted rays. As a consequence, traveltimes calculated by ray tracing are systematically late with respect to the Huygens-method traveltimes. The difference becomes significant for L/a greater than 10 to 20, it increases with ɛ, and it is more pronounced for exponential than for Gaussian media. For instance, the velocity shift (with respect to the inverse of the volume average of the slowness) for an exponential medium, L/a= 60 and ɛ= 3 per cent, is –0.5 per cent according to ray tracing, whereas it is + 1.3 per cent according to the Huygens method. For ɛ= 1 per cent the corresponding numbers are 0 and +0.3 per cent, i.e. the difference between ray tracing and the Huygens method is still significant.A conclusion from our calculations is that, even in the mildly laterally heterogeneous earth models of seismic tomography, ray tracing may give traveltimes that are significantly biased, i.e. overestimated. Another result is that, in random media, ray-tracing first-arrival traveltimes often have much stronger short-scale spatial variations than Huygens-method traveltimes which include wavefront healing due to diffractions. Both effects, traveltime bias and short-scale variations, limit the applicability of ray tracing already for weak random media.

Notes: Seismic waves in a random medium (with standard deviation ε and correlation distance a of the relative slowness fluctuations) prefer fast paths, and therefore the apparent velocity of wave propagation is larger than the velocity which corresponds to the volume average of slowness. This velocity shift can be determined by ray perturbation theory (Snieder & Sambridge 1992), by the Huygens method (Podvin & Lecomte 1991) and by wave theory (Müller, Roth & Korn 1992). We apply all three methods to plane-wave propagation through a 2-D acoustic medium with Gaussian or exponential autocorrelation function of the slowness fluctuations. Ray perturbation theory gives numerical and analytical results, but has path-length (L) limitations. The Huygens method, which also gives the ray-theoretical velocity shift, can be used for L/a ratios of seismological interest. Wave theory shows that the velocity shift also depends on the wavelength λ and that for λ/a less than about 0.1 the velocity shift agrees with the result of the Huygens method. For λ/a= 1 the wave-theoretical (i.e. true) shift is lower than the Huygens-method shift by a factor of 0.25 to 0.5. Simple formulae for the ε dependence of the Huygens-method shift at long path lengths (L/a≤ 80) are given, and a correction factor is derived which approximately transforms plane-wave 2-D into spherical-wave 3-D velocity shifts; the latter correspond to 3-D two-point ray tracing.For short-period seismic waves, propagating to teleseismic distances, mantle heterogeneity with ε= 1 per cent and a= 100 km produces a velocity shift of about 0.2 per cent. Shifts of this order can explain the difference in earth models, derived from free oscillations on the one hand and from short-period body waves on the other. A velocity shift (or velocity dispersion) due to anelasticity would be additional.

Notes: A ray-theoretical relation is established between the autocorrelation function of the slowness fluctuations of a random medium and the autocorrelation function of the traveltime fluctuations on a profile perpendicular to the general propagation direction of an originally plane wave. Although this relation can be inverted exactly, it is preferable for applications to use the results of a forward calculation for a modified exponential autocorrelation function which represents slowness fluctuations with zero mean. The essential parameters of this autocorrelation function, standard deviation ε and correlation distance a, follow by simple relations from the maximum and the zero crossing of the corresponding autocorrelation function of the traveltime fluctuations. The traveltime analysis of 2-D finite-difference seismograms shows that ε and a can be reconstructed successfully, if the wavelength-to-correlation-distance ratio is 0.5 or less. Otherwise, ε is underestimated and a overestimated; however, both effects can be compensated for.The average traveltime, as determined from the finite-difference seismograms, is slightly, but systematically shorter than the traveltime according to the average slowness, i.e. the wave prefers fast paths through the medium. This is in agreement with results of Wielandt (1987) for a spherical low-velocity inclusion in a full-space and with results of Soviet authors, summarized by Petersen (1990). The velocity shift is proportional to ε2, it has dispersion similar to the dispersion related to anelasticity, and it increases with the pathlength of the wave.

Notes: Under the minimum-phase condition attenuation operators are derived from arbitrary intrinsic or scattering Q as a function of frequency, and a simple method is described to calculate these operators with the aid of Fourier transformation. In the case of scattering attenuation, the medium may contain both 1-D, 2-D or 3-D heterogeneities. For illustration, the method is applied to a 1-D model of statistically layered media with 12 per cent standard deviation of relative velocity fluctuation. The theoretical scattering Q, deduced from single-scattering theory, is determined for a numerical autocorrelation function and an exponential autocorrelation function, as well as for a modified exponential autocorrelation function, which is introduced here. The corresponding attenuation operators are calculated. The theoretical Q and simulated seismograms, calculated with the attenuation operators, agree very well with the exact results of synthetic-seismogram calculations.

Notes: Fast frequency-wavenumber migration is used to migrate synthetic seismograms, calculated by a hybrid method for crustal models with complex 2-D scattering structures in the lower crust. Scatterers with predominantly horizontal or vertical orientation and scatterers without preferred orientation (isotropic scatterers) are investigated; horizontal scatterers or lamellae have frequently been suggested for the lower crust on the basis of modern reflection seismological experiments. In none of the cases studied here are the scattering structures imaged correctly. the reason is mainly multiple scattering which can produce coherent arrivals in the seismogram sections, and hence coherent signatures in the migrated sections, which have no relation to structure. Imaging is generally acceptable for horizontal scatterers, but for isotropic or vertical scatterers the migrated signatures are also horizontal and thus do not represent reality. It is concluded that the highly detailed line drawings, which are popular in crustal reflection seismology, are less reliable than believed, as far as the internal structure of scattering zones and the scatterer orientations are concerned. Horizontal or subhorizontal structures in the lower crust may be less common than assumed.The paper also briefly addresses a few methodical aspects of fast frequency-wavenumber migration for depth-dependent background structure, in particular the concept of sounding beams, their width and the construction of a migrated section from several sounding beams.

Notes: In August 1988 gravity measurements were made during 22 days in the Hornberg pumped-storage reservoir in the southern Black Forest, SW Germany. Water-level changes with daily variations of 5-22 m and the Earth tides produced gravity signals which were recorded digitally with six LaCoste-Romberg field gravimeters above and below the water level in a 60 m high tower. The reservoir geometry is well known, and water level could be measured continuously with high accuracy. The purpose of the experiment was to search in the gravity signals for deviations from Newton's gravitational law due to a newly postulated interaction (‘fifth force’) whose range is somewhere between 1 and 1000 m. The search technique is to construct residual signals, i.e. to subtract from observed gravity known effects such as the Newtonian attraction of the moving water masses and the Earth tides, and to search by regression analysis in the residual signal for a residual component proportional to the Newtonian attraction; this component could be of non-Newtonian origin. Residual water signals with amplitudes of 0. 25 ± 0.4 per cent of the Newtonian water signal were found. This value implies negative evidence for a residual water signal and, hence, for non-Newtonian gravitation. The experiment can also be considered as one for the measurement of the gravitational constant at effective mass separations of 40–70 m. The deviation from the laboratory value is also 0.25 ± 0.4 per cent and thus not significantly different from zero. The main limitation of the Hornberg experiment is due to calibration errors of the gravimeters used of 0.2–0.4 per cent, which were revealed by comparison of the records of neighbouring instruments.

Notes: The reflectivity method for computing synthetic seismograms can be applied to seismic prospecting problems with special focus on coal-mining problems. The method allows the calculation of reflected waves for point-source excitation and non-vertical incidence. It automatically includes all possible conversions of wave types and all inner multiple reflections. Synthetic horizontal- and vertical-component seismogram sections are given for a simple two-seam model and for a realistic seam sequence which is represented by 48 layers; the source-receiver distances range from 100 m to 1000 m. These seismograms show prominent PS reflections already at moderate source-receiver distances. These waves complicate the vertical-component records by producing arrivals of similar strength as the PP reflections. From this it is concluded that PS reflections in strongly layered media can cause problems in routine CDP stacking. On the horizontal-component records the PS reflections are dominant. Because of the lower velocities of S waves the time resolution of PS reflections is better than that of PP reflections. This suggests that horizontal-component recording may be useful in the investigation of subsurface regions with strong velocity contrasts, even with conventional energy sources producing mainly P waves.

Notes: The doubled haploid (DH) wheat line ‘dh 5841’ carrying two translocations from rye, 5DL.5RS and 1BL.1RS, has been crossed to the subline of wheat cultivar ‘Amadeus 7143’ with a 1BL.1RS translocation. The resulting F1 hybrid IJ 98 with a heterozygous 5DL.5DS-5DL.5RS chromosome pair has been used to produce doubled haploids. A total of 57 DH lines were obtained from plantlets regenerated in anther culture after successful colchicine treatment and seed set. These lines were identified regarding the constitution of chromosome 5D (5DL.5DS or 5DL.5RS) by means of isoenzyme marker analysis. Thirty DH lines possessed the 5DL.5DS chromosome, while the remaining 27 lines carried the 5DL.5RS translocation. For some of these lines, the 5DL.5RS chromosome was cytologically confirmed by C-banding. Furthermore, the DH lines were evaluated for their high molecular weight glutenin subunit composition. All possible combinations for the four independent loci —Skdh, Glu-Al, Glu-B1 and Glu-D1— were detected in only 57 DH lines and no segregation distortion was observed.