Abstract. ERS SAR amplitude images are utilized to map ground displacements from a sub-pixel correlation method. It yields a ground two-dimensional displacement field with independent measurements about every 128m in azimuth and 250m in range. The accuracy depends on the characteristics of the images. For the Landers test case, the 1-• uncertainty is 0.8m in range and 0.4m in azimuth. We show that this measurement provides a map of major surface fault ruptures accurate to better than lkm and information on coseismic deformation comparable to the 92 GPS measurements available. Although less accurate, this technique is more robust than SAR interferometry and provides complementary information since interferograms are only sensitive to the displacement in range.
Système pour l'Observation de la Terre images are used to map ground displacements induced by earthquakes. Deformations ͑offsets͒ induced by stereoscopic effect and roll, pitch, and yaw of satellite and detector artifacts are estimated and compensated. Images are then resampled in a cartographic projection with a low-bias interpolator. A subpixel correlator in the Fourier domain provides twodimensional offset maps with independent measurements approximately every 160 m. Biases on offsets are compensated from calibration. High-frequency noise ͑0.125 m Ϫ1 ͒ is ϳ0.01 pixels. Low-frequency noise ͑lower than 0.001 m Ϫ1 ͒ exceeds 0.2 pixels and is partially compensated from modeling. Applied to the Landers earthquake, measurements show the fault with an accuracy of a few tens of meters and yields displacement on the fault with an accuracy of better than 20 cm. Comparison with a model derived from geodetic data shows that offsets bring new insights into the faulting process.
The double-helical conformations of d(m5-C-G-C-G-m5-C-G) in aqueous solution were studied by circular dichroism and 1H NMR spectroscopy. In 0.1 M NaCl, only the B form is detected whereas the Z form is strongly predominant in 3 M NaCl. In the presence of 2 M NaCl, two resonance signals corresponding to the B and Z duplexes were observed for each proton below 50 degrees C, indicating a slow exchange between B and Z. However, the B-Z exchange becomes intermediate or fast in the 55-80 degrees C temperature interval. By contrast the exchange between B helix and single-stranded (or coil) forms is much faster for the same temperature conditions. The Z form is only detectable when the coil form is practically absent. With decreasing temperature the B form decreases in favor of the Z form. From proton line-width measurements under various experimental conditions, it was also shown that Z exchanges only with B, while the latter also exchanges with the single-stranded form (S): Z in equilibrium B in equilibrium S. The enthalpy value is about 8 +/- 1 kcal/mol for the B-Z transition and about 40 +/- 2 kcal/mol for the B-S dissociation (2 M NaCl solution). The activation energy is about 47 +/- 2 kcal/mol for the Z----B and 39 +/- 2 kcal/mol for the B----Z reaction. Very good agreement between the experimental results and computed data (based on the above kinetic reaction model) was found for the B, Z, and coil proportions. The B-Z transition of methylated d(C-G)n oligomers is only possible when the Watson-Crick hydrogen bonds between the CG base pairs are firmly maintained; otherwise, the transformation from B to Z would not occur, and B-S dissociation would take place instead.
Infrared spectroscopy in the 1750-700 cm-.' region is used to characterize the right-and left-handed helices of poly (dG-dC) .poly(dG-dC) with sodium counterions. The use of polymers selectively deuterated on the C8 of guanincs and methylated on the C5 of cytosines allows us to propose explanations for several spectroscopic modifications which occur under thc B + Z transition. Similar substitutions on nucleosides and nucleotides are used so as to assign base absorptions in poly(dGdC).poly(dG-dC). A set of ir bands characteristic of DNA conformations, which can be used in studies of interactions with this polynucleotide and to identify the left handed Z conformation in more complex systems, is proposed. J . A. TABOURY, J. LIQUIER, et E. TAILLANDIER. Can. J. Chem. 63, 1904Chem. 63, (1985. La spectroscopie infrarouge dans la region 1750-700 cm-' permet de caracttriser la forme droite et la forme gauche de la double hClice de poly(dG-dC) -poly(dG-dC). L'Ctude de dCrivCs du poly(dG-dC).poly(dG-dC) deutCrits sklectivement sur le C8 de la guanine ou mCthylCs sur le C5 de la cytosine permet d'expliquer diffkrentes modifications du spectre de ce polynuclCotide au cours de la transition B + Z. Des modifications similaires sur des nuclCotides ou nucltosides apportent Cgalement des informations pour I'attribution des bandes d'absorption des bases du poly(dG-dC).poly(dG-dC).Nous proposons un ensemble de bandes d'absorption caractkristiques des conformations de I'ADN. qui pourra 2tre utilisC pour 1'Ctude d'interactions avec ce polynuclCotide ou pour la mise en evidence de la conformation en double hklice gauche dans des systkmes plus complexes. IntroductionThe DNA molecule, which for a long time had been considered a rather rigid entity, is now known to be extremely flexible and capable of adopting a great variety of secondary structures. The study of purine-pyrimidine alternating copolymers has, moreover, shown that classical right-handed A and B helices can be turned into left-handed forms belonging to the so-called Z family. These novel structures were first characterized in the case of poly(dG-dC)-poly(dG-dC) by the modification of the uv absorbance spectrum and by the inversion of the cd (circular dichroism) signal (1). Their existence has been definitively proved by X-ray diffraction studies on d(C-G)3 crystals (2). Nuclear magnetic resonance (nmr) (3, 4) and Raman spectroscopy (5-9) have also been used to investigate Z DNA. Thamann et al. (6) showed that the Raman spectrum of the Z DNA d(C-G), crystal is essentially identical to the high salt
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