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Last but not least, earlier reports from indentation experiments showed that diamonds with lower levels of nitrogen can more easily be deformed than diamonds with higher levels of nitrogen These observations indicate that nitrogen impurity may have profound effects on the deformation behavior of diamond crystals. Systematic studies of such effects under controlled deformation are thus warranted for a comprehensive understanding of crystal plasticity of diamond.

The polycrystalline diamond powder was purchased from Microdiamant. The as-purchased powder is more than For deformation under confined high pressure, the two vertical anvils can be driven independently to introduce compressive or tensile uni-axial straining. The pressure medium is a mixture of amorphous boron and epoxy resin for x-ray transparency. The diamond powders were compacted in a boron nitride sleeve, which also isolates the sample from graphite furnace.

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Bulk differential stress was produced in the specimen with hard alumina pistons placed on both ends of the specimen. The sample was separated from the alumina pistons by nickel foils, which were used as strain markers for measuring the total strain. X-ray radiographs of the deformed column at corresponding deformation conditions were also taken by removing the collimation slits.

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This bulk information is used, as described next, to derive differential stress and strain for each experimental run. Note that the pressure was applied in this work because external pressure helps minimize flow of polycrystalline diamond along the radial direction when sample is under uni-axial loading. Within the stability filed of graphite pressure is also needed to stabilize diamond and hence to prevent partial graphitization of diamond under the present experimental temperatures.

Our work, however, was not intended to systematically study the pressure effect on the deformation mechanisms of diamond. The sample columns from X-ray radiographs are used to measure the changes in the sample length during the deformation experiment. Depending on the intensity contrast between sample and strain marker Ni foil , it is possible to measure the sample length changes within 1 microns.

In this work, the ambient diffraction data are chosen as a reference for zero strain. Since this stress represents the local contact stress between crystal grains, it is conventionally termed microscopic stress. Different from the microscopic stress which originates from the local grain-to-grain contact stress field, the macroscopic stress directly reflects the stress field applied to the entire sample, which can be quantified by measuring the peak position shift. The methods used here for macroscopic stress analysis are similar to those described by Uchida et al. The lattice strain, , is fitted to the Equation 2 to obtain the differential lattice strain,.

With a cylindrical symmetry of the stress field in the D-DIA pressure cell the differential stress is defined by , where and are the principal stresses in axial and radial directions, respectively. For a given lattice plane hkl , the differential strain can be converted into the differential stress by equation 3 :. Throughout this work, both the microscopic and macroscopic strains are derived from the lattice plane A Philips CM30 electron microscope operating at kV was used to investigate the specimens.

All authors reviewed the manuscript. National Center for Biotechnology Information , U. Sci Rep. Published online Nov Author information Article notes Copyright and License information Disclaimer. Received Sep 24; Accepted Oct All rights reserved. Abstract Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 's.

Results Microscopic and macroscopic strain-stress measurements Figs. Open in a separate window. Figure 1. Figure 2. Figure 3. TEM characterization and deformation mechanism at room temperature Although diamond has the highest hardness and shear modulus owing to sp 3 hybridization and directional bonding of carbon atoms, diamond crystals cleave quite easily on a certain crystallographic plane when undergoing uni-axial deformation at room temperature. Figure 4.

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Figure 5. Discussion Experimental determination of constitutive laws and flow mechanisms in diamond deformation has been a standing problem since synthetic diamond was made in 's.


Methods Uniaxial deformation experiments under confined high pressure The polycrystalline diamond powder was purchased from Microdiamant. Derivation of macroscopic strain and stress Different from the microscopic stress which originates from the local grain-to-grain contact stress field, the macroscopic stress directly reflects the stress field applied to the entire sample, which can be quantified by measuring the peak position shift. References Field J. The Properties of Natural and Synthetic Diamond.

Academic, London, Telling R. Theoretical Strength and Cleavage of Diamond. Ideal strength of diamond, Si, and Ge. B 64 , Structural deformation, strength, and instability of cubic BN compared to diamond: A first-principles study. B 73 , C , — Dissociation of Dislocations in Diamond. A , — Philosophical Magazine 13 , — Strength, fracture and friction properties of diamond. Optical transitions in diamond at ultrahigh pressures. Nature , — The strength of diamond. Raman study on the stress state of [] diamond anvils at multimegabar pressure.

Science , — Strength of Diamond. Fracture toughness of diamond single crystals.

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Information from three satellites gives the 3D position; data from the fourth is required because receivers on the ground don't use atomic clocks and we need to solve for the timing error. Using this method, the GNSS receiver in your phone or car will give your position to an accuracy of about 5 m — insufficient for measuring deformation at tectonic rates, which might be as slow as 1 mm a year. To get around this problem, scientists realized that they could ignore the code and instead track the wave on which it is encoded. These carrier waves have a wavelength of about 20 cm, and we can track the phase of these signals to an accuracy of about 2 mm as the satellites move along their orbits.

By measuring these phase data from lots of satellites over time we can obtain absolute positions with an accuracy of about 1 mm. There are now many thousands of GNSS instruments installed permanently at sites across the planet, and more sites whose positions are measured in regular campaigns.

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This has improved greatly since their first model Kreemer et al. However, there are large gaps in the coverage in many tectonic areas, particularly in developing countries that cannot afford the installation and maintenance costs of dense permanent GNSS networks. And even in Japan and California, which have the densest GNSS coverages on Earth, stations spaced between 10 and 50 km apart can be too far apart to distinguish between locked faults accumulating strain and those that creep steadily without building up strain.

A second satellite technology, interferometric synthetic aperture radar InSAR , can make observations of surface motions with millimetric precision, a spatial resolution of a few tens of metres, and without instruments on the ground. Satellite radars were launched as an imaging technology to provide images of the Earth.

Radar satellites provide an all-weather imaging tool, and with their own source of illumination they can acquire imagery at any time of day or night. We can also measure the phase of the waves that return. The difference between these two values is a function of the distance between the satellite and the ground. However, with wavelengths of 2—20 cm typical for radar systems in use today, the radar waves travel a distance equivalent to several tens of millions of wavelengths on their round-trip journey to the Earth's surface.

And we don't know the position of the satellite, and Earth's topography, well enough to know the nearest whole number of wavelengths along the radar beam's path: all we know is that the path length is equal to N whole wavelengths, where N is an unknown integer, plus some fraction of a wavelength, which we can measure very precisely from the phase of the wave.

Furthermore, the number of wavelengths, and hence the recorded phase, is also a function of the speed of propagation of the wave through the atmosphere and of any changes in phase that occur when the waves interact with the ground. Neither of these can be determined using independent data with sufficient precision to correct for their contributions to apparent changes in path length and phase. We solve these seemingly intractable problems using interferometry, comparing the relative phase differences measured in two radar images acquired from approximately the same position in space, at different times, and comparing the phase values between two different positions on the ground within this phase difference image called an interferogram.

After minor corrections for any changes in the satellite's position, and provided the ground surface hasn't changed significantly in the time between the two image acquisitions, the precise topography and the changes in phase that occur when the waves interact with the ground are nearly identical in the two images. These signals cancel out when forming the interferogram; also, any changes in overall path length do not matter. Changes in atmospheric conditions will cause phase variations, but they are relatively small and usually spatially smooth.

The interferograms show primarily a function of the change in distance between the satellite and the ground. InSAR was first used to measure the motion in earthquakes in the early s Massonnet et al. Many key observations of time-dependent deformation during the earthquake cycle have been made using InSAR Wright et al. The launch of ESA's Sentinel-1A satellite in April boosted the observational capacity — images are now being acquired every 12 days for most of the tectonic and volcanic areas of the planet Elliott The accuracy required of these geodetic techniques to be useful for seismic hazard assessment can be assessed in a number of ways. One is to compare geodetic strain rates, estimated from the global strain rate model, with a crude measure of the impact of earthquakes — the number of people who are killed because of earthquakes figure 4. Cumulative histogram comparing the 1.

Courtesy Matt Garthwaite, Geoscience Australia. These source models have some advantages over traditional models derived from seismology. Firstly, they provide very accurate location information, particularly if the earthquake is shallow; there are now several examples where InSAR results have led investigators in the field to an earthquake's surface rupture. Secondly, the source models do not suffer to the same degree from the ambiguity in fault plane orientiation inherent in many seismic methods Biggs et al.

Finally, the distribution of slip on the fault plane can be determined more reliably using geodetic observations than using seismic observations, particularly for shallow earthquakes with magnitudes in the range 6—8 e. Funning et al. The primary information from the coseismic phase relates to the seismogenic layer thickness.