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A P W Makepeace - One of the best experts on this subject based on the ideXlab platform.

  • elastic deformation in a crystal plate where lattice parameter mismatch is present between adjacent growth Sectors ii measurement of lattice tilts by synchrotron x ray reticulography
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2002
    Co-Authors: R G C Arridge, Andrew Richard Lang, A P W Makepeace
    Abstract:

    Synchrotron X–ray reticulography measures lattice–plane orientation variations point by point on the crystal with microradian resolution capability. A fine–scale X–ray–absorbing mesh placed close to the crystal in the back–reflected diffracted beam of ‘white’ X–rays splits the beam into an array of microbeams whose direction differences are measured from the mesh–bar shadow shifts that result from controlled changes of the distance between the mesh and the recording high–resolution photographic plate. In the present work, lattice tilts were measured on either side of a growth–Sector Boundary outcropping at the surface of a single–crystal synthetic diamond cut and polished parallel to (110) in which the displacements and strains due to lattice–parameter mismatch at coherent growth–Sector boundaries have been analysed in part I. Attention was concentrated on a crystallographically well–defined planar segment of a Boundary separating two Sectors, each of uniform, but significantly differing, concentration of substitutional nitrogen impurity, and for which the anisotropic elasticity theory of part I provided quantitative relations between the lattice–parameter relative difference, Δa/ā, and the lattice tilts due to coherency strains at the Boundary. This enabled a novel method for determining Δa/ā to be realized, using reticulographic measurements of tilts of near–surface lattice planes alone. The paper explains the reticulographic technique fully. Factors affecting the quality and reliability of reticulographic records are examined in detail. For the growth Sectors concerned, the reticulographic measurement Δa/ā = (1.10 ± 0.10) × 10−5 is in accord with an earlier finding by synchrotron X–ray double–crystal diffractometry, slightly revised as recommended in part I, Δa/ā = (1.20 ± 0.07) × 10−5. The closeness of the findings by two quite different methods confirms the conclusion from X–ray topography that the growth–Sector Boundary was free from misfit dislocations compensating the lattice–parameter mismatch. On mismatch boundaries in crystals too highly absorbing for transmission X–ray topography, such comparisons of reticulographic and diffractometric measurements would reveal information otherwise inaccessible by non–destructive methods.

  • elastic deformation in a crystal plate where lattice parameter mismatch is present between adjacent growth Sectors i anisotropic elasticity theory with application to lattice parameter measurements
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2002
    Co-Authors: R G C Arridge, Andrew Richard Lang, A P W Makepeace
    Abstract:

    A method is described for analysing strain in a plate–shaped crystal divided into growth Sectors differing in lattice parameter and joined together at coherent dislocation–free Sector boundaries running between the surfaces of the plate. The specimen studied was a large synthetic diamond, grown by the high–pressure hightemperature method, from which a near–central slice had been cut and polished parallel to (110). It contained dilatation–producing atomically dispersed substitutional nitrogen impurity, with adjacent growth Sectors alternating in nitrogen concentration. In order that stress functions could be used to approximate the exact solution of the three–dimensional problem, the configuration of crystal growth Sectors was modelled by an assembly of elongated rectangular parallelepipeds of alternating lattice parameter. Such a model is considered to be a good representation of the Sector configuration of special interest in the real crystal. Using this model, the strains induced by lattice–parameter mismatch were calculated by adapting the classical theory of initial stresses due to Timoshenko and Goodier. In the present application, this involved four stages of imaginary operations: disassembly of the crystal model into stress–free Sectors, deforming them by uniform lattice–matching strains, in planes parallel to the Sector boundaries, ‘welding’ them together, and restoration of the initial conditions by application of ‘annulling’ stresses to cancel those applied in the deformations. Because uniform strains were applied in the matching procedure, only forces on the free surfaces of the crystal were required in this final stage, and it is argued that these should be applied in plane strain in planes orthogonal both to the Sector boundaries and to the crystal–plate surface. Stress functions for orthorhombic symmetry are derived from first principles and applied to the geometry of the present problem, namely that of a cubic crystal under plane strain in which the cubic axes are rotated by 45 ° about the axis determined by the Sector–Boundary normal, [001]. Displacements and strains have been calculated at all points within the Sector cross–section of interest, and extended to include wide variations in ratios between Sector widths, and between Sector width and plate thickness; the physical reasons for the resultant changes in strain distributions are discussed. Convergence of the Fourier–series solution under this variation of parameters is examined in detail. Representative deformation profiles of (110) planes in the real crystal are exhibited. The calculation has enabled a close limit to be placed on systematic error due to coherency strains in the findings of earlier X–ray–diffractometric experiments on the specimen discussed in the present study. Those experiments compared the symmetrical 440 surface Bragg reflection from a large (11 bar 1) growth Sector fairly rich in substitutional nitrogen impurity with that from an adjacent, smaller, (11 bar 0) Sector, virtually nitrogen free. The measurements aimed to establish the proportionality factor between substitutional nitrogen concentration and dilatation. The present analysis supports the earlier X–ray diffractometry: it changes the finding for Δa 0 /ā 0 quite insignificantly from (1.18 ±) × 10 −5 to (1.20 ± 0.07) × 10 −5 . On the other hand, revision of the nitrogen–concentration difference between the two growth Sectors concerned, resulting from a more recent conversion factor between infrared absorption and nitrogen content (independent of the present study), raises that difference from ca .88 to ca .100 ppm atomic. Combining this large change with the small change in Δa 0 /ā 0 reduces the earlier finding for the ratio of the effective volume of a single substitutional nitrogen atom to the volume of the carbon atom it replaces from 1.41 ± 0.06 to 1.36 ± 0.1.

R G C Arridge - One of the best experts on this subject based on the ideXlab platform.

  • elastic deformation in a crystal plate where lattice parameter mismatch is present between adjacent growth Sectors ii measurement of lattice tilts by synchrotron x ray reticulography
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2002
    Co-Authors: R G C Arridge, Andrew Richard Lang, A P W Makepeace
    Abstract:

    Synchrotron X–ray reticulography measures lattice–plane orientation variations point by point on the crystal with microradian resolution capability. A fine–scale X–ray–absorbing mesh placed close to the crystal in the back–reflected diffracted beam of ‘white’ X–rays splits the beam into an array of microbeams whose direction differences are measured from the mesh–bar shadow shifts that result from controlled changes of the distance between the mesh and the recording high–resolution photographic plate. In the present work, lattice tilts were measured on either side of a growth–Sector Boundary outcropping at the surface of a single–crystal synthetic diamond cut and polished parallel to (110) in which the displacements and strains due to lattice–parameter mismatch at coherent growth–Sector boundaries have been analysed in part I. Attention was concentrated on a crystallographically well–defined planar segment of a Boundary separating two Sectors, each of uniform, but significantly differing, concentration of substitutional nitrogen impurity, and for which the anisotropic elasticity theory of part I provided quantitative relations between the lattice–parameter relative difference, Δa/ā, and the lattice tilts due to coherency strains at the Boundary. This enabled a novel method for determining Δa/ā to be realized, using reticulographic measurements of tilts of near–surface lattice planes alone. The paper explains the reticulographic technique fully. Factors affecting the quality and reliability of reticulographic records are examined in detail. For the growth Sectors concerned, the reticulographic measurement Δa/ā = (1.10 ± 0.10) × 10−5 is in accord with an earlier finding by synchrotron X–ray double–crystal diffractometry, slightly revised as recommended in part I, Δa/ā = (1.20 ± 0.07) × 10−5. The closeness of the findings by two quite different methods confirms the conclusion from X–ray topography that the growth–Sector Boundary was free from misfit dislocations compensating the lattice–parameter mismatch. On mismatch boundaries in crystals too highly absorbing for transmission X–ray topography, such comparisons of reticulographic and diffractometric measurements would reveal information otherwise inaccessible by non–destructive methods.

  • elastic deformation in a crystal plate where lattice parameter mismatch is present between adjacent growth Sectors i anisotropic elasticity theory with application to lattice parameter measurements
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2002
    Co-Authors: R G C Arridge, Andrew Richard Lang, A P W Makepeace
    Abstract:

    A method is described for analysing strain in a plate–shaped crystal divided into growth Sectors differing in lattice parameter and joined together at coherent dislocation–free Sector boundaries running between the surfaces of the plate. The specimen studied was a large synthetic diamond, grown by the high–pressure hightemperature method, from which a near–central slice had been cut and polished parallel to (110). It contained dilatation–producing atomically dispersed substitutional nitrogen impurity, with adjacent growth Sectors alternating in nitrogen concentration. In order that stress functions could be used to approximate the exact solution of the three–dimensional problem, the configuration of crystal growth Sectors was modelled by an assembly of elongated rectangular parallelepipeds of alternating lattice parameter. Such a model is considered to be a good representation of the Sector configuration of special interest in the real crystal. Using this model, the strains induced by lattice–parameter mismatch were calculated by adapting the classical theory of initial stresses due to Timoshenko and Goodier. In the present application, this involved four stages of imaginary operations: disassembly of the crystal model into stress–free Sectors, deforming them by uniform lattice–matching strains, in planes parallel to the Sector boundaries, ‘welding’ them together, and restoration of the initial conditions by application of ‘annulling’ stresses to cancel those applied in the deformations. Because uniform strains were applied in the matching procedure, only forces on the free surfaces of the crystal were required in this final stage, and it is argued that these should be applied in plane strain in planes orthogonal both to the Sector boundaries and to the crystal–plate surface. Stress functions for orthorhombic symmetry are derived from first principles and applied to the geometry of the present problem, namely that of a cubic crystal under plane strain in which the cubic axes are rotated by 45 ° about the axis determined by the Sector–Boundary normal, [001]. Displacements and strains have been calculated at all points within the Sector cross–section of interest, and extended to include wide variations in ratios between Sector widths, and between Sector width and plate thickness; the physical reasons for the resultant changes in strain distributions are discussed. Convergence of the Fourier–series solution under this variation of parameters is examined in detail. Representative deformation profiles of (110) planes in the real crystal are exhibited. The calculation has enabled a close limit to be placed on systematic error due to coherency strains in the findings of earlier X–ray–diffractometric experiments on the specimen discussed in the present study. Those experiments compared the symmetrical 440 surface Bragg reflection from a large (11 bar 1) growth Sector fairly rich in substitutional nitrogen impurity with that from an adjacent, smaller, (11 bar 0) Sector, virtually nitrogen free. The measurements aimed to establish the proportionality factor between substitutional nitrogen concentration and dilatation. The present analysis supports the earlier X–ray diffractometry: it changes the finding for Δa 0 /ā 0 quite insignificantly from (1.18 ±) × 10 −5 to (1.20 ± 0.07) × 10 −5 . On the other hand, revision of the nitrogen–concentration difference between the two growth Sectors concerned, resulting from a more recent conversion factor between infrared absorption and nitrogen content (independent of the present study), raises that difference from ca .88 to ca .100 ppm atomic. Combining this large change with the small change in Δa 0 /ā 0 reduces the earlier finding for the ratio of the effective volume of a single substitutional nitrogen atom to the volume of the carbon atom it replaces from 1.41 ± 0.06 to 1.36 ± 0.1.

Sd Bale - One of the best experts on this subject based on the ideXlab platform.

  • the heliospheric current sheet and plasma sheet during parker solar probe s first orbit
    The Astrophysical Journal, 2020
    Co-Authors: B Lavraud, A Szabo, Ap Rouillard, Td Phan, Jc Kasper, N Fargette, V Reville, Jia Huang, Nicholeen M Viall, Sd Bale
    Abstract:

    We present Heliospheric Current Sheet (HCS) and Plasma Sheet (HPS) observations during Parker Solar Probe's (PSP) first orbit around the Sun. We focus on the eight intervals that display a true Sector Boundary (TSB; based on suprathermal electron pitch angle distributions) with one or several associated current sheets. The analysis shows that (1) the main density enhancements in the vicinity of the TSB and HCS are typically associated with electron strahl dropouts, implying magnetic disconnection from the Sun, (2) the density enhancements are just about twice that in the surrounding regions, suggesting mixing of plasmas from each side of the HCS, (3) the velocity changes at the main boundaries are either correlated or anticorrelated with magnetic field changes, consistent with magnetic reconnection, (4) there often exists a layer of disconnected magnetic field just outside the high-density regions, in agreement with a reconnected topology, (5) while a few cases consist of short-lived density and velocity changes, compatible with short-duration reconnection exhausts, most events are much longer and show the presence of flux ropes interleaved with higher-β regions. These findings are consistent with the transient release of density blobs and flux ropes through sequential magnetic reconnection at the tip of the helmet streamer. The data also demonstrate that, at least during PSP's first orbit, the only structure that may be defined as the HPS is the density structure that results from magnetic reconnection, and its by-products, likely released near the tip of the helmet streamer.

  • The heliospheric current sheet and plasma sheet during Parker Solar Probe’s first orbit
    'American Astronomical Society', 2020
    Co-Authors: Lavraud B, Fargette N, Szabo A, Huang J, Ap Rouillard, Viall N, Td Phan, Jc Kasper, Sd Bale
    Abstract:

    We present heliospheric current sheet (HCS) and plasma sheet (HPS) observations during Parker Solar Probe's (PSP) first orbit around the Sun. We focus on the eight intervals that display a true Sector Boundary (TSB; based on suprathermal electron pitch angle distributions) with one or several associated current sheets. The analysis shows that (1) the main density enhancements in the vicinity of the TSB and HCS are typically associated with electron strahl dropouts, implying magnetic disconnection from the Sun, (2) the density enhancements are just about twice that in the surrounding regions, suggesting mixing of plasmas from each side of the HCS, (3) the velocity changes at the main boundaries are either correlated or anticorrelated with magnetic field changes, consistent with magnetic reconnection, (4) there often exists a layer of disconnected magnetic field just outside the high-density regions, in agreement with a reconnected topology, (5) while a few cases consist of short-lived density and velocity changes, compatible with short-duration reconnection exhausts, most events are much longer and show the presence of flux ropes interleaved with higher-β regions. These findings are consistent with the transient release of density blobs and flux ropes through sequential magnetic reconnection at the tip of the helmet streamer. The data also demonstrate that, at least during PSP's first orbit, the only structure that may be defined as the HPS is the density structure that results from magnetic reconnection, and its byproducts, likely released near the tip of the helmet streamer

E. K. J. Kilpua - One of the best experts on this subject based on the ideXlab platform.

  • multispacecraft observations of magnetic clouds and their solar origins between 19 and 23 may 2007
    Solar Physics, 2009
    Co-Authors: B J Lynch, E. K. J. Kilpua, P C Liewer, C J Farrugia, J G Luhmann, Christian Mostl, Ying Liu, C T Russell
    Abstract:

    We analyze a series of complex interplanetary events and their solar origins that occurred between 19 and 23 May 2007 using observations by the STEREO and Wind satellites. The analyses demonstrate the new opportunities offered by the STEREO multispacecraft configuration for diagnosing the structure of in situ events and relating them to their solar sources. The investigated period was characterized by two high-speed solar wind streams and magnetic clouds observed in the vicinity of the Sector Boundary. The observing satellites were separated by a longitudinal distance comparable to the typical radial extent of magnetic clouds at 1 AU (fraction of an AU), and, indeed, clear differences were evident in the records from these spacecraft. Two partial-halo coronal mass ejections (CMEs) were launched from the same active region less than a day apart, the first on 19 May and the second on 20 May 2007. The clear signatures of the magnetic cloud associated with the first CME were observed by STEREO B and Wind while only STEREO A recorded clear signatures of the magnetic cloud associated with the latter CME. Both magnetic clouds appeared to have interacted strongly with the ambient solar wind and the data showed evidence that they were a part of the coronal streamer belt. Wind and STEREO B also recorded a shocklike disturbance propagating inside a magnetic cloud that compressed the field and plasma at the cloud’s trailing portion. The results illustrate how distant multisatellite observations can reveal the complex structure of the extension of the coronal streamer into interplanetary space even during the solar activity minimum.

Tielong Shen - One of the best experts on this subject based on the ideXlab platform.