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J C Spence

Publications and source records attributed to J C Spence.

5 recordsLinked to original sources
PubMed1989

FORTRAN source listing for simulating three-dimensional convergent beam patterns with absorption by the Bloch wave method.

The FORTRAN source code is given for a computer program that calculates the two-dimensional intensity distribution in convergent-beam transmission electron microdiffraction (CBED) patterns from perfect crystals. The program uses the eigenvalue or Bloch-wave method. It allows three-dimensional dynamical diffraction, and so includes all higher-order Laue zone effects without approximation. No symmetry reduction is included. The program accepts noncentrosymmetric or centrosymmetric crystal structures and allows absorption corrections to be included. It uses the "EISPACK" subroutines for the diagonalisation of a general complex matrix. Up to 100 CBED disks may be included. The code is also available via "Bitnet."

Electron Probe Microanalysis↗
PubMed1988

Structural characterization of Ba2YCu3O7 by high resolution transmission electron microscopy.

We show that high-resolution transmission electron microscopy can be used directly to reveal the structure of the metal framework and its defects in Ba2YCu3O7. The use of dynamical effects under carefully selected and controlled conditions allows the detection of long-range order in the disposition of the oxygen vacancies, but inevitable misalignments make the quantification of the order parameter difficult. Specimen preparation methods are compared, and a wide-angle convergent-beam pattern is demonstrated.

Barium↗
PubMed1979

Vitiligo patterns simulating autoimmune and rheumatic diseases.

Several variants of generalised vitiligo can be recognised by their cutaneous distribution. In some, certain anatomical regions--e.g., hands--are predominantly affected while the cutaneous depigmentation in other variants shows a similar anatomical distribution to that of the internal structures affected in some of the autoimmune and rheumatic diseases. Five patients have been seen, and three described by others, with vitiligo affecting skin of eyelids and lower front of neck, reminiscent of the anatomical distribution of lesions in thyrotoxicosis with exophthalmos: two of these patients have thyrotoxicosis. Another variant of vitiligo mimicks the anatomical distribution of lesions in ankylosing spondylitis, Reiter's syndrome, and ulcerative colitis and there are cases simulating lupus erythematosus, rheumatoid arthritis, and psoriasis. It is suggested that the parts of the body affected in each vitiligo variant and its corresponding internal disease constitute a set os mosiac patches with distinctive shared characters. These may have morphogenetic functions during embryonic development and be potentially autoantigenic later in life.

Adolescent↗