Showing papers by "George Davey Smith published in 1976"

The Absorption Spectrum of Europium

Abstract: The europium absorption spectrum has been photographed at high resolution in the spectral region 7200-2100 A which includes the entire sharp-line spectrum longward q£ the first ionization limit. Wavelengths and wavenumbers have been determined by comparison with thorium standards. Since all transitions take place from the ground level the wavenumbers correspond to excitation energies of even-parity levels with total angular momentum ( J)of f , or f . /-values and gj-values have been determined for many of these levels from a study of the longitudinal Zeeman effect in the 5 T (50 kG) field of a superconducting solenoid magnet. The configurations 4f7 (8S) 6s 6p, 4f7 (8g) 6s 7p, 4f7 (8S) 5d 6p and 4f6 (7F) 5d 6s2 are discussed in detail. Levels of 4f6 5d2 6s and 4f7 (6I) 6s 6p are reported for the first time. Several long series and parts of series have been discovered among the highly excited levels. Some of these can be identified with levels arising from 4f7 6s (9S) np and 4f7 6s (7S) np but interpretation is complicated by the presence of several perturbations of unknown origin.

Enhancement of a tumor allograft in BALB/c x DBA/2 F1 mice by pyran copolymer.

Abstract: Pyran copolymer (NSC 46015) was evaluated with respect to its effect on the rejection of a murine leukemic allograft by BALB/c x DBA/2 F1 (CD2F1) mice. Significant prolongation of allograft survival with production of progressively growing lethal tumors was found following pyran administration. This phenomenon occurred at nontoxic doses of the drug and appeared to be closely related to the timing of pyran injection. Nonspecifically stimulated lymphocyte blast transformation by concanavalin A was not impaired by pyran when lymphocytes were exposed in vitro to the drug. The mechanism of tumor allograft enhancement remains obscure but may be related to allograft size at the time of pyran administration.

A helium gas flow cryostat and specimen airlock assembly for ultrahigh vacuum use (in field ion microscope)

Abstract: An ultrahigh vacuum field-ion microscope has been modified to incorporate both a continuous flow cryostat and a specimen airlock. The design is simple in construction and operation, robust, and needs only the minimum of facilities for its manufacture. Following the specimen change it is possible to image a specimen at a background pressure of better than 1 n Torr within 30 min. The economical operating temperature range is down to 12K with a stability better than +or-0.1K h-1. The design can be adapted, without difficulty, for a wide variety of ultrahigh vacuum applications.

Interaction of oxygen with nickel studied by field emission microscopy

Abstract: The reaction of oxygen with atomically clean nickel surfaces was studied by field emission microscopy at temperatures from 78 to 500 K, and oxygen pressures from 10–10 to 1.0 Torr. Epitaxial nickel single crystal specimens were prepared by vapour deposition onto tungsten field emitter substrates held at 550–700 K in ultra high vacuum (UHV) conditions. On exposure to oxygen, a series of reaction processes was observed prior to the nucleation of oxide. Two stages of intermediate reaction were identified subsequent to chemisorption. The first stage, which occurs homogeneously over certain regions of the surface, appears to involve the introduction of oxygen into the plane of the surface. The second stage is apparently a cooperative process, and involves the migration of oxygen to sub-surface sites. Oxide nucleation is believed to take place after the second stage of reaction, and therefore occurs within a relatively disordered surface layer.