Primary defects induced by 1 MeV electron irradiation have been quantitatively studied in semi-insulating ͑SI͒ GaAs by using normalized thermally stimulated current spectroscopy, a new technique. Defects identical to ͑or similar to͒ those known in the thermally stimulated current literature as T 6 *(0.13 eV), T 5 ͑0.34 eV͒, and T 4 ͑0.31 eV͒ are produced at rates 0.70, 0.08, and 0.23 cm Ϫ1 , respectively; T 5 is also a strong trap in unirradiated SI GaAs. The defects T 6 * and T 4 correspond closely to the irradiation-induced traps E2͑0.14 eV͒ and E3͑0.30 eV͒, studied extensively by deep-level transient spectroscopy and Hall-effect measurements and assigned to the As vacancy. We thus infer that traps T 6 * and T 4 ͑and probably also T 5 ͒ in SI GaAs have As-vacancy character. ͓S0163-1829͑97͒04503-7͔
We present a brief review of the subject of confined atoms, in which we emphasise the origins of the subject and its most recent applications. Emphasis is placed on the wide variety of situations to which the idealised quantum mechanical treatment is relevant. Both the nonrelativistic and relativistic methods are contrasted; an example of confinement in the Dirac‐Fock scheme is given and some special problems connected with relativistic confinement are mentioned. Finally, we present a discussion of the quantum pressure, and a novel, dimensionless choice of variables which allows universal atomic behaviour for confined atoms to be visualised.
We consider the concept of atomic pressure for atoms subjected to quantum
confinement. New scaling rules are introduced which allow the compressibility to
be expressed as the product of two factors. The first is a term independent of
compression, which varies widely from atom to atom, but can be computed in the
free atom limit. The second is a term expressed in dimensionless variables,
whose dependence on compression is in general nonlinear and may exhibit
discontinuities. However, it is shown not to vary much from one atom to
another and to follow general rules which are easily understood. We have
performed fully relativistic ab initio calculations to illustrate
these general rules of atomic compressibility, and we characterize the variation
of atomic compressibility for both soft and hard atoms.
The magnet lattice for the Siam Photon Source, the ®rst storage ring for synchrotron radiation research in Thailand, has been designed. The storage ring has a double-bend achromat lattice and fourfold symmetry with four straight sections. Although the magnet lattice is relaxed, an emittance value of 72 % nm rad has been obtained, which is only 1.4 times as large as the theoretical minimum emittance with eight bending magnets. The dynamic aperture is found to be much larger than the physical aperture.
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