General Electric

About: General Electric is a company organization based out in Boston, Massachusetts, United States. It is known for research contribution in the topics: Turbine & Signal. The organization has 76365 authors who have published 110557 publications receiving 1885108 citations. The organization is also known as: General Electric Company & GE.

Band Structure and Electron Transport of GaAs

Abstract: Existing experimental data on GaAs are reviewed and analyzed to yield the band structure in the vicinity of the band edges as well as the parameters characterizing the bands summarized in Fig. 1 of this paper. On the basis of presently existing experimental evidence, chiefly the behavior of the optical band gap in Ga(As, P) alloys and the deduced pressure shift and density of states effective mass, it is thought likely that the subsidiary conduction band minima lie along [100] directions. Analytical expressions including nonparabolic effects are given for the energy and density of states of the [000] conduction band and used to obtain a better value of the effective mass from optical reflectivity data. The experimentally observed structure in the Hall effect in $n$-type material at elevated temperatures is shown to result from excitation of carriers into the subsidiary conduction band. Changes of resistivity with pressure are explained on the basis of an increase of the [000] effective mass at low pressures and the transfer of carriers to the subsidiary minima at higher pressures. The scattering mechanisms, which are important in connection with transport phenomena, are shown to be polar lattice scattering and charged impurity scattering in the highest mobility samples. The transport calculations leading to the mobility and thermoelectric power as a function of temperature and impurity concentrations are performed using variational techniques, and shown to agree well with experiment. The apparently low mobility in the subsidiary minima is attributed at least in part to the large effective mass and relatively small anisotropy ratio. An estimate shows scattering between the two conduction bands probably to be unimportant.

Surface Reconstructions and Dimensional Changes in Single-Walled Carbon Nanotubes

Abstract: Dimensional stability is crucial to possible applications of single-walled nanotubes, as their properties are linked to size and topology. We observe nanotubes responding to uniform atom loss, through surface reconstruction and drastic dimensional changes. Experiments using electron irradiation evidence nanotube diameters shrinking from similar to 1.4 to 0.4 nm. Molecular dynamics simulations show that surface reconstruction and size reduction occur through dangling bond saturation, forming nonhexagonal rings and 5-7 defects in the lattice. Nonuniform atom removal results in inhomogeneous tube deformations and local necking, and formation of linear atomic carbon chains in the nanotube body.

System Level Concurrency Control for Distributed Database Systems

Abstract: A distributed database system is one in which the database is spread among several sites and application programs “move” from site to site to access and update the data they need. The concurrency control is that portion of the system that responds to the read and write requests of the application programs. Its job is to maintain the global consistency of the distributed database while ensuring that the termination of the application programs is not prevented by phenomena such as deadlock. We assume each individual site has its own local concurrency control which responds to requests at that site and can only communicate with concurrency controls at other sites when an application program moves from site to site, terminates, or aborts.This paper presents designs for several distributed concurrency controls and demonstrates that they work correctly. It also investigates some of the implications of global consistency of a distributed database and discusses phenomena that can prevent termination of application programs.