Operation of an electron-bombardment ion source using various gases

An electron-bombardment ion thruster of the SERT 2 type was operated with xenon, krypton, argon, neon, nitrogen, helium, and carbon dioxide. The discharge performance with xenon, krypton, and argon was similar to that obtained previously with mercury. Mass spectrometer data indicated that the xenon contained no significant multiple ionization. Restriction of the beam area, with an associated decrease in discharge potential, was necessary to reduce multiple ionization with argon to a negligible level. This modification also resulted in more stable operation of the thruster. Performance with the remaining gases was poor because the basic thruster designed was optimized for operation with mercury

Improved high voltage insulator for use in vacuum

High voltage insulator for electron bombardment ion thruster has electric field directed through dielectric material and electrons emitted by field emission are constrained in negative junction region. Surface flashover and unstable operation are eliminated, and maximum voltage is limited only by dielectric strength of material, aluminum oxide in this case

Theory of a Scanning Tunneling Microscope with a Two-Protrusion Tip

We consider a scanning tunneling microscope (STM) such that tunneling occurs through two atomically sharp protrusions on its tip. When the two protrusions are separated by at least several atomic spacings, the differential conductance of this STM depends on the electronic transport in the sample between the protrusions. Furthermore two-protrusion tips commonly occur during STM tip preparation. We explore possible applications to probing dynamical impurity potentials on a metallic surface and local transport in an anisotropic superconductor.Comment: revtex, 11 pages, 6 figures upon reques

HAMEV and SQRED: Fortran 77 Subroutines for Computing the Eigenvalues of Hamiltonian Matrices Using Van Loanss Square Reduced Method

This paper describes LAPACK-based Fortran 77 subroutines for the reduction of a Hamiltonian matrix to square-reduced form and the approximation of all its eigenvalues using the implicit version of Van Loan's method. The transformation of the Hamilto- nian matrix to a square-reduced Hamiltonian uses only orthogonal symplectic similarity transformations. The eigenvalues can then be determined by applying the Hessenberg QR iteration to a matrix of half the order of the Hamiltonian matrix and taking the square roots of the computed values. Using scaling strategies similar to those suggested for algebraic Riccati equations can in some cases improve the accuracy of the computed eigenvalues. We demonstrate the performance of the subroutines for several examples and show how they can be used to solve some control-theoretic problems

System Reliability: Exact Bayesian Intervals Compared With Fiducial Intervals

This paper compares numerically two different, widely used lower limit estimates for the reliability of a series system: Bayesian limits and fiducial limits. The fiducial limits are obtained by Monte Carlo simulation because of its simplicity and ease of computer programming. Subsystem failures are s-independent and exponentially distributed; life test data are available for estimating the failure rate of each system. Copyright © 1975 by The Institute of Electrical and Electronics Engineers, Inc

Multi-partnership mangrove rehabilitation of Dasol Bay strategies and results

The coastal waters and shoreline of Luzon Province, the Philippines, have not been spared the loss of large tracks of mangrove forest. A multi-partnership coastal resource management project was implemented in 2005 to mitigate further degradation of the ecosystem through rehabilitation of mangrove forests in the Dasol Bay area of Pangasinan in northern Luzon. This paper presents a snapshot of results from this continuing effort and expectations for future initiatives in the area. The work is supported by Tanggol Kalikasan (Defense of Nature), with special support from the mayor’s office of the Dasol local government unit (LGU) including the Dasol municipal agriculture office, and Washington State University’s Office of International Research and Development. The authors built on a coastal resources database generated from a project-supported rapid resource assessment of Dasol Bay. Educating stakeholders about mangrove rehabilitation has been found to have an early and encouraging impact. Institutionalization through use of a structure that involves the community, an NGO, a university and individuals has helped partners meet goals. Results point to early successes from increasing environmental awareness and encouraging local participation that subsequently (1) allows effective constituency-building; (2) eases the integration of technical experts into decision-making processes; (3) provides a mechanism to channel innovative ideas and technologies; and (4) promotes learning by seeing and doing. This paper describes how the design and implementation of the Dasol Bay project promotes adaptive resource management, improves opportunities for effective governance and generates greater public support for rehabilitation of the mangrove forest. The project’s participatory community-based approach engages stakeholders in direct project implementation and leads to continuously increasing involvement by members of the community. Environmental awareness and local participation are hallmarks of this effort. Insights are provided into the future of the Multi-partnership Mangrove Rehabilitation of Dasol Bay Project (Dasol 1) and its sister project, Upland and Rural-Urban Ecosystem Management for Dasol Bay Project (Dasol 2), begun in 2006

Who Contributes to the Knowledge Sharing Economy?

Information sharing dynamics of social networks rely on a small set of influencers to effectively reach a large audience. Our recent results and observations demonstrate that the shape and identity of this elite, especially those contributing \emph{original} content, is difficult to predict. Information acquisition is often cited as an example of a public good. However, this emerging and powerful theory has yet to provably offer qualitative insights on how specialization of users into active and passive participants occurs. This paper bridges, for the first time, the theory of public goods and the analysis of diffusion in social media. We introduce a non-linear model of \emph{perishable} public goods, leveraging new observations about sharing of media sources. The primary contribution of this work is to show that \emph{shelf time}, which characterizes the rate at which content get renewed, is a critical factor in audience participation. Our model proves a fundamental \emph{dichotomy} in information diffusion: While short-lived content has simple and predictable diffusion, long-lived content has complex specialization. This occurs even when all information seekers are \emph{ex ante} identical and could be a contributing factor to the difficulty of predicting social network participation and evolution.Comment: 15 pages in ACM Conference on Online Social Networks 201

Polarons and Solitons in Jahn-Teller Systems

Using a semiclassical continuum model of an electron in a deformable molecular crystal, some properties of multicomponent generalizations of the polaron--``vector polarons''-- are elucidated. Analytical solutions for the case of two electronic bands coupled to two vibrational modes are given in detail. Within the model considered, the vector polaron can be classified by its wavefunction into several types and can have features that include: (1) a spatial variation in the electronic and vibrational character, and (2) low-energy internal degrees of freedom. For the case of electronic and vibrational degeneracy, local Jahn-Teller interactions can also lead to a novel spatiotemporal soliton, a long-lived excited state of the many-electron system stabilized by the conservation law resulting from degeneracy.Comment: 10 pages, 0 figures. International Symposium on Jahn-Teller Effects, ICTP, Trieste, Ital