Producing persistent, high-current, high-duty-factor H- beams for routine 1 MW operation of Spallation Neutron Source (invited)

Since 2009, the Spallation Neutron Source (SNS) has been producing neutrons with ion beam powers near 1 MW, which requires the extraction of ～50 mA H(-) ions from the ion source with a ～5% duty factor. The 50 mA are achieved after an initial dose of ～3 mg of Cs and heating the Cs collar to ～170 °C. The 50 mA normally persist for the entire 4-week source service cycles. Fundamental processes are reviewed to elucidate the persistence of the SNS H(-) beams without a steady feed of Cs and why the Cs collar temperature may have to be kept near 170 °C.     

Substrate temperature and water vapour effects on structural and mechanical properties of TiO x N y coatings

Dc reactive sputtering was successfully implemented to deposit titanium oxynitride thin films using a titanium metallic target, argon, nitrogen and water vapour as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas that of the water vapour was systematically changed from 0 to 0.1 Pa. The study aims at comparing the structural and mechanical properties of the coatings deposited at room temperature (293 K) and at 673 K. Surface morphology of the film was examined by atomic force microscopy and showed different aspects according to the growth temperature. Topography mainly depends on the amount of water vapour introduced during the deposition process. Some significant changes of the crystallographic structure, due to the high substrate temperature were correlated with the evolution of the surface aspect and roughness parameters. Determination of the phase occurrence by X-ray diffraction was also carried out and appeared to be a significant parameter in understanding the evolution of mechanical properties like nanohardness (H _n) and Young’s modulus (E). H _n and E values obtained by nanoindentation ranged from 16.5 to 7 GPa and from 240 to 100 GPa, respectively. For both temperatures, mechanical properties of titanium oxynitride thin films were notably reduced as a function of the water vapour supply, especially for partial pressures higher than 4 × 10⁻² Pa. These mechanical behaviours were correlated and discussed with the phase occurrence and the amorphous structure of titanium oxynitride thin films.     

Obtaining mode mixity for a bimaterial interface crack using the virtual crack closure technique

We review, unify and extend work pertaining to evaluating mode mixity of interfacial fracture utilizing the virtual crack closure technique (VCCT). From the VCCT, components of the strain energy release rate (SERR) are obtained using the forces and displacements near the crack tip corresponding to the opening and sliding contributions. Unfortunately, these components depend on the crack extension size, Δ, used in the VCCT. It follows that a mode mixity based upon these components also will depend on the crack extension size. However, the components of the strain energy release rate can be used for determining the complex stress intensity factors (SIFs) and the associated mode mixity. In this study, we show that several—seemingly different—suggested methods presented in the literature used to obtain mode mixity based on the stress intensity factors are indeed identical. We also present an alternative, simpler quadratic equation to this end. Moreover, a Δ-independent strain energy release based mode mixity can be defined by introducing a “normalizing length parameter.” We show that when the reference length (used for the SIF-based mode mixity) and the normalizing length (used for Δ-independent SERR-based mode mixity) are equal, the two mode mixities are only shifted by a phase angle, depending on the bimaterial parameter ε.     

Ultrasonic measurements of microelectronic resins

The elastic moduli, measured with the ultrasonic technique, of commercial silica filled epoxy resins used in the electronic circuits are reported. Measurements of velocity propagation and attenuation were carried out in large temperature and frequency ranges. Predictions of the theoretical models were compared with the experimental values. Explicit expressions of the elastic moduli were derived as functions of filler content and the properties of the matrix and the fillers. The influences of frequency and temperature on the elastic moduli and attenuation are discussed.     

Three generations of asynchronous microprocessors

We trace the evolution of Caltech asynchronous processors from a simple proof of concept, to a high-performance MIPS-like processor using a different buffer circuit for better performance, to the latest 8051 clone targeting low-energy operation. We describe the control aspects of the evolving circuit styles. We describe these three generations of asynchronous microprocessors (Caltech asynchronous processors, MiniMIPS and Lutonium) and the corresponding circuit families and design methods. The asynchronous circuits we use are called quasidelay-insensitive (QDI) circuits. A QDI circuit involves no assumption about, or knowledge of, delays in operators and wires, except for isochronic forks, which the designer assumes have similar delays on the different branches. QDI circuits are the most conservative asynchronous circuits in terms of delays.     

Total Travel Cost in Stochastic Assignment Models

Deterministic assignment models are sometimes used to approximate properties of more complex stochastic models. One property that is of particular interest from a system optimization viewpoint is total travel cost. This paper looks at the approximation of mean total travel cost. It is shown that deterministic models will underestimate this quantity in many common situations. Furthermore, discrepancies between total travel cost under the different modelling frameworks can lead to situations in which network modifications which are detrimental according to a stochastic model appear beneficial when using the natural deterministic approximation. We conclude that estimation of mean travel cost in stochastic assignment is often best done using simulation. Some suggestions are made regarding the implementation of traffic assignment simulation.     

Mobile phones as computing devices: the viruses are coming!

Understanding existing threats against mobile phones helps us better protect our information and prepare for future dangers. Mobile phones have evolved from their roots as analog walkie-talkies to full-scale Internet-enabled computers. Today, mobile phone handsets are arguably the dominant computer form factor consumers purchase. But having such powerful networked computers leads to a new class of malware: viruses, worms, and trojans specifically designed for the mobile environment. Merely enumerating known attacks doesn't help us understand all possible threats. Instead, we present a taxonomy of attacks against mobile phones that shows known as well as potential attacks.     

Overt Anger in Response to Victimization: Attributional Style and Organizational Norms as Moderators.

Prior theory and research suggests a positive relation between perceived victimization and overt anger. The authors proposed and tested a theoretical extension of this link by investigating possible moderating effects of individual and contextual variables. A sample of 158 employees of a municipality was used to test hypotheses that the relationship between perceived victimization and overt anger is moderated by hostile attributional style and perceptions of organizational norms. The results showed that the relation between perceptions of direct victimization and overt anger was stronger when the employee had a more rather than less hostile attributional style and when the employee perceived the organizational norms as more rather than less oppositional. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microscopy under pressure--an optical chamber system for fluorescence microscopic analysis of living cells under high hydrostatic pressure

High hydrostatic pressure (HHP) becomes more and more interesting for life science research, since it can be employed to inactivate various cells. To directly monitor "cells under pressure," the development of an optical high-pressure chamber is required. Therefore, an optical pressure chamber that can be used for up to 300 MPa was constructed. This chamber has already been described as a tool for in situ observation of dynamic changes of microscopic structures in bright field as well as phase contrast. In combination with an inverted microscope, we obtained brilliant microscopic color pictures with an optical resolution more than 0.56 microm. Here, we demonstrate the capabilities of the HHP cell, in combination with epifluorescence microscopy. Using a nonadherent human B-cell line (Raji, ATCC CCL 86), stained with the fluorescent dyes propidium iodide, Hoechst 33342, or dihexyloxacarbocyanine iodide, we were able to show that the system is suitable to perform fluorescence microscopic analyses, with pressures up to 300 MPa, with viable mammalian cells.     

Synthesis and applications of new left handed microstrip lines with complementary split-ring resonators etched on the signal strip

A new type of left handed microstrip lines implemented by means of complementary split-ring resonators (CSRRs) is proposed. The CSRRs are etched on the signal strip alternating with series gaps. Additionally, shunt connected stubs are introduced for the first time to the previous structure. The combination of these three elements, that is, the series gaps, the CSRR and the shunt inductance, enhances design flexibility. By this means, the ground plane is left unaltered and narrow band artificial transmission lines with good performance and compact dimensions can be synthesised. The lumped element equivalent circuit model of the structure is proposed and validated. To demonstrate the applicability of these new left handed transmission lines, two compact microwave components have been designed and fabricated: (i) a narrow band power divider and (ii) a band pass filter. The resulting power divider is 75% smaller than the conventional implementation and 50% smaller than previous power dividers implemented by means of CSRRs. The band pass filter performance is comparable to that of previous CSRR-based filters with ground plane etching, whereas its size is smaller. This work represents a significant progress on the design of microwave components based on CSRRs, that is, the approach is opened to those systems where the ground plane cannot be etched.