MOEMS tuning element for a Littrow external cavity laser

A miniature grating-tunable external cavity laser diode constructed using microoptoelectromechanical systems (MOEMS) technology is described. The tuning element is a vertically etched blazed grating mounted on a compound flexure, which consists of a cantilever in series with a portal frame. The flexure is deflected using comb electrostatic drives to rotate and translate the grating. The tuning element is prototyped using deep reactive ion etching of bonded silicon-on-insulator (SOI) material. Interferometric measurements of electromechanical performance are presented, and departures from the ideal behavior are identified. Electrostatic tuning of a Littrow external cavity laser over a range of 20 nm using a 50-V drive is demonstrated.     

Synchronised carrier-based SVPWM signal generation scheme for the entire modulation range extending up to six-step mode using the sampled amplitudes of reference phase voltages

The issues in synchronised implementation of space vector-based pulse width modulation (SVPWM) signal generation are addressed on a conventional DSP platform. With the present day digital signal processors (DSPs) with clock over 10 MHz, it is possible to include additional tasks for synchronisation in the interrupt service routine (ISR). Also, the task of the synchronisation can be easily accommodated within the same ISR without disturbing the time critical pulse width modulation (PWM) operation. The authors systematically present the additional software requirements to determine the time period proportional to the half carrier switching time interval that is required for the synchronisation. First, the DSP implementation of the conventional multi-level SVPWM based on the sampled amplitudes of reference voltages is presented and then the additional requirements to maintain the PWM in synchronisation are discussed. The simulation results as well as experimental results are presented for a five-level PWM signal generation. A five-level inverter configuration, using a 1.5 kW open-end winding induction motor drive, is used for experimentally verifying the SVPWM     

The behavior of a cloud of emissions of high moisture content in the surface layer of the atmosphere

The propagation in the atmosphere of instantaneous emissions which largely consist of water vapor is treated in a three-dimensional formulation. The regularities are studied of the evolution of the hydrodynamic, concentration, and temperature fields depending on the parameters which define the state of the atmosphere (temperature and humidity), as well as on the temperature and moisture content of the cloud of emissions.     

Experimental and theoretical evidence for carbon-vacancy binding in austenite

Our research and results from the literature all consistently suggest a binding energy of nearest-neighbor carbon-vacancy (C-V) pairs of the order 35 to 40 kJ/mole in austenitic alloys. Results examined include point-defect anelasticity, self-diffusion, high-temperature creep, strain aging, strain-age hardening, radiation damage, and point-defect structure modeling. Increases in the height of carbon-based anelastic peaks by quenching, cold work, and electron irradiation are consistent with a substantial nonexclusive contribution of C-V complexes. Increased carbon content in austenite increases the iron self-diffusivity and the high-temperature creep rate of fcc Fe, implying a C-V binding energy of ∼40 kJ/mol. Dynamic strain aging of carbon-containing austenites occurs in temperature ranges too low to involve interstitial solute mobility and requires an interpretation of large C-V binding wherein the vacancy is the more mobile component. Strengthening in heavily deformed austenitic stainless steels associated with strain aging or long-term aging near room temperature implies solution hardening by tetragonal-like C-V complexes formed at these temperatures. Results on radiation damage of austenitic steels show effects of carbon on irradiation susceptibility. Finally, we have performed first-principles gradient-corrected density functional calculations to determine the binding energy of nearest-neighbor C-V pairs in fcc iron; a value of ∼35 kJ/mol is obtained. This article is based on a presentation in the symposium “Terence E. Mitchell Symposium on the Magic of Materials: Structures and Properties” from the TMS Annual Meeting in San Diego, CA in March 2003.     

The International Technology Alliance in Network and Information Sciences

In May 2006, the US Army Research Laboratory and UK Ministry of Defense created the international technology alliance. The consortium of 26 partners including the ARL and MoD offers an open research environment in which leading US and UK companies and universities can collaborate (see table 1). It will also fuse the best aspects of the US Army's Collaborative Technology Alliances and UK MoD's Defense Technology Centers on an international scale. The ITA aims to develop flexible, distributed, and secure decision-making procedures to improve networked coalition operations. Network science is a young discipline we have limited information models and network theories to describe the behavior and scaling of large, complex mobile ad hoc networks.1 moreover, you can't understand a coalition network's performance without understanding its cognitive and sociocultural aspects and physical characteristics. A key ITA goal is to perform basic research in network-centric coalition decision making across four technical areas: network theory, security across a system of systems, sensor information processing and delivery, and distributed coalition planning and decision making, 2. we focus on the last area because this is where intelligent systems will play the biggest role.     

A monotone multigrid solver for two body contact problems in biomechanics

The purpose of the paper is to apply monotone multigrid methods to static and dynamic biomechanical contact problems. In space, a finite element method involving a mortar discretization of the contact conditions is used. In time, a new contact-stabilized Newmark scheme is presented. Numerical experiments for a two body Hertzian contact problem and a biomechanical application are reported. This work was supported by the DFG Research Center Matheon.