A novel feedback control system – Controlling the material flow in deep drawing using distributed blank-holder force

The performance of a feedback control system is often limited by the quality of the model on which it is based, and often the controller design is based on trial and error due to insufficient modeling capabilities. A framework is proposed where the controller design is based on classical state space control theory and time series. The system plant has been modeled using non-linear finite element and the gain factors for the control loop were identified by solving the optimal control problem using a non-linear least square optimization algorithm.The proposed design method has been applied on a deep drawing operation where the objective was to control material flow throughout the part using only spatial information regarding flange draw-in. The control system controls both the magnitude and distribution of the blank-holder force.The methodology proved stable and flexible with respect to controlling the dynamic behavior of the system and the numerical tests showed that it is possible to control the material flow.Preliminary experimental results show that the proposed control system can eliminate process instability when the process is subject to a systematic error.     

A quantitative analysis of indicators of scientific performance

Condensing the work of any academic scientist into a one-dimensional indicator of scientific performance is a difficult problem. Here, we employ Bayesian statistics to analyze several different indicators of scientific performance. Specifically, we determine each indicator’s ability to discriminate between scientific authors. Using scaling arguments, we demonstrate that the best of these indicators require approximately 50 papers to draw conclusions regarding long term scientific performance with usefully small statistical uncertainties. Further, the approach described here permits statistical comparison of scientists working in distinct areas of science.     

Optical and electrical properties of zinc oxide films prepared by spray pyrolysis

Zinc oxide thin films were prepared on glass substrates from an aqueous solution of zinc acetate by spray pyrolysis. These films were characterized using X-ray diffraction, scanning electron microscopy and optical transmission. The films were highly transparent to the visible radiation and electrically conductive. Films deposited at optimum conditions exhibited a resistivity of 3·15×10⁻³ Ωm along with a transmittance of 98% at 550 nm.     

A survey on wireless ATM technologies and standardization

Growing emphasis on multimedia traffic has underlined the importance of broadband asynchronous transfer mode (ATM) networks which are capable of supporting demanding applications such as audio/video playback, image browsing, real-time voice/video transmission and interactive data exchange in a unified manner. However, the extension of ATM from wireline to wireless creates a new set of challenging issues. ATM standards are developed based on high data rates and reliable transmission links. This is in contrast to wireless channels where bandwidth is limited and error rates are high. Furthermore, existing ATM specifications are designed primarily to provide services to fixed end-terminals with little ability to adapt to mobile connections and the highly time-varying conditions associated with wireless networks. This paper surveys the major technical and service issues related to the deployment of ATM in third-generation wireless networks. It will also cover how international standards are progressing in this important area. This revised version was published online in August 2006 with corrections to the Cover Date.     

Organizing drug injectors against AIDS: Preliminary data on behavioral outcomes.

Describes a project based on organizing drug injectors to change their subculture in ways that promote lower risk behaviors. Initial and follow-up interviews were conducted with 368 Ss. Findings indicate a decline in high-risk behaviors such as renting or borrowing used syringes and an increase in risk-reducing behaviors such as using new syringes and condoms. Almost half the Ss entered drug abuse treatment during the follow-up period; 60% taught others to use bleach to decontaminate injecting equipment. Risk reduction was greater among Ss who attended group meetings. Thus, organizing drug injectors is a feasible intervention that should be adopted elsewhere. Drug injectors can take on responsibility in combating AIDS. All evaluations of interventions should measure Ss' efforts to spread the message to others. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unified overhead-aware schedulability analysis for slot-based task-splitting

Hard real- time multiprocessor scheduling has seen, in recent years, the flourishing of semi-partitioned scheduling algorithms. This category of scheduling schemes combines elements of partitioned and global scheduling for the purposes of achieving efficient utilization of the system’s processing resources with strong schedulability guarantees and with low dispatching overheads. The sub-class of slot-based “task-splitting” scheduling algorithms, in particular, offers very good trade-offs between schedulability guarantees (in the form of high utilization bounds) and the number of preemptions/migrations involved. However, so far there did not exist unified scheduling theory for such algorithms; each one was formulated in its own accompanying analysis. This article changes this fragmented landscape by formulating a more unified schedulability theory covering the two state-of-the-art slot-based semi-partitioned algorithms, S-EKG and NPS-F (both fixed job-priority based). This new theory is based on exact schedulability tests, thus also overcoming many sources of pessimism in existing analysis. In turn, since schedulability testing guides the task assignment under the schemes in consideration, we also formulate an improved task assignment procedure. As the other main contribution of this article, and as a response to the fact that many unrealistic assumptions, present in the original theory, tend to undermine the theoretical potential of such scheduling schemes, we identified and modelled into the new analysis all overheads incurred by the algorithms in consideration. The outcome is a new overhead-aware schedulability analysis that permits increased efficiency and reliability. The merits of this new theory are evaluated by an extensive set of experiments.     

Influence of hydrogen on microstructure and dynamic strength of lean duplex stainless steel

In this research dynamic strength is analyzed for the first time in a lean duplex stainless steel (LDS) uncharged and charged with hydrogen. In particular, the dynamic yield stress (Hugoniot elastic limit, HEL) and the dynamic tensile strength (spall strength) of LDS are studied. We also investigate the deformation mechanism of the LDS using metallurgical analysis. LDS was chosen since it has a mixed structure of ferrite (BCC, α) and austenite (FCC, γ), which allows an attractive combination of high strength and ductility. The dynamic loading was produced by accelerating an LDS impactor in a gas gun into an LDS target (uniaxial plate impact experiments). Data collection was performed by optical diagnostics through the velocity interferometer for any reflector device. The impact produces conditions of high pressure and high strain rate (~10⁵ s^?1), which can be comparable to explosions during extreme conditions of failure. In addition, investigations of hydrogen interaction with both crystal lattices were performed by means of X-ray diffraction (XRD) measurements. Several assessments can be made based on the results of this study. Using XRD analysis, it will be shown that even after hydrogen desorption some hydrogen remained trapped in the austenitic phase causing a small lattice expansion. After impact, a brittle spall was seen, which occurred through cavitation of cracks along both phases’ grain boundaries. Hydrogen increases the dynamic yield strength and when hydrogen content is sufficiently high it will also lead to higher spall strength. The relation between microstructure and dynamic strength of the LDS in the presence of hydrogen is discussed in detail.     

Gas transport in coextruded multilayered membranes with alternating dense and porous polymeric layers

Multilayered gas separation membranes with alternating layers of β crystalline polypropylene and PEBAX copolymers were produced via coextrusion and biaxial stretching for potential applications in modified atmosphere packaging. The number of layers and PEBAX compositions were varied to study the effect of various membrane configurations on pore formation in the polypropylene layers, which ideally serve as a mechanical support for the selective PEBAX layers. Gas permeabilities of multilayered films were compared to control PEBAX films using a simple model, which allowed inferences about the completeness of pore formation to be drawn. Preliminary results show that increasing the layer count degrades membrane throughput and separation capability, while varying PEBAX composition results in a tradeoff between these properties.     

Compact high-resolution spaceborne echelle grating spectrometer with acousto-optical tunable filter based order sorting for the infrared domain from 2.2 to 4.3 microm

A new compact spaceborne high-resolution spectrometer developed for the European Space Agency's Venus Express spacecraft is described. It operates in the IR wavelength range of 2.2 to 4.3 microm and measures absorption spectra of minor constituents in the Venusian atmosphere. It uses a novel echelle grating with a groove density of 4 lines/mm in a Littrow configuration in combination with an IR acousto-optic tunable filter for order sorting and an actively cooled HgCdTe focal plane array of 256 by 320 pixels. It is designed to obtain an instrument line profile of 0.2 cm(-1). First results on optical and spectral properties are reported.