A tool to analyze robust stability for model predictive controllers

A strategy based on Nonlinear Programming (NLP) sensitivity is developed to establish stability bounds on the plant/model mismatch for a class of optimization-based Model Predictive Control (MPC) algorithms. By extending well-known nominal stability properties for these controllers, we derive a sufficient condition for robust stability of these controllers. This condition can also be used to assess the extent of model mismatch that can be tolerated to guarantee robust stability. In this derivation we deal with MPC controllers with final time constraints or infinite time horizons. Also for this initial study we concentrate only on discrete time systems and unconstrained state feedback control laws with all of the states measured. To illustrate this approach we give two examples: a linear first-order dynamic system and a nonlinear SISO system involving a first order reaction. ©     

Dissolution of Lime in Synthetic ‘FeO’‐SiO2 and CaO‐‘FeO’‐SiO2 Slags

Dissolution of different CaO samples into molten synthetic ‘FeO’‐SiO₂ and ‘FeO’‐SiO₂‐CaO slags was carried out in a closed tube furnace at 1873 K. The slag was kept stagnant. It was found that the dissolution rate was very fast when CaO rod was dipped into ‘FeO’‐SiO₂ slag. In the case of ‘FeO’‐SiO₂‐CaO slag, the dissolution of CaO rod in the stagnant slag was retarded after the initial period (2 minutes). Only less than 16 percent CaO reacted with the slag, irrespective of the type of lime. Three phase‐regions were identified in the reacted part of the lime rod by SEM‐EDS analysis. The formation of these regions was explained thermodynamically. A dense layer of 2CaO · SiO₂ was found to be responsible for the total stop of the dissolution. It could be concluded that constant removal of the 2CaO · SiO₂ layer would be of essence to obtain a high dissolution rate of lime. In this connection, it was found necessary to study the dissolution of lime in moving slag to reach a reliable conclusion regarding the relevance of the reactivity obtained by water ATSM test to the real reactivity of lime in high temperature slag.     

Spatial encoding using a code division technique for fast ultrasound imaging

This paper describes a method for spatial encoding in synthetic transmit aperture ultrasound imaging. This allows several ultrasonic sources to be active simultaneously. The method is based on transmitting pseudorandom sequences to spatially encode the transmitters. The data can be decoded after only one transmission using the knowledge of the transmitted code sequences as opposed to other spatial encoding techniques, such as Hadamard or Golay encoding. This makes the method less sensitive to motion, and data can be acquired using fewer transmissions. The aim of this paper is to analyze the underlying theory and to test the feasibility in a physical system. The method has been evaluated in simulations using Field II in which the point-spread functions were simulated for different depths for a 7 MHz linear array transducer. A signal-to-noise ratio (SNR) simulation also was included in the study in which an improvement in SNR of approximately 1.5 dB was attained compared to the standard synthetic transmit aperture (STA) firing scheme. Considering the amount of energy transmitted, this value is low. A plausible explanation is given that is verified in simulation. The method also was tested in an experimental ultrasound scanner and compared to a synthetic transmit aperture ultrasound imaging scheme using a sinusoidal excitation. The performance of the proposed method was comparable to the reference with respect to axial and lateral resolution, but it displayed poorer contrast with sidelobe levels at approximately - 40 dB compared to the mainlobe.     

车床直线运动误差测试新技术的应用研究

本文阐述用序贯双测头法测量车床直线运动误差的原理,并给出了该方法与其他测试方法(水平仪法、三坐标法、激光干涉法)的对比试验洁果。大量试验结果表明:序贯双测头法的测量精度和测试效率都远远高于其它方法。该方法不仅能测量车床直线运动误差,而且为工件直线度误差在线测量提供了新的测试手段,很有开发应用前景。     

Antibiotic resistance and tolerance to simulated gastrointestinal conditions of eight hemolytic Bacillus pumilus isolated from pulque,a traditional Mexican beverage

Food Science and Biotechnology - Traditional fermented sap beverages from two provinces of Mexico were studied for the isolation of pathogenic bacteria from these beverages. Eight strains of...     

Dynamic response of an opening in jointed rock

A large-scale test was performed on a 0.4 m diameter lined cylindrical opening in a 2 m cube of jointed limestone for the purpose of gathering data to develop and validate computational models for the dynamic response of structures in jointed rock. The limestone cube was assembled from over four thousand 51 mm square×0.6 to 1.2 m long limestone bricks and was then embedded in a concrete test bed and loaded explosively with a 100 MPa, cylindrically diverging stress wave. The material velocity around the boundary of the jointed limestone cube was measured with accelerometers and these data were used to generate a continuous velocity boundary condition that can be used for computational simulations. Additional instrumentation measured stress in the limestone, joint slip and deformation of the opening. After the test, the limestone cube was recovered and carefully disassembled to reveal fracture patterns in the limestone bricks. Vertical fractures emanating from the springlines formed a chimney of bricks that slipped measurably relative to the rest of the rock mass above the opening and to a lesser degree below the opening.     

Radiation resistivity in silica optical fibers

Hydrogen treatment of optical fiber waveguides with pure silica cores and boron, fluorine codoped silica claddings was found to effectively reduce the y-ray induced loss increases in visible wavelength region. Germanium-doped core fibers free from metal impurities had good resistance against y-rays. The induced losses were shown to be dependent on the dose rate, a similar behavior to that of pure silica core fibers. Metal impurities such as phosphorus or alkalis added to germanium doped silica core were found to change the glass structure significantly, producing the precursors of a defect center related to the y-ray-induced loss and increasing sensitivity to y-irradiation