Phase Relations at Liquidus Temperatures in the System MgO-NiO-SiO2

The well-known "quenching technique" has been used to determine liquidus and solidus phase relations in the system MgO-NiO-SiO₂. Oxide mixtures were heated at selected temperatures for sufficient lengths of time for attainment of equilibrium, followed by quenching to room temperature, and phase identification by optical microscopy (transmitted-and reflected-light examination) and X-ray diffraction. Two ternary liquidus invariant points are present in the system. One is characterized by the coexistence of pyroxene (Mg-SiO₃-NiSiO₃ solid solution), olivine (Mg₂SiO₄-Ni₂SiO₄ solid solution), silica (cristobalite), and liquid at 1547°C. The other eutectic is at 1633°C and is characterized by the coexistence of olivine, oxide (MgO-NiO solid solution), silica, and liquid. There is a temperature maximum on the olivine-silica liquidus boundary curve at 1639°C. Reversals in the distribution ratios of magnesium and nickel between solid and liquid phases coexisting in equilibrium during crystallization of melts in this system may occur, depending on the compositions of the mixtures.     

Suspension Processing of Al2O3/SiC Whisker Composites

Homogeneous Al₂O₃ powder/SiC whisker compacts were prepared by suspension processing. By optimizing the conditions for particle/whisker codispersion, castable suspensions could be prepared at total-solids concentrations 50 vol%. Green bodies with high relative density (∼66% to 70%) were obtained with SiC whisker contents in the range of 5 to 30 vol%. Although densification was severely inhibited by the SiC whiskers, significantly higher sintered densities were obtained by suspension processing compared to dry processing.     

Imaging applications of synchrotron X-ray phase-contrast microtomography in biological morphology and biomaterials science. I. General aspects of the technique and its advantages in the analysis of millimetre-sized arthropod structure

Synchrotron‐generated X‐rays provide scientists with a multitude of investigative techniques well suited for the analysis of the composition and structure of all types of materials and specimens. Here, we describe the properties of synchrotron‐generated X‐rays and the advantages that they provide for qualitative morphological research of millimetre‐sized biological organisms and biomaterials. Case studies of the anatomy of insect heads, of whole microarthropods and of the three‐dimensional reconstruction of the cuticular tendons of jumping beetles, all performed at the beamline ID19 of the European Synchrotron Radiation Facility (ESRF), are presented to illustrate the techniques of phase‐contrast tomography available for anatomical and structural investigations. Various sample preparation techniques are described and compared and experimental settings that we have found to be particularly successful are given. On comparing the strengths and weaknesses of the technique with traditional histological thin sectioning, we conclude that synchrotron radiation microtomography has a great potential in biological microanatomy.     

Tectonic Gardens

The Tectonic Gardens initiative focuses on small, unremarkable, and often forgotten places adjacent to the lives of underserved people. Located in the boundary between architecture and landscape, these projects seek to create experiential delight out of small-scale design opportunities. Through the adaptive reuse and recycling of leftover urban space, Tectonic Gardens augment and enhance existing building infrastructures with new, primarily outdoor spaces that provide pragmatic functions, promote play, and exhibit a social and environmental conscience.     

MULTIVARIABLE CONSTRAINED ADAPTIVE GPC: THEORY AND EXPERIMENTAL EVALUATION

This paper deals with on-line identification and constrained long-range predictive control of multivariable systems. It extends a recently proposed augmented upper diagonal factorization identification (AUDI) algorithm to identify input–output models of multivariable systems with distinct time delays. The multi-input, multi-output (MIMO AUDI) algorithm can simultaneously identify the process model order and process parameters. The MIMO AUDI algorithm is implemented by decomposing a MIMO system into as many multi-input, single-output (MISO) subsystems as the number of outputs and then identifying each MISO subsystem separately. The performance of the new MIMO AUDI algorithm is demonstrated by application to input–output data from a real process. The extension of this algorithm by incorporating a variable forgetting factor with a lower bound in its value is implemented on real plant data to demonstrate ‘alertness’ of the estimator. This paper evaluates the performance of the MIMO adaptive generalized predictive control algorithm with and without constraints by experimental application on a computer-interfaced, pilot-scale process. The MIMO adaptive GPC is shown to have good regulatory plus servo-tracking properties. © 1997 John Wiley & Sons, Ltd.     

THERMAL INACTIVATION OF PEA FLOUR LIPOXYGENASE

Lipoxygenase (LOX) was determined in pea flour (9.6% moisture) samples which had been exposed to 90–130°C for 5–45 min, and in crude aqueous extracts (5%; pH 6.7) of previously unheated pea flour which had been exposed to 40–80°C for 5–30 min. The rate of thermal inactivation of pea LOX was shown to follow first-order reaction kinetics. The rate constants, k(min^?1), ranged from 0.005 to 0.252 for the flour, and from 0.068 to 0.267 (60–80°C) for the crude extract. The respective thermodynamic values were: for the energy of activation (E_a), 126.2 and 64.6 kJmole^?1; for the enthalpy of activation (ΔH^?), 123.1 and 61.8 kJmole^?1; for the free energy of activation (Δ^?), 118.0 and 101.4 kJmole^?1. The greater thermostability of LOX in the pea flour under dry-heat conditions, and the observed differences in the E_a, ΔH^? and ΔS^? values, may be accounted for by its possible complexation with other macromolecules and by the structure of the water surrounding the native enzyme.     

三角铣头强化了5轴加工中心的通用性

大、重型零件,例如透平轮毂、风力发电机或重型机械的齿轮,泵体、工业及船用发动机缸体、冲压成型模具的模板等等,主要是单件或小批量生产.这类零件大部分是由分包制造商和维修公司制造的.因此,这类工件不能使用专用夹具装夹.而且,在大型车床或加工中心上加工此类工件时,找正工作非常耗时耗力.     

ADAPTIVE CONTROL OF A HEAT EXCHANGER USING FUNCTION BLOCKS

Many adaptive control strategies require on-line identification, which implies that a digital computer is needed for implementation. The objective of the work presented in this paper is to demonstrate that adaptive process control can be accomplished by combining relatively simple digital control algorithms called function blocks. These function blocks are easily implemented in low-level microprocessor-based digital controllers without requiring a computer. The feasibility of these methods is illustrated through an industrial heat exchanger control example, and the performance benefits of this adaptive approach are illustrated by means of simulation results.     

MODEL REFERENCE ADAPTIVE CONTROL BASED ON LIAPUNOV'S DIRECT METHOD Part II: Hybrid Computer Simulation and Experimental Application

A Model Reference Adaptive Control (MRAC) system is evaluated via hybrid computer simulation and experimental application to a computer-controlled, pilot plant evaporator. In both the simulation and experimental studies, the MRAC system performed well and was insensitive to unmeasured process disturbances, to the choice of the initial control policy and to changes in plant operating conditions. In addition to providing an algorithm for adapting control systems to accommodate changing process parameters, MRAC also provides a systematic approach for tuning or developing multivariable control systems for time-invariant processes.     

MEASUREMENT OF FLUID FOOD VISCOSITY USING MICROFABRICATED RADIO FREQUENCY COILS

We report on the use and applicability of microfabricated radio frequency (r.f.) coils for viscosity measurements of fluid foods. The viscosity of fluid milk and milklike products was measured using nuclear magnetic resonance imaging based on microfabricated r.f. coils coupled to in‐line tubing with an inner diameter of 1.4 × 10^‐3 m. The fluid's apparent viscosity ranged from 0.002 to 0.08 Pa·s. The magnetic resonance‐based measurements were limited in shear rate range because of the small size of the coil. Magnetic resonance‐based measurements from 2 to 15 s^‐1 were obtained and were equivalent to off‐line rotational rheometry.