Fracture Characteristics of Torsion-Bending Fatigue and Impact Fatigue Failure of Two Steel Pins in a Crawler Excavator

The arms of crawler excavators used in diverse quarries work under extremely harsh conditions. A common failure during their operation is the fracture of the steel pin joints that permit free movement of the two adjacent booms closer to the machine housing, as well as the motion of the backhoe bucket against its nearest boom. This work presents examples of two steel pin joint failures. The pins had a diameter of 90 mm, and the failures resulted in high stand-by time for repairs. The first failure was caused by the combination of bending and torsion fatigue, and the second fracture occurred because of impact fatigue. Optical metallography and scanning electron microscopy/electron dispersive x-ray analysis (SEM/EDS) analysis provided a better understanding of the failure mechanism of the two steel pins, since these particular components exhibited excellent fatigue characteristics in both mating fracture surfaces.     

Time-discretization of nonlinear systems with delayed multi-input using Taylor series

This study proposes a new scheme for the sampled-data representation of nonlinear systems with time-delayed multi-input. The proposed scheme is based on the Taylor-series expansion and zero-order hold assumption. The mathematical structure of a new discretization scheme is explored. On the basis of this structure, the sampled-data representation of nonlinear systems including time-delay is derived. The new scheme is applied to nonlinear systems with two inputs and then the delayed multi-input general equation is derived. The resulting time-discretization provides a finite-dimensional representation of nonlinear control systems with time-delay enabling existing controller design techniques to be applied to them. In order to evaluate the tracking performance of the proposed scheme, an algorithm is tested for some of the examples including maneuvering of an automobile and a 2-DOF mechanical system.     

Gas permeation field tests of composite Pd and Pd–Au membranes in actual coal derived syngas atmosphere

Three large scale (with each a permeable area of 200 cm²) highly structured composite Pd and Pd–Au membranes were prepared and tested in an actual stream of coal derived, but desulfurized, syngas at the National Carbon Capture Center (NCCC) in Wilsonville, Al. The objective of the study was to investigate the long term membrane stability and to establish the long term effects of syngas contaminants in the coal derived syngas other than sulfur compounds on H₂ permeance and selectivity. The large scale membranes had thicknesses ranging from 7 to 14 μm, H₂ permeances ranging from 20 to 28 Nm³ m⁻² h⁻¹ bar^−0.5, and an undetectable He leak before the actual syngas test. In the syngas atmosphere, composite Pd and Pd–Au membranes showed an outstanding H₂ permeance stability at 450 °C and 12.6 bar for approximately 200 h albeit a fast initial decline upon syngas introduction. The fast permeance decline observed at the introduction of the actual syngas was attributed to possible surface and/or bulk poisoning. An exceptionally high H₂ purity level of 99.89% was achieved at 450 °C and 12.6 bar during the entire period of the measurement of over 200 h in syngas atmosphere representing a breakthrough result in the field never reported before with actual syngas from a coal gasification unit.     

Evaluation of selected publications on reference values for lead in blood

As a part of the global Tracy project, whose aim is to define metal concentrations in tissues and body fluids of reference populations, more than 1000 papers published from 1980 to 1994 were scrutinized that presented tentative reference values for lead in blood in occupationally unexposed adult populations. Ten studies exemplifying criteria for proper sampling, analysis and data treatment are presented and discussed. Levels of lead in blood are influenced by numerous factors. Accordingly, a wide variation in blood lead concentrations was observed. As an example, in a global study in 1983 of nonsmoking female schoolteachers, the geometric mean value for lead in blood varied from 52 micrograms. l-1 in Tokyo, Japan, up to 193 micrograms. l-1 in Mexico City. The Tracy survey demonstrates the importance of factors such as age, gender, ethnicity, food, drinking and smoking habits, hobbies, season and year of sampling, residential area, and geographic location. Lead in blood was shown to be both time and area specific. Thus it was not possible to establish a general reference value for lead in blood.     

A process dynamic modeling and control framework for performance assessment of Pd/alloy-based membrane reactors used in hydrogen production

In the present study a comprehensive, insightful and practical process dynamic modeling framework is developed in order to analyze and characterize the transient behavior of a Pd/alloy-based (Pd/Au or Pd/Cu) water-gas shift (WGS) membrane reactor. Furthermore, simple process control ideas are proposed aiming at enhancing process system performance by inducing the desirable dynamic characteristics in the response of the controlled process during start-up as well as in the presence of unexpected adverse disturbances (process upset episodes) or operationally favorable set-point changes that reflect new hydrogen production requirements. Finally, the proposed methods are evaluated through detailed simulation studies in an illustrative example involving a Pd/alloy-based WGS membrane reactor that exhibits complex dynamic behavior and is currently used for lab-scale pure hydrogen production and separation.     

Effect of harvest time and storage conditions on almond kernel oil and sugar composition

The effect of storage for 6 months at 5 °C (80% RH) versus 20 °C (60% RH) of shelled versus in‐shell almonds was studied on early versus late harvested nuts from ‘Ferragnes’ and ‘Texas’ trees. Kernel quality characteristics, oil composition and sugar composition were determined initially and after 6 months of storage. Early harvested almonds had similar kernel weight to but higher moisture content than late harvested almonds after 6 months of storage. Early harvested almonds also had similar oil quality (based on ultraviolet absorption coefficient measurements) and oil composition but lower sugar content and modified sugar composition compared with late harvested almonds. Storage of shelled almonds resulted in kernels with higher oil content, better oil quality, similar oil composition, similar sugar content and some modifications in sugar composition compared with in‐shell stored almonds. Finally, storage for 6 months at either 5 or 20 °C resulted in lower moisture content, higher oil content, similar oil quality and composition, similar sugar content and some modifications in sugar composition compared with freshly harvested almonds. Almonds stored at 5 °C retained higher kernel weight and moisture content than almonds stored at 20 °C. © 2003 Society of Chemical Industry     

Discrete-time nonlinear observer design using functional equations

The present research work proposes a new approach to the discrete-time nonlinear observer design problem. Based on the early ideas that influenced the development of the linear Luenberger observer, the proposed approach develops a nonlinear analogue. The formulation of the discrete-time nonlinear observer design problem is realized via a system of first-order linear nonhomogeneous functional equations, and a rather general set of necessary and sufficient conditions for solvability is derived using results from functional equations theory. The solution to the above system of functional equations can be proven to be locally analytic and this enables the development of a series solution method, that is easily programmable with the aid of a symbolic software package.     

A model-based characterization of the long-term asymptotic behavior of nonlinear discrete-time processes using invariance functional equations

The present research work proposes a new approach to the problem of quantitatively characterizing the long-term dynamic behavior of nonlinear discrete-time processes. It is assumed that in order to analyze the process dynamic behavior and digitally simulate it for performance monitoring purposes, the discrete-time dynamic process model considered can be obtained: (i) either through the employment of efficient and accurate discretization methods for the original continuous-time process which is mathematically described by a system of nonlinear ordinary (ODEs) or partial differential equations (PDEs) or (ii) through direct identification methods. In particular, nonlinear processes are considered whose dynamics can be viewed as driven: (i) either by an external time-varying “forcing” input/disturbance term, (ii) by a set of time-varying process parameters or (iii) by the autonomous dynamics of an upstream process. The formulation of the problem of interest can be naturally realized through a system of nonlinear functional equations (NFEs), for which a rather general set of conditions for the existence and uniqueness of a solution is derived. The solution to the aforementioned system of NFEs is then proven to represent a locally analytic invariant manifold of the nonlinear discrete-time process under consideration. The local analyticity property of the invariant manifold map enables the development of a series solution method for the above system of NFEs, which can be easily implemented with the aid of a symbolic software package such as MAPLE. Under a certain set of conditions, it is shown that the invariant manifold computed attracts all system trajectories, and therefore, the asymptotic process response and long-term dynamic behavior are determined through the restriction of the discrete-time process dynamics on the invariant manifold.     

Nonlinear observer design in the presence of delayed output measurements

The present work proposes a new approach to the nonlinear observer design problem in the presence of delayed output measurements. The proposed nonlinear observer possesses a state-dependent gain which is computed from the solution of a system of first-order singular partial differential equations, and in particular, consists of a chain of state observation algorithms that reconstruct the unmeasurable state vector at different delayed time-instants within the time-delay window introduced by the available output measurements. Therefore, the proposed nonlinear observer exhibits a chain-like structure that explicitly reflects and takes into account the magnitude of the output delay. Furthermore, a set of conditions is derived under which convergence of the estimation error to zero is established. Finally, the performance of the proposed observer and its convergence properties are evaluated in an illustrative biological reactor example.     

The use of between-session (homework) activities in psychotherapy: Conclusions from the Journal of Psychotherapy.

This article summarizes the special series. It notes both diversity and commonalities in approaches and highlights areas for future research. Conclusions include the fact that the use of homework appears to be increasingly widespread across a range of therapeutic approaches. However, more research is necessary to document features of homework that will assist practitioners from both a common factors model as well as within a specific approach. (PsycINFO Database Record (c) 2010 APA, all rights reserved)