Makespan estimation and order acceptance in batch process industries when processing times are uncertain

Batch process industries are characterized by complex precedence relationships between operations, which renders the estimation of an acceptable workload very difficult. A detailed schedule based model can be used for this purpose, but for large problems this may require a prohibitive large amount of computation time. We propose a regression based model to estimate the makespan of a set of jobs. We extend earlier work based on deterministic processing times by considering Erlang-distributed processing times in our model. This regression-based model is used to support customer order acceptance. Three order acceptance policies are compared by means of simulation experiments: a scheduling policy, a workload policy and a regression policy. The results indicate that the performance of the regression policy can compete with the performance of the scheduling policy in situations with high variety in the job mix and high uncertainty in the processing times. Correspondence to: C.V. Ivanescu     

A decoupled sliding mode control for a continuum arm

The paper treats the control problem of a class of robots constituted by a chain of continuum segments. The technological model basis is a central, long and thin, highly flexible and elastic backbone. The segment control system is a decoupled one. The main parameters of the arm control are determined by the curvature and curvature gradient. The dynamic model is inferred. The primary benefit of the proposed method is that the dynamic equations are represented by a set of ODE’s in time instead of PDE’s in time and space, and the new curvature gradient lumped parameter model is used. A sliding mode control system is used in order to achieve the desired shape of the arm. The stability of the closed-loop control system is proven. Numerical simulations and an experimental platform are also provided to verify the effectiveness of the presented approach.     

Microstructure,mechanical properties,and corrosion resistance of Ti-20Zr alloy in undoped and NaF doped artificial saliva

The corrosion behavior of a new, advanced Ti-20Zr alloy with α+β microstructure (determined by optical microscopy, XRD, and SEM) and very good mechanical properties (obtained from the stress-strain curve) is studied in this paper. The composition of the alloy native passive film was determined from a XPS analysis and the long-term corrosion resistance in undoped and doped states with 0.05M NaF artificial Carter-Brugirard saliva of different pH values, simulating the severe functional conditions of a dental implant, was analyzed by electrochemical methods. This alloy possesses an advantageous balance between good mechanical resistance and plasticity and Young’s modulus and exhibits more favorable electrochemical parameters and corrosion resistance than CP Ti due to its more resistant passive layer containing Ti₂O₃, TiO₂, and ZrO₂ protective oxides. After 1000 h of immersion in saliva, the protective properties of the alloy were enhanced due to the deposited surface layer that incorporated protective phosphates (shown by SEM and XPS).     

Microstructure, mechanical, and anticorrosive properties of a new Ti-20Nb-10Zr-5Ta alloy based on nontoxic and nonallergenic elements

For an alloy to be suitable for use as an implant material, it must have a low specific weight and Young??s modulus, good mechanical properties that are similar to those of bone, and very good corrosion resistance and biocompatibility. In this study, we have developed a novel Ti-20Nb-10Zr-5Ta alloy that is composed of nontoxic, nonallergenic, corrosion-resistant elements. This alloy has low specific weight and Young??s modulus and good mechanical properties. It has a fine microstructure with a matrix that is mainly composed of the ?? phase and some ?? phase due to recrystallization during cooling. It shows elastoplastic behavior with a fairly linear elastic behavior and low Young??s modulus (59 GPa). In addition, its ultimate tensile strength, 0.2% yield strength, and hardness are higher than those of CP Ti, commercial Ti-6Al-4V, and similar ??-type alloys. It exhibited a very stable passive state and its electrochemical parameters and corrosion and ion release rates were better than those of CP Ti in Ringer??s solutions of different pH values that simulate the severe functional conditions of an implant; this is attributable to the beneficial influence of the alloying elements and to the better protective properties of the coated passive film.     

Corrosion behaviour and biocompatibility of a new dental noble AuPdAgTi alloy

The aims of the study were to investigate the electrochemical response of a new dental Au‐20Pd‐10Ag‐5Ti alloy in artificial Carter‐Brugirard saliva and to assess its biocompatibility using gingival fibroblast culture. Electrochemical techniques of potentiodynamic and linear polarization were used. Also, the open circuit potentials and the corresponding open circuit potential gradients were monitored for 5000 exposure hours. The gingival fibroblast response to Au‐20Pd‐10Ag‐5Ti alloy was estimated by LDH‐cytotoxicity, MTT cell proliferation assays, the assessment of substrate‐dependent changes in extracellular fibronectin network, cell morphology and actin cytoskeleton organization. The cyclic potentiodynamic curves of Au‐20Pd‐10Ag‐5Ti alloy exhibited a passive behaviour with transpassive dissolution of silver, without pitting corrosion. Open circuit potentials were finally stable at noble values. Open circuit potential gradients have low values that could not generate galvanic or local corrosion. The new Au‐20Pd‐10Ag‐5Ti alloy did not promote cell damage and alterations in cell adhesion and morphological features, exhibiting a good biocompatibility.     

Fuzzy Logic Control of Parametrically Excited Rotating Beam Using Inverse Model

In this article the control of an elastic link with parametrically excited base in rotational motion was considered. A decoupled controller and an inverse model was designed and employed to suppress the vibrations of the elastic beam. The inverse model has a transfer function like the reciprocal of the plant transfer function and becomes the actuator for the original model. The decoupling controller separates the global system in several independent components. A sliding mode strategy using fuzzy logic was developed to control the independent components. Simulations for damped and undamped system were provided.     

Mechanical and corrosion behaviour of a Ti‐Al‐Nb alloy after deformation at elevated temperatures

The mechanical properties of Ti6Al7Nb alloy deformed and heat treated at elevated temperatures were correlated with its microstructure and corrosion behaviour in Ringer (of different pH values: 2.49, 6.9 and 8.9) and Ringer–Brown solutions. Microstructural analysis revealed a Widmanstatten structure for the alloys deformed at 1100 °C (β field) and structure with α grains at 930 °C (α + β field). The thermo‐mechanical processing improved the electrochemical behaviour of Ti6Al7Nb alloys, especially their passive state. Open circuit potential variations in time reflected more compact, stable, resistant passive films on the surface of the treated alloys. Open circuit potential gradients simulating the non‐uniformities of pH along the implant surface have very low values that cannot generate galvanic corrosion. Corrosion rates and ion release are very much reduced. Impedance spectra were fitted with a two time‐constants equivalent circuit for some alloys and with three time‐constants equivalent circuit for other alloys.     

Electrochemical and SEM studies of a new implant bioalloy in physiological electrolytes

A new implant Ti–7Al–3V–2Mo–2Fe alloy was elaborated and its behaviour in Ringer–Brown and Ringer solutions (of different pH values) was studied using cyclic potentiodynamic and linear polarisation, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) with its link energy dispersive X‐ray system (EDX). Cyclic potentiodynamic polarisation curves revealed that the Ti–7Al–3V–2Mo–2Fe alloy is self‐passivated in Ringer solutions. Pitting corrosion appeared in alkaline Ringer solution but at very electropositive values of the breakdown and pitting protection potentials and it is not possible to develop local corrosion on this alloy, even in extreme functional conditions. EIS spectra at open circuit potential exhibited two phase angles characterising a resistant passive film and some charge transfer reactions. SEM–EDX analysis shows the presence of some aggregates containing complex compounds of calcium, magnesium, phosphor, silicon deposited on the alloy surface.     

Characterization of the Ti-10Nb-10Zr-5Ta Alloy for Biomedical Applications. Part 1: Microstructure, Mechanical Properties, and Corrosion Resistance

Ti-10Nb-10Zr-5Ta alloy was investigated as possible material candidate for replacing Ti6Al4V in medical applications. The alloy was prepared in a levitation melting furnace and characterized in terms of elemental and phase composition, microstructure, mechanical properties, and corrosion resistance in simulated body fluid and Fusayama Meyer artificial saliva solutions. The characteristics of the new alloy were compared to those of the Ti6Al4V alloy. The Ti-10Nb-10Zr-5Ta system was found to posses of a polyhedral structure consisting in α′ and β phases. X-ray structural analysis revealed a mixture of hexagonal α′ martensite (main phase, with grain size of about 21 nm) and β bcc phase. The Ti-10Nb-10Zr-5Ta alloy exhibited some better mechanical properties (Young modulus, tensile properties) and corrosion resistance (polarization resistance, corrosion current density, and corrosion rate), as compared to Ti6Al4V alloy.     

Corrosion behaviour of a new Ti‐6Al‐2Nb‐1Ta alloy in various solutions

A new Ti‐6Al‐2Nb‐1Ta alloy was obtained for to satisfy the mechanical and anticorrosion requirements in neutral corrosive environment. The corrosion behaviour of this new Ti‐6Al‐2Nb‐1Ta alloy in 0.1 M Na₂SO₄, 3% NaCl solutions and synthetic sea water was studied in this paper, using potentiodynamic and linear polarisation method, electrochemical impedance spectroscopy (EIS) and monitoring of the open circuit potentials. The structure of the alloy represents an α + β uniform structure with un‐oriented grains. From the potentiodynamic polarisation curves it resulted that the studied alloy is self‐passivated in all three solutions having a very good and very easy tendency to passivation. The most favourable values of the electrochemical parameters were registered in 0.1 M Na₂SO₄ solution due to its reduced corrosivity. EIS measurements proved the improvement of the passive layer resistance with the immersion time. An electric equivalent circuit with two time constants was fitted. The values of the polarisation resistances showed very good protective capacities which improved in time. The open circuit potentials have the general tendency to ennoble in time, suggesting the thickening of the passive films and the increase of their protective capacities.