A restarted and modified simplex search for unconstrained optimization

In this paper we propose a simple but efficient modification of the well-known Nelder–Mead (NM) simplex search method for unconstrained optimization. Instead of moving all n simplex vertices at once in the direction of the best vertex, our “shrink” step moves them in the same direction but one by one until an improvement is obtained. In addition, for solving non-convex problems, we simply restart the so-modified NM (MNM) method by constructing an initial simplex around the solution obtained in the previous phase. We repeat restarts until there is no improvement in the objective function value. Thus, our restarted modified NM (RMNM) is a descent and deterministic method and may be seen as an extended local search for continuous optimization. In order to improve computational complexity and efficiency, we use the heap data structure for storing and updating simplex vertices. Extensive empirical analysis shows that: our modified method outperforms in average the original version as well as some other recent successful modifications; in solving global optimization problems, it is comparable with the state-of-the-art heuristics.     

Preparation of smallest microparticles of poly-D,L-lactide by modified precipitation method: influence of the process parameters

Biodegradable microspheres such as those made of poly-D,L-lactide (PDLLA) are widely investigated delivery systems for drugs or antigens. The aim of this study was to examine experimental conditions in order to produce PDLLA microspheres with the best properties for controlled and sustained drug delivery by the modified precipitation method. For this purpose, the following parameters were varied: co-solvent (methanol or ethanol), the concentration of stabilizer polyvinyl alcohol (PVA), chloroform-to-water ratio and the speed and time of homogenization. Scanning electron microscopy (SEM) and stereological analysis were used to characterize the particles. The average size and morphology of the microspheres varied substantially with preparation conditions from 8.44-1.25 microm. Results showed that the smallest particles were obtained with methanol, 1% PVA and with 10 min of homogenization at 21,000 rpm.     

Human-like behavior of robot arms: general considerations and the handwriting task—Part II: the robot arm in handwriting

This paper (Part II) investigates the motion of a redundant anthropomorphic arm during the writing task. Two approaches are applied. The first is based on the concept of distributed positioning which is suitable to model the “writing” task before the occurrence of fatigue symptoms. The second approach uses the concept of “virtual fatigue” (VF) which is a variable that dynamically behaves in a way analogous to the biological fatigue. VF enables the arm to reconfigure itself and take postures appropriate for the current level of fatigue. The study includes the analysis of legibility and inclination of handwriting, and a set of simulation results that show most practical aspects of robot human-like performance.     

Looking at Heterogeneous Catalysis at Atmospheric Pressure Using Tunnel Vision

This paper addresses the “pressure gap” between traditional surface science experiments and catalysis under practical conditions. We review high-pressure, microflow experiments at elevated temperatures during the catalytic oxidation of CO. Using a specially constructed “Reactor-STM” we simultaneously determine the surface structure of a model catalyst by scanning tunneling microscopy and the reaction kinetics by online mass spectrometry. For both Pt(110) and Pd(100) we find that under O₂-rich conditions surface oxides are formed on the otherwise metallic surfaces. The presence of the oxide is correlated with a superior catalytic activity. Whereas the reaction on the metal surfaces shows traditional Langmuir–Hinshelwood kinetics, the reaction on the oxides follows the Mars-Van Krevelen oxidation–reduction mechanism, as we conclude from the reaction kinetics and the reaction-induced roughening of the surface. We emphasize that in addition to a pressure gap there can also be a temperature gap, requiring experiments to be performed not only at high pressures but also at sufficiently high temperatures.     

Detecting correlation between server resources for system management

Efficient system management requires continuous knowledge about the state of system and application resources that are typically represented through time series obtained by monitors. Capacity planning studies, forecasting, state aggregation, anomaly and event detection would be facilitated by evidence of data correlations. Unfortunately, the high variability characterizing most monitored time series affects the accuracy and robustness of existing correlation solutions. This paper proposes an innovative approach that is especially tailored to detect linear and non-linear correlation between time series characterized by high variability. We compare the proposed solution and existing algorithms in terms of accuracy and robustness for several synthetic and real settings characterized by low and high variability, linear and non-linear correlation. The results show that our proposal guarantees analogous performance for low variable time series, and improves state of the art in finding correlations in highly variable domains that are of interest for the application context.     

Kinematic redundancy and sensor redundancy for enhancement of robot tracking performance

Imprecision of robot's internal sensors and its influence on trajectory tracking tasks along with high dynamic requirements are the main issues in this paper. The solution proposes redundancy introduction (in the shape of small mechanism at the top of the robot) for resolving both problems. The inverse kinematics of the redundant robot has been solved at the tactical level of control via the Distributed Positioning (DP) concept. The redundancy applied reduces the tracking error caused by dynamic requirements and partly by imprecision of internal sensors. However, additional solutions with external position sensor could be used in order to reduce sensor imprecision influence. All solutions are very conservative considering changes in basic (non-redundant) robot. Simulation results provide clear insight in the validity of proposed solutions.     

High‐Temperature Structural Evolution of the Disordered LiMn1.5Ni0.5O4

In this work, we present our recent results about the changes induced on a crystalline bulk LiMn_1.5Ni_0.5O₄ disordered cubic spinel phase by thermal treatments carried out under different back atmospheres (vacuum and air). Our aim is to describe the structural changes induced by temperature in various conditions both on the long range (by means of XRD) and on the short range around Mn/Ni metal sites (by means of EXAFS) and to investigate the reversible oxygen loss and adsorption upon heating and cooling, respectively. In summary, the LiMn_1.5Ni_0.5O₄ phase suffers large structural modifications above 650°C both under vacuum and air. These alterations are closely related to the occurrence of large oxygen vacancies in the anionic sublattice due to spontaneous oxygen loss via the gas phase. Apparently, local and long‐range distortions from the pristine disordered cubic spinel structure are completely reversible in air upon cooling from high temperature, whereas under vacuum, the structural alterations are permanent.