Evaluation of trace metal concentrations in some herbs and herbal teas by principal component analysis

Sixteen trace metallic analytes (Ba, Ca, Ce, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, P, Sr and Zn) in acid digests of herbal teas were determined and the data subjected to chemometric evaluation in an attempt to classify the herbal tea samples. Nettle, Senna, Camomile, Peppermint, Lemon Balm, Sage, Hollyhock, Linden, Lavender, Blackberry, Ginger, Galangal, Cinnamon, Green tea, Black tea, Rosehip, Thyme and Rose were used as plant materials in this study. Trace metals in these plants were determined by using inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry. Principal component analysis (PCA), linear discriminant analysis (LDA) and cluster analysis (CA) were used as classification techniques. About 18 plants were classified into 5 groups by PCA and all group members determined by PCA are in the predicted group that 100.0% of original grouped cases correctly classified by LDA. Very similar grouping was obtained using CA.     

Bacterial Foraging Optimization Algorithm for assembly line balancing

Assembly line balancing is the problem of assigning tasks to workstations by optimizing a performance measure while satisfying precedence relations between tasks and cycle time restrictions. Many exact, heuristic and metaheuristic approaches have been proposed for solving simple straight and U-shaped assembly line balancing problems. In this study, a relatively new optimization algorithm, Bacterial Foraging Optimization Algorithm (BFOA), based heuristic approach is proposed for solving simple straight and U-shaped assembly line balancing problems. The performance of the proposed algorithm is evaluated using a well-known data set taken from the literature in which the number of tasks varies between 7 and 111, and results are also compared with both an ant-colony-optimization-based heuristic approach and a genetic-algorithm-based heuristic approach. The proposed algorithm provided optimal solutions for 123 out of 128 (96.1 %) test problems in seconds and is proven to be promising.     

State‐Feedback Control for a Class of Timed Petri Nets Subject to Marking Constraints

The paper contributes with an original method of designing a control for discrete event systems modeled by a class of timed Petri nets. Precisely, this work deals with the closed loop control of Timed Event Graphs (TEGs) under specifications expressed with linear marking constraints. The objective of the controller is to limit the number of tokens in some places of these TEGs. The behavior of TEGs is represented by a system of difference equations that are linear in Min‐Plus algebra and the constraints are described by a set of inequalities, which are also linear in Min‐Plus algebra. A formal approach to design control laws that guarantee compliance with these marking constraints is proposed. For this, two sufficient conditions for the existence of control laws are proposed. The computed controls are causal feedbacks, which can be represented by a set of marked and timed places. The proposed method is illustrated in two applications: a manufacturing production line and an assembly system.     

High-performance oxygen reduction and evolution carbon catalysis: From mechanistic studies to device integration

The development of high-performance and low-cost oxygen reduction and evolution catalysts that can be easily integrated into existing devices is crucial for the wide deployment of energy storage systems that utilize O2-H2O chemistries,such as regenerative fuel cells and metal-air batteries.Herein,we report an NH3-activated N-doped hierarchical carbon (NHC) catalyst synthesized via a scalable route,and demonstrate its device integration.The NHC catalyst exhibited good performance for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER),as demonstrated by means of electrochemical studies and evaluation when integrated into the oxygen electrode of a regenerative fuel cell.The activities observed for both the ORR and the OER were comparable to those achieved by state-of-the-art Pt and Ir catalysts in alkaline environments.We have further identified the critical role of carbon defects as active sites for electrochemical activity through density functional theory calculations and high-resolution TEM visualization.This work highlights the potential of NHC to replace commercial precious metals in regenerative fuel cells and possibly metal-air batteries for cost-effective storage of intermittent renewable energy.     

Computational insights into charge transfer across functionalized semiconductor surfaces

Abstract

Photoelectrochemical water-splitting is a promising carbon-free fuel production method for producing H₂ and O₂ gas from liquid water. These cells are typically composed of at least one semiconductor photoelectrode which is prone to degradation and/or oxidation. Various surface modifications are known for stabilizing semiconductor photoelectrodes, yet stabilization techniques are often accompanied by a decrease in photoelectrode performance. However, the impact of surface modification on charge transport and its consequence on performance is still lacking, creating a roadblock for further improvements. In this review, we discuss how density functional theory and finite-element device simulations are reliable tools for providing insight into charge transport across modified photoelectrodes.     

Role of manufacturing towards achieving circular economy: The steel case

Circular economy (CE) has been promoted worldwide as a strategy to reduce material use and to increase the material use efficiency by closing material loops at the societal level. The core concept of CE is to improve the circularity of material use through turning materials at the end of their service life into resources for others, however, there is very little information about the role of manufacturing in achieving CE. Using the concepts of dynamic material flow analysis and stock dynamics, this paper proposes a methodological approach to help understand the role of manufacturing in achieving CE. A number of other strategies such as material efficiency in conjunction with CE are also tested using the case of global steel use to draw conclusions.     

Intuitive Material Distributions

Panagiotis Michalatos and Sawako Kaijima describe how the Optimisation Design team at Adams Kara Taylor (AKT) work with mathematical algorithms to develop interactive software applicatons that help inform structural behaviour in the early parts of the design process. This is exemplified by the project-specific software they developed for Thomas Heatherwick's British Pavilion at the 2010 Shanghai Expo. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative study of adatom manipulation on several fcc metal surfaces

For a set of fcc metals, our total energy calculations based on many body potentials show that activation barriers for lateral manipulation of an adatom at a step edge depend on the tip/substrate composition. Of the six homogeneous systems studied, manipulation on stepped Ag(111) showed the lowest energy barrier for adatom hopping toward the tip, although the relative probability for this process was largest on Cu(111). For a representative Cu/Pt heterogeneous system, we find lateral manipulation of a Pt adatom along a step on Pt(111) by a Cu(100) tip to be energetically much less favorable than the reverse case of a Cu adatom manipulated by a Pt(100) tip. In the case of vertical manipulation, atomic relaxations of the tip and its neighboring atoms are found to be prominent and tip-induced changes in the bonding of the adatom to its low coordinated surroundings help explain the relative ease with which an adatom next to a step edge or a kink site may be pulled as compared to that on a flat surface.     

Electrical properties of Poly(ethylene glycol dimethacrylate-n-vinyl imidazole)/Single Walled Carbon Nanotubes/n-Si Schottky diodes formed by surface polymerization of Single Walled Carbon Nanotubes

In this paper we report the electrical characteristics of the Schottky diodes formed by surface polymerization of the Poly(ethylene glycol dimethacrylate-n-vinyl imidazole)/Single Walled Carbon Nanotubes on n-Si. The Single Walled Carbon Nanotubes were synthesized by CVD method. The main electrical properties of the Poly(ethylene glycol dimethacrylate-n-vinyl imidazole)/Single Walled Carbon Nanotubes/n-Si have been investigated through the barrier heights, the ideality factors and the impurity density distribution, by using current-voltage and reverse bias capacitance voltage characteristics. Electrical measurements were carried out at room temperature. Poly(ethylene glycol dimethacrylate-n-vinyl imidazole)/Single Walled Carbon Nanotubes/n-Si Schottky diode current-voltage characteristics display low reverse-bias leakage currents and average barrier heights of 0.61 ± 0.02 eV and 0.72 ± 0.02 eV obtained from both current-voltage and capacitance-voltage measurements at room temperature, respectively.     

High efficiency graphene solar cells by chemical doping

We demonstrate single layer graphene/n-Si Schottky junction solar cells that under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%. This performance, achieved by doping the graphene with bis(trifluoromethanesulfonyl)amide, exceeds the native (undoped) device performance by a factor of 4.5 and is the highest PCE reported for graphene-based solar cells to date. Current-voltage, capacitance-voltage, and external quantum efficiency measurements show the enhancement to be due to the doping-induced shift in the graphene chemical potential that increases the graphene carrier density (decreasing the cell series resistance) and increases the cell's built-in potential (increasing the open circuit voltage) both of which improve the solar cell fill factor.