bluuebunny/crossref_metadata_2025 huggingface dataset:
Shortest Path Problem Algorithms
Authors: Nemani Ashish K. , Ahuja Ravindra K.
Published: February 2011

Theshortest path problem(SPP) is a fundamental combinatorial optimization problem that concerns finding the shortest paths between a source and a destination; it is also referred to as asingle‐source shortest path problem(SSPP). In some problem settings, shortest paths between all pairs of nodes are desired; these are referred to as all‐pairs shortest path problems (ASPP). The SPP arises in a number of applications, both as a stand‐alone problem and as a subproblem in more complex scenarios. Several applications have been described in the last chapter. In this article, we describe algorithmic methods to solve the SSPP, as well as the ASPP. In real‐life applications, networks vary in their characteristics such as in the presence of negative arcs, directed cycles, and so forth. We present both customized and the most extensively studied algorithms for each scenario, with an analysis of their individual complexities.
The Simplex Method and Its Complexity
Authors: Prabhu Nagabhushana
Published: February 2011

The article provides an overview of the simplex method and the research on polyhedra related to its worst case complexity.
Simultaneous Perturbation and Finite Difference Methods
Authors: Bhatnagar Shalabh
Published: February 2011

This article presents a survey of simultaneous perturbation and finite difference algorithms. One of the most important in this category of algorithms is the simultaneous perturbation stochastic approximation (SPSA) algorithm that has been used in a wide range of settings. The article presents an overview of the theory behind SPSA as well as the recent development of other finite‐difference algorithms along the lines of SPSA. The article also gives an overview of the applications of SPSA and SPSA‐type algorithms in various disciplines of engineering and science.
Single‐Search‐Based Heuristics for Multiobjective Optimization
Authors: Ehrgott Matthias
Published: February 2011

This article explains the single‐search‐based heuristics for multiobjective optimization. The most prominent heuristics of multiobjective simulated annealing, multiobjective tabu search, and Pareto local search are each explained with a detailed pseudocode and further summaries of algorithmic ideas. This is followed by a brief review of hybrid heuristics combining features of single search and population‐based heuristics. The article ends with brief conclusions and suggestions for further reading.
Nonlinear Multiobjective Programming
Authors: Engau Alexander
Published: February 2011

This introductory treatment of the theory and methodology of nonlinear multiobjective programming offers an annotated bibliographic overview of various concepts and approaches to solve continuous deterministic multicriteria optimization problems. First, the notions of Pareto optimality, efficiency, and nondominance are discussed and then related to approximate, epsilon, and proper efficiency. Second, after highlighting similarities and pointing out differences to first‐ and second‐order optimality conditions in classical nonlinear programming, several other topics including duality and sensitivity are also mentioned. Third, a number of solution approaches and generating methods are described with a particular focus on scalarizations using objective aggregation, prioritization, and norm or distance minimization to some utopian reference point.
Solving Stochastic Programs
Authors: Bayraksan Güzİn
Published: February 2011

This article reviews solution methods for stochastic programs. First, decomposition methods that exploit the special structure of stochastic programs are discussed. Then, approximate solution methods based on Monte Carlo sampling and bounding techniques are introduced. The algorithmic ideas are presented with a focus on two‐stage stochastic programs with recourse. Extensions to other class of stochastic programs are pointed out.
Minimum Spanning Trees
Authors: Nemani Ashish K. , Ahuja Ravindra K.
Published: February 2011

Theminimum spanning tree(MST) problem is one of the simplest and most studied classical optimization problems. It is concerned with finding a spanning tree of an undirected, connected graph such that the sum of the weight of selected arcs is at a minimum and, therefore, sometimes it is also referred to as theminimum weight spanning tree problem. The importance of MSTs can be derived from its wide range of both direct and indirect applications, some of which are described in this article. Several efficient solution techniques have been used effectively for many years, playing a central role in generating important ideas for designing algorithms for other combinatorial problems. We discuss two classical algorithms:Prim's algorithmandKruskal's algorithm, followed by recent developments that improve the asymptotic time bounds using advanced data structures.
Split Cuts
Authors: Andersen Kent
Published: February 2011

Split cuts were introduced by Cook and his colleagues in the 1990s. Split cuts are based on the following simple Observation. Given an integer vector π ∈ ℤ

n

, and an integer π
0
 ∈ ℤ, every integer point
x
 ∈ ℤ

n

satisfies the
split disjunction
: either π
T
x
 ≤ π
0
or π
T
x
 ≥ π
0
 + 1. Split cuts are a special case of the
disjunctive cuts
introduced by Balas . The set obtained by adding all split cuts to the linear program (LP) relaxation of a mixed integer program (MIP) is called the
split closure
. We show how split cuts can be obtained from a basis of the LP relaxation of a mixed integer program, and we describe the structure of the split closure. Furthermore, we give a summary of the computational results that have been obtained in the literature on the strength of the split closure as a relaxation of a MIP.
Statistical Methods for Optimization
Authors: Hong L. Jeff
Published: February 2011

Many statistical methods have been proposed to solve stochastic optimization problems where the objective functions are expected values of some random performances. In this article, we consider only ranking and selection: a collection of statistical procedures that intend to select the best solution from a finite (and often small) set of solutions, where the solutions can only be evaluated by running random computer experiments. We review two basic formulations of the problem and summarize how statistically valid procedures are designed to take into consideration the unique features of computer experiments.
Stochastic Hazard Process
Authors: Özekici Süleyman
Published: February 2011

The hazard function describes the probabilistic structure of failures in reliability models. It therefore plays a crucial role in reliability and maintenance of systems that are subject to failures. It is generally assumed to be some deterministic and increasing function of time that explains how a system deteriorates or ages as it is used. In this article, we consider hazard functions that are in fact stochastic. The aim is to demonstrate a variety of cases where this is true and to discuss issues related to computation of system reliability. Most of our discussions focus on stochastic hazard processes generated through modulation via random environments.
Stochastic Dynamic Programming Models and Applications
Authors: Begen Mehmet A.
Published: February 2011

We start with a short comparison of deterministic and stochastic dynamic programming models followed by a deterministic dynamic programming example and several extensions, which convert it to a stochastic one. We then present several applications and highlight some properties of stochastic dynamic programming formulations.
Continuous‐Time Control under Stochastic Uncertainty
Authors: Marti Kurt
Published: February 2011

Control problems from engineering and economics can be represented by a continuous‐time optimal control problem with a convex cost criterion, a nonlinear random differential equation, a stochastic initial state and deterministic or stochastic controls. Thus, the existence and uniqueness of a solution of systems of first‐order differential equations with random parameters is considered first. Then the most important control laws are discussed, such as open‐loop (OL), closed‐loop (CL) as well as the open‐loop feedback (OLF) controls. Since feedback controls can be approximated very efficiently by OLF controls, for practical applications one can confine to the construction of optimal OL controls.

Convex approximations of the underlying control problem are obtained then by “inner” linearization of the given control problem, that is, by a linearization of the dynamic equation. Considering the necessary and sufficient optimality condition for the convex approximation of the original problem, stochastic optimal controls may be represented by means of stochastic optimal control laws obtained by solving certain finite‐dimensional stochastic optimization problems. Using then a stochastic version of the Hamilton–Jacobi theory, stochastic optimal controls may be obtained by solving the related canonical or Hamiltonian system of first‐order differential equations, which is a two‐point boundary value problem with random parameters. Approximate solutions of the two‐point boundary value problem are constructed then by (i) discretization of the underlying probability distribution or (ii) by evaluations of the occurring expectations by means of Taylor expansions with respect to the vector of model parameters. The method is applied to the feedback control of mechanical systems (robots) under stochastic uncertainty.
Supply Chain Coordination
Authors: Zhang Fuqiang
Published: February 2011

Supply chain coordination is among the central issues in supply chain management. A supply chain is coordinated if all supply chain members adopt the actions that optimize the entire system's performance. However, in most cases, supply chain firms are independent, self‐interested entities that may deviate from the system‐optimal actions. This article provides an introductory review on how firms can use various contractual schemes to achieve supply chain coordination. Discussions on additional issues and potential research directions are also provided.
Systems Modeling to Inform Drug Policy
Authors: Caulkins Jonathan P.
Published: February 2011

Illegal drugs cause substantial harm and raise challenging policy problems. Operations research has made important contributions to modeling drug market operations and the effectiveness of various interventions. This article outlines some of the key contributions.
TheG/G/1 Queue
Authors: Foss Sergey
Published: February 2011

The article contains a summary of basic results for a single‐server queue. For the case where interarrival and service times are i.i.d., one can find results on stability and continuity, regenerative structure, moments of stationary waiting times, Little's laws, heavy‐traffic limits, and tail asymptotics (both for light and heavy tails). In the case of stationary and ergodic driving sequences, the key stability result is given.
TheG/G/sQueue
Authors: Breuer Lothar
Published: February 2011

This article provides a literature survey on results for the G/G/s multiserver queue with general interarrival and service time distributions. It further presents two fundamental aspects in a concise yet relatively self‐sufficient form. These are results on the waiting time vectors, derived by Kiefer and Wolfowitz, and the special case of the G/M/s queue with exponential service time distributions, first analyzed by Kendall.
The

G

/

M

/1 Queue
Authors: Perry David
Published: February 2011

The
M
/
G
/1 queue and the
G
/
M
/1 queue represent the mainstay of the single server queueing models. Both models are obtained as special cases of the
G
/
G
/1 queue for which most of the relevant measures and functionals cannot be expressed in closed form formulas. This review is a direct continuation of the encyclopedia entry “The
M
/
G
/1 queue”, and the spirit follows the same direction of that article in the sense that we focus on the same measure and functionals. The approach here is based on the special duality between the
M
/
G
/1 queue and the
G
/
M
/1 queue so that one can use known results of the
M
/
G
/1 queue to derive properties into the
G
/
M
/1 queue.
The Global Replenishment Problem
Authors: Bradley James R. , Guerrero Héctor H.
Published: February 2011

Long transit lead times in supply chains and the uncertainty of demand during the replenishment lead time present a difficult problem of how best to provide the correct assortment of goods at the right time to each destination in a distribution network. However, goods in global supply chains can follow any one of a number of routes from any overseas origin to a particular final destination (retail store or manufacturing site). These alternative routes, and also the choice of how to load shipments in highly assorted loads or in containers with only a small number of products, provide flexibility, which, if properly exercised, can reduce global supply chain costs. We describe replenishment in global supply chains in detail, and we also present a formulation of that replenishment decision problem. We relate that problem to existing literature and describe various simplifications and extensions to the problem.
TheM/G/sQueue
Authors: Kimura Toshikazu
Published: February 2011

This article provides a brief review of exact and approximate results for theM/G/squeue. The principal focus is on the standardM/G/squeue with homogeneous servers, unlimited waiting spaces, and the FCFS (first‐come first‐served) service discipline. According to some asymptotic properties, previously established approximations for the mean waiting time and the queue length distribution in steady state are classified in a unified way. As an application of theM/G/squeue with finite capacity, a buffer design problem is considered to obtain simple approximations for the optimal buffer capacity.
The
M
/
M
/1 Queue
Authors: Hlynka Myron
Published: February 2011

The M/M/1 queueing system is discussed. Key properties are stated, many with proofs. Steady state and transient probabilities are presented along with many other well‐known properties. A variety of analytical techniques are used in the presentation. Graphs are used to illustrate several aspects of this system.
The
M
/
M
/

s

Queue
Authors: Ulukus M. Yasin
Published: February 2011

This article describes the
M
/
M
/
s
queueing system, or Erlang delay model, which is a stochastic service system with a Poisson arrival process and
s
(1 ≤ 
s
 < ∞) independent and identical servers, each of which serves customers in an exponentially distributed amount of time. Arriving customers join an infinite queue if they find all of the
s
servers busy. The main purpose of this article is to summarize the characteristics of the
M
/
M
/
s
system, namely the steady‐state probability distribution of the number of customers in the system, the steady‐state performance parameters, and steady‐state delay probability which is computed using the well‐known Erlang C formula. As a special case of the
M
/
M
/
s
system, we also discuss the
M
/
M
/
s
/
c
queue. Computational issues and some structural properties of the Erlang C formula are also discussed.
Total Expected Discounted Reward
MDPS
: Existence of Optimal Policies
Authors: Feinberg Eugene A.
Published: February 2011

This article describes the results on the existence of optimal and nearly optimal policies for Markov Decision Processes (MDPs) with total expected discounted rewards. The problem of optimization of total expected discounted rewards for MDPs is also known under the name of discounted dynamic programming.
Transient Behavior of
CTMCs
Authors: Distefano Salvatore , Trivedi Kishor S.
Published: February 2011

Since their first specification, Markov models have been widely used for modeling many kinds of systems, in different environments, in application fields, and with different purposes. The success of the formalism of Markov chains is due to the simplicity and the effectiveness in (analytically) evaluating discrete state‐space systems, providing both transient and steady‐state analyses. But the Markovian assumption often limits the applicability of Markov chains. This limitation can be overcome by nonhomogeneous Markov chains and phase type distributions, allowing us to model more general behaviors. This further enhances the importance and the effectiveness of Markov chains and related formalisms. In this article, we focus on the transient behavior of Markov models, providing an overview of their solution techniques.
Transient Behavior of
DTMCs
Authors: Gautam Natarajan
Published: February 2011

The objective of this article is to describe the transient behavior of discrete‐time Markov chains (DTMC). We first provide some notation and terminology necessary for transient analysis. Then we provide a procedure for analyzing a DTMC and predicting the state after a finite number of jumps. Finally, we provide algorithms to efficiently perform transient analysis for DTMCs and obtain performance measures.
Understanding and Managing Variability
Authors: Ahn Hyun‐Soo
Published: February 2011

Variability exists in almost all production and manufacturing systems. Demand and product mix may vary over time, as may the processing capacity of the system and the availability of raw materials and components. Variability in demand or manufacturing processes makes seamless alignment of demand and supply impossible and degrades system performance. Understanding the effects of variability and how to effectively manage them are critical elements to the design and control of production and service systems. This article discusses the sources and types of variability, the effect of variability in manufacturing systems, and managerial tools to mitigate the adverse effects of variability.
Uniformization in
M
arkov Decision Processes
Authors: Alagoz Oguzhan , Ayvaci Mehmet U.S.
Published: February 2011

Continuous‐time Markov decision processes (CTMDP) may be viewed as a special case of semi‐Markov decision processes (SMDP) where the intertransition times are exponentially distributed and the decision maker is allowed to choose actions whenever the system state changes. When the transition rates are identical for each state and action pair, one can convert a CTMDP into an equivalent discrete‐time Markov decision process (DTMDP), which is easier to analyze and solve. In this article, we describe uniformization that uses fictitious transitions from a state to itself and hence enables the conversion of a CTMDP with nonidentical transition rates into an equivalent DTMDP. We first demonstrate the use of uniformization in converting a continuous‐time Markov chain into an equivalent discrete‐time Markov chain, and then describe how it is used in the context of CTMDPs with discounted reward criterion. We also present examples for the use of uniformization in continuous‐time Markov models.
Use ofLagrange Interpolating Polynomials in theRLT
Authors: Adams Warren P.
Published: February 2011

This article examines the use of Lagrange interpolating polynomials (LIPs) in constructing polyhedral outer‐approximations and convex hull representations of mixed‐discrete sets. The LIPs provide the theoretical foundation for extending the reformulation‐linearization technique (RLT), used for automatically computing tight relaxations of mixed‐binary programs, to handle discrete variables that can realize values within finite sets. The LIPs operate by generalizing the idempotent property of binary variablesxthatx2 = x, thereby promoting a hierarchy of progressively tighter forms that culminates in an explicit algebraic characterization of the convex hull of feasible solutions at the highest level. The methods of proof, which employ Kronecker products of transposes of Vandermonde matrices, both subsume and provide insight into the mixed‐binary RLT.
Exact Solution of the Capacitated Vehicle Routing Problem
Authors: Baldacci Roberto , Vigo Daniele , Toth Paolo
Published: February 2011

Vehicle routing problem (VRP) is a generic name given to a whole class of problems concerning the optimal design of routes to be used by a fleet of vehicles to serve a set of customers. The VRP generalizes one of the most famous and important combinatorial optimization problems: the traveling salesman problem (TSP). Since it was first proposed by Dantzig and Ramser in 1959, hundreds of papers in the areas of operations research were devoted to the exact and approximate solution of a member of the VRP class, known as the capacitated vehicle routing problem (CVRP), where a homogeneous fleet of vehicles is available and the only constraint considered is the vehicle capacity constraint. Real‐world applications of the VRP are, for instance, delivery and collection of goods, solid waste collection, street cleaning, school bus routing, dial‐a‐ride systems, transportation of handicapped persons, and routing of salesmen and of maintenance units. This article provides a review of the developments that had a major impact in the current state‐of‐the‐art of exact algorithms for the CVRP. The paper also reports a comparison of the computational performances of the recent exact methods.
Warranty Modeling
Authors: Thomas Marlin U.
Published: February 2011

Warranties have become an essential issue throughout the U.S. and global economy. Consumers rely on warranties for protection against low quality products, while manufacturers use them for marketing and building customer confidence in their products. The difficulties and challenges that manufacturers face in managing warranty programs are due to the risk of product failure and uncertainties in customer preferences and expectations. This article provides an overview of the quantitative models for examining economic decisions involving warranties. Cost models for various warranty policies including reserve fund allocation for future warranty costs are presented, along with models dealing with warranty and maintenance planning decisions.
MACBETH
(Measuring Attractiveness by a Categorical Based Evaluation Technique)
Authors: Bana e Costa Carlos A , de Corte Jean‐Marie , Vansnick Jean‐Claude
Published: February 2011

MACBETH (measuring attractiveness by a categorical based evaluation technique) is an interactive multicriteria decision aid approach used to build a quantitative (numerical) value model, based on qualitative (nonnumerical) pairwise comparison judgments. The MACBETH value‐elicitation procedure described in this article is composed of an input stage aimed at eliciting a consistent set of qualitative judgments of difference in attractiveness between options, and an output stage aimed at constructing an interval value scale from the set of judgments, which numerically measures the relative attractiveness of options for the person or group that made the judgments.
The Strategic Choice Approach
Authors: Friend John
Published: February 2011

The Strategic Choice Approach to planning under pressure has been developed by OR scientists as a means of facilitating communication among decision‐makers with diverse perspectives, allegiances and skills. Its function is to enable them to make sustained progress together in exploring the structure of complex decision problems, and in charting progress towards timely commitments to agreed actions. It offers a balanced set of communication tools which are primarily visual in form, yet are interlinked within a philosophy of planning that recognises the challenges that decision‐makers face in responding strategically to diverse sources of uncertainty, including those that call for a political or structural rather than an analytical response. The principles and leading tools of the approach are briefly introduced, with references to the growing range of applications in fields of collaborative planning ranging from local community action to national environmental policy.
Complementarity Problems
Authors: Konnov Igor V.
Published: February 2011

We consider complementarity problems in a finite‐dimensional space setting. We first describe existence and uniqueness results under norm and order monotonicity assumptions. Relations to some other general nonlinear problems are discussed. Then we describe basic solution methods utilizing the above monotonicity concepts and their convergence properties. We also discuss some extensions of the cases where variables satisfy box‐type constraints or the cost mapping is multivalued.
Sequential Quadratic Programming Methods
Authors: Schittkowski Klaus , Yuan Ya‐Xiang
Published: February 2011

We present a brief review on one of the most powerful methods for solving smooth constrained nonlinear optimization problems, the so‐called sequential quadratic programming (SQP) method. Started during the late 1970s, global and local convergence theorems were proved and efficient codes released. Today, SQP algorithms are the standard tool in academia and industry to solve highly complex application problems.
Tracking Technologies in Supply Chains
Authors: Monsreal Mario M. , Hongyan Dai , Mitchell Tseng , David Brock
Published: February 2011

In recent years, companies have been striving for increased visibility and transparency of activities performed in supply chains. Supply chain tracking systems can provide visibility, traceability, and associated information across different stages of a supply chain, which enables competitive advantages. The efficiency and effectiveness of a tracking system are mainly supported by identification, communication, and information technologies in the supply chain. A better understanding of the various tracking technologies is important due to the fact that there is no single technology that completely covers the entire spectrum of needs and operations in the supply chain. However, there are various relevant technologies available in the market for information registration, capturing, and exchange; and in addition, some technologies have different standards to fit into specific industry sector and operation environments. These technologies complement each other in many ways; for example, some are suitable for outer environments while others work seamlessly inside facilities; and some identify objects while others capture information. It is the intent of this article to understand the main characteristics of different technologies, which play a key role in implementing the tracking system in an effective way. We introduce concepts of tracking system architecture and review most relevant identification, communication, and information technologies. Ultimately, we want to provide an overview of tracking technologies in order to assist decision makers in the processes of evaluation and selection of adequate technology for a design of a tracking system.
Rent and Rent Loss in the Icelandic Cod Fishery
Authors: Arnason Ragnar
Published: February 2011

This article estimates current resource rents being generated in the Icelandic cod fishery and compares them to the maximum sustainable attainable ones. For this purpose, a simple aggregative model of the cod fishery is specified and empirically estimated. It is found that in spite of the cod stock being in a fairly depressed state, substantial economic rents are currently being generated in this fishery. No doubt this is primarily due to the effects of the ITQ system in this fishery. Current rents, however, are only about a third of the rents that would pertain in a profit maximizing sustainable position of this fishery. Thus, compared to the maximum, the Icelandic cod fishery appears to be subject to significant rent loss. Most of the rent gain from the current position of the fishery to the profit maximizing sustainable position is due to an increased cod stock. A much smaller part is due to reduced fishing effort.
Lipschitz Global Optimization
Authors: Sergeyev Yaroslav D. , Kvasov Dmitri E.
Published: February 2011

In this paper, a global optimization problem is considered where the objective function and constraints are multiextremal black‐box functions satisfying the Lipschitz condition over a hyperinterval and hard to evaluate. Such functions are frequently encountered in practice and that explains the great interest of researchers in the stated problem. Some known approaches to solving this problem are briefly described.
Deterministic Global Optimization
Authors: Pardalos Panos M. , Zheng Qipeng P. , Arulselvan Ashwin
Published: February 2011

Global optimization has a wide range of applications, including chemistry, engineering, biology, economics, and physics. It includes a broad range of optimization problems, where both continuous and discrete variables are involved. Unlike many optimization methods that find locally optimal solutions, global optimization methods guarantee a globally optimal solution that is intrinsically difficult to find as there might exists multiple local optima. In this survey article, we make an appraisal of the existing state of affairs in global optimization. We discuss the theoretical and algorithmic advances made in the past decades in the area of global optimization.
Biosurveillance: Detecting, Tracking, and Mitigating The Effects of Natural Disease and Bioterrorism
Authors: Fricker Ronald D.
Published: February 2011

Biosurveillance is the regular collection, analysis, and interpretation of health and health‐related data for indicators of diseases and other outbreaks by public health organizations. Motivated by the threat of bioterrorism, biosurveillance systems are being developed and implemented around the world. The goal of these systems has been expanded to include both, early event detection and situational awareness, so that the focus is not simply on detection, but also on response and consequence management. Whether they are useful for detecting bioterrorism or not, there seems to be consensus that these biosurveillance systems are likely to be useful for detecting and responding to natural disease outbreaks such as seasonal and pandemic flu and thus, they have the potential to significantly advance and modernize the practice of public health surveillance.
Cognitive load theory, modality of presentation and the transient information effect
Authors: Leahy Wayne , Sweller John
Published: February 2011

The modality effect occurs when audio/visual instructions are superior to visual only instructions. The effect was explored in two experiments conducted within a cognitive load theory framework. In Experiment 1, two groups of primary school students (N = 24) were presented with either audio/visual or visual only instructions on how to read a temperature graph. The group presented with visual text and a diagram rather than audio text and a diagram was superior, reversing most previous data on the modality effect. It was hypothesized that the reason for the reversal was that the transitory auditory text component was too long to be processed easily in working memory compared to more permanent written information. Experiment 2 (N = 64) replicated the experiment with the variation of a reduced length of both auditory and visual text instructions. Results indicated a reinstatement of the modality effect with audio/visual instructions proving superior to visual only instructions. Copyright © 2011 John Wiley & Sons, Ltd.
Charge‐Generating Mode Control in High‐Performance Transparent Flexible Piezoelectric Nanogenerators
Authors: Park Hyun‐Kyu , Lee Keun Young , Seo Ju‐Seok , Jeong Jin‐A , Kim Han‐Ki , Choi Dukhyun , Kim Sang‐Woo
Published: February 2011

In this work, we demonstrate the mode transition of charge generation between direct‐current (DC) and alternating‐current (AC) from transparent flexible (TF) piezoelectric nanogenerators (NGs), which is dependent solely on the morphology of zinc oxide (ZnO) nanorods without any use of an AC/DC converter. Tilted ZnO nanorods grown on a relatively low‐density seed layer generate DC‐type piezoelectric charges under a pushing load, whereas vertically aligned ZnO nanorods on a relatively high‐density seed layer create AC‐type charge generation. The mechanism for the geometry‐induced mode transition is proposed and characterized. We also examine the output performance of TF‐NGs which employ an indium zinc tin oxide (IZTO) film as a TF electrode. It is demonstrated that an IZTO film has improved electrical, optical, and mechanical properties, in comparison with an indium tin oxide (ITO) film. Enhanced output charge generation is observed from IZTO‐based TF‐NGs when TF‐NGs composed of only ITO electrodes are compared. This is attributed to the higher Schottky barrier and the lower series resistance of the IZTO‐based TF‐NGs. Thus, by using IZTO, we can expect TF‐NGs with superior mechanical durability and power generating performance.
Highly Conductive PEDOT:PSS Electrode with Optimized Solvent and Thermal Post‐Treatment for ITO‐Free Organic Solar Cells
Authors: Kim Yong Hyun , Sachse Christoph , Machala Michael L. , May Christian , Müller‐Meskamp Lars , Leo Karl
Published: February 2011

Highly conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as stand‐alone electrodes for organic solar cells have been optimized using a solvent post‐treatment method. The treated PEDOT:PSS films show enhanced conductivities up to 1418 S cm−1, accompanied by structural and chemical changes. The effect of the solvent treatment on PEDOT:PSS has been investigated in detail and is shown to cause a reduction of insulating PSS in the conductive polymer layer. Using these optimized electrodes, ITO‐free, small molecule organic solar cells with a zinc phthalocyanine (ZnPc):fullerene C60 bulk heterojunction have been produced on glass and PET substrates. The system was further improved by pre‐heating the PEDOT:PSS electrodes, which enhanced the power conversion efficiency to the values obtained for solar cells on ITO electrodes. The results show that optimized PEDOT:PSS with solvent and thermal post‐treatment can be a very promising electrode material for highly efficient flexible ITO‐free organic solar cells.
Bionanoelectronics: Bionanoelectronics (Adv. Mater. 7/2011)
Authors: Noy Aleksandr
Published: February 2011

Every cell in a living organisms performs a complex array of functions using a vast arsenal of proteins, ion channels, pumps, motors, signaling molecules, and cargo carriers. With all the progress that humankind has made to date in the development of sophisticated machinery and computing capabilities, understanding and communicating with living systems on that level of complexity lags behind. A breakthrough in these capabilities could only come if a way is found to integrate biological components into artificial devices. The central obstacle for this vision of bionanoelectronics is the absence of a versatile interface that facilitates two‐way communication between biological and electronic structures. 1D nanomaterials, such as nanotubes and nanowires, open up the possibility of constructing tight interfaces that could enable such bidirectional flow of information. This report discusses the overall progress in building such interfaces on the level of individual proteins and whole cells and focuses on the latest efforts to create device platforms that integrate membrane proteins, channels, and pumps with nanowire bioelectronics.
Synthesis, Immobilization, MAS and HR‐MAS NMR of a New Chelate Phosphine Linker System, and Catalysis by Rhodium Adducts Thereof
Authors: Guenther J. , Reibenspies J. , Blümel J.
Published: February 2011

A new class of tridentate phosphine ligands with the general formula [MeP{(CH2)xPPh2}3]+I− (x=4, 7, 11) and [MeP(CH2PPh2)3]+OTf−, has been synthesized and fully characterized. The linkers have been immobilized on silica with their phosphonium moieties via electrostatic interactions, and their mobility and leaching has been studied by solid‐state HR‐MAS (high‐resolution magic angle spinning) NMR in various solvents. Immobilized Wilkinson‐type rhodium complexes have been obtained by ligand exchange with the surface‐bound linkers. The activities and lifetimes of the catalysts have been tested with respect to the hydrogenation of 1‐dodecene. The rhodium catalyst precursor bound by the immobilized linker [MeP{(CH2)7PPh2}3]+I− led to material with the highest activity and lifetime, and it could be recycled for 30 times in a batchwise manner. The other catalysts show shorter lifetimes. For all catalysts the formation of rhodium nanoparticles with a narrow size distribution around 4 nm has been proven.
Palladium‐Catalyzed Hydroesterification of Alkynes Employing Aryl Formates without the Use of External Carbon Monoxide
Authors: Katafuchi Yuko , Fujihara Tetsuaki , Iwai Tomohiro , Terao Jun , Tsuji Yasushi
Published: February 2011

A highly efficient hydroesterification of alkynes employing aryl formates has been developed without the use of external carbon monoxide and at ambient pressure. The reaction in the presence of a palladium‐xantphos catalyst system selectively affords α,β‐unsaturated esters in good to high yields. Use of an aryl formate is crucial and alkyl formates did not react at all. The hydroesterification of norbornene and terminal alkenes also readily proceeded under similar reaction conditions. A mechanistic study showed that conversion of aryl formates to carbon monoxide and phenol derivatives occurred in the hydroesterification. Xantphos is highly effective as a ligand both in the conversion of aryl formates and the hydroesterification reactions.
Highly Selective Palladium‐Catalyzed Direct CH α‐Monoarylation of Carbonyl Compounds using Water Containing the Surfactant Polyoxyethylene‐α‐Tocopheryl Sebacate (PTS) as a Solvent
Authors: Lessi Marco , Masini Tiziana , Nucara Luca , Bellina Fabio , Rossi Renzo
Published: February 2011

Highly selective direct CH α‐monoarylation reactions of 4‐chromanones, ketones and 2‐phenylacetaldehyde with aryl halides have been performed in satisfactory yields by using a tris(dibenzylideneacetone)dipalladium(0)/tri‐tert‐butylphosphine tetrafluoroborate catalyst system, potassium bicarbonate as the base and a solvent consisting of pure water containing a small amount of polyoxyethylene‐α‐tocopheryl sebacate (PTS). Analogous reaction conditions have been employed in a tandem process leading to phenyl‐substituted isocoumarins from carbonyl compounds and methyl 2‐bromobenzoate.
Radiation grafting of VAc/HEMA binary monomers onto PFA films for biomedical applications
Authors: El‐Sawy Naeem M. , Abd El‐Rehim Hassan A. , Elbarbary Ahmed M.
Published: February 2011

Grafting of vinyl acetate (VAc), 2‐hydroxyethyl methacrylate (HEMA), and their binary monomer onto poly(tetraflouroethylene‐perflourovinyl ether) (PFA) copolymer films was performed by means of gamma rays from 60Co using the direct method. The factors affecting the grafting yield such as type of solvent, inhibitor concentration, monomer and comonomer concentrations, comonomer composition, and irradiation dose were investigated. It was found that the magnitude of the enhancement depends on the VAc/HEMA ratio in the comonomer feed solution; the grafting yield was higher when VAc‐rich comonomer feed solution is used. The TGA analysis indicated that the copolymerization grafting of VAc/HEMA binary monomers onto PFA matrix improves the thermal stability. The results obtained in this study suggest that PFA‐g‐p(VAc/HEMA) copolymers have the potential to be used as blood‐contacting devices in a broad range of biomedical applications. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30:21–32, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20204
A Systematic Approach to Solvent Selection Based on Cohesive Energy Densities in a Molecular Bulk Heterojunction System
Authors: Walker Bright , Tamayo Arnold , Duong Duc T. , Dang Xuan‐Dung , Kim Chunki , Granstrom Jimmy , Nguyen Thuc‐Quyen
Published: February 2011

The solubilities of 3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione (DPP(TBFu)2) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) in a series of solvents are measured, and this data is used to calculate the Hansen solubility parameters of the two materials. The dispersion, polar, and H‐bonding parameters of DPP(TBFu)2 and PC71BM were found to be (19.3, 4.8, 6.3) and (20.2, 5.4, 4.5) MPa1/2, respectively, with an error of ± 0.8 MPa1/2. Based on the solubility properties of the two materials, three new solvents (thiophene, trichloroethylene and carbon disulfide) were utilized for the DPP(TBFu)2:PC71BM system which, after device optimization, led to power conversion efficiencies up to 4.3%.
In‐situ‐Verfolgung der Bildung kristalliner Feststoffe
Authors: Pienack Nicole , Bensch Wolfgang
Published: February 2011

Die Prozesse, die in den frühen Stadien der Bildung kristalliner Feststoffe ablaufen, sind nur wenig verstanden, sodass eine rationale Synthese neuer Feststoffe weitgehend ausgeschlossen ist. Die Untersuchung der strukturbildenden Prozesse ist eine Herausforderung an analytische und theoretische Methoden, da vor und während einer Nukleation sehr kleine Teilchen oder Aggregate unterschiedlicher chemischer Zusammensetzung und Größe in komplexen und dynamischen Gleichgewichten untersucht werden müssen. Dieser Aufsatz gibt einen Überblick über die Methoden zur In‐situ‐Untersuchung der frühen Kristallisationsstadien von Feststoffen, die helfen können, eine gezieltere Synthese metastabiler Polymorphe, kurzlebiger Intermediate und von Präkursoren mit neuen oder verbesserten Eigenschaften zu erreichen. Beispiele aus aktuellen Forschungsarbeiten sollen die Notwendigkeit und die Potentiale, aber auch die Grenzen der In‐situ‐Verfolgung von Kristallisationsprozessen verdeutlichen.
Von konventionellen zu ungewöhnlichen Gerüsten für Enzyminhibitoren: das Streben nach Spezifität
Authors: Meggers Eric
Published: February 2011

Die enorme Herausforderung der spezifischen molekularen Erkennung einzelner biomakromolekularer Ziele innerhalb komplexer biologischer Systeme erfordert neuartige und kreative Strategien. Dieser Kurzaufsatz beschäftigt sich sowohl mit einigen konventionellen als auch mit ungewöhnlichen Herangehensweisen an die Entwicklung von selektiven Enzyminhibitoren mit besonderem Augenmerk auf die dazu verwendeten chemischen Grundgerüste. Diese beinhalten zum Beispiel komplizierte naturproduktähnliche organische Moleküle, stabile oktaedrische Metallkomplexe, Fullerene, Carborane, polymetallische Cluster und sogar Polymere. Somit ist das ganze Repertoire der organischen, anorganischen und makromolekularen Chemie verfügbar, um die Herausforderung der zielspezifischen Enzyminhibition anzugehen.
In‐Situ Monitoring of the Formation of Crystalline Solids
Authors: Pienack Nicole , Bensch Wolfgang
Published: February 2011

The processes occurring during the early stages of the formation of crystalline solids are not well understood thus preventing the rational synthesis of new solids. The investigation of the structure‐forming processes is an enormous challenge for both analytical and theoretical methods because very small particles or aggregates with different chemical composition and different sizes must be probed, both before and during nucleation. Furthermore, these precursors are present in a complex and dynamic equilibrium. This Review gives a survey of the in‐situ methods available for the study of the early stages of crystallization of solids and how they can help in the synthesis of metastable polymorphs, of transient intermediates, and/or precursors displaying new or improved properties. Examples of actual research demonstrate the necessity and potentials but also the limitations of in‐situ monitoring of the formation of crystalline solids.
Morphology and rheology of composites based on anisotropic polymer matrix and different clays
Authors: Vasilyev G. B. , Makarova V. V. , Rebrov A. V. , Picken S. J. , Smirnova N. M. , Malkin A. Ya. , Kulichikhin V. G.
Published: February 2011

Structure and rheological properties of hybrids with polymer matrix and layered silicates as filler were studied. Solution containing 60% wt of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycol (PEG) was used as a matrix. The peculiarity of this study is that the matrix depending on temperature can form different phase states including liquid‐crystalline (LC). So, a possibility of coexistence and superposition of different ordered structures can be realized at different temperatures. Three different fillers were used: natural Na‐montmorillonite (MMT) and organoclays obtained by treating MMT with surfactants varying in polarity of their molecules. Depending on the type of clay, materials with different morphology can be obtained. X‐ray data showed that PEG intercalates all types of clay used whereas penetration of HPC macromolecules into clay galleries during mixing does not occur. Clay modified with more polar surfactant should be treated as the most convenient material to be intercalated by PEG. Rheological studies (included steady‐state and dynamic shear properties in a wide temperature range) demonstrate that composites are viscoplastic materials and the yield stress is observed already at 5% fillers loading. The level of the yield stress depends on the phase state of the matrix being induced by the superposition of structures formed by clay particles as well as by the LC phase (if it exists). The same conclusion can be made on the base of linear oscillatory measurements because the existence of the LC phase and/or the presence of filler lead to a pseudo solid‐like behavior of a system as whole. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
The effect of carbon nanofiber on the thermo‐physical behavior of polyethylene oxide
Authors: Adhikari A. R. , Lozano K. , Chipara M. , Qualls J.
Published: February 2011

Composites of polyethylene oxide (PEO) filled with carbon nanofiber (CNF) were prepared using solution mixing followed by melt mixing. The morphology and thermophysical properties of these composites and of pristine polyethylene oxide were analyzed by scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamical mechanical analysis. Crystallization kinetic data were analyzed within the Avrami approximation for the primary stage of crystallization. The influence of CNF on the temperature dependence crystallization of PEO and the tendency of forming three‐dimensional crystallites at higher crystallization temperature were observed. The nucleation features of CNFs dispersed within PEO were investigated by using Lauritzen‐Hoffman nucleation theory. Crystallization activation energies were also computed; the results are in agreement with the Lauritzen–Hoffman theory. Thermogravimetric analysis and dynamical mechanical analysis showed a gradual increase of the thermal stability and of the storage modulus of the polymeric matrix due to the loading with CNFs and formation of a polymer–carbon nanofiber interface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Short‐term flexural creep behavior and model analysis of a glass‐fiber‐reinforced thermoplastic composite leaf spring
Authors: Subramanian C. , Senthilvelan S.
Published: February 2011

Present work investigated the short‐term flexural creep performance of fiber reinforced thermoplastic injection molded leaf springs. Unreinforced polypropylene, 20 wt % short and 20 wt % long glass fiber reinforced polypropylene materials were injection‐molded into constant thickness varying width mono leaf spring. Short‐term flexural creep tests were performed on molded leaf springs at various stress levels with the aid of in‐house developed fixture integrated with the servo‐hydraulic fatigue machine. Spring rate reduction is reported as an index for the accumulated damage. Experimental creep performance of molded leaf springs for 2 h was utilized to predict the creep performance with the aid of four parameter HRZ model and compared with 24‐h experimental creep data. Test results revealed that HRZ model is sufficient enough to predict short‐time flexural creep performance of engineering products over wide range of stress. Test results also confirmed the suitability of long fiber reinforced thermoplastic material for creep application over other considered materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011