bluuebunny/crossref_metadata_2025 huggingface dataset:
DEA models for two‐stage processes: Game approach and efficiency decomposition
Authors: Liang Liang , Cook Wade D. , Zhu Joe
Published: August 2008

Data envelopment analysis (DEA) is a method for measuring the efficiency of peer decision making units (DMUs). This tool has been utilized by a number of authors to examine two‐stage processes, where all the outputs from the first stage are the only inputs to the second stage. The current article examines and extends these models using game theory concepts. The resulting models are linear, and imply an efficiency decomposition where the overall efficiency of the two‐stage process is a product of the efficiencies of the two individual stages. When there is only one intermediate measure connecting the two stages, both the noncooperative and centralized models yield the same results as applying the standard DEA model to the two stages separately. As a result, the efficiency decomposition is unique. While the noncooperative approach yields a unique efficiency decomposition under multiple intermediate measures, the centralized approach is likely to yield multiple decompositions. Models are developed to test whether the efficiency decomposition arising from the centralized approach is unique. The relations among the noncooperative, centralized, and standard DEA approaches are investigated. Two real world data sets and a randomly generated data set are used to demonstrate the models and verify our findings. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008
Scheduling multiple products on parallel machines with setup costs
Authors: Krasik Vladimir , Leung Joseph , Pinedo Michael , Zhang Jiawei
Published: August 2008

We consider a class of production scheduling models with m identical machines in parallel and k different product types. It takes a time pi to produce one unit of product type i on any one of the machines. There is a demand stream for product type i consisting of ni units with each unit having a given due date. Before a machine starts with the production of a batch of products of type i a setup cost c is incurred. We consider several different objective functions. Each one of the objective functions has three components, namely a total setup cost, a total earliness cost, and a total tardiness cost. In our class of problems we find a relatively large number of problems that can be solved either in polynomial time or in pseudo‐polynomial time. The polynomiality or pseudo‐polynomiality is achieved under certain special conditions that may be of practical interest; for example, a regularity pattern in the string of due dates combined with earliness and tardiness costs that are similar for different types of products. The class of models we consider includes as special cases discrete counterparts of a number of inventory models that have been considered in the literature before, e.g., Wagner and Whitin (Manage Sci 5 (1958), 89–96) and Zangwill (Oper Res 14 (1966), 486–507; Manage Sci 15 (1969), 506–527). © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008
A novel modeling approach for express package carrier planning
Authors: Root Sarah , Cohn Amy
Published: August 2008

Express package carrier networks have large numbers of heavily‐interconnected and tightly‐constrained resources, making the planning process difficult. A decision made in one area of the network can impact virtually any other area as well. Mathematical programming therefore seems like a logical approach to solving such problems, taking into account all of these interactions. The tight time windows and nonlinear cost functions of these systems, however, often make traditional approaches such as multicommodity flow formulations intractable. This is due to both the large number of constraints and the weakness of the linear programming (LP) relaxations arising in these formulations. To overcome these obstacles, we propose a model in which variables represent combinations of loads and their corresponding routings, rather than assigning individual loads to individual arcs in the network. In doing so, we incorporate much of the problem complexity implicitly within the variable definition, rather than explicitly within the constraints. This approach enables us to linearize the cost structure, strengthen the LP relaxation of the formulation, and drastically reduce the number of constraints. In addition, it greatly facilitates the inclusion of other stages of the (typically decomposed) planning process. We show how the use of templates, in place of traditional delayed column generation, allows us to identify promising candidate variables, ensuring high‐quality solutions in reasonable run times while also enabling the inclusion of additional operational considerations that would be difficult if not impossible to capture in a traditional approach. Computational results are presented using data from a major international package carrier. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008
Replacing nonidentical vital components to extend system life
Authors: Shechter Steven M. , Bailey Matthew D. , Schaefer Andrew J.
Published: August 2008

We consider a system that depends on a single vital component. If this component fails, the system life will terminate. If the component is replaced before its failure then the system life may be extended; however, there are only a finite number of spare components. In addition, the lifetimes of these spare components are not necessarily identically distributed. We propose a model for scheduling component replacements so as to maximize the expected system survival. We find the counterintuitive result that when comparing components' general lifetime distributions based on stochastic orderings, not even the strongest ordering provides an a priori guarantee of the optimal sequencing of components. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008
Competitive location and capacity decisions for firms serving time‐sensitive customers
Authors: Kwasnica Anthony M. , Stavrulaki Euthemia
Published: August 2008

In this article we explore how two competing firms locate and set capacities to serve time‐sensitive customers. Because customers are time‐sensitive, they may decline to place an order from either competitor if their expected waiting time is large. We develop a two‐stage game where firms set capacities and then locations, and show that three types of subgame perfect equilibria are possible: local monopoly (in which each customer is served by a single firm, but some customers may be left unserved), constrained local monopoly (in which firms serve the entire interval of customers but do not compete with each other), and constrained competition (in which firms also serve the entire interval of customers, but now compete for some customers). We perform a comparative statics analysis to illustrate differences in the equilibrium behavior of a duopolist and a coordinated monopolist. © 2008 Wiley Periodicals, Inc. Naval Research Logistics, 2008
Minimising the effects of bolus dispersion in bolus‐tracking MRI
Authors: Willats L. , Connelly A. , Calamante F.
Published: August 2008

Bolus‐tracking perfusion measurements in patients with vascular abnormalities are often unreliable, because delay and/or dispersion of the bolus within the vessels distorts the measured arterial input function (AIF). Erroneous measurements of perfusion can be identified by examining the measured response function, the shape of which is determined by both the tissue and arterial retention. In this work, an accurate response function is extracted by combining maximum‐likelihood expectation‐maximisation deconvolution, regularised using an oscillation index, with subsequent wavelet thresholding. Simulations show that this method recovers both the smooth‐dispersed and the sharp‐delayed response functions. This enables regions where the bolus is delayed and/or dispersed to be identified when the methodology is applied to data from patients with vascular abnormalities. Simulations also demonstrate robust and accurate perfusion estimates when there is no bolus delay and/or dispersion. The presence of delay and/or dispersion in the response function suggests that the perfusion measurements are erroneous, and that the global AIF is an inaccurate approximation to the true AIF in these regions. Perfusion measurements are corrected within the affected regions by defining a regional AIF from the independent component analysis of the dynamic susceptibility contrast MRI data. The regional AIF is shown to remove the delay and dispersion, improving the accuracy of the perfusion maps. Copyright © 2008 John Wiley & Sons, Ltd.
First‐pass dynamic contrast‐enhanced MRI with extravasating contrast reagent: evidence for human myocardial capillary recruitment in adenosine‐induced hyperemia
Authors: Li Xin , Springer Charles S. , Jerosch‐Herold Michael
Published: August 2008

Human myocardial 1H2O T1‐weighted dynamic contrast‐enhanced MRI data were acquired during the brief first‐pass period after injection of a very small gadolinium diethylenetriaminepenta‐acetate (GdDTPA2−) dose. The shutter‐speed pharmacokinetic effects of both transendothelial and transcytolemmal equilibrium water exchange processes were investigated. Our results indicate that even for such a short acquisition window and relatively large pseudo‐first‐order rate constant (Ktrans) for plasma/interstitium contrast reagent (CR) transfer the kinetics of these water exchange processes cannot be treated as infinitely fast or slow. However, neither the intracellular water molecule lifetime (τi) nor its intravascular counterpart (τb) are among the parameters most influential in analysis of the noisy data typically associated with the cardiac perfusion application. Thus, the actual values of water exchange kinetic rate constants are relatively indeterminate as this experiment is usually conducted. Combining the Ktrans evaluations with independently determined flow (F) values allows us to estimate CR permeability coefficient surface area product (PCRS) values. The fact that the PCRS magnitudes almost equal the Ktrans values confirms that GdDTPA2− extravasation in resting human myocardial muscle is indeed permeation‐limited and supports the validity of the Ktrans and PCRS estimations. Nevertheless the model analysis is most consistent with the results if PCRS is not assumed to be constant with changing flow. The capillary blood volume fraction (vb) is a sensitive parameter in the analysis. We also compared resting and hyperemic cardiac conditions, the latter resulting from the volume flow increase induced by adenosine arteriolar vasodilation. We found that the PCRS value increases with flow probably mostly because of an S increase associated with capillary recruitment. The vb values also increased in hyperemia and showed a flow‐dependence with a clearly identifiable component due to capillary recruitment. Copyright © 2008 John Wiley & Sons, Ltd.
Effective condition number of Trefftz methods for biharmonic equations with crack singularities
Authors: Li Zi‐Cai , Lu Tzon‐Tzer , Wei Yimin
Published: August 2008

The paper presents the new stability analysis for the collocation Trefftz method (CTM) for biharmonic equations, based on the new effective condition number Cond_eff. The Trefftz method is a special spectral method with the particular solutions as admissible functions, and it has been widely used in engineering. Three crack models in Li et al. (Eng. Anal. Boundary Elements 2004; 28:79–96; Trefftz and Collocation Methods. WIT Publishers: Southampton, Boston, 2008) are considered, and the bounds of Cond_eff and the traditional condition number Cond are derived, to give the polynomial and the exponential growth rates, respectively. The stability analysis explains well the numerical experiments. Hence, the new Cond_eff is more advantageous than Cond. Besides since the bounds of Cond_eff and Cond involve the estimation of the minimal singular value σmin of the discrete matrix F, and since the estimation of σmin is challenging and difficult, the proof for lower bounds of σmin in this paper is important and intriguing. Copyright © 2008 John Wiley & Sons, Ltd.
Two classes of multisecant methods for nonlinear acceleration
Authors: Fang Haw‐ren , Saad Yousef
Published: August 2008

Many applications in science and engineering lead to models that require solving large‐scale fixed point problems, or equivalently, systems of nonlinear equations. Several successful techniques for handling such problems are based on quasi‐Newton methods that implicitly update the approximate Jacobian or inverse Jacobian to satisfy a certain secant condition.

We present two classes of multisecant methods which allow to take into account a variable number of secant equations at each iteration. The first is the Broyden‐like class, of which Broyden's family is a subclass, and Anderson mixing is a particular member. The second class is that of the nonlinear Eirola–Nevanlinna‐type methods.

This work was motivated by a problem in electronic structure calculations, whereby a fixed point iteration, known as the self‐consistent field (SCF) iteration, is accelerated by various strategies termed ‘mixing’. Copyright © 2008 John Wiley & Sons, Ltd.
On parallel multisplitting methods for symmetric positive semidefinite linear systems
Authors: Cao Guangxi , Song Yongzhong
Published: August 2008

In this paper we propose some parallel multisplitting methods for solving consistent symmetric positive semidefinite linear systems, based on modified diagonally compensated reduction. The semiconvergence of the parallel multisplitting method is discussed. The results here generalize some known results for the nonsingular linear systems to the singular systems. Copyright © 2008 John Wiley & Sons, Ltd.
Modeling shear bands in J2 plasticity using a two‐scale formulation via embedded strong discontinuity modes
Authors: D'hers Sebastián , Dvorkin Eduardo N.
Published: August 2008

A new two‐scale finite element formulation was developed for modeling J2 plastic deformation processes (2D) in which shear band localizations take place. The formulation is based on the use of embedded strong discontinuity modes, which are triggered using a stress‐based criterion. The new formulation does not require a specific mesh refinement to model the localization phenomena and provides mesh‐independent results. The shear bands constitutive behavior is derived from the continuum properties without the introduction of any ad hoc physical law. Copyright © 2008 John Wiley & Sons, Ltd.
Pointwise supercloseness of tensor‐product block finite elements
Authors: Liu Jinghong , Zhu Qiding
Published: August 2008

In this article, we first introduce interpolation operator of projection type in three dimensions, from which we then derive weak estimates for tensor‐product block finite elements of degree m ≥ 1. Finally, using estimates for the discrete Green's function and the discrete derivative Green's function, we prove that both of the gradient and the function value of the finite element solution uh and the corresponding interpolant Πmu of projection type and degree m are superclose in the pointwise sense of the L∞‐norm. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009
Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes
Authors: Sui G. , Zhong W. H. , Yang X. P. , Yu Y. H. , Zhao S. H.
Published: August 2008

In order to achieve dramatic improvements in the performance of rubber materials, the development of carbon nanotube (CNT)‐reinforced rubber composites was attempted. The CNT/natural rubber (NR) nanocomposite was prepared through solvent mixing on the basis of pretreatment of CNTs. Thermal properties, vulcanization characteristics, and physical and mechanical properties of the CNT/NR nanocomposites were characterized in contrast to the carbon black (CB)/NR composite. Through the addition of the CNTs treated using acid bath followed by ball milling with HRH (hydrated silica, resorcinol, and hexamethylene tetramine) bonding systems, the crystallization melting peak in differential scanning calorimetry (DSC) curves of NR weakened and the curing rate of NR slightly decreased. Meanwhile, the over‐curing reversion of CNT/NR nanocomposites was alleviated. The dispersion of the treated CNTs in the rubber matrix and interfacial bonding between them were rather good. The mechanical properties of the CNT‐reinforced NR showed a considerable increase compared to the neat NR and traditional CB/NR composite. At the same time, the CNT/NR nanocomposites exhibited better rebound resilience and dynamic compression properties. The storage modulus of the CNT/NR nanocomposites greatly exceeds that of neat NR and CB/NR composites under all temperature regions. The thermal stability of NR was also obviously improved with the addition of the treated CNTs. Copyright © 2008 John Wiley & Sons, Ltd.
Pt/SiO2 as addition to multilayer SPSU/PTFE composite membrane for fuel cells
Authors: Wang L. , Yi B. L. , Zhang H. M. , Xing D. M.
Published: August 2008

A multilayer composite membrane was prepared by reinforcing sulfonated polysulfone (SPSU) with porous polytetrafluoroethylene (PTFE), and adding Pt/SiO2–Nafion® membranes on both sides of the SPSU/PTFE membrane to self‐humidify and protect the inside membrane. The ex situ Fenton test and open circuit voltage (OCV) accelerated test show that the composite membrane has better stability than the initial membrane because of the protection of the outside Pt/SiO2–Nafion layers. The composite membrane has similar performance to that of NRE‐212 under the fully humidified condition and better performance than NRE‐212 without humidifying. The self‐humidifying membrane shows great potential for use in low humidifying conditions. Copyright © 2008 John Wiley & Sons, Ltd.
Lipase‐catalyzed polymerization of L‐lactide in ionic liquids
Authors: Yoshizawa‐Fujita Masahiro , Saito Chihiro , Takeoka Yuko , Rikukawa Masahiro
Published: August 2008

Lipase‐catalyzed polymerizations of L‐lactide were carried out in four kinds of ionic liquids (ILs) in order to investigate the effect of ILs on the conversion, molecular weight, and yield of the obtained poly(lactide) (PLLA). PLLA could be synthesized in ILs of 1‐butyl‐3‐methylimidazolium ([C4mim]) except in [C4mim][N(CN)2]. While the number‐average molecular weight (Mn) of the PLLA obtained in [C4mim][PF6] was below 4000 g mol−1 and the yield was below 10%, the Mn and yield of the PLLA obtained in [C4mim][BF4] reached 55000 g mol−1 and 35%, respectively. The Mn values of PLLAs in the ILs were clearly higher than those of PLLAs obtained in bulk and in toluene (<44000 g mol−1). The polymerization in the ILs proceeds even at lower temperatures as compared with that in bulk. The effect of lipase content on the Mn of PLLA was also investigated. When [C4mim][BF4] was used as the solvent, the highest Mn was obtained at a lipase content of 10 wt%. In the case of [C4mim][NTf2], the most suitable lipase content depended on the polymerization temperature. [C4mim][BF4] was suitable to obtain higher molecular weight PLLA and higher polymer yield at lower lipase contents. Copyright © 2008 John Wiley & Sons, Ltd.
Overexpression of TFAP2C in invasive breast cancer correlates with a poorer response to anti‐hormone therapy and reduced patient survival
Authors: Gee JMW , Eloranta JJ , Ibbitt JC , Robertson JFR , Ellis IO , Williams T , Nicholson RI , Hurst HC
Published: August 2008

The AP‐2γ transcription factor encoded by the TFAP2C gene is a member of a family of homologous DNA binding proteins that play essential roles during vertebrate embryogenesis but show a restricted pattern of expression in the adult. Elevated expression of the AP‐2α and AP‐2γ family members has been associated with a number of neoplasms, particularly breast cancer. Here we present an exploratory immunohistochemical study of an archival primary breast tumour series (n = 75) with parallel clinicopathological data using a new, well‐characterized antibody to AP‐2γ. Heterogeneous, exclusively nuclear expression of AP‐2γ was found in the epithelial and myoepithelial compartments of normal breast and within tumour epithelial cells. In the breast cancer series, the most notable association was a correlation between elevated levels of AP‐2γ and shortened patient survival (p = 0.0009*). This relationship was also conserved in ER‐positive and ErbB2‐negative patients; sub‐groups generally considered to have a relatively good prognosis. When patient data for survival and duration of treatment response on anti‐hormone therapy were examined by multivariate analysis, AP‐2γ was revealed in this study to be an independent predictor of outcome for both survival (p = 0.005) and response to anti‐hormone therapy (p = 0.046). Studies using in vitro models confirmed that while tamoxifen response is associated with lower levels of AP‐2γ, acquisition of resistance to this and other anti‐hormone measures (eg faslodex or oestrogen deprivation) is associated with high levels of nuclear AP‐2γ. Together these data suggest that elevated tumour AP‐2γ expression can contribute to the failure of cells to growth arrest following anti‐hormone treatment and lead to sustained growth and poorer patient outcome. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Role of Necl‐5 in the pathophysiology of colorectal lesions induced by dimethylhydrazine and/or dextran sodium sulphate
Authors: Abe A , Fukui H , Fujii S , Kono T , Mukawa K , Yoshitake N , Sekikawa A , Ichikawa K , Tomita S , Yamagishi H , Imai Y , Shinoda M , Ishizaki H , Tanaka‐Okamoto M , Kubota K , Miyoshi J , Takai Y , Fujimori T
Published: August 2008

Necl‐5 is an immunoglobulin‐like molecule that was originally identified as a poliovirus receptor. Although Necl‐5 expression is often up‐regulated in cancer cells, its pathophysiological significance in the development of cancer remains unclear. We investigated the roles of Necl‐5 in the development of colitis‐associated neoplasia. Necl‐5‐deficient mice were generated and treated with dimethylhydrazine (DMH) and/or dextran sodium sulphate (DSS) to induce colitis and its associated neoplasias. Colon tissues were examined for histology, Ki‐67 expression by immunohistochemistry and K‐ras gene mutation. Colon tumours occurred significantly less frequently in heterozygous (Necl‐5+/−) or homozygous Necl‐5‐deficient (Necl‐5−/−) mice than in wild‐type (WT) mice with DMH/DSS treatment. Total ulcer index and inflammatory cell infiltration were significantly lower in Necl‐5−/− mice than in WT mice with DSS alone or DMH/DSS treatment. Colon tumours in both WT and Necl‐5−/− mice showed high cell proliferation ability but lacked K‐ras mutation. The total Ki‐67 labelling index in non‐neoplastic colon epithelium was significantly higher in WT (45.9 ± 0.94) than in Necl‐5+/− (34.3 ± 1.40) or Necl‐5−/− (27.7 ± 1.15) mice with DMH/DSS treatment (p < 0.001). Necl‐5 plays a role in the development of colitis‐associated cancer by up‐regulating colonic mucosal cell proliferation. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
SAHA induces caspase‐independent, autophagic cell death of endometrial stromal sarcoma cells by influencing the mTOR pathway
Authors: Hrzenjak A , Kremser M‐L , Strohmeier B , Moinfar F , Zatloukal K , Denk H
Published: August 2008

Endometrial stromal sarcomas are rare and molecular mechanisms involved in their pathogenesis are poorly understood. Covalent modifications of histone proteins, in particular de/acetylation of lysine residues, play an important role in the regulation of gene transcription in normal and neoplastic cells, but there are only limited data about these processes in solid mesenchymal tumours. We treated endometrial stromal sarcoma cells (ESS‐1) and non‐malignant human endometrial stromal cells (HESCs) with suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor. SAHA was able to mediate the cell cycle and expression of genes related to the malignant phenotype of endometrial stromal tumours, eg p21WAF1 and HDAC7. SAHA led to dose‐dependent differentiation and death of ESS‐1 cells but not of HESCs. Exposure of HESCs to SAHA resulted only in slightly decreased cell proliferation. SAHA also increased the p21WAF1 expression and caused significant changes in the cell cycle by inhibiting the G1/S transition in ESS‐1 cells. Recovery experiments indicated that these changes became irreversible when the tumour cells were treated with SAHA for longer than 24 h. In our experimental system, not apoptotic but autophagic processes were responsible for the cell death. Monodansyl cadaverine accumulation in treated ESS‐1 cells and decreased expression of the mTOR and phospho‐S6 ribosomal protein (S6rp) additionally supported this observation. Taken together, our study indicates that HDACs might be considered as potential drug targets in the therapy of stromal sarcomas and that SAHA might be a promising therapeutic agent for endometrial stromal sarcoma. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Insulin‐like growth factor‐1 receptor acts as a growth regulator in synovial sarcoma
Authors: Friedrichs N , Küchler J , Endl E , Koch A , Czerwitzki J , Wurst P , Metzger D , Schulte JH , Holst MI , Heukamp LC , Larsson O , Tanaka S , Kawai A , Wardelmann E , Buettner R , Pietsch T , Hartmann W
Published: August 2008

Synovial sarcomas account for 5–10% of all soft tissue sarcomas and the majority of synovial sarcomas display characteristic t(X;18) translocations that result in enhanced transcription of the insulin‐like growth factor‐2 (IGF‐2) gene. IGF‐2 is an essential fetal mitogen involved in the pathogenesis of different tumours, leading to cellular proliferation and inhibition of apoptosis. Here we asked whether activation of IGF signalling is of functional importance in synovial sarcomas. We screened human synovial sarcomas for expression of IGF‐2 and the phosphorylated IGF‐1 receptor (IGF‐1R), which mainly mediates the proliferative and anti‐apoptotic effects of IGF‐2. Since both the phosphatidylinositol 3′‐kinase (PI3K)–AKT pathway and the MAPK signalling cascade are known to be involved in the transmission of IGF‐1R signals, expression of phosphorylated (p)‐AKT and p‐p44/42 MAPK was additionally assessed. All tumours expressed IGF‐2 and 78% showed an activated IGF‐1R. All tumours were found to express p‐AKT and 92% showed expression of activated p44/42 MAPK. To analyse the functional and potential therapeutic relevance of IGF‐1R signalling, synovial sarcoma cell lines were treated with the IGF‐1R inhibitor NVP‐AEW541. Growth was impaired by the IGF‐1R antagonist, which was consistently accompanied by a dose‐dependent reduction of phosphorylation of AKT and p44/42 MAPK. Functionally, inhibition of the receptor led to increased apoptosis and diminished mitotic activity. Concurrent exposure of selected cells to NVP‐AEW541 and conventional chemotherapeutic agents resulted in positive interactions. Finally, synovial sarcoma cell migration was found to be dependent on signals transmitted by the IGF‐1R. In summary, our data show that the IGF‐1R might represent a promising therapeutic target in synovial sarcomas. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Number‐average molecular weight of branched polymers from SEC with viscosity detection and universal calibration
Authors: Netopilík Miloš , Podešva Jiří , Lokaj Jan , Kratochvíl Pavel
Published: August 2008

BACKGROUND: Number‐average molecular weight, M̄n, is an important characteristic of synthetic polymers. One of the very few promising methods for its determination is size‐exclusion chromatography (SEC) using on‐line viscometric detection and assuming the validity of the universal calibration concept.

RESULTS: We have examined the applicability of this approach to the characterization of statistically branched polymers using 22 copolymers of styrene and divinylbenzene as well as 3 homopolymers of divinylbenzene with various degrees of branching. SEC with three on‐line detectors, i.e. concentration, light scattering and viscosity, enables us to evaluate experimental data by various computational procedures yielding M̄n and weight‐average molecular weight, M̄w. Analysis of the results has shown that the universal calibration theorem has limited validity, apparently due to the dependence of the Flory viscosity function on the molecular shape, the molecular weight distribution and the expansion of molecules.

CONCLUSION: For complex polymers, the universal calibration, i.e. the dependence of the product of intrinsic viscosity and molecular weight, [η]M, on elution volume, can differ in values of [η]M from those obtained for narrow molecular weight standards by 10–15%. The method studied is helpful for the determination of M̄n of polymers, in particular of those with very broad molecular weight distribution, such as statistically highly branched polymers. Copyright © 2008 Society of Chemical Industry
Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels
Authors: Liu Hongliang , Liu Mingzhu , Jin Shuping , Chen Shilan
Published: August 2008

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent.

RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy.

CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry
Computational (MP2 and DFT) modeling of the substrate/inhibitor interaction with the LDH active pocket in the gas phase and aqueous solution: bimolecular charged (pyruvate/oxamate–guanidinium cation) and neutral adducts (pyruvic/oxamic acids–guanidine)
Authors: Raczyńska Ewa D. , Makowski Mariusz , Hallmann Magorzata , Duczmal Kinga
Published: August 2008

Two types of bimolecular adducts were studied for the substrate and inhibitor of lactate dehydrogenase (LDH), one type of adducts between ionic species,α‐keto‐carboxylates (pyruvate and oxamate) and the guanidinium cation, and the other type of adducts between neutral species,α‐ketocarboxylic (pyruvic and oxamic) acids and guanidine. Calculations were performed in the gas phase and aqueous solution using the MP2 and PCM methods and the 6‐31++G** basis set. Application of the DFT(B3LYP) and PCM methods led to similar results. A change of the adducts' preference was observed when proceeding from the gas phase to aqueous solution. This change is in good agreement with the acidity–basicity scales in both phases. Formation constant (KHB) for adduct between neutral species is greater for pyruvic than for oxamic acid in the gas phase, whereas a reverse situation takes place in aqueous solution, where theKHBvalue for adduct between ionic species is smaller for pyruvate than for oxamate. The water molecules favor interactions of more polar oxamate with the guanidinium cation. Stronger interaction with this cation, a model of the arginine fragment of the LDH pocket, suggests that oxamate (inhibitor of LDH) has stronger binding properties in aqueous solution than pyruvate (substrate of LDH). Copyright © 2008 John Wiley & Sons, Ltd.
What governs nitrogen configuration in substituted aminophosphines?
Authors: Wodrich Matthew D. , Vargas Alfredo , Morgantini Pierre‐Yves , Merino Gabriel , Corminboeuf Clémence
Published: August 2008

The trigonal planar geometry of the nitrogen atom in commonly used phosphoramidite ligands is not in line with the traditional valence shell electron pair repulsion (VSEPR) model. In this work, the effects governing nitrogen configuration in several substituted aminophosphines, A2PNB2 (A or B = H, F, Cl, Br, Me, OMe, BINOP), are examined using modern computational analytic tools. The electron delocalization descriptions provided by both electron localization function (ELF) and block localized wavefunction analysis support the proposed relationships between conformation and negative hyperconjugative interactions. In the parent H2PNH2, the pyramidal nitrogen configuration results from nitrogen lone pair electron donation into the σ* PH orbital. While enhanced effects are seen for F2PNMe2, placing highly electronegative fluorine substituents on nitrogen (i.e., Me2PNF2) eliminates delocalization of the nitrogen lone pair. Understanding and quantifying these effects can lead to greater flexibility in designing new catalysts. Copyright © 2008 John Wiley & Sons, Ltd.
Quinoline formation via a modified Combes reaction: examination of kinetics, substituent effects, and mechanistic pathways
Authors: Sloop Joseph C.
Published: August 2008

This is the first reported investigation of the Combes condensation employing 19F NMR spectroscopy to monitor intermediate consumption and product formation rates. The reaction was found to be first order in both the diketone and aniline. Product regioselectivity and reaction rates were found to be influenced by substituents on the diketones and anilines with rates varying as much as five fold. The consumption rate of key imine and enamine intermediates mirrored quinoline formation rates, in accord with rate determining annulation. A ρ of −0.32 was determined for this cyclization. While the sign of the reaction constant is consistent with rate limiting electrophilic aromatic substitution (EAS), the magnitude is likely a composite value, resulting from opposing substituent effects in the nucleophilic addition and EAS steps. Mechanistic details and reaction pathways supporting these findings are proposed. Copyright © 2008 John Wiley & Sons, Ltd.
Syntheses, characterization, and functionalization of poly(ester amide)s with pendant amine functional groups
Authors: De Wit Matthew A. , Wang Zixi , Atkins Katelyn M. , Mequanint Kibret , Gillies Elizabeth R.
Published: August 2008

Poly(ester amide)s (PEAs) comprising α‐amino acids, diols, and diacids are promising materials for biomedical applications such as tissue engineering and drug delivery because of their tunability and potential for either hydrolytic or enzymatic degradation. Although a number of PEAs of different compositions have been reported, there is a significant need for the incorporation of amino acids with functional side chains. This will allow for the conjugation of drugs or cell signaling molecules in tissue engineering scaffolds, thus expanding the potential applications of these materials. The objective of this work was the incorporation of l‐lysine into PEAs to provide functionalizable pendant amine groups. Thus, varying percentages of lysine were incorporated into PEAs comprised of l‐phenylalanine, 1,4‐butanediol, and succinic acid by tuning the ratio of ε‐protected‐l‐lysine and l‐phenylalanine derived monomers. The polymers were characterized by nuclear magnetic resonance spectroscopy, infrared spectroscopy, size exclusion chromatography, and differential scanning calorimetry. The lysine ε‐protecting group was removed, then the reactivity of the pendant amines was demonstrated by reaction with amino acid and tri(ethylene glycol) derivatives. The degradation of thin films of polymers were studied using scanning electron microscopy and the incorporation of lysine was found to significantly accelerate both the hydrolytic and enzymatic degradation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6376–6392, 2008
Ethylene‐based copolymers with tunable content of polymerizable hindered phenols as nonreleasing macromolecular additives
Authors: Menichetti Stefano , Viglianisi Caterina , Liguori Francesca , Cogliati Clelia , Boragno Luca , Stagnaro Paola , Losio Simona , Sacchi Maria Carmela
Published: August 2008

Four comonomers bearing a highly efficient phenolic antioxidant unit and different methylene spacers between the aromatic ring and the double bond have been prepared and tested in copolymerization with ethylene using metallocene‐based catalysts. The possibility of obtaining a “masterbatch” suitable for melt blending with commercial polyolefins has been evaluated by modifying: (i) the structure of the functionalized comonomer, (ii) the kind of catalyst, and (iii) the polymerization conditions. Characterization of monomers and copolymers was accomplished by using 1H and 13C NMR, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Using the comonomer with the longest methylene spacer between the aromatic ring and the double bond, and rac‐(EBTHI)ZrCl2 as catalyst, adjustable amounts of the antioxidant moiety can be incorporated into the polyethylene chains. TGA analysis carried out on some of the copolymers containing the antioxidant group showed no oxygen uptake before decomposition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6393–6406, 2008
Synthesis and characterization of well‐defined cyclodextrin‐centered seven‐arm star poly(ε‐caprolactone)s and amphiphilic star poly(ε‐caprolactone‐b‐ethylene glycol)s
Authors: Gou Peng‐Fei , Zhu Wei‐Pu , Xu Ning , Shen Zhi‐Quan
Published: August 2008

Per‐2,3‐acetyl‐β‐cyclodextrin with seven primary hydroxyl groups was synthesized by selective modification and used as multifunctional initiator for the ring‐opening polymerization of ε‐caprolactone (CL). Well‐defined β‐cyclodextrin‐centered seven‐arm star poly(ε‐caprolactone)s (CDSPCLs) with narrow molecular weight distributions (≤1.15) have been successfully prepared in the presence of Sn(Oct)2 at 120 °C. The molecular weight of CDSPCLs was characterized by end group 1H NMR analyses and size‐exclusion chromatography (SEC), which could be well controlled by the molar ratio of the monomer to the initiator. Furthermore, amphiphilic seven‐arm star poly(ε‐caprolactone‐b‐ethylene glycol)s (CDSPCL‐b‐PEGs) were synthesized by the coupling reaction of CDSPCLs with carboxyl‐terminated mPEGs. 1H NMR and SEC analyses confirmed the expected star block structures. Differential scanning calorimetry analyses suggested that the melting temperature (Tm), the crystallization temperature (Tc), and the crystallinity degree (Xc) of CDSPCLs all increased with the increasing of the molecular weight, and were lower than that of the linear poly(ε‐caprolactone). As for CDSPCL‐b‐PEGs, the Tc and Tm of the PCL blocks were significantly influenced by the PEG segments in the copolymers. Moreover, these amphiphilic star block copolymers could self‐assemble into spherical micelles with the particle size ranging from 10 to 40 nm. Their micellization behaviors were characterized by dynamic light scattering and transmission electron microscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6455–6465, 2008
Efficient initiators for the ring‐opening polymerization of L‐lactide: Synthesis and characterization of NNO‐tridentate Schiff‐base zinc complexes
Authors: Hung Wen‐Chou , Huang Yong , Lin Chu‐Chieh
Published: August 2008

A series of efficient catalysts, based on zinc alkoxides coordinated with NNO‐tridentate Schiff‐base ligands (L1H‐L6H), for ring opening polymerization of L‐lactide have been prepared. The reactions of diethyl zinc (ZnEt2) with L1H‐L6H yielded [(μ‐L)ZnEt]2 (1a–6a), respectively. Further reaction of compounds 1a–6a with benzyl alcohol (BnOH) produced the corresponding compounds of [LZn(μ‐OBn)]2 (1b–6b), respectively. X‐ray crystal structural studies reveal that all of these compounds 1a–6a are dimeric bridging through the phenolato oxygen atoms of the Schiff‐base ligand. However, the molecular structures of 1b–6b show a dimeric character bridging through the benzylalkoxy oxygen atoms. Ring‐opening polymerization of L‐lactide, initiated by 1b–6b, proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. Experimental results show that the substituents on the imine carbon of the NNO‐ligand affect the reactivity of zinc complexes dramatically. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6466–6476, 2008
Novel fluorescent (p‐phenylene ethynylene)‐calix[4]arene‐based polymer: Design, synthesis, and properties
Authors: Costa Alexandra I. , Ferreira Luís F. V. , Prata José V.
Published: August 2008

A novel fluorescent (p‐phenylene ethynylene)‐calix[4]arene‐based polymer (CALIX‐PPE) has been successfully synthesized by cross‐coupling polymerization of bis‐calix[4]arene 1 with 1,4‐diethynylbenzene. The polycondensation was carried out in toluene/NEt3 at 35 °C for 24 h, using PdCl2(PPh3)2/CuI as the catalytic system, furnishing CALIX‐PPE in excellent isolated yields (higher than 95%, several runs). The yellow polymer is freely soluble in several nonprotic organic solvents. The GPC trace of the isolated polymer showed a monomodal distribution and a number‐average molecular weight of 23,300 g mol−1 (Mw/Mn = 2.05). No evidence was found in the structural analysis (FTIR and 1H/13C NMR) regarding the formation of alkyne homocoupled segments along the polymer chain. For comparative purposes, the synthesis of an analogous poly(p‐phenylene ethynylene) containing p‐t‐butyl‐phenoxymethyl side chains (TBP‐PPE) was also undertaken. A great similarity was found between the photophysical properties of CALIX‐PPE and TBP‐PPE in solution (UV–vis and laser induced luminescence), clearly demonstrating their unique dependence on the structure and conformation of the conjugated PPE backbone. The fluorescence spectra of polymers are of nearly identical shape, displaying their maximum emission around 420 nm. The calculated solution photoluminescence quantum yields of CALIX‐PPE and TBP‐PPE are of similar magnitude (ϕF(CALIX‐PPE) = 0.43; ϕF(TBP‐PPE) = 0.51). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6477–6488, 2008
Viscometric measurement of the thermodynamics of PAN terpolymer/DMSO/water system and effect of fiber‐forming conditions on the morphology of PAN precursor
Authors: Dong Ruijiao , Keuser Marcus , Zeng Xiaomei , Zhao Jiongxin , Zhang Youwei , Wu Chengxun , Pan Ding
Published: August 2008

The thermodynamics of polyacrylonitrile (PAN) terpolymer/dimethyl sulphoxide (DMSO)/water system was investigated by viscometric method. Fourier transform infrared (FTIR) measurement of the temperature dependence of polymer/solvent interaction was performed in the range of 25–80 °C, which was in good agreement with viscometric results. Meanwhile, the upper critical solution temperature (UCST) for PAN terpolymer/DMSO/water system, which is proved to be stable one, was determined from the temperature dependence of the expansion factor αη3. The morphology of PAN precursor prepared by dry‐jet‐wet spinning with different fiber‐forming conditions was examined with a scanning electron microscope (SEM). Judging from SEM photographs, not only the number and size of microvoids of PAN precursor gradually increase, with increasing the temperature of coagulation bath, but also the cross‐section shape of PAN precursor changes from nephroid shape to elliptical shape or circular shape. Therefore, PAN precursor with different microstructures can be fabricated at different quenching‐depths, suggesting that the final microstructure of the PAN precursor greatly depends on the phase separation in the fiber‐forming process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1997–2011, 2008
Effect of side groups of polymer glycol on microphase‐separated structure and mechanical properties of polyurethane elastomers
Authors: Kojio Ken , Nakamura Sadaharu , Furukawa Mutsuhisa
Published: August 2008

The effect of side methyl and dimethyl groups of the soft segment component on the microphase‐separated structure and mechanical properties of polyurethane elastomers (PUEs) was investigated. Poly(oxytetramethylene) glycol (PTMG), and PTMG incorporating dimethyl groups (PTG‐X) and methyl side groups (PTG‐L) were used as a polymer glycol, which forms a soft segment in the PUEs. The PUEs were synthesized with 4,4′‐dipheylmethane diisocyanate [1,1′‐methylenebis(4‐isocyanatobenzene)], 1,4‐butane diol, and 1,1,1‐trimethylol propane by a prepolymer method. The degree of microphase separation of the PUEs became weaker with increasing side group content in polymer glycols. Dynamic viscoelastic properties measurement showed reorganized‐crystallization and melting of the soft segment for the PUEs based on PTMG, PTG‐L, and PTG‐X with a lower content of the side groups, but not for a PTG‐L and PTG‐X with higher content of the side groups. Tensile testing revealed that increasing methyl group concentration made the PUEs soften and weaken. The PTMG‐based PUEs obviously exhibited strain‐induced crystallization of the soft segment chains during elongation process. In contrast, for the PTG‐L and PTG‐X‐based PUEs, crystallinity decreased with increasing side group content, and the PUEs with PTG‐L and PTG‐X with highest methyl group content did not crystallize even at a large strain. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2054–2063, 2008
Validation of proteomic‐based discovery with tissue microarrays
Authors: Hewitt Stephen M. , Takikita Mikiko , Abedi‐Ardekani Behnoush , Kris Ylaya , Bexfield Kathryn , Braunschweig Till , Chung Joon‐Yong
Published: August 2008

Proteomics is routinely utilized for biomarker discovery above and beyond its general use in basic science. Multiple platforms provide a robust pipeline of candidates that require verification and validation as biomarkers of disease. Within the field of oncology, tissue biomarkers are in high demand as tools of diagnosis, prognosis and prediction of response to therapy. By examining the proteome, rather than the transcriptome, there is the potential to directly interrogate the drug targets and define biomarkers at the most proximate level. Toward these ends, the tissue microarray has become a common platform for verification of results and validation of clinically relevant biomarkers. Immunohistochemistry remains the most common analytical method applied to TMA and provides a direct channel toward clinical application. The TMA stands at the crossroads of proteomics and pathology, combining formalin‐fixed paraffin‐embedded tissue as an analyte and IHC as a method of assay.