bluuebunny/crossref_metadata_2025 huggingface dataset:
Maternal age and depressive symptoms in a low‐income sample
Authors: Eshbaugh Elaine M.
Published: March 2008

In this study, depressive symptoms of 2,011 European‐American, African‐American, and Latina low‐income mothers at approximately 14 months after birth of the child were examined. Maternal age was used as a predictor of depressive symptoms. Overall, 31.9% of mothers were classified as depressed using the Center for Epidemiological Studies Depression Scale. Younger mothers tended to have more depressive symptoms among European‐American mothers only. Latina mothers had fewer depressive symptoms than African‐American and European‐American mothers. Number of children 5 years and under in the home was positively related to depressive symptoms. In addition, mothers with higher levels of self‐mastery reported fewer symptoms of depression. Implications for preventing maternal depressive symptoms are discussed. © 2008 Wiley Periodicals, Inc.
Efficient syntheses of 13C‐labelled erythromycin biosynthetic intermediates. 2: (2S,3S,4S,5R,6R,7R)‐3,6,7‐trihydroxy‐2,4,6‐trimethyl[1‐13C]nonan‐5‐olide and S‐2‐acetylaminoethyl (2R,3S,4S,5R,6S,7R)‐3,5,6,7‐tetrahydroxy‐2,4,6‐trimethyl[1‐13C]nonanethioate
Authors: Iida Katsumi , Kajiwara Masahiro , Fukui Mineo , Nakata Tadashi , Oishi Takeshi
Published: March 2008

The 13C‐labelled putative erythromycin biosynthetic intermediates, ((2S,3S,4S,5R,6R,7R)‐3,6,7‐trihydroxy‐2,4,6‐trimethyl[1‐13C]nonan‐5‐olide and S‐2‐acetylaminoethyl (2R,3S,4S,5R,6S,7R)‐3,5,6,7‐tetrahydroxy‐2,4,6‐trimethyl[1‐13C]nonanethioate), which would be useful for the investigation of the chain elongation mechanism in erythromycin biosynthesis, were efficiently synthesized via aldol condensation of aldehyde derived from (2S,3R,4R,5R)‐tert‐butyldimethylsilyloxy‐5‐3,4‐O‐isopropylidene‐2,4‐dimethylheptanol, which was obtained in our previous work on erythromycin A synthesis, and sodium [1‐13C]propionate (after conversion to ester). Copyright © 2008 John Wiley & Sons, Ltd.
The impact of the positive Indian Ocean dipole on Zimbabwe droughts
Authors: Manatsa D. , Chingombe W. , Matarira C. H.
Published: March 2008

A comparative study of the impact of the anomalous positive Indian Ocean SST gradient, referred to as the Indian Ocean Dipole/Zonal Mode (IODZM), and El Niño‐Southern Oscillation (ENSO) on Zimbabwe seasonal rainfall variability for the period 1940–1999, is documented. Composite techniques together with simple and partial correlation analyses are employed to segregate the unique association related to IODZM/ENSO with respect to the Zimbabwe seasonal rainfall.

The analysis reveals that the IODZM impact on the country's summer rainfall is overwhelming as compared to that of ENSO when the two are in competition. The IODZM influence remains high (significant above 99% confidence level), even after the influence of ENSO has been removed, while that of ENSO collapses to insignificance (even at 90% confidence level) when the IODZM contribution is eliminated. The relationship between ENSO and Zimbabwe seasonal rainfall seems to be sustained through El Niño occurring in the presence of positive IODZM events. However, when the co‐occurring positive IODZM and El Niño events are removed from the analysis, it is apparently clear that ENSO has little to do with the country's rainfall variability. On the other hand, positive IODZM is mostly associated with the rainfall deficits, whether or not it co‐occurs with El Niño. However, the co‐occurrence of the two events does not necessarily suggest that El Niño influences droughts through the positive IODZM events. The El Niño event components during co‐occurrence seem to be unrelated (at least linearly) to the droughts, while the positive IODZM events display a relatively strong relationship that is significant above the 95% confidence level. It thus becomes important to extend the study of this nature to cover the whole of southern Africa, so that the extent of the impact of the phenomena can be realized over the whole region. Copyright © 2008 Royal Meteorological Society
Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau
Authors: Prins Maarten A. , Zheng Hongbo , Beets Kay , Troelstra Simon , Bacon Patrick , Kamerling Ilse , Wester Wouter , Konert Martin , Huang Xiangtong , Ke Wang , Vandenberghe Jef
Published: March 2008

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.
Plasma Surface Modification of Chitosan Membranes: Characterization and Preliminary Cell Response Studies
Authors: Silva Simone S. , Luna Sandra M. , Gomes Manuela E. , Benesch Johan , Pashkuleva Iva , Mano João F. , Reis Rui L.
Published: March 2008

Surface modification of biomaterials is a way to tailor cell responses whilst retaining the bulk properties. In this work, chitosan membranes were prepared by solvent casting and treated with nitrogen or argon plasma at 20 W for 10–40 min. AFM indicated an increase in the surface roughness as a result of the ongoing etching process. XPS and contact angle measurements showed different surface elemental compositions and higher surface free energy. The MTS test and direct contact assays with an L929 fibroblast cell line indicated that the plasma treatment improved the cell adhesion and proliferation. Overall, the results demonstrated that such plasma treatments could significantly improve the biocompatibility of chitosan membranes and thus improve their potential in wound dressings and tissue engineering applications.

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Kinetics of Ultrasonic Polymer Degradation: Comparison of Theoretical Models with On‐Line Data
Authors: Akyüz Ali , Catalgil‐Giz Huceste , Giz Ahmet T.
Published: March 2008

PVP solutions were sonicated with high‐intensity ultrasound, and the weight‐average molecular weight was monitored by an ACOMP system. The use of continuous on‐line data to critically evaluate various models showed that the molecular weight decreased towards a limiting value. Theoretical and phenomenological models of evolution of the molecular weight during sonication are compared with the on‐line data. The Ovenall/Harrington/Madras and Giz and Tang models werer found to describe the results adequately. These models share the property of an initial rapid drop in molecular weight followed by a slowing down of the rate of molecular weight decrease.

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Trembling Shear Behavior of a Modified‐Chitosan Dispersed Suspension under an Electric Field and its Model Study
Authors: Ko Young Gun , Choi Ung Su , Chun Yong Jin
Published: March 2008

An electro‐rheological (ER) fluid showing trembling shear behavior was fabricated with chitosan particles that had benzene, amine and azo‐pendent side groups. This modified‐chitosan dispersed suspension showed four regions in a plot of shear stress against shear rate at high electric field. We analyzed this specific behavior with our suggested model. The model was developed with the spring‐damper model. Our suggested model equation treated the wide range of shear rate and specific behaviors of shear stress in ER fluids. In this study, we successfully obtained various ER fluids showing different behaviors just by changing the side functional groups of the particles in the ER fluids. All of the curves of the shear stress plotted against shear rate were fitted well by our spring‐damper model.

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Valuing information from mesoscale forecasts
Authors: Kok Kees , Schreur Ben Wichers , Vogelezang Daan
Published: March 2008

The development of meso‐γ scale numerical weather prediction (NWP) models requires a substantial investment in research, development and computational resources. Traditional objective verification of deterministic model output fails to demonstrate the added value of high‐resolution forecasts made by such models. It is generally accepted from subjective verification that these models nevertheless have a predictive potential for small‐scale weather phenomena and extreme weather events. This has prompted an extensive body of research into new verification techniques and scores aimed at developing mesoscale performance measures that objectively demonstrate the return on investment in meso‐γ NWP.

In this article it is argued that the evaluation of the information in mesoscale forecasts should be essentially connected to the method that is used to extract this information from the direct model output (DMO). This could be an evaluation by a forecaster, but, given the probabilistic nature of small‐scale weather, is more likely a form of statistical post‐processing. Using model output statistics (MOS) and traditional verification scores, the potential of this approach is demonstrated both on an educational abstraction and a real world example. The MOS approach for this article incorporates concepts from fuzzy verification. This MOS approach objectively weighs different forecast quality measures and as such it is an essential extension of fuzzy methods. Copyright © 2008 Royal Meteorological Society
Bicarbonate‐Induced phosphorylation of p270 protein in mouse sperm by cAMP‐Dependent protein kinase
Authors: Kaneto Masako , Krisfalusi Michelle , Eddy Edward M. , O'Brien Deborah A. , Miki Kiyoshi
Published: March 2008

Signaling by cAMP‐dependent protein kinase (PKA) plays an important role in the regulation of mammalian sperm motility. However, it has not been determined how PKA signaling leads to changes in motility, and specific proteins responsible for these changes have not yet been identified as PKA substrates. Anti‐phospho‐(Ser/Thr) PKA substrate antibodies detected a sperm protein with a relative molecular weight of 270,000 (p270), which was phosphorylated within 1 min after incubation in a medium supporting capacitation. Phosphorylation of p270 was induced by bicarbonate or a cAMP analog, but was blocked by the PKA inhibitor H‐89, indicating that p270 is likely a PKA substrate in sperm. In addition, phosphorylation of p270 was inhibited by stearated peptide st‐Ht31, suggesting that p270 is phosphorylated by PKA associated with an A‐kinase anchoring protein (AKAP). AKAP4 is the major fibrous sheath protein of mammalian sperm and tethers regulatory subunits of PKA to localize phosphorylation events. Phosphorylation of p270 occurred in sperm lacking AKAP4, suggesting that AKAP4 is not involved directly in the phosphorylation event. Phosphorylated p270 was enriched in fractionated sperm tails and appeared to be present in multiple compartments including a detergent‐resistant membrane fraction. PKA phosphorylation of p270 within 1 min of incubation under capacitation conditions suggests that this protein may have an important role in the initial signaling events that lead to the activation and subsequent hyperactivation of sperm motility. Mol. Reprod. Dev. 75: 1045–1053, 2007. © 2007 Wiley‐Liss, Inc.
Comparative transcriptome analysis of in vivo‐ and in vitro‐produced porcine blastocysts by small amplified RNA‐Serial analysis of gene expression (SAR‐SAGE)
Authors: Miles Jeremy R. , Blomberg Le Ann , Krisher Rebecca L. , Everts Robin E. , Sonstegard Tad S. , Van Tassell Curtis P. , Zuelke Kurt A.
Published: March 2008

Production of embryos in vitro has enormous potential for research and commercial applications. Unfortunately, in vitro production of porcine embryos is extremely inefficient. Despite the characterization of distinct phenotypes, little is known about the molecular mechanisms and altered physiological processes of in vitro‐produced embryos. The objective of this study was to compare global gene expression patterns from in vivo‐ (IVO) and in vitro‐produced (IVP) porcine embryos using small amplified RNA‐serial analysis of gene expression (SAR‐SAGE). Whole‐cell RNA from pools of Day 6 IVO and IVP blastocysts was used to construct SAR‐SAGE libraries. Sequence analysis of the IVO and IVP libraries yielded 98,771 and 98,408 tags, respectively. A total of 20,029 and 23,453 putative transcripts were detected in the IVO and IVP libraries, respectively. Statistical analyses of SAGE tag frequencies between the IVO and IVP libraries indicated that 938 and 193 tags were differentially expressed at a P < 0.05 and P < 0.001 level of significance, respectively, suggesting significant deviations in transcriptome profiles from IVO and IVP embryos. Categorization of differentially expressed transcripts into functional groupings indicated a significant deviation in gene expression from IVP blastocysts compared with IVO blastocysts for a number of biological processes including cellular metabolism, organization, and response to stress. Real‐time PCR confirmed differential expression for several transcripts from independent IVO and IVP blastocysts. These results demonstrate compromised gene expression in IVP blastocysts compared with IVO blastocysts for a number of biological processes, particularly processes involved in mitochondrial function; thereby providing potential target pathways for improvement of IVP methods. Mol. Reprod. Dev. 75: 976–988, 2007. © 2007 Wiley‐Liss, Inc.
A novel steady‐state genetic algorithm approach to the reliability optimization design problem of computer networks
Authors: Mutawa A. M. , Alazemi H. M. K. , Rayes Ammar
Published: March 2008

This paper introduces the development and implementation of a new methodology for optimizing reliability measures of a computer communication network within specified constraints. A genetic algorithm approach with specialized encoding, crossover, and mutation operators to design a layout topology optimizing source‐terminal computer communication network reliability is presented. In this work, we apply crossover at the gene level in conjunction with the regular chromosome‐level crossover operators that are usually applied on chromosomes or at boundaries of nodes. This approach provides us with a much better population mixture, and hence faster convergence and better reliability. Applying regular crossover and mutation operators on the population may generate infeasible chromosomes representing a network connection. This complicates fitness and cost calculations, since reliability and cost can only be calculated on links that actually exist. In this paper, a special crossover and mutation operator is applied in a way that will always ensure production of a feasible connected network topology. This results in a simplification of fitness calculations and produces a better population mixture that gives higher reliability rates at shorter convergence times. Copyright © 2008 John Wiley & Sons, Ltd.
A discontinuous‐Galerkin‐based immersed boundary method
Authors: Lew Adrián J. , Buscaglia Gustavo C.
Published: March 2008

A numerical method to approximate partial differential equations on meshes that do not conform to the domain boundaries is introduced. The proposed method is conceptually simple and free of user‐defined parameters. Starting with a conforming finite element mesh, the key ingredient is to switch those elements intersected by the Dirichlet boundary to a discontinuous‐Galerkin approximation and impose the Dirichlet boundary conditions strongly. By virtue of relaxing the continuity constraint at those elements, boundary locking is avoided and optimal‐order convergence is achieved. This is shown through numerical experiments in reaction–diffusion problems. Copyright © 2008 John Wiley & Sons, Ltd.
A strategy for parallel implementation of finite difference numerical schemes associated to evolution differential equations
Authors: Moura Carlos A. de , Castro M. Clicia S. de , Castro Vinicius B. de
Published: March 2008

Within the framework of parallel numerical treatment, there are many more results on stationary (or time‐frozen) PDE's than on their evolution (or time‐dependent) counterparts. This is justified as computer simulation of time flow – an intrinsically sequential phenomenum – leads naturally to a sequential algorithm, thus inhibiting any search for concurrent ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Calculation of effective mechanical properties of textiles by asymptotic approach
Authors: Nam Alexander , Orlik Julia
Published: March 2008

We consider plates with 2‐D periodic rod or fabric structure, used as geotextiles or textiles. The period of structure as well as the hight of a plate are much smaller compared to its depth and width. This makes a direct numerical computation of boundary value or contact elasticity problem too expensive. Three small parameters are introduced for the asymptotic analysis: the first one connected with the period of structure, the second one with the thickness of fibers or beams inside the periodicity cell and the last one – with the hight of a plate. The overcoming to the limit with respect to period of structure provides equivalent homogenized plate of the finite hight. Calculation of its outer‐plane stiffness is a new aspect of this work. The next overcoming to the limit with respect to the hight reduces the 3‐D problem to the homogenized equations, fourth order PDEs. The effective elasticity moduli and outer‐plane stiffness can be obtained numerically solving cell experiments. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface stability of nonlinear magnetoelastic solids
Authors: Ottenio M. , Destrade M. , Ogden R.W.
Published: March 2008

The present paper proposes to identify surface stability when a magnetoelastic half‐space is subjected to a pure homogeneous pre‐deformation and to a magnetic field normal to its (plane) boundary. Clearly, the aim is to find the critical stretch ratio beyond which surface instabilities may develop, or in other words, to establish a bifurcation criterion based on the incremental static solution of the boundary value problem. We want to analyse how the presence of a coupling between magnetism and nonlinear elasticity modify the conditions of stability. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surrogate modeling for geometry optimization in material design
Authors: Rojas Marielba , Abraham Yonas B. , Holzwarth Natalie A. W. , Plemmons Robert J.
Published: March 2008

We propose a new approach based on surrogate modeling for geometry optimization in material design. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of planar vortex clusters with binaries
Authors: Ting Lu , Knio Omar , Blackmore Denis
Published: March 2008

We study an N ‐vortex problem having J of them forming a cluster, which means the distances between the vortices in the cluster is much smaller by O (ε) than the distances, O (ℓ), to the N – J vortices outside of the cluster. With the strengths of N vortices being of the same order, the velocity and time scales for the motion of the J vortices relative to those of the N – J vortices are O (ε–1) and O (ε2) respectively. We show that this two‐time and two‐length scale problem can be converted to a standard two‐time scale problem and then the leading order solution of the N ‐vortex problem can be uncoupled to two problems, one for the motion of J vortices in the cluster relative to the center of the cluster and one for the motion of the N – J vortex plus the center of the cluster. For N = 3 and J = 2, the 3‐vortex problem is uncoupled to two binary vortices problems in the length scales ℓ and ℓε respectively. When perturbed in the scale ℓ, say by a fourth vortex even of finite strength, the binary problem becomes a 3‐vortex problem, admitting periodic solutions. Since 3‐vortex problems are solvable, the uncoupling enables us to solve 3‐cluster problems having at most three vortices in each cluster. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive importance sampling with prior information in dynamic process imaging
Authors: Watzenig Daniel , Steiner Gerald
Published: March 2008

The estimation of cross‐sectional material distributions from non‐stationary sparse tomographic measurement data is a demanding class of ill‐posed inverse problems. In this context, electrical capacitance tomography (ECT) is a well‐established modality that aims at monitoring and controlling dynamic industrial processes arising e.g. in pneumatic conveying or heterogeneous flow fields. By measuring the capacitances between certain electrodes that are arranged around the periphery, the permittivity distribution inside closed objects can be spatially resolved. In this paper, the main focus is on the robust estimation of time‐dependent material distributions given uncertain measurements. The underlying inverse problem is formulated in a Bayesian inferential framework, by specifying a prior parameter distribution, and characterizing the statistics of the measurement noise, to give a posterior distribution conditioned on measured data. Transitions between different material phases are described by means of a Fourier contour model of second order implying a geometric regularization. Sequential importance filtering – particle filtering – is applied to solve the non‐stationary ECT problem. A tracking experiment is presented in order to show the robustness of the Bayesian filtering approach to solve the non‐stationary inverse problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On pricing derivatives under nonlinear time series models
Authors: Siu Tak Kuen , Yang Hailiang
Published: March 2008

In this note, we summarize some of our recent works on pricing derivative securities under nonlinear time series models. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of the non‐isothermal flow between co‐ and counter‐rotating disks
Authors: Zielinski Artur , Tuliszka‐Sznitko Ewa
Published: March 2008

The 3D DNS computations are performed to study the isothermal and not‐isothermal transitional flow between two co‐ and counter‐rotating disks enclosed by two rotating cylinders. Computations have been performed for the wide range of Reynolds numbers and different end‐wall conditions including throughflow. For chosen examples 3D LES computations are performed. The flow is described by 3D Navier‐Stokes, energy and continuity equations. Numerical computations are based on a pseudospectral Chebyshev‐Fourier method. The time scheme is semi‐implicit and second‐order accurate. For LES computations, a Lagrangian dynamic sub‐grid model is used. In this paper we studied the spatial structures, which appeared in different stages of the lam.‐turb. transition process. We considered cavities of the aspect ratio 9 and curvature parameters Rm=1.5–3.0. Influence of the thermal Rossby number on lam.‐turb. transition process was also investigated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of a vehicle seat suspension system with pneumatic spring and viscous dampers
Authors: Chamera Sebastian , Maciejewski Igor , Krzyzynski Tomasz
Published: March 2008

The paper contains physical and mathematical model of the passive system of seat suspension, used in trucks and buses. Spring force in this system is performed by air spring, whereas damping force is generated by two viscous dampers. Based on the experimental research of characteristic parts of the suspension system, the parameters of mathematical model are determined. Both results of computer simulations and experiments are presented as power spectral density of acceleration courses, measured on seat, in comparison with courses measured on excitation platform in laboratory. Transmissibility of real system and its model are also presented in the paper. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Systematic characterization of the murine mitochondrial proteome using functionally validated cardiac mitochondria
Authors: Zhang Jun , Li Xiaohai , Mueller Michael , Wang Yueju , Zong Chenggong , Deng Ning , Vondriska Thomas M. , Liem David A. , Yang Jeong‐In , Korge Paavo , Honda Henry , Weiss James N. , Apweiler Rolf , Ping Peipei
Published: March 2008

Mitochondria play essential roles in cardiac pathophysiology and the murine model has been extensively used to investigate cardiovascular diseases. In the present study, we characterized murine cardiac mitochondria using an LC/MS/MS approach. We extracted and purified cardiac mitochondria; validated their functionality to ensure the final preparation contains necessary components to sustain their normal function; and subjected these validated organelles to LC/MS/MS‐based protein identification. A total of 940 distinct proteins were identified from murine cardiac mitochondria, among which, 480 proteins were not previously identified by major proteomic profiling studies. The 940 proteins consist of functional clusters known to support oxidative phosphorylation, metabolism, and biogenesis. In addition, there are several other clusters, including proteolysis, protein folding, and reduction/oxidation signaling, which ostensibly represent previously under‐appreciated tasks of cardiac mitochondria. Moreover, many identified proteins were found to occupy other subcellular locations, including cytoplasm, ER, and golgi, in addition to their presence in the mitochondria. These results provide a comprehensive picture of the murine cardiac mitochondrial proteome and underscore tissue‐ and species‐specification. Moreover, the use of functionally intact mitochondria insures that the proteomic observations in this organelle are relevant to its normal biology and facilitates decoding the interplay between mitochondria and other organelles.
Copolymerization of ethylene with cycloolefins by titanium complexes containing tridentate [o−NSR] ligands
Authors: Gao Ming‐Li , Sun Xiu‐Li , Gu Yue‐Feng , Yao Xiao‐Li , Li Chuan‐Feng , Bai Ji‐Ye , Wang Cong , Ma Zhi , Tang Yong , Xie Zuowei , Bu Shi‐Zheng , Qian Changtao
Published: March 2008

A family of titanium complexes of the general formula [N‐(3,5‐di‐tert‐butylsalicylidene)‐2‐alkylsulfanylanilinato]Ti(IV)Cl3
5a–f was prepared from the reaction of TiCl4 with the potassium salts of the corresponding ligands. These complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 5b and 5e were further confirmed by single‐crystal X‐ray analyses. Complexes 5a–f (except for 5c) exhibited good to high catalytic activities in ethylene copolymerization with cycloolefins such as norbornene, cyclopentene, dicyclopentadiene in the presence of modified methylaluminoxane. The reaction conditions and the steric hindrance of the alkyl substituents on sulfur atom in the precatalysts influenced strongly the copolymerization behaviors and the structures of the resultant copolymers. Complex 5c with bulky tert‐butylthio sidearm showed both low catalytic activity and comonomer incorporation ratio. The n‐alkylthio complexes 5a, 5d–f all exhibited good ethylene copolymerization capabilities with cycloolefins, which is superior to the corresponding phenylthio complex 5g. © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 2807–2819, 2008
Bidentate coordination effect on polycondensation of amino acid esters between metal triflates and methoxy groups
Authors: Nemoto Tadamasa , Naka Kensuke , Chujo Yoshiki
Published: March 2008

To study the bidentate coordination effect on the polycondensation of L‐valinates between metal triflates as a Lewis acid and methoxy groups, we carried out the polycondensation of 2‐methoxy‐4‐nitrophenyl L‐valinate (1a) and 2‐methoxyphenyl L‐valinate (1b) in the presence of the various kinds of rare‐earth triflates in DMF solution at room temperature. The polymerizations of 1a did not proceed without any metal triflates. In the presence of 5 mol% triflates, especially Sc(OTf)3, the polymerization proceeded effectively. After the reaction mixture was poured into water, the product was collected, which was recognized as poly(L‐valine)s by FTIR spectrum and GPC measurement. The yield of the product from the polymerization of 1a with Sc(OTf)3 was higher than that from the polymerization of 4‐nitrophenyl L‐valinate (1c) with Sc(OTf)3. This result indicates that the polymerization of 1a was promoted to introduce the methoxy group on the o‐position of the phenyl ring at the ester group with the aim of the bidentate coordination effect between metal triflates and L‐valinate. As a control experiment, we carried out the polycondensation of 1b in the presence of 5 mol% metal triflates; however, any polymerization did not proceeded. That reason is from the lower activity of activated L‐valinate (1b). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2864–2868, 2008
Living ring‐opening polymerization of ϵ‐caprolactone with Ti alkoxides derived from the Cp2TiCl‐catalyzed SET reduction of aldehydes
Authors: Asandei Alexandru D. , Chen Yanhui , Adebolu Olumide I. , Simpson Christopher P.
Published: March 2008

A series of substituted benzaldehydes were investigated as initiators for the living ring‐opening polymerization (LROP) of ε‐caprolactone (CL) mediated by titanium alkoxides obtained from the Cp2TiCl‐catalyzed single electron transfer (SET) reduction of the carbonyl group following the in situ reduction of Cp2TiCl2 with Zn. The aldehyde initiation was demonstrated (NMR) by the presence of the initiator derived fragment on the polycaprolactone (PCL) chain end. The effect of the nature of the aldehyde functionality (R‐Ph‐CHO, R = H, Cl, PhCH2O, NMe2, CH3O, NO2, and CHO), reagent ratios ([CL]/[aldehyde] = 50/1 to 400/1, [aldehyde]/[Cp2TiCl2] = 1/1 to 1/4, and [Cp2TiCl2]/[Zn] = 1/0.5 to 1/2), and temperature (T = 75–120 °C) was investigated over a wide range of values to reveal a living polymerization in all cases with an optimum observed at 90 °C with typical stoichiometric ratios of [CL]/[aldehyde]/[Cp2TiCl2]/[Zn] = 100/1/1/2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2869–2877, 2008
A novel nanoporous structure on the surface of bubbles in polycarbonate foams
Authors: Fukasawa Yoshihito , Chen Jienbin , Saito Hiromu
Published: March 2008

We found that novel nanoporous structures such as ellipsoidal‐ or string‐shaped nanopores were formed on the surface of the spherical bubbles in polycarbonate foams by annealing CO2‐saturated polycarbonate. The pores were surrounded by polycarbonate nanofibrils, and birefringence with spherical symmetry was seen on the surface of the spherical bubbles. Thus, the formation of such a characteristic structure might be attributed to orientation‐induced crystallization of CO2‐saturated polycarbonate on the surface of the bubbles and the exclusion of CO2 from the fibrillar crystals thus obtained. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 843–846, 2008
Thermomechanical and Morphological Characteristics of Cross‐Linked GAP and GAP–HTPB Networks with Different Diisocyanates
Authors: Mathew Suresh , Manu S. K. , Varghese T. L.
Published: March 2008

This paper describes the mechanical and thermal characterisation of cross‐linked glycidyl azide polymer (GAP) and GAP–hydroxyl terminated polybutadiene (HTPB) networks. Cross‐linked GAP and GAP–HTPB networks were prepared by reacting GAP diol and GAP–HTPB diol mixture with different diisocyanates. The physical and mechanical characteristics were found to be influenced by the type of isocyanate curing agents, [NCO]/[OH] equivalent ratios and concentration of GAP. For all the three types of curing agents, GAP–HTPB blends of 50 : 50 to 30 : 70 ratios show higher mechanical strength over the virgin networks of GAP or HTPB. Thermal decomposition of cross‐linked GAP–HTPB networks was evaluated by thermogravimetric analysis (TGA). The kinetic parameters for the decomposition of GAP–HTPB blends were found to be dependant on the concentration of GAP and HTPB in the blend. The cross‐linked GAP–HTPB blends were subjected to dynamic mechanical analysis (DMA). The glass transition characteristics of the blends were evaluated by DMA and it was found that blends prepared with GAP content up to 30% showed single transition in the loss tangent trace indicating no phase separation in the cured network.
Current treatments for age‐related macular degeneration
Authors: Patel Praveen , Tufail Adnan
Published: March 2008

There have been significant advances in the treatment of age‐related macular degeneration in recent years. Here, the authors describe how to diagnose AMD and discuss the available treatment options. Copyright © 2008 Wiley Interface Ltd
The role of combined addition of Ti and B in magnetic hardening of devitrified Pr2Fe14B/(Fe3B,α‐Fe) nanocomposite magnets
Authors: Zhang W. Y. , Stoica M. , Eckert J. , Chang H. W. , Chang W. C. , Ehrenberg H.
Published: March 2008

Pr2Fe14B/(Fe3B,α‐Fe) nanocomposite magnets with high coercivity have been prepared by devitrification of Pr9Fe88.5–xTi2.5Bx(x= 7, 9, 11, 13, and 15) amorphous ribbons. Similar to Zr and Nb, Ti substitutes rare earth sites and participates in forming the (Pr,Ti)2Fe14B phase. The increasing amount of nonmagnetic TiB2with increasingxin the nanocomposite magnets may precipitate along the grain boundaries and refine the microstructure by inhibiting the grain growth, and results in a continuous increase of coercivity. It also leads to an increase of the fraction of soft phases in the nanocomposites, which enhances the remanence. The squareness of the demagnetization curves is also improved by appropriate B addition. As a result, the energy product attains a maximum value of 129.6 kJ/m3forx= 13. A more obvious shoulder and significantly enhanced coercivity (2424 kA/m) in the hysteresis curves at 70 K was observed for the sample withx= 15 in comparison with the ribbon withx= 7. This further demonstrates that B addition promotes the formation of TiB2and the Fe3B soft phase in good agreement with XRD results. Accordingly, the introduction of a proper amount of nonmagnetic phases can enhance the magnetic properties of the nanocomposite magnets. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Correlation between optical properties of MBE films of AlN and morphology of their surface
Authors: Svitasheva S. N. , Mansurov V. G. , Zhuravlev K. S. , Nikitin A. Yu. , Sheglov D. V. , Pecz B.
Published: March 2008

In this work we revealed correlation between presence of surface defects and peculiarities in ellipsometric spectra and hence in optical properties of AlN films grown by ammonia MBE technique. We propose to use this fact for the fast and non‐destructive checking of film quality. Principal criterions of AlN films quality was both magnitude of phase deviation in maximum and/or a value of false (effective) absorption in transparency field of AlN calculated in according with our model. Our experiments were based on using of spectroscopic ellipsometry (SE). Atomic force microscopy (AFM) was used for determination of geometric size of overlayer roughness. Quantitative parameter related with surface morphology γs was proposed and influence of surface defects upon phase of light reflected was studied to evaluate surface quality from ellipsometric spectra at once, i.e. without any model calculations. Besides, an impact of surface defects upon film extinction coefficient is demonstrated in case when roughness is not taken into account. This approach could be useful for sorting identical films produced in routine growth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dielectric function representation by B‐splines
Authors: Johs Blaine , Hale Jeffrey S.
Published: March 2008

Accurate dielectric function values are essential for spectroscopic ellipsometry data analysis by traditional optical model‐based analysis techniques. In this paper, we show that B‐spline basis functions offer many advantages for param‐ eterizing dielectric functions. A Kramers–Kronig consistent B‐spline formulation, based on the standard B‐spline recursion relation, is derived. B‐spline representations of typical semiconductor and metal dielectric functions are also presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Immersion scatterometry for improved nano‐scale topography measurements
Authors: Liu Elson , Terry Fred L.
Published: March 2008

Spectroscopic ellipsometry measurement of periodic structures (“scatterometry”) has become a standard method for critical dimension and topography measurement in the integrated circuit industry. As dimensions are reduced, this method may not be adequate for research and process control. Use of immersion mode measurements may extend the usefulness of near UV specular scatterometry. In this paper, we present the first experimental measurements of gratings in water immersion and discuss the issues in achieving improved nano‐topography measurements with this method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectroscopic ellipsometry and photoluminescence investigation of Zn1–x –yBex Mgy Se and Cd1–x –yBex Zny Se crystals
Authors: Wronkowska A. A. , Skowroński Ł. , Wronkowski A. , Firszt F. , Me¸czyńska H. , Łe¸gowski S. , Strzałkowski K. , Arwin H.
Published: March 2008

Optical and luminescence properties of the Bridgman‐grown Cd1–x –y Bex Zny Se and Zn1–x –y Bex Mgy Se crystals are reported. Spectroscopic ellipsometry was employed for determination of spectral dependence of the complex dielectric function $ \tilde \epsilon $(E) in the photon energy range 0.75–6.5 eV. Below the absorption edge the refractive indices n (E) of the alloys were modelled using a Sellmeier‐type relation. The excitonic band‐gap energies were estimated from the ellipsometric and photoluminescence measurements. Compositional effects in the ellipsometric and photoluminescence spectra are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The nearly aligned rotating‐monoplate compensator
Authors: Asar M. , Aspnes D. E.
Published: March 2008

A rotating‐compensator polarimeter with a misaligned monoplate compensator generates first, third, and fifth harmonics as well as the zeroth (dc), second, and fourth harmonics that provide information about the sample. We outline a general procedure for calculating the detected intensity with mis‐ aligned components, then provide some results where multiple internal reflections in the component are ignored. The analysis involves several orders of tensors, and a quartic secular equation instead of the usual quadratic of a quadratic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploring the thermal transformation of mesoporous titania using spectroscopic ellipsometry
Authors: Choi S. Y. , Mamak M. , Ozin G. A. , Peiris F. C.
Published: March 2008

Spectroscopic ellipsometry was used to investigate the optical properties of a series of 2D‐hexagonal and 3D‐cubic mesoporous titania samples subjected to different annealing temperatures. Below a critical temperature, the dispersion of the index of refraction of the composite structure exhibits strong anisotropy, while above the critical temperature the structure reverts to an isotropic medium. Scanning electron microscopy and X‐ray measurements corroborate the ellipsometry results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized ellipsometry determination of non‐reciprocity in chiral silicon sculptured thin films
Authors: Schmidt D. , Schubert E. , Schubert M.
Published: March 2008

We report on angle‐resolved reflection‐type generalized ellipsometry investigations of form‐birefringent chiral silicon sculptured thin films. The nanodimensional structures within the sculptured thin films are designed in geometries of left‐handed hollow‐core three‐, four‐, and five‐fold, and solid‐core continuous screws. We identify their structurally induced non‐reciprocal optical properties by comparison between off‐diagonal Mueller matrix elements upon reversal of the light direction. The observed non‐reciprocity cannot be described by the piecewise homogeneous approximation scheme using chiral arrangements of dielectrically anisotropic layers. We show that a simple sequence of light interaction with an ideal isotropic chiral rotator and an arbitrarily anisotropic but non‐chiral surface produces non‐reciprocity. We provide estimates of the optical rotary power of the nanostructures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physics of plasma‐based ion implantation & deposition (PBIID) and high power impulse magnetron sputtering (HIPIMS): A comparison
Authors: Anders André
Published: March 2008

The emerging technology of High Power Impulse Magnetron Sputtering (HIPIMS) has much in common with the more established technology of Plasma‐Based Ion Implantation & Deposition (PBIID): both use pulsed plasmas, the pulsed sheath periodically evolves and collapses, the plasma‐sheath system interacts with the pulse‐driving power supply, the plasma parameters are affected by the power dissipated, surface atoms are sputtered and secondary electrons are emitted, etc. Therefore, both fields of science and technology could learn from each other, which has not been fully explored. On the other hand, there are significant differences, too. Most importantly, the operation of HIPIMS heavily relies on the presence of a strong magnetic field, confining electrons and causing their E × B drift, which is closed for typical magnetron configurations. Second, at the high peak power levels used for HIPIMS, 1 kW/cm2 or greater averaged over the target area, the sputtered material greatly affects plasma generation. For PBIID, in contrast, plasma generation and ion processing of the surface (ion implantation, etching, and deposition) are considered relatively independent processes. Third, secondary electron emission is generally considered a nuisance for PBIID, especially at high voltages, whereas it is a critical ingredient to the operation of HIPIMS. Fourth, the voltages in PBIID are often higher than in HIPIMS. For the first three reasons listed above, modelling of PBIID seems to be easier and could give some guidance for future HIPIMS models, which, clearly, will be more involved. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Silver nanocluster containing diamond like carbon
Authors: Schwarz F. , Thorwarth G. , Wehlus T. , Stritzker B.
Published: March 2008

Applying Diamond Like Carbon (DLC) as medical coating has become well established since large scale plasma processes like Plasma Immersion Ion Implantation and Deposition (PIII&D) are available. Now the focus of research lies on systematic modification of certain biological relevant properties and the most recent field of interest turned to generating antimicrobial behaviour. This is desirable for medical tools as well as for different types of medical implants. Since silver and copper are known to provide a bactericidal effect, one tries to introduce clusters of these noble metals into the carbon matrix.

The basic principle of the method presented is to convert a metal containing polymer film into DLC by ion bombardment. In this paper the hydrogenated DLC matrix is characterized and the evolution of the metal particles is studied. By means of film composition (RBS/ERD), bonding structure (Raman spectroscopy) and hardness (nanoindentation), the dependency of these material properties on ion species, energy and fluence is investigated. TEM imaging is used to visualize the film structure.

Upon ion irradiation of the polymer films, increased density and considerable loss of hydrogen can be observed, which both are controlled by ion fluence and mass. The crosslinking of the carbon network, caused by hydrogen drive out as well as atomic displacements in collision cascades, results in the formation of a‐C:H. The silver particles in the film some ion induced growth, but still remain as nanoclusters in the a‐C:H matrix. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conduction band filling in In‐rich InGaN and InN under hydrostatic pressure
Authors: Franssen G. , Kamińska A. , Suski T. , Gorczyca I. , Christensen N. E. , Svane A. , Lu H. , Schaff W. J. , Dimakis E. , Georgakilas A. , Che S.B. , Ishitani Y. , Yoshikawa A.
Published: March 2008

We demonstrate the effect of conduction band shape evolution of InGaN with increasing In content and applying hydrostatic pressure. The influence of conduction band filling on the hydrostatic pressure dependence of photoluminescence in In0.7Ga0.3N and InN is investigated. It is found that the PL pressure coefficient dEPL/dp of InN changes from ∼27 meV/GPa to ∼21 meV/GPa when the electron concentration increases from 3.6×1017 cm–3 to 1.1×1019 cm–3. In contrast, no significant change of dEPL/dp with electron concentration was observed for In0.7Ga0.3N. We conclude that the pressure sensitivity of the Fermi level, which is responsible for the lowering of dEPL/dp with respect to dEG/dp in InN, is much less prominent in In0.7Ga0.3N than in InN. We attribute this difference to the larger band gap of In0.7Ga0.3N, which lowers the pressure sensitivity of m*. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dislocation annihilation in GaN with multiple MgxNy/GaN buffer layers by metal organic chemical vapor deposition
Authors: Fu Y. K. , Tun C. J. , Kuo C. H.
Published: March 2008

Unintentionally doped GaN epitaxial layers with a conventional single low‐temperature (LT) GaN buffer layer and with multiple MgxNy/GaN buffer layers were grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD). X‐ray Photoelectron Spectroscopy (XPS) result reveals Mg 2p core‐level spectra from the 12 pairs of MgxNy/GaN buffer layers. The multiple MgxNy/GaN buffer layers exhibit a low nuclei density, increasing the volume of defect‐free regions and reducing the dislocations associated with the grain boundaries. Therefore, the GaN with multiple MgxNy/GaN buffer layers reveals an asymmetrical reflection (102) with a small full‐width at half‐maximum (FWHM), and a higher mobility, lower background concentration and lower etching pit density (EPD) than the GaN with the LT GaN buffer layer. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of nonpolar cubic GaN/AlN multiple quantum wells with intersubband transitions for 1.5 µm applications
Authors: As D. J. , Schörmann J. , Tschumak E. , Lischka K. , DeCuir E. A. , Manasreh M. O.
Published: March 2008

Cubic GaN/AlN short‐period multiple quantum well structures were grown at 720 oC by plasma‐assisted molecular beam epitaxy on free standing 3C‐SiC substrates. The samples consist of 100 nm thick GaN buffer and 20 periods of GaN/AlN active regions. The thickness of the AlN barrier is 1.35 nm for all samples, while the thickness of the GaN well varies between 1.6 nm–2.10 nm depending on the samples. The periodicity of the GaN/AlN active regions was confirmed by the presence of several peaks in the high resolution x‐ray diffraction (HRXRD) spectra. The thickness of the total period was estimated by fitting the HRXRD data using a dynamic scattering theory. Room temperature measurements of the optical absorption spectra of the intersubband transitions were obtained using a Bruker IFS‐125HR spectrometer. The peak position wavelengths of these transitions were observed in the spectral region of 1.5–2.0 µm and confirmed theoretically by using a self‐consistent Poisson‐Schrödinger model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)