bluuebunny/crossref_metadata_2025 huggingface dataset:
Microparticles for Drug Delivery Based on Functional Polycaprolactones with Enhanced Degradability: Loading of Hydrophilic and Hydrophobic Active Compounds
Authors: Vaida Cristian , Mela Petra , Kunna Katharina , Sternberg Katrin , Keul Helmut , Möller Martin
Published: June 2010

Microparticle drug carriers made of biodegradable functional polyesters were produced. The polyesters consist of a poly(ε‐caprolactone) backbone bearing pendant acryloyloxy and methacryloyloxy groups. Stable microparticles were prepared via an oil/water emulsion‐solvent evaporation technique eventually combined with a simultaneous crosslinking procedure. Crosslinked particles were obtained via photo‐crosslinking and Michael type addition using diamines as crosslinking agents. Encapsulation of a hydrophobic fluorescent dye and a hydrophilic protein, as model drugs, were performed and confirmed by optical microscopy and Raman spectroscopy. The presence of the functional groups allow for not only the tuning of the degradation rate, but also for further processing and (bio)functionalization.

magnified image
The Softer and More Hydrophobic the Better: Influence of the Side Chain of Polymethacrylate Nanoparticles for Cellular Uptake
Authors: Lorenz Steffen , Hauser Christoph P. , Autenrieth Benjamin , Weiss Clemens K. , Landfester Katharina , Mailänder Volker
Published: June 2010

Intracellular uptake of nanoparticles is highly interesting for labeling of cells, drug delivery, or non‐viral gene delivery. In this study we have synthesized a wide variety of poly(alkyl methacrylate) nanoparticles with the same size and investigated their uptake into cells. The nanoparticles were prepared from alkylmethacrylates with different linear and branched ester chains as well as from benzylmethacrylate using the miniemulsion polymerizaiton technique. By adding a fluorescent dye as a marker, the internalization of the nanoparticles could be investigated quantitatively with flow cytometry and qualitatively with confocal laser scanning microscopy. With increasing side chain of the ester and therefore increasing hydrophobicity and at glass transition temperature (Tg), below the incubation temperature of 37 °C the uptake of the nanoparticles into cells is favored.

magnified image
Bioresorbable Electrospun Fibers for Immobilization of Thiol‐Containing Compounds
Authors: Lösel Robert , Grafahrend Dirk , Möller Martin , Klee Doris
Published: June 2010

For the reconstruction of functional tissue, biodegradable scaffolds providing specific surface functionality and a three‐dimensional structure matching that of the damaged tissue are needed. Fibers capable of controlling cell‐fiber interaction were produced by electrospinning of PDLLA‐block‐PEG with thiol‐reactive end groups from a solvent mixture. The hydrophilic fibers uniquely combine minimized non‐specific protein adsorption and well‐defined surface reactivity allowing controlled immobilization of peptides and proteins. Human dermal fibroblasts show adherence and proliferation on the surface of RGDC‐functionalized electrospun PDLLA‐block‐PEG fibers.

magnified image
Enhanced Stereocomplexation by Enantiomer Adjustment for Stereo Diblock Polylactides with Non‐Equivalent D/L Ratios
Authors: Hirata Masayuki , Kobayashi Kaori , Kimura Yoshiharu
Published: June 2010

A stereo diblock polylactide di‐sb‐PLA consisting of PDLA and PLLA in a block ratio of 2:8 was prepared and mixed with PDLA to investigate the effect of enantiomer adjustment on the sc crystallinity. Each of these polymer blends was found to have improved stereocomplexibility which was changed with the PDLA compositions in the di‐sb‐PLA/PDLA blend systems. It was also revealed that melt blending is more highly efficient than solution blending in terms of enhancing the sc crystallinity. The blend samples prepared by the former process were found to retain high loss modulus above Tg as well as heat‐stability up to Tm (215 °C) of di‐sb‐PLA. These data hold promise for interesting applications of di‐sb‐PLA and its polymer blends as high‐performance bio‐based materials.

magnified image
Characterization and Properties of Poly[N‐(2‐cyanoethyl)pyrrole]
Authors: Aradilla David , Estrany Francesc , Armelin Elaine , Oliver Ramon , Iribarren José I. , Alemán Carlos
Published: June 2010

PNCPy was prepared by anodic polymerization and its properties in both doped and undoped state were characterized. The doping level of the oxidized material has been found to be larger than that of other conducting polymers; the more relevant electrochemical properties of the doped material were retained after undoping. SEM and AFM data are consistent with a lumpy surface and a multidirectional growing of the polymer chains. Finally, PNCPy has been combined with PEDOT to prepare three‐layer systems with enhanced electroactivity and electrostability. Results suggest that PNCPy is a potential candidate for the fabrication of electric circuit components that are able to block the current flow below a given potential.

magnified image
Relaxation Processes of Poly(tert‐butyl acrylate) Chemically Confined via Hydrogen Bonds
Authors: Schwabe Moritz , Rotzoll Robert , Küchemann Stefan , Nadimpalli Karthik , Vana Philipp , Samwer Konrad
Published: June 2010

In this work, tailored copolymers of tert‐butyl acrylate and acrylic acid (AA) with an ABA type structure were systematically analyzed via dynamic‐mechanical analysis with regard to their relaxations, in which the main focus was put on a chemical confinement (cc) mode caused by hydrogen bonds. Four different relaxation modes were detected, whereupon two modes seem to depend on the length of the inner B‐block and one on the length of the outer A‐blocks. One mode below room temperature could be identified as a secondary relaxation which belongs to the B‐block and is most likely induced by a cc. A softening of the polymer corresponding to the glass transition is found near to room temperature and surprisingly shifts to lower temperatures with increasing chain length of the B‐block. A second softening of the ABA type copolymers is caused by the AA containing A‐blocks and was found at higher temperatures.

magnified image
Nanoporous Films with Low Refractive Index for Large‐Surface Broad‐Band Anti‐Reflection Coatings
Authors: Wicht Gaëtan , Ferrini Rolando , Schüttel Stefan , Zuppiroli Libero
Published: June 2010

Nowadays, nanoporous films are widely employed in biochemical applications or in opto‐photonic devices such as displays, solar cells, or light‐guiding systems. In particular, the technological feasibility of nanoporous layers with low refractive indices has recently enabled the development of high‐efficiency anti‐reflection coatings. In this paper, we report on hybrid polymer nanoporous films that can be fabricated in a single coating step with an industrial aqueous‐based method on very large surfaces. Both high transparency and low refractive index are simultaneously achieved over the entire visible spectrum. We eventually demonstrate the potential of such films for broadband AR applications by combining them in a graded‐index multilayer that reduces the surface reflectivity of a polymer substrate from 10% to few ‰.

magnified image
Influence of Initial High Shearing on Electrical and Rheological Properties and Formation of Percolating Agglomerates for MWCNT/Epoxy Suspensions
Authors: Schulz Sonja Carolin , Schlutter Jana , Bauhofer Wolfgang
Published: June 2010

We report on shear‐induced nanotube agglomerate formation in low viscous multiwalled carbon nanotube/epoxy suspensions during steady shear rate step tests. A combined setup allows monitoring of the electrical, rheological, and optical properties of the system. High initial shearing was found to be necessary to achieve the insulator‐to‐conductor transition as well as low shear rate viscosity enhancement. Depending on the applied pre‐shear, conductivity improvement of about four orders of magnitude was observed. Different morphologies for shear‐induced agglomerates were detected before and after high shear. The critical minimal shear rate for the system was determined and a simple model using phase separation due to high shear forces is proposed.

magnified image
Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions
Authors: Kurek Alexander , Mark Stefan , Enders Markus , Kristen Marc O. , Mülhaupt Rolf
Published: June 2010

A ternary blend of the bisiminopyridine chromium (III) (Cr‐1) with the bisiminopyridine iron (II) (Fe‐2) post‐metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr‐3) was supported on mesoporous silica to produce novel multiple single‐site catalysts and polyethylene reactor blends with tailor‐made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO‐treated silica was Fe‐2 followed by Cr‐1 and Cr‐3. Cosupporting does not impair the single‐site nature of the blend components producing polyethylene fractions with $\overline M _{\rm w}$ = 104 g · mol−1 on Cr‐1, $\overline M _{\rm w}$ = 3 × 105 g · mol−1 on Fe‐2, and $\overline M _{\rm w}$ = 3 × 106 g · mol−1 on Cr‐3. As a function of the Fe‐2/Cr‐1/Cr‐2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor‐made polyethylene reactor blends with ultra‐broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe‐2/Cr‐1 was constant, the ultra‐high molecular polyethylene (UHMWPE, $\overline M _{\rm w}$ > 106 g · mol−1) content was varied between 8 and 16 wt.‐% as a function of the Cr‐3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe‐2/Cr‐3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr‐1. Due to the intimate mixing of low and ultra‐high molecular weight polyethylenes (UHMPEs) produced on cosupported single‐site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

magnified image
Supramolecular Aggregates of Water Soluble Dendritic Polyglycerol Architectures for the Solubilization of Hydrophobic Compounds
Authors: Kurniasih Indah N. , Liang Hua , Rabe Jürgen P. , Haag Rainer
Published: June 2010

Dendritic core–shell architectures which are based on hyperbranched polyglycerol for the solubilization of hydrophobic drugs have been synthesized and characterized. The core of hyperbranched polyglycerol has been modified with hydrophobic biphenyl groups or perfluorinated chains to increase the core hydrophobicity of the macromolecules. These amphiphilic core–shell type architectures were then used to solubilize pyrene, nile red, and a perfluoro tagged diazo dye, as well as the drug nimodipine in water. Specific host–guest interactions such as fluorous–fluorous interactions could be tailored by this flexible core design and determined by UV spectroscopy. The transport capacity increased 450‐fold for nile red, 47‐fold for nimodipine, and 37‐fold for pyrene at a polymer concentration of only 0.1 wt.‐%. Surface tension measurements and scanning force microscopy (SFM) were used to reveal the aggregation properties of these complexes. The formation of supramolecular aggregates with diameters of ≈20 nm and critical aggregate concentrations of 2 × 10−6 mol · L−1 have been observed. This indicates the controlled self‐assembly of the presented amphiphilic dendritic core–shell type architectures.

magnified image
Discrete Metal Catalysts for Stereoselective Ring‐Opening Polymerization of Chiral Racemic β‐Lactones
Authors: Carpentier Jean‐François
Published: June 2010

Poly(β‐hydroxyalkanoate)s (PHAs) are a class of aliphatic polyesters that can be efficiently synthesized by ring‐opening polymerization (ROP) of β‐lactones. The case of chiral racemic β‐substituted β‐lactones is particularly appealing since these monomers open the way to original tacticities and materials different from those biotechnologically produced. In this overview, after briefly surveying general considerations associated to the ROP of β‐lactones and metal‐based catalysts used in stereoselective ROP of racemic β‐butyrolactone, special emphasis is given to discrete rare earth catalysts that have allowed the preparation of highly syndiotactic poly(3‐hydroxybutyrate)s. Recent developments – such as preparation of stereocontrolled PHAs with pendant structural groups via (co)polymerization of functional β‐substituted β‐lactones, and highly alternating copolymers obtained by ROP of mixtures of enantiomerically pure but different monomers – are also discussed.

magnified image
Assembly of Anionic Conjugated Polymer with 6‐O‐Modified PNP‐β‐Galactoside for Fluorescence Logic‐signal‐based Multiplex Detections of Enzymes
Authors: Wang Ya‐juan , Xin Bao‐juan , Duan Xin‐rui , Xing Guo‐wen , Wang Shu
Published: June 2010

Anionic conjugated polymer (PFP‐SO) was assembled with a novel enzymatic substrate 6‐O‐modified PNP‐β‐galactoside (1) for sensitive multiplex enzyme detections. The PFP‐SO/1/lipase/β‐galactosidase system has two chemical input signals which are Input 1 (lipase) and Input 2 (β‐galactosidase), and output optical signals such as fluorescence emission at 416 nm or 450 nm. Four types of logic gates, including YES, INH, NAND and AND, were successfully constructed and utilized for multiplex detections of lipase and β‐galactosidase in one tube.

magnified image
Functional polymorphisms in cell death pathway genes and risk of renal cell carcinoma
Authors: Zhu Jian , Qin Chao , Wang Meilin , Yan Fu , Ju Xiaobing , Meng Xiaoxin , Ding Qi , Li Pu , Yang Jian , Cao Qiang , Zhang Zhengdong , Yin Changjun
Published: June 2010

The FAS/FAS ligand (FASL) system plays a key role in regulating apoptotic cell death, and corruption of this signaling pathway has been shown to participate in tumorigenesis. However, the effects of functional promoter polymorphisms of the CASP8, FAS, and FASL genes on risk of renal cell carcinoma (RCC) are unknown. In this study, we genotyped CASP8 ‐652 6N ins/del, FAS ‐1377 G > A, FAS ‐670 A > G, and FASL ‐844 C > T polymorphisms in a hospital‐based case–control study of 353 patients diagnosed with RCC and 365 cancer‐free controls in a Chinese population. Compared with CASP8 ‐652 ins/ins genotype, the del/del genotype had a significantly decreased RCC risk [adjusted odds ratio (OR) = 0.36, 95% confidence interval (CI) = 0.16–0.84]. For FAS ‐1377 G > A polymorphism, a significantly increased risk of RCC was found for AA (adjusted OR = 1.65, 95% CI = 1.03–2.64) and GA (adjusted OR = 1.41, 95% CI = 1.02–1.94) genotypes compared with GG genotype. When we combined these two polymorphisms together, we found that individuals carrying CASP8 ‐652 6N ins/del and FAS ‐1377 GG genotypes or CASP8 ‐652 6N del/del and FAS ‐1377 GG genotypes were associated with a statistically significantly decreased risk of RCC (adjusted OR = 0.46, 95% CI = 0.24–0.88 and OR = 0.12, 95% CI = 0.02–0.58, respectively) compared with individuals carrying CASP8 ‐652 6N ins/ins and FAS ‐1377 AA genotypes. These results suggest that the CASP8 ‐652 6N ins/del and FAS ‐1377 G > A polymorphisms are involved in the susceptibility to developing RCC in Chinese populations. © 2010 Wiley‐Liss, Inc.
Spiralometry: Computerized assessment of tremor amplitude on the basis of spiral drawing
Authors: Kraus Peter H. , Hoffmann Arndt
Published: June 2010

Spiral drawing has been used for the assessment of the impact of therapy on motor performance in various movement disorders (e.g. in Parkinson's disease, especially for tremor and hypokinesia). Nevertheless, there are only few guidelines available providing some kind of standardized interpretation. The published protocol with the highest standard is that of Bain and Findley. Kinetic tremor assessed by spiral drawing is not quantified by alternative approaches so far and is not even considered by most rating scales. However, kinetic tremor is quite common and represents a significant impairment in the everyday life of parkinsonian patients. More complex instrumental methods for the quantification of kinetic tremor have not been practical as they, e.g., require relatively expensive equipment or have an unfavourable effort/benefit ratio. We pursued an alternative approach, where we scan drawn spirals to a computer‐algorithm that calculates the tremor amplitude. Our standardized method can be applied without difficulty in patients needing only paper and pencil. The evaluation is fully automated, and therefore, it is appropriate for the assessment of therapeutic efficacy in very large populations. The objectivity of the approach represents a significant advantage. In the actual paper, we present how we analyzed the original spirals published by Bain and Findley to validate our computerized assessment. We found a highly significant connection between both methods (explained variance: 88.9%). © 2010 Movement Disorder Society
The Integrated Deconvolution Estimation Model: A Parameter Estimation Method for Ethylene/α‐Olefin Copolymers Made with Multiple‐Site Catalysts
Authors: Al‐Saleh Mohammad A. , Soares João B. P. , Duever Thomas A.
Published: June 2010

The integrated deconvolution estimation model (IDEM) to estimate the microstructural parameters of polyolefins made with multiple‐site catalysts is described. IDEM estimates ethylene/α‐olefin reactivity ratios for each site type in two‐steps. In the first step, the MWD of the whole copolymer is deconvoluted into several Flory's most probable distributions, to determine the number of site types and the weight fraction of copolymer made on each of them. In the second estimation step, the model deconvolutes the CSLD of the copolymer into its individual components per site type, and estimates their respective reactivity ratios. This is the first time that MWD and CSLD information is integrated to estimate the reactivity ratios of polyolefins made with multiple‐site catalysts.

magnified image
Imaging three‐dimensional myocardial mechanics using navigator‐gated volumetric spiral cine DENSE MRI
Authors: Zhong Xiaodong , Spottiswoode Bruce S. , Meyer Craig H. , Kramer Christopher M. , Epstein Frederick H.
Published: June 2010

A navigator‐gated 3D spiral cine displacement encoding with stimulated echoes (DENSE) pulse sequence for imaging 3D myocardial mechanics was developed. In addition, previously described 2D postprocessing algorithms including phase unwrapping, tissue tracking, and strain tensor calculation for the left ventricle (LV) were extended to 3D. These 3D methods were evaluated in five healthy volunteers, using 2D cine DENSE and historical 3D myocardial tagging as reference standards. With an average scan time of 20.5 ± 5.7 min, 3D data sets with a matrix size of 128 × 128 × 22, voxel size of 2.8 × 2.8 × 5.0 mm3, and temporal resolution of 32 msec were obtained with displacement encoding in three orthogonal directions. Mean values for end‐systolic mid‐ventricular mid‐wall radial, circumferential, and longitudinal strain were 0.33 ± 0.10, −0.17 ± 0.02, and −0.16 ± 0.02, respectively. Transmural strain gradients were detected in the radial and circumferential directions, reflecting high spatial resolution. Good agreement by linear correlation and Bland‐Altman analysis was achieved when comparing normal strains measured by 2D and 3D cine DENSE. Also, the 3D strains, twist, and torsion results obtained by 3D cine DENSE were in good agreement with historical values measured by 3D myocardial tagging. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
An optimized 3D spoiled gradient recalled echo pulse sequence for hemorrhage assessment using inversion recovery and multiple echoes (3D SHINE) for carotid plaque imaging
Authors: Zhu David C. , Vu Anthony T. , Ota Hideki , DeMarco J. Kevin
Published: June 2010

Intraplaque hemorrhage into the carotid atherosclerotic plaque has been shown to create instability and progression. We have developed an optimized 3D Spoiled Gradient recalled echo pulse sequence for Hemorrhage assessment using INversion recovery and multiple Echoes (3D SHINE) for carotid plaque imaging. The sequence was developed by incorporating multiecho acquisition to its clinically validated optimized single‐echo counterpart 3D inversion recovery prepared fast spoiled gradient recalled sequence. With similar scan time (4 min), 3D spoiled gradient recalled echo pulse sequence for hemorrhage assessment using inversion recovery and multiple echoes maintained comparable high‐resolution volumetric coverage, black‐blood effect, contrast, signal‐to‐noise and contrast‐to‐noise ratios, and similar sensitivity and specificity in detecting whether intraplaque hemorrhage was present on an artery. The multiple echoes acquired with 3D SHINE allowed the estimation of intraplaque hemorrhage T*2 and then the subsequent characterization of intraplaque hemorrhage (T*2 for type I < 14 msec, and for type II > 14 msec). The type I intraplaque hemorrhage size estimated by 3D SHINE was significantly and positively correlated with the size estimated manually by an expert reviewer using the histology‐validated multicontrast MRI technique (r = 0.836 ± 0.080, p < 0.001). With only one fast sequence, 3D SHINE can detect and characterize intraplaque hemorrhage that has previously required a multicontrast approach using a combination of black‐blood T1‐weighted, black‐blood T2‐weighted, and time‐of‐flight imaging techniques. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.
Deflated preconditioned conjugate gradient solvers for the pressure‐Poisson equation: Extensions and improvements
Authors: Löhner Rainald , Mut Fernando , Cebral Juan Raul , Aubry Romain , Houzeaux Guillaume
Published: June 2010

Extensions and improvements to a deflated preconditioned conjugate gradient technique for the solution of the pressure‐Poisson equation within an incompressible flow solver are described. In particular, the use of the technique for embedded grids, for cases where volume of fluid or level set schemes are required and its implementation on parallel machines are considered. Several examples are included that demonstrate a considerable reduction in the number of iterations and a remarkable insensitivity to the number of groups/ regions chosen and/or to the way the groups are formed. Copyright © 2010 John Wiley & Sons, Ltd.
A discrete mechanics approach to the Cosserat rod theory—Part 1: static equilibria
Authors: Jung Pascal , Leyendecker Sigrid , Linn Joachim , Ortiz Michael
Published: June 2010

A theory of discrete Cosserat rods is formulated in the language of discrete Lagrangian mechanics. By exploiting Kirchhoff's kinetic analogy, the potential energy density of a rod is a function on the tangent bundle of the configuration manifold and thus formally corresponds to the Lagrangian function of a dynamical system. The equilibrium equations are derived from a variational principle using a formulation that involves null‐space matrices. In this formulation, no Lagrange multipliers are necessary to enforce orthonormality of the directors. Noether's theorem relates first integrals of the equilibrium equations to Lie group actions on the configuration bundle, so‐called symmetries. The symmetries relevant for rod mechanics are frame‐indifference, isotropy, and uniformity. We show that a completely analogous and self‐contained theory of discrete rods can be formulated in which the arc‐length is a discrete variable ab initio. In this formulation, the potential energy density is defined directly on pairs of points along the arc‐length of the rod, in analogy to Veselov's discrete reformulation of Lagrangian mechanics. A discrete version of Noether's theorem then identifies exact first integrals of the discrete equilibrium equations. These exact conservation properties confer the discrete solutions accuracy and robustness, as demonstrated by selected examples of application. Copyright © 2010 John Wiley & Sons, Ltd.
Variation in health and socioeconomic status within the W. Montague Cobb skeletal collection: Degenerative joint disease, trauma and cause of death
Authors: Watkins R.
Published: June 2010

This paper examines health differences between two distinct samples within an African American skeletal population by investigating variation in osteoarthritis (OA) patterns, the presence of enthesopathies, fractures and cause of death. Surveys and statistical treatments tested the hypothesis that two samples within a population that have different socioeconomic contexts will present associated differences in health.

Binomial statistics were used to examine differences in OA patterns and prevalence within and between groups, and according to age and sex. These data were paired with information on the presence of enthesopathies at select muscle attachment and insertion sites to add another dimension to the assessment of mechanical strain. Finally causes of death, when available, were recorded to compare leading causes within and between samples, as well as with the larger population.

Data reveal significant differences in the prevalence of OA between groups. Significant differences also presented when comparing the prevalence of unilateral and bilateral affect. Although a number of differences in health status observed can be attributed to age, relationships between the presence of OA and enthesopathies in a portion of the sample indicates that degenerative change and hypertrophy in the samples reflect both systemic and non‐systemic change. The presence and pattern of fractures and causes of death are also suggestive of differences in social context between the two samples. Copyright © 2010 John Wiley & Sons, Ltd.
Time‐delay dependentH∞model simplification for singular systems with Markovian jumping parameters
Authors: Lu Hongqian , Zhou Wuneng , Xu Yuhua , Fang Jian'an , Tong Dongbing
Published: June 2010

The problem ofH∞model simplification for singular systems with Markovian jumping parameters and time‐delay is investigated. For a given stochastic stable system, our attention is focused on the construction of reduced‐order models which guarantee the corresponding error system to be admissible and have a prescribedH∞error performance. A robust admissibility condition and a robust bounded real lemma are developed based on which, sufficient conditions for the existence of desired reduced‐order models are proposed. Desired reduced‐order model can be constructed when the proposed conditions are satisfied. The effectiveness of the proposed model reduction method is illustrated via a numerical example. Copyright © 2010 John Wiley & Sons, Ltd.
Selected experimental methods for determining droplet parameters from the intensity distribution of scattered light: A review
Authors: Roth N. , Weigand B.
Published: June 2010

The present paper summarizes some experimental methods, which have been developed using the results of calculations based on the theory of Gustav Mie. As examples two regions of the scattered light are considered in more detail. The intensity distribution in the forward hemisphere for scattering angles 30 ≤ θ ≤ 60 shows maxima, which can be identified as regular fringes on a screen. The spacing between the fringes is a measure for the droplet size.

In the intensity distribution of the backward hemisphere the region of the first rainbow can be found. In the rainbow region a main maximum, subsidiary maxima and a ripple structure can be identified. The angular position of the main maximum is a measure for the refractive index of the droplet. The angular distance between the subsidiary maxima and the angular distance between the ripples both are a function of droplet size. A comparison with other size measurement methods gives information about the sphericity of the droplet.

An evaporating droplet shows for instance oscillations of the rainbow position due to morphology dependent resonances. The oscillation frequency is proportional to the evaporation rate.
Applicability of constitutive laws for simulations of shock wave‐loaded plates
Authors: Stoffel M. , Schmidt R. , Weichert D.
Published: June 2010

In the present study simulations using different constitutive laws are compared with each other in order to find a model which is most suitable to calculate the deformations of shock wave‐loaded plates.
Parameter Identification of a Finite Viscoplastic Material Model using different Deterministic Optimization Methods
Authors: Rieger A. , Scheday G. , Miehe C.
Published: June 2010

The efficiency of two deterministic optimization strategies are discussed in order to solve the arising least squares minimization problem. A sequential quadratic programming method is compared with a trust region enhanced simplex method. In particular we focus on the effort to determine the necessary gradients for the sqp‐method and compare the computational costs of the identification process. In the later development the identification problem is extended to account for inhomogeneous deformations using the finite element method for simulation purpose. Here, displacement fields are determined via an optical measurement technique. The accompanying modification of the solution procedure results in an extended least squares functional. The sensitivity analysis, needed for the gradient based method, is embedded in a distinct format in the finite element context.
Cross‐coupling and Unbalance Compensation of a Rigid Rotor
Authors: Hirschmanner Martin
Published: June 2010

The system under investigation is a rigid rotor supported by two active magnetic bearings. In this paper two coexisting sources of vibrations are considered. First, mass unbalance excitation as a synchronous periodic disturbance and second, destabilizing cross‐coupling forces as generated, for example, by fluid film mechanisms, annular pressure seals or labyrinths of a turbo machine. The basic AMB‐control is carried out by a simple PID controller while for the compensation of both excitation mechanisms two independent control algorithms are used. In order to compensate the destabilizing cross‐coupling forces a least square estimator estimates the unknown parameters of the cross‐coupling mechanism. The mass unbalance forces are compensated by a recursive gain scheduled algorithm. By combining these two algorithms a significant reduction of the vibration level is achieved.
An approach to the modelling of worm‐like motion systems with finite degree of freedom – First steps in technical realization
Authors: Zimmermann K. , Zeidis I. , Jianjun Huang , Steigenberger J.
Published: June 2010

The paper presents some investigations of worm‐like motion systems that have the earthworm as live prototype. The systems are modeled in form of straight chains of n interconnected mass points. The ground contact can be described by non‐symmetric dry friction. Analytical solutions using asymptotical methods are presented.
Phasebehaviour of a 3D–Stell–Hemmer Liquid
Authors: Mausbach P. , May H.‐O.
Published: June 2010

Investigations for one– and two–dimensional systems have shown that the Stell–Hemmer potential can produce liquid–state anomalies. By means of a Monte Carlo simulation for a N; V; T–ensemble we calculate the phase behaviour and show that these anomalies disappear in three dimensions.
Regelung eines elastischen Roboters mit Zwangskräften am Greifer
Authors: Mitterhuber Ralph , Bremer Hartmut
Published: June 2010

Bei einem Knickarmroboter mit 6 Gelenken und 2 schlanken, elastisch verformbaren Armen, dessen Greifer im Kontakt mit einer bewegten Zwangsfläche steht, werden die Greiferposition und ‐orientierung geregelt.
Arbitrary Pole Assignability by Static Output Feedback under Structural Contraints
Authors: Reinschke K. J.
Published: June 2010

Using a few elementary concepts from algebraic geometry such as multidimensional projective space, quadric hypersurface and its tangential variety, the known problem of arbitrary pole placement is transformed into a system of well‐structured (partly non‐linear) algebraic equations. Necessary and sufficient solvability conditions are derived. Finally, it is outlined how to calculate admissible output feedback matrices which ensure the desired pole assignment.
Enclosure of Algebraic Functions and Bounded–Input Bounded–Output Stability of Linear Time–Discrete Scalar Bivariate Dynamical Systems
Authors: Boese F. G.
Published: June 2010

An enclosure set for the general polynomial in two complex variables is expounded. Based thereupon, BIBO stability criteria for time–discrete, time–constant bivariate linear dynamical systems are set forth.
Electrical and luminescence properties of Mg‐doped p‐type GaPN grown by molecular beam epitaxy
Authors: Mitsuyoshi S. , Umeno K. , Furukawa Y. , Urakami N. , Wakahara A. , Yonezu H.
Published: June 2010

We have demonstrated the acceptor concentration control for p‐type GaPN grown by molecular beam epitaxy (MBE) using Mg as the acceptor element. The hole concentration increases up to 2×1019 cm‐3 at 300 K and does not remarkably vary after thermal treatment and thus Mg is successfully doped into GaPN. Subsequently, we have investigated the electrical and luminescence properties of Mg‐doped p‐type GaPN grown by MBE. The activation energy is estimated to be about 37 meV, indicating Mg is a shallow acceptor element for p‐type GaPN grown by MBE. When the hole concentration is larger than ∼1018 cm‐3, the photoluminescence (PL) intensity decreases with increasing the hole concentration. By time‐resolved PL (TRPL) measurement, this PL quenching is caused by the non‐radiative centres due to Mg doping when the hole concentration is larger than ∼1018 cm‐3. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of rugged 2 GHz power bars delivering more than 100 W and 60% power added efficiency
Authors: Waltereit P. , Bronner W. , Quay R. , Dammann M. , Müller S. , Köhler K. , Mikulla M. , Ambacher O. , Harm L. , Lorenzini M. , Rödle T. , Riepe K. , Bellmann K. , Buchheim C. , Goldhahn R.
Published: June 2010

In this work we systematically study the structural, optical and electrical properties of AlGaN/GaN heterostructures grown by MOCVD 3‐inch on SiC substrates The finally developed HEMTs demonstrate excellent high‐voltage stability, high power performance and large power added efficiencies. For a drain bias of 100 V an output‐power‐density around 26 W/mm with 25 dB linear gain is obtained. On 36 mm gate width devices an output power beyond 100 W is achieved with a power added efficiency above 60% and a linear gain around 17 dB. Ruggedness on these large devices is proven by successfully passing harsh intentional device mismatch tests during operation at 50 V. Reliability is tested at a drain bias of 50 V. Under DC conditions a drain‐current degradation below 20% after 20 years is extrapolated. Under RF stress the observed change in output power is well below 0.1 dB after a test duration of more than 500 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acoustic phonon effects on telecommunication‐band quantum dot exciton Rabi oscillation
Authors: Miyazawa Toshiyuki , Nakaoka Toshihiro , Kodera Tetsuo , Takagi Hiroyuki , Kumagai Naoto , Watanabe Katsuyuki , Arakawa Yasuhiko
Published: June 2010

We investigated the effect of acoustic phonon mediated damping on a telecommunication‐band excitonic Rabi oscillation in a single quantum dot (QD). The InAs/GaAs QDs were capped with an InGaAs strain‐reducing layer (SRL) to shift the exciton energy to the O‐band (the lowest dispersion band; 1.26‐1.36 mm). They were also embedded in an n ‐i ‐Schottky diode in order to prove the excitonic state in a single photo‐excited QD by photocurrent spectroscopy. The observed exciton linewidth increased linearly at the low temperature due to the exciton‐acoustic phonon coupling, and increased drastically above 40 K due to the nonlinear increment of the exciton‐LO phonon coupling. We successfully observed excitonic Rabi oscillation up to 40 K even though the acoustic phonon‐mediated damping increased with temperature. This result suggests that the telecommunication‐band QDs are useful in constructing the exciton‐based qubits under the influence of the coupling between excitons and acoustic‐phonons. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c‐plane sapphire by metal organic chemical vapor deposition
Authors: Xue J. S. , Hao Y. , Zhang J. C. , Yang L. A.
Published: June 2010

The effect of growth temperature of AlN interlayers on the properties of GaN epilayers grown on c‐plane sapphire by metal organic chemical vapor deposition has been investigated by high resolution X‐ray diffraction (HRXRD) and Raman spectroscopy. It is concluded that the crystalline quality of GaN epilayers is improved significantly by using the high temperature AlN (HT‐AlN) interlayer in GaN buffers. The density of threading dislocation is reduced especially for edge type dislocations. Higher compressive stress exists in GaN epilayers with HT‐AlN interlayer than with low temperature AlN (LT‐AlN) interlayer, which is related to the reduction of strain relaxation caused by the formation of misfit dislocation. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hg(1‐x)CdxTe from short to long wave infrared on Si substrates grown by MBE
Authors: Vilela M. F. , Olsson K. R. , Reddy M. , Peterson J. M. , Franklin J. J. , Vang T. , Lofgreen D. D. , Johnson S. M.
Published: June 2010

In this paper, we show the power of using molecular beam epitaxy (MBE) for the growth of the mercury cadmium telluride (HgCdTe) system. Abrupt composition profiles, changes in doping levels, or switching doping types are easily performed. It is shown that high quality material is achieved with Hg(1‐x)CdxTe grown by MBE from a cadmium mole fraction of x =0.15 to x =0.72. Doping elements incorporation as low as 1015 cm‐3 for both n‐type and p‐type material as well as high incorporation levels >1018cm‐3 for both carrier types were achieved. Secondary ion mass spectrometry (SIMS) data, x‐ray data, Hall data, the influence of doping incorporation with cadmium content and growth rate, etch pit density (EPD), composition uniformity determined from Fourier transform infrared (FTIR) transmission spectroscopy, and surface defect maps from low to high x values are presented to illustrate the versatility and quality of HgCdTe material grown by MBE. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Space‐charge‐limited current transport in nitride HFETs
Authors: Schimizzi R. D. , Trew R. J. , Bilbro G. L.
Published: June 2010

High‐voltage microwave AlGaN/GaN HFETs operating under high‐power conditions suffer from degraded RF performance and linearity due to a nonlinear resistance effect in the gate‐source region. During RF operation, the nonlinear resistance is due to the onset a of space‐charge‐limited current (SCLC) transport mechanism within the device channel. Under high current injection conditions, SCLC transport can set in and, consequently, the source resistance becomes a function of the injected charge causing a rapid increase and limiting device performance. The threshold for SCL current is dependent on the donor‐like states on the AlGaN surface which are responsible for supplying electrons to the channel. To alleviate the effect of nonlinear source resistance we show on an un‐gated HFET channel model that the critical current density of space‐charge effects and thus the onset of nonlinear source resistance can be shifted above the normal operating current density of the device by modification of the charge on the AlGaN surface. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear‐mode operation of the quantum‐dot avalanche photodiode (QDAP)
Authors: Ramirez David A. , Shao Jiayi , Hayat Majeed M. , Krishna Sanjay
Published: June 2010

We report new results on the design, fabrication and characterization of a novel midinfrared sensor called quantum dot avalanche photodiode (QDAP). The QDAP consists of a quantum dots‐in‐a‐well (DWELL) detector coupled with an avalanche photodiode (APD) through a tunnel barrier. In the QDAP, the photons are absorbed in the DWELL active region while the APD section provides gain.

Photocurrent and noise measurements at 77 K were taken to characterize the response of the device. The nonlinear increase in the photocurrent as the APD voltage increases support theoretical predictions about the QDAP capability to work in applications with low photon flux levels. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Short‐period AlN/GaN p‐type superlattices: hole transport use in p‐n junctions
Authors: Simon John , Cao Yu , Jena Debdeep
Published: June 2010

Hole transport properties of short‐period Mg‐doped AlN/GaN superlattices are compared with bulk Mg‐doped GaN layers. Due to polarization‐induced reduction in acceptor ionization energy, the superlattice structures are observed to result in a nearly temperatureindependent in‐plane p‐type conductivity as opposed to a 100‐fold decrease in bulk p‐type GaN as temperature drops from 300 K to 100 K.

Moreover, significant vertical p‐type conductivity is facilitated by the ultrathin AlN barriers due to possible hole tunneling & miniband formation: p‐n junctions are demonstrated by replacing the p‐type GaN layer by a superlattice. The results indicate the feasibility of enhancement of both vertical and lateral p‐type conductivity in bipolar transistors and deep‐UV optical devices. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Heterostructure engineering in Type II InAs/GaSb strained layer superlattices
Authors: Myers Stephen , Plis Elena , Kim Ha Sul , Khoshakhlagh Arezou , Gautam Nutan , Lee Sang Jun , Noh Sam Kyu , Krishna Sanjay
Published: June 2010

The background carrier concentration is an important factor in the performance of detectors. We have investigated the effect of a variable background doping concentration in the absorber region of an nBn type‐II InAs/GaSb superlattice infrared detector. The doping concentrations were 5 × 1016 cm‐3 (non‐intentionally doped, n.i.d.), 1.4 × 1017 cm‐3, 4.0 × 1017 cm‐3, and 3.5 × 1018 cm‐3. The specific detectivity of the detectors was found to dramatically decrease as the doping concentration was increased. This was caused by an increase in dark current density which is attributed to the presence of a quantum well (QW) formed in the valence band. This QW allowed for enhanced electron‐hole recombination at higher doping concentrations. Consequently the n.i.d. device demonstrated the best performance with a zero bias specific detectivity (D*) equal to 1.2 × 1011 Jones at 77 K. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of c‐axis oriented Ga‐doped MgZnO‐based UV transparent electrodes by molecular precursor method
Authors: Honda Tohru , Oda Takuto , Mashiyama Yoshihiro , Hara Hiroki , Sato Mitsunobu
Published: June 2010

MgZnO films were fabricated by the molecular precursor method (MPM) for their application as UV transparent electrodes. It was clarified that annealing under suitable conditions using an Ar gas flow is effective for the realization of c‐axis‐oriented MgZnO films in the time of a pyrolysis reaction. The resistivity of the Ga‐doped Mg0.1Zn0.9O film was 2.5 × 10‐2 Ω · cm. The resistivity of the c‐axis‐oriented MgZnO films was lower than that of polycrystalline films. This is due to the reduction of the potential barrier at the boundaries of the crystallites. The spontaneous polarization affects the potential barrier. The c‐axis orientation reduces the potential barrier along the deposition plane (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical Kerr signals of GaAs/AlAs multilayer cavities with two‐photon resonant quantum wells in the half‐wavelength layer
Authors: Isu Toshiro , Kanbara Toshiyuki , Takahashi Tomoya , Morita Ken , Kitada Takahiro
Published: June 2010

Optical Kerr signals from GaAs/AlAs multilayer micro‐cavities with GaAs/AlGaAs multi‐quantum wells (MQW) in the half‐wavelength cavity layer were investigated. The cavity‐mode‐wavelengths were set at the resonance region of two‐photon absorption of the MQWs in the 1.5‐μm band. The measured intensities of the signals depended strongly on the cavity‐mode wavelength, although the cavity layers including the MQW and multilayers maintained approximately the same structure. The nonlinearity of the MQW is considered to vary considerably at the resonant wavelength of the two‐photon absorption. The results indicate that the optical Kerr signal of the multilayer micro‐cavity is dominated by the nonlinearity of the cavity layer, although the cavity layer is only a small part of the total cavity thickness. This experimentally confirms the results of a previous simulation study on the multilayer cavities. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of the extraction of short diffusion lengths from simulated electron‐beam induced current
Authors: Wee D. , Parish G. , Nener B.
Published: June 2010

This paper reports on the investigations via 2‐D simulation into the accuracy of diffusion length extraction from scanning electron‐beam induced current measurements when the diffusion length, L is very short. L is extracted by using the direct method proposed by Chan et al. [1] and later refined by Kurniawan and Ong [2] to take finite junction depth into account. The 2‐D simulations were undertaken using Synopsys® Sentaurus TCAD and a realistic electron‐hole pair generation volume was created using CASINO v2.42 [3], a Monte Carlo Scanning Electron Microscope interaction simulation software, and imported into Sentaurus. The voltage and diameter of the electron beam and diffusion length and surface recombination velocity of the semiconductor materials were varied in the simulations to determine the errors in the diffusion length extracted from the EBIC signals as a function of these parameters. The results of the simulation show that the accuracy of the method proposed in [1] is reasonably accurate and that the beam voltage and spot size do not have significant effects on the accuracy (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of polar direction of AlN grown on (0001) sapphire and 6H‐SiC substrates by high‐temperature metal‐organic vapor phase epitaxy using coaxial impact collision ion scattering spectroscopy
Authors: Imura Masataka , Ohnishi Tsuyoshi , Sumiya Masatomo , Liao Meiyong , Koide Yasuo , Amano Hiroshi , Lippmaa Mikk
Published: June 2010

High‐crystalline quality AlN layers with an atomically flat surface are grown on (0001) sapphire and 6H‐SiC substrates by metal‐organic vapor phase epitaxy at 1400 °C without low‐temperature buffer layer. The polar direction of AlN layers is investigated by coaxial impact‐collision ion scattering spectroscopy (CAICISS). For AlN growth on sapphire substrate, trimethylaluminum (TMAl) is supplied for 10 sec before introducing ammonia (NH3). For AlN growth on SiC substrate, TMAl and NH3 are supplied at the same time. The CAICISS spectrum of AlN layers is analyzed by measuring the dependence of the Al atoms signal intensity on the angle of ion beam incidence considering the shadowing and focusing effects for determining the polar direction of AlN layers. The CAICISS spectra clearly indicate the polar direction of AlN layers and both AlN layers are found to be had the Al‐polarity. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Normally‐on/off AlN/GaN high electron mobility transistors
Authors: Chang C. Y. , Lo C. F. , Ren F. , Pearton S. J. , Kravchenko I. I. , Dabiran A. M. , Cui B. , Chow P. P.
Published: June 2010

We report on the novel normally‐on/off AlN/GaN high electron mobility transistors (HEMTs) grown by plasma‐assisted molecular beam epitaxy. With simple oxygen exposure, the threshold voltage can be tuned from ‐2.76 V to +1.13 V depending on the treatment time. The gate current was reduced and current‐voltage curves show metal‐oxide semiconductor diode‐like characteristics after oxygen plasma exposure. The extrinsic transconductance of HEMTs decrease with increasing oxygen plasma exposure time due to the thicker Al oxide formed on the gate area. The unity current gain cut‐off frequency, fT, and maximum frequency of oscillation, fmax, were 20.4 GHz and 36.5 GHz, respectively for an enhancement‐mode HEMT with the gate dimension of 0.4 × 100 μm2. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)