bluuebunny/crossref_metadata_2025 huggingface dataset:
MicroCT analysis of hydroxyapatite bone repair scaffolds created via three‐dimensional printing for evaluating the effects of scaffold architecture on bone ingrowth
Authors: Simon Joshua L. , Rekow E. Dianne , Thompson Van P. , Beam Heather , Ricci John L. , Parsons J. Russell
Published: August 2007

Recent studies have shown that it is now possible to construct tissue‐engineered bone repair scaffolds with tight pore size distributions and controlled geometries using 3‐D Printing techniques (3DP). This study evaluated two hydroxyapatite (HA) 8‐mm diameter discs with controlled architectures in a rabbit trephine defect at 8 and 16 weeks using a 2 × 2 factorial design. Input parameters were time and scaffold void volume at two levels. Three output variables were extracted from MicroCT data: bone volume ingrowth with respect to total region of interest, bone volume ingrowth with respect to available ingrowth volume, and soft tissue volume. The experiment measured two groups—Group 1: 500‐μm × 500‐μm channels parallel to the scaffold's long axis and penetrating up 3‐mm from the bottom. Group 2: 800‐μm × 800‐μm struts spaced 500 μm apart set perpendicularly to each other in each printed layer. Rendered 3‐dimensional MicroCT scans and undecalcified histological slides of implants revealed good integration with the surrounding tissue, and a sizeable amount of bone ingrowth into the device. Factorial analysis revealed that the effects of time were the greatest determinant of soft tissue ingrowth, while time and its interaction with void volume were the greatest determinants of bone volume ingrowth with respect to both total and available volume. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
Characterization of Staphylococcus aureus strains in a rabbit model of osseointegrated pin infections
Authors: Williams Dustin , Bloebaum Roy , Petti Cathy A.
Published: August 2007

Staphylococcus aureus is a common infecting agent of many surgical sites. As a commensal organism to humans and rabbits, the infection process may occur due to native or exogenous S. aureus. We applied exogenous S. aureus ATCC 49230 once weekly to the surgical site of an osseointegrated pin in 20 New Zealand white rabbits. Clinical signs of infection resulted in euthanasia and at necropsy samples were collected from putatively infected sites. The predominant organism cultured was S. aureus. We observed various β‐hemolysis patterns of S. aureus on culture media and used pulsed field gel electrophoresis (PFGE) to determine whether there were distinct strains of S. aureus collected from various sites of the rabbits. On the basis of PFGE results, we found that the exogenous S. aureus ATCC 49230 was not the S. aureus cultured during necropsy, but that S. aureus native to the rabbits was in fact the infecting agent. We conclude that this rabbit model for S. aureus infection, which has not been described previously, may contribute to understanding the pathogenesis of S. aureus infections in future studies with simulated osseointegrated pin infections secondary to S. aureus. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2008
Differentiation stage alters matrix control of stem cells
Authors: Hsiong Susan X. , Carampin Paolo , Kong Hyun‐Joon , Lee Kuen‐Yong , Mooney David J.
Published: August 2007

Cues from the material to which a cell is adherent (e.g., adhesion ligand presentation, substrate elastic modulus) clearly influence the phenotype of differentiated cells. However, it is currently unclear if stem cells respond similarly to these cues. This study examined how the overall density and nanoscale organization of a model cell adhesion ligand (arginine‐glycine‐aspartic acid [RGD] containing peptide) presented from hydrogels of varying stiffness regulated the proliferation of a clonally derived stem cell line (D1 cells) and preosteoblasts (MC3T3‐E1). While the growth rate of MC3T3‐E1 preosteoblasts was responsive to nanoscale RGD ligand organization and substrate stiffness, the D1 stem cells were less sensitive to these cues in their uncommitted state. However, once the D1 cells were differentiated towards the osteoblast lineage, they became more responsive to these signals. These results demonstrate that the cell response to material cues is dependent on the stage of cell commitment or differentiation, and these findings will likely impact the design of biomaterials for tissue regeneration. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Composites of poly(DL‐lactide‐co‐glycolide) and calcium carbonate: In vitro evaluation for use in orthopedic applications
Authors: Cotton Nicholas J. , Egan Melissa J. , Brunelle John E.
Published: August 2007

Biodegradable materials utilized in current orthopedic sports medicine fixation devices are required to maintain mechanical properties for at least 12 weeks to facilitate tissue healing and then ideally degrade with eventual replacement by surrounding tissue (bone). Current materials exhibit excessive longevity, which limit the potential for bone replacement, an ideal outcome in clinical procedures where revisions are a possibility. This study investigates material property modification of poly(DL‐lactide‐co‐glycolide) (PLGA) by calcium carbonate. Modification of the degradation rate of PLGA by calcium carbonate (16, 36, 51% w/w) was demonstrated and the percentage of calcium carbonate within the polymer optimized at 36% (w/w). The optimized formulation was molded into a fixation screw and in vitro degradation demonstrated a gradual loss in molecular weight but with a pull‐out strength retention beyond 12 weeks. Significant mass loss then occurred after 26 weeks. Physical testing, insertion torque, and failure torque indicated that this composite also had sufficient initial mechanical properties required for screw in type fixation devices. The combination of mechanical properties and degradation behavior suggests that this material may have potential to be utilized in orthopedic fixation devices that are placed in bone. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Closing capacity of segmental radius defects in rabbits
Authors: Bodde Esther W.H. , Spauwen Paul H.M. , Mikos Antonios G. , Jansen John A.
Published: August 2007

In the research of synthetic bone graft substitutes, the relevance for bone regeneration can be confirmed in a critical‐sized model. In this study the rabbit radial defect was investigated as an ingenious model of critical size, due to its defect immobilizing intact ulna. In addition, the influence of poly(DL‐lactic‐co‐glycolic acid) (PLGA) on bone regeneration was determined. Sixteen, 4‐month‐old rabbits received bilateral segmental radial defects of 15 or 20 mm. The osteotomy ends were marked with small titanium pins. Half of the group received injected PLGA microparticle/carboxymethylcellulose implants. Implantation time was 12 weeks. Evaluation consisted of radiographs after surgery and sacrifice, microcomputed tomography and histology. The radiographs revealed that the created defects were significantly smaller after sacrifice. Further a number of radii showed fibrocartilaginous interposition. Both findings indicated instability of the created defect. All evaluation techniques revealed that 15 and 20 mm were not of critical size, as most defects were more or less regenerated. PLGA microparticles did not influence bone regeneration significantly. In conclusion, 15‐ and 20‐mm radius defects in 4‐month‐old rabbits were not a suitable model for bone regeneration as these defects were neither critical size nor stable. PLGA‐microparticle degradation did not influence bone regeneration. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Enhanced osteoblast functions on anodized titanium with nanotube‐like structures
Authors: Yao Chang , Slamovich Elliott B. , Webster Thomas J.
Published: August 2007

Previous studies have demonstrated increased osteoblast (bone‐forming cells) adhesion on titanium and Ti‐6Al‐4V anodized to possess nanometer features compared with their unanodized counterparts. In this study, osteoblast long‐term functions (specifically, synthesis of intracellular proteins, synthesis of intracellular collagen, alkaline phosphatase activity, and deposition of calcium‐containing minerals) were determined on titanium anodized to possess either heterogeneous nanoparticles or ordered nanotubes. Titanium was anodized in dilute hydrofluoric acid at 20 V for 20 min to possess nanotubes, while titanium was anodized at 10 V for 20 min to possess nanoparticles. Most importantly, results showed that calcium deposition significantly increased on anodized titanium with nanotube‐like structures compared with unanodized titanium and anodized titanium with nanoparticulate structures after 21 days of osteoblast culture. In this manner, the results of the present in vitro study indicated that anodization might be a promising quick and inexpensive method to modify the surface of titanium‐based implants to induce better bone cell functions important for orthopedic applications. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Modeling of electric‐stimulus‐responsive hydrogels immersed in different bathing solutions
Authors: Luo Rongmo , Li Hua , Birgersson Erik , Lam Khin Yong
Published: August 2007

By reformulation of the fixed charge density and consideration of finite deformation, a previous model simulating the pH‐sensitive hydrogels is refined in this paper for extension to simulating the electric‐sensitive hydrogels, which is termed the refined multi‐effect‐coupling electric‐stimulus (rMECe) model. The rMECe model is based on the assumptions: (a) the hydrogel is isotropic and macroscopically homogeneous, (b) all the three phases are incompressible, including the polymeric solid matrix, interstitial water and mobile ions, (c) the effect of electro‐osmosis is neglected, (d) bath solution is ideal so that the variation of the activity coefficients with ionic strength can be negligible, i.e., its effect on the concentration profiles is negligible, (e) the smart hydrogel is immersed in an unstirred solution in vibration‐free experimental device; the bulk flow of fluid or hydrodynamic velocity can thus be eliminated and subsequently the convective flux is neglected, and (f) the pore of the present hydrogel is narrow enough so that the diffusion dominates the transmission of flux. The model consists of nonlinear coupled partial differential governing equations with the coupling effects of chemo‐electro‐mechanical multi‐energy domains and the fixed charge density with the effect of externally applied electric‐field. By comparing the simulating results with experimental data extracted from literature, a very good agreement is achieved and thus this validates the computing accuracy and stability of model. The present rMECe model shows the capability of efficiently predicting the ionic transport and the performance of the hydrogels when they are immersed in a bath solution subject to externally applied electric voltage. The model is used for quantitative analysis of the electric‐sensitive hydrogels and for discussion of the influences of several physical parameters on the response of the hydrogels, including the externally applied electric voltage, the initially fixed charge density, and the ionic strength and valence of surrounding solution. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2008
Helper‐dependent adenovirus for the gene therapy of proliferative retinopathies: stable gene transfer, regulated gene expression and therapeutic efficacy
Authors: Lamartina Stefania , Cimino Monica , Roscilli Giuseppe , Dammassa Ernesta , Lazzaro Domenico , Rota Rossella , Ciliberto Gennaro , Toniatti Carlo
Published: August 2007

Background

Ocular neovascular disorders, such as diabetic retinopathy and age‐related macular degeneration, are the principal causes of blindness in developed countries. Current treatments are of limited efficacy, whereas a therapy based on intraocular gene transfer of angiostatic factors represents a promising alternative. For the first time we have explored the potential of helper‐dependent adenovirus (HD‐Ad), the last generation of Ad vectors, in the therapy of retinal neovascularization.

Methods

We first analyzed efficiency and stability of intraretinal gene transfer following intravitreous injection in mice. A HD‐Ad vector expressing green fluorescent protein (GFP) under the control of the cytomegalovirus (CMV) promoter (HD‐Ad/GFP) was compared with a first‐generation (E1/E3‐deleted) Ad vector carrying an identical GFP expression cassette (FG‐Ad/GFP). We also constructed HD‐Ad vectors expressing a soluble form of the VEGF receptor (sFlt‐1) in a constitutive (HD‐Ad/sFlt‐1) or doxycycline (dox)‐inducible (HD‐Ad/S‐M2/sFlt‐1) manner and tested their therapeutic efficacy upon intravitreous delivery in a rat model of oxygen‐induced retinopathy (OIR).

Results

HD‐Ad/GFP promoted long‐lasting (up to 1 year) transgene expression in retinal Müller cells, in marked contrast with the short‐term expression observed with FG‐Ad/GFP. Intravitreous injection of HD‐Ad vectors expressing sFlt‐1 resulted in detectable levels of sFlt‐1 and inhibited retinal neovascularization by more than 60% in a rat model of OIR. Notably, the therapeutic efficacy of the inducible vector HD‐Ad/S‐M2/sFlt‐1 was strictly dox‐dependent.

Conclusions

HD‐Ad vectors enable stable gene transfer and regulated expression of angiostatic factors following intravitreous injection and thus are attractive vehicles for the gene therapy of neovascular diseases of the retina. Copyright © 2007 John Wiley & Sons, Ltd.
The cis/trans isomerization of Cu(II)–bis‐(glycinato) complex in solution: a computer aided multifrequency EPR and DFT/PCM calculation study
Authors: Pezzato M. , Lunga G. Della , Baratto M. C. , Sinicropi A. , Pogni R. , Basosi R.
Published: August 2007

In this paper the Cu(II)–bis‐(glycinato) complex has been analysed in solution by applying a combined approach of multifrequency EPR and DFT/PCM calculations. The accuracy in the determination of magnetic parameters has been reached by the use of a unique simulation program (COSMOS) for the whole range of temperatures analysed and by the error analysis. A change in magnetic parameters was envisaged in the 243–253 K range of temperature, and was interpreted in terms of stabilization, near the freezing point of the solution, of one of the isomers of the complex. A DFT/PCM computational model was crucial in assigning, on the basis of the experimental superhyperfine interaction value, the isomer to the trans form. Copyright © 2007 John Wiley & Sons, Ltd.
Fluorophore‐labeled myosin‐specific antibodies simplify muscle‐fiber phenotyping
Authors: Gregorevic Paul , Meznarich Norman A. , Blankinship Michael J. , Crawford Robert W. , Chamberlain Jeffrey S.
Published: August 2007

Skeletal muscles are frequently analyzed for composition of phenotypically distinct myofibers, as a functional determinant. We describe an improved myofiber phenotyping procedure, involving cryosection co‐incubation with fluorophore‐labeled myosin heavy‐chain (MyHC)‐isoform–specific antibodies. This technique identifies multiple fiber “types” on a single section, thereby reducing reagents and processing, and offers side‐by‐side comparison of samples from multiple species including mice. These advances are valuable for studying the physiological attributes of skeletal muscle in health and disease. Muscle Nerve, 2007
Glucose‐induced de novo synthesis of fatty acyls causes proportional increases in INS‐1E cellular lipids
Authors: Nyblom H. K. , Nord L. I. , Andersson R. , Kenne L. , Bergsten P.
Published: August 2007

Raised concentrations of glucose for extended periods of time have detrimental effects on the insulin‐producing β‐cell. As de novo synthesis of lipids has been observed under such conditions, it was hypothesized that newly formed lipids may preferentially contain saturated fatty acids, which in particular have been associated with impaired β‐cell function. Glucose‐induced de novo synthesis of fatty acids in INS‐1E cells cultured in 5.5, 11, 20 or 27 mM glucose for 5 days was assessed by high‐resolution magic‐angle‐spinning (HR‐MAS) NMR spectroscopy and gas chromatography‐mass spectrometry (GC‐MS). The glucose origin of the increase in fatty acyls was verified by replacing glucose with [1‐13C]glucose during culture followed by analysis with two‐dimensional 1H‐13C NMR spectroscopy. The composition of the fatty acyls was determined by GC‐MS. Fatty acyls determined by HR‐MAS 1H NMR spectroscopy were increased fivefold in INS‐1E cells cultured in 20 or 27 mM glucose compared with cells cultured in 5.5 mM glucose. The five most abundant fatty acids with their relative percentages in INS‐1E cells cultured in 5.5 mM glucose were oleate (33%), palmitate (25%), stearate (19%), octadecenoate (13%) and palmitoleate (4.4%). These proportions were not affected by glucose‐ induced de novo synthesis in INS‐1E cells cultured in 11, 20 or 27 mM glucose. It is concluded that glucose‐induced de novo lipid synthesis results in accumulation of both saturated and unsaturated fatty acids in specific proportions that are identical with those present under control conditions. Copyright © 2007 John Wiley & Sons, Ltd.
Electrical and microstructural properties of low‐resistance Ti/Re/Au ohmic contacts to n‐type GaN
Authors: Rajagopal Reddy V. , Choi Chel‐Jong
Published: August 2007

The microstructural and electrical properties of Ti/Re/Au (10 nm/10 nm/50 nm) ohmic contacts to moderately doped n‐type GaN (4.0 × 1018 cm–3) have been investigated by current–voltage (I –V), Auger electron microscopy (AES) and transmission electron microscopy (TEM). The electrical characteristics of as‐deposited and annealing at temperatures below 800 °C samples exhibit non‐linear behaviour. However, the sample showed ohmic behaviour when the contact is annealed at 900 °C for 1 min in nitrogen ambient. The Ti/Re/Au contacts give specific contact resistance as low as 8.6 × 10–6 Ω cm2 after annealing at 900 °C. It is shown that the surface of the as‐deposited contact is fairly smooth and slightly degraded when the contact is annealed at 900 °C. The Ti/Re/Au ohmic contact showed good edge acuity after annealing at 900 °C for 1 min. Based on the Auger electron microscopy and transmission electron microscopy results, possible ohmic formation mechanisms for the Ti/Re/Au contacts to the n‐type GaN are described and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of aluminum‐doped ZnO thin‐film deposition by magnetron sputtering for liquid crystal display applications
Authors: Minami Tadatsugu , Miyata Toshihiro , Ohtani Yuusuke
Published: August 2007

This paper describes the optimization of ZnO:Al (AZO) thin films formed by a magnetron sputtering method for the purpose of creating a substitute for the indium‐tin‐oxide (ITO) transparent electrodes used in liquid crystal display (LCD) applications. New AZO thin‐film preparation techniques for both decreasing resistivity as well as improving resistivity distribution have been investigated: magnetron sputtering deposition in a weakly reducing atmosphere and newly developed high‐rate magnetron sputtering deposition techniques. A low resistivity below 5 × 10–4 Ω cm and improvement of the resistivity distribution could be obtained using a commercially available high density sintered AZO target by introducing hydrogen gas into the deposition chamber during depositions with a dc magnetron sputtering method that incorporates rf power. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tuning the shape of macroporous silicon
Authors: Trifonov T. , Garín M. , Rodríguez A. , Marsal L. F. , Alcubilla R.
Published: August 2007

Macroporous silicon membranes, prepared by photo‐electrochemical etching, were subjected to pore widening performed by multiple oxidation/oxide‐stripping cycles. We study the dependence of pore cross section and diameter on the oxidation parameters. The anisotropy of the oxidation process allows us to correct the faceted pore shape after the etching and to obtain pores with circular cross section. The shown post‐treatment of macroporous silicon extends the possibilities of the electrochemical etching process to produce structures with a desired geometry. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An analytical approach to the tunnelling current of MOSFETs considering the barrier height reduction caused by the channel electron velocity due to the effective electron mass difference between silicon and oxide
Authors: Mao Ling‐Feng
Published: August 2007

The effects of the barrier height reduction caused by the channel electron velocity due to the effective electron mass difference between silicon and oxide on the gate leakage current in a MOSFET are discussed The calculations show such a barrier height reduction will have a large effect on the direct tunnelling current and the Fowler–Nordheim tunnelling current when the channel electron velocity is higher than 2 × 107 cm/s. The relative increase in the tunnelling current caused by such a barrier height reduction increases with increasing oxide electric field in the regime of the direct tunnelling, but decreases with increasing oxide electric field in the regime of the Fowler–Nordheim tunnelling. The A ‐factor in the Fowler–Nordheim expression increases but the B ‐factor decreases with channel electron velocity, and they remain constant when the channel electron velocity is less than 3 × 106 cm/s. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence of isoelectronically ion‐implanted SiO2 layers
Authors: Salh Roushdey , Fitting Kourkoutis L. , Schmidt B. , Fitting H.‐J.
Published: August 2007

Scanning electron microscopy (SEM) and cathodoluminescence (CL) in combination with scanning transmission electron microscopy (STEM) have been used to investigate thermally grown amorphous silicon dioxide layers implanted isoelectronically with group IV ions (C+, Si+, Ge+, Sn+, Pb+) as well as with group VI ions (O+, S+, Se+). Besides the main luminescent centers in a‐SiO2 layers: the red R luminescence (650 nm; 1.9 eV) of the non‐bridging oxygen hole centers (NBOHC), the blue B (460 nm; 2.7 eV) and the UV (290 nm; 4.3 eV) band of the oxygen deficient centers (ODC), in ion implanted silica additional emission bands are observed. E.g. in Ge+ implanted layers a huge violet band appears at 410 nm (3.1 eV) increasing with the thermal annealing process due to formation of Ge dimers, trimers or higher aggregates, finally leading to destruction of the luminescence centers by further growing to Ge nanoclusters. The Ge cluster size is shown by STEM cross section micrographs.

Generally, group IV element implantation and partial substitution of silicon increases the luminescence in the blue/violet region whereas group VI elements and additional oxygen increase the intensity in the red region, confirming the association of the blue and the red luminescence with oxygen deficient centers and oxygen excess centers, respectively. Thus, the cathodoluminescence spectra of sulfur and oxygen implanted SiO2 layers under special conditions show besides the characteristic luminescence bands a multimodal structure beginning in the green region at 500 nm and extending up to the near infrared region at 820 nm. The energy step differences of the sublevels amount in the average 120 meV and indicate vibronic‐electronic transitions, probably of O2– interstitial molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of substrate temperature on structural, optical and electrical properties of spray pyrolytically grown nanocrystalline SnO2 thin films
Authors: Chacko Saji , Sajeeth Philip Ninan , Vaidyan V. K.
Published: August 2007

SnO2 nanocrystalline thin films were prepared by a spray pyrolysis method on glass substrates at 375, 400, 425, 450 and 500 °C. Structural, optical and electrical properties of these films were studied by X‐ray diffraction, UV–visible and four‐probe methods. The change in electrical conductivity, band gap and optical transmittance was found to be a function of the change in lattice parameters Δa and Δc The samples prepared at 425 °C are found to have good figure of merit and maximum transmittance (96% at 550 nm). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploring and mapping Fermi surfaces of complex materials
Authors: Dugdale S. B.
Published: August 2007

The study of the electronic structure of crystalline materials, and specifically metallic systems, has formed the backbone of physics in the solid state. Our vision of the electronic ground state of a metallic system is dominated by the concept of the Fermi surface, which dictates many of the material properties. The momentum distribution can give invaluable access to information about the Fermi surface topology, and both positron annihilation and Compton scattering experiments can measure it. Here, recent progress in the field is discussed and illustrated with appropriate examples. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the curing temperature on the structure of epoxy/rectorite nanocomposites studied by positrons
Authors: Chen Z. , Liu L. M. , Fang P. F. , Wang H. M. , Wang S. J.
Published: August 2007

The epoxy‐rectorite nanocomposites were prepared at different curing temperature ranged from 70 °C to 200 °C and the effects of curing temperature on microstructure of material have been studied by positron annihilation lifetime spectroscopy (PALS), and X‐ray diffraction (XRD). The XRD patterns show that the intercalated structure existed in the samples cured at 70 °C and 90 °C, and the clay platelets were completely exfoliated while the curing temperature is higher than 110 °C. At low rectorite content the Ps is mainly formed and annihilated in the free volume of the epoxy matrix and the average size of the free volume is essentially unchanged with the curing temperature. With the increasing curing temperature from 70 °C to 110 °C, the dramatic increase in the intensity I2 of second lifetime component indicates the formation of interfacial layers between rectorite and epoxy matrix. The distributions of o‐Ps lifetime and the free volume size have the narrowest distribution for the samples cured at temperature 110 °C and 140 °C, which imply the most homogeneous structure existed in the nanocomposites. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Internal surfaces of voids and cavities in silicon probed by Positron Annihilation Spectroscopy
Authors: Potter N. R. , Coleman P. G.
Published: August 2007

Silicon with a layer of helium created nanovacanies is probed using Positron Annihilation Spectroscopy. Analysis of theS‐parameter and Gaussian fitting of the full γ‐energy spectra shows trapping in cavities both clean and oxygen‐decorated. Repeated measurements at 700 °C suggest that trapping may be occuring in smaller voids surrounding the nanovacancies themselves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of hydrogen bonding on low temperature positronium formation in frozen hexanol
Authors: Suzuki T. , Yu R. S. , Shantarovich V. P. , Ito Y. , Kondo K.
Published: August 2007

The increase of positronium (Ps) formation in polymers (polyethylene and PMMA) cooled below the freezing temperature of molecular motions has been widely accepted to be due to positron interaction with weakly bound (trapped) electrons. For the first time, we will present results on a more complicated effect for monomers: in frozen hexanol below 100 K increase of ortho‐Ps intensity (I3) with elapsed time of the experiment could be inhibited by bleaching and therefore had the traditional explanation. However, around 200 K the increase of I3 with elapsed time was not affected by light and had different nature, namely, reducing of inhibition effect due to formation of hydrogen bonds typical for the solid state structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature dependence of the free volume holes in polyhydroxybutyrate biopolymer: A positron lifetime study
Authors: Abdel‐Hady E. E. , Mohamed Hamdy F. M. , Fareed Somia S.
Published: August 2007

The size of the free volume holes and their distributuion in polyhydroxybutyrate (PHB) biopolymer have been studied using positron annihilation lifetime spectroscopy (PALS). The measurements were performed as a function of the temperature from 243 to 363 K. The temperature dependence of the free volume hole shows a glass transition temperature, Tg at 278 K. The free volume behaviour of PHB shows a small linear increase with temperature below Tg and a steeper increase above Tg. The thermal expansion coefficients of the free volume hole were determined to be 4.78 x 10–3 and 12.5 x 10–3 / K below and above Tg, respectively. The free volume hole distribution shows a narrow distribution below Tg. With increasing temperature, the maximum of the distributions of the free volume holes shifts to higher values. Meanwhile, widening of the distribution is smaller in lower temperature ranges and more pronounced at higher temperatures, especially above Tg. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal evolution of vacancy defects induced in 12 MeV H+ irradiated 6H‐SiC single crystals
Authors: Kerbiriou X. , Barthe M.‐F. , Gentils A. , Desgardin P.
Published: August 2007

In this work positron annihilation lifetime spectroscopy (PALS) has been used to investigate the evolution of the vacancy defects induced in 12 MeV H+ irradiated SiC as a function of the temperature. The irradiation has been performed at room temperature at a fluence of 4 x 1016 cm–2 in 6H‐SiC single crystals using the CERI‐Orléans cyclotron. Thermal treatments have been performed under an argon flux from 300 °C up to 1050°C. The positron lifetime has been measured as a function of the temperature in the range 15–600 K. After irradiation, positrons detect negative ions and two types of vacancy defects: VSi monovacancies and VSi–VC divacancies. After annealing, the lifetime behaviour as a function of the measurement temperature changes indicating different annealing stages. An increase of the long lifetime component is specially observed whereas the corresponding intensity decreases. These changes are correlated to the migration of VSi and the clustering with VSi–VC to form a new vacancy defect. The lifetime of this new defect has been determined and is equal to 235 ± 2 ps. We propose that it is related to VSi–VC–VSi. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Positron annihilation study of alloys for fission and fusion technology
Authors: Slugen Vladimir , Krsjak Vladimir , Petriska Martin , Zeman Andrej , Miklos Marek
Published: August 2007

Positron annihilation spectroscopy (PAS) based on positron lifetime measurements using the conventional positron annihilation lifetime set‐up and the Pulsed Low Energy Positron System (PLEPS) was applied for the investigation of defects of irradiated and thermally treated reactor pressure vessel (RPV) steels as well as for investigation of new materials foreseen for Generation‐IV and fusion facilities. PAS results obtained in framework of several scientific projects are summarised and correlated to other techniques. Possibilities for experimental modelling of irradiation effects using ion implantation instead of neutron irradiation are discussed in the paper. The actually running program of micro structural study of Fe–Cr binary alloys is presented in detail. For the next effective study of radiation degradation of fusion as well as fission materials, the experimental micro structural study of model alloys in combination to computer simulations is recommended. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coincidence Doppler broadening study of phase decomposition in a continuous cast AA 2037 Al alloy
Authors: Wu Y.C. , Wu S.L. , Chen Y.Q. , Wang S.J. , Zhai T.
Published: August 2007

Phase decomposition in hot band of a continuous cast AA 2037 Al alloy was investigated by coincidence Doppler broadening (CDB) of positron annihilation radiation and positron annihilation lifetime spectroscopy (PALS). It was found that there existed V–Cu and V–Cu–Mg complexes in the as‐received hot band at room temperature. At 200°C, positron average lifetime appeared to be a maximum value because of the formation of semi‐coherent precipitates. The shape of the CDB ratio curve was found to be characteristic of Mn, which indicated the formation of V‐Mn complexes or the existence of Mn clusters in the semi‐coherent precipitates. Above 250 °C, coarsening and dissolution of semi‐coherent precipitates resulted in a decrease in lifetime and disappearance of the Mn signal, but the Cu signal increased clearly with increase in annealing temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Continuous amorphization of Cu–Zr studied by positron lifetime and two‐dimensional Doppler broadening measurements
Authors: Puff W. , Rabitsch H. , Würschum R. , Wilde G.
Published: August 2007

Positron lifetime and 2‐dimensional Doppler broadening measurements were used to study the amorphization of Cu60Zr40 induced by consecutive folding and rolling. In an intermediate state of folding and rolling cycles a complex microstructure evolves with structural free volumes exhibiting a local environment with enhanced Zr content. In the fully amorphous state after 80 cycles, free volumes of the size of a few missing atoms occur which is contrast to amorphous alloys prepared by melt‐spinning. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pulsed low energy positron system (PLEPS) at the Munich research reactor FRM II
Authors: Egger W. , Sperr P. , Kögel G. , Dollinger G.
Published: August 2007

Currently, the Munich pulsed low energy positron beam‐system (PLEPS) is transferred to the high‐intensity positron source (NEPOMUC) at the Munich research Reactor FRM II. We expect count‐rates up to 106 cps. Several improvements to enhance the performance of the system have been implemented. Until now, PLEPS was employed exclusively for lifetime measurements. To enable also Doppler‐broadening, coincident Doppler‐broadening and AMOC experiments, two additional detector ports have been installed. An additional chopper allows to suppress pulses and, therefore, to extend the standard time window of 20 ns for precise measurements of longer lifetimes. The high event‐rate supports the use of smaller scintillators. Consequently an improvement in time resolution is expected. Also envisaged is the use of new detector materials. Various measures to further reduce background from back‐scattered positrons and a reduction of the beam diameter down to 1 mm will improve the overall performance of the system. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Digital positron lifetime spectrometer for measurements of radioactive materials
Authors: Jardin M. , Almazouzi A. , Lambrecht M. , Rempel A. , Nagai Y. , van Walle E.
Published: August 2007

A digital positron lifetime spectrometer for the measurements of 2 GBq level radioactive materials has been constructed and successfully tested. The equipment consists of a state‐of‐the‐art digital oscilloscope and three movable scintillation detectors operating in triple‐coincidence mode. The time resolution of 188 ps full‐width at half‐maximum (FWHM) is achieved for the positron lifetime measurements of radioactive specimens. Also by comparison of measurements of well‐known material with and without high 60Co background radiation the ability to measure radioactive specimens is proved. In this paper the performance, construction, installation, optimization and calibration of the setup is reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MBE growth of dilute magnetic (Zn,Mn)Se on Si substrates
Authors: Slobodskyy A. , Keller D. , Gould C. , Ossau W. , Schmidt G. , Molenkamp L. W.
Published: August 2007

We have demonstrated growth of the dilute magnetic II–VI semiconductor (Zn,Mn)Se on As‐passivated (100) oriented Si substrates. Low temperature epitaxy has been used to optimize the growth start. The morphology has been assessed by Nomarski and scanning electron microscopy (SEM). SQUID measurements show the full magnetic moment of the Mn ions and optical investigations show a clear Zeeman splitting of up to 30 meV. All observations indicate a high crystalline quality of the epitaxial layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase effects in HgTe quantum structures
Authors: König M. , Buhmann H. , Becker C. R. , Molenkamp L. W.
Published: August 2007

HgTe quantum well structures with high electron mobilities have been used to fabricate quantum interference devices. Aharonov‐Bohm oscillations have been studied in the low and high magnetic field regime. In the latter case a decrease of the effective ring radius is observed. Additionally, as a consequence of the strong Rashba spin‐orbit coupling within this material, it was possible to observe conductance oscillations which are due to the so‐called Aharonov‐Casher effect. These quantum interference effects are effectively controlled by the applied magnetic and electric field. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of liquid‐phase synthesis parameters on particle sizes and structural properties of nanocrystalline ZnO powders
Authors: Chory Christine , Neder Reinhard B. , Korsunskiy Vladimir I. , Niederdraenk Franziska , Kumpf Christian , Umbach Eberhard , Schumm Marcel , Lentze Michael , Geurts Jean , Astakhov Georgy , Ossau Wolfgang , Müller Gerd
Published: August 2007

In order to obtain well‐controlled size and optimized structural properties, ZnO nanoparticles were grown from ethanolic solutions using acetate, acetylacetonate and dimethylpropylendiamine as stabilizer molecules. The low‐temperature syntheses yield considerably large amounts of pure, nanocrystalline powder. Structural properties like particle size, crystal structure and quality were investigated by x‐ray diffractometry, photoluminescence, and Raman spectroscopy. Particle sizes down to 4 nm and a size dependent anisotropic shape are observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A weighted logistic regression for conjoint analysis and Kansei engineering
Authors: Barone Stefano , Lombardo Alberto , Tarantino Pietro
Published: August 2007

Customer needs for emotional satisfaction are increasingly being considered by product and service designers. While several existing methods such as conjoint analysis (CA), Kano model and quality function deployment support the translation of customer requirements into technical specifications, researchers are now working to develop methods aimed at integrating affective aspects into product design. Kansei engineering (KE) is a design philosophy that considers customer perceptions and emotions by adopting a multi‐disciplinary approach. CA is a useful tool within a KE project. This article presents a methodology for conducting a KE project in early development phases. This methodology is based on two new procedures. The first one is aimed at calculating attribute importance weights by using respondent choice time in controlled interviews. The second procedure allows the exploitation of such weights in an ordinal logistic regression model for analysing the results of CA experiments. By using the proposed methodology, it is possible to identify product/service attributes able to induce specific emotions and feelings in customers and consequently choose the right development strategy. An application of the method for the design of mobile phones is presented. Copyright © 2007 John Wiley & Sons, Ltd.
Effect of exposure misclassification on the mean squared error of population attributable risk and prevented fraction estimates
Authors: Walter S. D. , Hsieh C. C. , Liu Qin
Published: August 2007

Previous work has considered the effect of exposure misclassification on the bias of population attributable risk (AR) estimates, but little is known about the corresponding effects on their precision or mean squared error (MSE). This paper considers AR estimation in typical scenarios for case–control and cohort studies. The analogous index used when exposure reduces the risk—the prevented fraction (PF)—is also investigated.

It is shown, through both theoretical and simulation results, that even with quite modest levels of exposure misclassification, the MSE can increase substantially, relative to the variance of AR estimated without measurement error. When exposure assessment is perfectly sensitive, there is no bias in AR but lack of measurement specificity can still cause a substantial loss of precision. In a few cases, the AR or PF with misclassified exposure can actually have smaller MSE; these exceptional cases arise when sensitivity is poor and the bias in AR or PF is relatively large.

We conclude that while bias can be reduced by defining exposure on a highly sensitive basis, one must also consider the deleterious effect on precision by doing so. Loss of precision in the AR and PF estimates can be safely ignored only when the exposure measure is very accurate. Copyright © 2007 John Wiley & Sons, Ltd.
Mediation analysis via potential outcomes models
Authors: Albert Jeffrey M.
Published: August 2007

This paper develops a causal or manipulation model framework for mediation analysis based on the concept of potential outcome. Using this framework, we provide new definitions and measures of mediation. Effects of manipulations are modeled via the linear structural model. Corresponding structural equation models (SEMs), in conjunction with two‐stage least‐squares estimation and the delta method, are used to perform inference. The methods are applied to data from a study of nursing interventions for postoperative pain. We address the cases of more than two treatment groups, and an interaction among mediators. For the latter, a sensitivity analysis approach to handle unidentified parameters is described. Interpretative advantages of the potential outcomes framework for mediation are emphasized. Copyright © 2007 John Wiley & Sons, Ltd.
Comparing several means of dependent populations of count—A parametric robust approach
Authors: Tsou Tsung‐Shan , Chen Chien‐Hung
Published: August 2007

We propose a parametric robust procedure for comparing several means of dependent populations of counts. The validity of the proposed method requires no knowledge of the true underlying joint distributions so long as they have finite second moments. The efficacy of this novel technique is demonstrated by simulations and the analysis of a data set from the Taiwan National Health Insurance Research Database. Our new parametric robust method is also compared with the popular semi‐parametric generalized estimating equations approach. Copyright © 2007 John Wiley & Sons, Ltd.
Hierarchical Classes Modeling of Rating Data
Authors: Van Mechelen Iven , Lombardi Luigi , Ceulemans Eva
Published: August 2007

Hierarchical classes (HICLAS) models constitute a distinct family of structural models for N-way N-mode data. All members of the family include N simultaneous and linked classifications of the elements of the N modes implied by the data; those classifications are organized in terms of hierarchical, if–then-type relations. Moreover, the models are accompanied by comprehensive, insightful graphical representations. Up to now, the hierarchical classes family has been limited to dichotomous or dichotomized data. In the present paper we propose a novel extension of the family to two-way two-mode rating data (HICLAS-R). The HICLAS-R model preserves the representation of simultaneous and linked classifications as well as of generalized if–then-type relations, and keeps being accompanied by a comprehensive graphical representation. It is shown to bear interesting relationships with classical real-valued two-way component analysis and with methods of optimal scaling.
Corrective Osteotomy for Deformity of the Distal Radius Using a Volar Locking Plate
Authors: Peterson Brett , Gajendran Varun , Szabo Robert M.
Published: August 2007

Dorsally angulated malunions of the distal radius have historically been corrected with an opening wedge osteotomy fixed with a dorsal plate. Volar locking plates may facilitate a less morbid approach to corrective osteotomies of the wrist. Eight consecutive patients with an average age of 40 years (range, 15–52 years) underwent correction of a distal radius deformity through a volar approach. Clinical follow-up averaged 17.4 months (range, 7–41 months). Preoperative radiographs revealed an average of 24° of dorsal tilt in patients with dorsal deformity. Postoperatively, their average measurement was <3° of volar tilt. Patients were initially ulnar-positive with an average of 4 mm ulnar-positive variance (range, 2–7 mm). This corrected to less than 1 mm postoperatively. Postoperative disabilities of the arm, shoulder, and hand (DASH), SF-12, and Mayo Wrist scores averaged 10.8, 40.5, and 82.5, respectively. There were no nonunions, and no plates required removal. Distal radius deformity can be effectively addressed through a volar approach with the use of a locking plate.
Submonolayer Quantum Dots for High Speed Surface Emitting Lasers
Authors: Ledentsov NN , Bimberg D , Hopfer F , Mutig A , Shchukin VA , Savel’ev AV , Fiol G , Stock E , Eisele H , Dähne M , Gerthsen D , Fischer U , Litvinov D , Rosenauer A , Mikhrin SS , Kovsh AR , Zakharov ND , Werner P
Published: August 2007

We report on progress in growth and applications of submonolayer (SML) quantum dots (QDs) in high-speed vertical-cavity surface-emitting lasers (VCSELs). SML deposition enables controlled formation of high density QD arrays with good size and shape uniformity. Further increase in excitonic absorption and gain is possible with vertical stacking of SML QDs using ultrathin spacer layers. Vertically correlated, tilted or anticorrelated arrangements of the SML islands are realized and allow QD strain and wavefunction engineering. Respectively, both TE and TM polarizations of the luminescence can be achieved in the edge-emission using the same constituting materials. SML QDs provide ultrahigh modal gain, reduced temperature depletion and gain saturation effects when used in active media in laser diodes. Temperature robustness up to 100 °C for 0.98 μm range vertical-cavity surface-emitting lasers (VCSELs) is realized in the continuous wave regime. An open eye 20 Gb/s operation with bit error rates better than 10−12has been achieved in a temperature range 25–85 °Cwithout current adjustment. Relaxation oscillations up to ∼30 GHz have been realized indicating feasibility of 40 Gb/s signal transmission.
Strain Relief Analysis of InN Quantum Dots Grown on GaN
Authors: Lozano Juan G , Sánchez Ana M , García Rafael , Ruffenach Sandra , Briot Olivier , González David
Published: August 2007

We present a study by transmission electron microscopy (TEM) of the strain state of individual InN quantum dots (QDs) grown on GaN substrates. Moiré fringe and high resolution TEM analyses showed that the QDs are almost fully relaxed due to the generation of a 60° misfit dislocation network at the InN/GaN interface. By applying the Geometric Phase Algorithm to plan-view high-resolution micrographs, we show that this network consists of three essentially non-interacting sets of misfit dislocations lying along the "Equation missing" directions. Close to the edge of the QD, the dislocations curve to meet the surface and form a network of threading dislocations surrounding the system.