bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of swelling agent on the molecular weight of poly(2,6‐dimethyl‐1,4‐phenylene oxide) synthesized in an aqueous medium
Authors: Liu Qun , Shentu Baoqing , Weng Zhixue
Published: May 2008

The effects of the species and content of a swelling agent on the molecular weight of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that the molecular weight of PPO increases after introducing a certain amount of the swelling agent during the oxidative polymerization of 2,6‐dimethylphenol (DMP). Tg of the PPO/swelling agent mixture decreases with the increase of the swelling agent content, and the relation between Tg of the PPO/swelling agent mixture and the swelling agent content obeys Fox equation. After the introduction of the swelling agent during the oxidative polymerization of DMP, the molecular weight of PPO is correlated with Tg of the PPO/swelling agent mixture and it was revealed that Tg plays an important role in the molecular weight of PPO synthesized in the aqueous medium. The same molecular weight of PPO can be obtained only if Tg of the PPO/swelling agent mixture is the same, no matter what kind of swelling agent is introduced during the oxidative polymerization of DMP. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers
Synthesis and solution properties of poly(vinyl ether)s with long alkyl chain, biphenyl, and cholesteryl pendants
Authors: Seno Ken‐Ichi , Date Akiko , Kanaoka Shokyoku , Aoshima Sadahito
Published: May 2008

The judicious choice of reaction conditions permitted living cationic polymerization of vinyl ethers with bulky and strongly interacting pendant groups, such as crystalline long alkyl chains and liquid crystalline mesogenic structures, using appropriate combinations of Lewis acids with added bases. Thus, well‐defined random and block copolymers with various pendants were also synthesized. Highly sensitive UCST‐type phase separation in various organic solvents was achieved employing crystallization of octadecyl pendants of homopolymers and random copolymers. This phase separation behavior is unusual for a polymer‐organic solvent system. Furthermore, thermally induced reversible physical gelation was conducted using this thermosensitive behavior. These specific pendants were very effective not only in organic media but also in water, in obtaining hydrogels with relatively low polymer concentrations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4392–4406, 2008
Improved properties of polyfluorenevinylenes by introduction of carbazole units
Authors: Jin Youngeup , Lee Minjung , Kim Sun Hee , Song Suhee , Goo Youngran , Woo Han Young , Lee Kwanghee , Suh Hongsuk
Published: May 2008

New electroluminescent polyfluorenevinylenes (PFV) copolymers with carbazole group, CzPFVs, have been synthesized by the GILCH polymerization. The carbazole groups were introduced as pendant to increase the electron rich ability of the copolymers. All CzPFVs exhibited absorption spectra with maximum peaks at around 417 nm. In the PL emission spectra of CzPFVs, maximum peaks around 463 nm and shoulder peaks around 490–500 nm were exhibited. By adjusting the feed ratios of carbazole groups in the CzPFVs, it is possible to have the higher current density and brightness, and the lower turn‐on voltage due to increasing hole injection ability. The maximum luminescence of CzPFV9 was 2003 cd/m2 at 7 V. The introduction of carbazole contents in PFVs can enhance the device performance to result in stable PL and EL spectra with high current density and brightness due to the increased hole injection ability and reduced interchain interaction between polymer backbones. Especially, the 1:1 mixture of CzPFV10 and PVK didn't show aggregation effect in PL spectra even after annealing the thin film at 80 °C up to 60 min, since the interchain interaction among polymer backbones with fluorenevinylene units was reduced. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4407–4419, 2008
Fabrication and characterization of poly(butylene succinate)‐grafted carbon fiber/poly(L‐lactide) nanocomposites
Authors: Moon Sungil , Iji Masatoshi
Published: May 2008

A new poly(butylene succinate) (PBS)‐grafted vapor grown carbon fiber (VGCF)/poly(L‐lactide) (PLLA) nanocomposites were successfully prepared by an in situ condensation reaction between PBS (Mw = 6,000) and surface oxidized VGCF, followed by direct melt mixing technique, and their mechanical and thermal properties were evaluated. Fourier transform infrared spectroscopy and scanning electron microscopy studies indicate a chemical interaction between the PBS and the surface of VGCF. It was found that the maximum tensile strength and modulus of PBS‐grafted VGCF/PLLA nanocomposites were 135 MPa (27% increase relative to neat PLLA) and 4,400 MPa (29% increase relative to neat PLLA), respectively. The results indicate that significant improvement in the mechanical properties can be accomplished by optimizing the surface modification conditions for VGCF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4433–4441, 2008
Synthesis and characterization of side‐chain liquid crystalline ABC triblock copolymers with p‐methoxyazobenzene moieties by atom transfer radical polymerization
Authors: He Xiaohua , Sun Wuqiong , Yan Deyue , Xie Meiran , Zhang Yiqun
Published: May 2008

A series of novel side‐chain liquid crystalline ABC triblock copolymers composed of poly(ethylene oxide) (PEO), polystyrene (PS), and poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PMMAZO) were synthesized by atom transfer radical polymerization (ATRP) using CuBr/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as a catalyst system. First, the bromine‐terminated diblock copolymer poly(ethylene oxide)‐block‐polystyrene (PEO‐PS‐Br) was prepared by the ATRP of styrene initiated with the macro‐initiator PEO‐Br, which was obtained from the esterification of PEO and 2‐bromo‐2‐methylpropionyl bromide. An azobenzene‐containing block of PMMAZO with different molecular weights was then introduced into the diblock copolymer by a second ATRP to synthesize the novel side‐chain liquid crystalline ABC triblock copolymer poly(ethylene oxide)‐block‐polystyrene‐block‐poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] (PEO‐PS‐PMMAZO). These block copolymers were characterized using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatograph (GPC). Their thermotropic phase behaviors were investigated using differential scanning calorimetry (DSC) and polarized optical microscope (POM). These triblock copolymers exhibited a smectic phase and a nematic phase over a relatively wide temperature range. At the same time, the photoresponsive properties of these triblock copolymers in chloroform solution were preliminarily studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4442–4450, 2008
Regio‐regular structure high molecular weight poly(propylene carbonate) by rare earth ternary catalyst and Lewis base cocatalyst
Authors: Tao Youhua , Wang Xianhong , Chen Xuesi , Zhao Xiaojiang , Wang Fosong
Published: May 2008

Lewis base modification strategy on rare earth ternary catalyst was disclosed to enhance nucleophilic ability of active center during copolymerization of carbon dioxide and propylene oxide (PO), poly(propylene carbonate) (PPC) with H‐T linkages over 83%, and number–average molecular weight (Mn) up to 100 kg/mol was synthesized at room temperature using Y(CCl3OO)3‐ZnEt2‐glycerine catalyst and 1,10‐phenanthroline (PHEN) cocatalyst. Coordination of PHEN with active Zinc center enhanced the nucleophilic ability of the metal carbonate, which became more regio‐specific in attacking carbon in PO, leading to PPC with improved H‐T linkages. Moreover, the binding of PHEN to active Zinc center also raised the carbonate content of PPC to over 99%, whereas the PPC from common rare earth ternary catalyst was about 96%. Unlike the highly regio‐regular structure PPC but with relatively low molecular weight recently reported in the literature, our high molecular weight regio‐regular PPC did show significant improvement in thermal and mechanical performances. PPC with H‐T linkages up to 83.2% showed glass transition temperature (Tg) of 43.3 °C, while Tg of PPC with H‐T linkages of 69.7% was only 36.1 °C. When H‐T connectivity was raised from 69.7 to 83.2%, the modulus of PPC showed a 78% increase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4451–4458, 2008
Kinetics of self‐condensing vinyl hyperbranched polymerization in three‐dimensional space
Authors: He Xuehao , Tang Jing
Published: May 2008

Self‐condensing vinyl hyperbranched polymerization (SCVP) with A‐B* type monomer is simulated applying Monte Carlo method using 3d bond fluctuation lattice model in three‐dimensional space. The kinetics of SCVP with zero active energy of reaction is studied in detail. It is found that the maximal number–average and weight–average polymerization degrees and the maximal molecular weight distribution, at varying the initial monomer concentration and double bond conversion, are about 52, 190, and 3.93, respectively, which are much lower than theoretical values. The maximal average fraction of branching points is about 0.27, obtained at full conversion at the initial monomer concentration of 0.75. The simulation demonstrated the importance of steric effects and intramolecular cyclization in self‐condensing vinyl hyperbranched polymerization. The results are also compared with experiments qualitatively and a good agreement is achieved. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4486–4494, 2008
The Cancer Communication Assessment Tool for Patients and Families (CCAT‐PF): a new measure
Authors: Siminoff Laura A. , Zyzanski Stephen J. , Rose Julia Hannum , Zhang Amy Y.
Published: May 2008

Objectives: Caregivers and cancer patients frequently have conflicting and unmet communication needs. The Cancer Communication Assessment Tool for Patients and Families (CCAT‐PF) is a new instrument that assesses congruence in patient–family caregiver communication for both research and clinical purposes.

Methods: The scale was developed using a sample of 190 lung cancer patient–caregiver pairs. Standard psychometric procedures were used to develop and test the scale including qualitative item pool development, item reduction and ascertainment of scale properties.

Results: The multiple correlation of the 18‐item CCAT‐PF scale with the longer 30‐item scale was 0.94. All but three items had less than 20% variance accounted for when each item was regressed on the remaining 17, indicating that responses to an individual item were not readily predicted by the remaining items. Test re‐test reliability was 0.35 and Cronbach's alpha was 0.49 as the CCAT‐PF scale represents the sum of mostly independent items. Higher CCAT‐PF scores were significantly correlated with greater patient depression, greater patient perceived family conflict, lower patient–caregiver assessment and well‐being and less expressiveness and family cohesion. For both patients and caregivers, physical, functional and emotional well‐being were not associated with CCAT‐PF scores.

Conclusion: The CCAT‐PF is a brief but reliable and valid tool. Although administering both family and patient versions is optimal, administering it to a patient or family caregiver only also produces reliable information. Copyright © 2008 John Wiley Sons, Ltd.
Predictors of breast cancer‐related distress following mammography screening in younger women on a family history breast screening programme
Authors: Brain K. , Henderson B. J. , Tyndel S. , Bankhead C. , Watson E. , Clements A. , Austoker J. ,   for the PIMMS Study Management Group
Published: May 2008

Objective: This longitudinal study investigated pre‐screening factors that predicted breast cancer‐specific distress among 1286 women who were undergoing annual mammography screening as part of a UK programme for younger women (i.e., under 50) with a family history of breast cancer.

Methods: Women completed questionnaires one month prior to screening, and one and six months after receiving screening results. Factors measured were breast cancer worry, perceived risk, cognitive appraisals, coping, dispositional optimism, and background variables relating to screening history and family history.

Results: Pre‐screening cancer worry was the most important predictor of subsequent worry, explaining 56/61% and 54/57% of the variance at one and six months follow‐up, respectively. Other salient pre‐screening predictors included high perceived risk of breast cancer, appraisals of high relevance and threat associated with the family history, and low perceived ability to cope emotionally. Women who had previously been part of the screening programme and those with a relative who had recently died from breast cancer were also vulnerable to longer‐term distress. A false positive screening result, pessimistic personality, and coping efforts relating to religion and substance use predicted outcomes of screening at one month follow‐up, but were not predictive in the longer‐term.

Conclusion: Early intervention to ameliorate high levels of cancer‐related distress and negative appraisals would benefit some women as they progress through the familial breast screening programme. Copyright © 2008 John Wiley & Sons, Ltd.
Plasma‐Modified PTFE for Biological Applications: Correlation between Protein‐Resistant Properties and Surface Characteristics
Authors: Vandencasteele Nicolas , Nisol Bernard , Viville Pascal , Lazzaroni Roberto , Castner David G. , Reniers François
Published: May 2008

PTFE samples were treated by low‐pressure O2 RF plasmas. The adsorption of BSA was used as a probe for the protein‐resistant properties. Exposure of PTFE to an O2 plasma leads to an increase in chamber pressure. OES reveals the presence of CO, CO2 and F in the gas phase, indicating a strong etching of the PTFE surface by the plasma. Furthermore, the high‐resolution C1s spectra show CF3, CF and CCF components. WCA as high as 160° were observed, indicating a super‐hydrophobic behavior. AFM images of surfaces treated at high plasma power showed an increase in roughness. Lower amounts of BSA adsorption were detected on high power, O2 plasma‐modified PTFE samples compared to low power, oxygen plasma‐modified ones.

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Effects of Low‐Temperature Atmospheric Air Plasmas on the Activity and Function of Human Lymphocytes
Authors: Shi Xing‐Min , Zhang Guan‐Jun , Yuan Yu‐Kang , Ma Yue , Xu Gui‐Min , Yang Yun
Published: May 2008

Samples of peripheral blood lymphocytes from 20 healthy adult volunteers were treated by using low‐temperature plasmas produced by DBD to investigate their activity and function change as a result of plasma exposure. When the lymphocytes were more than 5 cm away from the electrode center or when the treatment time was shorter than 5 s, their activity and function did not significantly change. When the lymphocytes were less than 5 cm away from the electrode center, and the treatment time was longer than 5 s, the activity and function was significantly reduced. Furthermore, plasma action resulted in the protein, nucleic acid and K+ leakage from lymphocytes, and therefore in the apoptosis of lymphocytes.

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Plasma Modification of Solid and Porous Polyethylene
Authors: Walton Scott G. , Lock Evgeniya H. , Fernsler Richard F.
Published: May 2008

The use of electron beam generated plasmas to modify the surface of solid and porous polyethylene substrates is discussed. In both cases, the hydrophobicity of the material was increased by exposing the substrates to electron beam generated plasmas produced in Ar/SF6 mixtures. The solid material studies served as a basis for understanding the plasma‐induced changes at the substrate surface, while the porous material was treated using a system designed for two‐sided processing applications and proved to be the best way to maximize treatment. Plasma diagnostics were used to characterize the ion and neutral fluxes at the substrates and thereby obtain a better understanding of the plasma–polymer interaction.

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Progress in permafrost hydrology in the new millennium
Authors: Woo Ming‐Ko , Kane Douglas L. , Carey Sean K. , Yang Daqing
Published: May 2008

Increased attention directed at the permafrost region has been prompted by resource development and climate change. This review surveys advances in permafrost hydrology since 2000. Data shortage and data quality remain serious concerns. Yet, there has been much progress in understanding fundamental hydrologic processes operating in a wide range of environments, from steep mountainous catchments, to the Precambrian Shield with moderate relief, to the low‐gradient terrain of plains, plateaus and wetlands. Much of the recent research has focused on surface water, although springs and groundwater contribution to streamflow have also been studied. A compendium of water‐balance research from 39 high‐latitude catchments reveals the strengths and limitations of the available results, most of which are restricted to only a few years of study at the small watershed scale. The response of streamflow to climate receives continued if not increasing attention, from the occurrence of extreme hydrologic events to the changing regimes of river flow at a regional scale. The effect of climate change and the role of permafrost on the changing discharge of large boreal rivers are major topics for further investigation. Extended field and modelling research on physical processes will improve knowledge of permafrost hydrology and enhance its relevance to societal needs. Copyright © 2008 John Wiley & Sons, Ltd.
Recent advances in permafrost modelling
Authors: Riseborough Daniel , Shiklomanov Nikolay , Etzelmüller Bernd , Gruber Stephan , Marchenko Sergei
Published: May 2008

This paper provides a review of permafrost modelling advances, primarily since the 2003 permafrost conference in Zürich, Switzerland, with an emphasis on spatial permafrost models, in both arctic and high mountain environments. Models are categorised according to temporal, thermal and spatial criteria, and their approach to defining the relationship between climate, site surface conditions and permafrost status. The most significant recent advances include the expanding application of permafrost thermal models within spatial models, application of transient numerical thermal models within spatial models and incorporation of permafrost directly within global circulation model (GCM) land surface schemes. Future challenges for permafrost modelling will include establishing the appropriate level of integration required for accurate simulation of permafrost‐climate interaction within GCMs, the integration of environmental change such as treeline migration into permafrost response to climate change projections, and parameterising the effects of sub‐grid scale variability in surface processes and properties on small‐scale (large area) spatial models. Copyright © 2008 John Wiley & Sons, Ltd.
Advances in geophysical methods for permafrost investigations
Authors: Kneisel Christof , Hauck Christian , Fortier Richard , Moorman Brian
Published: May 2008

Geophysical techniques can be used to examine the spatial distribution of subsurface geophysical properties to delineate horizontally and vertically the active layer, permafrost and taliks. Spatial and temporal changes in subsurface geophysical properties due to permafrost cooling, warming, aggradation or degradation can also be assessed through geophysical monitoring. This paper reviews the geophysical methods most frequently applied in mountain and arctic/subarctic lowland permafrost investigations. Key results and recommendations based on the analysis of the applicability and reliability of different geophysical techniques for permafrost studies are summarised. Emphasis is put on the tomographic capabilities of geophysical methods. Recent advances in application and data interpretation are shown in relation to five case studies, and future perspectives are highlighted. Copyright © 2008 John Wiley & Sons, Ltd.
Lowland periglacial research: a review of published advances 2003–2007
Authors: Humlum Ole , Christiansen Hanne H.
Published: May 2008

Research on lowland periglacial landforms and processes is reviewed using papers published from 2003–2007, to identify current interests, trends and directions of advances in knowledge, and to help identify promising avenues for future research. For this period, the total number of identified published research papers was 72. Topics relating to ice wedges, thermokarst, palsas and patterned ground were characterised by high publication activity. Current trends suggest three main research thrusts in the near‐future: palaeoenvironmental reconstructions (including Mars) using current process and landform observations as analogues, year‐round monitoring of processes using automatic equipment and modelling based on Geographical Information Systems. Copyright © 2008 John Wiley & Sons, Ltd.
Real‐time ultrasound measurements of changes in suboccipital vertebral artery diameter and blood flow velocity associated with cervical spine rotation
Authors: Mitchell Jeanette , Kramschuster Kristin
Published: May 2008

Background and Purpose. The vulnerability of the vertebral artery (VA) to distortion with sustained, full‐range cervical spine rotation, resulting in compromised blood flow and possible vertebrobasilar ischaemia, is well recognized. However, few studies have measured such blood flow changes in the parts of the VA downstream from the region of maximum cervical spine rotation: the suboccipital (VA3) and intracranial vertebral arteries. The purpose of this experimental study was to visualize the VA3 and record the changes in its blood flow associated with cervical spine rotation. Method. VA3 diameters and blood flow velocities were measured in the neutral cervical spine position and with active full‐range rotation to the left and right, in 35 healthy female subjects, using colour‐coded real‐time ultrasound. Results. Both left and right VA3 diameters and blood flow velocities decreased significantly on ipsilateral rotation. These values increased non‐significantly in the left VA3 and decreased non‐significantly in the right VA3 on contralateral rotation. Conclusions. The results of this study suggest that the distortion or compression of VA3 demonstrated by the reduction in diameter on ipsilateral cervical spine rotation, particularly, was sufficient to result in compromised blood flow. A significant stretching effect of VA3, on contralateral rotation, was not demonstrated in these subjects. Nevertheless, these findings add evidence to support the recommendation that sustained, full‐range cervical spine rotation should be avoided in professional practice. Copyright © 2008 John Wiley & Sons, Ltd.
Physical findings in patients with dizziness undergoing a group exercise programme
Authors: Kvåle Alice , Wilhelmsen Kjersti , Fiske Heidi Ann
Published: May 2008

Background and Purpose. Although there have been studies on patients with persistent dizziness, physical findings have not been formerly focused. The aim of this study was to investigate localization and extent of physical dysfunctions in patients with long‐lasting dizziness. To investigate physical change, we re‐examined patients who had completed a vestibular rehabilitation (VR) programme. Methods. A longitudinal design was used. Patients with peripheral vestibular dysfunction were examined with the Global Physiotherapy Examination (GPE‐52) and the Vertigo Symptom Scale‐short form (VSS‐SF). The GPE‐52 consists of 52 standardized items within posture, respiration, movement, muscle and skin. Initially, 32 patients were included; 20 completed the VR programme. The programme, based upon traditional VR exercises combined with a body awareness approach, was administered as group sessions taking place once weekly for nine weeks. Results. The majority of patients had a flexed head posture, and their respiration was restricted. Reduced flexibility, reduced ability to relax, measured with passive movements, and restricted range of motion (ROM) were found in about half of the patients in the neck, jaw, shoulder girdle and thorax. On palpation of muscles, 70–94% of the patients had reduced stretch in the abdominals/diaphragm, upper trapezius, sternocleidomastoid and medial gastrocnemius muscles. After the VR programme, significant improvements (p < 0.05) were shown in the following areas: respiration, flexibility and passive movement tests in the shoulder and cervical region, and ROM in the neck and jaw. Significant improvement (p < 0.05) was also reported in the balance subscale of the VSS‐SF. Conclusions. This study documents that postural changes, restricted respiration, lack of flexibility, ability to relax and reduced muscular stretch seem quite common in patients with dizziness. A modified VR comprising body awareness significantly improved respiration and movements in the upper body as well as self‐reported balance. Copyright © 2008 John Wiley & Sons, Ltd.
Crystal orientations of InSb films grown on a Si(111) substrate by inserting AlSb buffer layer
Authors: Murata K. , Ahmad N. B. , Mori M. , Tambo T. , Maezawa K.
Published: May 2008

The heteroepitaxial growth of InSb film via AlSb buffer layer on a Si(111) substrate was performed in an ultra high vacuum. The grown InSb films were characterized by X‐ray diffraction and atomic force microscopy. XRD patterns (ϕ‐scan) of the samples showed different epitaxial relationship between InSb/Si and InSb/AlSb/Si. It is found that surface condition has a significant influence on the growth of InSb films and the surface of InSb films became rough due to the high mixture ratio of domains. The two‐step growth procedure was also tried to further improve the crystal quality of the InSb films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studies on dynamics of charge carrier in organic electroluminescent devices
Authors: Takada N. , Kamata T.
Published: May 2008

Under high current density, lots of organic electroluminescent devices (OELDs) exhibit a substantial decrease in an external quantum coefficient (ηext). Understanding the operating principles of the device is necessary to control the ηext roll off and achieve good performance of OELDs. In this study, we mainly discuss the possible dynamics of charge carrier in our device according to the transient behaviors of electroluminescence (EL) and current after voltage pulse was turn off. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical design of carrier injection rate and recombination rate in tunnel injection quantum well lasers
Authors: Higa Yasutaka , Miyamoto Tomoyuki , Nakajima Hiroshi , Fujimoto Kosuke , Koyama Fumio
Published: May 2008

Carrier injection rate in tunnel injection quantum well structures used in semiconductor lasers was investigated through theoretical analysis. Carrier capture time from 3D‐state to 2D‐state in a conventional quantum well was several ten picoseconds and it is almost uncontrollable characteristics. The tunnel injection structure can be designed to control the carrier injection rate. The carrier transition time from carrier reservoir‐region of the tunnel injection structure to the active well was a few picoseconds when the structure was designed for high speed transition. As results, carrier injection to ground state of the active well takes less than 10 picoseconds. The change of the radiative recombination rate in the active well also defines the optimal design of the tunnel injection structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Si doping on size of GaN quantum dots grown by molecular beam epitaxy under Ga‐rich conditions
Authors: Managaki Nobuto , Iizuka Norio
Published: May 2008

The size control of Si‐doped GaN/AlN quantum dots (QDs) was studied by using molecular beam epitaxy under Ga‐rich conditions that were widely used for high‐quality thin‐film growth. The formation of GaN QDs was affected by Si‐doping in contrast with that of the QDs under N‐rich condition. Atomic force microscopy images of Si‐doped GaN QDs and undoped GaN QDs were clearly different. Diameters of Si‐doped GaN QDs decreased with increase in Si concentration within 1 x 1017‐1020 cm–3, whereas heights were almost constant. Micro‐Raman spectroscopy showed that the LO phonon frequency shifted toward lower wavenumbers with increase in Si concentration. These results suggest that Si doping may affect the length of Ga‐N bonds related with the elastic strain and, as a result, influence the aspect ratio of QDs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Possible anomalous Hall effect of Be/Si pair delta‐doped GaAs structures
Authors: Noh J. P. , Jung D. W. , Islam A. Z. M. Touhidul , Otsuka N.
Published: May 2008

Beryllium/Silicon pair delta‐doped GaAs structures grown by molecular‐beam epitaxy exhibit Hall resistance which has highly nonlinear dependence on the applied magnetic field. The dependence of the occurrence of the nonlinear Hall resistance on the sample structure is investigated. A significantly large increase in the non‐linearity and magnitude of the Hall resistance is observed from a sample structure whose buffer layer is grown under the low As flux and thick buffer layer condition. The non‐linearity of the Hall resistance is found to depend on a single parameter B /T, where B and T are the magnetic field and temperature, respectively. From another sample structure in which an AlGaAs barrier with a single Be delta‐doped layer is placed near the Be/Si pair delta‐doped layer, a similar nonlinear Hall resistance is observed. On the basis of these results, it is suggested that the anomalous Hall effect results from interplay between itinerant holes in the valence band and localized spins in the delta‐doped layer in these structures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral width dependence of residual carrier effect on nonlinear optical response of weakly confined excitons
Authors: Kojima O. , Isu T. , Ishi‐Hayase J. , Sasaki M. , Kanno A. , Katouf R. , Tsuchiya M.
Published: May 2008

We report residual carrier effects on the nonlinear optical response of weakly confined excitons in GaAs thin films. The nonlinear response was investigated using a degenerate four‐wave mixing technique with an additional pulse to create the residual carriers. In the case of the additional‐pulse incidence, the signal intensity decreases with the time of incidence.

However, the ultrafast component comparable to the pulse width in the temporal profiles does not change appreciably. Our results imply the possibility of the realization of ultrafast switching using the exciton response. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ZnO nanowires: chemical growth, electrodeposition, and application to intracellular nano‐sensors
Authors: Willander M. , Klason P. , Yang L. L. , Al‐Hilli Safaa M. , Zhao Q. X. , Nur O.
Published: May 2008

In this paper we present our results on growth, characterization, and nano‐devices based on ZnO nano‐structures. The ZnO nano‐structures were grown by mainly two methods, the catalytic Vapor Liquid Solid (VLS) and the low temperature chemical growth. We show that by multiple coating combined with low temperature chemical growth, well aligned with size controlled ZnO nanowires on silicon substrates can be achieved. The dissolution, due to its important on the stability of ZnO nano‐structures in aqueous medium, is then discussed and some preliminary experimental results are shown. Basic Optical characteristics of ZnO nano‐rods are briefly discussed. Finally, electrochemical intracellular nano‐sensors based on ZnO nano‐wires are demonstrated as efficient nano‐sensors for monitoring the human cell activity with minute pH changes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of composition control and capping of MOVPE grown InGaN/InxAlyGa1–x–yN MQW structures
Authors: Ali M. , Suihkonen S. , Svensk O. , Törmä P. T. , Sopanen M. , Lipsanen H. , Odnoblyudov M. A. , Bougrov V. E.
Published: May 2008

We report on the growth and characterization of InGaN/ InxAlyGa1–x–yN multiple quantum well (MQW) structures emitting at 380 nm. The samples were grown by metalorganic vapour phase epitaxy (MOVPE) and were analyzed by using high resolution X‐ray diffraction (HRXRD), room and low temperature photoluminescence (PL) measurements. The effect of changing the indium precursor flow during the barrier and capping layer growth on the structural and optical quality of multiple quantum wells (MQWs) is explored. The HRXRD results show that the MQWs grown under the set of mentioned conditions are of very good structural quality. The temperature dependent PL results from our samples show that increasing the In content in the barriers enhances to a certain limit the internal quantum efficiency of the MQW structures. We also report that changing the In content in the capping layer effects the peak emission energy and does not have any significant impact on the optical quality of the MQW structures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and density control of GaN nanodots and nanopillars
Authors: Takeda S. , Inoue Y. , Ishida A. , Mimura H.
Published: May 2008

We have fabricated hexagonal pillar like GaN nanostructures on Si (111) substrate. The GaN nanopillars were grown by two step processes, including droplet epitaxy to form GaN nanodots as buffer, and hot wall epitaxy to grow GaN nanopillars. We proposed the growth mechanism of the GaN nanodot by droplet epitaxy. Density of the GaN nanopillars was controlled by changing the density of GaN nanodots. When the nanopillar density was so high as to coalesce with each other, the luminescence efficiency reduced. The deterioration of luminescence is considered to be due to increase of dislocations arising at the nanopillars interface. To obtain the high luminescence efficiency, it is important to increase density of nanopillars with no coalescing. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum well and cavity structures grown on (110)GaAs by MBE
Authors: Hey R. , Jahn U. , Wan Qian , Trampert A.
Published: May 2008

The structural perfection of (In,Ga)As‐ and GaAs quantum wells and distributed Bragg reflectors for cavity structures on (110)GaAs grown by molecular‐beam epitaxy is investigated. The relaxation mechanism of accumulated elastic strain is studied by transmission electron microscopy.

Differences to structures with (001) orientation are addressed. The use of short‐period superlattices for Bragg mirrors stabilizes the structures grown on (110)GaAs against relaxation‐based defect formation as well as degradation of bare sidewalls when exposed to ambient air. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of semi‐polar (11‐22)GaN on a (113)Si substrate by selective MOVPE
Authors: Tanikawa T. , Hikosaka T. , Honda Y. , Yamaguchi M. , Sawaki N.
Published: May 2008

MOVPE growth of uniform (11‐22)GaN layer was attempted on a patterned (113)Si substrate. The growth of GaN was achieved on (1‐11) facets of the Si selectively. The optimum design of the patterned substrate and the growth conditions were studied to get the semi‐polar GaN layer with high optical and crystalline quality. The cathode‐luminescence spectra showed a sharp edge emission peak of which half width was as narrow as 10 meV. The X‐ray rocking curves showed that the (11‐22) diffraction was as narrow as 300 arcsec. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Longitudinal‐commensurable resistance oscillations in the ballistic transport of electrons on cylindrical surfaces
Authors: Friedland K.‐J. , Hey R. , Kostial H. , Riedel A.
Published: May 2008

We observe a new type of resistance oscillations in the ballistic transport of two‐dimensional electrons on cylindrical surfaces with a tangentially directed magnetic field. The longitudinal resistance oscillates with a periodicity proportional to the square root of the magnetic field √B, which indicates a commensurability of longitudinal distances with a length scale related to the gradient of the perpendicular to the surface component of magnetic field B⊥.We show, that the length of the stripe with energetically free electrons, forming the so called ‘snake’‐like trajectories around the position where B⊥ = 0 is the basic length scale for the √B oscillations. We speculate, that ‘zitterbewegung’ of the one‐dimensional ‘skin’‐channel due to switching of the spin‐orbit interaction around the B⊥ = 0 position may cause this new type of resistance oscillations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current‐controlled wavelength tunability of a quantum cascade laser
Authors: Kim Gyungock , Jang Ki Seok , Kim In Gyoo , Lee Ki Joong
Published: May 2008

We report quantum cascade lasers (QCLs) which exhibit multiple peak structures in the emission spectra as a function of injected current, and provide the availability of additional laser lines in the single QCL. The emission spectra of quantum cascade lasers measured with varying current show emission wavelength peaks, separated by 110 nm, indicating the possibility of broad tuning range. The optical output power.vs. injected current curves also exhibit two separate thresholds at low duty cycles, indicating two different lasing conditions originating from the different transition levels. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Indian monsoon daily rainfall on subseasonal to multidecadal time‐scales using a hidden Markov model
Authors: Greene A. M. , Robertson A. W. , Kirshner S.
Published: May 2008

A 70‐year record of daily monsoon‐season rainfall at a network of 13 stations in central western India is analyzed using a 4‐state homogeneous hidden Markov model. The diagnosed states are seen to play distinct roles in the seasonal march of the monsoon, can be associated with ‘active’ and ‘break’ monsoon phases and capture the northward propagation of convective disturbances associated with the intraseasonal oscillation. Interannual variations in station rainfall are found to be associated with the alternation, from year to year, in the frequency of occurrence of wet and dry states; this mode of variability is well correlated with both all‐India monsoon rainfall and an index characterizing the strength of the El Niño Southern Oscillation. Analysis of low‐passed time series suggests that variations in state frequency are responsible for the modulation of monsoon rainfall on multidecadal time‐scales as well. Copyright © 2008 Royal Meteorological Society
The life cycle of convective‐shower cells under post‐frontal conditions
Authors: Weusthoff Tanja , Hauf Thomas
Published: May 2008

Seventeen days with post‐frontal shower precipitation are analysed by means of radar data obtained from the German Weather Service's C‐band radar network. The life cycle of clusters—defined here as contiguous rain areas including one or more radar‐reflectivity peaks (i.e. convection cells)—is investigated. To allow for the continuous tracking of clusters, sometimes over a time period of more than an hour, a new, specially adapted tracking algorithm has been developed. The life cycle of convective clusters comprises five different stages: genesis; growth (including merging); stagnation; decay (including splitting); and dissolving. The transition likelihoods from a cluster with n maxima to one with m maxima are determined (the case m > n corresponding to growth and m < n to decay). It is found that, predominantly, clusters grow or decay by one cell. Results relating to the temporal evolution of post‐frontal showers are presented, and a conceptual growth model is proposed. Although single cells are the most frequent cluster type, the spatial structure of the post‐frontal precipitation field is dominated by multi‐celled clusters. Their life cycle is essentially affected by cell merging and splitting. Although the transitions of all (about one million) identified clusters have been analysed and quantified, more research is necessary in order to understand the underlying principles of cluster growth. Copyright © 2008 Royal Meteorological Society
Observation of microcontaminants on pure chromium surface by AFM and their removal by UV light illumination
Authors: Wang Rongguang
Published: May 2008

Microcontaminants on a pure chromium surface were observed and confirmed by atomic force microscope (AFM). On the basis of surface observation, X‐ray photoelectron spectroscopy (XPS) analysis and wettability measurement, the removal of microcontaminants by ultraviolet (UV) light illumination was investigated. Particle‐ and film‐like microcontaminants on the specimen surface were observed. With an increase in air exposure time, particle‐like contaminants increased in size, and then film‐like contaminants almost covered the entire surface. Most organic substance in the contaminants was removed by UV light illumination in a sealed chamber, except water in the contaminants. The re‐adhesion of contaminants on the UV‐light‐illuminated surface seemed slower after compared to before UV light illumination. Copyright © 2008 John Wiley & Sons, Ltd.
Rationality in systems engineering: Beyond calculation or political action
Authors: Clausing Don P. , Katsikopoulos Konstantinos V.
Published: May 2008

This paper is written in favor of rationality in systems engineering. Operational rationality is the foundation for the improvement of quality, cost, and delivery (QCD) that leads to continued success in the market place. On both sides of operational rationality lie pitfalls that plague most systems‐engineering decision making. On one side lies hand waving and political action. On the opposite side lies mathematical certainty, very enticing to the educated mind, but lacking in broad decision‐making capability. In this paper we set forth the principles of operational rationality in systems engineering. These principles guide the evaluation, improvement, and development of systems‐engineering practices and methods. © 2008 Wiley Periodicals, Inc. Syst Eng
Interventions for twin–twin transfusion syndrome: a Cochrane review
Authors: Roberts D. , Gates S. , Kilby M. , Neilson J. P.
Published: May 2008

We performed a Cochrane review to assess which of the treatments for twin–twin transfusion syndrome (TTTS) improves fetal, childhood and maternal outcomes. This article represents a version of the review which includes additional data to the published version.

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (April 2007) and the Cochrane Central Register of Controlled Trials (The Cochrane Library, October 2007) for randomized and quasi‐randomized studies of amnioreduction, laser coagulation and septostomy and compared their outcomes. We also searched conference proceedings and contacted the authors of published trials for clarification and addtional data. No trials compared intervention with no intervention. Three studies (253 women) were included.

Laser coagulation resulted in less overall death (48% vs. 59%; relative risk (RR), 0.81; 95% CI, 0.65–1.01 adjusted for clustering; two trials, 364 fetuses), perinatal death (26% vs. 44%; RR, 0.59; 95% CI, 0.40–0.87 adjusted for clustering; one trial, 284 fetuses) and neonatal death (8% vs. 26%; RR, 0.29; 95% CI, 0.14–0.61 adjusted for clustering; one trial, 284 fetuses) when compared with amnioreduction. There was no difference in perinatal outcome between amnioreduction and septostomy. More babies were alive without neurological abnormality at the age of 6 months in the laser group than in the amnioreduction group (52% vs. 31%; RR, 1.66; 95% CI, 1.17–2.35 adjusted for clustering; one trial). There was no difference in the proportion of babies alive at 6 months that had undergone treatment for major neurological abnormality between the laser coagulation and the amnioreduction groups (4% vs. 7%; RR, 0.58; 95% CI, 0.18–1.86 adjusted for clustering; one trial).

The results suggest that endoscopic laser coagulation of anastomotic vessels should be considered in the treatment of all stages of TTTS to improve perinatal and neonatal outcome. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Non‐influence of fetal gender on ductus venosus Doppler flow in the first trimester
Authors: Teixeira L. S. , Leite J. , Castro Viegas M. J. B. , Faria M. M. L. , Pires M. C. , Teixeira H. C. , Teixeira R. C. , Pettersen H.
Published: May 2008

Objectives

Recent findings have suggested that ductus venosus blood flow may be influenced by fetal gender. The aim of this study was to investigate further the influence of fetal gender on ductus venosus Doppler flow in the first trimester.

Methods

This was a cross‐sectional and retrospective study performed between January 1998 and January 2003. A total of 932 fetuses at between 10 and 14 weeks' gestation were included. The following inclusion criteria were used: singleton gestation; crown–rump length between 39 and 84 mm; and absence of fetal anomalies. The following variables of the ductus venosus were evaluated: peak velocity during ventricular systole (S‐wave) and diastole (D‐wave); nadir during atrial contraction in late diastole (A‐wave); pulsatility index for veins (PIV); peak velocity index for veins (PVIV); and time‐averaged maximum velocity (TAMXV).

Results

Four hundred and forty‐eight (48.1%) female and 484 (51.9%) male fetuses were included in the study. Comparing males and females at between 10 and 14 weeks' gestation, there was no statistically significant difference in S‐wave, D‐wave, A‐wave, PIV, PVIV or TAMXV.

Conclusions

Our study suggests that fetal gender does not influence ductus venosus blood flow in the first trimester. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.
Monochorionic twins with selective intrauterine growth restriction and intermittent absent or reversed end‐diastolic flow (Type III): feasibility and perinatal outcome of fetoscopic placental laser coagulation
Authors: Gratacós E. , Antolin E. , Lewi L. , Martínez J. M. , Hernandez‐Andrade E. , Acosta‐Rojas R. , Enríquez G. , Cabero L. , Deprest J.
Published: May 2008

Objectives

To assess the feasibility and impact on perinatal outcome of fetoscopic laser coagulation of placental anastomoses in monochorionic twins with selective intrauterine growth restriction (sIUGR) and intermittent absent or reversed end‐diastolic flow (iAREDF) in the umbilical artery (Type III), in comparison with expectant management.

Methods

This is a descriptive study of the outcome of 18 cases of monochorionic twins with Type III sIUGR treated with laser, and 31 pregnancies managed expectantly over the same period. All newborns underwent neonatal brain ultrasound scans. Perinatal outcome and the incidence of neurological damage were compared between the two groups.

Results

Laser coagulation could be performed in only 88.9% (16/18) of cases owing to technical difficulties, and in 12.5% (2/16) a second procedure was required to achieve complete coagulation of the large artery‐to‐artery anastomosis. Mean gestational age at delivery was 31.0 (range, 26–33) weeks in the expectant management group and 32.6 (range, 23–38) weeks in the laser group (P = 0.32). Overall perinatal survival was 85.5% (53/62) and 63.9% (23/36), respectively (P = 0.02). Intrauterine demise of the smaller twin occurred in 19.4% (6/31) and 66.7% (12/18), respectively (P = 0.001), and was associated with death of the cotwin in 50% (3/6) and 0% (0/12) of these cases, respectively (P = 0.02). The prevalence of periventricular leukomalacia in the larger fetus was 4/28 (14.3%) in the expectant management group and 1/17 (5.9%) in the laser group (P = 0.63).

Conclusions

Laser coagulation in sIUGR‐iAREDF pregnancies is technically difficult and not always feasible. Placental dichorionization significantly increases the proportion of fetuses with intrauterine death of the growth‐restricted twin, but it protects the normal twin from its cotwin's death in the event of demise of the growth‐restricted twin. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.