bluuebunny/crossref_metadata_2025 huggingface dataset:
Addition of sucralose enhances the release of satiety hormones in combination with pea protein
Authors: Geraedts Maartje C. P. , Troost Freddy J. , Saris Wim H. M.
Published: February 2012

Scope Exposing the intestine to proteins or tastants, particularly sweet, affects satiety hormone release. There are indications that each sweetener has different effects on this release, and that combining sweeteners with other nutrients might exert synergistic effects on hormone release.

Methods and results STC‐1 cells were incubated with acesulfame‐K, aspartame, saccharine, sucralose, sucrose, pea, and pea with each sweetener. After a 2‐h incubation period, cholecystokinin(CCK) and glucagon‐like peptide 1 (GLP‐1) concentrations were measured. Using Ussing chamber technology, the mucosal side of human duodenal biopsies was exposed to sucrose, sucralose, pea, and pea with each sweetener. CCK and GLP‐1 levels were measured in basolateral secretions. In STC‐1 cells, exposure to aspartame, sucralose, sucrose, pea, and pea with sucralose increased CCK levels, whereas GLP‐1 levels increased after addition of all test products. Addition of sucrose and sucralose to human duodenal biopsies did not affect CCK and GLP‐1 release; addition of pea stimulated CCK and GLP‐1 secretion.

Conclusion Combining pea with sucrose and sucralose induced even higher levels of CCK and GLP‐1. Synchronous addition of pea and sucralose to enteroendocrine cells induced higher levels of CCK and GLP‐1 than addition of each compound alone. This study shows that combinations of dietary compounds synergize to enhance satiety hormone release.
An isolable acyclic hemiacetal of ansamitocin P‐3
Authors: Segraves Nathaniel L. , Yazzie Derrick , Deese Alan J.
Published: February 2012

During impurity analysis of maytansinol (2), produced from the reduction of ansamitocin P‐3 (AP‐3, 1), a surprisingly stable acyclic hemiacetal (4) was isolated. A combination of 1D and 2D NMR experiments, along with liquid chromatography–mass spectrometry data was used to confirm the structure. Comparison of NMR data to the previously reported bridged acetal (3), a by‐product of AP‐3 reduction, supports reassignment of the latter to the former. Additionally, ROESY data, in conjunction with minimum energy calculations, support intramolecular hydrogen bonding that is involved in stabilizing the hemiacetal. This report adds another example to the very short list of isolable acyclic hemiacetals. Copyright © 2012 John Wiley & Sons, Ltd.
Dynamic NMR of low‐sensitivity fast‐relaxing nuclei: 17O NMR and DFT study of acetoxysilanes
Authors: Fusaro Luca , Mameli Giulia , Mocci Francesca , Luhmer Michel , Cerioni Giovanni
Published: February 2012

17O NMR is not routinely used for structure characterization, and kinetic studies of fluxional organic compounds are seldom undertaken because poor sensitivity and fast quadrupole relaxation are frequently regarded as intractable issues. This work shows how, nowadays, quantitative 17O dynamic NMR studies on small organic molecules are feasible without enrichment being needed. It reports on acetoxysilanes, a class of fluxional compounds whose structure and dynamics were to be clarified. Natural abundance 17O NMR spectra were recorded over a wide range of temperatures using standard instrumentation. The analysis relies on simple linewidth measurements and directly provides the activation parameters. The activation enthalpy is found to decrease with increasing number of acetoxy groups bound to silicon. Density functional theory calculations properly predict this trend and show that a single oxygen atom of the acetoxy group is bound to silicon, excluding chelation as binding mode, and that the dynamic process involves the shift of the silicon atom between the two oxygen atoms of the acetoxy group. Copyright © 2012 John Wiley & Sons, Ltd.
Predictors of care seeking in women with urinary incontinence
Authors: Minassian Vatche A. , Yan Xiaowei , Lichtenfeld Marc J. , Sun Haiyan , Stewart Walter F.
Published: February 2012

Aims

To determine predictors of health care utilization in women with urinary incontinence (UI) from the population to specialty care.

Methods

The General Longitudinal Overactive Bladder Evaluation‐UI is a population‐based study on the natural history of UI in women ≥40 years of age. Prevalence of UI was estimated using the Bladder Health Survey (BHS). Survey data were linked with electronic health records (EHRs) to examine factors associated with a clinical UI diagnosis using logistic regression. Risk factors analyzed included: UI symptoms, subtypes, bother, severity, duration, and effect on quality of life, and demographic and other health characteristics. All statistical tests were two‐sided with a P‐value < 0.05 being significant.

Results

The overall prevalence of any UI based on responses to the BHS was 1,618/4,064 (40%). Of the 1,618 women with UI, there were only 398 (25%) women with EHR (clinical) diagnosis of UI. Women with UI versus those without UI were more likely to be have a BMI >25 kg/m2 (70% vs. 58%), more likely to be parous (91% vs. 87%) and college educated (54% vs. 46%), P < 0.001. After adjusting for confounders in the model, variables significantly associated with clinical UI diagnosis included: older age (OR = 1.96), higher parity (> 1 birth) (OR = 1.76), higher urgency UI (OR = 1.08), adaptive behavior (OR = 1.2), and UI bother scores (OR = 1.01), as well as more frequent outpatient visits (OR = 1.03), P < 0.05.

Conclusions

UI is a highly prevalent condition with only a minority of women seeking care. Factors associated with health care utilization include older age, parity (1+), number of doctor visits, urgency UI subtype, UI bother, and impact on behavior. Neurourol. Urodynam. 31:470–474, 2012. © 2012 Wiley Periodicals, Inc.
BUDGETING IN A TIME OF AUSTERITY: THE CASE OF THE ESTONIAN CENTRAL GOVERNMENT
Authors: Jõgiste Kadri , Peda Peeter , Grossi Giuseppe
Published: February 2012

Resulting from the global economic crisis, high budget deficits and debt burden characterise many economies looking for an exit strategy from current fiscal unbalances. The government of Estonia, having pursued a conservative fiscal policy for over a decade, reacted to the economic recession with radical budget adjustments, the latter constituting approximately 9% of gross domestic product in 2009. Consequently, Estonia took its chance and qualified for the euro in 2011. This study examines the behaviour of the Estonian central government and the basis of its budget decisions when planning drastic cost reductions through the theoretical lens of cutback management. The foremost results reveal that the crisis pushed the government to establish a different institutional framework that facilitated fast and effective decision‐making during the budget process. The savings proposals came from the Ministry of Finance; however, running a cash‐basis line‐item budgeting system in practice, the centre possessed only limited performance data for developing the proposals. Consequently, the long‐term impacts of the budget adjustments had not been assessed and are as yet unknown. A further conclusion is that the current budgeting framework should be revised and replaced step by step with a more advanced approach. Copyright © 2012 John Wiley & Sons, Ltd.
Imatinib mesylate causes growth deceleration in pediatric patients with chronic myelogenous leukemia
Authors: Rastogi Maynika V. , Stork Linda , Druker Brian , Blasdel Carolyn , Nguyen Thuan , Boston Bruce A.
Published: February 2012

Background

Imatinib mesylate, a tyrosine kinase inhibitor, is used in the treatment of chronic myelogeneous leukemia (CML). Given its ease of administration and manageable side effects in adults, imatinib mesylate was introduced as therapy for pediatric CML. Recently published case reports describe growth deceleration in children treated with imatinib. This study details the growth phenotype of seven pediatric patients maintained in remission on imatnib mesylate over an extended period of time.

Procedure

This study is a retrospective chart review of pediatric patients with CML at Oregon Health & Science University treated with imatinib. Height, weight, and body mass index (BMI) measurements were collected before and during treatment. Median standard deviation scores (SDS) were analyzed by Wilcoxon Rank‐Sum test and Wilcoxon signed rank cohort analysis.

Results

Individual patient analysis demonstrated five of seven subjects with a statistically significant decrease in height SDS pre versus during treatment. The whole group analysis showed a trend to significance for difference in median height SDS pre and during treatment (P = 0.078). Bone age was delayed in all four patients in whom bone ages were obtained. IGF‐1, IGFBP‐3, and thyroid levels during treatment were normal. Four patients experienced an improvement in height SDS during puberty. However, three patients approaching near final adult height failed to achieve genetic height potential determined by mid‐parental target height.

Conclusion

Growth in children with CML appears to be adversely impacted by imatinib therapy. BMI and IGF‐1/IGFBP‐3 are maintained during treatment, suggesting a direct effect of imatinib on the growth plate. Pediatr Blood Cancer 2012; 59: 840–845. © 2012 Wiley Periodicals, Inc.
Facile synthesis and responsive behavior of PDMS‐b‐PEG diblock copolymer brushes via photoinitiated “thiol‐ene” click reaction
Authors: Yang Muquan , Mao Jun , Nie Wei , Dong Zhixin , Wang Dapeng , Zhao Ziliang , Ji Xiangling
Published: February 2012

We present herein a mild and rapid method to create diblock copolymer brushes on a silicon surface via photoinitiated “thiol‐ene” click reaction. The silicon surface was modified with 3‐mercaptopropyltrimethoxysilane (MPTMS) self‐assembled monolayer. Then, a mixture of divinyl‐terminated polydimethylsiloxane (PDMS) and photoinitiator was spin‐coated on the MPTMS surface and exposed to UV‐light. Thereafter, a mixture of thiol‐terminated polyethylene glycol (PEG) and photoinitiator were spin‐coated on the vinyl‐terminated PDMS‐treated surface, and the sequent photopolymerization was carried out under UV‐irradiation. The MPTMS, PDMS, and PEG layers were carefully identified by X‐ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements. The thickness of the polydimethylsiloxane‐block‐poly(ethylene glycol) (PDMS‐b‐PEG) diblock copolymer brush could be controlled by the irradiation time. The responsive behavior of diblock copolymer brushes treated in different solvents was also discussed. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Novel conjugated copolymers based on dithiafulvalene moiety for bulk heterojunction solar cells
Authors: Chen Yung‐Chung , Hsu Chih‐Yu , Lin Jiann T.
Published: February 2012

New conjugated copolymers, P1‐P3, based on dithiafulvalene‐fused entity and different conjugated segments have been synthesized. Incorporation of electron‐deficient conjugated segments into the conjugated copolymers results in red shifting the absorption band and lowering the hole mobility. Bulk heterojunction solar cells using on these polymers as the donor and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) as the acceptor were fabricated by solution process. The cells based on the blend of P1‐P3/PC61BM (1:1, w/w) have power conversion efficiencies (PCEs) ranging from 0.53 to 0.93%. Among these, the cell of P1/PC61BM exhibited the highest open‐circuit voltage at 0.85 V, and the cell of P3/PC61BM exhibited the best PCE at 0.93% with the short‐circuit current (JSC) of 4.88 mA/cm2. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Cyclic polymers: Methods and strategies
Authors: Jia Zhongfan , Monteiro Michael J.
Published: February 2012

Cyclic polymers have different physical properties compared to their linear counterparts of the same molecular weight. These different properties could have potential impact in the production of new and exciting polymer products. For industry to commercialize such materials, cyclic polymers need to be made on large scales, have controlled molecular weight distributions, and have versatile chemical composition. This highlight article describes many of the synthetic methods and strategies for obtaining highly pure cyclic polymers, and presents kinetic attributes for some of the processes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Iron‐mediated AGET ATRP of methyl methacrylate using metal wire as reducing agent
Authors: Jiang Hongjuan , Zhang Lifen , Pan Jinlong , Jiang Xiaowu , Cheng Zhenping , Zhu Xiulin
Published: February 2012

Methyl methacrylate (MMA) were successfully polymerized by atom transfer radical polymerization with activator generated by electron transfer (AGET ATRP) using copper or iron wire as the reducing agent at 90°C. Well‐controlled polymerizations were demonstrated using an oxidatively stable iron(III) chloride hexahydrate (FeCl3·6H2O) as the catalyst, ethyl 2‐bromoisobutyrate (EBiB) as the initiator, and tetrabutylammonium bromide (TBABr) or triphenylphosphine as the ligand. The polymerization rate was fast and affected by the amount of catalyst and type of reducing agents. For example, the polymerization rate of bulk AGET ATRP with a molar ratio of [MMA]0/[EBiB]0/[FeCl3·6H2O]0/[TBABr]0 = 500/1/0.5/1 using iron wire (the conversion reaches up to 82.2% after 80 min) as the reducing agent was faster than that using copper wire (the conversion reaches up to 86.1% after 3 h). At the same time, the experimental Mn values of the obtained poly(methyl methacrylate) were consistent with the corresponding theoretical ones, and the Mw/Mn values were narrow (∼1.3), showing the typical features of “living”/controlled radical polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Peptide‐poly(ε‐caprolactone) biohybrids by grafting‐from ring‐opening polymerization: Synthesis, aggregation, and crystalline properties
Authors: Paira Tapas K. , Banerjee Sanjib , Mandal Tarun K.
Published: February 2012

Well‐defined peptide‐poly(ε‐caprolactone) (Pep‐PCL) biohybrids were successfully synthesized by grafting‐from ring‐opening polymerization (ROP) of ε‐caprolactone (CL) using designed amine‐terminated sequence‐defined peptides as macroinitiators. MALDI‐TOF‐MS and 1H NMR analyses confirmed the successful attachment of peptide to the PCL chain. The gel permeation chromatography (GPC) measurement showed that the Pep‐PCL biohybrids with controllable molecular weights and low polydispersities (PDI <1.5) were obtained by this approach. The aggregation of Pep‐PCL hybrid molecules in THF solution resulted in the formation of micro/nanospheres as confirmed through FESEM, TEM, and DLS analyses. The circular dichroism study revealed that the secondary structure of peptide moiety was changed in the peptide‐PCL biohybrids. The crystallization and melting behavior of Pep‐PCL hybrids were somewhat changed compared with that of neat PCL of comparable molecular weight as revealed by DSC and XRD measurements. In Pep‐PCL biohybrids, extinction rings were observed in the PCL spherulites, in contrast with the normal spherulite morphology of the neat PCL. There was a substantial decrease (4–5 folds) in the spherulitic growth rate after the incorporation of peptide moiety at the end of PCL chain as measured by polarizing optical microscopy. Pseudomonas lipase catalyzed enzymatic degradation was studied for Pep‐PCL hybrids and neat PCL. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
Biodegradable thermoset shape‐memory polymer developed from poly(β‐amino ester) networks
Authors: Lakhera Nishant , Laursen Christopher M. , Safranski David L. , Frick Carl P.
Published: February 2012

The purpose of this study was to develop a degradable thermoset shape‐memory polymer from poly(β‐amino ester) (PBAE) networks. PBAE was chosen to be the crosslinker as it is biodegradable and has been projected as a potential material for biomedical applications. The low glass transition temperature of PBAE was increased to a biomedically relevant range using methyl methacrylate and methyl acrylate as the linear chain builders. The thermo‐mechanical properties of the networks were tailored such that they exhibited onset of glass transition temperature in between the room temperature (22 °C) and the body temperature (37 °C). Free‐strain recovery tests under heating and isothermal conditions were performed to quantify shape‐memory behavior. Testing showed that sampled programmed at 10 °C initiated deformation recovery at a lower temperature and a faster rate as compared to programming at 60 °C. Higher thermal conductivity of water enabled the samples to recover faster in water than in air. Samples with higher PBAE crosslinking densities exhibited higher normalized mass loss under regular and accelerated conditions. The amount of water absorption in the networks also increased with the crosslinker concentration independent of the testing conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Psychosexual distress in women with gynecologic cancer: a feasibility study of an online support group
Authors: Classen Catherine C. , Chivers Meredith L. , Urowitz Sara , Barbera Lisa , Wiljer David , O'Rinn Susan , Ferguson Sarah E.
Published: February 2012

Objectives

The psychosexual concerns of gynecologic cancer patients are often unaddressed and there are limited resources available for women to deal with this highly sensitive topic. This feasibility study examines the participation rates and preliminary outcomes for an online support group designed specifically for women who are sexually distressed subsequent to gynecologic cancer treatment

Methods

A 12‐week online intervention was developed to address the psychosexual impact of gynecologic cancer. This intervention included a professionally moderated, asynchronous discussion forum as well as the provision of psycho‐educational materials addressing the psychosexual impact of gynecologic cancer. Each week, a new topic was introduced and relevant material was posted on the website. Women were encouraged to share their experiences related to the topic. Twenty‐seven, sexually distressed, remitted gynecologic cancer patients were randomly assigned to immediate treatment or a waitlist control condition. Participants completed questionnaires at baseline, 4‐month and 8‐month follow‐ups assessing sexual distress as the primary outcome as well as anxiety, depression, and illness intrusiveness.

Results

Participation rates differed between the two groups, with greater participation occurring in the second group. Exit interviews indicated that the majority of the participants were satisfied with the intervention. Intent‐to‐treat analyses suggest a small effect for reduction in sexual distress

Conclusions

This feasibility study suggests that women find this intervention acceptable. Further research is required to determine efficacy. Copyright © 2012 John Wiley & Sons, Ltd.
Non‐geometric fluxes in ten dimensions
Authors: Larfors M.
Published: February 2012

In ten‐ and four‐dimensional supergravities, the descriptions of non‐geometric configurations are different. In the former, non‐geometry arises as naively non‐single valued supergravity fields. In the latter, new terms, coming from “non‐geometric” Q‐ and R‐fluxes, appear in the four‐dimensional potential. We review how these different descriptions can be linked using a ten‐dimensional field redefinition, as proposed by [1]. This change of field basis results in a Q‐flux term in the ten‐dimensional Lagrangian, which can, for certain non‐geometric set‐ups, be dimensionally reduced to its four‐dimensional counterpart. We briefly discuss the global issues of this construction.
The Hirota equation for string theory in AdS5 × S5 from the fusion of line operators
Authors: Benichou R.
Published: February 2012

We present a perturbative derivation of the T‐system that is believed to encode the exact spectrum of planar 𝒩 = 4 SYM. The T‐system is understood as an operator identity between some special line operators, the quantum transfer matrices. By computing the quantum corrections in the process of fusion of transfer matrices, we show that the T‐system holds up to first order in a semi‐classical expansion. This derivation does not rely on any assumption. We also discuss the extension of the proof to other theories, including models describing string theory on various AdS spaces.
Generating higher‐derivative couplings in 𝒩 = 2 supergravity
Authors: Butter D. , Kuzenko S.
Published: February 2012

Using a recently developed off‐shell formulation for general 4D 𝒩 = 2 supergravity‐matter systems, we propose a construction to generate higher derivative couplings. We address here mainly the interactions of tensor and vector multiplets, but the construction is quite general. For a certain subclass of terms, the action is naturally written as an integral over 3/4 of the Grassmann coordinates of superspace.
Topics in 3D 𝒩 = 2 AdS supergravity in superspace
Authors: Tartaglino‐Mazzucchelli G.
Published: February 2012

We review some recent results on the construction in superspace of 3D 𝒩 = 2 AdS supergravities and on the formulation of rigid supersymmetric theories in (1,1) and (2,0) AdS superspaces.
Notes on the overall coefficient of the two‐loop superstring amplitude using pure spinor
Authors: Gomez H.
Published: February 2012

Using the results recently obtained for computing integrals over (non‐minimal) pure spinor superspace, we compute the coefficient of the massless two‐loop four‐point amplitude from first principles. This proceeding is a very short summary on the paper [arXiv:1003.0678 [hep‐th]], which was done with the collaboration of Carlos R. Mafra.
Light‐front higher‐helicity interactions
Authors: Bengtsson A.K.H.
Published: February 2012

The reformulation, using Fock space vertex operators, of the original light‐front cubic interaction terms for higher spin gauge fields is reviewed with comments on quantum higher spin gravity. The formalism is generalized to all orders in the interaction. The ensuing recursive equations for the higher order vertices, if they can be explicitly solved, will encode all interaction data into a denumerable set of rational functions of p+, the overall transverse momentum structure being fixed already at the kinematical level. A more thorough exposition can be found in the archive. This work was presented at the XVII European Workshop on String Theory, Padua, 5–9 September 2011.
Holography and condensed matter
Authors: Benini F.
Published: February 2012

This is a review of recent developments in the application of AdS/CFT methods to some condensed matter problems. In particular we present the holographic description of a local quantum critical state, related to (non)‐Fermi liquids and the strange metal, that appears in large N CFTs with a gravity dual at finite density and zero temperature, and explore its properties by probing it with fermionic operators. Further we discuss possible bosonic and fermionic instabilities, leading to s‐, p‐ or d‐wave holographic superconductors and “electron stars”. Finally we present a realization of local quantum criticality with an impurity problem.
Suppression of defect‐related luminescence in laser‐annealed InGaN epilayers
Authors: Tamulaitis G. , Dobrovolskas D. , Mickevičius J. , Kazlauskienė V. , Miškinis J. , Kuokštis E. , Onufrijevs P. , Medvids A. , Huang J.‐J. , Chen C.‐Y. , Liao C.‐H. , Yang C. C.
Published: February 2012

An In0.21Ga0.79N epilayer has been studied by using spatially‐resolved photoluminescence spectroscopy and Auger electron spectroscopy. The photoluminescence intensity is shown to be distributed highly inhomogeneously, while the epilayer also exhibits strong defect‐related emission. It is shown that laser annealing at high enough power densities causes redistribution of indium atoms and results in suppression of the defect‐related emission. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
III‐nitride grown on freestanding GaN nanostructures
Authors: Wang Yongjin , Hu Fangren , Zhu Hongbo , Hane Kazuhiro
Published: February 2012

We report here the epitaxial growth of III‐nitride on the freestanding GaN nanostructures by molecular beam epitaxy growth. Various GaN nanostructures are defined by electron beam lithography and realized on GaN‐on‐silicon substrate by fast atom beam etching. Silicon substrate beneath GaN nanostructures is removed from the backside to form the freestanding GaN slab, and the epitaxial growth of III‐nitride by MBE is performed on the prepared GaN template. The selective growth takes place with the assistance of GaN nanostructures and generates hexagonal III‐nitride pyramids. Thin epitaxial structures, depending on the shape and the size of GaN nanostructure, can produce the promising optical performance. This work opens the way to combine silicon micromachining with the epitaxial growth of III‐nitride by MBE on GaN‐on‐silicon substrate for further integrated optics (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs by quasi‐static C‐V measurement
Authors: Huang Sen , Yang Shu , Roberts John , Chen Kevin J.
Published: February 2012

The threshold‐voltage (Vth) instability in AlGaN/GaN MIS‐HEMTs with ALD‐Al2O3 (15 nm) as gate dielectrics is systematically investigated by dc current‐voltage (I‐V), high‐frequency capacitance‐voltage (C‐V) (HFCV), and quasi‐static C‐V (QSCV) characterizations. For Al2O3/GaN/AlGaN/GaN MIS diodes, tiny Vth hysteresis (ΔVth) appears in double‐mode (up and down sweep) HFCV measurements if the maximum forward bias (VF,max) is only set to 0 V, while an apparent clockwise ΔVth (as large as 0.9 V) emerges as VF,max is increased to +5 V. The stability of Vth in the corresponding MIS‐HEMTs is thus studied by increasing the maximum VGS (VGS,max) in the measurement of double‐mode transfer characteristics. Significant clockwise ΔVth also occurred once the VGS,max exceeds +1.1 V, and it increased to ∼1 V at VGS,max= +3 V. Such Vth‐instability is absent in AlGaN/GaN HEMTs. It is suggested that the acceptor‐like deep states at Al2O3/GaN interface account for the Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs, and their filling and emission processes are successfully captured by QSCV measurements. The interface state density detected is about 4.6×1012 cm‐2 using 1 Hz QSCV. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence changes in n‐type GaN samples after photoelectrochemical treatment
Authors: Fujii Katsushi , Koike Kayo , Atsumi Mika , Goto Takenari , Itoh Takashi , Yao Takafumi
Published: February 2012

Photoelectrochemical water splitting using semiconductors to produce hydrogen is a promising technique for converting sunlight to chemical energy. However, anodic photocorrosion occurs during the reaction even when n‐type GaN, a chemically stable material, is used for the photo‐illuminated working electrode. We previously demonstrated that the stability is related to the amount of Si doping used to make the GaN to be n‐type. This means that, the surface damage after photoelectrochemical reaction depends on the amount of Si. We have now investigated the relationship between this surface change and the optical properties especially for the near band edge peaks. With the peak shift by the strain relaxation due to the surface change from smooth to rough, new peaks around 3.4 eV were observed after photoelectrochemical treatment. These new peaks are defect‐related emission, which has been reported as Yi lines. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RF‐MBE growth of semipolar InN(10‐13) and InGaN(10‐13) on GaAs(110)
Authors: Orihara Misao , Yagi Shuhei , Hijikata Yasuto , Yaguchi Hiroyuki
Published: February 2012

We have studied InN and InGaN films grown on GaAs(110) substrates by RF‐assisted molecular beam epitaxy. Reflection high‐energy diffraction observation and X‐ray diffraction (XRD) measurements revealed that the InN films were epitaxially grown with InN(10‐13)// GaAs(110). From XRD pole figure measurements, only one InN(0002) peak was found at an angle of 31.8° from the pole, indicating that the semipolar InN films were free from twin crystals. This can be explained by the similarity in the anisotropic structure between InN(10‐13) and GaAs(110) surfaces. By using low‐temperature InN buffer layers, we could obtain semipolar InN films with a smooth surface. Polarization anisotropy in the photoluminescence peak observed at 0.67 eV from semipolar InN(10‐13) was weaker than that from a ‐plane InN, which is reasonable considering the smaller angle between the c‐axis and the perpendicular direction to the semipolar InN surface. We have also successfully grown In‐rich InGaN(10‐13) on GaAs(110) substrates with an InN(10‐13) intermediate layer, and observed strong photoluminescence from the semipolar InGaN films (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of flat p‐GaN contact layer by pulse flow method for high light‐extraction AlGaN deep‐UV LEDs with Al‐based electrode
Authors: Akiba Masahiro , Hirayama Hideki , Tomita Yuji , Tsukada Yusuke , Maeda Noritoshi , Kamata Norihiko
Published: February 2012

Improvement of light extraction efficiency (LEE) is strongly demanded in an AlGaN‐based deep ultraviolet (DUV) light‐emitting diode (LED), because the LEE of AlGaN DUV LED is low (usually below 10%) due to the light absorption at around p‐GaN contact layer and p‐type electrode. We have demonstrated improvement of LEE of AlGaN DUV LEDs by using thin p‐GaN contact layer and using Al‐based high‐reflectivity p‐electrode. It was difficult to grow thin and flat p‐type GaN layers with heavy Mg‐doping on high‐Al‐content AlGaN layers. We demonstrated the growth of flat and thin p‐GaN contact layer by using ‘an NH3 pulse‐flow growth method’. We investigated the growth conditions for thin p‐GaN contact layer with high‐hole‐concentration using the NH3 pulse‐flow growth method. The surface roughness of the p‐GaN layer on high‐Al‐content p‐AlGaN was markedly improved by using an NH3 pulse‐flow growth method. We fabricated 250 nm‐band AlGaN quantum well (QW) DUV LEDs with thin p‐GaN contact layers grown by an NH3 pulse‐flow growth method. We observed single‐peaked operation spectrum for the 251 nm AlGaN MQW LED. The maximum output power and external quantum efficiencies (EQE) were 17.7 mW and 1.32%, respectively, measured under room temperature cw operation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Atomically controlled chemical polishing of GaN using platinum and hydrofluoric acid
Authors: Sadakuni Shun , Murata Junji , Sano Yasuhisa , Yagi Keita , Okamoto Takeshi , Tachibana Kazuma , Asano Hiroya , Yamauchi Kazuto
Published: February 2012

We have developed a novel planarization method called catalyst‐referred etching (CARE), which utilizes platinum as a catalyst that is immersed in hydrofluoric (HF) acid solution. In this process, chemical etching occurs only near the surface of a platinum plate that has a flat surface. The protrusions on a GaN substrate that is in contact with the surface of the catalyst plate are the only parts that are removed by the platinum and HF solution. The surface is therefore flattened without damaging the crystal. Morphological characterization showed that CARE produced smooth surfaces with single bilayer atomic terracing throughout the substrate. Cross‐sectional transmission electron microscope observations revealed that the surface was atomically flat with no subsurface damage (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiarities of galvanomagnetic effects in GaN epilayers and GaN/InGaN quantum wells
Authors: Malinovskis P. , Mekys A. , Kadys A. , Malinauskas T. , Grinys T. , Bikbajevas V. , Tomašiūnas R. , Storasta J.
Published: February 2012

Temperature dependent Hall effect, magnetoresistivity and time resolved photoconductivity studies have been performed on GaN epilayers and GaN/InGaN multiple quantum wells (MQWs) grown on sapphire films by Metal Organic Chemical Vapor Deposition (MOCVD) method. The MQW structures consisted of different width or different amount of quantum wells. We related the electrical parameters with the quantum structure parameters and found that the geometrical variation of the quantum wells may be substituted by the variation of the amount of the quantum wells. The Hall and the magnetoresistivity measurements showed the complex behavior, which was attributed to the inhomogeneities of the samples, similarly to the case of the crystals with great size defects (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasma affected 2DEG properties on GaN/AlGaN/GaN HEMTs
Authors: Linkohr Stefanie , Pletschen Wilfried , Kirste Lutz , Himmerlich Marcel , Lorenz Pierre , Krischok Stefan , Polyakov Vladimir , Müller Stefan , Ambacher Oliver , Cimalla Volker
Published: February 2012

We investigated the impact of SF6 plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma conditions as well as annealing in nitrogen atmosphere at 425 °C. The electrical properties are characterized by Hall‐effect measurements while electron spectroscopy and X‐ray measurements are used to investigate changes in the surface chemical composition and in the layer structure, respectively. It is demonstrated that plasma treatments strongly affect the 2DEG properties of the heterostructure due to altering of the surface potential accompanied by the formation of a thin fluorinated amorphous film. Increasing the DC bias voltage for the plasma treatment leads to an additional degradation of the mobility caused by incorporation of fluorine into the heterostructure interface. Furthermore, the thin GaN cap layer is etched by plasma treatments with higher bias potential, which increases the carrier density at the interface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ab initio study of the properties of GaN(0001) surface at MOVPE and HVPE growth conditions
Authors: Kempisty Pawel , Strak Pawel , Krukowski Stanislaw
Published: February 2012

Density functional theory (DFT) is used to simulate the properties of GaN(0001) surface employing a finite slab with additional modifications of the non‐real side by termination with variously charged pseudo‐hydrogen atoms. Different terminations change the electric field inside the slab and causes a relative shift of the energy of the surface and band states, which is known as Surface States Stark Effect (SSSE). It is shown that single hydrogen atom is barrierlessly adsorbed on GaN(0001) surface in the on‐top position. Its adsorption energy strongly depends on the surface coverage by other hydrogen atoms, being above 3 eV and below 1.5 eV for the coverage lower and higher than 0.75 ML, respectively. This large difference is due to the difference of electronic occupation of the surface states. The adsorption energies indicate that hydrogen can be stably attached to the surface up to 0.75 ML coverage. It is shown that the adsorption energy of molecular hydrogen depends to some degree on the electric field at the surface, i.e. doping in the bulk. The dependence of hydrogen coverage on the pressure in the vapor shows that complete removal of hydrogen from GaN(0001) surface is difficult. Also chemical potential of hydrogen at the surface as a function of its coverage is determined. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of crack‐free thick AlN film on a‐plane sapphire by low‐pressure HVPE
Authors: Takagi Yuta , Miyagawa Reina , Miyake Hideto , Hiramatsu Kazumasa
Published: February 2012

The periodic trench patterning of sapphire substrates is useful for the growth of crack‐free AlN thick films. However, the in‐plane epitaxial relationship between AlN and a‐plane sapphire depends on the initial growth temperature. Therefore, two trench directions, the <0001>a‐plane sapphire and <1‐100>a‐plane sapphire directions are investigated in this study. We investigated the control of in‐plane epitaxial relationship between AlN and a‐plane sapphire by low‐pressure HVPE and the effect of the trench direction of AlN, which results in two different in‐plane epitaxial relationships on a‐plane sapphire (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and structural, optical and electrical properties study of bulk GaN
Authors: Gogova D. , Rudko G. , Siche D.
Published: February 2012

High‐quality GaN substrates with a thickness of 0.5 to 1.2 mm were prepared by halide vapor‐phase epitaxy (HVPE) on c‐plane sapphire and by means of a post‐growth laser‐induced lift‐off or natural stress‐induced (self‐) separation process. Structural, optical and electrical properties of the grown material were studied in detail. Resistivity and doping concentrations dependence on temperature were investigated and the results revealed a low donor concentration (2 × 1015 cm‐3 at 273 K) and a moderate resistivity (10‐48 Ωcm) of the samples. Several deep levels observed in the DLTS spectra were identified. The study shows that the GaN material is self‐compensated and a strong influence of point defects related to dislocations on electronic transport is observed. The HVPE growth on InGaN/GaN multi‐quantum wells buffer layers and subsequent self‐separation method was seen as advantageous, in comparison to the laser‐induced lift‐off one, in respect to a lower cost and better crystalline quality of the GaN material obtained (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessing Performance Risk for Complex Product Development: A Simulation‐Based Model
Authors: Xu Zhe , Li Hongbo
Published: February 2012

Assessing and managing performance risk is important for complex product development projects. The performance risk of complex product development can be defined as the probability failing to achieve desired performance level subject to cost and time constraints. This article presents a simulation model based on the graphical evaluation and review technique (GERT) and analyzes the complex product development project using simulation data. The model computes the probability distribution of project duration and cost in a GERT network with multifeedback branches considering activities rework that is caused by probabilistic failure to meet the planned design objective. A simulation strategy is designed to assess the performance risk in both subsystems and system development. With the performance risk assessment methodology, project managers can make a better decision and then minimize the performance risk of product development project. Finally, an obstacle clearance armored vehicle development project is used to illustrate the effectiveness of the proposed model. Copyright © 2012 John Wiley & Sons, Ltd.
The number of graphs and a random graph with a given degree sequence
Authors: Barvinok Alexander , Hartigan J.A.
Published: February 2012

We consider the set of all graphs on n labeled vertices with prescribed degrees D = (d1,…,dn). For a wide class of tame degree sequences D we obtain a computationally efficient asymptotic formula approximating the number of graphs within a relative error which approaches 0 as n grows. As a corollary, we prove that the structure of a random graph with a given tame degree sequence D is well described by a certain maximum entropy matrix computed from D. We also establish an asymptotic formula for the number of bipartite graphs with prescribed degrees of vertices, or, equivalently, for the number of 0‐1 matrices with prescribed row and column sums. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013
Percolation and limit theory for the poisson lilypond model
Authors: Last Günter , Penrose Mathew D.
Published: February 2012

The lilypond model on a point process in d ‐space is a growth‐maximal system of non‐overlapping balls centred at the points. We establish central limit theorems for the total volume and the number of components of the lilypond model on a sequence of Poisson or binomial point processes on expanding windows. For the lilypond model over a homogeneous Poisson process, we give subexponentially decaying tail bounds for the size of the cluster at the origin. Finally, we consider the enhanced Poisson lilypond model where all the balls are enlarged by a fixed amount (the enhancement parameter), and show that for d > 1 the critical value of this parameter, above which the enhanced model percolates, is strictly positive. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2012
Cryptanalysis of a secure and efficient authentication protocol for anonymous channel in wireless communications
Authors: Lee Cheng‐Chi , Lin Tsung‐Hung , Tsai Chwei‐Shyong
Published: February 2012

To enhance the efficiency and the security in an anonymous channel of wireless systems, Yang et al. proposed a secure and efficient authentication protocol for an anonymous channel in wireless communications. The protocol did not use asymmetric cryptosystems to protect the identity of the mobile user because the cryptosystems have high complex and high computation cost. Not only can the protocol resist some security attacks but also the computation cost is low. However, the authors shall point out that their protocol is vulnerable to key compromise attack. Through this attack, any adversary can obtain the secret key Kh, i shared between the home network (HN) and the mobile station (MS). Then, the adversary can wiretap any messages that he/she wants using the secret key between the HN and the MS. Copyright © 2012 John Wiley & Sons, Ltd.
Growth, Characterization, and Properties of Nanographene
Authors: Yang Wei , He Congli , Zhang Lianchang , Wang Yi , Shi Zhiwen , Cheng Meng , Xie Guibai , Wang Duoming , Yang Rong , Shi Dongxia , Zhang Guangyu
Published: February 2012

A systematic study on nanographene grown directly on silicon dioxide substrates is reported. The growth is carried out in a remote plasma‐enhanced chemical vapor deposition system at a low temperature of around 550 °C with methane gas as the carbon source. Atomic force microscopy is used to characterize the nanographene morphology, and Raman spectroscopy, X‐ray photoelectron spectroscopy, and scanning tunneling microscopy are exploited to identify the in‐plane sp2 bonding structures of nanographene samples. Electrical transport properties are measured at various temperatures down to 4 K. Tunneling effects, minimal conductance at the charge‐neutral point, sheet resistances, and Dirac point position at different channel lengths are investigated. In addition, nanographene film possesses high transmittance properties, as indicated by transmittance spectra. Nanographene devices are fabricated from rippled structures, and show great promise for strain‐gauge sensor applications.
Graphoepitaxy of Block‐Copolymer Self‐Assembly Integrated with Single‐Step ZnO Nanoimprinting
Authors: Kim Sarah , Shin Dong Ok , Choi Dae‐Geun , Jeong Jong‐Ryul , Mun Jeong Ho , Yang Yong‐Biao , Kim Jaeup U. , Kim Sang Ouk , Jeong Jun‐Ho
Published: February 2012

A highly efficient, ultralarge‐area nanaolithography that integrates block‐copolymer lithography with single‐step ZnO nanoimprinting is introduced. The UV‐assisted imprinting of a photosensitive sol–gel precursor creates large‐area ZnO topographic patterns with various pattern shapes in a single‐step process. This straightforward approach provides a smooth line edge and high thermal stability of the imprinted ZnO pattern; these properties are greatly advantageous for further graphoepitaxial block‐copolymer assembly. According to the ZnO pattern shape and depth, the orientation and lateral ordering of self‐assembled cylindrical nanodomains in block‐copolymer thin films could be directed in a variety of ways. Significantly, the subtle tunability of ZnO trench depth enabled by nanoimprinting, generated complex hierarchical nanopatterns, where surface‐parallel and surface‐perpendicular nanocylinder arrays are alternately arranged. The stability of this complex morphology is confirmed by self‐consistent field theory (SCFT) calculations. The highly ordered graphoepitaxial nanoscale assembly achieved on transparent semiconducting ZnO substrates offers enormous potential for photonics and optoelectronics.
Reversible Single‐Molecule Switching in an Ordered Monolayer Molecular Dipole Array
Authors: Li Huang Yu , Lu Yunhao , Niu Tian Chao , Huang Han , Kera Satoshi , Ueno Nobuo , Wee Andrew Thye Shen , Chen Wei
Published: February 2012

Making electronic devices using a single molecule has been the ultimate goal of molecular electronics. For binary data storage in particular, the challenge has been the ability to switch a single molecule in between bistable states in a simple and repeatable manner. The reversible switching of single molecules of chloroaluminum phthalocyanine (ClAlPc) dipolar molecules within a close‐packed monolayer is demonstrated. By pulsing an scanning tunneling microscopy tip, read–write operations of single‐molecular binary bits at ∼40 Tb/cm2 (∼250 Tb/in2) are demonstrated.
Synthesis and characterization of graft copolymers of Sago starch and acrylic acid
Authors: Kaur Inderjeet , Sharma Meenakshi
Published: February 2012

Sago starch has been graft copolymerized with acrylic acid (AAc) by mutual gamma radiation method. Reaction conditions such as total dose, monomer concentration and amount of methanol were optimized to obtain maximum grafting percentage. Maximum percentage of grafting, Pg (158.00%) was obtained at an optimum total dose of 62.64 kGy using 4.37 moles/L of AAc in 1 mL of methanol. Using optimum conditions, the effect of cross‐linker, glyoxal, on percent grafting was also studied and maximum grafting was obtained at [Glyoxal] = 54.70 moles/L. Characterization of the graft copolymer was carried out by FTIR, TGA, SEM, XRD analytical methods. The grafted Sago starch was found to have increased crystalline and improved thermal behavior. Swelling and solubility kinetics were measured for each of the samples and correlation between the effects of the reaction parameter on swelling‐solubility kinetics was evaluated. Maximum swelling (4192.3%) at 37°C in 8 h was observed for the sample with 59.9% graft level. Higher swelling percentage is indicative of the graft copolymer to have the properties of a hydro gels that can be utilized for use as drug delivery vehicle and purification of industrial effluents.
Amylopectin structure of heat–moisture treated starches
Authors: Jiranuntakul Wittawat , Puttanlek Chureerat , Rungsardthong Vilai , Puncha‐arnon Santhanee , Uttapap Dudsadee
Published: February 2012

The effects of heat–moisture treatment (HMT; moisture content of 25%, at 100°C for 24 h) on starch chain distribution and unit chain distribution of amylopectin in normal rice, waxy rice, normal corn, waxy corn, normal potato, and waxy potato starches were investigated. After HMT, starch chain distribution (amylose and amylopectin responses) of waxy corn and potato starches were identical to those of untreated starches, whereas the chromatographic response of waxy rice starch showed a slight decrease, but with a slight increase in peak tailing. This result indicated that HMT had no (or very limited) effect on the degradation of amylopectins. Analysis of unit chain distribution of amylopectins revealed that waxy characteristics affected the molecular structure of amylopectin in untreated starches, i.e., the CL of normal‐type starches was greater than that of waxy‐type starches. After HMT, the CL and unit chain distribution of all starches were no different than those of untreated starches. The results implied that changes in the physico‐chemical properties of HMT starches would be due to other phenomena rather than the degradation of amylopectin molecular structure. However, the thermal degradation of amylopectin molecules of waxy starches could occur by HMT at higher treatment temperatures (120 and 140°C).