bluuebunny/crossref_metadata_2025 huggingface dataset:
Initial growth stages of MOVPE InN studied by AFM and specular reflectivity
Authors: van der Lee A. , Salah F. , Harzallah B. , Ruffenach S. , Briot O.
Published: January 2007

The initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X‐ray specular reflectivity for five different thin films ranging from 57 to 750 Å. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two‐dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 Å the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High indium content AlInGaN films: growth, structure and optoelectronic properties
Authors: Nemoz M. , Beraudo E. , De Mierry P. , Vennéguès P. , Hirsch L.
Published: January 2007

Structural and optical properties of AlInGaN epilayers grown on GaN template on sapphire substrate by metalorganic vapour phase epitaxy (MOVPE) are investigated by photoluminescence (PL), photothermal deflection spectroscopy (PDS), X‐ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). At low substrate temperature during the growth two quaternary layers are presents along the growth axis. The interface layer strained on GaN contains about 12% Al and 24% In. The surface layer with a 3D morphology disappears increasing the substrate temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improved AlN buffer layer technologies for UV‐LEDs
Authors: Ranalli F. , Parbrook P. J. , Wang T. , Bai J. , Lee K. B. , Airey R. J. , Hill G. , Tahraoui A. , Cullis A. G.
Published: January 2007

Growth of AlGaN based structure on AlN buffers grown directly on sapphire is reported. Such buffers show excellent morphology but a high density of edge dislocations. Growth of GaN on such layers allows dislocation bending and annihilation. Improved UV emission compared to structures grown on GaN prepared conventionally has been observed. Using AlGaN on ALN gives significantly less dislocation reduction, but efficient 340 nm LEDs have been fabricated on this template. For further dislocation reduction overgrowth on a porous AlN film has been developed, leading to much improved room temperature luminescence, indicating the technology's potential for UV‐LED device fabrication (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the relation between leakage current and dislocations in GaN‐based light‐emitting devices
Authors: Lee S. W. , Oh D. C. , Goto H. , Ha J. S. , Lee H. J. , Hanada T. , Cho M. W. , Hong S. K. , Lee H. Y. , Cho S. R. , Choi J. W. , Choi J. H. , Jang J. H. , Shin J. E. , Lee J. S. , Yao T.
Published: January 2007

In order to understand the origin of leakage current, light emitting devices were grown on two different templates with apparently different dislocation density: one on thin GaN template (∼2 μm) with higher dislocation density (low × 109 cm–2) prepared by metal‐organic vapor‐phase epitaxy (sample A), and the other on thick GaN template (∼20 μm) with comparatively low dislocation density (high × 108 cm–2) by hydride vapor‐phase epitaxy (sample B). Especially, the template B showed very low value of the dislocation density for a screw component, 2.2 × 107 cm–2 evaluated by transmission electron microscope and 2.3 × 107 cm–2 approximated by the Williamson‐Hall plot which was evaluated by high resolution X‐ray diffraction, respectively. On the other hand, sample A showed one order higher, low × 108 cm–2, than that of sample B for a screw component. Sample A showed the larger leakage current (more than two orders of magnitude) than sample B in a forward‐biased region and a reverse‐biased region also. It is expected that the screw dislocation were strongly contributed to the leakage current of forward and reverse I‐V regions in LEDs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monolithic white light emitting diodes with a broad emission spectrum
Authors: Dussaigne A. , Brault J. , Damilano B. , Massies J.
Published: January 2007

Monolithic white light emitting diode (LEDs) grown by molecular beam epitaxy (MBE) is an original approach to realize white LEDs. Using a Ga0.8In0.2N/GaN multi‐quantum well (QW) structure with different QW thicknesses in the active region of a GaN p‐n junction leads to white light emission provided that the different QW emission wavelengths and relative intensities are properly adjusted. However, the color rendering index (CRI) and the output power are still a limitation for the development of these LEDs. In this study, we propose to use a broad emission spectrum – from blue to red – with the objective of improving the CRI. Carrier recombination mechanisms in the LEDs are studied by electroluminescence (EL) measurements at room temperature and discussed as a function of the structure design. Results show a strong modification of the EL spectrum as a function of the applied voltage and an enhancement of the red emission component with the insertion of a GaN undoped spacer layer between the active region and the p‐type layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical gain and saturation behavior in homoepitaxially grown InGaN/GaN/AlGaN laser structures
Authors: Świetlik T. , Perlin P. , Suski T. , Leszczyński M. , Czernecki R. , Grzegory I. , Porowski S.
Published: January 2007

Optical gain and losses in semiconductor laser epilayers are of profound importance in device optimization. We used both parameters to estimate the potential of InGaN/GaN/AlGaN epitaxial system to be used as a laser structure emitting in a blue region. The sample was grown homoepitaxially by MOVPE technique on high quality bulk GaN substrates obtained in high pressure growth process. These structures are characterized by very low dislocation density (around 105 cm–2). As a result the reduction of a nonradiative recombination is expected which is reflected in reduced excitation pump power and gain saturation processes described by means of saturation length and a product of the latter and a maximum modal gain. To determine gain value and its saturation behavior a variable stripe length method is used employing one dimensional amplifier model. Maximum gain value of 190 cm–1 together with internal losses of 15 cm–1 are determined for the studied structure. Low value of maximum saturation length of 320 um was found in our structures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ZnMgO‐ZnO quantum wells embedded in ZnO nanopillars: Towards realisation of nano‐LEDs
Authors: Bakin A. , El‐Shaer A. , Mofor A. C. , Al‐Suleiman M. , Schlenker E. , Waag A.
Published: January 2007

ZnO thin films, ZnMgO/ZnO heterostructures and ZnO nanostructures were fabricated using molecular beam epitaxy (MBE), vapour phase transport (VPT) and an aqueous chemical growth approach (ACG). The possibility to employ several fabrication techniques is of special importance for the realization of unique device structures. MBE was implemented for ZnO‐based layer and heterostructure growth. Pronounced RHEED oscillations were used for growth control and optimisation, resulting in high quality ZnO and Zn1–xMgxO epilayers and heterostructures, as well as ZnMgO/ZnO quantum wells on sapphire and SiC substrates. A novel advanced VPT approach is developed and sapphire, SiC, ZnO epitaxial layers, and even plastic and glass were implemented as substrates for ZnO growth. The VPT fabrication of ZnO nanopillars, leading to well aligned, c‐axis oriented nanopillars with excellent quality and purity is demonstrated. Successful steps were made towards device fabrication on ZnO basis. The nanopillar fabrication technique is combined with MBE technology: MBE‐grown ZnMgO/ZnO quantum well structures were grown on ZnO nanopillars presenting significant progress towards nano‐LEDs realization. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radiative lifetime in wurtzite GaN/AlN quantum dots
Authors: Bardoux R. , Bretagnon T. , Guillet T. , Lefebvre P. , Taliercio T. , Valvin P. , Gil B. , Grandjean N. , Damilano B. , Dussaigne A. , Massies J.
Published: January 2007

We study wurtzite GaN/AlN quantum dots (QDs) by time‐resolved photoluminescence. The properties of nitride based nano‐objects are significantly affected by strong built‐in electric fields existing in this crystalline phase. These fields induce a spatial separation of electrons and holes in the quantum dot, a Stark shift of the transition energy, and they slow their radiative recombination down to tens of microseconds of decay time for the largest quantum dots. Such long decay times are responsible for the screening of internal fields by using moderate excitation intensities, thus modifying drastically both the energy and the rate of photon emission. Consequently it is difficult to perform spectroscopic studies of these QDs in the regime where a single electron‐hole (e‐h) pair is present at the most in each dot. Using a pulsed laser excitation, we study the time‐resolved dynamics of carrier recombinations, waiting for complete recombination of all electron‐hole pairs in the dots. We clearly exhibit the conditions where no screening of the internal electric field occurs. We especially obtain the transition energy and the mono‐exponential decay, i.e the radiative recombination time, of the last e‐h pair present in the dot, for a wide range of QD sizes. These results are analyzed within an envelope function model for the electron and hole confinement. The effective electric field, averaged over the strain distribution in the dots, is determined to be of 9.0 ± 0.5 MV/cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum well‐free nitride‐based UV LEDs emitting at 380 nm
Authors: de Mierry Philippe , Tinjod Frank , Chenot Sébastien , Lancefield David
Published: January 2007

CVD. The bare chip device shows a strong UV emission at 380 nm, with a maximum output power of 1.6 mW at 140 mA, and a junction temperature of 120 °C. The saturation of the external quantum efficiency (EQE) occurs at 0.5 kA/cm2 (∼80 mA), a much higher value than the 10 A/cm2 commonly reported in quantum wells (QWs) based nitride LEDs. This behavior can be accounted for by a temperature dependent non‐radiative recombination rate which increases at high injection currents. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photonic crystals comprising selectively grown flat‐topped and sharp‐tipped GaN pyramids
Authors: Coquillat D. , Le Vassor d'Yerville M. , Boubanga Tombet S. A. , Liu C. , Bejtka K. , Watson I. M. , Edwards P. R. , Martin R. W. , Chong H. M. H. , De La Rue R. M.
Published: January 2007

Selective area growth offers the promise of producing III‐nitride photonic crystals (PhCs) without dry etching and concomitant surface damage. Two PhC structures were studied, one comprising an array of flat‐topped GaN micropyramids with micrometre‐scale periodicity, and the other made up of sharp‐tipped pyramids with sub‐micrometre periodicity. Angularly resolved reflection and transmission measurements revealed the presence of sharp resonances associated with resonant Bloch modes. As a result, the photonic band structure was determined along symmetry directions of the reciprocal lattice for the two PhC structures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strong coupling in bulk GaN microcavities grown on silicon
Authors: Réveret F. , Sellers I. R. , Disseix P. , Leymarie J. , Vasson A. , Semond F. , Leroux M. , Massies J.
Published: January 2007

We have studied GaN microcavities grown on silicon by angle resolved reflectivity at 5 and 300 K. A Bragg mirror made up of λ/4 AlGaN and AlN layers has been grown on a silicon substrate. The GaN active layer whose thickness is equal to λ/2 is covered by a 100 Å thick aluminium layer which acts as the top mirror. Transfer matrix simulations are carried out to interpret the reflectivity spectra from which crucial parameters of the active layer such as the oscillator strengths, the excitonic energies and the associated broadenings of A and B excitons are deduced. At low temperature the strong coupling regime between with A and B excitons and the cavity photonic mode is clearly observed. At room temperature the splitting is evaluated to 45 meV. In order to get further insight in the physics of nitride‐based microcavities and especially to improve the exciton‐photon coupling, the influence of the Bragg or metallic mirrors on the cavity is analysed. The inhomogeneous broadening of excitons together with the strain gradient experienced by the active layer along the growth axis are also investigated. All of these effects on the Rabi splitting are analysed and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature‐ and excitation density dependency of photoluminescence spectra in InGaN/GaN‐heterostructures
Authors: Vierheilig C. , Braun H. , Schwarz U. T. , Wegscheider W. , Baur E. , Strauß U. , Härle V.
Published: January 2007

We study the lateral diffusion of photogenerated carriers within InGaN/GaN quantum wells by scanning in the focal plane of our confocal microscope. The photoluminescence (PL) images are analyzed at varying excitation densities in the temperature range between 4 K and room temperature. The results of a blue and a green emitting sample are discussed in context of reported diffusion lengths for InGaN/GaN quantum wells. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficiency enhancement of 400 nm violet LEDs utilizing island‐like GaN thick film by HVPE technology
Authors: Tsay Jenq‐Dar , Liu Po Chun , Guo Yih‐Der , Wang Jing‐Mei , Liu Wen‐Yueh , Pan Shyi‐Ming , Wu Liang‐Wen , Heuken Michael
Published: January 2007

In this study, we develop a novel way to fabricate InGaN/GaN LED chips with special shape for improving the output power. Crack‐free shaped GaN islands were first prepared on c‐axis sapphire substrate by using HVPE selective area growth. By doing so, GaN islands with flat top surface and inclined side faces are obtained. Then, the InGaN/GaN LED structure was grown on the top surface of the GaN island subsequently. The output powers of the p‐side up and the p‐side down shaped LED chip are 1.4 and 2.2 times the output power of the cubic chip, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth kinetics and properties of ZnO/ZnMgO hetero‐ structures grown by radical‐source molecular beam epitaxy
Authors: Ivanov S. V. , El‐Shaer A. , Shubina T. V. , Listoshin S. B. , Bakin A. , Waag A.
Published: January 2007

A phenomenological approach to quantitative description of Zn(Mg)O growth by radical‐source molecular beam epitaxy, based on the experimental studies of RHEED intensity oscillations, has been developed. It allows a precise control of growth rate, composition and stoichiometry at any growth temperature, Along with optimization of a growth initiation procedure on a c‐sapphire, it is necessary condition for fabrication of high quality ZnO epilayers and ZnO/ZnMgO heterostructures in a wide Mg composition range. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Blue light emitting diodes on Si(001) grown by MOVPE
Authors: Schulze F. , Dadgar A. , Bertram F. , Bläsing J. , Diez A. , Veit P. , Clos R. , Christen J. , Krost A.
Published: January 2007

The cover picture of this issue of physica status solidi (c) has been taken from the article [1].
It's time to celebrate!
Authors: Stutzmann Martin
Published: January 2007

The beginning of the 19th century was a remarkable period for culture and science, indeed. Many of Beethoven's great works were performed for the first time, the first asteroids Ceres and Pallas were discovered, Alessandro Volta informed the Royal Society in London about a new source for electrical current, the industrial revolution began with the invention of punch card controlled weaving machines by Jacquard and the appearance of steam engines as power sources for ships or trains, and Alexander von Humboldt travelled and surveyed the New World. At the same time, also the foundations of modern crystallography and solid state science were laid, with the discovery of many metallic elements and, most notably, the first editions of René Just Haüy's “Traité de Minéralogie” in 1801 and the “Traité de Physique” in 1803.

On this scale of events, the opening of a small printing shop in lower Manhattan by Charles Wiley in 1807 remained practically unnoticed. However, in the following 200 years not only did solid state physics develop into one of the most active fields in modern science, but also the small printing shop did prosper into one of the largest science publishers worldwide. physica status solidi became part of the Wiley family with the acquisition of VCH in 1996 and, since then, has enjoyed the support and stimulating atmosphere as the largest solid state physics unit within Wiley. Thus, all members of the Editorial Office and all Editors of physica status solidi take great pleasure in congratulating Wiley on the occasion of the 2007 Bicentennial and expressing their best wishes for a prosperous future!

Also physica status solidi has continued its growth and positive development under the publishing agreement entered with Wiley in 2002. Thus, the number of submitted and published articles has again increased significantly in the past year, by 20% and 25%, respectively. Among the other notable events in 2006 was the completion of the Physics and Astronomy Backfile Collection, which now provides easy and complete access to more than 300 000 pages published in physica status solidi since the foundation of the journal at www.interscience.wiley.com/backfiles/physics. And last but not least, the Rapid Research Letter section of physica status solidi has just been launched as an independent journal, pss‐RRL, complementing pss (a), pss (b), and pss (c) by providing a special service for the fast publication of important new findings in all areas of solid state physics. Please have a look at the home page of the new journal www.pss‐rapid.com for further details.

As this year comes to an end, I would like to express my sincere thanks to our authors, referees, readers, and everybody involved in editing and producing physica status solidi for their continued interest, valuable contributions, and dedication. Good luck and all the best for 2007! And once again: Happy 200th anniversary, Wiley!

Garching, December 2006
Using electrospray‐assisted pyrolysis ionization/mass spectrometry for the rapid characterization of trace polar components in crude oil, amber, humic substances, and rubber samples
Authors: Hsu Hsiu‐Jung , Oung Jung‐Nan , Kuo Tseng‐Long , Wu Suh‐Huey , Shiea Jentaie
Published: January 2007

We describe the use of electrospray‐assisted pyrolysis ionization/mass spectrometry (ESA‐Py/MS) to selectively ionize trace polar compounds that coexist with large amounts of nonpolar hydrocarbons in crude oil, amber, humic substances, and rubber samples. Samples of different origins are distinguished rapidly by their positive ion ESA‐Py mass spectra without prior separation or chemical pretreatment. During ESA‐Py analysis, the samples in their solid or liquid states were pyrolyzed at 590, 630 or 940°C using a commercial Curie‐point pyrolysis probe. The gaseous pyrolysates were transferred into a glass reaction cell. The polar compounds (M) in the pyrolysates were then ionized by electrospray ionization (ESI), yielding protonated molecules (MH+). Although the major components of the pyrolysates are nonpolar hydrocarbons, their lack of functional groups that can receive a proton in the ESA‐Py source results in no hydrocarbon ion signals being produced; thus, the positive ions detected in ESA‐Py mass spectra all result from trace polar components in the pyrolysates. Copyright © 2007 John Wiley & Sons, Ltd.
A robustness approach to linear control of mildly nonlinear processes
Authors: Schweickhardt T. , Allgöwer F.
Published: January 2007

We present a novel approach toward linear control of nonlinear systems. Combining robust control theory and nonlinearity measures, we derive a method to (i) assess the nonlinearity of a given control system, (ii) derive a suitable linear model (not necessarily equivalent to the local linearization), and (iii) design a linear controller that guarantees stability of the closed loop containing the nonlinear process. A distinctive feature of the approach is that the nonlinearity analysis, linear model derivation and linear controller synthesis can be done on an operating regime specified by the designer. Examples are given to illustrate the approach. Copyright © 2007 John Wiley & Sons, Ltd.
Musical part separation based on perceptual hierarchy
Authors: Kinoshita Tomoyoshi , Handa Ibuki , Muto Makoto , Sakai Shuichi , Tanaka Hidehiko
Published: January 2007

There have been many studies of auditory scene analysis in which an attempt was made to understand external events through acoustic signals. In particular, when the target is limited to music, there have been several studies aiming at automatic music scoring. In most previous studies, however, the procedure is constantly limited to local processing. Even if the procedure continues along the time axis, it is confined to the local neighborhood on the time axis, and only limited processing performance is realized. The purpose of this paper is to improve this aspect. A method is proposed which focuses on the hierarchical structure in the perception of the acoustic stream and extracts a single note string corresponding to each part from the music. In the proposed method, phrases are formed as an intermediate step in extracting the parts. Local clues are used in forming the phrases, and global clues are used in forming the parts. By using this approach, the parts are successfully extracted without problems such as explosion of the computational complexity. In a preliminary experiment, the parts were successfully extracted with a reproduction rate of approximately 80% and a fit rate of approximately 85%. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(2): 91– 100, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10310
Incorporating environment models for improving vision‐based tracking of people
Authors: Suzuki Tatsuya , Iwasaki Shinsuke , Kobayashi Yoshinori , Sato Yoichi , Sugimoto Akihiro
Published: January 2007

This paper presents a method for real‐time 3D human tracking based on the particle filter by incorporating environment models. We track a human head represented with its 3D position and orientation by integrating the multiple cues from a set of distributed sensors. In particular, the multi‐viewpoint color and depth images obtained from distributed stereo camera systems and the 3D shape of an indoor environment measured with a range sensor are used as the cues for 3D human head tracking. The 3D shape of an indoor environment allows us to assume the existing probability of a human head (we call this probability the environment model). While tracking the human head, we consider the environment model to improve the robustness of tracking in addition to the multi‐camera's color and depth images. These cues including the environment model are used in the hypothesis evaluation and integrated naturally into the particle filter framework. The effectiveness of our proposed method is verified through experiments in a real environment. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(2): 71–80, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20612
A method for language‐specific Web crawling and its evaluation
Authors: Tamura Takayuki , Somboonviwat Kulwadee , Kitsuregawa Masaru
Published: January 2007

Many countries have created Web archiving projects aiming at long‐term preservation of Web information, which is now considered precious in cultural and social aspects. However, because of its borderless character, the Web poses obstacles to comprehensively gathering information originating in a specific nation or culture.

This paper proposes an efficient method for selectively collecting Web pages written in a specific language. First, a linguistic graph analysis of real Web data obtained from a large crawl is conducted in order to derive a crawling guideline, which makes use of language attributes per Web server. The guideline then is formed into a few variations of link selection strategies. Simulation‐based evaluation reveals that one of the strategies, which carefully accepts newly discovered Web servers, shows superior results in terms of harvest rate/coverage and runtime efficiency. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(2): 10–20, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20693
A self‐distributing software environment for immersive multiprojector displays
Authors: Hashimoto Naoki , Ishida Yoshihiko , Sato Makoto
Published: January 2007

In multiprojector displays which surround users with high‐resolution images, a PC‐Cluster is often used for realistic and real‐time image generation. However, it is quite troublesome to develop applications which support parallel processing on the PC‐Cluster. It is also difficult to acquire enough rendering performance because of the limited bandwidth of the PC‐Cluster. Therefore, we aim to achieve affordable and accessible software environments for the multiprojector displays. In this paper, we describe a self‐distributing software environment for inheriting existent game engines which provide basic functions of realizing virtual environments. This environment achieves minimum data communication based on a master–slave model. The communication mechanism is automatically applied to target applications by intercepting APIs. Hence, we can directly exploit high capability of the existing game engines on the multiprojector displays. © 2007 Wiley Periodicals, Inc. Syst Comp Jpn, 38(2): 1–9, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20705
Statistical evidence for GLM regression parameters: A robust likelihood approach
Authors: Blume Jeffrey D. , Su Li , Olveda Remigio M. , McGarvey Stephen T.
Published: January 2007

When a likelihood ratio is used to measure the strength of evidence for one hypothesis over another, its reliability (i.e. how often it produces misleading evidence) depends on the specification of the working model. When the working model happens to be the ‘true’ or ‘correct’ model, the probability of observing strong misleading evidence is low and controllable. But this is not necessarily the case when the working model is misspecified. Royall and Tsou (J. R. Stat. Soc., Ser. B2003;65:391–404) show how to adjust working models to make them robust to misspecification. Likelihood ratios derived from their ‘robust adjusted likelihood’ are just as reliable (asymptotically) as if the working model were correctly specified in the first place. In this paper, we apply and extend these ideas to the generalized linear model (GLM) regression setting. We provide several illustrations (both from simulated data and real data concerning rates of parasitic infection in Philippine adolescents), show how the required adjustment factor can be obtained from standard statistical software, and draw some connections between this approach and the ‘sandwich estimator’ for robust standard errors of regression parameters. This substantially broadens the availability and the viability of likelihood methods for measuring statistical evidence in regression settings. Copyright © 2007 John Wiley & Sons, Ltd.
A likelihood approach to estimating sensitivity and specificity for binocular data: application in ophthalmology
Authors: de Leon A. R. , Guo M. , Rudnisky C. J. , Singh G.
Published: January 2007

Binocular data typically arise in ophthalmology where pairs of eyes are evaluated, through some diagnostic procedure, for the presence of certain diseases or pathologies. Treating eyes as independent and adopting the usual approach in estimating the sensitivity and specificity of a diagnostic test ignores the correlation between eyes. This may consequently yield incorrect estimates, especially of the standard errors. The paper proposes a likelihood‐based method of accounting for the correlations between eyes and estimating sensitivity and specificity using a model for binocular or paired binary outcomes. Estimation of model parameters via maximum likelihood is outlined and approximate tests are provided. The efficiency of the estimates is assessed in a simulation study. An extension of the methodology to the case of several diagnostic tests, or the same test measured on several occasions, which arises in multi‐reader studies, is given. A further extension to the case of multiple diseases is outlined as well. Data from a study on diabetic retinopathy are analysed to illustrate the methodology. Copyright © 2007 John Wiley & Sons, Ltd.
Early stopping clinical trials of binomial response with an exact group sequential method
Authors: Zhao Zhen
Published: January 2007

In Phase II clinical trials much slower patient enrollment and intervening results of comparable trials can make it desirable to stop trials early when the data indicate no relevant effect. For a binomial response, we adopt an exact group sequential method as a decision tool to assess whether the trial could be stopped early or not. We have applied the exact group sequential method to a Phase II Tuberculosis clinical trial, and the results have been compared with that from error spending and conditional power approaches. We conclude that the exact group sequential method is more efficient for interim analysis in clinical trials than the error spending and conditional power approaches. Published in 2007 by John Wiley & Sons, Ltd.
Furan fatty acids: Occurrence, synthesis, and reactions. Are furan fatty acids responsible for the cardioprotective effects of a fish diet?
Authors: Spiteller Gerhard
Published: January 2007

Furan FA (F‐acids) are tri‐or tetrasubstituted furan derivatives characterized by either a propyl or pentyl side chain in one of the α‐positions; the other is substituted by a straight long‐chain saturated acid with a carboxylic group at its end. F‐acids are generated in large amounts in algae, but they are also produced by plants and microorganisms. Fish and other marine organisms as well as mammals consume F‐acids in their food and incorporate them into phospholipids and cholesterol esters. F‐acids are catabolized to dibasic urofuran acids, which are excreted in the urine. The biogenetic precursor of the most abundant F‐acid, F6, is linoleic acid. Methyl groups in the β‐position are derived from adenosylmethionine. Owing to the different alkyl substituents, synthesis of F‐acids requires multistep reactions. F‐acids react readily with peroxyl radicals to generate dioxoenes. The radical‐scavenging ability of F‐acids may contribute to the protective properties of fish and fish oil diets against mortality from heart disease.
Eicosapentaenoic acid, but not oleic acid, stimulates β‐oxidation in adipocytes
Authors: Guo Wen , Xie Weisheng , Lei TianGuang , Hamilton James A.
Published: January 2007

The beneficial roles of dietary fish oil in lowering serum TAG levels in animals and humans have been attributed in part to the high content of two n−3 polyunsaturated very long‐chain FA, EPA, and DHA. Recent studies show that EPA induces mitochondrial β‐oxidation in hepatocytes, which might contribute to the systemic lipid‐lowering effect. Whether EPA affects FA storage or oxidation in adipocytes is not clear. To investigate this possibility, 3T3‐L1 adipocytes incubated with EPA (100 μM) for 24 h were assayed for β‐oxidation, carnitine palmitoyl transferase 1 (CPT‐1) activity, protein, and mRNA expression of CPT‐1. For comparison, cells treated with oleic acid, octanoic acid, and clofibrate, a synthetic ligand for peroxisome proliferator‐activated receptor α were also analyzed. Mitochondria were isolated by differential centrifugation, and the mitochondrial membrane acyl chain composition was measured by GLC. EPA increased the oxidation of endogenous FA but did not inhibit lipogenesis. Oleic acid and clofibrate did not affect FA oxidation or lipogenesis, whereas octanoic acid suppressed the oxidation of endogenous FA and inhibited lipogenesis. Increased β‐oxidation by EPA was associated with increased CPT‐1 activity but without changes in its mRNA and protein expression. EPA treatment increased the percentage of this FA in the mitochondrial membrane lipids. We suggest that EPA increased the activity of CPT‐1 and β‐oxidation in adipocytes by altering the structure or dynamics of the mitochondrial membranes.
Effect of abomasal infusions of geometric isomers of 10,12 conjugated linoleic acid on milk fat synthesis in dairy cows
Authors: Sæbø Asgeir , Sæbø Per‐Christian , Griinari J. Mikko , Shingfield Kevin J.
Published: January 2007

The trans‐10, cis‐12 isomer of conjugated linoleic acid (CLA) decreases TAG accumulation in 3T3‐L1 adipocytes, reduces lipid accretion in growing animals, and inhibits milk fat synthesis in lactating mammals. However, there is evidence to suggest that other FA may also exert antilipogenic effects. In the current experiment, the effects of geometric isomers of 10,12 CLA on milk fat synthesis were examined using four Holstein‐British Friesian cows in a 4×4 Latin Square experiment with 14‐d periods. Treatments consisted of abomasal infusions of skim milk, or skim milk containing trans‐10, cis‐12 CLA (T1), trans‐10, trans‐12 CLA (T2), or a mixture of predominantly 10,12 isomers containing (g/100 g) trans‐10, cis‐12 (35.0), cis‐10, trans‐12 (23.2), trans‐10, trans‐12 (14.9), and cis‐10, cis‐12 (5.1). CLA supplements were prepared from purified ethyl linoleate and infused as nonesterified FA. Infusions were conducted over a 4‐d period with a 10‐d interval between treatments and targeted to deliver 4.5 g/d of 10,12 CLA isomers. Compared with the control, trans‐10, trans‐12 CLA had no effect (P>0.05) on milk fat yield, whereas treatments T1 and T3 depressed (P<0.05) milk fat content (19.8 and 22.9%, respectively) and decreased milk fat output (20.8 and 21.3%, respectively). Comparable reductions in milk fat synthesis to 4.14 and 1.80 g trans‐10, cis‐12/d supplied by treatments T1 and T3 indicate that other 10,12 geometric isomers of CLA have the potential to exert antilipogenic effects. The relative abundance of cis‐10, trans‐12 CLA in treatment T3 and the low transfer efficiency of this isomer into milk suggest that cis‐10, trans‐12 CLA was the active component.
Isolation and characterization of some hydroxy fatty and phosphoric acid esters of 10‐hydroxy‐2‐decenoic acid from the royal jelly of honeybees (Apis mellifera)
Authors: Noda Naoki , Umebayashi Kazue , Nakatani Takafumi , Miyahara Kazumoto , Ishiyama Kaori
Published: January 2007

The present work characterizes novel FA in the royal jelly of honeybees (Apis mellifera). TLC analysis showed that the chloroform/methanol extract obtained from royal jelly consists mainly of FA. The FABMS spectrum of this extract gave several ion peaks due to compounds with higher M.W. than those of the FA so far reported. The methanol extract was found to contain unknown phospholipids. By means of reversed‐phase HPLC with various solvent systems, 13 compounds were obtained in pure state. Their structures including absolute configurations were determined by chemical, NMR, and MS spectral analysis. Six compounds were identified as novel mono‐ or diesters of 10‐hydroxy‐2E‐decenoic acid in which the hydroxyl group was esterified by another FA unit, and one was hydroxy‐2E‐decenoic acid 10‐phosphate. In addition, we demonstrated that 9‐hydroxy‐2E‐decenoic acid exists as a mixture of optical isomers.
Synthesis and characterization of a series of carbamate‐linked cationic lipids for gene delivery
Authors: Liu Dongliang , Hu ianjun , Qiao Weihong , Li Zongshi , Zhan Shubiao , Cheng Lvbo
Published: January 2007

A series of pH‐sensitive lipids, 1a‐h [(2,3‐bis‐alkyl‐carbamoyloxy‐propyl)‐trialkylammonium halide] and 2a‐d (1‐dimethylamino‐2,3‐bis‐alkylcarbamoyloxy‐propane), with carbamate linkages between the hydrocarbon chains and an ammonium or tertiary amine head, were synthesized for liposome‐mediated gene delivery. The variable length of the carbon chains and the quaternary ammonium or neutral tertiary amine heads allowed us to identify the structure‐function relationship showing how these factors would affect cationic lipid in gene delivery performance.
A rapid method for the quantification of fatty acids in fats and oils with emphasis on trans fatty acids using fourier transform near infrared spectroscopy (FT‐NIR)
Authors: Azizian Hormoz , Kramer John K. G.
Published: January 2007

A rapid method was developed for classifying and quantifying the FA composition of edible oils and fats using Fourier Transform near infrared spectroscopy (FT‐NIR). The FT‐NIR spectra showed unique fingerprints for saturated FA, cis and trans monounsaturated FA, and all n−6 and n−3 PUFA within TAG to permit qualitative and quantitative comparisons of fats and oils. The quantitative models were based on incorporating accurate GC data of the different fats and oils and FT‐NIR spectral information into the calibration model using chemometric analysis. FT‐NIR classification models were developed based on chemometric analyses of 55 fats, oils, and fat/oil mixtures that were used in the identification of similar materials. This database was used to prepare three calibration models—one suitable for the analysis of common fats and oils with low levels of trans FA, and the other two for fats and oils with intermediate and high levels of trans FA. The FT‐NIR method showed great potential to provide the complete FA composition of unknown fats and oils in minutes. Compared with the official GC method, the FT‐NIR method analyzed fats and oils directly in their neat form and required no derivatization of the fats to volatile FAME, followed by time‐consuming GC separations and analyses. The FT‐NIR method also compared well with the official FTIR method using an attenuated total reflectance (ATR) cell; the latter provided only quantification of specific functional groups, such as the total trans FA content, whereas FT‐NIR provided the complete FA profile. The FT‐NIR method has the potential to be used for rapid screening and/or monitoring of fat products, trans FA determinations for regulatory labeling purposes, and detection of contaminants. The quantitative FT‐NIR results for various edible oils and fats and their mixtures are presented based on the FT‐NIR model developed.
Phytosterols, Cholesterol Absorption and Healthy Diets
Authors: Ostlund Richard E.
Published: January 2007

The purpose of this review is to outline the emerging role of dietary phytosterols in human health. Dietary saturated fat, cholesterol and fiber are currently emphasized in the reduction of low‐density lipoprotein cholesterol levels. However, other dietary components such as phytosterols may have equivalent or even larger effects on circulating cholesterol and need further study with respect to the potential for coronary heart disease risk reduction. Phytosterol effects were not considered in classic fat‐exchange clinical trials and may account for some of the differences attributed to the food fats studied. Phytosterols reduce cholesterol absorption while being poorly absorbed themselves and the effects can be studied in human subjects in single‐meal tests using stable isotopic tracers. Because phytosterols are insoluble and biologically inactive when purified, careful attention needs to be given to ensuring that commercial supplement products are rendered bioavailable by dissolution in fat or by emulsification. Recent work shows that phytosterols in natural food matrices are also bioactive. The retention of phytosterols during food manufacturing and the use of foods with high phytosterol content may constitute an alternative to the use of supplements.
Effects of α‐ and γ‐tocopherols on formation of hydroperoxides and two decomposition products from methyl linoleate
Authors: Kinen Marjukka M , Kamal‐Eldin Afaf , Lampi Anna‐Maija , Hopia Anu
Published: January 2007

The antioxidant effects of α‐and γ‐tocopherols (at 0, 10, 100, 500, and 1000 ppm) were evaluated in a model system based on the autoxidation of methyl linoleate in bulk for 4 d at 40°C. Samples were collected every 24 h and analyzed for the 9 cis,trans, 9 trans,trans, 13 cis,trans, and 13 trans,trans isomers of hydroperoxide, hydroxy, and ketodiene oxidation products by high‐performance liquid chromatography. Results showed that both α‐ and γ‐tocopherols are effective hydrogen donors as evidenced by their abilities to inhibit the formation of hydroperoxides, hydroxy compounds, and ketodienes and the cis,trans to trans,trans isomerization of hydroperoxides. Compared with γ‐tocopherol, α‐tocopherol was a more efficient antioxidant at very low concentrations (10 ppm) but a less efficient antioxidant at the high concentrations (100–1000 ppm). This paradoxical behavior is explained on the basis of differences in ease of hydrogen donation between the two tocopherol homologs. Although α‐tocopherol shows some loss of efficiency with increasing concentration, it is not a prooxidant when compared to the control void of antioxidants.
Behavior of phenolic antioxidants in a partitioned medium: Focus on linoleic acid peroxidation induced by iron/ascorbic acid system
Authors: Bondet Vincent , Cuvelier Marie‐Elisabeth , Berset Claudette
Published: January 2007

The peroxidation of linoleic acid was induced by the Fe2+/ascorbic acid system in a micellar medium, and the kinetics of the produced conjugated dienes to a weak level (0.7 μM) in order to initiate only the sequential oxidative reactions without superimposed antioxidant activity. Other conditions were established to obtain a simple kinetic profile. With a linoleic acid/Fe2+ ratio of 10 and an Fe2/ascorbic acid ratio of 23 in the medium emulsified by Tween and saturated in oxygen, no limiting effect of substrates was observed for several hours. Fe2+ disappeared in less than 5 min, while a linear propagation rate was reached after 1 h for up to 15 h. Two parameters were chosen to quantify the level of the oxidation: the slope of the linear phase, and the extrapolated absorbance of this step at zero time. These two parameters were used in order to compare the antioxidant power of different phenolic compounds in this partitioned medium.
Lipid components and enzymatic hydrolysis of lipids in muscle of Chinese freshwater fish
Authors: Kaneniwa Masaki , Miao Song , Yuan Chunhong , Lida Haruka , Fukuda Yutaka
Published: January 2007

The lipid and fatty acid composition of muscle of 10 species of freshwater fish obtained from a market of Shanghai City was examined. Total lipids (TL) ranged over 0.9–4.7% of muscle for all samples. The content of triacylglycerol (TG) in muscle ranged over 0.2–3.4% and that of polar lipids (PL) was 0.5–1.3%. Differences of TL content were dependent on TG contents. The predominant important fatty acids (>10% of the total fatty acids in TL) were 16∶0 and 18∶1n−9 with some 16∶1n−7, 18∶2n−6, and 22∶6n−3. The polyunsaturated fatty acids (PUFA) content was 10.2–43.4%, and especially Chinese sea bass contained above 20% of 22∶6n−3 in the total fatty acids. There were higher levels of PUFA such as 20∶5n−3 and 22∶6n−3 in PL than in neutral lipids. Muscle of the silver carp was stored at 20°C, and changes of lipid classes during storage were examined. Free fatty acids increased, and PL decreased during storage. This phenomenon was inhibited by heating the muscle, suggesting that lipid hydrolysis by phospholipase occurred in silver carp muscle.
Investigation of crude latex from various Carica papaya varietices for lipid bioconversions
Authors: Caro Yanis , Villeneuve Pierre , Pina Michel , Reynes Max , Graille Jean
Published: January 2007

The protein contents in crude latices from various varieties of papaya (Carica papaya) and their catalytic activities in proteolysis, lipolysis, and interesterification reactions were studied with regard to the variety, the geographic location of cultures, and the frequency of fruit tapping. Biocatalytic activities of these raw materials were compared to several commercially available crude and purified preparations of papain. These investigations were carried out in order to have a better physicochemical characterization of these raw materials, to select the adequate papaya latex for protein or lipid bioconversions, and to valorize them on an industrial scale. For the purified preparations of papain, only proteolytic activity was obtained. All crude papaya latices exhibit proteolytic, lipolytic, and interesterification activities, and no relationship between the proteolytic and lipolytic activities was observed. The high multiple correlation coefficient (R) on the order of R=0.93–0.99, obtained from the regression analysis for the lipolytic and interesterification activities for all crude papaya latices investigated suggested that there was a correlation between these enzyme activities. However, for the same lipase preparation, the interesterification activity differed substantially depending on the type of interesterification reaction.
Preparation of Glycinin and β‐Conglycinin from High‐Sucrose/Low‐Stachyose Soybeans
Authors: Deak Nicolas A. , Murphy Patricia A. , Johnson Lawrence A.
Published: January 2007

A new soybean line, known as high‐sucrose/low‐stachyose (HS/LS) soybeans, has been developed having elevated sucrose content and reduced content of flatus‐causing oligosaccharides, especially stachyose. There is also increased interest in understanding the health benefits, functional properties and potential applications for the two major storage proteins of soybeans, glycinin and β‐conglycinin. We evaluated the protein fractionation behavior of a HS/LS soybean line and compared it to normal soybeans when using the three‐step Wu procedure, which employs SO2, NaCl and precipitations at pH 6.4 and 4.8 and a new two‐step Deak procedure, which employs SO2, CaCl2 and precipitations at pH 6.4 and 4.8. Both soybean variety and fractionation procedure significantly affected fraction yields, purities and functional properties. The Wu procedure gave glycinin‐ and β‐conglycinin‐rich fractions with 100% purities and high yields of solids (15.4%) and protein (31.7%) from HS/LS soy flour, which were significantly higher than the purities and yields achieved with normal soybeans. The Deak procedure was less efficient in fractionating proteins from HS/LS soybeans than from normal soybeans, producing protein fractions from HS/LS soybeans with purities ranging from 71 to 80%. The Deak procedures yielded products with unique solubilities, surface hydrophobicities, and emulsification and foaming properties.