bluuebunny/crossref_metadata_2025 huggingface dataset:
A divergent approach to the preparation of cysteine and serine analogs
Authors: Masterson Douglas S. , Roy Kinkini , Rosado Dale A. , Fouche Marilyn
Published: July 2008

Malonate diesters containing a prochiral quaternary carbon have been successfully transformed into analogs of cysteine and serine. The chiral half‐esters are obtained in good yield, and enantioselectivity by selective hydrolysis using Pig‐Liver Esterase (PLE) as the catalyst. The resulting half‐ester intermediates are transformed into α2, 2‐, β2, 2‐, and β3, 3‐analogs of cysteine and serine. The methodology described here allows for the preparation of both enantiomers of the amino‐acid analogs by selective manipulation of the ester and acid functionalities. This divergent strategy allows a common synthetic strategy to be used to prepare a variety of unnatural amino‐acid classes from a common intermediate which should prove useful in the design of novel peptide libraries. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.
Multi‐walled carbon nanotubes production by ethane decomposition over silica‐supported iron‐catalysts
Authors: Messina Giacomo , Santangelo Saveria , Donato Maria G. , Lanza Maurizio , Milone Candida , Pistone Alessandro , Galvagno Signorino
Published: July 2008

Multi‐walled carbon nanotubes (MWCNTs) are prepared by chemical vapor deposition (CVD) in C2H6 + H2 mixture over 20%Fe/SiO2 catalysts. The effects, in terms of yield and selectivity of the growth process, of the changes in composition (H2 at 0–75%) and flow‐rate (100–150 sccm) of gas‐mixture, catalyst reduction‐temperature (400 °C and 650 °C), temperature (750–850 °C) and duration (0.5−6 h) of the synthesis‐reaction are investigated. Although yield to C deposits improves by increasing gas flow‐rate, temperature or duration of the synthesis‐reaction, and by diminishing H2 volume fraction in growth atmosphere, it never exceeds 90% due to the heavy catalyst encapsulation. Moreover, the results of morphological and structural analyses show that a loss of selectivity towards nanotubes and a deterioration of CNT crystalline quality generally accompany the yield enhancement. This suggests the unsuitability of the ethane decomposition over silica‐supported Fe‐catalysts to the large‐scale production of CNTs. Nevertheless, the nanotubes attained might be profitably used in all applications exploiting the magnetic properties originating from the encapsulated iron. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and characterization of gallium oxide thin films by radiofrequency magnetron sputtering
Authors: Marie P. , Portier X. , Cardin J.
Published: July 2008

Undoped and Neodymium‐doped gallium oxide (Ga2O3) thin films of about 500 nm thickness were successfully grown at different temperatures ranging from 100 up to 600 °C by radiofrequency magnetron sputtering. Post‐annealing treatments were carried out at 900 °C and 1000 °C. The obtained films were (400) textured and a grain size of a few tens of nanometres was found. Optical and electrical characterizations led to a figure of merit of about 1.9 × 10–4. These films were successfully doped with Neodymium by a co‐sputtering method. The photoluminescence experiments for the Nd‐doped β‐Ga2O3 films clearly showed the rare‐earth emitting signature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of tantalum dopant ions (Ta5+) on the efficiency of the tungsten trioxide photoelectrode
Authors: Enesca A. , Duta A. , Schoonman J.
Published: July 2008

The paper presents the influence of the tantalum dopant ions (Ta5+) on the properties of WO3 film, used as photoelectrode for water photolysis. The photoluminescence and photocurrent stability were recorded in a photoelectrochemical system having doped and, respectively, undoped WO3 films, deposited by spray pyrolysis on fluorine–doped tin oxide as photoanode and Pt as cathode, in electrolyte HCl (pH = 5). The crystalline structure, topography and electrical properties were investigated. The experiments confirm that the doping process double the photoelectrode efficiency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mosaicity and stress effects on luminescence properties of GaN
Authors: Toure A. , Bchetnia A. , Lafford T. A. , Benzarti Z. , Halidou I. , Bougrioua Z. , Jani B. El
Published: July 2008

High‐resolution X‐ray diffraction (HRXRD) of several GaN layers grown on Si/N treated c ‐plane sapphire substrate by metal‐organic chemical vapour phase deposition (MOCVD) were investigated. Photoluminescence (PL) measurements were carried out at 13 K. GaN mosaicity was studied at different growth stage with a thickness varying from 0.1 to 4.5 µm. Rocking curves of symmetric and asymmetric plane reflections were investigated to determine respectively the tilt and twist mosaic. Using PL spectra and HRXRD scattering a correlation were found between the intensity and the full width at half maximum (FWHM) of the bound exciton neutral donor (I2) with the GaN mosaicity. The I2 intensity increased significantly with increasing the interaction parameter (m) between tilt and twist mosaic, whereas the FWHM of I2 decreased with increasing m. The evolution of the compressive stress with thickness is extracted from HRXRD and correlated with PL measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interdiffusion in SiGe alloys with Ge contents of 25% and 50% studied by X‐ray reflectivity
Authors: Medunˇa M. , Novák J. , Bauer G. , Falub C. V. , Grützmacher D.
Published: July 2008

The interdiffusion in SiGe alloys has been studied by X‐ray specular reflectivity using ex‐situ and in‐situ annealing experiments. We report on the evolution of the Ge profile of strain‐compensated Si/SiGe multilayers due to high temperature annealing. These multilayers were grown pseudomorphically and strain‐symmetrized on relaxed Si0.75Ge0.25 and Si0.5Ge0.5 pseudosubstrates by molecular beam epitaxy at 330 °C. The multilayer structures were annealed at several temperatures around 590 °C and around 800 °C. From modelling the X‐ray specular reflectivity scans at various stages of the interdiffused structures, we obtained interdiffusion coefficients resulting in the activation energy and the prefactor for interdiffusion corresponding to Si0.75Ge0.25 and Si0.5Ge0.5. The results obtained ex‐situ for Si0.5Ge0.5 and in‐situ for Si0.75Ge0.25 provide accurate values of diffusion parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
One‐step electrochemical deposition of CuInSe2 absorber layers
Authors: Kois J. , Volobujeva O. , Bereznev S.
Published: July 2008

A new modified approach for the thermodynamics and kinetics constituents of the electrodeposition mechanism of CuInSe2 is presented. It is shown that the mechanism of CuInSe2 phase formation includes a number of consecutive reactions. Under the conditions of the one‐step electrochemical deposition process, the formation of Cu+Se phases are controlled by the diffusion of selenium and copper species, the insertion of indium into the film depends on the applied potential. The paper describes developed associated model used to determine the fluxes of copper, indium and selenium species to the cathode and relative concentrations of deposited solid phases. The distribution diagram of the final products in depending on applied potential and composition ratio of Se(IV)/Cu(II) in solution is build by the results of computations. The morphology of electrodeposited films is determined by the potential of deposition and the rate of mass transport in solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Decoupling crystalline volume fraction and VOC in microcrystalline silicon pin solar cells by using a µc‐Si:F:H intrinsic layer
Authors: Zhang Q. , Johnson E. V. , Djeridane Y. , Abramov A. , Cabarrocas P. Roca i
Published: July 2008

Microcrystalline silicon thin film pin solar cells with a highly crystallized intrinsic μc‐Si:F:H absorber were prepared by RF‐plasma enhanced chemical vapour deposition using SiF4 as the gas precursor. The cells were produced with a vacuum break between the doped layer and intrinsic layer depositions, and the effect of different subsequent interface treatment processes was studied. The use of an intrinsic μc‐Si:H p/i buffer layer before the first air break increased the short circuit current density from 22.3 mA/cm2 to 24.7 mA/cm2. However, the use of a hydrogen‐plasma treatment after both air breaks without an interface buffer layer improved both the open circuit voltage and the fill factor. Although the material used for the absorber layer showed a very high crystalline fraction and thus an increased spectral response at long wavelengths, an open‐circuit voltage (VOC) of 0.523 V was nevertheless observed. Such a value of VOC is higher than is typically obtained in devices that employ a highly crystallized absorber as reported in the literature (see abstract figure). Using a hydrogen‐plasma treatment, a single junction μc‐Si:F:H pin solar cell with an efficiency of 8.3% was achieved.

magnified image

(© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mountain torques and synoptic systems in the Mediterranean
Authors: Egger Joseph , Hoinka Klaus‐Peter
Published: July 2008

The mountains surrounding the Mediterranean exert torques T during the passage of North Atlantic systems which affect the angular momentum of the airflow passing over and around the massifs. The Alps, the Atlas range and the orographic block of Asia Minor are selected to investigate the typical flow conditions during torque events. These mountain ranges are small enough to justify a local angular momentum analysis. Both the zonal and the meridional components of a mountain's torque (Tλ and Tφ) are used as stratification parameters in a statistical investigation of the interaction of large‐scale perturbations with this mountain. How are these flows affected by the obstacle? A simple scheme is tested which attempts to interpret results.

The torque analysis singles out eastward‐moving large‐scale systems. Their isobars are oriented from southwest (northwest) to northeast (southeast) near the mountain in zonal torque Tλ (Tφ) cases. The massifs tend to generate a low‐level distortion of the pressure field such that the angular momentum of the flow over the mountain is reduced. These results can be explained within the framework of the scheme. The influence of the mountains on the pressure field is seen only at heights ≤4000 m. The low‐level distortions of the pressure field contribute positively to the total torque for lags τ≤0 in the Alps and for all lags − 2≤τ≤2 days in Asia Minor, where only Tλ is evaluated. The impact of the Atlas mountains is seen only at τ = 0. Copyright © 2008 Royal Meteorological Society
Axisymmetric, nearly inviscid circulations in non‐condensing radiative‐convective atmospheres
Authors: Caballero Rodrigo , Pierrehumbert Raymond T. , Mitchell Jonathan L.
Published: July 2008

We study the steady‐state axisymmetric circulation of nearly inviscid, compressible atmospheres with no condensible component. Assuming simplified non‐grey radiative transfer and instantaneous adjustment to convective neutrality, we present an analytical theory for the depth, width and strength of the Hadley cell in terms of the planetary radius and rotation rate, insolation, optical depth and atmospheric composition. Under equatorially symmetric insolation, the Hadley cell width predicted by the present theory is generally very close to the Boussinesq, Newtonian cooling result of Held and Hou. We also introduce a new scaling theory for Hadley cell width under solstitial insolation conditions. The theory compares favourably with axisymmetric numerical results and also with full general‐circulation model simulations of Mars and Snowball Earth. Copyright © 2008 Royal Meteorological Society
Dependence of vortex axisymmetrization on the characteristics of the asymmetry
Authors: Peng Jiayi , Peng Melinda S. , Li Tim
Published: July 2008

This study investigates how different characteristics of initial asymmetries, including their positions and profiles, can impact on the vortex axisymmetrization process for barotropic vortices. When an initial disturbance is placed near the core of a vortex, a new asymmetry is generated inside the original asymmetry and grows due to its upshear tilt. Differential basic‐state rotation then shifts the phase to a downshear tilt and the asymmetry weakens. As the initial radius of the imposed asymmetry is increased, the initial upshear tilt of the asymmetry decreases. There is also a decrease in the efficiency with which the differential rotation shifts the phase tilt from upshear to downshear. The latter is related to differential radial propagation of the asymmetry in the form of vortex Rossby waves. These two mechanisms that are position‐dependent act against each other. There is an optimal radius at which the energy exchange between the symmetric and asymmetric flows is maximized. For a range of very different basic‐state profiles examined here, the optimal radius is around 1.5 to 2 times the radius of the maximum wind. The initial growth of asymmetries with higher azimuthal wavenumbers is weaker than their lower‐wavenumber counterparts due to a smaller upshear phase tilt with their smaller azimuthal length‐scales.

Nonlinearity reduces the magnitude and multiple perturbations of the newly induced inner asymmetry, and also limits the radial propagation of the asymmetry. The further the asymmetry is away from the core, the slower the axisymmetrization is. Depending on the position of the initial asymmetry, the basic state can have an increase of the maximum wind, a double‐peak profile, or an increase of its outer wind profile through axisymmetrization. Copyright © 2008 Royal Meteorological Society
(E)‐4‐Alkoxycarbonylalkylthiochalcones: differentiation of isomeric derivatives by electron ionization mass spectrometry
Authors: Nowakowska Zdzisława , Pankiewicz Radosław
Published: July 2008

The principal fragmentation pathways of the molecular ions of 18 new (E)‐4‐alkoxycarbonylalkylthiochalcones have been investigated. It has been shown that the data derived from electron ionization mass spectra (the relative abundance of the fragment ions and values of coefficients µ) can be used to differentiate the isomers. The fragmentation rules deduced here could help in the characterization of other chalcones of these types. Copyright © 2008 John Wiley & Sons, Ltd.
Profiling of yew hair roots from various species using ultra‐performance liquid chromatography/electrospray ionization mass spectrometry
Authors: Ge Guang‐Bo , Luan Hong‐Wei , Zhang Yan‐Yan , He Yu‐Qi , Liu Xing‐Bao , Yang Li , Wang Zheng‐Tao , Yang Ling
Published: July 2008

An efficient and sensitive profiling approach to complex yew samples was developed using ultra‐performance liquid chromatography/electrospray ionization mass spectrometry (UPLC/ESI‐MS). The UPLC‐based method displayed short analytical time and improved peak capability, as well as high sensitivity. The appropriate in‐source collision‐induced dissociation (CID) energy was employed to produce informative characteristic ions which could be used for stereochemical and sub‐structural assignment of yew constituents. The method was successfully applied in the rapid screening of yew hair roots from various species, and 53 constituents including 47 taxoids were detected from partially purified root extract. Notably, C‐7 hydroxytaxane stereoisomers could be identified based on their different fragment ions under the optimal profiling conditions. It was also observed that hair roots from different Taxus species exhibited nearly identical chemical distribution, indicating they had similar metabolic frameworks. Additionally, Taxus root resources also display benign medicinal perspective because they have relatively simple chemical profiles and possess high yields of valuable taxanes such as paclitaxel, cephalomannine, 10‐deacetylpaclitaxel and 7‐xylosyltaxanes. Copyright © 2008 John Wiley & Sons, Ltd.
High‐throughput approaches towards the definitive identification of pharmaceutical drug metabolites. 1. Evidence for an ortho effect on the fragmentation of 4‐benzenesulfinyl‐3‐methylphenylamine using electrospray ionisation mass spectrometry
Authors: Holman Stephen W. , Wright Patricia , Langley G. John
Published: July 2008

A 50 m/z unit loss from protonated 4‐benzenesulfinyl‐3‐methylphenylamine has been observed and investigated using electrospray ionisation quadrupole ion trap mass spectrometry (ESI‐QIT‐MS). It was hypothesised that the specific fragmentation was affected by the presence of an ortho methyl group in relation to the sulfoxide functionality, i.e. an ortho effect influences the preferred dissociation pathway. This was because the des‐methyl homologue did not display a 50 m/z unit loss. This fragmentation was shown to be a two‐step process with sequential losses of a hydroxyl radical and a thiol radical. Molecular modelling calculations showed that the most favourable site of protonation for 4‐benzenesulfinyl‐3‐methylphenylamine was the sulfoxide oxygen, which would facilitate the loss of a hydroxyl radical. Subsequent deuterium‐exchange experiments confirmed that the loss was a hydroxyl radical and afforded definitive assignment of the site of protonation. Furthermore, the involvement of a single exchangeable hydrogen atom in the overall 50 m/z unit loss was demonstrated. Thus, supportive evidence was provided for the involvement of the ortho methyl group in the second stage of the fragmentation, leading to the loss of the thiol radical. Accurate mass measurements, performed using electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (ESI‐FTICR‐MS), verified the elemental formulae of the individual losses. The ion structure following the 50 m/z unit loss was proposed to be a protonated aminofluorene and was supported by comparing the product ion spectrum of commercially available protonated 2‐aminofluorene with the MS4 data of protonated 4‐benzenesulfinyl‐3‐methylphenylamine. Fragmentation mechanisms are proposed. The relevance of the loss with regards to pharmaceutical drug metabolite identification is discussed. Copyright © 2008 John Wiley & Sons, Ltd.
Robotic appendectomy in gynaecological surgery: technique and pathological findings
Authors: Akl Mohamed N. , Magrina Javier F. , Kho Rosanne M. , Magtibay Paul M.
Published: July 2008

Background

We evaluated the feasibility, safety and pathological findings of incidental robotic appendectomy in patients undergoing robotic gynaecological surgery.

Methods

Retrospective analysis of 107 consecutive cases of robotic appendectomy done in conjunction with other robotic gynaecological procedures between May 2004 and January 2007.

Results

All appendectomies were performed robotically in conjunction with other robotic procedures. Mean time for appendectomy was 3.4 min. No perioperative complications related to appendectomy were encountered. Among 90 patients with no gynaecological malignancy, 57 patients reported chronic pelvic pain preoperatively and 21 (37%) of them had an abnormal appendiceal pathology as compared to only 5 (15%) of the 33 patients with no pelvic pain (OR. 3.2; 95% CI, 1.1–9.7, p = 0.032). Of seven patients with ovarian malignancy, three (42%) had appendicular metastasis.

Conclusion

Incidental robotic appendectomy can be performed safely without the need for switching to conventional laparoscopy. It should be considered in patients undergoing robotic pelvic surgery for pelvic pain and ovarian malignancy. Copyright © 2008 John Wiley & Sons, Ltd.
More efficient queries in PCPs for NP and improved approximation hardness of maximum CSP
Authors: Engebretsen Lars , Holmerin Jonas
Published: July 2008

Samorodnitsky and Trevisan [STOC 2000, pp. 191–199] proved that there exists, for every positive integerk, a PCP forNPwithO(logn) randomness, query complexity 2k+k2, free bit complexity 2k, completeness 1 ‐ϵ, and soundness 2+ϵ. In this article, we devise a new “outer verifier,” based on the layered label cover problem recently introduced by Dinur et al. [STOC 2003, pp. 595–601], and combine it with a new “inner verifier” that uses the query bits more efficiently than earlier verifiers. Our resulting theorem is that there exists, for every integerf≥ 2, every positive integert≤f(f‐ 1)/2, and every constantϵ> 0, a PCP forNPwithO(logn) randomness, query complexityf+t, free bit complexityf, completeness 1 ‐ϵ, and soundness 2‐t+ϵ. As a corollary, there exists, for every integerq≥ 3 and every constantϵ> 0, aq‐query PCP forNPwith amortized query complexity 1 +$ 1 + \sqrt{2/q} + \varepsilon $+ϵ. This improves upon the result of Samorodnitsky and Trevisan with respect to query efficiency, i.e., the relation between soundness and the number of queries. Although the improvement may seem moderate—the construction of Samorodnitsky and Trevisan has amortized query complexity 1 + 2/$ 1 + 2/\sqrt{q} + \varepsilon $—we also show in this article that combining our outer verifier with any natural candidate for a corresponding inner verifier gives a PCP that is less query efficient than the one we obtain.© 2008 Wiley Periodicals, Inc. Random Struct. Alg., 2008
An overview of the Sirius satellite radio system
Authors: Akturan Riza
Published: July 2008

This paper presents the system architecture and expected link availability for the Sirius satellite radio system for both the contiguous United States (CONUS) and Canada service regions. Sirius delivers over 100 channels of talk and music to subscribers in CONUS. The service is available to different markets, such as vehicles, homes, portables, marine, and aviation, and is offered on a subscription basis. Descriptions and performance of the Sirius system are detailed herein. Copyright © 2008 John Wiley & Sons, Ltd.
Testing for the presence of multiple sources of informative dropout in longitudinal data
Authors: Crawford S. B. , Hanfelt J. J.
Published: July 2008

Longitudinal studies tracking the rate of change are subject to patient dropout. This dropout process might not only be informative but also heterogeneous in the sense that different causes might contribute to multiple patterns of informative dropout. We propose a random‐effects approach to test for homogeneity of informative dropout that accommodates the realistic situation where reasons for dropout are not fully understood, or perhaps are even entirely unknown. The proposed score test is robust in that it does not depend on the underlying distribution of the informative dropout random effects. The test allows for an additional level of clustering among participating subjects, as might be found in a family study, provided the informative dropout random effects have a known correlation structure. Copyright © 2008 John Wiley & Sons, Ltd.
A maximum likelihood latent variable regression model for multiple informants
Authors: Horton Nicholas J. , Roberts Kevin , Ryan Louise , Suglia Shakira Franco , Wright Rosalind J.
Published: July 2008

Studies pertaining to childhood psychopathology often incorporate information from multiple sources (or informants). For example, measurement of some factor of particular interest might be collected from parents, teachers as well as the children being studied. We propose a latent variable modeling framework to incorporate multiple informant predictor data. Several related models are presented, and likelihood ratio tests are introduced to formally compare fit. The incorporation of partially observed subjects is addressed under a variety of missing data mechanisms. The methods are motivated by and applied to a study of the association of chronic exposure to violence on asthma in children. Copyright © 2008 John Wiley & Sons, Ltd.
Estimation of risk factor associations when the response is influenced by medication use: An imputation approach
Authors: McClelland Robyn L. , Kronmal Richard A. , Haessler Jeffrey , Blumenthal Roger S. , Goff David C.
Published: July 2008

When the outcome of interest is a quantity whose value may be altered through the use of medications, estimation of associations with this outcome is a challenging statistical problem. For participants taking medication the treated value is observed, but the underlying ‘untreated’ value may be the measure that is truly of interest. Problematically, those with the highest untreated values may have some of the lowest observed measurements due to the effectiveness of medications. In this paper we propose an approach in which we parametrically estimate the underlying untreated variable of interest as a function of the observed treated value, and dose and type of medication. Multiple imputation is used to incorporate the variability induced by the estimation. We show that this approach yields more realistic parameter estimates than other more traditional approaches to the problem and that study conclusions may be altered in a meaningful way by using the imputed values. Copyright © 2008 John Wiley & Sons, Ltd.
Predicting impacts of mass‐screening policy changes on breast cancer mortality
Authors: Seppänen Johanna , Heinävaara Sirpa , Hakulinen Timo
Published: July 2008

The aim of this study is to present a methodology for taking into account the mass‐screening invitation data in breast cancer mortality predictions, particularly in assessing impacts of screening policy changes on the short‐term predictions. The methodology is applied to a database that includes observed year‐ and age‐specific screening invitation schemes in Finnish municipalities from the time period 1987–2001. The target year for predictions is 2012.

To predict mortality, breast cancer incidence and patients' survival from breast cancer are modelled with the screening data included. The knowledge of breast cancer survival together with the other cause survival is then used to calculate the number of breast cancer deaths caused by observed (1987–2001) and predicted (2002–2012) incident cases in Finland.

Survival from breast cancer was estimated with a parametric mixture model where the patient population is assumed to be a combination of cured and uncured patients. This approach provides a way of modelling the hazard of fatal cases and the proportion of cured cases simultaneously. In other cause survival, the patients' hazard was allowed to differ from that of the general population.

Breast cancer mortality predictions are presented according to three alternative future scenarios of screening policy. The results show no major differences between predictions yielded by alternative scenarios: Any policy change would have at the most a 3.0 per cent impact on breast cancer mortality in the near future. Copyright © 2008 John Wiley & Sons, Ltd.
Semi‐parametric maximum likelihood estimates for ROC curves of continuous‐scale tests
Authors: Zhou Xiao‐Hua , Lin Huazhen
Published: July 2008

In this paper, we propose a new semi‐parametric maximum likelihood (ML) estimate of a receiver operating characteristic (ROC) curve that satisfies the property of invariance of the ROC curve and is easy to compute. We show that our new estimator is$$ \sqrt {n} $$‐consistent and has an asymptotically normal distribution. Our extensive simulation studies show that the proposed method is efficient and robust. Finally, we illustrate the application of the proposed estimator in a real data set. Copyright © 2008 John Wiley & Sons, Ltd.
Marginalized models for longitudinal ordinal data with application to quality of life studies
Authors: Lee Keunbaik , Daniels Michael J.
Published: July 2008

Random effects are often used in generalized linear models to explain the serial dependence for longitudinal categorical data. Marginalized random effects models (MREMs) for the analysis of longitudinal binary data have been proposed to permit likelihood‐based estimation of marginal regression parameters. In this paper, we propose a model to extend the MREM to accommodate longitudinal ordinal data. Maximum marginal likelihood estimation is proposed utilizing quasi‐Newton algorithms with Monte Carlo integration of the random effects. Our approach is applied to analyze the quality of life data from a recent colorectal cancer clinical trial. Dropout occurs at a high rate and is often due to tumor progression or death. To deal with events due to progression/death, we used a mixture model for the joint distribution of longitudinal measures and progression/death times and use principal stratification to draw causal inferences about survivors. Copyright © 2008 John Wiley & Sons, Ltd.
Using tensor product splines in modeling exposure–time–response relationships: Application to the Colorado Plateau Uranium Miners cohort
Authors: Berhane Kiros , Hauptmann Michael , Langholz Bryan
Published: July 2008

An adequate depiction of exposure–time–response relationships is important in assessing public health implications of an occupational or environmental exposure. Recent advances have focused on flexible modeling of the overall shape of latency. Methods are needed to allow for varying shapes of latency under different exposure profiles. A tensor product spline model is proposed for describing exposure–response relationships for protracted time‐dependent occupational exposure histories in epidemiologic studies. The methods use flexible multi‐dimensional techniques to jointly model age, latency and exposure–response effects. In analyzing data from the Colorado Plateau Uranium Miners cohort, a model that allows for varying exposure‐dependent latency shapes is found to be superior to models that only allowed for an overall latency curve. Specifically, the model suggests that, at low exposure levels risk increased at short latencies followed by a slow decline for longer latency periods. On the other hand, risk was higher but did not change much by latency for higher exposure levels. The proposed methodology has the advantage of allowing for latency functions that vary by exposure levels and, conversely, exposure–response relationships that are influenced by the latency structure. Copyright © 2008 John Wiley & Sons, Ltd.
Estimation method of the semiparametric mixture cure gamma frailty model
Authors: Peng Yingwei , Zhang Jiajia
Published: July 2008

Mixture cure frailty model has been proposed to analyze censored survival data with a cured fraction and unobservable information among the uncured patients. Different from a usual mixture cure model, the frailty model is employed to model the latency component in the mixture cure frailty model. In this paper, we extend the mixture cure frailty model by incorporating covariates into both the cure rate and the latency distribution parts of the model and propose a semiparametric estimation method for the model. The Expectation Maximization (EM) algorithm and the multiple imputation method are employed to estimate parameters of interest. In the simulation study, we show that both estimation methods work well. To illustrate, we apply the model and the proposed methods to a data set of failure times from bone marrow transplant patients. Copyright © 2008 John Wiley & Sons, Ltd.
Comparison of the risk difference, risk ratio and odds ratio scales for quantifying the unadjusted intervention effect in cluster randomized trials
Authors: Ukoumunne Obioha C. , Forbes Andrew B. , Carlin John B. , Gulliford Martin C.
Published: July 2008

This paper evaluates methods for unadjusted analyses of binary outcomes in cluster randomized trials (CRTs). Under the generalized estimating equations (GEE) method the identity, log and logit link functions may be specified to make inferences on the risk difference, risk ratio and odds ratio scales, respectively. An alternative, ‘cluster‐level’, method applies the t‐test to summary statistics calculated for each cluster, using proportions, log proportions and log odds, to make inferences on the respective scales. Simulation was used to estimate the bias of the unadjusted intervention effect estimates and confidence interval coverage, generating data sets with different combinations of number of clusters, number of participants per cluster, intra‐cluster correlation coefficient ρ and intervention effect. When the identity link was specified, GEE had little bias and good coverage, performing slightly better than the log and logit link functions. The cluster‐level method provided unbiased point estimates when proportions were used to summarize the clusters. When the log proportion and log odds were used, however, the method often had markedly large bias for two reasons: (i) bias in the modified summary statistic used for cluster‐level estimation when a cluster has zero cases with the outcome of interest (arising when the number of participants sampled per cluster is small and the outcome prevalence is low) and (ii) asymptotically, the method estimates the ratio of geometric means of the cluster proportions or odds, respectively, between the trial arms rather than the ratio of arithmetic means. Copyright © 2008 John Wiley & Sons, Ltd.
Analysis of cross‐over designs with serial correlation within periods using semi‐parametric mixed models
Authors: Maringwa John T. , Geys Helena , Shkedy Ziv , Faes Christel , Molenberghs Geert , Aerts Marc , Van Ammel Karel , Teisman Ard , Bijnens Luc
Published: July 2008

The use of semi‐parametric mixed models has proven useful in a wide variety of settings. Here, we focus on the application of the methodology in the particular case of a cross‐over design with relatively long sequences of repeated measurements within each treatment period and for each subject. Other than an overall measure of the difference between each one of the experimental groups and the control group, specific time point comparisons may also be of interest. To that effect, we propose the use of flexible semi‐parametric mixed models, enabling the construction of simulation‐based simultaneous confidence bands. The bands take into account both between‐ and within‐subject variabilities, while simultaneously correcting for multiple time point comparisons. Owing to the relatively long sequences of measurements per subject, the presence of serially correlated errors is anticipated and investigated. We illustrate how several formulations of semi‐parametric mixed models can be fitted and the construction of simulation‐based simultaneous confidence bands using SAS PROC MIXED. Copyright © 2008 John Wiley & Sons, Ltd.
Incorporating validation subsets into discrete proportional hazards models for mismeasured outcomes
Authors: Magaret Amalia S.
Published: July 2008

Standard proportional hazards methods are inappropriate for mismeasured outcomes. Previous work has shown that outcome mismeasurement can bias estimation of hazard ratios for covariates. We previously developed an adjusted proportional hazards method that can produce accurate hazard ratio estimates when outcome measurement is either non‐sensitive or non‐specific. That method requires that mismeasurement rates (the sensitivity and specificity of the diagnostic test) are known. Here, we develop an approach to handle unknown mismeasurement rates. We consider the case where the true failure status is known for a subset of subjects (the validation set) until the time of observed failure or censoring. Five methods of handling these mismeasured outcomes are described and compared. The first method uses only subjects on whom complete data are available (validation subset), whereas the second method uses only mismeasured outcomes (naive method). Three other methods include available data from both validated and non‐validated subjects. Through simulation, we show that inclusion of the non‐validated subjects can improve efficiency relative to use of the complete case data only and that inclusion of some true outcomes (the validation subset) can reduce bias relative to use of mismeasured outcomes only. We also compare the performance of the validation methods proposed using an example data set. Copyright © 2008 John Wiley & Sons, Ltd.
Bayesian bootstrap estimation of ROC curve
Authors: Gu Jiezhun , Ghosal Subhashis , Roy Anindya
Published: July 2008

Receiver operating characteristic (ROC) curve is widely applied in measuring discriminatory ability of diagnostic or prognostic tests. This makes the ROC analysis one of the most active research areas in medical statistics. Many parametric and semiparametric estimation methods have been proposed for estimating the ROC curve and its functionals. In this paper, we propose the Bayesian bootstrap (BB), a fully nonparametric estimation method, for the ROC curve and its functionals, such as the area under the curve (AUC). The BB method offers a bandwidth‐free smoothing approach to the empirical estimate, and gives credible bounds. The accuracy of the estimate of the ROC curve in the simulation studies is examined by the integrated absolute error. In comparison with other existing curve estimation methods, the BB method performs well in terms of accuracy, robustness and simplicity. We also propose a procedure based on the BB approach to test the binormality assumption. Copyright © 2008 John Wiley & Sons, Ltd.
‘Smooth’ inference for survival functions with arbitrarily censored data
Authors: Doehler Kirsten , Davidian Marie
Published: July 2008

We propose a procedure for estimating the survival function of a time‐to‐event random variable under arbitrary patterns of censoring. The method is predicated on the mild assumption that the distribution of the random variable, and hence the survival function, has a density that lies in a class of ‘smooth’ densities whose elements can be represented by an infinite Hermite series. Truncation of the series yields a ‘parametric’ expression that can well approximate any plausible survival density, and hence survival function, provided the degree of truncation is suitably chosen. The representation admits a convenient expression for the likelihood for the ‘parameters’ in the approximation under arbitrary censoring/truncation that is straightforward to compute and maximize. A test statistic for comparing two survival functions, which is based on an integrated weighted difference of estimates of each under this representation, is proposed. Via simulation studies and application to a number of data sets, we demonstrate that the approach yields reliable inferences and can result in gains in efficiency over traditional nonparametric methods. Copyright © 2008 John Wiley & Sons, Ltd.
De‐stressing mommy: ameliorative association with dispositional optimism and resiliency
Authors: Baldwin Debora R. , Kennedy Donna L. , Armata Pamela
Published: July 2008

The purpose of this investigation was to examine the role of dispositional optimism on levels of stress, resiliency and salivary immunoglobulin A (IgA) in employed mothers. The participants, comprised of 37 mothers (26 married and 11 single), were asked to render a timed saliva sample and complete a questionnaire package (demographic sheet, stress, resiliency and optimism inventories). Results indicated that mothers who were more optimistic tended to report less distress and greater resiliency. Furthermore, life event stress was positively related to self‐reported levels of distress. Salivary IgA did not correlate significantly with the above psychological variables. These data provide additional support regarding the buffering effect of dispositional optimism on the stress experience and has practical implications for the cultivation of learned optimism in employed mothers. Copyright © 2008 John Wiley & Sons, Ltd.
Intrusive thoughts and everyday cognitive failures in Holocaust survivors
Authors: Boals Adriel
Published: July 2008

Past research has found that the experiencing of a traumatic event can lead to detriments in lab‐based measures of cognitive abilities. However, there is only limited research on the impact of trauma on everyday cognitive functioning. In the current study, 13 Holocaust survivors completed measures of intrusive and avoidant thoughts concerning the Holocaust, the Cognitive Failures Questionnaire and a measure of lifetime physical health. The results revealed that intrusive thoughts predicted the frequency of everyday cognitive failures, whereas avoidance of Holocaust memories predicted lifetime physical health. These findings suggest that trauma not only affects lab‐based measures of cognitive abilities but also impacts everyday cognitive functioning. Copyright © 2008 John Wiley & Sons, Ltd.
Psychological impact and associated factors after disclosure of genetic test results concerning hereditary non‐polyposis colorectal cancer
Authors: Yamashita Manami , Okamura Hitoshi , Murakami Yoshie , Sugano Kokichi , Yoshida Teruhiko , Uchitomi Yosuke
Published: July 2008

The purpose of this study is to elucidate the psychological impact of disclosure of genetic test results concerning hereditary non‐polyposis colorectal cancer (HNPCC) and to assess factors associated with it, with particular focus on memory function. The subjects were persons who were suspected of having HNPCC and given the choice of undergoing genetic testing. The post‐genetic testing psychological impact was evaluated by means of the Impact of Event Scale‐Revised (IES‐R), and personality tendencies and memory function were evaluated. Final data were obtained from 46 subjects. The results of the genetic testing were ‘mutation‐positive’ in 18 subjects, ‘uninformative’ in 18 subjects, and ‘mutation‐negative’ in 10 subjects. Comparison of the IES‐R scores showed that they tended to be higher in the mutation‐positive group, but the differences were not statistically significant. The personality tendency ‘nervousness’ and verbal memory assessed prior to disclosure were significantly associated with total score on the IES‐R. Based on the results of this study it seems possible to minimize the risk of a psychological impact of disclosure of genetic test results by reassessing the follow‐up system for persons at high risk of a psychological impact. Copyright © 2008 John Wiley & Sons, Ltd.
Psychosocial indicators and distress in immigrants living in Italian reception centres
Authors: Toselli Stefania , Gualdi‐Russo Emanuela
Published: July 2008

Despite the high rate of migration to Italy, there are still no comprehensive studies of psychosocial distress in the different groups of immigrants. The objective of the present study was to investigate the psychosocial status of immigrants living in Bologna (Italy). We conducted a cross‐sectional survey of 396 immigrants (313 males and 83 females) from Africa, Asia and eastern Europe (Senegalese, Moroccans, Tunisians, Pakistanis, Kosovars and Roma) using questionnaires administered by trained anthropologists. Except for Tunisians, the psychological distress and discomfort of the immigrant groups are low, and the perception of their quality of life and well‐being is good. In the groups that have spent more time in Italy, the percentage of subjects wishing to return to their native country is generally higher. Immigrants living in Bologna exhibit a good psychosocial state and seem to have positively interacted with their new environment. Copyright © 2008 John Wiley & Sons, Ltd.
Psychogenic heart disease—stress and the heart: a historical perspective
Authors: Stanley Robb O , Burrows Graham D
Published: July 2008

Although ‘stress’ is accepted by the general population and patients with cardiac disease as a contributor to acute cardiac events and to the disease itself, this has not been universally accepted by the scientific community over the last century. Historically, research is not always helpful because it is unclear whether what is being researched is the cause of the cardiac event (e.g. myocardial infarction) or the underlying disease. A great deal of effort had been put into researching the concept of the coronary prone personality (i.e. Type A) with somewhat modest results. The shift in focus to the involvement of negative affect in cardiac disease has moved the field forward significantly. Recently, research has furthered our understanding of the mechanisms whereby stressful life experiences may interact with predispositions to experience the negative affects of anxiety, anger and depression (i.e. a feature of personality) and inherited cardiac disease proneness to result in both disease and acute events. Copyright © 2007 John Wiley & Sons, Ltd.
Mental stress is a cause of cardiovascular diseases: from scepticism to certainty
Authors: Esler Murray , Schwarz Rosemary , Alvarenga Marlies
Published: July 2008

Integrating into the clinical practice of medicine the recent evidence that psychiatric illness and mental stress contributes to the development of cardiovascular disease has not been a seamless process. The evidence for such a link, in fact, had been slow in materializing. The importance of acute mental stress as a trigger for cardiac catastrophes (acute myocardial infarction, sudden death) and of depressive illness as a cause of coronary heart disease, however, is now firmly established. But the spectre of workplace litigation still does hang over the field, clouding the arguments and polarizing medical opinion. Now that a consensus finally seems to have been reached that mental stress, including in the workplace, is an important cause of coronary heart disease and hypertension, it is hoped that the primary outcome will be the implementation of preventive measures to reduce stress in the workplace, such as worker empowerment to end the very adverse high demand/low job control scenario, rather than a rash of lawsuits. Copyright © 2008 John Wiley & Sons, Ltd.
State‐of‐the‐art: anxiety management in patients with implantable cardioverter defibrillators
Authors: Sears Samuel F. , Vazquez Lauren D. , Matchett Melissa , Pitzalis Mariavittoria
Published: July 2008

Through large‐scale clinical trials, the implantable cardioverter defibrillator (ICD) has been established as the treatment of choice for primary and secondary prevention of sudden cardiac death. Although the ICD offers a confirmed mortality benefit, it may incite psychological adjustment issues within recipients. The most predominant form of psychological morbidity for ICD patients is anxiety. The prevalence of anxiety is well documented within the context of cardiac patients; however, ICD recipients often present with device‐specific concerns, including shock and death anxiety. Therefore, the interventions for these patients must be tailored to their unique concerns. This article will discuss forms and manifestations of anxiety within the ICD patient population, followed by an exploration of the components of psychosocial interventions found to be effective with these patients. Copyright © 2008 John Wiley & Sons, Ltd.
Impacts of disasters: comparisons of several worries in Turkey
Authors: Kasapoğlu Aytül , Turan Feryal , Dönmez Ali
Published: July 2008

The aim of this paper is to define respondents' levels of worries and to find out the main predictors of each worry factor by comparing the results of earthquake (2001) and bird flu (2006) studies carried out in Turkey. Assuming that the critical power‐conflict perspective was appropriate; several types of worries, namely, traffic accidents, natural disasters, unemployment, health and sickness, nuclear plants, war and terrorism, and environmental problems defined by Kamano have been analysed using parametric and non‐parametric statistical significance tests. The results revealed that earthquake hazards affected respondents' level of worries more than bird flu disease mainly because of the enormous economic and human losses of the 1999 earthquake. It was also found that the main predictors were not the same for both studies: the education variable was more effective on the level of worries of earthquake survivors, and gender was more influential for the bird flu study. Copyright © 2008 John Wiley & Sons, Ltd.