bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of Poly[oxy(ω,ω,ω‐trifluoroalkylsulfonylmethyl)ethylene]s: Effect of Terminal CF3 and CH3 Moieties on the Wettability of the Comb‐Like Polymers
Authors: Kim Byoung Gak , Sohn Eun‐Ho , Lee Jong‐Chan
Published: April 2007

Two CF3‐terminated polymers were synthesized by polymer analogous reactions in order to study the effect of the terminal CF3 groups on their surface properties. ESCA and NEXAFS showed that they contain highly ordered side chains oriented perpendicularly to the polymer surface. The CF3‐terminated polymers showed enhanced wettability by polar solvents as compared to the corresponding CH3‐terminated polymers, while the wettability by non‐polar dodecane showed the opposite trend. This was attributed to specific interactions between the oriented surface dipoles of the CF3‐terminated surfaces and the polar solvents. Thus, terminal CF3 groups in a polymer can increase its surface polarity.

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Ultrahigh‐Molecular‐Weight Polyethylene by Using a Titanium Calix[4]arene Complex with High Thermal Stability under Polymerization Conditions
Authors: Frediani Marco , Sémeril David , Comucci Alessandro , Bettucci Lorenzo , Frediani Piero , Rosi Luca , Matt Dominique , Toupet Loïc , Kaminsky Walter
Published: April 2007

The new complex 25,27‐dipropyloxy‐26,28‐dioxocalix[4]arene titanium (IV) dichloride (1) was evaluated as an ethylene polymerization catalyst. Activation with methylalumoxane resulted in an active system producing ultrahigh‐molecular‐weight polyethylene. As expected for a Ziegler‐Natta catalyst, the polymerization reaction follows first‐order kinetics. The most striking feature of the catalytic system (1/MAO) is its remarkably high thermal stability. This peculiarity probably relies on the electronic stabilization of the metal center by the two coordinating propoxy groups.

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Macromol. Chem. Phys. 8/2007
Authors: Zinck Philippe , Terrier Michaël , Mortreux André , Valente Andreia , Visseaux Marc
Published: April 2007

Back Cover: The picture presents the unprecedented insertion of styrene single units into polyisoprene and the corresponding spectroscopic data. Catalytic systems affording this single insertion as well as mechanistic details and physico‐chemical characterization of the copolymers can be found in the Full Paper by P. Zinck,* M. Terrier, A. Mortreux, A. Valente, and M. Visseaux* on page 973.
Über nichtlineare Eigenwertaufgaben in konvexen Mengen
Authors: Miersemann Erich
Published: April 2007

We consider the bifurcation problem of a general class of variational inequalities at the first igenvalue of the associated linear problem. Essentially we use a generalization of LJUSTERNIK's emma, MIERSEMANN [13]. We apply our results to buckling problems for the thin elastic plate.
Nonlinear Elliptic Variational Inequalities
Authors: Bose Deb K. , Brill Heinz
Published: April 2007

We consider the problem of finding a solution to a class of nonlinear elliptic variational inequalities. These inequalities may be defined on bounded or unbounded domains Ω, and the nonlinearity can depend on gradient terms. Appropriate definitions of sub‐and supersolutions relative to the constraint sets are given. By using a mixture of maximal monotone operator theory and compactness arguments we prove the existence of a H2(Ω) solution lying between a given subsolution φ1 and a given supersolution φ2≧φ1, when Ω is bounded, and a H1(Ω) solution when Ω is unbounded.
[Russian Text Ignored.]
Authors: [Russian Text Ignored.]
Published: April 2007

[Russian Text Ignored.].
On maximally unitarily mixed states on W*‐algebras
Authors: Alberti P. M.
Published: April 2007

The matter of discussion is the set of states on W*‐algebras. States are considered in relation to unitary mixing where the full group of unitary elements is used. Among all the states, one could talk about, we are mainly interested in studying those the degree of mixture of which is maximally. We give a general description of the set of maximally unitarily mixed states. For a finite W*‐algebra the set of states in question is identified as the set of unitarily invariant states and for each state there is precisely one maximally mixed state comparable with it in the sense of unitary mixture. The latter fact fails to be true in the general case of an infinite W*‐algebra. In this case the problem is more complicated. For a properly infinite W*‐algebra we introduce an interesting symmetric ideal, the c‐ideal. We prove that a state on a properly infinite W*‐algebra is maximally mixed if and only if its kernel contains the c‐ideal, i. e. maximally mixed states may be identified with the set of states on the quotient algebra generated by the c‐ideal. For a general infinite W*‐algebra the solution of the problem can be represented as a combination of both above mentioned cases. The point of view we adopted in handling the mixture relation has its origin in UHLMANN'S work.
Safety and tolerability of growth hormone therapy in multiple system atrophy: A double‐blind, placebo‐controlled study
Authors: Holmberg Björn , Johansson Jan‐Ove , Poewe Werner , Wenning Gregor , Quinn Niall P. , Mathias Chris , Tolosa Eduardo , Cardozo Adriana , Dizdar Nil , Rascol Olivier , Slaoui Tarik ,   Growth‐Hormone MSA Study Group,   European MSA Study Group (EMSA‐SG)
Published: April 2007

The objective of this study was to investigate tolerability and possible neurotrophic effects of growth hormone (GH) in treatment of multiple system atrophy (MSA). In this double‐blind pilot study, MSA patients were randomized to recombinant human growth hormone (r‐hGH, n = 22), 1 mg every second day (6 months) followed by alternating daily injections of 1 mg and 0.5 mg (6 months), or matched placebo (n = 21). Safety analysis demonstrated no obvious between‐group differences. In both groups, there was progressive worsening of Unified Parkinson's Disease Rating Scale total score, which tended to be less in r‐hGH‐treated patients (12.9% at 6 months, 25.3% at 12 months) than in placebo (17.0% and 35.7%). Similarly, there was a trend to less worsening in Unified MSA Rating Scale total score with r‐hGH (13.2% and 21.2%) than with placebo (21.1% and 36.5%). Cardiovascular reflex autonomic testing also tended to show less deterioration with r‐hGH than with placebo at 12 months. However, 95% CI did not indicate treatment differences for any efficacy measures. In conclusion, r‐hGH administration in MSA patients for up to 1 year appears safe and might influence disease symptoms, signs and, possibly, progression. The results support further studies utilizing higher doses in more patients. © 2007 Movement Disorder Society
Gender differences in patients with Parkinson's disease treated with subthalamic deep brain stimulation
Authors: Accolla Ettore , Caputo Elena , Cogiamanian Filippo , Tamma Filippo , Mrakic‐Sposta Simona , Marceglia Sara , Egidi Marcello , Rampini Paolo , Locatelli Marco , Priori Alberto
Published: April 2007

We investigated gender‐differences in clinical phenomenology and response to deep brain stimulation (DBS) of the subthalamic nucleus (STN) in a group of patients with advanced Parkinson's disease (PD). Thirty‐eight consecutive patients with PD (22 men and 16 women), bilaterally implanted for DBS of the STN, were evaluated 1 month before and 11 to 14 months after surgery. Gender differences in severity of the disease (HY and UPDRS), ability in the activities of daily living (ADL, UPDRS II), tremor and rigidity (UPDRS III), bradykinesia (UPDRS III and hand tapping test), levodopa‐induced dyskinesias (LIDs, UPDRS IV), and levodopa equivalent daily dosage (LEDD) were analyzed before and after intervention. We found a predominantly male population, with no gender‐related differences in age at onset, disease progression rate, or severity of disease. Nevertheless, women had more severe LIDs than men, only before the intervention. Bradykinesia was significantly less responsive to any kind of treatment (pharmacologic and neurosurgical) in women than in men. Finally, although STN‐DBS induced similar total benefits in both genders, postoperative assessment suggested that the ADL improved more in women than in men. Women and men with advanced PD appear to differ in some clinical features and in response to dopaminergic and STN‐DBS treatment. © 2007 Movement Disorder Society
A numerical procedure for predicting rainfall‐induced movements of active landslides along pre‐existing slip surfaces
Authors: Calvello Michele , Cascini Leonardo , Sorbino Giuseppe
Published: April 2007

A numerical model to predict landslide movements along pre‐existing slip surfaces from rainfall data is presented. The model comprises: a transient seepage finite‐element analysis to compute the variations of pore water pressures due to rainfall; a limit equilibrium stability analysis to compute the factors of safety along the slip surface associated with transient pore pressure conditions; an empirical relationship between the factor of safety and the rate of displacement of the slide along the slip surface; an optimization algorithm for the calibration of analyses and relationships based on available monitoring data. The model is validated with reference to a well‐monitored active slide in central Italy, characterized by very slow movements occurring within a narrow band of weathered bedrock overlaid by a clayey silt colluvial cover. The model is conveniently divided and presented in two parts: a groundwater model and a kinematic model. In the first part, monthly recorded rainfall data are used as time‐dependent flow boundary conditions of the transient seepage analysis, while piezometric levels are used to calibrate the analysis by minimizing the errors between monitoring data and computed pore pressures. In the second part, measured inclinometric movements are used to calibrate the empirical relationship between the rate of displacement along the slip surface and the factor of safety, whose variation with time is computed by a time‐dependent stability analysis. Copyright © 2007 John Wiley & Sons, Ltd.
Intracellular water‐specific MR of microbead‐adherent cells: the HeLa cell intracellular water exchange lifetime
Authors: Zhao L. , Kroenke C. D. , Song J. , Piwnica‐Worms D. , Ackerman J. J. H. , Neil J. J.
Published: April 2007

Quantitative characterization of the intracellular water 1H MR signal from cultured cells will provide critical biophysical insight into the MR signal from tissues in vivo. Microbeads provide a robust immobilization substrate for the many mammalian cell lines that adhere to surfaces and also provide sufficient cell density for observation of the intracellular water MR signal. However, selective observation of the intracellular water MR signal from perfused, microbead‐adherent mammalian cells requires highly effective suppression of the extracellular water MR signal. We describe how high‐velocity perfusion of microbead‐adherent cells results in short apparent 1H MR longitudinal and transverse relaxation times for the extracellular water in a thin slice selected orthogonal to the direction of flow. When combined with a spin‐echo pulse sequence, this phenomenon provides highly effective suppression of the extracellular water MR signal. This new method is exploited here to quantify the kinetics of water exchange from the intracellular to extracellular spaces of HeLa cells. The time constant describing water exchange from intracellular to extracellular spaces, also known as the exchange lifetime for intracellular water, is 119 ± 14 ms. Copyright © 2007 John Wiley & Sons, Ltd.
Preparation of polysaccharide–polymethacrylate hybrid materials by radical polymerization of cationic methacrylate monomer in the presence of anionic polysaccharide
Authors: Kadokawa Jun‐ichi , Saitou Shingo , Shoda Shin‐ichiro
Published: April 2007

This article describes preparation of polysaccharide–polymethacrylate hybrid materials by means of free‐radical polymerization of a cationic methacrylate monomer in the presence of anionic polysaccharides. In particular, synthesis of the hybrid material composed of carboxymethyl cellulose (CMC) and a cationic polymethacrylate, i.e. poly(2‐aminoethyl methacrylate) is disclosed. The formation of the materials was achieved by radical polymerization of 2‐aminoethyl methacrylate hydrochloride (AEMA‐HCl) in aqueous solution of CMC. The insoluble material was formed and the structure was determined by the IR spectra and elemental analysis to be composed of CMC and polymethacrylate. Thermal analyses such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed to confirm the network structure of the material. The dehydrative amidation occurred by heating the material at 200°C, giving rise to the new hybrid material hybridized by the amide linkages. Copyright © 2007 John Wiley & Sons, Ltd.
Investigation of swelling, drug release and diffusion behaviors of poly(N‐isopropylacrylamide)/poly (N‐vinylpyrrolidone) full‐IPN hydrogels
Authors: Seden Akdemir Z. , Kayaman‐Apohan Nilhan
Published: April 2007

The synthesis of sequential full interpenetrating polymer networks (IPNs) based on poly (N‐isopropylacrylamide) (PNIPAAm) and negatively charged poly(N‐vinyl‐2‐pyrrolidone) (PNVP) was described and their swelling, drug release, and diffusion studies were investigated. PNIPAAm was used as a host network. According to swelling experiments, IPNs gave relatively lower swelling ratios compared to PNIPAAm hydrogel due to the higher cross‐linking density. Lidocaine (LD) was used as a model drug for the investigation of drug release behavior of IPNs. LD uptake of the IPNs were found to increase from 24 to 166 (mg LD / g dry gel) with increasing amount of PNIPAAm and AMPS contents in the IPN structure. It was observed that the specific interaction between drug and AMPS co‐monomer influenced the drug release profile. In the diffusion transport mechanism study in water, the results indicated that the swelling exponents n for all IPNs are in the range from 0.50 to 0.72. This implies that the swelling transport mechanism was transferred from Fickian to non‐Fickian transport, with increasing AMPS content and NIPAAm character in the IPN structure. In addition, diffusion of LD within the IPNs showed similar trend. The incorporation of AMPS leads to an increase in electrostatic interaction between charge sites on carboxylate ions and cationic LD molecules. Therefore, the highest diffusion coefficient (D) of drug was found for IPN2 sample. Copyright © 2007 John Wiley & Sons, Ltd.
Differences in personality characteristics between body‐modified and non‐modified individuals: associations with individual personality traits and their possible evolutionary implications
Authors: Wohlrab Silke , Stahl Jutta , Rammsayer Thomas , Kappeler Peter M.
Published: April 2007

After a long history of negative stigmatisation, the practices of tattooing and body piercing have become fashionable in the last decade. Today, 10% of the population in modern western societies have some form of body modification. The aim of this study was to quantify the demographic and personality traits of tattooed and pierced individuals and to compare them with a control group of individuals without body modifications. These comparisons are based on questionnaires completed by 359 individuals that investigate the details of body modification, and which incorporate five personality scales. We describe several sex differences in ornament style and location. We found no relevant differences between modified and non‐modified individuals in relation to demographic variables. This indicates that some of the traditional attitudes towards tattoos and piercings appear to be outdated. However, we found striking differences in personality traits which suggest that body‐modified individuals are greater sensation seekers and follow a more unrestricted mating strategy than their non‐modified contemporaries. We discuss these differences in light of a potential signalling function of tattoos and piercings in the mating context. Copyright © 2007 John Wiley & Sons, Ltd.
Longitudinal changes in lung function and somatic growth in children with sickle cell disease
Authors: Koumbourlis Anastassios C. , Lee Donna J. , Lee Ada
Published: April 2007

Background

We studied the changes in the patterns of lung function and somatic growth over time in children and adolescents (10.6 ± 3.5 years at first test) with hemoglobin SS (Hb‐SS) sickle cell disease (SCD).

Methods

Lung function and somatic growth were measured twice with an interval of 42.3 ± 23.3 months in 45 children (25 females and 20 males) with Hb‐SS SCD.

Results

The lung volumes slightly decreased but remained borderline normal in both tests. All spirometric indices were within the normal range but significantly decreased (P < 0.001) at the time of the second test indicating development of lower airway obstruction (forced expiratory volume in the first second (FEV1): 87 ± 21 vs. 80 ± 15; FEV1/forced vital capacity (FVC): 89 ± 7 vs. 85 ± 6; FEF25–75: 89 ± 32 vs. 76 ± 24). “Normal” pattern of lung function was initially found in 56% of the patients, but in only 29% in the second test. In contrast, those with “obstructive” pattern increased from 22 to 44%, and those with “restrictive” pattern from 22 to 27%. There was no association between history of asthma and pattern of lung function. “Normal” Body Mass Index (BMI) was found in 64% of the patients, whereas 13% had “High” BMI and 22% “Low” BMI. The two latter patterns were associated with abnormal lung function but only patients with normal BMI showed actual decline overtime.

Conclusion

SCD is characterized by a predominantly obstructive pattern of lung function that increases in prevalence over time. There was no apparent causal relationship between the pattern of somatic growth and the pattern of lung function. Pediatr Pulmonol. 2007; 42:483–488. © 2007 Wiley‐Liss, Inc.
Clinical response to azithromycin in cystic fibrosis correlates with in vitro effects on Pseudomonas aeruginosa phenotypes
Authors: Nguyen Dao , Emond Mary J. , Mayer‐Hamblett Nicole , Saiman Lisa , Marshall Bruce C. , Burns Jane L.
Published: April 2007

A 6‐month clinical trial of azithromycin (AZM) in American cystic fibrosis (CF) patients with chronic Pseudomonas aeruginosa infection showed clinical improvement without significant reduction in bacterial density. Sub‐inhibitory AZM has been hypothesized to affect P. aeruginosa virulence, partly contributing to the mechanism of action of AZM. To correlate bacterial phenotypes of P. aeruginosa isolates with clinical response to AZM in CF patients. Pre‐treatment P. aeruginosa isolates from subjects randomized to AZM in the US trial were characterized for bacterial phenotypes: AZM minimal inhibitory concentration (MIC), mucoidy, and baseline and AZM effects on twitching and swimming motility, and production of pyocyanin, protease and phospholipase C (PLC). Initial analyses of a subset of subjects identified phenotypes most strongly associated with FEV1 response and pulmonary exacerbation. These phenotypes were subsequently characterized and tested in isolates from subjects of the complete AZM cohort. Exploratory analyses of the initial subset suggested that the MIC and in vitro change in PLC and swimming motility with AZM were the strongest candidates among the bacterial phenotypes. When tested, only the change in PLC was significantly correlated with the change in FEV1 (P = 0.05), and occurrence and time to pulmonary exacerbation (both P = 0.02). In the complete cohort, change in PLC continued to show significant correlation with FEV1 response (P = 0.006), but not exacerbation. The in vitro effect of AZM on PLC correlates with FEV1 response to AZM. This suggests that AZM anti‐virulence effects may be predictive of clinical response and play a role in the mechanism of action of AZM in CF patients. Pediatr Pulmonol. 2007; 42:533–541. © 2007 Wiley‐Liss, Inc.
Multiple asparagine deamidation of Bacillus anthracis protective antigen causes charge isoforms whose complexity correlates with reduced biological activity
Authors: Powell Bradford S. , Enama Jeffrey T. , Ribot Wilson J. , Webster Wendy , Little Stephen , Hoover Timothy , Adamovicz Jeffrey J. , Andrews Gerard P.
Published: April 2007

Protective antigen is essential for the pathology of Bacillus anthracis and is the proposed immunogen for an improved human anthrax vaccine. Known since discovery to comprise differentially charged isoforms, the cause of heterogeneity has eluded specific structural definition until now. Recombinant protective antigen (rPA) contains similar isoforms that appear early in fermentation and are mostly removed through purification. By liquid chromatography‐tandem mass spectrometry sequencing of the entire protein and inspection of spectral data for amino acid modifications, pharmaceutical rPA contained measurable deamidation at seven of its 68 asparagine residues. A direct association between isoform complexity and percent deamidation was observed such that each decreased with purity and increased with protein aging. Position N537 consistently showed the highest level of modification, although its predicted rate of deamidation ranked 10th by theoretical calculation, and other asparagines of higher predicted rates were observed to be unmodified. rPA with more isoforms and greater deamidation displayed lower activities for furin cleavage, heptamerization, and holotoxin formation. Lethal factor‐mediated macrophage toxicity correlated inversely with deamidation at residues N466 and N408. The described method measures deamidation without employing theoretical isotopic distributions, comparison between differentially treated samples or computational predictions of reactivity rates, and is broadly applicable to the characterization of other deamidated proteins. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Development and benchmarking of TASSERiter for the iterative improvement of protein structure predictions
Authors: Lee Seung Yup , Skolnick Jeffrey
Published: April 2007

To improve the accuracy of TASSER models especially in the limit where threading provided template alignments are of poor quality, we have developed the TASSERiter algorithm which uses the templates and contact restraints from TASSER generated models for iterative structure refinement. We apply TASSERiter to a large benchmark set of 2,773 nonhomologous single domain proteins that are ≤ 200 in length and that cover the PDB at the level of 35% pairwise sequence identity. Overall, TASSERiter models have a smaller global average RMSD of 5.48 Å compared to 5.81 Å RMSD of the original TASSER models. Classifying the targets by the level of prediction difficulty (where Easy targets have a good template with a corresponding good threading alignment, Medium targets have a good template but a poor alignment, and Hard targets have an incorrectly identified template), TASSERiter (TASSER) models have an average RMSD of 4.15 Å (4.35 Å) for the Easy set and 9.05 Å (9.52 Å) for the Hard set. The largest reduction of average RMSD is for the Medium set where the TASSERiter models have an average global RMSD of 5.67 Å compared to 6.72 Å of the TASSER models. Seventy percent of the Medium set TASSERiter models have a smaller RMSD than the TASSER models, while 63% of the Easy and 60% of the Hard TASSER models are improved by TASSERiter. For the foldable cases, where the targets have a RMSD to the native <6.5 Å, TASSERiter shows obvious improvement over TASSER models: For the Medium set, it improves the success rate from 57.0 to 67.2%, followed by the Hard targets where the success rate improves from 32.0 to 34.8%, with the smallest improvement in the Easy targets from 82.6 to 84.0%. These results suggest that TASSERiter can provide more reliable predictions for targets of Medium difficulty, a range that had resisted improvement in the quality of protein structure predictions. Proteins 2007. © 2007 Wiley‐Liss, Inc.
Anisotropic electrical response of mesoporous silicon to NO2
Authors: Borini S. , Boarino L. , Amato G.
Published: April 2007

The I–V characteristics of Mesoporous Silicon (mesoPS) samples have been studied both in vacuum and in presence of NO2 traces. By the use of different electrode configurations, the longitudinal (parallel to the sample surface) and transverse (perpendicular to the sample surface) components of the electrical conductance have been independently measured and compared. We show that the electrical response of mesoPS to NO2 is anisotropic, and that the best sensing performance is achieved by monitoring the longitudinal conductance variation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High efficient terahertz emission from InN surfaces
Authors: Cimalla Volker , Pradarutti Boris , Matthäus Gabor , Brückner Claudia , Riehemann Stefan , Notni Gunther , Nolte Stefan , Tünnermann Andreas , Lebedev Vadim , Ambacher Oliver
Published: April 2007

Terahertz radiation was measured from InN and compared to p‐InAs excited by femtosecond optical pulses at 1060 and 800 nm. At 800 nm, atomically smooth InN with low background electron concentration exhibit higher THz emission than the highly effective material p‐InAs. The higher THz emission efficiency of InN is caused by the absences of any intervalley scattering, which in the case of InAs increases the effective mass of the photo generated electrons and, thus, reduces the Dember field, which is responsible for THz emission. Consequently, InN is a promising material for THz emission; however, further improvement of the material quality (surface roughness and carrier concentration) is needed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From evidence of strong light–matter coupling to polariton emission in GaN microcavities
Authors: Sellers I. R. , Semond F. , Zamfirescu M. , Stokker‐Cheregi F. , Disseix P. , Leroux M. , Leymarie J. , Gurioli M. , Vinattieri A. , Réveret F. , Malpuech G. , Vasson A. , Massies J.
Published: April 2007

We present both experimental and theoretical results which outline our development of the molecular beam epitaxy of GaN microcavities on (111) silicon. In particular we show that although in this material system the strong‐light matter coupling regime can be observed at 300 K even with relatively low quality factor structures (Q = 60) in reflectivity measurements, it is necessary to increase the Q ‐factor by at least a factor of two to observe strong coupling in the emission. For an optimized microcavity structure (Q = 160), polaritonic emission is observed at 300 K, with the origin of the broadened luminescence features confirmed by co‐incident reflectivity measurements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient solar energy conversion using TiO2 nanotubes produced by rapid breakdown anodization – a comparison
Authors: Hahn R. , Stergiopoulus T. , Macak J. M. , Tsoukleris D. , Kontos A. G. , Albu S. P. , Kim D. , Ghicov A. , Kunze J. , Falaras P. , Schmuki P.
Published: April 2007

We report on dye‐sensitization of different TiO2 nanotube layers, their photoelectrochemical response and their efficiency for solar energy conversion. The tubes compared in this study were either grown by controlled Ti anodization in fluoride containing electrolytes or by rapid breakdown anodization (RBA) of Ti in fluoride free electrolytes. After converting the different tube layers to anatase and sensitizing with Ru‐dye (N719), clearly layers consisting of RBA‐NTs show a significantly higher photoresponse and conversion efficiencies than tubes formed under self‐ordering conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Straight to the bar: Molecular nanostructures, graphene, nanotubes. XXIst International Winterschool on Electronic Properties of Novel Materials (IWEPNM 2007), Kirchberg, Austria, 10–17 March 2007
Authors: Capaz Rodrigo B.
Published: April 2007

Conference Reports are meant to offer an authoritative view on a recently held scientific meeting rather than a comprehensive list of the conference presentations. Authors are invited to describe what they feel were the most interesting contributions. The Kirchberg Winterschool provided a platform for reviewing and discussing new developments in the field of electronic properties of molecular nanostructures and their applications such as carbon nanotubes, graphene and single molecules. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Understanding and managing iterative error and change cycles in construction
Authors: Lee SangHyun , Peña‐Mora Feniosky
Published: April 2007

Errors and changes in construction often result in significant schedule and cost overruns affecting project performance. To understand the nature of these errors and changes and to ultimately reduce their detrimental impacts on project performance, this paper presents a system dynamics‐based construction model, which focuses on the dynamics of error and change management in construction, including quality management, scope management, the request for information process, and the decision‐making process for the approval of changes, and their consequent detrimental impacts on project performance. In particular, the developed model integrates several concepts in traditional network‐based tools to enhance the applicability of the model. Describing the dynamic behaviors generated by the developed model and applying the model to a couple of real‐world construction projects, this paper concludes that: (1) realism should be added to schedule planning; (2) an efficient coordination process is needed; (3) proactive contingency plans need to be taken into consideration; and (4) integration of network‐based tools and system dynamics‐based models can contribute to management of errors and changes. Copyright © 2007 John Wiley & Sons, Ltd.
Statistical methods for short‐term projections of AIDS incidence
Authors: Brookmeyer Ron , Damiano Anne
Published: April 2007

Short‐term projections of AIDS incidence are critical for assessing future health care needs. This paper focuses on the method of back‐calculation for obtaining short‐term projections. The approach consists of back‐calculating from AIDS incidence data through use of the incubation period distribution to obtain estimates of the numbers previously infected. The numbers previously infected are then projected forward to obtain short‐term projections. An approach is suggested for accounting for new infections in short‐term projections of AIDS incidence. Back‐calculation requires accurate AIDS incidence data. A method which is computationally easy to implement is proposed for estimating the distribution of the delays in reporting AIDS cases. It was found that the reporting delay distribution in the United States varies by geographic region of diagnosis. Back‐calculation also requires a reliable estimate of the incubation period distribution. Statistical issues associated with estimating the incubation period distribution are considered. The methods are applied to obtain short‐term projections of AIDS incidence in the United States. The projected cumulative AIDS incidence in the U.S. by the end of 1992 was 287,100 under the assumption that there are no new infections after 1 July 1987, and 330,600 under the assumption that the infection rate remains constant. These projections do not account for the new broadened AIDS surveillance definitions or the underreporting of AIDS cases to the Centers for Disease Control.
The impact that group sequential tests would have made on ECOG clinical trials
Authors: Rosner Gary L. , Tsiatis Anastasios A.
Published: April 2007

Using designs that several authors proposed, we reanalysed a large number of completed phase III clinical trials of the Eastern Cooperative Oncology Group as if each had been designed with group sequential stopping rules. With survival the primary endpoint of the large multicentre trials, we discuss the relative merits of each design, as well as the feasibility of group sequential designs in general.
Assessing antiarrhythmic drug efficacy: Multivariate considerations
Authors: Ulm K. , Schmidt G. , Barthel P. , Linzmaier A.
Published: April 2007

The spontaneous variability of ventricular arrhythmias is the major problem in assessing antiarrhythmic drug efficacy. Efficacy is usually assessed on one form of ventricular premature beats, namely either single beats (VPC) or more complex forms like couplets or salvos. The reduction rates required to assume efficacy with a confidence of 95 per cent are 63 per cent for VPCs, 92 per cent for couplets or 96 per cent for salvos. These rates are valid for two Holter electrocardiogram recordings within one week; otherwise the rates are higher and close to 100 per cent. In this paper we extend our ratio method for calculating these criteria to consider two or all three forms of ventricular premature beats simultaneously. The method is based on the first principal component. For use in practice we decided to calculate fixed criteria for each form of ventricular premature beats. For the combination of VPCs and couplets and a confidence level of 95 per cent, reduction rates of 42 per cent for VPC and 87 per cent for couplets are required. Both criteria must be fulfilled to assume the efficacy of a drug. These criteria are lower than those for each form alone. For all three forms together, reduction rates of 28, 72 and 88 per cent for VPC, couplets and salvos respectively are required.
Meta‐analysis for 2 × 2 tables: A bayesian approach
Authors: Carlin John B.
Published: April 2007

This paper develops and implements a fully Bayesian approach to meta‐analysis, in which uncertainty about effects in distinct but comparable studies is represented by an exchangeable prior distribution. Specifically, hierarchical normal models are used, along with a parametrization that allows a unified approach to deal easily with both clinical trial and case‐control study data. Monte Carlo methods are used to obtain posterior distributions for parameters of interest, integrating out the unknown parameters of the exchangeable prior or ‘random effects’ distribution. The approach is illustrated with two examples, the first involving a data set on the effect of beta‐blockers after myocardial infarction, and the second based on a classic data set comprising 14 case‐control studies on the effects of smoking on lung cancer. In both examples, rather different conclusions from those previously published are obtained. In particular, it is claimed that widely used methods for meta‐analysis, which involve complete pooling of ‘O‐E’ values, lead to understatement of uncertainty in the estimation of overall or typical effect size.
Differential influence of prognostic factors on the occurrence of metastases at various anatomical sites in human breast cancer
Authors: Zedeler Karin , Keiding Niels , Kamby Claus
Published: April 2007

The present study was initiated by data on the anatomical occurrence of metastases from breast cancer. Metastases may occur at various organs, here grouped into ten categories, and simultaneous occurrences at several sites are common. Our aim was to identify and compare risk factors for development of metastases at each site.

The influence of the various risk factors for recurrence at one specific site can be modelled as a standard competing risk problem, using well‐established survival analysis techniques such as the Cox regression model. Recently a generalization to joint occurrences at more than one site has been proposed. The more general models allowcomparisonof the differential prognostic influence of various risk factors on recurrence at different sites.

We applied these methods to data from the Danish Breast Cancer Cooperative Group on recurrence after breast cancer, and examined the effect of degree of anaplasia, number of positive lymph nodes, size of primary tumour, skin or deep fascial invasion, age of the patient and adjuvant treatment regimen, as possible risk factors.

There were no differential effects of type of therapy on recurrence in different sites. However, chemotherapy had a marginally significant positive effect at all sites. Moreover the number of positive lymph nodes was associated with an increased risk of metastases, homogenous across sites, except for brain where an opposing trend was found. Similarly the degree of anaplasia was associated with a somewhat increased risk of metastases, homogenous except for brain. For brain metastases a significantly more pronounced effect of degree of anaplasia was found.

Comparison of the results obtained from the two types of models reveals that the new more general models confirm fewer differences between the influence of the prognostic factors than the traditional regression models suggest.
Which measures of skewness and kurtosis are best?
Authors: Royston Patrick
Published: April 2007

Indices of distributional shape based on linear combinations of order statistics have recently been described by Hosking. Their usefulness as tools for practical data analysis is examined. They are found to have several advantages over the conventional indices of skewness and kurtosis (√b1andb2) and no serious drawbacks. It is proposed, therefore, that they should replace √b1andb2in routine data analysis. To implement this suggestion, action by the developers of standard statistical software is needed.
Directory of registries of clinical trials
Authors: Easterbrook Philippa J.
Published: April 2007

Registries of clinical trials are a potentially useful resource for the planning of new studies, the promotion of communication and collaboration between researchers, the conduct of meta‐analyses, and the facilitation of patient access and recruitment to trials. However, many physicians and researchers are unaware of their existence, and as a result they remain underused. A directory of registries of clinical trials has been developed as a result of an international survey of 63 organizations and 51 individuals in 13 different countries to identify the existence of such registries. This is intended as a resource to keep physicians, researchers, trial organizers, funding bodies and government agencies abreast of the growing number of registries available, and to assist in the planning of future registries. Twenty‐four current and six planned registries of clinical trials have been identified. Most focus on AIDS or oncology, but such diverse areas as neurosurgery, cardiovascular disease, dentistry and perinatology are also represented. This paper presents a descriptive profile on each registry and discusses the relative merits of their different organizational features. Recommendations are given for the establishment of future registries.
The use of subjective rankings in clinical trials with an application to cardiovascular disease
Authors: Follmann Dean , Wittes Janet , Cutler Jeffrey A.
Published: April 2007

Evaluating a clinical trial can be problematic if the studied treatments affect patients in many ways. A possible method for evaluating treatments is to have raters rank all the patients' trial experiences and then test whether the distribution of ranks differ between treatments. Before one can advocate such a procedure, however, one would like to be assured that raters agree fairly well with one another. As a first step in examining whether raters tend to agree, we conducted a small study with 20 raters evaluating 43 trial experiences from an imaginary cardiovascular clinical trial. Raters showed a high degree of consensus. Moreover, the average ranks agreed fairly well with two quantitative ranking rules. On the other hand, the average ranks did not agree very well with weightings usually selected in cardiovascular trials. These results suggest ranking may be a feasible approach to analysing certain clinical trials with multiple outcomes.
Graphical representation of survival curves associated with a binary non‐reversible time dependent covariate
Authors: Feuer Eric J. , Hankey Benjamin F. , Gaynor Jeffrey J. , Wesley Margaret N. , Baker Stuart G. , Meyer Jason S.
Published: April 2007

The use of time dependent covariates has allowed for incorporation into analysis of survival data intervening events that are binary and non‐reversible (for example, heart transplant, initial response to chemotherapy). We can represent this type of intervening event as a three‐state stochastic process with a starting state (S), an intervening state (I), and an absorbing state (D), which usually represents death. In this paper we present three procedures for calculating survivorship functions which attempt to display the prognostic significance of the time dependent covariate. The first method compares survival from baseline for the two possible paths through the stochastic process; the second method compares overall survival to survival with stateIremoved from the process; and, the third method compares survival for those already in stateIat a landmark timexto those in stateSat timexwho will never enter stateI.We develop discrete hazard estimates for the survival curves associated with the three methods. Two examples illustrate how these methods can yield different results and in which situations one might employ each of the three methods. Extensions to applications with reversible binary time dependent covariates and models with both baseline and time dependent covariates are suggested.
Cross‐validation performance of mortality prediction models
Authors: Hadorn David C. , Draper David , Rogers William H. , Keeler Emmett B. , Brook Robert H.
Published: April 2007

Mortality prediction models hold substantial promise as tools for patient management, quality assessment, and, perhaps, health care resource allocation planning. Yet relatively little is known about the predictive validity of these models. We report here a comparison of the cross‐validation performance of seven statistical models of patient mortality: (1) ordinary‐least‐squares (OLS) regression predicting 0/1 death status six months after admission; (2) logistic regression; (3) Cox regression; (4–6) three unit‐weight models derived from the logistic regression, and (7) a recursive partitioning classification technique (CART).

We calculated the following performance statistics for each model in both a learning and test sample of patients, all of whom were drawn from a nationally representative sample of 2558 Medicare patients with acute myocardial infarction: overall accuracy in predicting six‐month mortality, sensitivity and specificity rates, positive and negative predictive values, and per cent improvement in accuracy rates and error rates over model‐free predictions (i.e., predictions that make no use of available independent variables). We developed ROC curves based on logistic regression, the best unit‐weight model, the single best predictor variable, and a series of CART models generated by varying the misclassification cost specifications.

In our sample, the models reduced model‐free error rates at the patient level by 8–22 per cent in the test sample. We found that the performance of the logistic regression models was marginally superior to that of other models. The areas under the ROC curves for the best models ranged from 0·61 to 0·63. Overall predictive accuracy for the best models may be adequateto support activities such as quality assessment that involve aggregating over large groups of patients, but the extent to which these models may be appropriately applied to patient‐level resource allocation planning is less claar.
On the use of the generalized t and generalized rank‐sum statistics in medical research
Authors: Blair R. Clifford , Morel Jorge G.
Published: April 2007

We have used Monte Carlo methods to compare the type I error properties of the conditional and unconditional versions of the generalized t and the generalized rank‐sum tests to those of the independent samples t and Wilcoxon rank‐sum tests. Results showed inflated type I errors for the conditional generalized tests but not for the unconditional tests. We also compared the power of the unconditional generalized tests to that of the t and Wilcoxon tests under a variety of conditions. Results showed the generalized tests to be much more efficient than their traditional counterparts in some circumstances, but substantially less powerful in others. Based on these and other considerations, we conclude that the application of these newer statistics in medical research needs further consideration.
Maximum likelihood estimation of between and within variations in energy and protein intakes from infancy to adolescence for the philippines
Authors: Bhargava Alok , Bouis Howarth
Published: April 2007

The assesment of subjects' ‘usual’ intake of nutrients is important in assessing relationships between diet and disease and in identifying malnourished sub‐groups of the populations. Estimation of the variation in intakes within subjects over time (‘within variation’) has importance in epidemiologic research; estimation of the between subject variation in the sample has use in defining the recommended dietary allowances that take into account the inter‐individual differences. This paper estimates the between and within variances in the energy and protein intakes of 1189 Filipino children, based on 4 rounds of 24‐hour recall data within a dynamic framework by means of maximum likelihood. The main findings are that the proportion of variation due to the within variance is higher for childern from poorer households. Also, from the estimates of dynamic regression models for nutrient intakes of children and adults, it appears that school programmes that provide subsidized foods with good sources of protein to the poorest among school attendees will be cost effective.
Optimum sample size determination in stratified case‐control studies with cost considerations
Authors: Nam Jun‐Mo , Fears Thomas R.
Published: April 2007

We investigate sample size determination for Cochran's test for stratified case‐control studies when samples of cases and controls are allocated to maximize the asymptotic efficiency of Cochran's test subject to fixed total cost with cost per control varying by strata. We consider two situations typical of strata‐matched case‐control studies: when one samples both cases and controls and when cases are given and one samples controls. In each situation we develop and study an asymptotic method for finding the sample size required for a specific power under the optimum allocation proposed by Nam and Fears. Also, for the second situation, we investigate an asymptotic method for determining the common ratio, k, in one‐to‐k stratamatched case‐control studies without cost consideration for a given power. When cases are given, neither the optimum nor the standard control sample sizes appear in a closed form; we present numerical methods for calculating these sample sizes and illustrate them with examples. We find the reduction in total cost obtained under the optimum allocation compared to standard allocation more pronounced as the differences in stratum‐specific costs of sampling controls increase.
Estimating transmission probabilities for chlamydial infection
Authors: Katz Barry P.
Published: April 2007

Estimates of transmission probabilities for sexually transmitted diseases historically come from studies of uninfected individuals exposed to those with a high disease prevalence (for example, prostitutes). However, changes in sexual behaviour, much of which relates to concerns about AIDS, has made identification of populations suitable for such studies extremely difficult. This paper presents a method for estimating these probabilities that utilizes a deterministic model and routinely collected data available in many clinics. Variance estimates for the estimators are also derived. Data for chlamydial infection and sensitivity analyses for the input parameters and assumptions illustrate the method.