bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis, characterizations, and biocompatibility of block poly(ester‐urethane)s based on biodegradable poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) and poly(ε‐caprolactone)
Authors: Qiu Handi , Li Dandan , Chen Xi , Fan Kaiyan , Ou Wenfeng , Chen Kevin C. , Xu Kaitian
Published: July 2012

A type of block poly(ester‐urethane)s (abbreviated as PUBC) based on bacterial copolyester poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) (P3/4HB) and biodegradable poly(ε‐caprolactone) (PCL) was synthesized by melting polymerization using 1,6‐hexamethylene diisocyanate (HDI) as the coupling agent, with different 3HB, 4HB and PCL contents and segment lengths. Stannous octanoate (Sn(Oct)2) was used as catalyst. The chemical structure, molecular weight and thermal property were characterized by1H NMR, FTIR GPC, DSC and TGA. DSC analysis revealed that the PUBC polyurethanes exhibit amorphous to semi‐crystalline (20.9% crystallinity degree) withTgrange from ‐39.7 to ‐21.5 °C. The hydrophilicity was investigated by static contact angle of deionized water and CH2I2. The obtained PUBCs are hydrophobic (water contact angle 73.7−90.2°). Platelet adhesion study and plasma recalcification time revealed that the block polyurethanes possess hemastasis ability. CCK‐8 assay illuminated that the no cytotoxic polyurethanes maintain rat aortic smooth muscle cells (RaSMCs) good viability. It was found that the 4HB content in the materials is an important factor to affect the sustainable cell viability. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A:75–86, 2013.
Behavior of primary human osteoblasts on trimmed and sandblasted Ti6Al4V surfaces functionalized with integrin αvβ3‐selective cyclic RGD peptides
Authors: Mas‐Moruno Carlos , Dorfner Petra M. , Manzenrieder Florian , Neubauer Stefanie , Reuning Ute , Burgkart Rainer , Kessler Horst
Published: July 2012

It is well known that functionalization of surfaces with cell adhesive peptides mimicking the integrin binding motif of extracellular matrix proteins is a feasible approach to improve osseointegration of implant materials. Also, modification of the surface properties of the material (e.g., roughness) strongly influences cell behavior. However, these two approaches are rarely studied together. This study addressed the hypothesis that the combination of peptide functionalization and surface roughness will have an enhancing effect on the adhesion process of osteoblasts. To test this hypothesis, a series of αvβ3‐selective cyclic RGD peptides were prepared and immobilized on trimmed (Sa= 0.74 μm, smooth) and sandblasted (Sa= 3.24 μm, rough) Ti6Al4V disks. Effects of these surface modifications were evaluated with respect to integrin αvβ3‐mediated adhesive capacity, cell morphology, and spreading of primary human osteoblasts. After 3 h of incubation, osteoblasts adhered more strongly on sandblasted than on trimmed noncoated Ti6Al4V surfaces. Their attachment efficiency was further enhanced in the presence of RGD peptides. However, peptide functionalization had a relatively stronger impact on osteoblast attachment on trimmed surfaces compared with sandblasted surfaces. Cell morphology after 3 h of culture was exclusively altered by surface topography. RGD coating was critical for osteoblast spreading on both trimmed and sandblasted materials after 1 h of incubation but it showed almost negligible effects after 3 h. The results of this study provide evidence that the alliance of RGD coating and surface topography on Ti6Al4V positively influences osteoblast adhesion and spreading, especially at very early adhesion times. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A:87–97, 2013.
Osseointegration assessment of chairside argon‐based nonthermal plasma‐treated Ca‐P coated dental implants
Authors: Giro Gabriela , Tovar Nick , Witek Lukasz , Marin Charles , Silva Nelson R. F. , Bonfante Estevam A. , Coelho Paulo G.
Published: July 2012

This study investigated the effect of an Argon‐based nonthermal plasma (NTP) surface treatment‐operated chairside at atmospheric pressure conditions applied immediately prior to dental implant placement in a canine model. Surfaces investigated comprised: Calcium‐Phosphate (CaP) and CaP + NTP (CaP‐Plasma). Surface energy was characterized by the Owens‐Wendt‐Rabel‐Kaelble method and chemistry by X‐ray photoelectron spectroscopy (XPS). Six adult beagles dogs received 2 plateau‐root form implants (n = 1 each surface) in each radii, providing implants that remained 1 and 3 weeks in vivo. Histometric parameters assessed were bone‐to‐implant contact (BIC) and bone area fraction occupancy (BAFO). Statistical analysis was performed by Kruskall‐Wallis (95% level of significance) and Dunn's post‐hoc test. The XPS analysis showed peaks of Ca, C, O, and P for the CaP and CaP‐Plasma surfaces. Both surfaces presented carbon primarily as hydrocarbon (CC, CH) with lower levels of oxidized carbon forms. The CaP surface presented atomic percent values of 38, 42, 11, and 7 for C, O, Ca, and P, respectively, and the CaP‐Plasma presented increases in O, Ca, and P atomic percent levels at 53, 12, and 13, respectively, in addition to a decrease in C content at 18 atomic percent. At 1 week no difference was found in histometric parameters between groups. At 3 weeks significantly higher BIC and BAFO were observed for CaP‐Plasma treated surfaces. Surface elemental chemistry was modified by the Ar‐based NTP. Ar‐based NTP improved bone formation around plateau‐root form implants at 3 weeks compared with CaP treatment alone. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A:98–103, 2013.
Defining Sets and Critical Sets in (0,1)‐Matrices
Authors: Cavenagh Nicholas J.
Published: July 2012

If D is a partially filled‐in (0, 1)‐matrix with a unique completion to a (0, 1)‐matrix M (with prescribed row and column sums), we say that D is a defining set for M. If the removal of any entry of D destroys this property (i.e. at least two completions become possible), we say that D is a critical set for M. In this note, we show that the complement of a critical set for a (0, 1)‐matrix M is a defining set for M. We also study the possible sizes (number of filled‐in cells) of defining sets for square matrices M with uniform row and column sums, which are also frequency squares. In particular, we show that when the matrix is of even order 2m and the row and column sums are all equal to m, the smallest possible size of a critical set is precisely m2. We give the exact structure of critical sets with this property. © 2012 Wiley Periodicals, Inc. J. Combin. Designs 21: 253–266, 2013
An asymptotically tight bound on the adaptable chromatic number
Authors: Molloy Michael , Thron Giovanna
Published: July 2012

The adaptable chromatic number of a multigraph G, denoted χa(G), is the smallest integer k such that every edge labeling, τ, of G from [k] = {1, 2, …, k} permits a vertex coloring, σ, of G from [k] such that no edge e = uv has τ(e) = σ(u) = σ(v). Hell and Zhu proved that for any multigraph G with maximum degree Δ, the adaptable chromatic number is at most . We strengthen this to the asymptotically best possible bound of for any ɛ>0. © 2012 Wiley Periodicals, Inc. J Graph Theory
Do Tourism Receipts Contribute to the Sustainability of Current Account Deficits: a Case Study of Barbados
Authors: Lorde Troy , Lowe Shane , Francis Brian
Published: July 2012

Given Barbados’ recent history of persistent current account deficits and reliance on tourism as a major source of foreign exchange and driver of the economy, this paper investigated the contribution of tourism receipts to the sustainability of Barbados’ current account deficits. Utilizing an inter‐temporal budget approach, it was found that Barbados’ current account deficits were weakly sustainable as a result of tourism's contribution, underscoring the island's dependence on the industry. Copyright © 2012 John Wiley & Sons, Ltd.
Quantum Chemical Investigation of Secondary Reactions in Poly(vinyl chloride) Free‐Radical Polymerization
Authors: Cuccato Danilo , Dossi Marco , Moscatelli Davide , Storti Giuseppe
Published: July 2012

Free‐radical polymerization of vinyl chloride is investigated computationally with special attention to the secondary reactions involving mid‐chain radicals (MCRs). Namely, the rate constants of backbiting, chain scission, chain transfer, and propagation reactions are evaluated using a density functional theory method. The rate coefficients of such reactions are estimated taking into account the position of the radical along the chain as well as its distance from the chain‐end. In particular 1:5, 5:1, and 5:9 backbiting are the most relevant secondary reactions, followed by the slower propagation of MCRs. Finally, a kinetic model of suspension polymerization including the investigated reactions is developed, in order to determine their impact on the quality of the final polymer.

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Graft Copolymers for Blend Compatibilization: Mathematical Modeling of the Grafting Process
Authors: Gianoglio Pantano Ioana A. , Asteasuain Mariano , Sarmoria Claudia , Brandolin Adriana
Published: July 2012

The grafting of PE onto PS through a Friedel‐Crafts reaction, which results in a mixture of PE‐g‐PS copolymer, unmodified PE, and modified PS, is investigated. The copolymer may be suitable for compatibilization of immiscible mixtures in the household plastic waste stream, where PE and PS are majority components. Since the compatibilization effect depends on the composition and block lengths in the copolymer, a model is presented for predicting the complete molecular weight distribution of the homopolymers and the chemical composition distribution of the graft copolymer. The model has potential for application in an optimization tool for the compatibilization process, as it is able to account for the opposing effects of competing reactions that characterize the graft reaction.

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Simultaneous single‐quantum and triple‐quantum‐filtered MRI of 23Na (SISTINA)
Authors: Fiege Daniel P. , Romanzetti Sandro , Mirkes Christian C. , Brenner Daniel , Shah N. Jon
Published: July 2012

The low MR sensitivity of the sodium nucleus and its low concentration in the human body constrain acquisition time. The use of both single‐quantum and triple‐quantum sodium imaging is, therefore, restricted. In this work, we present a novel MRI sequence that interleaves an ultra‐short echo time radial projection readout into the three‐pulse triple‐quantum preparation. This allows for simultaneous acquisition of tissue sodium concentration weighted as well as triple‐quantum filtered images. Performance of the sequence is shown on phantoms. The method is demonstrated on six healthy informed volunteers and is applied to three cases of brain tumors. A comparison with images from tumor specific O‐(2‐[18F]fluoroethyl)‐L‐tyrosine positron emission tomography and standard MR images is presented. The combined information of the triple‐quantum‐filtered images with single‐quantum images may enable a better understanding of tissue viability. Future studies can benefit from the evaluation of both contrasts with shortened acquisition times. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.
Toward cardiovascular interventions guided by magnetic particle imaging: First instrument characterization
Authors: Haegele Julian , Biederer Sven , Wojtczyk Hanne , Gräser Matthias , Knopp Tobias , Buzug Thorsten M. , Barkhausen Jörg , Vogt Florian M.
Published: July 2012

Magnetic particle imaging has emerged as a new technique for the visualization and quantification of superparamagnetic iron oxide nanoparticles. It seems to be a very promising application for cardiovascular interventional radiology. A prerequisite for interventions is the artifact‐free visualization of the required instruments and implants. Various commercially available catheters, guide wires, and a catheter experimentally coated with superparamagnetic iron oxide nanoparticles were tested regarding their signal characteristics using magnetic particle spectroscopy to evaluate their performance in magnetic particle imaging. The results indicate that signal‐generating and non‐signal‐generating instruments can be distinguished. Furthermore, coating or loading non‐signal‐generating instruments with superparamagnetic iron oxide nanoparticles seems to be a promising approach, but optimized nanoparticles need yet to be developed. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.
A standardized scan statistic for detecting spatial clusters with estimated parameters
Authors: Shu Lianjie , Jiang Wei , Tsui Kwok‐Leung
Published: July 2012

The scan statistic based on likelihood ratios (LRs) have been widely discussed for detecting spatial clusters. When developing the scan statistic, it uses the maximum likelihood estimates of the incidence rates inside and outside candidate clusters to substitute the true values in the LR statistic. However, the parameter estimation has a significant impact on the sensitivity of the scan statistic, which favors the detection of clusters in areas with large population sizes. By presenting the effects of parameter estimation on Kulldorff's scan statistic, we suggest a standardized scan statistic for spatial cluster detection. Compared to the traditional scan statistic, the standardized scan statistic can account for the varying mean and variance of the LR statistic due to inhomogeneous background population sizes. Extensive simulations have been performed to compare the power of the two cluster detection methods with known or/and estimated parameters. The simulation results show that the standardization can help alleviate the effects of parameter estimation and improve the detection of localized clusters. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012
Bayesian analysis of queues with impatient customers: Applications to call centers
Authors: Aktekin Tevfik , Soyer Refik
Published: July 2012

Queuing models have been extensively used in the literature for obtaining performance measures and developing staffing policies. However, most of this work has been from a pure probabilistic point of view and has not addressed issues of statistical inference. In this article, we consider Bayesian queuing models with impatient customers with particular emphasis on call center operations and discuss further extensions. We develop the details of Bayesian inference for queues with abandonment such as the M/M/s + M model (Erlang‐A). In doing so, we discuss the estimation of operating characteristics and its implications on staffing. We illustrate the implementation of the Bayesian models using actual arrival, service, and abandonment data from call centers. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2012
PROMIS pediatric measures in pediatric oncology: Valid and clinically feasible indicators of patient‐reported outcomes
Authors: Hinds Pamela S. , Nuss Suzanne L. , Ruccione Kathleen S. , Withycombe Janice S. , Jacobs Shana , DeLuca Holly , Faulkner Charisse , Liu Yang , Cheng Yao I. , Gross Heather E. , Wang Jichuan , DeWalt Darren A.
Published: July 2012

Background

Establishing the ability of children and adolescents with cancer to complete the NIH‐sponsored PROMIS pediatric measures electronically and the preliminary validity estimates of the measures (both full item banks and short forms) in pediatric oncology will contribute to our knowledge of the impact of cancer treatment on these young patients.

Procedures

A total of 203 8‐ to 17‐year olds were administered eight PROMIS pediatric measures in a cross‐sectional study design to establish known‐group validity. Of the 200 who completed all or most of the items, a slight majority were male (55.5%) and white (54%). Patients were either undergoing treatment for cancer (n = 93) or in survivorship following treatment for cancer (n = 107). Measures were completed using computer interface during an in‐person interaction with researchers.

Results

Only 3 of 203 participants did not complete the PROMIS pediatric measures. As hypothesized, participants in treatment were significantly different (worse) on parent‐reported clinical indicators (blood counts, fatigue, and appetite) and on seven self‐reported measures (depression, anxiety, peer relationships, pain interference, fatigue, upper extremity function, and mobility) from participants in survivorship. Females reported worse fatigue, anger, and pain interference than males. Worse patient‐reported outcomes for patients in active treatment persisted after adjusting for potential confounding variables.

Conclusions

Children and adolescents in treatment for cancer or in survivorship and ranging from 8 to 17 years of age can complete multiple PROMIS pediatric measures using a computer interface during an outpatient clinic visit or inpatient admission. Findings establish known‐group validity for PROMIS pediatric measures in pediatric oncology. Pediatr Blood Cancer 2013; 60: 402–408. © 2012 Wiley Periodicals, Inc.
Guiding of Reactive Plasma Species by Micro‐Channels
Authors: Li Yang‐Fang , Zimmermann Julia L. , Klämpfl Tobias , Morfill Gregor E.
Published: July 2012

We investigate the effect of the micro‐channel plate (MCP) on the diffusive transport of reactive plasma species generated by a cold atmospheric discharge. The diffusion of the reactive plasma species is guided by the micro‐channels and the side diffusion is consequently reduced. Therefore the reactive plasma species are more effectively transported to the target surface. A higher bactericidal efficiency is found in comparison with the open, unhindered configuration when the open area ratio of the MCP equals 50%. Furthermore, the experimental results show a significant UV reduction because of the shielding by the MCP.

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Comment on “Ion‐Assisted Processes of Polymerization in Low‐Pressure Plasmas”
Authors: d'Agostino Riccardo , Palumbo Fabio
Published: July 2012

Ions as building blocks in the deposition of plasma polymers, or as promoters and initiators of the polymerization process? Perchance the both, depending on the operative conditions.
Using layer of protection analysis to understand necessary safeguards for steam boiler operation
Authors: Morrison Delmar “Trey” , Fecke Mark , Ramirez Juan
Published: July 2012

Most chemical process plants, petrochemical facilities, and electrical power utilities rely on steam boilers to provide motive power, electricity, and process steam for operations. Safe operation, startup, and shutdown of these boilers require many levels of operational/controls safeguards. The design and selection of safeguards is often guided by the original design of the boiler, equipment manufacturers, internal company standards, and recognized authoritative standards. In the United States, the National Fire Protection Association (NFPA) has promulgated NFPA 85 Boiler and Combustion Systems Hazards Code. This prescriptive code identifies necessary safeguards along with “listing” and “labeling” requirements for some components used as safeguards; however, the Safety Integrity Levels for the multiple safeguard systems have not been quantified. In this article, we use Layer of Protection Analysis methods along with generally accepted probabilities and frequencies of failures to provide a quantitative framework for an owner, operator, or manufacturer to use in designing or evaluating the multiple safeguards necessary for safe steam boiler operation. As part of the analysis, we have provided case studies of boiler failures with a discussion of how additional layers of protection may be either ineffective or missing. © 2012 American Institute of Chemical Engineers Process Saf Prog, 2012
How to be effective in a process safety role
Authors: Klein James A.
Published: July 2012

Many factors contribute to being capable and effective in process safety roles. Certainly, understanding of engineering and process safety is desirable to establish basic technical competence. Ultimately, true capability and career success also requires the ability to work within an organization to help achieve superior and effective performance. This article discusses how to be effective in a process safety role by developing a strong foundation of technical knowledge and capability, by learning to influence the organization, and by thinking and communicating independently. The result should be career success as well as improved process safety performance, helping to prevent serious injuries and incidents. © 2012 American Institute of Chemical Engineers Process Saf, 2012.
High‐contrast 2D etched holes array obtained by direct laser writing on chalcogenide As2S3 films
Authors: Popescu Aurelian , Savastru Dan , Savastru Roxana , Miclos Sorin , Socol Gabriel , Mihailescu Ion N.
Published: July 2012

This paper studies optical, chemical and photoinduced changes in amorphous AsS films, obtained by nanosecond pulsed‐laser ablation of a As40S60 target. The arsenic content of the films is slightly higher than the target composition and depends on the ablation fluence. The photobleaching phenomenon appears after 1–2 min of bandgap laser irradiation. The refractive index diminishes by 0.07 and the transmission approximately doubles. It was established for the first time that films obtained by pulsed laser deposition exhibit a positive resist behavior in amine‐containing etchant. The etching rate of the irradiated film was 0.12 µm/min, while as‐deposited films have lower etching rate. The measured selectivity rate was of 14:1. A 2D high‐quality hole array was produced by direct laser writing and further etching. The unusual behavior can be a result of different glass network formation during the condensation of AsSn molecules sputtered from the bulk target. This is different from the case of thermally evaporated films where AsS1 molecules only were identified in gas‐phase by mass spectrometry.
Computational modeling of wet TiO2 (001) anatase surfaces functionalized by transition metal doping
Authors: Zhang Yuchi , Kilin Dmitri S.
Published: July 2012

Titanium dioxide anatase nanostructure is a photocatalyst under UV light. Our objective is to discover proper surface and functionalization, which facilitate the efficiency of photocatalytic water splitting on TiO2 crystals. We set up a periodic model of Ti32O64·8H2O as the neutral structure and expose the (001) crystallographic surface as it is more reactive. Using platinum, cobalt, and ruthenium to dope in the (001) crystallographic surface and get Ti30Me2O64·8H2O, which Me stands for either Pt, Co, or Ru. Based on density functional theory and Perdue Burke Ernzerhof functional (PBE) we calculate and optimize the doped nanostructures using VASP software. Through their density of states, we can analyze the possibility of charge transfer at the crystal surface and compare how the doping elements affect the charge transfer direction. A comparison of the computed absorption spectra and the charge density of the doping nanostructures help us in better understanding of the possibility of the bandgap tuning in photocatalytic energy nanomaterials. © 2012 Wiley Periodicals, Inc.
Time dependent wave packet treatment of 2ΠgN2− and 3Σ−NO− shape resonances using two‐dimensional surfaces for electron‐N2 and NO interactions
Authors: Shandilya Bhavesh K. , Sarma Manabendra , Adhikari Satrajit , Mishra Manoj K.
Published: July 2012

The 2ΠgN and 3Σ−NO− resonances in electron‐N2 and NO collisions have been treated using both nuclear and electronic degrees of freedom and a two‐dimensional (2D) time dependent wave packet approach to ascertain the importance of nonlocality in electron–nuclear interaction. The results so obtained are compared with vibrational excitation cross‐sections obtained experimentally and those from other theoretical/numerical approaches using 1D local complex potential, 2D model with a combination of the exterior complex scaling method and a finite‐element implementation of the discrete‐variable representation. The results obtained provide detailed insight into the nuclear dynamics induced by electron–molecule collision and reveal that while for resonant excitation of lower vibrational modes, the nonlocal effect may not be as critical but importance of nonlocal effects may increase with increase in quanta of resonant vibrational excitation. © 2012 Wiley Periodicals, Inc.
An improved CeO2 method for high‐precision measurements of 17O/16O ratios for atmospheric carbon dioxide
Authors: Mahata Sasadhar , Bhattacharya Sourandra K. , Wang Chung‐Ho , Liang Mao‐Chang
Published: July 2012

RATIONALE

The oxygen isotopic composition of carbon dioxide originating at the Earth's surface is modified in the stratosphere by interaction with ozone which has anomalous oxygen isotope ratio (Δ17O = 1000 * ln(1 + δ17O/1000) – 0.522 * 1000 * ln (1 + δ18O/1000) >0). The inherited anomaly provides a powerful tracer for studying biogeochemical cycles involving CO2. However, the existing methods are either too imprecise or have difficulty in determining the small Δ17O variations found in the tropospheric CO2. In this study an earlier published CeO2 and CO2 exchange method has been modified and improved for measuring the Δ17O values of atmospheric carbon dioxide with high precision.

METHODS

The CO2 fraction from air samples was separated by cryogenic means and purified using gas chromatography. This CO2 was first analyzed in an isotope ratio mass spectrometer, then artificially equilibrated with hot CeO2 to alter its oxygen isotopes mass‐dependently and re‐analyzed. From these data the 17O/16O and 18O/16O ratios were calculated and the Δ17O value was determined.

RESULTS

The validity of the method was established in several tests by using artificially prepared CO2 with zero and non‐zero Δ17O values. The published value of the CO2‐H2O equilibrium slope was also reproduced.

CONCLUSIONS

The CO2‐CeO2 equilibration method has been improved to measure the oxygen isotope anomaly (Δ17O value) of atmospheric CO2 with an analytical precision of ±0.12‰ (2σ). Copyright © 2012 John Wiley & Sons, Ltd.
Characterization of ethanolysis products of poly(dimethylsiloxane) species by electrospray ionization tandem mass spectrometry
Authors: Fouquet Thierry , Bour Jérôme , Toniazzo Valérie , Ruch David , Charles Laurence
Published: July 2012

RATIONALE

The partial and controlled degradation of insoluble cross‐linked silicon‐based polymers is a promising approach to enable their characterization by mass spectrometry. Providing that the chemolysis reaction specifically proceeds at cross‐linking sites, the size of linear poly(dimethylsiloxane)s (PDMS) produced during the treatment should reflect the length of linear segments between branching points in the original network. In this context, the specificity of ethanol to act as a nucleophilic agent towards tri‐functional silicon atoms in a D3TDnTD3 model was evaluated.

METHODS

Tandem mass spectrometry (MS/MS) combined with accurate mass measurements, MS3 experiments and collision‐induced dissociation of authentic compounds was used for structural characterization of D3TDnTD3 ethanolysis products. All MS/MS data were obtained from electrosprayed ammonium adducts, previously reported to provide the most informative data for silicon‐based polymers.

RESULTS

Since the expected ethanolysis products were hydroxy‐ and ethoxy‐terminated PDMS, the dissociation behavior of such polymeric species was established, using electrosprayed ammonium adducts as the precursor ions. Diagnostic product ions were identified, allowing four main D3TDnTD3 ethanolysis products to be structurally characterized. End‐group analysis of these polymeric distributions clearly indicated that ethanolysis was mostly occurring on tri‐functional silicon atoms but also, to a lesser extent, on those D atoms close to T silicons.

CONCLUSIONS

The size of the linear skeleton located between two tri‐functional silicon atoms could be accurately determined by mass spectrometric analyses of a polymeric model submitted to ethanolysis. This soft and rapid pre‐treatment is thus a promising approach for determining the length of linear segments between branching points in the original network of cross‐linked silicon‐based polymers. Copyright © 2012 John Wiley & Sons, Ltd.
The oscillations killer: a mechanism to eliminate undesired limit cycles in a class of nonlinear systems
Authors: Canudas‐de‐Wit C. , Aracil J. , Gordillo F. , Salas F.
Published: July 2012

In this paper, we present a mechanism, calledoscillation killer, intended to eliminate limit cycles that may occur as a consequence of unexpected external disturbances, interactions with the environment, changes in systems set‐points, physical parameters, and so on. Examples range from controlled systems with friction to electrical networks with varying loads and impedances. The proposed mechanisms is shown to be particulary appropriate for nonlinear systems displaying a locally asymptotically equilibrium point surrounded by a locally asymptotically stable limit set outside this local domain. Copyright © 2012 John Wiley & Sons, Ltd.
Nanometrical evaluation of direct laser implant surface
Authors: Ricci M. , Mangano F. , Tercio T. , Tonelli P. , Barone A. , Raspanti M. , Covani U.
Published: July 2012

The present study was designed to evaluate the characteristics and the topography of a new implant surface. Titanium discs were manufactured using master alloy powder (Ti‐6Al‐4V) with a particle size of 25–45 µm as the basic material (Leader Implants, Milan, Italy). We acquired images in three different dimensional ranges of decreasing dimensions: 30 (dimensional class A), 10 (dimensional class B), and 5 µm2 (dimensional class C). For each dimensional range, we collected five (dimensional classes A and B) to ten (dimensional classes C) different images, belonging both to the center and to the edge of the slide

Results

In dimensional class A, implant surface showed an average roughness value (Ra) of 0.6 µm, whereas the root mean square roughness (Rrms) value was 0.78 µm. In the dimensional class B, value of Ra was 133.4 µm and value of Rrms was 161.7 µm. Finally, at a smaller level as in dimensional class C, value of Ra was 68.5 µm and Rrms was 81.05 µm. Moreover, the peak to peak value was 369.5 µm and the average height value was 187.3 µm

Discussion

The surface which results from direct laser fabrication process has an ideal nano‐roughness to enhance protein adsorption and to facilitate precursor osteoblast adhesion. In conclusion, direct laser forming surface seems to be a promising technique for forming dental implants from titanium alloys. Copyright © 2012 John Wiley & Sons, Ltd.
Non‐hydrogenated amorphous germanium carbide with adjustable microstructure and properties: a potential anti‐reflection and protective coating for infrared windows
Authors: Han Jiecai , Jiang Chunzhu , Zhu Jiaqi
Published: July 2012

Amorphous non‐hydrogenated germanium carbide (a‐Ge1−xCx) films have been deposited using magnetron co‐sputtering technique by varying the sputtering power of germanium target (PGe). The effects of PGe on composition and structure of the a‐Ge1−xCx films have been analyzed. The FTIR spectrum shows that the C–Ge bonds were formed in the a‐Ge1−xCx films according to the absorption peak at ~610 cm−1. The Raman results indicate that the amorphous films also contain both Ge and C clusters. The XPS results reveal that the carbon concentration decreased as PGe increased from 40 to 160 W. The fraction of sp3 C–C bonds remains almost constant when increasing PGe from 40 to 160 W. The sp2 C–C content of a‐Ge1−xCx film decreases gradually to 35.9% with PGe up to 160 W. Nevertheless, sp3 C–Ge sites rose with increasing PGe. Furthermore, the hardness and the refractive index gradually increased with increasing PGe. The excellent optical transmission of annealed a‐Ge1–xCx double‐layer coating at 400 °C suggests that a‐Ge1−xCx films can be used as an effective anti‐reflection coating for the ZnS IR window in the wavelength region of 8–12 µm, and can endure higher temperature than hydrogenated amorphous germanium carbide do. Copyright © 2012 John Wiley & Sons, Ltd.
Construction and corrosion behaviors of a bilayer superhydrophobic film on copper substrate
Authors: Ou Junfei , Hu Weihua , Wang Ying , Wang Fajun , Xue Mingshan , Li Wen
Published: July 2012

A novel bilayer superhydrophobic film was constructed on Cu substrate by a simple multi‐step process. First, (3‐mercaptopropyl) trimethoxysilane (MPTMS) molecules were self‐assembled onto the pre‐etched Cu surface via covalent bonding followed by hydrolysis and condensation, then 1H, 1H, 2H, 2H‐perfluorodecyltrichlorosilane (PFDTS) were grafted onto the resultant hydroxyl terminated surface via the Si‐O‐Si bonding. The so‐prepared sample was defined as Cu‐MPTMS‐PFDTS. The structure and morphology of the samples were characterized by means of contact angle measurement, X‐ray photoelectron spectroscopy and scanning electron microscopy. The corrosion behaviors of the films were evaluated by Tafel plot and electrochemical impedance spectroscopy on an electrochemical work station. The results indicated that the bilayer superhydrophobic film possessed better corrosion protection as compared with the control samples. The superiority of the corrosion protection was mainly ascribed to the following two aspects: the superhydrophobicity and polysiloxane micro‐structures of the Cu‐MPTMS‐PFDTS. Copyright © 2012 John Wiley & Sons, Ltd.
Comparison of methods for imputing ordinal data using multivariate normal imputation: a case study of non‐linear effects in a large cohort study
Authors: Lee Katherine J. , Galati John C. , Simpson Julie A. , Carlin John B.
Published: July 2012

Background

Multiple imputation is becoming increasingly popular for handling missing data, with Markov chain Monte Carlo assuming multivariate normality (MVN) a commonly used approach. Imputing categorical variables (which are clearly non‐normal) using MVN imputation is challenging, and several approaches have been suggested. However, it remains unclear which approach should be preferred.

Methods

We explore methods for imputing ordinal variables using MVN imputation, including imputing as a continuous variable and as a set of indicators, and various methods for assigning imputed values to the possible categories (rounding), for estimating a non‐linear association between an ordinal exposure and binary outcome. We introduce a new approach where we impute as continuous and assign imputed values into categories based on the mean indicators imputed in a separate round of imputation. We compare these approaches in a simple setting where we make 50% of data in an ordinal exposure missing completely at random, within an otherwise complete real dataset.

Results

Methods that impute the ordinal exposure as continuous distorted the non‐linear exposure–outcome association by biasing the relationship towards linearity irrespective of the rounding method. In contrast, imputing using indicators preserved the non‐linear association but not the marginal distribution of the ordinal variable.

Conclusions

Imputing ordinal variables as continuous can bias the estimation of the exposure–outcome association in the presence of non‐linear relationships. Further work is needed to develop optimal methods for handling ordinal (and nominal) variables when using MVN imputation. Copyright © 2012 John Wiley & Sons, Ltd.
Simulating from marginal structural models with time‐dependent confounding
Authors: Havercroft W.G. , Didelez V.
Published: July 2012

We discuss why it is not always obvious how to simulate longitudinal data from a general marginal structural model (MSM) for a survival outcome while ensuring that the data exhibit complications due to time‐dependent confounding. On the basis of the relation between a directed acyclic graph and an MSM, we suggest a data‐generating process that satisfies both these requirements, the general validity of which we prove. Our approach is instructive regarding the interpretation of MSMs and useful in that it allows one to examine the finite sample performance of methods that claim to adjust for time‐dependent confounding. We apply our methodology to design a simulation study that emulates typical longitudinal studies such as the Swiss HIV Cohort Study so that competing methods of adjusting for time‐dependent covariates can be compared. Copyright © 2012 John Wiley & Sons, Ltd.
A conditional likelihood approach for regression analysis using biomarkers measured with batch‐specific error
Authors: Wang Ming , Dana Flanders W. , Bostick Roberd M. , Long Qi
Published: July 2012

Measurement error is common in epidemiological and biomedical studies. When biomarkers are measured in batches or groups, measurement error is potentially correlated within each batch or group. In regression analysis, most existing methods are not applicable in the presence of batch‐specific measurement error in predictors. We propose a robust conditional likelihood approach to account for batch‐specific error in predictors when batch effect is additive and the predominant source of error, which requires no assumptions on the distribution of measurement error. Although a regression model with batch as a categorical covariable yields the same parameter estimates as the proposed conditional likelihood approach for linear regression, this result does not hold in general for all generalized linear models, in particular, logistic regression. Our simulation studies show that the conditional likelihood approach achieves better finite sample performance than the regression calibration approach or a naive approach without adjustment for measurement error. In the case of logistic regression, our proposed approach is shown to also outperform the regression approach with batch as a categorical covariate. In addition, we also examine a ‘hybrid’ approach combining the conditional likelihood method and the regression calibration method, which is shown in simulations to achieve good performance in the presence of both batch‐specific and measurement‐specific errors. We illustrate our method by using data from a colorectal adenoma study. Copyright © 2012 John Wiley & Sons, Ltd.
Profile likelihood‐based confidence interval of the intraclass correlation for binary outcome data sampled from clusters
Authors: Saha Krishna K.
Published: July 2012

The intraclass correlation in binary outcome data sampled from clusters is an important and versatile measure in many biological and biomedical investigations. Properties of the different estimators of the intraclass correlation based on the parametric, semi‐parametric, and nonparametric approaches have been studied extensively, mainly in terms of bias and efficiency [see, for example, Ridoutet al.,Biometrics1999, 55:137–148; Paulet al.,Journal of Statistical Computation and Simulation2003, 73:507–523; and Lee,Statistical Modelling2004, 4: 113–126], but little attention has been paid to extending these results to the problem of the confidence intervals. In this article, we generalize the results of the four point estimators by constructing asymptotic confidence intervals obtaining closed‐form asymptotic and sandwich variance expressions of those four point estimators. It appears from simulation results that the asymptotic confidence intervals based on these four estimators have serious under‐coverage. To remedy this, we introduce the Fisher'sz‐transformation approach on the intraclass correlation coefficient, the profile likelihood approach based on the beta‐binomial model, and the hybrid profile variance approach based on the quadratic estimating equation for constructing the confidence intervals of the intraclass correlation for binary outcome data. As assessed by Monte Carlo simulations, these confidence interval approaches show significant improvement in the coverage probabilities. Moreover, the profile likelihood approach performs quite well by providing coverage levels close to nominal over a wide range of parameter combinations. We provide applications to biological data to illustrate the methods. Copyright © 2012 John Wiley & Sons, Ltd.
Optimal design of multi‐arm multi‐stage trials
Authors: Wason James M. S. , Jaki Thomas
Published: July 2012

In drug development, there is often uncertainty about the most promising among a set of different treatments. Multi‐arm multi‐stage (MAMS) trials provide large gains in efficiency over separate randomised trials of each treatment. They allow a shared control group, dropping of ineffective treatments before the end of the trial and stopping the trial early if sufficient evidence of a treatment being superior to control is found. In this paper, we discuss optimal design of MAMS trials. An optimal design has the required type I error rate and power but minimises the expected sample size at some set of treatment effects. Finding an optimal design requires searching over stopping boundaries and sample size, potentially a large number of parameters. We propose a method that combines quick evaluation of specific designs and an efficient stochastic search to find the optimal design parameters. We compare various potential designs motivated by the design of a phase II MAMS trial. We also consider allocating more patients to the control group, as has been carried out in real MAMS studies. We show that the optimal allocation to the control group, although greater than a 1:1 ratio, is smaller than previously advocated and that the gain in efficiency is generally small. Copyright © 2012 John Wiley & Sons, Ltd.
Predicting longitudinal trajectories of health probabilities with random‐effects multinomial logit regression
Authors: Liu Xian , Engel Charles C.
Published: July 2012

Researchers often encounter longitudinal health data characterized with three or more ordinal or nominal categories. Random‐effects multinomial logit models are generally applied to account for potential lack of independence inherent in such clustered data. When parameter estimates are used to describe longitudinal processes, however, random effects, both between and within individuals, need to be retransformed for correctly predicting outcome probabilities. This study attempts to go beyond existing work by developing a retransformation method that derives longitudinal growth trajectories of unbiased health probabilities. We estimated variances of the predicted probabilities by using the delta method. Additionally, we transformed the covariates’ regression coefficients on the multinomial logit function, not substantively meaningful, to the conditional effects on the predicted probabilities. The empirical illustration uses the longitudinal data from the Asset and Health Dynamics among the Oldest Old. Our analysis compared three sets of the predicted probabilities of three health states at six time points, obtained from, respectively, the retransformation method, the best linear unbiased prediction, and the fixed‐effects approach. The results demonstrate that neglect of retransforming random errors in the random‐effects multinomial logit model results in severely biased longitudinal trajectories of health probabilities as well as overestimated effects of covariates on the probabilities. Copyright © 2012 John Wiley & Sons, Ltd.
The ghosts of departed quantities: approaches to dealing with observations below the limit of quantitation
Authors: Senn Stephen , Holford Nick , Hockey Hans
Published: July 2012

A common but not necessarily logical requirement in drug development is that a ‘limit of quantitation’ be set for chemical assays and that observations that fall below the limit should not be treated as real data but should be labelled as below the limit and set aside for special treatment.

We examine five of seven approaches to analysing such data considered by Beal in 2001, concentrating in particular on two: one that treats the data as a truncated sample and another that treats them as a censored sample. In fact, using a pattern‐mixture framework, one can show that the former consists of using the conditional distribution of the ‘acceptable values’ and the latter adds the information from the marginal mixing distribution.

We illustrate these approaches with a real example, concentrating in particular on the two likelihood‐based methods, provide various formulae that may be used to compare these and other approaches, check these formulae using simulations and make some recommendations as to which approach one should use. Copyright © 2012 John Wiley & Sons, Ltd.
Adverse subpopulation regression for multivariate outcomes with high‐dimensional predictors
Authors: Zhu Bin , Dunson David B. , Ashley‐Koch Allison E.
Published: July 2012

Biomedical studies have a common interest in assessing relationships between multiple related health outcomes and high‐dimensional predictors. For example, in reproductive epidemiology, one may collect pregnancy outcomes such as length of gestation and birth weight and predictors such as single nucleotide polymorphisms in multiple candidate genes and environmental exposures. In such settings, there is a need for simple yet flexible methods for selecting true predictors of adverse health responses from a high‐dimensional set of candidate predictors. To address this problem, one may either consider linear regression models for the continuous outcomes or convert these outcomes into binary indicators of adverse responses using predefined cutoffs. The former strategy has the disadvantage of often leading to a poorly fitting model that does not predict risk well, whereas the latter approach can be very sensitive to the cutoff choice. As a simple yet flexible alternative, we propose a method for adverse subpopulation regression, which relies on a two‐component latent class model, with the dominant component corresponding to (presumed) healthy individuals and the risk of falling in the minority component characterized via a logistic regression. The logistic regression model is designed to accommodate high‐dimensional predictors, as occur in studies with a large number of gene by environment interactions, through the use of a flexible nonparametric multiple shrinkage approach. The Gibbs sampler is developed for posterior computation. We evaluate the methods with the use of simulation studies and apply these to a genetic epidemiology study of pregnancy outcomes. Copyright © 2012 John Wiley & Sons, Ltd.
Event‐weighted proportional hazards modelling for recurrent gap time data
Authors: Darlington G. A. , Dixon S. N.
Published: July 2012

The analysis of gap times in recurrent events requires an adjustment to standard marginal models. One can perform this adjustment with a modified within‐cluster resampling technique; however, this method is computationally intensive. In this paper, we describe a simple adjustment to the standard Cox proportional hazards model analysis that mimics the intent of within‐cluster resampling and results in similar parameter estimates. This method essentially weights the partial likelihood contributions by the inverse of the number of gap times observed within the individual while assuming a working independence correlation matrix. We provide an example involving recurrent mammary tumours in female rats to illustrate the methods considered in this paper. Copyright © 2012 John Wiley & Sons, Ltd.
Control of Cell Adhesion and Neurite Outgrowth by Patterned Gold Nanoparticles with Tunable Attractive or Repulsive Surface Properties
Authors: Gilles Sandra , Winter Silke , Michael Kristin E. , Meffert Simone H. , Li Pinggui , Greben Kyrylo , Simon Ulrich , Offenhäusser Andreas , Mayer Dirk
Published: July 2012

Guiding of neuronal cells on surfaces is required for the investigation of fundamental aspects of neurobiology, for tissue engineering, and for numerous bioelectronic applications. A modular method to establish nanostructured chemical templates for local deposition of gold nanoparticles is presented. A process comprising nanoimprint lithography, silanization, lift‐off, and gold nanoparticle immobilization is used to fabricate the particle patterns. The chemical composition of the surface can be modified by in situ adsorption of cell‐binding ligands to locally addressed particles. The versatility of this approach is demonstrated by inverting the binding affinity between rat cortical neurons and nanopatterned surfaces via wet‐chemical means and thereby reversing the pattern of guided neurons.