bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface structural characteristics and tunable electronic properties of wet-chemically prepared Pd nanoparticles
Authors: Cook S. C. , Padmos J. D. , Zhang P.
Published: April 2008

The ligand substitution reaction, Pd L3,2,1-edge and S K-edge x-ray absorption fine structure (XAFS), XAFS simulations, and valence-band and core-level x-ray photoelectron spectroscopy (XPS) have been used to systematically study the surface chemical and electronic properties of wet-chemically prepared Pd nanoparticles of varied size, molecular capping, and metal composition. It was found that the replacement of weakly interacting capping molecules (amine and tetra-alkylphosphonium bromide) with strongly binding thiols caused a considerable change in the surface bonding of Pd nanoparticles. However, the Pd d-electron counts (number of d electrons) remained almost unchanged before and after ligand substitution, which is unexpected since Pd atoms normally lose electrons to the more electronegative S atoms. XAFS results and simulations provided useful insights into the surface structural characteristics of Pd nanoparticles and satisfactorily accounted for the unexpected d-electron behavior involved in the ligand substitution process. XPS valence and core-level spectra further revealed a size-dependent d-band narrowing and presented complementary information to XAFS about the surface electronic properties of Pd atoms. The small weakly bound Pd nanoparticles seem inevitably to have a net d-electron depletion due to the influence of the surface effect (chemical adsorption by oxygen), which is more significant than the d-electron enriching nanosize effect. However, it was demonstrated that by forming Pd–Ag alloy nanoparticles, a net increase of the Pd d-electron counts can be realized. Therefore, it is illustrated that by manipulating the surface, size, and alloying effects, the electronic properties of Pd nanoparticles can be possibly tuned.
Interaction potentials for alumina and molecular dynamics simulations of amorphous and liquid alumina
Authors: Vashishta Priya , Kalia Rajiv K. , Nakano Aiichiro , Rino José Pedro
Published: April 2008

Structural and dynamical properties of crystalline alumina α-Al2O3 and amorphous and molten alumina are investigated with molecular dynamics simulation based on an effective interatomic potentials consisting of two- and three-body terms. Structural correlations are examined through pair distribution functions, coordination numbers, static structure factors, bond angle distributions, and shortest-path ring analyses. The calculated results for neutron and x-ray static structure factors are in good agreement with experimental results. Dynamical correlations, such as velocity autocorrelation function, vibrational density of states, current-current correlation function, and frequency-dependent conductivity, are also discussed.
Determination of the melting point of hard spheres from direct coexistence simulation methods
Authors: Noya Eva G. , Vega Carlos , de Miguel Enrique
Published: April 2008

We consider the computation of the coexistence pressure of the liquid-solid transition of a system of hard spheres from direct simulation of the inhomogeneous system formed from liquid and solid phases separated by an interface. Monte Carlo simulations of the interfacial system are performed in three different ensembles. In a first approach, a series of simulations is carried out in the isothermal-isobaric ensemble, where the solid is allowed to relax to its equilibrium crystalline structure, thus avoiding the appearance of artificial stress in the system. Here, the total volume of the system fluctuates due to changes in the three dimensions of the simulation box. In a second approach, we consider simulations of the inhomogeneous system in an isothermal-isobaric ensemble where the normal pressure, as well as the area of the (planar) fluid-solid interface, are kept constant. Now, the total volume of the system fluctuates due to changes in the longitudinal dimension of the simulation box. In both approaches, the coexistence pressure is estimated by monitoring the evolution of the density along several simulations carried out at different pressures. Both routes are seen to provide consistent values of the fluid-solid coexistence pressure, p=11.54(4)kBT∕σ3, which indicates that the error introduced by the use of the standard constant-pressure ensemble for this particular problem is small, provided the systems are sufficiently large. An additional simulation of the interfacial system is conducted in a canonical ensemble where the dimensions of the simulation box are allowed to change subject to the constraint that the total volume is kept fixed. In this approach, the coexistence pressure corresponds to the normal component of the pressure tensor, which can be computed as an appropriate ensemble average in a single simulation. This route yields a value of p=11.54(4)kBT∕σ3. We conclude that the results obtained for the coexistence pressure from direct simulations of the liquid and solid phases in coexistence using different ensembles are mutually consistent and are in excellent agreement with the values obtained from free energy calculations.
Band alignment of yttrium oxide on various relaxed and strained semiconductor substrates
Authors: Chiam S. Y. , Chim W. K. , Pi C. , Huan A. C. H. , Wang S. J. , Pan J. S. , Turner S. , Zhang J.
Published: April 2008

In this work, we report on the band offsets of yttrium oxide (Y2O3) on various relaxed and strained semiconductor substrates, such as silicon (Si), germanium (Ge), and silicon germanium (SiGe). By using the example of Y2O3/Si, important experimental aspects in using photoemission to determine band offsets are discussed. We then discuss the various values of band offsets of Y2O3 on the different substrates that we obtained by using x-ray photoelectron spectroscopy. Finally, we show that presputtering 3 Å of metallic Y [equivalent to 1 ML (monolayer) coverage] before the deposition of Y2O3 affects the band lineup by reducing the resultant valence band offsets. We explain the observed band offsets by using an interfacial layer model.
A highly tunable lateral quantum dot realized in InGaAs/InP by an etching technique
Authors: Larsson M. , Wallin D. , Xu H. Q.
Published: April 2008

We report on the realization of a quantum dot in a modulation doped InGaAs/InP heterostructure by electron beam lithography and chemical wet etching. Using etched trench defined in-plane gates and a local top gate, the tunneling barriers, electron density, and electrostatic potential of the dot can be tuned. Electrical measurements reveal clear Coulomb blockade behavior of the electron transport through the dot and the behavior of electron tunneling through its excited states.
Lattice engineering of dielectric heterostructures on Si by isomorphic oxide-on-oxide epitaxy
Authors: Schroeder T. , Costina I. , Storck P. , Wilke A. , Seifarth O. , Giussani A. , Müssig H.-J. , Zaumseil P.
Published: April 2008

The isomorphic oxide-on-oxide epitaxy of Y2O3 on cubic Pr2O3(111)∕Si(111) support systems was studied to tailor the lattice constant of the dielectric heterostructure for future integration of functional semiconductors via heteroepitaxy on the Si material platform. Laboratory- and synchrotron-based x-ray diffraction was applied to study the structure as well as the epitaxy mechanism of Y2O3 on the cubic Pr2O3(111)∕Si(111) support. The oxide heterostructure is characterized by the formation of closed single crystalline cubic Y2O3(111) films which are in especial twin-free and exhibit an exclusive type B epitaxy orientation on the cubic Pr2O3(111)∕Si(111) system. Nondestructive depth profiling x-ray diffraction reveals that the epitaxy mechanism of Y2O3 films on cubic Pr2O3(111)∕Si(111) systems is determined by the formation of a transition layer with variable lattice parameters, changing with increasing depth from the Y2O3 values towards the parameters of the isomorphic Pr2O3 support. This transition layer thus effectively accomodates the relatively large lattice misfit of 4.8% between the isomorphic oxides. X-ray photoelectron depth profiling studies are applied to discriminate between strain and interface reaction effects in the formation of this transition region at the Y2O3∕Pr2O3 boundary. An interface reaction, forming a compositionally graded Pr2−xYxO3 (x=0–2) buffer layer at the oxide/oxide boundary, results as the most probable physical origin.
Magnetic ordering effects in the Raman spectra of Sn1−xCoxO2
Authors: Kravets Vasyl G. , Poperenko Leonid V.
Published: April 2008

The room temperature ferromagnetism is observed in chemically synthesized powderlike samples of Sn1−xCoxO2 compound (x=0.07 and 0.1). The Raman spectra of the Sn1−xCoxO2 films were analyzed in terms of their structural and magnetic properties. In the Raman spectra of the Sn1−xCoxO2 films additional features were revealed which are associated with the excitation of phonon modes in the cobalt-oxide-defect complex. The intensities of the Raman bands showed a strong dependence on the doping concentration and on applied magnetic field. The softening of the ∼630cm−1 symmetric A1g mode and the field dependence of the intensity Raman scattering observed for Co-doped SnO2 films was ascribed to spin-phonon interaction. The absorption spectra show that there are changes of absorption edge toward low energy due to the influence of incorporated Co atoms on the electronic states of SnO2. These results can be described by the bound magnetic polarons theory.
Laser-induced damage of TiO2∕SiO2 high reflector at 1064nm
Authors: Yao Jianke , Ma Jianyong , Xiu Cheng , Fan Zhengxiu , Jin Yunxia , Zhao Yuanan , He Hongbo , Shao Jianda , Huang Huolin , Zhang Feng , Wu Zhengyun
Published: April 2008

A high laser-induced damage threshold (LIDT) TiO2∕SiO2 high reflector (HR) at 1064nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064nm with a 12ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR.
Anomalous Rashba spin-orbit interaction in InAs∕GaSb quantum wells
Authors: Li Jun , Chang Kai , Hai G. Q. , Chan K. S.
Published: April 2008

We theoretically investigate the Rashba spin-orbit interaction in InAs∕GaSb quantum wells (QWs). We find that the Rashba spin-splitting (RSS) sensitively depends on the thickness of the InAs layer. The RSS exhibits nonlinear behavior for narrow InAs∕GaSb QWs and the oscillating feature for wide InAs∕GaSb QWs. The nonlinear and oscillating behaviors arise from the weakened and enhanced interband coupling. The RSS also show asymmetric features respect to the direction of the external electric field.
Investigation of trap effects in AlGaN∕GaN field-effect transistors by temperature dependent threshold voltage analysis
Authors: Kordoš P. , Donoval D. , Florovič M. , Kováč J. , Gregušová D.
Published: April 2008

We report on a temperature dependent threshold voltage analysis of the AlGaN∕GaN heterostructure field-effect transistors (HFETs) and Al2O3∕AlGaN∕GaN metal-oxide-semiconductor HFETs (MOSHFETs) in order to investigate the trap effects in these devices. The threshold voltage of both types of devices decreases with increased ambient temperature up to 450°C. This indicates on donor traps to be present. The temperature induced threshold voltage shift is −1.6 and −8.5mV∕°C for the HFETs and MOSHFETs, respectively. A thermally activated energy level of ∼0.2eV is evaluated and attributed to the nitrogen vacancy in the AlGaN near surface. The trap density for the MOSHFETs is about two times higher than that for the HFETs. This might be due to the high-temperature treatment (∼600°C) of the MOSHFET structure during the gate insulator deposition.
Nonlinear measurement of mid-infrared absorption in AlOx waveguides
Authors: Ravaro M. , Guillotel E. , Le Dû M. , Manquest C. , Marcadet X. , Ducci S. , Berger V. , Leo G.
Published: April 2008

We report a quantitative study on the absorption of oxidized-AlAs (AlOx) integrated thin layers in the mid-infrared range (2–4μm). An AlOx absorption coefficient of 1600cm−1 is measured in a nonlinear waveguide, by investigating the phase-matching bandwidth of parametric fluorescence. Since mid-infrared optical losses of the idler mode are inferred from the corresponding signal features in the 1–2μm range, our technique takes advantage of common near-infrared sources and detectors.
Transport properties of organic field effect transistors modified by quantum dots
Authors: Nishioka Masaya , Chen Yu , Goldman A. M.
Published: April 2008

We have investigated the transport properties of organic field effect transistors (OFETs) with quantum dot layers between the organic semiconductor and the dielectric. An insulating dot layer changes the properties of OFETs, suggesting that OFET mobility will always be reduced by additional physical disorder. However, a metal dot layer causes a much larger reduction of the mobility and an increase of the activation energy. This phenomenon may be explained by more charge being induced on metal dots causing the carriers to be more localized.
The meteorological conditions associated with extreme fire risk in Italy and Greece: relevance to climate model studies
Authors: Good P. , Moriondo M. , Giannakopoulos C. , Bindi M.
Published: April 2008

The meteorological conditions associated with elevated and extreme long- and short-timescale forest fire risk are investigated by validating and diagnosing the Canadian Fire Weather Index (FWI) in the context of Tuscany in Italy, and Thessaloniki, Athens and Heraklion in Greece. The aim is to provide information to assist diagnosing experiments that use output from climate models to calculate FWI values. Links are made from fire risk to the widely used FWI, and then to the underlying meteorology, complementing other more complex fire risk model studies. First, the information about Mediterranean fire risk provided by the FWI is assessed by comparing the observed number of fires per day with FWI values based on the locally observed meteorology. This shows that the FWI provides some relatively consistent information for different locations, and suggests useful FWI thresholds indicating elevated and extreme fire risk. Then, the FWI system is split according to contributions from long- and short-timescale components, in a different way than usually adopted in the literature. Using the FWI thresholds suggested above, the long- and short-timescale meteorological conditions causing elevated and extreme FWI values are diagnosed. The results may help studies that investigate what aspects of projected climate change drive changes in fire weather risk, compare fire risk calculations from different climate models, or assess how climate models can be improved to provide better fire risk projections.
TRIM21 is an IgG receptor that is structurally, thermodynamically, and kinetically conserved
Authors: Keeble Anthony H. , Khan Zahra , Forster Alan , James Leo C.
Published: April 2008

The newly identified tripartite motif (TRIM) family of proteins mediate innate immunity and other critical cellular functions. Here we show that TRIM21, which mediates the autoimmune diseases rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's syndrome, is a previously undescribed IgG receptor with a binding mechanism unlike known mammalian Fcγ receptors. TRIM21 simultaneously targets conserved hot-spot residues on both Ig domains of the Fc fragment using a PRYSPRY domain with a preformed multisite interface. The binding sites on both TRIM21 and Fc are highly conserved to the extent that the proteins are functionally interchangeable through murine, canine, primate, and human species. Pre-steady-state analysis exposes mechanistic conservation at the level of individual residues, which make the same energetic and kinetic contributions to binding despite varying in sequence. Together, our results reveal that TRIM21 is a previously undescribed type of IgG receptor based on a non-Ig scaffold whose interaction at the fundamental level—structural, thermodynamic, and kinetic—is evolutionarily conserved.
The adolescent emotional maelstrom
Authors: Meuter Renata F.I. , Buckley Leigh
Published: April 2008

To determine how differences in emotion representation and/or inhibitory ability affect adolescents’ responses to emotion words, 13-yr and 16-yr olds, as well as adults, were compared on the processing of emotion-laden and neutral words. Word ratings revealed that 16-yr olds tended towards perceiving all words as more arousing than did adults, irrespective of valence. Also, they rated words more negatively than 13-yr olds. Performance on an Affective Simon task revealed a marked incongruency effect only for 13-yr olds (and then only for negative words) but not for 16-yr olds (who responded fastest) or adults. Performance on a sustained attention task confirmed the expected age-related increase in inhibitory ability and a concomitant increase in response latencies. Our conclusions are two-fold. First, there are age-related differences in lexical representation which appear more marked for 16-yr olds. Second, 16-yr olds are more reactive, irrespective of the emotional content they are processing, yet appear to control its impact as efficiently as adults.
Emotion words in the mental lexicon
Authors: Sutton Tina M. , Altarriba Jeanette
Published: April 2008

The representation of emotion words in memory is a relatively new area of research within the cognitive domain. In the present paper, these words will be examined with the use of the Stroop paradigm. In the past, this paradigm has been used to investigate a wide variety of word types, including color words and color-related words. Only a few studies have examined emotion words. The current study investigates a particular set of emotion words that were either congruent or incongruent with the color they were presented in (e.g., ENVY in green ink or red ink), much like standard Stroop stimuli (RED in red ink or green ink). The results of Experiment 1 revealed that emotion stimuli can be studied in the same manner as color words and color-related words, such as fire. When the congruent and incongruent items were presented together, within the same block in Experiment 2, the color items and color-related emotion items still produced a Stroop interference effect, but the color-related emotionally neutral items did not. The results of Experiment 2 suggest that evaluative information (i.e., negative valence) is automatically accessed regardless of the task at hand. The current study speaks to the need to include negative valence as an important factor in models of word recognition.
Words, feelings, and bilingualism
Authors: Marian Viorica , Kaushanskaya Margarita
Published: April 2008

Cross-linguistic differences in emotionality of autobiographical memories were examined by eliciting memories of immigration from bilingual speakers. Forty-seven Russian-English bilinguals were asked to recount their immigration experiences in either Russian or English. Bilinguals used more emotion words when describing their immigration experiences in the second language (English) than in the first language (Russian). Bilinguals’ immigration narratives contained more negative emotion words than positive emotion words. In addition, language preference (but not language proficiency) influenced results, with emotional expression amplified when speaking in the preferred language. These findings carry implications for organization of the bilingual lexicon and the special status of emotion words within it. We suggest that bilinguals’ expression of emotion may vary across languages and that the linguistic and affective systems are interconnected in the bilingual cognitive architecture.
AUSTRIA'S ITALIAN POLICY RECONSIDERED: REVOLUTION AND REFORM IN RESTORATION ITALY
Authors: Laven David
Published: April 2008

This article examines Austrian policy towards the Italian states from the Congress of Vienna to the revolutions of 1848. It argues that the paramount concern of Habsburg policy was not revolution, but rather the maintenance of a hegemonic position in the peninsula against threats from the Habsburgs’ traditional enemy - the French. Revolution caused significant concern only because it might provide the French with a pretext for intervention in the peninsula. Consequently a number of strategies were adopted both to forestall insurrection (vigorous policing, encouraging moderate reform programmes, armed intervention), and to retain influence over the peninsula's rulers (diplomatic pressure, dynastic and military alliances, promises of assistance against unrest). However, by the 1830s the Austrians were faced by increasing challenges to their position of dominance. This was in part because of the personal ambitions of individual Italian rulers, but it also reflected the changing situation in Paris after the July Revolution, and in Vienna after the death of Francis I.
REGION AND NATION
Authors: Thom Martin
Published: April 2008

Carl Levy (ed.), Italian Regionalism. History, Identity and Politics, Berg, Oxford 1996, 197 pp., ISBN 1–85975–131–7 hbk, 1–85973–156–2 pbk, £12.95.

It would seem to be self-evident that we cannot say what regions (and regionalism) are until we have said what nations (and nationalism) are, for the concept of region was formulated in response to, and to some degree in opposition to, that of nation. It would be overstating the case, even in the France of the Restoration or of the July Monarchy, to define ‘regionalism’ as belonging on the Right of the political spectrum, for there are liberal counter-examples to pit against de Gobineau, and yet many did indeed construe regional identity as a threat to the principle of nationality. Thus, in the Italian context, as David Hine observes in the volume under review, the real explanation for the limited nature of the challenge to the highly centralized state ‘probably lies, at least for the period from 1860 to 1922, in the cultural dominance of the myth of national popular resurgence on which the Risorgimento was based’ (p. 110). On this reading, critics of unity, who were often advocates of diversity also, were bound to remain unheeded.
Next to the Dog Pound: Institutional Discourses and Practices About Rom Refugees in Left-Wing Bologna
Authors: Però Davide
Published: April 2008

This article examines the institutional discourses and practices that have characterized the process of incorporation of a group of Rom refugees from the former Yugoslavia in Bologna, the ‘showcase’ of the Italian Left. Following an anthropology of policy approach, the article provides insights into both the conditions of refugees in Italy and the relationships which exist between the political Left and the ‘new’ immigrations. This is done by showing how the discourses and the practices of the Left can be oppressive and how such oppression is not merely due to an inescapable macro-structural order of things but has local ‘origins’, too. Thus it is argued that if social justice is still a priority in the political agenda of the mainstream Left in Italy, as is claimed, then the Left has some rethinking to do in order to avoid its entanglement and responsibility in processes of oppression and domination in the context of migration.
Coexistence in North Sea fish communities: implications for growth and natural mortality
Authors: Gislason Henrik , Pope John G. , Rice Jake C. , Daan Niels
Published: April 2008

Gislason, H., Pope, J. G., Rice, J. C., and Daan, N. 2008. Coexistence in North Sea fish communities: implications for growth and natural mortality. – ICES Journal of Marine Science, 65: 514–530. For a fish community to persist over time, all species must be able on average to replace themselves on a one-for-one basis over their lifetime. We use this principle and a size-based equilibrium model where asymptotic length is used as a functional trait to investigate how natural mortality should scale with size within and across pelagic and demersal species of North Sea teleosts. The model predicts natural mortality to scale with body length raised to a power of −1.66 at current levels of exploitation. Additionally, natural mortality of demersal species should be proportional to asymptotic length raised to a power of 0.80, so generating a higher natural mortality at a given length for large species than for small ones. The model also suggests that the exponent in the scaling of the von Bertalanffy growth parameter K with asymptotic length should be more negative for pelagic than for demersal species. We test our results by analysing independent estimates of predation mortality, the scaling of maximum recruitment per unit of spawning-stock biomass with asymptotic length, and the general relationship between K and asymptotic length for demersal and pelagic families of fish. All tests are consistent with our modelling results.
In situ target-strength measurements of Chilean jack mackerel (Trachurus symmetricus murphyi) collected with a scientific echosounder installed on a fishing vessel
Authors: Peña Hector
Published: April 2008

Peña, H. 2008. In situ target-strength measurements of Chilean jack mackerel (Trachurus symmetricus murphyi) collected with a scientific echosounder installed on a fishing vessel. – ICES Journal of Marine Science 65: 594–604. The use of commercial fishing vessels for scientific purposes has increased worldwide in the past 10 years. Many such studies have involved the collection of acoustic data from both uncalibrated and calibrated echosounders. However, few studies have involved investigations of in situ target strength (TS). During August/September 2003, in situ TS data on Chilean jack mackerel (Trachurus symmetricus murphyi) were collected on board a commercial purse-seiner during normal fishing operations off Chile, using a 38 kHz, Simrad EK60 scientific echosounder. The single-target detections of Chilean jack mackerel were filtered by depth, off-axis beam angle, and beam-compensation criteria to improve the quality of the data used for the TS calculations. Two methods, using raw data and tracked data, were employed to calculate the mean acoustic-backscattering cross section (σbs) and mean TS of Chilean jack mackerel. The results of the two approaches gave similar results, with a strong mode in the mean TS distribution between −35 and −37 dB for fish lengths ranging from 26 to 34 cm, indicating a b20 value of −66 dB. These results agreed well with most results published for this species and others of the same genus (i.e. T. trachurus, Trachurus t. capensis, and T. japonicus).
Scaling of xylem vessels and veins within the leaves of oak species
Authors: Coomes David A , Heathcote Steven , Godfrey Elinor R , Shepherd James J , Sack Lawren
Published: April 2008

General models of plant vascular architecture, based on scaling of pipe diameters to remove the length dependence of hydraulic resistance within the xylem, have attracted strong interest. However, these models have neglected to consider the leaf, an important hydraulic component; they assume all leaves to have similar hydraulic properties, including similar pipe diameters in the petiole. We examine the scaling of the leaf xylem in 10 temperate oak species, an important hydraulic component. The mean hydraulic diameter of petiole xylem vessels varied by 30% among the 10 oak species. Conduit diameters narrowed from the petiole to the midrib to the secondary veins, consistent with resistance minimization, but the power function scaling exponent differed from that predicted for stems. Leaf size was an organizing trait within and across species. These findings indicate that leaf vasculature needs to be included in whole-plant scaling models, for these to accurately reflect and predict whole-plant transport and its implications for performance and ecology.
Uniform asymptotics of the Pollaczek polynomials via the Riemann–Hilbert approach
Authors: Zhou Jian-Rong , Zhao Yu-Qiu
Published: April 2008

The Pollaczek weight is an example of the non-Szegö class. In this paper, we investigate the asymptotics of the Pollaczek polynomials via the Riemann–Hilbert approach. In the analysis, the original endpoints ±1 of the orthogonal interval are shifted to the Mhaskar–Rakhmanov–Saff numbers
α

n

and
β

n

. It is also shown, by analysing the singularities of the
ϕ
-function, that the endpoint parametrices constructed in terms of the Airy function are bound to be local. Asymptotic approximations are obtained in overlapping regions that cover the whole complex plane. The approximations, some special values and the leading and recurrence coefficients are compared with the known results.
A method of assessing the sensitivity of the Cochran–Mantel–Haenszel test to an unobserved confounder
Authors: Yu Binbing , Gastwirth Joseph L
Published: April 2008

Observational studies, including the case-control design frequently used in epidemiology, are subject to a number of biases and possible confounding factors. Failure to adjust with them may lead to an erroneous conclusion about the existence of a causal relationship between exposure and disease. The Cochran–Mantel–Haenszel (CMH) test is widely used to measure the strength of the association between an exposure and disease or response, after stratifying on the observed covariates. Thus, observed confounders are accounted for in the analysis. In practice, there may be causal variables that are unknown or difficult to obtain. Hence, they are not incorporated into the analysis. Sensitivity analysis enables investigators to assess the robustness of the findings. A method for assessing the sensitivity of the CMH test to an omitted confounder is presented here. The technique is illustrated by re-examining two datasets: one concerns the effect of maternal hypertension as a risk factor for low birth weight infants and the other focuses on the risk of allopurinol on having a rash. The computer code performing the sensitivity analysis is provided in appendix A.
Two-stage procedures for selecting the best diagnostic biomarkers
Authors: Liu Aiyi , Wu Chengqing , Yu Kai F
Published: April 2008

Considered in the paper is the problem of selecting a diagnostic biomarker that has the highest classification rate among several candidate markers with dichotomous outcomes. The probability of correct selection depends on a number of nuisance parameters from the joint distribution of the biomarkers and thus can be substantially affected if these nuisance parameters are misspecified. A two-stage procedure is proposed to compute the needed sample size that achieves the desired level of correct selection, as so confirmed by simulation results.
A Bayesian precision profile for measuring the quality of immunoassay experiments
Authors: O'Malley A. James
Published: April 2008

A precision profile, the relationship between the concentration of a substance and its measured precision, is a convenient way of conveying the ability of an immunoassay to accurately measure the concentration of a substance in blood serum. A precision profile is characterized by the definition of precision. Historically, precision has been evaluated as the standard error of an estimator of the concentration in a sample conditional on the true concentration. In this paper, Bayesian predictive inference is used to develop a new measure of precision based on the accuracy with which an assay could infer the concentration in a hypothetical new sample. This leads to a natural procedure for evaluating a precision profile that avoids using approximations such as those inherent in traditional methods.
Bayesian assessment of overtriage and undertriage at a level I trauma centre
Authors: DiDomenico Paul B , Pietzsch Jan B , Paté-Cornell M. Elisabeth
Published: April 2008

We analysed the trauma triage system at a specific level I trauma centre to assess rates of over- and undertriage and to support recommendations for system improvements. The triage process is designed to estimate the severity of patient injury and allocate resources accordingly, with potential errors of overestimation (overtriage) consuming excess resources and underestimation (undertriage) potentially leading to medical errors.

We first modelled the overall trauma system using risk analysis methods to understand interdependencies among the actions of the participants. We interviewed six experienced trauma surgeons to obtain their expert opinion of the over- and undertriage rates occurring in the trauma centre. We then assessed actual over- and undertriage rates in a random sample of 86 trauma cases collected over a six-week period at the same centre. We employed Bayesian analysis to quantitatively combine the data with the prior probabilities derived from expert opinion in order to obtain posterior distributions. The results were estimates of overtriage and undertriage in 16.1 and 4.9% of patients, respectively.

This Bayesian approach, which provides a quantitative assessment of the error rates using both case data and expert opinion, provides a rational means of obtaining a best estimate of the system's performance. The overall approach that we describe in this paper can be employed more widely to analyse complex health care delivery systems, with the objective of reduced errors, patient risk and excess costs.
Improving interval estimation of binomial proportions
Authors: Zhou X.H , Li C.M , Yang Z
Published: April 2008

In this paper, we propose one new confidence interval for the binomial proportion; our interval is based on the Edgeworth expansion of a logit transformation of the sample proportion. We provide theoretical justification for the proposed interval and also compare the finite-sample performance of the proposed interval with the three best existing intervals—the Wilson interval, the Agresti–Coull interval and the Jeffreys interval—in terms of their coverage probabilities and expected lengths. We illustrate the proposed method in two real clinical studies.
Multiple imputation inference for multivariate multilevel continuous data with ignorable non-response
Authors: Yucel Recai M
Published: April 2008

Methods specifically targeting missing values in a wide spectrum of statistical analyses are now part of serious statistical thinking due to many advances in computational statistics and increased awareness among sophisticated consumers of statistics. Despite many advances in both theory and applied methods for missing data, missing-data methods in multilevel applications lack equal development. In this paper, I consider a popular inferential tool via multiple imputation in multilevel applications with missing values. I specifically consider missing values occurring arbitrarily at any level of observational units. I use Bayesian arguments for drawing multiple imputations from the underlying (posterior) predictive distribution of missing data. Multivariate extensions of well-known mixed-effects models form the basis for simulating the posterior predictive distribution, hence creating the multiple imputations. The discussion of these topics is demonstrated in an application assessing correlates to unmet need for mental health care among children with special health care needs.
A mathematical approach for the transactivation of hERα
Authors: Castano Enrique , Flores-Saaib Ruben D
Published: April 2008

Several reports over the last few years have documented the dose–response curve for steroid hormone induction of gene transcription as a modulated property of a given receptor–agonist complex that varies with the changing concentration of a variety of factors including: homologous receptor, co-activators, co-repressors and selected co-factors. In each report, the dose–response curves are sigmoidal and show an excellent fit with the curve generated by Michaelis–Menten kinetics. In addition, even the overall function of human oestrogen receptors (hERs) can show a similar graph for the determination of sex versus oestrogen compounds in reptiles. Thus, the kinetic properties of the simple bimolecular reaction of A+B→C appear, surprisingly, to be sufficient to describe the dose–response curve of the multi-step process of steroid-regulated gene induction that involves several molecules. Any advance in explaining why the dose–response curve for steroid-regulated gene expression is sigmoidal would assist in understanding what parameters are key factors of the dose–response curve and can benefit in the design of new oestrogenic substances. We have constructed and analysed a multi-step model of hER-induced gene transcription that explains the multiple forms of a simple dose–response curve in an
in vitro
transcription system.
Validation of image segmentation by estimating rater bias and variance
Authors: Warfield Simon K , Zou Kelly H , Wells William M
Published: April 2008

The accuracy and precision of segmentations of medical images has been difficult to quantify in the absence of a ‘ground truth’ or reference standard segmentation for clinical data. Although physical or digital phantoms can help by providing a reference standard, they do not allow the reproduction of the full range of imaging and anatomical characteristics observed in clinical data.

An alternative assessment approach is to compare with segmentations generated by domain experts. Segmentations may be generated by raters who are trained experts or by automated image analysis algorithms. Typically, these segmentations differ due to intra-rater and inter-rater variability. The most appropriate way to compare such segmentations has been unclear.

We present here a new algorithm to enable the estimation of performance characteristics, and a true labelling, from observations of segmentations of imaging data where segmentation labels may be ordered or continuous measures. This approach may be used with, among others, surface, distance transform or level-set representations of segmentations, and can be used to assess whether or not a rater consistently overestimates or underestimates the position of a boundary.
Point and interval estimation of accuracies of a binary medical diagnostic test following group sequential testing
Authors: Shu Yu , Liu Aiyi , Li Zhaohai
Published: April 2008

When hypotheses concerning the sensitivity and specificity of a binary medical diagnostic test are simultaneously tested using a group sequential procedure, constructing point and interval estimates of the parameters is challenging because there is no unique way to order sample points in the two-dimensional space. In this paper, upon termination of a group sequential procedure, we compare the bias and mean squared errors of the maximum-likelihood and Rao–Blackwell unbiased estimators of sensitivity and specificity. Confidence intervals (CIs) of the two parameters were constructed using normal approximation and Woodroofe's pivot methods based on maximum-likelihood and Rao–Blackwell unbiased estimates. The coverage probability and the expected length of CIs for the parameters were compared by simulation studies.
The predictive receiver operating characteristic curve for the joint assessment of the positive and negative predictive values
Authors: Shiu Shang-Ying , Gatsonis Constantine
Published: April 2008

Binary test outcomes typically result from dichotomizing a continuous test variable, observable or latent. The effect of the threshold for test positivity on test sensitivity and specificity has been studied extensively in receiver operating characteristic (ROC) analysis. However, considerably less attention has been given to the study of the effect of the positivity threshold on the predictive value of a test. In this paper we present methods for the joint study of the positive (PPV) and negative predictive values (NPV) of diagnostic tests. We define the predictive receiver operating characteristic (PROC) curve that consists of all possible pairs of PPV and NPV as the threshold for test positivity varies. Unlike the simple trade-off between sensitivity and specificity exhibited in the ROC curve, the PROC curve displays what is often a complex interplay between PPV and NPV as the positivity threshold changes. We study the monotonicity and other geometric properties of the PROC curve and propose summary measures for the predictive performance of tests. We also formulate and discuss regression models for the estimation of the effects of covariates.
Estimation of vaccine efficacy in a repeated measures study under heterogeneity of exposure or susceptibility to infection
Authors: Valim Clarissa , Mezzetti Maura , Maguire James , Urdaneta Margarita , Wypij David
Published: April 2008

Vaccine efficacy (VE) is commonly estimated through proportional hazards modelling of the time to first infection or disease, even when the event of interest can recur. These methods can result in biased estimates when VE is heterogeneous across levels of exposure and susceptibility in subjects. These two factors are important sources of unmeasured heterogeneity, since they vary within and across areas, and often cannot be individually quantified. We propose an estimator of VE per exposure that accounts for heterogeneous susceptibility and exposure for a repeated measures study with binary recurrent outcomes. The estimator requires only information about the probability distribution of environmental exposures. Through simulation studies, we compare the properties of this estimator with proportional hazards estimation under the heterogeneity of exposure. The methods are applied to a reanalysis of a malaria vaccine trial in Brazil.
Alcohol dependence is associated with reduced plasma and fundic ghrelin levels
Authors: Badaoui A. , De Saeger C. , Duchemin J. , Gihousse D. , De Timary P. , Stärkel P.
Published: April 2008

Background  Conflicting data concerning the involvement of ghrelin in the pathophysiology of alcohol dependence have been reported. The aim of this study is to investigate how chronic alcohol ingestion influences plasma ghrelin levels and whether potential changes observed in plasma relate to modifications in ghrelin production in the stomach where this peptide is primarily synthesized.

Materials and methods  Fifty‐one consecutive alcoholics admitted for alcohol withdrawal were prospectively enrolled and compared to a control group of 32 healthy volunteers matched for age, sex, height and weight. All subjects underwent fasting plasma ghrelin determination. Twenty‐seven randomly selected alcoholics and 17 controls underwent gastroscopy for fundic and duodenal biopsies. Tissues were fixed for histology or frozen in liquid nitrogen for ghrelin protein and mRNA determinations by a radioimmunoassay and quantitative polymerase chain reaction, respectively. Alcohol consumption was normalized to body weight (BW) or body mass index (BMI) given the influence of BW and volume distribution on alcohol levels.

Results  Plasma and fundic ghrelin protein levels were significantly decreased in alcoholics. Fundic but not plasma ghrelin protein levels inversely correlated with alcohol consumption normalized to BW or BMI. Ghrelin mRNA levels in fundic biopsies were similar in alcoholics and controls. No significant differences in duodenal ghrelin protein and mRNA levels were found between both groups.

Conclusions  Alcoholism was associated with decreased plasma ghrelin levels partly due to reduced ghrelin production in the stomach. Alcohol affected ghrelin production on the post‐transcriptional level in the fundus, whereas duodenal ghrelin secretion did not respond in a similar manner to alcohol intake.
Cohort splitting in bluefish, Pomatomus saltatrix, in the US mid‐Atlantic Bight
Authors: CALLIHAN JODY L. , TAKATA LYNN T. , WOODLAND RYAN J. , SECOR DAVID H.
Published: April 2008

Atlantic bluefish exhibit cohort splitting, whereby two modes of juvenile recruits originate from spatially distinct spring‐ and summer‐spawning regions in US Atlantic shelf waters. We evaluate the pattern of cohort splitting in a transition area (US Maryland coastal region and Chesapeake Bay) between the two major spawning regions. Spring and summer cohorts were differentially represented in Maryland estuarine (Chesapeake Bay) and coastal waters. The spring cohort was dominant in Chesapeake Bay, but was not well represented in the ocean environment, and the converse true for the summer cohort. We hypothesized that ocean temperatures control the bimodal spawning behavior and extent of cohort splitting. As evidence, we observed an intervening early summer cohort produced in years when shelf temperatures during early summer were suitably warm for spawning. In most years however, two dominant cohorts were evident. We propose that vernal warming dynamics in the mid‐Atlantic Bight influence spawning behavior and the resultant bimodal pattern of seasonal juvenile cohort production commonly observed along the US east coast.
Using process‐oriented holonic (PrOH) modelling to increase understanding of information systems
Authors: Clegg Ben , Shaw Duncan
Published: April 2008

Abstract.  Methodologies for understanding business processes and their information systems (IS) are often criticized, either for being too imprecise and philosophical (a criticism often levied at softer methodologies) or too hierarchical and mechanistic (levied at harder methodologies). The process‐oriented holonic modelling methodology combines aspects of softer and harder approaches to aid modellers in designing business processes and associated IS. The methodology uses holistic thinking and a construct known as the holon to build process descriptions into a set of models known as a holarchy. This paper describes the methodology through an action research case study based in a large design and manufacturing organization. The scientific contribution is a methodology for analysing business processes in environments that are characterized by high complexity, low volume and high variety where there are minimal repeated learning opportunities, such as large IS development projects. The practical deliverables from the project gave IS and business process improvements for the case study company.
Research on couples: are feminist approaches useful?
Authors: Peters Kathleen , Jackson Debra , Rudge Trudy
Published: April 2008

Title.  Research on couples: are feminist approaches useful?

Aim.  This paper is an exploration of the utility and value of feminist approaches when undertaking narrative‐based research with partner dyads (within both heterosexual and same sex partnerships) and when researching sensitive issues.

Background.  Adverse life events or conditions experienced by individuals have been found also to have a negative impact on their partners. Most literature addressing partner issues uses quantitative methods, and existing qualitative research on couples has traditionally interviewed only one person in the partnership or coupled partners together. There is little discussion in the literature about the use of feminist research when researching male perspectives and experiences, and even less discussion of the possibilities that feminist research methods bring to the study of couple dyads.

Discussion.  Qualitative methodologies informed by feminist perspectives, including issues of reciprocity and self disclosure, can be used to unpack structural, personal and political issues related to couples’ experiences. A feminist approach allows us to show that the origin of oppression is not personal but very much about power and that men as well as women, regardless of their sexuality, may experience the effects of oppression. Narrative and story‐telling complements feminist research because of the value it assigns to the storytellers.

Conclusion.  To care for women effectively, we must also consider the experiences of their partners as the health of one partner has the potential to impact on the other. The concept of oppression is not absent, but indeed is illuminated, in the lives of some men. Gathering stories using feminist perspectives enhances respect and mutuality in the research process.