Bias in cross-sectional analyses of longitudinal mediation.

Most empirical tests of mediation utilize cross-sectional data despite the fact that mediation consists of causal processes that unfold over time. The authors considered the possibility that longitudinal mediation might occur under either of two different models of change: (a) an autoregressive model or (b) a random effects model. For both models, the authors demonstrated that cross-sectional approaches to mediation typically generate substantially biased estimates of longitudinal parameters even under the ideal conditions when mediation is complete. In longitudinal models where variable M completely mediates the effect of X on Y, cross-sectional estimates of the direct effect of X on Y, the indirect effect of X on Y through M, and the proportion of the total effect mediated by M are often highly misleading. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoelectrolysis of water using thin copper gallium diselenide electrodes

Thin CuGaSe₂ films were deposited by vacuum co-evaporation and characterized for their structure, properties and performance as hydrogen-evolving photoelectrodes. The 0.9 μm thick films were nearly stoichiometric with very slight copper deficiency and showed polycrystalline structure with grain sizes of tens of nanometers. An electrode based on such a film was demonstrated operating with outdoor 1-sun photocurrent of up to 13 mA/cm². Spectral response data show significant incident-photon-to-current efficiency throughout the visible spectrum, peaking at 63% at 640 nm. Photocurrent output under simulated 1-sun Air Mass 1.5 light was stable over 4 h. Unassisted water-splitting is not possible due to high band edge positions, but operation in tandem configuration with a suitable bottom junction is feasible.     

Compositionally graded ferroelectric multilayers for frequency agile tunable devices

Recently, there has been significant interest toward the development of tunable dielectric materials for voltage-controlled, frequency-agile phase shifters and filters operating in the microwave regime. The fundamental challenge in designing materials systems for such tunable devices is the simultaneous requirement of high dielectric tunability (>40%) over a large temperature interval (−10 °C to +90 °C) coupled with low dielectric losses (between 3.0 dB and 4.0 dB in operational bandwidths ranging from several hundred MHz up to 30 or more GHz). We show that a high- and temperature-insensitive tunability can be realized in compositionally graded ferroelectrics and provide a brief review of the results of experimental and theoretical studies on the dielectric properties of Barium Strontium Titanate (Ba_1−x Sr _x TiO₃ or BST) multilayer heterostructures. Theoretically, we discuss the role of thermal stresses on the dielectric properties using a non-linear thermodynamic model coupled with basic electrostatic considerations to describe the interlayer interactions between the ferroelectric layers. We show that the thermal strains arising from the thermal expansion coefficient mismatch between the multilayered film and the substrate may have a significant effect on the dielectric permittivity and tunability of BST multilayers. Experimentally, compositionally graded BST multilayers (5 mol% MgO doped and undoped) were grown via metallo-organic solution deposition (MOSD) on Pt–Si substrates and electrically characterized. Optimum conditions were found to exist in BST multilayers consisting of three distinct layers of ~220 nm nominal thickness with compositions corresponding to Ba_0.60Sr_0.40TiO₃ (BST 60/40), BST 75/25, and BST 90/10. At room temperature, the BST heterostructure has a small-signal dielectric permittivity of 360 with a dissipation factor of 0.012 and a dielectric tunability of 65% at 444 kV/cm. These properties exhibit minimal dispersion as a function of temperature ranging from 90 °C to −10 °C. Our results also show that MgO doping improves dielectric loss (tan δ = 0.008), but results in a moderate dielectric tunability of 29% at 444 kV/cm. Electrical measurements at microwave frequencies display a decrease in the dielectric permittivity and tunability for both undoped and MgO-doped BST multilayers. At 10 GHz, the dielectric response, tunability, and the loss characteristics for graded undoped BST are 261, 25% (at 1,778 kV/cm), and 0.078, respectively, and 189 and 15% (at 1,778 kV/cm), and 0.039, respectively, for the MgO-doped graded BST.     

Vertical dynamic behavior of three-piece bogie suspensions with two types of friction wedge

There are two common types of friction wedge in the suspension system of a three-piece bogie—the “constant damping” wedge and the variable damping wedge. A generic wagon–track dynamics interaction model has been developed to investigate the dynamic behavior of suspension systems with these two wedge types. The model differs from usual approaches in two aspects: (1) the mass of the wedge is considered in the model and, (2) the track is modeled as a flexible element with multiple degrees of freedom modeling sleepers, ballast and subgrade. The dynamic response characteristics of the two suspension-wedge systems are simulated, compared and discussed for different wedge friction conditions and track input frequencies.     

A Multiple-Criterion Model for Machine Scheduling

We consider a scheduling problem involving a single processor being utilized by two or more customers. Traditionally, such scenarios are modeled by assuming that each customer has the same criterion. In practice, this assumption may not hold. Instead of using a single criterion, we examine the implications of minimizing an aggregate scheduling objective function in which jobs belonging to different customers are evaluated based on their individual criteria. We examine three basic scheduling criteria: minimizing makespan, minimizing maximum lateness, and minimizing total weighted completion time. Although determining a minimum-cost schedule according to any one of these criteria is polynomially solvable, we demonstrate that when minimizing a mix of these criteria, the problem becomes NP-hard.     

Alloying with copper to reduce metal dusting of nickel

Copper is thought to be noncatalytic to carbon deposition from gas atmospheres, and owing to its extremely low solubility for carbon, inert to the metal dusting reaction. Thus, the addition of copper to nickel, which forms a near perfect solid solution, may be able to suppress or greatly retard the metal dusting of the alloy, without the need for a protective oxide scale on the surface. The dusting behaviour of Ni‐Cu alloys containing up to 50 wt% Cu, along with pure Cu, was investigated in a 68%CO‐31%H₂‐1%H₂O gas mixture (a_C: 19) at 680°C for up to 150 h. Surface analysis showed that two types of carbon deposits, graphite particle clusters and filaments, were observed on pure Ni and Ni‐Cu alloys with Cu contents of up to 5 wt%. Alloys with more than 10 wt% Cu showed very little coking, forming filaments only. SEM and TEM analyses revealed metal particles encapsulated by graphite shells within the graphite particle clusters, and metal particles at filament tips or embedded along their lengths. A kinetic investigation showed that alloy dusting rates decreased significantly with increasing copper levels up to 10 wt%. At copper concentrations of more than 20 wt%, the rate of metal dusting was negligible. Although pure copper is not catalytic to carbon formation, scattered carbon nanotubes were observed on its surface. The effect of copper on alloy dusting rates is attributed to a dilution effect.     

Modeling causal relations between academic and social competence and depression: a multitrait-multimethod longitudinal study of children

The authors obtained self-reports, peer nominations, teacher ratings, and parent reports of depression and social and academic competence on 490 3rd graders and 455 6th graders near the beginning and end of the school year. Confirmatory factor analysis and structural equation modeling revealed that (a) measures showed significant convergent and discriminant validity; (b) within-wave correlations between constructs were large and significant, although the depression-social competence correlation was larger than the depression-academic competence correlation; (c) the cross-wave stability of all constructs was remarkably high; and (d) social competence at Wave 1 predicted depression at Wave 2 for 6th graders after controlling for depression at Wave 1. Depression did not predict change in either academic or social competence over time. Implications for competence-based and failure-based models of child depression are discussed.     

High-dose proton pump inhibitor plus amoxycillin for the treatment or retreatment of Helicobacter pylori infection

BACKGROUND: The combination of 120 mg of omeprazole (40 mg t.d.s.) and amoxycillin has been reported to be effective for treating H. pylori infections. METHODS: Normal volunteers with H. pylori infection received high-dose omeprazole (40 mg t.d.s.) or lansoprazole (60 mg t.d.s.) plus amoxycillin 750 mg t.d.s. for 14 days. The studies were open label and not randomized as those receiving omeprazole plus amoxycillin had previously failed lower dose omeprazole (20 mg b.d.) plus amoxycillin therapy more than 6 months previously. Those receiving lansoprazole plus amoxycillin had not been previously treated. Four to 6 weeks after ending antimicrobial therapy, H. pylori status was determined by Genta stain of gastric mucosal biopsies. RESULTS: Forty-three volunteers entered the study and 41 completed it. The overall success with high-dose proton pump inhibitor plus amoxycillin was 34.9%. For the individual regimens the per-protocol results were 48% (95% CI = 28-69%) with lansoprazole and 12.5% (95% CI = 2-38%) with omeprazole. Compliance was > 95% for both regimens. Side-effects were experienced by four lansoprazole and three omeprazole subjects, and caused two omeprazole subjects to withdraw. Cure rates were similar among different races and ethnic groups, between men and women, and between smokers and non-smokers. The level of the pre-treatment urea breath test also did not predict outcome. CONCLUSION: High-dose proton pump inhibitor plus amoxycillin combinations for treatment of H. pylori infection yielded unacceptable results, as the 95% confidence intervals did not include an 80% cure rate. These combinations do not yield consistent results worldwide and cannot be recommended as primary therapy.