Sample sizes required to detect interactions between two binary fixed-effects in a mixed-effects linear regression model

Mixed-effects linear regression models have become more widely used for analysis of repeatedly measured outcomes in clinical trials over the past decade. There are formulae and tables for estimating sample sizes required to detect the main effects of treatment and the treatment by time interactions for those models. A formula is proposed to estimate the sample size required to detect an interaction between two binary variables in a factorial design with repeated measures of a continuous outcome. The formula is based, in part, on the fact that the variance of an interaction is fourfold that of the main effect. A simulation study examines the statistical power associated with the resulting sample sizes in a mixed-effects linear regression model with a random intercept. The simulation varies the magnitude (Δ) of the standardized main effects and interactions, the intraclass correlation coefficient (ρ), and the number (k) of repeated measures within-subject. The results of the simulation study verify that the sample size required to detect a 2×2 interaction in a mixed-effects linear regression model is fourfold that to detect a main effect of the same magnitude.     

Comparison of physical, chemical and cellular responses to nano- and micro-sized calcium silicate/poly(epsilon-caprolactone) bioactive composites.

In this study, we fabricated nano-sized calcium silicate/poly(epsilon-caprolactone) composite (n-CPC) and micro-sized calcium silicate/poly(epsilon-caprolactone) composite (m-CPC). The composition, mechanical properties, hydrophilicity and degradability of both n-CPC and m-CPC were determined, and in vitro bioactivity was evaluated by investigating apatite forming on their surfaces in simulated body fluid (SBF). In addition, cell responses to the two kinds of composites were comparably investigated. The results indicated that n-CPC has superior hydrophilicity, compressive strength and elastic modulus properties compared with m-CPC. Both n-CPC and m-CPC exhibited good in vitro bioactivity, with different morphologies of apatite formation on their surfaces. The apatite layer on n-CPC was more homogeneous and compact than on m-CPC, due to the elevated levels of calcium and silicon concentrations in SBF from n-CPC throughout the 14-day soaking period. Significantly higher levels of attachment and proliferation of MG63 cells were observed on n-CPC than on m-CPC, and significantly higher levels of alkaline phosphatase activity were observed in human mesenchymal stem cells (hMSCs) on n-CPC than on m-CPC after 7 days. Scanning electron microscopy observations revealed that hMSCs were in intimate contact with both n-CPC and m-CPC surfaces, and significantly cell adhesion, spread and growth were observed on n-CPC and m-CPC. These results indicated that both n-CPC and m-CPC have the ability to support cell attachment, growth, proliferation and differentiation, and also yield good bioactivity and biocompatibility.     

Development of a fouling monitor for safety-related heat exchangers

Periodic safety reviews (PSRs) are performed to verify and/or improve the safety of operating nuclear power plants. When the PSR of Gori Units 3/4 in South Korea was performed, a few safety-related heat exchangers were pointed out as components in need of an ageing management program. This study shares the motivation with the necessity of the ageing management program. We developed a condition monitoring methodology for identifying one of the ageing mechanisms in the safety-related heat exchangers and named it the fouling monitor. The fouling monitor is composed of (1) the model for determining the test fouling resistance and the projected design fouling resistance at a test condition, and (2) the monitoring and detection of their deviation. The mathematical model for determining the projected design fouling resistance at a test condition needs to be considered carefully because the heat exchanger, and particularly in this study, the letdown heat exchanger, is normally tested under operating conditions that differ considerably from the design conditions. This need was met by developing independent physical and empirical correction methods of which consistency is cross-checked. Either or both correction method(s) convert the design fouling resistance into a projected fouling resistance, which is finally comparable with the test fouling resistance. The monitoring and detection method tracks the deviation of the test fouling resistance and the projected fouling resistance. Considering the stochastic characteristics of fouling phenomena, we adopted the sequential probability ratio test to determine appropriate scheduling for cost- and safety-optimized maintenance of the heat exchanger.     

Microfluidic chip to produce temperature jumps for electrophysiology

We developed a microfluidic chip that provides rapid temperature changes and accurate temperature control of the perfusing solution to facilitate patch-clamp studies. The device consists of a fluid channel connected to an accessible reservoir for cell culture and patch-clamp measurements. A thin-film platinum heater was placed in the flow channel to generate rapid temperature change, and the temperature was monitored using a thin-film resistor. We constructed the thermal chip using SU-8 on a glass wafer to minimize the heat loss. The chip is capable of increasing the solution temperature from bath temperature (20 degrees C) to 80 degrees C at an optimum heating rate of 0.5 degrees C/ms. To demonstrate the ability of the thermal chip, we have conducted on-chip patch-clamp recordings of temperature-sensitive ion channels (TRPV1) transfected HEK293 cells. The heat-stimulated currents were observed using whole-cell and cell-attached patch configurations. The results demonstrated that the chip can provide rapid temperature jumps at the resolution of single-ion channels.     

Critical parameters of nylon and other fibres for spalling protection of high strength concrete in fire

This study investigated various types of fibre length, fibre diameter, fibre type and fibre content on the degree of spalling of concrete in fire. Four types of fibres, namely, polypropylene, polyvinyl alcohol, cellulose and nylon with various lengths and diameters were studied. Fibre contents ranged from 0.05 to 0.15% by volume of concrete. Fire tests were conducted according to the ISO 834 standard heating curve. Results showed that when comparing all the fibres under the same fibre content levels (% volume of concrete), the nylon fibre was the most effective in protecting concrete from spalling. This is because the diameter of the nylon fibres were significantly less than the other fibres, hence there were significantly more number of nylon fibres present for the same fibre content (% volume) in concrete. Analysis revealed, regardless of the amount of fibre, the type of fibre, diameter of and length of fibre, there is a strong relationship between the total number of fibres present per unit volume, length of fibres and the degree of spalling observed. Based on this relationship, the authors established a critical minimum for total number of fibres per unit volume for spalling protection in fire.     

Highly responsive sensor on a nanostructured surface via the self-assembly of a biomolecule with an evanescent wave technique

A self-assembled biomolecule was used to create a highly sensitive sensor surface for detecting toxic chemical species (polychlorinated biphenyls, PCBs). We fabricated the nanostructured sensor surface via the self-assembly of cytochrome c on a Au thin film. Surface plasmon resonance (SPR), an evanescent wave technique possessing maximum sensitivity on the surface and characterized by an exponential decay of sensitivity with distance from the surface, was utilized as the principle for signal transduction. When this sensor surface was used for the detection of PCB, even trace amounts of PCB (from 0.1 ppb to 8.0 ppb) in an aqueous solution were readily detectable.     

Synchrotron X-ray reflectivity study of high dielectric constant alumina thin films prepared by atomic layer deposition

High dielectric constant (high-k) gate dielectric alumina films were prepared with nanoscale thicknesses on p-type silicon substrates by atomic layer deposition (ALD) with alternating pulses of trimethyl aluminum, nitrogen, ozone and nitrogen, and some of them were further thermally annealed. These high-k gate dielectric films were characterized by synchrotron X-ray reflectivity (XR), and the XR data were quantitatively analyzed, providing the following structural parameters of each gate dielectric film: the surface roughness and interfacial roughness, the electron density profile, the number of layers, and the thickness of individual layers. These structural characteristics were then analyzed in detail by considering the ALD processing conditions and post-thermal annealing history.     

Decrease in work function of boron ion-implanted ZnO thin films

We have fabricated boron ion-implanted ZnO thin films by ion implantation into sputtered ZnO thin films on a glass substrate. An investigation of the effects of ion doses and activation time on the electrical and optical properties of the films has been made. The electrical sheet resistance and resistivity of the implanted films are observed to increase with increasing rapid thermal annealing (RTA) time, while decreasing as the ion dose increases. Without any RTA process, the variation of the carrier density is insensitive to the ion dose. With the RTA process, however, the carrier density of the implanted films increases and approaches that of the un-implanted ZnO film as the ion dose increases. On the other hand, the carrier mobility is shown to decrease with increasing ion doses when no RTA process is applied. With the RTA process, however, there is almost no change in the mobility. We have achieved the optical transmittance as high as 87% within the visible wavelength range up to 800 nm. It is also demonstrated that the work function can be engineered by changing the ion dose during the ion implantation process. We have found that the work function decreases as the ion dose increases.     

Localization algorithm using a virtual label for a mobile robot in indoor and outdoor environments

Scanning laser range sensors provide range data consisting of a set of point measurements. The laser sensor URG-04LX has a distance range of approximately 0.02–4 m and a scanning angle range of 240°. Usually, such an image range is acquired from one viewpoint by “moving” the laser beam using rotating mirrors/prisms. The orientation of the laser beam can easily be measured and converted into the coordinates of the image. This article conducts localization using virtual labels with data about distances in the environment obtained from 2D distance laser sensors. This method puts virtual labels on special features and points which are along the mobile robot’s path. The current location is calculated by combining the virtual label and the range image of the laser range finder.