Hydroxyapatite as a filler for dental composite materials: mechanical properties and in vitro bioactivity of composites

Hydroxyapatite (HAp) powder was treated with -methacryloxypropyltrimethoxy-silane (-MPS) using standard techniques in both non-polar and polar systems. Infrared spectra (DRIFT) and thermogravimetric analysis (TGA) confirmed the presence of -MPS on the surface of the HAp filler particles. Series of experimental composites consisting of bisphenol-a-glycidyl methacrylate (BisGMA) based resin and untreated or treated HAp filler were produced to determine the mechanical properties and in vitro bioactivity. The incorporation of HAp filler into the BisGMA base resin had an enhancing effect on the flexural strength and Young's modulus of the base resin, the latter being increased by a factor of three. The mechanical properties of the filled resin were not affected by the surface treatment of the HAp, but filler loading was found to have a significant effect on Young's modulus. Higher proportions of silane-treated HAp of smaller particle size could be incorporated in the monomer phase giving rise to composites of higher stiffness. Examination of the fracture surfaces showed that the silanized HAp particles maintained better contact with the polymer matrix. In vitro study revealed that the composites incorporating silanized HAp formed a compact and continuous calcium phosphate layer on their surface after 4 weeks immersion in a simulated body fluid (SBF). © 2001 Kluwer Academic Publishers     

Joint Detection and Tracking of Time-Varying Harmonic Components: A Flexible Bayesian Approach

This paper addresses the joint estimation and detection of time-varying harmonic components in audio signals. We follow a flexible viewpoint, where several frequency/amplitude trajectories are tracked in spectrogram using particle filtering. The core idea is that each harmonic component (composed of a fundamental partial together with several overtone partials) is considered a target. Tracking requires to define a state-space model with state transition and measurement equations. Particle filtering algorithms rely on a so-called sequential importance distribution, and we show that it can be built on previous multipitch estimation algorithms, so as to yield an even more efficient estimation procedure with established convergence properties. Moreover, as our model captures all the harmonic model information, it actually separates the harmonic sources. Simulations on synthetic and real music data show the interest of our approach     

Annotating mobile phone location data with activity purposes using machine learning algorithms

Individual human travel patterns captured by mobile phone data have been quantitatively characterized by mathematical models, but the underlying activities which initiate the movement are still in a less-explored stage. As a result of the nature of how activity and related travel decisions are made in daily life, human activity-travel behavior exhibits a high degree of spatial and temporal regularities as well as sequential ordering. In this study, we investigate to what extent the behavioral routines could reveal the activities being performed at mobile phone call locations that are captured when users initiate or receive a voice call or message.Our exploration consists of four steps. First, we define a set of comprehensive temporal variables characterizing each call location. Feature selection techniques are then applied to choose the most effective variables in the second step. Next, a set of state-of-the-art machine learning algorithms including Support Vector Machines, Logistic Regression, Decision Trees and Random Forests are employed to build classification models. Alongside, an ensemble of the results of the above models is also tested. Finally, the inference performance is further enhanced by a post-processing algorithm.Using data collected from natural mobile phone communication patterns of 80 users over a period of more than one year, we evaluated our approach via a set of extensive experiments. Based on the ensemble of the models, we achieved prediction accuracy of 69.7%. Furthermore, using the post processing algorithm, the performance obtained a 7.6% improvement. The experiment results demonstrate the potential to annotate mobile phone locations based on the integration of data mining techniques with the characteristics of underlying activity-travel behavior, contributing towards the semantic comprehension and further application of the massive data.     

In-situ studies of gas phase composition and anode surface temperature through a model DIR-SOFC steam–methane reformer at 973.15 K

A comparative study into the effects of total volume flow rate, methane ‘residency time’, methane volume flow rate, and steam-to-carbon ratio on the steam–methane reforming process was performed in a model Direct Internal Reforming SOFC (DIR-SOFC) reformer operating in steady state at a nominal temperature of 973 K. The spatial distributions of major gas species (CH₄, H₂O, CO, CO₂, and H₂) over the reformer surface were measured in-situ using Vibrational Raman Spectroscopy. Surface temperature measurements were recorded using IR thermometry. The effects of varying the intake mole fractions of methane and water were considered. The results of this work have demonstrated a strong positive correlation between the intake mole fraction of methane and the rate of the steam–methane reformation reaction. A weak negative correlation between the intake mole fraction of water and the rate of the reformation reaction was also shown.     

Greater rate of decline in maximal aerobic capacity with age in physically active vs. sedentary healthy women

Using a meta-analytic approach, we recently reported that the rate of decline in maximal oxygen uptake (VO2 max) with age in healthy women is greatest in the most physically active and smallest in the least active when expressed in milliliters per kilogram per minute per decade. We tested this hypothesis prospectively under well-controlled laboratory conditions by studying 156 healthy, nonobese women (age 20-75 yr): 84 endurance-trained runners (ET) and 72 sedentary subjects (S). ET were matched across the age range for age-adjusted 10-km running performance. Body mass was positively related with age in S but not in ET. Fat-free mass was not different with age in ET or S. Maximal respiratory exchange ratio and rating of perceived exertion were similar across age in ET and S, suggesting equivalent voluntary maximal efforts. There was a significant but modest decline in running mileage, frequency, and speed with advancing age in ET. VO2 max (ml . kg-1 . min-1) was inversely related to age (P < 0.001) in ET (r = -0.82) and S (r = -0.71) and was higher at any age in ET. Consistent with our meta-analysic findings, the absolute rate of decline in VO2 max was greater in ET (-5.7 ml . kg-1 . min-1 . decade-1) compared with S (-3.2 ml . kg-1 . min-1 . decade-1; P < 0. 01), but the relative (%) rate of decline was similar (-9.7 vs -9. 1%/decade; not significant). The greater absolute rate of decline in VO2 max in ET compared with S was not associated with a greater rate of decline in maximal heart rate (-5.6 vs. -6.2 beats . min-1 . decade-1), nor was it related to training factors. The present cross-sectional findings provide additional evidence that the absolute, but not the relative, rate of decline in maximal aerobic capacity with age may be greater in highly physically active women compared with their sedentary healthy peers. This difference does not appear to be related to age-associated changes in maximal heart rate, body composition, or training factors.     

Interannual variability of solar energy generation in Australia

Australia has an abundant solar energy resource that is likely to be used for energy generation on a large scale. Variable sources of electricity generation require knowledge of the nature of their variability at all time scales. This study examines the effect that El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) have on solar radiation in Australia, in order to establish the role for seasonal forecasting of solar power. Calendar years are classified into their ENSO state using a sea surface temperature index. The ERA-Interim and NCEP reanalysis products are then used to estimate the effect of ENSO on global horizontal solar irradiance over the continent. A bootstrap technique is used to obtain confidence regions for the effect in both winter and summer. The main impact of ENSO occurs during winter over a large part of eastern Australia. Little impact was observed over the continent during summer. A similar analysis is conducted for the Indian Ocean Dipole (IOD) to ensure that the observed ENSO effect is not a manifestation of the IOD. This study indicates that the ENSO phenomenon may account for solar energy changes of more than 10% in some locations on a seasonal basis. We show that the solar radiation analysis is directly applicable to solar energy yield. Knowledge of this variability may influence the location of large solar generation plants. Also, there is a potential to predict solar energy a few months ahead by means of seasonal forecasting systems, which would help to assist with planning for electricity grid.     

Incorporation of organic liquids into geopolymer materials - A review of processing,properties and applications

Geopolymers, composed of an amorphous three-dimensional inorganic network and synthesized by the activation of a solid alumino-silicate precursor with an alkaline activating solution, have attracted increasing attention because of their environmental benefits and favorable characteristics. This review deals with the development of organic/inorganic composite materials made by adding organic liquids into inorganic geopolymer matrices. Firstly, the incorporation processing approaches are presented and are divided into three categories: (i) Direct incorporation, (ii) Pre-emulsification (iii) Solid impregnation. Their main advantages and drawbacks are discussed in relation to the aimed properties. Secondly, this review highlights that geopolymers are low-cost candidates allowing technologically significant applications, through the incorporation of various organic liquids. Aside from the well-studied immobilization of industrial waste streams commonly known as stabilization/solidification (S/S), the development of highly porous geopolymer foams and the design of reinforced organic/inorganic composite matrices are being notably investigated. This review aims at summarizing the main published results, and fostering further investigations into innovative uses of organic liquids incorporated into geopolymers for a wide range of applications.     

Metal Nanocatalyst Sintering Interrogated at Complementary Length Scales

Metal nanoparticle (NP) sintering is a prime cause of catalyst degradation, limiting its economic lifetime and viability. To date, sintering phenomena are interrogated either at the bulk scale to probe averaged NP properties or at the level of individual NPs to visualize atomic motion. Yet, “mesoscale” strategies which bridge these worlds can chart NP populations at intermediate length scales but remain elusive due to characterization challenges. Here, a multi-pronged approach is developed to provide complementary information on Pt NP sintering covering multiple length scales. High-resolution scanning electron microscopy (HRSEM) and Monte Carlo simulation show that the size evolution of individual NPs depends on the number of coalescence events they undergo during their lifetime. In its turn, the probability of coalescence is strongly dependent on the NP's mesoscale environment, where local population heterogeneities generate NP-rich “hotspots” and NP-free zones during sintering. Surprisingly, advanced in situ synchrotron X-ray diffraction shows that not all NPs within the small NP sub-population are equally prone to sintering, depending on their crystallographic orientation on the support surface. The demonstrated approach shows that mesoscale heterogeneities in the NP population drive sintering and mitigation strategies demand their maximal elimination via advanced catalyst synthesis strategies.