Hydroxyapatite‐barium titanate piezocomposites with enhanced electrical properties

The present work aims to obtain Hydroxyapatite (HA) ‐ Barium Titanate (BT) piezocomposites with improved electrical properties by retaining OH^? ions and tuning BT grain size. Dense piezocomposites of HA‐BT were obtained, using single step Spark Plasma Sintering. The presence of OH^? ions in the sintered piezocomposites of HA‐BT was confirmed by thermal characterization and Fourier transform infrared transmittance. No decomposition/interaction between HA and BT phases were observed in the complete range of temperature studied. The dielectric and pyroelectric properties were studied as a function of temperature (100 K to 450 K) and frequency (100 Hz to 2 MHz). The influence of the ferroelectric grain size (300 and 500 nm) on the electrical properties of HA‐BT has been analyzed. The dielectric permittivity of HA‐BT ceramics can be enhanced with appropriate ferroelectric grain size and volume fraction of BT (<80%).     

Dietary Alkaloid Sequestration in a Poison Frog: An Experimental Test of Alkaloid Uptake in Melanophryniscus stelzneri (Bufonidae)

Several lineages of brightly colored anurans independently evolved the ability to secrete alkaloid-containing defensive chemicals from granular glands in the skin. These species, collectively referred to as ‘poison frogs,’ form a polyphyletic assemblage that includes some species of Dendrobatidae, Mantellidae, Myobatrachidae, Bufonidae, and Eleutherodactylidae. The ability to sequester alkaloids from dietary arthropods has been demonstrated experimentally in most poison frog lineages but not in bufonid or eleutherodactylid poison frogs. As with other poison frogs, species of the genus Melanophryniscus (Bufonidae) consume large numbers of mites and ants, suggesting they might also sequester defensive alkaloids from dietary sources. To test this hypothesis, fruit flies dusted with alkaloid/nutritional supplement powder were fed to individual Melanophryniscus stelzneri in two experiments. In the first experiment, the alkaloids 5,8-disubstituted indolizidine 235B' and decahydroquinoline were administered to three individuals for 104 days. In the second experiment, the alkaloids 3,5-disubstituted indolizidine 239Q and decahydroquinoline were given to three frogs for 153 days. Control frogs were fed fruit flies dusted only with nutritional supplement. Gas chromatography/mass spectrometry analyses revealed that skin secretions of all experimental frogs contained alkaloids, whereas those of all control frogs lacked alkaloids. Uptake of decahydroquinoline was greater than uptake of 5,8-disubstituted indolizidine, and uptake of 3,5-disubstituted indolizidine was greater than uptake of decahydroquinoline, suggesting greater uptake efficiency of certain alkaloids. Frogs in the second experiment accumulated a greater amount of alkaloid, which corresponds to the longer duration and greater number of alkaloid-dusted fruit flies that were consumed. These findings provide the first experimental evidence that bufonid poison frogs sequester alkaloid-based defenses from dietary sources.     

Activity density map visualization and dissimilarity comparison for eldercare monitoring

In this paper, we present a methodology for analyzing passive infrared motion sensor data logged in the homes of seniors. The objective is to capture activity patterns that represent different health conditions. Recognizing changes in the activity patterns can then be used to provide early detection of health changes. A visualization of motion sensor data is introduced in the form of a density map that uses different colors to show varying levels of activity. For evaluating the activity density level accurately, time away from home is determined first using a system of fuzzy rules. In addition, a dissimilarity between two density maps is computed using texture features for automatically determining changes in activity patterns, which may indicate a health problem. The activity density maps are being used in an aging in place senior housing community to aid clinicians in early illness detection. Three case studies of elderly residents are included to illustrate how the density map and dissimilarity measure can be used to track general activity level and daily patterns over time, showing changes in physical, cognitive, and mental health.     

Infants' meaning-making and the development of mental health problems.

We argue that infant meaning-making processes are a central mechanism governing both typical and pathological outcomes. Infants, as open dynamic systems, must constantly garner information to increase their complexity and coherence. They fulfill this demand by making nonverbal “meaning”—affects, movements, representations—about themselves in relation to the world and themselves into a “biopsychosocial state of consciousness,” which shapes their ongoing engagement with the world. We focus on the operation of the infant–adult communication system, a dyadic, mutually regulated system that scaffolds infants' engagement with the world of people, things, and themselves, and consequently their meaning-making. We argue that infant mental health problems emerge when the meanings infants make in the moment, which increase their complexity and coherence and may be adaptive in the short run, selectively limit their subsequent engagement with the world and, in turn, the growth of their state of consciousness in the long run. When chronic and iterative, these altered meanings can interfere with infants' successful development and heighten their vulnerability to pathological outcomes. Cultural variations in meaning-making and implications for clinical practice are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reference Resolution Challenges for Intelligent Agents: The Need for Knowledge

This paper presents a vision of how language-endowed, next-generation intelligent agents might resolve—that is, fully interpret—references to objects and events in language input. It describes some of the more difficult reference phenomena that are not being sufficiently treated by practical systems and suggests what kinds of knowledge must be available to intelligent agents to enable them to reach human competence in reference resolution.     

STRESS-STRAIN RELATIONS IN CERAMIC MATERIALS*

The electric strain gauge was used to study the deformation of several types of ceramic materials under stress. It was found that they behaved as elastic materials. The hard-fired materials exhibit straight-line deformation to failure while the softer-fired have a proportional elastic limit beyond which the stress-strain curve deviates from a straight line. Data indicate that engineering formulas based on elastic materials may be applied to ceramic materials.     

Nano-scale friction of polystyrene in air and in vacuum

Using atomic force microscopy (AFM), we measured friction between an AFM tip and a polystyrene surface at 25 °C, as a function of the sliding velocity and the applied normal load, both in air and under vacuum conditions. The objective was to analyze the influence of humidity on the frictional behavior of polystyrene. Our experimental results as a function of sliding velocity revealed a logarithmic increase of the friction force in air whereas a logarithmic decrease of this force is found in vacuum. Our comparative results unveil that two different dissipation mechanisms are dominating the frictional behavior of polystyrene in air and in vacuum. We propose a tentative explanation.     

重力下水道中混凝土的微生物诱导腐蚀及防护涂层(英文)

Microbiologically induced corrosion of concrete(MICC) and its protective coatings has a high economic impact on sewer maintenance and rehabilitation.A better understanding of the micro-organisms and the biogenic acids that are generated in the sewer is essential in controlling the corrosion of concrete pipes and protective coatings.The role of succession of micro-organisms growth in the corrosion of concrete and protective coatings was evaluated in this study.Examination of various sewer pipe materials exhibiting various extents of degradation,including concrete,cement based and epoxy based coating revealed the presence of both organic and biogenic sulphuric acids.This reflects the activity of fungi and the thiobacilli strains.Organism growth and metabolism were strongly related to the substrate pH.Fungi were found to grow and metabolise organic acids at pH from 2.0-8.0.Whilst the thiobacilli strains grew and generated sulphuric acids at pH below 3.0.The successive growth of the organisms provides an important bearing in developing improved strategies to better manage sewers.     

New epoxy thermosets obtained from diglycidylether of bisphenol a and modified hyperbranched polyesters with long aliphatic chains cured by diisocyanates

Hyperbranched polyesters modified with long aliphatic chains with vinyl or epoxy groups as chain ends were synthesized and added as modifiers to diglycidyl ether of bisphenol A/toluene‐2,4‐diisocyanate mixtures in the presence of benzyldimethylamine as catalyst. The influence of the addition of these modifiers on the curing was investigated by thermal analysis and infrared spectroscopy. The materials obtained were investigated by electron microscopy and some mechanical characteristics were determined by nanoindentation tests. Epoxy terminated hyperbranched led to homogeneous materials with high crosslinking densities, whereas vinyl terminated hyperbranched produced phase separated morphologies. The materials showing phase separation presented a tough fracture, whereas the homogeneous materials obtained with epoxidated hyperbranched showed increased brittleness on increasing the proportion of modifier. On increasing the proportion of vinyl terminated hyperbranched in the thermosets, Young's modulus and hardness decreased but the addition of epoxy terminated hyperbranched did not influence these parameters. The addition of vinylic hyperbranched to the formulations produced a decrease in the curing shrinkage, whereas the epoxidic hyperbranched did not. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Variation of Band Gap and Lattice Parameters of β−(AlxGa1−x)2O3 Powder Produced by Solution Combustion Synthesis

Single‐phase monoclinic aluminum–gallium oxide powders, β?(Al_xGa_1?x)₂O₃, have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. α?(Al_xGa_1?x)₂O₃ is observed for x = 1, with mixed α + β for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), respectively, and are compared with a first‐principles density‐functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.