Effect of processing induced particle alignment on the fracture toughness and fracture behavior of multiphase dental ceramics

Objective. To investigate the processing induced particle alignment on fracture behavior of four multiphase dental ceramics (one porcelain, two glass-ceramics and a glass-infiltrated-alumina composite). Methods. Disks (empty set12mm x 1.1 mm-thick) and bars (3 mm x 4 mm x 20 mm) of each material were processed according to manufacturer instructions, machined and polished. Fracture toughness (K(IC)) was determined by the indentation strength method using 3-point bending and biaxial flexure fixtures for the fracture of bars and disks, respectively. Microstructural and fractographic analyses were performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results. The isotropic microstructure of the porcelain and the leucite-based glass-ceramic resulted in similar fracture toughness values regardless of the specimen geometry. On the other hand, materials containing second-phase particles with high aspect ratio (lithium disilicate glass-ceramic and glass-infiltrated-alumina composite) showed lower fracture toughness for disk specimens compared to bars. For the lithium disilicate glass-ceramic disks, it was demonstrated that the occurrence of particle alignment during the heat-pressing procedure resulted in an unfavorable pattern that created weak microstructural paths during the biaxial test. For the glass-infiltrated-alumina composite, the microstructural analysis showed that the large alumina platelets tended to align their large surfaces perpendicularly to the direction of particle deposition during slip casting of green preforms. Significance. The fracture toughness of dental ceramics with anisotropic microstructure should be determined by means of biaxial testing, since it results in lower values. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Functional mapping of the periaqueductal gray matter involved in organizing tonic immobility behavior in guinea pigs

Tonic immobility behavior (TI) is an innate response characterized by profound motor inhibition that is exhibited by prey when physical contact with a predator is prolonged and the situation inescapable. The periaqueductal gray matter (PAG) is intimately associated with the somatic and autonomic components of defensive reactions. This study investigated whether the TI response was able to recruit specific functional columns of the PAG by examining c-fos immunolocalization in guinea pigs. In the TI group, the innate response was invoked in animals through inversion and physical contention for at least 15 min. In the control group, the animals were physically manipulated only. Our results demonstrate that the defensive behavior of TI is capable of promoting the expression of Fos protein in different areas of the PAG, with higher levels of staining in the ventrolateral (vI) and lateral (I) columns. In addition, our results demonstrate increased Fos immunoreactivity (FOS-IR) in the dorsal raphe nucleus, the Edinger-Westphal nucleus, the cuneiform nucleus and the superior colliculus. In contrast, there were no significant alterations in the number of FOS-IR cells in the inferior colliculus or the oculomotor nucleus. Analysis of the results suggests that neuronal activation after the TI response differs by functional column of the PAG. (C) 2010 Elsevier B.V. All rights reserved.

GABAergic antagonist blocks the reduction of tonic immobility behavior induced by activation of 5-HT(2) receptors in the basolateral nucleus of the amygdala in guinea pigs

Tonic immobility (TI) is a temporary state of profound motor inhibition induced by situations that generate intense fear, with the objective of protecting an animal from attacks by predators. A preliminary study by our group demonstrated that microinjection into the basolateral nucleus of the amygdala (BLA) of an agonist to 5-HT(1A) and 5-HT(2) receptors promoted a decrease in TI duration. In the current study, the effects of GABAergic stimulation of the BLA and the possible interaction between GABA(A) and 5-HT(2) receptors on TI modulation were investigated. Observation revealed that GABAergic agonist muscimol (0.26 nmol) reduced the duration of TI episodes, while microinjection of the GABAergic antagonist bicuculline (1 nmol) increased TI duration. Additionally, microinjection of 5-HT(2) agonist receptors (alpha-methyl-5-HT, 0.32 nmol) into the BLA decreased TI duration, an effect reversed by pretreatment with bicuculline (at the dose that had no effect per se, 0.2 nmol). Moreover, the activation of GABA(A) and 5-HT(2) receptors in the BLA did not alter the spontaneous motor activity in the open field test. These experiments demonstrated that the activation of GABA(A) and 5-HT(2) receptors of the BLA possibly produce a reduction in unconditioned fear that decreases the TI duration in guinea pigs, but this is not due to increased spontaneous motor activity, which could affect a TI episode nonspecifically. Furthermore, these results suggest an interaction between GABAergic and serotoninergic mechanisms mediated by GABA(A) and 5-HT(2) receptors. In addition, the GABAergic circuit of the BLA presents a tonic inhibitory influence on TI duration. (C) 2009 Elsevier Inc. All rights reserved.

The effect of resource aggregation at different scales: Optimal foraging behavior of Cotesia rubecula

Resources can be aggregated both within and between patches. In this article, we examine how aggregation at these different scales influences the behavior and performance of foragers. We developed an optimal foraging model of the foraging behavior of the parasitoid wasp Cotesia rubecula parasitizing the larvae of the cabbage butterfly Pieris rapae. The optimal behavior was found using stochastic dynamic programming. The most interesting and novel result is that the effect of resource aggregation within and between patches depends on the degree of aggregation both within and between patches as well as on the local host density in the occupied patch, but lifetime reproductive success depends only on aggregation within patches. Our findings have profound implications for the way in which we measure heterogeneity at different scales and model the response of organisms to spatial heterogeneity.

Natural selection and quantitative genetics of life-history traits in Western women: A twin study

Whether contemporary human populations are still evolving as a result of natural selection has been hotly debated. For natural selection to cause evolutionary change in a trait, variation in the trait must be correlated with fitness and be genetically heritable and there must be no genetic constraints to evolution. These conditions have rarely been tested in human populations. In this study, data from a large twin cohort were used to assess whether selection Will cause a change among women in contemporary Western population for three life-history traits: age at menarche, age at first reproduction, and age at menopause. We control for temporal variation in fecundity (the baby boom phenomenon) and differences between women in educational background and religious affiliation. University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population. We also estimate substantial heritable variation in fitness itself, with approximately 39% of the variance attributable to additive genetic effects, the remainder consisting of unique environmental effects and small effects from education and religion. We discuss mechanisms that could be maintaining such a high heritability for fitness. Most likely is that selection is now acting on different traits from which it did in pre-industrial human populations.

Thermal characterization of copolymers obtained by radiation grafting of styrene onto poly(tetrafluoroethyleneperfluoropropylvinylether) substrates: thermal decomposition, melting behavior and low-temperature transitions

Differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) have been used to study the thermal decomposition, the melting behavior and low-temperature transitions of copolymers obtained by radiation-induced grafting of styrene onto poly (tetrafluoroethylene- perfluoropropylvinylether) (PFA) substrates. PFA with different contents of perfluoropropylvinylether (PPVE) as a comonomer have been investigated. A two step degradation pattern was observed from TGA thermograms of all the grafted copolymers, which was attributed to degradation of PSTY followed by the degradation of the PFA backbone at higher temperature. One broad melting peak can be identified for all copolymers, which has two components in the samples with higher PPVE content. The melting peak, crystal-crystal transition and the degree of crystallinity of the grafted copolymers increases with radiation grafting up to 50 kGy, followed by a decrease at higher doses. No such decrease was observed in the ungrafted PFA samples after irradiation. This indicated that the changes in the heats of transitions and crystallinity at low doses are due to the radiation effects on the microstructure of PFA (chain scission), whereas at higher doses the grafted PSTY is the driving force behind these changes. (C) 2001 Elsevier Science Ltd. All rights reserved.

(Book review) Neuropsychotherapy and Community Integration: Brain Illness, Emotions, and Behavior. T. Judd. 1999. New York: Kluwer Academic/Plenum Publishers

As individuals gain expertise in a chosen field they can begin to conceptualize how what they know can be applied more broadly, to new populations and situations, or to increase desirable outcomes. Judd's book does just this. It takes our current understanding of the etiology, course, and sequelae of brain injuries, combines this with established psychotherapy and rehabilitation techniques, and expands these into a cogent model of what Judd calls “neuropsychotherapy.” Simply put, neuropsychotherapy attempts to address the cognitive, emotional and behavioral changes in brain-injured persons, changes that may go undiagnosed, misdiagnosed, or untreated.

A proposed maceral index to predict combustion behavior of coal

To predict the combustion performance in pulverized coal-fired boilers, this paper examines existing indices and develops a maceral index (MI). These indices were compared with the data of 68 coals and blends in a range of the mean vitrinite reflectance from 0.25 to 1.63. The results showed that the fuel ratio and the mean vitrinite reflectance could qualitatively indicate the burnout of the coals and blends. The new MI, MI = L + V/R-2/I-1.25(HV/30)(2.5), provides a useful correlation for the burnout of the coals and blends. The correlation coefficient (I-) is 0.982 for the EER data, and 0.808 for the ACIRL data. The MI also has potential to correlate ignition and flame stability of the coals and blends. The MI predicts the burnout better than the other indices. (C) 2001 Elsevier Science Ltd. All rights reserved.

Sexual recombination in Phytophthora cinnamomi in vitro and aggressiveness of single-oospore progeny to Eucalyptus

Fifty single oospore progeny were established from an in vitro mating of A1 and A2 mating type isolates of Phytophthora cinnamomi from South Africa. Forty-nine progeny were identified as F-1 hybrids using seven random amplified polymorphic DNA (RAPD) primers, and one was a selfed isolate of the A1 mating type parent. Among the hybrid progeny, 24 and 25 were A1 and A2 mating type, respectively. Aggressiveness of progeny and parental isolates was assessed on 1-year-old seedlings of Eucalyptus smithii. The mean aggressiveness of hybrid oosporic isolates, expressed as lesion length, was significantly (P = 0.0001) lower than that of the parental isolates. No significant difference in aggressiveness of A1 and A2 mating type F-1 hybrid isolates was observed. This is the first report demonstrating sexual recombination in vitro in P. cinnamomi.

Genetic monogamy in the absence of paternity guards: the Capricorn silvereye, Zosterops lateralis chlorocephalus, on Heron Island

We investigated the genetic mating system of a socially monogamous passerine bird, the Capricorn silvereye Zosterops lateralis chlorocephalus, on an island of the Great Barrier Reef. There were no cases of extrapair paternity (EPP) among 122 offspring from 53 broods detectable by minisatellite or microsatellite DNA fingerprinting. Behavioral observations of paired birds showed that this was not a consequence of efficacious paternity guards and that females did not engage in extrapair copulation (EPC). Frequency of intrapair copulations was also low, with only 14 cases observed during 199 hours of observations of the 11 focal pairs in the fertile periods of females, and this was consistent with anatomical features of the cloacal protuberance in males. In this population, young birds form life-time pair bonds soon after gaining independence but females are obviously not attempting EPC possibly to redress this early mate choice. This is despite the fact that they breed in high density with a synchronous start and asynchronous spread of laying in a protracted season and males do not positively exhibit mate guarding behavior when females are fertile. Our results support high fidelity of socially monogamous birds on islands and are consistent with the hypothesis that sexual selection is reduced where genetic variation in fitness is limited.