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Relative Density (relative + density)
Selected AbstractsFabrication of (Ca1,xLax)MnO3 Ceramics with a High Relative Density and their Power FactorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Hideki Taguchi Perovskite-type (Ca1,xLax)MnO3 powders were synthesized using a Pechini-type polymerized complex route, and (Ca1,x Lax)MnO3 ceramics with a high relative density (85.6%,98.5%) were fabricated using a planetary mill and cold-isostatic pressing (CIP) in order to improve the electrical and thermoelectric properties. The electrical conductivity (,) was independent of both x and the temperature, and the relationship between log ,T vs. 1000/T was linear. The Seebeck coefficient (S) was negative, and the absolute value of the Seebeck coefficient increased with temperature and decreased with increases of x. The highest value of the power factor (S2,) was 3,4 × 10,4 W/(K2·m) for the (Ca0.96La0.04)MnO3 ceramic. [source] Synthesis of Dense, High-Defect-Concentration B4C through Mechanical Activation and Field-Assisted CombustionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004E. M. Heian Dense fine-grained B4C was synthesized by the spark plasma sintering (SPS) method using mechanically activated elemental powders. Relative densities of up to 95% were achieved. When characterized by X-ray line broadening methods, the grains of the resulting product were determined to be nanometric in scale. However, transmission electron microscopy (TEM) observations showed the product to be composed of a mixture of fine (nanometric) crystallites and grains in the micrometer range. The TEM images showed a highly defective structure containing a high density of twins. Their presence is the reason for the discrepancy between the X-ray and TEM results. [source] Synthesis and Properties of Porous Single-Phase ,,-SiAlON CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2002Jian-Feng Yang Single-phase ,,-SiAlON (Si6,zAlzOzN8,z, z= 0,4.2) ceramics with porous structure have been prepared by pressureless sintering of powder mixtures of á-Si3N4, AlN, and Al2O3 of the SiAlON compositions. A solution of AlN and Al2O3 into Si3N4 resulted in the ,,-SiAlON, and full densification was prohibited because no other sintering additives were used. Relative densities ranging from 50%,90% were adjusted with the z -value and sintering temperature. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicated that single-phase ,,-SiAlON free from a grain boundary glassy phase could be obtained. Both grain and pore sizes increased with increasing z -value. Low z -value resulted in a relatively high flexural strength. [source] Biodiversity and biocontrol: emergent impacts of a multi-enemy assemblage on pest suppression and crop yield in an agroecosystemECOLOGY LETTERS, Issue 9 2003Bradley J. Cardinale Abstract The suppression of agricultural pests has often been proposed as an important service of natural enemy diversity, but few experiments have tested this assertion. In this study we present empirical evidence that increasing the richness of a particular guild of natural enemies can reduce the density of a widespread group of herbivorous pests and, in turn, increase the yield of an economically important crop. We performed an experiment in large field enclosures where we manipulated the presence/absence of three of the most important natural enemies (the coccinellid beetle Harmonia axyridis, the damsel bug Nabis sp., and the parasitic wasp Aphidius ervi) of pea aphids (Acyrthosiphon pisum) that feed on alfalfa (Medicago sativa). When all three enemy species were together, the population density of the pea aphid was suppressed more than could be predicted from the summed impact of each enemy species alone. As crop yield was negatively related to pea aphid density, there was a concomitant non-additive increase in the production of alfalfa in enclosures containing the more diverse enemy guild. This trophic cascade appeared to be influenced by an indirect interaction involving a second herbivore inhabiting the system , the cowpea aphid, Aphis craccivora. Data suggest that high relative densities of cowpea aphids inhibited parasitism of pea aphids by the specialist parasitoid, A. ervi. Therefore, when natural enemies were together and densities of cowpea aphids were reduced by generalist predators, parasitism of pea aphids increased. This interaction modification is similar to other types of indirect interactions among enemy species (e.g. predator,predator facilitation) that can enhance the suppression of agricultural pests. Results of our study, and those of others performed in agroecosystems, complement the broader debate over how biodiversity influences ecosystem functioning by specifically focusing on systems that produce goods of immediate relevance to human society. [source] Heat Transfer in Polypropylene-Based Foams Produced Using Different Foaming Processes,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo Antunes This paper presents the characterization of the cellular structure and thermal conduction behaviour of polypropylene foams produced using different foaming processes, with the aim of selecting the best possible PP foam thermal insulator. Thermal conductivity results have shown that the global heat transfer behaviour is controlled by the relative density. For relative densities higher than 0.2, thermal conductivity differences were insignificant, the data being predicted by the mixture's rule and Russell's model. In the low density range, all of the proposed models underestimated the overall conductivity, the effect of the processing method being more significant, slight differences being observed between foams produced by extrusion and those produced by gas dissolution with higher cell sizes and anisotropies. Foams with finer cellular structures showed to be better insulating materials. [source] The stress,life fatigue behaviour of aluminium alloy foamsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000McCullough The tension,tension and compression,compression nominal stress versus fatigue life responses of Alulight closed cell aluminium alloy foams have been measured for the compositions Al,1Mg,0.6Si and Al,1Mg,10Si (wt %), and for relative densities in the range 0.1,0.4. The fatigue strength of each foam increases with the relative density and with the mean applied stress, and is greater for the transverse orientation than for the longitudinal orientation. Under both tension,tension and compression,compression loading the dominant cyclic deformation mode appears to be material ratchetting; consequently, the fatigue life is highly sensitive to the magnitude of the applied stress. A micromechanical model is given to predict the dependence of life upon stress level and relative density. Panels containing a central hole were found to be notch insensitive for both tension,tension and compression,compression fatigue loading: the net-section strength equals the unnotched strength. [source] Effects of floods versus low flows on invertebrates in a New Zealand gravel-bed riverFRESHWATER BIOLOGY, Issue 12 2006ALASTAIR M. SUREN Summary 1. Floods and low flows are hydrological events that influence river ecosystems, but few studies have compared their relative importance in structuring invertebrate communities. Invertebrates were sampled in riffles and runs at eight sites along 40 km of a New Zealand gravel-bed river every 1,3 months over 2.5 years, during which time a number of large flood and low flow events occurred. Flows were high in winter and spring, and low in summer and autumn. Four flow-related variables were calculated from hydrological data: flow on the day of sampling (Qsample), maximum and minimum flow between successive samples (Qmax and Qmin, respectively), and the number of days since the last bed-moving flood (Ndays). 2. The invertebrate community was summarised by relative densities of the 19 most abundant taxa and four biotic metrics [total abundance, taxon richness, the number of Ephemeroptera, Plecoptera and Trichoptera taxa (i.e. EPT richness), and per cent EPT]. Invertebrate density fluctuated greatly, and was high in summer and autumn, and low during winter and spring. Stepwise multiple regression (SMR) analysis was used to investigate relationships between the invertebrate community and season, flow, habitat and water temperature. 3. Seasonal variables were included in almost 50% of the SMR models, while flow-related variables were included in >75% of models. Densities of many taxa were negatively correlated to Qmin and Qmax, and positively correlated to Ndays, suggesting that while high flows reduced invertebrate densities, densities recovered with increasing time following a flood. Although season and flow were confounded in this study, many of the taxa analysed display little seasonal variation in abundance, suggesting that flow-related variables were more important in structuring communities than seasonal changes in density associated with life-cycles. 4. Five discrete flood and low flow events were identified and changes to invertebrate communities before and after these events examined. Invertebrate densities decreased more commonly after floods than after low flows, and there was a significant positive relationship between the number of taxa showing reductions in density and flood magnitude. Densities of most invertebrates either remained unchanged, or increased after low flow events, except for four taxa whose densities declined after a very long period (up to 9 months) of low flow. This decline was attributed to autogenic sloughing of thick periphyton communities and subsequent loss of habitat for these taxa. 5. Invertebrate communities changed more after floods and the degree of change was proportional to flood magnitude. Community similarity increased with increasing time since the last disturbance, suggesting that the longer stable flows lasted, the less the community changed. These results suggest that invertebrate communities in the Waipara River were controlled by both floods and low flows, but that the relative effects of floods were greater than even extended periods of extreme low flow. 6. Hydraulic conditions in riffles and runs were measured throughout the study. Riffles had consistently faster velocities, but were shallower and narrower than runs at all measured flows. Invertebrate density in riffles was expressed as a percentage of total density and regressed against the flow-related variables to see whether invertebrate locations changed according to flow. Significant negative relationships were observed between the per cent density of common taxa in riffles and Qsample, Qmax and Qmin. This result suggests either that these animals actively drifted into areas of faster velocity during low flows, or that their densities within riffles increased as the width of these habitats declined. [source] Generalized trapezoidal numerical integration of an advanced soil modelINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2008Yunming Yang Abstract This paper investigates the numerical performance of the generalized trapezoidal integration rule by using an advanced soil model. The generalized trapezoidal integration rule can include many other integration algorithms by adjusting a single parameter , ranging from 1 to 0. The soil model used is the recently developed middle surface concept (MSC) sand model which simulates different soil response characteristics by using different pseudo-yield functions. The generalized trapezoidal rule and MSC sand model are used to simulate the responses of sand samples with different relative densities under various initial and loading conditions. Instead of a single step, multiple loading steps bring the sample to the vicinity of failure. These comprehensive investigations examine and compare the influences of various values of , on the numerical solution of integrated constitutive equations, the convergence of Newton's iterative scheme, and the integration accuracy. Copyright © 2007 John Wiley & Sons, Ltd. [source] Liquefaction and cyclic mobility model for saturated granular mediaINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2006S. López-Querol Abstract A new constitutive law for the behaviour of undrained sand subjected to dynamic loading is presented. The proposed model works for small and large strain ranges and incorporates contractive and dilative properties of the sand into the unified numerical scheme. These features allow to correctly predict liquefaction and cyclic mobility phenomena for different initial relative densities of the soil. The model has been calibrated as an element test, by using cyclic simple shear data reported in the literature. For the contractive sand behaviour a well-known endochronic densification model has been used, whereas a plastic model with a new non-associative flow rule is applied when the sand tends to dilate. Both dilatancy and flow rule are based on a new state parameter, associated to the stiffness degradation of the material as the shaking goes on. Also, the function that represents the rearrangement memory of the soil takes a zero value when the material dilates, in order to easily model the change in the internal structure. Proceeding along this kind of approach, liquefaction and cyclic mobility are modelled with the same constitutive law, within the framework of a bi-dimensional FEM coupled algorithm developed in the paper. For calibration purposes, the behaviour of the soil in a cyclic simple shear test has been simulated, in order to estimate the influence of permeability, frequency of loading, and homogeneity of the shear stress field on the laboratory data. Copyright © 2006 John Wiley & Sons, Ltd. [source] Demographic aspects of sympatric Praomys jacksoni and P. stella in a tropical lowland forest in Kakamega, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2004Catherine W. Waweru Abstract Populations of coexisting tropical forest rodents Praomys jacksoni and P. (Hylomyscus) stella were investigated to test whether lower relative densities in regenerating forest compared with mature forest were because of poor health and/or reduced chances for females to breed. Relative frequencies, litter size, mass, length of embryos, presence or absence of ecto- and/ or endoparasites, and liver condition were recorded and analysed. Higher numbers of either species occurred in the mature compared with regenerating forest. Mottled livers and endoparasites were associated with heavier rodents; litter size related positively to mass of pregnant females in both species. Litter size, embryo size, sex ratios, liver condition, and infestation of ecto- and endoparasites were independent of forest and species. Apparently, reduced female density in regenerating forest had no breeding cost on individual females occurring there. Résumé Les populations de rongeurs coexistants en forêt tropicale Praomys jacksoni et P. (Hylomyscus) stella ont étéétudiées pour vérifier si les densités relatives, plus faibles dans les forêts en voie de régénération que dans les forêts mâtures, étaient dues à une moins bonne santé et/ou à de plus faibles chances de se reproduire pour les femelles. On a noté et analysé les fréquences relatives, la taille des portées, le poids, la taille des embryons, la présence ou l'absence d'ecto- et/ou d'endoparasites et l'état du foie. On a constaté des nombres plus importants des deux espèces dans les forêts mâtures que dans les forêts en voie de règénération. Des foies tachetés et des endoparasites étaient associés à des rongeurs plus lourds; la taille des portées était positivement liée au poids des femelles pleines dans les deux espèces. La taille de la portée, le poids des petits, le sex-ratio, l'état du foie et l,infestation par des ecto- et endoparasites étaient indépendants de la forêt et de l'espèce. Apparemment, la densité réduite des femelles dans la forêt en voie de régénération n'avait aucun impact sur la reproduction locale des femelles prises individuellement. [source] Influence of boreal forest succession and dead wood qualities on saproxylic beetlesAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2007Joshua M. Jacobs Abstract 1,Saproxylic insects, a functional group dominated by beetles, are dependent on dead or moribund trees as habitat elements. 2,Although there are few studies of saproxylic insects from the North American boreal zone, European studies demonstrate that forest harvest can lead to a biologically significant decrease in saproxylic beetle diversity. 3,We studied saproxylic beetles in the North American boreal mixedwood forest using flight intercept traps established on naturally dead and girdled trembling aspen and spruce trees along a successional gradient of undisturbed stands from deciduous to coniferous overstory trees. 4,Composition and diversity of beetle assemblages differed among forest successional types. 5,Snag age class was an important determinant of composition for saproxylic beetle assemblages. 6,Multivariate regression analysis of these data indicated that saproxylic beetles are responding to changes in coarse woody debris, and not to the relative densities of canopy tree species, although these variables are strongly correlated. 7,Coarse woody debris management should be a primary concern in forest management plans seeking to conserve saproxylic organisms and the critical ecosystem functions (i.e. nutrient cycling) in which they participate. [source] Effect of Yttria and Yttrium-Aluminum Garnet on Densification and Grain Growth of Alumina At 1200°,1300°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2004Michael K. Cinibulk Densification and grain growth of alumina were studied with yttria or yttrium-aluminum garnet (YAG) additives at the relatively low temperatures of 1200°,1300°C. Yttria doping was found to inhibit densification and grain growth of alumina at 1200°C and, depending on dopant level, had a lesser effect at 1300°C. At 1200°C, yttria inhibits densification more than it hinders grain growth. The rate of grain growth increases faster with temperature than the rate of densification. Alumina-YAG particulate composites were difficult to sinter, yielding relative densities of only 65% and 72% after 100 h at 1200° and 1300°C, respectively. Pure YAG compacts exhibited essentially no densification for times up to 100 h at 1300°C. [source] Effect of Porosity on the Electrical Properties of Polycrystalline Sodium Niobate: I, Electrical ConductivityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2003Silvania Lanfredi The electrical behavior of NaNbO3 ceramic samples with different relative densities was investigated by ac impedance spectroscopy in a range of 13 MHz to 10,3 Hz between 400° and 800°C in dry air. Measurements were performed during heating and cooling cycles. The Nyquist impedance diagrams of dense sodium niobate exhibit only one semicircle representing the grain contribution with depression angles as small as 1°, indicating a high homogeneity of the specific electrical properties. In the case of porous samples, the data reveal an additional low-frequency semicircle related to microstructure. For all studied samples, the Arrhenius conductivity plots show a change in the activation energy around 640°C, attributed to the tetragonal-cubic phase transition. The electrical conductivity of porous samples appears to be higher than that of dense ones. [source] Transparent Sintered Corundum with High Hardness and StrengthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Andreas Krell Commercial corundum powder and a liquid-shaping approach are used for manufacturing complex hollow components and large flat windows of sintered and hot isostatically pressed Al2O3 ceramics having grain sizes of 0.4,0.6 ,m at relative densities of >99.9%. High macrohardness (HV10 = 20,21 GPa) and four-point bending strength (600,700 MPa; 750,900 MPa in three-point bending) are associated with a real in-line transmission of 55%,65% through polished plates. The submicrometer microstructure and the optical properties can be retained for use at >1100°C using dopants that shift the sintering temperature to high values without additional grain growth. [source] Synthesis of Dense TiB2 -TiN Nanocrystalline Composites through Mechanical and Field ActivationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001Jae Won Lee The synthesis of dense nanometric composites of TiN-TiB2 by mechanical and field activation was investigated. Powder mixtures of Ti, BN, and B were mechanically activated through ball milling. Some powders were milled to reduce crystallite size but to avoid initiating a reaction. In other cases powders were milled and allowed to partially react. All these were subsequently reacted in a spark plasma synthesis (SPS) apparatus. The products were composites with equimolar nitride and boride components with relative densities ranging from 90.1% to 97.2%. Crystallite size analyses using the XRD treatments of Williamson-Hall and Halder-Wagner gave crystallite sizes for the TiN and TiB2 components in the range 38.5,62.5 and 31.2,58.8 nm, respectively. Vickers microhardness measurements (at 2 N force) on the dense samples gave values ranging from 14.8 to 21.8 GPa and fracture toughness determinations (at 20 N) resulted in values ranging from 3.32 to 6.50 MPa·m1/2. [source] Turbid flow through a tropical reservoir (Lake Dalrymple, Queensland, Australia): Responses to a summer storm eventLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 4 2000John W. Faithful Abstract The first flood event following a prolonged dry period is described for an impoundment, Lake Dalrymple, in tropical north-eastern Australia. The event, in January 1996, generated substantial flow in the two main inflow sources: the Burdekin River from the north and the Suttor River from the south. Flow through the Burdekin River peaked early and then subsided to a lower level, but flow through the Suttor River persisted at a moderate level for over 15 days after the initial inflow. An extensive water quality survey was conducted on 16 January 1996 (seven days after the initial dam overflow) to determine the nature of the inflows originating from the two major subcatchments feeding the reservoir as they entered and passed through the impoundment. The inflow comprising waters of high turbidity and low conductivity occupied the mid-column region along the two major inflow channels through the impoundment to the dam wall. The suspended particulate material in the form of silt and clay sized particles remained in suspension as the flow passed through the reservoir, due in part to the low ionic strength of the inflow and the relative densities of the inflowing and receiving waters. For both river sources, more than 50% of the total nitrogen and almost all of the total phosphorus were bound to the suspended particulate matter. Much of this was exported in the flow over the spillway. The highly turbid nature of the inflow resulted in strong attenuation of down-welling photosynthetically active radiation (up to maximum attenuation values of 12.24 m,1 in the reservoir where the euphotic depth was only 0.38 m). The irradiance reflectance and the scattering coefficient were considerably higher than any reported for other Australian inland waters. Concentrations of viable chlorophyll a in the surface waters were very low (maximum value 3.4 ,g L,1) because of the highly turbid conditions and extensive dilution by the inflow. The results of this study provide an example of the significant impact a large inflow of turbid, low conductance water can have on a large reservoir in the arid tropics following a prolonged dry period. During inflow events such as the one described in this paper, the reservoir becomes riverine in nature, and large amounts of suspended particulate matter and associated nutrients are transported through the reservoir. [source] Vasotocin and mesotocin in the brains of amphibians: State of the artMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2001Wilhelmus J.A.J. Smeets Abstract Immunohistochemical studies during the last decade have revealed elaborate systems of vasotocinergic (AVT) and mesotocinergic (MST) neuronal elements in the brain of a variety of amphibians including anurans, urodeles, and gymnophionans. Apart from a well-developed hypothalamo-hypophysial system, the antibodies demonstrated the existence of extrahypothalamic AVT- and MST-immunoreactive cell groups as well as extensive extrahypothalamic networks of immunoreactive fibers. The wide distribution of AVT- and MST-immunoreactive fibers throughout the brains of amphibians suggests that the two neuropeptidergic systems are involved not only in hypothalamo-hypophysial interactions, but also in a variety of other brain functions. Moreover, there is now evidence that sex-related differences occur in amphibians as previously shown for amniotes. It should be noted, however, that substantial variation occurs in the relative densities of AVT- and MST-immunoreactive fibers and number of cells between species, even within a single order of amphibians. Similar observations have been made in other classes of vertebrates and prompt us, therefore, to critically evaluate conclusions with respect to specific functions of AVT and MST in the central nervous system of vertebrates. Microsc. Res. Tech. 54:125,136, 2001. © 2001 Wiley-Liss, Inc. [source] Loss of consumers alters the effects of resident assemblages on the local spread of an introduced macroalgaOIKOS, Issue 2 2009F. Bulleri Despite the great interest for the role played by resident assemblages in regulating biological invasions, few studies have assessed how these can influence the spread of exotic species that have successfully established or have included more than one trophic level. On shallow rocky reefs, we assessed how the effects of different benthic assemblages on the spread of an invasive alga, Caulerpa racemosa, are influenced by alterations in the density and species composition of the resident sea urchin assemblage. In order to simulate herbivore species loss scenarios, assemblages dominated by different morphological groups of algae (i.e. turfs or encrusting corallines) or experimentally cleared plots (i.e. bare rock) were exposed to grazing by different combinations of species (Arbacia lixula and Paracentrotus lividus) and densities (natural, ,50% and ,100% of natural densities) of urchins. Algal turfs and encrusting corallines generally facilitated C. racemosa. Manipulating urchins assemblages did not affect the cover and density of fronds of C. racemosa. In contrast, halving the density of P. lividus favoured the penetration of stolons of C. racemosa, consistently among algal assemblages. Other effects of urchins varied among algal assemblages, indicating interactions between trophic levels. In algal turfs, the total removal of urchins caused a decrease in the penetration of stolons, while it enhanced the length of fronds, indicating a shift in the growth form of this clonal plant and, ultimately, a depression of its spreading ability. In bare or encrusting corallines dominated surfaces, the removal of urchins had positive effects on the penetration of stolons and on the length of fronds of C. racemosa, irrespective of one or two species being manipulated and for the intensity of their removal. Our results show that tradeoffs between negative and positive effects of herbivores, varying according to relative densities of species and to the direction and strength of the effects of resident plant assemblages, can influence local rates of spread of C. racemosa. Thus, not only facilitation of exotics by natives can be key in enhancing the spread of exotic species, but it can occur between organisms at different trophic levels. Finally, our findings have important implications for the management of C. racemosa, in view of the progressive domination of shallow rocky reefs by algal turfs. [source] Competition between Eurasian otter Lutra lutra and American mink Mustela vison probed by niche shiftOIKOS, Issue 1 2004Laura Bonesi Interspecific competition is one of several constraints that might prevent an individual from maximising its energy intake. When an interspecific competitor is introduced, an individual is often forced to shift its diet according to the intensity of the competitive pressure. In this paper, we explore whether the introduced American mink (Mustela vison Schreber) shifts its diet when the density of its potential competitor, the Eurasian otter (Lutra lutra L.), is increased. We compared the diets of otter and mink at the same location but at two moments in time when the relative densities of these two species were different while controlling for the abundance of aquatic prey. Mink and otters are semi-aquatic mammals belonging to the same guild of mustelids and otters are expected to be the dominant competitor because they are larger and better at hunting underwater. The diets of otters and mink overlap to a great extent but while otters specialise mainly on aquatic prey, mink are able to exploit both aquatic and terrestrial prey. These observations prompted the hypothesis investigated in this work that at higher otter densities the diet of mink should change to include a higher proportion of terrestrial items. This hypothesis was supported by the data and at higher otter densities mink diet was observed to consist of a higher proportion of mammals and birds while fewer fish were present, although this pattern was present only in winter while no changes were observed in spring. Meanwhile the diet of otters remained basically unchanged. In the second part of the study, we investigated whether niche breadth and niche overlap between otter and mink changed at different otter densities. We found that niche overlap declined as the density of otters increased, in agreement with the prediction of habitat selection theory. [source] Thermoelectric properties of rapid hot pressed polycrystalline Ag1,xPb18SbTe20 synthesized from doping PbTe nanocrystalsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2010Xingliang Xin Abstract Polycrystalline thermoelectric (TE) materials of n-type and with compositions of Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) were prepared by rapid hot pressing from alloy powders, which were obtained by ball milling crystalline ingots. The ingots were synthesized from PbTe nanoparticles, made by solvothermal reactions, and Ag, Sb and Te powders via vacuum-sealed melting in quartz ampoules. Through rapid hot pressing at 748,K for 15,min under 80,MPa, the polycrystalline samples possessed 95% relative densities with the average grain size of 5,µm. The electrical resistivity, Seebeck coefficient and thermal conductivity of the Ag1,xPb18SbTe20 (x,=,0, 0.1, 0.2) samples were measured in the range from room temperature (RT) to 673,K. The thermal conductivity was dramatically decreased, caused by scattering of phonons from grain boundaries and interfaces. By optimizing the values of carrier concentration and carrier transference, the Ag1,xPb18SbTe20 (x,=,0.2) sample achieved a maximum ZT value of 1.019 at 673,K. [source] Changes in estrogen receptor alpha expression in the bursa of Fabricius during chick embryonic developmentANIMAL SCIENCE JOURNAL, Issue 1 2008Young-Ha SHIN ABSTRACT Sex steroid hormones have been reported to be modulators that augment or suppress immune functions. Applying estrogen to chick embryos has been reported to influence antibody production after hatching, suggesting that estrogen acts on B cell differentiation and proliferation in the bursa of chick embryos. We previously reported the presence of estrogen receptor , (ER,) in the bursa during the late period of embryogenesis. In the present study we examined the time course of ER, expression in the bursa of chick embryos at the late period of embryogenesis by ER,-messenger RNA (mRNA) expression analysis by reverse-transcription-polymerase chain reaction (RT-PCR) using primers for chicken ER,, and immunohistochemistry using an anti-ER antibody. The quantity of ER,-mRNA expressed, estimated from the relative densities of the ER, RT-PCR products to those of ,-actin, changed with time during the late period of embryogenesis (day 10 to day 21). ER,-mRNA expression was observed at all ages examined in the present experiment. The expression increased between day 10 and day 15 of embryogenesis and then the value was decreased between day 15 and day 21 of embryogenesis. The numbers of ER-positive cells in the bursa also changed with time during the late period of embryogenesis (day 14 to day 18). ER-positive cells showed the highest level on day 14 of embryogenesis, and then the value declined. ER-positive cells were observed in lymphoid follicular cells, stromal cells and epithelial cells, and the density of ER-positive cells was highest in epithelial cells among the three cell components of the bursa. The high level of ER expression in the bursa of Fabricius (BF) of chick embryos at the late period of embryogenesis suggests that this stage of embryogenesis is critical in B cell differentiation in the bursa in connection with estrogen effects on antibody production after hatching. [source] Harbour swimming nets: a novel habitat for seahorsesAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 5 2008B. G. Clynick Abstract 1.Artificial structures are becoming increasingly important in conserving biodiversity in urban ecosystems, by providing habitat for endangered or rare species. Their role in providing habitat for such species has, however, been largely unexplored. 2.In Sydney Harbour, Australia, seahorses were observed among the netting used to keep sharks out of swimming enclosures. Over a 2-year period, the relative densities of two species of seahorses observed on netting was measured at swimming enclosures with permanent netting and at swimming areas that were only enclosed with netting during the summer months. 3.The rate of colonization by seahorses to new netting was also examined over a period of 10 months. 4.Numbers of seahorses on permanent swimming enclosures were 10 to 100 times greater than numbers present on swimming enclosures that were only set up during the summer months. 5.This large difference may have been attributed to the slow rate of colonization of seahorses to new habitat. Seahorses were not observed at experimental nets that were deployed in two areas in the harbour until at least 4 months after the netting was deployed. 6.Swimming pool nets are a habitat for species of seahorses in Sydney Harbour and, consequently, the removal or disturbance of swimming nets may impact the survival of these fish. Management of these artificial habitats may therefore best be focused on providing a permanent habitat that may help to compensate for the loss of netting during winter months. Copyright © 2007 John Wiley & Sons, Ltd. [source] The value of georeferenced collection records for predicting patterns of mosquito species richness and endemism in the NeotropicsECOLOGICAL ENTOMOLOGY, Issue 1 2008DESMOND H. FOLEY Abstract 1.,Determining large-scale distribution patterns for mosquitoes could advance knowledge of global mosquito biogeography and inform decisions about where mosquito inventory needs are greatest. 2.,Over 43 000 georeferenced records are presented of identified and vouchered mosquitoes from collections undertaken between 1899 and 1982, from 1853 locations in 42 countries throughout the Neotropics. Of 492 species in the data set, 23% were only recorded from one location, and Anopheles albimanus Wiedemann is the most common species. 3.,A linear log,log species,area relationship was found for mosquito species number and country area. Chile had the lowest relative density of species and Trinidad-Tobago the highest, followed by Panama and French Guiana. 4.,The potential distribution of species was predicted using an Ecological Niche Modelling (ENM) approach. Anopheles species had the largest predicted species ranges, whereas species of Deinocerites and Wyeomyia had the smallest. 5.,Species richness was estimated for 1° grids and by summing predicted presence of species from ENM. These methods both showed areas of high species richness in French Guiana, Panama, Trinidad-Tobago, and Colombia. Potential hotspots in endemicity included unsampled areas in Panama, French Guiana, Colombia, Belize, Venezuela, and Brazil. 6.,Argentina, The Bahamas, Bermuda, Bolivia, Cuba, and Peru were the most under-represented countries in the database compared with known country species occurrence data. Analysis of species accumulation curves suggested patchiness in the distribution of data points, which may affect estimates of species richness. 7.,The data set is a first step towards the development of a global-scale repository of georeferenced mosquito collection records. [source] Processing of Carbon Nanofiber Reinforced ZrB2 Matrix Composites for Aerospace Applications,ADVANCED ENGINEERING MATERIALS, Issue 7 2010Jorge Barcena Ceramic matrix composites (CMCs) based on zirconium diboride (ZrB2) reinforced by vapor grown carbon nanofibers are a potential constituent of reusable thermal protection systems. A manufacturing procedure was devised that involved the fabrication of thin films by tape casting to obtain a layer that could be integrated into a more complex system. Higher thermal conductivities and improved toughness can be expected for nanofiber additions, as compared to the matrix alone. Consolidation by hot-pressing was more effective than pressureless sintering, in terms of the final relative density and flatness of specimens. Examination of microstructures showed that few carbon nanofibers were present in the matrix after consolidation by sintering, which was attributed to a reaction between the nanofibers and zirconium oxide present on the surface of the ZrB2 powder. As a solution, oxygen impurities from the boride powders were removed by reduction with carbon coatings derived from phenolic resin. The deleterious reaction was avoided, but residual carbon remained at the grain boundaries, likely from decomposition of the binder. The use of an alternative binder (PMMA vs. PVB) will be used in future studies to reduce the residual carbon content. Further, consolidation by Spark Plasma Sintering (SPS) will be explored to further reduce the reaction of surface oxides with the nanofibers. Finally, characterization of the microstructure at the nanometric level and further determination of the mechanical and thermal properties will be conducted as part of future studies. [source] Differential sensitivity of medium- and large-sized striatal neurons to NMDA but not kainate receptor activation in the ratEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2001Carlos Cepeda Abstract Infrared videomicroscopy and differential interference contrast optics were used to identify medium- and large-sized neurons in striatal slices from young rats. Whole-cell patch-clamp recordings were obtained to compare membrane currents evoked by application of N -methyl- d -aspartate (NMDA) and kainate. Inward currents and current densities induced by NMDA were significantly smaller in large- than in medium-sized striatal neurons. The negative slope conductance for NMDA currents was greater in medium- than in large-sized neurons and more depolarization was required to remove the Mg2+ blockade. In contrast, currents induced by kainate were significantly greater in large-sized neurons whilst current densities were approximately equal in both cell types. Spontaneous excitatory postsynaptic currents occurred frequently in medium-sized neurons but were relatively infrequent in large-sized neurons. Excitatory postsynaptic currents evoked by electrical stimulation were smaller in large- than in medium-sized neurons. A final set of experiments assessed a functional consequence of the differential sensitivity of medium- and large-sized neurons to NMDA. Cell swelling was used to examine changes in somatic area in both neuronal types after prolonged application of NMDA or kainate. NMDA produced a time-dependent increase in somatic area in medium-sized neurons whilst it produced only minimal changes in large interneurons. In contrast, application of kainate produced significant swelling in both medium- and large-sized cells. We hypothesize that reduced sensitivity to NMDA may be due to variations in receptor subunit composition and/or the relative density of receptors in the two cell types. These findings help define the conditions that put neurons at risk for excitotoxic damage in neurological disorders. [source] Heat Transfer in Polypropylene-Based Foams Produced Using Different Foaming Processes,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo Antunes This paper presents the characterization of the cellular structure and thermal conduction behaviour of polypropylene foams produced using different foaming processes, with the aim of selecting the best possible PP foam thermal insulator. Thermal conductivity results have shown that the global heat transfer behaviour is controlled by the relative density. For relative densities higher than 0.2, thermal conductivity differences were insignificant, the data being predicted by the mixture's rule and Russell's model. In the low density range, all of the proposed models underestimated the overall conductivity, the effect of the processing method being more significant, slight differences being observed between foams produced by extrusion and those produced by gas dissolution with higher cell sizes and anisotropies. Foams with finer cellular structures showed to be better insulating materials. [source] Numerical Modelling of Flow Boiling Heat Transfer in Horizontal Metal-Foam Tubes,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Wei Lu Abstract The flow boiling heat transfer performance in horizontal metal-foam tubes is numerically investigated based on the flow pattern map retrieved from experimental investigations. The flow pattern and velocity profile are generally governed by vapour quality and mass flow rate of the fluid. The porous media non-equilibrium heat transfer model is employed for modelling both vapour and liquid phase zones. The modelling predictions have been compared with experimental results. The effects of metal-foam morphological parameters, heat flux and mass flux on heat transfer have been examined. The numerical predictions show that the overall heat transfer coefficient of the metal-foam filled tube increases with the relative density (1-porosity), pore density (ppi), mass and heat flux. [source] Compressive Behavior of Pyramidal, Tetrahedral, and Strut-Reinforced Tetrahedral ABS and Electroplated Cellular Solids,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2009Samuel Markkula Fused deposition modeling combined with electroplating provides a novel manufacturing methodology for building low relative density engineered cellular topologies. Here the mechanical performance of tetrahedral, pyramidal, and strut-reinforced tetrahedral cellular solids manufactured from multiphase nickel-copper-ABS is studied. The novel processing and geometric optimization places these engineered topologies into an unoccupied location in the material universe. [source] Age-hardening Response of Replicated Microcellular Al-4.5%Cu,ADVANCED ENGINEERING MATERIALS, Issue 9 2008Y. Conde We study the response to age hardening of Al-4.5%Cu replicated foams having 75 and 400 ,m diameter cells and of relative density between 0.1 and 0.32, to show that the age-hardening response can depend on the cell size and morphology, and that open-celled replicated high-strength aluminium alloy foams can be made as strong as commercial closed-celled aluminium foams despite their inferior mesostructural features. [source] The stress,life fatigue behaviour of aluminium alloy foamsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2000McCullough The tension,tension and compression,compression nominal stress versus fatigue life responses of Alulight closed cell aluminium alloy foams have been measured for the compositions Al,1Mg,0.6Si and Al,1Mg,10Si (wt %), and for relative densities in the range 0.1,0.4. The fatigue strength of each foam increases with the relative density and with the mean applied stress, and is greater for the transverse orientation than for the longitudinal orientation. Under both tension,tension and compression,compression loading the dominant cyclic deformation mode appears to be material ratchetting; consequently, the fatigue life is highly sensitive to the magnitude of the applied stress. A micromechanical model is given to predict the dependence of life upon stress level and relative density. Panels containing a central hole were found to be notch insensitive for both tension,tension and compression,compression fatigue loading: the net-section strength equals the unnotched strength. [source] | ||||||||||||||||||||||