Different Densities (different + density)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Production of Nile Tilapia Oreochromis niloticus and Freshwater Prawn Macrobrachium rosenbergii Stocked at Different Densities in Polyculture Systems in Brazil

Marcel J. M. dos Santos
Twelve 0.01-ha earthen ponds were stocked with 1 tilapia/m2 and 0, 2, 4, or 6 postlarvae prawn/m2. Three replicates were randomly assigned to each prawn density. Postlarval prawns were stocked a week prior to tilapia juveniles and both were harvested 175 d after the beginning of the experiment. Tilapia final average weight, survival, production, and food conversion rates did not differ significantly among treatments (P > 0.05); the averages were 531 g, 67%. 3,673 kg/ha, and 1.91, respectively. Prawn survival rates did not differ for the three stocking densities (mean 90%). However, final weight and production were significantly different (P < 0.05) as follows: 34.0, 23.0, and 14.7 g and 639, 909, and 818 kg/ha, respectively for 2. 4, and 6 prawns/m2 densities. Stocking densities up to 6 prawn/m2 did not affect tilapia production and required neither additional feeding nor significant changes in management. The polyculture system allowed an increase in total production with the same amount of supplied feed, thus improving the system sustainability. [source]

Influence of reed stem density on foredune development

S. M. Arens
Abstract Vegetation density on foredunes exerts an important control on aeolian sediment transport and deposition, and therefore on profile development. In a long-term monitoring field experiment, three plots were planted with regular grids of reed bundles in three different densities: 4, 2 and 1 bundles per m2. This study reports on the differences in profile development under the range of vegetation densities. Topographic profiles were measured between May 1996 and April 1997. Results indicate important differences in profile development for the three reed bundle densities: in the highest density plot a distinct, steep dune developed, while in the lowest density a more gradual and smooth sand ramp was deposited. When the stems had been completely buried, differences in profile evolution vanished. After a second planting of reed stems in January 1997 the process was repeated. In May 1997, all plots had gained a sand volume ranging from 11·5 to 12·3 m3 m,1, indicating that the sediment budget is relatively constant, regardless of the particular profile evolution. The field evidence is compared with simulations of profile development, generated by the foredune development model SAFE. The model successfully reproduces the overall profile development, but in general, the equations used for vegetation,transport interaction overestimate the effect of vegetation. This causes some deviations between field and model results. Several reasons for this are discussed. Based on the experiments reported here, recommendations are given for further research. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Density-dependent polyphenism and geographic variation in size among two populations of lubber grasshoppers (Romalea microptera)

Abstract. 1. Density-dependent phase polyphenism occurs when changes in density during the juvenile stages result in a developmental shift from one phenotype to another. Density-dependent phase polyphenism is common among locusts (Orthoptera: Acrididae). 2. Previously, we demonstrated a longitudinal geographic cline in adult body size (western populations = small adults; eastern populations = large adults) in the eastern lubber grasshopper (Romalea microptera) in south Florida. As lubbers are confamilial with locusts, we hypothesised that the longitudinal size cline was partly due to density-dependent phase polyphenism. 3. We tested the effect of density, population, and density×population interaction on life-history traits (pronotum length, mass, cumulative development time, growth rate) of, and proportion surviving to, each of the five instars and the adult stage in a 2 × 3 factorial laboratory experiment with two lubber populations, each reared from hatchling to adult at three different densities. 4. The effect of density on life history and survival was independent of the effects of population on life history and survival. Higher densities led to larger adult sizes (pronotum, mass) and lower survivorship. The western population had smaller adult masses, fewer cumulative days to the adult stage, and higher survivorship than the eastern population. 5. Our data suggest that lubber grasshoppers exhibit density-dependent phase polyphenism initiated by the physical presence of conspecifics. However, the plastic response of adult size to density observed in the laboratory is not consistent with the relationship between phenotypes and adult density in the field. Genetic differences between populations observed in the laboratory could contribute to size and life-history differences among lubber populations in the field. [source]

Testing of the influenza virus purification by CIEF

Marie Horká
Abstract In virological practice, the pre-concentration, purification and subsequent determination of the purity and concentration of the viruses from the cultural medium and/or from the real sample are required. The conventional techniques used today are equipment demanding, time-consuming and laborious. In this study, the CIEF of influenza viruses with UV detection has been developed and subsequently used to test the purification of the virus from the biological samples. The equine and swine influenza viruses present in infected allantoic fluid of specific pathogen free embryonated chicken eggs were precipitated by using PEG 6000 and sodium chloride. The precipitated viruses were centrifuged at 14,000×g, and the impurities of different densities were removed by using the sucrose gradients. The efficiency of the virus purification technique was examined by the CIEF and compared to the results of real-time PCR. The pIs of both influenza viruses were determined. Simultaneously, the CIEF was found to be a suitable method for the rapid testing of the efficiency of the virus purification. [source]

Natal Dispersal Patterns of a Subsocial Spider Anelosimus cf. jucundus (Theridiidae)

ETHOLOGY, Issue 9 2003
Kimberly S. Powers
Species that alternate periods of solitary and social living may provide clues to the conditions that favor sociality. Social spiders probably originated from subsocial-like ancestors, species in which siblings remain together for part of their life cycle but disperse prior to mating. Exploring the factors that lead to dispersal in subsocial species, but allow the development of large multigenerational colonies in social species, may provide insight into this transition. We studied the natal dispersal patterns of a subsocial spider, Anelosimus cf. jucundus, in Southeastern Arizona. In this population, spiders disperse from their natal nests in their penultimate and antepenultimate instars over a 3-mo period. We tracked the natal dispersal of marked spiders at sites with clustered vs. isolated nests. We found that most spiders initially dispersed less than 5 m from their natal nests. Males and females, and spiders in patches with different densities of nests, dispersed similar distances. The fact that both sexes in a group dispersed, the lack of a sex difference in dispersal distance, and the relatively short distances dispersed are consistent with the hypothesis that natal dispersal results from resource competition within the natal nest, rather than inbreeding avoidance in competition for mates. Additionally, an increase in the average distance dispersed with time and with the number of spiders leaving a nest suggests that competition for nest sites in the vicinity of the natal nest may affect dispersal distances. The similar distances dispersed in patches with isolated vs. clustered nests, in contrast, suggest that competition among dispersers from different nests may not affect dispersal distances. [source]

Species-specific responses of planktivorous fish to the introduction of a new piscivore: implications for prey fitness

Summary 1. Antipredator behaviour by the facultative planktivorous fish species roach (Rutilus rutilus), perch (Perca fluviatilis) and rudd (Scardinius erythrophthalmus) was studied in a multi-year whole-lake experiment to evaluate species-specific behavioural and numerical responses to the stocking of pikeperch (Sander lucioperca), a predator with different foraging behaviour than the resident predators large perch (P. fluviatilis) and pike (Esox lucius). 2. Behavioural responses to pikeperch varied greatly during the night, ranging from reduced activity (roach and small perch) and a shift in habitat (roach), to no change in the habitat use and activity of rudd. The differing responses of the different planktivorous prey species highlight the potential variation in behavioural response to predation risk from species of similar vulnerability. 3. These differences had profound effects on fitness; the density of species that exhibited an antipredator response declined only slightly (roach) or even increased (small perch), whereas the density of the species that did not exhibit an antipredator response (rudd) decreased dramatically (by more than 80%). 4. The maladaptive behaviour of rudd can be explained by a ,behavioural syndrome', i.e. the interdependence of behaviours expressed in different contexts (feeding activity, antipredator) across different situations (different densities of predators). 5. Our study extends previous studies, that have typically been limited to more controlled situations, by illustrating the variability in intensity of phenotypic responses to predators, and the consequences for population density, in a large whole-lake setting. [source]

The relationship between Chironomus plumosus burrows and the spatial distribution of pore-water phosphate, iron and ammonium in lake sediments

Summary 1. To study the influence of chironomids on the distribution of pore-water concentrations of phosphate, iron and ammonium, we conducted a laboratory experiment using mesocosms equipped with two-dimensional pore-water samplers, filled with lake sediment and populated with different densities of Chironomus plumosus. 2. Specially designed mesocosms were used in the study. A 6-mm deep space between the front plate and the pore-water sampler at the back plate was just thick enough to allow the chironomids to live undisturbed, yet thin enough to force all the burrows into a two-dimensional plane. 3. The courses of the burrows were observed during the experiment as oxidised zones surrounding them, as well as being identified with an X-ray image taken at the end of the experiment. 4. We investigated the relationship between C. plumosus burrows and spatial patterns of pore-water composition. Concentrations of the three ions were significantly less around ventilated burrows (54% to 24%), as bioirrigation caused a convective exchange of pore-water enriched with dissolved species compared with the overlying water, and also because oxygen imported into the sediment resulting in nitrification of ammonium, oxidation of iron(II) and a co-precipitation of phosphate with Fe(III) oxyhydroxides. 5. In mesocosms with chironomids, new (redox) interfaces occurred with diffusive pore-water gradients perpendicular to the course of burrows and the site of major phosphate, ammonium and iron(II) release shifted from the sediment surface to the burrow walls. [source]

Determinants of within- and among-clutch variation in levels of maternal hormones in Black-Headed Gull eggs

Groothuis T. G.
Summary 1.,Females of egg-laying vertebrates may adjust the development of their offspring to prevailing environmental conditions by regulating the deposition of hormones into their eggs. Within- and amng-clutch variation in levels of steroid hormones were studied in the egg yolks of the Black-Headed Gull (Larus ridibundus, Linnaeus) in relation to environmental conditions at the nest site. This species breeds in colonies of different densities and in different habitats, and the chicks hatch asynchronously. 2.,Egg yolks contained very high levels of androstenedione, substantial levels of testosterone and moderate levels of 5,-dihydrotestosterone. Oestrogen (17,-oestradiol) was not detected. 3.,Androgen levels increased strongly with laying order, irrespective of egg or yolk mass. This may compensate for the disadvantages of the later hatching chicks. These results have implications for adaptive hypotheses that were proposed for asynchronous incubation. 4.,Eggs of lighter clutches contained more androgens, perhaps to compensate for a lower nutritional quality of these eggs. 5.,Birds breeding in the periphery of a colony, being relatively more aggressive and having relatively large territories, laid eggs that contained more androgens than those of birds breeding in the centre. These high yolk androgen levels may facilitate growth and motor development of the chicks, which may be especially important for chicks developing at the periphery of a colony. Reduced levels may be adaptive for birds breeding in the centre, where risk of infectious diseases is high, since steroids may be immunosuppressive. 6.,Corrected for nest distance, clutches of birds in high vegetation, where predation risk is less severe and therefore competition for nest sites perhaps high, contained relatively high levels of androgens. It is suggested that the level of yolk androgens reflects the hormonal condition of the female, that in turn is influenced by her characteristics such as her age and aggressiveness, and the level of social stimulation. [source]

Thermodynamics of Nanosystems with a Special View to Charge Carriers

ADVANCED MATERIALS, Issue 25-26 2009
Joachim Maier
Abstract Basic ingredients of interfacial thermodynamics are recapitulated with a special eye on the nanometer-size regime. Questions are then briefly tackled that arise if, in heterogeneous systems, the constituent phases shrink to atomistic dimensions. Particularly helpful in this context are thermodynamic approaches, in which the introduction of interfacial tension is avoided. While the first part addresses ground structure quantities, the second part deals with questions of size and confinement effects on entropy and energy of ionic and electronic defects. These defects represent the respective excitations within this ground structure. The article emphasizes the similarities between ions and electrons manifested in the statistics rather than elaborating on the discrepancies that are primarily reflected by different densities of states and mobilities. It is, therefore, not the intention of the article to address aspects of nanoelectronics that rely on quantum transport for which many reviews are available. Nonetheless all these discussed aspects are directly relevant for both nanoionics and nanoelectronics. [source]

Bond rolling resistance and its effect on yielding of bonded granulates by DEM analyses

M. J. Jiang
Abstract A discrete element modelling of bonded granulates and investigation on the bond effect on their behaviour are very important to geomechanics. This paper presents a two-dimensional (2-D) discrete element theory for bonded granulates with bond rolling resistance and provides a numerical investigation into the effect of bond rolling resistance on the yielding of bonded granulates. The model consists of mechanical contact models and equations governing the motion of bonded particles. The key point of the theory is that the assumption in the original bond contact model previously proposed by the authors (55th CSCE-ASCE Conference, Hamilton, Ont., Canada, 2002; 313,320; J. Eng. Mech. (ASCE) 2005; 131(11):1209,1213) that bonded particles are in contact at discrete points, is here replaced by a more reliable assumption that bonded particles are in contact over a width. By making the idealization that the bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring, dashpot, bond, slider or divider), we establish a bond rolling contact model together with bond normal/tangential contact models, and also relate the governing equations to local equilibrium. Only one physical parameter , needs to be introduced in the theory in comparison to the original bond discrete element model. The model has been implemented into a 2-D distinct element method code, NS2D. Using the NS2D, a total of 86 1-D, constant stress ratio, and biaxial compressions tests have been carried out on the bonded granular samples of different densities, bonding strengths and rolling resistances. The numerical results show that: (i) the new theory predicts a larger internal friction angle, a larger yielding stress, more brittle behaviour and larger final broken contact ratio than the original bond model; (ii) the yielding stress increases nonlinearly with the increasing value of ,, and (iii) the first-yield curve (initiation of bond breakage), which define a zone of none bond breakage and which shape and size are affected by the material density, is amplified by the bond rolling resistance in analogous to that predicted by the original bond model. Copyright © 2006 John Wiley & Sons, Ltd. [source]

The geographical range structure of the holly leaf-miner.


Summary 1The local population density structure of a phytophagous insect, the holly leaf-miner Phytomyza ilicis Curtis, was examined across its natural geographical range in Europe. 2The frequency distribution of the number of sample sites at which the leaf-miner attained different densities per tree was strongly right-skewed, with the species being absent from a large number of sites at which its host occurred, particularly in southern regions. 3There was a decline in the spatial autocorrelation of leaf-miner densities with increasing distance between sample sites, with negative autocorrelation at long lags resulting in part from high densities being attained at the north-eastern range limits and low densities at the southern range limits. 4Partial regression analysis was used to model leaf-miner densities in terms of spatial position within the geographical range and the broad climate experienced at the sample localities. This accounted for between 40 and 65% of the variation in densities, dependent upon how the leaf-miner's geographical range was defined. 5While overall these results are at odds with common and intuitively appealing assertions about the abundance structure of geographical ranges, they can readily be interpreted in terms of a simple modification of a general model of such structures. [source]

The joint effects of larval density and 14C-cypermethrin on the life history and population growth rate of the midge Chironomus riparius

Helen L. Hooper
Summary 1Chemical effects on organisms are typically assessed using individual-level endpoints or sometimes population growth rate (PGR), but such measurements are generally made at low population densities. In contrast most natural populations are subject to density dependence and fluctuate around the environmental carrying capacity as a result of individual competition for resources. As ecotoxicology aims to make reliable population projections of chemical impacts in the field, an understanding of how high-density or resource-limited populations respond to environmental chemicals is essential. 2Our objective was to determine the joint effects of population density and chemical stress on the life history and PGR of an important ecotoxicological indicator species, Chironomus riparius, under controlled laboratory conditions. Populations were fed the same ration but initiated at different densities and exposed to a solvent control and three concentrations of 14C-cypermethrin in a sediment,water test system for 67 days at 20 ± 1 °C. 3Density had a negative effect on all the measured life-history traits, and PGR declined with increasing density in the controls. Exposure to 14C-cypermethrin had a direct negative effect on juvenile survival, presumably within the first 24 h because the chemical rapidly dissipated from the water column. Reductions in the initial larval densities resulted in an increase in the available resources for the survivors. Subsequently, exposed populations emerged sooner and started producing offspring earlier than the controls. 14C-cypermethrin had no effect on estimated fecundity and adult body weight but interacted with density to reduce the time to first emergence and first reproduction. As a result, PGR increased with cypermethrin concentration when populations were initiated at high densities. 4Synthesis and applications. The results showed that the effects of 14C-cypermethrin were buffered at high density, so that the joint effects of density and chemical stress on PGR were less than additive. Low levels of chemical stressors may increase carrying capacity by reducing juvenile competition for resources. More and perhaps fitter adults may be produced, similar to the effects of predators and culling; however, toxicant exposure may result in survivors that are less tolerant to changing conditions. If less than additive effects are typical in the field, standard regulatory tests carried out at low density may overestimate the effects of environmental chemicals. Further studies over a wide range of chemical stressors and organisms with contrasting life histories are needed to make general recommendations. [source]

Food competition between 2+ tench (Tinca tinca L.), common carp (Cyprinus carpio L.) and bigmouth buffalo (Ictiobus cyprinellus Val.) in pond polyculture

Z. Adámek
Summary Natural diets of tench (Tinca tinca L.), carp (Cyprinus carpio L.) and bigmouth buffalo (Ictiobus cyprinellus Val.) were studied to determine food competition among them in polyculture stocks of two different densities. Tench diet consisted mainly of zooplankton (43.8%) and bottom sediments (21.2%). In contrast, carp diet consisted mainly of bottom items including plant debris and detritus (68.8%), which dominated over zooplankton (19.1%). In bigmouth buffalo, most food bulk comprised zooplankton (80.7%). Thus, the resulting food competition (i.e. similarity) was most pronounced between tench and carp (60.8%) and between tench and bigmouth buffalo (47.4%). When comparing growth performance of the three cultured species, the ratios between stocking and harvesting size were: in normal stocking density (392 kg ha,1) 1.72, 3.67 and 2.13, and in doubled stocking density (777 kg ha,1) 1.07, 2.33 and 2.16 in tench, carp and bigmouth buffalo, respectively. [source]

Virus infection and grazing exert counteracting influences on survivorship of native bunchgrass seedlings competing with invasive exotics

Summary 1,Invasive annual grasses introduced by European settlers have largely displaced native grassland vegetation in California and now form dense stands that constrain the establishment of native perennial bunchgrass seedlings. Bunchgrass seedlings face additional pressures from both livestock grazing and barley and cereal yellow dwarf viruses (B/CYDVs), which infect both young and established grasses throughout the state. 2,Previous work suggested that B/CYDVs could mediate apparent competition between invasive exotic grasses and native bunchgrasses in California. 3,To investigate the potential significance of virus-mediated mortality for early survivorship of bunchgrass seedlings, we compared the separate and combined effects of virus infection, competition and simulated grazing in a field experiment. We infected two species of young bunchgrasses that show different sensitivity to B/CYDV infection, subjected them to competition with three different densities of exotic annuals crossed with two clipping treatments, and monitored their growth and first-year survivorship. 4,Although virus infection alone did not reduce first-year survivorship, it halved the survivorship of bunchgrasses competing with exotics. Within an environment in which competition strongly reduces seedling survivorship (as in natural grasslands), virus infection therefore has the power to cause additional seedling mortality and alter patterns of establishment. 5,Surprisingly, clipping did not reduce bunchgrass survivorship further, but rather doubled it and disproportionately increased survivorship of infected bunchgrasses. 6,Together with previous work, these findings show that B/CYDVs can be potentially powerful elements influencing species interactions in natural grasslands. 7,More generally, our findings demonstrate the potential significance of multitrophic interactions in virus ecology. Although sometimes treated collectively as plant ,predators', viruses and herbivores may exert influences that are distinctly different, even counteracting. [source]

Responses to handling and confinement stressors in juvenile great sturgeon Huso huso

B. Falahatkar
The effects of acute stressors on physiological responses of juvenile great sturgeon or beluga Huso huso L. were investigated in two experiments. In the first experiment, fish were handled by placing them in containers at either low density (LD, one fish l,1) or high density (HD, four fish l,1) for 60 s. Concentrations of plasma cortisol, glucose and lactate were determined from blood collected at 0, 1, 3, 6 and 12 h after application of the stressor. Plasma cortisol concentrations increased after the disturbance in H. huso from both handling treatments, but changes were not significant. Plasma glucose rose significantly by 22·9 and 31·6% in LD and HD handling treatments, respectively, after 3 h. Significant increases in plasma lactate occurred within 1 h in both treatment groups, but that of the HD group was much higher. In the second experiment, fish were held at two different densities, LD (2 kg m,2 tank bottom surface area) and HD (7 kg m,2), for 8 weeks and then subjected to an aerial emersion handling stressor in a net for 60 s; blood samples were taken before handling (resting, 0 h) and at 1, 3, 6 and 9 h after handling. Plasma cortisol increased significantly in fish from the HD treatment from 8·8 ± 0·3 to 19·2 ± 2·4 ng ml,1 (mean ±s.e.) by 1 h after stress, but post-handling changes in the LD group were not significant. Significant increases in both plasma glucose and lactate were observed by 1 h in both treatment groups, with peak levels of plasma glucose evident at 3 h [69·4 ± 2·9 and 60·9 ± 1·7 mg dl,1 (mean ±s.e.) in LD and HD groups, respectively]. Plasma glucose levels were significantly higher in the LD group than in the HD group at 3 and 6 h. Post-handling haemoglobin content increased by 1 h and white blood cell numbers were reduced by 3 and 6 h in the HD treatment group compared with resting values, but changes in these blood features in the LD group were not significant. Acute handling did not affect haematocrit in either treatment. The results suggest that H. huso is relatively resistant to handling and confinement, and could tolerate normal hatchery practices associated with aquaculture. Because changes in cortisol concentrations were relatively low compared with those in most teleosts, glucose and lactate concentrations may be more useful as stress indicators in juvenile H. huso. This study also demonstrated that prior exposure to a chronic stressor, specifically high stocking density, could alter the physiological response to subsequent acute handling in H. huso. [source]

Dynamics of experimental production of Thelohanellus hovorkai (Myxozoa: Myxosporea) in fish and oligochaete alternate hosts

Y S Liyanage
Abstract The dynamics of development and production of Thelohanellus hovorkai (Myxozoa) were examined to investigate factors inducing haemorrhagic thelohanellosis in carp, Cyprinus carpio L. Fresh actinospores of T. hovorkai were harvested from the oligochaete alternate host, Branchiura sowerbyi, and used for infection experiments with myxosporean-free carp. Visualization of actinospores by fluorescent labelling revealed that sporoplasms penetrated the gill filaments of carp immersed in an actinospore suspension as early as 30 min post-exposure (PE). Plasmodia of T. hovorkai developed in the connective tissues of various organs and matured 3,5 weeks PE; dispersion of myxospores from degenerate plasmodia occurred 5,7 weeks PE. Challenges with a high dose of actinospores (4.5 × 106 spores per fish) resulted in the onset of disease, which was more easily achieved by the oral intubation of actinospores than by immersion in an actinospore suspension. Actinosporean-free B. sowerbyi were exposed to different densities of myxospores (104,106 spores per oligochaete) and subsequently reared at different temperatures (15, 20, 25 °C). At 20 and 25 °C, actinospore releases were first detected 40,43 days PE, with multiple peaks of release (max. 7 × 105 actinospores day,1) during the next 60 days. We concluded that the developmental cycle of T. hovorkai was completed within 3,5 months at 20,25 °C, and that the ingestion of large numbers of actinospores orally, possibly by feeding on infected oligochaetes, resulted in a disease condition in carp. [source]

Reproductive Allocation Patterns in Different Density Populations of Spring Wheat

Jing Liu
Abstract The effects of increased intraspecific competition on size hierarchies (size inequality) and reproductive allocation were investigated in populations of the annual plant, spring wheat (Triticum aestivum). A series of densities (100, 300, 1 000, 3 000 and 10 000 plants/m2) along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient (R2 = 0.927), which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition (100 plants/m2), individual reproductive allocation was size independent but, in high density populations (300, 1 000, 3 000 and 10 000 plants/m2), where competition occurred, individual reproductive allocation was size dependent: the small proportion of larger individuals were winners in competition and got higher reproductive allocation (lower marginal reproductive allocation; MRA), and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation (higher MRA). In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation (with a negative relationship between them). However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies. [source]

Microenvironment regulation of PRG4 phenotype of chondrocytes

Megan E. Blewis
Abstract Articular cartilage is a heterogeneous tissue with superficial (S), middle (M), and deep (D) zones. Chondrocytes in the S zone secrete the lubricating PRG4 protein, while chondrocytes from the M and D zones are more specialized in producing large amounts of the glycosaminoglycan (GAG) component of the extracellular matrix. Soluble and insoluble chemicals and mechanical stimuli regulate cartilage development, growth, and homeostasis; however, the mechanisms of regulation responsible for the distinct PRG4-positive and negative phenotypes of chondrocytes are unknown. The objective of this study was to determine if interaction between S and M chondrocytes regulates chondrocyte phenotype, as determined by coculture in monolayer at different ratios of S:M (100:0, 75:25, 50:50, 25:75, 0:100) and at different densities (240,000, 120,000, 60,000, and 30,000 cells/cm2), and by measurement of PRG4 secretion and expression, and GAG accumulation. Coculture of S and M cells resulted in significant up-regulation in PRG4 secretion and the percentage of cells expressing PRG4, with simultaneous down-regulation of GAG accumulation. Tracking M cells with PKH67 dye in coculture revealed that they maintained a PRG4-negative phenotype, and proliferated less than S cells. Taken together, these results indicate that the up-regulated PRG4 expression in coculture is a result of preferential proliferation of PRG4-expressing S cells. This finding may have practical implications for generating a large number of phenotypically normal S cells, which can be limited in source, for tissue engineering applications. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:685,695, 2007 [source]

Site-specific deposition of Ag nanoparticles on ZnO nanorod arrays via galvanic reduction and their SERS applications

Wei Song
Abstract A controllable heterostructure consisting of ZnO nanorod arrays with attached Ag nanoparticles at only one end has been synthesized via a facile and convenient galvanic reduction method. Scanning electron microscopic images of these nanostructures showed good selectivity of Ag deposition on the tip of ZnO nanorod arrays. The formation of these regular AgZnO heterogeneous nanorod arrays can be explained by a localization of the electrons at the ends of the ZnO nanorods after the electron transfer step. By tuning the reaction time and the concentration of silver nitrate, the density of Ag nanoparticles on the tip of ZnO nanorods can be well controlled. Owing to the introduction of Ag nanoparticles with different densities, the resulting AgZnO heterogeneous nanorod arrays have been proved to be a versatile substrate for surface-enhanced Raman scattering not only for common organic molecules but also for label-free protein detection. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Effects of Two Densities of Caged Monosex Nile Tilapia, Oreochromis niloticus, on Water Quality, Phytoplankton Populations, and Production When Polycultured with Macrobrachium rosenbergii in Temperate Ponds

Jason J. Danaher
The effects of different densities of caged Nile tilapia, Oreochromis niloticus, on water quality, phytoplankton populations, prawn, and total pond production were evaluated in freshwater prawn, Macrobrachium rosenbergii, production ponds. The experiment consisted of three treatments with three 0.04-ha replicates each. All ponds were stocked with graded, nursed juvenile prawn (0.9 ± 0.6 g) at 69,000/ha. Control (CTL) ponds contained only prawns. Low-density polyculture (LDP) ponds also contained two cages (1 m3; 100 fish/cage) of monosex male tilapia (115.6 ± 22 g), and high-density polyculture (HDP) ponds had four cages. Total culture period was 106 d for tilapia and 114 d for prawn. Overall mean afternoon pH level was significantly lower (P , 0.05) in polyculture ponds than in CTL ponds but did not differ (P > 0.05) between LDP and HDP. Phytoplankton biovolume was reduced in polyculture treatments. Tilapia in the LDP treatment had significantly higher (P , 0.05) harvest weights than in the HDP treatment. Prawn weights were higher (P , 0.05) in polyculture than prawn monoculture. These data indicate that a caged tilapia/freshwater prawn polyculture system may provide pH control while maximizing pond resources in temperate areas. [source]

Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell Systems

A. van den Noort
Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source]

Developmental shifts in watermelon growth and reproduction caused by the squash bug, Anasa tristis

Maciej Biernacki
Summary ,,Compared with leaf-feeding herbivores, little is known about how sap-feeding herbivores affect plant growth, morphology and reproduction. This study examines effects of the sap-feeding squash bug ( Anasa tristis ) on watermelon ( Citrullus lanatus ) root, leaf and reproductive structures. ,,Plants at the four-leaf stage were exposed to different densities of caged squash bugs for 67 d (to plant maturity). ,,Initial effects were on roots. Herbivory was associated with a significant reduction in mean total root length, root surface area and number of root tips, as well as an increase in root diameters. Herbivore-exposed plants had significantly more leaves, although leaf lifespan was decreased. Both total plant dry mass and fruit dry mass per unit leaf area were significantly greater in controls. Significant effects of herbivores on plant reproductive traits included delayed flower formation (by 7,12 d), change in floral sex ratio (in favor of femaleness), increased fruit abortion, and smaller fruit size. ,,Developmental consequences were related to changes in plant water relations, including decreased water-use efficiency. Water use in treated plants was three to nine times greater per unit of plant dry mass than in controls. [source]

Estuarine Restoration of Submersed Aquatic Vegetation: The Nursery Bed Effect

Angela Hengst
The historic decline of submersed aquatic vegetation (SAV) in mesohaline regions of Chesapeake Bay, United States involved a diversity of plant species. The recent modest recovery is mostly, however, associated with a single, prolific but ephemeral species, Ruppia maritima. Two previously abundant and more stable species, Potamogeton perfoliatus and Stuckenia pectinata, have shown virtually no evidence of recovery. Based on previous studies that demonstrated the ability of R. maritima stands to enhance water clarity and nutrient conditions for SAV growth, we hypothesized that these beds would serve as effective "nursery" areas to incite transplant success for other SAV. We conducted experiments in a two-phase study at small and large spatial scales designed to explore this "nursery effect" as a restoration approach to increase plant species diversity. The first phase was conducted at small spatial scales to test effects of patch density by planting P. perfoliatus and S. pectinata into bare, sparse, and densely vegetated areas within three similar R. maritima beds in a tributary of Chesapeake Bay. Mean seasonal percent survivorship and shoot density were significantly higher in bare patches compared to vegetated patches. In the second phase of the study, P. perfoliatus was transplanted into separate R. maritima beds of different densities to test the effect of bed scale plant density on P. perfoliatus survival and growth. Transplant success of P. perfoliatus was positively correlated with the density of R. maritima among all sites. [source]

The optimal density of atmospheric sounder observations in the Met Office NWP system

M. L. Dando
Abstract Large numbers of satellite observations are discarded from the numerical weather prediction (NWP) process because high-density observations may have a negative impact on the analysis. In current assimilation schemes, the observation error covariance matrix R is usually represented as a diagonal matrix, which assumes there are no correlations in the observation errors and that each observation is an independent piece of information. This is not the case when there are strong error correlations and this can lead to a degraded analysis. The experiments conducted in this study were designed to identify the optimal density and to determine if there were circumstances when exceeding this density might be beneficial to forecast skill. The global optimal separation distance of Advanced TIROS Operational Vertical Sounder (ATOVS) observations was identified by comparing global forecast errors produced using different densities of ATOVS. The global average of the absolute forecast error produced by each different density was found for a 3-week period from December 2004 to January 2005. The results showed that, when using the Met Office NWP system with a horizontal model resolution of ,60 km, the lowest global forecast errors were produced when using separation distances of 115,154 km. However, localized regions of the atmosphere containing large gradients such as frontal regions may benefit from thinning distances as small as 40 km and therefore the global optimal separation distance is not necessarily applicable in these circumstances. Copyright © 2007 Royal Meteorological Society [source]

Vertebral deformity in cultured Atlantic cod larvae: ontogeny and effects on mortality

Velmurugu Puvanendran
Abstract The effects of different egg incubation densities on the incidences of vertebral deformities in Atlantic cod larvae were investigated. Cod eggs were incubated at four different densities, 3, 6, 12 and 48 mL eggs L,1, of water. When all the eggs hatched, larvae were reared in 30 L glass aquaria. Larval samples were taken at 0, 14, 42 and 56 days post hatch (dph) for deformity analysis. Larval samples were stained using bone and cartilage staining methods to determine vertebral deformity. Incubation densities did not have any significant effects on vertebral deformities in Atlantic cod larvae. However, the incidence of larval vertebral deformity was high at hatch and decreased as the larvae grew older until 42 dph, indicating selective mortality of deformed larvae during this period. Larvae at 56 dph, however, showed an increase in the incidence of vertebral deformity, indicating a possible nutritional or prey-type effect. To our knowledge, no studies have documented the occurrence of variable patterns in vertebral deformities in cod at various developmental stages. Overall, our results suggest that broodstock husbandry, genetics and/or nutrition could play a major role in causing vertebral deformities in Atlantic cod at hatch; however, nutrition and prey type may play a major role during metamorphosis. [source]

Statistical criteria to establish optimal antibody dilution in flow cytometry analysis

CYTOMETRY, Issue 3 2007
Cesar J. G. Collino
Abstract Background: In direct techniques of flow cytometry, the optimal antibody dilution or titer point is established from the plateau area of the antibody titration curve. However, the plateau area is defined without any statistical criteria, which may lead to an incorrect selection of antibody dilution. Herein, we report statistical criteria to establish the optimal antibody dilution for CD14, CD8, CD4, and CD3 analysis by flow cytometry in peripheral whole blood. Methods: The unpaired t- test (two-tail P value) was used as statistical criteria to analyze the titration curve of the following monoclonal antibody panels: CD14-FITC, CD8-FITC, CD4-RD1, and CD3-PC5. Results: Using the unpaired t- test (two-tail P value), the plateau area from the antibody titration curve was fitted when two consecutive antibody volumes showed mean peak of channel fluorescence (MPCF) values not significantly different. When the antibody was used at volume corresponding to that of the antibody titration point, the flow cytometry analysis of whole blood samples with different density of cell antigens can be correctly discriminated. Conclusion: This statistical criteria allows the fitting of the plateau area of MPCF versus antibody volume and consequently, to define the optimal antibody dilution. © 2007 Clinical Cytometry Society [source]

Numerical modelling of fluid flow in microscopic images of granular materials

E. Masad
Abstract A program for the simulation of two-dimensional (2-D) fluid flow at the microstructural level of a saturated anisotropic granular medium is presented. The program provides a numerical solution to the complete set of Navier,Stokes equations without a priori assumptions on the viscous or convection components. This is especially suited for the simulation of the flow of fluids with different density and viscosity values and for a wide range of granular material porosity. The analytical solution for fluid flow in a simple microstructure of porous medium is used to verify the computer program. Subsequently, the flow field is computed within microscopic images of granular material that differ in porosity, particle size and particle shape. The computed flow fields are shown to follow certain paths depending on air void size and connectivity. The permeability tensor coefficients are derived from the flow fields, and their values are shown to compare well with laboratory experimental data on glass beads, Ottawa sand and silica sands. The directional distribution of permeability is expressed in a functional form and its anisotropy is quantified. Permeability anisotropy is found to be more pronounced in the silica sand medium that consists of elongated particles. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Improving Eulerian two-phase flow finite element approximation with discontinuous gradient pressure shape functions

A. H. Coppola-Owen
Abstract In this paper we present a problem we have encountered using a stabilized finite element method on fixed grids for flows with interfaces modelled with the level set approach. We propose a solution based on enriching the pressure shape functions on the elements cut by the interface. The enrichment is used to enable the pressure gradient to be discontinuous at the interface, thus improving the ability to simulate the behaviour of fluids with different density under a gravitational force. The additional shape function used is local to each element and the corresponding degree of freedom can therefore be condensed prior to assembly, making the implementation quite simple on any existing finite element code. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Linear polarized photoluminescence from GaN quantum dots imbedded in AlN matrix

K. S. Zhuravlev
Abstract We report microphotoluminescence studies of GaN/AlN quantum dots grown along the (0001) crystal axis by molecular-beam epitaxy on sapphire substrates. To obtain quantum dots with different density and size a nominal GaN coverage was varied from 1 to 4 monolayers. The highest density of quantum dots was about 1011 cm -2, so about 103 quantum dots was excited in experiments. We found that the photoluminescence intensity of a sample with the smallest amount of deposited GaN decreases in more than two orders of magnitude under continuous-wave laser exposure during about 30 minutes and then it remains stable. The photoluminescence intensity of the rest samples was time-independent quantity. The emission band of the former sample exhibits a prominent linear polarization along the growth plane. We assume that the quite high degree of polarization can be due anisotropy of strain and/or shape of the quantum dots formed near dislocations which act also as recombination centers causing photoluminescence quenching. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The optimal density of atmospheric sounder observations in the Met Office NWP system

M. L. Dando
Abstract Large numbers of satellite observations are discarded from the numerical weather prediction (NWP) process because high-density observations may have a negative impact on the analysis. In current assimilation schemes, the observation error covariance matrix R is usually represented as a diagonal matrix, which assumes there are no correlations in the observation errors and that each observation is an independent piece of information. This is not the case when there are strong error correlations and this can lead to a degraded analysis. The experiments conducted in this study were designed to identify the optimal density and to determine if there were circumstances when exceeding this density might be beneficial to forecast skill. The global optimal separation distance of Advanced TIROS Operational Vertical Sounder (ATOVS) observations was identified by comparing global forecast errors produced using different densities of ATOVS. The global average of the absolute forecast error produced by each different density was found for a 3-week period from December 2004 to January 2005. The results showed that, when using the Met Office NWP system with a horizontal model resolution of ,60 km, the lowest global forecast errors were produced when using separation distances of 115,154 km. However, localized regions of the atmosphere containing large gradients such as frontal regions may benefit from thinning distances as small as 40 km and therefore the global optimal separation distance is not necessarily applicable in these circumstances. Copyright © 2007 Royal Meteorological Society [source]