Size-dependent Changes Research Articles

Synthesis, structure and light scattering properties of tetraalkylammonium metal isothiocyanate salts

A series of ammonium and tetraalkylammonium metal isothiocyanate salts of the type Q(y)[M(NCS)x] (M = Cr(III), x = 6, y = 3, Q = NH4(+), Me4N(+), Et4N(+), n-Bu4N(+); M = Mn(II), x = 6, y = 4, Q = Me4N(+); M = Mn(II), x = 5, y = 3, Q = Et4N(+); M = Fe(III), x = 6, y = 3, Q = Me4N(+), Et4N(+), n-Bu4N(+); M = Co(II), x = 4, y = 2, Q = n-Bu4N(+); M = Eu(III), Gd(III), Dy(III), x = 6, y = 3, Q = Bu4N(+)) has been synthesized and structurally characterized. The octahedral Cr(III) salts are isostructural to previously and newly reported Fe(III) salts. The Ln(III)-containing anions are also octahedral. For Mn(II), although the Me4N(+) salt is octahedral, the Et4N(+) salt [Mn(NCS)5](3-) possesses a distorted trigonal bipyramidal geometry. For (Et4N)3[Fe(NCS)6] and (n-Bu4N)3[Fe(NCS)6], a solid-state size-dependent change in colour from red to green was observed and was attributed to a light scattering phenomenon in the crystalline samples.

Investigation of Catalytic Finite-Size-Effects of Platinum Metal Clusters.

In this paper, we use density functional theory (DFT) calculations on highly parallel computing resources to study size-dependent changes in the chemical and electronic properties of platinum (Pt) for a number of fixed freestanding clusters ranging from 13 to 1415 atoms, or 0.7-3.5 nm in diameter. We find that the surface catalytic properties of the clusters converge to the single crystal limit for clusters with as few as 147 atoms (1.6 nm). Recently published results for gold (Au) clusters showed analogous convergence with size. However, this convergence happened at larger sizes, because the Au d-states do not contribute to the density of states around the Fermi-level, and the observed level fluctuations were not significantly damped until the cluster reached ca. 560 atoms (2.7 nm) in size.

Flee or Fight: Ontogenetic Changes in the Behavior of Cobweb Spiders in Encounters With Spider-Hunting Wasps

An animal's body size plays a predominant role in shaping its interspecific interactions, and, in encounters between two predators, often determines which shall be predator and which shall be prey. Spiders are top predators of insects, yet can fall prey to mud-dauber wasps that provision their larval nests with paralyzed spiders. Here we examined predator-prey interactions between Chalybion californicum (Saussure) (Sphecidae), a mud-dauber wasp, and Parasteatoda tepidariorum C. L. Koch (Theridiidae), a cobweb spider. We examined whether a spider's size influences its response to an attacking wasp, and report a size-dependent change in spider behavior: small-sized spiders fled, whereas medium- and large-sized spiders fought in response to wasp attacks. From the wasps' perspective, we examined whether spider size influences a wasp's hunting behavior and capture success. We found that wasps commonly approached small spiders, but were much less likely to approach medium and large spiders. However, wasp capture success did not vary with spider size. We also report a strategy used by Chalybion wasps toward cobweb spiders that is consistent with an interpretation of aggressive mimicry.

Size effects in the elastic deformation behavior of metallic nanoparticles

In this work, the results of a series of molecular statics simulations to investigate the size dependence of the elastic properties of metallic nanoparticles are presented. The per-atom stiffness tensor was calculated from the derivative of the used embedded atom method potentials and, from it, lower order elastic parameters, such as the Young’s modulus or the Poisson ratio. The Young’s modulus decayed up to 30 % relative to the bulk values for 2.5 nm small particles, whereas the Poisson ratio showed an increase with decreasing particle size for most materials. Particles with a diameter of 30 nm approached the continuum values to around 1 %, marking the transition to continuum theory. The size-dependent Young’s modulus and several other material properties can be described by a simple algebraic function of the number of atoms per particle. By plotting the radial distribution of the local Young’s modulus within particles of different size, it is shown that only the outermost 2–3 atomic layers are responsible for the size-dependent change of elastic properties. Within these layers, the average atomic stiffness was found to decay linearly and independent of the particle size.

Atypical BCS-BEC crossover induced by quantum-size effects

Quantum-size oscillations of the basic physical characteristics of a confined fermionic condensate are a well-known phenomenon. Its conventional understanding is based on the single-particle physics, whereby the oscillations follow the size-dependent changes in the single-particle density of states. Here we present a study of a cigar-shaped ultracold superfluid Fermi gas, which demonstrates an important many-body aspect of the quantum-size effects, overlooked previously. The many-body physics is revealed in the atypical crossover from the Bardeen-Cooper-Schrieffer (BCS) superfluid to the Bose-Einstein condensate (BEC) induced by the size quantization of the particle motion. Quantized perpendicular spectrum results in the formation of single-particle subbands (shells) so that the aggregate fermionic condensate becomes a coherent mixture of subband condensates. Each time when the lower edge of a subband crosses the chemical potential, the BCS-BEC crossover is approached in this subband, and the aggregate condensate contains both the BCS and BEC-like components.

Oxygen and carbon isotope fractionation of marine ostracod calcite from the eastern Mediterranean Sea

Over the last two decades, non-marine ostracods have been intensively studied with respect to the stable isotopic composition (δ13C, δ18O) of their calcified valves, however, few data for marine taxa have been published so far. Here, we provide new data from recent and Pleistocene near-surface sediments of the Gulf of Taranto (recent) and the southern Aegean Sea (15ka, both in the Mediterranean Sea) helping to improve our understanding of ostracod stable isotopes in palaeoceanography. Results are compared to those of certain benthic foraminiferal taxa for which the living habitat and the isotopic disequilibrium from ambient sea-water are known. In addition, monospecific size fractions of three common ostracod species (Bairdia conformis, Bosquetina tarentina, Henryhowella sarsii) have been studied from the Gulf of Taranto in order to test the existence of a size-dependent change in the δ13C and δ18O composition of the valve calcite. Our results reveal positive average species-specific deviations from the δ18O of calcite equilibrium for two ostracod taxa (B. conformis 0.31‰, H. sarsii 0.33‰), while B. tarentina shows a negative off-set of −0.41‰. These values are substantially lower than those reported for most non-marine ostracods, which usually yield positive “vital effects” for δ18O of more than 2‰. Furthermore, B. tarentina is thereby the only ostracod taxon so far for which a negative “vital effect” has been reported, apart from the non-marine Eucypris mareotica. δ13C values cover a much larger range than δ18O with a negative off-set from sea-water by −1.8 to −5‰. Size-fraction data show no systematic change, although a statistically-significant positive covariance between δ13C and δ18O has been observed, consisting of a slope similar to a kinetically controlled fractionation effect as has previously been documented for asymbiotic planktic foraminifera and corals. The documented interspecific offsets can be primarily attributed to differences in diet for δ13C and for both δ13C and δ18O to fractionation processes related to different modes of calcification.

The role of growth hormone in growth, lipid homeostasis, energy utilization and partitioning in rainbow trout: Interactions with leptin, ghrelin and insulin-like growth factor I

The growth-promoting effects of in vivo growth hormone (GH) treatment were studied in relation to size and lipid content of energy stores including liver, mesentery, white muscle and belly flap in rainbow trout. In order to elucidate endocrine interactions and links to regulation of growth, adiposity and energy metabolism, plasma levels of GH, insulin-like growth factor I (IGF-I), leptin (Lep) and ghrelin, were assessed and correlated to growth and energy status. In addition tissue-specific expression of lepa1 mRNA was examined. Juvenile rainbow trout were implanted with sustained-release bovine GH implants and terminally sub-sampled at 1, 3 and 6 weeks. GH increased specific growth rate, reduced condition factor (CF) and increased feed conversion efficiency resulting in a redistribution of energy stores. Thus, GH decreased mesenteric (MSI) and liver somatic index (LSI). Lipid content of the belly flap increased following GH-treatment while liver and muscle lipid content decreased. Independent of GH substantial growth was accompanied by an increase in muscle lipids and a decrease in belly flap lipids. The data suggest that the belly flap may function as an energy buffering tissue during episodes of feeding and lean growth. Liver and muscle lipids were positively correlated to body weight, indicating a size-dependent change in adiposity. Hepatic lepa1 mRNA positively correlated to MSI and CF and its expression decreased following GH treatment, coinciding with decreased hepatic lipid content. Plasma Lep was positively correlated to MSI and belly flap lipid content, suggesting that Lep may communicate energy status. In summary, the observed GH tissue-specific effects on lipid metabolism in rainbow trout highlight the complex physiology of the energy reserves and their endocrine control.

Facile organic solvent-free synthesis of size-controlled hierarchically structured magnetic hollow spheres and potential application in adsorption for bovine serum album

A series of size-controllable hierarchically nanostructured magnetic hollow spheres (MHS) (250–2330nm) have been fabricated by using the hard-template method involving the coprecipitation of ferrite precursor over the pre-synthesized polystyrene spheres with varied sizes under organic solvent-free conditions followed calcinations. The SEM, TEM and HRTEM results indicate that the primary nanoparticles constructing hierarchically nanostructured MHS clearly show the template sphere size-dependent changes in morphologies and stacking modes from disorderly stacked globular and nanorodlike mixed particles, to orderly perpendicularly oriented nanorodlike particles, and to compact horizontally arranged nanospindle particles as the template size is increased. The N2 adsorption–desorption data reveal that the MHS spheres have a high BET surface area (48–83m2/g) and large pore volumes (0.37–0.66cc/g). The vibration sample magnetization analysis shows that the MHS spheres have moderate magnetization saturation of 24–37emu/g. The adsorption results show that the BSA adsorbance is greatly affected by the varied morphologies and stacking modes of primary nanoparticles constructing the MHS spheres and the maximum adsorption occurs on the MHS spheres mainly comprised of perpendicularly oriented nanorodlike primary particles.

Influence of particle size in hybrid solar cells composed of CdSe nanocrystals and poly(3-hexylthiophene)

Inorganic semiconductor nanoparticles, such as CdSe quantum dots, are considered to be a promising alternative to fullerene derivates for application as electron acceptors in polymer-based bulk heterojunction solar cells. The main potential advantage is the strong light absorption of CdSe nanoparticles with a spectral bandwidth, which can even be tuned, due to the quantum size effect. However, the impact of the particle size on the performance of polymer/CdSe solar cells has remained largely unexplored so far. Therefore, the influence of particle size in hybrid solar cells using a blend of poly(3-hexylthiophene) (P3HT) and quasi-spherical CdSe nanoparticles on relevant cell parameters and the overall solar cell performance is systematically studied in the present work. As the most important result, an increase of the open-circuit voltage (VOC) can be found for smaller nanoparticles and can be explained by an “effective bandgap” model. In contrast, no significant changes of the short-circuit current density with particle size are observed. Smaller particles were found to yield a lower fill factor, compensating the gain in VOC, so that the power conversion efficiency finally turned out to be independent of the particle size in this study. Spectral differences observed in the respective external quantum efficiency spectra of the solar cells can be attributed to size-dependent changes of the particle absorption. Temperature-dependent measurements of the current-voltage (I-V) characteristics suggest that the transport of photogenerated charge carriers in the bulk heterojunction is limited by localized states, with activation energy beyond thermal energy at room temperature.

Size-Dependent Phase Changes in Water Clusters.

We investigate melting behavior of water clusters (H2O)N (N = 7, 8, 11, and 12) by using multicanonical-ensemble molecular dynamics simulations. Our simulations show that the melting behavior of water clusters is highly size dependent. Based on the computed canonical average of the potential energy and heat capacity CV, we conclude that (H2O)8 and (H2O)12 exhibit first-order-like phase change, while (H2O)7 and (H2O)11 exhibit continuous-like phase change. The melting temperature range for (H2O)8 and (H2O)12 can be defined based on the peak position of CV(T) and dCV(T)/dT (where T is the temperature). Moreover, for (H2O)8 and (H2O)12, the solid- and liquid-like phases separate temporally in the course of simulation. In contrast, no temporal separation of solid- and liquid-like phases is observed for (H2O)7 and (H2O)11. In light of the notable temporal separation of solid- and liquid-like phases for(H2O)8 and (H2O)12, an alternative computer approach for estimating the melting temperature range is proposed based on the time-dependent Lindemann parameters. We find that the melting temperature range estimated from both definitions is consistent with each other for (H2O)8 and (H2O)12 but not for (H2O)7 and (H2O)11. We also find that the melting behavior of small water clusters can be conveniently assessed if the energy differences of neighbor-sized clusters at zero temperature are known.

Size dependent microstructure for Ag–Ni nanoparticles

The Ag–Ni system is characterized by large differences in atomic sizes (14%) and a positive heat of mixing (+23kJmol−1). The binary equilibrium diagram for this system therefore exhibits a large miscibility gap in both solid and liquid state. This paper explores the size-dependent changes in microstructure and the suppression of the miscibility gap which occurs when free alloy particles of nanometer size are synthesized by co-reduction of Ag and Ni metal precursors. The paper reports that complete mixing between Ag and Ni atoms could be achieved for smaller nanoparticles (<7nm). These particles exhibit a single-phase solid solution with face-centered cubic (fcc) structure. With increase in size, the nanoparticles revealed two distinct regions. One of the regions is composed of pure Ag. This region partially surrounds a region of fcc solid solution at an early stage of decomposition. Experimental observations were compared with the results obtained from the thermodynamic calculations, which compared the free energies corresponding to a physical mixture of pure Ag and Ni phases and a fcc Ag–Ni solid solution for different particle sizes. Results from the theoretical calculations revealed that, for the Ag–Ni system, solid solution was energetically preferred over the physical mixture configuration for particle sizes of 7nm and below. The experimentally observed two-phase microstructure for larger particles was thus primarily due to the growth of Ag-rich regions epitaxially on initially formed small fcc Ag–Ni nanoparticles.

On the role of the lateral lift force in poly-dispersed bubbly flows

An extensive experimental database comprising air–water as well as steam-water upwards vertical pipe flows for a pressure up to 6.5 MPa was used to investigate the effect of the lateral lift force on turbulent poly-dispersed flows with medium or high gas volume fraction. It was clearly shown that the lift force plays an important role also in such flows. Several effects such as bubble coalescence and breakup as well as fast rising large bubbles which push small bubbles towards the pipe wall superpose the effect of the lift force but can be separated from this effect. The critical bubble diameter, at which the lift force changes its sign, predicted by using Tomiyama’s correlation agrees well with experimental data obtained for turbulent air–water and steam-water flows with medium and high void fraction and a broad spectrum of bubbles sizes. The values for this critical bubble diameter are confirmed by the experimental data within the frame of the uncertainty of the data. Consequences of the action of the lateral lift force on flow structures in different flow situations are discussed. From the investigations it can be concluded that the lift force including the bubble size dependent change of its sign should be considered in a proper numerical 2D or 3D-simulation on flows in which bubbles in the range of several millimeters are present.

Energetic inequivalence in eusocial insect colonies

The energetic equivalence rule states that population-level metabolic rate is independent of average body size. This rule has been both supported and refuted by allometric studies of abundance and individual metabolic rate, but no study, to my knowledge, has tested the rule with direct measurements of whole-population metabolic rate. Here, I find a positive scaling of whole-colony metabolic rate with body size for eusocial insects. Individual metabolic rates in these colonies scaled with body size more steeply than expected from laboratory studies on insects, while population size was independent of body size. Using consumer-resource models, I suggest that the colony-level metabolic rate scaling observed here may arise from a change in the scaling of individual metabolic rate resulting from a change in the body size dependence of mortality rates.

Morphological and Ecological Adaptation of Basterotia Bivalves (Galeommatoidea: Sportellidae) to Symbiotic Association with Burrowing Echiuran Worms

The burrows created by benthos in tidal flats provide various habitats to other organisms. Echiuran burrows are unique among these in being persistently disturbed by the host's undulating activity, but little is known on how symbionts adapt to such a unique habitat. We report here the morphological and ecological adaptation by two bivalve species of Basterotia (Sportellidae), including one new species, which are commensals with burrowing echiuran worms. The burrows of Ikedosoma gogoshimense were inhabited by Basterotia gouldi at intertidal gravelly mud flats in the central Seto Inland Sea, whereas those of Ochetostoma erythrogrammon were inhabited by Basterotia carinata n. sp. at an intertidal gravelly coral-sand flat at Amami-Ohshima Island. Both bivalve species were found embedded in the burrow wall with their posterior inhalant and exhalant apertures gaping to the burrow lumen, suggesting that they utilize the water currents created by host echiurans. The posteriorly robust, laterally inflated shell with developed carina is considered an adaptation to symbiotic life, as it is exposed to pressure caused by the host's persistent undulating activity. Females of Basterotia bivalves were larger than males, suggesting size-dependent sex change, and possessed brooded veligers in the ctenidium. Our findings suggest that species-specific intimate association with echiurans may be widespread among the Sportellidae bivalves, whose biology remains poorly understood.

A preliminary study of digestive enzyme activities and amino acid composition of early juvenile yellowfin tuna ( Thunnus albacares)

The yellowfin tuna (YFT, Thunnus albacares) is a circumtropical/subtropical marine species that supports major fisheries throughout its range. Tuna ranching – an activity that currently relies on fish captured from the wild – has rapidly expanded, thus placing even greater pressure on wild tuna stocks worldwide. Although captive propagation of tunas has proven feasible, hatchery technologies for YFT need improvement to increase larval survival. The onset of exogenous feeding is a critical phase during which digestive processes develop rapidly. Therefore, the present research was undertaken to examine size-dependent changes in YFT fertilized eggs and in 23, 25 and 34 mm (total length) early juveniles with respect to the development of digestive capacity, biochemical composition and amino acid (AA) profiles as indicators of larval nutritional requirements for AAs. To this end, the activities of alkaline and acid phosphatases, pepsin, trypsin, chymotrypsin, aminopeptidase, lipase and α-amylase were determined spectrophotometrically. Activities of the analyzed enzymes were greater in the YFT than in similar-age/size marine fish of other species. In YFT, enzyme activities progressively increased as fish grew, resulting in significantly different ( P < 0.0001) enzyme profiles among size classes. With the exception of acid phosphatase, all enzymes displayed a precocious increase in specific activity concurrent with somatic growth. Proximate composition and AA patterns were generally similar within juveniles but distinctly different ( P ≤ 0.001–0.05) from that of eggs. Histidine, taurine and alanine were the most prevalent AAs in the free pool; whereas, arginine's free pool concentration increased substantially from egg to juvenile stages (2.2 to 12.7 nmol/mg, respectively). These results support the hypothesis of precocious digestive capacity for scombrid fish. Observed AA patterns suggest that strategies for feeding larval and juvenile YFT in aquaculture should incorporate higher levels of specific AAs during early development to support rapid growth and diminish the threat of starvation or cannibalism. Although this information is useful for understanding feeding processes in juvenile YFT, more research is necessary to fully characterize these processes in the various stages from egg to juvenile, leading to the development of balanced diets that would allow for early weaning from live prey.

Source-controlled yield and hardening of Cu(1 0 0) studied by in situ transmission electron microscopy

In the present work we investigate the mechanical properties of multiple slip oriented single crystal Cu(100) compression samples to shed light on size-dependent yield and hardening behavior at small-scales. Samples with diameters ranging from 90nm to 1700nm were fabricated using focused ion beam milling and tested in situ in a transmission electron microscope. The results demonstrate a dislocation source-limited size-dependent yield strength, as evidenced by size-dependent changes in the deformation morphology. Moreover, we report size dependency and strain dependency in the hardening behavior at these dimensions, where higher hardening is observed for smaller samples and at lower strains. This is explained by the source-limited nature of plasticity in small dimensions, which we demonstrate affects not just yield but also the hardening behavior in the nanopillars.

Fast and furious: effects of body size on strike performance in an arboreal viperTrimeresurus(Cryptelytrops)albolabris

Body size has a pervasive effect on animal functioning and life history with size dependent changes in performance and physiology throughout ontogeny being common in many ectothermic vertebrates. However, as selection on juvenile life history stages is strong, juveniles often offset the disadvantages of small body size by disproportionate levels of performance. Here, we investigate size-related changes in defensive strike performance in an arboreal pit viper, Trimerusurus (Cryptelytrops) albolabris. Our data show a significant negative allometry in the scaling of head dimensions and head mass to body mass. However, strike velocity and strike distance are independent of body mass, with juveniles in our sample striking as fast and as far as adults. In contrast to model predictions suggesting that acceleration capacity should decrease with increasing body mass, acceleration capacity increases with snake body mass. Our results suggest that this is the result of a negative allometric scaling of head mass combined with an isometric scaling of the dorsal epaxial musculature. Finally, our data show a significant sexual dimorphism in body size and strike velocity with females being heavier and striking faster independent of the dimorphism in body size.

Size-dependent sex change can be the ESS without any size advantage of reproduction when mortality is size-dependent

Almost all models of sex change evolution assume that reproductive rate increases with body size. However, size-dependent sex changing plants often show size-independent reproductive success, presumably due to pollen limitation. Can the observed size-dependent sex change pattern be the ESS in this case? To answer this question, we analyze a game model of size-dependent sex expression in plants. We assume: (1) reproductive rate is perfectly independent of size; (2) mortality decreases with size in the same way for both sexes; (3) growth rates decrease at maturity, more for females than males. We show that the ESS is size-dependent sex expression: small individuals are vegetative, intermediate individuals are male, and large individuals are female. These results demonstrate that mortality is important in size-dependent sex allocation even when mortality rate is independent of sex. They also offer an explanation of why we see populations in poor environments to have sex ratios more biased toward the first sex relative to high quality environments.

Stress, Sheet Resistance, and Microstructure Evolution of Electroplated Cu Films During Self-Annealing

Electroplated copper films are known to change their microstructure due to the self-annealing effect. The self-annealing effect of electroplated copper films was investigated by measuring the time dependence of the film stress and sheet resistance for different layer thicknesses between 1.5 and 20 ?m. While the sheet resistance was found to decrease as time elapsed, a size-dependent change in film stress was observed. Films with the thickness of 5 ?m and below decrease in stress, while thicker films initially reveal an increase in film stress followed by a stress relaxation at a later stage. This behavior is explained by the superposition of grain growth and grain-size-dependent yielding.

Size- and Site-Dependent Reconstruction in CdSe QDs Evidenced by 77Se{1H} CP-MAS NMR Spectroscopy

Evidence of size-dependent reconstruction in quantum dots leading to changes in bonding is observed through analysis of the (77)Se{(1)H} cross-polarization magic angle spinning and (77)Se spin-echo solid-state NMR for Cd(77)Se quantum dots. The CP-MAS and spin-echo data indicate discrete surface and core (77)Se sites exist with the QD, in which the surface is comprised of numerous reconstructed lattice planes. Due to the nearly 100% enrichment level for (77)Se, efficient spin coupling is observed between the surface (77)Se and sublayer (77)Se sites due to spin diffusion in the Cd(77)Se quantum dots. The observed chemical shift for the discrete (77)Se sites can be correlated to the effective mass approximation via the Ramsey expression, indicating a 1/r(2) size dependence for the change in chemical shift with size, while a plot of chemical shift versus the inverse band gap is linear. The correlation of NMR shift for the discrete sites allows a valence bond theory interpretation of the size-dependent changes in bonding character within the reconstructed QD. The NMR results provide a structural model for the QDs in which global reconstruction occurs below 4 nm in diameter, while an apparent self-limiting reconstruction process occurs above 4 nm.