The sandpaper frog, Lechriodus fletcheri, is a temperate anuran that has previously been shown to be virtually semelparous, with adults overwhelmingly reproducing in a single year of life. Yet, this ...species almost exclusively oviposits in highly ephemeral pools where there is a high chance of total reproductive failure due to hydroperiods often being unpredictable and too short for their offspring to reach metamorphosis. We sought to understand how L. fletcheri copes reproductively in such a risky breeding environment in the absence of a classical iteroparous life history. We investigated aspects of reproduction in wild and laboratory‐reared individuals to determine whether females are capable of intra‐seasonal multi‐clutching and/or clutch partitioning, and males of fertilizing multiple clutches. Direct field evidence was obtained that males participated in multiple mating events within season, while indirect evidence of this ability in females was obtained based on laboratory‐held individuals that produced an additional batch of mature oocytes weeks after an initial release of eggs. Our findings suggest that both males and females likely have the capacity to participate in multiple reproductive events within season and, while most adults may not reproduce more than once, that they are abbreviate iteroparous rather than truly semelparous. Our findings provide evidence that short‐lived anurans may exploit alternative bet‐hedging strategies that mimic the fitness benefits of multi‐year iteroparity.
Adult sandpaper frogs (Lechriodus fletcheri) overwhelmingly reproduce in a single breeding year of their short lives, despite depositing eggs in ephemeral waterbodies where there is a high chance of total reproductive failure. We show that individuals of both sexes likely have the capacity to participate in multiple reproductive events within a single breeding season. We thus suggest that L. fletcheri are abbreviate iteroparous rather than truly semelparous, providing evidence that short‐lived anurans may exploit alternative bet‐hedging strategies that mimic the fitness benefits of multi‐year iteroparity.
The absorption of hydrophobic drugs and nutrients from the intestine is principally determined by the amount that can be dissolved by the endogenous fluids present in the gut. Human intestinal fluids ...(HIFs) comprise a complex mixture of bile salts, phospholipids, steroids and glycerides that vary in composition in the fed and fasted state and between subjects. A number of simulated intestinal fluid (SIF) compositions have been developed to mimic fasted and fed state intestinal conditions and allow the in vitro determination of drug solubility as a proxy for the maximum dissolved concentration it is possible to reach. In particular these solvents are used during the development of lipophilic and poorly water-soluble drugs but questions remain around the differences that may arise from the source and methods of preparation of these fluids. In this work, a range of SIFs were studied using small-angle X-ray scattering (SAXS), cryogenic-transmission electron microscopy (cryo-TEM) and molecular dynamics (MD) simulations in order to analyze their structures. In-house prepared SIFs based on sodium taurodeoxycholate (NaTDC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) formed oblate ellipsoidal micelles irrespective of lipid concentration and preparation conditions. In contrast, commercially available SIFs based on sodium taurocholate and lecithin formed prolate ellipsoidal micelles in the fed state and vesicles in the fasted state. These structural variations are the likely reason for the dramatic differences sometimes observed in the solubility enhancements for hydrophobic drugs, nutrients and digestion products when using different SIFs. However, the structural homogeneity of the NaTDC/DOPC micelles makes them ideal candidates for standardizing SIF formulations as the structures of the solubilizing nanoaggregates therein are not sensitive to the preparation method.
Spontaneous formation of vesicles from the self-assembly of two specific surfactants, one zwitterionic (oleyl amidopropyl betaine, OAPB) and the other anionic (Aerosol-OT, AOT), is explored in water ...using small-angle scattering techniques. Two factors were found to be critical in the formation of vesicles: surfactant ratio, as AOT concentrations less than equimolar with OAPB result in cylindrical micelles or mixtures of micellar structures, and salt concentration, whereby increasing the amount of NaCl promotes vesicle formation by reducing headgroup repulsions. Small-angle neutron scattering measurements reveal that the vesicles are approximately 30–40 nm in diameter, depending on sample composition. Small-angle X-ray scattering measurements suggest preferential partitioning of OAPB molecules on the vesicle inner layer to support vesicular packing. Heating the vesicles to physiological temperature (37 °C) causes them to collapse into smaller ellipsoidal micelles (2–3 nm), with higher salt concentrations (≥10 mM) inhibiting this transition. These aggregates could serve as responsive carriers for loading or unloading of aqueous cargoes such as drugs and pharmaceuticals, with temperature changes serving as a simple release/uptake mechanism.
With the incidence of emerging infectious diseases on the rise, it is becoming increasingly important to identify refuge areas that protect hosts from pathogens and therefore prevent population ...declines. For the chytrid fungus Batrachochytrium dendrobatidis, temperature and humidity refuge areas for amphibian hosts exist but are difficult to manipulate. Other environmental features that may affect the outcome of infection include water quality, drying regimes, abundance of alternate hosts and isolation from other hosts. We identified relationships between water bodies with these features and infection levels in the free-living hosts inhabiting them. Where significant relationships were identified, we used a series of controlled experiments to test for causation. Infection loads were negatively correlated with the salt concentration of the aquatic habitat and the degree of water level fluctuation and positively correlated with fish abundance. However, only the relationship with salt was confirmed experimentally. Free-living hosts inhabiting water bodies with mean salinities of up to 3.5 ppt had lower infection loads than those exposed to less salt. The experiment confirmed that exposure to sodium chloride concentrations >2 ppt significantly reduced host infection loads compared to no exposure (0 ppt). These results suggest that the exposure of amphibians to salt concentrations found naturally in lentic habitats may be responsible for the persistence of some susceptible species in the presence of B. dendrobatidis. By manipulating the salinity of water bodies, it may be possible to create refuges for declining amphibians, thus allowing them to be reintroduced to their former ranges.
Human milk is critical for the survival and development of infants. This source of nutrition contains components that protect against infections while stimulating immune maturation. In cases where ...the mother's own milk is unavailable, pasteurized donor milk is the preferred option. Although pasteurization has been shown to have minimal impact on the lipid and FA composition before digestion, no correlation has been made between the impact of pasteurization on the FFA composition and the self-assembly of lipids during digestion, which could act as delivery mechanisms for poorly water-soluble components. Pooled nonpasteurized and pasteurized human milk from a single donor was used in this study. The evolving FFA composition during digestion was determined using GC coupled to a flame ionization detector. In vitro digestion coupled to small-angle X-ray scattering was utilized to investigate the influence of different calcium levels, fat content, and the presence of bile salts on the extent of digestion and structural behavior of human milk lipids. Almost complete digestion was achieved when bile salts were added to the systems containing high calcium to milk fat ratio, with similar structural behavior of lipids during digestion of both types of human milk being apparent. In contrast, differences in the colloidal structures were formed during digestion in the absence of bile salt because of a greater amount of FFAs being released from the nonpasteurized than pasteurized milks. This difference in FFAs released from both types of human milk could result in varying nutritional implications for infants.
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Organic light-emitting diodes (OLEDs) are subject to thermal stress from Joule heating and the external environment. In this work, neutron reflectometry (NR) was used to probe the effect of heat on ...the morphology of thin three-layer organic films comprising materials typically found in OLEDs. It was found that layers within the films began to mix when heated to approximately 20 °C above the glass-transition temperature (T g) of the material with the lowest T g. Diffusion occurred when the material with the lowest T g formed a supercooled liquid, with the rates of interdiffusion of the materials depending on the relative T g’s. If the supercooled liquid formed at a temperature significantly lower than the T g of the higher-T g material in the adjacent layer, then pseudo-Fickian diffusion occurred. If the two T g’s were similar, then the two materials can interdiffuse at similar rates. The type and extent of diffusion observed can provide insight into and a partial explanation for the “burn in” often observed for OLEDs. Photoluminescence measurements performed simultaneously with the NR measurements showed that interdiffusion of the materials from the different layers had a strong effect on the emission of the film, with quenching generally observed. These results emphasize the importance of using thermally stable materials in OLED devices to avoid film morphology changes.
The effect of varying the emitter concentration on the structural properties of an archetypal phosphorescent blend consisting of 4,4′‐bis(N‐carbazolyl)biphenyl and tris(2‐phenylpyridyl)iridium(III) ...has been investigated using non‐equilibrium molecular dynamics (MD) simulations that mimic the process of vacuum deposition. By comparison with reflectometry measurements, we show that the simulations provide an accurate model of the average density of such films. The emitter molecules were found not to be evenly distributed throughout film, but rather they can form networks that provide charge and/or energy migration pathways, even at emitter concentrations as low as ≈5 weight percent. At slightly higher concentrations, percolated networks form that span the entire system. While such networks would give improved charge transport, they could also lead to more non‐radiative pathways for the emissive state and a resultant loss of efficiency.
The distribution of triplet emitters in molecular hosts for organic light‐emitting diodes was investigated using a combination of simulations and experimentation. At relatively low guest concentrations, triplet emitters were found to cluster, forming possible percolation pathways for charge carriers.
We have recently shown that real-time monitoring of drug solubilization and changes to solid state of the drug during digestion of milk can be achieved using synchrotron small-angle X-ray scattering. ...A complementary laboratory-based method to explore such changes is low-frequency Raman spectroscopy, which has been increasingly used to characterize crystalline drugs and their polymorphs in powders and suspensions. This study investigates the use of this technique to monitor in situ drug solubilization in milk during the process of digestion, using a lipolysis model/flow-through configuration identical to that used previously for in situ synchrotron small-angle X-ray scattering studies. An antimalarial drug, ferroquine (SSR97193), was used as the model drug for this study. The Raman spectra were processed using multivariate analysis to extract the drug signals from the milk digestion background. The results showed disappearance of the ferroquine peaks in the low-frequency Raman region (<200 cm–1) after approximately 15–20 min of digestion when milk fat was present in the system, which indicated drug solubilization and was in good agreement with the in situ small-angle X-ray scattering measurements. This proof-of-concept study therefore suggests that low-frequency Raman spectroscopy can be used to monitor drug solubilization in a complex digesting milk medium because of the unique vibrational modes of the drug crystal lattices.
Engineering dielectric constants in organic semiconductors Armin, Ardalan; Stoltzfus, Dani M.; Donaghey, Jenny E. ...
Journal of materials chemistry. C, Materials for optical and electronic devices,
2017, Letnik:
5, Številka:
15
Journal Article
Recenzirano
The dielectric properties of three pairs of organic semiconductors that contain increasing numbers of cyclopentadithiophene- co -benzothiadiazole moieties (monomer, dimer and polymer) were studied ...and compared. The materials in each pair differed in the nature of the ‘solubilizing groups’, which are either alkyl- or glycol-based. At low frequencies (<MHz), dielectric constants of up to ∼9 were obtained for the glycolated materials. In addition, the optical- (high-) frequency dielectric constants for the glycolated dimer and polymer were 4.6 and 4.2 respectively, which are the highest values reported thus far for non-ionic organic semiconductors. The external and internal quantum efficiencies (EQE and IQE) of homojunction ( i.e. , single component) solar cells comprising the dimer and polymer glycolated materials both showed measurable improvements at wavelengths close to their optical gap when compared with the alkylated equivalents. The improvement is suggestive of an increase in the charge generation efficiency, potentially facilitated by the high optical-frequency dielectric constant.
Nanoparticle dispersions open up an ecofriendly route toward printable organic solar cells. They can be formed from a variety of organic semiconductors by using miniemulsions that employ surfactants ...to stabilize the nanoparticles in dispersion and to prevent aggregation. However, whenever surfactant-based nanoparticle dispersions have been used to fabricate solar cells, the reported performances remain moderate. In contrast, solar cells from nanoparticle dispersions formed by precipitation (without surfactants) can exhibit power conversion efficiencies close to those of state-of-the-art solar cells processed from blend solutions using chlorinated solvents. In this work, we use small-angle neutron scattering measurements and transient absorption spectroscopy to investigate why surfactant-free nanoparticles give rise to efficient organic solar cells. We show that surfactant-free nanoparticles comprise a uniform distribution of small semiconductor domains, similar to that of bulk-heterojunction films formed using traditional solvent processing. This observation differs from surfactant-based miniemulsion nanoparticles that typically exhibit core–shell structures. Hence, the surfactant-free nanoparticles already possess the optimum morphology for efficient energy conversion before they are assembled into the photoactive layer of a solar cell. This structural property underpins the superior performance of the solar cells containing surfactant-free nanoparticles and is an important design criterion for future nanoparticle inks.
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