Search

There is growing recognition of the importance of food quality over quantity for aquatic consumers. In streams and rivers, most previous studies considered this primarily in terms of the quality of terrestrial leaf litter and importance of microbial conditioning. However, many recent studies suggest that algae are a more nutritional food source for riverine consumers than leaf litter. To date, few studies have quantified longitudinal shifts in the nutritional quality of basal food resources in river ecosystems and how these may affect consumers.We conducted a field investigation in a subalpine river ecosystem in Austria to investigate longitudinal variations in diet quality of basal food sources (submerged leaves and periphyton) and diet source dependence of stream consumers (invertebrate grazers, shredders, filterers and predators, and fish). Fatty acid (FA) profiles of basal food sources and their consumers were measured.Our results indicate systematic differences between the FA profiles of terrestrial leaves and aquatic biota, that is periphyton, invertebrates and fish. Submerged leaves contained very low proportions of long‐chain polyunsaturated fatty acids (LC‐PUFAs), which were conversely rich in aquatic biota. While the FA composition of submerged leaves remained similar among sites, the LC‐PUFAs of periphyton increased longitudinally, which was associated with increasing nutrients from upstream to downstream.Longitudinal variations in periphyton LC‐PUFAs were reflected in the LC‐PUFAs of invertebrate grazers and shredders, and further tracked by invertebrate predators and fish. However, brown trout Salmo trutta contained a large proportion of docosahexaenoic acid (DHA, 22:6ω3), a LC‐PUFA almost entirely missing in basal sources and invertebrates. The fish accumulated eicosapentaenoic acid (EPA, 20:5ω3) from invertebrate prey and may use this FA to synthesize DHA.Our results provide a nutritional perspective for river food web studies, emphasizing the importance of algal resources to consumer somatic growth and the need to account for the longitudinal shifts in the quality of these basal resources. [ABSTRACT FROM AUTHOR]

Abstract: Many efforts have been made to incorporate our improved understanding of zooplankton physiology and behaviour into mathematical models. The increased complexity, however, has been a major impediment in integrating these advances into management-oriented models and thus bridging the gap between theoretical and applied ecology. In this study, we enhance an existing eutrophication model with a zooplankton somatic growth submodel that simulates the interplay among nitrogen, phosphorus, and highly unsaturated fatty acids (HUFAs) through the grazers’ digestive tracks. We calibrate the newly incorporated parameters (and associated processes) against observed data from the mesotrophic Lake Washington. We extrapolate the model to different trophic environments and tease out the underlying drivers of zooplankton growth. Our analysis suggests that both stoichiometric and HUFA based somatic growth limitations can modulate the zooplankton biomass in mesotrophic environments. Food abundance and mineral P limitation are critical factors of zooplankton growth under oligotrophic conditions, while HUFA availability is the main driving force of plankton dynamics in eutrophic states. Our zooplankton submodel downplays pre-gut regulation in favour of post-gut metabolic processing, which appears to shift the bulk of the non-limiting nutrient recycling from particulate to dissolved form. The homeostatic maintenance of somatic quotas and the dynamic nutrient recycling could also be an important mechanism for shedding light on the controversial hypothesis that the enrichment of natural ecosystems is a destabilizing factor of food web dynamics. [Copyright &y& Elsevier]

Abstract: We report the fabrication, characterisation, and electro-catalytic activity of <0.3 mg cm−2 platinum deposits onto ∼500 nm long nickel nanopillar substrates (NiNP) synthesised by glancing angle deposition (GLAD). This is the first reported study of GLAD-based Pt–Ni electro-catalysts and the first alcohol oxidation study on any GLAD based electro-catalyst. The Pt was deposited onto NiNP via either 1) an unconventional, self-limiting, relatively high current density galvanostatic deposition, with a Pt counter electrode as the source of Pt, or 2) via a conventional potentiostatic deposition from Pt salts dissolved in acidic electrolytes. X-ray Diffraction (XRD) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) confirm the successful deposition of Pt onto NiNP, while Scanning Electron Microscopy (SEM) shows that the nanopillar morphology is preserved but the Pt morphology is significantly different between the two methods. The galvanostatic procedure resulted in a conformal Pt deposition over the entire surface of the NiNP. The conventional procedure appeared to be mass-transfer limited, with most of the Pt being deposited on the tops of the NiNP. Cyclic voltammetry in 1 M KOH shows an enhancement of the surface area of the catalysts upon Pt deposition and corroborates the presence of Pt on the NiNP surface. Both prepared catalysts show high electro-catalytic activity towards 2-propanol oxidation in the KOH electrolyte at 60 °C. The activity enhancement below 300 mV vs. RHE (RHE = reversible hydrogen electrode) was attributed to the combined activity of the Pt and Ni components in the catalysts. At higher potentials, a bifunctional mechanism was suggested. Finally, a geometric/composition effect may be at work in the traditionally deposited catalyst, and requires further investigation. [Copyright &y& Elsevier]

Abstract: Fabrication of interdigitated organic photovoltaic (OPV) devices commonly involves filling a nanostructured thin film using solution-based methods. In these cases, the sensitivity of the nanostructured films to the solvents used needs to be studied in order to optimize the interface. Here, we study the ability of chlorobenzene (CB) and dichlorobenzene (DCB) to dissolve and recrystallize zinc phthalocyanine (ZnPc) thin films, while fabricating interdigitated active layers composed of ZnPc and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). Using glancing angle deposition (GLAD), we are able to construct slanted nanorod arrays of ZnPc, with nanorod diameters of nominally 40nm and lengths up to 450nm. We find that these films are recrystallized upon direct exposure to CB and DCB, regardless of initial morphology, yielding a variety of possible nanoscale formations. The crystallinity and absorbance of these recrystallized films changes as well, depending on solvent choice and exposure time. Through control of initial ZnPc film morphology and solvent choice for PCBM casting, we exploit the sensitivity of ZnPc to these organic solvents to optimize the photovoltaic performance of ZnPc/PCBM devices. Optimal OPV device performance is achieved with a 30nm thick GLAD-textured ZnPc film while using DCB as the PCBM solvent. In this case, power conversion efficiencies are up to 3.0%, compared to an average of 2.3% when using CB as the solvent on the same film, and 2.3% also for bilayer devices when using DCB as the solvent. A higher degree of material mixing at the ZnPc/PCBM interface is shown when using DCB over CB as the PCBM solvent, which may be the primary mechanism for the photovoltaic improvements seen in these devices. [Copyright &y& Elsevier]

Zooplankton transfer ecologically important fatty acids (FA) from their diets to upper trophic levels. We used diet-switching experiments with 13C-labeled food sources to determine the time scale at which dietary uptake is manifested in the FA profiles of Daphnia magna. Daphnia dramatically shifted their FA composition in response to diet change within only four days, however Daphnia switched from a high quality (i.e. Cryptomonas) to a moderate quality ( Scenedesmus) diet retained the most physiologically important FA from their original diet source even after 14 days. In particular, Daphnia exhibited long-term retention of eicosapentaenoic (EPA; 20:5ω3) and arachidonic acid (ARA; 20:4ω6) when switched from Cryptomonas to Scenedesmus. Similarly, when switched from Scenedesmus to Cryptomonas, Daphnia took up a high proportion of EPA and ARA after only two days. The phospholipid fatty acid (PLFA) fraction in Daphnia was preferentially enriched with stearic (18:0), oleic (18:1ω9), and linoleic acid (LIN; 18:2ω6). In contrast with studies of marine copepods, dietary FA also strongly affected the PLFA composition (structural lipids) of Daphnia. Results of δ13C signatures of individual FA provided evidence of elongation and desaturation of α-linolenic (ALA; 18:3ω3) or stearidonic acid (SDA; 18:4ω3) to EPA 10 days after a diet switch to EPA-deficient Scenedesmus. Differences in the ARA content of Daphnia fed Cryptomonas and Scenedesmus suggest Daphnia consuming Cryptomonas synthesized ARA via retroconversion of ω6-docosapentaenoic acid (ω6-DPA; 22:5ω6). Daphnia preferentially accumulate and retain, as well as bioconvert, those FA that are also most physiologically important for fish production. Our results also indicate Daphnia FA composition responds to their diet on a short temporal scale and analyses of lipid biomarkers in zooplankton provide strong insights into the food sources that support their production. [ABSTRACT FROM AUTHOR]

Abstract: The porous nature of high surface area and large aspect ratio nanorods arrays make them strong candidates for a range of applications from catalyst supports to energy scavenging devices. The glancing angle deposition (GLAD) technique is a straightforward and flexible method for ensuring control of morphology and porosity in nanorod arrays. Quantifying the porous nature of nanostructured columnar arrays, fabricated using the GLAD technique, is critical for understanding and optimizing the performance of devices fabricated using this method. The mesoporosity and pore volume of these GLAD nanorod arrays have thus been characterized using gas adsorption (krypton adsorption at 87.3K) and scanning electron microscopy (SEM) image analysis techniques. To characterize the obliquely deposited amorphous titanium dioxide (TiO2) and silicon dioxide (SiO2) samples, top-down SEM images of the films were also analyzed which allowed us to determine the mean distance between columns. SEM image analysis permitted for estimation of inter-column porosity of films deposited at angles from 65° to 85°, while krypton analysis allowed for the identification of mesoporosity in films from 45° to 85°. Our results provide a comprehensive characterization of GLAD film porosity which will be vital for the design of devices for a diverse set of applications from photonics to sensing to microfluidics. [Copyright &y& Elsevier]

Hydrogenation has proven to be an effective tool to open the band gap of graphene. In the present density functional study, we demonstrate that single-side-hydrogenated graphene is a semiconductor with an indirect band gap of 1.35 eV, which is in between the gapless graphene and wide band-gap graphane and surprisingly close to silicon. We show that its electronic structure and lattice characteristics are substantially different from those of graphene, graphone, or graphane. The lattice parameter and C-C bond length are found to be lengthened by 15% of those of graphene. Our binding-energy analysis confirms that such a single-sided hydrogenation leads to energetically stable material, making it a promising candidate as an organic semiconductor. [ABSTRACT FROM AUTHOR]

Abstract: Zinc oxide nanorod films produced by glancing angle deposition were fabricated within the parameter space defined by the process variables pitch (nanorod growth per substrate rotation), deposition rate, and throw distance to investigate the effect these parameters have on morphology and crystallinity. Statistical analysis was used to identify important relationships. Final film morphology depends on both pitch and deposition rate, where two growth regimes distinguished by deposition rate are observed and interpreted as arising from competition between geometric shadowing and crystalline growth kinetics. Optimal growth conditions for nanostructured films of isolated zinc oxide nanorods occurred for pitch values of approximately 1nm to 10nm. Pole-figure measurements confirm that the films consist of oriented single-crystal nanorods. Films deposited at all pitch values between 0.001nm to 6.5μm are crystalline and textured, and greater texturing is achieved for conditions of decreased surface diffusion. [Copyright &y& Elsevier]

Abstract: Glancing angle deposition (GLAD) was used to deposit controlled-porosity TiO2 thin films of varying pore size and shape. Hybrid materials were fabricated by infiltrating the TiO2 films with poly(3-hexylthiophene) (P3HT) using a spin casting process, which were either employed as-cast or subjected to thermal processing. Photovoltaic devices fabricated using these hybrid materials were characterized as a function of TiO2 pore size and shape, and thermal processing. It was found that the optimum pore size was dependent on the thermal history of the sample. When as-cast hybrid materials were employed conversion efficiencies decreased with increasing pore size. When hybrid materials annealed above the melting point of P3HT were employed the trend was reversed, with conversion efficiency increasing with increasing pore size. Trends in conversion efficiency were found to correlate with P3HT crystallinity, demonstrating that optimum pore sizes for hybrid devices of this type are dependent on sample processing. [ABSTRACT FROM AUTHOR]

We revisit the phosphorus-retention and nutrient-loading models in limnology using a Bayesian hierarchical framework. This methodological tool relaxes a basic assumption of regression models fitted to data sets consisting of observations from multiple systems, i.e., the systems are assumed to be identical in behavior, and therefore the models have a single common set of parameters for all systems. Under the hierarchical structure, the models are dissected into levels (hierarchies) that explicitly account for the role of significant sources of variability (e.g., morphometry, mixing regime, geographical location, land-use patterns, trophic status), thereby allowing for intersystem parameter differences. Thus, the proposed approach is a compromise between site-specific (where limited local data is a problem) and globally common (where heterogeneous systems in wide geographical areas are assumed to be identical) parameter estimates. In this study, we used critical values of the mean lake depth $$ \left( {\bar{z} = 10.3\,{\text{m}}} \right) $$ and the hydraulic residence time ( τw = 2.6 years) to specify the hierarchical levels of the models. Our analysis demonstrates that the hierarchical configuration led to an improvement of the performance of six out of the seven hypothesized relationships used to predict lake-phosphorus concentrations. We also highlight the differences in the posterior moments of the group-specific parameter distributions, although the inference regarding the importance of different predictors (e.g., inflow-weighted total phosphorus input concentration, and hydraulic retention time) of lake phosphorus or the relative predictability of the models examined are not markedly different from an earlier study by Brett and Benjamin. The best fit to the observed data was obtained by the model that considers the first-order rate coefficient for total phosphorus loss from the lake as an inverse function of the lake hydraulic retention time. Finally, our analysis also demonstrates how the Bayesian hierarchical framework can be used for assessing the exceedance frequency and confidence of compliance of water-quality standards. We conclude that the proposed methodological framework will be very useful in the policy-making process and can optimize environmental management actions in space and time. [ABSTRACT FROM AUTHOR]

Temporal variability in lake phytoplankton is controlled largely by a complex interplay between hydrodynamic and chemical factors, and food web interactions. We explored mechanisms underlying phytoplankton interannual variability in Lake Washington (USA), using a 25-yr time series of water quality data (1975–1999). Time-series analysis and PCA were used to decompose chlorophyll data into modes of variability. We found that phytoplankton dynamics in Lake Washington were characterized by four seasonal modes, each of which was associated with different ecological processes. The first mode coincided with the period when the system was light limited (January–March) and phytoplankton patterns were driven by the amount of available solar radiation. The second mode (April–June) coincided with the peak of the spring bloom and the subsequent decline of phytoplankton biomass, and was largely controlled by total phosphorus levels and grazing pressure from cladoceran zooplankton. Evidence of co-dependence and tight relationship between phytoplankton and cladoceran dynamics were also found from July to October when a large portion of the phosphorus supply in the mixed layer was provided by zooplankton excretion. The fourth mode (November–December) was associated with the transition to thermal and chemical homogeneity and the winter phytoplankton minima (2–2.5μg/l). Finally, we examined the effects of meteorological forcing and large-scale oceanic climate fluctuations (ENSO and PDO) on phytoplankton dynamics and assessed the significance of their role on the interannual variability in the lake. [Copyright &y& Elsevier]

Helical microstructures are of interest for MEMS devices because of their spring-like shape. However, helices with micron and submicron dimensions are difficult to engineer using conventional processing techniques where patterning is accomplished lithographically. In this paper, we report the fabrication of porous gold, nickel, and polystyrene thin films with helical pore architectures. All films were made using a replication process, in which a thin film comprised of independent helical microstructures acted as the template. Filling of the template with metals was achieved by electroplating through the microstructures, whereas filling with polystyrene was achieved by capillary action. Porous films were produced from these composites by wet etch removal of the template material. Typical helical pores were on the order of 100 nm in diameter and extended through a film 1 pm to 2 pm thick. These films were generally more robust than the films from which they were templated, since they consisted of a solid network with helical pores rather than individual structures. Polymer and metal films with helical pores could be used for sensor and catalytic devices that take advantage of the chemical properties of these materials. Polymer films are also of interest for mechanical sensor and actuator devices since they are expected to be more compliant than both traditional MEMS materials and the films from which they were templated. [ABSTRACT FROM AUTHOR]

An approach of using a current-controlled voltage source analogy to account for a general boundary condition of particle or thermal flux in transmission-line matrix (TLM) diffusion modelling has been developed. For mass diffusion, this boundary condition is expressed as D ∂C/∂x + αC = 0. where C is the concentration, D is the diffusion coefficient, and α is a parameter characterizing the out-diffusion mobility across the boundary of interest. Confirmation of the TLM numerical treatment through comparison with analytical solutions is presented. Besides the open-circuit and short-circuit boundaries, the matched-load boundary is also found to be a special case of the present boundary condition. This extension of the boundary treatment allows the highly flexible TLM method to be applied to a greater variety of diffusion problems. [ABSTRACT FROM AUTHOR]

According to the River Continuum Concept, headwater streams are richer in allochthonous (e.g. terrestrial leaves) than autochthonous (e.g. algae) sources of organic matter for consumers. However, compared to algae, leaf litter is of lower food quality, particularly ω‐3 polyunsaturated fatty acids (n‐3 PUFA), and would constrain the somatic growth, maintenance, and reproduction of stream invertebrates. It may be thus assumed that shredders, such as Gammarus, receive lower quality diets than grazers, e.g. Ecdyonurus, that typically feed on algae.The objective of this study was to assess the provision of dietary PUFA from leaf litter and algae to the shredder Gammarus and the grazer Ecdyonurus. Three different diets (algae, terrestrial leaves, and an algae–leaf litter mix) were supplied to these macroinvertebrates in a flume experiment for 2 weeks. To differentiate how diet sources were retained in these consumers, algae were isotopically labelled with 13C.Both consumers became enriched with 13C in all treatments, demonstrating that both assimilated algae. For Gammarus, n‐3 PUFA increased, whereas n‐6 PUFA stayed constant. By contrast, the n‐3 PUFA content of Ecdyonurus decreased as a consequence of declining algal supply.Results from compound‐specific stable isotope analysis provided evidence that the long‐chain n‐3 PUFA eicosapentaenoic acid (EPA) in both consumers was more enriched in 13C than the short‐chain n‐3 PUFA α‐linolenic acid, suggesting that EPA was taken up directly from algae and not from heterotrophic biofilms on leaf litter. Both consumers depended on algae as their carbon and EPA source and retained their EPA from high‐quality algae. [ABSTRACT FROM AUTHOR]

Porous chiral thin films composed of a nearly hexagonal-close-packed array of helical nanorods of tris-(8-hydroxyquinoline) aluminum (Alq3) are fabricated using glancing angle deposition and exhibit a one-dimensional polarization-dependent photonic stop band. These chiral thin films transmit only one handedness of circularly polarized light and emit highly circularly polarized photoluminescence. The strong circular Bragg phenomena exhibited by these films suggest potential for use of these films in low-threshold mirrorless lasing and circularly polarized emission applications, while the porosity of the films allows for infiltration by dyes or liquid crystals to enable the formation of unique hybrid materials. [ABSTRACT FROM AUTHOR]

Anisotropic properties of columnar nanoporous thin films were utilized to design and fabricate interference mirrors with lossless omnidirectional reflection in the visible spectral range. Index graded columnar films with distributed Bragg reflector (DBR), sinusoidal, and Gaussian refractive index profiles were studied using finite-difference frequency-domain and finite-difference time-domain methods, with an emphasis on maximizing the omnidirectional reflection bandwidth. Titanium dioxide columnar films with sixteen period sinusoidal refractive index profile were fabricated using the glancing angle deposition technique and characterized by angle resolved transmittance measurements. Simulations and experimental measurements have shown the presence of the omnidirectional reflection band up to 5% wide for a film with a maximum refractive index nmax=2.3 and refractive index contrast Δn=0.8. Simulations further showed that with the optimal choice of the refractive index variation range, the omnidirectional reflection band can reach 10.5% width in TiO2 films with a sinusoidal index profile, 14.5% with a DBR index profile, and 12% with a Gaussian profile. Due to the optical anisotropy of the columnar films, the reflection bandwidth exceeded the corresponding value, observed in isotropic analogs, by a factor of three to four depending on the choice of the refractive index profile. [ABSTRACT FROM AUTHOR]

Nanoimprint lithography was combined with glancing angle deposition (GLAD) of titanium dioxide to fabricate a square spiral columnar film with a bandgap in the visible spectral range. Nanoimprint stamps were fabricated with seed spacing ranging from 80 to 400 nm, and four periods of square spiral film were deposited on top of the 320 nm array of seeds. The ratio of lattice spacing, vertical pitch and spiral arm swing was chosen as a : P : A = 1 : 1.35 : 0.7 and the deposition angle was fixed at 86° to maximize the square spiral film's bandgap. Reflectivity measurements show that the fabricated structure exhibit a pseudo-gap centered at around 600 nm wavelength, in good agreement with finite difference electromagnetic simulations. The absence of a full 3D bandgap is due the deviation of GLAD columns' cross-section from the optimal one, which has to be highly elongated in the deposition plane. However, simulations show that a geometry close to the fabricated one will produce a full 3D bandgap, if the structure is inverted. The material refractive index in such an inverted photonic crystal can be as low as n = 2.15. [ABSTRACT FROM AUTHOR]

Columnar thin films exhibiting linear polarization selectivity have been theoretically investigated and fabricated using the glancing angle deposition (GLAD) technique. The film structure employed an s-shaped columnar morphology that may be either smoothly bent or composed of discrete segments. Finite-difference time-domain and frequency-domain methods have been used to model these thin film structures numerically. Simulation results have yielded optimal geometries in which the films exhibit either a single frequency band with polarization-selective transmittance or two separated frequency bands each transmitting one of two orthogonal linearly polarized modes. Based on these designs, a series of TiO2 films were grown by GLAD with continuous and discrete s-shaped columnar morphology. Experimental measurements by spectrophotometry verified the presence of selectivity for the orthogonal linearly polarized modes. Films with more then 24 periods were found to have polarization selectivity approaching unity. The agreement between the simulation and experimental results demonstrates the potential for future theoretical development of highly selective polarization filters based on GLAD thin films. [ABSTRACT FROM AUTHOR]

Postdeposition thermal annealing is used to enhance the form birefringence of nanostructured TiO2 thin films grown by electron-beam evaporation using the serial bideposition technique. Thin films were grown on fused silica substrates using oblique deposition angles between 60° and 75° and repetitive 180° substrate rotations to produce birefringent thin films that are structurally anisotropic. Postdeposition annealing in air, between 200 and 900 °C, was used to increase the form birefringence of the films by changing the TiO2 phase from the as-deposited amorphous state to a polycrystalline state that exhibits a greater inherent density and larger bulk refractive index. The optical properties, microstructure, and crystallinity were characterized by Mueller matrix ellipsometry, scanning electron microscopy, atomic force microscopy, and x-ray diffraction. It was found that the in-plane birefringence increased significantly upon thermal annealing, in some cases yielding birefringence values that doubled in magnitude, from 0.11 to 0.22 at a wavelength of 550 nm for films annealed at 400 °C. [ABSTRACT FROM AUTHOR]

Presents a study which developed a grain-boundary diffusion model using the transmission-line matrix (TLM) method. Application examples of titanium nitride as a useful diffusion barrier material; Description of a grain oriented film microstructure simulator; Treatment of various boundary conditions that play an essential role in the grain-boundary diffusion modeling.