Heterogeneous Substrates Research Articles

Heterogeneous Nb-Based Nuclei for the Grain Refinement of Al-Si Alloys

Nb-based intermetallics are, generally, low-density high-temperature materials used for structural applications or cryogenic superconductors. In this work, we report the development of an Al(96)-Nb(2)-B(2) master alloy where in situ-formed micrometric Nb-based intermetallics (i.e. NbB2 and Al3Nb) are used for a completely different purpose: to promote the refinement of Al-Si alloys by taking advantage of enhanced heterogeneous nucleation. Nb-based intermetallics have the right characteristics, like low density, stability at high temperature and good lattice match, to be used as heterogeneous nucleation substrates. It was found that the addition of these Nb-based intermetallics permits the significant refinement of the microstructural features of the Al-Si alloy studied. The enhanced heterogeneous nucleation makes the grain size of the material far less dependent on the cooling rate, which is one of the critical parameters influencing the variation of the properties of the alloy.

Fluctuations in complex networks with variable dimensionality and heterogeneity.

Synchronizing individual activities is essential for the stable functioning of diverse complex systems. Understanding the relation between dynamic fluctuations and the connection topology of substrates is therefore important, but it remains restricted to regular lattices. Here we investigate the fluctuation of loads, assigned to the locally least-loaded nodes, in the largest-connected components of heterogeneous networks while varying their link density and degree exponents. The load fluctuation becomes finite when the link density exceeds a finite threshold in weakly heterogeneous substrates, which coincides with the spectral dimension becoming larger than 2 as in the linear diffusion model. The fluctuation, however, diverges also in strongly heterogeneous networks with the spectral dimension larger than 2. This anomalous divergence is shown to be driven by large local fluctuations at hubs and their neighbors, scaling linearly with degree, which can give rise to diverging fluctuations at small-degree nodes. Our analysis framework can be useful for understanding and controlling fluctuations in real-world systems.

Molecular dynamics simulation of melt structure evolution during cooling process for lead on nickel substrate surface

The effect of heterogeneous substrates with micro-scale structure on the evolution of melt during the process of solidification is investigated, by molecular dynamics simulation on the structure evolution of lead melt on nickel substrate with a groove. During the cooling process, BCC structure forms firstly, and then FCC and HCP structures begin to form with the ratio reduction of BCC structure. Due to the existence of additional constraints by the substrate groove, the majority of the BCC structure inside the groove transforms into the metastable structure HCP, while the BCC structure outside the groove transforms into stable FCC structure mainly. At the end of the cooling process, a hybrid structure with FCC and HCP is formed from the lead melt, where FCC structure is dominant in the structure outside the groove, but HCP structure accounts for the majority in the groove.

RIM15 antagonistic pleiotropy is responsible for differences in fermentation and stress response kinetics in budding yeast.

Different natural yeast populations have faced dissimilar selective pressures due to the heterogeneous fermentation substrates available around the world; this increases the genetic and phenotypic diversity in Saccharomyces cerevisiae In this context, we expect prominent differences between isolates when exposed to a particular condition, such as wine or sake musts. To better comprehend the mechanisms underlying niche adaptation between two S. cerevisiae isolates obtained from wine and sake fermentation processes, we evaluated fermentative and fungicide resistance phenotypes and identify the molecular origin of such adaptive variation. Multiple regions were associated with fermentation rate under different nitrogen conditions and fungicide resistance, with a single QTL co-localizing in all traits. Analysis around this region identified RIM15 as the causative locus driving fungicide sensitivity, together with efficient nitrogen utilization and glycerol production in the wine strain. A null RIM15 variant confers a greater fermentation rate through the utilization of available glucose instead of its storage. However, this variant has a detrimental effect on fungicide resistance since complex sugars are not synthesized and transported into the membrane. Together, our results reveal the antagonist pleiotropic nature of a RIM15 null variant, positively affecting a series of fermentation related phenotypes, but apparently detrimental in the wild.

Palladium clusters deposited on the heterogeneous substrates

To improve the performance of the Pd composite membrane prepared by the cold spraying technology, it is extremely essential to give insights into the deposition process of the cluster and the heterogeneous deposition of the big Pd cluster at the different incident velocities on the atomic level. The deposition behavior, morphologies, energetic and interfacial configuration were examined by the molecular dynamic simulation and characterized by the cluster flattening ratio, the substrate maximum local temperature, the atom-embedded layer number and the surface-alloy formation. According to the morphology evolution, three deposition stages and the corresponding structural and energy evolution were clearly identified. The cluster deformation and penetrating depth increased with the enhancement of the incident velocity, but the increase degree also depended on the substrate hardness. The interfacial interaction between the cluster and the substrate can be improved by the higher substrate local temperature. Furthermore, it is found that the surface alloys were formed by exchanging sites between the cluster and substrate atoms, and the cluster atoms rearranged following as the substrate lattice arrangement from bottom to up in the deposition course. The ability and scope of the structural reconstruction are largely determined by both the size and incident energy of the impacted cluster.

Recent Strategies to Overexpress and Engineer Cellulases for Biomass Degradation

Bioenergy is one of the best options towards replacing fossil fuels with renewable, carbon-neutral alternatives. To generate bioenergy at an industrial scale, we must be able to design an optimized cell factory that will convert chemically complex residual biomass or lignocellulose to useful liquid fuels. Microorganisms have evolved a sophisticated enzymatic machinery to degrade these heterogeneous biomass substrates to soluble sugar. These enzyme cocktails are primarily composed of various glycoside hydrolases (GHs) and act synergistically to efficiently cleave the glycosidic linkages in the biomass. Here we review the current strategies to engineer and improve cellulases and the efforts to understand and create microbes with improved catalytic proficiencies. Keywords: Biomass, cellulase, lignocellulose, metabolic engineering, protein engineering.

A highly diverse siliceous sponge fauna (Porifera: Hexactinellida, Demospongiae) from the Eocene of north-eastern Italy: systematics and palaeoecology

A siliceous sponge fauna, consisting of more than 900 specimens, is described from an early Lutetian tuffite horizon in the Chiampo Valley, Lessini Mountains, north-eastern Italy. Thirty-two taxa (15 Hexactinellida, 17 Demospongiae) are determined and illustrated, belonging to 24 genera, two of which are new (Rigonia gen. nov. and Coronispongia gen. nov.). Among these, 10 new species are proposed: Stauractinella eocenica sp. nov., Rigonia plicata gen. et sp. nov., Hexactinella clampensis sp. nov., Camerospongia visentinae sp. nov., C. tuberculata sp. nov., Toulminia italica sp. nov., Coronispongia confossa gen. et sp. nov., Cavispongia scarpai sp. nov., Corallistes multiosculata sp. nov. and Bolidium bertii sp. nov. Of the genera identified at Chiampo, 14 range back to the Cretaceous, three to the Jurassic and one to the Triassic, while six are still extant. The studied fauna shows affinities with sponges from the Eocene of Spain and the Cretaceous of Germany. The sponge fossils are uncompressed and bodily preserved, but the original siliceous skeleton is dissolved and substituted by calcite. Delicate attachments can be nevertheless documented: some sponges attached to a hard substrate by encrustation, while others were anchored on soft sediments by root-like structures. The presence of different modes of attachment suggests heterogeneous substrate conditions. Small, possibly young, sponges are recorded too. The sponge fauna is essentially autochthonous and lived in the middle-outer part of a carbonate ramp, where it formed clusters. This study extends the geographical and stratigraphical range of many sponge taxa, including Camerospongia, Toulminia, Ozotrachelus and Bolidium, previously documented only from the Cretaceous. The Recent calcified demosponge genus Astrosclera is reported here in the Cenozoic for the first time, having been reported previously in the Triassic only. Additionally, this study documents the second worldwide occurrence of the Recent sphinctozoan genus Vaceletia in the Palaeogene, formerly recorded exclusively in Australia.http://zoobank.org/urn:lsid:zoobank.org:pub:B3466955-8E20-429A-89BE-42BAEB4002E8

A Generalized Cassie-Baxter Equation for Wetting Phenomena of Cylindrical Nano-Droplets on Heterogeneous Substrates

A Generalized Cassie-Baxter Equation for Wetting Phenomena of Cylindrical Nano-Droplets on Heterogeneous Substrates

Molecular dynamics study on the nucleation of Al-Si melts on sheet substrates at the nanoscale.

Molecular dynamics (MD) simulations are performed to study the freezing process of Al-Si melts on heterogeneous Si substrates in detail. We highlight the inherent nanostructure of both the Si primary phase and the Al-Si binary phase. It is found for the first time that the primary Si phase displays a "pyramidal configuration" when the Al-Si melt congeals. Experimental measurements could also verify our simulation results. It can be found that the binary Al-Si phase turns into a "Si-Al-Si sandwich construction" during solidification, regardless of freezing on a single substrate or in the restricted space between substrates. This peculiar phenomenon results from the combined effects of the van der Waals potential well and the interatomic interaction between Al and Si. Furthermore, it is also able to control the thickness of the Si atomic shell of the "sandwich construction", resulting in the silicene-like unilaminar Si nanostructure. Our findings provide novel strategies to fabricate desired shaped nanostructures by means of nanocasting in Al-Si melts at the nanoscale.

INTERACTION OF TECTONIC UPLIFT AND EXOGENOUS DESTRUCTION OF A SLOPE COMPOSED OF NON UNIFORM SUBSTRATES

Landform morphology created by combined action of endogenous deformations and exogenous (denudation) processes depends on whether these forces performed concurrently or in succession in this study, different formation scenarios for a tectonic arch composed of heterogenous substrates are analyzed based on kinematic modeling techniques. Following the start of the uplift, a lengthwise zone of softer rocks is being transformed into a gorge with a narrow outlet either in case of tectonic tilt and vertical (block) elevation. V-shaped cross-section is being preserved in the outlet as long as the elevation above base level increases. This scenario is valid for many young alpine regions such as Kopet Dag, Himalaya, etc. After the uplift has been finished, gorges start to widen and become trough-like in cross section, and a progressively widening step starts to form at the base of the arch slope (a pediment). In a block that contains a hard vertical dyke, a gently sloping crest is formed following the uplift start. After the uplift cessation, the crest preserves its form retreating together with the whole arch slope. Slow elevation of an arch containing a hard horizontal layer results in transformation of the upper part of the arch into a small spherical remnant. At the side of the hard layer, a steep cliff forms that passes below into a conical pedestal produced by denudation in softer rocks. In case if the arch contains a softer horizontal layer the surface of the raising block evolves rather to conical than to spherical form.

English

Abstract Stream habitat-use of female crayfish during brooding of eggs and hatchlings is a poorly studied aspect of crayfish life history and ecology. Our goal was to use passive integrated transponder (PIT) technology to describe diurnal habitat-use patterns of females of two crayfish species during reproductive seclusion. PIT tags were externally attached to female Cambarus friaufi in Pine Creek, Tennessee, USA and Orconectes meeki meeki in Rock Creek, Missouri, USA. Crayfish were tracked with a portable detector and habitatuse was assessed in 2008 for C. friaufi and 2009 for O. m. meeki. PIT tags proved to be a highly effective tool for relocating crayfish, with = 85% of tagged individuals located at least once. Substrate roughness was identified as the most important variable for both species during brooding, followed by additional substrate-related variables, water velocity, and water depth. Cambarus friaufi, however, was more of a generalist and used microhabitat variables in close proportion to availability, whereas O. m. meeki showed more specialized use of brooding habitat variables. Our results suggest that female crayfish reproductive seclusion is closely linked to sufficiently heterogeneous substrate. Reductions in substrate quality could potentially alter crayfish reproductive capacity, thus impacting biodiversity and productivity of streams.

Microscale measurements of oxygen concentration across the thickness of diffusion media in operating polymer electrolyte fuel cells

Although polymer electrolyte fuel cells (PEFCs) offer promise as efficient, low emission power sources, the large amount of platinum catalyst used for the cathode's oxygen reduction (ORR) results in high costs. One approach to using less Pt is to increase the oxygen concentration at the catalyst by reducing the oxygen transport resistances. An important resistance is that of the diffusion media (DM). The DM are highly heterogeneous porous carbon fiber substrates with a graded composition of additives across their thickness. In this work we use an oxygen microsensor with a micro-positioning system to measure the oxygen concentration and presence of liquid water in the pores at discrete points across the thickness of a commercial carbon felt DM in operating PEFCs. Under conditions with no liquid water, the DM accounts for 60% of the oxygen depletion, with 60–70% of that depletion being due to the thin microporous layer (MPL) on the catalyst layer (CL) side. Using concentration gradient data, we quantify the non-uniform local transport resistance across the DM and relate it to high resolution 3D X-ray computed tomography of the same DM.

Orthogonal chemical functionalization of patterned gold on silica surfaces.

Single-step orthogonal chemical functionalization procedures have been developed with patterned gold on silica surfaces. Different combinations of a silane and a thiol were simultaneously deposited on a gold/silica heterogeneous substrate. The orthogonality of the functionalization (i.e., selective grafting of the thiol on the gold areas and the silane on the silica) was demonstrated by X-ray photoelectron spectroscopy (XPS) as well as time-of-flight secondary ion mass spectrometry (ToF–SIMS) mapping. The orthogonal functionalization was used to immobilize proteins onto gold nanostructures on a silica substrate, as demonstrated by atomic force microscopy (AFM). These results are especially promising in the development of future biosensors where the selective anchoring of target molecules onto nanostructured transducers (e.g., nanoplasmonic biosensors) is a major challenge.

Generalized Cassie-Baxter Equation for Nanodroplet on Heterogeneous and Spherical Solid Substrates

Generalized Cassie-Baxter Equation for Nanodroplet on Heterogeneous and Spherical Solid Substrates

Improving impact toughness of a high chromium cast iron regarding joint additive of nitrogen and titanium

In this work, the effect of nitrogen on the as-cast microstructure and impact toughness of high chromium cast irons(HCCIs) mainly containing 2.2%C, 25.0%Cr and 0.8%Ti was studied (all compositions are in wt.% in this work). The experimental results showed that with the addition of N(0.028%, 0.075%, 0.2%, respectively), Ti(C,N) precipitates were formed in the high chromium cast irons, and dispersedly distributed in M7C3 carbides and austenite matrix. With the increase of nitrogen content, the microstructure was significantly refined, especially the M7C3 carbides, which was related to the heterogeneous nucleation of M7C3 carbide where Ti(C,N) precipitates act as the heterogeneous nuclei substrates. The Rockwell hardness of the specimen with 0.2% nitrogen increased to 49HRC in comparison to the specimen with 0.028% nitrogen (47HRC). The impact toughness of the specimen reached its peak value of 20.79J/cm2 with 0.075% nitrogen, improving almost 80% compared with the specimen with 0.028% nitrogen (11.80J/cm2).

Understanding β-mannanase from Streptomyces sp. CS147 and its potential application in lignocellulose based biorefining.

Hydrolytic enzymes such as cellulase and hemicellulase have been attracted in lignocellulose based biorefinery. Especially, mannanase has been a growing interest in industrial applications due to its importance in the bioconversion. In this study, an extracellular endo-β-1,4-D-mannanase was produced by Streptomyces sp. CS147 (Mn147) and purified 8.5-fold with a 43.4% yield using Sephadex G-50 column. The characterization of Mn147 was performed, and the results were as follows: molecular weight of ∼25 kDa with an optimum temperature of 50°C and pH of 11.0. The effect of metal ions and various reagents on Mn147 was strongly activated by Ca(+2) but inhibited by Mg(+2) , Fe(+2) , hydrogen peroxide, EDTA and EGTA. Km and Vmax values of Mn147 were 0.13 mg/mL and 294 μmol/min mg, respectively, when different concentrations (3.1 to 50 mg/mL) of locust bean gum galactomannan were used as substrate. In enzymatic hydrolysis of heterogeneous substrate (spent coffee grounds), Mn147 shows a similar conversion compared to commercial enzymes. In addition, lignocellulosic biomass can be hydrolyzed to oligosaccharides (reducing sugars), which can be further utilized for the production of biomaterials. These results showed that Mn147 is attractive in quest of potential bioindustrial applications.

Derivation of Generalized Cassie-Baxter Equation for Nano-Scale Wetting Phenomena of Nanodroplets on Heterogeneous Substrates

Derivation of Generalized Cassie-Baxter Equation for Nano-Scale Wetting Phenomena of Nanodroplets on Heterogeneous Substrates

Intercalation of HF, H2O, and NH3 Clusters within the Bilayers of Graphene and Graphene Oxide: Predictions from Coronene-Based Model Systems.

Understanding molecular interactions with monolayers and bilayers of graphene and its derivatized forms is very important because of their fundamental role in gas sensing and separation, gas storage, catalysis, etc. Herein, motivated by the recent realization of graphene-based sensors for the detection of single gas molecules, we use density functional theory to study the noncovalent interactions of molecules and molecular clusters with graphene, graphene oxide, and graphane, which are represented by coronene-based molecular model systems, C24H12 (coronene), C24OH12 (coroepoxide), and C24H36 (perhydrocoronene), respectively. The objective is to understand the structural and energetic changes that occur as a result of adsorption on monolayers and intercalation within bilayers. To begin with, the interactions of coronene, coroepoxide, and perhydrocoronene with a variety of small molecules like HF, HCl, HBr, H2O, H2S, NH3, and CH4 are studied. Subsequently, the binding of coronene and coroepoxide substrates with molecular clusters of HF, H2O, and NH3 is studied to understand the strength of adsorption on the substrates and the effect of substrates on hydrogen-bonding interactions within the molecular clusters. Further, bilayers of the model systems, namely, coronene-coronene, coronene-coroepoxide, and two configurations of coroepoxide-coroepoxide (one in which the oxygen atoms are facing each other and the other in which they do not face each other) are generated. The energetics for the nanoscale confinement or intercalation of the clusters within the bilayers along with the impact of the intercalation on the intermolecular hydrogen-bonding interactions are investigated. Our coronene-based model systems can provide a simple way of describing the rather complex events that occur in representative regions of graphene-based heterogeneous substrates.

Microbial population dynamics during long-term sludge adaptation of thermophilic and mesophilic sequencing batch digesters treating sewage fine sieved fraction at varying organic loading rates

BackgroundIn this research, the feasibility of, and population dynamics in, one-step anaerobic sequencing batch reactor systems treating the fine sieved fraction (FSF) from raw municipal wastewater was studied under thermophilic (55 °C) and mesophilic (35 °C) conditions. FSF was sequestered from raw municipal wastewater, in the Netherlands, using a rotating belt filter (mesh size 350 micron). FSF is a heterogeneous substrate that mainly consists of fibres originating from toilet paper and thus contains a high cellulosic fraction (60–80 % of total solids content), regarded as an energy-rich material.ResultsResults of the 656-day fed-batch operation clearly showed that thermophilic digestion was more stable, applying high organic loading rates (OLR) up to 22 kg COD/(m3 day). In contrast, the mesophilic digester already failed applying an OLR of 5.5 kg COD/(m3 day), indicated by a drop in pH and increase in volatile fatty acids (VFAs). The observed viscosity values of the mesophilic sludge were more than tenfold higher than the thermophilic sludge. 454-pyrosequencing of eight mesophilic and eight thermophilic biomass samples revealed that Bacteroides and aceticlastic methanogen Methanosaeta were the dominant genera in the mesophilic digester, whereas OP9 lineages, Clostridium and the hydrogenotrophic methanogen Methanothermobacter dominated the thermophilic one.ConclusionsOur study suggests that applying thermophilic conditions for FSF digestion would result in a higher biogas production rate and/or a smaller required reactor volume, comparing to mesophilic conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0355-3) contains supplementary material, which is available to authorised users.

Leaf-Nets (LN): A New Quantitative Method for Sampling Macroinvertebrates in Non-Wadeable Streams and Rivers

The ecological knowledge of large rivers is still scarce or highly fragmented mainly because of complex, laborious and expensive procedures to collect informative samples from the benthic biota. Standard sampling protocols for macroinvertebrates were mainly developed and calibrated for wadeable streams, while a number of heterogeneous non-standard sampling procedures are available for large rivers. We propose the new, easy-to-build and cost-effective leaf-nets (LN) method to quantitatively sample benthic invertebrates in non-wadeable waterways. The LN method uses Phragmites australis leaves as substrate and combines the characteristics of the leaf-bags and the Hester–Dendy (HD) multiplates methods. We compared the effectiveness of the LN and HD methods in a near-pristine and in an impacted stream-reach (downstream an aquaculture plant) of a non-wadeable second-order stream of Central Apennines (Italy). Twenty-five of the 34 cumulatively collected macroinvertebrate taxa were common to both methods, while seven taxa were found only on LN and two only on HD. Taxonomic richness and total macroinvertebrate abundance were higher for LN assemblages. Number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) also tended to be higher on LN. Assemblage composition was different on LN and HD. Both methods documented a significant decrease in EPT taxa and a concomitant increase in the total abundance of more pollution-tolerant taxa in the impacted stream-reach, but the LN method was more sensitive to impact-associated changes in macroinvertebrate assemblage structure. In contrast to the hardboard plates of HD, the assembled leaves of the LN may act as a direct or indirect food source and may better mimic the texture and composition of more heterogeneous natural substrates thus favouring the migration–colonization process from both bottom and littoral benthic invertebrates. The sampling efficiency, cost effectiveness and simplicity warrant the routine use of the new LN method in large-river ecological assessment. Copyright © 2015 John Wiley & Sons, Ltd.