Discretized Fast–Slow Systems with Canards in Two Dimensions

We study the problem of preservation of maximal canards for time discretized fast–slow systems with canard fold points. In order to ensure such preservation, certain favorable structure-preserving properties of the discretization scheme are required. Conventional schemes do not possess such properties. We perform a detailed analysis for an unconventional discretization scheme due to Kahan. The analysis uses the blow-up method to deal with the loss of normal hyperbolicity at the canard point. We show that the structure-preserving properties of the Kahan discretization for quadratic vector fields imply a similar result as in continuous time, guaranteeing the occurrence of maximal canards between attracting and repelling slow manifolds upon variation of a bifurcation parameter. The proof is based on a Melnikov computation along an invariant separating curve, which organizes the dynamics of the map similarly to the ODE problem.

Preparation and properties of an intelligent adjustable functional paper for organic cultural relics

Precious organic cultural relics are easily affected by temperature, humidity, and harmful gases in the environment, resulting in embrittlement, fading, mildew, moth damage and other aging forms. An energy-saving and environmentally friendly material is needed to stabilize humidity and adsorb harmful gases in the environment. In this paper, with an intelligent adjustment function, functional paper containing sepiolite and tourmaline natural minerals was successfully prepared. The component of 80 % of wingceltis and 20 % of straw in dry pulp as main raw material was conducive to the desorption of water molecules. As favorable structure inside functional paper, the adsorption point and the adsorption contact area increased by the rough surface of fiber bundles, the addition of sepiolite and the ordered molecular chains of copolymers destroyed. So, the relative humidity could be adjusted to 55 % ± 3 within 2 hours and was stable with functional paper. At the same time, 1.11 ppm sulfur dioxide and 2.98 ppm ammonia could be effectively adsorbed in 10 and 12 h, respectively, by 1 g of paper in a 5 L container. The pH of the paper was adjusted to neutral with tourmaline, even if the pH was changed by acidic or alkaline gas absorption. Therefore, for long-term organic cultural relic preservation, preparing a constant-humidity and clean environment is of great significance. This is possible through this paper.

Zinc Induced Aβ16 Aggregation Modeled by Molecular Dynamics

It is widely accepted that the addition of zinc leads to the formation of neurotoxic nonfibrillar aggregates of beta-amyloid peptides Aβ40 and Aβ42 and at the same time destabilizes amyloid fibrils. However, the mechanism of the effect of zinc on beta-amyloid is not fully understood. In this study, a fast zinc-induced aggregation of Aβ16 (as compared to a system without zinc) via the formation of Aβ16 dimers with one zinc ion coordinated in the metal-binding site 11EVHH14, followed by their polymerization, has been studied by molecular dynamics. The best aggregation was shown by the system composed of Aβ16 dimers bound by one zinc ion, with no additional zinc in solution. The presence of Aβ16 dimers was a major condition, sufficient for fast aggregation into larger complexes. It has been shown that the addition of zinc to a system with already formed dimers does not substantially affect the characteristics and rate of aggregation. At the same time, an excessive concentration of zinc at the early stages of the formation of conglomerates can negatively affect aggregation, since in systems where zinc ions occupied the 11EVHH14 coordination center and the His6 residue of every Aβ16 monomer, the aggregation proceeded more slowly and the resulting complexes were not as large as in the zinc-free Aβ system. Thus, this study has shown that the formation of Aβ16 dimers bound through zinc ions at the 11EVHH14 sites of the peptides plays an important role in the formation of neurotoxic non-fibrillar aggregates of beta-amyloid peptide Aβ16. The best energetically favorable structure has been obtained for the complex of two Aβ16 dimers with two zinc ions.

STUDY OF THE FORMATION OF THE STRUCTURE OF GRAY CAST IRON BY THE METHOD OF THERMOGRAPHIC ANALYSIS

The work is devoted to the study of the effect of an exothermic carbon-containing additive of a facing layer of a sandy-clay molding mixture on the eutectic transformation of cast iron. For this, the method of thermographic analysis was used and metallographic analysis of the metal under study was carried out. It is shown that the results obtained by thermographic analysis have a correlation with the structure of cast iron. The introduction of a carbon-containing additive into the composition of the facing mixture led to the formation of a favorable structure of the prototype, characteristic of gray cast iron.

Collaboratively boosting charge transfer and CO2 chemisorption of SnO2 to selectively reduce CO2 to HCOOH

In this paper, we have facilely developed a SnO2-based electrocatalyst (SnO2-VO@N-C), which can combine together the favorable structure features of oxygen vacancies, porosity, and fully-coating with N-doped carbon layers (N-C)....

Structure and properties of a tungsten-free hard alloy based on titanium carbonitride sintered from electroerosive powders obtained in a carbon-containing medium

The results of experimental studies of a KNT16 tungsten-free hard alloy sintered from electroerosive powders obtained in ethyl alcohol are presented. It is shown that the use of the spark plasma sintering method to produce products from powder obtained by electroerosive dispersion of the alloy KNT16 will ensure high performance of parts due to the uniformity of the surface, favorable structure and low porosity of the product.

Properties of WNiFe-95 pseudoalloy sintered from electroerosive powders obtained in kerosene

The results of experimental studies of the composition, structure, and properties of WNiFe-95 pseudoalloy sintered from electroerosive powders obtained in lighting kerosene are presented. It is shown that the use of the spark plasma sintering method to produce products from powder obtained by electrodispersing of this pseudoalloy will ensure high performance of parts due to the surface uniformity, favorable structure and low porosity of the product.

Designing Stable Bimetallic Nanoclusters via an Iterative Two-Step Optimization Approach

Determining the energetically most favorable structure of nanoparticles is a fundamentally important task towards understanding their stability. In the case of bimetallic nanoclusters, their vast configurational space makes it especially...

How does the sward condition in late winter influence the Marandu palisade grass (Urochloa brizantha cv. Marandu) structure during spring and summer?

Height and mowing of a sward in late winter can change its structure during the subsequent spring and summer seasons, which influences plant growth and animal performance. This work was conducted to evaluate the structural characteristics of Urochloa brizantha (syn. Brachiaria brizantha) cv. Marandu (marandu palisadegrass) during spring and summer in relation to the following sward conditions in late winter: short (15 cm), medium (23 cm), tall (31 cm) and tall (31 cm)/mowed to 8 cm. Stages of the grazing period (beginning, middle and end) in spring and summer were considered measures repeated over time. Leaf area index was lower in the tall pasture than in the other pastures and was lower at the beginning than at the end of the grazing period. Dead material mass was highest in the tall pasture, intermediate in the short and medium pastures and lowest in the tall/mowed pasture. Live stem mass was higher at the end than at the beginning and middle of the grazing period of the short, medium and tall/mowed pastures, contrary to that observed in the tall sward. At the end of the grazing period, tiller number did not vary among pastures. The tall pasture in late winter presents a limiting structure to animal consumption. Short and tall/mowed pastures in late winter show a favorable structure for forage plant growth and, probably, animal performance.

Preparation of xanthan gum-based composite hydrogels with aligned porous structure

Aligned hydrogels have received increasing attention in tissue engineering and electrochemical fields due to their favorable structure. In this work, xanthan gum-based hydrogels (XGH) with aligned pores were prepared via photoinitiated free radical irradiation that used sodium acetate crystals as template. The microstructure, compressive strength, porosity, and absorption capacity of the hydrogel were studied and compared with the non-aligned hydrogels. Scanning electron microscope analysis confirmed the aligned porous structure of the hydrogel. The maximum compressive strength for the aligned hydrogel prepared with 12% acrylamide and 1.5% xanthan gum reached 0.439 MPa at a strain of 95%. Furthermore, aligned XGH exhibited better flexibility than non-aligned hydrogels, as indicated by the Young’s compressive modulus. The porosity of the aligned hydrogels ranged from 94.9% to 88.8% as the acrylamide concentration increased from 12% to 20%. Simulated body fluid absorption showed that hydrogels with aligned pores could attain absorption equilibrium within 5 min, and the maximum absorption capacity reached 33.6 g/g for the sample made with 0.5% xanthan gum and 12% acrylamide. In addition, exhibited preferable biocompatibility, as demonstrated by the cytotoxicity test.