Isothermal crystallization of PLA: Nucleation density and growth rates of α and α' phases

From a technological point of view, poly(lactic acid) (PLA) is one of the most important polymers produced from renewable sources, due to its versatility, relatively acceptable processability, and low cost. However, a significant limitation exists in its slow crystallization kinetics, which results in amorphous products having low mechanical properties and thermal resistance. For this reason, quantitative knowledge of the phenomenon of crystallization kinetics is fundamental. In this work, the crystallization kinetics in quiescent conditions of a commercial grade of PLA was analyzed in terms of nucleation and growth rates by direct morphological observations at different crystallization temperatures (T_c) and by calorimetric analysis in isothermal and non-isothermal conditions. The optical analysis showed a spherulitic morphology with radial growth of the lamellae. The analysis of the growth rate evidenced the α/α'-crystals polymorphism with a transition temperature of ~120°C. Based on experimental observation, the crystallization kinetics of the two crystalline phases were assessed.     

Structural properties of nanocomposites based on resole-type phenol-formaldehyde oligomers and detonation nanodiamonds

Using the methods of infrared spectroscopy (IRS) and X-ray photoelectron spectroscopy (XPS), it was shown that short-term high-energy machining of detonation nanodiamonds (DND) leads to structural changes in the crystal structure and functional composition of the surface layer on particles. The possibility of spontaneous formation for stable colloidal systems with a narrow size distribution of mechanically activated DND in phenol-formaldehyde oligomers (PFO) was established. By molecular spectroscopy it was revealed that π → π* interactions of the aromatic rings of PFO are caused by orientational phenomena as a result of hydrogen bonds between an activated DND surface and functional groups of PFO. The effect of DND concentration on the curing reaction parameters ofpsgr the phenol-formaldehyde oligomer was determined by differential scanning calorimetry (DSC). The concentration effect of mechanically activated nanodiamonds on the physical and mechanical characteristics of a composite material based on phenol-formaldehyde binder and polyamide paper (Nomex) was studied. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48582.     

Ionic‐Liquid Gating of InAs Nanowire‐Based Field‐Effect Transistors

Here, the operation of a field‐effect transistor based on a single InAs nanowire gated by an ionic liquid is reported. Liquid gating yields very efficient carrier modulation with a transconductance value 30 times larger than standard back gating with the SiO₂/Si₊₊ substrate. Thanks to this wide modulation, the controlled evolution from semiconductor to metallic‐like behavior in the nanowire is shown. This work provides the first systematic study of ionic‐liquid gating in electronic devices based on individual III–V semiconductor nanowires: this architecture opens the way to a wide range of fundamental and applied studies from the phase transitions to bioelectronics.     

Moldless Printing of Silicone Lenses with Embedded Nanostructured Optical Filters

In this work, both light‐shaping and image magnification features are integrated into a single lens element using a moldless procedure that takes advantage of the physical and optical properties of mesoporous silicon (PSi) photonic crystal nanostructures. Casting of a liquid poly(dimethylsiloxane) pre‐polymer solution onto a PSi film generates a droplet with a contact angle that is readily controlled by the silicon nanostructure, and adhesion of the cured polymer to the PSi photonic crystal allows preparation of lightweight (10 mg) freestanding lenses (4.7 mm focal length) with an embedded optical component (e.g., optical rugate filter, resonant cavity, and distributed Bragg reflector). The fabrication process shows excellent reliability (yield 95%) and low cost and the lens is expected to have implications in a wide range of applications. As a proof‐of‐concept, using a single monolithic lens/filter element it is demonstrated: fluorescence imaging of isolated human cancer cells with rejection of the blue excitation light, through a lens that is self‐adhered to a commercial smartphone; shaping of the emission spectrum of a white light emitting diode to tune the color from red through blue; and selection of a narrow wavelength band (bandwidth 5 nm) from a fluorescent molecular probe.     

Simultaneous Achievement of Open and Closed Loop Diagonal Dominance Through Constant Feedback

This paper proposes a new and low complexity technique for the simultaneous achievement of open and closed loop diagonal dominance for uncertain plants. The method is based on the introduction of a static high gain inner feedback which modifies the plant to attain a diagonal dominant open loop compensated plant. The sufficient, easy to use, conditions derived for the open loop diagonal dominance also assure the simultaneous achievement of closed loop diagonal dominance under soft assumptions on the diagonal elements of the decoupled controller robustly stabilizing the plant. These assumptions agree with the usual closed‐loop performance specifications, so that closed‐loop diagonal dominance is achieved without any extra complication on the controller design procedure. The main merits of the present method are: applicability to uncertain plants, ease of implementation and low computational cost. Three examples taken from the relevant literature, are given to show the effectiveness of the proposed approach.     

Usage metrics vs classical metrics: analysis of Russia’s research output

This paper discusses the results of a pilot project investigating Russian scholarly publications using the altmetric indicators “Usage Count Last 180 days” (U1) and “Usage Count Since 2013” (U2) introduced by Web of Science. We explored the relationship between citation impact and both types of usage counts. The data set consisted of 37,281 records (publications) indexed by SCI-E in 2015. Seven broad research areas were selected to observe citation patterns and usage counts. A significant difference was found between mean citations and mean usage counts (U2) in a few research areas. We discovered a significant Kendall rank correlation between the citation metrics and usage metrics at the article level. This correlation is particularly strong for the longer period usage metric (U2). We also analyzed the relationship between usage metrics and traditional journal-level citation metrics. Very weak correlation was observed.     

Effect of hydrogenation on mechanical properties and tensile fracture mechanism of a high-nitrogen austenitic steel

Austenitic stainless steels are frequently used for hydrogen applications due to their high ductility at low temperatures and lower hydrogen environment embrittlement compared to ferritic steels. We study the effect of electrochemical hydrogen saturation up to 40 h on tensile behavior and fracture mechanisms in high-nitrogen austenitic 17Cr–24Mn–1.3V–0.2C–1.3N steel. Hydrogen saturation weakly influences the characteristic of stress–strain curves, but decreases steel ductility, yield stress, and ultimate tensile stress. Hydrogenation provides a change in steel fracture peculiarities—a hydrogen-assisted thin brittle surface layer of ≈5 μm and ductile subsurface layer of 50–150 μm in width in hydrogen-saturated specimens. The subsurface layer shows ductile transgranular fracture with elongated dimples and flat facets. The central parts of fracture surfaces for hydrogenated specimens show ductile fracture mode similar to hydrogen-free state, but they include numerous secondary cracks both for central part and for transition zone between ductile central part and subsurface layer associated with highest hydrogen saturation. The possible reasons of decrease in hydrogen-associated ductility and change in fracture character are discussed.