Effects of different cryoprotectants on morphology of lyophilized poly(ε-caprolactone) micro and nanospheres

A common limitation of using polymeric micro and nanoparticles in long-term conservation is due to their poor physical and chemical stability. Freeze-drying is one of the most convenient methods that enable further reconstitution of micro and nanoparticles for therapeutical use. Nevertheless, this process generates various stresses during freezing and desiccation steps. The aim of this study was to evaluate different cryoprotectants (protective excipients that are usually added to increase stability upon storage and protect the particles from freezing stress): sugars (glucose and sucrose) and polymers (PVA and PGA), on the outcome of freeze-dried poly(ε-caprolactone) micro and nanospheres. The best freeze-drying results in terms of morphological characteristics, analyzed with SEM, were achieved with glucose at concentration of 1%. The FTIR analysis confirmed that the molecular structure of PCL particles remained the same after the addition cryoprotectants

Preparation and Instability of Nanocrystalline Cuprous Nitride

Low-dimensional cuprous nitride (Cu3N) was synthesized by nitridation (ammonolysis) of cuprous oxide (Cu2O) nanocrystals using either ammonia (NH3) or urea (H2NCONH2) as the nitrogen source. The resulting nanocrystalline Cu3N spontaneously decomposes to nanocrystalline CuO in the presence of both water and oxygen from air at room temperature. Ammonia was produced in 60% chemical yield during Cu3N decomposition, as measured using the colorimetric indophenol method. Because Cu3N decomposition requires H2O and produces substoichiometric amounts of NH3\u3e, we conclude that this reaction proceeds through a complex stoichiometry that involves the concomitant release of both N2 and NH3. This is a thermodynamically unfavorable outcome, strongly indicating that H2O (and thus NH3 production) facilitate the kinetics of the reaction by lowering the energy barrier for Cu3N decomposition. The three different Cu2O, Cu3N, and CuO nanocrystalline phases were characterized by a combination of optical absorption, powder X-ray diffraction, transmission electron microscopy, and electronic density of states obtained from electronic structure calculations on the bulk solids. The relative ease of interconversion between these interesting and inexpensive materials bears possible implications for catalytic and optoelectronic applications

From evolutionary computation to the evolution of things

Evolution has provided a source of inspiration for algorithm designers since the birth of computers. The resulting field, evolutionary computation, has been successful in solving engineering tasks ranging in outlook from the molecular to the astronomical. Today, the field is entering a new phase as evolutionary algorithms that take place in hardware are developed, opening up new avenues towards autonomous machines that can adapt to their environment. We discuss how evolutionary computation compares with natural evolution and what its benefits are relative to other computing approaches, and we introduce the emerging area of artificial evolution in physical systems

Strategy for large???scale monolithic Perovskite/Silicon tandem solar cell: A review of recent progress

For any solar cell technology to reach the final mass-production/commercialization stage, it must meet all technological, economic, and social criteria such as high efficiency, large-area scalability, long-term stability, price competitiveness, and environmental friendliness of constituent materials. Until now, various solar cell technologies have been proposed and investigated, but only crystalline silicon, CdTe, and CIGS technologies have overcome the threshold of mass-production/commercialization. Recently, a perovskite/silicon (PVK/Si) tandem solar cell technology with high efficiency of 29.1% has been reported, which exceeds the theoretical limit of single-junction solar cells as well as the efficiency of stand-alone silicon or perovskite solar cells. The International Technology Roadmap for Photovoltaics (ITRPV) predicts that silicon-based tandem solar cells will account for about 5% market share in 2029 and among various candidates, the combination of silicon and perovskite is the most likely scenario. Here, we classify and review the PVK/Si tandem solar cell technology in terms of homo- and hetero-junction silicon solar cells, the doping type of the bottom silicon cell, and the corresponding so-called normal and inverted structure of the top perovskite cell, along with mechanical and monolithic tandemization schemes. In particular, we review and discuss the recent advances in manufacturing top perovskite cells using solution and vacuum deposition technology for large-area scalability and specific issues of recombination layers and top transparent electrodes for large-area PVK/Si tandem solar cells, which are indispensable for the final commercialization of tandem solar cells

Femtosecond tunneling of polarons in Pb5Cr3F19

The complex dielectric constant/ac electrical conductivity was investigated as a function of frequency and temperature in Pb5Cr3F19. The system undergoes a ferroelectric phase transition at higher temperatures. At lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response (UDR) σ′ ∝ νs, typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in Pb5Cr3F19. The value of the inverse attempt frequency τ0 indicates the femtosecond tunneling of polarons in the system similar to the Büttiker–Landauer transversal time

DIELECTRIC DISPERSION IN FERROELECTRIC LIQUID CRYSTALS

Nous avons effectué des mesures de relaxation diélectrique au voisinage de la transition ferroélectrique smectique-A smectique-C* d'un cristal liquide chiral. Ces mesures ont permis d'obtenir pour le DOBAMBC la partie basse fréquence du spectre de fluctuation du paramètre d'ordre lors de cette transition. Dans la phase ferroélectrique (C*), nous avons déterminé la fréquence et l'amplitude à vecteur d'onde nul du mode de Goldstone qui conserve la symétrie. Sa fréquence ne dépend que très légèrement de la température ; elle décroît en approchant de la transition par températures croissantes tandis que son amplitude diminue d'un ordre de grandeur et semble tendre vers 0.The low frequency order parameter fluctuation spectrum of chiral DOBAMBC has been studied at the ferroelectric smectic A → C transition by dielectric relaxation spectroscopy. The frequency and the dielectric strength of the symmetry recovering Goldstone mode for q = 0 in the ferroelectric phase have been determined. The frequency is approximately temperature independent, decreasing slightly when approaching Tc from below, while the intensity decreases for an order of magnitude and seems to go to zero at Tc

Polarons in magnetoelectric K

The ac electrical conductivity of magnetoelectric K3Fe5F15 was investigated as a function of frequency and temperature. While at higher temperatures charge transport is governed by a thermally activated process, at lower temperatures the real part of the complex ac electric conductivity was found to follow the universal dielectric response $\sigma^\prime\propto\nu^{s}$, being typical for hopping or tunnelling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunnelling of small polarons revealed that, below 80 K, this mechanism governs the charge transport in the K3Fe5F15 magnetoelectric fluoride system

Strain-induced ferroelectricity in KTaO

This paper has been formally withdrawn on ethical grounds because six of the co-authors listed (V. Bobnar, Z. Kutnjak, S. Glinšek, B. Kužnik, B. Malič, M. Kosec) had no knowledge or discussion of the content of the article, nor had given permission for it to be submitted, nor had given approval for inclusion of their names as co-authors. EPL submission policy states quite clearly that: “If several persons are listed as authors, the corresponding author takes full responsibility that the co-authors agree with the submission and further processing of the manuscript.” It is unfortunate that this misconduct was not detected before going to press. My thanks to the scientists named above for bringing this fact to my attention. Strain-induced ferroelectricity was observed directly at low temperatures in KTaO3 thin films and the temperature-strain phase diagram was determined. The values of εmax and Tmax of the ε′(T) curves change with the measuring electrical signal. The temperature dependence of the dielectric constant is fitted by the Curie-Weiss law