On hypercomplex pseudo-Hermitian manifolds

The class of the hypercomplex pseudo-Hermitian manifolds is considered. The flatness of the considered manifolds with the 3 parallel complex structures is proved. Conformal transformations of the metrics are introduced. The conformal invariance and the conformal equivalence of the basic types manifolds are studied. A known example is characterized in relation to the obtained results.Comment: 12 pages, presented on The Sixth International Workshop on Complex Structures and Vector Fields, St Konstantin, Bulgaria, 3-6 September 200

Hyperbolic Fibrations and PDE

2010 Mathematics Subject Classification: 35L10, 35L90.In this note we try to distinguish the hyperbolic fibrations from the Euclidean one with the help of the invariant action of partial differential operators on the fibration. Two examples are given

Mechanism of Formation and Chemical Structure of Graphene Oxide

© 2017 John Wiley & Sons, Ltd.This chapter presents the most recent view on fundamental aspects of graphene oxide (GO) chemistry. The mechanism of GO formation, its transformation during aqueous work-up and the fine chemical structure are introduced sequentially, in a way typical of textbooks. Re-examination of GO acidity overflows into discussion of the dynamic structural model. A new type of GO material with low density of defects, and thus termed "oxo-functionalized graphene" is introduced next. The challenges brought by the two-component GO structural model are then addressed. The chapter ends with a brief review of different bulk forms of graphite oxide

Functionalization and Reduction of Graphene Oxide

© 2017 John Wiley & Sons, Ltd.The chemistry of graphene oxide (GO) is a growing field of research. The modification of the surface properties of GO is the main goal in application-driven research. Successful functionalization protocols must be interpreted in accordance with the chemical structure of the original GO, and therefore, in this chapter, crucial aspects of the chemical structure of GO are introduced first. Next, the thermal and chemical stability of GO is reviewed, followed by introducing wet-chemical non-covalent and covalent reaction principles. The covalent functionalization of GO requires special attention. When chemical reaction principles, well known from organic chemistry, are applied to GO, it remains challenging to prove the successful accomplishment of reactions by analyzing the as-modified GO product. We pay special attention to the reactivity of the edges of defects and provide alternative explanations for interpreting experimental results, where necessary. Next, chemical reduction methods are summarized; special accent is placed on differentiating true chemical reduction from so-called "thermal reduction". Several examples for the functionalization of reduced graphene oxide (RGO) are considered next. While discussing GO chemical properties, in parallel with typical GO, we discuss these properties for the oxo-functionalized graphene (oxo-G1), a type of GO with very low density of structural defects. This sheds additional light on the role of defects in GO chemistry. Finally, additional properties of oxo-G1 are introduced. Oxo-G1 can act as a compound that enables the controlled chemistry for the design and synthesis of functional materials and devices

Graphene Oxide: Fundamentals and Applications

© 2017 John Wiley & Sons, Ltd. All rights reserved.Due to its unique properties, graphene oxide has become one of the most studied materials of the last decade and a great variety of applications have been reported in areas such as sensors, catalysis and biomedical applications. This comprehensive volume systematically describes the fundamental aspects and applications of graphene oxide. The book is designed as an introduction to the topic, so each chapter begins with a discussion on fundamental concepts, then proceeds to review and summarize recent advances in the field. Divided into two parts, the first part covers fundamental aspects of graphene oxide and includes chapters on formation and chemical structure, characterization methods, reduction methods, rheology and optical properties of graphene oxide solutions. Part Two covers numerous graphene oxide applications including field effect transistors, transparent conductive films, sensors, energy harvesting and storage, membranes, composite materials, catalysis and biomedical applications. In each case the differences and advantages of graphene oxide over its non-oxidised counterpart are discussed. The book concludes with a chapter on the challenges of industrial-scale graphene oxide production. Graphene Oxide: Fundamentals and Applications is a valuable reference for academic researchers, and industry scientists interested in graphene oxide, graphene and other carbon materials

Distribution of Gd(III) ions at the graphene oxide/water interface

© 2018 Elsevier Inc. Graphene oxide (GO) have emerged recently as a novel material for sorbing metal cations from aqueous media. However, the literature data on sorption capacity differ by more than one order in magnitude, and the nature of the chemical bonding between GO and metal cations remains unclear. In this work we show that Gd3+ ions are bound to GO by both coordinate-covalent bonding and electrostatic attraction with prevailing the former. We provide the complete account for the GO sorption toward Gd3+ as the function of the Gd3+/GO ratio and pH of solution. The upper limits of the strong bonding are determined as 0.70 and 0.16 mmol(Gd3+)/g(GO) in the neutral and in the intrinsically acidic solutions, respectively. At large excess of Gd3+ in the neutral solutions, the sorption capacity reaches 1.45 mmol(Gd3+)/g(GO). The effectiveness of water, hydrochloric acid and EDTA as desorbing eluents is compared. We experimentally demonstrate the existence of the Gd3+ concentration gradient within the diffuse layer at the GO/water interface, and its exponential character on the distance from the GO surface. The thickness of the diffuse layer and the position of the slipping plane are estimated. Such characteristics, typical for colloid systems, show that in solutions, GO flakes form distinct phase, even though they are just one atom thick

New Details to Relaxation Dynamics of Dielectric Composite Materials Comprising Longitudinally Opened Carbon Nanotubes

© 2017 American Chemical Society. The difference between intact and longitudinally opened multiwalled carbon nanotubes (referred to as CNT and OCNT) has been studied in their application as conductive filler in polymer composite materials. The dielectric properties have been studied in a broad frequency range at the temperatures varying from 293 K through 373 K. Introduction of as little as 0.5% and 1.0% of the conductive filler dramatically increased both parts of the complex permittivity. The percolation threshold is registered at ∼1.5% filling fraction. The main frequency dispersion of the dielectric permittivity lies in the low frequency end of the tested spectrum: from 10 2 Hz through 10 4 Hz. At equal filling fractions, the permittivity of the OCNT-based samples exceeds that of the intact CNT-based samples. The relaxation dynamics is largely affected by the nanoscale geometry of the filler: the temperature dependence of such parameters as dielectric strength, activation energy, and relaxation time demonstrated significant difference between the charge transfer mechanism in the CNT-based and OCNT-based samples. The obtained activation energy is 150 and 85 kJ/mol for materials comprising CNTs and OCNTs, respectively. The relaxation mechanism is complex, and the exact factors behind the macroscopic dielectric properties of the tested materials cannot be singled out with certainty. Several experimental data points suggest that the individual nanotubes, not their aggregates, play the major role in the observed electrical properties of the composites. At the low loading fractions, we attained the highest dielectric strength values among all the data reported by the present day for the CNT/polymer host systems