UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

Different nanocomposites have been attained by in situ polymerization based on ultra-high molecular weight polyethylene (UHMWPE) and mesoporous SBA-15, this silica being used for immobilization of the FI catalyst bis [N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium (IV) dichloride and as filler as well. Two distinct approaches have been selected for supporting the FI catalyst on the SBA-15 prior polymerization. A study on polymerization activity of this catalyst has been performed under homogenous conditions and upon heterogenization. A study of the effect of presence of mesoporous particles and of the immobilization method is also carried out. Moreover, the thermal characterization, phase transitions and mechanical response of some pristine UHMWPEs and UHMWPE/SBA-15 materials have been carried out. Relationships with variations on molar mass, impregnation method of catalyst and final SBA-15 content have been established

Some operators and Carleson measures on weighted norm spaces

Thesis (Ph. D.)--Michigan State University. Department of Mathematics, 1991Includes bibliographical references (pages 86-88

Ultra high molecular weight polyethylene and its reinforcement with Carbon Nanotubes in Medical Devices

This chapter discusses the advantages and complexities of ultra high molecular weight polyethylene(UHMWPE) when used as a bearing material for total joint arthroplasty (TJA) and total knee arthroplasty(TKA). The UHMWPE internal structure and its mechanical response depend strongly on a diversity offactors that include radiation crosslinking, fiber reinforcement, and the addition of antioxidants such asVitamin E or Vitamin C. All these manufacturing procedures induce morphological changes andsimultaneously alter the mechanical properties of UHMWPE. The importance of UHMWPE on arthroplasty,including the advantages, the limitations and the strategies devised to overcome the knowndrawbacks are discussed in the first section. The following sections revise and discuss thebiocompatibility, the manufacturing processes, the tribological behaviour, the aging by oxidation andirradiation of UHMWPE and UHMWPE-CNT nanocomposites. The last section analyses the viscoelasticbehavior of UHMWPE and its implications on the long-term survival of total joint arthroplasty

Modular impedance modeling and stability analysis of hybrid AC/DC power systems with grid-forming and grid-following converters

© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The renewable energy resources integrating HVDC transmission systems, consisting of grid-following and grid-forming converters, have complex physical and control dynamic interactions. Although the impedance analysis method is advisable to study these interactions, impedance modeling is still challenging when taking various converter control schemes into account. This article proposes a modular three-port admittance modeling framework for the hybrid AC/DC power systems. This approach separates the modeling process into three levels: controller, converter, and system levels. The current and voltage feedback loops are subdivided into multiple submodules at the controller level, and the submodule connection method is proposed to obtain the small-signal model of the unified main controller, which thus can eliminate the repetitive work caused by the diversity of control schemes. Due to the modular modeling advantage, the method is also versatile and scalable, as well as using unlimited and expandable interconnecting. In addition, the modeling separates the entire system into three components, and the stability criterion of the hybrid AC/DC power systems is derived by regrouping their transfer function matrix models. Then, the proposed modeling method is applied to assess the stability of hybrid power plants integrating HVDC systems with grid-following and grid-forming sources. The conclusions can be used to plan GFM converter capacity in power System plants, the installation location of HVDC transmission systems, and other scenarios. Simulations are carried out to validate the correctness of the impedance modeling method and stability criterion. Finally, the effect of the different capacity ratios of grid-forming sources to renewable energy power plants on system stability is discussed.This work was supported in part by the GuangDong Basic and Applied Basic Research Foundation (Offshore Wind Power Joint Fund) under Grant 2022A1515240030, and in part by the Shenzhen Science and Technology Innovation Commission through the Shenzhen Innovation and Entrepreneurship Project (Key Technologies R & D Program) under Grant JSGG20210802152540008.Postprint (published version

Negative Quantum Capacitance Induced By Midgap States In Single-Layer Graphene

We demonstrate that single-layer graphene (SLG) decorated with a high density of Ag adatoms displays the unconventional phenomenon of negative quantum capacitance. The Ag adatoms act as resonant impurities and form nearly dispersionless resonant impurity bands near the charge neutrality point (CNP). Resonant impurities quench the kinetic energy and drive the electrons to the Coulomb energy dominated regime with negative compressibility. In the absence of a magnetic field, negative quantum capacitance is observed near the CNP. In the quantum Hall regime, negative quantum capacitance behavior at several Landau level positions is displayed, which is associated with the quenching of kinetic energy by the formation of Landau levels. The negative quantum capacitance effect near the CNP is further enhanced in the presence of Landau levels due to the magnetic-field-enhanced Coulomb interactions.Scientific Reports 3. (2013)2045-232

Detection Of Interlayer Interaction In Few-Layer Graphene

Bernal-stacked few-layer graphene has been investigated by analyzing its Landau-level spectra through quantum capacitance measurements. We find that surface relaxation, which is insignificant in trilayer graphene, starts to manifest in Bernal-stacked tetralayer graphene. In trilayer graphene, the interlayer interaction parameters are generally similar to those of graphite. However, in tetralayer graphene, the hopping parameters of the two bulk layers are quite different from those of the two outer layers. This represents direct evidence of the surface relaxation phenomenon. Traditionally, the van der Waals interaction between the carbon layers is thought to be insignificant. However, we suggest that the interlayer interaction is an important factor in explaining the observed results, and the symmetry-breaking effects in graphene sublattice are not negligible.Physical Review B 92(7), 075408. (2015)1098-012