Manufacturing of Nanocomposite Carbon Fibers and Composite Cylinders

Pitch-based nanocomposite carbon fibers were prepared with various percentages of carbon nanofibers (CNFs), and the fibers were used for manufacturing composite structures. Experimental results show that these nanocomposite carbon fibers exhibit improved structural and electrical conductivity properties as compared to unreinforced carbon fibers. Composite panels fabricated from these nanocomposite carbon fibers and an epoxy system also show the same properties transformed from the fibers. Single-fiber testing per ASTM C1557 standard indicates that the nanocomposite carbon fiber has a tensile modulus of 110% higher, and a tensile strength 17.7% times higher, than the conventional carbon fiber manufactured from pitch. Also, the electrical resistance of the carbon fiber carbonized at 900 C was reduced from 4.8 to 2.2 ohm/cm. The manufacturing of the nanocomposite carbon fiber was based on an extrusion, non-solvent process. The precursor fibers were then carbonized and graphitized. The resultant fibers are continuous

Research on IFR of Technological Evolution Bifurcations

AbstractIdealization is a powerful tool in TRIZ, and it plays an important role in innovation processes. In the fierce market competition, in order to adopt new technology and make their product approach to ideal product, enterprises spare no effort to improve the degree of product's idealization. At the bifurcation points of product technology evolution, the ideal result that customers need changes, but because of the existence of conventional thinking and market competition, engineers always engage in designing according to the original target ideal result, finally the technology innovation opportunities are lost, so it is of great significance to study the Ideal Final Result (IFR) at the bifurcation points. According to different innovation processes of S-curves, the IFR for product's technology evolution bifurcations are divided into four classifications, Incremental Innovation Ideal Final Result(IFR_II), Radical Innovation Ideal Final Result(IFR_RI), Low-end Disruptive Innovation Ideal Final Result(IFR_LDI) and New-market Disruptive Innovation Ideal Final Result(IFR_NDI). Product's technology system consists of several technology sub-systems, correspondingly, ideal product is made up of several idealized technology sub-systems. It is the objective of product design that realizing the idealization of technology subsystem through innovation design, however, because the presence of conflicts and design constraints among technology sub-systems, the design aim for realizing ideal final results of each sub-system is almost impossible. Therefore, in designing processes, engineers always give priority to several mainstream technology sub-systems and realize their idealization first. This paper decomposes IFR into several ideal results of sub-systems based on a technical system decomposition method, researches a process of technology evolution and a changing process of sub-systems’ ideal results, determines evolution bifurcations’ direction of technology systems through the combination of the sub-systems’ ideal results and then realizes the technology forecasting at the evolution bifurcation points

Backstepping control with fixed-time prescribed performance for fixed wing UAV under model uncertainties and external disturbances

In this paper, a novel backstepping control scheme with fixed-time prescribed performance is proposed for the longitudinal model of fixed wing UAV subject to model uncertainties and external disturbances. The novel performance function with arbitrarily preassigned fixed-time convergence property is developed, which imposes priori performance envelops on both altitude and airspeed tracking errors. By using error transformed technology, the constrained fixed-time performance envelops are changed into unconstrained equivalent errors. Based on modified error compensation mechanism, a novel backstepping approach is proposed to guarantee altitude tracking equivalent error converges to the specified small neighborhood and presents excellent robustness against model uncertainties and external disturbances, and airspeed controller with fixed-time prescribed performance is designed. The proposed methodology guarantees the transient and steady-state performance of altitude and airspeed tracking errors within constrained fixed-time performance envelops in spite of lumped disturbances. Finally, numerical simulations are used to verify the effectiveness of the proposed control schem

Not all Minorities are Equal: Empty-Class-Aware Distillation for Heterogeneous Federated Learning

Data heterogeneity, characterized by disparities in local data distribution across clients, poses a significant challenge in federated learning. Substantial efforts have been devoted to addressing the heterogeneity in local label distribution. As minority classes suffer from worse accuracy due to overfitting on local imbalanced data, prior methods often incorporate class-balanced learning techniques during local training. Despite the improved mean accuracy across all classes, we observe that empty classes-referring to categories absent from a client's data distribution-are still not well recognized. This paper introduces FedED, a novel approach in heterogeneous federated learning that integrates both empty-class distillation and logit suppression simultaneously. Specifically, empty-class distillation leverages knowledge distillation during local training on each client to retain essential information related to empty classes from the global model. Moreover, logit suppression directly penalizes network logits for non-label classes, effectively addressing misclassifications in minority classes that may be biased toward majority classes. Extensive experiments validate the efficacy of FedED, surpassing previous state-of-the-art methods across diverse datasets with varying degrees of label distribution shift

Radiative thermal switch via metamaterials made of vanadium dioxide-coated nanoparticles

In this work, a thermal switch is proposed based on the phase-change material vanadium dioxide (VO2) within the framework of near-field radiative heat transfer (NFRHT). The radiative thermal switch consists of two metamaterials filled with core-shell nanoparticles, with the shell made of VO2. Compared to traditional VO2 slabs, the proposed switch exhibits a more than 2-times increase in the switching ratio, reaching as high as 90.29% with a 100 nm vacuum gap. The improved switching effect is attributed to the capability of the VO2 shell to couple with the core, greatly enhancing heat transfer with the insulating VO2, while blocking the motivation of the core in the metallic state of VO2. As a result, this efficiently enlarges the difference in photonic characteristics between the insulating and metallic states of the structure, thereby improving the ability to rectify the NFRHT. The proposed switch opens pathways for active control of NFRHT and holds practical significance for developing thermal photon-based logic circuits