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Epoxy resin based on carbon nanotubes with heating properties is studied to tune its heating performance by changing the applied voltage value. The developed self‐heating device, able to heat to high temperatures in a short time, can be applied in various areas. The electro‐thermal investigation shows the presence of both positive temperature coefficient (PTC) and negative temperature coefficient (NTC) behaviors with a predominance of NTC trend neat to the glass transition temperature of the epoxy matrix. [ABSTRACT FROM AUTHOR]

In anticipation of climate changes, strategic soil management, encompassing reduced tillage and optimized crop residue utilization, emerges as a pivotal strategy for climate impact mitigation. Evaluating the transition from conventional to conservative cropping systems, especially the equilibrium shift in the medium to long term, is essential. ARMOSA, a robust crop simulation model, adeptly responds to varied soil management practices such as no tillage, minimum tillage, and specific straw management options such as chopping and incorporating crop residue into the soil (with or without prior nitrogen and water addition before ploughing). It effectively captures dynamic fluctuations in total organic carbon over an extended period. While challenges persist in precisely predicting grain yield due to climatic intricacies, ARMOSA stands out as a valuable and versatile tool. The model excels in comprehending and simulating wheat cultivar responses in dynamic agricultural ecosystems, shedding light on phenological patterns, biomass accumulation, and soil organic carbon dynamics. This research significantly advances our understanding of the intricate complexities associated with past wheat cultivation in diverse environmental conditions. ARMOSA's ability to inform decisions on conservation practices positions it as a valuable asset for researchers, agronomists, and policymakers navigating the challenges of sustainable agriculture amidst climate change. Its real-world significance lies in its potential to guide informed decisions, contributing to global efforts in sustainable agriculture and climate resilience. [ABSTRACT FROM AUTHOR]

Polymer-matrix composites containing conductive nanoparticles are a potential means for achieving an appealing combination of multifunctional properties for their use as structural parts in the aerospace field. Carbon nanofibers (CNFs) have been being looked forward to as the next generation of new and avant-garde aircraft structures because they are exceptionally coveted competitor materials to replace traditional metal components for lightning strike protection. In this regard, nanocomposites at low concentration of CNFs ranging from 0.05% up to 2% by wt to impart electron conduction in tetrafunctional epoxy resin have been prepared and characterized. The aim of this work concerns the use of Tunneling AFM (TUNA) as revolutionary tool able to correlate the electrical current map with the correspondent local morphology of CNF/resins. TUNA technique has proven to play a leading role in the identification of current paths and electrical interconnections, even without altering the morphology with usual treatments employed to create electrical contacts to the ground. Summing up, the good electrical performance together with the high mechanical properties due to a conductive cross-linked network of CNFs inside the resin demonstrate a charming applicative potential for the formulated nanocomposites as structural materials capable to provide a safe conductive path on the exterior skin, preventing serious damage to the aircraft.

Epoxy nanocomposites fulfill tight and compelling industrial requirements in the field of structural material for aeronautical applications. In this paper the development and characterization of nanocomposites obtained by filling tetrafunctional epoxy resin (tetraglycidyl methylene dianiline cured with the aromatic diamine 4,4’-diaminodiphenylsulfone, named T20BD) with carbon nanofibers (CNF) is discussed. A filler amount ranging from 0.05% to 2%wt is considered. The DC volume conductivity and the dielectric characteristics (ϵ’) of the nanocomposites in the frequency range 100Hz-1MHz are analyzed and compared with those of the pure resin. Atomic force microscopy, mapping the local topography by means of tunneling effect, is used for recording the electrical percolation path for nanocomposites. In particular, the case 1.3wt% of CNF filled nanocomposites that exhibits a stable behavior of the conductivity in the full investigated frequency range, is here reported. The developed filled epoxy used in carbon fiber reinforced composites, shows enhanced electrical properties leading to better electromagnetic (EM) performances in EM coatings, EM shields and filters or radar absorber materials (RAMs).

In this paper, the effect of steep-fronted voltage waveshapes infringing on a pulse-width-modulated (PWM) inverter fed induction motor is studied. The system, composed of a feeder cable and a stator winding, is modeled and simulated by using multiconductor transmission line theory in order to predict the voltage distribution among the coils of the stator winding. A recently developed time-domain equivalent circuit is used; it allows one to correctly describe the dielectric losses and the skin-effect in the conductors. The relationship among the voltage distribution inside the electrical insulation and parameters like the rise time of the applied voltage, the cable length, and the distributed losses is deeply discussed. Good agreement has been found among experimental and numerical results. Index Terms--AC motors, electrical insulation, pulse-width modulation, windings.

The state-space modeling and related order reduction problems of switching dc-dc converters operating in discontinuous (D) mode are treated in this paper. A unified discrete-time full-order model is proposed assuming the discontinuous current and voltage mode (DCVM) as a general operation mode from which the discontinuous current mode (DCM), the discontinuous voltage mode (DVM), and continuous mode (CM) derive as special cases. Such model permits a straightforward study of the control-to-output response, in each operation mode. The order reduction of the transfer function is carried out by means of the principal component analysis considering the joint controllability and observability properties of the circuit. It is shown that a proper order reduction can be gained not only in DC mode, as expected, but also in DV and DCV modes. A substantial difference between DC and DV modes is also evidenced in terms of controllability. The frequency analysis and state-space model order reduction for a Cuk converter are proposed to show that the method is free of the limitations affecting other methods of analysis and that its predictions fit experimental measurements.

Several methods have been developed until today for the analysis of PWM converters operating in Discontinuous Conduction Mode (DCM) and many endeavours have been done in order to solve two well known problems: the nontrivial calculation of the internally controlled instant at which the current flowing into the diode falls to zero and the subsequent order reduction of the state-space model of the circuit due to the disappearance of one state variable. In this work a new approach to the modeling of PWM converters for the large signal analysis in DCM operation is presented. It is based on a closed-form discrete-time state-space model obtained by introducing a time-adaptive function for the calculation of the instant at which the diode current falls to zero, and an equivalent fictitious configuration of the circuit during the idle phase, in order to prevent the unconditioned order reduction of the state-space model. A four-terminal device is also introduced which allows a unified representation of the PWM buck, boost, buck-boost, and Cuk converters in DCM operation using the fictitious configuration. The model proposed can be used for circuit oriented simulations both in open and closed loop operation and for an accurate ripple inspection, automatically accounting for DCM to CCM transitions and vice versa.

PLA filaments filled with different percentages of commercial graphene nanoplates (GNP) and multi-walled carbon nanotubes (CNT), produced for Fused Deposition Modeling (FDM) 3D-printing, are here considered. In particular, the electromagnetic properties of the filament obtained with two different processes are compared in order to assess the influence of the different procedures, named solution blending (SB) and melt extrusion (ME), on the Ka-band (26-37 GHz) behavior of the nanocomposites. First, the method of measurements of electromagnetic response of rod-shaped samples in the instrumentation waveguide is studied and implemented. Then, the electromagnetic properties of filaments loaded with nanocomposites in a maximum of 6wt% are investigated, assuming for each filler the possible value of {0,3,6} wt%. The experimental results in terms of reflection and absorption are used to estimate the complex permittivity and the AC electrical conductivity in samples under study by using a suitable created code. Filaments prepared by ME show higher values of both components of dielectric permittivity compared to SB. The highest values of relative permittivity are obtained for the bi-filler filament (3wt% GNP and 3wt% CNT) in ME processes (max value 12.73), whereas a maximum of 11.84 is reached for the relative permittivity of SB produced filament. Maximal AC conductivity is observed for composites containing 6wt% of GNP and 6wt% of CNT for SB and ME respectively. Electrical percolation thresholds (EPT) consistent with literature available DC results are detected, ranging in the explored filler amount, except for the SB produced CNT-based filament. [ABSTRACT FROM AUTHOR]

The use of a one-dimensional model for analyzing nonlinear stress in cable terminations is of considerable engineering interest. This is because the approach utilizes two novel techniques for the evaluation of the voltage profile in the cable terminations, the first of which is a characteristic parameter for describing in quantitative mode the ability of the stress grading material to degrade the field strength at the shield cut. The second technique involves the analysis of the general nonlinear resistive-capacitive electric field control problem. However, the model is undermined by the fact that some meaningless approximations have been used in the evaluation of specific cases.