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New IEC standards for the measurement of sheet resistance on large-area graphene using the van der Pauw and the in-line four-point probe methods
Get PDFGraphene has evolved from a scientific research subject to an industrial product, in need of a normative basis for its key control characteristics. Recently two new IEC technical specifications that establish standardized procedures for assessing the sheet resistance R S of monolayer graphene have been published. These new standards, part of the IEC TS 62607-6-xx series, outline protocols for employing two contact methods: i) van der Pauw, and ii) in -line four -point probe. In the following we present and discuss illustrative examples of the scientific experiments designed and performed to inform the standardization process behind the presented standards. In particular we report about the investigation of mechanical contacting of chemical -vapor -deposited monolayer graphene and the measurement of the R S in cm 2 area graphene samples with non uniform resistivity distributions. This paper includes an overview of the broader IEC context, detailing the key steps in the development of the standards themselves
Experimental test of nonlocality limits from relativistic independence
Get PDFQuantum correlations, like entanglement, represent the characteristic trait of quantum mechanics and pose essential issues and challenges to the interpretation of this pillar of modern physics. Although quantum correlations are largely acknowledged as a major resource to achieve quantum advantage in many tasks of quantum technologies, their full quantitative description and the axiomatic basis underlying them are still under investigation. Previous works have suggested that the origin of nonlocal correlations is grounded in principles capturing (from outside the quantum formalism) the essence of quantum uncertainty. In particular, the recently introduced principle of relativistic independence has given rise to a new bound intertwining local and nonlocal correlations. Here, we test such a bound by realizing together sequential and joint weak measurements on entangled photon pairs, allowing us to simultaneously quantify both local and nonlocal correlations by measuring incompatible observables on the same quantum system without collapsing its state, a task typically forbidden in the traditional (projective) quantum measurement framework. Our results demonstrate the existence of a fundamental limit on the extent of quantum correlations, shedding light on the profound role of uncertainty in both enabling and balancing them
Assessment of permeability and microstructural parameters via fractal modelling in bioactive glass-derived scaffolds produced by vat photopolymerization
Get PDFPorosity-related characteristics of biomedical three-dimensional (3D) scaffolds govern mass transport properties which, in turn, dictate the success of implants in vivo. The accurate determination of permeability and microstructural properties in highly-porous materials - like implantable bone scaffolds - still represents a challenge due to the complex architecture of struts and voids in 3D. In the present study, the complete set of mass transport properties of bioactive glass scaffolds produced by vat photopolymerization was reliably determined by combining experimental assessment, advanced imaging and mathematical modelling based on the Ergun-Wu approach. Specifically, the intrinsic permeability of the scaffolds was experimentally estimated by acoustic measurements, and the pore diameter was calculated through implementing an innovative fractal model. An accurate statistical analysis of the results provided evidence of the robustness of the overall strategy, which can be potentially extended and adapted to the analysis of other types of sintered porous (bio)materials
Laboratory Replication of Low Power Quality Conditions Observed on the Field for Testing Active Energy Meters
No full textThis paper reports about a new proposed methodology,
where active energy meters are tested under conditions
directly recorded at installation sites. This allows for the reproduction
of specific, not only realistic, low power quality
as observed on the field. A portable instrument is employed
to sample on-field voltage and current waveforms, which are
then replicated in a laboratory setting using a phantom power
generator with a bandwidth covering up to the 40th harmonic.
The recording site chosen is the coupling section between the
distribution grid and a photovoltaic energy production facility
with a nominal power of 50 kW. Laboratory recreated waveforms
are used to tested three-phase commercial static energy meters.
The selected models encompass those utilized by energy providers
at the point of common coupling, as well as meters typically
employed for in-line monitoring by end users. The key focus
is on the reading error of the measured active energy when
subjected to conditions mimicked from on-field measurements,
in comparison with a reference meter
Synaptic Plasticity and Visual Memory in a Neuromorphic 2D Memitter Based on WS2 Monolayers
Get PDFNeuromorphic computing aims to leverage physical phenomena of adaptive materials for emulating information processing capabilities and effectiveness of biological neuronal circuits. In this framework, memristors (resistors with memory) based on 2D materials are demonstrated for the hardware implementation of highly integrated artificial neural networks. All the works reported thus far exploited electrical properties of 2D materials to emulate neuromorphic functionalities. Here, a 2D memitter (emitter with memory) is reported on that exploits the stimuli-responsive photoluminescence of a monolayer WS2 for neuromorphic-type of data processing. A combined experimental and modeling approach reveals that photoluminescent dynamics triggered by optical stimulation emulates Short-Term synaptic Plasticity and Visual Short-Term Memory typical of biological systems. While spatio-temporal processing capabilities of input signals can be used for information processing in the context of reservoir computing, the capability of the 2D memitter of sensing, processing, and memorizing-forgetting optical inputs in the same physical substrate can be utilized for in-sensor computing
Multicomponent Synergistic Contribution in Nanoengineered Nanofibers for Flexible Energy Storage
No full textLightweight and flexible energy storage devices are gaining interest due to their potential integration into wearable electronics. They might work for the long-term powering of sensors, for example, but they need to be operative after the application of different types of mechanical stress. Conductive and semiconducting nanomaterials have been largely investigated as active components for this type of application but need to be coupled to an elastic matrix, such as a polymeric one, in order to be functional in flexible technologies. In this work, we investigate the production of electrospun nanofibers based on a ternary blend of 2D layered WS2, multiwalled carbon nanotubes, and carbon black in poly(ethylene oxide) and characterize their electrochemical behavior in symmetric supercapacitor architectures within bendable pouch cells, in conjunction with a robust analysis of the active materials’ mechanical properties. We find optimized specific capacitance values of up to 9 F g-1 after mechanical adjustment of the device and excellent capacitance retention after multiple bending cycles, revealing the potential of similar scaffolds for use in wearable energy storage devices to activate low-power electronics
Gravitational and Coriolis forces in crystal neutron interferometry. I. Theory
Get PDFThe proof that neutron interference is possible using split-crystal interferometers opens the way to extended arm separation and length and to new experiments exploring quantum mechanics and gravity. Therefore, this paper reexamines the effect of gravitational and Coriolis forces on the Laue diffraction of neutrons by perfect crystals and the operation of crystal interferometers. We give in analytical form the transfer matrices for the propagation of the neutron quantum state, either pure or mixed and subjected to gravity and Coriolis force, in free space and perfect crystals. They are used to study the effect of interferometer aberrations on the quantum-mechanical phase due to the Earth's gravity. We also give an alternative way to understand the impact of gravitational and Coriolis forces in terms of the crystal displacements and tilts perceived by the neutron
Diffusion of light in structurally anisotropic media with uniaxial symmetry
Get PDFAnisotropic light transport is extremely common among scattering materials, yet a comprehensive picture of how macroscopic diffusion is determined by microscopic tensor scattering coefficients is not fully established yet. In this work, we present a theoretical and experimental study of diffusion in structurally anisotropic media with uniaxially symmetric scattering coefficients. Exact analytical relations are derived in the case of index-matched turbid media, unveiling the general relation between microscopic scattering coefficients and the resulting macroscopic diffusion tensor along different directions. Excellent agreement is found against anisotropic Monte Carlo simulations up to high degrees of anisotropy, in contrast with previously proposed approaches. The obtained solutions are used to analyze experimental measurements of anisotropic light transport in polystyrene foam samples under different degrees of uniaxial compression, providing a practical example of their applicability