Istituto Nazionale di Ricerca Metrologica
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Direct calibration of a true-rms ac voltmeter against a He-free pulsed Josephson standard
Get PDFStarting from 2019 a new central role is played by quantum standards, owing to the redefined SI, where electrical units are directly linked to the fundamental constants e (elementary charge) and h (Planck constant). Thus, metrologists are nowadays trying to extend the astonishing accuracy attainable in dc measurements to ac and beyond, moving towards calibrations aiming quantum ac voltage generation. Programmable Josephson Voltage Standards are nowadays capable of fulfilling primary metrology requirements only for stepwise-approximated voltage signals up to few hundreds Hz. Pulsed Josephson standards are instead capable of generating arbitrary waveforms at higher frequencies, so are generally called Josephson Arbitrary Waveform Standards (JAWS). Despite of the lower attainable voltage, JAWS are very promising and are the subject of intense research activity. In particular, the capability of generating high spectral purity signals allows high accuracy measurements especially at the low voltage levels (<100 mV rms), which are challenging to be performed by the traditional ac-dc transfer difference using thermal converters. We report in the following about our setup for quantum-based calibrations of a true-rms ac voltmeter with low uncertainty, first results obtained and unsolved issues
GPS-navigator: an advanced search engine to gather information and navigate through standards in the field of geometrical product specification
No full textThe Geometrical Product Specification (GPS) and the Geometrical Dimensioning and Tolerancing (GD&T) are communication languages to code the tolerable morphology of manufactured parts and assemblies. Both languages should be unambiguous tools to communicate such information between designers, process engineers, and Coordinate Measuring Machines operators (CMM). GPS is the one developed in the ISO (International Organization for Standardization) environment. GPS language is a complex code of 143 standard with further 15 under development. Moreover, as in each complex body of standards, most of them recalls other standards in a very intricate manner. So, the need to have a flexible tool to search and navigate through the standards is great, as is the need to optimize the work of the designer and to minimize the design, production, and control costs. The basic effort in building such a tool has been the development of the database and the structure for the search engine, called "GPS Navigator". In the following, the requirements for the coding phase have also been issued, to realize a powerful, efficient, fast, robust, and rigorous tool to navigate through the GPS standards. The final step of the "GPS-Navigator project" is the delivery of a software tool able to help and guide the designer to quickly consult the appropriate standard or set of standards
Authentication and/or identification method based on an artificial engraved fingerprint originated by a mask from block copolymers
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Design and Uncertainty Evaluation of a Calibration Setup for Turbine Blades Vibration Measurement
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An inorganic water-based paint for high-durability passive radiative cooling
Get PDFDue to the extreme reflectivity requirements of radiative cooling coatings, these materials often employ ceramic nanoparticles such as TiO2 due to their high refractive index and scattering efficiency. However, the bandgap of TiO2 (3.2 eV) is lower than the energy of the most energetic solar light, leading to significant absorption in the UV range (0.25–0.4 μm) and subsequent oxidation aging and yellowing of particles and/or organic binders. To overcome the conflict between high reflective efficiency and UV durability, formulations using high-bandgap materials can be used despite their lower refractive index. In this work, we describe an optimized PRC-Al2O3 coating by adjusting the ratio of low refractive index alumina particles to sodium methylsilicate adhesive. The PRC-Al2O3 exhibits a high solar reflectance above 0.96 and a high mid-infrared emissivity of 0.92, enabling it to achieve a maximum theoretical cooling power of 109 W/m2. Following continuous UV irradiation with a power of 0.7 kW/m2 for 72 hours, only a marginal 0.2% decline in solar reflectance occurred compared to the unaged coatings. The resulting anti-aging cooling paint is scalable and can be spray-coated onto outdoor structures and containers, providing durable radiative cooling towards real-world applications
Solvent role for the electrospinning of PVDF-HFP nanofibrous coatings for passive radiative cooling applications
Get PDFDue to the increasing demand of cooling systems, new techniques to produce materials with specific optical properties are being developed for innovative applications such as passive daytime radiative cooling (PDRC). In recent years, electrospun polymeric coatings have been proposed as one of the most promising and scalable techniques for PDRC, due to the high solar reflectivity induced by their nanofibrous structure. Specifically, electrospun poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) exhibit negligible absorption in the solar wavelength range, and a selective emissivity in the atmospheric transparency range provided by its C-F bonds. However, the production of these coatings by electrospinning involves the use of toxic or hazardous solvents. In this study, we explore the substitution of traditional solvents with a non-toxic one, i.e., dimethyl sulfoxide (DMSO), to produce PVDF-HFP electrospun coatings. Through an easy one-step electrospinning process, 35 μm-thick coatings composed of well-defined, cylindrical, uniform, and continuous fibers are obtained with comparable properties to those obtained using traditional solvents
Probabilities of true and false decisions in conformity assessment of a finite sample of items
Get PDFProbability of conforming items of a finite sample of items is evaluated when conformity assessment (CA) of each item is based on comparison of measured item property values with their acceptance and/or tolerance limits. Two models of probabilities of false decisions on conformity of the whole sample are developed. The first model considers a specific sample of items that already underwent a CA process. A Poisson binomial distribution is applied to calculate the number of the sample items having good (conforming) true property values. The second model, applying a multinomial distribution, treats a generic sample of items potentially drawn from a common population. This model allows evaluating probabilities of false decisions on conformity of the sample items (false positives and negatives), as well as probabilities of correct decisions (true positives and negatives). Applicability of both the models is demonstrated using data of simulated and experimental case studies. These methods extend the existing framework for evaluation of probabilities of true and false decisions in the CA of individual items to the whole sample. The proposed approach provides quality indexes for such a sample, that can be applied in quality inspection and CA of products and objects in industry and trade, environmental monitoring, and other fields. In particular, this approach may be helpful for solving the inspection problem of a production lot, when the minimal number of non-conforming items in a sample for rejecting the whole lot is to be determined
Nanoporous Film Layers to Enhance the Performance of Passive Radiative Cooling Paint Mixtures
No full textPassive radiative cooling (PRC) offers significant potential to reduce energy consumption and carbon emissions associated with cooling. Among various approaches, paint-like systems present several advantages in terms of cost effectiveness, scalability, and ease of application. In this study, we report on a PRC system composed of a paint mixture modified with 50% glass bubbles (GB) and a commercial polypropylene–polyethylene–polypropylene (PP–PE–PP) film, commonly used as a battery separator. The resulting material exhibits a solar reflectance of 94% and a broad emittance of over 95% in the sky-transparent window (STW) from 8 μm to 13 μm. The addition of glass bubbles enhances the solar reflectance of the base paint in the near-infrared wavelengths, while the nanoporous PP–PE–PP film (NPF) topcoat improves reflectance in the UV range, remains largely transparent in the IR, and renders the overall coating washable. The material was tested under realistic outdoor conditions, comparing the performance when the PP–PE–PP film was directly applied onto the wet paint layer versus when it was used as a separate windshield enclosing the sample test chamber. Despite its high solar reflectance, no radiative cooling was observed relative to ambient temperature during peak hours (solar irradiation >600 W/m2). However, below this threshold, a temperature drop of -3 °C and a cooling power exceeding 100 W/m2 were observed. Notably, even when a visibly opaque convection shield was used, the configuration in which the PP–PE–PP film sealed the sample slot resulted in significant overheating of the air pocket surrounding the sample during the day. This outcome suggests that experimental setups incorporating a windshield, commonly found in the literature, may introduce an artificial overheating effect, leading to biased measurements of passive radiative cooling