Istituto Nazionale di Ricerca Metrologica
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High-value resistance measurements for temperature sensitivity characterization of PLA composites with biochar from olive pruning biomass
No full textAnisotropic light propagation in human brain white matter
No full textSignificance
Accurate modeling of light diffusion in the human brain is crucial for applications in optogenetics and spectroscopic diagnostic techniques. White matter tissue is composed of myelinated axon bundles, suggesting the occurrence of enhanced light diffusion along their local orientation direction, which however has never been characterized experimentally. Existing diffuse optics models assume isotropic properties, limiting their accuracy.
Aim
We aim to characterize the anisotropic scattering properties of human white matter tissue by directly measuring its tensor scattering components along different directions and correlating them with the local axon fiber orientation.
Approach
Using a time- and space-resolved setup, we image the transverse propagation of diffusely reflected light across two perpendicular directions in a post-mortem human brain sample. Local fiber orientation is independently determined using light sheet fluorescence microscopy and two-photon fluorescence microscopy.
Results
The directional dependence of light propagation in organized myelinated axon bundles is characterized via Monte Carlo simulations accounting for a tensor scattering coefficient, revealing a weaker scattering rate parallel to the fiber orientation. The effects of white matter anisotropy are further assessed by simulating a typical time-domain near-infrared spectroscopy measurement in a four-layer human head model.
Conclusions
We provide a first characterization of the anisotropic scattering properties in post-mortem human white matter, highlighting its direct correlation with axon fiber orientation, and opening the way to the realization of quantitatively accurate anisotropy-aware human head 3D meshes for diffuse optics application
Cooling Potential Assessment of PRC Materials: Findings from a Full-Scale Prototype Study
No full textA full-scale radiant-capacitive cooling system (RCCS) was implemented in Arganda del Rey, Spain, to evaluate passive radiative cooling (PRC) materials. The hydronic system includes sky-exposed radiators, indoor radiant ceiling panels, and thermal energy storage. The thermal performance of the radiators was evaluated under two conditions: with and without PRC material. The cooling potential was assessed based on the water temperature difference between the radiator inlet and outlet. Multiple correlation models, incorporating the most influential climatic and operational factors, were developed to comparatively analyze the experimental series. Their application enabled the identification of the best-performing configurations and the conditions under which they are most effective. The application of PRC material increased cooling hours and maintained the daily cooling potential between 52.4 and 68.1 W/m2 . This cooling effect ensured that operating temperatures remained within the thermal comfort range, even under extreme conditions (~40 °C). These findings highlight the potential of PRC materials to enhance sustainable cooling solutions for buildings and improve energy efficiency
Preliminary characterisation of electrical and mechanical quantities on a MEMS-SPM device
No full textExperimental evidence for anisotropic diffusion of light in white matter tissue
No full textWe report on the observation of anisotropic propagation of light through ex vivo white matter from a human brain sample. White matter comprises bundles of axons which exhibit preferential alignment directions in different regions. This is associated with an anisotropic response which, however, has not been characterized yet in the field of biomedical optics. We test this hypothesis experimentally by probing transverse propagation of light across two perpendicular directions in a post-mortem human brain cortex sample. Using recently derived solutions to the anisotropic diffusive equation, we characterize the scattering properties along both directions at a probe wavelength of 820 nm, well within the near-infrared window of biological tissue, with the aim to improve the diagnostic value of near-infrared studies of light transport through brain tissue, and other structurally anisotropic tissues in general
Rules for Monte Carlo simulations through anomalous heterogeneous media
No full textUntil now, when describing transport through the vast class of anomalous media, researchers always assumed that it was sufficient to simply replace the classical step length distribution with an anomalous one of choice. The presented results reveal that this is not sufficient, leading to macroscopic violations of multiple physical quantities that were not recognized in the previous literature. In anomalous transport, light acquires a "memory"of its past trajectory, which requires the introduction of new rules for its propagation-especially when crossing boundaries between different regions. This work successfully identiffies the complete set of rules-a "recipe"for the correct modeling of anomalous light transport-validating it in a range of different scenarios and revealing some counter-intuitive consequences of its application to the case of finite heterogeneous media. These results represent a generalization of classical transport that can also be applied to all types of anomalous transport beyond light and optics, offering insights on both its physical interpretation and expected impact on experimental measurements
Influence of Multilayer Architecture on the Structural, Optical, and Photoluminescence Properties of ZnO Thin Films
No full textThe present work systematically investigates the impact of multilayer architecture—specifically 5, 10, and 15 layers—on the structural, morphological, optical, and dielectric properties of zinc oxide (ZnO) thin films, aiming to tailor their characteristics for optoelectronic applications. The films were characterized using a comprehensive suite of techniques. X-ray diffraction (XRD) analysis of the 15-layer sample confirmed the formation of polycrystalline ZnO with a hexagonal wurtzite crystal structure, showing prominent (100), (002), and (101) diffraction peaks. Measurements indicated that the film thickness progressively increased from 43.81 nm for 5 layers to 80.68 nm for 15 layers. Concurrently, the surface roughness significantly decreased from 5.54 nm (5 layers) to 2.00 nm (15 layers) with increasing layer count, suggesting enhanced film quality and densification. Optical studies using ultraviolet–visible (UV-Vis) spectroscopy revealed an increase in absorbance and a corresponding decrease in transmittance in the UV-Vis spectrum as the film thickness increased. The calculated optical band gap showed a slight redshift, decreasing from 3.26 eV for the 5-layer film to 3.23 eV for the 15-layer film. Photoluminescence (PL) spectra exhibited characteristic near-band-edge UV emission, with the 5-layer film demonstrating the highest PL intensity. Furthermore, analysis of optical constants revealed that the refractive index, extinction coefficient, optical conductivity, and both the real and imaginary parts of the dielectric constant generally increased with an increasing number of layers, particularly in the visible region, while more nuanced and non-monotonic trends were observed in the UV range. These results underscore the significant influence of layer number on the physical properties of ZnO thin films, providing valuable insights for optimizing their performance in various optoelectronic devices
Feasibility study of subject‐specific, brain specific‐absorption‐rate maps retrieved from MRI data
No full textIntroduction: Specific absorption rate (SAR) is crucial for monitoring radiofrequency power absorption during MRI. Although local SAR distribution is usually calculated through numerical simulations, they are impractical during exams, limiting real-time patient-specific SAR assessment. This study confirms the feasibility of deriving in vivo, subject-specific, image-based SAR and 10-g SAR maps directly from MRI data. Methods: Complex B1+ maps were derived by combining a B1+ product (XFL) magnitude sequence with balanced steady-state free precession phase. Anatomical information and tissue masking were obtained from a T1 magnetization-prepared rapid gradient echo sequence. Electrical conductivity maps were generated from balanced steady-state free precession phase. Whole-brain SAR maps were created from MRI data acquired at 3 T using a 32-channel head coil on 2 healthy volunteers. A correction factor was applied to account for underestimation due to reliance on measurable B1+ data. Numerical simulations compared image-based SAR with simulation-based SAR distributions. Results: A multi-slice image-based brain SAR map was obtained in 12 min (9-min acquisition, 3-min SAR reconstruction). In vitro experiments validated B1+ distribution and electrical conductivity values. Calculated electrical conductivities for in vitro and in vivo experiments were within reference ranges. Image-based SAR and 10-g SAR maps showed a distribution similar to simulation-based maps (r = 0.5) after correction. Conclusions: This study shows the feasibility of inline, subject-specific SAR and 10-g SAR maps from standard brain clinical sequences. Image-based SAR maps can be a practical alternative during MRI exams when simulations are not feasible
Buffer gas cooling of a continuous CO molecular beam
No full textWe characterize a continuous buffer gas cooled source using CO molecules. We show results about the source performance considering different parameters, like gas flow rate, nozzle size, and internal cell volume. The beam contains 2.5 × 1014 molecules/(s sr) at about 160 m/s. Moreover, for two rotational states we observe an unexpected population distribution that we tentatively attribute to a lower temperature inside the cell. Considering the importance of buffer-gas cooling for experiments on ultracold molecules prepared with direct laser cooling, we believe that our work will improve this key first-stage cooling, accelerating the adoption of molecules in the framework of quantum technologies
