Functional and structural reliability of optic nerve head measurements in healthy eyes by means of optical coherence tomography angiography

Background and Objectives: the aim of the study was to evaluate the repeatability and reproducibility of optical microangiography (OMAG)-based optical coherence tomography angiography (OCTA) in the optic nerve head (ONH) and radial peripapillary capillary (RPC) perfusion assessment of healthy eyes. Materials and Methods: in this observational study, a total of 40 healthy subjects underwent ONH evaluation, using an OMAG-based OCTA system at baseline (T0), after 30 min (T1), and after 7 days (T2). The main outcome measures were the vessel density (VD) and flux index (FI) of the RPCs, as well as peri-papillary retinal nerve fibre layer (pRNFL) thickness. The analysis was performed by two observers independently. The coefficient of repeatability (CR), within the subject coefficient of variation (CVw) and intrasession correlation coefficient (ICC), to evaluate intrasession repeatability of measurements was calculated for each observer. Results: the high intrasession and intersession repeatability and reproducibility were assessed in the two observers for all three outcome measures. Of note, the CRs for the first and the second observer were 0.011 (95% confidence interval (CI) 0.009–0.014) and 0.016 (95% CI 0.013–0.020) for FI, 0.016 (95% CI 0.013–0.021) and 0.017 (95% CI 0.014–0.021) for VD, and 2.400 (95% CI 1.948–3.092) and 3.732 (95% CI 3.064–4.775) for pRNFL thickness, respectively. The agreement between them was excellent for pRNFL assessment and very good for FI and VD. Conclusion: OCTA has a great potential in the accurate assessment of ONH and peri-papillary microcirculation. It allows for repeated and reproducible measurements without multiple scans-related bias, thus guaranteeing an independent operator analysis with good reproducibility and repeatability

Comparing the Chemical Models by Fan-Shen and by Bird through a 2D DSMC Code

The present work is the logical continuation of a paper by Zuppardi and Romano where the models by Bird and by Fan and Shen, evaluating the occurrence of a chemical reaction in a collision between two molecules, were compared in a Direct Simulation Monte Carlo (DSMC) process. The main difference between the models is in handling molecular vibration; the Bird model considers the vibrational energy only as a contribution to the collision energy, the Fan-Shen model considers a physical link between vibrational excitation and dissociation/exchange reactions. In order to make comparable the two models, a parameter similar to the steric factor by Bird, was introduced into the DSMC implementation of the Fan-Shen model. A “simple” DSMC code, computing just the occurrence of a reaction in the collision between two molecules, was written for that purpose. Computer tests considered three dissociation and two exchange reactions in air. The results verified that the direct influence of vibration increases the reactivity level. In order to get over the limitations of the code and therefore to provide a more precise analysis, in the present work both models have been implemented in a 2D DSMC code, allowing the simulation of the flow field on a flat plate and therefore making possible an evaluation of the influence of a different chemical composition (due to the different chemical models) on the aerodynamic parameters both along the surface and in the flow field. The present tests consider the dissociation reactions of oxygen and nitrogen. According to what already found, the reactivity level of the Fan-Shen model verifies to be greater than the one of the Bird model. No significant influence of the different gas composition is found on the aerodynamic parameters along the flat plate (heat flux, pressure and shear stress). On the contrary, a significant influence is found on the flow field parameters (Mach number, rotational and vibrational temperatures)

Sensitivity Analysis of the Gupta and of the Park Chemical Models on the Heat Flux by DSMC and by CFD Codes

The present study is the logical continuation of a former paper by the first author in which the influence of the chemical models by Gupta and by Park on the computation of heat flux on the Orion and EXPERT capsules was evaluated. Tests were carried out by the direct simulation Monte Carlo code DS2V and by the computational fluid-dynamic (CFD) code H3NS. DS2V implements the Gupta model, H3NS implements the Park model. In order to compare the effects of the chemical models, the Park model was implemented also in DS2V. The results showed that DS2V and H3NS compute a different composition both in the flow field and on the surface, even using the same chemical model (Park). Furthermore DS2V computes, by the two chemical models, different compositions in the flow field but the same composition on the surface, therefore the same heat flux. In the present study, in order to evaluate the influence of these chemical models also in a CFD code, the Gupta and the Park models have been implemented in FLUENT. Tests by DS2V and by FLUENT, have been carried out for the EXPERT capsule at the altitude of 70 km and with velocity of 5000 m/s. The capsule experiences a hypersonic, continuum low density regime. Due to the energy level of the flow, the vibration equation, lacking in the original version of FLUENT, has been implemented. The results of the heat flux computation verify that FLUENT is quite sensitive to the Gupta and to the Park chemical models. In fact, at the stagnation point, the percentage difference between the models is about 13%. On the opposite the DS2V results by the two models are practically equivalent

Computed vs. Measured Force Coefficients in a Small Arc Facility

Measurements of the aerodynamic forces acting on a 70◦ semiangle cone have been made in the small arc facility SPES at the Department of Aerospace Engineering in Naples. Two sets of measurements, with arc electrical currents of 300 and 400 A, respectively, are noted; the test gas was argon, the mass flow rate was 1 g/s. Because of the existing difficulties in measuring the free stream parameters in an arc wind tunnel, two procedures are proposed to calculate them: the first based on the one-dimensional theory and the second solving the flow field in the nozzle by a two-dimensional direct simulation Monte Carlo method (DSMC) code; the ‘continuum break-down limit’ is overcome just before the exit of the nozzle. The experimental force coefficients have been compared both with other experimental data available in the open literature and with the results from three-dimensional DSMC code. The comparison shows, as expected, some discrepancies among experimental and numerical data due to the uncertainties in the test parameters and to the interference, at high angle of attack, of the sting supporting the model

Active packaging based on coupled nylon/pe pouches filled with active nano-hybrid: Effect on the shelf life of fresh milk

The study reports on the preparation and characterization of an active packaging based on pouches composed of a coupled system nylon/polyethylene (PE). The PE layer was filled with and active nano-hybrid of layered double hydroxide (LDH) on which it was anchored salicylate, as antimicrobial molecule. The release of the salicylate anchored to the LDH was compared to the release of the molecule free dispersed into the PE and resulted much slower. It was evaluated the efficiency of the active packaging to inhibit Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, and Campylobacter. Global migration tests on the PE active layer, using ethanol (50% v/v) as food simulant, demonstrated the possibility of such active nanocomposite to be used for food contact being the migration limits in compliance with those imposed from the EU regulation. Fresh milk was packed into the active pouches and pouches with unfilled PE layer, as control. The pH reduction as function of the time, due to the production of lactic acid, resulted much slower in the active packaging. Total bacterial count (TBC) was evaluated on the milk, either packed into the active packaging or the control, up to 50 days of storage at 4 °C. Shelf life of the milk was evaluated using the Gompertz model. It was demonstrated an increasing of the shelf life of milk packaged in active pouches from 6 days up to 10 days

DSMC Aero-Thermo-Dynamic Analysis of a Sample-Return Capsule

Future exploration programs, promoted by the main world space agencies, deal with sample return missions to planets like Mars or to asteroids and comets. In this study, an aero-thermo-dynamic analysis of a possible Earth Return Capsule during the high energy, high altitude re-entry path from an exploration mission is presented. The altitude interval 70-120 km is considered, where the capsule experiences different flow fields. In fact, rarefaction ranges from the continuum low density regime to the near free molecular flow and, even though the free stream velocity has been considered constant (13 km/s) in the whole altitude interval, the Mach number changes from 44 to 32 and the Reynolds number, based on the capsule diameter, ranges from 4.92???104 to 9. The computations were carried out using two direct simulation Monte Carlo codes: the 2-D code DS2V to compute local quantities such as heat flux, thermal and aerodynamic loads at zero angle of attack and the 3-D code DS3V to compute global aerodynamic coefficients in the range of the angle of attack 0-60 deg.. The results verified that in this altitude interval the heat flux and the thermal load satisfy reasonably the requirements for the thermal protection system and that the capsule is longitudinally stable up to an angle of attack of about 40 deg.