Mixed Regime Research Articles

Functional response traits and altered ecological niches drive the disassembly of cloud forest bird communities in tropical montane countrysides.

Anthropogenic disturbance contributes to global change by reshaping the ecological niche space available to biological communities. Quantifying the range of functional response traits required for species persistence is central towards understanding the mechanisms underlying community disassembly in disturbed landscapes. We used intensive field surveys of cloud forest bird communities across seven replicate landscapes undergoing agricultural conversion in the Peruvian Andes to examine how a suite of 16 functional response traits related to morphology, diet, foraging behaviour and environmental niche breadth predict (1) species-specific abundance changes in countryside habitats compared to forest and (2) differential changes to the ecological niche space occupied by communities. Our analyses relied on (1) hierarchical distance sampling models to examine the functional predictors of abundance change across the agricultural land use gradient while accounting for imperfect detection and (2) n-dimensional hypervolumes to quantify the expansion and contraction of ecological niche space in countryside habitats. Key traits related to increased abundance in early successional and mixed-intensity agricultural areas included (1) morphological adaptations to dense understorey habitats, (2) plant-based diets (flowers, fruit and seeds) and (3) broad elevational range limits and habitat breadth. Species occupying mixed and high-intensity agricultural land use regimes had mean elevational range limits 20%-60% wider than species found within forests. Collectively, ecological niche space expanded within agricultural habitats for traits related to diet and environmental niche breadth, while contracting for foraging and dispersal traits. Such changes were driven by species with unique functional trait combinations. Our results reveal the dynamic changes to ecological niche space that underly community structure in disturbed landscapes and highlight how increased niche breadth can ameliorate disturbance sensitivity for generalist species. We emphasize that functional traits can be used to predict changes in community structure across disturbance gradients, allowing insights into specific mechanisms underlying community disassembly beyond emergent patterns of functional diversity. By identifying key functional trait groups that align with different countryside habitats, we demonstrate how conservation practitioners can contribute to the retention of avian functional diversity in agricultural landscapes throughout the world.

Hybrid Political Regime: The Problem оf Positioning

Introduction. This is not the first time a scientific attempt to position a hybrid political regime in the article has made, again unsuccessful due to the contradictory nature of this regime, pronounced national specifics of combining democratic and authoritarian components, decades of delays in transforming hybrid regimes towards democracies. The methodological basis on which the study is based is a systematic analysis combined with an interdisciplinary approach. The application of this interdisciplinary approach shows that the mixed political regime was called a “hybrid” not by chance - it also has a heterosis effect. Autocratic leaders and parties were well aware that military regimes and personal dictatorships looked too authoritarian and could face sanctions from the international community, so they sought ways to legitimize their autocratic advantages in order to remain in power for a long time. The most effective approach for essentially authoritarian governments has been to fill the hybrid regime with the appearance of democracy, avoiding or distorting, depleting the very essence of democracy. By gaining an externally presentable democratic configuration, an authoritarian regime can pretend to respect rights and freedoms by actually cutting or obstructing their enjoyment. Hybrid regimes can be stable, long-lasting and competitive – while meeting the demands of elites and the needs of society, setting an example of social compromise. The concept of a hybrid regime still has no theoretical basis, which would make it possible to distinguish its identity and clearly distinguish it from other types of political regimes. Conclusions. The study of types of political regimes, the development of the theory of hybrid political regime and the application of interdisciplinary approach gives grounds to define hybrid regime as a separate type of political regime, more stable and durable than pure democratic and undemocratic forms due to its hybrid nature (heterotic effect) and unique national combination of democratic and authoritarian elements. Key words: political regime, democracy, authoritarianism, hybrid political regime

Examination of Twisted Elliptical Tube Heat Enhancement Within the Mixed Convective Zone

Previously, the investigation of the heat transfer performance of twisted elliptical tubes has been restricted to the effects of forced convective conditions without considering the impact of buoyancy conditions. Therefore, this work investigates heat transfer enhancement of twisted elliptical tubes of different pitch lengths at different mixed convective regimes. The model continuity, momentum, and energy equations were solved using the finite volume technique and validated using both analytical and experimental results. Under the variation of Gr and Re, the results show that twisted elliptical tubes are better than smooth elliptical tubes for heat transfer but with a corresponding high drag coefficient. The heat enhancement of 48% was obtained at a twisted pitch length of 200 mm and Re of 2000 as compared to the plain tube. In addition, on the effect of twist pitch length, the results show that the more twisted a tube is the more its Nu and F. This indicates that induced secondary flow by the twist has a high impact on the Nu and F. The results show that heat enhancement of the elliptical tube depends on P, Gr, and Re. Similarly, there is a fluid-thermal-structure interaction interplay in the hydrothermal behavior of elliptical tubes.

Better sturdy or slender? Eurasian otter skull plasticity in response to feeding ecology.

Otters are semi-aquatic mammals specialized in feeding on aquatic prey. The Eurasian otter Lutra lutra is the most widely distributed otter species. Despite a low degree of genetic variation across its European range, the population from Great Britain exhibits distinct genetic structuring. We examined 43 skulls of adult Eurasian otters belonging to 18 sampling localities and three genetic clusters (Shetlands, Wales and Scotland). For each sample location, information regarding climate was described using bioclimatic variables from WorldClim, and information on otter diet was extracted from the literature. By using photogrammetry, 3D models were obtained for each skull. To explore any evidence of adaptive divergence within these areas we used a three dimensional geometric morphometric approach to test differences in skull size and shape between areas with genetically distinct populations, as well as the influence of diet, isolation by distance and climate. Males were significantly larger in skull size than females across all the three genetic clusters. Skull shape, but not size, appeared to differ significantly among genetic clusters, with otters from Shetland exhibiting wider zygomatic arches and longer snouts compared to otters from Wales, whereas otters from Scotland displayed intermediate traits. A significant relationship could also be found between skull shape variation, diet as well as climate. Specifically, otters feeding on freshwater fish had more slender and short-snouted skulls compared to otters feeding mostly on marine fish. Individuals living along the coast are characterised by a mixed feeding regime based on marine fish and crustaceans and their skull showed an intermediate shape. Coastal and island otters also had larger orbits and eyes more oriented toward the ground, a larger nasal cavity, and a larger distance between postorbital processes and zygomatic arch. These functional traits could also represent an adaptation to favour the duration and depth of diving, while the slender skull of freshwater feeding otters could improve the hydrodynamics.

Development of a predictive kinetic model with statistically analyzed parameters for Donnan Dialysis process

Donnan Dialysis (DD) utilizes ion exchange membranes that allow the selective transport of target ions from a feed solution to a concentrated receiver solution. The kinetics of DD involves boundary layer diffusion (BLD), diffusional membrane transport (MD), and a mixed regime where both mechanisms are active. The objective of the research was to develop an automated computational model that can predict nitrate, bicarbonate, and sulfate concentration profiles and transport mechanisms in DD processes. Experiments were conducted in a batch dialyzer in sole- and multi-component feed solutions and NaCl receiver solutions.Training of the model included numerical extraction of the BLD and MD coefficients from the experimental data; determination of the statistically significant parameters that affect the DD transport; development of correlations between these parameters and the kinetic coefficients; and mapping of the ratio between the boundary layer resistance and the membrane resistance to determine the transport mechanism.The predictive model, included the kinetic equations, i.e., the Nernst-Planck formulation, mass balances, and electro-neutrality, the correlations, and the mapping of the transport mechanism. The model was verified by the experimental data used for the model training and validated by independent datasets. Very good fits between the predicted and experimental concentration profiles were obtained, and the ability to determine the transport mechanism was demonstrated.

LES of HCCI combustion of iso-octane/air in a flat-piston rapid compression machine

Homogeneous Charge Compression Ignition (HCCI) engines promise better efficiency and cleaner emissions than conventional piston engines, but can be challenging to control. Rapid compression machines (RCM) provide a simplified configuration for investigating HCCI combustion behavior, which is necessary for effective control of engine ignition timing and peak pressures. In this study, we assess the utility of large eddy simulations (LES) for predicting HCCI combustion in a 3-D configuration. To this end, LES with finite-rate chemistry employing a 99-species iso-octane/air mechanism of two RCM operating conditions are performed. The RCM configuration under consideration was designed by Strozzi et al. (Combust. Flame, 2019) with a flat piston to introduce large amounts of thermal stratification representative of realistic HCCI engine conditions, through the generation of corner vortices. It is shown that the simulation provides reasonable agreement with temperature fluctuations (7% difference), as well as ignition delay in the short ignition case (1 ms difference), while the long ignition case (35 ms difference) highlights more substantial deficiencies that are still within the expected uncertainty from the employed chemical mechanism. Flame propagation modes predicted by LES agree with experimental observations: spontaneous ignition is seen in the short ignition case, while deflagration is more prominent in the long ignition case. Analysis of global and local quantities classify the short ignition case in a mixed ignition regime, and the long ignition case in the mild ignition regime. These results demonstrate the utility of FRC-LES for investigations of multimode combustion regimes of HCCI combustion in a 3-D configuration.

Designing a Simple Test to Measure and Rate Lubricant-Controlled Friction Reduction

The ability of a lubricant to reduce friction and increase machine efficiency is one of its main functions. However, a standardized test to measure the ability of a lubricant to reduce friction does not exist. In this work we take a common tribometer and design a test sequence to allow the friction reduction of any lubricant to be measured and rated, quickly and accurately. The kinematic viscosity values at 40 and 100 °C for the lubricant, along with the density, are used to calculate appropriate entrainment speeds to maintain a constant test severity for each lubricant. A set sliding distance is determined experimentally to ensure that the metal surfaces are run in and that a stable tribofilm is formed at both temperatures. The lubricants are then rated in terms of their ability to maintain low friction in the boundary, mixed, and full film regimes. The proposed method has been designed ensuring good repeatability, across a range of common lubricants (engine oils, transmission fluids, hydraulic fluids, gear oils). This new method simplifies friction measurement and rating of lubricants using Stribeck curves, supporting the development and qualification of new lubricants.

Numerical investigation of mixed convection and entropy production of nanofluid flow in a corrugated channel using a two‐phase mixture model

AbstractThe two‐dimensional mixed convection in a horizontal sinusoidal corrugated channel (CC) is investigated. The two‐phase mixture model (2PMM) is implemented in Ansys Fluent software to simulate the nanofluid (NF) flow. The mathematical formulation of the 2PMM shows the limitation of the single‐phase mixture model linked to the absence of the slip particle‐fluid velocity and, consequently, the parameters that depend on this factor, particularly the diffusion and the drag coefficients. The laminar mixed convection regime is studied, where the NF copper–water is considered under a uniform temperature wall. The simulation results agree with three published works on mixed laminar convection and forced laminar convection in horizontal CC. The effects of nanoparticles volume fraction (ϕ), Richardson number (Ri), wavelength (λ), and wave amplitude (α) are investigated. The results showed that for a mixed flow, the improvement of heat transfer in a horizontal CC could essentially be obtained for a low Ri, where for a given λ, the submits an apparent increase with the increase of λ, that is, for Ri = 0.05 (λ = 3, α = 0.3, ϕ = 3%), the enhancement is 29.7% for and 128.5% for average entropy production compared to the smooth channel. The effect of ϕ on or is weakly dependent on Ri. The use of a Cu–water NF with a volume fraction of 5% (α = 0.2, λ = 2) leads to an increase in the of 17.6% for Ri = 0.05 and 16.4% for Ri = 10 compared to conventional water fluid.

The effect of monochromatic, combined, and mixed light-emitting diode light regimes on growth traits, fear responses, and slaughter-carcass characteristics in broiler chickens.

This study aims to determine the effects of blue and green monochromatic, blue-green combination, and blue-green mixed led lighting systems on growth, fear, and carcass characteristics of broilers reared in an extensive indoor system. Experimental groups were formed as follows; 1-conventional (incandescent), 2-blue, 3-green, 4-blue-green combined (blue for the first 10days, then green), 5-green-blue combined (green for the first 10days, then blue), and 6-blue-green intermittent (alternating every 5min) monochromatic lightings. It was detected that the average values of the body weight of chickens at 42 and 56days of age in the green-blue group were higher than those of the other treatment groups (both P < 0.05). It was determined that the broilers in the green and green-blue groups had higher means of the β0 parameter of Gompertz model. The tonic immobility, emergence test, home cage avoidance test, a looming human test, and box plus experimenter test were applied to determine the fear responses. It was determined that the worst results for fear responses of broilers were in the intermittent lighting group and green-blue combined group. As a result, it was determined that the application of green monochromatic lighting in the first 10days of the fattening period and blue monochromatic lighting in the following period positively affected growth and slaughter-carcass characteristics. However, it was found that broilers reared under green-blue combined lighting had high fear levels.

Hydrologic Sensitivities and ENSO Variability Across Hydrological Regimes in Central Chile (28°–41°S)

AbstractThere is strong evidence of El Niño‐Southern Oscillation (ENSO) teleconnections in the South Pacific and related impacts on the precipitation regime in Chile; nonetheless, many aspects of the hydrological propagation and temperature responses to ENSO remain unclear in this region. We examine fluctuations across 59 near‐natural catchments in central Chile (28°–41°S) under contrasting ENSO phases during the period 1981–2019. Our results show statistically significant ENSO‐related hydroclimatic anomalies in almost all watersheds analyzed, which confirms the major influence of ENSO within this domain. By comparing El Niño phases against La Niña, we observe generally wetter conditions, warmer winters, cooler late springs, lower (higher) runoff ratios in snowmelt‐driven (rainfall‐driven) basins, and longer storm durations while storm frequencies (i.e., number of events of consecutive days with precipitation) are preserved. Additionally, low (high) elevation catchments are related to positive (negative) streamflow sensitivities to winter temperature, which increase in magnitude with the evaporative index; besides, catchments with sharp warm‐and‐dry conditions yield largely negative sensitivities to late spring temperature. Further, positive streamflow anomalies in rainfall‐driven catchments are explained by temperature and precipitation ENSO‐related amplitudes (El Niño minus La Niña) that separately favor streamflow; however, in mixed regimes and snowmelt‐driven basins these results are spatially scattered. Hence, this study supports that meteorological, hydrological, and physiographic attributes modulate the translation of climate variability into river hydrology. The results presented here unravel the joint effects of precipitation and seasonal temperature fluctuations through different hydrological regimes, across a region that encloses populated cities and water‐intensive activities.

Experimental Investigation for Tribological Properties in Mixed Regime of Lubrication with VG-46 and VG-32.

Experimental Investigation for Tribological Properties in Mixed Regime of Lubrication with VG-46 and VG-32.

Membrane assisted transport of thorium (IV) across bulk liquid membrane containing DEHPA as ion carrier: kinetic, mechanism and thermodynamic studies

Abstract Extraction and carrier mediated transport of thorium (IV) ions through bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as metal ion carrier. The feed comprised of thorium (IV) ions solutions containing various concentrations of hydrochloric acid, while sulfuric acid solutions of different concentrations are used as a stripping agent. Various parameters about thorium (IV) ion extraction and transport were investigated: the feed solution acidity, initial metal ions aqueous solution concentration, carrier concentration and stripping agent concentration. More than 85% thorium (IV) is recovered in 960 min using 0.2 M DEHPA/kerosene as carrier and 1.5 M H2SO4 as stripping agent from the 0.0001 M HCl solution containing 50 mg L−1 thorium (IV) as feed. Assuming a consecutive, irreversible extraction and back-extraction (stripping) reactions a simple kinetic model was proposed for estimating the reaction rate constant or reaction rate coefficient under the investigated experimental conditions. The activation energy values of extraction and back-extraction reactions were calculated to be 29.94 kJ mol−1 and 20.55 kJ mol−1, respectively, which indicates that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the back-extraction process was mainly controlled by diffusion process.

Effects of Thermocyclops decipiens and Artemia Nauplii for Larval Rearing of Macrobrachium rosenbergii (De Man, 1879)

This study examines the effects of the freshwater cyclopoid Thermocyclops decipiens and Artemia nauplii on the growth and survival of Macrobrachium rosenbergii (De Man, 1879) larvae during the rearing phase. M. rosenbergii larvae were divided into three groups and fed exclusively with either Artemia nauplii or T. decipiens, and a mixed diet (50% T. decipiens and 50% Artemia nauplii) in triplicate. The results indicated that M. rosenbergii larvae reached 90% post larvae (PL) on the 23rd day of the mixed diet feeding regime, followed by 88% and 82% PL on the 24th and 26th days when fed with Artemia nauplii and T. decipiens , respectively. The highest length and weight of M. rosenbergii PL were observed in the mixed diet treatment with 14.37±0.51mm and 0.76±0.04mg, respectively. The specific growth rate and percentage weight gain were significantly (p &amp;lt; 0.05) higher in the mixed feeding treatment. However, the survival of larvae was highest (69.89±4.55%) in the Artemia nauplii treatment. The larval stage index (LSI) of M. rosenbergii larvae fed on different feeding regimes was mixed diet &amp;gt; Artemia nauplii &amp;gt; T. decipiens. The biochemical constituents of M. rosenbergii PL showed that protein concentration was higher in the larvae fed with T. decipiens, while carbohydrate and lipid content were also high in mixed feeding regimes. Results indicated that the larval stage index and growth parameters of M. rosenbergii larvae were highest in the mixed diet treatment

Characterization of Nile Tilapia (Oreochromis niloticus) Farming Intensities in Liberia

Fish farming is a rapidly growing food sector in developing nations. Liberia is an example of a least developed country with a large population facing high poverty levels. This has led to the adoption of aquaculture as one of the most important strategies for solving malnutrition and food security problems. However, since the introduction of fish farming, fish yields have been persistently low. To address the shortcomings in fish yields in Liberia, a study was conducted to provide information on fish farming intensities, types, and quality of feeds used by farmers in the culture of O. niloticus in Bong, Lofa, Nimba, and Grande Gedeh counties. Using stratified purposive sampling, 120 farmers were interviewed, and their fish feeds were sampled for proximate nutrient analyses. The results demonstrated that fish farming of O. niloticus in Liberia is mostly semi-extensive (81.6%), mainly practiced in paddy, barrage, and earthen ponds. On average, farmers produce 165.7 kg ha−1 of O. niloticus annually, translating to USD 414.25. Farmers use mixed feeding regimes, comprising farmer-made, kitchen waste, and blended commercial feeds. Farmers, on average, spend 43% of their operation cost on feeds, which makes it unsustainable to maintain semi-intensive systems. The main feed ingredients used by Liberian fish farmers are rice bran, wheat bran, corn, palm kernel, and fishmeal. Crude protein levels in feed ingredients are as follows: rice bran (3.7 ± 1.3%), wheat bran (16.4 ± 1.5%), corn (6.3 ± 1.1%), palm kernel cake (14.8 ± 1.4%), and fishmeal (63.8 ± 1.3%). Crude proteins were low in formulated feeds, ranging from 8–15% CP. From this study, poor yields and the slow growth of O. niloticus can be attributed to low-protein diets, rendering farming ventures unprofitable and unsustainable for resource-poor farmers in Liberia.

Correlation Between Tribological and Vibration Behaviors in Sliding Lubricated Contacts

Abstract The tribological and vibration behaviors of a lubricated system are often studied separately. However, in recent years, the combination of tribology and mechanical vibration significantly contributes in analyzing and solving many practical problems. The main objective of this study is to establish empirical equations that describe friction–-vibration interactions under dynamic (sliding) lubricated contacts. The effects of operating conditions on the tribological and vibration behaviors of lubricating oils having different viscosities were experimentally investigated using a four-ball wear test machine. The results indicated that the vibration velocity tends to increase with the sliding velocity. With a lower combination of ratio of the vibration velocity to the sliding velocity and the specific film thickness, lower friction coefficients were observed in the boundary and mixed lubrication regimes. The mean wear scar diameters exhibited positive correlations with the amplitudes of vibration accelerations. The empirical equations provide basic information for the prediction of friction variation by measuring vibration signals.

Synthesis of N-doped carbon quantum dots as lubricant additive to enhance the tribological behavior of MoS2 nanofluid

In this study, a novel lubricant additive nitrogen-doped carbon quantum dot (N-CQD) nanoparticle was prepared by the solvothermal method. The synthesized spherical N-CQD nanoparticles in the diameter of about 10 nm had a graphene oxide (GO)-like structure with various oxygen (O)- and nitrogen (N)-containing functional groups. Then N-CQDs were added to MoS2 nanofluid, and the tribological properties for steel/steel friction pairs were evaluated using a pin-on-disk tribometer. Non-equilibrium molecular dynamics (NEMD) simulations for the friction system with MoS2 or MoS2 + N-CQD nanoparticles were also conducted. The results showed that friction processes with MoS2 + N-CQD nanofluids were under the mixed lubrication regime. And MoS2 nanofluid containing 0.4 wt% N-CQDs could achieve 30.4% and 31.0% reduction in the friction coefficient and wear rate, respectively, compared to those without N-CQDs. By analyzing the worn surface topography and chemical compositions, the excellent lubrication performance resulted from the formation of tribochemistry-induced tribofilm. The average thickness of tribofilm was about 13.9 nm, and it was composed of amorphous substances, ultrafine crystalline nanoparticles, and self-lubricating FeSO4/Fe2(SO4)3. NEMD simulation results indicated the interaction between S atoms in MoS2 as well as these O- and N-containing functional groups in N-CQDs with steel surfaces enhanced the stability and strength of tribofilm. Thereby the metal surface was further protected from friction and wear.

Flash boiling atomization triggered and driven by intensive radiation

• We propose a new method for spray generation, employing the flash boiling mechanism. • A liquid is subjected to intense volumetric radiation, causing rapid boiling. • The bubbles’ nucleation and growth rate were estimated. • We found that an increase of heating power will generate finer sprays. For many applications, the demand for a high-quality liquid spray is crucial. Flash boiling atomization is one of the most promising methods to generate such fine sprays with a high degree of droplet size uniformity. Several mechanisms were proposed to implement this method, which harnesses the liquid’s thermal energy to disintegrate it into droplets; the atomized liquid is brought to a highly energetic superheated state either by rapid heating of the liquid or by an abrupt pressure drop. In the present work, we propose and theoretically examine a novel method for spray generation which employs the flash boiling mechanism. By subjecting the liquid to intense volumetric heating and inducing significant homogeneous nucleation (i.e., nucleation flux of more than 10 12 1 / m 3 s ), the vapor bubbles nucleate, grow, and subsequently break down the liquid into a fine spray. We analyze the bubbles' expansion process and determine their size before bursting as a reasonable indication of the generated droplets' size. Here we consider a mixed regime where both heterogeneous and homogeneous nucleation may occur. Our results suggest that an increase in the heating power leads to a significant decrease in the bubbles' mean diameter, thus contributing to the refinement of the generated droplets. The study evaluates the energetic efficiency of the proposed novel mechanism, exposing a rather complex behavior. The model predicts a maximum efficiency of 0.05% when homogeneous nucleation is dominant, while the efficiency for systems governed by heterogeneous boiling aspires to near-zero values.

Thermal analysis on mutual interaction of temperature stratification and solutal stratification in the presence of non-linear thermal radiations

The mutual interaction of thermal stratification and solutal stratification in mixed convection flow regimes claims many thermal engineering standpoints in daily life and so holds the interest of researchers in the thermal science of fluid flows. Owning to such interest, the current attempt contains a comparative thermal case study on a non-Newtonian fluid flow field subject to inclined surfaces. The stagnation point temperature flow regime is manifested with non-linear radiations, magnetic field, and heat generation/absorptions effects. The physical problem is translated mathematically in terms of a non-linear coupled differential system. The solution is reported by using the shooting method for Jeffrey fluid flow. The surface quantities namely are Sherwood and Nusselt numbers are evaluated for various important physical domains namely radiative flow field, non-radiative flow field, stratified and non-stratified fields, magnetic and non-magnetic fields. We observed that the thermophysical characteristics of stagnation point flow of Jeffrey fluid are enriched in magnitude for the cylindrical surface. Further, the heat transfer normal to the cylindrical surface is higher in magnitude with temperature stratification in comparison with the flow regime without temperature stratification.

Methyltrioctylammonium Octadecanoate as Lubricant Additive to Different Base Oils

This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the miscibility of the FAIL in the base oils. The addition of the FAIL hardly changed the density of the base oils and the viscosity slightly increased at lower temperatures. The tribological performance of the base oils and their blends with the FAIL was determined using three different tests: Stribeck curve determination and tribofilm formation tests, both under sliding/rolling motion, and reciprocating wear tests. The M1 + FAIL blend showed the lowest friction values under the mixed lubrication regime due to its higher viscosity, while the E1 + FAIL showed the lowest friction values under the elastohydrodynamic lubrication regime, which may well have been due to its higher polarity. Only the E1 + FAIL blend outperformed the antiwear behavior of the base oil, probably because it has better chemical affinity (higher polarity) for the metallic surface. SEM images showed that the predominant wear mechanism was adhesive-type with plastic deformation and XPS studies proved that the presence of increasing amounts of organic oxygen on the wear scar caused better antiwear performance when the E1 + FAIL blend was used.

Flight regimes recognition in actual operating conditions: A functional data analysis approach

Helicopters need adequate monitoring to prevent dynamic failures from excessively affecting components’ health status, increase the level of safety, and reduce operative costs. Health and Usage Monitoring Systems have been developed to monitor helicopters during their lifetime in the last few decades. Recent works demonstrated that despite analyzing physical components’ behavior over time, tracking the regimes performed during each flight contributes to estimating the aircraft’s health and usage status, paving the way for designing accurate prognostics algorithms. However, today, most regime recognition systems rely on data recorded during certification flights. It follows that the training regimes differ from the ones proposed in the prediction phase, which are acquired during helicopter actual operating conditions. This affects these recognition system performances. Aiming at overcoming this limitation, in this work, we proposed an unsupervised regimes recognition system capable of better handling the actual helicopter usage spectrum. In detail, we proposed a system based on an unsupervised learning paradigm, which leverages a soft-membership classification technique to account even for mixed regimes and transitions. In addition, the system represents data according to functional data analysis theory, which allows for considering the temporal relationship between samples in the classification process, often neglected in state-of-the-art approaches. The proposed system was tested on experimental data, collected by Leonardo Helicopter Division, assessing outstanding capabilities in recognizing correctly standard and mixed regimes and transients. Also, the presented results demonstrate the approach capabilities in paving the way for the definition of new regimes, more consistent with the actual helicopter usage spectrum.