Robust surfaces capable of reducing flow drag, controlling heat and mass transfer, and resisting fouling in fluid flows are important for various applications. In this context, textured surfaces impregnated with a liquid lubricant show promise due to their ability to sustain a liquid–liquid interface that induces slippage. However, theoretical and numerical studies suggest that the slippage can be compromised by surfactants in the overlying fluid, which contaminate the liquid–liquid interface and generate Marangoni stresses. In this study, we use Doppler-optical coherence tomography, an interferometric imaging technique, combined with numerical simulations to investigate how surfactants influence the slip length of lubricant-infused surfaces with longitudinal grooves in a laminar flow. Surfactants are endogenously present in the contrast agent (milk) which is added to the working fluid (water). Local measurements of slip length at the liquid–liquid interface are significantly smaller than theoretical predictions for clean interfaces (Schönecker & Hardt 2013). In contrast, measurements are in good agreement with numerical simulations of fully immobilized interfaces, indicating that milk surfactants adsorbed at the interface are responsible for the reduction in slippage. This work provides the first experimental evidence that liquid–liquid interfaces within textured surfaces can become immobilised in the presence of surfactants and flow.

Taking the leap to the secondary and tertiary generations of the missions to Mars, a comprehensive outline was presented for a cluster of Martian Habitat Units (MHUs) designed for long-term settlements of research crew in Melas Chasma, Valles Marineris, Mars. Unlike initial exploration missions, where primary survival is ensured through basic engineering solutions, this concept targets later-stage missions focused on long-term human presence. Accordingly, the MHUs are designed not only for functionality but also to support the social and cultural well-being of scientific personnel, resulting in larger and more complex structures than those typically proposed for early-stage landings. To address the construction and structural integrity of the MHUs, the current work presents a comprehensive analysis of the feasibility of semi-3D-printed structural systems using in situ material to minimize the cost and engineering effort of logistics and construction of the units. Regolith-based additive manufacturing was utilized as the primary material, and the response of the structure, not only to the gravitational loads but also to those applied from the exterior flow field and wind pressure distributions, was simulated, as well as the considerations regarding the contribution of the extreme interior/exterior pressure differences. The full analyses and structural results are presented and discussed in this manuscript, as well as insights on manufacturing and its feasibility on Mars. The analyses demonstrate the feasibility of constructing the complex architectural requirements of the MHUs and their cost-effectiveness through the use of in situ resources. The manuscript presents an iterative structural optimization process, with results detailed at each step. Structural elements were modeled using FEM-based analysis in Karamba-3D to minimize near-yielding effects such as buckling and excessive displacements. The final structural system was integrated with the architectural design to preserve the intended spatial and functional qualities.

Optical coherence tomography (OCT) has become an indispensable tool for investigating mesoscopic features in soft matter and fluid mechanics. Its ability to provide high-resolution, non-invasive measurements in both spatial and temporal domains bridges critical gaps in experimental instrumentation, enabling the study of complex, confined, and dynamic systems. This review serves as both an introduction to OCT and a practical guide for researchers seeking to adopt this technology. A set of tutorials, complemented by Python scripts, is provided for both intensity- and Doppler-based techniques. The versatility of OCT is illustrated through case studies, including time-resolved velocimetry, particle-based velocity measurements, slip velocity characterization, detection of shear-induced structures, and analysis of fluid-fluid and fluid-structure interactions. Drawing on our experiences, we also present a set of practical guidelines for avoiding common pitfalls.

It is needless to say that travel to and settlement on Mars are associated with extreme levels of scientific and engineering issues. This will only be amplified with the long-term duration of the mission, not only due to scarcity of resources, but also as the psychological aspects of the dynamics among the crew increase drastically. It should be emphasized that this is a scientific crew, who have undergone high levels of confinement during space travel to Mars, O (102 Earth days), are living in semi-solitude and partial confinement conditions for durations of O (103 Earth days), and even at the nominal termination of the mission, foresee a high-risk and arduous travel time of O (102 Earth days) back to the Earth. The mental weight of the described mission with its slow pace and tardy episodes, puts the crew under severe psychological issues. Minimal and conservative design of spaces, lack of constant access to the exterior, and social solitude are among major factors contributing to the psychological well-being of the crew. Furthermore, the overall lower levels of natural light, accompanied by the minimum possible area of transparent facades, protecting the crew from harmful radiations and cold exterior, burden the mental conditions of the crew even more. Given the limited availability of data from the surface of Mars, study of the effects linked to the lighting and illumination design of the habitats is challenging. The current manuscript hopes to shed light on the illumination and lighting design and simulation procedure, required data, assumptions, and final results for the surface-level habitats on Mars. • Mars / Sub orbital configuration allows for limited natural lighting, however, upon site-specific analysis, it might be considerable as a base passive source. • Current simulation tools are design based on Earth-bound design requirements. These need to be re-oriented to match available planetary data.

The combination of flow elasticity and inertia has emerged as a viable tool for focusing and manipulating particles using microfluidics. Although there is considerable interest in the field of elasto-inertial microfluidics owing to its potential applications, research on particle focusing has been mostly limited to low Reynolds numbers (Re<1), and particle migration toward equilibrium positions has not been extensively examined. In this work, we thoroughly studied particle focusing on the dynamic range of flow rates and particle migration using straight microchannels with a single inlet high aspect ratio. We initially explored several parameters that had an impact on particle focusing, such as the particle size, channel dimensions, concentration of viscoelastic fluid, and flow rate. Our experimental work covered a wide range of dimensionless numbers (0.05 < Reynolds number < 85, 1.5 < Weissenberg number < 3800, 5 < Elasticity number < 470) using 3, 5, 7, and 10 µm particles. Our results showed that the particle size played a dominant role, and by tuning the parameters, particle focusing could be achieved at Reynolds numbers ranging from 0.2 (1 µL/min) to 85 (250 µL/min). Furthermore, we numerically and experimentally studied particle migration and reported differential particle migration for high-resolution separations of 5 µm, 7 µm and 10 µm particles in a sheathless flow at a throughput of 150 µL/min. Our work elucidates the complex particle transport in elasto-inertial flows and has great potential for the development of high-throughput and high-resolution particle separation for biomedical and environmental applications. (Figure presented.)

Thixo-elasto-viscoplastic (TEVP) fluids are very complex fluids. In addition to elasticity and viscoplasticity, they exhibit thixotropy, i.e., time-dependent rheology due to breakdown and recovery of internal structures at different length- and timescales. General and consistent methods for a priori flow prediction of TEVP fluids based on rheological characteristics are yet to be developed. We report a combined study of the rheology and flow of 18 samples of different TEVP fluids (three yogurts and three concentrations of Laponite and Carbopol, respectively, in water in both the unstirred and a stirred state). The rheology is determined both with standard protocols and with an ex situ protocol aiming at reproducing the shear history of the fluid in the flow. Micrometer resolution flow measurements in a millimeter scale rectangular duct are performed with Doppler Optical Coherence Tomography (D-OCT). As expected, the results show the existence of a plug flow region for samples with sufficiently high yield stress. At low flow rates, the plug extends almost all the way to the wall and the extent of the plug decreases not only with increased flow rate but also with increased thixotropy. The ex situ rheology protocol enables estimation of the shear rate and shear stress close to the wall, making it possible to identify two scaling laws that relates four different non-dimensional groups quantifying the key properties wall-shear stress and slip velocity. The scaling laws are suggested as an ansatz for a priori prediction of the near-wall flow of TEVP fluids based on shear flow-curves obtained with a rheometer.

Centered on the core idea of long duration habitat design for research crew on Mars, the Martian Habitat Units (MHUs) are designed as a cluster of 10 units each with the maximum capacity of 9 crew members to live and carry on with the local challenges of scientific and exploratory life, while enjoying their lives as intellectual, social individuals in the harsh environment of Mars for durations in the order of magnitude of several years. This approach to the concept of a living environment in sharp contradiction to that of a shelter with the minimal capabilities to meet the requirements of terrestrial life to the point of survival, has led the outcoming design to be a fulfilling environment for the inhabitants of the units to evolve and thrive culturally, while being on a years-long mission. This manuscript provides detailed insight on the lessons learned of the aforementioned comprehensive design attempt with, but not limited to, the following core concerns: • The initial stand-point of such a design procedure relies on an ever increasing and comprehensive list of concerns, be it classically discussed in the literature and predictable, or unforeseen on the face of it, but to be prevented anyhow. The manuscript discusses the most crucial ones of such criteria/concerns. • The infamous saying of “Whatever that can go wrong, will go wrong” demands a rather complex level of redundancies in all layers of the design and the thought procedure behind its all aspects. The manuscript addresses the adequate steps towards its realization. • Modularity in all layers of the design plays a key role in reducing construction, maintenance, and installation costs, as for any deep space mission the mentioned expenses are astronomically high themselves. The manuscript presents our solution for geometric modularity of the design.

In response to application demands in vehicle dynamics and control, traffic engineering, urban planning, and logistics, the generation of an adequate artificial road profile in terms of the diversity of geometric scenarios has been addressed in the current manuscript. The underlying mathematical principles for generating a geometrically comprehensive, yet logically meaningful, 3D road profile have been taken from high and unbiased sweeping factors of random number sequences over their domain of interest. And to generate such random number sequences, the mathematically manipulated output signal of a well-established chaotic system has been utilized, namely that of the Chua's circuit. Having defined the target road profile mathematically with all its geometrical complexities, a suitable scheme derived from the mentioned chaotic signal has been used to generate the required random number sequences as defining parameters of the road profile. The scheme has been otherwise tested and proven to show the demanded level of randomness in literature. Several attempts have been made to create a diverse range of road profiles. considering the constraints imposed by vehicle dynamics. To generate the road geometries, the limitations imposed by the vehicle's motion, such as the limitations on corresponding curvatures, slopes, and banking angles are negotiated, in terms of vehicle dynamics and available tire-road friction forces, by evaluating how close a vehicle will be to its tire force capacity limits as it travels on sections of the generated road.

We are living in a point in the history of science and technology, where space travel for research and settlement is inevitable. As the utmost crucial technology pieces for leaving Earth and travelling into the cosmos is being established one after another, it is just a matter of decades, until it all gets integrated together, solving the engineering problems ahead of the way and being able to step on the planets and moons of the solar system. In this quest, as has been the case for most of the technological advancements so far, there ought to be mind experiments, in which one skips one step, assumes the availability of responses to the skipped-over step, and searches for the solution to the questions of the next level. This way, by getting passed the first, i.e. current step, the solution to the next one is already available. The current manuscript is addressing this very 'next step', on the long path to eventually colonize Mars and inhabit it for long-term research-based missions; let it be for terraforming, or other agenda to be defined by the research strategists, then. And as mentioned earlier, the current step; being setting foot on Mars, is well-deservedly taken for granted, as is to come forth undoubtedly. Having that realized, we might find ourselves faced by the engineering complexities of surviving and thriving on Mars, which is the subject matter of the current research, from the aspect point of space technological and architectural design. The design procedure beginning from setting the philosophy of design upon the concerns of sustaining in the hostile environment of Mars, to the stepwise emergence of the final design of a cluster of Martian Habitat Units (MHUs) considering the high-criteria of the case, is the subject matter covered in this manuscript.

Addressing the subject matter of human missions on Mars, the Martian Habitat Units (MHUs) are presented as a comprehensive solution. MHUs are designed in clusters of 10 units, each capable of serving as long-term habitats for 9 scientific crew members. The life-style requirements of the units are targeted at an imitation of cultural thriving life we all know of, and not a mere survival-type shelter expecting the first people to step foot on Mars. One aspect of many challenging issues to be addressed in such complex settings is the lighting and illuminance condition of the said habitats, which in the context of Mars, and generally deep space missions being far from the sun will certainly lead to an arduous task. To check the validity of the argument and assess the extent to which the natural light level available on the surface of Mars will be sufficient for the daily requirements of the crew and mission in terms of illuminance, the current manuscript presents thorough and detailed simulations and analyses on the availability evaluation of natural lighting in the site location of MHUs, namely Valles Marineris, Melas Chasma. In this paper solar irradiation parameters on Mars are calculated based on the previous research which resulted in global, direct and diffuse irradiance at 12 different Martian solar times. The simulations are distributed over the Martian year and its day-time, and for two extreme orientations of MHUs in their circular surrounding cluster, namely East/West and South/North units. The distribution of illuminance for each case, and trend comparison studies are then accompanied by numerical values and analyses on the percentage to which the natural lighting conditions on Mars have been shown to be sufficient as a fraction of the whole lighting load of the habitats, which is to be compensated using artificial sources. The corresponding values are shown to fall well in the range of 35-45% of the total lighting loads. Also, as the results of the simulations show, due to the consistency of the glazed parts of the designed facade through all exterior surface of the MHU, natural lighting sufficiency percentage does not show a significant difference between two simulated orientations. This fact further approves the circular orientation premise of the MHUs in their cluster.