Water is essential for sustaining life and required for carrying out basic daily activities. Even though water covers the vast majority of the earth’s surface, the availability of fresh water, which is necessary to maintain human activities, is limited, making it a scarce resource. Climate change, overexploitation of groundwater, and population growth are all putting significant pressure on natural water sources, which pose a serious threat to various sectors of society, especially in agriculture. Future projections of freshwater availability indicate agriculture production will suffer a significant shock globally, including in India, leading to a threat to food security and sustainability. To ensure the sustainability of this vital resource, it is crucial to use water sensibly. Moreover, it is essential to adopt certain strategies to manage agricultural water use effectively. This includes adopting various water-efficient techniques such as ‘micro-irrigation’, ‘irrigation scheduling’, ‘conservation agriculture’, ‘crop switching’ and so on. In this review, firstly, we discuss water scarcity and its types, causes, crisis for water shortages and hindrance to sustainable development from a global perspective emphasizing the Indian scenario as a developing nation. Secondly, we elaborated our discussion on water scarcity in agriculture including the impacts of water scarcity on agricultural production and its connection to climate change, population growth, and overexploitation of natural resources globally focusing on the Indian scenario. In addition, innovative water management practices and adaptation strategies to manage agricultural water use, constraints, and the need for further research are also covered. It is anticipated that this review will benefit researchers and policymakers by providing useful information on the impacts of water limitation and adoption strategies.

We verify a long-standing conjecture on the membership of univalent harmonic mappings in the Hardy space, whenever the functions have a “nice” analytic part. We also produce a coefficient estimate for these functions, which is in a sense best possible. The problem is then explored in a new direction, without the additional hypothesis. Interestingly, our ideas extend to certain classes of locally univalent harmonic mappings. Finally, we prove a Baernstein-type extremal result for the function $\log (h'+cg')$, when $f=h+\overline {g}$ is a close-to-convex harmonic function, and c is a constant. This leads to a sharp coefficient inequality for these functions.

Compound droplets confined in a microfluidic channel often exhibit intriguing shapes, primarily attributable to complex hydrodynamic interactions over small scales. Here, we show that the effect of electrohydrodynamic interactions may modulate the shape evolution of the same in a somewhat non-trivial manner. By adopting a phase field formalism, our studies reveal that the combined influence of electrohydrodynamics and fluidic confinement eventually culminates towards influencing the droplet transients, distortion of the local field, as well as droplet stabilization or destabilization, allowing one to develop different regimes of shape evolution that are distinct from the ones reported in earlier studies on single droplet dynamics. Under the assumption of negligible fluid inertia and small shape deformation, we also develop an asymptotic model to predict the transient as well as the steady-state behaviour of the compound droplet for the limiting case of an unbounded suspending medium. The relative magnitude of the permittivity and conductivity of the system, in conjunction with the channel confinement, is seen to play an important role in altering the deformation characteristics of either of the interfaces. We further observe that, depending on these electrical properties, the inner droplet, if eccentrically located, may exhibit a to-and-fro or a simple translational motion. Remarkably, below a threshold confinement dimension, we unravel the onset of a definitive translational motion of the inner droplet instead of a more intuitive to-and-fro motion, thereby rendering its migration characteristics to be independent of any electrical properties. Furthermore, the viscosity contrast of the fluid phase also plays a vital role in controlling the motion and deformation dynamics of the droplet in both confined and unbounded domains. These results may bear far-reaching consequences towards understanding the control of cellular dynamics in confined in vivo physiological passages by introducing embedded electrical chips, as well as electrohydrodynamically modulated lab-on-a-chip devices for medical diagnostics on a cellular level.

Intricate manipulation of droplets in fluidic confinements may turn out to be critically important for achieving their controlled transverse distributions. Here, we study the migration characteristics of a suspended deformable droplet in a parallel plate channel under the combined influence of a constant temperature gradient in the transverse direction and an imposed pressure driven flow. An outstanding question concerning the resultant non-trivial dynamical features that we address here pertains to the nonlinearity that results as a consequence of the shape deformation, which does not permit us to analyse the combined transport as a mere linear superposition of the results for the thermocapillary and imposed flow driven droplet migration in an effort to obtain the final solution. For the analytical solution, an asymptotic approach is used, where we neglect any effect of inertia or thermal convection of the fluid in either of the phases. To obtain a numerical solution, we use the conservative level set method. We perform numerical simulations over a wide range of governing parameters and obtain the dependence of the transverse steady position of the droplet on different parameters. In order to address practical microfluidic set-ups, the influence of a bounding wall as well as the effect of thermal convection and finite shape deformation on the cross-stream migration of the droplet is investigated through numerical simulations. Increase in the thermal Marangoni stress shifts the steady-state transverse position of the droplet further away from the channel centreline, for any particular value of the capillary number (which signifies the ratio of the viscous force to the surface tension force). The confinement ratio, which is the ratio of the droplet radius to the channel height, plays an important role in predicting the transverse position of the droplet and thus has immense consequences for the design of droplet-based microfluidic devices with enhanced functionalities. A large confinement ratio drives the droplet towards the channel centre, whereas a smaller confinement ratio causes the droplet to move towards the wall. Moreover, for a fixed droplet radius and constant imposed temperature gradient, an increase in the channel height results in an increase in the time required for the droplet to reach the steady-state position. However, the final steady-state position of the droplet is independent of its initial position but at the same time dependent on the droplet phase thermal conductivity. A larger droplet thermal conductivity compared with the carrier phase results in a steady-state droplet position closer to the channel centreline. A higher fluid inertia, on the other hand, shifts the steady-state position towards the channel wall.

The motion of a viscous droplet in unbounded Poiseuille flow under the combined influence of bulk-insoluble surfactant and linearly varying temperature field aligned in the direction of imposed flow is studied analytically. Neglecting fluid inertia, thermal convection and shape deformation, asymptotic analysis is performed to obtain the velocity of a force-free surfactant-laden droplet. The droplet speed and direction of motion are strongly influenced by the interfacial transport of surfactant, which is governed by surface Péclet number. The present study is focused on the following two limiting situations of surfactant transport: (i) surface-diffusion-dominated surfactant transport considering small surface Péclet number, and (ii) surface-convection-dominated surfactant transport considering high surface Péclet number. Thermocapillary-induced Marangoni stress, the strength of which relative to viscous stress is represented by the thermal Marangoni number, has a strong influence on the distribution of surfactant on the droplet surface. The present study shows that the motion of a surfactant-laden droplet in the combined presence of temperature and imposed Poiseuille flow cannot be obtained by a simple superposition of the following two independent results: migration of a surfactant-free droplet in a temperature gradient, and the motion of a surfactant-laden droplet in a Poiseuille flow. The temperature field not only affects the axial velocity of the droplet, but also has a non-trivial effect on the cross-stream velocity of the droplet in spite of the fact that the temperature gradient is aligned with the Poiseuille flow direction. When the imposed temperature increases in the direction of the Poiseuille flow, the droplet migrates towards the flow centreline. The magnitude of both axial and cross-stream velocity components increases with the thermal Marangoni number. However, when the imposed temperature decreases in the direction of the Poiseuille flow, the magnitude of both axial and cross-stream velocity components may increase or decrease with the thermal Marangoni number. Most interestingly, the droplet moves either towards the flow centreline or away from it. The present study shows a critical value of the thermal Marangoni number beyond which the droplet moves away from the flow centreline which is in sharp contrast to the motion of a surfactant-laden droplet in isothermal flow, for which the droplet always moves towards the flow centreline. Interestingly, we show that the above picture may become significantly altered in the case where the droplet is not a neutrally buoyant one. When the droplet is less dense than the suspending medium, the presence of gravity in the direction of the Poiseuille flow can lead to cross-stream motion of the droplet away from the flow centreline even when the temperature increases in the direction of the Poiseuille flow. These results may bear far-reaching consequences in various emulsification techniques in microfluidic devices, as well as in biomolecule synthesis, vesicle dynamics, single-cell analysis and nanoparticle synthesis.

Three-dimensional (3D) printing of metallic materials involves the layerwise consolidation of feedstock materials in the form of powder, wire, or sheet using various energy sources to form complex shapes. The past two decades have witnessed significant advances in the field, in terms of both technologies and materials for metal 3D printing. This has led to widespread exploration and adoption of the technologies across industry, academia, and R&D organizations. This article presents an overview of the field of metal 3D printing. A brief history of metal 3D printing is followed by an overview of metal 3D printing methods and metallic material systems used in these methods. Microstructure and properties, and their relationship to process parameters are discussed next, followed by current challenges and qualification issues. The article concludes with future trends and a brief description of the invited articles included in this special issue.

Three-dimensional (3D) printing represents the direct fabrication of parts layer-by-layer, guided by digital information from a computer-aided design file without any part-specific tooling. Over the past three decades, a variety of 3D printing technologies have evolved that have transformed the idea of direct printing of parts for numerous applications. Three-dimensional printing technology offers significant advantages for biomedical devices and tissue engineering due to its ability to manufacture low-volume or one-of-a-kind parts on-demand based on patient-specific needs, at no additional cost for different designs that can vary from patient to patient, while also offering flexibility in the starting materials. However, many concerns remain for widespread applications of 3D-printed biomaterials, including regulatory issues, a sterile environment for part fabrication, and the achievement of target material properties with the desired architecture. This article offers a broad overview of the field of 3D-printed biomaterials along with a few specific applications to assist the reader in obtaining an understanding of the current state of the art and to encourage future scientific and technical contributions toward expanding the frontiers of 3D-printed biomaterials.

PS-b-PEO block co-polymers have been reported to form cylindrical, lamellar, gyroidic, and supramolecular architectures due to several reasons: some of the reasons include the chemical incompatibility between the lipophilic and lipophobic covalently cross-linked blocks resulting in a high Flory-Huggins interaction parameter, the annealing solvent, and the interfacial boundary conditions between the substrate and the phase separating blocks. We report here for the first time on the spontaneous formation of nanopores and nanorings in PS-b-PEO block co-polymers. The mean size and depth of the pores are about 150nm and 40nm, respectively, while the pores occur randomly placed in clusters of about 2-5 pores. The pore clusters leave behind a breath-like architecture replicated by the phase separating block co-polymer. These breath architectures, in the shape of nanorings, are formed during the initial period of phase separation and do not disappear after phase separation has been achieved, leaving behind a PS-enriched circular framework. The diameter of the nanorings is in the 200-700nm range, as measured from AFM phase and height images. This range falls within the reported size of water droplets forming breath structures on polymer films. The resulting nanoarchitectured materials could find potential applications where biocompatibility and water permeability of the PEO block within the nanopores is desirable. In addition, the slightly elevated nanorings could also provide semi-enclosed barriers that can serve as micro/nano-enclosed cell and tissue cultures.

We report on the laser interference patterning of as-spun block copolymer films on silicon and silicon dioxide substrates. Our process involves the use of a pulsed laser light source of 266 nm wavelength and any type of diblock copolymer as a positive tone photoresist, resulting in the generation of sub-micron domains of different geometries and periodicity. This non-solvent based method is robust, and when combined with the inherent nano-scaled periodicity in block copolymers, can produce hierarchical patterns on substrates with potential use in the electronics and semiconductor industries.

We report on the formation of hierarchical nanostructures of Au, Pt, Fe2O3 and PdO2 using a hybrid technique combining laser interference patterning (LIP) and block copolymer phase separation (BCPS). By varying the loading time of the block copolymer with metallic salts and the laser interference technique, different types of hierarchical square, triangular, linear and circular arrays can be formed. Such a robust method can be applied to other metallic and ceramic materials and has potential for use in the large-scale production of nano-catalysts, photonics, optoelectronics, MEMS devices and bio-sensors.

Visceral leishmaniasis (VL) is a major public health problem in the Indian subcontinent where the Leishmania donovani transmission cycle is described as anthroponotic. However, the role of animals (in particular domestic animals) in the persistence and expansion of VL is still a matter of debate. We combined Direct Agglutination Test (DAT) results in humans and domestic animals with Geographic Information System technology (i.e. extraction maps and scan statistic) to evaluate the exposure to L. donovani on these 2 populations in a recent VL focus in Nepal. A Poisson regression model was used to assess the risk of infection in humans associated with, among other factors, the proportion of DAT-positive animals in the proximities of the household. The serological results showed that both humans and domestic animals were exposed to L. donovani. DAT-positive animals and humans were spatially clustered. The presence of serologically positive goats (IRR=9·71), past VL cases (IRR=2·62) and the proximity to a forest island dividing the study area (IRR=3·67) increased the risk of being DAT-positive in humans. Even if they are not a reservoir, domestic animals, and specially goats, may play a role in the distribution of L. donovani, in particular in this new VL focus.

The flow field due to two normal impinging liquid jets is different from the flow field associated with a single normal impinging liquid jet, and even from the flow field around two normal impinging compressible fluid jets. Depending on the spacing between the two jets and their relative strengths, different kinds of hydraulic jump interactions are possible, resulting in a variety of flow patterns. The present study experimentally elucidates the jump--jump interactions formed in such cases, for different values of inter-jet spacings and for different strengths of the individual jets. Analogous flow fields associated with the interactions between a single impinging jet and a fence are also studied to allow convenient experimental flow vizualizations.

An obliquely inclined circular water jet, impinging on a flat horizontal surface, confers a series of hydraulic jump profiles, pertaining to different jet inclinations and jet velocities. These jump profiles are non-circular, and can be broadly grouped into two categories, based on the angle of jet inclination, φ, made with horizontal. Jumps corrosponding to the range (25° < φ≤ 90°) are observed to be bounded by smooth curves, whereas those corresponding to φ≤ 25° are characterized by distinct corners. The present work attempts to find a geometric and hydrodynamic characterization of the spatial patterns formed as a consequence of such non-circular hydraulic jump profiles. Flow-visualization experiments are conducted to depict the shape of demarcating boundaries between supercritical and subcritical flows, and the corresponding radial jump locations are obtained. Theoretical calculations are also executed to obtain the radial locations of the jumps with geometrically smooth profiles. Comparisons are subsequently made between the theoretical predictions and the experimental observations, and a good agreement between these two can be observed. Jumps with corners, however, turn out to be comprised of strikingly contrasting profiles, which can be attributed to the ‘jump–jet’ interaction and the ‘jump-jump’ interaction mechanisms. A phenomenological explanation is also provided, by drawing an analogy from the theory of shock-wave interactions.

Present tissue engineering practice requires porous, bioresorbable scaffolds to serve as temporary 3D templates to guide cell attachment, differentiation, and proliferation. Recent research suggests that scaffold material and internal architecture significantly influence regenerate tissue structure and function. However, lack of versatile biomaterials processing methods have slowed progress towards fully testing these findings. Our research investigates using selective laser sintering (SLS) to fabricate bone tissue engineering scaffolds. Using SLS, we have fabricated polycaprolactone (PCL) and polycaprolactone/tri-calcium phosphate composite scaffolds. We report on scaffold design and fabrication, mechanical property measurements, and structural characterization via optical microscopy and micro-computed tomography.

We present a concept for multi-material solid freeform fabrication of 2D and layered 3D heterogeneous components. This technique involves direct-write deposition of multiple, patterned powder materials followed by laser processing. The direct-write deposition system features miniature hopper-nozzles for depositing dry powdered materials by gravity or by high frequency vibration-assisted flow onto a movable substrate. A dual wavelength laser processing workstation was used to consolidate the deposited pattern to desired densities. The feasibility of this concept was proved by direct-writing and laser processing various powder material patterns.

Advanced and novel fabrication methods are needed to build complex three-dimensional scaffolds that incorporate multiple functionally graded biomaterials with a porous internal architecture that will enable the simultaneous growth of multiple tissues, tissue interfaces and blood vessels. The aim of this research is to develop, demonstrate and characterize techniques for fabricating such scaffolds by combining solid freeform fabrication and computational design methods. When fully developed, such techniques are expected to enable the fabrication of tissue engineering scaffolds endowed with functionally graded material composition and porosity exhibiting sharp or smooth gradients. As a first step towards realizing this goal, scaffolds with periodic cellular and biomimetic architectures were designed and fabricated using selective laser sintering in Nylon-6, a biocompatible polymer. Results of bio-compatibility and in vivo implantation studies conducted on these scaffolds are reported.