Root growth dynamics is an outcome of complex hormonal crosstalk. The primary root meristem size, for example, is determined by antagonizing actions of cytokinin and auxin. Here we show that RAV1, a member of the AP2/ERF family of transcription factors, mediates cytokinin signaling in roots to regulate meristem size. Therav1mutants have prominently longer primary roots, with a meristem that is significantly enlarged and contains higher cell numbers, compared with wild-type. The mutant phenotype could be restored on exogenous cytokinin application or by inhibiting auxin transport. At the transcript level, primary cytokinin-responsive genes like ARR1, ARR12 were significantly downregulated in the mutant root, indicating impaired cytokinin signaling. In concurrence, cytokinin induced regulation of SHY2, an Aux/IAA gene, andauxin efflux carrier PIN1 was hindered inrav1, leading to altered auxin transport and distribution. This effectively altered root meristem size in the mutant. Notably, CRF1, another member of the AP2/ERF family implicated in cytokinin signaling, is transcriptionally repressed by RAV1 to promote cytokinin response in roots. Further associating RAV1 with cytokinin signaling, our results demonstrate that cytokinin upregu-latesRAV1expression through ARR1, during post-embryonic root development. Regulation of RAV1expres-sion is a part of secondary cytokinin response that eventually represses CRF1 to augment cytokinin signaling. To conclude, RAV1 functions in a branch pathway downstream to ARR1 that regulates CRF1 expression to enhance cytokinin action during primary root development in Arabidopsis.

We report the impact dynamics of a ferrofluid droplet on a PDMS substrate in the presence of a non-uniform magnetic field. Based on high-speed imaging, we unravel the various characteristic behaviors of the impinging ferrofluid droplet under the influence of a vertically applied magnetic field. We show that the magnetic, viscous, inertial, and interfacial energies non-trivially affect the equilibrium shape of the impacting ferrofluid droplet. Consequently, we reveal that the collective role of these forces ensures the ferrofluid droplet exhibits essentially three typical equilibrium shapes, i.e., no spike, single spike, and multiple spikes assemblies. Based on a phase diagram, we demonstrate the role of various dynamic forces in dictating the droplet’s equilibrium shape. We report the universality constant exhibited by the non-dimensionalized droplet diameter (ratio of the droplet’s equilibrium diameter to the semi-minor axis width of the ellipsoidal droplet just before impact), irrespective of the magnetic Bond number, on a PDMS substrate to be around 1.3. Consequently, we investigated the internal flow domain of the ferrofluid flow field in the presence of a magnetic field, essentially to understand its characteristic spreading behavior. Following bright-field visualization, we observed chain-like clustering of the magnetic nano-particles inside the ferrofluid flow domain in a direction perpendicular to the magnet. Insights from bright field visualization enable us to qualitatively argue that the chaining phenomena of the nano-sized particles (present inside ferrofluid) in a direction perpendicular to the substrate ensure the formation of single/multiple assemblies of spikes. In addition, we also argue that the chain-formation of the magnetic nano-particles increases the viscous force of the ferrofluid droplet in the presence of a magnetic field. This augmented viscous energy of the fluid in the presence of a magnetic field ensures an inverse relationship of the spreading diameter with magnetic field strength. The inference of the present study could be beneficial in the rational design of wide-ranging applications, such as ink-jet printing or 3D printing, requiring controlled droplet spreading phenomena.

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We report the breakup dynamics of a magnetically active (ferrofluid) droplet in a T-shaped Lab on a Chip (LOC) device under the modulation of a non-uniform magnetic field.We adhere to high-speed imaging modalities for the experimental quantification of the droplet splitting phenomenon, while the underlying phenomenon is supported by the numerical results in a qualitative manner as well. On reaching the T-junction divergence,the droplet engulfs the intersection fully and eventually deforms into the dumbbell-shaped form, making its bulges move towards the branches of the junction. We observe that the asymmetric distribution of the magnetic force lines, acting over the T-junction divergence,induces an accelerating motion to the left of the moving bulge (since the magnet is placed adjacent to the left branch). We show that the non-uniform force field gradient allows the formation of a hump-like structure inside the left moving bulge, which triggers the onset of augmented convection in its flow field. We reveal that this augmented internal convection developed in the left moving volume/bulge, on becoming coupled to the various involved time scales of the flow field, leads to the asymmetric splitting of the droplet into two sister droplets. Our analysis establishes that, at the critical strength of the applied forcing, as realized by the critical magnetic Bond number, the flow time scale becomes minimum at the left branch of the channel, leading to the formation of larger sized sister droplets herein. Inferences of the present analysis, which demonstrates a plausible means of independently controlling the size of the sister droplet by manoeuvring the applied force field gradient, will provide a potential solution for rapid droplet splitting, which typically finds significant importance in point-of-care diagnostics.

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The salinity gradient energy or the ‘blue energy’ is one of the most promising inexpensive and abundant sources of clean energy, having immense capabilities to serve modern-day society. In this article, we overlay an extensive analysis of reverse electrodialysis (RED) for harvesting salinity gradient energy in a single conical nanochannel, grafted with a pH-tunable polyelectrolyte layer (PEL) on the inner surfaces.We primarily focus on the distinctiveness of the solution pH of the connecting reservoirs. In spite of acquiring a maximum power density of B1.2 kW m2 in the chosen configuration, we notice a counter-intuitive patterning of the ion transport for a certain span of pH, leading to diminishing power. To this end, we discuss the possible strategic avenues essentially to achieve a higher amount of power density.In order to achieve a desirable outcome within that pH zone, we employ two separate approaches intending to counter the underlying physics. Results reveal a great enhancement in the power density as well as in the efficiency even under the framework of both strategies proposed herein. Moreover, as shown, the window of solution pH has increased by three times, implicating the maximum power density mentioned above. We expect that the strategic procedure of augmented energy harvesting as discussed in this analysis can be of importance from the perspective of fabricating state-of-the-art nanodevices aimed at blue energy harvesting.

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A surface tension gradient resulting from the inhomogeneities in temperature (thermo-capillarity) or concentration (solutocapillarity) on the free surface of a pure or binary liquid has the ability to induce motion in its bulkphase. Typically known as the Marangoni instability, this phenomenon is frequently encountered in the small-scale systems (liquid films, droplets, liquid bridges etc.) where the surface effects dominate over the volumetric ones. The present thesis aims at understanding this instability phenomenon for thin films of Newtonian and viscoelastic liquids under the framework of liner stability analysis. The dynamics of both the long-wave and short-wave perturbations are studied here for the most classical system configuration ofa thin liquid film confined between its free surface and a poorly conducting rigid substrate. Besides exploring the basic instability modes for both the Newtonian and viscoelastic fluids, the physical conditions are also identified for which these instability modes become dominant in the system. Several novel instability modes are detected in this work that forms a strong basis for the future course investigation in such fluids.

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Ferrofluid is a type of magnetic liquid that is synthesized as a stable colloidal suspension of iron oxide particles in a carrier fluid. Ferrofluids have shown promising potential in several applications of emerging relevance, primarily due to its ability of being in control under the influence of a magnetic field. In the present study, some of the pertinent issues related to the transport phenomena of ferrofluid in small scale systems in the presence of a magnetic field are addressed. These include (a) exploring the thermal characteristics of ferrofluid flow in a heated channel in the presence of a constant and time-dependent magnetic field, (b) internal convections of a sessile ferrofluid droplet under the modulations of a time-dependent magnetic field, (c) mixing, and (d) evaporation characteristics of the ferrofluid droplet in a magnetically field-driven environment. All the problems as mentioned above have been systematically explored following comprehensive experimental techniques involving infrared thermography, bright field visualization, μPIV, and μLIF, respectively. Infrared thermography is performed for observing the thermal footprints of the ferrofluid flow. Bright field visualization is used to understand the qualitative behavior of the ferrofluid flow, while μPIV measurement is adopted for quantification of the internal flow dynamics. The experimental measurement technique consistent with μLIF is employed for quantification of the mass transfer occurring between fluids. In addition to that, numerical simulations have also been performed to support the experimental observations.

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Two-dimensional (2D) materials are one of the greatest invention of 21st century for which 2010 Nobel prizein physics was awarded to Prof. Andre Geimand Prof. Konstantin Novoselov. Considering the intriguing potential applicabilities of 2D materials two such 2D materials are considered namely grapheneand graphene oxide (GO). Usingl arge scale atomistic simulation, the potential applicabilities of these two nano materials are investigated. One of the interesting observations from these simulation results is that the performance of layered GO membranes can be efficiently be tuned by selecting appropriate geometric parameters for the membrane e.g. pore offset distance and interlayer distance. The presence of the cations inside the interlayer gallery also significantly influence the performance of the membrane. From the study of electro-osmotic flow (EOF) through graphene nanochannel, it is observed that the flow dynamics inside the nanochannel can be tuned by altering surface charge density. Also the flow inside the nanochannel is greatly influenced by the a typical interplay between van der Waals interactions and electrostatic interactions between the surface of the nanochannel and water molecules/ionic species. The observations will be significantly helpful for the future investigations on the applicabilities of 2D materials for various cutting edge applications

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Narrow-fluidic channels with built-in polyelectrolyte layers at the inner walls are widely used to transport bio-samples in on-chip applications. The grafted polyelectrolyte layer (PEL) demonstrates its profound efficacy in application-driven micro/nanofluidics. Unresolved issues on the underlying transport in PEL grafted narrow fluidic pathways are not only restricted to the transport of Newtonian fluids but also include the analysis of non-Newtonian fluids as well. In the present study, some of the pertinent issues are investigated. These include electroosmotic transport of non-Newtonian biofluids in PEL grafted narrow fluidic confinement, electroosmotic mixing in narrow-fluidic assay having walls grafted with patterned PEL, the Coriolis force induced micromixing in the soft narrow-fluidic channel, and the enhancement of electro-chemo-mechanical energy conversion in the narrow-fluidic batteries. The inferences obtained from these studies suggest that the complex interplay between the soft layer modulated rich interfacial electrochemistry and the non-Newtonian fluid rheology leads to the enhancement in the net throughput of bio-fluids. Such intricate dynamics, particularly for viscoelastic fluid transport through a narrow channel, contribute to the giant enhancement of the energy conversion efficiency. Besides, the stronger electroosmotic flow obtained due to the grafted PEL enhances the quality of vortices and the mixing performance in the rotating soft channels, and the channels having the walls grafted with the patterned PEL.

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