7 results on '"Gupta, Unmukt"'
Search Results
2. Revealing the atomic ordering of binary intermetallics using in situ heating techniques at multilength scales.
- Author
-
Yin Xiong, Yao Yang, Rui Zeng, DiSalvo, Francis J., Abruña, Héctor D., Xin Huang, Joress, Howie, Agyeman-Budu, David N., Brock, Joel D., Padgett, Elliot, Muller, David A., Gupta, Unmukt, Escobedo, Fernando A., Yarlagadda, Venkata, Moylan, Thomas E., and Anusorn Kongkanand
- Subjects
INTERMETALLIC compounds ,ELECTROCATALYSTS ,OXYGEN reduction ,CRYSTAL structure ,X-ray diffraction ,SUPERLATTICES ,ANNEALING of metals - Abstract
Ordered intermetallic nanoparticles are promising electrocatalysts with enhanced activity and durability for the oxygen-reduction reaction (ORR) in proton-exchange membrane fuel cells (PEMFCs). The ordered phase is generally identified based on the existence of superlattice ordering peaks in powder X-ray diffraction (PXRD). However, after employing a widely used postsynthesis annealing treatment, we have found that claims of "ordered" catalysts were possibly/likely mixed phases of ordered intermetallics and disordered solid solutions. Here, we employed in situ heating, synchrotron-based, X-ray diffraction to quantitatively investigate the impact of a variety of annealing conditions on the degree of ordering of large ensembles of Pt3Co nanoparticles. Monte Carlo simulations suggest that Pt3Co nanoparticles have a lower order-disorder phase transition (ODPT) temperature relative to the bulk counterpart. Furthermore, we employed microscopic-level in situ heating electron microscopy to directly visualize the morphological changes and the formation of both fully and partially ordered nanoparticles at the atomic scale. In general, a higher degree of ordering leads to more active and durable electrocatalysts. The annealed Pt3Co/C with an optimal degree of ordering exhibited significantly enhanced durability, relative to the disordered counterpart, in practical membrane electrode assembly (MEA) measurements. The results highlight the importance of understanding the annealing process to maximize the degree of ordering in intermetallics to optimize electrocatalytic activity. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Pneumatic Networks for Soft Robotics that Actuate Rapidly.
- Author
-
Mosadegh, Bobak, Polygerinos, Panagiotis, Keplinger, Christoph, Wennstedt, Sophia, Shepherd, Robert F., Gupta, Unmukt, Shim, Jongmin, Bertoldi, Katia, Walsh, Conor J., and Whitesides, George M.
- Subjects
PNEUMATICS ,ROBOTICS ,ELASTOMERS ,FATIGUE (Physiology) ,AMPLITUDE modulation - Abstract
Soft robots actuated by inflation of a pneumatic network (a 'pneu-net') of small channels in elastomeric materials are appealing for producing sophisticated motions with simple controls. Although current designs of pneu-nets achieve motion with large amplitudes, they do so relatively slowly (over seconds). This paper describes a new design for pneu-nets that reduces the amount of gas needed for inflation of the pneu-net, and thus increases its speed of actuation. A simple actuator can bend from a linear to a quasi-circular shape in 50 ms when pressurized at ΔP = 345 kPa. At high rates of pressurization, the path along which the actuator bends depends on this rate. When inflated fully, the chambers of this new design experience only one-tenth the change in volume of that required for the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
4. Control of soft machines using actuators operated by a Braille display.
- Author
-
Mosadegh, Bobak, Mazzeo, Aaron D., Shepherd, Robert F., Morin, Stephen A., Gupta, Unmukt, Sani, Idin Zhalehdoust, Lai, David, Takayama, Shuichi, and Whitesides, George M.
- Subjects
BRAILLE ,ACTUATORS ,BIOCHIPS ,MINIATURE electronic equipment ,MICROBIOLOGY ,CHEMICAL biology - Abstract
One strategy for actuating soft machines (e.g., tentacles, grippers, and simple walkers) uses pneumatic inflation of networks of small channels in an elastomeric material. Although the management of a few pneumatic inputs and valves to control pressurized gas is straightforward, the fabrication and operation of manifolds containing many (>50) independent valves is an unsolved problem. Complex pneumatic manifolds―often built for a single purpose―are not easily reconfigured to accommodate the specific inputs (i.e., multiplexing of many fluids, ranges of pressures, and changes in flow rates) required by pneumatic systems. This paper describes a pneumatic manifold comprising a computer-controlled Braille display and a micropneumatic device. The Braille display provides a compact array of 64 piezoelectric actuators that actively close and open elastomeric valves of a micropneumatic device to route pressurized gas within the manifold. The positioning and geometries of the valves and channels in the micropneumatic device dictate the functionality of the pneumatic manifold, and the use of multi-layer soft lithography permits the fabrication of networks in a wide range of configurations with many possible functions. Simply exchanging micropneumatic devices of different designs enables rapid reconfiguration of the pneumatic manifold. As a proof of principle, a pneumatic manifold controlled a soft machine containing 32 independent actuators to move a ball above a flat surface. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
5. Exploring the mechanism of interfacial self-assembly of colloidal quantum dot nanoparticles
- Author
-
Gupta, Unmukt
- Subjects
- Colloidal Nanoparticles, Molecular Dynamics, Quantum dots
- Abstract
Colloidal nanoparticles at the interface of two immiscible fluids experience certain restrictions on their position and orientation. This property is exploited to create long-range, coherent assemblies of quasi-2D super-structures that are known to possess strong correlations between their packing symmetries (structure) and the displayed opto-electronic properties (function). However, despite the recent advances in synthesis techniques, the underlying kinetic and thermodynamic factors governing the self-assembly process are not yet completely understood. The overarching goal of this work is to increase the repeatability, precision, and control over the self-assembly of constituent NPs into superstructures with programmable symmetry. In this work, I will take you through not only 1) the development of a set of design rules based on energetic arguments obtained from simulations and theoretical considerations, but equally importantly 2) the development of a simulation paradigm that is faithfully able to reproduce the inherent physics, in-silico. The first step in this process is to investigate the behavior of an isolated NP at the interface. For this purpose, I use both particle-based coarse-grained molecular simulation and a theoretical continuum model. I present the free-energy characteristics of the NPs as a function of their orientations and their vertical positions with respect to the interface. Meaningfully probing the self-assembly process at meso-scales requires simulation of O(10^3) NPs. However, this is infeasible in an explicit-solvent setting with the typically available computing resources. To this end, a key contribution of this work is to develop an efficient (implicit-solvent) model that is not only able to reproduce experimentally exhibited behavior by NPs at fluid-fluid interfaces but is also scalable to the experimentally relevant length scales. By explicitly modeling coarse-grained ligands that cap the nanoparticle surface, I show that changes in nanoparticle shape and ligand densities give rise to drastically different mechanisms. In agreement with experiments, formation of bilayer honeycomb and monolayer square lattices is observed. My results indicate that the choice of solvent and rate of evaporation have a significant impact on reversibility and ultimately the coherence of the finally obtained superstructure. The proposed simulation paradigm would pave the way forward for exploration of the vast phase space.
- Published
- 2021
6. Modeling the Orientational and Positional Behavior of Polyhedral Nanoparticles at Fluid-Fluid Interfaces
- Author
-
Gupta, Unmukt
- Subjects
- Free energy, Interface, Umbrella sampling, Molecular Dynamics, Self Assembly, nanoparticle, Chemical engineering
- Abstract
Using Molecular Dynamics simulations to explicitly model fluid molecules, we study the effect of solvent wetting on the behavior of polyhedral nanoparticles at a fluid-fluid interface. First, we quantify the positional and orientational free energy characteristics of an isolated nanoparticle. Our results suggest that the thickness of the interface can introduce non-trivial effects on the preferential particle orientations. A continuum model is proposed to account for the finite interfacial mixing region, and a qualitative comparison between the two approaches is presented. We examine the effect on the free energy of the system of changes in the particle’s solvation preference towards one fluid, and the degree of miscibility between the two fluids. By tuning these interaction parameters, we can potentially access and favor different orientations for the particle shapes examined. Further, we extend the insights gained from single particle analyses to the attachment of two particles. Our results reveal conditions that can drive the assembly of Cuboctahedra into either 2D Puckered Honeycomb lattices or linear rod-like structures.
- Published
- 2017
7. Soft Robotics: Pneumatic Networks for Soft Robotics that Actuate Rapidly (Adv. Funct. Mater. 15/2014).
- Author
-
Mosadegh, Bobak, Polygerinos, Panagiotis, Keplinger, Christoph, Wennstedt, Sophia, Shepherd, Robert F., Gupta, Unmukt, Shim, Jongmin, Bertoldi, Katia, Walsh, Conor J., and Whitesides, George M.
- Subjects
ROBOTICS ,PNEUMATIC actuators - Abstract
Four separate soft robotic fingers progressively curl to play notes on a keyboard. The finger‐like actuators are made of a silicone elastomer molded from 3D printed parts by G. M. Whitesides and co‐workers. On page 2163, these soft fingers are shown to be capable of bending fully in less than 50 ms, actuating over 1 million cycles, and bending along different paths based on their rate of pressurization. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.