479 research outputs found
Graphene: Microwave Enabled One‐Pot, One‐Step Fabrication and Nitrogen Doping of Holey Graphene Oxide for Catalytic Applications (Small 27/2015)
Get PDFPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112226/1/smll201570159.pd
Direct Production of Graphene Nanosheets for Near Infrared Photoacoustic Imaging.
No full textHummers method is commonly used for the fabrication of graphene oxide (GO) from graphite particles. The oxidation process also leads to the cutting of graphene sheets into small pieces. From a thermodynamic perspective, it seems improbable that the aggressive, somewhat random oxidative cutting process could directly result in graphene nanosheets without destroying the intrinsic π-conjugated structures and the associated exotic properties of graphene. In Hummers method, both KMnO4 and NO2þ (nitronium ions) in concentrated H2SO4 solutions act as oxidants via different oxidation mechanisms. From both experimental observations and theoretical calculations, it appears that KMnO4 plays a major role in the observed oxidative cutting and unzipping processes. We find that KMnO4 also limits nitronium oxidative etching of graphene basal planes, therefore slowing down graphene fracturing processes for nanosheet fabrication. By intentionally excluding KMnO4 and exploiting pure nitronium ion oxidation, aided by the unique thermal and kinetic effects induced by microwave heating, we find that graphite particles can be converted into graphene nanosheets with their π-conjugated aromatic structures and properties largely retained. Without the need of any postreduction processes to remove the high concentration of oxygenated groups that results from Hummers GO formation, the graphene nanosheets as-fabricated exhibit strong absorption, which is nearly wavelength-independent in the visible and near-infrared (NIR) regions, an optical property typical for intrinsic graphene sheets. For the first time, we demonstrate that strong photoacoustic signals can be generated from these graphene nanosheets with NIR excitation. The photo-to-acoustic conversion is weakly dependent on the wavelength of the NIR excitation, which is different from all other NIR photoacoustic contrast agents previously reported.This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in ACS Nano, copyright © American Chemical Society after peer review. To access the final edited and published work see https://dx.doi.org/10.1021/nn403429v
CCDC 1435119: Experimental Crystal Structure Determination
No full textRelated Article: Ashok Keerthi, Cunbin An, Mengmeng Li, Tomasz Marszalek, Antonio Gaetano Ricciardulli, Boya Radha, Fares D. Alsewailem, Klaus Müllen, Martin Baumgarten|2016|Polym.Chem.|7|1545|doi:10.1039/C6PY00023
STORM: Screw theory toolbox for robot manipulator and mechanisms
No full textScrew theory is a powerful mathematical tool for the kinematic analysis of mechanisms and has become a cornerstone of modern kinematics. Although screw theory has rooted itself as a core concept, there is a lack of generic software tools for visualization of the geometric pattern of the screw elements. This paper presents STORM, an educational and research oriented framework for analysis and visualization of reciprocal screw systems for a class of robot manipulator and mechanisms. This platform has been developed as a way to bridge the gap between theory and practice of application of screw theory in the constraint and motion analysis for robot mechanisms. STORM utilizes an abstracted software architecture that enables the user to study different structures of robot manipulators. The example case studies demonstrate the potential to perform analysis on mechanisms, visualize the screw entities and conveniently add new models and analyses
A coupled finite volume method and Gilbert-Johnson-Keerthi distance algorithm for computational fluid dynamics modelling
No full textWe investigate a novel technique to obtain the mesh porosity (volume and area) based on the Gilbert-Johnson-Keerthi (GJK) distance algorithm for flow modelling. The GJK algorithm is used to check collisions between two convex objects. This concept is applied to check the collision between an element of the computational mesh and the geometrical model where the element of the mesh is broken recursively to obtain refined values of the porosity. The approach has demonstrated that it can handle complex geometries within feasible computational time. The porosity values obtained using this methodology are coupled in the developed Navier-Stokes. Numerical findings are compared with selected benchmarking tests. Numerical findings agree with experimental data and the main features of the fluid flow are well captured352417436CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES140812/2014-8não te
Multi-wavelength Raman Spectroscopy of Ultra-narrow Nanoribbons Made by Solution-mediated Bottom-up Approach
Get PDFHere we present a combined experimental and theoretical study of graphene nanoribbons (GNRs), where detailed multi-wavelength Raman measurements are integrated by accurate ab initio simulations. Our study covers several ultra-narrow GNRs, obtained by means of solution-based bottom-up synthetic approach, allowing to rationalize the effect of edge morphology, position and type of functional groups as well as the length on the GNR Raman spectrum. We show that the low-energy region, especially in presence of bulky functional groups is populated by several modes, and a single radial breathing-like mode cannot be identified. In the Raman optical region, we find that, except for the fully-brominated case, all GNRs functionalized at the edges with different side groups show a characteristic dispersion of the D peak (8{22 cm-1/eV). This has been attributed to the internal degrees of freedom of these functional groups, which act as dispersion-activating defects. The G peak shows small to negligible dispersion in most of the cases, with larger values only in presence of poor control of the edges functionalization, exceeding the values reported for highly defected graphene.In conclusion, we have shown that the characteristic dispersion of the G and D peaks offer further insight on the GNR structure and functionalization, by making Raman spectroscopy an important tool for the characterization of GNRs
Synthesis of a quinoidal dithieno[2,3-D;2′,3′- d] benzo[2,1- b;3,4- b ′]-dithiophene based open-shell singlet biradicaloid
Get PDFA fused heteroacene derivative, bis(dicyanomethylene)-end-capped-dithieno[2,3-d;2′,3′-d]benzo[2,1-b;3,4-b′]-dithiophene (4CN-DTmBDT) was synthesized. Its open-shell biradical character in the ground state is studied by a combination of electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). Structural assignment was verified with single crystal X-ray diffraction analysis. A highly stable biradicaloid with a low energy gap and low LUMO level is achieved.</p
Smart Material Actuated Inkjet Printed Robotic Fish
No full textSeveral underwater activities like exploration, surveillance, measuring key characteristics like water current or temperature, and mapping seabed risk human lives as the underwater conditions are hostile. Developing underwater vehicles provides a solution to minimize risking human lives. The underwater robots developed based on conventional actuation tend to be bulky and inefficient, lacking the ability to swim through a complex environment. Using smart materials, efficient robots can be built to swim individually or in swarms through a complex environment. However, there is a huge gap in the performance of the underwater robots developed using smart materials in comparison with the ones actuated conventionally. This thesis fills the gap by elaborating on the development of a robotic fish using polyvinylidene fluoride (PVDF), a smart material, that is proven to produce higher strain per volt among other electro-active polymers (EAPs). To develop a robotic fish, different swimming styles are studied and the carangiform style is adapted to achieve good efficiency without compromising maneuverability. The robotic fish is designed as a monolithic structure with an integrated actuator. The carangiform swimming style is implemented by designing a bi-morph actuator that occupies one-third portion of the robotic fish. The actuator is designed to produce symmetric tail deflectionsin the lateral direction generating the vortices in the wake which can propel the robotic fish. In order to prove the usability of the actuator underwater, uni-morph actuators were manufactured using the inkjet printing technique. The actuator samples are developed on four different substrate materials, namely PEN, 25um Kapton, 50um Kapton, and Novele each with dimensions of 60mmx20.5mm. Experiments are conducted under various conditions to test their behavior before operating them underwater. The PVDF actuators developed using the Novele substrate successfully operated underwater at an operating frequency of 5.1Hz.Mechanical Engineering | Mechatronic System Design (MSD
Sparse support vector regression based on orthogonal forward selection for the generalised kernel model
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