Local Analysis of Dissipative Dynamical Systems

Linear transformation techniques such as singular value decomposition (SVD) have been used widely to gain insight into the qualitative dynamics of data generated by dynamical systems. There have been several reports in the past that had pointed out the susceptibility of linear transformation approaches in the presence of nonlinear correlations. In this tutorial review, local dispersion along with the surrogate testing is proposed to discriminate nonlinear correlations arising in deterministic and non-deterministic settings.Comment: 85 Pages, 13 Figure

Fabrication of piezoresistive Si nanorod-based pressure sensor arrays: a promising candidate for portable breath monitoring devices

This paper reports on the controlled fabrication of a highly sensitive piezoresistive sensor by using Si nanorod (NR) arrays. An efficient, large-area, scalable strategy was adopted to fabricate the pressure sensors by incorporating chemically etched, high-aspect-ratio, vertical Si NR arrays between two thin Au layers. The piezoresistive properties corresponding to dimension- and position-controlled and randomly etched, closely packed, and thin Si NR arrays were exploited to fabricate the small, portable, and device-compatible pressure sensors. The Si-NR-based piezoresistive sensors exhibited a high sensitivity of 0.49 MPa−1, thereby demonstrating its superiority over other unconventional piezoresistive nanomaterials such as Si with different configurations of nanostructures. Furthermore, the sensors exhibited a large variation (~45%) in the current at a constant bias voltage of 2 V under a weak applied pressure corresponding to an inert gas flow of 5 sccm. The excellent pressure sensing performance of the piezoresistive Si NRs enabled the efficient detection of changes corresponding to the human breathing pattern. In particular, the key advantages of such pressure sensors is the simple, inexpensive, and scalable fabrication process; high sensitivity with ultra-low-pressure detection; and excellent ambient stability (>several months) with a high durability pertaining to more than 1,000 cycles of pressure loading/unloading. Furthermore, we demonstrated the ability of the pressure sensor to act as a portable human breath sensor to monitor respiratory parameters in a noninvasive and personalized manner. The results can provide direction for the realization of next-generation breath-sensing gadgets and other leading-edge applications in the domain of electronic and healthcare devices

Ultrafast response humidity sensor using supramolecular nanofibre and its application in monitoring breath humidity and flow

Measuring humidity in dynamic situations calls for highly sensitive fast response sensors. Here we report, a humidity sensor fabricated using solution processed supramolecular nanofibres as active resistive sensing material. The nanofibres are built via self- assembly of donor and acceptor molecules (coronene tetracarboxylate and dodecyl methyl viologen respectively) involved in charge transfer interactions. The conductivity of the nanofibre varied sensitively over a wide range of relative humidity (RH) with unprecedented fast response and recovery times. Based on UV-vis, XRD and AFM measurements, it is found that the stacking distance in the nanofibre decreases slightly while the charge transfer band intensity increases, all observations implying enhanced charge transfer interaction and hence the conductivity. It is demonstrated to be as a novel breath sensor which can monitor the respiration rate. Using two humidity sensors, a breath flow sensor was made which could simultaneously measure RH and flow rate of exhaled nasal breath. The integrated device was used for monitoring RH in the exhaled breath from volunteers undergoing exercise and alcohol induced dehydration

Dynamic self-assembly of charge-transfer nanofibers of tetrathiafulvalene derivatives with F<inf>4</inf>TCNQ

One-dimensional charge-transfer nanostructures were constructed by the supramolecular coassembly of amphiphilic (Amph-TTF) and hydrophobic (TDD-TTF) tetrathiafulvalene (TTF) donor derivatives with the acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), in appropriate solvent composition mixtures. Microscopic analyses show that TDD-TTF retains its self-assembled fibrillar morphology even in the charge-transfer state, whereas Amph-TTF undergoes a spherical to nanorod transition upon coassembly. Time-dependent optical spectroscopy studies have shown a spontaneous change in molecular organization in TDD-TTF-based donor-acceptor costacks, which suggests a dynamic behavior, in contrast to the kinetically stable amphiphilic TTF assemblies. We have also tried to get an insight into the observed time-dependent change in molecular packing of these nanostructures through spectroscopic analyses by commenting on whether the TTF-TCNQ pair is cofacially arranged or present in the classical herringbone (orthogonal) fashion. Furthermore, our two-probe electrical measurements showed that these charge-transfer fibers are conducting. A supramolecular approach that yields 1D charge-transfer nanostructures of donor and acceptor molecules will be an alternative to existing crystalline substances with high conductivity and hence can be a viable tool for nanoelectronics. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Low cost, rapid synthesis of graphene on Ni: an efficient barrier for corrosion and thermal oxidation

Graphene because of its inert and impermeable nature holds a great promise as a protective coating against corrosion and oxidation. It is envisioned that graphene coated metals will be increasingly used in metal and electronic industries. To date, mainly expensive chemical vapor deposition methods are being employed for its synthesis over large area involving hydrogen at high reaction temperatures. Here we report, a simple and rapid method of Joule heating a Ni foil coated with naphthalene in rotary vacuum to produce graphene without hydrogen gas. The graphene thus grown protects the Ni surface against corrosion and oxidation even at elevated temperatures. This synthetic approach has a great potential for widespread use as it is low cost and adaptable to metal surfaces of complex curvatures

High-mobility field effect transistors based on supramolecular charge transfer nanofibres

Self-assembled charge transfer supramolecular nanofibres of coronene tetracarboxylate (CS) and dodecyl substituted unsymmetric viologen derivative (DMV) behave as active channel in field effect transistors exhibiting high mobility. These devices work in ambient conditions and can regenerate in the presence of a single drop of water. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Charge-transfer nanostructures through noncovalent amphiphilic self-assembly: extended cofacial donor-acceptor arrays

Charge‐transfer (CT) assemblies with mixed‐stack (MS) arrays of donor (D) and acceptor (A) molecules are important class of functional organic materials owing to their interesting optoelectronic properties. Construction of charge‐transfer nanostructures comprising cofacially stacked perylene/tetrathiafulvalene (TTF) donors and viologen acceptors by an efficient, noncovalent, amphiphilic approach is described. Optical properties were used to probe the CT coassembly and stoichiometry of molecular D/A components, whereas <SUP>1</SUP>H NMR and X‐ray diffraction studies provided insights into their face‐to‐face organization. The efficient equimolar coassembly between ionic D (perylene salt (PS) and TTF salt (TTFS)) and A (dodecylmethyl viologen (DMV) and hexadecylmethyl viologen (HDMV)) molecules in water through ground state CT interactions results in the formation of noncovalent amphiphiles. Microscopic studies provided structural insight into the hierarchical organization of these charge‐transfer D‐A amphiphiles into bilayers and one‐dimensional nanostructures. In addition, at higher concentrations PS‐HDMV amphiphiles form hydrogels due to strong hydrophobic interactions caused by the long hydrocarbon tails. Two probe devices fabricated from these CT nanostructures as channel elements showed impressive conductivity values without any external doping, thus validating the CT design for conducting organic wires