Nuclear spin-lattice relaxation in trans-polyacetylene (CH)x. A confined soliton model including nuclear spin flip diffusion

A « confined soliton model » in which the solitons move over a small part of the chain is developed. The on-chain nuclei are relaxed directly by contact hyperfine interactions whilst the remainder nuclei relax via nuclear spin flip diffusion. It is found that the proton spin-lattice relaxation data can be rationalized in terms of the fast and confined one-dimensional hopping motion of the soliton whilst that for enriched 13C one requires in addition a much more dominating mechanism that of nuclear spin flip diffusion.Un modèle de solitons confinés dans lequel les solitons se déplacent sur une petite partie de la chaîne a été développé. Les noyaux de la chaîne relaxent directement les interactions hyperfines de contact alors que les autres noyaux relaxent par une diffusion de l'aimantation des spins nucléaires. Les données sur la relaxation spin-réseau du proton peuvent être expliquées par un mouvement rapide et confiné de sauts à une dimension alors que celles relatives au 13C nécessitent en plus de tenir compte du mécanisme de diffusion de spin nucleaire

Effect of dopants on electron localization length in polyaniline

The electronic behavior of chemically synthesized polyaniline depends on the amount of disorder—whether homogeneous or inhomogeneous— created during synthesis and doping. Its physical properties are significantly affected by a number of parameters such as catalyst type, solution pH, oxidant/monomer ratio, solvent type, secondary doping, dopant type, dopant size and synthesis temperature. With the view of studying the dependence of electron localization behavior on the dopant type, all other factors remaining the same, we report in this paper a systematic study of NMR, EPR, magnetic susceptibility, and dc conductivity measurements for seven doping acids. The EPR lineshape in all these cases is close to a Lorentzian, but the linewidth is sensitively dependent on the type of the dopant. In spite of differences in the magnitude and the temperature dependences of dc conductivity and magnetic susceptibility data, the experiments reveal a localization length of approximately 30Å for all the samples. It is concluded that, unlike drastically different charge transport behaviors caused by the presence of substituent groups on phenyl rings of the polymer chains, dopant molecules belonging to a given family have virtually no effect on the electron localization length

Performance Evaluation of Distributed Co-Ordination Function for IEEE 802.11 Wireless LAN Protocol in Presence of Mobile and Hidden Terminals

This paper investigates the performance of IEEE 802.11 wireless local area network (WLAN) protocol's Distributed Coordination Function (DCF) in the presence of mobile and hidden terminals. In order to study the joint effect of hidden terminals and user mobility on the performance of IEEE 802.11 DCF, we extend Tobagi and Kleinrock's [14] hearing graph framework to model hidden terminals in a static environment. We derive a combined mobility and hidden terminal model using a Markov chain from the hearing graph of a given physical layout. The simple model uses two parameters: ff, which controls the number of hidden terminals in the steady state, and , which controls the rate of mobility of each terminal. By varying the values of ff and we can systematically generate scenario with different number of hidden terminals and different mobility rates for a particular physical layout with static obstructions. We have developed a discrete event simulator which uses the parameterized model to obt..

Electron localization length in polyaniline

Electrical DC conductivity, magnetic susceptibility, and EPR measurements are used to investigate the electron localization behavior of polyaniline as a function of the dopant type using seven sulfonic acid based doping acids. In spite of differences in the magnitude and the temperature dependences of DC conductivity and magnetic susceptibility data, the experiments reveal a localization length of approximately 30 A ° for all the samples. We conclude that this result is essentially due to disorder in the basic morphological structure of a polymer that seems to be determined, among other factors, by the nature of the monomeric units comprising the polymer chains

Nitrogen-doped flexible carbon cloth for durable metal free electrocatalyst for overall water splitting

Water electrolysis is one of the greenest ways to generate clean energy. However, it is critical to develop durable and cost-effective electrocatalysts using earth-abundant materials for overall water splitting. Here we report, a facile method to fabricate N-doped cotton cloth as an electrocatalyst. The N-doped cotton cloth showed outstanding performance as an electrocatalyst for overall water splitting. For oxygen evolution reaction (OER), N-doped cotton cloth requires a low overpotential of 351 mV to deliver 10 mA/cm2 of current density with a Tafel slope of 88 mV/dec. On the other hand, it requires 233 mV to achieve a current density of 10 mA/cm2 for hydrogen evolution reaction (HER) with a Tafel slope of 135 mV/dec. Furthermore, the electrocatalyst showed outstanding electrocatalytic stability and flexibility. The observed overpotential and stability are among the best for the metal-free electrocatalyst. Such a binder-free approach for fabrication of high performance, durable and flexible bi-functional (HER and OER) electrocatalyst could be a promising way to generate green energy from water

Electrochemical energy storage performance of electrospun CoMn2O4 nanofibers

Nanofibers of cobalt manganese oxide (CoMn2O4) were grown using an electrospun technique. Structural and microstructural characterizations confirm the formation of phase pure CoMn2O4with high porosity. The potential application of CoMn2O4nanofibers as an electrode material for energy storage device was studied using cyclic voltammetry and galvanostatic charge-discharge measurements. A specific capacitance of 121 F/g was observed with enhanced cyclic stability. Furthermore, an energy storage device was fabricated by sandwiching two electrodes separated by an ion transporting layer. The device showed a specific capacitance of 241 mF/cm2in 3 M NaOH electrolyte. The effect of temperature on the charge storage properties of the device was also investigated for high temperature applications. The device showed about 75% improvement in the charge storage capacity when the temperature was increased from 10 to 70 °C. This research suggests that nanofibers of CoMn2O4could be used for fabrication of energy storage devices which could operate in a wide temperature range with improved efficiency