The failure mechanism of a nickel electrode in a nickel-hydrogen cell

Studies on a number of types of nickel electrodes after cycle failure in a Ni/H2 cell showed that the failure is due to the loss of high rate discharge capability rather than an absolute capacity loss. The failure mechanism is speculated to be a combination of migration of the active material away from the current collecting nickel sinter, increased porosity of the active material caused by cycling, and an electrical isolation process of the active material during discharge

Long Life Nickel Electrodes for a Nickel-hydrogen Cell: Cycle Life Tests

In order to develop a long life nickel electrode for a Ni/H2 cell, cycle life tests of nickel electrodes were carried out in Hi/H2 boiler plate cells. A 19 test cell matrix was made of various nickel electrode designs including three levels each of plaque mechanical strength, median pore size of the plaque, and active material loading. Test cells were cycled to the end of their life (0.5v) in a 45-minute low earth orbit cycle regime at 80% depth-of-discharge. The results show that the active material loading level affects the cycle life the most with the optimum loading at 1.6 g/cc void. Mechanical strength did not affect the cycle life noticeably in the bend strength range of 400 to 700 psi. The best plaque type appears to be one which is made of INCO nickel powder type 287 and has a median pore size of 13 micron

KOH concentration effect on the cycle life of nickel-hydrogen cells. Part 4: Results of failure analyses

KOH concentration effects on cycle life of a Ni/H2 cell have been studied by carrying out a cycle life test of ten Ni/H2 boiler plate cells which contain electrolytes of various KOH concentrations. Failure analyses of these cells were carried out after completion of the life test which accumulated up to 40,000 cycles at an 80 percent depth of discharge over a period of 3.7 years. These failure analyses included studies on changes of electrical characteristics of test cells and component analyses after disassembly of the cell. The component analyses included visual inspections, dimensional changes, capacity measurements of nickel electrodes, scanning electron microscopy, BET surface area measurements, and chemical analyses. Results have indicated that failure mode and change in the nickel electrode varied as the concentration was varied, especially, when the concentration was changed from 31 percent or higher to 26 percent or lower

Properties of kinematic singularities

The locally rotationally symmetric tilted perfect fluid Bianchi type V cosmological model provides examples of future geodesically complete spacetimes that admit a `kinematic singularity' at which the fluid congruence is inextendible but all frame components of the Weyl and Ricci tensors remain bounded. We show that for any positive integer n there are examples of Bianchi type V spacetimes admitting a kinematic singularity such that the covariant derivatives of the Weyl and Ricci tensors up to the n-th order also stay bounded. We briefly discuss singularities in classical spacetimes.Comment: 13 pages. Published version. One sentence from version 2 correcte

Orbital and valley state spectra of a few-electron silicon quantum dot

Understanding interactions between orbital and valley quantum states in silicon nanodevices is crucial in assessing the prospects of spin-based qubits. We study the energy spectra of a few-electron silicon metal-oxide-semiconductor quantum dot using dynamic charge sensing and pulsed-voltage spectroscopy. The occupancy of the quantum dot is probed down to the single-electron level using a nearby single-electron transistor as a charge sensor. The energy of the first orbital excited state is found to decrease rapidly as the electron occupancy increases from N=1 to 4. By monitoring the sequential spin filling of the dot we extract a valley splitting of ~230 {\mu}eV, irrespective of electron number. This indicates that favorable conditions for qubit operation are in place in the few-electron regime.Comment: 4 figure

Making information accessible for the conservation and use of biodiversity. A novel initiative to facilitate access to information and use of agricultural and tree biodiversity

Poster presented at Science Week 2014 - Bioversity International HQ, Rome (Italy), 24-27 Feb 201

Observation of the single-electron regime in a highly tunable silicon quantum dot

We report on low-temperature electronic transport measurements of a silicon metal-oxide-semiconductor quantum dot, with independent gate control of electron densities in the leads and the quantum dot island. This architecture allows the dot energy levels to be probed without affecting the electron density in the leads, and vice versa. Appropriate gate biasing enables the dot occupancy to be reduced to the single-electron level, as evidenced by magnetospectroscopy measurements of the ground state of the first two charge transitions. Independent gate control of the electron reservoirs also enables discrimination between excited states of the dot and density of states modulations in the leads.Comment: 4 pages, 3 figures, accepted for Applied Physics Letter

Quantum Direct Communication with Authentication

We propose two Quantum Direct Communication (QDC) protocols with user authentication. Users can identify each other by checking the correlation of Greenberger-Horne-Zeilinger (GHZ) states. Alice can directly send a secret message to Bob using the remaining GHZ states after authentication. Our second QDC protocol can be used even though there is no quantum link between Alice and Bob. The security of the transmitted message is guaranteed by properties of entanglement of GHZ states.Comment: 9 pages, 3 figures and 2 table