Stability of small chemical groups on hexagonal-SiC(0001) surfaces: A theoretical study

Density functional theory (DFT) calculations are used to investigate the stability on SiC(0001) surfaces of different chemical groups -NH₂, -NO₂, -CH₃, -OH, -SH and -CN. The adsorption stability decreases in the order -NO₂ > ? OH > ? NH₂ > ? SH > ? CN > ? CH₃. The stability of the single molecule-substrate bond is strongly influenced by the polarizability, which in turn depends on different parameters such as the electronegativity, atomic size and chemical environment. In a further step, methyl (? ACH₃) and phenyl (? AC₆H₅) substituted groups are also considered and similar behaviour is observed. The inductive effect of the -CH₃ or -C₆H₅ groups modifies the polarization of the Si adatom-molecule bond and the steric hindrance due to their size influences the molecular orientation. These two parameters affect the calculated adsorption energy, and are more important for –C₆H₅ substituent. This study provides clear tendencies that can be applied to more complex systems. Comparison of the adsorption of two large molecules, H₂Pc (metal-free phthalocyanine) and PTCDI (perylene tetracarboxylic diimide) on the SiC(0001) surface is presented as an example.     

Liquid Marble Photosensor

A liquid marble is a liquid droplet coated by a hydrophobic powder. The liquid marble does not wet adjacent surfaces and therefore can be manipulated as a dry soft body. A Belousov-Zhabotinsky (BZ) reaction is an oscillatory chemical reaction exhibiting waves of oxidation. We demonstrate how to make a photo-sensor from BZ medium liquid marbles. We insert electrodes into a liquid marble, prepared from BZ solution and coated with polyethylene powder. The electrodes record a potential difference which oscillates due to oxidation wave-fronts crossing the electrodes. When the BZ marble is illuminated by a light source, the oxidation wave-fronts are hindered and, thus, the electrical potential recorded ceases to oscillate. We characterise several types of responses of BZ marble photosensors to various stimuli, and provide explanations of the recorded activity. BZ liquid marble photosensors may find applications in the fields of liquid electronics, soft robotics and unconventional computing.     

First-order strong variation algorithms for optimal control

Journal of Optimization Theory and Applications - This paper presents two demonstrably convergent, first-order, differential dynamic programming algorithms for the solution of optimal control...     

Some Reliability Models of Production Lines,with Special Reference to Computer Operation and Scheduling

A situation is considered where a machine or a production line, for example an electronic computer or a data-processing system, has alternate "good" and "bad" periods of operation. Two types of model are described which can be used to tackle this kind of situation and these form an approach to the practical problem of scheduling work through such a system. The two aspects considered are the probability of a preassigned schedule of operation being completed within some critical time, and the optimum assignment of the length of the scheduled operations.     

Random to deterministic transform

A method of transforming an ergodic random signal to its deterministic equivalent is presented. The transform requires that the spectral density of the random signal should be known. It also depends on the ability to obtain the inverse Fourier transform of a function. A specific relationship is developed to evaluate the root mean square of a random signal based on its deterministic equivalent. A sample application is presented to demonstrate that a step input can be equivalent to a hyperbolic spectral density. A linear system is subjected to the hyperbolic spectral density and the equivalent step. The calculated root mean square outputs are found to be identical. Deterministic equivalents for other random signals are also indicated.