Avoiding instabilities in antisymmetric tensor field driven inflation

Models of inflation with antisymmetric tensor studied in the past are plagued with ghost instability even in an unperturbed FRW background. We show that it is possible to avoid ghosts in an unperturbed FRW background by considering the most general kinetic term for antisymmetric tensor field. The kinetic part acquires a new gauge symmetry violating term whose effect on perturbed modes is to prevent the appearance of nondynamical modes, and thus avoid ghosts. For completeness, we perform a check for gradient instability and derive the conditions for perturbations to be free of gradient instability.

Motion Controller Design for Single Axis

In recent years, with the development of technical of numerical control, embedded system has been a hot topic of conversation of engineering control system... In order to solve the shortcoming ,such as complex structure,bad embedded quality and high cost ,of traditional motion controller, MCS-51 was used to control the step motor in this design. so the coordinate and the velocity of the kinetic part on the axis can be controlled easily, and it can satisfy the common demand of the single axis in transformation of numerical control.

FINITE NUMBER OF KALUZA–KLEIN MODES, ALL WITH ZERO MASSES

Kaluza–Klein modes of fermions in a five-dimensional toy model are considered. The number of Kaluza–Klein modes that survive after integration over extra dimensions is finite in this space. Moreover, the extra dimensional piece of the kinetic part of the Lagrangian in this space induces no mass for the higher Kaluza–Klein modes on contrary to the standard lore.