Effect of thermal ground state correlations on the statistical properties of the Lipkin model

The renormalized random phase approximation for hot finite Fermi systems is evaluated with the use of the thermo field dynamics formalism. This approximation treats vibrations of a hot finite Fermi system as harmonic ones but takes into account the Pauli principle in a more proper way than the usual thermal RPA, thus incorporating a new type of correlations in a thermal ground state. To demonstrate advantages of the approximation and to analyze a range of its validity, it is applied to the exactly solvable Lipkin model. A comparison is made with the exact grand canonical ensemble calculations, results of the thermal Hartree – Fock approximation and the thermal random phase approximation. The intrinsic energy of the system, the heat capacity, the average value of the quasispin operator z-projection and the particle number variance are calculated as functions of temperature. On the whole, the thermal renormalized RPA appears to be a better approximation than the other two. Its advantage is especially evident in the vicinity of the phase transition point. It is found that within TRRPA the phase transition occurs at lower temperature than in THFA and TRPA

Schematical shell model at finite temperature

info:eu-repo/semantics/publishe

Lipkin-Meshkov-Glick model at finite temperatures

info:eu-repo/semantics/publishe

A new approximation to treat collective vibrations in hot nuclei

info:eu-repo/semantics/publishe

Piezoelectric deformable mirror with adaptive multiplexing control

Electronic Instrumentation LaboratoryElectrical Engineering, Mathematics and Computer Scienc

Multiplexing control of a multichannel piezoelectric deformable mirror

Addressing of massive arrays of piezoelectric actuators is usually achieved by using separate high-voltage output drivers, one per channel. This approach applied to high-order adaptive optics systems results in complex, expensive and vulnerable to handling abuse driver electronics, hardly scalable to 103-104 actuators. To reduce the number of identical electronic units and simplify the control, we propose sequential multiplexing of piezoelectric actuators. The relatively large capacitance inherent in mirror piezo-actuators allows for storage of charge (high voltage) on a disconnected actuator retaining its displacement, while other actuators are addressed. As a demonstrator a 12-channel piezoelectric deformable mirror driven by a single high-voltage amplifier has been characterized experimentally. The multiplexing of actuators was accomplished by miniature optical switches. Temporal stability of ~?/100 was demonstrated at multiplexing frequency of 700 Hz with a full-range ~2 ?m inter-actuator stroke. The developed approach can be scaled to higher-order deformable mirrors.Electronic InstrumentationElectrical Engineering, Mathematics and Computer Scienc