653 research outputs found
Integrability of Nonholonomic Heisenberg Type Systems
We show that some modern geometric methods of Hamiltonian dynamics can be
directly applied to the nonholonomic Heisenberg type systems. As an example we
present characteristic Killing tensors, compatible Poisson brackets, Lax
matrices and classical -matrices for the conformally Hamiltonian vector
fields obtained in a process of reduction of Hamiltonian vector fields by a
nonholonomic constraint associated with the Heisenberg system
The Ferromagnetism in the Vicinity of Lifshitz Topological Transitions
We show that the critical temperature of a ferromagnetic phase transition in
a quasi-two-dimensional hole gas confined in a diluted magnetic semiconductor
quantum well strongly depends on the hole chemical potential and hole density.
The significant variations of the the Curie temperature occur close to the
Lifshitz topological transition points where the hole Fermi surface acquires
additional components of topological connectivity due to the filling of excited
size-quantization subbands. The model calculations demonstrate that the Curie
temperature can be doubled by a small variation of the gate voltage for the
CdMnTe/CdMgTe quantum well based device
Calculation of thermal parameters of SiGe microbolometers
The thermal parameters of a SiGe microbolometer were calculated using
numerical modeling. The calculated thermal conduction and thermal response time
are in good agreement with the values found experimentally and range between
2x10 and 7x10 W/K and 1.5 and 4.5 ms, respectively. High sensitivity
of microbolometer is achieved due to optimization of the thermal response time
and thermal conduction by fitting the geometry of supporting heat-removing legs
or by selection of a suitable material providing boundary thermal resistance
higher than 8x10 cmK/W at the SiGe interface.Comment: 11 pages, 6 figure
On bi-integrable natural Hamiltonian systems on the Riemannian manifolds
We introduce the concept of natural Poisson bivectors, which generalizes the
Benenti approach to construction of natural integrable systems on the
Riemannian manifolds and allows us to consider almost the whole known zoo of
integrable systems in framework of bi-hamiltonian geometry.Comment: 24 pages, LaTeX with AMSfonts (some new references were added
The Polarized H and D Atomic Beam Source for ANKE at COSY-J\"ulich
A polarized atomic beam source was developed for the polarized internal
storage-cell gas target at the magnet spectrometer ANKE of COSY-J\"ulich. The
intensities of the beams injected into the storage cell, measured with a
compression tube, are hydrogen atoms/s (two hyperfine
states) and deuterium atoms/s (three hyperfine states). For
the hydrogen beam the achieved vector polarizations are . For the deuterium beam, the obtained combinations of vector
and tensor () polarizations are (with a
constant ), and or (both with vanishing ). The paper includes a detailed
technical description of the apparatus and of the investigations performed
during the development.Comment: 18 pages, 26 figures, 4 table
Magnetic field study of exciton nonradiative broadening excitation spectra in GaAs/AlGaAs quantum wells
Exciton excited states in the quantum well are studied via their effect on
the nonradiative broadening of the ground exciton resonance. Dependence of the
nonradiative broadening of the ground exciton state on the photon energy of
additional laser excitation was measured. Applying magnetic field up to 6 T, we
could trace the formation of Landau levels and evolution of the exciton states
of size quantization in a 14-nm GaAs/AlGaAs quantum well. Sensitivity of the
technique allowed for observation of the second exciton state of size
quantization, unavailable for conventional reflectance and photoluminescence
spectroscopy. Our interpretation is supported by the numerical calculation of
the exciton energies of the heavy-hole and light-hole subsystems. The numerical
problems were solved using the finite-difference method on the nonuniform grid.
The ground Landau level of the free electron-hole pair was observed and
numerically analysed. In addition to energies of the excited states, electron
hole distances and exciton-light interaction constant was investigated using
the obtained in the numerical procedure exciton wave functions
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