21 research outputs found
Thermal equilibration between two quantum systems
Two identical finite quantum systems prepared initially at different
temperatures, isolated from the environment, and subsequently brought into
contact are demonstrated to relax towards Gibbs-like quasi-equilibrium states
with a common temperature and small fluctuations around the time-averaged
expectation values of generic observables. The temporal thermalization process
proceeds via a chain of intermediate Gibbs-like states. We specify the
conditions under which this scenario occurs and corroborate the quantum
equilibration with two different models.Comment: 10 pages, 9 figures, including supplementary materia
Quantum machine using cold atoms
For a machine to be useful in practice, it preferably has to meet two
requirements: namely, (i) to be able to perform work under a load and (ii) its
operational regime should ideally not depend on the time at which the machine
is switched-on. We devise a minimal setup, consisting of two atoms only, for an
ac-driven quantum motor which fulfills both these conditions. Explicitly, the
motor consists of two different interacting atoms placed into a ring-shaped
periodic optical potential -- an optical "bracelet" --, resulting from the
interference of two counter-propagating Laguerre-Gauss laser beams. This
bracelet is additionally threaded by a pulsating magnetic flux. While the first
atom plays a role of a quantum "carrier", the second serves as a quantum
"starter", which sets off the "carrier" into a steady rotational motion. For
fixed zero-momentum initial conditions the asymptotic carrier velocity
saturates to a unique, nonzero value which becomes increasingly independent on
the starting time with increasing "bracelet"-size. We identify the quantum
mechanisms of rectification and demonstrate that our quantum motor is able to
perform useful work.Comment: simplified notations, extended figure captions; 16 pages, 6 figure
Stress-strain state simulation of large-sized cable-stayed shell structures
This paper studies the opportunities for applying framed cable-stayed shell structures to generate innovative structures in civil engineering. Numerical solution methods for stress-strain state problems of these kinds of geometrically nonlinear structures were developed. Developed methods efficiency is presented by a range of large-dimensional space antenna reflectors
Tuning the mobility of a driven Bose-Einstein condensate via diabatic Floquet bands
We study the response of ultracold atoms to a weak force in the presence of a
temporally strongly modulated optical lattice potential. It is experimentally
demonstrated that the strong ac-driving allows for a tailoring of the mobility
of a dilute atomic Bose-Einstein condensate with the atoms moving ballistically
either along or against the direction of the applied force. Our results are in
agreement with a theoretical analysis of the Floquet spectrum of a model
system, thus revealing the existence of diabatic Floquet bands in the atom's
band spectra and highlighting their role in the non-equilibrium transport of
the atoms
Modelling large-sized mesh reflector with extended aperture
Offset large-sized deployable mesh reflector with symmetric frontal and rear nets is described in the paper. This reflector involves extended aperture area and reduced framework elements by applying beam elements in the peripheral areas of reflecting surface. Strain-stress analysis is conducted to calculate reflecting surface shape of required accuracy
Modeling large pneumatic reflectors based on innovative materials
Large pneumatic structures of deploying space reflector are highly efficient and significantly advantageous due to the following reasons: significant coverage at low material usage and deployment simplicity. At the same time experimental modeling of such structures is time-consuming and costly. So, numerical analysis of such structures is very important in preliminary design. This paper presents the mathematical problem statement of stress-strain state of pneumatic structures, as well as the modal analysis results for two pneumatic reflectors of 50 and 100 meters in size applying such materials as Kevlar and thin polyamide films. The above described problems were solved by well-known nonlinear finite element method
Stress-strain state simulation of large-sized cable-stayed shell structures
This paper studies the opportunities for applying framed cable-stayed shell structures to generate innovative structures in civil engineering. Numerical solution methods for stress-strain state problems of these kinds of geometrically nonlinear structures were developed. Developed methods efficiency is presented by a range of large-dimensional space antenna reflectors
Modelling large-sized mesh reflector with extended aperture
Offset large-sized deployable mesh reflector with symmetric frontal and rear nets is described in the paper. This reflector involves extended aperture area and reduced framework elements by applying beam elements in the peripheral areas of reflecting surface. Strain-stress analysis is conducted to calculate reflecting surface shape of required accuracy