284 research outputs found
nonlinear model predictive control strategy for steam turbine rotor stress
Abstract The paper proposes a Nonlinear Model Predictive Control strategy for the control of steam turbines rotor thermal stresses, which exploits the approximation of the turbine rotor as an infinite cylinder subjected to external convection. The Nonlinear Model Predictive Control allows optimizing the control strategy in the long term, by significantly reducing the machine start-up time during the power up ramp. This study proposes two different control strategies: the former one is based on the control of the Heat Transfer Coefficient, correlated to the inlet valve stroke. The latter one is based on the control of Heat Transfer Coefficient and the boiler steam temperature reference. Both strategies achieve good results in shortening the start-up time. The overall approach is validated and currently under development on Programmable Logic Controller platforms to the aim of code optimization
Transition from Collisionless to Hydrodynamic Behaviour in an Ultracold Atomic Gas
Relative motion in a two-component, trapped atomic gas provides a sensitive
probe of interactions. By studying the lowest frequency excitations of a two
spin-state gas confined in a magnetic trap, we have explored the transition
from the collisionless to the hydrodynamic regime. As a function of collision
rate, we observe frequency shifts as large as 6% as well as a dramatic,
non-monotonic dependence of the damping rate. The measurements agree
qualitatively with expectations for behavior in the collisionless and
hydrodynamic limits and are quantitatively compared to a classical kinetic
model.Comment: 5 pages, 4 figure
Expansion of a coherent array of Bose-Einstein condensates
We investigate the properties of a coherent array containing about 200
Bose-Einstein condensates produced in a far detuned 1D optical lattice. The
density profile of the gas, imaged after releasing the trap, provides
information about the coherence of the ground-state wavefunction. The measured
atomic distribution is characterized by interference peaks. The time evolution
of the peaks, their relative population as well as the radial size of the
expanding cloud are in good agreement with the predictions of theory. The 2D
nature of the trapped condensates and the conditions required to observe the
effects of coherence are also discussed.Comment: 4 pages, 3 figure
Collective oscillations of two colliding Bose-Einstein condensates
Two 87Rb condensates (F=2, m_f=2 and m_f=1) are produced in highly displaced
harmonic traps and the collective dynamical behaviour is investigated. The
mutual interaction between the two condensates is evidenced in the
center-of-mass oscillations as a frequency shift of 6.4(3)%. Calculations based
on a mean-field theory well describe the observed effects of periodical
collisions both on the center-of-mass motion and on the shape oscillations.Comment: 5 pages, 3 figures, revtex - revised versio
Shaking table tests for the experimental verification of the effectiveness of an automated modal parameter monitoring system for existing bridges in seismic areas
Reinforced concrete bridges represent a majority of the Italian stock and they play a primary role to ensure the efficiency of the transportation network and prompt rescue in the case of an emergency. However, most of them have been designed and built according to outdated codes, or even without any seismic detailing. The significant impact of strong motions on the road network as well as the human life and economy emphasizes the need for effective strategies for post-earthquake emergency management and to support rescue operations. The present paper aims at evaluating, against real data, the effectiveness of automated modal parameter monitoring for vibration-based Structural Health Monitoring (SHM) of existing bridges in earthquake prone areas. This objective has been pursued in the context of shaking table tests on a 1:3 scale single span bridge representative of existing highway bridges built in the 60's in Italy. The dynamic response of the structure before and after the application of asynchronous seismic input has been analyzed for damage detection and performance assessment. Results show that partially hidden damage can be remotely detected, thus validating the interesting applicative perspectives of automated output-only modal identification and modal-based damage detection for fast assessment of existing bridges in the early earthquake aftershock. The robustness of the SHM system to sensor overload due to earthquake shaking has been also assessed, demonstrating the applicability of modal-based SHM in seismic regions even in the absence of a measurement chain specifically designed to resolve the large amplitude vibrations induced by earthquakes. Finally, the possibility of complementing modal-based SHM with drift-based estimates is explored
Superfluidity of Bose-Einstein Condensate in An Optical Lattice: Landau-Zener Tunneling and Dynamical Instability
Superflow of Bose-Einstein condensate in an optical lattice is represented by
a Bloch wave, a plane wave with periodic modulation of the amplitude. We review
the theoretical results on the interaction effects in the energy dispersion of
the Bloch waves and in the linear stability of such waves. For sufficiently
strong repulsion between the atoms, the lowest Bloch band develops a loop at
the edge of the Brillouin zone, with the dramatic consequence of a finite
probability of Landau-Zener tunneling even in the limit of a vanishing external
force. Superfluidity can exist in the central region of the Brillouin zone in
the presence of a repulsive interaction, beyond which Landau instability takes
place where the system can lower its energy by making transition into states
with smaller Bloch wavenumbers. In the outer part of the region of Landau
instability, the Bloch waves are also dynamically unstable in the sense that a
small initial deviation grows exponentially in time. In the inner region of
Landau instability, a Bloch wave is dynamically stable in the absence of
persistent external perturbations. Experimental implications of our findings
will be discussed.Comment: A new section on tight-binding approximation is added with a new
figur
Critical velocities in two-component superfluid Bose gases
On the ground of the Landau criterion we study the behavior of critical
velocities in a superfluid two-component Bose gas. It is found that under
motion of the components with different velocities the velocity of each
component should not be lower than a minimum phase velocity of elementary
excitations (s_). The Landau criterion yields a relation between the critical
velocities of the components (v_{c1}, v_{c2}). The velocity of one or even both
components may exceed s_. The maximum value of the critical velocity of a given
component can be reached when the other component does not move. The approach
is generalized for a two-component condensate confined in a cylindrical
harmonic potential.
PACS numbers: 03.75.Kk,03.75.MnComment: 6 pages, 1 figure
The T.O.S.C.A. Project: Research, Education and Care
Despite recent and exponential improvements in diagnostic-
therapeutic pathways, an existing “GAP” has been revealed
between the “real world care” and the “optimal care”
of patients with chronic heart failure (CHF). We present the
T.O.S.CA. Project (Trattamento Ormonale dello Scompenso
CArdiaco), an Italian multicenter initiative involving different
health care professionals and services aiming to explore the
CHF “metabolic pathophysiological model” and to improve
the quality of care of HF patients through research and continuing
medical education
- …