14,819 research outputs found
Frequency domain criteria for lp-robust stability of systems with fuzzy parameters
The paper deals with the problem of determining stability margin of linear continuous-time system with fuzzy parametric uncertainty. Non-symmetric multivariate membership functions with lp -constraints describing the uncertainty of characteristic polynomial parameters are considered. An elegant solution, graphical in nature, based on generation of Tsypkin-Polyak plot is presented
Topological Superfluid Phase of a Dipolar Fermi Gas in a 2D Optical Lattice
In a dipolar Fermi gas, the anisotropic interaction between electric dipoles
can be turned into an effectively attractive interaction in the presence of a
rotating electric field. We show that the topological superfluid
phase can be realized in a single-component dipolar Fermi gas trapped in a 2D
square optical lattice with this attractive interaction at low temperatures.
The superfluid state has potential applications for topological
quantum computing. We obtain the phase diagram of this system at zero
temperature. In the weak-coupling limit, the p-wave superfluid phase is stable
for all filling factors. As the interaction strength increases, it is stable
close to filling factors or , and phase separation takes place in
between. When the interaction strength is above a threshold, the system is
phase separated for any . The transition temperature of the
superfluid state is estimated and the implication for
experiments is discussed.Comment: 10 pages, 4 figure
Policy Design for Controlling Set-Point Temperature of ACs in Shared Spaces of Buildings
Air conditioning systems are responsible for the major percentage of energy
consumption in buildings. Shared spaces constitute considerable office space
area, in which most office employees perform their meetings and daily tasks,
and therefore the ACs in these areas have significant impact on the energy
usage of the entire office building. The cost of this energy consumption,
however, is not paid by the shared space users, and the AC's temperature
set-point is not determined based on the users' preferences. This latter factor
is compounded by the fact that different people may have different choices of
temperature set-points and sensitivities to change of temperature. Therefore,
it is a challenging task to design an office policy to decide on a particular
set-point based on such a diverse preference set. As a result, users are not
aware of the energy consumption in shared spaces, which may potentially
increase the energy wastage and related cost of office buildings. In this
context, this paper proposes an energy policy for an office shared space by
exploiting an established temperature control mechanism. In particular, we
choose meeting rooms in an office building as the test case and design a policy
according to which each user of the room can give a preference on the
temperature set-point and is paid for felt discomfort if the set-point is not
fixed according to the given preference. On the other hand, users who enjoy the
thermal comfort compensate the other users of the room. Thus, the policy
enables the users to be cognizant and responsible for the payment on the energy
consumption of the office space they are sharing, and at the same time ensures
that the users are satisfied either via thermal comfort or through incentives.
The policy is also shown to be beneficial for building management. Through
experiment based case studies, we show the effectiveness of the proposed
policy.Comment: Journal paper accepted in Energy & Buildings (Elsevier
A vortex-filament and core model for wings with edge vortex separation
A method for predicting aerodynamic characteristics of slender wings with edge vortex separation was developed. Semiempirical but simple methods were used to determine the initial positions of the free sheet and vortex core. Comparison with available data indicates that: the present method is generally accurate in predicting the lift and induced drag coefficients but the predicted pitching moment is too positive; the spanwise lifting pressure distributions estimated by the one vortex core solution of the present method are significantly better than the results of Mehrotra's method relative to the pressure peak values for the flat delta; the two vortex core system applied to the double delta and strake wing produce overall aerodynamic characteristics which have good agreement with data except for the pitching moment; and the computer time for the present method is about two thirds of that of Mehrotra's method
Analysis of some aerodynamic characteristics due to wing-jet interaction
The results of two separate theoretical investigations are presented. A program was used which is capable of predicting the aerodynamic characteristics of both upper-surface blowing (USB) and over-wing blowing (OWB) configurations. A theoretical analysis of the effects of over-wing blowing jets on the induced drag of a 50 deg sweep back wing was developed. Experiments showed net drag reductions associated with the well known lift enhancement due to over-wing blowing. The mechanisms through which this drag reduction is brought about are presented. Both jet entrainment and the so called wing-jet interaction play important roles in this process. The effects of a rectangular upper-surface blowing jet were examined for a wide variety of planforms. The isolated effects of wing taper, sweep, and aspect ratio variations on the incremental lift due to blowing are presented. The effects of wing taper ratio and sweep angle were found to be especially important parameters when considering the relative levels of incremental lift produced by an upper-surface blowing configuration
A vortex-filament and core model for wings with edge vortex separation
A vortex filament-vortex core method for predicting aerodynamic characteristics of slender wings with edge vortex separation was developed. Semi-empirical but simple methods were used to determine the initial positions of the free sheet and vortex core. Comparison with available data indicates that: (1) the present method is generally accurate in predicting the lift and induced drag coefficients but the predicted pitching moment is too positive; (2) the spanwise lifting pressure distributions estimated by the one vortex core solution of the present method are significantly better than the results of Mehrotra's method relative to the pressure peak values for the flat delta; (3) the two vortex core system applied to the double delta and strake wings produce overall aerodynamic characteristics which have good agreement with data except for the pitching moment; and (4) the computer time for the present method is about two thirds of that of Mehrotra's method
Minimum induced drag configurations with jet interaction
A theoretical method is presented for determining the optimum camber shape and twist distribution for the minimum induced drag in the wing-alone case without prescribing the span loading shape. The same method was applied to find the corresponding minimum induced drag configuration with the upper-surface-blowing jet. Lan's quasi-vortex-lattice method and his wing-jet interaction theory was used. Comparison of the predicted results with another theoretical method shows good agreement for configurations without the flowing jet. More applicable experimental data with blowing jets are needed to establish the accuracy of the theory
Tunable negative permeability in a three-dimensional superconducting metamaterial
We report on highly tunable radio frequency (rf) characteristics of a
low-loss and compact three dimensional (3D) metamaterial made of
superconducting thin film spiral resonators. The rf transmission spectrum of a
single element of the metamaterial shows a fundamental resonance peak at
24.95 MHz that shifts to a 25 smaller frequency and becomes
degenerate when a 3D array of such elements is created. The metamaterial shows
an \emph{in-situ} tunable narrow frequency band in which the real part of the
effective permeability is negative over a wide range of temperature, which
reverts to gradually near-zero and positive values as the superconducting
critical temperature is approached. This metamaterial can be used for
increasing power transfer efficiency and tunability of electrically small
rf-antennas.Comment: 6 pages, 4 figure
Evolutionary optimization of a fed-batch penicillin fermentation process
This paper presents a genetic algorithms
approach for the optimization of a fed-batch penicillin
fermentation process. A customized float-encoding
genetic algorithm is developed and implemented to a
benchmark fed-batch penicillin fermentation process.
Off-line optimization of the initial conditions and set
points are carried out in two stages for a single variable
and multiple variables. Further investigations with online
optimization have been carried out to demonstrate
that the yield can be significantly improved with an
optimal feed rate profile. The results have shown that the
proposed approaches can be successfully applied to
optimization problems of fed-batch fermentation to
improve the operation of such processes
- …