1,601 research outputs found
Evolutionary design of a full-envelope full-authority flight control system for an unstable high-performance aircraft
The use of an evolutionary algorithm in the framework of H1 control theory is being considered as a means for synthesizing controller gains that minimize a weighted combination of the infinite norm of the sensitivity function (for disturbance attenuation requirements) and complementary sensitivity function (for robust stability requirements) at the same time. The case study deals with a complete full-authority longitudinal control system for an unstable high-performance jet aircraft featuring (i) a stability and control augmentation system and (ii) autopilot functions (speed and altitude hold). Constraints on closed-loop response are enforced, that representing typical requirements on airplane handling qualities, that makes the control law synthesis process more demanding. Gain scheduling is required, in order to obtain satisfactory performance over the whole flight envelope, so that the synthesis is performed at different reference trim conditions, for several values of the dynamic pressure, used as the scheduling parameter. Nonetheless, the dynamic behaviour of the aircraft may exhibit significant variations when flying at different altitudes, even for the same value of the dynamic pressure, so that a trade-off is required between different feasible controllers synthesized at different altitudes for a given equivalent airspeed. A multiobjective search is thus considered for the determination of the best suited solution to be introduced in the scheduling of the control law. The obtained results are then tested on a longitudinal non-linear model of the aircraft
Does the taste matter? Taste and medicinal perceptions associated with five selected herbal drugs among three ethnic groups in West Yorkshire, Northern England
In recent years, diverse scholars have addressed the issue of the chemosensory perceptions associated with traditional medicines, nevertheless there is still a distinct lack of studies grounded in the social sciences and conducted from a cross-cultural, comparative perspective. In this urban ethnobotanical field study, 254 informants belonging to the Gujarati, Kashmiri and English ethnic groups and living in Western Yorkshire in Northern England were interviewed about the relationship between taste and medicinal perceptions of five herbal drugs, which were selected during a preliminary study. The herbal drugs included cinnamon (the dried bark of Cinnamomum verum, Lauraceae), mint (the leaves of Mentha spp., Lamiaceae), garlic (the bulbs of Allium sativum, Alliaceae), ginger (the rhizome of Zingiber officinale, Zingiberaceae), and cloves (the dried flower buds of Syzygium aromaticum, Myrtaceae).
The main cross-cultural differences in taste perceptions regarded the perception the perception of the spicy taste of ginger, garlic, and cinnamon, of the bitter taste of ginger, the sweet taste of mint, and of the sour taste of garlic.
The part of the study of how the five selected herbal drugs are perceived medicinally showed that TK (Traditional Knowledge) is widespread among Kashmiris, but not so prevalent among the Gujarati and especially the English samples. Among Kashmiris, ginger was frequently considered to be helpful for healing infections and muscular-skeletal and digestive disorders, mint was chosen for healing digestive and respiratory troubles, garlic for blood system disorders, and cinnamon was perceived to be efficacious for infectious diseases.
Among the Gujarati and Kashmiri groups there was evidence of a strong link between the bitter and spicy tastes of ginger, garlic, cloves, and cinnamon and their perceived medicinal properties, whereas there was a far less obvious link between the sweet taste of mint and cinnamon and their perceived medicinal properties, although the link did exist among some members of the Gujarati group.
Data presented in this study show how that links between taste perceptions and medicinal uses of herbal drugs may be understood as bio-cultural phenomena rooted in human physiology, but also constructed through individual experiences and culture, and that these links can therefore be quite different across diverse cultures
Braess's Paradox in Wireless Networks: The Danger of Improved Technology
When comparing new wireless technologies, it is common to consider the effect
that they have on the capacity of the network (defined as the maximum number of
simultaneously satisfiable links). For example, it has been shown that giving
receivers the ability to do interference cancellation, or allowing transmitters
to use power control, never decreases the capacity and can in certain cases
increase it by , where is the
ratio of the longest link length to the smallest transmitter-receiver distance
and is the maximum transmission power. But there is no reason to
expect the optimal capacity to be realized in practice, particularly since
maximizing the capacity is known to be NP-hard. In reality, we would expect
links to behave as self-interested agents, and thus when introducing a new
technology it makes more sense to compare the values reached at game-theoretic
equilibria than the optimum values.
In this paper we initiate this line of work by comparing various notions of
equilibria (particularly Nash equilibria and no-regret behavior) when using a
supposedly "better" technology. We show a version of Braess's Paradox for all
of them: in certain networks, upgrading technology can actually make the
equilibria \emph{worse}, despite an increase in the capacity. We construct
instances where this decrease is a constant factor for power control,
interference cancellation, and improvements in the SINR threshold (),
and is when power control is combined with interference
cancellation. However, we show that these examples are basically tight: the
decrease is at most O(1) for power control, interference cancellation, and
improved , and is at most when power control is
combined with interference cancellation
Systematics of q anti-q states in the (n,M^2) and (J,M^2) planes
In the mass region up to M < 2400 MeV we systematise mesons on the plots
(n,M^2) and (J,M^2), thus setting their classification in terms of n^{2S+1}L_J
q anti-q states. The trajectories on the (n,M^2)-plots are drawn for the
following (IJ^{PC})-states: a_0(10^{++}), a_1(11^{++}), a_2(12^{++}),
a_3(13^{++}), a_4(14^{++}), pi(10^{-+}), pi_2(12^{-+}), eta(00^{-+}),
eta_2(02^{-+})$, rho(11^{--}), f_0(00^{++}), f_2(02^{++}). All trajectories are
linear, with nearly the same slopes. At the (J,M^2)-plot we set out meson
states for leading and daughter trajectories: for pi, rho, a_1, a_2 and P'.Comment: 6 pages, LaTeX, 16 EPS figures, epsfig.st
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The STAR detector magnet subsystem
The RHIC (Relativistic Heavy Ion Collider) Accelerator currently under construction at Brookhaven National Laboratory will have large detectors at two of its six intersection regions. One of these detectors, known as STAR (Solenoidal Tracker At RHIC), weighs 1100 tons and is being built around a large solenoid magnet. The magnet is 7.32 in in diameter, 7.25 m long and utilizes three different sizes of room temperature aluminum coils. The magnet will operate with a field set from 0.25 T to 0.5 T and have a field uniformity of better than 1000 ppm over a portion of its interior region. This paper describes the magnet design, fabrication and assembly requirements and presents the current construction status
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