28,342 research outputs found
A mathematical simulation model of the CH-47B helicopter, volume 1
A nonlinear simulation model of the CH-47B helicopter was adapted for use in the NASA Ames Research Center (ARC) simulation facility. The model represents the specific configuration of the ARC variable stability CH-47B helicopter and will be used in ground simulation research and to expedite and verify flight experiment design. Modeling of the helicopter uses a total force approach in six rigid body degrees of freedom. Rotor dynamics are simulated using the Wheatlely-Bailey equations including steady-state flapping dynamics. Also included in the model is the option for simulation of external suspension, slung-load equations of motion
Ground-simulation investigations of VTOL airworthiness criteria for terminal-area operations
Several ground-based simulation experiments undertaken to investigate concerns related to tilt-rotor aircraft airworthiness were conducted. The experiments were conducted on the National Aeronautics and Space Administration (NASA) Ames Research Center's Vertical Motion Simulator, which permits simulation of a wide variety of aircraft with a high degree of fidelity of motion cueing. Variations in conversion/deceleration profile, type of augmentation or automation, level of display assistance, and meteorological conditions were considered in the course of the experiments. Certification pilots from the Federal Aviation Administration (FAA) and the Civil Aviation Authority (CAA) participated, in addition to NASA research pilots. The setup of these experiments on the simulator is summarized, and some of the results highlighted
Partially composite 2-Higgs-doublet model
In the extra dimensional scenarios with gauge fields in the bulk, the
Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type
attractive four-fermion interactions, which can break electroweak symmetry
dynamically with accompanying composite Higgs fields. We consider a possibility
that electroweak symmetry breaking (EWSB) is triggered by both a fundamental
Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism
induced by a new strong dynamics. The resulting Higgs sector is a partially
composite two-Higgs doublet model with specific boundary conditions on the
coupling and mass parameters originating at a compositeness scale .
The phenomenology of this model is discussed including the collider
phenomenology at LHC and ILC.Comment: To appear in the proceeding of LCWS06, Bangalore, Indi
Ion exchange phase transitions in "doped" water--filled channels
Ion transport through narrow water--filled channels is impeded by a high
electrostatic barrier. The latter originates from the large ratio of the
dielectric constants of the water and a surrounding media. We show that
``doping'', i.e. immobile charges attached to the walls of the channel,
substantially reduces the barrier. This explains why most of the biological ion
channels are ``doped''. We show that at rather generic conditions the channels
may undergo ion exchange phase transitions (typically of the first order). Upon
such a transition a finite latent concentration of ions may either enter or
leave the channel, or be exchanged between the ions of different valences. We
discuss possible implications of these transitions for the Ca-vs.-Na
selectivity of biological Ca channels. We also show that transport of divalent
Ca ions is assisted by their fractionalization into two separate excitations.Comment: 16 pages, 27 figure
Majorana zero modes in a quantum Ising chain with longer-ranged interactions
A one-dimensional Ising model in a transverse field can be mapped onto a
system of spinless fermions with p-wave superconductivity. In the weak-coupling
BCS regime, it exhibits a zero energy Majorana mode at each end of the chain.
Here, we consider a variation of the model, which represents a superconductor
with longer ranged kinetic energy and pairing amplitudes, as is likely to occur
in more realistic systems. It possesses a richer zero temperature phase diagram
and has several quantum phase transitions. From an exact solution of the model
these phases can be classified according to the number of Majorana zero modes
of an open chain: 0, 1, or 2 at each end. The model posseses a multicritical
point where phases with 0, 1, and 2 Majorana end modes meet. The number of
Majorana modes at each end of the chain is identical to the topological winding
number of the Anderson's pseudospin vector that describes the BCS Hamiltonian.
The topological classification of the phases requires a unitary time-reversal
symmetry to be present. When this symmetry is broken, only the number of
Majorana end modes modulo 2 can be used to distinguish two phases. In one of
the regimes, the wave functions of the two phase shifted Majorana zero modes
decays exponentially in space but but in an oscillatory manner. The wavelength
of oscillation is identical to the asymptotic connected spin-spin correlation
of the XY-model in a transverse field to which our model is dual.Comment: 11 pages, 8 figures; brief clarifying comments added; few new
references; this version is accepted in Phys. Rev.
Control Force Compensation in Ground-Based Flight Simulators
This paper presents the results of a study that investigated if controller force compensations accounting for the inertial force and moment due to the aircraft motion during flight have a significant effect on pilot control behavior and performance. Seven rotorcraft pilots performed a side-step and precision hovering task in light turbulence in the Vertical Motion Simulator. The effects of force compensation were examined for two different simulated rotorcraft: linear and UH-60 dynamics with two different force gradient of the lateral stick control. Four motion configurations were used: large motion, hexapod motion, fixed-base motion, and fixed-base motion with compensation. Control-input variables and task performance such as the time to translate to the designated hover position, station-keeping position errors, and handling qualities ratings were used as measures. Control force compensation enabled pilot control behavior and performance more similar to that under high- or medium-fidelity motion to some extent only. Control force compensation did not improve overall task performance considering both rotorcraft models at the same time. The control force compensation had effects on the linear model with lighter force gradient, but only a minimal effect on pilots? control behavior and task performance for the UH-60 model, which had a higher force gradient. This suggests that the control force compensation has limited benefits for controllers that have higher stiffness
Hawking Radiation from Feynman Diagrams
The aim of this letter is to clarify the relationships between Hawking
radiation and the scattering of light by matter falling into a black hole. To
this end we analyze the S-matrix elements of a model composed of a massive
infalling particle (described by a quantized field) and the radiation field.
These fields are coupled by current-current interactions and propagate in the
Schwarzschild geometry. As long as the photons energy is much smaller than the
mass of the infalling particle, one recovers Hawking radiation since our
S-matrix elements identically reproduce the Bogoliubov coefficients obtained by
treating the trajectory of the infalling particle classically. But after a
brief period, the energy of the `partners' of Hawking photons reaches this mass
and the production of thermal photons through these interactions stops. The
implications of this result are discussed.Comment: 12 pages, revtex, no figure
Theory of superconductor-insulator transition in single Josephson junctions
A non-band theory is developed to describe the superconductor-insulator (SI)
transtition in resistively shunted, single Josephson junctions. The
characteristic is formulated by a Landauer-like formula and evaluated by the
path-integral transfer-matrix method. The result is consistent with the recent
experiments at around 80 . However, the insulator phase shrinks with
decreasing temperature indicating that the single Josephson junction becomes
all superconducting at absolute zero temperature, as long as dissipation is
present.Comment: 4 pages, 3 figure
Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals
Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD
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