6,187 research outputs found
Effects of dynamic aeroelasticity on handling qualities and pilot rating
Pilot performance parameters, such as pilot ratings, tracking errors, and pilot comments were determined for a longitudinal pitch tracking task using a large, flexible bomber with parametric variations in the undamped natural frequencies of the two lowest frequency symmetric elastic modes. This pitch tracking task was programmed on a fixed base simulator with an electronic attitude-director display of pitch command, pitch angle, and pitch error. Low frequency structural flexibility significantly affects the handling qualities and pilot ratings in the task evaluated
Studies of (GaAI)As injection lasers operating with an optical fiber resonator
The characteristics of an optical fiber external resonator in conjunction with (GaAl)As stripe geometry lasers are described. We have observed a 6â10% reduction in the threshold current and have obtained 150 ps pulses at gigahertz repetition rates. The fiber resonator has also been used to quench selfâpulsations in a (GaAl)As injection laser. In order to explain many of our results we have used a model that uses the conventional semiconductor rate equations modified by the addition of saturable electron traps and the effects of the external cavity. Our results predict many of the selfâlocking effects observed in injection lasers operating in an external cavity. Furthermore, the degree of selfâlocking will be a strong function of the external cavity length and the density of saturable absorbers
Gait Verification using Knee Acceleration Signals
A novel gait recognition method for biometric applications is proposed. The approach has the following distinct features. First, gait patterns are determined via knee acceleration signals, circumventing difficulties associated with conventional vision-based gait recognition methods. Second, an automatic procedure to extract gait features from acceleration signals is developed that employs a multiple-template classification method. Consequently, the proposed approach can adjust the sensitivity and specificity of the gait recognition system with great flexibility. Experimental results from 35 subjects demonstrate the potential of the approach for successful recognition. By setting sensitivity to be 0.95 and 0.90, the resulting specificity ranges from 1 to 0.783 and 1.00 to 0.945, respectively
Pressure-Temperature Phase Diagram of Multiferroic
The pressure-temperature phase diagram of multiferroic is
investigated for hydrostatic pressures up to 2 GPa. The stability range of the
ferroelectric phase associated with the incommensurate helical spin order is
reduced by pressure and ferroelectricity is completely suppressed at the
critical pressure of 1.64 GPa at 6.2 K. Thermal expansion measurements at
ambient pressure show strong step-like anomalies of the lattice parameters
associated with the lock-in transition into the commensurate paraelectric
phase. The expansion anomalies are highly anisotropic, the related volume
change is consistent with the high-pressure phase diagram
Strong spin-lattice coupling in multiferroic HoMnO: Thermal expansion anomalies and pressure effect
Evidence for a strong spin-lattice coupling in multiferroic HoMnO_3 is
derived from thermal expansion measurements along a- and c-axis. The
magnetoelastic effect results in sizable anomalies of the thermal expansivities
at the antiferromagnetic (T_N) and the spin rotation (T_{SR}) transition
temperatures as well as in a negative c-axis expansivity below room
temperature. The coupling between magnetic orders and dielectric properties
below T_N is explained by the lattice strain induced by the magnetoelastic
effect. At T_{SR} various physical quantities show discontinuities that are
thermodynamically consistent with a first order phase transition
Low temperature dielectric anomalies in HoMnO_3: The complex phase diagram
The dielectric constant of multiferroic hexagonal HoMnO_3 exhibits an
unprecedented diversity of anomalies at low temperatures (1.8 K< T <10 K) and
under external magnetic fields related to magnetic phase transitions in the
coupled system of Ho moments, Mn spins, and ferroelectric polarization. The
derived phase diagram is far more complex than previously assumed including
reentrant phases, phase transitions with distinct thermal and field hysteresis,
as well as several multicritical points. Magnetoelastic interactions introduce
lattice anomalies at the magnetic phase transitions. The re-evaluation of the
T-H phase diagram of HoMnO_3 is demanded.Comment: 12 pages, 3 figure
Marginally Trapped Surfaces in the Nonsymmetric Gravitational Theory
We consider a simple, physical approach to the problem of marginally trapped
surfaces in the Nonsymmetric Gravitational Theory (NGT). We apply this approach
to a particular spherically symmetric, Wyman sector gravitational field,
consisting of a pulse in the antisymmetric field variable. We demonstrate that
marginally trapped surfaces do exist for this choice of initial data.Comment: REVTeX 3.0 with epsf macros and AMS symbols, 3 pages, 1 figur
Progress towards quantum simulating the classical O(2) model
We connect explicitly the classical model in 1+1 dimensions, a model
sharing important features with lattice gauge theory, to physical models
potentially implementable on optical lattices and evolving at physical time.
Using the tensor renormalization group formulation, we take the time continuum
limit and check that finite dimensional projections used in recent proposals
for quantum simulators provide controllable approximations of the original
model. We propose two-species Bose-Hubbard models corresponding to these finite
dimensional projections at strong coupling and discuss their possible
implementations on optical lattices using a Rb and K Bose-Bose
mixture.Comment: 7 pages, 6 figures, uses revtex, new material and one author added,
as to appear in Phys. Rev.
Coupling of Magnetic Order, Ferroelectricity, and Lattice Strain in Multiferroic Rare Earth Manganites
Multiferroic rare earth manganites attracted recent attention because of the
coexistence of different types of magnetic and ferroelectric orders resulting
in complex phase diagrams and a wealth of physical phenomena. The coupling and
mutual interference of the different orders and the large magnetoelectric
effect observed in several compounds are of fundamental interest and bear the
potential for future applications in which the dielectric (magnetic) properties
can be modified by the onset of a magnetic (dielectric) transition or the
application of a magnetic (electric) field. The physical mechanisms of the
magnetoelectric effect and the origin of ferroelectric order at magnetic
transitions have yet to be explored. We discuss multiferroic phenomena in the
hexagonal HoMnO3 and show that the strong magneto-dielectric coupling is
intimately related to the lattice strain induced by unusually large spin-phonon
correlations.Comment: Proceedings of the ACERS Annual Meeting, April 200
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