3,585 research outputs found
Reducing AC impedance measurement errors caused by the DC voltage dependence of broadband high-voltage bias-tees
During the AC impedance characterization of devices, from the kHz-range up to the GHz-range, accuracy can be lost when a DC voltage is applied. Commercial high-voltage broadband bias-tees are often voltage-dependent, which can cause inaccuracies at low frequencies. A calibration technique with applied bias significantly improves the measurement accuracy.\ud
Additionally, a bias-tee has been developed with a voltageindependent capacitor, suitable for DC voltages up to 500 V showing excellent performance up to several gigahertz. PIN diode limiters protect the measurement equipment from damage in case of a device breakdown.\u
Rolling and sliding of a nanorod between two planes: Tribological regimes and control of friction
The motion of a cylindrical crystalline nanoparticle sandwiched between two
crystalline planes, one stationary and the other pulled at a constant velocity
and pressed down by a normal load, is considered theoretically using a planar
model. The results of our model calculations show that, depending on load and
velocity, the nanoparticle can be either rolling or sliding. At sufficiently
high normal loads, several sliding states characterized by different friction
forces can coexist, corresponding to different orientations of the
nanoparticle, and allowing one to have low or high friction at the same pulling
velocity and normal load.Comment: 5 figure
On the Trade-Off Between Quality Factor and Tuning Ratio in Tunable High-Frequency Capacitors
A benchmark of tunable and switchable devices at microwave frequencies is presented on the basis of physical limitations to show their potential for reconfigurable cellular applications. Performance limitations are outlined for each given technology focusing on the quality factor (Q) and tuning ratio (eta) as figures of merit. The state of the art in terms of these figures of merit of several tunable and switchable technologies is visualized and discussed. If the performance of these criteria is not met, the application will not be feasible. The quality factor can typically be traded off for tuning ratio. The benchmark of tunable capacitor technologies shows that transistor-switched capacitors, varactor diodes, and ferroelectric varactors perform well at 2 GHz for tuning ratios below 3, with an advantage for GaAs varactor diodes. Planar microelectromechanical capacitive switches have the potential to outperform all other technologies at tuning ratios higher than 8. Capacitors based on tunable dielectrics have the highest miniaturization potential, whereas semiconductor devices benefit from the existing manufacturing infrastructure
Metastability of persistent currents in trapped gases of atoms
We examine the conditions that give rise to metastable, persistent currents
in a trapped Bose-Einstein condensate. A necessary condition for the stability
of persistent currents is that the trapping potential is not a monotonically
increasing function of the distance from the trap center. Persistent currents
also require that the interatomic interactions are sufficiently strong and
repulsive. Finally, any off-center vortex state is shown to be unstable, while
a driven gas shows hysteresis.Comment: 7 pages, RevTex, 5 figure
Classical linear chain behavior from dipolar droplets to supersolids
We investigate the classicality of linear dipolar droplet arrays through a
normal mode analysis of the dynamical properties in comparison to the
supersolid regime. The vibrational patterns of isolated-droplet crystals that
time-evolve after a small initial kick closely follow the properties of a
linear droplet chain. For larger kick velocities, however, droplets may
coalesce and separate again, showing distinct deviations from classicality. In
the supersolid regime the normal modes are eliminated by a counter-flow of mass
between the droplets, signaled by a reduction of the center-of-mass motion
Nonequilibrium coupled Brownian phase oscillators
A model of globally coupled phase oscillators under equilibrium (driven by
Gaussian white noise) and nonequilibrium (driven by symmetric dichotomic
fluctuations) is studied. For the equilibrium system, the mean-field state
equation takes a simple form and the stability of its solution is examined in
the full space of order parameters. For the nonequilbrium system, various
asymptotic regimes are obtained in a closed analytical form. In a general case,
the corresponding master equations are solved numerically. Moreover, the
Monte-Carlo simulations of the coupled set of Langevin equations of motion is
performed. The phase diagram of the nonequilibrium system is presented. For the
long time limit, we have found four regimes. Three of them can be obtained from
the mean-field theory. One of them, the oscillating regime, cannot be predicted
by the mean-field method and has been detected in the Monte-Carlo numerical
experiments.Comment: 9 pages 8 figure
Density Functional Theory of Multicomponent Quantum Dots
Quantum dots with conduction electrons or holes originating from several
bands are considered. We assume the particles are confined in a harmonic
potential and assume the electrons (or holes) belonging to different bands to
be different types of fermions with isotropic effective masses. The density
functional method with the local density approximation is used. The increased
number of internal (Kohn-Sham) states leads to a generalisation of Hund's first
rule at high densities. At low densitites the formation of Wigner molecules is
favored by the increased internal freedom.Comment: 11 pages, 5 figure
Slice Stretching at the Event Horizon when Geodesically Slicing the Schwarzschild Spacetime with Excision
Slice-stretching effects are discussed as they arise at the event horizon
when geodesically slicing the extended Schwarzschild black-hole spacetime while
using singularity excision. In particular, for Novikov and isotropic spatial
coordinates the outward movement of the event horizon (``slice sucking'') and
the unbounded growth there of the radial metric component (``slice wrapping'')
are analyzed. For the overall slice stretching, very similar late time behavior
is found when comparing with maximal slicing. Thus, the intuitive argument that
attributes slice stretching to singularity avoidance is incorrect.Comment: 5 pages, 2 figures, published version including minor amendments
suggested by the refere
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