6,128 research outputs found
Transient dynamics of a superconducting nonlinear oscillator
We investigate the transient dynamics of a lumped-element oscillator based on
a dc superconducting quantum interference device (SQUID). The SQUID is shunted
with a capacitor forming a nonlinear oscillator with resonance frequency in the
range of several GHz. The resonance frequency is varied by tuning the Josephson
inductance of the SQUID with on-chip flux lines. We report measurements of
decaying oscillations in the time domain following a brief excitation with a
microwave pulse. The nonlinearity of the SQUID oscillator is probed by
observing the ringdown response for different excitation amplitudes while the
SQUID potential is varied by adjusting the flux bias. Simulations are performed
on a model circuit by numerically solving the corresponding Langevin equations
incorporating the SQUID potential at the experimental temperature and using
parameters obtained from separate measurements characterizing the SQUID
oscillator. Simulations are in good agreement with the experimental
observations of the ringdowns as a function of applied magnetic flux and pulse
amplitude. We observe a crossover between the occurrence of ringdowns close to
resonance and adiabatic following at larger detuning from the resonance. We
also discuss the occurrence of phase jumps at large amplitude drive. Finally,
we briefly outline prospects for a readout scheme for superconducting flux
qubits based on the discrimination between ringdown signals for different
levels of magnetic flux coupled to the SQUID.Comment: 15 pages, 9 figure
Phase Transition in a Stochastic Forest Fire Model and Effects of the Definition of Neighbourhood
We present results on a stochastic forest fire model, where the influence of
the neighbour trees is treated in a more realistic way than usual and the
definition of neighbourhood can be tuned by an additional parameter.
This model exhibits a surprisingly sharp phase transition which can be
shifted by redefinition of neighbourhood. The results can also be interpreted
in terms of disease-spreading and are quite unsettling from the epidemologist's
point of view, since variation of one crucial parameter only by a few percent
can result in the change from endemic to epidemic behaviour.Comment: 23 pages, 13 figure
Ohio's statewide land use inventory: An operational approach for applying LANDSAT data to state, regional and local planning programs
The programmatic, technical, user application, and cost factors associated with the development of an operational, statewide land use inventory from LANDSAT data are described. The LANDSAT multispectral data are subjected to geometrical and categorical processing to produce map files for each of the 200 fifteen (15) minute quads covering Ohio. Computer compatible tapes are rescanned to produce inventory tapes which identify eight (8) Level I land use categories and a variety of Level II categories. The inventory tapes are processed through a series of ten (10) software programs developed by the State of Ohio. The net result is a computerized inventory which can be displayed in map or tabular form for various geographic units, at a variety of scales and for selected categories of usage. The computerized inventory data files are applied to technical programs developed by the various state agencies to be used in state, regional, and local planning programs
Stereoscopic Polar Plume Reconstructions from Stereo/Secchi Images
We present stereoscopic reconstructions of the location and inclination of
polar plumes of two data sets based on the two simultaneously recorded images
taken by the EUVI telescopes in the SECCHI instrument package onboard the
\emph{STEREO (Solar TErrestrial RElations Observatory)} spacecraft. The ten
plumes investigated show a superradial expansion in the coronal hole in 3D
which is consistent with the 2D results. Their deviations from the local
meridian planes are rather small with an average of . By
comparing the reconstructed plumes with a dipole field with its axis along the
solar rotation axis, it is found that plumes are inclined more horizontally
than the dipole field. The lower the latitude is, the larger is the deviation
from the dipole field. The relationship between plumes and bright points has
been investigated and they are not always associated. For the first data set,
based on the 3D height of plumes and the electron density derived from
SUMER/\emph{SOHO} Si {\sc viii} line pair, we found that electron densities
along the plumes decrease with height above the solar surface. The temperature
obtained from the density scale height is 1.6 to 1.8 times larger than the
temperature obtained from Mg {\sc ix} line ratios. We attribute this
discrepancy to a deviation of the electron and the ion temperatures. Finally,
we have found that the outflow speeds studied in the O {\sc vi} line in the
plumes corrected by the angle between the line of sight and the plume
orientation are quite small with a maximum of 10 . It is
unlikely that plumes are a dominant contributor to the fast solar wind.Comment: 25 pages, 13 figure
Entangling flux qubits with a bipolar dynamic inductance
We propose a scheme to implement variable coupling between two flux qubits
using the screening current response of a dc Superconducting QUantum
Interference Device (SQUID). The coupling strength is adjusted by the current
bias applied to the SQUID and can be varied continuously from positive to
negative values, allowing cancellation of the direct mutual inductance between
the qubits. We show that this variable coupling scheme permits efficient
realization of universal quantum logic. The same SQUID can be used to determine
the flux states of the qubits.Comment: 4 pages, 4 figure
SU(4) Fermi Liquid State and Spin Filtering in a Double Quantum Dot System
We study a symmetrical double quantum dot (DD) system with strong capacitive
inter-dot coupling using renormalization group methods. The dots are attached
to separate leads, and there can be a weak tunneling between them. In the
regime where there is a single electron on the DD the low-energy behavior is
characterized by an SU(4)-symmetric Fermi liquid theory with entangled spin and
charge Kondo correlations and a phase shift . Application of an external
magnetic field gives rise to a large magneto-conductance and a crossover to a
purely charge Kondo state in the charge sector with SU(2) symmetry. In a four
lead setup we find perfectly spin polarized transmission.Comment: 4 pages, 4 figures, ReVTe
An Empirical Examination of Symptom Substitution Associated with Behavior Therapy for Tourette\u27s Disorder
Over the past six decades, behavior therapy has been a major contributor to the development of evidence-based psychotherapy treatments. However, a long-standing concern with behavior therapy among many nonbehavioral clinicians has been the potential risk for symptom substitution. Few studies have been conducted to evaluate symptom substitution in response to behavioral treatments, largely due to measurement and definitional challenges associated with treated psychiatric symptoms. Given the overt motor and vocal tics associated with Tourette’s disorder, it presents an excellent opportunity to empirically evaluate the potential risk for symptom substitution associated with behavior therapy. The present study examined the possible presence of symptom substitution using four methods: (a) the onset of new tic symptoms, (b) the occurrence of adverse events, (c) change in tic medications, and (d) worsening of co-occurring psychiatric symptoms. Two hundred twenty-eight participants with Tourette’s disorder or persistent motor or vocal tic disorders were randomly assigned to receive behavioral therapy or supportive therapy for tics. Both therapies consisted of eight sessions over 10 weeks. Results indicated that participants treated with behavior therapy were not more likely to have an onset of new tic symptoms, experience adverse events, increase tic medications, or have an exacerbation in co-occurring psychiatric symptoms relative to participants treated with supportive therapy. Further analysis suggested that the emergence of new tics was attributed with the normal waxing and waning nature of Tourette’s disorder. Findings provide empirical support to counter the long-standing concern of symptom substitution in response to behavior therapy for individuals with Tourette\u27s disorder
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