22,477 research outputs found
Risk aversion and bidding theory
Theory of bidding behavior and formation of bidding model with risk aversio
Enhanced Acoustic Emission in Relation to the Acoustic Halo Surrounding Active Region 11429
The use of acoustic holography in the high-frequency -mode spectrum can
resolve the source distributions of enhanced acoustic emissions within halo
structures surrounding active regions. In doing so, statistical methods can
then be applied to ascertain relationships with the magnetic field. This is the
focus of this study. The mechanism responsible for the detected enhancement of
acoustic sources around solar active regions has not yet been explained.
Furthermore the relationship between the magnetic field and enhanced acoustic
emission has not yet been comprehensively examined. We have used vector
magnetograms from the \Helioseismic and Magnetic Imager (HMI) on-board the
Solar Dynamics Observatory (SDO) to image the magnetic-field properties in the
halo. We have studied the acoustic morphology of an active region, with a
complex halo and "glories," and we have linked some acoustic properties to the
magnetic-field configuration. In particular, we find that acoustic sources are
significantly enhanced in regions of intermediate field strength with
inclinations no different from the distributions found in the quiet Sun.
Additionally we have identified a transition region between the active region
and the halo, in which the acoustic source power is hindered by inclined fields
of intermediate field strength. Finally, we have compared the results of
acoustic emission maps, calculated from holography, and the commonly used local
acoustic maps, finding that the two types of maps have similar properties with
respect to the magnetic field but lack spatial correlation when examining the
highest-powered regions.Comment: 19 pages, 8 figures, Accepted by Solar Physic
Fast Single-Charge Sensing with an rf Quantum Point Contact
We report high-bandwidth charge sensing measurements using a GaAs quantum
point contact embedded in a radio frequency impedance matching circuit
(rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to
charge, we demonstrate a conductance sensitivity of 5x10^(-6) e^(2)/h Hz^(-1/2)
with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron
double quantum dot is investigated in a mode where the rf-QPC back-action is
rapidly switched.Comment: related papers available at http://marcuslab.harvard.ed
Cotunneling Spectroscopy in Few-Electron Quantum Dots
Few-electron quantum dots are investigated in the regime of strong tunneling
to the leads. Inelastic cotunneling is used to measure the two-electron
singlet-triplet splitting above and below a magnetic field driven
singlet-triplet transition. Evidence for a non-equilibrium two-electron
singlet-triplet Kondo effect is presented. Cotunneling allows orbital
correlations and parameters characterizing entanglement of the two-electron
singlet ground state to be extracted from dc transport.Comment: related papers available at http://marcuslab.harvard.ed
Rapid Single-Shot Measurement of a Singlet-Triplet Qubit
We report repeated single-shot measurements of the two-electron spin state in
a GaAs double quantum dot. The readout scheme allows measurement with fidelity
above 90% with a 7 microsecond cycle time. Hyperfine-induced precession between
singlet and triplet states of the two-electron system are directly observed, as
nuclear Overhauser fields are quasi-static on the time scale of the measurement
cycle. Repeated measurements on millisecond to second time scales reveal
evolution of the nuclear environment.Comment: supplemental material at
http://marcuslab.harvard.edu/papers/single_shot_sup.pd
Two-way time transfers between NRC/NBS and NRC/USNO via the Hermes (CTS) satellite
At each station the differences were measured between the local UTC seconds pulse and the remote UTC pulse received by satellite. The difference between the readings, if station delays are assumed to be symmetrical, is two times the difference between the clocks at the two ground station sites. Over a 20-minute period, the precision over the satellite is better than 1 ns. The time transfer from NRC to the CRC satellite terminal near Ottawa and from NBS to the Denver HEW terminal was examined
Polarization and readout of coupled single spins in diamond
We study the coupling of a single nitrogen-vacancy center in diamond to a
nearby single nitrogen defect at room temperature. The magnetic dipolar
coupling leads to a splitting in the electron spin resonance frequency of the
nitrogen-vacancy center, allowing readout of the state of a single nitrogen
electron spin. At magnetic fields where the spin splitting of the two centers
is the same we observe a strong polarization of the nitrogen electron spin. The
amount of polarization can be controlled by the optical excitation power. We
combine the polarization and the readout in time-resolved pump-probe
measurements to determine the spin relaxation time of a single nitrogen
electron spin. Finally, we discuss indications for hyperfine-induced
polarization of the nitrogen nuclear spin
Planar ion trap (retarding potential analyzer) experiment for atmosphere explorer
The retarding potential analyzer and drift meter were carried aboard all three Atmosphere Explorer spacecraft. These instruments measure the total thermal ion concentration and temperature, the bulk thermal ion velocity vector and some limited properties of the relative abundance of H(+), He(+), O(+) and molecular ions. These instruments functioned with no internal failures on all the spacecraft. On AE-E there existed some evidence for external surface contamination that damaged the integrity of the RPA sweep grids. This led to some difficulties in data reduction and interpretation that did not prove to be a disastrous problem. The AE-D spacecraft functioned for only a few months before it re-entered. During this time the satellite suffered from a nutation about the spin axis of about + or - 2 deg. This 2 deg modulation was superimposed upon the ion drift meter horizontal ion arrival angle output requiring the employment of filtering techniques to retrieve the real data
Latched Detection of Excited States in an Isolated Double Quantum Dot
Pulsed electrostatic gating combined with capacitive charge sensing is used
to perform excited state spectroscopy of an electrically isolated
double-quantum-dot system. The tunneling rate of a single charge moving between
the two dots is affected by the alignment of quantized energy levels; measured
tunneling probabilities thereby reveal spectral features. Two pulse sequences
are investigated, one of which, termed latched detection, allows measurement of
a single tunneling event without repetition. Both provide excited-state
spectroscopy without electrical contact to the double-dot system.Comment: related papers available at http://marcuslab.harvard.ed
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