25,935 research outputs found
Observations of fast anisotropic ion heating, ion cooling, and ion recycling in large-amplitude drift waves
Large-amplitude drift wave fluctuations are observed to cause severe ion temperature oscillations in plasmas of the Caltech Encore tokamak [J. M. McChesney, P. M. Bellan, and R. A. Stern, Phys. Fluids B 3, 3370 (1991)]. Experimental investigations of the complete ion dynamical behavior in these waves are presented. The wave electric field excites stochastic ion orbits in the plane normal (perpendicular to) to B, resulting in rapid perpendicular to heating. Ion-ion collisions impart energy along (parallel to) B, relaxing the perpendicular to-parallel to temperature anisotropy. Hot ions with large orbit radii escape confinement, reaching the chamber wall and cooling the distribution. Cold ions from the plasma edge convect back into the plasma (i.e., recycle), causing further cooling and significantly replenishing the density depleted by orbit losses. The ion-ion collision period tau(ii)similar to Tau(3/2)/n fluctuates strongly with the drift wave phase, due to intense (approximate to 50%) fluctuations in n and Tau. Evidence for particle recycling is given by observations of bimodal ion velocity distributions near the plasma edge, indicating the presence of cold ions (0.4 eV) superposed atop the hot (4-8 eV) plasma background. These appear periodically, synchronous with the drift wave phase at which ion fluid flow from the wall toward the plasma center peaks. Evidence is presented that such a periodic heat/loss/recycle/cool process is expected in plasmas with strong stochastic heating
Real-time phase-selective data acquisition system for measurement of wave phenomena in pulsed plasma discharges
A novel data acquisition system and methodology have been developed for the study of wave phenomena in pulsed plasma discharges. The method effectively reduces experimental uncertainty due to shot-to-shot fluctuations in high repetition rate experiments. Real-time analysis of each wave form allows classification of discharges by wave amplitude, phase, or other features. Measurements can then be constructed from subsets of discharges having similar wave properties. The method clarifies the trade-offs between experimental uncertainty reduction and increased demand for data storage capacity and acquisition time. Finally, this data acquisition system is simple to implement and requires relatively little equipment: only a wave form digitizer and a moderately fast computer
Coherent control of microwave pulse storage in superconducting circuits
Coherent pulse control for quantum memory is viable in the optical domain but
nascent in microwave quantum circuits. We show how to realize coherent storage
and on-demand pulse retrieval entirely within a superconducting circuit by
exploiting and extending existing electromagnetically induced transparency
technology in superconducting quantum circuits. Our scheme employs a linear
array of superconducting artificial atoms coupled to a microwave transmission
line.Comment: 13 pages, 4 figures and some supplementary materia
Radiation-induced nucleic acid synthesis in L cells under energy deprivation
Radiation induced nucleic acid synthesis in energy deprived L cell
On Non-Commutative Integrable Burgers Equations
We construct the recursion operators for the non-commutative Burgers
equations using their Lax operators. We investigate the existence of any
integrable mixed version of left- and right-handed Burgers equations on higher
symmetry grounds.Comment: 8 page
Quantum walk on a line for a trapped ion
We show that a multi-step quantum walk can be realized for a single trapped
ion with interpolation between quantum and random walk achieved by randomizing
the generalized Hadamard coin flip phase. The signature of the quantum walk is
manifested not only in the ion's position but also its phonon number, which
makes an ion trap implementation of the quantum walk feasible.Comment: 5 pages, 3 figure
Quantum informatics with plasmonic metamaterials
Surface polaritons at a meta-material interface are proposed as qubits. The
SP fields are shown to have low losses, subwavelength confinement and can
demonstrate very small modal volume. These important properties are used to
demonstatre interesting applications in quantum information, i.e., coherent
control of weak fields and large Kerr nonlinearity at the low photon level
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A high resolution coupled hydrologic–hydraulic model (HiResFlood-UCI) for flash flood modeling
HiResFlood-UCI was developed by coupling the NWS's hydrologic model (HL-RDHM) with the hydraulic model (BreZo) for flash flood modeling at decameter resolutions. The coupled model uses HL-RDHM as a rainfall-runoff generator and replaces the routing scheme of HL-RDHM with the 2D hydraulic model (BreZo) in order to predict localized flood depths and velocities. A semi-automated technique of unstructured mesh generation was developed to cluster an adequate density of computational cells along river channels such that numerical errors are negligible compared with other sources of error, while ensuring that computational costs of the hydraulic model are kept to a bare minimum. HiResFlood-UCI was implemented for a watershed (ELDO2) in the DMIP2 experiment domain in Oklahoma. Using synthetic precipitation input, the model was tested for various components including HL-RDHM parameters (a priori versus calibrated), channel and floodplain Manning n values, DEM resolution (10 m versus 30 m) and computation mesh resolution (10 m+ versus 30 m+). Simulations with calibrated versus a priori parameters of HL-RDHM show that HiResFlood-UCI produces reasonable results with the a priori parameters from NWS. Sensitivities to hydraulic model resistance parameters, mesh resolution and DEM resolution are also identified, pointing to the importance of model calibration and validation for accurate prediction of localized flood intensities. HiResFlood-UCI performance was examined using 6 measured precipitation events as model input for model calibration and validation of the streamflow at the outlet. The Nash–Sutcliffe Efficiency (NSE) obtained ranges from 0.588 to 0.905. The model was also validated for the flooded map using USGS observed water level at an interior point. The predicted flood stage error is 0.82 m or less, based on a comparison to measured stage. Validation of stage and discharge predictions builds confidence in model predictions of flood extent and localized velocities, which are fundamental to reliable flash flood warning
Gyroscopes based on nitrogen-vacancy centers in diamond
We propose solid-state gyroscopes based on ensembles of negatively charged
nitrogen-vacancy () centers in diamond. In one scheme, rotation of
the nitrogen-vacancy symmetry axis will induce Berry phase shifts in the electronic ground-state coherences proportional to the solid angle
subtended by the symmetry axis. We estimate sensitivity in the range of
in a 1 sensor volume using
a simple Ramsey sequence. Incorporating dynamical decoupling to suppress
dipolar relaxation may yield sensitivity at the level of . With a modified Ramsey scheme, Berry phase shifts in the
hyperfine sublevels would be employed. The projected sensitivity
is in the range of , however the smaller
gyromagnetic ratio reduces sensitivity to magnetic-field noise by several
orders of magnitude. Reaching would represent
an order of magnitude improvement over other compact, solid-state gyroscope
technologies.Comment: 3 figures, 5 page
How rare are diffusive rare events?
We study the time until first occurrence, the first-passage time, of rare
density fluctuations in diffusive systems. We approach the problem using a
model consisting of many independent random walkers on a lattice. The existence
of spatial correlations makes this problem analytically intractable. However,
for a mean-field approximation in which the walkers can jump anywhere in the
system, we obtain a simple asymptotic form for the mean first-passage time to
have a given number k of particles at a distinguished site. We show
numerically, and argue heuristically, that for large enough k, the mean-field
results give a good approximation for first-passage times for systems with
nearest-neighbour dynamics, especially for two and higher spatial dimensions.
Finally, we show how the results change when density fluctuations anywhere in
the system, rather than at a specific distinguished site, are considered.Comment: 6 pages, 5 figures. Accepted for publication in Europhysics Letters
(http://www.iop.org/EJ/journal/EPL
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