35 research outputs found
Correlation potentials for molecular bond dissociation within the self-consistent random phase approximation
Self-consistent correlation potentials for H and LiH for various
inter-atomic separations are obtained within the random phase approximation
(RPA) of density functional theory. The RPA correlation potential shows a peak
at the bond midpoint, which is an exact feature of the true correlation
potential, but lacks another exact feature: the step important to preserve
integer charge on the atomic fragments in the dissociation limit. An analysis
of the RPA energy functional in terms of fractional charge is given which
confirms these observations. We find that the RPA misses the derivative
discontinuity at odd integer particle numbers but explicitly eliminates the
fractional spin error in the exact-exchange functional. The latter finding
explains the accurate total energy in the dissociation limit.Comment: 9 pages, 10 figure
Excited states of a dilute Bose-Einstein condensate in a harmonic trap
The low-lying hydrodynamic normal modes of a dilute Bose-Einstein gas in an
isotropic harmonic trap determine the corresponding Bogoliubov amplitudes. In
the Thomas-Fermi limit, these modes have large low-temperature occupation
numbers, and they permit an explicit construction of the dynamic structure
function . The total noncondensate number at zero
temperature increases like , where is the condensate radius measured
in units of the oscillator length. The lowest dipole modes are constructed
explicitly in the Bogoliubov approximation.Comment: 15 pages, REVTE
Quantization of Superflow Circulation and Magnetic Flux with a Tunable Offset
Quantization of superflow-circulation and of magnetic-flux are considered for
systems, such as superfluid He-A and unconventional superconductors, having
nonscalar order parameters. The circulation is shown to be the anholonomy in
the parallel transport of the order parameter. For multiply-connected samples
free of distributed vorticity, circulation and flux are predicted to be
quantized, but generically to nonintegral values that are tunably offset from
integers. This amounts to a version of Aharonov-Bohm physics. Experimental
settings for testing these issues are discussed.Comment: 5 two-column pages, ReVTeX, figure available upon request (to
[email protected]
Quantifying Ground Deformation in the Los Angeles and Santa Ana Coastal Basins Due to Groundwater Withdrawal
We investigate complex surface deformation within the Los Angeles and Santa Ana Coastal Basins due to groundwater withdrawal and subsequent aquifer compaction/expansion. We analyze an 18 year interferometric synthetic aperture radar (InSAR) time series of 881 interferograms in conjunction with global positioning system (GPS) data within the groundwater basins. The large data set required the development of a distributed time series analysis framework able to automatically decompose both the InSAR and GPS time series into shortâterm and longâterm signals. We find that shortâterm, seasonal oscillations of ground elevations due to annual groundwater withdrawal and recharge are unsteady due to changes in seasonal withdrawal by major water districts. The spatial pattern of seasonal ground deformation near the center of the basin corresponds to a diffusion process with peak deformation occurring at locations with highest groundwater production. Longâterm signals occur over broader areas and are ultimately caused by longâterm changes in groundwater production. Comparison of the geodetic data with hydraulic head data from major water districts suggests that different regions of the groundwater system are responsible for different temporal components in the observed ground deformation. Shortâterm, seasonal ground deformation is caused by compaction of shallower aquifers used for the majority of groundwater production whereas longâterm ground deformation is correlated with delayed compaction of deeper aquifers and potential compressible clay layers. These results demonstrate the potential for geodetic analysis to be an important tool for groundwater management to maintain sustainable pumping practices
The Impact of Contact Isolation on the Quality of Inpatient Hospital Care
Background: Contact Isolation is a common hospital infection prevention method that may improve infectious outcomes but may also hinder healthcare delivery. Methods: To evaluate the impact of Contact Isolation on compliance with individual and composite process of care quality measures, we formed four retrospective diagnosis-based cohorts from a 662-bed tertiary-care medical center. Each cohor