How Do Mortgage Subsidies Affect Home Ownership? Evidence from the Mid-century GI Bills

The largest 20th-century increase in U.S. home ownership occurred between 1940 and 1960, associated largely with declining age at first ownership. I shed light on the contribution of coincident government mortgage market interventions by examining home loan benefits granted under the World War II and Korean War GI Bills. The impact of veterans' housing benefits on home ownership is positive for young men, and declines with age. Veterans' benefits increased aggregate home ownership rates primarily by shifting purchase earlier in life, explaining 7.4 percent of the overall 1940-60 increase and 25 percent of the increase for affected cohorts. A rough extrapolation suggests that broader changes in mortgage terms may explain 40 percent of the 1940-60 increase.

Correlation potentials for molecular bond dissociation within the self-consistent random phase approximation

Self-consistent correlation potentials for H$_2$ 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

Statistical mechanics of Floquet systems: the pervasive problem of near degeneracies

The statistical mechanics of periodically driven ("Floquet") systems in contact with a heat bath exhibits some radical differences from the traditional statistical mechanics of undriven systems. In Floquet systems all quasienergies can be placed in a finite frequency interval, and the number of near degeneracies in this interval grows without limit as the dimension N of the Hilbert space increases. This leads to pathologies, including drastic changes in the Floquet states, as N increases. In earlier work these difficulties were put aside by fixing N, while taking the coupling to the bath to be smaller than any quasienergy difference. This led to a simple explicit theory for the reduced density matrix, but with some major differences from the usual time independent statistical mechanics. We show that, for weak but finite coupling between system and heat bath, the accuracy of a calculation within the truncated Hilbert space spanned by the N lowest energy eigenstates of the undriven system is limited, as N increases indefinitely, only by the usual neglect of bath memory effects within the Born and Markov approximations. As we seek higher accuracy by increasing N, we inevitably encounter quasienergy differences smaller than the system-bath coupling. We therefore derive the steady state reduced density matrix without restriction on the size of quasienergy splittings. In general, it is no longer diagonal in the Floquet states. We analyze, in particular, the behavior near a weakly avoided crossing, where quasienergy near degeneracies routinely appear. The explicit form of our results for the denisty matrix gives a consistent prescription for the statistical mechanics for many periodically driven systems with N infinite, in spite of the Floquet state pathologies.Comment: 31 pages, 3 figure

TURBULENCE MEASUREMENTS WITHIN A CYCLIC FLOW AND ANALYSIS IN THE MOMENTUM EQUATION

ABSTRACT Particle Image Velocimetry (PIV) measurements were performed within an optical water analog engine. A unique triggering and data collection system was developed to allow a CCD camera to acquire two consecutive image frames at predetermined crank angles. The water analog engine operated at 15 RPM and had a square cross-section with two circular valved inlets. Measurements were made throughout an entire cycle to determine mean and turbulence statistics and results at 60 crank angle degree are discussed in this paper. Different averaging techniques were used and results between the techniques were compared to provide a number of statistical quantities having large discrepancies in scales and distributions. A study of the equations of motion showed that different averaging techniques results in differing physical interpretations of the flow

The Innate Immune Receptor PGRP-LC Controls Presynaptic Homeostatic Plasticity

SummaryIt is now appreciated that the brain is immunologically active. Highly conserved innate immune signaling responds to pathogen invasion and injury and promotes structural refinement of neural circuitry. However, it remains generally unknown whether innate immune signaling has a function during the day-to-day regulation of neural function in the absence of pathogens and irrespective of cellular damage or developmental change. Here we show that an innate immune receptor, a member of the peptidoglycan pattern recognition receptor family (PGRP-LC), is required for the induction and sustained expression of homeostatic synaptic plasticity. This receptor functions presynaptically, controlling the homeostatic modulation of the readily releasable pool of synaptic vesicles following inhibition of postsynaptic glutamate receptor function. Thus, PGRP-LC is a candidate receptor for retrograde, trans-synaptic signaling, a novel activity for innate immune signaling and the first known function of a PGRP-type receptor in the nervous system of any organism

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 $S(q,\omega)$. The total noncondensate number $N'(0)$ at zero temperature increases like $R^6$, where $R$ 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 $^3$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]

Interstitials, Vacancies, and Supersolid Order in Vortex Crystals

Interstitials and vacancies in the Abrikosov phase of clean Type II superconductors are line imperfections, which cannot extend across macroscopic equilibrated samples at low temperatures. We argue that the entropy associated with line wandering nevertheless can cause these defects to proliferate at a sharp transition which will exist if this occurs below the temperature at which the crystal actually melts. Vortices are both entangled and crystalline in the resulting ``supersolid'' phase, which in a dual ``boson'' analog system is closely related to a two-dimensional quantum crystal of He$^4$ with interstitials or vacancies in its ground state. The supersolid {\it must} occur for $B\gg B_\times$, where $B_\times$ is the decoupling field above which vortices begin to behave two-dimensionally. Numerical calculations show that interstitials, rather than vacancies, are the preferred defect for $B\gg \phi_0/\lambda_\perp^2$, and allow us to estimate whether proliferation also occurs for B\,\lot\,B_\times.The implications of the supersolid phase for transport measurements, dislocation configurations and neutron diffraction are discussed.Comment: 53 pages and 15 figures, available upon request, written in plain TE

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 short‐term and long‐term signals. We find that short‐term, 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. Long‐term signals occur over broader areas and are ultimately caused by long‐term 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. Short‐term, seasonal ground deformation is caused by compaction of shallower aquifers used for the majority of groundwater production whereas long‐term 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