8,823 research outputs found
Following in Your Parents' Footsteps? Empirical Analysis of Matched Parent-Offspring Test Scores
In this paper, we explore whether an intergenerational relationship exists between the reading and mathematics test scores, taken at ages 7, 11 and 16, of a cohort of individuals born in 1958 and the equivalent test scores of their offspring measured in 1991. Our results suggest that how the parent performs in reading and mathematics during their childhood is positively related to the corresponding reading and mathematics test scores of their offspring as measured at a similar age. Our findings imply that parental ability in numeracy and literacy as a child is positively associated with the ability in numeracy and literacy of their offspring. With respect to gender, a father´s (mother´s) test score generally has a positive influence on the test scores of their daughter (son)
Solar Atmospheric Oscillations and the Chromospheric Magnetic Topology
We investigate the oscillatory properties of the quiet solar chromosphere in
relation to the underlying photosphere, with particular regard to the effects
of the magnetic topology. We perform a Fourier analysis on a sequence of
line-of-sight velocities measured simultaneously in a photospheric (Fe I 709.0
nm) and a chromospheric line (Ca II 854.2 nm). The velocities were obtained
from full spectroscopic data acquired at high spatial resolution with the
Interferometric BIdimensional Spectrometer (IBIS). The field of view
encompasses a full supergranular cell, allowing us to discriminate between
areas with different magnetic characteristics. We show that waves with
frequencies above the acoustic cut-off propagate from the photosphere to upper
layers only in restricted areas of the quiet Sun. A large fraction of the quiet
chromosphere is in fact occupied by ``magnetic shadows'', surrounding network
regions, that we identify as originating from fibril-like structures observed
in the core intensity of the Ca II line. We show that a large fraction of the
chromospheric acoustic power at frequencies below the acoustic cut-off,
residing in the proximity of the magnetic network elements, directly propagates
from the underlying photosphere. This supports recent results arguing that
network magnetic elements can channel low-frequency photospheric oscillations
into the chromosphere, thus providing a way to input mechanical energy in the
upper layers.Comment: 4 pages, 3 figure, A&A Letters in pres
An Examination of Informed Traders and the Market Microstructure of Real Estate Investment Trusts
A significant body of research exists documenting that REITs perform differently from other types of equity securities, although the reasons for these differences are unclear. This study examines the intraday trading behavior of Real Estate Investment Trusts (REITs). Specifically, intraday REIT returns, volume, trading activity, and bid/ask spread are examined in an attempt to better understand the patterns of intraday information flow for a sample of REITs trading on the NYSE. After controlling for differences in market capitalization, share price, and institutional holdings, this paper analyzes differences between REITs and non-REITs, and between REITs that are widely held by institutions and those that are not. The results suggest that, as a group, REITs exhibit lower average volumes and number of trades than do similar non-REITs. In addition, the findings suggest that mortgage REITs trade at spreads that are wider. Surprisingly, the analysis of institutional ownership suggests that equity REITs that are widely held by institutions exhibit the largest divergence from non-REITs in terms of both intraday trading activity and volume, but at the same time trade closer to non-REITs in terms of bid/ask spread. Overall, the results of this study confirm that REITs are treated differently by investors than similar non-REITs, and the institutional ownership findings suggest that trading activity is less important as a determinant of REIT performance than is the level of institutional ownership.
REIT Pricing Efficiency; Should Investors Still Be Concerned?
This study examines the impact of the REIT boom on the market microstructure of REIT common stocks. We analyze NYSE-traded REITs during the pre-boom period (1992) and the post-boom period (1994), and find significant reductions in bid/ask spreads over the period. We also find that the bid/ask spread differential between REITs and non-REITs has been roughly halved between 1991 and 1994. These reductions provide a direct benefit to REIT investors in terms of reduction in transaction costs and improved liquidity, and suggest that the level of uncertainty on the part of the REIT specialist has been reduced.
Quantum effects in the diffusion of hydrogen on Ru(0001)
An understanding of hydrogen diffusion on metal surfaces is important, not
just for its role in heterogeneous catalysis and hydrogen fuel cell technology,
but also because it provides model systems where tunneling can be studied under
well-defined conditions. Here we report helium spin-echo measurements of the
atomic-scale motion of hydrogen on the Ru(0001) surface between 75 and 250 K.
Quantum effects are evident at temperatures as high as 200 K, while below 120 K
we observe a tunneling-dominated temperature independent jump rate of
1.910 s, many orders of magnitude faster than previously
seen. Quantum transition state theory calculations based on ab initio
path-integral simulations reproduce the temperature dependence of the rate at
higher temperatures and predict a crossover to tunneling-dominated diffusion at
low temperatures, although the tunneling rate is under-estimated, highlighting
the need for future experimental and theoretical studies of hydrogen diffusion
on well-defined surfaces.Comment: 15 pages, 3 figure
Magnetic suspension and balance system advanced study
An improved compact design for a superconducting magnetic suspension and balance system for an 8 ft. x 8 ft. transonic wind tunnel is developed. The original design of an MSBS in NASA Cr-3802 utilized 14 external superconductive coils and a superconductive solenoid in the airplane test model suspended in a wind tunnel. The improvements are in the following areas: test model solenoid options, dynamic force limits on the model, magnet cooling options, structure and cryogenic designs, power supply specifications, and cost and performance evaluations. The improvements are: MSBS cost reduction of 28%, weight; reduction of 43%, magnet system ampere-meter reduction of 38%, helium liquifier capacity reduction by 33%, magnet system stored energy reduction by 55%, AC loss to liquid helium reduced by 76%, system power supply reduced by 68%, test coil pole strength increased by 19%, wing magnetization increased by 40%, and control frequency limit increased by 200% from 10 Hz to 30 Hz. The improvements are due to: magnetic holmium coil forms in the test model, better rare earth permanent magnets in the wings, fiberglass-epoxy structure replacing stainless steel, better coil configuration, and new saddle roll coil design
Fetal Cortical Transplants in Adult Rats Subjected to Experimental Brain Injury
Fetal cortical tissue was injected into injured adult rat brains following concussive fluid percussion (FP) brain injury. Rats subjected to moderate FP injury received E16 cortex transplant injections into lesioned motor cortex 2 days, 1 week, 2 weeks, and 4 weeks post injury. Histological assessment of transplant survival and integration was based upon Nissl staining, glial fibrillary acidic protein (GFAP) immunocytochemistry, and staining for acetylcholinesterase. In addition to histological analysis, the ability of the transplants to attenuate neurological motor deficits associated with concussive FP brain injury was also tested. Three subgroups of rats receiving transplant 1 week, 2 weeks, and 4 weeks post injury Were chosen for evaluation of neurological motor function. Fetal cortical tissue injected into the injury site 4 weeks post injury failed to incorporate with injured host brain, did not affect glial scar formation, and exhibited extensive GFAP immunoreactivity. No improvement in neurological motor function was observed in animals receiving transplants 4 weeks post injury. Conversely, transplants injected 2 days, 1 week, or 2 weeks post injury survived, incorporated with host brain, exhibited little GFAP immunoreactivity, and successfully attenuated glial scarring. However, no significant improvement in motor function was observed at the one week or two week time points. The inability of the transplants to attenuate motor function may indicate inappropriate host/transplant interaction. Our results demonstrate that there exists a temporal window in which fetal cortical transplants can attenuate glial scarring as well as be successfully incorporated into host brains following FP injury
Repulsive force support system feasibility study
A new concept in magnetic levitation and control is introduced for levitation above a plane. A set of five vertical solenoid magnets mounted flush below the plane supports and controls the model in five degrees of freedom. The compact system of levitation coils is contained in a space 2.4 m (96 in) diameter by 1 m (40 in) deep with the top of the levitation system 0.9 m (36 in) below the center line of the suspended model. The levitated model has a permanent magnet core held in position by the five parallel superconductive solenoids symmetrically located in a circle. The control and positioning system continuously corrects for model position in five dimensions using computer current pulses superimposed on the levitation coil base currents. The conceptual designs include: superconductive and Nd-Fe-B permanent magnet model cores and levitation solenoids of either superconductive, cryoresistive, or room temperature windings
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