2,338 research outputs found
Schooling, cognitive ability, and health
A large literature documents a strong correlation between health and educational outcomes. In this paper we investigate the role of cognitive ability in the health–education nexus. Using NLSY data, we show that cognitive ability accounts for roughly one quarter of the association between schooling and health. Both schooling and ability are strongly associated with health at low levels but less related or unrelated at high levels. Estimates treating schooling as endogenous to health suggest that most of the correlation between schooling and health is attributable to unobserved heterogeneity, except possibly at low levels of schooling for individuals with low cognitive ability. An implication is that policies which increase schooling will only increase health to the extent that they increase the education of poorly-educated individuals; subsidies to college education, for example, are unlikely to increase population health.education, health, intelligence, correlated random coefficient
Schooling, cognitive ability, and health
A large literature documents a strong correlation between health and educational outcomes. In this paper we investigate the role of cognitive ability in the health–education nexus. Using NLSY data, we show that cognitive ability accounts for roughly one quarter of the association between schooling and health. Both schooling and ability are strongly associated with health at low levels but less related or unrelated at high levels. Estimates treating schooling as endogenous to health suggest that most of the correlation between schooling and health is attributable to unobserved heterogeneity, except possibly at low levels of schooling for individuals with low cognitive ability. An implication is that policies which increase schooling will only increase health to the extent that they increase the education of poorly-educated individuals; subsidies to college education, for example, are unlikely to increase population health.education, health, intelligence, correlated random coefficient models
The existence and detection of optically dark galaxies by 21cm surveys
One explanation for the disparity between Cold Dark Matter (CDM) predictions
of galaxy numbers and observations could be that there are numerous dark
galaxies in the Universe. These galaxies may still contain baryons, but no
stars, and may be detectable in the 21cm line of atomic hydrogen. The results
of surveys for such objects, and simulations that do/do not predict their
existence, are controversial. In this paper we use an analytical model of
galaxy formation, consistent with CDM, to firstly show that dark galaxies are
certainly a prediction of the model. Secondly, we show that objects like
VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are
predicted by the model. Thirdly, we show that previous 'blind' HI surveys have
placed few constraints on the existence of dark galaxies. This is because they
have either lacked the sensitivity and/or velocity resolution or have not had
the required detailed optical follow up. We look forward to new 21cm blind
surveys (ALFALFA and AGES) using the Arecibo multi-beam instrument which should
find large numbers of dark galaxies if they exist
Using Capacitive Probes in Electromagnetic Nondestructive Testing
In an attempt to expand the scope of electromagnetic testing to include poorly conducting materials, we have tried using a low frequency capacitive probe. This probe has given promising performances in testing materials with resistivities of several hundred ohm-centimeters
Eddy Current Probe Design and Matched Filtering for Optimum Flaw Detection
Eddy current signals obtained from variations in the probe liftoff are in general much larger in amplitude than the useful flaw signals. Small flaw signals can, however, be detected in the presence of liftoff noise if a large enough phase angle exists between them. Figure 1(a) shows how this phase discrimination can help in liftoff noise suppression. Here, the oscilloscope traces the complex impedance of the probe. The impedance plane has been rotated so that the liftoff noise lies entirely in the horizontal channel. Now if we choose to look only at the signal in the vertical channel of the scope, or the Q channel (in phase quadrature with liftoff), there will be no liftoff noise. This, however, is not a very realistic picture. Figure 1(b) is obtained when we try to detect much smaller flaws (in this case a closed crack of 20 mils in aluminum). We see that the trace of the liftoff noise has a curvature and that there are also fluctuations along the Q channel axis. Both of these effects eventually limit the detectability of small flaws. Since this contribution of liftoff to the Q channel is in practice larger than circuit noise, we define the detection figure of merit for an EC probe as 1D=(ΔZf)sinβ(ΔZℓO)Q
Capacitive Arrays for Robotic Sensing
Electromagnetic arrays have been used effectively for many years in optimizing the responses of antenna systems. The basic principles that make arrayed antennas work and make them easy to control can also be applied to near field electromagnetic array sensors. The array factor allows for flexibility in sensor geometry. Firstly, by exciting only a portion of an array in a sequential fashion one can physically scan and interrogate a region of a sample without having to move the sample or the probe head itself. Secondly, the field configurations can be altered by selectively exciting electrodes of an array. Also, the information received can be selected by combining electrodes to form different effective receiver geometries. Thirdly, array configurations allow for real-time analog signal processing. For instance, one can perform pattern matching by choosing the spatial resolution of the probe to match the spatial resolution of the desired feature
{\sc CosmoNet}: fast cosmological parameter estimation in non-flat models using neural networks
We present a further development of a method for accelerating the calculation
of CMB power spectra, matter power spectra and likelihood functions for use in
cosmological Bayesian inference. The algorithm, called {\sc CosmoNet}, is based
on training a multilayer perceptron neural network. We compute CMB power
spectra (up to ) and matter transfer functions over a hypercube in
parameter space encompassing the confidence region of a selection of
CMB (WMAP + high resolution experiments) and large scale structure surveys (2dF
and SDSS). We work in the framework of a generic 7 parameter non-flat
cosmology. Additionally we use {\sc CosmoNet} to compute the WMAP 3-year, 2dF
and SDSS likelihoods over the same region. We find that the average error in
the power spectra is typically well below cosmic variance for spectra, and
experimental likelihoods calculated to within a fraction of a log unit. We
demonstrate that marginalised posteriors generated with {\sc CosmoNet} spectra
agree to within a few percent of those generated by {\sc CAMB} parallelised
over 4 CPUs, but are obtained 2-3 times faster on just a \emph{single}
processor. Furthermore posteriors generated directly via {\sc CosmoNet}
likelihoods can be obtained in less than 30 minutes on a single processor,
corresponding to a speed up of a factor of . We also demonstrate the
capabilities of {\sc CosmoNet} by extending the CMB power spectra and matter
transfer function training to a more generic 10 parameter cosmological model,
including tensor modes, a varying equation of state of dark energy and massive
neutrinos. {\sc CosmoNet} and interfaces to both {\sc CosmoMC} and {\sc
Bayesys} are publically available at {\tt
www.mrao.cam.ac.uk/software/cosmonet}.Comment: 8 pages, submitted to MNRA
Interaction of Lamb modes with two-level systems in amorphous nanoscopic membranes
Using a generalized model of interaction between a two-level system (TLS) and
an arbitrary deformation of the material, we calculate the interaction of Lamb
modes with TLSs in amorphous nanoscopic membranes. We compare the mean free
paths of the Lamb modes with different symmetries and calculate the heat
conductivity . In the limit of an infinitely wide membrane, the heat
conductivity is divergent. Nevertheless, the finite size of the membrane
imposes a lower cut-off for the phonons frequencies, which leads to the
temperature dependence . This temperature dependence
is a hallmark of the TLS-limited heat conductance at low temperature.Comment: 9 pages, 2 figure
Herbicide impacts on exotic grasses and a population of the critically endangered herb "Calystegia affinis" (Convolvulaceae) on Lord Howe Island
Introduced perennial grasses are capable of altering the habitat of native species, causing reductions in population size and vigour, and potentially affecting life-history processes such as survival, pollination and seedling recruitment. We examined the utility of herbicide treatment on two exotic grasses, Pennisetum clandestinum (Kikuyu) and Stenotaphrum secundatum (Buffalo grass) to restore the habitat of Calystegia affinis, a critically endangered species endemic to Lord Howe and Norfolk Islands. Using two herbicides, Asset (designed to affect only grasses) and Glyphosate (a general herbicide), we compared effectiveness in reducing grass cover on a population of Calystegia affinis. We protected Calystegia plants from the herbicides by ensuring their leaves were covered by plastic bags during herbicide application. Both herbicides were similarly effective in reducing grass cover after four weeks and had no noticeable adverse affect on Calystegia (suggesting the plastic bag protection was effective). After 26 weeks, Glyphosate was more effective in maintaining a reduced grass cover. Plots treated with either herbicide had a greater relative increase in abundance of Calystegia stems compared to untreated controls. The Glyphosate treatment resulted in the greatest relative increase in stem abundance, but this was not significantly greater than in the Asset treatment. We consider that spraying with Glyphosate treatment, with follow-up monitoring and spot-spraying, will assist the recovery of the Calystegia affinis population. Ultimately, the maintenance of a weed-free zone at the forest edge will provide suitable habitat for additional recruitment of this and other native species
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