4,893 research outputs found
You can't take it with you: asset run-down at the end of the life cycle
This article presents evidence on the extent to which households run down their assets after retirement. The authors show that, once corrections are made for several econometric problems, households engage in very little asset decumulation after retirement.Retirement ; Income ; Wealth
Molecular biology on a microfluidic chip
We have developed microfluidic chips for automating molecular biology processes such as gene ligation and gene transformation from nanolitre sample volumes with parallel architecture. Unlike conventional tube methods with cumbersome pipetting procedures, all processes, including metering of samples, ligation and transformation, were carried out in the microfluidic chips through pneumatic control of the nanofluid. The microfluidic devices presented here offer an illustration of some of the basic physics that arises when trying to miniaturize and automate biological techniques
Electrical microfluidic pressure gauge for elastomer microelectromechanical systems
We report on an electrical microfluidic pressure gauge. A polydimethylsiloxane microvalve closes at a characteristic applied pressure determined by the material's properties and the valve's dimensions. Hence, when the same pressure is applied to all valves of a heterogeneous valve array, some valves close while others remain open. The state of the array is combined with knowledge of the respective characteristic closing pressures of the individual valves to yield an estimate of the applied pressure. The state of each valve is obtained by electrical measurements, since the electrical resistance of the respective underlying fluid-filled channel increases by at least two orders of magnitude as the valve closes and its insulating elastomer material interrupts the electrical circuit. The overall system functions as a pressure gauge with electrical readout. This device would be a critical component in active pressure-regulation loops in future integrated microfluidic systems
Experimentally validated quantitative linear model for the device physics of elastomeric microfluidic valves
A systematic experimental study and theoretical modeling of the device physics of polydimethylsiloxane âpushdownâ microfluidic valves are presented. The phase space is charted by 1587 dimension combinations and encompasses 45â295 ”m lateral dimensions, 16â39 ”m membrane thickness, and 1â28 psi closing pressure. Three linear models are developed and tested against the empirical data, and then combined into a fourth-power-polynomial superposition. The experimentally validated final model offers a useful quantitative prediction for a valve's properties as a function of its dimensions. Typical valves (80â150 ”m width) are shown to behave like thin springs
Uranus and Neptune: Shape and Rotation
Both Uranus and Neptune are thought to have strong zonal winds with
velocities of several hundred meters per second. These wind velocities,
however, assume solid-body rotation periods based on Voyager 2 measurements of
periodic variations in the planets' radio signals and of fits to the planets'
magnetic fields; 17.24h and 16.11h for Uranus and Neptune, respectively. The
realization that the radio period of Saturn does not represent the planet's
deep interior rotation and the complexity of the magnetic fields of Uranus and
Neptune raise the possibility that the Voyager 2 radio and magnetic periods
might not represent the deep interior rotation periods of the ice giants.
Moreover, if there is deep differential rotation within Uranus and Neptune no
single solid-body rotation period could characterize the bulk rotation of the
planets. We use wind and shape data to investigate the rotation of Uranus and
Neptune. The shapes (flattening) of the ice giants are not measured, but only
inferred from atmospheric wind speeds and radio occultation measurements at a
single latitude. The inferred oblateness values of Uranus and Neptune do not
correspond to bodies rotating with the Voyager rotation periods. Minimization
of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by
the single occultation radii and gravitational coefficients of the planets,
leads to solid-body rotation periods of ~16.58h for Uranus and ~17.46h for
Neptune. Uranus might be rotating faster and Neptune slower than Voyager
rotation speeds. We derive shapes for the planets based on these rotation
rates. Wind velocities with respect to these rotation periods are essentially
identical on Uranus and Neptune and wind speeds are slower than previously
thought. Alternatively, if we interpret wind measurements in terms of
differential rotation on cylinders there are essentially no residual
atmospheric winds.Comment: Accepted for publication in Icarus, 20 pages, 4 tables, 9 figure
A Numerical Approach to Space-Time Finite Elements for the Wave Equation
We study a space-time finite element approach for the nonhomogeneous wave
equation using a continuous time Galerkin method. We present fully implicit
examples in 1+1, 2+1, and 3+1 dimensions using linear quadrilateral,
hexahedral, and tesseractic elements. Krylov solvers with additive Schwarz
preconditioning are used for solving the linear system. We introduce a time
decomposition strategy in preconditioning which significantly improves
performance when compared with unpreconditioned cases.Comment: 9 pages, 5 figures, 5 table
Spectral ergodicity and normal modes in ensembles of sparse matrices
We investigate the properties of sparse matrix ensembles with particular
regard for the spectral ergodicity hypothesis, which claims the identity of
ensemble and spectral averages of spectral correlators. An apparent violation
of the spectral ergodicity is observed. This effect is studied with the aid of
the normal modes of the random matrix spectrum, which describe fluctuations of
the eigenvalues around their average positions. This analysis reveals that
spectral ergodicity is not broken, but that different energy scales of the
spectra are examined by the two averaging techniques. Normal modes are shown to
provide a useful complement to traditional spectral analysis with possible
applications to a wide range of physical systems.Comment: 22 pages, 15 figure
Parallel Picoliter RT-PCR Assays Using Microfluidics
The development of microfluidic tools for high-throughput nucleic acid analysis has become a burgeoning area of research in the post-genome era. Here, we have developed a microfluidic chip to perform 72 parallel 450-pL RT-PCRs. We took advantage of Taqman hydrolysis probe chemistry to detect RNA templates as low as 34 copies. The device and method presented here may enable highly parallel single cell gene expression analysis
A new chronology for the Moon and Mercury
In this paper we present a new method for dating the surface of the Moon,
obtained by modeling the incoming flux of impactors and converting it into a
size distribution of resulting craters. We compare the results from this model
with the standard chronology for the Moon showing their similarities and
discrepancies. In particular, we find indications of a non-constant impactor
flux in the last 500 Myr and also discuss the implications of our findings for
the Late Heavy Bombardment hypothesis. We also show the potential of our model
for accurate dating of other inner Solar System bodies, by applying it to
Mercury.Comment: 27 pages, 13 figures, 1 table; accepted by A
Executive functioning (fully) and processing speed (mostly) mediate intelligence deficits in children born very preterm
Children born very preterm (<32 weeks gestational age) are known to be at increased risk of neurocognitive impairments, in domains including executive functioning, processing speed, and fluid and crystallised intelligence. Given the close association between these constructs, the current study investigated a specific model, namely whether executive functioning and/or processing speed mediates the relationship between preterm birth and intelligence. Participants were 204 children born very preterm and 98 full-term children, who completed a battery of tasks measuring executive functioning, processing speed, and fluid and crystallised intelligence. Independent-samples t-tests found significantly poorer performance by children born preterm on all measures, and a confirmatory factor analysis found preterm birth to be significantly related to each of the cognitive domains. A latent-variable mediation model found that executive functioning fully mediated the associations between preterm birth and both fluid and crystallised intelligence. Processing speed fully mediated the preterm birth-fluid intelligence association, but only partially mediated the preterm birth-crystallised intelligence association. Future research should consider a longitudinal study design to test whether these deficits and mediating effects remain throughout childhood and adolescence
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