12,670 research outputs found

    Rates of public health insurance coverage for children rise as rates of private coverage decline

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    This brief uses data from the 2008, 2009, and 2010 American Community Survey to document changes in rates of children’s health insurance, between private and public. The authors report that, nationally, private health insurance for children decreased by just under 2 percentage points, while public health insurance increased by nearly 3 percentage points. Rural places and central cities witnessed significant declines in rates of private health insurance for children in nearly every region. Rates of public insurance coverage rose in every region and place type. Children’s health insurance coverage overall continued to rise in 2010, increasing by 0.6 of a percentage point since 2009, and 1.9 percentage points since 2008

    Financial frictions and the monetary transmission mechanism: theory, evidence and policy implications

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    This paper provides a brief survey of the role of financial frictions in the monetary transmission mechanism. After noting some of the key stylised facts that any model of the transmission mechanisms must be consistent with, we discuss both the classical interest rate channel and the credit and bank lending channels of monetary transmission. We then review the empirical evidence relating to the relative importance of these channels. Finally we consider what impact the presence of significant financial frictions might have on the conduct of monetary policy JEL Classification: E52, E58, E44bank-lending channel, credit channel, monetary policy, transmission mechanism

    Reliability assessment of the 1964 mariner mars spacecraft

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    Numerical exercise of reliability model of Mariner Mars spacecraft and spacecraft subsystems reliabilit

    Prebiotic synthesis of nucleic acids

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    The origin of the first RNA polymers is central to most current theories regarding the origin of life. However, difficulties associated with the prebiotic formation of RNA have lead many researchers to conclude that simpler polymers, or proto-RNAs, preceded RNA. These earlier polymers would have been replaced by RNA over the course of evolution. A remaining difficulty for this theory is that the de novo synthesis of a feasible proto-RNA has not yet been demonstrated by plausible prebiotic reactions. This thesis focuses on two problems associated with prebiotic proto-RNA synthesis: The formation of nucleosides and the necessity of reversible backbone linkages for error correction in nucleic acid polymers. "The Nucleoside Problem", or the lack of success in forming pyrimidine nucleosides by plausible prebiotic reactions, represents a significant stumbling block to the RNA world hypothesis. Nearly four decades ago Orgel and coworkers demonstrated that the purine nucleosides adenosine and inosine are synthesized by heating and drying their respective bases and ribose in the presence of magnesium, but these reaction conditions do not yield the pyrimidine nucleosides uridine or cytidine from their respective bases. In this thesis a potential solution to The Nucleoside Problem is hypothesized based upon a proposed chemical mechanism for nucleoside formation. This hypothesis is supported by the successful synthesis of 2-pyrimidinone nucleosides by a plausible prebiotic reaction in good yield, demonstrating that pyrimidine nucleosides could have been available in the prebiotic chemical inventory, but that uridine and cytidine were likely not abundant. Reversible backbone linkages are necessary to provide a mechanism for error correction in non-enzymatic template-directed syntheses of proto-RNAs. In this thesis, acetals are explored as low-energy, reversible linkage groups for nucleosides in polymers. The synthesis of glyoxylate-acetal nucleic acids (gaNAs) through simple heating-drying reactions from neutral aqueous solutions is demonstrated, and these linkages are shown to be hydrolytically stable under a considerable range of solution conditions. Computational models demonstrate that the glyoxylate linkage is an excellent electronic and isosteric replacement for phosphate. Molecular dynamics simulations also indicate that a gaNA duplex would have structural properties that closely match a phosphate-linked RNA helix, suggesting the possibility for cross-pairing between gaNAs and RNAs, allowing for sequence transfer and genetic continuity through the evolution from proto-RNAs to RNA. The principles illustrated in this thesis by 2-pyrimidinone nucleoside and gaNA synthesis can be extended to other prebiotic condensation reactions. Factors affecting condensation yield, such as thermodynamics, kinetics, reactant solubility, and salt effects, are summarized herein.Ph.D.Committee Chair: Hud, Nicholas V.; Committee Member: Fox, Ronald F.; Committee Member: Lynn, David G.; Committee Member: Powers, James C.; Committee Member: Wartell, Roger M.; Committee Member: Williams, Loren D

    Letter from C. D. Bean to Representative Burdick Regarding Need for Barge to Ferry Trucks Across the Lake Created by the Garrison Dam, September 5, 1957

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    This letter, dated September 5, 1957, from Federal Supply Service Commissioner C. D. Bean to United States (US) Representative Usher Burdick responds to an inquiry related to transportation for the Three Affiliated Tribes across the Garrison Reservoir. The US Department of the Interior informed Bean\u27s office that the US Bureau of Indian Affairs does not have the authority to transfer ownership of property to the tribes. Bean recommends that the tribes purchase a surplus barge and jeeps as needed and encloses information about buying surplus property. The referenced enclosed booklet is not included with this document. See also: Letter from Representative Burdick to Clifton E. Mack Regarding Need for Barge to Ferry Trucks Across the Lake Created by the Garrison Dam, May 22, 1957https://commons.und.edu/burdick-papers/1350/thumbnail.jp

    Adiabatic instability in coupled dark energy-dark matter models

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    We consider theories in which there exists a nontrivial coupling between the dark matter sector and the sector responsible for the acceleration of the universe. Such theories can possess an adiabatic regime in which the quintessence field always sits at the minimum of its effective potential, which is set by the local dark matter density. We show that if the coupling strength is much larger than gravitational, then the adiabatic regime is always subject to an instability. The instability, which can also be thought of as a type of Jeans instability, is characterized by a negative sound speed squared of an effective coupled dark matter/dark energy fluid, and results in the exponential growth of small scale modes. We discuss the role of the instability in specific coupled CDM and Mass Varying Neutrino (MaVaN) models of dark energy, and clarify for these theories the regimes in which the instability can be evaded due to non-adiabaticity or weak coupling.Comment: 20 pages, 2 figures; final published versio

    Perturbation Theory in k-Inflation Coupled to Matter

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    We consider k-inflation models where the action is a non-linear function of both the inflaton and the inflaton kinetic term. We focus on a scalar-tensor extension of k-inflation coupled to matter for which we derive a modified Mukhanov-Sasaki equation for the curvature perturbation. Significant corrections to the power spectrum appear when the coupling function changes abruptly along the inflationary trajectory. This gives rise to a modification of Starobinsky's model of perturbation features. We analyse the way the power spectrum is altered in the infrared when such features are present.Comment: 20 pages, 1 figur

    Delayed Recombination and Cosmic Parameters

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    Current cosmological constraints from Cosmic Microwave Background (CMB) anisotropies are typically derived assuming a standard recombination scheme, however additional resonance and ionizing radiation sources can delay recombination, altering the cosmic ionization history and the cosmological inferences drawn from CMB data. We show that for recent observations of CMB anisotropy, from the Wilkinson Microwave Anisotropy Probe satellite mission 5-year survey (WMAP5) and from the ACBAR experiment, additional resonance radiation is nearly degenerate with variations in the spectral index, n_s, and has a marked effect on uncertainties in constraints on the Hubble constant, age of the universe, curvature and the upper bound on the neutrino mass. When a modified recombination scheme is considered, the redshift of recombination is constrained to z_*=1078\pm11, with uncertainties in the measurement weaker by one order of magnitude than those obtained under the assumption of standard recombination while constraints on the shift parameter are shifted by 1-sigma to R=1.734\pm0.028. Although delayed recombination limits the precision of parameter estimation from the WMAP satellite, we demonstrate that this should not be the case for future, smaller angular scales measurements, such as those by the Planck satellite mission.Comment: 9 pages, 9 figure

    Can the Universe escape eternal acceleration?

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    Recent astronomical observations of distant supernovae light-curves suggest that the expansion of the universe has recently begun to accelerate. Acceleration is created by an anti-gravitational repulsive stress, like that produced by a positive cosmological constant, or universal vacuum energy. It creates a rather bleak eschatological picture. An ever-expanding universe's future appears to be increasingly dominated by its constant vacuum energy. A universe doomed to accelerate forever will produce a state of growing uniformity and cosmic loneliness. Structures participating in the cosmological expansion will ultimately leave each others' horizons and information-processing must eventually die out. Here, we examine whether this picture is the only interpretation of the observations. We find that in many well-motivated scenarios the observed spell of vacuum domination is only a transient phenomenon. Soon after acceleration starts, the vacuum energy's anti-gravitational properties are reversed, and a matter-dominated decelerating cosmic expansion resumes. Thus, contrary to general expectations, once an accelerating universe does not mean always an accelerating universe.Comment: 6 pages, 2 figure

    A Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

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    A relativistic modified gravity (MOG) theory leads to a self-consistent, stable gravity theory that can describe the solar system, galaxy and clusters of galaxies data and cosmology.Comment: 16 pages. Latex file. Talk given at the International Workshop "From Quantum to Cosmos: Fundamental Physics in Space", 22-24 May, 2006, Warrenton, Virginia, USA. To be published in Int. J. Mod. Phys D. Equation correcte
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