35,701 research outputs found

    Household Saving Behaviour in New Zealand: A Cohort Analysis

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    This paper seeks to improve our understanding of household saving behaviour. It is based on an analysis of unit record data from March years 1984 to 1998 taken from the Household Economic Survey (HES). There are limitations of the data set but it provides the only available estimates of income and expenditure, from which saving is estimated as a residual. The HES is a series of cross-sectional surveys rather than a true panel, so we construct synthetic cohorts rather than tracking individual households. We use a range of regression models to separate out the effect of age, birth-year cohort and year on saving rates. The typical age profile for savings is hump-shaped, peaks around age 57 and does not become negative at older ages. Such a profile appears to have shifted down for the cohorts born between 1920 and 1939 relative to the younger and older cohorts studied. This pattern of cohort effects is robust to the inclusion of conditioning variables and to the trimming from the sample of households with either negative or very large ratios of savings to consumption. Preliminary investigation supports the hypothesis that changes in the economic and policy environment help explain the different saving behaviour of different birth cohorts. Tentative results suggest that more favourable environments are associated with lower rates of lifetime saving, although more research is needed to confirm this finding.Household saving, lifecycle, age, cohorts

    Household Saving Behaviour in New Zealand: Why do Cohorts Behave Differently?

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    The aim of this paper is to add to the understanding of saving decisions by households. The saving behaviour of households is found to differ depending on the birth cohort of the household head. This paper seeks to explain why this pattern might exist. It is based on an analysis of synthetic cohorts derived from unit record data taken from the Household Economic Survey (HES) for the March years 1984 to 1998. The need to use synthetic cohorts arises as the HES is not a longitudinal panel survey, but rather a time series of independent cross-sectional samples. We use a range of regression models to separate out the effect of age, birth-year cohort and year on saving rates. The typical saving rates for the cohorts born between 1920 and 1939 are found to be significantly lower relative to the younger and older cohorts studied. This pattern of cohort effects is robust to the inclusion of conditioning variables; to the trimming from the sample of households with either negative or very large ratios of savings to consumption, and to different definitions of saving. Some exploratory investigation supports the hypothesis that changes in the economic and policy environment help explain the different saving behaviour of different birth cohorts. Tentative results suggest that more ?favourable environments are associated with lower rates of lifetime saving.Household saving rates; cohort effects; New Zealand; economic and social policies

    Observationally-Motivated Analysis of Simulated Galaxies

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    The spatial and temporal relationships between stellar age, kinematics, and chemistry are a fundamental tool for uncovering the physics driving galaxy formation and evolution. Observationally, these trends are derived using carefully selected samples isolated via the application of appropriate magnitude, colour, and gravity selection functions of individual stars; conversely, the analysis of chemodynamical simulations of galaxies has traditionally been restricted to the age, metallicity, and kinematics of `composite' stellar particles comprised of open cluster-mass simple stellar populations. As we enter the Gaia era, it is crucial that this approach changes, with simulations confronting data in a manner which better mimics the methodology employed by observers. Here, we use the \textsc{SynCMD} synthetic stellar populations tool to analyse the metallicity distribution function of a Milky Way-like simulated galaxy, employing an apparent magnitude plus gravity selection function similar to that employed by the RAdial Velocity Experiment (RAVE); we compare such an observationally-motivated approach with that traditionally adopted - i.e., spatial cuts alone - in order to illustrate the point that how one analyses a simulation can be, in some cases, just as important as the underlying sub-grid physics employed.Comment: Accepted for publication in PoS (Proceedings of Science): Nuclei in the Cosmos XIII (Debrecen, Jul 2014); 6 pages; 3 figure

    On the Physical Origin of OVI Absorption-Line Systems

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    We present a unified analysis of the O{\sc vi} absorption-lines seen in the disk and halo of the Milky Way, high velocity clouds, the Magellanic Clouds, starburst galaxies, and the intergalactic medium. We show that these disparate systems define a simple relationship between the O{\sc vi} column density and absorption-line width that is independent of the Oxygen abundance over the range O/H \sim 10% to twice solar. We show that this relation is exactly that predicted theoretically as a radiatively cooling flow of hot gas passes through the coronal temperature regime - independent of its density or metallicity (for O/H \gtrsim 0.1 solar). Since most of the intregalactic O{\sc vi} clouds obey this relation, we infer that they can not have metallicities less than a few percent solar. In order to be able to cool radiatively in less than a Hubble time, the intergalactic clouds must be smaller than \sim1 Mpc in size. We show that the cooling column densities for the O{\sc iv}, O{\sc v}, Ne{\sc v}, and Ne{\sc vi} ions are comparable to those seen in O{\sc vi}. This is also true for the Li-like ions Ne{\sc viii}, Mg{\sc x}, and Si{\sc xii} (if the gas is cooling from T106T \gtrsim 10^6 K). All these ions have strong resonance lines in the extreme-ultraviolet spectral range, and would be accessible to FUSEFUSE at zz \gtrsim 0.2 to 0.8. We also show that the Li-like ions can be used to probe radiatively cooling gas at temperatures an order-of-magnitude higher than where their ionic fraction peaks. We calculate that the H-like (He-like) O, Ne, Mg, Si, and S ions have cooling columns of 1017\sim10^{17} cm2^{-2}. The O{\sc vii}, O{\sc viii}, and Ne{\sc ix} X-ray absorption-lines towards PKS 2155-304 may arise in radiatively cooling gas in the Galactic disk or halo.Comment: 25 pages, 5 figure

    Galactic Archaeology and Minimum Spanning Trees

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    Chemical tagging of stellar debris from disrupted open clusters and associations underpins the science cases for next-generation multi-object spectroscopic surveys. As part of the Galactic Archaeology project TraCD (Tracking Cluster Debris), a preliminary attempt at reconstructing the birth clouds of now phase-mixed thin disk debris is undertaken using a parametric minimum spanning tree (MST) approach. Empirically-motivated chemical abundance pattern uncertainties (for a 10-dimensional chemistry-space) are applied to NBODY6-realised stellar associations dissolved into a background sea of field stars, all evolving in a Milky Way potential. We demonstrate that significant population reconstruction degeneracies appear when the abundance uncertainties approach 0.1 dex and the parameterised MST approach is employed; more sophisticated methodologies will be required to ameliorate these degeneracies.Comment: To appear in "Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys and Wide Fields"; Held: Santa Cruz de La Palma, Canary Islands, Spain, 2-6 Mar 2015; ed. I Skillen & S. Trager; ASP Conference Series (Figures now optimised for B&W printing

    Laser microprobe study of cosmic dust (IDPs) and potential source materials

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    The study of cosmic dust or interplanetary dust particles (IDP) can provide vital information about primitive materials derived primarily from comets and asteroids along with a small unknown fraction from the nearby interstellar medium. The study of these particles can enhance our understanding of comets along with the decoding of the history of the early solar system. In addition the study of the cosmic dust for IDP particles can assist in the elucidation of the cosmic history of the organogenic elements which are vital to life processes. Studies to date on these particles have shown that they are complex, heterogeneous assemblages of both amorphous and crystalline components. In order to understand the nature of these particles, any analytical measurements must be able to distinguish between the possible sources of these particles. A study was undertaken using a laser microprobe interfaced to a quadrupole mass spectrometer for the analysis of the volatile components present in cosmic dust particles, terrestrial contaminants present in the upper atmosphere, and primitive carbonaceous chondrites. From the study of the volatiles released from the carbonaceous materials it is hoped that one could distinguish between components and sources in the IDP particles analyzed. The technique is briefly described and results for the CI, CM, and CV chondrites and cosmic dust particle W7027B8 are presented

    Comment on ``Validity of certain soft-photon amplitudes''

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    The criteria suggested by Welsh and Fearing (nucl-th/9606040) to judge the validity of certain soft-photon amplitudes are examined. We comment on aspects of their analysis which lead to incorrect conclusions about published amplitudes and point out important criteria which were omitted from their analysis.Comment: 6 pages plus 1 postscript figure, Revte
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