115,983 research outputs found
Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10
Anderson, et al. find the measured trajectories of Pioneer 10 and 11
spacecraft deviate from the trajectories computed from known forces acting on
them. This unmodelled acceleration (and the less well known, but similar,
unmodelled torque) can be accounted for by non-isotropic radiation of
spacecraft heat. Various forms of non-isotropic radiation were proposed by
Katz, Murphy, and Scheffer, but Anderson, et al. felt that none of these could
explain the observed effect. This paper calculates the known effects in more
detail and considers new sources of radiation, all based on spacecraft
construction. These effects are then modelled over the duration of the
experiment. The model reproduces the acceleration from its appearance at a
heliocentric distance of 5 AU to the last measurement at 71 AU to within 10
percent. However, it predicts a larger decrease in acceleration between
intervals I and III of the Pioneer 10 observations than is observed. This is a
2 sigma discrepancy from the average of the three analyses (SIGMA, CHASMP, and
Markwardt). A more complex (but more speculative) model provides a somewhat
better fit. Radiation forces can also plausibly explain the previously
unmodelled torques, including the spindown of Pioneer 10 that is directly
proportional to spacecraft bus heat, and the slow but constant spin-up of
Pioneer 11. In any case, by accounting for the bulk of the acceleration, the
proposed mechanism makes it much more likely that the entire effect can be
explained without the need for new physics.Comment: Final minor changes for publication - added explanation of acronyms,
added to RTG asymmetry argument.. Was: 12 pages, 9 figures, major revision.
Added discussion of gas leaks and spin history, a radiation based explanation
of spin changes, and references to re-analysis of Markwardt. Fixed radio
forces, tuned models. Was: 7 pages, 5 figures; added liklihood calculations
in body and abstract per suggestio
Effects of pregnancy, childbirth, and motherhood on high school dropout
This paper uses data from the National Longitudinal Survey of Youth to explore the effect of fertility on high school dropout, and differences in that effect by age at first birth. Fertility is conceptualized as a series of states: pregnancy, childbirth, postpartum, and motherhood. Pregnant students and mothers are much more likely to drop out than students who are not pregnant or mothers. Models including a wide variety of controls for social background, ability, schooling factors, and adolescent behaviors show that the net effects of pregnancy and motherhood on dropout are substantively and statistically significant. The effects of fertility on dropout are strongest for the youngest students.
Energetic particle flux experiment (IMP F and G)
The data reduction procedures and programs for analysis of the IMP F and G energetic particle flux experiments are summarized. The IMP-F experiment contained two thin-window Geiger-Mueller detectors and an ionization chamber. There were two IMP-G experiments: one with six Geiger-Mueller detectors and an ionization chamber, and the other with two funnel mouthed channeltrons in a parallel plate electrostatic analyzer. These experiments measured particles in the energy range above 20 keV (IMP-F) and above approximately 5 keV (IMP-G). A bibliography is presented of papers containing the scientific results. These data were predominantly used for the study of low energy solar particles from flares
Relation of energetic particles in the plasma sheet to the auroral zone
Relationship of plasma and energetic particles in geomagnetic tail to particle precipitation into auroral zon
Data reduction and analysis for ISEE-A and -B energetic particles flux experiment and ISEE-C electron and X-ray experiments
A summary of the data reduction and analysis activities from late 1979 to late 1983 is presented. A bibliography of publications is included
The distribution of species range size: a stochastic process
The major role played by environmental factors in determining the geographical range sizes of species raises the possibility of describing their long-term dynamics in relatively simple terms, a goal which has hitherto proved elusive. Here we develop a stochastic differential equation to describe the dynamics of the range size of an individual species based on the relationship between abundance and range size, derive a limiting stationary probability model to quantify the stochastic nature of the range size for that species at steady state, and then generalize this model to the species-range size distribution for an assemblage. The model fits well to several empirical datasets of the geographical range sizes of species in taxonomic assemblages, and provides the simplest explanation of species-range size distributions to date
Does Community and Environmental Responsibility Affect Firm Risk? Evidence from UK Panel Data 1994-2006
The question of how an individual firm’s environmental performance impacts its firm risk has not been examined in any empirical UK research. Does a company that strives to attain good environmental performance decreases its market risk or is environmental performance just a disadvantageous cost that increases such risk levels for these firms? Answers to this question have important implications for the management of companies and the investment decisions of individuals and institutions. The purpose of this paper is to examine the relationship between corporate environmental performance and firm risk in the British context. Using the largest dataset so far assembled, with Community and Environmental Responsibility (CER) rankings for all rated UK companies between 1994 and 2006, we show that a company’s environmental performance is inversely related to its systematic financial risk. However, an increase of 1.0 in the CER score is associated with only a 0.02 reduction in firm’s risk and cost of capital
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