12,221 research outputs found
Peace Through Prayer
As far back as he could remember he had been afraid of storms. Back there in the early years, some member of the family had set the pace of fear when a storm came. There was an old belief - probably a superstition - that if one sat on a feather bed, lightning wouldn\u27t strike. Anyway, there was a general migration to the bedrooms during a storm. Mother became nervous if the storm was severe, and sister would have a fit of trembling. Brother made a vain show of bravery, which only intensified the uneasiness. All through his seventeen years the boy had had a dread of storms. Perhaps the psychologists would say it was conditioned by those early experiences.
So that night he lay huddled among the covers, as the storm raged. The room was dungeon-black, lighted only by the vivid flashes of lightning. All other sound was swallowed up in the crash and rumble of the thunder. He could feel the house shake as the wind dashed against it, seemingly in a mad effort to tear it apart. The rain beat against the window pane in a solid phalanx. And he was scared a pointless, unreasoning, foolish fear
Checkmate
Six men sat around a table. They had been sitting there for two hours. The ash trays gave evidence of the intensity of their thought. The glasses had been emptied and refilled, and now, they were empty again. The silence of the room was as thick as the cigar smoke. The grandfather\u27s clock in the corner counted off the seconds with a heavy tread. The hour was past midnight
Empirical Uncertainty Estimators for Astrometry from Digital Databases
In order to understand the positional uncertainties of arbitrary objects in
several of the current major databases containing astrometric information, a
sample of extragalactic radio sources with precise positions in the
International Celestial Reference Frame (ICRF) is compared with the available
positions of their optical counterparts. The discrepancies between the radio
and various optical positions are used to derive empirical uncertainty
estimators for the USNO-A2.0, USNO-A1.0, Guide Star Selection System (GSSS)
images, and the first and second Digitized Sky Surveys (DSS-I and DSS-II). In
addition, an estimate of the uncertainty when the USNO-A2.0 catalog is
transferred to different image data is provided. These optical astrometric
frame uncertainties can in some cases be the dominant error term when
cross-identifying sources at different wavelengths.Comment: 12 pages including 2 figures and 1 table. Accepted for publication in
The Astronomical Journal, October 1999. Values in Table 1 for DSS I corrected
99-07-1
Fractional euler limits and their applications
© 2017 Society for Industrial and Applied Mathematics. Generalizations of the classical Euler formula to the setting of fractional calculus are discussed. Compound interest and fractional compound interest serve as motivation. Connections to fractional master equations are highlighted. An application to the Schlögl reactions with Mittag- Leffler waiting times is described
Analysis of direct segregated boundary-domain integral equations for variable-coefficient mixed bvps in exterior domains
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2013 World Scientific Publishing.Direct segregated systems of boundary-domain integral equations are formulated for the mixed (Dirichlet–Neumann) boundary value problems for a scalar second-order divergent elliptic partial differential equation with a variable coefficient in an exterior three-dimensional domain. The boundary-domain integral equation system equivalence to the original boundary value problems and the Fredholm properties and invertibility of the corresponding boundary-domain integral operators are analyzed in weighted Sobolev spaces suitable for infinite domains. This analysis is based on the corresponding properties of the BVPs in weighted Sobolev spaces that are proved as well.The work was supported by the grant EP/H020497/1 \Mathematical analysis of localised boundary-domain integral equations for BVPs with variable coefficients" of the EPSRC, UK
Forecasting emergency medical service call arrival rates
We introduce a new method for forecasting emergency call arrival rates that
combines integer-valued time series models with a dynamic latent factor
structure. Covariate information is captured via simple constraints on the
factor loadings. We directly model the count-valued arrivals per hour, rather
than using an artificial assumption of normality. This is crucial for the
emergency medical service context, in which the volume of calls may be very
low. Smoothing splines are used in estimating the factor levels and loadings to
improve long-term forecasts. We impose time series structure at the hourly
level, rather than at the daily level, capturing the fine-scale dependence in
addition to the long-term structure. Our analysis considers all emergency
priority calls received by Toronto EMS between January 2007 and December 2008
for which an ambulance was dispatched. Empirical results demonstrate
significantly reduced error in forecasting call arrival volume. To quantify the
impact of reduced forecast errors, we design a queueing model simulation that
approximates the dynamics of an ambulance system. The results show better
performance as the forecasting method improves. This notion of quantifying the
operational impact of improved statistical procedures may be of independent
interest.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS442 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Structural and chemical embrittlement of grain boundaries by impurities: a general theory and first principles calculations for copper
First principles calculations of the Sigma 5 (310)[001] symmetric tilt grain
boundary in Cu with Bi, Na, and Ag substitutional impurities provide evidence
that in the phenomenon of Bi embrittlement of Cu grain boundaries electronic
effects do not play a major role; on the contrary, the embrittlement is mostly
a structural or "size" effect. Na is predicted to be nearly as good an
embrittler as Bi, whereas Ag does not embrittle the boundary in agreement with
experiment. While we reject the prevailing view that "electronic" effects
(i.e., charge transfer) are responsible for embrittlement, we do not exclude
the role of chemistry. However numerical results show a striking equivalence
between the alkali metal Na and the semi metal Bi, small differences being
accounted for by their contrasting "size" and "softness" (defined here). In
order to separate structural and chemical effects unambiguously if not
uniquely, we model the embrittlement process by taking the system of grain
boundary and free surfaces through a sequence of precisely defined gedanken
processes; each of these representing a putative mechanism. We thereby identify
three mechanisms of embrittlement by substitutional impurities, two of which
survive in the case of embrittlement or cohesion enhancement by interstitials.
Two of the three are purely structural and the third contains both structural
and chemical elements that by their very nature cannot be further unravelled.
We are able to take the systems we study through each of these stages by
explicit computer simulations and assess the contribution of each to the nett
reduction in intergranular cohesion. The conclusion we reach is that
embrittlement by both Bi and Na is almost exclusively structural in origin;
that is, the embrittlement is a size effect.Comment: 13 pages, 5 figures; Accepted in Phys. Rev.
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
Regional engagement and spatial modelling for natural resource management planning
Changing unsustainable natural resource use in agricultural landscapes is a complex social–ecological challenge that cannot be addressed through traditional reductionist science. More holistic and inclusive (or transdisciplinary) processes are needed. This paper describes a transdisciplinary project for natural resource management planning in two regions (Eyre Peninsula and South Australian Murray-Darling Basin) of southern Australia. With regional staff, we reviewed previous planning to gain an understanding of the processes used and to identify possible improvement in plan development and its operation. We then used an envisioning process to develop a value-rich narrative of regional aspirations to assist stakeholder engagement and inform the development of a land use management option assessment tool called the landscape futures analysis tool (LFAT). Finally, we undertook an assessment of the effectiveness of the process through semi-structured stakeholder interviews. The planning process review highlighted the opinion that the regional plans were not well informed by available science, that they lacked flexibility, and were only intermittently used after publication. The envisioning process identified shared values—generally described as a trust, language that is easily understood, wise use of resources, collaboration and inclusiveness. LFAT was designed to bring the best available science together in a form that would have use in planning, during community consultation and in assessing regional management operations. The LFAT provided spatially detailed but simple models of agricultural yields and incomes, plant biodiversity, weed distribution, and carbon sequestration associated with future combinations of climate, commodity and carbon prices, and costs of production. Stakeholders were impressed by the presentation and demonstration results of the software. While there was anecdotal evidence that the project provided learning opportunities and increased understanding of potential land use change associated with management options under global change, the direct evidence of influence in the updated regional plan was limited. This project had elements required for success in transdisciplinary research, but penetration seems limited. Contributing factors appear to be a complexity of climate effects with economic uncertainty, lack of having the project embedded in the plan revision process, limited continuity and capacity of end users and limited after project support and promotion. Strategies are required to minimise the controlling influence that these limitations can have.Wayne S. Meyer, Brett A. Bryan, David M. Summers, Greg Lyle, Sam Wells, Josie McLean, Mark Siebentrit
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