22,891 research outputs found
Forecasting intermittent demand
Methods for forecasting intermittent demand are compared using a large data-set from the UK Royal Air Force (RAF). Several important results are found. First, we show that the traditional per period forecast error measures are not appropriate for intermittent demand, even though they are consistently used in the literature. Second, by comparing target service levels to achieved service levels when inventory decisions are based on demand forecasts, we show that Croston's method (and a variant) and Bootstrapping clearly outperform Moving Average and Single Exponential Smoothing. Third, we show that the performance of Croston and Bootstrapping can be significantly improved by taking into account that each lead time starts with a demand
Dynamics of the Kuiper Belt
Our current knowledge of the dynamical structure of the Kuiper Belt is
reviewed here. Numerical results on long term orbital evolution and dynamical
mechanisms underlying the transport of objects out of the Kuiper Belt are
discussed. Scenarios about the origin of the highly non-uniform orbital
distribution of Kuiper Belt objects are described, as well as the constraints
these provide on the formation and long term dynamical evolution of the outer
Solar system. Possible mechanisms include an early history of orbital migration
of the outer planets, a mass loss phase in the outer Solar system and
scattering by large planetesimals. The origin and dynamics of the scattered
component of the Kuiper Belt is discussed. Inferences about the primordial mass
distribution in the trans-Neptune region are reviewed. Outstanding questions
about Kuiper Belt dynamics are listed.Comment: 22 pages plus 8 figures added footnote, figure
The design and construction of the CAD-1 airship
The background history, design philosophy and Computer application as related to the design of the envelope shape, stress calculations and flight trajectories of the CAD-1 airship, now under construction by Canadian Airship Development Corporation are reported. A three-phase proposal for future development of larger cargo carrying airships is included
Pariah moonshine
Finite simple groups are the building blocks of finite symmetry. The effort
to classify them precipitated the discovery of new examples, including the
monster, and six pariah groups which do not belong to any of the natural
families, and are not involved in the monster. It also precipitated monstrous
moonshine, which is an appearance of monster symmetry in number theory that
catalysed developments in mathematics and physics. Forty years ago the pioneers
of moonshine asked if there is anything similar for pariahs. Here we report on
a solution to this problem that reveals the O'Nan pariah group as a source of
hidden symmetry in quadratic forms and elliptic curves. Using this we prove
congruences for class numbers, and Selmer groups and Tate--Shafarevich groups
of elliptic curves. This demonstrates that pariah groups play a role in some of
the deepest problems in mathematics, and represents an appearance of pariah
groups in nature.Comment: 20 page
A simplified PERT system
Modified PERT technique processes the input data and arranges it in familiar graphic form in a booklet which is issued at periodic intervals. The tabulated data provides readily available information to management personnel concerned with monitoring the progress of a program
Improved Pseudofermion Approach for All-Point Propagators
Quark propagators with arbitrary sources and sinks can be obtained more
efficiently using a pseudofermion method with a mode-shifted action.
Mode-shifting solves the problem of critical slowing down (for light quarks)
induced by low eigenmodes of the Dirac operator. The method allows the full
physical content of every gauge configuration to be extracted, and should be
especially helpful for unquenched QCD calculations. The method can be applied
for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert,
Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The
statistical properties of the method are examined and examples of physical
processes under study are presented.Comment: LateX, 26 pages, 10 eps figure
Advanced dendritic web growth development and development of single-crystal silicon dendritic ribbon and high-efficiency solar cell program
Efforts to demonstrate that the dendritic web technology is ready for commercial use by the end of 1986 continues. A commercial readiness goal involves improvements to crystal growth furnace throughput to demonstrate an area growth rate of greater than 15 sq cm/min while simultaneously growing 10 meters or more of ribbon under conditions of continuous melt replenishment. Continuous means that the silicon melt is being replenished at the same rate that it is being consumed by ribbon growth so that the melt level remains constant. Efforts continue on computer thermal modeling required to define high speed, low stress, continuous growth configurations; the study of convective effects in the molten silicon and growth furnace cover gas; on furnace component modifications; on web quality assessments; and on experimental growth activities
Crop Yield Prospects for 1960
The kind of weather we have often is the deciding factor on crop yields in Iowa. The moisture used by crops comes from two sources-soil reserves and crop-season rainfall. Here\u27s how we stand for the year ahead
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