79,879 research outputs found
Optimal spectral bandwidth for long memory
For long range dependent time series with a spectral singularity at frequency zero, a theory for optimal bandwidth choice in non-parametric analysis ofthe singularity was developed by Robinson (1991b). The optimal bandwidths are described and compared with those in case of analysis of a smooth spectrum. They are also analysed in case of fractional ARIMA models and calculated as a function of the self similarity parameter in some special cases. Feasible data dependent approximations to the optimal bandwidth are discussed
New methods for the analysis of long memory time series: application to Spanish inflation
Models for long-memory time series are considered, in which the autocovariance sequence is only parameterized at very long lags, or the spectral density is only parametized at very low frequencies. Various recently proposed methods for estimating the differencing parameters are reviewed, and applied to an economic time series of prices in Spain
Kinematics of the Broad Line Region in M81
A new model is presented which explains the origin of the broad emission
lines observed in the LINER/Seyfert nucleus of M81 in terms of a steady state
spherically symmetric inflow, amounting to 1 x 10^-5 Msun/yr, which is
sufficient to explain the luminosity of the AGN. The emitting volume has an
outer radius of ~1 pc, making it the largest broad line region yet to be
measured, and it contains a total mass of ~ 5 x 10^-2 Msun of dense, ~ 10^8
cm^-3, ionized gas, leading to a very low filling factor of ~ 5 x 10^-9. The
fact that the BLR in M81 is so large may explain why the AGN is unable to
sustain the ionization seen there. Thus, the AGN in M81 is not simply a scaled
down quasar.Comment: Accepted for Publication in ApJ 7/21/0
Design of a "Digital Atlas Vme Electronics" (DAVE) Module
ATLAS-SCT has developed a new ATLAS trigger card, 'Digital Atlas Vme
Electronics' ("DAVE"). The unit is designed to provide a versatile array of
interface and logic resources, including a large FPGA. It interfaces to both
VME bus and USB hosts. DAVE aims to provide exact ATLAS CTP (ATLAS Central
Trigger Processor) functionality, with random trigger, simple and complex
deadtime, ECR (Event Counter Reset), BCR (Bunch Counter Reset) etc. being
generated to give exactly the same conditions in standalone running as
experienced in combined runs. DAVE provides additional hardware and a large
amount of free firmware resource to allow users to add or change functionality.
The combination of the large number of individually programmable inputs and
outputs in various formats, with very large external RAM and other components
all connected to the FPGA, also makes DAVE a powerful and versatile FPGA
utility cardComment: 8 pages, 4 figures, TWEPP-2011; E-mail: [email protected]
An optimization method for nacelle design
A multi-objective optimiZation method is demonstrated using an evolutionary genetic algorithm. The applicability of this method to preliminary nacelle design is demonstrated by coupling it with a response surface model of a wide range of nacelle designs. These designs were modelled using computational fluid dynamics and a Kriging interpolation was carried out on the results. The NSGA-II algorithm was tested and verified on established multi-dimensional problems. Optimisation on the nacelle model provided 3-dimensional Pareto surfaces of optimal designs at both cruise and off-design conditions. In setting up this methodology several adaptations to the basic NSGA-II algorithm were tested including constraint handling, weighted objective functions and initial sample size. The influence of these operators is demonstrated in terms of the hyper volume of the determined Pareto set
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