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81.
82.
F R Johnston J E Boyland M Meadows E Shale 《The Journal of the Operational Research Society》1999,50(12):1267-1271
Simple (equally weighted) moving averages are frequently used to estimate the current level of a time series, with this value being projected as a forecast for future observations. A key measure of the effectiveness of the method is the sampling error of the estimator, which this paper defines in terms of characteristics of the data. This enables the optimal length of the average for any steady state model to be established and the lead time forecast error derived. A comparison of the performance of a simple moving average (SMA) with an exponentially weighted moving average (EWMA) is made. It is shown that, for a steady state model, the variance of the forecast error is typically less than 3% higher than the appropriate EWMA. This relatively small difference may explain the inconclusive results from the empirical studies about the relative predictive performance of the two methods. 相似文献
83.
84.
Wilmin P. Bartolini Catherine M. Bentzley Murray V. Johnston Barbara S. Larsen 《Journal of the American Society for Mass Spectrometry》1999,10(6):521-528
Elucidating structure function relationships of DNA in cellular processes requires fast, reliable methods that can be applied to picomole amounts of sample. Higher order structure can be inferred by distinguishing paired and unpaired regions. It is shown here that enzymatic digestion coupled with product analysis by matrix-assisted laser desorption ionization (MALDI) is able to identify unpaired bases within structured DNA regions. The method is demonstrated with DNA duplexes having a five nucleotide mismatch as a 5' overhang, a 3' overhang, and an internal loop. Exo- and endonuclease digestions are performed under solution conditions (temperature, annealing, and enzyme buffers) which promote base pairing and specific enzyme activity. For each type of mismatch, the length and sequence of the single stranded region can be inferred from MALDI spectra taken as a function of digestion time. 相似文献
85.
Ghizzo A. Bertrand P. Begue M.L. Johnston T.W. Shoucri M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1996,24(2):370-378
High-frequency beatwave simulations relevant to the University of California at Los Angeles (UCLA) experiment with relativistic eulerian hybrid Vlasov code are presented. These Hilbert-Masov simulations revealed a rich variety of phenomena associated with the fast particle dynamics induced by beatwave experiment for a high ratio of driver frequency to plasma frequency ωpump/ωplasma ≈33. The present model allows us to extend detailed modeling to frequency ratios greater than the current practical maximum of 10 or so, for Vlasov or particle-in-cell (PIC) codes, by replacing the Maxwell equations by mode equations for the electromagnetic Vlasov code. Numerical results, including beat frequency chirping (i.e., pump frequency linearly decreasing with time), show that the amplitude limit due to relativistic detuning can be enhanced with accelerated particles up to the ultrarelativistic energies with a high-acceleration gradient of more than 25 GeV/m 相似文献
86.
Bruce A. Kimball Rori K. Craver John J. Johnston Dale L. Nolte 《Journal of separation science》1995,18(4):221-225
In order to investigate the relationship between terpenoid content and black bear foraging preference, an analytical method was required to quantify mono- and sesquiterpenoids present in Douglas-fir sapwood. Sapwood samples were scraped from trees, immediately frozen in liquid nitrogen, and then homogenized. A simple extraction requiring no clean-up step was performed with ethyl acetate. Extracts were analyzed by gas chromatography with mass selective detection versus external standards. The recoveries of 22 terpenoids from fortified controls were approximately 90% with good precision (relative standard deviations of approximately 10%). 相似文献
87.
K. G. Johnston 《Semigroup Forum》1994,49(1):131-135
Communicated by Norman R. Reilly 相似文献
88.
89.
The influence of an inhibitor (CF3Br or Halon 1301) on the propagation of high-speed turbulent flames, quasi-detonations and the transition to detonation has
been investigated for methane-air, propane-air and acetylene-air mixtures. The experiments are carried out in a 13 m tube
(15 cm diameter) filled with regularly spaced orifice plates (blockage ratio of 0.39) to ensure rapid flame acceleration.
In all cases, the addition of the inhibitor reduces the turbulent flame velocity and extinguishes the flame with sufficient
inhibitor concentration (2.7% and 7.5% for methane-air and propane-air, respectively). For acetylene-air mixtures, the quasi-detonation
speed is progressively reduced with increasing inhibitor concentration and eventually causes the failure of the quasi-detonation
and transition back to a fast turbulent flame. The inhibitor also narrows the propagation limits in all cases. To elucidate
the inhibition mechanism, detailed modelling of both the turbulent flame structure as well as the chemical kinetics are required. 相似文献
90.
Dr. Christopher J. Heard Prof. Roy L. Johnston Prof. Dr. J. Christian Schön 《Chemphyschem》2015,16(7):1461-1469
The energy landscapes of sub‐nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low‐lying minima along with their permutational isomers are located for the Cu${_4 }$ Ag${_4 }$ cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo‐planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters. 相似文献