4,304 research outputs found
Evidence of crossover phenomena in wind speed data
In this report, a systematic analysis of hourly wind speed data obtained from
three potential wind generation sites (in North Dakota) is analyzed. The power
spectra of the data exhibited a power-law decay characteristic of
processes with possible long-range correlations. Conventional
analysis using Hurst exponent estimators proved to be inconclusive. Subsequent
analysis using detrended fluctuation analysis (DFA) revealed a crossover in the
scaling exponent (). At short time scales, a scaling exponent of
indicated that the data resembled Brownian noise, whereas for
larger time scales the data exhibited long range correlations (). The scaling exponents obtained were similar across the three locations.
Our findings suggest the possibility of multiple scaling exponents
characteristic of multifractal signals
A Multifractal Description of Wind Speed Records
In this paper, a systematic analysis of hourly wind speed data obtained from
four potential wind generation sites in North Dakota is conducted. The power
spectra of the data exhibited a power law decay characteristic of
processes with possible long range correlations. The temporal
scaling properties of the records were studied using multifractal detrended
fluctuation analysis {\em MFDFA}. It is seen that the records at all four
locations exhibit similar scaling behavior which is also reflected in the
multifractal spectrum determined under the assumption of a binomial
multiplicative cascade model
Post-flight analyses of the crystals from the M0003-14 quartz crystal microbalance experiment
Quartz Crystal Microbalances constructed by QCM Research were flown on the leading and trailing edges of LDEF as one of the sub-experiments of M0003. Response of the crystals coated with 150 A of In2O3 was recorded during the first 424 days of the mission. A second QCM with crystals coated with 150 A of ZnS was also flown but not monitored. After the flight, the QCM's were disassembled and analyzed in The Aerospace Corporation laboratories. The samples included the crystals from the leading and trailing edge samples of both types of coatings along with the reference crystals, which were inside the QCM housing. Analyses were performed by scanning electron microscopy, energy dispersive x-ray analyses, x-ray photoelectron spectroscopy, ion microprobe mass analysis, and reflectance spectroscopy in the infrared and UV/visible regions. The crystals are contaminated predominantly with silicone compounds. The contamination is higher on the leading edge than on the trailing edge and higher on the exposed crystals than on the reference crystals
Minimizing the effect of sinusoidal trends in detrended fluctuation analysis
The detrended fluctuation analysis (DFA) [Peng et al., 1994] and its
extensions (MF-DFA) [Kantelhardt et al., 2002] have been used extensively to
determine possible long-range correlations in self-affine signals. While the
DFA has been claimed to be a superior technique, recent reports have indicated
its susceptibility to trends in the data. In this report, a smoothing filter is
proposed to minimize the effect of sinusoidal trends and distortion in the
log-log plots obtained by DFA and MF-DFA techniques
A Note on the Intermediate Region in Turbulent Boundary Layers
We demonstrate that the processing of the experimental data for the average
velocity profiles obtained by J. M. \"Osterlund
(www.mesh.kth.se/jens/zpg/) presented in [1] was incorrect. Properly
processed these data lead to the opposite conclusion: they confirm the
Reynolds-number-dependent scaling law and disprove the conclusion that the flow
in the intermediate (`overlap') region is Reynolds-number-independent.Comment: 8 pages, includes 1 table and 3 figures, broken web link in abstract
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Length-weight relationship and certain biological aspects of the Indian white shrimp Fenneropenaeus indicus (H. Milne Edwards, 1837) exploited by trawls in the Arabian Sea off Kerala coast, India
Length-weight relationship (LWR), sex ratio and maturity of Fenneropenaeus indicus (H. Milne Edwards, 1837), was analysed based on samplings from coastal trawl fishing grounds in the Arabian Sea off Kerala coast, India. The male to female ratio (1:1.27) did not vary significantly from the hypothetical 1:1 ratio. Length at maturity (Lm50) was estimated at 122 mm total length for females. The LWR did not differ significantly between male and female shrimps. The information generated from this study will enhance knowledge on the biology of the species and assist in assessment and management of its stock
Pulsar activity and the morphology of supernova remnants
We use the recently introduced concept of a 'window' of magnetic field strengths in which pulsars can be active to explain the variation in morphology of supernova remnants. The striking difference between shell-type and filled-type remnants is attributed to differences in he magnetic field strengths of the neutron stars left by the respective Supernovae. Field strengths of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field values lead to strong magnetic dipole radiation and consequent shell formation (e.g. Cas A). Several apparent inconsistencies concerning pulsar-supernova associations appear to find a logical explanation on the basis of this hypothesis
Evidence for a large population of shocked interstellar clouds
A 21 cm absorption measurement over a long path length free of the effects of differential galactic rotation indicates the existence of two distinct cloud populations in the plane. One of them consisting of cold, dense clouds has been well studied before. The newly found hot clouds appear to be at least five times more numerous. They have a spin temperature of ˜ 300 K, an rms velocity of ˜ 35 km/s-1, twice the total mass, and hundred times the kinetic energy of the cold clouds. Over long path lengths, the hot clouds have NH/kpc ˜ 2 × 1021/cm-2 kpc-1, and are estimated to have individual column densities ≤ 1020/cm-2. We propose that they are shocked clouds found only within supernova bubbles and that the cold clouds are found in the regions in-between old remnants, immersed in an intercloud medium. We conclude that the solar neighborhood must be located between old supernova remnants rather than within one
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