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Scale Length (scale + length)

Distribution by Scientific Domains
Physics and Astronomy66%

Selected Abstracts

Impactites as a random medium,Using variations in physical properties to assess heterogeneity within the Bosumtwi meteorite impact crater

METEORITICS & PLANETARY SCIENCE, Issue 4-5 2007
Elizabeth L'HEUREUX
The damage induced by impact results in extensive fracturing and mixing of target materials. We discuss here a means of using sonic velocity and density logs from two boreholes through the Bosumtwi crater fill and basement to estimate the degree of heterogeneity and fracturing within the impacted target, in order to understand the discrepancy between the large impedances derived from the log data and the nonreflective zone of impactites observed in seismic sections. Based on an analysis of the stochastic fluctuations in the log data, the Bosumtwi impactites are characterized by vertical scale lengths of 2,3 m. From the resolution of the seismic data over the crater, horizontal scale lengths are estimated at <12 m. The impactites therefore fall within the quasi-homogeneous scattering regime, i.e., seismic energy will propagate through the medium with little disruption. Scale lengths as small as these are observed in the fractured basement rocks of impact structures, whereas non-impact related crystalline environments are characterized by scale lengths an order of magnitude larger. Assuming that the high-frequency fluctuations observed in the log data are more sensitive to fracture distribution than petrology, this suggests that the small scale lengths observed within impact structures are characteristic of impact-induced damage, and could be used to estimate the extent of fracturing undergone by the rocks at any depth below an impact structure. [source]

Using the Steepened Plasma Profile and Wave Breaking Threshold in Laser-Plasma Interaction

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 8 2008
P. Zobdeh
Abstract In this work we evaluate the interaction of high intense laser beam with a steepened density profile. During laser interaction with underdense plasma by freely expanding plasma regime, modification of density profile is possible. In this paper we have investigated the ultra short laser pulse interaction with nonisothermal and collisionless plasma. We consider self,focusing as an effective nonlinear phenomenon that tends to increase when the laser power is more than critical rate. By leading the expanded plasma to a preferred location near to critical density, laser reflection is obtained, so the density profile will be locally steepened. The electromagnetic fields are evaluated in this new profile. We show the amplitude and period of electrical field oscillation are increased by reducing the steepened scale length. Also our numerical results identify that by reducing the steepened scale length, the electrical field is increased to wave breaking threshold limit. This high gradient electrical field causes the effective beam loading during the wave breaking phenomenon. The wave breaking can be the initial point for other acceleration regime as cavity or channel guiding regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Donor/Spacer/Acceptor Block Copolymer Containing Poly(2,7-carbazole) and Perylenetetracarboxydiimide Subunits

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2010
Changduk Yang
Abstract A straightforward synthesis of a conjugated rod/spacer/rod-type block copolymer containing PCz electron-donor and PDI electron-acceptor blocks is described. Two chromophores are covalently connected through sebacate units as saturated spacer. The resulting donor/spacer/acceptor-type block copolymer (PCz-S-PDI) can be applied to limit charge recombination between donor/acceptor interfaces and to control the scale length of nanostructure formation. PCz-S-PDI was used to produce a solar cell with the power conversion efficiency of 0.004%. [source]

Impactites as a random medium,Using variations in physical properties to assess heterogeneity within the Bosumtwi meteorite impact crater

METEORITICS & PLANETARY SCIENCE, Issue 4-5 2007
Elizabeth L'HEUREUX
The damage induced by impact results in extensive fracturing and mixing of target materials. We discuss here a means of using sonic velocity and density logs from two boreholes through the Bosumtwi crater fill and basement to estimate the degree of heterogeneity and fracturing within the impacted target, in order to understand the discrepancy between the large impedances derived from the log data and the nonreflective zone of impactites observed in seismic sections. Based on an analysis of the stochastic fluctuations in the log data, the Bosumtwi impactites are characterized by vertical scale lengths of 2,3 m. From the resolution of the seismic data over the crater, horizontal scale lengths are estimated at <12 m. The impactites therefore fall within the quasi-homogeneous scattering regime, i.e., seismic energy will propagate through the medium with little disruption. Scale lengths as small as these are observed in the fractured basement rocks of impact structures, whereas non-impact related crystalline environments are characterized by scale lengths an order of magnitude larger. Assuming that the high-frequency fluctuations observed in the log data are more sensitive to fracture distribution than petrology, this suggests that the small scale lengths observed within impact structures are characteristic of impact-induced damage, and could be used to estimate the extent of fracturing undergone by the rocks at any depth below an impact structure. [source]

Reliability reconsidered: Cronbach's alpha and paediatric assessment in occupational therapy

AUSTRALIAN OCCUPATIONAL THERAPY JOURNAL, Issue 3 2009
Georgia Spiliotopoulou
Background/aim:,Using reliable outcome measures is a necessity for the occupational therapy profession in enabling valid assessments of clients. Although Cronbach's alpha is the most widely applied index of internal consistency reliability, there are misconceptions about its use and interpretation. This paper aims to guide assessment developers in paediatric occupational therapy, as well as practitioners who are evaluating outcome measures in using and interpreting the Cronbach's alpha estimates appropriately. This will enable them to decide on the tools' clinical value and incorporate them into their practice with children. Method:,Previously published papers reporting on internal consistency issues of outcome measures in paediatric occupational therapy were searched through the Allied and Complementary Medicine database. These papers were used as a basis to discuss possible reasons for reporting of low internal consistency. Results:,The analysis demonstrates that Cronbach's alpha reports are not always interpreted in a sound way. The paper emphasises that one should be cautious about judging estimates of internal consistency. Low size of the coefficient alpha might not always indicate problems with the construction of the tool; whereas large sizes do not always suggest adequate reliability. Instead, these reports might be related to the data characteristics of the construct. Conclusion:,In judging an outcome measure's internal consistency, researchers and practitioners in occupational therapy should report and consider the nature of data, the scale's length and width, the linearity and the normality of response distribution, the central response tendency, the sample response variability and the sample size. [source]