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排序方式: 共有166条查询结果,搜索用时 31 毫秒
1.
D L Neff 《The Journal of the Acoustical Society of America》1986,79(5):1519-1529
In some forward-masking conditions, signal thresholds may be elevated by the listener's inability to distinguish the signal from the preceding masker. In this study, such "confusion" effects are investigated for both sinusoidal and narrow-band noise forward maskers combined with sinusoidal signals of varying duration. Results for the sinusoidal maskers show effects of off-frequency listening for brief signals and possibly small effects of confusion for longer signals. Results for the narrow-band noise maskers show a marked influence of confusion over a wide range of signal durations. This range is in good agreement with that predicted from previous work with "pulsing" maskers [D. Neff, J. Acoust. Soc. Am. 78, 1966-1976 (1985)]. These results suggest that studies using narrow-band noise forward maskers or studies of psychophysical suppression should include direct tests for confusion effects in key conditions. 相似文献
2.
M. D. Glascock H. Neff K. S. Stryker T. N. Johnson 《Journal of Radioanalytical and Nuclear Chemistry》1994,180(1):29-35
An abbreviated NAA procedure has been developed to fingerprint obsidian artifacts in the Mesoamerican region. Despite the large number of available sources, an NAA procedure, which relies on producing short-lived isotopes, has been applied with a success rate greater than 90 percent. The abbreviated NAA procedure is rapid and cost competitive with the XRF technique more often applied in obsidian sourcing. Results from the analysis of over 1,200 obsidian artifacts from throughout Mesoamerica are presented. 相似文献
3.
Masked thresholds for a 1000-Hz sinusoidal signal were measured as a function of masker level in both forward and simultaneous masking for two types of maskers: a 1000-Hz sinusoid and a narrowband noise, 60-Hz wide, centered at 1000 Hz. In forward masking, the noise masker produced much steeper growth-of-masking functions than the sinusoid. Presenting a contralateral broadband noise "cue" with the forward masker dramatically reduced the slope of masking for the noise masker but did not influence results for the sinusoidal masker. The noise remained the more effective masker. The amount of masking produced by combinations of equally effective narrowband-noise and sinusoidal maskers was compared to that produced by each masker individually with and without the contralateral cue. No additional masking beyond that predicted by energy summation was measured for forward masking. Additional masking beyond energy-sum predictions was measured for analogous conditions in simultaneous masking. Comparisons of results obtained with and without the contralateral cue suggest that signal thresholds in the presence of narrowband-noise forward maskers can reflect nonperipheral auditory processes. 相似文献
4.
A new approach to the total, asymmetric synthesis of D -threo-L -talo-octose ((?)- 1 ) and its derivatives is presented. It is based on the chemoselective Wittig-Horner monoolefination of a 5-deoxy-D -ribo-hexodialdose derivative 4 obtained by selective reduction of (?)-5-deoxy-2.3-O-isopropylidene-/β-D -ribo-hexofuranurono-6,1-lactone ((?)- 3 ). Allylic bromination of the resulting methyl (E)-oct-6-enofuranuronate (+)- 5 followed by intramolecular nucleophilic displacement of the so-obtained bromides gave a 13.3:1 mixture of (?)-methyl (E)-l,4-anhydro-6,7-dideoxy-2,3-O-isopropylidene-β-L -talo-oct-6-enopyranuronate ((?)- 8 ) and methyl (E)-l,4-anhydro-6,7-dideoxy-2,3-O-isopropylidene-α-D -allo-oct-6-enopyranuronate ( 9 ). The double hydroxylation of the enoate (?)- 8 followed Kishi's rule and gave the corresponding D -threo-β-L -talo-octopyranuronate derivative (?)- 11 with a good diastereoselectivity. Reduction of ester (?)- 11 and deprotection led to pure (?)- 1 . 相似文献
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A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration. 相似文献
8.
J. Monnier S. Réguer D. Vantelon P. Dillmann D. Neff I. Guillot 《Applied Physics A: Materials Science & Processing》2010,99(2):399-406
The study and prediction of very long-term atmospheric corrosion behaviour of ferrous alloys is of great importance in different
fields. First the conservation of metallic artefacts in museum and the corrosion diagnosis on ferrous reinforcement used in
ancient monuments since medieval times needs reliable data to understand the mechanisms. Second, in the frame of the interim
storage of nuclear waste in France, it is necessary to model the long-term corrosion of low alloy steel overcontainer. The
nature of phases and elements constituting the corrosion layers can greatly influence the corrosion mechanisms. On the one
hand, it is crucial to precisely determine the nature of microscopic phases that can be highly reactive. On the other hand,
some elements as P and S could modify this reactivity. To clarify this point and complementary to other studies using Raman
micro spectroscopy technique, X-rays Absorption Spectroscopy (XAS) under synchrotron radiation plays a crucial role. It allows
one to precisely identify the reactive phases in the corrosion layers. Micro-XAS was required in order to refine the spatial
variation, at micrometer scale, of the predominant Fe oxidation state and to characterise the corresponding corrosion products.
Moreover, the role of minor elements on phase’s stability and the chemical form of these elements in the rust layer, especially
phosphorus and sulphur, was investigated. 相似文献
9.
10.
Alexandrou C de Forcrand P Neff H Negele JW Schroers W Tsapalis A 《Physical review letters》2005,94(2):021601
The magnetic dipole (M1), the electric quadrupole (E2), and the Coulomb quadrupole (C2) amplitudes for gammaN-->Delta are calculated in quenched lattice QCD. Using a new method, which combines an optimal choice of interpolating fields for the Delta and an overconstrained analysis, we obtain statistically accurate results for the dipole form factor and for the ratios R(EM)=E2/M1 and R(SM)=C2/M1, up to momentum transfer squared 1.5 GeV2. We show for the first time, using lattice QCD, that both R(EM) and R(SM) are nonzero and negative, in qualitative agreement with experiment and indicating the presence of deformation in the N/Delta system. 相似文献