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901.
A measurement of the absorption of neutrinos with energies in excess of 10 TeV when traversing the Earth is capable of revealing its density distribution. Unfortunately, the existence of beams with sufficient luminosity for the task has been ruled out by the AMANDA South Pole neutrino telescope. In this Letter we point out that, with the advent of second-generation kilometer-scale neutrino detectors, the idea of studying the internal structure of Earth may be revived using atmospheric neutrinos instead. 相似文献
902.
N.W. Ghonaim M. Nieradko L. Xi J.T. Francis K.K.C. Yeung Leo W.M. Lau 《Applied Surface Science》2008,255(4):1029-1032
The nondestructive nature of static secondary ion mass spectrometry (SIMS) in the context of studies of self-assembled monolayers (SAMs) of organic molecules has been examined by measuring the primary ion fluence dependence of secondary ion signals with two well-known SAMs, C18H37SH on Au(1 1 1) and C18H37PO3H2 on freshly cleaved mica. This SIMS analysis is challenging because the bonding nature is delicate and the areal molecular density is less than 1015 cm−2. In SIMS, it is prevalently assumed that if the primary ion fluence is confined to not more than 1 × 1012 cm−2, all secondary ion signals should not change by more than 10% and the practically defined static condition is satisfied. Our results from time-of-flight SIMS with the common primary ions of Bi3+, Bi+ and Ar+, indicate that this prevalent static assumption fails for both model SAMs. The SIMS results from the phosphyl case, which have been recently published, consistently display the evidence of bombardment-induced damage. In comparison, the thiol case presented here shows much more complex primary ion fluence dependence of SIMS signals. It is therefore concluded that practical static analysis should use primary ion fluence not more than 1 × 1011 cm−2 or should simply record and report the effects of primary ion fluence. 相似文献
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905.
Precision determination of high density polyethylene unit-cell dimensions are reported. The crystallographic analysis was carried out on pressure crystallized and subsequently solid-state extruded samples respectively, by means of x-ray photographic and diffractometric procedures. In all cases the crystal data was derived from a large number of independent reflections. It was shown that the unit-cell dimensions and the corresponding crystallographic densities of all the specimens are invariant with respect to either crystallization pressure or nominal draw ratio. The effects of deformation on macroscopic density are attributed, therefore, to changes of the degree of crystallinity and to an increase of the density of the amorphous phase. This interpretation is consistent with the experimental data in the framework of the two-phase model of polymer morphology. 相似文献
906.
Bigourd D Cuisset A Hindle F Matton S Fertein E Bocquet R Mouret G 《Optics letters》2006,31(15):2356-2358
Continuous-wave terahertz spectroscopy by photomixing is applied to the analysis of mainstream cigarette smoke. Using the wide tunability of the source, spectral signatures of hydrogen cyanide (HCN), carbon monoxide (CO), formaldehyde (H2CO), and water (H2O) have been observed from 500 to 2400 GHz. The fine spectral purity allows direct concentration measurement from the pure rotational transitions of HCN and CO. The quantification of the measurement was validated by the means of a calibration gas containing CO. The potential of this technique for trace gas detection is demonstrated with an estimated detection limit of HCN equal to 9 parts in 10(6). 相似文献
907.
Maria Chatzopoulou R. Fernando Martínez Nicky J. Willis Timothy D.W. Claridge Francis X. Wilson Graham M. Wynne Stephen G. Davies Angela J. Russell 《Tetrahedron》2018,74(38):5280-5288
Structural misassignments are often seen for complex natural products, but this can also be an issue with seemingly simpler structures. In this paper, we describe how, using a 15N-labelled analogue, we established that the Dimroth rearrangement can occur in imidazo[1,2-a]pyrimidines and result in an incorrect regiochemical assignment of such compounds. These studies supported a rearrangement mechanism involving addition of hydroxide ion followed by ring opening. It was also observed that C(2) and C(3) substituted regioisomers could be readily distinguished using 1H NMR spectroscopy. 相似文献
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