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991.
Coherent backscattering (CBS) of light in random media has been previously investigated by use of coherent light sources. Here we report a novel method of CBS measurement that combines low spatial coherence, broadband illumination, and spectrally resolved detection. We show that low spatial coherence illumination leads to an anomalously broad CBS peak and a dramatic speckle reduction; the latter is further facilitated by low temporal coherence detection. Thus CBS can be observed in biological tissue and other media that previously were beyond the reach of conventional CBS measurements. We also demonstrate, for the first time to our knowledge, spectroscopic analysis of CBS. CBS spectroscopy may find important applications in probing random media such as biological tissue in which depth-selective measurements are crucial. 相似文献
992.
33S solid-state NMR is reported from some model crystalline sulphides, sulphates, sulphites and thiosulphates. This is the first report of 33S NMR signals of the latter two species from a solid. Good quality spectra, which have distinct, well separated shift ranges can be identified for all these groupings, except for sulphites and hydrogen sulphites whose resonances are very broad. Nonetheless the presence of sulphites and hydrogen sulphites can be confirmed from their characteristic sharp, intense time domain echoes. 33S MAS NMR is also applied to a range of dry and hydrous silicate glasses with 1wt% 99 at% 33S-enriched sulphur. It is clear that in all these glasses sulphate is present, and in mixed cation systems there is some evidence of preferential association of sulphate with a specific cation. In a dry potassium silicate glass sample two resolved 33S resonances are observed, a sulphate, and the second from thiosulphate. Hence solid state 33S NMR is shown to be a feasible probe that can be applied to this problem that can readily distinguish different sulphur species. 相似文献
993.
Mukhopadhyay S Zerella M Bell AT Srinivas RV Smith GS 《Chemical communications (Cambridge, England)》2004,(4):472-473
Methane is transformed selectively to methanesulfonyl chloride at low temperature by liquid-phase reaction of methane with SO(2)Cl(2) in the presence of a free radical initiator and a promoter using 100% H(2)SO(4) as the solvent. 相似文献
994.
Nandhakumar IS Gabriel T Li X Attard GS Markham M Smith DC Baumberg JJ 《Chemical communications (Cambridge, England)》2004,(12):1374-1375
Direct liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride films which displayed good optical properties as evidenced by UV/VIS reflectance spectroscopy. 相似文献
995.
Pratontep S Preece P Xirouchaki C Palmer RE Sanz-Navarro CF Kenny SD Smith R 《Physical review letters》2003,90(5):055503
The deposition of size-selected clusters represents a new route to the fabrication of truly nanometer-scale surface architectures, e.g., nanopores. We report a systematic experimental study, coupled with molecular dynamics simulations, of the implantation depths of size-selected Au7, Ag7, and Si7 clusters in the model graphite substrate. For impact energies between 1.0 and 5.5 keV, we find that the implantation depth scales linearly with the momentum of the clusters for all three types of cluster. This "universal" behavior is consistent with a (viscous) retarding force proportional to the velocity of the cluster, akin to Stokes's law. 相似文献
996.
We report a robust and reliable platform source for visible-wavelength multiphoton microscopy that is based on nonlinear optical methods. We demonstrate a synchronously pumped, singly resonant optical parametric oscillator with simultaneous intracavity third-order quasi-phase matching in a single crystal that generates continuously tunable, visible, and femtosecond-pulsed radiation. The application of the system is demonstrated by two-photon laser-scanning fluorescence microscopy of rabbit cardiac myocytes loaded with the fluorescent Ca2+ indicator fura-2. 相似文献
997.
Neutron emission cross section for various elements from9Be to209Bi have been calculated using the hybrid model code ALICE-91 for proton induced reactions in the energy range 25 MeV to 105
Me V. An empirical expression relating neutron emission cross section to target mass number and incident proton energy has
been obtained. The simple expression reduces the computation time significantly. The trend in the variation of neutron emission
cross sections with respect to the target mass number and incident proton energy has been discussed within the framework of
the model used. 相似文献
998.
Gockel H Moore BC Patterson RD Meddis R 《The Journal of the Acoustical Society of America》2003,114(2):978-990
The influence of the degree of envelope modulation and periodicity on the loudness and effectiveness of sounds as forward maskers was investigated. In the first experiment, listeners matched the loudness of complex tones and noise. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz and were filtered into a frequency range from the 10th harmonic to 5000 Hz. The Gaussian noise was filtered in the same way. The components of the complex tones were added either in cosine phase (CPH), giving a large crest factor, or in random phase (RPH), giving a smaller crest factor. For each F0, subjects matched the loudness between all possible stimulus pairs. Six different levels of the fixed stimulus were used, ranging from about 30 dB SPL to about 80 dB SPL in 10-dB steps. Results showed that, at a given overall level, the CPH and the RPH tones were louder than the noise, and that the CPH tone was louder than the RPH tone. The difference in loudness was larger at medium than at low levels and was only slightly reduced by the addition of a noise intended to mask combination tones. The differences in loudness were slightly smaller for the higher than for the lower F0. In the second experiment, the stimuli with the lower F0s were used as forward maskers of a 20-ms sinusoid, presented at various frequencies within the spectral range of the maskers. Results showed that the CPH tone was the least effective forward masker, even though it was the loudest. The differences in effectiveness as forward maskers depended on masker level and signal frequency; in order to produce equal masking, the level of the CPH tone had to be up to 35 dB above that of the RPH tone and the noise. The implications of these results for models of loudness are discussed and a model is presented based on neural activity patterns in the auditory nerve; this predicts the general pattern of loudness matches. It is suggested that the effects observed in the experiments may have been influenced by two factors: cochlear compression and suppression. 相似文献
999.
Back BB Baker MD Ballintijn M Barton DS Becker B Betts RR Bickley AA Bindel R Budzanowski A Busza W Carroll A Decowski MP García E Gburek T George N Gulbrandsen K Gushue S Halliwell C Hamblen J Harrington AS Henderson C Hofman DJ Hollis RS Hołyński R Holzman B Iordanova A Johnson E Kane JL Khan N Kulinich P Kuo CM Lee JW Lin WT Manly S Mignerey AC Noell A Nouicer R Olszewski A Pak R Park IC Pernegger H Reed C Remsberg LP Roland C Roland G Sagerer J Sarin P Sawicki P Sedykh I Skulski W Smith CE 《Physical review letters》2003,91(7):072302
We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25
相似文献
1000.
A water-filled impedance tube capable of improved measurement accuracy and precision is reported. The measurement instrument employs a variation of the standardized two-sensor transfer function technique. Performance improvements were achieved through minimization of elastic waveguide effects and through the use of sound-hard wall-mounted acoustic pressure sensors. Acoustic propagation inside the water-filled impedance tube was found to be well described by a plane wave model, which is a necessary condition for the technique. Measurements of the impedance of a pressure-release terminated transmission line, and the reflection coefficient from a water/air interface, were used to verify the system. 相似文献