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111.
Sviatlana Viarbitskaya Linus Ryderfors Therese Mikaelsson Emad Mukhtar Lennart B.-?. Johansson 《Journal of fluorescence》2011,21(1):257-264
Multi-photon absorption induced luminescence (MAIL) from bare gold nanoparticles, silica-coated particles, as well as silica-coated agglomerated gold nanoparticles suspended in aqueous solution was studied by using time-resolved and steady-state luminescence spectroscopy. The nanoparticles were excited by femtosecond pulses of wavelengths ranging from 630 nm to 900 nm. The luminescence from the particles exhibits a broad spectrum in the UV and VIS region. The time-resolved measurements indicate a luminescence lifetime of a few ps, limited by the response of the experimental system. The studied dependence of the MAIL efficiency on the excitation wavelength showed that the luminescence from silica-coated agglomerates was enhanced over the whole range of excitation wavelengths, when compared to the luminescence from individual gold nanoparticles. The agglomerates show an almost excitation wavelength independent efficiency of the MAIL, while for individual nanoparticles a rapid decrease of the MAIL efficiency was observed with increasing excitation wavelength. The observed enhancement of the MAIL from the agglomerated nanostructures can be attributed to the presence of localized surface plasmon resonances in the spectral region corresponding to the excitation wavelengths. The high MAIL efficiency from the agglomerated nanoparticle structures in the near-infrared could be an advantage in the expanding field of luminescence-based-imaging, as well as in biosensor technology. 相似文献
112.
Maria McDonnell Johan Sundberg Joakim Westerlund Per-Åke Lindestad Hans Larsson 《Journal of voice》2011,25(5):526-531
Objectives/Hypotheses
Singers learn to produce well-controlled tone onsets by accurate synchronization of glottal adduction and buildup of subglottal pressure. Spectrographic analyses have shown that the higher spectrum partials are present also at the vowel onset in classically trained singers’ performances. Such partials are produced by a sharp discontinuity in the waveform of the transglottal airflow, presumably produced by vocal fold collision.Study Design
After hearing a prompt series of a triad pattern, six singer subjects sang the same triad pattern on the vowel /i/ (1) preceded by an aspirated /p/, (2) preceded by an unaspirated /p/, and (3) without any preceding consonant in staccato.Methods
Using high-speed imaging we examined the initiation of vocal fold vibration in aspirated and unaspirated productions of the consonant /p/ as well as in the staccato tones.Results
The number vibrations failing to produce vocal fold collision were significantly higher in the aspirated /p/ than in the unaspirated /p/ and in the staccato tones. High frequency ripple in the audio waveform was significantly delayed in the aspirated /p/.Conclusions
Initiation of vocal fold collision and the appearance of high-frequency ripple in the vowel /i/ are slightly delayed in aspirated productions of a preceding consonant /p/. 相似文献113.
A significant anisotropy of the magnetic-field driven superconductor-insulator transition is observed in thin films of amorphous indium-oxide. The anisotropy is largest for more disordered films which have a lower transition field. At higher magnetic fields the anisotropy reduces and even changes sign beyond a sample specific and temperature independent magnetic field value. The data are consistent with the existence of more than one mechanism affecting transport at high magnetic fields. 相似文献
114.
In this paper we present an improved algorithm for finding low-weight multiples of polynomials over the binary field using coding theoretic methods. The associated code defined by the given polynomial has a cyclic structure, allowing an algorithm to search for shifts of the sought minimum-weight codeword. Therefore, a code with higher dimension is constructed, having a larger number of low-weight codewords and through some additional processing also reduced minimum distance. Applying an algorithm for finding low-weight codewords in the constructed code yields a lower complexity for finding low-weight polynomial multiples compared to previous approaches. As an application, we show a key-recovery attack against that has a lower complexity than the chosen security level indicate. Using similar ideas we also present a new probabilistic algorithm for finding a multiple of weight 4, which is faster than previous approaches. For example, this is relevant in correlation attacks on stream ciphers. 相似文献
115.
Robert Reys Barbara Reys Gran Emanuelsson Bengt Johansson Alistair McIntosh Der Ching Yang 《School science and mathematics》1999,99(2):61-70
This paper reports selected findings from a study of number sense proficiency of students aged 8 to 14 years in Australia, Sweden, United States, and Taiwan. It comments on the meaning and importance of number sense, the development of the assessment instruments, and student responses to the items. Some implications for classrooms of the findings are then discussed. 相似文献
116.
In the region near 1 μm, we have found laser action in a quantum transition between highly excited states of Fe II, with its higher levels being optically pumped by the intense H Lyα radiation (1215 Å) formed in the ionized HII region of a gas condensation (blob B) in the close vicinity of the central star in η Carinae. 相似文献
117.
Stellan Jacobsson Anders Lundgren Joakim Johansson 《International Journal of Infrared and Millimeter Waves》1990,11(11):1251-1261
Computer generated Fourier transform phase holograms, known as kinoforms, have been synthesized, manufactured and their performance evaluated at a wavelength of 3 mm (100 GHz). The kinoforms were synthesized to give a prescribed far-field intensity distribution and manufactured by milling the computed kinoform surface relief into a Teflon plate, using a numerically controlled milling machine. The measured diffraction efficiencies exceed 50 percent. Millimeter-wave kinoforms can be used in various quasi-optical applications,e.g. distributing a local oscillator signal to an array of detector elements in heterodyne receivers. 相似文献
118.
M. S. Pedersen S. Mørup S. Sethi M. Hanson C. Johansson 《Hyperfine Interactions》1994,93(1):1433-1437
Ferrofluids with ultrafine magnetic particles of amorphous Fe1-xCx were studied by Mössbauer spectroscopy, transmission electron microscopy and magnetic measurements. Magnetic measurements showed that the initial susceptibility follows a Curie-Weiss law, indicating magnetic interaction between the particles. The influence of the magnetic interaction on the estimation of the particle size, made from the field dependence of the induced hyperfine splitting, is discussed. 相似文献
119.
The acylated guanine-glyoxal adduct (I) has been alkylated with 4-bromobutyl acetate and in the presence of sodium hydride the reaction was regioselective to give 7-alkylguanine. 相似文献
120.
Y. Gauthier I. Zasada V. Langlais C. Virojanadara L.I. Johansson 《Surface science》2007,601(16):3383-3394
Low energy electron diffraction, grazing incidence X-ray diffraction and photoemission were used to decipher the detailed structural arrangement and chemical composition of the surface region of a transition metal carbide, VC0.8(1 1 0). In agreement with previous scanning tunneling microscopy (STM) studies, we find that the surface reconstructs with a ridge-and-valley grating structure along the direction resulting from {0 0 1} faceting for the (3 × 1) and the (4 × 1) phases.Both superstructures terminate on the vacuum side with a nearly stoïchiometric VC region due to C segregation, in contrast with the conclusions drawn from this previous STM study. However, the present experiments clearly show that these phases are metastable, and slow cooling results in a (1 × 1) surface, which is highly C depleted, similarly to the (1 0 0) face. 相似文献