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51.
Imaging and quantifying transverse flow velocity with the Doppler bandwidth in a phase-resolved functional optical coherence tomography 总被引:2,自引:0,他引:2
The Doppler bandwidth extracted from the standard deviation of the frequency shift in phase-resolved functional optical coherence tomography (F-OCT) was used to image the velocity component that is transverse to the optical probing beam. It was found that above a certain threshold level the Doppler bandwidth is a linear function of flow velocity and that the effective numerical aperture of the optical objective in the sample arm determines the slope of this dependence. The Doppler bandwidth permits accurate measurement of flow velocity without the need for precise determination of flow direction when the Doppler flow angle is within +/-15 degrees perpendicular to the probing beam. Such an approach extends the dynamic range of flow velocity measurements obtained with the phase-resolved F-OCT. 相似文献
52.
Investigation of Brillouin effects in small-core holey optical fiber: lasing and scattering 总被引:6,自引:0,他引:6
We demonstrate for what is believed to be the first time a Brillouin laser based on a holey fiber (HF). Using a simple Fabry-Perot resonator scheme containing a 73.5-m-long highly nonlinear HF with an effective area of 2.85 microm(2) , we obtain a threshold of 125 mW and a slope efficiency of ~70% . Stimulated and spontaneous Brillouin scattering effects are investigated in the HF, and we show that the high lasing threshold is due mainly to reduction of the effective gain coefficient caused by structural nonuniformity along the fiber length. 相似文献
53.
J. H. Bowie J.
. Madsen S.-O. Lawesson R. G. Cooks 《Journal of mass spectrometry : JMS》1969,2(4):413-424
The mass spectra of thioglycollic acids and esters are reported and discussed. The spectra of compounds of the type X·CH(Y)·S·CH2·COOR(X > Y) contain skeletal rearrangement fragments with the composition R·Y·C2H3SO+. Ions produced by simple cleavage processes may be usefully correlated with structure. 相似文献
54.
55.
Jørgensen LV Amoretti M Bonomi G Bowe PD Canali C Carraro C Cesar CL Charlton M Doser M Fontana A Fujiwara MC Funakoshi R Genova P Hangst JS Hayano RS Kellerbauer A Lagomarsino V Landua R Lodi Rizzini E Macrì M Madsen N Mitchard D Montagna P Rotondi A Testera G Variola A Venturelli L van der Werf DP Yamazaki Y;ATHENA Collaboration 《Physical review letters》2005,95(2):025002
We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10(-9) mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10(-13) mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1.2 x 10(9) positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 x 10(6) positrons were compressed to a density of 2.6 x 10(10) cm(-3). This is a factor of 6 improvement over earlier measurements. 相似文献
56.
Nielsen M Thomsen AH Cló E Kirpekar F Gothelf KV 《The Journal of organic chemistry》2004,69(7):2240-2250
Rigid linear and tripoidal organic modules based on the oligo(phenylene ethynylene) backbone having salicylaldehyde-derived termini are synthesized. A highly functionalized 5-iodosalicyl aldehyde was prepared and coupled to each ethynyl group of 1,4-diethynylbenzene or 1,3,5-triethynylbenzene in Sonogashira couplings. The two or three termini of the compounds are functionalized for incorporation in linear and branched oligonucleotide strands. For the linear module (LM), the two termini are equipped with amide spacers, and one of these was functionalized with a DMTr (dimethoxytrityl)-protected hydroxy group and the other with a phosphoramidite. One of the tripoidal modules is prepared with DMTr groups in two of its three termini. A tripoidal module is also synthesized with three different groups on its hydroxy termini: a phosphoramidite, a DMTr group, and an Fmoc group. Extended studies have shown that these rigid linear and tripoidal organic modules can be incorporated into short oligonucleotides. Several of these modules can be applied for DNA-directed assembly and covalent coupling into structures of predetermined connectivity. Such structures have potential application for molecular electronics and nanotechnology. 相似文献
57.
Rémi?GribonvalEmail author Morten?NielsenEmail author 《Journal of Fourier Analysis and Applications》2004,10(1):51-71
We study various approximation classes associated with m-term approximation by
elements from a (possibly redundant) dictionary in a Banach space. The standard approximation
class associated with the best m-term approximation is compared to new classes defined by
considering m-term approximation with algorithmic constraints: thresholding and Chebychev approximation
classes are studied, respectively. We consider embeddings of the Jackson type (direct
estimates) of sparsity spaces into the mentioned approximation classes. General direct estimates
are based on the geometry of the Banach space, and we prove that assuming a certain structure of
the dictionary is sufficient and (almost) necessary to obtain stronger results. We give examples of
classical dictionaries in Lp spaces and modulation spaces where our results recover some known
Jackson type estimates, and discuss some new estimates they provide. 相似文献
58.
Single-fiber Bragg gratings designed to compensate for pure third-order dispersion are demonstrated. The devices are designed by use of a layer-peeling inverse-scattering technique and exhibit dispersion profiles across their reflection bandwidths of -20, +/- 40, and -225 ps/nm2 over bandwidths of 4.5, 6, and 3 nm, respectively. Furthermore, they have almost constant peak reflectivities of approximately 75% and are, respectively, only 8, 23, and 40 mm long. 相似文献
59.
By use of a near-field scanning optical microscope (NSOM) in collection mode, the intensity distribution along a 2 x 2 multimode interference coupler was directly imaged as a function of wavelength. Although calculations can predict the general trend of wavelength dependence and the approximate positions of multiple images in the coupler, the accuracy is poor because of uncertainties in the waveguide width. We show that direct imaging using a NSOM bypasses calculational uncertainties and proves to be a powerful technique for studying these waveguide devices. 相似文献
60.
Gutt C Ghaderi T Chamard V Madsen A Seydel T Tolan M Sprung M Grübel G Sinha SK 《Physical review letters》2003,91(7):076104
We report measurements of propagating capillary waves on a liquid water surface at T=5 degrees C with x-ray photon correlation spectroscopy. The experiment has been performed under grazing incidence conditions with an incoming x-ray beam below the critical angle of total external reflection. In the q region investigated the measured intensity-intensity autocorrelation functions of the liquid water surface were found to be heterodyne signals, i.e., a combination of first- and second-order correlation functions g(1)(tau) and g(2)(tau). 相似文献