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991.
We have set up a laser system which simultaneously provides synchronized picosecond pulses in the visible and at a wavelength of 1.06 m with a repetition rate of 76 MHz. The set-up consists of a dye laser synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser and a fiber-grating compressor for the fundamental wavelength of the Nd;YAG laser. Crosscorrelation measurments reveal the time jitter between the two pulse trains to be less than 10 ps. As a first application we have performed non-degenerate transient grating experiments in semiconductors. The non-degenerate technique allows to use excitation energies well above the bandgap energy and to separate non-linear refractive index effects from photoinduced absorption or transmission changes. 相似文献
992.
K. Kriŝtiaková O. Ŝauŝa J. Kriŝtiak Ŝ. Jánoŝ 《Zeitschrift für Physik B Condensed Matter》1989,75(2):197-199
We have measured the ac susceptibility of a wire with a Nb core (1.27 mm diam.) and a Cu cladding (0.37 mm thickness) atT50 K andB0.1 mG. Due to its proximity to Nb, the Cu becomes fully superconducting. From the data we find a breakdown fieldH
b
=1.2 (mG) and a coherence length =2.2T
–1/2 (m) for the Cu, as well as a field penetration depth -34T
1/2 (m) at the Cu/Nb interface. 相似文献
993.
J. Spinnewyn H. Strauven O. B. Verbeke 《Zeitschrift für Physik B Condensed Matter》1989,75(2):159-165
We report on a previously not observed behaviour of oscillations of the voltage over a hyperpure germanium sample, when increasing the sample current from 0.05 to 13 A, for a number of transverse magnetic fields ranging from 697 to 1746 gauss. The sample temperature was 7.54 K±0.02 K. For each magnetic field the first observed peaks in the frequency spectrum of the sample voltage go to chaos by the period-doubling route and simultaneously shift to lower frequencies (first scenario). Superimposed upon this chaotic spectrum a new peak emerges, which again shifts to lower frequencies with increasing sample current (second scenario). A complementary effect of the sample current and the magnetic field is detected for four properties: firstly, the sudden onset of high resistance in the current versus voltage diagram, secondly, the transition between the two frequency scenarios described above, thirdly the presence of certain frequencies in the sample voltage spectra and fourthly the occurrence of an amplitude maximum for the principal frequency of the first scenario. It is shown that the first two transitions are interrelated. 相似文献
994.
G. Lo Bianco K. P. Schmittgen K. O. Zell P. v. Brentano 《Zeitschrift für Physik A Hadrons and Nuclei》1989,332(1):103-104
The ratio of the B(E2) values for the 0 1 + → 2 1 + transitions in138Ce and142Ce was measured by Coulomb excitation with α-particles. From the known value of the transition probability in142Ce it results: B(E2,138Ce, 0 1 + → 2 1 + =0.45 +/?0.03 e2 b 2 相似文献
995.
996.
[reaction: see text] Allylically oxygenated vinyl alpha-triphenylstannanes such as 22 can be readily converted into vinyl iodides and thereafter stereodefined trisubstituted alkenes with retention of configuration. 相似文献
997.
Nanoscale organization of the pathogen receptor DC-SIGN mapped by single-molecule high-resolution fluorescence microscopy. 总被引:3,自引:0,他引:3
Bärbel I. de Bakker Dr. Frank de Lange Dr. Alessandra Cambi Dr. Jeroen P. Korterik Erik M. H. P. van Dijk Dr. Niek F. van Hulst Prof. Carl G. Figdor Prof. Maria F. Garcia‐Parajo Prof. 《Chemphyschem》2007,8(10):1473-1480
DC-SIGN, a C-type lectin exclusively expressed on dendritic cells (DCs), plays an important role in pathogen recognition by binding with high affinity to a large variety of microorganisms. Recent experimental evidence points to a direct relation between the function of DC-SIGN as a viral receptor and its spatial arrangement on the plasma membrane. We have investigated the nanoscale organization of fluorescently labeled DC-SIGN on intact isolated DCs by means of near-field scanning optical microscopy (NSOM) combined with single-molecule detection. Fluorescence spots of different intensity and size have been directly visualized by optical means with a spatial resolution of less than 100 nm. Intensity- and size-distribution histograms of the DC-SIGN fluorescent spots confirm that approximately 80 % of the receptors are organized in nanosized domains randomly distributed on the cell membrane. Intensity-size correlation analysis revealed remarkable heterogeneity in the molecular packing density of the domains. Furthermore, we have mapped the intermolecular organization within a dense cluster by means of sequential NSOM imaging combined with discrete single-molecule photobleaching. In this way we have determined the spatial coordinates of 13 different individual dyes, with a localization accuracy of 6 nm. Our experimental observations are all consistent with an arrangement of DC-SIGN designed to maximize its chances of binding to a wide range of microorganisms. Our data also illustrate the potential of NSOM as an ultrasensitive, high-resolution technique to probe nanometer-scale organization of molecules on the cell membrane. 相似文献
998.
Doz. Dr. Karl Gewald Gudrun Heinhold 《Monatshefte für Chemie / Chemical Monthly》1976,107(6):1413-1421
The alkylation of arylaminomethylenecyanamides1 or cyano-imidothiocarbamates2 with -halogen carbonyl compounds followed by base catalysed cyclization yields substituted 4-amino-imidazoles4. Imidazo[4,5-d]pyrimidones5, 6 and imidazo[4,5-b]pyridines7 can be obtained from4. 相似文献
999.
A novel two-dimensional coordination polymer containing infinite, coherently pitched single and triple helical motifs is formed by the self-assembly of Cd2+, succinate, water and a bipyridyl ligand. 相似文献
1000.
L. M. Khalilov M. É. Adler O. V. Shitikova M. S. Miftakhov G. A. Tolstikov 《Chemistry of Natural Compounds》1991,27(1):108-113
The diastereomeric effects on the13C NMR chemical shifts of thirteen epimeric pairs of 16-aryloxy-11-deoxyprostaglandins of the E1 and F1 series caused by the change in the configuration of the 15-hydroxy group, which are differential parameters for assigning epimers to the 15- and 15-stereochemical series, have been determined.For Communication (VIII), see [1].Institute of Chemistry, Bashkir Scientific Center, Urals Branch, Academy of Sciences of the USSR, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 123–128, January–February, 1991. 相似文献